United States

Environmental Protection

Agency

Office of Water (4203)

Washington, D.C. 20460

www.epa.gov/npdes

EPA 833-R-04-001

August 2004

Report to Congress

Impacts and Control of CSOs and SSOs
On the Cover

Large photo in background: Oklahoma City PVC sewer pipe stockpile. In response to problems from an aging sewer system 

made up of more than 2,000 miles of pipe, Oklahoma City implementing a capital improvement planning program with the 

goal of replacing sewer lines at the rate of 1% per year. The City opted for replacing aging pipes with PVC pipes as a more 

affordable, flexible and corrosion-resistant alternative. Photo courtesy of Julia Moore, Limno-Tech, Inc..

Top inset: Former Denny Way CSO outfall in Seattle, WA. The Denny Way outfall as shown was the largest volume CSO discharge 

in the King County System. Through a joint effort of King County and the City of Seattle, the Denny Way/Lake Union CSO 

Project was implemented to control over 600 million gallons of combined sewage from overflowing annually into Lake Union 

and Elliott Bay. Under way since May 2000, construction is expected to be complete in 2005. Progress to date includes the 

demolition of the pictured outfall, restoration of the shoreline, and revitalization of the surrounding public park. Photo courtesy 

of King County.

Second inset: Monitoring team responding to sewer overflow. Photo provided by ADS.

Third inset: City of Richmond, VA Canal Walk. The City of Richmond incorporated downtown revitalization, historical 

interpretation, and combined sewer overflow planning as part of a large-scale redevelopment of their downtown river front 

area. The riverfront redevelopment was made possible, in part, by the environmental improvements achieved by the Richmond 

CSO Control Program. The resulting Canal Walk extends for more than a mile along the Haxall and Kanawha Canals and includes 

under canal routing of combined sewage while providing a pathway of access to revitalized businesses, museums and new 

outdoor public vistas and arenas. Photo courtesy of City of Richmond.

Fourth inset: Orange County, CA. Orange County Health Care Agency’s Environmental Health Ocean Water Protection Program 

administers a beach water quality monitoring program to ensure public recreational waters meet bacteriological water quality 

standards for full body contact recreational activities such as swimming, surfing and diving. Beach closure or advisory signs are 

posted at Orange County beaches when high levels of bacteria are measured or when a sewage spill contamination of ocean or 

bay waters occurs. Photo courtesy of OCHCA EH Ocean Water Protection Program.
Table of Contents

Executive Summary—Report to Congress on the Impacts and Control of CSOs and SSOs . . . . . . . . . . . . ES-1

Chapter 1—Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 What are CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.1.1 CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.1.2 SSOs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1.2 How is this Report Organized? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Chapter 2—Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1 What is the History of Sewer Systems in the United States? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1.1 Combined Sewers and CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.1.2 Sanitary Sewers and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.2 What is the History of Federal Water Pollution Control Programs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.2.1 Secondary Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.2.2 Construction Grants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2.2.3 Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.2.4 Wet Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.2.5 Watershed-Based Permitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.3 What is the Federal Framework for CSO Control? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.3.1 CSO Case Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.3.2 The National CSO Control Stategy and the MAG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2.3.3 The CSO Control Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2.4 What is the Federal Framework for SSO Control? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2.5 What is the Wet Weather Water Quality Act? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Chapter 3—Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.1 What Study Objectives and Approach Did EPA Use to Prepare this Report? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2 What Data Sources Were Used? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.2.1 Federal Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.2.2 NPDES Authority and Other State Program Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.2.3 Community-Level Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.2.4 Non-Governmental Organization Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.3 What Data Were Collected? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.3.1 Characterization of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.3.2 Extent of Environmental Impacts Caused by CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

3.3.3 Extent of Human Health Impacts Caused by CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.3.4 Evaluation of Technologies Used by Municipalities to Address Impacts Caused by CSOs and SSOs . . . . . . . 3-8

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Report to Congress on the Impacts and Control of CSOs and SSOs

3.3.5 Assessment of Resources Spent by Municipalities to Address Impacts Caused by CSOs and SSOs . . . . . . . . . . 3-8

3.4 How Were Stakeholders Involved in the Preparation of this Report? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3.5 What Data Considerations Are Important? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3.6 What Quality Control and Quality Assurance Protocols Were Used? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11

3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

Chapter 4—Characterization of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1 What Pollutants are in CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.1.1 Microbial Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.1.2 BOD5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.1.3 TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.1.4 Toxics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.1.5 Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.1.6 Floatables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.2 What Factors Influence the Concentrations of the Pollutants in CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4.2.1 Factors Influencing Pollutant Concentrations in CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4.2.2 Factors Influencing Pollutant Concentrations in SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9

4.3 What Other Point and Nonpoint Sources Might Discharge These Pollutants to Waterbodies Receiving CSOs 

and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9

4.3.1 Wastewater Treatment Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

4.3.2 Decentralized Wastewater Treatment Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.3.3 Industrial Point Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.3.4 Urban Storm Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.3.5 Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.3.6 Domestic Animals and Wildlife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.3.7 Commercial and Recreational Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.4 What is the Universe of CSSs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.5 What are the Characteristics of CSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16

4.5.1 Volume of CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4.5.2 Frequency of CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4.5.3 Location of CSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4.6 What is the Universe of SSSs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

4.7 What are the Characteristics of SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

4.7.1 SSO Data Management System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

4.7.2 Statistical Technique Used to Estimate Annual National SSO Frequency and Volume . . . . . . . . . . . . . . . . . . 4-23

4.7.3 Frequency of SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24

4.7.4 Volume of SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-25

4.7.5 Location of SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.8 How Do the Volumes and Pollutant Loads from CSOs and SSOs Compare to Those from Other Municipal 

Point Sources? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

Chapter 5—Environmental Impacts of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.1 What is EPA’s Framework for Evaluating Environmental Impacts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2 What Overall Water Quality Impacts Have Been Attributed to CSO and SSO Discharges in National Assessments? . . 5-3

5.2.1 NWQI 2000 Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
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5.2.2 Analysis of CSO Outfalls Discharging to Assessed or Impaired Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

5.2.3 Modeled Assessment of SSO Impacts on Receiving Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

5.3 What Impacts on Specific Designated Uses Have Been Attributed to CSO and SSO Discharges in National 

Asssessments? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5.3.1 Recreation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5.3.2 Shellfish Harvesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

5.4 What Overall Water Quality Impacts Have Been Attributed to CSO and SSO Discharges in State and Local 

Assessments? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

5.4.1 Water Quality Assessment in New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

5.4.2 Water Quality Assessment of the Mahoning River Near Youngstown, Ohio . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

5.4.3 Water Quality Assessment in Indianapolis, Indiana . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

5.4.4 Water Quality Risk Assessment of CSO Discharges in King County, Washington . . . . . . . . . . . . . . . . . . . . . . 5-16

5.5 What Impacts on Specific Designated Uses Have Been Attributed to CSO and SSO Discharges in State and Local 

Assessments? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

5.5.1 Aquatic Life Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

5.5.2 Recreation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21

5.5.3 Shellfish Harvesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

5.6 What Factors Affect the Extent of Environmental Impacts Caused by CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5.6.1 Timescale Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

5.6.2 Receiving Water Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

Chapter 6—Human Health Impacts of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1 What Pollutants in CSOs and SSOs Can Cause Human Health Impacts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1.1 Microbial Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6.1.2 Toxics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6.1.3 Biologically Active Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

6.2 What Exposure Pathways and Reported Human Health Impacts are Associated with CSOs and SSOs? . . . . . . . . . . . . . 6-7

6.2.1 Recreational Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

6.2.2 Drinking Water Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

6.2.3 Fish and Shellfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

6.2.4 Direct Contact with Land-Based Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13

6.2.5 Occupational Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

6.2.6 Secondary Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15

6.3 Which Demographic Groups Face the Greatest Risk of Exposure to CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

6.3.1 Swimmers, Bathers, and Waders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

6.3.2 Subsistence and Recreational Fishers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

6.3.3 Wastewater Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6.4 Which Populations Face the Greatest Risk of Illness from Exposure to the Pollutants Present in CSOs and SSOs? . . 6-17

6.4.1 Pregnant Women . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6.4.3 Immunocompromised Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6.4.4 Elderly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6.5 How are Human Health Impacts from CSOs and SSOs Communicated, Mitigated, and Prevented? . . . . . . . . . . . . . . 6-18

6.5.1 Agencies and Organizations Responsible for Protecting Public Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6.5.2 Activities to Protect Public Health from Impacts of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6.6 What Factors Contribute to Information Gaps in Identifying and Tracking Human Health Impacts from CSOs 

and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24

6.6.1 Underreporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24
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6.6.2 Use of Indicator Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25

6.7 What New Assessment and Investigative Activities are Underway? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26

6.7.1 Investigative Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26

Chapter 7—Federal and State Efforts to Control CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1 What are States and EPA Regions Doing to Control CSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.1 Nine Minimum Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.1.2 Long-Term Control Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.2 What are States and EPA Regions Doing to Control SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.2.1 Application of Standard Permit Conditions to SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.2.2 Electonic Tracking of SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7.3 What Programs Have Been Developed to Control SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7.3.1 EPA Region 4’s MOM Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7.3.2 Oklahoma - Collection System Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7.3.3 California - Record Keeping and Reporting of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7.3.4 North Carolina - Collection System Permitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7.4 What Compliance and Enforcement Activities Have Been Undertaken? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7.4.1 National Municipal Policy on POTWs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.4.2 Enforcement Management System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.4.3 Compliance and Enforcement Strategy (2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.4.4 Compliance Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

7.4.5 Summary of Enforcement Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

Chapter 8—Technologies Used to Reduce the Impacts of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.1 What Technologies are Commonly Used to Control CSOs and SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8.1.1 Operation and Maintenance Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8.1.2 Collection System Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5

8.1.3 Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11

8.1.4 Treatment Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

8.1.5 Low-Impact Development Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17

8.2 How Do CSO and SSO Controls Differ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20

8.2.1 Common CSO Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20

8.2.2 Common SSO Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

8.3 What Technology Combinations are Effective? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

8.3.1 Inflow Reduction or Low-Impact Development Coupled with Structural Controls . . . . . . . . . . . . . . . . . . . . 8-22

8.3.2 Disinfection Coupled with Solids Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22

8.3.3 Sewer Rehabilitation Coupled with Sewer Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22

8.3.4 Real-Time Control Coupled with In-line or Off-line Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22

8.4 What New Technologies for CSO and SSO Control are Emerging? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

8.4.1 Optimization of Sewer System Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

8.4.2 Information Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

Chapter 9—Resources Spent Address the Impacts of CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.1 What Federal Framework Exists for Evaluating Resources Spent on CSO and SSO Control? . . . . . . . . . . . . . . . . . . . . . 9-1

9.2 What are the Past Investments in Wastewater Infrastructure? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2
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9.3 What Has Been Spent to Control CSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

9.4 What Has Been Spent to Control SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6

9.5 What Does it Cost to Maintain Sewer Systems? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

9.6 What are the Projected Costs to Reduce CSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8

9.7 What are the Projected Costs to Reduce SSOs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

9.8 What Funding Mechanisms are Available for CSO and SSO Control? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10

9.8.1 Self-financing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11

9.8.2 State and Federal Funding for CSO and SSO Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12

Chapter 10—Conclusions and Future Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

 Protecting Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

 Implementing the Watershed Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3

 Improving Monitoring and Information-Based Environmental Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4

 Building Strategic Partnerships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
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List of Figures

Figure ES.1—National Distribution of CSSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ES-5

Figure ES.2—National Distribution of SSSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ES-6

Figure ES.3—Sources of Pollution that Resulted in Swimming Beach Advisories and Closings . . . . . . . . . . . . . . . . . . . . . . . . ES-8

Figure 2.1—Typical Combined Sewer System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Figure 2.2—Typical Separate Sanitary and Storm Sewer Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Figure 2.3—National Distribution of Communities Served by CSSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Figure 2.4—National Distribution of Communities Served by SSSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Figure 4.1—Distribution of CSO Permits by Region and by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

Figure 4.2—Distribution of CSO Outfalls by Region and by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

Figure 4.3—Distribution POTW Facility Sizes Serving CSSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

Figure 4.4—Distribution of SSSs with Wastewater Treatment Facilities by Region and by State . . . . . . . . . . . . . . . . . . . . . . . . 4-21

Figure 4.5—Distribution of Satellite SSSs by Region and by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

Figure 4.6—States Providing Electronic Data on SSO Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

Figure 4.7—Total Number of SSO Events Reported by Individual Communities, January 1, 2001 - December 31, 2002 . . . 4-25

Figure 4.8—Distribution of SSO Volume Reported Per Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

Figure 4.9—Most Common Reported Causes of SSO Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

Figure 4.10—Reported Causes of SSOs in Communities Reporting More than 100 SSO Events During a 

 Single Calendar Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

Figure 4.11—Reported Cause of Blockage Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

Figure 5.1—NWQI 2000 Summary of Assessed Waters by Waterbody Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Figure 5.2—Sources of Pollution that Resulted in Beach Advisories and Closings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11

Figure 5.3—Sources of Water Quality Impairment in New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

Figure 5.4—Fish Species Found in the Chicago and Calumet River System, 1974 - 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

Figure 5.5—Sources of Contamination Resulting in California Beach Closures in 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

Figure 5.6—Beach Closures in California During 2000 Attributed to SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23

Figure 5.7—Average Number Days per Year Coastal Municipalities in Connecticut Closed One or More Beaches . . . . . . . . 5-24

Figure 5.8— Lake Michigan Beach Closures, 1998- 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

Figure 5.9— Movement of Bacteria Plume from SSO Discharge in Raritan Bay, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

Figure 6.1—Microbial Pathogens Linked to Outbreaks in Recreational Waters, 1985 - 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Figure 6.2—Microbial Pathogens Causing Outbreaks Linked to Drinking Water, 1985-2000 . . . . . . . . . . . . . . . . . . . . . . . . . 6-11

Figure 9.1—Annual Capital Expenditures on Wastewater Projects, 1970 - 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

Figure 9.2—State and Local Expenditures on Wastewater O&M, 1970 - 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

Figure 9.3—CWSRF Annual Expenditures for CSO Projects, 1988 - 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

Figure 9.4—CWSRF Annual Expenditures for I/I and Sewer Replacement/Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6

Figure 9.5—Changes in Estimated Needs Between 1996 and 2000 CWNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10

Figure 9.6—Revenue Sources for Municipal Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11

Figure 9.7—State and Local Expenditures Under the CWSRF Program for CSO Correction and SSO Capital Projects . . . 9-12
Table of Contents

vii

List of Tables

Table ES.1—Comparison of Estimated Annual Discharge Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ES-7

Table 4.1—Fecal Coliform Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

Table 4.2—BOD5 Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

Table 4.3—TSS Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

Table 4.4—Cadmium and Copper Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Table 4.5—Lead and Zinc Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Table 4.6—Nutrient Concentrations in Municipal Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Table 4.7—Volume Reduction Estimates Based on Implementation of CSO Control Policy . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

Table 4.8—SSO Event Volume by Cause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

Table 4.9—Estimated Annual Municipal Point Source Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

Table 4.10—Estimated Annual BOD5 Load from Municipal Point Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

Table 4.11—Estimated Annual TSS Load from Municipal Point Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

Table 4.12—Estimated Annual Fecal Coliform Load from Municipal Point Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

Table 5.1—Pollutants of Concern in CSOs and SSOs Likely to Cause or Contribute to Impairment . . . . . . . . . . . . . . . . . . . . . 5-3

Table 5.2—Pollutants and Stressors Most Often Associated with Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Table 5.3—Leading Sources of Pollutants and Stressors Causing Water Quality Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Table 5.4—Occurances of 305(b) Assessed Waters Within One Mile Downstream of a CSO Outfall . . . . . . . . . . . . . . . . . . . . 5-7

Table 5.5—Occurence of 303(d) Listed Waters Within One Mile Downstream of a CSO Outfall . . . . . . . . . . . . . . . . . . . . . . . 5-8

Table 5.6—Estimated Perentage of Time SSOs Would Cause Water Quality Standard Violations . . . . . . . . . . . . . . . . . . . . . . . 5-9

Table 5.7—NMDMP Marine Debris Survey Results from 1996 to 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

Table 5.8—Pollution Sources Reported for Harvest Limitations on Classified Shellfish Growing Waters in the 1990 and 1995 

 National Shellfish Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

Table 5.9—Harvest Limitations on Classified Shellfish Growing Areas Within Five Miles of a CSO Outfall . . . . . . . . . . . . . 5-15

Table 5.10—Relative Contributions of Pollutant Sources to Water Quality Problems in Indianapolis, Indiana . . . . . . . . . . . 5-17

Table 5.11—Fish Kills Reported in North Carolina: 1997 - 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

Table 5.12—Fish Kills Caused by Sewage Spills in North Carolina: 1997 - 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20

Table 5.13—Summary of Unauthorized Wastewater Discharges in Orange County, California, that

 Resulted in Beach Closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

Table 6.1—Common Pathogenic Bacteria Present in Sewage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

Table 6.2—Common Enteric Viruses Present in Sewage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

Table 6.3—Common Parasitic Protozoa Present in Sewage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

Table 6.4—Concentration of Indicator Bacteria and Enteric Pathogens Shed by an Infected Individual . . . . . . . . . . . . . . . . . . 6-5

Table 6.5—Participation in Water-Based Recreation in U.S. during July 1999 and January 2001 . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Table 6.6—Estimated Number of Illnesses per Year Attributed to CSOs and SSOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

Table 6.7—Association of CSO Outfalls with Drinking Water Intakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

Table 6.8—Examples of Secondary Transmission from Waterborne and Non-Waterborne Disease Outbreaks . . . . . . . . . . . 6-15
viii

Report to Congress on the Impacts and Control of CSOs and SSOs

Table 7.1—Summary of Electronic SSO Data by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

Table 8.1—Summary of Operation and Maintenance Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

Table 8.2—Summary of Collection System Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

Table 8.3—Summary of Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12

Table 8.4—Summary of Treatment Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15

Table 8.5—Summary of Low-Impact Development Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

Table 9.1—Annual Budget Expenditures in Sanitary Sewer Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

Table 9.2—O&M Costs for Sewers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
Table of Contents

ix

List of Appendices

Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Statutes, Policies, and Interpretative Memoranda

Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Human Health Expert and Stakeholder Meeting Summaries

Appendix C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Documentation of State and Municipal Interviews

Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . List of Active CSO Permits

Appendix E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GPRACSO Model Documentation

Appendix F . . . . . . . . . . . . . . . . . . . . . . . . . . .Analysis of CSO Receiving Waters Using the National Hydrography Dataset (NHD)

Appendix G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . National Estimate of SSO Frequency and Volume

Appendix H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Estimation of SSO Impacts in Streams and Rivers

Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Human Health Addendum

Appendix J . . . . . . . . . Estimated Annual Illness Burden Resulting from Exposure to CSOs and SSOs at BEACH Survey Beaches

Appendix K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Summary of Enforcement Actions

Appendix L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Technology Descriptions

Appendix M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Financial Information

CDC– Centers for Disease Control 

and Prevention

CFR– Code of Federal Regulations

cfs– Cubic Feet per Second

CIPP– Cured-in-place Pipe

CMOM– Capacity, Management, 

Operation, and Maintenance

CSO– Combined Sewer Overflow

CSS– Combined Sewer System

CTP– Central Treatment Plant

CWNS– Clean Watersheds Needs 

Survey

CWSRF– Clean Water State Revolving 

Fund

ECD– Enforcement and Compliance 

Docket

ENR– Engineering News Record

EPA– Environmental Protection 

Agency

FEB– Flow Equalization Basins

FAC– Federal Advisory Committee

FOG– Fats, Oils, and Grease

FR– Federal Register

FY– Fiscal Year

List of Acronyms

AIDS– Acquired Immune Disorder 

Syndrome

AMSA– Association of Metropolitan 

Sewerage Agencies

AO– Administrative Order

APO– Administrative Penalty Orders

APWA– American Public Works 

Association

ASCE– American Society of Civil 

Engineers

BAT– Best Available Technology 

Economically Achievable

BCT– Best Conventional Pollutant 

Control Technology

BEACH Program– Beaches 

Environmental Assessment and 

Coastal Health Program

BMP– Best Management Practice

BOD5– Biochemical Oxygen Demand 

(measured over 5 days)

CAFO– Concentrated Animal Feeding 

Operation

CATAD– Computer Augmented 

Treatment and Disposal

CBO– Congressional Budget Office

CCTV– Closed Circuit Television

ACR-1

FWPCA– Federal Water Pollution 

Control Act

GAO– Government Accounting Office

GIS– Geographic Information System

GPRA– Government Performance and 

Results Act

HUD– Housing of Urban 

Development

I/I– Infiltration & Inflow

ISSC– Interstate Shellfish Sanitation 

Conference

LGEAN– Local Government 

Environmental Assistance Network

LID– Low Impact Development

LOV– Letter of Violation

LTCP– Long-Term Control Plan

MAG– Office of Water Management 

Advisory Group

MDE– Maryland Department of the 

Environment

MDEQ– Michigan Department of 

Environmental Quality

MG– Million Gallons

mgd– Million Gallons per Day

ml– Milliliter
ACR-2

Report to Congress on the Impacts and Control of CSOs and SSOs

MMSD– Milwaukee Metropolitan 

Sewarage District

MOM– Management, Operation, and 

Maintenance

MPN– Most Probable Number

MWWSSB– Montegomery Water 

Works and Sanitary Sewer Board

MS4– Municipal Separate Storm 

Sewer System

NCDENR– North Carolina 

Department of Environmental and 

Natural Resources

NEEAR Water Study– National 

Epidemiological and Environmental 

Assessment of Recreational Water 

Study

NIH– National Institutes of Health

NHD– National Hydrography Dataset

NJDEP– New Jersey Department of 

Environmental Protection

NMC– Nine Minimum Controls

NMDSP– National Marine Debris 

Survey Program

NMP–National Municipal Policy

NOAA–National Oceanic and 

Atmospheric Administration

NPDES– National Pollutant Discharge 

Elimination System

NRDC– Natural Resources Defense 

Council

NURP– Nationwide Urban Runoff 

Program

NWQI– National Water Quality 

Inventory

O&M– Operation and Maintenance

ODEQ– Oklahoma Department of 

Environmental Quality

OMB– Office of Management and 

Budget

ORD– Office of Research and 

Development

PCBs– Polychlorinated biphenyls

PCS– Permit Compliance System

P.L.– Public Law

POTW– Publicly Owned Treatment 

Works

REAP– Rural Economic Assistance 

Program

RWQCB– Regional Water Quality 

Control Board

SRF– State Revolving Fund

SSO– Sanitary Sewer Overflow

SSS– Sanitary Sewer System

TKN– Total Kjeldahl Nitrogen

TMDL– Total Maximum Daily Loads

TSS– Total Suspended Solids

USGS– United States Geological 

Survey

UV– Ultraviolet

WATERS- Watershed Assessment, 

Tracking, & Environmental ResultS

WDR– Waste Discharge Requirements

WEF– Water Environment Federation

WERF– Water Environment Research 

Foundation

WISE– Watershed Initiative for a Safe 

Environment

WWTP– Wastewater Treatment Plant
Glossary

GL-1

This glossary includes a collection of the terms used in this manual and an explanation of each term. To the 

extent that definitions and explanations provided in this glossary differ from those in EPA regulations or other 

official documents, they are intended for use in understanding this manual only.

A

Acute Toxicity– The ability of 

a substance to cause severe 

biological harm or death soon 

after a single exposure or dose. 

Also, any poisonous effect 

resulting from a single short-term 

exposure to a toxic substance.

B

Bacteria– Microscopic, unicellular 

organisms, some of which 

are pathogenic and can cause 

infection and disease in animals 

and humans. Most often, nonpathogenic bacteria, such as fecal 

coliform and enterococci, are used 

to indicate the likely presence 

of disease-causing, fecal-borne 

microbial pathogens.

Best Available Technology 

Economically Achievable (BAT)– 

Technology-based standard 

established by the Clean Water Act 

as the most appropriate means 

available on a national basis for 

controlling the direct discharge 

of toxic and nonconventional 

pollutants to navigable waters.

Best Conventional Pollutant Control 

Technology (BCT)– Technologybased standard for the discharge 

from existing industrial point 

sources of conventional 

pollutants including BOD, TSS, 

fecal coliform, pH, oil and grease. 

The BCT is established in light of 

a two-part “cost reasonableness” 

test, which compares the cost 

for an industry to reduce its 

pollutant discharge with the cost 

to a POTW for similar levels of 

reduction of a pollutant loading. 

The second test examines the 

cost-effectiveness of additional 

industrial treatment beyond 

BPT. EPA must find limits, which 

are reasonable under both tests 

before establishing them as BCT.

Biochemical Oxygen Demand 

(BOD)– A measure of the 

amount of oxygen consumed 

by microorganisms from the 

decomposition of organic 

material in water over a specified 

time period (usually 5 days, 

indicated as BOD5). The 

BOD5 value is used for many 

applications, most commonly to 

indicate the effects of sewage and 

other organic wastes on dissolved 

oxygen in water.

C

Chronic Toxicity– The capacity of 

a substance to cause long-term 

poisonous health effects in 

humans, animals, fish, and other 

organisms.

Clean Water Act– The Clean Water 

Act is an act passed by the 

U.S. Congress to control water 

pollution. It was formerly 

referred to as the Federal Water 

Pollution Control Act of 1972 or 

Federal Water Pollution Control 

Act Amendments of 1972 (P.L. 

92-500), 33 U.S.C. 1251 et. seq., 

as amended by: P.L. 96-483; P.L. 

97-117; P.L. 95-217, 97-117, 

97-440, and 100-04.
GL-2

Report to Congress on the Impacts and Control of CSOs and SSOs

Combined Sewer Overflow (CSO)– A 

discharge of untreated wastewater 

from a combined sewer system at 

a point prior to the headworks of 

a publicly owned treatment works 

(POTW). 

Combined Sewer System (CSS)– A 

wastewater collection system 

owned by a municipality (as 

defined by Section 502(4) of the 

Clean Water Act) that conveys 

domestic, commercial and 

industrial wastewater and storm 

water runoff through a single pipe 

system to a POTW. 

Concentrated Animal Feeding 

Operation (CAFO)– New 

and existing animal feeding 

operations of a sufficient size 

that are required to develop 

and implement a nutrient 

management plan as a condition 

of a NPDES permit (defined at 40 

CFR 122.23). 

Construction Grants Program– 

Federal assistance program 

authorized under Section 201 

of the Clean Water Act intended 

to assist with the development 

and implementation of waste 

treatment management plans and 

practices that will achieve the 

goals of the Act. 

Conventional Pollutants– As 

defined by the Clean Water Act, 

conventional pollutants include: 

BOD, TSS, fecal coliform, pH, and 

oil and grease.

D

Dissolved Oxygen (DO)– The 

oxygen freely available in water, 

vital to fish and other aquatic 

life and for the prevention of 

odors. DO levels are considered 

a most important indicator of a 

water body’s ability to support 

desirable aquatic life. Secondary 

and advanced waste treatment 

are generally designed to ensure 

adequate DO in waste-receiving 

waters. 

Diurnal– Relating to or occurring 

in a 24-hour period, or daily. A 

pattern that repeats itself over a 

daily cycle.

Dry Weather CSO– An unauthorized 

discharge from a combined sewer 

system that occurs during dry 

weather conditions.

Dry Weather SSO– A sanitary sewer 

overflow that occurs during dry 

weather conditions, most often as 

a result of blockages, line breaks, 

or mechanical/power failures in 

the collection system.

E

Effluent Limits– Restrictions 

established by a state or EPA 

on quantities, rates, and 

concentrations in municipal or 

industrial wastewater discharges. 

Environmental Impact– Any change 

to the environment, whether 

adverse or beneficial, wholly 

or partially resulting from an 

organization’s activities, products 

or services.

Eutrophic Condition– The presence 

of excess nutrients in a receiving 

water body. During the later 

stages of eutrophication the water 

body can become choked by 

abundant plant life due to higher 

levels of nutritive compounds 

such as nitrogen and phosphorus. 

F

Federal Advisory Committee– Any 

committee, board, commission, 

council, conference, panel, task 

force, or other similar group, 

or any subcommittee or other 

sub-group thereof (hereafter 

in this paragraph referred 

to as “committee”), which 

in— (A) established by statute 

or organization plan, or (B) 

established or utilized by the 

President; or (C) established or 

utilized by one or more agencies; 

in the interest of obtaining 

advise and recommendations 

for the President or one or more 

agencies or offices of the Federal 

Government, except that such 

term excludes (i) any committee 

that is composed wholly of fulltime, or permanent part-time, 

officers or employees of the 

Federal Government, and (ii) any 

committee that is created by the 

National Academy of Sciences of 

the National Academy of Public 

Administration. 

First Flush– The occurrence of higher 

concentrations of pollutants in 
 Glossary

GL-3

storm water or CSO discharges at 

the beginning of a storm.

Floatables and Trash– Visible buoyant 

or semi-buoyant solids including 

organic matter, personal hygiene 

items, plastics, styrofoam, paper, 

rubber, glass and wood. 

H

Headworks of a Wastewater Treatment 

Plant– The initial structures, 

devices and processes provided 

at a wastewater treatment plant 

including screening, pumping, 

measuring, and grit removal 

facilities. 

Human Health Impacts– Damage 

to the health of an individual or 

individuals due to a given exposure 

or a series of exposures.

I

Indicator Bacteria– Bacteria that 

are common in human waste. 

Indicator bacteria are not harmful 

in themselves but their presence is 

used to indicate the likely presence 

of disease-causing, fecal-borne 

microbial pathogens that are more 

difficult to detect. 

Infiltration– Storm water and 

groundwater that enter a sewer 

system through such means 

as defective pipes, pipe joints, 

connections, or manholes. 

(Infiltration does not include 

inflow).

Infiltration/Inflow (I/I)– The total 

quantity of water from both 

infiltration and inflow.

Inflow– Water, other than wastewater, 

that enters a sewer system from 

sources such as roof leaders, 

cellar drains, yard drains, area 

drains, foundation drains, drains 

from springs and swampy areas, 

manhole covers, cross connections 

between storm drains and sanitary 

sewers, catch basins, cooling 

towers, storm waters, surface 

runoff, street wash waters, or 

other drainage. (Inflow does not 

include infiltration).

L

Long-Term Control Plan (LTCP)– 

Water quality-based CSO control 

plan that is ultimately intended 

to result in compliance with 

the Clan Water Act. Long-term 

control plans should consider the 

site-specific nature of CSOs and 

evaluate the cost effectiveness of a 

range of controls.

M

Major Facility– Classification for 

wastewater treatment plants 

that are designed to discharge 

more than 1 mgd. Some facilities 

with smaller design flows are 

classified as major facilities 

when the NPDES authority 

deems it necessary for a specific 

NPDES permit to have a stronger 

regulatory focus. 

Microbial Pathogens– Minute life 

forms including bacteria, viruses 

and parasites that can cause disease 

in aquatic biota and illness or even 

death in humans.

Million Gallons per Day (mgd)– A 

unit of flow commonly used for 

wastewater discharges. One mgd is 

equivalent to a flow rate of 1.547 

cubic feet per second over a 24-

hour period.

Minor Facility– A classification for 

wastewater treatment plants that 

are designed to discharge less than 

1 mgd.

N

National Pollutant Discharge 

Elimination System (NPDES)– The 

national program for issuing, 

modifying, revoking and reissuing, 

terminating, monitoring and 

enforcing permits, and imposing 

and enforcing pretreatment 

requirements, under Sections 307, 

318, 402, and 405 of the Clean 

Water Act.

Nine Minimum Controls (NMC)– 

Technology-based CSO controls 

that do not require significant 

engineering studies or major 

construction.

Nutrient– Any substance assimilated by 

living things that promotes growth. 

The term is generally applied 

to nitrogen and phosphorus in 

wastewater, but is also applied to 

other essential and trace elements.
GL-4

Report to Congress on the Impacts and Control of CSOs and SSOs

O

Oxygen Depleting Substances– 

Materials including human waste 

and other organic matter that 

cause a loss of oxygen in water and 

wastewater, typically measured in 

terms of BOD5.

P

Parasites– Animals or plants that live 

in and obtain nutrients from a 

host organism of another species. 

Pathogenic– Capable of causing 

disease. 

Point Source– Any discernible, 

confined, and discrete conveyance, 

including but not limited 

to any pipe, ditch, channel, 

tunnel, conduit, well, discrete 

fixture, container, rolling stock, 

concentrated animal feeding 

operation, landfill leachate 

collection system, vessel, or 

other floating craft from 

which pollutants are or may be 

discharged.

Primary Treatment– First steps in 

wastewater treatment wherein 

screens and sedimentation tanks 

are used to remove most materials 

that float or will settle. 

Publicly Owned Treatment Works 

(POTW)– A treatment works, 

as defined by Section 212 of the 

Clean Water Act that is owned 

by a state or municipality. This 

definition includes any devices 

and systems used in the storage, 

treatment, recycling, and 

reclamation of municipal sewage 

or industrial wastes of a liquid 

nature. It also includes sewers, 

pipes, and other conveyances only 

if they convey wastewater to a 

POTW treatment plant [40 CFR 

§403.3].

Q

Sanitary Sewer Overflow (SSO)– An 

untreated or partially treated 

sewage release from a sanitary 

sewer system. 

Sanitary Sewer System (SSS)– A 

municipal wastewater collection 

system that conveys domestic, 

commercial and industrial 

wastewater, and limited amounts 

of infiltrated ground water and 

storm water, to a POTW. Areas 

served by sanitary sewer systems 

often have a municipal separate 

storm sewer system to collect and 

convey runoff from rainfall and 

snowmelt. 

Satellite Sewer Systems– Combined 

or separate sewer systems that 

convey flow to a publicly owned 

treatment works owned and 

operated by a separate entity.

Secondary Treatment– 

Technology-based requirements 

for direct discharging 

municipal sewage treatment 

facilities. Standard is based 

on a combination of physical 

and biological processes for 

the treatment of pollutants in 

municipal sewage. Standards 

are expressed as a minimum 

level of effluent quality in terms 

of: BOD5, suspended solids, 

and pH (except as provided 

for special considerations and 

treatment equivalent to secondary 

treatment).

State Revolving Fund Program– A 

federal program created by the 

Clean Water Act Amendments in 

1987 that offers low interest loans 

for wastewater treatment projects.

T

Technology-Based Effluent Limit– 

Effluent limitations applicable to 

direct and indirect sources, which 

are developed on a category-bycategory basis using statutory 

factors, not including water quality 

effects.

Total Suspended Solids (TSS)– A 

measure of the filterable solids 

present in a sample of water or 

wastewater (as determined by the 

method specified in 40 CFR Part 

136).

Toxics– Materials contaminating the 

environment that cause death, 

disease, and/or birth defects in 

organisms that ingest or absorb 

them. The quantities and length of 

exposure necessary to cause these 

effects can vary widely.

W

Water Quality Standard– A law 

or regulation that consists of 

the beneficial use or uses of a 

waterbody, the numeric and 
 Glossary

GL-5

narrative water quality criteria that 

are necessary to protect the use or 

uses of that particular waterbody, 

and an antidegradation statement.

Water Quality-Based Effluent 

Limitations– Effluent limitations 

applied to dischargers when 

technology-based limitations 

insufficient to result in the 

attainment of water quality 

standards. Usually applied to 

discharges into small streams. 

Waters of the United States– All waters 

that are currently used, were used 

in the past, or may be susceptible 

to use in interstate or foreign 

commerce, including all waters 

subject to the ebb and flow of the 

tide. Waters of the United States 

include but are not limited to all 

interstate waters and intrastate 

lakes, rivers, streams (including 

intermittent streams), mudflats, 

sand flats, wetlands, sloughs, 

prairie potholes, wet meadows, 

play lakes, or natural ponds. [See 

40 CFR §122.2 for the complete 

definition.]

Watershed Approach– An initiative 

that promotes integrated 

solutions to address surface 

water, groundwater, and habitat 

concerns on a watershed basis. 

It is a decision-making process 

that reflects a common strategy 

for information collection 

and analysis and a common 

understanding of the roles, 

priorities and responsibilities of all 

stakeholders within a watershed.

Wet Weather Event– A discharge 

from a combined or sanitary 

sewer system that occurs in direct 

response to rainfall or snowmelt. 

Wet Weather SSO– A sanitary sewer 

overflow that results from the 

introduction of excessive inflow 

and infiltration into a sanitary 

sewer system, such that the total 

flow exceeds conveyance capacity.
of the Combined Sewer Overflow 

Control Policy (EPA 2001a). This 

second Report to Congress fulfills the 

requirement that: 

Not later than 3 years after 

the date of enactment of this 

Act, the Administrator of the 

Environmental Protection Agency 

shall transmit to Congress a report 

summarizing– 

(A) the extent of human health 

and environmental impacts 

caused by municipal combined 

sewer overflows and sanitary 

sewer overflows, including the 

location of discharges causing such 

impacts, the volume of pollutants 

discharged, and the constituents 

discharged; 

(B) the resources spent by 

municipalities to address these 

impacts; and

(C) an evaluation of the 

technologies used by municipalities 

to address these impacts.

Further, the technology information 

compiled for this Report to 

Congress will serve as a key element 

in developing the technology 

Executive Summary

The U.S. Environmental 

Protection Agency (EPA or 

“the Agency”) is transmitting 

this Report to Congress on the extent 

of human health and environmental 

impacts caused by municipal 

combined sewer overflows (CSOs) 

and sanitary sewer overflows (SSOs), 

including the location of discharges 

causing such impacts, the volume of 

pollutants discharged, the constituents 

discharged, the resources spent 

by municipalities to address these 

impacts, and the technologies used 

by municipalities to address these 

impacts. 

Overview and Background

Why is EPA Preparing this Report?

I

n the Consolidated Appropriations 

Act for Fiscal Year 2001, P.L. 106-

554 (or “2000 amendments to the 

Clean Water Act”), Congress requested 

two reports and the development of 

a technology clearinghouse. The first 

report was transmitted to Congress in 

December 2001 as Report to Congress–

Implementation and Enforcement 

ES-1

Report to Congress on the Impacts 

and Control of CSOs and SSOs

SSOs include untreated discharges from SSSs 

that reach waters of the United States, as 

well as overflows out of manholes and onto 

city streets, sidewalks, and other terrestrial 

locations.

Photo: EPA
ES-2

Report to Congress on the Impacts and Control of CSOs and SSOs

clearinghouse requested by P.L. 106-

554.

What are CSOs and Why are They a 

Problem?

Two types of public sewer systems 

predominate in the United States: 

combined sewer systems (CSSs) and 

sanitary sewer systems (SSSs). CSSs 

were among the earliest sewer systems 

constructed in the United States and 

were built until the first part of the 

20th century. As defined in the 1994 

CSO Control Policy (EPA 1994a), a 

CSS is:

A wastewater collection system 

owned by a state of municipality 

(as defined by Section 502(4) 

of the Clean Water Act) that 

conveys domestic, commercial, and 

industrial wastewaters and storm 

water runoff through a single 

pipe system to a publicly-owned 

treatment works (POTW).

During wet weather events (e.g., 

rainfall or snowmelt), the combined 

volume of wastewater and storm water 

runoff entering CSSs often exceeds 

conveyance capacity. Most CSSs are 

designed to discharge flows that 

exceed conveyance capacity directly to 

surface waters, such as rivers, streams, 

estuaries, and coastal waters. Such 

events are called CSOs.

A CSO is defined as:

The discharge from a CSS at 

a point prior to the POTW 

treatment plant.

Some CSO outfalls discharge 

infrequently, while others discharge 

every time it rains. Overflow 

frequency and duration varies from 

system to system and from outfall to 

outfall within a single CSS. Because 

CSOs contain untreated wastewater 

and storm water, they contribute 

microbial pathogens and other 

pollutants to surface waters. CSOs 

can impact the environment and 

human health. Specifically, CSOs 

can cause or contribute to water 

quality impairments, beach closures, 

shellfish bed closures, contamination 

of drinking water supplies, and other 

environmental and human health 

problems. 

What are SSOs and Why are They a 

Problem?

Since the first part of the 20th century, 

municipalities in the United States 

have generally constructed SSSs. 

For the purposes of this Report to 

Congress, an SSS is:

A municipal wastewater collection 

system that conveys domestic, 

commercial, and industrial 

wastewater, and limited amounts 

of infiltrated groundwater and 

storm water, to a POTW. 

SSSs are not designed to collect large 

amounts of storm water runoff from 

precipitation events. Areas served by 

SSSs often have a municipal separate 

storm sewer system (MS4) to collect 

and convey runoff from rainfall and 

snowmelt. 

Untreated or partially treated 

discharges from SSSs are commonly 

referred to as SSOs. SSOs have a 

variety of causes including blockages, 

line breaks, sewer defects that allow 

excess storm water and groundwater 

to overload the system, lapses in sewer 

system operation and maintenance, 

inadequate sewer design and 
 Executive Summary

ES-3

construction, power failures, and 

vandalism. An SSO is defined as:

An untreated or partially treated 

sewage release from a SSS.

The discussion of SSOs in this 

report, including national estimates 

of SSO volume and frequency, does 

not account for discharges from 

points after the headworks of the 

treatment plant, regardless of the 

level of treatment, or backups into 

buildings caused by problems in the 

publicly-owned portion of the SSS. 

EPA found that backups into buildings 

are not widely tracked by permitting 

authorities.

Generally speaking, SSOs can occur 

at any point in an SSS, during dry 

weather or wet weather. SSOs include 

overflows that reach waters of the 

United States. SSOs also include 

overflows out of manholes and onto 

city streets, sidewalks, and other 

terrestrial locations. A limited number 

of municipalities have SSOs that 

discharge from fixed points within 

their sewer system. SSSs can back 

up into buildings, including private 

residences. When sewage backups are 

caused by problems in the publiclyowned portion of an SSS, they are 

considered SSOs.

SSOs can range in volume from 

one gallon to millions of gallons. 

The microbial pathogens and other 

pollutants present in SSOs can 

cause or contribute to water quality 

impairments, beach closures, shellfish 

bed closures, contamination of 

drinking water supplies, and other 

environmental and human health 

problems. 

What Statutory and Regulatory 

Framework Applies to CSOs and 

SSOs?

With extensive and documented 

stakeholder support, EPA issued 

its final CSO Control Policy on 

April 19, 1994 (59 FR 18688). The 

CSO Control Policy “represents a 

comprehensive national strategy to 

ensure that municipalities, permitting 

authorities, water quality standards 

authorities, and the public engage in a 

comprehensive and coordinated effort 

to achieve cost-effective CSO controls 

that ultimately meet appropriate 

health and environmental objectives.”

When the CSO Control Policy was 

released, many stakeholders, key 

members of Congress, and EPA 

advocated for it to be endorsed in 

the Clean Water Act to ensure its full 

implementation. In the Consolidated 

Appropriations Act for Fiscal Year 

2001, P.L. 106-554, Congress stated 

that:

...each permit, order, or decree 

issued pursuant to this Act after 

the date of enactment of this 

subsection for a discharge from a 

municipal combined storm and 

sanitary sewer shall conform to the 

CSO Control Policy signed by the 

Administrator on April 11, 1994.

SSOs that reach waters of the United 

States are point source discharges, 

and, like other point source discharges 

from municipal SSSs, are prohibited 

unless authorized by an National 

Pollutant Discharge Elimination 

System (NPDES) permit. Moreover, 

SSOs, including those that do not 

reach waters of the United States, may 

be indicative of improper operation 

and maintenance of the sewer system, 

CSO outfalls were constructed in a wide 

variety of shapes and sizes, including the 

large box culvert shown here. In general, CSO 

outfalls discharge directly to receiving waters.

Photo: City of Wilmington, DE
ES-4

Report to Congress on the Impacts and Control of CSOs and SSOs

and thus may violate NPDES permit 

conditions. 

What Methodology Did EPA Use 

for this Report to Congress?

The basic study approach for this 

report was to divide the congressional 

request into a series of discrete study 

questions, then to identify and collect 

existing data appropriate to each study 

question. This effort entailed:

● Reviewing existing data collected 

by EPA and other federal agencies, 

state and local governments, and 

non-governmental organizations;

● Searching the existing literature 

for environmental and human 

health impacts attributable to 

CSOs and SSOs, as well as the cost 

and technologies used to control 

CSOs and SSOs;

● Organizing forums to work 

with EPA and external experts 

and stakeholders on the specific 

questions addressed in this report;

● Updating, verifying, and 

establishing latitude and longitude 

coordinates for the inventory of 

CSO outfalls developed as part 

of EPA’s 2001 Report to Congress–

Implementation and Enforcement 

of the Combined Sewer Overflow 

Control Policy;

● Collecting SSO event information 

from those states that compile 

data on the volume, frequency, 

and cause of SSO events in 

electronic data management 

systems;

● Developing national estimates 

of the volume and frequency of 

CSOs and SSOs; and

● Developing simple models to 

estimate environmental and 

human health impacts where there 

was an absence of direct causeand-effect data.

EPA emphasized the collection, 

compilation, and analysis of existing 

data for this report. This effort allowed 

the Agency to expand its knowledge 

about CSOs and SSOs, and to identify 

gaps in the existing data and in 

current systems that provide such data. 

This Report to Congress recognizes 

that EPA should and will continue 

to investigate the environmental and 

human health challenges posed by wet 

weather.

Response to Congress

EPA’s response to the 

congressional request set forth 

in P.L. 106-554 is presented 

below, organized into five themes 

addressing both CSOs and SSOs: 

● Characterization

● Environmental impacts

● Human health impacts

● Control technologies

● Resources spent

What are the Location, Volume of 

Pollutants, and Constituents of 

CSOs and SSOs?

Currently, 828 NPDES permits 

authorize discharges from 9,348 CSO 

outfalls in 32 states (including the 

District of Columbia). As shown in 

Figure ES.1, most CSSs are located in 

the Northeast and Great Lakes regions. 
 Executive Summary

ES-5

The estimated volume of CSO 

discharged nationwide is 850 billion 

gallons per year. The number of 

CSSs and CSO permits has decreased 

slightly since publication of EPA’s 2001

Report to Congress–Implementation 

and Enforcement of the Combined 

Sewer Overflow Control Policy. Further, 

the percentage of CSO long-term 

control plans (LTCPs) that have been 

submitted to permitting authorities 

has increased from 34 to 59 percent. 

This represents progress in controlling 

CSOs in the United States.

As shown in Figure ES.2, SSSs are 

located across the country. EPA’s 

2000 Clean Watersheds Needs Survey 

(CWNS) Report to Congress reported 

15,582 municipal SSSs with wastewater 

treatment facilities; an additional 

4,846 satellite SSSs collect and 

transport wastewater flows to regional 

wastewater treatment facilities. SSOs 

have the potential to occur in any of 

these SSSs. 

EPA estimates that between 23,000 

and 75,000 SSO events occur per year 

in the United States, discharging a 

total volume of three to 10 billion 

gallons per year. This estimate does 

not account for discharges occurring 

after the headworks of the treatment 

plant or backups into buildings caused 

by problems in the publicly-owned 

portion of an SSS. The majority 

of SSO events are caused by sewer 

blockages that can occur at any time. 

The majority of SSO volume appears 

to be related to events caused by wet 

weather and excessive inflow and 

infiltration. 

Figure ES.1

National Distribution 

of CSSs

The majority of CSO permits are 

held by communities located in 

the Northeast and Great Lakes 

regions.
ES-6

Report to Congress on the Impacts and Control of CSOs and SSOs

A comparison of the estimated annual 

CSO and SSO discharge volume with 

treated wastewater is presented in 

Table ES.1.

CSOs and SSOs contain untreated 

wastewater, and therefore the pollutant 

concentration depends on the service 

population, the characteristics of the 

sewer system, weather conditions, any 

treatment provided, and other factors. 

The principal pollutants present in 

CSOs and SSOs are:

● Microbial pathogens

● Oxygen depleting substances

● Total suspended solids (TSS)

● Toxics

● Nutrients

● Floatables and trash

Pollutant concentrations in CSOs 

and SSOs vary substantially, not only 

from community to community and 

event to event, but also within a given 

event. CSOs and SSOs contribute 

pollutant loadings to waterbodies 

where discharges occur. It is important 

to note that waterbodies also receive 

pollutants of the types found in CSOs 

and SSOs from other sources such as 

storm water runoff.

Figure ES.2

National Distribution 

of SSSs 

SSSs are widely distributed 

across the United States, serving 

municipalities in all 50 states. 

Approximately 75 percent of SSSs 

are shown, where location data 

(latitude/longitude) were available 

from EPA’s Permits Compliance 

System.
Executive Summary

ES-7

What is the Extent of 

Environmental Impacts Caused by 

CSOs and SSOs?

Pollutant concentrations in CSOs 

and SSOs may be sufficient to cause a 

violation of water quality standards, 

precluding the attainment of one or 

more of the designated uses (e.g., 

swimming, boating, fishing) for the 

waterbody.

CSOs and wet weather SSOs discharge 

simultaneously with storm water 

runoff and other nonpoint sources of 

pollution. EPA recognizes that this can 

make it difficult to identify and assign 

specific cause-and-effect relationships 

between CSOs, SSOs, and observed 

water quality problems. In addition, 

EPA found that the identification 

and quantification of environmental 

impacts caused by CSOs and SSOs 

at the national level is difficult 

because there is no comprehensive 

national data system for tracking the 

occurrence and impacts of CSOs and 

SSOs.

Nevertheless, CSOs and SSOs can 

by themselves affect the attainment 

of designated uses and cause water 

quality standards violations. Average 

bacteria concentrations in CSOs and 

SSOs may be several thousand times 

greater than water quality standard 

criteria, and waterbodies that receive 

CSO and SSO discharges may lack 

sufficient dilution or assimilative 

capacity. Based on modeling analysis 

conducted by EPA and summarized in 

Table 5.6 of this report, water quality 

standards are projected to be violated 

frequently, even in the absence 

of other sources of fecal coliform 

pollution, where discharges from SSO 

events include more concentrated 

wastewater (e.g., SSOs with limited 

I/I) or when SSOs discharge to smaller 

receiving waters such as a stream or 

small tributary.

As shown in Figure ES.3, CSOs were 

responsible for 1 percent of reported 

advisories and closings, and 2 percent 

of advisories and closings that had 

a known cause during the 2002 

swimming season. SSOs were reported 

to be responsible for 6 percent of 

reported advisories and closings, and 

12 percent of advisories and closings 

having a known cause. Studies also 

identify CSOs and SSOs as a cause 

of shellfish harvesting prohibitions 

and restrictions in classified shellfish 

growing areas. 

The environmental impacts of CSOs 

and SSOs are most apparent at the 

local level, and as the result of large 

or recurrent discharges. Examples of 

localized impacts due to CSOs and 

SSOs include:

Source Annual Discharge Volume Table ES.1

(billion gallons)

Treated wastewatera 11,425

CSOb 850

SSOc 3 - 10

a EPA 2000a

b GPRACSO model, Section 4.5.1 of this report

c Section 4.7.4 of this report

Estimated Annual 

Discharge Volumes 

On an annual basis, the volume 

of CSO and SSO discharged is a 

proportionally small amount 

compared to the total fl ow 

processed at municipal treatment 

facilities.
ES-8

Report to Congress on the Impacts and Control of CSOs and SSOs

● The City of Indianapolis assessed 

receiving waters in the city and 

ranked CSOs high in importance 

relative to other sources of 

pollution.

● The State of North Carolina has 

documented fish kills attributed to 

SSOs since 1997.

● The State of New Jersey closed 

over 30,000 acres of classified 

shellfish growing areas in the 

Raritan Bay area due to a large 

SSO in 2003.

What is the Extent of Human 

Health Impacts Caused by CSOs 

and SSOs?

Microbial pathogens and toxics can 

be present in CSOs and SSOs at levels 

that pose risks to human health. 

Human health impacts occur when 

people become ill due to contact with 

water or ingestion of water or shellfish 

that have been contaminated by CSO 

or SSO discharges. In addition, CSSs 

and SSSs can back up into buildings, 

including private residences. These 

discharges provide a direct pathway 

for human contact with untreated 

wastewater. Exposure to land-based 

SSOs typically occurs through the 

skin via direct contact. The resulting 

diseases are often similar to those 

associated with exposure through 

drinking water and swimming (e.g., 

gastroenteritis), but may also include 

illness caused by inhaling microbial 

pathogens.

Although it is clear that CSOs 

and SSOs contain disease-causing 

pathogens and other pollutants, EPA 

has limited information on actual 

human health impacts occurring as a 

result of CSO and SSO events. Further, 

CSOs and wet weather SSOs also tend 

to occur at times (e.g., storm events) 

when exposure potential may be lower. 

Identification and quantification 

of human health impacts caused 

by CSOs and SSOs at the national 

Figure ES.3

Sources of Pollution 

Resulting in Swimming 

Beach Advisories and 

Closings (EPA 2003a)

EPA’s Beaches Environmental 

Assessment and Coastal (BEACH) 

Program conducts an annual survey 

of the nation’s swimming beaches. 

During the 2002 swimming season, 

CSOs and SSOs (including sewer 

line blockages and breaks) were 

responsible for 1 and 6 percent of 

reported closings and advisories, 

respectively.

43

21

11

9

6

4

3

2

1

0 10 20 30 40 50

Unknown

Storm water runoff

Wildlife

Other

Septic system

Boat discharge

SSO

POTW

CSO

Pollution Sources

Percent
Executive Summary

ES-9

level is difficult due to a number of 

factors, including under-reporting and 

incomplete tracking of waterborne 

illness, contributions of pollutants 

from other sources, and the lack of a 

comprehensive national data system 

for tracking the occurrence and 

impacts of CSOs and SSOs. As an 

alternative to direct data on human 

health impacts, EPA modeled the 

annual number of gastroenteritis 

cases potentially occurring as a result 

of exposure to water contaminated 

by CSOs and SSOs at BEACH survey 

beaches. As shown in Table 6.6, 

EPA found that CSOs and SSOs are 

estimated to cause between 3,448 and 

5,576 illnesses annually at the subset 

of recreational areas included in the 

analysis.

What Technologies Have 

Municipalities Used to Reduce the 

Impacts of CSOs and SSOs?

Municipalities have many options in 

selecting technologies to reduce the 

impacts of CSOs and SSOs. These 

technologies range from large-scale 

structural projects (e.g., wet weather 

storage facilities) to operation and 

maintenance practices (e.g., sewer 

cleaning). Technology selection is 

determined by characteristics of the 

sewer system, problems identified in 

the sewer system, performance goals 

established for the sewer system, 

resources available, and other sitespecific considerations.

Municipalities employ a wide variety 

of technologies and operating 

practices to maintain existing 

infrastructure, minimize the 

introduction of unnecessary waste 

and flow into the sewer system, 

increase capture and treatment of 

wet weather flow reaching the sewer 

system, and minimize the impact of 

any subsequent discharges on the 

environment and human health. For 

this Report to Congress, technologies 

used to address CSOs and SSOs 

have been grouped into five broad 

categories:

● Operation and maintenance 

practices

● Collection system controls

● Storage facilities

● Treatment technologies

● Low-impact development 

techniques

EPA, states, and municipalities have 

made progress in developing tools and 

strategies for reducing the frequency 

and volume of CSOs and SSOs. 

Much remains to be done, however, 

to fully realize the objectives of the 

Clean Water Act and the CSO Control 

Policy. Municipalities have suggested 

that limited resources prevent them 

from acquiring and implementing 

technologies as quickly as they and 

regulatory agencies would prefer.

What Resources Have 

Municipalities Spent to Address 

the Impacts of CSOs and SSOs?

Municipal resources used to address 

CSOs and SSOs are documented in 

different ways. EPA’s estimates of 

municipal CSO expenditures rely 

on requests for Clean Water State 

Revolving Loan Fund (CWSRF) 

loans and on documents submitted 
ES-10

Report to Congress on the Impacts and Control of CSOs and SSOs

to EPA’s CWNS, which include CSO 

LTCPs and other facility planning 

documents. In addition, EPA uses a 

cost curve methodology to estimate 

costs for communities with CSSs 

that do not submit documentation. 

In communities served by SSSs, SSO 

control expenditures are generally 

a combination of general operation 

and maintenance (O&M) and 

capital expenditures. In total, EPA 

documented expenditures of more 

than $6 billion on CSO control 

(through 2002) and at least $4 billion 

on SSO control (1998-2002). EPA’s 

2000 CWNS estimated that at least an 

additional $50.6 billion is required to 

capture no less than 85 percent of the 

CSO by volume, and an additional 

$88.8 billion is required to control 

SSOs over the next 20 years (EPA 

2003b).

What Actions Should be Taken to 

Reduce the Impacts of CSOs and 

SSOs?

In its preparation of this report, EPA 

found that: 

Maintaining and improving the 

integrity of the nation’s wastewater 

infrastructure will protect the high 

level of environmental quality and 

public health enjoyed in the United 

States. Proper O&M of the nation’s 

sewers is integral to ensuring that 

wastewater is collected, transported, 

and treated at POTWs; and to 

reducing the volume and frequency 

of CSO and SSO discharges. Many 

existing structural and non-structural 

technologies are well suited for 

CSO and SSO control. Emerging 

technologies and innovative practices 

hold promise for even greater 

reductions in pollution. Municipal 

owners and operators of sewer systems 

and wastewater treatment facilities 

need to manage their assets effectively 

and implement new controls, where 

necessary, as this infrastructure 

continues to age. 

The impacts of CSOs and SSOs are a 

concern at the local watershed level. 

CSOs and SSOs are two among many 

sources of pollutants that contribute 

to urban water quality problems. 

The watershed approach is central 

to water quality assessments and the 

identification of control strategies 

must include all sources of pollution 

affecting water quality. The presence 

of sewer systems in most developed 

watersheds nationwide underscores 

the importance of considering 

potential SSOs impacts on water 

quality. Similarly, the presence of 

CSOs in 32 states places them in 

many watersheds across the country. 

EPA, states, and municipalities should 

strive toward better integration of 

wet weather programs with other 

NPDES, compliance assistance, 

and enforcement activities. Better 

integration of programs and activities 

at the watershed level will provide 

economies of scale with respect to 

monitoring and reporting, protecting 

water quality, and reducing the 

impacts of CSOs and SSOs. 

Improved monitoring and reporting 

programs would provide better 

data for decision-makers on CSO 

and SSO control. Better tracking 

of environmental impacts and the 

incidence of waterborne disease would 

increase national understanding of 

the environmental and human health 

impacts associated with CSOs, SSOs, 
Executive Summary

ES-11

and other sources of pollution. Use 

of standardized reporting formats 

for information on the occurrence 

and control of CSOs and SSOs would 

enable EPA, states, and others to track 

pollutant loads and the performance 

of controls. Recent EPA efforts such 

as WATERS (Watershed Assessment, 

Tracking, and Environmental 

ResultS) work to unite national 

water quality information that was 

previously available only from several 

independent and unconnected 

databases. EPA will continue to work 

to improve the information available.

The success that the nation has 

achieved in improving water quality 

since passage of the Clean Water Act is 

due to the collective efforts of federal 

and state agencies, municipalities, 

industry, non-governmental 

organizations, and citizens. Continued 

cooperation among these groups 

is essential to meet the challenges 

to clean water that lie ahead. As 

described in this Report to Congress, 

numerous pollutant sources threaten 

the environment and human health, 

but establishing direct cause-andeffect relationships is often difficult. 

The information necessary to manage 

water quality problems comes from 

many sources. EPA recognizes the 

value of working with stakeholders 

and has pursued a strategy of extensive 

stakeholder participation in its policymaking on CSO and SSO issues. 

Likewise, as communities continue 

to implement CSO and SSO controls, 

further cooperation with municipal, 

industry, and environmental 

organizations is essential to ensure 

successful development and 

implementation of environmental 

programs.
Typical CSO outfall discharge following a 

storm.

Photo: NJ Department of Environmental Protection

impacts, the volume of pollutants 

discharged, and the constituents 

discharged;

(B) the resources spent by 

municipalities to address these 

impacts; and

(C) an evaluation of the 

technologies used by municipalities 

to address these impacts.

EPA prepared this report between 

March 2002 and July 2004. During this 

time, EPA developed a methodology; 

collected data from federal, state, and 

local sources; performed analyses; 

coordinated with stakeholders; and 

wrote this report. Data collection was 

completed in early fall 2003, and select 

analyses were updated in mid-2004. 

This report is the second Report to 

Congress required as part of P.L. 106-

554. The first report was EPA’s Report 

to Congress–Implementation and 

Enforcement of the Combined Sewer 

Overflow Control Policy (EPA 833-R01-003).

P.L. 106-554 also requires EPA to 

develop and maintain a clearinghouse 

of technologies for addressing the 

impacts of CSO and SSO discharges. 

Chapter 1

This Report to Congress presents 

U.S. Environmental Protection 

Agency’s (EPA or “the Agency”) 

most recent and comprehensive 

characterization of combined sewer 

overflows (CSOs) and sanitary sewer 

overflows (SSOs), including the extent 

of human health and environmental 

impacts caused by CSOs and SSOs, 

the resources spent by municipalities 

to address these impacts, and the 

technologies used by municipalities to 

address these impacts. This report has 

been prepared in direct response to a 

congressional mandate established in 

December 2000 in the Consolidated 

Appropriations Act for Fiscal Year 

2001, P.L. 106-554, which requires 

that:

Not later than 3 years after 

the date of enactment of this 

Act, the Administrator of the 

Environmental Protection Agency 

shall transmit to Congress a report 

summarizing–

(A) the extent of human health 

and environmental impacts 

caused by municipal combined 

sewer overflows and sanitary 

sewer overflows, including the 

location of discharges causing such 

1-1

1.1 What are CSOs and 

SSOs?

1.2 How is this Report 

Organized?

Introduction

In this chapter:
1-2

Report to Congress on the Impacts and Control of CSOs and SSOs

EPA expects that information 

provided in this Report to Congress 

will be the basis for the clearinghouse 

when it is developed.

1.1 What are CSOs and SSOs?

I

n the United States, two types of 

public sewer systems predominate: 

combined sewer systems (CSSs) 

and sanitary sewer systems (SSSs).

A CSS is a wastewater collection 

system owned by a municipality (as 

defined by Section 502(4) of the Clean 

Water Act) that conveys domestic, 

commercial, and industrial wastewater 

and storm water runoff through a 

single pipe system to a publicly-owned 

treatment works (POTW).

An SSS is a wastewater collection 

system owned by a municipality that 

conveys domestic, commercial, and 

industrial wastewater, and limited 

amounts of infiltrated groundwater 

and storm water to a POTW. Areas 

served by SSSs often have a municipal 

separate storm sewer system (MS4) to 

collect and convey runoff from rainfall 

and snowmelt. 

1.1.1 CSOs

The term “CSO” refers to a discharge 

from a CSS at a point prior to the 

POTW treatment plant. CSOs 

generally occur in response to wet 

weather events; that is, during and 

following periods when rainfall or 

snowmelt drain to the CSS. Most CSSs 

are designed to discharge flows that 

exceed conveyance capacity directly to 

receiving waterbodies, such as rivers, 

streams, estuaries, and coastal waters. 

CSSs can also back up into buildings, 

including private residences. When 

backups are caused by problems in 

the publicly owned portion of a CSS, 

they are considered unauthorized 

discharges. 

CSO discharges include a mix of 

domestic, commercial, and industrial 

wastewater, and storm water runoff. 

As such, CSO discharges contain 

human, commercial, and industrial 

wastes as well as pollutants washed 

from streets, parking lots, and other 

surfaces. EPA’s 1994 CSO Control 

Policy (59 FR 18688) provides a 

comprehensive national strategy 

to ensure municipalities, NPDES 

permitting authorities, water quality 

standards authorities, EPA, and the 

public to engage in a coordinated 

planning effort to achieve costeffective CSO controls that ultimately 

meet the requirements of the Clean 

Water Act (EPA 1994a). The text of 

the CSO Control Policy is provided 

in Appendix A. In 2000, P.L. 106-554 

amended the Clean Water Act by 

adding the following to Section 402:

(q)(1) Each permit, order, or 

decree issued pursuant to this Act 

after the date of enactment of this 

subsection for a discharge from a 

municipal combined storm and 

sanitary sewer shall conform to the 

CSO Control Policy signed by the 

Administrator on April 11, 1994.

EPA’s Report to Congress–

Implementation and Enforcement 

of the Combined Sewer Overflow 

Control Policy identified CSSs in 

32 states (including the District of 

Columbia) across nine EPA regions 

(EPA 2001a). As of July 2004, those 32 

states had issued 828 permits to 746 

communities.
 Chapter 1—Introduction

1-3

1.1.2 SSOs

The term “SSO” refers to untreated or 

partially treated sewage releases from 

an SSS.

SSOs have a variety of causes, 

including, but not limited to, severe 

weather, blockages, line breaks, 

power failures, lapses in sewer 

system operation and maintenance, 

inadequate sewer design and 

construction, and vandalism. SSO 

discharges typically contain a mix of 

domestic, commercial, and industrial 

waste. SSOs can pose challenging 

public health and environmental 

issues when they occur. 

SSOs include those overflows that 

reach waters of the United States, as 

well as overflows out of manholes 

and onto city streets, sidewalks, and 

other terrestrial locations. A limited 

number of municipalities have regular 

SSO discharges from fixed points 

within the sewer system. SSSs can back 

up into buildings, including private 

residences. When backups are caused 

by problems in the publicly-owned 

portion of an SSS, they are considered 

SSOs.

SSOs that reach waters of the United 

States are point source discharges, 

and, like other point source discharges 

from municipal SSSs, are prohibited 

unless authorized by an National 

Pollutant Discharge Elimination 

System (NPDES) permit. Moreover, 

SSOs, including those that do not 

reach waters of the United States, may 

be indicative of improper operation 

and maintenance of the sewer 

system, and thus may violate NPDES 

permit conditions. EPA has focused 

on SSO problems with compliance 

assistance and enforcement activities 

in accordance with the Compliance 

and Enforcement Strategy Addressing 

Combined Sewer Overflows and 

Sanitary Sewer Overflows, issued 

April 27, 2000 (EPA 2000b). In 

addition, EPA is evaluating options 

for improving NPDES permit 

requirements for SSOs and municipal 

SSSs.

EPA’s 2000 Clean Watersheds Needs 

Survey Report to Congress reported 

15,582 municipal SSSs providing 

wastewater collection, conveyance, 

and treatment are presently operating 

within the 50 states and the District 

of Columbia (EPA 2003b). EPA also 

identified an additional 4,846 satellite 

SSSs providing only collection and 

conveyance. Not all of these hold 

NPDES permits (EPA 2003b). If not 

properly maintained, satellite systems 

have the potential to have an SSO 

or to cause an SSO in downsewer 

systems.

1.2 How is this Report 

Organized?

The purpose of this report is 

to respond to Congress with 

a current characterization of 

the volume, frequency, and location 

of CSOs and SSOs, the extent of 

human health and environmental 

impacts caused by CSOs and SSOs, 

the resources spent by municipalities 

to address these impacts, and the 

technologies used to address these 

impacts. The report contains 10 

chapters; the content and purpose of 

which are summarized below. 

Since the passage of the Clean Water Act in 

1972, all levels of government have made 

substantial investments in the nation’s 

wastewater infrastructure.

Photo: City of Chicago
1-4

Report to Congress on the Impacts and Control of CSOs and SSOs

Chapter 2 summarizes the history of 

regulatory efforts to control CSOs 

and SSOs. It describes federal water 

pollution control legislation, paying 

particular attention to Clean Water Act 

requirements for secondary treatment 

and pretreatment, the Construction 

Grants Program, and amendments to 

the Clean Water Act made by P.L. 106-

554. 

Chapter 3 describes the methodology 

used to develop this Report to 

Congress. In order to report on 

impacts, resources spent to address 

impacts, and the technologies 

applied to control CSOs and SSOs, 

EPA designed and implemented a 

comprehensive approach to gather 

the necessary data and information. 

This effort included an extensive 

literature search, site visits to EPA 

regional offices and states, interviews 

with state and local officials, an 

experts workshop, and outreach to 

stakeholders. 

Chapter 4 characterizes the pollutants 

present in CSO and SSO discharges 

and identifies other watershed sources 

of these pollutants. This chapter 

describes the universe of CSS and 

SSS permittees under the NPDES 

program. The chapter also summarizes 

information on the volume, frequency, 

and location of CSOs and SSOs, as 

well as the most common causes of 

SSOs.

Chapter 5 describes the types of 

environmental impacts attributable 

to CSO and SSO discharges in terms 

of water quality standards violations 

and lost uses (i.e., closures of shellfish 

beds and beaches). This chapter also 

discusses the extent of environmental 

impacts caused or contributed to by 

CSO and SSO discharges. National 

data are used to describe the extent of 

environmental impacts. State and local 

data are used to illustrate site-specific 

examples of impacts.

Chapter 6 describes waterborne 

diseases and other potential human 

health impacts associated with 

exposure to the pollutants found 

in CSO and SSO discharges. The 

chapter summarizes mechanisms 

at the federal, state, and local levels 

for reporting and tracking these 

impacts. In addition, the chapter 

describes different techniques used to 

communicate the risk associated with 

exposure to CSO and SSO discharges 

and how these risks can be minimized 

or prevented.

Chapter 7 summarizes federal and 

state activities to regulate CSOs and 

SSOs to minimize impacts associated 

with discharges. The chapter reports 

on the issuance of permits and 

other enforceable orders requiring 

control of CSOs or elimination of 

SSOs. This chapter also summarizes 

technical assistance provided by 

federal and state governments to assist 

municipalities in controlling CSOs 

and SSOs.

Chapter 8 surveys the technologies 

most widely used to control CSO and 

SSO discharges, including: operation 

and maintenance practices, sewer 

system controls, storage facilities, 

treatment technologies, and lowimpact development techniques. 

The chapter also describes effective 

combinations of technologies as 

well as emerging practices that show 

particular promise in the control of 

CSOs and SSOs.

Sewer separation is one of the most often 

used CSO controls. The separation project 

shown here is underway in Louisville, 

Kentucky.

Photo: Louisville-Jefferson County Metropolitan Sewer District
 Chapter 1—Introduction

1-5

Chapter 9 provides information on 

the resources spent by municipalities 

to control CSO and SSO discharges, 

including a discussion of the 

national investment in wastewater 

infrastructure. Specific information 

from select municipalities on 

expenditures related to CSO and SSO 

control is presented. The chapter 

summarizes projected financial needs 

for municipalities to meet current 

regulatory requirements for CSO and 

SSO control and discusses available 

sources of funding to address impacts 

of CSOs and SSOs.

Chapter 10 summarizes report 

findings and key considerations for 

EPA in shaping future regulations and 

program activities aimed at CSO and 

SSO control. 
repair procedures, which has led to 

considerable variability in the current 

condition of sewer infrastructure.

This chapter provides a brief history 

of sewer systems and wastewater 

treatment in the United States, using 

context provided by the Clean Water 

Act. Additional information on federal 

and state efforts related to the control 

of CSOs and SSOs is presented in 

Chapter 7. 

2.1 What is the History of 

Sewer Systems in the 

United States?

I

n the pre-sewer era, human waste 

was dumped into privy vaults and 

cesspools, and storm water ran 

into the streets or into surface drains. 

Population increases during the 1800s, 

particularly in urban areas, created 

the need for more effective sanitary 

systems. Between 1840 and 1880, 

the percentage of Americans living 

in urban areas rose from 11 percent 

to 28 percent (Burian et al 1999). 

This rapid urbanization resulted in 

increased quantities of wastewater that 

Chapter 2

Municipal sewer systems 

are an extensive and 

valuable part of the 

nation’s infrastructure. In 2000, 16,202 

wastewater treatment facilities and 

21,264 sewer systems (both CSS and 

SSS) were in operation in the United 

States. These systems serve about 208 

million people in the United States, 

as reported in EPA’s Clean Watersheds 

Needs Survey 2000 Report to Congress

(EPA 2003b). EPA estimates that 

publicly-owned sewer systems account 

for about 724,000 miles of sewer pipe 

and approximately 500,000 miles 

of privately-owned pipes deliver 

wastewater into these systems.

Much of the nation’s wastewater 

infrastructure is aging. Components 

of some sewer systems date back 

over 100 years, as evidenced by wood 

and brick sewers still in operation in 

some cities. A survey of 42 wastewater 

utilities indicated the age of sewer 

system components ranged from new 

to 117 years, with an average age of 

33 years (ASCE 1999). Over time, 

municipalities have used a wide variety 

of materials, design and installation 

practices, and maintenance and 

2-1

2.1 What is the History of 

Sewer Systems in the 

United States?

2.2 What is the History of 

Federal Water Pollution 

Control Programs?

2.3 What is the Federal 

Framework for CSO 

Control?

2.4 What is the Federal 

Framework for SSO 

Control?

2.5 What is the Wet Weather 

Water Quality Act?

Background

In this chapter:
2-2

Report to Congress on the Impacts and Control of CSOs and SSOs

overwhelmed privy vaults and cesspool 

systems. Consequently, municipalities 

began installing sewer systems to 

protect public health and to address 

aesthetic and flooding concerns 

(Melosi 2000). Little precedent existed 

for the construction of underground 

sewer systems, however, and engineers 

were reluctant to experiment with 

expensive capital works (Tarr 1996). 

In 1858, the first comprehensive sewer 

system was designed for the city of 

Chicago (Burian et al. 1999). Extensive 

construction of municipal sewer 

systems did not start until the 1880s. 

In the United States, municipalities 

installed sewer systems using two 

predominant design options: 

● Combined sewer systems – 

domestic, commercial, and 

industrial wastewater, and storm 

water runoff are collected and 

conveyed in a single pipe system, 

as shown in Figure 2.1; or

● Separate sanitary sewer and 

storm sewer systems – domestic, 

commercial, and industrial 

wastewater, and storm water 

runoff are collected and conveyed 

using two separate systems of 

pipe, as shown in Figure 2.2.

Combined sewer systems were less 

expensive for municipalities that 

needed both sanitary and storm 

sewers, while SSSs were less expensive 

Dry Weather Wet Weather

Sewer to POTW

Down

spout

Storm

drain

Sewer to POTW

Outfall pipe

to river

Combined

sewage and storm water

Sewage from domest commercial ic, , and industrial sources Dam Outfall pipe

to river

Dam

Down

spout

Storm

drain

Down

spout

Storm

drain

Separate storm sewer

Dry Weather

Sewer to POTW

Sewer to POTW

Down

spout

Storm

drain

Separate storm sewer

Outfall pipe

to river Outfall pipe

to river

Wet Weather

Figure 2.1

Typical Combined 

Sewer System

Combined sewer systems are 

designed to discharge directly to 

surface waterbodies such as rivers, 

estuaries, and coastal waters 

during wet weather, when total 

fl ows exceed the capacity of the 

CSS or treatment plant.

Typical Separate 

Sanitary and Storm 

Sewer Systems

Sanitary sewer systems are 

designed to collect and convey 

wastewater mixed with limited 

amounts of infi ltration and infl ow 

to a treatment plant. A separate 

storm sewer system is used in 

many areas to collect and convey 

storm water runoff directly to 

surface waterbodies.

Figure 2.2
 Chapter 2—Background

2-3

 

for municipalities that needed only a 

wastewater collection system. Sanitary 

sewers were sized to convey domestic, 

commercial, and industrial wastewater, 

and limited amounts of infiltrated 

groundwater and storm water inflow. 

Unlike CSSs, they were not intended 

to collect large amounts of runoff 

from wet weather events. In general, 

large cities tended to construct CSSs, 

given the flood control advantages 

offered by such systems. By the end 

of the 19th century, most of the large 

urban areas with sewer systems had 

CSSs. Smaller communities generally 

pursued construction of separate 

sanitary and storm sewers (Melosi 

2000). 

At the time, sanitary engineers 

thought that both CSSs and SSSs 

provided roughly equivalent health 

protection, as neither design included 

wastewater treatment (Tarr 1996). 

This view was supported by an 1881 

report to the National Board of 

Health that recommended that design 

choice be based on local conditions 

and financial considerations (Hering 

1977). 

Construction of sewer systems greatly 

improved local sanitary conditions 

and in many cases reduced illness. 

The direct discharge of untreated 

wastewater to local receiving 

waters, however, adversely impacted 

downstream communities. During 

the 1880s and 1890s, the rate of 

typhoid deaths rose in cities with 

drinking water intakes downstream 

of untreated wastewater discharges. 

Bacterial analysis confirmed the link 

between sewage pollution in rivers 

and epidemics of certain diseases 

(Tarr 1996). Large outbreaks of 

cholera, which claimed thousands 

of lives, were also linked to sewagecontaminated water supplies (Snow 

1936). As a result, views on the safety 

of discharging untreated wastewater 

directly to receiving waters began 

to shift toward the end of the 19th 

century. 

As the need to provide wastewater 

treatment was recognized, the major 

design difference between CSSs and 

SSSs became apparent. Although 

combined sewers offered an efficient 

means of collecting and conveying 

storm water and wastewater, they 

made treatment more difficult due to 

the large variation in flows between 

dry and wet weather conditions. 

Sanitary sewer systems simplified 

and lowered the cost of wastewater 

treatment, due to significantly 

smaller volumes of wet weather flows 

(Burian et al. 1999). Nonetheless, 

municipalities with CSSs often 

continued to utilize and expand the 

areas served by such systems (Tarr 

1996). 

Centralized municipal wastewater 

treatment was still in its infancy in 

the late 1800s (Burian et al. 1999). In 

1892, only 27 municipalities treated 

their wastewater; of these, 26 had SSSs. 

2.1.1 Combined Sewers and CSOs 

CSOs are primarily caused by wet 

weather events (e.g., rainfall or 

snowmelt), when the combined 

volume of wastewater and storm 

water entering the system exceeds the 

capacity of the CSS or treatment plant. 

When this occurs, combined systems 

overflow directly to a receiving water. 

Overflow frequency and duration 

varies both from system to system and 

Privy vaults and a water pump are located 

side by side in this Pittsburgh neighborhood, 

circa 1909.

Photo: Paul Underwood Kellog
2-4

Report to Congress on the Impacts and Control of CSOs and SSOs

from outfall to outfall within a single 

CSS. Some CSO outfalls discharge 

infrequently, while others activate 

every time it rains. When constructed, 

CSSs were typically sized to carry 

three to five times the average dry 

weather flow. Thus, there is usually 

considerable conveyance capacity 

within a CSS during dry weather. 

Discharges from a CSS during dry 

weather, referred to as dry weather 

overflows, are infrequent and are 

prohibited under the NPDES program. 

State and local authorities generally 

have not allowed the construction of 

new CSSs since the first half of the 

20th century. As shown in Figure 2.3, 

most of the communities served by 

CSSs are located in the Northeast and 

Great Lakes regions, while relatively 

few are located in the Midwest, 

Southeast, and Pacific Northwest. 

Currently, 828 NPDES permits 

authorize discharges from 9,348 CSO 

outfalls in 32 states (including the 

District of Columbia). 

2.1.2 Sanitary Sewers and SSOs 

SSOs include unauthorized discharges 

from SSSs that reach waters of the 

United States, as well as overflows out 

of manholes and onto city streets, 

sidewalks, and other terrestrial 

locations. A limited number of 

municipalities have SSO discharges 

Figure 2.3

National Distribution of 

Communities Served by 

CSSs

CSSs are found throughout the 

United States, but are most heavily 

concentrated in the Northeast and 

Great Lakes regions.
 Chapter 2—Background

2-5

from fixed points within the sewer 

system, similar to CSO outfalls.

SSOs, including those that do not 

reach waters of the Unites States, may 

be indicative of improper operation 

and maintenance of the sewer system. 

Causes of SSOs include, but are not 

limited to: 

● Blockages

● Structural, mechanical, or 

electrical failures

● Collapsed or broken sewer pipes

● Insufficient conveyance capacity

● Vandalism

In addition, high levels of infiltration 

and inflow (I/I) during wet weather 

can cause SSOs. Many SSSs that 

were designed according to industry 

standards experience wet weather 

SSOs because levels of I/I may exceed 

levels originally expected; removal 

of I/I has proven more difficult and 

costly than anticipated; or the capacity 

of the system has become inadequate 

due to an increase in service 

population without corresponding 

system upgrades. SSSs are located 

across the country, as presented in 

Figure 2.4. EPA believes that all SSSs 

have the potential to have occasional 

SSOs. 

Figure 2.4

National Distribution of 

Communities Served by 

SSSs

SSSs are located in all 50 states, but 

are concentrated in the eastern 

half of the United States and on the 

west coast. SSSs are shown for approximately 75 percent of systems, 

where locational data (latitude/

longitude) were available from EPA’s 

Permit Compliance System.
2-6

Report to Congress on the Impacts and Control of CSOs and SSOs

2.2 What is the History of 

Federal Water Pollution 

Control Programs?

The desire for a federal water 

pollution control program 

increased steadily through the 

first half of the 20th century. Congress 

and the public became more aware 

of the environmental and human 

health impacts resulting from direct 

discharges of untreated wastewater 

to local receiving waters. Recognizing 

the national interest in abating water 

pollution for the benefit of water 

supply and water resources, the 80th

Congress stated:

“The pollution of our water 

resources by domestic and 

industrial wastes has become an 

increasingly serious problem for 

the rapid growth of our cities 

and industries. . . Polluted waters 

menace the public health through 

the contamination of water and 

food supplies, destroy fish and 

game life, and rob us of other 

benefits of our natural resources.” 

(Senate Report No. 462 of the 80th 

Congress, 1948)

In 1948, Congress passed the 

Federal Water Pollution Control Act 

(FWPCA), P.L. 80-845, creating a 

legislative basis for water pollution 

control in the United States. The 

original FWPCA was amended many 

times (in 1956, 1961, 1965, 1966, 

1970, 1972, 1977, 1981, and 1987). 

Notably, the 1972 Amendments (P.L. 

92-500), commonly known as the 

Clean Water Act, restructured the 

authority for water pollution control 

and consolidated that authority in the 

Administrator of the EPA. The Clean 

Water Act provided a framework for: 

● Prohibition of point source 

discharges except as authorized by 

a permit; 

● Establishment of the National 

Pollutant Discharge Elimination 

System (NPDES), a regulatory 

program that requires “point 

source” dischargers, such as 

municipal wastewater collection 

and treatment plant operators, 

to obtain a permit and meet 

applicable regulations issued 

under the Clean Water Act; 

● Development of technologybased effluent limits, based on 

the pollutant reduction capacity 

of demonstrable treatment 

technologies, to be met by NPDES 

permit holders; and

● Water quality standards and water 

quality-based effluent limitations, 

where technology-based limits 

are inadequate to meet state water 

quality standards.

As a result of investment in wastewater 

treatment, the United States has 

realized major improvements in 

environmental quality and human 

health. Widespread epidemics of 

typhoid fever and cholera that 

killed thousands of people in the 

19th century and early 20th century 

were brought under control and 

have remained under control due to 

disinfection of drinking water supplies 

and advances in wastewater treatment. 

2.2.1 Secondary Treatment

Many of the first wastewater treatment 

facilities were designed to simply 

separate solids and floating debris 

from wastewater prior to discharge; 

this process is often referred to as 

San Francisco’s CSO Oceanside Water 

Pollution Control Plant treats an average 

of 17 million gallons per day (mgd) during 

dry weather and has 65 mgd of peak flow 

capacity.

Photo: San Francisco Public Utilities Commission
 Chapter 2—Background

2-7

primary treatment (Rowland and 

Heid 1976). This modest level of 

treatment, however, was unable 

to offset increased pollutant loads 

associated with rapidly growing urban 

populations and associated increases 

in the volume of wastewater generated. 

An additional level of treatment was 

needed to protect the quality of the 

nation’s waters.

The 1972 Clean Water Act provided 

the first statutory requirement for 

achievement of effluent limits based 

on secondary treatment by POTWs. 

Specifically, Section 301 of the Clean 

Water Act required POTWs to meet 

limits based on secondary treatment 

by July 1, 1977. EPA developed 

limits based on secondary treatment 

to include maximum allowable 

concentrations of key parameters as 

well as percent removal requirements. 

Limits based on secondary treatment 

include maximum acceptable 

concentrations for biochemical 

oxygen demand measured over five 

days (BOD5), total suspended solids 

(TSS), and pH. Percent removal 

requirements for BOD5 and TSS were 

also included. Adjustments to percent 

removal requirements are available, on 

a case-by-case basis, for POTWs with 

less-concentrated influent that may 

prevent compliance with the standard 

requirements (EPA 2000a). 

2.2.2 Construction Grants

In addition to establishing effluent 

limits for POTWs, the FWPCA and 

its amendments brought about 

substantial investment in wastewater 

treatment between the 1940s and the 

present. The 1956 Amendments (P.L. 

84-660) established the Construction 

Grants Program for the construction 

of wastewater treatment facilities and 

provided $150 million in funding for 

the program. Additional construction 

grant funding was authorized with the 

1961, 1965, and 1966 amendments. 

With passage of the Clean Water Act 

in 1972, funding for the Construction 

Grants Program dramatically 

increased. EPA’s Construction Grants 

Program distributed $100.7 billion 

(2002 dollars) to communities 

between 1970 and 1995 (EPA 2000a). 

The 1987 amendments to the Clean 

Water Act transformed the financial 

assistance from a grant program to 

a loan program. The Construction 

Grants Program was phased out 

by 1991 and replaced by the State 

Revolving Fund (SRF) program.

Federal funding provided a strong 

impetus for constructing and 

upgrading wastewater infrastructure. 

The level of treatment provided at 

POTWs improved substantially over 

the last 50 years (EPA 2000a): 

● 30 percent of POTWs (3,529 

of 11,784) provided secondary 

treatment in 1950.

● 72 percent of POTWs (10,052 

of 14,051) provided secondary 

treatment in 1968.

● 99 percent of 16,024 POTWs 

provided secondary or greater 

treatment, or were “no-discharge 

facilities,” in 1996.

High levels of compliance with 

secondary treatment requirements 

resulted in notable decreases in 

pollutant loadings from POTWs, even 

as the service population increased. 

As an example, the amount of BOD5

discharged from POTWs declined by 
2-8

Report to Congress on the Impacts and Control of CSOs and SSOs

about 23 percent between 1968 and 

1996, despite a 35 percent increase in 

influent loadings to POTWs during 

the same period (EPA 2000a). 

2.2.3 Pretreatment

In the mid-1980s, more than onethird of all toxic pollutants entering 

the nation’s waters were discharged 

from POTWs (EPA 1986a). POTWs 

are not typically designed to remove 

toxic pollutants, and in some cases 

constituents in industrial wastewater 

can actually interfere with the 

removal of conventional pollutants 

such as BOD5 and TSS. To address 

the discharge of toxic pollutants, 

EPA, pursuant to Clean Water Act 

Section 307, established the National 

Pretreatment Program. The National 

Pretreatment Program requires that 

industrial and commercial dischargers 

treat or control toxic pollutants in 

their wastewater prior to discharge to 

a municipal sewer system. 

The General Pretreatment Regulations 

require all large POTWs (i.e., 

those designed to treat flows of 

more than 5 million gallons per 

day (mgd)) and smaller POTWs 

with significant industrial users to 

establish local pretreatment programs. 

These local programs implement 

national pretreatment standards and 

requirements in addition to any more 

stringent local requirements necessary 

to protect site-specific conditions. 

More than 1,500 POTWs have 

developed and are implementing local 

pretreatment programs designed to 

control discharges from approximately 

30,000 significant industrial users. 

The National Pretreatment Program 

has made great strides in reducing the 

discharge of toxic pollutants to sewer 

systems and to waters of the United 

States (EPA 1999a).

2.2.4 Wet Weather

Initial implementation of the Clean 

Water Act during the 1970s and 1980s 

focused on discharges from traditional 

point sources of pollution, such as 

POTWs and industrial facilities. 

Beginning in the late 1980s, attention 

shifted to wet weather sources of 

pollution. Under the NPDES program, 

four program areas address wet 

weather discharges: CSOs, SSOs, storm 

water, and concentrated animal feeding 

operations (CAFOs).

Storm Water

EPA published Phase I of the NPDES 

Storm Water Program in 1990 (55 

FR 47990). Phase I applies to large 

dischargers; that is, those associated 

with industrial activities, municipal 

separate storm sewer systems 

serving 100,000 people or more, and 

construction projects disturbing 

more than five acres of land. In 1999, 

EPA published the Phase II Final 

Rule, which requires NPDES permit 

coverage for storm water discharges 

from smaller sources, including cities 

and towns in urban areas with separate 

storm sewer systems serving fewer 

than 100,000 people, and smaller 

construction projects that disturb less 

than five acres (64 FR 68722). 

CAFOs

CAFOs are point sources, as defined 

by Clean Water Act Section 502(14). 

On February 12, 2003, EPA published 

the Concentrated Animal Feeding 

Operations Rule to ensure that manure 

Some municipalities promote storm drain 

stenciling as a storm water pollution 

prevention measure.

Photo: EPA
 Chapter 2—Background

2-9

and wastewater from CAFOs are 

properly managed to protect the 

environment and public health (68 FR 

7175). 

2.2.5 Watershed-Based 

Permitting

On December 17, 2003, EPA 

published the Watershed-Based 

NPDES Permitting Implementation 

Guidance (EPA 2003c). Watershedbased permitting under the NPDES 

program emphasizes addressing 

all stressors (including CSOs and 

SSOs) within a watershed, rather 

than individual pollutant sources on 

a discharge-by-discharge basis. The 

watershed-based permitting approach 

is supported by EPA as a cost-effective 

mechanism for improving water 

quality and meeting watershed goals. 

The approach builds on watershed 

policy and guidance developed during 

the 1990s: EPA’s Watershed Strategy, 

Watershed Framework, and Clean 

Water Action Plan (EPA 1994b, 1996a, 

EPA and USDA 1998). In addition, 

the approach fulfills commitments 

articulated in recent initiatives such as 

EPA’s Trading Policy and WatershedBased Permitting Policy Statement 

(EPA 2003d, 2003e). 

Watershed-based permitting can 

encompass a variety of activities 

ranging from synchronizing NPDES 

permits within a basin to developing 

water quality-based effluent limits 

using a multiple discharger modeling 

analysis. Within a broader watershed 

management system, the watershedbased permitting approach is a tool 

that can assist with implementation 

activities such as monitoring, 

reporting, and assessment.

2.3 What is the Federal 

Framework for CSO 

Control?

CSOs are point source 

discharges and are subject to 

NPDES permit requirements. 

CSOs are not subject to limits based 

on secondary treatment requirements 

otherwise applicable to POTWs. 

Permits for CSOs must include 

technology-based effluent limits, 

based on the application of best 

available technology economically 

achievable (BAT) for toxic and 

non-conventional pollutants and 

best conventional pollutant control 

technology (BCT) for conventional 

pollutants. Additionally, like all 

NPDES permits, permits authorizing 

discharges from CSO outfalls must 

include more stringent water qualitybased requirements, when necessary, 

to meet water quality standards. The 

development of the federal framework 

to address CSOs is described in detail 

below.

2.3.1 CSO Case Law

In 1980, the U.S. Court of Appeals 

for the D.C. Circuit accepted EPA’s 

interpretation of the Clean Water 

Act that discharges at CSO outfalls 

are not discharges from POTWs 

and thus are not subject to the 

limits based on secondary treatment 

standards otherwise applicable to 

POTWs (Montgomery Environmental 

Coalition vs. Costle, 46 F2d 568 (D.C. 

Cir. 1980)). Following this decision, 

EPA and states renewed their focus 

on permit requirements for CSO 

discharges under the NPDES program.

The sewer utility serving Louisville, Kentucky, 

has restructured its organization to 

coordinate CSO control needs with other 

water quality improvement programs as part 

of an effort to move toward watershed-based 

permitting.

Photo: Louisville-Jefferson County Metropolitan Sewer District
2-10

Report to Congress on the Impacts and Control of CSOs and SSOs

2.3.2 The National CSO Control 

Strategy and the MAG

In 1989, EPA issued the National 

CSO Control Strategy (54 FR 

37371). The National CSO Control 

Strategy encouraged states to develop 

statewide permitting strategies to 

ensure all CSOs were subject to an 

NPDES permit and recommended six 

minimum measures for CSO control; 

additional controls could be required 

as necessary. As EPA, states, and 

municipalities worked to implement 

the National CSO Control Strategy in 

the early 1990s, the impacts of CSOs 

(discussed in Chapters 5 and 6 of this 

report) continued to receive national 

attention. Environmental interest 

groups pushed for further action, while 

municipal organizations, concerned 

that the National CSO Control Strategy 

did not provide sufficient clarity, 

sought a consistent national approach 

to CSO control. In response to these 

concerns, EPA formed a Management 

Advisory Group (MAG) in 1992. 

The MAG included representatives 

from states, municipalities, industry 

associations, and environmental 

interest groups. 

2.3.3 The CSO Control Policy

EPA published the CSO Control Policy 

on April 19, 1994 (59 FR 18688). The 

purpose of the CSO Control Policy was 

twofold: 1) to elaborate on EPA’s 1989 

National CSO Control Strategy; and 

2) to expedite compliance with Clean 

Water Act requirements. The policy 

sought to minimize adverse impacts 

from CSOs on water quality, aquatic 

biota, and human health (EPA 1994a). 

EPA’s CSO Control Policy assigns 

primary responsibility for its 

implementation and enforcement 

to NPDES authorities and water 

quality standards authorities. This 

policy also established objectives for 

CSO communities: 1) to implement 

the nine minimum controls (NMC) 

and submit documentation on NMC 

implementation; and 2) to develop 

and implement a long-term control 

plan (LTCP). Implementation status 

of the NMC and LTCPs is presented 

in Chapter 7. More information 

on the CSO Control Policy is 

provided in EPA’s Report to Congress–

Implementation and Enforcement of 

the Combined Sewer Overflow Control 

Policy (EPA 2001a).

2.4 What is the Federal 

Framework for SSO 

Control?

S

SOs that reach waters of the 

United States are point source 

discharges and, like other point 

source discharges from municipal 

SSSs, are prohibited unless authorized 

by an NPDES permit. Moreover, SSOs, 

including those that do not reach 

waters of the United States, may be 

indicative of improper operation and 

maintenance of the sewer system, 

and thus may violate NPDES permit 

conditions. In the 1989 National CSO 

Control Strategy, EPA explained that: 

A CSO outfall in Wilmington, Delaware.

Photo: Wilmington Department of Public Works
 Chapter 2—Background

2-11

“sanitary sewer systems must adhere 

to the strict design and operational 

standards established to protect the 

integrity of the sanitary sewer system 

and wastewater treatment facilities.” 

In 1994, a number of municipalities 

asked EPA to establish an SSO 

Federal Advisory Committee 

(FAC) of key stakeholders to make 

recommendations on how the NPDES 

program should address SSOs. The 

municipalities indicated a desire for 

greater national clarity, consistency 

in NPDES requirements applicable 

to SSOs, and a workable regulatory 

framework. Five general stakeholder 

groups were represented in the SSO 

FAC: sanitary sewer system operators, 

SSO-related health professionals, 

state regulatory agencies, technical 

professionals, and environmental and 

citizen groups. 

In 1995, EPA chartered an Urban Wet 

Weather Flows FAC with stakeholder 

representation to address crosscutting issues associated with wet 

weather discharges (i.e., CSOs, SSOs, 

and storm water). The Urban Wet 

Weather Flows FAC formed its SSO 

Subcommittee by reconvening the 

SSO FAC established in 1994. The 

SSO Subcommittee was tasked with 

developing a framework for addressing 

SSOs and their impacts through 

regulatory and non-regulatory actions.

Between 1995 and 1999, the SSO 

Subcommittee held 12 meetings and 

developed a number of documents, 

including a series of issue papers 

and a draft comprehensive guidance 

document. In January 2001, EPA 

prepared a notice of proposed 

rulemaking related to SSOs, which 

was withdrawn for review before it 

was published in the Federal Register. 

EPA is considering various options for 

moving forward.

2.5 What is the Wet Weather 

Water Quality Act?

I

n December 2000, as part of the 

Consolidated Appropriations Act 

for Fiscal Year 2001 (P.L. 106-554), 

Congress amended the Clean Water 

Act by adding Section 402(q). This 

amendment is commonly referred to 

as the Wet Weather Water Quality Act 

of 2000. Section 402(q) requires that 

each permit, order, or decree issued 

pursuant to the Clean Water Act after 

the date of enactment for a discharge 

from a municipal combined sewer 

system shall conform to the CSO 

Control Policy. It authorized a $1.5-

billion grant program for controlling 

CSOs and SSOs. Section 402(q) also 

required EPA to issue guidance to 

facilitate the conduct of water quality 

and designated use reviews for CSO 

receiving waters. EPA issued this 

guidance on August 2, 2001 (EPA 

2001b).
by municipalities to address these 

impacts; and the technologies used to 

address these impacts. Some new data 

were obtained through interviews in 

the development of this report, but 

EPA did not undertake surveys or 

field monitoring to characterize CSOs, 

SSOs, and their impacts. Instead, EPA 

primarily emphasized the collection, 

compilation, and analysis of existing 

data.

EPA used a two-tiered approach 

to address the questions posed by 

Congress. The first tier focused on 

national assessments, drawing on 

existing data collected by EPA and 

other federal agencies to the fullest 

extent possible. These data were 

supplemented with select data from 

non-governmental organizations 

that were also national in scope. 

The second tier focused on the use 

of anecdotal data to provide sitespecific examples of impacts, costs, 

and technology applications, and 

to demonstrate the significance of 

CSOs and SSOs at the local level. Sitespecific examples were largely drawn 

from state and local interviews and 

reports. 

Chapter 3

This chapter documents the 

methodology EPA used 

to prepare this Report to 

Congress. It presents EPA’s study 

objectives and analytical approach, 

and summarizes the steps EPA has 

taken to compile information on the 

impacts and control of CSOs and 

SSOs. This chapter describes EPA’s 

data sources, explains information 

collection methods, and outlines the 

steps EPA took to involve stakeholders 

in the development of this report. 

The chapter also summarizes data 

considerations and quality assurance 

measures used to enhance the accuracy 

and precision of results. 

3.1 What Study Objectives and 

Approach Did EPA Use to 

Prepare this Report?

The overall objective for 

this report is to respond 

to Congress with a current 

characterization of the volume, 

frequency, and location of CSOs and 

SSOs; the extent of human health 

and environmental impacts caused by 

CSOs and SSOs; the resources spent 

3-1

3.1 What Study Objectives 

and Approach Did EPA 

Use to Prepare this 

Report?

3.2 What Data Sources Were 

Used?

3.3 What Data Were 

Collected?

3.4 How Were Stakeholders 

Involved in the 

Preparation of this 

Report?

3.5 What Data 

Considerations Are 

Important?

3.6 What Quality Control 

and Quality Assurance 

Protocols Were Used?

3.7 Summary

Methodology

In this chapter:
3-2

Report to Congress on the Impacts and Control of CSOs and SSOs

3.2 What Data Sources Were 

Used? 

EPA developed a comprehensive 

list of potential data 

sources that could be used 

to characterize CSOs and SSOs, 

including environmental and human 

health impacts from the discharges, 

technologies used to control the 

discharges, and the costs of the control 

measures. This list included:

● Federal data sources

● NPDES authority and other state 

program data sources

● Community-level data sources

● Non-governmental organization 

data sources

The following sections describe 

specific data sources EPA used to 

develop this report. 

3.2.1 Federal Data Sources 

EPA researched its own files and 

library of CSO- and SSO-related 

documents for data that could be used 

to characterize CSOs and SSOs. Data 

and reports relevant to CSOs and 

SSOs developed by EPA’s permitting, 

compliance and enforcement, research 

and development, and water quality 

assessment programs were among 

those reviewed. Specific EPA data 

sources used in the analysis for this 

Report to Congress include: 

Beaches Environmental Assessment and 

Coastal Health (BEACH) Program.

The BEACH Program focuses 

on improving public health and 

environmental protection programs 

for beachgoers and providing the 

public with information about the 

quality of beach water.

Clean Watersheds Needs Survey 

(CWNS). The CWNS summarizes 

estimated capital costs for water 

quality projects including projects to 

control CSOs and SSOs.

Enforcement and Compliance Docket 

(ECD). The ECD is the central archive 

for all documents related to EPA’s 

enforcement and compliance activities. 

It contains regulatory, case settlement, 

and other policy related information.

EPA’s 2001 Report to Congress– 

Implementation and Enforcement of 

the Combined Sewer Overflow Control 

Policy. The 2001 Report to Congress 

provides a comprehensive national 

inventory of active CSO permits. 

Government Performance and Results 

Act (GPRA). EPA selected the CSO 

program as a GPRA pilot program 

for tracking programmatic benefits in 

1997.

Municipal Technology Fact Sheets. EPA 

maintains a series of more than 100 

technology fact sheets, including more 

than 20 with application to the control 

of CSOs and SSOs.

National Water Quality Inventory 

(NWQI). The biennial NWQI Report 

to Congress is the primary vehicle for 

informing Congress and the public 

about general water quality conditions 

in the United States.

Office of Research and Development 

(ORD) projects. ORD works with 

industry, universities, and other 

agencies to develop technologies and 
 Chapter 3—Methodology

3-3

 

techniques for protecting the nation’s 

freshwater and coastal resources and 

human health.

Permit Compliance System (PCS). PCS 

provides information on point sources 

holding NPDES permits, including 

permit issuance and expiration 

dates, discharge limits, and discharge 

monitoring data.

EPA also researched the programs 

and files of other federal agencies to 

ensure that relevant data from other 

federal programs and activities were 

assessed and included in this report, 

as appropriate. The agencies consulted 

included:

● Centers for Disease Control and 

Prevention (CDC)

● Congressional Budget Office 

(CBO)

● Government Accounting Office 

(GAO)

● National Institutes of Health 

(NIH)

● National Oceanic and 

Atmospheric Administration 

(NOAA) 

● United States Geological Survey 

(USGS)

3.2.2 NPDES Authority and Other 

State Program Data Sources

Individual NPDES authorities and 

associated state programs were the 

primary sources of data on the 

location of CSO outfalls as well as the 

frequency, volume, and cause of SSO 

events. EPA conducted interviews with 

states to assess the availability of data. 

State program data and interviews 

with program staff were also used to 

identify site-specific CSO- and SSOrelated examples of environmental 

and human health impacts such as fish 

kills, beach closures, and outbreaks of 

waterborne disease. 

3.2.3 Community-Level Data 

Sources

EPA identified relevant communitylevel data to supplement the national 

data and drew on local planning 

and monitoring studies, such as 

CSO LTCPs, to illustrate site-specific 

impacts and common technologies 

used to control CSOs and SSOs. 

Municipalities were interviewed 

to obtain additional data to 

characterize the volume, frequency, 

and constituents of CSO and SSO 

discharges; to identify the types of 

controls implemented and results 

achieved; and to quantify the resources 

spent. 

3.2.4 Non-Governmental 

Organization Data Sources

EPA also reviewed reports prepared by 

non-governmental organizations that 

contained national-level data relevant 

to the objectives of this report. These 

included: 

● American Public Works 

Association (APWA)

● American Society of Civil 

Engineers (ASCE) 

● Association of Metropolitan 

Sewerage Agencies (AMSA)

● The Ocean Conservancy

● Water Environment Federation 

(WEF)

● Water Environment Research 

Foundation (WERF)
3-4

Report to Congress on the Impacts and Control of CSOs and SSOs

3.3 What Data Were Collected?

Data collection involved 

identification and 

compilation of existing 

information. The primary data sources 

for this report were federal databases 

and reports as well as interviews with 

states and municipalities. In addition, 

EPA performed a comprehensive 

literature search and applied national 

assessment models, where appropriate.

In compliance with the Paperwork 

Reduction Act, EPA prepared and 

submitted Information Collection 

Request 2063.01, which was approved 

by OMB on September 16, 2002 

(OMB No. 2040-0248).

The following sections describe data 

collection and the key assessments 

carried out by EPA. 

3.3.1 Characterization of CSOs and 

SSOs

This report characterizes CSOs and 

SSOs by addressing the following key 

questions: 

● What pollutants are in CSOs and 

SSOs?

● What factors influence the 

concentrations of these pollutants in 

CSOs and SSOs?

● What other point and nonpoint 

sources might discharge these 

pollutants to waterbodies receiving 

CSOs and SSOs?

● What is the universe of combined 

sewer systems?

● What are the characteristics of 

CSOs?

● What is the universe of sanitary 

sewer systems?

● What are the characteristics of 

SSOs?

● How do the volumes and loads from 

CSOs and SSOs compare to those 

from other municipal point sources?

To address these questions EPA used 

NPDES permit files, state databases 

for tracking CSO and SSO events, and 

interviews with state and municipal 

officials. Specific efforts included 

updating data on the location of CSSs 

and CSO outfalls from the 2001 Report 

to Congress–Implementation and 

Enforcement of the Combined Sewer 

Overflow Control Policy (EPA 2001a), 

and compiling SSO volume, frequency, 

and cause data. This allowed 

assessment of: 

● Pollutants found in CSOs and 

SSOs

● Location of CSSs and individual 

CSO outfalls

● Volume and frequency of CSOs 

and SSOs

● Causes of SSOs

● Comparison of pollutant loads 

from CSOs and SSOs with other 

municipal point sources 

EPA relied on existing Agency data 

systems wherever possible. These 

include PCS, the CWNS, and NWQI. 

EPA data systems were the principal 

source of information used to locate 

CSSs, CSO outfalls, and SSSs. Data 

on the concentration of pollutants 

found in CSO and SSO discharges 

were developed from a number of 

sources, including engineering and 

scientific literature, EPA studies, 
 Chapter 3—Methodology

3-5

 

municipal reports including CSO 

LTCPs, and interviews with municipal 

sewer system owners and operators. 

EPA applied the GPRACSO model 

to calculate the annual volume 

of CSOs. Documentation of the 

GPRACSO model is included as 

Appendix E of this report. EPA used 

statistical techniques to develop 

national estimates of the frequency 

and volume of SSOs based on data 

reported electronically by states. 

Documentation of the statistical 

techniques is included in this report as 

Appendix G.

3.3.2 Extent of Environmental 

Impacts Caused by CSOs and 

SSOs

This report’s analysis of the extent 

of environmental impacts caused 

by CSOs and SSOs addresses the 

following key questions:

● What is EPA’s framework for 

evaluating environmental impacts?

● What overall water quality impacts 

have been attributed to CSO 

and SSO discharges in national 

assessments? 

● What impacts on specific designated 

uses have been attributed to CSO 

and SSO discharges in national 

assessments?

● What overall water quality impacts 

have been attributed to CSO and 

SSO discharges in state and local 

assessments?

● What impacts on specific designated 

uses have been attributed to CSO 

and SSO discharges in state and 

local assessments?

● What factors affect the extent of 

environmental impacts caused by 

CSOs and SSOs?

EPA used federal reports and data as 

the primary bases for reporting on 

environmental impacts from CSOs 

and SSOs on a national level. The 

assessment included identification 

of water quality impairments and 

environmental impacts associated with 

CSOs and SSOs with respect to:

● Impaired stream segments

● Impaired lakes 

● Impaired estuaries 

● Impaired ocean shoreline 

● Impaired Great Lakes shoreline

● Beach closures

● Shellfish bed closures

EPA also reviewed national resource 

assessments from NOAA and nongovernmental organizations such as 

the Ocean Conservancy. 

CSS location and individual CSO 

outfall information published 

in the 2001 Report to Congress–

Implementation and Enforcement of 

the Combined Sewer Overflow Control 

Policy was updated for this Report to 

Congress by contacting states and EPA 

regions to confirm active CSO permit 

data. The data system developed as 

part of the 2001 report effort contains 

latitude and longitude information for 

over 90 percent of the CSO outfalls 

currently permitted under the NPDES 

program. Having the latitude and 

longitude of the CSO outfalls allowed 

individual permitted outfalls to be 

associated with specific waterbody 

segments (called “reaches”) within 
3-6

Report to Congress on the Impacts and Control of CSOs and SSOs

the National Hydrography Dataset 

(NHD). The NHD is a comprehensive 

set of digital spatial data of surface 

water features that enables analysis 

of water-related data in upstream 

and downstream order. Associating 

CSO outfall locations with the NHDindexed assessed waters allowed for 

comparison of the outfalls to known 

impairments reported by states, as 

required under Clean Water Act 

Sections 303(d) and 305(b), and to the 

location of protected resources and 

sensitive areas. Additional detail on the 

CSO analysis using the NHD-indexed 

assessed waters is documented in 

Appendix F. 

SSOs are generally considered 

unpermitted discharges, and SSO 

locations are not typically included 

in NPDES permits. As described in 

Chapter 4, SSOs occur for a variety of 

reasons and at many locations within 

the sewer system, including manholes, 

roadways, and pump stations. Further, 

some SSOs discharge to land and not 

to waters of the United States. For 

these reasons, it was not possible to 

conduct a parallel analysis for SSOs 

using the NHD. EPA, however, did 

develop a simple model for estimating 

the likely impact of SSO events on 

streams and rivers based on reasonable 

assumptions about SSO event 

duration, pollutant concentrations, and 

waterbody characteristics. Additional 

detail on the model is provided in 

Appendix H.

National level assessments are unable 

to convey the circumstances that 

surround an individual CSO or SSO 

event, the nature of site-specific 

environmental impacts, and the 

consequences with respect to water 

quality criteria and designated uses. 

To account for these localized impacts, 

EPA used state and communitylevel data to document site-specific 

environmental impacts including 

water quality standards violations, 

shellfish bed closures, and fish kills. 

These examples are not comprehensive 

but are presented to illustrate the 

potential of CSOs and SSOs to 

cause or contribute to impacts and 

impairments.

3.3.3 Extent of Human Health 

Impacts Caused by CSOs and 

SSOs

This report’s analysis of the extent of 

human health impacts caused by CSOs 

and SSOs addresses the following key 

questions:

● What pollutants are present in 

CSOs and SSOs that can cause 

human health impacts?

● What exposure pathways and 

reported human health impacts are 

associated with CSOs and SSOs? 

● Which demographic groups face the 

greatest risk of exposure to CSOs 

and SSOs? 

● Which populations face the greatest 

risk of illness from exposure to the 

pollutants present in CSOs and 

SSOs?

● How are human health impacts 

from CSOs and SSOs prevented, 

communicated, and mitigated?

● What factors contribute to 

information gaps in identifying 

and tracking human health impacts 

from CSOs and SSOs?

Water quality data from state 305(b) reports 

were used in gathering information on the 

environmental impacts of CSOs.

Photo: P. Macneill
 Chapter 3—Methodology

3-7

● What new assessment and 

investigative activities are 

underway?

EPA began its effort to document 

human health impacts from CSOs 

and SSOs with a literature review. EPA 

searched on-line databases including 

PubMed, Toxline, LexisNexis, and 

the Washington Research Libraries 

Consortium for relevant reports and 

articles. A series of waterborne disease 

outbreak case studies developed from 

published literature is provided in 

Appendix I. EPA gathered data on the 

general incidence and characteristics 

of waterborne diseases as well as on 

other impacts associated with the 

pollutants found in CSO or SSO 

discharges. The primary source of 

data on the incidence of waterborne 

disease in the United States is a joint 

surveillance system operated by the 

CDC, EPA, and the Council of State 

and Territorial Epidemiologists (CDC 

2002). Summaries of data collected 

by CDC are published periodically 

and divided into waterborne-disease 

outbreaks resulting from drinking 

water, recreational waters, or, in some 

cases, cruise ships. EPA also reviewed 

reports from non-governmental 

organizations for data related to 

human health impacts. 

EPA identified experts in the fields 

of epidemiology, public health 

policy, and waterborne disease 

research and invited them to attend 

a workshop in August 2002. Experts 

represented EPA, CDC, local health 

departments, and academia. This 

workshop did not constitute an 

advisory committee under the Federal 

Advisory Committees Act. Rather, it 

solicited individual expert opinions 

and provided a forum for information 

exchange related to this Report to 

Congress. EPA shared the results of its 

initial data collection at this workshop, 

received feedback on and refined the 

study methodology, and sought to 

ensure that gaps and redundancies in 

the research effort did not exist. An 

abstract of this workshop is provided 

in Appendix B; the summary of this 

workshop was published separately 

(EPA 2002b).

EPA also estimated the illness burden 

resulting from exposure to CSOs 

and SSOs at beaches recognized by 

state authorities using data from the 

BEACH Program’s annual survey 

(BEACH Survey) and other sources. 

EPA analyzed data from responses 

to the 1999-2002 BEACH Surveys 

including the number of CSO and 

SSO events, number of swimmers, 

bacterial concentrations, and CSO 

and SSO event duration. An illness 

rate derived by Cabelli et al. (1983) 

and Dufour (EPA 1984a) was applied 

to estimate the number of swimmers 

who contract gastrointestinal 

illnesses. Additional details describing 

this methodology are included in 

Appendix J. 

EPA also conducted interviews with 

public health personnel, including 

state or territorial epidemiologists and 

local public health officials. States and 

communities were selected from each 

EPA region in an attempt to ensure 

geographic, climatic, and population 

variability among communities 

interviewed. Nevertheless, the sample 

is intentionally biased, targeting 

communities that were likely to have 

health data related to CSOs and SSOs, 

or that employed noteworthy water 

quality monitoring or waterborne 
3-8

Report to Congress on the Impacts and Control of CSOs and SSOs

disease outbreak tracking techniques. 

The results of the interviews are 

provided in Appendix I.

3.3.4 Evaluation of Technologies 

Used by Municipalities to 

Address Impacts Caused by 

CSOs and SSOs

This report’s evaluation of the 

technologies used by municipalities 

to address impacts caused by CSOs 

and SSOs addresses the following key 

questions:

● What technologies are commonly 

used to address CSOs and SSOs?

● How do CSO and SSO controls 

differ? 

● What are effective technology 

combinations? 

● What are emerging technologies for 

CSO and SSO control?

EPA conducted a literature review 

and collected reports on CSO and 

SSO abatement efforts to evaluate 

technologies used by municipalities 

to address the impacts of CSO and 

SSO discharges. These data included 

existing EPA fact sheets, technical 

reports covering relevant research, and 

wet weather demonstration studies. 

EPA also reviewed technical guidance 

manuals developed by states, as well 

as documentation of local programs, 

including CSO LTCPs. The literature 

review was supplemented with 

discussions of CSO and SSO programs 

in interviews with municipal sewer 

system owners and operators.

The analysis conducted by EPA 

included:

● Development of 23 technology 

descriptions, included as 

Appendix L of this report, that 

summarize available technologies 

and the factors that influence their 

applicability and effectiveness.

● Identification of common and 

promising technologies used by 

municipalities to control CSOs 

and SSOs.

EPA and non-EPA experts were 

called upon to provide peer review 

of technology descriptions, costs, 

and performance. It is anticipated 

that technology data gathered and 

presented in this report’s technology 

descriptions will support development 

of the technology clearinghouse 

required by the Wet Weather Water 

Quality Act of 2000 (P.L.106-554).

3.3.5 Assessment of Resources 

Spent by Municipalities to 

Address Impacts Caused by 

CSOs and SSOs

This report’s assessment of resources 

spent by municipalities to address 

impacts caused by CSOs and SSOs 

addresses the following key questions:

● What federal framework exists for 

evaluating resources spent on CSO 

and SSO control?

● What are the past investments in 

wastewater infrastructure?

● What has been spent to control 

CSOs?

● What has been spent to control 

SSOs?

● What does it cost to maintain sewer 

systems?
 Chapter 3—Methodology

3-9

● What are the projected costs to 

reduce CSOs?

● What are the projected costs to 

reduce SSOs?

● What mechanisms are available for 

funding CSO and SSO control?

EPA used several of its own reports 

and reviewed data from other federal 

agencies (e.g., CBO, GAO, and 

Census Bureau), states, and nongovernmental organizations to assess 

the national investment in wastewater 

infrastructure and future needs. EPA 

also reviewed data collected for the 

2000 CWNS (EPA 2003b). EPA used 

a variety of reports to quantify the 

resources spent by municipalities to 

control CSOs and SSOs, including: 

● EPA’s 1996 Clean Water Needs 

Survey (EPA 1997a) and 2000 

CWNS (EPA 2003b)

● EPA’s Clean Water and Drinking 

Water Infrastructure Gap Analysis

(EPA 2002a)

● Clean Water State Revolving Fund 

(CWSRF) records

● Negotiated enforcement actions 

● Interviews with municipal owners 

and operators of sewer systems

● CSO LTCPs

● Recent AMSA, ASCE, and WERF 

reports

EPA also used a variety of sources 

to assess available mechanisms for 

funding CSO and SSO control, 

including:

● EPA’s Clean Water and Drinking 

Water Infrastructure Gap Analysis

(EPA 2002a)

● EPA’s 2001 Report to Congress–

Implementation and Enforcement 

of the Combined Sewer Overflow 

Control Policy (EPA 2001a)

● EPA’s Fact Sheet: Financing Capital 

Improvements for SSO Abatement

(EPA 2001c)

● EPA’s Combined Sewer Overflows: 

Guidance for Funding Options

(EPA 1995a)

● GAO reports

● CSO LTCPs

3.4 How Were Stakeholders 

Involved in the Preparation 

of this Report?

EPA consulted and worked with 

a broad group of stakeholders 

for this report. EPA conducted 

site visits to several EPA regions 

and six states; developed a series 

of 23 technology descriptions in 

cooperation with municipalities; and 

sought review of sections of the report 

from experts internal and external 

to EPA. States and municipalities 

featured in this Report to Congress 

were provided the opportunity 

to review information specifically 

pertaining to them. 

Throughout 2002 and 2003, EPA 

met with representatives from key 

stakeholder groups such as AMSA, 

NRDC, and WEF. During these 

meetings, EPA presented an overview 

of the congressional directive and the 

Agency’s planned response. EPA then 

solicited feedback on its progress. 

The comments and suggestions of the 

stakeholder groups were incorporated 

into the preparation of this report.

In 1999, North Bergen Municipal Utilities 

installed numerous mechanical screen 

bars and netting systems to control solids 

and floatables in CSOs. The facilities cost 

$3.3 million and annually cost $57,373 to 

operate and maintain (2002 dollars).

Photo: NJDEP
3-10

Report to Congress on the Impacts and Control of CSOs and SSOs

As described in Section 3.3.3, EPA 

facilitated a workshop for public 

health experts in Arlington, Virginia. 

Experts represented EPA, CDC, local 

health departments, and academia. 

Observers of the workshop included 

representatives of many stakeholder 

groups.

EPA also sponsored stakeholder 

meetings during development of 

this report in Washington, DC (June 

2003), and in Huntington Beach, CA 

(July 2003). Participants included 

representatives from EPA regions; 

states; municipal sewer system owners, 

operators, and consultants; national 

and local environmental organizations; 

professional associations; and public 

health experts. The purpose of these 

meetings was to:

● Provide a preliminary description 

of the report methodology and 

findings

● Discuss the implications of 

preliminary findings

● Describe data availability and 

limitations

● Solicit additional data on impacts, 

costs, and technologies 

EPA presented preliminary data on 

all aspects of the report, received 

comments on data sources and 

data interpretation, and received 

input on the context within which 

these findings should be viewed. A 

summary of the stakeholder meetings 

is provided in Appendix B of this 

report. EPA also made presentations 

at numerous national meetings and 

conferences to provide progress 

reports and updates to stakeholders.

3.5 What Data Considerations 

Are Important? 

The information collection 

strategy used to support 

this report includes several 

important data considerations. First 

and foremost, EPA based this report 

on the collection, compilation, 

and analysis of existing data and 

program information. No surveys 

or field monitoring were conducted 

to quantify pollutant concentrations 

or environmental and human health 

impacts. Similarly, EPA did not 

undertake new research or analysis 

in the assessment of technologies or 

evaluation of costs.

Another important data consideration 

is state-to-state differences in the 

definition of “CSO event” and “SSO 

event” related to threshold volumes 

and duration of events that last 

beyond midnight or for more than 24 

hours. EPA also found that wastewater 

backups into buildings, including 

private residences, are not typically 

tracked by or reported to NPDES 

authorities.

A third consideration is that often 

the pollutants present in CSOs and 

SSOs have numerous sources within a 

given watershed. These sources include 

municipal wastewater treatment plants, 

storm water runoff, decentralized 

wastewater treatment systems, 

runoff from agricultural areas, and 

wildlife and domesticated animals. 

It can be difficult, if not impossible, 

to differentiate environmental and 

human health impacts caused by CSO 

and SSO discharges from those caused 

by these other sources.
 Chapter 3—Methodology

3-11

A fourth consideration is the potential 

underreporting of waterborne disease 

outbreaks. Existing systems for 

tracking these outbreaks often lack 

sufficient information on the cause 

of the outbreak to establish whether 

CSOs or SSOs are a suspected source.

A final data consideration is that 

the nature of many CSO and SSO 

control activities makes it difficult 

to separate their costs from routine 

municipal wastewater infrastructure 

expenditures. Further, local and state 

governments currently fund the 

majority of wastewater infrastructure 

costs. Mechanisms for compiling 

comprehensive national level 

information on expenditures on CSO 

and SSO control do not exist. The 

CWSRF is the most comprehensive 

source of information on state 

and local spending on wastewater 

projects. There are, however, several 

important limitations to using data 

from the CWSRF. First, operation 

and maintenance (O&M) costs are 

not reported. Second, many CSO 

communities do not participate in the 

CWSRF. Third, the CWSRF has no 

separate accounting categories for SSO 

control. Moreover, although many 

communities and states are making 

concerted efforts to report additional 

needs for CSO and SSO control, very 

few report the cost of implementing 

technologies.

Although the above considerations 

shaped the approach used to develop 

this report, the basic objectives—to 

respond to Congress with an accurate 

characterization of the volume, 

frequency, and location of CSOs and 

SSOs; the extent of human health 

and environmental impacts caused by 

CSOs and SSOs; the resources spent 

by municipalities to address these 

impacts; and the technologies used to 

address impacts—never varied. 

3.6 What Quality Control 

and Quality Assurance 

Protocols Were Used?

EPA applied a detailed data 

verification and interpretation 

process following data 

collection. Federal and state data 

sets were evaluated for missing and 

inconsistent data. Follow-up phone 

calls were made to data providers to 

verify the accuracy and completeness 

of EPA’s records. Likewise, site-specific 

examples of impacts and technology 

application were reviewed by local 

officials.

The data taken from reports prepared 

by external sources, such as ASCE and 

AMSA, were not obtained directly by 

EPA and were used as reported. These 

data were not subjected to the same 

quality control as data collected and 

compiled directly by EPA.

3.7 Summary

Chapters 4 through 9 provide 

a detailed assessment of the 

data and materials collected 

in support of this Report to Congress. 

The compilation of existing data led to 

development of several new analyses 

that previously did not exist. These 

include:

● National estimates of the 

frequency and volume of SSOs

● Analysis of causes of SSOs
3-12

Report to Congress on the Impacts and Control of CSOs and SSOs

● National modeling of SSO events 

to estimate violations of water 

quality standards

● Updated CSO permit information 

with latitude and longitude for 

over 90 percent of CSO outfalls

● Analysis linking CSO outfall 

locations with impaired waters and 

sensitive areas through the NHD 

● Modeling to estimate the number 

of gastrointestinal illnesses 

resulting from exposure to CSOs 

and SSOs at BEACH Survey 

beaches
is, those CSOs that are rainfall- or 

snowmelt-induced and occur at 

permitted CSO outfalls. Dry weather 

CSO discharges are prohibited under 

the NPDES program.

SSOs can be induced by rainfall or 

snowmelt when excess I/I causes the 

conveyance capacity of the SSS to be 

exceeded. SSOs also occur as a result 

of other, non-wet weather causes such 

as blockages, line breaks, vandalism, 

mechanical failures, and power failure. 

The terms “wet weather SSOs” and 

“dry weather SSOs” are used in this 

report to differentiate these two 

general types of SSOs because these 

events have different characteristics 

and respond to different control 

strategies. The discussion of SSOs 

in this report, including national 

estimates of volume and frequency, 

does not account for wet weather or 

dry weather discharges occurring after 

the headworks of the treatment plant, 

regardless of the level of treatment, 

or backups into buildings caused 

by problems in the publicly-owned 

portion of the SSS.

Chapter 4

Consistent with the 

congressional directive, 

this chapter provides a 

comprehensive description of 

CSOs and SSOs with respect to the 

location of discharges, the frequency 

and volume of discharges, and the 

constituents discharged. Similarities 

and differences in the character of 

CSO and SSO discharges are noted 

where they occur. Comparisons of 

CSOs and SSOs to other sources of 

pollution have been made where 

appropriate. The CSO and SSO 

characterization information provided 

in this chapter is important for 

assessing the environmental and 

human health impacts of CSOs and 

SSOs.

For purposes of this Report to 

Congress, the terms “wet weather” and 

“dry weather” are used to distinguish 

sewer overflows that are rainfall- or 

snowmelt-induced from those that are 

not caused by rainfall or snowmelt. 

The discussion of CSOs in this report 

is limited to wet weather CSOs. That 

4-1

4.1 What Pollutants are in 

CSOs and SSOs?

4.2 What Factors Influence 

the Concentrations of the 

Pollutants in CSOs and 

SSOs?

4.3 What Other Point and 

Nonpoint Sources Might 

Discharge These Pollutants 

to Waterbodies Receiving 

CSOs and SSOs?

4.4 What is the Universe of 

CSSs?

4.5 What are the 

Characteristics of CSOs?

4.6 What is the Universe of 

SSSs?

4.7 What are the 

Characteristics of SSOs?

4.8 How Do the Volumes 

and Pollutant Loads from 

CSOs and SSOs Compare 

to Those from Other 

Municipal Point Sources?

Characterization of 

CSOs and SSOs

In this chapter:
4-2

Report to Congress on the Impacts and Control of CSOs and SSOs

4.1 What Pollutants are in CSOs 

and SSOs?

The principal pollutants present 

in CSO and SSO discharges 

include:

● Microbial pathogens

● Oxygen depleting substances 

(measured as BOD5)

● TSS

● Toxics

● Nutrients

● Floatables

The pollutants in CSOs and SSOs 

come from a variety of sources. 

Domestic wastewater contains 

microbial pathogens, BOD5, TSS, 

and nutrients. Wastewater from 

industrial facilities, commercial 

establishments, and institutions can 

contribute additional pollutants such 

as fats, oils, and grease (FOG), and 

toxic substances including metals 

and synthetic organic compounds. 

Fungi do not have a major presence 

in wastewater (WERF 2003b). Storm 

water can also contribute pollutants to 

CSSs and, in some instances, SSSs. The 

concentration of pollutants in storm 

water is generally more dilute than in 

wastewater, but can contain significant 

amounts of microbial pathogens, 

BOD5, TSS, toxics (notably metals and 

pesticides), nutrients, and floatables. 

Pollutant concentrations in CSOs and 

SSOs vary substantially, not only from 

community to community and event 

to event, but also within a given event. 

Descriptions of the pollutants in CSOs 

and SSOs are provided in the following 

subsections and include comparisons 

of concentration data for discharges 

from different municipal sources. The 

comparisons include, where available, 

median pollutant concentrations 

and ranges of concentrations found 

in treated wastewater, untreated 

wastewater, CSOs, wet weather 

SSOs, dry weather SSOs, and urban 

storm water. The origin and relative 

availability of data on pollutant 

concentrations in discharges were not 

consistent for the different municipal 

sources. In general, adequate data 

were available to characterize treated 

and untreated wastewater, CSOs, and 

urban storm water. Monitoring data 

to characterize actual wet and dry 

weather SSO discharges, however, were 

less readily available. 

EPA compiled a limited dataset on 

pollutant concentrations in wet 

weather SSOs as part of municipal 

interviews conducted for this Report 

to Congress. EPA also identified a 

study conducted by the Wisconsin 

Department of Natural Resources 

that quantified the concentration 

of various constituents in wet 

weather SSOs from a number of 

federal and locally-sponsored studies 

(WDNR 2001). The findings of 

the WDNR study support the data 

EPA collected on wet weather SSOs 

for this Report to Congress. For 

the purposes of this report, EPA 

assumed that dry weather SSOs would 

have the same characteristics and 

pollutant concentrations as untreated 

wastewater.

The descriptions of pollutants in CSOs 

and SSOs include an overview of the 

types of impacts typically associated 

with these pollutants. The presence of 

pollutants in a CSO or SSO discharge 

in and of itself is not indicative of 
 Chapter 4—Characterization of CSOs and SSOs

4-3

environmental or human health 

impacts. The occurrence of actual 

impacts depends on the concentration 

of the pollutant present, the volume 

and duration of the CSO or SSO 

event, the location of the discharge, 

the condition of the receiving water at 

the time of the discharge, and, in the 

case of human health, exposure. More 

detailed discussions of environmental 

and human health impacts of CSOs 

and SSOs are presented in Chapters 5 

and 6, respectively.

4.1.1 Microbial Pathogens

Microbial pathogens are 

microorganisms that can cause disease 

in aquatic biota and illness or even 

death in humans. The three major 

categories of microbial pathogens 

present in CSOs and SSOs are 

bacteria, viruses, and parasites. These 

microbial pathogens are, for the most 

part, easily transported by water. A 

brief discussion of these pathogens, 

including the concentrations present 

in various municipal discharges, is 

presented below. A more detailed 

discussion of pathogens is presented in 

Chapter 6 of this report.

Bacteria

The two broad categories of bacteria 

associated with wastewater are 

indicator bacteria and pathogenic 

bacteria. Indicator bacteria are widely 

used as a surrogate for microbial 

pathogens in wastewater and water 

quality assessments. Indicator bacteria 

suggest the presence of disease-causing 

organisms, but generally are not 

pathogenic themselves. The principal 

indicator bacteria used to assess water 

quality are fecal coliform, E. coli, and 

enterococcus. All three are found in 

the intestines and feces of warmblooded animals. 

Fecal coliform concentrations from 

municipal sources are presented in 

Table 4.1. As shown, concentrations of 

fecal coliform found in CSOs and wet 

weather SSOs are generally less than 

the concentrations found in untreated 

wastewater and dry weather SSOs, 

and greater than the concentrations 

reported for urban storm water. 

Pathogenic bacteria are capable 

of causing disease. Examples of 

pathogenic bacteria associated with 

untreated wastewater, CSOs, and SSOs 

Table 4.1

Municipal Sources

Fecal Coliform (colonies/100 ml)

Number of 

Samples Range Median

Untreated wastewater/dry 

weather SSOs

-- 1,000,000a - 

1,000,000,000d

--

Wet weather SSOsa -- -- 500,000

CSOsb 603 3 - 40,000,000 215,000

Urban storm waterc 1,707 1 -5,230,000 5,081

Treated wastewater -- -- <200e

a WDNR 2001

b Data collected as part of municipal interviews

c Pitt et al. 2003

d NRC 1996

e Limit for disinfected wastewater

Fecal Coliform 

Concentrations in 

Municipal Discharges

The presence of fecal coliform 

bacteria in aquatic environments 

indicates that the water has been 

contaminated with fecal material 

of humans or other warm-blooded 

animals.
4-4

Report to Congress on the Impacts and Control of CSOs and SSOs

include Campylobacter, Salmonella, 

Shigella, Vibrio cholerae, and Yersina.

Viruses

More than 120 enteric (intestinal) 

viruses may be found in sewage (NAS 

1993). Concentrations of viruses 

reported in wastewater vary greatly 

and depend on the presence and 

amount of infection in the population 

served by a sewer system, season 

of the year, and the methods used 

for enumerating the virus counts. 

Examples of viruses associated with 

untreated wastewater, CSOs, and SSOs 

include poliovirus, infectious hepatitis 

virus, and coxsackie virus.

Parasites

The common parasites of human 

health concern in untreated 

wastewater are parasitic protozoa 

and helminths (NAS 1993). 

Parasitic protozoa include Giardia, 

Cryptosporidium, and Entamoeba. 

Giardia is the most common 

protozoan infection in the United 

States (NAS 1993). Giardia has been 

detected in treated and untreated 

wastewater at levels of 0.0002 to 0.011 

cysts per L and 2 to 200,000 cysts 

per L, respectively (Payment and 

Franco 1993; Yates 1994; NAS 1998; 

Rose et al. 2001b). Cryptosporidium

has also been detected in treated 

and untreated wastewater at 

concentrations of 0.0002 to 0.042 

oocysts per L and less than 0.3 to 

13,700 oocysts per L, respectively 

(Payment and Franco 1993; NAS 1998; 

Rose et al. 2001a; McCurin and Clancy 

2004).

Several recent studies have specifically 

investigated the presence of 

Cryptosporidium and Giardia in CSOs. 

Giardia concentrations ranging from 

2 to 225 cysts per L were measured in 

samples collected during two overflow 

events at each of the six CSO outfalls 

(EPA 2003f). A study conducted in 

Pittsburgh also found Cryptosporidium

(0 to 30 oocysts per L) and Giardia

(37.5 to 1,140 cysts per L) in CSOs 

(States et al. 1997). Given that both 

CSOs and SSOs include untreated 

wastewater, this suggests that CSOs 

and SSOs are also likely to contain 

significant concentrations of Giardia, 

and possibly Cryptosporidium. 

Helminths include roundworms, 

hookworms, tapeworms, and 

whipworms. These organisms are 

endemic in areas lacking inadequate 

access to hygiene facilities, including 

toilets. Their transmission is generally 

associated with untreated sewage and 

sewage sludge. However, there is very 

little documentation of waterborne 

transmission of helminths (NAS 

1993).

4.1.2 BOD5

BOD5 is widely used as a measure of 

the amount of oxygen-demanding 

organic matter in water or wastewater. 

The organic matter in sewage is a 

mix of human excreta, kitchen waste, 

industrial waste, and other substances 

discharged into sewer systems. 

When significant amounts of BOD5

are discharged to a waterbody, the 

dissolved oxygen can be depleted. This 

occurs principally through the decay 

of organic matter and the uptake of 

oxygen by bacteria. The depletion 

of dissolved oxygen in waterbodies 

can be harmful or fatal to aquatic 

life. Low levels of dissolved oxygen 

are responsible for many of the fish 
 Chapter 4—Characterization of CSOs and SSOs

4-5

kills reported and tracked by resource 

agencies. BOD5 concentrations from 

municipal sources are presented in 

Table 4.2. As shown, the median 

concentrations of BOD5 in CSOs and 

wet weather SSOs are typically five 

times greater than concentrations 

found in urban stormwater. Median 

BOD5 concentrations in CSOs and 

wet weather SSOs are typically 1.3 to 

1.4 times greater than concentrations 

found in treated wastewater.

4.1.3 TSS

TSS is a measure of the small particles 

of solid pollutants that float on the 

surface of, or are suspended in, water 

or wastewater. TSS in wastewater 

includes a wide variety of material, 

such as decaying plant and animal 

matter, industrial wastes, and silt. 

High concentrations of TSS can 

cause problems for stream health 

and aquatic life. TSS can clog fish 

gills, reduce growth rates, decrease 

resistance to disease, and impair 

reproduction and larval development. 

The deposition of solids can damage 

habitat by filling spaces between 

rocks that provide shelter to aquatic 

organisms. TSS can accumulate in 

the immediate area of CSO and 

recurrent SSO discharges, creating 

turbid conditions that smother the 

eggs of fish and aquatic insects. 

TSS concentrations from municipal 

sources are presented in Table 4.3. As 

shown, the median concentration of 

TSS in CSOs and wet weather SSOs is 

Municipal Sources

BOD5 (mg/l)

Number of Samples Range Median

Untreated wastewater/dry 

weather SSOsa

-- 88 - 451 --

Wet weather SSOsb 22 6 - 413 42

CSOsb 501 3.9 - 696 43

Urban storm waterc 3,110 0.4 - 370 8.6

Treated wastewaterd -- -- 30

a AMSA 2003a. 85 facilities reported annual average BOD5 concentration data; each facility based its value on an 

 unspecified amount of monitoring

b Data collected as part of municipal interviews

c Pitt et al. 2003

d Typical limit for wastewater receiving secondary treatment

Municipal Sources TSS (mg/l)

Number of Samples Range Median

Untreated wastewater/dry 

weather SSOsa

-- 118 - 487 --

Wet weather SSOsb 27 10 - 348 91

CSOsb 995 1 - 4,420 127

Urban storm waterc 3,396 0.5 - 4,800 58

Treated wastewaterd -- -- 30

a AMSA 2003a. 121 facilities reported annual average TSS concentration data; each facility based its value on an 

unspecified amount of monitoring

b Data collected as part of municipal interviews

c Pitt et al. 2003

d Typical limit for wastewater receiving secondary treatment

Table 4.2

BOD5 Concentrations in 

Municipal Discharges

The consequences of high BOD5

concentrations are the same as 

those for low dissolved oxygen: 

aquatic organisms become stressed, 

suffocate, and die.

Table 4.3

TSS Concentrations in 

Municipal Discharges

Over the long-term, the deposition 

of solids in the immediate area of 

CSO and SSO discharges can 

damage aquatic life habitat.
4-6

Report to Congress on the Impacts and Control of CSOs and SSOs

higher than concentrations in urban 

storm water.

4.1.4 Toxics

Toxics are chemicals or chemical 

mixtures that, under certain 

circumstances of exposure, present an 

environmental or human health risk. 

Toxics include metals, hydrocarbons, 

and synthetic organic chemicals. 

Concentrations of toxics in wastewater 

can be a concern in industrialized 

areas or where monitoring data 

indicate potential toxicity (Moffa 

1997). Storm water contributions 

to CSOs in urbanized areas can also 

contain significant concentrations 

of hydrocarbons and metals. Metals 

concentrations from municipal sources 

are presented in Tables 4.4 and 4.5.

In general, environmental problems 

related to toxicity fall into two 

categories: chronic or long-term 

exposure to toxics causing reduced 

growth and reproduction, and acute 

Municipal 

Sources

Lead (μg/l) Zinc (μg/l)

Number of 

Samples

Range Median Number of 

Samples

Range Median

Untreated 

wastewater/dry 

weather SSOsa -- 0.5 -250 -- -- 9.7 - 1,850 --

Wet weather 

SSOs -- -- -- -- -- 159

CSOsb 438 5 - 1,013 48 442 10 - 3,740 156

Urban storm 

waterc 2,954 0.2 - 1200 16 3,016 0.1 - 22,500 117

Treated 

wastewaterd 21 0.2 - 1.4 0.6 530 20.0 - 57.5 51.9

a AMSA 2003a. 101 and 109 facilities reported annual average Cd and Cu concentrations, respectively; each facility 

 based its value on an unspecified amount of monitoring

bData collected as part of municipal interviews

c Pitt et al. 2003

d WERF 2000

Municipal 

Sources

Cadmium (μg/l) Copper (μg/l)

Number of 

Samples

Range Median Number of 

Samples

Range Median

Untreated 

wastewater/dry 

weather SSOsa

−- 0.1 - 101 -- -- 1.8 - 322 --

Wet weather 

SSOs -- -- -- -- -- --

CSOsb 401 0.16 - 30 2 346 10-1,827 40

Urban storm 

waterc 2,582 0.04 - 16,000 1 2,728 0.6 - 1,360 16

Treated 

wastewaterd 465 0.01 - 3.0 0.04 596 2.8-16.0 5.2

a AMSA 2003a. 106 and 109 facilities reported annual average Pb and Zn concentrations, respectively; each facility based 

 its value on an unspecified amount of monitoring

bData collected as part of municipal interviews

c Pitt et al. 2003

d WERF 2000

Table 4.4

Cadmium and Copper 

Concentrations in 

Municipal Discharges

For many municipalities, the largest 

source of copper in wastewater is 

corrosion of copper pipes (PARWQCP 

1999). Other sources include 

industrial discharges, copper-based 

root killers, and cooling water 

discharges.

Table 4.5

Lead and Zinc 

Concentrations in 

Municipal Discharges

Municipal wastewater treatment 

facilities are reported to be the 

largest point source for zinc 

discharges to surface waters 

(WSDOH 1996).
 Chapter 4—Characterization of CSOs and SSOs

4-7

Nutrient Concentrations 

in Municipal Discharges

Nutrient additions can cause 

increased algae or aquatic weed 

growth that, in turn, can deplete 

dissolved oxygen, reduce biologic 

diversity, worsen aesthetics, and 

impair use for water supply (Moffa 

1997).

or short-term exposure at higher 

concentrations causing increased 

mortality. Chronic effects are subtle 

and difficult to identify, but can be 

observed by lower productivity and 

biomass (numbers of organisms), 

bioaccumulation of chemicals, or 

reduced biological diversity. Acute 

effects can be observed as immediate 

fish kills or severely reduced biologic 

diversity.

4.1.5 Nutrients

Nutrients is the term generally 

applied to nitrogen and phosphorus. 

Untreated wastewater contains 

significant amounts of nitrogen 

and phosphorus from domestic and 

industrial sources. CSSs also receive 

nutrients contained in urban runoff 

from street litter and chemical 

fertilizers applied to landscaped 

areas, lawns, and gardens. Nutrients 

are essential to the growth of plants 

and animals. Excess amounts of 

nitrogen and phosphorus can cause 

rapid growth of algae and nuisance 

plants, as well as eutrophic conditions 

that can lead to oxygen depletion. 

Total phosphorus and total kjeldahl 

nitrogen (a measure of ammonia 

and organic nitrogen) concentrations 

from municipal sources are presented 

in Table 4.6. As shown for total 

phosphorus, wet weather SSO 

concentrations are roughly equivalent 

to treated wastewater concentrations 

and are approximately one-third of 

untreated wastewater concentrations. 

Total phosphorus concentrations 

in CSO and urban stormwater are 

generally less than those in wet 

weather SSOs.

4.1.6 Floatables

Floatables is the term used to describe 

the trash, debris, and other visible 

material discharged when sewers 

overflow. In SSSs, floatables generally 

include sanitary products and other 

wastes commonly flushed down a 

toilet. In CSSs, floatables include litter 

and detritus that accumulate on streets 

and other paved areas that wash into 

CSSs during rainfall or snowmelt 

events. Floatables can have an adverse 

impact on wildlife, primarily through 

entanglement or ingestion. Floatables 

Table 4.6

Municipal 

Sources

Total Phosphorus (mg/l) Total Kjeldahl Nitrogen (mg/l)

Number of 

Samples

Range Median Number of 

Samples

Range Median

Untreated 

wastewater/dry 

weather SSOsa

-- 1.3 - 15.7 5.8 59 11.4 - 61 33

Wet weather 

SSOsb

-- -- 2 -- -- --

CSOsc 43 0.1 - 20.8 0.7 373 0 -82.1 3.6

Urban storm 

waterd

3,283 0.01 - 15.4 0.27 3,199 0.05 - 66.4 1.4

Treated 

wastewatera 72 0.07 - 6 1.65 64 0.5 - 32 3.95

a AMSA 2003a. 59 facilities reported annual average total P and TKN concentrations; each facility based its value on an 

 unspecified amount of monitoring

b WDNR 2001

c Data collected as part of municipal interviews

d Pitt et al. 2003
4-8

Report to Congress on the Impacts and Control of CSOs and SSOs

can also contribute to aesthetic impacts 

in recreation areas.

An extensive monitoring program 

conducted in New York City suggests 

that more than 90 percent of 

floatables in the city’s CSOs originate 

as street litter (NYCDEP 1997). The 

monitoring program specifically found 

that street trash, including plastics, 

polystyrene, and paper, accounted 

for approximately 93 percent of the 

floatables discharged. Personal hygiene 

items and medical materials accounted 

for approximately one percent of all 

floatables discharged into New York 

Harbor through CSOs. The remaining 

six percent of floatable items included 

glass, metal, wood, and cloth. 

4.2 What Factors Influence 

the Concentrations of the 

Pollutants in CSOs and 

SSOs?

The pollutant concentrations 

associated with CSO and SSO 

discharges are highly variable. 

Pollutant concentrations vary not 

only from site to site and event to 

event, but also within a given overflow 

event. Brief descriptions of some of 

the factors that influence pollutant 

concentrations in CSOs and SSOs are 

described in the following subsections. 

4.2.1 Factors Influencing Pollutant 

Concentrations in CSOs

The relative amounts of domestic, 

commercial, and industrial wastewater, 

and urban storm water carried by a 

CSS during specific wet weather events 

are the primary driver of pollutant 

concentrations in CSOs. Other factors 

that contribute to the variability 

include: 

● Elapsed time since the wet weather 

event began, with higher pollutant 

concentrations expected during 

the early stages of a CSO event 

(often termed the “first flush”);

● Time between the current 

and most recent wet weather 

events, with higher pollutant 

concentrations expected in CSOs 

occurring after lengthier dry 

periods; and

● Intensity and duration of the wet 

weather event.

The sudden rush of flow into a CSS 

brought on by rainfall, or in some 

instances, snowmelt, can create a 

first flush effect. The first flush effect 

occurs when pollutants washed from 

city streets and parking lots combine 

with pollutants re-suspended from 

settled deposits within the CSS. 

This combination can produce 

peak pollutant concentrations at 

the beginning of the CSO event, 

particularly if rainfall is intense. First 

flush effects are typically observed 

during the first 30 to 60 minutes of 

a CSO discharge (Moffa 1997). They 

are generally more pronounced after 

an extended dry period and in sewer 

systems with low gradients (slope). 

Many CSO control programs have 

been designed specifically to capture 

the first flush. 

4.2.2 Factors Influencing Pollutant 

Concentrations in SSOs

Wastewater flows generated by 

domestic, commercial, and industrial 

sources fluctuate on diurnal, weekend/

weekday, and seasonal cycles. Periods 
 Chapter 4—Characterization of CSOs and SSOs

4-9

of low and high flows are associated 

with water demand and use. SSSs 

carry varying amounts of I/I during 

wet weather periods, when the ground 

is saturated, and when the water table 

is elevated. The amount of I/I entering 

an SSS is influenced by:

● Age and condition of SSS 

components

● Local use of SSS for roof and 

foundation drainage

● Location of sewer pipes relative to 

the water table

● Characteristics of recent rainfall 

events

● Soil type and antecedent soil 

moisture conditions

The amount of I/I, in turn, influences 

the concentration of pollutants in SSO 

discharges. 

Dry weather SSOs consist mainly of 

domestic, commercial, and industrial 

wastewater, with limited amounts 

of I/I. Therefore, the pollutant 

concentrations in dry weather SSOs 

are most heavily influenced by the 

relative contribution from domestic, 

commercial, and industrial customers 

to the total flow.

4.3 What Other Point and 

Nonpoint Sources Might 

Discharge These Pollutants 

to Waterbodies Receiving 

CSOs and SSOs? 

CSOs and SSOs contribute 

to pollutant loadings where 

discharges occur. Waterbodies 

also receive pollutants of the types 

found in CSOs and SSOs from other 

point and nonpoint sources including: 

● Wastewater treatment facilities

● Decentralized wastewater 

treatment systems

● Industrial point sources

● Urban storm water

● Agriculture

● Domestic animals and wildlife 

● Commercial and recreational 

vessels

The contribution of pollutant loads 

from CSOs and SSOs relative to 

other point and nonpoint sources 

varies widely depending on the 

characteristics of the waterbody and 

the volume, frequency, and duration 

of CSO and SSO events. Each of these 

sources is discussed briefly below.

In 1999, the Augusta Sanitary District completed the first phase of a $40-million 

five-phase CSO Long Term Control Plan as part of an Administrative Order (AO). 

Phase One involved a $12.2-million upgrade of the wastewater treatment plant to 

increase the treatment capacity and to better treat excess wet weather flows from 

the CSS. Prior to the upgrade, excess wet weather flows received minimal treatment 

(sometimes bypassing primary and secondary treatment processes entirely) and 

were not disinfected prior to discharge. Since completion of the treatment plant 

upgrade, the District bypasses secondary treatment processes only during wet 

weather events, and has the capacity to provide primary treatment, chlorination, 

and dechlorination to the bypassed flows. Bypassing frequency has decreased by 

70 percent.

CSO-related Bypass at 

Wastewater Treatment Facility: 

Augusta, ME
4-10

Report to Congress on the Impacts and Control of CSOs and SSOs

4.3.1 Wastewater Treatment 

Facilities

Wastewater treatment facilities 

are designed to receive domestic, 

commercial, and industrial wastewater, 

and to treat it to the level specified in 

an NPDES permit. Permits typically 

define effluent concentration limits 

for BOD5 and TSS, and for indicator 

bacteria (typically fecal coliform, E. 

coli, or enterococci) when disinfection 

is required. Wastewater treatment 

facilities that discharge to impaired 

or sensitive waters may have more 

stringent effluent limits for BOD5,

TSS, or additional parameters (e.g., 

additional reduction of nutrients and 

metals). 

Wastewater treatment facilities in 

the United States are estimated to 

contribute to the impairment of 

four percent of the nation’s assessed 

rivers and streams; five percent of 

the nation’s assessed lakes, ponds, 

and reservoirs; and 19 percent of 

assessed estuaries (EPA 2002c). The 

concentrations of fecal coliform, 

BOD5, TSS, metals, and nutrients 

in treated and untreated wastewater 

can be compared using the tables in 

Section 4.1 of this report. 

Untreated and Partially Treated 

Discharges from Wastewater 

Treatment Facilities

In CSSs and to a lesser degree in 

SSSs, flows to wastewater treatment 

facilities increase during periods of 

wet weather. Significant increases in 

influent flow caused by wet weather 

conditions (e.g., due to I/I into the 

sewer system) can create operational 

challenges for treatment facilities 

and can adversely affect treatment 

efficiency, reliability, and control 

of treatment processes. Excess wet 

weather flows can result in discharges 

of untreated or partially treated 

wastewater at the treatment facility. 

Treatment plants are sometimes 

designed to route peak wet weather 

flows that exceed capacity around 

secondary treatment units and then 

blend them with treated wastewater to 

meet permit limits. Volumes associated 

with wet weather discharges can be 

substantial.

Treatment facilities serving CSSs 

may be allowed to discharge partially 

treated wastewater (e.g., wastewater 

having received primary treatment 

and disinfection, if necessary) during 

periods of wet weather, according to 

The Village Creek Wastewater Treatment Plant in Jefferson County, Alabama, 

routinely experienced peak wet weather flows greater than 10 times its annual 

average flow of 40 mgd. Due to extreme peak wet weather flows in the system, 

untreated wastewater was frequently diverted from the Village Creek plant and 

discharged without treatment. Between 1997 and 2001, excess wastewater flow 

was diverted and discharged an average of 41 times per year. Under a Consent 

Decree issued in 1996, Jefferson Country initiated corrective actions to address 

diversions of untreated wastewater from the Village Creek facility, as well as other 

problems within the system. The total cost for the improvements are estimated to 

approach $2.5 billion.

Wet Weather Bypass at 

Wastewater Treatment Facility 

Serving SSS: 

Jefferson County, AL
 Chapter 4—Characterization of CSOs and SSOs

4-11

the terms of their permit. Untreated 

wet weather discharges at treatment 

facilities serving CSSs are not 

permitted and are required to be 

reported to the NPDES authority 

within 24 hours of their occurrence.

With rare exception, treatment 

facilities serving SSSs are only 

permitted to discharge wastewater that 

has received appropriate treatment. 

Discharges of untreated wastewater 

at treatment facilities serving SSSs are 

required to be reported to the NPDES 

authority within 24 hours of their 

occurrence. 

4.3.2 Decentralized Wastewater 

 Treatment Systems

Decentralized wastewater treatment 

systems are on-site or clustered 

wastewater systems used to treat and 

dispose of relatively small volumes 

of wastewater, generally from private 

residences and businesses that are 

located in close proximity to each 

other. These systems serve individual 

residences as well as trailer parks, 

recreational vehicle parks, and 

campgrounds. They are commonly 

referred to as septic systems, private 

sewage systems, or individual 

sewage systems. Some decentralized 

systems are designed to have a 

surface discharge. Approximately 

25 percent of the total population 

of the United States is served by 

decentralized wastewater treatment 

systems, and about 33 percent of 

new residential construction employs 

this type of treatment (EPA 2003g). 

The 2001 American Housing Survey 

for the United States reported 

that approximately 6 percent of 

decentralized wastewater treatment 

systems fail annually. Depending 

on assumptions about persons per 

household and water use, these failures 

may result in improper treatment 

of 180 to 396 million gallons of 

wastewater daily, or 66 to 144 billion 

gallons discharged annually. Failing 

decentralized wastewater treatment 

systems can contribute to pathogen 

and nutrient contamination of surface 

water and groundwater (Bowers 2001).

4.3.3 Industrial Point Sources

Industrial point sources include nonmunicipal industrial and commercial 

facilities that treat and discharge 

wastewater, with attendant pollutants, 

directly to receiving waters. Unlike 

municipal wastewater treatment 

facilities, the types of raw materials, 

production processes, and treatment 

technologies utilized by industrial 

and commercial facilities vary 

widely. Consequently, the pollutants 

discharged by industrial point sources 

vary considerably and are dependent 

on specific facility characteristics (EPA 

1996b). In addition to wastewater, 

industrial point sources can also 

collect and discharge storm water 

runoff generated at their facility. 

Industrial point sources are regulated 

under the NPDES point source 

and storm water programs. Many 

discharges are governed by industryspecific effluent guidelines. Industrial 

point sources can be a major source 

of pollutants, particularly nutrients 

and toxics, in waters receiving the 

discharges.

4.3.4 Urban Storm Water

Urban storm water runoff occurs 

when rainfall does not infiltrate into 

the ground or evaporate. Urban storm 

water runoff flows onto adjacent 
4-12

Report to Congress on the Impacts and Control of CSOs and SSOs

land, directly into a waterbody, or 

is collected and routed through a 

separate storm sewer system. Urban 

storm water runoff is principally 

generated from impervious surfaces 

such as city streets and sidewalks, 

parking lots, and rooftops. In 

general, the degree of urbanization 

increases the variety and amount of 

pollutants carried by storm water 

runoff. Although concentrations of 

specific pollutants in urban storm 

water runoff vary widely, the most 

common pollutants include microbial 

pathogens from pet and wildlife 

wastes; TSS; metals, oil, grease, and 

hydrocarbons from motor vehicles; 

and nutrients, pesticides, and 

fertilizers from lawns and gardens 

(EPA 2003h). 

Urban storm water discharges are a 

leading cause of impairment of the 

nation’s surface waters (EPA 2002c). 

Storm water is estimated to contribute 

to the impairment of 5 percent of 

assessed river miles nationwide, 8 

percent of assessed lake acres, and 16 

percent of assessed estuarine square 

miles (EPA 2002). EPA has estimated 

that approximately 27.6 billion gallons 

of storm water runoff are generated 

daily from urbanized areas nationwide 

(EPA 2002c).

4.3.5 Agriculture

Agriculture is a major source of 

pollution in the United States and 

the leading source of impairment 

in assessed rivers and streams, as 

well as in assessed lakes, ponds, and 

reservoirs (EPA 2002c). Agricultural 

sources that contribute pollutant 

loads to waterbodies include row 

crops, pastures, feed lots, and holding 

pens. Agricultural practices that add 

pollution include over-application 

of manure, other fertilizers, and 

pesticides; tillage practices that leave 

the earth exposed to erosion; and 

pasture and range practices that 

provide livestock with direct access 

to waterways. These practices add 

microbial pathogens, BOD5, TSS, 

toxics, and nutrients to runoff from 

agricultural areas. More than 150 

microbial pathogens found in livestock 

manure are associated with health 

risks to humans. This includes the 

microbial pathogens that account 

for more than 90 percent of food 

and waterborne diseases in humans 

(EPA 2003i). These pathogens are 

Campylobacter, Salmonella (nontyphoid), Listeria monoctyogenes, 

pathogenic E. coli, Cryptosporidium, 

and Giardia.

4.3.6 Domestic Animals and 

Wildlife

Although livestock are believed to be 

the greatest contributor of animal 

waste to receiving waters, loads from 

pets, wild birds, and other mammals 

can be significant (EPA 2001d). This 

is particularly true in urban areas 

where there are no livestock, but pets 

and wildlife are common. In addition, 

the feces of waterfowl (e.g., geese 

and ducks) can contribute significant 

nutrient loads to waterbodies (Manny 

et al. 1994).

Animal waste associated with pets, 

wild birds, and small mammals can 

present significant risk to humans. 

Between 15 and 50 percent of pets and 

10 percent of mice and rats may be 

infected with Salmonella (NAS 1993). 

In addition, many wildlife species are 

reservoirs of microorganisms that can 

be pathogenic to humans. Beaver and 
 Chapter 4—Characterization of CSOs and SSOs

4-13

deer are large contributors of Giardia

and Cryptosporidium, respectively 

(EPA 2001d). Waterfowl such as geese, 

ducks, and heron can also contaminate 

surface waters with microbial 

pathogens (Graczyk et al. 1998). 

Bacteria source-tracking can be 

employed to establish the relative 

contribution of human and nonhuman sources to levels of indicator 

bacteria measured in a given 

waterbody. For example, watershed 

studies in the Seattle, Washington 

area found that nearly 20 percent of 

bacteria in receiving water samples 

were traceable to dogs (EPA 2001d). A 

study of Four Mile Run in Northern 

Virginia found that waterfowl 

accounted for 37 percent, humans 

and dogs together accounted for 26 

percent, and raccoons accounted for 

15 percent of the bacteria. Deer and 

rats contributed smaller percentages 

(NVPDC 2000).

4.3.7 Commercial and Recreational 

Vessels

Improper disposal of sewage by 

commercial and recreational vessels 

can spread disease, contaminate 

shellfish beds, and lower oxygen levels 

in receiving waters (CFWS 2003). 

Improper disposal is also a problem 

in marinas and harbors, despite 

the prohibition on the discharge of 

untreated sewage in the Great Lakes, 

in all navigable rivers, and within 

three miles of the U.S. coastline. 

Improper disposal of sewage occurs 

largely as a result of inadequate 

facilities on-board vessels and at 

docks, and a lack of education about 

safe handling and disposal of sewage. 

Boaters often illegally dump or dispose 

sewage improperly in marina toilets, 

overloading them (Baasel-Tillis 

1998). Impacts due to pollution from 

commercial and recreational vessels 

are highly localized. 

4.4 What is the Universe of 

CSSs?

Most CSSs are located in 

the Northeast and Great 

Lakes regions. Thirtytwo states (including the District of 

Columbia) have permitted CSSs in 

their jurisdiction. As of July 2004, 

these 32 states had issued 828 active 

CSO permits to 746 communities. 

These permits regulate 9,348 CSO 

discharge points. The distribution 

of CSO permits and CSO outfalls in 

each state are shown in Figures 4.1 

and 4.2, respectively. About 46 million 

people are served by CSSs, which 

include an estimated 140,000 miles of 

municipally-owned sewers.

CSO permits have been issued to the 

owners and operators of two types of 

CSSs:

● CSSs owned and operated by 

the same entity that owns and 

operates the receiving POTW; and

● CSSs that convey flows to a POTW 

owned and operated by a separate 

entity under a different permit.

Communities that operate and 

maintain a sewer system but send 

wastewater flows to a treatment plant 

owned and operated by another entity 

are referred to as “satellite systems.” 

The 828 active CSO permits include 

616 combined systems with POTWs, 

176 satellite systems, and 36 systems 

that EPA has been unable to classify 

due to insufficient data.
4-14

Report to Congress on the Impacts and Control of CSOs and SSOs

WA

OR

CA

MN

SD

KS

IA

MO

WI MI

IL IN

KY

TN

GA

WV VA

OH

PA

NY

ME

MA

RI

CT

NH

VT

NJ

DE

MD

DC

AK

NE

Region 10 Region 8 Region 5 Region 2 Region 1

Region 9 Region 7 Region 4 Region 3

Total Permits: 828

5

22

39

6 3 7

31

68

1 1

8

153

3

56

8

17

3

108 107

46

3

88

2

10

3

9

2

1

3

1 3

11

NJ NY CT MA ME NH RI VT

GA KY TN DC DE MD PA VA WV

IL IN MI MN OH WI

IA KS MO NE

SD

CA

AK OR WA

Figure 4.1

Distribution of CSO Permits by Region and by State

More than half of the nation’s 828 active CSO permits are held by communities in 

four states: Illinois, Indiana, Ohio, and Pennsylvania.
 Chapter 4—Characterization of CSOs and SSOs

4-15

WA

OR

CA

MN

SD

KS

IA

MO

WI

IL IN

KY

TN

GA

WV VA

OH

PA

NY

ME

MA

RI

CT

NH

VT

NJ

DE

MD

DC

AK

NE

MI

60 40 58

1,631

69

681

17

288

41

80 81

451

42 31

122

278

207

40 76 62

CT MA ME NH RI VT

255

1,032

NJ NY

GA KY TN DC DE MD PA VA WV

1,378

742

876

262

11

123

IL IN MI MN OH WI

IA KS MOa NE

1

SD

CA

3

86

224

AK OR WA

Region 10 Region 8 Region 5 Region 2 Region 1

Region 9 Region 7 Region 4 Region 3

Total Outfalls: 9,348

Figure 4.2

Distribution of CSO Outfalls by Region and by State

Similar to the distribution of CSO permits, CSO outfalls are also concentrated in the 

Northeast and Great Lakes regions.

aSince the 2001 Report to Congress—Implementation and Enforcement of the Combined Sewer Overflow Control Policy, the Missouri Department 

of Natural Resources has been working with its CSO communities to confirm the number of CSO outfalls for each NPDES permit. The significant 

increase in the number of CSO outfalls in Missouri is a result of this effort.
4-16

Report to Congress on the Impacts and Control of CSOs and SSOs

NPDES permittees are classified by 

regulatory authorities as “major” 

or “minor” dischargers. Facilities 

are classified as “major” when the 

wastewater treatment plant is designed 

to discharge more than 1 mgd. 

Facilities with flows less than 1 mgd 

may be classified as “major” when the 

NPDES authority determines that 

a specific permit needs a stronger 

regulatory focus. Classification as 

“major” is used to guide permitting, 

compliance, and enforcement activities 

to ensure that larger sources of 

pollutants are given priority. Major 

facilities are typically inspected 

annually and must report monthly 

effluent concentrations and loadings. 

Based on information available in 

EPA’s PCS for the 828 active CSO 

permits, EPA found that 57 percent 

were classified as major facilities. 

Facilities classified as “minor” usually 

have design flows less than 1 mgd. 

The CSO Control Policy established 

a population threshold of 75,000 to 

define small jurisdictions that may 

be held to less rigorous requirements 

in developing an LTCP for CSO 

control. EPA does not have population 

data by permit for CSSs. EPA has 

previously estimated that average daily 

wastewater flows are approximately 

100 gallons per capita per day (EPA 

1985). As a surrogate, plants treating 

7.5 mgd (75,000 x 100 gallons per 

capita per day) are used to define the 

upper limit of a small jurisdiction.

EPA obtained flow data for 398 of 

the 616 permits for CSSs that include 

a POTW. As shown in Figure 4.3, 73 

percent of CSO permits (with available 

flow data) are for POTWs with design 

flows less than 7.5 mgd, and therefore 

an estimated service population of less 

than 75,000.

4.5 What are the 

Characteristics of CSOs?

An accurate characterization 

of the frequency, volume, and 

location of CSO discharges, 

coupled with information on the 

pollutants present in the discharges, is 

9%

5%

13%

6%

24%

13%

30%

50 - 1600 mgd

20 - 50 mgd

7.5 - 20 mgd

5 - 7.5 mgd

2 - 5 mgd

1 - 2 mgd

<1 mgd

Small

Jurisdictions

73%

Distribution of POTW Treatment Capacities

Treated Flow (mgd)

Figure 4.3

Distribution of POTW 

Facility Sizes Serving CSSs

POTWs serving CSSs are designed to 

treat fl ows ranging from 0.1 mgd to 

1,600 mgd, but most treat less than 

7.5 mgd.
 Chapter 4—Characterization of CSOs and SSOs

4-17

needed to fully evaluate the potential 

for environmental and human health 

impacts from CSOs. This section 

describes the process EPA used to 

characterize CSO discharges at the 

national level.

4.5.1 Volume of CSOs

EPA applied the previously developed 

GPRACSO model to estimate 

the volume and pollutant loads 

attributable to CSOs nationwide. A 

summary of the GPRACSO model and 

how it was used to derive the national 

estimates presented in this report is 

provided in Appendix E. 

The GPRACSO model was applied to 

estimate the CSO volume associated 

with three planning-level scenarios. 

Corresponding BOD5 loads associated 

with the CSO volumes were also 

estimated. The three scenarios 

modeled are:

● Baseline scenario (1992) 

representing CSO volumes and 

pollutant loads prior to issuance 

of the CSO Control Policy.

● Current implementation scenario 

(2002) representing estimates 

of CSO volumes and pollutant 

loads with CSO controls that are 

currently in place.

● Full CSO Control Policy 

implementation scenario 

representing future CSO volume 

and pollutant loads assuming 

full implementation of the CSO 

Control Policy (e.g., four to six 

untreated overflows per year).

The three scenarios are compared in 

terms of CSO volume and pollutant 

load reduction in Table 4.7. National 

estimates of the annual volume of 

combined wastewater generated and 

treated are added for context. The 

volume of combined wastewater 

generated represents the volume of 

domestic, commercial, and industrial 

wastewater and storm water runoff 

that enters CSSs across the nation 

during wet weather periods under 

annual average conditions. The 

estimate of combined wastewater 

treated represents the amount of 

combined wastewater that receives the 

minimum treatment specified under 

Annual Volume 

(billion gallons/yr)

Annual Load 

(million pounds/yr)

Scenario

Combined 

Wastewater 

Generated 

Combined 

Wastewater 

Treated

Untreated 

CSO 

Discharged 

BOD5 from Untreated CSO 

Discharges

Baseline, prior to 

CSO Control Policy 4,250 3,180 1,070 445

Current level of CSO 

control 4,230 3,380 850 367

Full CSO 

Control Policy 

implementation

4,230a 4,070a 160 159

Table 4.7

Volume Reduction 

Estimates Based on 

Implementation of CSO 

Control Policy

EPA’s GPRACSO model was used to 

evaluate the potential reduction in 

discharges of untreated CSO and 

the attendant BOD5 loads based 

on current and future expected 

implementation of CSO controls.

a Assumes that the areas and populations served by CSSs will remain relatively constant at current levels through full 

implementation of the CSO Control Policy.
4-18

Report to Congress on the Impacts and Control of CSOs and SSOs

the CSO Control Policy (primary 

clarification or equivalent and 

disinfection, as necessary). The volume 

of combined wastewater treated under 

the three scenarios is not constant, 

as each reflects a different control 

condition.

EPA took a conservative approach 

in using the GPRACSO model to 

estimate reductions in CSO volumes 

and BOD5 loads. Only structural CSO 

controls, such as expanded capacity at 

a wastewater treatment facility, were 

considered. Non-structural controls, 

such as enhanced pretreatment 

requirements, inflow reduction, 

and pollution prevention, were not 

simulated with the GPRACSO model. 

The fact that sewer separation can 

lead to increased storm water volumes 

and loads was not factored into this 

analysis. 

The GPRACSO model estimates 

that prior to issuance of the CSO 

Control Policy (baseline scenario) 

approximately 1,070 billion gallons 

of untreated CSO and 445 million 

pounds of BOD5 were discharged 

annually from CSSs. Under the 

current implementation scenario, 

the GPRACSO model estimates that 

approximately 850 billion gallons 

of untreated combined sewage and 

367 million pounds of BOD5 are 

discharged from CSSs annually. The 

GPRACSO model estimates that the 

national CSO volume and associated 

BOD5 loads have decreased by 21 

percent and 18 percent, respectively, 

since issuance of the CSO Control 

Policy.

The full CSO Control Policy 

implementation scenario assumes 

that all CSO communities have, at a 

minimum, implemented the controls 

necessary to reduce the frequency of 

CSO events to an average of four to 

six untreated CSO events per year. The 

actual level of control needed to meet 

water quality standards may require 

measures beyond those needed for an 

average of four to six events per year. 

When full implementation is achieved 

under this scenario, the GPRACSO 

model predicts that approximately 

160 billion gallons of untreated CSO 

and 159 million pounds of BOD5

would be discharged annually from 

CSSs. Reaching a full implementation 

of CSO control will require 

communities with CSSs to provide 

the equivalent of primary clarification 

and disinfection, as necessary, to 

an estimated additional 690 billion 

gallons of currently untreated CSO 

discharges.

4.5.2 Frequency of CSOs

In the CSO Control Policy, a “CSO 

event” is defined as a discharge from 

one or more CSO outfalls in response 

to a single wet weather event. The 

frequency of CSO events in a given 

community can range from zero 

events to 80 or more per year. The 

frequency of CSO events in a given 

community can also vary considerably 

from year to year depending on 

weather conditions. The CSO Control 

Policy specifies that the evaluation 

of CSO control alternatives and 

development of LTCPs should be 

on a system-wide, annual average 

basis. Annual average conditions are 

typically established by performing a 

statistical analysis on local, long-term 

precipitation records that consider the 

number of precipitation events per 

year, maximum rainfall intensity, and 

average storm duration.
 Chapter 4—Characterization of CSOs and SSOs

4-19

In addition to estimating national 

CSO volumes and pollutant loads, 

the GPRACSO model was used to 

estimate the frequency of CSO events. 

Under the baseline scenario, prior to 

issuance of the CSO Control Policy, 

the GPRACSO model estimates that 

there were approximately 60,000 CSO 

events per year nationwide. Under 

the current implementation scenario 

with the current level of CSO control, 

the GPRACSO model estimates 

there are 43,000 CSO events per year 

nationwide, a reduction of 28 percent 

since the issuance of the CSO Control 

Policy.

4.5.3 Location of CSOs

A key EPA initiative undertaken 

as part of this Report to Congress 

was to update, verify, and digitally 

georeference the inventory of 

CSO outfalls documented as part 

of EPA’s 2001 Report to CongressImplementation and Enforcement of 

the CSO Control Policy. This effort 

resulted in establishing latitude and 

longitude coordinates for more than 

90 percent of CSO outfalls. 

With this new information, EPA 

was able to associate those CSO 

outfalls with latitude and longitude 

coordinates with specific waterbody 

segments (reaches) identified in the 

NHD. The NHD is a comprehensive 

set of digital spatial data of surface 

water features that enables analysis 

of water-related data in upstream 

and downstream order. Associating 

CSO outfall locations with the NHDindexed assessed waters allowed 

analysis of the types of waterbodies 

receiving CSO discharges. Through

 this analysis, EPA found:

● 75 percent of CSOs discharge to 

rivers, streams, or creeks;

● 10 percent of CSOs discharge to 

oceans, bays, or estuaries;

● 8 percent of CSOs discharge to 

waters that are unclassified or 

unidentified in the NHD;

● 5 percent of CSOs discharge to 

other types of waters (unnamed 

tributaries, canals, etc.); and

● 2 percent of CSOs discharge to 

ponds, lakes, or reservoirs.

Further, associating CSO outfall 

locations with the NHD-indexed 

assessed waters allowed comparison 

with impairments reported by states 

in the 303(d) program (waters not 

meeting water quality standards or not 

supporting their designated uses), and 

the location of protected resources 

and sensitive areas. These analyses are 

discussed in more detail in Section 

5.3 of this report. Additional detail on 

the CSO analysis using the NHD is 

presented in Appendix F. 

4.6 What is the Universe of 

SSSs?

EPA’s 2000 CWNS reported 

15,582 municipal SSSs with 

wastewater treatment facilities 

across the nation (EPA 2003b). EPA 

has also identified an additional 4,846 

satellite SSSs that collect and transport 

wastewater to regional treatment 

facilities (EPA 2003b). The number 

of SSSs with wastewater treatment 

facilities and the number of satellite 

systems are shown for each state in 

Figures 4.4 and 4.5, respectively. 
4-20

Report to Congress on the Impacts and Control of CSOs and SSOs

Distribution of SSSs with Wastewater Treatment Facilities by EPA 

Region and by State

SSSs are located in all 50 states. EPA’s 2000 CWNS reported 15,582 municipal SSSs with 

wastewater treatment facilities across the nation.

0 100 200 300 400 500 600 700 800

Region 3

Region 4

Region 2

Region 5

Region 6

Region 7

Region 8

Region 9

Region 10

Region 1

1500

1,363

CT

MA

ME

NH

RI

VT

NJ

NY

DE

MD

PA

VA

WV

AL

FL

GA

KY

MS

NC

SC

TN

IL

IN

MI

MN

OH

WI

AR

TX

NM

OK

LA

IA

KS

MO

NE

CO

MT

ND

SD

UT

WY

AZ

CA

HI

NV

AK

ID

OR

WA

Figure 4.4
 Chapter 4—Characterization of CSOs and SSOs

4-21

0 100 200 300 400 500 600 700 800

CT

MA

ME

NH

RI

VT

NJ

NY

DE

MD

PA

VA

WV

AL

FL

GA

KY

MS

NC

SC

TN

IL

IN

ME

MI

OH

WI

AR

TX

NM

OK

LA

IA

KS

MO

NE

CO

MT

ND

SD

UT

WY

AZ

CA

HI

NV

AK

ID

OR

WA

Region 3

Region 4

Region 2

Region 5

Region 6

Region 7

Region 8

Region 9

Region 10

Region 1

Figure 4.5

Distribution of Satellite SSSs by Region and by State

EPA identified 4,846 satellite SSSs that collect and transport flows to regional wastewater 

treatment facilities; such systems exist in all states, with the exception of Hawaii.
4-22

Report to Congress on the Impacts and Control of CSOs and SSOs

Figure 4.6

States Providing 

Electronic Data on SSO 

Discharges

EPA identified 25 states in which 

the NPDES authority is using an 

electronic data system to track the 

volume, frequency, location, and 

cause of SSO discharges within its 

jurisdiction. Data from these states 

were used to develop national 

estimates of SSO frequency and 

volume.

CA CO

WA

KS

OK

WI MI

IN

NC

GA

SC

ME

RI

NH

MD

AK

MA

FL HI

CT

NV UT

WY

ND

SD

MN

EPA estimates that 164 million people 

are served by municipal SSSs. EPA 

estimates that SSSs contain 584,000 

miles of municipally-owned sewer 

pipes and that approximately 500,000 

miles of privately-owned pipes deliver 

wastewater into SSSs (EPA 2003b).

As described in Section 4.4, NPDES 

permittees are commonly classified 

by NPDES authorities as “major” 

or “minor” dischargers. Based on 

information available in PCS for 

permits issued to SSSs with wastewater 

treatment facilities, EPA found that 

80 percent were classified as minor 

facilities, with average daily discharges 

less than 1 mgd.

4.7 What are the 

Characteristics of SSOs?

An accurate characterization 

of the frequency, volume, and 

location of SSO discharges, 

coupled with information on the 

pollutants present in the discharges, is 

needed to fully evaluate the potential 

for environmental and human health 

impacts from SSOs. Currently, there 

are no federal systems in place to 

compile data on the frequency, 

volume, and location of SSO 

discharges. This section describes the 

processes EPA used to characterize 

SSOs.
 Chapter 4—Characterization of CSOs and SSOs

4-23

4.7.1 SSO Data Management 

System

For the purposes of this report, EPA 

identified 25 states where the NPDES 

authority is using an electronic data 

system to track the volume, frequency, 

location, and cause of SSO discharges 

within its jurisdiction. As shown in 

Figure 4.6, these 25 states are spread 

across the nation.

EPA collected the individual state 

datasets and compiled them in a single 

SSO data management system. In its 

collection of SSO data from the states, 

EPA found that the definition of an 

“SSO event” varied. For example, 

some states include incidents such as 

secondary treatment bypasses which 

exceed NPDES permit limits by more 

than 50 percent at the main outfall, 

and spills from septic haulers as SSO 

events in their data systems. EPA also 

found that backups into buildings 

caused by problems in the publiclyowned portion of an SSS are not 

tracked by states. 

SSOs are untreated or partially treated 

releases from an SSS. The discussion 

of SSOs in this report does not 

include discharges occurring after the 

headworks of the treatment plant, 

regardless of the level of treatment; 

or backups into buildings caused 

by problems in the publicly-owned 

portion of an SSS. Datasets for each 

state were screened using these 

qualifiers. SSO events that did not 

meet the above criteria were omitted 

from the SSO data management 

system and from the analyses of 

SSO frequency, volume, and cause 

presented later in this chapter. 

Additional information on the data 

management system is provided in 

Appendix G of this report.

4.7.2 Statistical Technique Used 

to Estimate Annual National 

SSO Frequency and Volume 

National estimates of SSO frequency 

and volume were generated using 

reported data on 33,213 SSO events 

in 25 states that occurred in calendar 

years 2001, 2002, and 2003, combined 

with basic information describing 

the sewered universe in each state 

from the 2000 CWNS. This basic state 

information included:

● Total number of sewer systems 

by state (combined and separate 

sanitary);

● Number of SSSs by state; and

● Population served by SSSs by state.

To account for the uncertainty in the 

data reported by states, two separate 

scenarios were evaluated:

● The first scenario assumed that 

SSO events tracked in the state’s 

data system include all of the SSO 

events that occurred statewide 

during the reporting period.

● The second scenario assumed that 

SSO events tracked in the state’s 

data system include SSO events 

from only those communities that 

chose to report and are therefore 

a fraction of SSO events that 

occurred statewide during the 

reporting period.

Regression analyses demonstrated that 

the frequency of SSO events in a state 

is correlated both to the total number 

of SSSs as well as to the population 

served, although neither parameter 
4-24

Report to Congress on the Impacts and Control of CSOs and SSOs

is a perfect predictor. To account for 

the uncertainty as to which provides 

the better national estimate of SSO 

frequency, two additional subscenarios were analyzed: 

● Estimating SSO event frequency 

for non-reporting states based on 

total number of SSSs in each state; 

and

● Estimating SSO event frequency 

for non-reporting states based 

on the total population served by 

SSSs in each state.

National estimates of SSO volume 

were generated using the following 

five-step procedure:

1. Tabulate the total number of 

events and SSO volume for each 

of the reporting states.

2. Estimate the total number of SSO 

events per year for each nonreporting state based on a) the 

number of SSSs in the state, and 

b) the population served by SSSs 

in the state.

3. Divide the total number of events 

in each non-reporting state into 

different categories describing the 

cause of the SSO event, accounting 

for observed regional differences 

from the 25 reporting states.

4. Calculate SSO volume for each 

cause category in each nonreporting state, accounting for 

observed regional differences.

5. Calculate national estimates 

by summing the total number 

of events by state and the total 

volume across all states.

A detailed explanation of the statistical 

techniques applied to the SSO data 

provided by the 25 states is presented 

in Appendix G.

4.7.3 Frequency of SSOs

Between January 1, 2001, and 

December 31, 2003, 33,213 SSO 

events were reported by individual 

communities in the 25 states. 

During this three-year period, 2,663 

communities reported one or more 

SSO discharges. The number of 

SSO discharges reported by each 

community is presented in Figure 

4.7. As shown, most of the 2,663 

Figure 4.7

> 100

76 - 100

51 - 75

41 - 50

31 - 40

21 - 30

11- 20

8 - 10

5-7

2-4

1

1%

1%

2%

3%

7%

5%

9%

28%

40%

2%

2%

Percent Reported

Range of Reported SSOs

Total Number of SSO 

Events Reported by 

Individual Communities, 

January 1, 2001 - 

December 31, 2003

Nearly 70 percent of the 

communities in the 25 states 

reported between one and four 

SSO events during the three-year 

reporting period.
 Chapter 4—Characterization of CSOs and SSOs

4-25

communities reported between one 

and four SSO events during the 

three-year reporting period. One 

community reported more than 1,300 

SSOs over the three years. 

Using the statistical techniques 

described previously, and in Appendix 

G, SSO frequency information in 

the SSO data management system 

was extrapolated into a national 

estimate. This analysis suggests that 

between 23,000 and 75,000 SSO 

events per year occur in the United 

States. EPA evaluated the SSO 

frequency information in the SSO 

data management system for regional 

trends and found only marginal 

regional effects for overall event 

frequency. Therefore, EPA did not 

make adjustments to the estimated 

number of SSO events in nonreporting states based on geographic 

location. 

4.7.4 Volume of SSOs

Estimated SSO volumes were reported 

and available for 28,708 (86 percent) 

of the 33,213 events included in 

the SSO data management system. 

Between January 1, 2001, and 

December 31, 2003, a total of 2.7 

billion gallons of SSO was reported 

discharged in the 25 states. The 

reported volume for individual SSO 

events ranged from one gallon to 88 

million gallons. The distribution of 

reported SSO volumes for these events 

is presented in Figure 4.8. As shown:

● More than half of the reported 

SSOs were less than 1,000 gallons;

● More than 80 percent of the SSOs 

were less than 10,000 gallons; and

● Approximately 2 percent of the 

SSOs were greater than 1 million 

gallons.

Further, the 1,000 largest SSO events 

(3 percent of reported events) 

accounted for almost 90 percent of the 

total SSO volume reported.

> 10,000,000

gallons

1,000,001 - 10,000,000

gallons

100,001 - 1,000,000

gallons

10,001 - 100,000

gallons

1,001 - 10,000

gallons

101 - 1,000

gallons

1 - 100

gallons

1%

<1%

5%

12%

29%

36%

17%

SSO Volume

Distribution of SSO Volume Reported Figure 4.8

Distribution of SSO 

Volume Reported Per 

Event

Estimated SSO volumes were 

available for 86 percent of events in 

the SSO data management system. 

The reported volumes for individual 

SSO events ranged from one gallon 

to 88 million gallons.
4-26

Report to Congress on the Impacts and Control of CSOs and SSOs

Using the statistical techniques 

described in Appendix G, data on the 

volume discharged during individual 

SSO events were extrapolated into 

a national estimate of the annual 

volume of SSO discharged. This 

analysis suggests that the total SSO 

volume discharged annually is 

between three and 10 billion gallons. 

In an unpublished EPA report 

supporting a draft rulemaking on 

SSOs, EPA previously estimated that 

the national volume of SSO discharges 

caused by wet weather totaled 311 

billion gallons per year. That estimate 

was derived from a model designed 

to predict the relationship between 

the frequency of wet weather SSO 

events and the required national 

investment in SSO control measures. 

The model was based on variables 

such as sewer system capacity, acreage 

served by SSSs, and the percentage 

of rainfall that became I/I. Values 

assigned to each of these variables 

were based on very little empirical 

data, and the output of the model was 

not verified. EPA has a much higher 

degree of confidence in the national 

SSO volume estimates presented in 

this Report to Congress because the 

new estimates are based on a much 

larger empirical data set and rely on a 

simplified approach for extrapolating 

to a national estimate.

4.7.5 Location of SSOs

SSOs can occur at any location in the 

SSS, including: manholes, cracks and 

other defects in sewer lines, emergency 

relief outlets, and elsewhere. Reports 

of SSO events often include street 

addresses where the spill occurred. 

Because SSO events can occur at so 

many locations, gathering latitude and 

longitude for SSOs at a national level 

is impractical. Rather, it is more useful 

to look at the cause of the events, 

which is often linked to the type of 

location where it occurs. EPA grouped 

the reported SSO events into five 

broad cause categories: 

● Blockages

● Wet weather and I/I

● Power and mechanical failures 

● Line breaks

● Miscellaneous (e.g., vandalism, 

contractor error)

In general, SSOs attributed to 

wet weather and I/I are caused by 

insufficient sewer system capacity, 

while the other types of spills are 

attributable to sewer system operation 

and maintenance.

Cause information was available for 

77 percent of the SSO events included 

in the SSO data management system. 

As shown in Figure 4.9, 48 percent 

of all SSO events with a known cause 

were the result of the complete or 

partial blockage of a sewer line, and 

26 percent of SSO events were caused 

by wet weather and I/I. In general, the 

communities reporting large numbers 

of SSO events have programs that 

place a strong emphasis on tracking. 

As a result, EPA believes that these 

communities are likely to identify 

additional low-volume SSO events 

(e.g., SSOs resulting from blockages) 

that have the potential to go unnoticed 

or unreported in other jurisdictions.

EPA evaluated the reported causes 

of SSO events in the SSO data 

management system for regional 

trends and found significant 
 Chapter 4—Characterization of CSOs and SSOs

4-27

differences in the cause of SSO events 

between EPA regions. Specifically, 

EPA found that nearly three-quarters 

of SSO events in the arid Southwest 

were caused by blockages, while more 

than half of SSO events in Great 

Lakes states were attributed to wet 

weather and I/I. Therefore, average 

regional distributions for SSO cause 

were developed and applied in the 

estimation of SSO volume in nonreporting states. More information 

on regional trends in SSO cause is 

presented in Appendix G.

EPA found that individual SSO event 

volumes show a strong correlation 

with cause, with the smallest events 

attributed to blockages and the largest 

events occurring as a result of wet 

weather or excessive I/I. As shown 

in Table 4.8, the average volume of 

SSO events caused by wet weather or 

excessive I/I is much greater than the 

average volume for any other type of 

SSO event.

Additional analysis was performed 

on the cause of SSO events in those 

communities reporting more than 

100 events during a calendar year 

(either 2001 or 2002); this analysis 

was done to determine whether the 

distribution of causes was markedly 

different in municipalities reporting 

higher numbers of SSO events. As 

shown in Figure 4.10, EPA found 

that communities reporting higher 

numbers of SSO events attributed 

a significantly higher percentage of 

their SSO events to blockages and a 

correspondingly lower percentage of 

SSO events to wet weather and I/I.

More detailed information on cause 

was available for approximately 80 

percent of the more than 12,000 SSO 

events attributed to the complete or 

Causes of SSO Events

Blockages 48%

Wet weather and I/I 26%

Mechanical or power failures 11%

Line breaks 10%

Miscellaneous 5%

Total 100%

Percent

Figure 4.9

Most Common Reported 

Causes of SSO Events

Nearly 50 percent of all SSO events 

with a known cause were the result 

of complete or partial blockage of 

a sewer line.

Cause Average SSO 

Event Volume

(gallons)

Median SSO 

Event Volume

(gallons)

Total Volume

(million gallons)

Percent 

of Total 

Volume

Blockages 5,900 500 69 3

Wet weather and I/I 360,000 14,400 1,860 74

Mechanical or power 

failures

63,000 2,000 157 6

Line breaks 172,000 1,500 239 9

Miscellaneous 260,000 1,200 199 8

Table 4.8

SSO Event Volume by 

Cause

Although wet weather and I/I 

was listed as the cause for onequarter of SSO events, these events 

account for nearly three-quarters of 

the total SSO volume discharged.
4-28

Report to Congress on the Impacts and Control of CSOs and SSOs

partial blockage of a sewer line. As 

shown in Figure 4.11, grease from 

restaurants, homes, and industrial 

sources is the most common cause 

of reported blockages. Grease is 

problematic because it solidifies, 

reduces conveyance capacity, and 

blocks flow. Grit, rocks, and other 

debris that find their way into the 

sewer system account for nearly a 

third of the reported blockages. Roots 

are responsible for approximately 

one quarter of reported blockages. 

Roots are problematic because they 

penetrate weaknesses in sewer lines 

at joints and other stress points, and 

cause blockages.

4.8 How Do the Volumes and 

Pollutant Loads from 

CSOs and SSOs Compare 

to Those from Other 

Municipal Point Sources?

As described in Section 4.3, 

waterbodies receive pollutant 

loads of the types found in 

CSOs and SSOs from other urban and 

rural sources. Responsibility for two of 

these sources—wastewater treatment 

plants and urban storm water 

runoff—belongs almost exclusively 

to municipalities. Comparing 

information on annual discharges 

from municipal sources gives context 

Figure 4.10

Causes of Blockage Events

Grease 47%

Grit, rock, and other debris 27%

Roots 22%

Roots and grease 4%

Total 100%

Percent

Causes of SSO Events

Blockages 74%

Wet weather and I/I 14%

Line breaks 7%

Mechanical or power failures 3%

Miscellaneous 2%

Total 100%

Percent Reported Causes of 

SSOs in Communities 

Reporting More than 

100 SSO Events During a 

Single Calendar Year

EPA found that communities 

reporting higher numbers of SSO 

events (>100 per year) attributed a 

significantly higher percentage of 

their SSO events to blockages.

Figure 4.11

Reported Cause of 

Blockage Events

Grease--the most common cause 

of blockage--solidifies, reduces conveyance capacity, and can eventually block flow in sewers.
 Chapter 4—Characterization of CSOs and SSOs

4-29

to the magnitude of CSO and SSO 

discharges. At a national level, as 

shown in Table 4.9, the volume of 

CSOs and SSOs discharged is one to 

two orders of magnitude less than 

the total flow processed at wastewater 

treatment plants. The volume of urban 

storm water runoff generated annually 

is nearly equivalent to the volume of 

treated wastewater.

In addition to considering the volumes 

discharged by various municipal 

sources, it is also informative to 

consider their relative contributions 

in terms of pollutant loads at the 

national level. The comparisons of 

BOD5, TSS, and fecal coliform loads 

presented in Tables 4.10, 4.11, and 4.12 

are based on the volumes presented in 

Source Average Discharge Volume 

(billion gallons)

Percent of Total 

Municipal Discharges

Treated wastewatera 11,425 51%

CSOb 850 4%

SSOc 10 <1%

Urban storm water runoffd 10,068 45%

a EPA 2000a

b GPRACSO model, Section 4.5.1

c High estimate, Section 4.7.4

Source

Annual Discharge 

Volume 

(billion gallons)

Median BOD5 

Concentration 

(mg/L)

Total BOD5

Load 

(lbs. x 108)

% of Total 

Municipal 

BOD5 Load

Treated wastewater 11,425 30 28.5 72%

CSO 850 15-215a 3.7 9%

SSO 10 42 <0.1 <1%

Urban storm water runoff 10,068 8.6 7.2 19%

a BOD5 concentrations taken from the GPRACSO model vary with time, as described in Appendix E.

Table 4.10

Estimated Annual BOD5

Load from Municipal 

Point Sources

CSOs and SSOs contribute to a 

relatively low percentage of the 

total municipal BOD5 load disharged 

annually.

Table 4.9

Estimated Annual 

Municipal Point Source 

Discharges

On an annual basis, the volume 

of CSO and SSO discharged is a 

proportionally small amount of the 

total flow processed at municipal 

wastewater treatment facilities.

Source

Annual Discharge 

Volume 

(billion gallons)

Median TSS 

Concentration 

(mg/L)

Total TSS Load 

(lbs x 108)

% of Total 

Municipal 

TSS Load

Treated wastewater 11,425 30 28.5 33%

CSO 850 127 8.9 10%

SSO 10 91 < 0.1 < 1%

Urban storm water 

runoff

10,068 58 48.6 56%

Table 4.11

Estimated Annual TSS 

Load from Municipal 

Point Sources

Storm water discharges account for 

nearly 60 percent of the municipal 

TSS load discharged annually.

Source

Annual Discharge 

Volume 

(billion gallons)

Median FC

Concentration 

(#/100 ml)

Total FC Load 

(MPN x 1014)

% of Total 

Municipal 

FC Load

Treated wastewater 11,425 200a 865 1%

CSO 850 215,000 69,172 76%

SSO 10 500,000 1,892 2%

Urban storm water 

runoff

10,068 5,081 19,362 21%

a Assumes wastewater treatment includes disinfection

Table 4.12

Estimated Annual Fecal 

Coliform Load from 

Municipal Point Sources

CSOs appear to be the most 

significant source of fecal coliform 

when compared to other municipal 

point sources on an annual basis.
4-30

Report to Congress on the Impacts and Control of CSOs and SSOs

The District of Columbia Water and Sewer Authority quantified pollutant loads 

to receiving waters as part of its modeling analysis to support development of 

a CSO LTCP (DCWASA 2002). The CSO contribution to the tidal Anacostia River in 

Washington, D.C., was estimated to be 61 percent for fecal coliform and 14 percent 

for BOD5. Similarly, the CSO contribution to Rock Creek was estimated to be 41 

percent for fecal coliform and 6 percent for BOD5. Storm water from Washington, 

D.C., and suburban areas in Maryland as well as other upstream nonpoint sources 

accounted for the remaining loads in both watersheds.

Relative Contribution of CSOs 

to Bacterial Loads: 

Rouge River, MI

Relative Contribution of CSOs 

to Bacterial and BOD5 Loads: 

Washington, D.C.

Table 4.9, and on the concentrations 

presented in Tables 4.1, 4.2, and 4.3. 

As shown, CSOs and SSOs contribute 

a relatively low percentage of the 

total municipal BOD5 and TSS load 

discharged annually. CSOs, however 

appear to be the most significant 

municipal source of fecal coliform. 

Further, as shown earlier in Figure 4.1, 

most CSSs are located in the Northeast 

and Great Lakes regions. Therefore, 

the fraction of discharge volume and 

pollutant load attributed to CSOs in 

states with many CSSs and locally in 

communities with CSSs is likely to be 

much higher. Similarly, communities 

experiencing frequent and/or high 

volume SSO events are likely to 

attribute a larger percentage of the 

discharge volume and pollutant load 

to SSOs.

BOD5 , TSS, and fecal coliform loads 

from several important watershed 

sources of pollutants identified in 

Section 4.3 of this report, including 

agricultural practices and animal 

feeding operations, domestic animals 

and wildlife, and decentralized 

wastewater treatment systems, are not 

reflected in these comparisons. It is not 

practical to estimate the contributions 

of these various sources to the total 

annual load of BOD5, TSS, or fecal 

coliform on a national level; however, 

local examples provide some context.

A recent study on Michigan’s Rouge River (a river with a long history of CSOs and 

pollution problems) assessed the relative contributions of CSOs to overall bacterial 

indicator loads in the river (Murray and Bona 2001). This study conducted sampling 

for fecal coliform and fecal streptococci bacteria at 28 sites within the watershed. 

The results of the study suggest that CSOs contribute 10 to 15 percent of the total 

bacterial load in the watershed. The authors acknowledge the contributions of 

a variety of other sources, including non-CSO municipal sources and nonpoint 

sources. The nonpoint sources mentioned as other contributors included wildlife, 

domestic animals, rural runoff, contaminated groundwater, and faulty septic 

systems. 
other sources of pollution such as 

storm water runoff, decentralized 

wastewater treatment systems, and 

agricultural practices. This can make 

it difficult to identify and assign 

specific cause-and-effect relationships 

between CSO or SSO events and 

observed water quality impacts and 

impairments.

For the purpose of this report, 

environmental impacts do not include 

human health impacts. The extent of 

human health impacts due to CSOs 

and SSOs is discussed in Chapter 6.

5.1 What is EPA’s Framework 

for Evaluating 

Environmental Impacts?

EPA’s water quality standards 

program provides a framework 

for states and authorized tribes 

to assess and enhance the quality of 

the nation’s waters. Water quality 

standards define goals by designating 

uses for the water (e.g., swimming, 

boating, fishing) and setting pollutant 

Chapter 5

This chapter describes the 

extent to which CSOs and 

SSOs cause or contribute to 

environmental impacts. The chapter 

first discusses EPA’s framework for 

evaluating environmental impacts 

from CSOs and SSOs, using water 

quality standards. The chapter then 

summarizes environmental impacts 

from CSOs and SSOs as reported in 

national assessments and presents 

the results of new analyses completed 

by EPA. Next, site-specific examples 

are presented to illustrate the types 

of impacts that CSOs and SSOs have 

at the local watershed level. Lastly, 

the factors that affect the extent of 

environmental impacts caused by CSO 

and SSO discharges are described. 

In conducting data collection 

and research for this report, EPA 

found that CSOs and SSOs cause 

or contribute to environmental 

impacts that affect water quality and 

the attainment of designated uses. 

Pollutant concentrations in CSOs and 

SSOs alone may be sufficient to cause 

a violation of water quality standards. 

Impacts from CSOs and SSOs are 

often compounded by impacts from 

5-1

5.1 What is EPA’s Framework 

for Evaluating 

Environmental Impacts?

5.2 What Overall Water 

Quality Impacts Have Been 

Attributed to CSO and SSO 

Discharges in National 

Assessments?

5.3 What Impacts on Specific 

Designated Uses Have 

Been Attributed to CSO 

and SSO Discharges in 

National Assessments?

5.4 What Overall Water 

Quality Impacts Have Been 

Attributed to CSO and SSO 

Discharges in State and 

Local Assessments?

5.5 What Impacts on Specific 

Designated Uses Have 

Been Attributed to CSO 

and SSO Discharges 

in State and Local 

Assessments?

5.6 What Factors Affect the 

Extent of Environmental 

Impacts Caused by CSOs 

and SSOs?

Environmental Impacts of

CSOs and SSOs

In this chapter:
5-2

Report to Congress on the Impacts and Control of CSOs and SSOs

limits (criteria) necessary to protect 

the uses. 

Attainment of water quality standards 

is determined through a process of 

evaluation and assessment, as follows:

● States adopt water quality goals 

or standards that, once approved 

by EPA, serve as the foundation 

of the water quality-based control 

program mandated by the Clean 

Water Act. 

● States, EPA, and other federal 

agencies (e.g., U.S. Geological 

Survey) conduct water quality 

monitoring studies to measure 

water quality and assess changes 

over time.

● States compare measured water 

quality to goals or standards in 

a statewide assessment required 

under section 305(b) of the Clean 

Water Act and report conditions as 

good, threatened, or impaired. 

● Waters designated as impaired 

are included on a state’s 303(d) 

list. A total maximum daily load 

(TMDL) is required for each 

pollutant causing impairment. The 

TMDL establishes an allowable 

pollutant load that, when achieved, 

will result in the attainment of the 

water quality standard.

The discussion of environmental 

impacts in this chapter is focused on 

circumstances in which a designated 

use is not being attained due entirely 

or in part to CSO and SSO discharges. 

The pollutants found in CSOs and 

SSOs can potentially impact five 

designated uses:

● Aquatic life support, meaning the 

water provides suitable habitat for 

the protection and propagation of 

desirable fish, shellfish, and other 

aquatic organisms.

● Drinking water supply, meaning 

the water can supply safe 

drinking water with conventional 

treatment.

● Fish consumption, meaning the 

water supports fish free from 

contamination that could pose a 

significant human health risk.

● Shellfish harvesting, meaning 

the water supports a population 

of shellfish free from toxics 

and pathogens that could pose 

a significant health risk to 

consumers.

● Recreation, meaning waterbased activities (e.g., swimming, 

boating) can be performed 

without risk of adverse human 

health effects.

As discussed in Section 4.1 of this 

report, the principal pollutants 

present in CSOs and SSOs are: 

microbial pathogens, oxygen depleting 

substances, TSS, toxics, nutrients, 

and floatables. Table 5.1 summarizes 

designated uses likely to be impaired 

by each of these pollutants.
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-3

5.2 What Overall Water 

Quality Impacts Have Been 

Attributed to CSO and SSO 

Discharges in National 

Assessments?

S

tates are required to periodically 

assess the health of their waters 

and the extent to which water 

quality standards are being met. 

EPA compiles these reports into the 

NWQI, which offers a comprehensive 

review of water quality conditions 

nationwide. This section summarizes 

findings from the NWQI and describes 

two original analyses undertaken by 

EPA to identify potential water quality 

impacts from CSO and SSO discharges 

at the national level.

5.2.1 NWQI 2000 Report

Since 1975, EPA has prepared a series 

of biennial NWQI reports as required 

under Section 305(b) of the Clean 

Water Act. The NWQI 2000 Report, 

the most recently published report, is 

a compilation of assessment reports 

on the quality of state waters (EPA 

2002c). The NWQI Report categorizes 

assessed waters as follows: 

Good – fully supporting all uses 

or fully supporting all uses but 

threatened for one or more uses; or

Impaired – partially or not supporting 

one or more uses. 

Pollutants of Concern in CSOs 

and SSOs Likely to Cause or 

Contribute to Impairment

Aquatic life support

Drinking water 

supply

Fish consumption 

Shellfish harvesting

Recreation

Oxygen-demanding substances ●

Sediment (TSS) ●

Pathogens ●●●●

Toxics ● ●●

Nutrients ● ●

Floatables ●

Table 5.1

Pollutants of Concern in 

CSOs and SSOs Likely to 

Cause or Contribute to 

Impairment

The pathogens present in CSO and 

SSO discharges have the potential 

to impact several designated uses, 

including, drinking water supply, fish 

consumption, shellfish harvesting, 

and recreation.
5-4

Report to Congress on the Impacts and Control of CSOs and SSOs

Rivers and Streams (miles)

Percent assessed

Assessed as good

Assessed as impaired 19%

61%

39%

Total miles: 3,692,830

86%

14%

Ocean Shoreline (miles)

6%

Total miles: 58,618

Lakes, Reservoirs, and Ponds (acres)

Total acres: 40,603,893

55%

45%

43%

22%

78%

Great Lake Shoreline (miles)

Total miles: 5,521

36%

49%

51%

Estuaries and Bays (square miles)

Total sq. miles: 87,369

92%

Figure 5.1

NWQI 2000 Report: Summary of Assessed Waters by Waterbody Type 

(EPA 2002c)

Waterbody assessments are normally based on five broad types of monitoring data: biological 

integrity, chemical, physical, habitat, and toxicity. Monitoring data are then integrated for an overall 

assessment.

The national summary of the 

quality of assessed waters, by type, is 

presented in Figure 5.1. This summary 

shows that 19 percent of the nation’s 

total river and stream miles; 43 

percent of lake, reservoir, and pond 

acres; 36 percent of estuarine and 

bay square miles; 6 percent of ocean 

shoreline miles; and 92 percent of 

Great Lakes shoreline miles were 

assessed. 

EPA’s NWQI 2000 Report also 

identified the types of pollutants or 

stressors most often found to impair 

the assessed waters as well as the 

leading sources of these pollutants. 

These results are presented in Table 

5.2 and Table 5.3, respectively. Overall, 

EPA found that the three pollutants 

most often associated with impaired 

waters were solids, pathogens, and 

nutrients. All three are present in CSO 

and SSO discharges. Therefore, at a 

minimum, CSOs and SSOs contribute 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-5

Pollutant/Stressor

Rivers 

and 

Streams

Lakes, 

Ponds, 

and 

Reservoirs

Estuaries 

and Bays

Ocean 

Shoreline

Great

Lakes 

Shoreline

Habitat alterations 3

Metals 2 1

Nutrients 5 1 2

Oil and grease 5

Oxygen-depleting substances 4 5 3 2 5

Pathogens (bacteria) 1 4 1 3

Pesticides 2

Priority toxic organic 

chemicals

5 1

Siltation (sedimentation) 2 3 4

Suspended solids 4

Total dissolved solids 4

Turbidity 3

Pollutant Source

Rivers 

and 

Streams

Lakes, 

Ponds, 

and 

Reservoirs

Estuaries 

and Bays

Ocean 

Shoreline

Great

Lakes 

Shoreline

Agriculture 1 1 5 3

Atmospheric deposition 5 4 4

Contaminated sediment 1

Forestry 5

Habitat modifications 3 5

Hydrologic modifications 2 2

Industrial discharges 3

Land disposal 3

Municipal point sources 1 5

Nonpoint sources 4 2

Septic tanks 4

Urban runoff/storm sewers 4 3 2 1 2

Table 5.2

Pollutants and Stressors 

Most Often Associated 

with Impairment 

(EPA 2002c)

Overall, EPA found that the three 

pollutants most often associated 

with impaired waters were solids 

(i.e., suspended solids, siltation, 

and total dissolved solids), 

pathogens, and nutrients. This 

table ranks the top five pollutants 

(or stressors) for each waterbody.

Table 5.3

Leading Sources of 

Pollutants and Stressors 

Causing Water Quality 

Impairment 

(EPA 2002b)

Overall, EPA found that pollution 

from urban and agricultural land, 

transported by precipitation 

and runoff, is a leading source of 

impairment. This table ranks the 

top five pollutant sources causing 

water quality impairments.
5-6

Report to Congress on the Impacts and Control of CSOs and SSOs

to the loading of these pollutants 

where they occur. 

The NWQI 2000 Report did not cite 

CSOs or SSOs as a leading source 

of impairment in any of the five 

waterbody types listed in Table 5.3 

(EPA 2002c). CSOs were identified as a 

source of impairment for 1,466 square 

miles (5 percent) of assessed estuaries 

and 56 miles (1 percent) of Great 

Lakes shoreline.

The NWQI 2000 Report is based 

on a compilation of individual 

state assessments, and reporting 

of the source of impairment varies 

widely from state to state. The lack 

of uniformity in assessment and 

reporting makes it difficult to fully 

assess the magnitude of CSO and 

SSO impacts. Inconsistencies in 

state reporting of CSOs and SSOs as 

pollutant sources are described below.

Unknown sources and failure to 

classify: Some states cite unknown 

pollutant sources or do not attribute 

impairment to a specific source. 

Inconsistent source listing: CSOs are 

tracked as a specific pollutant source 

in many, but not all, states where they 

occur. Twenty of the 32 CSO states 

identified “combined sewer overflow” 

as a source of impairment, in the 

NWQI at least once. Where SSOs are 

identified by states, they are tracked 

in an inconsistent manner. States 

use categories such as “collection 

system failure (SSO),” “wet weather 

discharges,” and “spills” for tracking 

SSOs. 

Cumulative impacts from multiple 

pollutant sources: Impacts from CSOs 

and SSOs are often compounded 

by impacts from other sources of 

pollution, particularly during wet 

weather. As such, CSOs and SSOs may 

be grouped into municipal or urban 

source categories. 

EPA is working with the states to 

develop a framework to promote 

consistent listing of sources of 

impairment (EPA 2002d).

5.2.2 Analysis of CSO Outfalls 

Discharging to Assessed or 

Impaired Waters

As described in Section 4.5, a key 

EPA initiative undertaken as part of 

this report was to update, verify, and 

digitally georeference the inventory of 

CSO outfall locations documented as 

part of EPA’s 2001 Report to CongressImplementation and Enforcement of 

the CSO Control Policy. Through this 

effort, EPA established latitude and 

longitude coordinates for over 90 

percent of CSO outfalls. EPA then 

linked CSO outfall locations to other 

national-level data and assessments. 

For example, permitted CSO outfall 

locations were linked to 305(b)-

assessed waters and 303(d)-impaired 

waters. These analyses are presented 

in the following subsections. A similar 

analysis linking permitted CSO outfall 

locations with classified shellfish 

growing areas is presented in Section 

5.3.2. An analysis of CSO outfall 

proximity to drinking water intakes 

is presented in Chapter 6. More 

information on each of these analyses 

is provided in Appendix F.

As discussed in Chapter 4, SSOs 

do not necessarily occur at fixed 

locations. Therefore, a parallel effort 

to georeference SSO locations and 

evaluate their location with respect 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-7

Assessed Waters Total 

Assessed

Assessed as 

Good

Assessed as 

Impaired

Percent 

Impaired

Assessed 305(b) segments in CSO 

states with electronic 305(b) data 59,335 44,457 14,878 25%

Assessed segments within one mile 

downstream of a CSO outfall 733 181 552 75%

Table 5.4

Occurrence of 305(b) 

Assessed Waters Within 

One Mile Downstream of 

a CSO Outfall

EPA was able to complete this 

analysis only for states with 

electronic 305(b) data; that is, for 

19 of the 32 states with active CSO 

permits.

to other national-level data and 

assessments was not possible.

Analysis of CSO Outfalls Discharging 

to EPA’s 305(b) Assessed Waters

EPA was able to compare CSO outfall 

locations with assessed waters in the 

NWQI 2000 Report through the 305(b) 

assessment database for 19 CSO 

states with electronic 305(b) data. 

The purpose of this analysis was to 

determine the number of CSO outfalls 

discharging to waters classified as good 

or impaired. EPA limited the analysis 

to assessed water segments located 

within one mile downstream of a CSO 

outfall. The results of this analysis are 

summarized in Table 5.4. EPA found 

that of the 59,335 assessed water 

segments in CSO states with electronic 

305(b) data only a small number (733 

segments) were in close proximity 

to CSO outfalls. Of these, 75 percent 

(552 segments) were impaired. The 

proximity of a permitted CSO outfall 

to an impaired segment does not in 

and of itself demonstrate that the 

CSO is the cause of the impairment. 

CSOs generally are located in urban 

areas where waterbodies also receive 

relatively high volumes of storm water 

runoff and other pollutant loads. 

Nevertheless, the high percentage 

of impairment associated with CSO 

outfalls suggests some correlation 

between impairment and CSOs. 

Analysis of CSO Outfalls Discharging 

to EPA’s 303(d) Waters

EPA also compared CSO outfall 

locations to water segments identified 

in EPA’s Section 303(d) list of impaired 

waters in states with NHD-index 

data. For the purpose of this analysis, 

EPA assumed the causes of reported 

Section 303(d) impairment most likely 

attributed to or associated with CSOs 

were:

● Pathogens

● Organic enrichment, leading to 

low dissolved oxygen

● Sediment and siltation

Again, EPA limited the analysis to 

water segments located within one 

mile downstream of a CSO outfall. The 

results of this analysis are summarized 

in Table 5.5. EPA found that although 

less than one-tenth of one percent 

(1,560 of more than 1,495,000) of all 

waterbody segments in CSO states 

are within one mile of a CSO outfall, 

between five and 10 percent of the 

waters assessed as impaired are within 

that one mile. EPA believes the strong 

correlation between CSO location and 

impaired waters is due in part to the 
5-8

Report to Congress on the Impacts and Control of CSOs and SSOs

following factors: CSOs generally 

are located in urban areas where 

waterbodies also receive relatively 

high volumes of storm water runoff 

and other pollutant loads; and waters 

within urban areas are much are more 

likely to be assessed as part of the 

305(b) process.

As described in the 305(b) analysis, the 

existence of a permitted CSO outfall in 

close proximity to an impaired water 

does not in and of itself demonstrate 

that the CSO is the cause of the 

impairment. It does suggest, however, 

that CSOs should be considered as 

a potential source of pollution with 

respect to TMDL development. 

EPA has collected anecdotal data 

demonstrating that CSOs are being 

considered in TMDL development 

and that substantial load reductions 

have been assigned to CSOs in some 

communities as a result of the TMDL 

process. 

5.2.3 Modeled Assessment of SSO 

Impacts on Receiving Water 

Quality

The unpredictable nature of most SSO 

events makes it difficult to monitor 

and collect the data needed to measure 

the occurrence and severity of 

environmental impacts. As described 

in Section 4.7 of this report, however, 

EPA was able to compile a substantial 

amount of information on the 

frequency, volume, and cause of SSO 

events. From these data, EPA found 

72 percent of these SSO events reach a 

surface water. 

Using the national SSO data, EPA 

developed a simple model for 

estimating the likely impact of SSO 

events on different size receiving 

waterbodies, based on reasonable 

assumptions about SSO event 

duration and concentrations of fecal 

coliform bacteria in SSO discharges. 

For the purpose of this report, 

modeled impacts associated with 

SSO events are evaluated in terms 

of violations of the single sample 

maximum water quality criterion for 

fecal coliform. That is, a predicted 

concentration of greater than 400 

counts of fecal coliform per 100 mL of 

surface water would be considered to 

be a water quality standards violation. 

The model was run under three 

different scenarios: one that assumed 

the entire volume of each modeled 

SSO discharge reached a surface 

water (100% delivery), a second that 

assumed half the volume of each 

modeled SSO discharge reached a 

surface water (50% delivery), and 

a third that assumed ten percent of 

the volume of each modeled SSO 

discharge reached a surface water 

(10% delivery). 

 Reason or Cause of Listing

Listed Waters

 Pathogens Enrichment Leading 

to Low Dissolved 

Oxygen

Sediment 

and 

Siltation

Total number of listed waters in CSO 

states 3,446 1,892 3,136

Number of listed waters within one 

mile of a CSO outfall 191 163 149

Table 5.5

Occurrence of 303(d) 

Listed Waters Within 

One Mile Downstream 

of a CSO Outfall

Waters within one mile of a CSO 

outfall are much more likely to 

be assessed as impaired than a 

typical water in a CSO state.
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-9

Flow Rate 

(cfs)

Dilute Wastewater

(FC = 500,000 #/ml)

Medium Strength Wastewater 

(FC = 10,000,000 #/100 ml)

Concentrated Wastewater

(FC = 1,000,000,000 #/ml)

10% 

Delivery

50% 

Delivery

100% 

Delivery

10% 

Delivery

50% 

Delivery

100% 

Delivery

10% 

Delivery

50% 

Delivery

100% 

Delivery

50 12% 27% 36% 45% 68% 77% 95% 99% 100%

100 9% 20% 27% 36% 58% 68% 92% 98% 99%

250 5% 12% 18% 25% 45% 55% 84% 95% 97%

500 3% 9% 12% 18% 36% 45% 77% 92% 95%

1000 2% 6% 9% 13% 27% 36% 68% 86% 92%

5000 1% 2% 3% 5% 13% 18% 45% 68% 77%

10000 0% 1% 2% 3% 9% 13% 36% 58% 68%

Table 5.6

Estimated Percentage of 

Time SSOs Would Cause 

Water Quality Standard 

Violations

EPA developed a frequency 

distribution characterizing typical 

volumes of SSO events based on 

available data in order to estimate the 

likely impact of SSO events on water 

quality. 

Flow varies widely in receiving 

waters both from year to year and 

seasonally. Flow can also increase 

substantially in a particular receiving 

water during local wet weather 

events. The potential impact of a 

specific SSO discharge depends on a 

number of factors including flow and 

background pollutant concentrations 

in the receiving water at the time the 

discharge occurs, and the volume and 

strength of the discharge that reaches 

the receiving water.

The results of EPA’s simple model of 

SSO-related water quality impacts are 

presented in Table 5.6 for a range of 

flow conditions, wastewater strength, 

and delivery ratios. In general, SSOs 

consisting of concentrated wastewater 

are predicted to violate water quality 

standards the majority of the time, 

particularly under low flow conditions. 

In contrast, SSOs consisting of more 

dilute wastewater are much less likely 

to cause water quality standards 

violations, particularly under high 

flow conditions.

Flow in a particular waterbody can increase dramatically with a wet weather 

event. For example, after an extended period without rain, 2.6 inches of 

rain fell in the Washington, DC area over two days in late February, 2004. 

This, in turn, caused flow in local waterbodies to increase by varying 

amounts–e.g., to 63 times the median flow in the Anacostia River. The 

flows given reflect the peak daily flow observed due to this rainfall event.

Waterbody Median Flow 

(cfs)

February Storm Peak 

(cfs)

Peak Factor

Potomac River 8,490 79,300 9

Monocacy River 624 9,130 15

Goose Creek 250 4,480 18

Seneca Creek 91 1,630 18

Anacostia River 47 2,950 63

Example: Change in Flow 

in Washington, D.C. Area 

Waterbodies as a Result of Wet 

Weather
5-10

Report to Congress on the Impacts and Control of CSOs and SSOs

A detailed description of the 

methodology used to develop these 

estimates is presented in Appendix 

H. No comparable analysis of SSO 

discharges to lake or estuarine waters 

was undertaken.

5.3 What Impacts on Specific 

Designated Uses Have Been 

Attributed to CSO and SSO 

Discharges in National 

Assessments?

EPA, other federal agencies, 

and non-governmental 

organizations periodically 

conduct national assessments of 

environmental impacts that are framed 

in terms of the loss of a specific 

designated use. Examples include 

beach closures in waters designated 

for recreation and shellfish harvesting 

restrictions in waters designated for 

shellfishing. This section summarizes 

findings from a number of national 

assessments, with emphasis placed on 

environmental impacts identified as 

being caused, or contributed to, by 

CSOs or SSOs.

EPA was unable to identify national 

assessments that specifically consider 

the impacts of CSOs and SSOs on 

aquatic life, although EPA found 

several state and local watershed 

assessments which do so. These 

assessments are discussed in Section 

5.5 of this report. Also, for purposes 

of this report, impairment of drinking 

water supply as a designated use is 

considered to be a human health 

rather than an environmental impact. 

Consequently, drinking water supply is 

discussed in Chapter 6 of this report. 

5.3.1 Recreation

Recreation is an important designated 

use for most waters of the United 

States. The results of national 

assessments of recreational waters 

and the causes of impairment are 

described in the following subsections.

EPA BEACH Program

EPA’s Beaches Environmental 

Assessment and Coastal Health 

Program (BEACH Program) conducts 

an annual survey of the nation’s 

swimming beaches, the National 

Health Protection Survey of Beaches. 

Nearly 2,500 agencies representing 

beaches in coastal locations, the 

Great Lakes, and inland waterways 

participate in the survey. With respect 

to designated use impairment during 

the 2002 swimming season, 25 

percent of the beaches inventoried 

(709 of 2,823) had at least one 

advisory or closing (EPA 2003a). 

Elevated bacteria levels accounted 

for 75 percent of recreational use 

impairments, manifested as beach 

advisories and closings. As shown in 

Figure 5.2, a wide variety of pollutant 

sources were reported as causing 

beach advisories and closings. Nearly 

half of the advisories and closings, 

however, were reported as having an 

unknown cause. CSOs were reported 

to be responsible for 1 percent of 

reported advisories and closings, and 2 

percent of advisories and closings that 

had a known cause. SSOs (including 

sewer line blockages and breaks) 

were reported to be responsible for 

6 percent of reported advisories and 

closings, and 12 percent of advisories 

and closings that had a known cause.
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-11

Floatables

Floatables are visible buoyant or semibuoyant solids that originate from a 

variety of sources, including CSOs 

and SSOs. CSOs can be a source of 

floatables when debris in raw sewage 

and storm water is released into the 

receiving waterbody. The type of 

floatables typically found in CSOs 

include sewage-related items (e.g., 

condoms and tampons), street litter, 

medical items (e.g., syringes), and 

other material from storm drains, 

ditches, or runoff (EPA 2002c).

Floatables on beaches and waterways, 

also known as marine debris, create 

aesthetic impacts and safety issues that 

detract from the recreational value of 

beaches and other public shorelines. 

As defined by the EPA, marine debris 

includes all objects found in the 

marine environment that do not 

naturally occur there. The marine 

environment includes the ocean, salt 

marshes, estuaries, and beaches. 

The National Marine Debris 

Monitoring Program (NMDMP), 

coordinated by the Ocean Conservancy 

(formerly the Center for Marine 

Conservation) and funded by EPA, 

maintains a national marine debris 

database. The NMDMP has conducted 

monthly beach cleanups since 1996. 

Volunteers track information on 

specific marine debris items that are 

added to the national database. The 

most frequently collected marine 

debris items from 1996 to 2002 

are presented in Table 5.7 (Ocean 

Conservancy 2003). 

Medical and personal hygiene items 

are an important component of 

marine debris. Given the nature and 

use of these items and their disposal in 

toilets, CSOs and SSOs are considered 

a possible source. The Ocean 

Conservancy’s 2003 International 

Coastal Cleanup, a large one-day event, 

found a substantial amount of medical 

and personal hygiene items on U.S. 

beaches (Ocean Conservancy 2004). 

More than 7,500 condoms and 10,000 

tampons and tampon applicators were 

collected from 9,200 miles of U.S. 

shoreline during this event. While this 

Figure 5.2

43

21

11

9

6

4

3

2

1

0 10 20 30 40 50

Unknown

Storm water runoff

Wildlife

Other

Septic system

Boat discharge

SSO

POTW

CSO

Pollution Sources

Percent

Sources of Pollution 

that Resulted in Beach 

Advisories and Closings 

(EPA 2003a)

EPA’s BEACH Program conducts 

an annual survey of the nation’s 

swimming beaches. During the 

2002 swimming season, CSOs and 

SSOs were responsible for 1 and 6 

percent, respectively, of reported 

advisories and closings. 
5-12

Report to Congress on the Impacts and Control of CSOs and SSOs

years between 1966 and 1995. The 

last report, 1995 National Shellfish 

Register of Classified Growing Waters, 

provided an assessment of 4,230 

different classified shellfish growing 

areas in 21 coastal states (NOAA 

1997). Areas open for harvesting are 

rated as “approved” or “conditionally 

approved;” areas where harvesting 

is limited are rated as “restricted” or 

“conditionally restricted;” and areas 

where harvesting is not allowed are 

rated as “prohibited.” 

Findings from the 1995 report with 

respect to shellfish harvesting are as 

follows:

● 76 percent of all classified waters 

were approved or conditionally 

approved for harvest (14.8 million 

acres);

information is inconclusive on its own, 

it does suggest that CSOs and SSOs 

may contribute to the occurrence of 

medical and personal hygiene waste 

found on beaches and other shorelines. 

5.3.2 Shellfish Harvesting

Commercial and recreational 

shellfishing in populated coastal areas 

has declined steadily since the early 

1900s, when outbreaks of typhoid 

were linked to untreated wastewater. 

Environmental impacts that restrict 

shellfish harvesting as a designated use 

are discussed in the following section. 

Human health impacts related to the 

consumption of contaminated fish and 

shellfish are discussed in Chapter 6. 

NOAA National Shellfish Register

NOAA published assessments of 

classified shellfish growing waters 

in the contiguous states every five 

Marine Debris 

(excluding ocean-based)

Total Items

Straws 83,714

Plastic beverage bottles 60,426

Other plastic bottles 36,598

Balloons 34,355

Plastic food bottles 18,383

Plastic bottles 11,946

Condoms 1,675

Syringes 1,379

Plastic bags with seam <1 meter 422

Cotton swabs 171

Metal beverage cans 109

Plastic bags with seam > 1 meter 88

Tampon applicators 61

Motor oil containers 19

Six-pack rings 17

Table 5.7

NMDMP Marine Debris 

Survey Results from 

1996 - 2002 (Ocean 

Conservancy 2003) 

Funded by EPA is Office of Water, 

the NMDMP uses standardized 

data collection methods to 

determine the status of and 

trends in marine debris pollution. 

The data are compiled in a 

national database. 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-13

● 11 percent of all classified waters 

were restricted or conditionally 

restricted (3.9 million acres); and

● 13 percent of all classified waters 

were prohibited (2.8 million 

acres).

NOAA reported that the primary 

basis for harvest restrictions was 

the concentration of fecal coliform 

bacteria associated with untreated 

wastewater and wastes from livestock 

and wildlife. CSOs are one of many 

sources of fecal coliform that impact 

shellfish harvesting. A summary of 

all pollution sources identified in 

the 1990 and 1995 National Shellfish 

Registers as causing or contributing 

to restrictions and prohibitions is 

presented in Table 5.8. 

A cooperative effort between the 

Interstate Shellfish Sanitation 

Conference and NOAA has resulted 

in the development of a state Shellfish 

Information Management System. 

The system will summarize basic 

information about shellfish programs 

CSO controls implemented in Oswego, NY, 

have helped provide suitable habitat for 

desirable fish.

Photo: P. MacNeill

Table 5.8

Pollution Sources Reported for Harvest Limitations on Classified Shellfish Growing 

Waters in the 1990 and 1995 National Shellfish Registers (NOAA 1997)

Compared to the 1990 Register, the 1995 Register shows significant decreases in the acreage that is harvest-limited 

due to contributions from industry and wastewater treatment plants; the acreage impacted by CSOs remained 

relatively constant during the five-year period. 

Pollution Source 1990a 1995a

Urban Runoff

Precipitation-related discharges (e.g., septic leachate, animal wastes) from impervious surfaces, lawns, 

and other urban land uses

38% 40%

Upstream Sources

Contaminants from unspecified sources upstream of shellfish growing waters 46% 39%

Wildlife

Precipitation-related runoff of animal wastes from high wildlife concentration areas (e.g., waterfowl) 25% 38%

Decentralized Wastewater Treatment Systems

Discharge of partially treated sewage from malfunctioning on-site septic systems 37% 32%

Wastewater Treatment Plants

Routine and accidental sewage discharge from public and private wastewater treatment plants with 

varying levels of treatment

37% 24%

Agricultural Runoff

Precipitation- and irrigation-related runoff of animal wastes and pesticides from crop and pasture lands 11% 17%

Marinas

Periodic discharge of untreated or partially treated sewage from berthed vessels – 17%

Boating

Periodic discharge of untreated or partially treated sewage from vessels underway or anchored offshore 18% 13%

Industry

Routine and accidental discharges from production/manufacturing processes and on-site sewage 

treatment

17% 9%

CSOs

Discharge of untreated sewage/storm water when sewage system capacity is exceeded by heavy rainfall

7% 7%

Total harvest-limited area, in acres 6.4

million

6.7

million

a Harvest-limited areas are impacted by multiple pollution sources. Annual values do not total 100 percent.
5-14

Report to Congress on the Impacts and Control of CSOs and SSOs

Shellfish Harvest Classification Number of Classified Shellfish Growing Areas 

within 5 Miles of a CSO outfall

Prohibited 411

Restricted 80

Approved 154

Unclassified 14

Total 659

in each state, replacing NOAA’s 

national shellfish register. This system, 

which will provide spatial data through 

a web-based interface, is expected to be 

operational in 2004.

Analysis of CSO Outfalls Discharging 

Near Classified Shellfish Growing Areas 

EPA associated the location of 

individual CSO outfalls with classified 

shellfish growing areas as reported 

by NOAA in 1995, the last year for 

which national data were available. 

EPA limited the analysis to classified 

shellfish growing areas within five 

miles of a CSO outfall. The number 

of classified areas was tabulated by 

shellfish harvest classification. As 

shown in Table 5.9, harvesting was 

prohibited or restricted in most 

of the classified shellfish growing 

areas that are proximate to CSO 

outfalls. As discussed earlier under 

similar 305(b) and 303(d) analyses, 

the presence of a CSO outfall alone 

does not necessarily mean that the 

CSO is causing or contributing to 

the prohibition or restriction. Many 

classified shellfish growing areas 

where shellfish harvesting is currently 

prohibited or restricted are in urban 

areas in the Northeast where CSOs 

are one of several factors that might 

account for impairment. Nevertheless, 

the association between prohibited and 

restricted conditions and the presence 

of CSO outfalls is strong.

5.4 What Overall Water 

Quality Impacts Have Been 

Attributed to CSO and SSO 

Discharges in State and 

Local Assessments?

S

tate and local governments track 

environmental impacts and 

gather data for programmatic 

reasons that are not necessarily 

included in national assessments. 

Examples of environmental impacts 

included in this section were gathered 

from state and local reports and from 

watershed studies in which broad 

assessments of water quality were 

undertaken. These examples are not 

meant to be comprehensive. They are 

presented to illustrate environmental 

impacts attributed to CSO and SSO 

Table 5.9

Harvest Limitations 

on Classified Shellfish 

Growing Areas Within Five 

Miles of a CSO Outfall

Fifty-eight active CSO permits in nine 

states cover outfalls located within 

five miles of a classified shellfish 

growing area. Shellfish harvesting 

is prohibited or restricted in the 

majority of the 659 shellfish growing 

areas in proximity to CSO outfalls 

national database. 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-15

discharges, and, in some instances, 

the site-specific circumstances under 

which they occurred.

5.4.1 Water Quality Assessment in 

New Hampshire

In its 2000 Water Quality Report, New 

Hampshire reported that bacteria is 

the third leading cause of water quality 

impairment in the state, causing or 

contributing to 13 percent of the total 

miles of impaired rivers and streams 

in the state (NHDES 2000). Elevated 

levels of bacteria impaired recreational 

uses as well as shellfish harvesting 

uses in New Hampshire. The overall 

sources of water quality impairment to 

rivers and streams in New Hampshire 

are presented in Figure 5.3. As shown, 

unknown sources cause 79 percent of 

the 642 miles of impairment reported. 

A total of 24.1 miles were impaired 

due to CSOs; this represents 3 percent 

of all impaired waters in the state and 

19 percent of impaired waters with a 

known source of impairment.

5.4.2 Water Quality Assessment 

of the Mahoning River Near 

Youngstown, Ohio

Working in cooperation with 

the City of Youngstown, Ohio, 

USGS conducted a comprehensive 

assessment of water quality and 

habitat in the Mahoning River and 

its tributaries (USGS 2002). The 

City of Youngstown has 80 CSOs 

that discharge to local receiving 

waters. Water quality monitoring was 

conducted during 1999 and 2000. CSO 

discharges were found to contribute to 

bacterial and nutrient loads observed 

in the Mahoning River, but they were 

not the only factor adversely affecting 

water quality and habitat. USGS found 

that:

“Improvement of water quality in 

the lower reaches of the Mahoning 

River and Mill Creek (a tributary) 

to the point that each waterbody 

meets its designated-use criteria 

will likely require an integrated 

approach that includes not only 

abatement of sewer overflow 

loadings but also identification 

and remediation of other loadings 

in Youngstown and improvement 

of water quality entering 

Youngtown.”

Unknown

79%

Agriculture

7%

Other

5% Urban Runoff

2%

CSOs

3%

Municipal Point

Sources

2%

Industrial Point

Sources

2%

Figure 5.3

Sources of Water Quality 

Impairment in New 

Hampshire (NHDES 2000)

In 2000, New Hampshire reported 

a total of 24.1 miles of rivers and 

streams impaired by CSOs; this 

represents 3 percent of all impaired 

waters in the state and 19 percent of 

impaired waters with a known source 

of impairment. 
5-16

Report to Congress on the Impacts and Control of CSOs and SSOs

5.4.3 Water Quality in Indianapolis, 

Indiana

The City of Indianapolis, Indiana, is 

working to identify and implement 

CSO controls. The city identified 

specific water quality problems in 

waterbodies receiving CSO discharges 

(City of Indianapolis 2000). The 

city’s assessment of pollutant sources 

contributing to water quality problems 

is presented in Table 5.10. As shown, 

CSO discharges and wet weather 

bypasses at POTWs are ranked high 

relative to other sources of pollution.

5.4.4 Water Quality Risk 

Assessment of CSO 

Discharges in King County, 

Washington

King County, Washington, conducted 

a CSO water quality risk assessment 

for the Duwamish River and Elliot 

Bay, an estuary in Seattle (KCDNR 

1999). The water quality assessment 

consisted of three main parts. First, 

more than 2,000 environmental 

samples were collected and analyzed 

to determine pollutant concentrations 

in the water, sediment, and tissues of 

aquatic organisms. Six CSO locations 

within the estuary were included in 

this sampling. The samples were 

analyzed for 35 chemical, physical, 

and biological attributes. Next, a 

computer model was developed to 

describe water flow and contaminant 

transport within the estuary. The 

model was used to estimate current 

pollution levels in estuarine water 

and sediment as well as to predict 

pollution levels after CSO control. 

Finally, a risk assessment was 

conducted to determine the impacts 

of the various pollutants on aquatic 

life, wildlife, and people that use 

the estuary. Key study findings with 

respect to risk reduction resulting 

from CSO control are as follows:

● No predicted reduction in risks 

for water-dwelling organisms;

● Some predicted reduction in risks 

to sediment-dwelling organisms 

near the CSO discharges;

● A possible increase in the variety 

of benthic organisms near CSOs 

as the result of a decrease in 

organic matter;

● A possible reduction in impacts 

of localized scouring and 

sedimentation, which may be 

Pollutant Source Dissolved Oxygen 

Violations

Bacteria 

Violations

Aesthetic 

Problems

CSO Discharges High High High

Upstream Sources Low

Storm Water Low High

Wet Weather Bypass at POTW High High

Electric Utility Thermal Discharge Low

Sediment Oxygen Demand Low

Dams Low

Water Supply Withdrawals Low

Septic Tanks Low

Table 5.10

Relative Contributions 

of Pollutant Sources to 

Water Quality Problems in 

Indianapolis, Indiana (City 

of Indianapolis 2000)

Indianapolis ranked the contribution 

of CSO discharges and wet weather 

bypasses at POTWs high relative 

to other sources of pollution in 

local receiving waters. Blank 

spaces represent negligible or no 

contribution in comparison to other 

sources. 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-17

small compared to the overall 

scouring impacts of the river and 

sediment from other sources; and

● No predicted reduction in risks 

to wildlife as other sources 

contribute the majority of the 

risk-related chemicals.

A stakeholder committee composed 

of local citizens, business owners, 

environmental organizations, and 

tribal governments drew the following 

conclusions from the study results:

● Existing sediment quality and 

associated risks to people, wildlife, 

and aquatic life in the estuary are 

unacceptable; 

● Levels of human pathogens and 

fecal coliform in the estuary are 

unacceptable;

● Controlling CSOs according to the 

King County comprehensive sewer 

plan will improve some aspects of 

environmental quality; and

● Even if CSOs are completely 

eliminated, overall environmental 

quality of the estuary will 

continue to be unacceptable.

5.5 What Impacts on Specific 

Designated Uses Have Been 

Attributed to CSO and SSO 

Discharges in State and 

Local Assessments?

Examples of environmental 

impacts included in this section 

were gathered from state and 

local reports and watershed studies; 

the examples are presented according 

to the designated use impacted by 

CSO and SSO discharges. They are 

not meant to be comprehensive. 

They are presented to illustrate 

representative environmental impacts 

attributed to CSO and SSO discharges, 

and, in some instances, the sitespecific circumstances under which 

they occurred. CSO or SSO discharges 

are clearly the cause of documented 

environmental impacts in some cases, 

and are a contributing factor in others. 

Several examples summarize studies in 

which impacts from CSOs and SSOs 

were sought, but were not found.

5.5.1 Aquatic Life Support

The designated use for aquatic 

life support is achieved when the 

water provides suitable habitat for 

the protection and propagation 

of desirable fish, shellfish, and 

other aquatic organisms. Oxygendemanding substances are the 

principal pollutants found in CSOs 

and SSOs that can cause or contribute 

to impaired aquatic life support. 

CSO and SSO discharges can also 

contribute sediment, pathogens, 

nutrients, and toxics to receiving 

waters, but there is little evidence that 

levels of these pollutants in CSOs 

and SSOs are major causes of aquatic 

life impairment. Select examples 

of impacts or relevant studies are 

presented below.

Fish Kills in North Carolina

Reports of impaired aquatic life (i.e., 

fish kills) have been investigated 

and documented in North Carolina 

since 1997 (NCDENR 2003). A 

summary of fish kills attributed to 

sewage spills from 1997 to 2002 is 

presented in Table 5.11. As shown, 

SSOs are a relatively small cause of the 

documented fish kills. Other causes of 
5-18

Report to Congress on the Impacts and Control of CSOs and SSOs

fish kills include chemical spills, heavy 

rainfall, eutrophication, low dissolved 

oxygen due to unspecified causes, 

natural phenomena (e.g., temperature 

and salinity effects), and unknown 

causes. 

Individual fish kill events linked to 

sewage spills in North Carolina are 

presented in Table 5.12. Descriptive 

comments provided by field crews 

investigating the fish kills are listed in 

an abbreviated manner. The oxygendepleting substances in the spilled 

sewage appear to reduce oxygen 

levels to a point at which there is 

insufficient oxygen to support aquatic 

life, particularly when spills occur in 

relatively small streams. No North 

Carolina communities are served by 

CSSs.

Assessment of SSO Impacts on Fish 

and Aquatic Life at Camp Pendleton, 

California

In September 2000, an SSO occurred 

at the Marine Corps Base Camp 

Pendleton near Oceanside, California. 

The California State Water Resources 

Control Board investigated the spill, 

monitored water quality, and assessed 

the impact of the spill on fish and 

aquatic life (Vasquez 2003). The SSO 

occurred at a deteriorated access port 

in a sewer force main operated by 

the Marine Corps. An estimated 2.73 

million gallons of sewage was spilled 

over an eight-day period. Data showed 

that dissolved oxygen levels in the 

impacted area dropped below 1 mg/L, 

well below the numeric criteria of 5 

mg/L and levels needed to support 

most aquatic life, and remained low 

for several days. The assessment of 

impacted wildlife documented 320 

dead fish, 67 dead shrimp, 169 dead 

clams, 1 dead snail, and 1 dead bird.

Assessment of PCBs in the Buffalo 

River, New York

Polychlorinated biphenyls (PCBs) 

are a contaminant of concern for the 

Buffalo River in New York and the 

Great Lakes in general. PCB levels 

in the river often exceed state water 

quality criteria, and PCBs found in 

fish tissue exceed levels allowed by 

the Food and Drug Administration. 

In 1994, a study was conducted 

to identify sources of PCBs to the 

Buffalo River (Loganthan et al. 1997). 

Monitoring was conducted in the 700-

acre Babcock Creek sewershed, one 

of 27 sewersheds served by combined 

Year Total Number 

of Fish Kills

Number of Fish 

Kills Attributed to 

Sewer Spills

Total Number 

of Fish Killed

Number of Fish Killed 

in Events Attributed to 

Sewer Spills 

1997 57 8 91,998 8,384

1998 58 3 593,545 336

1999 54 1 1,298,472 200

2000 58 2 716,141 400

2001 77 2 1,369,140 490

2002 45 0 269,635 0

Table 5.11

Fish Kills Reported in 

North Carolina: 1997 - 

2002 (NCDENR 2003)

Between 1997 and 2002, NCDENR 

attributed the deaths of nearly 

10,000 fish to SSOs (sewer spills).
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-19

sewers in the City of Buffalo. The 

study detected the presence of PCBs 

in CSO discharges from the Babcock 

Creek CSO outfall and confirmed 

that the city’s CSS was a source of 

PCBs to the river. Monitoring at other 

study locations as well as watershed 

modeling indicated that the PCB 

loadings from unknown, non-CSO 

sources were more than 10 times 

greater than the loading from all of 

the CSOs in the lower Buffalo River 

(Atkinson et al. 1994).

Whole Effluent Toxicity of CSO 

Discharges in Toledo, Ohio

Whole effluent toxicity testing uses 

Ceriodaphnia dubia (water flea) 

and Pimephales promelas (fathead 

minnow) to measure if a discharge 

is toxic. The City of Toledo, Ohio, 

conducted whole effluent toxicity 

testing on samples collected at four 

separate CSO outfalls during wet 

weather conditions (Jones & Henry 

Engineers 1997). In comparison 

with laboratory control groups, 

acute (short-term) toxicity was 

observed in samples from two CSO 

Date 

Investigated

Waterbody Number of 

Fish

Killed

Comments

7/1/97 Tributary to Cokey Swamp 300 Spill of at least 23,000 gallons of sewage

7/14/97 Elerbee Creek 120 Sewer spill at storm drain due to sump overflow

7/29/97 Tributary to Elerbee Creek 100 30,000 gallon spill at pump station

8/13/97 Swift and Mahlers Creeks 1,000 500,000–1,000,000 gallon sewer line spill

8/14/97 Tributary to Northeast Creek 200 20,000 gallon sewer line spill

8/19/97 Coon Creek 3,500 1,200,000 gallon spill at pump station

9/23/97 Little Buffalo Creek 25 50,000 gallon sewage spill

10/7/97 Lovills Creek 3,099 Sewage leakage at junction in sewage lines

11/9/97 East Beaverdam Creek 40 500,000 spill at broken manhole

1/5/98 Cooper’s Pond 85 Sewage spill

3/16/98 Unnamed Lake 175 114,000 gallons spilled

7/6/98 Reedy Fork Creek 76 3,000 gallons spilled at pump station

6/29/99 Muddy Creek 200 Sewer overflow reported in area

4/13/00 South Fork Catawba River 200 3,000 gallons spilled

6/9/00 Town Branch 200 5,200 gallons spilled due to blockage

5/3/01 Subdivision Pond 400 Sewage overflow

10/23/01 Tributary to Hare Snipe Creek 90 40,000 gallon sewage spill

Table 5.12

Fish Kills Caused by Sewage Spills in North Carolina: 1997 - 2001 

(NCDENR 2003)

Oxygen-depleting substances in SSOs (sewer spills) can reduce in-stream dissolved oxygen to levels that 

are insufficient to support aquatic life. 
5-20

Report to Congress on the Impacts and Control of CSOs and SSOs

outfalls, and chronic (long-term) 

toxicity was observed in samples from 

the other two CSO outfalls. Some 

chronic toxicity effects were also 

observed in river samples taken above 

and below the CSO discharges. Parallel 

modeling analysis of CSO discharges 

by the City of Toledo identified copper, 

lead, silver, and zinc as pollutants of 

concern.

As a result of the testing, Toledo 

recently developed a draft Industrial 

Wastewater Release Minimization 

Plan with policies and procedures for 

minimizing the discharge of industrial 

wastewater during CSO events (City 

of Toledo 2003). The plan includes 

a variety of measures to reduce 

the volume and concentration of 

industrial wastewater discharged to the 

CSS during wet weather events. Eight 

industrial facilities identified as having 

the potential to contribute toxics to 

CSO discharges have implemented or 

scheduled changes to their operations 

to reduce flow, load, or both. The 

city plans to contact the remaining 

industrial facilities participating in its 

Industrial Pretreatment Program to 

encourage operational modifications to 

reduce the volume and concentration 

of wastewater discharged to the CSS 

during wet weather events. 

Analysis of Toxics in CSOs in 

Washington, D.C.

The District of Columbia Water and 

Sewer Authority monitored its CSO 

outfalls for nine months during 1999 

and 2000 (DCWASA 2002). The 

purpose of the monitoring was to 

characterize the chemical composition 

of CSO discharges in order to assess 

the potential for receiving water 

impacts. Monitoring was carried out 

for 127 priority pollutants including:

● Total recoverable metals and 

cyanide

● Dissolved metals

● Pesticides and PCBs 

● Volatiles and semivolatiles

The CSO monitoring data reported 

by the Water and Sewer Authority 

indicated that all results for priority 

pollutants were below the laboratory 

method reporting limits, except for 

cyanide, chloroform, and several 

metals. The cyanide and chloroform 

concentrations were found to be 

well below the applicable water 

quality criteria. Further evaluation of 

detected metals showed that all but 

dissolved copper and dissolved zinc 

were at acceptable levels. Additional 

analysis using the EPA-approved 

CORMIX and Biotic Ligand models 

indicated that the effective instream 

concentrations of dissolved copper and 

dissolved zinc were also at acceptable 

levels. Although Washington, D.C. is 

not a heavily industrialized city, 25 

permitted significant industrial users 

and approximately 3,000 smaller 

commercial dischargers (e.g., medical 

facilities, printing and photocopying 

facilities) discharge to its sewer system. 

Fish Diversity in Chicago-area 

Waterways

Prior to the implementation of 

wastewater treatment facility upgrades 

in the 1970s and CSO controls in 

the 1980s, aquatic life suffered in 

urban Chicago-area streams. The 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-21

ability of Chicago-area waterways to 

support a rich and diverse aquatic 

community was severely limited 

by inadequate levels of wastewater 

treatment, discharges of chlorinated 

effluent at treatment facilities, 

and CSO discharges. In particular, 

CSO discharges contributed large 

amounts of oxygen-demanding 

organic substances that depressed 

oxygen levels in the waterways, and 

the presence of chlorine in treatment 

plant effluent contributed to 

conditions that were toxic to aquatic 

life. Improved wastewater treatment, 

including facilities to dechlorinate 

treated wastewater, and CSO control 

over the past 30 years have improved 

the richness and diversity of aquatic 

life. As shown in Figure 5.4, the total 

number of fish species found and 

supported in the principal waterways 

in Chicago has expanded during this 

period (MWRD 1998).

5.5.2 Recreation

Primary contact and secondary 

contact recreation uses are protected 

when a waterbody supports swimming 

and other water-based activities, 

such as boating, without risk of 

adverse human health effects from 

contact with the water. The principal 

pollutants found in CSOs and SSOs 

that affect recreational uses at beaches 

are microbial pathogens and, to a 

lesser extent, floatables. Select local 

examples of impacts to recreational 

uses and relevant studies are presented 

below. Additional information about 

potential human health impacts 

from recreational exposure to water 

contaminated by CSO or SSO 

discharges is presented in Chapter 6.

Beach Closures in California

SSOs were identified by the California 

State Water Resources Control Board 

as one of several sources of beach 

pollution in its California Beach 

Closure Report 2000 (CSWRCB 

2001). Beach closures result from 

exceedences of bacterial standards. A 

closure provides the public with notice 

that the water is unsafe for contact 

recreation (i.e., swimming poses an 

unacceptable risk of illness). 

The majority of beach closures during 

2000 were attributed to unspecified 

creek and river sources. As shown in 

0

10

20

30

40

50

60

70

1974 1978 1982 1986 1990 1994 1998 2002

Number of Fish Species

Year

Figure 5.4

Fish Species Found in 

the Chicago and Calumet 

River System, 1974 - 2001 

(MWRD 1998; Dennisen 

2003)

The total number of fish species 

found in the Chicago and Calumet 

River system increased six-fold 

between 1974 and 2001. 
5-22

Report to Congress on the Impacts and Control of CSOs and SSOs

Figure 5.5, SSOs accounted for 42 

percent and CSOs accounted for less 

than one percent of all beach closures 

in California during 2000. California 

has only two communities with CSSs: 

San Francisco and Sacramento. 

A summary of beach closures due to 

SSOs in California in 2000 is presented 

in Figure 5.6. The total number of 

days that at least one beach was closed 

is presented in the map by county. 

The accompanying bar graph shows 

closures by county in beach-mile 

days, a measure of beach availability 

for recreation that integrates miles of 

beach closed with days of impairment.

Beach Closures in Connecticut

The Connecticut Council on 

Environmental Quality reported 

on beach closures in the state in its 

2001 Annual Report (CTCEQ 2002). 

Connecticut’s goal is to eliminate 

beach closures caused by discharges 

of untreated or poorly treated 

wastewater, which Connecticut 

identified as the most common cause 

of elevated bacteria levels. Currently, 

several towns close beaches following 

a heavy rainfall as a precaution, 

presuming that CSO, SSO, and 

storm water discharges will occur 

and contaminate water. The average 

number of days that beaches are closed 

depends largely on the frequency and 

amount of rainfall during the beach 

season. The long-term trend in beach 

closures reported by the Council is 

presented in Figure 5.7.

Beach Closures in Orange County, 

California

Orange County monitors and reports 

on bacteria levels along 112 miles of 

its ocean and bay coastline. Major 

findings documented in its Annual 

Ocean and Bay Water Quality Report

(Orange County 2002) are:

● The total number of SSOs 

reported to the Orange County 

Health Care Agency has steadily 

increased over the past 15 years.

● The total number of ocean and 

bay beach closures due to SSOs 

has increased each year since 1999.

● The total number of beach miledays lost as a result of sewage spills 

has remained constant since 1999.

Sources of Contamination

Resulting in Beach Closures

Unspecified river sources 58%

SSOs 42%

CSOs <1%

Unknown <1%

Total 100%

Percent

Figure 5.5

Sources of Contamination 

Resulting in California 

Beach Closures in 2000 

(CSWRCB 2001)

In California, problems with sewer 

lines such as line breaks; blockages 

due to grease, roots, or debris; 

and pump station failures have 

been identified as the cause of a 

to a significant number of beach 

closures. 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-23

San Luis Obispo

Ventura

Los Angeles

Orange

San

Diego

15 Mendocino

Sonoma

San Mateo

Monterey

4

217

16

1

12 45

152

310

Beach Mile-Days

2.6

0.1

0.4

0.7

3.9

33.6

41.9

53.4

187

Mendocino

San Luis Obispo

Sonoma

Ventura

Monterey

Los Angeles

San Mateo

Orange

San Diego

Beach Mile-Days is the product of the number

of miles of coastline and the number of days

of impairment.

0

1

2

3

4

5

6

7

8

1987 1989 1991 1993 1995 1997 1999 2001

Year

Days

Figure 5.7

Average Number of 

Days per Year Coastal 

Municipalities in 

Connecticut Closed One 

or More Beaches (CTCEQ 

2002)

Yearly variations in beach closures 

are a product of rainfall patterns 

and incidents such as sewer line 

ruptures. In 1999, a relatively 

dry summer led to less than two 

closings, on average. The sharp 

increase in beach closings in 2000 

was the result of a rainy summer. 

Figure 5.6

Beach Closures in 

California During 2000 

Attributed to SSOs 

(CASWRCB 2001)

During 2000, nine coastal counties 

in California reported beach 

closures as a result of SSOs. Beach 

closure statistics are presented two 

ways. The number shown in each 

county indicates the total number 

of days that are least one beach in 

the county was closed in 2000. The 

number of lost beach mile-days 

in each county is presented in the 

adjacent bar chart.
5-24

Report to Congress on the Impacts and Control of CSOs and SSOs

A summary of the specific types of 

unauthorized wastewater discharges 

that resulted in beach closures is 

presented in Table 5.13. As shown, 

the total number of unauthorized 

discharges resulting in beach closures 

increased steadily between 1999 and 

2002. However, during this same time 

period the total number of beach miledays lost as a result of sewage spills has 

remained constant, suggesting that the 

impacts from individual spills have been 

reduced. The Orange County Health 

Care Agency attributes the reduced 

impacts to improvements in wastewater 

utility response procedures and increased 

regulatory oversight. 

Lake Michigan Beach Closures

The Lake Michigan Federation tracks 

beach closures in Michigan, Indiana, 

Illinois, and Wisconsin based on 

data collected from local health 

departments, parks managers, and 

other municipal agencies. EPA and 

NRDC data were used to augment 

these sources prior to 2000. The 

Federation’s tabulation of beach 

closures from 1998 to 2002 for all of 

Lake Michigan is presented in Figure 

5.8. The Federation believes that CSOs 

are associated with a high percentage 

of the beach closures. Other sources 

of pathogens that cause or contribute 

to beach closures include wildlife, 

storm water runoff, direct human 

contamination, and re-suspension 

of bacteria in sediment (Brammeier 

2003).

To examine whether CSOs were 

responsible for beach closures and 

advisories along Lake Michigan 

in Cook County, Illinois, the 

Metropolitan Water Reclamation 

District of Greater Chicago conducted 

independent research into river 

reversals to Lake Michigan (MWRD 

2003). River reversals to Lake 

Michigan occur when, due to heavy 

rainfall, the gates that separate Lake 

Michigan and the Chicago River are 

opened. River water impacted by 

CSOs is discharged to the lake during 

river reversals. Swimming at nearby 

beaches is preemptively banned for 

two consecutive days by park officials 

when river reversals occur. 

In its report, the District noted hat 

river reversals (and thus the discharge 

of CSO-impacted waters) to Lake 

Michigan were infrequent and did 

not explain most beach closings and 

advisories (MWRD 2003). Other 

sources of bacteria at Chicago beaches 

include sea gulls and bacteria in sand 

deposits (USGS 2001).

Cause of Discharge 1999 2000 2001 2002

Line breaks 38 55 69 95

Blockages 210 288 308 409

Pump station failures 14 8 15 11

Treatment plant discharges 0 0 4 2

Miscellaneous 14 25 16 2

Total unauthorized discharges 276 377 412 522

Table 5.13

Summary of 

Unauthorized Wastewater 

Discharges in Orange 

County, California, 

that Resulted in Beach 

Closures (Mazur 2003)

Blockages were identified as the 

cause of approximately threequarters of all unauthorized 

wastewater discharges that resulted 

in beach closures in Orange County 

between 1999 and 2002. 
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-25

5.5.3 Shellfish Harvesting

The designated use of shellfish 

harvesting is achieved when a 

waterbody supports a population 

of shellfish free from toxics and 

pathogens that could pose a significant 

human health risk to consumers. 

Accordingly, the principal pollutants 

in CSO and SSO discharges found to 

impact this use are pathogens, and, to 

a lesser extent, toxics. An example of 

shellfishing restrictions imposed as a 

result of SSO discharges is presented 

below. 

Shellfish Harvest Limitations as a 

Result of SSO to the Raritan River, 

New Jersey

On March 2, 2003, a 102-inch 

diameter sewer in Middlesex 

County, New Jersey, ruptured and 

spilled untreated wastewater into 

residential areas and the Raritan River. 

Approximately 570 million gallons 

of wastewater were discharged over 

a nine-day period while the pipeline 

was being repaired. Daily monitoring 

tracked the movement of elevated 

bacteria levels in the river (NJDEP 

2003). The spill caused high levels of 

fecal coliform in nearby, downstream 

waters including Raritan Bay, Sandy 

Hook Bay, and the Navesink River. 

EPA and the New Jersey Department 

of Environmental Protection (NJDEP) 

sampled affected waters daily and 

determined that fecal coliform counts 

were highest in the Raritan Bay 

(2,400–4,500 fecal coliform counts 

per 100 mL); counts were also high 

in Sandy Hook Bay (up to 1,100 

fecal coliform counts per 100 mL). 

Once the spill was stopped, levels 

of fecal coliform dropped to below 

88 counts per 100 mL throughout 

the river and bay system. By March 

15, 2003 (two weeks after the spill 

began), the highest level reported was 

in the western end of Raritan Bay 

at an acceptable level of 43 counts 

per 100 mL. Fecal coliform was not 

detected at nearby ocean beaches. The 

movement of the bacteria plume and 

its dissipation and dilution over time 

are illustrated in Figure 5.9.

The spill forced NJDEP to close 

shellfish beds totaling approximately 

30,000 acres in Raritan and Sandy 

Hook Bays, as well as in the Navesink 

and Shrewsbury Rivers. Of the total 

acres closed, more than 6,000 acres 

were reopened after four weeks, 

and an additional 20,000 acres were 

reopened after six weeks (NJDEP 

2003). 

0

200

400

600

800

1000

1998 1999 2000 2001 2002

Year

Number of Closures

Figure 5.8

Lake Michigan Beach 

Closures, 1998 - 2002 

(Brammeier 2003)

During the 2002 swimming season, 

authorities issued a total of 919 

beach closures and advisories for 

Lake Michigan. Of the 34 Lake 

Michigan coastal counties, 65 

percent were monitored for beach 

pollution, up from 50 percent in 

2000. 
5-26

Report to Congress on the Impacts and Control of CSOs and SSOs

Navesink River

Staten Island

Raritan Bay

New York Waters

Sandy Hook

Bay

Sandy

Hook

March 4, 2003

Fecal Coliform Bacteria Levels

Monmouth

County

4000-5000

3500-4000

3000-3500

2500-3000

2000-2500

1500-2000

1000-1500

500-1000

88-500

0-88

Fecal Coliform Results

(MPN/1000mL)

Land

Movement of Bacteria 

Plume from SSO 

Discharge in Raritan Bay, 

New Jersey (NJDEP 2003)

This large SSO event (570 million 

gallons over nine days, beginning 

on March 2, 2003) resulted in the 

closure of more than 30,000 acres 

of shellfish beds for four to six 

weeks, until shellfish tissue was clear 

of fecal coliform, viral, and metal 

contamination. Data are not shown 

for the Navesink River and portions 

of Sandy Hook Bay.

Figure 5.9

Navesink River

Staten Island

Raritan Bay

New York Waters

Sandy Hook

Bay

Sandy

Hook

Monmouth

County

4000-5000

3500-4000

3000-3500

2500-3000

2000-2500

1500-2000

1000-1500

500-1000

88-500

0-88

Fecal Coliform Results

(MPN/1000mL)

Land

March 10, 2003

Fecal Coliform Bacteria Levels
 Chapter 5—Environmental Impacts of CSOs and SSOs

5-27

5.6 What Factors Affect the 

Extent of Environmental 

Impacts Caused by CSOs 

and SSOs?

Compiling and presenting 

information on the extent of 

environmental impacts caused 

by CSOs and SSOs is complicated by 

a number of factors. At the local level, 

site-specific water quality impacts 

vary depending on the volume and 

frequency of CSO or SSO discharges, 

the size and type of waterbody that 

receives the overflows, other sources 

of pollution, and the designated uses 

for the waterbody. Depending on 

the particular combination of these 

factors, impacts from CSOs and SSOs 

can be visible and intense or relatively 

minor. Further, because CSO and SSO 

discharges are intermittent and often 

occur during wet weather, resulting 

impacts can be transient and difficult 

to monitor. This section discusses 

key factors, including timescale and 

receiving water characteristics, that 

affect the extent of environmental 

impacts caused by CSOs and SSOs.

5.6.1 Timescale Considerations

Although CSO and SSO discharges 

are intermittent, the resultant impacts 

may not be temporary and can persist 

to varying degrees. Some impacts, 

such as aesthetic impairment due to 

the presence of floatable material, 

occur immediately when sewers 

overflow and are considered shortterm impacts. In contrast, nutrients 

discharged with CSOs and SSOs can 

contribute to eutrophication on a 

time scale of weeks or months; such 

impacts are classified as long-term 

impacts. Similarly, chronic toxicity 

impacts associated with metals, 

pesticides, and synthetic organic 

compounds that contaminate both 

waterbodies and sediments can affect 

aquatic systems over decades. 

5.6.2 Receiving Water 

Characteristics

The degree to which a CSO or SSO 

discharge produces an environmental 

impact in a particular waterbody 

depends on the rate and volume of the 

discharge, the degree of mixing and 

dilution, and the assimilative capacity 

of the waterbody (see Section 5.2.3). 

In general, the larger the waterbody 

and the smaller the discharge, the 

less likely it is that environmental 

impacts will occur. In contrast, 

small waters with little dilution and 

little assimilative capacity can be 

severely impacted by relatively small 

discharges. 

Once pollutants are discharged into 

a waterbody, fate and transport 

processes determine the extent and 

severity of environmental impacts. 

Small-scale hydraulics, such as water 

movement near a discharge point, 

determine the initial dilution and 

mixing of the discharge. Large-scale 

water movement due to river flow 

and tidal action largely determine the 

transport of pollutants over time and 

distance. Processes identified as most 

important in assessing the impacts of 

CSOs and SSOs include:

● Dilution and transport of 

pathogens and toxics in the water 

column;

● Deposition of settleable solids;

● Resuspension or scour of 

settleable solids; and

● Chemical exchange or dilution 

between the water column and 

sediment pore water (Meyland et 

al. 1998).
This chapter documents and expands 

the current understanding of human 

health impacts from CSOs and 

SSOs. The chapter first describes 

the pollutants commonly present in 

CSOs and SSOs that can cause human 

health impacts. The next sections 

discuss human exposure pathways; 

demographic groups and populations 

that face the greatest exposure and 

risk of illness; and ways in which 

human health impacts from CSOs and 

SSOs are communicated, mitigated, 

or prevented. The identification and 

tracking of illnesses associated with 

CSOs and SSOs are also discussed. 

Several examples of human health 

impacts are provided in the chapter. 

6.1 What Pollutants in CSOs 

and SSOs Can Cause 

Human Health Impacts? 

The principal pollutants present 

in CSOs and SSOs that can 

cause human health impacts 

are microbial pathogens and toxics. 

The presence of biologically active 

chemicals (e.g., antibiotics, hormones, 

Chapter 6

I

n addition to causing and 

contributing to the environmental 

impacts reported in Chapter 

5, CSOs and SSOs can cause or 

contribute to human health impacts. 

Microbial pathogens and toxics can 

be present in CSOs and SSOs at levels 

that pose a risk to human health. 

Human health impacts occur when 

people become ill due to contact 

with or ingestion of water or shellfish 

that have been contaminated with 

microbial pathogens or toxics. 

Although it is clear that CSOs 

and SSOs contain disease-causing 

pathogens and other pollutants, EPA 

found limited quantitative evidence 

of actual human health impacts 

attributed to specific CSO and 

SSO events. Factors such as underreporting and incomplete tracking 

of waterborne illness, the presence of 

pollutants from other sources, and 

the use of non-pathogenic indicator 

bacteria in water quality monitoring 

often make it difficult to establish a 

cause-and-effect relationship between 

human illnesses and CSO and SSO 

discharges.

6-1

6.1 What Pollutants in CSOs 

and SSOs Can Cause 

Human Health Impacts?

6.2 What Exposure Pathways 

and Reported Human 

Health Impacts are 

Associated with CSOs and 

SSOs?

6.3 Which Demographic 

Groups Face the Greatest 

Risk of Exposure to CSOs 

and SSOs?

6.4 Which Populations Face 

the Greatest Risk of Illness 

from Exposure to the 

Pollutants Present in CSOs 

and SSOs?

6.5 How are Human Health 

Impacts from CSOs and 

SSOs, Communicated, 

Mitigated, or Prevented?

6.6 What Factors Contribute 

to Information Gaps in 

Identifying and Tracking 

Human Health Impacts 

from CSOs and SSOs?

6.7 What New Assessments 

and Investigative Activities 

are Underway?

Human Health Impacts of CSOs 

and SSOs

In this chapter:
6-2

Report to Congress on the Impacts and Control of CSOs and SSOs

and steroids) is also a concern but is 

less well understood at this time. 

6.1.1 Microbial Pathogens

Microbial pathogens include hundreds 

of different types of bacteria, viruses, 

and parasites. Microbial pathogens 

of human and non-human origin are 

present in domestic and industrial 

wastewater. The presence of specific 

microbial pathogens in wastewater 

depends on what is endemic or 

epidemic in the local community and 

is often transient. Some microbial 

pathogens also have environmental 

sources. In general, microbial 

pathogens are easily transported 

by water. They can cause disease in 

aquatic biota and illness or even death 

in humans. The three major categories 

of microbial pathogens present in 

CSOs and SSOs are bacteria, viruses, 

and parasites. Fungi do not have a 

major presence in wastewater (WERF 

2003b), and thus in CSOs and SSOs.

Bacteria

Bacteria are microscopic, unicelluar 

organisms. Two broad categories 

of bacteria are associated with 

wastewater: indicator bacteria and 

pathogenic bacteria. Indicator bacteria 

are common in human waste and 

are relatively easy to detect in water, 

but they are not necessarily harmful 

themselves. Their presence is used 

to indicate the likely presence of 

disease-causing, fecal-borne microbial 

pathogens that are more difficult to 

detect. Enteric (intestinal) bacteria 

have been used for more than 100 

years as indicators of the presence 

of human feces in water and overall 

microbial water quality (NAS 1993). 

Enteric bacteria commonly used as 

indicators include total coliform, fecal 

coliform, E. coli, and enterococci. 

Further discussion of bacterial 

indicators is provided in Section 6.6.

Pathogenic bacteria are also common 

in human waste and are capable 

of causing disease. Human health 

impacts from pathogenic bacteria 

most often involve gastrointestinal 

illnesses. The predominant symptoms 

of pathogenic bacterial infections 

include abdominal cramps, diarrhea, 

fever, and vomiting. Pathogenic 

bacteria can also cause diseases such 

as typhoid fever, although this is 

not common in the United States. 

In addition to attacking the human 

digestive tract, the pathogenic bacteria 

present in CSOs and SSOs can 

cause illnesses such as pneumonia, 

bronchitis, and swimmer’s ear. 

Common pathogenic bacteria, typical 

concentrations present in sewage 

(where available), and associated 

disease and effects are summarized in 

Table 6.1. 

Viruses

Viruses are submicroscopic infectious 

agents that require a host in which 

to reproduce. Once inside the host, 

the virus reproduces and manifests 

in illness (EPA 1999c). More than 

120 enteric viruses are found in 

sewage (NAS 1993). The predominant 

symptoms resulting from enteric virus 

infection include vomiting, diarrhea, 

skin rash, fever, and respiratory 

infection. Most waterborne and 

seafood-borne diseases throughout 

the world are caused by viruses (NAS 

2000). Many enteric viruses, however, 

cause infections that are difficult to 

detect (Bitton 1999). A list of common 

enteric viruses, including typical 
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-3

concentrations present in sewage 

(where available), and associated 

disease and effects are summarized 

in Table 6.2. Infective doses are not 

reported; enteric viruses typically are 

very infectious.

Parasites

Parasites by definition are animals or 

plants that live in and obtain nutrients 

from a host organism of another 

species. The parasites in wastewater 

that pose a primary public health 

Virus Group Concentration 

in Sewagea

(per 100mL)

Diseaseb Effects b

Adenovirus 10 - 10,000 Respiratory disease, 

gastroenteritis,

pneumonia 

Various effects

Astrovirus Gastroenteritis Vomiting, diarrhea

Noraviruses (includes 

Norwalk-like viruses)

Gastroenteritis Vomiting, diarrhea

Echovirus Hepatitis, respiratory 

infection, aseptic meningitis

Various effects, 

including liver 

disease

Enterovirus (includes 

polio, encephalitis, 

conjunctivitis, and 

coxsackie viruses)

0.05 - 100,000 Gastroenteritis, 

heart anomalies, aseptic 

meningitis, polio

Various effects

Reovirus 0.1 - 125 Gastroenteritis Vomiting, diarrhea

Rotavirus 0.1 - 85,000 Gastroenteritis Vomiting, diarrhea

Bacteria Concentration 

in Sewagea

(per 100mL)

Diseaseb Effectsb Infective Dosec,d

Campylobacter3,700 -100,000 Gastroenteritis Vomiting, diarrhea 102 - 106

Pathogenic 

E. coli

30,000 - 

10,000,000

Gastroenteritis Vomiting, diarrhea, 

Hemolytic Uremic 

syndrome (HUS), 

death in susceptible 

populations

106 - 108

Salmonella 0.2 - 11,000 Salmonellosis Diarrhea, dehydration 104 - 107

S. typhi Typhoid fever High fever, diarrhea, 

ulceration of the small 

intestine

103 - 107

Shigella 0.1 - 1,000 Shigellosis Bacillary dysentery 101 - 102

Vibrio

cholera

Cholera Extremely heavy 

diarrhea, dehydration

103 - 108

Vibrio noncholera10 - 10,000 Gastroenteritis Extremely heavy 

diarrhea, nausea, 

vomiting

102 - 106

Yersinia Yersinosis Diarrhea 106

Table 6.1

Common Pathogenic 

Bacteria Present in 

Sewage

Infective dose is defined as the 

number of pathogens required to 

cause subclinical infection. Infective 

doses are typically given as ranges, 

as the actual infective dose depends 

on the pathogen strain and an 

individual’s health condition.

Table 6.2

Common Enteric Viruses 

Present in Sewage

Enteric viruses are typically very 

infectious: 1-10 virus particles can 

cause infection.

a Details in Appendix I c Yates and Gerba 1998

b EPA 1999C d Lue-Hing 2003

a Details in Appendix I c Yates and Gerba 1998

b EPA 1999C d Lue-Hing 2003
6-4

Report to Congress on the Impacts and Control of CSOs and SSOs

concern are protozoa and helminths 

(NAS 1993). Parasitic protozoa 

commonly present in sewage include 

Giardia lamblia, Cryptosporidium 

parvum, and Entamoeba histolytica. 

These protozoa cause acute and 

chronic diarrhea (NAS 1993). Giardia

causes giardiasis, which is one of the 

most prevalent waterborne diseases in 

the United States (EPA 2001e). 

Ranges of typical concentrations of 

protozoa in sewage and information 

on infective doses are summarized 

in Table 6.3. As shown, ingestion of 

a small number of parasitic protozoa 

is capable of initiating infection. 

Therefore, the presence of low levels 

of parasitic protozoa in wastewater 

is a greater health concern than are 

low levels of most pathogenic bacteria 

(NAS 1993).

Helminths, or parasitic worms, include 

roundworms, hookworms, tapeworms, 

and whipworms. These organisms are 

endemic in areas lacking adequate 

hygiene. Very little documentation of 

waterborne transmission of helminth 

infection is available (NAS 1993). 

Helminth infections can be difficult to 

diagnose and often exhibit no obvious 

symptoms.

Indicator Bacteria and Microbial 

Pathogens in Sewage

Microbial pathogen concentrations 

in sewage vary greatly depending on 

the amount of illness and infection in 

the community served by the sewer 

system. The time of year can also 

be important, as some outbreaks of 

viral disease are seasonal. Average 

concentrations of indicator bacteria 

(e.g., fecal coliform) and other 

microbial pathogens (enteric viruses 

and protozoan parasites) shed by 

an infected person are shown in 

Table 6.4. These high concentrations 

illustrate that a single person shedding 

pathogenic organisms can cause a 

large pathogen load to be discharged 

to a municipal sewer system.

6.1.2 Toxics

As described in Section 4.1 of this 

report, toxics are chemicals or 

chemical mixtures that, under certain 

circumstances of exposure, pose a 

risk to human health. Individuals can 

suffer chronic health effects resulting 

from prolonged periods of ingestion 

or consumption of water, fish, and 

shellfish contaminated with a toxic 

substance. Generally, metals and 

synthetic organic chemicals are the 

Parasitic

Protozoa

Concentration 

in Sewagea

(per L)

Diseaseb Effectsb Infective Dosec

Cryptosporidium 3 - 13,700 CryptosporidiosisDiarrhea 1 - 150

Entamoeba 4 - 52 Amedbiasis 

(amoebic 

dysentery)

Prolonged diarrhea 

with bleeding, abscess 

of the liver and small 

intestine

10 - 20

Giardia 2 - 200,000 Giardiasis Mild to severe diarrhea, 

nausea, indigestion

10 - 100

Table 6.3

Common Parasitic 

Protozoa Present in 

Sewage

Parasitic protozoa have very low 

infective doses, which makes their 

presence in CSO and SSO discharges 

an important public health 

concern.

a Details in Appendix I c Yates and Gerba 1998

b EPA 1999C 
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-5

toxic substances present in CSO and 

SSO discharges that can cause human 

health impacts. Metals and synthetic 

organic chemicals are introduced into 

sewer systems through a variety of 

pathways (Ford 1994). These include 

permitted industrial discharges, 

improper or illegal connections, 

improper drain disposal of chemical 

remnants, and urban runoff in areas 

served by CSSs. While the occurrence 

and concentration of specific toxics 

in CSOs and SSOs vary considerably 

from community to community and 

from event to event depending on sitespecific conditions (see Tables 4.4 and 

4.5), EPA found no evidence of human 

health impacts due to toxics in CSO 

and SSO discharges. 

Metals

The metals most commonly identified 

in wastewater include cadmium, 

chromium, copper, lead, mercury, 

nickel, silver, and zinc (AMSA 

2003a). In CSSs, storm water can also 

contribute metals. EPA’s Nationwide 

Urban Runoff Program (NURP) 

identified copper, lead, and zinc in 

91 percent of urban storm water 

samples collected (EPA 1983a). That 

is, all three metals were present in 

91 percent of samples. Other metals 

commonly detected in urban runoff 

include arsenic, cadmium, chromium, 

and nickel. The NURP Program 

focused on end-of-pipe samples and 

therefore did not consider receiving 

water impacts.

Metals are a human health concern 

for two reasons. First, metals are 

persistent in the environment. This 

creates an increased chance of longterm human exposure once metals are 

introduced to a waterbody. Second, 

metals such as arsenic, cadmium, 

lead, and mercury bioaccumulate 

in the human brain, liver, fat, and 

kidneys, causing detrimental effects. 

Other impacts that can be caused by 

metals include dermatitis, hair loss, 

gastrointestinal distress, bone disease, 

and developmental illnesses. 

Synthetic Organic Chemicals

The synthetic organic chemicals that 

have been identified in CSOs and 

SSOs include chlorinated aromatic 

hydrocarbons such as polychlorinated 

biphenyls (PCBs), chlorinated 

hydrocarbons such as pesticides, and 

polycyclic aromatic hydrocarbons. 

Synthetic organic chemicals can be 

ingested by drinking contaminated 

water or by eating contaminated 

fish that have bioaccumulated the 

chemical. Synthetic organic chemicals 

can also be absorbed through the skin. 

Their effects on humans range from 

skin rash to more serious illnesses 

including anemia, nervous system 

and blood problems, liver and kidney 

problems, reproductive difficulties, 

and increased risk of cancer. 

Organism Number per Gram of Feces

Fecal Coliform Bacteria 108 to 109

Enteric Viruses 103 to 1012

Protozoan Parasites 106 to 107

Table 6.4

Concentration of 

Indicator Bacteria and 

Enteric Pathogens Shed 

by an Infected Individual 

(Schaub 1995)

This table shows that a single 

infected person can shed a large 

number of pathogenic organisms.
6-6

Report to Congress on the Impacts and Control of CSOs and SSOs

6.1.3 Biologically Active Chemicals

Recent research efforts have begun to 

consider the presence of biologically 

active chemicals—antibiotics, caffeine, 

hormones, human and veterinary 

drugs, and steroids—in wastewater 

(Kümmerer 2001). For the most part, 

these chemicals have not undergone 

extensive analysis for environmental 

fate and transport, human health 

impacts, or ecological impacts. 

Concerns about the presence of these 

biologically active chemicals focus on 

abnormal physiological processes and 

reproductive impairments, increased 

incidence of cancer, development 

of antibiotic-resistant bacteria, 

and potential increased toxicity of 

chemical mixtures. Human health 

effects, however, are largely unknown 

(Kolpin et al. 2002). 

Little is known about the effectiveness 

of conventional wastewater treatment 

processes in the removal of these 

biologically active chemicals. The 

relative concentrations of these 

chemicals in CSOs and SSOs are also 

unknown. 

6.2 What Exposure Pathways 

and Reported Human 

Health Impacts are 

Associated with CSOs and 

SSOs?

Humans may be exposed 

to the pollutants found in 

CSOs and SSOs through 

several pathways. The most common 

pathways include recreating in waters 

receiving CSO or SSO discharges, 

drinking water contaminated by CSO 

The New York-New Jersey Harbor Estuary Program sponsored studies to estimate 

pollutant loads, including loads of synthetic organic chemicals to New York 

Harbor. As shown, the studies identified six sources of PCB inputs to the harbor. 

Application of a mass balance water quality food chain model for PCBs indicated 

that discharges of PCBs to the lower estuary from municipal point sources and 

CSOs are significant in causing PCB levels in striped bass to exceed the FDA 

standard for fish consumption (NYNJHEP 1996).

Tributaries/

upstream inputs

50%

Municipal

point sources

22%

Urban

storm water

15%

CSOs

10%

Atmospheric

deposition

3%

Landfill leachate

<1%

Sources of Synthetic Organic 

Chemicals Deposition:

NY/NJ Harbor
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-7

or SSO discharges, and consuming 

or handling fish or shellfish that 

have been contaminated by CSO 

or SSO discharges. Other pathways 

include direct contact with discharges, 

occupational exposure, and secondary 

transmission.

During wet weather events, CSO- and 

SSO-impacted waterbodies typically 

receive microbial pathogens and 

toxics from a variety of other sources 

including municipal and industrial 

wastewater discharges, urban storm 

water runoff, and agricultural 

nonpoint source discharges. These 

“interferences” can complicate the 

identification of specific cause-andeffect relationships between individual 

CSO or SSO discharges and human 

health impacts.

6.2.1 Recreational Water 

In the United States, millions of 

people use natural waters (e.g., oceans, 

lakes, rivers, and streams) each year 

for a variety of recreational activities. 

The National Survey on Recreation 

and the Environment, conducted by 

the U.S. Forest Service and NOAA, 

describes nationwide participation in 

50 categories of outdoor recreation 

activities (Leeworthy 2001). The 

survey estimates the percentage of the 

population, 16 years of age or older, 

participating in water-based recreation 

activities. Participation in more than 

one activity in a single water-based 

recreation category is possible (e.g., 

respondents may report both sailing 

and canoeing). Data from the most 

recent version of the survey (the 

period of July 1999 to January 2001) 

are presented in Table 6.5. 

A number of studies have documented 

the risks of gastroenteritis among 

people recreating in water 

contaminated with microbial 

pathogens (NAS 1993; Wade et al. 

2003). Recreational exposure generally 

comes from contaminants suspended 

in the water column entering the body 

via oral ingestion. Exposure can also 

occur through the eyes, ears, nose, 

anus, genitourinary tract, or dermal 

cuts and abrasions (Henrickson et 

al. 2001). Contact with and ingestion 

of ocean water near wastewater or 

storm drain outfalls have resulted in 

increases in reported respiratory, ear, 

and eye symptoms by ocean swimmers 

and surfers (Corbett et al. 1993; Haile 

et al. 1999). 

As described in Chapter 5, 25 percent 

of the beaches inventoried in EPA’s 

National Health Protection Survey of 

Beaches under the BEACH Program 

had at least one advisory or area 

closing during the 2002 swimming 

Table 6.5

Participation in WaterBased Recreation in U.S. 

between July 1999 and 

January 2001

The National Survey on Recreation 

and the Environment estimates 

nationwide participation in various 

outdoor recreation activities, 

including water-based recreation. 

Participation in more than one 

U.S. Population activity is possible.

(16 and Older)

Boating/Floating a Fishing Swimming b

Percent participating 36% 34% 61%

Number in millions 77 72 131

a Includes sailing, canoeing, kayaking, rowing, motor-boating, water skiing, personal watercraft use, wind 

surfing, and surfing. 

b Includes swimming in freshwater or saltwater, snorkeling, scuba, and visiting a beach. 
6-8

Report to Congress on the Impacts and Control of CSOs and SSOs

season. Elevated bacteria levels were 

cited as the primary cause for 75 

percent of these beach advisories or 

closures. CSOs were reported to be 

responsible for 1 percent of reported 

closings and advisories, and 2 percent 

of advisories and closures that had 

a known cause. SSOs (including 

sewer line breaks) were reported to 

be responsible for 6 percent of all 

reported advisories and closings, and 

12 percent of advisories and closing 

that had a known cause (EPA 2003a).

Reported Human Health Impacts

A review of CDC Surveillance 

Summaries identified 74 waterborne 

disease outbreaks linked to open 

recreational waters (i.e., rivers, streams, 

beaches, lakes, and ponds) from 1985 

to 2000. A waterborne disease outbreak 

is defined by CDC as two or more 

people experiencing similar illness after 

exposure to a waterborne pathogen. 

A total of 5,601 cases of illness were 

attributed to these 74 waterborne 

disease outbreaks (CDC 1988, 1990, 

1992, 1993, 1996a, 1998, 2000, 2002). 

The source of the pathogens causing 

these waterborne disease outbreaks 

was not identified in CDC’s reports. 

These waterborne disease outbreaks, 

however, were caused by the types of 

microbial pathogens found in CSOs 

and SSOs. Figure 6.1 shows that 

Shigella, which is present in CSOs 

and SSOs, caused the largest number 

of recreational water-associated 

outbreaks having a known cause.

Additional information from CDC 

Surveillance Summaries on outbreaks 

linked to recreational exposure in 

fresh or marine waters contaminated 

with microbial pathogens is presented 

in Appendix I. 

CDC Surveillance Summaries also 

identify outbreaks linked to swimming 

pools or hot tubs. For swimming 

pools and hot tubs, 191 recreational 

waterborne disease outbreaks with 

14,836 cases of illness were reported 

to CDC between 1985 and 2000 (CDC 

1988, 1990, 1992, 1993, 1996a, 1998, 

2000, 2002). This is 265 times the 

Figure 6.1

Microbial Pathogens 

Linked to Outbreaks 

in Recreational Waters, 

1985 - 2000

Shigella was the most commonly 

identified cause of waterborne 

disease outbreaks linked to 

recreational waters between 1985 

and 2000. Shigella has a relatively 

low infective dose of 10-100 and 

is typically found in wastewater in 

concentrations of 0.1-1,000 per 100 

mL of sewage.

Unknown Agent

23%

Shigella

21%

Naegleria fowleri

17%

Pathogenic E.coli

13%

Schistosoma spp.

7%

Crypotosporidium

4%

Giardia

4%

Norwalk-like

virus

4%

Other known agents

7%
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-9

number of illnesses reported for open 

recreational waters.

Estimated Illnesses at Recognized 

Beaches

In developing this Report to 

Congress, EPA found an absence of 

direct cause-and-effect data relating 

the occurrence of CSO and SSO 

discharges to specifi c human health 

impacts. Lacking comprehensive 

data, EPA was able to implement an 

alternate approach to estimate the 

annual number of illnesses caused 

by recreational exposure to CSO and 

SSO discharges at a small subset of 

the nation’s swimming areas—that is, 

those recreational beaches recognized 

by state authorities (“recognized 

beaches”). EPA’s illness estimate was 

based on existing environmental 

and recreational use databases. Data 

limitations made it impossible to 

develop a comprehensive estimate 

of illness at all swimming areas at 

this time, but EPA believes that a 

signifi cant number of additional 

illnesses occur in exposed swimmers 

at many inland and unrecognized 

beaches. 

EPA’s estimation of illness at 

recognized beaches was limited to 

gastrointestinal illness. EPA employed 

a multi-step process, including the 

following:

● Number of recognized beaches 

 using specific management 

 approaches;

● Number of CSO and SSO events 

impacting recognized beaches;

● Number of individuals exposed 

annually;

● Average concentration of fecal 

coliform bacteria at affected 

beaches;

● Rate of infection for exposed 

population; and

● Total annual number of 

gastrointestinal illnesses.

The number of highly credible 

gastrointestinal illnesses (HCGI) 

resulting from human exposure 

to SSOs and CSOs at recognized 

beaches was estimated by combining 

information on the number 

of exposed swimmer days, the 

concentration of indicator bacteria 

to which swimmers are exposed, and 

the Cabelli/Dufour dose-response 

functions for marine and fresh 

waters. First, EPA calculated the total 

number of illnesses caused by CSOs 

and SSOs, and then attributed them 

separately to CSO illnesses or SSO 

illnesses according to the ratio of CSO 

to SSO events in the BEACH Survey. 

A more detailed presentation of EPA’s 

methodology is included in Appendix 

J.

Results from the analyses are presented 

in Table 6.6. The range shown reflects 

differences in how compliance rates 

with beach advisories were estimated. 

The lower bound uses a compliance 

rate of 90 percent, and the upper 

bound uses a compliance rate of 36 

percent. As shown, CSOs and SSOs 

are estimated to cause between 3,448 

and 5,576 illnesses annually at the 

recognized beaches included in this 

analysis. This estimate captures only a 

portion of the likely number of annual 

illnesses attributable to CSO and SSO 

contamination of recreational waters.
6-10

Report to Congress on the Impacts and Control of CSOs and SSOs

6.2.2 Drinking Water Supplies

Public water systems regulated by EPA, 

states, and tribes provide drinking 

water to 90 percent of Americans (EPA 

2002e). Approximately 65 percent of 

the population served by these systems 

receive water primarily taken from 

surface water sources such as rivers, 

lakes, and reservoirs. The remaining 35 

percent drink water that originated as 

groundwater (EPA 1999d).

Reported Human Health Impacts

People can contract waterborne 

diseases through consumption of 

municipal drinking water, well 

water, or contaminated ice. Because 

drinking water is directly ingested, 

and it is generally ingested in larger 

quantities than recreational water that 

is accidentally ingested, drinking water 

is an important pathway of exposure. 

From 1985 to 2000, 251 outbreaks and 

462,169 cases of waterborne illness 

related to contaminated drinking 

water were reported to CDC (CDC 

1988, 1990, 1992, 1993, 1996a, 1998, 

2000, 2002). The vast majority of 

these cases of illness are from a 

1993 cryptosporidiosis outbreak in 

Milwaukee, Wisconsin, which affected 

an estimated 403,000 people; the CDC 

did not specifically identify untreated 

wastewater as contributing to the 

Milwaukee outbreak. 

As shown in Appendix I, EPA 

identified a subset of 55 of these 251 

outbreaks linked to drinking source 

water contaminated with human 

sewage or to drinking water taken 

Sourcee Lower Bound Upper Bound

SSOs 2,269 3,669

CSOs 845 1,367

CSO/SSOs 334 540

Total 3,448 5,576

Table 6.6

Estimated Illness 

Resulting from 

Recreational Exposure to 

CSOs and SSOs at Select 

Beaches

This table shows the portion of the 

estimated number of annual illnesses 

attributable to exposure to CSO and 

SSO contaminated water at staterecognized beaches in the U.S. and 

its territories.

Between December 15, 1989, and January 20, 1990, residents of and visitors to 

Cabool, Missouri, experienced 243 cases of diarrhea and four deaths (Swerdlow 

et al. 1992). The CDC conducted a household survey and concluded that persons 

drinking municipal water were 18.2 times more likely to develop diarrhea than 

persons using private well water (Geldreich et al. 1992). Observations suggested 

that Cabool’s SSS was prone to excessive storm water infiltration and therefore was 

unable to convey all of the wastewater to the treatment facility. As a result, frequent 

capacity-related SSOs occurred, spilling sewage onto the ground surface in areas 

over drinking water distribution lines and near water meter boxes. During the 

outbreak, the water distribution system was under construction, allowing untreated 

sewage to contaminate the drinking water system (Geldreich et al. 1992).

SSOs linked to Drinking 

Water Contamination: 

Cabool, MO
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-11

from rivers, streams, or lakes. Of 

these, EPA identified 11 outbreaks 

accounting for 7,764 cases of 

waterborne illness that CDC linked 

to drinking water contamination with 

sewage. Only one of these outbreaks 

was linked directly to CSOs or SSOs. 

The outbreaks were caused, however, 

by the types of microbial pathogens 

found in CSOs and SSOs. As shown in 

Figure 6.2, Giardia, which is present 

in significant concentrations in CSOs 

and SSOs, caused the largest number 

of outbreaks linked to drinking water. 

A summary of these outbreaks is 

provided in Appendix I.

Proximity of CSO Outfalls to Drinking 

Water Intakes

As described in Chapter 5 and 

documented in Appendix F, EPA georeferenced more than 90 percent of 

all CSO outfalls. EPA compared the 

locations of these CSO outfalls to 

drinking water intakes. Only drinking 

water systems that serve a community 

on a year-round basis and that use 

surface water as the primary source 

of water were considered in this 

analysis. Approximately 7,519 such 

systems operate in the United States, 

of which 6,631 (85 percent) have been 

Giardia

42%

Unknown agent

31%

Cryptosporidium

10%

Pathogenic E. coli

6%

Campylobacter

2%

Other known

agents

7%

Shigella

2%

Figure 6.2

In July 1998, a lighting strike and the subsequent power outage caused 167,000 

gallons of raw sewage to flow into Brushy Creek in Texas (TDH 1998). The sewage 

contaminated municipal drinking water wells that supplied the community of 

Brushy Creek. Although the wells are not in direct contact with surface waters (the 

wells are more than 100 feet deep and encased in cement), drought conditions at 

the time are thought to have caused water from Brushy Creek to be drawn down 

into the aquifer and into the wells through a geologic fissure. It is estimated that 60 

percent of Brushy Creek’s population of 10,000 were exposed to Cryptosporidium

and approximately 1,300 residents became ill with cryptosporidiosis. Residents of 

Brushy Creek were supplied water from the contaminated wells for approximately 

eight days (TDH 1998).

Drinking Water 

Contaminated by Sewage: 

Brushy Creek, TX

Microbial Pathogens 

Causing Outbreaks 

Linked to Drinking Water 

1985 - 2000

Giardia was responsible for 42 

percent of the outbreaks of 

waterborne disease linked to 

drinking water.
6-12

Report to Congress on the Impacts and Control of CSOs and SSOs

geo-referenced to the NHD and are 

included in this analysis. 

All of the drinking water systems 

within one mile of any CSO 

outfall were selected for further 

analysis. As shown in Table 6.7, EPA 

identified seven states with outfalls 

located within one mile upstream 

of a drinking water intake. Phone 

interviews were conducted with 

both the NPDES permit-holder 

and drinking water authority in 

the identified areas to confirm the 

location of the CSO outfall, the status 

of the CSOs (active/inactive), and the 

location of the drinking water intake. 

In many cases, the NPDES permitholder reported that the CSO was 

inactive, as a result of sewer separation 

or other CSO controls. 

EPA identified and confirmed 59 

active CSO outfalls within one mile of 

a drinking water intake. One NPDESpermit holder reported that receiving 

water modeling found that the 

drinking water intake (located within 

one mile, but on the opposite side 

of the river) was not affected by the 

CSO. Interviews with drinking water 

authorities found, where a primary 

drinking water intake was located 

within one mile of an active CSO, each 

drinking water authority was aware 

of the CSO. Further, in all cases, lines 

of communication existed between 

the drinking water authority and the 

NPDES permit-holder. In many cases 

the drinking water authority indicated 

adjustments are made to the treatment 

process during wet weather.

This assessment indicates that CSO’s 

generally do not pose a major risk 

of contamination to most public 

drinking water intakes. However, to 

understand the relationship between 

a discharge point and a downstream 

drinking water intake the transport 

and fate of the discharge between the 

two points must be modeled under the 

range of real world flow conditions for 

that stream reach. Such modeling is 

beyond the scope of this report. 

6.2.3 Fish and Shellfish

Fish and shellfish are widely 

consumed in the United States and 

are a valued economic and natural 

resource (NYNJDEP 2002a). In 1995, 

EPA Region State Number of CSO Outfalls within 1 mile 

upstream of a drinking water intake

1 ME 7

2 NY 7

3 PA 19

3 WV 9

4 KY 7

5 IN 3

5 OH 7

Total: 59

Table 6.7

Association of CSO 

Outfalls with Drinking 

Water Intakes

EPA identified 59 CSO outfalls in 

seven states with outfalls located 

within one mile upstream of a 

drinking water intake.

Note: EPA was unable to confirm data for an additional 14 outfalls in two states ( PA and WV); these outfalls 

are not included in this table.
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-13

the most recent year for which data 

are available, 77 million pounds of 

clams, oysters, and mussels were 

harvested in the coastal United States 

(NOAA 1997). Shellfish grown in 

contaminated waters concentrate 

microbial pathogens and can have 

higher concentrations than the 

waters in which they are found. 

Viable pathogens can be passed on 

to humans by eating whole, partially 

cooked, or raw contaminated shellfish.

Reported Human Health Impacts

The World Health Organization 

reported that seafood is involved in 11 

percent of all disease outbreaks from 

food ingestion in the United States 

(WHO 2001). The most common 

illness associated with eating sewagecontaminated raw shellfish and fish is 

gastroenteritis (CERI 1999). 

A review of CDC Surveillance 

Summaries identified eight 

waterborne disease outbreaks linked to 

the consumption of contaminated fish 

or shellfish for the period 1985-2000. 

These outbreaks resulted in 995 cases 

of illness (CDC 1990, 1995, 1996b, 

1997). More information on these 

outbreaks is provided in Appendix 

I. In most cases, the contaminated 

fish or shellfish were exposed to or 

grown in sewage-contaminated water. 

Waste dumped overboard by boaters 

and improperly treated sewage were 

the most commonly cited sources 

of fish and shellfish contamination. 

The New York State Department of Health compiled data on shellfish-associated 

illness (most commonly gastroenteritis) recorded in New York State from 1980 to 

1999 (NYNJHEP 2002b). The incidence of reported illness has dropped markedly 

since its peak in 1982. The study was able to trace most of the outbreaks in 1982 to 

Rhode Island shellfish. The study noted that it is often difficult to identify the source 

of the shellfish that induced the outbreak. Decreases in shellfish-associated disease 

are attributed to a number of factors including: improvements in wastewater 

treatment leading to reductions in concentrations of waterborne microbial 

pathogens; more restrictions on shellfish harvesting in contaminated areas; and 

more public awareness of the risks associated with consuming raw shellfish. The 

study also noted that although shellfish beds are carefully monitored for pathogenic 

contamination, the levels of toxic contaminants in shellfish, including impacts from 

marine algal toxins, need additional study. 

Number of Reported Outbreaks of Shellfish

Associated Illnesses, New York State

0

20

40

60

80

100

120

140

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

Year

# Outbreaks

Shellfish-Associated Illness:

New York State
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Report to Congress on the Impacts and Control of CSOs and SSOs

Direct links to CSO and SSO events 

as a cause of contamination were not 

made. 

6.2.4 Direct Contact with LandBased Discharges

Many SSOs discharge to terrestrial 

environments including streets, 

parks, and lawns. CSSs and SSSs 

can also back up into buildings, 

including residences and commercial 

establishments. These land-based 

discharges present exposure pathways 

that are different than those pathways 

associated with typical discharges to 

water bodies. Exposure to land-based 

SSOs and building backups typically 

occurs through dermal contact. The 

resulting diseases are often similar 

to those associated with exposure 

through drinking or swimming in 

contaminated water, but may also 

include illness caused by inhaling 

microbial pathogens (CERI 1999). 

Reported Human Health Impacts

In general, very few outbreaks 

associated with direct contact 

with land-based SSOs have been 

documented. Land-based SSOs 

tend to leave visible evidence of 

their occurrence, such as deposits of 

sanitary products and other wastes 

commonly flushed down a toilet. The 

presence of these items often acts as 

a deterrent to direct contact with the 

SSO. Further, municipal response 

to land-based SSOs often includes 

cleaning the impacted area by washing 

the sewage into a nearby manhole 

or storm drain and disinfecting as 

needed. This review identified one 

confirmed outbreak resulting from 

direct contact with a discharge of 

untreated sewage in Ocoee, Florida. 

This event resulted in 39 cases of 

hepatitis A (Vonstille 1993).

6.2.5 Occupational Exposures

Many occupational settings 

occasionally expose personnel to 

microbial pathogens. These include 

restaurants and food processing, 

agriculture, hospitals and healthcare, 

emergency response, and wastewater 

treatment. 

Wastewater treatment plant workers 

and public works department 

personnel operate and maintain 

wastewater treatment facilities and 

respond to CSO or SSO events. In 

doing so, they may be exposed to 

microbial pathogens present in CSOs 

and SSOs. Police, firefighters, rescue 

divers, and other emergency response 

personnel also face exposure to 

CSOs and SSOs. Depending on the 

context in which the overflow event 

occurs, exposure can occur through 

inhalation, ingestion, and dermal 

contact. Adherence to good personal 

hygiene and the appropriate use of 

personal protective equipment are 

important in minimizing the potential 

for injury or illness.

Reported Human Health Impacts

Comprehensive epidemiologic 

research on waterborne illness 

associated with occupational exposure 

to untreated wastewater is lacking. 

Some researchers believe that 

wastewater workers may experience 

increased numbers of bacterial, viral, 

and parasitic infections without 

exhibiting signs or symptoms of 

illness. These are called “sub-clinical” 

infections (AFSCME 2003). One 

study concluded that the lowest rates 
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-15

of illness are found among workers 

employed in wastewater treatment 

for less than five years, the highest 

rates in workers with five to 10 years 

of exposure, and lower rates again 

in workers with 15 years or more 

of exposure (Dowes et al. 2001). An 

explanation for this is that workers 

build immunity to many of the 

microbial pathogens present in the 

work environment over the course 

of their employment, and those who 

become very ill no longer work in the 

plant. This phenomenon is also known 

as the “healthy worker effect.”

In general, the effect of microbial 

pathogens, other than hepatitis A, on 

wastewater workers has been given 

little attention, and “there have been 

few epidemiologic studies conducted 

among sewage workers in the U.S. to 

determine the actual prevalence and 

types of infections” (AWR 2001). 

One confirmed waterborne disease 

outbreak through occupational 

exposure was identified from 

the review of CDC Surveillance 

Summaries. In 1982, 21 cases 

of gastrointestinal illness were 

identified among 55 police and fire 

department scuba divers training 

in sewage-contaminated waters 

(CDC 1983). The divers developed 

gastrointestinal disease more than 

four times as frequently as nondiving 

firefighters, the control group in the 

study. Although the causes of illness 

in many divers were not identified, 

gastrointestinal parasites were found 

in 12 divers: Entamoeba histolytica

in five divers, and Giardia lamblia in 

seven divers.

6.2.6 Secondary Transmission

An individual who contracts 

an infection from exposure to a 

waterborne microbial pathogen may, 

in turn, infect other individuals, 

regardless of whether symptoms are 

apparent in the first individual. This 

is commonly referred to as “secondary 

transmission.” The rate of secondary 

transmission depends largely on 

the particular microbial pathogen. 

Illnesses caused by secondary 

transmission are not included in CDC 

Surveillance Summaries, which list 

only primary illnesses. 

Reported Human Health Impacts

Secondary transmission statistics 

obtained from a variety of waterborne 

and non-waterborne disease outbreaks 

are shown in Table 6.8 (NAS 1998). As 

presented, the secondary attack ratio 

represents the ratio of secondary cases 

to primary cases.

6.3 Which Demographic 

Groups Face the Greatest 

Risk of Exposure to CSOs 

and SSOs? 

S

everal demographic groups 

face increased risk of exposure 

to the pollutants in CSOs and 

SSOs because they are more likely to 

spend time in locations impacted by 

such discharges. These groups include 

people recreating in CSO- and SSOimpacted waters, subsistence fishers, 

shellfishers, and wastewater workers. 

The sections that follow describe 

exposure risks for each of these groups 

in greater detail. This information is 
6-16

Report to Congress on the Impacts and Control of CSOs and SSOs

presented based on the availability of 

literature documenting each group’s 

potential for exposure, rather than 

on the relative sensitivity of each 

population to the pollutants in CSO 

and SSO discharges. 

6.3.1 Swimmers, Bathers, and 

Waders

Swimming in marine and fresh water 

has been linked directly to diseases 

caused by the microbial pathogens 

found in wastewater (Cabelli et 

al. 1982). For example, a 1998 

study comparing bathers and nonbathers found that 34.5 percent of 

gastroenteritis and 65.8 percent of ear 

infections reported by participants 

were linked to bathing in marine 

waters contaminated with sewage. 

The percentage of people who lost at 

least one day of normal activity due to 

contacting one of the illnesses studied 

ranged from 7 to 26 percent (Fleisher 

et al. 1998).

Many variables influence the exposure 

of people to pathogens in recreational 

water. These factors include whether 

people swim or wade, the type of 

pathogens present at the time of 

exposure, the route of exposure 

(ingestion or skin contact), and 

individual susceptibility to waterborne 

disease (WSDH 2002). 

6.3.2 Subsistence and Recreational 

Fishers

Subsistence and recreational fishers 

and their families tend to consume 

more fish and shellfish than the 

general population, and men tend to 

consume more fish and shellfish than 

women (Burger et al. 1999). Further, 

in areas conducive to fishing, people 

with lower education levels or lower 

income levels consume more fish and 

shellfish, as it is often an inexpensive 

source of protein (Burger et al. 1999). 

Cultural preferences influence the 

amount and frequency of fish as well 

as shellfish consumption and the 

methods for preparing and serving 

fish and shellfish. For example, a study 

of two Native American groups in 

Puget Sound in Washington found 

that these groups consumed fish at 

much higher rates than the general 

public and at rates greater than those 

recommended by EPA (Toy et al. 

1996). Asians and Pacific Islanders 

generally consume fish at much higher 

rates than the general United States 

population (Sechena et al. 1999). 

In addition, cooking methods and 

consumption rates of parts of the 

fish that tend to concentrate toxins 

(e.g., skin, head, organs, and fatty 

tissue) can increase the risk of human 

health impacts from consuming 

Microbial Pathogen Secondary Attack Ratio Source of Outbreak 

Cryptosporidium 0.33 Contaminated apple cider

Shigella 0.28 Child day care center

Rotavirus 0.42 Child day care center

Giardia 1.33 Child day care center

Unspecified virus causing 

viral gastroenteritis

0.22 Contaminated drinking water

Norwalk virus 0.5 - 1.0 Contaminated recreational water

Table 6.8

Examples of Secondary 

Transmission from 

Waterborne and NonWaterborne Disease 

Outbreaks (NAS 1998)

An individual who contracts an 

infection may, in turn, infect other 

individuals. This table shows for 

every two individuals infected with 

Norwalk virus, one to two individuals 

can become infected via secondary 

transmission.
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-17

contaminated fish and shellfish (e.g., 

Wilson et al. 1998; WDNR 2003). 

Fish and shellfish advisories target 

recreational and subsistence fishers. 

Despite warnings and advisories, 

however, many fishers consume 

their catch. May and Burger (1996) 

found that a majority of urban and 

suburban recreational fishers ignored 

warnings issued by the New York State 

Department of Health and the New 

Jersey Department of Environmental 

Protection.

6.3.3 Wastewater Workers

Wastewater workers are more likely 

to come into contact with untreated 

wastewater than the general public, 

but there is insufficient data to 

determine whether wastewater 

workers or their families face an 

increased risk of illness as a result 

of this exposure. Although there is 

disagreement regarding the benefits of 

additional immunization above those 

recommended by CDC for the adult 

general population (i.e., diptheria 

and tetanus), WERF (2003b) asserts 

that wastewater workers should be 

vaccinated for both Hepatitis A and B.

6.4 Which Populations Face 

the Greatest Risk of Illness 

from Exposure to the 

Pollutants Present in CSOs 

and SSOs? 

Certain demographic groups, 

including pregnant women, 

children, individuals with 

compromised immune systems, 

and the elderly, may be at greater 

risk than the general population for 

serious illness or a fatal outcome 

resulting from exposure to the types 

of pollutants present in CSOs and 

SSOs. Specific characteristics of 

these demographic groups that make 

them particularly susceptible to these 

illnesses are discussed in more detail in 

the following sections. These sensitive 

groups represent almost 20 percent 

of the U.S. population (Gerba et al. 

1996). Also, tourists and travelers may 

be more prone to waterborne illnesses 

than local residents (EPA 1983b). EPA 

research has found that when exposed 

to pathogens found in local sewage, 

local residents have been shown to 

develop fewer symptoms than nonresidents or visitors. 

6.4.1 Pregnant Women

During pregnancy, women appear 

to be at greater risk of more serious 

disease outcomes from exposure to 

the types of enteric viruses found 

in CSOs and SSOs (Reynolds 2000). 

Waterborne diseases contracted during 

pregnancy may result in transfer of 

the illness to the child either in utero, 

during birth, or shortly after birth 

(Gerba et al. 1996).

6.4.2 Children 

The incidence of several waterborne 

infectious diseases caused by the 

types of pollutants present in CSO 

and SSO discharges is significantly 

greater in infants and children than 

in the general population (Laurenson 

et al. 2000). Factors contributing to 

the susceptibility of children include 

children’s naturally immature immune 

systems and child-associated behaviors 

that result in abnormally high 

ingestion rates during recreational 

exposure to contaminated water 

(Laurenson et al. 2000). For example, 
6-18

Report to Congress on the Impacts and Control of CSOs and SSOs

children frequently splash or swim in 

waters that would be considered too 

shallow for full-body immersion by 

adults (EPA 2001b).

6.4.3 Immunocompromised Groups

People with compromised immune 

systems, such as those with AIDS, 

organ transplant recipients, and 

people undergoing chemotherapy, 

are more sensitive than the general 

public to infection and illness caused 

by the types of pollutants present 

in CSO and SSO discharges (Gerba

et al. 1996). Using Wisconsin death 

certificate data, Hoxie et al. (1997) 

analyzed cryptosporidiosis-associated 

mortality in AIDS patients following 

the 1993 Milwaukee outbreak that 

affected an estimated 403,000 people. 

The researchers found that AIDS 

was the underlying cause of death 

for 85 percent of post-outbreak 

cryptosporidiosis-associated deaths 

among residents of the Milwaukee 

area. Further, the researchers found 

that AIDS mortality increased 

significantly in the six months 

immediately after the outbreak, 

then decreased to levels lower than 

expected, and then returned to 

expected levels. This suggests that 

some level of premature mortality was 

associated with the outbreak. 

6.4.4 Elderly

The elderly are at increased risk for 

waterborne illness due to a weakening 

of the immune system that occurs 

with age (Reynolds 2000). Studies 

have found that people over 74 years 

old, followed by those between 55 

and 74, and then by children under 

5, respectively experience the highest 

mortality from diarrhea as a result of 

infection by waterborne or foodborne 

illness (Gerba et al. 1996). Studies 

of a giardiasis outbreak in Sweden 

that occurred when untreated sewage 

contaminated a drinking water supply 

found people over 77 years old faced 

an especially high risk of illness 

(Ljungstrom and Castor 1992).

6.5 How are Human Health 

Impacts from CSOs and 

SSOs Communicated, 

Mitigated, or Prevented? 

A variety of programs are in 

place to reduce human health 

impacts associated with 

exposure to microbial pathogens 

and toxics. These programs generally 

involve preventive measures enacted 

by public health officials, including: 

communication efforts to warn the 

public about risk and threats; and 

monitoring, reporting, and tracking 

activities. This section is focused on 

agencies, activities, and programs 

designed to communicate, mitigate, 

or prevent potential human health 

impacts from exposure to CSOs and 

SSOs. 

6.5.1 Agencies and Organizations 

Responsible for Protecting 

Public Health 

Numerous agencies and organizations 

have responsibilities for monitoring, 

tracking, and notifying the public of 

potential human health impacts. These 

include federal and state agencies, 

local public health officials, owners 

and operators of municipal wastewater 
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-19

collection and treatment facilities, and 

non-governmental organizations. 

Federal Agencies

EPA administers a national water 

quality standards program that 

establishes criteria to support 

designated uses including recreation, 

drinking water supply, and shellfish 

harvesting. EPA also administers a 

national safe drinking water program 

with a goal that, by 2005, 60 percent of 

the population served by community 

drinking water systems will receive 

their water from systems with active 

source water protection programs 

(EPA 1997b). In developing source 

water protection programs, EPA 

specifically encourages suppliers 

to consider CSOs, sewer system 

failures, and wet weather municipal 

effluent point source discharges as 

sources of microbial contamination. 

Further, drinking water intakes and 

their designated protection areas are 

identified as “sensitive areas” under the 

CSO Control Policy. The elimination, 

control, or relocation of CSO outfalls 

that discharge to sensitive areas 

are to be given high priority in the 

development and implementation of 

CSO LTCPs (EPA 1994a).

As discussed earlier in Section 5.5.2 

of this report, EPA’s BEACH program 

conducts an annual survey of the 

nation’s swimming beaches. The 

program was created to reduce health 

risks to swimmers due to contact 

with contaminated water by working 

to improve monitoring and public 

notification procedures at beaches.

CDC’s National Center for Infectious 

Diseases works to prevent illness, 

disability, and death caused by 

infectious diseases. Waterborne 

disease prevention is a priority for this 

program. Working with EPA, CDC 

coordinates national reporting of 

waterborne illness outbreaks through 

its Outbreak Surveillance System. 

This system compiles state-reported 

outbreaks to characterize waterborne 

outbreaks epidemiologically (e.g., to 

investigate the agents, reasons for the 

outbreak, and adequacy of various 

treatment methods) and to strengthen 

the public health community’s ability 

to respond. Outbreak summaries 

are produced biennially. With 

the cooperation of state health 

departments and other national 

partners, CDC’s Division of Parasitic 

Diseases and Division of Bacterial and 

Mycotic Diseases are responsible for 

the investigation, surveillance, and 

control of specific groups of diseases, 

including many pathogens linked to 

waterborne illness. 

NOAA works to protect and 

preserve U.S. living marine resources 

through scientific research, fisheries 

management, enforcement, and 

habitat conservation. As detailed in 

Section 5.3.2 of this report, NOAA 

is currently working with Interstate 

Shellfish Sanitation Conference 

(ISSC), EPA, and FDA to develop an 

information resource on shellfish 

safety. This data system will house 

shellfish growing area monitoring, 

survey, and classification data. 

FDA administers the National Shellfish 

Sanitation Program, an effort intended 

to standardize the inspection and 

monitoring of shellfish growing 

areas and shellfish packing/shucking 

facilities. Working with EPA, FDA 
6-20

Report to Congress on the Impacts and Control of CSOs and SSOs

publishes guidance on the safety 

attributes of fish and fishery products, 

including acceptable levels of organic 

and inorganic compounds such as 

mercury and PCBs. 

USGS plays an active role in 

monitoring and reporting the 

quantity and quality of the nation’s 

water resources. USGS helps to assess 

water quality problems and sources 

of pollution, including CSOs and 

SSOs, by studying how pathogens and 

other agents of waterborne disease 

interact with the environment and by 

monitoring and reporting the quality 

of the nation’s water resources.

State Agencies

State public health agencies track 

communicable diseases, perform 

outbreak investigations, and issue 

warnings to the public. These agencies 

integrate and compile findings 

from local efforts, and they provide 

coordination with other state and 

federal agencies and programs. This 

coordination includes providing 

data on waterborne illness and 

investigations to CDC.

State environmental agencies conduct 

water quality monitoring and 

assessment programs and require 

monitoring to be conducted by others, 

such as local sanitation districts, 

public water systems, regional 

planning agencies, and recreational 

facilities. State environmental or 

natural resource agencies also 

monitor fish and shellfish. These 

monitoring programs provide data 

for management decisions at the state 

level in response to environmental and 

public health concerns. In addition 

to monitoring, state agencies perform 

sanitary surveys to identify problems 

that could affect the safety of the 

drinking water supply. A sanitary 

survey is a physical inspection of the 

The Rhode Island Health Department requires every licensed beach to sample its 

water and test for the presence of fecal coliform bacteria. The Rhode Island water 

quality standard for recreation is 50 MPN per 100 ml of salt water and 200 MPN 

per 100 ml of fresh water. Results are posted on the department’s website, along 

with advisories on waterborne illness and beach closures and openings. Public 

notification of beach closures is accomplished in several ways, including the use 

of color-coded flags at beaches, press releases, and notices on the department 

website. The website also supports on-line reporting by the public of suspected 

beach-related illnesses.

The State of Connecticut has a comprehensive monitoring program for its coastal 

waters, with standards and guidelines set by the state. The state collects and 

analyzes samples taken at four coastal state parks on Long Island Sound. At least 

18 municipalities in the state’s four coastal counties monitor their own beaches, 

following the ocean and bay beachwater-quality monitoring protocol established 

by the Connecticut Departments of Public Health and Environmental Protection. In 

2002, Connecticut set aside a $226,000 grant to integrate monitoring at municipal 

beaches into a state-administered sampling and public notification plan for the 

entire state. The beach grant funded a courier service to bring municipal beach 

samples to the Department of Public Health lab, where the state analyzes the 

samples free of charge.

Coastal Beach 

Monitoring Program:

Connecticut

Beach Monitoring and 

Public Notification Program:

Rhode Island
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-21

water treatment and distribution 

system and a review of operation and 

maintenance practices. 

States also implement notification 

programs to warn citizens about 

human health impacts associated with 

recreation at contaminated beaches 

and consumption of contaminated 

water, fish, or shellfish. 

Local Agencies

Local public health agencies, regional 

planning authorities, and the owners 

and operators of wastewater collection 

and treatment facilities have distinct 

responsibilities to protect public 

health. Working with state oversight, 

city and county health departments 

often maintain separate divisions 

for tracking communicable diseases 

and for environmental health. The 

communicable disease divisions 

of these departments generally 

have responsibility for cataloging, 

investigating, and reporting cases of 

“reportable illness” to the appropriate 

state agency. The environmental 

health divisions generally have 

responsibility for monitoring, analysis, 

and posting of recreational waters, 

where needed. Owners and operators 

of municipal wastewater collection 

and treatment facilities have their 

own responsibilities, many of which 

are stipulated as NPDES permit 

requirements, including notifying 

the public when SSOs occur and 

reporting SSOs to state regulatory and 

public health agencies. Communities 

with CSSs are required to implement 

public notification programs as part of 

implementing the NMCs.

6.5.2 Activities to Protect Public 

Health from Impacts of CSOs 

and SSOs

The principal activities undertaken to 

protect the public from the impacts 

of CSOs and SSOs can be grouped 

into three areas: exposure pathway 

monitoring, public notification, and 

research. These activities protect 

public health by identifying possible 

sources of pathogens, reducing public 

exposure through notification and 

Local Public Health Activity: 

Orange County, CA

Local Public Health Activity: 

Allegheny County, PA

The Allegheny County Health Department in Pennsylvania implemented a public 

notification program designed to warn recreational users of health risks in 

CSO-impacted waters in the Pittsburgh area. The program includes publishing 

advisories in local newspapers and producing public service announcements on 

local television stations to educate the public about health risks associated with 

CSO discharges. The department also installed orange warning flags that read “CSO” 

at 30 locations near CSO outfalls. The flags are raised to warn recreational users 

whenever CSO discharges cause or contribute to elevated bacteria levels.

In California, the Orange County Health Care Agency’s Ocean Water Protection 

Program has a mission to ensure that all public recreational waters meet 

bacteriological water quality standards for full body contact recreation activities, 

such as swimming, surfing, and diving. Staff collect water samples at approximately 

150 locations along the shoreline of Orange County for laboratory analysis for 

indicator bacteria. Results of the analysis are reviewed by program specialists who 

determine if action needs to be taken to protect the public. Staff are available to 

respond on a 24-hour basis to investigate reports of contamination incidents, 

including SSOs, affecting Orange County’s public beaches.
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Report to Congress on the Impacts and Control of CSOs and SSOs

use restriction, when necessary, and 

continuing research by public health 

experts to better protect public health 

in the future. More detail on each 

activity is presented below.

Exposure Pathway Monitoring

Exposure pathway monitoring 

programs focus on recreational waters, 

public drinking water systems, and 

fish and shellfish in order to reduce 

the risk of human health impacts from 

exposure to contaminated water and 

food. 

Recreational waters are typically 

monitored using indicator bacteria to 

detect the presence of or the potential 

for microbial pathogen contamination. 

If the bacteria levels in a given water 

sample exceed the state standard for 

recreational waters, advisories are 

posted or the waterbody is closed. For 

example, EPA’s 2002 BEACH Program 

found that 91 percent of surveyed 

beaches had some type of water 

quality monitoring program. Though 

the frequency of monitoring varied, 63 

percent of the beaches were monitored 

at least once per week (EPA 2003a). 

Public water systems are governed 

by National Primary Drinking Water 

Standards, also known as primary 

standards (EPA 2003f). Primary 

standards are legally enforceable 

standards that protect public health 

by limiting the levels of specific 

contaminants in drinking water. 

To protect the health of those 

being served, public water systems 

have monitoring requirements. 

Contaminants monitored are as 

follows (EPA 2002f):

● Microorganisms including 

indicator organisms, enteric 

viruses, and parasitic protozoa; 

● Disinfectants including chlorine, 

chlorine dioxide, and chloramine;

● Disinfection byproducts including 

bromate, chlorite, haloacetic acids, 

and trihalomethanes;

● Inorganic chemicals including 

metals, nitrate, and nitrite;

● Organic chemicals including a 

broad list of agricultural and 

industrial products; and

● Radionuclides.

If monitoring shows the drinking 

water is contaminated, the owner or 

operator of the public water system 

is required to shut down the system 

and/or direct the public to take 

precautions, such as boiling water. 

Fish and shellfish monitoring is 

administered jointly by state agencies, 

EPA, NOAA, and FDA. Bacteriological 

monitoring is used to assess the 

potential presence of microbial 

pathogens in shellfish harvesting areas. 

States, U.S. territories, and authorized 

tribes have primary responsibility for 

protecting residents from the health 

risks of consuming contaminated, 

noncommercially caught fish. This 

is accomplished by issuing of fish 

consumption advisories. These 

advisories inform the public when 

high concentrations of contaminants 

have been found in local fish. They 

also include recommendations to 

limit or avoid eating certain fish 

species from specific waterbodies or 

waterbody types.
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-23

Public Notification 

Public notification programs provide 

information to communities regarding 

the occurrence of CSO and SSO 

events and ongoing efforts to control 

discharges. 

Public notification programs include 

posting temporary or permanent 

signs where CSOs and SSOs 

occur, coordinating with civic and 

environmental organizations, and 

distributing fact sheets to the public 

and the media. Notices in newspapers 

are used to publicize CSO or SSO 

discharges in some states. Radio and 

television announcements may be 

appropriate for CSOs and SSOs with 

unusually severe impacts. Distribution 

of information on websites is rapidly 

gaining wider use. Additional 

information on reporting and public 

notification is presented in Chapter 8 

of this Report to Congress and in the 

technology descriptions included as 

Appendix L.

Research

Several research activities are expected 

to improve the ability of public health 

programs to protect humans from 

impacts associated with CSOs, SSOs, 

and other sources of pollution. Two 

examples are provided below.

EPA’s National Epidemiological 

and Environmental Assessment of 

Recreational (NEEAR) Water Study 

is intended to develop a better 

understanding of water pollution at 

beaches, recreational use of beaches, 

and public health. As part of the 

BEACH Program, this effort seeks to 

improve beach monitoring by linking 

real-time monitoring results with 

meaningful risk-based guidelines. 

EPA’s Office of Research and 

Development has completed the 

first in a planned series of studies 

to estimate the urban contribution 

to the total Cryptosporidium and 

Giardia loads to receiving waters (EPA 

2003f). It is hoped that the studies will 

provide a basis for designing source 

water protection programs.

6.6 What Factors Contribute 

to Information Gaps in 

Identifying and Tracking 

Human Health Impacts 

from CSOs and SSOs?

S

ystematic data on human 

health impacts as a result of 

exposure to CSOs and SSOs 

are not readily available. The chief 

factors that account for the absence 

of direct cause-and-effect data 

In 1984, public drinking water for the community surrounding Braun Station, Texas, 

was drawn from an artesian well that was not filtered but was chlorinated prior 

to distribution. At the time, well water was not routinely sampled in this region 

of Texas. Community complaints, however, convinced authorities to begin testing. 

Fecal coliform level as high as 2,600/100 mL were measured in untreated well water 

samples. Subsequent dye tests indicated that the community’s SSS was leaking into 

the well water. When attempts to identify the exact site of contamination were not 

successful, an alternative water source was provided to the community (D’Antonio 

et al. 1985).

Monitoring Identifies SSS 

as Source of Drinking Water 

Contamination:

Braun Station, TX
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Report to Congress on the Impacts and Control of CSOs and SSOs

are underreporting of waterborne 

disease and the reliance of water 

quality monitoring activities on 

indicator bacteria instead of microbial 

pathogens. Both factors are discussed 

below. 

6.6.1 Underreporting

Reporting and tracking of outbreaks 

of waterborne disease are difficult 

under the best circumstances. 

Underreporting stems from a number 

of causes. CDC’s waterborne disease 

outbreak surveillance system depends 

on states to report outbreaks, and 

this reporting is often incomplete. 

Existing local systems for tracking 

these outbreaks often lack sufficient 

information on the cause of the 

outbreak to establish whether CSOs 

and SSOs are suspected source.

Factors that affect the likelihood that 

outbreaks will or will not be detected, 

investigated, and reported include 

(adapted from CDC 2000):

● Public awareness about illness 

symptoms, environmental 

conditions that might precipitate 

an outbreak, and where to report 

symptoms;

● The frequency with which people 

experiencing illnesses related to 

exposure to contaminated water 

seek medical care from the same 

provider;

● The adequacy of laboratory 

infrastructure to fully investigate 

outbreaks;

● The compatability of local 

reporting requirements for specific 

waterborne diseases with data 

tracking systems employed by the 

CDC; and

● The integration of state and 

local reporting and investigation 

protocols for waterborne disease 

outbreaks.

Large outbreaks are more likely 

to be noticed and reported than 

smaller outbreaks. Nevertheless, the 

source and exposure pathway of the 

1993 Milwaukee cryptosporidiosis 

outbreak, the largest documented in 

U.S. history, remained unidentified for 

more than two weeks (CDC 1996a). 

This outbreak, affecting an estimated 

403,000 people, was detected only 

“when increased sales of antidiarrheal 

medicines were observed and reported 

to the local public health agency” 

(Frost et al. 1995).

6.6.2 Use of Indicator Bacteria

Indicator bacteria are used to 

evaluate human health risks from 

contaminated water without sampling 

for every possible microbial pathogen. 

As described in Section 6.1.1, 

indicator bacteria are relatively easy 

to detect and are used to indicate 

the likely presence of fecal-borne 

microbial pathogens. There is ongoing 

scientific debate regarding the use of 

indicators and their ability to predict 

human health impacts. Some specific 

criticisms of the use of indicator 

bacteria are as follows:

● A single indicator organism 

may be insufficient to establish 

water quality standards. EPA’s 

current water quality criteria 

are targeted toward protecting 

people participating in 
 Chapter 6—Human Health Impacts of CSOs and SSOs

6-25

recreational activities from acute 

gastrointestinal illness (EPA 

2002g).

● Current bacterial detection 

methods are subject to false 

positives and false negatives 

(Griffin et al. 2001).

● Coliform bacteria can survive and 

replicate in waters and soils under 

certain environmental conditions. 

Their presence is not always due 

to recent fecal contamination. 

In addition, all current bacteria 

indicators are shed by animals. 

Their occurrence in the 

environment does not always 

indicate that human pathogens are 

present or that contamination was 

due to a human source (Griffin et 

al. 2001).

● Indicator bacteria do not directly 

indicate the presence of viruses, 

which survive longer in marine 

waters and have a low infective 

dose (Seyfried et al.1984; Freeman 

2001; Schvoerer et al. 2001).

Bacteriophages have shown merit 

for use as an alternative to indicator 

bacteria to identify human health 

risks. Specifically, Bacteroides fragilis 

bacteriophages have been found to be 

more resistant to chlorine than current 

indicator bacteria and are thought to 

be good indicators of enteric viruses. 

Bacteriodes also show potential for 

use as an indicator of recent fecal 

contamination (Griffin et al. 2001).

Although EPA recognizes the 

limitations of indicator bacteria, they 

continue to be used to assess potential 

human health risk because:

● Indicator bacteria area simple and 

inexpensive to measure (Griffin et 

al. 2001).

● Studies show that E. coli and 

enterococci exhibit a strong 

relationship to swimmingassociated gastrointestinal illness

(Fattal et al. 1987; Cheung et al.

1990; EPA 2002g).

● Indicator bacteria are present 

where fecal contamination occurs; 

they are always present in feces 

and at higher levels than most 

enteric pathogens (Griffin et al.

2001). 

EPA continues to encourage states 

and authorized tribes to use E. coli 

or enterococcci as the basis of their 

water quality criteria for protecting 

recreational waters.

6.7 What New Assessment and 

Investigative Activities are 

Underway?

S

everal local government agencies 

are implementing innovative 

programs to identify risks and 

to track the types of illness associated 

with the pathogens present in CSO 

and SSO discharges. Select examples 

are provided in this section.

6.7.1 Investigative Activities

Monitoring, modeling, and other 

investigative activities are useful 

tools in reducing human exposure 

to pathogens, identifying waterborne 

and foodborne disease outbreaks, 

and assessing illness patterns. Some 

innovative investigative programs 
6-26

Report to Congress on the Impacts and Control of CSOs and SSOs

intended to reduce human health 

impacts and risk are described below.

● In Texas, the Austin-Travis Health 

and Human Services Department 

has a predictive model for 

recreational water quality at the 

Barton Springs pool. If the Barton 

Creek watershed receives more 

than one inch of rainfall, the 

pool is closed until monitoring 

determines it is safe to reopen 

(Staudt 2002). 

● New York City has an advanced 

rainstorm modeling system that 

predicts the estimated amount of 

fecal matter that will contaminate 

beaches after a measurable rainfall. 

This information is used to make 

decisions on beach closures and is 

shared with all area beaches and 

neighboring states (Luke 2002).

● Orange County, California, 

maintains a passive reporting 

system for illnesses from 

recreational waters. Between 1998 

and 2002, Orange County received 

110 ocean and bay bather illness 

reports and one illness report 

from a freshwater lake (Mazur 

2002).

● Boston, Massachusetts, operates 

a waterborne surveillance project 

that monitors Cryptosporidium

and Giardia illnesses from 

drinking water. The program uses 

fixed populations within the city 

(schools, nursing homes, prisons) 

as control groups (Gurba 2002). 

● San Diego County, California 

Department of Environmental 

Health and a group called Surfers 

Tired of Pollution conducted a 

self-reported ocean illness survey. 

Between August 1, 1997, and 

December 31, 1999, 232 illnesses 

were reported. The county plans a 

second survey (Clifton 2002). 

● The Douglas County, Nebraska 

Health Department compares 

reported illnesses with a computer 

model that provides epidemiologic 

analysis for 1- to 10-year periods. 

Reported illnesses are compared 

with projected baselines and trends 

to determine if an outbreak is 

occurring (Kurtz 2002). 

● New York City has an active 

outbreak monitoring procedure. 

The Department of Health 

tracks reports of giardiasis and 

cryptosporidiosis by visiting labs 

in New York City on a weekly 

basis and making sure all samples 

testing positive for the pathogens 

are reported. The Department of 

Health receives weekly tallies of 

diarrheal medicine sold in the area 

and has a clinical lab monitoring 

system to track the number of 

stool samples tested. Finally, the 

city monitors hospital emergency 

rooms for the number of people 

complaining of diarrhea and 

vomiting (Seeley 2002).
7.1 What are States and EPA 

Regions Doing to Control 

CSOs?

On April 19, 1994, EPA 

published the CSO Control 

Policy that established 

objectives for CSO communities and 

expectations for NPDES permitting 

authorities (59 FR 18688). The CSO 

Control Policy also presented elements 

of an enforcement and compliance 

program to address dry weather CSO 

discharges and to enforce NPDES 

permit requirements. The four key 

principles of the CSO Control Policy 

that ensure that CSO controls are costeffective and meet the objectives of the 

Clean Water Act are:

1. Provide clear levels of control 

that would be presumed to 

meet appropriate health and 

environmental objectives;

Chapter 7

The federal and state regulatory 

framework for controlling 

CSOs and SSOs affects 

municipal decision-making on how 

to best protect human health and the 

environment from these discharges. 

This chapter describes the status of 

the federal framework used to address 

CSOs and SSOs. The discussion on 

CSO policies summarizes findings 

from the 2001 Report to Congress– 

Implementation and Enforcement of 

the CSO Control Policy (EPA 2001a) 

and updates data on the status of 

NPDES permit requirements for CSO 

control. A brief discussion of current 

SSO regulatory efforts follows. This 

chapter also describes a number of 

state programs to address CSOs and 

SSOs, and it presents an overview of 

federal compliance assistance and 

enforcement efforts related to CSOs 

and SSOs. 

7-1

7.1 What are States and 

EPA Regions Doing to 

Control CSOs?

7.2 What are States and 

EPA Regions Doing to 

Control SSOs?

7.3 What Programs Have 

Been Developed to 

Control SSOs?

7.4 What Compliance and 

Enforcement Activities 

Have Been Undertaken?

Federal and State Efforts to 

Control CSOs and SSOs

In this chapter:
7-2

Report to Congress on the Impacts and Control of CSOs and SSOs

2. Provide sufficient flexibility to 

municipalities, especially financially 

disadvantaged communities, to 

consider the site-specific nature 

of CSOs and to determine the 

most cost-effective means of 

reducing pollutants and meeting 

[Clean Water Act] objectives and 

requirements;

3. Allow a phased approach to 

implementation of CSO controls 

considering a community’s financial 

capability; and 

4. Provide for review and revision, 

as appropriate, of water quality 

standards and their implementation 

procedures when developing CSO 

control plans to reflect the sitespecific wet weather impacts of 

CSOs.

Objectives for CSO communities with 

NPDES permits are 1) to implement 

the NMC and submit documentation 

on NMC implementation; and 2) to 

develop an LTCP. 

7.1.1 Nine Minimum Controls

The NMC are:

1. Proper operation and regular 

maintenance programs for the 

sewer system and the CSOs

2. Maximum use of the collection 

system for storage

3. Review and modification of 

pretreatment requirements 

to assure CSO impacts are 

minimized

4. Maximizing flow to the POTW for 

treatment

5. Prohibition of CSOs during dry 

weather

6. Control of solids and floatable 

materials in CSOs

7. Pollution prevention

8. Public notification to ensure 

that the public receives adequate 

notification of CSO occurrences 

and CSO impacts

9. Monitoring to effectively 

characterize CSO impacts and the 

efficacy of CSO controls

Municipalities were expected to 

implement the NMC and to submit 

appropriate documentation to NPDES 

authorities as soon as reasonably 

possible, but no later than January 1, 

1997. Of the 828 active CSO permits 

identified by EPA in July 2004, 94 

percent (777 permits) required 

implementation of the NMC.

7.1.2 Long-Term Control Plans

In addition to implementing the 

NMC, CSO communities are expected 

to develop and implement an LTCP 

that includes measures to provide for 

attainment of water quality standards. 

The policy identified nine elements 

that an LTCP should include:

● Characterization, monitoring, and 

modeling of the CSS

● Public participation

● Consideration of sensitive areas

● Evaluation of alternatives

● Cost/performance considerations

● Operational plan
 Chapter 7—Federal and State Efforts to Control CSOs and SSOs

7-3

 

● Maximization of treatment at the 

POTW treatment plant

● Implementation schedule

● Post-construction compliance 

monitoring

LTCP implementation schedules were 

expected to include project milestones 

and a financing plan for design and 

construction of necessary controls as 

soon as practicable (EPA 1994a). 

In July 2004, EPA confirmed the status 

of LTCPs with states and regional 

NPDES authorities:

● 86 percent (708 of 828) of permits 

required development and 

implementation of an LTCP;

● 59 percent (490 of 828) of LTCPs 

have been submitted; and

● 35 percent (290 of 828) of LTCPs 

have been approved.

More information on the CSO Control 

Policy is provided in EPA’s 2001 Report 

to Congress–Implementation and 

Enforcement of the CSO Control Policy.

7.2 What are States and EPA 

Regions Doing to Control 

SSOs?

S

SOs that reach waters of the 

United States are point source 

discharges, and, like other 

point source discharges from SSSs, 

are prohibited unless authorized by 

an NPDES permit. Moreover, SSOs, 

including those that do not reach 

waters of the United States, may be 

indicative of improper operation and 

maintenance of the sewer system, 

and thus may violate NPDES permit 

conditions.

7.2.1 Application of Standard 

Permit Conditions to SSOs

The NPDES regulations establish 

standard permit conditions that are 

incorporated into all NPDES permits. 

Several existing standard permit 

conditions have particular application 

to SSOs. These include:

Noncompliance Reporting – When 

incorporated into a permit, the 

standard permit conditions for 

noncompliance reporting at 40 

CFR 122.41(l)(6) and (7) require 

permittees to report any instance 

of noncompliance to the NPDES 

authority. Unpermitted discharges 

from SSSs to waters of the United 

States constitute noncompliance, 

which the permittee would report 

under these provisions. 

Recordkeeping – The permit 

provisions required by 40 CFR 

122.41(j)(2) require permittees to 

retain copies of all reports required 

by the permit for a period of at least 

three years from the date of the report. 

This provision would require retention 

of records of noncompliance reports 

of SSOs.

Proper Operation and Maintenance 

Requirements – The standard permit 

conditions at 40 CFR 122.41(d) and 

(e) require proper operation and 

maintenance of permitted wastewater 

systems and related facilities to achieve 

compliance with permit conditions 

and that permittees take all reasonable 

SSOs can occur at numerous locations in the 

sewer system, including at manholes.

Photo: EPA
7-4

Report to Congress on the Impacts and Control of CSOs and SSOs

steps to minimize or prevent any 

discharge in violation of the permit 

that has a reasonable likelihood of 

adversely affecting human health 

or the environment. In a permit 

for a wastewater treatment facility 

and/or a sewer system, these two 

standard conditions would require 

the permittee to properly operate 

and maintain its collection system 

as well as take all reasonable steps to 

minimize or prevent SSO discharges. 

7.2.2 Electronic Tracking of SSOs

A growing number of states have 

increased data collection and 

tracking efforts for SSOs (excluding 

building backups) in recent years. 

As part of this report effort, EPA 

identified 25 states that track SSO data 

electronically. The states and the most 

commonly tracked SSO data elements 

are listed in Table 7.1.

Table 7.1

Summary of Electronic 

SSO Data by State

At a minimum, states with electronic systems for tracking SSOs 

compile information on the date, 

location, or cause of the overfl ow.

State

Date & 

Time 

Reported

Start Date 

& Time

End Date 

& Time/

Duration

Total 

Overfl ow 

Volume 

(gallons)

SSO 

Locationa

SSO 

Cause 

Response 

Measures 

Takenb 

 Receiving 

Water 

Identifi ed 

CA ●● ● ● ●● ● ●

CO ●● ● ● ●● ● ●

CT ● ● ● ●●

FL ● ● ●● ●

GA ●● ● ● ●

HI ●● ● ● ●● ● ●

IN ● ● ● ●●

KS ●● ●

MA ●● ● ● ●● ● ●

MD ● ● ● ●● ●

ME ●● ● ● ●● ● ●

MI ●● ● ● ●● ● ●

MN ●● ● ● ●● ●

NC ● ● ● ●● ●

ND ●● ● ● ● ● ●

NH ●● ● ● ●● ● ●

NV ●● ● ●● ● ●

OK ● ● ● ●● ●

RI ●● ● ● ●● ● ●

SC ● ●● ●

SD ●● ● ● ●● ● ●

UT ●

WA ● ● ●● ● ●

WI ● ● ● ●● ● ●

WY ● ●● ●

a May not include exact SSO location point

b May include cleanup activities, volume recovered, and corrective or preventive measures
 Chapter 7—Federal and State Efforts to Control CSOs and SSOs

7-5

 

SSO Data Publication via the Internet

Maryland and Michigan publish 

CSO and SSO data periodically on 

the Internet. In Maryland, owners or 

operators of an SSS must report any 

SSO that results in a discharge of raw 

or diluted sewage into the waters of 

the state to the Maryland Department 

of the Environment (MDE). This 

requirement is also applicable to 

CSOs and wastewater treatment 

plant bypasses. MDE coordinates 

reporting requirements with local 

health departments. Reports must 

include the volume spilled, duration, 

start and stop times, name of receiving 

waters, cause, corrective action taken, 

and information regarding public 

notification. CSO and SSO data 

reported to MDE can be found at http:

//www.mde.state.md.us/programs/

waterprograms/cso_sso.asp.

The Michigan Department of 

Environmental Quality (MDEQ) 

has broad statutory and regulatory 

authority for SSOs under Part 31, 

Water Resources Protection, and 

Part 41, Sewerage Systems, of the 

Natural Resources and Environmental 

Protection Act, 1994 PA 451, as 

amended. Facilities in Michigan are 

required to notify MDEQ within 

24 hours of when a CSO or SSO 

discharge begins. After the discharge 

ends, the facility must submit a 

complete report, including the 

location and volume of the discharge 

as well as the start/end date and time.

MDEQ’s CSO and SSO discharge 

information web page provides 

specific event information on CSOs 

and SSOs (http://www.deq.state.mi.us/

csosso/). In addition to providing 

final CSO and SSO reports, MDEQ’s 

website also displays records of recent 

events for which MDEQ has not 

yet received a final written report. 

Recently, MDEQ produced its first 

Combined Sewer Overflow (CSO) and 

Sanitary Sewer Overflow (SSO) Report, 

which compiled event information 

during the period from July 2002 

to December 2003. MDEQ expects 

that subsequent reports will be made 

available on a calendar-year basis.

7.3 What Programs Have Been 

Developed to Control 

SSOs?

Although there is no national 

regulatory program specific 

to SSOs, a number of EPA 

regions and state agencies have 

initiated efforts to address SSOs. 

Some agencies require that permittees 

assess sewer system condition or 

implement specific O&M practices. 

Other agencies have implemented 

programs requiring sewer system 

owners to obtain NPDES permit 

coverage, whether or not they operate 

a wastewater treatment facility. 

The following descriptions are not 

intended to be comprehensive, but 

represent some innovative approaches 

to addressing SSO issues.

7.3.1 EPA Region 4’s MOM Program

EPA Region 4’s Management, 

Operations, and Maintenance 

(MOM) Program is implemented in 

cooperation with states in the region. 

The MOM program encourages 

all NPDES permit-holders and 

any associated satellite utilities to 

participate in a proactive approach to 

managing, operating, and maintaining 

their sewer system. Utilities that 
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Report to Congress on the Impacts and Control of CSOs and SSOs

implement good MOM Programs 

benefit by reducing the likelihood of 

Clean Water Act violations, extending 

the life of their infrastructure, and 

providing better customer service 

through steady rates and greater 

efficiency. The goal of the MOM 

Program is to bring 100 percent of the 

POTWs handling domestic wastewater 

in Region 4 into compliance with the 

“proper operation and maintenance” 

provision of their NPDES permits by 

2011. 

The Region 4 MOM Program 

addresses SSO issues in sewer systems 

(including satellites) by concentrating 

on high priority watersheds. Region 

4 uses a Geographic Information 

System (GIS) to focus on watersheds 

categorized as having existing water 

quality problems or assessed as being 

vulnerable to stressors (e.g., coastal 

and shellfish harvesting areas). Based 

in part on recommendations made by 

states in the region, Region 4 selects 

at least one watershed in each state 

for each cycle of the MOM Program. 

Region 4 started the second cycle of its 

MOM Program in September 2003.

In the selected watersheds, the 

operators of all sewer systems are 

expected to provide a self-evaluation 

report to the region. This report 

identifies improvements that can be 

made and the schedules necessary to 

make those improvements. Region 4 

encourages participants to conduct the 

self-evaluation within seven months of 

receiving the initial requests. To assist 

participants with the process, Region 4 

provides checklists and other outreach 

information. Depending on the 

thoroughness of the self-evaluation, 

Region 4 may conduct follow-up 

inspections and initiate further 

discussions regarding the evaluated 

programs. Where the permittee does 

not conduct an evaluation, Region 

4 conducts its own site inspection. 

Through voluntary participation in 

the program and by self-disclosing any 

needed improvements, participants 

may be eligible for a reduction in civil 

penalties while under a remediation 

schedule.

Region 4 expects participants to 

develop a plan that addresses the 

MOM requirements, which the 

region typically includes in a Letter 

of Violation (LOV) or an AO. Region 

4 recently completed the first round 

of LOV inspections and found that 

many MOM Program participants 

have made significant positive and 

productive efforts (e.g., increased 

staff, purchased maintenance 

equipment, and increased cleaning 

frequency) toward the development 

and implementation of their MOM 

Programs.

7.3.2 Oklahoma – Collection 

System Program

The Oklahoma Department of 

Environmental Quality (ODEQ) 

has actively addressed SSO and 

sewer system issues for many years 

through its NPDES program. 

Program elements include permitting, 

compliance, enforcement, and 

education/outreach. 

Standard NPDES permit language 

in Oklahoma requires proper O&M 

of the sewer system and reporting 

of bypasses and SSOs. A state 

construction permit, which is distinct 

and different from an NPDES permit, 

is required for all new sewer lines 

to ensure that the sewer system has 
 Chapter 7—Federal and State Efforts to Control CSOs and SSOs

7-7

adequate capacity to accommodate 

the growth. When a request is made 

to ODEQ to expand an SSS, the 

capacity of pipes, pumps, and other 

system components is evaluated by 

ODEQ design and engineering staff 

during review of the construction 

permit. These requirements encourage 

municipalities to have a program in 

place to address capacity, management, 

operation, and maintenance issues in 

their sewer system. 

ODEQ evaluates system performance 

through compliance evaluation 

inspections, complaint and fish kill 

investigations, and database record 

reviews. Members of the general 

public can report SSOs by calling 

an ODEQ overflow hotline; ODEQ 

investigates all complaints of alleged 

SSOs. Oklahoma’s criterion for 

significant non-compliance due to 

SSOs is more than one SSO at the 

same location in a 12-month period. 

As of 2003, ODEQ has 60-70 active 

enforcement orders for SSOs.

ODEQ has maintained an SSO 

database and tracking system since 

1987. Over the last 15 years, the 

annual number of reported SSO 

events has decreased by 14 percent, 

and the number of enforcement 

orders issued annually has decreased 

by approximately 25 percent. During 

this same period, the number of 

municipalities reporting at least one 

SSO event has increased by 12 percent. 

ODEQ attributes the increase in the 

number of systems reporting SSOs 

to elevated awareness of SSO issues 

by the regulated community and 

the public. ODEQ’s education and 

outreach efforts include operator 

certification training, ODEQsponsored seminars, and staff 

presentations to municipal leagues, 

rural water associations, regulated 

communities, and other affected 

groups. 

7.3.3 California – Record Keeping 

and Reporting of Events

Some of California’s Regional Water 

Quality Control Boards (RWQCBs) 

use Waste Discharge Requirements 

(WDR), a form of discharge permit, 

to address SSOs. These orders 

prohibit all discharges of wastewater 

from a sewer system upstream of a 

wastewater treatment plant. Priorities 

in California are to address beach 

closures linked to SSOs, such as those 

occurring in Orange County, San 

Diego, and Los Angeles. 

The RWQCB Orders require proper 

O&M, sewer system management 

plans, capacity evaluations, and FOG 

programs. For example, in May 1996, 

the San Diego RWQCB adopted Order 

No. 96-04 prohibiting SSOs. This 

order was adopted as a mechanism 

to achieve a reduction in the number 

and volume of SSOs and to protect 

water quality, the environment, 

and public health. Order No. 96-04 

also brings satellite sewer systems 

under a regulatory framework. The 

order regulates 48 cities and special 

districts in the San Diego area 

that own and operate SSSs. It also 

requires a monitoring and reporting 

program with specific SSO reporting 

procedures. 

In addition, California has a statewide 

regulation requiring utilities to report 

SSOs greater than or equal to 1,000 

gallons and all SSOs that reach surface 

waters. Reports must be made within 

Advisory and closing signs are posted at 

beaches throughout Orange County, CA, to 

alert beachgoers of potential dangers, from 

elevated bacterial levels. 

Photo: OCHA Ocean Water Protection Program.
7-8

Report to Congress on the Impacts and Control of CSOs and SSOs

24 hours of becoming aware of the 

spill and followed up with a written 

report within five days. The RWQCBs 

have issued several large penalty 

orders for SSOs (generally one dollar 

per gallon spilled).

7.3.4 North Carolina – Collection 

System Permitting

In 1999, the North Carolina General 

Assembly ratified HB 1160 (1999 

NC Sessions Laws Chapter 329), 

a bill that requires SSSs to obtain 

a comprehensive permit separate 

from the NPDES permit obtained 

by wastewater treatment facilities. 

The North Carolina Department 

of Environment and Natural 

Resources (NCDENR) administers 

this permitting program through the 

Non-Discharge Permitting Branch in 

coordination with the Enforcement 

Group. The focus of the NCDENR 

program is proactive, preventive O&M 

of sewer systems.

NCDENR collection system permits 

contain five principal sections: 

performance standards, O&M, 

inspections, record keeping, and 

general conditions. Conditions 

are included for grease control, 

planned reinvestment in the SSS 

through a capital improvement 

plan, alarms for pump stations, 

spare parts, inspections, cleaning, 

mapping, observation, and preventive 

maintenance. The permits also include 

public notification and other reporting 

requirements. NCDENR has provided 

guidance for reporting SSOs that 

includes a standardized calculation for 

estimating the volume of SSOs when 

they occur. 

NCDENR is using a phased approach 

to permit all SSSs over a five-year 

period (20 percent/year). This 

program incorporates a number of 

older satellite systems that have never 

been permitted. The first round of 

permits was issued in 2001. Sewer 

systems that fail to meet the standard 

permit conditions may be subject to 

enforcement action by NCDENR. The 

1999 legislation dramatically increased 

the potential civil penalties that may 

be assessed against the municipality 

for unauthorized discharges (G.S. 143-

215.6A).

7.4 What Compliance and 

Enforcement Activities 

Have Been Undertaken?

The goal of EPA’s water 

compliance and enforcement 

program is to ensure 

compliance with the Clean Water Act. 

EPA’s compliance and enforcement 

program has five major objectives: 

● Provide compliance assistance 

tools and information to the 

regulated community;

● Identify instances of 

noncompliance; 

● Return violators to compliance;

● Recover any economic advantage 

obtained by the violator’s 

noncompliance; and 

● Deter other regulated facilities 

from noncompliance.

EPA established “wet weather” 

(i.e., CSOs, SSOs, storm water, 

and concentrated animal feeding 

operations) as a national enforcement 

priority for FY 2002 and FY 2003. 
 Chapter 7—Federal and State Efforts to Control CSOs and SSOs

7-9

The compliance and enforcement 

policies and strategies used to address 

CSOs and SSOs are discussed in the 

following subsections. In addition, 

a summary of related enforcement 

actions as of October 2003 is 

presented.

7.4.1 National Municipal Policy on 

POTWs

EPA’s 1984 National Municipal 

Policy on Publicly-Owned Treatment 

Works (NMP) provided an impetus 

for control of all discharges from 

municipal sewer systems, treated or 

otherwise (EPA 1984b). The NMP 

encouraged a collaborative effort 

between EPA and states in addressing 

compliance with the Clean Water Act 

at POTWs. The NMP focused EPA’s 

compliance efforts on three types 

of POTWs: those that had received 

federal funding and were out of 

compliance, and all major POTWs, 

and minor POTWs that discharged 

to impaired waters. The NMP 

recommended that each EPA region 

draft a strategy to bring POTWs into 

compliance with the Clean Water Act. 

The NMP was intended to facilitate 

compliance at all POTWs by July 1, 

1988. While the main focus of the 

NMP was to ensure that POTWs 

complied with secondary treatment 

and water-quality based NPDES 

requirements, many enforcement 

actions brought under the NMP also 

addressed improvements to sewer 

systems.

7.4.2 Enforcement Management 

System

EPA’s national enforcement guidance, 

Enforcement Management System, 

recommends using a scaled response 

to noncompliance considering such 

factors as the nature, frequency, and 

severity of the violation; potential 

harm to the environment and public 

health; and the compliance history 

of the facility. Chapter X: Setting 

Priorities for Addressing Discharges 

From Separate Sanitary Sewers includes 

a list of priorities for dealing with 

SSOs to ensure that enforcement 

resources are used in ways that result 

in maximum environmental and 

public health benefit (EPA 1996c). The 

complete text of Chapter X is provided 

in Appendix A. EPA’s enforcement 

response guidelines range from 

informal actions such as telephone 

calls or warning letters to formal 

administrative or civil judicial actions. 

7.4.3 Compliance and Enforcement 

Strategy (2000)

On April 27, 2000, EPA issued the 

Compliance and Enforcement Strategy 

Addressing Combined Sewer Overflows 

and Sanitary Sewer Overflows (EPA 

2000b). This strategy was designed to 

ensure that CSO and SSO violations 

are properly addressed by promoting 

the enforcement and compliance 

assistance components of the 

following:
7-10

Report to Congress on the Impacts and Control of CSOs and SSOs

● CSO Control Policy (EPA 1994a);

● Joint Office of Enforcement 

and Compliance Assistance/

Office of Water memorandum 

“Enforcement Efforts Addressing 

Sanitary Sewer Overflows” (March 

7, 1995); and 

● Chapter X of the Enforcement 

Management System (EPA 1996c). 

The strategy also supports the 

Memorandum of Agreement for 

EPA’s regional office performance 

expectations, EPA’s Clean Water Action 

Plan, and EPA’s Strategic Plan. 

The strategy calls for each EPA 

region to develop compliance and 

enforcement plans addressing CSOs 

and SSOs. The plans should include: 

● A systematic approach to address 

wet weather violations through 

compliance assistance;

● The identification of compliance 

and enforcement targets; and 

● Details on NPDES state 

participation, including tracking 

of state CSO and SSO compliance 

and enforcement activities. 

Specifically, the SSO response plan 

should describe the process and 

criteria that the region and states 

use to identify priority systems each 

year and include an inventory of SSO 

violations (EPA 2001a). As of August 

2003, all regions except Region 4 had 

developed and begun implementation 

of their strategies.

7.4.4 Compliance Assistance

EPA has developed a number of tools 

for tracking and sharing compliance 

assistance and other information for 

addressing CSOs and SSOs internally 

among EPA staff and externally 

with states, local governments, and 

others. Several of these tools have 

specific references and guidance for 

implementing the NMC; developing 

an LTCP; and implementing capacity, 

management, operations, and 

maintenance (CMOM) and asset 

management approaches to eliminate 

or reduce SSOs. Examples include:

Local Government Environmental 

Assistance Network (LGEAN) – The 

EPA-sponsored compliance assistance 

center for local municipal governments 

provides environmental management, 

planning, and wet weather regulatory 

and legislative information for elected 

and appointed officials, managers, and 

staff (http://www.lgean.org). 

National Environmental Compliance 

Assistance Clearinghouse – This 

clearinghouse provides compliance 

assistance tools, contacts, and other 

wet weather (including CSO-specific) 

resources available from EPA as well as 

other public and private compliance 

assistance providers 

(http://www.epa.gov/clearinghouse). 

Statistically Valid Non-Compliance 

Study – EPA’s Office of Enforcement 

and Compliance Assistance (OECA) 

completed the Statistically Valid 

Non-Compliance Study to assess 

compliance with NMC requirements. 

EPA has a goal of ensuring that all 

CSO communities have an enforceable 

mechanism requiring implementation 

of the NMC, are in compliance with 

those controls, and, if needed, have 

developed and are implementing an 

LTCP. Determination of the current 

compliance rate of CSO communities 

with the NMC was an EPA priority in 
 Chapter 7—Federal and State Efforts to Control CSOs and SSOs

7-11

FY 2002. OECA found the national 

compliance rate with the NMC was 

39 percent. OECA plans to repeat the 

assessment of NMC compliance in 

FY 2004. The new analysis will also 

assess the status of CSO communities 

with respect to development and 

implementation of LTCPs.

Permit Compliance System – EPA is 

working to modernize PCS. When 

complete, this database of NPDES 

point source dischargers will track 

information specifically related to 

CSOs and SSOs. 

CSO Implementation Guidance – EPA 

has released eight guidance documents 

to assist in implementation of the 

CSO Control Policy. The eight 

guidance documents explain technical, 

financial, and permitting issues related 

to implementation of the policy and 

are as follows:

● Combined Sewer Overflows 

Guidance for Funding Options

(EPA 1995a)

● Combined Sewer Overflows 

Guidance for Long-Term Control 

Plans (EPA 1995b)

● Combined Sewer Overflows 

Guidance for Nine Minimum 

Control Measures (EPA 1995c)

● Combined Sewer Overflows 

Guidance for Permit Writers (EPA 

1995d)

● Combined Sewer Overflows 

Screening and Ranking Guidance

(EPA 1995e)

● Combined Sewer Overflows 

Guidance for Financial Capability 

Assessment and Schedule 

Development (EPA 1997c)

● Combined Sewer Overflows 

Guidance for Monitoring and 

Modeling (EPA 1999e)

● Guidance: Coordinating Combined 

Sewer Overflow (CSO) Long-Term 

Planning with Water Quality 

Standards Reviews (EPA 2001b) 

7.4.5 Summary of Enforcement 

Activities

Federal and state enforcement actions 

concluded against municipalities for 

CSO- and SSO-related violations 

are summarized below. Individual 

enforcement actions are listed in 

Appendix K.

Summary of Federal Judicial Actions

Thirty-six federal judicial enforcement 

actions have been concluded against 

municipalities in Regions 1-5 as a 

result of CSO violations. The relevant 

state served as a co-plaintiff with the 

EPA region in most cases. Since 1995, 

26 judicial actions have been brought 

against municipalities in Regions 1-6 

and Region 9 for SSO violations. As in 

the CSO judicial actions, many of the 

SSO actions were initiated by the EPA 

region in cooperation with the state.

Summary of Federal Administrative 

Actions

Sixty Federal AOs have been issued for 

CSO violations in Regions 1, 3, and 5 

since 1987. Two CSO Administrative 

Penalty Orders (APOs) were issued 

to municipalities in Massachusetts. 

Between 1994 and 2003, 78 AOs were 

issued to municipalities in Regions 

1-7 and Region 10 for SSO violations. 

Twelve SSO APOs were issued during 

the same period.

United States

Environmental Protection

Agency

EPA 832-B-99-002

January 1999

Combined Sewer Overflows

Guidance For Monitoring

And Modeling
7-12

Report to Congress on the Impacts and Control of CSOs and SSOs

Summary of State Judicial Actions

EPA’s review of available state-initiated 

CSO enforcement cases yielded 16 

CSO civil judicial actions. EPA’s review 

of available state-initiated enforcement 

cases found six judicial actions against 

municipalities for SSO violations.

Summary of State Administrative 

Actions

A number of states have initiated 

administrative enforcement actions 

to address CSO violations. A list of 53 

state-initiated administrative actions 

for CSO violations is included in 

Appendix K. EPA’s review of available 

state-initiated enforcement cases 

found 597 administrative actions 

against municipalities for SSO 

violations. In addition, EPA identified 

18 CSO administrative penalty orders 

and 137 SSO administrative penalty 

orders issued by states.
Most technologies and operating 

practices are designed to reduce, not 

eliminate, the discharge of pollutants 

and attendant impacts because it is 

generally not feasible to eliminate all 

discharges.

This chapter provides an overview of 

technologies used to control CSOs and 

SSOs. In addition, the chapter also 

discusses:

● Factors that can influence the 

effectiveness of specific technology 

applications;

● Combinations of technologies 

that have proven more effective 

than application of individual 

technologies; and

● Emerging technologies that show 

promise in controlling CSOs and 

SSOs.

A complete set of detailed technology 

descriptions is contained in Appendix 

L of this report.

Chapter 8

S

ince the enactment of the Clean 

Water Act in 1972, federal, 

state, and local governments 

have made substantial investments 

in the construction, operation, and 

maintenance of wastewater collection 

and treatment systems. Municipalities 

employ a wide variety of technologies 

and operating practices to maintain 

existing infrastructure, minimize the 

introduction of unnecessary waste 

and flow into the sewer system, 

increase capture and treatment of 

wet weather flows reaching the sewer 

system, and minimize the impact of 

any subsequent discharges on the 

environment and human health. 

For the purposes of this Report to 

Congress, technologies used to control 

CSOs and SSOs are grouped into five 

broad categories:

● Operation and maintenance 

practices

● Collection system controls

● Storage facilities

● Treatment technologies

● Low-impact development 

techniques

8-1

8.1 What Technologies are 

Commonly Used to Control 

CSOs and SSOs?

8.2 How Do CSO and SSO 

Controls Differ?

8.3 What Technology 

Combinations are 

Effective?

8.4 What New Technologies 

for CSO and SSO Control 

are Emerging?

Technologies Used to Reduce the 

Impacts of CSOs and SSOs

In this chapter:
8-2

Report to Congress on the Impacts and Control of CSOs and SSOs 

8.1 What Technologies are 

Commonly Used to Control 

CSOs and SSOs?

Municipalities have used 

numerous technologies 

and operational practices 

to reduce the volume, frequency, 

and impacts of CSO and SSO 

events. The performance and costeffectiveness of these technologies 

is often related to a number of sitespecific factors. Technologies deemed 

highly effective in one location may 

prove inappropriate in another. 

Specific factors that may influence 

the selection of a given technology 

include: 

● Current condition of the sewer 

system;

● Characteristics of wet weather 

flows (e.g., peak flow rate, flow 

volume, concentration of key 

pollutants, frequency and duration 

of wet weather events);

● Hydraulic and pollutant loading 

to a particular facility;

● Climate, including seasonal 

variations in temperature and 

rainfall patterns; 

● Implementation requirements 

(e.g., land or space constraints, 

surrounding neighborhood, noise, 

disruption, etc.); and

● Maintenance requirements.

This section describes 23 of the 

technologies and operational practices 

most commonly used to control CSOs 

and SSOs, including considerations 

for determining the applicability 

of different controls for individual 

locations. More detailed information 

on each technology, including cost 

and performance considerations, 

is presented in the technology 

descriptions provided in Appendix L 

of this report.

8.1.1Operation and 

Maintenance Practices

Over time, CSSs and SSSs can 

deteriorate structurally or become 

clogged by FOG and other 

obstructions introduced into the 

sewer system. Left uncorrected, 

these conditions can result in dry 

weather CSOs and SSOs. Further, 

these conditions often are exacerbated 

during wet weather when the capacity 

of sewer systems and treatment 

facilities can be severely taxed.

The objective of O&M practices is 

to ensure the efficient and effective 

collection and treatment of wastewater 

and to minimize the volume and 

frequency of CSO and SSO discharges. 

For purposes of this report, O&M 

practices include activities designed 

to ensure that sewer systems 

function as designed and strategies 

that rely on public education and 

participation. The specific O&M 

practices considered for this report are 

summarized in Table 8.1 and include:

● Inspecting and testing of the sewer 

system to track condition and 

identify potential problems;

● Cleaning or flushing deposits of 

sludge, sediment, debris, and FOG 

from the sewer system;

● Working with customers to reduce 

pollutant loads delivered to the 

sewer system; and
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-3

● Establishing procedures for 

notifying the public in the event 

of a CSO or SSO.

Sewer Inspection and Testing

Sewer inspection is used to determine 

the condition of sewer lines and 

identify potential problems. Common 

sewer system inspection techniques 

can be grouped into two categories: 

manual and remote. Manual 

inspection techniques, such as visual 

inspection and lamping, are simple 

and typically limited to the first few 

feet of pipe upstream and downstream 

of each accessible manhole. Remote 

inspection techniques, such as closedcircuit television and sonar, use units 

that are either self-propelled or pulled 

through the sewer line to capture 

information on sewer condition. 

In general, sewer testing techniques 

are used to identify leaks that allow 

unwanted infiltration into the sewer 

system and to determine the location 

of direct connections of storm water 

sources to the sewer system (e.g., roof 

leaders, area drains, basement sump 

pumps). Sewer testing techniques fall 

into three categories:

● Air testing

● Hydrostatic testing

● Smoke testing

Air testing and hydrostatic testing 

identify cracks and other defects in the 

sewer system that might allow storm 

water or groundwater to infiltrate. 

Smoke testing is used to identify 

connections that allow direct storm 

water inflow to the sewer system. 

Sewer Cleaning

Sewer cleaning and flushing 

techniques remove blockages caused 

by solids, FOG, and root intrusion. 

Sewer cleaning techniques are 

particularly important because 

blockages are the leading cause of 

SSO events (see Section 4.7). Cleaning 

techniques fall into three categories: 

● Hydraulic

● Mechanical

● Chemical

Hydraulic cleaning techniques employ 

the cleansing action of high velocity 

water. Cleansing velocities are achieved 

by allowing water pressure to build 

in a sewer line or by using a pump to 

produce water pressure. In general, 

hydraulic cleaning techniques tend 

to be simpler and more cost-effective 

in removing deposited solids when 

compared to other sewer cleaning 

techniques (CSU 2001). Alternatively, 

mechanical cleaning methods rely on 

a scraping, cutting, pulling, or pushing 

action to remove obstructions from 

sewer lines. Mechanical techniques 

Technology Type of System Pollutants/Problems Addressed

Sewer inspection and testing CSS, SSS I/I

Sewer cleaning CSS, SSS BOD5, TSS, nutrients, toxics, pathogens, 

floatables, FOG

Pollution prevention CSS, SSS Nutrients, toxics, FOG

Water quality monitoring and 

public notification

CSS, SSS BOD5, TSS, nutrients, toxics, pathogens

Table 8.1

Summary of Operation 

and Maintenance 

Practices

The objective of O&M practices 

is to ensure that sewer systems 

function as designed and convey 

the maximum amount of flow 

practicable to a treatment facility.
8-4

Report to Congress on the Impacts and Control of CSOs and SSOs 

are typically used in areas where the 

volume, size, weight, or type of debris 

limits the effectiveness of hydraulic 

techniques. Chemicals can be used to 

control roots, grease, odors, concrete 

corrosion, rodents, and insects (CSU 

2001). Chemicals can be helpful aids 

for cleaning and maintaining sewers, 

though chemical applications often are 

localized or coupled with a hydraulic 

or mechanical technique.

Pollution Prevention

Pollution prevention is defined as 

any practice that reduces the amount 

of pollutants, hazardous substances, 

or contaminants entering the waste 

stream, which in turn would mean 

fewer pollutants in potential CSO or 

SSO discharges (EPA 2002b). Pollution 

prevention practices most often take 

the form of simple, individual actions 

that reduce the pollutants generated 

by a particular process. Therefore, 

pollution prevention programs 

must be implemented with broad 

participation to realize a discernible 

reduction in pollutant loads 

discharged to sewer systems. Public 

education is a key component of 

most pollution prevention activities. 

Education programs are most 

successful when tailored to a specific 

audience (i.e., residential, institutional, 

or commercial). 

Pollution prevention activities usually 

focus on best management practices 

for both commercial/industrial 

facilities and residential customers to 

reduce pollutant loads discharged to 

sewer systems. Pollutants of concern 

include FOG, household hazardous 

wastes, fertilizers, pesticides, and 

herbicides. In particular, the effective 

management of FOG has recently 

received attention as an important 

technique for controlling SSOs. 

As reported in Chapter 4, FOG is 

the leading cause of blockages in the 

United States, and blockages account 

for nearly half of all SSO discharges. 

The best way to prevent blockages 

due to FOG is to keep FOG out of the 

sewer system. Many municipalities 

have adopted regulations controlling 

the introduction of FOG into the 

sewer system. Education programs 

are important in making residents 

and owners of institutional and 

commercial establishments, especially 

restaurants, aware of their role in 

managing FOG. Grease trap design 

and maintenance is a vital part of any 

The SSS for the City of Sioux Falls, South Dakota, consists of 578 miles of pipes 

ranging in size from six to 66 inches in diameter. The sewer system is divided 

into 20 drainage basins, and the maintenance program provides that the entire 

system is cleaned once every three years. Maintenance records are stored in a 

database that generates work orders by date and drainage basin. Sanitary sewer 

maintenance includes high pressure jetting, vacuuming to remove loosened debris, 

and mechanical and chemical root control. Closed circuit television (CCTV) is used 

to identify trouble spots. This results in more frequent cleaning than the scheduled 

three-year interval requires in problem areas. In 2001, 372 miles of sewer (64 percent 

of the sewer system) were televised and cleaned. The cost for these activities was 

approximately $236 per inch-diameter mile of pipe. Assuming an average pipe 

diameter of ten inches, inspection and cleaning costs about $0.45 per linear foot. 

Sewer Cleaning: 

Sioux Falls, SD
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-5

education program for commercial 

and institutional customers. 

Water Quality Monitoring and Public 

Notification

Water quality monitoring and public 

notification practices are important in 

minimizing potential human health 

impacts that can result from exposure 

to pathogens and other pollutants 

in CSO and SSO discharges. Water 

quality monitoring is used routinely 

to verify the suitability of a particular 

waterbody for fishing, swimming, or as 

a drinking water source; and to identify 

whether a specific CSO or SSO event 

has impaired water quality. Public 

notification programs are intended to 

communicate water quality monitoring 

results, general information regarding 

the occurrence of CSO and SSO events, 

and municipal efforts to control 

discharges. Public notification program 

activities include posting temporary 

or permanent signs where CSOs and 

SSOs occur, coordinating with civic 

and environmental organizations, and 

distributing fact sheets to the public 

and the media. Monitoring and public 

notification programs should be a 

high priority at beaches or recreational 

areas, whether directly or indirectly 

affected by CSOs and SSOs, due to the 

increased risk of human contact with 

pollutants and pathogens (EPA 2002i). 

When developing a monitoring and 

public notification program, the 

lag time that often occurs between 

collecting water samples and providing 

the public with results is important 

to consider. This lag is due to the 

time required (from 24 to 72 hours) 

to test for the presence of bacterial 

indicators of contamination. During 

this time, pathogen levels, weather, 

and water conditions, and related 

environmental or human health risks 

may change. This means that decisions 

regarding beach and recreational water 

postings, closings, and re-openings 

using bacterial indicators often reflect 

conditions as they were one to three 

days earlier (EPA 2002i). Further, 

contaminants may no longer be 

present once test results are available, 

and safe beaches may be closed 

needlessly. As described in Chapter 

6, some communities and beaches 

have procedures to close beaches 

proactively when a CSO-producing 

rainfall event has occurred.

8.1.2 Collection System Controls

Collection system controls are 

designed to maximize the capacity of 

the sewer system to transport or store 

domestic, commercial, and industrial 

wastewater. This is accomplished by 

adjusting hydraulic control points 

to maximize available sewer system 

capacity and by implementing 

programs and practices to minimize 

the volume of I/I that enters the sewer 

system. The specific collection system 

controls considered for this report are 

summarized in Table 8.2, and include:

● Maximizing flow to the treatment 

plant;

● Installing a network of flow 

monitors to better understand and 

manage the response of the sewer 

system to wet weather events;

● Identifying and eliminating direct 

connections of storm water to the 

sewer system (inflow);

● Separating combined sewer 

systems into storm and sanitary 

systems; and

This CSO notification sign is 

posted along Brandywine Creek in 

Wilmington, Delaware, as part of a 

public notification program. It warns 

swimmers of the presence of a CSO 

outfall and advises that raw sewage 

and bacteria may be present after a 

storm.

Photo: City of Wilmington Department of Public Works
8-6

Report to Congress on the Impacts and Control of CSOs and SSOs

● Rehabilitating sewer system 

components. 

Collection system controls are 

designed to maintain the structural 

integrity of CSSs and SSSs, and to 

maximize available capacity for 

transporting wastewater to a treatment 

plant. Some municipalities have found 

combining various rehabilitation 

techniques with inflow reduction 

activities to be a cost-effective and 

successful means of controlling SSOs. 

Other municipalities have found 

that implementing one or more of 

these collection system controls in 

conjunction with storage facilities or 

treatment a cost-effective CSO control. 

Maximizing Flow

EPA encourages plants serving CSSs 

and SSSs to minimize CSOs and SSOs 

during wet weather events by using 

existing infrastructure to maximize 

flow to the treatment plant (EPA 

1994a; NYSDEC 1997). Maximizing 

flow to the treatment plant often 

involves simple and low-cost measures, 

including:

● Capacity evaluations of the sewer 

system and pumping stations to

 determine the maximum amount 

of flow that can be transported 

(Sherrill et al. 1997).

● Sewer investigations to identify 

bottlenecks or constrictions that 

limit flow in specific areas and 

prevent downstream treatment 

capacity from being fully utilized.

● Targeted O&M activities to 

address structural deterioration, 

obstructions due to FOG and 

sediment buildup and excessive 

I/I.

The benefits of maximizing wet 

weather flows to the existing treatment 

plant depend on the ability of the 

plant to accept and provide treatment 

to increased flows. The consequences 

of mismanaging extreme flows at 

the treatment plant include flooding 

the treatment plant and washing 

out biological treatment processes, 

which can result in reduced treatment 

capacity and efficiency at the plant for 

extended periods of time. Likewise, 

changes in sewer system operation 

without a careful analysis of transport 

capacity can result in increased 

building backups or street flooding.

Technology Type of 

System

Pollutants/Problems 

Controlled

Maximizing flow to the 

treatment plant

CSS, SSS BOD5, TSS, nutrients, toxics, pathogens, 

floatables

Monitoring and real-time 

control

CSS, SSS Peak wet weather flow rate

Inflow reduction CSS, SSS I/I, peak wet weather flow rate

Sewer separation CSS I/I, peak wet weather flow rate

Sewer rehabilitation CSS, SSS I/I, peak wet weather flow rate

Service lateral 

rehabilitation

CSS, SSS I/I, peak wet weather flow rate

Manhole rehabilitation SSS I/I, peak wet weather flow rate

Table 8.2

Summary of Collection 

System Controls

Collection system controls are 

designed to maximize the use 

of existing sewers to collect and 

convey wastewater to a treatment 

facility.
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-7

Monitoring and Real-Time Control

Basic flow monitoring is an important 

component of O&M programs in 

most systems. Effective monitoring 

programs enable evaluations 

of diurnal and day-to-day flow 

patterns as well as I/I in a sewer 

system. Moreover, monitoring is 

extremely valuable in establishing 

maintenance schedules, developing 

hydraulic models, planning related to 

capital improvements, and ensuring 

regulatory compliance. 

Enhanced monitoring programs in 

SSSs and real-time control systems 

in CSSs use more complex flow 

monitoring networks to optimize 

sewer system performance. In SSSs, 

enhanced monitoring information 

can be used to identify blockages or 

capacity-constrained areas of the 

sewer system where wet weather SSOs 

are likely to occur. In CSSs, integration 

of real-time flow, regulator, pump, and 

storage information can be used to 

maximize use of storage capabilities 

and to maximize flow to the treatment 

plant.

Inflow Reduction

Inflow is the entry of extraneous 

storm water into a sewer system from 

sources other than infiltration, such 

as basement drains, roof leaders, 

manholes, and storm drains. Inflow 

reduction refers to the identification 

and elimination of these sources to 

reduce the amount of storm water 

that enters CSSs and SSSs. By reducing 

the volume of storm water entering 

the sewer system, more conveyance, 

storage, and treatment capacity is 

available for sanitary flows during 

wet weather. This, in turn, aids in 

reducing the frequency, volume, and 

duration of wet weather CSO and SSO 

events. Common inflow reduction 

techniques include the disconnection 

of roof leaders, redirection of area and 

foundation drains and basement sump 

pumps, and elimination of crossconnections between separate sanitary 

and storm water systems (EPA 1999f). 

Inflow reduction techniques can be 

an efficient way to improve sewer 

system performance, especially when 

the diverted storm water can be 

conveniently directed either to surface 

waters or to open land for infiltration 

or detention (EPA 1999f). For SSSs, 

inflow reduction techniques usually 

target specific areas with chronic SSOs. 

For CSSs, these techniques are applied 

more broadly to minimize the size of 

structural controls.

Sewer Separation 

Sewer separation is the practice of 

separating the single-pipe CSS into 

separate systems for sanitary and 

storm water flows. Full separation 

can be applied on a system-wide basis 

to eliminate the CSS. This approach 

is most practical for communities 

with small areas served by combined 

sewers. Separation of select areas 

within a CSS is widely used by large 

and small CSO communities as an 

element of a broader LTCP.

Sewer separation can be highly 

effective in controlling the discharge 

of untreated wastewater. Under ideal 

circumstances, full separation can 

eliminate CSO discharges. A survey 

of readily available information in 

NPDES files indicates that sewer 

separation is the most widely used 

CSO control, accounting for half of 

CSO control measures found in LTCP 

The Milwaukee Metropolitan Sewer District 

uses real-time data to monitor the flow in its 

sewer system tunnels and pipes. 

Photo: Milwaukee Metropolitan Sewer District
8-8

Report to Congress on the Impacts and Control of CSOs and SSOs

documentation (EPA 2001a). This 

suggests that many CSO communities 

identify portions of their CSS in which 

separation is a cost-effective CSO 

control. Under these circumstances, 

separation is often implemented in 

conjunction with other public works 

projects, including road work and 

redevelopment. Sewer separation on 

its own, however, does not always lead 

to an overall reduction in pollution 

or the attainment of water quality 

standards. Storm water discharges 

from the newly created separate 

storm sewer system can contain 

substantial pollutant loads that may 

cause or contribute to water quality 

problems. Implementation of storm 

water controls may be necessary 

following sewer separation in order to 

achieve the pollutant load reductions 

necessary for attainment of water 

quality standards.

In practice, there are three distinct 

approaches to sewer separation:

● Full separation wherein 

new sanitary sewer lines are 

constructed with the existing CSS 

becoming a storm sewer system. 

This is probably the most widely 

used form of separation.

● Full separation wherein an 

entirely new storm sewer system 

is constructed with the existing 

CSS remaining as a sanitary sewer 

system. This form of separation 

is not often used because the 

capacity of the existing CSS was 

designed to accommodate storm 

water runoff, which is more than 

what is required to accommodate 

sanitary flows.

● Partial separation wherein a new 

storm sewer system is constructed 

for street drainage, but roof 

leaders and basement sump 

pumps remain connected to the 

existing CSS.

Sewer Rehabilitation/Replacement

The structural integrity of many sewer 

system components deteriorates with 

use and age. This gradual breakdown 

allows more groundwater and storm 

water to infiltrate into the sewer 

system. This increases the hydraulic 

load and, in turn, reduces the system’s 

ability to convey all flows to the 

treatment plant. During wet weather 

Seattle was one of the first U.S. communities to implement and operate an advanced 

real-time control system to control CSO discharges. Seattle’s system, called Computer 

Augmented Treatment and Disposal (CATAD), began operating in 1971. In the late 

1980s, treatment plant computer hardware was upgraded, remote telemetry units 

at regulators and pump stations were replaced by programmable logic controllers, 

and graphical displays used by operators were improved. Based on the success of 

the CATAD technology, Seattle implemented a new, predictive real-time control 

system that went on-line in early 1992. Rainfall prediction capabilities that utilize 

rain gage data and a runoff model were added. A global optimization program 

was introduced that computed optimal flow and corresponding gate position for 

each regulator within the CSS. A distributed network allows control decisions to be 

implemented without operator intervention. The computer program uses real-time 

operation and system performance data to predict or forecast conditions through 

the system and directs control elements to utilize in-line storage during periods of 

high flow. 

Monitoring and RealTime Control: 

Seattle, WA

The direct connection of roof leaders (shown 

above) and other inflow sources can limit 

sewer system capacity for conveying sanitary 

wastewater during wet weather. 

Photo: Milwaukee Metropolitan Sewer District
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-9

events, excessive infiltration can cause 

or contribute to CSOs and SSOs. 

Sewer rehabilitation/replacement 

restores and maintains the structural 

integrity of the sewer system, in 

part by reducing or mitigating the 

effects of infiltration. Common 

sewer rehabilitation and replacement 

techniques include: 

● Removal and replacement of 

defective lines;

● Trenchless technologies that use 

the existing sewer to support a 

new pipe or line;

● Shotcrete, wherein a mixture of 

cement, sand, and water is applied 

to sewer walls; and

● Grouting and epoxy injections to 

seal leaks and cracks.

Inspecting and evaluating current 

sewer condition is necessary before 

a sewer rehabilitation technique 

is chosen, as the condition of the 

sewer may favor specific techniques. 

Removing and replacing defective 

lines is the most commonly used 

rehabilitation technique when the 

sewer line is structurally deficient 

(CSU 2001). Complete replacement is 

often the most effective rehabilitation 

method in areas where increased 

conveyance capacity is needed (WEF 

1999a). 

Trenchless technologies are especially 

well-suited to urban areas where the 

traffic disruption associated with 

large-scale excavation projects can be a 

significant obstacle to a project (WEF 

1999a). In addition, many sewers 

are located near other underground 

utilities in urban areas, which can 

complicate traditional dig-and-replace 

methods; trenchless technologies avoid 

underground utilities by using the 

existing sewer to support a new pipe 

or line. Trenchless technologies include 

sliplining, cured-in-place pipe (CIPP), 

modified cross-section liners, and pipe 

bursting. 

Shotcrete, a non-invasive rehabilitation 

method, is often used to rehabilitate 

sewers with major structural problems. 

Shotcrete, however, can be used only 

in pipe with a diameter of at least 36 

inches (CSU 2001). 

Grouting and epoxy injections are 

most appropriate when the sewer is 

structurally stable but experiencing 

infiltration.

Service Lateral Rehabilitation

Private building service laterals are 

the pipes that convey wastewater from 

individual buildings, including houses, 

to the municipal sewer system. Recent 

studies indicate that a significant 

component of the infiltration in any 

sewer system is the result of service 

lateral defects that contribute varying 

quantities of I/I (WEF 1999b). During 

wet weather events, excessive I/I can 

cause or contribute to CSOs and SSOs. 

In general, service lateral rehabilitation 

techniques are similar to those used for 

larger diameter sewers and include:

● Removing and replacing defective 

service laterals;

● Applying trenchless technologies 

that use the existing service lateral 

to support a new pipe or liner; and

● Using grouting and epoxy 

injections to seal leaks and cracks.
8-10

Report to Congress on the Impacts and Control of CSOs and SSOs

Assigning responsibility for the repair 

or replacement of service laterals is 

often cited as the biggest obstacle to 

correcting known defects. Notably, 

several studies highlighted significant 

problems in gaining access to private 

property until the municipality 

assumed full financial responsibility 

for the repair or replacement costs 

(Paulson et al. 1984; Curtis and 

Krustsch 1995). 

Manhole Rehabilitation

Manholes must be maintained 

and kept in working condition. 

Structurally defective manholes can 

be a significant source of I/I that 

otherwise would not enter an SSS. 

Damage to manhole covers and rims 

often occurs during road work, and 

it can allow storm water runoff from 

roads and sidewalks to flow directly 

into the sewer system. Further, cracks 

and openings in the sidewalls and base 

of the manhole can allow groundwater 

and storm water to infiltrate into the 

sewer system. Manhole rehabilitation 

can reduce I/I, restore the structural 

integrity of the manhole, and 

preserve SSS capacity for transporting 

wastewater. Common manhole 

rehabilitation methods include (ASCE 

1997): 

● Sealing pick holes in the manhole 

cover and installing gaskets 

between the manhole cover and 

frame to eliminate storm water 

inflow;

● Implementing spot repairs with 

chemical grout or fast-drying 

cement to patch defects in 

manhole sidewalls or bases;

● Coating systems to rebuild 

structural integrity and protect 

concrete, steel, and masonry 

manhole structures against 

deterioration;

In Alabama, the Montgomery Water Works and Sanitary Sewer Board (MWWSSB) 

evaluated nearly 2.2 million linear feet of its sewer system, identifying 3,394 defects. 

Eighty-five percent of these defects were in service laterals; 97 percent of lateral 

defects identified have been repaired.

Lateral repairs necessary within the city street right-of-way are made by MWWSSB 

with consent and release of liability from the property owner. MWWSSB replaces 

missing clean-out covers for a minimal cost with written permission from the 

property owner. The property owners are responsible for the cost of all lateral repair 

and replacement on their property. 

Property owners initially received a 60-day notice of lateral repair requirements. 

Another 10-day notice was sent if the property failed to respond to the initial 

notice. Finally, if the property owner failed to respond to either notice, water service 

to the property was shut off. Sixty-five percent of property owners responded after 

receiving the initial notice. The remaining property owners corrected their defects 

under threat of having their water service discontinued.

In selected areas where service lateral rehabilitation has been completed, the I/I 

was reduced by an average of 42 percent. It is estimated that the annual I/I volume 

in the MWWSSB service area has been reduced by 36 million gallons. The cost 

of establishing the I/I program was approximately $150,000. MWWSSB spends 

$207,000 annually to operate the program.

Service Lateral 

Rehabilitation: 

Montgomery, AL
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-11

● Reconstructing manholes in 

cases of substantial structural 

degradation; and

● Placing inserts and liners in 

deteriorated manholes.

Inspection of the manhole components 

is a necessary first step in selecting an 

appropriate rehabilitation technique. 

Spot repairs of manhole components 

are most appropriate for addressing 

minor defects, and chemical grouts 

are commonly used for rehabilitating 

structurally sound manholes made of 

brick. Coating systems are applicable 

for manholes with brick structures 

that show little or no evidence of 

movement or subsidence and at sites 

not conducive to excavation or major 

reconstruction. Structural linings 

are applicable for standard manhole 

dimensions (48- to 72-inch inner 

diameter) where substantial structural 

degradation has occurred. Structural 

linings tend to be more expensive than 

other rehabilitation techniques.

8.1.3 Storage Facilities

Many sewer systems experience 

increased flow during wet weather. In 

systems that are unable to transport or 

provide full treatment for wet weather 

flows, storage facilities are often used 

to reduce the volume, frequency, and 

duration of CSO and SSO events. 

Storage facilities fill during wet 

weather and are drained or pumped to 

the wastewater treatment plant once 

conveyance and treatment capacity 

have been restored following the wet 

weather event. Specific types of storage 

facilities considered for this report are 

summarized in Table 8.3. 

Storage facilities have seen wide 

application as a CSO control because 

of the large and frequent volumes of 

combined sewage requiring control; 

however, a number of communities 

have also found storage facilities, 

especially flow equalization basins, 

to be an effective wet weather SSO 

control.

In-line Storage

In-line or in-system storage is the 

term used to describe storage of wet 

weather flows within the sewer system. 

Taking advantage of storage within the 

sewer system has broad application 

and can often reduce the frequency 

and volume of CSOs and SSOs 

without large capital investments. 

Maximization of storage in the 

sewer system is also one of the NMC 

required of all CSO communities. The 

amount of storage potentially available 

in the sewer system largely depends 

on the size or capacity of the pipes 

that will be used for storage and on 

the suitability of sites for installing 

regulating devices. 

Damaged manholes, such as the broken 

cover shown above, can be a significant 

source of storm water I/I into an SSS.

Photo: Limno-Tech, Inc.

Technology Type of 

System

Pollutants/Problems Addressed

In-line storage CSS, SSS Peak wet weather flow rate, BOD5, TSS, nutrients, toxics, 

pathogens, floatables

Off-line storage CSS, SSS Peak wet weather flow rate, BOD5, TSS, nutrients, toxics, 

pathogens, floatables

On-site storage and flow 

equalization basins

CSS, SSS Peak wet weather flow rate, BOD5, TSS, nutrients, toxics, 

pathogens, floatables

Table 8.3

Summary of Storage 

Facilities

Storage facilities have seen wide 

application in attenuating peak 

wet weather flows in both CSS and 

SSS.
8-12

Report to Congress on the Impacts and Control of CSOs and SSOs

In-line storage techniques include the 

use of flow regulators, in-line tanks 

or basins, and parallel relief sewers. 

Flow regulators optimize in-line 

storage by damming or limiting flow 

in specific areas of the sewer system. 

Storage tanks and basins constructed 

in-line are typically governed by flow 

regulators. Dry weather flows pass 

directly through in-line storage tanks 

or basins, and flow regulators limit 

flow exiting the facility during wet 

weather periods. In-line capacity can 

also be created by installing relief 

sewers parallel to existing sewers or 

by replacing older sewers with larger 

diameter pipes. Again, flow regulators 

are used to optimize storage within 

these facilities.

Areas where the sewer slope is 

relatively flat typically offer the best 

opportunities for in-line storage. One 

factor that limits the applicability of 

in-line storage is the possibility that 

this approach can increase basement 

backups and street flooding (EPA 

1999g). Use of in-line storage may 

also slow flow, allowing sediment and 

other debris to settle in the sewer. If 

allowed to accumulate, sediment and 

debris can reduce available storage 

and conveyance capacity. Therefore, an 

important design consideration for inline storage is to ensure that minimum 

flow velocities are provided to flush 

and transport solids to the wastewater 

treatment plant.

Off-line Storage

Off-line storage is the term used 

to describe facilities that store wet 

weather flows in near-surface storage 

facilities, such as tanks and basins or 

deep tunnels located adjacent to the 

sewer system. Off-line storage facilities 

have broad applicability and can be 

adapted to many different site-specific 

conditions by changing the basin size 

(volume), layout, proximity to the 

ground surface, inlet or outlet type, 

and disinfection mechanism. For 

these reasons, off-line storage facilities 

are one of the most commonly 

implemented CSO controls (EPA 

2001a). The use of off-line storage 

tends to be more expensive than inline storage; it is usually considered 

in areas where in-line storage is 

insufficient or unavailable. 

A typical near-surface storage facility 

is a closed concrete structure built 

at or near grade alongside a major 

interceptor. Deep tunnel storage 

facilities are used where large 

storage volumes are required and 

opportunities for near-surface storage 

are unavailable. As their name implies, 

deep tunnels are typically located 

100 to 400 feet below ground. Tunnel 

diameters range from 10 to 50 feet, and 

many are several miles in length.

During dry weather, untreated 

wastewater is routed around, not 

through, off-line storage facilities. In 

contrast, during wet weather, flows 

are diverted from the sewer system 

to the off-line storage facilities by 

gravity drainage or with pumps. The 

wastewater is detained in the storage 

facility and returned to the sewer 

system once downstream conveyance 

and treatment capacity become 

available. Overflows can occur if the 

capacity of off-line storage structures is 

exceeded. Some treatment is provided 

through settling; however, the primary 

function of such facilities is storage 

and the attenuation of peak wet 

weather flows.
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-13

On-site Storage

On-site storage, which is storage 

developed at the wastewater treatment 

facility, is often an effective control 

for managing wet weather flows 

in systems where sewer system 

conveyance capacity exceeds that 

of the treatment plant. On-site 

storage can play an important role in 

improving treatment plant operations 

by providing operators with the 

ability to manage and store excess 

flows. The costs associated with the 

development of on-site storage are, 

on average, considerably lower than 

the construction costs for typical near 

surface off-line storage facilities built 

outside the bounds of the treatment 

plant. Much of the cost savings derive 

from siting storage facilities on land 

already owned by the utility. It should 

be noted, however, that sewer system 

conveyance capacity may limit the 

amount of wet weather flow that 

can be brought to an on-site storage 

facility, and expanding conveyance 

capacity can be extremely expensive.

The two most common forms of onsite storage are flow equalization basins

 (FEBs) and converted abandoned 

treatment facilities. FEBs are used to 

attenuate peak wet weather flows and 

to improve wet weather treatment 

plant operations (Metcalf and Eddy 

2003). Abandoned treatment facilities 

can function in a manner similar to 

FEBs in attenuating peak wet weather 

flows. Abandoned facilities that have 

been successfully converted for storage 

include old clarifiers, treatment or 

polishing lagoons, and abandoned 

pretreatment facilities at industrial 

sites near the treatment plant. 

8.1.4 Treatment Technologies

In many systems, wet weather flows 

can exceed the existing conveyance 

and treatment capacity. The 

development of wet weather treatment 

systems presents a viable alternative 

to storing excess flows. Treatment 

technologies are end-of-pipe controls, 

used to provide physical, biological, 

or chemical treatment to excess wet 

weather flows immediately prior to 

discharge from a CSS or SSS. Specific 

treatment technologies can address 

different pollutants, such as settleable 

solids, floatables, and pathogens.

As part of Philadelphia’s effort to control CSOs, the City Water Department plans 

to install three inflatable dams in large diameter sewers that have available in-line 

storage. The dams will range from 11 to 15 feet high and will be automatically 

controlled for both dry and wet weather conditions. The three dams will enable 16.3 

MG of flow that might otherwise discharge to local receiving waters to be stored in 

existing sewers per storm event, reducing CSO volumes by 650 MG per year.

The first inflatable dam, located in the city’s main relief sewer, will be operational by 

the end of 2004. The associated civil work projects including sewer rehabilitation 

have been completed for this project. When operational, the dam will have the 

ability to store up to 4 MG of combined sewage, and it is expected to reduce the 

number of CSO discharges to the Schuylkill River from 32 per year to four per year. 

Another inflatable dam will be installed in Rock Run during the summer of 2005. The 

total cost for the installation of the dams and sewer rehabilitation is approximately 

$4.8 million, or $0.29 per gallon of storage. 

In-line Storage: 

Philadelphia, PA
8-14

Report to Congress on the Impacts and Control of CSOs and SSOs

For the purposes of this Report to 

Congress, treatment technologies are 

assumed to operate intermittently, 

with dry weather flows from the 

CSS or SSS handled by the existing 

wastewater treatment plant. Treatment 

technologies considered here include 

strategies for developing wet weather 

treatment capacity at remote locations 

in the sewer system and for enhancing 

the performance of the existing 

treatment facility when flows exceed 

the rated capacity of the plant. Specific 

technologies and operational practices 

are summarized in Table 8.4 and 

include:

● Constructing supplemental 

treatment facilities for treating 

excess wet weather flows;

● Modifying the POTW to better 

accommodate high flows;

● Disinfecting excess wet weather 

flows;

● Using vortex separators to provide 

partial treatment for excess wet 

weather flows; and

● Constructing facilities to remove 

floatables from CSO discharges.

In general, treatment technologies have 

not been as widely applied as other 

CSO and SSO controls, partly due 

to cost and the difficulty of remote 

control. Also, the requirements for 

permitting treated discharges from offsite SSO facilities during wet weather 

are somewhat unclear. 

Supplemental Treatment

As the name implies, supplemental 

treatment technologies are intended 

to supplement existing wastewater 

treatment capacity during periods of 

wet weather. Example applications 

include installing a small scale 

treatment facility in a capacityconstrained area of the sewer system, 

or adding a parallel treatment process 

at the existing treatment plant to be 

operated only during wet weather. 

Selection of a supplemental treatment 

technology is determined by the 

level of treatment required and the 

characteristics of the wet weather flow. 

Technologies commonly considered 

as potential supplemental treatment 

processes for excess wet weather flows 

include: 

● Ballasted flocculation or 

sedimentation using a fine-grained 

The sewer system in Oakland, Maine, consists mainly of combined sewers. The city 

has been implementing CSO controls since 1997. These efforts include separating a 

portion of the CSS and targeted inflow reduction activities. As a result, Oakland has 

been able to eliminate both of its CSO outfalls and transport all wet weather flows 

to its wastewater treatment plant. Although the city had sufficient sewer system 

capacity to transport these wet weather flows, it did not have facilities capable of 

treating the peak wet weather flow. The city was able to use an FEB installed at a 

nearby textile mill that is no longer operating. The FEB was built in 1990 by the 

textile mill as part of their pretreatment program and had not been used since the 

plant closed. Oakland is able to store 0.2 MG of excess wet weather flows in the 

FEB, and release it back to the wastewater plant for treatment as capacity becomes 

available. The FEB is mainly used to control excess wet weather flow during spring 

snowmelts. Bringing the FEB back into operation cost approximately $27,610, or 

$0.14 per gallon of storage. 

On-site Storage:

Oakland, ME
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-15

sand, or ballast, and a coagulant to 

accelerate settling of solids from 

wastewater;

● Chemical flocculation using metal 

salts and polymers to accelerate 

settling of solids from wastewater;

● Deep bed filtration with coarse 

sand to filter wastewater; and

● Microscreens.

Supplemental treatment technologies 

must have quick start-up times after 

extended periods of no flow (or 

low flow) conditions, accommodate 

sudden increases in flow at unplanned 

times, and provide adequate treatment 

despite significant variation in 

flow rates and influent pollutant 

concentrations. 

Plant Modifications

Simple modifications to existing 

wastewater treatment facilities can 

increase their ability to handle wet 

weather flows. Modifications can 

involve changes to the physical 

configuration of various treatment 

processes and the operation of 

specific plant processes during 

wet weather. Most modifications 

require the active involvement of the 

treatment plant operator to ensure 

effective implementation. Example 

modifications that maximize the 

treatment of wet weather flows 

include:

● Ensuring the even distribution of 

flow among treatment units; 

Technology Type of 

System

Pollutants/Problems Controlled

Supplemental treatment CSS, SSS Peak wet weather flow rate, BOD5, TSS, pathogens

Plant modifications CSS, SSS Peak wet weather flow rate, BOD5, TSS

Disinfection CSS, SSS Pathogens

Vortex separators CSS TSS, floatables

Floatables controls CSS Floatables

Table 8.4

Summary of Treatment 

Technologies

Based on life-cycle cost evaluations, 

treatment technologies may be an 

effective technique for handling 

excess wet weather flows.

The Central Treatment Plant (CTP) for the City of Tacoma, Washington, receives 

flow from an SSS serving a population of 208,000. The CTP has a peak biological 

treatment capacity of 78 mgd. The sewer system, however, can deliver up to 110 

mgd to the CTP. Tacoma plans to install a ballasted flocculation process at the CTP, 

in parallel with the existing processes, to handle wet weather flows in excess of 

the peak biological treatment capacity. The ballasted flocculation process will cost 

approximately $12.4 million. All related peak wet weather flow facilities upgrades 

are estimated at $50.7 million. In comparison, expanding the existing activated 

sludge processes would cost an estimated $130 million; this estimate does not 

include the cost for additional primary clarification capacity. When the ballasted 

flocculation process is brought on-line for wet weather treatment, effluent from 

the process will be separately disinfected and blended with disinfected biologically 

treated effluent prior to discharge. The blended effluent is expected to meet permit 

limits. The ballasted flocculation process is expected to operate a maximum of 5.5 

days in a row, 8 days in a month, and 21 days per year (Parametrix 2001).

Supplemental Treatment: 

Tacoma, WA
8-16

Report to Congress on the Impacts and Control of CSOs and SSOs

● Installing baffles to protect 

clarifiers from hydraulic surges 

(NYSDEC 2001);

● Using metal salts and polymers to 

increase suspended solids removal; 

● Switching the mode of delivering 

flow from the primary to the 

secondary treatment units; 

● Switching from “series” operation 

of unit processes during dry 

weather flows to “parallel” 

operation during wet weather 

flows; and

Performance evaluations are 

conducted to determine whether 

additional capacity can be obtained 

from existing facilities. While plant 

modifications are generally more 

cost effective than new construction, 

some modifications that improve wet 

weather performance may result in 

increased concentrations of pollutants 

in treatment plant effluent during dry 

weather. For example, if not properly 

designed, a clarifier modified for wet 

weather flows may have inadequate 

settling characteristics during dry 

weather (Metcalf and Eddy 2003). 

Further, modifications that require 

operator attention before and after 

a wet weather event may interrupt 

regular dry weather operations and 

potentially compromise the quality of 

treated wastewater during dry weather.

Disinfection

Disinfection of wastewater is necessary 

for public health protection when the 

public may come into contact with 

wastewater discharges. Wastewater 

treatment plants typically include 

a disinfection process designed 

specifically to inactivate bacteria, 

viruses, and other pathogens in the 

treated wastewater. The application 

of disinfection to CSO and SSO 

discharges has been limited. 

Achieving adequate disinfection 

of excess wet weather flows can be 

difficult. High flow rates can result 

in reduced exposure of wastewater 

to the disinfecting agent and 

possibly reduced effectiveness of 

the disinfection process. Among 

conventional disinfection processes, 

chlorine disinfection has been used 

most often to successfully disinfect wet 

weather flows. Effects of this method, 

however, include toxic residual 

chlorine and chlorine disinfection 

by-products that limit the utility of 

chlorination for disinfection in some 

areas. Experience with ultraviolet 

(UV) light and other alternatives has 

increased considerably in recent years 

and may be practical for wet weather 

flow receiving a minimum of primary 

treatment.

Vortex Separators

Vortex separators (swirl concentrators) 

are designed to concentrate and 

remove suspended solids and 

floatables from wastewater or 

storm water. Applications of 

vortex separators, for the most 

part, have been limited to CSSs. 

Vortex separators use centripetal 

force, inertia, and gravity to divide 

combined sewage into a smaller 

volume of concentrated sewage, solids, 

and floatables; and a large volume of 

more dilute sewage and surface runoff. 

Typically, the concentrated sewage and 

debris are conveyed to the treatment 

plant, and the dilute mix is discharged 

to a receiving water. This discharge 

may or may not receive disinfection. 

Ultraviolet light is used to disinfect wet 

weather flows as part of the Columbus, 

Georgia, Water Works CSO Technology 

Testing Program.

Photo: Columbus Water Works
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-17

Vortex separators provide a modest 

level of treatment for a modest 

cost. They are useful in controlling 

suspended solids and floatables and 

in reducing pollutants associated 

with solids such as metals bound to 

sediments. Vortex separators have 

limited ability to reduce dissolved 

pollutant or bacteria concentrations 

unless, in the latter case, disinfection 

is applied in conjunction with vortex 

separation (Brashear et al. 2002). 

When used in combination with 

other CSO controls, the placement of 

vortex separators is very important. 

Because they are designed to remove 

suspended solids and floatables, 

vortex separators should not be placed 

downstream of other facilities that 

perform the same function, such as 

sedimentation basins or grit chambers. 

(Moffa 1997).

Floatables Controls

Floatables controls are principally 

applied in CSSs and are designed to 

mitigate aesthetic impacts of CSO 

discharges by minimizing the amount 

of litter and other debris entrained in 

the CSO. Floatables controls are widely 

used to control solids and floatables 

in urban storm water discharges 

from separate storm sewer systems. 

Improvements in water quality from 

floatables controls may be secondary. 

The CSO Control Policy recognized 

the importance of controlling solid 

and floatable material by including 

it under the NMC (EPA 1994a). 

Floatables controls can be grouped 

into three categories: 

● Source controls that work to 

prevent solids and floatables from 

entering the CSS.

● Collection system controls that 

keep solids and floatables in the 

sewer system, so they can be 

collected and removed at strategic 

locations or transported to the 

wastewater treatment plant.

● End-of-pipe controls, such as 

containment booms and skimmer 

boats, capture solids and floatables 

as they are discharged from 

the sewer system. End-of-pipe 

controls can create temporary 

unsightly conditions near CSO 

outfalls and may be undesirable 

in areas with waterfront 

development. 

Ensuring the efficient and effective 

operation of all types of floatables 

controls requires proper maintenance. 

The optimal period between 

maintenance activities ranges from a 

few weeks to semi-annually, depending 

on the technology employed. 

8.1.5 Low-Impact Development 

 Techniques

Low-impact development (LID) 

techniques seek to control the timing 

and volume of storm water discharges 

from impervious surfaces (e.g., 

building roofs and parking lots) to the 

sewer system as well as the volume of 

wastewater generated by residential, 

commercial, and industrial customers. 

Controlling the timing and volume 

of storm water discharges can be an 

important component of a program 

to control CSOs. Reducing the volume 

of wastewater generated within the 

service area frees capacity within 

both CSSs and SSSs for transport of 

additional flows during wet weather. 

Specific LID techniques considered for 

this report are summarized in Table 

8.5.
8-18

Report to Congress on the Impacts and Control of CSOs and SSOs

While the concept of using LID to 

control storm water runoff is familiar, 

the application of LID techniques 

for CSO control has been limited 

(University of Maryland 2002). It is 

unlikely that LID techniques alone are 

sufficient to fully control CSOs, yet 

they have shown promise as part of 

larger programs in reducing the size of 

structural controls (e.g. storage). The 

use of LID as an SSS control is limited 

to situations in which LID might 

contribute to inflow control. LID 

has great potential as a storm water 

control for the separate storm sewer 

system that complements an SSS. 

Porous Pavement

Porous pavement is an infiltration 

system in which storm water 

runoff enters the ground through a 

permeable layer of pavement or other 

stabilized permeable surface (EPA 

1999h). The use of porous pavement 

reduces or eliminates impervious 

surfaces, thus reducing the volume of 

storm water runoff and peak discharge 

volume generated by a site. Reducing 

the amount of stormwater that enters 

the CSS increases conveyance and 

storage capacity. This in turn leads 

to reductions in the volume and 

frequency of CSOs.

Porous pavement is used as 

an alternative to conventional 

impervious pavement, under certain 

conditions. The success of porous 

pavement applications depends 

on design criteria including site 

conditions, construction materials, 

and installation methods. Typically, 

porous pavement is most suitable for 

areas with sufficient soil permeability 

and low traffic volume. Common 

applications include parking lots, 

residential driveways, street parking 

lanes, recreational trails, golf cart and 

pedestrian paths, shoulders of airport 

runways, and emergency vehicle and 

fire access lanes. This technology is not 

recommended for areas that generate 

highly contaminated runoff such as 

commercial nurseries, auto salvage 

yards, fueling stations, marinas, 

outdoor loading and unloading 

facilities, and vehicle washing facilities, 

as contaminants could infiltrate into 

groundwater (SMRC 2002).

Green Roofs

Green roofs use rooftop vegetation 

and underlying soil to intercept storm 

water, delay runoff peaks, and reduce 

runoff discharge rates and volume. 

Their use can lead to reductions in the 

volume or occurrence of CSOs. Green 

roofs are becoming an important 

tool in areas with dense development 

where the use of other space-intensive 

storm water management practices, 

such as detention ponds and large 

infiltration systems, is impractical. 

Technology Type of System Pollutants/Problems Controlled

Porous pavement CSS Peak wet weather flow rate

Green roofs CSS Peak wet weather flow rate

Bioretention CSS Peak wet weather flow rate

Water conservation CSS, SSS Peak wet weather flow rate

Table 8.5

Summary of Low-Impact 

Development Techniques

Low-impact development 

techniques are most useful in 

attenuating peak wet weather flow 

rates associated with urban and 

suburban storm water runoff.
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-19

There are two basic types of green 

roofs: intensive and extensive. 

Intensive green roofs, also known 

as conventional roof gardens, are 

landscaped environments developed 

for aesthetic and recreational uses that 

require high levels of management. 

Extensive green roofs, or eco-roofs, 

make use of a continuous, thin layer 

of growing medium that sustains lowmaintenance vegetation tolerant of 

local climatic conditions.

Intensive and extensive green roofs 

have been successfully installed in 

cities across the United States, both 

as part of new building design and 

retrofitted to existing buildings 

(e.g., Chicago, IL; Philadelphia, PA; 

Portland, OR). Green roofs can be 

designed for commercial buildings, 

multi-family homes, industrial 

structures, and single-family homes 

and garages. Factors that must be 

considered before installing a green 

roof include the load-bearing capacity 

of the roof deck, the moisture and 

root penetration resistance of the 

roof membrane, roof slope and shape, 

hydraulics, and wind shear.

Bioretention

Bioretention is a soil and plantbased storm water management 

practice used to filter and infiltrate 

runoff from impervious areas such 

as streets, parking lots, and rooftops. 

Bioretention systems are essentially 

plant-based filters designed to mimic 

the infiltrative properties of naturally 

vegetated areas, reducing runoff rates 

and volumes. Their use can lead to 

reductions in CSO and SSO volume 

and frequency. The complexity of 

bioretention systems depends on the 

volume of runoff to be controlled, 

available land area, desired level of 

treatment, and available funding. 

Bioretention systems can be used as 

a stand-alone practice (off-line) or 

connected to a separate storm sewer 

system (on-line). 

Bioretention systems can be 

implemented in new development or 

be retrofitted into developed areas. 

Bioretention systems are easier to 

incorporate in new developments, 

due to fewer constraints regarding 

siting and sizing. They can be 

applied in heavily urbanized areas, 

including commercial, residential, 

and industrial developments. For 

example, bioretention can be used as 

a storm water management technique 

in median strips, parking lots with 

or without curbs, traffic islands, 

sidewalks, and other impervious areas 

(EPA 1999i). 

The effectiveness of bioretention 

systems depends on infiltration 

capacity and treatment capability. 

Systems must be sized to match 

expected runoff. Runoff volumes in 

excess of the system’s capacity must 

be handled in such a way as to avoid 

erosion and destabilization of the 

site. Typical maintenance activities 

for bioretention systems include 

re-mulching void areas; treating, 

removing, and replacing dead or 

diseased vegetation; watering plants 

until they are established; inspecting 

and repairing soil, as needed; and 

removing litter and debris.

Water Conservation

Water conservation is the efficient 

use of water in a manner that extends 

water supplies, conserves energy, 

and reduces water and wastewater 

In-system netting can provide floatables 

control at strategic locations in the sewer 

system.

Photo: New Jersey Department of Environmental Protection
8-20

Report to Congress on the Impacts and Control of CSOs and SSOs

treatment costs. Reducing water use 

can decrease the total volume of 

domestic sewage conveyed by a sewer 

system, which can increase conveyance 

and treatment capacity during periods 

of wet weather and potentially 

reduce the volume and frequency of 

CSOs and SSOs. Numerous indoor 

and outdoor practices reduce water 

consumption, including (GBS 2002):

● High efficiency fixtures and 

appliances such as low-flow toilets, 

urinals, showerheads, and faucets, 

and water-efficient washing 

machines and dishwashers.

● Water recycling and reuse of 

wastewater from sinks, kitchens, 

tubs, washing machines, and 

dishwashers for landscaping, 

flushing toilets, and other nonpotable purposes.

● Waterless technologies such as 

composting toilets and waterless 

urinals. 

● Rain harvesting, in which roof 

runoff is collected, stored, and 

used primarily for landscaping.

In most instances, money saved 

from reduced water and sewer bills 

offsets installation costs over time. 

Among high efficiency fixtures and 

appliances, low-flow showerheads 

and faucet aerators are almost always 

cost-effective to install due to their 

relatively low cost and minimal 

labor requirements. Low-flow toilets 

also have widespread application, 

particularly in commercial and 

institutional settings, because the 

economic offset period can be 

relatively short. The cost effectiveness 

of the other water conservation 

technologies mentioned depends on 

site-specific considerations. 

8.2 How Do CSO and SSO 

Controls Differ?

Although many of the 

technologies considered 

in this report have proven 

useful in controlling overflows from 

both CSSs and SSSs, EPA found that 

applications of certain technologies 

were more common to a particular 

type of system. This section highlights 

technologies with particular 

application in either CSSs or SSSs.

8.2.1 Common CSO Control 

Measures 

Implementation of the NMC was 

expected to be one of the first steps 

taken by CSO communities in 

response to the CSO Control Policy. 

In general, the NMC are controls that 

reduce CSOs and their impacts on the 

environment and human health, but 

do not require significant engineering 

studies or major construction, and 

are implemented in a relatively 

short period (e.g., within a few 

years). Most activities completed 

as part of implementing the NMC 

are considered O&M practices or 

collection system controls. The most 

common NMC activities include (EPA 

2001a):

● Sewer cleaning

● Pollution prevention

● Inflow reduction

In developing and implementing a 

CSO LTCP, municipalities are expected 

to consider more significant structural 

Bioretention systems can reduce the 

amount of storm water runoff generated by 

impervious surfaces, such as parking lots, 

that enters a CSS during wet weather.

Photo: Prince George’s County, MD
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-21

controls. Specifically, municipalities 

are asked to evaluate the applicability 

of more comprehensive collection 

system controls, storage facilities, and 

treatment technologies.

Sewer separation is the CSO control 

most widely implemented as part of 

an LTCP (EPA 2001a). Complete or 

limited sewer separation has been 

implemented or planned by the 

majority of CSO communities for 

which CSO controls were documented 

in the NPDES authority files that EPA 

reviewed as part of data collection to 

support its 2001 Report to Congress–

Implementation and Enforcement of the 

CSO Control Policy. Other common 

CSO control measures identified in 

LTCPs include:

● Off-line storage facilities

● Plant modifications

● Sewer rehabilitation

● Disinfection facilities

8.2.2 Common SSO Control 

Measures

There is no national standard 

equivalent to the LTCP for 

communities with SSSs that are 

working to control SSOs, so it is 

difficult to determine the prevalence of 

specific controls. Based on interviews 

EPA conducted to support the 

development of this report, it appears 

that communities with recurrent dry 

weather SSOs tend to rely on O&M 

activities, while communities with wet 

weather SSOs rely more heavily on 

collection system controls (e.g., inflow 

reduction, rehabilitation). 

8.3 What Technology 

Combinations are 

Effective?

M ost communities evaluate 

and use a wide variety of 

technologies for their CSO 

and SSO programs. Some technologies 

have proven to be advantageous 

when applied together. This section 

describes several examples of 

beneficial technology pairings; 

this list should not be construed 

as an exhaustive list of technology 

combinations.

8.3.1 Inflow Reduction or LowImpact Development Coupled 

with Structural Controls

Inflow reduction and LID techniques 

reduce the quantity of storm water 

runoff that enters a sewer system. 

Since these controls can reduce both 

the peak flow rate and volume of 

storm water delivered to a sewer 

Low-flow plumbing fixtures were installed in a 60-unit low income multi-family 

housing complex in Houston, Texas. The average number of occupants per unit was 

4.4. Devices installed in each unit included low-flow toilets (1.6 gallons per flush), 

low-flow aerators on faucets (2.2 gallon per minute) and new water meters. Faucet 

leaks were repaired, and tenants were educated on conservation techniques. The 

project resulted in a reduction in average monthly water consumption for the 

complex from 1.3 MG pre-installation to 367,000 gallons post-installation. Average 

monthly water bills for the complex decreased from $8,644 to $1,810, resulting in 

savings of approximately $6,834 each month. Due to the success of the project, 

Houston retrofitted four other low income housing developments with low-flow 

plumbing fixtures.

Water Conservation: 

Houston, TX
8-22

Report to Congress on the Impacts and Control of CSOs and SSOs

system, the size of more capitalintensive downstream control 

measures, such as storage facilities 

or treatment technologies, can be 

reduced, or, in some cases, eliminated 

completely.

8.3.2 Disinfection Coupled with 

Solids Removal

A number of the pollutants present 

in wastewater can interfere with 

disinfection processes and reduce 

their efficacy. High concentrations of 

BOD5, ammonia, and iron can reduce 

the effectiveness of disinfection. 

These substances can consume or 

otherwise prevent the disinfectant 

from reaching microbial pathogens. 

Solids in wastewater can also interfere 

physically with the disinfection 

process. Pathogens can be “shielded” 

by larger solids that surround and 

insulate microbial pathogens from the 

disinfectant (Hoff and Akin 1986). 

Physical interference can be significant 

for both chlorine and UV disinfection. 

In general, solids removal enhances 

disinfection by removing interfering 

substances and by physically 

removing the pathogens themselves. 

The performance of disinfection 

facilities to treat CSO and SSO 

discharges can be improved through 

the use of technologies that provide 

solids control. Technologies with 

demonstrated abilities to remove 

solids include off-line storage facilities, 

vortex separators, and supplemental 

treatment facilities. 

8.3.3 Sewer Rehabilitation Coupled 

with Sewer Cleaning

Sewer rehabilitation is undertaken 

to restore the structural integrity 

of sewers and reduce infiltration. 

The presence of debris and roots 

within sewer systems can limit the 

effectiveness of sewer rehabilitation 

efforts, particularly where Shortcrete 

or trenchless technologies are 

employed. Therefore, it is essential 

that sewer cleaning techniques are 

employed prior to any scheduled sewer 

rehabilitation efforts.

8.3.4 Real-Time Control Coupled 

with In-line or Off-line 

Storage Facilities

Real-time control technology is 

used to maximize storage within the 

collection system and maximize flow 

to the POTW, thereby reducing the 

volume and frequency of untreated 

discharges. Real-time control systems 

use monitoring data, operating rules, 

and customized software to operate 

system components (e.g., weirs, 

gates, dams, valves, and pumps) in a 

dynamic manner to optimize storage 

and treatment. Real-time control is 

most often applicable in CSSs, as these 

systems tend to have substantial inline storage in large diameter pipes 

designed to transport excess wet 

weather flows. CSSs may also have offline storage facilities (e.g., tunnels and 

basins), which can be incorporated 

into a real-time control strategy. The 

dynamic operation possible under 

real-time control tends to require less 
 Chapter 8—Technologies Used To Reduce the Impacts of CSOs and SSOs

8-23

storage than would be required for 

similar performance without real-time 

control.

8.4 What New Technologies for 

CSO and SSO Control are 

Emerging?

This section describes two 

different broad types of 

measures that have potential 

for widespread implementation in 

controlling the impacts of CSOs or 

SSOs. These controls are viewed as 

“emerging” for the following reasons: 

techniques are evolving and warrant 

further study; and, in general, 

applications to date have been limited 

to larger municipalities, although the 

technologies appear to have value for 

use in smaller systems. Again, this 

should not be construed to be an 

exhaustive list. 

8.4.1 Optimization of Sewer 

System Maintenance

Sewer system maintenance is critical 

to providing safe and efficient service. 

Optimizing sewer system maintenance 

involves allocating labor, equipment, 

and materials to maximize system 

performance, so that the system 

can efficiently collect and transport 

wastewater to the treatment plant. 

Determining how much maintenance 

is enough is rarely straightforward, 

however. Currently, there is no 

standard approach for determining 

the optimal frequency of various 

maintenance procedures except 

through experience and professional 

judgement (ASCE 1999). Several 

EPA regions and states, as well as 

professional organizations, have 

initiated efforts to develop such an 

approach. These include Region 4’s 

MOM Program (Section 7.3.1) and 

the toolkit of effective O&M practices 

recently published by WERF (WERF 

2003a).

8.4.2 Information Management

Effective sewer system management 

largely depends on the availability 

of accurate, easily accessible data. 

Manual, paper-based data systems 

are used to some degree in all 

sewer systems (Arbour and Kerri 

1998). Many utilities have been 

and continue to be operated and 

managed in an effective manner 

without the assistance of computerbased systems. The use of a computer 

system, however, can improve data 

storage and processing. Previously, 

the considerable expense of such 

systems limited their applicability to 

larger sewer systems. As the costs of 

computers and customized software 

have decreased, however, these 

systems are now available to most 

utilities (CSU 2002). An information 

management system can be designed 

to meet multiple needs, including:

● Simplifying maintenance planning 

and scheduling;

● Tracking workforce productivity;

● Developing accurate unit costs for 

specific maintenance activities;
8-24

Report to Congress on the Impacts and Control of CSOs and SSOs

● Measuring the impact of resource 

allocation to various maintenance 

activities; and

● Developing and tracking sewer 

system performance measures.

A number of vendors have designed 

software packages specifically to 

assist utility staff in sewer system 

management. The software is typically 

a tailored database program that 

provides a means for efficient data 

organization, storage, and analysis. 

Most software packages include 

basic tools for sorting and filtering 

maintenance data; many also offer 

report generation capabilities. Other 

software packages contain basic tools 

as well as more advanced decision 

support systems. Most packages 

offer the ability to link to other 

external data systems such as a GIS or 

computer models.
industry reports, such as the AMSA’s 

triennial financial survey (AMSA 

2003a).

All cost figures in this chapter are 

presented in 2002 dollars, unless 

otherwise noted. Unadjusted costs are 

included in Appendix M.

9.1 What Federal Framework 

Exists for Evaluating 

Resources Spent on CSO 

and SSO Control?

At the national level, two EPA 

programs provide information 

on the monies spent on CSO 

and SSO control, as well as anticipated 

needs:

● Clean Water State Revolving Fund 

(CWSRF)

● Clean Watersheds Needs Survey 

(CWNS)

The CWSRF is a national program 

established in 1987 under the Clean 

Water Act to fund water quality 

projects. Through the CWSRF, all 

50 states and Puerto Rico maintain 

Chapter 9

This chapter responds to 

the congressional directive 

to report on the resources 

spent by municipalities to address 

environmental and human health 

impacts of CSOs and SSOs. The 

chapter presents information on 

historical investments in wastewater 

infrastructure, resources spent on CSO 

and SSO control to date, projected 

costs to reduce CSOs and SSOs, and 

financing mechanisms available to 

municipalities. 

Most municipalities are not required 

to explicitly report costs to implement 

CSO and SSO controls. Therefore, 

financial information on resources 

spent to address CSOs and SSOs 

was drawn from alternative sources, 

including: LTCPs and other facility 

planning documents; municipal 

interviews described in Appendix 

C; information on state and 

local expenditures on wastewater 

infrastructure from the U.S. Census 

Bureau (2002, 2003a); specific 

reporting categories associated with 

the CWNS (EPA 2003b) and the 

CWSRF (EPA 2003j); other loan and 

grant programs; and federal, state, and 

9-1

9.1 What Federal Framework 

Exists for Evaluating 

Resources Spent on CSO 

and SSO Control?

9.2 What are the Past 

Investments in Wastewater 

Infrastructure?

9.3 What Has Been Spent to 

Control CSOs?

9.4 What Has Been Spent to 

Control SSOs?

9.5 What Does it Cost to 

Maintain Sewer Systems?

9.6 What are the Projected 

Costs to Reduce CSOs?

9.7 What are the Projected 

Costs to Reduce SSOs?

9.8 What Funding Mechanisms 

are Available for CSO and 

SSO Control?

Resources Spent to Address the 

Impacts of CSOs and SSOs

In this chapter:
9-2

Report to Congress on the Impacts and Control of CSOs and SSOs 

revolving loan funds to provide 

low-cost financing for these projects 

through low-interest loans. The 

CWSRF is primarily used to fund 

wastewater treatment projects, but it 

can also be used for nonpoint source 

pollution control and watershed and 

estuary management (EPA 2003j). 

The CWSRF tracks state and local 

expenditures on these projects on 

an annual basis, and it includes a 

separate reporting category for CSO 

expenditures. 

The CWNS, a joint effort between 

states and EPA, includes a survey of 

needs of facilities for control of CSOs 

along with other wastewater and 

watershed needs (EPA 2003b). Survey 

data are maintained in a database and 

used to produce a CWNS Report to 

Congress, which provides a national 

estimate of needs. The CWNS and the 

CWSRF do not specifically track costs 

related to SSO control. 

The CSO Control Policy provides 

a regulatory framework for CSO 

control. Under the CSO Control 

Policy, communities are required 

to develop and implement LTCPs. 

In developing an LTCP, the CSO 

Control Policy recommends that 

the community complete a detailed 

evaluation of CSO control alternatives 

and develop a financing plan to 

fund implementation of the selected 

controls. This means that communities 

that have completed LTCPs usually 

report the anticipated cost of CSO 

control in their plan. 

The costs of addressing SSO problems 

can vary significantly among 

communities. Currently, there is no 

national framework for SSO control 

that requires communities to develop 

and report projected or realized costs. 

Therefore, more financial information 

is available for CSOs than SSOs. For 

the purposes of this report, the costs 

to address SSOs were estimated using 

information from the CWSRF, the 

CWNS, and recent EPA efforts.

9.2 What are the Past 

Investments in Wastewater 

Infrastructure?

Municipalities, states, and 

the federal government 

have been investing in the 

nation’s wastewater infrastructure 

since the late 19th century (EPA 

2000a, 2000c). With passage of the 

Clean Water Act in 1972, investment 

in wastewater infrastructure increased 

markedly. The Clean Water Act 

dramatically increased funding for 

the Construction Grants Program, 

establishing a national policy to 

provide federal grants for the 

construction and upgrade of POTWs. 

The Construction Grants Program 

provided grants for as much as 75 

percent of the total capital cost for 

construction of wastewater treatment 

facilities from 1970 to 1995. During 

this period, the Construction Grants 

Program provided a total of more 

than $100 billion in federal funding 

for new construction and POTW 

upgrades (EPA 2000a). In 1981, 

amendments to the Clean Water Act 

cut the authorization for POTW 

grants in half and reduced the 

maximum federal match to 55 percent. 

Legislation was amended to phase out 

the Construction Grants Program by 

1991 and replace it with the CWSRF. 

Federal funding for the CWSRF 

totaled more than $21 billion from 
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-3

infrastructure exceeded $535 billion 

between 1970 and 2000. EPA estimates 

that the current capital investment 

in wastewater infrastructure from all 

public sources—federal, state, and 

local—is just over $13 billion annually 

(EPA 2002a). Today, according 

to industry organizations, local 

governments and utilities pay as much 

as 90 percent of capital expenditures 

on wastewater infrastructure (AMSA 

and WEF 1999).

1988 to 2002, and states have made 

over $47 billion available through the 

CWSRF for investment in wastewater 

infrastructure; both figures are in 

unadjusted dollars.

As shown in Figure 9.1, federal grant 

funding for capital wastewater projects 

peaked in 1977 at $14.1 billion 

dollars. The U.S. Census Bureau 

(2002, 2003a) reported that total local 

and state spending on wastewater 

Figure 9.1

Annual Capital 

Expenditures 

on Wastewater 

Infrastructure, 1970-

2000

Federal funding for capital 

wastewater projects peaked in 

1977. At that time, federal funding 

accounted for more than 60 percent 

of annual capital expenditures 

on wastewater projects; by 2000, 

federal funding represented 

about 15 percent of annual capital 

expenditures. Details on annual 

federal, state, and local expenditures 

are shown in Appendix M (Tables 

M.2, M.3).

Sources: Construction Grants Program and CWSRF expenditures (EPA 2000a, 2000c, 2003j); and 

U. S. Census Bureau (2002). 

Year

Billions of Dollars

0.0 3.0 6.0 9.0 12.0 15.0

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Federal

State and local
9-4

Report to Congress on the Impacts and Control of CSOs and SSOs 

As the value of the nation’s wastewater 

infrastructure increased, O&M (noncapital) expenditures at wastewater 

facilities have increased from $1.3 

billion in 1970 to $18.0 billion in 

2000 (Figure 9.2). O&M expenditures 

now account for 60 percent of total 

spending on wastewater services 

(U.S. Census Bureau 2003a). AMSA 

(2003b) cites a “combination of aging 

infrastructure, expectations of higher 

quality service, a growing population, 

and increasingly expensive federal 

regulations” as contributing to 

increased O&M costs.

Since 1970, total public investment in 

wastewater infrastructure (capital) and 

O&M exceeded $658.4 billion (EPA 

2001f). According to ASCE, water and 

wastewater systems are the second 

largest public works infrastructure 

in the country (ASCE 2003). This 

infrastructure includes: Figure 9.2

State and Local 

Expenditures on 

Wastewater O&M, 1970-

2000 (EPA 2000c, U.S. 

Census Bureau 2002, 

2003b)

The majority of O&M expenditures 

are borne by local governments. The 

Census Bureau does not, however, 

report state and local expenditures 

separately.

$0 $2 $4 $6 $8 $10 $12 $14 $16 $18

Billions of Dollars

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Year
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-5

● 16,202 wastewater treatment 

facilities; 

● 21,264 sewer systems (both CSS 

and SSS);

● 100,000 major pumping stations; 

● 584,000 miles of sanitary sewers; 

● 200,000 miles of storm sewers; 

and

● 140,000 miles of combined sewers 

(EPA 2001g and 2003b).

9.3 What Has Been Spent to 

Control CSOs?

F

ederal funding for CSO control

projects began in 1965. 

Although some communities 

financed CSO controls through 

the Construction Grants Program, 

investment in wastewater 

infrastructure during the 1970s and 

1980s was focused on POTW upgrades 

to secondary and advanced treatment 

and expansion (EPA 2001a). Federal 

funding for CSO projects through the 

Construction Grants Program totaled 

$3.4 billion.

Since 1988, the CWSRF has been used 

to provide loans to CSO communities. 

CSO projects financed under the 

CWSRF total $3 billion (EPA 2003j). 

As shown in Figure 9.3, total state and 

local expenditures reported under the 

CWSRF program for CSO projects 

have increased to $0.44 billion per 

year in 2002. The exact percentage of 

total annual municipal investment 

in CSO control projects funded 

through the CWSRF is not known. 

Some communities participate in 

the CWSRF for only a portion of 

their CSO financing; others do not 

participate in the program at all.

Statewide information on past 

expenditures for CSO control 

is available in some states. Two 

coordinated surveys were conducted 

in Michigan in 1999 to obtain 

community and state information 

on CSOs, SSOs, and other water 

pollution control efforts (SEMCOG 

$0.00 $0.01 $0.02

$0.13

$0.19

$0.26

$0.20

$0.17

$0.14

$0.28

$0.20

$0.16

$0.41

$0.44

$0.41

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Billions of Dollars (2002)

Year

Figure 9.3

CWSRF Annual 

Expenditures for CSO 

Projects, 1988 - 2002 

(EPA 2003b)

This figure shows state and local 

expenditures reported under CWSRF 

Category V (CSO correction). Some 

communities participate in CWSRF 

for a portion of their CSO financing; 

other CSO communities do not 

participate at all.
9-6

Report to Congress on the Impacts and Control of CSOs and SSOs

2001; PSC & ECT 2002). Capital CSO 

control expenditures by 63 Michigan 

communities exceeded $1 billion 

between 1989 and 1999 (PSC & ECT 

2002). It should be noted that few of 

Michigan’s CSO communities began 

implementing controls prior to 1989.

No comprehensive source of 

individual municipal expenditures 

for CSO control exists. Through this 

report effort, however, EPA compiled 

expenditures to date for 48 CSO 

communities (Appendix M). These 

expenditures total $6 billion, ranging 

from $134,000 to $2.2 billion per 

community. Information on the unit 

costs of specific control technologies 

used by communities to reduce 

CSOs is available in the technology 

decriptions provided in Appendix L.

9.4 What Has Been Spent to 

Control SSOs?

Many of the expenditures 

associated with controlling 

SSOs are costs associated 

with renewing aging sewer system 

infrastructure. This makes separating 

costs specifically associated with SSO 

control from standard sewer system 

O&M costs difficult. 

The CWSRF does not explicitly track 

expenditures related to SSO control. 

The CWSRF, however, does track 

“I/I correction” and “sewer system 

replacement and rehabilitation” 

expenditures. For the purposes of this 

report, these CWSRF categories of 

expenditures are used as a surrogate 

for SSO capital projects, with 

the understanding that they may 

HUD and CWSRF Funding 

Used to Fund Sewer 

Separation: 

Agawam, MA

The Town of Agawam, Massachusetts had 132 miles of combined sewer and found 

sewer separation to be a cost-effective CSO control. The town spent a total of 

$5.85 million to implement CSO-control measures. Funding was provided through 

a Housing and Urban Development (HUD) grant in the 1970s for limited sewer 

separation. CWSRF loans provided $2 million for a pump station upgrade (1996-

1997) and $3.5 million to complete the sewer separation (1999).

$0.001

$0.04 $0.06

$0.10 $0.13

$0.16

$0.42

$0.26 $0.25 $0.27

$0.32

$0.41

$0.62

$0.38

$0.53

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

I/I correction

Sewer system replacement and

rehabilitation

Billions of Dollars (2002)

Year

Figure 9.4

CWSRF Annual 

Expenditures for I/I and 

Sewer Replacement/

Rehabilitation (EPA 2003j)

Although the CWSRF does not 

specifically track expenditures 

related to SSO control, spending 

related to I/I correction and 

sewer system replacement and 

rehabilitation may serve as a 

surrogate for SSO capital projects. 

These categories, however, may 

overestimate CWSRF expenditures 

on SSO control.
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-7

overestimate CWSRF expenditures 

on SSO control. As shown in Figure 

9.4, total state and local spending 

through the CWSRF on I/I correction 

(Category III-A) and sewer system 

replacement and rehabilitation 

(Category III-B) was $0.53 billion in 

2002. From 1988 to 2002, expenditures 

totaled $4.0 billion. Spending in these 

areas has increased over the last several 

years and now exceeds expenditures 

for CSO projects under the CWSRF 

program (EPA 2003j). It should be 

noted that communities may have 

reported expenditures on SSO projects 

under other categories, and not 

all communities participate in the 

CWSRF.

Some local cost information on 

expenditures to control SSOs was 

obtained as part of the municipal 

interviews conducted for this report 

(Appendix C). These communities 

had service populations ranging 

from 75 to 615,000 people. Of the 

45 communities with SSSs that 

participated, 29 communities provided 

cost information on either capital 

or O&M annual expenditures on 

SSO control. As shown in Table 9.1, 

the total annual capital and O&M 

expenditures for these 29 communities 

totaled $196.8 million. The total 

annual expenditures varied with 

population served, from a minimum 

of $20,000 in one small village 

to nearly $96 million in a major 

metropolitan area. 

The cost of SSO control can vary 

significantly, depending on the 

size and condition of the SSS, the 

technologies chosen to reduce 

SSOs, and regulatory requirements. 

Information on the unit costs of 

specific control technologies used 

by communities to reduce SSOs 

is available in the technology 

descriptions provided in Appendix L.

9.5 What Does it Cost to 

Maintain Sewer Systems?

As discussed in Section 9.2, the 

current capital investment by 

federal, state, and local sources 

in wastewater infrastructure is $13 

billion dollars per year. O&M costs 

exceed $18 billion per year, more than 

60 percent of total spending. 

As shown in Table 9.2, average annual 

O&M costs per mile of sewer are 

highly varible. Various studies have 

estimated average O&M costs between 

$3,100-$12,500 per year per mile of 

Type of Cost Number of 

Communities

Minimum Maximum Total

Capital 19 $6,000 $75M $154.5M

O&M 26 $12,500 $20.9M $42.3M

Total 

(capital + O&M)

29 $20,000 $95.9M $196.8M

Annual Expenditures in 

Sanitary Sewer Systems

This table shows annual capital 

and O&M expenditures for 29 

communities with SSSs, which 

service populations ranging from 75 

to 615,000.

Table 9.1
9-8

Report to Congress on the Impacts and Control of CSOs and SSOs

sewer. A study commissioned by ASCE 

and EPA on optimizing maintenance 

of SSSs estimated that utilities should 

spend, on average, $8,009 per mile 

annually (ASCE 1999). This study 

found that it is often difficult to 

develop comparable unit costs for 

different O&M techniques.

Communities participating in the 

interviews for this report also provided 

information on O&M expenditures. 

On average, these communities spent 

$33,000 per mile of sewer per year on 

capital projects. O&M expenditures 

averaged $7,886 per mile. These 

findings are consistent with the 

aforementioned ASCE, WERF, and 

AMSA findings.

9.6 What are the Projected 

Costs to Reduce CSOs?

The CWNS is the primary 

source of data on anticipated 

capital needs for CSO control 

at the national level. 

In the 2000 CWNS, EPA estimated 

future capital financial needs for 

CSO control at $50.6 billion (2000 

The City of Somersworth, New Hampshire, maintains 24.4 miles of sewers. Prior to 

obtaining CWSRF for SSO projects, the city typically cleaned less than one mile of 

sewer each year. CWSRF funding was used to purchase a $325,000 flushing truck. 

In 2002, the city was able to clean 15 miles of older sewer lines for $140,000. The 

city currently anticipates spending at least $15,000 per year on O&M. The city also 

anticipates spending $100,000 to analyze the SSS and the separate storm sewer 

system and to enter that information into a GIS. These efforts have helped reduce 

the frequency of SSOs, which cost an average of $1,200 per event for cleanup.

The Santa Margarita Water District 

in California serves 134,000 people, 

and owns and operates three 

wastewater treatment plants and 

539 miles of SSSs; the District 

also maintains unknown miles of 

private laterals. The current O&M 

budget for sewer system work is 

approximately $5 million a year, 

with more than one-third covering 

labor costs.

Labor

41%

Power

28%

Supplies 8%

Contract

services

7%

Pipe replacement 7%

Lift station

maintenance

6%

Vehicles Sewer System Operation 3%

and Maintenance Costs:

Santa Margarita Water 

District, CA

Sewer System Operation 

and Maintenance Costs:

Somersworth, NH

Source Annual Average O&M 

costs per mile

Range of O&M 

costs per mile

WERF (1997) $8,667 $1,033 - $51,051

ASCE (2000) $3,100

WERF (2003) $12,503

AMSA (2003a) $6,212 $300 - $57,000

Table 9.2

O&M Costs for Sewers

This table shows the average annual 

O&M costs per mile of sewer. Studies 

have found that O&M costs can vary 

widely.
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-9

dollars). This estimate is based on 

LTCPs and CSO planning documents 

(which indicate varying levels of 

control) and a model used to estimate 

missing costs. Thirty-four facilities 

from 10 states documented CSO 

needs using LTCPs. These needs, 

totaling $3.9 billion, account for 7.7 

percent of the CSO needs reported in 

the CWNS. EPA also reviewed other 

materials (e.g., capital improvement 

program budgets) submitted by states 

as part of the CWNS process which 

documented municipal CSO needs. In 

compiling this information EPA found 

documentation of approximately 

$16.7 billion in needs. The CWNS 

reports that a cost curve methodology 

was used to estimate the cost of CSO 

control where documented needs 

were not provided. The cost curve 

methodology is based on communities 

providing primary treatment and 

disinfection, where necessary, for no 

less than 85% of the CSO by volume. 

Compliance with current state water 

quality standards could, however, 

require a higher level of control 

resulting in additional needs.

Some organizations have compiled 

information at the state level on 

estimated capital needs for CSO 

control. Recent analyses conducted 

for Michigan estimated that $1.7-

$3.4 billion will be needed for CSO 

communities in Michigan over the 

next 12 years (PSC & ECT 2002). 

Estimated costs to control CSOs 

in West Virginia exceed $1 billion 

(Mallory 2003).

Community-specific information on 

projected CSO needs is available from 

several sources, including LTCPs, the 

Report to Congress–Implementation 

and Enforcement of the Combined 

Sewer Overflow Control Policy (EPA 

2001a) and the 2000 CWNS (EPA 

2003c). Together, these sources 

provide information on the future 

capital needs for CSO control in 71 

communities (see Appendix M). 

Information on O&M costs for CSO 

control is not available at the national 

level. 

9.7 What are the Projected 

Costs to Reduce SSOs?

The 2000 CWNS identified 

$3.5 billion in I/I correction 

needs (Category III-A) for 

facilities reported by states as having 

SSO problems (EPA 2003b). A further 

$10.4 billion in needs were reported 

for sewer system replacement or 

rehabilitation (Category III-B). The 

total needs for Category III-A and 

III-B were reported at $8.2 and 

$16.8 billion, respectively. Needs for 

Category III-A and III-B account for 

only 14 percent of the total CWNS. 

As shown in Figure 9.5, needs for 

Category III-A and III-B have 

more than doubled since the 1996 

CWNS. This increase demonstrates 

that communities are planning for 

the correction of problems that are 

symptomatic of SSOs (EPA 2003b).

In addition to the documented needs, 

national modeled cost estimates for 

reducing SSOs to one overflow every 

five years for each SSS were prepared 

for the 2000 CWNS (EPA 2003b). 

EPA estimated that it would require 

$88.5 billion in capital improvements 

to reduce the frequency of SSOs 

caused by wet weather and other 

conditions, such as blockages, line 
9-10

Report to Congress on the Impacts and Control of CSOs and SSOs

Change in Estimated 

Needs Between 1996 and 

2000 CWNS (EPA 2003b)

Between the 1996 and 2000 

CWNS estimated needs related to 

I/I correction and sewer system 

replacement and rehabilitation have 

more than doubled, increasing by 

122% and 118%, respectively.

breaks, or mechanical/power failures. 

This estimate does not include costs 

associated with improved system 

management and O&M activities 

necessary to actually achieve the 

desired level of control. A case-bycase analysis of each SSS is needed 

to determine the actual level of 

investment required to control SSOs. 

EPA notes that these modeled needs 

should not be added to documented 

needs because the documented needs 

may already include costs to address 

SSOs.

SSSs, including newer systems, 

typically require significant, ongoing 

investment in O&M to reduce SSOs. 

O&M costs in individual communities 

vary significantly depending on 

community size, sewer system 

characteristics, local geology, and 

climate. EPA believes that needs will 

be greatest in communities that lack 

regular preventive maintenance or 

asset management programs. EPA 

estimates that the gap between 

projected needs and current O&M 

spending over the next 20 years is 

between $72 billion and $229 billion 

(with a point estimate of $148 billion), 

if current spending and operations 

practices are maintained. However, if 

municipalities increase spending at the 

rate of expected economic growth, the 

gap largely disappears (EPA 2002a).

9.8 What Funding Mechanisms 

are Available for CSO and 

SSO Control?

S

ignificant capital and O&M 

expenditures are often required 

to control CSOs and SSOs. 

Detailed descriptions of various 

finance mechanisms and case studies 

can be found in EPA’s SSO Fact Sheet 

Financing Capital Improvements for 

25%

5%

122%

118%

19%

24%

2%

9%

-33% VI Storm water

I Secondary

II Advanced

III-A I/I correction

III-B Sewer replacement/rehab

IV-A New collector sewers

IV-B New intercepor sewers

V CSO correction

management

VII Nonpoint source

treatment

treatment

Figure 9.5
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-11

SSO Abatement (EPA 2003k) and in 

CSO Guidance for Funding Options 

(EPA 1995a). The following sections 

provide an overview of common 

financing options for capital projects, 

including self-financing, CWSRF loans, 

and federal and state grants. Financing 

options for debt repayment and O&M 

costs are more limited and often rely 

solely on self-financing.

9.8.1 Self-financing

Self-financing is the most common 

financing option used for CSO and 

SSO control. Self-financing relies on 

local revenue sources including:

● Fees – user charges, property taxes, 

hookup fees, development charges, 

assessments, permit fees, and 

special levies.

● Bonds – general obligation and 

revenue bonds.

● Other local income sources –

reserves or fund transfers, interest 

payments, sales, and other 

mechanisms.

The AMSA Financial Survey–2003 

documents that local sources (i.e., 

fees, bonds, and other sources) have 

been used to fund between 90 and 

95 percent of capital investment 

and operating funds for wastewater 

infrastructure between 1992 and 2001 

(AMSA 2003a). The distribution of 

revenue sources based on AMSA’s most 

recent financial survey is presented in 

Figure 9.6.

AMSA’s recent financial survey notes 

that, when adjusted for inflation, 

residential service rates have decreased 

slightly since 1999, while rates for 

industrial customers have increased 

for some pollutants and decreased 

for others (AMSA 2003a). Specifically 

AMSA stated:

“The overall average residential 

sewer service charge from 1999 

to 2002 rose 7.6 percent from 

$216.02 to $232.59 per year 

($19.38 per month) for a singlefamily residence (for common 1999 

and 2002 survey respondents the 

increase was only 6.0 percent). 

Adjusting for inflation, average 

residential sewer rates have actually 

decreased by 0.3 percent from 1999 

to 2002 (1.9 percent for common 

agencies). For industrial customers, 

inflation-adjusted rates for volume 

(in dollars per 1,000 gallon) and 

BOD have increased by 1 and 4 

percent, respectively, since 1999, 

while inflation-adjusted rates for 

suspended solids have decreased by 

2 percent from 1999 to 2002.”

Revenue Sources

Local fees 66%

Other sources 16%

Bonds 13%

CWSRF loans 4%

Federal & state grants 1%

Total 100%

Percent

Figure 9.6

Revenue Sources for 

Municipal Wastewater 

Treatment (AMSA 2003a)

Self-financing is the most common 

option used to fund capital 

investments and O&M activities for 

wastewater treatment systems.
9-12

Report to Congress on the Impacts and Control of CSOs and SSOs

The costs associated with the control 

of CSOs and SSOs can be substantial 

and are likely to be borne mainly at 

the local level. Planning is needed to 

spread costs over time, as appropriate, 

in developing comprehensive, longterm programs.

9.8.2 State and Federal Funding for 

CSO and SSO Control

State and federal funding can offset 

some expenditures for capital projects 

needed to control CSOs and SSOs. A 

local match is typically required for 

state and federal funding, which can 

create debt repayment pressures for 

some communities (EPA 2002d). 

Clean Water State Revolving Fund

CWSRF programs operate much like 

banks that are capitalized with state 

and federal contributions. CWSRF 

monies are loaned to communities for 

planning, design, and construction of 

environmental infrastructure. Loan 

repayments are recycled back into the 

program to fund additional projects. 

The CWSRF is the federal 

government’s major funding 

mechanism for financing capital 

improvements in wastewater 

infrastructure, including projects to 

address CSOs and SSOs. The CWSRF 

is used by states to provide loans at or 

below market interest rates, purchase 

existing local debt obligations, and 

guarantee local debt obligations. Loans 

are not available for O&M or other 

non-capital I/I reduction activities 

(e.g., downspout disconnection 

programs). As shown in Figure 9.7, the 

total expenditures under the CWSRF 

have increased since 1986, as has the 

amount being spent on CSO control 

(Category V) and on I/I correction 

and sewer repairs or rehabilitation 

(Category III-A and III-B, a proxy for 

SSO capital) projects.

Total assets of the CWSRF program 

exceed $42 billion. States have 

significant control over the CWSRF 

funds. States set loan terms, including 

maximum loan amount, fees, interest 

rates (from zero percent to market 

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Year

CSO correction

SSO capital projects (I/I correction and

sewer rehabilitation)

All other CWSRF expenditures

Billions of Dollars (2002)

$0.02

$0.6

$1.3

$2.9 $2.9

$2.5

$3.9

$3.4

$2.9 $3.1

$3.5 $3.5

$5.1

$4.3

$5.0

Figure 9.7

State and Local 

Expenditures Under 

the CWSRF Program for 

CSO Correction and SSO 

Capital Projects 

Total expenditures under the CWSRF 

have generally increased since 

program inception in the late 1980s.
 Chapter 9—Resources Spent to Address the Impacts of CSOs and SSOs

9-13

CWSRF Loans Fund SSO 

Control:

Lawton, OK

rate, sometimes on a sliding scale 

based on community economics), 

repayment periods (up to 20 years), 

requirements on repayment dollars, 

prioritization requirements, and 

many other features of the program. 

In some cases, legislative approval is 

required for changes. Twenty-six states 

are leveraging the federal funding by 

issuing bonds. States can also tailor 

their CWSRF programs to leverage 

a number of financing mechanisms 

to make funding opportunities more 

attractive for communities. Options 

include loans; refinancing, purchasing, 

or guaranteeing local debt; and 

purchasing bond insurance. 

Federal Grants

As discussed in Section 9.3 of this 

report, federal water pollution 

control grants for CSO control were 

available as early as 1965. The federal 

Construction Grant Program was 

used extensively during the 1970s 

and 1980s to fund construction of 

wastewater infrastructure, and several 

communities used this program to 

fund CSO projects. The program was 

phased out in the late 1980s in favor of 

the CWSRF.

Several other grant programs—the 

Rural Utilities Service Grant 

Program, the Economic Development 

Administration Grant Program, and 

Community Development Block 

Grants—also are used for CSO and 

SSO control projects, but they are only 

available to small and economically 

disadvantaged communities. 

State Grants for CSO Control

Twenty-eight states have grant 

programs specifically to help 

communities implement CSO 

projects (EPA 2001a). These programs 

vary significantly in funding level 

and restrictions; many incorporate 

CWSRF loan funding. Most of these 

state programs are targeted at small 

The City of Lawton, Oklahoma, is using CWSRF loans along with utility rate increases 

to fund rehabilitation and replacement of the SSS. The project is separated into 

three 7-year phases. The first phase ends in 2004. By establishing a Sanitary Sewer 

Technical Division for design in May 1998 and a Construction Division in January 

1999, the city has been able to complete many of the tasks associated with this 

project on its own. While costs for Phase I were estimated to be $22 million, actual 

costs held to $16.8 million (see table below). This cost difference is the result of city 

efforts to use in-house designers and contractors. Actual costs for the remaining 

phases of this project are expected to be substantially lower.

Contract and Actual Costs for Lawton, OK SSS Rehablitation Project

Phase Contract 

Cost

Actual 

Cost

Projected 

Acutal 

Cost

SRF 

Loan

I $22M $16.8M -- $15M

II $37M -- $28M $28M*

III $40M -- ** --

 * Lawton has qualified for this loan but has not borrowed the money yet.

 ** It is too early for a projected cost for Phase III.
9-14

Report to Congress on the Impacts and Control of CSOs and SSOs

and/or economically disadvantaged 

communities, and often have fairly low 

funding levels. 

States with grant programs for CSO 

control include Connecticut, Vermont, 

and Maine. Connecticut established 

a CSO grant program in 1986 that 

provides grants for 50 percent of the 

federal eligible project costs, and a 

CWSRF loan at 2 percent interest for 

the remaining costs. Vermont has a 

similar program that requires a 25 

percent local match, provides a 25 

percent grant for construction costs, 

and allocates CWSRF loans for the 

remainder. Maine has a state bond 

issue for $2.4 million that funds grants 

awarded for 25 percent of the cost of 

development of CSO Master Plans, the 

functional equivalent of an LTCP.

State Grants for SSO Control

Oklahoma and North Carolina are 

examples of states with targeted grant 

programs, primarily aimed at making 

funding more readily available for 

rural areas, that have been used for 

SSO control projects. Oklahoma’s 

Water Resources Board administers 

the CWSRF, provides low-interest 

bonds, and provides competitive 

funding through a Rural Economic 

Assistance Program (REAP). REAP 

provides grants between $50,000 and 

$100,000 for towns with populations 

between 500 and 1,000. The state has 

awarded 379 REAP grants for a total 

of $32.7 million. North Carolina’s 

General Assembly funded a program 

of grants called the High Unit Cost 

Program through issuance of state 

bonds in 1987 and again in 1993.

Nowata, Oklahoma, secured $250,000 from the Community Development Block 

Grant Program and $79,000 from the Oklahoma REAP grant program to replace 

7,000 feet of failing sanitary sewer line. Prior to receiving the grants, Nowata was 

able to replace 3,000 feet of sewer. The city plans to replace an additional 3,000 feet 

in the next five years. The grants represented a significant source of funding to the 

Maintenance Department, which operates with a $190,000 annual budget.

State Grants for SSO 

Control:

Nowata, OK

Vermont’s grant program helped the Town of Springfield make CSO projects more 

acceptable to voters. The town recently finished a $4 million project for which it 

received $1 million in state grant funds and a 50-percent loan at close to zeropercent interest. In Rutland, the Commissioner of Public Works also stated that grant 

funds were beneficial and helped keep user rates down (EPA 2002d).

Connecticut’s state grant program for CSOs has provided $173 million to eight 

communities. Without this funding, the City of Hartford would have been unable 

to proceed with CSO control, because independently the city could not issue $80 

million in debt. The state grant program also allowed the City of New Haven to meet 

its 12 to 15-year schedule for the LTCP, and the program kept user rates below EPA’s 

affordability cap (EPA 2002d).

State Grants for CSO 

Control:

Hartford and 

New Haven, CT

State Grants for CSO 

Control:

Springfield and 

Rutland, VT
water and other nonpoint source 

pollutant loads are delivered to 

surface waters. This often makes 

it difficult to directly attribute 

specific water quality impacts to 

CSOs and SSOs. This suggests that 

a holistic approach should be used 

to address wet weather impacts. 

● There are many existing structural 

and non-structural technologies 

that are well-suited for CSO and 

SSO control. Implementation 

of emerging technologies 

and improved information 

management hold promise 

for increased effectiveness and 

efficiency. 

● Costs associated with the 

technologies for controlling CSOs 

and SSOs are often substantial. 

Planning is needed to spread 

costs over time, as appropriate, in 

developing comprehensive, longterm programs.

These findings are consistent with 

programmatic initiatives currently 

being implemented by EPA’s Office 

of Water. They correspond with 

emerging needs and the findings 

Chapter 10

This report has been prepared 

in response to a request by 

Congress for information 

related to CSOs and SSOs. EPA 

collected data and performed 

technical analyses to determine the 

environmental and human health 

impacts of CSOs and SSOs; the 

location, volume, frequency, and 

constituents of such discharges; the 

technologies used by municipalities 

to address CSOs and SSOs; and the 

resources spent by municipalities on 

CSO and SSO control.

In its preparation of this report, EPA 

found that: 

● The occurrence of CSOs and 

SSOs is widespread. CSOs and 

SSOs contain pollutants that 

are harmful to the environment 

and human health, and there is 

evidence that CSOs and SSOs 

may cause or contribute to 

environmental and human health 

impacts.

● CSOs and many SSOs are caused 

by wet weather conditions and 

occur at the same time that storm 

10-1

Protecting Infrastructure

Implementing the Watershed 

Approach

Improving Monitoring 

and Information-Based 

Environmental Management

Building Strategic 

Partnerships

Conclusions and 

Future Challenges

In this chapter:
10-2

Report to Congress on the Impacts and Control of CSOs and SSOs

of other recent studies such as the 

National Water Quality Inventory, the 

BEACH Program, the Gap Analysis, 

and the Clean Watersheds Needs 

Survey. Further, they support EPA’s 

position that discharges from urban 

areas—particularly wet weather 

discharges resulting from rainfall or 

snowmelt—continue to be significant 

contributors to water quality 

impairments nationwide. 

Current challenges for clean water 

encompass CSO and SSO control, and 

include: 

● Protection of existing 

infrastructure;

● Development, approval, and 

implementation of CSO LTCPs 

under the CSO Control Policy;

● Development and implementation 

of SSO controls;

● Implementation of Best 

Management Practices (BMPs) 

to reduce pollution from storm 

water runoff in accordance with 

EPA’s Storm Water Phase I and II 

Programs;

● Integration of wet weather 

programs to increase the value of 

monitoring, reporting, tracking, 

and permitting to support 

information-based environmental 

management;

● Coordination of permits on a 

watershed basis; and

● Maintenance of valued 

partnerships with key stakeholder 

groups.

Several initiatives and actions that will 

enable EPA, states, municipalities, and 

citizens at large to achieve success in 

meeting these future challenges are 

described below.

Protecting Infrastructure

S

ince 1972, EPA has worked to 

implement the Clean Water Act 

as it relates to the collection, 

conveyance, and treatment of 

wastewater. The national investment 

in municipal wastewater infrastructure 

has been substantial. This investment 

has resulted in water quality and 

human health improvements 

throughout the United States. Today, 

however, the nation’s wastewater 

infrastructure is aging and in need 

of attention. The continued ability of 

existing infrastructure to safeguard the 

clean water accomplishments realized 

since 1972 is at risk. Further, its ability 

to serve as the platform for future 

expansion of wastewater collection 

and treatment capacity is jeopardized.

Proper O&M of the nation’s sewers is 

integral to ensuring that wastewater 

is collected, transported, and treated 

at POTWs; and to reducing the 

volume and frequency of CSO and 

SSO discharges. Municipal owners 

and operators of sewer systems and 

wastewater treatment facilities need 

to manage their assets effectively 

and implement new controls, where 

necessary, as this infrastructure 

continues to age. Innovative responses 

from all levels of government and 

consumers are needed to close the gap.
 Chapter 10—Conclusions and Future Challenges

10-3

Implementing the Watershed 

Approach

CSOs and SSOs are two among 

many sources of pollution that 

can impact receiving water 

quality. The watershed approach is 

central to water quality assessments 

and the identification of control 

strategies that include all sources of 

pollution that affect water quality. 

The presence of sewer systems in 

most developed watersheds across 

the country underscores the potential 

for SSOs to affect water quality on 

a widespread basis. Similarly, the 

presence of CSOs in 32 states places 

them in many watersheds across the 

country. 

As described in this Report to 

Congress, CSOs and wet weather 

SSOs occur simultaneously with 

the generation of storm water and 

other forms of nonpoint source 

pollution, making it difficult to 

identify and assign specific causeand-effect relationships to observed 

water quality problems. Attainment 

and maintenance of water quality 

standards requires that appropriate 

attention is given to all sources. 

Better integration of all of EPA’s wet 

weather programs will provide for 

Sanitation District No. 1 of Northern Kentucky received an EPA grant to work 

with the State of Kentucky to develop a watershed permitting approach and to 

investigate the feasibility of implementing the approach. The District includes 

Campbell, Kenton, and Boone counties, and covers an area of 580 square miles. 

Located on the southern bank of the Ohio River, directly across from Cincinnati, 

Ohio, this three-county area contains approximately 40 incorporated cities, each 

with its own political and administrative structure. 

Prior to July 1995, the operation and maintenance of the sewer systems in these 

counties was the responsibility of the respective municipal jurisdictions. Ownership 

for most of the sewer systems in Northern Kentucky was transferred to the District in 

1995 as a result of revisions to state legislation. With this consolidation, the District 

became responsible for managing 1,400 miles of combined and separate sanitary 

sewers, one major wastewater treatment facility, eight small wastewater treatment 

facilities, and approximately 100 CSO outfalls. Recently, with the development of a 

regional facilities plan, the District has embarked on a program to construct two 

new regional wastewater treatment facilities at a cost of more than $200 million 

over the next 10 years. In addition, the District is responsible for implementing a 

CSO LTCP that includes an integrated watershed approach to planning and an 

SSO Plan (requested by the Kentucky Division of Water) to reduce the number of 

unauthorized discharges. 

At this time, the District and the Kentucky Division of Water have agreed to pursue 

additional dialog on the development of a draft watershed permit for Banklick 

Creek. This watershed was selected because it is impacted by urban storm water 

runoff, CSOs, SSOs, septic systems, and rural runoff. It should be noted that the 

District’s wastewater treatment plant does not discharge into the Banklick Creek 

watershed. The new watershed permit will enable the District to invest resources 

(time, labor, and money) more effectively in water quality improvement projects. 

The watershed permitting approach will also take advantage of the extensive 

database of water quality and GIS information that the District has compiled for 

its service area. Further, it provides an opportunity to consolidate monitoring and 

reporting activities.

Implementing the 

Watershed Approach: 

Kentucky
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Report to Congress on the Impacts and Control of CSOs and SSOs

some economies of scale in achieving 

this end. Similarly, concentration 

of resources under the watershed 

approach will help advance the control 

of CSOs and SSOs in a cost-effective 

manner. 

Improving Monitoring 

and Information-Based 

Environmental Management

I

n developing this Report to 

Congress, EPA found that 

the data necessary to answer 

many of Congress’ questions were 

limited. Improved monitoring 

and reporting programs would 

provide better data for decisionmakers to assess the frequency and 

magnitude of CSO and SSO events, 

the impact these discharges have on 

the environment and human health, 

and the importance of CSO and 

SSO discharges with respect to other 

pollution sources. 

Numerous federal, state, and local 

government agencies as well as nongovernmental organizations and 

citizens are involved in monitoring. 

Monitoring and reporting efforts 

include collection of water quality 

information, tracking impacts of 

known activities affecting water 

quality, linking water quality to human 

health, and other activities. Effective 

monitoring programs provide the data 

and information needed to support 

sound decision making. Too often, 

however, the monitoring data do not 

meet the needs of specific programs 

or are not readily available. Better 

alignment of monitoring programs to 

address environmental management 

and human health issues is needed. 

Improved monitoring and reporting 

may foster a better understanding of 

cause-and-effect relationships. It may 

also improve state/local government 

and citizen access to environmental 

information. 

Along with improved monitoring and 

reporting, data need to be effectively 

managed. Modernization of EPA’s 

PCS will help in this regard. Use 

of standardized reporting formats 

for information on the occurrence 

A cooperative effort between the Milwaukee Metropolitan Sewerage District 

(MMSD), the Wisconsin Department of Natural Resources, USGS, and several 

academic institutions resulted in the development of a single database for 

environmental data. The project team is compiling data sets from various federal, 

state, and local agencies in a centralized database of hydrology, water chemistry, 

macroinvertebrate, fish, habitat, and GIS information for stream corridors in the 

MMSD service area. The database is available on-line and allows the user to run 

queries and retrieve data currently in the system.

The database serves as a comprehensive inventory of stream corridor conditions, 

allowing for an improved understanding of the inter-relationship between the 

various types of data and establishing a baseline of existing conditions. Using these 

baseline conditions, impairments can be identified and assessed, and strategies can 

be developed to address the most significant problems. MMSD plans to use the 

database as a tool to prioritize future efforts to control CSO, SSO, and storm water 

discharges. Future data incorporated into the database will allow verification of 

improvements and identification of necessary adjustments or additional steps.

Improving Monitoring 

and InformationBased Environmental 

Management:

Wisconsin
 Chapter 10—Conclusions and Future Challenges

10-5

and control of CSOs and SSOs will 

enable EPA, states, and others to track 

pollutant loads and performance 

measures. Further, recent EPA efforts 

such as Watershed Assessment, 

Tracking, and Environmental ResultS 

(WATERS) are working to unite 

national water quality information 

that was previously available only from 

several independent and unconnected 

databases.

Building Strategic Partnerships

The success that the nation 

has achieved in improving 

water quality since passage 

of the Clean Water Act is due to the 

The Watershed Initiative for a Safer Environment (WISE) was started by the Cities 

of Elkhart, Mishawaka, and South Bend, Indiana. These cities have 102 CSO outfalls 

that discharge to 48 miles of the St. Joseph and Elkhart Rivers. Land use within the 

two-county area is 72 percent rural. Concentrations of E. coli in the main stem and 

at the mouths of the tributaries routinely exceed water quality standards. A single 

watershed tool was needed to educate the public and to assist in the selection of 

cost-effective strategies to reduce point and non-point pollutant sources, including 

CSOs. WISE utilized a stakeholder-driven approach to watershed planning involving 

numerous stakeholders, including:

• Indiana Department of Environmental Management 

• City of Elkhart Public Works & Utilities

• City of Goshen Wastewater Utility

• City of Mishawaka Wastewater Utility

• City of South Bend Wastewater Utility 

• Elkhart County Planning Division

• Jimtown Community School Corporation

• Juday Creek Task Force

• Local Farm Bureau Agency

• Michiana Area Council of Governments

• St. Joseph County Area Plan Commission

• St. Joseph County Surveyor

• St. Joseph and Elkhart County Health Departments

• St. Joseph and Elkhart County Soil and Water Conservation Districts

• Concerned citizens

WISE secured federal funding through the Clean Water Act 205(j) grant program 

to conduct coordinated river sampling and to develop a calibrated water quality 

model of the two rivers. WISE also expects to receive a 104(b)(3) grant in January 

2004 to continue development of the model, including:

• Isolating the sources of E. coli;

• Identifying additional types of appropriate controls;

• Displaying the anticipated improvements in river water quality from 

 different source controls along with the cost for implementation; and

• Evaluating whether refined water quality standards are appropriate.

This work will provide a single model that can be used in NPDES programs to 

further refine contaminant sources and assist in the selection of cost-effective 

strategies toward meeting, and possibly refining, water quality standards.

Strategic Partnerships:

Indiana
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Report to Congress on the Impacts and Control of CSOs and SSOs

collective efforts of federal and state 

agencies, municipalities, industry, 

non-governmental organizations, and 

citizens. Maintenance and enhancing 

existing cooperation among these 

groups is essential to meet the 

challenges to clean water that lie ahead. 

As described in this Report to 

Congress, threats to water quality 

and human health have numerous 

origins and sources; establishing direct 

cause-and-effect relationships is often 

difficult. The information necessary to 

manage water quality problems also 

comes from many sources. 

EPA recognizes the value of working 

with stakeholders and has pursued 

a strategy of extensive stakeholder 

participation in its policy-making 

on CSO and SSO issues. This 

effort should continue to improve 

knowledge on the impacts of CSOs 

and SSOs. Similarly, as communities 

continue to implement CSO and 

SSO controls, further cooperation 

with municipal, industry, and 

environmental organizations 

is essential to ensure successful 

development and implementation of 

environmental programs.
Appendix A 

Statutes, Policies, and Interpretive 

Memoranda

A.1 Consolidated Appropriations Act 

 for Fiscal Year 2001 (P.L. 106-554)

A.2 Combined Sewer Overflow 

 (CSO) Control Policy

A.3 Memorandum: Addition 

 of Chapter X to Enforcement 

 Management System

A.4 Enforcement Management 

 System–Chapter X: Setting 

 Priorities for Addressing 

 Discharges from Separate 

 Sanitary Sewers

 Appendix A

A-1
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A-2
 Appendix A

A-3
Report to Congress on the Impacts and Control of CSOs and SSOs

A-4
 Appendix A

A-5
Report to Congress on the Impacts and Control of CSOs and SSOs

A-6

 Chapter 1—Introduction
 Appendix A

A.-7
Report to Congress on the Impacts and Control of CSOs and SSOs

A-8
 Appendix A

A-9
Report to Congress on the Impacts and Control of CSOs and SSOs

A-10
 Appendix A

A-11
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A-12
 Appendix A

A-13
A-14

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix A

A-15

 March 7, 1996

MEMORANDUM

SUBJECT: Addition of Chapter X to Enforcement Management

 System (EMS): Setting Priorities for Addressing

 Discharges from Separate Sanitary Sewers

FROM: Steven A. Herman [SIGNED]

 Assistant Administrator

 

TO: Water Management Division Directors, Regions I-X

 NPDES State Enforcement Directors

 Regional Counsels, Regions I-X

 I am pleased to transmit to you a new chapter in final form 

for the Enforcement Management System (EMS) Guide. This new chapter 

provides a method of setting priorities for addressing discharges 

of untreated sewage from separate sanitary sewer collection systems 

prior to the headworks of a sewage treatment plant. Included with 

this chapter is an Enforcement Response Guide, specifically tailored 

to these types of discharges.

 I want to express my appreciation to those Regional, 

Headquarters, State personnel, and the members of the Federal 

Advisory Sub-Committee for Sanitary Sewer Overflows (SSO) who helped 

develop this document. The Advisory Sub-Committee reviewed it at 

two public meetings in August and October, 1995. The cooperation 

and hard work of all interested parties has produced this final 

document which I believe will help protect public health and the 

environment from these serious sources of water pollution.

 This guidance supplements the current EMS by establishing 

a series of guiding principles and priorities for use by EPA 

Regions and NPDES States in responding to separate sanitary sewer 

discharge violations. The guidance allows sufficient flexibility 

to alter these priorities based on the degree of public health 

or environmental risk presented by specific discharge conditions. 

Implementation of this guidance by EPA and the States will promote 

national consistency in addressing discharges from separate sanitary 

sewers. Implementation will also ensure that
Report to Congress on the Impacts and Control of CSOs and SSOs

A-16

- 2 -

enforcement resources are used in ways that maximize public health 

and environmental benefits. 

 The Regions should ensure that all approved States are aware 

of this additional EMS guidance, and the Regions and NPDES States 

should begin the process of modifying their written EMS documents 

to include it. Both Regions and States should have these documents 

revised and implemented no later that November 15, 1996.

 If you have questions about this document, please feel free to 

contact Brian J. Maas, Director, Water Enforcement Division (202/

564-2240), or Kevin Bell of his staff (202/564-4027). 

cc: Mike Cook, OWM
 Appendix A

A-17

THE ENFORCEMENT MANAGEMENT SYSTEM

NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM

(CLEAN WATER ACT)

CHAPTER X: Setting Priorities for Addressing Discharges 

from Separate Sanitary Sewers 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF REGULATORY ENFORCEMENT 

1996

ENFORCEMENT MANAGEMENT SYSTEM - CHAPTER X
Report to Congress on the Impacts and Control of CSOs and SSOs

A-18

Setting Priorities for Addressing Discharges from 

Separate Sanitary Sewers 

Discharges of raw or diluted sewage from separate sanitary 

sewers before treatment can cause significant public health and 

environmental problems. The exposure of the public to these 

discharges and the potential health and environmental impacts are 

the primary reasons EPA is developing this additional guidance on 

these discharges. This document provides a method of setting 

priorities for regulatory response, and serves as a supplement to 

the Enforcement Management System guidance (EMS, revised February 

27, 1986). As such, this document addresses only those 

discharges which are in violation of the Clean Water Act. As a 

general rule, the discharges covered by this guidance constitute 

a subset of all discharges from separate sanitary sewer systems. 

Legal Status 

In the context of this document, a "discharge from a 

separate sanitary sewer system" (or "discharge") is defined as 

any wastewater (including that combined with rainfall induced 

infiltration/inflow) which is discharged from a separate sanitary 

sewer that reaches waters of the United States prior to treatment 

at a wastewater treatment plant. Some permits have specific 

requirements for these discharges, others have specific 

prohibitions under most circumstances, and still other permits 

are silent on the status of these discharges. 

The legal status of any of these discharges is specifically 

related to the permit language and the circumstances under which 

the discharge occurs. Many permits authorize these discharges 

when there are no feasible alternatives, such as when there are 

circumstances beyond the control of the municipality (similar to 

the concepts in the bypass regulation at 40 CFR Part 122.41 (m)). 

Other permits allow these discharges when specific requirements 

are met, such as effluent limitations and monitoring/reporting. 

Most permits require that any non-compliance including 

overflows be reported at the end of each month with the discharge 

monitoring report (DMR) submittal. As a minimum, permits 

generally require that overflow summaries include the date, time, 

duration, location, estimated volume, cause, as well as any 

observed environmental impacts, and what actions were taken or 

are being taken to address the overflow. Most permits also 

require that any non-compliance including overflows which may 

endanger health or the environment be reported within 24 hours, 

and in writing within five days. Examples of overflows which may 

endanger health or the environment include major line breaks, 

overflow events which result in fish kills or other significant 

harm, and overflow events which occur in environmentally 

sensitive areas. 
 Appendix A

A-19

3

For a person to be in violation of the Clean Water Act: 

1) a person must own, operate, or have substantial control over 

the conveyance from which the discharge of pollutants occurs, 

2) the discharge must be prohibited by a permit, be a violation 

of the permit language, or not be authorized by a permit, and 3) 

the discharge must reach waters of the United States. In 

addition, discharges that do not reach waters of the United 

States may nevertheless be in violation of Clean Water Act permit 

requirements, such as those requiring proper operation and 

maintenance (O&M), or may be in violation of state law. 

Statement of Principles 

The following six principles should be considered as EPA 

Regions and States set priorities for addressing violating 

discharges from separate sanitary sewers: 

1. All discharges (wet weather or dry weather) which cause or 

contribute significantly to water quality or public health 

problems (such as a discharge to a public drinking water supply) 

should be addressed as soon as physically and financially 

possible. Other discharges may, if appropriate, be addressed in 

the context of watershed/basin plans (in conjunction with state 

or federal NPDES authorities). 

2. Discharges which occur in high public use or public access 

areas and thus expose the public to discharges of raw sewage 

(i.e., discharges which occur in residential or business areas, 

near or within parks or recreation areas, etc.) should be 

addressed as soon as physically and financially possible. 

3. Dry weather discharges should be addressed as soon as 

physically and financially possible. 

4. Discharges due to inadequate operation and routine 

maintenance should be addressed as soon as possible. (Physical 

and financial considerations should be taken into account only in 

cases where overflow remedies are capital intensive.) 

5. Discharges which could be addressed through a comprehensive 

preventive maintenance program or with minor capital investment 

should be addressed as soon as physically and financially 

possible.

6. With respect to principles 1 through 5 above, schedules of 

compliance which require significant capital investments should 

take into account the financial capabilities of the specific 
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4

municipality, as well as any procedures required by state and 

local law for publicly owned facilities in planning, design, bid, 

award, and construction. (See later sections on Schedules). 

Causes of Sanitary Sewer Discharges 

Discharges from separate sanitary sewers can be caused by a 

variety of factors including, but not limited to: 

1. Inadequate O&M of the collection system. For example, 

failure to routinely clean out pipes, failure to properly seal or 

maintain manholes, failure to have regular maintenance of 

deteriorating sewer lines, failure to remedy poor construction, 

failure to design and implement a long term replacement or 

rehabilitation program for an aging system, failure to deal 

expeditiously with line blockages, or failure to maintain pump 

stations (including back-up power). 

2. Inadequate capacity of the sewer system so that systems 

which experience increases in flow during storm events are unable 

to convey the sewage to the wastewater treatment plant. For 

example, allowing new development without modeling to determine 

the impact on downstream pipe capacity, insufficient allowance 

for extraneous flows in initial pipe design (e.g. unapproved 

connection of area drains, roof leaders, foundation drains), or 

overly optimistic Infiltration/Inflow reduction calculations. 

3. Insufficient capacity at the wastewater treatment plant so 

that discharges from the collection system must occur on a 

regular basis to limit flows to the treatment plant. For 

example, basic plant designs which do not allow sufficient design 

capacity for storm flows. 

4. Vandalism and/or facility or pipeline failures which occur 

independent of adequate O&M practices. 

Applicable Guidance 

For many years, EPA and the States have been working with 

municipalities to prevent discharges from separate sanitary sewer 

systems. The preferred method has been to use the general policy 

on responding to all violations of the Clean Water Act which is 

contained in the EMS guidance. Factors which are considered are 

the frequency, magnitude, and duration of the violations, the 

environmental/public health impacts, and the culpability of the 

violator. This guidance sets up a series of guiding principles 

for responding to separate sanitary sewer discharge violations, 
 Appendix A

A-21

5

and it supplements the current EMS. 

Every EPA Region and State uses some form of this general 

enforcement response guidance as appropriate to the individual 

state processes and authorities. Under the guidance, various EPA 

Regions and States have taken a large number of formal 

enforcement actions over the past several years to address 

sanitary sewer discharge problems across the country. Responses 

have included administrative orders and/or civil judicial actions 

against larger municipalities to address sanitary sewer discharge 

problems, resulting in substantial injunctive relief in some 

cases.

As a result of EPA Region and State enforcement efforts, a 

number of municipalities have invested substantial resources in 

diagnostic evaluations and designing, staffing, and implementing 

O&M plans. Other municipalities have undertaken major 

rehabilitation efforts and/or new construction to prevent 

sanitary sewer discharges. 

Priorities for Response 

There are approximately 18,500 municipal separate sanitary 

sewage collection systems (serving a population of 135 million), 

all of which can, under certain circumstances, experience 

discharges. Given this fact, the Agency has developed a list of 

priorities in dealing with the broad spectrum of separate 

sanitary sewer discharges to ensure that the finite enforcement 

resources of EPA and the States are used in ways that result in 

maximum environmental and public health benefit. However, these 

priorities should be altered in a specific situation by the 

degree of health or environmental risks presented by the 

condition(s).

In the absence of site-specific information, all separate 

sanitary sewer discharges should be considered high risk because 

such discharges of raw sewage may present a serious public health 

and/or environmental threat. Accordingly, first priority should 

be given within categories (such as dry weather discharges and 

wet weather discharges) to those discharges which can be most 

quickly addressed. The priority scheme listed below takes this 

into account by first ensuring that municipalities are taking all 

necessary steps to properly operate and maintain their sewerage 

systems. Corrective action for basic O&M is typically 

accomplished in a short time, and can yield significant public 

health and environmental results. 

Risk again becomes a determinant factor when conditions 
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6

warrant long term corrective action. The goal here should be to 

ensure that capital intensive, lengthy compliance projects are 

prioritized to derive maximum health and environmental gains. 

The priorities for correcting separate sanitary sewer 

discharges are typically as follows: 

1) Dry weather, O&M related: examples include lift stations or

pumps that are not coordinated, a treatment plant 

that is not adjusted according to the influent flow, poor 

communication between field crews and management,

infiltration/inflow, and/or pretreatment problems.

2) Dry weather, preventive maintenance related: examples include

pumps that fail due to poor maintenance, improperly calibrated

flow meters and remote monitoring equipment, insufficient

maintenance staff, deteriorated pipes, and/or sewers that are not

cleaned regularly.

3) Dry weather, capacity related: examples include an

insufficient number or undersized pumps or lift stations,

undersized pipes, and/or insufficient plant capacity.

4) Wet weather, O&M related: examples include excessive inflow

and/or infiltration (such as from improperly sealed manhole

covers), inadequate pretreatment program (i.e. excessive

industrial connections without regard to line capacity),

uncoordinated pump operations, treatment plant operation that is

not adjusted according to the influent flow, poor coordination

between field crews and management, illegal connections, and/or

no coordination between weather forecast authorities and sewer

system management.

5) Wet weather, preventive maintenance related: examples

include poor pump maintenance leading to failure, improperly

calibrated flow meters and remote monitoring equipment,

insufficient maintenance staff, and/or sewers that are not

cleaned regularly.

6) Wet weather, O&M minor capital improvement related: examples

include the upgrading of monitoring equipment, pumps, or computer

programs, and/or repair or replacement of broken manholes or

collapsed pipes.

7) Wet weather capacity, quick solution related: examples

include a known collection system segment that is a "bottleneck",

pumps beyond repair in need of replacement, and/or need for

additional crews or technical staff.
 Appendix A

A-23

7

8) Wet weather, capacity, health impact related requiring long 

term corrective action: examples include frequent discharges to 

public recreational areas, shellfish beds, and/or poor 

pretreatment where the total flow is large. 

9) Wet weather, capacity, sensitive area related requiring long 

term corrective action: examples include discharges to 

ecologically and environmentally sensitive areas, as defined by 

State or Federal government. 

Selecting A Response 

The appropriate regulatory response and permittee response 

for separate sanitary sewer discharges will depend on the 

specifics of each case. The regulatory response can be informal, 

formal, or some combination thereof. Typical regulatory 

responses include a phone call, Letter of Violation (LOV), 

Section 308 Information Request, Administrative Order (AO), 

Administrative Penalty Order (APO), and/or judicial action. The 

permittee response can range from providing any required 

information to low cost, non-capital or low capital improvements 

to more capital intensive discharge control plans. 

The attached chart lists some categories of separate 

sanitary sewer noncompliance along with the range of response for 

each instance. The chart is intended as a guide. The responses 

listed on the chart are not to be considered mandatory responses 

in any given situation. EPA and the States should use the full 

range of regulatory response options (informal, formal, or some 

combination thereof) to ensure that the appropriate response or 

remedy is undertaken by the permittee or municipality. All 

regulatory responses should be in accordance with the concept of 

the EMS regarding orderly escalation of enforcement action. 

Developing Compliance Schedules 

A compliance schedule should allow adequate time for all 

phases of a sanitary sewer discharge control program, including 

development of an O&M plan, diagnostic evaluation of the 

collector system, construction, and enhanced O&M. 

Municipalities should be given a reasonable length of time to 

develop schedules so they can realistically assess their 

compliance needs, examine their financing alternatives, and work 

out reasonable schedules for achieving compliance. Nevertheless, 

timelines for schedules should be as short as physically and 

financially possible. 

Short Term Schedules 
Report to Congress on the Impacts and Control of CSOs and SSOs

A-24

-------

8

In general, short term schedules would be appropriate for 

sanitary sewer discharges involving O&M problems, or where only 

minor capital expenses are needed to correct the problem. The 

schedule should have interim dates and a final compliance date 

incorporated in the administrative order or enforcement 

mechanism.

Comprehensive Discharge Control Schedules 

Comprehensive discharge control schedules should be used 

where specific measures must be taken to correct the discharges, 

and the measures are complicated, costly, or require a 

significant period of time to implement. If appropriate, these 

schedules should include the use of temporary measures to address 

high impact problems, especially where a long term project is 

required to correct the sanitary sewer discharge violation. 

When working with municipalities to develop comprehensive 

schedules, EPA Regions and States should be sensitive to their 

special problems and needs, including consideration of a 

municipality's financial picture. Factors that should be 

considered are the municipality's current bond rating, the amount 

of outstanding indebtedness, population and income information, 

grant eligibility and past grant experience, the presence or 

absence of user charges, and whether increased user charges would 

be an effective fund-raising mechanism, and a comparison of user 

charges with other municipalities of similar size and population. 

Physical capability should be considered when schedules are 

developed. Schedules should include interim milestones and 

intermediate relief based on sound construction techniques and 

scheduling such as critical path method. Compliance schedules 

should be based on current sewer system physical inspection data 

adequate to design sanitary sewer discharge control facilities. 

Schedules should not normally require extraordinary measures such 

as overtime, short bidding times, or other accelerated building 

techniques. Where possible, schedule development should be 

completed according to normal municipal government contracting 

requirements.

Financial capability should also be considered in schedule 

development, including fiscally sound municipal financing 

techniques such as issuing revenue bonds, staging bond issuance, 

sequencing project starts, sensitivity to rate increase 

percentages over time. 
 Appendix A

A-25

9

Note: The intent of this guidance is to aid the Regions and 

States in setting priorities for enforcement actions based on 

limited resources and the need to provide a consistent level of 

response to violations. This does not represent final Agency 

action, but is intended solely as guidance. This guidance is not 

intended for use in pleading, or at hearing or trial. It does 

not create any rights, duties, obligations, or defenses, implied 

or otherwise, in any third parties. This guidance supplements 

the Agency's Enforcement Management System Guide (revised 

February 27, 1986). 
Report to Congress on the Impacts and Control of CSOs and SSOs

A-26
 Appendix A

A-27
Appendix B 

Human Health Expert and Stakeholder 

Meeting Summaries

B.1 Summary of the August 14 - 15, 2002, 

 Experts Workshop on Public 

 Health Impacts of Sewer Overflows 

 (Abstract and Background)

B.2 Stakeholder Meeting Summary, 

 Washington, D.C.

B.3 Stakeholder Meeting Summary, 

 Huntington Beach, CA

 Appendix B

B-1

United States Office ofWastewater Management EPA 833-R-02-002 

Environmental Protection Washington, D.C. 20460 November 2002 

Agency www.epa.gov/npdes 

EPA Summary of the August 14 – 15, 2002, 

Experts Workshop on Public Health 

Impacts of Sewer Overflows 
B-2

Report to Congress on the Impacts and Control of CSOs and SSOs

Summary of the August 14 – 15, 2002, Experts Workshop on Public 

Health Impacts of Sewer Overflows 

Table of Contents

Abstract............................................................................................................................................1

Background......................................................................................................................................1

Rationale for the Workshop.............................................................................................................1

Opening Remarks.............................................................................................................................3

Review of Goals and Agenda ..........................................................................................................3

Overview of the 2001 and 2003 Reports to Congress .....................................................................5

The Public Health Chapter of the 2003 CSO/SSO Report to Congress:

Questions and Proposed Methods....................................................................................................8

Discussion Session 1: Characterizing Pathogens and Pollutants...................................................13

Discussion Session 2: Pathways of Exposure................................................................................22

Discussion Session 3: Open Discussion Session ...........................................................................25

Welcome and Structure of Day Two .............................................................................................26

Breakout Session A: Significance of the CSO and SSO Problem.................................................26

Breakout Session B: Options for the Current Study ......................................................................28

General Discussion ........................................................................................................................30

Final Comments and Next Steps....................................................................................................31

Appendices

Appendix A: Attendee List 

Appendix B: Agenda 

Appendix C: Clarifying Questions from Observers 

Appendix D: The Public Involvement Process for the 2001 and 2003 Reports to Congress 
 Appendix B

B-3

Abstract

In embarking upon the task of assessing the human health impact portion of Congress' request for 

a report on the impacts and control of sewer overflows in the United States, initial research 

revealed that relatively little data were available that linked waterborne illness or other exposures 

to combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs). In response to these 

challenges, EPA held a Public Health Impacts Experts Workshop on August 14 and 15, 2002. A

group of nine external and EPA experts in public health, epidemiology, and wastewater treatment 

attended the workshop. Observers included representatives of stakeholder groups and EPA 

personnel. This workshop did not constitute an advisory committee under the Federal Advisory 

Committees Act (FACA), but rather solicited individual opinions and provided a forum for 

information exchange related to this Report to Congress. 

Background

In the Consolidated Appropriations Act for fiscal year 2001, also known as the “Wet Weather 

Water Quality Act of 2000”or “2000 Amendments to the Clean Water Act” (CWA), Congress 

made several changes to the CWA regarding combined sewer overflows (CSOs) (P.L. 106-554). 

Among these changes was a requirement for the U.S. Environmental Protection Agency (EPA) to 

provide two Reports to Congress. The first report, Implementation and Enforcement of the 

Combined Sewer Overflow Control Policy (EPA 833-R-01-003), was delivered on January 29, 

2002. The second report, which is due to Congress on December 15, 2003, is to investigate: 

• The extent of the human health and environmental impacts caused by municipal 

CSOs and sanitary sewer overflows (SSOs), including the location of discharges 

causing such impacts, the volume of pollutants discharged, and the constituents 

discharged;

• The resources spent by municipalities to address these impacts; and 

• An evaluation of the technologies used by municipalities to address these impacts. 

Rationale for the Public Health Experts Workshop 

In embarking upon the task of assessing the human health impact portion of Congress’ request, 

initial research revealed that relatively little data were available that linked waterborne illness or 

other exposures to CSOs and SSOs. Factors complicating collection of information and data in 

this arena include public perception of reporting overflows in recreational areas; difficulty in 

contributing CSO/SSO loadings of pathogens in our nation’s waters from other background 

sources; multiple possible pathways for fecal-related illness; underreporting of certain types of 

waterborne illnesses; and a lack of comprehensive local or national tracking for such illnesses. 

1
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Report to Congress on the Impacts and Control of CSOs and SSOs

In response to these challenges, EPA held a Public Health Impacts Experts Workshop on August 

14 and 15, 2002. The purpose of this workshop was to enlist technical and subject matter experts 

from federal agencies, local health departments, and academia to ensure that EPA frames the 

study questions correctly, benefits from all pertinent data, and develops a methodology that bears 

out actual experiences. A group of recognized experts in the field of public health and interested 

observers met with the goals and objectives of: 

• Fully elucidating the issues and the magnitude of those issues associated with 

health impacts of CSOs and SSOs; 

• Reviewing and supplementing data and information sources identified to date; and 

• Critiquing the proposed methodology for gathering and analyzing the public health 

information and data for the 2003 report. 

The experts were asked to give individual opinions relating to the study questions. No consensus 

opinions or policy recommendations were solicited. 

This Public Health Experts workshop is part of a larger public involvement process for the 2001 

and 2003 CSO/SSO Reports to Congress. It occurs between two broader stakeholders’ meetings 

(June 2001 and summer 2003, anticipated), at which a broad range of stakeholders discuss and 

provide input on draft report findings and recommendations, experiences in CSO control, and 

future policy and program directions. For a more detailed discussion of the overall stakeholder 

approach, please refer to Appendix D of this summary. 

2
 Appendix B

B-5

2003 Report to Congress on the Impacts and Control of Combined Sewer 

Overflows and Sanitary Sewer Overflows

Stakeholder Meeting Summary

Washington, D.C. 

On June 23 and 24, 2003, the U.S. Environmental Protection Agency held a meeting in Washington, 

D.C., to discuss the upcoming Report to Congress on the impacts and control of CSOs and SSOs. The 

meeting held at the Renaissance Hotel, 999 9th St. NW, provided an opportunity for EPA to present the 

results of the data collection, request verification of information and data sources, and solicit feedback on 

preliminary findings and interpretation.

The main goals of the meeting were to:

● Discuss the data, report methodology, and analysis of the 2003 Report to Congress;

● Discuss implications of the major analyses in the report; and

● Discuss participants’ experiences in controlling impacts from CSOs and SSOs.

The summary below describes the presentations given to outline the contents of the report and recounts 

the resulting discussions. The summary is organized into the following major sections, which correspond 

to the meeting agenda:

● Opening Remarks

● Background on the Report

● Characterization of CSOs and SSOs

● Environmental Impacts of CSOs and SSOs

● Closing Remarks, Day One

● Recap of Day One and Agenda Review for Day Two

● Welcome and Opening Remarks, Day Two

● Human Health Impacts of CSOs and SSOs

● Technologies for CSO and SSO Control

● Resources Spent Addressing CSOs and SSOs

● Common Themes Heard During the Meeting

● Closing Remarks, Day Two 

Opening Remarks

James A. Hanlon – Director, Office of Wastewater Management, EPA

Mr. Hanlon opened the meeting by welcoming the participants to Washington, D.C., and providing 

an overview of the 2000 Wet Weather Water Quality Act, the 2001 CSO Report to Congress, and its 

associated stakeholder meeting. Mr. Hanlon reminded the participants that this Report was not intended 

to set policy, instead it was intended to present data and cite additional data sources that Congress 

could look to when entering into policy discussions. He mentioned that responding to the charge from 

Congress had proven difficult, specifically in identifying loadings and in correlating discharges with 

environmental and human health impacts.
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Report to Congress on the Impacts and Control of CSOs and SSOs

Background on the 2003 Report to Congress

Kevin DeBell – Office of Wastewater Management, EPA

Mr. DeBell presented the background to the 2003 Report to Congress. He started by mentioning 

the near-term EPA policies that directly led to the request for the 2003 Report to Congress. First, he 

described the 1994 National CSO Control Policy which formalized EPA’s management expectations for 

CSS communities. Next, a summary of the 2001 Report to Congress – Implementation and Enforcement of 

the Combined Sewer Overflow Control Policy was presented. This report acted as a program evaluation in 

which success of CSO Control Policy implementation was assessed; one useful product of the 2001 Report 

is the CSO database, which includes information on all CSO permits. Mr. DeBell then mentioned the 

draft SSO Notice of Proposed Rulemaking, and the 2000 Wet Weather Water Quality Act, which required 

the 2003 Report. The statutory requirements for the 2003 Report are stated below: 

The Administrator of the Environmental Protection Agency shall transmit to Congress a report 

 summarizing:

 a. the extent of human health and environmental impacts caused by municipal combined 

sewer overflows and sanitary sewer overflows, including the location of discharges causing 

such impacts, the volume of pollutants discharged, and the constituents discharged; 

 b. resources spent by municipalities to address these impacts; and 

 c. an evaluation of the technologies used by municipalities to address these impacts.

Mr. DeBell next explained that EPA is not required to have a public review of Reports to Congress, but 

that this particular program has a legacy of stakeholder collaboration, which EPA values. 

Finally, Mr. DeBell presented the report outline. The report is organized as follows:

● Introduction

● Background

● Methodology

● Characteristics of CSOs and SSOs

● Environmental Impacts of CSOs and SSOs

● Human Health Impacts of CSOs and SSOs

● Federal and State Actions to Control CSOs and SSOs

● Technologies Used to Reduce the Impacts of CSOs and SSOs

● Findings and Recommendations

Stakeholder Questions and Comments on the Background Presentation 

Questions and comments received after the background presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● Are data collected during the Report to Congress effort also being used to inform the SSO economic 

analysis?

● Is EPA still attempting to make an economic model to justify the SSO Rule, despite the fact that the 

public health experts (during the August 2002 Experts Workshop) said that an economic model was 

not feasible?

● In relation to municipalities’ actions on CSOs and SSOs, will the Report to Congress help 

municipalities prioritize resources spent on CSO/SSO versus other wet weather events?

● Regarding the Pretreatment Rule streamlining, enforcement of this rule may reduce the human health 

risks associated with CSOs and SSOs fed by industrial wastewater flows during wet weather. Has EPA 

consulted with municipalities regarding enforcement of this rule?

● Will the SSO/CSO data (compiled for both Reports to Congress) be publicly available? When? 

● Some stakeholders were worried about the lack of representation at the stakeholder meeting from 

certain stakeholder groups (i.e., NOAA and public health officials) and urged EPA to try to increase 

representation from each group.
 Appendix B

B-7

● A stakeholder pointed out that many enforcement actions and consent decrees are currently in place 

(for CSO and SSO violations), and wanted to ensure that these actions were represented in the report. 

Characterization of CSOs and SSOs

Kevin DeBell – Office of Wastewater Management, EPA

Mr. DeBell presented data on the location of CSO and SSO discharges, the volume of pollutants 

discharged, the constituents discharged, and the frequency of discharge events.

This presentation defined a CSO as a mixture of untreated sewage and storm water discharged from a 

combined sewer system at a point prior to the headworks of the POTW. Generally, CSOs occur during 

wet weather when the CSS becomes overloaded. SSO is defined as a discharge of untreated or partially 

treated wastewater from a sanitary sewer system at any point prior to the headworks of a POTW. Backups 

of wastewater to private property are not included in the definition of SSO used for this Report to 

Congress.

Data Sources for the Characterization Chapter

EPA used the following data sources to characterize CSOs and SSOs.

● State databases for tracking CSO and SSO events;

● NPDES permit files;

● Approximately 80 interviews with state and municipal officials;

● LTCPs and other capital improvement documentation; 

● Literature review; and

● Existing EPA documentation, including technical reports and products of cooperative 

agreements.

Key Research Questions for the Characterization Chapter

This presentation introduced three key research questions for the characterization chapter:

● How many NPDES permits exist for combined sewer systems and sanitary sewer systems?

● What are the common pollutants found in CSOs and SSOs?

● What are the volume, frequency, and location of CSOs and SSOs?

Stakeholder Questions and Comments for the Characterization Chapter

Questions and comments received after the characterization presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● With respect to the pollutants and pathogens found in CSOs and SSOs, specifically concentrations, 

stakeholders questioned the accuracy of the data presented in the meeting and asked that it be 

verified. Stakeholders identified possible data sources, including the Nationwide Urban Runoff 

Program and Hydraulic Characteristic Reports (needed for NPDES permits). 

● The concentrations of constituents within CSOs, SSOs, and storm water vary widely, depending 

on many factors, such as the amount of precipitation or sources contributing to the wastewater. 

Therefore, it is very difficult to present general characteristics. Stakeholders questioned whether CSOs 

and SSOs should be characterized in this fashion. Some suggested concentrating on specific and acute 

impacts.

● Stakeholders suggested that EPA take a look at “hot spots” or incidents of the most dangerous, 

concentrated CSOs and SSOs.

● Stakeholders suggested that EPA express to Congress what can be supported by available data– local, 

acute impacts can be terrible, while the national impact looks relatively small; both are very difficult 

to track or assess.
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Report to Congress on the Impacts and Control of CSOs and SSOs

● Stakeholders said the information presented in this section needed to be placed in the context of the 

environmental and human health impacts.

● Do not present data in aggregate format. For example, separate wet weather and dry weather SSO 

data.

● Characteristics of the receiving water need to be addressed.

● More specificity is needed. Add community data where available, including volume, cause, and 

receiving water information. A stakeholder thought that this would help Congress better understand 

why national data are and are not representative.

● Stakeholders asked for clarification of the charge from Congress. Was the directive to look at 

municipalities only or also at decentralized wastewater treatment systems?

● Stakeholders were concerned that describing the volume of current CSO discharges as “a large 

amount” would give Congress the impression that municipalities were not doing anything to correct 

the CSO problem.

● Were small communities contacted and interviewed in this methodology?

● A clarifying question was asked regarding the statistic on the amount of SSOs that reach waterbodies 

and how researchers were estimating the impact on sensitive areas.

● Concerns were raised about how information presented in this report was going to inform Congress’s 

decisions regarding wet weather policy as a whole.

Environmental Impacts of CSOs and SSOs

Julia Moore – Limno-Tech, Inc.

Ms. Moore began by defining “environmental impacts” as water quality, aquatic life, and aesthetic 

impacts that affect designated uses. Violations of water quality standards were used as an indicator 

for environmental impacts. While researching this chapter, EPA used previously completed national, 

state, and local assessments. Literature and web searches were performed and interviews with state and 

municipal officials were carried out. 

EPA sought to characterize types of environmental impacts from CSOs and SSOs. First, EPA presented 

ranges in concentrations of the constituents typically found in CSOs and SSOs. EPA presented the results 

of assessments of environmental impacts caused by CSOs and SSOs. EPA acknowledged that while beach 

closures and shellfish bed closures have been traced to CSOs and SSOs, the data are not complete. 

EPA described planned national assessments in which CSO outfall locations will be integrated with EPA’s 

WATERS database. This will allow CSO locations to be associated with information such as 303(d) 

impaired reaches and drinking water intakes.

Conclusions for the Environmental Impacts Chapter

EPA presented preliminary conclusions regarding the environmental impacts from CSOs and SSOs. 

These included:

 

● CSOs and SSOs contain pollutants that cause impairments to designated uses, as reported in 

national assessments.

● CSOs and SSOs can be a principal cause or a contributing cause of an environmental impact.

● National data are inconsistent in tracking CSOs and SSOs as a direct cause of impairment. 

● While data are not comprehensive, some national estimates of use impairment have been 

made.

● State and local examples of cause and effect exist where CSO and SSO reporting and tracking 

are undertaken.

EPA asked the stakeholders present at the meeting for additional information on documented 

environmental impacts from CSOs and SSOs.
 Appendix B

B-9

Stakeholder Questions and Comments on the Environmental Impacts Chapter

Questions and comments received after the environmental impacts presentation are summarized below. 

The comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● Need to put a greater emphasis on water quality impacts.

● Need to do a better job of conveying that the data are all anecdotal.

● Researchers have only presented suspicion of impacts. 

● Regarding the concentrations of metals in CSOs, some stakeholders commented that most metal 

contamination comes from storm water and that CSO controls would not make a difference.

● In the presentation, it was stated that dry weather SSOs were responsible for 7 percent of the total 

volume discharged annually. Stakeholders were interested in the characteristics of the other 93 

percent of the SSO events contributing to the volume to determine if dry weather overflows are a 

problem. 

● Some stakeholders expressed the opinion that in urban watersheds, current water quality standards 

are impossible to meet during wet weather and that even without CSO or SSO discharges, 

waterbodies would exceed water quality standards.

● Stakeholders questioned the source of pathogen data. They stated that municipalities would argue 

strongly against the source allocation and mentioned the new Santa Ana Regional Water Quality 

Control Board beach closure study in California, which attributed most beach closures to urban 

runoff. The stakeholders also mentioned the Four Mile Run TMDL study, in Virginia, in order 

to clarify pathogen source information. As a follow up to this comment, it was mentioned that 

stormwater may be impacted by cross-connections or SSOs.

● Stakeholders reiterated the need to characterize both dry and wet weather SSOs and CSOs, specifically 

stating that the sources of pathogens vary widely depending on whether the event takes place during 

dry weather or wet weather.

● A stakeholder commenting on the North Carolina example stated that none of the overflows 

highlighted in the presentation appeared to be attributed to wet weather.

● Stakeholders questioned the concentration of metals being contributed to receiving waters via CSOs.

● Regarding shellfish advisories, stakeholders commented that over 90 percent of these were due to 

stormwater, not CSOs. 

● Stakeholders challenged the research team to find fish kills that occurred during wet weather as a 

result of CSOs or SSOs. They doubted this had happened.

● Regarding the Ohio River study, stakeholders commented that urban runoff contributes more 

pollutants and pathogens than the CSOs, so removal of CSOs will not show different results.

● Stakeholders stated that many pathogen source studies performed to date showed that primary 

sources of pathogens were not of human origin (specifically mentioned studies in Chicago, Detroit, 

and Milwaukee). Other stakeholders disagreed, citing Lake Michigan studies.

● Stakeholders pointed out that constituents in CSOs and SSOs can vary. One stakeholder was 

particularly concerned about hospital sewage and radionuclide contamination.

● One stakeholder mentioned that it is still very difficult to attribute pathogens to their source. The 

stakeholder said that source tracking is still in the research stage and suggested that the technology be 

used to monitor CSOs and SSOs. The stakeholder did not agree that current data “show no human 

impact” and mentioned that some studies have shown higher human viral concentrations at overflow 

sites. 

● From a local perspective, stakeholders mentioned that there are other wet weather sources about 

which Congress needs to know in order to prioritize funding. Stakeholders wanted to know if this 

report would help Congress do that. 

● Stakeholders wanted to know what studies were chosen and why.

● Can we make gross estimates about how often CSOs or SSOs will push waterbodies into nonattainment?

● Regarding the amount of Great Lakes shoreline reported impaired, does EPA know the amount of 

shoreline assessed?
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Report to Congress on the Impacts and Control of CSOs and SSOs

● Regulations currently focus on the most easily regulated communities. There is much disagreement 

over how much implementing control regulations will cost. Will the Report to Congress help remedy 

this?

Closing Remarks, Day One

Benita Best-Wong – Office of Wastewater Management, EPA

Ms. Best-Wong stated that stakeholder comments would inform the report. She also reminded the 

audience that the report was not intended to cover all wet weather events and policy, and therefore, some 

of the stakeholder questions were beyond the scope of this report. Ms. Best-Wong then touched on the 

Office of Water’s watershed management approach, which focuses on many of the other issues raised 

during the first day.

Recap of Day One & Agenda Review for Day Two

Linda Manning – Facilitator, SRA International 

Ms. Manning described some of the main themes from the previous day, which centered around the 

accuracy of data. The themes included:

● Do not oversell the data or paint with too broad a brush;

● Get a local flavor; it is important to present local impacts;

● Fully explain the limitations in the data and be clear about the data gaps;

● Do not have interpretational bias;

● Be clear about the data gaps and provide the clear message that more data are needed;

● Make sure the report is useful by providing context and placing the issues in relation to other 

wet weather events;

● Acknowledge variability in the data; and

● Address big picture policy questions.

Welcome and Opening Remarks, Day Two

Ben Grumbles – Deputy Assistant Administrator for Water, EPA

Mr. Grumbles talked about the importance of the report as well as the importance of the stakeholder 

involvement process. He mentioned the challenges confronting the Office or Water in the 21st century 

and the resulting shift of EPA’s focus from point source controls to a more holistic watershed approach. 

Mr. Grumbles touched on the history of the Wet Weather Water Quality Act and Congress’s intention for 

the Report. He stressed the need for increased monitoring and data gathering to make more informed 

policy decisions. Mr. Grumbles addressed the following comments and questions from the stakeholders.

Question/Comment: Progress needs to be made regarding EPA’s policy on the blending of treated and 

partially untreated wastewater at POTWs during wet weather.

Response: EPA is very much engaged in the blending issue and asked the stakeholders to provide any 

information they have on the use of blending to manage wet weather flows.

Question/Comment: Too much government regulation and intervention runs the risk of dictating 

technology, which, in turn, may stymie development of innovative alternatives.

Response: The current EPA leadership is very sensitive to the danger of dictating too much and 

understands that EPA needs to be open-minded when considering technologies in order to achieve water 

quality standards. But, wet weather issues also need to be addressed. We will do our best to be cost 

effective and environmentally responsible.

Question/Comment: We currently have decades of data from California, yet will never have enough data. 
 Appendix B

B-11

Please do not continue to say that we lack enough data. Instead, take our collective knowledge and make 

conclusions carefully. Do not skew the data one way or the other.

Question/Comment: At the Expert Workshop, public health officials said that is was not feasible to make 

an economic argument for preventing SSOs. What is happening with the EA?

Response: EPA is looking to the report to inform policy decisions. 

Human Health Impacts of CSOs and SSOs

Greg Frey – SRA International

Mr. Frey began by introducing the key questions addressed in this chapter:

● What constituents of CSOs and SSOs cause human health impacts?

● Of what consequence are these impacts?

● Which exposure pathways are the most significant and what populations are most sensitive?

● What are the impediments to understanding the linkages between CSOs and SSOs, exposures, 

and the human health impacts?

● What is the institutional framework to assess and address potential human health impacts of 

CSOs and SSOs?

Mr. Frey explained that EPA first performed an extensive literature review. Then, EPA held an experts 

workshop in order to verify the accuracy of data already collected, find new sources, and ascertain an 

understanding of experts’ opinions of the human health impacts of CSOs and SSOs. EPA next performed 

a series of state and community interviews for the purpose of understanding local and state health agency 

staff’s opinions of the impacts of CSOs and SSOs and to characterize the current activities being carried 

out that address this potential threat.

Mr. Frey went on to present the range of human health symptoms resulting from exposure to the 

pollutants typically found in CSOs and SSOs. Next, Mr. Frey discussed exposure pathways and the groups 

facing the most frequent exposure, as well as the groups most sensitive to waterborne illnesses. 

Mr. Frey described the limitations of the major data sources used to identify and describe waterborne 

disease outbreaks, one potential indicator of human health impacts from CSOs and SSOs. He next 

presented local, site specific examples of outbreaks attributed to exposure to sewage in order to illustrate 

the potential for acute health impacts. 

Next, EPA outlined the challenges to identifying the human health impacts of CSOs and SSOs. These 

include:

 

● The lack of connectivity in the monitoring and reporting systems for CSO and SSO events, 

human exposures, and human health impacts.

● The difficulty identifying the source of pathogens.

● The difficulty in attributing disease outbreaks to specific CSO and SSO events.

● The fact that outbreak reporting to CDC is voluntary.

● The understanding that many people who become ill do not seek medical treatment due to 

the nature of such illnesses. 

● There are inconsistent probabilities of diagnoses within the health care system. 

● The general tendency towards underreporting. 

Conclusions for the Human Health Impacts Chapter

Finally, Mr. Frey identified the actions that are currently being taken by state and local governments 

to address the human health impacts from CSOs and SSOs and EPA’s preliminary conclusions. These 

include:
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Report to Congress on the Impacts and Control of CSOs and SSOs

● The pathogens and pollutants found in CSOs and SSOs have the potential to cause human 

health impacts. 

● Exposures to the pathogens and pollutants resulting from CSOs and SSOs occur, but are 

difficult to quantify. 

● Human health impacts from waterborne diseases are underreported. 

● Responsibilities for protecting human health from waterborne illnesses are distributed among 

many agencies and institutions.

Stakeholder questions and comments on the Human Health Impacts Chapter 

Questions and comments received after the human health presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● Regarding the Austin example, there are no CSOs in Austin, and since there is no source attribution, 

the slide on the predictive closings at Barton Springs makes the observer think that all the pathogens 

are due to CSOs or SSOs. Be careful which examples you use.

● Does EPA have data on bacterial concentrations in different effluents? If so, add it.

● In the slide that attempts to put the outbreaks of E. coli into perspective, shellfish pathways would be 

listed under foodborne, but actually may be exacerbated by an SSO or CSO issue.

● Why did EPA not include shellfish advisories for the Great Lakes?

● Remember to add specific information whenever possible. 

● Some stakeholders questioned whether the Brushy Creek, Texas, incident was related to an SSO. 

Because it was caused by a power failure, they did not think it was a good example. 

● Stakeholders debated how much disease and antibody production could be attributed to SSOs or 

CSOs (i.e., how may cases are from human sources). 

● Was the Milwaukee outbreak due to a CSO? If so, please clarify. 

● There is a Great Lakes Watershed pathogen source study underway, but it will not be completed in 

time to inform the Report to Congress.

● Stakeholders questioned the proportion of illness attributable to CSOs or SSOs and thought the 

presentation was misleading.

● Rather than stating that quantification of exposure is difficult, EPA should say why it is difficult. 

EPA has data about what is “coming out of the pipe” but needs to better understand receiving water 

characteristics. 

● Regarding the responsibilities slide, there has been a 25-year lag between legislation and the 

production of a comprehensive communication system. Will EPA state who should take responsibility 

for this?

● Are the pathogen measurements from the sediment or do they just represent the water column 

concentrations?

● Why did EPA not include aerosols as a pathway?

● Some stakeholders said that there is no way to attribute a portion of mercury loadings to CSOs and 

SSOs. 

● Has EPA found characteristics from the different agencies that lead to communication difficulties? 

● How do our pathogen concentrations compare to concentrations internationally? Should we 

be concerned with migration if pathogen concentration and type is partially dependent on 

demographics?

● Make sure that EPA’s findings are not biased. Everything presented in the report should be definitely 

attributed to CSOs and SSOs.

● How did EPA come up with those populations who are most frequently exposed to pathogens from 

CSOs and SSOs? It looks like the majority of illnesses are from drinking water.

● What about the risks to people who are exposed to mold after basement backups?

● Clarify difference between storm water and sewer overflows.

● There is potential to contract the SARS virus from CSOs that are contaminated with hospital waste.

● Include all state and community interviews in the Report to Congress, giving specific examples.

● There have been thousands of beach water samples that show CSOs are not a problem. Attainment 

issues are wet weather problems.
 Appendix B

B-13

● Beach closures are based on a 24-hour time lag from the time the sample is collected. There have 

been 150-200 closures in Indiana and yet no one has reported sicknesses (despite this time lag); 

therefore, the indicators are wrong.

● Need to remove the fish advisories from PCBs and mercury since these constituents are not in CSOs 

and SSOs.

● Make a distinction between events occurring during dry weather and wet weather.

● Maybe drinking water monitoring and treatment should be improved, rather than spending on CSO 

and SSO controls. 

● How would proper enforcement of the long-term surface drinking water rule address 

Cryptosporidium issues, especially since so much is attributable to animals?

● Two percent of beach closures are due to CSOs. This may mislead people, since CSOs are 

concentrated geographically and therefore the local impacts may be much more significant. 

● The report should comment on the relative risks of human versus non-human bacteria. 

Technologies for CSO and SSO Control

Kevin DeBell – Office of Wastewater Management, EPA 

Mr. DeBell described the key data sources for the technology chapter. These included:

● Extensive literature reviews of existing EPA documentation as well as other sources;

● Interviews with municipal officials; 

● Meetings with key EPA staff; and

● Informal peer review by internal and external experts.

Key Questions for the Technologies Chapter

Mr. DeBell introduced the key questions that were addressed:

● What technologies have been used by municipalities to control CSOs and SSOs?

● What factors influence the effectiveness of these technologies?

● Have there been any recent technological innovations in the control of CSOs and SSOs?

While researching this chapter, EPA identified common and promising technologies used by 

municipalities to address CSOs and SSOs. From this research, EPA developed technology descriptions 

summarizing available technologies and factors influencing their effectiveness. Mr. DeBell explained that 

it is very difficult to compare certain types of technologies, as they are designed to deal with different 

aspects of wet weather challenges. Therefore, the technologies were not ranked for effectiveness against 

each other within this chapter. 

Presentation of Technologies

Mr. DeBell said that a wide range of technologies are available and that, within the report, they had been 

grouped into five key categories:

● Operations and maintenance activities;

● Collection system controls;

● Storage facilities;

● Treatment technologies; and 

● Low impact development techniques. 

Mr. DeBell mentioned that EPA developed case studies on each of the researched technologies, and 

presented preliminary findings pertaining to the relative cost of implementing the systems, the type 

of system for which the technology was designed, and the pollutants or problems controlled by the 

technology.
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Report to Congress on the Impacts and Control of CSOs and SSOs

Stakeholder Questions and Comments on the Technologies Chapter

Questions and comments received after the technologies presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● This information is not useful from a policy perspective, as it does not evaluate the technologies. 

At least “tell the story” on a community basis. Things that should be included in these evaluations 

include volume, flow, constituents, what the community did to address the problem, results, etc.

● Available technologies are dependent on what EPA allows communities to use, so defining the 

technology type takes decisions out of municipalities’ hands.

● How will the technology clearinghouse be managed?

● What about technologies used for satellite facilities?

● What about blending technologies?

● Most of the technologies were better suited to combined sewer systems. Stakeholders were concerned 

that SSO control was not looked at extensively enough.

● Some pollution prevention activities should be the responsibility of the individual and not the 

municipality, but municipalities still have to enforce the regulations and the ultimate responsibility is 

theirs.

● EPA needs to get more specific. This report needs a discussion of the effectiveness of technologies. 

● EPA needs to add data on collateral damage from implementing technologies, for example, in- or offline storage can lead to contamination of groundwater.

Resources Spent on CSO and SSO Control 

Kevin DeBell – Office of Wastewater Management, EPA

 

Mr. DeBell outlined the methodological approach to this chapter which included:

● Data analysis which tabulated information of past investments in clean water infrastructure 

and compiled information on what has been spent on CSO and SSO control. 

● EPA’s estimate of the investment needed to meet the current requirements for CSO and SSO 

controls.

● EPA’s acknowledgement of the fact that costs of CSO and SSO control are borne almost 

exclusively by local governments and utilities but local governments and utilities have not 

been requested to report the costs incurred for CSO and SSO control.

Stakeholder Questions and Comments on the Resources Chapter

Questions and comments received after the resources presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● EPA cited funding of $9.1 billion in 1980 (in the presentation) – the stakeholder believed that 

Congress never appropriated more than $2.4 billion through construction grants.

● All State Revolving Funds money has to be paid back, so these really are local expenditures, not 

federal. 

● At least one community had money earmarked from the federal government. EPA needs to 

distinguish between local and federal expenditures.

● EPA should do an analysis of per capita costs. 

● Stakeholders questioned the term “significant” with respect to past grant funding.

● Emphasize the need for grants to move things forward, especially for communities with small 

populations. Expanding grant money to small communities can result in huge benefits to water 

quality.

● The “knee of the curve” diagram is right on target. EPA needs to understand that it is not cost 

effective to eliminate all overflows. EPA should understand how the level of CSO control compares 
 Appendix B

B-15

to water quality – four overflows per year would be cost effective and we would have improved water 

quality (provided that we capture the first flush). See Akron Regional Sewer District for more “knee 

of the curve” information. 

● Make sure to reflect what caused the environmental benefits. Is it CSO and SSO prevention or 

controls for other wet weather events?

● There are many agencies and organizations that have done financial analyses, including the Army 

Corps of Engineers

● The reference to EPA’s Gap Analysis is good. Stakeholders suggested that EPA include a summary of 

the Gap Analysis in this report. 

● EPA should reference growing interest in a clean and safe water trust fund.

● Qualify the reference to 106 grants and how they contribute to CSO or SSO control. 

● Community cost estimates are larger than in the Gap Analysis. Will both be reflected in the report?

● Distinguish between points of fact and policy suggestions.

● In the presentation, the Gap Analysis information was presented two different ways, make sure that 

this information is presented in such a way that it can be compared. Use a common denominator. 

● All of the analysis is based on anecdotal evidence; there are no real data. 

● Put numbers in the context of per capita flow and the time frame of the project. 

● Estimates will be different if blending is allowed. EPA should indicate the difference in cost if 

blending is allowed.

● A goal of the CSO Control Policy was to move forward with realistic plans and make sure that they 

are economically sound.

 

Common Themes Heard During the Meeting

The following comments are paraphrases and summaries of actual stakeholder comments that emerged at 

many points throughout the meeting. They reflect recurring themes. Because the statements came from 

different stakeholders at the meeting, there are conflicts and disagreements among them. Additionally, all 

of the comments listed below are stakeholder opinion(s) and may not reflect EPA’s position.

Specific Policy and Program-Related Questions and Comments

● The report should help municipalities prioritize resources spent on CSOs and SSOs versus 

other wet weather events.

● The report should help Congress make more informed decisions about wet weather issues 

and other water quality issues as a whole, not just look at CSOs and SSOs in a vacuum.

● The report should help Congress prioritize funding for wet weather issues.

● The report states that there is a significant lag (25 years) between the development of water 

quality laws and the comprehensive communication system regarding detecting, reporting 

and tracking waterborne diseases related to water quality issues. 

● Are data collected during the Report to Congress effort also being used to inform the SSO 

economic analysis?

● Enforcement of the Pretreatment Rule may reduce the human health risks associated with 

CSOs and SSOs, which include an industrial wastewater component. This was brought up 

with regard to hospital waste. 

● Does EPA have an understanding of the total costs of all of the regulations that are coming?

● Are all wet weather events extreme events? What are acceptable levels of discharge?

Across the presentations, there were questions related to the completeness, accuracy, and representation 

of the information and data. While some of the comments are a product of the limited amount of 

information that can be conveyed in presentation format during a two-day meeting, they are all included 

here. All of the comments listed below are stakeholder opinion(s) and may not reflect EPA’s position.

● Make sure that the data EPA uses are as current, correct, and complete as possible. When 

a clear source of information is not apparent, feel free to provide Congress with conflicting 

data, but explain them.
B-16

Report to Congress on the Impacts and Control of CSOs and SSOs

● Make sure that data are unbiased in selection and presentation. On one hand, make sure 

that EPA does not lead the reader to draw unsupported conclusions of the negative impacts 

of CSOs and SSOs – avoid guilt by association. On the other hand, do not limit inclusion of 

information and data to national-scale, complete data sets. Local information and experience 

is valuable. 

● Draw conclusions that are appropriate for the scale of the available data. 

● Whenever possible, provide ranges in your data and interpretations in order to adequately 

describe the variability. All data should be transparent and the reader should be able to 

understand how EPA is using the data.

● Provide context to your information. For example, if the report states that something is 5 

percent of something else, make sure that the overall universe is clear.

● Describe data in a manner that is useful to Congress, municipalities, and other stakeholders.

● Because the data are so variable and include so much anecdotal evidence, it is important to 

present it in a useful way. While there may not be enough information to completely inform 

policy decisions, there are conclusions that EPA should draw to help Congress, municipalities, 

and other stakeholders understand the data presented. One of the biggest findings of this 

report may be that we have a serious lack of data and an incomplete picture.
 Appendix B

B-17

Report To Congress

Stakeholder Meeting Attendee List

Washington D.C.

June 24-25, 2003

 

Name, Office/Organization

Angela Akridge, Louisville & Jefferson County Metropolitan Sewer District

David Baron, Earthjustice

Benita Best-Wong, USEPA

Steve Bieber, Metropolitan Washington Council of Governments

Joe Boles, New Iberia (Louisiana) Municipal Government 

Karl Boone, ADS Corporation

Linda Boornazian, USEPA

Walter Brodtman, USEPA

Jason Brooks, Knoxville Utilities Board

Ted Brown, Center for Watershed Protection of Ellicott City MD

Thomas Brueckner, Narragansett Bay Commission 

Deb Caraco, Center for Watershed Protection of Ellicott City MD

Sharie Centilla, USEPA

Shellie Chard McClary, Oklahoma Department of Environmental Quality

John Chorlog, Miami-Dade County Water and Sewer Department

Victoria Cluck, Indianapolis Department of Public Works

Gary Cohen, Hall & Associates

Hubert Colas, BPR CSO

Anna Collery, Engineering Field Activities (EFA) Chesapeake

Lamont “Bud” Curtis, The TAF Group

Kimberly V. Davis, Hazen and Sawyer

Kevin DeBell, USEPA

Mike Domenica, Black & Veatch

Gary A. DuVal, City of Richmond Public Utilities

Janet Faulk, New Iberia (Louisiana) Municipal Government 

Erin Flanagan, Rockefeller Family Fund

Ruth Fontenot, New Iberia (Louisiana) Municipal Government 

Peter Fortin, City of Norfolk, VA 

Tom Franza, San Francisco Public Utilities Commission

Greg Frey, SRA

Wil Garland, ADS Corporation

Heather Gewandter, SRA

Paul Greenfield, University of Queensland

Frank Greenland, Northeast Ohio Regional Sewer District

Ben Grumbles, USEPA

Ahmad Habibian, Ph.D., P.E., Black & Veatch Corporation

Art Hamid, MWH Americas, Inc.

Jim Hanlon, USEPA

Eric M. Harold, P.E., Buchanan Street Consulting

Marvin Hayes, Parsons

Jim Heist, CDS Technologies Inc.

Roy A. Herwig, Brown and Caldwell

John Hills, Irvine Ranch Water District

Bud Hixson, Friends of Beargrass Creek

Lisa E. Hollander, Northeast Ohio Regional Sewer District

Chris Hornback, AMSA 

Carol Hufnagel, Tetra Tech

J. Leonard Ignatowski, P.E., EFA Chesapeake
B-18

Report to Congress on the Impacts and Control of CSOs and SSOs

Rick Karasiewicz, PBS&J

Rachel Katonak, Michigan State University

Ifty Khan, Wastewater Collection Division, DPWES

Don Killinger, Cuyahoga County Board of Health

Carol Kocheisen, National League of Cities

Fred Krieger 

Jane Lavelle 

Norman E. LeBlanc, Hampton Roads Sanitation District

Stewart T. Leeth, McGuireWoods LLP

Carol Leftwich, Environmental Council of the States

Roger Lemasters, Tennessee Department of Environment and Conservation

Federico Maisch, Greeley and Hansen LLC

Linda Manning, SRA

George L. Martin, Greenwood Metropolitan District

Bob Matthews, CDM, Inc

Michael J. McCabe, Milwaukee Metropolitan Sewerage District

Nate McConoughey, Cuyahoga County Board of Health

Jane McLamarrah, MWH

Heather McTavish, American Public Works Association

James B. Meyer, Meyer & Wyatt, P.C.

Sarah Meyland, Citizens Campaign for the Environment 

Peter Moffa, Brown and Caldwell

Julia Moore, Limno-Tech, Inc. 

John Murphy, P.E., City of Bangor

Gary Nault, United States Air Force

Sharon Nicklas 

Paul Novak, U.S. Environmental Protection Agency, Ohio

Jan Oliver, Allegheny County Sanitary Authority (ALCOSAN)

Laurel O’Sullivan, Lake Michigan Federation

Betsy Otto, American Rivers

Karen L. Pallansch, Alexandria Sanitation Authority

Stacy Passero, P.E., Water Environment Federation

Tom Ripp, USEPA

J. Alan Roberson, P.E., American Water Works Association

Dr. Joan Rose, Michigan State University

Nelson Ross, Tennessee Izaak Walton League

Lesley Schaaff, U.S. Environmental Protection Agency

Nancy Schultz, CH2M

Eric Seaman, Department of Natural Resources

Michael J. Sharp, Sonny Callahan and Associates, LLC

Mohsin R. Siddique, DC Water and Sewer Authority

Nancy Stoner, Natural Resources Defense Council

Mike Sullivan, Limno-Tech, Inc.

Chris Swann, Center for Watershed Protection of Ellicott City MD

Rod Thornhill, White Rock Consultants

Peter Trick, SRA

Betsy Valente, Limno-Tech, Inc.

Tara Van Atta, SRA

Lynn Vendinello, EPA, Evaluation Support Division

Mark G. Wade, P.E., Wade & Associates, Inc.

Robert C. Weaver, Kelly & Weaver, P.C.

Neil Weinstein, The Low Impact Development Center, Inc. 

Nancy Wheatley, Water Resources Strategies
 Appendix B

B-19

Clyde Wilber, Greeley and Hansen LLC

Gus Willis, CDS Technologies Inc.

George Zukovs, XCG Consultants Ltd.

 
B-20

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix B

B-21

2003 Report to Congress on the Impacts and Control of Combined Sewer 

Overflows and Sanitary Sewer Overflows

Stakeholder Meeting Summary

Huntington, CA

On July 8, 2003, the U.S. Environmental Protection Agency held a meeting in Huntington Beach, 

California, at the Huntington Beach Public Library to discuss the upcoming Report to Congress on the 

impacts and control of CSOs and SSOs. The meeting provided an opportunity for EPA to present the 

results of the data collection, request verification of information and data sources, and solicit feedback on 

preliminary findings and interpretations.

The main goals of the meeting were to:

● Discuss the data, report methodology, and analyses for the 2003 Report to Congress;

● Discuss implications of the major analyses in the report; and

● Discuss participants’ experiences in controlling impacts from CSOs and SSOs.

The summary below describes the presentations that outline the contents of the Report to Congress and 

the resulting discussions. The summary is organized into the following major sections which correspond 

to the meeting agenda:

● Welcome

● Goals and Agenda for the Meeting

● Background on the Report

● Characterization Presentation

● Environmental Impacts Presentation

● Human Health Presentation

● Resources Spent Addressing CSO and SSO Issues

● Technology Presentation

● Presentation of Stakeholder Comment and Question Themes

 

 

Welcome

Benita Best-Wong – Office of Wastewater Management, EPA

Ms. Best-Wong thanked the Orange County Sanitation District for alerting EPA to the region’s interest 

in the Report to Congress. She mentioned that this meeting was the second of two – the first was held in 

Washington, D.C., the previous week. She next answered some of the questions that were repeatedly heard 

at the previous meeting but would not be covered during the presentations. 

Ms. Best-Wong gave updates on the blending issue, the SSO Rule, and the Storm Water Phase II Rule.

Ms. Best-Wong next touched on the desire of Assistant Administrator for Water, Tracy Mehan, to ensure 

policy that facilitates a watershed approach. He would like EPA to focus on efficient ways of doing things 

and be aware of areas where EPA can help municipalities economize and make the best decisions possible. 

She went on to say that EPA hopes to focus on environmental outcomes, such as water quality and 

swimmer safety, and not outputs. She reminded the participants that the information gathered for this 

report forms a baseline and is something from which to work. EPA hopes that the report can be used not 

only to inform decision making but also for stakeholders to use as a resource.
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Report to Congress on the Impacts and Control of CSOs and SSOs

Goals and Agenda for the Meeting

Linda Manning – Facilitator, SRA International

Ms. Manning began by setting “ground rules” for the meeting. The ground rules were as follows:

● Do not repeat points. This meeting is simply a way to collect perspectives and the number of 

times a comment was made will not be presented.

● Remember that participants are only being presented with representational data.

● Please provide us with additional information sources.

● Remember that this is the first effort to pull together all available information on this topic. 

The data are incomplete. 

Background on the 2003 Report to Congress

Kevin DeBell – Office of Wastewater Management, EPA

Mr. DeBell presented the background to the 2003 Report to Congress. He started by mentioning 

the near-term EPA policies that directly led to the request for the 2003 Report to Congress. First, he 

described the 1994 National CSO Control Policy which formalized EPA’s management expectations for 

CSS communities. Next, a summary of the 2001 Report to Congress – Implementation and Enforcement 

of the Combined Sewer Overflow Control Policy was presented. This report acted as a program evaluation 

in which success of CSO Control Policy implementation was assessed; one useful product of the 2001 

Report is the CSO database, which includes information on all CSO permits. Mr. DeBell then mentioned 

the draft SSO Notice of Proposed Rulemaking, and the 2000 Wet Weather Water Quality Act, which 

required the 2003 Report. The statutory requirements for the 2003 Report are stated below: 

The Administrator of the Environmental Protection Agency shall transmit to Congress a report 

summarizing:

a. the extent of human health and environmental impacts caused by municipal combined sewer 

overfl ows and sanitary sewer overfl ows, including the location of discharges causing such 

impacts, the volume of pollutants discharged, and the constituents discharged; 

b. resources spent by municipalities to address these impacts; and 

c. an evaluation of the technologies used by municipalities to address these impacts.

Mr. DeBell next explained that EPA is not required to have a public review of reports to Congress, but 

that this particular program has a legacy of stakeholder collaboration, which EPA values. 

Finally, Mr. DeBell acknowledged the research team and presented the report outline. The Report to 

Congress is organized as follows:

● Introduction

● Background

● Methodology

● Characteristics of CSOs and SSOs

● Environmental Impacts of CSOs and SSOs

● Human Health Impacts of CSOs and SSOs

● Federal and State Actions to Control CSOs and SSOs

● Technologies Used to Reduce the Impacts of CSOs and SSOs

● Findings and Recommendations

Stakeholder Questions and Comments on the Background Presentation 

Questions and comments received after the background presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.
 Appendix B

B-23

● Is EPA taking this opportunity to weigh in on the blending rule?

● In the Wet Weather Water Quality Act of 2000, is there a context for larger wet weather events in the 

act language?

Characterization of CSOs and SSOs

Kevin DeBell – Office of Wastewater Management, EPA

Mr. DeBell presented data on the location of CSO and SSO discharges, the volume of pollutants 

discharged, the constituents discharged, and the frequency of discharge events.

This presentation defined a CSO as a mixture of untreated sewage and storm water discharged from a 

combined sewer system at a point prior to the headworks of the POTW. Generally, CSOs occur during 

wet weather when the CSS becomes overloaded. SSO is defined as a discharge of untreated or partially 

treated wastewater from a sanitary sewer system at any point prior to the headworks of a POTW. 

Backups of wastewater to private property are not included in the definition of SSO used for this Report 

to Congress.

Data Sources for the Characterization Chapter

EPA used the following data sources to characterize CSOs and SSOs.

● State databases for tracking CSO and SSO events;

● NPDES permit files;

● Approximately 80 interviews with state and municipal officials;

● LTCPs and other capital improvement documentation; 

● Literature review; and

● Existing EPA documentation, including technical reports and products of cooperative 

agreements.

Key Research Questions for the Characterization Chapter

This presentation introduced three key research questions for the characterization chapter:

● How many NPDES permits exist for combined sewer systems and sanitary sewer systems?

● What are the common pollutants found in CSOs and SSOs?

● What are the volume, frequency, and location of CSOs and SSOs?

Stakeholder Questions and Comments for the Characterization Chapter

A list presenting the questions and comments received after the characterization presentation are 

summarized below. The comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● The term “basement backup” is misleading. EPA should replace it with “private property” backup, as 

many areas of the county do not have basements. The critical link in this phenomenon is the laterals. 

Private citizens do not know how to clean the laterals and plumbers do not report the problem.

● EPA needs to highlight the lack of consistency between different jurisdictions. There is no baseline 

for SSO reporting. It is important to let Congress understand that this information is missing. 

● Look at WERF reports for other estimates on pollutant concentrations and other CSO/SSO 

characteristics. 

● Differentiate between major and minor sources. 

● Make sure to assess benefits versus the costs of elimination, so that we know where we can best put 

our resources to help the environment. 

● Can the federal government fund this collection system program like they did for secondary 

treatment? Municipalities cannot do it. 

● Stakeholders commented that communities had SSO tracking systems. 
B-24

Report to Congress on the Impacts and Control of CSOs and SSOs

● How were sewer systems rated in the report? Some stakeholders wanted to know if they would be 

able to see how their system compared to a national average. 

● Characterize SSO by volume per 100 miles of pipe in order to compare systems. 

● Present SSO events by cause. EPA may also want to break out events regionally. Doing this will help 

identify extreme weather events.

● SSO should only be defined based on what agencies are responsible for (i.e., agencies are not 

responsible for all laterals).

● It will be very difficult to compare systems nationally, due to the differences in reporting 

requirements.

● In the slides, how do the volume and frequencies of SSOs compare to the amount of sewage 

collected? 

● Is EPA distinguishing between the SSO effluent that actually gets to surface water versus how much is 

collected and disposed of properly? 

● Does EPA have details about how many of the SSOs in the database were due to wet weather and I/I?

● It is not possible to design sewers based on every potential storm event. The report should address 

what can not be contained in the system. 

● The conclusion “On a local scale, pollutant loads from CSOs and SSOs can be significant”– the 

opposite can also be true. On a local scale, pollutant loads may not have significant impacts. 

● Regarding reporting thresholds, maybe there is a reason for thresholds, the report should discuss the 

rationale. 

● Excluded from the study is storm water, but a significant source of pathogens found in storm water 

are from SSOs.

● Need to understand the water quality issues in receiving waters. 

● In the SSO database, has EPA identified repeated, chronic, or preventable spills? Sewage collection 

agencies are responsible for these incidents and they need to correct them. This type of spill may 

skew or misrepresent the real problem. 

● EPA could describe money spent versus pipe miles versus spills to compare communities.

● What percent of the spills reach receiving waters? A stakeholder said that during wet weather, very 

little of the amount spilled was contained, but during dry weather most was contained.

● Stakeholders mentioned that flood control systems are designed to withstand 195-year floods but 

there are no standards for sewer systems.

● Stakeholders said that the report needed to focus on impacts and focus on specifics.

Environmental Impacts of CSOs and SSOs

Hans Holmberg – Limno-Tech, Inc.

Mr. Holmberg began by defining “environmental impacts” as water quality, aquatic life, and aesthetic 

impacts that affect designated uses. Violations of water quality standards were used as an indicator 

for environmental impacts. While researching this chapter, EPA used previously completed national, 

state, and local assessments. Literature and web searches were performed and interviews with state and 

municipal officials were carried out. 

EPA sought to characterize types of environmental impacts from CSOs and SSOs. First, EPA presented 

ranges in concentrations of the constituents typically found in CSOs and SSOs. EPA presented the results 

of assessments of environmental impacts caused by CSOs and SSOs. They acknowledged that while 

beach closures and shellfish bed closures have been traced to CSOs and SSOs, the data are not complete. 

EPA described planned national assessments in which CSO outfall locations will be integrated with EPA’s 

WATERS database. This will allow CSO locations to be associated with information such as 303(d) 

impaired reaches and drinking water intakes.
 Appendix B

B-25

Conclusions for the Environmental Impacts Chapter

EPA presented preliminary conclusions regarding the environmental impacts from CSOs and SSOs. 

These included:

 

● CSOs and SSOs contain pollutants that cause impairments to designated uses, as reported in 

national assessments.

● CSOs and SSOs can be a principal cause or a contributing cause of an environmental impact.

● National data are inconsistent in tracking CSOs and SSOs as a direct cause of impairment. 

● While data are not comprehensive, some national estimates of use impairment have been 

made.

● State and local examples of cause and effect exist where CSO and SSO reporting and tracking 

are undertaken.

EPA asked the stakeholders present at the meeting for additional information on documented 

environmental impacts from CSOs and SSOs.

Stakeholder Questions and Comments on the Environmental Impacts Chapter

Questions and comments received after the environmental impacts presentation are summarized below. 

The comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● Most impacts seem very locally specific. 

● Because of the ambiguity of the data, should you split them into separate categories in order to direct 

policy talks and funding allocations?

● There may be a time lapse between the event and the environmental impact. Does the report 

measure that?

● The beach closure chart should clarify miles by including the total miles of beach. 

● Is EPA saying that municipal point sources, specifically CSOs and SSOs, are leading sources of water 

quality impairment? 

● Stakeholders said that within their jurisdictions, a significant amount of water contamination is due 

to failing septic tanks.

● Stakeholders thought that EPA should try to gain an understanding of the concentration of pathogens 

from SSO to storm water, which leads to beach closing. 

● Distinguish between beach advisories, which (in California) are based on bacteria levels from ongoing 

water quality monitoring, and beach closures, which (in California) happen after every reported SSO/

CSO event. 

● For SSO, EPA cannot blame natural phenomenon, such as rain and snowmelt, for overflows.

Human Health Impacts of CSOs and SSOs

Heather Gewandter – SRA International

Ms. Gewandter began by introducing the key questions addressed in this chapter:

● What constituents of CSOs and SSOs cause human health impacts?

 Of what consequence are these impacts?

● Which exposure pathways are the most significant and what populations are most sensitive?

● What are the impediments to understanding the linkages between CSOs and SSOs, exposures, 

and the human health impacts?

● What is the institutional framework to assess and address potential human health impacts of 

CSOs and SSOs?
B-26

Report to Congress on the Impacts and Control of CSOs and SSOs

Ms. Gewandter explained that EPA first performed an extensive literature review. Then, EPA held an 

experts workshop in order to verify the accuracy of data already collected, find new sources, and ascertain 

an understanding of experts’ opinions of the human health impacts of CSOs and SSOs. EPA next 

performed a series of state and community interviews for the purpose of understanding local and state 

health agency staff’s opinions of the impacts of CSOs and SSOs and to characterize the current activities 

being carried out that address this potential threat.

Ms. Gewandter went on to present the range of human health symptoms resulting from exposure to the 

pollutants typically found in CSOs and SSOs. Next, she discussed exposure pathways and the groups 

facing the most frequent exposure, as well as the groups most sensitive to waterborne illnesses. 

Ms. Gewandter described the limitations of the major data sources used to identify and describe 

waterborne disease outbreaks, one potential indicator of human health impacts from CSOs and SSOs. 

She next presented local, site specific examples outbreaks attributed to exposure to sewage in order to 

illustrate the potential for acute health impacts. 

Next, EPA outlined the challenges to identifying the human health impacts of CSOs and SSOs. These 

include:

 

● The lack of connectivity in the monitoring and reporting systems for CSO and SSO events, 

human exposures, and human health impacts.

● Difficulty identifying the source of pathogens.

● The difficulty in attributing disease outbreaks to CSO and SSO events.

● The fact that outbreak reporting to CDC is voluntary.

● The understanding that many people who become ill do not seek medical treatment due to 

the nature of the illness. 

● There are inconsistent probabilities of diagnoses within the health care system. 

● The general tendency towards underreporting. 

Conclusions for the Human Health Impacts Chapter

Finally, Ms. Gewandter identified the actions that are currently being taken by state and local governments 

to address the human health impacts from CSOs and SSOs and EPA’s preliminary conclusions. These 

conclusions include:

● The pathogens and pollutants found in CSOs and SSOs have the potential to cause human 

health impacts. 

● Exposures to the pathogens and pollutants resulting from CSOs and SSOs occur, but are 

difficult to quantify. 

● Human health impacts from waterborne diseases are underreported. 

● Responsibilities for protecting human health from waterborne illnesses are distributed among 

many agencies and institutions.

Stakeholder Questions and Comments on the Human Health Impacts Chapter 

Questions and comments received after the human health impacts presentation are summarized below. 

The comments represent stakeholder opinion(s) and may not reflect EPA’s position.

 

● Comment on warnings: In California, in event of SSO, beaches close immediately and there is no lag 

time.

● Clarify between postings, advisories, and closures.
 Appendix B

B-27

● CDC released a paper in 1999 that said there were 300 cases of Cryptosporidiosis annually. This is 

contradictory to the information EPA presented and shows that there is a lot of uncertainty. 

● The information regarding sensitive populations is all speculation. 

● EPA needs to distinguish between large and small potential exposures; break out one-time exposure 

risk (metals) versus chronic exposures. 

● There are no criteria for metals for recreational use. 

● Just because a person has Cryptosporidiosis does not mean they get sick.

● Did EPA coordinate with the new epidemiology studies? 

● Did EPA do risk assessment with pathogen data? Has EPA put the risk (of health impacts from CSO 

and SSO) in context with other risks? 

● Did the literature review find epidemiological studies on WWTP workers? Did they build immunity? 

● The material is inconclusive. 

● Tie in anticipated exposure levels. 

● Make sure to qualify that the pathogens and pollutants are coming from human waste and wastewater 

in the table.

● If groundwater impacts are a concern, many parameters are attenuated.

 

Resources Spent on CSO and SSO Control 

Kevin DeBell – Office of Wastewater Management, EPA

Mr. DeBell outlined the methodological approach to this chapter which included:

● Data analysis which tabulated information of past investments in clean water infrastructure 

and compiled information on what has been spent on CSO and SSO control. 

● EPA’s estimate of the investment needed to meet the current requirements for CSO and SSO 

controls.

● EPA’s acknowledgement of the fact that costs of CSO and SSO control are borne almost 

exclusively by local governments and utilities but local governments and utilities have not 

been requested to report the costs incurred for CSO and SSO control.

Stakeholder Questions and Comments on the Resources Chapter

Questions and comments received after the resources presentation are summarized below. The comments 

represent stakeholder opinion(s) and may not reflect EPA’s position.

● Are SSO control expenditure needs distinguished from overall needs? 

● Is the cost EPA has designated as SSO cost incremental or is it the total cost of running the sewage 

collection system? Since all money spent on the sewage collection system is aimed at getting sewage 

to the plant and preventing sewage spills, the total number may be more accurate.

● Do you plan to use other financial studies besides EPA’s Gap Analysis (i.e., Waste Infrastructure 

(WIN) report)? The two studies have contradictory findings and a stakeholder did not want 

Congress to be confused if it heard the findings from the WIN report and they were not mentioned 

in this report.

● Stakeholders were concerned about private spills. Since municipalities do not pay for those, some 

stakeholders did not want them included, or they wanted these estimates to at least be called out. 

 

Technologies for CSO and SSO Control

Kevin DeBell – Office of Wastewater Management, EPA 

Mr. DeBell described the key data sources for the technology chapter. These included:

● Extensive literature reviews of existing EPA documentation as well as other sources;

● Interviews with municipal officials; 
B-28

Report to Congress on the Impacts and Control of CSOs and SSOs

● Meetings with key EPA staff; and

● Informal peer review by internal and external experts.

Key Questions for the Technologies Chapter

Mr. DeBell introduced the key questions that were addressed:

● What technologies have been used by municipalities to control CSOs and SSOs?

● What factors influence the effectiveness of these technologies?

● Have there been any recent technological innovations in the control of CSOs and SSOs?

While researching this chapter, EPA identified common and promising technologies used by 

municipalities to address CSOs and SSOs. From this research, EPA developed technology descriptions 

summarizing available technologies and factors influencing their effectiveness. Mr. DeBell explained that 

it is very difficult to compare certain types of technologies, as they are designed to deal with different 

aspects of wet weather challenges. Therefore, the technologies were not ranked for effectiveness against 

each other within this chapter. 

Presentation of Technologies

Mr. DeBell said that a wide range of technologies are available and that, within the report, they had been 

grouped into five key categories:

● Operations and maintenance activities;

● Collection system controls;

● Storage facilities;

● Treatment technologies; and 

● Low impact development techniques. 

Mr. DeBell mentioned that EPA developed case studies on each of the researched technologies and 

presented preliminary findings pertaining to the relative cost of implementing the systems, the type of 

system for which the technology was designed, and the pollutants or problems controlled.

Stakeholder Questions and Comments on the Technologies Chapter

Questions and comments received after the technologies presentation are summarized below. The 

comments represent stakeholder opinion(s) and may not reflect EPA’s position.

● There is a lack of innovative technologies investigated, especially the decentralized technologies.

● Did EPA discuss odor control? 

● What about the fats, oils, and grease requirements, will they be included in the SSO rule? 

● Do you have any understanding about the total cost of all of the regulations that are coming? 
 Appendix B

B-29

Report To Congress

Stakeholder Meeting Attendee List

Huntington Beach, CA

July 8, 2003

Name, Office/Organization

Andy Aguilar, Surfrider Foundation

Richard Alcorn, City of Rancho Cucamonga

Jody Allen, Sacramento County

Ric Amador, City of San Diego

Rodney Andersen, City of Burbank

Nick Arhontes, Orange County Sanitation Districts

Daniel Askenaizer, MWH

Regan Bailey, City of Riverside

Dennis Baker, Earth Resource Foundation

Richard Bardin, Boyle Engineering Corporation

Danilo Batson, City of Glendale

Cindy Beck, Irvine Ranch Water District

Matthew Bequette, City of Los Angeles

 Benita Best-Wong, USEPA

Thomas Blanda, Orange County Sanitation Districts

M. Todd Broussard, City of Huntington Beach

Bryan Brown, City of Los Angeles

Ray Burk, City of Santa Ana

Ed Burt, City of Newport Beach

John Butcher, NCPI

Olson Childress, City of Chino Hills

Marvin Chiong, Los Angeles County Department of Public Works

James Clark, Black & Veatch

Daniel Cooper, Lawyers for Clean Water

Lee Cory, Yorba Linda Water District

 Kevin DeBell, USEPA

Jim Delicce, City of Newport Beach

Bill Denhart, City of San Diego

Parivash Dezham, Inland Empire Utilities Agency

Dick Dietmeier, South Coast Water District

Rick Donahue, City of San Diego

Mike Dunbar, South Coast Water District

Bill Echols, Central Contra Costa County Sanitary District

Michele Farmer, Orange County Sanitation Districts

Tom Fauth, Costa Mesa Sanitary District

Michael Feroz, Jacobs Civil Inc.

Ken Fischer, City of Burbank

Michael Flores, HDR

Paul Forsthoefel, ADS Environmental Services

Phil Friess, LACSD

Kevin Gensler, City of San Diego

 Heather Gewandter, SRA

Marco Gonzalez, Surfrider Foundation

Chris Gray, City of Huntington Beach

Don Greek, DGA Consultants

Ken Greenberg, U.S. EPA, Region 9

Paul Guzman, Costa Mesa Sanitary District
B-30

Report to Congress on the Impacts and Control of CSOs and SSOs

Roy Hafar, City of Folsom

Roger Ham, Union Sanitary District

Robin Hamers, Costa Mesa Sanitary District

Daniel Hardgrove, City of Glendale

Alan Harrell, Coachella Valley Water District

F. Patrick Hassey, Sacramento County

Jonathan Hasson, ADS Environmental Services

Brent Hayes, Garden Grove Sanitary District

Jeannie Heimberger, City of Fountain Valley

Penny Hill, Los Angeles County Sanitation Districts

 Hans Holmberg, Limno-Tech, Inc.

Larry Honeybourne, County of Orange

Lisa Marie Kay, MEC Analytical Systems Inc.

Zeki Kayiran, AKM Consulting Engineers

Bill Knitz, DGA Consultants

Ruth Kolb, City of San Diego

Bob Kreg, Southern California Alliance of Publicly Owned Treatment Plants

Patty Lambaren, City of Fullerton

Winnie Lee, PBS&J

Sylvie Lee, Inland Empire Utilities Agency

Albert Lee, Jr., City of Glendale

Keith Linker, City of Anaheim

Russell Maguire, City of Anaheim

 Linda Manning, SRA

Lisa Mattert, City of Orange

Ziad Mazboudi, City of San Juan Capistrano

Monica Mazur, County of Orange

Joe McDivitt, South Coast Water District

Charles McGee, Orange County Sanitation Districts

Patrick McNelly, Orange County Sanitation Districts

Dayna Michaelsen, Midway City Sanitary District

Victor Moraga, City of Ontario

Andy Morrison, Union Sanitary District

Margie Nellor, Sanitation Districts of Los Angeles County

Bryan Ortega, City of Glendale

Ralph Palomares, El Toro Water District

Diann Pay, AKM Consulting Engineers

Ken Payne, City of Folsom

John Perry, City of San Bernardino

Michele Pla, CH2M Hill

Denis Pollock, MGD Technologies Inc.

Craig Proctor, Inland Empire Utilities Agency

Lloyd Prosser, EMA

Ronn Rathbun, City of Huntington Beach

Robert Reid, West Valley Sanitation District

Don Rhoads, Central Contra Costa County Sanitary District

Kenny Robbins, Midway City Sanitary District

Manuel Romero, City of Santa Barbara

Dick Runge, South Coast Water District

Jeff Sadler, ECA

Dale Schindler, Crestline Sanitation District

Kathy Schindler, Crestline Sanitation District
 Appendix B

B-31

Don Schulz, Surfrider Foundation

John Shaffer, Environmental Engineering & Consulting

David Shissler, City of Laguna Beach

Mike Shope, Camp Pendleton

Gary Skipper, MGD Technologies Inc.

Mary Snyder, County of Sacramento

Stan Steinbach, Environmental Engineering & Consulting

Ken Theisen, California Regional Water Quality Control Board

Leo Truttmann, LTEC

Roger Turner 

 Tara Van Atta, SRA

Clarence Van Corbach, City of Manhattan Beach

Gonzalo Vazquez, City of Cypress

Konya Vivanti, Garden Grove Sanitary District

Jeff Walker, City of Chino Hills

Dan Wall, City of Burbank

Stephanie Warren, Surfrider Foundation

Jason Wen, City of Downey

Dave Williams, East Bay Municipal Utility District

James Wilson, City of Fresno

Rick Wilson, Surfrider Foundation

Hu Yi, Los Angeles County
Appendix C 

Documentation of State and 

Municipal Interviews

 Appendix C

C-1

Documentation of State and Municipal Interviews

Data collection for this report involved a series of site visits and telephone interviews. Such data collection efforts 

were conducted in accordance with an Information Collection Request (ICR 2063.01), which was approved by 

OMB on September 16, 2002 (OMB No. 2040-0248). 

Site Visits

EPA conducted site visits to seven states to obtain specific information regarding CSOs and SSOs for the report. 

The states visited include Connecticut, Kansas, Maryland, Missouri, North Carolina (SSO only), Oklahoma (SSO 

only), and Rhode Island. While there, EPA met with permitting staff to discuss programmatic issues related to 

CSO and SSO discharges. EPA also accessed the NPDES authority’s electronic data management system for SSOs, 

where available.

North Carolina was specifically visited to obtain information on its collection system permitting program. 

Oklahoma was selected for a site visit to collect information on the state’s collection system program used to 

address SSOs and other sewer system issues. The five states with both CSSs and SSSs– Connecticut, Kansas, 

Maryland, Missouri, and Rhode Island– were selected for site visits, because CSO permit file reviews were not 

conducted in these states for the 2001 Report to Congress–Implementation and Enforcement of the CSO Control 

Policy (EPA 2001). The information gathered from these states was used to update the inventory of CSO outfalls, 

documented in Appendix D of this report. 

EPA also conducted site visits to regional offices, municipal governments, sewer utilities and non-governmental 

organizations. EPA visited EPA Region 4 offices in Atlanta, GA, to collect pertinent information about the region’s 

Management, Operation and Maintenance (MOM) program, and to review program files. EPA conducted site 

visits to Orange County and San Francisco, California. In Orange County, EPA met with the Orange County 

Sanitation District to gather SSO information and met with the Orange County Health Care Agency to collect 

beach monitoring data (including beach closings and postings). In San Francisco, EPA met with the San 

Francisco Public Utilities Commission to discuss CSO and environmental impact data. Moreover, EPA met with 

Save the Bay in Rhode Island and Heal the Bay in the greater Los Angeles-area to collect CSO and SSO-related 

information.

Public Health State and Municipal Phone Interviews

EPA also conducted interviews with public health personnel. State or territorial epidemiologists and local public 

health officials were the primary sources of data. During these interviews, EPA gathered data on pathogen 

sources, contaminated water exposures, and illness tracking. In addition, EPA inquired about innovative local 

programs in place to monitor CSOs or SSOs and/or waterborne illnesses. Through these interviews, EPA sought 

a clearer understanding of the roles and responsibilities of these agencies in preventing, tracking, and monitoring 

potential human health impacts associated with CSO and SSO discharges within their jurisdiction. 

States and communities were selected from each EPA region in an attempt to ensure geographic, climatic, and 

population variability among communities interviewed. Nevertheless, the sample was intentionally biased, 

targeting communities that were likely to have health data related to CSOs and SSOs, or which employed 

noteworthy water quality monitoring or waterborne disease outbreak tracking techniques. In total, officials from 

even states and 23 municipalities, as shown in Appendix I, were interviewed. 
C-2

Report to Congress on Impacts and Control of CSOs and SSOs

CSO and SSO Municipal Telephone Interviews

In order to gather representative information to characterize CSOs and SSOs, EPA interviewed officials with 85 

sewer agencies, 40 with CSSs and 45 with SSSs, which varied widely in terms of service area, population served, 

and sewer age. For example, EPA interviewed officials representing systems that served as few as 75 people 

to systems that served over one million people. In total, EPA interviewed municipal officials in 27 states by 

telephone. In some states, both CSO and SSO interviews were conducted. State NPDES authorities were contacted 

in advance of any interviews conducted within their states. At that time, EPA briefly interviewed state officials to 

gather information about environmental and human health impacts as well as cost information relevant to CSO 

and SSO discharges.

Potential CSO and SSO interviewees was selected as follows. For the CSO interviews, a list of CSO permittees that 

had developed and/or implemented CSO controls were extracted from the inventory of CSO permits (Appendix 

D). A list of unique entities with SSSs, which have reported at least one SSO, was extracted from the SSO data 

management system described in Appendix G. SSO communities studied in EPA fact sheets (EPA 2003) were 

excluded from consideration. A random sampling was taken from the CSO and SSO lists to create the pool of 

potential interviews. Municipal officials unable or unwilling to participate in the survey were replaced with 

alternate candidates.

Through the CSO interviews, EPA gathered information about collection systems, treatment plants (if applicable), 

operational responsibility, CSO events, environmental and human health impacts from CSO discharges, LTCP 

implementation, and funding. As part of the SSO interviews, EPA collected information about collection systems, 

treatment plants (if applicable), operational responsibility, SSO events, environmental and human health impacts 

from SSO discharges, O&M, and funding. 

References

EPA. 2003. Office of Water. “Featured Factsheets, Case Studies, and Other Information.” Retrieved October 3, 

2003. http://cfpub2.epa.gov/npdes/sso/featuredinfo.cf.

EPA. 2001. Office of Water. Report to Congress- Implementation and Enforcement of the Combined Sewer Overflow 

Control Policy. EPA 833-R-01-003.
Appendix D 

List of Active CSO Permits

 Appendix D

D.1

List of Active CSO Permits, Sorted by Region and State

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

1 CT CT0100056 Bridgeport-West WPCF 32

1 CT CT0100251 Hartford MDC WPCF 44

1 CT CT0100366 New Haven East Shore WPCF 19

1 CT CT0100412 Norwich WPCF 15

1 CT CT0101010 Bridgeport-East WPCF 12

1 MA MA0102997 Worcester Combined Overflow Facility 1

1 MA MA0101168 Palmer WPCF 6

1 MA MA0101192 Boston Water and Sewer Commission 37

1 MA MA0101338 Town of Ludlow CSOs 1

1 MA MA0101621 Haverhill WWTF 21

1 MA MA0101877 Chelsea 4

1 MA MA0101974 City of Cambridge 11

1 MA MA0100986 Fitchburg WWTF 27

1 MA MA0102351 MWRA, Deer Island WWTP 14

1 MA MA0101508 Chicopee WPCF 31

1 MA MA0103331 Springfield CSOs 25

1 MA MA0101982 Somerville DPW 2

1 MA MA0100455 South Hadley WWT 3

1 MA MA0101630 Holyoke WPCF 15

1 MA MA0100897 Taunton WWTPs 1

1 MA MA0100137 Montague WPCF 2

1 MA MA0100382 Fall River WWTP 19

1 MA MA0100447 Greater Lawrence Sanitary District 5

1 MA MA0100552 Lynn WWTF 4

1 MA MA0100625 Gloucester WPCF 5

1 MA MA0100633 Lowell Regional WWU 9

1 MA MA0100781 New Bedford WWTF 35

1 ME ME0100625 Skowhegan WPCP 9

1 ME ME0100633 City of South Portland 8

1 ME ME0102369 Fort Kent Utility District 1

1 ME ME0100617 Sanford Sewerage District 2

1 ME ME0100951 Paris WWTP 1

1 ME ME0100781 Bangor WWTP 12

1 ME ME0100846 Westbrook/Portland Water District 5

1 ME ME0100854 Kennebec Sanitary District 3

1 ME ME0100722 Winslow Sanitary District 2

1 ME ME0101117 Saco WWTP 5

1 ME ME0101214 Bar Harbor WWTF 3

1 ME ME0101478 Lewiston-Auburn WPCA 1

1 ME ME0101494 Fairfield 2

1 ME ME0101681 Madawaska PCF 2

1 ME ME0102075 Portland Water District 23

1 ME ME0100595 Rockland WWTF 4

1 ME ME0101702 City of Gardiner 2

1 ME ME0100897 Hamden 1

1 ME ME0101532 Belfast WWTF 2

1 ME ME0100153 Corrina Sewer District 1

1 ME ME0102466 Bar Harbor Hulls Cove 1

1 ME MEU508074 Randolf 1

1 ME ME0101435 City of Portland 12

1 ME ME0100005 Auburn Sewerage District 6

1 ME ME0100013 Augusta Sanitary District 24

1 ME ME0100021 Bath WWTP 4
D.2

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

1 ME ME0100048 Biddeford Wastewater Department 11

1 ME ME0100072 City of Brewer 7

1 ME ME0100501 Town of Dover-Foxcroft Wastewater Department 4

1 ME ME0100994 Lewiston 30

1 ME ME0100196 Town of East Millinocket 1

1 ME ME0100285 Town of Kittery 3

1 ME ME0100307 Lisbon WWTF 2

1 ME ME0100323 Machias WWTP 2

1 ME ME0100391 Mechanic Falls Sanitary District 1

1 ME ME0100439 Milo Water District 3

1 ME ME0100471 Old Town PCF 3

1 ME ME0100498 Orono Water Pollution Control Facility 1

1 ME ME0100111 Bucksport WWTF 2

1 NH NH0100234 City of Portsmouth 2

1 NH NH0100366 City of Lebanon WWTF 6

1 NH NH0100871 Exeter 1

1 NH NH0100170 Nashua WWTF 8

1 NH NH0100013 Berlin PCF 1

1 NH NH0100447 City of Manchester WWTF 22

1 RI RI0100072 Narragansett Bay - Bucklin 28

1 RI RI0100315 Narragansett Bay - Fields Point 45

1 RI RI0100293 Newport City Hall 3

1 VT VT0100153 Burlington Main WWTF 1

1 VT VT0100196 Montpelier WWTF 15

1 VT VT0100285 Randolph WWTF 3

1 VT VT0100374 Springfield WWTF 21

1 VT VT0100404 Vergennes WWTF 0

1 VT VT0100579 St. Johnsbury WWTF 19

1 VT VT0100871 Rutland WWTP 3

2 NJ NJ0108731 City of Rahway 0

2 NJ NJ0108766 City of Hackensack 2

2 NJ NJ0021016 Passaic Valley Sewerage Commissioners 0

2 NJ NJ0111244 Town of Kearny 10

2 NJ NJ0108782 City of Elizabeth 33

2 NJ NJ0109118 Ridgefield Park Village 6

2 NJ NJ0108791 Camden County MUA 1

2 NJ NJ0108812 City of Camden 31

2 NJ NJ0108847 Gloucester City 7

2 NJ NJ0108871 Town of Harrison 7

2 NJ NJ0108880 City of Paterson 31

2 NJ NJ0108723 Jersey City MUA 27

2 NJ NJ0108758 Newark 27

2 NJ NJ0025321 North Hudson SA-West NY (River Road) 2

2 NJ NJ0109240 City of Bayonne CSOs 28

2 NJ NJ0117846 East Newark 1

2 NJ NJ0020028 Bergen County WWTP Utilities Authority 0

2 NJ NJ0020141 Middlesex County Utility Authority 0

2 NJ NJ0020141a Perth Amboy 16

2 NJ NJ0020591 Edgewater MUA 0

2 NJ NJ0024741 Joint Meeting of Essex & Union Counties 0

2 NJ NJ0024643 Rahway Valley Sewerage Authority 0

2 NJ NJ0108715 Guttenberg Town 1
 Appendix D

D.3

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

2 NJ NJ0026085 North Hudson SA-Hoboken (Adams Street) 11

2 NJ NJ0026182 Camden County MUA 1

2 NJ NJ0029084 North Bergen MUA (Woodcliff) 1

2 NJ NJ0034339 North Bergen MUA (Central) 0

2 NJ NJ0034517 Fort Lee 2

2 NJ NJ0108707 Passaic Valley Sewerage Commissioners 0

2 NJ NJ0020923 Trenton Sewer Utilities Authority 1

2 NJ NJ0108898 North Bergen MUA (Central) 9

2 NY NY0027081 Syracuse Metro WWTP 62

2 NY NY0029114 City of Oswego, East Side STP 6

2 NY NY0029106 Oswego-West Side STP 1

2 NY NY0029050 Glens Falls WWTP 1

2 NY NY0028410 Bird Island WWTF 58

2 NY NY0028339 Frank E. VanLare STP 6

2 NY NY0027961 Dunkirk WWTP 1

2 NY NY0248941 City of Mechanicville CSO 3

2 NY NY0027545 Clayton Village WTF 2

2 NY NY0029807 Canastota WPCF 1

2 NY NY0027073 Red Hook WPCP 34

2 NY NY0027057 Lockport WWTP 30

2 NY NY0026689 Yonkers Joint WWTP 26

2 NY NY0026336 Niagara Falls WWTP 9

2 NY NY0026310 Newburgh WPCP 12

2 NY NY0027766 Lewiston Master S.D. 1

2 NY NY0031208 Dock Street STP 0

2 NY NY0183695 Washington County S.D. 2 11

2 NY NY0099309 Troy CSO 49

2 NY NY0087971 Rensselaer County 0

2 NY NY0036706 Ticonderoga S.D. #5 WPCP 2

2 NY NY0035742 Chemung County-Elmira S.D. STP 11

2 NY NY0033545 Village of Coxsackie STP 3

2 NY NY0029173 Waterford WWTP 4

2 NY NY0031429 Utica CSO 82

2 NY NY0029351 Kingston WWTF 7

2 NY NY0031194 Massena WWTP 10

2 NY NY0031046 Cohoes CSO 16

2 NY NY0030899 Watervliet CSO 5

2 NY NY0029939 Tupper Lake WPCP 3

2 NY NY0029831 Ogdensburg WWTP 17

2 NY NY0026247 North River WPCF 50

2 NY NY0033031 Green Island CSO 3

2 NY NY0020818 Potsdam WPCP 1

2 NY NY0026280 North Tonawanda WWTP 13

2 NY NY0023981 Village of Johnson City CSO 2

2 NY NY0023256 Village of Holley STP 0

2 NY NY0022403 Little Falls WWTP 3

2 NY NY0022136 Erie County S.D. #6 1

2 NY NY0022039 Hudson STP 10

2 NY NY0024481 Lewiston ORF 1

2 NY NY0021873 Medina WWTP 13

2 NY NY0025747 Albany CSO 12

2 NY NY0020621 Wellsville WWTP 3
D.4

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

2 NY NY0020516 Schenectady WPCP 2

2 NY NY0020494 Boonville WWTP 1

2 NY NY0020389 Catskill WWTP 6

2 NY NY0020290 Amsterdam WWTP 3

2 NY NY0020117 Gouverneur STP 1

2 NY NY0021903 Auburn STP 9

2 NY NY0026131 Wards Island WPCP 78

2 NY NY0026239 Tallmans Island WPCP 21

2 NY NY0026221 NYCDEP Rockaway WWTP 27

2 NY NY0026204 Newtown Creek WPCP 85

2 NY NY0026191 NYCDEP-Hunt's Point WPCP 42

2 NY NY0026182 NYCDEP Coney Island WPCP 4

2 NY NY0026174 NYCDEP Oakwood Beach WPCP 1

2 NY NY0024406 Binghamton CSO 10

2 NY NY0026158 NYCDEP Bowery Bay WPCP 49

2 NY NY0026255 Poughkeepsie WPCP 6

2 NY NY0026115 NYCDEP Jamaica WPCP 6

2 NY NY0026107 Port Richmond WPCF 36

2 NY NY0026026 Rensselaer CSO 8

2 NY NY0026018 Plattsburgh WPCP 14

2 NY NY0025984 Watertown WPCP 17

2 NY NY0025780 Oneida County WPCP 1

2 NY NY0026166 NYCDEP Owls Head WPCP 16

2 NY NY0026212 NYCDEP 26th Ward 4

3 DC DC0021199 District of Columbia WWTP 60

3 DE DE0020320 Wilmington 40

3 MD MD0067547 LaVale CSOs 3

3 MD MD0021571 Salisbury City 2

3 MD MD0021598 Cumberland WWTP 18

3 MD MD0021601 Patapsco WWTP 1

3 MD MD0021636 Cambridge WWTP 14

3 MD MD0067384 Westernport Town 2

3 MD MD0067407 Allegany County CSOs 3

3 MD MD0067423 Frostburg CSOs 15

3 PA PA0036820 Galeton Borough Authority 4

3 PA PA0036650 Titusville City 4

3 PA PA0028673 Borough of Gallitzin WWTP 6

3 PA PA0028631 Mid-Cameron Authority 1

3 PA PA0028436 Elizabeth Borough STP 6

3 PA PA0028223 Corry City Municipal Authority 3

3 PA PA0039489 Garrett Boro SIP 2

3 PA PA0028401 Dravosburg Borough STP 1

3 PA PA0037044 Ford City WTP 3

3 PA PA0037711 Everett Borough Municipal Authority 5

3 PA PA0028207 Reynoldsville Sewer Authority 7

3 PA PA0038920 Burnham Borough 4

3 PA PA0027421 Norristown MWA 2

3 PA PA0042234 Kittanning Borough STP 9

3 PA PA0043273 Hollidaysburg Regional WWTP 4

3 PA PA0043877 Greater Pottsville Area Sewer Authority (West End) 4

3 PA PA0043885 Greater Pottsville Area Sewer Authority 56

3 PA PA0070041 Mahanoy City (MCSA) STP 3
 Appendix D

D.5

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

3 PA PA0037818 Saltsburg Borough STP 6

3 PA PA0027227 Farrell City 4

3 PA PA0027049 Williamsport Sanitary Authority West Plant 1

3 PA PA0027057 Williamsport Sanitary Authority Central 3

3 PA PA0027065 Lackawanna River Basin Sewer Authority-Archbald 6

3 PA PA0027081 Lackawanna River Basin Sewer Authority-Clinton 9

3 PA PA0027090 Lackawanna River Basin Sewer Authority-Throop 20

3 PA PA0027103 DELCORA Chester STP 26

3 PA PA0027111 New Kensington STP 5

3 PA PA0027456 Greater Greensboro STP 39

3 PA PA0027197 Harrisburg Authority 60

3 PA PA0027693 Minersville Sewer Authority 7

3 PA PA0027324 Shamokin-Coal Township Joint Sewer Authority 5

3 PA PA0027391 Upper Allegheny Joint Sanitary Authority STP 19

3 PA PAG064801 Shamokin City 33

3 PA PA0027430 Jeannette WWTP 5

3 PA PA0070386 Shenandoah STP 13

3 PA PA0027570 Brush Creek STP 3

3 PA PA0027626 Kiski Valley STP 32

3 PA PA0027651 West Newton Borough STP 13

3 PA PA0027120 Warren City 4

3 PA PAG066127 Munhall Boro 4

3 PA PAG066116 West View Borough 2

3 PA PAG066117 City of Uniontown 28

3 PA PAG066118 Borough of Turtle Creek 10

3 PA PAG066119 Borough of Etna 8

3 PA PAG066120 Borough of East Pittsburgh 3

3 PA PAG066123 Borough of West Homestead 2

3 PA PA0027014 Altoona City Authority-East 1

3 PA PAG062201 Easton City 2

3 PA PAG066126 Carnegie Borough 1

3 PA PAG066113 Borough of Aspinwall 3

3 PA PAG066128 Borough of Swissvale 1

3 PA PAG066129 Mayview State Hospital 1

3 PA PAG066130 Export Borough 5

3 PA PAG066131 Freedom Borough 3

3 PA PAG066132 East Rochester Borough 1

3 PA PAG066134 Township of Lett 1

3 PA PAG066122 East Conemaugh Borough 2

3 PA PAG066121 City of Arnold 2

3 PA PAG066125 Sharpsburg Borough 6

3 PA PAG066105 Borough of Rankin 2

3 PA PA0096229 Marianna-West Bethlehem STP 1

3 PA PA0217611 City of Pittsburgh 217

3 PA PA0027022 Altoona West STP 1

3 PA PAG062202 Lackawanna River Basin Authority-Moosic 3

3 PA PAG066124 Dale Borough 7

3 PA PAG064802 Coal Township 33

3 PA PAG066101 Pitcairn Borough 1

3 PA PAG066102 Braddock Borough 8

3 PA PAG066115 Ferndale Borough 5

3 PA PAG066104 Bureau of Wilmerding 9
D.6

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

3 PA PAG066114 Borough of North Braddock 1

3 PA PAG066106 Girty's Run JSA, Millvale 9

3 PA PAG066107 Township of Stowe 7

3 PA PAG066108 Township of Wilkins 2

3 PA PAG066109 McDonald Sewage Authority 20

3 PA PAG066110 Borough of Crafton 4

3 PA PAG066111 Emsworth Borough 1

3 PA PAG066112 Borough of McKee Rocks 3

3 PA PA0092355 North Belle Vernon WPCP 16

3 PA PAG066103 Borough of Homestead 1

3 PA PA0023701 Midland Borough Municipal Authority STP 1

3 PA PA0024490 Rockwood Boro STP 5

3 PA PA0022306 Brownsville Municipal Authority-Shady Avenue STP 4

3 PA PA0022331 West Elizabeth WWTP 1

3 PA PA0023175 Kane Borough 2

3 PA PA0023248 Berwick Area Joint Sewer Authority 4

3 PA PA0022209 Bedford Borough Municipal Authority 2

3 PA PA0023558 Ashland Borough 9

3 PA PA0021814 Mansfield WWTP 4

3 PA PA0023736 Tri-Borough Municipal Authority WWTP 2

3 PA PA0024163 Cambria Township Sewer Authority (Revloc STP) 1

3 PA PA0024341 Canton Borough Authority 1

3 PA PA0024406 Mt. Carmel Municipal Authority 19

3 PA PA0024449 Youngwood Borough STP 2

3 PA PA0020125 Boro of Monaca STP 6

3 PA PA0023469 Honesdale STP 9

3 PA PA0021237 Newport Borough Municipal Authority 3

3 PA PA0020397 Bridgeport Borough 6

3 PA PA0020613 Waynesbug STP 2

3 PA PA0020681 Sewickley WWTP 4

3 PA PA0020702 Fayette City WWTP 2

3 PA PA0020940 Tunkhannock Borough Municipal Authority 1

3 PA PA0022292 Ebensburg WWTP 2

3 PA PA0021148 Mt. Pleasant STP 6

3 PA PA0024511 Redbank Valley Municipal Authority 1

3 PA PA0021407 Point Marion WWTP 6

3 PA PA0021521 Smethport Borough 1

3 PA PA0021539 Williamsburg Borough 1

3 PA PA0021571 Marysville Municipal Authority 3

3 PA PA0021610 Blairsville Borough STP 16

3 PA PA0021687 Wellsboro Municipal Authority 2

3 PA PA0021113 Glassport STP 5

3 PA PA0026492 Scranton WWTF 78

3 PA PA0024481 Meyersdale STP 5

3 PA PA0026204 Oil City STP 16

3 PA PA0026301 Erie City STP 15

3 PA PA0026310 Clearfield Municipal Authority 9

3 PA PA0026352 Coraopolis WPCF 6

3 PA PA0026182 Lansdale Borough 2

3 PA PA0026476 Coaldale Landsford-Summitt Hill TP 6

3 PA PA0026174 Franklin City General Authority 5

3 PA PA0026557 Municipal Authority of the City of Sunbury 6
 Appendix D

D.7

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

3 PA PA0026581 Scottsdale STP 8

3 PA PA0026662 Philadelphia Water Department-Southeast 35

3 PA PA0026671 Philadelphia Water Department-Southwest 83

3 PA PA0026743 Lancaster City 5

3 PA PA0026689 Philadelphia Water Department-Northeast 59

3 PA PA0026361 Lower Lackawanna Valley Sanitary Authority 26

3 PA PA0025950 City of Monongahela 1

3 PA PA0024589 Leetsdale STP 6

3 PA PA0024686 Mid Mon Valley WPCP 8

3 PA PA0024716 Freeland WWTP 1

3 PA PA0024864 Ligonier Boro STP 2

3 PA PA0025224 St. Clair S.A. WWTP 7

3 PA PA0026191 Huntington Borough 6

3 PA PA0025810 Shade-Central City STP 3

3 PA PAG066133 Rochester Borough 5

3 PA PA0025984 Allegheny County Sanitary Authority 21

3 PA PA0026042 Bethlehem WWTP 3

3 PA PA0026069 Latrobe Borough 18

3 PA PA0026107 Wyoming Valley Sewer Authority 54

3 PA PA0026140 Rochester Area Joint Sewer Authority WTP 1

3 PA PA0026158 Monongahela Valley WWTP 21

3 PA PA0025755 Borough of Freeport STP 6

3 PA PA0026832 Ellwood City Borough 1

3 PA PA0027006 Tamaqua Borough Sewer Authority 13

3 PA PA0026981 City of Duquesne STP 4

3 PA PA0026921 Hazelton WTP 14

3 PA PA0026913 McKeesport WPCP 28

3 PA PA0026905 Connellsville STP 16

3 PA PA0026891 Charleroi STP 12

3 PA PA0020346 Punxsutawney Sewer Authority STP 4

3 PA PA0026824 Clairton STP 5

3 VA VA0024970 Lynchburg STP 36

3 VA VA0063177 Richmond WWTW 29

3 VA VA0087068 Alexandria CSOs 4

3 WV WV0023167 Martinsburg 1

3 WV WV0020648 City of Benwood 14

3 WV WV0027324 Monongah 2

3 WV WV0026832 Wellsburg 10

3 WV WV0025461 City of Bridgeport 12

3 WV WV0027472 New Martinsville 10

3 WV WV0028088 Weston 5

3 WV WV0020621 Montgomery 5

3 WV WV0084042 Flatwoods-Canoe Run PSD 5

3 WV WV0020109 Town of West Union 7

3 WV WV0020028 City of Elkins 19

3 WV WV0020150 Moorefield 2

3 WV WV0024856 Thomas 1

3 WV WV0020273 City of Follansbee 5

3 WV WV0105279 City of Piedmont 7

3 WV WV0029289 City of Belington 7

3 WV WV0084310 Greater Paw Paw Sanitary District 7

3 WV WV0024848 Town of Davis 3
D.8

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

3 WV WV0081434 Town of Barrackville 12

3 WV WV0054500 City of Shinnston 10

3 WV WV0035939 Boone County PSD 5

3 WV WV0035912 City of Kenova 2

3 WV WV0035637 Cedar Grove 1

3 WV WV0028118 Dunbar 17

3 WV WV0033821 City of Logan 10

3 WV WV0100901 Nutter Fort 2

3 WV WV0023175 St. Albans 3

3 WV WV0021865 City of Farmington 1

3 WV WV0021857 City of Philippi 13

3 WV WV0021822 Grafton 39

3 WV WV0023094 Princeton 1

3 WV WV0022080 Town of Bethany 3

3 WV WV0022063 City of Parsons 5

3 WV WV0022039 Point Pleasant 2

3 WV WV0024732 City of Hinton 6

3 WV WV0022004 Richwood 2

3 WV WV0032336 Buckhannon 5

3 WV WV0021881 Kingwood 3

3 WV WV0021750 Marmet 3

3 WV WV0021741 Smithers 4

3 WV WV0023124 City of Morgantown 40

3 WV WV0023299 Nitro 6

3 WV WV0024589 Welch 26

3 WV WV0024562 City of Wayne 3

3 WV WV0024473 Marlington 1

3 WV WV0024449 City of Westover 5

3 WV WV0024392 Keyser 1

3 WV WV0020681 Mullens 3

3 WV WV0023302 City of Clarksburg 55

3 WV WV0023159 Huntington 25

3 WV WV0023264 City of Moundsville 6

3 WV WV0023230 Wheeling 137

3 WV WV0023205 Charleston 55

3 WV WV0023183 Beckley 1

3 WV WV0020141 McMechen 3

3 WV WV0023353 Fairmont 43

4 GA GA0037109 Atlanta-Tanyard Creek 1

4 GA GA0037168 Atlanta-Intrenchment and Custer Avenue 2

4 GA GA0037133 Atlanta-McDaniel Street 1

4 GA GA0037117 Atlanta-Proctor Creek/North 1

4 GA GA0036871 Atlanta-Clear Creek 1

4 GA GA0036854 City of Albany CSOs 8

4 GA GA0036838 Columbus CSO 2

4 GA GA0037125 Atlanta-Proctor Creek/Greenferry 1

4 KY KY0020095 Owensboro-West 8

4 KY KY0022373 Ashland WWTP 8

4 KY KY0027413 Prestonsburg WWTP 1

4 KY KY0020257 Maysville WWTP 11

4 KY KY0020711 Henderson WWTP 15

4 KY KY0021440 Morganfield WWTP 2
 Appendix D

D.9

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

4 KY KY0021466 Northern Kentucky S.D. #1 71

4 KY KY0021512 Vanceburg WWTP 5

4 KY KY0026115 Loyall WWTP 6

4 KY KY0026093 Harlan WWTP 1

4 KY KY0022411 Morris Forman WWTF 115

4 KY KY0035467 Catlettsburg WWTP 5

4 KY KY0025291 Pikeville WWTP 3

4 KY KY0024058 Pineville STP 3

4 KY KY0022926 Worthington WWTP 3

4 KY KY0022861 E.C. McManis WWTP 20

4 KY KY0022799 Paducah WWTP 11

4 TN TN0020575 Nashville 30

4 TN TN0020656 Clarksville 2

4 TN TN0024210 Chattanooga 9

5 IL IL0029815 City of Mason City 1

5 IL ILM580035 Village of Niles CSOs 8

5 IL IL0022471 Glenbard WW Authority-Lombard 2

5 IL IL0028070 MWRDGC-Lemont WRP 1

5 IL ILM580031 City of Blue Island CSOs 5

5 IL ILM580034 Lincolnwood CSOs 2

5 IL ILM580003 Village of Melrose Park CSO 1

5 IL ILM580030 Village of North Riverside CSOs 2

5 IL IL0066818 Hinsdale CSOs 4

5 IL IL0068365 Marshall STP 2

5 IL ILM580012 Wilmette CSO 1

5 IL IL0070505 City of Elgin CSOs 12

5 IL IL0021253 Monmouth Main WWTP 6

5 IL ILM580009 Village of LaGrange CSOs 3

5 IL ILM580023 Village of Stickney CSOs 1

5 IL IL0072001 Bloomington CSOs 6

5 IL IL0030660 City of Peru STP 22

5 IL IL0034495 Pekin STP 1 4

5 IL IL0033618 Village of Villa Park CSOs 4

5 IL ILM580008 LaGrange Park CSOs 3

5 IL IL0033472 East St. Louis CSOs 2

5 IL IL0031852 Wood River STP 1

5 IL IL0031356 Taylorville S.D. STP 2

5 IL IL0045039 Village of Western Springs CSOs 4

5 IL IL0030783 Rock Island 6

5 IL IL0037800 City of Peoria CSOs 16

5 IL IL0030503 Quincy STP 6

5 IL IL0030457 Pontiac STP 5

5 IL IL0030384 Ottawa STP 14

5 IL IL0030015 Morton STP 2 2

5 IL IL0029874 City of Metropolis STP 1

5 IL IL0029831 Mattoon WWTP 4

5 IL IL0031216 Spring Valley WWTP 9

5 IL ILM580011 Dixmoor CSO 1

5 IL ILM580036 Skokie CSOs 3

5 IL IL0045012 Chicago CSOs 231

5 IL ILM580007 Village of Riverdale CSOs 4

5 IL ILM580021 Village of River Grove CSO 6
D.10

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 IL ILM580013 Village of Schiller Park CSO 1

5 IL ILM580032 Brookfield CSOs 6

5 IL IL0035084 City of Casey STP 1

5 IL ILM580014 Park Ridge CSOs 4

5 IL ILM580002 City of Evanston CSOs 15

5 IL ILM580026 Des Plaines CSO 2

5 IL ILM580037 Posen CSO 1

5 IL IL0043061 Prophetstown STP 2

5 IL ILM580018 Village of Burnham CSOs 3

5 IL IL0039551 Village of Lemont CSOs 2

5 IL ILM580028 City of Markham CSO 1

5 IL IL0029424 LaSalle WWTP 3

5 IL ILM580025 City of Calumet City CSOs 7

5 IL IL0022004 City of Streator STP 17

5 IL IL0029564 Lincoln STP 2

5 IL IL0023272 Milford STP 4

5 IL IL0023141 Galesburg Sanitary District 40

5 IL IL0022675 Carlinville STP 1

5 IL IL0022519 City of Joliet-Eastside STP 9

5 IL IL0022462 Farmer City STP 2

5 IL IL0023388 Havana STP 2

5 IL IL0022161 Watseka STP 6

5 IL IL0023825 Cairo STP 3

5 IL IL0021989 Spring Creek STP 6

5 IL IL0021971 Sugar Creek STP 2

5 IL IL0021873 City of Belleville STP #1 15

5 IL IL0021792 Wenona WWTP 1

5 IL IL0021661 Jacksonville STP 2

5 IL IL0021601 Fairbury STP 11

5 IL IL0021423 Village of Hartford CSO 1

5 IL IL0022331 Granville STP 4

5 IL IL0028053 MWRDGC Stickney, West-Southwest STP 15

5 IL ILM580015 Riverside CSOs 5

5 IL IL0028657 Fox River WRD-South STP 1

5 IL IL0028622 Effingham STP 3

5 IL IL0028592 Metro East S.D. CSOs 4

5 IL IL0028321 S.D. of Decatur Main STP 4

5 IL IL0028231 Cowden STP 1

5 IL IL0023281 Gibson City STP 1

5 IL IL0028061 MWRDGC Calumet Water Reclamation Plant 13

5 IL IL0029467 Lawrenceville STP 4

5 IL IL0027839 Canton-West STP 2

5 IL IL0027731 Bloomington/Normal WRD/STP 9

5 IL IL0027464 City of Alton STP 6

5 IL IL0027367 Addison 1

5 IL IL0026450 Dixon STP 4

5 IL IL0025135 Beardstown S.D. 1

5 IL IL0024996 City of Oglesby STP 7

5 IL IL0028088 MWRDGC-Northside Water Reclamation Plant 9

5 IL IL0047741 MWRDGC James C. Kire WRP 1

5 IL ILM580020 City of Harvey CSOs 7

5 IL ILM580006 Village of Arlington Heights CSO 1
 Appendix D

D.11

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 IL ILM580016 Village of Calumet Park CSO 1

5 IL ILM580004 Village of Lyons CSOs 3

5 IL ILM580019 Village of Forest Park CSOs 2

5 IL ILM580005 Village of Morton Grove CSOs 2

5 IL ILM580029 Franklin Park CSOs 4

5 IL ILM580022 Village of Maywood CSOs 8

5 IL IL0048518 Aurora CSOs 16

5 IL ILM580033 Summit CSOs 4

5 IL IL0072389 Golf CSOs 1

5 IL IL0021113 City of Morris STP 5

5 IL IL0021059 Marseilles STP 1

5 IL ILM580024 Village of River Forest CSOs 2

5 IL IL0020621 Litchfield STP 1

5 IL ILM580017 Village of Dolton CSOs 3

5 IL IL0072834 Phoenix CSOs 1

5 IL IL0072508 Town of Normal CSOs 0

5 IL ILM580010 Village of South Holland CSOs 5

5 IL IL0020818 Fox Metro Water Reclamation District 1

5 IN IN0035696 Mt. Vernon WWTP 3

5 IN IN0024520 City of South Bend WWTP 44

5 IN IN0023183 Indianapolis-Belmont 131

5 IN IN0024473 City of Seymour WWTP 1

5 IN IN0024414 Rensselaer 17

5 IN IN0020044 City of Alexandria WPCP 3

5 IN IN0024406 Town of Redkey POTW 6

5 IN IN0024023 Paoli Municipal STP 8

5 IN IN0033073 Evansville East WWTP 8

5 IN IN0023914 City of New Castle WWTP 8

5 IN IN0023752 Michigan City 2

5 IN IN0023736 Markle WWTP 2

5 IN IN0023621 Lowell Municipal STP 1

5 IN IN0023604 City of Logansport WWTP 16

5 IN IN0023582 Ligonier WWTP 6

5 IN IN0024554 City of Sullivan WWTP 5

5 IN IN0050903 City of Aurora WW Collection System 5

5 IN IN0024805 Warsaw WWTP 1

5 IN IN0038318 Milford 1

5 IN IN0039314 City of Decatur WWTP 4

5 IN IN0023302 Jeffersonville 16

5 IN IN0032719 Elwood 15

5 IN IN0031950 Indianapolis-South Port 2

5 IN IN0032191 City of Fort Wayne WWTP 42

5 IN IN0032328 City of Peru WWTP 16

5 IN IN0032336 Connersville 5

5 IN IN0032468 Lafayette 15

5 IN IN0024775 Wakarusa WWTP 7

5 IN IN0032573 City of Columbus POTW 3

5 IN IN0025674 City of Elkhart WWTP 39

5 IN IN0032875 City of Kokomo Municipal Sanitation Utility 30

5 IN IN0032956 Evansville Westside WWTP 15

5 IN IN0032964 City of Crawfordsville WWTP 2

5 IN IN0032972 Civil Town of Speedway WWTP 2
D.12

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 IN IN0023132 City of Huntington WWTP 15

5 IN IN0023060 Hammond WWTP 20

5 IN IN0032476 Anderson WWTP 17

5 IN IN0025607 City of Terre Haute POTW 10

5 IN IN0024660 Elden Kuehl Pollution Control Facility 2

5 IN IN0024716 Veedersburg WWTP 1

5 IN IN0024741 City of Wabash WWTP 8

5 IN IN0024791 Warren 3

5 IN IN0024821 West Lafayette WWTP 5

5 IN IN0025232 Town of Akron WWTP 3

5 IN IN0025763 City of Crownpoint WWTP 5

5 IN IN0025585 City of Marion WWTP 9

5 IN IN0025755 City of Goshen WWTP 6

5 IN IN0025615 William Edwin Ross WWTP 4

5 IN IN0025631 Muncie Sanitary District 25

5 IN IN0025640 City of Mishawaka WWTP 19

5 IN IN0025658 Washington Municipal STP 5

5 IN IN0025666 City of Madison WWTP 7

5 IN IN0024562 Summitville 2

5 IN IN0025577 LaPorte Municipal STP 1

5 IN IN0020427 Bremen WWTP 2

5 IN IN0020109 Greenfield 0

5 IN IN0020907 Rossville 2

5 IN IN0020877 North Judson Municipal STP 2

5 IN IN0020770 Middletown 3

5 IN IN0020745 Ossian WWTP 6

5 IN IN0020711 Waterloo Municipal STP 2

5 IN IN0020672 Auburn WWTP 4

5 IN IN0020664 Avilla WWTP 1

5 IN IN0020656 City of Kendallville WWTP 1

5 IN IN0020567 South Whitley Municipal STP 2

5 IN IN0020991 Plymouth Municipal STP 10

5 IN IN0020451 North Vernon WWTP 2

5 IN IN0021016 Tell City WWTP 5

5 IN IN0020362 North Manchester STP 8

5 IN IN0020346 New Haven STP 4

5 IN IN0020222 Attica 2

5 IN IN0020176 Monticello Municipal STP 5

5 IN IN0020168 City of Noblesville WWTP 7

5 IN IN0020133 Greensburg WWTP 1

5 IN IN0020125 Royal Center WWTP 1

5 IN IN0020117 Montpelier WWTP 4

5 IN IN0020095 Portland Municipal STP 16

5 IN IN0020001 Ridgeville WWTP 3

5 IN IN0022977 Gary WWTP 14

5 IN IN0020516 Winamac Municipal STP 5

5 IN IN0021628 Hartford City 17

5 IN IN0022829 East Chicago S.D. 3

5 IN IN0022683 Town of Crothersville WWTP 2

5 IN IN0022535 Centerville Municipal STP 0

5 IN IN0022624 Columbia City WWTP 12

5 IN IN0022608 City of Clinton POTW 6
 Appendix D

D.13

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 IN IN0022578 Chesterton Municipal STP 1

5 IN IN0022560 Chesterfield WWTP 0

5 IN IN0022462 Butler 1

5 IN IN0022420 Boonville 2

5 IN IN0022411 City of Bluffton WWTP 1

5 IN IN0020958 Fortville WWTP 7

5 IN IN0021652 Eaton 2

5 IN IN0022934 Frankfort 1

5 IN IN0021474 Tipton Municipal STP 7

5 IN IN0021466 Nappanee 13

5 IN IN0021385 City of Knox WWTP 1

5 IN IN0021369 Berne 3

5 IN IN0021342 Oxford WWTP 3

5 IN IN0021296 City of Angola WWTP 3

5 IN IN0021270 Rushville 2

5 IN IN0021245 Town of Brownsburg WWTP 2

5 IN IN0021211 Brazil Municipal STP 3

5 IN IN0021202 Plainfield Municipal STP 5

5 IN IN0021105 Fairmount 16

5 IN IN0021067 Rockport WWTP 1

5 IN IN0022144 Albion 2

5 MI MI0048046 Bloomfield Village CSO 1

5 MI MI0026735 St. Joseph CSO 5

5 MI MI0025453 Martin RTB 2

5 MI MI0025500 Milk River CSO 1

5 MI MI0025534 Birmingham CSO 1

5 MI MI0025542 Dearborn CSO 19

5 MI MI0025577 Saginaw WWTP 7

5 MI MI0025585 Chapaton RTB 1

5 MI MI0025631 Menominee WWTP 1

5 MI MI0026069 Grand Rapids WWTP 10

5 MI MI0026077 Grosse Pointe Farms CSO 7

5 MI MI0024058 Sault Ste Marie WWTP 6

5 MI MI0026115 Oakland County SOCSDS 12 Towns RTF 1

5 MI MI0028819 River Rouge CSO 1

5 MI MI0036072 Southgate/Wyandotte CSO RTF 2

5 MI MI0048879 Crystal Falls CSO 2

5 MI MI0051462 Wayne County/ Inkster/Dearborn Heights CSO 2

5 MI MI0051471 Wayne County/Inkster CSO 10

5 MI MI0051489 Wayne County/Dearborn Heights CSO 7

5 MI MI0051535 Wayne County/Redford/ Livonia CSO 8

5 MI MI0051811 Dearborn Heights CSO 1

5 MI MI0051829 Redford Township CSO 1

5 MI MI0051837 Inkster/Dearborn Heights CSO 1

5 MI MI0037427 Oakland County-Acacia Park CSO 1

5 MI MI0026085 Grosse Pointe Shores CSO 0

5 MI MI0022284 Bay City WWTP 5

5 MI MI0023973 Saginaw Township WWTP 0

5 MI MI0020214 Norway WWTP 1

5 MI MI0020362 Manistee WWTP 4

5 MI MI0020591 St. Clair WWTP 0

5 MI MI0020656 Marysville WWTP 1
D.14

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 MI MI0021083 Croswell WWTP 1

5 MI MI0021440 Wakefield WWSL 1

5 MI MI0021695 Blissfield WWTP 2

5 MI MI0022152 Adrian WWTP 2

5 MI MI0022802 Detroit WWTP 86

5 MI MI0022853 East Lansing WWTP 2

5 MI MI0022918 Essexville WWTP 1

5 MI MI0023001 Gladwin WWTP 1

5 MI MI0023205 Iron Mountain-Kingsford WWTP 1

5 MI MI0023400 Lansing WWTP 30

5 MI MI0023515 Manistique WWTP 1

5 MI MI0023647 Mt. Clemens WWTP 1

5 MI MI0023701 Niles WWTP 8

5 MI MI0023833 Port Huron WWTP 14

5 MI MI0043982 North Houghton County W&SA CSO 2

5 MN MN0025470 MCWS-St. Paul 2

5 MN MN0024571 Red Wing 1

5 MN MN0046744 MCWS-Minneapolis 8

5 OH OH0023981 City of Avon Lake 14

5 OH OH0026671 Newark WWTP 25

5 OH OH0026565 Village of Mingo Junction 6

5 OH OH0026522 Middletown WWTP 8

5 OH OH0026514 Middleport WWTP 13

5 OH OH0026352 Marion Water Pollution Control 3

5 OH OH0026263 City of McComb WWTP 2

5 OH OH0026069 City of Lima WWTP 19

5 OH OH0026026 Lancaster WWTP 31

5 OH OH0026018 Lakewood WWTP 9

5 OH OH0025852 Ironton WWTP 9

5 OH OH0025771 Hicksville 5

5 OH OH0024732 Columbus-Jackson Pike 31

5 OH OH0025291 Fremont WWTP 13

5 OH OH0024139 City of Bowling Green 1

5 OH OH0025160 Fort Recovery WWTP 4

5 OH OH0025151 Forest WWTP 3

5 OH OH0025135 Findlay Water Pollution Control Center 18

5 OH OH0025127 Fayette WWTP 15

5 OH OH0025003 City of Elyria WWTP 27

5 OH OH0024929 Delphos WWTP 6

5 OH OH0024899 Defiance 44

5 OH OH0024759 Columbus Grove 4

5 OH OH0024741 Columbus-Southerly 1

5 OH OH0058971 Luckey STP 4

5 OH OH0026841 Oak Harbor 9

5 OH OH0024686 City of Clyde WWTP 3

5 OH OH0025364 City of Girard WWTP 4

5 OH OH0031062 Euclid 18

5 OH OH0020826 Village of Leipsic 1

5 OH OH0126268 Lisbon WWTP 9

5 OH OH0105457 Hamilton County Commissioners 213

5 OH OH0094528 Village of Malta 9

5 OH OH0020893 Napoleon WWTP 3
 Appendix D

D.15

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 OH OH0058408 Metamora 4

5 OH OH0023884 Village of Ansonia WWTP 2

5 OH OH0052922 City of Bucyrus 22

5 OH OH0052876 Port Clinton 2

5 OH OH0052744 City of Fostoria 5

5 OH OH0052604 City of Norwalk 3

5 OH OH0049999 Eastern Ohio Regional Wastewater Authority 47

5 OH OH0052949 Tiffin 30

5 OH OH0043991 Northeast Ohio Regional Sewer District 126

5 OH OH0027197 Portsmouth 10

5 OH OH0029122 Village of Gibsonburg 3

5 OH OH0028240 Zanesville WWTP 21

5 OH OH0028223 City of Youngstown WTP 101

5 OH OH0028185 Wooster 3

5 OH OH0028177 Woodsfield WWTP 5

5 OH OH0028118 City of Willard 3

5 OH OH0027987 Warren 4

5 OH OH0027952 Wapakoneta WWTP 4

5 OH OH0027910 Van Wert 6

5 OH OH0027740 Toledo 37

5 OH OH0027511 Steubenville 16

5 OH OH0027481 Springfield STP 58

5 OH OH0027332 City of Sandusky 15

5 OH OH0048321 Dunkirk 6

5 OH OH0020192 Village of Bradford 9

5 OH OH0020974 Delta WWTP 9

5 OH OH0023833 City of Akron 38

5 OH OH0020117 North Baltimore 2

5 OH OH0020214 Toronto WWTP 7

5 OH OH0020338 Village of Paulding 2

5 OH OH0020451 City of Milford WWTP 2

5 OH OH0020486 Village of Greenwich WWTP 10

5 OH OH0020524 Village of Swanton 13

5 OH OH0020559 Village of Caldwell WWTP 22

5 OH OH0020591 Woodville 17

5 OH OH0020613 Village of New Boston 2

5 OH OH0020664 Crestline WWTP 1

5 OH OH0020851 Bluffton WWTP 20

5 OH OH0020940 Arcanum WWTP 14

5 OH OH0021831 Montpelier WWTP 3

5 OH OH0020001 Upper Sandusky 1

5 OH OH0023400 City of Wauseon 4

5 OH OH0023396 Ohio City 2

5 OH OH0022471 Deshler WWTP 7

5 OH OH0021008 Perrysburg Water Pollution Control 4

5 OH OH0022110 Newton Falls WWTP 28

5 OH OH0022578 Green Springs WWTP 1

5 OH OH0021725 Pomeroy 13

5 OH OH0021491 Bremen 1

5 OH OH0021466 McConnelsville 11

5 OH OH0021326 Village of Payne WWTP 2

5 OH OH0021148 Village of Pandora WWTP 7
D.16

Report to Congress on Impacts and Control of CSOs and SSOs

EPA

Region

State NPDES Permit 

Number

Facility Name Number of 

Outfalls

5 OH OH0021105 Hamler WWTP 6

5 OH OH0022322 Put-In-Bay WWTP 3

5 WI WI0025593 Superior Sewage Disposal System 3

5 WI WI0024767 Milwaukee MSD-Jones Island 120

7 IA IA0076601 Des Moines CSOs 18

7 IA IA0058611 Ottumwa STP 10

7 IA IA0047961 City of Wapello STP 2

7 IA IA0043079 City of Burlington STP 12

7 IA IA0042609 City of Keokuk STP 9

7 IA IA0035947 City of Clinton STP 10

7 IA IA0027219 City of Ft. Madison STP 9

7 IA IA0021059 City of Spencer STP 4

7 IA IA0020842 City of Lake City STP 1

7 IA IA0023434 City of Muscatine STP 5

7 KS KS0042722 Topeka City of Oakland STP 6

7 KS KS0039128 Atchison City WWTP 9

7 KS KS0038563 Kansas City WWTP (and Wyandotte County) 66

7 MO MO0050580 Cape Girardeau WWTP 0

7 MO MO0025178 MSD, Bissell Point WWTP 56

7 MO MO0024929 Kansas City, Westside STP 6

7 MO MO0023027 Sedalia North WWTP 1

7 MO MO0024911 Kansas City, Blue River STP 218

7 MO MO0023221 Macon WWTF 2

7 MO MO0023043 St. Joseph WWTP 15

7 MO MO0117960 Moberly East WWTP 4

7 MO MO0025151 MSD, Lemay WWTP 149

7 NE NE0133680 City of Omaha CSS 31

7 NE NE0021121 Plattsmouth WWTF 0

8 SD SD0027481 City of Lead 1

9 CA CA0079111 Sacramento Regional County S.D. 6

9 CA CA0037681 Oceanside WPCP and Westside Wet Weather CSO System 7

9 CA CA0037664 Bayside WW Facilities WPCP & SF Southeast 29

10 AK AK0023213 Juneau-Douglas WWTP 3

10 OR OR0026361 City of Corvallis WWRP 4

10 OR OR0026905 City of Portland Columbia Blvd WWTP 44

10 OR OR0027561 City of Astoria WWTP 38

10 WA WA0024473 City of Spokane 24

10 WA WA0037061 City of Olympia 3

10 WA WA0031682 City of Seattle 113

10 WA WA0029548 Snohomish WWTP 2

10 WA WA0029289 Bremerton WWTP 16

10 WA WA0024490 City of Everett 14

10 WA WA0024074 City of Mt. Vernon WWTP 2

10 WA WA0023973 City of Port Angeles WWTP 5

10 WA WA0023744 City of Bellingham WWTP 2

10 WA WA0020257 City of Anacortes WWTP 3

10 WA WA0029181 Metropolitan King County - West Point 40
Appendix E 

GPRACSO Model Documentation

 Appendix E

E-1

E.1 GPRACSO Database and GPRACSO Model

EPA developed the GPRACSO Database and GPRACSO Model to estimate CSO volume and the attendant 

pollutant loads on a national level. The GPRACSO Database contains information for all CSO communities in 

the United States. The GPRACSO Model estimates CSO volume and the BOD5 load in CSOs for communities 

with combined sewer systems (CSSs). This documentation presents background on the sources of information 

and the methodology used to develop the GPRACSO Database and Model.

The GPRACSO Database includes information on all of the CSO communities across the United States. The 

primary sources of community-specific information include: 

• EPA’s CWNS (1992, 1996, and 2000)

• EPA’s PCS database

• EPA’s 2001 Report to Congress- Implementation and Enforcement of the CSO Control Policy

• EPA-sponsored municipal interviews with select CSO communities during 2002 and 2003

• Individual CSO community long-term control plan documentations

• Internet searches

The GPRACSO database contains information on how the CWNS Facility identifying numbers relate to CSO 

community names and NPDES numbers, and how complex CSO community systems connect to discharge into 

single regional POTWs. For highly detailed assessments of a single CSO community, the GPRACSO database 

may not have sufficiently accurate information. However, for EPA’s efforts to summarize national conditions, the 

combination of the GPRACSO Database and the GPRACSO Model is sufficient for policy, cost, and technology 

assessments.

Each CSO community is represented as a specified land area within the GPRACSO Model, and each is associated 

with a known quantity of dry weather flow, and a known quantity of wet and dry weather treatment and wet 

weather storage. The GPRACSO Model is applied to represent annual average conditions. Typical rainfall years 

were developed from long-term meteorologic records for each CSO community. The key inputs to the GPRACSO 

model include: service area, population served, impervious cover, rainfall, temperature, treatment plant capacity, 

and wet weather storage. A detailed description of each of these parameters, including database sources, is 

provided in Table E.1

A “CSO community” is used herein to generically refer to the entity that terminates at a single POTW. Each 

POTW is evaluated as a single entity whether it is an individual sewer system or a totaled regional system. 

Wherever multiple CSO communities comprise a single regional system, a single data record, representing 

the total treatment capacity, wet-weather storage, and combined sewer service area of all the combined sewer 

communities in the regional system, is included in the GPRACSO Database. 

The GPRACSO Model was used to estimate CSO volumes and BOD5 concentrations for three national planninglevel scenarios: baseline (1992) prior to CSO Control Policy, current level of control, and (future) full CSO 

Control Policy implementation. To accomplish this, the GPRACSO Model generates rainfall-derived runoff 

from each combined sewer area on an hourly basis, adds the runoff to dry weather flow, calculates the volume of 

combined sewage delivered to the POTW, and estimates CSO volume based on storage and treatment capacities. 

Hourly estimates of BOD5 concentrations within CSSs are used to calculate the pollutant loads in CSOs and 

treated effluent from POTWs. The following sections provide more detail on the GPRACSO model algorithms 

and key assumptions.
E-2

Report to Congress on Impacts and Control of CSOs and SSOs

E.2 Simulation of Dry Weather Sanitary Flows

Average daily dry weather sanitary flows for CSO communities are based on discharge monitoring reports 

available in PCS. Typical flow peaking factors based on literature values are used to represent the hourly variation 

of sanitary flows relative to the average daily flow rate within the CSS and entering the POTW (Metcalf & Eddy 

1991). For example, the GPRACSO model sets the minimum and maximum hourly sanitary inflows to 32 

percent and 141 percent of the average daily reported POTW inflow. Wherever PCS or other data on both average 

and maximum POTW capacity are available for a CSO community, GPRACSO peaking factors are modified 

accordingly. Regardless of the conditions encountered, simulated average dry weather sanitary inflow into a 

POTW always matches the average inflow obtained from the best available source for each CSO community. The 

maximum daily dry weather inflow never exceeds the reported maximum daily POTW treatment capacity.

E.3 Dry Weather Sanitary Pollutant Concentration Estimation

For the purposes of this report, the GPRACSO Model was used to estimate the BOD5 load associated with CSO 

discharges. The GPRACSO Model assumes that the average dry weather BOD5 concentration entering the POTW 

is 158 mg/L, with minimum and maximum hourly values of 40 and 290 (mg/L), respectively. The average dry 

weather concentration and the diurnal (i.e., hourly) variations in pollutant concentration are based on the trend 

Combined Sewer System Description Parameters

Service area acreage and 

population information

Estimated CSO service area data for 1992, 1996, and 2000 were obtained from a myriad of sources 

including CWNS. Where necessary, either population served or miles of sewer pipe were used to 

estimate source area. For a small fraction of the communities, other sources of service area included 

direct responses in EPA-sponsored interviews, published reports, and LTCPs.

Runoff coefficient This coefficient was set to the impervious fraction of each community. Land use/land cover GIS layers 

from the USGS (EPA 2001) were used to aerial weight imperviousness based on five urban land use types. 

The boundary of each community was identified and was graphically superimposed on the USGS data.

Meteorologic data

Rainfall The United States was divided into 84 common hydrologic zones based on average annual precipitation, 

mean January air temperature, geography, and peak 2-year, 6-hour rainfall. For modeling purposes, 

rainfall is represented in terms of hourly rainfall amounts. It is presumed that all communities located in 

common zone would experience the same hydrologic conditions, including snow generation and melt. 

(EPA 2001) 

Temperature Once a “typical” rainfall year was identified for each of the 84 hydrologic zones, the associated hourly 

temperature record was taken from National Weather Service records such that snow generation and 

melting could be assessed. Estimated (modeled) snow accumulation and snow melt was based on hourly 

air temperatures using degree-day methodology (McCuen 1998). 

Treatment System/Management System Parameters

Dry weather and 

maximum wet weather 

POTW flow rates

Multiple sources have been reviewed to establish current and historic POTW treatment levels. The bulk 

of the information on POTWs originated from EPA’s PCS database. For use in the GPRACSO model, the 

median value was calculated for both average and maximum design POTW flow based on up to two 

years of reported daily average and daily peak discharge rates. 

End-of-pipe wet-weather 

treatment capacity

Data was obtained from the internet, published literature, responses in EPA-sponsored interviews, and 

LTCPs.

Secondary bypass with 

flow recombination

Data was obtained from the internet, published literature, responses in EPA-sponsored interviews, and 

LTCPs.

Wet weather storage 

capacity

Data was obtained from the internet, published literature, responses in EPA-sponsored interviews, and 

LTCPs. 

Table E.1 Summary of Key Inputs to the GPRACSO Model
 Appendix E

E-3

reported by Metcalf & Eddy (1991) for the City of Chicago. There were no other influences on hourly dry weather 

concentrations unless there were additional inflow from snowmelt or from stored combined sewage returned 

from wet weather storage facilities. Algorithms associated with these two inputs are:

Flow source #1: The GPRACSO Model identifies that there is a snow pack present in the CSO community and 

that hourly air temperature is above 32 degrees.

Flow source #2: A CSO community has dedicated wet weather storage available to capture any wet weather flows 

in excess of the POTW maximum treatment capacity. 

E.4 Estimation of CSO Volume

The GPRACSO Model performs many hydrologic computations as it evaluates the potential and actual wetweather inflow into the CSS. The data sources used and the computations performed are as follows.

 

Typical meteorological conditions were estimated for each CSO community based on a review of long-term data 

from the National Weather Service. CSO communities were geographically grouped based on hydrology into 84 

common zones, and a typical rainfall year was identified for each zone. As a rule, the typical year contained within 

+/-10 percent of the annual average precipitation for that zone or location, and had no single rainfall event larger 

than the two-year return period rainfall. Depending on the zone evaluated, the typical rainfall year presents 

between 30 and 80 potential overflow-producing events for each CSO community within the zone. Hourly 

temperature records was associated with rainfall records for each zone so that snow accumulation and melting 

could be included in the GPRACSO Model simulation.

Runoff calculations were performed using the rational method, which multiplies hourly rainfall by a single 

coefficient to calculate the runoff. The coefficient was set to equal the overall impervious cover of each CSO 

community. As described in Table E.1 under runoff coefficient, land use/land cover GIS layers from the USGS 

were used to help estimate the geographically weighted imperviousness for the land area found within the 

political boundaries of the CSO communities.

Snow accumulation and melting were calculated using a degree-day approach applied on an hourly basis 

(McCuen 1989). The GPRACSO Model monitors the conditions in each CSO community to determine if snow 

pack is present and if it is aggregating or shrinking in any simulated hour. Each hour’s temperature was evaluated 

to establish the potential snowmelt, and snowmelt was simulated if a snow pack existed. 

Model Response Assumptions

From the calculated melt rate, an estimate of the snowmelt is made, all of which 

is assumed to flow into the CSS. The relative volumes of dry weather sewage and 

snowmelt are used to calculate a reduction in the BOD5 concentration entering the 

POTW.

It is assumed that snowmelt contains 

zero pollutant and as a result dilutes the 

inflow entering the POTW.

Model Response Assumptions

The GPRACSO model tracks all of the storage 

volume along with the amount of pollutant 

(BOD5) it contains on an hourly basis.

GPRACSO assumes that the stored flow is discharged to the POTW as soon 

as there is available treatment capacity (i.e., the hourly POTW inflow is less 

than the reported maximum POTW treatment capacity).
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Report to Congress on Impacts and Control of CSOs and SSOs

POTW wet weather treatment capacity is an important management feature. The GPRACSO model assumes 

the average event-period wet weather POTW treatment capacity is 130 percent of the reported maximum daily 

treatment rate. Rainfall and CSO events often occur over a period between two and eight hours, a period short 

enough for POTWs to “max-out” their systems at a greater rate than possible for a full 24-hour period. For 

example, if DMR data for a single POTW indicates 100 MGD is the maximum daily discharge rate (the median of 

maximum monthly values reported in PCS), then GPRACSO assumes that the POTW can actually treat 130 MGD 

over the short-term (i.e., during wet weather conditions). This 130 percent rule was developed from in-depth 

comparison between GPRACSO simulations and the results of local models/studies for four CSO communities. 

The GPRACSO simulation assumes the POTW secondary treatment capacity above the simulated hourly dry 

weather inflow (the annual average daily POTW inflow multiplied by the appropriate hourly peaking factor) is 

available for treating potential CSO. So a POTW with a daily 100 MGD maximum secondary treatment capacity 

and an estimated hourly dry weather flow rate of 76 MGD (at 2 pm) would have 54 MGD capacity available 

between 2 and 3 pm to manage any wet weather flows (resulting from 100 MGD *1.3 - 76 MGD). At 3 pm, the 

estimated dry weather flow would be about 71 MGD, so any wet weather flows entering the system between 3 and 

4 pm would be treated up to 59 MGD (resulting from 100 MGD *1.3 - 71 MGD).

Wet weather end-of-pipe (EOP) treatment was assumed to occur only after both the maximum wet weather 

treatment capacity of the POTW and any wet weather storage is fully utilized during a CSO event. The GPRACSO 

Model uses EOP as a last resort treatment, and it cannot be used to drain stored wet weather flows. EOP treatment 

technologies considered by the GPRACSO Model include things like vortex treatment facilities.

Wet weather storage was simulated using a built-in algorithm within the GPRACSO Model. The algorithm assesses 

the operation of wet weather storage facilities designed to capture and hold wet weather flows until treatment 

capacity is available. The operation of wet weather storage is simulated such that any hourly flows in excess of 

POTW treatment would go directly to wet weather storage. Only after all available wet weather storage is filled 

and EOP treatment capacity is exceeded will GPRACSO simulate a CSO discharge. Available POTW capacity for 

draining storage is defined as the difference between the maximum POTW treatment rate and the flow entering 

the simulated POTW for any given hour.

Conveyance limits for combined sewer interceptor systems are not considered by the GPRACSO Model. The 

GPRACSO Model assumes that the total interceptor system discharging into a POTW has a capacity greater than 

the maximum treatment rate of the POTW. As a result, the limiting factor within the GPRACSO Model is the 

POTW wet weather treatment capacity. While it is acknowledged that this assumption is not appropriate for some 

CSO communities, maximization of flows to the POTW is a required minimum control measure under EPA’s CSO 

Control Policy.

E.5 Estimation of CSO Pollutant Loads

The GPRACSO Model attempts to recognize the major influences on CSS pollutant concentration on an hour-tohour basis. The influences accounted for include:

• Flushing of accumulated materials from the CSS

• Dilution of sanitary fl ows by storm water infl ow late in the overfl ow periods

• Variation in sanitary fl ow rate and concentration through the day

The first two influences are lumped into a single load or calculation referred to as “storm water pollutant load”. 

This load represents the combination of pollutants flushed from pipes and pollutants washed from the urban surface, 
 Appendix E

E-5

independent of any sanitary inflow rates. In order to estimate the BOD5 loadings attributable to storm water 

(including the flushing of settled pollutant in pipes), the following exponential relationship between time and 

BOD5 concentration was applied:

 Equation 1. C = (200 * 10 -1.5*(t)) + 15

 Where:

 C = the BOD5 concentration in mg/L used to calculate the storm water load

 t = time in hours since the overflow started

 15 = the BOD5 concentration in mg/L assumed to be in urban storm water

Information from two data sources was used to develop the above relationship. The first data source is multievent CSO monitoring results of first-flush concentrations in combined sewers for a medium-sized east 

coast CSO community. The second data source was from 90th percentile event mean concentration BOD5

concentrations reported in EPA’s Nationwide Urban Runoff Program (EPA 1985). The first data source suggests 

that BOD5 concentrations (grab samples in sewers) at the very start of runoff events range between 200 and 400 

mg/L, but that concentrations decrease rapidly within the first hour of runoff. As a result, the average first hour 

BOD5 concentration is set to be 215 mg/L, using the equation above. The second data source suggests a highend long-term urban runoff BOD5 concentration in the absence of CSOs is approximately 15mg/L, a feature also 

provided by the equation above.

Calculation of hourly overflow concentration in storm water/sanitary mix. While the first flush effect results in a 

high concentration of BOD5, later in the CSO event storm water dilutes the more concentrated sanitary flows. As 

a result, the GPRACSO Model continuously mixes the sanitary flow/pollutant load with the storm water runoff/

pollutant load each hour to calculate the average hourly concentration. It is assumed that the mixing of sanitary 

and storm water is 100 percent complete for each hour simulated and that any CSOs that occur will contain the 

same pollutant concentration as what enters the simulated POTW. The logic used to select the uniform BOD5

concentration for any particular hour is: 

The CSCConc(ttt,0) value is used to compute the CSO BOD5 load, the inflow load entering the POTW, and the 

pollutant load stored in any wet weather storage that may be present in the system. For BOD5, the assumed 

storm water concentration for the first hour when overflow occurs is 215 mg/L regardless of when it occurs in 

the day. For any subsequent hour in which overflow can occur, the BOD5 concentration is the greater of (1) the 

If EventTime = 0 (the runoff has just started entering the CSS), then

CSCConc(ttt,0) = (200 * 10 -1.5*(event time)) + 15

If EventTime > 0 (the overflow event is progressing), then 

CSCConc(ttt,0) = (200 * 10 -1.5*(event time)) + 15

If CSCConc(ttt,0) < DWBODconc * hours, then 

CSCConc(ttt,0) = (HRDischarge(ttt,0) - HRDWF(ttt,0)) * (CSCConc(ttt,0) +

 HRDWF(ttt,0) * DWBODconc * hours) / HRDischarge(ttt,0)

 

EventTime = time since the start of the overflow event (hours)

CSCConc = uniform concentration of the storm water/sanitary mixture (mg/L) from the combined sewer 

 community

DWBODconc * hours = the sanitary flow concentration in the absence of overflow (mg/L) for the “hour” under 

 simulation

HRDischarge(ttt,0) = the simulated total hourly flow in the combined sewer (MGD) 

HRDWF(ttt,0) = the hour’s sanitary flow rate in the absence of overflow (MGD)
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Report to Congress on Impacts and Control of CSOs and SSOs

value taken from Equation 1 based on the time elapsed since the start of the overflow, or (2) the flow weighted 

combination of Equation 1 and the dry weather sanitary flow concentration based on hourly variation. The first 

flush is recognized as the strongest influence on concentration at the beginning of the event, the dominant role 

of storm water dilution is recognized later in the event, and the daily variation in sanitary flow concentration is 

accounted for throughout the event.

E.6 Comparison with Other Estimates

EPA compared GPRACSO results against those of “local CSO models” of varying complexity and sophistication 

in five CSO communities. While there is no guarantee that they are correct, the local CSO models were developed 

to support LTCPs, and were assumed to be reasonably accurate. EPA used the departure from local CSO model 

estimates to gage the relative accuracy of the GPRACSO Model. Based on the local CSO model results, EPA 

established the following error brackets for GPRACSO estimates:

• CSO volumes are within +/- 50 percent of local CSO model estimates

• CSO community-wide average annual pollutant EMCs are at +/- 80 percent of local CSO model estimates

• CSO pollutant loads are within +/- 80 percent of local model estimates

Overall, errors originate from two principal sources: inaccuracies in data describing CSO communities, and 

errors resulting from the GPRACSO Model algorithms. EPA believes that the larger error is associated with the 

first source; that the bulk of the model error originates from errors in the basic system data (e.g., the combined 

sewer service area in each CSS). For several years, EPA has collected data to improve its understanding of historic, 

current, and future conditions in communities with combined sewers, obtaining better data each year. Additional 

investigation of CSO communities is anticipated to improve the assessment with the GPRACSO Model and its 

associated database.

To date, an in-depth comparison of local models and GPRACSO algorithms has not been performed. For the 

GPRACSO Model, extensive efforts were made to account for the majority of physical and hydrologic factors 

encountered in the generation of sanitary and storm water flows. Reasonable data sources are used to estimate the 

performance of POTWs and the operation of wet weather treatment and storage. However, the GPRACSO Model 

greatly simplifies the influence of geographic dissimilarities to each city, e.g., network of sewer pipes and pump 

stations are not explicitly modeled. 

E.7 Summary

The GPRACSO Database and application of the GPRACSO Model have been applied to estimate the CSO 

volume and annual BOD5 load for all combined sewer communities nationwide. The GPRACSO Model has 

been applied to estimate the current annual performance expected under rainfall that are both local to each 

community and typical on an annual basis. In addition, GPRACSO model results are conditions based on historic 

POTW performance data. Recent POTW upgrades and/or new wet weather management facilities may not be 

incorporated within the current version of the GPRACSO database. (Note: EPA is continuously collecting data on 

CSS facilities that can be used to update the GPRACSO database). For this reason, the estimates produced by the 

GPRACSO simulation may not fully recognize current management. 

For its analysis of CSO regulations, EPA has used the typical or average meteorologic conditions faced by each 

community to analyze annual CSO management performance, and then summed all communities to obtain 

a national total performance. The GPRACSO Model estimates of the typical performance will vary from the 

actual performance measured at a specific place and time, in a single community. This is because the actual 
 Appendix E

E-7

meteorologic conditions (e.g., the weather at 12 PM on May 1, 2002) will vary from that found in the matching 

hours meteorologic record for the selected typical year.

References

EPA. 1983. Results of the Nationwide Runoff Program, Vol 1, Final Report. NTIS PB84-185552.

EPA. Office of Science and Technology. 2001. Better Assessment Science Integrating Point and Nonpoint Sources: 

BASINS Version 3.0, User’s Manual. EPA 823-B-01-001.

McCuen, R.H. 1989. Hydrologic Analysis and Design, 2nd edition. Prentice-Hall. Upper Saddle River, NJ.

Metcalf & Eddy. 1991. Wastewater Enginnering Treatment, Disposal, Reuse, 3rd edition. McGraw Hill International.

Water Environment Federation (WEF) and American Society of Civil Engineers (ASCE). 1998. Urban Runoff 

Quality Management. WEF Manual of Practice No. 23. ASCE Manual and Report on Engineering Practice No. 87. 

Reston, VA: ASCE.
Appendix F 

Analysis of CSO Receiving Waters 

Using the National Hydrography 

Dataset (NHD)

 Appendix F

F-1

F.1 Background

EPA compiled a national inventory of NPDES permits for CSO facilities during the development of the Report 

to Congress–Implementation and Enforcement of the Combined Sewer Overflow Control Policy (EPA 2001). Data 

collection, management, and analysis are documented in Appendix F of the 2001 report. The national CSO 

inventory was developed from a review of permit files and information provided by NPDES authorities. The 

resulting inventory included a summary of total CSO outfalls per permit and, where available, a narrative 

descriptions of CSO outfall location (e.g., “near intersection of Water and Main Streets”) and/or by spatial 

coordinates (i.e., latitude and longitude). This inventory was reviewed by states and EPA regions to determine if 

the total number CSO outfalls was correct, but the information on outfall location was not verified as part of the 

2001 report effort.

F.2 Objectives

As specified in the Consolidated Appropriations Act for Fiscal Year 2001 (P.L. 106-554):

..the Environmental Protection Agency shall transmit to Congress a report summarizing—

(1) the extent of the human health and environmental impacts caused by municipal combined sewer 

overflows and sanitary sewer overflows, including the location of discharges causing such impacts, the 

volume of pollutants discharged, and the constituents discharged; ...

Given this requirement, and with the CSO permit inventory in-place from the 2001 report, EPA established a 

goal of updating the CSO data to include geographical locations for CSO outfalls included in CSO permits. EPA’s 

overriding objective for this effort was to provide a framework for identifying areas at and downstream of CSO 

outfalls to examine potential environmental and human health impacts.

F.3 Development of a National CSO Outfalls GIS Database

EPA began the process of geographically locating CSO outfalls by building on data originally collected for the 

2001 report. The CSO permit inventory was updated through a review by states and EPA regions. Based on 

the latest data updates, EPA obtained latitude and longitude for outfalls included in more than two-thirds of 

active CSO permits. Most of the other permits had narrative descriptions locating CSO outfalls. These narrative 

descriptions varied, but generally mentioned the nearest cross-street or public landmark and often included the 

name or description of the receiving waterbody.

EPA extracted CSO outfalls with narrative location descriptions. EPA utilized ESRI ArcGIS for the geo-spatial 

processing and analysis of these outfalls. EPA developed a GIS base map of land areas, transportation networks, 

and local waterbodies for each CSO permit to help locate outfalls based on narrative data. The analysis utilized 

the Census 2000 Topologically Integrated Geographic Encoding and Referencing (TIGER®) database of the U.S. 

Census Bureau for reference mapping. The geographic data for the TIGER® database is freely available from ESRI 

in ArcGIS format. The TIGER® database includes geographic data for roads, railroads, hydrography, utility lines, 

and government entities (e.g., places and counties).

EPA extracted TIGER® base map data for over 200 areas to match the more than 2,000 narrative outfall locations 

to a spaital location. A combination of ArcGIS address mapping (where street data were available) and visual 

identification were employed to match the narrative location to a geographic point. Once located, additional 

descriptive information was used to verify the position. This included comparing the ArcGIS mapped position 

relative to receiving waters or distance from landmarks recorded in the CSO inventory. Narrative locations 
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Report to Congress on Impacts and Control of CSOs and SSOs

not identifiable within the ArcGIS analysis were excluded, and points that could not be confirmed with other 

narrative descriptive locators were flagged for follow-up with the NPDES authority and were updated as 

necessary. Upon completion of identification and updates, the spatially-referenced CSO outfall latitude and 

longitude coordinates were computed and exported. 

With this procedure, over 90 percent of CSO outfalls were geographically mapped. These outfalls were then tested 

for data quality and consistency. The CSO outfalls were intersected with available GIS data (states, watersheds, 

and waterbodies). CSO permits were linked to PCS to supplement data for descriptive outfall locations within the 

CSO inventory. Spatially-referenced CSO outfalls with state, watershed 8-digit HUC, or waterbody information 

from PCS inconsistent with that obtained from the ArcGIS base data were flagged for review by the NPDES 

authority. Upon completion of review and incorporation of available updates, the CSO outfalls associated with 

nearly 95 percent of active CSO permits were geographically referenced, as shown in Figure F.1. The spatiallyreferenced CSO outfalls served as a data source for evaluating and assessing potential environmental and human 

health impacts from CSO discharges.

F.4 Available EPA Data Sources

EPA conducted literature reviews and developed an inventory of possible data sources at the federal, state, and 

local levels that could be used to assess potential impacts from CSOs. The listing below reflects national scale 

data sources used to assess potential impacts from CSOs. These descriptions include website citations where the 

data source is described in more detail, including references to data dictionaries and/or other metadata, analyses 

conducted, and findings. The application of these data sources for this Report to Congress is presented in the next 

section.

Figure F.1 Location of CSO Outfalls
 Appendix F

F-3

Permit Compliance System (PCS) - http://www.epa.gov/enviro/html/pcs/

Discharge of pollutants into waters of the United States is regulated under the NPDES program, a mandated 

provision of the Clean Water Act. To assist with the regulation process, state and federal regulators use an 

information management system known as PCS. PCS stores data about NPDES facilities, permits, compliance 

status, and enforcement activities for up to six years. PCS includes data on CSO permits but lacks data on location 

of outfalls for most permits. EPA is currently working with the regions and states to develop an approach for 

including and maintaining CSO outfall locations within the existing PCS framework. While PCS is a tool for EPA 

and state use only, public data are made available through EPA’s Envirofacts website http://www.epa.gov/enviro/, 

which provides a single point for accessing EPA’s facility dataset.

National Assessment Database (NADB) - http://www.epa.gov/305b/2000report/

The National Assessment Database contains information on the attainment of water quality standards. 

Assessed waters are classified as “fully supporting,” “threatened,” or “not supporting,” their designated uses. This 

information is reported in the NWQI Report to Congress under Section 305(b) of the Clean Water Act. Analyses 

presented in this report use EPA’s 2000 NWQI Report to Congress and the NHD-referenced data as means of 

assessing areas downstream of CSO outfalls.

Water Quality Standards Database (WQSDB) - http://www.epa.gov/wqsdatabase/

The WQSDB contains information on the designated uses for waterbodies. Designated uses set a regulatory goal 

for the waterbody, define the level of protection assigned to it, and establish scientific criteria to support that 

use. While not directly used for this report, the WQSDB provides supporting reference and data for EPA’s 305(b) 

NWQI.

303(d) Total Maximum Daily Load (TMDL) Tracking System - http://www.epa.gov/tmdl/

The TMDL Tracking System contains information on waters that are not supporting their designated uses. These 

waters are listed by the state as impaired under Section 303(d) of the Clean Water Act. The status of TMDLs is 

also tracked. This report uses the April 1, 2002 NHD-referenced data to consider 303(d) listed waters downstream 

of CSO outfalls and to examine TMDLs in place for those areas.

Safe Drinking Water Information System (SDWIS)

The Safe Drinking Water Act requires that states report information to EPA about public water systems, 

including violations of EPA’s drinking water regulations. The Safe Drinking Waters Act regulations and their 

enabling statutes establish maximum contaminant levels, compliance guidelines, and monitoring and reporting 

requirements to ensure that water provided to customers is safe for human consumption. This information is 

stored in SDWIS. Data as of June 25, 2003, was provided by EPA’s Office of Ground Water and Drinking Water in 

an NHD-referenced format to facilitate comparison with known CSO outfall locations.

National Shellfish Register of Classified Growing Waters

The classification of shellfish-growing waters is based on the National Shellfish Sanitation Program (NSSP), 

a cooperative effort involving states, the shellfish industry, and the FDA. Since 1983, it has been administered 

through the Interstate Shellfish Sanitation Conference (ISSC). The ISSC was formed to promote shellfish 

sanitation, adopt uniform procedures, and develop comprehensive guidelines to regulate the harvesting, 

processing, and shipment of shellfish. In 1995, the NSSP and coastal states listed over 33,000 square miles of 

marine and estuarine waters as classified shellfish-growth areas and published the coverage for distribution in 

ArcGIS geographically referenced areas. The areas are very site-specific and not a part of a hydrography network. 

Nonetheless, the data were easily linked to nearby CSO outfalls via standard ArcGIS geoanalysis detailed later in 

this appendix.
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Report to Congress on Impacts and Control of CSOs and SSOs

F.5 Technical Approach

The technical approach taken to link a digital CSO outfall dataset to other EPA data and program assessments is 

summarized below. The key activities undertaken for this effort include converting CSO outfall data to a spatially 

referenced digital format, relating the outfall locations to the NHD, and using the NHD stream network to look 

at areas at and downstream of the CSO outfalls through comparative analysis of other EPA data referenced to 

the NHD. EPA maintains program data including 303(d) lists, 305(b) assessments, and drinking water intake 

data linked to the NHD in its Reach Address Database (RAD). RAD provides the linkage from EPA datasets to 

the NHD referenced water reaches. EPA’s Watershed Assessment, Tracking, & Environmental ResultS (WATERS) 

initiative serves as a common platform for linking data from all of EPA’s surface water programs. These 

relationships are discussed in more detail below.

National Hydrography Database (NHD) - http://nhd.usgs.gov/

NHD is a nationally consistent hydrography dataset for the United States. A culmination of recent cooperative 

efforts between EPA and USGS, it combines elements of USGS digital line graph hydrography files and the EPA 

Reach File (RF3). NHD is designed to serve three simultaneous functions for surface waters:

 1. Provide a standard unique identifier (reach code) for each part of the surface water network. 

Reach codes act like street addresses in a road network, providing a unique identifier for streams 

and other waterbodies. 

 2. Contain a tabular routing (navigation) network of these features.

 3. Include a digital map representation of these features.

The analyses conducted for this report use the three functions of NHD. With NHD, CSO outfall locations are 

described by reach, the network is used to examine downstream conditions, and a visual representation of the 

locations and downstream pathway is given.

NHD is currently available in 1:100,000 (1:100K) scale format from USGS for the continental United States. 

Although some states are moving to higher resolution representations of their waters (e.g., the 1:24,000 (1:24K) 

scale), the 1:100,000 scale NHD was used for the analyses presented in this report.

Reach Address Database (RAD) - http://www.epa.gov/waters/about/rad.html

EPA’s RAD stores program data linked to NHD reaches, including information on the spatial extent of various 

program data. Datasets in RAD include, but are not limited to, the 303(d) and 305(b) programs. RAD stores only 

locational information for stream addresses (i.e., position of the listing within the NHD reach network). The 

details of that reach, such as designated use, monitoring results, assessment scores, or impairment type, remain 

in the program database. This report uses RAD as the gateway for linking CSO outfalls referenced to NHD with 

other EPA program data.

Reach Index and Reach Navigation of the Digital CSO Outfalls

A Reach Indexing Tool (RIT) was used to designate CSO outfall locations to the nearest point of an NHD reach, 

creating a CSO outfall stream address. These data were transferred to the RAD to provide instant linkage to other 

RAD program data. In order to access the other data, the CSO outfall addresses were then ‘reach walked’ to other 

RAD data. The reach walk is a service available within the WATERS system that allows upstream or downstream 

navigation of the NHD network, and thus a traverse of any data in the RAD/WATERS system. The reach walk 

was conducted to provide information on the distance between the CSO outfall stream address and other EPA 
 Appendix F

F-5

program data within RAD.

Downstream Analysis, Impacts, and Pollutants of Concern

For analysis of the reach walked NHD data, a downstream distance of one mile was considered to be a point 

where CSO impacts would be most discernable. Where pollutant or stressor information was available, the 

primary pollutants found in CSOs (pathogens, solids (TSS), and oxygen-demanding organic materials measured 

as BOD5) were included in the analysis. 

F.6 Analysis and Results

305(b) Analysis and 303(d) Analysis

Electronic data were available via WATERS within the RAD framework for 305(b) (assessment) and 303(d) 

(listing) information, as part of the Clean Water Act requirements. While 303(d) listed waters were available 

electronically for all states except Alaska, electronic 305(b) assessments were available for 13 of the 32 CSO states 

(as shown in Figure F.2). Data comparisons were made only for states where data were available.

State assessed waters within one mile downstream of CSO outfalls were evaluated. Waters in that distance with 

a cited impairment (pathogens, sediment/siltation, and organic enrichment causing low dissolved oxygen) were 

further examined. For example, existing TMDLs were reviewed to explore the relationship between impairment 

and source load allocation, including CSOs, as part of the existing TMDL. The tables on the next page summarize 

the findings.

Figure F.2 CSO States with Electronic NHD-Indexed 305(b) Assessed Waters

CSO States

CSO States w/ electronic 305(b) data
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Report to Congress on Impacts and Control of CSOs and SSOs

Drinking Water Analysis

The SDWIS database and the CSO database were geospatially cross-referenced using the NHD. The location of 

drinking water intakes downstream of a CSO was determined and their proximity was assessed. 

The database was queried selecting the drinking water intakes within one mile of a CSO outfall. Phone interviews 

were conducted with both the NPDES and drinking water authorities for cities with CSOs located within one mile 

upstream of a drinking water intake to confirm the location of the CSO outfall, whether the CSOs are active, and 

the location of the drinking water intake. Two facilities were eliminated from the analysis because their drinking 

water intake or their CSO outfalls were not located within the one-mile analysis radius. The results of this analysis 

are summarized in Table F.5.

# of NHD Reaches

In CSO States 1,495,853

within 1 mile downstream of a CSO Outfall 1,560

 Reason or Cause of Listing

Listed Waters

 Pathogens Enrichment Leading 

to Low Dissolved 

Oxygen

Sediment 

and 

Siltation

Total number of listed waters in CSO 

states 3,446 1,892 3,136

Number of listed waters within one 

mile of a CSO outfall 191 163 149

Assessed Waters Total 

Assessed

Assessed as 

Good

Assessed as 

Impaired

Percent 

Impaired

Assessed 305(b) segments in CSO 

states with electronic 305(b) data 59,335 44,457 14,878 25%

Assessed segments within one mile 

downstream of a CSO outfall 733 181 552 75%

Table F.2 Waters Considered in this Analysis

Table F.3 2000 NWQI Assessment within 1 mile of CSO Outfall

Table F.4 303(d) Listed Waters by Cause Categories aligning with impacts from CSOs
 Appendix F

F-7

Table F.5 Association of CSO Outfalls with Drinking Water Intakes

EPA Region State CSO Outfalls within 1 Mile Upstream 

of a Drinking Water Intake

1 ME 7

2 NY 7

3 PA 19

3 WV 9

4 KY 7

5 IN 3

5 OH 7

 Total: 59

Note: EPA was unable to confirm data for an additional 14 outfalls in two states (PA and WV); 

these outfalls are not included in this table.

Classified Shellfish-Growing Areas Analysis

Classified shellfish-growing areas are not georeferenced to the NHD. The geographic coverage available from NOAA 

provides spatial locations of the shellfish-growing areas and associated attribute data. The attribute data include 

information such as the shellfish classification and suspected sources of pollution including wastewater treatment 

plants and CSOs. 

Given the geospatial location of the CSOs and shellfish-growing areas, it is possible to analyze the distance between 

the two datasets using a buffer. A buffer creates an area around a geospatial dataset for a specified distance. It is 

then possible to intersect the buffer with another dataset to determine if they coincide spatially. This buffer process 

was used to determine how many CSOs are located within five miles of a shellfish-growing area. The results of this 

analysis are summarized in Table F.6 below.

Table F.6 Classified Shellfish-Growing Areas Within Five Miles of a CSO Outfall

Shellfish Harvest Classification Number of Classified Shellfish Growing Areas 

within 5 Miles of a CSO outfall

Prohibited 411

Restricted 80

Approved 154

Unclassified 14

Total 659
Appendix G 

National Estimate of SSO 

Frequency and Volume

 Appendix G

G-1

G.1 Summary

National estimates of SSO frequency and volume were generated based on reporting data for more than 33,000 

SSO events provided by 25 states during calendar years 2001, 2002, and 2003. The discussion of SSOs in this 

report does not account for discharges from points after the headworks of the treatment plant, regardless of 

the level of treatment, or backups into buildings caused by problems in the publicly-owned portion of the 

SSS. Therefore, these estimates of SSO volume and frequency do not account for discharges occurring after the 

headworks of the treatment plant or backups into buildings. Estimates were generated by extrapolating these 

data across the remaining 25 states and Washington, D.C., through a five-step procedure:

1. Tabulate the total number of SSO events and the SSO volume for each of the reporting states.

2. Estimate the total number of SSO events per year for each non-reporting state based on the number 

of sewer systems in the state or the population served by sewer systems in the state.

3. Divide the total number of events in each non-reporting state into different categories describing 

the cause of the SSO event based on observed regional differences among the 25 reporting states.

4. Calculate the SSO volume for each cause category in each non-reporting state to account for 

observed regional differences.

5. Calculate national estimates by summing the total number of events by state and the total volume 

across all states.

A range of estimates corresponding to different assumptions regarding the nature of the reported data was 

generated. Results of the analysis indicate that the annual frequency of SSO events is between 23,000 and 

75,000 events per year, with a corresponding volume of 3 to 10 billion gallons per year. This relatively large 

range is due to uncertainty regarding the extent to which the reported SSO events reflect all SSO events that 

occurred during calendar years 2001, 2002, and 2003.

This appendix summarizes how the estimates of SSO frequency and volume were generated. The discussion is 

grouped into the following sections:

G.2 Data Available

The national estimates of SSO frequency and volume were based on data provided by 25 states over three years 

(January 1, 2001 to December 31, 2003). Data were provided by: 

• California • Maryland • Rhode Island

• Colorado • Massachusetts • South Carolina

• Connecticut • Michigan • South Dakota

• Florida • Minnesota • Utah

• Georgia • New Hampshire • Washington

• Hawaii • Nevada • Wisconin

• Indiana • North Carolina • Wyoming

• Kansas • North Dakota

• Maine • Oklahoma

• Data available • Assumptions • Results

• Inital data assessment • Calculation procedure
Report to Congress on Impacts and Control of CSOs and SSOs

G-2

These data were obtained directly from the NPDES authority in each of these states. Data were typically compiled 

in either a database or spreadsheet. Specific data elements tracked by NPDES authorities are summarized in Table 

G.1.

A total of 36,325 SSO event records were collected from the NPDES authorities and compiled into a single data 

management system. No attempt was made to verify the quality or accuracy of the data with the individual 

jurisdictions reporting the SSOs; however, a quality check of the data was performed to identify discrepancies 

(e.g., gallons versus million gallons, dates outside of the 2001-2003 range, and records with no dates). Reported 

events with missing event volumes were used to generate frequency estimates, but were not used for volume 

a May not include exact SSO location point

b May include cleanup activities, volume recovered, and corrective or preventive measures

Table G.1 Data Elements Tracked by NPDES Authorities with Electronic Systems

State

Date & 

Time 

Reported

Start Date 

& Time

End Date 

& Time/

Duration

Total 

Overfl ow 

Volume 

(gallons)

SSO 

Locationa

SSO Cause Response 

Measures 

Takenb 

 Receiving 

Water 

Identifi ed 

CA ●●● ● ●● ● ●

CO ●●● ● ●● ● ●

CT ●● ● ●●

FL ● ● ●● ●

GA ●● ● ● ●

HI ●●● ● ●● ● ●

IN ●● ● ●●

KS ●● ●

MA ●●● ● ●● ● ●

MD ●● ● ●● ●

ME ●●● ● ●● ● ●

MI ●●● ● ●● ● ●

MN ●●● ● ●● ●

NC ●● ● ●● ●

ND ●●● ● ● ● ●

NH ●●● ● ●● ● ●

NV ●● ● ●● ● ●

OK ●● ● ●● ●

RI ●●● ● ●● ● ●

SC ● ●● ●

SD ●●● ● ●● ● ●

UT ●

WA ● ● ●● ● ●

WI ●● ● ●● ● ●

WY ● ●● ●
 Appendix G

G-3

estimates. Reported events with dates outside of the 2001-2003 range and events with no dates were not used 

to estimate SSO frequency or volume. After the screening, a total of 33,213 records remained describing event 

frequency, and 28,708 records remained describing event volumes.

Some states did not provide data for the entire three-year period. SSO frequency data for these states were 

adjusted proportionally to account for the missing months. For example, the number of observed events for a 

state providing 21 months of reports out of the 36-month period were scaled up by a factor of 36/21.

Basic information describing the sewered universe in each state was obtained from the 2000 CWNS and 

included:

• Total number of collection systems by state

• Number of SSSs by state

• Population served by SSSs by state

Lastly, data for each state were grouped by EPA Region to facilitate analysis of regional differences. The number 

of SSSs and the population served are presented by Region in Table G.2.

Table G.2 Number of SSSs and the Population Served by the SSSs for each Region

EPA Region Total number of SSSs Population served by SSSs 

(in millions)

1 705 6.18

2 1,518 14.51

3 2,149 15.49

4 2,678 29.89

5 4,296 27.05

6 2,983 25.67

7 2,619 7.58

8 1,437 7.78

9 1,003 33.38

10 823 6.36

G.3 Initial Data Assessment

Several analyses were conducted to assess the data prior to estimating SSO frequency and volume. The initial 

data assessment included:

• Analysis of climatic conditions

• Analysis of the variability of discharge volume, number of systems reporting at least one event, 

population served, and SSO event frequency

• Regional characterization of frequency, volume, and cause category

• Analysis of volume discharged by cause category

• Statistical regressions to predict frequency of events for non-reporting states
Report to Congress on Impacts and Control of CSOs and SSOs

G-4

These analyses are discussed in more detail below.

Analysis of Climatic Conditions

Annual precipitation statistics developed by the National Climatic Data Center (NCDC) suggest that no obvious 

bias towards wet or dry conditions was observed. Climatic conditions in the reporting states over the three-year 

period ranged from record drought to record rainfall. The results of NCDC’s analysis for 2001-2003 are presented 

in Table G.3 for the 24 of the reporting states. Data for Hawaii were not available.

Analysis of Variability

The first data assessment step was to statistically characterize the variability in the parameters used to generate 

the national estimates. The first parameter evaluated was SSO event discharge volume. A frequency distribution 

was generated for the reported volume data and goodness-of-fit tests were conducted to determine the type of 

statistical distribution that the data exhibited. The volume distribution was reasonably described with log-normal 

distributions. 

Three additional parameters related to event frequency were investigated, and each was characterized with a 

single value for each state. The parameters were: 1) number of systems with events; 2) population served; and 3) 

number of events per year. Frequency distributions were generated for each of these parameters and goodness-ofState 2001 2002 2003

CA Near normal Below normal Near normal

CO Near normal Record driest Below normal

CT Below normal Near normal Much above normal

FL Near normal Above normal Above normal

GA Below normal Near normal Above normal

IN Above normal Above normal Above normal

KS Near normal Below normal Near normal

MA Near normal Near normal Much above normal

MD Much below normal Near normal Record wettest

ME Record driest Near normal Near normal

MI Much above normal Near normal Near normal

MN Above normal Above normal Below normal

NC Much below normal Near normal Record wettest

ND Near normal Below normal Below normal

NH Much below normal Near normal Above normal

NV Near normal Much below normal Near normal

OK Near normal Near normal Below normal

RI Near normal Near normal Above normal

SC Much below normal Near normal Above normal

SD Above normal Below normal Near normal

UT Near normal Much below normal Near normal

WA Near normal Below normal Near normal

WI Above normal Above normal Below normal

WY Below normal Much below normal Below normal

Table G.3 National Precipitation Summary by State for 2001-2003
 Appendix G

G-5

fit tests were conducted to determine the type of statistical distribution. Log-normal distributions were found to 

adequately describe each parameter.

Regional Characterization

The data for SSO frequency, volume, and cause were stratified by EPA region to determine if geographical 

differences in SSO characteristics existed. The cause of SSO events was found to vary significantly by region. 

Box and whisker plots were initially generated to provide a visual depiction of differences in volume by region. 

Analysis of variance (ANOVA) testing was then conducted to verify that significant differences existed between 

regions. Once these differences were confirmed, additional Bonferroni-adjusted ANOVA testing was conducted 

to identify individual differences between regions. Analyses were conducted on log-transformed data, consistent 

with the determination of log-normality discussed earlier. Based on these results, all subsequent analyses for 

cause category were conducted on a region-specific basis. State-specific cause information was used for the 25 

states in EPA’s data management system. Distributions for SSO cause were developed and applied by region to 

states without state-specific information in EPA Regions 1, 3, 4, 5, 9, and 10. One average cause distribution was 

used for Regions 6, 7, and 8 because the cause of SSO events reported by the states in these regions was very 

similar. Finally, none of the 25 states in EPA’s data management system are in EPA Region 2, so an average cause 

distribution was developed and applied from the reporting states in Regions 1, 3 and 5. The cause distributions, 

by region, for non-reporting states are summarized in Table G.4.

Less significant regional differences were observed for SSO event frequencies and the volume of individual spills; 

therefore, subsequent analyses regarding SSO event frequencies and volumes were not stratified on a regional 

basis.

Analysis of Volume Discharged by Cause Category 

The next data assessment step was to determine whether a relationship existed between volume discharged 

and cause of the SSO event. SSO volumes were found to vary significantly across most cause categories. Boxand-whisker plots were generated to provide a visual depiction of differences in volume by cause category. 

No significant differences in volume discharged were observed across the cause categories of Line Break and 

Miscellaneous. These two categories were therefore combined into a single category, as shown in Table G.4. 

ANOVA testing was conducted to verify that significant differences existed between the remaining categories. 

Once these differences were confirmed, additional Bonferroni-adjusted ANOVA testing was conducted to identify 

Region Blockage Line Break/Misc. Mechanical/Power 

Failure Wet Weather – I/I Unknown

1 41% 13% 10% 30% 6%

2 25% 12% 11% 36% 17%

3 36% 13% 7% 13% 30%

4 34% 11% 7% 12% 35%

5 8% 10% 16% 58% 8%

6 48% 9% 7% 21% 15%

7 48% 9% 7% 21% 15%

8 48% 9% 7% 21% 15%

9 69% 15% 6% 1% 9%

10 22% 13% 16% 6% 43%

Table G.4 Percentage of SSO Events, by Cause, by Region
Report to Congress on Impacts and Control of CSOs and SSOs

G-6

individual differences between cause categories. Analyses were conducted on log-transformed data, consistent with 

the determination of log-normality discussed earlier. 

Statistical Regression to Estimate SSO Frequency

In order to estimate national SSO frequency, the frequency data from the reporting states were extrapolated to 

estimate the non-reporting states. For this final data assessment step, a series of linear regressions were developed 

allowing event frequencies to be estimated for each state. Several regressions (both in linear and log-log space) were 

conducted to evaluate potential predictors of event frequency. The independent variables evaluated were:

• Number of SSSs in the state reporting at least one SSO event

• Total number of SSSs in the state

• Population served by SSSs in the state

Based upon these analyses, the two best predictors of event frequency were:

1) Log-log regression of number of SSO events per year as a function of the number of SSSs in the state with 

events, linked to a second regression of number of SSSs in the state reporting at least one SSO event with 

events, as a function of total number of SSSs in the state; and

2) Log-log regression of number of events per year as a function of total population.

Both methods provided a similar level of accuracy, explaining approximately 40 percent of the variability in the 

observed frequency data; therefore, both the system-based and population-based methods were used in generating 

the national estimates.

G.4 Assumptions

Estimating the national SSO frequency and volume from available data required a number of assumptions. The two 

primary assumptions that have the greatest potential to affect the estimates are:

• The degree to which reported SSO events in a specific time period represent all SSO events that occurred 

statewide during the same period; and 

• The degree to which the number of SSSs in a state serves as a predictor of SSO frequency and volume, 

compared to population served. 

To account for the uncertainty caused by these assumptions, separate analyses were conducted using a range of 

values. The range of results obtained from these alternative analyses helps to bound the uncertainty in the estimates 

generated.

Scenarios Evaluated

Different assumptions can be made regarding the degree to which the reported data represent statewide conditions. 

It could be assumed that each state’s reporting data reflect all SSO events that occurred in that state. Alternatively, 

it could be assumed that the data reflect SSO events that occurred only for those communities that chose to 

report SSO events. It is not clear at this time which of these assumptions is most appropriate. To account for the 

uncertainty caused by these alternate assumptions, two separate scenarios were simulated: 

• Scenario 1: Available reporting data reflect all SSO events that occured statewide

• Scenario 2: Available reporting data reflect events that occured for only those communities that chose to 

report
 Appendix G

G-7

These scenarios were further evaluated using two different predictors of SSO frequency for states that do not 

track SSOs electronically:

• Predictor a: Event frequency based on total number of separate sewer systems in state

• Predictor b: Event frequency based on population served by separate sewers in state

The two pairs of assumptions discussed above result in four possible combinations of scenarios: 1a, 1b, 2a, and 

2b. Scenario 2b, however, could not be evaluated as it requires data on population served by separate sewers in 

each municipal jurisdiction reporting at least one SSO event. These data were available only on a statewide basis. 

Consequently, only three scenarios were evaluated: 1a, 1b, and 2a. 

G.5 Calculation Procedure

National estimates of SSO frequency and volume were generated by extrapolating the available data across the 

remaining 25 states (and Washington, D.C.) through the following five-step procedure:

1. Tabulate the total number of SSO events and the SSO volume for each of the reporting states.

2. Estimate the total number of SSO events per year for each non-reporting state.

3. Divide the total number of SSO events in each non-reporting state into different categories describing 

the cause of the SSO event.

4. Calculate the SSO volume for each cause category in each non-reporting state.

5. Calculate national estimates by summing across all states.

Step 1. Data Tabulation

Data tabulation was described earlier. 

Step 2. Estimate total number of SSO events per year for each state

The total number of SSO events per state was calculated for all three scenarios. Scenarios 1a and 1b assume 

that the available reporting data reflect all SSO events statewide, so the reported frequencies were not adjusted 

when calculating frequencies for the non-reporting states. Scenario 2a assumed that the available reporting data 

reflect only those communities that choose to report. For Scenario 2a estimates, the expected frequencies were 

scaled upward to represent the ratio of separate sewer systems reporting SSO events to the total number of sewer 

systems. Non-reporting communities in each state were assumed to experience SSOs in a frequency distribution 

that matched the reporting communities.

Step 3. Divide total number of SSO events into respective cause categories

The initial data assessment calculated the relative frequency of the cause of SSO events by EPA region. Regionspecific ratios are applied in Step 3 to define the number of events by cause category for each non-reporting state, 

as presented in Table G.4.

Step 4. Calculate SSO volume for each cause category

The initial data assessment defined SSO event volume as a function of cause. These region-specific cause and 

cause-specific volumes were applied in Step 4 to the frequency of events to define the total volume of SSO by 

cause category for each of the non-reporting states.
Report to Congress on Impacts and Control of CSOs and SSOs

G-8

Step 5. Calculate national estimates

SSO event frequency and cause-specific volumes for each non-reporting state were generated in Steps 2 

through 4. These estimates were combined with the data from the reporting states and were summed to 

provide a national estimate of SSO frequency and volume for each of the three scenarios examined.

G.6 Results

The results of the analyses for each of the three scenarios are summarized in Table G.5. These results 

indicate that the annual frequency of SSO events is between 23,000 and 75,000 events per year, with a 

corresponding volume of 3 to 10 billion gallons per year. The methodology used in developing this estimate 

results in an average volume per spill of approximately 125,000 gallons, while the average volume per spill 

in EPA’s data management system is approximately 94,000 gallons per spill. This occurs as a direct result of 

a methodology that accounts for regional differences in the cause of SSO events. Of the six states with the 

highest populations and numbers of systems that did not provide data for this analysis, fi ve (IL, NJ, NJ, OH, 

and PA) are in areas of the country where higher volume wet weather SSO events are more common.

The relatively large range is due to the uncertainty regarding the extent to which communities reporting at 

least one SSO event reflect all communities that had an SSO event, as the differences between Scenario 1a 

and Scenario 2a are much greater than the differences between Scenario 1a and Scenario 1b. Absence of a 

Scenario 2b does not seem to affect the overall range. As seen for Scenario 1, the population-based estimates 

are lower than the systems-based estimates. This suggests that Scenario 2a would be greater than Scenario 

2b. It is important to note that the ranges provided in Table G.5 are not necessarily all-encompassing, as the 

estimates contain additional assumptions that could either raise or lower the values provided. For example, 

this estimate assumes that reporting communities report every SSO event that occurred within their 

community; that is, no SSO event went unnoticed and unreported. If reporting communities failed to report 

any number of their SSO events, the estimates provided in Table G.5 would underestimate the true frequency 

and volume of SSOs. The estimate also assumes that non-reporting communities have SSOs in the same 

frequency distribution as reporting communities; this assumption could over-estimate the frequency and 

volume of SSOs for non-reporting communities. There is no way to quantify the significance of these types 

of assumptions, but the uncertainty introduced by these assumptions is anticipated to be small compared to 

the variability already considered in the analysis. Further, EPA believes that the alternative assumptions are 

more likely to affect SSO event frequency, rather than volume estimates.

Scenario Estimated Number of Events 

per Year 

Estimated SSO Volume 

(billion gallons)

Scenario 1a– systems based 24,564 3.06

Scenario 1b– population based 23,103 2.85

Scenario 2a– systems based 74,813 9.74

Table G.5 National Estimates of SSO Frequency and Volume
Appendix I 

Human Health Addendum

I.1 Selected Waterborne Disease 

Outbreaks Documented by the Center 

for Disease Control and Prevention

I.2 Interviewed Communities’ and States’ 

Roles and Responsibilities Matrix

I.3 Selected Case Studies

I.4 Documented Concentrations of 

 Bacteria, Enteric Viruses, and Parasitic 

 Protozoa in Sewage

 Appendix I

I-1

I.1 Selected Waterborne Disease Outbreaks Documented by the Center for Disease Control and 

Prevention

The CDC routinely publishes reports of waterborne disease outbreaks as part of their Mortality and 

Morbidity Weekly Report Surveillance Summaries. These reports include incidents of waterborne disease 

contracted through exposure to contaminated recreational waters or consumption of contaminated 

drinking water, fi sh, or shellfi sh. EPA compiled reports from the Surveillance Summaries for etiologic 

agents that are known to be present in untreated wastewater; however, in doing so EPA does not intend to 

imply that all outbreaks listed in the following tables are related to untreated wastewater or CSO or SSO 

discharges. Outbreaks are indicated in bold when untreated wastewater was specifi cally identifi ed by the 

CDC as contributing to the outbreak.

Table I.1 Selected Outbreaks from Exposure to Contaminated Drinking Water

Etiologic Agent Cases State(s)/Territory Year Type of Source Water

Salmonella typhii 60 Virgin Islands 1985 Suspected cross connection between 

water and sewer line.1 

Giardia 12 Maine 1986 River2

Acute Gastrointestinal Illness (AGI) 36 New Mexico 1986 River2

Giardia 44 New York 1986 Lake2

Campylobacter 250 Oklahoma 1986 Lake2

Giardia 68 Vermont 1986 River2

AGI 71 New Hampshire 1987 Lake2

Giardia 513 Pennsylvania 1987 River2

AGI 1,400 Puerto Rico 1987 Community water supply.2 

Shigella sonnei 1,800 Puerto Rico 1987 Contamination of a reservoir with 

sewage following a rain event and 

power failure.2 

Norwalk-like virus 5,000 Pennsylvania, 

Delaware, and New 

Jersey

1987 For cases in Pennsylvania and Delaware, 

outbreak is due to commercially 

manufactured ice produced from a 

contaminated water well. The outbreak 

in New Jersey is also from ice from a 

contaminated water well.2

Cryptosporidium 13,000 Georgia 1987 River2

Giardia 90 Colorado 1988 River2

AGI 7 Colorado 1988 River2

Giardia 172 Pennsylvania 1988 Lake2

Norwalk-like virus

(Setting: Resort)

900 Arizona 1989 Outbreak due to “effluent from 

sewage treatment facility seeping 

directly into resort’s well through 

cracks in the subsurface rock.”3

Giardia 19 Colorado 1989 River3 

AGI 31 Idaho 1989 Untreated surface water from a lake.3 

Giardia 308 New York 1989 Reservoir3

Giardia

(Setting: Prison)

152 New York 1989 Treatment deficiencies for drinking 

water from a reservoir.3
I-2

Report to Congress on the Impacts and Control of CSOs and SSOs

Etiologic Agent Cases State(s)/Territory Year Type of Source Water

Giardia 53 New York 1989 Lake3

E. coli O157:H7 243 Missouri 1989 SSO contamination of municipal 

drinking water well. This outbreak 

resulted in four deaths.3

Giardia 18 Alaska 1990 River3 (Setting: Lodge)

AGI 109 Missouri 1990 Lake3

AGI 63 Pennsylvania 1990 Lake3 (Setting: Inn)

Giardia 24 Vermont 1990 Lake3 (Setting: Resort)

AGI 202 Puerto Rico 1991 Deficiency with penitentiary 

distribution system for drinking water 

taken from a river.4

AGI 9,847 Puerto Rico 1991 River4

AGI 250 Minnesota 1992 Lake4

Giardia 80 Nevada 1992 Lake4

Cryptosporidium 3,000 Oregon 1992 Wastewater discharges and low flow 

in a river used for drinking water.4 

AGI 28 Pennsylvania 1992 River4

Cryptosporidium 27 Minnesota 1993 River5

Cryptosporidium parvum 103 Nevada 1993 Lake5

Cryptosporidium parvum 403,000 Wisconsin 1993 Treatment deficiencies and decline in 

raw water quality.5

Giardia lamblia 20 Pennsylvania 1993 Well contaminated with sewage.5

Giardia lamblia 18 New Hampshire 1994 Reservoir5

Giardia lamblia 36 New Hampshire 1994 Lake5

Giardia lamblia 304 Tennessee 1994 Reservoir5

Cryptosporidium parvum 134 Washington 1994 Well contaminated with wastewater.5 

Giardia lamblia 10 Alaska 1995 Surface water contaminated by 

unknown source.6

Giardia lamblia 1,449 New York 1995 Lake6

Viral outbreak (small, roundstructured virus)148 Wisconsin 1995 Lake6

Shigella sonnei 83 Idaho 1995 Sewage leak contaminated drinking 

water well.6

Giardia intestinalis 50 New York 1997 Lake7

AGI 123 New Mexico 1997 Sewage leak contaminated drinking 

water well.7

Cryptosporidium parvum 1,400 Texas 1998 Sewage spill contaminated drinking 

water wells.7 

AGI 6 Florida 1999 River/Stream8

AGI 4 Florida 1999 River/Stream8

AGI 46 Washington 1999 River/Stream8

E. coli O157:H7 5 California 2000 River/Creek8

Giardia intestinalis 27 Colorado 2000 River/Creek8

Giardia intestinalis 12 Minnesota 2000 Well contaminated with sewage.8

Giardia intestinalis 4 New Mexico 2000 River8

Norwalk-like virus 123 West Virginia 2000 Well contaminated with sewage.8

Table I.1 continued
 Appendix I

I-3

1Center for Disease Control (CDC). 1988. Water-Related Disease Outbreaks, 1985. Morbidity & Mortality Weekly Report Surveillance Summaries. 37 

(SS-2): 16-17.

2 CDC. 1990. Waterborne-Disease Outbreaks, 1986-1988. Morbidity & Mortality Weekly Report Surveillance Summaries. 39 (SS-1): 1-13.

3 CDC. 1991. Waterborne-Disease Outbreaks, 1989-1990. Morbidity & Mortality Weekly Report Surveillance Summaries. 40 (SS-3): 1-21.

4 CDC. 1993. Surveillance for Waterborne-Disease Outbreaks - United States, 1991-1992. Morbidity & Mortality Weekly Report Surveillance 

Summaries 42 (SS-5): 1-22.

5 CDC. 1996. Surveillance for Waterborne-Disease Outbreaks - United States, 1993-1994. Morbidity & Mortality Weekly Report Surveillance 

Summaries 45 (SS-1): 1-33.

6 CDC. 1998. Surveillance for Waterborne-Disease Outbreaks - United States, 1995-1996. Morbidity & Mortality Weekly Report Surveillance 

Summaries 47 (SS-5): 1-34.

7 CDC. 2000. Surveillance for Waterborne-Disease Outbreaks - United States, 1997-1998. Morbidity & Mortality Weekly Report Surveillance 

Summaries 49 (SS-4): 1-35.

8 CDC. 2002. Surveillance for Waterborne-Disease Outbreaks - United States, 1999-2000. Morbidity & Mortality Weekly Report Surveillance 

Summaries 51 (SS-8): 1-28.
I-4

Report to Congress on the Impacts and Control of CSOs and SSOs

Table I.2 Selected Outbreaks from Exposure to Contaminated Recreational Waters

Etiologic Agent Number 

of cases

Location Date Type of Recreational Water

AGI 21 New York 1982 Diving in waters known to be 

contaminated with human sewage 

caused outbreak among New York 

City Police scuba divers.

Shigella sonnei and boydii 68 California 1985 Lake2

Norwalk-like virus 41 California 1986 Lake2

Leptospira 8 Hawaii 1987 Stream2 

Shigella sonnei 130 South Carolina 1987 Lake2

Shigella sonnei 22 Georgia 1988 Lake2

Shigella sonnei 138 Pennsylvania 1988 Lake2

AGI 300 Vermont 1988 Lake – Recreational Area2

AGI 36 Vermont 1988 Lake – Swimming Area2

AGI 24 Minnesota 1988 Lake2

AGI 22 Maine 1989 Lake3

AGI 17 New Jersey 1989 Lake3 (Setting: Park)

AGI 26 New Jersey 1989 Lake3 (Setting: Swimming Area)

AGI 18 Minnesota 1990 Lake3

Shigella sonnei 7 New York 1990 Lake3

Shigella sonnei 9 Oregon 1990 Lake3

AGI 60 Pennsylvania 1990 Lake3

Shigella sonnei 68 North Carolina 1990 Lake3

AGI 244 Washington 1990 Lake3

AGI 79 Wisconsin 1990 Lake3

Leptospira 6 Illinois 1991 Pond4

Adenovirus 595 North Carolina 1991 Pond linked to outbreak of 

pharyngitis.4

E.coli 80 Oregon 1991 Lake4

Shigella sonnei 203 Pennsylvania 1991 Lake4

Shigella sonnei 23 Rhode Island 1991 Lake4

Giardia 4 Washington 1991 Lake4

AGI 15 Maryland 1992 Creek4

Giardia 43 New Jersey 1993 Lake5

Giardia 12 Maryland 1993 Lake5

Shigella sonnei 160 Ohio 1993 Lake5

Giardia 6 Washington 1993 River5

Shigella sonnei 35 Minnesota 1994 Lake5

Shigella sonnei 242 New Jersey 1994 Lake5

Cryptosporidium parvum 418 New Jersey 1994 Lake5

E. coli 166 New York 1994 Lake5

E. coli 12 Illinois 1995 Lake6

AGI 12 Minnesota 1995 Lake6
 Appendix I

I-5

Etiologic Agent Number 

of cases

Location Date Type of Recreational Water

E. coli 6 Minnesota 1995 Lake6

E. coli 2 Minnesota 1995 Lake6

AGI 17 Pennsylvania 1995 Lake6

Shigella sonnei 70 Pennsylvania 1995 Lake6

E. coli 8 Wisconsin 1995 Lake6

Shigella sonnei 39 Colorado 1996 Lake6

Shigella sonnei 81 Colorado 1996 Lake6

Cryptosporidium parvum 3 Indiana 1996 Lake6

AGI 4 Indiana 1996 Lake6

E. coli 6 Minnesota 1996 Lake6

AGI 32 Oregon 1996 Lake6

E. coli 8 Missouri 1997 Lake7

Schistosoma spindale 2 Oregon 1997 Lake7

AGI 650 Maine 1998 Lake7

E. coli 5 Minnesota 1998 Lake7

Norwalk-like virus 30 Ohio 1998 Lake7

Cryptosporidium parvum 8 Pennsylvania 1998 Lake7

AGI 41 Washington 1998 Lake7

AGI 248 Washington 1998 Lake7

Norwalk-like virus 18 Wisconsin 1998 Lake7

Leptospira 375 Illinois 1998 Outbreak among triathletes exposed 

to a lake.7

Shistosomes 2 Oregon 1999 Lake8

E. coli O121:H19 11 Connecticut 1999 Lake8

AGI 25 Illinois 1999 Lake8

Giardia intestinalis 18 Massachusetts 1999 Swimming at a pond.8

Norwalk-like virus 168 New York 1999 Lake8

E. coli O157:H7 36 Washington 1999 Lake8

E. coli O157:H7 5 Wisconsin 1999 Lake8

E. coli O157:H7 5 California 1999 Lake 8

AGI 2 Florida 2000 Lake8

AGI 4 Florida 2000 Lake - Summary states that this 

outbreak occurred from an outdoor 

spring.8

AGI 32 Maine 2000 Lake/pond8

Cryptosporidium parvum 220 Minnesota 2000 Lake8

Shigella sonnei 15 Minnesota 2000 Lake/pond8

Shigella sonnei 25 Minnesota 2000 Lake8

Leptospira 21 Guam 2000 Lake8

Schistosomes 6 California 2000 Pond8

Schistosomes 4 California 2000 Pond8

Schistosomes 2 Oregon 1999 Lake 8

Table I.2 continued
I-6

Report to Congress on the Impacts and Control of CSOs and SSOs

1 CDC. 1983. Epidemiologic Notes and Reports: Gastrointestinal Illness among Scuba Divers – New York City. Morbidity & Mortality Weekly 

 Report 32 (44): 576-577.

2 CDC. 1990. Waterborne-Disease Outbreaks, 1986-1988. Morbidity & Mortality Weekly Report Surveillance Summaries 39 (SS-1): 1-13.

3 CDC. 1991. Waterborne-Disease Outbreaks, 1989-1990. Morbidity & Mortality Weekly Report Surveillance Summaries 40 (SS-3): 1-21.

4 CDC. 1993. Surveillance for Waterborne-Disease Outbreaks - United States, 1991-1992. Morbidity & Mortality Weekly Report Surveillance 

 Summaries 42 (SS-5): 1-22.

5 CDC. 1996. Surveillance for Waterborne-Disease Outbreaks - United States, 1993-1994. Morbidity & Mortality Weekly Report Surveillance 

 Summaries 45 (SS-1): 1-33.

6 CDC. 1998. Surveillance for Waterborne-Disease Outbreaks - United States, 1995-1996. Morbidity & Mortality Weekly Report Surveillance 

 Summaries 47 (SS-5): 1-34.

7 CDC. 2000. Surveillance for Waterborne-Disease Outbreaks - United States, 1997-1998. Morbidity & Mortality Weekly Report Surveillance 

 Summaries 49 (SS-4): 1-35.

8 CDC. 2002. Surveillance for Waterborne-Disease Outbreaks - United States, 1999-2000. Morbidity & Mortality Weekly Report Surveillance 

 Summaries 51 (SS-8): 1-28.
 Appendix I

I-7

Table I.3 Selected Outbreaks from Consumption of Contaminated Fish or Shellfish

Etiologic Agent Number of 

cases

Location Date Exposure Pathway

AGI 150 New York 1982 Fourteen separate outbreaks 

of gastroenteritis due to the 

consumption of raw clams. It appears 

that the outbreak originated from 

coastal waters in Massachusetts, 

Rhode Island, and New York due to 

harvesting beds being contaminated 

as a result of heavy rains during May 

and June.1

Norwalk-like virus 20 N/A 1983 Consumption of raw clams.2

AGI 42 Maine 1984 Consumption of Seafood Newburg.2

Hepatitis A 61 Multiple states 1988 Consumption of raw oysters 

harvested from water contaminated 

by human feces.3

Vibrio cholerae 26 Guam 1990 Consumption of contaminated reef 

fish.3

Norwalk-like virus 73

103

Louisiana

Multiple States

1993 A shellfish harvester with high levels 

of immunoglobulin A to Norwalk-like 

virus reported having been ill before 

the outbreak and admitted dumping 

sewage directly into harvest waters.4

Viral gastroenteritis N/A Florida and 

Georgia

1994-

1995

December 1994 to January 1995, 34 

clusters of cases of viral gastroenteritis 

were traced to shellfish harvested to 

beds in Florida’s Apalachicola Bay. The 

source of the Norwalk-like virus was 

attributed to sewage contamination 

either from land-based sources or 

recreational or commercial vessels, 

according to preliminary findings.5

Viral gastroenteritis 493 Alabama, Florida, 

Georgia, Louisiana, 

and Mississippi

1996-

1997

Consumption of oysters thought 

to have been contaminated by 

harvesters improperly disposing of 

sewage. 6

1CDC. 1982. Epidemiologic Notes and Reports: Enteric Illness Associated with Raw Clam Consumption – New York. Morbidity & Mortality Weekly Report 31 (33): 

449-451.

2CDC. 1990. Foodborne Disease Outbreaks, 5-Year Summary, 1983-1987. Morbidity & Mortality Weekly Report Surveillance Summaries 39 (SS-01): 15-23.

3 CDC. 1996. Surveillance for Foodborne–Disease Outbreaks, United States, 1988-1992. Morbidity & Mortality Weekly Report Surveillance Summaries 45 (SS-05): 1-55.

4 CDC. 1993. Multistate Outbreak of Viral Gastroenteritis Related to Consumption of Oysters – Louisiana, Maryland, Mississippi, and North Carolina,1993. Morbidity 

& Mortality Weekly Report 42 (49): 945-948.

5 CDC. 1995. Epidemiologic Notes and Reports: Multistate Outbreak of Viral Gastroenteritis Associated with Consumption of Oysters – Apalachicola Bay, Florida, 

December 1994-January 1995. Morbidity & Mortality Weekly Report 44 (2): 37-39.

6 CDC. 1997. Viral Gastroenteritis Associated with Eating Oysters – Louisiana, December 1996-January 1997. Morbidity & Mortality Weekly Report 46 (47): 1109-1112.
I.10

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix I

I-11

I.2 Interviewed Communities’ and States’ Roles and Responsibilities Matrix

As part of this report effort, EPA conducted a series of interviews with officials in state and local 

governments. Through the interviews, EPA sought a clearer understanding of the roles and responsibilities 

of these agencies in preventing, tracking, and monitoring for potential human health impacts associated 

with CSO and SSO discharges within their jurisdiction. The results of these interviews are summarized in 

the following two tables.

Table I.4 Local Agency Responsibilities Related to Human Health as Identified During Community 

Interviews

Community Waterborne 

Illness 

Investigations

Recreational 

Water Monitoring 

& Posting

Wastewater 

Treatment

Drinking Water 

Monitoring

Monitoring Fish 

and Shellfish

Boston, MA City Health Metropolitan 

District 

Commission and 

MWRA

MWRA MWRA

Portland, ME City Health 

Department

State Health 

Department

State 

Environmental 

Agency

Public Works Water District State DEP

Cape May, NJ County Health County Health County 

Municipal 

Utilities 

Authority 

Individual Water 

Utilities, County 

Health State 

Environmental 

Agency

State 

Environmental 

Agency

New York, NY City Health 

Department

City 

Environmental 

Agency

State 

Environmental 

Agency

City Public 

Works

State 

Environmental 

Agency

City 

Environmental 

Agency

State 

Environmental 

Agency

State 

Environmental 

Agency

Arlington, VA County Health 

Department

N/A County 

Environmental 

Health 

Department

Public Works State 

Environmental 

Agency

Erie County, PA County Health 

Department

County Health 

Department

Public Works Water District N/A

Pittsburgh, PA County Health 

Department

State 

Environmental 

Agency

Drinking and 

Wastewater 

Agency

Drinking and 

Wastewater 

Agency

N/A

Atlanta, GA County Health 

Epidemiology & 

Environmental 

Division

County Health 

Environmental 

Division

Each 

municipality

Each 

municipality

Local Level 

Environmental 

Health

Ft. Pierce, FL County Health 

Departments

County Health 

Departments

County Health 

Dept, State 

Environmental 

Agency

County Health 

Department

State 

Environmental 

Agency

Akron, OH City Health 

Department

N/A

Milwaukee, WI City Health 

Department

City Health 

Department

Waste Treatment 

Agency

State 

Environmental 

Agency
I-12

Report to Congress on the Impacts and Control of CSOs and SSOs

Community Waterborne 

Illness 

Investigations

Recreational 

Water Monitoring 

& Posting

Wastewater 

Treatment

Drinking Water 

Monitoring

Monitoring Fish 

and Shellfish

Austin, TX City/County 

Health 

Department

Watershed 

Protection Division

Little Rock, AR State Health 

Department 

State 

Environmental 

Department

local 

municipalities

State 

Environmental 

Department

State 

Environmental 

Department

Tulsa, OK County Health 

Department 

& State Health 

Department

State 

Environmental 

Department

City Government City Government State 

Environmental 

Department

Omaha, NE County Health 

Department 

County

St. Louis, MO City Health 

Department

Denver, CO City/County 

Environmental 

Agency

City/County 

Environmental 

Agency

Public Works

Las Vegas, NV County Health 

Department, 

Water Authority 

Water Authority 

National Parks 

Service 

Local 

Wastewater 

Treatment

Water Authority County Health 

Department

Los Angeles, CA State Health 

Department, 

City Health 

Department

City Health 

Department

Local sanitation 

districts

State Health 

Department, 

City Health 

Department

State Health 

Department

Orange County, CA County Health 

Department 

Epidemiology

County Health 

Department 

Environmental 

County Sanitation 

District Wastewater 

Authority

Local water 

and sanitation 

districts

Water Authority 

under 

jurisdiction 

of State 

Department of 

Health 

State 

Department of 

Health Services/

Biotoxin 

Monitoring 

San Diego, CA County 

Environmental 

Health, 

Department 

of Health 

Epidemiology

County 

Environmental 

Health

Municipal 

POTWs

Local water 

purveyor 

and State 

Department of 

Health

State 

Department 

of Health 

and County 

Environmental 

Health

Portland, OR State Health 

Department

State Health 

Department 

(ocean beaches 

only) State 

Environmental

Agency

State 

Environmental 

Agency (or 

the Native 

American tribes, 

if treatment is 

associated with 

tribal lands)

State Health 

Department 

– monitor 

groundwater in 

general

State 

Environmental 

Agency 

Department of 

Agriculture 

Seattle, WA County Health 

Department

Table I.4 continued
 Appendix I

I-13

Table I.5 State Agency Responsibilities Related to Human Health, as Identified During Interviews 

State Waterborne 

Illness 

Investigations

Recreational 

Water 

Monitoring & 

Posting

Wastewater 

Treatment

Drinking Water 

Monitoring

Monitoring Fish 

and Shellfish

New Jersey State Department 

of Health

State 

Environmental 

Agency and 

Local Health 

Departments

State 

Environmental 

Agency

State 

Environmental 

Agency and 

Local Health 

Departments

State 

Environmental 

Agency

Pennsylvania State Health State 

Environmental 

Protection, State 

Department of 

Health

State 

Environmental 

Protection

State 

Environmental 

Protection, State 

Department of 

Health

Department of 

Agriculture

Florida State Department 

of Health

County health 

officers

State 

Environmental 

Agency permits 

the wastewater 

program 

State 

Environmental 

Agency 

oversight for 

drinking water 

suppliers 

The Dept. of 

Agriculture, 

DOH issues 

the health 

advisories. State 

environmental 

agency 

does tissue 

monitoring

Massachusetts Local Boards 

of Health, State 

Department of 

Health

Local Boards 

of Health, State 

Department of 

Health

Local Boards 

of Health, State 

Environmental 

Agency 

State 

Environmental 

Agency 

State 

Environmental 

Agency- Division 

of Marine 

Fisheries, State 

Department of 

Health

Missouri Department of 

Health

State 

Environmental 

Agency

State 

Environmental 

Agency

Wisconsin State Department 

of Health and local 

health agencies

Local or state 

agency that “owns 

the beach”

Local 

Government

Local 

Government 

State 

Environmental 

Agency

Oregon State Health 

Department State 

Environmental 

Agency

State Health 

Department 

(ocean beaches 

only)

State 

Environmental 

Agency (or 

the Native 

American tribes, 

if treatment is 

associated with 

tribal lands)

State Health 

Department 

– monitor 

groundwater in 

general

State 

Environmental 

Agency 

Department of 

Agriculture 
I-14

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix I

I-15

I.3 Selected Case Studies

A Case Study of the 1993 Milwaukee Cryptosporidiosis Outbreak 

Background

In the spring of 1993, the City of Milwaukee, Wisconsin and surrounding areas saw a marked increase 

in absenteeism and reported cases of diarrhea (MacKenzie 1994). Clinical investigations found that 

residents were suffering from Cryptosporidiosis, a diarrheal disease caused by a microscopic parasite, 

Cryptosporidium parvum. This parasite can live in the intestines of humans and other mammals and 

can be passed in the feces of an infected individual (CDC 2003a). It is estimated that more than 400,000 

people were infected during this outbreak; more than 600 persons had laboratory confirmed cases 

(MacKenzie 1994). 

Exposure Pathway and Source of Parasite

The Milwaukee Cryptosporidiosis outbreak was caused by ingestion of contaminated water from Lake 

Michigan. The Milwaukee Water Works (MWW) supplies water, obtained from Lake Michigan, to the 

City of Milwaukee and nine surrounding municipalities via two water treatment plants, one located in the 

northern part of the district and the other in the south.

Beginning on approximately March 21, 1993, and continuing through April 9, the southern treatment 

plant reported increases in the turbidity of treated water, rising from a low of 0.25 NTU to a peak of 1.7 

NTU. This finding, coupled with the fact that a majority of the laboratory and clinically confirmed cases 

About Cryptosporidiosis

Cryptosporidiosis, caused by the parasite Cryptosporidium parvum, is a disease affecting many 

large mammals. Its symptoms include, diarrhea, abdominal cramps, loss of appetite, low-grade 

fever, nausea, and vomiting (CDC 2003a). Cryptosporitiosis is highly contagious and is passed via 

fecal oral contamination from one host to another. Cryptosporidium oocysts are very resistant to 

disinfection and can survive outside of a host for a long period of time. Cryptosporidium oocysts 

are found throughout the United States in soil, animal waste, and water (CDC 2003a). Once 

ingested by the host, the parasite attacks the small intestine and rapidly reproduces.

Incubation takes two to fourteen days from the initial infection. For individuals with healthy 

immune systems, the infection will last approximately two weeks; however, symptoms may 

cycle and the individual can appear to get better and then experience a relapse (CDC 2003a). 

The disease is potentially fatal for immunocompromised individuals. In those individuals the 

symptoms may last longer, and the disease may reappear after white blood cell numbers drop 

(CDC 2003b). 

It is estimated that in industrialized countries, approximately 0.4% of the population pass 

Cryptosporidium parvum oocysts at any one given time, and of patients admitted to hospitals for 

diarrhea, 2-2.5% have Cryptosporidiosis. Further, 30-35% of the U.S. population has antibodies 

for Cryptosporidium parvum, evidence that they have been exposed to the parasite at some point 

(Upton 2001).
I-16

Report to Congress on the Impacts and Control of CSOs and SSOs

of Cryptosporidiosis were from households predominately supplied by the southern water treatment 

plant, led investigators to conclude that contaminated water from Lake Michigan was not properly 

filtered and was supplied to, and ingested by, residents in the southern plant treatment service area. 

(MacKenzie 1994) Although the environmental source of the parasite is not known, inferences include 

agricultural run-off, slaughterhouses, and untreated wastewater leaks (MacKenzie 1994).

Tracking, Reporting, and Response

On April 5, 1993, the Milwaukee Department of Health contacted the Wisconsin Division of Health 

after widespread absenteeism in key professions was reported. On April 7, 1993, two laboratories in 

the Milwaukee area identified Cryptosporidium oocysts in stool samples. On the evening of April 7, 

1993, a boil water advisory was issued and the southern plant was temporarily closed on April 9, 1993 

(MacKenzie 1994). Although the MWW was within required water quality limits, a streaming-current 

monitor, which helps determine the amount of coagulant needed for filtration, was not installed 

correctly. This was quickly fixed.

Impact

It is estimated that over 400,000 people were infected with Cryptosporidiosis (MacKenzie 1994). 

Their symptoms included: cramps, malaise, nausea, decreased appetite, weight loss, muscle pain, and 

rash (Frisby 1997). These symptoms resulted in decreased productivity and it was reported that the 

“gastrointestinal illness resulted in widespread absenteeism among hospital employees, students, and 

schoolteachers” (MacKenzie 1994).

Additional Comment

The Milwaukee outbreak helped identify shortcomings of the waterborne disease outbreak surveillance 

system that was in operation in the United States. Researchers suggested that laboratories should perform 

routine stool tests for Cryptosporidium when patients’ symptoms warranted (Mac Kenzie 1994). They 

also suggested that the Cryptosporidium tests were not sensitive enough and should be repeated in order 

to account for the time needed for the Cryptosporidium oocysts to enter the feces (Cicirello 1997). Most 

importantly, at the time of the Milwaukee outbreak, Cryptosporidiosis was not legally required to be 

reported to state health officials. As a result of this, and other outbreaks, Cryptosporidiosis is now a 

“reportable illness” in many jurisdictions. 
 Appendix I

I-17

A Case Study of the 1998 Brushy Creek Cryptosporidiosis Outbreak 

Background

On July 13, 1998, a lightning strike during a thunderstorm incapacitated the controls at a wastewater lift 

station located upstream from the Brushy Creek Municipal Utility District’s (MUD) five drinking water 

wells. This power outage caused 167,000 gallons of raw sewage to flow into Brushy Creek (TDH 1998). 

Beginning on July 24, 1998, the Texas Department of Health Infectious Disease Epidemiology and 

Surveillance Division (IDEAS) and the Williamson County and Cities Health Districts began to receive 

calls from Brushy Creek residents complaining of nausea, diarrhea, and abdominal cramps. It was later 

determined that residents of Brushy Creek were suffering from Cryptosporidiosis. It is estimated that 60 

percent of Brushy Creek’s population of 10,000 were exposed to the parasite and approximately 1,440 

residents contracted Cryptosporidiosis (TDH 1998).

Exposure Pathway and Source of Parasite

The Brushy Creek Cryptosporidiosis outbreak was caused by ingestion of contaminated water from 

the Brushy Creek MUD wells. It was reported that MUD customers whose water came from the 

contaminated wells were five times more likely to be ill than MUD customers whose water came from 

treated surface water (TDH 1998). Fecal coliform tests performed on raw water samples taken from the 

five wells after the sewage leak showed high levels of E. coli and helped to confirm that the wells had been 

contaminated (four of the five wells were positive)(TDH 1998).

Tracking, Reporting, and Response

In response to the massive sewage spill, the Texas Natural Resources Conservation Commission (TNRCC) 

instructed the Brushy Creek MUD to test its five water wells for fecal coliform (July 17). Based on results 

of those tests, received on July 21, the Brushy Creek MUD was ordered to take all the wells off-line and 

purchase water from the city of Round Rock. On July 24, 1998, the Texas Department of Health and local 

health districts began receiving residents’ complaints of symptoms related to gastrointestinal disease, 

and TNRCC contacted the Texas Department of Health to request assistance with a possible waterborne 

disease outbreak in Williamson County (TDH 1998). In cooperation with local health departments, 

IDEAS distributed specimen containers to Brushy Creek residents in order to obtain stool samples. Twelve 

of the specimen containers were returned, all were tested and found negative for viral and bacterial 

pathogens, six however, were positive for Cryptosporidium parvum (TDH 1998). 

Impact

It is estimated that 1,440 people suffered from Cryptosporidiosis during this outbreak (there were 89 

laboratory confirmed cases). The infected persons complained of nausea, diarrhea, and abdominal 

cramps. Based on a residents survey, the mean duration of the illness was seven days (range 1- 45 days) 

(TDH 1998).

Additional Comments

Brushy Creek MUD wells are 100 feet deep and encased in cement. It is generally thought that these types 

of wells would not be influenced by surface water. This presumption is probably the reason residents 

of Brushy Creek were supplied water from the contaminated well for approximately eight days. This 

outbreak illustrates that even wells with this degree of protection can be contaminated by surface water 

(TDH 1998). 
I-18

Report to Congress on the Impacts and Control of CSOs and SSOs

Forty-five additional cases of Cryptosporidiosis were reported in the Brushy Creek area between 

September 1 and December 31, 1998. It was not possible to determine if these cases would have occurred 

without the earlier water contamination because no reliable data were collected to establish a normal rate 

of Cryptosporidiosis in Texas.
 Appendix I

I-19

A Case Study of the 1995 Idaho Shigellosis Outbreak 

Background

In August 1995 the local health department requested that the Idaho Department of Health investigate 

reports of diarrheal illness among resort visitors in Island Park, Idaho. Clinical investigations found that 

these individuals were suffering from Shigellosis, a diarrheal disease caused by a microscopic parasite, 

Shigella sonnei (CDC 1996). This parasite can live in the intestines of humans and other mammals and 

can be passed in the feces of an infected organism. (CDC 2003c). Eighty-two cases were identified among 

visitors to the resort as well as a few cases among local residents (CDC 1996). 

Exposure Pathway and Source of Parasite

The Island Park Shigellosis outbreak was probably caused by the ingestion of contaminated well water. 

Testing of wells in the neighborhood indicated that a number of the wells were contaminated with 

fecal coliform bacteria (CDC 1996). While cultures did not indicate the presence of Shigella sonnei, it 

is known that Shigella organisms are rarely successfully isolated from water sources. Identification of a 

waterborne source is generally based on epidemiologic evidence (CDC 1996). Plasmid profile analyses 

indicated that the Shigella organisms were of the same strain in both the infected resort visitors and the 

infected neighbors. This suggests that the organisms may have been transmitted from multiple wells in 

the same area through common groundwater (CDC 1996). The water table in the area was higher than 

normal due to increased rainfall levels during the spring. Inspection of a nearby sewer line found that the 

wastewater was not draining properly, but no specific leaks were identified when sections were excavated 

for inspection (CDC 1996).

About Shigellosis

Shigellosis, caused by the parasite Shigella sonnei, is a well-recognized cause of gastrointestinal 

illness in humans and is the most common cause of bacillary dysentary in the United States 

(CDC 2003c). Symptoms include diarrhea, fever, abdominal pain, and blood or mucus in the 

stool. Most outbreaks of Shigellosis are attributed to person-to-person transmission, however, 

the disease has also been reported to spread through food, water, and swimming (CDC 2003c). 

Waterborne outbreaks are commonly associated with wells that have been fecally contaminated. 

However, because Shigella organisms rarely are isolated from water sources, the identification of a 

waterborne source usually is based on epidemiologic evidence (CDC 2003c). 

Most people who are infected with Shigella develop diarrhea, fever, and stomach cramps starting 

a day or two after they are exposed. The diarrhea usually resolves in fi ve to seven days. In some 

persons, especially young children and the elderly, the diarrhea can be so severe that the patient 

needs to be hospitalized. Some persons who are infected may have no symptoms at all, but may still 

pass the bacteria to others. 

Approximately 14,000 laboratory confirmed cases of shigellosis and an estimated 448,240 total 

cases (mostly due to Shigella sonnei) occur in the United States each year (CDC 2003d). This 

disease is very common in developing countries and, depending on the strain, can be deadly. 

Further, Shigella has, in some areas, become resistant to antibiotics.
I-20

Report to Congress on the Impacts and Control of CSOs and SSOs

Tracking, Reporting, and Response

After receiving reports of diarrheal illness among guests at the resort, the local health department 

recommended several prevention measures before initiating the investigation (CDC 1996). On August 

17, the resort posted warning signs at water taps cautioning against drinking water; on August 19, food 

service was terminated; and on August 21, bottled water was placed in every room. Resort water is 

supplied by one well, which was dug in 1993 (CDC 1996). Samples of water obtained from the well on 

August 23 were positive for fecal coliform bacteria; however, cultures were negative for Shigella. After this 

testing was completed the local health department required that the resort provide bottled or boiled water 

to visitors and recommended that persons residing in the area have their well water tested and boil all 

drinking water. Since the investigation, the resort has drilled a new and deeper well (CDC 1996). 

Impact

Eighty-two cases were identified among resort visitors and six cases were identified among individuals in 

neighboring houses. After testing well water throughout the neighborhood the local health department 

recommended that residents have their well water tested and a boil water advisory was put into effect. No 

specific source of Shigella organisms was ever identified.

Additional Comments

Routine water-quality testing, including testing for fecal coliform bacteria, is the most practical indicator 

of possible bacterial contamination of drinking water from both community and private water supplies. 

However, many privately owned wells are never tested for fecal coliform bacteria (CDC 1996). In 

addition, timely testing, reporting, and follow-up in cases of contaminated public water systems are often 

constrained by limited resources available to local health departments (CDC 1996). 
 Appendix I

I-21

A Case Study of the 1993 Las Vegas Cryptosporidiosis Outbreak 

Background

Over a seven month period in 1993 and 1994, Clark County, Nevada, which includes Las Vegas, 

experienced a rise in the number of HIV-infected individuals with diarrheal disease. Clinical 

investigations found that these individuals were suffering from Cryptosporidiosis. There was no estimate 

of the number of individuals infected during the course of this outbreak (Goldstein 1996). 

Exposure Pathway and Source of Parasite

The Clark County Cryptosporidiosis outbreak was most likely caused by ingestion of contaminated water 

from Lake Mead. The water treatment plant serving Clark County supplies water, obtained from Lake 

Mead, to the City of Las Vegas and the rest of the county (Goldstein 1996). It was not reported to be 

malfunctioning at any point during the seven month outbreak period. The maximum recorded turbidity 

value during the outbreak period reached 0.17 NTU, as compared with the 1.7 NTU value recorded 

during the 1993 Milwaukee Cryptosporidiosis outbreak (Goldstein 1996).

Due to the widespread geographic nature of the infected patients, it is assumed that the municipal 

drinking water supply was contaminated before reaching the treatment plant (Goldstein 1996). While 

the water was filtered and chlorinated at the treatment plant some Cryptosporidium oocysts survived 

the process and entered the municipal drinking water system. This is not surprising considering the 

resistance of Cryptosporidium oocysts to chlorination. Individuals then were exposed. The lack of positive 

test results for this parasite in the water supply, coupled with the persistence of this outbreak suggest an 

intermittent, low-level of contamination of the water. 

Tracking, Reporting, and Response

Because water quality exceeded all standards, waterborne transmission of this parasite was not suspected 

and no advisory warning residents to boil their water was issued. This situation remained unchanged for 

approximately fourteen weeks after the possible outbreak was first noted in mid-March 1993 (Goldstein 

1996).

The fact that Cryptosporidiosis is a reportable disease in Nevada combined with the awareness of 

physicians regarding the sensitivity of immunocompromised patients to exposure to this disease led to 

recognition of an outbreak that might have otherwise not been reported (Goldstein 1996). Generally, 

the appropriate laboratory tests that would identify Cryptosporidiosis infection are not carried out 

unless a physician is aware of a source of contamination in the community or if they are dealing with an 

individual who is particularly sensitive to this type of disease.

Impact

There is no estimate of the number of people infected during the course of this outbreak. A much higher 

incidence of reported infections occurred among HIV-infected individuals. The short-term mortality rate 

for the HIV-infected adults who had cryptosporidiosis was high. Two thirds of those who died during 

or shortly after the outbreak had cryptosporidiosis listed on their death certificates. These data do not 

differentiate dying “of” from dying “with” cryptosporidiosis. For these HIV-infected case-patients early 

mortality was higher, but one year mortality was not when compared with a HIV-positive, but nonCryptosporidium exposed control group (Goldstein 1996). 
I-22

Report to Congress on the Impacts and Control of CSOs and SSOs

Additional Comments

Laboratories do not routinely test for this type of infection as this diagnosis is rarely considered when 

not dealing with an immunosuppressed patient. Researchers suggest that the public health significance 

of waterborne-Cryptosporidium infection in the United States must be determined. To accomplish this 

task epidemiologists need more sensitive and rapid methods for detecting oocysts in water, workable 

surveillance systems able to detect cases associated with low-level transmission of Cryptosporidium, 

and epidemiologic studies specifically designed to address the risk for waterborne transmission of 

Cryptosporidium in nonoutbreak settings (Goldstein 1996).
 Appendix I

I-23

A Case Study of the 1985 Braun Station, Texas Cryptosporidiosis Outbreak 

Background

In a period between May and July 1984 two distinct gastroenteritis outbreaks were identified in the 

community surrounding Braun Station, Texas (D’Antonio 1985). Clinical investigations found that 

individuals impacted during the first outbreak were suffering from Norwalk virus and those impacted 

during the second outbreak were suffering from Cryptosporidiosis. This parasite can live in the intestines 

of humans and other mammals and can be passed in the feces of an infected organism. (CDC 2003a). 

Cryptosporidium oocysts were identified in 47 of 79 tested Braun Station patients (D’Antonio 1985). 

Oocycsts were also identified in samples from 12 patients suffering from gastroenteritis, but who did not 

reside in Braun Station.

Exposure Pathway and Source of Parasite

No geographical clustering or age-related patterns emerged upon examination of the July 

Cryptosporidiosis outbreak in Braun Station. However, consumption of tap water was greater among 

those afflicted and individuals who were not in the area during the month of July were generally not 

infected (D’Antonio 1985). Public drinking water is drawn from an artesian well that is not filtered, but 

is chlorinated shortly before distribution. The outbreak was investigated as it occurred. Well water is 

generally not tested in this region of Texas, but community complaints convinced authorities to begin 

testing in mid-June. Chlorinated water samples were found to be coliform-negative. However, untreated 

well water samples tested had fecal coliform counts as high as 2600/100 mL (D’Antonio 1985). A boil 

water advisory was put into effect. Subsequent dye tests indicated that the community’s wastewater system 

was leaking into the well water. Attempts to identify the exact site of contamination were not successful. 

The pattern of repeated outbreak but differing major causative agent suggested that contamination of the 

water supply was intermittent (D’Antonio 1985). The community was provided with an alternate water 

supply. 

Tracking, Reporting, and Response

A cluster of patients suffering from gastroenteritis in Braun Station led to the recognition of both 

outbreaks. Community-requested water testing and subsequent dye tests identified wastewater 

contamination of the community’s well water. A boil water advisory was issued after evidence of 

contaminated water was gathered. When the source of the wastewater could not be identified and 

stopped, an alternative water source was provided to the community. The differing types of causative 

agents at the root of each outbreak suggested intermittent water supply contamination.

Impact

Symptoms associated with Cryptosporidiosis infection were experienced by an estimated 2,006 patients 

in Braun Station. Once the source of infection was identified, proper steps were taken to ensure that the 

community was supplied with a healthy water supply. 
I-24

Report to Congress on the Impacts and Control of CSOs and SSOs

References for Case Studies

Bitton, G. 1980. Introduction to Environmental Virology. New York, NY: John Wiley & Sons.

Centers for Disease Control and Prevention (CDC). 1996. Shigella sonnei Outbreak Associated with 

Contaminated Drinking Water- Island Park, Idaho, August 1995. Morbidity and Mortality Weekly Report

45(11): 229-234. 

CDC. 2003a. “Parasitic Disease Information Fact Sheet: Cryptosporidiosis.” Retreived May 12, 2003b.

http:://www.cdc.gov/ncidod/dod/parasites/cryptosporidiosis/factsheet_cryptosporidiosis.htm. 

CDC. 2003b. “Preventing Cryptosporidiosis: A Guide for People With Compromised Immune Systems.” 

Retreived May 12, 2003c. 

http://www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/factsht_crypto_prevent_ci.htm.

CDC. 2003c. “Disease Information: Shigellosis”. Retrieved September 2003.

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/shigellosis_g.htm.

Cicirello H.G., et. al. 1997. Cryptosporidiosis in Children During a Massive Waterborne Outbreak in 

Milwaukee, Wisconsin: Clinical, Laboratory, and Epidemiologic Findings. Epidemiol Infect 119(1):53-60.

D’Antonio, R.G., et al. 1985. A waterborne outbreak of cryptosporidiosis at Brushy Creek. Epidemiology 

in Texas, 1999 Annual Report. Annals of Internal Medicine 103(6): 886-888.

Frisby, H.R. 1997. Clinical and Epidemiologic Features of a Massive Waterborne... Journal of Acquired 

Immune Deficiency Syndromes and Human Retrovisrus 16 (4-5): 223-422. 

Goldstein, S.T., et al. 1996. Cryptosporidiosis: An Outbreak Associated with Drinking Water Despite Stateof-the-Art Water Treatment. Annals of Internal Medicine 124(5):459-968.

MacKenzie W.R., et. al. 1994. A Massive outbreak in Milwaukee of Cryptosporidium infection transmitted 

through the public water supply. N English journal of Medicine. 331:161-7.

Texas Department of Health (TDH). 1998. Cryptosporidiosis at Brushy Creek. Epidemiology in Texas, 

1999 Annual Report.

http://www.tdh.state.tx.us/epidemiology/98annual/reports/crypto.pdf.

Upton, S.J. 2001. Cryptosporidium: they probably taste like chicken. Presented at the Cryptosporidium from 

Molecules to Disease Conference, Fremantle, Western Australia, October 7-12, 2001. (Cited in Text Box 1: 

About Cryptosporidiosis)
 Appendix I

I-25

I.4 Tables showing various concentrations of pathogenic bacteric, enteric viruses, and parasitic protozoa 

 in sewage.

Table I.6 Concentrations of Common Pathogenic Bacteria in Sewage

Bacteria Concentration in Sewage (per 100mL) Reference

Camplyobacter 3,700 Holler 1988

10,000-100,000 WHO 2003

Pathogenic E.coli 1,321,594 (30,000-6,200,000) Payment 2001

1,000,000-10,000,000 WHO 2003

1,190,000 Gore et al. 1999

2,500,000

3,180,000

4,120,000

2,880,000

1,600,000

2,170,000

Salmonella 2.3-8,000 NAS 1993

240-1,200 Koivunen 2003

93-1,100

1,100-11,000

150-1,100

100-10,000 NRC 1998

400-8,000 EPA 1992

8,000 NRC 1996

528 Bitton 1980

400-1,200 Pettygrove and Asano 1985

500-8,000 Yates 1994

418 Payment and Franco 1993

0.2-8,000 WHO 2003

13 Gore et al. 1999

62

>190

45

<20

170

<40

S. typhi -- --

Shigella 1-1,000 NAS 1993

1-1,000 EPA 1992

1,000 NRC 1996

1-1000 NRC 1998

0.1-1,000 WHO 2003

Vibrio cholera -- --

Vibrio non-cholera 10-10,000 NAS 1993

Yersinia -- --
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Report to Congress on the Impacts and Control of CSOs and SSOs

 Table I.7 Concentrations of Enteric Viruses Present in Sewage

Virus Group Concentration in Sewage 

(per 100mL)

Reference

Adenovirus 10-10,000 NAS 1993

Astrovirus -- --

Noravirus (includes Norwalk-like 

viruses)

-- --

Echovirus -- --

Enterovirus (includes polio, 

encephalitis, conjunctivitis, and 

coxsackie viruses)

18.2-9,200 NAS 1993

>0.720 Rose 2001a

>11

23

4.5

96.2 (0.4-1,251) Payment et al. 2001

1,000-10,000 NRC 1998

1.085

1

7

5

40

2

1

1.1 Rose 2001 (WER article)

100-50000 EPA 1992

7 (0.75-80) Hejkal 1984

1.98 Smith and Gerba 1982

0.05

14.8

3.95

6.91

3.95

50,000 NRC 1996

100-49,200 Pettygrove and Asano 1985

10,000-100,000 Yates 1994

0.284 Payment and Franco 1993

0.42 Rose 1996

10,000 Wyn-Jones and Sellwood 2001
 Appendix I

I-27

 Table I.7 continued

Virus Group Concentration in Sewage (per 

100mL)

Reference

Reovirus 0.1-124.7 NAS 1993

Rotavirus 40.1 NAS 1993

0.98 (0.1-32.1) Hejkal et al. 1984

9.6 Smith and Gerba 1982

9.6

6.7

17.4

8

1.5

400-85,000 WHO 2003
I-28

Report to Congress on the Impacts and Control of CSOs and SSOs

 Table I.8 Concentrations of Common Parasitic Protozoa Present in Sewage

Parasitic Protozoa Concentration in Sewage (per L) Reference

Cryptosporidium 10-1000 NAS 1993

47.7 Chauret 1999

6 (1-560) Payment 2001

<40-625 Mahin and Pancorbo 1999

226.0

60 (3-400)

20 (0-3,000)

20 Rose 2001a

17

<4.348

8.16

9.52

14.84 NRC 1998

15

0.3

2

1

15

15 Rose 2001b

7.42 Payment and Franco 1993

40 LA County SD 2003

280

160

80

120

3.7 Rose 1996

69.1 Gennaccaro et al. 2003

1-390 WHO 2003

<2-24 McCuin and Clancy 2004

0

0

<2

2

<2-8

<2-8

<2-24

4.1-13,700

Entamoeba 28-52 NAS 1993

0-100 EPA 1992

4.0 Bitton 1980

4 WHO 2003
 Appendix I

I-29

 Table I.8 continued

Parasitic Protozoa Concentration in Sewage (per L) Reference

Giardia 530-100,000 NAS 1993

82.5 Chauret 1999

1,165 (100-9,200) Payment 2001

390 Mahin and Pancorbo 1999

315

10-13,600

642-3,375

354 (90-2,830)

290 (40-1,140)

200 Rose 2001a

480

200

220

42.86

490 NRC 1998

69

39

325

2

69

490 Rose 2001b

13.76 Payment and Franco 1993

29,000 LA County SD 2003

19,000

16,000

27,000

32,000

4,760

5,080

15,560

9,760

19,280

500-100,000 EPA 1992

100,000 NRC 1996

9,000-200,000 Yates 1994

39 Rose 1996

125-200,000 WHO 2003
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Report to Congress on the Impacts and Control of CSOs and SSOs

References for Tables I.6 - I.8

Bitton, G. 1980. Introduction to Environmental Virology. New York, NY: John Wiley & Sons.

Chauret, C., et al. 1999. Fate of Cryptosporidium oocysts, Giardia cysts, and microbial indicators during 

wastewater treatment and anaerobic sludge digestion. Canadian Journal of Microbiology 45:257-151.

Environmental Protection Agency (EPA). 1992. Manual: Guidelines for Water Reuse. EPA 625/R-92/004.

Gennaccaro, A.L., et al. 2003. Infectious Cryptosporidium parvum oocysts in final reclaimed effluent. Applied 

and Environmental Microbiology 69(8): 4983-4984.

Gore, R., et al. 1999. Report No. 99-17: Bacteria in raw sewage and viable helminth ova in raw sewage and 

primary sludge at the water reclamation plants of the Metropolitan Water Reclamation District of Greater 

Chicago. Metropolitan Water Reclamation District of Greater Chicago Research and Development 

Department. Chicago, IL.

Hejkal, T.W., et al. 1984. Seasonal occurrence of rotavirus in sewage. Applied and Environmental Microbiology

47(3): 588-590.

Holler, C. 1988. Quantitative and qualitative investigations of Campylobacter in a sewage treatment plant. 

Zentralblatt für Bakteriologie, Mikrobiologie und Hygiene. Serie B 185: 326-339.

Koivunen, J., et al. 2003. Elimination of enteric bacteria in biological-chemical wastewater treatment and 

tertiary fi ltration units. Water Research 27: 690-698.

Los Angeles County Sanitation Districts. 2003. Memo containing a summary of various Giardia cyst and 

Cryptosporidium oocyst data sets compiled by the San Jose Creek Water Quality Laboratory over the previous 

nine years. July 21, 2003.

Mahin, T., and Pancorbo, O. 1999. Waterborne pathogens: more effective analytical and treatment methods 

are needed for pathogens in wastewater and stormwater. Water Environment and Technology 11(4): 51-55.

McCuin, R.M. and Clancy, J.L. 2004. Cryptosporidium Occurrence, Removal and Inactivation Methods for 

Wastewaters. Final Report: Water Environment Research Foundation, Project 98-HHE-1, Alexandria, VA. In 

press.

National Academy of Sciences (NAS). 1993. Managing Wastewater in Coastal Urban Areas. Washington, D.C: 

The National Academies Press.

National Research Council (NRC), Committee on the Use of Treated Municipal Wastewater Efflents and 

Sludge in the Production of Crops for Human Consumption. 1996. Use of Reclaimed Water and Sludge in 

Food Crop Production. Washington, D.C: The National Academies Press.

National Research Council (NRC), Committee to Evaluate the Viability of Augmenting Potable Water 

Supplies with Reclaimed Water. 1998. Issues in Potable Reuse: The Viability of Augmenting Drinking Water 

Supplies with Reclaimed Water. Washington, D.C: The National Academies Press.
 Appendix I

I-31

Payment, P., and Franco, E. 1993. Clostridium perfringens and somatic coliphages as indicators of the 

efficiency of drinking water treatment for viruses and protozoan cysts. Applied and Environmental 

Microbiology 59(8): 2418-2424.

Payment, P., et al. 2001. Removal of indicator bacteria, human enteric viruses, Giardia cysts, and 

Cryptosporidium oocysts at a large wastewater primary treatment facility. Canadian Journal of 

Microbiology 47: 188-193.

Pettygrove, G.S., and Asano, T. 1985. Irrigation with Reclaimed Municipal Wastewater—A Guidance 

Manual. Prepared by the Department of Land, Air, and Water Resources, University of California, Davis 

for the California State Water Resources Control Board. Ann Arbor: Lewis Publishers, Inc. (Reprint).

Rose, J.B., et al. 1996. Removal of pathogenic and indicator microorganisms by a full-scale water 

reclamation facility. Water Research 30(11): 2785-2797.

Rose, J.B., et al. 2001a. Reduction of pathogens, indicator bacteria, and alternative indicators by wastewater 

treatment and reclamation processes. Water Environment Research Federation. Project Number 00-PUM2T.

Rose, J.B., et al. 2001b. Reduction of enteric microorganisms at the Upper Occoquan Sewage Authority 

Water Reclamation Plant. Water Environment Research 73(6): 711-720.

Smith, E.M., and Gerba, C.P. 1982. Development of a method for detection of human rotavirus in water 

and sewage. Applied and Environmental Microbiology 43(6): 1440-1450.

World Health Organization (WHO). 2003. Guidelines for Safe Recreational Water Environments, Volume I: 

Coastal and Fresh Waters. Geneva: World Health Organization.

Wyn-Jones, A.P., and Sellwood, J. 2001. Enteric viruses in the aquatic environment. Journal of Applied 

Microbiology 91: 945-962.

Yates, M.V. 1994. Monitoring concerns and procedures for human health effects. In: Wastewater Reuse for 

Golf Course Irrigation. Ann Arbor: Lewis Publishers.
Appendix J 

Estimated Annual Illness Burden 

Resulting from Exposure to CSOs and 

SSOs at BEACH Survey Beaches

 Appendix J

J-1

This appendix provides a detailed description of the data and methodology used by EPA to estimate the annual 

illness burden associated with exposure to CSO and SSO discharges in recreational waters at state-recognized 

beaches. The analysis does not capture all of the likely annual illnesses attributable to CSOs and SSOs at beaches. 

EPA believes that CSO and SSO contamination at swimming areas other than those included in this analysis 

causes additional illnesses in exposed swimmers. A lack of information on these swimming areas, including 

water quality reporting data, precludes developing a more complete estimate of annual human illness frequency 

from beach exposure to CSO or SSO contaminants at this time. Moreover, this analysis accounts only for 

gastrointestinal illnesses. 

J.1 National Health Protection Survey of Beaches

EPA’s BEACH Survey served as the primary data source for estimating exposure to CSO and SSO discharges to 

recreational waters, as noted in Section 6.2.1.

BEACH Survey data include beach-specific information on advisories and closings for 3,067 beaches from 274 

federal, state, and local agencies; not all beaches provided data for the four-year period. Beaches included in the 

survey are located in 34 states and the U.S. territories of Guam, Puerto Rico, and the U.S. Virgin Islands. These 

beaches are primarily marine water beaches, but some freshwater beaches are included. Table J.1 shows the 

number of beaches covered in the BEACH Survey for each state and the number of beaches with and without 

pre-emptive actions or monitoring programs. 

As shown in Table J.2, California accounts for a signifi cant portion of the total number state-recognized beaches, 

closure events, and closure events attributed to CSO and SSO discharges. As a result, California may exert a 

disproportionate infl uence on illness estimates. There are several possible explanations for this, including that 

California has a longer swimming and monitoring season and has more rigorous monitoring programs than 

many other beaches in the nation, resulting in the discovery of more events than at beaches with less frequent 

monitoring and with an abbreviated swimming season. However, EPA lacks the data to make these comparisons at 

the time.

Although the BEACH Survey was initiated in 1998 (for the 1997 swim season), only data for the 1999, 2000, 2001, 

and 2002 swimming seasons were used. Data from the 1997 swimming season were excluded from this analysis 

because the initial BEACH Survey did not request information from respondents on the source, reason, or cause 

of advisories or closings. Further, information from the 1998 swimming season was not used due to an error in 

the data recording procedures. 

The BEACH Surveys have been modifi ed over time, including changes to the wording of some questions between 

1999 and 2002. Furthermore, the rate of participation by beach authorities has changed somewhat with each 

BEACH Survey. Nonetheless, EPA believes these differences do not preclude using data from the four most recent 

surveys.

EPA recognizes the limitations of the BEACH Survey. Specifi cally, although the data provided by the respondents 

are reviewed by EPA for potential gross errors, the quality and accuracy of the information may vary signifi cantly 

with each respondent. In addition, because the BEACH Survey data used in the analysis cover only four years 

signifi cant climatological events such as La Nina, which caused a severe drought in southern California during 

1999, could have a disproportionate affect on the number of CSOs and SSOs reported in the database. Despite 

these shortcomings, EPA believes that the BEACH Survey is the most accurate and comprehensive source of 

information on beach contamination and beach authority responses to contamination events. For the purposes 
J-2

Report to Congress on Impacts and Control of CSOs and SSOs

State Number of beaches 

in BEACH survey1

Beaches with pre-emptive 

actions and/or monitoring

Beaches with no preemptive actions or 

monitoring

Alabama 38 22 16

California 1,078 803 275

Delaware 70 70 0

Florida 962 858 104

Georgia 16 16 0

Guam 160 160 0

Hawaii 288 288 0

Illinois 153 153 0

Indiana 185 185 0

Iowa 102 102 0

Louisiana 16 16 0

Maine 25 18 7

Maryland 200 199 1

Massachusetts 783 748 35

Michigan 812 771 41

Minnesota 74 61 13

Mississippi 9 9 0

New Hampshire 689 689 0

New Jersey 906 906 0

New York 893 837 56

North Carolina 80 80 0

Northern Mariana Islands 3 3 0

Ohio 252 252 0

Pennsylvania 60 60 0

Puerto Rico 47 47 0

Rhode Island 480 480 0

South Carolina 105 105 0

Texas 65 44 21

Vermont 133 132 1

Virgin Islands 145 145 0

Virginia 56 35 21

Washington 202 184 18

Wisconsin 196 138 58

Total 9,671 9,002 669

1 The number of total beaches include beaches that reported in any of the four years of the BEACH survey used in this analysis: 1999, 

2000, 2001, 2002; thus, a beach that reported in all four years would be counted four times.

Table J.1. Number of BEACH Survey Beaches and Type of Program by State
 Appendix J

J-3

of this analysis, EPA contacted a limited number of BEACH Survey respondents to collect additional data on 

monitoring practices and levels of contamination resulting from SSO events. Other data were obtained from 

publicly available sources including beach authority websites, where available.

J.2 Methodology for Counting a CSO or SSO Event

In the BEACH Survey, beach authorities were asked to select the sources of pollution that caused any closures or 

advisories. Respondents could choose the following:

• SSO

• CSO

• CSO/SSO

• POTW

• Septic systems

• Sewer line/blockage/break

• Boat discharge

• Storm water runoff

• Wildlife

• Unknown

• Other (please specify)

For advisories and closings where “SSO” or “sewer line/blockage/break” were identifi ed, the event was classifi ed as 

an SSO.

J.3 Categorizing BEACH Survey Beaches

Based on the management practices used to address contamination events, each beach authority and its 

CA All other states Total Percent

1999 Beach Survey

Number of Beaches 256 1,795 2,051 12.5%

Number of all events 1,277 665 1,942 65.8%

Number of SSO/CSO events 22 102 124 17.7%

2000 Beach Survey

Number of Beaches 281 2,073 2,354 11.9%

Number of all events 1,545 1,214 2,759 56.0%

Number of SSO/CSO events 61 148 209 29.2%

2001 Beach Survey

Number of Beaches 272 2,171 2,443 11.1%

Number of all events 1,495 2,184 3,679 40.6%

Number of SSO/CSO events 268 59 327 82.0%

2002 Beach Survey

Number of Beaches 269 2,554 2,823 9.5%

Number of all events 1,057 2,157 3,214 32.9%

Number of SSO/CSO events 76 196 272 27.9%

Table J.2. Comparison of California reporting to all other states in the Beach Survey
J-4

Report to Congress on Impacts and Control of CSOs and SSOs

corresponding beach(es) were assigned to one of the following categories: 

(1) Beaches where the sewer authority reports CSO and SSO events to the beach authority. 

(2A) Beaches that preemptively initiate advisories or closures due to wet weather events. 

(2B) Beaches where advisories or closure decisions are based on monitoring data or preemptive actions 

due to wet weather events. 

(3) Beaches where advisory or closure decisions are made based on beach monitoring alone. 

(4) Beaches that have reported advisories and closures, but do not have programs described in 

Categories 1, 2, and 3.

J.4 Calculation of Swimmer Days

The number of swimmers per typical day at beaches where either a closing or advisory action had been 

implemented (due to CSOs or SSOs) was estimated by using beach attendance data included in the BEACH 

Survey. The BEACH Survey contained the following responses to the question on attendance per day:

• Less than 100

• 100 - 499

• 500 - 999

• 1,000 - 9,999

• More than 10,000

• Don’t know 

Respondents provided answers for weekdays, weekend days and holidays, during the summer season, and during 

other seasons. Respondents also estimated the length of their swimming season and the percentage of beach 

visitors that go into the water. 

To calculate the number of swimmers per day on weekdays, on weekend days, for the summer season, and for the 

“other season” category, a midpoint value was selected to represent each numeric response range. For example, 50 

was assigned for the “less than 100” response, and 5,500 for the “1,000 - 9,999” response. For a beach where the 

response was “more than 10,000,” EPA assumed an average summer weekday attendance value of 10,000. For a 

beach where the response was “don’t know”, the overall average for beaches who supplied data was used.

The difference between the weekday and weekend values was estimated separately for each year of data. For 

example, the BEACH Survey data for the 2002 BEACH Survey indicated that during the summer, the average 

weekend attendance levels were on average 62 percent greater than during the weekdays. For the other seasons, 

weekend attendance was on average 31 percent greater than the weekday.

A daily summer average was estimated by multiplying the summer weekday value by fi ve, multiplying the summer 

weekend value by two and dividing the sum by seven. This procedure was repeated to estimate the daily average 

for “other seasons.” EPA next calculated a daily average for the year, which consisted of summer and other season 

daily averages. EPA estimated the proportion of the values for “summer weekday,” “summer weekend,” “other 

weekday,” and “other weekend” based on the length of the season of the beach. If a beach authority reported that 

the swim season was six months long, the summer values were counted for six months of the year and the other 

values were counted for six months of the year. Similarly, if a beach authority noted that the swim season was only 

three months long, summer values were counted for three months of the year, and other values were counted for 

nine months of the year. 

The percentage of swimmers that enter the water was calculated for each beach, because it was assumed that only 

the people who actually go in the water are at risk from CSO- and SSO-related contamination. The percentage 

of swimmers was estimated for each beach based on the beach authority’s response to the question: “What 

percentage of people who use this beach go into the water?” If a beach did not respond to this question the overall 
 Appendix J

J-5

average (calculated for all beaches that answered in that survey year) was substituted. Some beaches responded 

with a range. In these cases, the midpoint of the range was used. In other cases, beaches responded with either less 

than or greater than a number. In these cases, the midpoint between the number provided and 0 or 100 was used 

(e.g., if a beach responded greater than 95 percent, then the value used was 97.5). The percent of swimmers was 

applied to the attendance for each beach to yield the number of swimmers at each beach. 

J.5 Extrapolation Method

This section describes the methods used to extrapolate the exposure estimates for swimmers at BEACH Survey 

beaches to other state-recognized beaches that did not participate in the BEACH Survey.

From responses to BEACH Survey questions about visitation and the fraction of visitors who swim, EPA estimated 

that 315 million swimmer days per year occur at the BEACH Survey beaches. The BEACH Survey, however, 

does not cover all swimming at state-recognized beaches. For example, approximately 13 percent of the beach 

authorities to whom the survey was mailed did not respond. 

To estimate 1) the number of swimmers at state-recognized beaches not accounted for in the BEACH Survey and 

2) the number of swimmers not accounted for at beaches where authorities received a survey and did not respond, 

EPA compared selected BEACH Survey attendance data with corresponding state attendance data estimates 

reported on the U.S. Life Savers Association and state web sites. A comparison of the Beach Survey data with 

the other state attendance data is shown in Table J.3. EPA used an adjustment factor of 1.362 to extrapolate the 

number of swimmer days from the BEACH Survey beaches to all state-recognized beaches in the United States.

EPA applied an approach based on attendance to estimate the fraction of all beach swimmer days represented by 

BEACH Survey respondents. The Agency did not have suffi cient data to support the assumption that visitation 

and swimmer days are proportional to mileage of beaches. EPA believes that heavily-used beaches are more likely 

to be surveyed by and respond to the BEACH Survey than are lightly-attended beaches. EPA also assumes that 

BEACH Survey beaches likely account for a substantially larger fraction of total beach visitation than the fraction 

of total beach mileage accounted for by these beaches. Using the attendance-based approach, EPA estimated 

that BEACH Survey beaches account for 73 percent of total national visitation and swimmer days at all staterecognized beaches.

This approach resulted in the following estimated distribution of the estimated 429 million days per year of 

outdoor non-pool swimming:

• 315 million swimmer days at BEACH Survey beaches

• 114 million swimmer days at other formal beaches that either were not sent or did not respond to the 

BEACH Survey

 State Estimated Attendance in BEACH 

Survey

Total Attendance Including 

Alternate Sources

California 143,283,136 171,146,608

Delaware 2,479,627 6,000,000

Hawaii 9,462,739 17,285,810

Illinois 5,399,233 24,885,197

Maryland 3,353,142 4,000,000

Total 163,977,877 223,317,615

Adjustment factor 1.362

Table J.3 Attendance Adjustment Calculations
J-6

Report to Congress on Impacts and Control of CSOs and SSOs

These swimmer days are distributed among categories as shown in Table J.4.

J.6 Exposure/Noncompliance Rates

It is important to note that each jurisdiction has its own defi nition of an advisory. EPA defi nes an advisory as “a 

recommendation to the public to avoid swimming in water that has exceeded applicable water quality standards 

to reduce the potential of contracting a swimming related illness.” Although each jurisdiction’s defi nition may 

vary, most authorities use an advisory to recommend that visitors not swim in the water. Closures, on the other 

hand, usually require that visitors do not enter the water or beach area. The degree to which a closure is enforced, 

however, can vary widely.

Different jurisdictions also have different policies regarding when they issue a closure or an advisory. South 

Carolina, for example, issues advisories only and does not issue closures. California generally issues an advisory 

on a preemptive basis when there is heavy rain; posts a beach warning when monitoring indicates a standard 

is exceeded, but there is no known source of human sewage; and closes a beach when there is a CSO, SSO, or 

repeated exceedances of standards. The State of New Jersey issues closures only. And, in many states, individual 

communities have policies on advisories and closures that can differ from the state’s policy regarding state-owned 

beaches.

For this analysis, EPA found it was not feasible to standardize the BEACH Survey data and adjust for differences 

in how jurisdictions defi ne and use advisories and closures. Instead, EPA aggregated advisories and closures and 

refers to them collectively as “actions.” Among the “actions” taken by beach authorities in response to CSO or SSO 

events, 63 percent were denoted as closures and 37 percent were denoted as advisories.

Effectiveness of actions was estimated by requesting information on the actual effectiveness of beach closures 

and advisories in preventing swimming from several local lifeguard offi ces. There was consensus that closures are 

typically well enforced and effective in preventing swimming. Based on this input, EPA assumes that 95 percent 

of potential swimmers at a closed beach would comply. The effectiveness of advisories estimate was based on 

information in the report, Coastal Beach Water Quality and Public Health: Preliminary Steps Toward Improving 

Public Notifi cation in Wisconsin Under the Federal Beach Act (Vail, 2002). It reports results from a social survey 

conducted at Wisconsin’s public beaches in 2002, in which survey respondents were shown a sign stating “Alert, 

Elevated Bacteria Levels, Swim at your own Risk.” The survey respondents were asked, “If you saw this sign posted 

at this beach, would you swim here?” and could answer either “yes,” “no,” or “don’t know.” Results were obtained 

for several different counties in Wisconsin. For this analysis, EPA weighted the responses by population and used 

the response rate for “no” as the lower bound of compliance; the upper bound was calculated by adding percent 

“no” and “don’t know”. For example, in Door County, 6 percent of the respondents answered “yes,” 9 percent 

Number of 

Swimmers/Year

Category 1 Category 2A Category 2B Category 3 Category 4 Total

BEACH Survey 

beaches 135,049,677 3,674,342 41,754,509 114,619,121 19,763,032 314,860,682

Beaches not in 

Survey 48,871,303 1,319,658 15,109,975 41,477,965 7,151,776 113,940,677

Total 48,871,303 1,319,658 15,109,975 156,097,086 26,914,808 428,801,359

Table J.4 Number of Swimmer Days Per Year, by Category
 Appendix J

J-7

answered “no,” and 85 percent responded “don’t know.” The upper bound of compliance was calculated by adding 

the response rate for no (9 percent) and don’t know (85 percent) to yield 94 percent, and the lower bound of 

compliance only accounts for the “no” responses (9 percent). Survey results and populations from 12 counties are 

shown in Table J.5. 

In estimating the overall effectiveness of actions, EPA developed a weighted average of the effectiveness of closures 

(95 percent effective) and advisories (36 to 90 percent effective), weighted by the proportion of CSO- or SSOcaused actions in the baseline that are closures (63 percent) and advisories (37 percent). This results in an estimate 

that 73 to 93 percent of potential swimmers, on average, will not swim at a beach when the beach is under a CSOor SSO-related action. Conversely, 7 to 27 percent would swim at a beach when a beach is under a CSO- or SSOrelated action. 

J.7 Monitoring Data Analysis 

Figure J.1 presents a timeline that shows the relevant events in detecting and responding to beach contamination 

from a CSO or SSO discharge and the duration between these events. The timeline is portrayed for instances in 

which contamination from a CSO or SSO is detected through monitoring at the beach.

The monitoring data from the beach authorities were analyzed to determine approximately when the 

contamination was discovered, when the existence of the contamination was confi rmed by analysis of an 

additional sample by a beach authority, when the beach authority issued the action, and the period during which 

the action remained in effect. The results of this analysis are summarized, by category, on the next page and are 

shown in Table J.6.

 Category 1 Beaches with preemptive programs close beaches upon notifi cation of CSO or SSO discharges. 

It is assumed that the beach is closed prior to contamination and lasts until contamination ends. To 

calculate exposure duration, duration data from the 2001 and 2002 BEACH Survey (end date subtracted 

County Lower Bound Upper Bound Population* Percent of Population

Kenosha 41 95.5 156,209 9.22

Racine 192,284 11.36

Milwaukee 933,221 55.11

Ozaukee 27 73 84,772 5.01

Sheboygan 113,376 6.70

Manitowac 82,065 4.85

Kewaunee 20,455 1.21

Door County 9 94 28,402 1.68

Iron 9 72 6,727 0.40

Ashland 16,561 0.98

Bayfield 15,114 0.89

Douglas 44,093 2.60

Weighted 

Average

36.42 90.33 1,693,369

* Population estimates obtained from U.S. Census 2003.

Table. J.5 Calculations for Advisory Compliance Rates 
J-8

Report to Congress on Impacts and Control of CSOs and SSOs

CSO/SSO

occurs

Contamination

begins at the 

beach

Detection of

contamination Confirmation

Beach

posted

Contamination

ends

y1

y3

x

y4

y2

x = The length of time that contamination from the CSO or SSO exists at the beach.

y1 = The period between the onset of contamination at the beach and when it was detected.

y2 = The period between the detection of contamination and its confirmation by the beach authority.

y3 = The period between confirmation and action (e.g. , beach posting, closure, public notification).

y4 = The period during which the action remains in effect.

from start date) were averaged for all Category 1 beaches. The average length of exposure duration was 5.1 

days. 

 Category 2A The preemptive programs for precipitation events (where beaches automatically close or 

post an advisory due to a precipitation event) prevent the full duration exposure to CSOs and wet weather 

SSOs, but not dry weather SSOs. Because there is no monitoring or other means to detect dry weather 

SSOs, it was assumed that exposure to these SSOs occurs. The estimated exposure duration for these 

events is 2.1 days.

 Category 2B Similar to Category 2A, preemptive programs for precipitation events eliminate exposure due 

to wet weather CSOs and SSOs. Some percent of dry weather SSOs would be detected and actions would 

be taken; however, some exposure occurs due to the delay from monitoring. For the purposes of this 

analysis, EPA assumed that the percentage of SSO events that were dry weather and that were wet weather 

were the same as the percentage of such events reported in the BEACH Survey. That is 34 percent of the 

events in Category 2B occurred during dry weather and 66 percent were wet weather related. Exposure to 

contamination due to dry weather events was estimated to last 8.7 days, and exposure during wet weather 

contamination events was estimated to last 4.5 days. 

 Category 3 CSOs and SSOs at these beaches are acted upon once monitoring results confi rm 

contamination, and therefore exposure is avoided only during the period of closure. Exposure during the 

actions is 4.5 days and exposure during the lag period is 4.2 days, for a total exposure period of 8.7 days.

Figure J.1 Timeline for Response Activities to CSO and SSO Discharges
 Appendix J

J-9

 Category 4 Although there were no reported mechanisms in place to detect CSOs and SSOs for these 

beaches in the BEACH Survey, some of these beaches reported advisories and closings caused by CSOs or 

SSOs. EPA calculated the duration reported from these beaches to be 10 days. 

EPA combined information on the number of baseline CSO- and SSO-related contamination events documented 

in the BEACH Survey, the duration of events and days of exposure, and the number of swimmer-days, to estimate 

the number of swimmer-days of exposure to CSOs and SSOs that would occur at the beaches included in this 

analysis. The results of this analysis are summarized in Table J.7.

Category

Time Periods 1 2A 2B 3 4 Explanation

Y1 NA NA 2.56 2.56 NA

For beaches for which there were monitoring data 

(categories 2b and 3), the value was calculated 

by subtracting the date of the first contaminated 

sample from the date of the last clean sample and 

dividing by 2.

Y2 NA NA 1.00 1.00 NA

For beaches for which there were monitoring data 

(categories 2b and 3), the value was calculated by 

subtracting the date of confirmation from the date 

of the first contaminated sample.

Y3 NA NA 0.68 0.68 NA

For beaches for which there were monitoring data 

(categories 2b and 3), the value was calculated by 

subtracting the start date of the action from the 

date of confirmation.

Y4 5.13 2.1 4.45 4.45 10.07

For beaches for which there were monitoring data 

(categories 2b and 3), the value was calculated by 

subtracting midpoint between the end date as 

reported in the beach report and the last sample 

showing contamination from the start date of 

the action. For beaches for which there was no 

monitoring data (Categories 1, 2a, and 4), the end 

date was subtracted from the start date reported in 

the beach survey.

TOTAL 5.15 2.1 8.69 8.69 10.07 Calculated by adding Y1-Y4

Table J.6. Duration Calculations by Category
J-10

Report to Congress on Impacts and Control of CSOs and SSOs

Table J.7 Calculations for Exposed Swimmer-Days

Category

Step 1 2A 2B 3 4 Total 1999-2002 Beach Survey Data

Number of beaches 3,907 91 985 4,020 668 9,671

Average number of beaches per year 977 23 246 1,005 167 2,418

Number of SSO and CSO events 

acted upon in survey 118 5 14 77 20 234

Number of events per year, per 

beach 0.121 0.209 0.055 0.076 0.117 --

Number of swimmer days/year for 

beaches 183,920,980 5,004,000 56,864,485 156,097,056 26,914,808 428,801,329

Exposure during noncompliance

Days of exposure during 

noncompliance (per event) 5.13 2.10 4.45 4.45 10.07 --

Number of such events per year, per 

beach 0.121 0.209 0.055 0.076 0.117 --

Number of days of exposure during 

non-compliance 0.622 0.438 0.244 0.339 1.175 --

Percent of year 0.17% 0.12% 0.07% 0.09% 0.32% --

Number of swimmer days exposed 

(7-27% of swimmers do not comply)

21,068-

83,552

404-

1,604

2,555-

10,133

9,738-

38,620

5,830-

23,122

39,596-

157,030

Exposure before detection

Days of exposure before detection 0 0 4.25 4.25 0 --

Number of such events per beach 0 0 0.019 0.076 0 --

Number of days of exposure per year 

per beach 0 0 0.079 0.323 0 --

Percent of year NA NA 0.022% 0.089% NA --

Number of swimmer days (100 

percent swimmers are exposed) 0 0 12,329 138,209 0 150,538

Total number of swimmer days occurring 

during the contamination period

21,068-

83,552

404-

1,604

14,884-

22,462

147,948-

176,830

5,830-

23,122

190,135-

307,568

The fi rst fi ve rows of Table J.7 present information from the 1999-2002 BEACH Surveys. On average, 153 CSOand SSO-related closure/advisory actions were reported in the BEACH Survey at these beaches between 1999 and 

2002. The number of swimmer days includes swimmer days at state-recognized beaches not in the BEACH Survey, 

as described in Section J.5.

The middle section of the table estimates the level of exposure that occurs when non-compliant swimmers 

are exposed to CSO and SSO contamination. Multiplying this amount of exposure prevention per event by 

the frequency of such events gives an estimate for the average number of days of exposure per beach per year 

occurring for noncompliant swimmers. The number of exposed days is then divided by 365 to calculate the 

percent of the year when contamination is present at a beach. Next, the percent of the year is multiplied by the 

number of swimmer days and by 7 percent and 27 percent (to account for the range of noncompliance exposure 

rates) to estimate the total number of swimmer days of exposure to CSO and SSOs during closures and advisories.
 Appendix J

J-11

The third section of Table J.7 (exposure before detection) estimates the days of exposure occurring during CSO 

and SSO contamination events before they are detected. In this case, exposure occurs only during the lag time 

between actual contamination and when the action begins at Category 2B and 3 beaches. Again, the amount 

of exposure occurring per event is multiplied by the frequency with which such events occur, to estimate the 

average number of days of exposure per beach per year occurring during the lag-time between contamination and 

detection. The number of days is divided by 365 to calculate the percent of the year contamination is present at 

these beaches. This percentage is multiplied by the number of swimmer days to estimate the number of swimmer 

days of exposure to CSOs and SSOs before the advisories and closings are in effect. 

The last row of the table presents the number of exposed swimmer days for the two different scenarios of exposure. 

J.8 SSO Events Excluded From Exposure Duration Calculations

Several SSO actions were removed from the exposure duration analysis because they were determined to be nonrepresentative of typical SSO events. Actions were considered to be non-representative of typical SSO events when:

• Action durations were greater than 100 days for a single event.

• Survey entries were found to be erroneous, based on information supplied by the beach authorities or 

based on internal quality control checks performed by technical reviewers.

Action durations greater than 100 days for a single event were removed from the analysis or adjusted when 

appropriate, because EPA assumed that such extended SSO contamination likely represented a continuous SSO 

problem that was well known, and therefore human exposure is less likely. Additional actions were removed from 

Categories 1 and 2B calculations. By defi nition, beach actions issued for these categories were issued preemptively. 

However, closer review of 2001 BEACH Survey responses indicated that several actions for these categories had 

been issued based on monitoring data alone. The actions in Categories 1 and 2B that were based on monitoring 

data alone were not included in these category calculations. In addition, these data were not used in any other 

duration categories. All of the actions (four in total) were removed from Category 2B because they were issued 

based on monitoring data alone; therefore, no duration estimates could be calculated for this category based on 

those four actions. 

J.9 Pathogen Concentrations

EPA estimated the average level of pathogens at beaches during closures attributed to CSO and SSO events 

and through analysis of monitoring data obtained from the states and reported in the 2001 and 2002 BEACH 

Survey. EPA obtained additional monitoring data from relevant state or county websites and by contacting beach 

authorities. EPA estimated the in-water concentration during an event by averaging monitoring data observations 

obtained during the event including: the fi rst monitoring result indicating exceedance of the bacteria standard and 

the presence of contamination, and all subsequent monitoring results until the fi rst monitoring result indicating 

that bacteria concentrations had fallen to an acceptable level. The monitoring data indicated similar, highly variable 

bacteria concentrations for both CSO- and SSO-contaminated recreational waters and were therefore averaged. 

• For salt water closures/advisories, data were obtained for 26 actions. The average enterococci concentration 

during these events was 532/100 mL.

• For freshwater closures/advisories, data were obtained for 29 actions. This E. coli concentration was 695/

100 mL. 

To account for bacteria levels present at times when SSO and CSO events are not occurring, EPA estimated 

background levels. This was accomplished by averaging concentration levels from the last monitoring result 

not below the bacteria standard preceding a contamination event at each beach for which there were data. The 

monitoring data showed similar, highly variable bacteria concentrations for both CSO- and SSO-contaminated 
J-12

Report to Congress on Impacts and Control of CSOs and SSOs

recreational waters and were therefore averaged. 

• The average background enterococci concentration was 12/100 mL

• For freshwater the background E. coli concentration was 71/100 mL

J.10 Dose Response Equations

The following dose-response functions derived by Cabelli (1983) and Dufour (EPA 1984) were used by EPA 

to relate highly-credible gastrointestinal illness (HCGI) symptoms among swimmers to the concentrations of 

enterococci (for marine water and for freshwater) or E. coli (for freshwater only):

For marine water: 

HCGI symptoms/1000 swimmers = 0.2 + 12.17 log(mean enterococci/100 mL)

For freshwater: 

HCGI symptoms/1000 swimmers = -11.74 + 9.4 log(mean E. coli/100 mL) 

These equations derive from epidemiological studies sponsored by EPA at several beach locations in the late 1970s 

and early 1980s, and provide the basis for EPA’s current water quality criteria for recreational waters. EPA’s marine 

water quality criterion of 35 enterococci per 100 mL, for example, was derived by solving the fi rst equation for 

the water quality that would yield the traditionally accepted illness rate of 19 cases per 1000 swimmers. Several of 

Cabelli’s and Dufour’s fi ndings are notable:

• The clearest statistical relationships between water quality and swimmer illness rates were found for 

gastrointestinal illness. The statistical relationships were even more defi nitive when only “highly credible” 

gastrointestinal symptoms were considered, in contrast to all gastrointestinal symptoms.

• Enterococci (marine water and freshwater) and E. coli (freshwater) were found to be the best indicator 

parameters. They correlated with swimmer illness rates more closely than did other possible indicator 

parameters (e.g., fecal coliform).

Despite EPA’s adoption of the Cabelli/Dufour dose-response functions as the basis for recreational water quality 

criteria, a great deal of uncertainty is associated with the number of illnesses predicted by these functions, as 

discussed above. EPA believes most other studies generally support the Cabelli/Dufour conclusion that enterococci 

and E. coli are the best indicators (EPA 1984). A comprehensive recent review of epidemiological studies on health 

effects from exposure to recreational water conclude similarly that enterococci/fecal streptococci for both marine 

and freshwater, and E. coli for freshwater, correlate best with health outcomes (Pruss 1998).

EPA’s Offi ce of Research and Development recently reviewed the Cabelli/Dufour studies and the other swimmer 

illness studies conducted since 1984, when the last of Cabelli/Dufour’s studies were published. The review 

concluded:

In examining the relationships between water quality and swimming-associated gastrointestinal 

illness, the epidemiological studies conducted since 1984 offer no new or unique principles that 

signifi cantly affect the current water quality criteria EPA recommends for protecting and maintaining 

recreational uses of marine and freshwaters. Many of the studies have, in fact, confi rmed and 

validated the fi ndings of EPA’s studies. Thus, EPA has no new scientifi c information or data justifying 

a revision of the Agency’s recommended 1986 water quality criteria for bacteria at this time (EPA 

2002).
 Appendix J

J-13

In light of these fi ndings, EPA concluded that Cabelli/Dufour remained the most reliable set of dose-response functions 

available to estimate swimmer illness rates in the United States. 

Cabelli and Dufour found a statistically signifi cant relationship between indicator bacteria density and gastrointestinal 

symptoms for some beaches. However, they found a stronger statistical relationship between indicator bacteria density 

and HCGI symptoms, and decided therefore to express their preferred dose-response relationship in terms of HCGI 

symptoms rather than total gastrointestinal symptoms. The implication for this analysis is that the Cabelli/Dufour doseresponse relationships may understate by a factor of two to four the total number of gastrointestinal cases that are likely 

occurring. This factor may result in EPA substantially underestimating the number of illnesses resulting from exposure 

to beach water contaminated by CSO and SSO discharges.

J.11 Illness Calculations and Results

The number of HCGI illnesses resulting from exposure to beach water contaminated by CSOs and SSOs was estimated 

by combining information on the number of exposed swimmer-days, the concentration of indicator bacteria to which 

swimmers are exposed, and the Cabelli/Dufour dose-response functions for marine and freshwaters. Table J.8 shows how 

the number of illnesses was calculated from the number of person days exposed to beach water contaminated by CSO 

and SSO discharges at beaches included in this analysis. 

Table J.8 Derivation of Number of HGCI Cases

Category

Steps Water Type

(per dose-response functions) 1 2A 2B 3 4 Total

Person Days of Exposure 21,068-

83,552

404-

1,604

14,884-

22,462

147,948-

176,830

5,830-

23,122

190,135- 

307,568

Allocation of Exposure 

Days

Percent in marine waters 83 83 83 83 83 83

Percent in freshwaters 17 17 17 17 17 17

Person Days of 

Exposure

In marine waters 17,487-

69,348

336-

1,331

12,534-

18,643

122,797-

146,769

4,839-

19,191

157,813-

255,282

In freshwaters 3,582-

14,204

69-

273

2,530-

3,818

25,151-

30,061

991-

3,931

32,323-

52,287

Pathogen Level 

During Contamination

Marine waters (EN/100 mL) 532 532 532 532 532 532

Freshwaters (E. coli/100 mL) 695 695 695 695 695 695

Rate of HCGI Cases Marine waters (per 1,000 swimmers) 33 33 33 33 33 33

Freshwaters (per 1,000 swimmers) 15 15 15 15 15 15

Background Pathogen 

Level 

Marine waters (EN/100 mL) 12 12 12 12 12 12

Freshwaters (E. coli/100 mL) 71 71 71 71 71 71

Rate of HCGI Cases

Marine waters (per 1,000 swimmers) 13 13 13 13 13 13

Freshwaters (per 1,000 swimmers) 6 6 6 6 6 6

Illness Rate for 

Contamination Events 

- Background Levels

Marine waters (per 1,000 swimmers) 20 20 20 20 20 20

Freshwaters (per 1,000 swimmers) 9 9 9 9 9 9

Number of Primary 

HCGI Cases

In marine waters 350-

1,387

7-

27

247-

373

2,456-

2,935

97-

384

3,157-

5,106

In freshwaters 32-128 1-2 23-34 226-271 9-35 291-470

Total estimated primary HCGI occuring due to human 

exposure to SSO and CSO contamination

382-

1,515

8-

29

270-

407

2,682-

3,206

106-

419

3,448-

5,576
J-14

Report to Congress on Impacts and Control of CSOs and SSOs

References

Cabelli, V.J. et al. 1983. A marine recreational water quality criterion consistent with indicator concepts and risk 

analysis. Journal of Water Pollution Control Federation 55(10):1306-1314.

EPA. 1984. Offi ce of Research and Development. Health Effects Criteria for Fresh Recreational Waters. EPA 600/1-

84-004. 

May, H., and J. Burger. 1996. Fishing in a polluted estuary: fi shing behavior, fi sh consumption, and potential risk. 

Risk Analysis 16(4):459-471.

National Sporting Goods Association (NSGA).1992. Sports participation in 1990, Series I and II.

Prüss, A. 1998. Review of Epidemiological Studies on Health Effects From Exposure to Recreational Water. 

International Journal of Epidemiology 27:1-9.

US DOC, Census (U.S. Department of Commerce, Bureau of the Census). 2004. State and County QuickFacts. 

Retrieved July 28, 2004. http://www.census.gov

Vail, B. J. 2002. Coastal Beach Water Quality and Public Health: Preliminary Steps Toward Improving Public 

Notifi cation in Wisconsin Under the Federal BEACH Act. Wisconsin Department of Natural Resources.

 
Appendix K 

Summary of Enforcement Actions

K.1 Federal CSO Judicial Orders

K.2 Federal SSO Judicial Orders

K.3 Federal CSO Administrative Orders

K.4 Federal SSO Administrative Orders

K.5 Federal CSO Administrative Penalty Orders

K.6 Federal SSO Administrative Penalty Orders

K.7 State CSO Judical Orders

K.8 State SSO Judicial Orders

K.9 State CSO Administrative Orders

K.10 State SSO Administrative Orders

K.11 State CSO Administrative Penalty Orders

K.12 State SSO Administrative Penalty Orders

 Appendix K

K-1

K.1 Federal CSO Judicial Orders

Region State Case Name/City Name Effective Date Description

1 MA Boston Harbor (MWRA) 1987 MWRA has completed four hydraulic relief projects including, 

CAM005, BOS017, Chelsea Trunk, and Chelsea Branch. They have 

completed CSO facility upgrades at Cottage Farm, Prison Point, 

Commercial Point, Fox Point and Summerville-Marginal. They have 

completed upgrades to the floatables removal facility and have 

closed outfalls. Under construction are the East Boston Branch 

Sewer relief and Union Park Detention/Treatment facility. Sewer 

separation is proceeding in South Dorchester, Stony Brook and 

Neponset River. Still in the design phase are Fort Point Channel 

Storage, the BOS019 storage conduit and parts of the East Boston 

Branch Sewer relief and, the South Dorchester and Stony Brook 

separation projects.

1 MA City of Lowell 11/10/88; 

Amended

06/29/01

The Consent Decree required that the City complete construction of 

the Southwest Bank Interceptor Project and eliminate all discharges 

from outfalls 001 and 003 by 12/15/88. It further required that the 

City complete construction of the Northwest Bank Interceptor 

Project, eliminate all discharges from outfalls 005 and 006, and 

complete construction of Storm Water Diversion Structure Number 

Two by 09/01/88. The City was required to eliminate all dry weather 

discharges from its West Street Pump Station by 01/15/89 and also 

eliminate discharges from outfall 004 by 04/15/89. Finally, they were 

required to complete construction for rehabilitation of Marginal 

Street Interceptor and eliminate all discharges from outfall 032 by 

01/15/90. The City was required to submit a completed Combined 

Sewer Overflow (CSO) Facilities Plan to EPA and the Department of 

Environmental Quality Engineering of the Commonwealth of 

Massachusetts (DEQE) which would address further CSO 

abatement.

1 MA City of New Bedford 12/07/87; 

Amended - 

4/28/95

The Consent Decree required the City to prepare and submit a CSO 

Facilities Plan by 07/01/89. The Plan identified all of the projects 

necessary to meet permit requirements and CSO discharge 

requirements. The City was required to construct whatever projects 

necessary to eliminate dry weather discharges from CSO outfalls by 

03/01/90.

1 MA Gloucester 11/30/88 The Order addressed noncompliance by failing to complete a CSO 

study and treatment plan.

1 MA Lynn Water and Sewer 

Commission

11/02/89;

Amended

11/15/94;

Amended

06/29/01

The Order required that by 12/31/03, the Commission would 

complete construction of the Summer Street Sewer Separation 

Project and complete 100% of the sewer separation for outfall 006 

thereby eliminating discharges of combined sewage to outfall 006. 

The Order also required that by 12/31/06, the Commission would 

complete the sewer separation for outfall 005 eliminating discharges 

of combined sewage to outfall 005. Also, by 12/31/09, the 

Commission would complete the sewer separation for outfall 004 

eliminating discharges of combined sewage to outfall 004.

1 MA Swampscott 05/05/88 The Order required the completion of a CSO analysis and 

development of a schedule for construction of CSO facilities.
K-2

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

1 ME City of Bangor 04/09/91; 

Modified06/28/91

The Order required a CSO facility's plan and CSO abatement 

projects implementation.

1 ME City of Bangor 6/30/87; 

Amended

12/01/87

This Order addressed certain NPDES permit violations.

1 ME City of South Portland 04/16/92; 

Amended08/18/94

This Order required a Publicly Owned Treatment Work (POTW) 

upgrade and a CSO abatement program for NPDES permit 

compliance.

1 NH City of Portsmouth No date 

provided

This Order required the implementation of a Long-Term Control 

Plan (LTCP).

2 NJ North Bergen Township No date 

provided

This Order addressed the failure to meet the construction schedule 

for CSO abatement.

2 NY Niagara Falls 03/13/87 This Order required the City to eliminate all dry weather overflows 

and submit final plans for repairs necessary to the combined sewer 

system (CSS).

2 NY Poughkeepsie 03/31/88 This Order required the City to eliminate all dry weather overflows.

2 NY Utica 06/22/77 This Order required the City to eliminate dry weather overflows and 

conduct a Sewer System Evaluation Study (SSES).

3 MD City of Baltimore 09/30/02 The Consent Decree required the City to separate the CSS and 

eliminate all CSO structures from the Warbrook neighborhood by 

06/30/02 and in the Forest Park neighborhood by 06/30/05. This 

represented elimination of all CSOs in Baltimore.

4 GA City of Atlanta 07/13/98 The Consent Decree required Atlanta to perform an evaluation of 

their existing CSO control facilities, perform studies and testing of 

their CSS and receiving waters and prepare a remedial measures 

report which will evaluate appropriate alternatives for CSO control. 

The City was required to perform various other studies to evaluate 

the efficacy of previous CSO control efforts. The Consent Decree 

required that the City prepare CSO Management, Operation, and 

Maintenance Plans by 12/01/98.

4 GA City of Atlanta 09/24/98 This Order addressed the nonattainment of water quality standards 

resulting from CSOs and it required an evaluation of CSO 

discharges and remedial action plan. All construction will be 

complete by 07/11/14.

4 GA City of Atlanta 07/29/99 This Order required the City to complete construction for the 10th 

Ward Trunk Sewer Improvements (Plan 6) by 07/31/00, complete 

construction for the Fairmont/Glidden CSO Separation by 09/30/01, 

complete construction for the Phase III Relief Sewer by 08/31/02, 

complete construction for the Veterans Hospital Trunk Sewer 

Improvements by 11/30/02, complete construction for the Peachtree 

Interceptor Relief Sewer by 12/31/02, complete construction for the 

Pine Meadows Sewer Improvements by 01/31/03, and complete 

construction for the North Fork Peachtree Creek Relief Sewer and 

Nancy Creek Sewer System Rehabilitation; the 10th Ward Trunk 

Sewer Improvements (Part 1-5); the South Fork Peachtree Creek 

Trunk Relief Sewer; and the Indian Creek Trunk Relief Sewer by 

02/28/03.

Region State Case Name/City Name Effective Date Description

1 ME City of Bangor 04/09/91; 

Modified06/28/91

The Order required a CSO facility's plan and CSO abatement 

projects implementation.

1 ME City of Bangor 6/30/87; 

Amended

12/01/87

This Order addressed certain NPDES permit violations.

1 ME City of South Portland 04/16/92; 

Amended08/18/94

This Order required a Publicly Owned Treatment Work (POTW) 

upgrade and a CSO abatement program for NPDES permit 

compliance.

1 NH City of Portsmouth No date 

provided

This Order required the implementation of a Long-Term Control 

Plan (LTCP).

2 NJ North Bergen Township No date 

provided

This Order addressed the failure to meet the construction schedule 

for CSO abatement.

2 NY Niagara Falls 03/13/87 This Order required the City to eliminate all dry weather overflows 

and submit final plans for repairs necessary to the combined sewer 

system (CSS).

2 NY Poughkeepsie 03/31/88 This Order required the City to eliminate all dry weather overflows.

2 NY Utica 06/22/77 This Order required the City to eliminate dry weather overflows and 

conduct a Sewer System Evaluation Study (SSES).

3 MD City of Baltimore 09/30/02 The Consent Decree required the City to separate the CSS and 

eliminate all CSO structures from the Warbrook neighborhood by 

06/30/02 and in the Forest Park neighborhood by 06/30/05. This 

represented elimination of all CSOs in Baltimore.

4 GA City of Atlanta 07/13/98 The Consent Decree required Atlanta to perform an evaluation of 

their existing CSO control facilities, perform studies and testing of 

their CSS and receiving waters and prepare a remedial measures 

report which will evaluate appropriate alternatives for CSO control. 

The City was required to perform various other studies to evaluate 

the efficacy of previous CSO control efforts. The Consent Decree 

required that the City prepare CSO Management, Operation, and 

Maintenance Plans by 12/01/98.

4 GA City of Atlanta 09/24/98 This Order addressed the nonattainment of water quality standards 

resulting from CSOs and it required an evaluation of CSO 

discharges and remedial action plan. All construction will be 

complete by 07/11/14.

4 GA City of Atlanta 07/29/99 This Order required the City to complete construction for the 10th 

Ward Trunk Sewer Improvements (Plan 6) by 07/31/00, complete 

construction for the Fairmont/Glidden CSO Separation by 09/30/01, 

complete construction for the Phase III Relief Sewer by 08/31/02, 

complete construction for the Veterans Hospital Trunk Sewer 

Improvements by 11/30/02, complete construction for the Peachtree 

Interceptor Relief Sewer by 12/31/02, complete construction for the 

Pine Meadows Sewer Improvements by 01/31/03, and complete 

construction for the North Fork Peachtree Creek Relief Sewer and 

Nancy Creek Sewer System Rehabilitation; the 10th Ward Trunk 

Sewer Improvements (Part 1-5); the South Fork Peachtree Creek 

Trunk Relief Sewer; and the Indian Creek Trunk Relief Sewer by 

02/28/03.
 Appendix K

K-3

Region State Case Name/City Name Effective Date Description

5 IL Metropolis No date 

provided

The Consent Decree required correction of the CSO overflow 

structure.

5 IL Paris No date 

provided

The Order addressed NPDES permit violations, resulting in CSO 

separation, testing, and first flush treatment.

5 IL Rock Island WWTP 08/21/03 The Order addressed permit violations. Rock Island was required to 

prepare and submit a LTCP. A penalty of $150,000 was assessed.

5 IN Anderson 07/18/02 The Consent Decree required that by 12/31/09, they will complete 

construction for all improvements.

5 IN City of Bonnville 04/16/87; 

Amended

08/13/01

The 1987 Consent Decree required the City to adequately maintain 

the CSS and improve plant operations.

5 IN Hammond 04/23/99 The Consent Decree required Hammond to maximize combined 

sewage flow through the collection system and treatment plant and 

implement their LTCP. They were directed to construct facilities as 

needed to eliminate three of their CSOs, including but not limited to: 

a storage reservoir, pump station improvements, sewer separation, 

sewer interceptors, and sewer interceptor improvements by 

05/01/09.

5 IN Madison No date 

provided

The Consent Decree required development of a CSO management 

plan.

5 MI Menominee 04/21/88 The Order addressed unauthorized CSO discharges.

5 MI Wayne County 1994 The Order addressed CSOs contributing to public health advisories 

against swimming and nutrient loading stimulating plant and algae 

growth in downstream water bodies including Lake Erie.

5 OH Bedford 09/30/85 This Order required City to conduct a CSO facility study and 

implement a plan for appropriate treatment of CSOs.

5 OH Cincinnati Metropolitan 

Sewer District

No date 

provided

This Order addressed unauthorized dry weather discharges from 

CSOs.

5 OH City of Akron No date 

provided

This Consent Decree addressed CSOs causing violation of effluent 

limits and failure to meet schedule for elimination of CSOs.

5 OH City of North Olmsted 07/31/91 Under this Order they were required to achieve consistent 

compliance with its permit within 40 days of the Order.

5 OH Port Clinton 09/08/99 This Order required monitoring and scheduled CSO abatement. 

Port Clinton was required to submit a plan for permanent CSO 

improvement or closure by 11/01/99.

5 OH Portsmouth 1992 This Order addressed CSOs causing water quality standard 

exceedances in the Scioto and Ohio Rivers.

5 OH Toledo 12/19/02 The Toledo Consent Decree addressed both CSO issues and 

Sanitary Sewer Overflow (SSO) issues. Regarding CSOs, Toledo 

was required to design and construct certain "Phase I" CSO control 

measures including: East Side and Bay View Pump Stations 

improvements, secondary treatment backup power, a 60 MG 

equalization basin, an additional secondary clarifier, and a 185 

MGD capacity ballasted flocculation wet weather treatment system. 

These "Phase I" projects were estimated to cost $157 million, and 

were to be complete within approximately 40-45 months of decree 

entry (depending on plan review and approval). Toledo was also 

required to develop and implement a LTCP. The LTCP control 

measures were to be completed by August 2016.

Region State Case Name/City Name Effective Date Description

5 IL Metropolis No date 

provided

The Consent Decree required correction of the CSO overflow 

structure.

5 IL Paris No date 

provided

The Order addressed NPDES permit violations, resulting in CSO 

separation, testing, and first flush treatment.

5 IL Rock Island WWTP 08/21/03 The Order addressed permit violations. Rock Island was required to 

prepare and submit a LTCP. A penalty of $150,000 was assessed.

5 IN Anderson 07/18/02 The Consent Decree required that by 12/31/09, they will complete 

construction for all improvements.

5 IN City of Bonnville 04/16/87; 

Amended

08/13/01

The 1987 Consent Decree required the City to adequately maintain 

the CSS and improve plant operations.

5 IN Hammond 04/23/99 The Consent Decree required Hammond to maximize combined 

sewage flow through the collection system and treatment plant and 

implement their LTCP. They were directed to construct facilities as 

needed to eliminate three of their CSOs, including but not limited to: 

a storage reservoir, pump station improvements, sewer separation, 

sewer interceptors, and sewer interceptor improvements by 

05/01/09.

5 IN Madison No date 

provided

The Consent Decree required development of a CSO management 

plan.

5 MI Menominee 04/21/88 The Order addressed unauthorized CSO discharges.

5 MI Wayne County 1994 The Order addressed CSOs contributing to public health advisories 

against swimming and nutrient loading stimulating plant and algae 

growth in downstream water bodies including Lake Erie.

5 OH Bedford 09/30/85 This Order required City to conduct a CSO facility study and 

implement a plan for appropriate treatment of CSOs.

5 OH Cincinnati Metropolitan 

Sewer District

No date 

provided

This Order addressed unauthorized dry weather discharges from 

CSOs.

5 OH City of Akron No date 

provided

This Consent Decree addressed CSOs causing violation of effluent 

limits and failure to meet schedule for elimination of CSOs.

5 OH City of North Olmsted 07/31/91 Under this Order they were required to achieve consistent 

compliance with its permit within 40 days of the Order.

5 OH Port Clinton 09/08/99 This Order required monitoring and scheduled CSO abatement. 

Port Clinton was required to submit a plan for permanent CSO 

improvement or closure by 11/01/99.

5 OH Portsmouth 1992 This Order addressed CSOs causing water quality standard 

exceedances in the Scioto and Ohio Rivers.

5 OH Toledo 12/19/02 The Toledo Consent Decree addressed both CSO issues and 

Sanitary Sewer Overflow (SSO) issues. Regarding CSOs, Toledo 

was required to design and construct certain "Phase I" CSO control 

measures including: East Side and Bay View Pump Stations 

improvements, secondary treatment backup power, a 60 MG 

equalization basin, an additional secondary clarifier, and a 185 

MGD capacity ballasted flocculation wet weather treatment system. 

These "Phase I" projects were estimated to cost $157 million, and 

were to be complete within approximately 40-45 months of decree 

entry (depending on plan review and approval). Toledo was also 

required to develop and implement a LTCP. The LTCP control 

measures were to be completed by August 2016.
K-4

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

5 OH Wellston 10/13/87 This Order addressed CSO discharges due to improper Operation 

and Maintenance (O&M) and unpermitted bypasses.

5 OH Youngstown 03/05/02 Youngstown was required by the Consent Decree to: eliminate an 

outfall in a local park (Outfall 6108) by 05/06; eliminate two small 

direct sewage discharges ("Tod & Irving East & West") by 08/03; 

develop a LTCP by 01/03; remove accumulated sediment from the 

Mill Creek Collector Sewer by 06/02; and implement various shortterm operational (i.e., Nine Minimum Controls (NMCs)) 

improvements and pump station upgrades/ replacements by 2007.

Region State Case Name/City Name Effective Date Description

5 OH Wellston 10/13/87 This Order addressed CSO discharges due to improper Operation 

and Maintenance (O&M) and unpermitted bypasses.

5 OH Youngstown 03/05/02 Youngstown was required by the Consent Decree to: eliminate an 

outfall in a local park (Outfall 6108) by 05/06; eliminate two small 

direct sewage discharges ("Tod & Irving East & West") by 08/03; 

develop a LTCP by 01/03; remove accumulated sediment from the 

Mill Creek Collector Sewer by 06/02; and implement various shortterm operational (i.e., Nine Minimum Controls (NMCs)) 

improvements and pump station upgrades/ replacements by 2007.
 Appendix K

K-5

K.2 Federal SSO Judicial Orders

Region State Case Name/City Name Effective Date Description

1 CT Greenwich 01/15/02 This Consent Decree required that construction be complete by 

12/08.

1 CT Waterbury 11/21/02 The Consent Decree was issued to prevent future Sanitary Sewer 

Overflows (SSOs) from occurring. Multiple construction schedules 

were established in the Order and were pending EPA approval.

1 MA Winchendon 07/29/02 This Consent Decree required that construction for the SSO 

improvements be complete by 01/04 and construction for the 

Publicly Owned Treatment Works (POTW) improvements be 

complete by 07/05.

2 Puerto 

Rico

Puerto Rico Aqueduct

and Sewer Authority

(PRASA)

Lodged 03/13/03 This Consent Decree required specific remedial actions at a defined 

list of pump stations. PRASA was required to submit the detailed list 

of actions to be performed at each station and a proposed schedule 

for same, within 90 days of entry date of Consent Decree. All 

remedial actions at these stations were to be complete within 32 

months of the date of final approval of the list. All pump stations 

were to be subject to an Operation and Maintenance (O&M) plan, 

which was to be developed by PRASA. A Spill Response and 

Cleanup Plan was required to be submitted within 90 days of date of 

entry of Consent Decree. The Plan was to be reviewed annually and 

updated as necessary. 

3 MD City of Baltimore 09/30/02 Remedial actions included: elimination or modification of designated 

SSO structures; reporting of SSO events; identification of all SSO 

structures, flow monitoring, collection system evaluation and 

sewershed planning, Infiltration and Inflow (I/I) evaluation; 

elimination of cross connections between sanitary and storm sewers; 

peak flow modeling; inspection of all gravity sewers 8-inches and 

larger and all force mains, manholes, etc.; evaluation of long-term 

capacity; identification and elimination of illegal private connections; 

rehabilitation of certain pump stations; inspection of all pump 

stations twice daily until SCADA is installed; update of maintenance 

information management system; performing pump station 

preventive maintenance; updating existing O&M manuals; 

implementing a maintenance program for the collection system and 

an overall information management system program; inspection of 

all valves in the collection system; development of an Emergency 

Response Plan; and reporting both orally and in writing any 

unauthorized discharges to waters.

3 PA Borough of Indiana 06/17/02 Objectives of the Consent Decree included compliance with final 

effluent limits, elimination of bypasses at the treatment plant, and 

elimination of SSOs. The remedial action for SSO elimination was to 

implement the EPA-approved SSO Response Plan that was 

previously submitted. With regard to the other issues, by 07/01/03, 

the Borough was supposed to have completed the wastewater 

treatment plant expansion projects, including the entire Wastewater 

Detention Tank. The Borough was also supposed to complete the 

Main Plant Interceptor project by 08/01/03.

3 PA Bradford 04/11/03 This Consent Decree addressed NPDES permit violations and 

assessed a $40,000 civil penalty.

3 VA Galax 01/30/03 This Consent Decree required the City to implement a 

Comprehensive Management, Operation and Maintenance (CMOM) 

program. All construction was to be complete by 03/03.
K-6

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 AL Jefferson County 12/15/96 The Consent Decree laid out a three-phase plan. Phase I required 

the County to develop a series of planning documents that would 

identify the scope, methodologies, time frames, and resources to be 

allocated to evaluate the condition and capacity of the collection 

system, identify sources of I/I, and develop remedial measures. 

Phase II consisted of analyses and reports to determine the extent of

rehabilitative needs and corrective actions necessary. Phase III was 

the implementation phase, in which specific improvements were to 

be made according to the Capacity Improvement Schedules and the 

Performance Improvement Plans developed in Phase II. 

4 AL Mobile 01/24/02 The Consent Decree required them to develop both Short-Term and 

Long-Term Capacity Assurance Programs. They were required to 

implement an EPA-approved SSO Reporting, Notification, and 

Record Keeping Program and submit a semi-annual report to EPA 

analyzing information available through its information management 

systems. They were also required to submit and implement Legal 

Support Programs, including an ordinance for grease control, as well 

as develop and submit a Contingency Plan for Sewer and 

Wastewater Treatment Facilities. They also had to submit and 

implement the following programs: Scheduled Pump Station 

Operation Program, Electrical Maintenance Program, Mechanical 

Maintenance Program, Force Main Preventive Maintenance (PM) 

Program, Gravity Line PM Program, Scheduled Hydraulic Cleaning 

Program, Root Control Program, Unscheduled Maintenance 

Program, revised Grease Control Program. A wet weather and dry 

weather water quality monitoring program was also required. 

4 FL Miami-Dade 

(Second and Final Partial 

Consent Decree)

04/95 This Consent Decree required an I/I evaluation and rehabilitation 

program; identification of a service area for each pump station; 

complete evaluations of 6.96 million feet of sewer lines and 

associated manholes; addressing I/I on private property; 

identification and elimination of illegal storm sewer connections to 

the sanitary sewer; development of a program to identify illegal 

storm sewer connections; inspection and, where necessary, repair of 

each pump station; repair or other improvements to pump stations 

that caused or contributed to SSOs; completion of the installation for 

the online remote monitoring equipment; submission of a Short-Term 

Collection System Operating Plan and a Long-Term Collection 

System Operation Plan; development of and implement a 

computerized collection and transmission system model; 

development of a program of pump station upgrades and collection 

system improvements; implementation of a collection system 

maintenance program; development of an inventory management 

system; and develop a program to optimize wastewater treatment 

efficiency and effectiveness. 

4 GA City of Atlanta 12/20/99 This Consent Decree required that construction for all improvements 

be complete by 07/01/14.
 Appendix K

K-7

Region State Case Name/City Name Effective Date Description

4 GA City of Atlanta 07/29/99 This Consent Decree required the City to complete construction for 

the 10th Ward Trunk Sewer Improvements (Plan 6) by 07/31/00, 

complete construction for the Fairmont/Glidden CSO Separation by 

09/30/01, complete construction for the Phase III Relief Sewer by 

08/31/02, complete construction for the Veterans Hospital Trunk 

Sewer Improvements by 11/30/02, complete construction for the 

Peachtree Interceptor Relief Sewer by 12/31/02, complete 

construction for the Pine Meadows Sewer Improvements by 

01/31/03, and complete construction for the North Fork Peachtree 

Creek Relief Sewer and the Nancy Creek Sewer System 

Rehabilitation, the 10th Ward Trunk Sewer Improvements (Part 1-5), 

the South Fork Peachtree Creek Trunk Relief Sewer, and the Indian 

Creek Trunk Relief Sewer all by 02/28/03. 

4 GA City of Atlanta 07/13/98 This Consent Decree addressed violations of its NPDES permits by 

discharging untreated wastewater containing raw sewage and 

partially treated wastewater into the Chattahoochee and South 

Rivers and their tributaries.

4 GA Dalton Lodged 

01/18/01;

Entered

03/28/01

This Consent Decree covered SSO, sludge, land application, and 

pretreatment. Construction was expected to be complete by 12/03.

5 IN New Albany 06/18/93; 

Amended

05/03/02

This amended Consent Decree required the City to develop a 

computerized collection system model, a SSO response plan, and a 

capacity assurance plan. They were also required to identify and 

remove all I&I sources unless exempted by EPA, perform wet 

weather survey and sampling, identify and remove any cross 

connections, and remove or separate any combined sewers. The 

capacity assurance plan included proposed remedial measures and 

a schedule for their design and construction. A comprehensive 

preventive maintenance program and a grease control program were 

also required to be developed and implemented. All piped overflows 

were to be flow metered. Flow volumes and rates of sanitary sewage 

input to a flood control pump station were to be estimated and 

sampled, and results submitted to EPA. Bypasses at these locations 

were to be reported to EPA within 24 hours. Alternative power 

sources and lightning protection at pump stations were to be 

provided to prevent overflows and the City was required to 

demonstrate for one year that all capacity related overflows had 

been eliminated.

5 IN South Haven Sewer 

Works

Lodged 07/17/03 This Consent Decree addressed permit violations. 

5 OH Akron 07/28/95 This Consent Decree required them to have construction complete 

for all improvements by 12/31/96.
K-8

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

5 OH Hamilton County (Interim 

Partial Consent Decree)

Lodged 02/15/02 This Consent Decree required Interim Remedial Measures (IRM) to 

include expenditure of $10-$15 million on an overflow treatment and 

storage facility for "SSO 700" and development of an IRM Plan 

evaluating system, including cost/performance, design storm 

parameters, etc., and schedule for completion by no later than 

12/31/07. After its completion, the County was to conduct an 

Effectiveness Study of the treatment and storage facility. Permanent 

Remedial Measures included a Remedial Plan due 12/31/09, with a 

goal of eliminating the "SSO 700" discharge point. The Remedial 

Plan was to specify proposed measures, estimated costs, annual 

O&M costs and expected performance during various storms. It also 

required a Comprehensive SSO Remediation Program to deal with 

SSOs in other parts of the system. This included modeling, capacity 

assessment, SSO response program, SSO monitoring and reporting 

plan, pump station operation program, industrial waste SSO/CSO 

management, etc.

5 OH Toledo 12/19/02 This Consent Decree addressed NPDES permit violations, including 

failure to implement a Long-Term Control Plan (LTCP). They were 

required to have construction complete for all improvements by 

12/16. This Consent Decree only addressed those that were point 

source discharges to waters, referred to as Sanitary Sewer 

Discharges (SSDs). Provisions that apply to SSDs include 

performing a Sanitary Sewer Evaluation Study (SSES), development 

of schedule for construction of sanitary sewer improvements; 

elimination of all known points of illegal discharge by 11/01/06; 

development of a Separate Sewer System Monitoring and Reporting 

Plan; development of an SSD response plan; development of an 

Industrial Wastewater Release Minimization Plan to reduce 

discharge of industrial pollutants through SSDs; and development of 

a Sewer System Management, Operation and Maintenance Plan to 

include gravity sewers, force mains, pump stations.

6 LA City/Parish of East Baton 

Rouge

12/23/88;

Modified

07/23/97

Remedial measures in this Consent Decree included elimination of 

cross connections, development of preventive maintenance program 

and SSO response plans, reporting unauthorized discharges, and 

monitoring environmental results. Also, a collection system remedial 

program was to be selected and completed. The components of this 

program were to include construction of storage basins and tanks, 

construction, modification or elimination of pump stations, 

construction of deep underground sewers and construction of 

treatment facilities. A treatment facility assessment was to be 

performed to evaluate whether improvement or expansion of three 

existing plants, or changes in plant O&M, were needed to comply 

with NPDES permits and handle future loading. 

6 LA City/Parish of East Baton 

Rouge

03/14/02 The environmental benefit of this Consent Decree was that 1.2 billion

gallons will be eliminated annually. A $1.12 million SEP was to be 

performed by the City and a penalty of $945,500 was assessed.
 Appendix K

K-9

Region State Case Name/City Name Effective Date Description

6 LA New Orleans 04/08/98 This Consent Decree required the Board to operate the fluidized bed 

incinerator with the EPA-approved O&M plan, have backup pumps 

for the pump stations, have the SCADA installed at all but one of the 

pump stations, operate a 24-hour manned central dispatch center, 

and certify that most known cross connections have been 

permanently sealed. Some cross connections were permitted to be 

retained, for these, the Cross Connection Security Plan would be 

followed and a physical barrier such as a valve or gate would be 

between the storm and sanitary sewers. They were also required to 

comply with the EPA-approved Preventive Maintenance Program 

and the Sewer Overflow Action Plan, track and report all 

unauthorized discharges, undertake a Remedial Action Program 

which would include flow monitoring, development of a computerized 

model, identification of construction projects, performance of 

collection system evaluation studies, and development of a 

Remedial Measures Action Plan (RMAP). Additionally, they will 

develop a storm sewer monitoring program.

9 CA San Diego 06/09/97 

Judicial ruling as 

to liability and 

penalties,

settlement and 

injunctive relief

This Consent Decree required them to have all construction 

complete by 12/07.

9 HI Honolulu 05/15/95 This Consent Decree required implementation of the EPA-approved 

pretreatment program, and included a requirement to develop 

technically based local limits for any pollutants of concern. They 

were also required to submit annual goals for reduction of SSOs for 

the years 1994 through 1999, and submit a Spill Reduction Action 

Plan by 12/31/95. This Plan was to include a Preventive 

Maintenance Plan, procedures for conducting grease trap 

inspections, evaluation of staffing needs, and equipment inventory. 

Interim preventive maintenance activities were also specified, 

including inspection and cleaning of at least 300 miles of sewer per 

year, semi-annual grease trap inspections, and inspection and 

cleaning of SSO hot- spots. Additionally, they were required to 

implement a computerized wastewater information and management 

system by 12/31/95 and developed an I/I program to prevent wet 

weather overflows.

9 HI Maui 09/09/99 This Consent Decree required the County to submit a Spill 

Reduction Action Plan (SRAP) to include implementation schedules, 

a spill response plan, a sewer preventive maintenance plan, a pump 

station spill reduction plan, an employee training program, a Fats, 

Oil, and Grease (FOG) control program, and a construction spills 

prevention plan by 01/01/00. They were also required to update its 

information management system to include systematic recording of 

collection system O&M activities and information obtained from 

sewer inspections and grease interceptor inspections and implement 

a Long-Term Sewer Line System Analysis and Rehabilitation Plan. A 

long-term treatment plant and pump station plan was required for 

rehabilitation, replacement and expansion of these facilities. Both of 

these plans have varying schedules depending on area and quarterly

reporting.
K-10

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-11

K.3 Federal CSO Administrative Orders

Region State Case Name/City Name Effective Date Description

1 MA Chicopee WPCF 06/06/97 This Order required them to complete construction of eliminating 

dry weather overflows at CSOs 027 and 037 and to complete river 

inflow improvements. Chicipee WPCF has constructed a CSO 

related bypass at the WWTP, allowing additional wet weather flow 

to receive primary treatment at the WWTP, thereby reducing CSOs. 

1 MA Chicopee WPCF 06/03/99 The Order required them to complete construction to eliminate dry 

weather overflows at CSO 027 (Front Street), CSO 037 (East Main 

Street), and River inflow improvements and to complete the 

cleaning of the second siphon at CSO 024 (V).

1 MA City of Chicopee 09/95 This Order required an abatement schedule for CSOs to 

Connecticut River.

1 MA City of Fall River 1987 This Order addressed unauthorized CSO discharges.

1 MA City of Fall River 1988 This Order addressed unauthorized CSO discharges.

1 MA City of Fall River 05/05/90 This Order required submittal of a report detailing the causes of the 

violations, including recommendations for bringing the discharge 

into compliance with the permitted limitations and a schedule for 

implementing the recommendations and achieving full compliance.

1 MA City of Fall River 08/29/91 This second Order required a detailed engineering report 

evaluating the City's ability to comply with the NPDES permit 

requirements.

1 MA City of Fall River 05/05/94 This third Order required, among other things, that the City submit a 

plan and schedule for bringing its discharge into compliance by 

11/01/95.

1 MA City of Fall River 05/05/97 Under this Order, the City was required to complete construction 

and attain operational level of the dechlorination system to comply 

with the permits effluent limits for total residual chlorine and 

coliform.

1 MA City of Fitchburg 08/31/94 This Order required them to submit a scope of work and an 

implementation schedule to complete a Long-Term Control Plan 

(LTCP).
K-12

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

1 MA City of Fitchburg 02/2/96; 

Amended

07/02/96

This Order required the immediate implementation of the Nine 

Minimum Controls (NMCs), submission of a report documenting 

NMC implementation by 07/31/96, submission of a draft Long-Term 

Control Plan by 04/30/98, submission of a final LTCP by 08/29/98, 

and then implementation of the approved LTCP. The City is 

proposing separation.

1 MA City of Fitchburg 12/01/00 This Order required that the City identify appropriate measures to 

prevent all dry weather CSO discharges from the Collection 

System. The Order required the City to submit a report that 

described those measures and provided a schedule for their 

implementation "as soon as possible". The report was to be 

submitted within 30 days of receipt of the Order.

1 MA City of Haverhill 08/09/99 This Order addressed CSO discharges in violation of permit 

requirements. The Order required the City to complete and submit 

to EPA and MADEP a draft LTCP by 08/31/00, and a final LTCP by 

01/15/01.

1 MA City of Haverhill 12/17/01, 

supercedes

11/02/01

The Order required the City to submit a Final LTCP by 08/02/02. 

The Order also required the City, by 04/01/03, to submit plans and 

specifications to EPA for: a parallel force main, measures to 

increase the WWTP peak wet weather capacity (through primary 

treatment), and primary bypass disinfection. Once approved by 

EPA, the City was to implement these measures within 28 months. 

The Order also required the City to submit plans for the structural 

modifications of Bradford-Side CSOs by 05/03/03, and complete 

those modifications within 15 months. The Order also required 

submission and implementation of a CS monitoring program. 

1 MA City of Holyoke 12/08/00 The Order required the City to complete construction of the Green 

Brook Sewer Separation Project, remove Green Brook flow from 

the combined sewer system (CSS) and eliminate all dry weather 

overflows from CSO discharge points.

1 MA City of Holyoke 04/11/01 The Order required the City to complete construction of Day Brook 

detention basin project and complete construction of the upgrade to 

the wastewater treatment facility.

1 MA City of Holyoke 09/95 Under this Order, they were required to prepare an abatement 

schedule for CSOs to Connecticut River.

1 MA City of Holyoke WPCF 03/27/97 This Order required the City to: initiate the appropriation of funds 

needed to complete the LTCP by 04/15/97; complete the 

appropriation of those funds by 05/06/97; submit a SRF application 

by 06/01/97; submit to EPA and MADEP a CSO monitoring plan by 

08/01/97; begin implementing the CSO monitoring plan by 

09/01/97; submit to EPA and MADEP a CSO optimization plan by 

10/01/97; complete implementation of the CSO monitoring plan by 

06/30/98; complete implementation of the CSO optimization plan by 

03/01/99; complete calibration of a computer model of the collection 

system by 03/31/99; submit to EPA and MADEP a draft LTCP by 

10/01/99; and submit a final LTCP to EPA and MADEP by 

04/01/00.
 Appendix K

K-13

Region State Case Name/City Name Effective Date Description

1 MA City of Taunton 01/29/96 The Order required the City to submit to EPA and to the 

Massachusetts Department of Environmental Protection (MADEP) 

a revised Scope of Work for conducting long-term improvement 

projects addressing Infiltration and Inflow (I/I) reduction, combined 

sewer overflow (CSO) abatement, and the Wastewater Facilities 

Capital Improvements Plan, all by 02/15/96. The Order also 

required the implementation of short-term improvements including: 

installation of a tide gate on the Water Street CSO by 03/01/96, 

submission of a high flow management plan by 03/15/96, updating 

of the sewer mapping system by 05/01/96, and submission of 

collection system and WWTP operating budgets by 05/01/96. 

1 MA City of Worcester 09/18/00 The Order required the City to submit a Scope of Work for 

development of a Phase I LTCP within 4 weeks of the Order date. 

The Order required submission of the Phase I LTCP within one 

year of EPA and MADEP approval of the LTCP SOW. The Phase I 

LTCP was to include a SOW for development of a Phase II LTCP. 

Submission of the Phase II LTCP was required 12 months following 

approval of the Phase I LTCP by EPA and MADEP. 

1 MA Gloucester 1989 The 1989 Consent Decree required a LTCP development. The 

LTCP was received 04/01.

1 MA Greater Lawrence 

Sanitary District, North 

Andover

06/24/99 This Order required the District to submit to USEPA and MADEP a 

revised NMC report, and to develop and submit to EPA and 

MADEP for approval, draft (due 06/31/01) and final (due 12/31/01) 

LTCP report.

1 MA Massachusetts Water 

Resources Authority 

(MWRA)

05/13/96 Under this Order, they were required to plan and implement actions 

to attain water quality standards.

1 MA Springfield Water and 

Sewer Commission, 

Springfield

04/26/02 This Order required the Commission to: submit a BMP Plan for the 

Watershops Pond by 03/31/02; submit a final LTCP to EPA and 

MADEP by 03/15/03; and complete construction of the approved 

Chicopee River CSO abatement program by 11/15/07.

1 MA Springfield Water and 

Sewer Commission, 

Springfield

09/95 This Order required an abatement schedule for CSOs to 

Connecticut River.

1 MA Springfield Water and 

Sewer Commission, 

Springfield

03/21/97 The Order required the Commission to: secure funding necessary 

to develop and implement the LTCP by 04/01/97; submit to EPA 

and MADEP a report documenting implementation of the NMCs by 

04/15/97; submit to EPA and MADEP a CSO monitoring plan and 

LTCP Work Plan by 07/01/97; engage a consultant to develop the 

LTCP by 08/15/97; begin implementing the CSO monitoring plan by 

03/01/98; complete implementation of the CSO monitoring plan by 

06/30/98; complete calibration of a computer model of the collection 

system and submit to EPA and MADEP a draft LTCP by 05/31/99; 

and submit a final LTCP by 08/31/99. 
K-14

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

1 MA Springfield Water and 

Sewer Commission, 

Springfield

11/14/00 Under this Order, the Commission was required to begin 

construction of interceptor relief conduits and a local storage 

conduit for CSO 019 by 06/01/02; complete construction of those 

interceptor relief conduits and local storage conduit for CSO 019 by 

12/31/03. Additionally, the Order required the Commission to begin 

improvements to the York Street Pump Station by 03/01/01; begin 

improvements to the Union Street Pump Station by 02/01/02; and, 

complete the pump station improvements by 03/01/04. The City 

was required to submit a final LTCP by 03/15/02. 

1 MA Town of Agawam 09/21/95 Under this Order, the Town was required to submit a Scope of 

Work and schedule for CSO facilities planning activities. 

1 MA Town of Agawam 12/30/96 Under this Order, the Town was required to submit a report 

documenting its implementation of the NMCs by 03/30/97. 

Following completion of the then-ongoing Little Canada Sewer 

Separation Project, the Town was then required to implement its 

existing CSO monitoring plan. Following completion of monitoring, 

the Town was then required to either submit a plan for additional 

CSO control, or for the sealing of all CSOs. 

1 MA Town of Ludlow 09/95 This Order required an abatement schedule for CSOs to 

Connecticut River.

1 MA Town of Ludlow WTP 12/30/96 Under this Order, they were required to submit a report on the 

implementation of the NMCs as part of controlling discharges from 

its CSOs. The Town will implement the CSO monitoring plan.

1 MA Town of Palmer 01/06/97 This Order addressed CSO discharges in violation of permit and a 

penalty of $5,000 was assessed.

1 MA Town of South Hadley 09/95 This Order required an abatement schedule for CSOs to 

Connecticut River.

1 MA Town of South Hadley, 

WTP

03/14/97 This Order required the Town to: apply for SRF funds by 03/31/97; 

complete construction of the Falls Sewer Separation Project by 

05/03/99; submit plans and a schedule for the East Side sewer 

separation project by 03/14/98 ; and complete construction of the 

Mount Holyoke I/I project, the Silver Street catch basin elimination 

project, and eliminate CSOs #10 and #14 all by 01/01/01.

1 MA West Springfield 09/01/95 This Order addressed CSO discharges in violation of permit. The 

Order required a CSO abatement schedule.

1 ME Augusta Sanitary District 07/20/97 This Order required the District to: complete "Phase I" WWTP wet 

weather flow capacity improvement projects by 10/31/98; and 

complete adjustments to the regulators tributary to CSOs 010, 019, 

023, 032, and regulators 029B, 029C, 029D, 029E, 029F, and 029G 

by 08/01/95. Where those adjustments and "flow slipping", are 

insufficient to control CSOs, the District must complete separation 

projects by 06/01/98.
 Appendix K

K-15

Region State Case Name/City Name Effective Date Description

1 ME Biddeford 04/22/94 This Order required a CSO abatement schedule.

1 ME City of South Portland 11/10/97 Under this Order, the City was required to not bypass secondary 

treatment at flows less than 22.9 MGD. Bypassing was to occur in 

accordance with a "High Flow Management Plan" approved by 

MEDEP. Bypassed flow was to receive the equivalent of at least 

primary treatment and be disinfected during the disinfection season. 

This requirement was to remain in effect until either: the permit was 

modified to incorporate a generic bypass provision; expiration of 

that permit; compliance by the blended effluent with secondary 

limits; or elimination of the need to bypass as a result of the sewer 

separation phase of the CSO abatement project.

1 ME Lincoln Sanitary District 12/17/98 Under this Order, the District was required to implement the 

collection system and wastewater treatment facility (WWTF) 

improvements and CSO abatement projects in accordance with the 

approved Implementation Schedule. Immediate and continued 

compliance with the NMCs was also required. Also under this 

Order, the District was required to not bypass secondary treatment 

at flows less than 2.8 MGD (instantaneous flow) or 1.07 MGD (daily 

average flow). Bypassing was to occur in accordance with a "High 

Flow Management Plan" approved by MEDEP. Bypassed flow was 

to receive the equivalent of at least primary treatment and be 

disinfected during the disinfection season. This requirement was to 

remain in effect until either: the permit was modified to incorporate 

a generic bypass provision; compliance by the blended effluent with 

secondary limits; or elimination of the need to bypass as a result of 

sewer separation projects.

1 ME Sanford Sewerage 

District, Town of Sanford

07/13/98 The Order required the District to submit a "Draft CSO Master Plan" 

within 180 days of receipt of the order, and further required 

completion of the approved Master Plan in accordance with the 

schedule included therein. Immediate and continued compliance 

with the NMCs was also required.

1 NH City of Nashua 04/16/99 Under this Order, the City was required to implement the 

construction of specified combined sewer separation projects, as 

well as to implement a yet-to-be-completed Combined Sewer 

Separation Plan (due within five years of the Order's effective date. 

The City will eliminate all CSOs by 2019. The City was also 

required to revise and implement its WWTF High Flow 

Management plan.

1 NH City of Portsmouth 07/11/02 This Order required the City to submit a LTCP and an updated 

NMC plan by 08/01/02. The City was required to submit a 

preliminary design report for the CSO measures recommended by 

the LTCP by 02/08/03, and advertise for bids for the construction of 

a particular project in the vicinity of Outfalls 010A and 010B by 

03/03/03 (two of the three CSOs in the City's CS).
K-16

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

1 NH Lebannon WWTP & City 

STP

06/06/00 The Order required them to design and construct combined sewer 

separation projects to eliminate six CSOs (CSOs 010, 027, 026, 

005, 022, and 023) by 12/31/08. Additionally, the City was required 

to submit a plan to EPA to eliminate the seventh CSO (CSO 024) 

by 12/31/12.

1 NH Manchester STP 03/08/99 Action was taken to address nonattainment of water quality 

standards caused by CSOs. The Order required the City to submit 

plans and specifications for WWTP wet weather treatment 

modifications within 6 months of the Order's effective date, and to 

complete construction of those modifications within 12 months of 

plans and specifications approval. Completion of specified CSO 

abatement projects ("Phase I" projects) within 10 years of the 

Order's effective date, completion of a study of CSO #44 within 5 

years of Order issuance, provision of a revised ("Phase II") LTCP 

within 11 years of the Order's effective date, and a $5.6 million 

supplemental environmental project (SEP) were also required. 

1 NH Town of Exeter 02/03/97 The Order required the City to submit a report documenting the 

Town's implementation of the NMCs by 04/30/97.

3 PA Connellsville Municipal 

Authority

09/30/02 Under this Order, the Authority was required to provide, within 15 

days, an explanation of actions taken to comply with the CSO 

policy's NMCs requirements and to implement the Authority's 

existing NMCs Report. Within 30 days, the Authority was required 

to submit a detailed plan and schedule for fully implementing the 

NMCs. The order also required the Authority to, within 30 days, 

identify the resources needed to properly operate and maintain 

collection system, and to describe any actions the Authority was 

planning to take to further minimize CSO discharges and water 

quality impacts.

3 PA Export Borough 05/15/97 This Order addressed the Borough's failure to obtain and 

implement the requirements in the CSO general permit. This Order 

required the Borough to apply to PADEP for a NPDES permit for 

CSO discharges.

3 PA Lower Lackawanna Valley 

Sewer Authority (LLVSA)

12/06/01 This Order required the Authority to submit, within 60 days of 

receipt of the order, a plan and schedule that identified specific 

measures to eliminate dry weather overflows. The Authority was 

required to submit, within 60 days, a plan and schedule detailing 

how the Authority was expected to fulfill the CSO-related monitoring 

requirements in its NPDES permit. The Authority was also required 

to submit, within 180 days, a report identifying critical CSO points 

and identifying root causes and preventive measures to prevent 

and/or minimize the impact of discharges from the critical CSO 

points. Within 45 days of each submittal, the Authority was required 

to implement that plan.
 Appendix K

K-17

Region State Case Name/City Name Effective Date Description

3 PA Pittsburgh Water and 

Sewer Authority

11/20/96 This Order addressed the Authority's failure to obtain and 

implement the requirements in the CSO general permit. This Order 

required the Authority to apply to PADEP for a NPDES permit for 

CSO discharges.

3 PA Scranton 11/27/02 Under this Order, they were required to submit appropriate 

documentation demonstrating implementation of and compliance 

with the 1998 NMCs Plan. They were also required to complete and 

submit to the Pennsylvania Department of Environmental Protection 

(PADEP) and EPA a revised LTCP and a schedule for 

implementation.

3 WV City of Marmet 09/04/02 The Order required the City to submit within 60 days: a plan and 

schedule for complying with the water quality monitoring 

requirements of its NPDES permit, and a plan and schedule for 

reducing I/I levels in the collection system.

3 WV City of McMechan 09/30/02 The Order required the City to submit within 60 days plans and 

schedules for complying with: the water quality monitoring 

requirements of its NPDES permit, the collection system O&M 

provisions of its NPDES permit, the pollution prevention 

requirements of its NPDES permit, and the CSO monitoring and 

characterization requirements of its NPDES permit. The Order 

required implementation of each of these plans within 90 days of 

the issuance of the order. 

3 WV Kenova 06/10/03 No additional information provided.

5 IL City of Lawrenceville 09/30/02 The Order required City to construct and operate an oil collection 

device at the storm sewer outfall to ensure the discharge of oil and 

pollutants is minimized. Upon completion and after proper operation 

of the new replacement sewer, the City had the option of removing 

the oil collection device. The City was also required to submit a 

New Sewer Work Plan to EPA by 10/30/02, and shall complete 

construction by 10/30/03.

5 IL City of Rock Island 02/13/98 This Order addressed CSOs to environmentally sensitive areas and 

failure to implement the NMCs. The Order also required plant and 

sewer improvements to reduce CSOs.

5 IN Bluffton POTW 06/06/00 The Order addressed failure to submit CSO plan. An Administrative 

penalty order required a SEP and assessed a $60,000 penalty.

5 IN Bluffton Utilities 03/19/98 The Order addressed permit violations.

5 IN Fort Wayne 1995 and 1996 The Order required them to identify all CSO outfalls and to submit a 

sanitary sewer overflow (SSO) elimination plan and implement the 

SSO elimination plan.

5 OH Columbus WWTP 07/17/98 The Order addressed permit violations.

5 OH Port Clinton 1995 The Order addressed CSOs in violation of permit. This Order 

eventually resulted in a judicial referral.
K-18

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-19

K.4 Federal SSO Administrative Orders

Region State Case Name/City Name Effective Date Description

1 MA Town of Winchendon 10/16/00 This Order required the permitee to implement a block testing 

program to determine the frequency of Sanitary Sewer Overflow 

(SSO) occurrence and report these results to EPA and 

Massachusetts Department of Environmental Protection (MADEP). 

The order also required that an update to the 1998 Preliminary 

Design Report be submitted to include recommendations on 

measures necessary to ensure compliance with the NPDES permit.

2 Puerto 

Rico

PRASA Bayamon WWTP 11/20/02 The order required that Puerto Rico Aqueduct and Sewer Authority 

(PRASA) take immediate steps to unclog and clean all sewer 

pipelines and manholes causing sewage bypasses.

2 Puerto 

Rico

PRASA Bayamon WWTP 12/23/02 The order required that PRASA take immediate steps to unclog and 

clean all sewer pipelines and manholes causing sewage bypasses

2 Puerto 

Rico

PRASA Puente Blanco 

Pump Station & 

Collection System

12/23/02 A $104,000 penalty was assessed for failure to provide proper 

operation and maintenance leading to the discharge of partially or 

untreated pollutants to waters of the U.S.

2 Puerto 

Rico

PRASA Puente Blanco 

Pump Station & 

Collection System

01/16/01 The Order addressed NPDES permit violations.

3 PA Prospect Borough 04/27/01 This Order required them to install and operate the flow 

equalization tank to eliminate overflows of their sewage. The Order 

further required the City submit a detailed Compliance Plan, 

conduct an SSES and establish actions to address deficiencies 

detected in the SSES, and establish a comprehensive 

management, operation and maintenance (CMOM) program.

4 KY City of LaGrange 05/09/01 The Order required them to establish numerous programs and 

evaluate and revise existing programs to achieve continuous 

compliance with its Permit.

4 KY City of Radcliff Sewerage 

System

05/09/01 The Order required them to establish engineering, continuing sewer 

assessment, infrastructure rehabilitation, system capacity 

assurance, and pump station operation programs and to evaluate 

and revise existing programs to remediate the causes of the 

discharges of untreated pollutants to waters of the U.S.
K-20

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 MS City of Moss Point Sewer 

System

09/28/01 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 MS City of Ocean Springs 06/05/01 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 MS City of Pascagoula Sewer 

System

12/04/01 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 MS City of Pass Christian 

Sewerage System

09/09/02 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 MS Gautier Utility District 

Sewer System

03/26/01 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 SC City of Simpsonville 02/04/03 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 SC City of Travelers Rest 11/15/02 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 SC Diamondhead Water & 

Sewer District Sewer 

System

10/18/02 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 SC Fountain Inn 06/27/02 The Order required the City to review, evaluate, and revise its 

current Management Program. Additionally, a Training Program, a 

Safety Program, and the Engineering Program were to be revised 

and/or developed within 18 months. 

4 SC Gantt 04/29/03 No additional information provided.

4 SC Georgetown 04/01/03 No additional information provided.

4 SC Greer 03/20/03 No additional information provided.

4 SC Laurens County Water 

and Sewer Commission

08/12/02 The Order required them to establish numerous programs with 

respect to collection system assessment, operations and 

maintenance, and evaluate and revise existing programs to achieve 

continuous compliance with the Permit.

4 SC Marietta Water, Fire, 

Sanitation and Sewer 

District

09/06/02 The Order required the City to review, evaluate, and revise its 

current Management Program. Additionally, a Training Program, a 

Safety Program, and the Engineering Program were to be revised 

and/or developed within 18 months. 

4 SC Piedmont 05/27/03 No additional information provided.

4 SC Taylors 03/04/03 No additional information provided.

4 SC Wade Hampton Fire and 

Sewer District

12/16/02 The Order required them to develop a financing and cost analysis 

program and a contingency plan for sewer. 

4 TN Rockwood Water and 

Gas

02/19/02 The order required review, evaluate, revise and/or develop 

collection system management programs, including Engineering 

Programs.The City was required to maintain a Pump Station 

Maintenance and Grease Control Program.
 Appendix K

K-21

Region State Case Name/City Name Effective Date Description

4 TN West Knox Utility District 10/29/01 The order required the establishment of numerous collection 

system management programs, including the Information 

Management Systems/Programs and Engineering Programs, to be 

implemented within 12 months.

5 IL City of Rock Island, Rock 

Island

02/13/98 The Order required that a plan of action for achieving compliance 

must be submitted to EPA for approval within 11 months

5 IN Fort Wayne 01/17/96 The order required the City to prepare and submit an SSO 

elimination plan to be implemented upon approval or within 45 days 

of submittal, whichever came first.

5 IN Fort Wayne 1995 No additional information provided.

5 IN Lawrence STP 09/30/02 The Order addressed permit violations.

5 IN Town of West College 

Corner

03/22/02 The Order required that the City submit certain information to EPA 

stating: the current status of compliance for each item on the IDEM 

approved action plan and the costs associated with each activity, 

and the needed plant improvements to come into consistent 

compliance with the NPDES permit, including proposed time to 

construct and the costs of construction. 

5 IN Town of West College 

Corner

12/08/97 The Order required that the Town will submit a Compliance Plan 

(CP) to the Indiana Department of Environmental Management 

(IDEM) for approval within 30 days.

5 OH City of Fostoria 09/27/01 The Order required the City to submit a detailed Plan of Action 

containing a fixed date schedule describing actions taken, or, to be 

taken, to eliminate Outfall 009E which are not in accordance with 

the NPDES permit.

5 OH City of Willoughby Hills 09/26/01 The order required the City to eliminate the discharge of raw or 

partially treated sewage within 20 days. The City plans to install 

sanitary sewers in the Oak Street area to alleviate the failing septic 

system.

5 OH Lake County 09/26/01 The Order required the County to eliminate the discharges of raw or 

partially treated source within 20 days.

5 OH Licking County Buckeye 

Lake Sewer District No. 1 

WWTP

02/05/97 The order required the preparation of a detailed plan of action to 

eliminate SSOs.

5 OH Village of College Corner 03/22/02 The Order required that the City submit certain information to EPA.

5 WI City of South Milwaukee 03/19/01 The Order required that by 11/30/01, the City will eliminate the 

sanitary flow restrictive junction at 15th Avenue and Manitowac 

Avenue, install manhole liners in 1,000 manholes and upgrade the 

Lake Drive Lift Station. 

6 AK City of Hot Springs 06/02/00 Within one month of this Order, the City will submit a 

comprehensive plan for the expeditious elimination and prevention 

of unauthorized discharges and overflows of wastewater from its 

collection system. The plan will provide specific actions to be taken 

and include a schedule for achieving compliance.
K-22

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 LA City of Opelousas 06/06/02 The Order required that the City provide a comprehensive 

construction progress summary to EPA for Phase I and Phase II 

rehabilitation activities within one month 

6 LA City of Opelousas 04/30/99 This Order required that all projects for the Phase I, Collection 

System Rehabilitation will be complete by 08/31/99. The Order also 

required that all projects for the Phase II, Collection System 

Rehabilitation will be complete by 09/31/01 and that all projects for 

the Phase III, Collection System Rehabilitation will be complete by 

07/31/02.

6 LA City of Rayne 2002 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 LA City of Shreveport 07/29/97 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 LA City/Parish of East Baton 

Rouge

09/09/94 This Order was issued requiring the City to report past SSOs from 

its collection system and to continue reporting those SSOs in 

tabular form along with its monthly Discharge Monitoring Report 

(DMRs).

6 LA City/Parish of East Baton 

Rouge

01/30/98 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 NM City of Carlsbad 08/29/00 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 TX City of Austin 06/10/99 A penalty of $27,500 was assessed based on, among other things, 

the number of violations the City committed.

6 TX City of Austin 10/25/99 The civil penalty of $21,000 listed in this Order settles all violations.

6 TX City of Austin 04/29/99 The Order required that the City perform numerous pump station 

upgrades, carry out infiltration and inflow (I/I) and SSES studies, 

and implement remedial actions. The Order required that 

compliance be achieved by 12/31/07.
 Appendix K

K-23

Region State Case Name/City Name Effective Date Description

6 TX City of Austin 09/11/98 The Order required that the City take whatever corrective action 

was possible to eliminate and prevent recurrence of the SSOs 

within one month. If one month was not possible, then the City was 

to submit an action plan detailing how the City intended to eliminate 

overflows in the collection system in the shortest amount of time 

possible. This plan will include a schedule for eliminating overflows 

in the collection system.

6 TX City of Dallas 10/25/00 Within one month of this Order, the City will take whatever 

corrective action is possible to eliminate and prevent recurrence of 

the violations. If one month is not possible, then the City will submit 

an action plan detailing how the City intends to eliminate overflows 

in the collection system in the shortest amount of time possible. 

This plan will include a schedule for eliminating overflows in the 

collection system. A $27,500 penalty was assessed.

6 TX City of Dallas 08/08/00 This Order was issued requiring the City to take corrective action to 

prevent a discharge to occur again and set up a meeting with EPA.

6 TX City of Denton 07/26/02 The City will complete construction of Pecan Creek WWTP 

improvements by 01/04. The City will complete construction of 

Cooper Creek Lift Station Improvements and the Pecan Creek 

Interceptor Phase I by 06/04. The City will complete construction of 

Pecan Creek Interceptor Phase II by 10/05.

6 TX City of Denton 09/19/02 A $137,500 penalty was assessed.

6 TX City of Denton 06/30/99 EPA provided the City with a list of scheduled activities. The City 

will follow the schedule so that the violations due to 

overflows/unauthorized discharges from the collection system of the 

POTW will be corrected. 

6 TX City of Denton 01/14/99 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 TX City of Galveston 05/18/01 This Order modified the schedule for construction improvements. 

Complete the Lift Station Improvements and the Trunk Sewer 

Improvements (trunk sewers without adequate capacity) by 

12/31/01. Complete the Trunk Sewer Improvements (to prevent 

overflows under surcharge conditions) by 12/31/02. All overflows 

and bypasses of the collection system will be eliminated by 

01/31/03.

6 TX City of Galveston 12/18/00 A $14,850 penalty was assessed.

6 TX City of Galveston 07/26/99 The Order modified the schedule for construction improvements. It 

required the completion of the Lift Station Number One Upgrade by 

03/31/00. It required the completion of the Trunk Sewer 

Improvements (trunk sewers without adequate capacity and Lift 

Station Improvements) by 12/31/01. All overflows and bypasses of 

the collection system must be eliminated by 01/01/02.
K-24

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 TX City of Galveston 12/09/96 This Order required that the City complete the Port Industrial Main 

improvements, the 10th Street Trunk replacement/Jones Drive 

replacement, manhole rehabilitation and structural repairs, and 

trunk sewer improvements. All improvements were to be complete 

by 06/30/01.

6 TX City of Galveston 10/07/96 This Order incorporated a compliance schedule, submitted by the 

City, for the elimination of wet weather and dry weather overflows 

throughout the collection system. 

6 TX City of Humble 1998 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 TX City of Jacksonville 02/22/99 The Order required that the City complete the rehabilitation of the 

western portion of the collection system by 06/01/99, complete the 

Sewer System Improvements, Line B4 by 11/01/00, complete the 

Sewer System Improvements, Line B2 by 04/01/02, and complete 

more specified improvements on an annual basis.

6 TX City of Jacksonville 10/22/97 The Order required that by 08/31/98, the City submit to EPA a 

construction schedule for all improvements necessary to eliminate 

overflows from their collection system.

6 TX City of Nederland 05/30/97 The Order required that the City will complete a SSES and submit a 

schedule for the rehabilitation of all system defects not completed 

during the SSES by 07/98.

6 TX City of Nederland 09/16/96 This Order was issued for overflows from the sewer system.

6 TX City of Nederland 01/31/95 This Order was issued requiring, among other things, that the City 

submit a plan and schedule for mitigating of the effects of the I/I on 

the system and the immediate elimination of the bypass located on 

Avenue C.

6 TX City of South Houston 09/17/98 Within one month of this Order, the City will take whatever 

corrective action is possible to eliminate and prevent recurrence of 

the violations. If one month is not possible, then the City will submit 

an action plan detailing how the City intends to eliminate overflows 

in the collection system in the shortest amount of time possible. 

This plan will include a schedule for eliminating overflows in the 

collection system.

6 TX City of South Houston 06/25/96 The Order required that the City take whatever corrective action is 

possible to eliminate and prevent recurrence of the violations within 

one month. If one month is not possible, then the City will submit an 

action plan detailing how the City intends to eliminate overflows in 

the collection system in the shortest amount of time possible. This 

plan will include a schedule for eliminating overflows in the 

collection system.

6 TX City of South Houston 01/23/96 This Order was issued requiring compliance with a schedule for 

Activity Numbers One thru Four in the Industrial User Survey 

submittals.

6 TX San Antonio Water 

System

07/11/96 The Order required that the System perform an I/I study of their 

collection system to include flow monitoring. A submission of 

schedules for rehabilitation was required when the studies were 

complete.
 Appendix K

K-25

Region State Case Name/City Name Effective Date Description

6 TX San Antonio Water 

System

04/14/94 The Order contained a schedule for the installation of permanent 

flow meters and a study of the collection system. The schedule was 

modified 04/11/96.

7 MO City of Campbell 04/04/01 Action taken to eliminate SSOs. 

7 MO City of Platte City 05/22/02 A $60,000 penalty was assessed.

7 MO City of Platte City 12/10/02 The City will immediately pay a $15,000 penalty. Upon satisfactory 

completion of multiple SEPs projects, the remaining $45,000 of the 

total ($60,000) will be suspended. The SEPs were intended to 

serve as significant environmental or public health protection and 

improvement.

10 AK City and Borough of 

Juneau, Alaska, 

Mendenhall Wastewater 

Treatment Facility

09/11/00 The Order required that a written plan for the elimination of 

unauthorized discharges be submitted to EPA within one month. 

The plan must include provisions for a thorough study of the 

collection system, a plan for addressing the problems identified and 

a schedule of completion for activities

10 WA Lummi Indian Business 

Council of the Lummi 

Nation, WA

07/29/02 The Order required that the Council perform various wastewater 

treatment plant upgrades and to investigate and seek available 

funding mechanisms for the Lummi Shore collection system 

upgrade by 12/31/02.
K-26

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-27

K.5 Federal CSO Administrative Penalty Orders

Region State Case Name/City Name Effective Date Penalty Amount

1 MA City of Fitchburg 02/02/96; 

Amended

07/02/96

$208,800

1 MA Town of Palmer 01/06/97 $5,000 
K-28

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-29

K.6 Federal SSO Administrative Penalty Orders

Region State Case Name/City Name Effective Date Penalty Amount

2 Puerto 

Rico

PRASA Puente Blanco Pump Station & 

Collection System 

12/23/02 $27,500

3 PA Monaca Borough 05/20/99 $18,000

5 IN Town of West College Corner 12/08/97 $24,062 

6 TX City of Austin 10/25/99 $21,000 

6 TX City of Austin 06/10/99 $27,500 

6 TX City of Dallas 10/25/00 $27,500 

6 TX City of Denton 09/19/02 $137,500 

6 TX City of Galveston 12/18/00 $14,850 

7 MO City of Campbell 04/04/01 $87,500 

7 MO City of Platte City 05/22/02 $60,000 

10 AK City and Borough of Juneau, Mendenhall 

Wastewater Treatment Facility

09/11/00 $60,000 

10 AK City and Borough of Juneau, Mendenhall 

Wastewater Treatment Facility

08/15/01 $30,000 
K-30

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-31

Region State Case Name/City Name Effective Date Description

1 ME City of Bangor and State 

of Maine

Entered

06/30/87;

Amended

12/01/87

This Order addressed NPDES permit violations. The City was 

required to pay a $40,000 civil penalty which provide other relief for 

certain violations of the NPDES permit requirements.

1 ME City of Bangor and State 

of Maine

04/09/91 The City completed a short-term sewer rehabilitation project for a 

previous State Consent Order and has begun long-term sewer 

rehabilitation and Combined Sewer Overflow (CSO) abatement 

projects.

2 NJ Borough of East Newark 02/11/99 The Order required that within 12 months of East Newark's receipt 

of the Department's Stage II/III TWA, the Borough will complete the 

required construction and commence operation of the approved 

treatment works. 

2 NJ Borough of Fort Lee 08/16/95 The Order addressed failure to meet the discharge of 

solids/floatable requirements established in the 1995 Administrative 

Consent Order.

2 NJ City of Bayonne 08/24/00 This was a settlement between both parties stating that both parties 

had voluntarily agreed to a settlement and that the agreement fully 

disposed of all issues in controversy and was consistent with the 

law.

2 NJ City of Bayonne 08/01/00 The Order required that construction of the Group One CSO Points 

006 and 015 will be complete by 07/22/99. Within 15 months from 

the Department's issuance of the Stage II/III Treatment of Works 

Approval (TWA) for the Group I CSO points, construction will be 

complete and the Solids/Floatables control measures will be 

implemented. Within 15 months of Bayonne's receipt of the 

Department's Stage II/III TWA, the Group Two CSO Points required 

construction will be complete.

2 NJ City of Kearny 02/11/99 The Order required that within 12 months of the City's receipt of the 

Department's Stage II/III TWA, the City will complete the required 

construction and commence operation of the approved treatment 

works. By 01/31/00, the City will complete construction for the 

Storm Sewer System 1A (Sewer Separation Project).

2 NJ City of Paterson 05/22/02 The Order required the City to complete construction of Romag 

CSO Points 30 and 31 by 06/01/05. The City will complete 

construction of Romag CSO Point 16 by 06/01/04. The City will 

complete construction of Romag CSO Points 25, 27, and 29 by 

12/01/07. The City will complete construction of the sewer 

separation by 12/31/04.

2 NJ Village of Ridgefield Park 08/20/99 The Order required, among other things, construction of the 

approved Long-term Solids/ Floatables Control Measures will be 

complete within nine months of receipt of Department's Stage II/III 

approval. Construction will be complete for the Solids/Floatables 

Control Facilities at outfall 001 and outfall 002 by 01/17/00, at 

outfall 003 by 11/30/99, at outfall 005 by 12/01/99, and at outfall 

006 by 11/09/99.

2 NJ Village of Ridgefield Park 07/22/98 The Order addressed permit violations.

K.7 State CSO Judicial Orders
K-32

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

2 NY Onondaga County 

Department of Drainage 

and Sanitation and, 

Onondaga County

01/20/98 The County was required to design, test, and construct 

modifications and additions to the Metro facility, including diversion 

of the Metro's effluent to the Seneca River. By 11/01/03, the County 

will complete construction of the Full Scale Ammonia Removal 

Project. By 04/01/05, the County will complete construction of the 

Phosphorus Removal/ Effluent Filtration Project. By 06/01/02, the 

County will complete construction and commence full operations of 

all projects to achieve Stage III effluent limits, or achieve revised 

effluent limits.

2 NY Onondaga County 

Department of Drainage 

and Sanitation and, 

Onondaga County

02/01/89 The County was obligated to develop a Municipal Compliance Plan 

that would bring the County's effluent discharges from the Metro 

facility and the CSOs into compliance with the State's effluent 

limitations and water quality standards, and then implement such a 

plan.

3 MD Frostburg (The Mayor 

and Town Council of )

12/14/01 Immediately following the Department's approval of its LTCP, 

Frostburg will begin implementation of the LTCP and then complete 

implementation of the LTCP in accordance with the approved 

schedule.

3 MD The City of Cambridge 

(The Mayor and 

Commissioners of)

02/05/99 This Order stated that within 11 months of the notice to proceed 

construction, the City will complete construction of the interceptor 

work along Water Street and complete separation of the combined 

sewer and storm water lines along Mill Street and Vue de L'eau 

Street. Within seven months of the respective notice to proceed 

with construction of the Phases II, III, IV, V, and VI improvements, 

complete construction of Phases II, III, IV, V, and VI improvements.

3 MD The City of Cambridge 

(The Mayor and 

Commissioners of)

11/23/93 The Order required the City to improve the Cambridge Wastewater 

Treatment Plant and the sewer system. The City will also submit a 

study, plan and schedule for improvements to the sewer system 

design to alleviate wastewater discharges into any and all streets.

3 MD Westernport (The Mayor 

and Town Council of)

08/23/02 Within one month after this Consent Decree, Westernport will 

implement all elements of the Nine Minimum Controls (NMCs). 

Within one month following the Department's approval of its LongTerm Control Plan (LTCP) and schedule, Westernport will 

implement its LTCP.
 Appendix K

K-33

K.8 State SSO Judicial Orders

Region State Case Name/City Name Effective Date Description

2 NJ Rahway Valley Sewerage 

Authority (RVSA)

07/09/01 Within 31 months of this Order, RVSA will complete construction of the 

Final Effluent Polishing Facilities, Disinfection Facilities, Pumping 

Facilities, Sampling Chambers, and Auxiliary Power. Within 31 months 

of completion of Phase I, Phase II construction will be complete. 

3 VA District of Columbia, 

Fairfax

01/25/02 In this Order, the District agreed to pay the Commonwealth $325,000 

in settlement of violations and close the Lorton facility.

3 WV Crab Orchard/ MacArthur 

Public Service District

02/04/00 This Consent Decree was issued for failure to comply with State water 

quality standards and effluent limitations for discharging pollutants into 

the Piney Creek and other waters of the State, for violating their 

NPDES Permit, and for failure to comply with several orders.

3 WV St. Albans Municipal Utility 

Commission, City of St. 

Albans

10/13/98 This Consent Decree was issued for failure to comply with state water 

quality standards and effluent limitations for discharging pollutants into 

the Kanawha River and other waters of the State, for violating their 

NPDES Permit, and for failure to comply with several orders.

4 AL The City of Brent, Brent 

Water and Sewer Board, 

City of Centreville, and the 

Centreville Waterworks 

and Sewer Board

01/30/02 Within 12 months of this Order, they will repair Pump Stations 

Numbers One, Two, Three, Four, and Five in the Centreville and Brent 

collection system.

4 AL The Water Works and 

Sewer Board of the City of 

Prichard

01/30/97 Within 420 days of this Order, the construction of the Gumtree Branch 

replacement sewer line or any other cost-effective remedy approved 

by Alabama Department of Environmental Management will be 

complete. Within 1,230 days of this Order, the construction of the new 

side stream storage facility will be complete.
K-34

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-35

K.9 State CSO Administrative Orders

Region State Case Name/City Name Effective Date Description

1 ME City of Bath 01/09/92 Before 06/01/93, the City will submit to the Department for review 

and approval a master plan for abatement of Combined Sewer 

Overflows (CSOs) from its sewerage system, including a schedule. 

The City will also develop a long-term Pump Stations Facility Plan, 

including a schedule. By 07/01/92, develop a Comprehensive 

Treatment Plant Facilities Plan to address the current and future 

needs of the City to achieve state of the art wastewater treatment 

consistent with its discharge license limitations.

1 ME City of Biddeford 07/22/91 The Order required, among other things, that by 01/01/93, they will 

complete sewer system improvement projects in order to eliminate 

or abate CSO discharges. Beginning in 01/92, the City will complete 

all other CSO abatement projects described in the approved interim 

and final Sewer System Master Plan.

1 ME City of Brewer and 

Eastern Fine Paper 

Company

02/27/92 The Order required a CSO Master Plan will be submitted to the 

Department before 06/01/93. This master plan will include a 

schedule for implementation and construction of all projects.

1 ME City of Westbrook, 

Portland Water District, 

Westbrook

10/21/91 The Order required that by 12/91, Westbrook and Portland Water 

District will complete all projects listed and described in the Final 

Sewer System Master Plan.

1 ME The City of Portland and 

Portland Water District

02/13/91 The Order required that by 12/93, Portland and Portland Water 

District will complete sewer system improvement projects in order to

eliminate or abate CSO discharges.

1 ME Town of Bucksport 03/01/90 The Order required that by 02/01/90, the Town will submit to the 

Department for review and approval, plans and a schedule for the 

installation of chlorination/dechlorination facilities. By 02/15/90, the 

Town will submit to the Department for review and approval a plan 

monitoring CSOs from its sewage system.

1 ME Town of Lisbon 05/24/90 The Order required that by 05/01/90, the Town will submit to the 

Department for review and approval, a process control plan to 

specifically deal with filamentous bulking. The Town will also submit 

to the Department for review and approval, a pump station and 

sewer maintenance program, including a time schedule for 

implementation of this pump station and sewer maintenance plan.

1 ME Town of Lisbon 04/13/88 The Order addressed upgrading the Town's secondary wastewater 

treatment facilities.
K-36

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

2 NJ Borough of Fort Lee 06/01/95 The Order required that within 15 months of the Borough's receipt 

of the New Jersey Department of Environmental Protection's 

(NJDEP's) Stage II/III approval, the Borough will complete 

construction and commence operation of the approved Long-term 

Solids/Floatables Control Measures.

2 NJ Camden County 

Municipal Utilities 

Authority

02/27/98 The Order addressed, among other things, permit violations.

2 NJ Camden County 

Municipal Utilities 

Authority

03/31/97 The Order addressed, among other things, permit violations.

2 NJ City of Camden 08/23/99 The City was required to fully implement the O&M Program and 

develop and implement the CSO Pollution Prevention Plan by 

09/30/99.

2 NJ City of Camden 03/31/97 The Order addressed, among other things, permit violations.

2 NJ City of Gloucester 07/22/99 The Order addressed, among other things, permit violations. The 

City was supposed to plan, design, improve, operate and maintain 

its combined sewer system (CSS) as required and set forth by its 

permit.

2 NJ City of Gloucester 03/31/97;

Amended

06/30/98

The Order addressed, among other things, permit violations.

2 NJ City of New Brunswick 04/25/94 The Order required that within six months from the start of 

construction for the backflow prevention device, the construction 

will be complete. Additionally, the City was required to submit a time 

table for attaining the completion of the sewer separation project by 

12/01/94.

2 NJ City of Newark 05/21/01 Under this Order, the City was required to complete construction 

and commence operation of the Long-Term Solids/ Floatable 

Control Plan for all its CSO points within 15 months of the City's 

receipt of the Department's Treatment of Works Approval (TWA).

2 NJ City of Newark 12/07/98 The Order addressed the City's noncompliance with its permit.

2 NJ City of Paterson 02/01/99 The Order addressed permit violations.

2 NJ City of Perth Amboy 07/26/95 The City was required to complete construction and eliminate the 

illegal discharges from the homes located on High and Hartford 

Streets at the corner of Buckingham Avenue, complete construction 

for the Budapest sewer separation project, eliminate the raw 

sanitary waste water discharge from DSN 001, and permanently 

close the seal at DSN 001. The City was also required to complete 

the upgrades/ repairs to the State Street, Front Street, and Amboy 

Avenue pump stations within 12 months of beginning construction 

and complete the repair of the CSO pipes at DSN 002 and DSN 

017 within six months.

Region State Case Name/City Name Effective Date Description

2 NJ Borough of Fort Lee 06/01/95 The Order required that within 15 months of the Borough's receipt 

of the New Jersey Department of Environmental Protection's 

(NJDEP's) Stage II/III approval, the Borough will complete 

construction and commence operation of the approved Long-term 

Solids/Floatables Control Measures.

2 NJ Camden County 

Municipal Utilities 

Authority

02/27/98 The Order addressed, among other things, permit violations.

2 NJ Camden County 

Municipal Utilities 

Authority

03/31/97 The Order addressed, among other things, permit violations.

2 NJ City of Camden 08/23/99 The City was required to fully implement the O&M Program and 

develop and implement the CSO Pollution Prevention Plan by 

09/30/99.

2 NJ City of Camden 03/31/97 The Order addressed, among other things, permit violations.

2 NJ City of Gloucester 07/22/99 The Order addressed, among other things, permit violations. The 

City was supposed to plan, design, improve, operate and maintain 

its combined sewer system (CSS) as required and set forth by its 

permit.

2 NJ City of Gloucester 03/31/97; 

Amended

06/30/98

The Order addressed, among other things, permit violations.

2 NJ City of New Brunswick 04/25/94 The Order required that within six months from the start of 

construction for the backflow prevention device, the construction 

will be complete. Additionally, the City was required to submit a time

table for attaining the completion of the sewer separation project by 

12/01/94.

2 NJ City of Newark 05/21/01 Under this Order, the City was required to complete construction 

and commence operation of the Long-Term Solids/ Floatable 

Control Plan for all its CSO points within 15 months of the City's 

receipt of the Department's Treatment of Works Approval (TWA).

2 NJ City of Newark 12/07/98 The Order addressed the City's noncompliance with its permit. 

2 NJ City of Paterson 02/01/99 The Order addressed permit violations.

2 NJ City of Perth Amboy 07/26/95 The City was required to complete construction and eliminate the 

illegal discharges from the homes located on High and Hartford 

Streets at the corner of Buckingham Avenue, complete construction 

for the Budapest sewer separation project, eliminate the raw 

sanitary waste water discharge from DSN 001, and permanently 

close the seal at DSN 001. The City was also required to complete 

the upgrades/ repairs to the State Street, Front Street, and Amboy 

Avenue pump stations within 12 months of beginning construction 

and complete the repair of the CSO pipes at DSN 002 and DSN 

017 within six months.
 Appendix K

K-37

Region State Case Name/City Name Effective Date Description

2 NJ City of Perth Amboy 09/30/93 The City was required to complete construction and implementation 

of a project that is used to control the discharge of solids/ floatables 

and properly dispose of solids/ floatables by 03/01/97.

2 NJ City of Rahway 05/08/00 This Order required the City to complete construction necessary to 

remove the identified sources of inflow contributing to outfalls 001, 

004 and 005 by 11/01/03. Additionally, the City was required to 

complete construction necessary for the separation of the combined 

sewer tributary to outfalls 003 and 004 by 03/01/03. The City was 

required to complete construction necessary to remove the 

identified sources of inflow contributing to outfalls 002 and 003 by 

05/01/04. The City was also required to complete construction 

necessary for the separation of the combined sewer tributary to 

outfall 002 by 03/01/04.

2 NJ Edgewater Municipal 

Utilities Authority

09/30/93 The Order required the City to complete construction and 

implement measures to control the discharge of solids/ floatables 

and properly dispose of these solids/floatables by 03/01/97.

2 NJ Hoboken/Union

City/Weehawken

Sewarage Authority 

(HUCWSA)

09/30/93 Under this Order, HUCWSA will complete construction and 

implementation of a project that is used to control the discharge of 

solids/ floatables and properly dispose of solids/ floatables by 

07/01/97.

2 NJ Middlesex County Utilities 

Authority

04/13/95 This Order addressed violations of the Water Pollution Control Act 

(WPCA), implementing regulations, and its permit.

2 NJ Middlesex County Utilities 

Authority (MCUA)

06/05/96 The Order required MCUA to complete the upgrade of the worse 20 

metering chambers to accurately measure all flows, including peak 

flows during storm events by 10/01/97. MCUA was also required to 

complete the upgrade of all of the remaining metering chambers to 

accurately measure all flows, including peak flows during storm 

events by 04/01/98, .

2 NJ Rahway Valley Sewerage 

Authority (RVSA)

09/30/93 RVSA was required to complete construction and implementation of 

a project that is used to control the discharge of solids/ floatables 

and properly dispose of solids/ floatables by 03/01/97.

2 NJ Town of Guttenberg 09/30/93 This Order addressed the failure to comply with its permit, the 

WPCA, and the SIIA.

2 NJ Town of North Bergen 

Municipal Utilities 

Authority (NBMUA), 

Town of Guttenberg/ 

Woodcliff Sewage 

Treatment Plant

12/13/95 This Order required NBMUA to complete construction and 

commence operation of the control measures in the Interim Solids/ 

Floatables Control plan within 12 months of the NBMUA's receipt of 

NJDEP's Stage II/III approval. Also, NBMUA will complete 

construction and commence operation of the Long-Term Solids/ 

Floatables Control measures within 15 months of receipt of 

NJDEP's Stage II/III approval.

2 NJ Town of North Bergen 

Municipal Utilities 

Authority (NBMUA), 

Town of Guttenberg/ 

Woodcliff Sewage 

Treatment Plant

09/30/93 This Order addressed the failure to comply with its permit, the 

WPCA, and the Sewage Infrastructure Improvement Act (SIIA).

Region State Case Name/City Name Effective Date Description

2 NJ City of Perth Amboy 09/30/93 The City was required to complete construction and implementation 

of a project that is used to control the discharge of solids/ floatables 

and properly dispose of solids/ floatables by 03/01/97.

2 NJ City of Rahway 05/08/00 This Order required the City to complete construction necessary to 

remove the identified sources of inflow contributing to outfalls 001, 

004 and 005 by 11/01/03. Additionally, the City was required to 

complete construction necessary for the separation of the combined 

sewer tributary to outfalls 003 and 004 by 03/01/03. The City was 

required to complete construction necessary to remove the 

identified sources of inflow contributing to outfalls 002 and 003 by 

05/01/04. The City was also required to complete construction 

necessary for the separation of the combined sewer tributary to 

outfall 002 by 03/01/04.

2 NJ Edgewater Municipal 

Utilities Authority

09/30/93 The Order required the City to complete construction and 

implement measures to control the discharge of solids/ floatables 

and properly dispose of these solids/floatables by 03/01/97.

2 NJ Hoboken/Union 

City/Weehawken

Sewarage Authority 

(HUCWSA)

09/30/93 Under this Order, HUCWSA will complete construction and 

implementation of a project that is used to control the discharge of 

solids/ floatables and properly dispose of solids/ floatables by 

07/01/97.

2 NJ Middlesex County Utilities

Authority

04/13/95 This Order addressed violations of the Water Pollution Control Act 

(WPCA), implementing regulations, and its permit.

2 NJ Middlesex County Utilities

Authority (MCUA)

06/05/96 The Order required MCUA to complete the upgrade of the worse 20 

metering chambers to accurately measure all flows, including peak 

flows during storm events by 10/01/97. MCUA was also required to 

complete the upgrade of all of the remaining metering chambers to 

accurately measure all flows, including peak flows during storm 

events by 04/01/98, .

2 NJ Rahway Valley Sewerage 

Authority (RVSA)

09/30/93 RVSA was required to complete construction and implementation of 

a project that is used to control the discharge of solids/ floatables 

and properly dispose of solids/ floatables by 03/01/97.

2 NJ Town of Guttenberg 09/30/93 This Order addressed the failure to comply with its permit, the 

WPCA, and the SIIA.

2 NJ Town of North Bergen 

Municipal Utilities 

Authority (NBMUA), 

Town of Guttenberg/ 

Woodcliff Sewage 

Treatment Plant

12/13/95 This Order required NBMUA to complete construction and 

commence operation of the control measures in the Interim Solids/ 

Floatables Control plan within 12 months of the NBMUA's receipt of 

NJDEP's Stage II/III approval. Also, NBMUA will complete 

construction and commence operation of the Long-Term Solids/ 

Floatables Control measures within 15 months of receipt of 

NJDEP's Stage II/III approval.

2 NJ Town of North Bergen 

Municipal Utilities 

Authority (NBMUA), 

Town of Guttenberg/ 

Woodcliff Sewage 

Treatment Plant

09/30/93 This Order addressed the failure to comply with its permit, the 

WPCA, and the Sewage Infrastructure Improvement Act (SIIA).
K-38

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

2 NJ West New York Municipal 

Utilities Authority 

(WNYMUA)

09/30/93 Under this Order, WNYMUA will develop and implement technologybased control measures to address the minimum technology-based 

limitations by 10/01/95. Additionally, WNYMUA will complete 

construction/ implementation of the Long-Term Solids/ Floatables 

Control Measure Strategy by 03/01/97.

2 NY New York City, 

Department of 

Environmental Protection 

(NYDEP)

06/26/92 The Order required the NYDEP to establish an environmental 

benefit program, costing $250,000; continue its CSO abatement 

program, including the Track One CSO Abatement (DO and 

Coliform) and the Track Two CSO Abatement (Floatables); and 

supplement the data collection gathered as part of the NY/NJ 

Harbor Estuary Program and gather additional information 

concerning the contribution of heavy metals to the Harbor from 

CSOs.

2 NY New York City, 

Department of 

Environmental Protection 

(NYDEP)

Modification

03/96

In addition to the CSO Abatement Program required by the 1992 

Order, this modification required the NYDEP to add another 

program which consisted of the inspection, inventory, mapping, 

replacement of missing hoods, and cleaning to facilitate inspection 

and hood replacement of those catch basins located in Phases I & 

II areas identified in this Order. They were required to retain a 

consulting firm to perform the inspections of each of the catch 

basins identified. Additionally, they were required to submit a scope 

of work to determine an appropriate and cost-effective catch basin 

cleaning program for floatables capture and flood control in specific 

locations throughout the City.

3 DE City of Wilmington 02/06/03 The Order required the City to modify the significant industrial users 

(SIUs) permits, determine whether any dry weather flow from a 

CSO is an overflow or infiltration, and notify the citizens of when 

and where CSOs occur.

3 MD Mayor and City Council 

of Frostburg

12/30/96 This Order was issued requiring them to implement a CSO Control 

Program or a plan to enable it to comply with the EPA CSO Control 

Policy, including NMCs by 07/01/97.

4 TN Metropolitan Government 

of Nashville and 

Davidson County

09/17/99 The City and County was required to have all CSO controls, 

including but not limited to, floatable material and debris removal, 

combined sewage storage and/or detention and CSO elimination, in 

place by 07/01/01. The City and County will eliminate all overflows 

or bypassing from its sanitary sewers to all waters of the state by 

07/01/01. Of the total $600,000 penalty, $100,000 will be due within 

one month of this Order. However, in lieu of the $100,000, a SEP 

may be performed by the City and the County.

5 IN City of Bluffton 06/24/03 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates.

5 IN City of Boonville 11/25/02 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates.

5 IN City of New Castle 01/27/03 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates.

5 IN City of Sullivan 01/22/03 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates. Also, the City was 

required to submit to IDEM a Compliance Plan, including a 

construction schedule by 03/01/03.

Region State Case Name/City Name Effective Date Description

2 NJ West New York Municipal 

Utilities Authority 

(WNYMUA)

09/30/93 Under this Order, WNYMUA will develop and implement technologybased control measures to address the minimum technology-based 

limitations by 10/01/95. Additionally, WNYMUA will complete 

construction/ implementation of the Long-Term Solids/ Floatables 

Control Measure Strategy by 03/01/97.

2 NY New York City, 

Department of 

Environmental Protection 

(NYDEP)

06/26/92 The Order required the NYDEP to establish an environmental 

benefit program, costing $250,000; continue its CSO abatement 

program, including the Track One CSO Abatement (DO and 

Coliform) and the Track Two CSO Abatement (Floatables); and 

supplement the data collection gathered as part of the NY/NJ 

Harbor Estuary Program and gather additional information 

concerning the contribution of heavy metals to the Harbor from 

CSOs.

2 NY New York City, 

Department of 

Environmental Protection 

(NYDEP)

Modification

03/96

In addition to the CSO Abatement Program required by the 1992 

Order, this modification required the NYDEP to add another 

program which consisted of the inspection, inventory, mapping, 

replacement of missing hoods, and cleaning to facilitate inspection 

and hood replacement of those catch basins located in Phases I & 

II areas identified in this Order. They were required to retain a 

consulting firm to perform the inspections of each of the catch 

basins identified. Additionally, they were required to submit a scope 

of work to determine an appropriate and cost-effective catch basin 

cleaning program for floatables capture and flood control in specific 

locations throughout the City.

3 DE City of Wilmington 02/06/03 The Order required the City to modify the significant industrial users 

(SIUs) permits, determine whether any dry weather flow from a 

CSO is an overflow or infiltration, and notify the citizens of when 

and where CSOs occur.

3 MD Mayor and City Council 

of Frostburg

12/30/96 This Order was issued requiring them to implement a CSO Control 

Program or a plan to enable it to comply with the EPA CSO Control 

Policy, including NMCs by 07/01/97.

4 TN Metropolitan Government 

of Nashville and 

Davidson County

09/17/99 The City and County was required to have all CSO controls, 

including but not limited to, floatable material and debris removal, 

combined sewage storage and/or detention and CSO elimination, in 

place by 07/01/01. The City and County will eliminate all overflows 

or bypassing from its sanitary sewers to all waters of the state by 

07/01/01. Of the total $600,000 penalty, $100,000 will be due within 

one month of this Order. However, in lieu of the $100,000, a SEP 

may be performed by the City and the County.

5 IN City of Bluffton 06/24/03 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates.

5 IN City of Boonville 11/25/02 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates.

5 IN City of New Castle 01/27/03 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates.

5 IN City of Sullivan 01/22/03 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates. Also, the City was 

required to submit to IDEM a Compliance Plan, including a 

construction schedule by 03/01/03.
 Appendix K

K-39

Region State Case Name/City Name Effective Date Description

5 IN Town of Centerville 11/25/02 This Order required the Town to submit to Indiana Department of 

Environmental Management (IDEM) the CSO Operational Plan and 

the Stream Reach Characterization Evaluation Report as soon as 

possible but no later than 06/01/03, and complete the LTCP.

5 IN Town of Remington 06/06/03 The Order required the Town to complete construction, cease 

overflows from Outfall 004, and provide IDEM a certification 

statement of completion of construction within nine months of this 

Order.

5 IN Town of Ridgeville 09/11/02 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates.

5 IN Town of Ridgeville 10/15/01 This Order required the Town to submit to the IDEM its complete 

Stream Reach Characterization and Evaluation Report by 09/30/01 

and submit its LTCP for approval by 03/15/02.

5 IN Town of Summitville 01/29/03 This Order required the City to immediately implement the approved 

LTCP and adhere to the milestone dates.

7 MO City of Macon, MO 05/29/01 This Order required that a schedule for the Nine Minimum Controls 

(NMCs) be submitted by 06/01/01. Upon review and approval of the 

LTCP and the schedule for implementation of the LTCP, the City 

will complete each phase of the LTCP in accordance with the 

approved schedule.

7 MO City of Sedalia, MO 06/15/92;

Amended

02/10/03

This Order required the City to complete construction of Phase I by 

12/01/04, complete construction of Phase II by 12/01/05, and 

complete construction of Phase III by 09/15/07.

10 OR City of Astoria 01/07/93 The City has completed the studies and planning activities required 

by the Order, and on 09/30/98, submitted a CSO Facilities Plan to 

the Department.

10 OR City of Astoria 08/05/02 This Order required the City to eliminate all untreated CSO 

discharges within 15 months of Department approval of the Plans 

and Specifications.

10 OR City of Corvallis 11/09/92 Under this Order the City was required to eliminate discharges that 

violate applicable water quality standards, subject to storm return 

frequencies at five CSO discharge points by 12/31/01.

10 OR City of Portland 08/11/94 Under this Order, the City was required to eliminate untreated CSO 

discharges at 20 of the CSO discharge points, including discharges 

to Columbia Slough by 12/01/01, eliminate untreated CSO 

discharges at 16 of the remaining discharge points by 12/01/06, 

and eliminate untreated CSO discharges at all remaining CSO 

discharge points by 12/01/11.

10 OR City of Portland 08/05/91 Under this Order, they were required to carry out necessary studies 

and corrective actions to eliminate the discharge of untreated 

overflows from the combined sewer system, up to one in ten year 

summer storm event and up to a one in five year winter storm 

event. The City was required to submit scope of study for the 

facilities plan and for an interim control measures study.

10 WA City Of Spokane 12/13/99 This Order addressed untreated sewage discharging from the City's 

CSO outlet #15. A penalty of $15,000 was eventually assessed for 

the violation.

Region State Case Name/City Name Effective Date Description

5 IN Town of Centerville 11/25/02 This Order required the Town to submit to Indiana Department of 

Environmental Management (IDEM) the CSO Operational Plan and 

the Stream Reach Characterization Evaluation Report as soon as 

possible but no later than 06/01/03, and complete the LTCP.

5 IN Town of Remington 06/06/03 The Order required the Town to complete construction, cease 

overflows from Outfall 004, and provide IDEM a certification 

statement of completion of construction within nine months of this 

Order.

5 IN Town of Ridgeville 09/11/02 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates.

5 IN Town of Ridgeville 10/15/01 This Order required the Town to submit to the IDEM its complete 

Stream Reach Characterization and Evaluation Report by 09/30/01 

and submit its LTCP for approval by 03/15/02.

5 IN Town of Summitville 01/29/03 This Order required the City to immediately implement the approved

LTCP and adhere to the milestone dates.

7 MO City of Macon, MO 05/29/01 This Order required that a schedule for the Nine Minimum Controls 

(NMCs) be submitted by 06/01/01. Upon review and approval of the 

LTCP and the schedule for implementation of the LTCP, the City 

will complete each phase of the LTCP in accordance with the 

approved schedule.

7 MO City of Sedalia, MO 06/15/92; 

Amended

02/10/03

This Order required the City to complete construction of Phase I by 

12/01/04, complete construction of Phase II by 12/01/05, and 

complete construction of Phase III by 09/15/07.

10 OR City of Astoria 01/07/93 The City has completed the studies and planning activities required 

by the Order, and on 09/30/98, submitted a CSO Facilities Plan to 

the Department.

10 OR City of Astoria 08/05/02 This Order required the City to eliminate all untreated CSO 

discharges within 15 months of Department approval of the Plans 

and Specifications.

10 OR City of Corvallis 11/09/92 Under this Order the City was required to eliminate discharges that 

violate applicable water quality standards, subject to storm return 

frequencies at five CSO discharge points by 12/31/01.

10 OR City of Portland 08/11/94 Under this Order, the City was required to eliminate untreated CSO 

discharges at 20 of the CSO discharge points, including discharges 

to Columbia Slough by 12/01/01, eliminate untreated CSO 

discharges at 16 of the remaining discharge points by 12/01/06, 

and eliminate untreated CSO discharges at all remaining CSO 

discharge points by 12/01/11.

10 OR City of Portland 08/05/91 Under this Order, they were required to carry out necessary studies 

and corrective actions to eliminate the discharge of untreated 

overflows from the combined sewer system, up to one in ten year 

summer storm event and up to a one in five year winter storm 

event. The City was required to submit scope of study for the 

facilities plan and for an interim control measures study.

10 WA City Of Spokane 12/13/99 This Order addressed untreated sewage discharging from the City's 

CSO outlet #15. A penalty of $15,000 was eventually assessed for 

the violation.
K-40

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-41

K.10 State SSO Administrative Orders

Region State Case Name/City Name Effective Date Description

1 NJ Bergen County Utilities 

Authority Sewage 

Treatment, Bergen 

County

12/17/91;

Amended

05/20/97;

Amended

02/01/99

This Order required Bergen County Utilities Authority to complete 

the Municipal Sewer Operations and Maintenance Program and 

submit a final report to the Department by 10/01/05.

1 NJ Cliffside Park Borough, 

Bergen County

06/22/01 This Order required the Borough to plan, design, construct, 

operate, and/or implement modifications to the collection and 

conveyance facilities that will result in the elimination of major storm 

water contributions to the CSOs from Sanitary Sewer Outlet Plan, 

Regulator Ten. Construction was required to be completed by 

06/01/02.

2 NJ Borough of Flemington 10/20/99 The Borough was required to immediately cease all unpermitted 

discharges of pollutants emanating from its wastewater collection 

system.

2 NJ Borough of Flemington 04/08/03 This Order addressed permit violations.

2 NJ City of Summit 05/28/99 The City was required to immediately cease all unpermitted 

discharges from the System and seal the overflow point from the 

Chatham Road Pump Station holding tank.

2 NJ City of Summit 07/23/02 This Order required the city to submit a comprehensive upgrade 

plan with a time schedule by 08/01/02; within 12 months of 

issuance of the Treatment Of Works Approval (TWA), the City was 

to complete construction and installation and commence operation 

of the additional pump(s).

2 NJ Englewood Cliffs Borough 05/15/97 This Order required the Borough to complete construction of 

Category 1A by 04/01/02, and complete construction of Category 

1B by 04/01/09. 

2 NJ Ewing-Lawrence 

Sewerage Authority, 

Trenton

09/14/00 Under this Order, Ewing-Lawrence Sewerage Authority was 

required to complete private property I/I corrective action for all 

properties which discharge into the sewage collection system 

upstream of Jacobs Creek Diversion Chamber by 07/01/02.

2 NJ West Milford Township 

Municipal Utilities 

Authority

03/28/00 This Order required the Authority to complete construction of the 

recommendations of the Phase I Report by 10/16/02.

2 NY City of Oneida 01/04/01 This Order required the City to submit for review an approvable 

composite correction program with a proposed schedule of work 

within two months of this Order, after Department approval of the 

comprehensive performance evaluation final report.

2 NY City of Sherrill 04/09/90 This Order required the City to submit to the Department for 

approval a plan and implementation schedule for bringing the City 

into compliance with its flow limits of its State Pollutant Discharge 

Elimination System (SPDES) permit within nine months of this 

Order.

2 NY County of Westchester 08/17/98 The County was required to complete all repairs to the Public I/I by 

12/31/02, and complete construction of the SSO Treatment 

Facilities for New Rochell S.D. Outfalls 003 and 005 by 04/01/04. 
K-42

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

2 NY Mount Vernon Sewer 

District, Hamburg

10/22/01 This Order required the District to submit an engineering report for 

abatement of all SSOs, including an approvable schedule, within six 

months of this Order.

2 NY Town of Coeymans 05/04/01 The Order required the Town to submit to the Department for 

approval an I/I reduction plan to address excessive I/I within the 

Town. They were also required to submit to the Department for 

approval a detailed Wet Weather Operations Plan to minimize the 

discharge of pollutants during wet weather and to prevent/minimize 

upset conditions.

2 NY Town of East Greenbush 11/08/00 This Order required the Town to submit to the Department for 

approval an I/I investigation plan by 01/15/01.

2 NY Town of Greenport 06/06/01 This Order required the Town to submit to the Department for 

approval an I/I remedial plan and expeditious schedule by 08/01/02.

2 NY Town of North Greenbush 11/27/00 This Order required that by 10/15/00, the Town would submit to the 

Department for approval an I/I removal plan that will result in the 

elimination of excessive I/I within the sewer system.

2 NY Town of North Greenbush Modified 10/2/01 The Order required the Town to submit to the Department for 

approval an I/I remedial plan which was to include the results of the 

I/I investigation by 01/01/02.

2 NY Town of Owasco 06/11/01 This Order required the Town to complete construction of Contract 

Number One by 10/26/01, as well as complete construction of 

Contract Number Two and eliminate existing sewer overflows by 

02/28/02.

2 NY Town of Sand Lake 07/21/00 This Order required the Town to submit to the Department for 

approval an I/I investigation plan which will include a schedule for 

implementation by 08/15/00.

2 NY Town of Tonawanda 01/02/87; 

Revised

03/22/95

The Town was required to install 4,400 new sump pumps and 

correct 1,650 existing sump pumps and 6,600 downspouts by 

12/31/05.

2 NY Town of Tonawanda 07/05/95 The Town was required to submit to the Department for approval a 

City Sanitary and Storm Sewer Management Plan by 09/01/95, and 

eliminate 322 of the 446 cost effective private sources of inflow 

identified in the City by 06/30/95.

2 NY Town of Tonawanda 02/87 This Order required the Town to submit a report detailing costeffective work which would minimize raw sewage overflows to 

surface waters and the complete the required work established in 

the schedule of this Order.

2 NY Village of Attica 09/18/97 This Order required the Village to submit certification from a 

professional engineer that the inflow removal Compliance Actions 

would be completed according to the Schedule of Compliance 

outlined in the permit by 11/01/97. The Order also required them to 

submit a Plan of Study prepared by a professional engineer to 

identify and remove all sources of excessive infiltration in the 

Village's sanitary sewer collection system by 12/01/97.
 Appendix K

K-43

Region State Case Name/City Name Effective Date Description

2 NY Village of Cobleskill 07/22/98 This Order required that within 12 months of this Order, 

construction of Phase I would be complete, within 24 months of this 

Order, construction of Phase II would be complete, within 36 

months of this Order, construction of Phase III would be complete, 

and Phase IV would be complete within 48 months of this Order if 

Phases I-III do not adequately address I/I.

2 NY Village of Cobleskill Modified 

05/31/01

This Order required that by 12/31/01, the design and construction 

of walls and additional piping in the aeration tanks would be 

complete and by 06/15/01, bypasses to the wastewater treatment 

facility would be eliminated. Additionally, construction of Phase I 

was required to be complete within six months of this Order and 

construction of Phase II would be complete within 24 months of this 

Order.

2 NY Village of Endicott 02/01/90 This Order required the Village to submit to the Department a plan 

to locate, install, and monitor newly installed wells by 03/15/90. The 

Village was also required to submit to the Department for approval, 

a Scope of Services report by 02/15/90 and within the appropriate 

time frame, complete the Phase I and Phase II of the I/I 

investigation.

2 NY Village of Fort Ann 08/07/01 This Order addressed permit violations and assessed a $17,000 

penalty. Within 12 months of construction start, all corrective 

measures were supposed to be complete.

2 NY Village of Hancock 01/31/02 This Order required the Village to have the valves located upstream 

of the Brooklyn and Pennsylvania Avenue pump stations be 

permanently closed by 06/01/02.

2 NY Village of Kenmore 01/28/87; 

Modified

06/09/95

This Order required the Village to install sump pumps, if necessary, 

by 05/01/89. 

2 NY Village of Saranac Lake 10/03/00 The City was required to implement all improvements to manhole 

number ten by 11/30/00. The City will submit an approvable plan for 

continuous ongoing sewer system assessment, flow monitoring, 

correction and maintenance, including a schedule for each, by 

02/28/01.

2 NY Village of Schuylerville 04/04/01 The Village was required to submit to the Department, within 14 

months after completion of "the project," an engineering report that 

evaluates the effectiveness of sump pump removal and 

replacement of sanitary sewers and manholes at reducing I/I.

2 NY Village of Stamford 01/24/00 The Order required the Village to begin the I/I remedial work and 

complete all work by 06/30/02.

2 NY Village of Stamford Modified 

06/05/00

This Order required that by 06/30/00, the Village would submit to 

the Department for approval an I/I investigation plan.
K-44

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

2 NY Village of Williamsville 04/13/98 This Order required the Village to submit to the Department for 

approval a plan for continuous ongoing sewer system assessment, 

flow monitoring, correction and maintenance, including a 

compliance schedule by 09/01/97, as well as an engineering report 

for abatement of discharges from sanitary sewer outfalls 001 thru 

008 by 09/01/98.

3 VA Caroline County Regional 

WWTP, Caroline County

04/01/02 This Order addressed violations of its permit for an unpermitted 

discharge, failure to take reasonable steps to minimize or prevent 

any discharge which has a likelihood of adversely affecting human 

health or the environment, and failure to properly operate and 

maintain systems. The County was required to develop and 

implement written procedures for identification of potential collection 

system problems; review and evaluate operation and maintenance 

staffing; update all O&M manuals for the pumping stations and the 

WWTP; and develop and implement an inspection program.

3 VA Commander, Navy 

Region, Mid-Atlantic 

(Regional Engineer)

 This Order resolved certain violations of the State Water Control 

Law and Regulations of the State Water Control Board. To correct 

these violations, the Navy was supposed to install a cured-in-place 

lining in the sewer line adjacent to pump station 1958; submit a 

maintenance plan for grease traps for approval; submit a linecleaning plan for specific lines for approval; and submit a map and 

list of all gravity sewer lines that have experienced overflow 

problems all by 03/01/03.

3 VA Henrico County Water 

Reclamation Facility, 

Henrico County

 This Order addressed violations of environmental laws and 

regulations, which required the County to begin implementation of 

the Operation and Maintenance (O&M) manual and maintenance 

schedule within three months of Department approval of the 

manual. A schedule for completion of specific I/I projects was 

supposed to be submitted for approval within two months of this 

Order.

3 VA Henrico County Water 

Reclamation Facility, 

Henrico County

02/19/98 A Consent Order was issued to Henrico County due to SSOs of 

sewage from its collection system. In a letter dated 01/08/02, the 

County reported that all projects outlined in the Consent Order had 

been completed except for one, which the Order required this 

project to be completed by 01/01/03.

3 VA Lorton Correctional 

Complex STP, District of 

Columbia Department of 

Corrections, Fairfax 

County

08/24/89;

Amended

08/20/92 and 

08/25/95 and 

Canceled

04/28/00

The 1989 Order required the District to upgrade the STP in phases 

to achieve compliance with more stringent permit effluent limits. In 

1992, the construction schedule was amended at the District's 

request and the 1995 Amendment was in response to the District's 

decision to construct the pumpover system and bring the STP offline.
 Appendix K

K-45

Region State Case Name/City Name Effective Date Description

3 VA Lorton Correctional 

Complex STP, District of 

Columbia Department of 

Corrections, Fairfax 

County

05/09/97;

Amended

8/15/00

The 1997 order required the District to, among other things, 

eliminate overflows from the STP and collection system. The 

District also had to comply with the permit and interim effluent limits 

and eliminate the STP's discharge or, at a minimum, 0.5 MGD of 

the discharge, by 08/01/99. A penalty of $25,000 was assessed. 

The amended order required the District to maintain an adequate 

staff of operators at the STP, secure the services of a consultant 

engineering firm, and install a high-level alarm at the manhole that 

overflowed at the corrections facility.

3 VA Massaponax WWTP, 

County of Spotsylvania

02/19/98 The Order required the County to pay a civil penalty of $53,200 for 

permit violations. The Order also required, among other things, that 

the County operate the WWTP in a workman-like manner, in 

compliance with the WWTP's Permit and O&M manual, in order to 

ensure that overflows of raw or partially treated sewage are 

eliminated.

3 VA Massaponax WWTP, 

County of Spotsylvania

Amendment

11/25/98

This amendment required the County to submit revised plans, 

specifications, and a schedule for review and approval for 

upgrading and expanding the WWTP to meet specific permit limits; 

operate the WWTP in a workman-like manner, and complete 

construction of the upgrade and expansion by 01/15/03.

3 VA Town of Vinton This Order addressed I/I issues that occurred in the collection 

system. Three projects were initiated as a result of this order. The 

first project was the Wolf Creek Sanitary Sewer Improvements 

which called for the pump station and part of a gravity sewer pipe to 

be replaced by 04/01/04. The second project was the Chestnut 

Mountain Subdivision Sewer System Evaluation and Repairs which 

called for the Town to complete repairs of the sewer line and 

associated manholes serving that area by 02/15/05. The third 

project is the Lindenwood Subdivision Sewer System Evaluation 

and Repairs which required the Town to complete repairs of the 

sewer line and the associated manholes in that area by 02/15/08.

3 VA U.S. Marine Corps, 

Marine Corps Base 

Quantico, Quantico 

Mainside WWTP

 This Order resolved certain violations of the State Water Control 

Law and Regulations, particularly violations of exceeding effluent 

limitations. By 08/30/02, the Department of Environmental Quality 

(DEQ) was notified by Quantico that the WWTP's upgrade was 

completed in accordance to approved plans.

3 WV City of Parkersburg Utility 

Board, Parkersburg

08/26/02 In this Order, the City and Parkersburg Utility Board will maximize 

flows to the treatment plant during both dry and wet weather 

conditions in order to reduce the number, volume, and duration of 

discharges from the City's SSOs. The City plans on completing 

construction of the Long-term SSO Abatement Improvements by 

10/31/09. A penalty of $12,500 was assessed.
K-46

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

3 WV City of South Charleston 

Sanitary Board and South 

Charleston Sewage 

Treatment Company, 

South Charleston

12/18/98 The City was required to submit a CSO plan, complete and 

implement the technology based controls established in the Order, 

and complete an evaluation of water quality impacts. By 06/01/99, 

they will submit a revised corrective action plan and compliance 

schedule for the elimination of the 26 SSOs.

3 WV North Putnam Public 

Service District, Scott 

Depot

11/01/00 This Order required the District to proceed with the continued 

implementation of the I/I identification and elimination measures 

needed to eliminate extraneous flows, and, in the interim, utilize the 

temporary sanitary sewer system overflow to alleviate potential 

adverse conditions.

3 WV North Putnam Public 

Service District, Scott 

Depot

Amended

04/13/01

This amendment requested an extension to the compliance 

schedule outlined in the 2000 Order.

3 WV Town of Athens 06/23/99 This Order required the Town to immediately comply with the 

interim limitations established in the Order. By 06/30/01, the Town 

will either cease operation of their existing WWTP or have it 

upgraded to meet the Permit requirements. Construction of the 

treatment plant upgrade will be complete by 06/30/01.

3 WV Town of Winfield 04/16/02 The Town was required to immediately proceed with the continued 

implementation of the I/I identification and elimination measures 

needed to eliminate extraneous flows, and, in the interim, utilize the 

temporary sanitary sewer system overflow to alleviate potential 

adverse conditions.

3 WV Town of Winfield Amended 

06/06/03

This amendment requested a temporary SSO, actively pursued the 

necessary processes for identifying and eliminating sources of I/I 

within the Town's wastewater collection system, and requested an 

extension to complete the wastewater system improvements and 

cessation of the temporary SSO.

4 AL Arab Sewer Board (Arab 

Riley Maze Creek 

WWTP)

04/28/00 This Order required them to have a professional, licensed engineer 

prepare a compliance plan for them to submit. The plan was to 

evaluate the causes of the bypass and overflow discharges of raw 

sewage at the treatment plant and make recommendations on how 

to eliminate or significantly reduce the discharges. A civil penalty of 

$2,300 was assessed.

4 AL Arab Sewer Board 

(Gilliam Greek WWTP)

04/28/00 This Order required them to have a professional, licensed engineer 

prepare a compliance plan for them to submit. The plan was to 

evaluate the causes of the bypass and overflow discharges of raw 

sewage at the treatment plant and make recommendations on how 

to eliminate or significantly reduce the discharges. A civil penalty of 

$1,300 was assessed.

4 AL City of Attalla, Attalla 

Wastewater treatment 

lagoon

02/26/02 This Order required the City to pay a civil penalty of $1,200 plus 

remove pollutants from their discharge during wet weather to the 

maximum extent possible. Additionally, the City was required to 

conduct and complete a thorough investigation of the existing 

treatment works and maintenance and operating procedures of the 

facility and, prepare and submit a compliance plan.
 Appendix K

K-47

Region State Case Name/City Name Effective Date Description

4 AL City of Cullman, Cullman 

WWTP

Modification

11/10/99

This Order required the City to execute the necessary contracts for 

the construction of the new or additional treatment works or 

modification of existing treatment works necessary to achieve 

compliance.

4 AL City of Cullman, Cullman 

WWTP

10/29/98 This Order established certain deadlines for the City to achieve 

compliance, which the City later requested extensions for those 

deadlines due to conditions beyond its reasonable control.

4 AL City of Moulton 06/19/97 This Order required the City to submit a compliance plan which 

evaluated the causes of SSOs at the manhole near the intersection 

of Alabama Highway 24 and 33 and the City and made 

recommendations on how to eliminate or significantly reduce SSOs 

and achieve compliance. They were also required to employ a 

registered professional engineer to inspect the entrance bridge and 

service road to determine the need for repairs and replacement to 

ensure reliable access to the facilities.

4 AL City of Tuscaloosa 11/07/01 The Order required the City to complete the ultraviolet disinfection 

project and have a substantially complete and operational 

ultraviolet disinfection system at the wastewater treatment plant by 

10/01/03.

4 AL Decatur Utilities 11/09/00 The Order required them to have a registered professional engineer 

prepare and submit a compliance plan which evaluated the causes 

of the bypasses or overflows and made recommendations on how 

to eliminate or significantly reduce the bypasses or overflows to 

achieve compliance.

4 AL Demopolis Water Works 

and Sewer Board, City of 

Demopolis

11/23/98 The Order addressed violations of the limitations established in the 

Permit as indicated by the Discharge Monitoring Reports (DMRs) 

submitted to the Department by the City. Interim limitations on 

discharge of pollutants from Outfall 001 into the Tombigbee River 

were established.

4 AL Demopolis Water Works 

and Sewer Board, City of 

Demopolis

08/02/01 This Order rescinded the 1998 Order and required the City to pay a 

civil penalty of $5,300. An engineering report investigating the 

needs for changes in maintenance and operation procedures and 

the need for modification of existing treatment works or the need for 

any new or additional treatment works was supposed to be 

submitted to the Alabama Department of Environmental Protection 

(ALDEP) within three months of this Order.

4 AL Stevenson Utilities Board, 

Stevenson Wastewater 

Treatment Lagoon, 

Stevenson

01/09/02 This Order required them to complete construction and start up the 

new or additional treatment works or modification of existing 

treatment works necessary to achieve compliance with Fecal 

Coliform discharge limitations by 10/14/03. They were also required 

to complete construction and start up of new pumping stations, 

SCADA System and upgrade of sewage collection system by 

08/30/03. Construction of any additional sewer system rehabilitation 

was to be complete by 10/22/04.

4 AL The Water Works and 

Sewer Board of the City 

of Anniston, Choccolocco 

Creek WWTP

06/25/98 This Order required the City to immediately make revisions to the 

overflow weirs at the headworks of the WWTP and at the 

Southeastern Area Lift Station to eliminate any leaking of untreated 

wastewater that resulted in continuous bypasses. They were also 

required to have a professional, licensed engineer prepare a report 

outlining the causes of noncompliance and they were supposed to 

later implement those preventative measures listed in the report.
K-48

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 AL Utilities Board of the City 

of Athens

08/06/97 The City was required to have a professional engineer prepare a 

compliance plan for the City to submit to the Department no later 

than 09/30/97. The compliance plan was to evaluate the causes of 

the SSO's at the cited manholes near the Athens Limestone 

Hospital and the L&N Railroad overpass and make 

recommendations on how to eliminate or significantly reduce the 

SSO's.

4 AL Utilities Board of the City 

of Bayou La Batre

01/08/99 The City was required to prepare and submit a Compliance Plan to 

the Department for approval no later than 03/31/99. The plan will 

identify causes of effluent limitations violations and describe 

corrective actions, as well as provide a schedule implementing the 

Compliance Plan.

4 AL Utilities Board of the City 

of Helena

12/03/01 The 1997 Order was rescinded. These Order required them to have 

a registered professional engineer prepare and submit the plans 

and specifications to upgrade the existing Helena WWTP to a 4.95 

MGD. All construction was supposed to be complete by 11/30/03. In

lieu of paying the $100,000 civil penalty, they performed a 

Supplemental Environmental Project (SEP) which consisted of the 

construction of a new pump station in the park area. 

4 AL Utilities Board of the City 

of Helena

08/22/97 This Order to addressed 53 SSOs in 1996 at several manhole 

locations in the collection system. The 53 SSO's resulted in a total 

of 29,330,000 gallons of raw sewage overflow from its collection 

system. They were required to submit a compliance plan schedule 

to resolve the violations. They failed to meet the milestones of two 

engineering activities, did not complete the replacement of the main 

pumping station at the scheduled date, and failed to expand the 

existing Helena WWTP to a 4.95 MGD plant.

4 FL South Cross Bayou 

WWTF, Pinellas County, 

Clearwater

04/20/94 The Order authorized the County to proceed with the corrective 

actions outlined in the document and temporarily operate the 

WWTP and injection well system for a period of five years. They 

were also required to pursue construction and implementation of a 

County regional reuse system and upgrade the Facility to Advanced 

Wastewater Treatment (AWT) to include surface water discharge 

for backup disposal. A stipulated penalty of $36,000 was assessed.

4 NC Belmont City-A Sludge/ 

Lars

10/30/01 

4 NC Mebane Bridge WWTP 01/25/02 

4 NC Morrisville TownCarpenter04/11/00 

4 NC Murfreesboro Town 

WWTP

10/11/00 

4 NC Neuse Crossing WWTP 02/17/00 

4 NC Pond Creek WWTP 01/25/02 

4 NC Sanford WWTP 11/25/02 

4 NC Sanford WWTP 07/09/03 

4 NC Town of Canton 03/27/00 

4 NC Town of Green Level 03/16/01 

4 NC Warsaw WWTP 08/03/00 
 Appendix K

K-49

Region State Case Name/City Name Effective Date Description

4 SC Bath and Water and 

Sewer District, Aiken 

County

08/21/97 This Order required the County to clean out the sewer line within 

three days of the Order and replace the section of sewer line from 

the main trunk line to the edge of the property at 15 Hill Street 

within four months of the Order. A $10,000 civil penalty was 

suspended.

4 SC Berkeley County Water 

and Sanitation Authority, 

Lower Berkely WWTF, 

Berkeley County

05/07/02 The Order required the County to submit a summary report of 

corrective actions taken to prevent future unauthorized discharges. 

A civil penalty of $9,900 was assessed.

4 SC City of Hanahan 03/20/00 The City was required in this Order to complete development of a 

comprehensive CMOM program and implementation of the initial 

system audit and by 09/01/00, submit a summary detailing the 

findings of the initial audit. A civil penalty of $11,200 was assessed.

4 SC City of Hardeeville 02/28/02 The Order addressed the discharge of sewage into the environment 

not in compliance with their permit and failure to properly operate 

and maintain, at all times, all waste treatment systems. An $8,000 

civil penalty was assessed.

4 SC City of Lancaster 01/27/97 This Order addressed raw sewage leaking from an exposed 

polyvinyl chloride (PVC) line under a bridge and from an 

abandoned line adjacent to the bridge decreased dissolved oxygen 

levels below stream standards resulting in a fish kill. As a result of 

this violation, the City was required to submit a schedule to survey 

the collection system as well as a schedule to inspect the collection 

system on a routine basis. A civil penalty of $12,000 was assessed 

plus $3,061.35 for the cost of the fish kill.

4 SC City of Lancaster 07/31/01 The Order required the City to begin developing a Capacity, 

Management, Operation, and Maintenance (CMOM) audit for the 

wastewater collection system. A summary report of corrective 

actions addressing deficiencies in the wastewater collection system 

and ammonia-nitrogen and toxicity were also to be submitted.

4 SC City of Lancaster, 

Catawba River Plant, 

Lancaster County

11/30/99 This Order addressed an unauthorized discharge caused by an 

overflowing manhole. The City was required to submit a SSES 

study plan outlining plans for evaluation of the deficiencies within its 

sewer system.

4 SC City of Rock Hill/ 

Manchester Creek

01/09/01 This Order required the City to submit a corrective action plan for 

compliance with the permitted discharge limits for fecal coliform. A 

corrective action plan and schedule was also required to address 

priority deficiencies in the wastewater collection system (pump 

stations, manholes, line breaks/ deteriorations, etc.). Within six 

months of the Order and every six months until the Order is closed, 

they were supposed to submit a summary report of corrective 

actions addressing deficiencies in the wastewater collection 

system. A civil penalty of $23,000 was assessed.
K-50

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 SC City of Rock Hill/ 

Manchester Creek

06/19/97 This Order addressed, among other things, violations of the 

permitted discharge limits for fecal coliform bacteria, total residual 

chlorine, and total suspended solids.

4 SC East Richland County 

Public Service District, 

Richland County

07/27/01 The Order required the County to begin development of a CMOM 

audit and to submit a corrective action plan and schedule to 

address priority deficiencies in the wastewater collection system 

(pump stations, manholes, line breaks/deterioration, etc.). Within 

six months of the Order and every six months until the Order is 

closed, the County was also supposed to submit a summary report 

of corrective actions addressing deficiencies in the wastewater 

collection system.

4 SC East Richland County 

Public Service 

District/Gills Creek 

WWTP, Richland County

06/29/98 The Order required the County to submit an administratively 

complete Preliminary Engineering Report addressing upgrade of 

the effluent pump station and the elimination of the Gills Creek 

discharge point. They were also required to submit an I/I study, 

outlining deficiencies in the waste disposal system and a schedule 

for completion of the study and of any necessary repairs.

4 SC McCormick County Water 

and Sewer, McCormick 

County

07/21/03 This Order required the County to implement and re-evaluate the 

approved MOM program, submit a schedule for lift station 

inspections, submit a report of reduction of SSOs during the most 

recent 12 months, and submit a schedule plan to pump out 

interceptor tanks in Savannah Lakes Village including disposal 

sites.

4 SC McCormick County Water 

and Sewer, McCormick 

County

08/19/02 The Ordered required the County to immediately begin inspecting 

all lift stations on a daily basis or have them equipped with 

telemetry monitoring. The lift station inspection records were 

supposed to be maintained for at least three years. Additionally, the 

Order required the County to submit a report identifying the 

reduction of SSOs since 01/01/00, as a result of compliance 

requirements of the 1999 Consent Order, as well as submit a five 

year on-going schedule to pump out interceptor tanks in Savannah 

Lakes Village, and submit "Sanitary Sewer Overflow or Pump 

Station Failure Forms" for unreported SSOs identified.

4 SC McCormick County Water 

and Sewer, McCormick 

County

12/14/99 The County agreed to operate and maintain the wastewater 

collection system, develop and implement a CMOM program, 

evaluate all lift stations and take corrective actions accordingly, 

report all SSOs, and pay a penalty.
 Appendix K

K-51

Region State Case Name/City Name Effective Date Description

4 SC Spartanburg Sanitary 

Sewer District/Fairforest 

Plant, Spartanburg 

County

06/09/99 The Order required the County to submit a Sewer System 

Evaluation Survey (SSES) study plan and later results for both, 

Camp Croft collection system and Fairforest Drainage Basin. The 

plans were supposed to have an implementation schedule for the 

phases of the SSES. A comprehensive Management, Operation, 

and Maintenance program (MOM) for the entire wastewater 

collection system was also to be submitted along with a corrective 

action plan detailing operation and maintenance procedures and/or 

pretreatment program modifications. At civil penalty of $36,000 was 

assessed.

4 SC Town of Carlisle 09/02/99 This Order required the Town to obtain a generator capable of 

operating the lift stations during power outages, submit a SSES 

study plan for the Westwood and Clearbranch subsystems along 

with an implementation schedule for the phases of the SSES, 

submit the results of the Phase I of the SSES, and submit a MOM 

plan for the entire wastewater collection system.

4 SC Town of Chesterfield 10/01/02 The Order required the Town to submit a summary of corrective 

actions taken to prevent SSOs, implement temporary measures to 

prevent SSOs at the high school lift stations and submit a summary 

report detailing the measures taken, submit a corrective action plan 

for the upgrade of the high school lift station, begin development of 

CMOM audit, submit a corrective action plan and schedule to 

address priority deficiencies in the wastewater collection system, 

and within six months of the Order and every six months after the 

Order is closed, submit a summary report of corrective actions 

addressing deficiencies in the wastewater collection system.

4 SC Town of Fort Mill 05/03/00 The Order required the Town to begin development of a CMOM 

audit and to submit a corrective action plan and schedule to 

address priority deficiencies in the wastewater collection system 

(pump stations, manholes, line breaks/ deterioration, etc.). Within 

six months of the Order and every six months until the Order is 

closed, the County was also supposed to submit a summary report 

of corrective actions addressing deficiencies in the wastewater 

collection system. A civil penalty of $11,200 was assessed.

4 SC Town of McColl 07/22/02 The Town was required to begin development of a cMOM audit, 

submit a corrective action plan and schedule to address priority 

deficiencies in the wastewater collection system, and within six 

months after the Order and every six months after the Order is 

closed, submit a summary report of corrective actions addressing 

deficiencies in the wastewater collection system. 

4 SC Town of Pamplico 05/17/00 The Order required the Town to submit a corrective action plan 

detailing measures taken or to be taken to prevent overflows. They 

were also required to submit detailed reports of all I/I work 

performed, including flow isolation and visual manhole inspections. 

A civil penalty of $10,200 was assessed.
K-52

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 SC Town of Varnville 08/11/97 The Order addressed the Town allowing unauthorized discharges 

of untreated wastewater into the environment. As a result, the Town 

was required to notify the Department verbally within 24 hours of a 

spill and follow-up with a written description within five days. A civil 

penalty of $3,500 was assessed.

4 SC Western Carolina 

Regional Sewer Authority, 

Greenville County

06/09/99 This Order required the County to submit a study plan for instream 

water quality assessment of fecal coliform bacteria, implement the 

water quality assessment for fecal coliform bacteria, submit a study 

plan for a biological assessment around the collection systems, and 

pay a civil penalty of $82,000.

4 TN Athens Utilities Board 01/05/99 The Order required the City to submit to the Chattanooga 

Environmental Assistance Center (CEAC) an engineering report by 

08/15/99.

4 TN City of Alexandria 07/19/00 The City was required to complete construction of the approved 

wastewater treatment plant (WWTP) additions and/or 

improvements by 08/31/01.

4 TN City of Alexandria 10/02/02 The City was required to complete construction of the WWTP 

facility by 10/31/02. Of the total $104,000 penalty, $7,500 will be 

due within one month of this Order and the remainder will be 

contingent with fulfilling the remaining tasks.

4 TN City of Bluff City 07/28/98 This Order required the City to complete construction of the sewer 

connection by 05/15/98, and complete closure of the WWTP, 

without the bypass of sewage, within three months of the systems 

connection to the City of Bristol Utilities. A penalty of $17,750 was 

assessed, of which $2,250 was due within one month of this Order, 

and the remainder was contingent upon fulfilling required tasks.

4 TN City of Church Hill 04/02/97 This Order required the City to notify the Tennessee Department of 

Environment and Conservation (TNDEC) of all sewage facility 

projects constructed or under construction without the Department's 

approval within one month of this Order. A penalty of $5,000 was 

due within one month of this Order.

4 TN City of Copperhill 10/21/99 The City was required to have two adequately sized and 

operational pumps installed at the City's lift station by 12/01/99, as 

well as have two adequately sized and operational return activated 

sludge pumps installed at the WWTP.

4 TN City of East Ridge 04/29/96 This Order required the City to complete the approved Corrective 

Action Plan by 12/31/98. A $30,000 contingent penalty was 

assessed.

4 TN City of Franklin 10/26/99 The Order addressed, among other things, permit violations. The 

City was required to pay a damage fee of $6,326 and a civil penalty 

of $3,750.

4 TN City of Franklin 11/13/00 This Order required the City to implement all remedial measures 

detailed in the approved report within six months of this Order. Of 

the total $57,500 civil penalty, $15,000 will be due within one month 

of this Order and the remainder will be contingent of fulfilling the 

remaining tasks.

4 TN City of Greenbrier 03/20/00 This Order required the City to complete the WWTP 

upgrade/expansion and interceptor improvements within nine 

months of start of construction or, by 03/01/01. Of the total 

$141,750 penalty, $1,500 will be due within one month of this Order 

and the remainder will be contingent with fulfilling the remaining 

tasks.
 Appendix K

K-53

Region State Case Name/City Name Effective Date Description

4 TN City of Harriman 06/28/00 This Order required the City to complete the WWTP 

upgrade/expansion and interceptor improvements within 14 months 

of start of construction or, by 03/01/03. Of the total $266,250 

penalty, $30,000 will be due within one month of this Order and the 

remainder will be contingent with fulfilling the remaining tasks.

4 TN City of Harriman 07/23/02 The City was required to complete construction of Woodyard Pump 

Station/Force Main by 06/31/03, complete 

construction/rehabilitation of the South Harriman Pump Stations by 

12/15/03, and complete construction of WWTP project by 03/01/04. 

A penalty of $30,000 will be due within one month of this Order.

4 TN City of Jefferson City 06/04/01 The City was required to complete construction of the WWTP 

improvement project by 01/31/02.

4 TN City of Jellico 10/03/97 This Order required the City to complete collection system repairs 

and treatment plant upgrades/ expansion, and implement an 

ongoing program for collection system rehabilitation. Of the total 

$11,500 penalty, $1,500 will be due within one month of this Order 

and the remainder will be contingent with fulfilling the remaining 

tasks.

4 TN City of Kingston 11/30/01 This Order required the City to complete the implementation of the 

Corrective Action Plan and within three months of complete 

implementation, the City will be in full compliance with its NPDES 

permit. Of the total $207,000 penalty, $5,000 will be due within one 

month of this Order and the remainder will be contingent with 

fulfilling the remaining tasks.

4 TN City of Lafayette 04/22/03 The City was required to complete construction of the WWTP 

upgrade. Of the total $92,500 penalty, $7,500 will be due within one 

month of this Order and the remainder will be contingent with 

fulfilling the remaining tasks.

4 TN City of LaVergne 11/08/99 This Order addressed the discharge of wastewater and raw sewage 

overflowing from manholes. A civil penalty fee of $2,500 will be due 

within one month of this Order.

4 TN City of LaVergne 10/24/00 The Order addressed, among other things, permit violations. A civil 

penalty fee of $2,000 will be due within one month of this Order.

4 TN City of Lawrenceburg 11/19/98 This Order required the City to complete repairs to the WWTP and 

collection system by 02/15/99.

4 TN City of Lawrenceburg 03/27/01 This Order required the City to complete the installation of the new 

sludge filter belt press in the WWTP by 03/01/01. A penalty fee of 

$9,375 will be due within one month of this Order..

4 TN City of Middleton 11/10/98 The Order required the City to complete construction by 09/30/00.

4 TN City of Middleton 08/25/00 The Order required the City to complete construction of the 

proposed upgrades to the existing lagoon, the modifications to the 

force main, and the replacements of the effluent pumps. 

Additionally, within six months of this Order, the City will complete 

construction of the parallel force main. Of the total $47,750 penalty, 

$5,000 will be due within one month of this Order and the 

remainder will be contingent with fulfilling the remaining tasks.
K-54

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

4 TN City of Murfreesboro 08/21/99 The City was required to complete the expansion of the sewer 

treatment plant and place the sewer treatment plant into full 

operation by 01/31/00. As a result, the Town was charged a 

damage fee of $12,107 in addition to the penalty of $400,000. Of 

the total penalty, $50,000 was due within one month of this Order 

and the remainder was to be contingent upon fulfilling the required 

tasks.

4 TN City of Murfreesboro 05/22/01 The Order requested that the City perform a Supplemental 

Environmental Project (SEP) in lieu of paying the $50,000 civil 

penalty. The City was to purchase a five acre lot, which had a 

wetland and protect, in perpetuity, the aesthetic, educational, or 

ecological values of this wetland.

4 TN City of Portland Public 

Works

08/02/02 The Order addressed discharges into waters of the U.S. without a 

NPDES permit and causing a condition of pollution that resulted in 

a fish kill. The damage fee totaled $541.11 and the penalty fee 

totaled $5,000.

4 TN City of Pulaski 05/08/98 The Order required the City to submit to the Division of Water 

Pollution Control a plan to eliminate permit limit violations by 

06/15/98.

4 TN City of Red Bank 02/25/97 The Order required the City to implement and complete the 

approved 1997 Sewer Rehabilitation and Corrective Action Plan 

and, if necessary, additional collection system improvements by 

09/30/01. Of the total $164,500 penalty, $10,000 will be due in 

increments by 09/01/97.

4 TN City of Rockwood 10/29/98 This Order required the City to complete the Corrective Action Plan 

and obtain full compliance with its NPDES permit by 08/01/01. Of 

the total $16,750 penalty assessed, $1,500 was due within one 

month of this Order and the remainder was to be contingent upon 

fulfilling required tasks.

4 TN City of Sparta 10/04/00 The Order required the City to submit a report evaluating the 

effectiveness of the WWTP upgrade/expansion. Additionally, the 

city was required to submit a Corrective Action Plan to address the 

collection system I/I problems. Of the total $62,000 penalty, $7,500 

will be due within one month of this Order and the remainder will be 

contingent with fulfilling the remaining tasks.

4 TN City of Watertown 02/08/00 This Order addressed effluent discharge violations. A civil penalty 

of $1,100 will be due within one month of this Order.

4 TN City of Watertown 06/03/03 This Order required the City to complete construction of the 

wastewater collection system and WWTP improvements by 

08/31/03. Of the total $87,500 penalty, $10,500 will be due in 

increments by 03/31/04.

4 TN Knoxville Utilities Board 05/20/03 This Order required a Phase I Corrective Action Plan/Engineering 

Report to be submitted within ten months of receiving comments 

from the Department. A Phase II Corrective Action 

Plan/Engineering Report was required to be submitted by 06/30/06. 

A contingent penalty was assessed at $475,000.

4 TN Lenoir City Utilities Board 01/03/01 This Order required the Board to complete collection system 

improvements by 07/31/01 and to complete all planned WWTP 

improvements by 12/31/01. They were also required to complete 

construction of approved additions and/or improvements within 18 

months of start of construction or, by 06/30/05.

4 TN Lynnwood Utility 

Corporation

No date 

provided

The Order addressed permit violations. A civil penalty of $5,000 will 

be due within one month of this Order.
 Appendix K

K-55

Region State Case Name/City Name Effective Date Description

4 TN Metropolitan Government 

of Nashville and 

Davidson County

09/17/99 The City and County were required to have all CSO controls, 

including but not limited to, floatable material and debris removal, 

combined sewage storage and/or detention and CSO elimination, in 

place by 07/01/01. The City and County were also supposed to 

eliminate all overflows or bypassing from its sanitary sewers to all 

waters of the state by 07/01/01. Of the total $600,000 penalty 

assessed, $100,000 was due within one month of this Order. 

However, the City and County had the option to perform a SEP in 

lieu of paying the $100,000.

4 TN Town of Collierville 06/03/98 The Town was required to complete the installation of the new 

return sludge pumping system within three months of this Order.

They were also required to complete the new aerated lagoon 

treatment plant within two months of this Order. Of the total 

$118,500 penalty, $5,000 was due within one month of this Order 

and the remainder was contingent with fulfilling the remaining tasks.

4 TN Town of Gainesboro 11/22/00 The Order required the Town to complete construction on the 

WWTP upgrade/expansion by 09/01/02. Of the total $67,625 

penalty, $6,500 will be due within one month of this Order and the 

remainder will be contingent of fulfilling the remaining tasks.

4 TN Town of Gainesboro 03/27/01 This Order required the Town to complete construction on the 

WWTP upgrade/expansion by 03/01/03. A penalty of $5,500 will be 

due within one month of this Order.

4 TN Town of Monterey 09/11/02 The Town was required to complete the implementation of the 

Corrective Action Plan and obtain full compliance with its NPDES 

permit within three years of approval. As a result, the Town was 

charged a damage fee of $6,413 in addition to the penalty of 

$115,500. Of the total penalty, $12,500 was be due within one 

month of this Order and the remainder was to be contingent upon 

fulfilling required tasks.

4 TN Town of Mosheim 04/25/01 The Order required the Town to complete construction on the 

WWTP upgrade/ expansion by 06/01/01 and complete the I&I 

rehabilitation by 12/31/01. A civil penalty of $3,000 will be due 

within one month of this Order.

4 TN Town of Pikeville 01/09/00 This Order required the Town to submit a pretreatment program for 

approval and, within one year of this Order, be in compliance with 

its NPDES permit. Of the total $58,250 penalty, $4,125 will be due 

within one month of this Order and the remainder will be contingent 

with fulfilling the remaining tasks.

4 TN Town of Spring City 07/31/03 The Order required the Town to submit a plan for approval to 

comply with permit requirements and within 12 months of approval, 

the plan will be implemented. Of the total $15,000 penalty, $5,000 

will be due within one month of this Order and the remainder will be 

contingent with fulfilling the remaining tasks.

4 TN Town of Spring Hill 06/04/99 The Town was required to implement a plan to prevent any future 

bypassing in the Pipkin Hills subdivision area by 09/01/99.

4 TN Town of Spring Hill 01/26/00 The Order required the Town to complete the Corrective Action 

Plan and obtain full compliance with its NPDES permit by 01/01/01. 

Of the total $73,312 penalty, $1,312 will be due within one month of 

this Order and the remainder will be contingent with fulfilling the 

remaining tasks.
K-56

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

5 IN City of Batesville 03/23/01

5 IN City of Brazil 12/09/93; 

Amended 10/95

5 IN City of Brazil 12/07/99

5 IN City of Charlestown 04/03/02

5 IN City of Dunkirk 05/28/93 

5 IN City of Elwood 10/04/93 

5 IN City of Garrett 12/13/02

5 IN City of Gas City 03/25/91 

5 IN City of Gas City 11/07/02

5 IN City of Greencastle 05/11/99

5 IN City of Greenwood 07/25/97 

5 IN City of Indianapolis Referred to EPA 08/20/02. 

5 IN City of Jasonville 12/20/93 The City was required to submit a Compliance Plan, including a 

schedule with fixed dates for each milestone and a reasonable date 

for final compliance. They were also required to initiate the work 

detailed in the plan within 30 days of being fully approved and 

complete the work according to the plan's schedule.

5 IN City of Lawrence 01/04/99; 

Amended

9/26/00

The City was required to develop and submit to IDEM its 

Compliance Plan for IDEM approval.

5 IN City of Madison 12/10/97 

5 IN City of New Albany 05/09/97 

5 IN City of Portland 03/30/93 

5 IN City of Rockport 01/29/03

5 IN City of Salem 09/18/96 

5 IN City of Salem 08/18/98

5 IN City of Scottsburg 07/23/03

5 IN Community University of 

Gary

08/07/91 

5 IN Henryville 10/31/01

5 IN Town of Advance 07/28/03

5 IN Town of Albany 11/30/00

5 IN Town of Ashley 09/11/01

5 IN Town of Austin 05/11/98 

5 IN Town of Bristol 11/10/98

5 IN Town of Brooklyn 10/20/98

5 IN Town of Carthage 01/12/99

5 IN Town of Cedar Lake 03/04/99

5 IN Town of Churubusco 06/24/03

5 IN Town of Clay City 03/05/02

5 IN Town of Converse 02/23/99

5 IN Town of Cumberland 02/01/02

5 IN Town of Dillsboro 05/01/03 The Town was required to submit a Compliance Plan detailing the 

construction of the new oxidation ditch wastewater treatment 

system, including an implementation and construction schedule 

within three months of this Order.

5 IN Town of Elizabethtown 11/27/91; 

Amended

05/20/98

5 IN Town of Farmersburg 08/08/02
 Appendix K

K-57

Region State Case Name/City Name Effective Date Description

5 IN Town of Farmland 05/09/03

5 IN Town of Flora 04/30/92; 

Amended

06/20/03

5 IN Town of Fort Branch 03/23/01

5 IN Town of Fountain City 09/30/02 The Town was required to develop and submit to Indiana 

Department of Environmental Management (IDEM) for approval a 

Compliance Plan which identified actions the Town was to take in 

order to achieve compliance within six months of this Order. This 

included eliminating sewer system overflows (SSOs).

5 IN Town of French Lick 11/12/93 This Order required the Town to complete construction of its I/I 

removal project by 12/21/94, complete construction of its sewage 

treatment plant by 06/30/97, and complete the necessary actions to 

assure that the downspouts and the sump pumps do not connect 

with the sewage treatment plant.

5 IN Town of Galveston 07/02/02 The Town was required to immediately implement the approved 

Compliance Plan and adhere to the milestone dates.

5 IN Town of Geneva 04/29/03

5 IN Town of Grabill 02/07/02

5 IN Town of Grandview 01/21/99

5 IN Town of Greentown 03/18/98 

5 IN Town of Hanover 03/07/01

5 IN Town of Hartsville 01/27/00

5 IN Town of Haubstadt 08/10/94 The Town was required to submit to IDEM a Compliance Plant 

which included an implementation schedule.

5 IN Town of Jonesboro 06/17/94 

5 IN Town of LaGrange 03/18/98 

5 IN Town of Lapel 11/21/97 

5 IN Town of Leavenworth 07/23/01 This Order required the City to develop and submit to IDEM its 

Compliance Plan for IDEM approval.

5 IN Town of Lynnville 07/28/03

5 IN Town of Milan 05/22/98 

5 IN Town of Montpelier 09/20/93 

5 IN Town of Moores Hill 09/26/00

5 IN Town of Mt. Etna 11/16/98

5 IN Town of Mulberry 10/18/98

5 IN Town of New Providence 12/28/98

5 IN Town of Palmyra 01/02/01

5 IN Town of Paoli 05/12/97 The Town was required to complete sludge handling improvements 

to assure NPDES compliance, complete a Sewer System 

Evaluation Study (SSES), and submit a list of I/I sources found and 

corrected.

5 IN Town of Parker City 05/23/94 

5 IN Town of Parker City 01/02/01

5 IN Town of Pierceton 11/18/98; 

Amended

06/24/03

5 IN Town of Remington 06/06/03

5 IN Town of Riley 12/12/02

5 IN Town of Rockville 07/22/97 

5 IN Town of Rome City 05/12/00

5 IN Town of Santa Claus 06/01/01
K-58

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

5 IN Town of Schererville 08/15/91 

5 IN Town of Sellersburg 12/14/00

5 IN Town of Staunton 09/26/00 The Town was required to develop and submit to IDEM a 

Compliance Plan for approval.

5 IN Town of Sweetser 01/29/02

5 IN Town of Trafalgar 01/26/95 

5 IN Town of Upland 06/06/94; 

Amended 12/01

5 IN Town of Upland 01/12/01

5 IN Town of West College 

Corner

12/18/97 Later referred to EPA. 

5 IN Town of Whitestown 05/01/01

5 IN Town of Wolcottville 06/20/02

6 LA City of Pineville 05/31/02 The Order required them to submit a comprehensive plan for the 

expeditious elimination and prevention of non-complying discharges 

and complete a written report to include a detailed description of the 

circumstances of the violations, the actions taken to achieve 

compliance, and corrective or remedial actions taken to mitigate 

any damages. 

6 LA City of Ruston 12/16/99 Under this Order, they were required to cease all unauthorized 

discharges, meet and maintain compliance with their Permit, submit 

a written report to include a detailed description of the 

circumstances for the violations and the actions taken to achieve 

compliance, and to submit a schedule for corrections.

6 LA City of Ruston 05/31/01 This Order required them to immediately cease unauthorized 

discharges to the waters of the state or any unenclosed areas that 

drain to the waters of the state, submit a comprehensive plan for 

the expeditious elimination and prevention of the noncomplying 

discharges, complete a written report to include a detailed 

description of the circumstances for the violations, the actions taken 

to achieve compliance, and any corrective or remedial actions 

taken.

6 LA City of Ruston Amendment 

11/29/2001

The Order required the City to complete repairs/replacement of 

U.S. Highway 80 East force main by 06/15/02, complete 

rehabilitation of the clarifiers by 01/15/03, and complete 

construction of the WWTF/pump station/ force main by 12/31/06.

6 LA City of Ruston 07/11/97 This Order required the City to immediately cease all unauthorized 

discharges from the facility to the waters of the state, submit a 

comprehensive plan for the expeditious elimination and prevention 

of noncomplying discharges, and submit a completed Louisiana 

permit application.

6 LA City of Ruston 04/29/98 This Order addressed the discharge of inadequately treated 

sanitary wastewater.

6 LA City of Ruston 12/16/99 This Order required the City to submit a written report detailing the 

circumstances for the violations, actions taken to achieve 

compliance, and corrective or remedial actions taken to mitigate 

damages. They were also required to submit a comprehensive plan 

for the expeditious elimination and prevention of noncomplying 

discharges.

6 LA City of Westwego 04/27/98 This Order addressed the City's O&M deficiencies, sampling 

deficiencies, and violations of effluent limitations.
 Appendix K

K-59

Region State Case Name/City Name Effective Date Description

6 LA City of Westwego 04/24/01 This Order addressed the City's the violation of effluent limitations, 

operation and maintenance requirements, and self-monitoring 

programs. The Order required them to immediately cease 

unauthorized discharges to the waters of the state, submit a written 

report to include the circumstances for the violations, and submit a 

comprehensive plan for the elimination and prevention of such noncomplying discharges.

6 LA City of Westwego 08/29/02 This Order required them to immediately cease unauthorized 

discharges to the waters of the state, submit semi-annual progress 

reports until completion of proposed improvements, and to 

complete a written report to include a detailed description of the 

circumstances for the violations, the actions taken to achieve 

compliance, and corrective or remedial actions taken to mitigate 

any damages resulting from the violations.

6 LA City of Westwego 12/24/02 This Order addressed the City's failure to properly operate and 

maintain its facility.

6 OK Bethany/Warr Acres 

Public Works Authority

03/09/00

Closed

This Order addressee bypasses of untreated wastewater.

6 OK Bixby Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Bixby Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Blackwell Municipal 

Authority

 This Order addressed unpermitted bypasses.

6 OK Bokoshe Public Works 

Authority

05/23/02 This Order addressed discharges without a permit. The Authority 

was required to complete construction of the new collection system 

by 01/01/04.

6 OK Carney Public Works 

Authority

06/01/98

Closed

This Order addressed exceeding discharge limits.

6 OK Checotah Public Works 

Authority

12/17/99

Closed

This Order addressed discharges without a permit.

6 OK Checotah Public Works 

Authority

10/01/95

Closed

This Order addressed discharge violations.

6 OK Chouteau Public Works 

Authority

04/11/97

Closed

This Order addressed violation of discharge permit.

6 OK City + A153 of McAlester 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Ada 03/08/01 

Closed

This Order addressed the City discharging without a permit.

6 OK City of Altus 06/14/95 

Closed

This Order addressed unpermitted discharges.

6 OK City of Apache 11/30/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Ardmore 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Atoka 01/11/94 

Closed

This Order addressed discharges without a permit.

6 OK City of Bartlesville 07/12/93 

Closed

This Order addressed unauthorized bypasses.

6 OK City of Bethany 06/12/02 This Order addressed discharges without a permit. The City was 

required to complete construction of the lift station upgrades by 

04/01/03.

6 OK City of Blackwell This Order addressed failure to report bypasses.

6 OK City of Broken Bow This Order addressed discharges without a permit.
K-60

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 OK City of Bulter 07/28/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Chandler This Order addressed discharges without a permit.

6 OK City of Claremore 07/26/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Claremore This Order addressed discharges without a permit.

6 OK City of Cleveland This Order addressed discharges without a permit.

6 OK City of Clinton This Order addressed discharges without a permit.

6 OK City of Clinton 10/10/94 

Closed

This Order addressed violation of discharge permit.

6 OK City of Cordell 12/01/99 

Closed

This Order addressed violation of discharge permit.

6 OK City of Corn 10/16/98 

Closed

This Order addressed discharges without a permit.

6 OK City of Coweta 04/11/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Davis 12/15/99 

Closed

This Order addressed unpermitted bypass from manholes.

6 OK City of Del City 11/19/98 

Closed

This Order addressed discharges without a permit.

6 OK City of Durant This Order addressed discharges without a permit.

6 OK City of Durant 01/26/96 

Closed

This Order addressed discharges without a permit.

6 OK City of Durant 10/10/95 

Closed

This Order addressed unpermitted bypasses.

6 OK City of El Reno This Order addressed discharges without a permit.

6 OK City of El Reno 04/24/00 

Closed

This Order addressed discharges without a permit.

6 OK City of El Reno 11/16/00 

Closed

This Order addressed unreported sewage bypasses.

6 OK City of El Reno 07/10/95 

Closed

This Order addressed discharges without a permit.

6 OK City of El Reno This Order addressed discharges without a permit.

6 OK City of El Reno 07/10/95 

Closed

This Order addressed discharges without a permit.

6 OK City of El Reno 08/01/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Elgin This Order addressed discharges without a permit.

6 OK City of Elk City 02/13/97 

Closed

This Order addressed exceeding discharge limits.

6 OK City of Elk City 10/01/95 

Closed

This Order addressed exceeding discharge limits.

6 OK City of Elmore City 10/21/02 This Order addressed discharges without a permit. The City was 

required to complete construction on the collection system 

upgrades by 12/01/03.

6 OK City of Enid 02/05/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Enid 06/12/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Fairview 07/10/95 

Closed

This Order addressed discharge violations.

6 OK City of Fairview 05/19/95 

Closed

This Order addressed violation of discharge permit.

6 OK City of Glenpool 03/06/01 

Closed

This Order addressed exceeding discharge limits.

6 OK City of Guthrie This Order addressed bypasses.
 Appendix K

K-61

Region State Case Name/City Name Effective Date Description

6 OK City of Haileyville 03/15/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Haileyville 08/27/96 

Closed

This Order addressed discharges without a permit.

6 OK City of Hartshorne 02/22/96 

Closed

This Order addressed bypass from manhole.

6 OK City of Healdton 08/01/02 This Order addressed discharges without a permit. The City was 

required to complete construction on the collection system 

upgrades by 12/01/03.

6 OK City of Heavener 05/25/99 

Closed

This Order addressed discharge of sewer, failure to sample, and 

bypassing.

6 OK City of Heavener 05/25/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Henryetta This Order addressed discharges without a permit.

6 OK City of Henryetta 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Henryetta 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Hobart This Order addressed discharges without a permit.

6 OK City of Hobart This Order addressed discharges without a permit.

6 OK City of Holdenville 11/07/02 This Order addressed discharges without a permit. The City was 

required to complete construction of improvements at the Heritage 

Village by 09/01/03, and complete construction of improvements to 

eliminate the connections between the storm sewer and the 

sanitary sewer systems within 12 months of obtaining adequate 

funding.

6 OK City of Holdenville 05/30/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Holdenville 07/11/95 

Closed

This Order addressed discharges of sewage effluent.

6 OK City of Hollis 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Hooker 10/29/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Hugo 09/25/98 

Closed

This Order addressed discharges without a permit.

6 OK City of Hugo 02/01/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Hugo 08/14/98 

Closed

This Order addressed discharges without a permit.

6 OK City of Hugo 06/21/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Idabel 07/01/96 

Closed

This Order addressed discharges without a permit.

6 OK City of Kingfisher This Order addressed discharges without a permit.

6 OK City of Kingfisher 12/17/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Konawa 11/14/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Lawton 01/17/03 The City was required to complete construction/rehabilitation of 

Phase I by 07/01/05, and complete the flow monitoring assessment 

for Phase I by 01/01/06. The City was also required to complete 

construction/rehabilitation of Phase II by 07/01/12, and complete 

the flow monitoring assessment for Phase II by 01/01/13.

6 OK City of Lawton This Order addressed discharges without a permit.
K-62

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 OK City of Madill 08/27/96 

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK City of Marland 10/10/95 

Closed

This Order addressed discharge permit violations.

6 OK City of McAlester 04/15/98 

Closed

This Order addressed discharges without a permit.

6 OK City of McAlester 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK City of McAlester 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Minco 10/01/95 

Closed

This Order addressed the discharge of sewage effluent to Buggy 

Creek.

6 OK City of Moore This Order addressed discharges without a permit.

6 OK City of Moore 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Morris This Order addressed failure to obtain a discharge permit.

6 OK City of Noble This Order addressed discharges without a permit.

6 OK City of Noble This Order addressed discharges without a permit.

6 OK City of Norman 05/24/96 

Closed

This Order addressed bypass violations.

6 OK City of Nowata 05/18/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Nowata This Order addressed unpermitted bypasses.

6 OK City of Oklahoma City 03/21/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Oklahoma City This Order addressed noncompliance with discharge procedures.

6 OK City of Okmulgee 09/23/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Okmulgee 06/20/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Okmulgee 04/17/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Okmulgee 11/01/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Okmulgee This Order addressed discharges without a permit.

6 OK City of Owasso This Order addressed bypass of untreated wastewater from 

manholes.

6 OK City of Pawhuska This Order addressed discharges without a permit.

6 OK City of Pawhuska This Order addressed unpermitted bypasses.

6 OK City of Pawhuska This Order addressed discharges without a permit.

6 OK City of Pawnee This Order addressed sewage bypasses.

6 OK City of Pawnee 09/07/01 

Closed

This Order addressed exceedings of discharge limits.

6 OK City of Picher 09/15/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Piedmont 10/01/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Ponca 12/01/99 

Closed

This Order addressed sewage treatment discharges.

6 OK City of Poteau 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Poteau 09/26/00 

Closed

This Order addressed discharges without a permit.
 Appendix K

K-63

Region State Case Name/City Name Effective Date Description

6 OK City of Poteau 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Sand Springs 05/03/01 

Closed

This Order addressed unpermitted bypasses.

6 OK City of Sand Springs 11/10/94 

Closed

This Order addressed unpermitted bypasses.

6 OK City of Sapulpa 06/20/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Sapulpa 09/26/02 This Order addressed discharges without a permit. The City was 

required to complete construction of the collection system 

improvements by 04/01/03.

6 OK City of Seminole 03/15/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Seminole This Order addressed eliminating defects contributing to bypasses.

6 OK City of Spencer This Order addressed discharges without a permit.

6 OK City of Stillwater 04/12/01 

Closed

This Order addressed discharges without a permit.

6 OK City of Sulphur 10/16/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Sulphur This Order addressed discharges without a permit.

6 OK City of Tonkawa 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK City of Valliant 10/03/97 

Closed

This Order addressed discharges without a permit.

6 OK City of Watonga This Order addressed discharges without a permit.

6 OK City of Waynoka 05/31/95 

Closed

This Order addressed violations of discharge permit.

6 OK City of Weleetka This Order addressed, among other things, bypasses.

6 OK City of Wetumka This Order addressed discharges without a permit.

6 OK City of Wetumka This Order addressed discharges without a permit.

6 OK City of Wetumka This Order addressed discharges without a permit.

6 OK City of Wetumka 06/21/00 

Closed

This Order addressed discharges without a permit.

6 OK City of Wetumka 10/10/95 

Closed

This Order addressed violations of discharge permit.

6 OK City of Wewoka This Order addressed discharges without a permit.

6 OK City of Wewoka 10/07/99 

Closed

This Order addressed discharges without a permit.

6 OK City of Wewoka This Order addressed bypasses.

6 OK City of Wewoka 10/07/99 

Closed

This Order addressed violations of discharge.

6 OK City of Wilburton 02/08/02; 

Amended

10/14/02

This Order addressed discharges without a permit. The City was 

required to complete the previously approved Environmental 

Enhancement Project (EEP) by 04/01/04, and complete 

construction of the approved wastewater treatment facility (WWTF) 

Number S-20104 and associated lift stations at Facility Numbers S20103 and S-20105 by 11/01/04.

6 OK City of Wilson 07/11/95 

Closed

This Order addressed violations of discharge permit.

6 OK City of Wilson 07/11/95 

Closed

This Order addressed violations of discharge permit.

6 OK City of Woodward This Order addressed discharges without a permit.

6 OK City of Woodward This Order addressed discharges without a permit.
K-64

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 OK City of Woodward This Order addressed discharges without a permit.

6 OK City of Wynnewood 10/01/95 

Closed

This Order addressed discharges without a permit.

6 OK Delaware Public Works 

Authority

07/10/95

Closed

This Order addressed discharges without a permit.

6 OK Fairfax Public Works 

Authority

12/20/99

Closed

This Order addressed violation of discharge permit.

6 OK Fairfax Public Works 

Authority

10/10/95

Closed

This Order addressed discharges without a permit.

6 OK Grand Lake Public Works 

Authority

12/01/99

Closed

This Order addressed discharges without a permit.

6 OK Grand Lake Public Works 

Authority

05/26/95

Closed

This Order addressed discharges without a permit.

6 OK Green Country Sewer 

Company

 This Order addressed discharges without a permit.

6 OK Haskell County Water 

Company

06/04/97

Closed

This Order addressed discharges without a permit.

6 OK Haskell Public Works 

Authority

01/11/01

Closed

This Order addressed discharges without a permit.

6 OK Heavener Public Works 

Authority

07/11/95

Closed

This Order addressed discharges without a permit.

6 OK Helena Public Works 

Authority

07/11/95

Closed

This Order addressed discharges without a permit.

6 OK Hinton Public Works 

Authority

04/05/94

Closed

This Order addressed lagoon sewage effluent.

6 OK Hominy Public Works 

Authority

04/14/00

Closed

This Order addressed discharges without a permit.

6 OK Hugo Municipal Authority 07/11/95 

Closed

This Order addressed bypassing collection system.

6 OK Hugo Municipal Authority 12/01/99 

Closed

This Order addressed bypassing untreated sewage.

6 OK Hugo Municipal Authority 10/01/95 

Closing

This Order addressed unpermitted bypasses.

6 OK Hulbert Public Works 

Authority

08/04/93

Closed

This Order addressed discharges without a permit.

6 OK Jay Utilities Authority This Order addressed discharges without a permit.

6 OK Jay Utilities Authority This Order addressed discharges without a permit.

6 OK Jay Utilities Authority 10/10/95 

Closed

This Order addressed permit violations.

6 OK Jenks Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Jenks Public Works 

Authority

07/11/95

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Jenks Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Keota Public Works 

Authority

06/10/99

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Krebs Utilities Authority This Order addressed discharges without a permit.

6 OK Lakeland Water System 11/14/99 

Closed

This Order addressed discharges without a permit.

6 OK Marietta Public Works 

Authority

10/16/93 Closed This Order addressed unpermitted discharges.

6 OK Marietta Public Works 

Authority

10/16/93 Closed This Order addressed discharges without a permit.

6 OK Marietta Public Works 

Authority

06/19/98

Closed

This Order addressed discharge permit violations.
 Appendix K

K-65

Region State Case Name/City Name Effective Date Description

6 OK Muskogee Municipal 

Authority

 This Order addressed discharges without a permit.

6 OK Muskogee Municipal 

Authority

07/15/98

Closed

This Order addressed chronic bypasses.

6 OK Muskogee Municipal 

Authority

07/11/95

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Ochelata Utilities 

Authority

 This Order addressed systems overflows and bypasses.

6 OK Okay Public Works 

Authority

10/06/00

Closed

This Order addressed unpermitted bypasses.

6 OK Okemah Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Okemah Public Works 

Authority

01/26/00

Closed

This Order addressed discharges without a permit.

6 OK Okemah Utilities Authority 07/11/95 

Closed

This Order addressed unpermitted bypasses.

6 OK Owasso Public Works 

Authority

10/04/01

Closed

This Order addressed discharges without a permit.

6 OK Panama Public Works 

Authority

 This Order addressed unpermitted bypasses.

6 OK Pensacola Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Pocola Municipal 

Authority

08/24/99

Closed

This Order addressed unpermitted bypasses.

6 OK Pocola Municipal 

Authority

10/02/02 This Order addressed discharges without a permit.

6 OK Pocola Municipal 

Authority

11/22/94

Closed

This Order addressed discharges without a permit.

6 OK Quinton Public Works 

Authority

07/11/95

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Regional Metropolitan 

Utility Authority

07/11/95

Closed

This Order addressed discharge violations.

6 OK Ringling Municipal 

Authority

10/10/95

Closed

This Order addressed violations of discharge permit.

6 OK Sapulpa Municipal 

Authority

 This Order addressed discharges without a permit.

6 OK Sapulpa Public Works 

Authority

12/21/00

Closed

This Order addressed discharges without a permit.

6 OK Savanna Public Works This Order addressed discharges without a permit.

6 OK Savanna Public Works 

Authority

10/10/95

Closed

This Order addressed bypasses/permit limits.

6 OK Savanna Public Works 

Authority

12/21/00

Closed

This Order addressed discharges without a permit.

6 OK South Coffeyville Public 

Works Authority

 This Order addressed discharges without a permit.

6 OK Stroud Utilities Authority 09/23/97 

Closed

This Order addressed violations of discharge permit.

6 OK Tahlequah Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Town + A304 of Freedom This Order addressed unpermitted bypasses.

6 OK Town of Achille 08/27/96 

Closed

This Order addressed the Town discharging without a permit.

6 OK Town of Alderson 12/09/98 

Closed

This Order addressed the Town discharging without a permit.
K-66

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 OK Town of Alex 10/01/95 

Closed

This Order addressed, among other things, the Town discharging 

without a permit.

6 OK Town of Antlers 09/20/95 

Closed

This Order addressed bypasses/discharges without a permit.

6 OK Town of Antlers 12/01/99 

Closed

This Order addressed bypass and discharge violations.

6 OK Town of Antlers This Order addressed unpermitted bypasses.

6 OK Town of Antlers This Order addressed unpermitted bypasses.

6 OK Town of Antlers 03/10/00 

Closed

This Order addressed unpermitted bypasses.

6 OK Town of Arapaho 09/14/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Arkoma This Order addressed discharges without a permit.

6 OK Town of Atoka 08/15/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Blair 10/23/96 

Closed

This Order addressed discharges without a permit.

6 OK Town of Bokoshe This Order addressed discharges without a permit.

6 OK Town of Boswell 11/22/94 

Closed

This Order addressed discharges without a permit.

6 OK Town of Boynton 04/20/95 

Closed

This Order addressed unpermitted bypasses.

6 OK Town of Caddo This Order addressed discharges without a permit.

6 OK Town of Canute 06/23/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Canute This Order addressed discharges without a permit.

6 OK Town of Chelsea This Order addressed discharges without a permit.

6 OK Town of Cimarron City 07/27/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Copan 07/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Covington 10/10/01 

Closed

This Order addressed discharges without a permit.

6 OK Town of Crescent 05/18/95 

Closed

This Order addressed violation of discharge permit.

6 OK Town of Dacoma This Order addressed unpermitted bypasses.

6 OK Town of Davenport 07/18/94 

Closed

This Order addressed discharges without a permit.

6 OK Town of Deer Creek 07/10/95 

Closed

This Order addressed discharge permit violations.

6 OK Town of Deer Creek 07/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Devol 11/07/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Dill City 08/17/01 

Closed

This Order addressed discharges without a permit.

6 OK Town of Dougherty 10/01/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Dougherty This Order addressed discharges without a permit.

6 OK Town of East Duke 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Fairmont 10/10/95 

Closed

This Order addressed violation of discharge permit.

6 OK Town of Fargo 10/03/95 

Closed

This Order addressed discharges without a permit.
 Appendix K

K-67

Region State Case Name/City Name Effective Date Description

6 OK Town of Freedom 09/17/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Freedom 07/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Ft. Towson 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Gans 05/30/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Garvin 10/13/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Geronimo 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Gore This Order addressed unpermitted bypasses.

6 OK Town of Inola This Order addressed discharges without a permit.

6 OK Town of Jennings 07/11/95 

Closed

This Order addressed the exceeding discharge limits.

6 OK Town of Jet 09/14/92 

Closed

This Order addressed violation of discharge permit.

6 OK Town of Keota 01/18/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Kingston 10/06/94 Closed This Order addressed bypasses and discharges without a permit.

6 OK Town of Kingston 10/06/94 Closed This Order addressed discharges without a permit.

6 OK Town of Kiowa This Order addressed discharges without a permit.

6 OK Town of Krebs 09/12/97 

Closed

This Order addressed discharges without a permit.

6 OK Town of Kremlin 09/04/01 

Closed

This Order addressed discharges without a permit.

6 OK Town of Lamont This Order addressed unpermitted bypasses.

6 OK Town of Langston 01/09/03 This Order addressed discharges without a permit. The City was 

required to complete construction of the upgrades to the 

wastewater treatment plant within 14 months from the start of 

construction.

6 OK Town of Lone Wolf 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Mannford This Order addressed discharges without a permit.

6 OK Town of Maud This Order addressed discharges without a permit.

6 OK Town of Meeker 04/11/95 

Closed

This Order addressed bypassing.

6 OK Town of Meeker 04/10/92 

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Town of Muldrow 06/06/97 

Closed

This Order addressed discharges without a permit.

6 OK Town of Muldrow This Order addressed discharges without a permit.

6 OK Town of Nash This Order addressed discharges without a permit.

6 OK Town of Okarche 04/04/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Okarche This Order addressed discharges without a permit.

6 OK Town of Oktaha This Order addressed plant overload, no operator, and discharges.

6 OK Town of Panama 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Panama 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Panama 07/11/95 

Closed

This Order addressed violations of discharge permit.
K-68

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

6 OK Town of Pond Creek 09/12/95 

Closed

This Order addressed violations of discharge permit.

6 OK Town of Quinton 09/14/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Quinton This Order addressed discharges without a permit.

6 OK Town of Ralston 06/11/96 

Closed

This Order addressed discharges without a permit.

6 OK Town of Ratliff City 12/05/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Salina 10/20/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Salina 11/21/01 

Closed

This Order addressed unpermitted bypasses.

6 OK Town of Salina This Order addressed discharges without a permit.

6 OK Town of Skiatook 07/11/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Soper 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Soper 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Soper This Order addressed discharges without a permit.

6 OK Town of Soper 08/10/01 

Closed

This Order addressed discharges without a permit.

6 OK Town of Spiro 07/06/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Spiro This Order addressed discharges without a permit.

6 OK Town of Springer 11/25/96 Closed This Order addressed discharges without a permit.

6 OK Town of Temple 02/22/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Tipton 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Tryon 03/11/97 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wakita 09/19/94 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wanette This Order addressed discharges without a permit.

6 OK Town of Wanette 01/12/01 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wanette 12/01/99 

Closed

This Order addressed discharges without a permit.

6 OK Town of Washington 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wayne 12/09/98 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wayne 10/10/95 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wayne This Order addressed violations of discharge permit.

6 OK Town of Wellston 03/15/94 

Closed

This Order addressed the inadequate facility to treat sewage 

effluent.

6 OK Town of Wellston 03/15/94 

Closed

This Order addressed violations of discharge permit.

6 OK Town of Wister 02/01/87 

Closed

This Order addressed bypass of raw sewage.
 Appendix K

K-69

Region State Case Name/City Name Effective Date Description

6 OK Town of Wister 07/06/00 

Closed

This Order addressed discharges without a permit.

6 OK Town of Wright City 01/08/02 

Closed

This Order addressed discharges without a permit.

6 OK Tulsa Metropolitan Utility 

Authority

08/20/91

Closed

This Order addressed discharges without a permit.

6 OK Tulsa Metropolitan Utility 

Authority

 This Order addressed discharges without a permit.

6 OK Tulsa Metropolitan Utility 

Authority

08/08/98

Closed

This Order addressed discharges without a permit.

6 OK Valliant Public Works 

Authority

07/19/96

Closed

This Order addressed violations of discharge permit.

6 OK Wagoner Public Works 

Authority

 This Order addressed discharges without a permit.

6 OK Wagoner Public Works 

Authority

06/04/93

Closed

This Order addressed infiltration problems and bypasses.

6 OK Warner Utilities Authority This Order addressed discharges without a permit.

6 OK Warner Utilities Authority This Order addressed discharges without a permit.

6 OK Warr Acres Public Works 

Authority

07/01/93

Closed

This Order addressed discharges without a permit.

6 OK Warr Acres Public Works 

Authority

07/01/93

Closed

This Order addressed discharges without a permit.

6 OK Weleetka Public Works 

Authority, City of 

Weleetka

10/14/02 This Order addressed discharges without a permit. The City was 

required to complete construction of the collection system 

improvements by 12/01/03.

6 OK Wilburton Public Works 

Authority

10/10/95 Closed This Order addressed violations of discharge permit.

6 OK Wright City Public Works 

Authority

10/01/95

Closed

This Order addressed violations of discharge permit.

6 OK Wright City Public Works 

Authority

01/25/99

Closed

This Order addressed violations of discharge permit.

9 CA City of Chico, Central 

Valley Region

2000 The Order required the City to submit a detailed workplan and 

timeline which were supposed to include dates for submission of 

progress reports and for completion of the Supplemental 

Environmental Project (SEP). A $50,000 civil liability penalty was 

assessed.

9 CA City of Crescent City, 

North Coast Region

2000 This Order established a schedule for the City to complete the longterm planning process to provide adequate wastewater treatment 

capacity.

9 CA City of Folsom, Central 

Valley Region

2000 This Order addressed discharges of pollutants without waste 

discharge requirements. A civil liability penalty of $70,000 was 

proposed.

9 CA City of Los Angeles, Los 

Angeles Region

2000 This Order required the City to upgrade sewers in the Hyperion 

service area, such upgrades included: implement the corrective 

measures for Boyle Heights and Silver Lake, construct the North 

Hollywood Interceptor Sewer, the North Outfall Relief Sewer (NOS)-

East Central Interceptor Sewer (ECIS), the Northeast Interceptor 

Sewer (NEIS) - Eagle Rock Blvd. to Mission Rd., and the Eagle 

Rock Area Relief Sewer Phases 2B, 2C, and 2D. Additionally, the 

City was required to reduce the risk of SSOs by bypassing filtration 

processes at the Tillman and LA/Glendale Plants under specified 

conditions until completion of the ECIS and NEIS projects.
K-70

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

9 CA City of Pacifica, Calera 

Creek Water Recycling 

Plant

 This Order required the City to either pay a civil liability in the 

amount of $125,033 or, pay a $10,000 and complete a SEP in the 

amount of $115,033.

9 CA Coachella Valley Water 

District, Colorado River 

Basin Region

2001 This Order addressed the discharge of untreated wastewater to the 

Coachella Branch of the All American Canal and Lake Cahuilla.

9 CA Fort Bragg Municipal 

Improvement District No. 

1, WWTF

03/22/01 This was a Cease and Desist Order which modified the time 

schedule of a previous Order to reflect a nine month delay in the 

NPDES permit renewal. 

9 CA Fort Bragg Municipal 

Improvement District No. 

1, WWTF

03/28/02 This Order addressed their request to adjust the 2001 time 

schedule to reflect delay in permit renewal, with the exception of 

those tasks already completed.

9 CA Long Beach Water 

Reclamation Plant, Long 

Beach

07/11/02 The Order required them to complete construction of the modified 

process for nitrification and de-nitrification, submit a pollution 

prevention plan (PPP) workplan with a time schedule for 

implementation of the construction, achieve compliance with its 

permit, and submit quarterly progress reports.

9 CA Los Coyotes Water 

Reclamation Plant, 

Cerritos

07/11/02 The Order required them to complete construction of the modified 

process for nitrification and de-nitrification, submit a PPP workplan 

with a time schedule for implementation of the construction, achieve 

compliance with its permit, and submit quarterly progress reports.

9 CA Orange County Sanitation 

District (OCSD), Fountain 

Valley

 This Order addressed the release and spill of approximately 

122,000 gallons of sewage. An estimated 20,000 gallons was 

recovered and an estimated 102,000 gallons entered Newport Bay. 

As a result of this spill a precautionary beach closure for all 

beaches within the western half of Newport Bay was issued for six 

days.

9 CA Orange County Sanitation 

District (OCSD), Fountain 

Valley

10/12/00 This Order addressed an estimated 60,600 gallons of sewage 

overflowing from a manhole in Beach Blvd., approximately 200 feet 

south of Imperial Highway. As a result, sewage flowed 

approximately 1,000 feet to a storm drain drop inlet and eventually 

entered Coyote Creek. An estimated 1,000 gallons of sewage was 

recovered, and approximately 59,600 gallons were not recovered.

9 CA Sonoma County 

Sanitation District, City of 

Sonoma

05/23/01 Two Administrative Orders were issued addressing violations of its 

NPDES permit limits during two separate periods. Action was taken 

to address their pollution prevention/ source reduction and 

pretreatment programs not being managed adequately or 

implemented aggressively enough.

9 CA Sonoma County 

Sanitation District, City of 

Sonoma

04/01/02 This Order required them to cease and desist from discharging 

wastes in violation of its NPDES permit and, they were required to 

continue and expand its current "Zinc Source Identification and 

Reduction Study." The Order also indicated that if they were 

successful in identifying the sources of zinc in its effluent, then a 

workplan identifying all necessary courses of actions to reduce the 

zinc in its treatment plant influent and effluent.
 Appendix K

K-71

Region State Case Name/City Name Effective Date Description

9 CA Whittier Narrows Water 

Reclamation Plant, El 

Monte

08/29/02 The Order required them to complete construction of the modified 

process for nitrification and de-nitrification, submit a PPP workplan 

with a time schedule for implementation of the construction, achieve 

compliance with its permit, and submit quarterly progress reports.

9 CA Yucaipa Valley Water 

District, Yucaipa

01/24/03 This Order addressed 28 effluent limit violations and a penalty of 

$84,000 was assessed. They agreed to perform a SEP that would 

benefit the Upper Santa Ana Watershed, contributing $49,500 

towards the cleanup of the perchlorate contamination in the ColtonRialto area.

10 OR City of Albany 05/16/01 The City was required to complete constructin and attain 

operational level of the Maple Street pump station and force main 

upgrades by 10/31/02, and complete construction and attain 

operational level of the approved treatment facility improvements by 

12/31/09. A $107,5000 civil liability was imposed.

10 OR City of Amity 03/01/00 Under this Order, the City was required to submit construction plans 

and specifications for upgrading the drinking water system and 

complete the necessary upgrades or improvements within 22 

months of this Order. They were also required to submit a 

Reclaimed Water Use Plan outlining the minimum rule 

requirements for how the City will achieve compliance and a final 

Phase I and Phase II construction plans and specifications for 

completing improvements to the WWTP.

10 OR City of Amity Amendment 

04/12/00

This amendment to the March 2000 Order approved the City's 

request for an extension to one compliance date requiring the City 

to submit a Reclaimed Water Use Planby 10/01/00.

10 OR City of Amity Amendment

11/02/00

This amendment to the March 2000 Order approved the City's 

request for an extension to one compliance date requiring the City 

to submit a Reclaimed Water Use Planby 02/01/01.

10 OR City of Amity Amendment

03/28/02

This amendment required them to, among other things, complete all 

necessary upgrades to the drinking water system by 09/01/02. 

Additionally, by 05/20/02, they were required to submit engineering 

plans and specifications for the entire wastewater improvement 

project and by 10/01/03, complete the upgrades to the wastewater 

treatment facilities.

10 OR City of Amity Amendment 

05/17/02

This amendment approved the request for an extension to the 

engineering plans and specifications from 05/20/02 to 07/30/02.

10 OR City of Ashland 02/06/95 This Order required the City to submit to the Department for 

approval a complete facilities plan by 10/95.

10 OR City of Brookings 04/16/92 Under this Order, the City was required to complete construction on 

the facultative sludge lagoon(s) and associated structures by 

11/01/93, and complete construction on the Wastewater Treatment 

Plant Improvement Project by 12/01/94.
K-72

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

10 OR City of Coos Bay, WWTF 

#1

08/21/03 This Order addressed the prevention of future waste discharge 

violations. The Order required that within 12 months of approval of 

the final engineering Plans and Specifications, the City will 

complete construction of the wastewater control facilities.

10 OR City of Coos Bay, WWTF 

#2

08/21/03 This Order required that within two years after award of a contract 

for construction, the City will complete construction of the approved 

wastewater control facilities and initiate operations.

10 OR City of Falls City, OR 04/04/00 This Order required that within six months following the 

Department's approval of the Final Plans and Specifications, the 

City will complete the removal of the Fair Oaks Pump Station and 

replace it with a gravity line. They were also required to complete 

the necessary optimization/upgrades to the WWTF.

10 OR City of Garibaldi 10/01/02 The Order required the City to complete the upgrades/expansion to 

the WWTFs as specified in the approved engineering Plans and 

Specifications and comply with all permit requirements, State, and 

Federal regulations and water quality standards by 05/31/04.

10 OR City of Glendale 11/03/98 This Order required the City to complete the necessary upgrades or 

improvements to the drinking water system and achieve compliance 

with all applicable drinking water requirements by 09/30/01, 

complete the removal of inflow sources identified and prioritized in 

the Inflow Evaluation and Reduction Report for the WWTFs by 

10/01/00, and complete the necessary upgrades/expansion to the 

WWTFs and comply with all permit requirements, State, and 

Federal regulations and water quality standards by 12/31/03.

10 OR City of Grants Pass 10/24/01 The Order required that within two years of Department approval of 

diffuser Plans and Specifications, the City will complete 

construction of the effluent diffuser.

10 OR City of Lowell, OR 11/08/01 This Order required that within 18 months after award of the 

construction contract, the City will complete construction 

upgrades/expansions required by the approved engineering Plans 

and Specifications.

10 OR City of McMinnville 04/05/93 The Order required the City to upgrade and repair its sewage 

collection system pursuant to the approved overall I/I Correction 

Plan by 10/31/99.

10 OR City of Medford 12/27/02 This Order required the City to complete construction of Phase I of 

the City's Best Management Practices (BMPs) by 06/02/03, and 

complete construction of Phase II of the City's BMPs by 03/01/04.

10 OR City of Monroe 11/03/98 This Order required the City to complete the necessary upgrades or 

improvements to the drinking water system by 01/02/01, install and 

operate an influent flow meter at the treatment plant site by 

10/31/98, complete the removal of all inflow sources identified in 

the approved Pre-Design Report by 11/01/03, and complete the 

necessary upgrades/expansion to the WWTFs by 11/01/06.
 Appendix K

K-73

Region State Case Name/City Name Effective Date Description

10 OR City of Myrtle Creek 05/30/02 This Order required the City to have wastewater control facilities in 

operation to comply with water quality standards immediately upon 

approval of Plans and Specifications and have the WWTF will be 

constructed and operational by 12/31/04.

10 OR City of Powers 12/29/00 This Order required the City to complete Phase I by 10/01/03, and 

no later than the same time as completion of Phase I, the City will 

complete monitoring of flows in the collection lines, complete Phase 

II by 10/01/02, and complete all upgrades to the WWTP and 

comply with all NPDES permit conditions by 10/01/05.

10 OR City of Rainier 12/15/95 The City was required to complete the upgrades to the drinking 

water treatment facility within 15 months following approval of the 

Plans and Specifications. Additionally, they were required to 

complete Phase I of the interim improvements to the WWTF by 

01/02/96, complete Phase II of the interim improvements to the 

WWTF by 01/02/97, and complete the decommissioning of the 

underground storage tanks (USTs) within four months of approval 

of the decommissioning plan.

10 OR City of Salem 01/21/98 This Order required the City to complete construction and initiated 

operation of the approved facilities and complete construction for all 

projects identified in the Salem Master Plan for the purposes of 

eliminating overflows to tributary streams by 01/01/00, and 

eliminate all SSOs by 12/31/09.

10 OR City of Sweet Home 01/19/99 This Order required the City to complete the removal of all 

reasonably removable inflow sources into the City's wastewater 

collection system by 01/15/00. Within two years after award of 

construction contracts, the City will complete construction of the 

wastewater improvements.

10 OR City of Sweet Home Modification 

1/19/01

This Order required the City to submit a draft facility plan and time 

schedule that evaluates alternatives for either increasing treatment 

capacity or reducing raw sewage flows down to the current 

treatment capacity by 10/31/05.

10 OR City of Sweet Home 05/09/01 This was a modification approving the City's request to extend the 

compliance deadlines.

10 OR City of Tillamook 01/06/03 This Order required the City to complete construction of a new 

digester supernatant pump station and modifications and repairs for 

the RBCs as required in the approved Plans and Specifications for 

the expanded Corrective Action Plan by 05/01/03. Additionally, the 

City was required to complete construction of the modifications to 

the facilities and repairs to the wastewater treatment facilities as 

required by the approved plans and specifications for the expanded 

Corrective Action Plan by 07/31/03.

10 OR City of Toledo 11/15/00 This Order required that within 24 months after award of the 

construction contract, the City will complete construction of the 

necessary improvements.

10 OR City of Warrenton 12/24/01 This Order required that within 15 months of awarding contracts for 

construction, the construction of the approved Plans and 

Specifications will be complete.
K-74

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Description

10 OR City of Willamina 09/26/96 This Order required that within 12 months following the award of the 

construction contract, the City will complete construction of the 

necessary Phase I and Phase II improvements. By 07/01/03, the 

City will complete inflow corrective work.

10 OR Clackamas County 

Service District #1, 

Oregon City

01/13/94 The Order required the County to have their wastewater control 

facilities in compliance with the water quality standards for chlorine 

by 12/31/94.

10 OR Oak Lodge Sanitary 

District, Clackamas 

County

05/17/95 This Order required the District to have wastewater control facilities 

in operation to comply with the water quality standards for chlorine 

by 12/31/98.

10 OR Roseburg Urban Sanitary 

Authority, Douglas County

06/27/94 This Order required the Authority to complete construction and 

installation of the back-up power generators at the Goedeck Waste 

Water Treatment Plant by 02/15/95.

10 OR Roseburg Urban Sanitary 

Authority, Douglas County

09/30/92 This Order required that within eighteen months after approval of 

the engineering Plans and Specifications, the City will complete 

construction of the necessary improvements.

10 OR Tri-City Service District, 

Clackamas

02/28/94 This Order required the District to complete the planning, designing, 

financing, and construction to increase the pump station capacity to 

accommodate a one in five year event and thereby substantially 

relieve bypass/overflows from certain discharge points by 07/01/97.

FL FL City of St. Petersburg 02/04/00 The Order required the City to budget appropriate monies, 

implement, and complete the recommendations for improvements 

to the Facilities and Systems established in the Final Report. They 

were also required to immediately initiate the capital improvements 

set forth in the Order, which were expected to be complete within 

seven years. In lieu of a $391,533 civil penalty, they elected to 

implement several in-kind penalty projects.
 Appendix K

K-75

K.11 State CSO Administrative Penalty Orders

Region State Case Name/City Name Effective Date Penalty Amount

1 ME City of Bath 01/09/92 $14,000 

1 ME City of Biddeford 07/22/91 $24,000 

1 ME City of Brewer 02/27/92 $75,000 

1 ME Town of Lisbon 05/24/90 $10,400 

2 NJ Camden County Municipal Utilities Authority 07/11/98 $1,886 

2 NJ City of Camden 08/23/99 $17,680 

2 NJ City of Gloucester 07/22/99 $9,875 

2 NJ City of Newark 05/09/01 $30,709 

2 NJ City of Paterson 02/01/99 $15,000 

2 NJ City of Rahway 05/08/00 $8,953 

2 NJ Middlesex County Utilities Authority 04/13/95 $336,750 

2 NJ Middlesex County Utilities Authority (MCUA) 06/05/96 $54,000 

4 TN Metropolitan Government of Nashville and 

Davidson County

09/17/99 $600,000

5 IN Bluffton POTW 06/06/03 $60,000

5 IN City of Sullivan 01/22/03 $575 

5 IN Town of Remington 06/06/03 $825 

5 IN Town of Ridgeville 10/15/01 $750 

5 IN Town of Sullivan 01/22/03 $2,625 
K-76

Report to Congress on the Impacts and Control of CSOs and SSOs
 Appendix K

K-77

K.12 State SSO Administrative Penalty Orders

Region State Case Name/City Name Effective Date Penalty Amount

4 AL Demopolis Water Works and Sewer Board, City of 

Demopolis

08/02/01 $5,300 

4 AL Stevenson Utilities Board, Stevenson Wastewater 

Treatment Lagoon, Stevenson 

01/09/02 $1,300 

4 NC Belmont City-A Sludge/Lars 10/30/01 $4,234

4 NC Mebane Bridge WWTP 01/25/02 $1,774

4 NC Morrisville Town-Carpenter Plant 04/11/00 $7,421

4 NC Murfreesboro Town-WWTP 10/11/00 $4,240

4 NC Neuse Crossing WWTP 02/17/00 $10,801

4 NC Pond Creek WWTP 01/25/02 $4,100

4 NC Sanford WWTP 11/25/02 $18,214

4 NC Sanford WWTP 07/09/03 $19,423

4 NC Town of Canton 03/27/00 $21,742

4 NC Town of Green Level 03/16/01 $5,862

4 NC Warsaw WWTP 08/03/00 $12,517

4 NC Wrenn Road Spray Irrigation Facility 03/16/01 $7,295

4 TN City of Alexandria 10/02/02 $104,000 

4 TN City of Bluff City 07/25/98 $17,750 

4 TN City of Church Hill 04/02/97 $5,000 

4 TN City of East Ridge 04/29/96 $30,000 

4 TN City of Franklin 10/26/99 $6,326 - Damage Fee; $3,750 - 

Civil Penalty

4 TN City of Franklin 11/13/00 $78,295 - Damage Fee; $57,500 

Civil Penalty

4 TN City of Greenbrier 03/20/00 $141,750 

4 TN City of Harriman 06/28/00 $266,250 

4 TN City of Harriman 07/23/02 $30,000 

4 TN City of Jellico 10/03/97 $11,500 

4 TN City of Kingston 11/30/01 $207,000 

4 TN City of Lafayette 04/22/03 $92,500 

4 TN City of LaVergne 11/08/99 $2,500 

4 TN City of LaVergne 10/24/00 $2,000 

4 TN City of Lawrenceburg 03/27/01 $9,375 

4 TN City of Middleton 08/25/00 $47,750 

4 TN City of Murfreesboro 08/21/99 $400,000 

4 TN City of Murfreesboro 05/22/01 In lieu of paying the $50,000 

civil penalty, the City agreed 

to perform a Supplemental 

Environmental Project (SEP). 

The City was supposed to 

purchase a five-acre lot which 

had a wetland.

4 TN City of Portland Public Works 08/02/02 $541 - Damage Fee; $5,000 - 

Penalty Fee

4 TN City of Red Bank 02/25/97 $164,500 

4 TN City of Rockwood 10/29/98 $16,750 

4 TN City of Sparta 10/04/00 $62,000 

4 TN City of Watertown 02/08/00 $1,100 

4 TN City of Watertown 06/03/03 $87,500 
K-78

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Penalty Amount

4 TN Knoxville Utilities Board 05/20/03 $475,000 

4 TN Lynnwood Utility Corporation $5,000 

4 TN Metropolitan Government of Nashville and 

Davidson County

09/17/99 Of the total $600,000 penalty, 

$100,000 was due within one 

month of this Order. However, 

in lieu of the $100,000, they 

agreed to perform a SEP.

4 TN Town of Collierville 06/03/98 $118,500 

4 TN Town of Gainesboro 11/22/00 $67,625 

4 TN Town of Gainesboro 03/27/01 $5,500 

4 TN Town of Monterey 09/11/02 $115,500 

4 TN Town of Mosheim 04/25/01 $3,000 

4 TN Town of Pikeville 01/09/00 $58,250 

4 TN Town of Spring City 07/31/03 $15,000 

4 TN Town of Spring Hill 01/26/00 $73,312 

6 OK City of Holdenville 11/07/02 $5,000 

9 CA California Department of Corrections, Sierra 

Conservation Center WTF, Tuolumne County

06/01/01 $96,000 

9 CA California Department of Parks and 

Recreation, Angel Island State Park

 $33,000

9 CA California Department of Parks and 

Recreation, Big Basin Redwoods State Park 

WWTP

09/20/02 $135,000

9 CA California Men's Colony San Luis Obispo 

County and Indirect Dischargers and Local 

Sewering Entities of Camp San Luis Obispo, 

Cuesta College, San Louis Obispo County 

Educational Center, and San Luis Obispo 

County Operational Facility 

10/26/01 $87,000 

9 CA Carpinteria Sanitary District, Santa Barbara 

County

04/09/01 $6,000 

9 CA Cedars-Sinai Medical Center, Imaging 

Building

09/27/02 $3,000

9 CA Centinela State Prison WWTF, Imperial 

County

04/30/01 $33,000 

9 CA Centinela State Prison WWTF, Imperial 

County

2000 $9,000 

9 CA Central Marin Sanitation Agency, San Rafael, 

Marin County

 $15,000

9 CA Central Marin Sanitation District, San Rafael, 

Marin County

2001 $6,000 

9 CA Cities of South San Francisco and San Bruno 

Water Quality Control Plant

07/16/03 $81,000

9 CA City and County of San Francisco, Southeast 

Water Pollution Control Plant

 $3,000
 Appendix K

K-79

Region State Case Name/City Name Effective Date Penalty Amount

9 CA City of Anderson Water Pollution Control 

Plant, Shasta County

 $3,000

9 CA City of Anderson Water Pollution Control 

Plant, Shasta County

 $10,000 

9 CA City of Anderson Water Pollution Control 

Plant, Shasta County

2000 $3,000 

9 CA City of Anderson Water Pollution Control 

Plant, Shasta County

 $10,000 

9 CA City of Atwater WWTF, Merced County 2000 $36,000 

9 CA City of Atwater WWTF, Merced County 04/27/01 $30,000 

9 CA City of Benicia WWTP, Solano County 2000 $3,000 

9 CA City of Benicia WWTP, Solano County 2000 $9,000 

9 CA City of Benicia WWTP, Solano County 10/29/2001 $18,000 

9 CA City of Brawley WWTF, Imperial County 03/15/02 $33,000

9 CA City of Brawley WWTF, Imperial County 2001 $6,000

9 CA City of Brawley WWTF, Imperial County 2000 $3,000 

9 CA City of Brentwood WWTP, Contra Costa 

County

07/26/01 $243,000 

9 CA City of Burlingame, San Mateo County 12/21/01 $3,000 

9 CA City of Chico WWTF, Butte County 01/29/00 $6,000 

9 CA City of Chico WWTF, Butte County $100,000 

9 CA City of Corona 2000 $15,000 

9 CA City of Corona 2001 $288,000 

9 CA City of Coronado, Glorietta Bay Pump Station 

Construction Dewatering

10/09/02 $39,000

9 CA City of El Centro WWTP $15,000 

9 CA City of Escondido Hale Avenue Resource 

Recovery Facility, San Diego County

07/27/00 $3,000 

9 CA City of Escondido, San Diego County 09/29/00 $6,000 

9 CA City of Lakewood, Department of Water 

Resources

05/09/02 $3,000

9 CA City of Livermore, Alameda County $15,000

9 CA City of Morro Bay and Cayucos Sanitary 

District WWTP, San Luis Obispo County

10/07/03 $12,000

9 CA City of Palo Alto, Santa Clara County $12,000

9 CA City of Pasadena Department of Water and 

Power (Power Plant)

08/19/02 $6,000

9 CA City of Petaluma, Sonoma County 02/01/02 $30,000

9 CA City of Redondo Beach, Seaside Lagoon 03/29/02 $51,000

9 CA City of Rialto 08/02/02 $30,000

9 CA City of Rio Vista Trilogy WWTF, Solano 

County

07/10/02 $3,000

9 CA City of Rio Vista WWTF, Solano County 07/10/02 $6,000

9 CA City of San Diego, San Diego Convention 

Center Dewatering

04/25/02 $81,000 

9 CA City of San Mateo Wastewater Treatment 

Plant, San Mateo County

01/24/03 $39,000

9 CA City of Santa Cruz 07/30/02 $40,000

9 CA City of Santa Rosa, Laguna Subregional 

WWT, Reuse, and Disposal Facilities

04/30/02 $15,000
K-80

Report to Congress on Impacts and Control of CSOs and SSOs

Region State Case Name/City Name Effective Date Penalty Amount

9 CA City of Santa Rosa, Subregional Wastewater 

Treatment, Reuse and Disposal Facilities

05/02/02 $12,350

9 CA City of Vacaville WWTP, Solano County 07/10/02 $27,000

9 CA Coachella Sanitary District WWTF Coachella, 

Riverside County

 $45,000

9 CA Coachella Sanitary District WWTF, Riverside 

County

04/30/01 $27,000 

9 CA Coachella Sanitary District WWTF, Riverside 

County

04/30/01 $3,000 

9 CA Coachella Sanitary District WWTF, Riverside 

County

2001 $51,000 

9 CA Coachella Sanitary District, Owner/Operator 

Coachella Sanitary District WWTF Coachella, 

Riverside County

03/15/02 $24,000

9 CA Coachella Valley Water District WWTP $20,000 

9 CA Colton/San Bernardino Regional Tertiary 

Treatment and Water Reclamation Authority

08/02/02 $54,000

9 CA County of Los Angeles Department of Parks 

and Recreation, Val Verde County Park 

Swimming Pool

09/23/02 $21,000

9 CA County of Los Angeles Department of Public 

Works Alamitos Barrier Project (San Gabriel 

River), Long Beach

09/27/02 $24,000

9 CA County of Los Angeles Department of Public 

Works Storm Drain Project 9037

12/05/02 $6,000

9 CA Department of Public Works City of Los 

Angeles, Marina Interceptor Sewer

09/27/02 $51,000

9 CA East Bay Municipal Utility District, Orinda 

WTP, Contra Costa County

 $9,000

9 CA East Bay Municipal Utility District, Orinda 

WTP, Contra Costa County

 $25,000 

9 CA Eastern Municipal Water District 06/22/00 $10,000 

9 CA Fairfield Suisun Sanitary District, Solano 

County

 $9,000

9 CA Fallbrook Public Utility District 12/11/02 $87,000

9 CA Fallbrook Public Utility District WWTP No.1, 

San Diego

10/24/02 $87,000

9 CA Harris Water Conditioning, Inc., Culligan Soft 

Water

02/07/02 $9,000

9 CA Las Virgenes Municipal Water District, Tapia 

Water Reclamation Plant, Calabasas

03/27/02 $12,000

9 CA Mt. View Sanitary District, Contra Costa 

County

 $3,000

9 CA Napa Sanitation District, Napa County $153,000

9 CA Natural History Museum of Los Angeles 

County

08/19/02 $3,000
 Appendix K

K-81

Region State Case Name/City Name Effective Date Penalty Amount

9 CA Rancho California Water District, Santa Rosa 

Water Reclamation Facility, Riverside County

03/13/02 $66,000

9 CA Rancho California Water District, Well No. 

121

12/11/02 $3,000

9 CA Rodeo Sanitary District, Contra Costa County $33,000

9 CA San Francisco International Airport, Water 

Quality Control Plant

 $27,000

9 CA Sewerage Agency of Southern Martin, Mill 

Valley, Marin County

 $6,000

9 CA Southern California Water Company, Yukon 

Plant

01/11/02 $21,000

9 CA State of California Department of Corrections, 

Centinela State Prison WWTF, Imperial 

County

 $6,000

9 CA The City of Chico WWTF, Butte County $9,000

9 CA The City of Santa Cruz 09/20/02 $40,000

9 CA University of California at Los Angeles 03/06/01 $6,000

9 CA West County Wastewater District, Contra 

Costa County

 $192,000

9 CA Western Riverside County Regional 

Wastewater Authority

01/18/02 $96,000

9 CA Yucaipa Valley Water District $39,000

9 CA Yucaipa Valley Water District $48,000

10 OR City of Albany 05/16/01 $5,080 
Appendix L 

Technology Descriptions

L.1 Operation and Maintenance 

 Practices

Sewer Testing and Inspection 

 Techniques

 Sewer Cleaning Techniques

 Pollution Prevention

Monitoring, Reporting, and 

 Public Notification

L.2 Collection System Controls

Maximizing Flow to Treatment 

 Plant

 Monitoring & Real-Time Control

 Inflow Reduction

 Sewer Separation

 Sewer Rehabilitation

 Service Lateral Rehabilitation

 Manhole Rehabilitation

L.3 Storage Facilities

In-line Storage

 Off-line Storage

 On-site Storage

L.4 Treatment Technologies

Supplemental Treatment

 Plant Modifications

 Disinfection

 Vortex Separators

 Floatables Control

L.5 Low-Impact Development 

 Techniques

Porous Pavement

 Green Roofs

 Bioretention

 Water Conservation

TECHNOLOGY DESCRIPTION

Sewer Testing and 

Inspection Techniques

OPERATION & MAINTENANCE

Overview

Operations and maintenance practices, such as sewer 

testing and inspection, enhance sewer system performance. 

Specifically, testing and inspection practices ensure that 

new connections are made correctly, help locate and protect 

against unwanted inflow and infiltration (I/I), and assess 

the structural condition of the sewer system. Inspection 

techniques can also be useful in identifying locations 

where grease and debris accumulate or where roots intrude 

into the sewer, which can cause sewer blockages resulting 

in unexpected CSOs and SSOs. The keys to a successful 

sewer testing and inspection program are identification 

of potential or current problem locations; correction of 

the problem; and evaluation of the effectiveness of the 

corrective measures.

Sewer Testing Techniques

In general, sewer testing techniques are used to identify 

leaks which allow unwanted infilitration into the sewer 

system and determine the location of illicit connections 

and other sources of storm water inflow. Air testing and 

hydrostatic testing are used to identify leaks in the sewer 

system. Smoke testing is used to determine connectivity 

and to identify points where inflow to the sewer system can 

occur. These testing techniques are described in further 

detail below.

Air Testing

Air testing is used to determine if a particular section 

of sewer line has leaks that would allow unwanted 

groundwater to infi ltrate into the system or sewage 

to exfi ltrate into the surrounding soil. Plugs, such 

as infl atable stoppers, are placed at either end of the 

test section, and in all service connections to the 

section. The test section is pressurized with air. After 

the pressure is allowed to stabilize, it is monitored 

for a predetermined amount of time. The acceptable 

range of pressure drop and the duration of the test are 

based on the pipe material and diameter, detailed in 

American Society for Testing and Materials (ASTM) 

standards. An unacceptable drop in the pressure 

indicates that the pipe has leaks that could lead to 

excessive infi ltration. To isolate the leaks, air testing can 

be repeated on smaller sections of line.

Hydrostatic Testing

Hydrostatic testing is another technique used to detect 

and locate leaks in a sewer system. As with air testing, 

the sewer reach of interest is isolated using plugs. The 

test section is fi lled with standing water and the water 

level is monitored. A drop in the water level over time 

indicates the presence of leaks. The acceptable decrease 

in water level and the test duration are specifi ed in 

ASTM standards based on pipe material. 

Smoke Testing

Smoke testing is commonly used to detect sources of 

unwanted infl ow such as down spouts, or driveway 

and yard drains. With each end of the sewer of interest 

plugged, smoke is introduced into the test section, 

usually via a manhole. Sources of infl ow can then be 

identifi ed when smoke escapes through them. This 

technique can also be used to identify cross connections 

between sanitary and storm sewer systems. The smoke 

can be tracked through the sewer system for a limited 

distance. The length of the sewer that can be tested at 

one time is dependent on a number of environmental 

factors affecting smoke dissipation, such as wind and 

the number of sewer and surface connections to the 

system. 

Sewer Inspection Techniques

Sewer inspection is an important component of any 

maintenance program. Sewer inspections establish the 

current condition of sewer lines and identify potential 

problems. The most common sewer system inspection 

techniques are described in detail below.

Visual Inspection

Visual inspection, which is the most basic sewer 

Sewer inspection (NJ Dep. of Environmental Protection).
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-2

inspection technique, can include surface and internal 

inspections. In either case, the manhole cover is 

removed and an inspection of the manhole condition, 

as well as the fl ow characteristics in the pipe, is made. 

For smaller pipes, mirrors and lights can be used 

to inspect the fi rst few feet of pipe upstream and 

downstream of each accessible manhole. For larger 

pipes, a maintenance crew member can enter the pipe 

to inspect the inside of the pipe.

Lamping

Lamping involves lowering a still camera into a 

maintenance shaft or manhole. The camera is lined 

up with the centerline of the junction of the manhole 

frame and the sewer. A picture is then taken down the 

pipe using a strobe-like fl ash. This method can typically 

be used to inspect the fi rst 10-12 feet of the pipe 

upstream and downstream from the access point. 

Camera Inspection

Camera inspection is slightly more comprehensive 

than lamping. In camera inspections, a still camera is 

mounted on a fl oatable raft that is released into a pipe. 

As it fl oats down in the sewer, the camera takes pictures 

of the pipe using a strobe-like fl ash. Camera inspections 

can be performed in any pipe that is large enough to 

accommodate the camera and raft device. 

Closed-Circuit Television

Closed-circuit television (CCTV) is the most 

commonly used technique for inspecting the internal 

condition of a sewer (EPA 1999). A closed-circuit 

camera with a light is self-propelled or pulled down the 

pipe. As it moves, it records the interior of the pipe. The 

focus of the camera can be controlled remotely for a 

clear image of points of interest. The distance traveled 

is recorded so that the location of any irregularities 

can be noted. This technique can be used in lines with 

a diameter ranging from 4-inches to 48-inches (CSU 

2001). 

Sonar

Sonar is a newer technology available for inspecting 

sewer lines. Sonar is deployed in the same manner as 

CCTV cameras and, therefore, can be used in the same 

diameter pipes. Sonar works by emitting a pulse that 

is bounced off the walls of the sewer. The time it takes 

for the pulse to bounce back is a function of the wall 

geometry. This wall geometry can then be analyzed to 

develop an image of the interior of the pipe. At low 

frequencies, less than 200 kHz, the pulse can penetrate 

the walls and provide information on the structural 

condition of the pipe.

Sewer Scanner and Evaluation Technology

Sewer Scanner and Evaluation Technology (SSET) is an 

experimental sewer line inspection technology. A full digital 

picture of the interior of a pipe can be produced by using a 

probe with a 360 degree scanner.

Key Considerations

Sewer Testing Techniques

The location and elimination of leaks in a sewer system 

are the major concern of system operators (CSU 2001). An 

effective sewer testing and inspection program will identify 

existing leaks and prevent other leaks from developing. Key 

considerations, including advantages and disadvantages, in 

selecting appropriate testing and inspection techniques are 

detailed below.

Air Testing

Air testing tests the entire circumference of the pipe 

for leaks by exerting the same amount of pressure in all 

directions on the pipe. Air can leak through a smaller 

crack than wastewater, therefore air testing helps fi nd 

vapor leaks which may attract roots. In addition, in 

areas with steep terrain, air tests are better than water 

tests because of excessive hydrostatic pressure created at 

the lower end of the sewer line (CSU 2001). However, 

air testing can be diffi cult to apply in areas that have 

numerous service lateral connections as each one must 

be individually plugged, and the test section must be 

taken out of service during air testing. Due to safety 

concerns, air testing can also only be used in 4-inch to 

24-inch pipes. For example, pressure on a 24-inch plug, 

even during a low pressure test, is enough to cause an 

improperly installed plug to explode (Rinker Material 

2002). 

Hydrostatic Testing

Hydrostatic testing also requires that the test section be 

taken out of service during testing. Individual service 

lateral connections do not need to be plugged as long 

as the water level at which the test is conducted is below 

that of the lowest basement in the test area. However, if 

residential taps are not plugged, the service laterals will 

be included in the test area. Further, since the release of 

pressure due to a failure of a plug in the hydrostatic test 

is much lower than in an air test, it can be conducted 

in larger diameter pipes. The principle disadvantages 

of hydrostatic testing are the time, money, and water 

wasted in conducting these tests (CSU 2001).

Smoke Testing

Smoke testing does not require the test section to be 

removed from service. However, all fl oor and sink 

drains must be fi lled with water prior to introducing 
Operation & Maintenance: Sewer Testing and Inspection Techniques

O&M-3

smoke to the system. Use of smoke testing is best done 

when the groundwater levels are low (i.e., below the 

elevation of the pipe) so that any cracks will leak smoke. 

It is important to realize that the location of smoke on 

the ground surface does not necessarily reveal where the 

smoke is escaping underground, but rather the point of 

exit at the ground surface (CSU 2001).

Sewer Inspection Techniques

Logging and recording inspections is critical to ensuring 

their utility. Typically, each municipality will have a standard 

log sheet for recording observations made through any of 

the inspection techniques described below. In cases where 

old sewers are to be inspected, it may be important to clean 

the lines before inspection. Ideally, sewer line inspections will 

take place during low flow conditions. Key considerations for 

different inspection techniques are discussed below. 

Visual Inspections

In conducting visual inspections of sewer interiors, the 

maintenance crew is required by law to have confi ned 

space entry training and to strictly follow confi ned 

space entry procedures. Safety concerns also arise when 

attempting visual inspections in sewers with access 

points more than 600 feet apart. 

Lamping

Lamping does not require confi ned space entry. 

Additionally, little equipment and set-up time are 

needed. Inspection is only possible, however, in the areas 

clearly captured in the photograph. Further, lamping has 

limited use in small diameter sewers (CSU 2001).

Camera Inspection

Camera inspection is often a viable alterative to visual 

inspections in larger sewers when the access points 

are more than 900 feet apart. The main disadvantage 

of camera inspection, similar to lamping, is that the 

pictures are not comprehensive and portions of the 

pipe may be missed. Additionally, there must be fl ow in 

the pipe for the raft to fl oat. If there is fl ow in the pipe 

usually the invert of the pipe cannot be seen and is not 

photographed. Therefore, this method of inspection 

does not fully capture the condition of the invert of the 

pipe. 

Closed-Circuit Television

One of the primary advantages of CCTV over stillphotography methods, such as lamping and camera 

inspections, is that the camera can be stopped and 

pulled back or forth for a more precise observation. 

A footage meter can also be used in conjunction with 

CCTV equipment to keep track of the location of any 

irregularities. CCTV, however, cannot capture pipe 

condition below the water. In addition, CCTV-based 

assessment is subjective and can be error prone as its 

accuracy depends heavily on the skill and concentration 

of the operator.

Sonar Technology

Sonar technology is able to map the sewer condition 

both above and below the level of fl ow. The primary 

use for sonar equipment is to inspect and assess the 

structural condition of otherwise inaccessible or fl ooded 

sections of sewer lines. The disadvantage is that it 

requires more power and heavy equipment than the 

CCTV, and therefore tends to be more expensive. 

Sewer Scanner and Evaluation Technology

Similar to sonar, SSET also offers the benefi ts of a 

more complete image of the pipe than CCTV, but this 

technology is still in the experimental phase. SSET 

does not identify all types of sewer defects, such as 

infi ltration and corrosion, equally. Also, it is not possible 

to see laterals, and SSET is slow compared to CCTV 

(CERF 2000). It appears that comprehensive data on 

the condition of the pipeline can be determined by 

combining SSET with CCTV. 

Cost

Costs for testing and inspection will vary based on 

location and technique used. CCTV is the most commonly 

used inspection technique and the costs are presented in 

Table 1.

Location CCTV1

Los Angeles, CA $0.57 

Sacramento, CA $1.63

Santa Rosa, CA $0.27

Honolulu, HI $3.24

Boston, MA $1.89 - $2.70

Laurel, MD $1.72

Albuquerque, NM $1.56

Charleston, SC $0.39

Fort Worth, TX $0.48

Fairfax County, VA $0.81

Norfolk, VA $1.62

Virginia Beach, VA $1.56 - $1.73

Average $1.44

Table 1. CCTV costs per linear foot, includes labor 

 and equipment costs.

1

 Costs in 2002 dollars.
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-4

The City of Fort Worth Water Department created a Preventative Maintenance 

Section and a Technical Service Section in 1998. The Preventive Maintenance 

Section was tasked with implementing a system-wide small diameter (less 

than 18 inches) sewer cleaning and inspection program. Larger pipes are 

cleaned and inspected by private contractors, due to technical logistics and 

the specialized equipment needed. The Sewer Maintenance Section handles 

all other sewer maintenance activities such as cleaning blockages, and pipe installation and repair. The sewer system is divided 

into nine major drainage basins containing 167 subbasins. Each subbasin, along with its SSO and maintenance histories, is tracked 

in a Geographic Information System (GIS) database. Spatial analysis based on information from the GIS database and baseline 

performance criteria is used to prioritize the cleaning and inspection of the subbasins. Once a subbasin is selected for cleaning, 

approximately two-thirds of the cleaned lines are evaluated by CCTV. This information is used as part of the decision making 

process for determining whether or not further maintenance is needed. During 2001-2002, 176 miles of pipe were televised. The 

cost for inspection of small diameter sewers by city employees was $0.48 per linear foot including labor and equipment.

Contact: Darrell Gadberry, City of Fort Worth Water Department, Field Operations Division

FORT WORTH, TX Sewer Maintenance and Service Program

Responsible Agency: City of Fort Worth

Population Served: 880,000

Service Area: 291 sq. mi.

Sewer System: 2,589 mi. of sewer

Implementation Examples

Fairfax County believes that improved record keeping, along with 

the reorganization and streamlining of their sewer maintenance 

program, has resulted in signifi cant reductions in SSOs in recent 

years. By tracking the number of inspections and cleanings, as well 

as the number of overfl ows in each individual line, the county has 

established and prioritized inspection and cleaning schedules for 

each line. This customized cleaning and inspection schedule, along with the resulting decrease in SSOs, led to a decrease in overall 

sewer maintenance costs. Inspection activities include visual inspection using a mirror attached to a pole, a portable camera, and 

CCTV. The sewers are then cleaned based on the regular schedule or sooner, as determined by the inspection results. In 2002, the 

cost of visual inspection and cleaning was $0.87 per linear foot. The cost of CCTV inspection was $0.78 per linear foot. 

Contact: Ifty Khan, Fairfax County Department of Public Works & Environmental Services, 

Wastewater Collection Division

Improved Sewer Maintenance Program

Responsible Agency: Fairfax County

Population Served: 835,000

Service Area: 234 sq. mi.

Sewer System: 3,100 mi. of sewer

FAIRFAX COUNTY, VA
Operation & Maintenance: Sewer Testing and Inspection Techniques

O&M-5

References

California State University (CSU), Sacramento, College 

of Engineering and Computer Science, Office of Water 

Programs. 2001. Operation and Maintenance of Wastewater 

Collection Systems. Vol. 1, 5th ed. Prepared for EPA Office 

of Water Programs, Municipal Permits and Operations 

Division. Sacramento, CA: CSU, Sacramento Foundation.

Civil Engineering Research Foundation (CERF). 2000. 

Sewer Scanner & Evaluation Technology (SSET). Retrieved 

July 28, 2003. 

http://www.cerf.org/ceitec/eval/ongoing/sset.htm

EPA Office of Water. 1999. Collection System O&M Fact 

Sheet: Sewer Cleaning and Inspection. EPA 832-F-99-031.

Rinker Materials. 2002. Information Series: Low Pressure Air 

Testing. Retrieved July 28, 2003. 

http://www.rinker.com/hydroconduit/infobriefs/i105.htm

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Sewer Cleaning 

Techniques

OPERATION & MAINTENANCE

Overview

Operations and maintenance practices, such as sewer 

cleaning, enhance sewer system performance. Specifically, 

sewer cleaning can remove blockages caused by the 

deposition of solids and grease, as well as root intrusion. 

Sewer cleaning is important in maintaining sewer system 

capacity and can reduce the frequency and volume of CSOs 

and SSOs. 

The three major techniques used to clean wastewater sewer 

systems are hydraulic, mechanical, and chemical. Some 

of the more widely used technologies in each of these 

categories are described below. 

Hydraulic Cleaning Techniques

Jetting

Jetting involves aiming a high-pressure stream of water 

at the blockage or debris in the pipe. The shape of the 

nozzle can be changed depending on the surface in 

need of cleaning (CSU 2001). Jet cleaners can either be 

truck- or trailer-mounted. Jet cleaners are very effi cient, 

require minimal staff, and are able to handle most types 

of sewers and blockages. Jetting is the most common 

hydraulic cleaning technique due to its comparatively 

low cost and effective cleaning results.

Balling

Balling involves inserting a rubber ball with a diameter 

slightly smaller than the interior diameter of the pipe 

into a sewer line. The ball is placed in the upstream end 

of the sewer line and reduces the area through which 

wastewater can pass, causing it to fl ow at a higher 

velocity. This increased velocity fl ow scours the interior 

of the pipe. Additional cleaning can also be achieved by 

threading the ball so that it spins as water fl ows past, 

scrubbing the interior of the pipe. 

Kites

Kites are cone shaped devices that resemble a windsock 

and are used to hydraulically clean sewers. Kites work 

similar to balling, increasing the velocity of the fl ow so 

that it scours the sewer line. They are made of a canvas 

material that traps and funnels the wastewater so that 

it is released as a high velocity stream. This wastewater 

stream works to break up deposits in the line.

Scooters

Scooters consist of a metal shield attached to a wheeled 

framework and are designed to be self-propelled. The 

shields are available in various sizes for use in different 

diameter pipes. Similar to the balling technique, the 

scooter blocks the fl ow in the pipe and forces it to go 

around the edges of the shield at a high velocity. The 

wheeled framework allows the scooter to be pushed 

by the wastewater built up behind it. The depth of 

wastewater behind the scooter is controlled by a spring 

system that adjusts the angle of the shield relative to 

the walls of the pipe. By adjusting the angle of the 

shield, the fl ow around the edges is either increased or 

decreased. The high velocity water fl owing around the 

shield breaks up and moves debris down the pipe.

Flushing

There are two methods used in fl ushing sewers: manual 

fl ushing and self-fl ushing. Manual fl ushing involves 

introducing large volumes of low velocity water at the 

upstream end of the sewer. The large fl ow volume 

is capable of transporting fl oatables and low density, 

loose debris to the downstream manhole for removal, 

but not necessarily heavy or attached debris. This 

method is most effective when used in combination 

with a mechanical method such as rodding. Selffl ushing techniques use the fl ow within the sewer for 

hydraulic cleaning. A gate or other device is used to 

store a volume of wastewater and then release it in a 

fl ood wave that washes deposits out of the sewer line. 

Mechanical Cleaning Techniques

Rodding

Power rodding machines use an engine to force a 

Sewer cleaning truck (Black and Veatch).
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-8

small diameter rod (less than one inch) through the 

sewer line. The rod turns as it passes through the pipe. 

Usually a cleaning attachment made of multiple small 

blades is located at the end of the rod. The attachment 

works to loosen and break up debris; it also cuts 

through roots that protrude into the interior of the 

pipe. In addition, power rodding can be used to thread 

cables for closed-circuit television (CCTV) inspection 

or bucket cleaning. 

Bucket Machines

Bucket machines use a steel bucket that is pulled 

through the sewer along a cable threaded between two 

manholes. The front of the bucket has jaws that open 

and scrape the debris and deposits from the interior 

of the pipe capturing them in the bucket for removal. 

Bucket machines are available in a range of sizes to 

allow for cleaning of both small and large diameter 

pipes. The power of the equipment being used to pull 

the bucket determines the size of the pipe that can be 

cleaned with this method. 

Chemical Grouting Techniques

Herbicides

Roots can inhibit fl ow, collect debris, and reduce 

the line’s capacity. Herbicides are used to kill roots 

protruding into the sewer line and inhibit future root 

growth. Herbicides are typically applied by one of two 

methods: soaking the roots inside the sewer with a 

liquid solution for a short time period, or fi lling the 

sewer with a herbicidal foam. Chemical root control 

must be used in combination with some other cleaning 

technique to remove the roots killed by the herbicides.

Enzyme Additives

Enzyme additives can be used to break up scum, 

grease, and other accumulated organic matter. These 

additives can control odors in the sewer system as well 

as removing blockages. The additives usually come in a 

dry fl aky form and are applied in small doses. 

Key Considerations

Selection of the most appropriate sewer cleaning technique 

will need to be made on a site-specific basis. In general, 

hydraulic cleaning techniques tend to be simpler and 

more cost-effective in removing deposited solids when 

compared to other sewer cleaning techniques (CSU 

2001). Mechanical techniques are typically used in areas 

where the volume, size, weight, or type of debris limit the 

effectiveness of hydraulic techniques. Chemicals can be 

helpful aids for cleaning and maintaining sewers, but most 

chemical applications are localized or used to enhance 

the effectiveness of other cleaning techniques. Specific 

considerations for each of the aforementioned cleaning 

techniques are described below.

Applicability

Hydraulic Cleaning Techniques

Jetting

Jetting is most effective in cleaning fl at, slow-fl owing, 

smaller pipes (less than 15 inches in diameter). As the 

pipe diameter increases, the distance between the high 

velocity nozzle and the interior of the pipe increases, 

which decreases its cleaning potential. Jetting is often 

more effective in low fl ow pipes as the jets can easily 

penetrate shallow fl ow to clean the deposits in the 

invert of the pipe. Jetting must be used with caution 

in pipes with fi xtures such as gauges and valves as they 

may be damaged by the jets. Basement backups can 

occur if the jetting hose is mistakenly fed into a service 

line, or if the volume of water introduced exceeds the 

capacity of the sewer line. 

Balling

Balling is best suited for removing deposits of inorganic 

material and grease (CSU 2001). Balling can only be 

used in areas where suffi cient hydraulic capacity is 

available to pressurize the water fl owing around the 

ball without causing sewer backups, and it is most 

successful in 24-inch or smaller diameter pipes. It 

cannot be used in sewer lines that have large offsets, 

service connections, or roots protruding into the 

sewer line since the ball can get caught. The required 

frequency of balling varies from six months to three 

years (CSU 2001).

Kites

Kites clean in a manner similar to balling, but they are 

commonly used to clean larger diameter sewers. Kites 

require only a small amount of hydraulic pressure to 

create a cleansing velocity. Yet, they can only be used in 

areas where suffi cient hydraulic capacity is available to 

pressurize the water fl owing around the kite without 

causing sewer backups. Some accommodation for 

hydraulic capacity can be made by feeding the kite 

through the system at a faster rate. However, this faster 

rate may not allow for suffi cient pressurization of the 

water fl owing out of the end of the kite. A kite cannot 

be used in pipes with large offsets, which could cause 

the kite to become lodged in the line. 

Scooters

Scooters are capable of removing large objects and 

heavy materials (i.e., brick, sand, gravel, and rocks). 

Scooters are considered more effective in larger lines, 

over 18 inches in diameter (CSU 2001). The operation 

of a scooter is quite simple, and the cost is often 
Operation & Maintenance: Sewer Cleaning Techniques

O&M-9

considerably less than other cleaning operations. Since 

scooters depend on the build-up of water pressure, 

caution must be used where sewers are shallow or the 

danger of fl ooding homes or businesses exists. A scooter 

cannot be used in lines with protruding pipes or service 

lateral connections, and it may not be appropriate for 

lines with signifi cant root intrusion, where it could 

become entangled. 

Flushing

Flushing is most often used in conjunction with other 

mechanical techniques, especially rodding. Mechanical 

devices are used to cut roots and grease from the walls 

and joints of pipes. This is followed by fl ushing to 

remove the cut material. Flushing is not as effective 

as balling or jetting because suffi cient velocities are 

not developed to remove grease, grit, or heavy debris. 

It is also important to note that the amount of water 

required to clean a line is dependent on the size, length, 

and slope of the line. Flushing is not a common practice 

due to poor results and large volumes of water required 

for cleaning, which ultimately fl ow to the wastewater 

treatment plant.

Mechanical Cleaning Techniques

Rodding

Rodding is one of the most widely used methods for 

cleaning sewers. Rodding is typically used to handle 

stubborn stoppages of roots, grease, and debris (CSU 

2001). This method works best when applied in pipes 

with diameters of 12 inches or less. When used in larger 

diameter pipes, the rod tends to bend and coil up on 

itself. Rodding is most effective when it is applied in 

conjunction with some form of fl ushing because it 

works to loosen and break up debris, but rodding itself 

does not remove debris from the line. If the rod happens 

to break in the sewer line, retrieval and repair may be 

very diffi cult.

Bucket Machines

Bucket machines are most often used to clean a line 

after a pipe breaks or debris that cannot be removed 

by hydraulic cleaning techniques accumulates. They 

should not be used as a routine cleaning tool. Bucket 

machines are heavy, and set-up of the equipment is more 

time consuming than for other mechanical methods. 

In addition, if the sewer line is completely blocked, the 

pull cable cannot be threaded through the line, making 

this method ineffective. Bucket machines are costly 

to operate and maintain, and they can be potentially 

damaging to sewer pipes.

Chemical Cleaning Techniques

Herbicides

Proper application of chemical root control is essential 

in ensuring their effectiveness. Root control using 

chemicals is not as fast as cutting roots with a power 

rodder, however, it is more permanent. Effective 

chemical application can control roots in a sewer for 

two to fi ve years (CSU 2001). It is important to take into 

consideration how the toxicity of the herbicide will affect 

the biological treatment process at the downstream 

wastewater treatment plant. 

Enzyme Additives

The addition of enzyme additives to control grease and 

scum are effective under specifi ed conditions in specifi c 

locations. Careful comparison of the results produced 

by the additives with those achieved via mechanical or 

hydraulic cleaning methods should be made to ensure 

that the most appropriate technique is selected.

Cost

Representative costs for various cleaning methods are 

summarized in Table 1. The relative effectiveness of the 

cleaning techniques is presented in Table 2.
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-10

Table 2. Effectiveness of sewer cleaning techniques (CSU 2001).

Maintenance Issue 

(Effectiveness scaled from 1=low to 5=high)

Cleaning Technique Emergency 

Stoppage Grease Roots Sand, Grit, 

Debris Odors

Jetting1 5 5-43

Balling - 4 - 4 3

Kiting - 4 - 4 3

Scooters - 3 - 3 -

Flushing - - - - 2

Rodding 4 1 3 - -

Bucket Machines - - - 4 -

Chemicals - 2 - 5 5

Microorganisms - 4 - - -

1

 Effectiveness decreases as pipe diameter increases.

Municipality Cleaning Method Average Cost per Linear 

Foot1

Los Angeles, CA Hydraulic - Jetting $0.27 

Mechanical - Rodding $0.41 

Mechanical - Manual Rodding $1.32 

San Diego, CA Overall Cleaning $0.54 

Hammond, IN Overall Cleaning $1.26 

Afton, OH Overall Cleaning $0.42 

Sioux Falls, SD Overall Cleaning $0.45 

Fort Worth, TX Overall Cleaning $0.61 - $1.02

Fairfax, VA Hydraulic - Jetting $0.44 

Mechanical - Rodding $0.86 

Table 1. Cleaning costs per linear foot.

1

 Costs include labor and equipment.
Operation & Maintenance: Sewer Cleaning Techniques

O&M-11

The City of Sioux Falls’ sewer system consists of 578 miles of sanitary pipe. The 

pipes range in size from 6-66 inches in diameter. The sewer system is divided 

into 20 drainage basins, and the current maintenance program provides that 

the entire system is cleaned once every three years. Maintenance records are 

stored in an Oracle database that generates work orders by date and drainage 

basin. Sanitary sewer maintenance includes high pressure jetting, vacuuming 

to remove loosened debris, and mechanical and chemical root control. Closed circuit televising (CCTV) is used to identify trouble 

spots, where more frequent cleaning is required than the scheduled three year intervals. In 2001, 372 miles of sewer (64 percent of the 

system) were cleaned and televised. The cost for these maintenance activities equates to $236 per 5,280 feet (1 mile) of inch-diameter 

pipe . Using a ten-inch diameter pipe as an average, maintenance costs are about $0.45 per linear foot. 

Contact: Richard McKee, M.O.U. Public Works, Water Reclamation Division

Sewer Cleaning and Maintenance

Responsible Agency: City of Sioux Falls

Population Served: 120,000

Service Area: 70 sq. mi.

Sewer System: 578 mi. of sewer

SIOUX FALLS, SD

Implementation Examples

The City of Fort Worth’s sewer system consists of approximately 2,589 miles 

of pipe. The pipes range in size from 6-96 inches in diameter. Ninety percent 

of the system is composed of pipes with diameters of18 inches or less. The 

city has established maintenance goals which include cleaning all sewers 18 

inches or smaller once every eight years and all sewers larger than 18 inches 

once every 15 years. The cleaning and maintenance of the smaller diameter 

pipes is conducted by city employees, while the cleaning of larger diameter pipes is outsourced due to technical logistics and the 

specialized equipment needed.

The sewer system is divided into nine major drainage basins containing 167 subbasins. Each subbasin, along with its SSO and 

maintenance histories, is contained in a Geographic Information System (GIS) database. Spatial analysis of the GIS database is 

compared to baseline performance indicators to prioritize the cleaning order of the subbasins. In 2001-2002, 1.15 million linear 

feet of pipe were cleaned by the city. The cost for city cleaning activities during this time, including labor and equipment, was $0.61 

per linear foot (in 2002 dollars) and the cost for cleaning of larger pipes by private contractors was $1.02 per linear foot (in 2002 

dollars). 

Contact: Darrell Gadberry, City of Fort Worth, Water Department, Field Operations Division 

FORT WORTH, TX Sewer Cleaning Efforts

Responsible Agency: City of Fort Worth

Population Served: 880,000

Service Area: 291 sq. mi.

Sewer System: 2,589 mi. of sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-12

References

Arbour, Rick, and Ken Kerri. 1998. Collection Systems: 

Methods for Evaluating and Improving Performance.

Prepared for EPA, Office of Water Programs, Municipal 

Permits and Operations Division and developed under EPA 

Grant No. CX924908-01-0. Sacramento, CA: California 

State University, Sacramento Foundation. 

California State University (CSU), Sacramento - College 

of Engineering and Computer Science, Office of Water 

Programs. 2001. Operation and Maintenance of Wastewater 

Collection Systems. Vol. 1, 5th ed. Prepared for EPA Office 

of Water Programs, Municipal Permits and Operations 

Division. Sacramento, CA: CSU, Sacramento Foundation.

EPA Office of Research and Development. 1998. Sewer and 

Tank Sediment Flushing: Case Studies. Prepared by Pisano, 

William C., et al. EPA 600-R-98-157.

EPA Office of Water. 1999. Collection System O&M Fact 

Sheet: Sewer Cleaning and Inspection. EPA 832-F-99-031.

Fan, Chi-Yuan, Richard Field, William C. Pisano, James 

Barsanto, James Joyce, and Harvey Sorenson. 2001. 

“Sewer and Tank Flushing for Sediment, Corrosion, and 

Pollution Control.” Journal of Water Resources Planning and 

Management. May/June: 194-201.

Mitchell, Scott E. 2001. “Benchmarking Operations for 

Sewer Cleaning vs. Private Contractor - Cost Analyses, 

1997-2001.” Retrieved July 28, 2003. 

http://www.ci.hammond.in.us/sewer/paper.html

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Pollution Prevention

OPERATION & MAINTENANCE

Overview

Pollution prevention is defined as any practice that 

reduces the amount of pollutants, hazardous substances, 

or contaminants entering the waste stream (EPA 2002). 

Pollution prevention focuses on source control, seeking to 

reduce the pollutants generated by a particular process. It 

relies on individual action, and therefore, public education 

and awareness. A range of pollution prevention activities 

including best management practices (BMPs) for fats, oils, 

and grease; household hazardous waste; and commercial 

and industrial facilities are detailed below.

Fat, Oil, and Grease Control Programs

Fat, oil, and grease (FOG) are a by-product of many food 

items that are prepared in homes and restaurants. Often, 

when used for cooking, FOG is improperly disposed of by 

pouring it down a sink drain. FOG can also enter the sewer 

system when dishes are washed. Over time, FOG builds up 

in sewers, leads to blockages, and can cause combined and 

sanitary sewer overflows (CSOs and SSOs). 

Nationally, EPA believes that FOG is one of the leading 

causes of SSOs contributing to approximately one out of 

every five SSOs. The best way to prevent these blockages is 

to keep FOG out of the sewer system. Education programs 

are important in ensuring residents, institutional, and 

commercial establishments, especially restaurants, are 

aware of their role in managing FOG. In addition, many 

municipalities have adopted regulations controlling the 

introduction of FOG into the sewer system.

In commercial areas, grease traps or interceptors are often 

used to remove FOG from wastewater before it enters the 

sewer system. Grease traps slow the flow of wastewater, 

allowing it to cool and FOG to float to the top of the trap. 

Baffles are located at the beginning and end of the trap to 

prevent FOG from escaping as shown in Figure 1. The size 

of the trap depends on the anticipated flow and the amount 

of FOG in the wastewater. Grease trap capacities range from 

small units (less than 10 gallons) located in the kitchen area 

to 5,000 gallon tanks installed underground outside the 

building (NCDPPEA 2002). Often, for restaurants, the size 

of the trap is determined by the number of seats.

Household Hazardous Waste Management

Household hazardous waste includes products that 

are corrosive, toxic, reactive, or flammable. Household 

hazardous waste management focuses on the proper 

application and disposal of these otherwise hazardous 

materials. Common household hazardous waste are paint 

thinners, auto batteries, pesticides, and oven cleaners. 

Household hazardous waste collection programs highlight 

the importance of proper disposal of these materials and 

potential hazards resulting from improper disposal (i.e., 

pouring down kitchen sinks or storm drains and thus into 

the sewer system). Collection programs typically include 

schedules for home pick-up or drop-off points for the 

waste.

Outlet

Clean-out

Inlet

FOG

Settled Solids

Baffles

Figure 1. A schematic showing the collection of FOG by a 

grease trap located within a sewer line.

Root and grease build-up in sewer (NCDNR).
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-14

The inappropriate or excessive application of fertilizer and 

pesticide can allow large amounts of these chemicals to 

be washed off lawns and other landscaped areas during 

wet weather events. Fertilizer contains nitrogen and 

phosphorous that can contribute to the eutrophication 

of receiving waters. Pesticides contain chemicals that are 

toxic to aquatic life and can impact the biological processes 

used at the wastewater treatment plant. In areas served by 

combined sewers, runoff contaminated with fertilizer and 

pesticides may be discharged during a CSO event. Drain 

disposal of chemical remnants can also introduce the 

fertilizer or pesticide into the sewer system.

Integrated pest management (IPM) programs can be 

effective in limiting fertilizer and pesticide application. IPM 

programs teach residents the difference between insects that 

are beneficial and harmful to plants to avoid the over use of 

pesticides. For example, if one branch of an azalea bush is 

infected with an azalea lace bug, that branch can be cut out 

of the bush eliminating the pest and reducing the need for 

pesticide (NVPDC 1996). Further, IPM programs advocate 

using a diverse selection of native plants and maintaining 

a healthy plant bed by using organic compost instead of 

fertilizer.

Commercial and Industrial Waste Management

Commercial and industrial facilities can discharge large 

amounts of pollutants to sewer systems through direct 

disposal or storm water runoff (EPA 1999). Pollution 

prevention plans that incorporate storm water BMPs 

and water conservation measures can play an important 

role in reducing the pollutants discharged directly to the 

sewer system, as well as those washed-off commercial 

and industrial sites during wet weather events. BMPs for 

commercial and industrial sites can be used to control the 

volume or quality of storm water runoff. BMPs may include 

using temporary covers for outside storage areas, installing 

covered bays for vehicle maintenance, purchasing rain proof 

dumpsters, and adopting environmentally-friendly building 

and grounds maintenance practices. Water conservation 

measures at commercial and industrial facilities often 

include installing water efficient fixtures such as low-flow 

toilets and faucets and reusing or recycling cooling water. 

For more information on water conservation activities, 

refer to the “Water Conservation Technology Description” 

in Appendix B of the Report to Congress on the Impacts and 

Controls of CSOs and SSOs.

Key Considerations

Pollution prevention practices most often take the form 

of simple, individual actions which reduce the pollutants 

generated by a particular activity. Therefore, pollution 

prevention programs must be implemented with broad 

participation in order for there to be a discernible 

reduction in pollutant loads discharged to sewer systems. 

Specific considerations for each of the pollution prevention 

practices described above are provided below.

Applicability

Fat, Oil, and Grease Control Programs

FOG is a common problem in both combined sewer 

systems (CSSs) and sanitary sewer system (SSSs). 

Numerous municipalities have invested in programs to 

educate customers about the proper handling and disposal 

of FOG. Education programs are most successful if they are 

tailored to a specific audience (i.e., residential, institutional, 

or commercial). 

 

Education programs should make residents aware that 

FOG can block private laterals, in addition to municipal 

sewers, resulting in basement backups. Utility bill inserts, 

direct mailings, newspaper articles, and community events 

are ways to reach residential customers (NCDPPEA 2002). 

Outreach materials can include a “Do and Don’t” list such 

as the following: 

Do: 

● Collect FOG in a container and dispose of it with the 

trash ● Scrape grease and food from cooking/serving ware 

before washing

● Encourage neighbors and friends to help eliminate 

FOG from the sewers

Don’t:

● Pour FOG down the sink drain or toilet

● Put greasy waste or food down garbage disposals

● Place FOG wastes in the toilet

Education for commercial and institutional customers 

can take the form of workshops, mailings, and web 

information. Workshops provide a forum for disseminating 

information concerning environmental and health effects 

of FOG, BMPs for controlling FOG, and any municipal 

ordinances that pertain to FOG. Workshops can emphasize 

the important link between employee behavior and possible 

FOG blockages. If new ordinances are put into place, direct 

mailings can be used to inform those effected of their new 

responsibilities, as well as techniques for controlling FOG.

A vital part of any education program for commercial and 

institutional customers is discussion of grease trap design 

and maintenance. Grease traps do not remove all the FOG 

in the wastewater; proper design and regular maintenance is 

critical for effective grease trap performance. The effective 

separation of water and grease is based on four design 

criteria (NCDPPEA 2002): 
Operation & Maintenance: Pollution Prevention

O&M-15

● Sufficient volume to allow the wastewater to cool for 

separation

● Proper retention time for the FOG to separate from 

the wastewater

● Low turbulence to prevent FOG and solids from 

resuspending

● Adequate volume to handle the accumulation of FOG 

and solids between cleanings 

Household Hazardous Waste Management

Programs that promote appropriate disposal of household 

hazardous waste and the proper application of fertilizers and 

pesticides can be instituted in any community. 

Household hazardous waste collection programs provide 

information to residents about materials that are considered 

hazardous and provide opportunities for proper disposal. 

State or local governments can establish a network of 

regional, local, or mobile household hazardous waste 

collection facilities providing residents with multiple options 

for disposing of the waste (MPCA 2002). Municipalities may 

organize simple or elaborate drop off events that incorporate 

other environmental education programs.

The control of fertilizer and pesticide levels involves 

convincing residents, institutions, and municipal 

departments to adhere to handling and application 

techniques that limit pollutant runoff. Public education 

programs should emphasize that “more is not better,” and 

that the lowest effective dose listed on the label for any one 

application should always be used. Education programs 

can also include information on IPM and other alternative 

pest control measures. The caretakers of large parcels of 

urban land, including local park departments and other 

institutions, should be encouraged to demonstrate the 

responsible use of fertilizers and pesticides.

Commercial and Industrial Waste Management

The development and implementation of a pollution 

prevention plan can benefit almost any commercial or 

industrial facility. Pollution prevention plans can reduce 

operating costs and improve the facility’s public image, while 

reducing the quantity of pollutants generated. Technical 

assistance and incentives may also be used to encourage 

commercial and industrial facilities to participate.

Some states, regional agencies, and counties have developed 

programs to aid businesses in developing pollution 

prevention plans. These programs typically include a waste 

analysis to determine which portions of the commercial 

or industrial facility’s production could benefit from waste 

reduction measures and services to help implement the 

suggested measures.

Water conservation measures can be an important 

component of a pollution prevention plan helping to 

reduce the amount of water consumed by commercial and 

industrial operations. This in turn reduces the amount of 

water discharged to the sewer system. When establishing a 

water conservation plan, a facility should perform a water 

audit to survey its water use. The true cost of water usage 

can then be calculated by considering the water and sewer 

costs, on-site wastewater treatment costs, if any, and energy 

costs to heat or pump water. After water use is characterized, 

areas for improvement can be identified and prioritized. 

Changes in behavior, as well as the replacement or retrofit of 

equipment, can be used to implement more efficient water 

use practices.

Cost

Pollution prevention measures are site-specific, and it is 

therefore difficult to compare costs between programs. 

Tables 1 and 2 provide cost examples for pollution 

prevention practices. Table 2 specifically details commercial 

and industrial pollution prevention measures including 

potential cost savings.
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-16

Technology Program Typical Costs

Fats, Oil, Grease Education Program

Grease Trap/Interceptor

Raleigh, NC- Budgeted $100,000 for program set-up and $50,000 annually 

for implementation.

Wisconsin - Grease traps can cost $750 per cubic foot or $211,000 per 

structure .2.

Household Waste 

Management

Hazardous Household 

Waste Management

Fertilizer and Pesticide 

Control

Jefferson County, KY - Operates a permanent collection facility for 

hazardous household materials. The annual operation budget is $250,000 

and they collect approximately 150,000 lbs. per year ($3,333/ton or $1.67/

lb.).

Greater Detroit Resource Recovery Authority - Collected 60 tons of waste in 

1995 for $223,000 ($3,716/ton or $1.86/lb.).2

Lovinia, MI - Spent an average of $80,918 annually for their hazardous 

household materials collection program from 1991- 1995. The average 

disposal cost was $12.19/gallon. 2

Prince William County, VA - Provides soil test kits to residents for $10, which 

includes analysis for fertilizer needs. 2

Commercial and Industrial 

Management

Waste Management King County, WA - Operates the Industrial Materials Exchange, which helps 

businesses find markets for their surplus materials, wastes, and industrial byproducts. The annual operating budget is $250,000.

Waste Reduction Partners of the Land-of-Sky Regional Council, Ashland, 

NC - Annual budget for 2001 was $132,097. In 2001, the program diverted 

10,609 tons of solid waste from landfills. 3

1

 EPA 1999, 2 Ferguson, et al. 1997, 3 Land-of-Sky 2001

Table 1. Example costs associated with pollution prevention programs.

Company State Program Activity Capital 

Cost

Cost 

Savings/Yr. Results

Air Products and 

Chemicals, Inc.

OH Wastewater 

Discharge 

Reduction

Batch seal pot water is 

recovered and reused 

in continuous emulsion 

process

$1,000 $2,000 Reduced waste flow to sewer 

system by 56% annually.

Cooper Hand 

Tools

NC Reuse Hazardous 

Waste Reduction

Concentrate chromic acid 

rinse water for reuse and 

recover nickel from nickel 

electroplating bast sludge

N/A $68,000 Reduced purchase of new 

chromic acid by 10,000 lbs. 

annually. Eliminated generation 

of 12 tons of hazardous waste 

annually.

Frigo Cheese 

Corporation

WI Reuse Salt whey recovery and 

reuse by evaporation

$2,000 N/A Not Available

Lockheed Martin GA Hazardous Waste 

Reduction

Minimized paint waste 

through improved planning

$4,000 $120,649 Reduced hazardous waste 

stream by 2,020 gallons 

annually.

Quality Metal 

Products/Sheet 

Metal Shop

CO Hazardous Waste 

Reduction

Installed solvent recovery 

unit

$14,700 $13,000 Prevented formation of 375 

gallons of hazardous liquid 

waste annually.

Small Engine 

Manufacturer

WI Hazardous Waste 

Reduction

Replaced chlorinated 

solvents with aqueous 

cleaners for parts cleaning.

$10,000 N/A Not Available

Unilever Home 

and Personal 

Care, Inc.

GA Water 

Conservation Plan

Reuse of cooling water and 

collected rainwater used in 

the manufacturing process.

N/A $20,000 Reduced wastewater effluent 

by 77%. No longer a Significant 

Industrial User in relation to 

pretreatment program.

Table 2. Examples of commercial and industrial pollution prevention programs.
Operation & Maintenance: Pollution Prevention

O&M-17

Implementation Examples

In 1999, the City of Raleigh passed an ordinance that made it unlawful to

dispose of grease by pouring it into the sewer system. To educate the public

about this ordinance and their responsibilities, the city launched the “Can

Can” Campaign in 2000. The city developed a website; produced television 

and newspaper advertisements and radio spots; sponsored a poster contest

during the

City of Raleigh’s annual Water Fest; and developed informational

brochures. The website contains information about grease and

its affect on the sewer system including a “Do and Don’t” list.

The first newspaper advertisement run by the city is shown.

The city’s efforts continue to educate the public on the proper

disposal of grease. Currently, a video is being developed for

civic groups and students. Public service announcements

on grease management will air on community and network

television stations. Press releases reminding citizens about

the problems grease can cause in the sewer system will also

continue. Also, water bills will contain informational inserts.

During 2001, the city experienced 51 SSO events, a 22 percent

reduction from the previous year. The city attributes this reduction

to the FOG education program and an aggressive sewer maintenance

program. The “Can Can” Program operates on an annual budget

of $50,000; the start-up cost of the program was $100,000.

More information at http://www.raleigh-nc.org/pubaffairs/cancan/index.htm

RALEIGH, NC Public Education “Can Can” Campaign

Responsible Agency: City of Raleigh Department 

of Public Works

Population Served: ~315,000

Service Area: Not Available

Sewer System: 1,525 mi. of sewer

The Upper Trinity Regional Water District in the Dallas/Fort Worth 

area provides drinking water, wastewater, hazardous waste 

management, biosolids management, and non-potable water 

supply services. Approximately 13 cities have contracts with the 

district for the specific services they need. In 1998, a household

hazardous waste collection program was established to provide 

the district’s customers with ways to dispose of their hazardous wastes in an environmental-friendly manner. The collected waste is 

then transported in a specially modified cargo trailer to a regional disposal facility. The trailer was purchased in 1998 using a grant 

from the Texas Commission on Environmental Quality. During collection events, residents can drop off batteries, used car oil, solvents, 

antifreeze, herbicides, pesticides, aerosols, mercury, and paint. Paint is the most disposed item. The district charges each city $80 per 

participating household for disposal fees and administration costs. The first collection event was held in June 1999. In 1999, a total of 

375 households handed in 51,468 pounds of material. The total cost for the participating cities was approximately $26,250.

More information at http://www.utrwd.com/HHW.HTM

Household Hazardous Waste Collection 

Responsible Agency: Upper Trinity Regional Water District

Population Served: ~158,000

Service Area: Not Available

Sewer System: Not Available

DENTON COUNTY, TX
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-18

A two-phase FOG control study is currently being conducted by

the Orange County Sanitation District. The first phase, completed 

in March 2003, consists of a set of 13 building blocks that can be 

used interchangeably to create FOG programs specific to local 

conditions. The building blocks are grouped into four categories: 

programmatic, best management practices, best available 

technologies, and regional and watershed. A summary of the 

draft report that details the building blocks of a FOG control program is presented. The second phase is on-going and involves field 

studies and pilot tests of FOG control technologies.

Cost comparisons of the various technologies that will be pilot tested as part of the FOG control study are not currently 

available. The first phase of the study cost $268,000. It is expected that another $1 million will be spent on pilot tests and system 

characterization.

Contact: Adriana Renescu

Programmatic Building Blocks Description

FOG Characterization Characterization of local FOG conditions including the extent and nature of SSO problems;

identification of current or potential “hot spots”. 

Ordinance Provides the legal framework for implementing a FOG program; establishes monitoring requirements,

enforcement conditions, and fees.

Monitoring and Enforcement Ensures that FOG control requirements are being followed. Enforcement: penalize entities that fail to 

correctly implement FOG controls.

Fees and Incentives Fees, often in the form of increased sewer fees, pay for the FOG program. Reduced fees may be

used as an incentive if commercial and institutional establishments can prove they are successfully

implementing controls.

Education and Outreach Many different stakeholders contribute to the success of FOG programs, it is important to identify 

and target key partners. Also, it is necessary to take into consideration language barriers (multilingual 

programs are required).

Best Management Practices g

Kitchen BMPs Practices to reduce and eliminate residential FOG before it enters the sewer system. 

Collection System Cleaning Collection system cleaning and TV-monitoring should focus on areas in the sewer system where FOG is

most problematic.

Best Available Technologies

Grease Interceptors Grease interceptors located outside of buildings that have a minimum volume of 750 gallons.

Passive Grease Traps Small collection devices with volumes less than 50 gallons, which are installed under sinks and must be 

cleaned manually.

Automatic Grease Traps Automatic grease traps are self-cleaning.

Biological Additives and Services Biological additives digest FOG and prevent it from blocking sewer lines or overloading traps.

Chemical Additives Chemical additives break down FOG and have been found to be useful in solving lift station grease

problems.

Regional and Watershed g

Grease Disposal Practices and

Alternatives

Once FOG controls have been put in place, there must be grease disposal mechanisms available to 

customers. Such disposal methods include converting grease into biofuels and feeding the waste into

POTW digesters. Also, it is important to regulate haulers and disposal sites to avoid illicit dumping.

ORANGE COUNTY, CA FOG Control Study

Responsible Agency: Orange County Sanitation District

Population Served: 2.4 million

Service Area: 470 sq. mi., 23 cities

Sewer System: 650 mi. of sanitary sewer

Building blocks of Orange County Sanitation District’s FOG control study.
Operation & Maintenance: Pollution Prevention

O&M-19

Since the early 1990s, the Prince William County Cooperative Extension has 

administered a water quality program that educates residents about the 

effects of over fertilizing their lawns and using too many pesticides. Residents 

are recruited using direct mailings and programs with civic and homeowner 

associations. Once a resident registers with the program, they complete a pre-program survey and attend educational seminars such 

as “Fall Fertilization” and “IPM Basics”. Upon completing the program, a master gardener volunteer visits with the residents to ensure 

that they are implementing the IPM and fertilization practices correctly. Finally, the resident completes a post-program survey. To 

date, over 2,000 households have completed Prince William’s turf care and management program. To determine the effectiveness of

the program, Prince William compared 1996 survey results from 600 participating households pre- and post-program. Results of the 

survey is summarized below.

Participant Activities Pre-Program Post-Program

Tested soil to determine fertilizer rates 17% 78%

Linked excessive nutrients to water quality problems 60% 86%

Considered IPM to be important 42% 62%

Followed a fall fertilization schedule 50% 82%

The survey results showed reductions in fertilizer and pesticide application. The average amount of nitrogen applied to lawns was 

reduced by 40 percent, pesticide and water use were reduced by 25 percent, and the volume of yard trimmings sent to the landfi ll 

was reduced by 25 percent. The program is facilitated by a part-time water quality technician and master gardener volunteers. Prince 

William County’s operating cost for the program ranges between $5,000-$10,000 annually. Except for the $10 soil test, the program is 

free for residents.

More information at http://www.co.prince-william.va.us/vce/enr/enr.htm

Horticulture and Water Quality Program

Responsible Agency: Prince William County 

Cooperative Extension

PRINCE WILLIAM 

COUNTY, VA

Turf care and management program participant responses.

Sara Lee Knit Products Corporation produces an array of finished 

textiles, many of which include cotton material dyed with reactive 

dyestuff. Cotton dying produces large waste streams, composed 

mostly of color and salt. The dyestuff has a low affinity to the cotton fabric, even with the help of the salts used to bind the color to 

the fabrics. Almost all of the salt and approximately half of the dye ends up in discharges to the sewer system. 

To reduce the amount of chemicals purchased and wastewater generated, Sara Lee Knit Products investigated a pilot-scale 

ultrafiltration and nanofiltration system. The filtration system separates the salts from other impurities for reuse and generates 

a concentrated color waste stream that can be more efficiently treated. The pilot study revealed that the system removes most 

pollutants of concern while allowing sodium chloride to remain in the permeate. Also, the polymer treatment scheme applied to 

the filtrate was successful and economical.

Projections from the pilot study suggest that the facility, which generates 240,000 gallons per day of wastewater, would reduce its 

water use by 120,000 gallons per day and salt discharges by 26,000 pounds per day. The filtration system will remove an estimated 

60 percent of the dyestuff and 50 percent of the salt typically discharged. The total capital cost for the filtration and treatment 

system would be $990,000 with annual operating costs of $180,000. Savings on salt purchases were estimated at $335,000 annually. 

An additional annual savings of $460,000 could be achieved using the color removal process.

Contact: Donald Brown, Sara Lee Knit Products Corporation

WINSTON-SALEM, NC Ultrafiltration for Pollution Prevention

Responsible Agency: Sara Lee Knit Products Corporation
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-20

References

EPA Office of Prevention, Pesticides, and Toxic Substances. 

2002. “Definitions National Prevention Pollution Policy.” 

Retrieved November 22, 2002.

http://www.epa.gov/p2/p2policy/definitions.htm.

EPA Office of Water. 1999. Combined Sewer Overflow 

Management Fact Sheet: Pollution Prevention. EPA 832-F99-038.

Ferguson, T. et al. 1997. “Rouge River National Wet Weather 

Demonstration Project: Cost Estimating Guidelines 

Best Management Practices and Engineering Controls.” 

Retrieved December 9, 2002. 

http://www.rougeriver.com/pdfs/stormwater/sr10.pdf.

Land-of-Sky Regional Council. 2001. “Waste Reduction 

Partners Annual Report 2001.” December 10, 2002. 

(Retrieved July 10, 2003.)

http://www.landofsky.org/publications/annual_report2001/

default.htm.

Minnesota Pollution Control Agency (MPCA). 2002. 

“Household Hazardous Waste.” Retrieved November 25, 

2002.

http://www.pca.state.mn.us/waste/hhw.html#map. 

North Carolina Division of Pollution Prevention 

and Environmental Assistance (NCDPPEA). 2002. 

“Considerations for the Management of Discharge of Fats, 

Oil, and Grease (FOG) to the Sanitary Sewer Systems.” 

Retrieved November 22, 2002. 

http://www.p2pays.org/ref/20/19024.pdf. 

Northern Virginia Planning District Commission 

(NVPDC). 1996. Nonstructural Urban BMP Handbook. 

Prepared for the Department of Conservation and 

Recreation/Division of Soil and Water Conservation. 

Annandale, VA: NVPDC Coastal and Chesapeake Bay 

Program.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Monitoring, Reporting, 

and Public Notifi cation

OPERATION & MAINTENANCE

Overview

Operation and maintenance practices are intended to 

enhance sewer system performance and minimize or 

reduce the occurrence of CSOs and SSOs and the potential 

impacts they have on receiving waters. Monitoring, public 

notification, and reporting of CSOs and SSOs and their 

impacts do not directly accomplish these objectives, but 

they are essential to: 

● Understand sewer system performance and impacts of 

CSOs and SSOs on receiving waters;

● Provide the potentially impacted public with 

information about overflow locations, specific events, 

and performance trends; ● Improve oversight by the National Pollutant Discharge 

Elimination System (NPDES) authority; and

● Improve operations and maintenance (O&M) program 

efficiency.

Monitoring Techniques

Monitoring of both the sewer system and receiving waters 

provides valuable information for the operation and 

maintenance of sewer systems and the control of CSOs and 

SSOs. Monitoring provides knowledge of:

● The hydraulic characteristics of a sewer system and 

how it responds to a range of rainfall events; and

● The degree of impact caused by CSOs and SSOs on 

receiving waters.

Results from monitoring programs can also be used to 

track improvements associated with control efforts. The 

basic components of a monitoring program include:

● Rainfall;

● Sewer system flows and overflow frequency, duration 

and magnitude; and

● Water quality in both CSOs and SSOs and receiving 

waters.

Techniques for monitoring each of these components are 

briefly described below. Additional guidance on monitoring 

can be found in Combined Sewer CSOs and SSOs: Guidance 

for Monitoring and Modeling (EPA 1999).

Rainfall

Precipitation is the primary cause of CSOs and a 

major contributor to SSOs. Consequently, rainfall 

measurements are an integral part of a monitoring 

program. 

Monitoring rainfall is fairly simple and provides 

valuable information in assessing the response of a 

sewer system to various rainfall events. Advanced 

techniques that merge radar data with rain gage data 

are available and can provide better rainfall estimates 

than either radar or a rain gage can provide alone.

Sewer System Flow

Flow measurements in the sewer system provide 

essential information related to the magnitude, 

duration, and frequency of CSOs and SSOs. This 

information can be used to design structural controls 

and to better operate and maintain the system, all in an 

effort to reduce CSOs and SSOs. Flow measurements 

following construction of controls and improved 

O&M practices can be used to assess the performances 

of controls and track improvements. Techniques 

for measuring fl ow in sewer systems vary greatly in 

complexity, expense, and accuracy.

Manual methods are the simplest technique for 

measuring fl ow and are most useful for instantaneous 

fl ow measurement or for determining whether or not 

an overfl ow occurred during or between measurements. 

Manual methods can be labor intensive and do not 

provide continuous fl ow records. 

Primary fl ow devices control fl ow in a portion of a 

pipe such that the fl ow rate can be calculated from 

fl ow depth. Relationships between depth and fl ow are 

Storm drain stenciling (NJ Dept. Environmental Protection).
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-22

accurate as long as surcharging or backfl ow does not 

occur. Manual or automatic measurements of the depth 

can be made. Depth-sensing devices can be used to 

measure water depth behind a primary fl ow device to 

determine fl ow rates. 

Velocity meters use ultrasonic or electromagnetic 

technology to sense the velocity of fl ow in the sewer 

system. The velocity measurement is combined with 

a depth measurement from a depth-sensing device to 

calculate fl ow rates. Velocity meters can be used without 

the need for a primary fl ow device and in situations 

where surcharging or backfl ow occurs. 

Pressurized fl ow rates can be estimated from the length 

of time pumps are on and the specifi cations for the 

pumps. Alternatively, full pipe fl ow can be measured 

using orifi ces, venturi fl ow meters, fl ow nozzles, 

turbines, and ultrasonic, electromagnetic, and vortex 

shedding meters.

Water Quality

Monitoring water quality in both the sewer system and 

receiving waters provides essential information for: 

● Characterizing CSOs and SSOs

● Assessing the attainment of water quality standards

● Defi ning baseline conditions ● Assessing the relative impacts of CSOs and SSOs 

on receiving water quality

Water quality monitoring programs can also be used to 

track improvements associated with control efforts. 

Data characterizing the water quality in the sewer 

system and receiving waters during both dry and wet 

weather conditions is needed. The water quality data 

can be analyzed to identify pollutants of concern, their 

concentrations, and likely sources of such pollutants. 

Pollutant concentrations along with sewer system 

fl ows can be used to calculate pollutant loadings to the 

receiving waters. 

In addition to pollutant characteristics, monitoring in 

the receiving waters may include:

● Biological assessment (including habitat 

assessment)

● Sediment monitoring (including metals and other 

toxics)

● Flow conditions

In many cases, the primary parameter of concern 

with respect to CSOs and SSOs will be pathogens, 

represented by an indicator bacteria such as fecal 

coliform or E. coli. Observations of fl oatables, 

objectionable deposits, or algal growths may also 

provide relative measures of CSO and SSO impacts.

Two distinct types of water quality samples can be 

collected:

● Grab samples: a discrete, individual sample 

representing the conditions at one location at the 

time the sample is taken.

● Composite samples: a combination of samples 

collected over a period of time from one location 

or combination of samples from more than one 

specifi c location.

Grab and composite samples can be collected using 

either manual or automatic sampling methods. Manual 

samples are collected by a trained individual using 

a hand-held container. Automated samplers can be 

programmed to collect multiple discrete samples as 

well as single or multiple composited samples. Many 

automated samplers can be connected to fl ow meters 

that will activate fl ow-weighted compositing programs, 

and some samplers are activated by inputs from rain 

gages.

A Quality Assurance Project Plan (QAPP) is an essential 

component of any monitoring program to ensure 

precise, accurate, and reliable data. EPA guidance for 

the development of a QAPP should be followed (EPA 

2002c). The QAPP should address fi eld sampling 

methods and protocols as well as laboratory analytical 

methods and quality assurance/quality control (QA/

QC). Data management techniques and responsible 

personnel should also be addressed in a QAPP.

Public Notification

Public notification programs provide information to the 

potentially impacted community regarding the occurrence 

of CSO and SSO events and on-going efforts to control 

the discharges. The Nine Minimum Controls (NMC) 

outlined in EPA’s CSO Control Policy specifically require 

implementation of a public notification program to ensure 

that the public receives adequate notification of CSO 

occurrence and CSO impacts. Public notification programs 

can assume a variety of forms, including posting temporary 

or permanent signs where CSOs and SSOs occur (Figure 1), 

coordinating with civic and environmental organizations, 

distributing fact sheets to the public and the media, and 

stenciling storm drains. Notices in newspapers are required 

to report occurrences of CSOs or SSOs in some states. 

Radio and TV announcements may be appropriate for 

CSOs or SSOs with unusually severe impacts. Distribution 
Operation & Maintenance: Monitoring, Reporting, and Public Notification

O&M-23

of information on websites is another technique that is 

rapidly gaining wider use.

Posting Signs

Signs are one of the most common mechanisms used to 

communicate the potential hazard posed by CSO and 

SSO discharges. Signs can be posted in the area where 

the use is affected (e.g., along a beach front) or at select 

public places (e.g., a public information center at a park 

where recurrent SSOs have occurred). EPA specifi cally 

recommends posting at visible CSO outfalls and in 

locations where affected shoreline areas are accessible 

to the public. In addition to notifying the public of the 

potential risk of exposure to CSO or SSO discharges, 

signs may provide contact information for citizens 

interested in obtaining additional information or to 

submit concerns. Call centers may be established to 

receive sign-prompted calls.

Coordinating with Civic Organizations

There are a number of ways that a municipality can 

involve public interest or civic and environmental 

groups in various aspects of programs to control CSOs 

and SSOs. One way is to involve the public in the 

process of evaluating technologies for controlling CSOs 

and SSOs. Involvement in assessing willingness to pay, 

determining the implementation schedule, and selecting 

or modifying the method of fi nancing for the controls 

are other ways to involve these groups. Public meetings 

or hearings allow public interest or civic groups to 

offi cially comment or pose questions to the municipality 

regarding a control program.

For example, the State of Wisconsin organized a 

workgroup including representatives from state and local 

health departments and citizen groups with an interest 

in beach health. This group worked to gather data on 

beach use and potential sources of contamination. They 

also interviewed beachgoers and collected suggestions 

for improvement of beach health. As a result of 

this program, Wisconsin’s 180 coastal beaches were 

categorized into high, medium, and low priority based 

on popularity and risk of contamination by sources 

including CSOs and SSOs. Higher priority beaches 

are tested more frequently, including 25 high-priority 

beaches that are tested fi ve times per week. Every day, the 

high-priority beaches post one of three signs to advise 

beachgoers of water quality for that day – good, poor, 

or closed. In addition, bathers can also check a website 

to view daily water quality reports for all high-priority 

beaches along the Great Lakes.

Distributing Fact Sheets

Another method of outreach to the public is through 

the dissemination of fact sheets on CSOs and SSOs. 

Municipalities often use these fact sheets to describe 

what CSOs or SSOs are, address specifi c local issues, 

and discuss impacts to local water bodies. Local issues 

addressed in the fact sheets can include disconnecting 

downspouts from the sewer system, local monitoring 

programs, and system improvements that are planned 

or are being implemented to address CSOs and SSOs. 

Fact sheets can also be developed to target specifi c 

commercial or industrial sewer customers encouraging 

best management practices, explaining regulatory 

requirements, or highlighting important pollution 

prevention measures.

EPA’s Offi ce of Wastewater Management has also 

developed a series of outreach materials and fact sheets 

to help municipalities educate citizens on important 

wastewater issues. These materials are available online 

at: http://cfpub.epa.gov/npdes/wastewatermonth.cfm. 

The materials include space to insert local contact 

information for citizens to fi nd more information. Local 

governments can inexpensively produce custom versions 

of the materials with their own addresses and phone 

numbers. 

Stenciling Storm Drains

Storm drain stenciling is frequently used in separate 

storm sewer systems to educate the public that wastes 

disposed of in storm drains fl ow directly to receiving 

waters without treatment. Similarly, municipalities with 

CSSs can use storm drain stenciling as part of a public 

Figure 1. CSO warning sign (King 

County, WA)
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-24

education program (Figure 2). Stenciling the name of 

the water body to which the street inlet drains provides 

a concrete link to the public to the consequences 

of dumping or littering. Storm drain stenciling 

programs can also generate useful information for the 

municipality. Since cities often have more storm drain 

inlets than can be effi ciently inspected by city staff, 

program volunteers may be asked to note drains than 

are clogged with debris or show signs of dumping. 

The municipality can then target these drains for 

maintenance.

Reporting

An essential element of a proper O&M program is 

documentation of accurate and reliable records related 

to CSOs and SSOs. Reporting requirements related to 

CSO and SSO events are typically included in the NPDES 

permit issued to a wastewater utility. Current reporting 

requirements for CSOs and SSOs are not always consistent 

from state-to-state; however, reporting typically involves 

notifying the appropriate regulatory agencies in a timely 

manner after a CSO or SSO event. Several states require 

that the duration and frequency of every CSO event be 

reported in a discharge monitoring report and submitted 

on a monthly basis. Twenty-four hour oral reporting of 

SSO events is generally required, and must be followed by a 

written report within five days of the SSO event. States may 

also require an annual report estimating the volume of CSO 

or SSO discharged over the past year, identifying known or 

potential water quality impacts, and, in the case of SSOs, 

the cause of the spill. Several states compile information 

on reported SSO events in databases or spreadsheets; at 

least two states, Michigan and Maryland, publish lists of 

reported CSO and SSO events on their websites. 

The CSO Control Policy states that the municipality should 

submit to the NPDES permitting authority documentation 

on the implementation of the NMC. Documentation 

should include information that demonstrates:

● The alternatives considered for each minimum control

● The actions selected and the reasons for their selection

● The selected actions already implemented

● A schedule showing additional steps to be taken

● The effectiveness of the minimum controls in 

reducing/eliminating water quality impacts.

The Guidance for Nine Minimum Controls (EPA 1995) 

presents examples of the information that should be 

documented for the NMCs.

Key Considerations

Responsibility for monitoring, public notification, and 

reporting efforts is often shared by a number of agencies 

within a single jurisdiction. These can include:

● Wastewater utility operators

● City, county, or state health department

● City, county, or state environmental agencies

● Drinking water providers

● Public works departments 

This potential overlap can lead to a duplication of efforts 

(e.g., multiple agencies monitoring water quality conditions 

in a single location). Good communication between these 

agencies can help ensure cost-effective data collection and 

a coordinated response to those CSO and SSO events with 

potential to impact the environment or human health. 

Other key considerations related specifically to monitoring, 

public notification, and reporting are discussed below.

Monitoring

Developing the extent of the monitoring program and 

selecting the most appropriate monitoring techniques will 

depend on site characteristics, budget constraints, and 

availability of trained personnel. The development of the 

monitoring program should be closely coordinated with the 

NPDES permitting authority to make sure that monitoring 

results will be acceptable and satisfy the regulatory 

requirements. Some specific considerations for monitoring 

rainfall, sewer system flow, and water quality are discussed 

below.

Figure 2. Community education on the 

importance of storm drain stenciling (King 

County, WA)
Operation & Maintenance: Monitoring, Reporting, and Public Notification

O&M-25

Rainfall

Rainfall conditions may vary signifi cantly over a sewer 

system. Suffi cient rain gages should be located to 

provide data representative of the entire study area.

Rain gages should be located in open spaces away 

from trees or buildings that may shield the gage from 

rainfall. Installing the gages at ground level is preferred, 

rooftops are also an option. Police and fi re stations 

and other public buildings are desirable locations as 

vandalism is prevented.

Sewer System Flow

Monitoring fl ows in sewer systems can be diffi cult 

because of surcharging, backfl ow, tidal fl ows, and 

the intermittent nature of CSOs and SSOs. Although 

some metering installations are designed to operate 

automatically, they are prone to clogging in sewer 

systems and should be checked as often as possible. 

Monitoring locations should be selected to identify 

which structures in the sewer system limit hydraulic 

capacity and should target portions of the system 

that are most likely to have CSOs and SSOs or receive 

signifi cant pollutant loadings. A representative range 

of land uses and basin sizes should be monitored. As 

many overfl ow outfall locations as possible should be 

monitored with an emphasis on discharges to sensitive 

areas. Flow measurement devices can be rotated 

between locations to obtain more comprehensive 

coverage of the sewer system. 

For CSOs and SSOs dependent on rainfall, a suffi cient 

number of storms should be monitored to accurately 

predict the sewer system’s response to a range of rainfall 

conditions.

Water Quality

Flow-weighted composite samples should be collected 

from the sewer system or outfalls to determine the 

average pollutant concentration from an overfl ow 

event (also known as the event mean concentration or 

EMC). Discrete samples from the same location over 

the course of an overfl ow can help determine whether 

a pattern of pollutant concentration exists, such as a 

fi rst-fl ush phenomenon. A range of rainfall events and 

receiving water conditions should be monitored. 

In developing a water quality monitoring plan, the 

location and impacts of all sources of pollutant 

loadings should be considered, and monitoring 

locations should be selected to isolate the impacts 

from CSOs and SSOs as best as possible. Monitoring to 

characterize the pollutant loadings from sources other 

than CSOs and SSOs may be needed. Sensitive areas 

should be given priority for monitoring, such as waters 

with drinking water intakes or recreational uses. The 

implementation of water quality monitoring programs 

should be a high priority at beaches or recreational 

areas directly or indirectly affected by CSOs and 

SSOs due to the increased risk of human contact 

with pollutants and pathogens. Finally, the safety and 

accessibility of monitoring locations should be given 

consideration.

One of the key considerations related to conventional 

water quality monitoring is the lag time between 

collecting water samples and providing the public 

with results. This lag is due to the time it takes (from 

24 to 72 hours) to test for the presence of bacterial 

indicators of CSO or SSO contamination. During this 

time, pathogen levels, weather, and water conditions 

may change, and related environmental or human 

health risks may also change. This means that decisions 

regarding beach and recreational water postings, 

closings, and reopenings using bacterial indicators 

often refl ect conditions as they were one to three days 

earlier (EPA 2002). Further, contaminants may no 

longer be present once test results are available and 

safe beaches may be posted needlessly. Recent studies 

of southern California beach closures showed that 70 

percent of the postings of water quality exceedences last 

less than one day, meaning that water quality is likely to 

have already returned to acceptable levels by the time 

laboratory results are available and warning signs are 

posted (Leecaster and Weisberg 2001).

To address this time lag problem, a number of 

municipalities are using time-relevant water quality 

monitoring and receiving water quality models. These 

techniques seek to shorten analysis times, use quicker 

predictive methods, and communicate water quality 

information to the public on a timely (e.g., near-daily) 

basis so the public can make more informed decisions 

regarding recreational water use (EPA 2002). Specifi c 

activities undertaken to support these objectives 

include monitoring more frequently or at additional 

locations, using analytical methods that provide 

results sooner, using a predictive model to supplement 

monitoring, and improving public notifi cation 

programs.

Public Notification

The principal advantage of a public notification program 

is the potential to reduce exposure of the general public to 

health risks associated with exposure to CSOs and SSOs. 

Well-designed public notification programs also offer 

wastewater utilities an opportunity to educate customers 

and seek assistance from the public in identifying problems, 
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-26

such as dry weather CSOs and SSOs. It can be challenging, 

however, to interest and involve the public in municipal 

efforts to control CSOs and SSOs. 

Public notification programs may be developed 

cooperatively with other agencies and organizations 

including city, county, or state health departments; 

shoreline owner associations; boating and fishing 

associations; or local planning and zoning authorities. 

Cooperative efforts can be a valuable mechanism for 

leveraging resources, as well as enhancing the quality, 

credibility, and success of public notification programs 

(EPA 2002). Experience shows that it may also be valuable 

for the wastewater utility to establish a relationship with 

the local media to help promote efforts to control CSO 

and SSO events, as well as to distribute time-relevant 

recreational water quality information. More extensive 

experience working with the local news media can also help 

ensure minimal misinterpretation regarding the occurrence 

of CSO and SSO events. 

The public is often not interested in the details behind 

the monitoring project, but rather if the water body is 

safe to use. Therefore, it is important that information 

is disseminated in a clear and concise format so that 

the public can consider the relative risk associated with 

exposure to the water body. Unless beachgoers are informed 

about current water quality conditions in a particular 

area, they will be unable to make informed choices about 

destinations or how to avoid exposure to pollutants, if 

necessary.

Reporting

The timely reporting of CSO and SSO events is a regulatory 

requirement; therefore, penalties are assessed for failing to 

report. It is important to maintain regular communication 

with the regulatory authority to ensure that submissions 

comply with permit requirements and meet the 

expectations of the permitting authority.

As municipalities, NPDES permitting authorities, and 

the public undertake efforts to control CSOs and SSOs, 

consideration should be given to developing and reporting 

on performance measures such as:

● End-of-pipe measures that show trends in the 

discharge of CSOs and SSOs, such as reduction in 

pollutant loadings and the frequency, duration, and 

magnitude of CSOs and SSOs;

● Receiving water measures that show trends in relevant 

water quality parameters, such as bacteria and 

dissolved oxygen concentrations; and ● Measures of the use of the receiving waters including 

beach closures, shellfish bed closures, and fish 

populations. ● Administrative measures that track programmatic 

activities;

Reporting on performance measures will allow 

municipalities, states, and EPA to demonstrate the benefits 

and long-term success of CSO and SSO control efforts.

Cost

The cost of monitoring will vary greatly based on the size 

and complexity of the sewer system and receiving waters, 

the number of CSO and SSO events that occur, and the 

techniques used. The costs of monitoring can be significant, 

especially for a large sewer system, a large number of 

outfalls, or frequent occurrences of CSO or SSO events. 

A small scale monitoring program may necessitate more 

conservative assumptions or result in more uncertainty 

when reporting on overflow events and when selecting 

and designing CSO or SSO controls. It should be noted 

that large sums of money spent on monitoring should be 

avoided if the additional data will not significantly enhance 

understanding of how a sewer system responds to a range 

of rainfall events, and to what extent receiving waters are 

impacted by CSOs and SSOs.

Analysis of water samples for the presence of indicator 

bacteria typically costs about $35 per sample (EPA 2003). 

Bacteria data tend to be highly variable; therefore, samples 

may need to be collected in duplicate or triplicate from a 

single location. Additionally, if a CSO or SSO event occurs 

over an extended period of time, multiple samples may 

need to be collected over time. 

EPA believes that, in general, costs for public notification 

programs should be nominal (EPA 1995), but will vary 

with the size of the potentially-impacted population. Costs 

for reporting should be nominal as well, if a well-designed 

O&M plan is carried out.
Operation & Maintenance: Monitoring, Reporting, and Public Notification

O&M-27

Implementation Examples

CSOs have historically caused use restrictions in large 

areas of the upper Narragansett Bay. There are several 

beach areas in the upper bay that are used by the 

public for swimming, diving, and water skiing. The 

occurrence of recreational use in areas with use restrictions is a public health concern.

To address this public health issue, the Rhode Island Department of Health’s (RIDOH’s) Beaches Monitoring Project samples 23 

sites in the upper bay. RIDOH conducts weekly beach monitoring from mid-May through mid-September to coincide with the 

summer beach season. Beaches are closed based on exceedances of bacterial water quality standards. RIDOH also closes beaches 

preemptively, without waiting for sampling results, if a CSO or SSO occurs near a beach. If a beach is closed because of high bacteria 

levels, it is resampled daily until bacteria levels fall below the water quality criteria. The beach is reopened if fi ve consecutive 

samples are collected at least 24 hours apart that are at or below the bacterial water quality standard. Upon reopening, at least 

three samples are collected each week for three months. The public is notifi ed of beach closures using the following procedures:

● Appropriate municipal and state offi cials are notifi ed

● An advisory or closure notice is posted at the beach, as needed

● A press release is issued and the project website and hotline are updated with current conditions

Many of these sites sampled were found to display consistently poor water quality, exceeding the state bacteria standard more 

than 50 percent of the time. 

More information at: http://www.health.state.ri.us/environment/beaches/index.html

Responsible Agency: Rhode Island Department of Health

Population Served: 360,000

NARRAGANSETT BAY, RI

The King County Wastewater Treatment Division works jointly with the 

Seattle Public Utilities and the Seattle-King County Health Department in 

posting warning signs at CSO locations and undertaking public outreach. 

The Health Department maintains a CSO information line and website to 

answer any health concerns about CSOs or questions such as, “How long 

does water stay contaminated after a discharge?” In early 1999, King County

and the City of Seattle posted signs near CSO outfalls. The signs warn people 

not to swim or fi sh at these outfalls during or following rainstorms. The signs also include the phone number of the CSO Information 

Line operated by the Seattle-King County Health Department. The Health Department recommends that people not go in the water 

near these signs for 48 hours after a heavy rain.

Contact: Bob Swarmer, King County Wastewater Treat,emt Division

KING COUNTY, WA

Responsible Agency: King County Wastewater 

Treatment Division

Population Served: 1.3 million

Service Area: 420 sq. mi.

Sewer System: 275 mi. of sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

O&M-28

The Allegheny County Health Department (ACHD) 

implemented a public notifi cation program designed to 

warn the public of possible river contamination as a result 

of CSO events, and advise limited contact while engaging 

in recreational activities on the river during periods 

immediately following wet weather events. The frequency 

and duration of the alerts varies depending on the amount of 

rainfall. ACHD publishes river water advisories in local newspapers and produces public service announcements on local television 

stations to educate the public of the dangers attributable to the CSO discharges. When an alert is in effect, marinas, docks, and other 

sites along the rivers fl y an orange-colored fl ag with black CSO lettering. Thirty-four sites participated in the program during the 2003 

recreation season - seventeen on the Allegheny River, eight each on the Monongahela and Ohio Rivers, and one on the Youghiogheny 

River. The fl ags are lowered when “safe” levels have returned. The public can also call the river water advisory hotline or visit the ACHD 

website to obtain updates 24 hours a day.

Thirteen alerts were issued during the wet summer of 2002, lasting 83 days altogether or an average of six days each. By contrast, 

during the dry summer of 1999, 11 alerts were issued and lasted a total of 33 days or an average of three days each.

More information at http://www.achd.net/

Responsible Agency: Allegheny County Health Department

Population Served: 850,000

Service Area: 311 sq. mi.

Sewer System: 85 mi. of interceptor sewer

PITTSBURGH/

ALLEGHENY COUNTY, PA

One of the monitoring objectives of the Charles River Basin/Boston Harbor 

Beaches Project was to develop a predictive model that would supplement the 

water quality monitoring program and provide quick, conservative estimates 

of bacteria levels at four Boston Harbor beaches. The four beaches are sampled 

seven times per week; rain gages have been installed close to the beaches. 

Analysis of data collected at the beaches showed that the previous day’s rainfall was a better predictor of water quality than the 

previous 24-hour bacteria measurement. Therefore, a simple rainfall model was developed for each of the beaches, and combined 

results from the rainfall model and bacteria monitoring are used to determine when to post the beaches. Beaches are reopened only 

when monitoring results indicate attainment of the bacterial water quality standard. The project uses several different types of public 

notifi cation techniques to communicate the results of the monitoring program. These include:

● Availability of daily water quality conditions on the Metropolitan District Commission website

● A telephone hotline that provides updated water quality conditions for Boston Harbor beaches on a daily basis 

throughout the beach season

● Posters, water bottles, and brochures that explain and highlight the beach monitoring program

● Notifi cation and other communications with the Massachusetts Department of Public Health and local boards of health

More information at http://www.crwa.org

BOSTON, MA

Responsible Agency: Charles River Watershed 

Association, Metropolitan District Commission, 

and Massachusetts Water Resources Authority
Operation & Maintenance: Monitoring, Reporting, and Public Notification

O&M-29

References

Allegheny County Health Department. “Topic: Water 

Pollution - Surface and Underground Sources of Water.” 

Retrieved June 3, 2003.

http://trfn.clpgh.org/achd/sewage.html.

Bartram, J., and G. Rees, eds. 2000. Monitoring Bathing 

Waters: A Practical Guide to the Design and Implementation 

of Assessments and Monitoring Programmes. London and 

New York: E&FN SPON.

Boehm, A.B., et. al. 2002. Decadal and shorter period 

variability and surf zone water quality at Huntington Beach, 

California. Environmental Science and Technology. 36:3885-

3892.

Citizens Environmental Research Institute (CERI). 1999. 

Assessment Strategy for Evaluating the Environmental and 

Health Impacts of Sanitary Sewer CSOs and SSOs from 

Separate Sanitary Sewers. EPA Cooperative Agreement CX824848-01-1.

EPA Office of Water. 1995. Combined Sewer CSOs and SSOs: 

Guidance for Nine Minimum Controls. EPA 832-B-95-003.

EPA Office of Wastewater Management. 1999. Combined 

Sewer CSOs and SSOs: Guidance for Monitoring and 

Modeling. EPA 832-B-99-002.

EPA Office of Water. 2001. Report to Congress: 

Implementation and Enforcement of the Combined Sewer 

Overflow Control Policy. EPA 833-R-01-003.

EPA Office of Water. 2001a. Source Water Protection 

Practices Bulletin: Managing Sanitary Sewer CSOs and 

SSOs and Combined Sewer CSOs and SSOs to Prevent 

Contamination of Drinking Water. EPA 916-F-01-032.

EPA Office of Research and Development and Office of 

Water. 2001. National Coastal Condition Report. EPA 620-R01-005.

EPA Office of Research and Development. 2002a. TimeRelevant Beach and Recreational Water Quality Monitoring 

and Reporting. EPA 625-R-02-0017.

EPA Office of Water. 2002b. National Beach Guidance and 

Required Performance Criteria for Grants. EPA-823-B-02-

004.

EPA Office of Environmental Informantion. 2002c. 

Guidance for Quality Assurance Project Plans (EPA QA/G-5). 

EPA 240-R-02-009.

EPA Office of Water. 2003. Guidelines establishing test 

procedures for the analysis of pollutants; analytical 

methods for biological pollutants in ambient water: Final 

rule. Federal Register 68, no. 139, July 21, 2003.

King County Department of Natural Resources and 

Parks Wastewater Treatment Division. “The CSO 

Control Program.” Retrieved June 3, 2003. http://

www.dnr.metrokc.gov/wtd/cso/page02.htm.

King County Department of Natural Resources and Parks 

Wastewater Treatment Division. March 2002. “Regional 

Wastewater Services Plan - Water Quality Report.” Retrieved 

October 1, 2003.

http://dnr.metrokc.gov/wtd/rwsp/documents/WQ2002.pdf.

King County Department of Natural Resources and 

Parks Wastewater Treatment Division. 2002. “2001/2002 

Combined Sewer Overflow Report.” Retrieved October 1, 

2003.

http://dnr.metrokc.gov/WTD/cso/2001-02-intro.htm.

Leecaster, M.K., and S.B. Weisberg. 2001. Effect of sampling 

frequency on shoreline microbiology assessments. Marine 

Pollution Bulletin 42:1150-1154.

Southern California Coastal Water Research Project 

(SCCWRP). 2003. “Research Plan 2003-2004.” Retrieved 

July 7, 2003. 

http://www.sccwrp.org/about/rspln2003-2004.html.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Maximizing Flow to

Treatment Plant

Collection System Controls

Overview

Maximizing the amount of wet weather flow transported 

to the wastewater treatment plant (WWTP) is a common 

technique for reducing the volume and frequency 

of CSO and SSO discharges. Maximizing the use of 

existing facilities to treat wet weather flows that would 

otherwise overflow without treatment is constructive in 

all circumstances. The various technologies available for 

maximizing the amount of flow conveyed to the WWTP 

include minimum measures that can be implemented 

without capital investment, and more capital intensive 

projects that require planning, design, and construction. 

Maximizing flow to the WWTP is one of the nine 

minimum controls (NMC) established under EPA’s 1994 

CSO Control Policy. As an NMC, maximization of flow 

to the WWTP includes measures that do not require 

significant engineering studies or major construction. 

Simple modifications to existing facilities such as 

adjustment of regulators to divert more flow to the WWTP 

can be done rather inexpensively. The CSO Control Policy 

also encourages municipalities to consider use of WWTP 

capacity for CSO control as part of developing a longterm control plan (LTCP). In doing so, municipalities may 

consider more capital intensive measures to maximize the 

wet weather flow delivered to the WWTP, including pump 

station enhancements and construction of relief sewers in 

areas with insufficient system capacity. 

Many of the techniques for maximizing flow to the WWTP 

specifically referenced and expected for combined sewer 

systems (CSSs) have broad utility and can also be applied 

to sanitary sewer systems (SSSs). EPA recommends that 

the measures listed in Table 1 be considered as part of any 

effort to maximize flow to the WWTP (EPA 1995).

Effective implementation of controls to maximize flow 

to the WWTP requires a thorough understanding of the 

sewer system and how it functions during wet weather. This 

often includes a concurrent assessment of the sewer system 

and treatment plant operations to ensure that increased 

flows do not have adverse consequences, such as flooding 

within the system or at the WWTP, or upset of biological 

Table 1. Considerations in maximizing flow to the WWTP.

Location Measures

Sewer System Determine the capacity of the major interceptor(s) and pumping station(s) that deliver flows to the 

treatment plant.

Treatment Plant Develop cost estimates for any planned physical modifications and any other additional operations 

and maintenance (O&M) costs at the treatment plant due to increased wet weather flow.

Compare the current flows with the design capacity of the overall facility, as well as the capacity of 

individual unit processes. Identify the location of available excess capacity.

Determine the ability of the facility to operate acceptably at incremental increases in wet weather 

flows and estimate the effect on the WWTP’s compliance with the effluent limits in its permit. 

For example, increased flows may upset biological processes and decrease performance for an 

extended period after the wet weather flows have subsided.

Determine whether inoperative or unused treatment facilities on the WWTP site can be used to 

store or treat wet weather flows.

Analyze existing records to compare flows processed by the plant during wet weather events and 

dry periods and determine the relationships between performance and flow.

Sewer system maintenance practices (NJ Dept. of Environmental Protection).
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-2

treatment processes. This technology description is focused 

on the modifications and operational changes within the 

sewer system. Specific measures discussed include:

● Regulator adjustments ● Pump station operation and maintenance practices

● Sewer system operation and maintenance practices

● Conveyance capacity evaluations

● Real-time control and monitoring

Additional information on optimizing WWTP 

performance during periods of wet weather is presented 

in the “Plant Modifications Technology Description” in 

Appendix B of the 2003 Report to Congress on the Impacts 

and Control of Combined Sewer Overflows and Sanitary 

Sewer Overflows.

Regulator Adjustments

Simple modifi cation to regulating devices in CSSs, 

such as weirs, can be useful in maximizing fl ow to 

the WWTP. Adding stop planks or raising brick/

concrete weirs through the construction of either 

temporary or permanent structures, can increase the 

volume of wet weather fl ows stored in the CSS and 

eventually delivered to the WWTP for treatment. Such 

modifi cations should be made incrementally with 

careful observation of resultant changes in wet weather 

fl ow patterns in the CSS to prevent fl ooding.

Pump Station Operation and 

Maintenance Practices

Routine pump station O&M can also improve the 

conveyance of wet weather fl ows to the WWTP; 

this includes regular maintenance of pumps and 

accessories, as well as periodic cleaning of wet wells 

to remove grit, scum, and debris. Where emergency 

generators are provided, generators should be exercised 

weekly (NYSDEC 2003). Automatic transfer switches 

for transferring power from emergency generators 

or backup utility power feeds should be tested and 

exercised periodically. To be sure that all equipment 

is ready for service when wet weather arrives, regular 

maintenance of all equipment should be provided in 

accordance with the manufacturer’s recommendations. 

In addition to routine O&M, more detailed assessment 

of pump station performance can be made to ensure 

that the maximum fl ow is delivered to the WWTP. 

These include evaluating whether the pumps are 

currently able to achieve their rated pumping capacities 

and whether improved wet weather operating 

procedures would increase the fl ow volume delivered 

to the WWTP. Rehabilitation or replacement should be 

considered for pumps that are no longer able to achieve 

their rate pumping capacity. Wet weather operating 

procedures can include adjustment to pump stations 

and their control systems to increase in-system storage 

during wet weather. For example, if the inlet sewer to 

the pumping station is not normally submerged and 

has available storage capacity, pump controls can be 

adjusted to allow the wet well level to rise above the 

feed pipe elevation, resulting in storage in the sewer 

system (NYSDEC 2003).

Sewer System Operation and 

Maintenance Practices

Operations and maintenance activities are necessary 

for sewer systems to function as designed and to deliver 

the maximum fl ow possible to the WWTP. Over time, 

sewer systems can deteriorate structurally or become 

clogged through the introduction of oil and grease and 

other obstructions into the sewers. Grit buildup reduces 

the hydraulic capacity of sewers and interceptors 

by reducing the cross-sectional area and increasing 

frictional resistance. 

O&M practices include pollution prevention, sewer 

cleaning, monitoring, testing, inspection, and repair or 

rehabilitation. These activities enhance sewer system 

performance and are important for maintaining 

conveyance capacity. Some states include specifi c O&M 

requirements in NPDES permits for sewer systems in 

order to maximize the transport of wet weather fl ow to 

the WWTP for treatment. For additional information 

on proper O&M, see the series of O&M Technology 

Descriptions in Appendix B of the 2003 Report to 

Congress on the Impacts and Control of Combined Sewer 

Overfl ows and Sanitary Sewer Overfl ows.

Conveyance Capacity Evaluations

Quantifying sewer system transport capacity is 

valuable for communities seeking to maximize fl ow to 

their WWTPs. Evaluating transport capacity involves 

determining the maximum amount of fl ow that can 

be transported by the primary trunk sewers and 

interceptors without raising water elevations in these 

sewers to levels which increase the risk of basement or 

street fl ooding (Sherrill et al. 1997).

Models, varying from simple to complex, are 

commonly applied to rate a sewer system’s transport 

capacity. Historical information can be used to identify 

target water levels within the system that do not cause 

problems such as SSOs, basement backups, or street 

fl ooding. Transport capacity is determined through 

evaluation of modeled fl ows at fl ow rates less than or 

equal to the target water levels. Interceptor sewers and 

trunk lines are usually rated separately. 
Collection System Controls: Maximizing Flow to Treatment Plant

CSC-3

It is important to consider site-specifi c characteristics 

of the sewer system when evaluating conveyance 

capacity. Conveyance of fl ow through a sewer is 

dependent on the difference in water level from the 

upstream to the downstream end, pipe slope, sewer size 

(length, shape, and cross-sectional area), and roughness 

characteristics. Under ideal conditions, a single sewer 

pipe may be able to convey fl ow at its entire capacity. 

However, real-system boundary conditions such as 

river elevations, downstream sewer capacities, regulator 

capacities, and pump station wet well levels will affect 

the transport of fl ow (Sherrill et al. 1997). 

The presence of bottlenecks in a sewer system is also 

an important consideration in conveyance capacity 

evaluations. Bottlenecks may occur at any point in the 

sewer system; they limit the amount of fl ow that can be 

transported to the WWTP for treatment during periods 

of high fl ow. Chronic bottlenecks typically occur as a 

result of insuffi cient interceptor capacity that causes 

fl ow to backup in connecting sewers. An example of 

a bottleneck resulting from insuffi cient interceptor 

capacity during a wet weather event is presented in 

Figure 1. As shown, the hydraulic response to the 

bottleneck is a decrease in fl ow velocity and an increase 

in water level. In acute situations, water levels increase 

until they rise above an overfl ow point (in this case the 

manhole rim) and an SSO occurs (ASCE 2000). Both 

velocity and water level return to normal once the high 

wet weather fl ow rates subside. 

Bottlenecks may also occur when the sewers delivering 

fl ow to the WWTP have less capacity than the 

individual unit processes at the plant. For example, if 

interceptors leading to the WWTP have a conveyance 

capacity of 50 MGD, yet unit processes (e.g., primary 

treatment, secondary treatment, and disinfection) at 

the plant can treat 75 MGD, a hydraulic bottleneck 

exists in the sewer system. This bottleneck prevents 

the treatment capacity of the plant from being fully 

utilized. In order to maximize fl ow to the WWTP, 

bottlenecks need to be reduced or removed. Potential 

modifi cations include (Field et al. 1994): 

● Increasing interceptor, pumping station, and/or 

trunk line transport capacity by replacing, 

rehabilitating, or adding parallel sewer 

components;

● Injecting polymers into the sewer system to reduce 

sewer roughness and increase carrying capacity in 

surcharged areas; and

● Improving operations and management 

procedures to remove obstructions. 

 

Real-Time Control and Monitoring

Monitoring and the use of real-time control 

technologies can also assist in maximizing fl ows to 

the WWTP. An effective monitoring program that 

gathers information on rainfall, fl ow, and storage 

at major hydraulic control points enhances the 

overall understanding of system performance. In 

SSSs, enhanced monitoring information can be used 

operationally to identify blockages or rainfall induced 

SSOs. In CSSs, the linkage of real time fl ow, regulator, 

pump, and storage information can be used effectively 

to maximize use of the sewer system for storage and to 

maximize fl ow to the WWTP for treatment. Additional 

information on real-time control technologies is 

presented in the “Monitoring and Real-Time Control 

Technology Description” in Appendix B of the 

2003 Report to Congress on the Impacts and Control 

of Combined Sewer Overfl ows and Sanitary Sewer 

Overfl ows.

Key Considerations

Applicability

Maximizing flow to the WWTP requires attention to both 

regulatory issues (e.g., NPDES permit requirements) and 

technical considerations (i.e., conveyance and treatment 

capacity). WWTPs are generally subject to EPA’s secondary 

treatment regulations. Secondary treatment requirements 

specify effluent concentration limits for biochemical 

oxygen demand (BOD) and total suspended solids (TSS), 

as well as a minimum removal percent (85 percent). These 

requirements are enforceable conditions in WWTP permits. 

The regulations provide some flexibility for WWTPs in 

communities receiving elevated flows (and more dilute 

influent) during wet weather by allowing for waivers of the 

Figure 1. Schematic showing water levels and velocity 

 conditions at a manhole when a bottleneck 

 occurs (ASCE 2000).

Manhole rim elevation

Increase in Time

Water Level and Velocity

Depth

Velocity
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-4

percent removal requirement. Waivers are not available, 

however, from effluent concentration limits (EPA 1995). 

Therefore, the optimal volume of wet weather flow 

transported to the plant may be constrained by provisions 

in existing discharge permits and the ability to modify 

provisions for increased flows during wet weather events. 

Understanding the link between sewer system and 

WWTP operation can be the difference between effective 

treatment of wet weather flows and adverse environmental 

and financial consequences. Operational and structural 

modifications to maximize flow transport to the WWTP 

should only be made if the WWTP can accept the increased 

flows. Otherwise, consequences may include flooding 

the treatment plant and reducing treatment efficiency at 

the plant for extended periods of time. Likewise, changes 

in sewer system operation without a careful analysis of 

transport capacity could result in an increase in basement 

backups or street flooding. For these reasons, both sewer 

system and WWTP capacity issues should be evaluated 

when implementing this control (see Table 1).

Cost

Maximization of flow to the WWTP can be a very costeffective technique for controlling CSOs and SSOs. This 

control seeks to optimize use of existing sewer system and 

treatment plant capacity, which can lessen the need for 

construction of new facilities. The value of maximizing 

flow to the WWTP is dependent on the system-specific 

availability of underutilized conveyance and treatment 

capacity. Although some cost increases can be expected for 

WWTP operation, optimizing the use of existing facilities 

is likely to be more cost-effective than construction of 

structural controls at one or more upstream locations.

Implementation Examples

The fi rst phase of the Philadelphia Water Department (PWD) CSO

strategy focused on the implementation of the nine minimum

controls (NMC), including increasing the transport of fl ow to the

WWTP for treatment. To garner information for PWD’s NMC program

(and eventually the long term control plan), PWD instituted a

$6.5 million project to upgrade its comprehensive system fl ow

monitoring network in its three drainage districts. This fl ow

monitoring program provided information to monitor system performance and enhance operation of the system through existing

infrastructure (PWD 1997).

PWD also took steps to maximize fl ow to their wastewater treatment facilities in the second phase (capital improvement) of their

CSO program. For example, analysis of the Northeast Drainage District Collector System, which conveys fl ow from almost half of

the combined sewer area, showed that sewer operation modifi cations could signifi cantly increase the volume of wet weather

fl ow transported for treatment. Potential modifi cations included (1) reduction of hydraulic constraints in the system that limit

the conveyance capacity of the sewers; and (2) modifi cation of large sewers to provide additional wet weather fl ow storage and

conveyance capacities.

PWD has implemented a range of projects to maximize conveyance to their treatment plants including adding a real-time control

system, replacing pipes and raising dams at regulators, and cleaning and modifying the hydraulic control point regulators along the

main level gravity sewers. A major goal of PWD’s LTCP strategy also includes optimizing interceptor sewer system performance by

maximizing the conveyance capacity of existing interceptors. Example projects are provided below.

● Somerset Interceptor Conveyance Improvements: Removal of grit, sediment, and debris from the interceptor enabled the full

hydraulic capacity of the interceptor to be utilized, allowing for increased capture and representing an approximately 10

percent reduction in CSO volume. The project budget was $300,000.

● Cobbs Creek Low Level Control Projects: Grit accumulation reduced the hydraulic capacity in an interceptor that conveys fl ow

to the low-level pumping station. The grit was removed; fl ow was also rerouted with a 30-inch pipe, increasing the capacity

from 11.8 MGD to15 MGD. This project was completed at a cost of $200,000.

More information at http://www.phila.gov/water/

PHILADELPHIA, PA Maximizing Conveyance Capacity

Responsible Agency: Philadelphia Water Department

Population Served: 2.1 million

Service Area: Not Available

Sewer System: 1,600 mi. of combined sewer;1,200 mi. 

of separate sanitary and storm sewer
Collection System Controls: Maximizing Flow to Treatment Plant

CSC-5

The WWTP for the City of Detroit receives wastewater via three interceptors. The city 

conducted an extensive study which rated its sewer system for both conveyance and 

storage of combined sewage. Rating the conveyance capacity involved determining 

the maximum amount of fl ow that can be transported by the primary trunk sewers 

and interceptors without raising water elevations in these sewers to levels that 

increase the risk of basement or street fl ooding. Historical information was used to 

establish these water levels throughout the CSS. In addition, design data at specifi c locations were used, and detailed risk evaluations 

were conducted at specifi c locations in the system.

System rating included use of the Greater Detroit Regional Sewer System model to simulate fl ow throughout the sewer system for 

a range of storm events. Target water levels determined from the historic information were compared against the resulting water 

levels produced by the model. Flow rates, which predicted water levels equal to or less than target water levels, were used to establish 

the transport ratings. Trunk sewers and four interceptor sewers were rated separately (Sherrill et al. 1997).

More information at http://www.wadetrim.com/resources/pub_conf_collrate.pdf

DETROIT, MI Assessing Transport Capacity

Responsible Agency: Detroit Water and 

Sewage Department

Population Served: 3 million

Service Area: 921 sq. mi.

Sewer System: 3,000 mi. of sewer

Massachusetts Water Resources Authority’s (MWRA) CSO plan was developed as part 

of an overall master plan that recommended interceptor system projects to eliminate 

bottlenecks that contribute to CSOs and to optimize existing facility operation 

during wet weather. Between 1988-2000, several transport-related projects were 

conducted to maximize wet weather fl ow conveyance to Deer Island Treatment 

Plant. This included rehabilitation of trunk sewers, improved pumping at Deer Island 

Treatment Plant, replacement of other pump stations within the collection system, 

and construction of a new pumping station. This component of MWRA’s CSO program provided reductions in CSO discharge from 

approximately 3.3 billion gallons (BG) annually in 1988 to approximately 1.0 BG in 2000 (MWRA 2000).

More recently, MWRA has begun work on the Braintree-Weymouth Relief Facilities Project. This project will expand and improve the 

Braintree-Weymouth System, which is MWRA’s network of sewer pump stations, interceptors, and siphons that serves six Boston area 

communities. Wastewater generated by the six communities currently must pass through the Braintree-Weymouth pump station. 

The 54 MGD capacity at this pump station, however, is not suffi cient to handle peak fl ows and presents a hydraulic bottleneck. The 

project will increase the Braintree-Weymouth System’s peak fl ow capacity by approximately 19 MGD, streamlining the fl ow route 

from South Shore communities to the Nut Island Headworks and the Deer Island Treatment Plant. Specifi cally, the project includes 

constructing an intermediate pump station and a multi-use deep rock tunnel, replacing and rehabilitating the Braintree pump 

station, and adding new interceptors and siphons. The total project cost is estimated at $150 million (MWRA 2001).

More information at http://www.mwra.state.ma.us 

BOSTON, MA Elimination of Bottlenecks and System Optimization

Responsible Agency: Massachusetts 

Water Resources Authority

Population Served: 2.5 million

Service Area: 228sq. mi.

Sewer System: Not Available
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-6

References

American Society of Civil Engineers (ASCE). 2000. Protocols 

for Identifying Sanitary Sewer Overflows. Prepared by Black 

& Veatch under EPA, Office of Wastewater Management 

Cooperative Agreement. EPA Cooperative Agreement #CX 

826097-01-0. Reston, VA: ASCE.

EPA Office of Water. 1995. Combined Sewer Overflows–

Guidance for Nine Minimum Controls. EPA 832-B-95-003.

Field, R., et al. 1994. Optimization of CSO Storage and 

Treatment Systems. Presented at “A Global Perspective for 

Reducing CSOs: Balancing Technologies, Costs, and Water 

Quality” Water Environment Federation (WEF) Specialty 

Conference, Louisville, Kentucky. July 10-13, 1994.

Massachusetts Water Resources Authority (MWRA). 2000. 

MWRA Business Plan Strategy #17: Implement CSO Control 

Plan by FY09 - Draft. v. 1.2. Retrieved September 1, 2003

http://www.mwra.state.ma.us/org/busplan/17.pdf

MWRA. 2001. Facts about the Braintree-Weymouth Relief 

Facilities Project. Boston, MA: Massachusetts Water 

Resources Authority. Retrieved September 4, 2003

http://www.mwra.state.ma.us/03sewer/graphic/

braintreeweyFS01.pdf

NYSDEC. 2003. Wet Weather Operating Practices for POTWs 

with Combined Sewers: “Technology Transfer Document.” 

Retrieved September 1, 2003

http://www.dec.state.ny.us/website/dow/bwcp/ww_

techtran.pdf

Philadelphia Water Department (PWD). 1997. CSO 

Documentation Long Term Control Plan. Submitted to: 

Pennsylvania Department of Environment Protection 

Bureau of Water Quality Management in partial fulfillment 

of NPDES Permit Nos. PA 0026689, 002662, 0026671 

(January 27, 1997).

Sherrill, J.D., et al. 1997. Rating and Optimization of 

Collection System Transport and Storage. Presented at 

Water Environment Federation Technical and Exhibition 

Conference in Chicago, IL. October 18-22, 1997.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Monitoring & 

Real-Time Control

Collection System Controls

Overview

Effective monitoring programs enable evaluations of 

diurnal and day-to-day flow patterns as well as inflow and 

infiltration (I/I) in the system. Such programs also provide 

a basis to assess the need for, or effect of, maintenance 

efforts. Monitoring has the potential to provide insight 

into operational issues and problems, including the 

identification of CSO and SSO events, in a timely 

manner. Moreover, monitoring is valuable in establishing 

maintenance schedules, in developing hydraulic models 

for planning related to capital improvements, and for 

regulatory compliance. 

In sanitary sewer systems (SSSs), enhanced monitoring 

information can be used operationally to identify blockages 

or capacity constrained areas of the system where wet 

weather SSOs may occur. The use of rainfall-derived 

infiltration and inflow (RDII) quantification methods can 

also serve as a predictive tool to control SSOs. In combined 

sewer systems (CSSs), the linkage of real-time flow, 

regulator, pump, and storage information can effectively 

maximize use of in-system and off-line storage facilities 

and maximize flow to the treatment plant. It should be 

noted that real-time control can also have substantial value 

in some SSSs (e.g., those sized for future growth or I/I). 

However, for practical as well as operational purposes, 

enhanced monitoring is discussed herein as an SSO control, 

and real-time control is discussed as a CSO control. 

Enhanced Monitoring

Enhanced monitoring takes routine monitoring of 

system conditions a step further by using monitoring 

information to track patterns and guide operations and 

maintenance (O&M) decisions. Enhanced monitoring 

generally consists of a network of rain gages, fl ow 

meters, pump station, and storage measurement 

devices that are fully integrated into an information 

management system. The components of the 

information management system can include:

 

● Hardware to measure system conditions (i.e., 

rainfall, sewer fl ow, pumping rate, storage level, 

etc.);

● Software, a central processor, and work stations 

to house management programs and to track, 

analyze, and display system information;

● Reporting mechanisms for compliance purposes; 

and

● Established procedures to respond to problems as 

they are identifi ed.

In practice, enhanced monitoring is typically applied 

systemwide as an SSO control. Abnormal wastewater 

fl ow patterns indicative of a blockage, pump station 

failure, or excessive I/I can be detected automatically. 

In sewer systems with enhanced monitoring programs 

(e.g., fl ow monitoring alarm systems), problematic 

conditions and blockages may be identifi ed in advance 

so that prompt attention and repair may prevent SSOs 

from occurring. In cases where SSOs have already 

occurred due to blockage or power failure, early remote 

detection by an enhanced monitoring network can 

lead to a prompt response that minimizes the volume 

and duration of the overfl ow as well as any potential 

environmental and human health impacts. Enhanced 

monitoring can be an economical way to identify 

and track SSO events that were previously largely 

unpredictable. 

RDII Quantifi cation

During dry weather, fl ow in SSSs primarily consists of 

domestic, commercial, and industrial wastewater mixed 

with some groundwater infi ltration. During periods of 

rainfall and snowmelt, however, dramatic increases in 

wastewater fl ows are often noted and can contribute 

to SSOs and increased treatment costs. The portion 

of sewer fl ow above normal dry weather fl ow is called 

RDII. Most communities served by SSSs are challenged 

to fi nd effective means for predicting sewer system 

response to wet weather events; enhanced monitoring 

Real-time monitoring of a sewer system (MMSD). 
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-8

programs often exceed their fi nancial and staffi ng 

capabilities (WERF 1999).

RDII quantifi cation methods are a tool for estimating 

the magnitude (frequency, location, and volume) of 

RDII and can inform efforts to improve sewer system 

performance. RDII quantifi cation often precedes the 

development of enhanced monitoring programs

The Water Environment Research Federation (WERF) 

recently funded an extensive study that identifi ed eight 

RDII hydrograph generation or RDII quantifi cation 

categories (WERF 1999): 

● Constant unit rate methods 

● Percentage of rainfall volume (R-value) methods

● Percentage of streamfl ow methods

● Synthetic unit hydrograph methods

● Probalistic methods (frequency analysis of peak 

RDII)

● Predictive equations based on rainfall/fl ow 

regression 

● Predictive equations based on synthetic streamfl ow 

and basin characteristics ● RDII as a component of hydraulic software 

These methods were tested under varying climatic and 

sewer operation conditions. With the goal of improved 

prediction and control of SSOs, the study found that 

no single RDII quantifi cation method was universally 

applicable. Availability of data and experience of the 

research team were among the factors that infl uenced 

the usefulness of each method (WERF 1999). 

A hydraulic (routing) analysis, which models the 

existing sewer system’s ability to transport RDII, is 

recommended with RDII quantifi cation to determine 

where SSOs will likely occur in the system. Once 

problems are characterized, RDII methods may also 

be used to evaluate and size appropriate control 

technologies and capacity relief scenarios. Because the 

same storms (including the same antecedent conditions 

and rainfall distributions) are unlikely to occur before 

and after controls are implemented, sewer system 

evaluations must rely on RDII quantifi cations (WERF 

1999).

Real-Time Control

Real-time control seeks to optimize sewer system 

performance during wet weather events as fl ow 

and storage conditions change within the system. 

Many of the same information management system 

components described as part of enhanced monitoring 

are also required for real-time control. Real-time 

control is typically most applicable in CSSs, as these 

systems tend to have substantial in-system storage in 

large pipes designed to transport excess wet weather 

fl ows. In addition to large pipes, CSSs may also have 

additional storage space (e.g., tunnels and tanks) 

that can be incorporated into a real-time control 

strategy. Maximizing system performance may lead to 

substantial savings in capital improvement programs 

if evaluated during the development of a long-term 

control plan (LTCP) (Field et al. 2000). Using feedback 

loops and rules to optimize storage, pumping, and 

treatment, real-time control technologies are capable of 

reducing the frequency, duration, and volume of CSOs 

through optimization of sewer system operations. 

CSSs that use real-time control technology have system 

regulator elements such as weirs, gates, dams, valves, or 

pumps that can function in a real-time environment. 

Real-time control systems rely on monitoring data and 

use a customized software program to operate regulator 

elements without a signifi cant time delay. Figure 1 

shows a monitoring network used to operate a realtime control system.

The regulator elements function according to operating 

rules that are generally based on fl ow level, storage, or 

pumping rates monitored at points within the CSS. In a 

simple example, a regulator element can be controlled 

locally based on conditions that are monitored within 

the vicinity of that element. Alternatively, in a more 

complex example, global control of regulator elements 

would rely on a centralized control device that analyzes 

system-wide monitoring data. Centralized control 

systems can rely on either human operators or fully 

automated computer controls. Real-time control 

regulators that operate based on monitoring inputs are 

Figure 1. Schematic of a monitoring network.

Monitoring

Network

Pump

station

Rain

gauge

Flow

monitor

Control center
Collection System Controls: Monitoring & Real-Time Control

CSC-9

referred to as reactive systems. Predictive systems, in 

contrast, include additional forecast data in the control 

process. Some predictive real-time control systems 

include a sewer system model as a component of the 

control device. In some instances, rainfall forecasts have 

been used successfully to optimize system operations in 

anticipation of rainfall. 

Key Considerations

Applicability

The use of enhanced monitoring and real-time control 

is consistent with the goals and objectives of many O&M 

programs and EPA’s 1994 CSO Control Policy. Enhanced 

monitoring and real-time control can be used to ensure 

that the public receives adequate notification of CSO and 

SSO events and potential impacts. Further, use of real-time 

control technologies for CSO control addresses two of the 

nine minimum controls (NMC). These are: maximizing 

use of the sewer system for storage; and maximizing 

flow to the wastewater treatment plant. In comparison, 

RDII quantification methods have lesser information 

requirements than enhanced monitoring techniques. RDII 

hydrograph generation methods can be used to predict 

RDII in different portions of an SSS and to evaluate source 

control scenarios, and in some cases, to develop enhanced 

monitoring programs.

Enhanced Monitoring

Sewer system monitoring is an essential component 

of an O&M program in most systems. An enhanced 

monitoring network utilizes fact-based knowledge 

to optimize sewer system performance. Enhanced 

monitoring can be used to determine the magnitude 

of the I/I and to better defi ne locations where it is 

occurring. It can also provide direction for maintenance 

activities, detection of illicit storm water connections to 

the SSS, and in some cases, the detection of SSO events. 

The size and complexity of the monitoring network 

usually depend on the size and complexity of the 

sewer system as well as fi nancial considerations. In 

general, automated monitoring technologies are more 

applicable in larger systems, while simpler monitoring 

devices are better suited to smaller systems. In either 

case, the use of enhanced monitoring techniques 

can lead to better decisions on capital improvements 

required for wet weather control facilities.

Many municipalities have supervisory control and 

data acquisition (SCADA) systems already in place, 

which can be operated in an enhanced monitoring 

role if they are linked to broader information 

technology management systems. The information 

collected by existing SCADA systems is often used 

locally rather than globally. Sharing relevant SCADA 

system information among many linked facilities as 

part of an information management system makes 

the information more meaningful; it also presents 

opportunities for detection of SSOs that would not 

otherwise exist. 

RDII Quantifi cation

Many communities do not have the resources necessary 

to implement enhanced monitoring programs. 

However, over-reliance on limited data and/or the 

rough interpretation of monitored fl ows can lead to 

oversimplifi cation of RDII causes and implementation 

of inadequate control technologies. Selection of an 

appropriate technique for estimating RDII is critical. 

Usefulness of a given RDII quantifi cation method 

depends on availability of data, experience of the 

analysis team, and purpose of the RDII evaluation 

(e.g., source control evaluation). Further, regardless of 

the RDII method selected, WERF (1999) found that 

testing on multiple storms is necessary to evaluate the 

true potential of the RDII quantifi cation method for 

extrapolation or comparison with other wet weather 

events. Table 1 presents a number of factors that may 

confound the interpretation of monitoring data in SSSs.

Real-time Control

Real-time control, in general, works best for CSO 

communities with populations greater than 50,000. 

Local, rather than centralized, real-time control systems 

may be cost-effective for smaller CSO communities 

with limited control points. Real-time control tends 

to be more effective in areas with level, as opposed 

to steep, terrain where it is more practical to store 

wastewater in existing sewers. Further, a CSS that is 

already operating at or near capacity will not benefi t 

from real-time control; systems which have capacity 

that is not being used effectively stand to gain more. 

Real-time control has also proved useful for 

communities with both sanitary and combined sewers 

(e.g., Milwaukee, WI; Louisville, KY; and Quebec, 

Ontario, Canada). In such systems, real-time control 

is used to divert fl ows to and from storage systems 

during wet weather. For example, real-time control is 

used to prevent storage systems from fi lling entirely 

with combined sewage, reserving space for separate 

sewage. This is achieved by incorporating separate 

sewer volume predictions into the real-time operational 

strategies, where the goal is eliminating SSOs and 

minimizing CSOs (Schultz et al. 2001).
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-10

Some advantages of real-time control include: 

● Storage facilities can be dynamically operated and 

continuously optimized in response to changing 

conditions;

● Runoff and hydraulic models can be integrated 

into operating rules and control algorithms;

● System response can be predicted through use of 

rainfall forecast data and a local rain gage network 

with adequate spatial coverage; and

● Seasonal and spatial variation in rainfall and 

receiving water fl ows and volumes can be 

accounted for in the system.

Communities that do not experience much spatial 

or seasonal rainfall variation or that utilize receiving 

waters with a static assimilative capacity may not be 

able to take advantage of some these real-time control 

features.

Cost

The capital cost of implementing an enhanced monitoring 

or real-time control scheme depends on the quality and 

quantity of control, the measurement devices required 

for successful implementation, as well as any software 

needed to manage or process the data (Field et al. 2000). 

Monitoring and control schemes may not be sufficient as a 

stand-alone solution to completely control CSOs or SSOs; 

therefore, they should be evaluated as part of the solution. 

O&M costs are dependent on the characteristics of the 

system being monitored and include regular inspection 

of the monitors. In systems using real-time control, O&M 

costs also include mechanical maintenance of the regulator 

elements.

The initial costs of enhanced monitoring or real-time 

control can be significant and may be prohibitive for small 

communities. The monitoring costs, however, may be a 

fraction of the cost of large capital projects that would 

achieve similar levels of CSO and SSO reduction, such 

as construction of additional conveyance, storage, or 

treatment facilities.

Monitoring Data Observation Common Interpretation Confounding Factors

Dry weather flow consistently 

higher than expected sanitary 

flow contribution

Infiltration through leaky 

pipes

● Leakage from an adjacent lake or river directly into sanitary 

sewer

● Underground spring intercepted by the sanitary sewer

● Seasonal fluctuation in groundwater

Rapid, dramatic rise in flow 

coincides with rainfall initiation

Unauthorized direct 

connection of roof or yard 

drains

● Leaking manhole lids or corbels in depressions that collect 

runoff

● Leaky pipes along stream banks

● Cross-connection with storm water systems

● Interconnection of the sanitary sewer with underground 

solution channels (common in karst topography)

Delayed and prolonged flow rise 

occurs after rain

Unauthorized connection of 

sump pumps or foundation 

drains to sanitary sewer

● Granular backfill in the sanitary sewer trench acting as a french 

drain

● Seasonal fluctuation in groundwater; response may be rapid 

depending on soils and trenches

Flows rise proportionately 

to rainfall, but only up to an 

observable maximum

Direct connections with 

capacity restrictions

● Further flow increases restricted by downstream blockages, 

backwater, or lift station capacity

● Further flow increases relieved by upstream overflows

Table 1. Common interpretations of flow monitoring data (WERF 1999).
Collection System Controls: Monitoring & Real-Time Control

CSC-11

Implementation Examples

Seattle was one of the fi rst U.S. communities to implement and operate 

an advanced real-time control system. Seattle’s system, called Computer 

Augmented Treatment and Disposal (CATAD), began operating in 1971. CATAD 

manages 13,120 acres of fully combined sewer area as well as 28,000 acres of

partially-separated sewers. The network included 17 regulator structures and

one major pumping station. CATAD has reduced CSO volume between 9 and 

49 percent at different outfall locations. The actual reduction realized depends on the rainfall volume and patterns during each 

individual year.

The capital cost for CATAD was $16.8 million, and O&M costs were approximately $16 per acre (2002 dollars). Estimated costs for 

sewer separation or construction of additional storage capacity to achieve equivalent reductions in overfl ow volume range between 

$127-$760 million (2002 dollars). In the late 1980s, treatment plant computer hardware was upgraded, remote telemetry units at 

regulators and pump stations were replaced by programmable logic controllers, and operators’ graphical displays were improved. 

Based on the success of the CATAD technology, Seattle implemented a new, predictive real-time control system that went online 

in early 1992. Rainfall prediction capabilities that utilized rain gage data and a runoff model were added at this time. A global 

optimization program was introduced that computed optimal fl ow and corresponding gate position for each regulator. Currently, 

the system’s centralized computer hardware is being upgraded. 

Contact: Bob Swarmer, King County Wastewater Treatment Division

SEATTLE, WA Real-Time Sewer System Controls

Responsible Agency: Seattle Public Utilities

Population Served: 1.4 million

Service Area: 64 sq. mi.

Sewer System: 335 mi. sewer

In 1986, Milwaukee Metropolitan Sewerage District (MMSD) designed and

installed real-time sewer system controls. The MMSD sewer system includes 

the Metropolitan Interceptor Sewer System (MIS) that collects fl ow from the 

local sewers; an Inline Storage System (ISS) that temporarily stores excess 

fl ows until treatment capacity is available, and a computer-based central 

control system. The MIS system collects wastewater from both sanitary and 

combined sewers and conveys fl ow to two wastewater treatment plants.

MMSD uses remote and local sensors to control intra-system fl ow diversions to both relief interceptors and temporary storage. 

Flows can be rerouted to avoid surcharging the system or to maximize treatment capacity during wet weather events. Routing is 

performed by adjusting diversion gates, which are controlled by monitoring multi-level sensors located at critical points in the MIS. 

Importantly, MMSD’s real-time control system is used to prevent storage systems from fi lling entirely with combined sewage and to 

reserve space for the separate sanitary sewage. This is achieved by incorporating sanitary sewer volume predictions into the realtime operational strategies, where the goal is eliminating SSOs and minimizing CSOs. Precipitation and meteorological forecasts are 

used to calculate the storage volume that must be reserved for anticipated sanitary sewage fl ows.

MMSD’s system was implemented to address chronic CSO and SSO problems cited in national and state court actions in the 1970s. 

In the mid-1970s, the city regularly experienced hundreds of SSOs and over 100 CSOs during wet weather; many homes in the 

sanitary sewer service area also faced sewage backups one or more times per year. MMSD has seen dramatic reductions in CSOs, 

SSOs, and backups in the last few decades. Furthermore, the real-time control system has provided much-needed fl exibility in system 

operation, allowing MMSD to better accommodate variable precipitation patterns, growth patterns, and lake and groundwater levels 

(Schultz et al. 2001).

Contact: Nancy Schultz, CH2M Hill

MILWAUKEE, WI Real-Time Sewer Sytem Controls

Responsible Agency: Milwaukee 

Metropolitan Sewerage District 

Population Served: 1.1 million

Service Area: 420 sq. mi.

Sewer System: 2,200 mi. of collector sewer; 

310 mi. of intercepting and main sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-12

In 1998-1999, the City of Quebec implemented a centralized, or 

global, optimal and predictive real-time control (GO RTC) system 

in its westerly sewer system. Quebec Urban Community’s (QUC’s) 

westerly catchment drains 82,000 acres and contains 41 miles of

interceptor and 22 regulators; it is served by an 82 MGD treatment 

plant. The GO RTC equipment consists of fi ve control stations, four 

monitoring stations, thirteen rainfall stations, and one central control station (Colas et al. 2001). The GO RTC system improves the fl ow 

management of the westerly system by taking advantage of 3.7 million gallons of in-line storage as well as wet weather treatment 

capacity at the plant. Pressure fl ow conditions that occur in the system are also eliminated, thereby protecting downstream areas 

against basement backups. The cost of the western installation GO RTC system was approximately $2 million. Operation costs are low 

because existing staff were trained to operate and maintain the system (Colas 2003).

In the late 1990s, EPA funded a demonstration study of three real-time control scenarios in the westerly QUC catchment (Field et.al.

2000). Using modeling tools and rainfall data from the summer of 1998, Field et al. (2000) found that the automated central control 

system, eventually implemented as GO RTC, performed better as system complexity increased. Actual reductions in CSO volume 

have exceeded those predicted by Field et al.(2000)–i.e., reductions of 24-47 percent. Compared to simulations of past system 

confi gurations, CSO volumes were reduced by 60 percent in 1999, 75 percent in 2000, and 83 percent in 2001. At some sites, CSOs 

were eliminated. In other areas, where storage was limited, CSO frequency was reduced by more than 40 percent (Colas 2003).

Contact: H. Colas, BPR CSO

Real-Time Control System

QUEBEC, ONTARIO, 

CANADA

Responsible Agency: Quebec Urban Community

Population Served: 500,000

Service Area: 213 sq. mi.

Sewer System: Not Available

The City of San Diego MWWD installed a Flow Metering Alarm System 

(FMAS) in September 2000. FMAS uses fl ow meters to monitor wastewater 

fl ow conditions, which provides real-time event notifi cation through the 

land-line telemetry system. Specifi cally, 92 alarmed fl ow meters provide 

coverage for 95 percent of MWWD’s sewers with a diameter of 15 inches or 

greater. Flow meters are also used by MWWD to meter fl ows from San Diego 

and its 15 satellite agencies, collect data for sewer modeling, evaluate trunk

sewer capacities, and investigate I/I issues. MWWD hired a maintenance contractor to maintain all the fl ow meters in their system 

including those used for FMAS. In addition, MWWD created a new section of three to four staff (with supplemental help on nights 

and weekends) to monitor the sewer system, analyze data, and dispatch crews to investigate potential spills and/or minimize active 

SSOs.

The purpose of FMAS is to help prevent, detect, and minimize the impact of major SSOs in the MWWD system. An alarm signals 

when a FMAS meter experiences a 25 percent loss of fl ow. For some areas where the base fl ow is more consistent, the alarms can be 

set to activate when a 15 percent fl uctuation in fl ow occurs. MWWD installed FMAS largely as a result of a large spill that occurred 

in February 2000 when the Alvarado Trunk Sewer was damaged during a winter storm, causing a 34 million gallon spill in an 

inaccessible canyon that went undetected for seven days. This spill forced beach closures, a highly undesirable situation for the City

of San Diego and surrounding communities. 

The FMAS has allowed MWWD to concentrate on specifi c areas of the SSS: trunk sewers where capacity is critical, remote areas, and 

sensitive areas including areas that would trigger beach closures. Although FMAS is principally used to detect major SSOs, it has also 

provided early warning of potential spills allowing crews to be dispatched in time to alleviate blockages. Over the past three years, 

MWWD has also considerably expanded its maintenance and cleaning program and is embarking on a 10-year capital improvement 

program to replace or rehabilitate structurally defective pipe, all in an effort to reduce future SSOs.

Contact: G. Hwang, City of San Diego Metropolitan Wastewater Division

SAN DIEGO, CA Flow Metering Alarm System

Responsible Agency: City of San Diego 

Metropolitan Wastewater Department

Population Served: 1.3 million

Service Area: 310 sq. mi.

Sewer System: 2,300 mi. sewer
Collection System Controls: Monitoring & Real-Time Control

CSC-13

In 2002, Atlanta installed a web-based information system that automates 

data collection from fl ow meters and rain gages. One hundred twenty fl ow 

meters and 35 rain gages provide coverage of the city’s entire sewer system 

and supply data to the information system. This system enables city staff

to view pipe capacities, fl ow levels, and fl oat positions (in the pumping

stations) via the Internet. Alarms calibrated to the system activate when 

fl ow velocities or depths reach predefi ned critical levels, where the potential 

for SSO events is high. 

Flow meters and rain gages have been used in the Atlanta sewer system for a number of years. In the past, fi eld crews were required 

to collect the data, and it often took many weeks for the data to be analyzed. Without alarms or real-time data, the city was frequently

faced with responding to spills after they had been reported by the public or detected by fi eld crews. By automating data collection, 

the city is better able to analyze the data in a timely manner. Crews may be sent to investigate potential problems and act to prevent 

SSOs rather than respond to an overfl ow event.

In addition, the system has helped the city better allocate its resources and focus on sewer lines that need repair, areas where fl ow 

capacity is frequently exceeded, and sections where recurrent blockages occur. If grease build-up is identifi ed as a chronic problem 

in a certain section of pipe, the crew that handles oil and grease issues will be dispatched to investigate (e.g., check grease traps). 

The city reports that businesses, such as restaurants, are more receptive to preventative operation and maintenance changes when 

shown evidence (provided by the monitoring data and CCTV) of the recurrent problem. 

Contact: K. Toomer, Atlanta Department of Public Works

ATLANTA, GA Automated Monitoring System

Responsible Agency: Atlanta Department 

of Public Works

Population Served: 1.2 million

Service Area: 131.4 sq. mi.

Sewer System: 2,000 mi. of sanitary and 

combinedsewer

References

Colas, H., et al. 2001. Operation and Performance of an 

Optimized Real time Control System for Wet Weather 

Pollution Control, Vulnerability of Water Quality in 

Intensively Developing Watersheds, Making the Case for 

High-Performance Integrated Control. Presented at the 

University of Georgia, Athens, Georgia, May 14-16, 2001.

Colas, H. BPR CSO. E-mail correspondence with LimnoTech, Inc., 2003. Washington, DC.

Field, R., Villenueve, E., Stinson, M.K. 2000. “Get Real!” 

Water Environment & Technology. Vol. 12, No. 4: 64-67.

Hwang, G., City of San Diego Metropolitan Wastewater 

Division (MWWD). Interview by Limno-Tech, Inc., 

February 2003. Washington, DC.

Schultz, N., et al. 2001. Milwaukee’s Experience in 

Collection System Controls. Proceedings of WEF Speciality 

Conference, A Collection System Odyssey, Bellevue, 

Washington, July 2001.

Schultz, Nancy, CH2M Hill. E-mail correspondence with 

Limno-Tech, Inc., 2003. Washington, DC.

Stevens, Pat, ADS Environmental Services. Interview by 

Limno-Tech, Inc., January 2003. Washington, DC. 

Swarmer, Bob, King County, WA Wastewater Treatment 

Division. Interview by Limno-Tech, Inc., December 2002. 

Washington, DC.

Toomer, K., Atlanta Department of Public Works. Interview 

by Limno-Tech, Inc., February 2003. Washington, DC.

Water Environment Research Foundation. 1999. Using Flow 

Prediction Technologies to Control Sanitary Sewer Overflows.

Prepared by D. Bennett, et al. Project 97-CTS-8. Alexandria, 

VA: Water Environment Research Foundation.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Infl ow Reduction

Collection System Controls

Overview

Inflow is the direct introduction of storm water into 

a sewer system; common sources include roof leaders, 

basement sump pumps, area drains in yards and driveways, 

foundation drains, cracked or broken manhole covers, 

and cross connections with a separate storm water system. 

Inflow occurs by design, through disrepair, and via illicit 

connections. Inflow reduction refers to techniques used to 

reduce the amount of storm water that enters a combined 

sewer system (CSS) or a sanitary sewer system (SSS). 

 

This technology description focuses on inflow associated 

with direct connections of storm water sources to the 

sewer system. Much of the inflow to CSSs is intentional as 

these systems were designed to convey excess storm water 

away from dwellings and to reduce localized flooding. 

Inflow to SSSs is generally not by design and is often 

illicit. By reducing the volume of storm water entering 

a sewer system, inflow controls free conveyance capacity 

and available storage. This, in turn, aides in reducing the 

frequency, volume, and duration of wet weather CSO and 

SSO events. Inflow reduction is particularly applicable in 

areas where open land is available to receive redirected 

storm water for infiltration or detention, or where storm 

water can be diverted to surface waters either directly or via 

a separate storm water system.

Specific inflow reduction techniques that will be discussed 

in this technology description include disconnection 

of roof leaders; redirection of area drains, foundation 

drains, and basement sump pumps; and cross connection 

elimination.

Disconnection of Roof Leaders

Roof leaders or down-spouts convey rain that falls on 

residential and commercial roofs directly to the sewer 

system. The use of this practice in CSSs is usually 

intentional, and in some instances, required by local 

ordinance. Use of roof leaders to convey rainwater to an 

SSS is generally considered to be an illicit connection 

in most, but not all, communities. In SSS areas, 

roof leaders may have been connected to the SSS by 

builders or homeowners to alleviate localized fl ooding 

associated with wet weather events. The disconnection 

of roof leaders from the sewer system and redirection 

to lawns, dry wells, or drain fi elds, where fl ows can 

infi ltrate into the soil, reduces the amount of storm 

water entering the sewer system. Disconnection of 

roof leaders works best in residential areas where open 

land is available. City-wide surveys are often necessary 

to determine the extent of roof leader connections to 

the sewer system. This infl ow reduction technique can 

be introduced as a voluntary effort or as a mandatory 

requirement. Guidance can be offered to individual 

homeowners on how to redirect the infl ow from 

roof leaders, and it can be combined with other 

infl ow reduction techniques such as area drain and 

basement sump pump redirection. Some communities 

have offered fi nancial incentives to homeowners to 

disconnect roof leaders and have prequalifi ed local 

contractors to provide this service. 

Redirection of Area and Foundation Drains and 

Basement Sump Pumps

Many buildings have a system of area and foundation 

drains and basement sump pumps to alleviate drainage 

problems. As with roof leaders, area and foundation 

drains and basement sumps are typically connected 

to CSSs by design. In some parts of the country, both 

area drains and foundation drains are connected 

to the SSS by design, but in most instances they are 

considered to be illicit connections to the SSS. Flows 

from area and foundation drains and basement sumps 

can generally be redirected away from the sewer system 

to lawns, dry wells, drain fi elds, or an existing separate 

storm water system. However, redirection may require 

additional pumping. City-wide surveys often need to 

be conducted to determine where area drains and sump 

pumps are located, whether they discharge directly to 

the sewer system, and whether it is feasible to redirect 

them.

A roof leader or down-spout connected to the sewer system (MMSD). 
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-16

Elimination of Cross Connections

Cross connections are direct connections between an 

SSS and a separate storm water system. By defi nition, 

it is not possible to have a cross connection in a CSS. 

Cross connections most commonly occur where the 

sanitary service lateral from a home or commercial 

establishment is inappropriately connected to the 

storm water system. Cross connections also often exist 

as remnants of incomplete sewer separation projects. 

Detection and elimination of cross connections 

between separate sanitary and storm water systems can 

reduce infl ow during wet weather events and reduce 

the concentration of bacteria, nutrients, and oxygen 

demanding substances contained in storm water 

discharges. 

Key Considerations

Applicability

There are a number of different sewer testing and 

inspection approaches that are useful for locating sources 

of inflow. These include visual inspections, smoke testing, 

dye-water flooding, water sampling from manholes, 

interpretation of public complaints, and video inspection. 

The most appropriate technique will depend on suspected 

inflow sources and site-specific conditions. Additional 

information on techniques for locating sources of inflow 

is provided in the “Testing and Inspection Technology 

Description” in Appendix B of the Report to Congress on the 

Impacts and Control of CSOs and SSOs.

Inflow reduction can be an efficient way to reduce the 

volume of storm water delivered to both CSSs and SSSs, 

and can result in improved sewer system performance. 

Provided below are specific considerations for each of the 

inflow reduction techniques described above.

Disconnection of Roof Leaders

Disconnection of roof leaders is a relatively simple 

and low-cost technique for reducing infl ow. It is more 

feasible in residential areas where houses are detached, 

yards are suffi ciently large to accommodate increased 

overland fl ow and soils have relatively high infi ltration 

rates. In order for a roof leader disconnection 

program to be successful the public must be educated 

about the benefi ts of disconnection and methods 

for implementing the program. This can be timeconsuming and will most likely require some type of 

rebate program or other incentive for compliance. 

Communities who have experimented with voluntary 

disconnection programs found that approximately 20 

percent of property owners are willing to participate 

(NBC 2000). In addition, because the effect per 

individual roof leader is small, this program must be 

implemented with broad participation across entire 

neighborhoods in order for there to be a discernible 

reduction in sewer system fl ow.

Redirection of Area and Foundation Drains and 

Basement Sump Pumps

In general, area and foundation drains and sump 

pumps are a less common source of infl ow than roof 

leaders, and their location may be harder to determine. 

The feasibility of redirecting drains and sump pumps 

depends on soil type, land slope, and the drainage 

conditions around the home or building. If a separate 

storm water system does not exist, then the excess 

rainwater must be conveyed to a distance far enough 

away and at a reverse slope from the building so that 

water is not allowed to migrate back into the building. 

Similar to the redirection of roof leaders, the volume 

controlled per individual drain or sump pump is small. 

Consequently, the program must be implemented with 

broad participation across neighborhoods in order for 

there to be a discernible reduction in sewer system fl ow. 

Implementation of this type of redirection program can 

be time-consuming and may necessitate use of a rebate 

program or other incentives for compliance.

Elimination of Cross Connections

Several methods exist for detecting and eliminating 

cross connections. Common sewer testing and 

inspection approaches are often appropriate 

for identifying storm water sources that were 

inappropriately connected to the SSS. In addition, 

there are a number of useful indicators for detecting 

connections between private building service laterals 

and the separate storm water system. These include 

inspections to determine the presence of unexpected 

dry weather fl ow in storm sewer lines, and fi nding 

biological indicators that denote the presence of 

human fecal matter in storm drain outfalls. Once cross 

connections are detected, excavation and correction are 

necessary. In addition to detection and elimination of 

existing cross connections, plans for new development 

should be carefully reviewed and inspections should 

be conducted during construction in order to prevent 

future cross connections from being placed.

Cost

The actual cost associated with implementation of an 

inflow reduction program varies considerably and is 

dependent on site-specific conditions. Disconnection of 

roof leaders and redirection of basement sump pumps 

can be quite economical under some circumstances. 

Disconnecting area and foundation drains typically requires 
Collection System Controls: Inflow Reduction

CSC-17

excavation around homes, and is therefore more expensive 

and disruptive than other inflow controls. Key parameters 

in determining the effectiveness of inflow reduction 

techniques are the infiltration rate of the soil in the area 

where flows will be redirected and the land area available 

to infiltrate the wet weather flow. Typical cost ranges for 

various techniques discussed in this technology description 

are presented in Table 1. 

a

 EPA 1999

b

 Arbour and Kerri 1998

Table 1. Costs of inflow reduciton activities

Implementation Examples

Wet weather SSOs were a frequent occurrence in Johnson 

County in the early 1980s. A comprehensive system-wide 

evaluation was conducted in 1983, which included smoke and 

dye-water testing of sewer lines, fl ow and rainfall monitoring, 

visual pipe inspections, and closed circuit television 

inspections. The survey identifi ed infl ow as a major contributor to wet weather SSOs. JCW’s response was to launch an infl ow 

reduction and sewer system rehabilitation program. An ordinance was passed by the Johnson County Board of Commissioners that 

made it illegal for residents to make connections from surface or groundwater sources to the SSS. This ordinance provided JCW with 

the legal authority to require removal of unpermitted infl ow sources, and to prohibit construction of new ones.

As part of the disconnection program, JCW initiated private property inspections to

identify infl ow sources and advise property owners on removal actions. Inspectors

toured commercial and residential building interiors and grounds, and they gathered

data on the location of foundation and area drains, roof leaders, and other apparent

connections to the SSS. Sources suspected of contributing to storm water infl ow

were subjected to smoke and/or dye-water testing, and all unpermitted sources

were scheduled for disconnection. As shown on the right, the most common sources

of infl ow were foundation drains, area drains, sump pumps, and roof leaders. JCW

established informal fi xed-price contracts with local contractors to complete the

work. To help JCW prioritize its remedial efforts, a hydraulic model was developed with

the data from the survey. The infl ow reduction program was completed in 1994. The

infl ow reduction and sewer rehabilitation program resulted in signifi cant reductions

in capacity-related SSOs; wet weather fl ow rates in the sewer system were reduced by

an average of 280 MGD during the 10-year, 6-hour storm. The total cost of the program

was $48.8 million, which includes $11.2 million for the reduction of infl ow from private

property. 

More information at http://cfpub2.epa.gov/clearinghouse/preview.cfm?RESOURCE_ID=253743

JOHNSON COUNTY, KS Inflow Reduction Program

Responsible Agency: Johnson County Wastewater (JCW)

Population Served: 500,000

Service Area: 20 sq. mi.

Sewer System: 1,700 mi. of sanitary sewer

22%

59% 13%

6%

Area

Drains

Sump

Pumps

Roof

Leaders

Foundation

Drains

Types and distribution of inflow 

Technology Cost

Disconnection of roof 

leaders

$45-$75 for individual 

homeowners 

Redirection of area and 

foundation drains and 

basement sump pumps

Varies based on site-specific 

requirements. 

Sump pump redirection costs 

$300-$500 per home a

Cross connection 

elimination

Varies depending on location.

Typical point repairs costs $600-

$8,500 b
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-18

The City of South Portland invested almost $2.5 million 

between 1986 and 1995 to reduce wet weather infl ow into 

their CSS. The program involved surveying 6,000 residential 

buildings. The survey identifi ed approximately 380 roof 

leaders and 300 sump pumps that were connected to 

the CSS. Property owners were notifi ed and offered the 

following incentives to disconnect the infl ow sources: $75 for roof leader redirection and $400 for sump pump redirection. At the 

program’s completion in 1995, 64.5 percent of all known sources had been redirected. The program resulted in a reduction in CSO

volume of 58 MG per year, a three percent reduction in annual fl ow to the local wastewater treatment plant, and fewer reported 

residential backups. The total cost of the rebate program was $128,000. The infl ow reduction program eliminated more than 420 

gallons per year of storm water from the CSS for every dollar spent.

Contact: Dave Pineo, Engineering Department, City of South Portland

Rebate Program to Reduce Inflow

Responsible Agency: City of South Portland

Population Served: 23,200

Service Area: 12 sq. mi.

Sewer System: 16.6 mi. of combined sewer

SOUTH PORTLAND, ME

The Rock River Water Reclamation District in Rockford conducted a survey of a 

portion of its service area that was experiencing SSOs during periods of heavy 

rainfall. The purpose of the survey was to determine the extent of infl ow and 

to recommend 

a plan for 

m i t i g a t i o n 

that included a 

cost-effectiveness analysis to justify the recommended work. 

Infl ow sources were identifi ed by smoke testing all sanitary sewers 

(approximately 77,000 linear feet) by dye-water testing storm 

systems adjacent to sanitary sewers, and with voluntary inspections 

of approximately 1,300 buildings for sources on private property. 

Infi ltration and infl ow (I/I) data were collected and analyzed in terms 

of location, pipe condition, fl ow rate, potential rehabilitation method, and cost. The relative cost-effectiveness calculations, using 

ratios of rehabilitation costs versus treatment-transport costs, provided the basis for rehabilitation recommendations. The primary 

sources of infl ow identifi ed were roof leaders, foundation drains, and sump pumps. This investigation identifi ed 68 infl ow sources 

that contributed an estimated 421 gallons per minute, based on a 5-year storm event (1.7 inches per hour). The investigation also 

determined that 75 percent of the I/I originated on private property.

More information at http://www.rrwrd.dst.il.us/

ROCKFORD, IL Sewer System Evaluation Survey

Responsible Agency: The Rock River Water 

Reclamation District

Population Served: 250,000

Service Area: 80 sq. mi.

Sewer System: 1,100 mi. of sanitary sewer

Area Number of 

Defective Sites

Inflow 

(Gallons Per 

Minute)

Cherry Valley 7 38.0

Dawson Avenue 26 167.6

Pepper Drive 35 147.8

a WEF 1999

Number of identified inflow sources.a
Collection System Controls: Inflow Reduction

CSC-19

References

Arbour, Rick, and Ken Kerri. 1998. Collection Systems: 

Methods for Evaluating and Improving Performance.

Prepared for EPA, Office of Water Programs, Municipal 

Permits and Operations Division and developed under EPA 

Grant No. CX924908-01-0. Sacramento, CA: California 

State University, Sacramento Foundation. 

EPA Office of Water. September 1999. Combined Sewer 

Overflow Technology Fact Sheet: Inflow Reduction. EPA-F-99-

035.

Narragansett Bay Commission (NBC). April 2000. 

Stormwater Attenuation Study - Technical Memorandum 

No. 3, Evaluation of Alternatives. Prepared by the Maguire 

Group Inc. Rhode Island: NBC.

Water Environment Federation (WEF). 1999. Control of 

Infiltration and Inflow in Private Building Connections. 

Alexandria, VA: WEF. 

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Sewer Separation

Collection System Controls

Overview

Sewer separation is the practice of separating the single 

pipe system of a combined sewer system (CSS) into 

separate systems for sanitary and storm water flows. Sewer 

separation, like other types of CSO control, is intended to 

reduce CSO volume, the number of CSO outfalls, or both. 

In practice, there are three distinct approaches to sewer 

separation:

● Full separation wherein new sanitary sewer lines are 

constructed with the existing CSS becoming a storm 

sewer system. This is probably the most widely used 

form of separation.

● Full separation wherein an entirely new storm sewer 

system is constructed with the existing CSS remaining 

as a sanitary sewer system. This form of separation is 

not often used because the capacity of the existing CSS 

was designed to accommodate storm runoff, which is 

more than what is required to accommodate sanitary 

flows. ● Partial separation wherein a new storm sewer system 

is constructed for street drainage, but roof leaders 

and basement sump pumps remain connected to the 

existing CSS allowing flow to enter the CSS during wet 

weather periods.

Full separation can be applied on a system-wide basis to 

eliminate the CSS. This approach is often practical only for 

communities with small areas served by combined sewers. 

Partial separation of select areas within the CSS is widely 

used in large and small CSO communities. In fact, a survey 

of readily available information in NPDES files indicates 

that sewer separation is the most widely used CSO control 

(EPA 2001). This suggests that most CSO communities 

opportunistically find portions of their CSS where 

separation is a cost-effective CSO control. Under these 

circumstances, separation is often implemented in 

conjunction with other public works projects, including 

road work and redevelopment.

Key Considerations

Sewer separation can be highly effective in controlling 

the discharge of untreated sewage to water bodies. Under 

ideal circumstances, full separation can eliminate CSO 

discharges. However, sewer separation on its own does not 

always lead to an overall reduction in pollutant loads or 

the attainment of water quality standards. Discharges of 

urban runoff from the newly separate storm sewer system 

often contain substantial pollutant loads that contribute to 

water quality problems. A comparison of average pollutant 

concentrations from a variety of sources is presented in 

Table 1. As shown, the pollutant concentrations in urban 

runoff can be quite high. From a management standpoint, 

the implementation of storm water controls is usually 

required following sewer separation in order to achieve the 

necessary pollutant load reductions for attainment of water 

quality standards.

From a regulatory standpoint, implementation of 

sewer separation satisfies the requirements of the CSO 

Control Policy. However, the newly-created sanitary and 

storm water systems become subject to existing NPDES 

requirements for storm water and separate sanitary sewer 

systems.

Table 1. Typical pollutant concentrations.

a

 AMSA 2003

b

 NRC 1996

c

 Chapter 4 of EPA’s 2003 Report to Congress on the Impacts and Control 

 of CSOs and SSOs 

d

 Pitt et al. 2003 e

 EPA 2000

Contaminant 

Source

BOD5

(mg/L)

TSS 

(mg/L)

Fecal Coliform 

(#/100mL)

Untreated 

wastewater 88 - 451a 118 - 487a 1,000,000 - 

1,000,000,000b

CSOc 4 - 699 4 - 4,420 1,100 - 1,645,000

Urban runoffd 0.41 - 370 0.5 - 4,800 1 - 5,230,000

Treated 

wastewatere

(disinfected)

12 - 140 0.5 - 35 <200

Sewer separation construction (NJ Dep. of Environmental Protection
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-22

Some CSO communities find that more cost-effective 

overall reductions in pollutant loads can be achieved with 

the implementation of other CSO controls such as storage 

and treatment, instead of sewer separation. Having the 

storm water collected and conveyed in a CSS does present 

some environmental advantages if most of the wet weather 

flow is given the minimum treatment required by the CSO 

Control Policy (i.e., the equivalent of primary treatment 

and disinfection, if necessary).

From both cost and design standpoints, it is often difficult 

to fully separate CSSs. The occurrence of occasional 

residual overflows is common in many CSSs that have been 

separated. The cost of full separation can be prohibitive, 

and some communities opt for partial separation for this 

reason. Several states require sewer separation to the extent 

necessary to eliminate CSOs under specific design storm 

conditions (i.e., the 2-year, 24-hour storm). This leaves 

a legacy of infrequent but substantial CSOs during large 

wet weather events or periods of snow melt. The difficulty 

in achieving full separation can leave a community with 

residual overflows that may be subject to potentially more 

stringent requirements for SSOs.

Applicability

A major benefit of sewer separation is that it has the 

potential to completely eliminate the CSOs and the 

unwanted discharge of raw sewage to receiving waters from 

an antiquated sewer system. Consequently, public health, 

water quality, ecological, and aesthetic benefits can be 

achieved through sewer separation. Another advantage of 

sewer separation is the reduction of wet weather flows to 

the wastewater treatment plant. Sewer separation diverts 

storm water to a separate storm water system during 

rainfall periods. The diversion of storm water reduces 

system-wide stress and frees up sewer system conveyance 

and wastewater treatment capacity. Sewer separation also 

offers a solution to localized flooding and basement backup 

problems caused by excess water entering the sewer system. 

Public health and aesthetic benefits accrue where public 

exposure to raw sewage in homes, businesses, and other 

public areas is reduced.

Cost

Sewer separation is expensive relative to other CSO 

controls, and full sewer separation is typically the most 

expensive CSO control alternative evaluated in most 

communities. Example unit costs for sewer separation are 

presented in Tables 2 and 3.

Sewer separation can also be very disruptive. Disturbances 

caused by construction activities required to implement 

sewer separation are widespread and relatively long-lasting; 

and include digging up roads, altering traffic patterns, and 

potentially disrupting other utility services.

Table 2. Sewer separation costs per linear foot of CSS.

a

 Costs are in 2002 dollars

b

 Not available

c Estimated costs; community found other CSO controls to be more cost 

 effective (NBC 2000)

Table 3. Sewer separation costs per acre of service area.

CSO 

Community

CSS Area 

(Acres)

Reported Costsa

(Million)

Cost Per 

Acre

Seaford, DE 1,260 $2.2 $1,750

Skokie/

Wilmette, IL

6,784 $2132 $31,397

St. Paul, MN and 

surrounding 

areas

21,117 $374 $17,730

Portland, OR N/Ab N/A $19,000

Providence, RI 180 $14.6c $81,000

CSO Community Cost per Linear Foota

Detroit, MI: 

Rouge River Projectb

$175 - $220

Syracuse, NY:

Onondaga Lake 

Improvement Projectc

$490 for residential areas 

(estimate)

$610 for commercial areas

a

Costs are in 2002 dollars

b

Includes removing existing pavement, laying a new sewer line, re- 

 paving, and re-sodding

c

Includes a 25 percent contingency for mobilization, bonds, permits, 

 survey, stakeout, and drawings; does not include internal building 

 plumbing modifications 
Collection System Controls: Sewer Separation

CSC-23

Implementation Examples

Randolph, a town of approximately 2,270, is located on the White River in

central Vermont. In 1990, the State of Vermont developed a CSO Control

Policy that encouraged sewer separation. Compliance requires elimination

of CSO discharges during any storm with precipitation less than 2.5 inches of rain over a 24-hour period. Randolph completed a

sewer separation program during the mid-1990s that consisted of construction of a new separate storm water system throughout 

much of the downtown commercial district and adjacent residential areas. A total of 44 storm water catch basins were separated

from the CSS, which was approximately 85 percent of the catch basins that were known or suspected to be connected. 

Since completion of the main CSO abatement program in 1996, Randolph has continued to implement additional CSO control

through separation of smaller combined sewer areas as part of road improvements under its capital improvement plan. This has

resulted in the separation of six additional catch basins. Currently, the town has separated 95 percent of its combined sewers. Postsewer separation monitoring has shown an 80 percent reduction in the duration of CSO events recorded at the CSO outfall located

at the wastewater treatment facility. This reduction is based upon data collected from a 20-month period from 1998-2000 compared 

with data collected prior to CSO control. As of 1997, approximately $2.66 million had been spent on the town’s CSO abatement

program.

Though signifi cantly reduced, CSOs still occur, and Randolph plans to further its CSO abatement efforts through a plan that spans

six years (2001-2006) at a projected cost of $500,000. Planned projects include sewer line replacement and upgrades as well as

continued sewer separation.

Contact: Joe Voci, Town of Randolph

RANDOLPH, VT Sewer Separation

Responsible Agency: Town of Randolph

Population Served: 2,270

The City of Seaford, a community of 5,900, is located in southwestern 

Delaware. In 2002, Seaford completed a major sewer separation program 

covering approximately 1.97 square miles. The goal of this program was to 

eliminate untreated CSO discharges into the Nanticoke River, a tributary of the 

Chesapeake Bay, during periods of wet weather. Compliance with Delaware and 

EPA regulations and water quality initiatives provided the driving force for this 

program. In addition, the program was designed to benefi t city residents and recreational users of the Nanticoke River. Prior to sewer 

separation, Seaford’s wastewater treatment plant was unable to process all the combined sewage captured by the CSS during wet 

weather events. This led to frequent discharges at four CSO outfalls located in downtown residential and commercial areas. 

The initial plan to separate the combined sewers of Seaford was developed in 1984 with the objective of complete separation. 

Implementation of the entire program was scheduled in eight phases and took 18 years to complete, due to construction and 

fi nancial constraints. The entire combined sewer area has been separated (approximately 40 percent of the city). Efforts to control 

the resulting storm water discharges to the Nanticoke River are currently underway. The cost of the sewer separation program was 

$2.2 million.

Contact: Charles Anderson, City of Seaford

SEAFORD, DE City-wide Sewer Separation

Responsible Agency: City of Seaford

Population Served: 6,699

Service Area: Not Available

Sewer System: 22.7 mi. of sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-24

Working cooperatively under the Metropolitan 

Council’s Environmental Services Division (MCES), 

the cities of St. Paul, South St. Paul, and Minneapolis 

completed a 10-year, $331 million dollar sewer 

separation program in 1996 (MCES 1996). The 

goal of this program was to reduce the pollutant 

load delivered to the Mississippi River from CSO 

discharges. Prior to sewer separation, the average volume of untreated CSO discharges from the metro areas was estimated at 4.6

BG per year, with discharges occurring on average once every three days. Separation of St. Paul, South St. Paul, and Minneapolis 

combined sewers began in 1985 as part of an on-going capital improvement program, with construction initially scheduled to be 

complete in 2025. Due to public demand, the Minnesota Legislature adopted an accelerated program aimed at completing the sewer 

separation by 1995. Implementation of the program resulted in the installation of 189 miles of separate storm sewers and 11.9 miles 

of new sanitary sewers. This amounted to separation of approximately 33 square miles of combined sewer areas: 6.66 square miles

in Minneapolis, 24.53 square miles in St. Paul, and 1.8 square miles in South St. Paul. The disconnection of roof leaders was also an 

important component of the program as it was estimated that they contributed 20 percent of the CSO volume in St. Paul. 

By design, the sewer separation program provided the opportunity to implement other municipal infrastructure improvements 

during construction. These included:

 ● Repair of existing sewers

 ● Disconnection of 21,900 residential rain leaders from the CSS

 ● Replacement of 3,500 lead water services with copper pipes

 ● Upgrade of other local utilities

 ● Installation of 8,200 new street lights

 ● Installation of handicapped-accessible ramps

As a result of sewer separation, water quality in the Mississippi River and other local waterbodies has improved. MCES noted lower 

fecal coliform bacteria levels in the river, the return of the pollution-sensitive Hexagenia Mayfl y, and increases in fi sh populations. 

Sewer separation is believed to be the major reason for the decrease in fecal coliform levels from an average of 500 MPN/100 mL

in 1976 to an average of 150 MPN/100 mL in 1995 in the waters below Minneapolis. The program also benefi tted local waterfront 

development along the Mississippi River.

Contact Tim O’Donnell, Metropolitan Council

Full Sewer Separation

Responsible Agency: Metropolitan Council Environmental Services 

Division (MCES) and the cities of St. Paul, South St. Paul, and Minneapolis

Population Served: 2.5 million

Service Area: 3,000 sq. mi.

Sewer System: 600 mi. of sewer

ST. PAUL, SOUTH ST. PAUL, 

AND MINNEAPOLIS, MN
Collection System Controls: Sewer Separation

CSC-25

References

Association of Metropolitan Sewerage Agencies 

(AMSA). 2003. The AMSA 2002 Financial Survey: A 

National Survey of Municipal Wastewater Management 

Financing and Trends. Washington, DC.

EPA. 2001. Report to Congress: Implementation and 

Enforcement of the Combined Sewer Overflow Control 

Policy. EPA/833-R-01-003.

EPA Office of Water. 2000. Progress in Water Quality: 

An Evaluation of the National Investment in Municipal 

Wastewater Treatment. EPA-832-R-00-008.

Metropolitan Council Environmental Services 

(MCES). 1996. Separating Combined Sewers to Improve 

and Protect Mississippi River Water Quality: A TenYear Commitment, Annual Progress Report to the 

Public - Year Ten. St. Paul, MN: MCES and Cities of 

Minneapolis, St. Paul, South St. Paul.

The Narragansett Bay Commission (NBC). 

2000. Storm Water Attenuation Study: Technical 

Memorandum No.3 Evaluation Alternatives. Prepared 

by MacGuire Group, Inc. Rhode Island: NBC.

National Research Council (NRC), Committee on 

the Use of Treated Municipal Wastewater Effluents 

and Sludge in the Production of Crops for Human 

Consumption. 1996. Use of Reclaimed Water and 

Sludge in Food Crop Production. The National 

Academies Press. 

Pitt, R. et al. 2003. “The National Stormwater Quality 

Database (NSQD, version 1.0).” Retreived August 6, 

2003. Tuscaloosa, AL: University of Alabama.http:

//www.eng.ua.edu/~rpitt/Research/ms4/Paper/

Mainms4paper.html

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Sewer Rehabilitation

Collection System Controls

Overview

The structural integrity of many sewer system components 

has deteriorated from use and age. This gradual breakdown 

allows greater amounts of groundwater and storm water 

to infiltrate into the sewer system, which increases the 

hydraulic load, and in turn, reduces the system’s ability to 

convey all flows to the treatment plant. During wet weather 

events, excessive infiltration can cause or contribute to 

CSOs and SSOs. There are many reasons why a system 

may deteriorate to the point where infiltration becomes a 

problem. These include (WEF 1999):

● Inadequate design and construction practices ● Inadequate or improper bedding material

● Root intrusion

● Pipe breakdown from chemical corrosion

● Traffic loadings ● Soil movement and settling ● Groundwater fluctuations ● Cracking and aging

● Inadequate installation and maintenance

Sewer rehabilitation helps restore and maintain the 

structural integrity of a sewer system, in part by reducing 

or mitigating the effects of infiltration. Specific sewer 

rehabilitation techniques discussed in this description 

include: 

● Removing and replacing defective lines ● Shotcrete

● Trenchless methods 

The presence of debris will limit the effectiveness of sewer 

rehabilitation efforts; therefore, before initiating sewer 

rehabilitation, it is essential to remove any debris or roots 

that may be present in the sewer line. When rehabilitating 

a sewer line, it is also important to consider rehabilitation 

of system components, such as manholes and service 

laterals, since these may also be subject to infiltration. More 

information on sewer cleaning and manhole and service 

lateral rehabilitation is presented in additional technology 

descriptions included in Appendix B of Report to Congress 

on the Impacts and Control of Combined Sewer Overflows 

and Sanitary Sewer Overflows.

 

Removing and Replacing Defective Lines

In many cases, it is not practical or desirable to rehabilitate 

existing sewers. Removing and replacing part or all of a 

defective sewer is the most common and proven method 

for eliminating inflow and infiltration (I/I), as well as 

correcting other structural problems. Often called “dig-andreplace,” the original pipe is excavated and disconnected 

from the sewer system. The pipe is then removed and 

replaced with a new, often larger, pipe. Alternatively, a new 

pipe may also be positioned parallel to the existing sewer 

and connected to the sewer system.

Shotcrete

Shotcrete is a mix of cement, sand, and water that is applied 

to the walls of the sewer using air pressure. Shotcrete 

generally consists of 30 percent cement and 70 percent 

sand (Shotcrete 2001). A welded wire mesh screen is often 

constructed over the section to be rehabilitated to provide 

additional support for the shotcrete mixture. The screen is 

covered by at least one inch of shotcrete to create a smooth 

surface. To apply shotcrete, the sand and cement mixture is 

forced through a hose to a mixing chamber that contains 

water. The mixture is then “shot” into place using air 

pressure. Major structural problems can often be remedied 

using shotcrete (CSU 2001). 

Trenchless Technologies

Trenchless sewer rehabilitation technologies use the existing 

sewer to support a new pipe or a liner. As the name implies, 

trenchless technology requires less surface interruption 

than to dig-and-replace a defective sewer line. Trenchless 

technologies include sliplining, cured-in-place pipe (CIPP), 

modified cross-section liners, and pipe bursting.

Installing lining in an aging sewer (NJ Dep. of Environmental Protection).
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-28

Sliplining

Sliplining involves placing a new, smaller diameter liner 

in the existing sewer. The new liner is then grouted to 

the existing pipe to improve structural integrity and 

prevent leaks (EPA 1999). The sliplining process can 

be continuous, segmented, or spiral wound. During 

continuous installation, the total length of lining is 

inserted at strategic locations. Segmented installation 

requires the pipe liner to be broken into portions and 

then assembled at access points in the sewer system. As 

shown in Figure 1, spiral wound lining is interlocked 

forming a spiral that is inserted into the pipe from a 

manhole or other access point. Sliplining may require 

access to the sewer line beyond that which a manhole 

can provide; an insertion pit may need to be created. 

Therefore, sliplining is not always a completely 

trenchless technology, but it is much less intrusive than 

traditional dig-and-replace methods (EPA 1999). Also, 

sliplining is not applicable in force mains. 

Cured-in-Place Pipe

During CIPP rehabilitation, a fl exible fabric liner 

coated with a thermosetting resin is inserted into the 

existing sewer and then cured (EPA 1999). The most 

common techniques for installing the liners are the 

winch-in-place and invert-in-place methods. In the 

former, a winch is used to pull the liner into place. The 

liner is then fi lled with air to push it against the existing 

pipe. When using the invert-in-place technique, the 

resin is applied to the inside of the liner. Water or air 

pressure is used to invert the liner so that the resin 

covered side “fl ips out” to meet the existing pipe. For 

both methods, heat is used to seal the liner to the pipe 

(EPA 1999). CIPP liners can be installed from existing 

manholes, making it a true trenchless technology, as 

shown in Figure 2.

Modifi ed Cross Section Lining

Modifi ed cross section lining rehabilitation methods 

modify the cross-sectional area of the liner to facilitate 

its installation. The three most common techniques 

are SwageliningTM, deform and reform, and roll down. 

SwageliningTM uses heat and a chemical dye to reduce 

the size of the liner. After the liner is pulled through 

the pipe and allowed to cool, it returns to its original 

diameter. In the deform and reform method, a fl exible 

pipe is deformed, often forming a U shape, and is then 

inserted into the existing pipe. The roll down technique 

minimizes the size of the liner using a series of rollers. 

Heat is used to reform the liner for both the deform 

and reform and rolldown methods (EPA 1999).

 

Pipe Bursting

Pipe bursting uses the existing pipe as a guide for 

an expansion head. A cable rod and winch pull the 

expansion head, which cracks the existing pipe by 

pushing it radially outwards. The new sewer line is 

pulled behind the expansion head, as shown in Figure 

3. Expansion heads are either static or dynamic; the 

dynamic head provides additional pneumatic or 

hydraulic force to counter the pressure created by 

pulling the expansion head through the existing pipe 

(EPA 1999).

Figure 1. Schematic of a spiral wound lining.

Existing

pipe

Spiral wound pipe

with interlocking

edges

Figure 2. Schematic of a cured-in-place technique (O’Brien 

 and Gere 2002)

Circulation

pump

Heated water

Roller truck

Existing pipe

Manhole
Collection System Controls: Sewer Rehabilitation

CSC-29

Key Considerations

Applicability

In selecting a sewer rehabilitation technique, site-specific 

conditions, project goals, and sewer system characteristics 

should be evaluated. Inspection and evaluation of the 

current sewer condition are necessary before a sewer 

rehabilitation technique is chosen, as the condition of the 

sewer may favor specific techniques. Additional information 

on sewer inspection techniques is provided in the “Sewer 

Testing and Inspection Technology Description” located 

in Appendix B of Report to Congress on the Impacts and 

Control of Combined Sewer Overflows and Sanitary Sewer 

Overflows.

Removing and Replacing Defective Lines

Removing and replacing defective lines is the most 

commonly used rehabilitation technique when the sewer 

line is structurally deficient. Replacing defective lines 

results in a line segment design life that exceeds any other 

rehabilitation method. Also, in areas in need of increased 

conveyance capacity, complete replacement provides an 

opportunity for installation of a larger-diameter sewer 

(WEF 1999). Sewer replacement can be quite disruptive to 

automotive and pedestrian traffic, however. Construction 

times and service interruptions for replacement are 

typically lengthy compared to other rehabilitation 

methods. In addition, sewer flows must be rerouted during 

construction. Construction costs are also considerably 

higher for dig-and-replace than for other rehabilitation 

methods (EPA 1991).

Shotcrete

Shotcrete is often used to rehabilitate sewers with major 

structural problems. As with dig-and-replace, flow must be 

completely diverted during construction since equipment 

and personnel must access the pipe. Shotcrete may only be 

used in pipes with a diameter greater than 36 inches.

The advantages of using shotcrete include (CSU 2001):

● Rehabilitation can be accomplished using manholes to 

access the sewer system; ● Restoration of the original pipe strength; and ● Method is safer for crews than grouting and epoxy 

injections.

Disadvantages of shotcrete include (CSU 2001):

● A long curing time; ● Complete diversion of the flow during application; and

● Reduction in hydraulic capacity because the diameter 

of the sewer is reduced.

Trenchless Technologies

Trenchless technologies are especially well-suited to urban 

areas where the traffic disruption associated with largescale excavation projects can be a significant obstacle to a 

project (WEF 1999). In addition, many sewers are located 

near other underground utilities in urban areas which can 

Figure 3. Schematic of pipe bursting technique.

Pulling

device

Cable or

chain

New pipe

Bursting head

Expander (if used)

Pipe fragments

Method Diameter 

Range (in.)

Maximum 

Installation 

(ft.)

Grouting and Epoxy Injections

Remote Application

Manual Application Not Available

Sliplining

Continuous 4-63 1,000

Segemented 12-158 5,600

Spiral wound 4-100 300

CIPP

Invert-in-Place 4-54 500

Winch-in-Place 4-100 3,000

Modified Cross Section Liners

SwageliningTM 4-24 300

Deform and Reform 4-64 300

Rolldown 4-24 300

Pipebursting

Pneumatic Head 2-24 475

Static Head 4-24 650

Table1. Sewer system characteristics for trenchless 

 technologyies (CSU 2001).
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-30

complicate traditional dig-and-replace methods; trenchless 

technologies avoid underground utilities.

Advantages of trenchless technologies include (EPA 1999):

● Reduced air pollution from construction equipment ● Fewer traffic detours

● Decreased construction noise

● Reduced vegetation disturbance ● Limited areas where safety concerns must be identified

Table 1 highlights conditions for which various trenchless 

technologies are most applicable. Trenchless technologies 

are not without limitations, however, and they are 

summarized in Table 2.

Cost

Selection of a cost-effective sewer rehabilitation technique 

depends on the present condition of the sewer and other 

site-specific considerations. In general, grouting is the least 

expensive of the sewer rehabilitation methods presented. 

Further, trenchless sewer rehabilitation techniques are often 

less expensive than open-cut methods because the amount 

of excavation for the trenchless technology is minimal 

(EPA 1999). A representative range of costs for several 

trenchless technologies (CIPP, sliplining, and pipe bursting) 

is presented in Table 3; actual costs for sewer rehabilitation 

projects undertaken by a number of municipalities are 

summarized in Table 4. As shown in Table 4, there is 

considerable variation in the cost per foot for an individual 

technology; the diameter of the pipe drives much of this 

variation. Figure 4 illustrates the increase in cost of CIPP 

Method Disadvantage replacement as a function of increasing sewer diameter.

Grouting and Epoxy 

Injections

● Utilize harsh chemicals that may be 

dangerous for installation crews

● Will not prevent further pipe 

movement, and may crack if pipe shifts

Sliplining ● Requires an insertion pit ● Reduces pipe diameter ● Cannot be used with small diameter 

pipes

CIPP ● Curing can be difficult for long pipe 

sections

● Requires diversion of flow ● Resin can clump together ● Reduces pipe diameter

Modified Cross ● Liner may shrink after installation

Section Liners ● Infiltration may occur between pipe 

and liner 

● Liner may not provide adequate 

structural support

● Requires dversion of flow ● Reduces pipe diameter

Pipe Bursting ● Insertion pit needed ● Dynamic head may cause soil settling 

around the newly installed pipe

● Requires diversion of flow ● Not suitable for all pipe materials

Table 2. Disadvantages of trenchless sewer rehabilitation 

 technologies (EPA 1999).

Technology Cost ($/foot)

CIPP 42-1200

Sliplining 10-560

Pipe Bursting 46-260

Table3. Cost of selected trenchless technologies.

0

100

200

300

400

500

20 25 30 35 40 45 50

Pipe Diameter (inches)

Unit Cost ($/ft)

cost is in 2002 dollars

Figure 4. CIPP cost versus pipe diameter (Zhao et al. 2001).
Collection System Controls: Sewer Rehabilitation

CSC-31

1

 All costs are converted to 2002 dollars based on the ENR Construction Cost Index

2

 Costs include traffi c control, which increase the cost per linear foot; total construction cost was $530,000 (Ringland 2003)

Municipality Technology Project Characteristics Year 

Constructed

Costs1

 

Buffalo, NY Shotcrete Shotcrete was applied to 1,465 linear feet of 

the Military Road sewer that was over 50 years 

old. The pipe diameter tapered down from 53 

to 48 inches. 

1997 Approximate cost: 

$280,552 or $192 per foot

Indianapolis, IN Shotcrete

Trenchless

After sewer evaluation was performed a 

total of 12,495 feet for sewer have been 

rehabilitated using Shotcrete, CIPP, and 

sliplining.

1998-2002 $4 million or $317 per foot

St. Louis, MO Open-Cut 1,560 feet of sewer were replaced, providing 

surcharge relief to upstream sewer system. 

Costs include all excavation, refill, and 

engineering costs.

2002 $535,000 or $343 per foot

Austin, TX Open-Cut

Trenchless

The Austin Clean Water Program is a 

comprehensive project to eliminate SSOs from 

the city’s sanitary sewer system. 

The project will be complete by 2007.

2002 

(construction 

started)

Cost for Crosstown Tunnel 

Service Area: 

$44 million or $530 per foot

Torrence, CA2 Open-Cut

Trenchless

8,400 feet of pipe was rehabilitated.

90 percent of the sewers were repaired using 

machine spiral wound PVC pipe liner.

Open-cut methods were used for the 

remaining sewers.

2002 Total construction cost: 

$530,000

Open-cut: 

$191,000 or $955 per foot

Trenchless: 

$339,000 or $41 per foot

DuPage 

County, IL

Trenchless U-liner to rehabilitate 24,000 feet of 8-inch and 

4,000 feet of 10-inch VCP mains.

1994 8- to12-inch U-Liner:

$34-$44 per foot

Glendale, WI Trenchless U-Liner was used to repair 3,462 feet of eight 

to 10 inches pipes; CIPP was used for 1,966 

feet of 15-inch pipes..

1999 8-to 10-inch U-Liner: 

$29-$33 per foot

15-18 inches CIPP: 

$58-68 per foot

Muscatine, IA Trenchless CIPP method was used to rehabilitate 3,800 

feet of 24- to 27-inch diameter pipes and 187 

feet of 8-inch clay pipes.

2001 24-to 27-inch CIPP: 

$67-$103 per foot 

South Fayette 

Township, PA

Grouting Pilot program grouting a total of 2,788 feet was 

conducted. 

A total of 303 gallons of acrylmide grout was 

used.

1997 $33,475 or $12 per foot

Dallas, TX Grouting Approximately 10,000 feet of pipe were 

cleaned, tested, and sealed as part of a project 

to eliminate I/I.

2000 $89,331 or $9 per foot

Table 4. Costs of municipal sewer rehabilitation projects.
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-32

Implementation Examples

In April 1999, the City of Austin received an Administrative Order from EPA 

requiring it to eliminate SSOs by 2007. The order stemmed from a review of 

Austin’s sewer system performance following a 170,000 gallon SSO to Bushy

Creek, a tributary of the San Gabriel River. To comply with the order, the city 

created the Austin Clean Water Program. The order requires inspection of

approximately 40 percent of the city’s 2,200 mile sewer system, and, where 

appropriate, the rehabilitation of failing sewer lines. The project is broken 

up into three areas, Crosstown Tunnel Service Area, Onion Creek Service Area, and Govalle Tunnel Service Area, which are being

inspected and rehabilitated in a phased approach. To date, 500,000 linear feet have been rehabilitated using sliplining and open-cut 

methods.

The total cost estimate for the Austin Clean Water Program is $150 million, which includes an I/I study and sewer system evaluation 

and rehabilitation projects in each service area. Estimated cost for the rehabilitation completed in the Crosstown Tunnel Service Area 

is approximately $44 million or $530 per linear foot.

More information at http://www.ci.austin.tx.us/acwp/

AUSTIN, TX Clean Water Program to Control SSOs

Responsible Agency: City of Austin Water and 

Wastewater Utility

Population Served: 1 million

Service Area: 364 sq. mi.

Sewer System: 2,262 mi. of sewer

The Miami-Dade Water and Sewer Department (MDWASD) initiated

an infiltration/inflow and rehabilitation (I/I & R) program in 1995 in 

response to an EPA consent decree. The I/I & R program established 

an ongoing sewer evaluation and rehabilitation schedule to 

preserve the sewer system’s integrity and maintain acceptable 

levels of I/I. The I/I & R program includes sewer cleaning, CCTV 

inspection, smoke testing, dye water flooding, and system rehabilitation.

Approximately 14.5 million feet of sanitary sewer have been inspected and rehabilitated. Sewer rehabilitation methods include digand-replace, sliplining, and grouting. Over 32,000 repairs have been completed, helping to reduce SSO volumes by 90 percent and I/I 

by an estimated 118 MGD since program inception. MDWASD believes the I/I & R program is working; for example, in June and July 

2002, the area received more than 20 inches of rain, but the sewer system experienced no capacity-related SSOs. The total cost of the 

I/I & R program, since its inception, has been approximately $174 million or $12 per foot of sewer inspected or rehabilitated.

More infromation at http://www.co.miami-dade.fl.us/wasd/

MIAMI, FL I/I and Rehabilitation Program

Responsible Agency: Miami-Dade Water and Sewer 

Department

Population Served: 2.1 million

Service Area: Not Available

Sewer System: 2,441 mi. of gravity sanitary sewer
Collection System Controls: Sewer Rehabilitation

CSC-33

In 1995, the City of Columbus initiated a sewer line inspection and rehabilitation 

program. To assure the quality of products used by contractors in the program, 

the city developed a list of approved rehabilitation technologies. When a new 

technology or product of interest emerges, the manufacturer may request to 

have their product added to the approved list. The city has developed a process 

to standardize the introduction of new products. The process requires that:

● The products meet and conform to American Society for Testing and Materials (ASTM) and other professionally

recognized standard specifications.

● The products must have been used successfully by three municipalities over a minimum of three years. ● The city visits both construction sites and product manufacturing facilities to inspect operation and observe standard

construction practices.

● The manufacturer provides information on the expected service life of the product with supporting data.

When a product is selected for preliminary review, it is installed in a small portion of the

city’s sewer system. The product’s effectiveness is then monitored for three years. Once

the product is judged effective, it can be placed on the list of approved technologies.

The current list of approved technologies includes several CIPP products, sliplining,

and shotcrete. These technologies have been utilized to repair numerous sections of

structurally impaired combined sewers. The city has recently started rehabilitating

sanitary sewers using the approved technologies.

Sewer rehabilitation is a priority for Columbus, and the program has been funded

accordingly. The dollars spent on sewer rehabilitation between 1996 and 2001

are shown in the table on the right. Costs presented do not include construction,

administration, and inspection costs. 

Contact: Miriam Siegfried, Department of Public Utilities, City of Columbus

COLUMBUS, OH Sewer Inspection and Rehabilitation Program

Responsible Agency: Department of Public 

Utilities, Division of Sewage and Drainage

Population Served: 1 million

Service Area: 219 sq. mi.

Sewer System: 4,000 mi. of sanitary and combined sewer

Year Construction Dollars Spent1

(Millions)

1996 $6.5

1997 $2.6

1998 $5.9

1999 $2.6

2000 $6.8

2001 $9.3

1

 All costs are converted to 2002 dollars based 

on the ENR Construction Cost Index
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-34

In 1987, the Texas Natural Resource Conservation Commission and EPA 

mandated that Houston eliminate the 200 known SSO points that were 

part of their sanitary sewer system by 1997. The fi rst step the city took was 

to inspect over 27 million linear feet of sewer. The results of the inspections 

were used to rate each sewer segment. The rating took into account the 

severity of I/I, roots, concrete deterioration, and structural defects. The 

inspection program found that 50 percent of the inspected sewer segments 

were in need of rehabilitation or replacement.

To help prioritize the numerous rehabilitation projects, the city developed a numeric sewer rehabilitation rating system, which

considered:

● Accessibility of the line

● Potential future capacity requirements

● Surrounding environment ● Cost

Prior to rehabilitation, a second analysis was performed to determine the most appropriate technique. The analysis considered: 

● Current condition of the sewer line ● Maximum service capacity

● Hydraulics

● Site constraints

In areas that were fully built-out, with no future plans for redevelopment, trenchless technologies were generally used for sewer 

rehabilitation. Where trenchless technologies were utilized, a hydraulic analysis was performed to determine if reducing the inner 

diameter of pipe would cause capacity constraints that could lead to SSOs. For sewers where the use of trenchless technologies 

yielded an unacceptable reduction in pipe diameter, or areas where undeveloped land was still available, lines targeted for 

rehabilitation were typically replaced with a larger pipe to add additional capacity.

Technologies approved for use by the city included sliplining, cured-in-place pipe, pipe bursting, and limited use of modifi ed crosssection liners. The city rehabilitates approximately 120 miles of sewers annually using trenchless technologies. The city committed 

to spend a total of $300 million on sewer rehabilitation as part of the settlement with EPA.

Contact: Teresa Battenfi eld, City of Houston, Department of Public Works and Engineering

HOUSTON, TX Greater Houston Wastewater Program

Responsible Agency: City of Houston 

Department of Public Works and Engineering

Population Served: 1.9 million

Service Area: 600 sq. mi.

Sewer System: 5,000 mi. of sanitary sewer
Collection System Controls: Sewer Rehabilitation

CSC-35

The Indianapolis Combined Sewer Infrastructure Assessment Project 

investigated the integrity of approximately 50 miles of sewer with diameters 

of 60 inches or larger. The city used the study to identify sewers in need of 

immediate rehabilitation and to develop the basis for a more integrated 

Capital Improvement Program. This project was also important to the city 

in developing its CSO long-term control plan. The city wanted to maximize 

storage in the existing sewer system, but needed to be sure that the pipes 

used to store fl ows were structurally sound. If a weak sewer pipe was stressed to the point of failure in using it for storage, the 

environmental impacts could be much larger than those attributed to a single CSO event. Approximately 253,000 feet of brick, 

concrete, and vitrifi ed tile combined sewer were physically inspected and rated based on their structural integrity between 1994 and 

1998. The study found that the majority of sewers were in good condition, identifying approximately 71,000 feet (28 percent of the 

assessed length) in need of rehabilitation. Since the Assessment Project was completed in 1998, a total of 12,495 feet of sewer have 

been rehabilitated. The city has used shotcrete, CIPP, and sliplining techniques to rehabilitate their large diameter combined sewers.

The total cost for the Assessment Project was $1.1 million. An additional $4 million or $317 per foot has been invested in targeted 

sewer rehabilitation.

Contact: T.J. Short, Greeley and Hansen

INDIANAPOLIS, IN Combined Sewer Infrastructure Assessment

Responsible Agency: City of Indianapolis 

Department of Public Works

Population Served: 800,000

Service Area: 58.4 sq. mi. 

Sewer System: 82.2 mi. of combined sewer

References

EPA. 1991. Sewer System Infrastructure Analysis and 

Rehabilitation. EPA 625-6-91-010. 

EPA. 1999. Collection Systems O&M Fact Sheet: Trenchless 

Sewer Rehabilitation. EPA 832-F-99-032.

California State University (CSU), Sacramento - College 

of Engineering and Computer Science, Office of Water 

Programs. 2001. Operation and Maintenance of Wastewater 

Collection Systems. Vol. 1, 5th ed. Prepared for EPA Office 

of Water Programs, Municipal Permits and Operations 

Division. Sacramento, CA: CSU, Sacramento Foundation.

National Research Council Canada (NRC). 2002. 

Construction and Rehabilitation Costs for Buried Pipe with 

Focus on Trenchless Technologies. Research Report No. 101. 

Ottawa, Canada: National Research Council Canada.

O’Brien & Gere. 2002. ‘Wastewater Management: Trenchless 

Technologies.’ Viewed December 17,2002. 

http://www.obg.com/wastewater/pdf/Trenchless_Syr(1).pdf

Shotcrete Technologies, Inc. 2001. “Shotcrete Tips and 

Tricks: Mix Design and Quality Control.” Retrieved 

February 21,2003.

http://www.shotcretetechnologies.com/tips.html 

Ringland, David, City of Torrence. Interview with LimnoTech, Inc., March 2003. Washington, DC.

Water Environment Federation (WEF). 1999. Prevention 

and Control of Sewer System Overflows: WEF Manual of 

Practice No. FD-17. Prepared by Gray, W. et al. Alexandria, 

VA: Water Environment Federation.

Zhao, J. Q. et al. 2001. Guidelines for Condition Assessment 

and Rehabilitation of Large Sewers. Ottawa, Canada: 

Institute for Research in Construction, National Research 

Council Canada. Report No. NRCC-45130.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Service Lateral 

Rehabilitation

Collection System Controls

Overview

Private building service laterals (herein referred to as 

“service laterals”) are the pipe or pipes used convey 

wastewater from individual buildings to the municipal 

sewer system. Typical service laterals are four to six inches 

in diameter, with lengths ranging from 15-100 feet. Service 

laterals are often thought of in two segments: the upper 

lateral, which includes the section of pipe between the 

building and private property boundary; and the lower 

lateral, which includes the section of pipe between the 

private property boundary and the municipal sewer system.

For many years, the effect of leaking service laterals was 

considered insignificant because it was assumed that 

most service connections were above the water table, and 

therefore, subject to infiltration only during periods of 

excessive rainfall or high groundwater levels (EPA 1991). 

More recent studies indicate that a significant component 

of the infiltration in any sewer system is the result of 

service lateral defects that contribute varying quantities 

of inflow and infiltration (I/I) to the sewer system. 

Many of these defects are traceable to poor design, pipe 

selection, and improper construction (WEF 1999). Further, 

fluctuating groundwater levels, variable soil characteristics 

and conditions, traffic, erosion, and washouts stress service 

lateral pipes and joints. As shown in Figure 1, the most 

common problems found in service laterals include:

● Improper connections ● Faulty pipe joints

● Root intrusion

● Failure of service lateral bedding or backfill to support 

the pipe ● Pipe material failure in aging service laterals

● Missing or broken cleanout caps

Service lateral testing is an important first step in any 

rehabilitation program. Testing is used to assess the 

structural condition of the service lateral and to help locate 

defects. Additional information on sewer testing practices is 

provided in the “Sewer Testing and Inspection Technology 

Description” in Appendix B of Report to Congress on the 

Impacts and Control of Combined Sewer Overflows and 

Sanitary Sewer Overflows.

There are a number of techniques available for repairing 

defective service laterals. These include: 

● Removing and replacing defective service laterals

● Spot repairs

● Trenchless technologies

● Eliminating inflow sources

These four techniques are discussed in some detail below.

Removing and Replacing Defective Service Laterals

In many cases, it is not practical or desirable to rehabilitate 

existing sewers. Removing and replacing part or all of a 

defective service lateral is the most common and proven 

method for eliminating I/I from private property. A key 

factor to a successful program using remove and replace is 

Improper

connection

Faulty joint

Root intrustion

Cracked pipe

Missing

cleanout

cap

Collector

sewer

Figure 1. Common defects in service laterals.

Installing cured-in-place lining (Reynold’s Inc.)
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-38

obtaining the private property owners’ consent to access the 

property for construction.

Spot Repairs

Spot, or point, repairs are typically used to correct isolated 

or severe problems in relatively short portions of a service 

lateral. Spot repairs can also be made as an initial step 

in the use of other rehabilitation methods (NASSCO 

1996). Spot repairs can be made using either open cut or 

trenchless technologies. The open-cut technique involves 

excavating and removing the defective section, and then 

installing new pipe with proper seals to ensure watertight 

connections to the existing service lateral and/or municipal 

sewer system. Trenchless technologies for spot repairs 

typically use epoxy or resin to fill defects; in general, their 

use is limited to service laterals with a diameter of six 

inches or more.

Trenchless Technologies

Trenchless service lateral rehabilitation uses the existing 

pipe to support a new pipe or a liner. Generally, the use 

of trenchless technology methods is neither as widespread 

nor extensive as open cut techniques for repairing service 

laterals (WEF 1999). As the name implies, trenchless 

technology requires less surface interruption than complete 

replacement of a defective line. Therefore, trenchless 

technologies show particular promise in areas where 

construction impacts on trees, shrubbery, and other 

landscaping materials would make open-cut service lateral 

repair costs prohibitive. Trenchless rehabilitation techniques 

include lining, cured-in-place pipe (CIPP), pipe bursting, 

grouting, and epoxy injections.

Lining Service Laterals

Lining service laterals is typically used to extend 

the life of an existing service lateral by increasing 

its strength and/or protecting it from corrosion or 

abrasion (NASSCO 1996). Lining involves sliding a 

fl exible liner pipe of slightly smaller diameter into the 

existing lateral. The space between the liner and the 

existing service lateral is then grouted. Lining is most 

often used to rehabilitate extensively cracked laterals, 

especially those in unstable soil conditions. The most 

popular materials used to line sewers are polyolefi ns, 

reinforced thermosetting resins, and PVC (EPA 1991). 

The lateral must be thoroughly cleaned prior to lining. 

Typically, lining the service lateral requires excavating 

an entry point at both upstream and downstream ends 

to be able to insert and move the liner into position. 

Therefore, similar to remove and replace and open-cut 

spot repairs, lining service laterals requires private 

property access.

Cured-in-Place Pipe

The cured-in-place pipe (CIPP) process involves 

installing and curing a resin-saturated, fl exible fabric 

liner inside the service lateral. The liner is installed 

using air or water inversion or a pull-in process. With 

water inversion, the lining is inverted using water 

pressure; air inversion uses air pressure to invert the 

liner. The pull-in process involves winching the liner 

into place and using an air bladder to “infl ate” the liner. 

The liner is then cured by circulating low pressure hot 

water or steam. The lateral must be thoroughly cleaned 

prior to installing the CIPP, and areas with excessive 

infi ltration must be sealed. Typically, installing CIPP 

liners requires excavating an entry point at either the 

upstream or downstream end. Therefore, installing 

CIPP liners may not require private property access. 

Pipe Bursting

Pipe bursting replaces the existing lateral with a pipe of 

similar or larger diameter by fragmenting the existing 

pipe into the surrounding soil, thereby creating a cavity 

for the new pipe. Pipe bursting has been used in the 

gas industry for some time, but only more recently has 

been looked at for rehabilitating service laterals. Similar 

to lining a lateral, excavated entry points at both the 

upstream and downstream ends of the service lateral 

are required, which requires private property access.

Grouting and Epoxy Injections

Grouting and epoxy injections are most commonly 

used for sealing leaking joints in pipes that are 

otherwise structurally sound (NASSCO 1996). 

Small holes and radial cracks may also be sealed by 

grouting or epoxy injections. Grouts and epoxies are 

applied internally within a pipe and are a trenchless 

rehabilitation method. 

Eliminating Infl ow Sources

Service lateral cleanouts allow access to the lateral 

for routine maintenance. Often, the cap used to 

prevent storm water infl ow into the service lateral at 

the cleanout is broken or missing. One study found 

that almost 25 percent of service lateral defects were 

related to missing or damaged cleanout caps (Rowe 

and Holmberg 1995). Replacing missing or defective 

cleanout caps can result in substantial reductions in 

infl ow into the sewer system.

Although disconnecting infl ow sources is not a repair 

of the service lateral per se, elimination of direct 
Collection System Controls: Service Lateral Rehabilitation

CSC-39

connections of extraneous storm water is important. 

Other, often signifi cant infl ow sources include:

● Roof leaders

● Area, foundation, yard, patio, and driveway drains ● Basement sump pumps

● Cross-connections to separate storm sewers

Additional information on disconnecting infl ow 

sources is provided in the “Infl ow Reduction 

Technology Fact Sheet” in Appendix B of Report to 

Congress on the Impacts and Control of Combined Sewer 

Overflows and Sanitary Sewer Overflows.

Key Considerations

Applicability

Assigning responsibility for the repair or replacement of 

service laterals has often been cited as the biggest obstacle 

to correcting known defects. Notably, several studies 

highlighted significant problems in gaining access to private 

property until the municipality assumed full financial 

responsibility for the repair or replacement of service 

laterals (Curtis and Krustsch 1995; Paulson et al. 1984). 

Removing and Replacing Defective Service Laterals

The removal and replacement of a service lateral is 

usually more expensive than other rehabilitation methods. 

Replacing a defective service lateral, however, ensures that 

the design capacity of the lateral is maintained, whereas 

rehabilitation may result in an unacceptable reduction in 

capacity. Construction activities associated with removal 

and replacement involve a greater risk of damage to or 

interruption of other utilities than most trenchless lateral 

rehabilitation techniques. 

Spot Repairs

Spot repairs are often a cost-effective means of addressing 

minor defects in service laterals. While spot repairs 

eliminate infiltration at the location of the repair they are 

typically not an appropriate approach for rehabilitating 

a lateral with multiple defects. Without correcting all of 

the defects in a given lateral, groundwater will simply 

find another location to enter the pipe. Depending on 

the number and type of defects in a given lateral, it 

may be more cost-effective to address the infiltration by 

rehabilitating the entire length of the lateral.

Trenchless Technologies

Trenchless sewer rehabilitation techniques require 

substantially less construction work than traditional 

remove-and-replace methods (EPA 1999). However, with 

the exception of pipe bursting, trenchless technologies 

reduce the lateral diameter, resulting in decreased capacity. 

Lining Service Laterals

To date, there has been limited experience using liners 

to rehabilitate service laterals, although application 

is expected to increase (WEF 1999). In lining service 

laterals, particular attention must be paid to local 

plumbing codes, specifi cally, whether changes will be 

required to accommodate the reduced interior diameter 

of the lateral after it is lined.

Pipe Bursting

The primary advantage of pipe bursting is that the fl ow 

carrying capacity of the existing lateral does not have to 

be reduced; further, pipe bursting allows the new lateral 

to be up-sized, if needed. In addition, the amount of 

surface disruption associated with pipe bursting is less 

than that required for total lateral replacement. The soil 

type surrounding the existing lateral is an important 

variable when considering pipe bursting. In soils that 

are predominated by sand, the soil “relaxes” almost 

instantaneously onto the new pipe causing very slow 

progress. It is also important to ensure that no large 

boulders or rock formations are located in the path of 

the pipe bursting equipment. Finally, the forces exerted 

by the bursting equipment may adversely affect other 

pipes near the lateral being replaced. Unit replacement 

costs with pipe bursting are typically 20-40 percent 

lower than traditional open cut methods. 

Cured-in-Place Pipe

The use of CIPP for rehabilitating laterals with 

diameters as small as four inches is common (NASSCO 

1996). Unlike other types of lining, CIPP does not 

require grouting. Although the installation of a CIPP 

liner is rapid, the curing period can be extensive, and 

fl ow and groundwater infi ltration in the lateral will 

need to be controlled during installation. CIPP also has 

relatively high set-up costs for small projects.

Grouting and Epoxy Injections

Grouting is relatively inexpensive. Grouting does not 

improve the structural strength of the lateral, and for 

that reason, should not be considered when the pipe 

is severely cracked, crushed, or badly broken (EPA 

1991). Epoxy injections, although similar to grouting in 

most respects, provide the added benefi t of improving 

somewhat the structural integrity of the rehabilitated 

pipe. Because epoxy is more viscous than grout, it 

cannot be pumped as far (WEF 1999). The service life 

of grout is an important consideration. The average 

service life of grouts is seven years (NASSCO 1996). 
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-40

Implementation Examples

Grouting requires fl ow control, because the section 

being grouted cannot transport fl ow until the grout 

has cured. Therefore, it is also diffi cult to line service 

laterals if infi ltration is present. Most coatings cannot 

be successfully applied to either water leaks or ponded 

water (NASSCO 1996). Large cracks, badly offset joints, 

and misaligned pipes may not be sealable using grouts 

or epoxies.

Eliminating Infl ow Sources

Eliminating sources of infl ow can be an effi cient way 

to reduce the volume of storm water delivered to 

both combined and separate sanitary sewer systems. 

The feasibility of disconnecting infl ow sources 

depends on the soil type, land slope, and drainage 

conditions around the home. Additionally, for an 

infl ow disconnection program to be successful, the 

public must be educated about the benefi ts of and the 

methods for disconnecting sources. This can be timeconsuming and will likely require some sort of rebate 

program or other incentive for compliance. 

Cost

Often, very little specific data are available to compare the 

I/I contribution from service laterals with that from other 

sewer system components. Flow meters are rarely used to 

monitor individual service laterals for reasons including 

it is physically difficult to isolate service laterals from the 

sewer system for installing flow meters; placing flow meters 

in a service lateral requires significant and often expensive 

modifications; and the large number of service lateral 

connections can make sampling representative locations 

costly. Rehabilitating service laterals, however, has proven 

to be a critical component of an I/I reduction program. 

Studies have found that service lateral rehabilitation can 

reduce the introduction of extraneous I/I into the sewer 

system from 45-87 percent (Rowe and Holmberg 1995; 

Curtis and Krustsch 1993; EPA 1985; Roberts 1979). 

Actual I/I reductions achieved, however, are dependent on 

a number of factors, and therefore the cost-effectiveness 

of lateral rehabilitation will vary from community to 

community.

Costs associated with the various techniques available for 

rehabilitating or replacing service laterals vary considerably 

and are driven by site-specific conditions. Table 1 presents 

the relative costs of the various techniques discussed in this 

technology description. For example, replacing a service 

lateral, either using open cut or pipe bursting techniques, 

is almost always more expensive than other rehabilitation 

alternatives. The exact cost of replacing the lateral, however, 

will be driven by the landscape and length of the lateral 

among other factors.

Technique Relative Cost 

Removing and replacing service laterals $$$$

Spot repairs $

Lining service laterals $$

Pipe bursting $$$

Grouting and epoxy injections $$

Eliminating inflow sources $$

Table 1. Relative cost of various service reheabilitation costs.

In the early 1990s, the DuPage County Public Works Division initiated efforts to 

control I/I in the Hinsbrook Subdivision, which suffered from frequent SSOs. A 

study of the sewer system determined that 25-30 percent of the I/I was entering 

from the sewer system service laterals. Rehabilitation of the service laterals was 

necessary, but politically complicated as it involved coordinating three groups: 

the Public Works Division of DuPage County, the Public Works Department of the City of Darien, and the property owners. DuPage 

County owns the SSS, while the City of Darien is responsible for storm water control in the subdivision, and property owners are 

responsible for the portion of the service lateral on their property.

Pipe bursting was used to rehabilitate the majority of the service laterals in the subdivision. Property owners were informed in 

advance of the replacement and given the option of hiring their own contractor or allowing the county to make the needed repairs. 

Only 35 homeowners chose to hire their own contractor. For the pipe bursting, a small pit was excavated at the foundation of each 

home. The pipe bursting head and new pipe were pulled with a winch from a pit located near the main pipe. The new service 

lateral was then connected to the house and the service main. Installation time averaged two hours limiting the time service was 

interrupted. Property owners who chose to have the county rehabilitate their service lateral paid the county $966.

More information at http://www.dupageco.org/publicworks/index.cfm

DARIEN, IL Hinsbrook Subdivision I/I Rehabilitation

Responsible Agency: DuPage County Public 

Works Division

Population Served: 585 single family homes
Collection System Controls: Service Lateral Rehabilitation

CSC-41

Montgomery Water Works and Sanitary Sewer Board (MWWSSB) 

evaluated the condition of its sewer system in the early 1990s and 

discovered infl ow sources could be cost-effectively eliminated in 

86 percent of the system. Nearly 2.2 million linear feet of pipe were 

investigated in the fi rst fi ve years of the program. Of the 3,394 sewer 

system problems detected, 85 percent were service lateral problems; a 

defect was found in approximately every 700 feet of sewer inspected. Of 

the 113 subbasins served by MWWSSB, 35 were smoke tested in the fi rst six years of the program; 97 percent of the lateral defects 

identifi ed have been repaired.

Lateral maintenance and repair has always been the responsibility of the property owner, who was notifi ed when defects were 

discovered. Due to the number of defects identifi ed, MWWSSB adopted a more aggressive maintenance and repair policy. Property 

owners initially received a 60-day notice of the lateral repair requirements. If they failed to respond to the initial notice, a 10-day 

notice was sent to the property owner. Finally, if the property owner had not responded to either notice, their water service was 

shut-off.

Lateral repairs necessary within the city street right-of-way are made by MWWSSB with consent and release of liability from the

property owner. MWWSSB also replaces missing clean-out covers for a minimal cost with written permission from the property 

owner.

To help manage the numerous service lateral repairs, MWWSSB created a sewer maintenance database. The database includes 

information regarding when smoke testing was initiated, any defects found during testing, digital photos of the defect, when the 

fi rst owner notice was generated, and any repairs that were performed. 

The public notice process was implemented in the Fall of 1994; 65 percent of property owners responded after receiving the 60-day 

notice. The remaining property owners repaired their defects under threat of having their water service discontinued. In selected 

subbasins where service lateral rehabilitation is complete, a 42 percent reduction of I/I has been measured. It is estimated that the 

annual I/I volume in the MWWSSB service area has been reduced by 36 million gallons. The initial cost of establishing the I/I program 

was approximately $150,000; MWWSSB annual program operation costs are $207,000.

Contact: Danny Holmberg, Montgomery Water Works and Sanitary Sewer Board

I/I Tracking and Service Lateral Rehabilitation

Responsible Agency: Montgomery Water Works and 

Sanitary Sewer Board

Population Served: 225,000

Service Area: 150 sq. mi.

Sewer System: 1,098 mi. of sewer

MONTGOMERY, AL
 Report to Congress on the Impacts and Control of CSOs and SSOs

CSC-42

The City of San Luis Obispo was experiencing I/I problems 

during their rainy season. At the time, the city treatment plant 

was suffering from wastewater fl ows that would increase from 

a daily average of 4.5 MGD to over 30 MGD during wet weather 

events, pushing the city’s wastewater treatment facility over its 

design limit. A fl ow monitoring study of the city sewer system was 

conducted to identify the extent of I/I and its sources.

Flow monitoring data showed that a residential area served by sewers built between 1930 and 1965 was the major contributor of I/I. 

The city then video inspected the sewer mains to determine the locations of the I/I within this area. The inspection phase occurred from 

1991-1994 and concluded that service laterals were the main source of the I/I. A small sample of laterals revealed that failures were 

mainly due to aging construction materials and failed mortar joints, particularly where laterals were constructed from orangeburg or 

clay pipe. Service lateral defects identifi ed included root intrusion, misaligned joints, broken pipes, holes, and missing pipes. Based on 

these fi ndings, the city adopted and implemented the Voluntary Sewer Lateral Rehabilitation Program (VSLRP) in 1997.

The VSLRP was developed to mutually benefi t the city and homeowners. Homeowners who participate in the program received free 

lateral inspection, construction permits, technical advice, and a rebate of half the cost of the replacement or repair up to $1,000 per 

property from the city. The lateral rehabilitation methods used by the city were removal and replacement, the most popular method, 

as well as trenchless rehabilitation methods of pipe bursting and lining.

More information at http://www.ci.san-luis-obispo.ca.us/utilities/vslrp_technical.asp

Voluntary Service Lateral Program

Responsible Agency: City of San Luis Obispo Utilities 

Department

Population Served: 44,613

Service Area: 10.7 sq. mi.

Sewer System: 130 mi. of combined sewer

SAN LUIS OBISPO, CA

The City of Orlando Public Works Department (PWD) is responsible for the 

maintenance and repair of the city’s sewer system. Service laterals in the sewer 

system are made from several different materials, including clay (45 percent), 

PVC (35 percent), and concrete (20 percent). PWD found that the clay and 

concrete pipes were particularly prone to I/I problems and that root intrusion 

was the most common defect in service laterals.

PWD began to excavate and replace laterals from the property line to the main sewer. Excavation was expensive and disturbed the

local landscape and traffi c patterns, frustrating residents. PWD looked into various trenchless technology options and selected CIPP 

liners installed using an air inversion system to rehabilitate laterals.

PWD only rehabilitates laterals from the property line to the main sewer. Lateral rehabilitation begins when city crews excavate the 

lateral at the property line. The crew then performs an initial inspection, and the proper length of liner is prepared and impregnated 

with resins. The liner is installed into the host pipe by infl ating a bladder that forces the liner into the pipe and causes it to adhere to 

the walls of the host pipe. After a two-hour curing period, the bladder is defl ated and removed. After a fi nal inspection, the pipe is 

reconnected and the excavation site is resodded. It is estimated that this process takes four to fi ve hours per lateral. It is believed that 

this system will help mitigate SSOs by controlling I/I into the system and will reduce service calls. The equipment for this program 

cost $21,500, and it is estimated that rehabilitation will cost $800 per lateral.

Contact: Ron Proulx, Public Works Department, City of Orlando

ORLANDO, FL Lateral Lining Program

Responsible Agency: City of Orlando Public 

Works Department, Wastewater Bureau

Population Served: 200,000

Service Area: 104 sq. mi.

Sewer System: 500 mi. of sanitary sewer
Collection System Controls: Service Lateral Rehabilitation

CSC-43

References

Curtis, N. M., and Krustsch, A.H. “Trying on Flow 

Reduction for Size.” Water Environment Technology. 3 (No. 

4): 48.

Curtis, N. M., and Krustsch, A.H. 1995. Sewer Rehabilitation 

Using Trenchless Technology on Mainlines and Service 

Laterals. Conference proceedings at Water Environment 

Federation WEFTEC, Anaheim, CA. October 1993.

EPA. 1985. Demonstration of Service Lateral Testing and 

Rehabilitation Techniques. Prepared by C. H. Steketee. EPA 

600-2-85-131.

EPA. 1991. Sewer System Infrastructure Analysis and 

Rehabilitation. EPA 625-6-91-030. 

EPA. 1999. Collection Systems O&M Fact Sheet: Trenchless 

Sewer Rehabilitation. EPA 832-F-99-032.

National Association of Sewer Service Companies 

(NASSCO). 1996. Manual of Practices - Wastewater 

Collection Systems. 2nd ed. Baltimore, MD: NASSCO.

Institute for Research in Construction, National Research 

Council Canada. 2002. Construction and Rehabilitation 

Costs for Buried Pipe with a Focus on Trenchless Technologies. 

Prepared by Jack Q. Zhao and Balvant Rajani. Research 

Report No. 101.

Paulson, R. I., et al. 1984. “Attacking Private Infiltration/

Inflow Sources.” Public Works. 115 (2):54-59

Roberts, G. C. 1979. “Expediting Sewer Studies.” Water 

Sewer Work. 126 (No. 2): 52.

Rowe, R., et al. 1995. Data Handling Procedures Expedite 

Sewer Evaluation and Repair of Service Laterals. Proceedings 

of the National Conference on Sanitary Sewer Overflows, 

Washington, DC, April 1995.

Water Environment Federation (WEF). 1999. Control of 

Infiltration and Inflow in Private Building Sewer Connections. 

Alexandria, VA: WEF.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Manhole Rehabilitation

Collection System Controls

Overview

Manhole rehabilitation is one of several sewer system 

controls that can be implemented as part of an on-going 

maintenance or sewer rehabilitation program. Structurally 

defective manholes can be a source of significant 

infiltration and inflow (I/I) to a sewer system. Manhole 

rehabilitation is one way to reduce or eliminate I/I and 

preserve sewer system capacity for transporting wastewater. 

Manhole rehabilitation can range from spot repairs of 

structural components to complete manhole replacement. 

A typical manhole and its components are presented in 

Figure 1. Descriptions of manhole components and a 

summary of common defects are presented in Table 1. 

The most common manhole rehabilitation methods are: 

chemical grouting, spot repairs, coating systems, and 

structural reconstruction (ASCE 1997; NASSCO 1996). 

These methods are described in more detail below. 

Chemical Grouting

Chemical grouting applications are used to fi ll and 

repair cracks and openings in manhole components, 

primarily in the frame, chimney, and cone. There 

are variety of grouts available including acrylamide, 

acrylate, acrylic, urethane gel, and urethane foam. 

The selection of a grout type should be based on 

site-specifi c considerations. A single grout or a 

combination of grout types may be used depending on 

the manhole’s depth. The ideal ambient temperature 

for applying grout is about 40EF. Grouts need to be 

chemically stable; be resistant to acids, alkalis, and 

organics; have controlled reaction times; and have a 15 

percent shrinkage control (ASCE 1997). For projects 

using a combination of grout types, urethane foam is 

typically used in the upper fi ve feet of the manhole, 

while urethane gel or acrylamide are used for the 

lower section (ASCE 1997). Careful inspection of 

the grouting work and dye testing is recommended 

to ensure adequate sealing. The effectiveness of this 

method depends on soil conditions, groundwater table 

elevation, type of grouting mixture applied, pattern 

of injection, experience of the grout crew, and project 

quality control (ASCE 1997).

Spot Repair

Spot repairs include a variety of activities intended 

to restore damaged manhole components to a proper 

functional condition that prevents or minimizes I/I. 

Spot repairs may include: restoration or overhaul of 

specifi c components, or patch work depending on the 

degree of damage and the availability of replacement 

parts. The types of manhole I/I that can be addressed 

with spot repairs include surface water entering 

through holes in the manhole cover and the space 

between the manhole cover and frame, and subsurface 

water entering from under the manhole frame and 

chimney. Damaged manhole covers can be sealed by 

replacing them with a new watertight cover; sealing the 

existing cover with asphaltic mastic and plugging vent 

and pick hole plugs; installing watertight inserts under 

the existing manhole cover; or by installing rubber 

gaskets. Damaged frame-chimney joint areas can be 

sealed internally, without excavation, when frame 

alignment and chimney conditions permit. 

Figure 1. Schematic of a typical manhole

Cover or Insert

Frame

Frame Seal or

Chimney Seal

Cone

Wall

Base

Bench Channel

Joint

Broken manhole (Limno-Tech, Inc.).
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Coating Systems

Coating systems have been used successfully for 

manhole rehabilitation for over 20 years. The 

application of coating systems to the inner surface 

of the manhole protects concrete, steel, masonry, 

and fi berglass structures against chemical attack, 

abrasion, high temperatures, infi ltration, and erosion. 

There are numerous coating systems available under 

various trade names, but in general they have similar 

basic components: rapid set patching, plugging, and 

coating compounds. The coating is applied in one or 

more layers to the manhole interior either by machine 

(spraying) or by hand. Surfaces that need coating 

require proper cleaning and preparation. If there 

is a potential for the presence of hydrogen sulfi de, 

corrosion-resistant additives should be included in 

the coating mixture. Careful monitoring of cleaning, 

preparation, coating, and clean-up is important, as is 

testing for effectiveness after rehabilitation, using dyewater fl ooding, water exfi ltration, or vacuum air testing. 

Structural Reconstruction

Structural reconstruction is a rehabilitation method 

that completely restores the structural integrity 

of manhole walls through in-situ reconstruction 

methods. Structural reconstruction can be done with 

the following: poured-in-place concrete; prefabricated 

fi berglass, PVC rib-lock liner, prefabricated reinforced 

plastic mortar, spiral wound liner, cured-inplace structural liners, prefabricated high-density 

polyethylene, and spray-applied systems (NASSCO 

1996). Selection criteria for using this rehabilitation 

method include substantial structural degradation and 

life-cycle cost justifi cations. When completed, the wall 

should be a minimum of 36 inches in diameter and 

three inches thick. The use of Type II Portland cement 

mix and calcium aluminate or other special cement 

mixes or linings for corrosion resistance is generally 

recommended (ASCE 1997). 

Key Considerations

The first step in selecting an appropriate manhole 

rehabilitation method is to conduct a thorough inspection 

of the manhole and its components. Selection of the 

appropriate method depends on several factors including:

● The type of problem to be remediated;

● Physical characteristics of the structure such as 

construction material, age, and condition of manhole;; 

and

● Location with respect to traffic and accessibility, risk 

of damage or injury associated with current condition, 

and cost/value in terms of rehabilitation performance 

(NASSCO 1996).

Table 1. Summary of manhole components and common defects1.

Component Description Typical Defects Defect Result

Bench Concrete or brick floor which 

directs incoming flows to the 

outlet piping and minimizes 

solids buildup. Includes bench/

channel joint.

Cracked, loose, missing pieces, leaking 

channel/bench seal, deteriorated, or 

debris/deposition

Infiltration

Chimney Narrow vertical section built from 

brick or from concrete adjusting 

rings that extends from the top 

of the cone to the frame and 

cover.

Cracked, broken, or deteriorated Infiltration

Cone Reducing section which tapers 

concentrically or eccentrically 

from the top wall joint to the 

chimney or the frame and cover. 

Cracked, loose, missing mortar, leaking 

cone/wall joint, or deteriorated

Infiltration

Cover Lid which provides access to the 

interior of the manhole.

Open vent or pick holes subject to 

ponding, bearing surface worn or 

deteriorated, poor fitting, cracked or 

broken, or missing

Inflow

Frame The cast or ductile ring which 

supports the cover.

Bearing surface worn or deteriorated, 

no gasket for gasketed frames, cracked 

or broken, or frame offset from chimney

Infiltration and 

Inflow

1

 ASCE 1997
Collection System Controls: Manhole Rehabilitation

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Applicability

Selection of an appropriate manhole rehabilitation 

technique is based on site-specific conditions. Chemical 

grouts are commonly used for rehabilitating manholes 

made of brick that are structurally sound. Spot repairs 

of manhole components are most appropriate for 

addressing minor defects. Coating systems are applicable 

for manholes with brick structures that show minimal 

or no evidence of movement or subsidence, since the 

coatings have minimal shear or tensile strength, and at 

sites not conducive to excavation or major reconstruction. 

Structural reconstruction is applicable for standard 

manhole dimensions (48-72 inches inner diameter) where 

substantial structural degradation has occurred. Structural 

reconstruction methods tend to be more expensive than 

other rehabilitation techniques.

Advantages

The primary advantage of manhole rehabilitation is a 

reduction in the capacity demanding I/I entering the sewer 

system through damaged manholes. Many municipalities 

have successfully implemented manhole rehabilitation 

programs as part of larger efforts aimed at reducing I/I and 

other extraneous flows into sewer systems. For manholes 

experiencing inflow from the surface, repairing or replacing 

individual components can be the most efficient and 

cost-effective rehabilitation method. For example, rubber 

gaskets are inexpensive and can effectively seal the cover 

without costly excavation. On a similar note, chemical 

grouting which seals cracks and voids along the manhole 

walls, is significantly less expensive than applying a coating 

system. Structural relining is often the most appropriate 

rehabilitation method for severely deteriorated manholes. 

An added benefit of structural relining is the renewal of 

manhole structural integrity and extended service life of the 

entire manhole.

Disadvantages

Manhole rehabilitation methods that require excavation can 

be significantly more expensive. For example, replacement 

of a manhole frame, rebuilding of a chimney and cone, and 

structural relining all require more extensive construction 

procedures including pavement replacement and surface 

restoration. Structural relining can reduce the diameter 

of the manhole and may entail higher initial costs. On 

the other hand, spot repairs or chemical grouting do not 

improve the structural integrity, and in some cases, may not 

be the most cost-effective long-term solution, especially for 

older manholes. In addition, the location of the manhole 

can entail significant safety risks for the work crew as some 

manholes are located in busy intersections and subject to 

considerable vehicle traffic.

Cost

The cost of rehabilitating individual manholes varies 

depending on the method selected and other site-specific 

conditions. A range of average costs for specific methods 

along with the anticipated useful life of the rehabilitated 

manhole or component are presented in Table 2. Selection 

of the most appropriate rehabilitation method often 

involves an assessment of cost and cost-effectiveness. If the 

amount of I/I controlled through manhole rehabilitation 

is known, then the cost of manhole rehabilitation can 

be compared directly with the cost of transporting and 

treating the I/I. When assessed in this manner, replacing 

or sealing of manhole covers is often cost-effective if 

substantial I/I enters the sewer system at manhole covers. 

However, in some situations, it may be more cost-effective 

to conduct a system-wide, comprehensive rehabilitation 

instead of assessing the need for repair or replacement of 

individual components. In addition to the volume of I/I 

removed, other important considerations include life-cycle 

cost, risk of failure, damage to surface from unrepaired 

manholes, disruption during construction, and life 

expectancy.

Rehabilitation Method Initial Cost 

Range ($)b

Anticipated 

Life (Years)

Seal existing cover 20-50 8

Replace cover 120-240 50

Adjust frame

 with excavation 150-640 50

 without excavation 150-200 25

Seal frame/applied seal 250-350 7

 gasket (applied seal) 250-415 7

 manufactured seal 250-415 25

Replace frame 415-685 50

Coating systems

 with corrosion

 protection

500-850 15

 without corrosion 

 protection

350-650 15

Chemical grouting 540-835 15

Structural lining 1,600-3,500 50

Replace manhole 2,400-5,500 50

Table 2. Manhole rehabilitation costs and life expectancies.a

a

 Based on a standard 9-foot, 48-inch diameter manhole (ASCE 

1997)

b

 Costs are in 2002 dollars
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The Perkasie Borough Authority provides water and sewer services to Perkasie 

Borough and three neighboring communities in southeastern Pennsylvania. It is 

also one of six municipal members who have their sewage treated at a regional 

sewage treatment plant. In the early 1990s, the regional plant rated at 4 MGD 

was receiving 6-7 MGD of fl ow during wet weather. Concerned about the I/I, 

the Pennsylvania Department of Environmental Protection (DEP) implemented 

a moratorium on new sewer connections until I/I was substantially reduced. 

Perkasie Borough found that manhole rehabilitation provided a simple, economical, and acceptable means to reduce I/I and get the 

moratorium on development lifted. 

Perkasie Borough conducted a comprehensive study to determine the extent to which I/I contributed to high fl ow rates. As part of 

the study, fl ow monitoring was carried out at eight representative locations over a three month period which included extended 

dry periods, small to medium storm events, and three storms greater than one inch. The extent of I/I was determined through 

comparison of water use data with monitored fl ow data. Sewersheds were ranked from best to worst and prioritized for corrective 

action. A second fl ow monitoring effort was undertaken to determine the amount of I/I attributable specifi cally to manholes. Flow 

was measured in a sewershed serving 230 homes that had relatively new PVC piping. The fl ow monitoring showed that most of the 

infl ow was entering the sewer system through manhole covers, frames, and connecting seals. Further, pilot tests showed that the 

installation of new seals would produce dramatic reductions in I/I. The evidence was so persuasive that the Pennsylvania DEP agreed 

that for every 3.2 seals installed, one new dwelling unit could be constructed in the service area. Perkasie Borough handles its own 

installations, and has found that the average cost-per-manhole is $310 for components and installation. Installation of the seal is an 

economical and effective way to reduce I/I and has become a standard procedure for new manholes. 

Contact Gary Winton, Perkasie Borough Authority

Manhole Sealing

PERKASIE 

BOROUGH, PA

Responsible Agency: Perkasie Borough 

Authority

Population Served: 10,000

Service Area: 2.5 sq. mi.

Sewer System: 33.5 mi. of sanitary sewer

The Broward County Southern 

Regional Sewer Authority completed 

a comprehensive sewer system 

rehabilitation program in 1996. The 

rehabilitation program eliminated 

approximately 5.64 MGD of extraneous 

fl ow via 429 manholes repairs, 427 

sewer line point repairs covering approximately 179,360 linear feet of lined or grouted 

main sewer line, and 314 private service lateral repairs. The sewer rehabilitation program 

reached its goal of eliminating 35 percent of the total system I/I. The construction cost for 

this project was $6.9 million.

More information at http://www.avantigrout.com/literature/casestudymiamil.pdf

Manhole Rehabilitation

Responsible Agency: Broward County 

Southern Regional Sewer Authority

Population Served: 288,600

Service Area: 106 sq. mi.

Sewer System: 536 mi. of collection sewer

BROWARD

COUNTY, FL

Manhole Rehabilitation 

Method

Number 

Completed

Cementitious liner 333

Realign manhole cover 59

Install cover inserts 58

Replace frame and cover 32

Install fiberglass liner 10

Implementation Examples
Collection System Controls: Manhole Rehabilitation

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References

American Society of Civil Engineers (ASCE). 1997. Manhole 

Inspection and Rehabilitation. In Manuals and Reports on 

Engineering Practice No. 92. Prepared by the Committee 

on Manhole Rehabilitation of the Pipeline Division of the 

ASCE. New York, NY: ASCE.

EPA Office of Research and Development, Center for 

Environmental Research Information. 1991. Handbook: 

Sewer System Infrastructure Analysis and Rehabilitation. 

Cincinnati, OH: EPA Office of Research and Development. 

EPA/625/6-91/030.

Johnstone, Ralph. Interview by Limno-Tech, Inc., December 

2002. Washington, D.C.

Larson, J.P., and C. Garcia-Marquez. 2000. Broward County, 

Florida – Successful I/I Rehabilitation Programs. Presented at 

the Water Environment Federation WEFTEC Conference, 

Anaheim, CA, 2000.

National Association of Sewer Service Companies 

(NASSCO). 1996. Manual of Practices: Wastewater Collection 

Systems. 2nd ed. Maitland, FL: NASSCO.

Metropolitan Sewer District of Greater Cincinnati (MSDGC). “MSD Receives Trenchless Technology Award.” 

Retrieved December 9, 2002. 

http://www.msdgc.org/news/archives/trenchless_tech_

award/ 

Winton, Gary. Interview by Limno-Tech, Inc., March 2003. 

Washington, D.C.

The Metropolitan Sewer District of Greater Cincinnati (MSD-GC) provides 

wastewater treatment services to more than 800,000 customers in Hamilton 

County, Ohio. Faced with I/I problems, MSD-GC conducted a demonstration 

project to evaluate various manhole rehabilitation products as part of a larger 

sewer system rehabilitation program. In 2001, over 35 different manhole 

rehabilitation products were installed and tested. The knowledge gained from the 

demonstration project allowed MSD-GC to develop specifi cations to maximize the 

success of future manhole rehabilitation efforts. These specifi cations involved the 

development of guidelines on substrate preparation, material application, frost-line protection, testing and inspection, and contract 

warranty requirements. Manholes requiring rehabilitation of the invert (fl ow channel) were found to be more costly due to the need 

to plug and bypass fl ows.

Following the demonstration project, MSD-GC launched a project to evaluate the performance and cost of three particular manhole

rehabilitation methods (i.e., cementitious coatings, spray-on epoxy coatings, and cured-in-place manhole liners). This project will result 

in the rehabilitation of 150-300 brick and concrete manholes per year, at an annual cost of approximately $1 million. This project also 

allows MSD-GC to test the effectiveness of its current manhole rehabilitation specifi cations and to make necessary adjustments based 

on performance results. Initial post-rehabilitation fl ow monitoring data indicate improvement as a result of the manhole rehabilitation. 

The data show that cementitious coatings and spray-on epoxy are less effective than cured-in-place methods in reducing I/I.

Contact Ralph Johnstone, Metropolitan Sewer District of Greater Cincinnati

CINCINNATI, OH Manhole Rehabilitation Project

Responsible Agency: Metropolitan Sewer 

District of Greater Cincinnati

Population Served: 800,000

Service Area: 400 sq. mi.

Sewer System: Over 3,000 mi. of sanitary and combined sewer

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

In-Line Storage

STORAGE FACILITIES

Overview

Many sewer systems experience high flow rates during wet 

weather periods. The use of storage facilities to attenuate 

and store peak wet weather flows is widely implemented to 

reduce or eliminate CSOs and SSOs. In-line or in-system 

storage is the term used to describe facilities that depend on 

existing, available storage in the sewer system to control wet 

weather flows. In-line storage techniques include the use of 

flow regulators, in-line tanks or basins, and parallel relief 

sewers. Each of these types of in-line storage is described 

below.

Flow Regulators

Flow regulators are used to optimize in-line storage 

by damming or limiting fl ow in specifi c areas of the 

sewer system. Flow regulators can be grouped into two 

categories: fi xed and adjustable. 

Fixed regulators, as their name implies, are stationary 

and do not adjust to variations in fl ow. They are ideally 

located at key hydraulic control points. With fewer 

moving parts and sensors, fi xed regulators tend to be 

less expensive to install, operate, and maintain than 

adjustable regulators. Fixed regulators include:

● Orifi ces ● Weirs

● Flow throttle valves

● Restricted outlets

● Vortex throttle valves

One specifi c type of fi xed regulator is the vortex 

throttle valve shown in Figure 1. Low fl ows pass 

through vortex throttle valves without restriction. Once 

the fl ow reaches a pre-determined level, an air-fi lled 

vortex is automatically created that reduces the area 

through which fl ow can pass, damming the fl ow behind 

the valve (John Meunier/USFilter 2002). The vortex 

does not create a constriction. Trash and debris fl ow 

through the valve easily after excess fl ows subside (EPA 

1993).

Adjustable regulators are more complex and can be 

operated in a dynamic mode. Consequently, they offer 

a greater potential to maximize the available in-system 

storage by reacting to the variable nature of fl ow in 

the sewer system (Moffa 1997). Adjustable regulators 

include:

● Infl atable dams

● Reverse-tainter gates

● Float-controlled gates

● Sluice-type gates

● Tilting plate regulators

An example of an adjustable regulator is the infl atable 

dam, shown in Figure 2. Infl atable dams are typically 

made of rubberized fabric and are infl ated and defl ated 

to control fl ow. Automatic sensors are often used to 

activate the dams. The dams can be fi lled with air, 

Vortex

throttle

Outfall

Inflow pipe

to throttle

Figure 1. Schematic of a vortex throttle.

Inflatable dam installation (LJCMSD)
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-2

water, or a combination of both. Air control is generally 

less costly, but water provides better control over dam 

shape (EPA 1993). With the dam infl ated, fl ow can be 

stored in upstream pipes. 

In-Line Storage Tanks or Basins

Storage tanks and basins constructed in-line within the 

sewer system can also be used to attenuate and store 

fl ows during wet weather periods. Dry weather fl ows 

pass directly through in-line storage tanks or basins. 

Storage within the in-line tanks or basins is typically 

governed by a fl ow regulator which limits fl ow exiting 

the facility during wet weather periods. The primary 

function of in-line storage structures is the attenuation 

of peak fl ows, not treatment. Flows exiting the storage 

structure are conveyed downstream for treatment. 

Therefore, unlike off-line retention basins and deep 

tunnel storage facilities, in-line tanks and basins are 

rarely equipped with disinfection, and may not have an 

outlet to discharge directly to a receiving water.

Parallel Relief Sewers

In-line capacity can also be created by installing relief 

sewers parallel to existing sewers, or by replacing older 

sewers with larger diameter pipes. The installation of 

parallel relief sewers, or larger pipes, is accomplished 

in the same manner as installing new pipes – using 

traditional open-cut construction methods or 

trenchless technologies. Trenchless technologies refer 

to several types of construction methods that minimize 

the environmental and surface impacts of sewer 

installation. More information on these techniques 

is provided in the “Sewer Rehabilitation Technology 

Description,” in Appendix B of the 2003 Report to 

Congress on the Impacts and Control of CSOs and SSOs.

Key Considerations

Applicability

Taking advantage of existing storage within the sewer 

system has broad application in CSSs and SSSs. It is 

regarded as a cost-effective way to reduce the frequency 

and volume of CSOs and SSOs, often without large capital 

investments. Maximization of storage in the sewer system 

is one of the NMC required of all CSO communities. EPA 

guidance describes maximization of storage as “making 

relatively simple modifications to the CSS to enable the 

system itself to store wet weather flow until downstream 

sewers and treatment facilities can handle them” (EPA 

1995).

The physical condition of the sewer system must be 

considered when examining potential in-line storage. The 

amount of storage potentially available in the sewer system 

largely depends on the size or capacity of the pipes that will 

be used for storage, and the suitability of sites for installing 

regulating devices. The trunk sewers and many interceptors 

within CSSs are often designed to convey flows 5-10 times 

greater than average dry weather flows, and often provide 

some potential capacity for storage. Also, areas where the 

pipe slope is relatively flat often offer opportunities for 

storage.

An important component of successful in-line storage 

applications is proper operation and maintenance. By 

maintaining the initial condition of the sewer system (i.e., 

not allowing sediment build up within the pipes), the 

complete capacity of the sewer is available for storing and 

transporting excess wet weather flows. Similarly, CSO and 

SSO volumes can be reduced by removing obstructions that 

decrease the capacity of the sewer system. Larger objects 

often must be removed by hand, whereas sewer flushing can 

be used to remove smaller obstructions and sediment build 

up (EPA 1999). Additional sewer cleaning techniques are 

discussed in the “Sewer Cleaning Technology Description,” 

in Appendix B of the 2003 Report to Congress on the Impacts 

and Controls of CSOs and SSOs.

Certain factors limit the applicability of in-line storage; for 

example it can increase the possibility of basement backups 

and street flooding (EPA 1999). Basement backups occur 

when the level of the flow in the sewer is higher than the 

level of the connection between the service lateral and 

the building basement. Storing flow in existing pipes may 

exacerbate this condition because damming devices raise 

the level of the flow in the sewer system. Field surveys and 

investigations of sewer maps and as-built drawings are 

required in order to prevent the throttling back of flows to 

a degree that causes flooding and backups.

Figure 2. Schematic of an inflatable dam system.

Inflatable dam

CSO

outfall

Dam

controls
Storage Facilities: In-Line Storage

STR-3

Use of in-line storage may also slow flows and allow 

sediment and other debris present in wastewater or urban 

runoff to settle out in the pipes. If allowed to accumulate, 

the sediment and debris can reduce available storage and 

conveyance capacity. Therefore, an important design 

consideration for in-system storage is to ensure that 

minimum flow velocities are provided to flush and transport 

solids to the wastewater treatment plant.

Advantages

Advantages of in-line storage include:

● Maximum utilization of existing capacity, which may 

reduce size or scope of other controls;

● Development of in-line storage in parallel relief or 

upsized sewers can be coupled with other sewer 

rehabilitation projects;

● Relatively inexpensive in comparison to other types of 

storage;

● Attenuates peak wet weather flows and equalizes loads 

to the treatment facility; and

● Reduces frequency and volume of CSOs and SSOs 

during light to moderate rainfall events.

Disadvantages

Disadvantages of in-line storage include:

● Provides little treatment of wet weather flows on its 

own;

● May be difficult to construct large storage volumes 

typically required for complete CSO control; and ● Increased potential for basement backups and street 

flooding.

Cost

The largest expenditure for most types of storage facilities 

is the construction of the actual storage volume. By taking 

advantage of underutilized capacity that may currently exist 

within the sewer system, costs are limited to flow regulators 

and other equipment needed to optimize the attenuation 

and storage of wet weather flows. The costs associated with 

construction of in-line storage range from approximately 

$0.06 per gallon to more than $1 per gallon. Cost 

information from a number of in-line storage applications is 

presented in Table 1 and 2.

The cost information shows that per gallon costs of storage 

developed using flow regulators are significantly less than 

storage developed through the installation of large diameter 

or parallel relief sewers.

Municipality Technology Characteristics Year 

Constructed Cost

Washington, DC Inflatable Dam • Total Storage = 36 MG

• 2 dams in 8 locations throughout the system

• Fully inflated under low pressure during dry

 weather

1990 Construction Cost:

$2.2 million or 

$0.06/gallon 

Louisville, KY Inflatable Dam • Total Storage = 2.5 MG

• Sneads Branch Relief Sewer collects wet weather 

flow from 11 CSOs

2001 Construction Cost:

$1.07 million or 

$0.43/gallon 

Saginaw, MI Flow Control 

Chamber with a 

Vortex Throttle

• Total Storage = 1.4 MG 1986 Construction Cost:

Less than $290,000 

or $0.21/gallon 

Philadelphia, PA Inflatable Dam • Total Storage = 16.3 MG

• 3 large inflatable dams located in large sewers

 11-15 ft. high

• Can inflate in 15 minutes and deflate in 5 minutes

Planned Dam Cost: $650,000

Civil Construction 

Cost: $4.2 million

Total Cost:

$4.8 million or 

$0.29/gallon 

Houston, TX Parallel Relief 

Sewer 

• Total Storage = ~ 0.64 MG

• Diameter: 36 in., 18 in., and 15 in.

• Length: over 6,000 ft.

• Installed parallel to the existing system which was 

abandoned in place

• Part of a plan to eliminate overflows from sewer 

system

1995 Construction Cost:

$436,126 or 

$0.68/gallon 

Table 1. Summary of costs of inflatable dam installed in select communities.
 Report to Congress on the Impacts and Control of CSOs and SSOs

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The Massachusetts Water Resources Authority (MWRA) provides sewer services 

for 43 communities in the Boston metropolitan area. The City of Boston and 

three surrounding communities have combined sewer areas. MWRA developed 

a system optimization plan in 1993, which included operational modifications 

and simple, low-cost structural changes to reduce CSO frequency. Structural 

alterations included repairing regulators, raising weir heights, and installing

new weirs and regulators to increase storage within the sewer system. All 103 

projects outlined in the system optimization plan have been completed. MWRA has since completed other system evaluations that 

have resulted in more simple structural alterations to reduce the occurrence of CSOs. As of 1997, MWRA had spent a total of $3.1 

million on structural alterations, which have reduced average annual CSO discharges by 400 MG. The typical capital costs for brick 

and mortar weirs, formed concrete weirs, and stop logs are $3,650, $13,525, and $20,315, respectively.

More information at http://www.mwra.state.ma.us/sewer/html/sewcso.htm

Implementation Examples

BOSTON, MA System Optimization Plan

Responsible Agency: Massachusetts 

Water Resources Authority

Population Served: 2.5 million

Service Area: 406 sq. mi.; 13 sq. mi. of combined sewers

Sewer System: 228 mi. of interceptor sewer

Municipality Technology Characteristics Year 

Constructed

Cost

Bangor, ME In-line Basin • In-line storage tunnel

• Made from V-bottom precast box sections

Davis Brooke Storage Facility

Total Storage = 1.2 MG

Barkersville Storage Facility

Total Storage = 1.4 MG

1998

2002

Construction Cost: 

$1.4 million or 

$1.17/gallon 

Construction Cost:

$2 million or 

$1.43/gallon

Houston, TX Parallel Relief 

Sewer 

• Total Storage = ~ 0.64 MG

• Diameter: 36 in., 18 in., and 15 in.

• Length: over 6,000 ft.

• Installed parallel to the existing system which 

was abandoned in place

• Part of a plan to eliminate overflows from 

sewer system

1995 Construction Cost:

$436,126 or 

$0.68/gallon 

Portland, OR Parallel Relief 

Sewer

• Total Storage = ~ 42 MG

• Conveyance pipe that is 6 ft. in diameter and a 

storage pipe that is 12 ft. in diameter

• Total length is 3.5 mi.

2000 Design and Construction 

Cost: $76 million or 

$1.81/gallon 

Syracuse, NY In-line Basin • Total Storage = 5 MG

• Erie Boulevard Storage Facility

• Box culvert with sluice gate control 

Dimensions: 7.5 ft. wide, 10.5 ft. high, and 8,640 

ft. long

1970s; 

refurbished 

2002

Approximate Cost of 

Refurbishment:

$2.6 million or 

$0.53/gallon

Table 2. Summary of costs of in-line basins and relief sewers in communities.
Storage Facilities: In-Line Storage

STR-5

The Sneads Branch Relief Sewer is an 11 foot semi-elliptical tunnel that 

was built in 1951 to control flooding. The relief sewer receives no dry 

weather flow, which was one of the reasons it was selected for storage of 

wet weather events. An inflatable rubber dam was installed to maximize 

storage in the relief sewer; minimal tunnel modifications were necessary. 

During normal flow conditions, the dam is half inflated. During wet weather 

events, it is inflated to full height. A water level sensor just above the dam activates the inflation. The relief sewer captures flow from 

11 upstream CSOs, and it can store up to 2.5 MG of combined sewage. It is predicted that the inflatable dam will reduce the average 

annual CSO volume by 63 percent from 43 MG per year to 18 MG per year. The cost of the Sneads Branch Relief Sewer Inflatable Dam 

was $1.07 million or $0.43/gallon of storage.

Contact: Angela Akridge, Louisville and Jefferson Metropolitan Sewer District

Snead Branch Relief Sewer Inflatable Dam

Responsible Agency: Louisville and Jefferson 

County Metropolitan Sewer District

Population Served: 600,000

Service Area: 205 sq. mi.

Sewer System: ~ 2,800 mi. of sewers

LOUISVILLE, KY

As part of Philadelphia’s effort to control CSOs, the City Water 

Department plans to install three inflatable dams in large sewers 

that have available in-line storage. The dams will range from 11 to 15 

feet high and will be automatically controlled for both dry and wet 

weather conditions. The three dams will enable 16.3 MG of flow that 

might otherwise discharge to local receiving waters to be stored in 

existing sewers, reducing CSO volumes by 650 MG per year.

The first inflatable dam, located in the city’s main relief sewer, will 

be operational by the end of 2004. The associated civil work projects such as sewer rehabilitation have been completed for this

project. When operating, the dam will have the ability to store up to 4 MG of combined sewage, and it is expected to reduce the

number of CSO discharges to the Schuylkill River from 32 per year to four per year. Another inflatable dam will be installed in

Rock Run during the summer of 2005. The total cost for the installation of the dams and sewer rehabilitation is approximately $4.8 

million, or $0.29/gallon of storage. 

More information at http://www.forester.net/sw_0011_innovative.html and http://www.phila.gov/water/index.html

Responsible Agency: Philidelphia Water 

Department

Population Served: 2 million

Service Area: 335 sq. mi.

Sewer System: 1,600 mi. of combined 

sewers

PHILADELPHIA, PA Inflatable Dams
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-6

In 1972, the City of Portland’s CSS was estimated to release 10 BG of CSO 

annually into local receiving waters. In 1991, the city started a 20-year 

program to curb CSOs to the Willamette River by 94 percent, and to the 

Columbia Slough by over 99 percent. The plan includes actions to fully utilize 

storage in the existing sewer system by modifying 32 diversion structures. 

The city has also invested in the construction of parallel relief sewers to store 

combined sewage that would otherwise be discharged to the Columbia Slough. Specifically, the city constructed 3.5 miles of six 

foot diameter conveyance pipe and a 12 foot diameter parallel relief sewer. It took three years to construct this relief sewer, which 

became operational in September 2000. It captures 100 percent of the overflows from the eight CSO outfalls in its drainage area and 

an average of 440 MG of combined sewage per year. The cost of the Columbia Slough Consolidation Conduit was approximately $76 

million or $1.81/gallon of storage.

More information at http://www.cleanriverworks.com/

Parallel Relief Sewers

Responsible Agency: City of Portland

Population Served: 500,000

Service Area: 133 sq. mi.

Sewer System: 2,256 mi. of sewer

PORTLAND, OR

The Erie Boulevard Storage System was originally constructed in the 1970s as a

separate storm water system. The facility is a box culvert that is 7.5 feet by 10.5

feet and 8,640 feet long. It has a storage volume of 5 MG, and an additional 1 MG

of storage is available in ancillary conveyance pipes. It was retrofitted in 1985

with four sluice gates to facilitate the storage of combined sewage, and reduce

CSO discharges to Onondaga Creek.

The original sluice gate control system was located within underground concrete

vaults. Moisture and road salt severely damaged the control system requiring a facility upgrade. The upgrade was completed in July

2002, and included refurbishment of the sluice gates, construction of an above ground control center, and installation of a realtime control system. It is estimated that the Erie Boulevard Storage System will now capture 220 MG of wet weather flow annually.

Upgrades to the Erie Boulevard Storage System cost $2.6 million or $0.52/gallon of storage.

More information at http://www.lake.onondaga.ny.us/ol3113.htm

SYRACUSE, NY Erie Boulevard Storage System

Responsible Agency: Onandaga County 

Department of Water Environment 

Protection

Population Served: 400,000

Service Area: 13 sq. mi.; 11 sq. mi. of combined sewer

Sewer System: 3,000 mi. of sewer
Storage Facilities: In-Line Storage

STR-7

References

City of Portland, Oregon, Bureau of Environmental 

Services. 2002. “Action 4: Upgrading Portland’s Eastside 

Sewer System.” Retrieved October 2, 2002. http://

www.cleanrivers-pdx.org/pdf/action4.pdf

Dahme, J. and J. Sullen. 2000. “Innovative Strategy Helps 

Philadelphia Manage Combined Sewer Overflows.” 

Retrieved October 7, 2002. 

http://www.forester.net/sw_0011_innovative.html 

District of Columbia Water and Sewer Authority. 2002. 

“Final Report: Combined Sewer System Long Term Control 

Plan.” Retrieved October 9, 2002. 

http://www.dcwasa.com/education/css/

longtermcontrolplan.cfm

EPA Office of Research and Development. 1993. Manual: 

Combined Sewer Overflow Control. EPA 625-R-93-007.

EPA Office of Water. 1995. CSO Guidance for Nine 

Minimum Controls. EPA-832-B-95-003. 

EPA Office of Water. 1999. Combined Sewer Overflow 

Technology Fact Sheet: Maximization of In-line Storage. EPA 

832-F-99-036.

Gray, W. et al. 1999. Prevention and Control of Sewer System 

Overflows: WEF Manual of Practice No. FD-17. Alexandria: 

Water Environment Federation. 

John Meunier/USFilter. 2002. “CSO/Stormwater 

Management: Hydrovex Product Line.” Retrieved 

December 9, 2002. 

http://www.johnmeunier.com/2002/en/products/pdf/

hydrovex_line_card.pdf

Moffa, Peter. 1997. Control and Treatment of Combined 

Sewer Overflows. New York: Van Nostrand Reinhold.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Off-Line Storage

STORAGE FACILITIES

Overview

Many sewer systems experience high flow rates during wet 

weather periods. The use of storage facilities to store and 

attenuate peak wet weather flows is widely implemented 

to reduce or eliminate CSOs and SSOs. Off-line storage 

is the term used to describe facilities that store or treat 

excess wet weather flows in tanks, basins, tunnels, or other 

structures located adjacent to the sewer system. During dry 

weather, wastewater is passed around, not through, off-line 

storage facilities. During wet weather, flows are diverted 

from the sewer system to these off-line storage facilities by 

gravity drainage or with pumps. The stored wastewater is 

temporarily detained in the storage facility and returned 

to the sewer system once downstream conveyance and 

treatment capacity become available. Most off-line storage 

structures provide some treatment through settling, but 

their primary function is storage and the attenuation of 

peak flows. The use of off-line storage is usually considered 

to be a good option where in-line storage is insufficient or 

unavailable.

Near-Surface Storage Facilities

Near-surface storage facilities are typically located at 

key hydraulic control points. In CSSs, they are often 

located near a CSO outfall; in SSSs, they are often 

situated in areas where infl ow and infi ltration (I/I) 

problems are severe and diffi cult to otherwise control. 

A typical near-surface storage facility is a closed 

concrete structure with a simple design that is built at 

or near grade alongside a major interceptor. As shown 

in Figure 1, the basic components of near-surface 

storage facilities are:

● Basin or tank

● Flow regulating device to divert wet weather fl ows 

to the basin or tank

● Flow regulating device or pumps to drain the basin 

or tank

● Emergency relief or overfl ow point

Near-surface storage facilities in CSSs are sometimes 

designed for both storage and treatment. When 

designed and operated for these purposes, they can 

provide primary treatment or its equivalent including 

primary clarifi cation, capture of solids and fl oatables, 

and disinfection of effl uent, where necessary, to meet 

water quality standards (EPA 1994). Consequently, 

screens and disinfection equipment are sometimes 

added to those near-surface storage facilities designed 

to discharge directly to receiving waters. 

An illustration of a more complex near-surface storage 

facility with multiple tanks that is designed to provide 

both storage and treatment is presented in Figure 2. As 

shown, screens are employed to remove fl oatables and 

coarse solids, and fl ows receive disinfection prior to 

discharge. Multiple tanks are used to enhance pollutant 

removal and facilitate maintenance activities. The 

benefi ts of using multiple tanks include:

Figure 1. Basic components of near-surface storage facility.

Near-Surface

Storage Basin

Regulator

Regulator

Emergency

Relief

Flow-Through

Interceptor

Deep tunnel construction (City of Richmond Dep. of Public Works)
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-10

● The “fi rst fl ush” of pollutants can be retained in 

one or more of the tanks long enough to settle 

suspended solids, BOD, and nutrients, while the 

remainder of the fl ow is handled in subsequent 

compartments

● Allows portions of the facility to remain in service 

while maintenance is performed on other portions 

of the facility. The number of compartments 

used can vary from storm-to-storm according 

to the volume of excess wet weather fl ow 

generated, potentially reducing the area requiring 

maintenance after smaller storms, which in turn 

reduces costs

In a multiple tank confi guration, excess wet weather 

fl ows can either pass through each compartment 

sequentially (i.e., the fl ow proceeds through chamber 

one, followed by chamber two, and then chamber 

three) or through each compartment simultaneously 

(i.e., there is fl ow in compartments one, two, and three 

at the same time). Both operational strategies are 

illustrated in Figure 2. However, near-surface storage 

facilities with multiple compartments are typically 

operated in a sequential manner. Specifi c advantages of 

sequential operation include:

● Tanks are only fi lled as the capacity of a preceding 

tank is exceeded; and

● Only that fl ow reaching the fi nal tank is 

disinfected, saving on chemical costs.

Deep Tunnels

Deep tunnel storage facilities are typically used where 

large storage volumes are required and opportunities 

for near-surface storage are unavailable. Deep tunnels 

are primarily implemented as controls in CSSs, but 

have had some application in SSSs. As their name 

implies, deep tunnels are typically located 100-400 feet 

below ground. Tunnel diameters range from 10-50 feet, 

and many are several miles in length. Construction 

usually requires large tunnel boring machines. Most 

deep tunnels are built in hard rock, but some have 

been built in unconsolidated material. Lining the 

tunnel with concrete or other impermeable material 

to prevent infi ltration and exfi ltration is required in 

unconsolidated material, and is recommended for hard 

rock. Like near-surface storage facilities, stored fl ow is 

typically conveyed from deep tunnels to a wastewater 

treatment plant (WWTP) after wet weather events, as 

capacity becomes available. 

An illustration of a deep tunnel, as constructed in 

Milwaukee, WI, is presented in Figure 3. The basic 

components of deep tunnels include: 

● Storage tunnel;

● Flow regulating devices to divert wet weather fl ows 

to the tunnel;

● Coarse screening to protect tunnel facilities from 

large debris;

● Vertical drop shafts to convey wet weather fl ows to 

the tunnel; ● Pumps to drain and de-water the tunnel; 

● Vent shafts to balance air pressure in the tunnel;

● Access shafts that give maintenance personnel 

access to the tunnel;

● Solids removal system for areas where grit may 

accumulate; and

● Odor control system, if necessary.

Figure 2. Flow paths for sequential and simultaneous 

 storage facilities.

Mechanical

Bar Screen

Tank 1

Tank 2

Tank 3

Excess Flow

from Sewers

Disinfected

Flow to

Receiving

Stream

Sequential Flow Pattern

Simultaneous Flow

Separate Sewer

System

Combined Sewer

System

Dropshafts

DEEP TUNNEL

Interceptor

Outfall WWTP

Regulator

Figure 3. Deep tunnel storage (MMSD 2001).
Storage Facilities: Off-line Storage

STR-11

Key Considerations

Applicability

Near-Surface Storage Facilities

Near-surface storage facilities have broad applicability 

and can be adapted to many different site-specifi c 

conditions by changing the basin size (volume), layout, 

proximity to the ground surface, inlet or outlet type, 

and, where required, disinfection mechanism. They are 

particularly applicable in areas where land is readily 

available and the disruption, due to construction, will 

be minimal. The adaptability of near-surface storage 

facilities has led to their use throughout the country. The 

fl exibility of the basin design makes near-surface storage 

facilities practical for utilities, both large or small, in all 

climates.

Deep Tunnels

Deep tunnels provide an alternative to near-surface 

storage facilities where space constraints, potential 

construction impacts, and other issues make 

constructing near-surface facilities challenging. Deep 

tunnels can be constructed in a variety of mediums, 

but geotechnical exploration is needed to assess the 

suitability of subsurface conditions. 

The major construction concerns are the structural 

integrity of the tunnel, infi ltration of groundwater, 

and exfi ltration of the stored fl ows. Tunneling in hard 

rock tends to be more economical because such tunnels 

need minimal, temporary, or permanent structural 

supports. Hard rock tunnels also require less lining to 

prevent infi ltration and exfi ltration (NBC 1998). When 

tunneling in soft rock or soil, the tunneling equipment is 

more expensive. Special equipment is needed to support 

the tunnel during construction to prevent the ground 

from collapsing. In addition, the cost of lining the tunnel 

can be greater because the lining is used to maintain the 

shape of the tunnel as well as to prevent infi ltration. 

Advantages

Near-Surface Storage Facilities

Advantages of near-surface storage facilities include:

● Structural design is simple compared to tunnels and 

supplemental treatment facilities;

● Construction and O&M costs are favorable relative 

to other structural approaches such as sewer 

separation (EPA 1999);

● Operation and response to intermittent and 

unpredictable wet weather events is automatic to a 

certain extent;

● Operators are allowed the fl exibility of returning 

the stored wastewater fl ow to the treatment facility 

where it can receive full treatment; maximizing 

utilization of existing treatment facilities;

● Helps equalize the delivery of pollutants to the 

treatment plant, which tends to improve effl uent 

quality at the treatment facility as well as treatment 

effi ciency;

● Treatment of excess wet weather fl ows consistent 

with the CSO Control Policy can be achieved in 

CSSs; and

● Aesthetic benefi ts and other locally defi ned 

objectives can be realized with imaginative design. 

For example, Wayne County, MI, constructed two 

covered near-surface storage facilities that were 

landscaped with recreation facilities including 

soccer fi elds and basketball courts (Wayne County 

2000).

Deep Tunnels

Advantages of deep tunnel storage include: 

● Large volumes can be stored and transported while 

having a minimal effect on the existing surface 

features (EPA 1993); ● Disruptions that occur with the open-cut 

excavations associated with near-surface storage 

facilities can be avoided (EPA 1993); and

● Valuable surface land area is saved by building deep 

under the ground’s surface.

Disadvantages

Near-Surface Storage Facilities

Disadvantages of near-surface storage facilities include:

● Costs can be substantial relative to non-structural 

controls such as I/I reduction;

● Land required for basins and tanks is often located 

in premium waterfront locations ; ● Construction activities are disruptive;

● On-going maintenance with attendant costs is 

required to keep facilities operating; and ● Solids and captured fl oatables must be removed and 

properly disposed to maintain storage capacity.

Deep Tunnels

Disadvantages of deep tunnel storage include:

● Diffi cult to map subsurface;

● Budget overruns can occur when boring does not 

proceed as planned;

● Tunnels may require substantial, on-going 

maintenance activities, including the disposal of 

built-up sediment deposits;
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-12

Municipality Facility Name Facility Characteristics Year Initiated Construction Cost1

Washington, DC Total Storage = 194 MG

3 deep rock tunnels

To be constructed $761 million or

$3.92/gallon

Atlanta, GA Intrenchment 

Creek

Total Storage = 34 MG

26 ft. diameter

9,293 ft. long

1985 $42.2 million or 

$1.24/gallon 

Chicago, IL TARP Project Total Storage = 2.3 BG

109 mi. of deep rock tunnels

150-350 ft. below ground

1976 (Near 

completion)

$2.51 billion or 

$1.09/gallon

Rochester, NY Total Storage = 175 MG 1993 $690 million or 

$3.94/gallon 

Providence, RI Total Storage = 56 MG

200-300 ft. below ground

26 ft. in diameter

13,500 ft long

2001 (Under 

construction)

$258 million or

$4.61/gallon 

Milwaukee, WI Total Storage = 405 MG

Depth up to 325 ft.

1994 $866 million or

$2.13/gallon 

Table.1. Deep tunnel costs from select communities.

1

 All costs are in 2002 dollars. 

• Exfi ltration from deep tunnels has the potential 

to adversely affect the quality of groundwater in 

adjacent aquifers; and

• Construction schedules for deep tunnels may be 

lengthy, allowing considerable time to pass between 

the initial investment and any measured water 

quality improvements.

Cost

The costs associated with construction of off-line storage 

facilities range from less than $0.10 per gallon to $4.61 per 

gallon. In general, costs for near-surface storage facilities were 

considerably less than those for deep tunnels. The average 

cost for deep tunnels was $2.82 per gallon, while the average 

cost for near-surface storage was $1.75 per gallon. Tables 1 

and 2 present cost information for near-surface and deep 

tunnel storage facilities, respectively.

Municipality Facility Name Facility Characteristics Year Initiated Construction Cost1

Atlanta, GA McDaniel CSO 

Facility 

Underground basin

Total Storage = 2 MG

1986 $9.2 million or 

$1.53/gallon 

Chicago, IL TARP Project Three retention basins

Total Storage = 15.7 BG

1976 (Under 

construction)

$1.11 billion or 

$0.07/gallon 

Bangor, ME Made from pre-cast concrete 

sections 

Total Storage = 1.2 MG

2000 $2.5 million or 

$2.08/gallon

Birmingham, MI Two compartment retention basin

Flow is simultaneous

Total Storage = 5.5 MG

1997 $14.4 million or

$2.61/gallon

Grand Rapids, MI Market Avenue Three compartment

retention basin; flow is sequential

Total Storage = 30.5 MG

1992 $39 million or

$1.24/gallon 

Fairport Harbor, 

OH 

Retention Basin Old oil tank converted for wet 

weather storage

Total Storage = 3.2 MG

1994 $3.1 million or

$0.97/gallon 

Seattle, WA Total Storage = 1.6 MG 1984 $6.1 million or

$3.80/gallon 

Richmond, VA Shockoe Basin Covered and uncovered retention 

basin

Total Storage= 41 MG

 ~1988 $70 million or

$1.73/gallon

Table 2. Near-surface storage costs from select communities.

1

 All costs are in 2002 dollars. 
Storage Facilities: Off-line Storage

STR-13

Construction of Chicago’s Tunnel and Reservoir Plan (TARP) began in 1976. The

TARP contains both deep tunnels and a system of three large reservoirs that act

as near-surface storage facilities. TARP has been implemented in two phases. The

fi rst phase focused on reducing CSOs. The second phase provides fl ood control

benefi ts as well as further increases CSO capture. When completed, the TARP

will have 18 BG of total storage between the three reservoirs and multiple deep

tunnels. The three reservoirs hold 15.7 BG; the plan also includes 109 miles of deep

rock tunnels, located 150-350 feet beneath the ground surface. One reservoir is

located on the site of an abandoned quarry. This siting reduces the amount of excavation needed for the reservoir, but does not

eliminate it. The tunnels are lined to prevent infi ltration and exfi ltration. Pumping and treating the total volume stored in the TARP

facilities will take two to three days. Since construction started, water quality in the Chicago area receiving waters has improved.

Mass loadings of BOD5, TSS, and volatile suspended solids have dropped by 13, 62, and 60 percent, respectively. Once the system is

completed, tunnels in 2006 and reservoirs in 2014, it is believed that further water quality improvements will be observed. The total

predicted cost of TARP is $3.62 billion. The cost of the reservoirs is $1.11 billion or $0.07/gallon. The deep tunnels when completed ,

will cost $2.51 billion or $1.09/gallon.

More information at http://www.mwrdgc.dst.il.us/plants/tarp.htm

Implementation Examples

CHICAGO, IL Tunnel and Reservoir Plan (TARP)

Responsible Agency: Metropolitan Water 

Reclamation District of Greater Chicago

Population Served: 5.1 million

Service Area: 873 sq. mi.

Sewer System: 4,300 total miles of sewer

Twenty percent of Atlanta’s sewershed is composed of combined sewers, which 

includes the most highly developed area of downtown Atlanta. The city started to 

control CSOs in the mid-1980s, using a mix of near-surface storage facilities, deep 

tunnels, and sewer separation projects. The Intrenchment Creek Tunnel, which

has a diameter of 26 feet and is 1.76 miles long, can store 30-34 MG of excess wet 

weather fl ows. It can be de-watered in one to two days, by sending the stored 

fl ows for physical and chemical treatment at the associated Intrenchment Creek

Treatment Facility. During a study performed from August 1999 to January 2000, fecal 

coliform levels in the effl uent from the Intrenchment Creek Facility were below the water quality standard that requires a geometric 

mean of 1,000 MPN col/100 mL. 

The city also maintains one near-surface storage facility at the McDaniel CSO Facility. This near-surface storage basin holds 2 MG of

combined sewage. The combination of tunnel and near-surface storage creates a total storage volume of 36 MG. This storage has 

reduced the frequency of CSO events from 50-60 times per year to approximately 17 per year. The Intrenchment Creek CSO project 

cost was approximately $42.2 million or $1.24/gallon. The McDaniel CSO Facility was constructed for $9.2 million or $1.53/gallon.

More information at http:/www.atlantapublicworks.org

ATLANTA, GA Near-Surface Storage Facilities and Tunnels

Responsible Agency: City of Atlanta 

Department of Public Works

Population Served: 1.5 million

Service Area: 260 sq. mi. 

Sewer System: 230 mi. of combined sewer 

and 1,970 mi. of separate sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-14

The Combined Sewer Overfl ow Abatement Program being implemented by 

the Narragansett Bay Commission will reduce the frequency of CSO events 

from 71 to four per year. The plan includes sewer separation projects as well 

as construction of storage and treatment facilities. The project is divided into 

three phases. The main component of the fi rst phase is a deep tunnel. The 

tunnel is 27 feet in diameter, 200-300 feet below the ground surface, and 

2.5 miles long. The tunnel’s storage volume is 56 MG, and it is designed to 

be de-watered within 24 hours. Phase I is expected to reduce CSO volume by 40 

percent; the entire project is expected to reduce CSOs by 98 percent. Construction of Phase I started in 2002 and will be completed 

in 2009. Phase I will be followed by a two-year monitoring period to assess improvements in water quality as a result of the tunnel. 

The fi nal completion date of the entire project is contingent on the success of Phase I. It is anticipated that the reduction in CSOs to 

Narragansett Bay will contribute to reductions in shellfi sh bed closures. The estimated construction cost for the deep tunnel is over 

$258 million or $4.61/gallon.

More information at http://www.narrabay.com/CSO.asp

Deep Tunnel Storage

Responsible Agency: Narrangasett Bay 

Commission

Population Served: 360,000

Service Area: 110 sq. mi.

Sewer System: 89 mi. of interceptor sewer

PROVIDENCE, RI

Bangor began development of a CSO long-term control plan in 1992. Initially, 

the city separated a portion of its sewer system. The sewer separation 

projects were followed by the installation of three storage facilities, 

including the Kenduskeag East CSO Storage Facility. The 1.2 MG nearsurface storage facility is located underneath an existing public parking lot. 

Stored fl ows are released back into the sewer system for treatment at the 

WWTP. The basin has a small on-line portion through which dry weather 

fl ows pass everyday. During a wet weather event, when levels rise to 3.5 feet in 

the on-line portion of the basin, wastewater spills over into the off-line portion. The off-line portion is comprised of fi ve box section 

rows that are 360 feet long and 8 feet wide. The basin’s fl ushing system utilizes stored fl ow to create waves that clean settled solids 

from the bottom of each section. The wastewater level in the basin is monitored electronically, and if the basin reaches capacity, the 

monitoring system opens control gates that allow for a controlled and measured CSO event. The construction cost of the storage tank 

was $2.3 million or $1.92/gallon.

More information at http://www.precast.org/pages/Solutions/Summer_2002/overfl ow_in_bangor.html

Kenduskeag East CSO Storage Facility

Responsible Agency: City of Bangor Sewer 

Division

Population Served: 33,000

Service Area: 6.4 sq. mi.

Sewer System: 33.21 mi. of sewer, 30 percent combined

BANGOR, ME
Storage Facilities: Off-line Storage

STR-15

The Grand Rapids wastewater service area includes the city of Grand 

Rapids and six other surrounding towns. The CSS area is small and 

consists of only a half percent of the entire service area. In the early 

1990s, the city created a plan to deal with the excess wet weather fl ows 

from this area. Part of this plan was the Market Avenue near-surface 

storage facility. The design included a multi-stage basin with treatment 

facilities to control the 10-year, one-hour storm. The 30.5 MG basin has three compartments which are operated sequentially. The fi rst 

compartment allows for primary settling and grit removal. Once this compartment is full, the second compartment begins to fi ll. The 

bottom of the second compartment is equipped with a fl oor wash system. If the second compartment reaches its capacity, the excess 

fl ow spills over into the third compartment where sodium hypochlorite is added for disinfection. The third compartment discharges 

the partially treated and disinfected fl ow to the Grand River. The near-surface storage facility came on-line in 1992. Since this time, 

there has been a noticeable decline in fecal coliform levels in the Grand River. As an example, in 1989, the annual geometric mean for 

fecal coliform was 500 MPN/100 mL, and in 1996, the value was 75 MPN/100 mL. The city believes the reduction can be attributed to 

the 90 percent reduction in discharges of untreated CSOs. The construction cost for the Market Avenue near-surface storage facility 

was $39 million or $1.24/gallon. Operation and maintenance costs are approximately $40,000/year or $0.001/gallon.

More information at http://www.epa.gov/owm/mtb/csoretba.pdf

Responsible Agency: Grand Rapids Public Works

Population Served: 261,000

Service Area: 750 sq. mi., 3.9 sq. mi. is combined

Sewer System: 850 mi. of sewer

GRAND RAPIDS, MI Market Ave. Near-Surface Storage Facility

Fairport Harbor Village is a historic town located on 

Lake Erie in Ohio. The separate sewer system that serves 

the city receives considerable I/I, which can be linked 

to the system’s aged clay pipes. In 1994, engineering 

investigations determined that 1.8 MG of storage was 

needed to contain the wet weather fl ows associated with 

a fi ve-year design storm event. The original proposal to build a near-surface storage facility near a major overfl ow point was rejected 

largely on the basis of citizen complaints. An alternative industrial site with an aging oil storage tank built in the 1940s was viewed 

more favorably, and had the potential to provide 3.2 MG of storage. Further investigations demonstrated the feasibility of converting 

the oil tank into an off-line storage tank. It was also found that even with extensive rehabilitation, the tank would provide a savings 

of $170,000-$500,000 when compared to the construction of a new facility. Rehabilitation of the oil tank included the removal of 

lead-based paint, asbestos-covered exterior piping, crude oil sludge, and interior pipes. A majority of the vertical and horizontal 

welds were replaced to meet current standards. In addition to rehabilitation of the tank, a new 5 MGD pump station and a one mile 

long force main were installed to convey fl ows to the tank. The cost of the Fairport Harbor storage facility was $3.1 million or $0.97/

gallon.

Contact: Phillip Shrout, CT Consultants

Responsible Agency: Lake County Regional Sewer District

Population Served: 3,180

Service Area: Not available

Sewer System: Separate sewer system

FAIRPORT HARBOR, OH Converted Surface Storage Facility
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-16

References

EPA Office of Research and Development. 1993. Manual: 

Combined Sewer Overflow Control. EPA 625-R-93-007.

EPA Office of Water. 1994. Combined Sewer Overflow (CSO) 

Control Policy. EPA-830-B-94-001. 

EPA Office of Water. 1999. Combined Sewer Overflow 

Technology Fact Sheet - Retention Basins. EPA-832-F-99-042. 

http://www.epa.gov/owm/mtb/csoretba.pdf

Gray, W. et al. 1999. Prevention and Control of Sewer System 

Overflows: WEF Manual of Practice No. FD-17. Alexandria: 

Water Environment Federation.

Milwaukee Metropolitan Sewerage District. “Sewer 

Operations Under Different Weather Conditions.” Retrieved 

September 20, 2002. 

http://www.mmsd.com/deeptunnel/sewersystem.asp

Narragansett Bay Commission. 1998. Combined Sewer 

Overflow Abatement Program Concept Design Report 

Amendment. Providence, RI: Narragansett Bay Commission. 

Wayne County Department of Environment. “CSO 

Demonstration Projects.” Retrieved September 17, 2002. 

http://rougerivercom.readyhosting.com/cso/projects.html

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

On-Site Storage

STORAGE FACILITIES

Overview

Many sewer systems experience high flow rates during wet 

weather periods. The use of storage facilities to attenuate 

and store peak wet weather flows is widely implemented to 

reduce or eliminate CSOs and SSOs. On-site storage, that 

is storage developed at the wastewater treatment facility, is 

often an effective control for managing excess wet weather 

flows in systems where sewer system conveyance capacity 

exceeds that of the treatment plant. 

The two most common forms of on-site storage are flow 

equalization basins (FEBs) and converted abandoned 

treatment facilities. Flow equalization is used to overcome 

operational problems caused by flow rate variations, to 

improve the performance of downstream processes, and to 

reduce the size and cost of downstream facilities (Metcalf 

& Eddy 2003). FEBs are typically located downstream of 

screening and grit removal facilities, but they can be placed 

just before the headworks of the treatment plant. FEBs 

can be configured in two general ways. The FEB can be 

placed within the flow path, meaning that all flow reaching 

the treatment plant passes through the basin, or it can be 

placed outside the flow path, where wet weather flows that 

exceed plant design capacity are diverted into the basin. 

Both configurations are shown in Figure 1. 

On-site storage capabilities may also be developed in 

abandoned treatment facilities such as: old clarifiers that 

have since been replaced; treatment lagoons or polishing 

ponds no longer needed after the construction of more 

modern treatment facilities; or pretreatment facilities at 

industrial sites near the treatment plant. Storing flows 

in abandoned facilities may require modification of the 

current wastewater flow path; a flow control device and 

piping may be needed to transport flows to and from the 

storage facility. It may be possible to retrofit existing piping 

for this purpose, otherwise new piping and a pump, if 

needed, will have to be installed.

There are three primary design considerations related to 

on-site storage facilities: sizing and locating the facility, 

handling settled solids, and pumping systems to return 

stored flows for treatment. The best location for an onsite storage facility will vary with the characteristics of the 

sewer system, the wastewater, and the type of treatment 

required (Metcalf & Eddy 2003). The size of the storage 

facility will depend on the wet weather volume it is 

designed to hold, and the amount of land available at the 

treatment plant for construction, if needed.

On-site storage facilities must be designed to handle the 

solids present in the wastewater. For example, in Oklahoma 

the state design standards require storage facilities to 

be constructed with a minimum of two compartments 

(OKDEQ 2002). One compartment, which is lined with 

concrete or asphalt, is where the solids are allowed to 

settle. The other compartment holds overflow from the 

first, during moderate or large wet weather events. The 

Figure 1. Alternative locations for flow equalization basins 

 (Metcalf & Eddy 2003).

Entering

Flow

(A)

Bar Screen Grit Removal Equalization

Basin

Pump

Station Remaining

Process

Entering

Flow

Bar Screen Grit Removal

Equalization

Basin

Pump

Station

Remaining

Process

(B)

Flow equalization basin (Borough of Lansdale)
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-18

settled solids are washed back into the headworks of the 

treatment plant, allowing them to receive full treatment. 

Other facilities utilize mixing to prevent the deposition of 

solids. Mixing equipment requirements can be minimized 

by constructing on-site storage downstream of grit removal 

facilities. Examples of effective mixing mechanisms for 

storage facilities include tipping weirs and flushing gates. 

Aeration systems may be necessary if storage basins are 

susceptible to becoming oxygen-deprived and septic. 

Variable or constant speed pumps may be used to return 

stored flows to the treatment plant. A constant speed 

pump will return flows at the same speed independent of 

the volume of flow stored, whereas a variable speed pump 

can be adjusted depending on the stored volume. A flowmeasuring device should be installed to monitor the return 

of the stored flow.

While the volume of an on-site storage facility can be very 

large, there will be occasions when wet weather flows will 

exceed storage capacity. A mechanism to discharge flows 

that exceed facility capacity, with or without treatment, 

must be available.

Key Considerations

Applicability

On-site storage at the wastewater treatment plant can be 

a viable alternative for reducing or eliminating CSOs and 

SSOs. There are a number of important considerations 

that must be evaluated to determine the applicability of 

on-site storage at a given wastewater treatment plant. These 

include: 

● Maximum flow that can be conveyed to the treatment 

plant;

● Maximum flow that can be treated with the existing 

treatment processes; 

● Availability of land on site for the construction of a 

new FEB; and

● Location and volume of abandoned treatment facilities.

Advantages

On-site storage can play an important role in improving 

wet weather treatment plant operations. It provides 

operators with the ability to manage and store excess flows, 

which helps maintain treatment efficiency and ensures that 

all flows reaching the plant receive the maximum treatment 

possible. Development of on-site storage can also facilitate 

operation and maintenance activities. If problems occur at 

on-site facilities, it is likely that they will be detected earlier, 

and that many of the tools required to make the needed 

repairs will already be at the treatment plant. 

Constructing storage outside the bounds of the wastewater 

treatment plant typically requires an environmental site 

assessment. Site assessments are less likely to be required for 

on-site storage facilities because the storage is being placed 

in a location that has already been approved for such use. 

If an assessment is needed, the requirements may be less 

rigorous since environmental conditions at the wastewater 

treatment plant are known and may have already been 

investigated. 

Disadvantages

There are limitations to on-site storage that must also be 

considered. Development of a large FEB uses space that 

might be needed for future plant expansion. Restored 

facilities, because of their age, may deteriorate faster than 

a new facility. The conveyance system or plant headworks 

may limit the amount of wet weather flow that can be 

brought to the treatment plant. The headworks can be 

expanded, but it can be costly to expand the conveyance 

system capacity. Finally, as with any storage facility, on-site 

storage has finite capacity which may not be sufficient to 

prevent CSOs and SSOs during extreme wet weather events.

Cost

The costs associated with the development of on-site 

storage facilities range from as little as $0.01 per gallon to 

more than $1.00 per gallon. These costs are, on average, 

considerably lower than the construction costs for typical 

near-surface storage facilities built outside the bounds 

of the treatment plant. Much of the cost savings derives 

from being able to site the storage facilities on land already 

owned by the utility. The following table presents cost 

information from a number of on-site storage applications.
Storage Facilities: On-site Storage

STR-19

Municipality Technology Characteristics Year

Initiated

Approximate 

Construction Cost1

Auburn, NY Restored Storage Total Storage = 0.2 MG

Cleaned annually

1997 $930,000 or

$4.65/gallon

Barlesville, OK Flow Equalization 

Basin

Total Storage = 20 MG

Sewer system also 

includes two other FEBs

1986 $1.70 million or

$0.08/gallon

Cleveland, OH Restored Storage Total Storage = 6 MG

Converted Imhoff Tanks

1985 $18.3 million or 

$3.05/gallon

Covington, LA Flow Equalization 

Basin

Total Storage = 6 MG

Cleaned annually

1997 $1.22 million or 

$0.20/gallon

Idabel, OK Flow Equalization 

Basin

Total Storage = 10 MG 1999 $450,000 or 

$0.05/gallon

Lafayette, LA Flow Equalization 

Basin

East WTTP:

Total Storage = 3 MG

West WTTP:

Total Storage = 3.5 MG

1999

1999

$1.6 million or 

$0.53/gallon

$1.9 million or 

$0.54/gallon

Oakland, ME Restored Storage Total Storage = 0.2 MG

FEB from a closed textile 

mill

1998 $27,610 or 

$0.14/gallons

South Paris, ME Restored Storage Total Storage = 1.5 MG

Clarifiers from old 

tannery

1995 Annual Debt Service: 

$110,000 or 

$0.07/gallon

Tulsa, OK Flow Equalization 

Basin

Total Storage = 13 MG 1994 $3.81 million or

$0.35/gallon

Vinita, OK Holding Ponds Total Storage = 7MG

Two holding ponds with 

capacity of 3.5 MG each

1996 $94,000 or 

$0.01/gallon

1

 All costs aren in 2002 dollars.

2

 South Paris, ME, reported negligible construction costs associated with restoring their abandoned on-site facilities. The cost numbers 

 presented reflect annual operation and maintenence for the facilities.

3 Vinita, OK, approximate construction cost does not include land or other facility improvement costs.

Table. 1. Summary of on-site storage costs.
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-20

Implementation Examples

In 1993, the City of Auburn began efforts to control both their CSOs and I/I within 

the separate sewer portion of their system. This included the conversion of primary 

settling tanks, originally built in the 1930s, into storage for wet weather events. When 

wet weather fl ows exceed the treatment plant’s 25 MGD capacity, excess infl uent is 

directed to the settling tanks. Four tanks, with a combined capacity of approximately 

158,000 gallons, serve as storage. When the capacity of the storage tanks is fully 

utilized, two additional tanks are used to provide high-rate disinfection and dechlorination before fl ows are discharged.

To modify the tanks, the primary sludge collectors were removed. A fl ushing system was then installed to wash the system after a wet 

weather event. Weirs were installed to permit fl ow between the tanks. Odors associated with the facility are minimized by returning 

the entire stored volume to the treatment plant within 24 hours of the wet weather event. Annually, the retrofi tted primary settling 

tanks capture 5.8 MG of excess fl ow. The facility captures 76 percent of the possible overfl ows, which are returned to the plant for full 

treatment; the volume that does overfl ow receives primary treatment and disinfection. The conversion of the primary settling tanks 

into wet weather storage facilities cost $930,000 or $4.65/gallon.

Contact: Frank DeOrio, City of Auburn

Responsible Agency: City of Auburn 

Department of Municipal Utilities

Population Served: 35,000

Service Area: Not Available

Sewer System: Not Available

AUBURN, NY Reusing Primary Treatment Facilities

In order to reduce CSO discharges, NEORSD refurbished old Imhoff tanks 

located at the Westerly wastewater treatment plant to store combined 

sewage. The Imhoff tanks required reconfi guration for CSO storage;. In 

addition, sludge removal equipment, bar screens, fl ow control gates, 

and an effl uent conduit and pump were installed. The tanks can store 

approximately 6 MG and the related interceptor can hold an additional 6 

MG, for a total storage of approximately 12 MG. Volumes which exceed the 

storage capacity are disinfected and then discharged. The conversion of the tanks was completed in 1985. The storage at the Westerly 

plant has helped reduce CSO discharges to the Edgewater State Park swimming beach on Lake Erie. The conversion of the Imhoff 

tanks into CSO storage facilities cost $18.3 million or $1.53/gallon.

Contact: Frank Greenland, Northeast Ohio Regional Sewer District

Responsible Agency: Northeast Ohio Regional 

Sewer District (NEORSD) 

Population Served: 500,000

Service Area: 355 sq. mi.

Sewer System: Not Available

CLEVELAND, OH Reusing Imhoff Tanks
Storage Facilities: On-site Storage

STR-21

In the mid 1990s, the Lafayette Consolidated Government started to look at

infl ow and infi ltration (I/I) problems prevalent in their sanitary sewer system.

After surveying, rehabilitating, and maximizing fl ow to the treatment plants,

the Utilities decided to construct FEBs at their East and South wastewater

treatment plants. The FEBs were constructed as part of a larger project that

included other plant upgrades. The East and South wastewater treatment

plants’ FEBs can hold 3 MG and 3.5 MG, respectively. When fl ows exceed the maximum fl ow rate which can be handled by the plant, a

portion of the fl ow is diverted to the FEB, to protect the treatment processes. Once the wet weather fl ows subside, the plants continue

to operate at maximum capacity while the basins are drained. Emptying the FEBs can take one to three days. Since the FEBs have

been in operation, hydraulic overload violations have been reduced from an average of six to nine annually to zero. The estimated

cost for the East FEB was $1.6 million or $0.53/gallon. The estimated cost for the South FEB was $1.9 million or $0.54/gallon.

More information at http://www.lus.org/site.php?pageID=2

LAFAYETTE, LA Flow Equalization Basins

Responsible Agency: Lafeyette Utilities System

Population Served: 37,500

Service Area: 38 sq. mi. 

Sewer System: 650 mi. of separate sewer

Oakland’s sewer system consists mainly of combined sewers. The city has 

been implementing CSO controls since 1997. These efforts include separating 

a portion of the combined sewer system and other targeted infl ow reduction 

activities. As a result, Oakland has been able to eliminate both of its CSO 

outfalls and transport all remaining wet weather fl ows to its wastewater 

treatment plant. Although the city had suffi cient sewer system capacity to 

transport these wet weather fl ows, it did not have treatment facilities capable of handling the peak wet weather fl ow. The city was 

able to utilize an FEB installed at the treatment plant for a nearby textile mill that had since ceased operation. The FEB was built in 

1990 by the textile mill as part of their pretreatment program, but had sat unused since the mill closed shortly afterwards. Oakland is 

able to store 0.2 MG of excess wet weather fl ows in the basin, and then bleed it back to the wastewater plant for treatment as capacity 

becomes available. The FEB is available to the city year-round, but is mainly used during spring snow melts. To bring the FEB back into 

operation will cost approximately $27,610 or $0.14/gallon; operational costs are minimal. 

Contact: Jim Fitch, Woodard and Curran

Restored Flow Equalization Basin

Responsible Agency: Oakland Public Works

Population Served: 6,000

Service Area: Not Available

Sewer System: 7 mi. of sewer

OAKLAND, ME
 Report to Congress on the Impacts and Control of CSOs and SSOs

STR-22

Tulsa’s separate sanitary sewer system is divided into three major sewersheds, 

with a wastewater treatment plant located in each. Multiple sanitary sewer 

evaluations have been performed to help Tulsa establish a plan for controlling

SSOs. SSO abatement efforts in the Northside Sewershed have facilitated on the 

attenuation of storage of excess wet weather fl ows. Tulsa has constructed three 

near-surface storage basins located remotely in the Northside Sewershed, and 

one FEB located within the bounds of the wastewater treatment plant. The four basins together provide a total of 83.2 MG of storage, 

with the treatment plant FEB accounting for 13 MG. The treatment plant site is large enough to accommodate the FEB as well as all 

anticipated future additions to the plant. The Northside FEB is used when a large wet weather event overwhelms the capacity of the 

three upstream storage basins. The construction cost for the Northside FEB was approximately $3.81 million or $0.35/gallon.

More information at http://www.cityoftulsa.org/Public+Works/wastewater/wastewater+treatment+process.htm

TULSA, OK Flow Equalization Basins

Responsible Agency: Tulsa Public Works

Population Served: 85,000

Service Area: Not Available

Sewer System: 1,800 mi. of sewer

The combined sewer system owned and operated by the Paris Utility District 

has one overfl ow point. Utilization of an unused pretreatment facility for 

storing excess wet weather fl ows has enabled the District to reduce the 

frequency of CSO events. The District’s wastewater system was designed 

with pretreatment facilities for the two major industries in the city, a tannery 

and a cannery. The tannery pretreatment facility is considered part of the 

South Paris wastewater treatment plant. The tannery closed in 1985. In the mid 1990s, the tannery pretreatment facility was brought 

back into service to store excess wet weather fl ows from the District’s CSS and provide primary treatment during extreme events. The 

tannery facility provides a total storage volume of 1.5 MG. Costs for returning the tannery facility to service were minimal because the 

infrastructure was already in place; operation and maintenance costs are also quite small. The only true cost of the tannery storage is 

its portion of the facilities debt service for plant modifi cations, which costs approximately $110,000 annually or $0.07/gallon.

Contact: John Barlow, Paris Utility District

Clarifiers from Old Tannery Storage

Responsible Agency: Paris Utility District

Population Served: 1,000

Service Area: Not Available

Sewer System: 16.3 mi. of combined sewer

SOUTH PARIS, ME
Storage Facilities: On-site Storage

STR-23

References

Metcalf and Eddy, Inc. 2003. Wastewater Engineering: 

Treatment, Disposal, and Reuse, 4th ed. Boston: Irwin 

McGraw Hill.

Oklahoma Department of Environmental Quality 

(OKDEQ). 2002. “Title 252: Oklahoma Administrative 

Code Chapter 656 Water Pollution Control Facility 

Construction.” Retrieved January 27, 2003. 

http://www.deq.state.ok.us/rules/656-correction.pdf

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Supplemental Treatment

Treatment Technologies

Overview

When wet weather flow rates exceed available sewer system 

or treatment capacity, constructing supplemental treatment 

facilities may be a cost-effective alternative to expanding 

existing conveyance capacity or treatment facilities. 

Supplemental treatment facilities are designed solely 

to treat excess wet weather flows; the level of treatment 

provided is typically driven by regulatory requirements.

Supplemental treatment facilities can be located and 

configured in multiple ways, including:

● Providing treatment at established overflow locations 

by installing a small scale treatment process at or near 

a known CSO or SSO location. For example, a vortex 

separator with disinfection capabilities might be 

installed near a CSO outfall. The treated effluent would 

be discharged directly to a receiving water.

● Constructing a separate treatment facility upstream 

of the existing treatment plant. Such a facility would 

accept and treat excess wet weather flows that might 

otherwise result in untreated CSOs or SSOs from one 

or more locations in the sewer system; for example, a 

ballasted flocculation treatment process constructed 

in a capacity-constrained area of the sewer system. 

Effluent would be discharged directly to a receiving 

water from this facility.

● Adding parallel treatment process(es) at the existing 

treatment plant that would operate as necessary during 

wet weather. To be successful, this requires sufficient 

sewer system capacity to deliver wet weather flows to 

the existing treatment plant. Effluent from the parallel 

treatment process would be discharged directly or 

recombined with flows from existing treatment units 

prior to discharge.

For any of these configurations, the selection of a specific 

supplemental treatment technology will be driven by wet 

weather flow characteristics. Important characteristics to 

consider include:

● Frequency of wet weather events requiring 

supplemental treatment;

● Limited event duration, often lasting less than 24 

hours;

● High flow rate and volume with potential peak wet 

weather flows of four to 20 times the average daily 

flow; and

● Weak influent pollutant concentrations, diluted by 

storm water inflow/infiltration (I/I).

These flow characteristics can pose technical challenges to 

efficient and effective treatment. Supplemental treatment 

facilities must be able to handle sudden increases in flow at 

unplanned times, have quick start-up time, or in the case of 

biological processes, quick acclimation time after extended 

periods of no flow (or low flow conditions), and provide 

adequate treatment despite significant variation in influent 

pollutant concentrations.

The technologies best suited for treating excess wet 

weather flows commonly involve physical or chemical 

processes rather than biological processes. The applicability 

of biological treatment processes is limited by factors 

including: 

● Biological processes do not respond well to adverse, 

intense, and intermittent flow conditions typical of wet 

weather events. 

● Rapid changes in the amount and quality of the 

influent reduce biological process treatment efficiency. 

In some cases, large hydraulic loads can wash out the 

microorganisms necessary for treatment. ● Microorganisms need a minimum level of food (i.e., 

organic matter) in the influent to survive. Therefore, 

it is often technologically and operationally difficult, 

if not impossible, to maintain a large enough 

microorganism population during dry weather or low 

flow periods, so that there is a sufficient population 

available for biological treatment of large wet weather 

flows.

Trash screens at one of Atlanta’s CSO Centers (Atlanta Dept. of Public Works).
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-2

Trickling filters are the biological treatment technology 

option considered most operationally feasible for treating 

excess wet weather flows. This is based on their ability to 

handle peak flow conditions with less likelihood of upset, 

relative to conventional activated sludge processes (WEF 

1998). In a trickling filter system, microorganisms are 

maintained as a biological film attached to a fixed media. 

In contrast, microorganisms in an activated sludge process 

are suspended in a less stable, liquid media. Nonetheless, 

supplemental treatment facilities with any biological 

process must operate continuously with a minimum flow 

rate to maintain the biomass necessary for treatment of wet 

weather flows. During dry weather, effluent from biological 

supplemental treatment facilities is typically returned to the 

sewer system for further treatment and discharged at the 

wastewater treatment plant. 

A number of physical and chemical treatment technologies 

are suited for use as supplemental treatment facilities 

handling excess wet weather flows. These include: 

Primary clarifi cation

Excess wet weather fl ows enter a large basin where the 

velocity of fl ow decreases, allowing solids to settle to the 

bottom of the tank and fl oatable materials (e.g., grease 

and debris) to rise. Mechanical equipment skims the 

fl oating material, while other mechanical devices collect 

and remove settled material from the bottom of the 

basin. 

Screening

Excess wet weather fl ows are strained through a mesh 

of metal, plastic, ceramic, or cloth. Solids are collected 

on the surface of the screen where they are removed by 

mechanical scraping, a spray mechanism that washes 

solids off the screen, or by gravity. Various screen 

aperture sizes are available; solids removal effi ciency 

decreases as the aperture increases.

Vortex separators

Vortex separators use centripetal force, inertia, and 

gravity to remove fl oatables, trash, and other settleable 

solids from excess wet weather fl ows. Additional 

information on vortex separators is presented in 

“Vortex Separators Technology Description” in 

Appendix B of the Report to Congress on Impacts and 

Control of Combined Sewer Overfl ows and Sanitary 

Sewer Overfl ows.

Ballasted fl occulation

In ballasted fl occulation or sedimentation, a metal salt 

coagulant is added to the excess wet weather fl ows to 

aggregate suspended solids. Then, fi ne-grained sand, 

or ballast, is added along with a polymer. The polymer 

acts like glue which bonds the aggregated solids and 

sand. The process increases the particles’ size and mass 

which allows them to settle faster. The high dosages of 

fl occulent may require pH adjustments.

Chemical fl occulation

Similar to ballasted fl occulation, chemical fl occulation 

is a high-rate treatment process that adds metal salts 

and polymers to clump particles together. Depending 

on their density, the clumps will either sink to the 

bottom or fl oat to the surface where they can be 

removed. 

Deep bed fi ltration

A deep bed fi lter system consists of a series of large 

tanks (depths greater than 6 feet) fi lled with coarse 

medium (typically sand or anthracite). Excess wet 

weather fl ows are directed to the top of each tank and 

exit at the bottom of the tank. Pollutants can either 

attach to the fi lter media or become trapped in the 

interstitial space of the fi lter; the fi lter is later cleaned 

through backwashing. Chemical additives can be used 

to improve removal rates.

Key Considerations

Applicability

Supplemental treatment facilities are not intended to 

treat dry weather flows from combined or sanitary 

sewer systems, although biological facilities will need 

to be operated continually. The type and location of 

supplemental treatment facilities will be driven by sitespecific considerations, which include: 

● State and federal permit requirements and effluent 

limits;

● Characteristics of the excess wet weather flows;

● Land or space constraints; ● Capacity constraints within the existing sewer system 

or treatment facility; ● Anticipated population growth; and

● Financial resources.

For example, if available land is a constraint, a facility with 

a large “footprint” would not be appropriate. Alternatively, 

if the existing sewer system cannot convey all of the wet 

weather flow to the WWTP, a supplemental treatment 

facility upstream of the plant may be the most practical 

alternative.

It should be noted that primary clarification and trickling 

filter technologies can have a difficult time handling 

the highly variable flows associated with wet weather 
Treatment Technologies: Supplemental Treatment

TMT-3

events; these technologies may, therefore, require some 

type of flow equalization to operate efficiently. Adequate 

disinfection of treated excess wet weather flows is also a 

concern. High flow rates can result in reduced exposure to 

the disinfecting agent and reduced pathogen inactivation. 

Increased solid concentrations may also exist in treated wet 

weather flows, which can shield pathogens from exposure 

to the disinfectant. Specific wet weather considerations 

related to disinfection technologies are discussed in more 

detail in the “Disinfection Technology Description” in 

Appendix B of the Report to Congress on Impacts and 

Control of Combined Sewer Overflows and Sanitary Sewer 

Overflows. The advantages and disadvantages of each of 

the aforementioned supplemental treatment processes are 

summarized in Table 1.

Technology Advantages Disadvantages

Primary Clarification ● Little manual operation ● Large “footprint”

● Reduced retention and settling time (i.e., residence 

time) and possible short circuiting during high flow 

rates

● Lack of removal of dissolved or soluble pollutants

● Need for significant periodic maintenance 

requirements

Screening ● Small “footprint”

● Little manual operation

● High reliability with proper operations and 

maintenance (O&M)

● Low energy consumption

● Susceptible to clogging or poor solids removal

● Require regular operator observation, especially 

microscreens

● Prompt solids disposal required due to potential odor 

problems

● Incomplete removal of solids from wastewater 

(coarse and fine screens generally only remove 

floatables and visible solids)

● High cost for high performance microscreens

Vortex Separation ● Small “footprint”

● Ability to handle high hydraulic loading rate

● No moving parts (no mechanical 

maintenance)

● Low construction cost

● Inability to remove fine solids and dissolved or 

soluble pollutants

● Loss of floatables to overflow during extremely high 

flows

● Potential loss of foam and floatables in initial 

overflow

● Manual cleaning needs for settled solids

Ballasted Flocculation ● Small “footprint” (typically 5-15 percent of 

the space required for conventional primary 

clarification)

● Ability to handle high hydraulic loading 

rate(s)

● Reduced capital cost relative to 

conventional clarification

● Ability to treat rapidly varying flows

● Ability to consistently achieve secondary 

treatment concentration standards for BOD 

and TSS

● Limited ability to remove soluble pollutants

● Increased operational cost relative to biological 

treatment or conventional clarification due to the 

cost of the chemicals and sludge disposal along with 

ballasted media

Chemical Flocculation ● Production of concentrated sludge, 

requiring no additional thickening 

equipment

● Ability to handle high hydraulic loading rate

● Ability to treat rapidly varying flows

● Limited ability to remove soluble pollutants

● Potential increase in sludge produced due to the 

addition of treatment chemicals

● Increased operational costs relative to biological 

treatment or conventional clarification due to the 

cost of the chemicals

Deep Bed Filtration ● Ability to treat high and rapidly varying 

flows

● Ability to consistently achieve secondary 

treatment concentration standards for BOD 

and TSS

● High initial construction costs

● Limited ability to remove soluble pollutants

● Frequent backwash requirements to avoid clogging

Trickling Filters ● Small “footprint”

● Ability to achieve all secondary treatment 

requirements

● Rapid reduction of soluble BOD in wet 

weather flow

● Ability to treat high and rapidly varying 

flows

● Continuous operation required

● Degraded removal efficiencies when excess biomass 

exists

● High clogging potential

● Regular operator supervision and maintenance 

requirements

● Potential odor and snail population problems

Table 1. Advantages and disadvantages of various supplemental treatment technologies.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-4

Cost

Performance information for each of these technologies is 

presented in Table 2. Screening data are presented according 

to screen aperture size in millimeters. Typical performance 

for hydraulic loading capacity, BOD removal, and TSS 

removal is presented where available. The range in observed 

performance is largely due to changes in either hydraulic 

loading rates or influent characteristics (e.g., concentration, 

fraction of soluble pollutants). Where typical ranges were 

not available, data for performance at a single location are 

provided with notation.

Capital cost information for each supplemental treatment 

technology is summarized in Table 3. Cost per gallon of 

capacity is provided where possible. 

The capital costs for biological trickling filters are generally 

greater than capital costs for physical and chemical 

alternatives. In comparing daily operating costs, biological 

processes are typically significantly less expensive to operate 

Technology Source(s) Hydraulic Capacity 

(gpd/ft2

)

BOD Removal

(Percent)

TSS Removal

(Percent)

Primary Clarification Metcalf and Eddy 1991;

NEIWPCC 1998; WEF 1996

600-3,000 25-40 50-70

Screening Metcalf and Eddy 1991

Coarse (5-25 mm) 21,000-86,000 Not Available 15-30

Fine (0.1-5 mm) 150-1,400 Not Available 40-50

Micro (less than 0.1 mm) 150-1,400 Not Available 40-70

Vortex Separation EPA 1996;

Boner et al. 1995;

WERF 2002

Up to and greater than 

100,000

Up to 55 a 5-60

Ballasted Flocculation Radick et al. 2001;

Scruggs et al. 2001;

Vick 2000;

Poppe et al. 2001

Up to 90,000 65-80 70-95

Chemical Flocculation Metcalf and Eddy 1991;

Moffa 1997

Up to 20,000 40-80 60-90

Deep Bed Filtration Ellard et al. 2002 Not Available 65b 87 b

Trickling Filters (with 

settling)c

Metcalf and Eddy 1991;

WEF 1998

Up to 11,000 40-90 Not Available

a

 Based on two monitored events (Boner et. al. 1995); limited data exist since BOD is not a common performance indicator for vortex 

 separators. 

b

 Average performance based on pilot test data from Jefferson County, Alabama (Ellard et al. 2002). c

 High-rate trickling fi lters achieve 65-85 percent BOD removal. Related technologies, including rotating biological contactors and packed- 

 bed reactors, use the same processes as trickling fi lters and have similar removal rates, advantages, and disadvantages.

Table 2. Performance data summary for supplemental treatment technologies.
Treatment Technologies: Supplemental Treatment

TMT-5

because of the chemical costs associated with physical or 

chemical treatment. Supplemental biological treatment 

processes need to be operated continuously, however, so the 

actual annual operating costs for a biological supplemental 

process will likely be greater than for a physical or chemical 

supplemental process. For example, annual operation and 

maintenance (O&M) costs for a 10 MGD trickling filter 

facility are estimated at $150,000 (EPA 2000). Assuming it 

operates 365 days per year, daily operating costs are $411 

per day. In comparison, annual O&M costs for a 10 mgd 

ballasted flocculation facility are estimated at $49,000 

(Wendle 2002). Assuming this facility operates eight days 

per year (a conservative estimate based on an expected two 

to four events per year in Lower Paxton Township), daily 

operating costs are $6,125 per day.

Technology echnology Source Capacity apacity 

(MGD)

Estimated Total stimated Total 

Capital Cost apital Cost 

a

Unit Cost nit Cost 

a

(Per Gallon/Day Per Gallon/Day 

of Capacity) f Capacity)

Primary Clarification Hufford 2001 78 $11.0 million $0.14

Screening EPA 1999 0.75-375 $40,800-$2.2 million $0.01-$0.05

Vortex Separation Sacramento 1999 1.8 - 16.2b $10,000-$50,000 $0.01

Vortex Separation with 

Screening

Sacramento 1999 0.71-194 $13,000-$630,000 $0.01-$0.02

Ballasted Flocculation Wendle 2002 15 $5.5 million $0.37

Hufford 2001 78 $12.4 million $0.16

WERF 2002 100 $20.0 million $0.20

Bremerton 2002 20 $4.0 millionc $0.20

Chemical Flocculation - 

Aluminum as Additive

Hewing et.al. 1995 Not 

Available

$0.50 (cost per pound) $0.04 (per gallon 

treated) d

Chemical Flocculation -

Ferrous Sulfate as Additive

Hewing et.al. 1995 Not 

Available

$0.17 (cost per pound) $1.03 (per gallon 

treated) d

Deep Bed Filtration Chandler 2001 360 $55 millione $0.15

Trickling Filters EPA 2000 1-100 $760,000-$63.4 million $0.63-$0.76

a Costs in 2002 dollars.

b

 Vortex separator capacities are hydraulic capacities. Manufacturer recommended design capacities for optimal TSS removal 

 are generally 25 percent of the hydraulic capacities.

c

 Includes costs for a 20 MGD Ultraviolet (UV) disinfection process. Cost for ballasted fl occulation alone was not available. d Capital costs for chemical feed mechanisms not available. Treatment costs include chemical costs and sludge handling costs. 

 Ferrous sulfate generates larger sludge volumes than aluminum, signifi cantly increasing treatment costs. e

 Includes costs for a 360 MGD UV disinfection process. Cost for deep bed fi ltration alone was not available. 

Table 3. Performance data summary for supplemental treatment technologies.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-6

Implementation Examples

Jefferson County’s Village Creek Wastewater Treatment Plant receives an average daily 

fl ow of 40 MGD; peak fl ows exceed 400 MGD once per year on average. Exceedence of 

available 120 MGD of primary treatment and disinfection capacity at the treatment plant 

occurs an average 41 times per year (based on data from 1997-2001). Flows exceeding 

the 60 MGD of secondary capacity occur more frequently. Elevated wet weather fl ows 

have continuously exceeded treatment capacity for as long as six days. A combination of 

rainfall patterns, topography, 

geology, and sewer system 

age have contributed to extreme peak wet weather fl ow issues for the 

county.

Under consent decree, Jefferson County will spend approximately $200 

million for the construction of a deep bed fi lter supplemental treatment 

facility. The deep bed fi lter facility will be constructed on a 450-acre site 

and will discharge through a separate outfall. Construction is scheduled 

for completion in late 2003. During pilot testing of the fi lter technology, 

the best effl uent and longest fi lter runs were achieved with no chemical 

addition. Pilot testing performance showed average removals of 87 

percent of TSS and 65 percent of BOD, on average.

To prevent fi lter clogging from high infl uent fl ow and solids loadings, new 

methods of operating and backwashing were developed during the pilot 

study. These methods are now patented or patent-pending. 

Contact: Harry Chandler, Assistant Director of Environmental Services, Jefferson County

Deep Bed Filter to Manage Peak Wet Weather Flows

JEFFERSON 

COUNTY, AL

Responsible Agency: Jefferson 

County Environmental Services

Population Served: 232,000

Service Area: Not Available

Sewer System: 3,100 mi. of sewer

Component Contract Cost

(Million)

Influent tunnel (15 foot diameter) $17.0

Pump station (360 MGD) $46.0

Surge basins (20 basins, total capacity: 

90 MG)

$54.2

Deep bed filters plus UV disinfection 

(360 MGD) (22 filters, each at 1,167 ft2

)

$55.0

24 megawatt generator building and 

equipment (primarily for pump station 

and UV operation)

$22.0

Site work/access, road, and 

miscellaneous

$14.3

Total: $208.4

Deep bed filter construction costs.

The Syracuse demonstration program evaluated the treatment of CSOs 

with screening. Three screening units, ranging from an aperture size of 

23 microns to 105 microns, were used in this program. The table on the 

left lists the hydraulic loading rates and average TSS removal effi ciencies 

associated with each of these microscreens. These results show that as 

aperture increases, hydraulic loading rates also increase. As aperture 

increases, however, the TSS removal effi ciencies decrease. 

Contact: Rich Field, EPA Offi ce of Research and Development, Edison, NJ

SYRACUSE, NY Microscreens to Treat CSOs

Responsible Agency: Onondaga 

County Public Utilities

Aperture (microns) 23 71 105

Hydraulic loading rate 

(gpd/ft2)

2,500-

11,000

4,000-

18,000

16,000 - 

95,000

Average influent TSS 

concentration (mg/L) 619 308 284

Average effluent TSS 

concentration (mg/L) 290 172 196

Average TSS removal 

(Percent) 58 45 32

Microscreen performance data (EPA 1979).
Treatment Technologies: Supplemental Treatment

TMT-7

The City of Tacoma’s Central Treatment Plant (CTP) receives fl ow from a separate sanitary 

sewer system serving a population of 208,000. The CTP has a hydraulic capacity of 103 

MGD (primary plus disinfection), and a peak biological treatment capacity of 78 MGD. The 

sewer system can currently deliver up to 110 MGD to the CTP.

The CTP has reached the criterion specifi ed in their permit that triggers a requirement 

to develop a plan for maintaining adequate capacity. The city plans to install a 78 

MGD ballasted fl occulation process at the CTP parallel to the existing processes. The ballasted fl occulation process alone will cost 

approximately $12.4 million. All related peak wet weather fl ow facility upgrades are estimated at $50.7 million. In comparison, to 

expand the existing activated sludge processes by 78 MGD would cost an estimated $130 million; this estimate does not include the 

cost for additional primary clarifi cation capacity.

During pilot testing, the ballasted fl occulation process reached acceptable performance levels within 10-15 minutes of start-up. Pilot 

testing performance data, collected over a nine-day period, indicate effl uent TSS concentrations below 30 mg/L (with the exception 

of the fi rst day) and percent removals for TSS ranging from 79-92 percent. Effl uent BOD concentrations ranged from approximately 

20-42 mg/L, and removal rates for BOD ranged from 63-73 percent (Tacoma 2000). The lower percent removals generally occurred 

during weaker infl uent conditions.

When the actual ballasted fl occulation process is constructed and operated for wet weather treatment, effl uent from the process 

will be separately disinfected and blended with disinfected biologically treated effl uent prior to discharge. The blended effl uent 

is expected to meet permitted effl uent concentrations and removal effi ciencies. The ballasted fl occulation process is expected to 

operate a maximum of 5.5 days in a row, 8 days in a month, and 21 days per year (Tacoma 2001).

Contact: David Hufford, Division Manager, Environmental Services/Wastewater Management, City of Tacoma

TACOMA, WA Ballasted Flocculation to Manage Wet Weather Flow

Responsible Agency: City of Tacoma

Population Served: 258,000

Service Area: Not Available

Sewer System: 700 mi. of sewer

The City of Bremerton maintains a partially combined sewer system that 

provides service to approximately 37,000 people. The WWTP receives an average 

annual fl ow of 7.6 MGD and has a peak hydraulic capacity of 29.5 MGD. During 

periods of wet weather, however, fl ows in excess of 38 MGD have been delivered 

to the plant. Currently, Bremerton has 16 permitted CSO outfalls. As part of their 

CSO long term control plan, the city constructed the Pine Road Eastside CSO 

Treatment Facility. The CSO treatment facility was completed in December 2001. 

The facility uses ballasted fl occulation in combination with UV disinfection. Total construction costs were $4 million. The CSO treatment 

facility also includes a 100,000 gallon storage tank that was constructed in 2000 for an additional $400,000 (Bremerton 2002).

No performance data are currently available for the constructed facility (Bremerton 2002). Pilot testing performance showed a 71 

percent removal of TSS, 63 percent removal of total BOD, and 46 percent removal of soluble BOD, on average. During pilot testing, the 

ballasted fl occulation unit reached peak effi ciency within 10 minutes of start-up.

Contact: John Poppe, Wastewater Manager, City of Bremerton

BREMERTON, WA Ballasted Flocculation to Treat CSOs

Responsible Agency: City of Bremerton

Population Served: 37,000

Service Area: 5.2 sq. mi.

Sewer System: Not Available
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-8

References

Boner, M.C., et al. 1995. “Modified Vortex Separator and 

UV Disinfection for Combined Sewer Overflow Treatment.” 

Water Science and Technology. Vol. 31( No. 3-4).

Bremerton, City of 2002. “City of Bremerton Public 

Works and Utilities’ Wastewater/CSO Update.” Retrieved 

December 11, 2002. 

http://www.cityofbremerton.com/content/ww_

csoupdate.html.

Chandler, Harry, Assistant Director of Environmental 

Services, Jefferson County. Interview by Limno-Tech, Inc., 

Birmingham, AL. Fall/Winter 2001.

Ellard, Gregory, Meek, R., and H. Chandler. 2002. Direct 

Filtration for Wet Weather Conditions. Presented at 

Water Environment Federation Technical Exhibition 

and Conference (WEFTEC) Chicago, IL. September 29 - 

October 2, 2002. 

EPA. 1979. Disinfection/Treatment of Combined Sewer 

Overflows - Syracuse, New York. Prepared by O’ Brien and 

Gere Engineers, Inc. EPA 600-2-79-134.

EPA. 1996. Assessment of Vortex Solids Separators for the 

Control and Treatment of Wet-Weather Flow. EPA 832-B-96-

006. 

EPA, Office of Water. 1999. Combined Sewer Overflow 

Technology Fact Sheet: Screens. EPA 832-F-99-040.

EPA, Office of Water. 2000. Wastewater Technology Fact 

Sheet: Trickling Filters. EPA 832-F-00-014.

Hewing, Albert, et al.1995. “Reducing Plating Line Metal 

Waste.” Pollution Engineering.

Hufford, David, Division Manager, Environmental Services/

Wastewater Management, City of Tacoma. Interview by 

Limno-Tech, Inc., October 2001. Tacoma, WA.

Metcalf and Eddy, Inc. 1991. Wastewater Engineering: 

Treatment, Disposal, and Reuse. 3rd Ed. Boston: Irwin 

McGraw Hill.

Moffa, P.E. (Ed.). 1997. Control and Treatment of Combined 

Sewer Overflows. 2nd ed. New York: Van Nostrand Reinhold.

New England Interstate Water Pollution Control 

Commission (NEIWPCC). 1998. Technical Report #16: 

Guides for the Design of Wastewater Treatment Works. 

Wilmington, MA: NEIWPCC.

Poppe, John, Wastewater Manager, City of Bremerton. 2002. 

Interview by Limno-Tech, Inc., Fall 2002. Washington, DC.

Poppe, John, et al. 2001. “High-Rate Wet Weather Solution.” 

Public Works. Vol. 132 (No. 8). 

Radick, Keith A. and Morgan, Marc A. Ocotber 2001. 

Ballasted Flocculation: A Technology for Long Term CSO 

Control. Presented at Water Environment Federation 

WEFTEC Conference Atlanta, GA. October 13 - 17, 2001.

Sacramento, County of. 1999. Stormwater Management 

Program: Investigation of Structural Control Measures for 

New Development. Prepared by Larry Walker Associates, Inc. 

Retrieved December 12, 2002

www.sacstormwater.org/const/manuals/pdf/scm99_

scm99.pdf

Scruggs, Caroline and C. Wallis-Lage. 2001. Ballasted 

Flocculation: A Wet-Weather Treatment Solution? Presented 

at Water Environment Federation WEFTEC Conference 

Atlanta, GA. October 13 - 17, 2001.

Tacoma, City of. 2000. Ballasted Sedimentation Pilot 

Study Report and Feasibility Analysis, Central Wastewater 

Treatment Plant, City of Tacoma. Prepared by Parametrix, 

Inc. Sumner, WA: Parametrix.

Tacoma, City of. 2001. Facilities Plan: Central Wastewater 

Treatment Plant, City of Tacoma - Draft Final Edits. 

Prepared by Parametrix, Inc. Sumner, WA: Parametrix.

Vick, Rebecca Chambers. 2000. “High-Rate Clarification 

Takes the Prize.” Pollution Engineering. Vol. 32 (No. 10).

Water Environment Federation (WEF). 1996. Operation of 

Municipal Wastewater Treatment Plants, Manual of Practice 

No. 11. 5th Ed, Vol. 2. Alexandria, VA: WEF.

Water Environment Federation (WEF). 1988. Design of 

Municipal Wastewater Treatment Plants, Manual of Practice 

No. 8. 4th Ed., Vol. 2. Alexandria, VA: WEF.

Water Environment Research Foundation (WERF). 2002. 

Best Practices for the Treatment of Wet Weather Wastewater 

Flows. Prepared by Brashear, Robert, et. al. WERF Project 

No.00-CTS-6. Alexandria, VA: Water Environment 

Foundation; London, United Kingdom: IWA Publishing.

Wendle, Jeff, CTE Engineering Services. Interview about 

Lower Paxton Township, PA by Limno-Tech, Inc., August 

2001. Ann Arbor, MI.
Treatment Technologies: Supplemental Treatment

TMT-9

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Plant Modifi cations

Treatment Technologies

Overview

Excess wet weather flows can cause sudden hydraulic surges 

and changes in pollutant loads that adversely affect the 

performance of wastewater treatment plants (WWTP). 

Excess wet weather flows can disrupt treatment processes 

and result in the discharge of untreated or partially treated 

sewage. As an alternative to constructing supplemental 

treatment units to handle excess wet weather flows, 

modifications of existing facilities may be sufficient to 

achieve the needed capacity and treatment efficiencies. 

In general, these modifications involve either process 

control changes or physical reconfiguration of unit 

processes. Process control changes are operational; 

examples include the addition of chemicals to a clarifier 

to enhance settling and the modification of return sludge 

flow rates. Physical reconfiguration of unit processes 

involves actual modification of the internal components 

of a process. For example, a clarifier’s internal components 

would be redesigned to improve its hydraulics and expand 

the range of flow and solids load it is able to handle. 

In addition to unit process modifications, system-wide 

or overall plant modifications can be used to improve 

performance with respect to treatment of excess wet 

weather flows; examples include flow distribution and realtime control. 

A generalized schematic of a WWTP depicting typical unit 

processes and the associated sludge handling is shown in 

Figure 1. This technology description first describes unit 

process modifications and then overall plant modifications 

which can improve the ability of a WWTP to provide 

treatment for excess wet weather flows. 

Unit Process Modifications

Clarifi cation Processes

The performance of both primary and secondary 

clarifi ers impacts the performance of biological 

secondary treatment units. The modifi cations described 

below pertain to both primary and secondary clarifi ers, 

unless otherwise noted.

Chemical enhancement can improve solids removal 

in primary and secondary clarifi ers. Two classes 

of chemicals used are coagulants and fl occulants. 

Coagulants neutralize the charge associated with 

suspended solids in wastewater. This is important 

since most suspended solids in water are negatively 

charged and particles with the same charge repel 

each other. With the charges neutralized, the particles 

are able to stick together and form larger, heavier 

particles which settle faster. Flocculants (also referred 

to as coagulant aids) can help bridge and bind solids 

together, further increasing particle size, density, and 

settleability. Treatment plant operators may choose to 

use one or both types of chemicals depending on the 

wastewater characteristics, chemical costs, and other 

factors. Common coagulants include: aluminum sulfate 

(alum), polyaluminum chloride, ferric chloride, ferric 

sulfate, ferrous sulfate, calcium hydroxide carbonate 

(slaked lime), calcium oxide (quicklime), and sodium 

aluminate. The degree of clarifi cation obtained when 

chemicals are added to untreated wastewater depends 

on the quantity of chemicals used, characteristics of 

the wastewater, and the care with which the process is 

Figure 1. Schematic of a typical WWTP.

Screening/

Grit removal

Influent

Primary

clarifier

Aeration

basin

Secondary

clarifier

Disinfection

Effluent

Return

sludge

Waste sludge

to processing

Lateral weir trough in a rectangular clarifier (Warminster Fiberglass).
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-12

monitored and controlled. For any chemical application 

to be effective, the chemicals must adequately mix with 

the wastewater. 

Baffl es are most commonly used to interrupt or 

disperse density currents. Density currents travel at a 

higher velocity than surrounding waters and can carry 

solids through a clarifi er and over its effl uent weir, 

reducing effl uent quality. The occurence of density 

currents is also referred to as short-circuiting. These 

currents may exist in both circular and rectangular 

clarifi ers, and may become more apparent and 

problematic during peak fl ows (NYSDEC 2001). Dye 

testing can be used to identify the existence of density 

currents and assist in determining the best baffl e 

confi guration. Baffl es can be of any size and confi gured 

in multiple ways (e.g., placed in the top, middle, or 

bottom of the tank; constructed of one solid board or 

several boards with gaps in between). Various materials 

can be used to construct the baffl e, including wood, 

fi berglass, plastic, and metal. In a rectangular clarifi er, 

a baffl e is a thin, vertical wall of material placed across 

the width of a clarifi er. It may span up to the entire 

width and a portion of the depth of the clarifi er. In 

a circular clarifi er, baffl es are commonly angled at 

45-60 degrees along the perimeter of the clarifi er wall, 

but they can also be placed perpendicular to the wall. 

Cross-section views of both placements in a circular 

clarifi er are shown in Figure 2.

Lengthening weirs can reduce the loss of solids during 

periods of excess wet weather fl ow. For rectangular 

clarifi ers, weirs can be lengthened by placing additional 

lateral weir troughs. In circular clarifi ers with one 

peripheral effl uent weir, weir lengths are normally 

suffi cient under average as well as peak fl ow conditions. 

For circular clarifi ers with double-sided effl uent weir 

troughs, eliminating identical V-notch spacing on outer 

and inner weirs can reduce solids loss during periods of 

excess wet weather fl ow. This can be accomplished by 

blocking alternating V-notches on the outer weir with 

plywood or other materials.

Biological Suspended Growth (Activated Sludge) 

Processes 

Maintaining a concentration of biological solids in 

the activated sludge system higher than necessary for 

proper treatment will increase the potential for solids 

loss during peak fl ow periods. Operators should try 

to maintain the solids concentration that is necessary 

to ensure adequate treatment. The concentration of 

solids is managed primarily by controlling the total 

sludge mass in the system. Although long-term changes 

in total sludge mass must be made by adjusting the 

sludge wasting rate, short-term changes can be brought 

about by adjusting the return rate. Shifting the mode 

of operation to step feed or contact stabilization can be 

particularly effective, as described below.

Return sludge fl ow rate control is used to manage 

the sludge mass and detention time in the aeration 

basin of the activated sludge process. The return 

sludge fl ow is settled biomass that is removed from 

secondary clarifi ers and recycled or returned back 

into the aeration basin (see Figure 1). It is necessary 

to return a portion of the secondary clarifi er sludge 

to the aeration basin because the sludge contains the 

bacteria needed to maintain the biological treatment 

process. It is important to note that the rate at which 

the sludge is returned must be managed in accordance 

with infl uent conditions, sludge settling characteristics, 

and the dynamics of the biomass inventory which is 

continuously shifting between the clarifi ers and the 

aeration basin. Understanding when to increase or 

decrease the return sludge fl ow can assist in maximizing 

secondary treatment capacity during periods of excess 

wet weather fl ow and improve effl uent quality. 

The step feed mode of operation introduces settled 

wastewater at several points in the aeration tank, as 

shown in Figure 3. Step feed mode can be used to 

handle increased organic loads by distributing them 

evenly across the aeration basin, but primarily provides 

more capability for handling hydraulic surges. To be 

effective, this approach generally requires three or more 

parallel channels in the aeration basin.

Contact stabilization is an operational modifi cation 

in which the feed point is moved downstream in the 

Figure 2. Example baffle replacement in circular clarifiers.

Water surface Water surface

45-60 degree angle 90 degree angle Circular clarifier wall

Baffle

Outlet weir

Wastewater flow

Wastewater flow

Baffle

Outlet weir

Flow

Circular

clarifier wall
Treatment Technologies: Plant Modifications

TMT-13

aeration tank approximately one-half to two-thirds 

the length of the tank or into a separate tank. This 

confi guration is shown in Figure 4. Return activated 

sludge is added to the basin inlet upstream of the feed 

point and aerated before being blended with infl uent. 

Similar to step feed, contact stabilization can reduce 

solids loss during hydraulic surge events. Solids in the 

reaeration basin are protected from the direct infl uent 

fl ow, thereby minimizing the potential for solids 

loss. Contact stabilization provides a relatively short 

detention time, which increases system stability.

Biological Fixed Film Processes

The biomass of fi xed fi lm processes, such as trickling 

fi lters and rotating biological contactors (RBCs), is 

not as easily washed out as the biomass of suspended 

growth processes. Nonetheless, their performance is 

impacted by excess wet weather fl ows. Techniques for 

improving the performance of fi xed fi lm processes 

under wet weather fl ow conditions are described below.

For trickling fi lters, recirculation of fl ow is commonly 

practiced to provide adequate wetting of the biological 

media. For RBCs, recirculation of sludge may be 

practiced to encourage some suspended growth and 

maintain dissolved oxygen and hydraulic loading. 

During peak fl ow periods, however, recirculation is 

generally not necessary and can be temporarily reduced 

or halted to allow increased capacity for peak fl ows.

Trickling fi lter fl ow distributors are used to spread 

wastewater infl uent evenly over the biological media. 

Distributor arms that are hydraulically driven may turn 

at excessive speeds during peak fl ow periods, but can be 

slowed by installing nozzles on the arms that discharge 

in the opposite direction. The new nozzles can be 

capped to return the arm to normal speed during 

normal fl ow conditions. In practice, such changes are 

not made routinely.

Trickling fi lters are sometimes operated in series or 

sequentially. Pipes and pumping may be confi gured 

between units, however, such that during peak fl ow 

periods, the units could be converted to parallel 

operation allowing fl ows to pass through all fi lters 

simultaneously. This would increase the biological 

treatment capacity by reducing the hydraulic loading 

rate. Biochemical oxygen demand (BOD) removal 

effi ciency may be reduced by placing the units in 

parallel operation; however, the reduced effi ciency 

would be offset somewhat by the fact that each unit will 

operate at or below design loading rates.

Chemical Disinfection Processes

During periods of excess wet weather fl ow, infl uent 

exposure time to chemical disinfectants may be 

insuffi cient for adequate disinfection. Key operational 

variables for optimizing performance of disinfection 

facilities include mixing and dosage. Poor disinfectant 

mixing or poor diffuser placement can signifi cantly 

reduce effectiveness. For chlorine disinfection, 

it is possible to provide adequate disinfection at 

detention times of less than 15 minutes with the 

appropriate dosage (NYSDEC 2001). Determining 

the optimal dosage at high fl ows, however, requires 

some experimentation. Additional information on 

disinfecting wet weather fl ow is provided in the 

“Disinfection Technology Description” in Appendix 

Figure 3. Step feed mode of operation.

Compressed air

Secondary Reactor clarifier

Primary effluent

Return sludge

Primary

effluent

Figure 4. Contact stabilizer mode of operation.

Waste sludge

Influent Primary

clarifier

Contact

tank

Reaeration

tank

Secondary

clarifier

Effluent

Return

sludge
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-14

B of Report to Congress on the Impacts and Control 

of Combined Sewer Overfl ows and Sanitary Sewer 

Overfl ows. 

Overall Plant Modifications

Flow Distribution and Control

Treatment facilities that have multiple treatment 

units used in a process must be able to control 

the distribution of fl ow. In general, uneven fl ow 

distribution can affect the hydraulic capacity in one 

or more of the treatment units, which can have a 

negative impact on performance (e.g., solids loss from 

a secondary clarifi er) (NYSDEC 2001). Flow control 

can be incorporated into an existing facility through 

the addition of adjustable control weirs or appropriate 

valves. 

Equal distribution of solids to the treatment processes, 

such as return sludge, is also important. Unless 

provided for in the design, equal distribution of solids 

to the treatment units may not occur coincidentally 

with the equal distribution of fl ow.

Sidestream Control

A sidestream is a liquid or sludge fl ow that is produced 

by a treatment process; wastewater treatment plants 

typically produce several sidestreams. Sidestreams are 

either handled separately from the wastewater fl ow, 

or returned to a specifi c unit process for additional 

treatment or to support operation. Controlling 

the timing and location of sidestream returns can 

prevent overload of the treatment facility. Specifi cally, 

consideration should be given to reducing or halting 

sidestream returns during peak wet weather fl ows 

(NYSDEC 2001).

Real-Time Automated and Remote Controls

Automated and remote operation controls, based on 

real-time system information, can improve preparation 

for and response to wet weather events. Real-time 

information from the sewer system can allow operators 

to anticipate the need for operational changes before 

excess wet weather fl ows reach the treatment facility, 

thereby optimizing the effi ciency and effectiveness 

of mode shifts or operational changes. Additional 

information on the use of real-time control is provided 

in the “Monitoring and Real-Time Control Technology 

Description” in Appendix B of Report to Congress on the 

Impacts and Control of Combined Sewer Overfl ows and 

Sanitary Sewer Overfl ows.

At the treatment plant, automated or remote control 

systems optimize adjustments to gates, valves, and 

weir levels during wet weather events. Such real-time 

controls have been shown to improve wet weather 

operations by reducing CSO events and maximizing 

sewer system storage capacity (Batzell 1994; Field 

et al. 2000). Real-time control within individual 

processes can also optimize unit process operation. For 

example, real-time information on dissolved oxygen 

concentrations in the aeration basin can optimize the 

performance of an activated sludge process.

Key Considerations

Applicability

A performance evaluation should be done prior to any 

plant modifications to determine whether it is feasible to 

obtain the needed capacity from the existing unit processes. 

Plant modifications are preferred over new construction 

since the cost of plant modifications is relatively small 

compared to new construction. Some of the recommended 

modifications for improving peak wet weather flow 

capacity, however, may result in increased effluent 

concentrations of BOD or other constituents. The ability to 

increase the capacity of existing processes must be balanced 

with the need to meet short- and long-term permit limits. 

In addition, modifications that require operator attention 

before and after a wet weather event may interrupt regular 

dry weather operations and potentially compromise the 

quality of treated effluent during dry weather.

Cost

In general, the costs for the modifications described 

above are low. Some modifications require only simple 

changes in operation and no additional treatment process 

units. Construction materials (e.g., lumber) for unit 

reconfiguration are typically simple and readily obtainable. 

Material costs for density current baffles built in-house, 

for example, are quite low. In an article by the New York 

State Department of Environmental Conservation, the 

highest cost for a density current baffle reported was $300 

(NYSDEC 2002). Further, the addition of baffles can often 

be implemented by plant staff. Baffles commonly result 

in TSS reductions of 25-35 percent under average flow 

conditions and 40-50 percent under peak flow conditions 

(NEFCO 2002).

Of the potential modifications presented, chemical 

enhancement and real-time controls are expected to be the 

most expensive. Chemical enhancement represents an ongoing cost that will vary depending on the chemicals used, 

and the frequency and volume of usage. Sludge volume 

and handling costs may also increase as a result of chemical 

addition. Nonetheless, chemical enhancement in primary 
Treatment Technologies: Plant Modifications

TMT-15

clarifiers has been demonstrated to improve TSS removal 

from the normal range of 50-70 percent to 80-90 percent. 

Real-time control costs are summarized and presented in the 

Monitoring and Real-Time Control Technology Description in 

Appendix B of the Report to Congress on Impacts and Control 

of Combined Sewer Overflows and Sanitary Sewer Overflows.

Case studies for larger sewer systems indicated capital 

costs in millions of dollars. These systems represent highly 

sophisticated automated and predictive technology. Simpler 

Implementation Examples

In March 1996, the NYSDEC and Washington County jointly conducted studies 

to investigate methods for increasing the wet weather treatment capacity of the 

existing secondary treatment process at the Sewer District #2 WWTP. The WWTP is 

an activated sludge facility designed to treat an average dry weather fl ow of 2.28 

MGD. The actual dry weather fl ow averages 2.1 MGD. However, during wet weather, 

fl ow to the WWTP can exceed 15 MGD. Operators only allow 7.5 MGD to enter the 

plant in order to protect unit processes. Prior to the study, fl ow to the activated 

sludge process was further restricted to 5 MGD. During periods of wet weather, fl ows 

entering the plant in excess of 5 MGD were bypassed around the activated sludge units and received only primary treatment and 

disinfection. 

Two techniques for increasing secondary treatment capacity were investigated: operating the activated sludge process in contact

stabilization mode; and evaluating primary and secondary clarifi ers for short-circuiting. The studies found that the contact stabilization 

mode could treat a higher fl ow rate than conventional operation. Conventional operations failed to meet permit limits at fl ow rates 

greater than 7 MGD. The contact stabilization mode, however, was able to treat 7.5 MGD and meet permit limits.

Both the rectangular primary and circular secondary clarifi ers exhibited short-circuiting. Baffl e systems were designed for each, but 

installation was delayed for the secondary clarifi er. The system initially installed in the primary clarifi er was a seven-foot high, solid, 

mid-tank baffl e that consisted of a used belt press supported by a wooden frame. The construction cost was less than $50. After 

installation, testing showed no improvement in clarifi er performance. The baffl e was modifi ed by cutting a six-inch opening every six 

inches. This confi guration reduced the density currents and reduced effl uent suspended solids by 10 percent (NYSDEC 2001). This also 

reduced the solids loading to the activated sludge process, improving overall treatment effi ciency.

Contact: Joe McDowell, Washington County Sewer District

Use of Contact Stabilization and Baffles 

WASHINGTON 

COUNTY, NY

Responsible Agency: Washington 

County Sewer District #2

Population Served: 15,000

Service Area: 5.8 sq. mi.

Sewer System: 90 percent of combined sewer; 10 percent of sanitary sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-16

The Village of Granville WWTP investigated methods for improving biological 

trickling fi lter and secondary clarifi er performance during periods of wet weather. 

The WWTP experiences dramatic and prolonged peak fl ow events. Flows can rise 

quickly from a dry weather fl ow of 0.3 MGD to more than 3 MGD, and the elevated 

fl ows may last for up to a week. During periods of wet weather, the trickling fi lter 

distributor arm speed would increase and result in sloughing of biomass from the 

fi lter media. Effl uent quality was often degraded for a period of time beyond the wet weather event, as much of the biomass necessary 

for treatment was washed out. 

During periods of high fl ow, the arm speed would increase from two revolutions per minute to more than seven revolutions per 

minute. Two retro nozzles (pointing in the opposite direction of existing nozzles) were installed on each trickling fi lter arm. The retro 

nozzles successfully slowed the arm speed to less than three revolutions per minute during periods of excess wet weather fl ow 

(greater than 2 MGD) (NYSDEC 2001). Excess sloughing and loss of biomass was reduced, resulting in higher effl uent quality.

Suspended solids removal was problematic in the rectangular secondary clarifi ers during both dry and wet weather periods. Extensive 

dye testing was conducted, and baffl es were designed and installed. The initial baffl e was installed at the one-third point in the tank. 

The baffl e was solid at the top with staggered 2 x 8 lumber at the bottom. Dye test results after installation showed a 6 percent 

reduction in effl uent solids. An additional baffl e was designed and installed at the two-thirds point of the clarifi er. This baffl e was solid 

from top to bottom, but left a 14-inch opening at the bottom of the tank and a smaller area for fl ow at the top. With the second baffl e, 

effl uent solids concentrations were reduced by 19 percent (NYSDEC 2001).

Contact: Dan Williams, Village of Granville

GRANVILLE, NY Plant Modifications Increase Capacity

Responsible Agency: Village of Granville

Population Served: 2,646

Service Area: 1 sq. mi.

Sewer System: Not Available

The Clatskanie WWTP is an activated sludge treatment facility that 

underwent a two-year full-scale performance evaluation of its wet 

weather treatment capabilities. High infl ow and infi ltration in its 

separate sanitary sewers resulted in the delivery of excess wet weather 

fl ows. During the evaluation, the plant was operated in the conventional 

mode during dry weather conditions. The average dry weather fl ow 

was 0.2 MGD and the peak dry weather fl ow was 0.5 MGD. During wet 

weather fl ows, the activated sludge process was operated in contact stabilization mode. By switching operational modes during 

wet weather conditions, six to 12 times the average dry weather fl ow rate (approximately 1.25-2.3 MGD) was treated. For fl ows of 

up to 1.25 MGD, the mean suspended solids and BOD5

 effl uent concentrations ranged from 2-24 mg/L and 6-11 mg/L, respectively. 

Removal effi ciencies for wet weather fl ows ranging from 0.5-2.3 MGD were 71 percent and 73 percent for suspended solids and 

BOD5

, respectively (Benedict and Roelfs 1981).

CLATSKANIE, OR

Responsible Agency: Clatskanie People’s Utility 

District

Population Served: 4,300

Service Area: 3.5 sq. mi.

Sewer System: Not Available

Contact Stabilization Used for Treatment
Treatment Technologies: Plant Modifications

TMT-17

References

Batzell, Russell W. 1994. “Computer Control of CSOs,” Civil 

Engineering. Vol 64 (No.11): 58-59.

Benedict, A.H. and Roelfs, V.L. 1981. Joint Dry/Wet Weather 

Treatment of Municipal Wastewater at Clatskanie, Oregon.

EPA-600/2-81-061, NTIS PB 81-187262.

Field, R., Villeneuve, E., and Stinson, M. K. 2000. “Get 

Real!” Water Environment & Technology. Vol 12 (No. 4): 64-

68.

NEFCO, Inc. 2002. “Baffle Basics...A Brief Tutorial.” 

Retrieved December 30, 2002.

http://www.nefcoinc.com/torial.html.

New York State Department of Environmental 

Conservation (NYSDEC). 2001. “Wet Weather Operating 

Practices for POTWs with Combined Sewers.” Retrieved 

June 26, 2003. 

http://www.dec.state.ny.us/website/dow/bwcp/ww_

training.pdf

NYSDEC. 2002. “Clarifier Baffles Work.” Retrieved 

December 30, 2002. 

http://www.dec.state.ny.us/website/dow/bwcp/tt_baffles.pdf

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Disinfection

Treatment Technologies

Overview

Disinfection of wastewater is necessary for the protection of 

public health. Therefore, municipal wastewater treatment 

processes are typically followed by a disinfection process 

that is designed specifically to inactivate bacteria, viruses, 

and other pathogens in the treated wastewater. The 

application of disinfection to CSOs and SSOs has been 

more limited, however, owing to uncertainties in process 

design, performance, and regulatory requirements. This 

technology description describes two processes that have 

been used to treat wet weather CSOs and SSOs: chlorine 

disinfection and ultraviolet (UV) light. Other technologies 

that have had more limited application in disinfecting 

CSOs and SSOs include ozonation, chlorine dioxide, 

peracetic acid, and electron beam irradiation. These will 

not be discussed in this fact sheet; more information is 

available in EPA’s “Alternative Disinfection Methods” fact 

sheet (EPA 832-F-99-033).

Chlorine Disinfection

Chlorine disinfection involves the application of 

chlorine to wastewater to inactivate microorganisms. 

Wastewater disinfection most often employs gaseous 

chlorine. The gas is usually supplied in either 150-

pound or 1-ton cylinders. When added to wastewater, 

gaseous chlorine undergoes hydrolysis and forms 

a mixture of hypochlorous acid (HOCl) and 

hydrochloric acid (HCl); some of the HOCl further 

dissociates to hypochlorite ion (OCl-). Hypochlorous 

acid and hypochlorite ion provide the majority of the 

disinfection. When ammonia is present, chloramines 

are also formed, although they are less potent as 

disinfectants.

Chlorine can also be applied in hypochlorite form. 

The chemistry of hypochlorination is very similar 

to gaseous chlorine in that the main agents of 

disinfection are hypochlorous acid and, to a lesser 

extent, hypochlorite ion. The two most commonly used 

hypochlorites are sodium hypochlorite, a clear, yellow 

liquid, and calcium hypochlorite, a dry solid that comes 

in powder, granular, or tablet form.

Sodium hypochlorite, also known as bleach, is available 

in strengths ranging from 1-16 percent, but typically 

contains 12.5 percent available chlorine. Solutions 

of less than one percent strength can be generated 

electrochemically from salt brine solution, but must 

be done on-site. Calcium hypochlorite is a solid 

that contains 65-70 percent available chlorine. It is 

commonly used in tablet erosion systems, which pass a 

stream of water over the tablets and generate a solution 

of generally less than one percent available chlorine.

The performance of a chlorine disinfection system can 

be characterized in terms of the product of the chlorine 

concentration in milligrams per liter (mg/L) and the 

contact time in minutes, usually referred to as “CT.” 

Disinfection effi ciencies are usually fairly consistent for 

a given CT, and increase in proportion to increasing 

CT. Decreased contact time can therefore be offset by 

increased disinfectant concentration and vice versa.

Ultraviolet Light

Ultraviolet (UV) light disinfection involves the direct 

exposure of the wastewater stream to UV light, which 

alters genetic material in microbial cells and prevents 

them from reproducing. Germicidal wavelengths range 

from 200-320 nanometers (nm), with peak effectiveness 

at approximately 260 nm. In UV disinfection systems, 

a relatively thin fi lm of wastewater fl ows past the UV 

lamps, and for a few seconds, the microorganisms are 

exposed to a dosage of UV energy.

Ultraviolet radiation is generated by striking an electric 

arc through mercury vapor contained in a lamp. 

Because ordinary glass absorbs UV light, the lamp is 

made of special UV light transmitting quartz, polymer, 

or silica. Factors that infl uence the level of radiation 

emitted from UV lamps include mercury vapor 

UV disinfection process (Columbus Water Works).
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-20

pressure, chemical composition of the quartz sleeve, 

and electrical power input (Acher et al. 1997).

Low-pressure, low-intensity lamps have found the 

greatest application in disinfection of wastewater 

treatment plant effl uents, primarily because they emit 

around 85 percent of their UV output at 254 nm, which 

is close to the most effective germicidal wavelength of 

around 260 nm. Due to their low-intensity, however, 

the number of lamps required is relatively large, which 

makes them impractical for high-rate applications such 

as disinfecting CSOs and SSOs. There is effectively 

no economy of scale in UV disinfection; much of the 

capital and operating costs are directly proportional 

to the number of bulbs, and the number of bulbs is 

directly proportional to the fl ow being disinfected. 

Medium-pressure, high-intensity lamps are becoming 

more widely available and have been shown to be more 

effective on lower-quality wastewaters such as CSO and 

SSO discharges. In addition, higher intensity means that 

fewer bulbs are required, which makes these systems 

more economical for CSO and SSO applications.

Ultraviolet disinfection technologies fall into two 

categories: closed systems and open channel systems. 

Closed system contact units consist of UV lamps 

encased in quartz around which wastewater fl ows. 

Open channel systems consist of submerged UV lamps 

either vertically or horizontally suspended in an open 

channel. Both systems are typically modular in design 

and are applicable to a wide range of fl ows.

To achieve inactivation, UV radiation must be absorbed 

into the microorganism. Therefore, anything that 

prevents UV light from reaching the microorganism 

will decrease the disinfection effi ciency. Other factors 

that have been determined to affect disinfection 

effi ciency include (EPA 1999):

● Chemical and biological fi lms that develop on the 

surface of UV lamps

● Dissolved organics and inorganics in the 

wastewater, especially iron

● Clumping or aggregation of microorganisms

● Turbidity

● Color

● Incomplete exposure of wastewater to UV light

The effectiveness of UV disinfection is typically 

characterized by the UV dose. The dose is most often 

expressed in milliwatt-seconds per square centimeter 

(mW-s/cm2), and is defi ned as the product of the 

average intensity of UV energy emitted by the lamps (in 

mW/cm2) and the exposure time (in seconds). UV dose 

is analogous to the CT concept used to characterize 

chlorine disinfection and is of similar use in comparing 

results from studies.

Key Considerations

Applicability

Chlorine Disinfection

Chlorine is a fairly stable disinfectant that provides 

continuous disinfection. Chlorine disinfection often has 

signifi cant space requirements; large tanks are usually 

required to allow for suffi cient contact time between 

the chlorine and the wastewater. Chemical storage and 

the location of feed equipment must also be considered. 

Chlorine reacts quickly with many constituents of 

wastewater including, but not limited to, pathogens, 

such that not all of the chlorine added is available 

for disinfection. The difference between the amount 

added and the residual concentration (that is, the 

concentration that persists long enough to provide 

disinfection) is called the “chlorine demand” (White 

1999). The initial chlorine demand of the wastewater 

must be known to some extent so that enough chlorine 

can be added to satisfy initial demand and still provide 

a suffi cient residual concentration.

Chlorine disinfection leaves residual chlorine in the 

treated wastewater, which is highly toxic to aquatic 

organisms. In addition, it may react with organics and 

inorganics in wastewater to form toxic compounds 

that can have long-term adverse effects on the receiving 

waters. For these reasons, residual chlorine levels are 

sometimes restricted by a facility’s discharge permit, 

and must be reduced by dechlorination. Dechlorination 

is typically done with either sulfur dioxide (a gas) or 

sodium bisulfi te (a liquid).

Another effect of the chlorine disinfection process is 

the formation of disinfection by-products (DBPs), 

specifi cally halogenated organics such as total 

trihalomethanes (THMs) and haloacetic acids. DBPs 

form when natural organic matter reacts with free 

chlorine added for disinfection or free bromine 

that results from the chlorine disinfectant oxidizing 

bromide ions in the wastewater. DBP formation is 

affected by the type and concentration of natural 

organic matter, chlorine form and dose, time, bromide 

ion concentration, pH, organic nitrogen concentration, 

and temperature. The utility of chlorine for disinfection 

may be limited where DBPs are subject to regulatory 

limits. Removal of DBP precursors, modifi cation of the 
Treatment Technologies: Disinfection

TMT-21

chlorine disinfection strategy, or changing disinfectants 

are typically used to lessen DBP formation.

UV Disinfection

UV disinfection requires no chemical storage and 

is very stable in this sense. Space requirements are 

relatively small due to short wastewater contact times 

and the lack of chemical storage.

Power consumption is an important consideration 

in UV applications. The process is energy-intensive 

compared to chemical methods. High-fl ow situations 

present high power demands, and will usually require 

an on-site generator, adding to the total construction 

and operating cost.

Advantages

Chlorine Disinfection

The primary advantage of gaseous chlorine is its 

low cost in relation to its overall effectiveness as a 

disinfectant. The technology is well-developed and 

straightforward to apply, and the chemical itself is 

widely available. 

Hypochlorination acts in a similar fashion as gaseous 

chlorine and shares most of its advantages and 

disadvantages. It provides reliable inactivation of 

bacteria, it is widely available, and the technology is 

fully developed. Liquid sodium hypochlorite is usually 

somewhat more expensive than gas per pound of 

available chlorine.

UV Disinfection

UV disinfection is attractive for disinfection of CSOs 

and SSOs for several reasons. The disinfection process 

requires much shorter detention times than chemical 

methods, on the order of seconds as compared to 

10 minutes or greater for chlorine. There are also no 

chemicals to transport, handle, or store, which appeases 

numerous concerns, including worker and public safety, 

environmental impacts, and degradation of chemical 

strength during storage. UV also does not form any 

known, potentially toxic byproducts, nor does it leave 

any toxic residuals.

Disadvantages

Chlorine Disinfection

Disadvantages of gaseous chlorine include poor 

inactivation of viruses and protozoan cysts and 

oocysts relative to bacteria, the formation of DBPs, 

and reactions with ammonia that result in combined 

chlorine residuals that are less effective disinfectants. 

These issues are especially important when treating 

CSOs and SSOs, since in many cases suspended solids 

and ammonia levels are elevated in these fl ows. In 

addition, the hazards posed by leaking chlorine gas may 

make it infeasible for use at satellite locations, which 

could be in heavily populated areas. Fire and building 

codes may require scrubbers or other equipment to 

mitigate leaks.

Hypochlorination shares some disadvantages with 

gaseous chlorine, including lesser inactivation of 

viruses and protozoa, the formation of DBPs, and 

reactions with ammonia that lessen its effectiveness at 

a given residual concentration. Although liquid sodium 

hypochlorite is highly corrosive and must be handled 

with care, it is generally considered to pose less of a 

safety hazard than gaseous chlorine. 

Solutions of sodium hypochlorite will decay in strength 

over time, especially at higher concentrations and 

temperatures. This can be a signifi cant disadvantage for 

CSO and SSO facilities that are operated infrequently 

and which would require chemicals to be stored for 

potentially long periods of time. Decay rates can be 

attenuated by diluting the hypochlorite after delivery 

to 10 percent or even 5 percent, although this requires 

additional storage facilities. Calcium hypochlorite, 

used in tablet erosion systems, has a much longer shelf 

life than liquid sodium hypochlorite. Tablet erosion 

systems, however, may not be able to provide large 

enough volumes of chlorine solution with the short 

notice given by CSOs and SSOs during many wet 

weather events.

UV Disinfection

A major disadvantage of UV light disinfection of CSOs 

and SSOs has been its sensitivity to wastewater quality. 

Its effi ciency is reduced by increased suspended solids 

and turbidity. The buildup of mineral deposits on the 

lamp sleeves also reduces effectiveness by reducing 

the applied dose of UV light. Recent advances are 

addressing these issues, however, by using higher 

intensity lamps and more effective self-cleaning 

mechanisms.

Cost

Chlorine Disinfection

Table 1 summarizes fecal coliform data for two 

chlorine disinfection facilities (more information on 

these facilities is provided in the case studies below): 

Washington, D.C., and Acacia Park in Oakland County, 

MI. The Washington, D.C., Northeast Boundary Swirl 

Facility (NEBSF) also tests for enterococci, and these 

results are also shown in Table 1. Samples at NEBSF are 

taken both in the disinfection chamber and at the river 

outfall.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-22

The table shows the variability of performance that is 

often the case when treating CSOs and SSOs. A major 

operational issue is optimizing the addition of chlorine; 

the experience at these facilities and others has been 

that inadequate pathogen reduction is usually the result 

of insuffi cient chlorine levels. Achieving the desired 

chlorine level requires reliable fl ow measurement and 

knowledge of the strength of the chlorine solution.

Capital costs for construction of chlorine disinfection 

facilities are usually proportional to the peak design 

fl ow. The majority of the cost is in the construction of a 

basin that provides suffi cient contact time (for example, 

15 minutes); a smaller portion consists of equipment, 

such as feed pumps, mixers, and storage tanks. Analysis 

of construction costs of CSO detention and treatment 

facilities in the River Rouge area in southeast Michigan 

showed that the equipment portion of the chlorine 

disinfection costs were approximately three to four 

percent of the total project cost (Tetra Tech MPS 

2002). These facilities generally included signifi cant 

storage volume beyond what would be needed solely 

for chlorine disinfection, however. If the basin costs 

are adjusted to provide a 15-minute detention time, 

the costs for the facilities average around $14,000 per 

MGD of peak fl ow. Reducing the detention time to 10 

minutes, which is feasible if highly effi cient chemical 

mixing is provided, reduces this cost to about $9,500 

per MGD. Actual construction costs vary considerably 

because of site-specifi c conditions.

Ultraviolet Light

UV systems do not have as long a record as chlorine 

disinfection facilities in disinfecting CSOs and SSOs. 

Pilot studies have shown, however, that fecal coliform 

levels of 1,000 #/100 mL can be met consistently by 

medium-pressure, high-intensity units operating 

within their normal range of power usage (CDM 1997; 

Curtis and Blue 1999). In another study, E. coli levels 

of 126 #/100 mL were met by both low- and mediumpressure systems treating effl uent from a physical/

chemical process using alum as the coagulant (Matson 

et al. 2002). The desired E. coli level was not met when 

ferric chloride was used, however.

Capital costs for construction of UV disinfection 

facilities are not well known, due to a lack of data 

for this relatively new technology. As part of a CSO 

disinfection pilot study, capital costs for construction of 

UV disinfection facilities were projected by the US EPA 

Offi ce of Research and Development. In this study, it is 

estimated that a UV disinfection facility that results in a 

four-log reduction in fecal coliform with a peak fl ow of 

88 MGD will cost approximately $27,600 per MGD of 

peak fl ow (EPA 2002).

Period Number of 

Samples

Geometric Mean Fecal Coliform (#/100 mL) Geometric Mean Enterococci 

(#/100mL)

Acacia Park

NEBSF NEBSF

Disinfection 

Chamber River Disinfection Chamber River

1997 13 5.4 -- -- -- --

1998 57 2,220 -- -- -- --

1999 31 2,430 -- -- -- --

Jan-Mar 2001 -- -- 2,240 9,230 68 496

Apr-Jun 2001 -- -- 6,620 26,500 1,700 23,800

Jul-Aug 2001 -- -- 1,600 8,940 593 7,080

Table 1. Pathogen removal performance for chlorine disinfection facilities.
Treatment Technologies: Disinfection

TMT-23

Implementation Examples

The District of Columbia Water and Sewer Authority (WASA) operates a sewer 

system that includes combined sewers serving approximately 12,478 acres. 

Among its existing CSO controls is the NEBSF, which provides treatment and 

disinfection for up to 400 MGD of CSO before discharging to the Anacostia 

River. The facility provides mechanical screening followed by three 57 foot 

diameter swirl concentrators. The effl uent from the swirl concentrators fl ows 

to a mixing chamber where sodium hypochlorite is added, usually at a dose 

of 5 mg/L. Sodium bisulfi te is added at the end of the outfall for dechlorination, usually at a dose of 2 mg/L. Flows above 400 MGD 

receive no treatment and are discharged through the same outfall as treated fl ows.

Samples taken during CSO events at the mixing chamber and at the river outfall are analyzed for enterococcus and fecal coliform. 

Reported counts range from less than 10 MPN/100 mL to in excess of 250,000 MPN/100 mL. The high numbers are associated with 

events in excess of 400 MGD and represent a comingling of treated and untreated CSO.

Annual operating costs for the NEBSF are estimated to be about $230,000. This is based on $180,000 for labor and $50,000 for chemicals. 

Labor includes two full-time operators, a part-time supervisor, and other part-time support for cleaning and maintenance. The facility 

discharges on average about 100 times per year, with an average total volume of approximately 1,500 MG.

Contact: Mohsin Siddique, CSO Control Program Manager, DC WASA

WASHINGTON, DC Northeast Boundary Swirl Facility (NEBSF)

Responsible Agency: District of Columbia Water 

and Sewer Authority

Population Served: 572,000

Service Area: 19.50 sq. mi.

Sewer System: 1,800 mi. of sanitary and combined 

sewer

The Jefferson County Environmental Services Division owns and operates 

nine wastewater treatment facilities, collecting and treating wastewater from 

the City of Birmingham and some 20 neighboring municipalities. These nine 

plants, along with about 658 miles of separate sewers, serve an approximate 

population of 376,000 at an average daily fl ow of 97 MGD. The Village Creek 

WWTP has at times received peak fl ows greater than ten times its annual 

average fl ow (in excess of 400 MGD versus an average of 40 MGD). Currently, a 

350 MGD peak excess fl ow treatment facility is under construction.

The Village Creek Peak Flow Wastewater Treatment Plant (PFWWTP) includes a pump station with 360 MGD capacity, 20 surge 

basins with surface aeration for mixing (total capacity of 90 MG), granular monomedia deep bed fi lters with 350 MGD capacity, UV 

disinfection, and a 24-megawatt generating facility (primarily to power the pump station and UV). The entire facility is scheduled to 

be completed in the summer of 2003.

The Village Creek PFWWTP uses a UV disinfection system with a total of 2,688 lamps and has a peak power requirement of 7,526 kW. 

The total installed cost of the UV facility at Village Creek is estimated to be $13 million; the cost for the UV equipment is approximately 

$10.7 million. Operating costs are not available.

Contact: Harry Chandler, Assistant Director, Environmental Services, Jefferson County

BIRMINGHAM, AL UV Disinfection at Peak Flow WWTP

Responsible Agency: Jefferson County 

Environmental Services Division

Population Served: 376,000

Service Area: Not Available

Sewer System: 3,100 mi. of sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-24

The Offi ce of the Oakland County Drain Commissioner (OCDC) 

currently operates three CSO retention basins in southeastern 

Michigan, all of which provide treatment and disinfection of 

fl ows that exceed their storage capacity. The Acacia Park CSO 

Retention Treatment Basin (RTB) is a 4 MG basin that serves 

a combined area of approximately 816 acres. Disinfection is 

by sodium hypochlorite, which is stored at about 6 percent to 

reduce the rate of degradation during storage. The feed system 

is designed to provide a dose of 10 mg/L at a CSO fl ow rate of 426 MGD. The hypochlorite is fed at the discharge of the infl uent 

pumps, which provides suffi cient mixing. Dechlorination is not currently provided at this facility.

Extensive monitoring of the basin performance was conducted during a three-year demonstration period from1997-1999 (Johnson 

et al. 2000). The disinfection target was a fecal coliform count of less than 400 #/100 mL at a total residual chlorine (TRC) level of 1.0 

mg/L. The purpose of the TRC goal is to ensure that a suffi cient dose of chlorine is delivered to the basin.

Five of the nine events monitored had average TRC levels above 1.0 mg/L, and the fecal coliform target was met in four of these fi ve 

events. The four events with average TRC levels less than 1.0 mg/L did not meet the fecal coliform target. Low TRC was generally 

attributed to sodium hypochlorite solutions being weaker than anticipated either because of degradation or inaccurate dilution of 

the chemical.

Annual operating costs for the Acacia Park facility are estimated to be $120,000. This includes $58,600 for labor, $24,800 for energy and 

utilities, $26,000 for chemicals, and $10,500 for laboratory and other services. These costs refl ect some additional expense associated 

with startup, testing, and performance evaluation. Over the three-year demonstration period, the facility captured approximately 

60 percent of the fl ow it received; that is, treated overfl ows represented 40 percent of fl ow into the facility. The total volume of fl ow 

into the facility was estimated at 146 MG, with 88 MG retained and returned to the sewer system and 58 MG treated and discharged. 

Overfl ows occurred on average four to fi ve times per year, and ranged in volume from 0.13-17 MG. 

Contact: Dan Mitchell, Hubbell, Roth, and Clark, Michigan

OAKLAND COUNTY, MI

Responsible Agency: Oakland County Drain 

Commissioner

Population Served: 4,500

Service Area: 1.28 sq. mi.

Sewer System: Not Available

Chlorine Disinfection at Acacia Park

The City of Bremerton has recently constructed a CSO treatment facility that 

uses high-rate clarifi cation, followed by UV disinfection, to treat fl ows up to 

45 MGD. The facility uses a medium-pressure, high-intensity UV system that 

employs a total of 90 bulbs. A 500 kilowatt generator is located on site to supply 

power to the UV system as well as pumps, mixers, and other appurtenances. 

The clarifi cation system uses a polyaluminum chloride coagulant, which was 

selected over the equally effective ferric chloride to avoid UV interferences by residual iron. The primary reason for choosing UV over 

chlorination was to avoid the degradation of hypochlorite between discharge events, which are estimated to occur approximately 20 

times per year. Bremerton installed a UV system at a cost of about $600,000 to disinfect CSO discharges. The annual operation cost for 

the entire facility is estimated to be about $50,000; UV power costs and bulb replacement are a portion of this. 

Contact: John Poppe, Wastewater Division Manager, City of Bremerton

BREMERTON, WA UV Disinfection at CSO Treatment Facility

Responsible Agency: City of Bremerton

Population Served: 40,000

Service Area: 10 sq. mi.

Sewer System: 250 mi. of sewer
Treatment Technologies: Disinfection

TMT-25

Columbus Water Works (CWW) operates a sewer system and treatment plant that 

includes 5,200 acres of combined sewer service area. Pilot studies aimed at gathering 

more information for controlling CWW’s CSOs grew, in part with the aid of an 

appropriation from Congress, into the Uptown Park Advanced Demonstration Facility 

(ADF). The ADF included vortex separators, compressed media fi ltration, and chemical 

and UV disinfection systems. Chemicals evaluated included sodium hypochlorite, 

chlorine dioxide and peracetic acid; vortex separators were used as contact chambers 

for chemical disinfection. The UV system used medium pressure, high-intensity lamps.

The study demonstrated the challenges to chemical disinfection posed by the variation of chemical oxidant demand in CSO. In 

general, no direct relationships were observed between effl uent fecal coliform concentrations and CT values based on disinfectant 

dose alone. Useful relationships were obtained, however, when CT values were normalized by both CSO ammonia concentration and 

the mass of chemical oxygen demand (COD) removed. The results were used to develop control algorithms for disinfectant dosing that 

are based on CSO infl uent conditions, rather than relying on residual chlorine measurements that can be diffi cult to obtain reliably 

under rapidly changing fl ow conditions.

UV disinfection performance was characterized by the inactivation of E. coli. The inactivation increased with increasing UV dose, which 

was calculated as the product of applied lamp power, UV percent transmittance, and contact time. UV transmittance of the fi ltered 

effl uent was typically less than 60 percent, and at levels less than 40 percent, effl uent bacteria increased by an order of magnitude 

(from hundreds to thousands). In contrast, the unfi ltered CSO UV transmittance was as low as 20 percent.

Capital and operating costs were developed for an optimized treatment train consisting of screening and grit removal, vortex 

separation, fi ltration, and combined chemical and UV disinfection. UV and chlorine disinfection/dechlorination accounted for about 28 

percent of the capital cost and 39 percent of the operating cost. Capital costs for a treatment system designed for 63 percent removal 

of TSS were estimated to be approximately $10,000 per acre of combined sewer service area; annual operating costs were estimated 

to be about $163 per acre. Designing the system for 80 percent removal of TSS increased the capital cost nearly threefold, with annual 

operating costs doubling.

Contact: Cliff Arnett, Columbus Water Works

COLUMBUS, GA Chlorine and UV Disinfection Demonstration Project

Responsible Agency: Columbus Water 

Works

Population Served: 186,000

Service Area: 95 sq. mi.

Sewer System: 8.1 mi. of combined sewer
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-26

References

Acher, A., et al. 1997. “Ecologically Friendly Wastewater 

Disinfection Techniques.” Water Research. 31(6):1398-1404. 

Camp, Dresser & McKee (CDM). 1997. “Spring Creek 

AWPCP Upgrade - CSO Disinfection Pilot Study - Final 

Report.” Location: Publisher.

Curtis, M. and K. Blue. City of Unalaska Ultraviolet 

Disinfection of a Primary Effluent. Conference proceedings 

at Water Environment Federation WEFTEC New Orleans, 

LA, 1999.

EPA Office of Research and Development. 2002. CSO 

Disinfection Pilot Study: Spring Creek CSO Storage Facility 

Upgrade. EPA 600-R-04-077.

EPA Office of Water and Office of Ground Water and 

Drinking Water. 1999. Alternative Disinfectants and 

Oxidants Guidance Manual. EPA 815-R-98-009.

Johnson, C. E., et al. Operating Experience with Large 

CSO Control Facilities. Conference proceedings at Water 

Environment Federation WEFTEC Anaheim, CA, 2000.

Matson, B., et al. Meeting SSO Requirements with a High 

Rate Process Train: Pilot Results Lead the Way. Conference 

proceedings at Water Environment Federation WEFTEC 

Chicago, IL 2002.

Poppe, John. Wastewater Division Manager, City of 

Bremerton, WA. Interview by Limno-Tech, Inc., December 

2002. Ann Arbor, MI.

Siddique, Mohsin. CSO Control Program Manager, District 

of Columbia Water and Sewer Authority. Interview by 

Limno-Tech, Inc, December 2002. Ann Arbor, MI.

Tetra Tech MPS. Interview by Limno-Tech, Inc., December 

2002. Ann Arbor, MI.

White, G.C. 1999. Handbook of Chlorination and Alternative 

Disinfectants. 4th Ed. New York: Wiley and Sons, Inc.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Vortex Separators

Treatment Technologies

Overview

Vortex separators are designed to concentrate and remove 

suspended solids and floatables from wastewater or storm 

water. Sometimes referred to as swirl concentrators, vortex 

separators use centripetal force, inertia, and gravity to 

provide treatment. The vortex design induces solids to 

settle out into a sump; floatables are captured by screens. 

In combined sewer systems (CSSs), vortex separators are 

used at hydraulic control points (regulators) to separate 

combined sewage into a small volume of concentrated 

sewage and solids, and a large volume of more dilute 

sewage and storm water runoff. The concentrated sewage 

is typically conveyed to a wastewater treatment plant 

(WWTP) for treatment, and the dilute mix is discharged 

directly to a receiving water. This discharge may or may not 

be disinfected. In storm water systems, vortex separators are 

used to capture solids and floatables at storm water outfalls. 

In storm water applications, captured material needs to be 

cleaned out and removed for disposal on a regular basis. In 

general, vortex separators are not used to provide treatment 

at remote locations in sanitary sewer systems (SSSs). The 

focus of this technology description is the use of vortex 

separators for controlling wet weather discharges from 

CSSs. 

Vortex separators are flow-through structures that usually 

have one inlet and two outlets: one for concentrated sewage 

and solids, and one for more dilute sewage. Different 

vendors provide different design features to optimize 

liquid-solid separation and pollutant removal. Many vortex 

separators use screens and baffles to collect floatables. 

Floating sorbent materials are also used in some designs 

to capture oil and grease. The range of size and capacity of 

vortex separators is quite large. 

A simple diagram of a vortex separator is shown in Figure 

1. The basic operation of a vortex separator is as follows:

● Excess wet weather flow enters the separator 

tangentially through an inlet pipe.

● Velocity causes flow to move through the separator in a 

circular path, forming a vortex.

● Inertia, gravity, and centripetal forces cause the heavier 

solid particles to move to the center and bottom of 

the swirling flow. Clearer water rises and discharges 

through the outlet.

● The concentrated sewage, including heavier solids and 

debris, becomes underflow and is discharged through 

a foul sewer outlet at the bottom of the separator and 

routed to a WWTP.

When the separator is full, the more dilute and clarified 

effluent is discharged through an overflow outlet at the top 

of the separator and conveyed to local receiving waters.

At the end of an event, as excess wet weather flows subside 

and the water level in the separator drops below the level of 

the overflow outlet, the separator ceases to discharge to the 

receiving water. 

Disinfection of the discharge from vortex separators 

is sometimes added for public health reasons (Boner 

et al. 1995). Sodium hypochlorite can be injected into 

Figure 1. Simplified diagram of a vortex separator.

Overflow to

recieving water

Underflow

To wastewater

treatment plant

Inflow

Construction of a vortex separator (Columbus Water Works.).
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-28

the separator basin, allowing the wet weather flows to 

be disinfected as the solids are removed. Chlorinated 

discharges may also need to be dechlorinated to prevent 

toxicity. Discharges from a vortex separator can also be 

treated using ultraviolet (UV) disinfection. If the separator 

design includes a sump to capture solids, the solids should 

be removed in advance of the next wet weather event. 

Some designs enable buoyant floatables to be skimmed 

from the dilute overflow and mixed with the underflow for 

conveyance to the treatment plant.

Key Considerations

Applicability

Vortex separators provide a modest level of treatment 

for a modest cost. In CSS, they can be used as a “standalone” CSO control, or in conjunction with other controls. 

When used on their own, they are useful in controlling 

suspended solids and floatables and in reducing pollutants 

associated with solids, such as metals bound to sediments. 

Their ability to reduce floatables in CSO discharges is 

valuable in situations where control of aesthetic impacts 

is important to the public. They have limited ability to 

reduce the strength of dissolved pollutants or bacteria 

unless disinfection is applied in conjunction with vortex 

separation. When used in combination with other CSO 

controls, the placement of vortex separators is important. 

Because they are designed to remove suspended solids 

and floatables, vortex separators should not be placed 

downstream of other facilities that perform the same 

function, such as sedimentation basins or netting systems. 

Vortex separators are often retrofitted within CSSs to 

provide some level of treatment where none had existed 

before. Considerations in implementing vortex separators 

include:

● Vortex separators do not require a power source 

because the energy of the flowing water is used to 

separate the solids. Therefore, the utility of vortex 

separation technologies is diminished in situations 

where the velocity of wet weather flows is limited.

● Space requirements are minimal relative to storage 

units because they separate rather than store sewage.

● Units can range in diameter from 2 feet to more than 

40 feet and are typically installed underground. 

● Soil conditions and depth to bedrock at potential sites 

influence site suitability and construction costs.

● Vortex separators can be either pre-fabricated or built 

on-site. They can be constructed of concrete, highdensity polyethylene (HDPE), aluminum, or stainless 

steel, depending on the manufacturer.

Advantages

The major advantage of vortex separators is their ability 

to remove suspended solids and floatables, which are the 

most visible and aesthetically displeasing components of 

CSO discharges. Vortex separators begin to separate out 

suspended solids and floatables as soon as inflow begins to 

move through the unit. Additional advantages include: 

● Maintenance requirements are low. Vortex separators 

have no moving parts to wear out or break. They can 

be allowed to go dry between storms without affecting 

performance. 

● Vortex separators have a high hydraulic loading 

capacity.

● Space requirements at implementation sites are low. 

Disadvantages

The principal disadvantage in the use of vortex separators 

for CSO control is that they do not eliminate CSOs or 

reduce CSO volume; they just reduce the strength of the 

CSO discharge with respect to suspended solids, pollutants 

associated with suspended solids, and floatables. Other 

disadvantages include:

● Removal rates of fine solids and soluble pollutants are 

low or negligible in vortex separators. 

● Disinfection is difficult because of the large volumes of 

excess wet weather flow received by vortex separators, 

short contact time for disinfection, and space and 

security requirements associated with disinfectants. 

● Floatables may be lost during extremely high flows or 

in the initial overflow, when the surge of inflow could 

carry them around and over the baffles and weirs 

designed to remove them. 

● Vortex separators with sumps require periodic cleaning 

to achieve optimal removal performance. 

Cost

The performance of vortex separators with respect to 

pollutant removal is based on the difference in pollutant 

load, not volume, that is discharged to a receiving 

water over time, with and without a vortex separator. 

Performance is directly related to the nature of the solids 

and floatables in the influent wastewater, as well as the 

influent concentrations and loading rates. Qualitatively, 

vortex separators can be expected to provide “good” 

removal of heavier particles and floatables and “fair to 

poor” removal of lighter weight materials such as oil and 

grease, nutrients, and colloidal material (WERF 2002). 

Some common performance characteristics are as follows:

● Vortex separators perform better for concentrating 

larger or heavier suspended solids for treatment 
Treatment Technologies: Vortex Separators

TMT-29

than smaller or lighter suspended solids. Removal of 

dissolved solids or dissolved fractions of pollutants is 

negligible. 

● Site specific design matched to particle size and settling 

velocity profiles of suspended solids is essential to 

optimize performance. 

● Floatables capture decreases as hydraulic loading 

increases.

Available data for basic vortex separation suggest widely 

varying performance, with total suspended solids (TSS) 

removal ranging from five percent to 60 percent (EPA 

1996; Boner et. al. 1995; WERF 2002). The higher removal 

rates are comparable to primary clarification, but can 

be achieved in a vortex separator that is one-fourth the 

volume and one-fifth the surface area of a conventional 

sedimentation basin (Boner et. al. 1995). TSS removal 

rates of up to 80 percent have been achieved when units 

are operated at one-fourth of the hydraulic capacity (Larry 

Walker Associates 1999). In a survey of vortex separator 

performance documented by Moffa (1997), removal 

efficiencies were shown to vary substantially from stormto-storm, and from one facility to another.

Additional vortex separation performance information for 

other pollutants is as follows:

● BOD5

 removal rates have ranged from 20 percent and 

79 percent in laboratory studies (Moffa 1997). Actual 

BOD5 removal rates for two storms in Columbus, GA, 

reached 55 percent (Boner et. al. 1995). Data for the 

Northeast Boundary Swirl Facility in Washington, D.C., 

indicate BOD5 removal efficiencies of up to 28 percent 

(WERF 2002). ● Manufacturer laboratory tests show that vortex 

separators can remove 80 percent of oil and grease; 

however, no data are available for oil and grease 

removal rates under actual, full-scale operating 

conditions. 

● UV disinfection of vortex discharges can achieve a 

90-99 percent reduction in the concentration of fecal 

coliform bacteria (WERF 1994). 

Costs for purchasing a basic vortex separator range from 

approximately $8,000 for a 1.8 MGD unit to $40,000 for 

a 16 MGD unit. Installation costs typically from 25-50 

percent of the purchase costs (Larry Walker Associates 

1999). A summary of products from various manufacturers 

with ranges in available hydraulic capacities and costs is 

presented in Table 1.

Maintenance costs for vortex separators vary depending on 

cleaning frequency, travel distances, and disposal costs for 

captured solids and floatables.

Product 

(Manufacturer)

 Available Hydraulic 

Capacity Sizes (MGD) Purchase Costs

Continuous Deflective Separation (CDS Technologies) 0.7-193.8 $9,600 - $332,500

Downstream Defender (H. I. L. Technology, Inc.) 1.9-7.8 $10,300 - $26,000

V2B1 (Kistner Concrete) 1.8-16.3 $8,000 - $40,000

Vortechs Storm Water Treatment System (Vortechnics) 1.0-16.2 $10,500 - $40,000

Table 1. Comparison of vortex separation products and costs.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-30

Implementation Examples

The Burlington Main Wastewater Treatment Facility (WTF) treats municipal

wastewater from the city’s CSS and discharges treated fl ow through an outfall into

Lake Champlain. The WTF also has a CSO treatment system on-site which includes

vortex separation, mechanical screening, and disinfection; the system was installed

in the early 1990s. The CSO treatment system is designed to handle wet weather

instantaneous fl ows greater than 11 MGD, but not exceeding 86 MGD.

The vortex separation process, combined with the capacity of the treatment plant, is designed to provide a relatively high level

of treatment for the “fi rst fl ush” generated during the early stages of storm events that usually contains the highest pollutant

concentrations. Chemical disinfectant is added to the CSO fl ow prior to and after treatment by the vortex separator. The concentrated

underfl ow from the vortex separator, approximately 2 MGD, is diverted to the WTF for full treatment. During wet weather events

when the instantaneous storm fl ow rate exceeds 75 MGD, ultrasonic sensors allow fl ows to bypass the vortex separator. According to

self-monitoring reports from January 1995 through December 1999, the CSO system was activated an average of 32 times per year,

13 times on average during the “beach season” of June through August.

More information at http://www.dpw.ci.burlington.vt.us/

RANDOLPH, VT Vortex Separator Used to Treat CSOs

Responsible Agency: Burlington Main 

Wastewater Treatment Facility

Population Served: 37,712

Service Area: Not Available

Sewer System: 100 mi. of sewer

The Columbus CSS extends over the old downtown area draining into the 

Chattahoochee River. Prior to CSO control, elevated levels of fecal coliform bacteria 

and visible sewage debris often plagued the Chattahoochee. Columbus began to 

implement CSO controls in 1995, including construction of two water resource 

facilities (WRFs). One of the WRFs, in Uptown Park, also serves as a national CSO 

technology testing facility used to demonstrate and evaluate alternative methods 

of CSO pollutant removal and disinfection.

A fi ve year CSO testing program was conducted at the Uptown WRF to analyze the performance, operation and maintenance (O&M), 

costs, and applications of CSO treatment technologies, including vortex separators. At this facility, Columbus installed six vortex 

separators, each 32 feet in diameter, with a conical ring bottom where grit and concentrated solids are removed. All six vortex vessels 

start empty and fi ll with CSO fl ow as CSS capacity is exceeded. The vessels have no moving parts. The vortex vessels serve as storage for 

small events, pollutant reduction during medium events, and grit removal and chemical disinfection for all events. Chemical disinfectant 

is added once the vortex vessels are full. For loading rates of 5 gallons per minute per square foot (gpm/sf ) of surface area, the vortex 

separators functioned similar to a primary clarifi er. For loading rates above 5 gpm/sf, however, the removal of pollutants was reduced 

to zero except for grit and oil and grease. The study also found that the use of vortex separators in combination with media fi lters was 

an effective treatment method in terms of load reduction and cost. The annual O&M for the vortex separators is estimated at $16,320, 

which is about 7 percent of the total O&M costs at the Uptown Park WRF. The capital cost of the vortex separators was $4.8 million.

Contact: Cliff Arnett, Columbus Water Works

COLUMBUS, GA National Demonstration Project

Responsible Agency: Columbus Water Works

Population Served: 186,000

Service Area: 2,400 sq. mi.

Sewer System: Not Available
Treatment Technologies: Vortex Separators

TMT-31

References

Boner, M. C., et. al. 1995. “Modified Vortex Separator and 

UV Disinfection for Combined Sewer Overflow Treatment.” 

Water Science Technology. 31: 263-274.

EPA Office of Wastewater Management, Municipal 

Support Division and National Risk Management Research 

Laboratory (Cincinnati) Water Supply and Water Resources 

Division. 1996. Assessment of Vortex Solids Separators for the 

Control and Treatment of Wet-Weather Flow. EPA 832-B-96-

006. 

Larry Walker Associates, Inc. 1999. “Investigation of 

Structural Control Measures for New Development. 

Prepared for the Sacramento Storm water Management 

Program.” Retrieved December 12, 2002.

www.sacstormwater.org/const/manuals/pdf/scm99_

scm99.pdf

Moffa, P.E. (Ed.). 1997. Control and Treatment of Combined 

Sewer Overflows. 2nd ed. New York, NY: Van Nostrand 

Reinhold.

Water Environment Research Federation (WERF). 1994. 

Optimization of Vortex Separator Removal Efficiencies for 

CSO Treatment. Prepared by Boner, M. C., et al. Alexandria, 

VA: WERF. Project 92-TCR-2.

WERF. 2002. Best Practices for Treatment of Wet Weather 

Wastewater Flows. Prepared by Brashnear, R., et. al. 

Alexandria, VA: WERF. Project 00-CTS-6.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Floatables Control

Treatment Technologies

Overview

Solids and floatables are the trash, debris, and other visible 

materials that are discharged when sewers overflow. In 

sanitary sewer systems (SSSs), solids and floatables are 

generally limited to human waste and sanitary products 

that are flushed down a toilet. In combined sewers systems 

(CSSs), solids and floatables can also include litter and 

detritus that accumulates on streets and parking lots that 

are washed into storm drains during rainfall events. The 

presence of solids and floatables in receiving waters causes 

aesthetic impacts that can threaten wildlife, cause beach 

closures, and pollute recreational areas. 

Floatables control technologies are principally applied in 

CSSs because of the recurring nature of CSOs. They are 

also used to control solids and floatables in urban storm 

water discharges from separate storm water systems. 

Floatables controls are most often designed to lessen 

aesthetic impacts that affect recreational uses. Water 

quality benefits from floatables controls, if they occur, 

are secondary. The CSO Control Policy recognized the 

importance of controlling solids and floatables by including 

it as part of the nine minimum controls. Floatables controls 

can be grouped into three categories: 

● Source controls work to prevent solids and floatables 

from entering the sewer system. ● Sewer system controls work to keep solids and floatables 

in the sewer system, so that they can be collected and 

removed at strategic locations or transported to a 

wastewater treatment plant. ● End-of-pipe controls work to capture solids and 

floatables as they are discharged from the sewer system.

Source Controls

Source controls collect solids and fl oatables before 

they enter the sewer system. Two of the most common 

source controls are street sweeping and catch basin 

modifi cations. Street sweeping is a pollution prevention 

activity that removes litter, debris, dirt, and other 

fl oatables materials from streets and other paved 

surfaces before it can be washed into a CSS during 

wet weather events. Paved surfaces can be swept using 

manual, mechanical, or vacuum sweepers (WEF 1999). 

The degree of fl oatables control achieved by street 

sweeping is infl uenced by the frequency of cleanings, 

local climate, and parked vehicle control (EPA 1999b).

 

Catch basins are the surface-level wells or chambers 

that serve as an entrance to CSSs and separate storm 

water systems for street runoff and overland fl ow. Catch 

basins are designed to trap grit and solids before they 

enter the sewer system (Moffa 1997). There are several 

modifi cations that can be made to catch basins to 

improve the capture of solids and fl oatables. Inlet grates 

installed at the entrance to the catch basin can reduce 

the amount of street litter and debris that enters the 

catch basin. If fl oatables enter the basin through these 

grates, they can be collected in colander-like structures 

called trash buckets installed beneath the grate. 

Other catch basin modifi cations, such as hoods and 

submerged outlets (Figure 1), modify the connection 

between the catch basin and the CSS to trap fl oatables 

Floatables control with netting (NJ Dept. of Environmental Protection).

Figure 1. Typical hood design in a catch basin.

Hood

Inlet

Outlet

Catch Basin

Ground

level
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-34

in the catch basin. Submerged outlets are located below 

the elevation of the sewer system and are connected by 

a riser pipe. Hoods are vertical cast iron baffl es installed 

over the outlet pipe in the catch basin.

Collection System Controls

Collection system controls are designed to keep solids 

and fl oatables in the sewer system so that they can 

be collected and removed at strategic locations or 

transported to a wastewater treatment plant. Screens, 

baffl es, and in-system netting are types of collection 

system controls. 

Screens can be installed near CSO outfalls or at other 

strategic locations in the CSS. Screens trap fl oatables 

behind metal bars or mesh, allowing wastewater to 

pass through. Screen openings typically range in size 

from 0.1 inch to 6 inches. The type of screen and size of 

openings determine the amount and size of fl oatables 

captured (EPA 1999c). Major categories of screens 

include:

● Bar screens or trash racks with openings greater 

than 1 inch;

● Coarse screens with 0.25-1 inch openings; and 

● Fine screens with 0.001-0.25 inch openings.

The nature and quantity of fl oatables in wet weather 

fl ows makes them likely to clog fi ne screens therefore 

their utility may be limited. Screens are usually set 0-30 

degrees from vertical and may be cleaned manually or 

mechanically.

Baffl es can be installed at fl ow regulators in CSSs or at 

outlets from storage facilities. Baffl es are commonly 

made from concrete beams, steel plates, wood, or 

plastic, and, as shown in Figure 2, extend from the top 

of the sewer to just below the regulating weir. As fl ow 

rises in the CSS or storage facility, water passes under 

the baffl e and over the regulator to the CSO outfall. 

Most fl oatables are trapped behind the baffl e and 

remain in the CSS where they are transported to the 

treatment plant (EPA 1999a).

In-system netting is installed at strategic locations 

in the sewer system in concrete vaults, often near 

regulators in the outfall pipe. One or more nylon mesh 

bags are supported by a metal frame. Netting system 

design, including the aperture of the mesh nets, is based 

on the size and types of fl oatables targeted for capture 

and the anticipated volume of fl ow. Wet weather 

fl ows carry fl oatables into the nets, which are replaced 

periodically (EPA 1999a). 

End-of-Pipe Controls

End-of-pipe controls use netting systems or 

containment booms and skimmer vessels to capture 

fl oatables in the receiving water after they have been 

discharged from the sewer system. 

End-of-pipe netting systems consist of an in-water 

containment area that funnels CSO discharges through 

a series of nylon mesh bags attached to a modular 

pontoon structure. Also referred to as a fl oating netting 

system, nets are located a short distance from the CSO 

outfall, allowing the fl oatables to rise to the water 

surface after the discharge mixes with the receiving 

water (EPA 1999a). As with in-system nets, the size of 

the mesh net used will depend on the volume and type 

of fl oatables targeted for capture (EPA 1999a). After the 

nets become full, they are removed and disposed.

Containment booms can be located in a receiving water 

downstream of one or more CSO outfalls. The booms 

are fl oatation structures with a suspended curtain 

that captures buoyant materials. Booms are typically 

anchored to the shoreline and bottom of the waterbody. 

They may also be designed to absorb oils and grease. 

The size of the boom is determined by the volume of 

fl oatables expected from a design storm event. After 

a storm, fl oatables and other debris trapped by the 

boom will need to be removed with a vacuum truck, 

manually, or using a skimmer vessel (EPA 1999a).

Skimmer vessels are boats designed to gather 

fl oatables in lakes, harbors, or bays, and can be used in 

conjunction with containment booms. Skimmer vessels 

capture fl oatables using either a capture plate located at 

the bow of the boat that collects debris on a conveyor 

Figure 2. Baffle placement at a CSO regulator.

Baffle

Regulating

weir

Discharge
Treatment Technologies: Floatables Control

TMT-35

belt system or by lowering large nets into the water. 

Skimmer vessels may require companion equipment to 

transport the debris for land disposal.

Key Considerations

Applicability

Source Controls

Street sweeping can be performed on any paved surface 

and is often already part of a municipality’s standard 

activities. In colder climates, sweeping during the 

spring snow-melt reduces the road salt and sand load 

delivered to the CSS (EPA 2002). The optimal timing 

between street sweepings ranges from a few weeks to 

a month based on the amount of debris present on 

the street. The sediment removal effi ciency of street 

sweeping as a function of the time between sweeps is 

illustrated in Figure 3.

Catch basin modifi cations increase the capture of 

solids and fl oatables, which often necessitates more 

frequent maintenance. Without proper maintenance, 

catch basin performance can be compromised. The 

more solids and fl oatables that are collected and held 

in a catch basin, the less effective the basin becomes 

at trapping additional material. A catch basin fi lled 

with solids and fl oatables can have the unintended 

consequence of blocking the inlet to the sewer system. 

Catch basin cleaning frequencies vary greatly, with 

some municipalities performing maintenance annually 

and others scheduling catch basin cleaning once every 

fi ve to six years. Often, individual basins are cleaned 

as specifi c needs arise, such as citizen complaints 

of localized street fl ooding. In general, a cleaning 

frequency of at least twice per year maintains the 

effectiveness of catch basins for pollutant removals 

(Moffa 1997). Manual and vacuum cleaning are two 

methods available to remove accumulated debris from 

catch basins (EPA 1999b).

Collection System Controls

Screens can be used effectively for CSO control because 

they capture a signifi cant amount of the fl oatables 

contained in CSO discharges. Removal effi ciencies 

are tied closely to the spacing between bars or mesh 

aperture and can range from 25-90 percent of the 

total solids. The effectiveness of screening is reduced 

signifi cantly by the presence of oil and grease in the 

fl ow (EPA 1999a). Many screens are self-cleaning 

but regular maintenance is required to ensure their 

effectiveness. Finer screens have higher removal 

effi ciencies, but are more susceptible to clogging and 

tearing and may require maintenance after every 

CSO event. Additional information on fi ne screens is 

presented in the “Supplemental Treatment Technology 

Description” included in Appendix B of the Report to 

Congress on the Impacts and Control of Combined Sewer 

Overfl ows and Sanitary Sewer Overfl ows.

The design of existing regulators or storage facilities 

will determine the effectiveness of baffl es, as well as 

the cost to retrofi t the structure. In some retrofi ts, the 

addition of baffl es may restrict access to the regulators 

making maintenance more diffi cult. When a new 

structure is installed, baffl es can be included in the 

design. Maintenance requirements for baffl es are low 

compared to other fl oatables controls, requiring only 

occasional cleaning to remove debris and reduce odors.

In-line netting units are widely applicable and can 

be adapted to most CSSs (EPA 1999a). Access to insystem netting is important since the mesh bags must 

be inspected after each overfl ow event and changed 

when full. The frequency of bag changing depends on 

site-specifi c conditions, including the frequency and 

volume of CSO events and the volume of fl oatables 

in the discharges. Cities report changing the mesh 

bags between 12 to 36 times a year. Field tests indicate 

netting can provide removal effi ciencies of up to 90 

percent for fl oatables (EPA 1999a).

End-of-Pipe Controls

The nature of the receiving water infl uences the 

applicability of end-of-pipe controls. End-of-pipe 

netting systems are most suitable for lakes, estuaries, 

and tidal waters (EPA 1999a). Netting systems are 

sized based on the peak fl ow expected, the maximum 

fl ow velocity, and the quantity of fl oatables and other 

debris per million gallons of CSO. End-of-pipe netting 

systems require a minimum water depth of two feet and 

should not be located near heavily traveled waterways. 

As described in the discussion of in-line netting 

0%

20%

40%

60%

80%

0 10 20 30 40 50 60

Weeks Between Sweeping

Sediment Removal

Figure 3. Cumulative sediment removal by street sweeping.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-36

Category Technology Capital Cost Maintenance 

Requirements

Floatables Capture 

Efficiency

Source Controls Street Sweeping H1 M L

Catch Basin Modifications L M M

Collection System Controls Screens and Trash Racks M L M

Baffles M L M

In-System Netting M H H

End-of-Pipe Netting M H H

End-of-Pipe Controls Containment Booms H M H

Skimmer Vessels H1 M M

Table 1. Comparison of floatables control technologies.

1

 Assumes program would require vehicle/vessel purchase.

systems, end-of-pipe systems have relatively high 

maintenance requirements.

Site conditions, such as receiving water velocity, should 

be considered when evaluating containment boom 

design, placement, and anchoring. Although booms 

fl oat and can therefore accommodate some fl uctuation 

in water level, high river velocities and winds may 

dislodge them. Furthermore, booms cannot be used 

during winter months in waters that are subject to 

freezing. Maintenance requirements for containment 

booms are moderate relative to other fl oatables 

controls; fl oatables trapped behind booms will need to 

be removed periodically.

Skimmer vessels are used to clean broad areas of 

open water. As a result, the fl oatables and other debris 

collected are likely to come from a variety of sources 

including CSOs, separate storm water systems, and 

upstream sources. Ice and high wind can impede 

skimmer vessel navigation and the collection of 

fl oatables. It is also important to be aware of minimum 

depth and clearance height requirements specifi c to 

each vessel (EPA 1999a). 

All end-of-pipe systems can create temporary unsightly 

conditions near CSO outfalls, and therefore, may be 

inappropriate in areas with waterfront development. 

Cost

A summary of cost and maintenance considerations, as well 

as the relative capture efficiency, for each of the floatables 

control technologies is presented in Table 1. Representative 

costs from actual applications are presented in Table 2.
Treatment Technologies: Floatables Control

TMT-37

Category Technology Cost

Source Controls Street Sweeping Costs depend on frequency of cleaning, volume of litter, enforcement of 

parking regulations, and other labor costs.1

Contracted street sweeping costs $130-$150 per curb mile.2

Plymouth Township, MI, swept 511 miles of curb at a cost of $68 per 

mile.2

Vacuum sweeping trucks cost between $150,000-$200,000 depending 

on the material holding capacity. Maintenance costs range from 

$12,500-$15,000 per truck per year.1

Collection 

System Controls

Screens and Trash Racks Cost for screens depends on the size of the screen, the means of 

cleaning, construction materials, flow rate, and whether construction 

is new or a retrofit. Costs can range from $40,000 to $9 million per 

screen.4

Seattle, WA, installed 25 MGD rotary screen for approximately $1.7 

million.4

Baffles Steel or aluminum curtains are usually used for retrofits at an average 

cost of less than $10,000 each.3

Catch Basin Modifications Costs range from $65-$100 per basin.1

Trash buckets can cost an average of $100 per basin to install.3

Contracted catch basin cleaning costs range from $50-$170 per hour.3

In-Line Netting Netting system costs range from $75,000-$300,000 per site.5

Operations and maintenance (O&M) costs for changing full nets are 

$1,000 per site.3

End-of-Pipe 

Controls

End-of-Pipe Netting Netting system costs range from $25,000-$300,000 per site.5

Containment Booms Installation costs for booms range from $100,000-$150,000 per site.3

O&M costs for changing full nets are approximately $1,000 per site.3

Skimmer Vessels Skimmer vessels cost between $300,000-$700,00 depending on vessel 

features.3

O&M costs can range between $75,000-$125,000 per year per boat.3

A pier conveyor to remove debris from the vessel can cost $37,000.6

1

 EPA 1999b

2 Ferguson 1997

3

 EPA 1999a

4

 EPA 1999c

5

 EPA 1999d

6

 Shenman 2003

Table 2. Cost comparison of floatable control technologies.
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-38

Implementation Examples

The City of Portland Sweeping Program sweeping crews work fi ve nights a 

week from late March to the beginning of December. During the sweeping 

season, the crews routinely sweep a total of 480 curb miles. The city tries 

to sweep each street at least once a month and twice a month if the street 

is more heavily traffi cked. One section of town has daytime sweeping at 

the request of the area residents. A parking program is in effect in the 

downtown portion of the city and an odd/even parking program is used 

in residential areas. The sweepers are effective in removing debris from the streets of Portland. It is estimated that during the spring 

street cleaning, up to 9,000 tons of sand and salt are caught before entering the sewer system.

The sweeping fl eet consists of eight sweepers with an annual maintenance budget of $125,000. The total annual budget of the 

program is $412,000 or $51,500 per sweeper. 

More information at http://www.ci.portland.me.us/publicworks/street.htm

PORTLAND, ME Street Sweeping

Responsible Agency: City of Portland Public 

Works Department

Population Served: 190,000

Service Area: 17.7 sq. mi.

Sewer System: Not Available

New York City studied street sweeping extensively in the early 1990s, as 

part of a city-wide effort to reduce CSO discharges of fl oatable material 

to New York Harbor (NYCDEP 1995). The study found that the primary 

sources of fl oatables were trees, littering, and spilled trash receptacles. 

Most debris was found within 3.5 feet of the curb. As shown in the table 

below, plastics were the most prevalent fl oatable material by volume.

Enhanced mechanical sweeping 

within a 450-acre study area (increased from two times per week to six times per week) 

produced a 42 percent reduction in fl oatables on an item count basis, and a 54 percent 

reduction on a weight basis. Using a city-wide model, it was estimated that street sweeping 

twice per week would reduce fl oatables loadings to New York Harbor by 29 percent from 

current levels, and that increasing the frequency to three times per week would bring the total 

reduction in fl oatables to 49 percent. 

In addition to street sweeping, the city has implemented various other fl oatables control 

practices. The city also retrofi tted numerous catch basins with hoods. NYCDEP has installed 

23 containment booms near CSO outfalls. Once fl oatables are collected by the containment 

booms, they are removed using the city’s fl eet of skimmer vessels. The city operates four 

skimmers designed for smaller tributary streams and one designed for open water conditions. 

Some areas have also been equipped with end-of-pipe netting systems, including the Fresh 

Creek outfall, one of the city’s largest. Studies have shown that the Fresh Creek net has a 

capture effi ciency of 90-95 percent. 

Program costs include $6.5 million to purchase and engineer the containment booms/nets; $6.8 million to purchase and operate the 

skimmer vessels; and $6.7 million to purchase 41 catch basin cleaning trucks or $164,000 per truck.

More information at http://home.nyc.gov/html/dep/html/fl oat.html

NEW YORK CITY, NY City-Wide Floatables Study

Responsible Agency: New York City Department of 

Environmental Protection

Population Served: 7.6 million

Service Area: 297 sq. mi.

Sewer System: 4,200 mi. of combined sewer, 1,800 

mi. of sanitary sewer

Type of 

Material

Volume of 

Floatables (%)

Plastic 56

Glass 12

Metal 7

Styrene 7

Cloth 6

Paper 5

Wood 4

Misc 2

Rubber 1
Treatment Technologies: Floatables Control

TMT-39

In 1999, North Bergen installed numerous solids and fl oatables control 

technologies, including a mechanical screen bar, four in-system netting 

systems, and fi ve end-of-pipe netting systems. An Army surplus boom 

truck was purchased for net removal. A dump truck then transports 

the nets to the wastewater treatment plants, where the fl oatables are 

disposed of with the screenings taken from fl ows entering the plant. A 

portable vacuuming system is available to remove fi ne solids. 

Replacement of the nets depends on the physical characteristics of the CSS upstream of the netting system. The in-line nets in 

relatively fl at areas of the sewer system collect more silt and grit than those downstream of areas with steeper terrain. Changing the 

nets at a single location usually takes two hours, but can take up to four hours if the site must be vacuumed. The least active CSO 

facility is serviced four times a year, whereas the most active is serviced an average of once per month. A total of 90 tons of fl oatables 

were collected between 1999-2002.

The actual construction cost for the CSO facilities was $3.3 million. Supporting equipment such as the boom truck and vacuum unit 

cost $80,000; it is estimated that annual operation and maintenance costs are $57,373.

Contact: Frank Bruno, Maintenance Supervisor, City of North Bergen

NORTH BERGEN, NJ

Responsible Agency: North Bergen Municipal Utilities 

Authority

Population Served: 48,000

Service Area: 1.8 sq. mi.

Sewer System: Not Available

CSO Floatables Control Facilities

Baltimore’s Inner Harbor has become a symbol of success for waterfront 

revitalization efforts around the country. With more people visiting the harbor, 

it is important to remove the 

debris and trash discharged 

into the harbor from the 

city’s CSS and separate storm 

water systems. In 1988, the 

city purchased its fi rst skimmer vessel and currently maintains a fl eet of four boats. 

The original skimmers were made of machine steel, which have been refurbished 

using stainless steel because of the brackish nature of the harbor. The boats remove 

fl oatables, such as styrofoam cups and soda bottles, as well as large and unusual items, 

such as refrigerators. Once the fl oatables are collected, they are off loaded using a 

pier-conveyor into dumpsters for later disposal. Patrolling 25 miles of coastline, the 

skimmers collect approximately 394 tons of fl oatables per year. The city has seen marked improvement in the appearance of the water 

in Inner Harbor with the use of the skimmer vessels. Over the years, Baltimore has purchased skimmer vessels of varying capacity; costs 

for individual boats have ranged from $200,000 to over $500,000. 

Contact: Tom Finnerty, Manager, Marine Operations in Baltimore Department of Public Works

BALTIMORE, MD Keeping Inner Harbor Clean

Responsible Agency: Department of Public 

Works, Bureau of Water and Wastewater

Population Served: 1.8 million

Service Area: Not Available

Sewer System: 3,100 mi. of sewer

United Marine International, LLC
 Report to Congress on the Impacts and Control of CSOs and SSOs

TMT-40

References

EPA Office of Water. 1999a. Combined Sewer Overflow 

Technology Fact Sheet: Floatables Control. EPA 832-F-99-008.

EPA Office of Water. 1999b. Combined Sewer Overflow 

Management Fact Sheet: Pollution Prevention. EPA 832-F99-038.

EPA Office of Water. 1999c. Combined Sewer Overflow 

Technology Fact Sheet: Screens. EPA 832-F-99-040.

EPA Office of Water. 1999d. Combined Sewer Overflow 

Technology Fact Sheet: Netting System for Floatable Control. 

EPA 832-F-99-037.

EPA. 2002. “Pollution Prevention/Good Housekeeping for 

Municipal Operations: Parking Lot and Street Cleaning.” 

Retrieved December 9, 2002. http://cfpub.epa.gov/npdes/

stormwater/menuofbmps/poll_10.cfm

Ferguson, T. et al. 1997. “Rouge River National Wet Weather 

Demonstration Project: Cost Estimating Guidelines 

Best Management Practices and Engineering Controls.” 

December 9, 2002. 

http://www.rougeriver.com/pdfs/stormwater/sr10.pdf

Moffa, P.E. (Ed.). 1997. Control and Treatment of Combined 

Sewer Overflows. 2nd ed. New York, NY: Van Nostrand 

Reinhold.

New York City Department of Environmental Protection 

(NYCDEP). 1995. City-Wide Floatables Study. Prepared by 

HydrQual, Inc. Mahwah, NJ: NYCDEP.

Shenman, Lou, President - United Marine International 

(UMI). Interview by Limno-Tech, Inc., 2003. Washington, 

DC.

Water Environment Federation (WEF). 1999. Prevention 

and Control of Sewer System Overflows: Manual of Practice 

No. FD-17. Edited by Gray, W. et al. Alexandria, VA: WEF.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Porous Pavement

LOW IMPACT DEVELOPMENT

Overview

Porous pavement is an infiltration system where storm 

water runoff is infiltrated into the ground through a 

permeable layer of pavement or other stabilized permeable 

surface (EPA 1999a). Porous pavement is considered a low 

impact development (LID) control intended to replicate 

pre-existing hydrologic site conditions through application 

of innovative land planning and engineering design. The 

use of porous pavement reduces or eliminates impervious 

surfaces, thus reducing the volume of storm water runoff 

and peak discharge volume generated on a site. This 

curtailment in storm water generation can keep storm 

water from entering combined sewer systems and taking up 

valuable conveyance and storage capacity. This in turn can 

lead to reductions in the volume or frequency of CSOs or 

stormwater discharges. 

There are several types of porous pavement. Porous asphalt 

consists of an open-graded coarse aggregate that is bonded 

together by asphalt cement with enough interconnected 

voids and sufficient permeability to allow water to infiltrate 

through the medium and into the underlying soil quickly 

(EPA 1999b). 

Porous concrete consists of uniform, open-graded, 

coarse aggregate and a lower water-to-cement ratio, 

which produces a pebbled, open surface that is roller 

compacted. Similar to porous asphalt, porous cement has 

interconnected voids that increase its permeability. Porous 

pavers are pre-fabricated units, rather than a medium, that 

come in two general types: block pavers and grass pavers. 

Block pavers consist of interlocking paving materials where 

the void areas are filled with pervious materials such as 

sand or grass (GSMM 2001). Grass pavers are mats of high 

strength plastic grids (often made of recycled materials) 

that are filled with gravel. An engineered aggregate material 

or a sand and soil mixture is installed beneath the grid and 

gravel that allows grass to grow through the gravel to the 

surface (TBS 2002). The grids function as mini-holding 

ponds where storm water is collected and infiltrated into 

the ground. 

Installation techniques for porous pavement vary 

depending on the type of porous pavement utilized. As 

shown in Figure 1, a typical porous pavement system 

consists of the following layers: (1) porous pavement; 

(2) gravel or coarse sand; (3) filter fabric; (4) reservoir 

consisting of 1.5-3 inch diameter stones; (5) gravel or 

sand layer; (6) optional filter fabric; and (7) undisturbed 

existing soil (EPA 1999b). The water storage capacity of the 

stone reservoir beneath the pavement can vary. Perforated 

overflow pipes may be installed near the top of the reservoir 

to drain excess storm water when the reservoir is full. 

Key Considerations

Applicability

Porous pavement can be used in place of conventional 

impervious pavement under certain conditions. Typically, 

Parking lot with porous pavement (North Carolina State University).

Porous Pavement (0.5 - 4 ")

Gravel or Sand (6")

Stone Reservoir (min. 9")

(may include underdrain pipe)

Undisturbed existing soil

Filter fabric

Filter fabric

Not drawn to scale

Adapted from EPA 1999a

Gravel or Sand (6")

Figure 1. Porous pavement cross-section.
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-2

porous pavement is most suitable for areas with sufficient 

soil permeability and low traffic volume. Porous pavement 

is a useful option in urban areas where little pervious 

surface exists, provided that the grade, subsoil, drainage 

characteristics, and groundwater conditions are suitable 

(EPA 1999b). Common applications include: parking lots, 

shoulders of airport runways, residential driveways, street 

parking lanes, recreational trails, golf cart and pedestrian 

paths, and emergency vehicle and fire access lanes. Use of 

this technology may be more limited in arid regions with 

high wind erosion and cold regions where sand can clog 

pores and road salt can contaminate groundwater. Also, 

they should not be installed in areas that generate highly 

contaminated runoff such as commercial nurseries, auto 

salvage yards, fueling stations, marinas, outdoor loading 

and unloading facilities, and vehicle washing facilities as 

the contaminants could infiltrate into the groundwater 

(SMRC 2002). The success of porous pavement applications 

depends on several key design criteria including site 

conditions, construction materials, and installation 

methods. These criteria are further described in Table 1.

Advantages

The primary advantage of porous pavement is a reduction 

in the volume of storm water runoff generated on site. By 

reducing runoff, porous pavement can reduce the need 

for storm water holding systems; allow the use of smaller, 

less expensive storm water collection systems; reduce the 

need for curbs, gutters, and inlets; maximize waste water 

conveyance capacity in combined sewer systems; and reduce 

puddling and flooding. A secondary advantage of porous 

pavement is that it can remove both soluble and particulate 

pollutants such as total phosphorus, total nitrogen, and 

heavy metals via natural filtration through the underlying 

soil (GSMM 2001). By promoting pollutant treatment, 

porous pavements reduce the potential impact of storm 

water runoff on local receiving waters.

Disadvantages

A major disadvantage of porous pavement is its tendency 

to clog. This can occur as a result of improper design 

or construction, but it occurs most commonly from a 

lack of maintenance (WMI 1997). Proper maintenance 

includes periodic vacuum sweeping followed by highpressure hosing to remove sediment from the pores (EPA 

1999b). Once clogged, it is very difficult and expensive to 

rehabilitate porous pavement, often requiring complete 

replacement (EPA 1999a). Another disadvantage is the lack 

of expertise of pavement engineers and contractors with 

this technology. In addition, some building codes may not 

allow installation. Since not all soils are absorptive enough 

to provide proper drainage, selection of the technology 

must be based on site-specific considerations (TBS 2002). 

If the underlying soils are unable to dry out between storm 

events, anaerobic conditions may develop which can result 

in odors. 

 Design Criterion Guidelines

Site Evaluation • Take soil samples by boring to a depth of at least 4 feet below bottom of stone reservoir to check 

permeability, porosity, depth of seasonally high water table, and depth to bedrock

• Not recommended on slopes greater than 5% and best with slopes closer to 0%.

• Minimum depth to bedrock and seasonally high water table: 4 feet

• Minimum infiltration rate of 3 feet below bottom of stone reservoir: 0.5 inches per hour

• Minimum setback from water supply wells: 100 feet

• Minimum setback from building foundations: 10 feet downgradient, 100 feet upgradient

• Not recommended in areas where wind erosion supplies significant amounts of windblown 

sediment

• Drainage area should be less than 15 acres

Traffic Conditions • Use for low-volume automobile parking area and lightly used access roads

• Avoid moderate to high traffic areas and significant truck traffic

Design Storage Volume • Highly variable; depends upon regulatory requirements. Typically designed for storm water runoff 

volume produced in the drainage area by the 6-month, 24-hour storm event

Drainage Time for Design 

Storm

• Minimum: 12 hours

• Maximum: 72 hours

• Recommended: 24 hours

Construction • Excavate and grade with light equipment with tracks or oversized tires to prevent soil compaction

Pretreatment • Pretreatment, such as bioretention or vegetative swales, recommended for runoff with high levels of 

suspended solids

Table 1. Design criteria for porous pavement (EPA 1999b).
Low Impact Development: Porous Pavement

LID-3

Cost

Porous pavement can initially cost more than traditional 

pavement. The overall cost-effectiveness varies depending 

on the site conditions, design requirements, and local 

installation and long-term maintenance costs. For porous 

asphalt and cement, the raw materials are the same as those 

utilized in conventional paving operations, but contractors 

may charge higher prices for jobs that involve unfamiliar 

formulas or techniques. For porous pavers, the cost can vary 

depending on the type utilized. Both grass pavers and block 

pavers require a high level of construction workmanship 

and expertise to ensure proper installation (GSMM 2001). 

The range of costs estimated for basic installation of porous 

pavement is summarized in Table 2.

Estimated cost for an average annual maintenance program 

for a porous pavement parking lot is approximately $200 per 

acre per year (EPA 1999b). This cost estimate assumes four 

inspections each year with appropriate vacuum sweeping 

and jet hosing. Savings from reduced investments in storm 

sewer extensions and costs associated with storm drain 

systems (i.e. repair and maintenance) have the potential to 

offset the initial costs. 

Paver System Cost (Sq. Ft) Life Span1

Traditional & Porous Asphalt $0.50 to $1.00 20 yrs

Traditional & Porous Concrete $2.00 to $6.50 20 yrs

Grass Pavers $1.50 to $5.75 ~20 yrs

Block Pavers $5.00 to $10.00 ~20 yrs

1Actual values may vary as life span is site specifi c and maintenance 

dependent

Table 2. Estimated costs for installation.

Implementation Examples

The University of Washington Center for Urban Water Resources untertook a 

pilot test of porous pavement in the King County Department of Public Works 

building parking lot in Renton, WA. Four types of porous pavement were 

installed in sections of the lot: (1) grass pavers with virtually no impervious 

surface, (2) plastic grid pavers with grass and gravel in-filling with 60 percent impervious surface, (3) concrete pavers with grass infilling with 60 percent impervious surface, and (4) concrete block pavers with 90 percent 

impervious surface. There were sections of the parking lot that were unmodified and thus left 

as impervious surfaces (asphalt). Runoff volumes from the porous and impervious sections 

were monitored during several storm events in 1996 and in a follow-up evaluation in 2002. 

Monitoring during the 1996 study and the 2002 follow-up study showed that the impervious 

asphalt surface generated a significant amount of runoff for the majority of precipitation 

events. Whereas, minimal storm runoff was generated on the porous pavers as virtually all 

precipitation from the observed storms was infiltrated. Therefore, replacing asphalt with 

pervious pavement would decrease surface runoff and attenuate peak discharges. The 

study found no significant differences in the performance of different types of pavers. The 

follow-up study in 2002 demonstrated that the porous pavement systems were structurally functional after six years of daily use. The 

concrete pavers and block pavers were found to be particularly robust, while the grass and gravel pavers did undergo some minor wear.

Contact: Derek B. Booth, Center for Urban Water Resources Management, University of Washington

Responsible Agency: University of 

Washington Center for Urban Water Resources

RENTON, WA Porous Pavers Pilot Test

Photo: University of Washington
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-4

A porous pavement parking lot was designed as a demonstration project,

monitoring the amount of storm water runoff controlled by both block pavers

and grass pavers. The parking lot was 9,340 square ft and was considered an ideal candidate because it was not a high traffi c area, the

in situ soil had suffi cient capacity, and there was no indication of a seasonally high water table within fi ve feet of the surface. Modular

and grass pavers were installed in separate areas of the lot, and runoff volumes were monitored from June 1999 through July 2001.

Monitoring results indicated that runoff from the concrete paver parking lot occurred only 11 

out of the 48 wet weather events recorded (less than 25 percent of total storms during study 

period). In addition, rational method runoff coeffi cients for the permeable pavement used in 

this study were calculated. Rational method runoff coeffi cients (0-1.0) are a way of describing 

the amount of runoff generated during a wet weather event; a coeffi cient of 0 refl ects 

maximum rainfall infi ltration, whereas a coeffi cient of 1.0 refl ects maximum runoff generation. 

The estimated runoff coeffi cient for the permeable pavement in this study ranged from 0.1-

0.48, depending on method used and amount of precipitation recorded. The project cost was 

estimated to be 25 percent more than the cost of building a conventional asphalt parking lot.

Contact: Bill Hunt, North Carolina State University

KINSTON, NC

Responsible Agency: NC State University

Parking Lot Demonstration Project

Photo: North Carolina State University

The 11.25 acre parking lot at the Florida Aquarium in Tampa, FL, was modifi ed 

for a study that compared storm water runoff reduction rates from several 

different porous pavement applications including swales, asphalt pavement 

with swales, asphalt pavement without swales, and cement pavement with swales. Swales, which are areas of vegetation, were 

placed between the rows of parking stalls without reducing the total number of stalls. Results showed that for all rainfall events 

that produced fl ow, the basin with pervious paving and a swale reduced runoff by over 60 percent compared to asphalt pavement 

with no swale. Also, the area with porous pavement reduced the average amount of runoff by 41 percent compared to the other 

areas with swales and impervious pavement. Porous pavement was found to be more effective for small storms; for rainfall events

less than 0.8 inch, the area with porous pavement and a swale had 80-90 percent less runoff than the asphalt pavement without a

swale.

Contact: Betty Rushton, Southwest Florida Water Management District

Responsible Agency: Florida Aquarium

TAMPA, FL Florida Aquarium Storm Water Study
Low Impact Development: Porous Pavement

LID-5

References

Booth, D. B. and J. Leavitt, 1999. “Field Evaluation 

of Permeable Pavement Systems for Improved Storm 

Water Management”. Journal of the American Planning 

Association. 65:314-325.

Booth, D.B. and Ben Brattebo, 2002. “Permeable Parking 

Lot Demonstration Project–The Six-Year Follow-Up”. Draft 

submitted to Water Research.

EPA Offi ce of Water. 2000. Low Impact Development (LID) 

A Literature Review. EPA-841-B-00-005.

EPA Offi ce of Water. 1999a. Preliminary Date Summary of 

Urban Storm Water Best Management Practices. EPA-821-

R-99-012.

EPA Offi ce of Water. 1999b. Storm Water Technology Fact 

Sheet Porous Pavement. EPA 832-F-99-023. 

Georgia Storm Water Management Manual 

(GSMM)(Volume 2). 2001. 

http://www.georgiastormwater.com

Low Impact Development Center. “Permeable Paver Costs.” 

Retrieved October 25, 2002. http://www.lid-stormwater.net/

permeable_pavers/permpaver_costs.htm

Storm Water Manager’s Resource Center (SMRC). “Storm 

Water Management Fact Sheet: Porous Pavement.” October 

25, 2002. 

http://www.stormwatercenter.net

Tool Base Services (TBS). “Permeable Pavements” Retrieved 

October 25, 2002. 

http://www.toolbase.org/tertiaryT.asp?TrackID=&CategoryI

D=38&DocumentID=2160

Watershed Management Institute (WMI), 1997. 

Operation, Maintenance, and Management of Storm Water 

Management Systems. Ingleside, MD.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Green Roofs

LOW IMPACT DEVELOPMENT

Overview

A green roof is a type of low impact development (LID) 

control that uses soil and plant growth for the purpose of 

rooftop runoff management. The rooftop vegetation and 

underlying soil serve to intercept storm water, delay runoff 

peaks, and reduce runoff discharge rates and volume. This 

can lead to reductions in the volume or occurrence of 

CSOs. A green roof is intended to minimize the impact 

of development on hydrologic site conditions through 

application of innovative building and engineering design. 

Green roof technology has been used in Europe for over 

25 years and is gaining increased recognition in the United 

States. As shown in Figure 1, the series of engineered layers 

that make up a green roof, from bottom to top, typically 

include (GBS 2002): 

● Waterproof membrane to protect the roof deck

● Root barrier to prevent roots from penetrating the 

waterproof membrane ● Optional insulation

● Drainage layer to direct excess water from the roof

● Filter fabric to keep fine soil from clogging the layers 

below

● Engineered soil substrate or growing medium

● Vegetation

There are two basic types of green roofs: intensive and 

extensive (Peck and Kuhn 2002). Factors to consider when 

choosing which type of green roof to install include: 

location, structural capacity of the building, budget, 

material availability, and client and/or tenant needs. 

Intensive Green Roofs

Intensive green roofs, more commonly known 

as conventional roof gardens, can be landscaped 

environments developed for aesthetics and recreational 

uses. The landscaped roofs are likely to include gardenvariety and food producing plants requiring high levels 

of management, though the degree of maintenance 

can be reduced by using tolerant plants that would 

deal well with the micro-climate of the particular 

roof (Beckman et al 1997). As ten inches or more of 

soil depth is necessary for growing larger trees and 

shrubs, intensive green roofs can add as much as 80-

150 pounds per square foot of load to the underlying 

structure (Sholz-Barth 2002) and often require an 

irrigation and drainage system. Food-producing plants 

are usually planted in containers rather than directly 

onto the rooftop. Intensive roofs are usually installed 

on fl at roofs.

Extensive Green Roofs

In contrast to intensive green roofs, extensive green 

roofs (also called eco-roofs) are primarily utilized for 

their environmental benefi ts (Beckman 1997). This 

type of roof is composed of a continuous thin growing 

medium which sustains low-maintenance vegetation 

tolerant of local climatological conditions. Extensive 

roofs require little maintenance after the vegetation 

is established, typically within the fi rst year or two 

after installation, and irrigation systems are generally 

Figure 1. Typical layers of a green roof.

Waterproof

membrane

Root barrier

Insulation

Drainage system

Filter fabric

Soil medium

Vegetation

Roof surface

Green roof in Chicago (City of Chicago).
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-8

unnecessary. Suitable for large roofs, vegetated cover 

will extend across the entire roof and should only 

be accessed to perform periodic maintenance. The 

extensive green roof can be more readily retrofi tted 

to an existing structure due to smaller loads, typically 

ranging between 15-50 pounds per square foot 

(Sholz-Barth 2001). In addition, extensive roofs can be 

installed on roofs with slopes up to about 25 percent 

(MUSS Manual 2001).

Design considerations for waterproofi ng, drainage, 

and soil type are important in any type of green roof. 

Common waterproofi ng options are rubber, modifi ed 

bituminous membrane, polyvinyl chloride (PVC), 

rubberized asphalt, thermal polyolefi ns (TPO), and 

coal tar pitch (GBS 2002; Miller 2002). The two 

most common waterproofi ng materials are PVC and 

modifi ed bituminous membranes (Miller 2002). To 

discourage roots from penetrating the waterproofi ng 

in intensive roof systems, a physical or chemical root 

barrier is usually installed over the protective layer. 

The key to moisture management and drainage is the 

use of absorptive growth media (Miller 2002). There 

are various drainage materials that can be used for 

moisture management including a synthetic sheet such 

as polystyrene or a granular drainage media. Depth 

of the drainage layer varies, depending on the level of 

runoff management desired and roof loading capacity. 

A geosynthetic fi lter mat is usually placed between 

the soil and drainage material to prevent the drainage 

system from becoming clogged with fi ne particles 

from the soil. Soils used for vegetated roofs are lighter 

in weight than typical soil mixes; they are usually 75 

percent mineral aggregate and 25 percent organic 

material (MUSS Manual 2001). 

Key Considerations

Applicability

Green roofs can be incorporated into new building design 

or retrofitted to existing buildings. Green roofs can be fitted 

to commercial buildings, multi-family homes, industrial 

structures, as well as single-family homes and garages. 

Depending on whether the system is intensive or extensive, 

green roofs can be installed on either flat or sloping roofs. 

Newly developed synthetic drainage materials have made 

green roofs feasible to install on most conventional flat 

roofs. The appropriate choice of vegetation is determined 

by substrate type, soil thickness, regional climate, and 

expected precipitation. Intensive and extensive green roofs 

have been successfully installed in cities with varying 

climatic conditions across the United States. Some factors 

that must be considered are the load-bearing capacity of the 

roof deck, the moisture and root penetration resistance of 

the roof membrane, roof slope and shape, hydraulics, and 

wind shear. In regions of the country where snow is part 

of the expected annual precipitation, the maximum roof 

design loads must incorporate expected snow accumulation 

and drifting patterns. 

Green roofs can be an important tool to reduce storm 

water runoff and subsequent CSOs in areas with dense 

development. Heavy development in urbanized areas may 

preclude the use of other space-intensive storm water 

management practices such as storm water management 

detention ponds and large infiltration systems. In these 

situations, green roofs may be a cost-effective technique 

for reducing storm water volumes. They can also be a 

component of an integrated runoff management program 

using a combination of low impact development practices. 

Advantages

In a green roof system, storm water is released slowly over a 

period of several days rather than discharging immediately 

into a sewer system (Beckman et al 1997). Studies show 

that both extensive and intensive green roofs can absorb 

as much as 75 percent of the precipitation during a typical 

rainfall event (Sholz-Barth 2001), while runoff from low 

volume storms may be eliminated entirely. The choice of 

soil substrates and vegetation will determine the storm 

water retention capacity of the roof. When fully saturated, 

storm water runoff is filtered through the vegetative layer 

to a drainage outlet. The following formula estimates the 

potential gallons of precipitation captured based on acres 

of green roof area and average annual rainfall (City of 

Portland 2002):

[(Acres of Green Roof) x (43,560 foot2/acre) x (144 inch2/foot)2 / 

(231 inch3/gallon)] x (60 % of Annual Rainfall in Inches) 

= Gallons Rainfall Captured

The gallons of runoff potentially captured by green roofs 

in various cities can be calculated based on annual rainfall 

statistics and assuming 100 acres of vegetated roof cover. 

Table 1 shows hypothetical results for green roofs in 

Atlanta, GA; Chicago, IL; Philadelphia, PA; and Portland, 

OR. These results will vary depending on rainfall patterns 

and whether the rainfall was preceded by a dry period, 

which affects absorption. 

An additional benefit to green roofs is they can filter airborne pollutants that are deposited via precipitation on 

the roof (i.e., nitrogen and particulate matter). They can 

also help counteract the “urban heat island effect,” created 

when the natural environment is replaced by pavement 
Low Impact Development: Green Roofs

LID-9

and buildings; green roofs provide a cooling effect as 

the plants’ foliage evaporate moisture via the process of 

evapotranspiration. In addition, green roofs can help 

City

Avg. Annual 

Rainfall (Inches)

Potential Gallons 

Captured (Millions)

Atlanta, GA 48 78

Chicago, IL 35 57

Philadelphia, PA 45 73

Portland, OR 37 60

reduce the roof temperature and insulate the building, as 

well as have aesthetic benefits. Vegetated covers can prolong 

the life of a roof by providing ultraviolet protection and 

reducing impacts resulting from extreme temperature 

fluctuations and high winds. The typical life-span of a 

green roof is about 40 years, significantly longer than 

a conventional roof. When used as accessible park-like 

building amenities, roof gardens can provide substantial 

aesthetic benefits. Where self-sufficient native vegetation 

tolerant of natural elements is used in green roofs, minimal 

maintenance is required. 

Disadvantages

Potential disadvantages of green roofs include the difficulty 

of repairing possible leaks that are buried under the plant 

and soil substrate layers; additional structural support load 

requirements for substrate and vegetation layers; and cost 

considerations due to increased initial capital outlay. Roof 

slope can be a limiting factor as horizontal roofs will require 

a system that drains excess water from the root zones, while 

sloped roofs may need erosion control measures. Also, 

maintenance costs may exceed those of a conventional roof. 

Buildings that are retrofitted with green roof covers are likely 

to incur more costs than a building that incorporates green 

roofs in its construction. For example, a building may need 

upgraded structural support for the added weight of the 

green roof. 

Cost

The average cost of a green roof is estimated at $10-$25 per 

square foot compared to conventional roofs that cost $3-$20 

per square foot (LIDC 2002; City of Portland 2002). Factors 

influencing cost include: the size of the installation; design 

complexity; local expertise and suppliers; type and depth of 

growing medium; selected vegetation and planting methods 

(seed, plug, or pot); and irrigation requirements.

Costs associated with intensive vegetated roofs tend to 

be higher compared to extensive roofs due to increased 

development and maintenance needs including more 

water, fertilizer, weeding, and clipping (Beckman et al

1997). Although green roofs may initially cost more than 

conventional roofs, the increase in membrane life-span 

and the decreased frequency of replacement make the 

green roof a cost-effective choice (City of Portland 2002). 

Costs of green roof installation may decrease with further 

development of the green roof market in the United States. 

In Europe, costs are typically one-fourth of those in the 

United States due to a more established green roof market. 

Table 1. Hypothetical gallons of storm water captured, 

 assuming 100-acres of green roof cover.
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-10

A green roof demonstration 

project was installed at the 

Fencing Academy of Philadelphia. 

Like many urban areas on the east coast, 90 percent of all rainfall in Philadelphia occurs 

during storms with 24-hour volumes of two inches or less. The 3,000 square foot extensive 

green roof was installed on the existing roof with the goal of replicating natural processes 

in detaining and treating a rainfall volume. The green roof was designed to reduce the 

peak runoff rate of a standard two year, 24-hour design storm. The overall depth of the 

green roof is three inches, featuring a synthetic 

under-drain layer; thin and lightweight growth 

media; and, vegetation selected for their hardiness and 

tolerance of the local climate. Perennial Sedum varieties create a meadow-like setting and 

require no irrigation or regular maintenance. The green roof weighs less than five pounds 

per square foot when dry, and approximately 17 pounds per square foot when saturated. 

The light weight allows installation on the existing conventional roof without the need for 

structural adjustments. The saturated infiltration capacity is 3.5 inches per hour. A pilot-scale 

test monitoring rainfall and runoff found that the green roof was able to detain 65% of the 

rainfall over a nine-month period. Runoff was negligible for storm events with less than 0.6 

inch of rainfall. Based on typical costs of green roofs, the cost of the green roof at the Fencing 

Academy is estimated at $18,000 or $6/sq. ft. 

Contact: Charlie Miller, Roofscapes, Inc.

PHILADELPHIA, PA Green Roof Demonstration Project

Responsible Agency: Fencing Academy of 

Philadelphia

Photo: Roofscapes, Inc.

Photo: Roofscapes, Inc.

The Housing Authority of Portland, in cooperation with the City of Portland’s 

Bureau of Environmental Services (BES), installed an 8,500 square foot 

extensive green roof atop the 10-story Hamilton Apartment building. The 

type of vegetation used is hardy plants species such as Sedum, native wild 

flowers, and grasses. The Hamilton Apartment green roof system covers 60 

percent of the total roof surface area and is comprised of two plots: the first is two inches thick and another is four inches thick. 

Storm events and runoff volumes are being monitored. During August 2001, a storm event was monitored for 9.5 hours by the 

BES. From a total measured rainfall of 1,485 gallons, 890 gallons ran off the two-inch 

plot and only 80 gallons ran off the four-inch plot. These runoff measurements do not 

take into consideration runoff generated from the remaining impervious areas of the 

roof (areas without green roof cover) that may be flowing into the green roof plots 

or directly into the drainage system. The estimated cost for the project was $70,200.

The City of Portland acknowledges green roofs can play an important role in 

storm water management and have included them in their “Clean River Incentive 

and Discount Program,” which is still under development. This program will offer 

incentives and discounts to commercial, industrial, institutional, and residential 

properties implementing storm water mitigation measures such as green roofs.

Contact: Tom Liptan, City of Portland Storm Water Specialist

Green Roof Demonstration Project

Responsible Agency: City of Portland 

Housing Authority and Portland Bureau 

of Environmental Services 

Photo: City of Portland Housing Authority

PORTLAND, OR

Implementation Examples
Low Impact Development: Green Roofs

LID-11

References

Beckman, S.; Jones, S.; Liburdy, K.; and Peters, C., Greening 

Our Cities: An Analysis of the Benefits and Barriers 

Associated with Green Roofs. Planning Workshop at Portland 

State University, 1997. 

http://www.greenroofs.com/Ecotrust%20Article.pdfhttp:

//www.lsdg.net/EcoRoofs.pdf

City of Chicago. “The components and design report of 

City Hall’s Rooftop Garden.” Retrieved December 2002. 

http://www.ci.chi.il.us/Environment/rooftopgarden/

designpage.html

City of Portland. “Ecoroof: Question and Answers” 

Retrieved December 2002.

http://www.cleanrivers-pdx.org/pdf/eco_questions.pdf

Green Building Services (GBS). “Green Rooftop 

Technology.” Retrieved November 2002.

http://www.greenbuildingservices.com/green_resources/

pdfs/ecoroofs.pdf

Low Impact Development Center (LIDC). “General 

Information on Green Roofs.” Retrieved November 2002.

http://www.lid-stormwater.net/intro/

sitemap.htm#greenroofs

Miller, Charlie. Interviewed by Limno-Tech, Inc. 2002. 

Minnesota Urban Small Sites (MUSS). 2001. BMP Manual: 

Storm Water Best Management Practices for Cold Climates.

Prepared for the Metropolitan Council Environmental 

Services by Barr Engineering Company.

Peck, Steven and Monica Kuhn. “Design Guidelines for 

Green Roofs.” Retrieved October 18, 2002.

http://www.cmhc-schl.gc.ca/en/imquaf/

himu/loader.cfm?url=/commonspot/security/

getfile.cfm&PageID=32570

Sholz-Barth, Katrin. 2001. “Green Roofs: Stormwater 

Management from the Top Down.” Environmental Design & 

Construction Magazine. Jan-Feb. 2001:1-11.

Twelve stories above ground, the demonstration green roof on Chicago’s City 

Hall covers 20,300 of the 38,800 square foot roof surface area (one square city 

block). This roof was retrofitted as part of an urban heat island effect study initiated by EPA (City of 

Chicago 2002). The thickness of this green roof ranges from a 2.4 to 3.4-inches deep. Based on the 

structural capacity of the roof, it was determined that the roof could support an extensive system 

overall with intensive localized systems over the support columns. Given constraints such as snow load, 

the structural capacity for the roof was determined at an average of 30 pounds per square foot. The 

precipitation storage capacity was an average of one inch of rain. About 20,000 plants were used for the 

green roof, including those native to the Chicago region and tolerant of dry soil and sunny conditions. 

A drip-irrigation system, partially served by roof runoff collected in storage tanks, was installed as a 

supplemental water source for the plants during roof establishment and dry periods. Monitoring plant 

survival and environmental benefits related to energy and “urban heat island effect” is in process. Due 

to the expense of installing flow meters, storm water runoff is not being monitored at this site. The 

vegetated cover cost was $500,000 of the entire re-roofing project cost, which totaled $1.5 million.

Contact: Mark Farina, City of Chicago

Responsible Agency: City of Chicago

CHICAGO, IL City Hall Green Roof

Photo: City of Chicago

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.

TECHNOLOGY DESCRIPTION

Bioretention

LOW IMPACT DEVELOPMENT

Overview

Bioretention is a soil and plant-based storm water 

management practice used to filter and infiltrate runoff 

from impervious areas such as streets, parking lots, and 

rooftops. Essentially, bioretention systems are engineered 

plant-based filters designed to mimic the infiltrative 

properties of naturally vegetated areas, which in turn can 

reduce the volume and frequency of CSOs. Bioretention is 

considered a low impact development (LID) practice and 

was developed in the early 1990s. 

One of the unique qualities of bioretention is the flexibility 

of design themes. Bioretention systems can range in 

complexity depending on available funding, volume of 

runoff to be controlled, available land area, and the desired 

level of treatment. Bioretention systems can be used as a 

stand-alone practice (off-line) or connected to a storm 

drainage system (on-line). It is important to note that 

changes and improvements to a bioretention system design 

are continually being made as use of the practice becomes 

more developed. 

On-line Bioretention System

A typical on-line bioretention system, as shown in 

Figure 1, includes components designed to capture, 

temporarily store, infi ltrate, and treat storm water 

runoff. A graded surface conveys the runoff from 

impervious areas (i.e. roofs, driveways, parking lots) 

toward an optional grass buffer or swale. The grass 

buffer pretreats the runoff by reducing the runoff 

velocity, fi ltering particulates, and evenly distributing 

the incoming runoff. The rain garden, the main 

treatment component of an on-line bioretention 

system, is located in a depressed area that allows the 

runoff to pond and infi ltrate, as well as evaporate from 

the surface. The rain garden is usually designed to 

hold up to six inches of standing water for one or two 

days, and consists of a mix of woody and herbaceous 

species planted in a soil mixture designed to optimize 

percolation and pollutant removal. The best type of 

vegetation is native plant species that are tolerant of 

both wet and dry conditions. The planting soil should 

be two to four feet deep topped with an organic layer. 

This confi guration allows the rain garden to maximize 

biological activity and enhance root growth. Factors 

affecting depth of the system include size of plants 

and depth to groundwater. Under the planting soil 

layer is a gravel layer that blankets an underdrain and 

serves to increase porosity of the system (Figure 1). 

The underdrain, a perforated pipe that collects and 

carries the runoff to the storm water system, ensures 

proper drainage for the plants and proper infi ltration 

rates. Earlier bioretention system designs included a 

fi lter fabric between the soil and gravel layers, however 

this was found to cause premature clogging that led to 

infi ltration problems. Replacing the fi lter fabric with 

a pea gravel diaphragm is an option. For storm fl ows 

exceeding the system’s storage capacity, the excess 

Planting Soil

Gravel

Blanket

Underdrain

Organic

Layer

Pavement Ponding Zone

(0.5')

Filtration Zone

(2'-4')

Recharge Zone

(1')

Runoff Berm

Adapted from PGC 2002

Figure 1. Cross-section of an on-line bioretention system.

Parking lot utilizing bioretention (Prince George’s County).
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-14

runoff is allowed to fl ow over a grassy berm swale into 

an inlet pipe connected to the storm drain system. 

Other system designs allow the treated storm water to 

percolate back into the groundwater.

Off-line Bioretention Systems

Off-line bioretention systems possess similar general 

features to on-line systems, but are more simplistic 

and tend to be smaller in scale. One common design is 

where the bioretention areas (i.e. fl ower beds or other 

landscaping) are depressed so ponding and infi ltration 

of storm water runoff can occur. Such designs do not 

include underdrains. Excess runoff overfl ows onto the 

adjacent surface areas. Another design is a bioretention 

“trap area” used in tree box areas, behind curbing, 

sidewalks, and pathways. With this technique, the paved 

surface is graded toward the adjoining grass areas to 

intercept runoff as it fl ows towards a drain or gutter 

(PGC 2002). Bioretention trap areas are common in 

urban areas with limited open space and high fl ow 

rates. In turn, tree boxes can be designed to serve as 

localized bioretention systems. This is done by creating 

a shallow ponding storage area by “dishing” mulch 

around the base of the tree or shrub (Figure 2).

Successful bioretention systems may also include soil 

amendments, which aim to improve health of the soil 

and its environmental functions. As a result of urban 

development, soils become compacted, which reduces 

soil porosity and ability to absorb water (ODEQ 2001). 

One type of soil amendment that can improve runoff 

absorption and treatment is the addition of compost. 

According to the Natural Resources Conservation 

Services (NRCS) hydrologic soils classifi cation, 

compacted urban soils are classifi ed under Group D 

due to their limited ability to infi ltrate runoff. Compost 

amendments can upgrade the compacted urban soils 

to Group B, soil with moderate infi ltration rates, by 

increasing soil porosity (AACED 2002; City of Portland 

2002). The soil is amended by spreading a layer of 

compost on the surface and tilling both the soil and 

compost to a total depth of 12 inches. The general soil 

to compost ratio rule is 2:1 by unit volume (ODEQ 

2001). 

Key Considerations

Applicability

Both on-line and off-line bioretention can be utilized in 

new developments or be retrofitted into developed areas. 

However, there is much more latitude to incorporate 

bioretention practices in new developments because there 

are fewer constraints regarding siting and sizing. In fact, 

good planning and design may result in an integrated sitewide bioretention system that decreases both initial project 

costs and long-term maintenance expenses. Bioretention 

practices are applicable in heavily urbanized areas such 

as commercial, residential, and industrial developments. 

For example, bioretention can be used as a storm water 

management technique in median strips, parking lots 

with or without curbs, traffic islands, sidewalks, and other 

impervious areas (EPA 1999). 

The effectiveness of a bioretention system is a function of 

its infiltration and treatment ability and so the system must 

be sized to match the expected runoff. Miscalculating the 

capacity limits in the system design can lead to erosion and 

stabilization issues, particularly for on-line systems. The 

following criteria can be used to determine the suitability of 

bioretention:

● Drainage area - 0.25 to one acre per bioretention 

system (multiple systems may be required for larger 

areas); ● Space required - Approximately five percent of the 

impervious area that will contribute runoff; and

● Minimum depth to water table - No less than two feet 

between ground surface and seasonally high water 

table.

Typical maintenance activities for any bioretention system 

are re-mulching void areas; treating, removing, and 

replacing dead or diseased vegetation; watering plants until 

they are established; soil inspection and repair; and litter 

and debris removal.

Planting Soil

Mulch Grassy or Paved Area

Adapted from PGC 2002

Figure 2. Schematic diagram of a tree-pit, which is a type of 

 off-line bioretention system
Low Impact Development Technology: Bioretention

LID-15

Advantages

Bioretention reduces storm water runoff and can 

consequently help reduce the size and cost of storm water 

control facilities, and the volume and frequency of CSOs. 

Bioretention can be an effective LID retrofit, especially 

in urban areas with minimal open space and extensive 

impervious area. Bioretention systems have also shown 

promise in the removal of pollutants via physical and 

biological processes of adsorption, filtration, plant uptake, 

microbial activity, decomposition, sedimentation, and 

volatilization (EPA 1999). Types of pollutants removed 

include metals, phosphorus, hydrocarbons, suspended 

solids, nitrogen, organic matter, and oils (EPA 1999). Also, 

bioretention systems can reduce on-site flooding, improve 

groundwater recharge, help maintain stream baseflows, 

provide habitat, and have aesthetic value. On-line systems 

are most cost-effective when incorporated into the initial 

design or into the repair/reconstruction process of an area 

(i.e. parking lots). Off-line bioretention systems are costeffective as retrofits in urban areas as they require little space 

and can be incorporated into existing urban landscapes.

Disadvantages

Functional problems of bioretention systems may arise 

such as clogging of the ponding area with sediment over 

time. Thus, pretreatment and regular maintenance are 

necessary components to the overall implementation. In 

many cases, maintenance tasks can be completed by a 

landscaping contractor. Systems with compost amendments 

require regular replacement of the compost. Additional soil 

amendments, such as lime or gypsum, may also be necessary 

to replenish nutritional deficiencies and correct unsuitable 

alkalinity levels (Chollak and Rosenfeld 1998). 

Cost

The cost of a residential off-line bioretention system 

averages about $3-$4 per square foot, depending on the 

soil conditions and the density and types of plants used, 

whereas the cost of commercial, industrial, and institutional 

applications of bioretention systems range between $10-$40 

per square foot, based on the need for control structures, 

curbing, storm drains, and underdrains (LID 2003). 

Landscaping costs required regardless of bioretention 

installation should be subtracted when determining the net 

cost of the bioretention system. As the size of bioretention 

systems can vary, so can the associated installation costs. 

In addition, in residential areas, storm water management 

controls become a part of each property owner’s landscape, 

reducing the public burden to maintain large centralized 

facilities (LID 2003).

Retrofitting a site may entail additional costs (EPA 1999). 

The higher cost of a retrofit is attributed to the demolition 

of existing concrete, asphalt, and other structures and 

replacing fill material with planting soil. The costs of soil 

amendments are site specific as well. For a shallow (up to an 

8-inch depth) compost amendment that incorporates in-site 

soil in a small area, the estimated cost is $1-$3 per square 

foot (LID 2002). 

Bioretention has the potential for cost savings compared 

to other types of storm water drainage techniques, such 

as curbs and gutters. The operation and maintenance 

costs for a bioretention facility are comparable to that of 

typical landscaping. Additional costs beyond the normal 

landscaping fees will be site specific, but can include soil 

testing, planting soil installation, and soil amendment 

components.
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-16

The City of Maplewood launched a storm water management project that 

implemented rain gardens instead of traditional curb and gutter systems 

in three neighborhoods. This decision was prompted by a combination of positive results of previously completed rain garden pilot 

projects, the need for road upgrades, and existing drainage problems in several neighborhoods. Considering bioretention as an 

environmentally friendly and aesthetically pleasing alternative, the city decided to focus on demonstration, education, and outreach 

to convey the benefits of using rain gardens for runoff management. Each bioretention system incorporated rain gardens and grass 

swales to collect runoff from streets and yards with a holding capacity of 0.5 inch of rain (85 percent of the local rainfall occurs during 

storms totaling 0.5 inch or less) (NSN 2001). The utilization of rain gardens in the neighborhoods was on a voluntary basis. However, 

the city offered incentives providing homeowners with plants, landscape plans, educational materials, and demonstrations free of

charge. The three standard garden sizes offered were 12 foot by 24 foot, 10 foot by 20 foot, and 8 foot by 16 foot. At least 130 rain 

gardens are expected to be installed by the end of 2003. Within the project neighborhoods, the city is installing rain garden systems 

at schools, nature centers, and neighborhood parks. The city is providing necessary regrading or curb work to achieve the proper 

slope for each system. Volunteers for disabled or elderly residents wishing to participate in the program are being provided as well. 

Whether the residents utilize the gardens or not, all residents must pay an annual assessment to cover the costs of the projects.

This bioretention project costs 75-85 percent of the cost of traditional curb and gutter systems (NSN 2001). Each garden costs $600-

$700 including excavation, rock infiltration sump, scarifying of the soils, bedding material, shredded wood mulch, and vegetation. 

Costs were kept low by recycling and using street material in lieu of gravel, by obtaining the plants from a local correctional facility 

green house program, and by having residents be responsible for the planting. Otherwise, the cost of each garden was estimated to 

be between $1,200-$1,500. The potential long-term savings are more difficult to quantify, but include reduced demand on the city’s 

downstream storm sewer infrastructure.

Contact: Chris Cavett, Assistant City Engineer, City of Maplewood

Implementation Examples

Rain Gardens in Residential Development 

Photo: City of Maplewood Photo: City of Maplewood

MAPLEWOOD, MN

Responsible Agency: City of Maplewood
Low Impact Development Technology: Bioretention

LID-17

An 80-acre residential development site in Prince George’s County, 

MD, consisting of 199 homes on 10,000 square foot lots was designed 

featuring bioretention rain gardens. One to two rain gardens were built 

on each lot in the development. Each garden is 300-400 square feet in size and consists of ornamental grasses, mulch, shrubs, and 

trees. The rain gardens were implemented as means of storm water attenuation. The gardens control storm water quantity and 

quality by collecting runoff from driveways and rooftops for infiltration into the ground. Each garden generally includes a mulch layer 

underlain by a sandy loam or loamy sand planting media with a minimum depth of two feet. A one-foot sand layer was placed below

the planting media to help store the runoff at sites with low porosity subsurface soils. Grassy swales were used to connect the rain 

gardens to storm drain inlets and provided additional quantity and quality management compared to a traditional curb and gutter

system. Water was allowed to pool to a depth of six inches in the rain garden after each rain event. The basins provided a maximum 

of 48-hour storage onsite. 

Analysis of the project costs showed the rain gardens were a cost-effective storm water management strategy. Each garden cost 

approximately $500, which consisted of $150 for excavation and $350 for vegetation. The total cost of the project was $100,000 

compared to the projected cost of $400,000 for a pond system which was the other storm water management alternative considered 

for the development. In addition, this allowed the developer to recover six lots that otherwise would have been used for the pond 

system. The area’s naturally sandy soil was suitable for the sand base required in the rain garden profile, which kept the costs of 

the gardens down. Homeowners are responsible for replacing dead vegetation, regulating soil pH, removing filter clogs and excess 

sedimentation, keeping the storm water intake open, and repairing erosion damage. The overall savings to the developer from the

use of bioretention was over $4,000 per lot. 

Contact: Larry Coffman, Prince George’s County Department of Environmental Resources

Residential Rain Garden Program

Responsible Agency: Prince George’s 

Department of Environmental Resources

PRINCE GEORGE’S 

COUNTY, MD

Photo: Prince George’s County DER Photo: Prince George’s County DER
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-18

References

Anne Arundel County Environmental Demonstration 

(AACED). “Revitalizing Compacted Soils.” Retrieved 

November 11, 2002.

http://www.srlt.org/compactsoils.shtml

Chollak, Tracy and Paul Rosenfeld. 1998. Guidelines for 

Landscaping with Compost-Amended Soils. Prepared for City 

of Redmond Public Works.

City of Portland. 2002. Storm Water Management Manual. 

Environmental Services City of Portland Clean Water 

Works. Portland: City of Portland.

Coffman, Larry. Interview by Limno-Tech, Inc., 2002. 

EPA. 1999. Storm Water Technology Fact Sheet: Bioretention. 

EPA 832-F-99-012.

Lehner, Peter, George Aponte Clark, Diane Cameron, 

Andrew Frank. 1999. Storm water Strategies: Community 

Responses to Runoff Pollution. New York: Natural Resources 

Defense Council.

Low Impact Development Center (LID) “Bioretention Cell 

Costs” Retrieved April 30, 2003.

http://www.lid-stormwater.net/bioretention/bio_costs.htm

Low Impact Development Center (LID) “Soil Amendment 

Costs.” Retrieved November 21, 2002. 

http://www.lid-stormwater.net/soilamend/soilamend_

costs.htm

Nonpoint Source News-Notes. “Landscaped Rain Gardens 

Offer Stormwater Control.” In Notes on Watershed 

Management. No. 66. October 2001. Retrieved November 

14, 2002.

http://notes.tetratech-ffx.com/newsnotes.nsf

 

Oregon Department of Environmental Quality (ODEQ). 

2001. Restoring Soil Health To Urbanized Lands: The Crucial 

Link between Waste Prevention, Land Use, Construction, 

Stormwater Management and Salmon Habitat Restoration.

Portland: Oregon Department of Environmental Quality. 

Prince George’s County Department of Environmental 

Resource, Programs and Planning Division (PGC) 2002. 

The Bioretention Manual. Prince George’s County, MD: 

Department of Environmental Resource, Programs and 

Planning Division.

The Navy demonstrated LID effectiveness and applicability by installing 

a number of storm water retrofits, including both on-line and off-line 

bioretention systems, throughout the Washington Navy Yard (Lehner et al. 1999). These retrofits complement the Navy’s effort to 

update the 150-year old separate storm sewer system. Video investigation, cleaning, and system modernization were conducted 

prior to the installation of ten pilot projects demonstrating the use of LID techniques in urban areas. Currently, the projects are 

undergoing monitoring and evaluation of maintenance requirements and pollution control effectiveness. Engineers designed the 

bioretention retrofits to treat the first one-half inch of rain, at a minimum. The two main retrofits were at the Willard Park and Dental 

Clinic parking lots, and cover a total of three acres of impervious surface. The Willard Park parking area incorporated the on-line 

bioretention retrofits in the replacement and repair of the parking lot. Bioretention was utilized to temporarily store and slowly 

release storm water to reduce the peak discharge. In an effort to maximize parking area, the bioretention systems were installed as 

strips between parking rows. Each unit is designed to treat 0.5 acre of impervious surface.

The Dental Clinic project is an example of implementing a combination of LID practices as part of a major reconstruction of the

parking lot. Bioretention islands, sand filter gutter strips, and permeable pavers were installed between parking rows. Also, a tree box 

was installed within the property and soil amendments were made in some open space areas to increase infiltration capabilities of 

the soil. 

Contact: Camille Destafney, Naval District Washington

Responsible Agency: U.S. Navy

WASHINGTON, DC Bioretention System Retrofits

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
TECHNOLOGY DESCRIPTION

Water Conservation

LOW IMPACT DEVELOPMENT

Overview

Water conservation is the careful and efficient use of 

water in a manner that extends water supplies, conserves 

energy, and reduces water and wastewater treatment costs. 

As such, it is considered to be a low impact development 

(LID) control. With regard to CSO and SSO control, the 

reduced use of water through water conservation can 

decrease the total volume of dry weather sanitary sewage 

flowing through a sewer collection system. This produces 

an increase in conveyance and treatment capacity which 

then prevents some sewage from being discharged during 

periods when runoff, infiltration, and blockage exacerbate 

capacity constraints within wastewater collection systems. 

Water conservation can be an important component of 

a program to control sewer overflows. It is not often a 

solution on its own, but can be effective when implemented 

in combination with other control methods.

There is a broad group of indoor and outdoor practices 

that reduces water consumption. Several of the important 

water conservation practices to reduce CSOs and SSOs are 

described below.

Water Effi cient Fixtures and Appliances 

Low-fl ow fi xtures include low-fl ow toilets and urinals, 

showerheads, and faucets. Aerators, which break the 

fl owing water into fi ne droplets by incorporating air 

without affecting wetting effectiveness, can be attached 

to showerheads and faucets to reduce water use. Selfclosing and sensored faucets with automated water fl ow 

are available for commercial facilities (PNNL 2001). 

Installation of pressure-reducing valves can lower water 

consumption by reducing water fl ow and the likelihood 

of leaking pipes and faucets. Water effi cient clothes 

and dish washers are also available. For example, high 

performance clothes washers can reduce water use from 

35-55 to 18-25 gallons per load (PNNL 2001).

Water Recycling

Water recycling is the reuse of water for benefi cial 

purposes (EPA 1998). Greywater, which is wastewater 

from sinks, kitchens, tubs, clothes and dish washers, 

can be reused for home gardening, lawn maintenance, 

cooling tower or boiler makeup water, landscaping, 

toilets, and exterior washing. More elaborate treated 

effl uent recycling measures can also be implemented 

for residential, agricultural, and industrial uses.

Waterless Technology

Some available technologies eliminate the need for 

water for operation. Composting toilets treat domestic 

sewage (also food scraps, paper, lawn clippings, 

and grease) by composting and dehydration. This 

technology does not require hook-up to sewage or 

septic systems, and the end-product can be used as 

fertilizer. Waterless urinals use a liquid with a lower 

specifi c gravity than urine, such as barrier oil or other 

sealant liquid, that allows waste to pass through while 

an airlock cartridge in the base of the urine bowl 

prevents any malodor (GBS 2002). 

Rain Harvesting

Rain harvesting is an interception practice that collects 

and stores roof runoff before it enters the sewer or 

storm water system. Typical components of a rain 

collecting system are a gutter or down spout; holding 

vessels (i.e., cisterns, rain barrels, or tanks); and a fi lter 

or screen (TWDB et al. 1997). Most often, harvested 

water is for home gardening or lawn care. More 

complex systems designed to collect water for in-home 

use require a water treatment system to settle, fi lter, and 

disinfect the water, as well as a gravity or pump system 

to transport the treated water (TWDB et al. 1997).

Rainbarrel attached to a rowhouse (DC WASA).
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-20

Key Considerations

Applicability

Water conservation makes sense for many reasons. 

One important reason is the contribution that water 

conservation can make to reducing the volume of CSO and 

SSO discharges. A few considerations regarding specific 

practices are discussed in the paragraphs below.

Water Effi cient Fixtures and Appliances

Water effi cient fi xtures can be installed or retrofi tted in 

residential, commercial, institutional, and recreational 

facilities. Buildings undergoing construction or 

remodeling have great potential for incorporating 

water-wise technologies, and most of these technologies 

are readily available in the U.S. Water effi cient fi xtures 

can be a practical and economical alternative for 

homes. 

Toilets, showers, and faucets account for approximately 

60% of all indoor residential water use (EPA 1995). 

In most instances, money saved from reduced water 

and sewer bills can offset installation costs over time, 

and the reduction of wastewater places less stress on 

sewer systems. Toilets in particular are one of the 

greatest residential water uses and have considerable 

water saving potential. By installing low-fl ow toilets, 

toilet water use can be reduced from more than 3.5 

gallons to 1.6 or less gallons per fl ush (gpf). Low-fl ow 

toilets function similar to conventional toilets, and 

are therefore easy to substitute. Since low-fl ow toilets 

were fi rst introduced in the 1980s, manufacturers 

have made signifi cant improvements in toilet design, 

thus reducing the need to double fl ush, which was a 

source of customer dissatisfaction and a reduction 

in effi ciency among earlier models (EPA 2002). In 

fact, current federal law requires that residential 

toilets manufactured after January 1, 1994, must use 

no more than 1.6 gpf; and that commercial toilets 

manufactured after January 1, 1997, must use no more 

than 1.6 gpf; and urinals must use no more than 1 gpf 

(FEMP 2002). Similar to low-fl ow toilets, low-fl ow 

showerheads conserve water by reducing water use 

from 4.5 to 2.5 gallons per minute (gpm) (EPA 1995). 

These showerheads are simple to install and relatively 

inexpensive, but fl ow can be reduced over time by scale 

buildup (EPA 1995). Various cities throughout the U.S. 

have established incentive programs, such as rebates, 

promoting the use of low-fl ow or water effi cient 

technologies.

Water Recycling and Reuse

Water recycling and reuse have the potential to satisfy 

many household water needs and have numerous 

potential applications. In general, water recycling 

provides a locally controlled water supply that can 

be developed in both residential and non-residential 

facilities. Benefi ts to users of greywater systems 

are reduced water and sewer bills due to lowered 

wastewater discharge and water usage. Reuse of 

greywater also can improve local water quality by 

reducing greywater pollution (i.e. organics) that may 

otherwise be discharged into local rivers and streams 

during sewer overfl ow events. The disadvantages 

are mainly in the costs of equipment and labor to 

install the system. For more complex systems, the 

economic payback period may extend beyond the life 

of the system. Periodic maintenance is required, and 

contaminants such as paint, bleach, and dye must 

not enter the system. Some local regulations may 

not be adapted for such systems. Sanitary engineers, 

inspectors, and boards of health may lack familiarity 

with such systems as well.

Cooling tower water recycling is most useful for 

commercial, institutional, and industrial facilities such 

as hospitals, factories, nuclear power plants, apartment 

buildings, and chemical plants. The recycling of cooling 

water reduces wastewater discharge, lowers water and 

sewer bills, and reduces the discharge of chemicals 

to wastewater collection systems. The operation of 

recirculating cooling towers in industrial buildings, 

however, can reduce production effi ciency as the 

system pumps consume power. Regular maintenance is 

required to ensure effi cient application of cooling tower 

technologies. 

Waterless Technology 

Technologies that eliminate the need for water all 

together are the ultimate water conservation tool. 

Composting toilets are particularly suitable for use 

in recreational facilities such as parks, although there 

are residential and commercial applications as well. 

The advantages include eliminating the need for 

potable water to fl ush the toilet and reduced sewer 

bills. Composting toilets, however, are not ideal in cold 

climates, can require some energy (i.e., ventilation and 

heating) to optimize composting, and need regular 

maintenance. Waterless urinals are another product line 

that conserve water. While suitable for commercial and 

other public facilities, their use can be limited because 

they are not always socially acceptable, and they require 

regular maintenance.

Institutions such as hospitals can benefi t from ozonated 

laundering which provides disinfection but does 

not require detergent or rinsing. Ozone generation 

is power-intensive, requiring signifi cant amounts 
Low Impact Development: Water Conservation

LID-21

of electricity that may reduce its cost-effectiveness 

in certain applications. Also, ozone is reactive and 

corrosive and thus requires resistant material such as 

stainless steel (NSFC 1998).

Rain Harvesting

Important considerations for rain harvesting include 

age and type of roof, amount of canopy overhang, and 

availability of space to position rain barrels or other 

storage units. Rain harvesting costs vary depending on 

the complexity of the system. Rainwater yield varies with 

the size and texture of the catchment area. Systems can 

be custom designed and built or purchased as a package. 

Minimal costs are associated with simple systems 

consisting of a gutter and collection barrel serving a 

home. Applications of rain harvesting can be limited to 

certain geographical regions, as some western states have 

water laws that may impose restrictions on the practice 

of rain harvesting. 

Cost

Important considerations in evaluating the effectiveness 

of water conservation technologies include determining 

if the water conservation savings offset the costs of 

implementing the technology; assessing the feasibility of 

the technology given local restrictions and building codes; 

size and complexity of installation; location (residential 

vs. non-residential); and local water and sewer rates. Costeffectiveness of specific technologies varies greatly depending 

on water use and geography. It is also important to consider 

the water conservation potential of combining the various 

technologies.

Among water efficient fixtures and appliances, low-flow 

showerheads and faucet aerators are almost always costeffective due to the relative low cost and minimal labor 

required. Low-flow toilets also have widespread application, 

particularly in commercial and institutional settings, 

because the economic offset period can be relatively short. 

The cost-effectiveness of other technologies mentioned 

in this fact sheet, however, will be based on site-specific 

considerations. Major factors affecting the cost-effectiveness 

of water efficient landscaping include landscape area, type of 

vegetation, geography, and climate. The cost-effectiveness of 

rain harvesting is controlled by the amount of rainfall and 

storage capacity. For greywater systems, the cost-effectiveness 

will vary based on flow rate, water quality, temperature, 

local building regulations (TBS 2002), and size of the 

reuse system. Due to the various types of applications for 

cooling towers, cost-effectiveness calculations are system 

specific. The cost-effectiveness of waterless technology will 

be controlled by the availability of connections to water and 

sewer lines. Table 1 provides general estimates of the costs 

and benefits of each water conservation technology.

Table 1. Water conservation technology cost and performance1.

1These estimates are for illustrative purposes and may not be applicable to a given situation. Estimates are from 

 various sources including PNNL 2001 and CUWCC 2002.

2 Percentage of water saved when compared to conventional water use application (no conservation measures 

 taken).

Category Technology % Water 

Conserved2 Approximate Cost ($)

Life Span 

(yrs.)

Water Efficient 

Fixtures and 

Appliances

Ultra low-flow toilet 54-68% $200-300 15-25

Low-flow showerhead 45% $23 2-10

Faucet aerator 40% $13 1-3

Clothes washer 49-55% $1000 12

Recycling/

Reuse

Residential greywater 

reuse

up to 54% $400-$5000 Not Available

Cooling tower up to 90% Not Available Not Available

Waterless Composting toilet 100% $1000-$2000 Not Available

Waterless urinal 100% $300-$500 Not Available

Rain Harvesting Rain barrels or cisterns Varies $100-$20,000 Not Available
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-22

The City of Sierra Vista established a water management team in September 

2000 to assess the public’s perception of local water issues, educate and 

involve the public on water management issues, provide incentive-based

conservation alternatives, identify and address new water conservation opportunities, and implement water conservation programs. 

The water conservation programs include a toilet rebate program to encourage residents to voluntarily install low-fl ow toilets, free 

in-home retrofi ts of high-use water fi xtures, a leak detection program, an internal “Water Watch” program to monitor municipal water 

use, public education and surveying, and partnerships with the Chamber of Commerce to involve the business community. For the 

toilet rebate program, qualifi ed participants received $100 for each unit replaced with a limit of two units per household. Sierra 

Vista has approximately 13,400 homes built prior to 1987 that may have high-fl ow toilets and fi xtures. Replacement of all high-fl ow 

fi xtures could save the city up to 261 million gallons of water annually. The old high-fl ow fi xtures collected by the city through this 

rebate program were crushed and used as road-base material for various city projects. For fi scal year 2002, 195 toilets were replaced 

through the rebate program saving two million gallons of water, while 110 homes were retrofi tted with low-fl ow fi xtures saving an 

additional 3.3 million gallons of water. The program provided homeowners the opportunity to have their high-fl ow fi xtures modifi ed 

with low-fl ow alternatives at no cost to the homeowner. Sierra Vista has also taken regulatory measures by adding the following code 

requirements:

• New commercial car washes must recycle 75% of their water

• Waterless urinals in all commercial facilities with urinals

• Turf limits for new golf courses and new developments

• Commercial landscapes must feature low water use plants from city-approved list

• New irrigation standards for steep slopes and medians

 • Hot water recirculating pumps in new homes

• Independent water meters required for each multi-family unit

In addition, the “Water Watch” program involved internal monitoring and evaluation aimed at reducing water consumption in the 

city’s facilities. Monthly water invoices from the city’s use of water from its wells and from private water companies were checked for 

anomalies. Trained personnel also conducted inspections at virtually all of the city’s facilities, providing an inventory of water fi xtures 

and identifying leaks and ineffi ciencies. The city was also involved in an internal retrofi tting program where water fi xtures were 

replaced with low-fl ow units. A study by the city showed the total acre-feet of water consumed between calendar year 2000 to 2001 

decreased from 2.5 billion gallons to 2.3 billion gallons of water for Sierra Vista.

Contact: Patrick J. Bell, Environmental Services Manager, City of Sierra Vista

SIERRA VISTA, AZ

Responsible Agency: Sierra Vista Water 

Management Team

“Water Watch” Program

Implementation Examples

Sandia National Laboratory has established several water 

conservation programs within its facilities, one of which is located 

at the Compound Semiconductor Research Laboratory (CSRL). The CSRL replaced its cooling system used for its laser installations 

from a once-through water cooling system to a cooling loop cooling system. By reusing cooling water, CSRL is able to save fi ve to 

ten million gallons of water per year based on normal usage. The water bill savings are estimated at $10,000-$30,000 per year. The 

project cost was $200,000.

Contact: Darrell Rogers, Sandia National Laboratories

Responsible Agency: U.S. Department of Energy

ALBUQUERQUE, NM Water Recycling in Cooling System
Low Impact Development: Water Conservation

LID-23

Low-flow plumbing fixtures were installed in a 60-unit low income multifamily 

housing complex in Houston, owned and managed by the Housing Authority of 

the City of Houston (HACH). The average number of occupants per unit was 4.4. 

Devices installed in each unit included low-flow toilets (1.6 gpf ), low-flow aerators 

on faucets (2.2 gpm), and new water meters for each unit. Faucet leaks were repaired, and tenants were educated on conservation

techniques. The project resulted in a reduction in average monthly water consumption for the complex from 1.3 million gallons 

pre-installation to 367,000 gallons post-installation. Average monthly savings on water bills for the complex was $6,834. Due to the 

success of the project, HACH (funded by HUD) has retrofitted four of its other low income housing developments. 

Contact: Pat Truesdale, City of Houston Public Works and 

Engineers Water Conservation Branch

Responsible Agency: City of Houston and 

Houston Housing Authority Joint Water 

Conservation Project

HOUSTON, TX Water Efficient Fixtures in Housing Project

Before After

Water Use Comparison

Avg Monthly Consumption 1,300,000 gals. 376,000 gals.

Avg Monthly Consumption/Unit 21,666 gals. 6,116 gals.

Avg Monthly Consumption/Person 4,924 gals. 1,390 gals.

Avg Consumption/Person/Day 146 gals. 46 gals.

Water Bill Comparison

Avg Monthly Bill $8,644.00 $1,810.00

Avg Monthly Bill/Unit $144.00 $30.17

Due to rapid urban growth on Florida’s west coast, Hillsborough County’s 

water resources were experiencing signifi cant stress. To address this 

problem, the county established a comprehensive water conservation 

program. The program is composed of public education and regulatory, operational, and fi nancial incentive/disincentive 

components. Examples of some of the program’s projects include full-time enforcement of water use restrictions, rebates for water 

effi cient devices, and educating communities on water conservation. The program has effectively reduced the per capita water 

consumption in the county from 146 to 105 gallons per person per day; well below the regional requirement of 130 gallons. The 

low-fl ow toilet rebate program that was started in 1994 replaced 75,200 fi xtures, saving an estimated 1.7 MGD. The county also 

established a reclaimed water program where approximately 11 million gallons of reclaimed water are used by approximately 

7,000 residential and commercial customers daily, and the numbers are growing. This program has helped reduce the need for 

groundwater withdrawals and wastewater discharges.

Contact: Norman Harcourt Davis IV, Water Conservation Manager, 

Hillsborough County Water Department

Responsible Agency: Hillsborough County 

Water Department

HILLSBOROUGH 

COUNTY, FL Water Conservation Program

Water use and bill comparison before and after project.
 Report to Congress on the Impacts and Control of CSOs and SSOs

LID-24

In 2001, the DC Water and 

Sewer Authority undertook a 

study of the effectiveness of 

rain harvesting in controlling storm water runoff from rooftops within its combined sewer 

service area. Rooftops are a major type of impervious surface whose runoff can contribute 

to CSO events. Rain barrels were analyzed as a means for capturing storm water runoff 

from rooftops, thereby reducing fl ow in the combined sewer system. The 75-gallon rain 

barrels were installed at two types of homes (detached and rowhouse), each with distinct 

roof confi gurations, and were monitored over a nine-month period. For the study area, 

under a design rainfall of 0.19 inch, the study showed that approximately 27,521 gallons 

out of a total of 211,950 gallons of runoff generated would be controlled using rain barrels. 

Rain harvesting from roofs on rowhouses appeared to be more cost-effective than on 

detached homes. Calculations indicated that for a one million gallon reduction in storm 

water volume, rain barrels would need to be installed in 20 percent of the rowhouses at an 

estimated cost of $1.7 million (MWCOG 2001). 

Contact: Phong Trieu, Peter Guillozet, John Galli, or Matt Smith, 

Metropolitan Washington Council of Governments

Responsible Agency: DC Water and Sewer 

Authority (WASA)

WASHINGTON, DC Rain Harvesting Study

Fort Carson’s Central Vehicle Wash Facility services

approximately 4,000 military vehicles using recycled

water and has been in operation for over 11 years. This facility is an example of

a closed loop recycling water treatment system that consists of grit chambers,

sand fi lters, oil skimmers, and aeration basins, and has a storage capacity of 9.6

million gallons. Grass carp were introduced in the aeration and stilling basins to

control aquatic vegetation and to avoid use of algacides. On a given day, up to

491 vehicles can be washed, using 10 million gallons of water. As this treatment

system is essentially self-sustaining, there is minimal impact on Fort Carson’s

sewage and industrial wastewater treatment systems. The yearly rainfall is usually

suffi cient to make-up for evaporation losses. Each year, the system conserves

150-200 million gallons of water. The facility was built at a cost of $7 million.

Contact: Richard Pilatzke, Fort Carson

Responsible Agency: U.S.Army

COLORADO SPRINGS, CO Water Reuse at Vehicle Wash

Photo: US Army

Photo: DC WASA
Low Impact Development: Water Conservation

LID-25

References

California Urban Water Conservation Council. “H2Ouse.” 

Retrieved October 16, 2002.

http://www.h2ouse.net/action/index.cfm

EPA Offi ce of Water. “High Effi ciency Toilets.” Retrieved 

June 28, 2002.

http://www.epa.gov/OW-OWM.html/water-effi ciency/

toilets.htm

EPA Water Division Region 9. 1998. Water Recycling and 

Reuse: The Environmental Benefi ts. EPA 909-F-98-001.

EPA Offi ce of Water. 1995. Cleaner Water Through 

Conservation. EPA 841-B-95-002.

Federal Energy Management Program. “Water-Conservation 

Best Management Practices.” Retrieved October 10, 2002. 

http://www.eren.doe.gov/femp/techassist/best_

practices.html

Green Building Services. “Green Technology Brief: Water 

Conservation.” Retrieved June 14, 2003.

http://greenbuildingservices.com/images/PDF/

WaterConWeb.pdf

Metropolitan Washington Council of Governments 

(MWCOG). 2001. Combined Sewer Overfl ow Rooftop Type 

Analysis and Rain Barrel Demonstration Project. Prepared 

for The District of Columbia Water and Sewer Authority. 

Washington DC: Metropolitan Washington Council of 

Governments.

National Small Flows Clearinghouse (NSFC). 1998. 

Environmental Technology Initiative Fact Sheet: Ozone 

Disinfection. National Small Flows Clearinghouse Item 

#WWFSGN100. Morgantown, WV, West Virginia University.

Pacifi c Northwest National Laboratory (PNNL). 2001. 

Market Assessment for Capturing Water Conservation 

Opportunities in the Federal Sector. Prepared for the US 

Department of Energy Federal Energy Management 

Program. Richland, WA: Pacifi c Northwest National 

Laboratory.

Tool Base Services. “Water Conservation.” Retreived October 

11, 2002.

http://www.toolbase.org/secondaryT.asp?TrackID=&Catego

ryID=1002

Texas Water Development Board (TWDB) and Center for 

Maximum Potential Building Services (CMPBS)CMPBS. 

1997. Texas Guide to Rainwater Harvesting. Austin, TX: 

TWDB and CMPBS.

Inclusion of this technology description in this Report to 

Congress does not imply endorsement of this technology 

by EPA and does not suggest that this technology is 

appropriate in all situations. Use of this technology does 

not guarantee regulatory compliance. The technology 

description is solely informational in intent.
Appendix M 

Financial Information

M.1 Cost Escalation Factors

M.2 Past Investments in Wastewater 

 Infrastructure

M.3 Projected Needs for CSO Control

 Appendix M

M-1

Year Capital O&M

1970 126 0.2849

1971 132.3 0.2992

1972 137.2 0.3132

1973 144.1 0.3271

1974 165.4 0.3504

1975 182.4 0.3867

1976 192.1 0.4140

1977 204.1 0.4451

1978 218.8 0.4756

1979 238.7 0.5142

1980 261.2 0.5599

1981 297 0.6142

1982 314 0.6572

1983 317 0.6861

1984 323 0.7114

1985 325 0.7349

1986 318 0.7526

1987 324 0.7733

1988 343 0.7986

1989 355 0.8293

1990 357.6 0.8605

1991 361.3 0.8940

1992 358.2 0.9174

1993 359.2 0.9393

1994 368.1 0.9596

1995 381.1 0.9804

1996 381.7 1.0000

1997 386.5 1.0195

1998 389.5 1.0339

1999 390.6 1.0477

2000 394.1 1.0679

2001 394.3 1.0940

2002 395.6 1.1080

Table M.1 Cost Escalation Factors

M.1 Cost Escalation Factors

All cost information presented in this Report to Congress is in 2002 dollars unless otherwise noted. Capital costs 

were adjusted using the Chemical Engineering Plant Cost Index (CEPCI); O&M Costs were adjusted using the Gross 

Domestic Product Implicit Price Deflator (GDPIPD). A summary of these cost factors from 1970 to 2002 is provided 

in Table M.1.
M-2

Report to Congress on Impacts and Control of CSOs and SSOs
 Appendix M

M-3

Table M.2 Federal Funding for Wastewater Infrastructure, 1970 - 2000 

 (billions of dollars)

Year Construction 

Granta CWSRFb EPA Line 

Item

Unadjusted 

Total

Total

(2000 Dollars)

1970 < $0.1 0 0 < $0.01 < $0.1

1971 < $0.1 0 0 < $0.01 < $0.1

1972 $0.1 0 0 $0.1 $0.4

1973 $3.0 0 0 $3.0 $8.4

1974 $2.5 0 0 $2.5 $6.0

1975 $4.3 0 0 $4.3 $9.4

1976 $4.6 0 0 $4.6 $9.5

1977 $7.3 0 0 $7.3 $14.1

1978 $2.8 0 0 $2.8 $5.1

1979 $5.1 0 0 $5.1 $8.5

1980 $3.8 0 0 $3.8 $5.8

1981 $3.6 0 0 $3.6 $4.8

1982 $2.3 0 0 $2.3 $2.8

1983 $4.0 0 0 $4.0 $5.0

1984 $4.6 0 0 $4.6 $5.6

1985 $2.1 0 0 $2.1 $2.6

1986 $2.3 0 0 $2.3 $2.9

1987 $2.4 0 0 $2.4 $3.0

1988 $3.1 $0.3 0 $3.4 $3.8

1989 $1.3 $1.2 0 $2.5 $2.7

1990 $0.9 $1.4 0 $2.3 $2.6

1991 $0.3 $2.0 0 $2.3 $2.5

1992 $0.3 $1.9 $0.4 $2.6 $2.8

1993 $0.1 $1.9 $0.4 $2.4 $2.7

1994 $0.1 $1.3 $0.4 $1.8 $1.9

1995 < $0.1 $1.3 $0.6 $1.9 $2.0

1996 0 $1.7 $0.1 $1.8 $1.9

1997 0 $0.8 $0.1 $0.9 $0.9

1998 0 $1.2 $0.2 $1.4 $1.4

1999 0 $1.3 $0.2 $1.5 $1.5

2000 0 $1.4 $0.2 $1.6 $1.6

Total $60.9 $17.7 $2.6 $79.5 $122.2

a EPA 2000

b EPA 2003

M.2 Past Investments in Wastewater Infrastructure

The federal government has been investing in the nation’s wastewater infrastructure since the late 19th century. 

With the passage of the Clean Water Act in 1972, federal investment markedly increased, peaking in 1977. As 

shown in Table M.2, between 1970 and 2000, the federal government invested more than $122 billion in the 

nation’s wastewater infrastructure. 
M-4

Report to Congress on Impacts and Control of CSOs and SSOs

Year Capitala,b Adjusted 

Capital (2002 

Dollars)

O&Ma,b Adjusted O&M (2002 

Dollars)

Total 

(2002 

Dollars)

1970 $1.4 $4.4 $0.4 $1.6 $6.0

1971 $1.7 $5.1 $0.8 $3.0 $8.0

1972 $2.2 $6.3 $1.0 $3.5 $9.9

1973 $2.4 $6.6 $1.2 $4.1 $10.7

1974 $2.6 $6.2 $1.4 $4.4 $10.6

1975 $3.6 $7.8 $1.7 $4.9 $12.7

1976 $4.0 $8.2 $2.0 $5.4 $13.6

1977 $4.2 $8.1 $2.3 $5.7 $13.9

1978 $4.4 $8.0 $2.8 $6.5 $14.5

1979 $5.6 $9.3 $3.2 $6.9 $16.2

1980 $6.3 $9.5 $3.6 $7.1 $16.7

1981 $6.9 $9.2 $4.2 $7.6 $16.8

1982 $5.9 $7.4 $4.9 $8.3 $15.7

1983 $5.8 $7.2 $5.4 $8.7 $16.0

1984 $5.7 $7.0 $5.8 $9.0 $16.0

1985 $5.9 $7.2 $6.3 $9.5 $16.7

1986 $6.5 $8.1 $6.8 $10.0 $18.1

1987 $7.5 $9.2 $7.4 $10.6 $19.8

1988 $8.3 $9.6 $8.0 $11.1 $20.7

1989 $8.3 $9.2 $8.7 $11.6 $20.9

1990 $8.4 $9.3 $10.0 $12.9 $22.2

1991 $9.1 $10.0 $11.0 $13.6 $23.6

1992 $8.9 $9.8 $11.4 $13.8 $23.6

1993 $10.3 $11.3 $12.4 $14.6 $26.0

1994 $8.0 $8.6 $13.6 $15.7 $24.3

1995 $8.9 $9.2 $14.7 $16.6 $25.9

1996 $9.3 $9.6 $15.3 $17.0 $26.6

1997 $9.6 $9.8 $16.1 $17.5 $27.3

1998 $9.1 $9.2 $16.6 $17.8 $27.0

1999 $9.7 $9.8 $17.3 $18.3 $28.1

2000 $10.1 $10.1 $18.0 $18.7 $28.8

Total $200.2 $260.3 $234.4 $316.0 $276.9

a U.S. Census Bureau. 2003. State and Local Government Finances by Level of Government. Retrieved October 2003.

 http://www.census.gov/govs/www/estimate.html. 

b EPA. 2000. Office of Water and Office of Policy, Economics, and Innovation. “A Retrospective Assessment of the 

 Costs of the Clean Water Act: 1972 to 1997. Final Report.” Retrieved October 2, 2003. 

 http://www.epa.gov/ost/economics/costs.pdf

EPA estimates that current combined capital investment in wastewater infrastructure from federal, state, and 

local governments is just over $13 billion annually (EPA 2002). Today, according to industry organizations, 

individual utilities can pay as much as 90 percent of capital expenses (AMSA and WEF 1999). As shown in 

Table M.3, capital expenditures by state and local governments have remained relatively constant since 1988; 

annual O&M expenditures have more than doubled.

Table M.3 State and Local Expenditures on Wastewater Infrastructure, 1970 - 2000

 (billions of dollars)
 Appendix M

M-5

Many municipalities have made signifi cant investments in CSO control within their jurisdictions. As part of 

the data gathering for this report, EPA was able to document expenditures on CSO control in 48 communities. 

To date, these expenditures total more than $6 billion, ranging from $134,000 to $2.2 billion per community. 

(Table M.4)

Table M.4 Community Expenditures on CSO Control

State Community

Capital 

Expenditure 

($M)a

Annual 

O&M ($M) Sources

CA San Francisco, CA $1,450.0 $20.3 EPA 2001, EPA 2003 PA 2001, EPA 2003

DC Washington, D.C. $35.0b $13.7 EPA 2001 PA 2001

GA Atlanta, GA $759.0 EPA 2001

GA Columbus, GA $95.0 $1.0 EPA 2001, AMSA 2003

IA Burlington, IA $2.9 EPA 2001

IA Washington, IA $0.6 CSO Municipal Interview 

IL Alton, IL $4.0 CSO Municipal Interview

IL Chicago, IL $2,200.0 $8.2 EPA 2001, EPA2003

IL City of Batavia, IL $10.9 CSO Municipal Interview

IL Decatur, IL $14.6 CSO Municipal Interview

IL Galesburg, IL $9.7 CSO Municipal Interview

IL Havana, IL $0.6 CSO Municipal Interview

IL Lincoln, IL $3.1 CSO Municipal Interview

IN Goshen, IN $12.3 CSO Municipal Interview 

IN Hammond, IN $13.7 CSO Municipal Interview 

IN Muncie, IN $20.5 EPA 2001

KY Louisville, KY $25.0 EPA 2001

MA Agawam, MA $5.9 CSO Municipal Interview 

MA Fitchburg, MA $0.1 CSO Municipal Interview 

MA MWRA, Boston, MA $110.0 $2.0 EPA 2001, EPA 2003

MA South Hadley, MA $2.5 CSO Municipal Interview 

ME Biddeford, ME $24.5 CSO Municipal Interview 

ME Hamden, ME $2.0 CSO Municipal Interview 

ME South Portland, ME $9.0 $0.4 EPA 2001

MI Armada, MI $1.3 CSO Municipal Interview 

MI Rouge River, MI $350.0 $5.1 EPA 2001

MI Saginaw, MI $105.2 EPA 2001, EPA 2003

MI East Lansing, MI $20.0 EPA 2003, CSO Municipal Interview 

MI Scottvile, MI $0.3 CSO Municipal Interview 
M-6

Report to Congress on Impacts and Control of CSOs and SSOs

State Community

Capital 

Expenditure 

($M)a

Annual 

O&M ($M) Sources

MO Cape Girardeau, MO $34.5 CSO Municipal Interview 

NJ East Newark, NJ $0.4 CSO Municipal Interview 

NJ North Bergen, NJ $3.9 EPA 2001

NJ Perth Amboy, NJ $6.0 EPA 2003, CSO Municipal Interview

NY Salamanca, NY $1.0 CSO Municipal Interview 

OH Fremont, OH $15.9 CSO Municipal Interview 

OH Perrysburg, OH $7.6 EPA 2003, CSO Municipal Interview 

OR Portland, OR $76.0b EPA 2001

PA Altoona, PA $13.5 CSO Municipal Interview 

PA Freeland, PA $3.0 CSO Municipal Interview 

PA Wyoming Valley, PA $12.0 CSO Municipal Interview 

VA Richmond, VA $221.0 $6.8 EPA 2001

VT Randolph, VT $2.9 EPA 2001

VT Richford, VT $3.2 CSO Municipal Interview 

VT Windsor, VT $1.6 CSO Municipal Interview 

WA Bellingham, WA $17.0 CSO Municipal Interview 

WA Bremerton, WA $17.0 $4.6 to $6.1 EPA 2001

WA King County, WA $266.0 CSO Municipal Interview 

WA Spokane, WA $50.0b EPA 2003

a Capital Expenditure reflects the total amount (in unadjusted dollars) spent by the community on CSO control.

b Includes updated information from the community’s LTCP or other documents.

Table M.4 continued
 Appendix M

M-7

M.3 Projected Needs for CSO Control

Community-specific information on projected CSO needs was available from several sources including:

● Report to Congress - Implementation and Enforcement of the CSO Control Policy

● 2000 Clean Watersheds Needs Survey Report to Congress

Together, these sources provide information on projected capital needs for CSO control in 71 communities, less than 10 

percent of the CSO universe. The individual community needs, presented in Figures M.1, M.2, and M.3, total more than 

$22 billion.

New York, NY

Cleveland, OH

Washington, DC

Atlanta, GA

Providence, RI

King County, WA

Cincinnati, OH

Boston, MA

San Francisco, CA

New Haven, CT

Lynchburg, VA

Nashville & Davidson Cnty, TN

Richmond, VA

Hoboken, NJ

Manchester, NH

Lowell, MA

Akron, OH

Louisville/Jefferson Cnty, KY

Nashua, NH

Springfield, MA

Chicopee, MA

Lansing, MI

Hartford, CT

Haverhill, MA

Wilmington, DE

Millions of Dollars

$6,545

Data Source

LTCPs in EPA CWNS 2000

Other documented needs (EPA CWNS 2000)

Other LTCPs pending regulatory approval

$0 $200 $400 $600 $800 $1,000 $1,200 $1,400 $6,500

Figure M.1 Communities with Projected Capital Needs for CSO Control Exceeding 

 $100 million
M-8

Report to Congress on Impacts and Control of CSOs and SSOs

Figure M.2 Communities with Projected Capital Needs for CSO Control Between 

 $10 and $100 million

$0 $20 $40 $60 $80 $100

Cumberland, MD

Lynn, MA

Newark, NJ

Saginaw, MI

Morgantown, WV

Everett, WA

Portsmouth, NH

Holyoke, MA

Lima, OH

Defiance, OH

Augusta, ME

Lebanon, NH

Gloucester, MA

Auburn, ME

Westernport, MD

East Lansing, MI

Bangor, ME

Middletown, OH

Saco, ME

Waterloo, IA

Sault St. Marie, MI

Millions of Dollars

Data Source

LTCPs in EPA CWNS 2000

Other documented needs (EPA CWNS 2000)

Other LTCPs pending regulatory approval
 Appendix M

M-9

Figure M.3 Communities With Projected Capital Needs for CSO Control Ranging 

 from $735,000 to 10 million

$0 $1 $2 $3 $4 $5 $6 $7 $8 $9 $10

Palmer, MA

Marion, OH

Wakefield TWP, MI

Nitro, WV

Jacksonville, IL

Bucyrus, OH

Perrysburg, OH

Kennebec, ME

Maysville, KY

Port Clinton, OH

Lancaster, OH

Newark, OH

Juneau-Douglas, AK

Alexandria, VA

Belfast, ME

Oregon, IL

St. Joseph, MI

Morganfield, KY

Monmouth, IL

Van Wert, OH

Catlettsburg, KY

Lewiston- Auburn, ME

Jewett City, CT

Essexville, MI

Reynoldsville, PA

Millions of Dollars

Data Source

LTCPs in EPA CWNS 2000

Other documented needs (EPA CWNS 2000)

Other LTCPs pending regulatory approval
M-10

Report to Congress on Impacts and Control of CSOs and SSOs

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