Street Storage System

for

Control of Combined Sewer Surcharge

Retrofitting Stormwater Storage

Into

Combined Sewer Systems

by

Stuart G. Walesh

Valparaiso, IN 46385-2979

Contract No. 8C-R416-NTSX

Project Officer

Carolyn R. Esposito

Water Supply and Water Resources Division

National Risk Management Research Laboratory

Edison, NJ 08837

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cinncinnati, OH 45268
ii

Disclaimer

The U.S. Environmental Agency through its Office of Research and Development

funded and managed the research described here under Contract No. 8C-R416-NTSX. 

It has been subjected to the Agency’s peer and administrative review and has been

approved for publication as an EPA document. Mention of trade names or commercial

products does not constitute endorsement or recommendations for use.

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iii

Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the

Nation’s land, air and waste resources. Under a mandate of national environmental

laws, the Agency strives to formulate and implement actions leading to a compatible

balance between human activities and the ability of natural systems to support and

nurture life. To meet this mandate, EPA’s research program is providing data and

technical support for solving environmental problems today and building a science

knowledge base necessary to manage our ecological resources wisely, understand how

pollutants affect our health, and prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory is the Agency’s center for

investigation of technological and management approaches for reducing risks from

threats to human health and the environment. The focus of the Laboratory’s research

program is on methods for the prevention and control of pollution to air, land, water and

subsurface resources; protection of water quality in public water systems; remediation

of contaminated sites and ground water; and prevention and control of indoor air

pollution. The goal of this research effort is to catalyze development and

implementation of innovative, cost-effective environmental technologies; develop

scientific and engineering information needed by EPA to support regulatory and policy

decisions; and provide technical support and information transfer to ensure effective

implementation of environmental regulations and strategies.

This publication has been produced as part of the Laboratory’s strategic long-term

research plan. It is published and made available by EPA’s Office of Research and

Development to assist the user community and to link researchers with their clients.

E. Timothy Oppelt, Director

National Risk Management Research Laboratory

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iv

Abstract

A case study approach, based primarily on two largely implemented street storage

systems, is used to explain the concept through construction and operation aspects of

street storage systems. More specifically, the case studies address analysis and

design approaches, the regulatory and funding framework, public involvement,

construction costs, operation and maintenance procedures, and system performance. 

Street storage refers to the technology of temporarily storing stormwater in urban areas

on the surface (off-street and on-street) and, as needed, below the surface close to the

source. Close to the source means where the water falls as precipitation and prior to its

entry into the combined, sanitary, or storm sewer system. The idea is to accept the full

volume of stormwater runoff into the sewer system but greatly reduce the peak rate of

entry of stormwater into the system. System components include street berms, flow

regulators, and surface and subsurface stormwater storage sites.

By eliminating or greatly reducing surcharging in combined sewer systems, street

storage has the potential to cost effectively and simultaneously mitigate basement

flooding and CSO’s. Other possible benefits of street storage are mitigating SSO’s,

eliminating surface flooding, reducing peak flows at WWTP’s, and controlling non-point

source pollution.

This report was submitted in fulfillment of Contract No. 8C-R416-NTSX by prime

contractor Stuart G. Walesh with the assistance of subcontractors Earth Tech, Inc. and

Donald Roecker under the sponsorship of the U.S. Environmental Protection Agency. 

This report covers a period from July 7, 1998 to May 1, 1999, and work was completed

as of May 1, 1999.

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v

Table of Contents

Disclaimer...................................................................................................................ii

Forward.....................................................................................................................iii

Abstract.....................................................................................................................iv

Table of Contents.......................................................................................................v

Tables......................................................................................................................xvi

Figures....................................................................................................................xvii

Abbreviations and Acronyms....................................................................................xx

Acknowledgments...................................................................................................xxii

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

Combined Sewer System Challenge in the U.S. .............................1-1

CSO Policy of the USEPA................................................................1-1

Objectives of the Policy..........................................................1-1

Nine Minimum Controls...........................................................1-2

Long-Term CSO Control Plan.................................................1-3

Traditional Approach: Store/Treat Combined Sewage or

Separate the Sewer System...................................................1-3

A New Approach: Store Stormwater Before it Combines With

Sanitary Sewage.....................................................................1-5

Scope of this Evaluation..................................................................1-5

Case Study Approach.............................................................1-5

Quantity and Quality: Seeking Optimum Means of

Simultaneously Mitigating Flooding and Pollution..............1-5

Retrospective Details with Prospective Purpose....................1-9

Initiatives...............................................................................1-10

Terminology.........................................................................1-10
vi

Abbreviations, Acronyms and Glossary.........................................1-12

Chapter 2 Case Study Communities: Skokie and Wilmette, IL.........................2-1

Basis of Selection of Case Study Communities..............................2-1

Familiarity of the Investigators with the Projects....................2-1

On-Going Relationships with Personnel in the Case

Study Communities......................................................2-1

Opportunity to Study a Large, Long-Standing Street

Storage Project............................................................2-1

Supplemental Communities.............................................................2-2

Description of Skokie, IL..................................................................2-2

Location..................................................................................2-2

Relationship to the Metropolitan Water Reclamation

District of Greater Chicago...........................................2-2

Land Use and Population.......................................................2-7

Soils and Groundwater...........................................................2-7

Topography and Drainage Patterns........................................2-7

Climate....................................................................................2-8

Brief History of Skokie with Emphasis on Development of

Its Drainage System................................................................2-8

Skokie’s Historic Combined Sewer System Basement

Flooding Problems................................................................2-12

Previous Studies of Ways to Solve Skokie’s Combined Sewer

System Basement Flooding Problems..................................2-13

Study Completed in 1967 Recommending Relief Sewers....2-13

Study Completed in 1973 Recommending Deep

and Shallow Tunnels..................................................2-14

Study Completed in 1974 Recommending Downspout

Disconnection and Catch Basin Restrictors...............2-15

Study Completed in 1978 Recommending Deep and

Shallow Tunnels and Relief Sewers..........................2-17

Study Completed in 1981 Providing Additional

Insight into System Inadequacies..............................2-18

Study Completed in 1981 Suggesting Combinations of

Traditional and Innovative Measures.........................2-21
vii

Study Completed in 1982 Recommending a Street

Storage System..........................................................2-22

Observations Regarding the Studies to Solve Skokie’s

Combined Sewer System Basement Flooding Problem.......2-24

Occurrence of a Series of Evolving Studies.........................2-24

Initial Focus on Traditional Solutions....................................2-24

Gradual Recognition of the Water Pollution Control

Purpose of TARP.......................................................2-24

Description of Wilmette, IL.............................................................2-25

Location...........................................................................2-25

Relationship to the Metropolitan Water Reclammation

District of Greater Chicago.........................................2-25

Land Use and Population.....................................................2-27

Topography and Drainage Patterns......................................2-27

Brief History of Wilmette with Emphasis on Development of

Its Drainage System..............................................................2-29

Wilmette’s Historic Combined Sewer System Basement

Flooding and Peak Discharge Problem................................2-29

Previous Studies of Ways to Solve Wilmette’s Combined

Sewer System Problems.......................................................2-30

Study Completed in 1991 Recommending Relief

Sewers.......................................................................2-30

Value Engineering Study Completed in 1992

Recommending Street Storage..................................2-31

Study Completed in 1992 Recommending Street

Storage......................................................................2-31

Study Completed in 1992 Recommending Refined

Street Storage............................................................2-31

Observations Regarding Studies to Solve Wilmette’s

Combined SewerSystem Problems........................................2-32

Chapter 3 The Concept Through Construction Process for Street

Storage Systems: Skokie and Wilmette, IL......................................3-1

Status of Urban Stormwater Management....................................3-1
viii

Two Fundamentally Different Approaches: ConveyanceOriented and Storage-Oriented................................3-1

Conveyance-Oriented Approach.............................3-1

Storage-Oriented Approach......................................3-3

Comparison of Features..........................................3-3

Historic Development of the Storage-Oriented

Approach.................................................................3-4

Emergency and Convenience Systems..............................3-5

The Convenience (Minor) System............................3-5

The Emergency (Major or Overflow) System...........3-7

Combined Convenience and Emergency System....3-7

The Possibility of Retrofitting Stormwater Storage Into

Already Developed Areas...................................................3-10

Distinction Between Analysis and Design: Diagnosis and

Then Prescription.................................................................3-10

Chronological Mode of Presentation..........................................3-11

The Concept of Street Storage..................................................3-14

Conveyance Capacity of Urban Streets............................3-14

Street Cross Sections............................................3-14

Analysis Procedure................................................3-14

Results...................................................................3-18

Storage Capacity of Urban Streets.....................................3-20

Analysis Procedure................................................3-20

Results...................................................................3-24

Using Street Storage and Conveyance Capacity in

Combined Sewer Systems.........................................3-24

Bringing the Street Storage Concept to Reality: Berms, Flow

Regulators, and Subsurface Storage...............................3-26

Berms...............................................................................3-26

Berms Contrasted with Bumps and Humps...........3-26

Berms: The Negative Perception Problem.............3-32
ix

The Possibility of Integrating Stormwater 

Berms and Speed Hump Functions.............3-33

Flow Regulators................................................................3-34

Combined Function of Berms and Flow Regulators..........3-38

Subsurface Storage...........................................................3-41

Apply Screening Criteria to Determine Likely Applicability of a

Street Storage System.......................................................3-46

Select an Initial Pilot or Implementation Area Within the

Combined Sewer System.....................................................3-46

Need for Phased Implementation.....................................3-46

Prioritization Factors.........................................................3-46

Establish Performance Criteria......................................................3-48

Need for Performance Criteria: Analysis and Design...........3-48

Variation in Performance Criteria.........................................3-48

Skokie Performance Criteria................................................3-49

Wilmette Performance Criteria.............................................3-50

Analyze Existing System Using Monitoring....................................3-51

Skokie Monitoring.................................................................3-52

Wilmette Monitoring..............................................................3-53

Analyze Existing System and Perform Preliminary Design

Using Computer Models.......................................................3-53

A Complex System: Need for Computer Modeling...............3-53

Analysis and Preliminary Design for the HSSD in

Skokie.......................................................................3-54

Phase I - Analysis of Static Conditions.....................3-54

Phase II - Analysis of Sewer Capacity......................3-55

Phase III - Preliminary Design of Street Storage......3-57

Results......................................................................3-59

Analysis and Preliminary Design in Wilmette......................3-61

Modification of the Stormwater Management 

Model..............................................................3-61

Application of the Model...........................................3-63

Results......................................................................3-64
x

Review Flow Regulator Availability and Performance...................3-64

Essentiality of Flow Regulators............................................3-64

Skokie Flow Regulator Study..............................................3-64

Purpose......................................................................3-65

Literature Search and Interviews...............................3-65

Design of the Field Study...........................................3-67

Equipment Acquisition and Installation......................3-67

Observation Procedures...........................................3-72

Rainfall.......................................................................3-72

Resistance to Plugging..............................................3-72

Costs..........................................................................3-72

Maintenance..............................................................3-74

Conclusions for Skokie...................................3-74

Complete Design of the Street Storage System............................3-74

Construction...................................................................................3-76

Skokie Construction.............................................................3-76

Wilmette Construction..........................................................3-79

Phase 1: Greenleaf Avenue Relief Sewer.................3-79

Phase 2: Eastside Relief Sewer................................3-79

Phase 3: Eastside Relief Sewer................................3-79

Phase 4.....................................................................3-79

Phase 5.....................................................................3-80

Chapter 4 Other Examples of Street Storage Systems....................................4-1

Purpose............................................................................................4-1

Cleveland, OH: Puritas Avenue - Rock River Drive Area.................4-2

Background.............................................................................4-2

Results....................................................................................4-2

Parma, OH: Ridge Road Area..........................................................4-4

Background.............................................................................4-4

Results....................................................................................4-5

Chicago, IL: Jeffery Manor Neighborhood.......................................4-5
xi

Background.............................................................................4-5

Results....................................................................................4-6

Chapter 5 Regulatory and Financial Framework: Complying with

Regulations and Funding Construction.......................................5-1

Motivated by Need but Subject to Regulatory and Financial

Constraints and Opportunities...........................................5-1

Federal and State Regulatory and Funding Framework

Within Which Skokie and Wilmette Functioned................5-3

Today’s Regulatory and Funding Framework: Review of Outside

Capital Funding Programs, Techniques and Strategies....5-4

Overview............................................................................5-4

Outside Capital Funding from Users..................................5-5

Outside Capital Funding from State and Federal

Agencies..................................................................5-5

Outside Capital Funding from the U.S. Congress:

Direct Legislation.........................................................5-8

Initial Capital Funding for the Skokie Street Storage System........5-11

On-Going Local Capital Funding of the Skokie Street Storage

System Through the Bond Market........................................5-12

Skokie Downspout Disconnection Ordinance and Program...........5-14

The Downspout Problem......................................................5-14

The Downspout Solution.......................................................5-14

Educational Value.................................................................5-17

Downspout Disconnection Process Used in Skokie.............5-17

Skokie Stormwater Control Ordinance...........................................5-18

Regulations of the Metropolitan Water Reclammation

District of Greater Chicago...................................................5-19

Chapter 6 Stakeholder Involvement..................................................................6-1

Two Public Works Challenges........................................................6-1

Purpose of this Chapter..................................................................6-1
xii

A Characteristic of Wet Weather Problems: Widely 

Fluctuating Public Interest.....................................................6-2

More on the Need for Stakeholder Involvement..............................6-2

Identification of Stakeholders..........................................................6-4

Types of Stakeholder Involvement..................................................6-6

Examples of Stakeholder Involvement Techniques.......................6-11

Skokie and Wilmette Approaches.........................................6-11

Additional Tactics.................................................................6-12

Chapter 7 Inspection and Maintenance............................................................7-1

Essentiality of Inspection and Maintenance.....................................7-1

Inspection and Maintenance Procedures for Skokie’s Street

Storage System.....................................................................7-2

Surface and Subsurface Storage and Dewatering

Facilities.....................................................................7-2

Flow Regulators....................................................................7-3

Street Berms...........................................................................7-4

Street Ponding Areas............................................................7-5

Safety of Inspection and Maintenance Personnel..........................7-6

Chapter 8 Construction Costs...........................................................................8-1

Purpose............................................................................................8-1

Skokie Construction Costs...............................................................8-1

Wilmette Construction Costs...........................................................8-5

Unit Costs.......................................................................................8-5

Skokie and Wilmette Unit Costs............................................8-5

Discussion of Unit Costs.......................................................8-7

Intangible Costs..............................................................................8-8
xiii

Chapter 9 Performance of Street Storage Systems..........................................9-1

Performance: The Ultimate Test......................................................9-1

Broad Interpretation of Performance................................................9-1

Means of Assessing Performance....................................................9-2

Summary of Interviews with Skokie, IL Officials...............................9-3

Participants.............................................................................9-3

Process...................................................................................9-3

Results....................................................................................9-4

Financing................................................................................9-4

Effectiveness of the System in Mitigating Basement 

Flooding ......................................................................9-4

Public Education and Involvement.........................................9-5

Litigation................................................................................9-5

Claims....................................................................................9-5

Operation of Emergency Vehicles.........................................9-5

Operation of Motor Vehicles..................................................9-6

Operation and Maintenance (O&M).......................................9-6

Monitoring..............................................................................9-8

Downspout Disconnection.....................................................9-8

Pavement Deterioration.........................................................9-9

Icing of Streets When Rainfall or Snowmelt Occurs 

During Freezing Temperatures.................................9-9

Interaction With Other Government Entities........................9-9

Summary of Interviews With Wilmette, IL Officials........................9-10

Participants.......................................................................9-10

Process.................................................................................9-10

Results.............................................................................9-11

Financing..............................................................................9-11

Effectiveness of the System in Mitigating Basement

Flooding.....................................................................9-11

Public Education and Involvement........................................9-11

Litigation...............................................................................9-12

Claims...................................................................................9-12

Operation of Emergency Vehicles........................................9-12

Operation of Motor Vehicles.................................................9-12

Operation and Maintenance (O&M)......................................9-13

Downspout Disconnection....................................................9-13

Pavement Deterioration........................................................9-13

Icing of Street When Rainfall or Snowmelt Occurs

During Freezing Temperatures..................................9-13
xiv

Interaction With Other Government Entities.........................9-14

Rainfall - Flooding Incidents......................................................9-14

Typical Limited Data.........................................................9-14

June 20-21, 1987 Rainfall - Flooding Event in Skokie......9-14

August 13-14, 1987 Rainfall - Flooding Event in

Skokie....................................................................9-15

August 4, 1989 Rainfall - Flooding Event in 

Skokie and Wilmette, IL..........................................9-15

May 8, 1996 Rainfall - Flooding Event in Skokie..................9-18

August 5, 1999 Rainfall - Flooding Event in Skokie..............9-18

Economic and Financial Impact on Skokie....................................9-19

Potential Impact of a Street Storage System on the

Frequency and Volume of Combined Sewer Overflows.......9-20

Chapter 10 Discussion...................................................................................10-1

Lessons Learned: How Other Communities Might Benefit

From A Street Storage System.............................................10-1

Lessons Learned About Analysis and Design......................10-1

Lessons Learned About Regulatory Compliance and

Project Financing.......................................................10-2

Lessons Learned About Stakeholder Involvement...............10-3

Lessons Learned About Evaluating System

Performance.............................................................10-4

Lessons Learned About Operation and Maintenance.........10-4

Criteria For Screening Applicability of Street Storage..................10-4

Purpose of Screening Criteria..............................................10-4

Qualifications of Evaluators.................................................10-5

Interpreting the Screening Information................................10-5

Chapter 11 Conclusions and Recommendations............................................11-1
xv

Street Storage: A New Technology for Affordable Mitigation

of CSS Problems.................................................................11-1

Recommended Research..............................................................11-2

Integration of Speed Humps and Street Berms....................11-2

Street Storage to Reduce CSOs and Peak Flows at

WWTPs......................................................................11-3

Costs and Benefits of Street Storage Versus

Traditional Approaches..............................................11-3

Further Improvement to Hanging Traps................................11-4

Street Storage as Part of New Combined Sewer

Systems.....................................................................11-5

Impact of a Street Storage on Non-Point Source

Pollution.....................................................................11-6

Appendices

A Questions Used to Prompt Discussion With Skokie

Officials........................................................................A-1

B Criteria for Screening the Applicability of Street

Storage........................................................................B-1

C Trouble Shooting Guide for Underground and Surface

Storage Basins with Gravity Dewatering.....................C-1

D Trouble Shooting Guide for Stormwater Storage

Basins - Dewatering Pump Stations...........................D-1

E Standard Maintenance Procedures for Submersible

Dewatering Pumps - Stormwater Storage Basins........E-1

F Exploratory Analysis of the Impact of a Street Storage

System on the Frequency and Volume of

Combined Sewer Overflows.........................................F-1

G Construction Costs for Skokie Street Storage System

Adjusted to 1999........................................................G-1

Glossary

Cited References

Bibliography

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xvi

Tables

1-1 Proven methods are available to solve pollution and/or flooding problems

in combined sewer systems..........................................................................1-4

1-2 Seven of 22 large CSS communities explicitly reported basement or

street and other surface flooding .................................................................1-8

3-1 Depth, cross-sectional area, and cumulative volume data for half of Easy

Street .........................................................................................................3-22

3-2 Rainfall and depth of ponding for Easy Street......................................................3-22

3-3 Components of the Skokie street storage system.................................................3-77

8-1 Total construction costs for the Skokie, IL street storage system..........................8-2

8-2 Unit construction costs for the Skokie and Wilmette street storage systems.........8-6
xvii

Figures

1-1 Control of peak rates of stormwater runoff can, in concept, mitigate

surcharging of combined sewer systems......................................................1-6

2-1 Skokie and Wilmette, IL lie immediately north of the City of Chicago.....................2-3

2-2 Map of Skokie, IL....................................................................................................2-4

2-3 The North Shore Channel, which bounds Skokie on the east, and its

contiguous linear parks provide an amenity for area residents..................2-5

2-4 The deep tunnel is primarily a pollution control system in that it mitigates

combined sewer overflows to the North Shore Channel...............................2-6

2-5 Each Skokie catch basin is a manhole-type structure with a sump........................2-9

2-6 Skokie is partitioned into three easterly draining combined sewer districts..........2-10

2-7 Map of portion of Wilmette, IL served by combined sewer system.......................2-26

2-8 Brick streets account for half of the street length in Wilmette that was

targeted for street storage..........................................................................2-28

3-1 Conveyance and storage approaches to stormwater management........................3-2

3-2 Historic development and use of storage facilities for stormwater

management in the U.S. ..............................................................................3-6

3-3 Emergency and convenience system applied to an urban street............................3-9

3-4 Emergency and convenience system applied along a channel and 

floodplain......................................................................................................3-9

3-5 Successful application of a street storage system requires a systematic 

analysis and design process that begins with understanding the 

concept and concludes with construction.........................................3-12 - 3-13

3-6 The photographs of urban streets in Skokie (top) and Wilmette (bottom) 

suggest their potential stormwater conveyance and storage function........3-15

3-7 Selected street cross sections from Skokie, IL.....................................................3-16

3-8 Typical street and lawn cross section representative of actual Skokie cross 

sections......................................................................................................3-17

3-9 Depth versus discharge relationships for typical street and lawn cross 

sections......................................................................................................3-19

3-10 Typical urban street plan showing the area tributary to the east side of a 

one block segment of Easy Street..............................................................3-21

3-11 Depth versus volume relationship for Easy Street and lawn cross section...........3-23
xviii

3-12 Control of peak rates of stormwater runoff can, in concept, mitigate 

surcharging of combined sewer systems....................................................3-25

3-13 Mid-block berm in Skokie intended to direct the flow of stormwater runoff...........3-27

3-14 Berm across an intersection in Skokie..................................................................3-28

3-15 A berm under construction in Skokie showing relocated inlet, raised 

curb and gutter, milled concrete surface and an asphalt lift.......................3-29

3-16 Bumps and humps are vehicle control devices and the gentler berm is a 

stormwater control device...........................................................................3-30

3-17 Typical configuration of an inlet, catch basin and manhole in the Skokie

combined sewer system.............................................................................3-36

3-18 A flow regulator installed in a catch basin illustrates the basic function 

of the regulator...........................................................................................3-37

3-19 Longitudinal profile of a street showing how a berm and flow regulator 

function as the outlet works of a temporary street storage facility..............3-39

3-20 Strategic placement of berms and flow regulators along a street facilitates 

use of the street’s capacity to temporarily and in a controlled fashion 

store stormwater.........................................................................................3-40

3-21 The street storage approach uses temporary, controlled ponding of 

stormwater in contrast with the common unintentional, uncontrolled 

and unexpected ponding resulting in damage and vehicular 

interference.................................................................................................3-42

3-22 Actual street ponding in Skokie (top) and Wilmette (bottom)................................3-43

3-23 Subsurface storage facilities are positioned within the right of way, above 

the combined sewer and temporarily store stormwater, not combined 

sewage.......................................................................................................3-44

3-24 Subsurface storage facilities range from simple oversized lengths of storm 

sewer to, as shown here, large structures assembled from precast 

reinforced concrete sections......................................................................3-45

3-25 Phase I, a simple static condition analysis, was used to determine if high

stages on the North Shore Channel caused basement flooding in the 

HSSD.........................................................................................................3-56

3-26 Computer model used for analysis and preliminary design in the Skokie 

HSSD..........................................................................................................3-58

3-27 Depth and duration of street ponding as a function of recurrence interval...........3-60

3-28 Examples of Hydro-Brake flow regulators available in the early 1980's

illustrating the basic operation of vortex-type regulators............................3-66

3-29 Photograph of Scepter flow regulator...................................................................3-68

3-30 Photograph of solid cover with orifices.................................................................3-69

3-31 Photographs of horizontal orifice plate flow regulator before and after

installation..................................................................................................3-70

3-32 Hanging trap flow regulator...................................................................................3-71

3-33 Streets were intentionally flooded to test the performance of flow regulators......3-73

3-34 Typical street berm design in Skokie, IL...............................................................3-75

3-35 Street storage accounts for half of the total stormwater storage in Skokie...........3-78
xix

4-1 Street storage system proposed for the Jeffery Manor neighborhood in

Chicago, IL...................................................................................................4-7

5-1 Downspouts connected to the house sewer, as shown on the left side, 

permit roof water to directly and immediately enter the combined 

sewer system and increase surcharging....................................................5-15

5-2 A disconnected downspout...................................................................................5-16

6-1 The “Hydroillogical” cycle......................................................................................6-3

6-2 Breadth of stakeholder involvement......................................................................6-5

6-3 A street storage project is likely to have many stakeholders, all of whom

should be involved from the outset.............................................................6-7

6-4 No communication and announcing decisions are increasingly unacceptable

ways of serving the public..........................................................................6-8

6-5 The goal in stakeholder involvement goes beyond providing information, 

it is meaningful interaction.........................................................................6-9

8-1 Distribution of construction costs for the Skokie street storage system

showing the relatively small cost of the berm-flow regulator

installations.................................................................................................8-3

8-2 Construction costs for Skokie’s street storage system are about one-third

the estimated cost of sewer separation......................................................8-4

9-1 Shear gate with orifice flow regulator as used in Wilmette, IL..............................9-14

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xx

Abbreviations and Acronyms

CCI Construction Cost Index (provided by ENR)

cfs Cubic feet per second

CMP Corrugated metal pipe

CSO Combined sewer overflow

CSS Combined sewer system

CUP Chicago Underflow Plan

CWA Clean Water Act

DPW Director of Public Works

EDA U.S. Department of Commerce Economic Development

Administration

ELSSD Emerson-Lake Streets Sewer District

ENR Engineering New Record (Source of the CCI)

EPA Environmental Protection Agency (same as USEPA)

gpd Gallons per day

HSSD Howard Street Sewer District

HUD U.S. Department of Housing and Urban Development

IDOT Illinois Department of Transportation

IEPA Illinois Environmental Protection Agency

ILLUDAS Illinois Urban Drainage Area Simulator

ITE Institute of Transportation Engineers

mph Miles per hour

MSDGC Metropolitan Sanitary District of Greater Chicago (now the

MWRDGC)

MSSD Main Street Sewer District

MWRDGC Metropolitan Water Reclamation District of Greater Chicago

(formerly MSDGC)

NMC Nine minimum controls

POTW Publicly-owned treatment works

RHS Rural Housing Service

RUS Rural Utilities Service

SAM System Analysis Model

SASAM Surface and Street Analysis Model

SRF State Revolving Fund

SSS Sanitary sewer system

SWMM Storm Water Management Model

TARP Tunnel and Reservoir Plan

USDA U.S. Department of Agriculture
xxi

USEPA U.S. Environmental Protection Agency (same as EPA)

WWF Wet weather flow

WWTF Wastewater treatment facility

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xxii

Acknowledgments

The support of the project by the Office of Research and Development, U.S.

Environmental Protection Agency is acknowledged and appreciated.

Mr. Robert W. Carr and Mr. Michael C. Morgan of Earth Tech conducted the computer

simulation study of the effect of street storage on the volume and frequency of

combined sewer overflows. They also participated in interviews; provided construction

costs, implementation schedules and other information about the Skokie and Wilmette

projects; and reviewed all chapters of this report. Mr. Donald F. Roecker, Special

Project Consultant, prepared most of the funding text in Chapter 5 and reviewed related

sections of this report. Ms. Vicki Farabaugh of Creative Computing created or

assembled the graphical content of this report and did the word processing.

Many Skokie and Wilmette, IL officials gave generously of their time and knowledge as

part of interviews conducted for this project. Their efforts are acknowledged and

appreciated.

Also worthy of recognition are personnel of Donohue and Associates and Rust

Environment and Infrastructure, predecessor firms of Earth Tech. Many individuals in

all three firms contributed to the creation and implementation of street storage systems

in Skokie and Wilmette.

The cooperation of Ms. Carolyn R. Esposito, Work Assignment Officer, Water Supply

and Water Resources Division, National Risk Management Research Laboratory, U.S.

Environmental Protection Agency, is appreciated and acknowledged.

wp/epastack
1 - 1

CHAPTER 1

INTRODUCTION

Combined Sewer System Challenge in the U.S.

Much work remains to be done to solve the overflow and basement flooding problems

caused by surcharging of combined sewer systems (CSS) in approximately 1000 U.S.

communities. These communities, 60% of which are small in that they have

populations of less than 10,000, have a total population of about 40 million or

approximately 15% of the country’s total. About 85% of the CSS municipalities are in

eleven northeastern, midwestern and far western states. Within these communities are

10,000 combined sewer overflow (CSO) points and an unknown number of historic and

potential basement flooding situations (Dwyer, T. 1998).

Most combined sewer municipalities face the challenge of how to mitigate overflows

and/or basement flooding and the attendant water pollution, health risks, and monetary

damages. The challenge is further defined by recognizing that the combined sewer

problem must be solved to comply with state and federal regulations, recognize the

realities of fiscal responsibility, and earn public acceptance.

Presented in this manual is a description and evaluation of what has proven, within a

specific set of circumstances, to be one way of meeting the CSS challenge. More

specifically, the technology described in this manual solved surcharging, complied with

regulations, proved to be cost effective and earned public support.

CSO Policy of the USEPA

Objectives of the Policy

Three objectives guide the U.S. Environmental Protection Agency’s (USEPA) CSO

policy (USEPA 1994). They are:

• “...ensure that if CSOs occur, they are only as a result of wet weather.”
1 - 2

• “...bring all wet weather CSO discharge points into compliance with the

technology-based and water quality-based requirements of the Clean Water

Act (CWA).”

• “...minimize water quality, aquatic biota, and human health impacts from

CSOs.”

According to the USEPA (1994):

Permitees with CSSs that have CSOs should immediately

undertake a process to accurately characterize their sewer

systems, to demonstrate implementation of the nine

minimum controls, and to develop a long-term CSO control

plan.

Nine Minimum Controls

Permitees with CSOs should, according to the EPA (1994), submit appropriate

documentation demonstrating implementation of the nine minimum controls (NMCs),

including any proposed schedules for completing minor construction activities. The

nine minimum controls are:

2. proper operation and regular maintenance programs for the sewer system and

the CSOs;

3. maximum use of the collection system for storage;

4. review and modification of pretreatment requirements to assure CSO impacts

are minimized;

5. maximization of flow to the publicly-owned treatment works (POTW) for

treatment;

6. prohibition of CSOs during dry weather;

7. control of solid and floatable materials in CSOs;

8. pollution prevention;

9. public notification to ensure that the public receives adequate notification of

CSO occurrences and CSO impacts; and

10. monitoring to effectively characterize CSO impacts and the efficacy of CSO

controls.

John and Wheatley (1998) focus on the minimum and interim aspects of the NMCs

when they state that the NMCs were:

...not expected to require major capital expenditures and

directed state environmental agencies to formulate their own

strategies for bringing CSOs into compliance with water

quality standards and other CWA requirements. The

minimum controls can reduce CSO impacts on water quality

but were not seen as a long-term solution.
1 - 3

Long-Term CSO Control Plan

Permitees with CSOs are, according to the EPA (1994), responsible for developing and

implementing long-term CSO control plans that will ultimately result in compliance with

the requirements of the CWA. The long-term plans should consider the site-specific

nature of CSOs and evaluate the cost effectiveness of a range of control

options/strategies. The minimum elements of the long-term control plan are:

• Characterization, monitoring, and modeling of the combined sewer system.

• Public participation.

• Consideration of sensitive areas.

• Evaluation of alternatives.

• Cost/performance considerations.

• Operational plan.

• Maximizing treatment at the existing POTW treatment plants.

• Implementation schedule.

• Post-construction compliance monitoring program.

Traditional Approach: Store/Treat Combined Sewage or Separate the Sewer

System

Traditional and proven structural methods for resolving CSS flooding and pollution

problems include, as shown in Table 1-1, separation, in-system storage, end-of-pipe

storage, and deep tunnels. All the traditional solutions address the pollution problem

while separation and in-system storage can also mitigate flooding problems, especially

basement flooding caused by surcharging of combined sewers.

The premise of the traditional and proven solutions is to generally accept the rate of

stormwater flow into the system. The resulting mixture of stormwater, sanitary sewage

and other components is then controlled with methods such as in-system storage, endof-pipe storage, and deep tunnels.

The Association of Metropolitan Sewage Agencies, in a study of 21 large U.S.

communities having CSS’s, reported that “storage is the most common approach taken

to reduce the volume and frequency of overflows” (AMSA, 1994, p. 17). Storage in this

context includes the in-system, end-of-pipe, and deep tunnels approaches listed in

Table 1-1. Interestingly, nine of the 21 communities have constructed (Chicago, IL and

Milwaukee, WI) or plan to construct tunnels. Two of the 21 studied communities,

Minneapolis-St. Paul, MN and Hartford, CT have made major commitments to sewer

separation.
1 - 4

Table 1-1. Proven methods are available to solve pollution and/or flooding problems in

 combined sewer systems.

Method Problem Solved

Pollution Flooding

Separation U U

In-System Storage1 U U

End-of-pipe Storage1 U

Deep Tunnels U

1) Storage of combined sewage.
1 - 5

A New Approach: Store Stormwater Before It Combines With Sanitary Sewage

Wet weather problems in CSSs are caused by the peak rate of stormwater runoff, not

necessarily by the runoff volume. Wet weather flooding and pollution problems would

often not occur, or would be much less severe, if the peak flows of stormwater could be

lessened. Peak flows are often the principal culprit, not the volume of stormwater

runoff.

This suggests a fundamentally different approach having the following premise: reduce

the peak flow rates of stormwater before it enters the combined sewer system. Accept

the full volume of stormwater into the CSS, but greatly reduce the peak rate of entry. 

Figure 1-1 illustrates, in conceptual fashion, this stormwater-oriented approach to

reducing surcharging in CSS and, therefore, mitigating flooding and pollution. Chapter

3 includes a detailed description of the conceptualization, development, design and

construction of the street storage approach.

Scope of This Evaluation

Case Study Approach

This manual documents a case study-based evaluation of the use of on-street and

related storage of stormwater to reduce the surcharging of combined sewers and, in

turn, mitigate basement flooding and CSOs. The focus of the evaluation is capturing,

analyzing, and presenting what has been learned through the concept-throughoperation process over 18 years in primarily two communities. Synopses of several

other applications are included as supplemental ways to learn about the street storage

system approach.

The scope of this manual is broad. The evaluation includes many and varied aspects

of the case studies such as analysis and design approaches, regulatory and funding

framework, public involvement, operation and maintenance procedures and costs,

construction costs, and performance of the system. The scope of this manual is also

deep, that is, detailed. Each of the preceding topics are covered in depth. The scope

of this manual is also broad in that it addresses both flooding and pollution caused by

surcharging of CSS’s. This quantity and quality issue is discussed in the next section.

Quantity and Quality: Seeking Optimum Means of Simultaneously Mitigating

Flooding and Pollution

Most CSS studies, reports and guidelines that are not community or site-specific,

address only or mainly the need to reduce pollution caused by CSOs. Lost in this focus

on pollution caused by surcharging of CSSs is the frequent parallel problem of

basement and other flooding caused by surcharging of CSSs.
Figure 1-1. Control of peak rates of stormwater runoff can, in concept, mitigate

 surcharging of combined sewer systems.

1-6

Premise:

Do not accept peak flow rates

(mostly stormwater) into

the combined sewer system

Turf, Concrete,

Asphalt Surface

Combined

Sewer

Surcharged

Is Not

Inlet/Catchbasin

Dry Weather

Turf, Concrete,

Asphalt Surface

Combined

Sewer

Surcharged

Is

Inlet/Catchbasin

Wet Weather without

Stormwater Control

Turf, Concrete,

Asphalt Surface

Temporary

Storage

Combined 

Sewer

Inlet/Catchbasin

Wet Weather with

Stormwater Control

Surcharged

Is Not
1 - 7

As an indication of the possible local importance of basement and other flooding in

CSS communities, consider the community-specific information provided in an

assessment report prepared by the Association of Metropolitan Sewerage Agencies

(AMSA, 1994). Described in this report are “CSO control programs” in 21 communities

across the U.S. Although the focus of the report is clearly on CSS water quality, that is,

pollution problems, water quantity problems, that is, flooding, are clearly evident in

some of the 21 communities. The report states (AMSA, 1994, p. 15):

In many of the cities, basement flooding during

wet weather is also a problem that influences

CSO improvements and frequently impacts

the selected control strategy (emphasis

added).

Flooding data on the previously mentioned 21 communities plus others is summarized

in Table 1-2. Some type of flooding attributed to the CSS is explicitly reported by seven

of the communities. Given the preceding quote, flooding problems may be under

reported.

As an example of emphasis on pollution control in CSSs to the essential exclusion of

flood control, consider the USEPA manual on combined sewer overflow control

(USEPA, 1993). The stated purpose is to provide “...information to assist in selecting

and designing control measures for reducing pollutant discharges from CSOs” (USEPA,

1993, p. 1). Although most of the report focuses on controlling combined sewage, there

are scattered brief references to components of street storage. Examples are inlet

restriction and attendant street ponding (p. 7), flow slipping (p. 7) and regulators (p. 38).

Several possible explanations can be offered for the strong focus on pollution caused

by CSSs to the exclusion of addressing basement and other flooding problems.

First, pollution will almost always be a problem in CSSs while basement and other

flooding problems are less likely to occur as evidenced by the AMSA (1994)

assessment. Basements are essentially not present in some communities because of

factors such as high groundwater levels and the presence of shallow bedrock. The

actual severity and frequency of basement flooding, regardless of cause, is likely to be

greater than reported because building owners may fear loss of property value if

flooding of their basements is documented. However, when basements exist within a

CSS, the resulting flooding by combined sewage can be a serious and repeated health

risk and create large monetary losses.
1 - 8

Table 1-2. Seven of 22 large CSS communities explicitly reported basement or street

and other surface flooding (AMSA, 1994 except where other source is indicated).

City Type of Flooding Explicitly Reported As being Attributed to the CSS

Street and/or Other

Surface Flooding

Basement Flooding Undifferentiated

Flooding

Atlanta, GA

Boston, MA

Chicago, IL M

Cincinnati, OH

Cleveland, OH M

Columbus, GA

Detroit, MI

Fort Wayne, IN1 M

Hartford, CT M

Louisville, KY M M

Milwaukee, WI

Minneapolis-St. Paul,

MN

New York, NY

Philadelphia, PA

Portland, OR

Providence, RI

Richmond, VA

Sacramento, CA M M

San Francisco, CA

Seattle, WA

Washington, DC M

Wayne County, MI

1) WERF, 1998, pp. 14-15
1 - 9

Second, the USEPA and counterpart state “environmental” agencies (e.g., Indiana

Department of Environmental Management) tend to be concerned with pollution

abatement. In contrast, flood control and drainage are within the mission of the COE

and counterpart state agencies (e.g., Indiana Department of Natural Resources).

These flood control oriented agencies typically do not address problems in CSSs. 

Agency missions understandably drive agency programs. A possible negative aspect of

exclusive or excessive focus on pollution abatement in CSSs is that less than optimum

solutions may result. For example, a community’s CSO problem may be successfully

resolved by end-of-pipe storage or end-of-pipe connection to “deep tunnels” while the

basement flooding problem continues.

Optimum solutions are more likely to arise if the entire drainage system or watershed is

examined from the outset in terms of defining the problem (pollution and flooding),

determining the causes, and then finding the most cost-effective solution. The scope of

this manual is holistic in that it stresses the possibility of simultaneously addressing

quality and quantity, that is, pollution abatement and flood control.

Retrospective Details With Prospective Purpose

Because of the case study approach, the details of this manual are retrospective. That

is, the emphasis is on history—what was done, why it was done, how it worked. 

However, in as much as municipal officials are the principal audience of this manual, the

overall thrust is prospective. That is, how could other communities benefit from the

concept-through-operation experience of the case study communities? 

Each municipality has a unique meteorological, physical, socio-economic, political and

regulatory profile. Therefore, only some of the knowledge gained from the case studies

described in this manual will be transferable to any given community. However, given

the breadth and depth of knowledge presented in this manual, if even a small part is

directly applicable to a given municipality, that municipality will gain much. Stated

differently, the specifics documented in this manual should prevent “reinventing the

wheel” in other communities. The theme of relevance to other CSS municipalities is

woven throughout this manual. Perhaps some communities will investigate the street

storage option as a result of successes enjoyed by the case study municipalities.

In addition to having a prospective thrust to serve municipalities, this manual is also

prospective for the benefit of researchers. Possible research topics are identified, (see

Chapter 11), based on the case study experience, with the hope that additional

investigations might be conducted.
1 - 10

Initiatives

As noted, this is a case study-based manual and, therefore, the details are largely

retrospective. Accordingly, new research efforts were generally beyond the scope of the

evaluation, with two specific exceptions. 

The first exception to the retrospective focus of this manual is a literature search. Efforts

were made to find, document and incorporate relevant papers, articles, and personal

contacts not already discovered during the conduct of the two projects. Because the

technology was considered innovative when first applied to the case study communities

in the 1980's, a major effort was undertaken at that time to find relevant literature and

knowledgeable individuals. Results of those efforts were included in early project

documents and are summarized in this manual. The additional literature and resource

search carried out for this evaluation was conducted to enhance the value of the

manual. Findings of the literature search are included throughout this manual as

supplements to the two case studies.

The second exception to the retrospective focus of this manual is the special analysis of

the hypothetical impact of the control technology on the volume and frequency of CSOs

and on peak flows at wastewater treatment plants. Basement flooding by combined

sewage, not CSOs, was the major CSS concern in the two case study communities. 

However, the implemented solution may have the potential to mitigate CSOs and related

problems. Therefore, that potential was studied in an exploratory fashion to further

enhance the value of this manual. That study is described in Appendix F and the results

are summarized in Chapter 9.

Terminology

Several terms have been used in recent years to describe controlling peak rates of

stormwater flow as a means of reducing surcharging in CSS’s. Utilization of different

terms for essentially the same system can and probably has led to some confusion. 

Accordingly, various terms are discussed here for purposes of clarification and to show

commonality among various research, development and engineering design efforts in

the U.S. and elsewhere. A specific terminology and its definition is then set forth for use

in this manual.

Terms in use include:

• Runoff Control. This terminology has been in use in the U.S. since at least the

early 1980's. In fact, it was used in most of the written and spoken

communication throughout the two principal case studies which are described in

this manual. See for example, the numerous Donohue & Associates citations in

the Cited References. However, this term, while suggesting stormwater, is too

general. Many aspects of stormwater management could be called “runoff
1 - 11

control.”

• Inlet Control. This terminology appears in the title of writings by Hides (1994)

and Pisano (1989) and is also used by Harza Engineering (1981). While inlet

modification may be part of the overall stormwater control system, it is typically

just one component. For example, other possible components are street berms

and subsurface storage tanks. Therefore, the term inlet control is undesirable

because it suggests an unrealistically simple approach.

• Source Control. This term, which was used by Kaufman and Lai (1978) and

Walesh (1996), has appeal because the stormwater is to be temporarily stored

as close as possible to the source, that is, to where it falls as precipitation. 

Unfortunately, this quantity-oriented use of “source control” conflicts with the

predominantly quality-oriented use of “source control” in amendments to the

Clean Water Act. In these amendments, “source control” is strongly associated

with non-point source pollution. 

• Micromanagement of Stormwater. This terminology, used by Carr and

Walesh (1998), focuses on the local, detailed, intersection-by-intersection

analysis and design process that is needed when attempting to reduce peak

stormwater flows in existing urban areas. This analysis and the resulting design

and construction of numerous, small structures may be characterized as “micro”

when compared to the “macro” approach typically used in stormwater system

analysis and design. “Macro,” in this context, refers to larger subbasins used in

the analysis and the smaller number of larger structures, such as detention or

retention facilities, typically designed and constructed. On the negative side,

the term “micromanagement” is not, in and of itself, very descriptive. Additional

description is needed to communicate the concept.

• Street Storage. This term has proved to be highly descriptive. It readily

suggests the unconventional, but potentially effective use of streets to

temporarily store stormwater. On the negative side, while on-street storage is

typically an important aspect of reducing peak stormwater flow into a CSS, it is

not the only form of storage. Other possibilities include off-street surface

storage and storage below streets and parking lots. The short hand term “street

storage” was selected for use in this manual. It appears in the title.

Street storage means:

a system that mitigates surcharging of CSSs,

SSSs and stormwater systems by temporarily

storing stormwater in a controlled fashion on the

surface (mainly on-street but some off-street)

and, as needed, below streets. Stormwater is

stored close to the source, that is, where it falls

as precipitation, and prior to its entry into the
1 - 12

sewer system. The full volume of stormwater

runoff is accepted into the sewer system but

peak rates are reduced, as a result of the

storage, to flow that can be accommodated

without surcharging.

Abbreviations, Acronyms and Glossary

Many abbreviations and acronyms are used, for the purposes of efficiency and

communication, in this manual. In the interest of assisting the reader, the first use of an

abbreviation or acronym in the manual is accompanied by its definition. After that

introduction, the abbreviation or acronym is used in the remainder of the manual. For

easy reference, a complete list of abbreviations and acronyms is included near the front

of this manual.

Some readers may not be familiar with all the technical, regulatory and other terms used

in this manual. Accordingly, a Glossary appears near the end of this document. 

Selected definitions were drawn from the “Glossary of Wet Weather Flow Terms”

(USEPA, 1998) and from other sources, as indicated in the Glossary.

wp/epastch1
2 - 1

CHAPTER 2

CASE STUDY COMMUNITIES:

SKOKIE AND WILMETTE, IL

Bases of Selection of Case Study Communities

Skokie and Wilmette, IL, the two principal case study communities, were chosen for this

manual primarily for three reasons, as described here. Because this manual describes

case studies of a newer technology, an opportunistic approach was taken to finding

principal and supplemental case study communities whose experiences could be of

value to other communities. The identified case study communities in effect provided

“laboratories” in which the new street storage technology could be studied.

Familiarity of the Investigators With the Projects

Each member of the four-member engineer team that conducted this investigation

contributed significantly to the engineering, financing or other aspects of one or both of

the two principal street storage system projects. By choosing the Skokie and Wilmette,

IL as the two principal case study communities, optimum use was made of the first

hand experience of the investigators.

On-Going Relationships With Personnel in the Case Study Communities

Three of the four engineer members of the team that conducted this investigation have

maintained on-going relationships with personnel in at least one of the two principal

case study communities. This proved to facilitate ready access to data, information,

and suggestions originating within the two communities.

Opportunity to Study a Large, Long-Standing Street Storage Project

The Skokie, IL street storage system is the largest known application of this technology

in the U.S. and possibly beyond. Furthermore, parts of the Skokie system have been in

operation since 1983, providing many years of operating experience. By choosing

Skokie for this case study, the manual captures the best known overall example of the

street storage technology.
2 - 2

Supplemental Communities

As a supplement to using Skokie and Wilmette as the principal case study

communities, other smaller scale applications of street storage, or components of it,

were sought. These applications is presented in Chapter 4.

The remainder of this chapter is devoted to detailed descriptions of Skokie and

Wilmette, IL. Pertinent information on supplemental communities that have

implemented street storage or some aspect of it is presented when those communities

are discussed.

Description of Skokie, IL

A detailed description of Skokie, IL is presented to provide context and data for

understanding the case studies. Included in the description are physical attributes,

meteorology, and history of CSS problems and proposed solutions to them.

Location

The general location of the 8.6 square mile Village of Skokie is shown on Figure 2-1. It

is immediately north of the City of Chicago. Figure 2-2 is a map of Skokie showing

major features. Skokie is bounded on the south by Lincolnwood, on the west by Niles 

and Morton Grove, on the north by Wilmette, and on the east by the North Shore

Channel and Evanston. As suggested by Figure 2-3, which is a photo of the North

Shore Channel, the channel and its associated linear parks are an amenity for area

residents.

Relationship to the Metropolitan Water Reclamation District of Greater Chicago

Skokie lies entirely in the service area of the Metropolitan Water Reclamation District of

Greater Chicago (MWRDGC). At the beginning of the Skokie street storage project,

this agency was named the Metropolitan Sanitary District of Greater Chicago (MSDGC).

Essentially all of Skokie is served by a CSS. Combined stormwater runoff and sanitary

sewage generated within Skokie flow generally eastward to interceptors and TARP

(Tunnel and Reservoir Plan), also called the deep tunnel system, which is owned and

maintained by the MWRDGC. As shown schematically on Figure 2-4, the interceptor

parallels the North Shore Channel. The tunnel, which parallels and lies 200 feet below

the North Shore Channel, is intended to capture, via drop shafts, combined sewage that

is in excess of the interceptor capacity. As suggested by Figure 2-4, the deep tunnel is

primarily a pollution control system. It mitigates CSOs but has minimal impact on

basement flooding caused by surcharged combined sewers.
WI

IL

IL

IN

Lake Michigan

N

0 10 M I

Chicago

Skokie

Wilmette

Figure 2-1. Skokie and Wilmette, IL lie immediately north of the City of Chicago.

2-3
North Shore Channel

Figure 2-2. Map of Skokie, IL (Source: Donohue, 1982b, p. 13).

2-4
Figure 2-3. The North Shore Channel, which bounds Skokie on the east, and its

contiguous linear parks provide an amenity for area residents.

2-5
Building with

Basement Building without

Basement

Interceptor

Sewer

Deep

Tunnel

Combined

Trunk

Sewer Normal

Stage

North Shore

Channel

Figure 2-4. The deep tunnel is primarily a pollution control system in that it mitigates

combined sewer overflows to the North Shore Channel.

2-6
2 - 7

Most drop shaft connections were provided to relieve the MWRDGC interceptors and

not directly serve individual communities. However, proactive Chicago area

communities such as Arlington Heights, Evanston, Niles, Skokie, and Wilmette were

able to negotiate with the MWRDGC to provide drop shaft connections with agreed

upon capacities to serve their CSSs. As a condition of placing these drop shafts, the

communities were required to limit peak discharges to TARP. These conditions gave

added impetus to Skokie and Wilmette, the two principal case study communities, to

consider the street storage system.

Land Use and Population

Skokie is completely developed. Land use is about 80 percent residential, 10 percent

industrial and 10 percent commercial. The population is about 60,000 persons with an

overall population density of 11 people per acre and a population density in residential

areas of approximately 14 people per acre (Nakai and Carr, 1993). There are about

20,000 single family residences in Skokie (Raasch, 1989b).

Soils and Groundwater

Skokie soils are primarily from glacial deposits of the Pleistocene series. These glacial

deposits have an approximate depth of 60 feet and consist of many types of materials. 

About 25 percent of the community has sandy soils, while the remainder has clay soils. 

Groundwater levels are generally 10 to 15 feet below ground level in sandy areas. An

exception is isolated perched lenses of shallower ground water (Nakai and Carr, 1993).

Topography and Drainage Patterns

“The land ...generally slopes eastward toward the North Shore Channel. Slopes vary

from 0.1 to 1 percent and the overall slope in many areas of the Village is a flat 0.2

percent. Surface runoff ...flows from the front lawn and driveway areas to the street. 

Flow in the street is along the curb line and gutters to the nearest inlet. Inlets are

generally located midblock and at intersections. Due to the extremely flat conditions,

few areas have a continuous drainage pattern from block to block” (Nakai and Carr,

1993).

Trunk sewers in the combined system range in diameter from 30 inches to a maximum

of 84 inches. Lateral sewers which are connected to trunk sewers vary in diameter

from 12 to 27 inches. Combined sewage is carried from Skokie through three 84-inch

trunk sewers to the MWRDGC interceptor sewer. When the interceptor capacity is

exceeded each trunk sewer overflows first to the MWRDGC deep tunnel and then to

the North Shore Channel (Nakai and Carr, 1993).

Stormwater leaves the street by flowing into an inlet, none of which have sumps, and
2 - 8

generally there are two inlets connected to a catch basin. As shown in Figure 2-5,

catch basins are manhole-type structures containing some standing water in a sump at

all times. The pipe conveying flow from the catch basin to the combined sewer is

configured so as to form a trap preventing backup of sewer gases into the catch basin. 

Catch basins are generally located between the curb and sidewalk and have either a

grated or solid manhole cover (Walesh and Schoeffmann, 1984).

Skokie is partitioned into three combined sewer districts. They are, as illustrated in

Figure 2-6, the 1,255 acre Howard Street Sewer District (HSSD) in the southern part of

the community; the 2,300 acre Main Street Sewer District (MSSD) in the central part,

and the 1,955 acre Emerson Lake Streets Sewer District (ELSSD) in the northern part. 

As indicated earlier, the three districts drain generally easterly and flow into an

interceptor sewer along the deep tunnel beneath the North Shore Channel (Nakai and

Carr, 1993).

Climate

Skokie’s climate is classified as continental, typical of a location in middle latitudes (42

degrees north latitude), but somewhat modified by the proximity of Lake Michigan which

is two miles east of the community. Because of the lake, the climate is moderated

relative to inland locations. Nevertheless, winters are cold, with an average snowfall of

about 36 inches as snow, and summers are warm and sometimes humid. “All seasons

are marked by occasionally intense storms that accompany changes from one air mass

to another. Runoff from these storms, particularly in the spring and early summer,

causes flooding in the Skokie area” (Donohue, 1982a, p. 29-31).

Nakai and Carr (1993) indicate that precipitation “...occurs as rain, sleet, hail, and snow

and ranges from showers of trace quantities to brief intense storms to longer duration

rainfall or snowfall events. Precipitation is distributed throughout the year with an

average annual total of 33.3 inches.” For a one-hour storm, the 1, 10, and 100-year

recurrence interval rainfall amounts are 1.18, 2.10, and 3.56 inches, respectively. For a

24-hour storm, the 1, 10, and 100-year amounts are 2.51, 4.47 and 7.58 inches,

respectively (Huff and Angel, 1989, pp. 29-30).

Brief History of Skokie with Emphasis on Development of Its Drainage System

Sewer surcharging and basement flooding problems that gradually developed in Skokie

can be traced back to the unique circumstances associated with development of the

community. Most of what is now Skokie was under waters of Lake Michigan in

prehistoric times. The community lies between two ridges approximately three miles

apart and the area was mostly swamp when the first explorers arrived in the sixteen

hundreds and found the Potawatomi Indians living there.
Catch Basin

Inflow Pipe

from Inlet

Outlet Pipe to

Combined Sewer

Figure 2-5. Each Skokie catch basin is a manhole-type structure with a sump.

2-9
Emerson-Lake

Streets District

Emerson-Lake

Streets District

Main Street

District

Main Street

District

Howard Street

District

Howard Street

District

N

0 1 M I

North Shore

Channel

North Shore

Channel

Figure 2-6. Skokie is partitioned into three easterly draining combined sewer districts.

2-10
2 - 11

As the area became populated in the 1800's, the need for drainage and sanitary waste

disposal became critical. Construction of the North Shore Channel in 1910, as part of

the overall plan to provide the Chicago metropolitan area with an adequate drainage

system, provided an outlet for sewers to serve Skokie. The first trunk sewer was

constructed in 1886 to drain what is now the downtown area and carried both

stormwater and sewage to the channel. Skokie’s combined sewer system had begun.

The prime reason for the severity of the present basement flooding problem in Skokie is

tied to the 1920's—the land boom days in Skokie. Major roads from Chicago were

being paved and a rapid transit line extended through Skokie. As farm land was

subdivided into building lots, population rose from 760 in 1920 to 4,200 in 1930. In

preparation for the anticipated building boom, the majority of streets, sidewalks, water

mains and sewers were constructed. The contemporary technology resulted in the

construction of a combined sewer system with its outfall at the North Shore Channel. In

1927, a treatment plant and interceptor sewer system were constructed to handle dry

weather sanitary flows, but the remaining mainly combined sewage flowed into the

channel.

The depression of the 1930's brought the land boom in Skokie to an immediate halt. 

The constructed infrastructure was left essentially unused for the next 20 years. 

However, development anticipated in the 1920's finally occurred in the years following

World War II. The majority of development and building took place in the 1950's as

Skokie’s population exploded from 14,800 in 1950 to 59,400 in 1960 (Walesh and

Schoeffmann, 1984).

Not only did the community commit to an entire CSS but, trunk sewers were,

unfortunately, undersized. More specifically (Consoer, Townsend & Associates, 1967):

Because of limitations on financing, the original

trunk sewer improvements were of an

introductory nature and restricted in size. The

lateral sewers were, however, installed to then

standard practice. All of these sewers were

combined storm and sanitary type.

It had been anticipated that additions to the

combined sewers would be installed at

intervals as buildings were constructed in the

vacant areas. However, this program was not

followed and as of today, all of the trunk

sewers are deficient in capacity for an

acceptable level of service. Basement flooding

is prevalent during medium to heavy storms,

and damaging street flooding also occurs
2 - 12

during the heavier storms.

In summary, this brief history highlights the community’s early commitment to combined

sewers and the need, driven by finances, to undersize trunk sewers. This history also

provides a seque to the next major section of this chapter which describes problems

caused by Skokie’s undersized CSS.

Skokie’s Historic Combined Sewer System Basement Flooding Problems

Several surveys over about a decade in the 1960's and 1970's documented widespread

basement flooding in Skokie. According to Donohue (1982a):

Previous studies by Consoer, Townsend &

Associates, 1967 and 1973; the Village of

Skokie, 1974; and by Harza Engineering

Company, 1978, have included surveys to

determine the extent of basement backup

flooding in the Village of Skokie. These

surveys were generally conducted by sending

post cards to residences requesting

information on their flooding history.

The 1967 survey received responses from over

9,000 residences with slightly in excess of 54

percent indicating that they had basement

backup problems during major storms.

The 1978 survey resulted in about 2,500

responses, a response rate of only 11 percent. 

Approximately 15 percent of those responding,

indicated they had basement flooding from

recent rains which were less intense than a 2-

year frequency storm. These backup problems

were spread somewhat uniformly over most of

the community. Interestingly, about 20 percent

of the residences having flooding problems

also indicated they had at least one flood

protection device that obviously didn’t work

properly.

The 1974 survey by the Village was conducted

only in the Fairview South area. During the

survey, a questionnaire was mailed to each

residence and Village personnel attempted to

interview every homeowner. These efforts

resulted in a 72 percent coverage of the 471
2 - 13

units and 47 percent indicated they had

basement flooding during heavy rainfall. 

Again, a large percent of the people with some

type of flood control equipment indicated they

still had basement backup flooding problems.

Viewed collectively, the three surveys (1967, 1974 and 1978) suggest a communitywide basement flooding problem caused by surcharging of the CSS. At least half of the

residences appeared to experience basement flooding in larger storms. Furthermore,

basement flooding occurred in a smaller but significant fraction of residences during

frequent, minor storms.

Previous Studies of Ways to Solve Skokie’s Combined Sewer System Basement

Flooding Problems

Skokie commissioned or conducted studies over a 15 year period to find a costeffective solution to the growing basement flooding problem. Summarized here are the

essential aspects of seven studies including the recommendations. This summary

serves to illustrate how traditional solutions were repeatedly proposed but not

implemented. This process, in turn, set the stage for Skokie’s receptivity to a new

approach.

Study Completed in 1967 Recommending Relief Sewers

Consoer, Townsend & Associates (1967) conducted this community-wide investigation. 

Donohue (1982a, pp. 15-16) provides this summary:

This study reviewed the sewer system

deficiencies and backup problems in

basements throughout the Village. It reviewed

several alternative solutions to these sewer

backup problems and recommended an

overflow relief sewer system for the entire

Village with an estimated 1967 cost of $22.0

million (Note: The 1999 cost would be $123

million using the Engineering News Record

[ENR] Construction Cost Index [CCI]). In the

Howard Street Sewer District the report

recommended a major relief sewer along

Laramie Avenue from Farwell Avenue to

Brummel Street (48-inch to 102-inch diameter),

then eastward along Brummel Street from

Laramie Avenue to Hamlin Avenue (108-inch

to 144-inch diameter), then two blocks south

along Hamlin Avenue to Howard Street, and
2 - 14

east along Howard Street to the North Shore

Channel (144-inch diameter). These sewers

were never installed.

The proposed relief sewers were designed so

that the combined capacity of the existing trunk

sewers and the new relief sewers would be

such that runoff from about a 15-year storm

could be accepted from non-restricted areas

and the actual maximum possible runoff could

be accepted from restricted flat areas.

Study Completed in 1973 Recommending Deep and Shallow Tunnels

With the “deep tunnel” being imminent, Skokie retained Consoer, Townsend &

Associates (1973) to carry out another community-wide investigation with emphasis on

solving basement flooding problems. The following summary is provided by Donohue

(1982a, pp. 16-17):

In October 1972, the Board of Trustees of the

Metropolitan Sanitary District of Greater

Chicago (MSDGC) adopted the “Chicago

Underflow Plan” (CUP). (This plan is later

referred to as Tunnel and Reservoir Plan,

TARP). The plan consisted of construction of

120 miles of conveyance tunnels intercepting

the overflows from all existing combined

sewers in the Chicago land area. One of the

planned underflow tunnels paralleled the North

Shore Channel and was scheduled for

installation in the first phase of construction of

the underflow plan. This provided a new outlet

for the combined sewage flow from the Skokie

sewer system and radically changed relief

sewer concepts for the Village of Skokie. The

1973 Consoer, Townsend study analyzed the

sewer facility needs for the Village of Skokie in

conjunction with the CUP.

This report recommended a system of deep

and shallow tunnels connecting to the MSDGC

main tunnel along the North Shore Channel. 

The 1973 estimated cost was $31 to $35

million (Note: The 1999 cost range would be
2 - 15

$98 to $111 million using the ENR CCI). The

system within the Village of Skokie included a

major deep tunnel in an east-west direction

down Main Street draining towards the North

Shore Channel and several shallow tunnels in

north-south directions draining to this deep

tunnel. The Howard Street area would be

served by shallow tunnels leading north along

Laramie Street and Keeler Avenue. The report

presented design data and cost estimates on

systems sized for both the 10-year and 100-

year storms. None of these deep or shallow

tunnels have been constructed.

The study also analyzed the effect that the

CUP would have on the existing trunk sewers if

no relief sewers were provided. The report

concludes that the North Shore Channel

underflow tunnel will have a minor impact on

Skokie flooding without supplementary

channels or relief sewers being installed,

except for several blocks near the outlet.

Study Completed in 1974 Recommending Downspout Disconnection and Catch

Basin Restrictors

Unlike all the other studies summarized in this section, this one was conducted by

Skokie personnel. Donohue (1982b, pp. 17-18) contains this summary:

This study was completed by the Village of

Skokie to determine the probable relief that

could result from downspout disconnection in

the Fairview South area and catch basin

restrictions. The restrictors were “half-moons”

inserted into catch basin outlet pipes which

effectively reduce their discharge capacity by

one half. Twenty-seven percent of the

downspouts in the area were found to be

disconnected at the beginning of the study.

Detailed surveys were conducted by mailing

questionnaires to residents of the Fairview

South area and collecting these questionnaires

by survey teams in the field. The survey
2 - 16

covered 72 percent of the residences and

showed that of those surveyed, 47 percent

have basement backup problems during heavy

rainfalls. The survey also asked if residences

had some type of flood control equipment

installed. Of the 355 residences surveyed, 86

percent indicated that they had some type of

flood control equipment installed. However, a

large percentage of these residences still

experienced sewer backup problems due to

inadequacies or malfunctioning of their flood

control equipment. Another question checked

the citizen response to the acceptability of a

future downspout disconnection program. 

Sixty-nine percent of the 355 residences

surveyed voiced a willingness to participate in

a downspout disconnection program.

Recommendations of the study were: 1) New

catch basin restrictors should be installed at 86

locations to reduce the pipe diameter from

eight inches to four inches thereby reducing

the discharge capacity of the catch basins by

75 percent. The cost was estimated to be

$1,274. 2) A downspout disconnection

program should be instituted and all

residences in the study area except those

fronting on Laramie and Pratt Avenues should

be disconnected. Cost for this program was

estimated at $19,728. The net effect of this

downspout disconnection program would be a

49 percent reduction in the demand placed on

the sewer system. The study stated that the

additional stormwater directed into the street

by the disconnected downspouts and stored in

the street by the restricted catch basins could

be stored without causing major hazards to

vehicular traffic in all areas of Fairview South

except the west and south boundary streets,

Laramie Avenue and Pratt Avenue,

respectively. This study used the five and 10-

year storms to analyze street flooding

characteristics.
2 - 17

As a result of this study, Skokie proceeded with a downspout disconnection program

with the goal of disconnecting 95 percent of those in the HSSD in 1982. Also in

keeping with the study’s innovative recommendation, some restrictors were installed in

catch basins. Unfortunately, most were removed because of plugging and

maintenance problems (Donohue, 1982b, p. 18).

Study Completed in 1978 Recommending Deep and Shallow Tunnels and Relief

Sewers

The entire Skokie CSS was the target of another study, this one conducted by Harza

Engineering Company (1978). As with the 1973 study, this investigation was carried

out with the understanding that TARP would eventually be a reality and, therefore,

provide an improved outlet for Skokie’s CSS. The following summary is provided by

Donohue (1982b, pp. 18-19):

This study analyzed the combined sewer

system in the Village of Skokie and reviewed

alternative ways to improve the system

performance and mitigate existing problems. 

The study related that the lateral sewers,

characteristically about two blocks long with a

maximum diameter of 18 inches, would have

sufficient capacity such that backups in

basements would occur only about once in 25

years if the downstream branch sewers were

adequate to handle the lateral sewer

discharges. These existing branch sewers,

however, have about one-half of the capacity

needed to convey the flow which the lateral

sewers can deliver. The large trunk sewers

into which the branch sewers flow have less

than one-half of the capacity required to

convey the flow from the branch and lateral

sewers. Thus, the overall sewer system

capacity decreases drastically in a downstream

direction causing a flow constraint and

resulting in under utilization of the upstream

features of the sewer system.

Mitigation concepts that were investigated

included homeowner protection devices,

reduced rate of stormwater runoff into the

sewer system, separate storm sewer systems,

and increased capacity of the existing sewers. 
2 - 18

The report recommended that the Village

proceed with a program to increase the

capacity of the existing sewers. This increased

capacity would be accomplished by

construction of a system of deep and shallow

tunnels connecting to the MSDGC main stream

tunnel system. Installation of some parallel

branch sewers to convey additional flow to the

tunnel system was also recommended. This

system was sized to provide conveyance

capacity for runoff from a 10-year frequency

storm with Phase I of TARP in place and

functioning. The 1978 cost estimate for these

improvements was $78 million (Note: The 1999

cost would be $168 million using the ENR

CCI). None of the improvements have been

constructed.

Study Completed in 1981 Providing Additional Insight Into System Inadequacies

The MSDGC (now the MWRDGC) studied the performance of the ESSD after two

summer of 1981 storms caused basement and street flooding (Paintal, 1981). This

investigation, as summarized in the following Donohue description (1982b, pp. 19-21),

characterizes the capacity problems in and other aspects of the CSS:

The MSDGC completed a study analyzing the

performance of the Emerson Street Sewer

District during two heavy storms that occurred

over the Skokie area in the months of July and

August 1981. These storms produced runoff

rates which exceeded the capacity of the local

sewer system resulting in street and basement

flooding. The purpose of this study was to

analyze those storms relative to the capacity of

the Emerson Street sewer system. This

system is a 1,740 acre area in the northern

part of the Village of Skokie and is fairly similar

in structure to the Howard Street system. The

study analyzed the following:

• The frequency of the July 12 and

August 14, 1981 storms.

• The sensitivity to flooding of the local
2 - 19

sewer system relative to the water

level elevation in the North Shore

Channel.

• The effects of downspout

disconnection and house flood

control-pumping systems on lateral

sewer flows.

Although this analysis was performed on the

Emerson Street District, most of the results and

conclusions are pertinent to the Howard Street

Sewer District and are summarized as follows:

• Submergence of the sewer outlet at

the North Shore Channel does not

affect the sewer capacity

significantly if the water level in the

channel does not rise above

elevation 5+/- Chicago City Datum.

• The storms of July 12 and August 14

had a frequency of recurrence of

once in 40 years and once in five

years, respectively. The Emerson

Street sewer, had it been designed

for a five-year storm, would have

adequate capacity to handle the

flows generated by the above

storms. The Lawler Avenue sewer

(a local lateral similar to the laterals

in the Howard Street District), had it

been designed for a two-year storm,

would have conveyed the flows

generated by these storms.

• In order to negotiate the storms, the

Emerson Street sewer should have a

capacity of 1 to 1.2 cubic feet per

second (cfs) per acre in comparison

to the actual capacity of 0.13 to 0.2

cfs per acre. The capacity of the

sewer is about one-fifth of what was

required.

• Had the sewer been of adequate

capacity, the flow at the outlet would
2 - 20

have been 1,600 cfs from its service

area of 1,740 acres. That is equal to

0.92 cfs per acre. It is noted that

TARP (Phase I) is designed for 1.0

cfs per acre drainage intensity.

• The results of an analysis of the

Lawler Avenue (south) sewer to

study the effect of downspout

disconnection and individual house

flood control pumping systems on

the performance of the sewer system

indicated that:

< For short duration storms the

disconnection of downspouts

from the sewer system reduces

the flow in the sewer

significantly if the flow from the

downspouts is directed to lawns

and other porous areas.

< The flood control pumping

system protects the house but

overloads the sewer system due

to pumping during periods of

peak flow and wet weather. If

every house in the area has this

kind of system, the pumpage

alone will account for about 50

percent of sewer capacity

depending on the size of the

lateral sewer.

Additional analyses were completed in an

addendum to this report. The addendum

reviewed the effect that TARP - Phase I would

have in reducing sewer surcharging particularly

in the lower reaches of the Emerson Street

District. This analysis concluded, had TARP -

Phase I been in place during the July 12, 1981

storm, sewer surcharging and basement

flooding would have been eliminated or

considerably reduced within about 10 percent
2 - 21

or 170 acres of the Emerson Street sewer

service area which is near the sewer outfall at

the North Shore Channel. A similar reduction

in surcharging would be felt in the Howard

Street Sewer District with TARP - Phase I

completed. The actual reduction in number of

basements flooded will be somewhat less in

the Howard Street district since development

nearest the North Shore Channel is

predominately industrial and commercial with

no basements.

Study Completed in 1981 Suggesting Combinations of Traditional and Innovative

Measures

Harza Engineering Company, which had completed a system wide study in 1978, was

called on again to explore options (Harza, 1981). Now the principal stimulus for another

study was greatly reduced probability of USEPA funding. The following summary is

provided by Donohue (1982b, pp. 21-22):

Harza Engineering Company completed a

supplemental study of flood control alternatives

in 1981. This was a follow-up to their 1978

report which recommended implementation of

a system of relief sewers that would connect to

the Metropolitan Sanitary District of Greater

Chicago’s main tunnel under the North Shore

Channel. Implementation of the relief sewers

was predicated on a significant amount of

funding coming from the USEPA. Since

funding from the USEPA was no longer

probable, this supplemental study was

undertaken to identify solutions that could be

implemented without federal aid.
2 - 22

Alternatives discussed in the study were

grouped into conveyance, flood protection,

inlet control, and combinations of these

concepts. The conveyance concepts included

relief tunnels and sewers (estimated cost of

$160 million for 10-year capacity), separate

sewers (estimated cost of $120 million), and

sewer lining (not adequate alone). Flood

protection consisted of individual flood

protection devices such as overhead sewers

(estimated cost of $75 million). The review of

inlet control looked at some typical depths of

street flooding that would be anticipated if inlet

controls were installed at the inlets without

significant subsurface or other off-street

storage. The cost of inlet controls alone,

without storage, was estimated at $2 million. 

Combinations of the above were packaged to

provide alternatives with the best features of

each single approach to maximize benefits for

targeted expenditure levels. Various

combinations of inlet controls with storage and

conveyance improvements were estimated to

range as high as $60 million (Note: The 1999

cost of the separate storm sewers would be

$203 million using the ENR CCI. This is

consistent with earlier IEPA (Park, 1990)

estimates).

Study Completed in 1982 Recommending a Street Storage System

Skokie retained Donohue and Associates in January 1982 to undertake a preliminary

engineering study of what was then called runoff control but, for purposes of this case

study manual and as explained in Chapter 1, is referred to as a street storage system. 

The HSSD was selected for this preliminary engineering project as an initial study area. 

Included in the scope of services for this project, which was completed in July 1982,

were data inventory, hydrologic-hydraulic modeling, development of alternatives with

cost estimates, and implementation recommendations (Donohue, 1982a, 1982b).

As the preliminary engineering project proceeded, nine alternatives were created for the

HSSD. They ranged from flow regulators only to various combinations of flow

regulators, underground storage and relief sewers. All alternatives “...were intended to

minimize sewer backup into basements and maximize utilization of available street

flooding capacity” (Donohue, 1982b, p. 3). This was the first time that utilization of

street storage was the sole basis for solving Skokie’s basement flooding problem. The

series of previously discussed studies had evolved to the point where the innovative,
2 - 23

lower cost, street storage concept was explored in detail. The idea was to focus on the

cause of CSS surcharging, that is, stormwater runoff, and explore ways to intentionally

store stormwater on streets in a controlled fashion. Traditional approaches were, at

least for the duration of this preliminary engineering study, held in abeyance.

The recommended street storage system consisted of approximately 1200 flow

regulators, 24 supplemental storage facilities, and a relief sewer. (The constructed

project required only 10 supplemental storage facilities). The storage and sewer

facilities were sized, in this preliminary engineering study, for a 10-year recurrence

interval storm. Flow regulators would range in location and function from modification

of existing inlet grates to orifice type or energy dissipating type flow regulators installed

in the sewer lines leading from catch basins or inlets to the sewer system.

Storage facilities were recommended for all areas where street ponding would exceed

the depth at which damage to adjacent private property could occur. This below street

or off-site storage will reduce street ponding depths to just below damaging levels. 

The estimated mid-1982 construction cost for the recommended HSSD street storage

system was $11,220,000. This cost was much less than the cost of traditional

approaches and, as a result, was attractive to community decision makers. 

Opportunities to improve the cost-effectiveness of the design and reduce the total

construction cost would be available as more detailed designs were prepared. 

Additional maintenance costs associated with the recommended street storage system

were projected to be minimal.

A pilot program was recommended during the design and initial construction phase of

implementation. The pilot program would evaluate various types of flow regulating

devices and assess their operational aspects and maintenance requirements.

A monitoring program was recommended to evaluate the existing uncontrolled system

and the performance of the pilot street storage system. The following five types of data

collection and analyses were recommended: rainfall, sewer flow, street ponding, depth

in storage facilities, and foundation drainage flow.

Unlike the recommendations in previous studies, the preceding recommendations were

implemented. The commitment to finally take action was probably due to a combination

of growing severity of the basement flooding problem and the promised low cost of the

street storage system. The gradual, successful implementation of the

recommendations in the preliminary engineering study, led to more recommendations

which were in turn implemented. As of 1999, the street storage system has been

almost completely implemented throughout the 8.6 square mile community. And, as

explained in Chapter 9, the system performs very well. The details of the planning,

design, testing, construction, financing and operation of the Skokie street storage

system are presented in the remainder of this manual.

Observations Regarding the Studies to Solve Skokie’s Combined Sewer System

Basement Flooding Problem
2 - 24

The Skokie experience in conducting a series of studies to solve its basement flooding

problem contain ideas that can be advantageously transferred to other communities. 

Consider the three observations discussed here.

Occurrence of a Series of Evolving Studies

In an attempt to solve its growing basement flooding problem, Skokie commissioned or

conducted a series of seven evolutionary studies over a period of 15 years. This

pattern of serial, evolutionary studies is common in the public works environment.

The evolutionary nature of the Skokie studies is readily illustrated. For example, the

1967 study recommended relief sewers whereas the 1973 study, informed by the

MSDGC’s adoption of TARP, recommended tunnels that could connect to the TARP

system. Recognizing that USEPA funding was probably no longer available, the 1981

study explored more innovative, low cost options, including street storage.

The study-no action, study-no action, etc. pattern is especially characteristic of wet

weather problems. This is caused by the random, episodic nature of such problems. 

One or more damaging episodes occur, adversely affected citizens express concern,

and community officials take action by initiating a study. By the time the study is

completed and recommendations made, the intensity of interest in solving the problem

has diminished, especially in light of implementation costs. In contrast with the random,

episodic nature of CSS, SSS, stormwater system and other wet weather problems,

most public service problems persist or at least are much less episodic, until solved. 

Examples are deteriorating streets, poorly performing schools, deteriorating quality of

water supply, and inadequate police protection.

Initial Focus on Traditional Solutions

Most of the earlier studies considered and recommended traditional solutions to

Skokie’s basement flooding problem. Examples are relief sewers and tunnels. 

Widespread consideration of—but not necessarily recommendation of—innovative

options was stimulated by lack of external funding. Reductions in or limitations of

financial resources encourages creativity. 

Gradual Recognition of the Water Pollution Control Purpose of TARP

The series of studies and the improved understanding of TARP gradually led to the

realization that while the massive, expensive TARP would mitigate CSOs it would have

minimal impact on the basement flooding problem. For example, the MSDGC’s 1981

study concluded that basement flooding would have been eliminated in less than 10

percent of Skokie buildings had TARP been in place during the two summer 1981

storms. Unless something was done, post-TARP Skokie would still have a massive

basement flooding problem because of its CSS.
2 - 25

Description of Wilmette, IL

A description of Wilmette, IL is presented as a basis for understanding the case

studies. Less detail is provided for Wilmette than for the previously described Skokie,

for three reasons. First, some of what applies to Skokie also applies to Wilmette given

that the latter is contiguous with and north of the latter. Second, more background

information is needed for the much larger and longer duration Skokie project because it

is emphasized in this case study manual. Third, less background documentation is

available for Wilmette.

Location

As indicated on Figure 2-1, the Village of Wilmette is contiguous with and immediately

north of Skokie. Figure 2-7 is a map of Wilmette showing major features. Besides

being bounded on the south by Skokie and Evanston, Wilmette is bounded on the west

by Glenview, on the north by Kenilworth and Northfield and on the east by Lake

Michigan. The North Shore Channel, which as previously noted forms the east

boundary of Skokie, passes through an eastern extremity of Wilmette before

discharging into Lake Michigan. As also is the case in Skokie, the North Shore

Channel, or more specifically, land paralleling it is an amenity for Wilmette. These

lands include a public golf course and Gillson Park.

Relationship to the Metropolitan Water Reclammation District of Greater Chicago

Combined sewers serve the 2.0 square mile portion of Wilmette lying east of Ridge

Road. Note that this CSS area is slightly less than one fourth of the CSS area in

Skokie. The rest of Wilmette, which lies west of Ridge Road, is served by a separate

sewer system (Loucks and Morgan, 1995). The Wilmette description presented in the

remainder of this section applies primarily to the CSS area.

Wilmette’s CSS lies in the service area of the MWRDGC. Combined sewers generally

flow eastward. Connections to MWRDGC interceptors occur in the central portion of

the CSS along Green Bay Road and on the east end of the CSS along Sheridan Road

and the North Shore Channel. The Wilmette CSS is connected to TARP via two drop

shafts along the North Shore Channel (SEC Donohue, December 1992, pp. 4-5). The

initial CSS did not contain many trunk sewers because of the large number, relative to

Skokie, of connections to MWRDGC interceptors.
Figure 2-7. Map of a portion of Wilmette, IL served by combined sewer system.

2-26

N

R idge Rd.

G reen Bay Rd.

Village

Limits

Sheridan R d.

Lake Street

North

Shore

Channel

Village Limits Isabella Street

Lake M ichigan
2 - 27

Land Use and Population

Approximately 80 percent of the fully developed Wilmette CSS is occupied by single

family residences. The remainder is commercial and multiple family dwelling units. The

2.0 square mile CSS has a population of 11,300 and contains approximately 3500

buildings. The overall population density is 9 people per acre and the population

density in residential areas is about 11 people per acre. To reiterate, the area is

completely developed (SEC Donohue, December 1992, p. 4).

Note that the Wilmette and Skokie CSSs are similar when compared on the basis of

type and intensity of land use. Each is fully developed, about 80 percent single family

residential, and has an overall density of about 10 people per acre (Skokie: 11,

Wilmette: 9).

Topography and Drainage Patterns

As noted earlier, the general drainage direction within the Wilmette CSS is eastward. 

Longitudinal street slopes are very flat. For example, 364 street segments within the

CSS having a total length of 36.2 miles were examined. A street segment would

typically be one block in length. Because of traffic volume, safety considerations or

steep longitudinal slopes, 24% of the streets were determined to be not suitable for

street storage. However, of the remaining 76% of street segments, 66% had

longitudinal slopes of less than 0.25% (0.25 feet per 100 feet), 21% had longitudinal

slopes of 0.25% to 0.50%, and only 13% had longitudinal slopes in excess of 0.50%

(SEC Donohue, June, 1992, pp. 12-16).

One way in which Wilmette differs from Skokie is the presence of some brick streets. 

Of the 26.2 lineal miles of streets available for street storage, 50% are constructed of

brick, 48% of asphalt, and 2% of concrete (SEC Donohue, June, 1992, p. 15). Figure

2-8 shows one of Wilmette’s brick streets. They are highly valued because of their

appearance. The brick streets were fully incorporated into the street storage system

without compromising their aesthetic values. For example, a mid-block berm is shown

on Figure 2-8.

The CSS contains about 33 miles of sewers that vary from eight to 72 inches in

diameter. Smaller sewers—less than 30 inches in diameter—are generally formed of

clay tile while the sewers larger than 48 inches in diameter are made of reinforced

concrete. Combined sewers in the 30 to 48 inch diameter range could be clay or

concrete. No combined sewers are constructed of brick (SEC Donohue, December,

1992, p. 4).
Figure 2-8. Brick streets account for half of the street length in Wilmette targeted for

street storage.

2-28
2 - 29

Brief History of Wilmette with Emphasis on Development of Its Drainage System

Partly as a result of the Chicago fire of 1871, the population of what is now Wilmette

increased to over 300 which was the number required for incorporation. Wilmette was

incorporated in 1872 and its first water and sewer systems were built in 1893-94. The

combined sewer system, which was the accepted type of sewer system at that time,

discharged into Lake Michigan.

As noted earlier, Wilmette, contrasted with Skokie, originally did not contain many trunk

sewers because of numerous connections to MWRDGC interceptors. The entire

system was generally under capacity. Relief sewers were constructed prior to 1960, but

they were also undersized.

This discharge location and the shape of the Wilmette lakefront changed in the 1908 to

1910 period with construction of the North Shore Channel and the interceptor system. 

Spoil from the channel construction was used to create a landfill, north of the North

Shore Channel, which is now Gillson Park. Therefore, Wilmette, like Skokie and many

other Chicago area communities, made a major historic commitment to combined

sewers and they proved to be undersized.

Wilmette’s Historic Combined Sewer System Basement Flooding and Peak

Discharge Problem

Like Skokie, Wilmette had a long-standing, widespread basement flooding in its CSS. 

SEC Donohue (December, 1992, p. 2) provides this description:

The combined sewer area of the Village of

Wilmette... experiences basement flooding

during moderate and heavy rainfalls. A

postcard survey conducted following a heavy

rain in August 1989 reported that nearly 800

buildings (23%) in the combined sewer area

were flooded during this storm. More recent

community surveys indicate that a substantially

greater number of homes are actually

impacted. These surveys indicate that over

60% of the buildings in the combined sewer

area have been affected by basement flooding

at one time or another.

A subsequent report by Rust (November, 1993, p. 1) reports the preceding and notes

that, besides property damage, flooding of basements with combined sewage exposes

residents to health problems. According to this report, basement and street flooding

problems “...occur regularly every one to two years during intense rain storms.” The
2 - 30

report also notes that, as a result of uncontrolled street flooding, emergency vehicles

have been delayed during storms.

As Wilmette sought a solution to its basement and street flooding problem in the early

1990's, it also had to resolve a related problem. As explained by Loucks and Morgan

(1995), Wilmette needed to reduce the peak discharge from its sewer system:

...to facilities of the MWRDGC. The MWRDGC

is responsible for transportation, treatment and

eventual discharge of sewage flows in

Wilmette and 185 other communities. 

Approval from MWRDGC is required for all

system modifications and new discharge

connections. Projects consisting only of relief

sewers are generally unacceptable. Hydraulic

simulations were used to demonstrate a

reduction of 28 percent in the peak discharge

from the village. A maximum total peak

release rate was negotiated with MWRDGC

which serves as a constraint on the system

design.

Reduction in peak flow from the CSS, which was not an issue in the planning and early

design of the Skokie street storage system, was a factor in the planning and design of

the Wilmette system. The added value achieved in Wilmette is significant. It points to

the potential for a street storage system to serve other functions such as reducing peak

flows in interceptor sewers and at WWTFs.

Previous Studies of Ways to Solve Wilmette’s Combined Sewer System Problems

Several studies were carried out in the early 1990's. Key studies are briefly described

here as an explanation of how and why Wilmette decided to implement a street storage

system in its 2.0 square mile CSS.

Study Completed in 1991 Recommending Relief Sewers

According to SEC Donohue (June, 1992, p. 5), RJN Environmental Associates, Inc.

completed a facility plan for Wilmette in 1991. Focusing on solving the basement

flooding problem, the plan “...recommended construction of combined relief sewers to

increase the existing combined sewer system capacity to transport a 10-year storm

event without surcharging.” The estimated 1991 construction cost was $65,000,000. 

The 1999 cost would be $81 million using the ENR CCI.

Value Engineering Study Completed in 1992 Recommending Street Storage
2 - 31

Donohue & Associates, Inc. and Lewis & Zimmerman Associates, Inc. were retained by

Wilmette to participate in a value engineering study of the previous study (SEC

Donohue, June 1992, p. 5; SEC Donohue, December 1992, p. 2). Completed in

January 1992, the value engineering study concluded that what is defined as street

storage in this report “...appeared to offer a higher level of protection against basement

flooding at a cost of $46,000,000 or substantially less than the $65,000,000

recommended in the RJN facility plan.”

Study Completed in 1992 Recommending Street Storage 

Wilmette retained Donohue & Associates in March of 1992 to “...determine the

technical and economic feasibility of using runoff control techniques such as temporary

street ponding to relieve basement flooding problems in the east side areas” (SEC

Donohue, June 1992, p. 5). The scope of services for this project was similar to that of

the preliminary engineering study completed by Donohue for Skokie in 1982.

Completed in June 1992, the study concluded that “...a stormwater runoff control

program consisting of temporary street ponding along with relief sewers will provide a

cost-effective level of protection against basement flooding in the combined sewer area

east of Ridge Road” (SEC Donohue, June 1992, p. 1). The report went on to point out

significant potential cost savings over the previously recommended conventional relief

sewer system. More specifically, the report stated:

The estimated cost for a system of temporary

street ponding berms and relief sewers which

provide full protection against basement

flooding and dedicated runoff storage capacity

for a 10-year event is $28,000,000. ...The

estimated cost of the 10-year ...capacity runoff

control program ...is substantially less than the

$65,000,000 10-year capacity combined relief

sewer alternative recommended in the 1991

RJN facility plan.

Study Completed in 1992 Recommending Refined Street Storage

Wilmette commissioned SEC Donohue (formerly Donohue & Associates) to conduct

this preliminary engineering study based on the favorable findings of the previous

feasibility study. One change in approach was to use a more sophisticated hydrologichydraulic model. The USEPA Stormwater Management Model (SWMM) was now used

rather than the Illinois Urban Drainage Area Simulator (ILLUDAS). The principal

purpose of SWMM was to represent the dynamics of flow in the system, that is, to

rigorously simulate surcharging and backwater effects and the interaction between

sewer flows and storage. Also used for the first time in Wilmette was SEC Donohue’s
2 - 32

Surface and Street Analysis Model (SASAM). It simulated on-street conveyance and

storage of stormwater (SEC Donohue, December 1992, pp. 8-9).

This refined study concluded that a system of street storage and relief sewers could

control the 10-year storm for a construction cost of $31,000,000. The 1999 cost would

be $37 million using the ENR CCI. Thus, this refined study essentially confirmed the

preceding study (SEC Donohue, December 1992, p. 9). Details of additional planning,

design, financing and construction of the Wilmette street storage system are presented

in the remainder of this manual.

Observations Regarding Studies to Solve Wilmette’s Combined Sewer System

Problems

As with Skokie, a series of studies led to the decision to implement street storage in

Wilmette’s CSS. Also like Skokie, some of what was learned in the process of

conducting the studies might be transferrable to other communities faced with CSS

problems. Two observations based on Wilmette’s experience are essentially the same

as the first two of the three observations presented earlier based on Skokie’s

experience. They are:

• Occurrence of a series of evolving studies prior to making a commitment.

• Initial focus on traditional solutions.

Wilmette’s studies differed from Skokie’s in one way: they sought to solve flooding while

also reducing the peak discharge from the Wilmette CSS to the MWRDGC system. 

This gave added impetus, as the studies proceeded, to exploring means to temporarily

store stormwater for gradual release. Relief sewers alone would not suffice.

wp/epastch2
3-1

CHAPTER 3

THE CONCEPT THROUGH CONSTRUCTION PROCESS

FOR

STREET STORAGE SYSTEMS

Status of Urban Stormwater Management

As briefly noted in Chapter 1, the street storage system mitigates surcharging of CSSs

by managing stormwater—by reducing peak rates of stormwater before it enters the

combined sewer system. Accordingly, a brief review of the status of urban stormwater

management, with emphasis on detention, that is, temporary storage of stormwater, is

appropriate. The following review is taken from Walesh (1989, pp. 20-31) and other

sources as indicated.

Two Fundamentally Different Approaches: Conveyance-Oriented and

Storage-Oriented

The state of the art of stormwater management has evolved to the point where there

are two fundamentally different approaches to controlling the quantity, and to some

extent the quality, of stormwater runoff. Using a “before and after” format. Figure 3-1

illustrates selected characteristics of the two available approaches.

Conveyance-Oriented Approach

The first to the two approaches is the more traditional conveyance-oriented stormwater

system. Systems designed in accordance with this approach provide for the collection

of stormwater runoff, followed by the immediate and rapid conveyance of the

stormwater from the collection area to the discharge point to minimize damage and

disruption within the collection area. Principal components of conveyance-oriented

stormwater systems are culverts, storm sewers, and channels supplemented with inlets

and catch basins.
Figure 3-1. Conveyance and storage approaches to stormwater management

(Source: Walesh, 1989, p. 26).

3-2
3-3

A potentially effective, newer approach to stormwater control is the storage-oriented

system. Its function is to provide for the temporary storage of stormwater runoff at or

near the point of origin, with subsequent slow release to downstream storm sewers or

channels. This approach minimizes damage and disruption both within and

downstream of the site. One or more storage facilities are the principal elements in a

storage-oriented system. These principal elements are often supplemented with

conveyance facilities, such as culverts, storm sewers, inlets, and catch basins, which

transport stormwater to storage facilities and gradually convey flow from those facilities.

Comparison of Features

A principal advantage of the traditional conveyance-oriented approach is applicability to

both existing and newly developing urban areas, contrasted with the storage-oriented

approach. Storage is more difficult to retrofit into already developed areas because of

space limitations. Although retrofitting storage into developed areas is difficult, it is not

impossible and it is sometimes cost effective as clearly demonstrated by the Skokie and

Wilmette projects.

Other advantages of the conveyance-oriented approach are rapid removal of

stormwater from the service area, minimal operation and maintenance requirements

and costs, and accepted analysis and design procedures. Principal advantages of the

storage-oriented approach are possible cost reductions in newly developing urban

areas, prevention of downstream adverse flooding and pollution associated with

stormwater runoff, and potential for multiple-purpose uses.

Neither the conveyance-oriented approach nor the storage-oriented approach is

inherently better. Both approaches should be considered, at least when a project or

development is at the conceptual level.

The conveyance- and storage-oriented approaches to stormwater management are not

necessarily mutually exclusive within the same hydrologic-hydraulic system. Depending

on the circumstances, the two approaches may be compatible and integrated use of the

two approaches may lead to a more optimum stormwater management system. One

example of the joint use of the conveyance-oriented facilities in one portion of a

watershed and storage-oriented facilities in another portion. Another example of the

combined use of the two approaches is to use conveyance-oriented facilities for the

convenience system and storage-oriented facilities for the emergency system. The

later approach is illustrated by the Skokie and Wilmette projects where the preexisting

combined sewers are the convenience system and new street surface storage and

underground tank storage constitute the emergency system. The convenience (minor)

and emergency (major) systems are discussed in a later section of this chapter.

Historic Development of the Storage-Oriented Approach
3-4

Understanding of the status of stormwater management is informed by its history. 

Furthermore, to the extent that contemporary use of storage sometimes targets both

the quantity and quality of stormwater, that history is very relevant to street storage and

possible implication of street storage for control of nonpoint source pollutants. The

following historical account is based on Walesh (1989, pp. 29-31) and other cited

sources.

The original motivation for using the newer storage-oriented approach over the

traditional conveyance-oriented approach was that the former offered cost advantages. 

Most documented examples of the cost advantage of the storage-oriented approach

over the conveyance-oriented approach relate to newly developing areas (e.g.,

Poertner, 1974). More recently, however, there have been situations in which already

developed areas are being retrofitted with a storage-oriented system at significantly less

cost than that of a traditional conveyance-oriented system. Examples include the

Skokie and Wilmette projects.

A complete comparison of conveyance-oriented and storage-oriented systems for a

particular location must consider all costs and benefits, tangible and intangible. For

example, reduction in developable land and possible safety hazards to children with the

storage-oriented system are costs, while increased land values for areas contiguous to

attractive storage facilities are a benefit. Cost analyses must be conducted on a

case-be-case basis. Documented case studies and experience suggest that storage

facilities should be at least considered for controlling the quantity of stormwater runoff

because of the potential for cost savings.

After initial use of storage facilities for the single purpose of controlling the quantity of

stormwater runoff, storage facilities found increased use as multiple-purpose

developments. In addition to their primary surface water control function, storage

facilities were designed to provide, or be part of, sites for recreation including such

activities as fishing, boating, tennis, jogging, ski touring, sledding, and field sports. 

Well-planned, well-designed, and well-operated storage facilities were also found to

have aesthetic value for contiguous and nearby residential areas.

In addition to the obvious erosion and sedimentation problems often associated with

urbanization, studies conducted in the 1970's indicated that urban stormwater runoff

contributes a significant part of some of the pollutants finding their way to surface

waters. For example, an early study conducted in Durham, NC, compared the quality of

urban runoff with that of secondary municipal sewage treatment effluent on the basis of

weight per unit area per year (Colston, 1974). On an annual basis, the urban runoff

contributed 91 percent of the chemical oxygen demand, 89 percent of ultimate

biochemical oxygen demand, and 99 percent of the suspended solids.

Many measures were suggested for controlling urban area nonpoint-source pollution in

general and erosion and sedimentation in particular. The use of storage was one of

these measures. The state of the art of using storage facilities to control the quality of

urban stormwater runoff is still under development.
3-5

In summary, storage facilities are being increasingly used for controlling the quantity of

runoff because of the cost advantages and because of their recreation and aesthetic

values. They are also being increasingly designed to accomplish a third function of

controlling the quality of stormwater runoff.

The evolution of using the storage-oriented approach in surface water management is

summarized in Figure 3-2. Beginning with the single quantity control function, storage

facilities have evolved so that they now can serve three compatible functions: quantity

control; recreation, aesthetic, and other supplemental uses; and quality control.

Street storage systems, which make heavy use of storage, have served the quantity

control function as demonstrated by the Skokie and Wilmette applications. Street

storage also has the potential to serve the quality control function relative to nonpoint

source pollution. This possibility is discussed in Chapter 11.

Emergency and Convenience Systems

The increasingly accepted emergency and convenience system approach to

stormwater management is an integral part of the street storage approach. 

Accordingly, a brief overview of the emergency-convenience system is provided. This

overview is taken from Walesh (1989, pp. 31-34) and other cited sources.

The stormwater system may be thought of as two systems, one functionally and

physically superimposed on the other. One system, the convenience or “minor” system,

contains components that accommodate frequent, small runoff events. The other

system, the emergency or “major” or overflow system, consists of components that

control infrequent but major runoff events. Although many of the components are

common to both the convenience and emergency system, their relative importance in

the two systems varies significantly.

The Convenience (Minor) System

Stormwater systems have traditionally been designed to convey all the design runoff

without street flooding, parking lot or other ponding, or basement backup associated

with frequent, small runoff events—up to about the five- or 10-year recurrence

interval—from an urban area with no damage and little or no disruption or even
1970’s

1980’s

1990’s

Figure 3-2. Historic development and use of storage facilities for stormwater

management in the U.S. (Source: Walesh, 1989, p. 31).

3-6
3-7

unimportant.

The Emergency (Major or Overflow) System

Major runoff events—such as 50- or 100-year recurrence interval events—will also

inevitably occur in urban areas. Accordingly, some stormwater control systems are

designed to control major event runoff rates and volumes in such a manner that

although temporary disruptions and inconvenience will occur, widespread danger and

damage will be avoided. This is accomplished by allowing for temporary storage and

conveyance of stormwater on parking lots and streets, within public open space areas,

and in other suitable low-lying areas; by establishing building grades well above street

grades; and by designing streets and roadways to serve as open channels providing for

the temporary storage and conveyance of runoff as it moves through the urban area

toward a safe discharge point.

The emergency system is sometimes called the major system because it is designed to

control runoff from “major” rainfall events. Sometimes the emergency system is

referred to as the overflow system because it is the system that begins to function when

the capacity of the convenience system is exceeded and it overflows.

Most surface water control systems, however, are not explicitly designed to

accommodate major runoff events. Nevertheless, major runoff events occur and the

emergency system will, by default, function during such events with sometimes

catastrophic damage and disruption.

Combined Convenience and Emergency System

The ideal surface stormwater system is planned and designed to include both the

emergency and convenience systems in anticipation of the inevitable occurrence of

both major and minor runoff events. In a combination system, essentially complete

control of minor runoff events is achieved to minimize disruption and damage during

smaller, frequently occurring rainfall events. Emergency components of the system are

designed to accept some temporary disruption and inconvenience during relatively

infrequent events. Jones (1967) provided a very readable and convincing early

explanation of the convenience-emergency system concept.

Figure 3-3 illustrates the emergency and convenience system concept applied to a

typical urban street cross section. This is essentially the manner in which the

emergency system appears in the street storage system described in this report. The

variation is that with street storage system, the receiving sewer is a combined

sewer—not a separate storm sewer. Figure 3-4 illustrates the emergency and

convenience system applied to a channel-floodplain passing through an urban area.

Components in the stormwater system can be examined from the perspective of

whether or not they function, how they function, and the relative importance of their
3-8

functioning under both convenience and emergency conditions. Consider, for example,

stormwater inlets located along the curbs and gutters of urban streets. For minor runoff

events, such inlets are normally designed to pass essentially all the discharge conveyed

to them, but under major events they should be expected to intercept only a small

portion of the flow moving along the gutter. Thus, whereas inlets are key elements in a

convenience system, they are of little importance in an emergency system.

Note, however, that catch basins—inlets with sumps—are of great importance in the

Skokie and Wilmette street storage systems. Their operation is not left to chance. 

Flow regulators are installed in the catch basins.

Streets are graded longitudinally and laterally to provide, during minor runoff events, for

rapid runoff of stormwater to curbs and inlets or to roadside ditches. During major

events, however, the longitudinal slope of the streets and the relative elevation of the

streets and contiguous residences and commercial and industrial structures must be

designed such that the street functions as a large, paved open channel or reservoir

which temporarily conveys or stores stormwater runoff. Thus, whereas the street is one

of many components in a surface water system during minor runoff events, it becomes

a key element in the surface water system during major events.

Streets are certainly key elements in the street storage systems described in this report. 

However, unlike the situation in the design of new development, the basic topography

of the streets and contiguous areas is already defined. It provides a physical constraint

within which the street storage system must be designed. That design includes some

refinements in the topography in the form of street berms.
Figure 3-4. Emergency and convenience system applied along a channel and

floodplain (Source: Walesh, 1989, p. 33).

3-9

Figure 3-3. Emergency and convenience system applied to an urban street

(Source: Walesh, 1989, p. 33).
3-10

Stormwater storage facilities have, as described in the preceding section, proven to be

technically sound, economically attractive, and environmentally acceptable elements in

urban stormwater management systems. However, they have been used primarily as

preventive measures in newly developing areas in contrast with use as remedial

measures in developed areas.

Widespread, frequent—one or more times per year—basement flooding is common in

existing, old, and intensely developed urban areas, served by CSSs. Traditional and

proven remedial measures to CSS basement and surface flooding problems include, as

noted in Chapter 1, separation and in-system storage of combined sewage.

A fundamentally different alternative to remedying combined sewer surcharging and

surface flooding is retrofitting the existing system to include storage. More specifically,

it is feasible under certain conditions to implement a carefully engineered system of

surface and sub-surface storage facilities to control the rate at which stormwater flows

into the combined sewer system so it does not exceed the capacity of the existing

sewers, thereby mitigating basement and other flooding.

The largely implemented Skokie and Wilmette projects have demonstrated the

technical and economic feasibility of retrofitting stormwater storage into CSSs. 

Furthermore, retrofitted stormwater storage can also have other benefits such as

reducing peak flows of combined sewage to regional wastewater agencies, mitigating

inflow to SSSs, solving flooding problems in separate sewer systems, and managing

nonpoint source pollution.

Retrofitting is not limited to CSSs. It can also be applied to the stormwater portion of

separate sewer systems for purposes such as improving quantity and/or quality control,

reducing safety hazards and enhancing recreation facilities and aesthetic values. 

Retrofitting stormwater facilities has been explored by and reported on by Walesh

(1991, 1992, 1993 and 1998).

Distinction Between Analysis and Design: Diagnosis and Then Prescription

An important integrating theme of this chapter is describing, using mainly case studies,

tools and techniques for analyzing the root causes of problems in CSSs and

designing solutions to these problems. A medical analogy helps to appreciate the

difference between analysis and design. Analysis in engineering, like diagnosis in

medicine, strives to get beyond symptoms. In medicine, symptoms may be a fever or

pain. In CSSs, symptoms may be flooded basements or overflows into surface waters. 

In both medicine and engineering, symptoms may appear to be problems or, in fact, be

problems to those who are adversely affected, but they are not the root causes. In

medicine, the cause of fever may be an infection and in engineering the cause of a

symptom like basement flooding may be inadequate flow carrying capacity of selected

sections of combined sewers.
3-11

Once the medical diagnosis or engineering analysis has gotten beyond symptoms to

causes, remedies or solutions can be explored. Medical doctors prescribe solutions

and engineers design solutions.

Walesh (1989, p. 317) elaborates on this two step analysis and design, or diagnosis

and prescription, process. His discussion is directly applicable to CSSs. Two

fundamental questions must be addressed in all but the most trivial CSSs. First, how

does the existing system function, that is, what is the cause or what are the causes of

the CSS problems such as basement flooding, surface flooding and CSOs? This, the

problem definition phase, must use but look way beyond and below symptoms such as

the number of basements flooding, the location of street inundation, and the frequency

of overflows. The first step, that is, the analysis or diagnosis phase, focuses on finding

causes. A clear understanding of the cause of a problem tends to lead to its solution.

The second fundamental question is: How can the CSS be modified or altered to

eliminate or mitigate the causes of the problems and to prevent similar or new problems

from occurring in the future? The process of answering this question may be called

design or prescription.

Why the emphasis on the two part analysis and design, or diagnosis and prescription

process? Answer: CSSs are complex and there is a tendency to rush to judgement as

to causes so that a community can “get on” with implementing solutions. Furthermore,

there is also a pattern, as shown by the Skokie and Wilmette studies discussed in

Chapter 2, to favor, if not exclusively consider, traditional solutions to CSS problems. 

Superficial analyses combined with a predisposition to employ traditional solutions can

lead to unnecessarily costly solutions to CSS problems.

Ideas and information presented in this chapter are intended to show the long term

value of a careful, deliberate, multi-faceted (e.g., monitoring, computer modeling, pilot

studies) analysis and design process. The “pay off” for a community can be a

cost-effective solution to its CSS problems.

Chronological Mode of Presentation

The remainder of this chapter is structured in a chronological fashion. Using Skokie,

Wilmette and, occasionally other communities, the steps that may be needed to

implement a street storage system are described in the approximate order they would

occur. Figure 3-5 illustrates the overall process. The description begins with the

understanding of the concept of a street storage system and concludes with
Study the concept

of a street storage system

Apply screening criteria

to determine

likely applicability

of a street storage system

Street

storage likely

to be

applicable

?

Explore other

solutions

Select

an initial

pilot or

implementation

area within

the CSS

Yes

No

Figure 3-5 (1 of 2). Successful application of a street storage system requires

a systematic analysis and design process that begins with understanding the

concept and concludes with construction.

3-12
Establish performance

criteria

Analyze existing

system and

perform preliminary

engineering using

computer models

Street

storage likely

to be

applicable

?

Yes

No

Analyze existing

system using

monitoring

Explore other

options

Review flow regulator

availability and

performance

Complete design of

street storage

system

Construct street

storage system

Figure 3-5 (2 of 2). Successful application of a street storage system requires a

systematic analysis and design process that begins with understanding the concept

and concludes with construction.

3-13
Fundamental to understanding the street storage system concept is appreciating the

capacity of urban streets to carry and store stormwater. Accordingly, this section begins

with discussions of the flow capacity and the storage capacity of an urban street. 

Figure 3-6 shows one photograph of a typical asphalt covered street in Skokie and a

typical brick street in Wilmette. These photographs suggest the potential stormwater

conveyance and storage functions of urban streets.

Conveyance Capacity of Urban Streets

Urban streets can be a vital element in the previously described emergency stormwater

system by conveying stormwater to a safe discharge point during a major rainfall-runoff

event. The Manning open channel flow equation is available for calculating depth

versus discharge relationships for urban streets.

Street Cross Sections

Some Skokie street cross sections, including the adjacent parkway, sidewalk and lawn

up to the street side of residences, are shown in Figure 3-7. A typical half cross section

of a street, based in part on the configurations of the actual street cross sections shown

in Figure 3-7, is presented in Figure 3-8. Longitudinal slopes, So, of 0.1, 1.0, and 3.0

percent are assumed for the subsequent analysis.

Analysis Procedure

The objective is to determine, assuming normal depth, the flow capacity of the street

cross section for a range of depths and a range of longitudinal slopes. The total flow in

the half section can be determined as the sum of the flow in subsection A of Figure 3-8,

the street portion of the cross section, and subsection B, the lawn portion of the cross

section. With this approach, the Manning equation becomes

constructing the system.

All of the steps followed in Skokie, the first large scale application of street storage, are

not likely to be needed in other communities. For example, the laboratory and field

testing of various flow regulators that was necessary for the Skokie project would

probably not be needed in other applications. However, the Skokie laboratory and field

testing is fully described here so that the process and especially the results are

available for possible use by others.

The Concept of Street Storage
Figure 3-6. The photographs of urban streets in Skokie (top) and Wilmette (bottom)

suggest their potential stormwater conveyance and storage function.

3-15
Figure 3-7. Selected street cross sections from Skokie, IL (Source: Donohue,

1982b, p. 65)

3-16
Figure 3-8. Typical street and lawn cross section representative of actual Skokie

cross sections (Source: Walesh, 1989, p. 191).

3-17
3-18

QQ Q S

A R

n

A R

n A B

A A

A

B B

B

=+= 



 + 

 1.49  0.5

0

23 23 / /

where QA = discharge in subsection A

QB = discharge in subsection B

So = longitudinal slope for both subsections (dimensionless)

AA = flow cross-section area in subsection A

RA = hydraulic radius for subsection A = AA /PA, where PA = the wetted

perimeter

nA = Manning roughness coefficient for subsection A

AB = flow cross-sectional area in subsection B

RB = hydraulic radius for subsection B = AB / PB, where PB = the wetted

perimeter

nB = Manning roughness coefficient for subsection B

Assume the depth of flow at the gutter of 0.5 ft. Then

( )( )( )

( )

( )

A ft

P ft

R ft

A

QQ Q S S

A

A

A

B

A B

= =

=+ + =

= =

=

=+=

×

+ =

05 05 20 5

05 20 05 205

5

205 0 244

0

149

5 0 244

0 013 0 224

2

2 2 0 5

2 3

0

0 5

0

1 2

. .

. ..

. .

. .

.

.

/

. /

Substituting S0 = 0.1, 1.0, and 3.0 percent yields half-street discharges of 7.1, 22.4,

and 38.8 ft3/sec, respectively. The corresponding average velocities are, 1.42, 4.48,

and 7.76 ft/sec, respectively. The preceding process is repeated for depths at the

gutter of 1.0 and 2.0 ft.

Results

Depth versus discharge relationships for the complete street cross section, including

adjacent lawns, are summarized in graphic form in Figure 3-9. A separate curve is

presented for each of the three longitudinal slopes.
Figure 3-9. Depth versus discharge relationships for typical street and lawn cross

sections (Source: Walesh, 1989, p. 192).

3-19
3-20

The analysis indicates that streets can carry very large flows relative to typical storm

sewers at similar slopes. For example, consider the case with a depth at the gutter of

1.0 ft. For the three longitudinal slopes, flows on the full width of street and adjacent

lawn areas are approximately 14 to 18 times greater than those that would be carried in

a 24-inch diameter reinforced-concrete pipe laid at the same slope and flowing full. 

The preceding analysis suggests that better use could be made of streets by designing

them to be channels that function as part of the emergency stormwater system. Using

streets for temporary stormwater conveyance is one aspect of the street storage

system.

Storage Capacity of Urban Streets

Urban streets can also constitute a vital element in the emergency stormwater system

by temporarily storing stormwater until it can be safely discharged to storm or combined

sewers. Actual street cross sections shown in Figure 3-7 suggest the volume of storage

available.

Analysis Procedure

Consider again the typical street cross section presented in Figure 3-8 and cross

sectional areas calculated and presented in the previous section titled “Conveyance

Capacity of Urban Streets.” A plan view of a typical single-family residential area with

paved streets and curb and gutter is shown in Figure 3-10.

Consider the east half of the 600-ft-long section of Easy Street and the directly tributary

area of 67,500 ft2

. The runoff coefficient for the area is 0.5; that is, half of the rainfall on

the total tributary area is directed toward the east half of Easy Street.

Assuming that the street has a zero longitudinal slope, the cross-sectional area of the

east side of the street and cumulative storage on the east side of the street may be

calculated as a function of depth of water relative to the gutter. Results are presented

in Table 3-1 and Figure 3-11. The depth versus volume relationship for the east side of

the 600-ft-long street has a shape similar to the depth versus volume relationship for a

natural river valley. That is, as depth increases, the relative volume of incremental

storage per unit of depth increases at least over the first one foot of depth.

Assume rainfall amounts of 0.5, 1.0, 2.0, and 4.0 in., which may be typical of moderate

to very severe rainfall events. Assuming that half of the rainfall is directed to and

remains in the street, the depth versus storage relationship presented in Figure 3-11

can be used to determine the depth of ponded water or each rainfall amount. The

results are presented in Table 3-2.
Figure 3-10. Typical urban street plan showing the area tributary to the east side

of a one block segment of Easy Street (Source: Walesh, 1989, p. 193).

3-21
3-22

Table 3-1. Depth, cross-sectional area, and cumulative volume data for half of Easy

Street (Source: Walesh, 1989, p. 194).

Depth at

Gutter (ft)

Cross-Sectional Area

on East Side of Street

(ft3)

Cumulative Storage on East

Side of Street1

(ft3) (acre-ft)

0.0 0.0 0 0

0.5 5.0 3,000 0.07

1.0 18.33 11,000 0.25

2.0 65.00 39,000 0.90

1) for 600-ft. street segment and assuming zero longitudinal grade.

Table 3-2. Rainfall and depth of ponding for Easy Street1

 (Source: Walesh, 1989, p.

194).

Rainfall

(in.)

Runoff Depth of Ponding

in Street Relative

to Gutter (ft.) (in.) (ft3

)

0.50 0.25 1,410 0.30

1.00 0.50 2,810 0.45

2.00 1.00 5,625 0.75

4.00 2.00 11,250 1.00

1) Assumes zero longitudinal grade.
Figure 3-11. Depth versus volume relationship for Easy Street and lawn cross

section (Source: Walesh, 1989, p. 194).

3-23
3-24

Results

As indicated, even with four inches of rainfall, and assuming that two inches of runoff is

stored in the street, the peak depth of street ponding relative to the gutter would be one

foot. 

The simple analysis suggests that streets with low longitudinal grades have the capacity

to store large volumes of stormwater runoff. Situations may arise where new streets

can be designed to store stormwater, or existing streets can be retrofitted to serve a

storage function as part of the emergency system. The latter retrofitting idea is one

aspect of the street storage system.

Using Street Storage and Conveyance Capacity in Combined Sewer Systems

Attention now turns to CSSs. As briefly noted in Chapter 1, wet weather problems in

CSSs, such as basement flooding, street flooding, and CSOs, are caused by peak rates

of stormwater runoff, not necessarily by the runoff volumes. Midwestern experience

suggests that wet weather flooding and pollution problems would often not occur, or

would be much less severe, if the peak flows of stormwater could be lessened. Peak

flows are often the principal culprit, not the volumes of stormwater runoff.

This suggests a fundamentally different approach having the following premise: reduce

the peak flow rates of stormwater before it enters the combined sewer system. Accept

the full volume of stormwater into the stormwater runoff into the CSS, but greatly

reduce the peak rate of entry. Figure 3-12 illustrates, in conceptual fashion, this

stormwater-oriented approach to reducing surcharging in CSS and, therefore, mitigating

flooding and pollution.

But where and how can stormwater runoff be temporarily stored and otherwise

controlled to reduce peak flows into the CSS? Urban streets have significant storage

and conveyance capacity, as just illustrated, in this chapter. That storage capacity and

conveyance capacity can be effectively utilized to answer the question of where and

how to temporarily store stormwater. 

Because of their storage capacity, some streets can be used to temporarily store

stormwater before it mixes with sanitary sewage and surcharges the CSS. Because of

their conveyance capacity, other streets can be used to convey stormwater from street

segments with low surface storage capacity to street segments with high surface

storage capacity. Streets in effect become a rectilinear conveyance and storage

system that are activated under emergency conditions, that is, when the capacity on

one or more segments of the CSS is exceeded.
Figure 3-12. Control of peak rates of stormwater runoff can, in concept, mitigate

 surcharging of combined sewer systems.

3-25

Turf, Concrete,

Asphalt Surface

Combined

Sewer

Surcharged

Is Not

Inlet/Catchbasin

Dry Weather

Turf, Concrete,

Asphalt Surface

Combined

Sewer

Surcharged

Is

Inlet/Catchbasin

Wet Weather without

Stormwater Control

Premise:

Do not accept peak flow rates

(mostly stormwater) into

the combined sewer system

Turf, Concrete,

Asphalt Surface

Temporary

Storage

Combined 

Sewer

Inlet/Catchbasin

Wet Weather with

Stormwater Control
3-26

Bringing the Street Storage Concept to Reality: Berms, Flow Regulators, and

Subsurface Storage

Capitalizing on street storage and conveyance capacity requires three elements that

operate in a integrated fashion. These elements are berms, flow regulators and

subsurface tanks. In this section, first berms and then regulators are described. Their

integrated function is then explained. Finally, subsurface storage facilities, which also

use regulators, are discussed.

Berms

Berms Contrasted With Bumps and Humps

A berm is a low structure constructed across a street, from curb to curb, and intended

to temporarily impound water on its upstream side. The crest or top of the berm, when

viewed along the longitudinal axis of the street, is horizontal. It is, in effect, a spillway.

Figure 3-13 is a photograph of a mid-block berm in Skokie. The berm is identified by

the asphalt overlay. A berm that lies across a Skokie intersection is shown in Figure

3-14. This berm may also be identified by the asphalt overlay. A berm under

construction is shown in Figure 3-15. The construction process typically consists of:

• Relocating inlets, if needed.

• Raising the curb and gutter, which has been done in Figure 3-15.

• Milling the street surface. The concrete has been milled in Figure 3-15.

• Placing lifts of asphalt to form the berm. At least one lift has been placed

in Figure 3-15.

The term berm was selected early in the Skokie street storage project to distinguish it

from bumps and humps, two established types of vehicle speed control devices. The

essential features of bumps, humps and berms are illustrated in Figure 3-16. 

According to the Institute of Transportation Engineers (1997, p. 1):
Purpose:

Direct the flow

of stormwater

Figure 3-13. Mid-block berm in Skokie intended to direct the flow of stormwater

runoff.

3-27
Figure 3-14. Berm across an intersection in Skokie.

3-28

Purpose:

Temporarily

store

stormwater
Place asphalt lift

Mill concrete

Raise curb and gutter

Relocate inlet

Figure 3-15. A berm under construction in Skokie showing relocated inlet, raised curb

and gutter, milled concrete surface and an asphalt lift.

3-29
Bump

Purpose: Low Speed

Control

3” - 4”

2’

Berm

7” - 9” (at gutter)

32’

Purpose: Stormwater Control

Hump

3” - 4”

12’

Purpose: Intermediate

Speed

Control 

Figure 3-16. Bumps and humps are vehicle control devices and the gentler berm

is a stormwater control device.

3-30
3-31

of three to six inches with a length (in the

direction of vehicle movement) of one to three

feet. Speed bumps are typically found on

private roadways and parking lots and do not

tend to exhibit consistent design parameters

from one installation to another... A bump

causes significant driver discomfort at typical

residential speeds and generally results in

vehicles slowing to five mph or less at the

bump.

Also, according to the ITE (1997, p. 1):

A speed hump is a raised area in the roadway

pavement surface extending transversely

across the travel way... speed humps normally

have a maximum height of three to four inches

with a travel length of approximately 12 feet... 

Within typical residential speed ranges, humps

create a gentle vehicle rocking motion that

causes some driver discomfort and results in

most vehicles slowing to 15 mph or less at

each hump and 25 to 30 mph between

properly spaced humps in a system.

Some speed humps have a flat top, that is, a plateau shape with gradual approaches

on both ends. This configuration tends to protect long wheel base vehicles like fire

trucks (Velazquez, 1992). Recognizing that speed humps control vehicle speeds

without the presence of police personnel, the humps have been called “sleeping

policemen” (ITE, 1997, p. 1).

In the interest of more fully understanding speed humps, consider their benefits and

drawbacks, as noted by Elizer (1996), and Haynes (1998). Some of these positive and

negative features can also be applied to berms when they are viewed from a vehicular

perspective.

Principal speed hump benefits are:

1. Reduced vehicle speeds.

2. Less accidents.
3-32

3. Diversion of traffic to more desirable routes; for example, from a local

street being used as a short cut to an arterial street.

4. Less traffic noise with the possible exception of more noise from trucks.

5. Less air quality impact and energy use than stop signs.

6. Support by most local residents.

Some speed hump drawbacks include:

1. Undesired traffic diversions; for example, from arterial to local streets.

2. Interference with the rapid response of police, firefighters, paramedics

and other emergency vehicles.

3. Negative aesthetic impact of humps and related signs and markings.

4. Concern with street sweeping and plowing, ice formation and other

maintenance and repair functions.

5. Fear of increased liability exposure attributed to claims of vehicle damage

and injury to bicyclists.

6. Poor design and construction resulting from the misperception that humps

are simple. ITE (1997) provides detailed design guidance.

Given the possible benefits and drawbacks to speed humps, some municipalities have

taken a systematic approach to optimize their use. During the 1994 to 1997 period, 217

people were killed in automobile crashes in Montgomery County (Haynes, 1998). 

Accordingly, the county installed more than 1000 humps on 300 residential streets as a

partial solution to the excessive number of automobile accidents. Thousand Oaks, CA,

which is one of the first U.S. cities to use speed humps, installed them and studied their

effects. Their conclusion: if the hump is more than two inches high, drivers will seek

alternate routes (Velazquez, 1992). Boulder, CO addressed the issue of interference

with emergency vehicles by banning speed humps on emergency routes (Haynes,

1998).

Berms: The Negative Perception Problem

The suggestion of building structures across streets to control stormwater often elicits

negative reactions, especially from engineers and other personnel responsible for the

design, construction and maintenance of streets. The driving public may also express

concern. One way to deal with this is to note that across street structures are

commonly used in urban areas to control the speed of vehicles. For example, ITE

(1997, p. 5) provides a “partial listing of jurisdictions with speed hump experience” in the

United States and Canada. Included in the partial list are 52 communities in 17 states

and three provinces. (ITE (1997, p. 5) also notes that speed humps are also used in at

least 14 countries outside of the U.S. In other words, humps, engineered cross-street

structures, are widely used in the transportation field.

Note that a berm has a much gentler slope than a hump in the direction of travel. 
3-33

Accordingly, berms cause even less discomfort than humps. Clearly, berms are vastly

different than bumps when measured in terms of driver discomfort.

The Possibility of Integrating Stormwater Berms and Speed Hump

Functions

Although the berms, as used extensively in Skokie and Wilmette, differ markedly in

function from the humps used widely in traffic control, berms and humps are very

similar in form. This suggests that traffic engineers and other personnel responsible for

urban streets should be receptive to the idea of using berms to control stormwater. In

fact, the convergence of the stormwater berm and the speed hump suggests the

possibility of retrofitting existing urban areas with these simple structures for the dual

purposes of stormwater and traffic control. Going one step further, convergence of the

form and function of berms and humps opens the possibility of designing these

structures into new urban development to optimize stormwater and traffic management.

The previously mentioned ITE (1997) document is described as a recommended

practice of the ITE. Interestingly, the only mention of stormwater in this document is a

brief caution to not interfere with drainage. More specifically, ITE (1997, p. 20) states:

Speed humps should be installed with

appropriate provisions made for roadway

drainage... Ideally, a hump should be installed

immediately on the downside of an existing

drain inlet. If this is not feasible the

construction of a bypass drain or other

treatment to route water around the hump

should be considered.

On the more positive side, and in keeping with the idea integrating stormwater

berms/speed hump structures into new development, ITE notes that speed humps

could be designed into new streets. The guidelines state (ITE, 1997, p. 27):

It is desirable in the planning of new residential

subdivisions to configure and design local

streets to minimize excessive speed, excessive

volumes, and cut-through traffic from outside

the immediate neighborhood. However, where

adequate subdivision planning and street

design control cannot be achieved, and one of

the aforementioned problems is considered

likely, it may be appropriate to include speed

humps as part of new street construction after

consideration of less restrictive design or traffic
3-34

control techniques.

Flow Regulators

For purposes of this manual, a flow regulator is a passive, gravity device that regulates

the flow of stormwater into a combined sewer. Because it restricts flow, a flow regulator

must be designed in combination with storage which is usually located immediately

upstream.

Donohue (March 1984a, p. 3-1) identifies three common features of flow regulators: 

A common feature of flow regulators is that

they are gravity devices operating without

external energy sources or external control. 

That is, they are intended to be simple devices

requiring no control and minimal attention.

A second characteristic shared by most flow

regulators is that they are designed and

installed to achieve the desired flow reduction

while minimizing the likelihood of blockage by

debris relative to that which could occur with a

conventional orifice. Some flow regulators

result in less flow passing the control section

for a given head or head range than would

occur with a simple orifice.

A third feature of flow regulators is the need to

specify three parameters for design. The first

parameter is the maximum discharge and the

second parameter is the corresponding design

head. The third parameter is installation

requirements such as available space and

expected orientation of the device.

Many flow regulators have been developed and tested. A discussion of the

configuration and performance of various flow regulators appears later in this chapter. 

For the purposes of this section, flow regulators are viewed as a generic device having

the preceding three features.

As further explained by Donohue (March 1984a, p. 3-1), “flow regulators may be

installed in a variety of locations in an urban stormwater-wastewater system including:

in storm inlets and catch basins to cause temporary ponding on streets or in depressed
3-35

areas; at the outlets of subsurface and surface detention facilities to induce temporary

subsurface and surface storage; and within ...sewers to utilize available in-system

storage.”

The meaning of the terms inlet and catch basin, as used for example in the preceding

paragraph, are important for purposes of this report. As explained by Donohue (March

1984a, p. 3-1):

Inlets collect runoff from the land surface and

discharge via a pipe. Inlets do not have a

sump. That is, the discharge pipe is at the

bottom of the inlet. Catch basins receive flow

from inlets and, occasionally, directly from the

land surface and discharge to the sewer

system. Catch basins have a sump created by

the outlet pipe being several feet above the

bottom of the basin. This sump serves to trap

leaves and other debris and requires periodic

removal and cleaning.

A typical Skokie configuration of an inlet, a catch basin and a manhole on a combined

sewer is shown in Figure 3-17. The configuration is shown in plan and section. Note

that, in a properly operating system, the transition from stormwater runoff to combined

sewage occurs in the pipe connecting the catch basin to the manhole. A trap, as

shown in Figure 3-17, is required to prevent sewer gases from being a problem near the

catch basins.

Figure 3-18 uses a flow regulator installed in a catch basin to illustrate the regulator’s

function. Comparison of the two head-discharge relationships indicates that for any

given head on the catch basin outlet, the flow regulator results in significantly less flow

out of the catch basin. This flow restriction or reduction must be accomplished without

blocking of the flow regulator with debris carried by the stormwater.

Although the function of a flow regulator is illustrated in Figure 3-18 using a catch basin

installation, flow regulators can be installed in other places. Example locations, as

noted earlier, are in stormwater inlets and at the outlets of surface and subsurface

storage facilities.
Figure 3-17. Typical configuration of an inlet, catch basin and manhole in the Skokie 

combined sewer system (Source: Donohue, March, 1984a, p. 3-2).

3-36
With

regulator

Without

regulator

Discharge

Head

Catch Basin

Inflow Pipe

from Inlet

Street

Flow

Regulator 

Outlet Pipe to

Combined Sewer

Static

Level 

Figure 3-18. A flow regulator installed in a catch basin illustrates the basic function

of the regulator.

3-37
catch basins needed only to be fitted with flow regulators. Existing inlets often had to

be moved or new ones installed. In Wilmette, new catch basins, which also served as

inlets, had to be constructed as did new manholes on the adjacent combined sewer.

Combined Function of Berms and Flow Regulators.

Functioning together, berms and flow regulators become, in what more traditional

stormwater management is called, an outlet works. The berm-flow regulator

combination, like the outlet works on a traditional stormwater detention basin, is sized

and configured to temporarily store stormwater to achieve a desired attenuation of the

stormwater runoff hydrograph.

Figure 3-19 shows how a berm on a street and a flow regulator in a catch basin cause

temporary ponding of water on the street during and immediately after a runoff event. 

During and immediately after the event, the peak flow from the catch basin is limited, by

the design of the flow regulator and the berm, to what can be conveyed by the receiving

combined sewer without surcharging. After, the event, the temporarily stored water

drains by gravity through the catch basin.

Figure 3-20 takes the description of the combined function of berms and flow regulators

one step further. Shown here is a hypothetical profile, with great vertical exaggeration,

along the longitudinal axis of a street. Berms and flow regulators (the flow regulators

are not shown) are strategically placed to take advantage of the storage capacity along

the length of the street. Low points, which are also storage areas, are used with peak

outflow of stormwater to the CSS also being governed by flow regulators.

Recall the earlier brief discussion of a common adverse reaction to constructing berms

across streets. This was answered, in part, by noting that stormwater berms have even

less impact on vehicles than do the engineered and widely used speed humps.

A similar negative reaction is frequently expressed in response to the suggestion of

intentionally storing stormwater on streets. Experiences in Skokie, Wilmette and

elsewhere indicate that this initial objection may be offset by offering the following three

points for consideration:

In Wilmette’s CSS, a pair of special catch basins were constructed immediately

upstream of berms and fitted with flow regulators. These catch basins were connected

to a single new manhole on the adjacent combined sewer. In some cases, as

described in the Chapter 9 section titled “Summary of Interviews with Wilmette, IL

Officials,” shear gate flow regulators were placed at the downstream end of pipes

connecting the catch basins to the combined sewer manholes.

In summary, suitable catch basins and manholes already existed in Skokie and the
Street Storage

of Stormwater

Berm Overflow

Longitudinal

Street Profile

Catch Basin

Flow Regulator

Controlled

Discharge to

Combined

Sewer System

Berm

Figure 3-19. Longitudinal profile of a street showing how a berm and flow regulator

function as the outlet works of a temporary street storage facility (Source: Adapted

from Loucks and Morgan, 1995).

3-39

Note: Not to scale and great vertical exaggeration
Figure 3-20. Strategic placement of berms and flow regulators along a street

facilitates use of the street’s capacity to temporarily and in a controlled fashion

store stormwater.

3-40

ROADWAY BERMS

PEAK STAGE

NOTE: GREATLY EXAGGERATED VERTICAL SCALE
3-41

• Urban Streets often flood anyway, especially in flat topography typical of

CSSs. That flooding is unintentional, uncontrolled and unexpected and

can cause damage and excessive disruption of vehicular traffic as

indicated by the upper portion of Figure 3-21.

• Stormwater “flooding” in the street storage system is controlled, that is,

the peak stage and lateral extent are predetermined by the design of

berms and flow regulators. The idea of street temporary controlled

storage of stormwater is illustrated in the lower portion of Figure 3-21. 

The goal is to prevent damage to adjacent properties and not

unnecessarily disrupt vehicular traffic.

• Controlled stormwater on streets is much preferred over uncontrolled

combined sewage in basements.

Shown in Figure 3-22 are photographs of actual street storage in Skokie and Wilmette. 

Note that the ponding is shallow, does not prevent vehicular movement, and is

contained within the public right-of-way.

Subsurface Storage

Subsurface storage facilities are expensive, but sometimes necessary, components of

a street storage system. They are used for temporary storage of stormwater beneath

those streets and parking lots where the required surface storage would cause damage. 

Subsurface storage is used only where absolutely needed because of the typical high

cost per unit volume of storage. Accordingly, street storage systems will typically have

very few subsurface storage facilities relative to on-street and other surface facilities. 

Skokie’s 8.6 square mile street storage system, for example, contains only 83

subsurface storage facilities compared to 871 berms and 2,900 flow regulators.

Figure 3-23 illustrates the function of subsurface storage. The facility lies within the

public right-of-way and is positioned above the combined sewer. Its outlet is controlled

by a flow regulator. Stormwater, not combined sewage, is temporarily stored in the

facility.

Actual subsurface storage facilities range from simple to complex configurations

depending on the volume of storage required and site constraints. Some facilities are

simply oversized lengths of storm sewer while others are large rectangular structures

extending the length of a block and the width of the street. An example of the latter is

illustrated in Figure 3-24. Shown is the construction of a subsurface storage facility

composed of precast, reinforced concrete sections.
Unintentional, uncontrolled and

unexpected surface flooding

Temporary, controlled surface ponding

within street right-of-ways

Figure 3-21. The street storage approach uses temporary, controlled ponding of

stormwater in contrast with the common unintentional, uncontrolled and unexpected

ponding resulting in damage and vehicular interference.

3-42
Figure 3-22. Actual street ponding in Skokie (top) and Wilmette (bottom).

3-43
Dry Weather

Reinforced

Concrete Box

Combined

Sewer

Depth

Flow

Regulator

Wet Weather

Reinforced

Concrete Box

Combined

Sewer

Depth

Flow

Regulator

Depth

Combined

Sewer Flow

Regulator

Reinforced

Concrete Box

Figure 3-23. Subsurface storage facilities are positioned within the right of way, abo

the combined sewer and temporarily stored stormwater, not combined sewage.

3-44
Figure 3-24. Subsurface storage facilities range from simple oversized lengths

of storm sewer to, as shown here, large structures assembled from precast

reinforced concrete sections.

3-45
3-46

Apply Screening Criteria to Determine Likely Applicability of A Street Storage

System

Refer to the section in Chapter 10 titled “Criteria for Screening the Applicability of Street

Storage.” The screening criteria are based largely on ideas and information presented

in this report, that is, the criteria reflects experience with the successful implementation

of street storage systems. Included in the previously noted section of Chapter 10 are

an explanation of the purpose of the screening criteria, comments about the

qualifications of evaluators, reference to the actual criteria which are presented in

Appendix B, suggestions for interpreting the information.

Select an Initial Pilot or Implementation Area Within the Combined Sewer System

Need for Phased Implementation

Traditional public works projects, such as streets and highways, wastewater collection

and treatment, and water supply treatment and distribution, are often implemented in a

phased manner. Budgetary constraints are usually the reason for prioritization and

phasing. That is, there is a need to spread capital costs over a period of years so that

they match revenues.

Phasing means prioritization. If costs are the principal reason for phasing, then a

phased public works project begins with the most cost-effective component. However,

other factors can establish priorities including physical constraints, regulatory

compliance, and political considerations.

When non-traditional approaches, such as street storage, are an integral part of a

public works project, another important reason arises for phasing. That reason is the

need to be cautious as the new technology is gradually conceptualized, planned,

designed, tested, refined, understood, and accepted. Phased implementation was

heavily used in the Skokie street storage project because it is the first large scale

application of the street storage system in the U.S.

The key to effective phasing is selection of the first or pilot implementation area. The

purpose of this section of the chapter is to offer suggestions, based on the Skokie,

Wilmette and other experiences, on factors to consider in selecting the physical area for

the first phase of a street storage project and then prioritizing subsequent phases.

Prioritization Factors

Many factors could be weighed in selecting an initial implementation area and

prioritizing subsequent areas. Factors to use and their relative weights will depend on a

given community’s physical, regulatory, and socio-economic situation. In picking an

initial implementation area or the next area in order of decreasing priority, consider
3-47

selecting an area that:

• Includes a complete drainage system or watershed. The analysis and

design process requires, for any point in the system, consideration of all

significant conveyance and storage components upstream of that point. 

The entire 1255 acre HSSD, one of three combined sewer districts in

Skokie, was selected as the initial area. It is a CSS watershed that

discharges to the interceptor sewer system of the MWRDGC. While

selecting a head water portion of this sewer district would have been

acceptable, choosing a middle or lower portion of the district would conflict

with this factor.

• Best satisfies the screening criteria for street storage. These criteria are

introduced in the preceding section of this chapter, elaborated on in

Chapter 10, and attached as Appendix B.

• Has a high concentration of basement flooding or other problems. By

using this approach, and assuming implementation proceeds through

construction, the selected area is likely to be very cost effective. That is,

the ratio of problems solved to dollars expended should be higher than if

other areas with less concentrated problems are selected.

• Reflects stakeholder input. An advisory committee of stakeholders might

be formed to help select the initial implementation area. Stakeholder

groups to be represented on the advisory committee might include

homeowners, business people, educators, environmentalists, and

regulators. Technical and other support should be provided by the

community possibly with the assistance of their engineering consultant. In

Skokie, the HSSD was selected by the community and then a consulting

engineering firm was retained (Donohue, 1982a, p. 11).

• Has characteristics typical of other areas. Skokie, for example, selected

portions of four streets covering approximately ten blocks within the HSSD

for testing of flow regulators. The referenced pilot study is discussed in

detail later in this chapter. One requirement for the testing of flow

regulators was that the selected areas have a number of inlets and catch

basins per unit area approximating that of the HSSD. In addition, street

cross sections and widths in the selected areas were to be representative

of the HSSD (Donohue, 1984a, pp. 3-13, 3-14). As further suggested by

this Skokie example, use of one or more small pilot study areas within the

overall initial implementation area may be prudent. 

• Offers cost or other advantages if quick action is taken. As an example of

this opportunity factor, one of several candidate CSS drainage areas may

be slated for near future street resurfacing. Given that street geometry is
3-48

critical to street storage, that CSS drainage area may be the logical place

to begin implementation of street storage.

Establish Performance Criteria

Need for Performance Criteria: Analysis and Design

Before a CSS can be diagnosed, that is, analyzed to determine the cause of problems,

the desired performance must be defined. The desired performance serves as the

benchmark against which the severity of CSS problems and the nature of their causes

can be measured.

Likewise, the prescription of solutions to a CSS’s problems, that is, planning and

design, cannot be undertaken until the desired performance of the CSS is defined.

Variation in Performance Criteria

Presented in this section of the chapter are examples of performance criteria used in

the Skokie and Wilmette and other street storage systems. While there are some

commonalities, the presented performance criteria show significant variations. This is

to be expected for the following three reasons:

1. The street storage technology is relatively new and, therefore, rapidly

evolving. Something learned in one project, or one phase of a given

project, may change the performance criteria for the next project, or next

phase of a given project.

2. Special circumstances. For example, a community with many tree-lined

streets is likely to include in their performance criteria provisions intended

to protect that amenity.

3. Different level of service expectations. Some communities have higher

expectations for the level of public services that they receive and are

willing to pay for.

Performance criteria presented here are not necessarily recommended for other

communities. Rather, they are offered as examples of what some communities have

developed to be consistent with their familiarity with the street storage technology, their

special circumstances and their level of service expectations. Each community

contemplating use of the street storage system should formulate their own performance

criteria, possibly using the criteria presented here as a guideline.

Skokie Performance Criteria
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Performance criteria for Skokie’s street storage system were first formulated in 1982 as

part of the preliminary engineering for the HSSD (Donohue, 1982a, p. 5-1). They were

slightly modified as part of a refinement of the HSSD preliminary engineering

(Donohue, 1984, pp. 5-1, 5-2), the preliminary engineering for the MSSD (Donohue,

1987b, pp. 6-1, 6-2) and the preliminary engineering for the Emerson and Lake Streets

Sewer District (Donohue, 1987a, pp. 5-1, 5-2). These criteria changed relatively little

during this five year preliminary engineering period. Therefore, the performance criteria

for the Emerson and Lake Streets are presented here as being representative of the

Skokie approach.

The explicitly documented Skokie performance criteria may be summarized as follows:

1. The street storage system should be designed for the 10-year recurrence

interval storm.

2. Reduce surcharging of sewers to prevent sewage backup caused by

overloading of the municipal sewer system. The preliminary design of the

alternatives is developed with the concept of defining maximum

stormwater runoff rate into the sewers while preventing damaging sewer

surcharging.

3. Make utilization of available street ponding capacity without causing flood

damage to adjacent private development. Berms are to be used to detain

stormwater on upland streets.

4. Minimize ponding on state and county highways. Stormwater ponding is

discouraged on such streets. In locations where street storage on nearby

streets could increase ponding depth on or near state and county

highways, roadway berms are to be use to prevent ponding on the state or

county highways. Storage facilities or relief sewers are to be used in

no-pond areas to accommodate stormwater in excess of sewer capacity.

5. Establish maximum permissible flood stage for each street on a

block-by-block basis. This stage, referred to as the “critical” elevation, is

the highest stage which can be tolerated on the block without incurring

flood damage such as first floor flooding and the flow of surface water

through windows into basements or into below grade garages. In most

cases the sidewalk elevation at the lowest point in the block is the critical

elevation.

6. Confine temporarily stored stormwater within the right-of-way during the

10-year recurrence interval design storm. Right-of-way typically extends

from the back of the sidewalk on one side of the street to the back of the
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sidewalk on the other side. Limit the maximum depth of ponding for the

10-year storm to the lesser of six inches at the street centerline or nine

inches at the gutter invert.

7. TARP Phase I provides a discharge point that will carry the stormwater

runoff from a 10-year recurrence interval storm.

8. A gravity operated stormwater system is preferred to a pumped system. 

Minimal use of electrical and mechanical controls and equipment is

desirable. A simple gravity operated system reduces the likelihood of

failure and minimizes future operation and maintenance costs.

9. Storage of excess runoff should be accomplished first in off-street areas,

second on streets, and last in underground storage facilities. Park and

private property may also be considered assuming proper arrangements

can be made.

10. Downspouts from one and two family residences are assumed to be

disconnected from the CSS and to discharge to the land surface or storm

sewer system in all street storage areas and in all areas without street

storage but having storm sewers and/or stormwater storage facilities. 

Industrial, commercial and multi-family buildings and any buildings with

internal drainage systems are excluded from this assumption.

Wilmette Performance Criteria

The explicitly documented performance criteria for Wilmette’s street storage system

may be summarized as follows:

1. “Alleviate basement flooding for the 10-year frequency storm event” (Rust,

November 1993, p. 1).

2. “Reduce private property flooding (outside of the Village right-of-way) for

the 10-year frequency storm event” (Rust, 1993, p. 1).

3. “Limit inconvenience to residents in accessing their property during major

rainfall events” (SEC Donohue, December 1992, p. 7).

4. Confine street storage to public right-of-way (SEC Donohue, June 1992,

p. 6).

5. Limit ponding depths to a maximum of six inches on the crown of a street

and a maximum 12 inches above the gutter invert. Allow no ponding on

sidewalks (SEC Donohue, June 1992, p. 7).

6. Exclude designated streets or street segments from ponding. These
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streets were selected based on high traffic volume and/or proximity to

schools, places of business, and access to or from elderly housing or fire

and police stations (SEC Donohue, June 1992, pp. 7-8).

7. Generally consider berms only on streets with flat longitudinal

grades—0.5% or less (SEC Donohue, June 1992, p. 16).

8. “Limit inconvenience to the community during the construction process”

(SEC Donohue, December, 1992, p. 7).

9. “Limit increases in hydraulic loading on the North Shore Channel” (SEC

Donohue, December 1992, p. 7).

10. “Limit increases in pollutant loading on the North Shore Channel” (SEC

Donohue, December 1992, p. 7).

11. Limit peak flow discharged to TARP to the negotiated rate for the 10-year

design rainfall events (Morgan, 1999).

Although not documented in the available Wilmette reports (SEC Donohue, June 1992;

SEC Donohue, December 1992; and Rust, November 1993) other important

performance criteria, in addition to the preceding list, were apparently applied in

Wilmette. These seem to include the previously presented Skokie performance criteria

8, 9 and 10.

Analyze Existing System Using Monitoring

The suggested systematic analysis and design process for a street storage system

should include, as shown in Figure 3-5, monitoring data. That data may already exist

from previous studies, may be collected as part of a special monitoring effort, or be a

combination of the two. Regardless of data origin, the data should be used in parallel

with the previous described computer modeling. Ideally, iteration should occur between

modeling and monitoring as suggested by the dashed two-way arrow in Figure 3-5. 

For example, monitoring data should be used to calibrate hydrologic-hydraulic models. 

Initial modeling results should be used to identify gaps in the monitoring program. See

Walesh (1989, Chapter 10) for a detailed discussion of the interplay between modeling

and monitoring. Both Skokie and Wilmette used monitoring during the analysis and

preliminary engineering process. Their efforts are described in the following sections.

Skokie Monitoring

This summary of the initial monitoring program is taken from Walesh and Schoeffmann

(1984). The monitoring program was conducted in 1983 to:

• Better define the behavior of the existing CSS.
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• Provide baseline information to evaluate the performance of the street

storage system, which would eventually be implemented.

• Provide data for refinement of the ongoing computer modeling effort.

An overriding consideration was selection of equipment, training of Skokie personnel,

and installation of equipment in such a fashion that it could be moved to other sewer

districts, after one or more years of service in the HSSD.

A 41 unit monitoring system was installed. It consisted of three rainfall monitoring

stations; nine sewer flow monitoring stations with bottle racks installed at all nine

monitoring stations and continuous monitors installed in six of the stations; 20 street

ponding monitoring stations composed of 15 stations equipped with bottle racks and

five with specially designed recording devices; and 10 footing drain flow monitoring

stations, three of which were located in the HSSD and seven in adjacent sewer districts.

Installation, startup and calibration of equipment was carried out from January through

March, 1983. Training of the Village staff, which occurred in the February through April,

1983 period, included chart changing, battery replacement, calibration, parts

replacement and recording procedures. The monitoring system was operated as a joint

effort between Skokie and Donohue & Associates, its consulting engineering firm, until

the end of October, 1983. Additional, selective monitoring was conducted in 1984

within and outside of the HSSD.

The monitoring program revealed that precipitation exhibits significant spatial variation

across the HSSD with half of 16 monitored major storms exhibiting such a variation. 

Dry weather flow values were found to be similar to those assumed in preliminary

analyses (which relied solely on computer modeling as described in subsequent

sections of this chapter) but exhibited significant spatial variation which was

subsequently included in the refined analyses. Foundation drain flows were determined

to be about one-third of the values assumed in the preliminary analysis. Accordingly,

foundation drain contributions were reduced from about 2,900 gallons per day per

house to about 1000 gallons per day per house.

Wilmette Monitoring

Flow monitoring was performed primarily to obtain data for calibration of SWMM. SEC

Donohue (December 1992, p. 8) describes the monitoring program as follows:

Flow meters were installed at five locations in

the... sewer system and operated from July 10,

1991 through September 9, 1991. Rainfall

over the flow metering period was measured

using a continuous recording rain gauge. Total
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rainfall for the flow monitoring period was 5.3

inches, the largest storm event was 1.6 inches,

and a number of smaller events were also

recorded.

A second purpose of the Wilmette monitoring program focused on system behavior

along the west boundary of the CSS. There was concern that MWRDGC interceptors

along this boundary might surcharge and impact the tributary portion of the CSS. No

surcharging occurred during the monitoring period. However, this observation was

qualified by the fact that no severe rainfalls occurred during the monitoring. This is an

example of using monitoring to diagnose system behavior.

Analyze Existing System and Perform Preliminary Design Using Computer

Models

A Complex System: Need for Computer Modeling

A typical combined sewer system is complex with its many and varied sanitary,

stormwater and other inflows and its tendency to surcharge. Overlay a rectilinear

system of street storage and conveyance components and the complexity increases.

Because of the complexity of the existing and possibly modified CSS, computer

modeling has proven to be a necessity. Hydrologic-hydraulic computer modeling was

heavily used in the Skokie and Wilmette projects. Computer modeling has been used

for both analysis and preliminary design, that is, diagnosis of problems and

development and prescription of solutions.

The models used and the manner in which they were used has naturally evolved, given

the approximately 15 year period during which analysis and design occurred in the

Skokie and Wilmette projects. Much was learned during this period as indicated by the

subsequent sections. Presented here are summaries of computer modeling

approaches used at various stages of the Skokie and Wilmette projects. Hopefully, the

ideas and information presented will be helpful to CSS communities contemplating the

use of computer modeling and the street storage approach.

Assuming a discrete event, contrasted with a continuous computer model (Walesh,

1989, pp. 321-324) is to be used, a design storm or design storms must be selected as

part of the modeling. This typically includes decisions on recurrence interval, duration,

volume, and hyetograph shape. Sensitivity analyses should be part of the process of

formulating the design storm or storms. Detailed discussion of design storms is beyond

the scope of this manual.

For in-depth discussion of design storms, see Walesh (1989, pp. 98-99, 112-113, 129,

304) and ASCE-WEF (1992, pp. 69-78, 226). An example of a sensitivity analyses
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used to determine the critical duration for a design storm is provided by Walesh (1989,

pp. 361-363).

Analysis and Preliminary Design for the HSSD in Skokie 

A three-phased approach was used in the modeling and the analysis and preliminary

design of the HSSD. The following description of the approach is taken from Walesh

and Schoeffmann (1984).

Phase I was a simple static condition analysis, done without computer modeling, to

determine the effect of North Shore Channel flood stages on flooding in the HSSD. 

Phase II was the steady-state hydraulic analysis of the sewer system, using a computer

modeling, to determine the capacity available for stormwater runoff. Phase III was the

determination of the location and extent of street flooding which would occur for various

recurrence interval storms and the location and size of supplemental surface storage

and relief sewers. This, the last phase was heavily dependent on computer modeling of

the dynamic hydrologic-hydraulic system.

Phase I - Analysis of Static Conditions

This analysis determined if flood levels on the North Shore Channel, the ultimate

receiving water for the HSSD CSS, would cause basement flooding solely as a result of

backwater. The analysis was motivated by the observation that surface and subsurface

storage of stormwater in the HSSD could not resolve basement flooding that resulted

solely from North Shore Channel backwater effects. The analysis was conducted to

determine if there were portions of the HSSD in which flood control could not be

achieved by a street storage system within the HSSD.

The procedure used in this analysis is illustrated in Figure 3-25. North Shore Channel

flood levels were obtained from the Corps of Engineers (Stadler, 1982) and the

MWRDGC (MSDGC, 1981). Elevations of inverts and crowns of sewers in the HSSD,

which were determined from sewer atlas maps and field surveys, were used to estimate

the elevations of basement floors. Basement floor elevations were then compared to

the flood levels.

The analysis concluded that there are no significant areas in which basement flooding

would result solely from backwater of the North Shore Channel. Therefore, flood

control within the HSSD might be achieved by an in-HSSD street storage system.

Phase II - Analysis of Sewer Capacity

The portion of the CSS capacity available for carrying stormwater runoff is a function of:

the total hydraulic capacity of the system as determined by pipe size, slope, and
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material; the quantity of sanitary flow, infiltration, and foundation drainage entering the

system; and the level to which the sewer can surcharge without causing basement

flooding or other damage. Capacity is also affected by the backwater effect of

downstream sewers. The maximum allowable surcharge level was set at the crown of

the sewers to avoid backup of combined sewage into basements.

For the sewer capacity analysis, flows representing foundation, sanitary and infiltration

components were established based on a concurrent monitoring program. Roof drains

were assumed to discharge to the land surface and no longer be directly connected to

the CSS as a result of the Village’s largely completed downspout disconnection

program. The following flow components were used:

• Foundation flow: 5,000 gpd/acre or 0.0075 cfs per acre based primarily

on monitoring.

• Sanitary and infiltration flow in residential areas: a total of 3,000 gpd/acre

or 0.0047 cfs/acre for the western 90 percent of the HSSD and 6,000

gpd/acre or 0.0093 cfs/acre were used for the remainder of the HSSD

based on monitoring.

• Sanitary and infiltration flow in industrial areas comprising the eastern

approximately 10 percent of the HSSD: 11,000 gpd/acre or 0.017 cfs/acre

based on monitoring.
Building

with

Basement

Building

without

Basement

Flood Stage

Combined

Trunk

Sewer

Interceptor

Sewer

Normal

Stage

Figure 3-25. Phase I, a simple static condition analysis, was used to determine if

high stages on the North Shore Channel caused basement flooding in the HSSD.

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subbasin basis until the hydraulic grade line in the sewer met the established allowable

surcharge level.

The allowable runoff rates represent design conditions, that is, the maximum rate at

which stormwater can be released into the CSS without causing sewer surcharge and

basement flooding. For this no-surcharge condition, the maximum allowable

stormwater runoff rate ranged from 0.1 to 0.2 cfs per acre.

The resulting allowable stormwater runoff rates are extremely low. These unit area

rates are equivalent to the runoff from an impervious surface that would be generated

by a continuous rainfall intensity of only 0.1 inches per hour. Stated differently, the

computer modeling diagnosis revealed that the HSSD combined sewers had very little

capacity available for conveying stormwater runoff when allowance was made for

sanitary sewage, foundation flow and infiltration.

Phase III - Preliminary Design of Street Storage

This analysis determined the street ponding which would occur as a result of regulating

the rate at which stormwater runoff could enter the CSS. More specifically, this analysis

determined the location, depth, lateral extent, and duration of street ponding subject to

the allowable stormwater release rate and other constraints as described below.

The intent of the analysis was to determine the maximum rate at which stormwater

runoff could be released into the CSS without exceeding the established surcharge

level. The analysis is analogous to establishing the maximum allowable release rate

from a conventional stormwater storage facility based on the capacity of downstream

conveyance works.

The sewer capacity analysis was carried out using the computer program System

Analysis Model (SAM), which permitted simulation of the entire HSSD and provided the

computational means of accounting for system surcharges and hydraulic grade lines for

each trunk and branch sewer (CH2M Hill, 1980). Refer to Figure 3-26 for a overview of

the computer modeling procedure. The dry weather module of SAM was used to

develop and input flows to the sewer system and the transport module was used to

combine and route the flows through the sewer system. The HSSD was represented in

the model as 101 subbasins, having an average area of 12 acres, and 161 sewer

segments, having an average length of 300 feet.

Foundation, sanitary and infiltration flows were input to the CSS. Increasing stormwater

runoff rates were then progressively added to the sewer system on a subbasin by
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Figure 3-26. Computer model used for analysis and preliminary design in the

Skokie HSSD (Source: Donohue, 1982a, p. 45).
analyses using storm durations ranging from 30 minutes to 12 hours indicated that a six

hour duration was most critical.

The lowest sidewalk elevation in each block was selected as the critical elevation for

the block. The critical elevation is the maximum allowable ponding elevation under

design storm conditions.

The modeling process moved on a block-by-block basis in the downstream direction. 

Excess water from each street was transferred to one or more adjacent downstream

streets. In this manner, ponding was maximized for each block. Use of street surface

berms was assumed for achieving stage control. Subsurface storage tanks were

strategically placed to store excess stormwater from groups of streets having

insufficient ponding capacity.

Results

Largely as a result of the preceding three phased analysis and preliminary design

process, the engineer recommended moving ahead with a street storage system

throughout the HSSD. Skokie accepted the recommendation and implementation of

street storage approach eventually encompassed the entire 8.6 square mile community.

A computer program, Street and Sewer Analysis Model (SASAM) was used for the

analysis. Refer again to Figure 3-26. Note the relationship between SASAM and SAM. 

SASAM accepted historic or design rainfall hyetographs and computed runoff

hydrographs as a function of subbasin area, time of concentration, and type of land

cover using the British Road Research Laboratory Method (Stall, 1972). Flow in streets

and on adjacent parkways was routed using the Manning equation plus conservation of

mass to account for the conveyance capability of any given street section. Stormwater

which ponded on street surfaces and adjacent parkways and lawn was accounted for

by a reservoir routing procedure. Release of flow from the street surface to the sewer

system was set at the maximum allowable release rates which could be handled by the

sewer system as determined by Phase II. Examples of stage hydrographs produced by

SASAM are presented in Figure 3-27.

The HSSD was partitioned into 278 subbasins having an average size of 2.4 acres for

the Phase III analysis. Drainage area, percent directly connected impervious area, and

time of concentration were determined for each subbasin. The street system was

represented on a block-by-block basis requiring the use of 278 street segments. 

Representative street cross-sections, some of which are shown in Figure 3-15, were

surveyed. Cross-sections extended from the street face of buildings on one side of the

street to the street face of buildings on the opposite side and varied significantly.

The first quartile storm distribution developed on the basis of historic rainfall data in the

Chicago area was used in the analysis (Illinois State Water Survey, 1976). Sensitivity
Figure 3-27. Depth and duration of street ponding as a function of recurrence interva

(Source: Walesh and Shoeffmann, 1984).

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The three phased analysis and preliminary design approach developed for the HSSD

was subsequently used, with refinements, on the other two districts comprising Skokie. 

Preliminary engineering was completed for both the MSSD and the ELSSD in 1987

(Donohue, May 1987a; Donohue, May 1987b). Thus, the substantial investment in

developing the computer modeling-based analysis and preliminary design methodology

for the HSSD yielded returns, not only on that district but also on the other two. As

described in the next section, some of the modeling approach developed for Skokie

was used in Wilmette.

Analysis and Preliminary Design in Wilmette

The USEPA Stormwater Management Model (SWMM) (Huber and Dickinson, 1992)

was modified for analysis and preliminary design of the Wilmette street storage system

(Loucks and Morgan, 1995). The modeling approach consisted of:

• Hydrologic simulation using the SWMM RUNOFF module.

• Street storage simulation using the SWMM EXTRAN module.

• Sewer system simulation using the SWMM EXTRAN module.

The EXTRAN model of the Wilmette street storage system is a surface network of

storage junctions and berm overflows connected to a subsurface combined and relief

sewer system.

Modification of the Stormwater Management Model
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Street storage simulator required three innovations, including two modifications. As

explained by Loucks and Morgan (1995):

Three innovations were required in the

development of the street storage model. 

First, the EXTRAN code was modified to

accept input of stage-storage relations for

storage junctions and to generate descriptive

storage junction output summaries of storage

junction levels and outflow. Second, it was

determined that the standard EXTRAN orifice

formulation did not adequately represent field

conditions for flow through a catch basin

restrictor. An alternate to the equivalent pipe

formulation was developed for use in the

EXTRAN model. Third, the EXTRAN weir

code was used to model flow overtopping of

the berms into adjacent street storage sites.

Each of the three SWMM innovations are now explained. This somewhat detailed

explanation is provided primarily because SWMM is widely used in modeling urban wet

weather conditions. Accordingly, communities contemplating a street storage system

may also be thinking of using SWMM.

In the standard use of EXTRAN, storage junction data are input in the form of a depth

and surface area relationships. Such a relationship is difficult to develop directly from

street storage sites. This problem was resolved as follows (Loucks and Morgan, 1995):

Available street storage volumes are from

street cross-sections using the end area

method. Software is available to compute

street storage at depth intervals of 0.1 feet. 

The EXTRAN code was modified to accept

stage verus storage volume input and to print

an enhanced summary of storage junction

results. The summary provides the maximum

depth, storage and discharge for each storage

site and identifies whether an overflow from the

junction occurred.

The software referred to in the preceding quote is SASAM, the previously described

computer model used in the Skokie modeling. It was used to develop stage-storage

relationships in the Wilmette project.
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EXTRAN uses an equivalent pipe to represent an orifice. This representation differed

greatly from the manner in which flow regulators were to be installed in Wilmette catch

basins. For example, inherent in EXTRAN is the assumption that the water depth in the

upstream junction exceeds the orifice diameter and that upstream and downstream

junction elevations are about the same. This differs markedly from the expected

Wilmette flow regulator installations, as shown in Figure 3-19, where the flow regulators

are 1.5 to 4.5 feet below street grade and the receiving combined sewer is three to nine

feet below the flow regulators. EXTRAN provided no way to position an orifice well

below the storage junction invert. As explained by Loucks and Morgan (1995), the

complication was resolved as follows:

Laboratory tests by Spring (1983)

demonstrated that a PVC tee-restrictor in a

catch basin behaves as a classical orifice for a

wide range of heads. The flow for a particular

orifice area and head is given by formula

Q=Cda(2gh)1⁄2, where g is acceleration due to

gravity and Cd is a discharge coefficient found

to be 0.60 to 0.65. In the context of the

EXTRAN model, this formula is much better

suited to the EXTRAN weir code rather than an

equivalent pipe representation. The EXTRAN

weir code was modified to accept a new type

of weir representing a catch basin restrictor. 

Data inputs are the orifice diameter, the depth

of the orifice below the ground, and the

discharge coefficient. This approach is

superior as long as there is no downstream

submergence. Even then it is still more

accurate than the equivalent pipe, but not as

stable computationally.

Berm overflow and flow exchange between adjacent street storage areas are important

phenomena in the street storage system. All stormwater flow and volume must be

accounted for. As explained by Loucks and Morgan (1995):

Berm overflow is employed to fully utilize

available storage and to convey stormwater to

relief sewer locations from individual ponding

areas, which may not have sufficient storage

volume. Simulation of berm overflow has been

implemented in the EXTRAN model using the

standard transverse weir input.
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Application of the Model

The previously described model was used for analysis, preliminary design, final design,

and post-construction verification. More specifically (Loucks and Morgan, 1995):

In the feasibility analysis, storage sites were

grouped together using a single storage

junction to represent ten or more ponding

areas. During design and construction, the

planning level models were refined to support

and verify the design of street storage location,

relief sewer configurations, relief sewer

connections to existing combined sewers, and

restrictor sizes. These models stretched the

traditional data limits of EXTRAN. Current

models representing the two completed

phases feature over 250 pipes and 350

junctions including more than 100 storage

junctions.

The model was calibrated against precipitation and flow data for July 13 and July 30,

1992 storm events, each of which had recurrence intervals of about three months. 

Analyses of sensitivity of the system to design storm duration revealed that the six hour

event “...produced the greatest amount of system overflow and the most prolonged time

of widespread sewer surcharge.” System analysis indicated that one-year frequency

and larger storm events surcharge the CSS and cause basement and street flooding

(Rust, November 1993, p. 4). This finding was consistent with Wilmette’s historic

basement and street flooding problems.

Results

The engineer recommended implementing the street storage system in Wilmette as a

result of the previously described computer modeling based analysis and design

process. Wilmette accepted the recommendation and implementation of the street

storage approach will eventually encompass the entire 2.0 square mile CSS. 

Review Flow Regulator Availability and Performance

Essentiality of Flow Regulators

Flow regulators, as explained earlier in this chapter, are an integral part of the street

storage system. They must be properly sized to achieve the desired stage-discharge

relationship at any given storage location.
3-65

Equally important is selection of the type of flow regulator for a particular application. 

Reason: relative to berms, subsurface tanks, relief sewers and other components, flow

regulators are most prone to failure. The most common failure mechanism is partial or

total plugging by debris carried in stormwater runoff. Plugging can, in turn, lead to

excessive upstream storage and stage and, after a rainfall event, prevent the gravity

drainage of stored stormwater. Therefore, the type of flow regulator selected must fit

the environment within which it is installed.

Skokie Flow Regulator Study

A flow regulator testing program was carried out in the early stages of the Skokie street

storage project. It had been recommended in the preliminary engineering study for the

HSSD (Donohue, 1982a, p. 115). At that time, in the early 1980's, little was known

about flow regulators. Flow regulators were viewed as likely pivotal components of the

evolving Skokie street storage program, and, therefore, a special flow regulator study

was warranted.

Presented here is a synopsis of the testing program based largely on Donohue (March

1984a). The first purpose of the synopsis is to sensitize potential uses of flow

regulators to flow regulator features so that informed decisions can be made. The

second purpose of this synopsis is to provide information about specific flow regulators.

Purpose

The overall purpose of the flow regulator study was an equitable and objective

evaluation of flow regulators under field conditions likely to be encountered in a

system-wide application of regulators in Skokie. Sometimes laudatory and occasionally

conflicting claims of equipment manufacturers and suppliers pointed to the need for a

comparative field test. Based on a literature search and personal contacts, such a test

had apparently never been carried out.

More specifically, the purpose of the flow regulator study was to: determine the initial

cost of commercially available flow regulators and devices specially fabricated by the

Village and others: evaluate flow regulator installation, removal and adjustment

requirements: and observe and evaluate the hydraulic and other performance

characteristics of flow regulators under a variety of field conditions.

Literature Search and Interviews

A literature survey and personal interviews identified the following five types of flow

regulators potentially applicable to the HSSD:

1. The commercially available Hydro-Brake unit as illustrated in Figure 3-28. 

Flow enters the unit perpendicular to the outlet pipe, is turned through 90

degrees, and is discharged. The resulting turbulent flow pattern causes a
3-66

much higher energy loss than would occur through an orifice of similar

diameter. Therefore, for a given head, the discharge through a

Hydro-Brake was half or less than half that which would occur through an

orifice having a cross-sectional area equal to the smallest free opening of

the Hydro-Brake. That is, although the Hydro-Brake and the orifice would

have similar ability to pass debris, the Hydro-Brake would reduce flows by

one-half or more.

As noted by Pisano (1989), the Hydro-Brake is an example of a vortex

flow throttling device. Vortex regulators were first developed in Denmark

in the mid 1970's. They were used in Denmark and Sweden to mitigate

basement flooding within CSSs.
Figure 3-28. Examples of Hydro-Brake flow regulators, available in the early 1980’s,

illustrating the basic operation of vortex type regulators (Source: Hydro Group, 1982).

3-67
3-68

2. The commercially available Scepter units. A photograph of one is shown

in Figure 3-29. The orifice is diamond shaped with a rectangular keyway

at the bottom. The principal purpose of the keyway is to keep buoyant

debris below the bottom of the diamond during dry periods. At the onset

of a runoff event, the device is expected to function such that buoyant

debris jammed against the keyway will rise, encounter the wider diamond

portion of the orifice, and immediately flow through the regulator.

3. Specially fabricated solid cover with orifices. Figure 3-30 is a photograph

of one of these devices. For a given head, a few small orifices reduce the

flow significantly compared to the flow through a standard inlet grate with

its many larger openings.

4. Horizontal orifice plate beneath the inlet grate as shown in the

photographs in Figure 3-31. The single, small orifice helps to trap leaves,

twigs and other debris carried by the stormwater before the material

reaches the underlying orifice.

5. Hanging trap flow regulator, as illustrated in Figure 3-32. This device,

which can be assembled from inexpensive, standard PVC units, features

an orifice that is always submerged.

Design of the Field Study

Portions of four streets, covering approximately ten lineal blocks on the west side of the

HSSD, were selected for the field phase of the flow regulator study. Factors considered

in selecting the test areas included: a variety of topographic features such as streets

with uniform and non-uniform longitudinal slopes; a range in type of street

cross-sections and street widths; an aerial density of inlets and catch basins similar to

that of the entire HSSD; a mix of residential and commercial streets; and the presence

of trees.

Equipment Acquisition and Installation

A total of 29 flow regulators were installed in the study area during the period of

January through April 1983. The Hydro-Brake and Scepter units were installed in both

catch basins and inlets. The hanging trap unit was applicable only to catch basins. 

The orifice in the inlet grate and the horizontal orifice plate beneath the grate were

suited only to inlet installations.
Figure 3-29. Photograph of Scepter flow regulator.

3-69
Figure 3-30. Photograph of solid cover with orifices.

3-70
Figure 3-31. Photographs of horizontal orifice plate flow regulator before and after

installation.

3-71
Figure 3-32. Hanging trap flow regulator (Source: Donohue, 1982a).

3-72
Rainfall

The average intensity of 60 percent of the rainfall events occurring during the six month

field tests exceeded 0.1 inches per hour which approximately corresponds to a unit

runoff rate of about 0.1 cfs per acre, the rate above which flow regulators had to

function as part of the HSSD street storage system to prevent damaging surcharging. 

Therefore, the majority of rainfall events, and all intentional flooding tests, simulated

operational conditions.

Resistance to Plugging

From a plugging perspective, flow regulators were much more resistant to plugging

when placed in catch basins than inlets—the latter installations were 20 times more

likely to plug than the former. There was no significant difference in the operation

characteristics of Hydro-Brakes, Scepter units, and hanging traps placed in catch

basins—they all performed very well.

Although there were significant differences in the anti-plugging performance of inlet

installations of Hydro-Brakes, Scepter units, grate modifications and horizontal orifice

plates, the difference was of little practical significance because the incidence of

plugging was too high. That is, even a relatively low plugging frequency of inlet

installation is unacceptable for the street storage system. Leaves appeared to be the

principal cause of plugging of flow regulators. This dominance probably reflects the

large supply of leaves relative to other materials.

Costs

The cost of purchasing flow regulators varied widely. Cost ranges per unit in 1983 for

units appropriate to Skokie inlet or catch basin installations were:

Observation Procedures

The system of 29 flow regulators was observed by Skokie and Donohue personnel

during or immediately after a total of 15 rainfall-runoff events between March 18 and

September 20, 1983. In addition, regulator performance was observed during

intentional flooding tests conducted on October 18 and November 16, 1983. A

photograph of the intentional street flooding is shown in Figure 3-33. The field

observations of flow regulators focused on operation and maintenance factors such as

the tendency of the regulators to plug with leaves and other debris and the ease of

removing material from plugged regulators.
Figure 3-33. Streets were intentionally flooded to test the performance of flow

regulators.

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3-75

• Hydro-Brake: $300 - $800

• Scepter: $100 - $130

• Solid cover with orifice: $10 - $50

• Horizontal orifice plate beneath inlet grate: $50 - $150

• Hanging trap: $25 - $50

Given the good and similar operating characteristics of Hydro-Brakes, Scepter units,

and hanging traps, the hanging traps were clearly preferable because of their very low

costs.

Maintenance

The ease with which debris can be removed from plugged flow regulators was difficult

to quantify. The debris removal effort, listed in order of increasing difficulty, is

approximately as follows: modified grate flow regulators; horizontal orifice plate

positioned beneath the inlet grates; Hydro-Brake and Scepter flow regulators installed

in inlets; and Hydro-Brakes, Scepter units, and hanging traps installed in catch basins.

Conclusions for Skokie

1. Flow regulators should be installed in catch basins, rather than inlets.

2. Hanging trap flow regulators should be used throughout the HSSD, except

where the desired reduction and resulting orifice size is beyond the

effective lower range of the hanging trap regulator, in which case

Hydro-Brake flow regulators should be used.

3. A field-oriented flow regulator design process should be used to minimize

costs.

4. The design and installation of flow regulators should be done in

conjunction with other components of recommended street storage

system including roadway berms, subsurface storage tanks, and relief

sewers.

Complete Design of the Street Storage System

The goal of final design is to produce a set of plans and specifications to be used by

contractors for bidding and by the selected contractors for construction. Additional

hydrologic-hydraulic modeling is needed for tasks such as final sizing of flow regulators

and refinement of berm locations and heights. However, the final design process is

typical of that which might be done for an urban street. An example of the kind of detail

that results is shown in Figure 3-34.
Figure 3-34. Typical street berm design in Skokie, IL (Source: Walesh, 1989, p. 401)

3-76
factors, refer to the earlier section of the chapter titled “Select an Initial Implementation

Area Within the Combined Sewer System.”) Each community’s overall implementation

schedule, with emphasis on construction, is summarized here.

Skokie Construction

Skokie implemented the physical aspects of its street storage system according to the

following schedule:

• 1981: Initiate downspout disconnection

• 1983: Begin stakeholder involvement

• 1983: Test flow regulators in pilot areas

• 1983: Initiate base line monitoring

• 1983-1986: Construct HSSD

• 1988-1997: Construct MSSD

• 1989-1999: Construct ELSSD

Table 3-3 summarizes the components of the Skokie street storage system. Note the

heavy reliance on berm-flow regulator installations, which suggest, in turn, widespread

use of temporary, controlled street ponding.

The relative importance of street storage versus other storage is shown in Figure 3-35. 

Overall, street storage accounts for half of the total stormwater storage capacity in

Skokie, the other half being subsurface storage and off-street surface storage. 

Incidentally, in Wilmette essentially all of the storage is street storage because there

are no subsurface or off-street storage facilities.

The preceding observations about the dominance of street storage in Skokie and

Wilmette reinforce the discussion near the beginning of this chapter about the

significant storage and conveyance capacity of street, especially in a CSS. With

carefully engineered retrofitting, that storage and conveyance can be the basis for

cost-effective solutions to flooding and perhaps other wet weather problems in CSSs.

Construction

Both Skokie and Wilmette are using a phased approach to construction. (For a

discussion of the advisability of phased implementation and suggested prioritization
3-78

Table 3-3. Components of the Skokie street storage system (Source: Carr, 1999).

Component Number Length

(Feet)

Flow Regulators 2,900 - - -

Berms 871 - - -

Off-Street

Surface Storage

10 - - -

Subsurface

Storage

83 - - -

Storm Sewer - - - 64,000

Combined Sewer - - - 29,000
Storage in Acre-Feet

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

Howard Main EmersonLakeAll 3

Districts

SupplementalOn-Street

Figure 3-35. Street storage accounts for half of the total stormwater storage

in Skokie (Source: Carr, 1999).

3-79
3-80

Wilmette Construction

A five-phased construction program is underway in Wilmette. Three phases are

completed and two are planned. Two major considerations determined the priorities. 

The first was functional dependence. For example, downstream relief sewers were

constructed before upstream relief sewers. The second of the two key prioritization

factors was cost effectiveness. That is, higher priority was given to areas with the most

severe problems. The five phases, with their actual construction costs (Phases 1, 2

and 3) and projected construction costs (Phases 4 and 5) are described below.

Phase 1: Greenleaf Avenue Relief Sewer

Included installation of approximately 6300 lineal feet of relief sewer (48" - 96") in

Greenleaf Avenue, connection to the deep tunnel, emergency overflow to the North

Shore Channel, and 165 berms and associated catch basins and flow regulators.

Cost: $10,358,000

Phase 2: Eastside Relief Sewer

Consisted of the continuation of relief sewers from Greenleaf Avenue, along 9th Street

and Forest Avenue to 15th Street. This tunneled sewer project consisted of

approximately 5600 lineal feet of 72", 54", and 48" diameter sewers. This phase also

included the construction of 50 berms and related catch basins and flow regulators.

Cost: $4,586,000

Cumulative Cost: $14,944,000

Phase 3: Eastside Relief Sewer

Included both construction of relief sewer to the south from Greenleaf Avenue and a

storm sewer system (including an outfall to the North Shore Channel) in the

Maple/Dupee portion of the Village. This Phase included the construction of 37 berms

and related catch basins and flow regulators.

Cost: $8,425,000

Cumulative Cost: $23,369,000

Phase 4: Eastside Lateral Relief Sewer

Will consist of the construction of relief sewers in 9th Street from Forest Avenue to

Chestnut; Ashland Avenue from 9th Street to 8th Street; 8th Street from Ashland
3-81

Avenue to Chestnut Avenue; 12th Street from Forest Avenue to Ashland Avenue with

one block stubs on Elmwood, Greenwood, and Ashland; 17th Street from Lake Avenue

to Forest; and 17th Street from Forest Avenue to Elmwood Avenue. These sewers will

range in size from 18" to 36" in diameter.

Cost: $4,500,000

Cumulative Cost: $27,869,000

Phase 5: Eastside Lateral Relief Sewer

Will consist of relief sewers in 6th Street from Greenleaf Avenue to Elmwood Avenue;

Forest Avenue from 6th Street to Michigan Avenue; Elmwood Avenue from Sheridan

Road to Michigan Avenue; and Washington Avenue from Prairie to Green Bay Road. A

portion of the Phase 5 sewers will be constructed in Green Bay Road as part of the

Green Bay Road resurfacing project. This phase will also include storm sewers at

various locations across the Village. These sewers are proposed to pick up primarily

surface drainage from low lying areas.

Cost: $7,300,000

Cumulative Cost: $35,169,000

In summary, as of early 1999, the constructed three phases of the street storage

system in Wilmette’s two square mile CSS consist of:

• 252 berms - catch basins - regulator installations. Over 98% of the

intended 717,540 ft3

 (16.5 acre-feet) of street storage has already been

achieved.

• Over 11,900 lineal feet of tunneled or conventionally constructed relief

sewer.

• Incidental storm sewers.

The $23,369,000 total cost of the three completed phases consists of $18,946,000 or

81.1%, for relief sewers and $4,423,000 or 18.9%, for berms and associated catch

basins and flow regulators.

Because the CSS is essentially one system, all phases must be completed to achieve

the intended degree of flood control. The last two phases of the five phased program

are not yet constructed.

wp/epastch3
4-1

CHAPTER 4

OTHER EXAMPLES

OF

STREET STORAGE SYSTEMS

Purpose

Using the well established and on-going Skokie and Wilmette, IL project; the previous

chapter presents a proven and practical street storage system concept through

construction and operation and maintenance process. Provided in this chapter of the

manual, are synopses of other street storage studies, designs and implementation. 

The intent is to use other examples as supplemental, mini-case studies which provide

additional insight into street storage. Some of the additional examples were carried

through to implementation while other did not move or have not yet moved past the

feasibility stage. Nevertheless, each of the mini-case studies offers additional useful

ideas and information that may be useful to municipal officials.

In the early 1980's, near the beginning of the Skokie project, Donohue and Associates

personnel learned much about flow regulators from other communities. For example,

research revealed that vortex regulators had been installed in at least a dozen

Canadian and U.S. communities. Contacts were made with municipal personnel in six

communities that had vortex regulator experience. Donohue personnel also

communicated with Canadian and U.S. communities about their experience with other

types of flow regulators (Donohue, 1984a, pp. 3-3 to 3-13).

Missing, at that time, were completed, or largely completed, street storage systems that

included flow regulators, berms, surface and subsurface storage. The Skokie and

Wilmette case studies in the previous chapter provide examples of largely completed

street storage systems. This chapter’s synopses of other projects which are, in effect,

street storage systems, provide additional examples.
4-2

Cleveland, OH: Puritas Avenue - Rock River Drive Area

Background

This mid 1980's investigation was undertaken primarily to “...evaluate the ability of the

Hydro-Brake to effectively regulate specific design flows from stormwater storage

structures to such an extent that receiving sewers could be protected from surcharging

and creating CSO conditions” (Mathews et al., 1983, p. 2, see also Mathews et. al.,

1984). Although the study focused on the Hydro-Brake, one of the commercially

available flow regulators discussed earlier in Chapter 3, the study does provide insight

into the street storage system.

The overall combined sewer study area covered 115 acres of medium density

residential originally developed in the 1920's. Basement flooding caused by

surcharging of combined sewers was a problem. Within this area, three subsurface

tanks were constructed serving separate subareas having a total area of 9.0 acres

(Mathews et al., 1983, p. 2). The three tanks were located within the street curb lines

and above the combined sewers, that is, they were intended to be gravity devices and

to temporarily store stormwater runoff. The three tanks were constructed of corrugated

metal pipe (CMP). The first tank used 163 feet of 48 inch diameter CMP and provided

2000 cubic feet of storage. The second tank was formed from two parallel 87 by 63

inch corrugated metal arch pipes each 156 feet long for a total storage volume of

10,000 cubic feet. The third tank consisted of 170 feet of 95 by 67 inch corrugated

metal arch pipe and contained 5,800 cubic feet of storage. Inlets conveyed stormwater

to the subsurface tanks and flow regulators controlled flow out of the tanks (Mathews et

al., 1983, pp. 12-15). 

The study included:

• Filling and draining each tank to determine Hydro-Brake stage-discharge

relationships.

• Monitoring of precipitation, water levels in tanks, and stormwater quality.

• Simulation of tank inflow and outflow hydrographs for design storms of

prescribed recurrence intervals.

• Pre and post-construction surveys of area residents with emphasis on

basement flooding.

Results

Numerous findings were reported. Some of the more significant observations relative to

this manual are (Mathews et. al., 1984):
4-3

Hydro-Brake regulated storage tanks are

effective in alleviating sewer surcharge and

basement flooding problems.

By reducing the peak flow in the sewer system,

combined overflow pollutant loadings are

reduced because the first flush effect is

dampened.

For effective application of the Hydro-Brake

regulated technology, the design approach

must include accurate characterization of

drainage areas and sewer hydraulics to

properly identify site-specific release rate

requirements. The level of control desired

determines the required storage volume, and

the characteristics of the site determine

whether to employ above-grade or belowgrade storage, or a combination thereof.

Where surface ponding is an acceptable form

of stormwater storage, the application of

Hydro-Brakes alone is more cost-effective than

Hydro-Brakes used in conjunction with off-line,

below-grade storage structures. Both

applications, however, appear to be more costeffective than the other evaluated alternatives

where both surcharging and overflows are the

prevailing problems.

During the first 18 months of operation, the

Hydro-Brake control/detention structures

exhibited minimal maintenance requirements. 

Solids deposition in the storage tanks was

negligible and did not increase significantly

with time.

Potentially useful ideas and information drawn from this Cleveland, OH project include:

• Use of CMP for subsurface tanks.

• Reduction of the first flush effect.
4-4

• Desirability, from a cost perspective, of using on-street storage rather than

below-street storage.

• The likely cost-effectiveness and multiple purpose benefits (reducing

basement flooding and CSO’s) of a street storage system.

Parma, OH: Ridge Road Area

Background

Ridge Road area “...is a topographic “dished” shaped area (30 acres) situated within the

lower portion of a 290 acre drainage system. The terrain in the watershed is hilly with

deep valleys...” (Pisano, 1989). The 290 acre area is highly developed in that it

contains 1200 homes and many commercial buildings. An over/under sewer system

serves the area. This is a special form of a combined sewer system common

throughout the Cleveland metropolitan area. The storm sewer is laid immediately

above the typically smaller diameter sanitary sewer. The two sewers share the same

trench and manholes and, therefore, there is a high likelihood of flow between the two

conduits..

As explained by Pisano (1989), the 30 acre area, known as the Triangle:

...endured severe basement flooding resulting

from the surcharging sanitary sewers during

heavy rainstorms (at least three to four

episodes per year). The cause of surcharge

stems from the undersized storm systems

which cannot handle storm flows, [they]

pressurize, surcharge and leak significant

amounts of clear water into the rock filled

“french drains” trench section. Since the sewer

joints in the sanitary sewer are invariably

cracked or broken, the surcharge condition

within the rock filled trench adversely affects

the sanitary sewer piping, ultimately resulting

in basement flooding. Basement flooding in

the Triangle is further exacerbated by the poor

hydraulic outlet conditions of the local sanitary

systems...

Due to the rolling terrain, there are numerous

“low valley pockets” throughout the entire 290

acre area. The storm drains are generally

inadequate. Surface water which cannot
4-5

escape via major overload routes... 

accumulates and severe street flooding results.

Therefore, the 290 acre drainage basin, and especially the Triangle, experienced

frequent and simultaneous basement and street flooding. The problems needed to be

solved.

Results

One partial solution was “...to construct a large underground off-line detention basin for

relieving the sanitary trunk sewer coming into the study area and to construct sanitary

relief sewers throughout the Triangle.” This $2,200,000 project (mid 1980's costs)

would solve only the basement flooding problem. The surface flooding problem would

remain.

The alternative, which was implemented, is what is referred to in this manual as a street

storage system. The system includes downspout disconnection, berms, reconstructed

curbs, flow regulators, new catch basins, subsurface storage tanks, manhole

rehabilitation, and relief sewers. Construction costs in 1984 totaled $875,000 (or about

$3000 per acre in 1984 dollars) which is 40% of the cost of the partial solution.

According to Pisano (1989), “The project has mitigated surface water ponding and has

provided basement flooding protection throughout the entire 290 acre area... Although

not intended, spring sanitary sewer infiltration has been significantly reduced.”

Possible valuable ideas and information based on the Parma, OH project are:

• Potential applicability of the street storage system to hilly terrain.

• Use of the street storage system to simultaneously mitigate basement and

surface flooding.

• Cost effectiveness of the street storage system approach.

Chicago, IL: Jeffery Manor Neighborhood

Background

Jeffery Manor is a 470 acre CSS area on the southeast part of the City of Chicago. 

Residential land use dominates with commercial, industrial and undeveloped land on

the perimeter. Streets have curb and gutter, are paved and most have sidewalks and

tree lined parkways. Local combined sewers, owned by the City of Chicago, range from

10 to 42 inches in diameter, and discharge to MWRDGC interceptor sewers. The entire

area is very flat (SEC Donohue, 1993).
4-6

Jeffery Manor has a serious basement flooding problem caused by surcharging of the

CSS. Local and interceptor sewers do not have the capacity needed to carry flows

received during rainfall events. An additional exacerbating factor is excessive dry

weather flow in interceptor sewers that originate outside of and flow through Jeffery

Manor. Sewer crowns are about eight feet below street level and most basement floors

are five to six feet below street level. Therefore, a few feet of surcharging above sewer

crowns forces combined sewage into basements.

Results

Results of the feasibility study, as quoted (parenthetic comments added) from SEC

Donohue (1993, pp. 1-1 to 1-2) are:

...a temporary street storage system would

alleviate sewer surcharging in the Jeffery

Manor area caused by overloading of the local

collection system. The system was developed

under the assumption of greatly reduced flows

in the MWRDGC interceptor sewer entering

the Jeffery Manor area. This reduction in flow

will occur when tunnels or other relief sewer

projects are constructed. However, if flows in

the MWRDGC interceptor continue at current

levels, the proposed street storage system will

provide some relief to the existing flooding

problem, but will not perform to its maximum

capability.

The analysis for the five-year storm event

showed that the storage required to eliminate

sewer surcharging is 455, 280 cubic feet (970

cubic feet per acre). The proposed temporary

street ponding system entails development of

ponding areas on 74 city blocks ...to provide

328,570 cubic feet of storage. The ponded

stormwater would be held in place by 120

berms to be constructed across the streets

(See Figure 4-1). Construction required for 
Figure 4-1. Street storage system proposed for the Jeffery Manor neighborhood in

Chicago, IL (Source: SEC Donohue, 1993, p. 5-3).

4-7
Although temporary ponding alone will greatly

improve the system capacity in Jeffery Manor,

additional facilities are required to provide a full

five-year level of protection. Approximately

60,000 cubic feet of additional storage is

needed in the southern part of the

neighborhood... This storage could possibly

be provided on the property of a closed

elementary school... Also a relief sewer is

needed... To provide a five-year level of

protection for the area after flows in the

MWRDGC interceptor are reduced by other

projects, street ponding, other storage and a

relief sewer are required at a probable

construction cost of $2,481,600 (or $5280 per

acre in 1993 dollars)... Street storage reduces

the required capacity of relief sewers, and can

result in millions of dollars in savings for

construction of sewers.

The recommended project has not been implemented. Possibly useful ideas and

information drawn from the Jeffery Manor feasibility study are:

• The need to address interceptor sewer capacity as affected by contributions

from outside of the CSS area.

• Cost effectiveness of the street storage system approach.

wp/epastch4 4-8

implementation consists of berm construction,

removal of existing stormwater inlets and

installation of new inlets with flow restrictors. 

The estimated construction cost for the street

storage components is $1,860,000 (or $3960

per acre in 1993 dollars).
5-1

CHAPTER 5

REGULATORY AND FINANCIAL FRAMEWORK:

COMPLYING WITH REGULATIONS AND

FUNDING CONSTRUCTION

Motivated by Need But Subject to Regulatory and Financial Constraints and

Opportunities

The principal reason to undertake the street storage projects in the communities of

Skokie and Wilmette, IL was to solve the serious problems of widespread flooding of

basements by combined sewage. Skokie and Wilmette had flooding problems that had

grown and festered long enough and the time for action had arrived, regardless of

regulatory requirements. 

This stands in stark contrast to the situation in many CSS communities where projects

are planned and implemented primarily to comply with regulations and court,

administrative or consent orders intended to prevent pollution of receiving waters. The

fundamental challenge in Skokie and Wilmette was to take basement flooding, a

serious, widely shared local concern, and come up with an affordable alternative to the

proposed unaffordable relief sewers.

The initial objective in Skokie and Wilmette was to create a project that solved several

problems and package the project in such a way that it:

• Eliminated basement flooding

• Was compatible with MWRDGC policy 

• Was affordable to the community

• Was supported by residents and users

• Was supported by state agencies which control NPDES compliance

• Might be eligible for outside capital agency funding.

With these objectives in mind, planning, design and construction could not proceed in a

vacuum. Many challenges had to be met, not the least of which were regulatory

requirements and related legal matters and the means by which construction would be

financed to make the improvements affordable. Some of the regulatory framework
5-2

proved to be advantageous in that it offered opportunities to pursue certain funding

options. 

Regulatory and financial issues are discussed together in this chapter because they are

highly interrelated. For example:

• Federal and state regulations sometimes define a community’s eligibility

for external funding in the form of loans and grants.

• Past state and federal funding programs required ties to NPDES

compliance and schedules of implementation for identified construction

projects. In the case of Skokie and Wilmette, both projects were originally

expected to construct large relief sewers to flow into TARP. TARP was

grant eligible and the large relief sewers were not.

• Working through the wastewater and stormwater permitting process

brings together local, regional, state and federal agency personnel. This

connection expands the local communities access to unique project

technical solutions as well as access to alternative funding sources.

• Home rule jurisdiction, as defined by Illinois law, meant that Skokie’s

elected and appointed officials did not have to get new voter approval on

some local borrowing. However, in the case of Skokie and Wilmette,

focusing on basement flooding elimination made proceeding with the

project easier at the local level.

• Should the agency permitting process result in the creation of an

unaffordable project solution, the agency permitting staff themselves

become advocates for special funding. That special funding can come

from a change in program eligibilities or direct legislative appropriations.

Other crucial issues, such as analysis and design procedures, public involvement, and

inspection and maintenance are discussed in, respectively, Chapters 3, 6, and 7.

The next three major sections of this chapter focus primarily on complying with federal

and state regulations and obtaining funding through federal and state programs. 

Sources for these sections are Roecker (1993, 1997, 1998a, and 1998b) plus additional

sources cited within these sections.
5-3

Federal and State Regulatory and Funding Framework Within Which Skokie and

Wilmette Functioned

During the late 1970's, the Skokie and Wilmette combined sewer systems were

expected to be reconstructed and connected to the future Chicago TARP project. A

CWA Section 201 Facility Plan was prepared for both Skokie and Wilmette which

showed the cost of combined sewer correction program, consisting of large relief

sewers, to be very expensive. In the case of Skokie, the estimate was $100,000,000

based on 1980 dollars. Because of TARP’s need for construction capital and the

MWRDGC’s ability to win USEPA Construction Grant eligibility for the TARP project,

Skokie, Wilmette and all other MWRDGC contract communities combined sewer

separation projects were classified as ineligible for grant monies.

This ineligibility determination and the continued basement flooding stalled remedial

action in Skokie and Wilmette until affordable alternatives could be developed. In the

early 1980's, Skokie began looking for alternatives to the construction of relief sewers. 

Working with their engineering firm, they began looking at their challenge in terms of a 

stormwater management problem, rather than a relief sewer problem. This process

resulted in the creation of the Skokie street storage system approach.

Meetings were held at the state to review the concept and determine how Skokie and

the state could create a partnership. The partnership was necessary to change the

regulatory requirements associated with the existing CWA Section 201 Facility Plan and

to try to find a way to change or eliminate current funding ineligibility determinations. 

Initial meetings with the state focused on the following;

• Change the regulatory requirements associated with the previously

approved CWA Section 201 Facility Plan to eliminate NPDES compliance

issues associated with eliminating the relief sewers.

• Look for local, state or federal funding sources which could assist in

demonstrating the new technologies or lower local cost impacts.

• Look for state level project support which would later help bring in other

state and federal agency funding.

Today, the path cut by Skokie and followed by Wilmette, is different. The differences

can be characterized as follows and can be used by others to assess the regulatory and

financial process;

• The initial regulatory challenge facing Skokie and Wilmette related to

TARP using all available USEPA Construction Grant dollars for their

project and leaving the two communities with an NPDES requirement to

build expensive relief sewers with no access to grant or low interest loan

money. Today, large percentage grants are not available to projects like

TARP and, therefore, communities are forced to focus on alternative,

lower cost and smarter projects at their initial stages of project planning.

• The USEPA Construction Grants program has been replaced with the
5-4

USEPA State Revolving Fund (SRF) program. In general, this program

provides low interest loans which must be paid back by the communities. 

A new sense of fiscal responsibility has entered projects which has

resulted in longer term phased projects that become more affordable to

the users.

• Demonstration projects, like Skokie and Wilmette, have become

showcases of what stormwater management can accomplish in CSS and

how it can save costs. More alternative technologies are becoming

available to those who seek them.

• At the national level, the U.S. Congress has begun providing direct grant

assistance to those projects which can demonstrate unique qualities or

have unique characteristics. Most recently, successful projects tend to

deal with the large issue of “watersheds” as opposed to single issue

wastewater or stormwater challenges. The Skokie and Wilmette projects

provide good examples of a multi purpose, watershed-based approach. 

Today’s Regulatory and Funding Framework: Review of Outside Capital Funding

Programs, Techniques and Strategies 

Overview 

Since the 1950's, the U.S. Congress has provided capital funding for municipal water

related infrastructure. The capital funding assistance has ranged from full project

grants to subsidized long term loans. In the recent past, communities and authorities

have found that their water related projects have become more expensive and

government funding has diminished. 

Based on recent Congressional actions, the future of state and federal sponsored water

related funding programs and initiatives are becoming known. That future includes

continued capital water related project funding opportunities for those communities and

projects that meet the criteria of a changing funding landscape.

Ideas, suggestions and insights contained in this chapter provide the tools needed by

communities to win needed capital water related funding. Addressed here is the

movement of available local, state and federal funds through existing and proposed

water related funding programs. Presented is information on the location of both

traditional and nontraditional funding opportunities. Communities are encouraged to

expand their water related project objectives to match the funding program objectives. 

Both state and federal funding program objectives are highlighted in this chapter to give

community leaders important strategic information that can save time in review of

possible funding avenues.

Outside Capital Funding from Users
5-5

The creative use of "special assessments" and "developer funds" offer unique capital

funding opportunities. Use of both "special assessments" and "developer funds" can

accomplish the following:

• The ability to assess acreage that is receiving a benefit from an area-wide

project. In the case of an urban stormwater project, area-wide benefit can

easily be defined and assessed on a more uniform basis than the

traditional per-foot basis.

• The ability to assess the capacity of a storage or treatment facility to all

users of the facilities on a uniform basis. 

• Since "special assessments" are property liens, federal agencies are

available to pay the assessments for the poor and elderly. Programs

continue to provide monies for these special user groups to make the

improvements affordable. 

• Including the needs of developers as a project planning objective can

enhance the project’s usefulness, and bring a secondary benefit of

outside funding from the developer. Long term phased projects tend to

have the time available to search out these developers and negotiate 

reasonable financial contributions which benefit the developer and the

community.

In the past several years, there is increased concern with making sure that all project

“stakeholders” are paying their fair share. In developing an outside capital funding

strategy, community leaders should make sure that all those benefitting or those who

will benefit are accounted for.

Outside Capital Funding from State and Federal Agencies

In order to understand what agency funds are available, a community must learn why a 

agency provides funding. The following five points were developed from experience

and provide some insights: 

• Funding agencies fund their program objectives, not a community’s

project

• A community should develop its project's uniqueness during planning

• Keep working with the agency until someone says "maybe"

• Once funding is obtained, other agencies will follow

• Spend some time getting to know representatives of agencies

To reiterate, of all the issues that are important to winning outside capital funding, the

single most important issue is understanding the funding program objective. As

community leaders start thinking about outside agency funding, they should define how
5-6

their project will help the agency further its objectives.

The following list of funding programs contain current (1999) information regarding their

objective, funding, administration, and current program status. These programs provide

more than 90% of water related infrastructure funding throughout the country.

# U.S. Department of Agriculture (USDA), Rural Utilities Service (RUS) & Rural

Housing Service (RHS). 

Objective: To provide safe and sanitary housing, including water related facilities

to small, rural municipalities ( less than 10,000 pop.) serving lower income

persons.

Funding: FY 1999 funding levels were $763,977,000 in low interest loans and

$500,000,000 in direct grants for project costs and $25,000,000 in direct loans

and $25,000,000 in direct grants to low income elderly rural home owners for

special assessments. 

Administration: Through a federal agency state headquarters office and several

district offices. The district offices review, screen and recommend individual

projects to the state office. If the state allocation is committed, a state can

submit a project to a national office for special funding consideration.

Status: These programs continue to receive increased funding. The district staff

engineers provide a very detailed review of proposed infrastructure and work to

lower capital costs and limit eligibilities on each project. 

# U.S. Department of Housing & Urban Development Block Grant Program (HUD). 

Objective: To provide viable urban communities with decent housing, a suitable

living environment and expanding economic opportunities for low to moderate

income residents.

Funding: FY 1999 set funding levels of $3,103,100,000 for their large

community entitlement program and $62,222,000 for their small community block

grant program.

Administration: Through a state agency normally located in the state capital.

Status: Past historic influence by Congress is said to have ended. Entitlement

recipients tend to receive small allotments that are spread over numerous 

competing infrastructure needs with little money available for new water related

infrastructure, while the state-wide small community competition tends to provide

a more meaningful opportunity for water related funding.

# U.S. Department of Commerce Economic Development Administration (EDA). 

Objective: To promote long-term economic development and assist in the

construction of infrastructure, including water related facilities, needed to initiate

and encourage the creation or retention of permanent jobs
5-7

Funding: FY 1999 saw program funding of $160,000,000 for this program.

Administration: Through a federal agency headquartered in the federal regional

city with a very small state or multi state office. In addition, individual states also

have their own version of this job creation program that can provide direct state

assistance to worthy projects.

Status: While EDA was slated for termination by the 104th Congress, it remains

intact. Before funding water related infrastructure, EDA will want very detailed

information from the job creator and limits funding to projects that generally cost

less than $10,000 per permanent job created. 

# U.S. Environmental Protection Agency (USEPA). 

Objective: To provide financial incentives to communities to obtain and maintain

NPDES compliance and provide a long term source of financing for water related

infrastructure. 

Funding: FY 1999 saw program funding of $2,125,000,000 for their water

related State Revolving Loan programs with additional grant monies available

from the USEPA Budget itself. 

Administration: Through a federal agency headquartered in the federal regional

city with direct allocation of loan and grant monies to individual state pollution

control agencies.

Status: The State Revolving Fund programs are viable funding programs and

are beginning to expand eligibilities for watershed projects. Reauthorization of

the Clean Water Act was pending as of early 1999. However, the reauthorization

is expected to further expansion of the eligibilities to innovative watershed

programs that meet the objectives of pollution reduction together with flood

protection.

In addition to the USEPA’s State Revolving Fund program several areas of the U.S.

Budget contain demonstration and implementation funding programs that can provide

grant assistance to projects that meet the specific funding objective contained in that

particular section. The USEPA (1993, EPA-814) provides the list of funding sources

which follows. Note: Section numbers refer to the Section of the existing Clean Water

Act and the numbers in parentheses refers to the funding program as described by the

Executive Office of the President and U.S. General Services Administration (U. S. GSA,

1998).

• Section 106 (66.419): This program provided state and interstate agencies

and Indian tribes with more than $115,000,000 in 1999 for prevention and

abatement of surface and groundwater pollution.

• Section 604(b) (66.454): This program provided States with $12,000,000 in

1999 to carry out water quality management planning.
5-8

• Section 603(d) (66.458): This program provides States with up to 4% of their

State Revolving Fund (SRF) allocation to manage their programs. Nationally

this amounts to more than $80 million annually, and if the State's SRF

program involves water resource projects, the administration of these water

resource projects can come from this fund.

• Section 319(h) (66.460): This program provided $200,000,000 in 1999 to

State-designated lead non-point source (NPS) agencies to fund

implementation or construction of water resource related practices or

infrastructure. The 1999 federal allocation represents a 100% increase over

1998.

• Section 320(g) (66.456): This program provided $12,300,000 in 1999 to any

agency or individual for planning activities in designated estuaries.

• Section 104(b)(3) (66.463): This program provided $19,000,000 in 1999 to

any agency or individual for one to two year demonstration type projects,

including combined sewer overflow and stormwater discharge control

programs.

• Regional Initiatives: The USEPA regions spend in the area of $2 to $4 million

annually on projects that address watershed protection. Communities can

obtain a listing of current objectives from their regional USEPA office.

Working through these federal agencies and their state counterparts will provide

community leaders with an understanding of the administrative funding possibilities for

both current and future water related projects. In addition, the effort will produce the

background information needed by a community to consider taking their project to the

next step in the funding road. That step is the U.S. Congress.

Outside Capital Funding from the U.S. Congress: Direct Legislation

Over the past several years, a growing number of communities have sought direct

funding of their projects from Congress through the U.S. Congress’ appropriations

process. In addition, various State Legislatures have begun providing direct funding of

special and unique projects.
5-9

Since 1992, the U.S. Congress has provided $3,579,425,000 in direct grants for water,

watershed, groundwater and wastewater projects across the nation. If a community

works through the existing local, state and federal agency funding programs and the

project is still truly unaffordable or if it has some unique feature that distinguishes it from

other projects attempting to accomplish the same objectives, elected officials can help. 

Certain projects may fall through the cracks either by poor management or

circumstances beyond their control. The U. S. democratic process has a strong sense

of fairness and when a case can be made demonstrating that the project has not had a

fair shake for available public funds, both the state and federal legislatures can help. 

Special attention to the issues of the day and the concept of "fairness" leads to success

in the legislative arena. When dealing with its legislature, community leaders should

keep the following objectives in mind:

• Legislatures provide direct funding to win favor with large population areas for

future political purposes by correcting an actual or perceived public policy

injustice and removing unreasonable regulatory barriers which preclude

sound projects from proceeding. 

• Legislatures provide direct funding to correct actual or perceived public policy

injustices for a project which would have been eligible for significant grant

funds in the past and was delayed beyond the control of the community. 

As can be seen from a review of these two concepts, the key is to have spent the time

to review all funding options and have a project packaged to the point that

congressional funding is the last, but potentially promising resort. Using the information

provided in this chapter as an overall checklist for local, state, and federal agency

funding opportunities will serve communities well in covering the “other funding” bases. 

Spending appropriate time to prepare a well written, concise project history, scope and

objectives document will serve to focus a community’s project objective. The 

community, its engineer, and state and congressional representatives should be

involved in the packaging process.

Below is a checklist of items to review before a community goes to the U.S. Congress

with its project. Community leaders should remember that they are looking to get their 

representative's attention and have their project meet the objectives of the current line

item funding written and unwritten criteria. 

I. Project factors to be completed before taking a project to U.S. Congress

A. Past site, environmental, and water quality issues addressed

1. The project is planned and on its way to being designed.

2. The community has reviewed other funding and understands why it is not

available.
5-10

3. The state has supported the project in writing and has given it high priority.

B. Past agency issues have been addressed

1. The community addressed state concerns raised during the planning

process.

2. The community has or is continuing to work to secure all project permits.

C. The project is packaged

1. Unique project qualities have been determined.

2. The community knows all its lost opportunities for funding and the reasons.

3. The community has a well written one to two page summary describing the

project and needs.

4. Parallels to past congressionally funded projects have been developed by the

community.

5. The project’s objectives have been packaged in a user-friendly format.

 II. Recommended Washington-based activities

A. Develop the right team to present and monitor congressional actions

1. Set up a team representing the community that includes:

State congressional delegation representative

Local elected representative

Governor's office

Project owner’s staff

Consulting engineer

Governmental affairs manager or consultant.

2. Make specific assignments to team members.

B. Make sure that the team understands the project and its objectives.

C. Meet with and/or communicate frequently with the community’s congressional

delegation

D. Use the team's past experience to create new relationships with influential

congressional leaders, appropriate committee members and staff

E. Monitor the schedule of both the authorizing and appropriations committees

F. Develop, manage, and communicate with project team members frequently

G. Make responding to questions, inquiries, or requests a high priority

III. When a community “wins” funding
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A. Make sure that the entire congressional delegation gets credit

B. Work with the appropriate funding agency in the grant release process

1. That agency has control over grant percentages, the application or nonapplication of rules, regulations, and program guidance.

2. Most funding agencies burdened with the grant release process are

understaffed and need community technical assistance to move quickly.

3. Be willing to share a small portion of the grant to cover necessary funding of

agency administrative costs of grant administration.

4. Keep very accurate records during the project because federal audits are

likely years after the project is complete.

Initial Capital Funding for the Skokie Street Storage System

As discussed earlier in this chapter, Skokie’s initial capital funding plan had the

following two objectives:

• Lessen the cost or eliminate the need to construct the $100,000,000 relief

sewer system that was recommenced by its existing CWA Section 201

Facility Plan.

• Develop an innovative technical alternative to the relief sewers, work with

State and Federal agencies to win approval and secure some outside

funding to make the alternative affordable. 

Skokie began work with the regional consulting engineering firm Donohue and

Associates, Inc., of Milwaukee, WI (now Earth Tech, with corporate offices in Long

Beach, CA), who developed the innovative street storage system. Once this system

was documented in a feasibility study and the estimated capital cost was shown to be

only a quarter to a third of the cost of the relief sewers, Skokie called a meeting with the

State of Illinois. 

The state was impressed with the technical approach and quickly realized that this

innovative technical alternative could be applied to other communities in the area and

result in a significant lowering of capital infrastructure cost. With this being the case,

the state became a partner in the project and began working with Skokie to find ways to

assist with making the project a reality.

While the USEPA’s Construction Grants Program specifically made the relief sewer

alternative an ineligible project, the state had begun work on the new USEPA State

Revolving Loan Program which allowed the State more flexibility in making eligibility

decisions. After reviewing the water quality impacts and evaluating the technical merits

of the project, the state made the project and technology eligible for its low interest loan

program. Low interest loans were important catalysts in both the Skokie and Wilmette
5-12

street storage projects.

The new funding program was entitled the “State of Illinois Water Pollution Control

Revolving Fund” (WPCRF). At its inception, it offered communities 20 year loan rates

equal to one-half the interest rate for which the State of Illinois could borrow monies. 

Once Skokie began the project, it recognized that expanding the project objectives and

building a partnership with the state helped bring in outside capital to lower the cost of

the project and create a new project partner. This process was continued with the State

of Illinois Department of Transportation (IDOT). Skokie had a need to build street

storage infrastructure in and near to IDOT facilities. Working with IDOT and

demonstrating the positive impact of the street storage project on their facilities resulted

in the Village’s receipt of additional direct grant dollars from the IDOT’s own funding

programs. Another phase of Skokie’s partnership with the state is grants received

under the Build Illinois program.

In the fourteen years Skokie has continued with the project, they have used a

combination of SRF loan monies, direct grant monies from the State of Illinois

Department Transportation, Build Illinois grants, and General Obligation local bond

monies to bring the project to where it is today. A general breakdown of these four

funding sources, is as follows:

• Water Pollution Control Revolving Fund = $18,700,000

• IDOT grants = 1,100,000

• Build Illinois grant = 500,000

• General Obligation bonding = 56,000,000

• Total $76,300,000

On-Going Local Capital Funding of the Skokie Street Storage System Through the

Bond Market

Fishman (1998) reviewed the history of the Skokie street storage project with emphasis

on how it was financed on the local, non-agency front. As the project neared

completion in 1998, Fishman’s paper provides a contemporary, insightful, outsider’s

view of the systematic, prudent and persistent process followed by community leaders

to use the municipal bond market to finance project costs outside of agency funding

sources. The paper reviews the advantages of the phased implementation of the

system over an approximately 14 year period and provides insights into the

marketability and the investors desire to purchase municipal bonds for projects such as

this.

Even though the cumulative capital cost of the innovative street storage system was to
5-13

be only about one-third the cost of more traditional sewer separation approaches, this 

was the most expensive project ever undertaken by the community. Skokie faced a

great financial challenge.

From the outset, according to Fishman (1998, p. 181), Skokie enjoyed at least two

project financing advantages. First, the community had a high credit rating so that bond

issues typically drew multiple bidders. This yielded favorable interest rates. Second, as

an Illinois home-rule community, the community leaders did not have to get voter

approval for general obligation bonding.

As part of the street storage financing process, the community retained an individual

financial advisor. According to Fishman (1998, p. 182), the financial advisor’s

responsibility was:

...to structure bond offerings on behalf of

issues so that they are legal and fair, as well

as attractive to both investors and dealers. 

Then, at a pre-set time and under terms put

forth in his offering documents, he invites

would-be dealers to bid on the issue.

Moody’s Investors Service was retained by Skokie to determine the community’s

financial health. This is where the new and innovative nature of the street storage

system could have affected the capital financing process. Fishman (1998, p. 182)

explains that the soundness of any particular project in a community usually doesn’t

affect the financial health assessment conducted by Moody’s and other rating agencies:

...but in Skokie’s case, the review would have

to account for the largely experimental and

expensive technology involved in the project.

...Moody’s even made a few house calls to get

a feel for the intangibles that might not be

captured by the town’s financials.

Apparently the “experimental” technology passed muster. Skokie funded the capital

cost of the project largely with a series of eight general-obligation bonds, the first of

which was issued in 1985. A total of $56 million was borrowed at interest rates ranging

from 4.5 to 7.2 percent. In 1998, Skokie:

...completed the last round of borrowing. 

Seven bidders sought to issue bonds, and

Skokie got the lowest interest rates since the

project began over a decade ago (Fishman,

1998, p. 185).

Skokie Downspout Disconnection Ordinance and Program
5-14

As suggested in the preceding sections of this chapter, federal and state regulations

often require that a community undertake costly projects. On the positive side, these

regulations also provide the creative, proactive community with opportunities for outside

funding.

While a community has little if any control over state and federal regulations, it does

have overall control over the creation and enforcement of local regulations. Skokie

created and enforced a special local regulation to successfully implement downspout

disconnection, the first concrete step in its program to mitigate basement flooding

caused by surcharging of combined sewers. Described here is the community’s

systematic program, which started with information gathering and education, ended with

strict enforcements, and resulted in the disconnection of essentially all downspouts. 

Portions of Skokie’s approach may be useful to other communities.

The Downspout Problem

As shown in Figure 5-1, when downspouts are connected to the house sewer, they

permit roof water to directly and immediately enter the CSS. This aggravates combined

sewer surcharging and basement flooding problems.

The Downspout Solution

The adverse effects of directly connected downspouts can be partly mitigated by

disconnection the downspouts at ground level and directing their outlets toward

landscaped areas. A photograph of a disconnected downspout is provided as Figure 5-

2.

Paintal (1981), in his study of Skokie’s ESSD, concluded that “for short duration storms

the disconnection of downspouts from the sewer system reduces the flow in the sewer

significantly if the flow from the downspouts is directed to lawns and other porous

areas.” Skokie’s 1974 study of a pilot area concluded that downspout disconnection

would substantially reduce the hydraulic load on the combined sewer system.
*

*

SUBSURFACE TANK OPTION

Used Where Street Ponding

Capacity is Inadequate Combined

Sewer

House

Sewer

Disconnected

Downspout

Downspout 

Connected

to Sewer

Catch

Basin

Inlet

Flow

Regulator

EXISTING CONDITIONS STREET STORAGE SYSTEM

Figure 5-1. Downspouts connected to the house sewer, as shown on the left side,

permit roof water to directly and immediately enter the combined sewer system and

increase surcharging.

5-15
Figure 5-2. A disconnected downspout.

5-16
5-17

Educational Value

Even if downspout disconnection does not achieve a major reduction in the load on a

combined sewer system, it can have a positive community-wide educational effect. 

Success of a downspout disconnection program requires participation, that is, specific

action, by essentially all property owners. Accordingly, they are likely to gain additional

understanding of the cause and effect relationship between stormwater runoff and

surcharging of the CSS. Armed with this knowledge, citizens are more likely to

understand the need for and give support to other much more costly components of a

street storage system. Examples of those other components are berms, flow

regulators, and underground tanks.

Downspout Disconnection Process Used in Skokie

This description is based on a paper by Walesh and Schoeffman (1984) which was

presented near the end of the disconnection program. The Skokie program began in a

regulatory manner with the September 1981 passage by the Board of Trustees of an

ordinance requiring the disconnection of all downspouts on one and two family

residences.

However, the initial strategy was to gather information and encourage volunteer action,

rather than emphasize enforcement. Questionnaires were sent to every involved

residence. This questionnaire set the groundwork for the subsequent two year

implementation effort. Residents were asked if their downspouts were already

disconnected, whether they needed assistance or advice, and whether they felt that

special circumstances made them eligible for an exception from the ordinance.

Based on the response from this survey, Skokie personnel began a comprehensive

program of assistance and inspection to determine where exceptions could be granted

and to find where compliance had been achieved. The initial inspection effort found

that volunteer action in response to previous recommendations to disconnect

downspouts had resulted in almost 50% compliance with the ordinance before its

passage.

In order to make the program manageable, residential areas of the community were

broken down into 21 housing districts, each containing approximately 700 residences

and covering an area of approximately one-half square mile. Each housing district was

dealt with separately and given a specific compliance date. Owners or occupants of

residences determined through inspection to be violating the ordinance were notified by

letter of the compliance date for their district. After expiration of the compliance date,

another inspection was made and a “warning citation” left at the residence by the

inspector. Two weeks after this warning, a final letter was sent to all non-complying

residents and citations requiring court appearances were issued.
5-18

For a two year period, except during winter months, this process continued. At the

conclusion of the program, 99.9% compliance was achieved in that all but 18

residences out of the total of almost 14,000 satisfied the requirements. A total of 169

citations were issued requiring court action and 19 judgments of up to $500 were

entered by the court.

A review of the small number of exceptions granted under the ordinance indicates that

more than 90% of the roof water from one and two family homes in Skokie were

disconnected from the sewer systems. One reason for this small number of exceptions

is the specific criteria used to evaluate the need for an exception. Exceptions were

granted only if the downspout water could not be directed to a location where it would

drain away from all building structures with the use of an extension up to ten feet long

or where a necessary downspout extension would block a sidewalk or driveway.

Skokie Stormwater Control Ordinance

As explained by Donohue (1987a, p. 3-2):

Skokie adopted a stormwater control ordinance

in August 1977. This ordinance requires that

all new development limit the peak runoff rate

from the site to that of an undeveloped 2-year

frequency storm (C = 0.15). Excess

stormwater runoff, as determined by the

difference between the stormwater runoff from

the undeveloped area with a 2-year storm and

from the developed area with a 100-year

storm, shall be stored onsite in a stormwater

retention or detention facility.

All development that existed prior to the

effective date of the ordinance was exempt

from the stormwater control requirement

except certain off-street parking facilities and

developments that are destroyed or improved

by greater than 50 percent of the original value

of the structure before such damages were

incurred or improvements were made. The

ordinance also outlines minimum design and

construction criteria for onsite stormwater

retention/detention facilities and discusses

maintenance, administration, and enforcement.

This ordinance focuses primarily on new development but also applied to

redevelopment. Given that Skokie is essentially fully developed, as are many CSS

areas or communities, stormwater ordinances intended to prevent increased runoff

rates from new development will not typically have remedial effects. They can,

however, prevent aggravation of existing surcharging and related problems.

Skokie’s stormwater ordinance provided a “safety factor” for the street storage system. 
5-19

In designing the street storage system to prevent combined sewer surcharging, the

ordinance allowed the assumption that any redevelopment in the community would be

restricted by the two year criterion.

Regulations of the Metropolitan Water Reclammation District of Greater Chicago

The “Manual of Procedures for Administration of the Sewer Permit Ordinance” was

adopted by the MWRDGC in 1970. Included are guidelines and criteria for the design

of sewerage within the agency’s jurisdictional area. An MWRDGC permit is required for

a sewer system to discharge to the agency’s system. The following provisions (quoted

from Donohue, 1982a, pp. 28-29) related to CSS:

1. Complete separation of sewers shall be provided within the property lines.

2. Detention shall be provided and/or permanent constrictions shall be built on

the stormwater sewer system to control flow into the existing combined

system in accordance with the requirements of the local government.

3. All downspouts or roof drains shall be discharged onto the ground or be

connected to storm or combined sewer.

4. Footing drains shall be connected to sump pumps and discharge shall be

made into storm sewers, combined sewers, or drainage ditches.

5. Floor drains in basements shall be connected to sump pumps and

discharged to sanitary or combined sewers.

6. Sump pumps shall be used for only one function, either to discharge

stormwater or to discharge sanitary sewage. If both functions are used in

one building, two pumps are required.

wp/epastch5
6-1

CHAPTER 6

STAKEHOLDER INVOLVEMENT

Two Public Works Challenges

Two major challenges face today’s public works personnel. The first is the challenge of

finding cost-effective solutions to increasingly complicated urban problems. The

second is communicating effectively with the public, recognizing the public’s

increasingly elevated expectations relative to public facilities and services and the

public’s growing understanding of technology and the environment. A premise of this

chapter is that many and varied stakeholders want to be involved in public works

decisions and should be given the opportunity to do so.

In retrospect, there was great need for meaningful communication with stakeholders in

the Skokie and Wilmette street storage projects. Two factors heightened the need for

stakeholder involvement. First, the technology was very new, especially for Skokie. 

Second, many individuals, especially residents and business people scattered

throughout the CSS, would be directly affected. These were not remote projects.

Interestingly, and fortunately, both Skokie and Wilmette recognized the need for intense

communication. From the outset, both communities mounted proactive efforts to

interact with stakeholders. These efforts apparently played a major role in the success

of the two projects. As evidence of this, read the Chapter 8 summary of interviews and

comments with Skokie and Wilmette officials.

Purpose of this Chapter

Given the apparent importance of stakeholder involvement in the two street storage

projects described in this manual, the purpose of this chapter is to describe those

efforts. This documentation may be helpful to other communities. While communities

with a CSS should benefit from some of the specifics, many of the stakeholder

involvement efforts in Skokie and Wilmette are applicable to a wide range of public

works projects. Therefore, this chapter, unlike most other chapters of this manual, is

not focused primarily on street storage systems.
6-2

A Characteristic of Wet Weather Problems: Widely Fluctuating Public Interest

The interest of the public and some elected and appointed government officials in wet

weather problems and opportunities tends to fluctuate widely, as illustrated in Figure 6-

1. The fluctuations parallel the random nature of major meteorologic events. Interest

usually is most intense during and immediately after a destructive problematic water

event such as basement or surface flooding, or CSOs.

Later, typically months later, when the initial studies/plans/preliminary engineering are

completed and recommendations made, interest has subsided. The zeal that

commissioned the investigations is not complemented with similar zeal to implement

the recommendations of those investigations. Maintaining stakeholder interest is one

challenge of a stakeholder involvement program.

The widely fluctuating interest associated with wet weather problems contrasts with a

morel level and continuous concern with most other areas of public works and services. 

Examples are water supply pressure; condition of streets, especially presence of

potholes; level of police protection; and quality of public schools. Once problems

develop in these areas, they tend to persist and to receive persistent public attention

until they are solved.

More on the Need for Stakeholder Involvement

A public works effort that fails to include a stakeholder involvement program plans to

fail. Although said over a century ago, and in an entirely different context, the following

words of President Abraham Lincoln are appropriate: “With public sentiment, nothing

can fail; without it nothing can succeed. Consequently, he who molds sentiment goes

deeper than he who enacts statutes or pronounces decisions” (Helweg, 1985).

Grigg (1986) defines planning as “studying what to do” and distinguishes planning from

decision making or “deciding what to do.” The point is that studying and deciding are

two different activities or processes, and, as exemplified by the preparation of a street

storage plan, the studying and deciding processes are usually carried out by different

groups. A team of professionals and technicians prepares the plan. Another group of

primarily appointed and elected officials, usually influenced by the public, typically

makes decisions based on the findings of the plan.

Because planning and deciding are different functions done by different groups, public

works personnel and their consultants must not be so presumptuous as to think that

their recommendations will be fully embraced by decision makers. The professionals

can greatly enhance the probability of acceptance of the recommendations if the work

is of high quality and if the professionals effectively communicate with all interested

individuals and groups.
Procrastination

Plan

Wet Weather

Event

Figure 6-1. The “Hydroillogical” cycle

Panic

6-3
6-4

A public interaction program, or lack thereof, is often the principal reason for the

successful implementation of a public works program or the failure to implement it. This

observation is supported by the work of Kurz (1973) and Rubin and Carbajal-Quintas

(1995) who describe six unsuccessful urban area planning efforts (not all water-related)

and conclude why they were not implemented. Deficiencies identified include a lack of

clearly presented objectives and standards; poor public involvement efforts; inadequate

coordination between government units and agencies; and a myopic approach to the

identification, development, and testing of alternatives. Kraft (1997) concludes that

failure to build public consensus is the reason for the failure of several public projects

that would have incorporated new ideas. Street storage is an example of a new idea. 

Kraft lists causative “common pitfalls” similar to the preceding deficiencies. Avoiding

such deficiencies and pitfalls is the goal of a public interaction program, especially when

new, innovative technology is contemplated.

Perry (1996) advocates the preceding ideas using a “pro and con” model of public

communication. When the desirable “pro” approach is used, public works professionals

are proactive, proficient, and pro-people. In the undesirable “con” mode, the situation is

confrontational and confusing and messages are contrived.

Herrin and Whitlock (1992) somewhat harshly, but perhaps accurately, suggest that the

cause of some communication failures lies with engineers’, and perhaps other

professionals’, formal and informal education. According to them:

Engineers are taught very few skills in

interpersonal relationships, much less those of

public interface and involvement. We spend

little, if any, time addressing it at our

conferences and conventions. We then spend

thousands of hours and millions of dollars

defending our projects when threatened by

delays and possible blockage by public

intervention.

As noted by Viessman (1989), public sector problems “cannot be solved in the

technologic area only... Engineers must be society-wise as well as technology-wise.”

Identification of Stakeholders

The success of a stakeholder involvement effort is determined more by the number of

different, legitimate stakeholders involved then by the total number of individuals

involved. Many subgroups with very different, often competing agendas typically

constitute the stakeholders. Breadth of stakeholder representation and involvement is

crucial as suggested by Figure 6-2.
Our Community

Figure 6-2. Breadth of stakeholder involvement is crucial (Source: USEPA, 1997).

6-5
6-6

Public works officials should be especially wary of the temptation to exclude what they

regard as “extremist” elements from the deliberation process. These groups have a

right to be part of the process and to express their views. Attempts to exclude them are

likely to aggravate matters and precipitate or elevate conflict. In addition to affording

them their rights, inclusion of “extremist” organizations may lead to moderation of their

positions as their representatives are gradually exposed to data and information

developed during the management program and as they interact with spokespersons

for other segments of the public.

Presented in Figure 6-3 is a likely set of stakeholders for a street storage project. Note

the breadth of interests that are represented.

Types of Stakeholder Involvement

Priscoli (1989) suggests that interaction between public works professionals and the

public refers to a continuum of activities, programs, and techniques. The continuum

ranges from proactive public involvement (e.g., public information, advisory groups,

workshops) at one end of the spectrum to reactive conflict management (e.g.,

mediation, collaborative problem-solving, negotiation, and arbitration) at the other end. 

The preceding suggests that stakeholder involvement should employ many and varied

programs and events.

Unfortunately, some professionals with public works responsibilities fail to appreciate

the importance of the communication challenge, or they recognize the challenge but are

not prepared to meet it. The traditional DAD approach, that is, public works

professionals adopt a decide-announce-defend mentality, is no longer appropriate. The

much more progressive and inclusive POP approach, that is, public owns project, is

more likely to be effective given the changing nature of the public’s expectations and

knowledge (Walesh, 1999).

Speaking directly to civil engineers, and indirectly to all public project professionals,

Wakeman (1997) describes today’s situation this way: “...broad sections of today’s

public are concerned, vocal, and actively engaged in the formulation and

implementation of public policy, particularly policies regarding public facility construction

projects. Today’s civil engineer must be ready to work on infrastructure projects from

many more perspectives than were required in earlier years.”

Furthermore, stakeholder involvement is explicitly intended to be an iterative, two-way

process. The old DAD strategy is out. It is being replaced by the two-way POP

strategy in which concerns, ideas, and information flow freely between water resource

professionals and the individuals and organizations representing various interests. 

Public interaction goes way beyond no communication (Figure 6-4) and announcing

decisions (Figure 6-4). Interaction even goes beyond public information (Figure 6-5),
Citizens

Business

Persons

Regulatory

Personnel1

Funding

Personnel1

Representatives

of

Contiguous

Engineering Communities

and Other

Consultants

Elected 

State and

Federal

Representatives

Operation

and Maintenance

Personnel

Appointed

Officials

Local

Elected

Officials

Street

Storage

Project

1) Local, regional, state, and federal entities.

Figure 6 - 3. A street storage project is likely to have many stakeholders, all

of whom should be involved from the outset.

6 - 7
Consultants

and Public

Works

Personnel

Public

Figure 6-4. No communication and announcing decisions are increasingly unacceptable

ways of serving the public.

NO COMMUNICATION

Consultants

and Public

Works

Personnel

Public

ANNOUNCING DECISIONS

DECISIONS

6-8
Consultants

and Public

Works

Personnel

Public

ppt/fig5-5

Figure 6-5. The goal in stakeholder involvement goes beyond providing information,

it is meaningful interaction.

PROVIDING INFORMATION

Consultants

and Public

Works

Personnel

Public

INTERACTION

6-9
6-10

which implies one-way communication from water professionals to the public. Public

interaction is truly two-way communication (Figure 6-5).

The importance of conducting the public interaction effort throughout a public works

program—from beginning to end—must be emphasized. Astrack et al (1984), Rubin et

al (1995) and Walesh (1993) emphasize the need to repeatedly interact with various

elements of the public beginning on “Day 1" and extending throughout the process. In

addition, the process should be highly visible to and easily accessible by the public. 

Sargent (1972) uses the term “fishbowl planning” to suggest frequent and open

stakeholder involvement as the plan is being prepared.

The stakeholder paradigm presented in this chapter has three objectives (Walesh,

1989, 1993, 1999). They are:

• The first objective is to demonstrate to the stakeholders that the public

works professionals are aware of the problems, at least in a general

sense; want to learn more about them; and want to seek solutions. In

other words, public works professionals need to demonstrate empathy

and concern. The public’s position in the early part of a planning process

might be represented by the anonymous statement, “I don’t care how

much you know until I know how much you care.” Sometimes the most

vociferous citizens need an opportunity to vent their frustration with public

works problems and the apparent inability of responsible parties to solve

those problems. As stated by P. S. Hale, “We earned the public’s distrust. 

We’ll have to work even harder to regain their trust” (Eschenbach and

Eschenbach, 1996). The interaction process must provide opportunities

to express frustration, to find empathy among the public works

professionals, and, hopefully, to enable frustrated individuals to become

positive participants in the problem defining and solving process.

• The second objective of a stakeholder involvement program is to gather

supplemental data and information pertinent to the effort. Interested

citizens and officials, if informed about what they believe to be a

potentially useful public works effort, are likely to contribute photographs,

information on problems, ideas on solutions and other useful data and

information. Similarly, but on a larger scale and in a more formal manner,

various government units and agencies are likely to offer potentially useful

data, reports, funding opportunities and other information if they are

informed about the effort, are invited to contribute, and believe they will

benefit.
6-11

• The third and final objective of stakeholder involvement is to build a base

of support for rapid plan implementation. Enlightened citizens and

officials, who have been informed about a public works program and have

been given an opportunity to participate in it, are likely to become

supporters of the program, to help interpret it for others, and to otherwise

help implement it. Worthy goals are to have stakeholders exhibit pride of

authorship and a sense of ownership in the public works program.

Essential to the success of a public works effort is agreement between the public and

the professionals on what problems are to be mitigated or prevented. As stated by

Silberman (1977), “The objectives of a public participation program should be to assure

that the planners and the public have the same understanding of what the problems are

and that the proposed solutions are perceived as solutions by both the planners and the

public.” Concurrence on problem definition is not as simple as it may seem. For

example, basement flooding in a CSS might be viewed as “the problem” by the public. 

In contrast, public works personnel might view such flooding as the “symptom” of the

“real problem,” namely, an inadequately sized CSS or localized constrictions in the

system.

Examples of Stakeholder Involvement Techniques

Skokie and Wilmette Approaches

Skokie and Wilmette used, and continue to use, an effective mix of stakeholder

involvement programs, events and supporting devices. Some of their strategies and

tactics may be of value to other communities.

Both communities used the strategy of starting the stakeholder involvement effort at the

beginning of the street storage projects, that is, when the projects were in the concept

stage. Second, the stakeholder involvement process was and is being continued

throughout the projects. A third shared strategy is that both communities used a variety

of communication tactics.

Stakeholder involvement tactics used or being used in Skokie and Wilmette include:

• Articles in the community’s newsletter—“Newskokie” in Skokie and the

“Communicator” in Wilmette.

• Cable television programs.

• Surveys of residents. Wilmette had an excellent response on its survey of

residents in the CSS.

• Letters to residents.
6-12

• Public meetings which were usually held at the Village Hall. In a spirit of

outreach, Wilmette conducted some meetings in resident’s homes.

• Use of a committee of senior personnel, such as Skokie’s Flood Task

Committee, to monitor and guide the engineering consultant’s efforts (Walesh

and Schoeffmann, 1984).

• Physical models, like an operating, table top device created under the Skokie

project to illustrate surface and subsurface storage.

• Assigning one public works person to answer telephone inquiries.

• Special brochures

• Conduct of high visibility field pilot studies that included the construction of

berms, so that citizens can drive over and experience them, and the

temporary flooding of streets, so that citizens could observe the depth and

lateral extent of ponding.

• Video taping, for subsequent informational use, construction of facilities,

ponding on streets, and vehicles driving over berms (Walesh and

Schoeffmann, 1984).

• Brief discussions of the evolving street storage system as part of new

resident receptions. This approach was used in Wilmette.

Additional Tactics

Many and varied other tactics have been used for interacting with stakeholders. Ideas,

in addition to those presented in the preceding section, are (Walesh, 1999):

• Presentations to service clubs and other community groups: Knowledgeable

and influential community leaders are typically members of one or more civic

organizations such as service clubs, environmental groups, and professional

associations. Because of the frequency of their regular meetings—

sometimes two or more times per month—these groups are often receptive to

suggestions for speakers and programs. Such presentations can help to

expand knowledge of and support for a water management effort.

• School programs: By educating school children about water issues, a two-fold

result can be achieved. The students gain understanding and, to the extent

they share what they learned with their parents, the knowledge is

disseminated.

• Guided and self-guided tours: Interested individuals and groups, including
6-13

news people, can be provided with guided tours of a project area, such as a

CSS. A single bus or van, preferably equipped with a public address system,

should be used for a guided tour so that all participants can easily travel

together and can be provided with an informative narrative between stops. 

Self-guided tours are also possible if a written tour guide is available. Guided

and self-guided tours enhance understanding of the location and severity of

wet weather problems. Well-meaning citizens often have strong opinions

about environmental problems (e.g., combined sewer overflows) that they

have never seen or experienced. Tours also provide an opportunity for the

public works officials and their consultants to explain and show remedial and

preventive measures that are under consideration in the planning program. 

Another benefit of guided tours is the spirit of camaraderie that typically

develops and the new interpersonal relationships that often result.

• Briefings for newly-appointed or elected public officials: By being introduced

to issues and being provided with basic information on proposed, on-going or

completed public works projects, new public officials are more likely to be

supportive (Gilbert et al, 1981). Tactics include inviting them to join advisory

committees or to attend public meetings and providing them with special

briefings.

• Preparation of media packages: Example contents are summaries of

regulations; descriptions with photographs of problems; brief discussions,

supplemented with photographs or graphics, of potential solutions; and

experiences of other communities.

• Workshops: Public works officials and their consultants can conduct

workshops for interested citizens and public officials. These events provide

an opportunity for in-depth exploration of substantive topics such as issues,

findings, alternatives, recommendations, funding, and operations.

• Electronic-based access and input: Email and websites (e.g., Tam and

Murillo, 1997) offer exciting possibilities.

wp/epastch6
7-1

CHAPTER 7

INSPECTION AND MAINTENANCE

Essentiality of Inspection and Maintenance

The experience of Skokie and Wilmette indicate that systematic maintenance is

essential to the effective functioning of a street storage system. Such a storageoriented system will malfunction, at least locally, if inlets or flow regulators become

obstructed with leaves, twigs, Styrofoam containers and other debris.

The preceding observation is also applicable to more traditional stormwater storage

facilities. It is not unique to a street storage system. The outlet works of a typical

stormwater detention basin should be carefully designed to minimize the potential for

blockage. Nevertheless, a systematic inspection and maintenance program is usually

required to further reduce the likelihood of malfunctioning to an acceptable level.

The point is that any stormwater storage system requires some sort of outlet control

structure or device. Even with thoughtful design, that outlet structure or device is

subject to failure without proactive inspection and maintenance.

Both Skokie and Wilmette report increased inspection and maintenance after

installation of their street storage systems. Refer, for example, to the Chapter 9

summaries of interviews with personnel from these communities. Quantifying the

increased inspection and maintenance effort is difficult, although Skokie personnel

described the overall effort as being “doubled.” The increased effort is significant.

In considering the increased inspection and maintenance effort, the pre-system status

should be considered. Skokie, for example, carried out minimal catch basin inspection

and maintenance prior to construction of the street storage system. Evidence included

many completely filled sumps. Wilmette inspected and maintained catch basin sumps

only once every three years prior to the street storage system. These levels of

inspection and maintenance are substandard because they render the sumps

ineffectual in trapping solids. However, the catch basins functioned hydraulically. 

Under street storage system conditions, sumps must be largely free of debris. Leaves,

twigs, Styrofoam containers and other debris trapped in catch basin sumps, if allowed

to accumulate too much, will begin to plug the orifices in the hanging traps. Stated
7-2

differently, catch basin sump cleaning may be viewed as hydraulically optional in the

pre-street storage system mode. However, it is mandatory with the street storage

system in place.

Inspection and Maintenance Procedures for Skokie’s Street Storage System

Recognizing the importance of system operation, Skokie commissioned the preparation

of a manual (Rust, September, 1995) to guide inspection and maintenance. This

manual was first prepared in June 1993, revised in November 1994 and September

1995, and was being revised again in 1999 as this manual was being written. The

specific purpose of the manual is to provide Department of Public Works personnel with

information needed to operate and maintain the street storage system. 

Included in the manual are a synopsis of the history and function of the street storage

system, detailed description of system components, and detailed inspection and

maintenance procedures. This chapter draws on the detailed inspection and

maintenance procedures with the idea that they may be of interest to other CSS

communities contemplating a street storage system.

Inspection and maintenance procedures are arranged in the manual according to the

following six categories (quoted from Rust, September, 1995, Section 3.0).

1. Underground and surface storage basins - normal operation, inspection, and

trouble shooting.

2. Stormwater storage basins and dewatering pump stations - inspection and

trouble shooting guide.

3. Submersible dewatering pumps - standard maintenance procedures.

4. Flow regulators and catch basins - standard operating and maintenance

procedures.

5. Street berms and diverters - standard operating and maintenance

procedures.

6. Street ponding areas - standard operating and maintenance procedures.

Surface and Subsurface Storage and Dewatering Facilities

Summaries of the inspection and maintenance procedures for the first three categories

are presented, respectively, in Appendices C, D, and E of this manual. Referred to as

trouble shooting guides (the first two) or standard procedures (the third one), these

three inspection and maintenance procedures are made available in laminated card

format for Department of Public Works Personnel.
7-3

Flow Regulators

Recall that two types of flow regulators are used in Skokie. They are the hanging trap,

which is widely used, and the vortex (Hydro-Brake and other) regulator, which is used

when the required orifice size is too small for use of the hanging trap. Flow regulator

inspection and maintenance procedures, quoted from Rust (September, 1995, Section

3.4), are:

1. Catch basins with hanging trap regulators should be inspected on a minimum

annual basis and maintained as required.

2. The best time for inspection is during the fall leaf season.

3. With a sounding pole, check the structure for an accumulation of grit in the

catch basin. There should be no accumulation of grit within one foot of the

bottom of the orifice.

4. Excessive floating material in the catch basin that reaches the orifice inlet

should also be removed.

5. Clean catch basins with hanging traps, and grit or floating material

accumulations, in the same manner as a normal catch basin.

6. Ponded water in the vicinity of a catch basin with a flow regulator is an

indicator of a clogged orifice.

7. If a street area is flooded because of a plugged regulator, dewater the area

and catch basin with a pump.

8. Clear the clogged trap by removing and replacing it, or by removing the plug

in the tee and rodding. Use confined space entry procedures if a person has

to enter the catch basin structure for any reason.

9. Use a similar strategy for inspection and maintenance of vortex regulators

installed in catch basins. To correct a clogged condition from a vortex

regulator, the entire device might have to be removed.

10. Record inspection and maintenance information on form provided.
7-4

Street Berms

Inspection and maintenance procedures for berms, quoted from Rust (September

1995, Section 3.5), are:

1. At a minimum, the condition of the street berms should be inspected on an

annual basis. Inspect bituminous areas for the following features indicating

deterioration:

Rutting. A depression in the pavement parallel to the side of the street. A

depth of 1⁄2 inch is slight; 1⁄2 to 1 inch is moderate; greater than 1 inch, or such

to affect vehicle steering, is severe.

Raveling. Breaking of the surface with visibly loose pieces of aggregate.

Flushing. Asphalt mixture covers the aggregate on the pavement surface.

Corrugations. Ripples are visible in the pavement perpendicular to the

direction of traffic.

Alligator Cracking. Pavement cracks in a wire mesh-like pattern. Slight when

barely visible; moderate when some cracks exceed 1/4 inch in width; severe

when the sides of cracks become fully separated.

Transverse Cracking. Cracks in the pavement perpendicular to the direction

of traffic. Severity criteria the same as for alligator cracking.

Longitudinal Cracking. Cracks in the pavement parallel to the direction of

traffic. Severity criteria the same as for alligator cracking.

Patched Areas. Evidence of repaired potholes, utility cuts, or other failed

areas. Slight when level with the pavement with no sign of deterioration;

moderate when deteriorated, but not enough to slow traffic; severe when

deteriorated and deep enough to slow traffic.

2. Repair minor deteriorated areas in street berms in the same manner as a

typical street area.

3. For major damage to roadway berm areas, the surface should be scarified

down to the point where a stable sub-base is reached, and resurfaced to the

original grade. This work would typically not be done by Village staff, but

rather by an outside contractor.

4. Reference the record contract drawings to obtain the design grade

characteristics of each berm area.
7-5

5. Record inspection and maintenance data on the form provided.

Street Ponding Areas

Procedures for inspection and maintenance of street ponding areas, quoted from Rust

(September 1995, Section 3.6) are:

1. At a minimum, the condition of the street ponding areas should be inspected

on an annual basis. Inspect bituminous areas for the following features

indicating deterioration:

Rutting. A depression in the pavement parallel to the side of the street. A

depth of 1⁄2 inch is slight; 1⁄2 to 1 inch is moderate; greater than 1 inch, or such

to affect vehicle steering, is severe.

Raveling. Breaking of the surface with visibly loose pieces of aggregate.

Flushing. Asphalt mixture covers the aggregate on the pavement surface.

Corrugations. Ripples are visible in the pavement perpendicular to the

direction of traffic.

Alligator Cracking. Pavement cracks in a wire mesh-like pattern. Slight when

barely visible; moderate when some cracks exceed 1/4 inch in width; severe

when the sides of cracks become fully separated.

Transverse Cracking. Cracks in the pavement perpendicular to the direction

of traffic. Severity criteria the same as for alligator cracking.

Longitudinal Cracking. Cracks in the pavement parallel to the direction of

traffic. Severity criteria the same as for alligator cracking.

Patched Areas. Evidence of repaired potholes, utility cuts, or other failed

areas. Slight when level with the pavement with no sign of deterioration;

moderate when deteriorated, but not enough to slow traffic; severe when

deteriorated and deep enough to slow traffic.

2. Repair minor deteriorated areas in street ponding areas in the same manner

as a typical street area.

3. For major damage to street ponding areas, the surface should be scarified

down to the point where a stable sub-base is reached, and resurfaced to the

original grade. This work would typically not be done by Village staff, but

rather by an outside contractor.
7-6

4. Reference the design drawings to obtain the design grade characteristics of

each ponding area.

5. Record inspection and maintenance data on the form provided.

Safety of Inspection and Maintenance Personnel

The Skokie Department of Public Works uses a Safety Manual (Skokie, 1992) which

contains procedures to be followed by Village personnel. Much of the manual’s content

is applicable to inspection and maintenance of the street storage system. As stated by

Rust (September, 1995, Section 4.0), with respect to safety and the street storage

system, “Topics of concern that should be reviewed by all workers performing

maintenance procedures include: traffic control; worksite safety; confined space entry;

safety equipment; and emergencies, first aid and hygiene.”

wp/epastch7
8-1

CHAPTER 8

CONSTRUCTION COSTS

Purpose

This chapter’s purpose is to provide construction cost ideas and information which

might be useful to other CSS communities contemplating street storage. Accordingly,

presented are the total construction costs for those systems. Also included, for both

Skokie and Wilmette, are estimated construction costs if traditional solutions had been

implemented. These costs are compared to the much lower costs for the street storage

systems. Street storage costs are normalized and compared to normalized costs for

other options. The chapter concludes with a discussion of intangible costs.

Skokie Construction Costs

As shown in Table 8-1, the total construction cost for the Skokie street storage project,

which was to be completed in 1999, is projected to be $67 million. (This is the

cumulative construction costs not adjusted for inflation. As shown in Appendix G, total

construction costs converted to 1999 dollars using the ENR CCI is $78 million.) The

graphical presentation in Figure 8-1 emphasizes the differences in the relative costs of

berm-flow regulator installations, sewers and supplemental storage.

Comparison of Figure 8-1, which summarizes construction cost data, with Figure 3-35,

storage location data, suggests the cost effectiveness of temporary, controlled storage

of stormwater on streets. The berm-flow regulator installations in Skokie account for

only nine percent of the total construction cost while providing about half of the total

stormwater storage. In Wilmette, the berm-flow regulator installations account for all of

the stormwater storage.

A generalization to many CSS cannot be made based largely on in-depth experience

with two communities. Nevertheless, the Skokie and Wilmette case studies suggest

that retrofitted storage of stormwater on streets may be very cost effective. Therefore,

it should be at least considered at the outset of any urban project involving the control

of stormwater runoff.

Figure 8-2 compares actual construction costs for the Skokie street storage system to

the estimated cost if a traditional sewer separation project had been implemented. 
8-2

Table 8-1. Total construction costs for the Skokie, IL street storage system (Source:

Carr, 1999).

Element

Construction Cost

(Million $) % of Total

Berm-flow regulator installations 6 8.9

Storm and combined sewers 20 29.9

Supplemental storage 41 61.2

Total: 67 100.0
0

10

20

30

40

50

60

70

Cost in Million $

Berms

Sewers

Supplemental Storage

Figure 8-1. Distribution of construction costs for the Skokie street storage system

showing the relatively small cost of the berm-flow regulator installations (Source:

Carr, 1999).

8-3
0

50

100

150

200

250

Cost in Million $

Sewer Separation Source Control

Figure 8-2. Construction costs for Skokie’s street storage system are about one-third

the estimated cost of sewer separation (Source: Carr, 1999).

8-4
8-5

These costs are adjusted to account for inflation during the Skokie construction period. 

As noted, the projected construction cost of the Skokie street storage system, when

expressed in 1999 dollars as developed in Appendix G, is $78 million. As explained in

Chapter 2, sewer separation costs, expressed in 1999 dollars, were estimated to be

$203 million. Therefore, the street storage system cost was about 38% of sewer

separation. Skokie achieved a major construction cost saving by using the street

storage system approach.

Wilmette Construction Costs

The projected total construction cost for the Wilmette street storage system, with three

of five phases already constructed as of early 1999, is $35,169,000. As explained in

Chapter 3, this system will eventually include about 250 berm-flow regulator

installations, essentially all of which have been constructed, and tunneled and

conventionally constructed relief and storm sewers.

For cost comparison purposes, a 1991 facilities plan examined sewer separation and

relief combined sewer options (SEC Donohue, 1992, p. 5). Relief combined sewers

were recommended at an estimated construction cost then of $65 million. The 1999

cost would be $81 million using the ENR CCI. Therefore, the projected construction

cost of Wilmette’s street storage system is about 43% the cost of the next best

identified option.

Unit Costs

One way to compare the costs of street storage to more traditional solutions of CSS

problems is to normalize the costs, that is, develop unit construction costs. Examples

of ways construction costs can be expressed on a unit basis are cost per acre, cost per

person, and cost per building. While normalization of costs helps with cost

comparisons, it does not reflect any economies of scale which may occur in the design

or construction process. For example, construction costs are likely to be less per unit

area if one contract is let for a large area than if two or more contracts are let.

Skokie and Wilmette Unit Costs

Table 8-2 presents various unit construction costs for the Skokie and Wilmette street

storage systems. As a point of reference, AMSA (1994, p. 19) reports the following unit

costs for sewer separation:

• Range: $15,000 - $176,000/acre

• Median: $21,000

According to AMSA, these costs are based on CSO work completed as of about 1994. 
8-6

Table 8-2. Unit construction costs for the Skokie and Wilmette street storage systems.

Item Skokie Wilmette

Total Projected

Construction Cost (million $)

781 35

Area (square miles) 8.6 2.0

Construction Cost per Acre ($/acre) 14,200 27,300

Population in the CSS 60,000 11,300

Construction Cost per Person

($/person)

1,300 3,100

Number of Single Family Residences 20,000 - - -

Construction Cost per Single Family

Residence ($/residence)

3,900 - - -

Number of Buildings - - - 3,500

Construction Cost per Building

($/building)

- - - 10,000

1) Adjusted to 1999 using the ENR CCI.
8-7

Adjusting the unit costs to 1999, using the ENR CCI, yields:

• Range: $16,600 - $195,000/acre

• Median: 23,300

The Skokie and Wilmette street storage unit costs of, respectively, $14,200/acre and

$27,300/acre are at the low end of the AMSA range. The Skokie unit cost is much less

than the AMSA median and the Wilmette unit cost is slightly above the AMSA median.

Discussion of Unit Costs

The preceding street storage system unit costs must be used cautiously. They are

based on construction experience in only two communities. The two communities are

similar in some ways. For example, flat street grades, the same climate and

approximately equivalent performance criteria such as the 10-year recurrence interval

design storm.

However, significant differences occur between the two communities and those

differences may affect unit costs. For example, while both street storage systems

include berms and relief sewers, Skokie’s also includes subsurface storage.

Although both communities make intensive use of berms, many of Wilmette’s are on

the highly valued brick streets and required very labor-intensive construction. 

Furthermore, most of the required catch basins and combined sewer manholes already

existed in Skokie but had to be constructed in Wilmette, further adding to costs.

Having presented the previous caveat and with it in mind, this case study strongly

suggests that street storage, where physically feasible, is likely to be much less costly

than sewer separation and relief sewers, a traditionally more common means of solving

basement and other flooding. Stated differently, if basement and surface flooding is the

only or principal CSS problem faced by a community, street storage should be viewed,

from the outset, as a potential solution. So should separation and any other potential

solution. If CSO’s are a problem, with or without basement and other flooding, street

storage should again be considered as an option, either alone or in combination with

traditional technologies.

Omitting street storage as an option in cases like preceding, either because of lack of

information about it or negative perception of it, could result in a community incurring

construction costs that are unnecessarily high. The suggested question to be asked by

a community and its stakeholders is: What is the most cost-effective means of

achieving the agreed-upon level of performance?
8-8

Intangible Costs

The preceding costs are tangible, that is, they are quantifiable in monetary terms. They

are real costs. Other costs connected with resolving wet weather problems are

intangible. They cannot be expressed in monetary terms. Nevertheless, these costs

are very real. Lack of quantification does not make intangible costs less important but

does mean that they are more difficult to weigh by stakeholders in the comprehensive

decision-making process increasingly used in public works projects.

Stakeholders should identify and weigh all possible intangible costs associated with any

alternative. Examples of intangible costs that might be associated with one or more

potential solutions to CSS problems are:

• Noise, dust and other disruption during construction.

• Construction outside of the public right-of-way, that is, on private property.

• Loss of trees and the resulting aesthetic impact.

• Interference with or adverse re-routing of vehicular traffic after construction. 

This could be the case with improperly designed berms.

• Few, if any, options for future physical adjustments.

Consider an example, recognizing that generalizations are problematic. Compare the

intangible costs of a sewer separation approach to a street storage system. Sewer

separation will probably result in much more noise, dust and other disruptions than

street storage. For example, separation is likely to involve opening up a street over the

length of many blocks. In contrast, street storage is constructed at discrete locations. 

Sewer separation may require construction or reconstruction of building laterals outside

of the public right-of-way. Street storage construction is typically and readily confined to

the right-of-way. Separate sewers offer little opportunity for future, low cost

adjustments. In contrast, flow regulator changes and even berm modifications are

easily accomplished.

wp/epastch8
9-1

CHAPTER 9

PERFORMANCE OF STREET STORAGE SYSTEMS

Performance: The Ultimate Test

The proof of a public works structure, facility or system is “in the doing.” Does it

perform? Elected and appointed officials in CSS communities are much more likely to

consider a new process or technology if it has been proven in other similar

communities. Favorable performance will be even more highly valued if it is reported by

or originates with other public works officials.

This chapter documents available information on the performance (not projected

performance as has been done with computer modelling) of the street storage system

approach to mitigating basement and other flooding problems caused by CSS

surcharging. Most of the performance information is drawn from up to 15 years of

experience with the Skokie and Wilmette, IL systems. Supplemental performance

information is presented from other communities that have applied, usually on a smaller

scale, street storage technology.

Broad Interpretation of Performance

The word “performance” is broadly interpreted in the chapter as it should be given the

realities of the public works field. A public works structure, facility or system must meet

many criteria to be acceptable, especially if the structure, facility or system embodies a

fundamentally new approach.

Clearly, the street storage system should perform in a functional sense. That is, it

should substantially mitigate basement and other flooding caused by surcharged

combined sewers. A street storage system may also be expected, as was the case in

Wilmette, to reduce peak flows to the entity that operates an interceptor sewers system

and wastewater treatment plants. Another possible performance test of a street

storage system is its reduction in the frequency and volume of CSOs. Other likely

important performance factors are:

• Economic feasibility, that is, do the benefits warrant the costs?

• Financial feasibility, that is, can the system be financed?
9-2

• Public acceptance

• Economic and financial impact on the community.

• Likelihood of generating claims or prompting legal actions.

• Impact on the effective operation of emergency and other vehicles.

• Feasibility and cost of operation and maintenance.

• Acceptance by local, regional, state and federal government agencies

having a stake in the system.

In searching for ideas on ways to evaluate performance of street storage in CSS,

reference was made to a summary of a series of five regional, AMSA-sponsored

workshops on the theme of CSO performance measures (AMSA and Limno-Tech,

1996). As is often the case with these events and the resulting documentation, the

summary report is totally devoted to the CSO problem. No mention is made of

basement flooding in CSSs, solutions to that problem, or ways of evaluating the

performance of implemented measures.

Means of Assessing Performance

Unlike a controlled laboratory test of a small prototype of a new device, testing of a new

large scale public works system is not typically carried out with intensive data collection. 

Street storage and related storage of stormwater is such a large scale public works

system. 

Accordingly, varied, qualitative and semi-quantitative means must be used to evaluate

the performance of the street storage system. Means of evaluation reported in this

chapter are:

• Interviews with Skokie, IL officials

• Interviews with Wilmette, IL officials

• Rainfall event incidents

• Study of economic and financial impacts
9-3

Summary of Interviews With Skokie, IL Officials

Participants

Five Village of Skokie officials kindly agreed to be interviewed on December 14, 1998

as part of the EPA project. Interviewees were:

• Ms. Jacqueline Gorell, Mayor

• Mr. Albert J. Rigoni, Village Manager

• Mr. Dennis York, Director of Public Works (DPW)

• Mr. Eddy Nakai, Village Engineer

• Mr. Frank Didier, Superintendent, Water and Sewer Division

Interviewees may be contacted through:

Village Hall

5127 Oakton Street

Skokie, IL 60077

Tel: 847-673-0500

Process

Stuart G. Walesh, Consultant, and Robert W. Carr of Earth Tech conducted two

interviews. The first involved Mayor Gorell and Manager Rigoni. The second interview

included DPW York, Engineer Nakai, and Superintendent Didier.

The objective of the comprehensive interviews was to obtain first hand ideas and

information on many aspects of the community’s street storage system. Because four

of the five interviewees have been Skokie employees (A. Rigoni, E. Nakai and F. Didier)

or an elected official (J. Gorell) throughout the life of the project, the interviews proved

to be very fruitful. Value was added to the interview process by the participation of

DPW York who had been employed by Skokie for only several years and, therefore,

offered a fresh perspective and an objective review.

A list of questions was prepared by the interviewers prior to the interviews to facilitate a

thorough, wide-ranging discussion. The list was not given to the interviewees but was

used by the interviewers as an aid during the interviews. The questions are included as

Appendix A.

Interviewees were encouraged to be open and frank. As suggested by the wording of

most of the questions in Appendix A, both positive and negative views were sought in

the hope of extracting ideas and information that would be useful to representatives of

other communities contemplating street and related storage of stormwater.

Results
9-4

Partly as a result of the prepared questions and the use of open-ended inquires, the

interviewees were generous, frank and informative with their comments. Key ideas and

information obtained or verified during the interviews are presented below.

Financing:

• Bonding is the dominant means of financing, usually without referenda. Some

low interest loans have been obtained under the State Revolving Fund program

through the State of Illinois as described in Chapter 5.

• There have been no large increases in taxes partly as a result of the phased

construction of the system.

• On-going capital expenditures for system construction have been accepted

partly because of the system’s success in solving problems and partly because

of the stability of the Board of Trustees and Skokie staff and citizen confidence

in the Board and staff.

Effectiveness of the System in Mitigating Basement Flooding:

• Mayor Gorell: “Ultimately it makes your life easier... worth time, effort and

money.”

• Street storage is generally viewed as not a perfect solution. However, there

are no perfect solutions to stormwater and wet weather problems given the

random, episodic nature of meteorological events.

• A serious storm might generate 60 telephone calls from residents and property

owners. In some cases, reported basement flooding may be caused by

seepage of infiltrated stormwater through basement floors and wall—not

necessarily back up of combined sewage.

• They “would do it again” according to Mayor Gorell and Manager Rigoni.

• DPW York, noting that the Skokie approach retrofits stormwater storage into

the system, stated that the project “makes good use of what is there.”

• One measure of the effectiveness of the street storage system is that news

media no longer come to Skokie when heavy rainstorms occur.
9-5

• Some building owners have installed their own systems, such as standpipes in

basement floor drains or overhead sewers as a backup system. Such building

owner actions tend to be prompted by major rainfall events—such as the

August, 1989 storm—in the interest of providing an “insurance policy.” There is

concern with such actions, even though on private property, because they may

be implemented without adequate knowledge and result in serious structural

damage and risk to occupants. For example, as a result of standpipe

installation, excessive hydrostatic pressure may build-up under basement

floors and against basement walls. The floor may be raised and/or the walls

collapse inward.

Public Education and Involvement:

• Although a major public education effort was mounted early in the project to

explain the function and benefit of the street storage system, on-going public

education is needed. 

• On-going public education mechanisms used in Skokie include letters to

citizens, cable television, and “Newskokie,” the Village’s newsletter (e.g.,

“Board Report” section, map of proposed street storage projects).

Litigation:

• There has been no litigation as a result of the street storage system.

Claims:

• One or two claims have been made to the Village.

• In one case, the owner of an automobile requested reimbursement for alleged

water damage to his/her parked vehicle. The community denied the claim and

referred the individual to their automobile insurance carrier.

Operation of Emergency Vehicles:

• There have been no complaints from any member of departments that use

emergency vehicles (e.g., fire, police).

• There has been no damage to emergency vehicles as a resulting of driving

over berms.
9-6

Operation of Motor Vehicles:

• There have been no claims for damage to vehicles as a result of driving over

berms.

• No accidents are known to have been caused by ice or water directly related to

the street storage system.

Operation and Maintenance (O&M):

• Much more O&M is needed for effective operation of the street storage system

than was practiced prior to construction of the system.

• Although complete statistics are not available to quantify the increased O&M,

the overall effort is described as having been doubled. One index is a doubling

of O&M personnel (from two to four) and an addition of a second Vac All. 

Another way to portray the increased O&M effort is to note that, as a result of

the street storage system, Village personnel have progressed from cleaning

about 3000 catch basins to cleaning and maintaining approximately 10,000

structures (i.e., catch basins, inlets, berms and storage facilities.

• About one-half of the approximately 3100 catch basins are cleaned each year

during the March through November period.

• One reason for more maintenance is a reduction in flushing action

characteristic of CSS’s and a corresponding increase in settling and

accumulation of solids in inlets, catch basins, and pipes connecting inlets to

catch basins. That is, the intentional, widespread introduction of street and

related stormwater storage reduces stormwater flow rates into and through

inlets, catch basins, connecting pipes and combined sewers. Thus the flow

reduction, which is highly desirable for mitigating basement flooding and

possibly CSO’s, appears to be undesirable from the perspective of reducing

self cleaning of the CSS.

• Catch basin sumps, which were not systematically cleaned prior to

implementation of the street storage project, are cleaned now because catch

basins are an even more essential part of the system.

• A manual is being prepared to increase the effectiveness of O&M.
9-7

• The existence of only four pumping facilities in the entire system facilitates

O&M. Note: With the preceding exception, and as explained in Chapter 3, the

street storage system operates solely by gravity.

• When plugging occurs, hanging trap flow regulators are much easier to rectify

than vortex regulators. If any difficulty is encountered in removing debris from

a hanging trap, the inexpensive device is simply broken off after which the

catch basin drains and a new hanging trap is inserted. A tee, on which the two

ends of the handle have been bent 90°, is used in an upside down fashion to

reach into the catch basin beneath the water level, “grab” the hanging trap and

pull up on it to break it off.

• A problem peculiar to vortex regulators is that sticks tend to bridge across the

openings which, in turn, accumulates other debris. The initial bridging of vortex

regulator openings probably occurs because the openings are not always

submerged. In contrast, orifices on hanging trap regulators are always

submerged by at least a few inches of water and, therefore, are less likely to be

plugged by buoyant debris.

• Newer model vortex regulators have two gaskets on the cylindrical portion

which inserts into the exit pipe from the catch basin. This has proven to be

better than the earlier model, which had one gasket. Two gaskets are

preferable because the regulator fits tighter and is less likely to fall out.

• Because of the superior O&M performance of hanging trap flow regulators, the

Village would prefer to use more of them and less vortex regulators. This

would be feasible if the minimum orifice diameter for hanging traps could be

reduced to one inch.

• Hanging trap resistance to plugging might be improved further and/or smaller

diameter orifices might be permissible by fitting the orifice end with a “bubble”

or hemispherically shaped screen or grate. 

• Plugging of regulators during any storm is relatively rare. For example, only

five to ten of the approximately 3000 regulators will experience blockage in a

runoff event.

• A positive O&M feature of the street storage system, with emphasis on

continuous improvement in system operation, is the ability to make low cost,

physical adjustments to the system. Examples of such adjustments, which can

be motivated by observation of the system, are changing flow regulator sizes

and modifying, adding or removing berms. Low cost system adjustments or

“tweaking” may lead to higher levels of protection.

• Because the street storage system has so many components distributed over a

large area (8.6 square miles), a user-friendly mapping system is very desirable. 
9-8

For example, one approach would be interactive computer-based maps that

would enable the user to easily obtain information about any component (e.g.,

the type and size of a particular flow regulator and the last time its catch basin

was cleaned) and to readily update the data base (e.g., document the cleaning

of a below-street tank).

Monitoring:

• Occasional, focused monitoring of parameters such as rainfall intensity, and

dry and wet weather discharge in combined sewers, is very useful. It has, for

example, revealed great spatial rainfall variability over the 8.6 square mile

Village of Skokie.

• Monitoring of stormwater levels in subsurface tanks, which has not been done,

is now desired. The principal interest is in determining if optimum use is being

made of available tank capacities.

• If a system similar to Skokie’s were to be planned, designed and constructed

“from scratch,” consideration should be given to incorporating permanent

monitoring devices. An example of such a device would be pressure sensors

in the floors of tanks or other device to monitor the depth of stored water. 

Another example would be permanent flow monitors in selected sewers.

Downspout Disconnection:

• Refer to Chapter 5 for a description of Skokie’s early 1980's community-wide

downspout disconnection program.

• This measure helps the public understand the functioning—and

malfunctioning—of combined sewer systems when receiving high rates of

stormwater runoff. That is, more residents recognize the cause and effect

relationship between excessive rates of stormwater runoff and basement

flooding.

• A mandatory downspout disconnection program should include an appeal

process. Some properties have special physical circumstances precluding

surface discharge of downspouts. For example, discharged stormwater may

flow onto neighboring properties.
9-9

• Skokie was too lenient with bringing business and commercial properties into

compliance with the community’s downspout disconnection program. This was

done, in part, because of the larger cost of disconnecting downspouts within

some business and commercial buildings.

Pavement Deterioration:

• There is no evidence of accelerated deterioration of asphalt or concrete

pavement as a result of the presence of the berms or the temporary ponding of

stormwater on the street. As noted in Chapter 3, street storage of stormwater

has occurred since 1985 in the Howard Street District, the first district in which

the street storage system was implemented.

Icing of Streets When Rainfall or Snowmelt Occurs During Freezing

Temperatures:

• This is not a problem provided the system is maintained, that is, obstructions

do not prevent or greatly restrict stormwater flow into inlets.

• Because it generates water slowly, snowmelt is not a problem.

• Breaks in water mains during winter have occasionally caused freezing

conditions.

• If an inlet or catch basin blockage exists during freezing conditions, a solution

is to dump a mixture of hot water and snow melting compound and “rod it” with

a jet truck. 

Interaction With Other Government Entities:

• The Illinois Environmental protection Agency (IEPA), after some discussion

and deliberation, decided to support the Skokie street storage system by

providing low interest loans under the state’s revolving fund program. Refer to

Chapter 5 for details.

• The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) is

a strong supporter of the Skokie project. One reason for MWRDGC support is

that the street storage type systems resolve the basement flooding problem

that remains after implementation of the Tunnel and Reservoir Plan (TARP). 

Control of CSO’s to protect surface water quality is TARP’s primary purpose

and, as a result, there is a major residual basement flooding problem.

• The Illinois Department of Transportation (IDOT) and Cook County, in contrast

with the preceding agencies, have not been supportive of the street storage

system. Their concern should be viewed in the context of these agencies’

roadway responsibilities and potential problems resulting from ponding of water
9-10

on arterials under their jurisdiction. 

Summary of Interviews With Wilmette, IL Officials

Participants

Three Village of Wilmette officials kindly agreed to be interviewed. Interviewees were:

• Mr. George Sullivan, Chair, Wilmette Sewer Commission

• Ms. Donna Jakubowski, Director of Public Works (DPW)

• Mr. Robert S. Lewis, Village Engineer

• Mr. Brad Enright, Sewer/Water Superintendent

Interviewees may be contacted through:

Village Hall

1200 Wilmette Avenue

Wilmette, IL 60091-0040

Tel: 847-853-7627

Process

Stuart G. Walesh, Consultant interviewed Chair Sullivan by telephone on February 4,

1999. S. Walesh and Michael C. Morgan, Earth Tech interviewed DPW Jakubowski

and Superintendent Enright in Wilmette on February 9, 1999. The second interview

that day was with Engineer Lewis.

As with Skokie, the objective of the comprehensive interviews was to obtain first hand

ideas and information on many aspects of the community’s street storage system. 

Because three interviewees have been Wilmette employees (D. Jakubowski and B.

Enright) or an elected official (G. Sullivan) throughout the life of the project, the

interviews proved to be very fruitful. Engineer Lewis, who had been with the community

less than a year at the time of the interview, provided fresh insight.

The previously mentioned list of questions (Appendix A) used for the earlier Skokie

interviews were subsequently used for the Wilmette interviews. The list was not given

to the interviewees but was used by the interviewers as an aid during the interviews.

Interviewees were encouraged to be open and frank. Both positive and negative views

were sought, as suggested by the wording of most of the questions in Appendix A. The

goal was to obtain ideas and information that would be useful to representatives of

other communities contemplating street and related storage of stormwater.

Results
9-11

The interviewees were generous, frank and informative with their comments. Key ideas

and information obtained or verified during the interviews are presented below.

Financing:

• Low interest loans were obtained through the State of Illinois as part of the

State Revolving Loan Fund is described in Chapter 5. Wilmette applied for

these loans based, in part, on learning of Skokie’s success with this financing

mechanism. All of the street storage project was funded in this manner.

• Sewer service charges, which are based on water use, have gradually

increased to generate needed revenue. However, the rates are still low relative

to similar neighboring communities

Effectiveness of the System in Mitigating Basement Flooding:

• Chair Sullivan: “Excellent, demonstrably better...” However, the community is

waiting for a “huge rain” to further evaluate the performance of the system

before proceeding with implementation of the fourth and fifth phases of the five

phase program.

• Few, if any complaints, about basement flooding were received from residents

of the CSS as a result of the August 1998 rainfall when about 2.75 inches fell. 

Many streets filled with water, as expected, and this caused some citizen

concern. However, flooding was “drastically reduced” and the system “worked

just great.”

Public Education and Involvement:

• Chair Sullivan: “Get out in front in interacting with the public.” The sewerage

commission budgeted specifically for information and publicity.

• On-going public interaction efforts used in Wilmette include a survey of

residents; assigning one person in Public Works to answer telephone inquiries;

articles in the local weekly newspaper; new resident receptions; items in the

“Communicator,” the Village’s newsletter; programs on cable TV and meetings

at the Village hall and in citizen’s homes.

• There was little difficulty in earning community acceptance and approval of the

street storage system. This favorable result probably reflects the proactive

approach of community leaders in interacting with the public.

Litigation:
9-12

• There has been no litigation as a result of the street storage system.

• A potential lawsuit did not materialize. In this situation a driver drove over a

berm, apparently at excessive speed, and damaged the vehicle’s under

carriage. The initial issue, which was not pursued, was that the berms are

speed control devices and, therefore, require appropriate signs and street

markings. While it is true that signs and street markings are recommended by

ITE (1997, pp. 17-19), Wilmette’s position was that the berms are designed

solely for flood control.

Claims:

• No claims have been made as a result of the street storage system.

Operation of Emergency Vehicles:

• One police car was damaged by “bottoming out” on one of the first berms

constructed in the community. This was attributed to an excessive longitudinal

slope on the first Wilmette berms. The vertical distance between the gutter

invert and the street crown is generally much greater in Wilmette than in

Skokie. That is, Wilmette streets typically have much more camber. 

Therefore, in order to hold the same maximum longitudinal slope in Wilmette

as proved successful in Skokie, the longitudinal length of the Wilmette berms

must be longer than the Skokie berms. Stated differently, berm longitudinal

slope governs design, not berm longitudinal length. The problem with the initial

Wilmette berms was rectified by altering them.

• There have been no subsequent problems with emergency vehicles.

Operation of Motor Vehicles:

• There has been no unfavorable rerouting of vehicular traffic onto side streets. 

However, berms are not generally located on high volume streets.

• No accidents are known to have been caused by ice or water directly related to

the street storage system. Icing has not occurred.

• Berms function as speed humps and favorably reduce speeds on some streets. 

The berms do not impair driving when vehicles travel at speeds at or below the

established speed limit.

• Parking patterns have been slightly altered by berms in that drivers tend to park

on or downstream of berms. Recall, as explained in Chapter 3 in the section

“Wilmette Performance Criteria,” that street ponding depths for the design

storm are limited to a maximum of six inches on the street crown and a
9-13

maximum of 12 inches above the gutter invert.

Operation and Maintenance (O&M):

• Much more O&M is needed for effective operation of the street storage system

than was practiced prior to construction of the system.

• Before the street storage system, catch basin sumps were cleaned about once

every three years. Now they are cleaned annually. Some sumps are probably

too shallow.

• If precipitation lasts more than a couple of hours, crews usually are called out

to remove blockage of catch basin grates which is typically caused by leaves. 

Crews drive the streets after most rainfalls.

• Berms have not interfered with snow plowing and street sweeping operations.

• Some flow regulators have become totally or partially plugged. Causes include

shallow catch basin sumps and leaves being raked into catch basins by area

residents. A negative result is stormwater being ponded on streets until the

blockage is removed by maintenance personnel. This problem was resolved

with a two step modification. Visualize an inlet-catch basin structure at the curb

line connected by a pipe to a manhole on the combined sewer. The first step

in the modification was to remove the hanging trap from the catch basin end of

the connecting pipe. The second step, as shown in Figure 9-1, was to add a

shear gate to the outfall end of the connecting pipe, that is, in the manhole on

the combined sewer. The shear gate is normally kept in the closed position but

contains an orifice sized to provide the allowable maximum flow of stormwater

into the combined sewer. If the orifice becomes blocked, the handle mounted

above it is used to open the shear gate and release the debris.

Downspout Disconnection:

• Some property owners objected to the effort and cost of downspout

disconnection.
8”FLEXIBLE BOOT

8”DUCTILE IRON PIPE

8”BAND SEAL

C O U PLIN G

8”PVC PIPE

FRO M CATCH

BASIN

H AND LE

ORIFIC E

SHEAR G ATE

BO LTED FLAN G E

CO NNECTIO N

COM BINED

SEW ER

Figure 9-1. Shear gate with orifice flow regulator as used in Wilmette, IL.

9-14
9-15

functioning—and malfunctioning—of combined sewer systems when receiving

high rates of stormwater runoff. They gained more appreciation of the cause

and effect relationship between stormwater runoff and basement flooding.

Pavement Deterioration

• No pavement deterioration was reported. However, the Wilmette street

storage system has only been in place for several years. No streets segments

on which berms are located have been resurfaced since the berms were

constructed.

Icing of Streets When Rainfall or Snowmelt Occurs During Freezing

Temperatures:

• No problems have occurred.

Interaction With Other Government Entities:

• The IEPA supported the Wilmette street storage system by providing low

interest loans under the state’s revolving fund program. 

• The MWRDGC is a strong supporter of the Wilmette project. According, to

Chair Sullivan, the MWRDGC “thinks it’s wonderful.”

Rainfall - Flooding Incidents

Typical Limited Data

Neither Skokie nor Wilmette have kept systematic records of rainfall event

characteristics (e.g., depth, duration, spatial variation, intensity, recurrence interval) or

basement flooding characteristics (e.g., number of buildings affected, location). This is

not unusual. Communities typically have neither the high priority need nor the

equipment and personnel means to obtain and analyze such data on an essentially

continuous basis over an extended period of time (e.g., years).

Instead, the rainfall event - flooding database in most communities is sporadic. It tends

to focus on major rainfall events because they are more likely to cause problems. 

Flooding incident data is typically derived from citizen complaints and is limited in detail. 

Under favorable circumstances, such information consists of the number of complaints

received and the corresponding location. Under less favorable circumstances, only

anecdotal information is available.

In spite of the typical paucity of rainfall event - flooding data, some value can be derived

from it in terms of assessing the performance of the system. The purpose of this

• Downspout disconnection helped other citizens understand the
9-16

section is to present and interpret some of the limited rainfall event and flooding data

that are available for the case study communities.

June 20 - 21, 1987 Rainfall - Flooding Event in Skokie

This event occurred during the special HSSD post-construction monitoring program. 

Construction of the HSSD street storage system was completed in April 1987. The

monitoring program was conducted within the 1255 acre HSSD from June through

September 1987. The monitoring program’s purpose was to assess the performance of

the street storage system and determine causes of scattered residual flooding

(Donohue, 1988, p. 1-1).

The event was determined to have a recurrence interval of 10 years on the east side

community and one year on the west side (Donohue, 1988, p. 5-1).

Village officials received about 20 reports of flooding as a result of the June 1987 event. 

Most reported problems were in the eastern portion of the district. “Complaints included

sewer backups; street ponding areas too deep and extending into yards; and basement

flooding” (Donohue, 1988, p. 5-1, 5-4). At that time, approximately 4600 single family

residences were in the HSSD based on proportioning the community’s single family

residences according to sewer district areas.

The system had performed very well based, in part, on the small number of complaints

relative to the number of single family residences. Furthermore, the number of HSSD

complaints with the street storage system in place was minuscule compared to the prestreet storage system flooding problems described in Chapter 2.

However, given that this storm event was within the 10-year recurrence interval design

of the street storage system, a high degree of performance is expected. Causes of

flooding were determined to be the intentional absence of flow regulators on some

arterial streets, incorrect flow regulator sizes, improper berm construction and

obstructions in existing combined sewers. Specific corrective actions were

recommended (Donohue, 1988, p. 6-1).

August 13 - 14, 1987 Rainfall - Flooding Event in Skokie

Also occurring during the special four month HSSD post-construction monitoring

program, this event greatly exceeded the design criteria for the street storage system. 

A total of 7.5 inches of rainfall fell in 11 hours over an 18 hour period. The estimated

recurrence interval was 300 years (Donohue, 1988, p. 4-1). In addition to the extreme

rainfall, an extreme high stage occurred on the North Shore Channel, the ultimate

receiving stream for the HSSD. Backwater effects of this stage, which was four feet

higher than the stage used in designing the street storage system, probably caused

some of the flooding (Donohue, 1988, p. 5-4).
9-17

Given the extreme severity of the August 13-14, 1987 rainfall relative to the design

conditions, the event provided an opportunity to assess the robustness of the street

storage system. About 85 reports of flooding within the HSSD were received by Skokie

officials. As with the June 1987 event, complaints included sewer backups, excessive

street ponding and basement flooding. Conclusion: The system performed very well

given that the storm greatly exceeded the design conditions.

August 4, 1989 Rainfall - Flooding Event in Skokie and Wilmette, IL

According to Skokie personnel (Rigoni, 1989), the August 4, 1989 storm generated 54

complaints from residents of the 1255 acre HSSD. Recall that approximately 4600

single family residences were in the HSSD. Therefore, flooding was reported for about

one percent of the residences. The complaints appeared to be “spread across the

entire HSSD without any noticeable pattern.”

For comparison purposes Wilmette which, as explained in Chapter 2 is immediately

north of Skokie, experienced widespread basement flooding as a result of the same

August 1989 storm. Based on a postcard survey, nearly 800 buildings, or 23% of the

total in the CSS, were flooded (SEC Donohue, 1992, p. 2). About 0.63 structures per

acre in Wilmette reported basement flooding.

While Skokie was progressing with its street storage system, Wilmette had not yet

begun. Recall that Skokie residents reported 54 basement floodings throughout the

HSSD in their CSS or about 0.04 per acre. Therefore, the density of reported flooded

basements in Wilmette’s CSS, which did not yet have a street storage system, was

about 16 times that of Skokie which had a street storage system in place in the HSSD.

In response to Skokie’s request, Donohue & Associates “...reviewed the reported

basement flooding problems... and evaluated possible causes...” (Raasch, 1989a). 

Contrary to the initial view that the flooding incidents lacked “any noticeable pattern,”

the Donohue analysis concluded that (Raasch, 1989a):

The largest cause of the continued flooding

problems was identified as runoff from streets

which do not have flow regulators to control

the rate at which runoff enters the sewer

system.

The review letter goes on to explain that Skokie and Donohue had decided during the

planning and design of the HSSD street storage system that “stormwater runoff on

selected streets or street segments would not be controlled with flow regulators

because intentional ponding was not desirable.” Streets or street segments where

intentional street storage was deemed undesirable fell into three categories. They were

streets or street segments:

• with high traffic volumes.
9-18

• under the jurisdiction of Cook County or IDOT, two government entities that

do not allow the new street storage technology.

• on Skokie borders where street storage on the Skokie side of a street might

adversely affect neighboring communities.

In addition, street storage was not applied to those few streets or street segments

served by separate sanitary sewers. Other supplemental circumstances cited in the

Donohue letter were the possible impact of isolated combined sewage flow from

outside the HSSD, contributions of parks which were assumed in the system design to

not contribute runoff, and the recognition that some downspouts had not been

disconnected from the CSS.

To reiterate, the conclusion of reviewing the August 4, 1989 rainfall - flooding event was

that the scattered basement flooding incidents were attributed to the absence of street

storage on some streets and street segments plus other factors. Stated differently,

basement flooding was not caused by a failure of the street storage technology but

rather by the “failure” to apply it totally to the HSSD.

The Donohue review concluded recommending various refinements and remedial

actions. The principal suggestion was to revisit the original reasons for not applying

street storage to some streets and street segments and, if appropriate, add street

storage.

May 8, 1996 Rainfall - Flooding Event in Skokie

This rainfall was spatially varied with the most severe rainfall segment being 2.0 inches

in just over an hour at the west end of the HSSD which was an eight-year recurrence

interval. Wet antecedent soil conditions prevailed, because of intermittent rainfall over

the preceding two days, which increased the volume of stormwater runoff.

About 75 basement flooding calls were received from across the community with

approximately two-thirds occurring in the HSSD. Recall that there are about 20,000

single family residences in Skokie. If all 75 basement flooding complaints were from

single family residents, then basement flooding was reported for about 0.4% of the

residences. Factors causing basement flooding included unregulated inlets on IDOT

arterials, wet antecedent moisture conditions, and the fact that, as of 1996, the street

storage system was still being implemented in the MSSD and the ELSSD (Carr, 1999).

August 5, 1999 Rainfall - Flooding Event in Skokie

This rainfall was of one to three hours duration, as measured at five rain gauge

locations in Skokie. The event was rated as having a one to 16-year recurrence interval

depending on location. The storm was most severe in the HSSD. 

Of the complaints received, 72 were determined to be basement flooding caused by

back-up of combined sewage through floor drains. Most were in the HSSD and MSSD. 
9-19

Given the small number of complaints, the street storage system performed well in light

of the severity of the storm. It exceeded the 10-year recurrence interval design criterion

for the street storage system. Additional explanatory factors include those noted under

the discussion of the May 8, 1996 event. They were unregulated inlets on the IDOT

arterials and the on-going construction of the street storage system in the ELSSD (Carr,

1999).

Economic and Financial Impact on Skokie

Fishman (1998) studied the history of Skokie’s street storage project with emphasis on

how it was financed (as discussed in Chapter 5) and on the financial and economic well

being of the community. He notes the project was the most expensive ever undertaken

by Skokie. His findings highlight another dimension of the positive performance of the

street storage system in that it significantly enhanced the community’s economic and

financial status.

Already at the beginning of the street storage project, Skokie had earned “high credit

ratings” because of excellent financial management. It was “one of only 232

municipalities in the nation with Moody’s coveted Aa2 rating.” Moody’s refers to

Moody’s Investor Services, an agency that rates a community’s financial health for the

benefit of bond investors (Fishman, 1998, pp. 181-182). Now with the street storage

project almost completely implemented, “...Skokie’s credit rating has been raised

another notch by Moody’s...” apparently based, in part, in the success of the flood

control efforts (Fishman, 1998, p. 186).

Economic benefits of the street storage system include rejuvenation of downtown

businesses. Fishman (1998, p. 186) concluded that:

Downtown Skokie, where errant water once

drove businesses away, no longer looks

dilapidated; instead, it now resembles the

handsome, high-rent business districts of the

surrounding suburbs...

Individual homeowners have also reaped economic benefits. Anecdotal evidence from

real estate agents suggests that the street storage project has added $40,000 to the

value of an average house (Fishman, 1998, p. 186). The bottom line, according to

Fishman (1998, p. 178), is that “Skokie is cleaner, safer and much richer” as a result of

the street storage system.
9-20

Potential Impact of a Street Storage System on the Frequency and Volume of

Combined Sewer Overflows

Chapter 1 of this manual explains that one of the initiatives undertaken during the

preparation of this manual is an exploratory analysis of the street storage system

technology on the volume and frequency of CSOs and peak flows at wastewater

treatment plants. Reductions in CSO volume and frequency and wastewater treatment

plant peak flows would enhance the performance of the street storage system.

The exploratory analysis is documented in Appendix F. Included are a description of

the methodology, presentation of results, and conclusions. Findings of the exploratory

study suggests that street storage systems have the potential to provide benefits

beyond mitigating basement flooding. Street storage technology may be able to

significantly reduce the volume and frequency of CSOs and peak flows at wastewater

treatment plants. 

wp/epastch9
10-1

Chapter 10

Discussion

Lessons Learned: How Other Communities Might Benefit From a Street Storage

System

In keeping with the theme of this manual—possible applicability of street storage as a

cost-effective solution to CSS problems in many communities—this chapter begins with

a lessons learned section. The lessons flow from ideas and information presented in

preceding chapters. The lessons learned section is directed primarily at elected and

appointed officials in communities having CSS flooding and/or overflow problems. For

convenience sake, the lessons learned are summarized here by the following six

categories:

• Analysis and Design

• Regulatory Compliance and Project Financing

• Stakeholder Involvement

• Evaluating System Performance

• Operation and Maintenance

Lessons Learned About Analysis and Design

1. Establish and obtain concurrence on system performance criteria

before beginning the analysis and design process. Involve stakeholders in

defining the desired level of service.

2. Initial studies of CSS problems should focus on finding and defining the

causes. This diagnostic step should look beyond symptoms and seek out

causes. Computer modeling is likely to be needed given the complexity of

the typical CSS. Failure to conduct a thorough system analysis may lead to

subsequent misguided efforts targeted at solving the “wrong problem.”

3. Consider, especially at the outset of the planning and preliminary design

phase, a wide range of potential solutions. Do not presume that

traditional, and very costly solutions, like separation, relief sewers and

tunnels are necessarily needed. Several to many years elapsed while

Skokie and Wilmette conducted a series of studies that contemplated only
10-2

traditional solutions to their CSS problems.

4. Adopt, at least at the beginning of the analysis and design effort, a

multipurpose posture. Become aware of and define the causes of all CSS

problems—not just CSOs or basement flooding. Thinking globally is more

likely to lead to a cost effective, multipurpose project. 

5. Use a phased approach to the concept through construction process. This

optimizes technical refinements and earns stakeholder acceptance.

6. Carefully prioritize the phases. Consider factors such as proceeding

downstream in each watershed, consistency with screening criteria

(Appendix B), severity of problems, stakeholder input, and windows of

opportunity.

7. In CSSs, view streets as potential partial solutions to flooding, CSO and

other problems. Given the typical low longitudinal grades of streets in CSS,

streets have significant potential storage capacity in a retrofit scenario.

8. Consider integrating the stormwater berm function and the speed hump

function into one stormwater management-speed control structure.

9. Avoid mechanical-electrical controls. Try to develop a simple, gravity

driven stormwater storage system.

10. Select flow regulators having a very low probability of plugging and

offering ease of maintenance.

Lessons Learned About Regulatory Compliance and Project Financing 

1. View regulations positively. For example, they often help support a

community’s eligibility claim for external funding in the form of loans and

grants from regulatory agencies.

2. Seek a comprehensive and innovative technical approach because it is

most likely to attract external funding.

3. Explore a wide range of established funding sources and seek ways to

meet the objectives of each. Investigate state and federal agencies as

sources of project grants and low interest, long term loans. Skokie, for

example received external financial assistance from IEPA, IDOT and Build

Illinois sources.

4. Consider seeking financial support in the form of a site specific line item

appropriation from the U.S. Congress. Having a distinctive project helps
10-3

as does a team approach involving the community, its engineer, and state

and congressional representatives.

5. Phase the project because this enables the community staff and their

consultants to seek and leverage external financing in an optimum fashion. 

This approach avoids needing a massive amount of funds in a short period

of time and allows “small wins” to spark new project and funding supporters.

6. Establish a downspout disconnection program using a combination of

education and ordinance enforcement. Expect the program to reduce

stormwater flow into the CSS and to increase citizen understanding of the

cause and effect relationship between stormwater and CSS surcharging.

7. Create a stormwater control ordinance. While it won’t mitigate existing

CSS problems it can prevent exacerbation of those problems.

Lessons Learned About Stakeholder Involvement

1. Recognize that a street storage project has many and varied

stakeholders. This occurs because of the large areal extent of such a

project and because of regulatory compliance needs and external funding

possibilities.

2. Proactively plan, budget for and implement a stakeholder interaction

program. Begin at the outset of the street storage program and continue

through the program. Avoid a reactive position. Both Skokie and Wilmette

used this proactive, continuous approach.

3. Use a variety of communication mechanisms. Examples are

informational meetings, focus groups, surveys, newspaper and newsletter

articles, television and radio programs and websites.

4. Anticipate and respond proactively to likely initial negative reaction to

intentional storing of stormwater on streets. Note the streets often flood

anyway in an uncontrolled fashion, that street storage uses highly controlled,

temporary ponding and that stormwater in streets is preferred over combined

sewage in basements.

5. Expect and be prepared to proactively respond to initial negative

reaction to stormwater berms. They are likely to be incorrectly confused

with speed bumps. Explain that engineered speed humps (not bumps) are

widely used in urban areas throughout the U.S. and that stormwater berms

cause even less driver discomfort than speed humps.
10-4

Lessons Learned About Evaluating System Performance

1. Think broadly when choosing criteria to evaluate the performance of a

street storage system. In Skokie, for example, the system performed very

well in reducing basement flooding. It also performed very well in that it had

a favorable economic impact on the community.

2. Obtain input from all stakeholders. Examples are elected and appointed

officials, citizens, business people, operation and maintenance personnel,

emergency vehicle operators, finance experts, and regulators.

3. Use the number and location of citizen complaints received during and

after storm events, along with storm severity data, as an index of system

performance. Consider doing pre- and post-project surveys.

Lessons Learned About Operation and Maintenance

1. Recognize that much more system wide maintenance is likely to be

needed once a street storage system is installed. Maintenance that may

have been optional before the street storage system, such as catch basin

cleaning, is mandatory with the street storage system in place.

2. Develop an operation and maintenance manual or other written

guidelines to encourage a systematic approach.

Criteria for Screening the Applicability of Street Storage

Purpose of Screening Criteria

Based largely on ideas and information presented in this manual, a set of street storage

screening criteria were created. These criteria appear as Appendix B. They are offered

for possible use by municipal officials and their consultants in making a preliminary

determination about the likely applicability of street storage as a solution to CSS

flooding and/or overflow problems in a particular community. Also included in the

screening criteria are sections for screening sanitary sewer and storm water systems. 

These are included, because as noted in this manual, the street storage system could

be used to solve wet weather problems in sanitary sewer and stormwater systems. 
10-5

Assume that application of the preliminary screening criteria suggests that street

storage may be suited to a particular community, or a portion of the community. The

next steps might include, as they were in Skokie, selection of a pilot area; data

collection; hydrologic-hydraulic modeling, possibly including water quality modeling, with

and without street storage. If street storage continues to be promising, then the effort

might move to preliminary engineering, cost estimating, comparison to other options

and expansion to other areas. A detailed discussion of the street storage analysis and

design process is presented in Chapter 3.

Qualifications of Evaluators

Community officials, consultants or other persons responsible for applying the

screening criteria included as Appendix B should be very knowledgeable about the

physical aspects of the community. If they are, very little time—a matter of hours—will

be needed to fill in the form which follows and assess its significance. With few

exceptions, such as the short general information section, a simple and quick “checkoff” format is used.

In order to appreciate why certain information is being requested, individuals involved in

the screening should understand the premise, components, and benefits of street

storage. For that reason, these three aspects of street storage are summarized at the

beginning of the screening instrument.

Interpreting the Screening Information

Assume that the evaluator is, as suggested, knowledgeable about the physical features

of the community. Further assume that the evaluator understands, as also suggested,

the premise, components and benefits of a street storage system. Then the evaluator

should be in a good position to judge whether or not street storage is likely to be

applicable. If there is uncertainty, advice could be obtained from personnel in a

community that has a street storage system. Another approach would be a request

assistance from an engineering consultant experienced with street storage.

wp/epastch10
11-1

Chapter 11

Conclusions and Recommendations

Street Storage: A New Technology for Affordable Mitigation of CSS Problems

Street storage, as documented in this manual using a largely case study approach, is a

relatively new and promising concept. Proven to be technically and cost effective in the

few communities where it has been systematically applied, street storage is becoming

one more technology in the array of technologies available for remedial or preventive

actions in CSSs.

Unlike traditional solutions to CSS problems, street storage may provide benefits that

transcend CSO control. That is, street storage has the potential to provide multiple

benefits in CSS communities. The first is mitigation of basement flooding caused by

surcharging of combined sewers. This potential benefit has been clearly demonstrated

by years of experience in Skokie, and Wilmette, IL. 

The second problem that may be mitigated by the street storage system is CSOs and

excessive peak flows at WWTPs. Preliminary modeling studies conducted as part of

this case study project suggest that street storage alone or in combination with

traditional approaches, may cost effectively reduce the annual number and volume of

overflows.

Because a street storage system targets stormwater for control, the third benefit is the

potential to mitigate other stormwater related problems. Examples are inflow to sanitary

sewers and stormwater flooding.

Finally, because a street storage system contains many small storage facilities,

scattered throughout a system, it has the potential to manage non-point source

pollution. This observation is based on the premise that suspended solids are a major

component of non-point source pollution and that other potential pollutants tend to be

absorbed onto or adsorbed into the solids. The numerous well-maintained sumps in a

street storage system provide a means for removing solids and other pollutants in

stormwater. When the street storage approach is planned early and carefully tied to

water quality and health benefits, state revolving fund (low interest loan) eligibility can

be obtained.

Recommended Research
11-2

Achieving the full potential of street storage for mitigation of flooding and for other

purposes requires research. Presented here are recommendations, informed by this

case study manual, for street storage research.

Integration of Speed Humps and Street Berms

Street berms, one component of the street storage system, are physically similar to

speed humps, which have proven to be effective devices for controlling vehicular

speeds on urban streets. This idea is developed in Chapter 3 in the section titled

“Berms and Humps: Different Functions But Similar Form.”

While both speed bumps and street berms have been independently designed by civil

engineers and both have been constructed on urban streets, they apparently have

never been planned and designed in an integrated fashion to control vehicles and wet

weather flow. This conclusion is based on the literature review and information search

conducted for this case study. No evidence was found of traffic specialists and wet

weather specialists teaming to design an integrated hump-berm system.

Several possible explanations for this absence of a connection between speed humps

and street berms may be offered. First, street berms are relatively new and, therefore,

there has been little opportunity for a collaboration between hump and berm designers. 

Second, a traditional principle of street and highway design is to remove stormwater

and snowmelt as quickly as possible from and beneath the pavement surface. 

Reasons include vehicular safety and prevention of damage to pavements and their

bases. Therefore, the thought of intentionally storing water on a street may be viewed,

at least initially, as unacceptable. Recall that no incidents of risk to vehicles or damage

to pavement as a result of properly designed street storage of stormwater have been

reported in Skokie or Wilmette.

Therefore, preliminary research into the technical and economic feasibility of the 

integrating planning and design of speed humps and street berms is

recommended. Each component has proven to be cost-effective and that cost

effectiveness might be enhanced if the two devices are part of an integrated design.

Joint application of humps for vehicle speed control and berms for stormwater control

should be examined in two nodes. One is retrofitting existing urban areas where speed

control and wet weather flow management are needed. Retrofitting is usually the way

these two devices are typically separately implemented. The other is integrating the

design of the form and function of humps and berms into new urban development to

optimize traffic and stormwater management.

Envisioned are traditional looking concrete or asphalt streets in a new development

which, on closer examination, are seen to include numerous berm-hump structures. 
11-3

Strategically placed and configured, the berm-hump structures were planned and

designed for the dual purpose of stormwater runoff vehicular speed management.

The recommended preliminary research into the integration of berms and humps

should include consideration of planning and design criteria and methodologies, public

agency acceptance, public acceptance, constructability, cost, and maintenance.

Street Storage to Reduce CSOs and Peak Flows at WWTPs

As noted, special hydrologic-hydraulic modeling conducted for this case study project

suggests that the street storage technology may help to significantly reduce the annual

number and volume of CSOs. Given the proven capability of a street storage system to

cost-effectively mitigate basement flooding, the need for some communities to mitigate

both basement flooding and CSOs, and the limited funds available to communities, the

possibility of using the street storage technology to cost-effectively solve two or more

problems warrants further study.

Consider, for example, a community where end-of-pipe storage is being considered to

mitigate CSOs. Assume the community also has a basement flooding problem. A

street storage system, implemented alone or in combination with reduced end-of-pipe

storage, might provide the most cost-effective overall solution to the hypothetical

community’s two problems. Therefore, additional primarily modeling studies of the

role of street storage in reducing CSOs and peak flows at WWTPs is

recommended. The approach described in Appendix F is suggested, that is, select

actual CSSs and use computer modeling to determine the annual frequency and

volume of CSOs and the magnitude and frequency of peak flows with and without street

storage systems. These modeling studies could be integrated with the modeling

studies suggested under the next recommended research topic.

Costs and Benefits of Street Storage Versus Traditional Approaches

The Skokie and Wilmette case studies suggest that street storage, where physically

feasible, is likely to be much less costly than sewer separation and relief sewers in

solving basement and other flooding. Stated differently, if basement and surface

flooding is the only or principal CSS problem faced by a community, economics

indicates that street storage should be viewed, from the outset, as a potential solution. 

So should separation and any other potential solution. If CSOs are a problem, with or

without basement and other flooding, street storage should again, because of costs, be

considered as an option, either alone or in combination with traditional technologies.

Needed is a rigorous comparison of the costs and benefits of street storage, sewer

separation, relief sewers, and end-of-pipe storage. While tangible and intangible costs

are obviously important in such a comparison, tangible and intangible benefits also

must be considered. This is because traditional CSS remedial methods tend to be
11-4

single purpose (usually reduction of CSOs), whereas street storage is likely to be

multiple purpose. The lower cost of street storage coupled with more benefits may

make yield a very high economic advantage. However, relevant data, information and

insight are needed.

Therefore, research into the tangible and intangible costs and benefits of street

storage compared to traditional approaches is recommended. One approach

would be to retrofit, “on paper,” street storage into one or more CSSs in which sewer

separation, relief sewers, or end-of-pipe storage has already been applied. Determine

tangible and intangible retrofit costs and compare to actual costs already incurred. 

Similarly identify tangible and intangible benefits. Draw conclusions based on the costs

and benefits. Another approach would be to draw on historic tangible cost data for all

types of methodologies. Normalize the costs by presenting them on a unit cost basis

where the units might be acres, buildings, or persons. Again, make comparisons.

Further Improvement to Hanging Traps

Hanging traps have proven, based on years of experience in Skokie and Wilmette, IL,

to be a very effective way of controlling the rate of flow from catchbasins into combined

sewers. Positive attributes include low cost, very little maintenance and ease of

replacement. As noted in the Chapter 9 section titled “Summary of Interviews With

Skokie, IL Officials,” maintenance personnel prefer the simple, low cost hanging trap

flow regulators over the much more costly vortex regulators.

More hanging trap regulators could be used if the minimum orifice diameter for hanging

traps could be reduced to one inch. Furthermore, as explained in Chapter 9, this might

be possible if the hanging traps were fitted with a “bubble” or hemispherically shaped

screen or grill. This screen or grill would prevent debris from reaching and blocking the

small orifice.

Therefore, research leading to development of an effective, low cost screen or

grill for hanging trap regulators is recommended. Various configurations could be

performance tested in a laboratory setting. Testing should include various sizes and

shapes of sumps, recognizing that sump depth and shape probably affect hanging trap

performance. A promising subset could then be field tested.

The hanging trap research might be extended to include optimizing the entire catch

basin. Water quality management would be the focus of this part of the research. For

ideas on improving catch basins, see Grottker (1989). There may be room for

improvement. Consider this conclusion based on Swiss studies (Conradin, 1989):

...the construction and operation of catch

basins is not really feasible from the economic

point of view. Nor would catch basins probably
11-5

have much justification in the combined sewer

system, for ecological reasons, when streets

are cleaned frequently by the vacuum method. 

Street Storage as Part of New Combined Sewer Systems

Since the 1930's and 1940's, U.S. sewage policy has embraced constructing separate,

as opposed to combined, sewer systems in newly urbanizing areas (Burian et al, 1999,

p. 7). Selection of this policy for new urban areas led to some major sewer separation

projects in the CSS portions of U.S. communities. Examples are Minneapolis-St. Paul,

MN and Hartford, CT (AMSA, 1994, p. 17).

While separate sewers have been the “system of choice” in the U.S. for several

decades, which may appear to be a long time, CSSs have been used throughout

western and eastern civilizations for many centuries. As an example, Burian et al

(1999, p. 4) states:

The Indus civilization, circa 3000 BC, presents

one example of a sewage system ahead of its

time. The dwellers of the city of Mohenjo-Daro

(now part of West Pakistan) used a simple

sanitary sewer system and had drains to

remove stormwater from the streets. The ruins

of this ancient system illustrate care taken to

construct the sewers that would make the

engineer of today envious. One feature of

note was the use of a cunette in the storm

drain to accommodate sanitary wastewater

flows, while the remaining capacity of the

channel was available for WWF.

Furthermore, CSSs are being constructed today in various countries. Examples are

Germany, Japan and Switzerland. Rather than continue to embrace a rigid SSS or

CSS stance, there appears to be some interest in the U.S. and elsewhere to consider

CSSs for certain types of new development (Burian et at., 1999, p. 11).

Interest in CSS for new development gets added impetus when the adverse water

quality impact of stormwater runoff is considered. With a CSS, at least some of the

stormwater would be captured and routed through treatment before release into the

receiving waters. Using a portion of Elizabeth, NJ, Kaufman and Lai (1978) studied

various types of sewer systems for pollution abatement and flood control purposes. 

Hypothetical systems studied were a conventional separate storm and sanitary sewer

system; a conventional CSS; and an advanced CSS meaning that it included in-pipe

storage, satellite storage, and controlled flow routing. Unlike the street storage system
11-6

described in this manual, storage meant storage of combined sewage, not stormwater. 

One conclusion with respect to the advanced CSS was that a “combined sewer system

can be designed to discharge less pollutant than a conventional separate system in

which the storm sewers discharge all urban runoff directly to water courses” (Kaufman

and Lai, 1978, p. 4). 

Given the apparent openness to at least considering CSSs in some types of new urban

development, the street storage technology becomes even more relevant. Its potential

function in new CSSs would be to reduce peak flows of stormwater into the CSS thus

reducing the size and cost of the combined sewers.

Therefore, integrating street storage into any known proposed or on-going

studies of new CSS is recommended. If such studies are not proposed or underway,

they should be.

Impact of a Street Storage System on Non-Point Source Pollution

As noted earlier in this chapter, the many well maintained sumps strategically placed

around a street storage system offer the potential to remove suspended solids as well

as absorbed and adsorbed potential pollutants from stormwater. This suggests the

value of knowing the pollutant removal performance of street storage systems for

possible multipurpose use in existing or new CSS and separate sewer systems. 

Therefore, research into the pollutant removal effectiveness of street storage

systems is recommended. This research might include computer modeling,

laboratory, and field monitoring elements.

wp/epastch11
A-1

Appendix A

Questions Used to

Prompt Discussion in

Interviews of Skokie Officials

1. Intentionally storing stormwater on streets is unusual, but, in your case, effective. 

How do you explain the benefits of street storage to citizens and/or elected

officials? Stated differently, how do you know that street storage “works?”

2. In your view, what are the key guiding principles in dealing with the public on

problems and solutions in the public works field?

3. Street and supplemental storage of stormwater seems to be a cost-effective

(lowest cost) solution to basement flooding in Skokie. If you could go back to the

beginning of the project (early, 1980's), would you do it again? Or would you

“hold out” for a more traditional and more costlier solution?

4. When street storage of stormwater was initially proposed, concern was expressed

over accelerated deterioration of pavement. What is your experience?

5. When street storage of stormwater was initially proposed, concern was expressed

over dangerous icing of streets during freezing temperatures. What is your

experience?

6. Are you aware of any accidents caused by standing water?

7. When street storage of stormwater was initially proposed, concern was expressed

over interference with normal movement of vehicles. What is your experience?

8. When street storage of stormwater was initially proposed, concern was expressed

over interference with operation of emergency vehicles (e.g., police cars, fire

engines). What is your experience?
A-2

9. Are you aware of any damage to vehicles directly related to the system or its

components?

10. What is the weakest “link” (e.g., hanging traps, berms, subsurface tanks, etc.) in

the physical system?

11. Has the Village encountered any legal (e.g., liability) problems as a direct result of

street storage?

12. Street and related storage of stormwater typically requires careful maintenance of

the drainage system. Examples include keeping inlet grates clear of debris,

removing sediment and other deposits from catch basin sumps, and cleaning

clogged flow regulators. To what extent has increased maintenance been a

financial/personnel burden?

13. How has your method of resolving basement flooding been received by

regulatory/operating agencies? That is, has your approach been an advantage,

disadvantage or “wash” with other governmental units?

14. How have you funded your “street storage” system? Anything

special/different/unique about this means of funding vis-a-vis other public works

projects?

15. Have there been any favorable or unfavorable effects on traffic flow such as

excessive speed reduction and unwanted diversion of vehicles to other streets?

wp/epastappa
B-1

Appendix B

Criteria

For

Screening Applicability

Of

Street Storage

Note: Before using this screening instrument, please read the section in Chapter 10 

titled “Criteria for Screening the Applicability of Street Storage.” In order to appreciate

why certain information is being requested, the person(s) involved in the screening

should understand the premise, components, and benefits of street storage. For that

reason, these three aspects of street storage are summarized here.

PREMISE OF A STREET STORAGE SYSTEM

Temporarily store stormwater on the surface (off-street and on-street) and, as needed,

below the surface close to the source, that is, where it falls as precipitation and prior to

its entry into the combined, sanitary, or storm sewer system. Accept the full volume of

stormwater runoff into the sewer system but greatly reduce the peak rate of entry of

stormwater into the system.

COMPONENTS OF A STREET STORAGE

• Downspout disconnection to slow down and possibly infiltrate

stormwater

• Off-street surface storage of stormwater (conventional

detention/retention) with regulated outflow

• On-street surface storage with regulated outflow achieved by an

optimum combination of on-street berms and catchbasin flow restrictors

• Sub-surface storage of stormwater (tanks or oversized sewer segments

beneath streets and parking lots) with regulated outlet control using

restrictors
B-2

BENEFITS OF A STREET STORAGE SYSTEM

Street storage technology has the potential, depending on the situation, to costeffectively mitigate one or more of the following wet weather condition problems:

• Basement flooding caused by surcharging of combined and/or sanitary

sewers

• Overflow of combined and/or sanitary sewers and resulting pollution of

receiving waters

• Excessive peak flow at wastewater treatment plants

• Nonpoint source pollution

• Surface flooding caused by stormwater runoff and/or surcharging of

combined or sanitary sewers.

General Information About the Community

1. Name of community/government entity:

__________________________________________________________

2. Name and affiliation of person(s) responsible for conducting screening:

Person Affiliation Telephone

Fax/

______ ________ Email 

__________________ ________________ ____________

__________________ ________________ ____________

__________________ ________________ ____________

__________________ ________________ ____________

3. Dates or period of screening:

__________________________________________________________

4. Population of community/government entity:
B-3

__________________________________________________________

5. Area of community/government entity:

__________________________________________________________

6. Overall longitudinal street grades (select one):

• < 0.2% (0.2 feet per 100 ft. along the street centerline)

• 0.2 < 0.5%

• 0.5 < %

Comment: _________________________________________________

__________________________________________________________

Combined Sewer System Information

QUESTION YES

OR

OFTEN

MAYBE

OR

SOMETIMES

NO

OR

RARELY

COMMENTS

Are combined sewers

present in at least part

of the community?

If the answer to the first

question is “no,” go to

the section titled

“Concluding Comments”

or go to the set of

questions under the

section titled “Sanitary

Sewer System

Information”

If the answer to the first

question is “yes,” the

following questions

apply only to the areas

served by combined

sewers.

Are combined sewers

structurally sound?

Do basements flood

because of combined

sewer surcharging?
B-4

Do streets flood

because of combined

sewer surcharging?

Do combined sewers

overflow into surface

waters?

Are off-street sites

available for surface

detention/retention of

stormwater?

Is nonpoint source

pollution a concern?

Is the wastewater

treatment plant

operating at or over its

treatment capacity?

Is the wastewater

treatment plant

operating at or over its

treatment capacity?

Has the community

already decided on a

solution to its combined

sewer problems or is the

community still “open” to

alternative solutions?

Sanitary Sewer System Information

QUESTION YES

OR

OFTEN

MAYBE

OR

SOMETIMES

NO

OR

RARELY

COMMENTS

Is a separate sanitary

sewer system present in

at least part of the

community?
B-5

If the answer to the first

question is “no,” go to

the section titled

“Concluding Comments”

or go to the set of

questions under the

section titled

“Stormwater System

Information”

If the answer to the first

question is “yes,” the

following questions

apply only to the areas

served by sanitary

sewers.

Are sanitary sewers

structurally sound?

Do basements flood

because of backup or

sanitary sewage?

Do sanitary sewers

overflow into surface

waters?

Is infiltration (of

groundwater) into

sanitary sewers a

problem/cause of

problems?

Is inflow of stormwater

into sanitary sewers a

problem/cause of

problems?

Is the wastewater

treatment plant

operating at or over its

treatment capacity?

Has the community

already decided on a

solution to its sanitary

sewer problems or is the

community “open” to

alternative solutions?
B-6

Stormwater System Information

QUESTION YES

OR

OFTEN

MAYBE

OR

SOMETIMES

NO

OR

RARELY

COMMENTS

Is a separate

stormwater system

present in at least part

of the community?

If the answer to the first

question is “no,” go to

the section titled

“Concluding

Comments.”

If the answer to the first

question is “yes,” the

following questions

apply only to the areas

served by separate

stormwater system.

Are the storm sewers

structurally sound?

Are residential, business

and other buildings and

property damaged by

stormwater?

Are off-street surface

sites available for

surface

detention/retention of

stormwater?

Is nonpoint source

pollution a concern?

Does the community

have an erosion/

sedimentation/

stormwater control

ordinance?

Does the community

have a separate

stormwater service fee?
B-7

Has the community

already decided on a

solution to its

stormwater problems or

is the community “open”

to alternative solutions?

CONCLUDING COMMENTS

Additional ideas/concerns/questions/suggestions/etc.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

wp/epastappb
C-1

Appendix C

Trouble Shooting Guide

for

Underground and Surface Storage Basins

with

Gravity Dewatering

wp/epastappc
C-2

UNDERGROUND AND SURFACE STORAGE BASINS WITH GRAVITY DEWATERING

NORMAL OPERATION, INSPECTION AND TROUBLESHOOTING GUIDE

Skokie, Illinois

NORMAL OPERATION

Storage structures with gravity drainage include relief sewers, underground vaults, and surface storage basins. The normal operating segravity drainage during a storm event is:

 ̃ Rainfall runoff from the streets in these areas drains directly from the inlets to the underground or surface storage basins. ̃ The basins provide additional sotrmwater runoff storage and protection from combined sewer surcharging and basement flooding. ̃ The water is discharged by gravity from the storage basin to the combined sewer system. The discharge rate from the storage ba

restrictor device at the outlet end. A check valve at the outlet pipe prevents backflow of combined sewage into the separated stor

INSPECTION AND TROUBLESHOOTING

CONDITION OBSERVED POSSIBLE CAUSE CORRECTIVE ACTION

 ̃ Streets for basin area flooded Very heavy rainfall filled storage basin.

Associated street inlets plugged.

Extremely heavy rainfall could cause pCheck for free flow of stormwater at inareas. Clear street inlets.

 ̃ Rain stopped, streets not draining Restrictor orifice is clogged

Basin has filled. Combined sewer stillsurcharged.

Check for free discharge at manhole wenters combined sewer system. Open for emergency drainage. Rod or flush or discharge pipe to combined sewer. area with city water.Drainage will resume when combined surcharged. No action needed.

 ̃ Sewage odor after basins have drained Stagnant water in basin. Check valve not

working.

Check manholes with check valve. Chdebris lodged in check valve.

Dry Weather Inspection and Maintenance

 ̃ Inspect street inlets for area basins

(Annually in fall).

Clean out any debris that would inhibit 

 ̃ Inspect condition of check valve and

orifice (Annually in fall).

Clear out any debris lodged in check v

 ̃ Exercise bypass drain valve (Annually in

fall).

With valve open, inspect for accumulaFlush out any excess accumulations w
D-1

Appendix D

Trouble Shooting Guide

for

Stormwater Storage Basins -

Dewatering Pump Stations

wp/epastappd
D-2

STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS

INSPECTION AND TROUBLESHOOTING GUIDE

Skokie, Illinois

CONDITION OBSERVED POSSIBLE CAUSE CORRECTIVE ACTION

STORMWATER BASINSRain Period - Basin Filling ̃ Streets for area basins flooded Very heavy rainfall filled basin.

Associated street inlets plugged.

Extremely heavy rainfall could cause pSecure appropriate traffic controls.Check for free flow of stormwater at inareas. Clear street inlets.

 ̃ Rainfall without basins filling Combined sewers not surcharged. Rain not sufficient to surcharge combi

checking that water level is below dividinlet structures: 8Z.1 - Area 8; 9P.0 - A

 ̃ Area 9 - light rain, combined sewer not

surcharged, pumps running

Pumping low flow from Dempster Street. All flow entering the north basin in Are

must be pumped by the dewatering pucombined sewer on Skokie Boulevard

Rain Over - Basin Draining

 ̃ Rain stopped, basin not gravity draining Restrictor orifice is clogged.

Plug valve failed closed (Area 9)

Check for free discharge at manhole wenters combined sewer system: Area Street at Skokie Boulevard); Area 9 - Sgravity and pumped discharge). Dislorodding or flushing. In Area 8, bypass opened.Depress RESET at control panel to cleremains, open plug valve using manuaservice contractor if valve operator or 
D-3

STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS

INSPECTION AND TROUBLESHOOTING GUIDE

Skokie, Illinois

CONDITION OBSERVED POSSIBLE CAUSE CORRECTIVE ACTION

STORMWATER BASINS (Continued)Basin Draining (Continued) ̃ Basin drained to gravity point, pumps

won’t start

Additional rain surcharged the combinedsewer.Pump Float Switch No. 6 or other controls notworking.

Pumps won’t start if combined sewers that water level is at top of divider wallCheck float condition and levels. Manpike pole. Check for other pump failur

 ̃ Pumps operating, basin not draining Restrictor orifice is clogged.

Pumps not pumping capacity.

See above for no gravity draining.See pumping guidelines below.

 ̃ Sewage odor after basins have drained Stagnant water in siphon. Check valve not

working.

Check manholes with check valve. Chdebris lodged in check valve. Dewatevalve to remove stagnant water.

Dry Weather Inspections

 ̃ Prevent basin drain clogging Clear any accumulated debris from ba

debris from perimeter of basin.
D-4

STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS

INSPECTION AND TROUBLESHOOTING GUIDE

Skokie, Illinois

CONDITION OBSERVED POSSIBLE CAUSE CORRECTIVE ACTION

PUMPING STATIONS ̃ Pump operating with severe noise or

vibration

Pump not seated properly. Pull pump and re-seat on guide rail sy

 ̃ Pumps operating but not pumping

capacity

Pump impeller or volute clogged.Pump discharge clogged.Basin dewatering drain plugged.

Pull pump and unclog.Check first manhole for pump dischargrod out or flush discharge line.Verify by low sump level but considerabasin to pump. Rod out or flush basin alternate pump if necessary.

Panel Alarm Indicators:

 ̃ Pump Fail Power failure.

Other conditions indicated by specific alarmlights:

Pump RESET switch must be depresspumps in AUTOMATIC mode upon respower failure, circuit breaker trip, or anlisted.

 ̃ Pump High Temperature Low cooling oil level.

Debris in impeller.

Pull pump and check cooling oil if pumPull pump and remove debris from imp

 ̃ Pump High Moisture Pump motor seal failed. Pull pump and inspect stator casing fo

service representative if moisture is in 

 ̃ Low Sump Level Low level or normal pump cutout float switch

not working or hung up.

With pumps in AUTOMATIC, use a lonfloats by hand to trip. Check for correcelectrical service contractor if pump floinoperative.

 ̃ High Basin Level Very heavy rainfall filled basin. Extremely heavy rainfall could cause p

Secure appropriate traffic controls.

 ̃ Plug Valve Fail (Area 9) Valve will not reach limit position (open or

close). Debris clogging valve.Limits of valve out of adjustment.

Manually open valve with override and flush out debris.Refer to Limitorque valve operator maservice contractor.
E-1

Appendix E

Standard Maintenance Procedures

for

Submersible Dewatering Pumps -

Stormwater Storage Basins

wp/epastappe
E-2

SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS

STANDARD MAINTENANCE PROCEDURES

Skokie, Illinois

EQUIPMENT CONTRACTORS

PUMP SUPPLIER:Hydroaire Incorporated834 West MadisonChicago, IL 60607Phone: 312-738-3000Fax: 312-738-3226Project No.: AKFL 10280

ELECTRICAL PANEL INSTALLATION

Aldridge Electric28572 N. Bradley RoadLibertyville, IL 60048Phone: 708-680-5200Fax: 708-680-5298

PUMP LIST

LOCATION: AREA 4 AREA 8 AREA 8 ITEM

Pump Tag No.MakeModel No.Impeller No.Impeller SizeHorsepowerFlow, gpmHead, feet

P-4-1, 4-2

Flygt

CP-3085

438

4"

2.0

210

12.0

P-8-1

Flygt

CP-3152

624

10"

14

2250

11.5

P-8-2

Flygt

CP-3102

442

6"

5

450

18.5

SAFETY PRECAUTIONS

1. Always lock out and tag the submersible pumping equipment before removing it from the sump for inspection or maintenance.2. Use only the hoisting equipment recommended by the equipment manufacturer to remove the pumps from the sump.3. Rinse the pump thoroughly with clean water before handling or inspecting the pump.4. The pumps are designed to be removed from the sumps without anyone entering.5. If for any reason it becomes necessary to enter the sump, follow proper confined space entry procedures.6. If checking or changing the oil, hold a rag over the oil casing screw when removing it.
E-3

SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS

STANDARD MAINTENANCE PROCEDURES (Continued) Skokie, Illinois

MAINTENANCE PROCEDURES

DESCRIPTION1. Inspect impeller and volute2. Inspect motor seal for proper oil level and possible

contamination. Replace oil containing water or ifcream-like.

3. Inspect the stator casing.4. Complete pump overhaul

FREQUENCY12 months12 months24 months5 years

LUBRICANT/PARTSCooling OilSeal

REMARKSReplace severely worn impellers. remove debris if needed. Have seimpeller clearance if needed.Use MobIl Whiterex 309 or ordinarIf oil or water is in the stator housinrepresentative.Interval recommended by manufacperformed for Skokie during winter 

STATION INSPECTIONS

1. Inspect stations weekly during wet weather months or more frequently during heavy rain events. Note general condition of structure

grass area, control panel, and signs of forced entry or vandalism.

2. Record the pump hour meter readings and electric meter readings.3. Observe the electrical panel for any alarm conditions: High water level, low water level, high temperature fail, seal leak. Record alar

inspection form.

4. Check bottom of sump for debris buildup. Remove excess debris as required.5. Alternate the pump sequence with the LEAD/LAG switches to obtain equal running time for the pumps at Area 9.

Notes:a. The pump station for Area 8 should always have Pump No. 1 as the lead pump and Pump No. 2 as the lag pump. On this sta

always have unequal run times.

b. When the pumps at the Area 4 station are set in the ALTERNATE position on the control panel, they will automatically alterna

REFERENCEFlygt Model CP Submersible Pump Installation and Maintenance Manual (provided with each pump).Village of Skokie Operation and Maintenance Manual, Stormwater Runoff Control Facilities.
E-4

SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS

INSPECTION FORM

Skokie, Illinois

Hour Meters

Date Pump 1 Pump 2 Electric Meter Comments

PUMP STATION AREA: _________ AREA 4 (OAKTON AND FLORAL)

_________ AREA 8 (GABION POND)_________ AREA 9 (EVANSTON GOLF CLUB)
F-1

Appendix F

Exploratory Analysis

of the

Impact of a Street Storage System

on the

Frequency and Volume

of

Combined Sewer Overflows

Note:

This analysis and its documentation was

prepared by Robert W. Carr, PE and Michael

C. Morgan, PE of Earth Tech.
F-2

Introduction

Street storage has been proven to substantially reduce basement flooding in various

communities.

It is reasonable to expect that street storage would have a positive impact on the

frequency and volume of CSOs and could be used to meet the Nine Minimum Controls

established by EPA. The primary purpose of this study was to complete an analysis to

evaluate the potential benefits of street storage with respect to reductions in the

frequency and volume of CSOs. The analysis was completed using hydrologic and

hydraulic computer modeling to represent the performance of the combined sewer

system. XP-SWMM computer modeling software was utilized to conduct the analysis.

To efficiently perform the analysis, data previously developed for the Village of Skokie

was utilized. The Village of Skokie has implemented a street storage program to

provide 10-year protection from basement flooding. The street storage improvements

were designed to function with TARP (the Tunnel and Reservoir Plan), deep tunnels

constructed to provide an overflow for flows in excess of the interceptor system

capacity. During dry weather, flows go from the Village’s system to the MWRDGC’s

interceptor system. During wet weather, flows fill the interceptor sewer system, and

then overflow into TARP. CSOs occur to the North Shore Channel when the capacity of

the connections between the local systems and TARP is exceeded or when TARP is

full. 

Street storage combined with a deep tunnel solution to sewer capacity problems is

effective in reducing CSOs to waterways, but is not an option in most communities. 

Therefore, the impacts the use of street storage independent of a TARP system need

to be evaluated. This study utilized the data developed for Skokie modified to exclude

TARP and replace it with discharge to a WWTP with CSOs to the adjacent waterway. 

This provided information about a combined sewer system discharging directly to a

WWTP, as is the case for most existing combined sewer systems.

Two scenarios were evaluated in the study. The first scenario consisted of “pre-project”

conditions, or the combined sewer system without implementation of street or

subsurface storage. The second scenario represented conditions with street storage

and subsurface storage that has been implemented in a basin in Skokie with

characteristics representative of other combined sewer areas. The analysis

incorporated flows for dry and wet weather conditions with and without street storage

and was completed using the Emerson Street Sewer District (ESSD) basin of the

Village (see Figure F-1). A 45-year rainfall record was used as the basis for evaluating

potential CSO reductions attainable with street storage. The occurrence of CSOs was

defined using “typical” wastewater treatment plant capacity. The number and volumes

of combined sewer overflows was determined for scenarios with and without the street

storage.
Figure F

1

Sewer Districts in Skokie

F-3
F-4

 

Study Area Description

The Village of Skokie is located adjacent to and directly north of the City of Chicago. 

The 5,510 acre area of the Village is divided into three sewer districts: the 1,255 acre

Howard Street Sewer District (HSSD) in the southern part of the Village; the 2,300 acre

Main Street Sewer District (MSSD) in the central part of the Village; and the 1,955 acre

Emerson and Lake Street Sewer District (ELSSD) in the northern part. As discussed

above, the 840 acre Emerson District was included in this analysis.

Precipitation occurs as rain, sleet, hail, and snow and ranges from showers of trace

quantities to brief intense storms to longer duration rainfall or snowfall events. 

Precipitation is distributed throughout the year with an average annual total of

33.3 inches. Circular 172 prepared by the Illinois State Water Survey (1989) estimates

that for a one hour storm, the 1, 10, and 100 year recurrence interval rainfall amounts

are 1.49, 1.94, and 2.08 inches, respectively. For a 24 hour storm, the 1, 10, and 100

year amounts are 2.21, 3.86 and 6.70 inches, respectively.

Soils in the area are primarily from glacial deposits of the Pleistocene series. These

glacial deposits have an approximate depth 60 feet and consist of many types of

materials. About 25 percent of the study area are sandy soils, while the remainder has

clay soils. Ground water levels tend to remain 10 to 15 feet below ground level in

sandy areas with the exception of isolated perched lenses of shallower ground water. 

The land in the ESSD generally slopes eastward toward the North Shore Channel. 

Slopes vary from 0.1 to 1 percent and the overall slope in many areas of the Village is a

flat 0.2 percent. Surface runoff flows from the front lawn and driveway areas to the

street. Flow in the street is along the curb line and gutters to the nearest inlet. Inlets

are generally located midblock and at intersections. Due to the extremely flat

conditions, few areas have a continuous drainage pattern from block to block. Trunk

sewers in the combined system range in diameter from 30 inches to a maximum of 84

inches. Lateral sewers which are connected to trunk sewers range in diameter from 12

to 27 inches. 

Study Approach

Analysis Objectives

The focus of this study was to quantitatively evaluate the potential benefits of street

storage with respect to control of CSOs. The approach adopted for this study included

components intended to consider “typical” combined sewer systems. The following

study objectives were identified and incorporated into the impact analysis:

1. Evaluate the potential effects of street and underground storage for a typical
F-5

community that contains a combined sewer service area. Use one sewer district in

the Village of Skokie as the basis for the analysis.

2. Assume that an overflow collection system such as TARP does not exist. The flows

discharged from the combined sewer system will be directed to the wastewater

treatment plant or overflow to a receiving stream.

3. Evaluate the effect of street storage on a community’s ability to meet the Nine

Minimum Controls, that have been developed by USEPA for control of CSOs.

4. Evaluate the effect of street storage on the frequency and volume of combined

sewer overflows.

5. Evaluate the effect of street storage on the community’s wastewater treatment

facilities.

Analysis Methodology

As previously discussed, detailed models were developed using SWMM to represent

the performance of the combined sewer system in the ESSD. Models were developed

to simulate performance of the system before and after the runoff control program was

implemented. SWMM is an excellent tool for conducting sewer system analysis,

however there are limitations to using the EXTRAN module of SWMM for continuous

simulation. 

To overcome the limitations of the EXTRAN module while utilizing historical

precipitation, a two part approach was adopted for this analysis. The first part of the

analysis consisted of completing simulations using the SWMM models developed for

scenarios with and without street storage. Simulations were conducted to define the

minimum rainfall event threshold causing combined sewer overflow. Simulations were

completed for both scenarios using rainfall events selected to represent the range of

events contained in the historical series. The results of the simulations were used in

the second part of the analysis, which consisted of deriving CSO statistics from the

entire record of rainfall events. CSO occurrences, volumes and peak flows were

derived based on regression techniques applied to the simulation results of the

strategically selected rainfall events. 

An outline of the procedure used for the impact study is summarized below:

1. Develop SWMM models for the ESSD basin to represent scenarios with and

without street storage.

2. Incorporate dry weather flows quantified from previously conducted flow

monitoring programs.
F-6

3. Incorporate wet weather flows with runoff control facilities.

4. Verify model performance for the 10-year, 6-hour design rainfall event. Adjust

parameters as necessary to correctly represent expected system discharge and

storage volumes for the design event. 

5. Develop model parameters to represent the scenario without runoff control

facilities.

6. Verify model performance for the 10-year, 6-hour design rainfall event using

earlier study results that quantified approximate surcharging depths.

7. Use the RAIN module of SWMM to convert the 45-year historical continuous

precipitation record from the NOAA station at O’Hare International Airport to

defined rainfall events. 

8. Complete model simulations to determine which rainfall events will result in

CSOs for wet weather flows with and without runoff control facilities.

9. Select rainfall events for simulation that are representative of the historical

precipitation record. Complete model simulations for both scenarios using the

selected rainfall events. Tabulate model results to determine CSO peak flow

and CSO volume for each simulated rainfall event simulated.

10. Determine relationship for each scenario between CSO peak flows and CSO

volumes with corresponding rainfall event characteristics. Use defined

relationship to estimate CSO peak flow and CSO volume for all rainfall events in

the 45-year historical series (See no. 7 above).

11. Develop statistics to describe the occurrence of CSO peak flows and CSO

volumes to quantify the effects of street storage on CSOs.

Hydrologic and Hydraulic Computer Modeling

Hydrologic and hydraulic modeling supporting the runoff control program dates back to

the late 1980's. The original analysis of the ESSD was completed in 1987 using the

System Analysis Model (SAM) computer modeling software, which was originally

developed by CH2MHill. The analysis was limited to the major interceptors in the

ESSD. The SAM model was run on a VAX computer system. In 1992, the sewer

system model was converted into the HYDRA model, developed by Pizer, Inc.

XP-SWMM modeling software was used for this analysis. SWMM was selected

because it offers advantages in evaluating CSOs when compared to the capability of

models that were previously used for the ESSD. The hydraulic analysis capability of

the EXTRAN module of SWMM is superior to the other models. For example, SWMM
F-7

explicitly solves the St. Venant equations for each model element at each time step

during the model simulation. The ability to explicitly represent system surcharging,

storage and volume are essential components to evaluating CSOs for a wide range of

rainfall events. 

Model Parameters

Pipe and manhole data (pipe diameters, inverts and lengths, and manhole rim

elevations) were taken from the existing HYDRA model and input into the EXTRAN

module of SWMM. The dry weather flows, consisting of sanitary sewage and infiltration

were input as constant point flows into the EXTRAN module of SWMM. The wet

weather flows from foundation drains (0.007cfs/acre) and existing on-site detention

facilities (41 cfs) were input into the model as a constant flow in the EXTRAN module. 

A flow rate of 2.0 cfs/acre was applied to the identified 26 acres of internal roof drains

using the acreage and the rainfall hyetograph in the RUNOFF module of SWMM. 

Surface stormwater runoff was represented using the RUNOFF module. The ESSD

was divided into 73 subbasins, which were tributary to manholes in the model. The

area and percent impervious values were taken from previously completed analysis. 

The subbasin widths were derived from measurements of each basin and a general

slope of 0.2 percent was used. The regulated catch basin flows were represented in

the EXTRAN module at each manhole by defining orifice links to control release rates

from each storage junction during the analysis. The non-regulated catch basin flows

were developed in the RUNOFF module and directed to the appropriate modeled

manholes in EXTRAN. The storage volume in each basin were determined and input

into the EXTRAN module using the stepwise linear area method.

Dry Weather Flow

Dry weather flows were considered to be sanitary sewage and infiltration. Sanitary

sewage is flow from residential, commercial or industrial buildings. The base average

daily residential flow was estimated based on the land use and the population served. 

A per acre contribution was developed for each type of residential land, single family,

multi-family (2 to 4) and apartments. Residential flows varied from 0.006 to 0.02

cfs/acre. 

The non-residential sanitary flows were divided into industrial and commercial flows.

Commercial flows are those flows from offices, gyms, laundries, schools, and other

commercial buildings. Sanitary flows from commercial buildings were estimated using

the size of the property. Industrial flows are those flows from manufacturing facilities,

warehouses, and other industrial buildings. Sanitary flows from industrial buildings

were also estimated using the size of the property. Commercial and industrial flows

varied from 0.04 - 0.02 cfs/acre. 

Infiltration is primarily groundwater which enters the system through defective pipe and

manholes or other openings. Infiltration tends to be a steady-state flow as far as
F-8

system modeling is concerned. The dry weather flows were all input as constant flows

because these flows are very small as compared to the wet weather flows.

Wet Weather Flows

Wet weather flows were considered to be foundation drains, roof drains, on-site

detention release rates and surface stormwater runoff. The first three components

were determined using flow monitoring and existing data. As part of the flow monitoring

program, foundation drains from individual homes in ESSD were monitored. This data

was determined to be similar to previous foundation flow monitoring data from the

Howard Street and Main Street Sewer Districts. The foundation flow was estimated to

be 0.007 cfs/acre and was input into the model as a constant flow. 

The second wet weather flow component are roof drains. The Village required all

single-family residences to disconnect their downspouts. Buildings without downspouts

were assumed to have internal roof drains. It was decided to allow internal roof drains

to be connected directly to the combined sewer because of the cost to disconnect them. 

A maximum peak flow rate of 2.0 cfs/acre was applied to the identified 26 acres of

internal roof drains. To maintain the rainfall dependent characteristics of flow from roof

drains, the roof area was represented as impervious tributary area in the model.

The third wet weather flow is the flow from existing on-site detention facilities. These

flows were represented by the design outflow rate as provided by the Village. Eighty

one (81) acres of existing on-site detention facilities were identified with a total release

rate of 41 cfs which was input into the model as constant point flows. 

Stormwater Runoff

The first three wet weather flow inputs described above are considered to be fixed

flows, that is these flows can not be regulated or changed. The fourth and final wet

weather flow input is surface stormwater runoff. While the other types of wet weather

flows cannot be regulated, the street storage and subsurface storage system was

designed to control stormwater runoff component of wet weather flow.

Stormwater runoff was divided into two components, regulated catch basin flows and

non-regulated catch basin flows. Regulated catch basin flows require storage of the

surplus water not immediately allowed into the sewer within the project area. The

regulated catch basin flows and associated storage volumes were determined as part of

the runoff control program for the ESSD of Skokie. Non-regulated catch basin areas

allow the runoff from rainfall events up to the 10-year design rainfall event to enter the

sewer system without any restrictions. These non-regulated flows were only allowed on

arterial streets.

Regulated Catch Basin Flows

The first step of the analysis was to determine the capacity of the sewer system
F-9

available for carrying stormwater runoff. The total hydraulic capacity of the sewer

system depends on the quantity of dry and wet weather flows and the level to which a

sewer can surcharge without causing basement flooding or other damage. This

capacity is also affected by the back water effect from limited capacity of downstream

sewers. The maximum allowable rates at which runoff can be released into the sewer

system were determined for all areas of the ESSD. These runoff rates ranged from

0.08 to 1.0 cfs per acre. Using the regulated runoff rate (cfs/acre) and the tributary

area, a maximum allowable regulated flow from each catch basin was determined. 

Results of this analysis formed the basis for the design of the runoff control system and

for determining the sewer capacity available for those areas which could not be

regulated. 

The second step was to determine the location and extent of intentional street ponding

which can be achieved through flow regulators and minor street grade modifications

(berms). Higher flows were allowed on streets with little storage available. Conversely,

on streets which could pond large stormwater volumes, the flows were regulated to use

the available storage capacity. The sewer capacity and the storage analyses were

conducted concurrently with each analysis providing input to the other. The product of

this analysis included delineation of street ponding elevations in allowable areas and

identification of the volume of additional runoff which must be detained in other storage

locations. 

The third step was to site and size the additional storage facilities necessary to store

flows in excess of street ponding capacity and where street ponding was not feasible to

store runoff in excess of the regulated runoff rate. The locations and volumes of

detention facilities needed to store the remaining volume from step two were

determined. This step insured that the runoff control system for the ESSD would

reduce sewer surcharging to prevent sewer backup into the basement during the 10-

year recurrence interval storm.

Non-regulated Catch Basin Flows

The final component of the wet weather flows is the flow from non-regulated catch

basins. These catch basins are located on arterial streets and allow the runoff from a

10-year recurrence interval storm to enter the combined sewer system. The Village

designated the streets within the ESSD that were to be non-regulated streets. 

Currently, the Village has reconsidered this assumption and is installing regulators to

restrict the runoff into the sewer system to that of a 10-year storm.

Wastewater Treatment Plant Description

The Village of Skokie does not own or operate a wastewater treatment plant (WWTP). 

Conveyance and treatment facilities are provided by the MWRDGC. Dry weather flows

from the ESSD discharge to the MWRDGC interceptor located under McCormick

Boulevard. Wet weather flows discharge first to the interceptor sewer system, then to
F-10

the TARP and if TARP is full, then to the North Shore Channel. To determine the

impact of street storage on the number and volumes of CSOs, a theoretical WWTP was

included in the analysis. Earth Tech recently completed a facility plan for the WWTP in

Gary, Indiana. Since Gary has a large combined sewer service area, it was used as a

basis for the theoretical WWTP for the ESSD. Theoretical ESSD flows were developed

by prorating average and peak flows from the Gary WWTP. The Gary WWTP treats an

average of 35.6 cfs on a dry day with a peak WWTP flow of 186 cfs. Flows larger than

186 cfs are bypassed into either the Little Calumet River or the Calumet River. The

average dry weather flow from the ESSD is 12 cfs. Using the same ratio of average dry

weather flow to peak capacity, the peak wet weather flow through the ESSD WWTP

would be 65 cfs. A review of the Skokie flows showed that the flows from on-site

detention facilities add up to 41 cfs. Therefore, the constant flows equal 53 cfs (12 cfs

dry weather and 41 cfs on-site detention facilities. The roof and foundation drains and

regulated catch basins also add additional flow. It was determined that 65 cfs was too

small to use for this analysis. Because many communities with large peaking factors,

both separate and combined systems, ie, Racine, WI, Kenosha, WI, Milwaukee, WI and

the Greater Metropolitan Water Reclamation District of Greater Chicago, IL provide

either storage or a flow through clarifier (typically with disinfection) for a portion of the

flows that exceed the WWTP capacity. Therefore, it was decided to provide a flow

through clarifier to allow the ESSD facility to handle a peak wet weather flow of 100 cfs. 

Therefore, the ESSD treatment facility assumed for this analysis accepts up to 100 cfs

prior to the occurrence of a combined sewer overflow.

Model Verification

Flow Monitoring Program

In 1986, a flow monitoring program was conducted in the ESSD. A total of __ flow

meters, __rain gauges, and two foundation monitors were installed for __ months. This

flow monitoring program provided dry weather and wet weather flow data at strategic

points in the districts. In addition to sewer flows, a foundation drain monitoring program

was also done. This data was used to develop dry weather flows and verify wet

weather flows used in the hydraulic models. The parameter development completed

during previous analysis and observed system performance was used as the basis for

completing the SWMM models used in this analysis.

Design Storm Simulation

In addition to the flow monitoring data described above, simulation of the system design

rainfall event was used for model verification. The 10-year, 6-hour recurrence interval

rainfall event was the design storm for the design of the ESSD runoff control system. 

Therefore, the 10-year, 6-hour rainfall event was simulated. The simulated storage

volumes and flows (sanitary, foundation drains, roof drains, existing on-site detention

facilities, and regulated catch basin flows) were compared and confirmed with expected
F-11

results for the 10-year design storm. The regulated flows were confirmed by comparing

design parameters with simulation results for storage volumes and peak flows at

regulated manholes. The non-regulated catch basin flows were verified when the

simulated peak flow at the outfall matched the design peak flow of 300 cfs. At this point

the model was considered to be verified for use in performing additional analysis.

Combined Sewer Overflow Simulation

As previously discussed, detailed SWMM models were developed to represent the

performance of the combined sewer system in the Emerson Street study area. Models

were developed to simulate performance of the system before and after the runoff

control program was implemented. SWMM is an excellent tool for conducting sewer

system analysis, however there are limitations to using the EXTRAN Block of SWMM

for continuous simulation. Therefore, a two part approach was adopted for this analysis

to utilize the rigorous hydraulic analysis capability of the SWMM EXTRAN Block and

still obtain results for a long term period of recorded precipitation data. The first part of

the analysis consisted of completing simulations using the SWMM models developed

for both the pre-project scenario and the street storage scenario. Simulations were

conducted to define the minimum rainfall event threshold causing combined sewer

overflow. Simulations were then completed for both scenarios for approximately 25

rainfall events. The results of the simulations were used in the second part of the

analysis, which consisted of deriving CSO statistics from the entire record of rainfall

events. CSO occurrences, volumes and peak flows were derived based on the

regression techniques applied to the simulation results of the strategically selected the

rainfall events.

Historic Precipitation Record

Historic precipitation data from the NOAA station at Chicago O’Hare International

Airport (ORD) was obtained for the period WY1949 to WY1993. Initially, the

precipitation record was processed using the RAIN Block of SWMM. The RAIN Block

was used to read the continuous rainfall record and define individual rainfall events. 

For the purpose of this study, a rainfall event was characterized as durations of

measured precipitation surrounded by 12-hour intervals during which precipitation was

not measured. The 12-hour interval was an arbitrary choice and deemed to be a

sufficient recovery time for the Emerson Street system. The continuous record was

processed by the RAIN block to gain information such as rainfall depth, maximum

rainfall intensity and average rainfall intensity to describe each rainfall event. This

information was used to correlate CSO occurrences with defined rainfall events. Table

F-1 presents a summary of the defined rainfall events according to rainfall depth and

maximum rainfall intensity.

The graphs depicted in Figure F-2, F-3 and F-4 were developed using the rainfall

events extracted from the historical precipitation record using the RAIN Block of

SWMM. The graphs include plots of rainfall depth, maximum rainfall intensity and
F-12

average rainfall intensity for the rainfall events defined in the historical record. As one

would expect, the graphs show significant scatter among the simple descriptors such

as rainfall depth and rainfall intensity. However, the graphs do indicate trends, upper

and lower limits and frequency characteristics that describe the historical rainfall events. 

Use of rainfall events from a long term precipitation record was advantageous for a

number of reasons. For example, realistic rainfall patterns and system response is

represented with the use of recorded rainfall events instead of synthetic design rainfall

distributions. The frequent occurrence of CSOs also is better addressed by using a

historical precipitation record to derive frequency and performance statistics than by

using design rainfall events. Verification of the performance of a street storage system

with a variety of rainfall depths, durations and intensities was also an advantage gained

from using recorded rainfall.

Correlation of Combined Sewer Overflows and Rainfall 

Rainfall events from the record were strategically selected to characterize CSO

occurrence for the study area while minimizing the number of simulations required. 

Initially, simulations were conducted to define the minimum rainfall event threshold

causing combined sewer overflow. Simulations were then completed for both scenarios

for approximately 25 rainfall events. The simulated events were selected to be

representative of the variety in rainfall depth, maximum intensity and average intensity

present in the historical precipitation record. Particular emphasis was placed on

simulating rainfall events near the threshold at which overflows occur. This approach

was adopted to define performance for the most frequent rainfall events, which were

also believed to dominate the annual CSO statistics. The results of the simulations

were used as the basis for deriving CSO statistics from the entire record of rainfall

events. Table F-2 includes summary information for the simulated rainfall events and

Table F-3 presents simulation results for each rainfall event.

Table F-1

Rainfall Event Summary

Rainfall

Depth

(inches)

Number of

Occurrences

Cumulative

Subtotals

Maximum

Rainfall

Intensity

(inches/hour)

Number of

Occurrences

Cumulative

Subtotals

10.00 -- -- 10.00 -- --

9.00 1 1 9.00 0 0
F-13

8.00 0 1 8.00 0 0

7.00 0 1 7.00 0 0

6.00 0 1 6.00 0 0

5.00 0 1 5.00 0 0

4.00 5 6 4.00 0 0

3.00 15 21 3.00 1 1

2.50 27 48 2.50 0 1

2.00 37 85 2.00 2 3

1.50 96 181 1.50 13 15

1.00 241 422 1.00 37 52

0.50 575 997 0.50 205 257

0.20 888 1885 0.20 657 914

0.10 624 2509 0.10 687 1601

0.05 490 2999 0.05 689 2290

0.02 532 3531 0.02 761 3051

0.01 280 3811 0.01 413 3464

0.00 456 4267 0.00 805 4267
Figure F-2

Rainfall Depth vs. Maximum Rainfall Intensity

0

0.5

1

1.5

2

2.5

3

3.5

4

0.50 2.50 4.50 6.50 8.50 

Rainfall Depth (in)

Maximum Rainfall 

Intensity (in/hr)

F-14
Figure F-3

Maximum Rainfall Intensity vs. 

Average Rainfall Intensity

01234

0 0.2 0.4 0.6 0.8 1 1.2 

Average Rainfall Intensity (in/hr)

Maximum Rainfall 

Intensity (in/hr)

F-15
Figure F-4

Rainfall Depth vs. Rainfall Intensity

01234

0.50 2.50 4.50 6.50 8.50 

Rainfall Depth (in)

Rainfall Intensity 

(in/hr)

Maximum Intensity (in/hr) Average Intensity (in/hr)

F-16
F-17

Table F-2

Simulated Rainfall Events

Event Start Date Event Duration

(hours)

Event Volume

 (inches)

Maximum

Intensity

(inches/hour)

Average

Intensity

(inches/hour)

3/19/48 19 5.00 2.39 0.26

10/9/69 33 4.68 1.10 0.14

4/24/54 8 3.70 0.57 0.10

8/17/90 10 3.01 1.55 0.15

11/26/90 10 2.98 0.33 0.08

8/31/89 18 2.56 1.85 0.11

8/29/55 16 2.46 0.60 0.22

6/13/50 4 1.99 1.16 0.40

9/24/61 22 1.98 0.46 0.11

11/4/88 7 1.50 0.92 0.30

4/12/83 18 1.49 0.42 0.03

9/15/92 15 1.25 1.19 0.63

6/4/53 23 1.25 0.52 0.06

9/25/93 11 1.25 0.29 0.07

8/17/83 1 1.00 0.74 0.17

11/13/51 5 1.00 0.32 0.07

9/12/77 11 1.00 0.15 0.04

9/17/49 23 0.75 0.42 0.11

3/28/51 5 0.75 0.17 0.01

12/16/87 20 0.75 0.07 0.02

6/20/68 4 0.60 0.60 0.60

9/23/63 18 0.60 0.30 0.10

7/18/57 12 0.60 0.09 0.02

5/27/56 16 0.55 0.51 0.14

7/1/83 3 0.55 0.33 0.06

12/7/78 3 0.55 0.13 0.03
F-18

Table F-3

Overflow Simulation Results

Event Start

Date

Pre-project Scenario Street Storage Scenario

Peak

Overflow

(cfs)

Overflow

Volume

(acre-feet)

Peak

Overflow

(cfs)

Overflow

Volume

(acre-feet)

Overflow

Volume

Reduction

(%)

3/19/48 464.5 115.2 278.3 111.3 3.36

10/9/69 353.1 110.6 229.7 101.3 8.45

4/24/54 116.2 39.0 86.3 35.6 8.72

8/17/90 427.7 67.4 233.7 60.3 10.64

11/26/90 61.8 19.3 55.3 16.9 12.61

8/31/89 418.9 50.1 223.7 44.8 10.60

8/29/55 114.0 31.6 82.7 27.9 11.86

6/13/50 225.7 30.9 150.2 27.2 12.03

9/24/61 66.8 8.8 16.9 0.1 99.06

11/4/88 177.8 19.7 113.3 16.7 15.48

4/12/83 67.1 7.7 -- -- 100.00

9/15/92 199.5 15.7 119.0 12.8 18.58

6/4/53 51.2 5.6 26.0 3.0 45.73

9/25/93 45.1 5.6 33.9 4.2 25.35

8/17/83 141.6 14.4 95.9 11.1 22.65

11/13/51 34.8 4.2 25.9 2.8 33.15

9/12/77 -- -- -- -- --

9/17/49 37.1 3.6 22.1 2.0 44.30

3/28/51 -- -- -- -- --

12/16/87 -- -- -- -- --

6/20/68 73.1 5.2 42.3 3.2 38.32

9/23/63 21.7 1.7 11.4 0.6 66.13

7/18/57 -- -- -- -- --

5/27/56 35.8 1.6 9.1 0.3 83.04

7/1/83 -- -- -- -- --

12/7/78 -- -- -- -- --
F-19

The simulation results presented in Table F-3 formed the basis for determining CSO

occurrence and assigning CSO volumes to rainfall events contained in the historical

record. The relationship between rainfall event characteristics and CSO occurrence,

flow and volume was determined by regression of the simulated results. A third order

polynomial was fitted to the simulated CSO volumes using rainfall depth, maximum

intensity and average intensity. Figure F-5, F-6 and F-7 demonstrate the consistency

between simulated CSO data and predicted CSO data based on the regression

relationship.

Analysis Results

Annual statistics were generated for WY1949 to WY1993. Table F-4 presents the

computed statistics, which include annual number of CSO occurrences, annual CSO

volume without street storage, annual CSO volume with street storage, annual percent

reduction in CSO volume with street storage. In addition to the regression that was

completed to assign CSO occurrence and volume to historic rainfall events, the data

was further analyzed to investigate the relationships defining CSO peak flow and

reductions in CSO volume and peak flow attainable with provision of street storage. 

Curve fitting techniques available in Microsoft EXCEL were used to quantify the

apparent relationships between various data sets.

Figure F-8 presents pre-project overflow volume plotted against overflow volume

reduction. The plot shows a well defined relationship between overflow volume

reduction and pre-project overflow volume and is well represented by the fitted power

function also shown in the figure. The data indicated significant reductions in overflow

volumes, especially for events producing overflow volumes that were less than 20 acrefeet. As indicated in Figure F-8, street storage resulted in reductions of at least 20% for

overflow volumes of approximately 20 acre-feet. The trend in percent reduction

resulting with street storage increased dramatically as overflow volume decreases. The

potential benefits from street storage become even more apparent considering that the

average overflow volume for pre-project conditions was 15.9 acre-feet and the median

overflow volume was 10.0 acre-feet. Applying the fitted curve in Figure F-8, street

storage reduced overflow volumes for over half of the individual events by 30% or

greater.

Graphs were also developed to examine possible relationships between provision of

street storage and reductions in CSO peak flows. As shown in Figure F-9, there does

not appear to be a well defined trend between CSO peak flow and rainfall depth. 

However, there does appear to be a trend in comparisons between CSO peak flow and

maximum rainfall intensity. Figure F-10 presents the CSO peak flows resulting from the

simulations compared with maximum rainfall intensity from each respective rainfall

event incorporated in the simulation. Figure F-10 also contains second order

polynomial curves fitted to the CSO peak flows for the pre-project scenario and the 
Figure F-5

Overflow Volume vs. Rainfall Depth

Pre-project Scenario

0

50

100150200

0.00 2.00 4.00 6.00 8.00 

Rainfall Depth (in)

Overflow Volume 

(af)

Predicted OF Simulated OF

F-20
Figure F-6

Overflow Volume vs. Maximum Rainfall Intensity

Pre-project Scenario

0

50

100150200

0 0.5 1 1.5 2 2.5 3 3

Maximum Rainfall Intensity (in/hr)

Overflow Volume 

(af)

Predicted OF Simulated OF

F-21
Figure F-7

Overflow Volume vs. Average Rainfall Intensity

Pre-project Scenario

0

50

100150200

0 0.2 0.4 0.6 0.8 1 1.2 

Average Rainfall Intensity (in/hr)

Overflow Volume 

(af)

Predicted OF Simulated OF

F-22
F-23

Table F-4

Annual Overflow Statistics

Annual CSO

Statistics

Pre-project Scenario Street Storage Scenario

 Number of

CSOs

CSO Volume

 (acre-feet)

 Number of

CSOs

CSO Volume

 (acre-feet)

CSO Volume

Reduction

(%)

Annual 

Average

12.62 197.98 11.24 162.44 19.23

Annual

Median

12 187.91 10 147.54 18.79

Annual

Maximum

23 478.42 22 415.68 29.48

Annual

Minimum

6 86.92 5 63.77 9.24

Annual

Standard

Deviation

4.00 92.57 3.69 82.05 4.40
Figure F-8

Overflow Volume Reduction vs. Overflow Volum

y = 120.98x-0.639

R2 = 0.7644

0

20406080

100120

0 20 40 60 80 100 12

Overflow Volume (af)

Overflow Vol Reduction 

(%)

F-24
Figure F-9

Peak Overflow vs. Rainfall Depth

0

100200300400500

012345

Rainfall Depth (in)

Peak Overflow (cfs)

Peak OF with Storage Peak OF without Storag

F-25
Figure F-10

Peak Overflow vs. Maximum Rainfall Intensity

0

200400600800

0123

Maximum Rainfall Intensity (in/hr)

Peak Overflow 

(cfs)

Peak OF with Storage Peak OF without StoraPoly. (Peak OF without Storage) Poly. (Peak OF with St

F-26
F-27

street storage scenario.

Conclusions

The graphs and tables summarizing the CSO simulation and annual statistics clearly

demonstrate that street storage does contribute to reducing both CSO volumes and

peak flows. The data indicated that street storage resulted in a reduction of overflow

volume of 30% or greater for approximately half of the overflow occurrences. This

trend is consistent with objectives included in the Nine Minimum Controls such as

treating the first flush and maximizing system storage. 

Unfortunately, the results of this analysis did not indicate significant reduction in CSO

occurrence and frequency. The study area selected for this case study was based on

an area where street storage improvements have actually been constructed. This fact

lends credibility to the improvement components and street storage volumes

incorporated into the SWMM models developed for this study. It should be noted,

however, that the improvements in the Emerson Street study area were conceptualized

and developed to function with the MWRDGC TARP system. As a result, this system

provides significantly greater capacity to accept system discharge than would normally

be received by typical treatment plant capacities. The street storage system analyzed

for this study was optimized to work in conjunction with improved sewer system

capacity to provide protection to the residents for the 10-year design rainfall event. The

street storage system was not specifically developed or optimized for the specific

purpose of eliminating and reducing CSO impacts. It is probable that even greater

benefits might have been realized had control of CSOs been an original objective

during development of the street storage system.

Provision of street storage as a CSO control technology clearly offers benefits beyond

simply controlling CSO impacts. Street storage can provide a cost-effective means for

addressing capacity limitations in combined sewer systems that are not addressed by

any current CSO control technologies. Based on the potential identified in this case

study for street storage to contribute to reductions in both CSO volumes and peak

flows, additional research and investigation is recommended to further explore and

quantify the benefits of street storage with respect to CSO impacts. Additional research

and investigation should be formulated to quantify the benefits of street storage to

address CSO water quality, CSO impacts and compatibility with other CSO control

technologies. The following are specific examples of additional research and

investigation: 

C Conduct monitoring of CSO effluent from areas with and without street

storage to evaluate potential water quality benefits attainable with

provision of street storage.

C Conduct analysis to determine the significance of different land use types

on the potential water quality benefits attainable with provision of street
F-28

storage.

C Conduct analysis to evaluate the compatibility of street storage with other

identified CSO control technologies. Evaluate potential design and cost

reductions for CSO control technologies resulting from implementation

with street storage.

C Evaluate design modifications required for street storage systems

optimized for CSO control compared to street storage systems optimized

to prevent basement and surface flooding.

C Conduct analysis to investigate the potential for implementing street

storage in various regions of the United States. Identify possible regional

limitations for implementing street storage for CSO control.

C Conduct a sensitivity analysis to evaluate the impact of the size of the

WWTP along with the street storage on the amount of overflows. This will

allow us to further evaluate the effect of street storage on the community’s

wastewater treatment facilities.

wp/epastappf
Appendix G

Construction Costs

for

Skokie Street Storage System

Adjusted to 1999

G-1
SYSTEM YEARS ORIGINAL ENR CONSTRUCTION

COMPONENT OF CONSTRUCTION INDEX COST

CONSTRUCTION COST(1) FOR ADJUSTED

 YEAR(S) TO

OF 1999(3)

CONSTRUCTION(2)

 $ $

Roadway Berms 1984 42450 4146 61351

Roadway Berms 1985 1325415 4195 1893179

Tanks, Sewer 1985 1689577 4195 2413336

Relief Sewer 1986-87 4930781 4351 6790448

Roadway Berms 1988 1547510 4519 2051932

Surface Detention Facility 1989 835771 4615 1085144

Tanks, Sewer, Surface

 Detention Facility 1989 7834524 4615 10172149

Tanks, Sewer, Surface

 Detention Facility 1990 4992485 4732 6321845

Roadway Berms 1990 1170665 4732 1482381

Tanks, Sewer, Surface

 Detention Facility 1991-92 4712949 4910 5751526

Tanks, Sewer 1992 2998451 4985 3604156

Surface Detention Facility 1994 946480 5408 1048689

Tanks, Sewer 1993-94 3153684 5309 3559404

Tanks, Sewer, Surface

 Detention Facility 1994-95 4422855 5440 4871645

Tanks, Sewer 1995 1686775 5471 1847406

Tanks, Sewer 1995 766109 5471 839065
 78232393

Tanks, Sewer

Relief Sewer 1996-97 13100078 5723 13715825

Sewer 1997-98 6887763 5873 7027324

Tanks, Sewer

Water Main 1998 185023 5920 187273

 1999 3508316 5992 3508316

 

TOTALS: 66737661

Footnotes:

1) Based on actual costs with the exception of 19999 which is the engineer’s estimate.

 Source: Carr, 1999.

2) Engineering News Record (ENR) Construction Cost Indices were obtained from www.enr.com.

 The annual average value was used for one year construction periods.

 The average of annual averages was used for two year construction periods.

3) ENR index used for 1999 (February) is: 5992 

File Name: SkokieStreetStorageCosts
1

Glossary

Note: Definitions are quoted from USEPA (August, 1998) except for terms denoted with

(*) at the end of the definition. Definitions of these terms are developed in this report or

taken from indicated sources.

Berm: A low structure constructed across a street, from curb to curb, and intended to

temporarily impound water on its upstream side. The crest or top of the berm when

viewed along the longitudinal axis of the street, is horizontal. It is in effect, a spillway.

(*)

Catch Basin: A chamber or well, usually at the street curbline, for the admission of

surface water to a sewer or subdrain, having at its base a sediment sump to retain grit

and below detritus the point of overflow; whereas, a stormwater inlet does not have a

sump and does not trap sediment.

Combined Sewer: A sewer receiving intercepted surface (dry- and wet-weather) runoff,

municipal (sanitary and industrial) sewage, and subsurface waters from infiltration.

Combined Sewer Overflow (CSO): Discharge of a mixture of stormwater and

domestic waste when the flow capacity of a sewer system is exceeded during

rainstorms.

Computer Model: A model in which the mathematical operations are carried out on a

computer.

Cost-Effective Solution: A solution to a problem that has been identified as being

financially optional (e.g., the solution associated with the knee-of-the-curve of a costbenefit relationship).

Detention: The slowing, dampening, or attenuating of flows either entering the sewer

system or within the sewer system by temporarily holding the water on a surface area,

in a storage basin, or within the sewer itself.

Flow Regulator: A passive, gravity device that regulates the flow of stormwater into a

combined sewer. (*)
2

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,

402, 318, and 405 of the Clean Water Act.

Nonpoint Source: Diffuse pollution sources (i.e., without a single point of origin or not

introduced into a receiving stream from a specific outlet). The pollutants are generally

carried off the land by stormwater. Common nonpoint sources are agriculture, forestry,

urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city

streets.

Permit: An authorization, license, or equivalent control document issued by EPA or an

approved state agency to implement the requirements of an environmental regulation;

e.g., a permit to operate a wastewater treatment plant or to operate a facility that may

generate harmful emissions.

Pollutant: A contaminant in a concentration or amount that adversely alters the

physical, chemical, or biological properties of the environment. The term includes

pathogens, toxic metals, carcinogens, oxygen-demanding materials, and all other

harmful substances. With reference to nonpoint sources, the term is sometimes used

to apply to contaminants released in low concentrations from many activities that

collectively degrade water quality. As defined in the federal Clean Water Act, pollutant

means dredged spoil; solid waste; incinerator residue; sewage; garbage; sewage

sludge; munitions; chemical wastes; biological materials; radioactive materials; heat;

wrecked or discarded equipment; rock; sand; cellar dirt; and industrial, municipal, and

agricultural waste discharged into water.

Pollution: Generally, the presence of matter or energy whose nature, location, or

quantity produces undesired environmental effects. Under the Clean Water Act, for

example, the term is defined as the man-made or man-induced alteration of the

physical, biological, chemical and radiological integrity of water.

Publicly Owned Treatment Works (POTW): Any device or system used in the

treatment (including recycling and reclamation) of municipal sewage or industrial wastes

of a liquid nature that is owned by a state or municipality. This definition includes

sewers, pipes, or other conveyances only if they convey wastewater to a POTW

providing treatment.

Receiving Waters: Natural or man-made water systems into which materials are

discharged.
3

Sewer: A channel or conduit that carries wastewater and stormwater runoff from the

source to a treatment plant or receiving stream. “Sanitary” sewers carry household,

industrial, and commercial waste. “Storm” sewers carry runoff from rain or snow. 

“Combined” sewers handle both.

Source Control: A method of abating storm-generated or CSO pollution at the

upstream, upland source where the pollutants originate and/or accumulate.

Storm Sewer: A sewer that carries intercepted surface runoff, street wash and other

wash waters, or drainage, but excludes domestic sewage and industrial wastes except

for unauthorized cross-connections.

Stormwater: Stormwater runoff, snowmelt runoff, and surface runoff and drainage;

rainfall that does not infiltrate into the ground or evaporate because of impervious land

surfaces but instead flows onto adjacent land or watercourses or is routed into

drain/sewer systems.

Street Storage. A system that mitigates surcharging of CSSs, SSSs and stormwater

systems by temporarily storing stormwater in a controlled fashion on the surface (mainly

on-street but some off-street) and, as needed, below streets. Stormwater is stored

close to the source, that is, where it falls as precipitation, and prior to its entry into the

sewer system. The full volume of stormwater runoff is accepted into the sewer system

but peak rates are reduced, as a result of the storage, to flow that can be

accommodated without surcharging. (*)

Surface Runoff: Precipitation, snowmelt, or irrigation water in excess of what can

infiltrate the soil surface and be stored in small surface depressions; a major transporter

of nonpoint source pollutants.

Surface Water: All water naturally open to the atmosphere (rivers, lakes, reservoirs,

ponds, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other

collectors directly influenced by surface water.

Watershed Protection Approach (WPA): The U.S. EPA’s comprehensive approach to

managing water resource areas, such as river basins, watersheds, and aquifers. WPA

has four major features: targeting priority problems, stakeholder involvement, integrated

solutions, and measuring success.

Watershed: A drainage area or basin in which all land and water areas drain or flow

toward a central collector such as a stream, river, or lake at a lower elevation.
4

Wet-Weather Flow: Usually referred to as the flow in a combined sewer system with

stormwater, but may also constitute the flow in a separate storm or sanitary drainage

system with stormwater.

wp/epastglos
1

Cited References

American Society of Civil Engineers and Water Environment Federation, Design and

Construction of Urban Stormwater Management Systems, 1992.

Association of Metropolitan Sewerage Agencies, Approaches to Combined Sewer

Overflow Program Development: A CSO Assessment Report, Washington, DC,

November, 1994. 

Association of Metropolitan Sewage Agencies and Limno-Tech, CSO Performance

Measures as a Method of Tracking the Success of Control Efforts - Summary Report,

December, 1996. 

Astrack, R. F., N. A. Baumann and G. L. Reynolds, “Managing a Public Involvement

Program,” Water Resources Planning and Management Division Journal, American

Society of Civil Engineers, Vol. 110, No. 2, 1984, pp. 153-166. (*)

Burian, S. J., S. J. Nix, S. R. Durrans, R. E. Pitt, C. Y. Fan and R. Field, “Historical

Development of Wet-Weather Flow Management;” Journal of Water Resources

Planning and Management, American Society of Civil Engineers, Vol. 125, No. 1,

January/February, 1999, pp. 3-13. 

Carr, R. W. and S. G. Walesh, “Micromanagement of Stormwater for Wet Weather

Control,” Poster paper presented at WEFTEC ‘98, Water Environment Federation,

Orlando, FL, October, 1998.

Carr, R. W., Earth Tech, personal communication regarding Skokie street storage

system components and construction costs, 1999.

CH2M Hill, Inc., SAM Wastewater Collection System Analysis Model, Users Manual.,

August, 1980.

Colston, N. V., Jr., Characterization and Treatment of Urban Land Runoff, EPA-670/2-

74-096, 1974. 
2

Conradin, F., “Study on Catch Basins in Switzerland,” In Proceedings of Urban

Stormwater Quality Enhancement - Source Control, Retrofitting, and Combined Sewer

Technology, Engineering Foundation Conference, American Society of Civil Engineers,

Davos Platz, Switzerland, October 22-29, 1989, pp. 199-214.

Consoer, Townsend & Associates, Comprehensive Engineering Study of the Storm

Flooding Problems in Skokie, IL, August 1967.

Consoer, Townsend & Associates, Engineering Report on Sewer Facilities Needed for

Conveyance of Skokie Combined Sewer Overflows to Main Tunnels of the Chicago

Underflow Plan, Village of Skokie, IL, December, 1973. 

Donohue & Associates, Flow Regulator Pilot Study: Runoff Control Program - Howard

Street Sewer District, Village of Skokie, IL, March, 1984a. 

Donohue & Associates, Preliminary Engineering: Runoff Control Program - Emerson

and Lake Street Sewer Districts - Village of Skokie, IL, May, 1987a.

Donohue & Associates, Preliminary Engineering: Runoff Control Program - Howard

Street Sewer District - Village of Skokie, IL, July, 1982a.

Donohue & Associates, Preliminary Engineering: Runoff Control Program - Howard

Street Sewer District - Village of Skokie, IL, Summary Volume, July 1982b.

Donohue & Associates, Preliminary Engineering: Runoff Control Program - Main Street

Sewer District - Village of Skokie, IL, May, 1987b.

Donohue & Associates, Post-Construction Monitoring - 1987, Runoff Control Program,

Howard Street Sewer District, Village of Skokie, IL, April, 1988.

Dwyer, T., “Overview of the CSO policy and Guidance Documents,” Paper presented at

the Small Communities Combined Sewer Overflow Workshop, Indianapolis, IN,

February 24-25, 1998.

Elizer, Jr., R. M. “Speed Bumps: Speed Bumps are Effective Strategy When

Addressing Residential Safety and Quality of Life Issues,” Excerpts from an earlier

article, APWA Report, September, 1996, pp. 10-15.

Eschenbach, R. C. and T. G. Eschenbach, “Understanding Why Stakeholders Matter,”

Journal of Management in Engineering, American Society of Civil Engineers, Vol. 12,

No. 6, 1996, pp. 59-64.
3

Fishman, T. C., “At the Corner of Wall Street and Main: The Flood of Money,” Worth,

November, 1998, pp. 176-186.

Gilbert, J. B., W. O. Maddaus and J. A. Yost, “Public Decision Making in Water

Conservation,” Proceedings of Water Forum ‘81, American Society of Civil Engineers,

New York, NY, 1981, pp. 757-764.

Grigg, N. S., Urban Water Infrastructure: Planning, Management and Operation. Wiley

& Sons, New York, NY, 1986.

Grottker, M., “Pollutant Removal by Catch Basins in West Germany: State of the Art -

New Design,” In Proceedings of Urban Stormwater Quality Enhancement - Source

Control, Retrofitting, and Combined Sewer Technology, Engineering Foundation

Conference, American Society of Civil Engineers, Davos Platz, Switzerland, October

22-29, 1989, pp. 199-214.

Harza Engineering Company, “Study of Flood Control Alternatives,” Prepared for the

Village of Skokie, IL, October, 1981.

Harza Engineering Company, Study of the Combined Sewer Conveyance Problems:

Supplemental Study to the Infiltration/Inflow Analysis Portion of MSDGC Facilities

Planning, May, 1978.

Haynes, V. D., “Speed Bumps Raise Praise and Ire Among Communities,” Chicago

Tribune, October 25, 1998.

Helweg, O. J., Water Resources Planning and Management, Wiley & Son, New York,

NY, 1985.

Herrin, J. C. and A. W. Whitlock, “Interfacing With the Public on Water-Related Issues:

What TVA is Doing,” Proceedings of Saving a Threatened Resource, American Society

of Civil Engineers, New York, NY, 1992, pp. 293-298.

Hides, S. P., “The Inlet Control System: A Common Sense Approach for Reducing CSO

Impacts,” In Proceedings - A Global Perspective for Reducing CSO’s: Balancing

Technologies, Costs, and Water Quality, Louisville, KY, July 10-13, 1994.

Huber, N. C. and R. Dickinson, Stormwater Management Model Version 4 User’s

Manual, 2nd Printing, October, 1992.

Huff, F. A. and J. R. Angel, Frequency Distribution and Hydroclimate Characteristics of

Heavy Rainstorms in Illinois, Bulletin 70, State of Illinois Department of Energy and

Natural Resources, Champaign, IL, 1989.
4

Hydro Group, “Hydro-Brake: Liquid Flow Controls,” Brochure, February, 1982.

Illinois State Water Survey, Hydrometeorology of Heavy Rainstorms in Chicago and

Northeastern Illinois, Phase I - Historical Studies., Report on Investigation 82, 1976.

Institute of Transportation Engineers, Guidelines for the Design and Application of

Speed Humps, Washington, DC, 1997.

John, S. F. and N. J. Wheatley, “Environmental Negotiation: Lessons From the

Combined Sewer Overflow Policy,” Paper presented at the Small Communities

Combined Sewer Overflow Workshop, Indianapolis, IN, February 24-25, 1998.

Jones, D. E., Jr., “Urban Hydrology - A Redirection,” Civil Engineering, American

Society of Civil Engineers, August, 1967, pp. 58-62.

Kaufman, H. L. and F. Lai, Conventional and Advanced Sewer Design Concepts for

Dual Purpose Flood and Pollution Control: A Preliminary Case Study, Elizabeth, NJ,

EPA - 600/2-78-090, May 1978.

Kraft, W. H., “Building Consensus: How Tos and How Not Tos,” Journal of Management

in Engineering, American Society of Civil Engineers, Vol. 13, No. 3, 1997, pp. 20-22.

Kurz, J. W., “Transformation of Plans Into Actions,” Urban Planning and Development

Division Journal, American Society of Civil Engineers, Vol. 99, No. 2, 1973, pp. 184-

191.

Loucks, E. D. and M. C. Morgan, “Evaluation of the Wilmette Runoff Control Program,”

Proceedings of Integrated Water Resources Planning for the 21st Century, American

Society of Civil Engineers, Cambridge, MA, May 7-11, 1995.

Matthews, T. M., P. D. Pitts, Jr., and R. C. Larlham; Hydro Brake Regulated Storage

System for Stormwater Management - Project Summary, EPA-600/s2-83-097, January

1984.

Matthews, T. M., P. D. Pitts, Jr., and R. C. Larlham, Hydro Brake Stormwater Detention

System Demonstration in Cleveland, OH, EPA - 600/2-83-097, 1983.

Metropolitan Sanitary District of Greater Chicago, Emerson Street Sewer Study -

Including Addendum, October, 1981.

Morgan, M. C., Earth Tech, personal communications regarding Wilmette performance

criterial and construction costs, 1999.

Nakai, E. H. and R. W. Carr, “Urban Stormwater Runoff Control System, Village of
5

Skokie, IL,” In Proceedings of the 20th Anniversary Conference of the Water Resources

Planning and Management Division, American Society of Civil Engineers, Seattle, WA,

May, 1993.

Paintal, A., “Emerson Street Sewer Study,” Metropolitan Sanitary District of Greater

Chicago, October, 1981.

Park, J. B., “IEPA Loan Project Number L170181,” memorandum to Village of Skokie

from Illinois Environmental Protection Agency, September 7, 1990.

Perry, S. D., “Rx for Risk Communication,” Civil Engineering, American Society of Civil

Engineers, August, 1996, pp. 61-63.

Pisano, W. C., “Inlet Control Concepts on Catchbasins: U.S. Experience,” In

Proceedings of Urban Stormwater Quality Enhancement - Source Control, Retrofitting,

and Combined Sewer Technology, Engineering Foundation Conference, American

Society of Civil Engineers, Davos Platz, Switzerland, October 22-29, 1989.

Poertner, H. G., Practices in Detention of Urban Storm Water Runoff, Special Report

No. 43, American Public Works Association, Chicago, IL, 1974.

Priscoli, J. D., “Public Involvement, Conflict Management: Means to EQ and Social

Objectives,” Water Resources Planning and Management Division Journal, American

Society of Civil Engineers, Vol. 115, No. 1, 1989, pp. 31-42.

Raasch, G. E., Project Manager, Donohue & Associates, “Letter to A. J. Rigoni, Village

Manager, Skokie, IL,” October 30, 1989a.

Raasch, G. E., “Urban Storm Runoff Control System Case Study - Skokie, IL,”

Presented as part of the course Optimizing Your Storm Drainage System, Department

of Engineering Professional Development, University of Wisconsin, Denver, CO, April

24-26, 1989b.

Rigoni, A. J., Village Manager, Skokie, IL, “Letter to G. E. Raasch, Project Manager,

Donohue & Associates,” September 7, 1989.

Roecker, D. F., “1997 Capital Wastewater Funding Opportunities: A Survey of Available

State, Federal and Congressional Funding,” Presented WEFTEC ‘97, the Water

Environment Federation’s 70th Annual Conference & Exposition, Chicago, IL, 1997.
6

Roecker, D. F., “1998 Capital Funding Sources,” Utility Executive, Water Environment

Federation, Vol. 1, No. 1, May/June, 1998a.

Roecker, D. F., “Case Studies in Capital Wastewater Funding Using Innovative Funding

Techniques,” Presented at WEFTEC ‘98, the Water Environment Federation’s 71th

Annual Conference, Orlando, FL, October, 1998b.

Roecker, D. F., “Securing Capital Funds for Water Resources Projects,” Presented at

the American Water Resources Association’s 29th Annual Conference and Symposium,

Tucson, AZ, 1993.

Rubin, R. A. and B. Carbajal-Quintas, “Environmental Regulation and Public

Participation in Project Planning,” Journal of Professional Issues in Engineering

Education and Practices, American Society of Civil Engineers, Vol. 121, No. 3, 1995,

pp. 183-186.

Rust Environment and Infrastructure, Amendment to 1991 Wastewater Facilities Plan

Appendix C, Design Memorandum, Preliminary Engineering for Stormwater Runoff

Control, Combined Sewer Area East of Ridge Road - Village of Wilmette, IL, November

1993.

Rust Environment & Infrastructure, Stormwater Runoff Control Facilities Operation and

Maintenance Manual, Village of Skokie, IL, September, 1995.

Sargent, H. L., Jr., “Fishbowl Planning Immerses Pacific Northwest Citizens in Corps

Projects,” Civil Engineering, American Society of Civil Engineers, Vol. 42, No. 9, 1972,

pp. 54-57.

SEC Donohue, Amendment to the 1991 Wastewater Facility Plan, Village of Wilmette,

IL, December, 1992.

SEC Donohue, Stormwater Management Study and Feasibility Report for the Jeffery

Manor Area, Prepared for the Department of Sewers, City of Chicago, March, 1993.

SEC Donohue, Stormwater Runoff Control Feasibility Analysis, Combined Sewer Area

East of Ridge Road, Village of Wilmette, IL, June, 1992.

Silberman, E., “Public Participation in Water Resource Development,” Water Resources

Planning and Management Division Journal, American Society of Civil Engineers, Vol.

103, No. 1, 1977, pp. 111-123.

Skokie, Village of, Department of Public Works, Safety Manual, August, 1992.

Spring, B. H., Hanging Trap and Scepter Orifice Tests, Department of Civil Engineering,
7

Valparaiso University, December, 1983.

Stadler, Gerald, U. S. Army Corps of Engineers, Chicago District, Personal

Communication, March 17, 1982.

Tam, W. and B. Murillo, “LA Story: Providing Public Services Online With GIS,” Geo

Info Systems, Vol. 7, No. 7, 1997, pp. 26-27.

USEPA, Combined Sewer Overflow (CSO) Control Policy, EPA 830-B-94-001, April

1994.

USEPA, “Glossary of Wet Weather Flow Terms,” www.epa.gov/ednnrmrl/gloss.htm,

August 3, 1998.

USEPA, Manual: Combined Sewer Overflow Control, EPA/625/R-93/007, September

1993.

USEPA, “Top 10 Watershed Lessons Learned,” EPA 840-F-97-001, October 1997, p.

50.

USEPA, Watershed Protection: Catalog of Federal Programs, EPA-841-B-93-002.

1993.

United States General Services Administration & Executive Office of the President,

1998 Catalog of Federal Domestic Assistance, Updated through December, 1998.

Velazquez, F., “Even a Lowly Hump Takes Good Engineering,” Engineering Times, May

1992, p. 8.

Viessman, W. J., Jr., “Technology, Society and Water Management,” Water Resources

Planning and Management Division Journal, American Society of Civil Engineers, Vol.

115, No. 1, 1989, pp. 48-51.

Wakeman, T. H., “Engineering Leadership in Public Policy Resolution,” Journal of

Management in Engineering, American Society of Civil Engineers, Vol. 13, No. 1, 1997,

pp. 57-60.

Walesh, S. G., “DAD Is Out, POP Is In, Journal of the American Water Resources

Association, Vol. 35, Nol. 3, June 1999.
8

Walesh, S. G., “Interaction With the Public and Government Officials in Urban Water

Planning,” Proceedings of Hydropolis - The Role of Water in Urban Planning, UNESCOIHP Workshop, Wageningen, The Netherlands and Emscher Region, Germany, MarchApril, 1993, pp. 164-176.

Walesh, S. G., “Retrofitting Storm Water Detention Facilities for Quantity and Quality

Control,” In Proceedings of the International Conference on Urban Drainage

Technologies, Dubrovnik, Yugoslavia, June, 1991.

Walesh, S. G., “Retrofitting Storm Water Facilities for Quantity and Quality Control,”

Presented at ASCE’s Water Forum ‘92, American Society of Civil Engineers, Baltimore,

MD, August 1992.

Walesh, S. G., “Retrofitting a Detention Facility for Improved Quantity Control,” Paper

presented at the International Symposium on Engineering Hydrology, American Society

of Civil Engineers, San Francisco, CA, July 1993.

Walesh, S. G., “Retrofitting Storm Water Facilities for Quantity and Quality Control,”

Seminar presented to the Indiana Society of Professional Land Surveyors, Valparaiso,

IN, July, 1998.

Walesh, S. G., “Source Control to Reduce Combined Sewer Surcharging,” Paper

presented at the Annual Conference of the Michigan Water Environment Federation,

Mackinac Island, MI, June, 1996.

Walesh, S. G. and M. L. Schoeffmann, “Surface and Sub-Surface Detention In

Developed Urban Areas: A Case Study,” Paper presented at the conference Urban

Water - ‘84, American Society of Civil Engineers, Baltimore, MD, May 28-31, 1984.

Walesh, S. G., Urban Surface Water Management, John Wiley & Sons, New York, NY,

1989.

Water Environment Research Foundation, Wet Weather: Information for Wet Weather

Decision Makers, Vol. 3, Issue 2, 1998.

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1

Bibliography

Aeppel, T., “Giant Sewage Storage Tank Shakes City,” Wall Street Journal, January 22,

1996. 

Association of Metropolitan Sewage Agencies and Limno-Tech, CSO Performance

Measures as a Method of Tracking the Success of Control Efforts - Workshop

Workbook, October and November, 1996. 

Bingham, D., E. Driscoll, J. Golden, and D. Walker, Manual: Combined Sewer

Overflow, EPA/625/R-93/007, September 1993. 

Carr, R. W. and E. H. Nakai, “Optimum Use of Existing Combined Sewer Systems,

Urban Stormwater Runoff Control Project,” Village of Skokie, IL, Paper presented at

WEFTEC 94, 67th Annual Conference of the Water Environment Federation, Chicago,

IL, October 15-19, 1994.

Carr, R. W., and E. H. Nakai, “Runoff Control,” Water Environment and Technology

Magazine, Vol. 7, No. 4, April 1995.

Des Plaines, IL, City of, “Flood Information Handbook: A Guide to Local, Interim

Solutions to a Regional Problem,” February, 1973. 

Donohue & Associates, Construction Cost Refinement, Runoff Control Program, Main

Street Sewer District, Main Street Sewer District, Village of Skokie, IL, January, 1989. 

Donohue & Associates, Preliminary Engineering Addendum: Runoff Control Program -

Howard Street Sewer District - Village of Skokie, March, 1984. 

Donohue & Associates, Monitoring - 1983 Runoff Control Program - Howard Street

Sewer District - Village of Skokie, IL, March, 1984b. 

Donohue & Associates, Monitoring - 1984 Runoff Control Program - Howard Street

Sewer District, Village of Skokie, IL, April, 1985. 

Donohue & Associates, Monitoring - 1985 Runoff Control Program - Main Street Sewer

District, Village of Skokie, IL, February, 1986. 

Donohue & Associates, Monitoring - 1986 Runoff Control Program - Emerson & Lake

Street Sewer Districts, Village of Skokie, IL, December, 1986. 

Evanston, City of, “Evanston’s Flood and Pollution Problem,” a brochure, no date but
2

probably late 1970's. 

Milligan, J. E., “Effective Subsurface Retention/Detention Systems,” In North American

Water and Environment Congress, American Society of Civil Engineers, 1996.

Raasch, G. E., “Stormwater Detention - Controlling Peak Runoff,” Paper presented at

the conference Designing the Future, Illinois Concrete Pipe Association, Carol Stream,

IL, April 13, 1988.

Rust Environment and Infrastructure, “Amendment to 1991 Wastewater Facilities Plan,”

Village of Wilmette, IL, November, 1995. 

Rust Environment & Infrastructure, Combined Sewer Interceptor Outfall Flow Monitoring

Study, Village of Skokie, IL, May, 1993. 

Rust Environment & Infrastructure, Project Manual for Combined Sewer Interceptor

Flow Meter Installation for the Village of Skokie, Cook County, IL, August, 1993.

Schoeffmann, M. L. and S. G. Walesh, “One Alternative to Flooded Basements,” APWA

Reporter, American Public Works Association, Vol. 52, No. 3, March, 1985, pp. 6-7.

Stall, J. B. and M. L. Terstriep, Storm Sewer Design - An Evaluation of the BRRL

Method, Prepared for the Office of Research and Monitoring of the USEPA, October,

1972.

Stauss Engineering, 95% Plan Completion Valve Engineering Study Report -

Stormwater Detention Facilities - 1992 Construction Program, Village of Skokie, IL,

December, 1991.

Walesh, S. G. and R. W. Carr, “Controlling Storm Water Close to the Source: An

Implementation Case Study,” Paper presented at APWA Congress, American Public

Works Association, Las Vegas, NV, September, 1998.

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