United States

Environmental Protection

Agency

Drinking Water Treatment Plant Residuals 

Management Technical Report

Summary of Residuals Generation, Treatment, and 

Disposal at Large Community Water Systems

December 2011 

EPA 820-R-11-003
Drinking Water Industry Report

i

DISCLAIMER

This report on the drinking water treatment industry does not set forth any regulatory 

requirements under the Clean Water Act. It is intended solely as a presentation of information of 

which the U.S. Environmental Protection Agency (EPA) is currently aware concerning the 

generation, treatment, and disposal of wastewater and solid residuals at water treatment plants 

(WTPs). Thus, it does not impose any requirements on any party, including EPA, states, 

permitting authorities, publicly-owned treatment works (POTWs), or the regulated community. 

This report was prepared using information from the following sources: review of selected 

literature, reports, and other materials; meetings with several interested parties; site visits at 

WTPs; an industry questionnaire; and other information solicited from stakeholders. 

References made in this report to any specific method, product or process, vendor, or corporation 

do not constitute or imply an endorsement, recommendation, or warranty by the U.S. EPA. EPA 

does not assume any legal liability or responsibility for any third party’s use of, or the results of 

such use of, any information discussed in this report, or represents that its use by such a third 

party would not infringe on privately owned rights. 
Drinking Water Industry Report Contents

ii

CONTENTS

Page 

SECTION 1 INTRODUCTION ..................................................................................................... 1-1

SECTION 2 DATA SOURCES ..................................................................................................... 2-1

2.1 Summary of EPA’s Water Treatment Plant Site Visits ........................... 2-1

2.2 EPA DWT Industry Questionnaire .......................................................... 2-2

2.2.1 Overview of Industry Questionnaire ............................................ 2-2

2.2.2 Description of Questionnaire ....................................................... 2-6

2.2.3 Development of the Questionnaire Mailing List ......................... 2-8

2.2.4 Sample Selection .......................................................................... 2-8

2.2.5 Questionnaire Response ............................................................... 2-9

2.2.6 Protection of Confidential Business Information ...................... 2-10

2.3 EPA’s Ground Water and Drinking Water Data .................................... 2-10

2.3.1 Safe Drinking Water Information System ................................. 2-11

2.3.2 2000 Community Water System Survey.................................... 2-12

2.3.3 Information Collection Rule, 40 CFR Part 141 ......................... 2-13

2.3.4 Other Ground Water and Drinking Water Data ......................... 2-15

2.4 Other Information Collection Activities ................................................ 2-15

2.4.1 Literature Search ........................................................................ 2-15

2.4.2 Current NPDES Permits ............................................................ 2-16

2.4.3 NPDES Discharge Monitoring Reports (DMRs) ....................... 2-18

2.4.4 Other EPA Data ......................................................................... 2-19

2.4.5 Industry Data .............................................................................. 2-20

2.4.6 American Water Works Association (AWWA) Surveys and 

Reports ....................................................................................... 2-20

2.5 Stakeholder Meetings............................................................................. 2-22

2.6 Drinking Water Treatment Technology Review.................................... 2-24

2.7 References .............................................................................................. 2-24

SECTION 3 INDUSTRY PROFILE ............................................................................................... 3-1

3.1 Overview of DWT Industry ..................................................................... 3-1

3.1.1 Types of Drinking Water Systems ............................................... 3-3

3.1.2 How EPA Classifies Drinking Water Systems ............................ 3-3

3.2 Summary of Questionnaire Responses .................................................... 3-4

3.2.1 System and WTP Classification................................................... 3-4

3.2.2 WTP Characteristics (Summary of Responses to Technical 

Questions) .................................................................................... 3-6

3.3 Drinking Water Industry Economic Overview ...................................... 3-45

3.3.1 Major Sources of Information .................................................... 3-45

3.3.2 Public Water System Characteristics ......................................... 3-47

3.3.3 Financial Characteristics of Drinking Water Treatment 

Systems ...................................................................................... 3-52

3.3.4 Customer Profile ........................................................................ 3-63

3.4 References .............................................................................................. 3-73
Drinking Water Industry Report Contents

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SECTION 4 CURRENT STATE NPDES PERMIT REQUIREMENTS FOR WATER TREATMENT 

PLANT RESIDUALS ................................................................................................ 4-1

4.1 Overview of State and Federal NPDES Regulatory Requirements for 

Water Treatment Plants............................................................................ 4-1

4.2 Summary of Current Pollutant Limitations and Requirements for 

Water Treatment Plants: General and Individual Permits ....................... 4-7

4.3 References .............................................................................................. 4-11

SECTION 5 SOURCE WATER QUALITY .................................................................................... 5-1

5.1 Factors That Influence Source Water Quality ......................................... 5-1

5.2 Comparison of Ground Water and Surface Water Quality ...................... 5-4

5.3 Source Water Protection Under the SDWA............................................. 5-5

5.4 References ................................................................................................ 5-6

SECTION 6 SOURCE WATER TREATMENT TECHNOLOGIES ...................................................... 6-1

6.1 Conventional Filtration, Direct Filtration, and Filtration Only ................ 6-2

6.1.1 Presedimentation .......................................................................... 6-4

6.1.2 Coagulation, Flocculation, and Sedimentation ............................ 6-4

6.1.3 Filtration ....................................................................................... 6-5

6.2 Precipitative (Lime) Softening ................................................................. 6-7

6.3 Membrane Separation .............................................................................. 6-8

6.3.1 Reverse Osmosis and Nanofiltration ........................................... 6-9

6.3.2 Microfiltration and Ultrafiltration .............................................. 6-10

6.3.3 Electrodialysis and Electrodialysis Reversal ............................. 6-11

6.4 Ion Exchange ......................................................................................... 6-12

6.5 Adsorptive Media—Activated Carbon .................................................. 6-13

6.6 Disinfection ............................................................................................ 6-14

6.6.1 Disinfection with Chlorine (Chlorination) ................................. 6-15

6.6.2 Disinfection with Chlorine Dioxide ........................................... 6-16

6.6.3 Disinfection with Chloramines (Chloramination) ..................... 6-16

6.6.4 Ozone Disinfection .................................................................... 6-17

6.6.5 Ultraviolet Light Disinfection .................................................... 6-18

6.7 Other Chemical Additions ..................................................................... 6-18

6.7.1 Corrosion and Scale Control ...................................................... 6-19

6.7.2 Solids Removal Using Sequestering Agents.............................. 6-19

6.7.3 pH Adjustment ........................................................................... 6-20

6.7.4 Water Additives ......................................................................... 6-20

6.8 References .............................................................................................. 6-20

SECTION 7 TYPES OF RESIDUALS PRODUCED BY SOURCE WATER TREATMENT ..................... 7-1

7.1 Presedimentation ...................................................................................... 7-1

7.2 Residuals from Coagulation, flocculation, and sedimentation ................ 7-2

7.3 Residuals from Precipitative (Lime) Softening ....................................... 7-4

7.4 Residuals from Filtration ......................................................................... 7-6

7.4.1 Filters (non-membrane) ............................................................... 7-6

7.4.2 Low-Pressure Membranes ........................................................... 7-7
Drinking Water Industry Report Contents

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iv

7.5 Residuals from Membrane Desalination .................................................. 7-9

7.6 Residuals from Ion Exchange ................................................................ 7-12

7.7 Residuals from Adsorption (Activated Carbon) .................................... 7-13

7.8 References .............................................................................................. 7-14

SECTION 8 POLLUTANTS IN WATER TREATMENT PLANT RESIDUALS ..................................... 8-1

8.1 Overview of Pollutants in Water Treatment Plant Residuals .................. 8-3

8.2 Solids In Water Treatment Plant Residuals ............................................. 8-4

8.3 Priority and Nonconventional Metals In Water Treatment Plant 

Residuals .................................................................................................. 8-5

8.3.1 Aluminum and Iron ...................................................................... 8-9

8.3.2 Arsenic ......................................................................................... 8-9

8.3.3 Calcium and Sodium .................................................................... 8-9

8.3.4 Fluoride ...................................................................................... 8-10

8.3.5 Manganese and Potassium ......................................................... 8-10

8.3.6 Additional Metals with DMR Data ............................................ 8-10

8.4 WTP Pollutants from Disinfection......................................................... 8-11

8.4.1 Chemistry of Chlorine Disinfection ........................................... 8-12

8.4.2 Residual Disinfectants in Finished Drinking Water .................. 8-14

8.4.3 Disinfection By-Products ........................................................... 8-14

8.5 Parameters Measuring Organic Matter and Oxygen in the Water In 

WTP Residuals....................................................................................... 8-15

8.5.1 Biochemical Oxygen Demand ................................................... 8-15

8.5.2 Dissolved Oxygen ...................................................................... 8-16

8.6 Other Pollutants in WTP Residuals ....................................................... 8-17

8.6.1 Chloride...................................................................................... 8-17

8.6.2 Nitrogen ..................................................................................... 8-17

8.6.3 pH ............................................................................................... 8-18

8.6.4 Phosphorus ................................................................................. 8-18

8.6.5 Radionuclides ............................................................................. 8-18

8.7 References .............................................................................................. 8-19

SECTION 9 WATER TREATMENT PLANT POLLUTANT DISCHARGE ESTIMATES ....................... 9-1

9.1 Data Sources for the Pollutant Loadings Analysis .................................. 9-3

9.2 Methodology to Estimate Pollutant Loadings Using Model Plants ......... 9-4

9.2.1 Model Plant Development ........................................................... 9-4

9.2.2 Estimation of Model Plant Pollutant Loadings ............................ 9-6

9.3 Model Plant Concentration Estimation .................................................... 9-8

9.3.1 Selection of Pollutant Parameters for Pollutant Loadings 

Analysis........................................................................................ 9-8

9.3.2 Development of Long-Term Average Concentrations for 

Pollutants.................................................................................... 9-12

9.3.3 DMR Data Limitations .............................................................. 9-16

9.4 Model Plant Flow Rate Estimation ........................................................ 9-17

9.4.1 Review of DMR and Questionnaire Data .................................. 9-18
Drinking Water Industry Report Contents

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9.4.2 Model Plant Effluent Flow Rate Results ................................... 9-19

9.5 Results of the Pollutant Loadings Estimate for Model Plants ............... 9-20

9.6 National Pollutant Discharge Estimates................................................. 9-39

9.7 References .............................................................................................. 9-43

SECTION 10 POTENTIAL SCOPE OF ENVIRONMENTAL IMPACTS OF POLLUTANT DISCHARGES 10-1

10.1 Review of Publicly Available Information ............................................ 10-1

10.2 Summary of Environmental Impact of WTP Residuals by Pollutant .... 10-2

10.2.1 Environmental Impact of Solids ................................................ 10-2

10.2.2 Environmental Impact of Metals ............................................... 10-3

10.2.3 Environmental Impact of Chlorine and Chloramines ................ 10-3

10.2.4 Environmental Impact of Oxygen Demand ............................... 10-4

10.2.5 Environmental Impact of Chlorides ........................................... 10-4

10.2.6 Environmental Impact of Nitrogen ............................................ 10-4

10.2.7 Environmental Impact of pH Changes ....................................... 10-6

10.2.8 Environmental Impact of Phosphorus ........................................ 10-6

10.2.9 Environmental Impact of Radionuclides ................................... 10-6

10.3 References .............................................................................................. 10-7

SECTION 11 TECHNOLOGIES AND PRACTICES FOR PREVENTING, TREATING, DISPOSING OF,

AND DISCHARGING SOURCE WATER TREATMENT RESIDUALS ............................ 11-1

11.1 Pollution Prevention and Waste Reduction ........................................... 11-2

11.1.1 Optimize Intake Water Conditions ............................................ 11-4

11.1.2 Optimize Filter Media ................................................................ 11-4

11.1.3 Optimize pH to Reduce Coagulant Chemicals .......................... 11-5

11.1.4 Reduce Softening Chemicals by Monitoring Source Water 

Hardness ..................................................................................... 11-6

11.1.5 Return Backwash Water and Filter-to-Waste to the Head of 

the Source Water Treatment Plant for Reuse ............................. 11-6

11.1.6 Reuse of Precipitative Softening Chemicals .............................. 11-7

11.1.7 Recovery of Treatment Chemicals ............................................. 11-8

11.2 Residuals Treatment............................................................................. 11-10

11.2.1 Solids Removal (Separation of Solids and Water) .................. 11-11

11.2.2 Chemical Precipitation ............................................................. 11-20

11.2.3 Increased Oxygen Content by Aeration ................................... 11-20

11.2.4 Dechlorination.......................................................................... 11-20

11.2.5 pH Adjustment ......................................................................... 11-21

11.2.6 Nonwater Quality Environmental Impact Considerations ....... 11-21

11.3 Disposal Practices for Treatment Residuals ........................................ 11-23

11.3.1 Land Application of Residuals................................................. 11-23

11.3.2 Disposal of Residuals to Landfills or Deep Injection Wells .... 11-24

11.4 Wastewater Discharges of Treatment Residuals .................................. 11-24

11.5 References ............................................................................................ 11-26
Drinking Water Industry Report Contents

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vi

SECTION 12 TREATMENT TECHNOLOGY COST CONSIDERATIONS FOR RESIDUALS 

THICKENING AND DEWATERING ......................................................................... 12-1

12.1 Residuals Thickening And Dewatering Treatment Train ...................... 12-1

12.2 Cost Data Sources Identified ................................................................. 12-4

12.2.1 Drinking Water Treatment Technology Review Group ............ 12-4

12.2.2 AWWA 2008 Cost Estimates .................................................... 12-6

12.2.3 EPA’s Work Breakdown Structure (WBS) Cost Models .......... 12-7

12.3 Treatment Units: Description and Capacity ........................................... 12-8

12.3.1 Typical Ranges of Solids Content and Flow in Residuals 

from Conventional Filtration and Softening Plants ................... 12-8

12.3.2 Spent Filter Backwash Equalization and Clarifier Capacity .... 12-10

12.3.3 Gravity Thickener Capacity ..................................................... 12-12

12.3.4 Sludge Dewatering Centrifuges and Equalization Tanks ........ 12-13

12.3.5 Ancillary Equipment ................................................................ 12-14

12.4 Costs to Install And Operate Residuals Treatment Systems ................ 12-15

12.4.1 Capital Costs for Treatment Units ........................................... 12-15

12.4.2 Indirect Capital Costs ............................................................... 12-16

12.4.3 Annual Operating Costs ........................................................... 12-16

12.4.4 Additional Costs that Vary Between WTPs............................. 12-17

12.5 References ............................................................................................ 12-20

SECTION 13 ECONOMIC CONSIDERATIONS FOR PERMIT WRITERS .......................................... 13-1

13.1 Introduction ............................................................................................ 13-1

13.2 A Methodology for Determining the Economic Achievability of Best 

Professional Judgment Effluent Limitations for A Public Water 

System .................................................................................................... 13-2

13.2.1 Estimate Increase in Water Rates to Household Customers ...... 13-4

13.2.2 Estimate Increase in Annual Water Service Cost for 

Household Customers .............................................................. 13-10

13.2.3 Estimate Number and Percentage of Households, by Water 

System, for which the Annual Household Water Service Cost 

Increase Exceeds a Percent of Income Achievability 

Threshold ................................................................................. 13-12

13.2.4 Assessing the Impact of Rate Structure on the Achievability 

Determination .......................................................................... 13-19

13.3 References ............................................................................................ 13-20

SECTION 14 GLOSSARY, ACRONYMS, AND ABBREVIATIONS .................................................. 14-1

APPENDIX A: QUESTIONNAIRE DESIGN AND CALCULATION OF NATIONAL ESTIMATES

APPENDIX B: COMPOSITION OF COMMON DRINKING WATER TREATMENT CHEMICALS 

ILLUSTRATING PRODUCTION IMPURITIES

APPENDIX C: POTW PERCENT REMOVALS
Drinking Water Industry Report Contents

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APPENDIX D: TOXIC WEIGHTING FACTORS (TWFS) 

APPENDIX E: NATIONAL ESTIMATES: WATER TREATMENT PLANT COUNTS FOR POLLUTANT 

LOADINGS ESTIMATES
Drinking Water Industry Report List of Tables

viii

LIST OF TABLES

Page 

Table 2-1. EPA Site Visits to Drinking Water Treatment Plants ................................................ 2-3

Table 3-1. Discharge Status for Water Treatment Plants Serving More than 10,000 People ...... 3-2

Table 3-2. Industry National Estimates: Numbers of WTPs and Systems .................................. 

Table 3-3. Number of People Served per WTP in 2006 (National Estimates Based on 

Responses to Question 2b) ................................................................................... 3-9

Table 3-4. Estimated Water Production per WTP in 2006 (National Estimates Based on 

Responses to Questions 2b and 2c) .................................................................... 3-10

Table 3-5. Operating Days per WTP in 2006 (National Estimates Based on Responses to 

Question 2c) ....................................................................................................... 

Table 3-6. WTP Age (National Estimates Based on Responses to Question 2d) ...................... 3-12

Table 3-7. Estimated Number of WTPs Using Presedimentation (National Estimates 

Based on Responses to Question 2f) .................................................................. 3-16

Table 3-8. Estimated Numbers of WTPs Using Various Primary Disinfection Methods 

(National Estimates Based on Responses to Question 2f) ................................. 3-17

Table 3-9. Disinfection Residuals in Filter Backwash and Filter-to-Waste (National 

Estimates Based on Responses to Question 2f) ................................................. 3-18

Table 3-10. Primary Disinfectants (National Estimates Based on Responses to Question 

2f) ....................................................................................................................... 3-19

Table 3-11. Residuals Treatment Methods (National Estimates Based on Responses to 

Question 2h) ....................................................................................................... 3-22

Table 3-12. Pollution Prevention Methods (National Estimates Based on Responses to 

Question 2i) ........................................................................................................ 3-23

Table 3-13. Estimated Numbers of WTPs Using Direct, Indirect, or Zero Residuals 

Discharge Practices (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-30

Table 3-14a. Estimated Numbers of WTPs by Types of Residuals Discharged and 

Discharge Practice (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-31

Table 3-14b. Estimated Numbers of WTPs by Types of Residuals Discharged and 

Discharge Practice (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-32

3-6

3-11
Drinking Water Industry Report List of Tables

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Table 3-15. Estimated Number of WTPs by Discharge Frequency for Direct and Indirect 

Discharges (National Estimates Based on Responses to Question 2k).............. 3-33

Table 3-16. Estimated Number of Batch and Emergency Dischargers by DirectDischarging WTPs (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-34

Table 3-17. Estimated Numbers of WTPs Directly Discharging to Various Types of 

Receiving Waters (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-35

Table 3-18. Estimated Number of WTPs with Indirect Discharge and Release Volumes 

for Continuous Discharges (National Estimates Based on Responses to 

Question 2k) ....................................................................................................... 3-36

Table 3-19. Estimated Number of WTPs with Indirect Discharge and Release Volumes 

for Batch Discharges (National Estimates Based on Responses to Question 

2k) ...................................................................................................................... 3-37

Table 3-20. Estimated Number of WTPs Employing Various Zero Discharge Disposal 

Methods (National Estimates Based on Responses to Question 2k) ................. 3-38

Table 3-21. Estimated Number of WTPs Using Copper Sulfate and Application Rate 

(National Estimates Based on Responses to Question 3) .................................. 3-41

Table 3-22. Estimated Number of WTPs Using Chelated Copper Complexes and 

Application Rate (National Estimates Based on Responses to Question 3) ...... 3-42

Table 3-23. Estimated Number of WTPs Using Copper Sulfate and Amount of Metallic 

Copper Used in Pounds (National Estimates Based on Responses to 

Question 3) ......................................................................................................... 3-43

Table 3-24. Estimated Number of WTPs Using Chelated Copper Complexes and .................. 

Table 3-25. Number of PWSs and Total Population Served by System Type, SDWIS ............ 3-47

Table 3-26. Summary of the Number of PWSs by System Type and Size, SDWIS ................. 3-47

Table 3-27. Number of Systems that Report Water Sales to Different Customer 

Categories, DWT Industry Questionnaire.......................................................... 3-48

Table 3-28. Number of Water Systems by Ownership Type and Size, SDWIS ........................ 3-49

Table 3-29. Number of Water Systems by Water Source and System Size, SDWIS ................ 3-50

Table 3-30. Summary of CWSs by Water Source and Population Served, CWSS ................... 3-52

3-44
Drinking Water Industry Report List of Tables

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Table 3-31. Reported 2006 Water Quantity Sold (MGY), per System, DWT Industry 

Questionnaire ..................................................................................................... 3-54

Table 3-32. Summary of Annual CWS Revenues by Ownership Type ($1,000), CWSS ......... 3-54

Table 3-33. Summary of Total Revenues of CWSs that Discharge ($/1,000 gallons) .............. 3-55

Table 3-35. Reported 2006 Water Sales Revenue per Volume, per System, DWT Industry 

Questionnaire ..................................................................................................... 3-56

Table 3-36. Average System Expenses and Expense Breakdown by Major Category, 

CWSS ................................................................................................................. 3-58

Table 3-37. Summary of Total Expenses by System Size and Ownership Type ...................... 3-58

($/1,000 gallons produced), CWSS ........................................................................................... 3-58

Table 3-38. Reported 2006 Total Expenses, per System, DWT Industry Questionnaire .......... 3-60

Table 3-39. Reported 2006 Expenses per MGY, Total and Operating, per System, DWT 

Industry Questionnaire ....................................................................................... 

Table 3-40. Reported 2006 Hourly and Total Wages for All Employees, per System, 

DWT Industry Questionnaire ............................................................................. 3-62

Table 3-41. Number and Percentage of CWSs Serving Different Customer Types, CWSS ..... 3-64

Table 3-42. Amount of Water Delivered by Customer and Ownership Type and System 

Size (billion gallons; 2000), CWSS ................................................................... 3-65

Table 3-43. Reported 2006 Water Sales to Residential Customers, by System, DWT 

Industry Questionnaire ....................................................................................... 3-66

Table 3-44. Revenues by Customer Type (in million $), CWSS............................................... 3-67

Table 3-45. Median Revenue per 1000 Gallons of Water Delivered by Customer Type, 

Ownership Type, and System Size ($/1000 gallons), CWSS ............................ 3-68

Table 3-46. Summary of Median Annual Residential Water Bill, CWSS................................. 3-69

Table 3-47. Number of Systems Using Various Billing Methods for All Customers, 2006, 

DWT Industry Questionnaire ............................................................................. 3-70

Table 3-48. Number and Percentage of Systems with Lower Rates for Low- or FixedIncome Households, CWSS ............................................................................... 3-71

3-61
Drinking Water Industry Report List of Tables

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Table 3-49. Reported 2006 Household Participation in System Assistance Programs and 

Income Requirements, DWT Industry Questionnaire ....................................... 

Table 3-50. Number of Households with Lower Rates and Range of Qualifying 

Household Incomes, CWSS ............................................................................... 

Table 4-1. Summary of Permit Information in the 2004 Permit Compliance System ................. 4-2

Table 4-2. Wastewater Discharges from WTPs Covered by General Permits ............................ 4-6

Table 4-3. Range of Pollutant Limitations From a Sample of General and Individual 

NPDES Permits .................................................................................................... 4-8

Table 5-1. Common Source Water Contaminants and Sources ................................................... 5-2

Table 7-1. Typical Chemical Coagulation Sludge Volumes ....................................................... 7-4

Table 7-2. Typical Lime Softening Sludge Volumes .................................................................. 7-5

Table 7-3. Typical Characteristics of Low-Pressure Membrane Backwash Residuals ............... 7-8

Table 7-4. Typical Characteristics of Spent Low-Pressure Membrane Chemical 

Cleaning Solutions ............................................................................................... 7-9

Table 7-5. Membrane Desalination: Typical Target Contaminants by Source Water ............... 7-11

Table 7-6. Typical Membrane Desalination System (RO and NF) Design Parameters ............ 7-11

Table 7-7. Typical Ion Exchange Concentrate Volumes ........................................................... 7-13

Table 7-8. Typical Chemical Concentrations in Ion Exchange Waste Concentrate .................. 7-13

Table 8-1. Priority Pollutant List ............................................................................................... 8-2

Table 8-2. Evaluation of Priority and Nonconventional Metals in Water Treatment Plant 

Residuals .............................................................................................................. 8-6

Table 9-1. Pollutants Included in the Loadings Estimates ........................................................... 9-9

Table 9-2. Type of Source Water Treatment and Residuals in Place (Solid/Water 

Separation) for WTPs with DMR Data .............................................................. 9-11

Table 9-3. Type of Source Water Treatment and Residuals in Place (Dechlorination) for 

WTPs with DMR Data ....................................................................................... 9-12

Table 9-4. Long-Term Average Concentrations from DMR Data by Source Water 

Treatment Type and Residuals Treatment (mg/L) ............................................. 9-14

3-72

3-72

a
Drinking Water Industry Report List of Tables

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Table 9-5. Long-Term Average Concentrations for Pollutants Resulting from 

Disinfection with Chlorine ................................................................................. 9-16

Table 9-6. Model Plant Effluent Flow Rates ............................................................................. 9-19

Table 9-7. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for 

Direct and Indirect (Pass Through) Discharges: Population Served of 

10,001 to 50,000 People..................................................................................... 9-21

Table 9-8. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for 

Direct and Indirect (Pass Through) Discharges: Population Served of 

50,001 to 100,000 People................................................................................... 9-24

Table 9-9. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for 

Direct and Indirect (Pass Through) Discharges: Population Served of 

100,001 to 500,000 People................................................................................. 9-28

Table 9-10. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for 

Direct and Indirect (Pass Through) Discharges: Population Served of 

More than 500,000 People .................................................................................

Table 9-11. Model Plant Pollutant Loadings for WTPs Performing Chlorination by 

Source Water Treatment Type and Residuals Treatment Type (With and 

Without Dechlorination) for Direct and Indirect (Pass Through) 

Discharges: Population Served of 10,001 to 100,000 People ............................ 9-34

Table 9-12. Model Plant Pollutant Loadings for WTPs Performing Chlorination by 

Source Water Treatment Type and Residuals Treatment Type (With and 

Without Dechlorination) for Direct and Indirect (Pass Through) 

Discharges: Population Served Greater than 100,000 People ........................... 9-37

Table 9-13. Pollutant Loadings a for WTPs: National Estimates by Source Water 

Treatment Type and Pollutant ............................................................................ 9-41

Table 9-14. Pollutant Loadings a for WTPs Serving More than 10,000 People: National 

Estimate by Source Water Treatment Type and WTP Size (as Population 

Served) ............................................................................................................... 9-43

Table 11-1. Distribution of Residuals Treatment Technologies at Drinking Water 

Treatment Plants .............................................................................................. 11-10

Table 11-2. Comparison of Solids Removal Technologies: Solids Concentration After 

Treatment by Residuals Type .......................................................................... 11-12

9-31
Drinking Water Industry Report List of Tables

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Table 11-3. Laboratory Results for Mechanical Dewatering Operations for Various 

Drinking Water Treatment Residuals .............................................................. 11-17

Table 12-1. Available Residuals Management Cost Equations ................................................. 12-6

Table 12-2. Ranges of Residuals Production Estimated for AWWA 2008 Study ..................... 

Table 12-3. SFBW Equalization Basin Capacity ..................................................................... 12-11

Table 12-4. Indirect Cost Factors and Selected Unit Costs for WTP Residuals Treatment 

System Planning............................................................................................... 12-18

Table 13-1. Example of Income Distribution from the 2000 U.S. Census .............................. 13-13

Table 13-2. Example of Income Distribution Provided by the U.S. Census With Ranges 

Updated to Current Year (10% increase in income) ........................................ 13-14

Table 13-3. Example of Income Distribution Provided by the U.S. Census With Ranges 

and Number of Households Updated to Current Year (10% increase in 

income and 3% increase in population) ........................................................... 13-15

Table 13-4. Example of the Calculation of Number and Percent of Households above an 

Achievability Threshold (1.0% of Median Household Income) ...................... 13-18

Table 13-5. Example of the Calculation of Number and Percent of Households above an 

Achievability Threshold (1.0% of Median Household Income) assuming a 

Lifeline Rate Structure for Income Below $16,500 ......................................... 13-20

12-9
Drinking Water Industry Report List of Figures

xiv

LIST OF FIGURES

Page 

Figure 3-1. Question 2b: Population Served by the WTP in 2006 .............................................. 3-5

Figure 3-2. Question 2e: Source Water Type .............................................................................. 

Figure 3-3. Questions 2b-d: WTP Operating Characteristics ...................................................... 3-8

Figure 3-4. Question 2f: Source Water Treatment and Chemical Addition: 

Presedimentation ................................................................................................ 3-13

Figure 3-5. Question 2f: Source Water Treatment and Chemical Addition: Primary 

Disinfection and Dechlorination ........................................................................

Figure 3-6. Question 2f: Source Water Treatment and Chemical Addition: Disinfection 

Residuals ............................................................................................................ 3-14

Figure 3-7. Question 2f: Source Water Treatment and Chemical Addition: Primary 

Disinfectant ........................................................................................................ 3-15

Figure 3-8. Question 2h: Residuals Treatment .......................................................................... 3-20

Figure 3-9. Question 2i: Pollution Prevention ........................................................................... 3-21

Figure 3-10. Question 2k: Residuals Discharge Method ........................................................... 3-25

Figure 3-11. Question 2k: Type of Residuals Discharged ......................................................... 3-26

Figure 3-12. Question 2k: Frequency of Residuals Discharge .................................................. 3-27

Figure 3-13. Question 2k: Direct Discharge—Continuous, Batch or Emergency and Type 

of Receiving Stream ........................................................................................... 3-27

Figure 3-14. Question 2k: Indirect Discharge—Continuous, Batch or Emergency and 

Volume Discharged ........................................................................................... 3-28

Figure 3-15. Question 2k: Zero Discharge Methods ................................................................. 3-29

Figure 3-16. Question 3: Use of Copper-Based Chemicals to Treat Source Water .................. 

Figure 6-1. Typical Conventional Filtration Treatment Plant Flow Diagram (U.S. EPA, 

2002a) .................................................................................................................. 6-3

Figure 6-2. Reverse Osmosis Cross-Flow Membrane (The Merit Partnership, 2002) .............. 6-10

Figure 6-3. Ozone Disinfection Process Flow Diagram (U.S. EPA, 1986) ............................... 6-18

3-6

3-14

3-40
Drinking Water Industry Report List of Figures

(Continued)

Page 

xv

Figure 7-1. Residuals from Source Water Solids Removal (U.S. EPA/ACSE/AWWA, 

1996) .................................................................................................................... 7-2

Figure 7-2. Residuals from Precipitative Softening WTP ........................................................... 7-6

Figure 7-3. Residuals from Membrane Desalination ................................................................. 7-10

Figure 8-1. Chemistry of Compounds Resulting from Chlorine Disinfection (CDC, 2006; 

Block, 2000) ....................................................................................................... 

Figure 11-1. WTP Pollution Prevention and Waste Reduction Practices in the U.S. in 

2006.................................................................................................................... 11-3

Figure 11-2. Gravity Thickener (U.S. EPA, 2003) .................................................................. 11-14

Figure 11-3. Belt Filter Press (U.S. EPA, 2000a) .................................................................... 11-16

Figure 11-4. Sand Drying Bed Section (U.S. EPA, ASCE, and AWWA, 1996) .................... 

Figure 12-1. Residuals Treatment Technology Train ................................................................ 12-3

8-12

11-19
1-1

SECTION 1

INTRODUCTION

The purpose of this report is to summarize information EPA collected to assess 

drinking water treatment plant (WTP) discharges of treatment residuals to surface water. EPA 

identified WTPs for analysis in its 2004 Effluent Guidelines Program Plan based on public 

comments and preliminary review of available data. In addition to literature review and site 

visits, EPA collected technical and financial information about WTPs through a national survey. 

After considering extensive information about WTPs, the production and management of 

treatment residuals, the characteristics of residuals waste streams, and resource availability in the 

context of other priorities, EPA determined that discharges of treatment residuals are best 

addressed through National Pollutant Discharge Elimination System (NPDES) permits. 

Accordingly, this report provides information about drinking water treatment technologies and 

residuals best management practices that may be useful to NPDES permit writers and WTPs with 

NPDES permits. Sections 2, 3, 9, 10, and 11 of this report summarize the data that EPA 

collected. Sections 4 through 8 and Sections 12 and 13 provide technical information particularly 

relevant to NPDES permitting of treatment residuals.

The DWT industry serves to provide potable water to its customers. The DWT 

industry falls under Standard Industrial Classification (SIC) code 4941, which crosswalks with 

North American Industry Classification System (NAICS) code 22131. In addition to drinking 

water, SIC code 4941 includes other water supply plants—those that treat water for use in 

commercial and industrial applications. NAICS code 22131 includes all of SIC code 4941 plus 

irrigation systems (defined by SIC code 4971). For this industry review, EPA focused on 

drinking water systems that serve more than 10,000 people. Most systems that serve more than 

10,000 people are defined as community water systems (CWSs) under the Safe Drinking Water 

Act. CWSs serve the same customer base year round (e.g., city water authority). 

Drinking water systems may obtain their water supply either directly from the 

source (e.g., river, lake, reservoir for surface water sources or via wells for ground water sources) 

or may purchase from wholesalers. Systems may treat the source water (i.e., intake water) prior 
Drinking Water Industry Report Section 1 – Introduction

1-2

to distribution or only provide delivery of the drinking water. If the system treats the source 

water prior to delivery, the system operates one or more WTPs. 

Based on EPA’s industry questionnaire, 2,151 WTPs serve populations greater 

than 10,000 people and generate waste streams from the treatment of source water. Sixty-eight 

percent (1,464 plants) serve between 10,001 and 50,000 people, and on average produce 3.49 

million gallons per year of finished drinking water. The remaining 32 percent (688 plants) serve 

more than 50,000 people and produce between three and 55,000 million gallons per year of 

finished drinking water. The average drinking water production per day for the 688 WTPs is 

23.46 million gallons. For all 2,151 WTPs, the average quantity of drinking water produced per 

person per year is over 53,000 gallons. 

During the treatment of source water, WTPs remove contaminants that are

unhealthy or undesirable for consumption. The generated waste streams are treatment residuals. 

EPA estimates that approximately 31 percent of the 2,151 WTPs directly discharge to surface 

water. An additional 7 percent discharge both directly to surface water and indirectly by 

transferring residuals to POTWs. The discharge of treatment residuals is the issue of interest in 

this industry review. 

Since 2004, EPA has conducted site visits, completed an industry questionnaire, 

worked with the industry (e.g., American Water Works Association), and collected other 

information. EPA produced this technical report to summarize the collected information and our 

analysis. Section 2.0 summarizes EPA’s activities to identify and collect data as part of the 

industry review. Subsequent sections of this report summarize analyses conducted using data 

from these sources. In particular: 

• Section 3.0 characterizes the water treatment industry by size of 

population served, primary water source (e.g., ground, surface), treatment 

method(s) used (e.g., precipitative softening, conventional filtration, 

membrane desalination, ion exchange), and discharges. It provides an 

overview of financial characteristics of the industry and a discussion of 

water consumption and rates. 

• Section 4.0 analyzes state permit requirements including both general 

and individual permits, pollutants regulated (e.g., aluminum, iron, 
Drinking Water Industry Report Section 1 – Introduction

1-3

manganese, pH, settleable solids), range of pollutant limitations, and 

special requirements for systems based on treatment technologies used. 

• Section 5.0 discusses source water quality and the factors that 

influence it. Influencing factors include naturally-occurring attributes 

(climate, geology, soil type, land cover, hydrology, precipitation and 

runoff, and wildlife) and man-made attributes (land management practices 

and runoff or upstream discharge from point and nonpoint sources). 

• Section 6.0 reviews source water treatment technologies including 

conventional filtration, direct filtration, and filtration only; precipitative 

softening; membrane separation; ion exchange; activated carbon; 

disinfection; and other chemical additions. 

• Section 7.0 examines residuals produced by each of the source water 

treatment technologies. Residuals generated by WTPs include solids 

contaminants removed during precipitative softening (softening sludge) 

and coagulation, flocculation, and sedimentation (coagulation sludge); 

filter backwash water; concentrates from membrane desalination; spent 

membrane cleaning solutions; ion exchange waste concentrates; and 

regeneration wastes from adsorption processes. 

• Section 8.0 discusses pollutants in drinking water treatment residuals 

including suspended and dissolved solids, metals (e.g., aluminum, iron, 

lead, and manganese), disinfection by-products (e.g., trihalomethanes and 

haloacetic acids), and other pollutants. 

• Section 9.0 provides EPA’s national estimate of pollutant discharges 

from WTPs. In addition to the estimate, this section describes data 

sources and methodology used; selection of pollutants to include in the 

loadings estimates; development of long-term averages for pollutants; and 

pollutant loadings estimates for model plants.

• Section 10.0 describes the potential environmental impacts of 

pollutant discharges. EPA completed a literature review to gather data on 

potential environmental impacts from discharges of WTP residuals. The 

majority of studies focused on discharges of lime sludge and alum sludge 

from lime softening and conventional filtration plants. This section 

summarizes EPA’s review of environmental impacts from WTP 

discharges.

• Section 11.0 discusses best management practices for handling, 

minimizing, and preventing source water treatment residuals. 

Example best management practices include source reduction activities 

(e.g., optimization of surface water intake to reduce suspended solids, 

optimization of filter media for finished water), and treatment of residuals, 

recycling and reuse of residuals, and land application of residuals. 
Drinking Water Industry Report Section 1 – Introduction

1-4

• Section 12.0 reviews cost considerations for residuals thickening and 

dewatering. Technology options exist to reduce discharges of residuals.

This section examines the factors that affect the cost of installing and 

operating residuals treatment systems for conventional filtration (i.e., 

coagulation and filtration) and lime softening plants.

• Section 13.0 discusses the methodology to assess economic 

achievability. EPA outlines an approach to determine the economic 

achievability of installing new technology to treat residuals at WTPs. 

• Section 14.0 includes a glossary, acronyms, and abbreviations used in 

this report. 
2-1

SECTION 2

DATA SOURCES

EPA conducted a number of data collection activities and reviewed a number of 

data sources in support of the drinking water treatment (DWT) industry review. Section 2.1 

describes EPA’s site visits and Section 2.2 describes EPA’s industry questionnaire. Section 2.3 

discusses ground water and drinking water data collected by EPA under the Safe Drinking Water 

Act (SDWA). Section 2.4 presents other information collection activities and data sources, 

including literature searches, National Pollutant Discharge Elimination System (NPDES) 

permits, NPDES Discharge Monitoring Reports (DMRs), other EPA data sources, and industry 

data. Section 2.5 describes EPA’s outreach efforts through stakeholder meetings and Section 2.6 

describes the DWT technology review.

2.1 SUMMARY OF EPA’S WATER TREATMENT PLANT SITE VISITS 

EPA conducted site visits to 31 drinking water treatment plants (WTPs) and a 

technology vendor research and manufacturing plant to gather information about industry 

operations, sources of residuals, residuals management practices, and residuals treatment 

technologies. EPA used information collected from literature searches and contact with trade 

association members to identify representative WTPs for site visits. In general, EPA considered 

the following when selecting WTPs to visit: 

• Size of plant (medium and large plants); 

• Geographic location (variable source water qualities); and

• Residuals management practices (for treatment technologies that generate 

residuals).

Plant-specific selection criteria are contained in site visit reports prepared for each 

plant visited by EPA. During the site visits, EPA collected the following information:

• Plant description (e.g., size, production volume, location); 

• Source water treatment technologies;
Drinking Water Industry Report Section 2 – Data Sources

2-2

• Residuals generation, treatment, and management; and 

• Permitting requirements.

This information is documented in the site visit report for each WTP visited. Table 2-1 lists the 

site visits EPA performed and the document control number (DCN) for the site visit report. 

2.2 EPA DWT INDUSTRY QUESTIONNAIRE 

2.2.1 Overview of Industry Questionnaire

EPA used an industry questionnaire to collect site-specific technical and 

economic information for Community Water Systems (CWSs) and WTPs operated by the 

systems. CWSs are drinking water systems that serve the same customer base year round (e.g., 

city water authority). The majority of drinking water is distributed by CWSs. 

EPA published a notice in the Federal Register on July 5, 2005 (70 FR 38675) 

announcing its intent to submit a survey Information Collection Request (ICR) to the Office of 

Management and Budget (OMB). The notice requested comment on the draft ICR and two draft 

survey questionnaires (screener and detailed)..EPA subsequently obtained OMB approval to 

administer one survey questionnaire (71 FR 41012, July 19, 2006). 
Drinking Water Industry Report Section 2 – Data Sources

2-3

Table 2-1. EPA Site Visits to Drinking Water Treatment Plants

Water Treatment Plant (WTP) 

Name

Date of EPA Site 

Visit Type of Source Water Treatment Type of Residuals Treatment

Site Visit 

Report DCN

James J. Corbalis WTP

(Fairfax County, VA)

November 3, 2004 Conventional filtration of surface water; 

disinfection using chlorine and chloramines

Solids dewatering: gravity 

thickening and plate and filter press; 

Water from dewatering recirculated 

to the head of the plant

DW00178

Bexar Metropolitan Ultrafiltration 

WTP

(San Antonio, TX)

November 18, 2004 Ultrafiltration with coagulation/sedimentation 

of surface water; disinfection using chlorine

Equalization;

Evaporation ponds; 

Filter backwash recirculated to the 

head of the plant

DW03706

Washington Aqueduct: Dalecarlia 

WTP (Washington, DC)

November 30, 2004 Conventional filtration of surface water; 

disinfection using chloramines

Dewatering facility is under 

construction

DW03707

Rivanna Water and Sewer 

Authority: South Rivanna WTP 

(Charlottesville, VA)

March 31, 2005 Conventional filtration of surface water; 

disinfection using chlorine

Equalization, clarification, and 

wastewater recirculation to the head 

of the plant; 

Solids dewatering: belt filter press 

DW03708

Rivanna Water and Sewer 

Authority: Scottsvillle WTP 

(Charlottesville, VA)

March 31, 2005 Conventional filtration of surface water; 

disinfection using chlorine

Equalization, clarification, and 

wastewater recirculation to the head 

of the plant; 

Settling in lagoons prior to discharge

Evitts Creek WTP

(Cumberland, MD)

July 14, 2005 Direct filtration of surface water, including use

of dissolved air flotation (DAF); disinfection 

using chlorine (ammonia added to distribution 

system to form chloramines)

Solids dewatering: thickening and 

belt filter press

DW03709

F.B. Leopold Company

(Zelienople, PA)

July 15, 2005 Vendor research and manufacturing facility DW00223

Fleur Drive WTP 

(Des Moines, IA)

October 6, 2005 Source water: surface water (Aspects of this report are claimed by the facility to be 

Confidential Business Information)

DW00918

Newport News Water Works: Lee 

Hall Facility 

(Newport News, VA)

October 7, 2005 Conventional filtration of surface water (with 

DAF); 

Reverse osmosis of ground water; 

Disinfection of finished water from both plants 

using chlorine or ozone

Equalization and gravity thickeners;

Thickening sludge treated off-site in 

centrifuges

DW03710
Drinking Water Industry Report Section 2 – Data Sources

2-4

Table 2-1. EPA Site Visits to Drinking Water Treatment Plants

Water Treatment Plant (WTP) 

Name

Date of EPA Site 

Visit Type of Source Water Treatment Type of Residuals Treatment

Site Visit 

Report DCN

City of Melbourne: Joe Mullins 

Reverse Osmosis WTP 

(Melbourne, FL)

October 14, 2005 Reverse osmosis of ground water; disinfection 

of finished water using chlorine 

Concentrate is degasified to remove 

hydrogen sulfide and carbon 

dioxide; 

Acid is added to lower the pH; 

Air injected prior to discharge to 

increase dissolved oxygen levels

DW00903

City of Melbourne: John A. 

Buckley Surface WTP

(Melbourne, FL)

October 14, 2005 Conventional filtration (activated carbon filters) 

of surface water; disinfection of finished water 

using chlorine

Equalization (filter backwash);

Solids dewatering: filter presses; 

Wastewater recirculated to the head 

of the plant.

DW00903

E.M. Johnson WTP

(Raleigh, NC)

October 17, 2005 Conventional filtration of surface water; 

disinfection using chlorine (sodium 

hypochlorite) and chloramine (at clear well)

Clarification of filter backwash;

Solids dewatering: gravity 

thickening and belt filter press

DW00905

Val Vista WTP

(Mesa, AZ)

January 18, 2006 Conventional filtration of purchased water 

(surface water); disinfection using chlorine

Filter backwash clarifiers;

Solids dewatering: gravity 

thickeners and centrifuges

DW00891

Alvarado WTP 

(San Diego, CA)

January 19, 2006 Conventional filtration of purchased and surface 

water; disinfection using chlorine but plans to 

introduce ozone disinfection

None: residuals returned to intake 

reservoir (source water)

DW00907

Puerto Rico Aqueduct and Sewer 

Authority (PRASA): Arecibo 

WTP

August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

None DW03711

PRASA: El Yunque WTP August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Sludge drying: vacuum-assisted

PRASA: Canovanas WTP August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Recirculation to the head of the plant

PRASA: Enrique Ortega (La 

Plata) WTP 

August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Sludge drying: vacuum-assisted

PRASA: Los Filtros (Guaynabo) 

WTP

August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Sludge drying: vacuum-assisted

PRASA: Sergio Cuevas 

Bustamante WTP

August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Sludge drying: vacuum-assisted
Drinking Water Industry Report Section 2 – Data Sources

2-5

Table 2-1. EPA Site Visits to Drinking Water Treatment Plants

Water Treatment Plant (WTP) 

Name

Date of EPA Site 

Visit Type of Source Water Treatment Type of Residuals Treatment

Site Visit 

Report DCN

Thames Water: Superaqueduct 

WTP

August 8 – 10, 2006 Conventional filtration of surface water; 

disinfection using chlorine

Solids dewatering: lagoon

Missouri American Water 

Company: St. Joseph Plant

(St. Joseph, MO)

October 16, 2006 Precipitative (lime) softening of ground water; 

disinfection using chlorine

Filter backwash recirculated to the 

head of the plant; 

Settling basin prior to discharge

DW03772

Kansas City WTP

(Kansas City, MO)

October 17, 2006 Precipitative (lime) softening of surface and 

ground water; disinfection using chloramine

None

Courtney Bend Water Plant

(Independence, MO)

October 17, 2006 Precipitative (lime) softening of ground water; 

disinfection using chloramines

Filter backwash recirculated to the 

head of the plant

Boonville WTP

(Boonville, MO)

October 18, 2006 Direct filtration of surface water None

Missouri American Water 

Company: Jefferson City Plant

(Jefferson City, MO)

October 18, 2006 Precipitative (lime) softening of surface water None

St. Louis Water Division:

Chain of Rocks WTP

(St. Louis, MO)

October 19, 2006 Precipitative (lime) softening of surface water; 

disinfection using chlorine 

None

St. Louis Water Division: Central 

Plant (St. Louis, MO)

October 19, 2006 Precipitative (lime) softening of surface water; 

disinfection using chlorine

None

St. Louis Water Division: Howard 

Bend Plant (St. Louis, MO)

October 19, 2006 Precipitative (lime) softening of surface water; 

disinfection using chlorine

None

St. Louis Water Division: PWSD 

#2 (St. Louis, MO)

October 19, 2006 Precipitative (lime) softening and aeration of 

ground water; disinfection using chlorine

None

St. Louis Water Division: North 

Plant (St. Louis, MO)

October 19, 2006 Precipitative (lime) softening of surface water; 

disinfection using chlorine

None

Illinois American Water 

Company: Alton Plant (Alton, IL)

October 19, 2006 Conventional filtration of surface water, 

disinfection using chloramines (ammonia and 

chlorine)

Dechlorination DW03781

Source: Site Visit Reports. 

Conventional filtration includes coagulation/flocculation, sedimentation, and filtration processes.

Direct filtration includes coagulation/flocculation and filtration processes.

DCN – Document control number (for project record).
Drinking Water Industry Report Section 2 – Data Sources

2-6

2.2.2 Description of Questionnaire

In February 2007, EPA performed a survey (not census) of WTPs to represent the 

entire industry. EPA distributed the Water Treatment Plant Questionnaire to 616 CWSs that 

distribute water to greater than 10,000 people. EPA designed the questionnaire to collect systemand plant-specific information. The questionnaire included three parts: 1) the first part identified 

the system and asked screening questions to determine if the remainder of the questionnaire 

should be completed; 2) the second part requested information on WTPs operated by the CWS 

that generate residuals and serve more than 10,000 people; and 3) the third part requested 

financial data about the system.

EPA excluded small systems (serving less than 10,000 people) from the 

questionnaire mailing list. Even though there are a large number of small systems—over 48,000 

small CWSs (U.S. EPA, 2008), EPA estimated that these systems contribute a small percent of 

residuals generated and discharged by the industry. In its supporting statement to the ICR, EPA 

estimated that CWSs that serve less than 50,000 people would contribute less than nine percent 

of the residuals from the industry. 

The first part of the questionnaire (question 1) requested system information 

(system name, address, and contact information) and asked questions to determine if the system 

was included in the scope of the questionnaire. A system was considered in scope if it was 

classified as a community water system and if one or more of the WTPs operated by the CWS 

met two criteria: 1) generated residuals in 2006; and 2) served a population greater than 10,000 

people. Because the CWS could operate more than one WTP, EPA only wanted to collect data 

on the larger WTPs that generated residuals. If the respondent answered “no” to any of the 

questions, the respondent was not required to proceed with completion of the questionnaire. This 

part also asked whether the system conducted or participated in any monitoring or other studies 

to assess potential impacts from discharges of residuals. 

The second part of the questionnaire (questions 2 and 3) requested general 

treatment plant information, production data, and current residuals treatment and disposal 

practices:
Drinking Water Industry Report Section 2 – Data Sources

2-7

• Plant address;

• Population served; 

• Annual production; 

• Age of plant and any current upgrades; 

• Source water types (i.e., ground water, surface water, or purchased water); 

• Source water treatment;

• Treatment chemicals used;

• Types and quantities of residuals generated, along with any treatment or 

disposal practices;

• Pollution prevention practices; 

• Discharge information; and 

• NPDES permit and 2004 through 2006 DMR data for direct dischargers. 

EPA used the collected data to develop a profile of the industry and to evaluate 

relationships between production factors (e.g., population served, source water treatment 

operations) and residuals quantity, characteristics, and waste management practices. The Agency 

also used data received in response to these questions to identify treatment technologies in place 

and zero discharge practices. 

The last part of the questionnaire (questions 4 through 13) requested financial data 

on the parent utility. Questions included production data, population served, and water sales 

revenue; drinking water systems that purchase water from that utility; other revenue sources; 

total revenue; residential customers and sales revenue from 2004 to 2006; residential customer 

zip codes; billing structure; programs to lower cost for low- or fixed-income households; 

expenses; and cost for capital improvements, repairs, or expansions. EPA used this information 

to characterize the economic profile of the industry. 
Drinking Water Industry Report Section 2 – Data Sources

2-8

2.2.3 Development of the Questionnaire Mailing List

The questionnaire focused on CWSs that operate treatment plants that serve more 

than 10,000 people (estimated based on system population served and corresponding plant 

production) and generate residuals. To develop the list of potential questionnaire recipients, EPA 

identified CWSs that serve more than 10,000 people using EPA’s Safe Drinking Water 

Information System (SDWIS) database from November 9, 2006 (U.S. EPA, 2006). In addition, 

EPA identified wholesale systems in SDWIS (e.g., list service population of 25) and determined 

the systems’ downstream population served by reviewing EPA’s 2000 Community Water System 

Survey (U.S. EPA, 2002) and system websites (ERG, 2005). If a wholesale system served a 

downstream population exceeding 10,000 people, EPA included that system in its questionnaire 

mailing list. EPA identified 4,115 CWSs that serve more than 10,000 people. 

EPA then identified whether these systems operated WTPs that potentially 

generated residuals. To identify treatment operations, EPA used data from SDWIS, the 2000 

Community Water System Survey, Internet searches, and the OGWDW Information Collection 

Rule Auxiliary 1 database.

1

 EPA excluded systems with plants that perform only disinfection or 

addition of chemicals such as flocculants as these plants do not generate residuals. EPA’s final 

list of potential questionnaire recipients included 2,290 CWSs. EPA used the mailing addresses 

listed in SDWIS. For more information about SDWIS and other OGWDW data sources, see 

Section 2.3. 

2.2.4 Sample Selection

EPA focused its analysis on the characteristics of large systems serving more than 

50,000 people and those that primarily use surface water because these systems (and their WTPs) 

are expected to discharge the majority of the WTP residuals, i.e., pollutant loadings. 

Consequently, EPA sampled a greater percentage of systems serving more than 50,000 people 

and surface water systems than systems serving 10,001 to 50,000 people and ground water 

 

1 Data collected by the Information Collection Rule (U.S. EPA, 2000) pertains to the Safe Drinking Water Act and 

differs from EPA’s Information Collection Request performed as part of this industry review.
Drinking Water Industry Report Section 2 – Data Sources

2-9

systems. Appendix A provides information on how the Agency designed the questionnaire, 

developed the sample size, and extrapolated the questionnaire results.

2.2.5 Questionnaire Response

EPA mailed 616 electronic questionnaires, and received 552 responses for a 90 

percent response rate. Of the 552 responses, 482 were in scope based on responses to Questions 

1c to 1e, on generation of residuals in 2006, operation of one or more WTPs serving more than 

10,000 people, and classification as community water system. 

As part of its technical analysis, EPA developed a questionnaire review checklist 

to determine whether the responses received for the second part of the questionnaire (questions 2 

and 3) were complete. If questionnaire responses were not complete or unclear, EPA contacted 

the system or WTP representative for clarification. 

Follow-up included review of responses and personal communication with system 

contacts if questionnaire responses were incomplete or if there were questions concerning the 

data reported. Based on the questionnaire review and follow-up communication, EPA 

incorporated changes to the questionnaire response to the extent possible. All in-scope and 

complete responses were combined into a single questionnaire response database. In addition, 

EPA included a subset of technical responses for an additional 104 questionnaires. The 

questionnaire response database – technical data included 482 in-scope responses. Of these, 378 

systems had complete responses (U.S. EPA, 2009a). 

As part of its economic analysis, EPA reviewed the third part of the questionnaire 

(questions 4 through 13). These questions allowed respondents to provide information for the 

parent utility (i.e., representing multiple systems). EPA included economic data for 482 systems

in the questionnaire response database – financial data (U.S. EPA, 2010). Not all the DWT 

systems included in the questionnaire response database – financial data were included in the 

database with technical responses. For the DWT systems not included in the questionnaire 

response database – technical data, EPA reviewed a subset of the technical responses to 
Drinking Water Industry Report Section 2 – Data Sources

2-10

determine the types and sizes of the systems. These data were used for the national estimates (see 

Appendix A). 

2.2.6 Protection of Confidential Business Information

EPA recognizes that certain data submitted by the industry has been claimed as 

confidential business information (CBI). The Agency has withheld CBI from this report, 

including aggregate data that represents a small number of systems or WTPs. The Agency’s 

approach to CBI protection ensures that data made available to the public explain the industry 

review without compromising data confidentiality.

2.3 EPA’S GROUND WATER AND DRINKING WATER DATA

EPA, along with delegated states and tribes, implements the requirements of the 

Safe Drinking Water Act, which safeguards drinking water delivered to consumers’ taps. EPA

regulates 90 percent of the public drinking water supply in the United States. Public water is 

supplied by publicly- or privately-owned systems that serve at least 25 people or at least 15 

service connections for 60 days or more per year. EPA does not regulate private water supplies 

that serve one or a few homes, such as household wells (U.S. EPA, 2003). 

EPA maintains the SDWIS database (Section 2.3.1); collects system- and plantlevel data from the industry (Sections 2.3.2 and 2.3.3); and provides other data on the industry 

(Section 2.3.4). EPA used these data to identify systems that serve more than 10,000 people, 

including system and treatment plant characteristics. EPA created the questionnaire mailing list 

for the industry questionnaire using these data. 
Drinking Water Industry Report Section 2 – Data Sources

2-11

2.3.1 Safe Drinking Water Information System 

EPA maintains basic information about the nation’s drinking water supply in 

SDWIS2

. States and EPA regional offices report data to EPA quarterly on all public water 

systems. Each public water system is identified in SDWIS using a nine character identification 

number, which includes the identification of the state or EPA regional office that oversees the 

system’s compliance. Data reported include basic information on the systems such as the 

following: 

• System name and address;

• Retail population served; 

• Number of service connections; 

• Primary county or city served; 

• Type of system (i.e., CWS or other); 

• Ownership; 

• Primary source water type (ground water or surface water); and

• Enforcement data.

SDWIS includes both mandatory and optional reporting components. Optional 

reporting components include ownership and type of treatment. Because providing some data is 

discretionary, EPA does not have complete data on every system for these parameters. If 

treatment is included in SDWIS, the data are on a plant-specific basis and include treatment 

objectives such as the following:

• Corrosion control; 

• Dechlorination; 

• Disinfection;

• Disinfection by-products control;

• Inorganics removal;

• Iron removal; 

• Manganese removal;

• Organics removal;

• Particulate removal;

• Radionuclides removal; 

• Taste/odor control; 

 

2 U.S. EPA maintains SDWIS/Federal database which is described in Section 2.3.1. In addition to the federal 

database, SDWIS/State is maintained by the drinking water primacy agency (e.g., state) and may contain additional 

data not available in the federal database. 
Drinking Water Industry Report Section 2 – Data Sources

2-12

• Softening (hardness removal); and 

• Other.

SDWIS does not include data on the type and quantity of residuals generated, 

residuals treatment method, or residuals disposal method. Therefore, EPA gathered data on 

residuals generation, treatment, and disposal using the industry questionnaire (see Section 2.2). 

SDWIS is continually updated, but EPA maintains snapshots (or freezes) of the 

database. In 2006, there were 156,644 public drinking water systems (U.S. EPA, 2008): 

• 52,339 community water systems (i.e., systems that supply water to the 

same population throughout the year) serving 282 million people. 

• 19,045 non-transient, non-community water systems (i.e., systems that 

regularly supply water to at least 25 of the same people for six months or 

more per year, such as schools) serving 6 million people. 

• 85,260 transient, non-community water systems (i.e., systems that supply 

water at locations where people do not remain for an extended time 

period, such as a campground) serving 14 million people. 

2.3.2 2000 Community Water System Survey 

To support the development and evaluation of drinking water regulations, EPA

collected industry data in the 2000 Community Water System Survey (CWSS). EPA collected 

operational and financial characteristics in the CWSS. Because CWSs are a very diverse group, 

CWSS is stratified to represent the complete population of CWSs across the United States, based 

on a list of approximately 52,000 systems from SDWIS. For the 2000 CWSS, questionnaires 

were mailed to 1,200 medium and large systems, and 600 site visits to small systems (serving 

3,300 people or fewer) were conducted.3 Operational data requested include the following: 

• System ownership type; 

• Source water type (ground water, surface water, or purchased water) and 

description of source; 

 

3 Site visits were used instead of mailed questionnaires from small CWSs to reduce the burden of the information 

collection effort on small systems.
Drinking Water Industry Report Section 2 – Data Sources

2-13

• Raw water concentrations;

• Production quantity, flow rate, and capacity for plants; 

• Type of source water treatment;

• Filter backwash technique;

• Residuals treatment and management;

• Discharge type;

• Operator information; and

• Storage and distribution information. 

Financial characteristics collected include customer type, revenue, billing structure, expenses, 

and source of funds. The overall response rate was 69 percent. Responses from CWSS were then 

weighted to develop estimates from the CWS community as a whole. 

The 2000 CWSS data included a report, an MS Access® database of the 

questionnaire information, and an MS Excel® spreadsheet containing treatment plant-specific 

data. The 2000 CWSS includes data on 2,603 WTPs at 1,246 systems. EPA used information 

from the 2000 CWSS to assist in sample frame development and to characterize the economic 

profile of the industry. 

2.3.3 Information Collection Rule, 40 CFR Part 141 

EPA used data from the Information Collection Rule Auxiliary 1 Database (U.S. 

EPA, 2000), along with supporting documentation, to characterize systems and treatment plants 

in the DWT industry as part of the questionnaire mailing list development. The purpose of the 

EPA Information Collection Rule, 40 CFR Part 141 (May 14, 1996), was to generate and provide 

EPA with the following information from drinking water systems:

• Monitoring data on microbiological contaminants; 

• Monitoring data on disinfection by-products; 
Drinking Water Industry Report Section 2 – Data Sources

2-14

• General water quality data; and

• Treatment plant design and operating information to characterize the 

system.

EPA collected these data from drinking water systems and analytical laboratories 

and entered them in the Information Collection Rule Federal Database. To facilitate review of 

the data, EPA designed seven auxiliary databases to store subsets of data extracted from the 

Information Collection Rule Federal Database. The Auxiliary 1 Database includes information 

for 296 systems (all but nine systems serve populations greater than 50,000 people). Data 

available in the Auxiliary 1 Database include the following:

• System design (e.g., EPA region, storage volume, distribution time, 

number of booster stations and dose range); 

• System monitoring (e.g., population served, average flow rate—wholesale 

and retail);

• Wholesale purchase flow rate;

• Treatment plant design (e.g., treatment process, average percent solid, 

solid handling capacity, clearwell data, and minimum temperature); 

• Plant monitoring data (e.g., alum dose (parts per million, ppm), iron dose 

(ppm), coagulant type, source water type (surface water or ground water), 

sludge production, sludge percent solids, disinfection type, average 

influent flow rate, sampling event influent flow rate, chlorine (Cl ) 

demand, effluent flow rate (average and sample event), wastewater 

residuals treatment performed, wastewater treatment flow rate (average 

and sample event));

• Unit process data (e.g., sequence in treatment train, volume, filtration 

surface area, residence times, process flow rate, filtration media type and 

depth, granular activated carbon (GAC) depth, disinfectant name and dose 

(ppm));

• Chemical feed information (e.g., alum, iron, Cl2);

• Ozone chamber data; 

• Sampling data;

• Water quality monitoring data; and

2
Drinking Water Industry Report Section 2 – Data Sources

2-15

• Intake information (e.g., latitude and longitude, reach). 

2.3.4 Other Ground Water and Drinking Water Data

EPA staff and the EPA website provided additional information to support this

industry review. The EPA website includes the following information: 

• Basic drinking water treatment references;

• Drinking water regulations and standards; 

• List of drinking water contaminants and maximum contaminant levels 

(MCLs) allowed in drinking water; 

• Guidance on drinking water regulations and standards; and

• Additional data on the Safe Drinking Water Act. 

2.4 OTHER INFORMATION COLLECTION ACTIVITIES

EPA collected other data to supplement information gathered through the 

aforementioned site visits, questionnaires, and EPA data sources, to obtain information on the 

documented environmental impacts of discharges from WTPs, water treatment operations, 

residuals characteristics, pollution prevention practices, residuals treatment technology 

innovation, and best management practices. These other data collection activities included a 

review of literature sources, current NPDES permits, NPDES monitoring reports, other EPA data 

sources, industry data (on-line data from drinking water system web pages), and AWWA 

questionnaires and reports. 

2.4.1 Literature Search

EPA conducted a literature search to obtain information on various aspects of the 

DWT industry. EPA performed several Internet and literature searches to identify papers, 

presentations, and other applicable materials. Literature collected by EPA covers such topics as:

• Source water treatment technologies;
Drinking Water Industry Report Section 2 – Data Sources

2-16

• Water quality and treatment;

• Pollution prevention; 

• Characterization of WTP residuals;

• Residuals treatment, including performance and costs; 

• Disposal practices and waste management of residuals (e.g., sludge, 

concentrate streams);

• Recycling and reuse of waste streams;

• Industry trends; 

• Environmental impacts; and

• Effect of discharges on the environment. 

EPA used data from these literature sources to develop the industry questionnaire, 

identify and characterize residuals, determine applicability of pollution prevention techniques, 

identify residuals treatment technologies, and identify best management practices (BMPs).

2.4.2 Current NPDES Permits

EPA collected available permit information to determine current practices in 

setting discharge limits for WTPs. States and, in some cases, EPA regions, issue NPDES permits 

to WTPs that allow direct discharge of wastewater. States might issue general permits for groups 

of plants that have similar operations and wastewater characteristics. States issue individual 

permits for specific plants that do not meet the requirements of the states’ general permits. 

Section 4.1.7 provides an overview of NPDES permits. Depending on the permit requirements, 

dischargers report compliance with NPDES permits via monthly discharge monitoring reports 

(DMRs) submitted to the permitting authority.

EPA’s Permit Compliance System (PCS) database contains monitoring and 

NPDES permit data from some permittees that discharge wastewater directly to surface waters.

States (or other permitting authority) have some discretion as to which data they make available 
Drinking Water Industry Report Section 2 – Data Sources

2-17

to PCS.4 For example, permitting authorities enter DMR and permit information for facilities 

that are considered major dischargers. However, they do not necessarily enter DMR or permit 

information into PCS for minor dischargers (as opposed to major dischargers) or facilities 

covered by a general permit. 

Permitting authorities designate which facilities are considered major dischargers 

or minor dischargers by assessing six characteristics including toxic pollutant potential and 

conventional pollutant loading (U.S. EPA, 2009b). Facilities designated as major dischargers 

must submit monthly DMRs to the permitting authority, who enters the reported DMR data into 

PCS. States have the option to enter DMR data for minor discharges into PCS, however, EPA 

does not require states to enter the data. For this reason, the permitting authority may choose to 

include data only for a limited set of minor dischargers in PCS. Similarly, EPA does not require 

DMRs for facilities covered under general permits, and PCS may include limited or no data on 

general permits.

Therefore, the completeness of the data in the PCS system is much higher for 

larger facilities that are more likely to impact surface waters. Information on smaller facilities

with less likelihood to impact surface waters is not consistently tracked in PCS. Also, 

information may not be available for facilities with discharges covered under a general permit. 

Despite the expected data limitations, EPA extracted available information from 

PCS to identify WTPs with NPDES permits. The extraction was performed by searching PCS 

using the Standard Industrial Classification (SIC) code 4941 for the drinking water treatment and 

supply industry. EPA found that PCS contains information on approximately 3,000 WTPs with 

NPDES permits; however only 20 plants are major dischargers. As a result, only limited data 

were available on WTP NPDES permits in PCS. EPA used this information as part of its initial 

screening process to determine the number of plants that discharge directly to waters of the 

United States.

 

4 EPA used DMR data from 2005, when DMR data were still maintained solely in PCS. Starting in 2006, states 

began reporting their data to the Integrated Compliance Information System for NPDES (ICIS-NPDES). However, 

this system was not in use at the time of this study.
Drinking Water Industry Report Section 2 – Data Sources

2-18

EPA expanded its search for WTP permit information beyond PCS, obtaining 

permits available online and those collected by other EPA activities (i.e., site visits and 

questionnaires). EPA used these permits to study permit requirements and treatment in place at 

WTPs that had certain water treatment operations. The majority of the limits in NPDES permits 

for WTPs were based on best professional judgment (BPJ). EPA summarized the current permit 

discharge requirements based on best professional judgment (BPJ)-based permit limitations (see 

Section 5). 

2.4.3 NPDES Discharge Monitoring Reports (DMRs)

NPDES-permitted plants submit DMRs to their permitting authority (state or EPA 

Region). DMRs summarize the quality and volume of wastewater discharged from plants with 

NPDES permits. They are critical for determining compliance with NPDES permit provisions for 

reporting and monitoring and for generating national trends in Clean Water Act compliance. 

DMRs may be submitted monthly, quarterly, or annually depending on the requirements of the 

NPDES permit. 

EPA requested DMR data (for years 2004, 2005, and 2006) as part of the 2007 

industry survey. EPA received primarily 2006 DMR data. EPA used the DMR data to identify 

pollutants of concern (pollutants currently included in NPDES permits) and to calculate pollutant 

loading estimates. EPA received 2006 DMR data for 140 WTPs (U.S. EPA, 2007). 

Indirect dischargers file compliance monitoring reports with their control 

authority (e.g., POTW) at least twice a year as required under the General Pretreatment 

Standards (40 CFR Part 403), while direct dischargers file DMRs with their permitting authority 

at least once a year. For the purposes of this rulemaking analysis, EPA did not collect 

compliance monitoring reports for WTPs that are indirect dischargers. This information is less 

centralized and therefore more difficult to collect than information on direct dischargers. 
Drinking Water Industry Report Section 2 – Data Sources

2-19

2.4.4 Other EPA Data

EPA reviewed two additional databases, the Facility Registry System (FRS) and 

the Resource Conservation and Recovery Act (RCRA) database, to gather additional data on the 

DWT industry. These databases classify facilities using a four-digit Standard Industrial 

Classification (SIC) code or five-digit North American Industry Classification System (NAICS) 

code. EPA used SIC code 4941 or NAICS code 22131 (Drinking Water Treatment and Supply 

Industry) to search the databases. 

2.4.4.1 Facility Registry System (FRS) 

EPA used the FRS to assist in identifying NPDES permit IDs (i.e., direct 

dischargers) for inclusion in the questionnaire mailing list. The FRS is a centrally managed 

database that identifies facilities, sites, or places subject to environmental regulations or of 

environmental interest. This database links the various identification numbers from federal and 

state environmental programs for a single facility. At the time of EPA’s review of the FRS data, 

the public water system identification numbers from SDWIS were not all matched to FRS 

identification numbers. The matching is complicated by the fact that a water system (assigned a

single Public Water System identification number, PWSID, in SDWIS) may operate more than 

one plant subject to environmental regulations (e.g., multiple NPDES permit IDs may apply to a 

single PWSID). The FRS database includes information for over 8,000 plants in SIC code 4941. 

EPA matched FRS IDs (and corresponding NPDES permit IDs) to specific WTPs (and their 

PWSID) where possible. 

2.4.4.2 Resource Conservation and Recovery Act (RCRA)

EPA determined that WTP residuals could be characterized as RCRA hazardous, 

based on searching for RCRA idenfication numbers in FRS. Under RCRA, WTP residuals could 

be characterized as RCRA hazardous based on characteristics of toxicity or corrosivity. EPA 

could then determine whether constituents of the WTP residuals would need to be disposed of as 

RCRA-hazardous waste.
Drinking Water Industry Report Section 2 – Data Sources

2-20

If a WTP generates solid waste, it may be subject to RCRA storage, treatment, 

and disposal requirements. RCRA provides guidelines for the management of solid and 

hazardous wastes. In order to be classified as hazardous, wastes must be listed under 40 CFR 

Part 261 of RCRA. To be considered a RCRA hazardous waste, drinking water residuals must 

either contain a constituent listed as a hazardous waste in RCRA, or exhibit certain 

characteristics of ignitability, corrosivity, reactivity, or toxicity. The FRS database lists 457 

WTPs assigned a RCRA identification number. RCRA waste management requirements, and any 

associated costs, may be part of the review process when developing BMPs or considering 

alternatives to effluent discharges. 

2.4.5 Industry Data

EPA used industry data, such as system websites and consumer confidence 

reports, to supplement data on specific systems and their operations. For example, EPA 

identified wholesale systems (i.e., those that sell drinking water to other systems but do not 

distribute to retail customers) serving more than 10,000 people by reviewing system websites. 

EPA also used on-line data to gather information on a plant-specific level, such as treatment 

performed and source water type. These industry data filled data gaps or confirmed data 

provided by other data sources (e.g., OGWDW data sources). 

2.4.6 American Water Works Association (AWWA) Surveys and Reports 

The AWWA trade association represents water treatment systems and service 

providers (e.g., consultants, manufacturers of water treatment products, etc.), as well as 

individual members who are most often professionals in the drinking water industry. AWWA 

provides regulatory support, technology updates, and other services to its members. EPA 

reviewed reports and other data available from AWWA. A summary of the AWWA surveys and 

resulting reports is provided below. 
Drinking Water Industry Report Section 2 – Data Sources

2-21

2.4.6.1 2004 Water and Wastewater Rate Survey 

The 2004 Water and Wastewater Rate Survey includes summary data and systemspecific data for water and wastewater systems. Data from the questionnaire include the 

following: 

• Rate trends;

• Rates by geographic area;

• Utility characteristics (e.g., population served, daily gallons sold, daily 

capacity, maximum daily production, number of employees, and financial 

data, including annual capital needs, total assets, long-term debt, and total 

equity); 

• Rate structure, monthly water charges, other water charges (e.g., minimum 

monthly charge for residential and industrial, connection charge, system 

development charge), total revenues, and total operating expenses;

• Indication of whether utilities provide water outside the municipal or 

district boundaries (e.g., wholesale) and retail differential (i.e., how much 

more “outside” customers pay compared to “inside” customers); and

• Median household affordability index. 

Survey participants include 266 water treatment utilities from 50 states and six 

Canadian provinces. For comparison, the survey contains international utility data from 44 cities 

in 27 countries (AWWA, 2004). EPA reviewed the survey results for background data on the 

industry; however, EPA did not make additional use of the survey results for this report. 

2.4.6.2 2002 AWWA Recycle Survey Analysis 

AWWA surveyed WTPs to determine their recycling practices for spent filter 

backwash water and other waste streams. AWWA compiled and analyzed data from 333 plants 

that responded to the survey and indicated recycling of one or more streams. The survey gathered 

data on the following: 

• Size of treatment plant (capacity and population served); 

• Location (state);
Drinking Water Industry Report Section 2 – Data Sources

2-22 

• Source water type and its treatment;

• Percent recycled backwash;

• Treatment performed on waste stream prior to recycling back into plant;

• Point where recycled stream reenters the source water treatment;

• Discharge permit availability for the waste stream; and

• Indication of whether monitoring data on the waste stream are available.

The analysis included determination of whether each plant’s equalization basin 

was adequately sized for the recycle stream and whether each plant’s sedimentation basin was 

adequately sized to serve as the equalization basin for the recycle stream (AWWA, 2002). EPA 

reviewed the survey results for background data on the industry; however, EPA did not make 

additional use of the survey results for this report. 

2.4.6.3 Residuals Management Costing Analysis 

To evaluate the cost considerations to construct and operate residuals treatment

systems, EPA reviewed an AWWA-sponsored report entitled Costing Analysis to Support 

National Drinking Water Treatment Plant Residuals Management Regulatory Options, dated 

April 2008 (AWWA, 2008). In this report, AWWA estimated costs to install and operate a 

typical sludge treatment system at model plants. AWWA developed cost curves for conventional 

filtration plants and lime softening plants, over a range of flows and solids loadings. AWWA 

presented their results as a series of curves, showing cost relative to population served, by plant 

type and solids loading. EPA used the costing analysis to augment its summary of cost 

considerations for residuals treatment (see Section 12).

2.5 STAKEHOLDER MEETINGS 

From 2004 through 2008, EPA participated in several meetings with other EPA 

offices, permitting authorities, industry representatives, industry associations, technology 

vendors, and other interested parties to gather technical information on environmental and 

operational issues related to drinking water treatment and supply operations. The purpose of the 

meetings was to gather current detailed information about the industry. These meetings also 

served as forums for the transfer of information between EPA and industry representatives on all 

aspects of WTP operations.
Drinking Water Industry Report Section 2 – Data Sources

2-23 

EPA coordinated with EPA Regions and Headquarter offices as well as the 

following industry and stakeholder groups: 

•

•

Trade associations and industry representatives:

— American Water Works Association,

— Association of Metropolitan Water Agencies,

— American Membrane Technology Association,

— Water and Wastewater Equipment Manufacturer Association,

— Wateruse,

— Passaic Valley Water Commission,

— National Association of Clean Water Agencies,

— Greater Cincinnati Water Works,

— East Bay Municipal Utility District, and

— Los Angeles Department of Water and Power.

Drinking water treatment technology vendors and/or consultants: 

— F.B. Leopold Company, 

— US Filter, 

— General Electric, and

— Black & Veatch.

• Other interested parties:

— Natural Resources Defense Council.

In addition to the meetings, EPA also attended several AWWA conferences 

including the following: 

• AWWA Water Quality Technology Conference, November 2004; 

• AWWA Annual Meeting and Conference, June 2005; 

• Water Environment Technical Exhibit and Conference, October 2005; and

• AWWA Annual Meeting and Conference, June 2006. 

By participating in these meetings and conferences, EPA was able to obtain up-todate information about source water treatment methods; residuals generation, collection, 

treatment, and disposal practices; and economic and financial aspects of the industry. EPA used 

this information throughout its industry review. 
Drinking Water Industry Report Section 2 – Data Sources 

2-24

2.6 DRINKING WATER TREATMENT TECHNOLOGY REVIEW

As part of the industry review, EPA solicited early individual input from 

stakeholders on technical issues related to the management of drinking water residuals. Goals for 

this stakeholder review included the following: 

• Characterization of typical residuals; 

• Identification of pollutants of concern; 

• Identification of pollution prevention and treatment technologies for 

residuals;

• Evaluation of 1993 and 1987 cost estimates developed by EPA and 

AWWA, respectively, for these residuals treatment technologies (U.S. 

EPA, 1993; AWWA, 1987); and

• Application of prevention and treatment technologies. 

From 2005 through 2007, EPA held several meetings and provided stakeholders 

with various technical papers to review. EPA reviewed the comments received from stakeholders 

and prepared technical paper comment-response documents (U.S. EPA, 2006c). 

Stakeholders included personnel from American Membrane Technology 

Association, AMWA, Association of State Drinking Water Administrators (ASDWA), AWWA, 

Black & Veatch, CH2M Hill, EE&T, East Bay Municipal Utility District, Carollo Engineers, 

P.C., Cincinnati Water Works, City of St. Louis Water Division, Environmental Law and Policy 

Center of the Midwest, F.B. Leopold Co., Los Angeles Department of Water and Power, 

NACWA, US Filter, and Water Environment Research Federation, as well as EPA’s OGWDW 

and ORD.

2.7 REFERENCES

American Water Works Association (AWWA), 1987. Water Treatment Plant Waste 

Management. Document Control Number (DCN) DW00186. 

AWWA, 2002. 2002 Recycle Survey Analysis. Submitted by Environmental Engineering & 

Technology, Inc. for AWWA. Document Control Number (DCN) DW00926. 
Drinking Water Industry Report Section 2 – Data Sources

2-25

AWWA, 2004. AWWA and Raftelis Financial Consultants, Inc, 2004 Water and Wastewater 

Rate Survey. DCN DW03765. 

AWWA, 2008. Costing Analysis to Support National Drinking Water Treatment Plant Residuals 

Management Regulatory Options, Submitted by Environmental Engineering & Technology, Inc., 

Newport News, VA. DCN DW03766. 

Eastern Research Group (ERG), 2005. Memorandum: Review of Wholesale Drinking Water 

Treatment Systems, Chantilly, VA. August 1, 2005. DCN DW03783. 

U.S. Environmental Protection Agency (EPA), 1993. Large Water System Byproducts Treatment 

and Disposal Cost Document (EPA 811-D-93-002), Office of Water, Washington, DC. DCN 

DW00058. 

U.S. EPA, 2000. Information Collection Rule (ICR) Auxiliary 1 Database. Office of Water, 

Washington, DC. DCN DW03723. 

U.S. EPA, 2002. Community Water System Survey 2000 (EPA 815-R-02-005), Office of Water, 

Washington, DC. DCN DW00001. 

U.S. EPA, 2003. Water on Tap: What You Need to Know (EPA 816-K-03-007), Office of Water, 

Washington, DC. DCN DW00653. 

U.S. EPA, 2006a. SDWIS Inventory 2006-11-09 (MS Excel® file), Office of Water, 

November 9, 2006. DCN DW03717.

U.S. EPA, 2006b. Survey Sample Frame Version 4. Office of Water, Washington, DC, 

December 2006. DCN DW03716. 

U.S. EPA, 2006c. Memorandum entitled Summary of Three Technology Review Conference 

Calls held on 27 February to 31 March 2006. Office of Water, Washington, DC, July 21, 2006. 

DCN DW00692. 

U.S. EPA, 2007. Phase I DMR Database. Office of Water, Washington, DC, December 2007. 

DCN DW03703. 

U.S. EPA, 2008. FACTOIDS: Drinking Water and Ground Water Statistics for 2006 (EPA 816-

K-06-012). Office of Water, Washington, DC. DCN DW03755. 

U.S. EPA, 2009a. Drinking Water Survey Response Database – Technical Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03790. 

U.S. EPA, 2009b. Technical Support Document for the Annual Review of Existing Effluent 

Guidelines and Identification of Potential New Point Source Categories. EPA-821-R-09-007. 

Washington, DC. (October). 

U.S. EPA, 2010. Drinking Water Survey Response Database – Financial Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03789. 
3-1

SECTION 3

INDUSTRY PROFILE

The purpose of the drinking water treatment (DWT) industry is to provide potable 

water to its customers. The DWT industry falls under Standard Industrial Classification (SIC) 

code 4941, which crosswalks with North American Industry Classification System (NAICS) 

code 22131. In addition to drinking water, SIC code 4941 includes other water supply plants—

those that treat water for use in commercial and industrial applications. NAICS code 22131 

includes all of SIC code 4941 plus irrigation systems (defined by SIC code 4971). For this 

industry review, EPA focused on drinking water systems that serve more than 10,000 people. 

Most systems that serve more than 10,000 people are defined as community water systems 

(CWSs) under the Safe Drinking Water Act. CWSs serve the same customer base year round 

(e.g., city water authority). 

Drinking water systems may obtain their water supply either directly from the 

source (e.g., river, lake, reservoir for surface water sources or via wells for ground water sources) 

or may purchase from wholesalers. Systems may treat the source water (i.e., intake water) prior 

to distribution or only provide delivery of the drinking water. If the system treats the source 

water prior to delivery, the system operates one or more water treatment plants (WTPs). 

3.1 OVERVIEW OF DWT INDUSTRY

As discussed in Section 2.3.1, there are 52,339 community water systems (CWSs) 

in the United States. EPA determined that 4,115 CWSs serve more than 10,000 people.5 EPA’s 

industry questionnaire collected data on CWSs that operate large WTPs (i.e., plants that produce 

drinking water for more than 10,000 people). After collecting responses from the questionnaire, 

EPA determined that 1,441 CWS were in-scope (i.e., operated large WTPs that generate 

residuals (e.g., wastewater, slurry)). See Appendix A. The other 58 percent of CWSs either 

 

5 2006 data from EPA’s Safe Drinking Water Information System and on-line review of wholesale systems (U.S. 

EPA, 2006; ERG, 2005). 
Drinking Water Industry Report Section 3 – Industry Profile

3-2

operate only small WTPs (produce drinking water for less than 10,000 people) or do not generate 

residuals at the large WTPs (e.g., perform disinfection of the source water only). 

WTPs may dispose of residuals by discharging into waters of the United States 

(direct discharge) or by discharging via sewer to a publicly-owned treatment works (indirect 

discharge). Of the WTPs serving more than 10,000 people and generating residuals, EPA 

estimates that 31 percent are direct dischargers, 37 percent are indirect dischargers, and 7 percent 

are both direct and indirect dischargers. The Agency estimates that the remaining 25 percent of

WTPs are zero dischargers (i.e., do not discharge directly or indirectly). Zero discharge methods 

include recycling, evaporation, composting, landfill disposal, spray irrigation, underground 

injection, and land application. Table 3-1 summarizes the number of WTPs operated by CWSs 

by source water treatment method and discharge status (see Appendix A). 

Table 3-1. Discharge Status for Water Treatment Plants Serving More than 10,000 People

Size of CWS 

Population 

Served

Primary 

Water 

Source

Source Water 

Treatment Method

Total 

Number 

of WTPs a,b

Estimated Number of WTPs by Discharge Type

Direct 

Discharge a

Indirect 

Discharge a

Zero Discharge

Only c

10,001 –

50,000

Ground Any 526 121 307 107

Surface Any 938 406 405 206

More than 

50,000

Ground Precipitative softening 66 31 2 32

Conventional filtration 14 [CBI Redacted] [CBI Redacted] [CBI Redacted]

Membrane d 19 2 6 13

Ion exchange 8 [CBI Redacted] [CBI Redacted] [CBI Redacted]

Other treatment e 4 [CBI Redacted] [CBI Redacted] [CBI Redacted]

Surface Precipitative softening 168 90 55 40

Conventional filtration 383 167 142 123

Membrane d 19 4 12 2

Ion exchange 0 0 0 0

Other treatment e 6 [CBI Redacted] [CBI Redacted] [CBI Redacted]

Total 2,151 a,b 832 a 943 a 531

Source: Appendix A. 

a – WTPs may handle residuals using multiple methods; therefore, totals for each column exceed the total number of plants (e.g., 

155 WTPs discharge both directly and indirectly).

b – The counts presented here include updated data compared to Appendix A. For example, Appendix A, Table A-1, classifies 

more facilities under “Other” treatment type. After EPA received questionnaire data, some of the “other” facilities were classified 

as different treatment types.

c – Zero discharge methods include recycling, evaporation, composting, landfill disposal, spray irrigation, underground injection, 

and land application. Direct and indirect dischargers may also use these methods, however, those WTPs are not included in the 

zero discharge only plant counts.
Drinking Water Industry Report Section 3 – Industry Profile

3-3

d – Membrane treatment method includes microfiltration, ultrafiltration, and membrane desalination (reverse osmosis, 

nanofiltration, electrodialysis, and electrodialysis reversal).

e – Other treatment methods include filtration without coagulation and adsorption processes. This group also includes plants that 

did not indicate any treatment operation in the questionnaire (classified as “none”).

3.1.1 Types of Drinking Water Systems 

Drinking water systems that provide water to at least 25 people or 15 service 

connections are defined as “public water systems” (Section 1401(4)(a)). Public water systems

encompass a wide variety of systems and plants. In total, there are 155,693 active public water 

systems serving 307 million people in the United States (U.S. EPA, 2007). These systems differ 

in terms of the type of population that they serve (residential, non-residential, transient, or 

permanent) and in terms of the entity that owns them (public, private, or a mixture of both). 

 

EPA further defines public water systems into the following three types: 

• Community water system (CWS): supplies water to the same population 

year round. 

• Non-transient, non-community water system (NTNCWS): regularly 

supplies water to at least 25 of the same people six months or more per 

year, but not year round (e.g., schools, factories, offices, and hospitals 

with their own water system).

• Transient, non-community water system (TNCWS): supplies water in such 

places as a gas stations or campgrounds where people do not remain for an 

extended time period. 

These are the drinking water systems usually associated with tap water. 

Households outside the service area of a water system obtain drinking water from private wells. 

3.1.2 How EPA Classifies Drinking Water Systems

EPA classifies the size of a drinking water system by population served (size), 

ownership type, and source water type. Other measurements for classifying the size include 

finished water production volume and number of employees. The population served often 

corresponds to the production volume and number of employees needed to run the system. The 

majority of the drinking water systems serve 10,000 people or less; however, the majority of the 
Drinking Water Industry Report Section 3 – Industry Profile

3-4

drinking water is produced by larger systems (those serving more than 10,000 people) (U.S. 

EPA, 2008a). 

3.2 SUMMARY OF QUESTIONNAIRE RESPONSES

This section summarizes the responses to the industry questionnaire about WTP 

and system conditions in 2006. Because EPA used statistical procedures to select systems for the 

questionnaire to be representative, the responses can be used to derive statistical estimates for all 

systems and WTPs in the target population6. For this questionnaire, the target population is 

defined as all systems that operate WTPs that have the capability to generate (and potentially 

treat) residuals and serve populations greater than 10,000 people. In addition, the systems must 

be community water systems (CWSs). 

The following subsections present a series of tables with the results of the 

statistical analysis of the questionnaire data. Each table presents national estimates based upon 

responses from systems and WTPs statistically selected for the questionnaire. Section 3.2.1 

describes the classification7

 of systems and WTPs by population served, source water, and 

treatment type. Section 3.2.2 summarizes WTP characteristics reported in responses to questions 

2 and 3 of the questionnaire. Section 3.2.3 summarizes the system characteristics reported in 

response to economic and financial questions 4 through 13. Appendix A describes the sample 

design, the selection procedure, response rates, and the development of the national estimates. 

3.2.1 System and WTP Classification 

EPA used the responses to classify the WTPs by the size of the population served, 

primary water source, and the source water treatment method. Systems, however, sometimes 

have WTPs assigned to different classifications. For example, the system may operate two small 

WTPs and one larger WTP. In another example, it may operate WTPs using different treatment 

technologies. To assign each system into a single classification, EPA used the information 

associated with the largest WTP reported in its response. Thus, each system is classified by the 

 

6 The target population for a data system is the specific population about which information is desired.

7 As explained in Appendix A, classifications are “domains” in statistical nomenclature.
Drinking Water Industry Report Section 3 – Industry Profile

3-5

population served, primary water source, and treatment method of its largest WTP. EPA 

estimates that there are 2,151 WTPs in 1,742 systems in the target population. 

Table 3-2 provides a summary of the number of WTPs and systems in each 

classification. Because ion exchange operations were not reported for larger WTPs (i.e., serving 

populations more than 50,000) using surface water, Table 3-2 shows the estimated number of 

WTPs and systems to be zero. Because EPA does not have any data on such WTPs or systems, 

the classification has been excluded from all other tables presented in this section.

To determine size classifications for Table 3-2 and the other tables in this section, 

EPA used the response to question 2b (shown below in Figure 3-1) about the number of people 

served by the WTP.

Figure 3-1. Question 2b: Population Served by the WTP in 2006 

To assign each WTP to a single water source, EPA used the response to question 

2e that asks about the percentages of water used from different sources (see Figure 3-2). Most 

WTPs reported the majority of the water was either surface or ground water. For the seven WTPs 

that only reported purchased water, EPA assigned them to surface water as their source because 

it was the most likely source to require treatment after purchase. For two WTPs reporting other 

water sources and one WTP with an even ground water/surface water allocation, EPA used the 

most commonly reported source water in their size category.

2.b. Please indicate the number people served by the water treatment plant in 2006.

Report your estimate to the nearest thousand (e.g., round 21,854 people served to 

22,000). If you do not have this data readily available, see the instructions and example in 

Question 1.d on page 2 to learn how to estimate the population served by your water 

treatment plant.

_ _ _, _ _ _, 0 0 0 people
Drinking Water Industry Report Section 3 – Industry Profile

3-6

Figure 3-2. Question 2e: Source Water Type

In assigning WTPs to treatment methods, EPA evaluated their responses to 

treatment and the types of chemicals reported in question 2.f of the questionnaire. 

Table 3-2. Industry National Estimates: Numbers of WTPs and Systems

Classification Estimated Number of:

Size of Population 

Served

Primary Water 

Source Treatment Method Systems WTPs

10,001-50,000 Ground Any 378 526

Surface Any 811 938

Subtotal 1,189 1,464

More than 50,000 Ground Conventional Filtration 8 14

Membrane 19 19

Other 2 2

Softening 57 66

Ion Exchange 8 8

None 2 2

Subtotal 97 111

Surface Conventional Filtration 295 383

Membrane 17 19

Other 4 4

Softening 139 168

Ion Exchange 0 0

None 2 2

Subtotal 456 576

Subtotal 554 688

Total 1,742 2,151

3.2.2 WTP Characteristics (Summary of Responses to Technical Questions) 

This section provides national estimates based upon the responses to questions 2 

and 3 that addressed WTP operations. The following information is summarized in each section: 

2.e. Please describe the type(s) of water used as the drinking water source in 2006.

Type of Source Water Percentage of Total Source Water

Surface Water

Ground Water

Purchased Water

Other (specify):________________

Total 100%
Drinking Water Industry Report Section 3 – Industry Profile

3-7

• Section 3.2.2.1: basic WTP operating characteristics (Questions 2b – 2d); 

• Section 3.2.2.2: source water treatment operations (Question 2f); 

• Section 3.2.2.3: residuals treatment and pollution prevention practices 

(Questions 2h and 2i); 

• Section 3.2.2.4: residuals discharge practices (Question 2k); and 

• Section 3.2.2.5: copper usage (Question 3). 

The tables appear at the end of each subsection.

3.2.2.1 WTP Operating Characteristics (Question 2)

The questionnaire collected basic operating characteristics data, including 

produced water volume, number of people served, plant age, and water source in response to 

questions 2b, 2c, and 2d. Figure 3-3 shows the wording of the questions and the responses are 

summarized in this section.

Table 3-3 presents the number of people served by WTP classification. Based 

upon the responses, the target population served approximately 143 million people (i.e., 2,151 

WTPs, each serving an average of 66,430 people). 

Table 3-4 presents the total volume of finished water, the amount per person, and 

water per day. The target population produced approximately 7.5 trillion gallons of finished 

water per year (i.e., 2,151 WTPs, each producing an average of 3,490.2 million gallons per year). 

Table 3-5 reports the minimum and maximum number of operating days based 

upon the responses to question 2c. It also estimates the mean (average) number of days that the 

WTP operated during the year. Most WTPs operate all or most of the year, although one WTP 
Drinking Water Industry Report Section 3 – Industry Profile

3-8

reported only 12 days of operation. According to its website, it generally operates only when its 

sister WTP is not operating.8

Table 3-6 identifies when WTPs were built and most recently upgraded. The 

oldest WTP in the questionnaire was built in 1867, making it 140 years old in 2006 (i.e., year 

reported in the questionnaire). The median age of all WTPs was 36 years old (built in 1970). The 

WTP operating the longest since its last upgrade has been doing so since 1885 (121 years). The 

median time since the last upgrade was 12 years.

Figure 3-3. Questions 2b-d: WTP Operating Characteristics

 

8 Erie Water Works, http://www.eriewater.org/our-water/, retrieved December 15, 2008.

2.b. Please indicate the number people served by the water treatment plant in 2006. 

Report your estimate to the nearest thousand (e.g., round 21,854 people served to 

22,000). If you do not have this data readily available, see the instructions and example in 

Question 1.d on page 2 to learn how to estimate the population served by your water 

treatment plant.

_ _ _, _ _ _, 0 0 0 people

2.c. Please indicate the total amount of finished water produced at the water treatment 

plant in 2006.

Report your estimate to the nearest million gallons (e.g., round 6,432,100 gallons 

produced to 6,000,000).

_ _ _, _ _ _ , _ _ _ , 0 0 0, 0 0 0 gallons of finished water produced in 

2006

Number of days in operation in 2006:

□ 365 days

□ _ _ _ days

2.d.i. Please indicate the year that this plant was first built (e.g., 1956).

_ _ _ _

Year

2.d.ii. Please indicate the year of the last treatment upgrade or significant expansion of 

water treatment operations at this plant. A significant expansion is one that increases 

capacity by 50% or more.

 
Drinking Water Industry Report Section 3 – Industry Profile

3-9 

Table 3-3. Number of People Served per WTP in 2006 

(National Estimates Based on Responses to Question 2b) 

Classification

Estimated 

Number of 

WTPs

Number of People Served (in thousands)

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Minimum 

Reported

Maximum 

Reported

Estimated 

Mean

Std Error 

of Mean

10,001-

50,000

Ground Any 526 10 50 18.86 1.72

Surface Any 938 10 50 25.19 0.88

Subtotal 1464 10 50 22.92 0.95

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 59 132 79.37 5.53

Other 2 [CBI Redacted]

Softening 66 52 333 87 6.18

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal a 111 52 490 101.79 7.29

Surface Conventional 

Filtration

383 51 850 165.29 7.56

Membrane 19 56 104 82.14 5.52

Other 4 [CBI Redacted]

Softening 168 51 1,128 183.49 15.13

None 2 [CBI Redacted]

Subtotal a 576 51 1,128 170.1 6.74

Subtotal a 688 51 1,128 159.05 6.21

Total a 2,151 10 1,128 66.43 2.89

a – CBI redacted counts of people served are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-10

Table 3-4. Estimated Water Production per WTP in 2006 (National Estimates Based on Responses to Questions 2b and 2c)

Classification

Estimated 

Number of 

WTPs

Total Amount of Finished Water

(million gallons per year (MGY))

Estimated Water for 

Each Person Served 

Per Year

(gal/person/yr)

Estimated Water 

Produced per Day

(MG/Day)

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Min. Max.

Estimated 

Mean

Std Error 

of Mean Mean Std Error Mean Std Error

10,001-

50,000

Ground Any 526 28 2,776 748.25 139.55 40,866.72 7,547.49 2.12 0.39

Surface Any 938 79 7,061 1,482.26 78.42 58,655.62 2,416.70 4.26 0.21

Subtotal 1,464 28 7,061 1,218.54 88.45 52,264.40 3,593.76 3.49 0.25

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 37 4,462 2,265.77 215.84 28,648.91 4,640.99 6.21 0.59

Other 2 [CBI Redacted]

Softening 66 840 17,000 4,243.80 1,064.31 48,447.97 11,779.86 11.68 2.93

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal a 111 37 17,000 4,170.62 642.52 42,127.70 6,421.41 12.05 1.92

Surface Conventional 

Filtration

383 60 55,000 8,668.41 414.86 55,553.16 1,209.13 24.62 1.23

Membrane 19 2,165 7,000 4,355.71 265.22 54,155.94 3,006.79 12.19 0.68

Other 4 [CBI Redacted]

Softening 168 3 44,000 10,003.66 665.05 61,044.84 3,625.78 27.63 1.84

None 2 [CBI Redacted]

Subtotal a 576 3 55,000 9,128.09 353.52 57,329.19 1,381.09 25.66 1.02

Subtotal a 688 3 55,000 8,326.38 364.13 54,870.84 1,774.75 23.46 1.04

Total a 2,151 3 55,000 3,490.24 172.10 53,097.43 2,529.14 9.87 0.49

a – CBI redacted water production estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-11

Table 3-5. Operating Days per WTP in 2006 (National Estimates Based on Responses to 

Question 2c)

Classification

Estimated 

Number of 

WTPs

Operating Days in 2006

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Minimum 

Reported

Maximum 

Reported Est. Mean

Std. Error 

of Mean

10,001-

50,000

Ground Any 526 92 365 347.08 5.79

Surface Any 938 73 365 350.42 4.07

Subtotal 1,464 73 365 349.22 3.32

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 365 365 365 0

Other 2 [CBI Redacted]

Softening 66 349 365 364.5 0.3

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal a 111 202 365 359.18 2.97

Surface Conventional 

Filtration

383 12 365 354.54 1.86

Membrane 19 292 365 354.75 4.77

Other 4 [CBI Redacted]

Softening 168 250 365 360.8 1.24

None 2 [CBI Redacted]

Subtotal a 576 12 365 356.49 1.3

Subtotal a 688 12 365 356.93 1.19

Total a 2,151 12 365 351.68 2.31

a – CBI redacted operating days are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-12

Table 3-6. WTP Age (National Estimates Based on Responses to Question 2d)

Classification WTP Built (Year) Last upgrade (Year)

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Earliest

Most 

Recent Median Earliest

Most 

Recent Median

10,001-

50,000

Ground Any 1928 2006 1991 1946 2006 1992

Surface Any 1881 2006 1966 1912 2007 1994

Subtotal 1881 2006 1973 1912 2007 1994

More than 

50,000

Ground Conventional 

Filtration

[CBI Redacted]

Membrane 1977 2002 1992 1986 2002 2002

Other [CBI Redacted]

Softening 1953 2003 1992 1953 2006 2004

Ion Exchange [CBI Redacted]

None [CBI Redacted]

Subtotal a 1928 2005 1992 1953 2006 2002

Surface Conventional 

Filtration

1873 2004 1967 1885 2007 1996

Membrane 1939 2006 2003 1998 2006 2003

Other [CBI Redacted]

Softening 1867 2003 1956 1906 2006 1990

None [CBI Redacted]

Subtotal a 1867 2006 1965 1885 2007 1995

Subtotal a 1867 2006 1967 1885 2007 1996

Total a 1867 2006 1970 1885 2007 1994

a – CBI redacted WTP years built and upgraded are included in subtotal and total rows.

3.2.2.2 Source Water Treatment Operations (Question 2f)

This subsection summarizes the responses to Question 2f which collected data 

about source water treatment operations employed at the WTP, chemicals used in the operations, 

and the amounts of the chemicals used. Section 3.2.1 describes the assignment of WTPs to each 

treatment method based upon information in question 2f. Tables 3-7 through 3-10 provide 

national estimates about source water treatment operations. If the respondent did not check a 

particular box, EPA assumed that the answer was ‘no’ (e.g., if the respondent did not check the 

box for presedimentation, EPA assumed that this procedure was not conducted at the WTP). 

Each table provides the estimated total number of WTPs in the classification and the smaller 

subset that performed each different operation in 2006. For example, an estimated 38 of the 526 
Drinking Water Industry Report Section 3 – Industry Profile

3-13

ground water plants that serve less than 50,000 people use presedimentation (Table 3-7). The 

discussion below identifies the specific portions of the question related to each table. 

Table 3-7 estimates the number of WTPs that use presedimentation as part of their 

source water treatment operations. Of the estimated 2,151 WTPs in the target population, 

approximately 141 WTPs (7 percent) use presedimentation.

Figure 3-4. Question 2f: Source Water Treatment and Chemical Addition: 

Presedimentation 

Table 3-8 estimates the number of WTPs using primary disinfection and the type 

of disinfection. The estimates are based upon responses to two parts of Question 2f as shown in 

Figure 3-5. Based upon the responses, 93 percent of the WTPs in the target population perform 

primary disinfection (i.e., 2,002 of the 2,151 WTPs). No respondent selected hydrogen peroxide, 

which appeared as one option in the questionnaire. Thus, it does not appear in the table. Table 3-

8 also shows the estimated 230 WTPs, by classification, that perform dechlorination. 

□ Presedimentation Average Amount Per Day 

(number, e.g., 20)

Units

□ Polymer coagulant □ tons □ lbs

□ Other (specify):___________ □ tons □ lbs
Drinking Water Industry Report Section 3 – Industry Profile

3-14

Figure 3-5. Question 2f: Source Water Treatment and Chemical Addition: Primary 

Disinfection and Dechlorination 

Table 3-9 provides information about disinfection residuals in the filter backwash 

and filter-to-waste. The estimates are based upon responses to two parts of Question 2f as shown 

in Figure 3-6. For each of these two items, WTPs were asked to check whether they had free 

chlorine, chloramination, other, or no backwash or filter-to-waste at the plant. EPA estimates that 

most WTPs generate filter backwash and filter-to-waste (i.e., 1,906 and 1,809, respectively, of 

the 2,151 WTPs). 

Figure 3-6. Question 2f: Source Water Treatment and Chemical Addition: Disinfection 

Residuals 

□ Primary Disinfection (Please indicate type)

□ Free chlorine

□ Chloramination

□ Ozone

□ Ultraviolet light

□ Hydrogen peroxide (H2O2)

□ Other (specify):__________________

Note: Primary disinfection is intended to remove or inactivate harmful microorganisms at the 

treatment plant, often conducted at the head of the plant or prior to filtration. This 

disinfection treatment is different from secondary disinfection, which is conducted as one of 

the final steps prior to distribution of the finished water. Secondary disinfection provides a 

residual level of disinfection to help protect finished water as it travels through the system’s 

distribution network.

□ Dechlorination Average Amount Per 

Day (number, e.g., 20)

Units

□ Sodium metabisulfite (Na2S2O5) □ tons □ lbs

□ Other (specify):_______________ □ tons □ lbs

□ What type of disinfection residual is in the filter backwash? (Please indicate 

type)

□ Free chlorine

□ Chloramination

□ Other (specify):__________________

□ No filter backwash at this plant

□ What type of disinfection residual is in the filter-to-waste? (Please indicate 

type)

□ Free chlorine

□ Chloramination

□ Other (specify):__________________

□ No filter to-waste at this plant
Drinking Water Industry Report Section 3 – Industry Profile

3-15

Table 3-10 provides the estimated number of WTPs using different types of 

chemicals for primary disinfection. The questionnaire identified five primary categories that the 

WTP could select, with one of the categories (ammonia) subdivided into four options as shown 

in Figure 3-7. For the sake of summary, all ammonia responses were combined. EPA estimated 

that approximately two-thirds of the WTPs (i.e., 1,418 of the 2,151 WTPs) use chlorine gas as a 

primary disinfectant.

Figure 3-7. Question 2f: Source Water Treatment and Chemical Addition: Primary 

Disinfectant

Please indicate below the type and 

amount of the chemicals used for primary 

disinfection.

Average Amount Per Day 

(number, e.g., 20)

Units

□ Chlorine dioxide (ClO2) □ tons □ lbs

□ Chlorine gas (Cl2, gas) □ tons □ lbs

□ Calcium hypochlorite (Ca(OCl)2) □ tons □ lbs

□ Sodium hypochlorite (NaOCl) □ tons □ lbs

□ Ammonia (Please indicate form) □ tons □ lbs

□ Anhydrous (NH3) □ tons □ lbs

□ Ammonium sulfate ((NH4)2SO4) □ tons □ lbs

□ Aqua ammonia (NH4

+) □ tons □ lbs

□ Other (specify):_____________ □ tons □ lbs

□ Other (specify):_______________ □ tons □ lbs
Drinking Water Industry Report Section 3 – Industry Profile

3-16

Table 3-7. Estimated Number of WTPs Using Presedimentation (National Estimates 

Based on Responses to Question 2f) 

Classification

Estimated Number of 

WTPs in Classification

Estimated Number of 

WTPs with 

Presedimentation

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method

10,001-50,000 Ground Any 526 38

Surface Any 938 66

Subtotal 1,464 104

More than 

50,000

Ground Conventional Filtration 14 [CBI Redacted]

Membrane 19 [CBI Redacted]

Other 2 [CBI Redacted]

Softening 66 [CBI Redacted]

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal 111 [CBI Redacted]

Surface Conventional Filtration 383 [CBI Redacted]

Membrane 19 [CBI Redacted]

Other 4 [CBI Redacted]

Softening 168 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal 576 [CBI Redacted]

Subtotal a 688 37

Total a 2,151 141

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-17

Table 3-8. Estimated Numbers of WTPs Using Various Primary Disinfection Methods (National Estimates Based on 

Responses to Question 2f) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs with 

Primary 

Disinfection

Estimated Number of WTPs Using:*

Estimated 

Number of 

WTPs that 

Dechlorinate

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Free 

Chlorine Chloramination Ozone UV Other

10,001-

50,000

Ground Any 526 452 331 118 0 0 0 64

Surface Any 938 895 771 74 7 2 68 79

Subtotal 1,464 1,347 1,102 192 7 2 68 143

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted] [CBI Redacted]

Membrane 19 11 5 6 0 0 0

Other 2 [CBI Redacted]

Softening 66 66 21 44 0 0 0

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal 111 101 43 51 2 2 4

Surface Conventional 

Filtration

383 377 316 37 46 2 19

Membrane 19 15 12 0 0 0 6

Other 4 [CBI Redacted]

Softening 168 159 122 39 10 0 10

None 2 [CBI Redacted]

Subtotal 576 554 454 76 56 2 35

Subtotal a 688 655 496 126 58 4 39 87

Total a 2,151 2,002 1,599 318 65 6 107 230

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-18

Table 3-9. Disinfection Residuals in Filter Backwash and Filter-to-Waste (National Estimates Based on Responses to 

Question 2f) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs with 

Primary 

Disinfection

Est. Number of WTPs Backwash a Est. Number of WTPs with Filter-to-Waste a

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Total

Free 

chlorine

Chloramination Other None TotalFree 

Chlorine

Chloramination Other None

10,001-

50,000

Ground Any 526 452 433 315 63 2 52 423 254 19 0 169

Surface Any 938 895 847 674 114 52 15 775 464 56 69 201

Subtotal 1,464 1,347 1,279 989 178 54 67 1,198 718 75 69 370

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 11 5 0 0 0 5 5 0 0 0 5

Other 2 [CBI Redacted]

Softening 66 66 66 17 48 0 0 66 4 44 2 17

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal b 111 101 95 32 56 0 7 95 18 44 2 33

Surface Conventional 

Filtration

383 377 362 263 87 15 10 352 221 23 29 82

Membrane 19 15 15 13 2 0 0 15 6 0 0 9

Other 4 [CBI Redacted]

Softening 168 159 152 88 58 11 0 146 62 18 10 58

None 2 [CBI Redacted]

Subtotal b 576 554 532 368 147 27 10 516 293 41 39 148

Subtotal b 688 655 627 400 203 27 17 611 311 86 41 181

Total b 2,151 2,002 1,906 1,388 380 80 84 1,809 1,028 161 110 552

a – WTPs may have more than one method of backwash or filter-to-waste. As a result, the sum of the number of WTPs in each of the three chemical categories may exceed the 

value in the corresponding total column.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-19

Table 3-10. Primary Disinfectants (National Estimates Based on Responses to Question 2f)

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs with 

Primary 

Disinfection

Estimated Number of WTPs Using Various Chemicals a

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method ClO2 Cl2 gas Ca(OCl)2) NaOCl Ammonia Other

10,001-

50,000

Ground Any 526 452 0 330 . 102 44 0

Surface Any 938 895 43 648 8 249 185 29

Subtotal 1,464 1,347 43 979 8 351 228 29

More than 

50,000

Ground Conventional Filtration 14 [CBI Redacted]

Membrane 19 11 0 0 0 5 0 0

Other 2 [CBI Redacted]

Softening 66 66 0 40 0 25 25 0

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal b 111 101 4 59 0 36 35 0

Surface Conventional Filtration 383 377 31 239 2 116 129 23

Membrane 19 15 4 8 0 7 2 0

Other 4 [CBI Redacted]

Softening 168 159 4 131 0 24 67 14

None 2 [CBI Redacted]

Subtotal b 576 554 39 380 2 147 198 37

Subtotal b 688 655 42 439 2 182 233 37

Total b 2,151 2,002 85 1,418 10 533 462 66

a – WTPs may use more than one chemical as primary disinfectant (e.g., ammonia and chlorine source to produce chloramines). As a result, the sum of the number of WTPs in 

each of the chemical categories may exceed the value in the corresponding total column.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-20

3.2.2.3 Residuals Treatment and Pollution Prevention Practices (Questions 2h and 

2i) 

This subsection summarizes the responses to Questions 2h and 2i that address 

residuals treatment and pollution prevention practices.9 The responses are used to estimate the 

number of WTPs within the target population with the different practices. If the respondent did 

not check a particular box, EPA assumed that the answer was ‘no’ (e.g., if the respondent did not 

check drying as a residuals treatment option, EPA assumed that drying operations were not 

conducted at the plant). 

Table 3-11 estimates different residuals management practices based upon the 

responses to question 2h as shown in Figure 3-8. In the table, the term “non-mechanical 

dewatering” also includes sedimentation tanks and ponds, thickening, evaporation ponds, and 

drying. After excluding WTPs with pH adjustment, aeration, and hydrogen sulfide removal, EPA 

estimates that approximately three-fourths of the WTPs in the target population treat residuals. In 

other words, an estimated 522 of the 2,151 WTPs do not treat residuals. 

2.h. Please indicate () below which residual treatment options were performed at the water 

treatment plant in 2006. Treatment of residuals refers to any activity designed to change the 

character or composition of liquid and solid residuals streams from water treatment processes as 

needed to render it amenable to recycle/recovery, reduce its volume, or prepare it for 

transportation, storage, disposal, or discharge.

□ No treatment □ Thickening □ Aeration

□ Drying □ Mechanical dewatering □ Hydrogen sulfide removal

□ pH adjustment □ Non-mechanical dewatering □ Evaporation ponds

□ Equalization of residuals prior to treatment or disposal □ Dechlorination

□ Sedimentation tanks and ponds

□ Other (specify):_______________________________

Table 3-12

Figure 3-8. Question 2h: Residuals Treatment

 estimates different pollution prevention practices based upon the 

responses to question 2i as shown in Figure 3-9. The responses options include no pollution 

prevention, recovery of treatment chemicals, recycling filter backwash, optimizing surface water 

intake to reduce suspended solids intake, reuse of precipitative softening chemicals by recycling 

 

9 Because few plants had affirmative responses, EPA did not provide national estimates for question 2g (“Is the 

primary water treatment objective of the plant to remove salt from the source water (i.e., desalination)?”
Drinking Water Industry Report Section 3 – Industry Profile

3-21

softening residuals to the head of the plant, recycling filter-to-waste, and other. EPA estimates 

that approximately half of the WTPs in the target population (i.e., 1,036 of the 2,151 WTPs) 

practice pollution prevention. 

2.i. Please indicate () below which pollution prevention practices were performed at the water 

treatment plant in 2006. Pollution prevention refers to the use of materials, processes, or practices 

that reduce or eliminate the creation of pollutants or residuals.

□ No pollution prevention

□ Recovery of treatment chemicals

□ Recycling filter backwash

□ Optimizing surface water intake to reduce suspended solids intake

□ Reuse of precipitative softening chemicals by recycling softening residuals to head of the plant

□ Recycling filter-to-waste 

□ Other (specify):_______________________________

Figure 3-9. Question 2i: Pollution Prevention 
Drinking Water Industry Report Section 3 – Industry Profile

3-22

Table 3-11. Residuals Treatment Methods (National Estimates Based on Responses to Question 2h)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated Number of WTPs With:

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

No 

treatment

Equalization 

only

Mechanical 

dewatering

Non-mechanical 

dewatering Other

10,001-50,000 Ground Any 526 253 31 8 225 14

Surface Any 938 193 84 40 651 25

Subtotal 1,464 447 115 47 876 39

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 6 5 0 6 2

Other 2 [CBI Redacted]

Softening 66 2 0 15 61 0

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal a 111 12 7 19 89 2

Surface Conventional 

Filtration

383 32 25 88 308 8

Membrane 19 4 0 9 11 2

Other 4 [CBI Redacted]

Softening 168 27 12 28 123 6

None 2 [CBI Redacted]

Subtotal a 576 63 37 129 448 16

Subtotal a 688 75 44 148 537 18

Total a 2,151 522 159 195 1,413 57

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-23

Table 3-12. Pollution Prevention Methods (National Estimates Based on Responses to Question 2i)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated Number of WTPs With:

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

No pollution 

prevention

Recovery of 

treatment 

chemicals

Recycling 

filter 

backwash

Optimizing 

surface 

water intake

Recycle 

softening 

chemicals

Recycling 

filter-towaste Other

10,001-

50,000

Ground Any 526 368 5 138 0 25 84 15

Surface Any 938 514 39 285 140 31 159 42

Subtotal 1,464 882 43 423 140 56 243 57

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 11 0 6 2 6 0 0

Other 2 [CBI Redacted]

Softening 66 27 4 36 0 16 12 2

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal a 111 46 4 59 2 22 20 4

Surface Conventional 

Filtration

383 111 0 222 82 0 157 42

Membrane 19 10 0 7 2 0 2 5

Other 4 [CBI Redacted]

Softening 168 64 4 80 27 16 40 12

None 2 [CBI Redacted]

Subtotal a 576 187 4 310 110 16 198 61

Subtotal a 688 233 8 369 112 39 219 65

Total a 2,151 1,115 51 792 253 95 461 122

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-24

3.2.2.4 Residuals Discharge Practices (Question 2k)

This subsection summarizes the responses to Question 2k which collected data 

about direct, indirect, and zero discharge streams. Tables 3-13 through 3-20 present national 

estimates based upon the questionnaire responses. The following paragraphs describe the tables 

and identify the specific portions of the question related to each table. If the respondent did not 

check a particular box, EPA assumed that the answer was ‘no’ (e.g., if a WTP did not check the 

box for direct discharge, EPA assumed that none of its residuals were discharged in this manner). 

Table 3-13 shows the estimated number of WTPs with each of the three discharge 

methods: direct, indirect, and zero. It also estimates the number of WTPs that use one, two, or all 

three discharge methods in their operations. The columns “Total Direct,” “Total Indirect,” and 

“Total Zero” include WTPs that are estimated to discharge at least some of the residuals by that 

method. The table also provides mutually exclusive estimates for each of the seven possible 

combinations of discharge methods (e.g., “Direct Only” and “Direct and Zero”). For example, a 

WTP that discharges some residuals to a stream and the rest to a POTW will form the basis of 

the national estimates in the columns “Total Direct,” “Total Indirect,” and “Direct and Indirect.” 

It will not be part of the estimates for any of the other columns for direct and/or indirect 

dischargers. Figure 3-10 shows the portions of Question 2.k that were used to determine the 

discharge type. EPA estimates that approximately 70 percent of the target population uses zero 

discharge methods for some or all of its residuals (i.e., 1,502 of 2,151 WTPs). (See Table 3-20 

for more details about zero discharge.) 
Drinking Water Industry Report Section 3 – Industry Profile

3-25

Figure 3-10. Question 2k: Residuals Discharge Method

Tables 3-14a and 3-14b provide national estimates of the types of residuals 

discharged in 2006. Although they are located under different sections of question 2k, the 

choices are essentially the same for each discharge method and are shown in Figure 3-11. EPA 

estimated the number of WTPs with residuals from four management practices: water treatment 

operations, presedimentation operations, dewatering operations, and brines. EPA divided the 

information into two tables to be more readable. The tables do not include national estimates for 

the other questionnaire options: residuals from stormwater, ion exchange resins, and other 

management practices. 

Dewatering operations generate more residuals than other types (1,402 of the 

2,151 WTPs have residuals from dewatering operations). Some facilities indicated that they 

operate presedimentation in Questions 2f (treatment operations) but not in Question 2k (residuals 

discharge), which resulted in 141 WTPs indicating presedimentation operations, but only 70 

WTPs with residuals from presedimentation. EPA chose to use the responses in Question 2f to 

represent the number of WTPs operating presedimentation (141 WTPs) for the following 

reasons:

• For Question 2f, plants would indicate operating presedimentation. The 

residuals from presedimentation might then be discharged (directly or 

indirectly), managed via zero discharge method (e.g., evaporation lagoon), 

or sent to the residuals treatment plant for dewatering. 

2.k. Please indicate () in 2.k.i, 2.k.ii, and 2.k.iii below the method(s) of residuals discharge

performed in 2006 at the water treatment plant and identify the year that this discharge method

started. Please select all categories that apply. (See Definitions of Key Terms on page 26 for 

explanations of discharge types, pollutants, and residuals.)

i.  Direct discharge of treated and/or untreated residuals. Do not select direct

discharge if your plant only discharges non-contact stormwater to surface waters.

Select direct discharge if your plant has a permit that regulates or monitors the 

discharge of treated and/or untreated residuals to surface waters. 

ii.  Indirect discharge of treated and/or untreated residuals. Select indirect discharge 

if your plant has a permit that regulates or monitors the discharge of treated and/or 

untreated residuals to a treatment works (POTW, PrOTW, FOTW). Indirect 

discharge does not include spent filter backwash discharged to surface water.

iii.  Zero discharge.
Drinking Water Industry Report Section 3 – Industry Profile

3-26

• Plants may not indicate presedimentation residuals in Question 2k. If the 

WTP dewaters the residuals from presedimentation, the WTP could select

“discharges from residuals treatment” instead of presedimentation 

residuals. The WTP would make this selection especially if the residuals 

from presedimentation are commingled with other waste streams. 

EPA used responses to Question 2k to represent the discharges from 

presedimentation that are directly discharged, indirectly discharged, or managed via zero 

discharge method. 

Figure 3-11. Question 2k: Type of Residuals Discharged 

Table 3-15 presents the number of direct and indirect WTPs with different 

discharge frequencies: continuous, batch, and emergency. Because a WTP could discharge more 

than one of these types of releases, the sum of the estimated number of WTPs within each of the 

three categories may be greater than the total number of direct or indirect discharging WTPs. As 

shown in Figure 3-12, question 2k uses slightly different ways to collect the information from 

direct and indirect dischargers, but the three discharge frequencies (continuous, batch, 

emergency) were the same. As shown in the tables, batch discharges are estimated to be the most 

common practice for both direct and indirect dischargers. 

Types of Residuals Disposed of by the Specified Residuals Management Option(s) in 2006.

Please check all that apply.

 Residuals from water treatment operations including coagulation, filter backwashing 

operations, filter-to-waste, precipitative softening, iron and manganese removal, and slow sand and 

diatomaceous earth filtration. These include accumulated residuals for batch discharge.

 Residuals from presedimentation water treatment operations.

 Discharges from residuals treatment including mechanical dewatering (e.g., thickener decant, 

centrate, and filtrate from belt or plate-and-frame presses) and non-mechanical dewatering (e.g., 

discharges from dewatering lagoons).

 Concentrate (brines) from ion exchange regeneration and salt water conversion, membrane 

reject water and spent backwash, activated alumina waste regenerate, and membrane cleaning fluid.

 Stormwater collected from areas associated with water treatment operations.

 Stormwater collected from areas not associated with water treatment operations.

 Ion exchange resins, spent GAC, and spent filter media.

 Other
Drinking Water Industry Report Section 3 – Industry Profile

3-27

Figure 3-12. Question 2k: Frequency of Residuals Discharge 

For direct dischargers, Tables 3-16 and 3-17 provide more information about 

discharge practices. Table 3-16 presents the estimated number of batch and emergency 

discharges in 2006 by direct dischargers. Table 3-17 presents the number of WTPs discharging 

into different types of waterbodies: river, creek, wetland, ocean, lake and other. Based upon the 

responses, the most common destinations for direct dischargers are likely to be rivers or creeks. 

Figure 3-13 shows the portions of question 2k used to derive the national estimates in Tables 3-

16 and 3-17. 

Figure 3-13. Question 2k: Direct Discharge—Continuous, Batch or Emergency and Type of 

Receiving Stream

If the water treatment plant directly discharged its residuals to surface water bodies in 2006, please 

indicate () below the frequency of the discharge. In the blank spaces below the batch and 

emergency discharge categories, please specify the number of times residuals were discharged to 

surface waters in 2006. Please indicate () below both ‘Continuous discharge’ and ‘Batch 

(intermittent) discharge’ if you are doing both types of discharges (e.g., continuous filter backwash 

and batch discharge of residuals in settling basins).

 Continuous discharge

 Batch (intermittent) discharge

Residuals were discharged ________ times in 2006. 

 Emergency discharge only

Residuals were discharged ________ times in 2006.

If the water treatment plant indirectly discharged its residuals to a treatment works (POTW, 

PrOTW, FOTW) in 2006, please indicate () below the frequency and volume of the discharge to 

the nearest 1,000 gallons. In the blank spaces below the batch and emergency discharge categories, 

please specify the number of times residuals were discharged in 2006.

 Continuous discharge

Volume of discharge ________ gallons per day.

 Batch (intermittent) discharge

Residuals were discharged ________ times in 2006.

Volume of discharge ________ gallons per day.

 Emergency discharge only

Residuals were discharged ________ times in 2006.

Volume of discharge ________ gallons per day

If the water treatment plant directly discharged its residuals to surface water bodies in 2006, ...

 Continuous ... 

 Batch ... 

 Emergency discharge only

Residuals were discharged ________ times in 2006.

Type of Receiving Water (See Definitions of Key Terms on page 26 for explanations of types.)

 River  Creek  Wetland  Ocean  Lake

 Other (specify):____________________
Drinking Water Industry Report Section 3 – Industry Profile

3-28

For indirect dischargers, Tables 3-18 and 3-19 provide more information about 

discharge practices. They provide national estimates for the number of WTPs and daily volumes 

for continuous and batch discharges. (Only one WTP provided volumes for emergency 

discharges.) The information was collected from the portion of question 2k shown in Figure 3-

14. 

If the water treatment plant indirectly discharged its residuals to a treatment works (POTW, 

PrOTW, FOTW) in 2006, please indicate () below the frequency and volume of the discharge to 

the nearest 1,000 gallons. In the blank spaces below the batch and emergency discharge categories, 

please specify the number of times residuals were discharged in 2006.

 Continuous discharge

Volume of discharge ________ gallons per day.

 Batch (intermittent) discharge

Residuals were discharged ________ times in 2006.

Volume of discharge ________ gallons per day.

 Emergency discharge only

Residuals were discharged ________ times in 2006.

Volume of discharge ________ gallons per day

Figure 3-14. Question 2k: Indirect Discharge—Continuous, Batch or Emergency and 

Volume Discharged

Table 3-20 provides the national estimates for the number of WTPs using 

alternative discharge methods by one or more “zero discharge” disposal methods: recycling, 

evaporation, composting, landfill disposal, spray irrigation, underground injection, land 

application, and other. The relevant part of the question is shown in Figure 3-15. Based upon the 

responses, more than half of the WTPs recycle and/or use landfills to reduce or eliminate 

wastewater discharges. Of the estimated 1,502 WTPs using zero discharge methods, an estimated 

790 recycle waste streams and 792 use landfills. 
Drinking Water Industry Report Section 3 – Industry Profile

3-29

If the water treatment plant operated as a zero-discharge plant in 2006, please identify () the 

disposal method(s) for the residuals.

 Recycle (i.e., return to water treatment plant pre-coagulation)

 Evaporation

 Composting

 Landfill disposal

 Spray irrigation

 Underground injection

 Land application (e.g., soil amendment)

 Other (specify):______________________________

 Other (specify): ______________________________

 Other (specify): ______________________________

Figure 3-15. Question 2k: Zero Discharge Methods
Drinking Water Industry Report Section 3 – Industry Profile

3-30

Table 3-13. Estimated Numbers of WTPs Using Direct, Indirect, or Zero Residuals Discharge Practices (National Estimates 

Based on Responses to Question 2k)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated Number

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Direct 

only

Indirect 

only

Zero 

only

Direct 

and 

Indirect

Direct 

and 

Zero

Indirect 

and Zero

Direct, 

Indirect, 

and Zero

Total

Direct

Total

Indirect

Total 

Zero a

10,001-

50,000

Ground Any 526 49 195 107 8 63 103 0 121 307 273

Surface Any 938 49 173 206 50 279 154 28 406 405 666

Subtotal 1,464 98 368 312 59 342 257 28 527 711 939

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 0 4 13 2 0 0 0 2 6 13

Other 2 [CBI Redacted]

Softening 66 2 0 32 0 29 2 0 31 2 64

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal b 111 4 5 54 2 34 13 0 40 20 100

Surface Conventional 

Filtration

383 15 18 123 32 103 74 18 167 142 318

Membrane 19 0 6 2 0 4 7 0 4 12 13

Other 4 [CBI Redacted]

Softening 168 14 17 40 8 59 21 8 90 55 129

None 2 [CBI Redacted]

Subtotal b 576 32 41 165 40 168 104 26 266 211 463

Subtotal b 688 36 47 219 42 202 117 26 305 231 563

Total b 2,151 134 415 531 100 544 374 54 832 943 1,502

a – Number of WTPs using one or more zero discharge method (e.g., landfill disposal, recycling). WTP may also discharge some residuals directly or indirectly.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-31

Table 3-14a. Estimated Numbers of WTPs by Types of Residuals Discharged and Discharge Practice (National Estimates 

Based on Responses to Question 2k)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated Number of WTPs with Residuals from:

Source water treatment operations Presedimentation operations

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Total Direct Indirect Zero a Total Direct Indirect Zero a

10,001-50,000 Ground Any 526 281 45 179 84 0 0 0 0

Surface Any 938 351 91 227 61 39 15 15 8

Subtotal 1,464 632 136 407 145 39 15 15 8

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 0 0 0 0 0 0 0 0

Other 2 [CBI Redacted]

Softening 66 26 2 0 24 0 0 0 0

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal b 111 34 4 2 29 0 0 0 0

Surface Conventional 

Filtration

383 150 35 69 81 13 0 0 13

Membrane 19 6 0 6 0 0 0 0 0

Other 4 [CBI Redacted]

Softening 168 86 35 37 28 17 8 2 6

None 2 [CBI Redacted]

Subtotal b 576 244 72 111 110 32 8 2 21

Subtotal b 688 278 76 114 138 32 8 2 21

Total b 2,151 910 212 520 283 70 24 18 29

a – Number of WTPs using one or more zero discharge method (e.g., landfill disposal, recycling). WTP may also discharge some residuals directly or indirectly.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-32

Table 3-14b. Estimated Numbers of WTPs by Types of Residuals Discharged and Discharge Practice (National Estimates 

Based on Responses to Question 2k)

Classification

Estimated Number 

of WTPs in 

Classification

Estimated Number of WTPs with Residuals from:

Dewatering Operations Concentrates (i.e., Brines)

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Total Direct Indirect Zero a Total Direct Indirect Zero a

10,001-50,000 Ground Any 526 197 44 69 173 107 32 78 25

Surface Any 938 662 289 161 585 21 2 17 9

Subtotal 1,464 859 334 230 758 127 34 95 34

More than 

50,000

Ground Conventional 

Filtration

14 [CBI Redacted]

Membrane 19 6 0 0 6 19 2 6 13

Other 2 [CBI Redacted]

Softening 66 60 29 2 60 0 0 0 0

Ion Exchange 8 [CBI Redacted]

None 2 [CBI Redacted]

Subtotal b 111 86 32 4 85 30 4 14 13

Surface Conventional 

Filtration

383 318 129 95 266 0 0 0 0

Membrane 19 13 4 2 13 7 0 5 7

Other 4 [CBI Redacted]

Softening 168 122 53 25 114 0 0 0 0

None 2 [CBI Redacted]

Subtotal b 576 457 186 124 396 7 0 5 7

Subtotal b 688 542 218 128 481 36 4 19 20

Total b 2,151 1,402 552 358 1,239 164 38 113 54

a – Number of WTPs using one or more zero discharge method (e.g., landfill disposal, recycling). WTP may also discharge some residuals directly or indirectly.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-33

Table 3-15. Estimated Number of WTPs by Discharge Frequency for Direct and Indirect Discharges (National Estimates 

Based on Responses to Question 2k)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

Direct and 

Indirect 

WTPs

Estimated Number of WTPs with:

Direct Discharge a Indirect Discharge a

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method Total Cont. Batch

Emergency Total Cont. BatchEmergency

10,001-

50,000

Ground Any 526 419 121 35 86 0 307 44 265 0

Surface Any 938 732 406 158 220 35 405 129 271 4

Subtotal 1,464 1,151 527 194 306 35 711 173 537 4

More than 

50,000

Ground Conventional 

Filtration

14 8 [CBI Redacted]

Membrane 19 6 2 2 0 0 6 6 0 0

Other 2 2 [CBI Redacted]

Softening 66 33 31 2 27 2 2 0 2 0

Ion Exchange 8 8 [CBI Redacted]

None 2 0 [CBI Redacted]

Subtotal b 111 57 40 8 29 2 20 7 13 0

Surface Conventional 

Filtration

383 260 167 78 76 15 142 48 102 0

Membrane 19 17 4 4 0 0 12 6 7 0

Other 4 4 [CBI Redacted]

Softening 168 129 90 44 45 8 55 24 31 0

None 2 2 [CBI Redacted]

Subtotal b 576 412 266 126 123 25 211 78 141 0

Subtotal b 688 469 305 135 152 27 231 85 154 0

Total b 2,151 1,620 832 328 458 62 943 258 691 4

a – WTPs may use more than discharge flow type (continuous, batch or emergency). As a result, the sum of the number of WTPs in each of the three discharge 

flow types may exceed the value in the corresponding total column.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-34

Table 3-16. Estimated Number of Batch and Emergency Dischargers by Direct-Discharging WTPs (National Estimates Based 

on Responses to Question 2k)

Classification Estimated

Number of 

WTPs in 

Classification

Estimated 

Number of 

Direct 

Dischargers

Estimated Number of WTPs and Frequency of Residual Discharges

Batch Discharge (Times in 2006) Emergency Discharge (Times in 2006)

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Estimated 

Number of 

WTPs Min Max Median

Estimated 

Number of 

WTPs Min Max Median

10,001-

50,000

Ground Any 526 121 86 50 365 365 0 0 0 0

Surface Any 938 406 220 2 19,000 365 35 0 218 2

Subtotal 1,464 527 306 2 19,000 365 35 0 218 2

More than 

50,000

Ground Conventional 

Filtration

14 4 [CBI Redacted] [CBI Redacted]

Membrane 19 2 0 - - - 0 - - -

Other 2 2 [CBI Redacted] [CBI Redacted]

Softening 66 31 27 21 1,500 1,000 2 0 0 0

Ion Exchange 8 0 -- --

None 2 0 -- --

Subtotal a 111 40 29 21 1,500 1,000 2 0 0 0

Surface Conventional 

Filtration

383 167 76 2 70,810 455 15 0 6 0

Membrane 19 4 0 - - - 0 - - -

Other 4 2 [CBI Redacted] [CBI Redacted]

Softening 168 90 45 1 36,000 1,095 8 0 12 0

None 2 2 [CBI Redacted] [CBI Redacted]

Subtotal a 576 266 123 1 70,810 589 25 0 12 0

Subtotal a 688 305 152 1 70,810 848 27 0 12 0

Total a 2,151 832 458 1 70,810 365 62 0 218 1

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-35

Table 3-17. Estimated Numbers of WTPs Directly Discharging to Various Types of Receiving Waters (National Estimates 

Based on Responses to Question 2k)

Classification Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

Direct 

Dischargers

Estimated Number of WTPs Directly Discharging to Receiving 

Waters

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method River Creek Wetland Ocean Lake Other

10,001-

50,000

Ground Any 526 121 57 55 0 2 0 6

Surface Any 938 406 167 157 0 8 67 0

Subtotal 1,464 527 224 212 0 10 67 6

More than 

50,000

Ground Conventional 

Filtration

14 4 [CBI Redacted]

Membrane 19 2 0 0 0 0 2 0

Other 2 2 [CBI Redacted]

Softening 66 31 23 8 0 0 0 0

Ion Exchange 8 0 --

None 2 0 --

Subtotal a 111 40 28 8 0 0 2 2

Surface Conventional 

Filtration

383 167 61 60 0 0 39 8

Membrane 19 4 0 2 0 0 0 0

Other 4 2 [CBI Redacted]

Softening 168 90 47 25 0 0 12 2

None 2 2 [CBI Redacted]

Subtotal a 576 266 109 87 0 0 51 13

Subtotal a 688 305 137 95 0 0 53 15

Total a 2,151 832 361 307 0 10 119 21

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-36

Table 3-18. Estimated Number of WTPs with Indirect Discharge and 

Release Volumes for Continuous Discharges (National Estimates Based on Responses to Question 2k) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

Indirect 

Dischargers

Continuous

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method

Est # 

WTPs

Gallons/Day

Min. Max. Median

10,001-50,000 Ground Any 526 307 44 720 1,000,000 50,000

Surface Any 938 405 129 5000 610,000 80,000

Subtotal 1,464 711 173 720 1,000,000 1,000,000

More than 

50,000

Ground Conventional Filtration 14 4 [CBI Redacted]

Membrane 19 6 6 122,200 997,000 260,000

Other 2 0 0 - - -

Softening 66 2 0 - - -

Ion Exchange 8 8 [CBI Redacted]

None 2 0 0 - - -

Subtotal a 111 20 7 122,020 997,000 260,000

Surface Conventional Filtration 383 142 48 6,375 1,404,000 173,337

Membrane 19 12 6 111,233 341,000 226,117

Other 4 2 [CBI Redacted]

Softening 168 55 24 3,562 1,056,960 300,000

None 2 0 0 - - -

Subtotal a 576 211 78 3,562 1,404,000 200,000

Subtotal a 688 231 85 3,562 1,000,000 1,404,000

Total a 2,151 943 258 720 1,000,000 99,800

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

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Table 3-19. Estimated Number of WTPs with Indirect Discharge and Release Volumes for Batch Discharges (National 

Estimates Based on Responses to Question 2k) 

Classification

Estimated 

Number of WTPs 

in Classification

Estimated 

Number of 

Indirect 

Dischargers

Batch

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method Est # WTPs

Gallons/Day

Min. Max. Median

10,001-

50,000

Ground Any 526 307 265 157 700,000 15,000

Surface Any 938 405 271 110 1,234,000 60,000

Subtotal 1,464 711 537 110 1,234,000 16,000

More than 

50,000

Ground Conventional Filtration 14 4 [CBI Redacted]

Membrane 19 6 0 - - -

Other 2 0 0 - - -

Softening 66 2 2 270,000 270,000 270,000

Ion Exchange 8 8 [CBI Redacted]

None 2 0 0 - - -

Subtotal a 111 20 13 1,600 270,000 51,305

Surface Conventional Filtration 383 142 102 246 730,000 45,000

Membrane 19 12 7 8,000 2,265,900 8,000

Other 4 2 [CBI Redacted]

Softening 168 55 31 26,000 1,000,000 350,000

None 2 0 0 - - -

Subtotal a 576 211 141 246 2,265,900 70,000

Subtotal a 688 231 154 246 2,265,900 67,641

Total a 2,151 943 691 110 2,265,900 25,000

a – CBI redacted WTP estimates are included in subtotal and total rows.
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Table 3-20. Estimated Number of WTPs Employing Various Zero Discharge Disposal Methods (National Estimates Based on 

Responses to Question 2k)

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs using 

Zero 

Discharge 

Methods a

Estimated Number of WTPs Using Zero Discharge Methods a:

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

RecycleEvaporationCompostLandfillSpray IrrigationUnderground InjectionLand ApplicationOther

10,001-

50,000

Ground Any 526 273 151 74 0 143 0 3 52 48

Surface Any 938 666 284 141 12 388 14 0 166 25

Subtotal 1,464 939 434 216 12 531 14 3 218 73

More than 

50,000

Ground Conventional 

Filtration

14 11 [CBI Redacted]

Membrane 19 13 6 0 0 6 0 11 2 0

Other 2 2 [CBI Redacted]

Softening 66 64 36 7 0 16 0 0 48 4

Ion Exchange 8 8 [CBI Redacted]

None 2 2 [CBI Redacted]

Subtotal b 111 100 59 12 0 37 0 11 50 13

Surface Conventional 

Filtration

383 318 211 69 10 165 8 0 74 17

Membrane 19 13 7 0 0 9 0 0 6 2

Other 4 2 [CBI Redacted]

Softening 168 129 77 20 8 46 0 0 48 15

None 2 2 [CBI Redacted]

Subtotal b 576 463 297 88 18 224 8 0 130 33

Subtotal b 688 563 356 101 18 261 8 11 180 46

Total a,b 2,151 1,502 790 316 29 792 21 14 399 119

a – Number of WTPs using one or more zero discharge method (e.g., landfill disposal, recycling). WTP may also discharge some residuals directly or indirectly.

b – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

3-39

3.2.2.5 Copper Usage (Question 3)

This subsection summarizes the responses to question 3 about the WTP’s usage of 

copper-based chemicals to treat source water. For example, WTPs might use copper-based 

chemicals to control nuisance algae in reservoirs. Tables 3-21 through 3-24 estimate copper 

usage by the target population based upon the responses to the question shown in Figure 3-16. If 

the respondent did not check a particular box, EPA assumed that the answer was ‘no.’ 

Tables 3-21 and 3-22 estimate the application rate of the copper sulfate and 

chelated copper complexes for WTPs in the target population that use copper. The application 

rate is expressed in pounds per acre-foot and was calculated as:

Reservoir volume

Annual amount Rate = (Eq. 3-1) 

Tables 3-23 and 3-24 estimate the metallic copper content of the treatments based 

upon the responses from WTPs using copper. For each response, EPA calculated the amount of 

metallic copper in one of two ways, depending upon whether the metallic content of the copper 

was expressed by weight or by volume. For weight-based metallic copper, the metallic copper 

was calculated as follows:

100

P

WW W

cm ⋅= (Eq. 3-2) 

where Wm is the weight of metallic copper (lbs), Wc is the total weight of chemical (lbs), and PW

is the percentage of metallic copper by weight. For volume-based metallic copper, the weight of 

metallic copper was calculated as follows:

(P 8.92/100) ( ) /100P1

P 8.92/100 WW

V V

V

cm −+⋅

⋅ ⋅= (Eq. 3-3) 

where PV is the percentage of metallic copper by volume.
Drinking Water Industry Report Section 3 – Industry Profile

3-40

3. Were copper-based chemicals used at the plant to treat the source water in 

2006?

 Yes

 No (Skip to Question 4.)

Please indicate () the type(s) of chemical(s) used at the plant to promote a 

better source of drinking water (e.g., control nuisance algae).

 Copper sulfate (CuSO4)

 Chelated copper complexes (i.e., copper citrate, copper ethanolamine, 

copper ethylene)

 Other (specify):

 Other (specify):

 Other (specify):

If more than one chemical was selected above, please photocopy this page and 

provide the following information for each chemical.

Name of chemical or product____________________________

Amount of this chemical used at this plant in 2006: ___________lbs

Volume of treatment reservoir: _____________acre-feet

Percent of metallic copper (label will note as Cu++ or Cu+2): _____________% 

by  weight



Figure 3-16. Question 3: Use of Copper-Based Chemicals to Treat Source Water

 

 

 
Drinking Water Industry Report Section 3 – Industry Profile

3-41

Table 3-21. Estimated Number of WTPs Using Copper Sulfate and Application Rate (National Estimates Based on Responses 

to Question 3) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated Number 

of WTPs Using 

Copper-based 

Chemicals

Copper Sulfate

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Estimated 

Number of 

WTPs

Application Rate (lbs/acre-ft)

Min. Max. Est. Mean

Std Err of 

Mean

10,001-

50,000

Ground Any 526 0 0 - - - -

Surface Any 938 95 87 0.02 1,000 102.89 88.61

Subtotal 1,464 95 87 0.02 1,000 102.89 88.64

More than 

50,000

Ground Conventional 

Filtration

14

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 2

Softening 66

Ion Exchange 8

None 2

Subtotal a 111 5 5 0.46 4.11 2.18 1.25

Surface Conventional 

Filtration

383

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 4

Softening 168

None 2

Subtotal a 576 92 64 0 50,000 2,355.9 2,195.4

Subtotal a 688 96 69 0 50,000 2,167.9 2,021.4

Total a 2,151 191 156 0 50,000 978.12 8,81.43

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

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Table 3-22. Estimated Number of WTPs Using Chelated Copper Complexes and Application Rate (National Estimates Based 

on Responses to Question 3) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs Using 

Copper-based 

Chemicals

Chelated copper complexes

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Estimated Number 

of WTPs

Application Rate (lbs/acre-ft)

Min Max Est. Mean

Std Err of 

Mean

10,001-

50,000

Ground Any 526 0 0 - - - -

Surface Any 938 95 18 0 0.03 0.01 0.01

Subtotal 1,464 95 18 0 0.03 0.01 0.01

More than 

50,000

Ground Conventional 

Filtration

14

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 2

Softening 66

Ion Exchange 8

None 2

Subtotal a 111 5 2 0 0 0 0

Surface Conventional 

Filtration

383

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 4

Softening 168

None 2

Subtotal a 576 92 29 0 25.25 2.6 1.93

Subtotal a 688 96 32 0 25.25 2.37 1.77

Total a 2,151 191 50 0 25.25 1.45 1.19

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

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Table 3-23. Estimated Number of WTPs Using Copper Sulfate and Amount of Metallic Copper Used in Pounds (National 

Estimates Based on Responses to Question 3) 

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs Using 

Copperbased 

Chemicals

Copper Sulfate

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Estimated 

Number of 

WTPs

Amount of metallic copper (lbs/yr)

Minimum Maximum

Estimated 

Mean

Std err of 

mean

10,001-

50,000

Ground Any 526 0 0 - - - -

Surface Any 938 95 87 1 2,000 515 164

Subtotal 1,464 95 87 1 2,000 515 164

More than 

50,000

Ground Conventional 

Filtration

14

[CBI 

Redacted] [CBI Redacted]

Membrane 19

Other 2

Softening 66

Ion Exchange 8

None 2

Subtotal a 111 5 5 1,969 3,465 2,674 512

Surface Conventional 

Filtration

383

[CBI 

Redacted] [CBI Redacted]

Membrane 19

Other 4

Softening 168

None 2

Subtotal a 576 92 64 21 34,520 3,322 1,558

Subtotal a 688 96 69 21 34,520 3,269 1,431

Total a 2,151 191 156 1 34,520 1,666 655

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

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Table 3-24. Estimated Number of WTPs Using Chelated Copper Complexes and

Amount of Metallic Copper Used in Pounds (National Estimates Based on Responses to Question 3)

Classification

Estimated 

Number of 

WTPs in 

Classification

Estimated 

Number of 

WTPs Using 

Copper-based 

Chemicals

Chelated copper complexes

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Estimated 

Number of 

WTPs

Amount of metallic copper (lbs/yr)

Minimum Maximum

Estimated. 

Mean

Std Err of 

Mean

10,001-

50,000

Ground Any 526 0 0 - - - -

Surface Any 938 95 18 0 24 12 8

Subtotal 1,464 95 18 0 24 12 8

More than 

50,000

Ground Conventional 

Filtration

14

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 2

Softening 66

Ion Exchange 8

None 2

Subtotal a 111 5 2 0 0 0 0

Surface Conventional 

Filtration

383

[CBI Redacted] [CBI Redacted]

Membrane 19

Other 4

Softening 168

None 2

Subtotal a 576 92 29 0 5,533 1,298 580

Subtotal a 688 96 32 0 5,533 1,165 534

Total a 2,151 191 50 0 5,533 717 398

a – CBI redacted WTP estimates are included in subtotal and total rows.
Drinking Water Industry Report Section 3 – Industry Profile

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3.3 DRINKING WATER INDUSTRY ECONOMIC OVERVIEW

This economic overview compiles and analyzes economic and operational data 

for public water systems (PWSs) and provides a general overview of the types and characteristics 

of public drinking water systems. The purpose of this section is to provide an overview of the 

financial characteristics of PWSs that operate WTPs serving at least 10,000 people, as well as the 

variability of financial strength across drinking water systems. The remainder of this section is 

organized as follows: 

• Section 3.3.1 describes the major data sources used for this profile. 

• Section 3.3.2 presents a general overview of PWSs, including population 

served, ownership type, water source, and discharge characteristics.

• Section 3.3.3 reviews financial characteristics of PWSs. 

• Section 3.3.4 provides an overview of water system customers, with focus 

on water consumption and rate payments by residential customers. 

3.3.1 Major Sources of Information 

EPA used three primary sources of data to characterize the universe of PWSs: the 

Safe Drinking Water Information System (SDWIS), the Community Water System Survey 

(CWSS), and the responses to the EPA DWT Industry Questionnaire. 

3.3.1.1 Safe Drinking Water Information System 

As discussed in Section 2.3.1, the SDWIS is a database compiled and maintained 

by EPA. It contains data on all PWSs including system location, system type (such as 

community or non-community water systems), primary raw water source (ground water or 

surface water), and violations. Optional reporting fields include type of treatment and ownership 

type. Because providing some data is discretionary, EPA does not have complete data on every 

system for these parameters. This is particularly common for non-community water systems 

(NCWSs).
Drinking Water Industry Report Section 3 – Industry Profile

3-46

Because SDWIS is continuously being updated, EPA used 155,693 records of 

active PWSs from the third quarter of 2007 for this economic profile (U.S. EPA, 2007).

3.3.1.2 Community Water System Survey 

The second source of information, the CWSS, is a periodically updated detailed 

EPA survey of surface and ground water community water systems (CWSs). The most recent 

survey was conducted in 2000 and published in 2002 (U.S. EPA, 2002). See Section 2.3.2 for 

more details. Since there is no survey equivalent to CWSS for non-community water systems, 

the operational and financial information presented later in this profile is only available for 

CWSs (U.S. EPA, 2002). 

3.3.1.3 EPA DWT Industry Questionnaire

The EPA DWT Industry Questionnaire, conducted in 2007, is a survey of WTPs

specifically created for this study to gather data on the operation, financial characteristics, and 

residuals discharges from the industry. The technical operations questions were posed at the 

water treatment plant level. The financial portion of the questionnaire (questions 4 through 13) 

asked for system or utility level data depending on whether the costs for a treatment technology 

would be spread amongst consumers at the system level or across all the customers of the larger 

utility. For the purpose of determining the financial strength of the larger corporate entity which 

owns the individual drinking water treatment plant being surveyed in the engineering portion of 

the questionnaire and the impacts to the large corporate entity’s customer base EPA must look to 

the level of the system. It is at the system level that the costs of technology improvements are 

financed and it is the system that can spread the costs of upgrades to a specific plant or plants 

across its total customer base. In some instances a larger utility may own more than one system

and spreads the cost of technology improvements across those systems. In this case the proper 

level of financial assessment is at the level of the utility.

10 See Section 2.2 for further details. 

 

10 In the EPA DWT Industry Questionnaire respondents were instructed to give either system or utility level 

information in their financial survey responses depending on which characterization was most appropriate. The 

competed responses to the financial portion of the survey are all at the system level. They may also be referred to as 

single system utility level data. 
Drinking Water Industry Report Section 3 – Industry Profile

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3.3.2 Public Water System Characteristics 

As discussed in Section 3.1, there are two major types of PWSs: community and 

non-community water systems (CWSs and NCWSs). This section discusses the different types of 

PWSs and the major characteristics used to classify them. Basic characteristics such as 

population served, ownership, and water source are discussed first, followed by operational 

characteristics such as water treatment and residual management. The purpose of this section is 

to provide a snapshot of the public water system industry. Table 3-25 provides a breakdown of 

PWSs by system type, according to SDWIS. 

Table 3-25. Number of PWSs and Total Population Served by System Type, SDWIS 

System Type Systems Population Served

CWS 52,110 33% 286,451,204 93%

NCWS 103,583 67% 20,086,152 7%

Total a 155,693 100% 306,537,356 100%

Source: U.S. EPA, 2007.

a – Four systems of an “unspecified” system type are included in these totals.

3.3.2.1 Population Served 

Table 3-26 presents the number of systems by type and by the number of people 

(as a range) served by each system, according to SDWIS. The table shows that the vast majority 

of both community and non-community water systems are fairly small, serving a population of 

less than 3,000 people. Only 8 percent of CWSs and 0.04 percent of NCWSs are large (serve 

more than 10,000 people). 

Table 3-26. Summary of the Number of PWSs by System Type and Size, SDWIS

System Type

System Size (Population Served)

<100 101 - 500 501 - 3k 3k - 10k 10k - 50k >50k Total a

CWS 13,270 16,012 13,906 4,822 3,175 925 52,110

NCWS 71,170 26,737 5,413 222 33 8 103,583

Total 84,440 42,749 19,319 5,044 3,208 933 155,693

Source: U.S. EPA, 2007. 

a – components may not add up to totals due to rounding.
Drinking Water Industry Report Section 3 – Industry Profile

3-48

Table 3-27 shows the number of systems, by source water and population served, 

reporting water sales for each customer category. This data is from the EPA DWT Industry 

Questionnaire; the total number of systems listed, 285, is a subset of the SDWIS systems.

11) 

This table shows that 95 percent of systems serve residential customers, 89 percent of systems 

serve non-residential customers, and 65 percent of systems sell water to other systems.

 

Table 3-27. Number of Systems that Report Water Sales to Different Customer Categories, 

DWT Industry Questionnaire

Primary 

Source* Population Served

Sold to Other 

Systems

Residential 

Customers

Non-Residential 

Customers Other

Surface 10,000-50,000 48 73 67 59

More than 50,000 123 155 151 142

Ground 10,000-50,000 4 17 15 14

More than 50,000 10 25 21 22

Total 185 270 254 237

Note: Systems serve more than one customer type—totals are not of unique systems. All systems report at least one 

customer type.

*Systems that use purchased water as their primary source are not presented in this table because of the potential for 

revealing Confidential Business Information Source: Appendix A.

3.3.2.2 Ownership

PWSs are owned by a variety of public and private entities. Public PWSs may be 

owned by a federal, state, or local entity, or by a Native American tribe. Private PWSs may be 

owned by non-profit or for-profit firms, or may be operated as ancillary businesses to other 

enterprises. Some PWSs are also co-owned by public and private entities. 

Table 3-28 summarizes the number of PWSs by ownership type and size of the 

population served, according to SDWIS. Public entities such as federal, state, and local 

government agencies and Native American tribes own approximately 27 percent of all PWSs in 

the U.S. Privately-owned PWSs make up approximately 69 percent of all PWSs. The majority of 

privately-owned PWSs, however, are small with over 71 percent serving fewer than 10,000 

people. They make up only 15 percent of PWSs serving over 50,000 people. In total, privately 

 

11 285 is the number of completed system responses to the financial portion of the EPA DWT Industry 

Questionnaire without those systems that primarily resell water that is purchased from other systems. The purchased 

water source category has been omitted from the results presented in this section because of the potential for 

revealing Confidential Business Information.
Drinking Water Industry Report Section 3 – Industry Profile

3-49

owned PWSs provide water to only 18 percent of the population served by PWSs, while 

publicly-owned systems serve about 80 percent (U.S. EPA, 2007). 

Table 3-28. Number of Water Systems by Ownership Type and Size, SDWIS 

Type of Ownership

System Size (Population Served)

<10k 10k - 50k >50k Total Population Served

Public 38,601 2,722 789 42,112 245,085,282

 Federal Government 3,736 66 5 3,807 3,038,437

 State Government 5,370 40 6 5,416 5,957,549

 Local Government 28,560 2,604 778 31,942 235,112,533

 Native American 935 12 0 673 976,763

Private 106,899 437 134 107,470 56,238,197

Mixed public/private 6,052 49 10 6,111 5,213,877

Total 151,552 3,208 933 155,693 306,537,356

Source: U.S. EPA, 2007. 

Table 3-28 does not present systems according to the type of population served, 

but groups these systems together. In general, a larger percentage of NCWSs than CWSs are 

privately owned. Privately-owned PWSs account for approximately 82 percent of TNCWSs and 

69 percent of NTNCWSs, as compared to only 48 percent of CWSs. 

3.3.2.3 Water Source

In addition to the type and size of population served and the type of ownership, 

water systems can be classified by their primary water source. PWSs may rely on ground water, 

surface water, or water purchased from other water systems. Table 3-29 presents the number of 

PWSs that draw water from each type of water source, by the size of the population served 

according to SDWIS.

12 The table also presents the total number of people that receive water 

from each type of water source. The vast majority of PWSs draw water from ground sources. 

The percent of PWSs utilizing ground water decreases significantly, however, as the size of the 

population served increases. The percentage of PWSs utilizing surface water, on the other hand, 

increases with the increase in the population served. In total, about 92 percent of PWSs draw 

water from ground sources. These systems, however, distribute water to only 36 percent of the 

 

12 SDWIS classifies a water system as relying on surface water if any of its water comes from surface water sources.
Drinking Water Industry Report Section 3 – Industry Profile

3-50

total populations served by PWSs. Sixty-four percent of PWSs’ customers receive water drawn 

from surface sources. 

Table 3-29 does not present PWSs according to the type of population served, but 

groups these systems together. PWSs that draw from ground water account for approximately 74 

percent of CWSs, as compared to only 13 percent of NCWSs. PWSs that draw from surface 

water account for approximately 97 percent of CWS, as compared to only 2 percent of NCWSs. 

Table 3-29. Number of Water Systems by Water Source and System Size, SDWIS 

Type of Source 

Water

System Size (Population Served)

<10k 10k - 50k >50k Total Population Served

Ground water 137,371 1,344 231 138,946 105,598,776

Surface water 4,043 938 455 5,436 137,577,368

Purchased 10,100 925 247 11,272 63,298,151

 Ground water 3,669 60 7 3,736 4,676,746

 Surface water 6,431 865 240 7,536 58,621,405

Total a 151,552 3,208 933 155,693 306,537,356

Source: U.S. EPA, 2007. 

a – Totals include 12 systems in the “< 10k” category that use an “unspecified” water type.

As identified in Table 3-27 within the EPA DWT Industry Questionnaire in the 

10,000 to 50,000 population category, approximately 17 percent of the systems draw from 

ground water and 83 percent draw from surface water. Within the greater than 50,000 population 

category, approximately 14 percent of the respondent systems draw from ground water and 86 

percent draw from surface water. 

3.3.2.4 Operational Characteristics: Water Treatment and Direct Discharge to 

Surface Water

This section presents CWSS data on two characteristics: water treatment and 

residuals management. Because SDWIS does not provide data on either treatment practices or 

residuals management, this information is not available for NCWSs. This section also does not 

present the characteristics for systems surveyed by the EPA DWT Industry Questionnaire; 

national estimates for WTPs are presented in Section 3.2. 
Drinking Water Industry Report Section 3 – Industry Profile

3-51

• Water Treatment: Not all CWSs treat water prior to distributing it to their 

customers. Some CWSs purchase water that has already been treated from 

other drinking water systems while other CWSs draw their water from 

sources that are pure enough to satisfy federal drinking water guidelines, 

eliminating the need for treatment. Systems that do not treat water are 

assumed not to discharge to surface water. CWSS asks respondents to 

report whether or not they treat water and several detailed questions 

regarding the treatment technology used. Overall, 75 percent of ground

water systems, 99.6 percent of surface water systems, and 17 percent of 

systems purchasing water provide treatment (U.S. EPA, 2002). 

• Residual Management: CWSs use a variety of technologies to dispose of 

water treatment residuals such as sludge, sediment, and chemicals. Some 

of the residual management techniques used by water systems include 

mechanical dewatering, land application, deep well injection, and direct 

discharge to surface water. Overall, 3 percent of ground water systems, 10

percent of surface water systems, and 6 percent of systems purchasing 

water perform residuals treatment (U.S. EPA, 2002). 

Table 3-30 presents the number of large CWSs (serving more than 10,000 people) 

that provide treatment and the number of CWSs that discharge directly to surface water, 

according to CWSS. The information is presented for all systems and by water source. 
Drinking Water Industry Report Section 3 – Industry Profile

3-52

Table 3-30. Summary of CWSs by Water Source and Population Served, CWSS 

System Size (Population Served)

10k-50k >50k Total >10k

Ground Water

All Systems 1,340 307 1,647

Provide Treatment 983 233 1,216

Discharger 217 50 267

Surface Water

All Systems 988 440 1,428

Provide Treatment 977 434 1,411

Discharger 387 142 529

Purchased Water

All Systems 685 238 923

Provide Treatment 385 100 485

Discharger 27 19 46

Total

All Systems 3,013 985 3,998

Provide Treatment 2,345 767 3,112

Discharger 631 211 842

Source: U.S. EPA, 2002.

Table 3-31 presents the 2006 water quantity sold, in million gallons per year 

(MGY), per system, reported at the 25th, 50th, and 75th quartiles, according to the EPA DWT 

Industry Questionnaire responses. The median quantity sold in 2006 across all respondent 

surface and ground water source systems was 4,297 million gallons. 

3.3.3 Financial Characteristics of Drinking Water Treatment Systems

In order to gauge the ability of PWSs to comply with environmental regulations, 

EPA conducts analyses that assess the financial health of the industry. This section provides a 

snapshot of the financial state of large CWSs (serving over 10,000 people). 

Basic data on revenue, expenses, capital expenditures, and funding sources 

available to water systems was obtained from CWSS and responses to the EPA DWT Industry 

Questionnaire questions 4 through 13. Because SDWIS does not provide any data on finances of 

the encompassed systems, no such information was available for non-community systems. This 
Drinking Water Industry Report Section 3 – Industry Profile

3-53 

section first presents system revenues and revenue sources, followed by system expenses and 

funding availability. 

3.3.3.1 Water System Revenues

Water sales are the primary source of revenue for the vast majority of water 

systems.13 CWSs supply water to private homes, businesses, agricultural and other nonresidential customers. A portion of CWS revenues also comes from connection fees, inspections, 

penalties and fines, and other non-consumption based charges.

Total CWS revenues came to $39 billion in 2000 (2000$). Revenues of publiclyowned systems accounted for 88 percent of this total. Water sales revenues contributed $33 

billion (85 percent) of total CWS revenues, and residential water sales accounted for about 60 

percent of total water sales for CWSs of all sizes. Overall, residential revenues have increased 

slightly since 1995 (U.S. EPA, 2002). 

Table 3-32 presents the 25th percentile. median, and 75th percentile values for

revenue by ownership type and system size, according to CWSS. The table shows that private 

systems earn slightly higher revenues than public systems. 

 

13 Although some smaller systems may be run as ancillary businesses, this was not true for any of the systems with a 

population of greater than 10,000 served. 
Drinking Water Industry Report Section 3 – Industry Profile

Table 3-31. Reported 2006 Water Quantity Sold (MGY), per System, DWT Industry Questionnaire

Primary Source a Population Group

Number of 

Systems

Water Quantity Sold (MGY)

25th Percentile 50th Percentile 75th Percentile

Surface 10,000-50,000

More than 50,000

74

166

657

4,403

1,351

8,488

2,274

17,333

Ground 10,000-50,000

More than 50,000

18

27

594

2,026

758

3,700

1,435

5,871

Total Systems/Quantity Across All Categories 285 1,664 4,297 11,242

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 

Table 3-32. Summary of Annual CWS Revenues by Ownership Type ($1,000), CWSS 

System Size

(Population Served)

Ownership Type

Public Private All Systems

P25 P50 P75 P25 P50 P75 P25 P50 P75

10k-50k $1,566 $2,302 $3,373 $1,454 $2,465 $4,100 $1,566 $2,313 $3,386 

50k-100k $5,344 $7,126 $11,254 $8,086 $10,133 $14,830 $5,440 $7,313 $11,802 

100k-500k $9,674 $16,444 $27,767 $15,217 $15,970 $36,579 $9,885 $16,187 $27,811 

>500k $61,899 $89,897 $193,345 $121,339 $122,075 $171,568 $62,103 $99,807 $188,013 

Source: U.S. EPA, 2002. 

P25 – 25th percentile.

P50 – 50th percentile (median).

P75 – 75th percentile.

3-54 
Drinking Water Industry Report Section 3 – Industry Profile

3-55 

Table 3-33 presents the median revenue per 1,000 gallons (and the 25th and 75th

percentiles), also by ownership type and system size, for those CWSs identified as discharging, 

according to CWSS. Similar to annual revenue, private systems also earn significantly more per 

gallon than their public counterparts. This discrepancy decreases with system size. For both private 

and public systems, revenue per 1,000 gallons generally declines as system size grows. 

Table 3-33. Summary of Total Revenues of CWSs that Discharge ($/1,000 gallons) 

System Size

Ownership Type

Public Private All Systems

(Population Served) P25 P50 P75 P25 P50 P75 P25 P50 P75

10k-50k $1.40 $1.93 $2.83 $3.16 $3.26 $3.36 $1.41 $2.51 $3.07 

50k-100k $1.12 $1.58 $1.71 $0.93 $2.42 $4.24 $1.12 $1.71 $1.74 

100k-500k $1.36 $1.82 $2.24 $2.17 $2.18 $2.58 $1.45 $1.95 $2.25 

>500k $1.37 $1.69 $1.71 N/A N/A N/A $1.37 $1.69 $1.71 

Source: U.S. EPA, 2002.

P25 – 25th percentile.

P50 – 50th percentile (median).

P75 – 75th percentile.

Table 3-34 presents the 2006 total revenue per system (in millions), reported at the 

25th, 50th, and 75th quartiles, according to responses to the EPA DWT Industry Questionnaire. 

Median total annual revenue across all source water and population size categories was $14 million. 

Surface source water systems serving both populations between 10,000 and 50,000, and those 

serving greater than 50,000 people reported higher median revenues, $4.5 and $25.3 million 

respectively, than their ground water counterparts. Table 3-35 presents 2006 revenues per volume 

(dollars per million gallons) from the EPA questionnaire. Unlike the total revenue values in Table 3-

34 the per unit water sales median values show that ground water systems receive higher per unit 

revenues than surface water systems. Ground water systems serving between 10,000 and 50,000 

people sell water at a median price of $4,021 per million gallons while surface water systems serving 

the same number of people receive a median sale value of $3,379. Systems serving more people and 

dealing in greater amounts of delivered water generally sell water at lower per unit prices. The 

median 2006 revenue per million gallons across all systems that responded to the DWT Industry 

Questionnaire was $3,082. 
Drinking Water Industry Report Section 3 – Industry Profile

3-56

Table 3-34. Reported 2006 Revenues by Population Served and Primary Water Source, per System, DWT Industry 

Questionnaire

a Primary Source Population Group Number of 

Systems 25th Percentile

Revenues ($ Millions)

50th Percentile 75th Percentile

Surface 10,000-50,000

More than 50,000

74

166

$3.2

$13.8

$4.5

$25.3

$6.8

$49.5

Ground 10,000-50,000

More than 50,000

18

27

$2.4

$9.9

$3.2

$14.9

$3.8

$23.3

Total Systems/ Revenues Across All Categories 285 $6.2 $14 $32.7

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 

Table 3-35. Reported 2006 Water Sales Revenue per Volume, per System, DWT Industry Questionnaire

Primary a Source Population Group Number of 

Systems

Water Sales Revenue per Volume ($/MGY)

25th Percentile 50th Percentile 75th Percentile

Surface

Ground

10,000-50,000

More than 50,000

10,000-50,000

More than 50,000

74

166

18

27

$2,230

$2,043

$2,202

$2,655

$3,379

$2,826

$4,021

$3,867

$5,216

$3,765

$5,893

$6,723

Total Systems/ Sales Revenue Across All Categories 285 $2,199 $3,082 $4,599

Source: Appendix A. 

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 
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3-57

3.3.3.2 Expenses

CWSs spent a total of $32 billion in 2000 on routine operating expenses, 

including water treatment, water distribution, and residuals management. Expenses of systems 

with a population of greater than 10,000 served totaled $13.3 billion (U.S. EPA, 2002). 

According to CWSS employee compensation – including salary, benefits, and 

contractor payments – accounts for about 31 percent of total system expenditures. Other routine 

operating and maintenance expenses account for another 45 percent. In total, operating expenses 

(employee expenses and other operating and maintenance expenditures) account for about 75 

percent of total system expenditures. Debt service payments and other expenses, contribute 

another 19 percent (U.S. EPA, 2002). 

Table 3-36 presents average total system expenditures by ownership type and 

system size, according to CWSS. The table also presents a breakdown of expenses by major 

category (employee, routine operating, debt service expenditures, and other expenses). 
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3-58 

Table 3-36. Average System Expenses and Expense Breakdown by Major Category, CWSS 

System Size (Population Served)

10k- 50k 50k-100k 100k –500k > 500k

Total

Across Alla

All Systems

Average System Expenses ($000) $2,673 $7,617 $18,561 $129,320 $7,539

b Employee 28% 30% 32% 34% 31%

Routine Operating 70% 62% 52% 48% 45%

Debt Service 2% 6% 12% 14% 19%

Other Expenses 1% 3% 4% 5% 6%

Public Systems

Average System Expenses ($000) $2,675 $7,630 $18,408 $131,490 $7,805

b Employee 34% 32% 32% 33% 30%

Routine Operating 45% 52% 52% 46% 44%

Debt Service 16% 11% 12% 16% 20%

Other Expenses 5% 6% 3% 5% 6%

Private Systems

Average System Expenses ($000) $2,664 $7,470 $20,466 $94,419 $5,355

b Employee 28% 29% 32% 40% 34%

Routine Operating 72% 69% 53% 56% 51%

Debt Service 1% 3% 10% 4% 9%

Other Expenses 1% 1% 6% 3% 8%

Source: U.S. EPA, 2002.

a – Components may not add up to 100% due to rounding.

b – Employee expenses include contractor expenses.

Table 3-37 presents the median and bounding quartiles for total expenses per 

1,000 gallons of water produced by ownership type and system size for CWSs, according to 

CWSS. 

Table 3-37. Summary of Total Expenses by System Size and Ownership Type 

($/1,000 gallons produced), CWSS 

System Size

(Population Served)

Ownership Type

Public Private Across All Systems

P25 P50 P75 P25 P50 P75 P25 P50 P75

10k-50k $1.27 $2.05 $2.95 $1.99 $2.30 $2.68 $1.29 $2.11 $2.79

50k-100k $1.16 $1.67 $2.32 $1.66 $2.11 $2.99 $1.16 $1.67 $2.41

100k-500k $1.20 $1.93 $2.48 $1.42 $2.09 $2.85 $1.22 $1.93 $2.48

>500k $1.09 $1.70 $2.06 $1.49 $2.05 $2.17 $1.21 $1.71 $2.10

Source: U.S. EPA, 2002.

P25 – 25th percentile. P50 – 50th percentile (median). P75 – 75th percentile.
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Table 3-38, Table 3-39, and Table 3-40 report the 25th, 50th, and 75th quartiles for 

2006 total expenses per system, total and routine operating expenses per million gallons a year 

for each system, and total employee wages per system, respectively from the DWT Industry 

Questionnaire. 

Based on the subset of EPA DWT Industry Questionnaire responses representing 

285 systems,14 median total annual expenses equaled $15.6 million. Seventy-five percent of 

systems reported total costs of operation below $39.6 million. Median total expenses per million 

gallons of produced water ranged from $3,272 to $4,815 across the source water and population 

served categories. Routine per unit operating expenses were highest for ground water systems 

serving more than 50,000 people, at $3,268. Surface water systems serving more than 50,000 

people had the lowest per unit routine expenditures, $1,897. Across all respondent categories 

median total per unit expenses equaled $3,522. Median routine operating expenses across all 

respondents was $2,034 or about 58% of the total median expenditures value. 

Table 3-40 shows that the median hourly wage rate paid in 2006 among EPA’s 

questionnaire responders equals $26. The median hourly wage rate ranged from $23 an hour paid 

by surface water producers serving between 10,000 and 50,000 residents, and $27 an hour paid 

by surface water suppliers serving greater than 50,000 people. Median total annual wages paid 

by the surveyed drinking water systems in 2006 was $1,447,000. Fifty percent of the 251 

respondents to this question paid between $616,000 and $3,535,000 in wages for the year 2006. 

 

14 As stated in earlier footnote, 285 is the number of completed system responses to the financial portion of the EPA 

DWT Industry Questionnaire without those systems that primarily resell water that is purchased from other systems. 

The purchased water source category has been omitted from the results presented in this section because of the 

potential for revealing Confidential Business Information.
Drinking Water Industry Report Section 3 – Industry Profile

Table 3-38. Reported 2006 Total Expenses, per System, DWT Industry Questionnaire

Primary Source a Population Group

Number of 

Systems

Total Expenses ($in millions)

25th Percentile 50th Percentile 75th Percentile

Surface 10,000-50,000

More than 50,000

74

166

$2.8

$14.5

$4.7

$30.2

$7.5

$58.1

Ground 10,000-50,000

More than 50,000

18

27

$2.0

$12.0

$3.0

$16.8

$4.6

$36.3

Total Systems/ Expenses Across All Categories 285 $6.4 $15.6 $39.6

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business

Information. 

3-60 
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3-61 

Table 3-39. Reported 2006 Expenses per MGY, Total and Operating, per System, DWT Industry Questionnaire

Primary a Source Population GroupNumber of 

Systems

Total Expenses ($/MGY) Routine Operating Expenses ($/MGY)

25th Percentile 50th Percentile 75th Percentile 25th Percentile 50th Percentile 75th Percentile

Surface

Ground

10,000-50,000

More than 50,000

10,000-50,000

More than 50,000

74

166

18

27

$2,186

$2,377

$2,196

$3,231

$3,272

$3,406

$3,900

$4,815

$5,653

$4,906

$6,762

$10,489

$1,342

$1,324

$1,267

$2,046

$2,105

$1,897

$2,516

$3,268

$3,244

$2,847

$3,407

$4,810

Total Systems/ Expenses 

Across All Categories 285 $2,357 $3,522 $5,474 $1,378 $2,034 $3,186

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information 
Drinking Water Industry Report Section 3 – Industry Profile

3-62 

Table 3-40. Reported 2006 Hourly and Total Wages for All Employees, per System, DWT Industry Questionnaire 

Primary a SourcePopulation 

Group

Number of b SystemsNumber of 

Employees

Hourly Wage ($) Total Wages Annually ($ in thousands)

25th 

Percentile

50th 

Percentile

75th 

Percentile

25th 

Percentile

50th 

Percentile

75th 

Percentile

Surface

Ground

10,000-50,000

More than 50,000

10,000-50,000

More than 50,000

69

139

18

26

 1,249 

 15,433 

 249 

 1,126 

$20

$22

$19

$23

$23

$27

$25

$26

$26

$33

$27

$30

$398

$1,441

$323

$765

$579

$2,694

$543

$1,454

$1,088

$5,142

$645

$1,927

Total Systems/ Wages 

Across All Categories 251 18,579 $22 $26 $30 $616 $1,447 $3,535

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 

b – There is a smaller number of systems in this table as some systems did not report wages, or reported them in an unclear manner.
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3-63

3.3.4 Customer Profile

Most CWSs, especially the ones serving the larger populations, are expected to be 

able to pass on any technology costs to their customers through rate increases. As a result, it is 

important to conduct an assessment of the likely burden on households served by CWSs. 

This section provides information on the customers of regulated CWSs, including 

customer types and water deliveries, revenues, and water rates by customer type. For residential 

customers, this section also discusses average annual water bills per household, information on 

the billing structures utilized, the availability of subsidized rates for low income families, and the 

average annual income of households served by regulated CWSs. 

3.3.4.1 Customer Types

CWSs serve three primary customer types: (1) other water suppliers, who resell 

water to the final customers, (2) residential customers, and (3) non-residential customers. Nonresidential customers can be further divided into commercial, industrial, agricultural, and other 

customers (e.g., hospitals and schools, prisons, or governments). 

According to the CWSS, of the systems with a population of greater than 10,000 

served, 1,680 (or 43 percent) sell water to other water suppliers, 3,242 (or 83 percent) serve 

residential customers, and 3,024 (or 77 percent) serve non-residential customers. Of the systems 

that serve non-residential customers, 91 percent serve commercial/industrial customers, 10 

percent serve agricultural customers, and 32 percent serve other non-residential customers. Table 

3-41 presents the number and percentage of systems with a population of greater than 10,000 that 

serve the different types of customers, by system size, according to CWSS. The majority of all 

systems, irrespective of size, serve residential and non-residential customers, while the largest 

systems (serving 500,000 people and more) are more likely to sell water to other water systems 

than the smaller-sized systems.
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Table 3-41. Number and Percentage of CWSs Serving Different Customer Types, CWSS 

System Size (Population Served)

10k - 50k 50k - 100k 100k - 500k > 500k Totala

Sold to Other PWS 1,107 37% 247 53% 251 60% 75 88% 1,680 43%

Residential 2,478 84% 384 82% 314 75% 66 78% 3,242 83%

Non-Residential 2,282 77% 371 79% 302 72% 69 82% 3,024 77%

Commercial/Industrial 2,112 93% 346 93% 232 77% 52 75% 2,742 91%

Agricultural 214 9% 38 10% 48 16% 9 12% 309 10%

Other 603 26% 143 39% 173 57% 37 53% 956 32%

Total 2,952 100% 470 100% 421 100% 85 100% 3,928 100%

Source: U.S. EPA, 2002.

a – Fifteen of the 2,283 systems with a population of greater than 10,000 served are excluded from these numbers 

because of removal of outliers in the CWSS data.

3.3.4.2 Water Deliveries, Revenues, and Rates by Customer Type

In 2000, the CWSs with a population of greater than 10,000 served supplied over 

17,317 billion gallons of water to their customers.15 Thirty-eight percent of this amount was 

delivered to residential customers, 22 percent was delivered to non-residential customers, 23 

percent was sold to another CWS, and 7 percent of the water was unaccounted for. Systems 

serving over 500,000 people accounted for the largest share of total water deliveries, with 40 

percent, followed by systems serving 100,000 to 500,000 people, with 26 percent. 

Table 3-42 presents year 2000 water deliveries by population served and customer 

type, according to CWSS. The table also distinguishes between systems owned by private and 

public entities. Privately-owned systems deliver 49 percent of water that they produce to 

residential customers, whereas 37 percent of the water delivered by public systems goes to 

residential customers. This difference is especially pronounced in the largest size category (more 

than 500,000 people served). Conversely, public systems deliver 25 percent of their water to 

other CWSs, compared to only 6 percent for private systems.

 

15 These numbers are based on 2,268 of the 2,283 regulated systems, that provided information on water deliveries 

to the 2000 Community Water System survey.
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3-65

Table 3-42. Amount of Water Delivered by Customer and Ownership Type and System 

Size (billion gallons; 2000), CWSS 

System Size (Population Served)

10k - 50k 50k - 100k 100k - 500k > 500k Total

All Systems

Sold to Other PWS 468 12% 180 9% 638 14% 2,774 40% 4,061 23%

Residential 1,700 43% 878 45% 1,762 40% 2,191 31% 6,530 38%

Non-Residential 893 23% 542 28% 1,004 23% 1,377 20% 3,816 22%

Unaccounted for 290 7% 187 10% 320 7% 480 7% 1,278 7%

Totala 3,930 100% 1,960 100% 4,436 100% 6,991 100% 17,317 100%

Public Systems

Sold to Other PWS 443 13% 165 9% 610 15% 2,759 42% 3,976 25%

Residential 1,440 42% 762 43% 1,616 40% 1,989 30% 5,807 37%

Non-Residential 832 24% 487 28% 899 22% 1,313 20% 3,531 22%

Unaccounted for 245 7% 166 9% 283 7% 461 7% 1,155 7%

Totala 3,402 100% 1,753 100% 4,072 100% 6,623 100% 15,850 100%

Private Systems

Sold to Other PWS 25 5% 16 8% 29 8% 15 4% 85 6%

Residential 260 49% 116 56% 146 40% 202 55% 724 49%

Non-Residential 61 11% 54 26% 105 29% 64 18% 285 19%

Unaccounted for 45 9% 21 10% 37 10% 19 5% 122 8%

Totala 529 100% 207 100% 364 100% 367 100% 1,467 100%

Source: U.S. EPA, 2002. 

a – Sum of individual components may not add up to total due to missing data in some of the subaccounts.

Table 3-43 presents the 25th percentile, median, and 75th percentile values for 

water sales for residential customers, in millions of gallons per year, according to the EPA DWT 

Industry Questionnaire respondents. 
Drinking Water Industry Report Section 3 – Industry Profile

3-66 

Table 3-43. Reported 2006 Water Sales to Residential Customers, by System, DWT Industry Questionnaire

Primary a Source Population GroupNumber of b Systems

Estimated Water Sold (MGY)

25th Percentile 50th Percentile 75th Percentile

Surface

Ground

10,000-50,000

More than 50,000

10,000-50,000

More than 50,000

73

155

17

25

332

2,094

273

1,601

654

3,800

331

2,819

1,090

7,889

484

4,113

Total 270 740 2,187 4,933

Source: Appendix A.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information.

b – There are fewer systems in this table than in the others as only systems with residential sales are reported.
Drinking Water Industry Report Section 3 – Industry Profile

3-67 

Table 3-44 presents 2000 water sales revenue of CWSs, by population served and 

customer type, according to CWSS.16 The table also distinguishes between systems owned by 

private and public entities. In 2000, these large CWSs received $27.2 billion in water sales 

revenue. Public systems accounted for almost 89 percent of this total percent of revenue. Similar 

to water deliveries discussed above, residential customers account for the largest share of water 

sales revenues. However, while residential customers accounted for 38 percent of water 

deliveries in 2000, they accounted for 48 percent of revenues, indicating higher average rates for 

this customer group. 

Table 3-44. Revenues by Customer Type (in million $), CWSS 

3

0 100

10k - 50k 50k - 100k 100k - 500k > 500k Total

All Systems

Sold to Other PWS $40 6% $212 7% $852 12% $2,922 29% $4,388 16%

Residential $3,796 57% $1,795 55% $3,719 52% $3,894 38% $13,204 48%

Non-Residential $1,601 24% $761 23% $1,973 28% $2,348 23% $6,683 25%

Totala $6,715 100% $3,250 100% $7,150 100% $10,127 100% $27,242 100%

Public Systems

Sold to Other PWS $351 6% $192 7% $822 13% $2,911 32% $4,277 18%

Residential $3,235 56% $1,506 53% $3,283 51% $3,389 37% $11,413 47%

Non-Residential $1,525 26% $694 24% $1,715 27% $2,148 23% $6,082 25%

Totala $5,774 100% $2,840 100% $6,411 100% $9,176 100% $24,202 100%

Private Systems

Sold to Other PWS $51 5% $20 5% $30 4% $10 1% $111 4%

Residential $561 60% $289 71% $436 59% $504 53% $1,790 59%

Non-Residential $76 8% $67 16% $258 35% $199 21% $601 20%

Totala $941 100% $409 100% $738 100% $951 100% $3,04 %

Source: U.S. EPA, 2002.

a – Sum of individual components may not add up to total due to missing data in some of the subaccounts.

Table 3-45 presents median revenue (per 1,000 gallons of water delivered) of 

CWSs, by population served and customer type, according to CWSS.17 Similar to Table 3-44 

above, Table 3-45 also distinguishes between systems owned by private and public entities. The 

table shows that non-residential customers served by privately-owned CWSs have the highest 

 

16 These numbers are based on 2,063 of the 2,283 regulated systems that provided information on water sales 

revenues.

17 These numbers are based on 2,014 of the 2,283 regulated systems that provided information on water sales 

revenues and water deliveries.
Drinking Water Industry Report Section 3 – Industry Profile

3-68

median water rates of $4.27 per 1,000 gallons. For all customer groups, private systems charge 

higher rates than public systems. 

Table 3-45. Median Revenue per 1000 Gallons of Water Delivered by Customer Type, 

Ownership Type, and System Size ($/1000 gallons), CWSS 

System Size (Population Served)

10k-50k 50k-100k 100k-500k >500k Total

All Systems

Sold to Other PWS $1.54 $1.61 $1.09 $1.09 $1.57

Residential $2.80 $2.61 $2.05 $1.89 $3.20

Non-Residential $2.10 $2.14 $1.86 $1.74 $1.75

Totala $2.02 $1.65 $1.79 $1.62 $2.73

Public Systems

Sold to Other PWS $1.32 $1.43 $1.09 $1.02 $1.57

Residential $2.72 $2.49 $2.02 $1.85 $3.03

Non-Residential $2.09 $1.93 $1.79 $1.66 $1.73

Totala $1.86 $1.61 $1.73 $1.56 $2.48

Private Systems

Sold to Other PWS

Residential

$2.30

$2.87

$2.00

$3.45

$1.28

$3.26

$1.16

$2.60

$1.44

$3.55

Non-Residential $2.96 $2.91 $2.36 $3.06 $4.27

Totala $2.47 $3.09 $2.47 $2.66 $3.22

Source: U.S. EPA, 2002. 

a – Total quantity (denominator) includes unaccounted for water for which no revenues were received.

3.3.4.3 Households

CWSs derive approximately 50 percent of their water sales revenue from 

residential customers, with smaller CWSs depending more heavily on this customer class than 

the larger CWSs. The average annual residential water bill for systems of every size, ownership 

type, and water source category is $266 in the year 2000. Based on this average annual 

residential water bill, and the national median household income of $42,151, most households 

spend less than 1 percent of their annual income on water services (U.S. EPA, 2002). 

Table 3-46 presents the median annual water bill for systems with a population of 

greater than 10,000 served, by system size, ownership type, and water source, according to the 

CWSS. In general, the median annual residential water bill is higher for privately-owned systems 

than for publicly-owned systems, at $280 and $240, respectively. Additionally, across all 

population size categories systems using ground water have the lowest median annual water 

bills, followed closely by surface water systems, with purchased water systems having 
Drinking Water Industry Report Section 3 – Industry Profile

significantly higher median annual residential water bills. These generalizations do not hold for 

the 50,000 to 100,000 and the greater than 500,000 categories where surface water systems have 

lower median residential water bills than ground water systems. 

 

Table 3-46. Summary of Median Annual Residential Water Bill, CWSS 

System Size (Population Served)

10k-50k 50k-100k 100k-500k >500k Total

Overall $269 $267 $224 $236 $266

By Ownership Type

Public $240 $260 $211 $223 $240

Private $260 $395 $350 $350 $280

By Water Source

Ground Water $211 $262 $144 $251 $211 

Surface Water $264 $240 $234 $211 $249 

Purchased Water $360 $300 $299 $255 $338 

Source: U.S. EPA, 2002.

Table 3-47 shows the estimated number of systems using various billing methods 

for all customers, according to the EPA DWT Industry Questionnaire. Seventy-five percent of 

systems use rates based on metered water usage. Approximately 50 percent of the systems that 

reported a billing method have uniform rates. Peak seasonal rates are not common. Smaller 

systems are more likely to use declining block rates than increasing block rates. As for larger 

systems serving more than 50,000 people the story is mixed with surface water systems tending 

towards declining block rates and ground water systems strongly skewed to the use of increasing 

block rates. 

Some of the variance in median annual residential water bills may be attributed to 

the fact that some CWSs provide reduced rates to low- and fixed-income households (i.e., 

lifeline rates). Table 3-48 presents the number and percentage of systems that offer reduced rates 

to low- and fixed-income households, according to CWSS. Overall, 3 percent of CWSs offer 

reduced rates to qualifying household, while 69 percent do not (28 percent did not provide this 

information). By ownership type, publicly-owned systems are more likely to offer lifeline rates 

than privately-owned CWSs: 1,503 of 25,510 publicly-owned systems (6 percent) offer reduced 

rates compared to only 18 of 26,675 privately-owned systems. 

3-69 
Drinking Water Industry Report Section 3 – Industry Profile

Table 3-47. Number of Systems Using Various Billing Methods for All Customers, 2006, DWT Industry Questionnaire 

Metered Charges Unmetered Charges

Combined 

Flat Fee for 

Peak Annual Water and Separate 

Primary Population Declining Increasing Season Uniform Total Connection Other Flat Fee for Total a Source Group Block rate Block Rate Rate Rate Metered Fee Services Water Unmetered Other

10,000-50,000 26 20 2 36 84 5 2 23 30 10

Surface More than

50,000 58 50 9 93 210 8 1 35 44 32

10,000-50,000 7 4 0 10 21 0 1 6 7 2

Ground More than

50,000 5 17 3 13 38 2 0 6 8 2

Total b 96 91 14 152 353 15 4 70 89 46

Source: Appendix A.

Note: Systems utilize more than one billing method—totals are not of unique systems. All systems report at least one billing method. 

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 

b – The number of respondents to a particular question in the questionnaire may differ. In addition, EPA’s questionnaire allowed respondents to answer financial 

questions on a utility basis. A single utility can operate more than one surveyed system.. 

3-70 
Drinking Water Industry Report Section 3 – Industry Profile

3-71 

Table 3-48. Number and Percentage of Systems with Lower Rates for Low- or FixedIncome Households, CWSS 

 

System Size (Population Served)

10k - 50k 50k - 100k 100k - 500k > 500k Total

No. % No. % No. % No. % No. %

All Systems

Lower Rates Available 244 8% 43 9% 30 7% 18 22% 1,521 3%

Lower Rates Not 

Available

2,552 85% 377 80% 360 84% 49 58% 35,958 69%

Did Not Report 217 7% 50 11% 41 9% 17 20% 14,707 28%

Total 3,013 100% 470 100% 430 100% 85 100% 52,186 100%

Public Systems

Lower Rates Available 232 9% 40 10% 30 8% 16 20% 1,503 6%

Lower Rates Not 

Available

2,144 84% 328 79% 326 83% 45 59% 19,563 77%

Did Not Report 166 7% 47 11% 37 9% 16 21% 4,444 17%

Total 2,542 100% 415 100% 393 100% 76 100% 25,510 100%

Private Systems

Lower Rates Available 12 3% 3 6% - 0% 3 33% 18 0%

Lower Rates Not 

Available

408 87% 49 89% 34 91% 4 51% 16,395 61%

Did Not Report 51 11% 3 6% 3 9% 1 16% 10,263 38%

Total 471 100% 55 100% 37 100% 8 100% 26,675 100%

Source: U.S. EPA, 2002. 

Table 3-49 shows the number of systems in 2006 that had a low income assistance 

program, the 25th, 50th, and 75th quartiles for the number of low-income households qualifying 

for the program, and the mean highest annual qualifying income for these programs (if the 

system supplied the number), according to the EPA DWT Industry Questionnaire respondents. 

Nearly 13 percent of systems offer some type of assistance program.

As shown in Table 3-50 according to the CWSS data, approximately 411,000 

households were eligible for reduced rates in 2000, with qualifying household incomes ranging 

from $0 to $54,000. Table 3-50 summarizes the number of households with reduced rates and the 

qualifying income ranges by system size and ownership type. The table shows that most of the 

households that qualify for the reduced rates receive their water from CWSs that serve greater 

than 500,000 people or 10,000 to 50,000 people, with 189,770 households and 56,962 

households in each group, respectively. 
Drinking Water Industry Report Section 3 – Industry Profile

3-72 

Table 3-49. Reported 2006 Household Participation in System Assistance Programs and Income Requirements, DWT Industry 

Questionnaire 

Primary a Source Population Group

Number of Households Highest Annual Income Requirement

Number of 

Systems

25th 

Percentile

50th 

Percentile

75th 

Percentile

Number of 

Systems Median (50th Percentile)

Surface

Ground

10,000-50,000

More than 50,000

10,000-50,000

More than 50,000

8

24

1

3

 

 

 

 

75 

467 

 9 

146 

 291 

 1,500 

 9 

 150 

 1,000 

 3,100 

 9 

 779 

1

11

0

2

$25,000 

$35,000 

NA

$18,800 

Total 36 148 704 2,567 14 $25,200 

Source: Appendix A.

Note: Non-responses to this question were assumed to indicate that the system had no assistance program.

a – Systems that use purchased water as their primary source are not presented in this table because of the potential for revealing Confidential Business 

Information. 

Table 3-50. Number of Households with Lower Rates and Range of Qualifying Household Incomes, CWSS 

System Size (Population Served)

10k - 50k 50k - 100k 100k - 500k > 500k Total

# of

Households

Min. - Max. 

Inccome

# of

Households

Min. - Max. 

Inccome

# of

Households

Min. - Max. 

Inccome

# of

Households

Min. - Max. 

Inccome

# of

Households

Min. - Max. 

Inccome

Public 56,962 $0-29k 26,985 $10-54k 41,959 $15-33k 189,770 $17-29k 411,155 $0-54k

Private n/a n/a n/a n/a n/a n/a a a a a

All 

Systems 56,962 $0-29k 26,985 $10-54k 41,959 $15-33k 189,770 $17-29k 411,155 $0-54k

Source: U.S. EPA, 2002.

a – Data not provided.
Drinking Water Industry Report Section 3 – Industry Profile

3-73 

3.4 REFERENCES

Eastern Research Group (ERG), 2005. Memorandum: Review of Wholesale Drinking Water 

Treatment Systems, Chantilly, VA. August 1, 2005. Document Control Number (DCN) 

DW03783. 

ERG, 2006. Memorandum: Drinking Water Treatment Residuals as RCRA Hazardous Waste. 

Chantilly, VA. April 14, 2006. DCN DW00288. 

U.S. EPA, 2002. Community Water System Survey 2000 (EPA 815-R-02-005), Office of Water, 

Washington, DC. DCN DW00001. 

U.S. EPA, 2006. SDWIS Inventory 2006-11-09 (MS Excel® file), Office of Water, November 9, 

2006. DCN DW03717. 

U.S. EPA, 2007. SDWIS Inventory (third quarter 2007) (MS Excel® file), Office of Water,

Washington, DC. 

U.S. EPA, 2008a. FACTOIDS: Drinking Water and Ground Water Statistics for 2006 (EPA 816-

K-06-012). Office of Water, Washington, DC, March 2008. DCN DW03755.
4-1

SECTION 4

CURRENT STATE NPDES PERMIT REQUIREMENTS FOR 

WATER TREATMENT PLANT RESIDUALS 

This section presents the current wastewater discharge requirements for drinking 

water treatment plant (WTP) residuals. Currently, there are no national effluent limitation 

guidelines and standards, direct or indirect, to regulate discharges of residuals to waters of the 

United States. Therefore, regulation of pollutants being discharged in residuals is decided by the 

state (or other permitting authority) for direct dischargers and by the publicly-owned treatment 

works (POTW) for indirect dischargers. Topics discussed in this section include an overview of 

the state and federal National Pollutant Discharge Elimination System (NPDES) permit program 

for WTPs (Section 4.1) and a summary of current pollutant limitations in NPDES permits for 

WTPs (Section 4.2). 

4.1 OVERVIEW OF STATE AND FEDERAL NPDES REGULATORY 

REQUIREMENTS FOR WATER TREATMENT PLANTS 

The NPDES permit program regulates residuals discharged directly to waters of 

the United States. The permits are issued by EPA regional offices or authorized states 

(permitting authority). WTPs may be authorized to discharge process wastewater (i.e., residuals) 

under an individual or general NPDES permit. Individual NPDES permits are developed and 

issued on a site-specific basis to manage the discharges at individual plants. General NPDES 

permits are developed and issued for multiple plants with similar activities or effluent 

characteristics. For both permit types, states apply water quality-based pollutant limitations 

where required and develop technology-based best professional judgment (BPJ) limitations for 

other pollutants. 

EPA reviewed the 2004 Permit Compliance System (PCS) database to determine 

how states are permitting discharges from WTPs. As discussed in Section 2.4.2, larger facilities 

are more likely to appear in the PCS system as they are expected to impact surface waters to a 

greater extent. Information on smaller facilities with less likelihood to impact surface waters is 
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-2

not consistently tracked in PCS. Also, information might not be available for facilities with 

discharges covered under a general permit. 

The 2004 PCS database included 20 WTPs identified as major dischargers and 

2,806 WTPs identified as minor dischargers. Of the 2,826 permit identification numbers in PCS, 

971 WTPs (34%) have general permits and 1,855 WTPs (66%) have individual permits (ERG, 

2005). Table 4-1 presents a summary of the PCS database 

(http://www.epa.gov/enviro/html/pcs/pcs_subj.html) review by state. 

Table 4-1. Summary of Permit Information in the 2004 Permit Compliance System

State

WTPs in EPA’s Permit 

Compliance System a

General Permits for WTP Discharges 

General 

Permits

Individual 

Permits

Alabama 0 85 No general permit.

Alaska 0 3 No general permit.

Arizona 0 11 No general permit. 

Arkansas 107 9 ARG640000: Water Treatment Plants

California None listed 

in PCS

33 Desalination concentrates covered under:

CAG9930001: Dewatering and Other Low Threat Discharges 

(Central Coast Region)

Colorado 72 (COG64)

4 (COG38)

10 COG640000: General Permit for Water Treatment Plants

COG380000: Treated Water Distribution Systems

Connecticut None listed 

in PCS

1 GP-002: General Permit for the Discharge of Water Treatment 

Wastewater Into Waters of the State of Connecticut

Delaware 0 None listed in 

PCS

No general permit.

DC (Region 3) 0 1 No general permit.

Florida 1 (FLG07)b 32 No general permit.

Georgia 0 1 No general permit.

Hawaii 0 1 No general permit.

Idaho (Region 

10)

0 10 No general permit.

Indiana 0 101 No general permit.

Illinois 48 175 ILG640000: General Permit for Public Water Supply 

Wastewaters

Iowa 0 14 No general permit.

Kansas 0 9 No general permit.

Kentucky 138 

(KYG64)

2 (KYG20) b

15 KYG64: General Permit for Wastewater Discharges Associated 

with Drinking Water Plant Activities
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-3

Table 4-1. Summary of Permit Information in the 2004 Permit Compliance System

State

WTPs in EPA’s Permit 

Compliance System a

General Permits for WTP Discharges 

General 

Permits

Individual 

Permits

Louisiana 2 (LAG38)

1 (LAG53)

12 LAG380000: Potable Water Treatment Plant

LAG530000: Waste Water Treatment Plant

Maine 0 12 No general permit.

Maryland 9 26 MDG670000: General Permit for Tanks and Pipes, and Other 

Liquid Containment Structures at Facilities other than Oil 

Terminals

Massachusetts 55 (MAG64)

8 (MAG07)

6 MAG640000: Water Treatment Facility Discharges

MAG070000: Construction Dewatering

Michigan 34 8 MIG640000: Wastewater Discharge from Potable Water Supply

Minnesota 38 (MNG64)

1 (MNG82) b

22 MNG640000: Treated Filter Backwash Water from Water 

Treatment Facilities

Mississippi 0 19 No general permit.

Missouri 142 

(MOG640)

7 (MOG641)

1 (MOG25) b

37 MOG640000 - Water Treatment Plant Filter Backwash

MOG641000 - Backwash Water from Water Softening Units

Montana 1 15 MTG770000: Disinfected Water Discharges

Nebraska 0 27 No general permit.

Nevada 0 3 No general permit.

New Hampshire 3 None listed in 

PCS

NHG640000: Water Treatment Facility Discharges

New Jersey 0 33 No general permit.

New Mexico 0 7 No general permit.

New York 0 52 No general permit.

North Carolina 0 170 No general permit.

North Dakota 0 26 No general permit.

Ohio 0 142 No general permit.

Oklahoma 4 31 OKG38: Filter Backwash Discharges from Potable Water 

Treatment Plants

Oregon 63 (ORG38)

1 (ORG75) b

5 OR38 (OR-200-J on website): Discharge/Land Application of 

Filter Backwash, Settling Basin, and Reservoir Cleaning Water

Pennsylvania 0 139 No general permit.

Puerto Rico 0 109 No general permit.

Rhode Island 0 5 No general permit.

South Carolina 58 (SCG64)

1 (SCG25)

11 SCG641000: Water Treatment Plant Discharges

With Maximum Total Residual Chlorine (TRC) Limits

SCG643000: Water Treatment Plant Discharges With Median 

TRC Limits

SCG645000: Water Treatment Plant Discharges With the Lowest 

TRC Limits

SCG250000: Utility Water Discharge

South Dakota 21 9 SDG07: Temporary Dewatering Activities
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-4

Table 4-1. Summary of Permit Information in the 2004 Permit Compliance System

State

WTPs in EPA’s Permit 

Compliance System a

General Permits for WTP Discharges 

General 

Permits

Individual 

Permits

Tennessee None listed 

in PCS

111 TNG640000: Filter Backwash and Sedimentation Basin 

Washwater from Water Treatment Plants

Texas 0 126 No general permit.

Utah 31 1 UTG640000: General Permit for Drinking Water Treatment 

Plants

Vermont 0 2 No general permit.

Virginia 0 128 No general permit.

Virgin Islands 0 14 No general permit.

Washington 30 None listed in 

PCS

WAG-64: Water Treatment Plant General Permit

West Virginia 86 (WVG64)

1 (WVG55) b

24 WVG64 (WV0115754 on website): Water Treatment Plant 

Wastewater Disposal Systems

Wisconsin None listed 

in PCS

None listed in 

PCS

WI-0046540-4 (Process wastewater discharges): Potable Water 

Treatment and Conditioning

Wyoming 1 12 WYG71: General Permit for Temporary Discharges

Total 971 1,855

Source: ERG, 2005.

a – Additional WTPs included in PCS, but omitted from table because of low flow or not applicable activities (by 

state):

Arkansas: Eight additional plants have discharge coverage under general permit ARG550000 - Individual 

Treatment Facilities with maximum design flow of ≤ 1,000 gallons/day.

Colorado: 12 additional plants have discharges covered under COG60 - Minimal Discharges (not specific to 

drinking water treatment).

Massachusetts: One plant had discharges covered under a general permit for noncontact cooling water 

(MAG25)

Minnesota: One plant had discharges covered under a general permit for noncontact cooling water (MNG25)

Missouri: One plant had discharges covered under a general permit for noncontact cooling water (MOG35)

North Carolina: Four additional plants discharge under general permit NCG510000, Groundwater Remediation

b – Permit not found on-line; discharge coverage unknown.

States commonly issue general permits for certain waste streams discharged by 

WTPs. The most common waste stream covered by general permits is filter backwash water. 

Residuals from solids settling (e.g., clarifiers, lagoons) are the second most common waste 

stream covered. Residuals less commonly covered by general permits include water softening 

discharges, membrane desalination concentrates, and ion exchange regeneration waste. Sections 

6 and 7 of this document discuss the source water treatment operations and residuals generated in 

more detail.
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-5

Table 4-2 lists the process wastewater discharges covered by drinking water 

treatment industry-specific general permits identified in Table 4-1. In addition to the information 

presented in the table, the Louisiana General Permit (LAG380000) also covers wastewater from 

disinfection of source water, the South Carolina (SCG641000, SCG643000, and SCG645000) 

and Tennessee (TNG640000) general permits also cover wash water from sedimentation basins. 

Some general permits specifically prohibit discharges (or exclude them from permit coverage). 

For example, the Oklahoma general permit (OKG38) requires no residual disinfectant in the 

discharge (i.e., completely diluted in the backwash water during storage in detention ponds). 

General permits may further limit applicability beyond type of WTP discharge. 

Applicability requirements include providing general permit coverage for existing plants only 

(MAG640000 and NHG640000) and limiting coverage to smaller dischargers using discharge 

flow rate limits or production limits. General permits that limit coverage based on discharge 

quantities, include the following: 

• The Oklahoma general permit (OKG38) requires discharge of no more 

than one million gallons per day; 

• The California Central Coast general permit (CAG993001) requires 

continuous maximum discharges to be specified in the permit, including 

limiting desalination concentrate to 50,000 gallons per day; and

• The Washington general permit (WAG-64) requires a maximum 

production capacity of 50,000 gallons per day (peak output based on 24-

hour production). 

Other applicability requirements are also used to protect the receiving water. For 

example, the Wisconsin general permit (WI-0046540-4) does not cover discharges containing 

radium and arsenic (present in water supply). Additionally, a number of general permits do not 

cover discharges to certain receiving streams (e.g., impaired waters); in those cases, WTPs need 

to apply for an individual permit. 

If the WTP does not meet the applicability of the general permit, an individual 

permit must be obtained prior to discharge. The types of waste streams and pollutants covered by 
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-6

an individual permit depend on the source water treatment operations, treatment chemicals, and 

source water contaminants at a particular plant.

Table 4-2. Wastewater Discharges from WTPs Covered by General Permits

State

NPDES Permit 

Number

Wastewater Discharges Covered by General Permit

Filter 

Backwash

Solids 

Removal a

Water 

Softening b

Ion Exchange 

Regeneration 

Reverse 

Osmosis 

Concentrate

Wastewater 

from Sludge 

Dewatering

AR ARG640000 X X

CA CAG9930001 X c

CO COG640000 X X

CT GP-002 X X X X X

IL ILG64 X X X

KY KYG640000 X

LA LAG380000 X X X

MA MAG640000 X X d

MD MD670000 Overflow, flushing, disinfection, mechanical cleaning, or dewatering discharges

MI MIG640000 X X e

MN MNG640000 X

MO MO-G640000 X

MO-G641000 X f X f

MT MTG770000 Disinfected water discharges

NH NHG640000 X X d

OK OKG38 X

OR OR-200-J X

SC SCG641000, 

SCG643000, 

and SCG645000

X X

SD SD070000 X g

TN TN640000 X

UT UTG640000 Not specified

WA WAG-64 X X

WV WV0115754 X h X h

WI WI-0046540-4 X i X i X i

WY WYG710000 Not specified (temporary discharges)

Source: ERG, 2005.

a – Residuals from solids removal include sludge/blowdown from clarifiers, lagoons, etc. and filter sludge. The filter 

sludge may be part of iron and/or manganese removal operations.

b – Water softening residuals may include ion exchange wash/rinse concentrates and sludge from sedimentation 

basins or filters.

c – The California Central Coast Regional general permit covers discharges of desalination concentrate up to 50,000 

gallons per day to ocean waters. This general permit does not cover discharges of desalination concentrate to inland 

surface waters.
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-7

d – The Massachusetts and New Hampshire general permits cover the discharge of treated presedimentation 

underflow and treated underflow from coagulation/settling processes using aluminum compounds or polymers as 

coagulants.

e – The Michigan general permit No. 649000 (expires April 1, 2005) includes water softening discharges, except 

from batch regenerated potassium permanganate iron removal and sodium zeolite softening. The general permit 

effective April 1, 2005 does not cover any discharges from water softening.

f – The Missouri general permit (G641000) covers discharges of backwash water from water softening.

g – South Dakota general permit covers discharges from temporary dewatering activities. The discharges “must be 

relatively uncontaminated and must not contribute nonconventional or toxic pollutant loadings to the receiving 

stream.” 

h – The West Virginia general permit covers treatment wastewater discharges and describes minimum treatment 

requirements for sediment removal and total residual chlorine removal.

i – Discharges covered by the Wisconsin general permit (WI-0046540-4) include those from iron removal filters 

(excluding batch regeneration by potassium permanganate (KMnO4) to surface water), demineralizers (excluding 

sodium or potassium cycle ion exchange softeners), lime softeners, alum coagulation units, granular media filters, 

reverse osmosis units, and other systems with similar discharges.

4.2 SUMMARY OF CURRENT POLLUTANT LIMITATIONS AND 

REQUIREMENTS FOR WATER TREATMENT PLANTS: GENERAL 

AND INDIVIDUAL PERMITS

The most common pollutants regulated in general permits include aluminum, iron, 

manganese, pH, settleable solids, total residual chlorine (TRC), and total suspended solids (TSS). 

In addition, NPDES permits for membrane desalination and ion exchange plants may also 

require limits or monitoring of chlorides and total dissolved solids (TDS) (ERG, 2005). 

WTPs not covered under a general discharge permit must apply for an individual 

NPDES permit. EPA reviewed individual permits from the following states:

• Alabama;

• Alaska;

• Arizona; 

• California;

• Florida; 

• Illinois;

• Indiana;

• Iowa;

• Kansas;

• Massachusetts;

• Missouri;

• Montana; 

• Nebraska;

• Nevada;

• North Carolina; 

• Ohio; 

• Pennsylvania; 

• Puerto Rico; 

• Texas;

• Washington, DC; and 

• Wisconsin. 

The common pollutants regulated in individual permits include aluminum, copper, dissolved 

oxygen, iron, lead, pH, temperature, TRC, TSS, and turbidity. Other pollutants that may be 

included in WTP permits based on source water characteristics or treatment chemicals used 
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-8

include ammonia, arsenic, biochemical oxygen demand (BOD), cadmium, manganese, oil and 

grease, settleable solids, total phosphorus, and zinc. In addition, NPDES permits for membrane 

desalination and ion exchange plants may also require limits or monitoring of chlorides and 

TDS. Table 4-3 lists the range of pollutant limitations in general and individual NPDES permits 

reviewed by EPA as part of the industry review (ERG, 2005 and ERG, 2008). 

Table 4-3. Range of Pollutant Limitations From a Sample of General and Individual 

NPDES Permits

Pollutant

General NPDES Permits Individual NPDES Permits

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation a

Daily 

Maximum 

Limitation a

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation b

Daily 

Maximum 

Limitation b

Aluminum Majority of 

state general 

permits

0.75 to 1 

mg/L

1.5 to 10 

mg/L

California

Missouri

Montana

Pennsylvania

Washington, DC

1 to 4 mg/L 1.5 to 8 mg/L

Ammonia Colorado Report only California

Puerto Rico

Report only 1 mg/L

Arsenic Michigan 0.150 mg/L 0.680 mg/L Alaska

Arizona

California

Puerto Rico

0.036 mg/L 0.00018 to 

0.080 mg/L

Biochemical 

oxygen 

demand 

(BOD)

None — — California

Florida

Illinois

Puerto Rico

10 to 20 mg/L 5 to 30 mg/L

Cadmium None — — California

Florida

Missouri

0.002 to 

0.0093 mg/L

0.004 to 

0.042 mg/L

Chlorides Illinois

Louisiana

Missouri

— 250 to 1,000 

mg/L

California

Florida

— 150 mg/L

Copper Connecticut

Wisconsin

— <1.09 mg/L Arizona

California

Florida

Massachusetts

Puerto Rico

0.0031 to 

0.007 mg/L

0.0029 to 

0.500 mg/L

Dissolved 

oxygen

None — — Alaska

California

Florida

Puerto Rico

Minimum: 2.0 to 7.0 mg/L
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-9

Table 4-3. Range of Pollutant Limitations From a Sample of General and Individual 

NPDES Permits

Pollutant

General NPDES Permits Individual NPDES Permits

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation a

Daily 

Maximum 

Limitation a

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation b

Daily 

Maximum 

Limitation b

Iron Majority of 

state general 

permits

1 to 5 mg/L 2 to 10 mg/L Alaska

Florida

Illinois

Indiana

North Carolina

Pennsylvania

Washington, DC

1.8 to 2 mg/L 0.3 to 4.1 

mg/L

Lead Wisconsin — — Arizona

California

Missouri

Puerto Rico

0.003 to 

0.0081 mg/L

0.0044 to 

0.210 mg/L

Manganese Majority of 

state general 

permits

0.0043 to 1 

mg/L

0.019 to 3 

mg/L

Arizona

Pennsylvania

Puerto Rico

1 mg/L 0.05 to 2 

mg/L

Oil and 

grease

California

Colorado

25 mg/L 10 to 75 mg/L California

Massachusetts

Puerto Rico

10 mg/L 10 to 15 mg/L

pH Majority of 

state general 

permits

6.0 to 9.0 s.u. Majority of states 

reviewed

6.0 to 11.0 s.u.

Phosphorus Michigan 1 mg/L — California

Florida

Missouri

Puerto Rico

1 mg/L 1 mg/L

Settleable 

solids

California

Missouri

Oregon

Tennessee

Washington

0.1 to 2.0 

mL/L

0.1 to 3.0 

mL/L

California

Missouri

North Carolina

0.1 mL/L 0.2 to 0.3 

mL/L

Temperature None — — California

Massachusetts

Nevada

Puerto Rico

— 86 to 100°F

±5°F: effect 

on receiving 

stream

Total 

dissolved 

solids (TDS)

Colorado

Connecticut

Illinois

— 1,000 to 

1,500 mg/L

Alaska

California

Illinois

Nevada

80 to 800 

mg/L

95 to 1,500 

mg/L

Total residual 

chlorine 

(TRC)

Majority of 

state general 

permits

0.03 to 1 

mg/L

<0.02 to 1 

mg/L c

Majority of states 

reviewed

0.01 to 0.29 

mg/L

0.002 to 1.3 

mg/L

Total 

suspended 

solids (TSS)

Majority of 

state general 

permits

15 to 30 mg/L 20 to 60 mg/L Majority of states 

reviewed

15 to 70 mg/L 5 to 150 mg/L
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-10

Table 4-3. Range of Pollutant Limitations From a Sample of General and Individual 

NPDES Permits

Pollutant

General NPDES Permits Individual NPDES Permits

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation a

Daily 

Maximum 

Limitation a

States with 

Limitations or 

Reporting 

Requirements

Monthly 

Average 

Limitation b

Daily 

Maximum 

Limitation b

Turbidity California 75 NTU 225 NTU California

Massachusetts

Nevada

Puerto Rico

6 to 50 NTU 5 to 150 NTU

Zinc Connecticut

Wisconsin

— <2.0 mg/L California

Missouri

Puerto Rico

0.061 to 

0.093 mg/L

0.09 to 50 

mg/L

Sources: ERG, 2005; ERG, 2008.

NTU—Nephelometric turbidity units 

a – Limitations may be less than range presented for certain receiving streams (e.g., small streams, impaired waters).

b – Some states may only require monitoring and reporting (i.e., no numerical limitations).

c – One general permit allows up to 3.0 mg/L TRC discharge to ground water. 

One of the trends in the drinking water treatment industry is the increased use of 

membrane desalination operations. Between 1992 and 1999, the number of desalination plants in 

the United States with production of 25,000 gallons per day or more increased from 103 to 203 

plants (Mickley, 2001). Residuals from desalination include concentrates. Due to large volumes 

and high TDS concentrations, WTPs have difficulty disposing of concentrates unless discharge 

to surface water is an option. Most membrane desalination plants do not treat the concentrate 

prior to discharge. Other waste management options include indirect discharge, land application, 

landfill disposal, and underground injection (Malmrose, et al., 2004). These other waste 

management options often include certain regulations that must be met by the WTP. 

Typical permit limitations for direct discharge of desalination concentrate include 

TDS, TSS, salinity, and contaminants specific to the source water such as nutrients (nitrogen and 

phosphorus), arsenic, barium, and radionuclides. If the discharge is potentially highly saline, 

WTPs may dilute the discharge with source water, wastewater treatment plant effluent, or 

cooling water. Also, concentrates for membrane systems treating ground water may contain low 

dissolved oxygen levels that can adversely impact the receiving stream (Malmrose, et al., 2004). 
Drinking Water Industry Report Section 4 – Current State NPDES Permit Requirements

4-11

4.3 REFERENCES

Eastern Research Group (ERG), 2005. Memorandum, Summary of State 

Requirements/Prohibitions for DWT Facilities, March 15, 2005. DCN DW00149. 

ERG, 2008. MS Excel Spreadsheet: Permit Summary Individual, May 2008. DCN DW03733. 

Malmrose, et al., 2004. Paul Malmrose, Jim Lozier, Michael Mickley, Robert Reiss, Jerry 

Russell, James Schaefer, Sandeep Sethi, Jennifer Manuszak, Robert Bergman, and Khalil Z. 

Atasi, Residual Management Research Committee Subcommittee on Membrane Residual 

Management, “2004 Committee Report: Residuals Management for Desalting Membranes,” 

Jour. AWWA, 96:12:73. American Water Works Association (AWWA), December 2004. 

Document Control Number (DCN) DW00032. 

Mickley, 2001. Michael C. Mickley. Membrane Concentrate Disposal: Practices and 

Regulations. Prepared for U.S. Department of the Interior by Mickley and Associates. Boulder, 

Co. September. DCN DW00028. 
5-1

SECTION 5

SOURCE WATER QUALITY

Drinking water sources include ground water and surface water. Ground water 

comes from wells drilled into underground aquifers (geologic formations containing water). 

Surface water is obtained from rivers, lakes, and reservoirs open to the atmosphere. 

Source water may contain undesirable contaminants that must be removed from 

the drinking water. These contaminants enter the water supply via natural sources or from human 

activities. Table 5-1 presents common source water contaminants and their environmental, 

agricultural, and industrial sources. Source water quality can also vary based on geographic 

region. This section discusses factors that influence source water quality (Section 5.1), compares 

ground water and surface water quality (Section 5.2), and discusses how the Safe Drinking Water 

Act (SDWA) addresses source water protection (Section 5.3).

5.1 FACTORS THAT INFLUENCE SOURCE WATER QUALITY 

The factors that influence the quality of source water—both ground water and 

surface water—include naturally-occurring attributes (climate, geology, soil type, land cover, 

hydrology, precipitation and runoff, and wildlife) and man-made attributes (land management 

practices and runoff or discharge from point and nonpoint sources). The Safe Drinking Water 

Act (SDWA) Amendments of 1996 required states to develop and implement source water 

assessment programs (SWAPs) to analyze existing and potential threats to the quality of the 

public drinking water throughout the state. Using these programs, most states have completed 

source water assessments for public water systems - from major metropolitan areas to the 

smallest towns (http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm?action=Programs#swap).

Using baseline water quality data, water treatment plants (WTPs) are designed with the treatment 

technologies necessary to produce potable water (U.S. EPA, 1999a). Source water quality 

impacts the design of the WTP, the treatment chemicals used, and the quantity and composition 

of the residuals generated. 
Drinking Water Industry Report Section 5 – Source Water Quality

5-2

Table 5-1. Common Source Water Contaminants and Sources

Contaminant Sources

Naturally Occurring

Microorganisms Wildlife and soils; microorganism-containing wastes in runoff from 

nonpoint sources, including animal wastes; and other point source 

discharges which are not disinfected

Radionuclides: All except beta particles 

and photon emitters

Erosion of natural deposits

Metals (e.g., arsenic, cadmium, 

chromium, lead, and selenium)

Erosion of natural deposits

Nitrates and nitrites Erosion of natural deposits

Fluoride Erosion of natural deposits

From Human Activities

Microorganisms Human and animal wastes

Radionuclides: Beta particles and photon 

emitters

Decay of man-made deposits

Metals (e.g., arsenic, barium cadmium, 

chromium, fluoride, mercury, selenium, 

and thallium) 

Mining; construction; industrial discharges; runoff from orchards, 

croplands, and landfills; lead and copper from household plumbing 

materials

Nitrates and nitrites Runoff from fertilizer use; leaching of septic tanks or sewage

Organic chemicals Runoff from herbicide and pesticide use, industrial discharges; 

emissions from incineration or combustion; household wastes such as 

cleaning solvents

Source: U.S. EPA, 2008.

Source water quality may vary over time or in seasonal cycles. Land uses, such as 

agriculture, urban development, and industrial sites, and the watershed management (i.e., the 

management of the land around a waterway) are the variables that most affect the source water 

quality conditions over time. For example, agricultural practices that affect source water quality 

include irrigation, field drainage, and chemical and biosolids application to crops and soil. 

Industrialization and urbanization within the watershed may affect source water quality due to 

changes in storm water runoff. As the land management practices change, WTPs adjust their 

operations and treatment chemical usage to meet drinking water quality standards. Changes in 

the source water quality (e.g., additional solids due to increased soil runoff; increased nutrient 

content in the source water due to fertilizer use) also affect the generation and composition of 

residuals. These land management practices are responsible for additional treatment over the 

baseline conditions of the source water. 
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5-3

Watershed management includes strategies and plans to assess and maintain a 

water resource within a specified drainage area. The overall strategy is to maintain or improve 

the quality of water (drinking, recreational, or industrial) that is derived from the watershed and 

to comply with the various statutes like the Clean Water Act (CWA), the SDWA, and state/local 

requirements. 

The industrialization and urbanization of rural land increases the amount of runoff 

into source water (U.S. EPA, 2001). The increased runoff of silt and sediment increases the 

amount of solids that WTPs must remove from source water, and, ultimately, the amount of 

residual solids. To remove these additional solids from drinking water, WTPs may need to spend 

additional money on operations, treatment chemical usage, residuals treatment operations, and 

residuals disposal costs. One way to reduce these costs is to have a strong cooperative watershed 

management program that maintains the quality of the source water.

Some of the less obvious runoff effects are caused by landscaping chemicals from 

lawns and gardens, as well as oil and hydrocarbons from roadways. The increased impervious 

surfaces of urban and industrial areas do not retain runoff, and the quality and quantity of both 

surface and ground water are adversely impacted. Increased runoff can lead to other watershed 

related problems such as flow modifications, erosion, introduction of chemical and 

microbiological pollutants, accumulation of sediments, habitat loss, ecosystem disruption, and 

the possible introduction of invasive species. The additional pollutants present in the source 

water must be removed by WTPs to meet drinking water standards and customer demands. 

Watershed protection can be a key pollution prevention option to reduce residuals 

from source water treatment. For example, New York City is investing $1.2 billion to safeguard 

its upstate reservoir system in hopes of reducing or eliminating the estimated $6 to 8 billion 

required for a filtration plant to treat an unprotected watershed. Also, New Jersey has a multiyear 

master plan for long-term funding and acquisition of watershed properties to protect source water 

quality (Ernst, 2004). 
Drinking Water Industry Report Section 5 – Source Water Quality

5-4

5.2 COMPARISON OF GROUND WATER AND SURFACE WATER 

QUALITY

Ground water is often, but not always, naturally filtered as it passes through layers 

of the earth into underground reservoirs known as aquifers. Ground water generally contains less 

organic material than surface water and may not need to undergo as many treatment steps. 

Surface water collects a wide variety of contaminants from watershed drainage, agricultural 

practices, and urban sources. Thus, surface water has more variable and extensive treatment 

requirements.

EPA’s Office of Ground Water and Drinking Water (OGWDW) completed a 

review of contaminant occurrences in the source water for drinking water systems (U.S. EPA, 

1999b). The purpose of the review was to enhance the scientific understanding of the occurrence 

of chemical contaminants in public drinking water systems and to refine the basis for the 

monitoring of these contaminants. The review found the following occurrence results for ground 

water and surface water:

• Volatile organic compounds (VOCs) are more common in surface water; 

however, exceedances of the EPA MCLs are nearly equal for surface and 

ground water systems. 

• Some VOCs are not geographically centralized (i.e., they are present in 

source water in all states18 studied). These VOCs include ethylbenzene, 

cis-1,2-dichloroethane, tetrachloroethylene (PCE), trichloroethylene 

(TCE), vinyl chloride, 1,1,1-trichlorethane, and xylenes.

• Inorganic chemicals are common in both surface and ground water, but 

ground water concentrations tend to be higher. 

• Synthetic organic chemicals (SOC) are more common in surface water.

Section 8 of this report discusses pollutants of concern for surface water and 

ground water.

 

18 The study included source water for drinking water systems in the following states: Alabama, California, Illinois, 

Indiana, Iowa, Massachusetts, Michigan, Montana, New Jersey, New Mexico, Ohio, and Oregon.
Drinking Water Industry Report Section 5 – Source Water Quality

5-5

5.3 SOURCE WATER PROTECTION UNDER THE SDWA

In addition to establishing drinking water requirements, the 1996 Amendments to 

the SDWA outlined measures to ensure the quality of drinking water by protecting the source 

water. The measures include source water assessments, providing information to the public 

(consumer confidence reports), and providing federal funds for source water assessments and 

protection. 

To give water systems and community members the information needed to decide 

how to protect their drinking water sources, the SDWA requires states to develop EPA-approved 

programs to carry out assessments of all source waters in the state. The source water assessment 

is a study that defines the land area contributing water to each public water system, identifies the 

major potential sources of contamination that could affect the drinking water supply, and then 

determines how susceptible the public water supply is to this potential contamination. Water 

systems and communities can then use the publicly-available study results to reduce potential 

sources of contamination and protect the source water. 

Community water systems are also required to provide consumer confidence 

reports, or annual water quality reports, to the public each year. The report explains where the 

supplied drinking water comes from and what contaminants might be in the drinking water. The 

consumer confidence reports summarize information regarding sources used (e.g., rivers, lakes, 

reservoirs, or aquifers), any detected contaminants, compliance, and educational information. 

EPA provides funding to states through the Drinking Water State Revolving Fund 

(DWSRF) for source water assessment and protection activities. Source water protection 

approaches are tailored to each unique local situation. Although most source water protection 

efforts are primarily led by the system (or utility), state, or locality, a variety of federal tools can 

be used, such as those available through the CWA, Underground Injection Control Program, and 

various agricultural programs. In addition, a number of national nongovernmental organizations, 

such as the American Water Works Association (AWWA), the National Rural Water Association 

(NRWA), the National Association of Counties (NACo), and the Trust for Public Lands (TPL), 
Drinking Water Industry Report Section 5 – Source Water Quality

5-6

are active in the realm of source water protection. One of EPA's roles is to encourage 

partnerships and provide information to those directly involved in source water protection. 

5.4 REFERENCES

Ernst, Caryn, 2004. Protecting the Source: Land Conservation and the Future of America’s 

Drinking Water. Published by the Trust for Public Land and AWWA. DCN DW03759. 

U.S. EPA, 1999a. Guidance Manual for Conducting Sanitary Surveys of Public Water Systems; 

Surface Water and Ground Water Under the Direct Influence (GWUDI) (EPA 815-R-99-016), 

Office of Water, Washington, DC. DCN DW01147. 

U.S. EPA, 1999b. A Review of Contaminant Occurrence in Public Water Systems (EPA 816-R99-006), Office of Water, Washington, DC. DCN DW00941. 

U.S. EPA, 2001. Protecting and Restoring America’s Watersheds: Status, Trends, and Initiatives 

in Watershed Management (EPA 840-R-00-001), Office of Water, Washington, DC. DCN 

DW00934. 

U.S. EPA, 2008. National Primary Drinking Water Standards (List of Drinking Water 

Contaminants and MCLs) (original document published in 2003, DCN DW00657), Office of 

Ground Water and Drinking Water, Washington, DC. Retrieved from 

http://www.epa.gov/safewater/contaminants/index.html Accessed April 2008 for updates.
6-1

SECTION 6

SOURCE WATER TREATMENT TECHNOLOGIES

Treatment of source water removes contaminants that are unhealthy or 

undesirable for consumption. The type of treatment operation performed at a drinking water 

treatment plant (WTP) and treatment chemicals used depend on the contaminants present in the 

source water. The removed contaminants and treatment chemical composition impact the content 

and quantity of residuals generated. This section discusses the source water treatment operations 

and treatment chemicals used that impact the content and quantity of residuals generated. 

WTPs strive to add sufficient treatment chemicals to source water to remove 

contaminants without adding excessive levels of additional pollutants (i.e., treatment chemical 

active ingredients and impurities). AWWA began assembling consensus standards for different 

aspects of drinking water production about 100 years ago and updates them periodically. 

Included in those consensus standards are best engineering judgments for the different chemicals 

added to drinking water. 

About 20 years ago, the National Sanitation Foundation (NSF) and a consortium 

of stakeholders established minimum human health effects requirements for any chemicals added 

directly to drinking water. The American National Standards Institute (ANSI)/NSF Standard 60 

recommends, when available, that EPA MCLs (U.S. EPA, 2008b) be used to determine the 

acceptable level for a treatment chemical in the finished drinking water. If an MCL is not 

available, ANSI/NSF Standard 60 provides criteria to conduct a toxicological risk assessment for 

the chemical. 

There are many different approaches to removing source water contaminants. In 

addition to the characteristics of the source water, the size of the system or plant may be a factor 

when selecting or implementing new source water treatment operations. For example, larger 

systems have in general a larger number of technology options to select from and can take 

advantage of economies of scale that can reduce both capital and operational expenses, allowing 

for a lower per unit of treated water cost. The larger systems can also spread the costs incurred to 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-2

install and operate source water treatment over a larger customer base. Common treatment 

operations for all system sizes that affect residuals content and quantity generated are discussed 

in this section. The source water treatment operations discussed include the following: 

• Conventional filtration, direct filtration, and filtration only (Section 6.1); 

• Precipitative softening (Section 6.2); 

• Membrane separation (Section 6.3); 

• Ion exchange (Section 6.4); 

• Activated carbon (Section 6.5); 

• Disinfection (Section 6.6); and 

• Other chemical additions (Section 6.7). 

6.1 CONVENTIONAL FILTRATION, DIRECT FILTRATION, AND 

FILTRATION ONLY

Conventional filtration is the most common treatment train at WTPs and is the 

primary treatment used at 63 percent of WTPs. It is a series of processes including coagulation, 

flocculation, sedimentation, and filtration that result in substantial particulate removal from the 

source water. Figure 6-1 shows a typical conventional filtration treatment plant flow diagram. 

Direct filtration is another treatment train operated at WTPs, where plants perform 

coagulation, flocculation, and filtration without sedimentation. Unlike conventional filtration, the 

floc is removed at the filter rather than at the sedimentation basin (National Drinking Water 

Clearinghouse, 1996b). Some treatment plants perform filtration without coagulation or 

flocculation, referred to as filtration only. 

The types of processes used at the WTP depend on the characteristics of the 

source water. Source water with high solids content may require pretreatment, or 

presedimentation. The following subsections focus on the individual processes that WTPs use to 

remove particulates (or solids) from the source water either as stand-alone processes or in series.
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6-3

Coagulation 

(rapid mix 

process)

Flocculation 

(separates 

suspended solids 

from water by 

creating “floc”)

Sedimentation 

(heavy particles 

settle to bottom)

Filtration 

(removes finer 

particles)

Finished Water to 

Storage and 

Distribution

Settled Solids 

(continuously or 

periodically 

removed)

Coagulant

Raw Water

Disinfectant

Clarified 

Water

Filter Backwash (recycled)

Figure 6-1. Typical Conventional Filtration Treatment Plant Flow Diagram (U.S. EPA, 2002a) 
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Residuals generated by solid removal processes include filter backwash water, 

filter-to-waste, and coagulation sludge (i.e., underflow streams removed from sedimentation or 

settling tanks). The residuals contain solids from the source water and chemicals added by the 

WTP to aid in solids removal. In addition, filter backwash and filter-to-waste streams may 

contain residual disinfectants. 

6.1.1 Presedimentation

Presedimentation is a pretreatment process operated at the head of the WTP (e.g., 

in a sedimentation basin) or prior to intake (e.g., within a reservoir). Its primary purpose is to 

remove a significant amount of readily settleable and suspended solids and other contaminants in 

the source water prior to other water treatment operations (e.g., coagulation and filtration). WTPs 

might add treatment chemicals during presedimentation; however, the primary removal 

mechanism is gravity settling. The process removes relatively high concentrations of easily 

settled solids (e.g., sand and silt). By allowing adequate detention time in the basin, coarser and 

other easily settleable particles drop out of the source water. To aid settling, WTPs may add 

polymers and other coagulants. The settled solids are removed continuously (or in frequent 

batches) via an underflow pipe. 

6.1.2 Coagulation, Flocculation, and Sedimentation 

Coagulation, flocculation, and sedimentation are water treatment processes 

performed in mixing tanks and sedimentation basins. WTPs operate one or more of the processes 

to remove as much source water solid matter as possible. Most plants follow coagulation, 

flocculation, and sedimentation with filtration to remove finer solid particles such as suspended 

solids, colloids, and color (indicative of dissolved organic material). 

At the clarification basins, coagulants and flocculants are added to the source 

water. Agitation of the water causes collisions between suspended particles, forming 

agglomerated solids. The solids settle to the bottom of the basin and are removed via an 

underflow pipe. An additional sedimentation basin may be used to allow further solids settling. 
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Coagulants and flocculants added to the raw water include metal salts (e.g., 

aluminum sulfate and ferrous sulfate) and polyelectrolytes. To optimize solids removal, plants 

may adjust the pH. Coagulant chemicals carry multivalent positive charges, which, when 

dissolved in water, tend to neutralize the negative charges on the surface of the particulate 

matter. This allows the small particles to approach each other, overcome electrostatic repulsion, 

and combine. As the particles grow larger, they become heavier and gravity aids their settling to 

the bottom of the tank. 

Inorganic coagulants (e.g., aluminum sulfate, aluminum chloride, ferrous sulfate, 

and ferric chloride) are used by many WTPs. The trivalent forms of aluminum and iron (Al+++, 

Fe+++) are insoluble at normal drinking water treatment operating conditions so very little metal 

is carried into the finished product (Tchobanoglous, et al., 2003). In addition to inorganic 

chemicals, a large variety of organic-based polymers are employed as coagulant aids either 

independently or in concert with the inorganic coagulation aids. About 1,100 different 

formulations of polymer beads, polyacrylamide, polyamines, and polydimethylammonium 

chloride are listed in ANSI/NSF Standard 60 and used to promote the removal of turbidity from 

drinking water. Some of these chemicals are also referred to as filtration aids, but function the 

same way as coagulants. 

Residuals are generated as underflow discharges from the sedimentation tanks. 

These residuals contain source water contaminants, as well as chemicals added to aid solid 

removal and formulation impurities in the added treatment chemicals. 

6.1.3 Filtration

After solids settling, the source water passes through filters to remove finer 

particles and metals. Various types of filter media may be used by WTPs, including permeable 

fabric and porous beds. The types of filters used by WTPs include the following: 

• Slow sand: consists of a bed of fine sand above a gravel layer and 

underdrain system. This type of filter is used for low-flow rates and might 

be performed without other solids removal treatment steps (i.e., filtration 
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6-6

only). Slow sand filters are not suitable for high turbidity source waters. 

(National Drinking Water Clearinghouse, 1996b) 

• Rapid sand: consists of a bed of sand above several layers of gravel in 

varying sizes.

• Pressure: similar to rapid sand filters but the operation is housed within a 

cylindrical tank and the water passes through the filter while under 

pressure generated by a pump rather than by gravity. 

• Diatomaceous earth: consists of a layer of diatomaceous earth above a 

septum or filter element. Most suitable for low turbidity and low bacterial 

count source water. Coagulants and filter aids are required for effective 

virus removal. (National Drinking Water Clearinghouse, 1996b) 

• Multimedia: consists of layers of various sizes of gravel, high-density 

garnet, sand, and anthracite coal. 

• Membrane filters: include ultrafilters and microfilters. These membranes 

use pressure as the driving force and are designed to remove particulates 

smaller than 10 micrometers (discussed in Section 6.3).

The filtration process removes suspended solids by mechanical straining—

trapping them between grains of the filter medium (e.g., bed of sand). Filtration also uses 

adhesion to remove solids; suspended solids stick (or adhere) to the surface of the filter material 

or previously deposited solids. In addition to mechanical removal, slow sand filters trap 

microorganisms that break down algae, bacteria, and other organic matter. (National Drinking 

Water Clearinghouse, 1996b) 

Slow sand and diatomaceous earth filtration are older filtration techniques that are 

effective in removing suspended particles and some microbes. Many older systems abandoned 

the use of these filter media due to slower filtration rates and the larger required size of the slow 

sand and diatomaceous earth filter beds (about 10 times that of the newer systems). Low 

filtration rate and large filter size both translate into higher operating costs. As a result, WTPs 

have switched to other fine particle removal systems like membranes or multimedia filters. 

WTPs may operate filtration systems without coagulation; these plants are 

typically smaller (less than 50,000 people served) and treat ground water (U.S. EPA, 2008a). 
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6-7

Smaller WTPs may also use adsorption (e.g., activated carbon), rather than filtration to remove 

certain contaminants (see Section 6.5). 

Residuals from filtration operations include filter backwash (finished drinking 

water flushes out solids and contaminants trapped in the filter) and filter-to-waste (initial 

permeate after the filter has been brought on line). The residuals may contain source water 

contaminants (e.g., solids), treatment chemical active ingredients and impurities, and residual 

disinfectant added prior to filtration or in the finished water used to backwash the filter. 

6.2 PRECIPITATIVE (LIME) SOFTENING

Drinking water that contains elevated levels of divalent cations, mostly calcium 

and magnesium, can produce customer complaints that revolve around appliance malfunctions 

(pipe scaling) and aesthetic concerns (water spots). These compounds present in the source water 

contribute to the water’s “hardness.” Plants remove these compounds from the water by 

precipitative, or chemical, softening. 

Precipitative softening is the removal of divalent cations by increasing the pH and 

altering the bicarbonate equilibrium. As the pH increases to about 9.5, the increased alkalinity 

extracts a hydrogen atom from the bicarbonate and forces the equilibrium toward the carbonate 

species, resulting in a precipitate of insoluble calcium carbonate. The chemical reaction is shown 

in Equation 6-1 (Manahan, 1993). 

Ca2+ + 2HCO3

- + Ca(OH)2 → 2CaCO3 (solid) + 2H2O (Eq. 6-1) 

If the pH is increased to about 11, magnesium is precipitated as a hydroxide, as shown in 

Equation 6-2. 

Mg2+ + 2OH- → Mg(OH)2 (solid) (Eq. 6-2) 

The softening process increases pH and leaves excess calcium hydroxide in the 

water. After softening, pH is reduced by the conversion of excess calcium hydroxide to solid 

calcium carbonate using carbon dioxide, as shown in Equation 6-3. 
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6-8

CO2- + Ca(OH)2 → CaCO3 (solid) + H2O (Eq. 6-3) 

Calcium oxide (lime) is usually the chemical of choice to affect the pH changes 

necessary for precipitative softening, but in some cases, sodium carbonate (soda ash) is used. 

Plants add lime to remove carbonate hardness―bicarbonates of calcium and magnesium, or 

plants add lime and soda ash to remove carbonate hardness and non-carbonate 

hardness―sulfates, chlorides, or nitrates of calcium and magnesium. The precipitative softening 

process is usually integrated with other treatment processes, particularly conventional or direct 

filtration (see Section 6.1). The precipitated solids are removed from the bottom of sedimentation 

or settling tanks (underflow), generating a residual waste stream—referred to as softening 

sludge. 

Due to cost and operating concerns, not all of the hardness is removed. By a 

combination of pH control, treatment bypass, and blending, plants customize the precipitative 

softening operation to the initial water quality conditions and the customer demands. The 

hardness level in the drinking water typically ranges between 80 and 100 mg/L (ASCE/AWWA, 

1997). 

6.3 MEMBRANE SEPARATION

Membranes are used to separate components of a liquid stream into useable and 

waste products. Membrane systems are characterized by the driving force needed to effect 

separation (e.g., pressure-driven or electrical-driven separation). Membrane separation 

techniques used to treat source water include the following: 

• High-pressure technologies, such as reverse osmosis (RO) and 

nanofiltration (NF); 

• Low-pressure technologies, such as microfiltration (MF) and ultrafiltration 

(UF); and

• Electrical-driven technologies, such as electrodialysis (ED) and 

electrodialysis reversal (EDR).
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6-9

WTPs using membrane separation are typically smaller plants (serving less than 

50,000 people). From EPA’s 2007 industry questionnaire, all plants that operated membranes 

served less than 150,000 people (U.S. EPA, 2008a). 

WTPs may use membrane operations to remove salt from saline or brackish 

water. Brackish water typically contains between one and 35 parts per thousand (ppt) salt. 

Seawater typically contains approximately 35 ppt of salt19 (USGS, 2007). The removal of salt 

from source water is called desalination. Desalination processes include RO, NF, ED, and EDR. 

Residuals from MF and UF include filter backwash and spent cleaning solutions. 

Residuals from membrane desalination include the concentrate or “reject” stream and spent 

cleaning solutions. The following subsections discuss the desalination processes and MF and UF 

processes in more detail.

6.3.1 Reverse Osmosis and Nanofiltration 

Most membranes use pressure as the driving separation force. Generally the 

smaller the pore size in the membrane, the higher the driving force (pressure) required to 

accomplish separation. For source water treatment, the application determines the driving force 

and thus the type of membrane. If the treatment application is removal of dissolved contaminants 

(hardness, salinity, arsenic, radioactive cations), then WTPs use high pressure systems like NF or 

RO. These systems also can remove dissolved organic material, biological contaminants, and 

suspended solids. 

Pretreatment is typically used to remove biological material and particulates. The 

use of NF or RO requires clean source water, with a significant amount of pretreatment to 

remove the majority of suspended solids so that the membrane will not quickly clog. The high 

pressure and additional pretreatment needed to operate RO and NF systems can translate into 

high operating and maintenance costs. 

 

19 Fresh water contains less than one ppt (or 1,000 parts per million) salt (USGS, 2007).
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-10

NF and RO use semipermeable membranes to remove contaminants from the 

source water. These systems operate at pressures between 75 pounds per square inch gauge 

(psig) and 1,200 psig (Malmrose, et al., 2003). Figure 6-2 presents a cross-section of a reverse 

osmosis membrane. 

Figure 6-2. Reverse Osmosis Cross-Flow Membrane (The Merit Partnership, 2002)

6.3.2 Microfiltration and Ultrafiltration

If the treatment application is particulate and suspended solids removal, lower 

pressure membrane systems may be used. MF and UF systems can effectively remove turbidity, 

metals such as iron, manganese and arsenic, as well as protozoan like Cryptosporidium. 

Dissolved organics may be removed when assisted by an adsorption agent (e.g., powdered 

activated carbon). UF systems can also remove viruses from the source water without additional 

treatment (Malmrose, et al., 2003). 

Pretreatment of source water is desirable but if the source is relatively clean, 

pretreatment may not be necessary. Applications of MF and UF systems are becoming more 

common as replacement for small, older conventional treatment systems. Lower capital costs, 

lower operating costs, and improved performance are reasons for their increased use. 
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6-11

MF and UF systems use porous, hollow-fiber membranes to remove source water 

contaminants. The membrane pore size for MF systems typically ranges between 0.1 and 10 

micrometers (μm). UF pore size is smaller, ranging from 0.01 to 0.4 μm. These systems typically 

operate at pressures less than 40 psig (Malmrose, et al., 2003). 

6.3.3 Electrodialysis and Electrodialysis Reversal

Dissolved contaminants in the source water may be removed using electrodialysis 

membranes, which are ion exchange membranes that use electrical current to separate the 

contaminants from the water (Malmrose, et al., 2004). This operation is primarily used to desalt 

brackish water. Electrodialysis is not effective in removing non-charged solutes, such as silica, 

pathogens, and dissolved organics. 

Electrodialysis uses alternating pairs of cation (positively charged) and anion 

(negatively charged) membranes positioned between two oppositely charged electrodes. 

Channeled spacers between the membranes create parallel flow streams across the membrane 

surface. The source water is pumped into the flow channels. When voltage is applied, the 

electrical current causes ions from the source water to migrate toward the oppositely charged 

electrodes, where the ions become restrained in the polarized membranes. Cations are attracted 

to the negatively charged electrodes, pass through the positively charged membranes, and 

become restrained by the negatively charged membrane. Anions are attracted to the positively 

charged electrodes, pass through the negatively charged membranes, and become restrained by 

the positively charged membranes. (Malmrose, et al., 2004) 

The EDR membrane system is constructed the same as the electrodialysis process, 

but the EDR system reverses direction of the charge and ion movement several times hourly. The 

direction of the charge is changed frequently to reverse the electrical polarity and flush fouling 

ions from the membrane. (Malmrose, et al., 2004) 

The electricity cost to operate ED/ EDR may inhibit the use of this source water 

treatment technique. ED and EDR are not common to large WTPs—those serving more than 

10,000 people (U.S. EPA, 2008a). 
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6.4 ION EXCHANGE

In ion exchange, ions are transferred between different substances with an 

exchange between solid and liquid being the most common. A precondition for using this 

process is that the substances must be ionized when exchanged. In drinking water applications, 

naturally occurring zeolites were first used for hardness removal, but modern ion exchange 

technology uses resin materials that can be customized to remove specific contaminants of 

interest. Ion exchange selectively removes a charged inorganic species (i.e., specific drinking 

water contaminant) from the source water using an ion-specific resin (U.S. EPA, 1998). 

Resins act as a repository of loosely held ions (cation or anion) that are exchanged 

for like-charged ions that have a greater affinity for the resin than the currently held ions. Resins 

are categorized as anion exchange or cation exchange resins. Anion exchange resins selectively 

remove anionic species such as nitrate (NO3

-

) and fluoride (F-). Cation exchange resins 

selectively remove cationic species such as radium from the water and replace with protons (H+

), 

sodium ions (Na+

), and potassium ions (K+). This process continues until all of the exchange 

sites are used (i.e., saturated with the contaminant). (U.S. EPA, 1998) 

Ion exchange often generates a backwash stream (or concentrate waste stream). 

After the exchanger has exhausted all of the exchange sites, it must be regenerated or replaced. 

Regeneration requires a reverse ion exchange and it is accomplished with a concentrated solution 

of a common ion, usually a salt, so that the pH of the water is not affected. The contaminated 

ions are exchanged for the concentrated salt common ions, and a waste stream requiring 

treatment and/or disposal is created. Anion exchange resins may be regenerated using sodium 

hydroxide or sodium chloride solutions by replacing the contaminant ions with a hydroxide 

(OH-

) or chloride (Cl-) ion (U.S. EPA, 1998). Cation exchange resins may be regenerated using 

acid (i.e., replacing the contaminant with a proton, H+). 

Some WTPs may not operate their ion exchange systems year-round. For 

example, the Des Moines Water Works Fleur Drive Plant operates a lime softening system year-
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-13

round and adds nitrate removal through ion exchange during spring and summer months, when 

nitrate concentrations are elevated in the river source water (U.S. EPA, 2006). 

6.5 ADSORPTIVE MEDIA—ACTIVATED CARBON

While many adsorptive media are available, WTPs most commonly use activated 

carbon. Plants use activated carbon filtration systems primarily to remove organic compounds 

from source water. Organic compounds removed include those that may cause objectionable 

taste or odor and those that pose potential negative health effects (e.g., pesticides). The most 

common type of system is granular activated carbon (GAC), but WTPs also use powdered 

activated carbon (PAC).

Activated carbon can adsorb ions or molecules on its surface from any 

environmental media, with water and air being the most common. Activated carbon has a 

random structure that is highly porous and exhibits different types of intramolecular forces. 

Intramolecular attractions overcome the attractive forces of the liquid for the substance (i.e., 

source water contaminant), and the substance is deposited on the surface of the carbon. The large 

surface area of activated carbon (1 gram = 1,000 square meters) allows removal of trace 

quantities of contaminants from drinking water (ASCE/AWWA, 1997). Unlike filtration, 

activated carbon plants do not remove the contaminants by straining; the removal is based on 

adsorption rather than the size of the particulate. Detailed descriptions of the two activated 

carbon forms follow. 

GAC is a more coarse material than PAC and is usually employed later in the 

treatment process to remove dissolved organic compounds as well as disinfection by-products. 

GAC is usually used in a fixed bed, which water passes through for treatment. The carbon bed is 

backwashed or surface washed to prevent buildup of solids and prevent fouling. As with other 

treatment technologies, there is a finite amount of surface material that can adsorb impurities, 

and when exceeded, “break through” occurs (i.e., contaminants are no longer removed from the 

source water). At this point, the spent GAC must be replaced; the spent material may be 

thermally reconditioned (regenerated) or discarded (U.S. EPA, 2000). 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-14

PAC is usually added early in the treatment process and is used to remove organic 

contaminants that are associated with taste and odor. On a limited basis, PAC is also used to 

remove seasonal contaminants like pesticides. PAC grains are 10 to 100 times smaller than GAC 

grains. Use of PAC is less efficient than GAC due to less carbon material per unit volume 

treated. The PAC is mixed with the water to create a suspension. The PAC continues along with 

the treated water to sedimentation or filtration and becomes part of the residuals. Care must be 

taken when using the small PAC particles so that they do not interfere with the application of 

other treatment chemicals and treatment processes. For example, PAC can adsorb free and 

combined chlorine, chlorine dioxide, and potassium permanganate, thereby reducing their 

effectiveness (U.S. EPA, 1998). 

6.6 DISINFECTION

Both surface and ground water sources typically require disinfection to eliminate 

or inactivate microbiological contamination. Historically, chlorine was the disinfectant used, but 

more recently other chemicals such as chlorine dioxide, chloramines, and ozone have been used 

to purify water. Non-chemical methods of disinfection include heat and radiation (e.g., 

ultraviolet light). The general disinfection reaction mechanism is chemical or physical 

interference with the microorganism structure and cell membrane function. 

If the microorganism cell membrane is compromised or penetrated, the 

microorganism dies. Disinfection does not totally destroy pathogens, but eliminates the ability to 

cause disease or interfere with normal body functions. 

WTPs perform two kinds of disinfection: 1) primary disinfection, and 2) 

secondary disinfection. Primary disinfection achieves the desired level of microorganism kill or 

inactivation. Secondary disinfection maintains a disinfectant residual in the finished drinking 

water to prevent regrowth of microorganisms as water passes through the distribution system. 

WTPs may use different chemicals for the two kinds of disinfection. Both kinds of disinfection 

might affect chemicals in the residuals.
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-15

Primary disinfection occurs early in the source water treatment, prior to 

sedimentation or filtration. Although no residuals are generated during this treatment step, the 

disinfectant used (e.g., chlorine) or disinfection by-products may be present in the WTP residual 

waste streams (e.g., filter backwash). Chlorine, ozone with another secondary disinfectant, and 

UV light with another secondary disinfectant are effective primary disinfectants (National 

Drinking Water Clearinghouse, 1996a). 

Secondary disinfection occurs at the end of source water treatment, either at the 

finished drinking water clear well or at various points in the distribution system. This 

disinfection step is used to maintain a disinfectant residual in the finished drinking water to 

prevent regrowth of microorganisms. The secondary disinfection process does not result in 

residuals generation; however, water from the clear well may be used to backwash filters. As a 

result, disinfectant added to the finished drinking water may become part of the filter backwash. 

Chlorine and chloramines are effective secondary disinfectants (National Drinking Water 

Clearinghouse, 1996a). 

Almost all WTPs disinfect the source water prior to delivery—98 percent of the 

ground water plants and 99 percent of the surface water plants (U.S. EPA, 2002b). The common 

methods of disinfection are discussed in subsections below. 

6.6.1 Disinfection with Chlorine (Chlorination)

When dissolved in water, chlorine gas quickly forms hypochlorous acid (HOCl), 

which in turn, dissociates into hypochlorite ion (OCl-

) (ASCE/AWWA, 1997). The hypochlorous 

acid form of chlorine is a more effective disinfectant that the dissociated form, hypochlorite ion. 

Chlorine gas, however, is toxic and has a density greater than air, therefore gas leaks accumulate 

and present significant safety concerns. Properly engineered gas handling systems, continuous 

training, or switching to a non-gaseous chlorine form like calcium hypochlorite reduce safety 

concerns. 

In the early 1970s, researchers discovered that the use of chlorine for disinfection 

of drinking water produced microgram per liter (μg/L) quantities of halogenated methane 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-16

compounds (e.g., trihalomethane). The halogenated methane compounds, known as disinfection 

by-products, are suspected to be carcinogens (U.S. EPA, 2008b). EPA limits the amount of total 

trihalomethanes (TTHMs) in the drinking water to 0.08 mg/L (U.S. EPA, 2008b). The balance 

between producing microbiologically safe drinking water without long term health effect 

implications from disinfection by-products became a major problem for some systems. 

Alternatives to chlorine disinfection have been known for a long time, and the discovery of 

halogenated methane compounds in chlorine-treated drinking water increased the pressure to 

explore these alternatives.

6.6.2 Disinfection with Chlorine Dioxide

Chlorine dioxide has been used in some drinking water systems where an elevated 

pH (>7) of the processed water has reduced the effectiveness of chlorine. Chlorine dioxide is 

formed when chlorine (gaseous or liquid form) is mixed with sodium chlorite. As with chlorine, 

WTPs must safely handle chlorine dioxide: it must be generated when used because it can not be 

safely stored due to explosive characteristics. Also, reaction by-products or waste materials can 

be toxic, such as chlorite (ClO2, MCL 1.0 mg/L) and chlorate (Cl2O2) ions (U.S. EPA, 2008b). 

On the positive side, chlorine dioxide does not dissociate or disproportionate under normal 

drinking water treatment conditions, is a strong oxidant, and does not form halogenated 

disinfection by-products. It is sometimes used in conjunction with ozone systems as a residual 

disinfectant. 

6.6.3 Disinfection with Chloramines (Chloramination)

Chloramines (or combined residual chlorine) result when chlorine reacts with 

ammonia. The ammonia can be natural or added to ensure the production of chloramines. 

Chloramines have been demonstrated as disinfectants, but are not as effective as other germicidal 

agents. The combined residual from chloramines lasts longer than chlorine residuals; therefore, 

chloramines are typically used as secondary disinfectants. In addition, the use of chloramines for 

disinfection results in very few disinfection by-products; however WTPs may need to 

periodically switch to free chlorine for biofilm control in the water distribution system (U.S. 

EPA, 1999d). 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-17

From EPA national estimates (see Section 3.3), EPA determined that 2,002 WTPs 

perform primary disinfection. Approximately 80 percent of the WTPs disinfect with free 

chlorine. 318 WTPs (or 16 percent) use chloramines for primary disinfection (see Appendix A). 

6.6.4 Ozone Disinfection

Ozone (O3) is an energetic species generated by electrical discharge through dry 

air or pure oxygen and tends to oxidize anything it contacts. Ozone disinfects microbes 

effectively and can easily penetrate the sturdy cell membranes of protozoa like Cryptosporidium 

(Tchobanoglous, et al., 2003). In addition to the on-site generation safety concerns, the main 

concern with using ozone as a disinfectant is that its “half life” in water is only 30 minutes 

(Lenntech, 2006). If ozone alone is used as the disinfectant in large distribution systems 

(characterized by a residence time of 2 to 3 days), this residual concentration “half life” is 

insufficient to maintain the microbiological integrity of the finished water. Use of ozone 

disinfection at large drinking water systems requires booster ozone additions or supplemental 

disinfection. Ozone disinfection is more commonly used to disinfect wastewater. EPA estimated 

that 65 WTPs (only three percent) use ozone for primary disinfection (see Appendix A). Figure 

6-3 shows an ozone disinfection process flow diagram. 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-18

Ozone Destruction

Ozone Generation Ozone Contact Basin

Feed Gas Preparation

• Oxygen Production

• Oxygen Storage

• Air/Oxygen Treatment

Recycle

Off-Gases

Disinfected 

Water

Raw Water In

Figure 6-3. Ozone Disinfection Process Flow Diagram (U.S. EPA, 1986) 

6.6.5 Ultraviolet Light Disinfection

In ultraviolet (UV) disinfection, electromagnetic energy (UV radiation) is 

transferred from a mercury arc lamp to an organism’s genetic material. The UV radiation 

penetrates microorganism cell membranes and destroys the microorganisms’ ability to 

reproduce. The application of UV disinfection for source water treatment is limited because 

turbidity and suspended solids can render UV disinfection ineffective (U.S. EPA, 1999c). As 

with ozone disinfection, UV disinfection requires large drinking water systems to add a 

secondary disinfectant to maintain the microbiological integrity of the finished water.

6.7 OTHER CHEMICAL ADDITIONS

In addition to disinfection, coagulation, and precipitative softening chemicals, 

drinking water systems add other chemicals to drinking water to control corrosion and scaling, 

facilitate solids removal, adjust pH, and impart properties to the drinking water. The process of 

adding the chemicals does not generate residuals; however, portions of the chemicals may 

become part of the residuals at a downstream operation (e.g., sedimentation tank underflow). 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-19

6.7.1 Corrosion and Scale Control

To maintain pipes and tanks in the drinking water distribution system, systems 

add chemicals to control corrosion (i.e., deterioration of material) and scale (i.e., film build-up). 

Systems use chemicals such as phosphates and zinc for the control of scaling and corrosion. 

Corrosion and scale control occurs at 26 percent of the ground water plants and 58 percent of the 

surface water plants (U.S. EPA, 2002b). 

Selected chemicals minimize scaling and corrosion by forming a protective film 

that reduces the electrochemical reactions between the plumbing material and the water. pH 

control with lime or strong bases, such as sodium hydroxide (NaOH) and potassium hydroxide 

(KOH) contribute to the stability of the water and assist in reducing corrosion. About 45 different 

blended phosphate chemicals listed in ANSI/NSF Standard 60 can be used for corrosion control 

and 12 miscellaneous zinc products can be custom blended to serve different water quality 

conditions. Zinc does not have a primary standard (no MCL), but does have a secondary standard 

of 5 mg/L (U.S. EPA, 2008b). ANSI/NSF Standard 60 recommends that zinc not exceed 2 mg/L 

in the finished water. 

6.7.2 Solids Removal Using Sequestering Agents

Iron and manganese are metals found in many drinking water supplies, especially 

ground water. EPA has secondary standards for iron (0.3 mg/L) and manganese (0.05 mg/L) 

(U.S. EPA, 2008b) and both metals can cause off-tastes and staining of customer sinks. If iron 

and manganese concentrations are low, the aesthetic problems can be addressed by adding a 

sequestering agent that will tie up the soluble form of the metal and inhibit precipitation 

(staining). Blended phosphates, sodium silicate, and sodium polyphosphate are sequestering 

agents listed in ASNI/NSF Standard 60. 

The use of sequestering agents occurs at 45 percent of the ground water plants and 

32 percent of the surface water plants (U.S. EPA, 2002b). 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-20

6.7.3 pH Adjustment

Adjusting the pH of a drinking water treatment process is often necessary to 

ensure the proper interactions between chemicals and contaminants. WTPs add lime or a strong 

base such as sodium hydroxide or potassium hydroxide to raise the pH. Sodium hydroxide is 

listed in ANSI/NSF Standard 60. In cases where the pH must be lowered, plants use carbon 

dioxide or purified mineral acids, such as hydrochloric acid (HCl). 

6.7.4 Water Additives

Small amounts of fluoride (~1.0 mg/L) in the drinking water can play a significant 

role in reducing tooth decay. Sodium fluoride, sodium fluorosilicate, and fluorosilicic acid are 

used by the drinking water systems and all three are covered by AWWA Standards. Fluoridation 

is used by 21 percent of the ground water plants and 49 percent of the surface water plants (U.S. 

EPA, 2002b). 

6.8 REFERENCES

American National Standards Institute (ANSI)/National Sanitation Foundation (NSF) Standard 

60, 2007. Drinking water Treatment Chemicals-Health Effects, Purchased from www.nsf.org. 

Document Control Number (DCN) DW00960. 

American Society of Civil Engineers (ASCE)/American Water Works Association (AWWA), 

1997. Water Treatment Plant Design, 3rd Edition. New York: McGraw-Hill. DCN DW00961. 

Chlorine Chemistry Council, 2003. Drinking Water Chlorination: A Review of Disinfection 

Practices and Issues, Arlington, VA, February 2003. DCN DW00651. 

Lenntech, 2006. FAQs Ozone. Retrieved from http://www.lenntech.com/faqozone.htm. DCN 

DW00639. 

Malmrose, et al., 2003. Paul Malmrose, Jim Lozier, Jason Marie, Michael Mickley, Robert Reiss, 

Jerry Russell, James Schaefer, Sandeep Sethi, Jennifer Worley, Residual Management Research 

Committee Subcommittee on Membrane Residual Management, “2003 Committee Report: 

Residuals Management for Low-Pressure Membranes,” Jour. AWWA, 95:6:68. AWWA, June 

2003. DCN DW00003. 

Malmrose, et al., 2004. Paul Malmrose, Jim Lozier, Michael Mickley, Robert Reiss, Jerry 

Russell, James Schaefer, Sandeep Sethi, Jennifer Manuszak, Robert Bergman, and Khalil Z. 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-21

Atasi, Residual Management Research Committee Subcommittee on Membrane Residual 

Management, “2004 Committee Report: Residuals Management for Desalting Membranes,” 

Jour. AWWA, 96:12:73. AWWA, December 2004. DCN DW00032. 

Manahan, Stanley E., 1993. Section 13.7. “Removal of Calcium and Other Metals.” In 

Fundamentals of Environmental Chemistry, pages 463-464. Chelsea, MI: Lewis Publishers. 

DCN DW03757. 

The Merit Partnership, 2002. Reverse Osmosis Applications for Metal Finishing Operations. 

Merit Partnership P2 Project for Metal Finishers. January 2002. DCN DW003774. 

National Drinking Water Clearinghouse, 1996a. Tech Brief: Disinfection (#DWBRPE47), June 

1996. DCN DW03758. 

National Drinking Water Clearinghouse, 1996b. Tech Brief: Filtration (#DWBRPE50), 

September 1996. DCN DW00874. 

Tchobanoglous, et al., 2003. George Tchobanoglous, Franklin L. Burton, H. David Stensel,

Wastewater Engineering Treatment & Reuse, 4th edition. Metcalf & Eddy, Inc., New York: 

McGraw-Hill. DCN DW00871. 

U.S. Environmental Protection Agency (EPA), 1986. Design Manual: Municipal Wastewater 

Disinfection (EPA 625-1-86-021), Office of Research and Development, Cincinnati, Ohio. 

U.S. EPA, 1998. Small System Compliance Technology List for the Non-Microbial 

Contaminants Regulated Before 1996 (EPA 815-R-98-002), Office of Water, Washington, DC. 

DCN DW00883. 

U.S. EPA, 1999c. Wastewater Technology Fact Sheet: Ultraviolet Disinfection (EPA 832-F-99-

064), Office of Water Municipal Technology Branch, Washington, DC. DCN DW00677. 

U.S. EPA, 1999d. Alternative Disinfectants and Oxidants Guidance Manual (EPA 815-R-99-

014), Office of Water, Washington, DC. DCN DW00647. 

U.S. EPA, 2000. Wastewater Technology Fact Sheet: Granular Activated Carbon Adsorption and 

Regeneration (EPA 832-F-00-017), Office of Water, Washington, DC. DCN DW00650. 

U.S. EPA, 2002a. Filter Backwash Recycling Rule: Technical Guidance Manual (EPA 816-R02-014), Office of Ground Water and Drinking Water, Washington, DC. DCN DW00064. 

U.S. EPA, 2002b. Community Water System Survey 2000 (EPA 815-R-02-005), Office of Water, 

Washington, DC. DCN DW00001. 

U.S. EPA, 2006. Drinking Water Treatment Plant Site Visit Report: Des Moines Water Works 

Fleur Drive Water Treatment Plant, Office of Water, Washington, DC. DCN DW00918. 
Drinking Water Industry Report Section 6 – Source Water Treatment Technologies

6-22

U.S. EPA, 2008b. National Primary Drinking Water Standards (List of Drinking Water 

Contaminants and MCLs) (original document published in 2003, DCN DW00657), Office of 

Ground Water and Drinking Water, Washington, DC. Retrieved from 

http://www.epa.gov/safewater/contaminants/index.html Accessed April 2008 for updates.

U.S. EPA, 2009. Drinking Water Survey Response Database – Technical Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03790. 

U.S. Geological Survey (USGS), 2007. “Saline water,” Water Science for Schools. Retrieved 

July 2007, from http://ga.water.usgs.gov/edu/saline.html. DCN DW03761. 
7-1

SECTION 7

TYPES OF RESIDUALS PRODUCED BY SOURCE WATER 

TREATMENT

The previous section discusses the treatment processes and common treatment 

trains that are used at water treatment plants (WTPs) to produce drinking water. The treatment 

processes used to produce drinking water may generate waste streams (or residuals) that the 

WTP must manage. Two of the treatment processes presented in the previous section, 

disinfection and other chemical addition, may contribute chemicals to the residuals, but do not 

generate waste streams themselves. Therefore these two processes are not specifically discussed 

in this section. This section discusses residuals generated by the following water treatment

processes: 

• Presedimentation (Section 7.1); 

• Coagulation, flocculation, and sedimentation (Section 7.2); 

• Precipitative softening (Section 7.3); 

• Filtration, microfiltration, and ultrafiltration (Section 7.4); 

• Membrane desalination (Section 7.5); 

• Ion exchange (Section 7.6); and 

• Activated carbon (adsorption process) (Section 7.7). 

Water treatment plants (WTPs) may use more than one of the treatment processes 

listed above and may generate multiple types of residuals. The volume and characterization of 

the residuals generated depends on the quality of the source water, the drinking water production 

rate, efficiency of the source water treatment system, the amount of treatment chemical used, and 

type of source water treatment. The residuals volume at a WTP may vary seasonally or monthly 

(U.S. EPA, 1993). EPA collected data through literature searches, EPA and state sources, and the 

2006 industry questionnaire to quantify residuals generation rates and composition before 

residuals treatment. An overview of the data sources is presented in Section 2 of this document. 

7.1 PRESEDIMENTATION

As discussed in Section 6, presedimentation is a sedimentation basin operated at 

the head of the WTP. Presedimentation uses gravity to remove suspended solids from source 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-2

water. The residence time, which depends on the WTP design, capacity, and production rate, is 

an important factor in the efficiency of solids separation and removal. Clay and organics settle 

slowly and are not removed during presedimentation; these contaminants require coagulants to 

assist settling. Silt also has a slow settling velocity; 2-micron silt particles settle at a rate of 10 

millimeters per hour (0.4 inches per hour). Sand and grit settle more rapidly; 600-micron sand 

particles settle at a rate of 900 meters per hour (50 feet per minute) (New Zealand Ministry of 

Health, 2005). If the presedimentation basin has a residence time of two days, then all of the sand 

and grit will be in the sludge, but very little of the clay and silt. The composition of the solids in 

the sludge is site-specific. Depending on the composition, settling basins can remove between 50 

and 90 percent of the influent solids (U.S. EPA, 1999). Following presedimentation, WTPs 

remove smaller particles during the coagulation, flocculation, sedimentation, and filtration 

processes, as shown in Figure 7-1. 

Figure 7-1. Residuals from Source Water Solids Removal (U.S. EPA/ACSE/AWWA, 1996) 

7.2 RESIDUALS FROM COAGULATION, FLOCCULATION, AND 

SEDIMENTATION

During coagulation, flocculation, and sedimentation, solids settle to the bottom of 

clarifiers and sedimentation basins. Coagulation is the addition of chemical agent(s) to the solids 

settling process to reduce the negative surface charges by introducing positive ions, which allows 

the particulates to agglomerate and settle. Aluminum and iron salts are common coagulant aids 

whose positive trivalent forms are insoluble at normal conditions for drinking water treatment 

and precipitate along with the neutralized suspended solids (Tchobanoglous, et al., 2003). The 

charge neutralization reactions begin immediately, necessitating a rapid mix chamber. 

Raw 

Water

Grit Pre-Sedimentation 

Waste

Pre-Sedimentation Basin Rapid Mix

Coagulant Sludge Filter Backwash 

Waste

Finished 

Water

Flocculation Final Sedimentation Basin Filters
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-3

The term flocculation is the agglomeration of small finely separated particles into 

larger particles that become heavier than water. Optimum floc formation is best carried out under 

conditions of gradually reducing energy: turbulent rapid mix is reduced to gentle agitation, which 

is further reduced to quiescent deposition. 

Within sedimentation basins, solids settle by gravity to the bottom. The underflow 

sludge is removed from the basin on either a continuous or batch basis. In continuous sludge 

removal, rakes or blades push the sludge along the bottom of the settling basin to an outlet. In 

batch removal, basins are drained and the sludge is removed with the remaining basin water and 

cleaning water. Batch removal occurs when the settling volume in the basin is no longer effective 

(i.e., sludge displaces too much settling volume). The time between batch removals varies from a 

few weeks to over a year.

The volume of coagulation sludge generated depends on the plant production, 

amount of coagulant or other treatment chemical added (dose), and amount of suspended solids 

in the source water. Table 7-1 presents typical coagulation sludge volumes generated (U.S. EPA, 

1993). The characteristics of coagulation sludge vary depending on initial water quality and the 

amount and type of coagulant used (e.g., higher aluminum concentration in the sludge using 

aluminum-based coagulant). Coagulation sludge predominately contains the coagulant metal 

hydroxides along with source water natural organic matter, suspended solids, microorganisms, 

radionuclides, and other organic and inorganic constituents. The metals found in coagulation 

sludge include aluminum, arsenic, and occasionally cadmium, chromium, copper, iron, lead, 

manganese, nickel, and zinc (Cornwell, 1999). 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-4

Table 7-1. Typical Chemical Coagulation Sludge Volumes 

Population Served 

Range

Average Water 

Treatment Plant 

Flow (MGD)

Water Treatment 

Plant Design Flow 

(MGD)

Typical Sludge 

Volume Range 

(GPD)

Average Sludge

Volume

(GPD)

1,001 to 3,300 0.23 0.7 7 – 2,600 770

3,301 to 10,000 0.7 1.8 18 – 6,700 2,000

10,001 to 25,000 2.1 4.8 48 – 17,800 5,300

25,001 to 50,000 5 11 110 – 40,900 12,100

50,001 to 75,000 8.8 18 180 – 66,800 19,800

75,001 to 100,000 13 26 260 – 96,600 28,600

100,001 to 500,000 27 51 510 – 189,400 56,200

500,001 to 1,000,000 120 210 2,100 – 779,900 231,300

Greater than 1,000,000 270 430 4,300 – 1,596,900 473,500

Source: U.S. EPA, 1993. 

MGD – Million gallons per day.

GPD – Gallons per day.

If the source water has a high concentration of total suspended solids (TSS), then 

the coagulant sludge will contain a high percentage of gelatinous, hydroxide precipitates. The 

alum and ferric (or iron) sludge exhibit poor compaction traits, ranging from 0.5 to 2 percent 

solids (ASCE/AWWA, 1997). Consequently, coagulation sludge usually requires additional 

processing such as thickening, dewatering, or drying prior to disposal. Because of their low 

solids content, these sludges are difficult to dewater. They are also biologically inert with little 

organic content and have little value as a fertilizer or soil conditioner. Section 11 discusses 

residuals treatment and management practices.

7.3 RESIDUALS FROM PRECIPITATIVE (LIME) SOFTENING

WTPs use precipitative softening to remove divalent ions in water, particularly 

calcium and magnesium, by the addition of lime. The concentration of the divalent ions in the 

water is often referred to as the water’s “hardness.” The lime increases the pH and reacts with the 

ions to form a precipitate of insoluble calcium carbonate and magnesium hydroxide. Softening 

sludge (or carbonate residuals) settles to a solids content ranging from 2 to 15 percent 

(ASCE/AWWA, 1997). Softening sludge is easier to dewater and compact than coagulation 

sludge (see Section 7.2). Table 7-2 presents typical lime softening sludge volumes produced by 

WTPs (U.S. EPA, 1993). 
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7-5

Table 7-2. Typical Lime Softening Sludge Volumes 

Population Served 

Range

Average Water 

Treatment Plant 

Flow (MGD)

Water Treatment

Plant Design Flow 

(MGD)

Typical Sludge Volume 

Range 

(GPD)

Average Sludge 

Volume 

(GPD)

1,001 to 3,300 0.23 0.7 2,800 – 10,700 8,500

3,301 to 10,000 0.7 1.8 7,200 – 27,400 21,900

10,001 to 25,000 2.1 4.8 19,300 – 73,100 58,300

25,001 to 50,000 5 11 44,200 – 167,500 133,600

50,001 to 75,000 8.8 18 72,300 – 274,100 218,600

75,001 to 100,000 13 26 104,400 – 395,900 315,800

100,001 to 500,000 27 51 204,800 – 776,600 619,400

500,001 to 1,000,000 120 210 843,400 – 3,198,000 2,550,600

Greater than 1,000,000 270 430 1,726,900 – 6,548,200 5,222,700

Source: U.S. EPA, 1993. 

MGD – Million gallons per day.

GPD – Gallons per day.

Softening sludge is biologically inert and has a high pH (typically greater than 

10.5) due to unreacted lime and high alkalinity. The sludge contains calcium carbonate, 

magnesium hydroxide, other divalent ions, natural organic matter from the source water, 

inorganics, suspended solids, microorganisms, and radionuclides. Metals found in the softening 

sludges include calcium, magnesium, arsenic, barium, cadmium, chromium, lead, mercury, 

selenium, and silver (Cornwell, 1999). 

In lime softening, sludge generation rates depend on the ratio of calcium 

carbonate to magnesium hydroxide and the type of clarifier/sedimentation basin. Conventional 

gravity sedimentation basins generate sludge with solids concentrations of only 2 to 4 percent, 

whereas, sludge blanket clarifiers generate sludge with solids concentrations up to 30 percent 

(U.S. EPA/ASCE/AWWA, 1996). 

Softening sludges are generally dense, stable, and inert materials that dewater 

easily to a solids content up to 50 to 60 percent. However, if the hardness is due to magnesium, 

the hydroxide sludge is more difficult to handle and dewater (Cornwell, 1999). Figure 7-2 

presents the sources of residuals from a typical precipitative softening plant. 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-6

Raw 

Water

Grit Pre-Sedimentation 

Waste

Pre-Sedimentation Basin Rapid Mix

Lime Softening 

Sludge

Filter Backwash 

Waste

Finished 

Water

Flocculation Final Sedimentation Basin Filters

Figure 7-2. Residuals from Precipitative Softening WTP 

7.4 RESIDUALS FROM FILTRATION

WTPs use filtration to remove finer particles and metals. At some WTPs, 

filtration is the only solids removal step. Filter types include non-membrane filters such as multimedia, slow sand, and diatomaceous earth and low-pressure membranes such as microfiltration 

(MF) and ultrafiltration (UF). 

7.4.1 Filters (non-membrane)

Filtration removes suspended material in the source water by allowing water to 

pass through the filter media while suspended solids accumulate in the interstices of the filter 

media. As the filter run continues and more particles are removed, it becomes more difficult for 

the inlet water to easily make its way through the filter. This condition is called filter head loss 

and is an indication of waning filter performance. At a predetermined filter head loss value, the 

filter is taken out of service for backwash. 

Backwashing is the process of using finished water to reversely expel the particles 

collected on the filter media. The plant collects the filter backwash water (containing the 

particles) in an area separated from the filter inlet. Due to the relatively low level of filtered 

particles and the relatively large volume of water necessary to clean the filter, the resulting 

backwash residuals water is dilute (50 to 400 mg/L of suspended solids) and difficult to dewater 

(U.S. EPA/ASCE/AWWA, 1996). 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-7

Filter backwash contains particulates including clay and silt particles, 

microorganisms (bacteria, viruses, and protozoan cysts), colloidal and precipitated humic 

substances, and other natural organic particulates from the decay of vegetation. At conventional 

and direct filtration plants, filter backwash also contains precipitates of aluminum or iron used in 

coagulation (Cornwell, 1999). 

The volume of filter backwash wastewater generated depends on the number of 

filters, frequency of backwash, and duration of backwash events. The volume is typically 

between 2 and 5 percent of the finished water produced (U.S. EPA/ASCE/AWWA, 1996). This 

is a sizeable residuals volume. Consequently, many WTPs employ a flow equalization system to 

settle and remove some of the solids and recycle the backwash water to the head of the source 

water treatment plant. 

After backwashing, WTPs may wash the filter to ensure adequate filter 

performance. The spent wash water is called “filter-to-waste.” By generating the filter-to-waste 

stream, WTPs can check the effluent quality from the filter prior to bringing the filter back online. Filter-to-waste is the filter effluent for the first 15 to 60 minutes after startup (following 

backwash). The filter-to-waste stream is equalized and returned to the head of the treatment 

plant, rather than distributed to customers (U.S. EPA/ASCE/AWWA, 1996). 

7.4.2 Low-Pressure Membranes

Low-pressure membranes (MF/UF) generate filter backwash waste streams, 

similar to other filtration processes, and spent chemical cleaning solutions. MF and UF systems

remove suspended solids, turbidity, inorganic and organic colloids, microorganisms (protozoan 

cysts and bacteria), viruses (UF only), and some organic fractions (UF only) from the source 

water. The volume of backwash generated is typically between 2 and 15 percent of the plant flow 

rate. The backwash stream represents the majority of residuals generated from MF/UF treatment 

process (95 to 99 percent of the total volume of residuals). The remaining 1 to 5 percent of 

membrane residuals is generated by chemical cleaning procedures (Malmrose, et al., 2003). 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-8

Table 7-3 presents typical characteristics of low-pressure membrane backwash 

residuals. These characteristics vary with feed flow rate and backwash frequency. (Malmrose, et 

al., 2003) 

Table 7-3. Typical Characteristics of Low-Pressure Membrane Backwash Residuals

Frequency of application Every 10 to 60 minutes.

Volume of backwash 

residuals generated/ 

waste produced

2 to 15% of plant feed flow rate for recoveries of 85 to 98%.

(Daily chemically-enhanced backwash (CEBW) wastes might be 0.2 to 0.4% of plant 

feed flow rate.)

Characteristics of 

backwash residuals

Algae, precipitated solids, possible chemical residues if using CEBW 

Total organic carbon (TOC) concentration of 1 to 2 times the feed water 

concentration (if no coagulant or absorbent is used).

If coagulant is used, the TOC could be 5 times the feed water concentration.

For recoveries of 85 to 98%, backwash will have a concentration factor of 7 to 50 

times the feed water for total suspended solids (TSS) and Cryptosporidium.

If using CEBW (with chlorine, acid, or base), pH may be <6 or >9, and chlorine 

residual may be up to 1,000 mg/L as Cl2.

Source: Malmrose, et al., 2003.

Some systems use coagulants, powdered activated carbon (PAC), or other 

chemicals (e.g., potassium permanganate) as pretreatment to membrane filtration to remove 

some solids prior to the membrane. This pretreatment helps to reduce fouling of the membrane 

and reduce the backwash frequency. The characteristics of the resulting residuals from these 

pretreatment operations closely resemble those of coagulation sludge (Malmrose, et al., 2003). 

MF/UF systems also generate spent chemical cleaning solution residuals during 

the membrane cleaning processes used to control fouling (CEBW and clean in place (CIP)). 

Cleaning solution residuals reflect the chemicals used in the cleaning process. Only a portion of 

the active chemical ingredient is consumed during the cleaning process, so the resulting chemical 

cleaning waste includes some remaining active chemical ingredient, as well as salts from 

chemical reactions between the chemicals and foulants, dissolved organic materials, and 

suspended solids. While some plants refresh the active ingredient in spent cleaning solutions and 

reuse it to minimize waste quantities, this practice can result in more concentrated waste cleaning 

solutions. Table 7-4 summarizes the characteristics of some typical waste chemical cleaning 

solutions (Malmrose, et al., 2003). 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-9

Table 7-4. Typical Characteristics of Spent Low-Pressure Membrane Chemical 

Cleaning Solutions 

Frequency of application Daily to once every 3 or 4 months.

Volume of residuals 

generated

Monthly CIP wastes normally <0.05% of plant feed flow rate.

Daily CEBW wastes might be 0.2 to 0.4% of plant feed flow rate.

Chemicals commonly 

used

Sodium hypochlorite – 500 to 1,000 mg/L as Cl2.

Citric or hydrochloric acid – pH 1 to 2.

Caustic soda – pH 12 to 13.

Surfactant – 0.1% by weight.

Characteristics of spent 

cleaning solutions

pH from 2 to 14.

Chlorine residual up to 1,000 mg/L as Cl2.

Low concentrations of surfactants.

TSS up to 500 mg/L (neutralization may precipitate additional solids).

TOC 10 to 30 times the feed water concentration.

5-day biochemical oxygen demand (BOD5) up to 5,000 or 10,000 mg/L (if citric acid 

is used).

Source: Malmrose, et al., 2003.

7.5 RESIDUALS FROM MEMBRANE DESALINATION 

As discussed in Section 6 of this document, membrane desalination technologies 

include reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and electrodialysis 

reversal (EDR). Membranes are typically used to remove dissolved solids and ions. In addition to 

dissolved solids and ions, membranes can also remove dissolved organics, dissolved gases, 

biological contaminants, and suspended solids (U.S. EPA/ASCE/AWWA, 1996). However, 

industry practice is to remove biological material and particulates via pretreatment. Plants 

typically pretreat the source water prior to membrane desalination to protect and extend the life 

of the membrane. Pretreatment steps commonly include:

• Acid addition – lowering pH to between 5.5 and 7.0. 

• Anti-scalant addition – to prevent membrane fouling. 

• Filtration – remove suspended particles. 

The filtration step generates a backwash waste stream. Figure 7-3 presents typical 

residuals generated from membrane desalination plants. 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-10

Raw Water Pretreatment Membrane Finished Water 

(Permeate)

Pretreatment Residuals 

(e.g., filter backwash)

Concentrate Cleaning Waste

(intermittent)

Figure 7-3. Residuals from Membrane Desalination 

Membrane desalination systems generate a clean permeate stream that passes 

through the membranes and a reject stream (or concentrate) containing the contaminants that are 

retained by the membranes for separate disposal. The types of contaminants in the concentrate 

are generally the same as those in the source water (i.e., very few process-added chemicals). 

Contaminant concentrations in the concentrate are typically 4 to 10 times feed 

water concentrations and depend upon the rejection characteristics of the membrane and finished 

drinking water (i.e., permeate) production. If pretreatment is used, then the feed water to the 

desalting membranes will have lower levels of certain constituents and particles; however, feed 

water levels of other constituents may increase. For example, coagulation pretreatment will 

increase the inorganic ions, such as sulfate, iron, and aluminum, and polymer or sulfuric acid 

pretreatment may increase residual organics. Table 7-5 lists the target contaminants typically 

removed by membrane desalination (Malmrose, et al., 2004). 

The rejection rate for a contaminant is the percentage of the contaminant in the 

source water that does not pass through the membrane, but becomes part of the concentrate 

stream. The rejection rate depends on the contaminant size and interaction with the membrane. In 

general, the larger the pore size of the membrane, the lower the rejection rate. RO systems have 

rejection rates from 90 to 99.8 percent for monovalent ions and from 98 to 99.9 percent for 

divalent ions (e.g., hardness) (Malmrose, et al., 2004). NF membranes have rejection rates from 

40 to 90 percent for monovalent ions and from 80 to 98 percent for divalent ions (Malmrose, et 

al., 2004). The ED/EDR process can reject more than 90 percent of dissolved ions (U.S. 

EPA/ASCE/AWWA, 1996). 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-11

Table 7-5. Membrane Desalination: Typical Target Contaminants by Source Water 

Source Water Typical Target Contaminants

Surface water Total Organic Carbon (TOC)

Disinfection By-product (DBP) Precursors

Microorganisms (or pathogens)

Pesticides / Synthetic Organic Compounds (SOCs)

Taste & Odor Compounds

Ground water Hardness

Color (indicative of dissolved organic material)

TOC

Inorganic and organic compounds / chemicals

Brackish surface water and ground water Total Dissolved Solids (TDS)

Hardness

Chloride and sodium

Seawater TDS

Chloride and Sodium

Bromide

Boron

Source: Malmrose, et al., 2004. 

Table 7-6 presents typical design parameters for RO and NF membrane 

desalination treatment plants (Malmrose, et al., 2004). The water recovery rate for a membrane is 

the percentage of the feed water that passes through the membrane as permeate (finished water).

Table 7-6. Typical Membrane Desalination System (RO and NF) Design Parameters

Parameter Surface Water

Fresh Ground

Water

Brackish Ground

Water Seawater

Feed total dissolved solids 

(TDS) (mg/L)

200-400 400-500 500-10,000 30,000-40,000

Water recovery 

(% of feed)

80-90 80-90 65-85 40-60

Concentrate quantity

(% of feed)

10-20 10-20 15-35 40-60

Concentrate TDS (mg/L)

(at example recovery)

1,330-2,660 

(85%)

2,660-3,330 

(85%)

2,000-40,000

(75%)

60,000-80,000

(50%)

Concentration factor a 5-10 5-10 2.9-6.7 1.7-2.5

Source: Malmrose, et al., 2004.

a – Ratio of total dissolved solids in concentrate to total dissolved solids in feed, assuming 100 percent salt rejection.

mg/L – Milligrams per liter.
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-12

Membrane desalination plants also clean the equipment and generate spent 

cleaning solutions every three to 12 months. Typically, the waste cleaning solution volume 

generated during a clean in place of NF and RO is about 3 gallons per 100 square feet (1.2 

liters/square meter). Typical waste cleaning solution volume is estimated by adding the total 

empty vessel volume and pipe volume. In addition to spent cleaning solution, the plant may 

generate one to two volumes of rinse water. Typical cleaning solutions, which may be diluted 

with rinse water (feed or permeate), for NF and RO systems include acid (mineral or citric) to 

remove inorganic contaminants and alkaline solutions (e.g., caustic soda with detergents or 

surfactants) to remove organic contaminants and biofilms.20 ED/EDR system cleaning solutions 

typically include concentrated hydrochloric acid and sodium chlorine solutions. Occasionally, 

chlorine solutions may be used to clean ED/EDR systems for organic contaminant and biofilm 

removal. The waste cleaning solution volume is extremely small compared to treated flow (<0.1 

percent) (Malmrose, et. al., 2004). 

ED/EDR systems also produce a low flow waste stream called “electrode waste,” 

which contains significant levels of hydrogen and chlorine gases that are typically stripped from 

the electrode waste stream using a degasifier (which is part of the EDR system) (Malmrose, et 

al., 2004). 

7.6 RESIDUALS FROM ION EXCHANGE

Ion exchange may be used by WTPs to reduce hardness by replacing calcium and 

magnesium ions in source water with sodium ions that are contained in the ion exchange resin. 

Ion exchange can also remove nitrates, barium, radium, arsenate, selenate, excess levels of 

fluoride, lead, and chromate (U.S. EPA/ASCE/AWWA, 1996). Once all the ion exchange sites 

reach capacity, the plant must regenerate the ion exchange material, thus producing waste 

concentrate that contains the source water contaminants. In addition to the waste concentrate, the 

ion exchange process also generates backwash water and rinse water that is used before and after 

the regeneration of the ion exchange resin, respectively. Waste concentrate generation rates from 

ion exchange for water softening ranges from 1.5 to 10 percent of the water softened (U.S. 

 

20 Biofilms are an accumulated mixture of microorganisms, organic contaminants, and inorganic contaminants.
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-13

EPA/ASCE/AWWA, 1996). Table 7-7 presents typical ion exchange concentrate generation 

rates for WTPs (U.S. EPA, 1993). 

Table 7-7. Typical Ion Exchange Concentrate Volumes 

Population Served 

Range

Average Water 

Treatment Plant Flow 

(MGD)

Water Treatment Plant 

Design Flow (MGD)

Range of Typical Concentrate 

Generation Rates (GPD)

1,001 to 3,300 0.23 0.7 12,300 – 63,200

3,301 to 10,000 0.7 1.8 31,500 – 162,500

10,001 to 25,000 2.1 4.8 84,000 – 433,300

25,001 to 50,000 5 11 192,500 – 993,000

50,001 to 75,000 8.8 18 315,000 – 1,624,900

75,001 to 100,000 13 26 455,000 – 2,347,100

100,001 to 500,000 27 51 892,600 – 4,604,000

500,001 to 1,000,000 120 210 3,675,200 – 18,957,700

Greater than 1,000,000 270 430 7,525,400 – 38,818,100

Source: U.S. EPA, 1993.

MGD – Million gallons per day.

GPD – Gallons per day.

Table 7-8 lists typical concentrations of ions in ion exchange waste concentrate 

(U.S. EPA/ASCE/AWWA, 1996). 

Table 7-8. Typical Chemical Concentrations in Ion Exchange Waste Concentrate 

Constituent Average Concentration Range (mg/L)

Total dissolved solids 15,000 – 35,000

Calcium (Ca++) 3,000 – 6,000

Magnesium (Mg++) 1,000 – 2,000

Hardness (as CaCO3) 11,600 – 23,000

Sodium (Na+) 2,000 – 5,000

Chlorine (Cl-) 9,000 – 22,000

Source: U.S. EPA, ASCE, AWWA, 1996. 

7.7 RESIDUALS FROM ADSORPTION (ACTIVATED CARBON)

Adsorption removes ions or molecules from the source water by adsorbing the 

chemicals in the source water onto the treatment media. Adsorption is used to remove naturally 

occurring organic materials, taste, odor, synthetic organic compounds, as well as disinfection by-
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-14

products. Adsorption can use different types of adsorptive media, and the most common is 

granular activated carbon (GAC). Residuals generated by GAC include backwash water (or 

surface wash water) and spent media. 

As the treatment process goes on, adsorption sites become filled. Once all the 

adsorption sites are filled, breakthrough of the contaminant occurs (i.e., pollutants are no longer 

removed from the influent but continue through to the GAC filter effluent). WTPs then perform 

backwashing of the GAC filter bed. The time it takes for breakthrough to occur depends on the 

concentration of the pollutant contaminants being removed. 

Plants perform backwashing to disengage solids that have been entrapped in the 

filter bed. Backwashing of GAC filter-adsorbers is essential to remove solids and to maintain the 

desired hydraulic properties of the bed. Backwash water generally contains the removed 

contaminants such as suspended solids, biological films, organics, and some filter media. The 

volume and quantity of the GAC backwash stream depends on the influent source water quality. 

The spent media (or carbon) is sent off site for regeneration or disposal. 

Regeneration of the spent carbon is accomplished by thermal means (e.g., rotary kiln, hearth 

furnace) and does not generate a wastewater stream. 

7.8 REFERENCES

American Society of Civil Engineers (ASCE)/American Water Works Association (AWWA), 

1997. Water Treatment Plant Design, 3rd Edition. New York: McGraw Hill. Document Control 

Number (DCN) DW00961. 

Cornwell, D.A., 1999. Water Treatment Plant Residual Management, In Water Quality and 

Treatment: A Handbook of Community Water Supplies, 5th edition. New York: McGraw Hill. 

DCN DW00247. 

Malmrose, et al., 2003. Paul Malmrose, Jim Lozier, Jason Marie, Michael Mickley, Robert Reiss, 

Jerry Russell, James Schaefer, Sandeep Sethi, Jennifer Worley, Residual Management Research 

Committee Subcommittee on Membrane Residual Management, “2003 Committee Report: 

Residuals Management for Low-Pressure Membranes,” Jour. AWWA, 95:6:68. AWWA, June 

2003. DCN DW00003. 
Drinking Water Industry Report Section 7 – Types of Residuals Produced by Source Water Treatment

7-15

Malmrose, et al., 2004. Paul Malmrose, Jim Lozier, Michael Mickley, Robert Reiss, Jerry 

Russell, James Schaefer, Sandeep Sethi, Jennifer Manuszak, Robert Bergman, and Khalil Z. 

Atasi, Residual Management Research Committee Subcommittee on Membrane Residual 

Management, “2004 Committee Report: Residuals Management for Desalting Membranes,” 

Jour. AWWA, 96:12:73. AWWA, December 2004. DCN DW00032. 

New Zealand Ministry of Health, 2005. Draft Guidelines for Drinking Water Quality 

Management for New Zealand, Chapter 12, October 2005. Retrieved from 

www.moh.govt.nz/moh.nsf. DCN DW00930. 

Tchobanoglous, et al., 2003. George Tchobanoglous, Franklin L. Burton, H. David Stensel,

Wastewater Engineering Treatment & Reuse, 4th edition. Metcalf & Eddy, Inc., New York: 

McGraw-Hill. DCN DW00871. 

U.S. Environmental Protection Agency (EPA), 1993. Large Water System Byproducts Treatment 

and Disposal Cost Document (EPA 811-D-93-002), Office of Water, Washington, DC. DCN 

DW00058. 

U.S. EPA, 1999. Storm Water Technology Fact Sheet: Wet Detention Ponds (EPA 832-F-99-

048), Office of Water, Washington DC. DCN DW00899. 

U.S. EPA, ASCE, and AWWA, 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals (EPA 625-R-95-008), Office of Research and Development, 

Washington, DC. DCN DW03736. 
8-1

SECTION 8

POLLUTANTS IN WATER TREATMENT PLANT RESIDUALS

This section identifies and discusses the pollutants present in WTP residuals 

including the source of these pollutants. Section 9 presents pollutant loadings estimate for 

discharges of these residuals and Section 10 discusses the environmental impacts of the 

pollutants on discharge receiving streams. 

EPA reviewed data sources to determine the presence of priority, conventional, 

and nonconventional pollutant parameters in water treatment plant (WTP) residuals. EPA defines 

priority pollutant parameters in Section 307(a)(1) of the Clean Water Act (CWA). Table 8-1 lists 

the 126 specific priority pollutants listed in 40 CFR Part 423, Appendix A. For this industry 

review, most of the priority pollutants listed in Table 8-1 were not identified as significant 

contributors to WTP residuals. Section 304(a)(4) of the CWA defines conventional pollutant 

parameters to include biochemical oxygen demand (BOD), total suspended solids (TSS), oil and 

grease, pH, and fecal coliform bacteria. Nonconventional pollutant parameters are those that are 

neither priority nor conventional pollutant parameters. This group includes nonconventional 

metal pollutants, nonconventional organic pollutants, and other nonconventional pollutant 

parameters such as chemical oxygen demand (COD). 

EPA gathered data on pollutants from literature sources, including composition of 

source water treatment chemicals (Cornwell, 2002) and pollutants identified by EPA’s Drinking 

Water Program as a contaminant in finished drinking water (U.S. EPA, 2008), and discharge 

monitoring reports (DMRs) from effluent discharges (U.S. EPA, 2007). Pollutants in WTP 

residuals come from two sources: 1) treatment chemical addition (including by-product 

formation); and 2) source water. The following subsections identify the pollutants commonly 

found in residuals and wastewater discharged from WTPs. 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-2

Table 8-1. Priority Pollutant List a

1 Acenaphthene

2 Acrolein

3 Acrylonitrile

4 Benzene

5 Benzidine

6 Carbon tetrachloride 

(tetrachloromethane)

7 Chlorobenzene

8 1,2,4-Trichlorobenzene

9 Hexachlorobenzene

10 1,2-Dichloroethane

11 1,1,1-Trichloroethane

12 Hexachloroethane

13 1,1-Dichloroethane

14 1,1,2-Trichloroethane

15 1,1,2,2-Tetrachloroethane

16 Chloroethane

17 Removed

18 Bis(2-chloroethyl) ether

19 2-Chloroethyl vinyl ether (mixed)

20 2-Chloronaphthalene

21 2,4,6-Trichlorophenol

22 Parachlorometa cresol (4-chloro3-methylphenol)

23 Chloroform (trichloromethane)

24 2-Chlorophenol

25 1,2-Dichlorobenzene

26 1,3-Dichlorobenzene

27 1,4-Dichlorobenzene

28 3,3'-Dichlorobenzidine

29 1,1-Dichloroethylene

30 1,2-Trans-Dichloroethylene

31 2,4-Dichlorophenol

32 1,2-Dichloropropane

33 1,3-Dichloropropylene (trans-1,3-

dichloropropene)

34 2,4-Dimethylphenol

35 2,4-Dinitrotoluene

36 2,6-Dinitrotoluene

37 1,2-Diphenylhydrazine

38 Ethylbenzene

39 Fluoranthene

40 4-Chlorophenyl phenyl ether

41 4-Bromophenyl phenyl ether

42 Bis(2-Chloroisopropyl) ether

43 Bis(2-Chloroethoxy) methane

44 Methylene chloride 

(dichloromethane)

45 Methyl chloride (chloromethane)

46 Methyl bromide (bromomethane)

47 Bromoform (tribromomethane)

48 Dichlorobromomethane 

(bromodichloromethane)

49 Removed

50 Removed

51 Chlorodibromomethane 

(dibromochloromethane)

52 Hexachlorobutadiene

53 Hexachlorocyclopentadiene

54 Isophorone

55 Naphthalene

56 Nitrobenzene

57 2-Nitrophenol

58 4-Nitrophenol

59 2,4-Dinitrophenol

60 4,6-Dinitro-o-cresol (phenol, 2-

methyl-4,6-dinitro)

61 N-Nitrosodimethylamine

62 N-Nitrosodiphenylamine

63 N-Nitrosodi-n-propylamine (dinpropylnitrosamine)

64 Pentachlorophenol 

65 Phenol 

66 Bis(2-ethylhexyl) phthalate

67 Butyl benzyl phthalate

68 Di-n-butyl phthalate

69 Di-n-octyl phthalate

70 Diethyl phthalate

71 Dimethyl phthalate

72 Benzo(a)anthracene (1,2-

benzanthracene)

73 Benzo(a)pyrene (3,4-

benzopyrene)

74 Benzo(b)fluoranthene (3,4-benzo 

fluoranthene)

75 Benzo(k)fluoranthene (11,12-

benzofluoranthene)

76 Chrysene

77 Acenaphthylene

78 Anthracene

79 Benzo(ghi)perylene (1,12-

benzoperylene)

80 Fluorene

81 Phenanthrene

82 Dibenzo(a,h)anthracene (1,2,5,6- 

dibenzanthracene)

83 Indeno(1,2,3-cd)pyrene (2,3-ophenylenepyrene)

84 Pyrene

85 Tetrachloroethylene 

(tetrachloroethene)

86 Toluene

87 Trichloroethylene 

(trichloroethene)

88 Vinyl chloride (chloroethylene)

89 Aldrin

90 Dieldrin

91 Chlordane (technical mixture & 

metabolites)

92 4,4'-DDT (p,p'-DDT)

93 4,4'-DDE (p,p'-DDX)

94 4,4'-DDD (p,p'-TDE)

95 Alpha-endosulfan

96 Beta-endosulfan

97 Endosulfan sulfate

98 Endrin

99 Endrin aldehyde

100 Heptachlor

101 Heptachlor epoxide

102 Alpha-BHC

103 Beta-BHC

104 Gamma-BHC (lindane)

105 Delta-BHC

106 PCB-1242 (Arochlor 1242)

107 PCB-1254 (Arochlor 1254)

108 PCB-1221 (Arochlor 1221)

109 PCB-1232 (Arochlor 1232)

110 PCB-1248 (Arochlor 1248)

111 PCB-1260 (Arochlor 1260)

112 PCB-1016 (Arochlor 1016)

113 Toxaphene

114 Antimony (total)

115 Arsenic (total)

116 Asbestos (fibrous)

117 Beryllium (total)

118 Cadmium (total)

119 Chromium (total)

120 Copper (total)

121 Cyanide (total)

122 Lead (total)

123 Mercury (total)

124 Nickel (total)

125 Selenium (total)

126 Silver (total)

127 Thallium (total)

128 Zinc (total)

129 2,3,7,8-Tetrachloro-dibenzo-pdioxin (TCDD)

Source: 40 CFR Part 423, Appendix A.

a – Priority pollutants are numbered 1 through 129 but include 126 pollutants, because EPA removed three 

pollutants (17, 49, and 50) from the list.
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-3

8.1 OVERVIEW OF POLLUTANTS IN WATER TREATMENT PLANT 

RESIDUALS 

WTP residuals contain pollutants from the source water (concentrated when 

removed from drinking water) and from treatment chemicals (including impurities and 

disinfection by-products). Source water pollutants removed from potable drinking water include 

solids, metals, and microorganisms. Pollutants from treatment chemical formulations include 

active treatment chemical ingredients such as aluminum, calcium, and ammonia compounds, and 

formulation impurities. Water treatment chemical impurities can concentrate into detectable 

levels in residuals and recycle streams over time (Cornwell, 2002). Disinfection by-products 

include bromate, chlorite, haloacetic acids, and trihalomethanes.

Common treatment chemicals listed in responses to the 2006 industry 

questionnaire include the following (U.S. EPA, 2009):

• Chlorine (disinfection); 

• Chlorine and ammonia (disinfection with chloramines);

• Conventional treatment: 

— Aluminum chlorohydrate/polyaluminum chloride (PACl), 

— Aluminum sulfate (alum),

— Iron-based coagulants (ferric chloride and ferric sulfide),

— Potassium permanganate,

— Polymer coagulants.

• Lime (precipitative) softening: 

— Hydrated lime (Ca(OH)2),

— Caustic soda/sodium hydroxide (NaOH), 

— Quick lime (CaO),

— Sodium carbonate/soda ash (Na2CO3).

• Powdered activated carbon;

• Granular activated carbon; and

• Fluoride. 

Appendix B lists the compositions for some of the common treatment chemical 

formulations. 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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8.2 SOLIDS IN WATER TREATMENT PLANT RESIDUALS

Solids are the most common pollutant in WTP residuals. WTP residuals contain 

both suspended and dissolved solids, which are also known as filterable and nonfilterable 

residue. Suspended and dissolved solids concentrations are determined by filtering the solids 

with a standard glass fiber filter and then drying them to a constant weight. The solids retained 

on the filter are considered suspended solids, and the solids passing through the filter are 

considered dissolved solids. Total solids are the sum of suspended and dissolved solids. 

Suspended solids in WTP residuals include inorganic (e.g., silt, sand, clay, and 

insoluble hydrated metal oxides) and organic matter (e.g., flocculated colloids and compounds 

that contribute to color). Suspended solids may be measured using the parameters total 

suspended solids or turbidity. Dissolved solids consist primarily of dissolved inorganic 

compounds and can be found in ion exchange and membrane desalination concentrate waste 

streams at high concentrations. One of the primary functions of WTPs is to remove solids from 

the source water. 

Solids in WTP residuals primarily come from the source water, but the addition of 

treatment chemicals can add to the measured value (e.g., metals present in coagulants). Solids 

from the source water may be concentrated in the residuals resulting in a higher solids 

concentration than the source water solids concentration. 

DMR data collected with the 2007 industry questionnaire includes TSS 

concentrations for precipitative softening, conventional filtration (i.e., coagulation/filtration), 

filtration only (includes microfiltration and ultrafiltration), membrane desalination, and ion 

exchange plants. DMR data includes total dissolved solids (TDS) concentrations for ion 

exchange plants. EPA included TSS and TDS in the pollutant loadings analysis (see Section 9). 

A portion of the solids in WTP residuals are metals.
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-5

8.3 PRIORITY AND NONCONVENTIONAL METALS IN WATER 

TREATMENT PLANT RESIDUALS

A number of metals may be present in WTP residuals from the source water and 

from source water treatment chemicals (and their impurities). Table 8-2 summarizes EPA’s 

evaluation of the presence of priority metals and nonconventional metals in WTP residuals. 

Metals, including iron, manganese, and mercury, listed in Table 8-2, may be present in source 

water from natural erosion, land runoff, and industrial discharges. Aluminum salts, iron salts, and 

polymers are commonly used as coagulants. Potassium permanganate is added to control taste 

and odors, remove contaminants that cause color, control biological growth in treatment plants, 

and remove iron and manganese. Lime products and caustic soda are added to reduce hardness. 

Depending on the formulation, these treatment chemicals may contain metal impurities as listed 

in Table 8-2. 

WTPs remove metals from the source water to meet maximum contaminant levels 

(MCLs) in the finished drinking water. The removed metals and metal constituents of treatment 

chemicals become part of the residual waste streams. Permit writers select the appropriate 

pollutants of concern when issuing discharge permits based on the pollutants in the source water 

and type of treatment chemicals being added at the plant.

The following subsections discuss the active ingredient metals and other metals in 

more detail.
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-6

Table 8-2. Evaluation of Priority and Nonconventional Metals in Water Treatment Plant Residuals

Pollutant

Source Water 

Contaminant

Removed from 

Drinking Water a

Present in Treatment Chemicals? b

Aluminum-Based 

Coagulant

Iron-Based 

Coagulant

Potassium 

Permanganate

Organic 

Polymers Lime Products Caustic Soda

Priority Metals

Antimony, total Yes No Yes—Treatment 

chemical impurity 

No No No No

Arsenic, total Yes No—Not present.

Beryllium, total Yes No—No data.

Cadmium, total Yes No Yes—Treatment 

chemical impurity

No No Yes—Treatment 

chemical impurity

No

Chromium, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity 

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity 

Copper, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity 

No No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Cyanide, total Yes No—No data.

Lead, total Yes No Yes—Treatment 

chemical impurity 

No No No No

Mercury, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity 

Yes—Treatment 

chemical impurity

No No No

Nickel, total No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Selenium, total Yes No No Yes—Treatment 

chemical impurity

No No No

Silver, total Yes No No Yes—Treatment 

chemical impurity

No No No

Thallium Yes No—No data.

Zinc, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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Table 8-2. Evaluation of Priority and Nonconventional Metals in Water Treatment Plant Residuals

Pollutant

Source Water 

Contaminant

Removed from 

Drinking Water a

Present in Treatment Chemicals? b

Aluminum-Based 

Coagulant

Iron-Based 

Coagulant

Potassium 

Permanganate

Organic 

Polymers Lime Products Caustic Soda

Nonconventional Metals (Limited to those potentially in DWT Residuals)

Aluminum, total Yes Yes—Treatment 

chemical addition 

(active ingredient)

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Barium, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Calcium, total c No f Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical addition 

(active ingredient)

Yes—Treatment 

chemical impurity

Cobalt, total No e No Yes—Treatment 

chemical impurity

No No Yes—Treatment 

chemical impurity

No

Fluoride, total Yes No—No data

Iron, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical addition 

(active ingredient)

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Magnesium, total No f Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Manganese, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical addition 

(active ingredient)

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Molybdenum No e No Yes—Treatment 

chemical impurity 

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Potassium, total No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical addition 

(active ingredient)

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Silicon No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Sodium, total d No (but may be 

present in source 

water)

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical addition 

(active ingredient)
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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Table 8-2. Evaluation of Priority and Nonconventional Metals in Water Treatment Plant Residuals

Pollutant

Source Water 

Contaminant

Removed from 

Drinking Water a

Present in Treatment Chemicals? b

Aluminum-Based 

Coagulant

Iron-Based 

Coagulant

Potassium 

Permanganate

Organic 

Polymers Lime Products Caustic Soda

Strontium, total No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Tin, total No e No Yes—Treatment 

chemical impurity

No No No No

Titanium, total No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Vanadium, total Yes Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No No Yes—Treatment 

chemical impurity

No

Yttrium, total No e No No Yes—Treatment 

chemical impurity

No Yes—Treatment 

chemical impurity

No

Zirconium, total No e Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

Yes—Treatment 

chemical impurity

No

Sources: U.S. EPA, 2008 and Cornwell, 2002. 

a – Identified by EPA as a contaminant in drinking water. 

b – “Yes” indicates that the metal was detected in at least one formulation sample. Specific formulation details are included in Appendix B.

c – Also an active ingredient in calcium hypochlorite (may be used for chlorination).

d – Also an active ingredient in sodium hypochlorite (may be used for chlorination).

e – Although not identified by EPA as a drinking water contaminant, metal may be present in certain source waters from natural materials (e.g., ores) or 

industrial discharges.

f – Calcium and magnesium ions may be present in source water and removed via lime softening.
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-9

8.3.1 Aluminum and Iron

As discussed in Section 6, WTPs use aluminum and iron salts as coagulants. 

These metals are active ingredients in coagulants; and their use occurs at precipitative softening 

and conventional filtration plants. These metals, along with coagulant impurities, become part of 

the residual waste stream. In addition, the metals can be found in some source waters. Also, 

DMR data collected with the 2007 industry questionnaire demonstrate the presence of aluminum 

and iron in WTP discharges. As a result, EPA included aluminum and iron in the pollutant 

loadings analysis (see Section 9). 

8.3.2 Arsenic

Arsenic may be present at potentially high levels in the source water, especially 

ground water sources. Sources of arsenic include natural sources (e.g., rocks, soil) and industrial 

sources (e.g., use as a wood preservative). Higher concentrations of arsenic are typically found in 

ground water compared to surface water. States in the western part of the United States tend to 

have more public water systems with arsenic levels exceeding the MCL of 10 parts per billion 

(ppb) for finished drinking water. Most of the systems in the Midwest and Northeast have arsenic 

levels between 2 and 10 ppb (U.S. EPA, 2006a). Most systems with high levels of arsenic are 

small systems (serving less than 10,000 people). 

Of the systems affected by the OGWDW final arsenic rule (66 FR 6976, 

January 22, 2001), 97 percent were small systems. EPA’s 2007 industry questionnaire focused 

on large WTPs and the DMR data collected did demonstrated that arsenic was not present at 

measurable concentrations. Therefore, EPA did not include arsenic in the pollutant loadings 

analysis (see Section 9).

8.3.3 Calcium and Sodium

Calcium and sodium are active ingredients in lime products and caustic soda, 

respectively. Lime products and caustic soda are added to reduce hardness (i.e., remove calcium 

and magnesium from the source water). EPA has not set MCLs for these two pollutants in 

drinking water. DMR data collected with the 2007 industry questionnaire demonstrated the 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-10

presence of calcium, but no sodium. Therefore, EPA included only calcium in its pollutant 

loadings analysis (see Section 9).

8.3.4 Fluoride

Fluoride can occur naturally in source water. WTPs may add fluoride to the 

drinking water to promote healthy teeth; however, fluoride addition typically occurs at the end of 

the source water treatment process. WTPs use finished drinking water to backwash filters; 

fluoride may be present in residuals if added prior to finished water use as backwash. At the 

majority of WTPs, the concentration of the fluoride in the wastewater is similar to the 

concentration in the finished drinking water. DMR data collected with the 2007 industry 

questionnaire demonstrated the presence of fluoride in discharges. EPA included fluoride in its 

pollutant loadings analysis (see Section 9).

8.3.5 Manganese and Potassium 

Manganese and potassium are active ingredients in potassium permanganate. 

Potassium permanganate is added to control taste and odors, remove contaminants that cause 

color, control biological growth in treatment plants, and remove iron and manganese from the 

source water. EPA set secondary standards for manganese at 0.05 mg/L for drinking water. DMR 

data collected with the 2007 industry questionnaire demonstrated the presence of manganese, but 

not potassium. Therefore, EPA included only manganese in its pollutant loadings analysis (see 

Section 9). 

8.3.6 Additional Metals with DMR Data

As summarized in Table 8-2, metals may be present in the source water (and 

concentrated in the WTP residuals) or in the treatment chemicals. The following metals are trace 

contaminants in common WTP treatment chemicals and monitored by WTPs in the DMR data 

collected by EPA:

• Barium;

• Cadmium;
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-11

• Copper; 

• Lead; 

• Magnesium; 

• Nickel; and 

• Zinc.

EPA included these metals in its pollutant loadings analysis (see Section 9).

8.4 WTP POLLUTANTS FROM DISINFECTION 

As discussed in Section 6.6, WTPs add disinfecting agents during source water 

treatment to eliminate or inactivate microbiological populations. Primary disinfection occurs at 

the front of the source water treatment process; disinfecting chemicals and any resulting byproducts might be found in WTP residuals generated later in the treatment process. Secondary 

disinfection occurs at the clear well or in the distribution system to prevent microbiological 

regrowth. If secondary disinfection occurs at the clear well, disinfecting chemicals and any 

resulting by-products might be found in wastewaters where finished water is used for washing or 

cleaning (e.g., filter backwash).

Chlorine is the most commonly used disinfectant. To disinfect with chlorine (or 

chlorination), WTPs can use gaseous chlorine; calcium hypochlorite (Ca(OCl)2), an easily 

dissolved solid containing 65 percent available chlorine; or sodium hypochlorite (NaOCl), a 

solution with 5 to 15 percent chlorine. Other disinfectant chemicals include chloramines 

(chlorine gas and ammonia), chlorine dioxide, and ozone. Most U.S. WTPs use gaseous chlorine 

to disinfect drinking water (U.S. EPA, 2009). 

Disinfection by-products (DBPs) form when disinfectants react with substances in 

the source water, such as bromide and/or natural organic matter. EPA promulgated maximum 

contaminant levels (MCLs) in drinking water for DBPs because they are potentially carcinogenic 

(71 FR 478). 

The DMR data collected with the 2007 industry questionnaire includes 

concentrations for total residual chlorine and four DBPs: 1) bromodichloromethane, 2) 

chloroform, 3) dibromochloromethane, and 4) trihalomethane. EPA did not have DMR data for 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-12

chloramines discharges, but did have DMR data for ammonia concentrations in the effluent. EPA 

included ammonia, total residual chlorine, the four DBPs listed above, and two additional DBPs, 

bromoform and haloaectic acids, in the pollutant loadings analysis (see Section 9).

8.4.1 Chemistry of Chlorine Disinfection 

Depending on the chemistry of the source water and wastewater, various forms of 

chlorine and disinfection by-products may be present in WTP residuals. Figure 8-1 shows the 

chemistry of how chlorine reacts when added during source water for disinfection (primary or 

secondary) purposes (CDC, 2006; Block, 2000). 

Chlorine Added

Total Residual Chlorine

The chlorine remaining 

after the chlorine demand

Free Chlorine

Concentration of chlorine 

available for disinfection 

as HOCl or OClCombined Chlorine

The concentration of 

chlorine bound to nitrogen 

compounds in the water, 

forming chloramines

Chlorine Demand

Reactions with organic 

material, metals, other 

compounds present in 

water prior to disinfection

Organic By-Products

such as:

Trihalomethanes

Haloacetic acids

Inorganic By-Products

such as: 

MnOCl3

FeCl3

Rapid 

reaction

Slower reaction dependent 

on the concentration of 

free chlorine

Figure 8-1. Chemistry of Compounds Resulting from Chlorine Disinfection (CDC, 2006; 

Block, 2000) 

The chlorine chemistry shown above includes the following three components: 1) 

chlorine added; 2) chlorine demand; and 3) total residual chlorine. 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-13

8.4.1.1 Chlorine Added

As discussed above, chlorine may be added at several points during source water 

treatment for disinfection. Primary disinfection is the addition of a disinfectant before 

sedimentation or filtration to achieve desired inactivation of microorganisms. Secondary 

disinfection is the addition of a disinfectant at the clear well and/or various points in the 

distribution system to maintain a disinfectant residual in the finished water, preventing regrowth 

of microorganisms. 

8.4.1.2 Chlorine Demand

Chlorine demand is the chlorine consumed by inorganic and organic substances in 

the water, not including amines. Chlorine reacts rapidly with inorganic substances, such as 

metals (manganese and iron), hydrogen sulfide, and nitrites. Chlorine reacts more slowly with 

organic substances, and the reaction depends on the amount of free chlorine available (U.S. EPA, 

1999a). By-products formed during chlorination include inorganic chlorine compounds, such as 

FeCl3 and MnOCl3 and organic chlorine compounds, such as trihalomethanes and haloacetic 

acids. 

8.4.1.3 Total Residual Chlorine

Total residual chlorine (TRC) is the amount of chlorine remaining after chlorine 

demand. TRC includes combined chlorine and free chlorine. Combined chlorine is the chlorine 

that has combined with amines to form chloramines. Although chloramines are a weaker 

disinfectant than chlorine, some WTPs use them for secondary disinfection. To perform 

disinfection with chloramines, WTPs inject chlorine, followed by ammonia into the distribution 

main. Chloramines are more stable than free chlorine in distribution systems and therefore more 

effective in controlling microorganism regrowth. 
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There are three chloramine compounds, formed in the following conditions: 

1. Monochloramine (NH2Cl): NH3 + HOCl → NH2Cl + H2O; pH near 6

2. Dichloramine (NHCl2): NH2Cl + HOCl → NHCl2 + H2O; pH near 5

3. Nitrogen trichloride (NCl3) : NHCl2 + HOCl → NCl3 + H2O; Uncommon; undesirable

Free chlorine is the chlorine that is available for disinfection after other chlorine 

compounds are formed, found as HOCl or OCl-, depending on pH. 

8.4.2 Residual Disinfectants in Finished Drinking Water

Under the Safe Drinking Water Act (SDWA), EPA set requirements for drinking 

water systems to ensure safe levels of disinfectants in the finished drinking water. The Total 

Coliform Rule requires a minimum residual disinfectant level of 0.2 mg/L of total residual 

chlorine for treated water entering the distribution system. Drinking water systems maintain 

residual disinfectants in the finished water to ensure disinfection throughout the distribution 

system. 

EPA also set primary standards for the finished drinking water including the 

maximum residual disinfectant levels (MRDLs) allowed. The MRDLs are:

• Chlorine: 4.0 mg/L; 

• Chloramines (as chlorine): 4.0 mg/L; and 

• Chlorine dioxide: 0.8 mg/L. 

8.4.3 Disinfection By-Products

EPA identified four parameters in its microbial and DBP (M/DBP) rules: 

chlorite, bromate, haloacetic acids, and trihalomethanes (71 FR 478). EPA set standards for these 

because they are good indicators of DBPs in disinfected drinking water, and because they are 

usually found at measurable concentrations (71 FR 478). Haloacetic acids include 

monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and 

dibromoacetic acid. Trihalomethanes include chloroform (CHCl2, trichloromethane), 
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8-15

bromodichloromethane (CHCl2Br), bromoform (tribromomethane), and dibromochloromethane 

(CHClBr2). 

Chlorite is a by-product from disinfection with chlorine dioxide. Bromate is a byproduct from disinfection with ozone. Trihalomethanes and haloacetic acids by-products form 

primarily from disinfection with chlorine, but also form when other disinfectants are used (71 FR 

478). 

WTPs can control DBPs by three methods: 1) removal of DBP precursors (i.e., 

natural organic matter), 2) modifying chlorination strategy, or 3) removing DBPs after 

formation, where the last of these is the most difficult process. Most plants typically focus on 

removing DBP precursors prior to chlorination. In general, aggregate DBP formation will 

decrease as the removal of total organic carbons (TOCs) increases. Studies have found that 

adding chlorine later (downstream) in the source water treatment process (e.g., adding after 

sedimentation) results in a reduction of DBP formation. However, some plants use the addition 

of chlorine to promote other pollutant removals prior to sedimentation (e.g., iron removal, 

manganese removal, taste/odor control, and color removal). Plants may also decrease DBP 

formation by the use of enhanced coagulation (U.S. EPA, 1999b).21 

8.5 PARAMETERS MEASURING ORGANIC MATTER AND OXYGEN IN 

THE WATER IN WTP RESIDUALS

Plants can measure organic matter and oxygen content in the wastewater using 

various parameters. Permit writers select which parameter works best for their NPDES 

permitting program. 

8.5.1 Biochemical Oxygen Demand 

BOD is an estimate of the oxygen-consuming requirements of organic matter 

decomposition under aerobic conditions. When WTP wastewaters are discharged to surface 

 

21 “Enhanced coagulation” is the term used to define the process of improving removal of DBP precursors (natural 

organic matter) by conventional filtration. “Enhanced softening” is the term used to define the process of improving 

removal of DBP precursors by precipitative softening.
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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waters, the microorganisms present in the naturally occurring microbial ecosystem decompose 

the organic matter contained in the wastewater. The decomposition process consumes oxygen 

and reduces the amount available for aquatic animals. 

BOD determinations include estimates of the amount of oxygen required for the 

degradation of both particulate and dissolved organic matter. Separation of these estimates is 

accomplished by first filtering the sample to remove particulate organic matter and then 

determining the BOD of the filtrate and dissolved BOD. The difference between BOD and 

dissolved BOD (DBOD) is an estimate of the contribution of particulate matter to total BOD. 

Also, BOD5 typically measures carbonaceous oxygen demanding organic material in the 

wastewater (CBOD). Nitrogenous oxygen demanding material (NBOD or NOD) is not likely to 

be a major concern for WTP wastewaters, as it is for certain nitrogen-containing industrial and 

municipal wastewaters and associated treatment systems.

DMR data collected with the 2007 industry questionnaire includes concentration 

of BOD in effluent discharges from conventional filtration plants. The data also includes CBOD 

concentrations in effluent discharges from membrane desalination and ion exchange plants. EPA 

included BOD and CBOD in the pollutant loadings estimate (see Section 9).

8.5.2 Dissolved Oxygen 

Dissolved oxygen (DO) measures the amount of oxygen in the water. Water 

bodies both produce and consume oxygen. A water body gains oxygen from the atmosphere and 

from plants as a result of photosynthesis. Running water, because of its churning, dissolves more 

oxygen than still water. Respiration by aquatic animals, decomposition, and various chemical 

reactions consume oxygen. 

WTP residuals may contain organic materials that are decomposed by 

microorganisms, using oxygen in the process. The amount of oxygen used is measured as BOD 

(discussed above). If more oxygen is consumed than produced, DO levels decline and some 

sensitive animals may move away, weaken, or die. 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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DO levels fluctuate seasonally and over a 24-hour period. The level also varies 

with water temperature and altitude. Cold water holds more oxygen than warm water, and water 

holds less oxygen at higher altitudes. 

EPA received DO data with the DMR data collected with the 2007 industry 

questionnaire. Because DO requirements are to maintain a minimum level, EPA did not include 

this pollutant in the pollutant loadings estimate (see Section 9).

8.6 OTHER POLLUTANTS IN WTP RESIDUALS

Other pollutant parameters found in residuals are primarily contaminants removed 

from the source water to produce finished drinking water. The pollutants discussed in this section

include chloride, nitrogen, pH, phosphorous, and radionuclides. 

8.6.1 Chloride

Chloride (Cl-) is a common anion in wastewaters and natural waters. Excessively 

high chloride concentrations in surface waters can impair their use as source waters for potable 

water supplies. If sodium is the predominant cation present, the water will have an unpleasant 

taste due to the corrosive action of chloride ions. Chloride is a constituent of TDS; dissolved 

solids are removed using membrane desalination and ion exchange processes. DMR data 

collected with the 2007 industry questionnaire includes concentrations of chlorides in effluent 

discharges from membrane desalination and ion exchange plants. EPA used these concentrations 

in its pollutant loadings analysis (see Section 9).

8.6.2 Nitrogen

Nitrogen may be present in WTP residuals (removed from the source water). 

WTPs are required to meet primary drinking water standards for nitrate (measured as nitrogen) 

and nitrite (measured as nitrogen). There are several parameters to measure forms of nitrogen, 

including total nitrogen, total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH4-N), and nitrite 

plus nitrate nitrogen (NO2 + NO3-N). TKN is defined as the sum of organic nitrogen and free 

ammonia. DMR data collected with the 2007 industry questionnaire includes total nitrogen 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-18

concentrations and ammonia concentrations. EPA used these concentrations in its pollutant 

loadings analysis (see Section 9).

8.6.3 pH

WTPs adjust the pH to optimize source water treatment, and the addition of lime 

for softening raises the pH of the water. The hydrogen-ion concentration in an aqueous solution 

is represented by the pH, which is defined as the negative logarithm of the hydrogen-ion 

concentration in a solution. On the pH scale ranging from zero to 14, a value of seven represents 

neutral conditions—the concentrations of hydrogen (H+) and hydroxyl ions (OH-) are equal. pH 

values less than seven indicate acidic conditions and values greater than seven represent basic 

conditions. 

EPA received pH data with the DMR data collected with the 2007 industry 

questionnaire. Because pH cannot be expressed as pounds in the discharge, EPA did not include 

this pollutant in the pollutant loadings estimate (see Section 9).

8.6.4 Phosphorus

The sources of phosphorus in WTP residuals and wastewater discharges include 

the source water and treatment chemicals for scale and corrosion control. In marine waters, 

phosphorus is not as much of a concern because of relatively high naturally occurring 

phosphorus concentrations. The impact of phosphorus in wastewater discharges into estuaries 

varies—in general, impacts decrease as salinity levels increase. DMR data collected with the 

2007 industry questionnaire includes phosphorus concentrations in effluent discharges. EPA 

used these concentrations in its pollutant loadings analysis (see Section 9).

8.6.5 Radionuclides

Low levels of radioactive contaminants, or radionuclides, occur in most drinking 

water sources and do not pose a public health risk. However, some drinking water sources have 

elevated radionuclide levels, usually occurring naturally (from certain rock types). Radionuclides 

regulated by EPA include the following: 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

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• Combined radium -226/-228: occurs naturally in some drinking water 

sources.

• (Adjusted) Gross alpha: occurs naturally in some drinking water sources. 

• Beta particle and photon radioactivity: contamination from facilities using 

or producing radioactive materials.

• Uranium: occurs naturally in some drinking water sources. 

Some drinking water sources located in the Midwest have elevated levels of 

radium -226/-228, while some sources in the West have elevated uranium levels (U.S. EPA, 

2006c). DMR data collected with the 2007 industry questionnaire includes concentration for 

radionuclides at some WTPs. However, since the presence of radionuclides is dependent on the 

source water, EPA did not use the DMR data to estimate pollutant loadings for the industry (see 

Section 9).

8.7 REFERENCES

American Public Health Association (APHA), 1995. Standard Methods for the Examination of 

Water and Wastewater, 19th edition, Washington, DC. 

Cornwell, 2002. David A. Cornwell, Michael J. Macphee and Richard Brown Trace 

Contaminants in Drinking Water Chemicals, American Water Works Association (AWWA) 

Research Foundation. Document Control Number (DCN) DW03737. 

Block, 2000. Disinfection, Sterilization, and Preservation. Block, Seymour S. Stanton. 

Lippincott (ISBN 0683307401). 2000. DCN DW03744. 

Center for Disease Control (CDC), 2006. Chlorine Residual Testing Fact Sheet, CDC SWS 

Project. Retrieved from http://cdc.gov/safewater/publications_pages/pubs_factsheets.htm. May 

23, 2006. DCN DW03745. 

U.S. Environmental Protection Agency (EPA), 1983. Methods for Chemical Analysis of Water 

and Wastes (EPA 600-4-79-020), Office of Research and Development, Washington, DC. 

U.S. EPA, 1999a. Disinfection Profiling and Benchmarking Guidance Manual. EPA 815-R-99-

013. August 1999. DCN DW03743. 

U.S. EPA, 1999b. Alternative Disinfectants and Oxidants Guidance Manual (EPA 815-R-99-

014), Office of Water, Washington, DC. DCN DW00647. 
Drinking Water Industry Report Section 8 – Pollutants in Water Treatment Plant Residuals

8-20

U.S. EPA, 2006a. Arsenic in Drinking Water (website), Office of Water. Retrieved from 

http://www.epa.gov/safewater/arsenic/basicinformation.html, last updated February 28, 2006. 

DCN DW01070. 

U.S. EPA, 2006c. Radionuclides in Drinking Water (website), Office of Water. Retrieved from 

http://www.epa.gov/safewater/standard/pp/radnucpp.html, last updated February 28, 2006. DCN 

DW00943. 

U.S. EPA, 2007. Phase I Discharge Monitoring Report (DMR) Database, Office of Water, 

Washington, DC. DCN DW03703. 

U.S. EPA, 2008. National Primary Drinking Water Standards (List of Drinking Water 

Contaminants and MCLs) (original document published in 2003, DCN DW00657), Office of 

Ground Water and Drinking Water, Washington, DC. Retrieved from 

http://www.epa.gov/safewater/contaminants/index.html Accessed April 2008 for updates.

U.S. EPA, 2009. Drinking Water Survey Response Database – Technical Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03790. 
9-1

SECTION 9

WATER TREATMENT PLANT POLLUTANT DISCHARGE 

ESTIMATES

As part of its effluent guidelines review process, EPA developed a variety of tools 

and methodologies to evaluate effluent discharges from various industrial categories. One of the 

main tools EPA used is an estimate of pollutant loadings being discharged from facilities within 

an industry sector. This section discusses how EPA estimated pollutant loadings for the drinking 

water treatment (DWT) industry. 

Pollutant loadings are the estimated amount of pollutants in water treatment plant 

(WTP) residuals currently being discharged to surface waters, whether directly from the plant or 

indirectly from publicly owned treatment works (POTWs) after taking POTW treatment 

effectiveness into account (i.e., pollutants that pass through the POTW). As part of the drinking 

water industry review, EPA estimated pollutant loadings from water treatment plants (WTPs) in 

the U.S. that serve more than 10,000 people. These loadings include contaminants in the source 

water that are removed to produce drinking water, and ingredients present in treatment chemicals 

added by the WTP. EPA did not have data to quantify the pollutant discharges attributed to 

source water contaminants and those attributed to treatment chemical addition. 

EPA estimated discharges for bulk parameters and chemical-specific parameters. 

Bulk parameters for the DWT pollutant loadings analysis include biochemical oxygen demand 

(BOD), carbonaceous BOD (CBOD), total nitrogen, total dissolved solids (TDS) and total 

suspended solids. The pollutant loadings estimated for bulk parameters may include the 

chemical-specific pollutant loading (e.g., TSS loadings include metals such as aluminum 

loadings). Because some portion of the chemical-specific pollutants are included in the bulk 

pollutant estimates, the two estimates should never be summed as this would constitute double 

counting of pollutants and result in an overestimate of the total pollutant loadings from DWT. 

EPA presents both bulk and chemical-specific parameters in this report since they offer different 

types of information but these estimates will always be presented separately to emphasize the 

non-additive nature of the data. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-2

Overall, EPA estimated that the discharges from the industry are 574 million 

pounds of bulk parameters per year and 352 million pounds per year of chemical-specific 

parameters, including metals and pollutants from disinfection with chlorine (chlorination). The 

majority of the bulk parameter loadings (over 98 percent) are TSS: 314 million pounds per year, 

primarily from precipitative softening plants, and TDS: 252 million pounds per year, primarily 

from ion exchange/adsorption plants. In EPA’s loadings analysis most of the chemical-specific 

parameter releases (over 98 percent) are due to the following five pollutants: 

1. Chlorides: 326 million pounds per year from membrane desalination and 

ion exchange/adsorption plants; 

2. Calcium: 14.4 million pounds per year from precipitative softening and 

coagulation/filtration plants;

3. Magnesium: 4.2 million pounds per year from precipitative softening and 

coagulation/filtration plants;

4. Lead: 1.97 million pounds per year, primarily from coagulation/filtration 

plants; and 

5. Aluminum: 1.48 million pounds per year, primarily from 

coagulation/filtration plants.

In addition to the pounds per year, EPA also estimated the toxic-weighted pound 

equivalent (TWPE) for the loadings parameters to determine the relative toxicity of DWT 

discharges22. EPA used toxic weighting factors (TWFs) that are specific to each chemical. EPA 

estimated 415,000 toxic-weighted pounds per year. Most of the TWPE (85 percent) is due to five 

pollutants: 

1. Total Residual Chlorine: 120,000 pound equivalents per year (lb-eq/yr);

2. Aluminum: 88,600 lb-eq/yr;

3. Copper: 60,700 lb-eq/yr;

4. Manganese: 41,800 lb-eq/yr; and

 

22 The DWT discharges include both the source water contaminants removed to produce drinking water and 

ingredients in treatment chemicals added by the WTP. EPA does not have sufficient source water characteristic data 

to determine the proportion of the total discharge loadings that come from source water contaminates versus 

material added by the WTP facilities as part of the drinking water treatment process.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-3

5. Fluoride: 41,100 lb-eq/yr.

This section describes EPA’s pollutant loadings analysis in the following 

subsections: 

• Section 9.1: Data sources used for the pollutant loadings analysis; 

• Section 9.2: Methodology to estimate pollutant loadings using model 

plants; 

• Section 9.3: Selection of pollutants to include in the loadings estimates;

• Section 9.4: Development of long-term averages for pollutants; 

• Section 9.5: Pollutant loadings estimate for model plants; and

• Section 9.6: National discharge estimate of pollutants from WTPs serving 

more than 10,000 people. 

9.1 DATA SOURCES FOR THE POLLUTANT LOADINGS ANALYSIS

For this analysis, EPA estimated pollutant loadings discharged in the base year of 

the questionnaire (2006). EPA used the following data sources as part of the pollutant loadings 

analysis:

• Discharge monitoring report (DMR) data from WTPs (U.S. EPA, 

2007): These data were used to calculate average pollutant concentrations 

in the discharges for model plants by source water treatment type and type 

of residuals treatment. EPA also used the flow rates reported to calculate 

average direct discharge flow rates for model plants by source water 

treatment type. EPA used data from 108 WTPs (direct dischargers with 

completed questionnaire responses and submitted DMR data). EPA 

supplemented pollutant concentration data for pollutants resulting from 

chlorination using four additional WTPs with DMR data.

• 2006 WTP Questionnaire Response Database – Technical Data (U.S. 

EPA, 2009a): EPA used the questionnaire responses to classify WTPs 

with DMR data into the four characteristics used to define model plants 

(see below). EPA also used the flow rates for indirectly-discharging plants 

to calculate average indirect discharge flow rates for model plants by 

source water treatment type.
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9-4

• EPA published maximum contaminant levels (MCLs) (U.S. EPA, 

2008b): MCLs are the maximum amount of a source water contaminant 

allowed in the finished drinking water. For one pollutant without DMR 

data (haloacetic acids), EPA used the MCL to estimate the average 

concentration discharged by model plants. 

• EPA National Estimates: WTP Counts for Pollutant Loadings (see 

Appendix A) EPA used the questionnaire responses to classify all WTPs 

in the sample frame into the four characteristics used to define model 

plants (see below).

9.2 METHODOLOGY TO ESTIMATE POLLUTANT LOADINGS USING 

MODEL PLANTS 

EPA used a model plant approach to estimate pollutant loadings from the drinking 

water treatment industry. EPA estimated the pollutant loadings being discharged from each of

the model plants and then calculated national discharges by multiplying the model treatment 

plant loadings by the number of WTPs represented by that model plant. A WTP may represent 

multiple types of source water treatment, but was counted only one time in the totals.

9.2.1 Model Plant Development

EPA used four factors representing the different types of WTPs in the U.S. to 

develop the model plants. EPA selected these four major factors because they govern the amount 

of pollutants discharged in residuals. The four factors are: 

• Type of WTP (such as coagulation and filtration or precipitative 

softening); 

• Type of residuals treatment in place;

• WTP size; and

• Discharge status (i.e., direct or indirect). 

Applying these four factors led to the development of distinct model plants. Each of the factors is 

described in detail below. 
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9.2.1.1 Type of WTP 

Based on data collected for the industry review, EPA determined that pollutant 

concentrations in residuals would vary by source water treatment type and type of residuals 

treatment in place. The five source water treatment types that EPA included in its analysis are the 

following: 

• Precipitative (i.e., lime) softening: includes all plants performing 

precipitative softening.

• Coagulation & filtration: includes conventional filtration plants, direct 

filtration plants, microfiltration (MF) plants also performing coagulation; 

and ultrafiltration (UF) plants also performing coagulation.

• Filtration only: includes plants performing filtration, MF, and UF without 

coagulation. 

• Membrane desalination: includes reverse osmosis (RO), nanofiltration 

(NF), electrodialysis (ED), and electrodialysis reversal (EDR) plants.

• Ion exchange & adsorption: includes plants performing ion exchange or 

adsorption (e.g., granular activated carbon). 

9.2.1.2 Type of Residuals Treatment

EPA identified two groups of residuals treatment that would affect the pollutant 

concentration in the effluent: 1) solid/water separation and 2) dechlorination. For most 

pollutants, WTPs use solid/water separation to treat residuals. For pollutants resulting from 

disinfection with chlorine, WTPs use dechlorination to treat the residuals. EPA determined that 

pollutant concentrations in residuals would vary by the type of residuals treatment in place. For 

pollutants other than those from disinfection with chlorine, EPA used two residuals treatment 

types for model plants: 1) solid/water separation or 2) no solid/water separation. For pollutants 

resulting from disinfection with chlorine, EPA also used two residuals treatment types for model 

plants: 1) dechlorination; and 2) no dechlorination. 
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9.2.1.3 WTP Size/Flow Rate 

In addition to the two characteristics affecting pollutant concentrations in 

discharges (source water treatment and residuals treatment), pollutant loadings are based on the 

volume of wastewater residuals generated. EPA determined that the discharge flow rate would 

vary by source water treatment type, plant size (correlated to population served), and discharge 

status (direct or indirect). EPA used the following population served size categories for the 

model plants:

• Population served between 10,001 and 50,000 people; 

• Population served between 50,001 and 100,000 people; 

• Population served between 100,001 and 500,000 people; and 

• Population served greater than 500,000 people. 

9.2.1.4 Discharge Status

In addition to using the discharge status (direct or indirect) to determine model 

plant effluent flow rates, EPA also used the discharge status when calculating pollutant loadings. 

For model plants discharging indirectly (i.e., wastewater treated by a POTW prior to discharge in 

waters of the U.S.), EPA accounted for the pollutants removed by the POTW (i.e., loadings are 

for pollutants that pass through the POTW). 

9.2.2 Estimation of Model Plant Pollutant Loadings 

EPA estimated pollutant loadings for each model plant and pollutant parameter

for the base year of 2006 using the equations below: 

Model Plant Load = (Concentration × Flow × Conversion Factor) (Eq. 9-1) 

where:

Model Plant Load = Pollutant loadings, in pounds per year (lbs/year).

Concentration = Annual average pollutant concentration, in milligrams per 

liter (mg/L).

Flow = Production-based discharge flow rate, in million gallons per 

day.

Conversion factor = 8.345 (to convert the loadings into lbs/year; derived from 

3.784 L/gal × 2.2 lbs/kg) x 365 days per year. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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EPA estimates the pollutant loadings from indirect dischargers to account for 

pollutant discharges that pass through the POTW to surface waters. Indirect discharges are 

treated at POTWs prior to discharge and EPA takes that treatment into account when calculating 

pollutant loadings. For indirect dischargers, EPA uses the results from Equation 9-1 and accounts 

for treatment at the POTW prior to discharge to surface waters using Equation 9-2: 

LoadPOTW = (1 – POTW % Removal) × Model Plant Load (Eq. 9-2) 

where:

LoadPOTW = Pollutant loadings discharged to surface water after 

treatment at the POTW, in pounds per year (lb/year). 

Model Plant Load = Pollutant loadings discharged to the POTW from Equation 

9-1 for each indirect discharger, in pounds per year 

(lb/year).

POTW % Removal = Percent removal at the POTW, shown in Appendix C 

Most of the POTW percent removal values are based on data from the Fate of 

Priority Pollutants in Publicly Owned Treatment Works and National Risk Management 

Research Laboratory (NRMRL) Treatability Database (U.S. EPA, 1982 and U.S. EPA, 1994) 

and are presented in Appendix C. The pollutant loadings and associated removals for indirect 

dischargers presented in this report represent pass through discharge from POTWs to receiving 

streams using the above equation.

EPA also estimated toxic-weighted pound equivalent (TWPE) pollutant loadings. 

To calculate TWPE, EPA multiplied the annual load (lb/yr) by a toxic weighting factor (TWF). 

TWFs account for differences in toxicity across pollutants and provide the means to compare 

mass loadings of different pollutants on the basis of their toxic potential. EPA multiplies a mass 

loading of a pollutant in pounds per year (lb/yr) by a pollutant-specific weighting factor to derive 

a "toxic-equivalent" loading (lb-equivalent/yr), or TWPE. EPA has developed TWFs for more 

than 1,900 pollutants based on aquatic life and human health toxicity data, as well as 

physical/chemical property data. EPA calculated TWPE using Equation 9-3. TWPEs do not 

apply to conventional pollutants or bulk parameters. 

TWPE (lb-eq-yr) = Annual Load (lb/yr) × TWF (Eq. 9-3) 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-8

The TWFs used for the pollutant loading estimates are presented in Appendix D 

(U.S. EPA, 2006). 

9.3 MODEL PLANT CONCENTRATION ESTIMATION

To estimate model plant loadings, Equation 9-1 lists two variables: concentration 

and flow rate. This section discusses how EPA estimated pollutant concentrations in the model 

plant effluent discharges and Section 9.4 discusses how EPA estimated effluent discharge flow 

rates for the model plants.

9.3.1 Selection of Pollutant Parameters for Pollutant Loadings Analysis 

EPA identified two groups of pollutant parameters for the loadings analysis based 

on type of residual treatment that affects the pollutant discharges: 1) pollutants resulting from the 

disinfection with chlorine (chlorination); and 2) all other pollutants. Chlorination pollutants 

include: total trihalomethanes, chloroform, bromodichloromethane, bromoform, 

dibromochloromethane, haloacetic acids, chloramines, and total residuals chlorine. To treat 

chemicals resulting from disinfection with chlorine, WTPs perform dechlorination. To treat all 

other pollutants, WTPs perform solid/water separation. 

EPA selected a subset of pollutants for the model plant loadings estimates based 

on three main factors: 1) ability to estimate pollutant loadings in pounds per year (lbs/yr), 2) 

availability of concentration data from the DMR submittals, and 3) presence of the pollutant in 

the residuals for the source water treatment type.

23 

EPA included three pollutants without DMR data in the pollutant loadings 

analysis. Bromoform, haloacetic acids, and chloramines are by-products of disinfection with 

chlorine. EPA estimated loadings for bromoform and haloacetic acids using a mass balance 

approach, which allows the estimation of pollutant loadings without DMR data. For bromoform, 

 

23 The memorandum entitled Pollutant Loadings Estimates for Drinking Water Treatment Plants: Model Plants and 

National Estimates (ERG, 2009) details the selection of pollutants for the loadings analysis. 
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9-9

EPA transferred the effluent concentration from chloroform. For haloacetic acids, EPA used the 

drinking water MCL to estimate pollutant loadings. For chloramines, EPA performed a 

qualitative review of the discharges of chloramines from WTPs. 

EPA selected 27 pollutants to include in the loadings analysis. For pollutants 

resulting from chlorination, EPA estimated discharge concentrations based on two factors: 1) 

whether the WTP disinfects with chlorine and 2) whether residuals are treated using 

dechlorination prior to discharge). If the WTP does not use chlorine for disinfection, EPA set the 

loadings for the chlorination pollutants equal to zero. EPA assumed that WTPs that do not 

disinfect with chlorine would not discharge pollutants resulting from chlorination. EPA did not 

differentiate between source water treatment types (e.g., assumed concentrations would be the 

same for precipitative softening plants as for plants with only filtration). Table 9-1 presents the 

pollutants selected for the loadings estimates for each source water treatment type.

Table 9-1. Pollutants Included in the Loadings Estimates 

Parameter

Precipitative 

Softening

Coagulation 

and Filtration

Filtration 

Only

Membrane 

Desalination

Ion Exchange 

and Adsorption 

Conventionals

BOD X a X X a

CBOD5 X X

TSS X X X X X

Other Solids

TDS c X

Chlorides X X

Nitrogen

Nitrogen, Total c X a X X a X X

Ammonia X a X X a X X

Metals

Aluminum X X X

Barium X a X 

Cadmium X X

Calcium X a X 

Copper X a X X X

Fluoride X X X X X

Iron X X X X X

Lead X a X X a X

Magnesium X a X

Manganese X X X X
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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Table 9-1. Pollutants Included in the Loadings Estimates 

Parameter

Precipitative 

Softening

Coagulation 

and Filtration

Filtration 

Only

Membrane 

Desalination

Ion Exchange 

and Adsorption 

Nickel X a X 

Phosphorus X a X X a X X

Zinc X a X X

Pollutants from Chlorination and Disinfection By-Products

Bromodichloromethane X b

Bromoform X b

Chlorine, Total Residual X b

Chloroform X b

Dibromochloromethane X b

Haloacetic acids X b

Trihalomethane X b

a – Transfer concentrations from coagulation/filtration source water treatment type. Note that all but three of the 

questionnaire respondents that perform precipitative softening also perform coagulation and filtration (U.S. EPA, 

2009a); therefore EPA included the same pollutants in the loadings analysis for each model plant type. For filtration 

only, EPA transferred pollutant concentrations from coagulation and filtration for source water contaminant 

pollutants that may be concentrated in the residuals.

b – Pollutant discharges expected only from WTPs that disinfect with chlorine. For pollutant loading estimates, EPA 

did not group chlorination chemical concentrations by source water treatment type. 

c – Bulk parameters represent more than one pollutant. For example, Total Nitrogen includes ammonia nitrogen 

(NH3) as well as organic nitrogen, nitrate, and nitrite. EPA estimated loads for total nitrogen in lbs/yr. EPA 

estimated loads for ammonia nitrogen in lbs/yr and TWPE/yr. EPA does not estimate TWPE for bulk parameters, 

because TWFs apply to specific chemicals. TDS is also a bulk parameter that includes chlorides.

In addition to grouping DMR data by source water treatment type, EPA used the 

questionnaire response database (U.S. EPA, 2009a) to determine whether the WTP performed 

residuals treatment prior to discharge. WTPs use solid/water separation to remove most 

pollutants from the residuals. Three of the plants fell under two source water treatment types. 

EPA used the plant’s DMR data to characterize discharges from both source water treatment 

types. Table 9-2 summarizes the WTPs with DMR data and whether solid separation is used to 

treat residuals. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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Table 9-2. Type of Source Water Treatment and Residuals in Place (Solid/Water 

Separation) for WTPs with DMR Data 

Source Water Treatment Type

Total Number of 

Plants

Number of Plants without 

Solid/Water Separation 

(Untreated)

Number of Plants with 

Solid/Water Separation 

(Treated)

Precipitative softening 24 6 18

Coagulation/filtration 76 6 70

Filtration only (including MF and 

UF)

5 1 4

Membrane desalination a 2 2 0

Ion exchange and adsorption b 4 1 3

Total c 108 15 93

Source: U.S. EPA, 2009a and U.S. EPA, 2007.

a – DMR data available for high pressure membrane (reverse osmosis and nanofiltration) plants. Data were not 

available for electrodialysis and electrodialysis reverse plants; assume discharge similar pollutants and at similar 

concentrations to high pressure membrane plants. Desalination membrane plants typically do not treat the 

concentrate prior to discharge (Malmrose, et al., 2004).

b – DMR data available for ion exchange plants. Data were not available for adsorption plants; assume discharge 

similar pollutants and at similar concentrations to ion exchange plants.

c – A WTP may represent multiple types of source water treatment, but was counted only one time in the totals.

To remove pollutants resulting from disinfection with chlorine, WTPs use 

dechlorination to treat residuals. Table 9-3 summarizes the WTPs with DMR data including 

whether the WTP uses chlorine for disinfection and whether dechlorination is used to treat 

residuals.
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Table 9-3. Type of Source Water Treatment and Residuals in Place (Dechlorination) for

WTPs with DMR Data

Source Water 

Treatment Type

Total 

Number of 

Plants

Number of Plants 

Performing 

Chlorination

Number of Plants 

without Dechlorination 

(Untreated)

Number of Plants 

with Dechlorination 

(Treated)

Lime softening 24 22 17 5

Coagulation/filtration 76 69 47 22

Filtration only (including 

MF and UF)

5 4 3 1

Membrane desalination a 2 2 1 1

Ion exchange and 

adsorption b

4 4 2 2

Total c 108 d 98 68 30

Source: U.S. EPA, 2009a and U.S. EPA, 2007.

a – DMR data available for high pressure membrane (reverse osmosis and nanofiltration) plants. Data were not 

available for electrodialysis and electrodialysis reverse plants; assume discharge similar pollutants and at similar 

concentrations to high pressure membrane plants. 

b – DMR data available for ion exchange plants. Data were not available for adsorption plants; assume discharge 

similar pollutants and at similar concentrations to ion exchange plants.

c – A WTP may represent multiple types of source water treatment, but was counted only one time in the totals.

d – EPA used DMR data collected with the 2007 industry questionnaire from an additional four WTPs to 

characterize discharge of disinfection by-products (U.S. EPA, 2007). These four WTPs are not included in the above 

total because a complete survey review was not completed for the four WTPs; therefore, these four WTPs are not 

included in the technical questionnaire response database (U.S. EPA, 2009a).

9.3.2 Development of Long-Term Average Concentrations for Pollutants 

EPA estimated the annual average pollutant concentrations (long-term averages) 

for each model plant, based on source water treatment type and residuals treatment in place. EPA 

does not expect WTP size or discharge status to affect the concentration in the effluent discharge. 

EPA used DMR data from WTPs in the questionnaire database with matching source water 

treatment type and residuals treatment in place to estimate long-term average concentrations. 

EPA used alternate approaches for two pollutants without DMR data: 

1. Bromoform (tribromomethane): Transfer from similar trihalomethane 

(chloroform); and

2. Haloacetic acids (5HAA’s): Use MCL as concentration.

EPA used the DMR data supplied with the 2007 industry questionnaire response 

to estimate annual averages for each WTP and pollutant. To calculate the annual average 

pollutant concentration, EPA took the arithmetic mean of the samples taken in 2006. For samples 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-13

showing presence of a chemical but at concentrations below detection limits, EPA used one-half 

of the method detection limit value to estimate pollutant loadings. For chemicals never detected 

in the effluent, EPA used a concentration of zero for the loadings estimates. 

EPA averaged the DMR pollutant concentrations for each source water treatment 

type and residuals treatment in place (i.e., model plant). For most pollutants, EPA calculated 

annual average pollutant concentrations by the source water treatment type and whether the WTP 

treated residuals using solid/water separation. For pollutants resulting from disinfection with 

chlorine, EPA differentiated the average pollutant concentration only by whether or not the plant 

used chlorine for disinfection and performed dechlorination. EPA describes the long-term 

average calculations in more detail in the memorandum entitled, Pollutant Loadings Estimates 

for Drinking Water Treatment Plants (ERG, 2009). 

Table 9-4 presents the model plant long-term average concentrations for all 

pollutants except those resulting from chlorination. These are grouped by source water treatment 

type and residuals treatment in place. EPA did not apply any toxic weighting factors (TWFs) to 

the long-term averages; TWFs are applied to the pounds per year loadings. 

Table 9-5 presents the long-term average concentrations for pollutants resulting 

from chlorination. These are grouped only by the presence of dechlorination as part of residuals 

treatment. EPA did not apply any toxic weighting factors (TWFs) to the long-term averages; 

TWFs are applied to the pounds per year loadings. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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Table 9-4. Long-Term Average Concentrations from DMR Data by Source Water Treatment Type and Residuals Treatment 

(mg/L) 

Pollutant

Precipitative Softening

Coagulation and 

Filtration Filtration only Membrane Desalination

Ion Exchange and 

Adsorption

Solids 

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Solids

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Conventionals

BOD 1.44 (b) 1.44 (b) 1.44 1.44 (e) 1.44 (b) 1.44 (b) (d) (d) (d) (d)

CBOD5 (d) (d) (d) (d) (d) (d) 1.00 (f) 1.00 1.00 (f) 1.00

TSS 5.89 1,430 54.5 135 2.62 22.5 2.86 (f) 2.86 6.38 (a)

Other Solids

TDS (d) (d) (d) (d) (d) (d) (d) (d) 8,570 8,570 (e)

Chlorides (c) (c) (c) (c) (c) (c) 7,120 (f) 7,120 2,930 7,120

Nitrogen

Nitrogen, Total 3.64 (b) 3.64 3.64 3.64 (e) 3.64 (b) 3.64 (b) 2.95 (f) 2.95 0.472 0.908

Ammonia 0.482 (b) 0.482 (b) 0.482 0.482 (e) 0.482 (b) 0.482 (b) 1.55 (f) 1.55 0.0894 0.0894 (e)

Metals

Aluminum 0.177 (a) 2.16 (a) 0.919 0.919 (e) (d) (d) (d) (d)

Barium 0.0100 (b) 0.0100 (b) 0.0100 0.0100 (e) (d) (d) (d) (d) (d) (d)

Cadmium (d) (d) (d) (d) (d) (d) 0.00104 (f) 0.00104 0.00104 (f) 0.00104

Calcium 8.73 (b) 8.73 (b) 8.73 8.73 (e) (d) (d) (d) (d) (d) (d)

Copper (g) 0.0693 (b) 0.0693 (b) 0.0693 0.0693 (e) (d) (d) 0.000891(f) 0.000891 0.00149 (a)

Fluoride 0.665 1.14 0.684 0.684 (e) 0.183 0.183 (e) 2.11 (f) 2.11 2.11 (f) 2.11

Iron 0.115 0.115 (e) 2.73 4.31 0.128 0.128 (e) 1.46 (f) 1.46 0.361 (a)

Lead (g) 0.00569 (b) 0.00569 (b) 0.00569 0.00569 (e) 0.00569 (b) 0.00569 (b) (d) (d) 0.00 0.00

Magnesium 2.58 (b) 2.58 (b) 2.58 2.58 (e) (d) (d) (d) (d) (d) (d)

Manganese 0.346 0.346 (e) 0.442 (a) 0.0574 0.0574 (e) (d) (d) 0.368 0.368 (e)

Nickel (g) 0.00 (b) 0.00 (b) 0.00 0.00 (e) (d) (d) (d) (d) (d) (d)
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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Table 9-4. Long-Term Average Concentrations from DMR Data by Source Water Treatment Type and Residuals Treatment 

(mg/L) 

Pollutant

Precipitative Softening

Coagulation and 

Filtration Filtration only Membrane Desalination

Ion Exchange and 

Adsorption

Solids 

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Solids

Separation

No Solids 

Separation

Solids 

Separation

No Solids 

Separation

Phosphorus, 

Total

0.423 (b) 0.423 (b) 0.423 0.423 (e) 0.423 (b) 0.423 (b) 0.0678 (f) 0.0678 0.0965 (a)

Zinc (g) 0.316 (b) 0.316 (b) 0.316 0.316 (e) (d) (d) (d) (d) 0.00473 0.00473 (e)

Source: U.S. EPA, 2007

a – EPA calculated average concentration using all plants within the source water treatment type group regardless of residuals treatment in place. The average concentration for 

WTPs without solid/water separation was less than the average concentration for WTPs with solid/water separation.

b – Transferred pollutant concentration from coagulation and filtration because no other data were available. 

c – DMR data available for ion exchange/membrane desalination plants only. Note that one plant with data also listed coagulation and filtration; however the chlorides load is 

expected to be due to ion exchange.

d – No DMR data were available for this pollutant and model plant. EPA did not estimate loadings for this pollutant and model plant.

e – DMR data available only for WTPs that perform solid/water separation. EPA used the treated concentration to estimate untreated pollutant loadings.

f – DMR data available only for WTPs that do not perform solid/water separation. EPA used the untreated concentration to estimate treated pollutant loadings.

g – Percent of non-detect samples in DMR databases exceeds 10 percent. Nickel was not detected above the detection limit for any sample; therefore EPA set the LTA equal to 

zero (0).
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Table 9-5. Long-Term Average Concentrations for Pollutants Resulting from Disinfection 

with Chlorine

Pollutant

Dechlorination 

Performed

No Dechlorination 

Performed

Source for 

Concentration

Total trihalomethanes 0 mg/L (a) 0.00223 mg/L DMR Data 

Chloroform (CHCl2) 0 mg/L (a) 0.050 mg/L DMR Data

Bromodichloromethane (CHCl2Br, 

Dichlorobromomethane)

0 mg/L (a) 0.010 mg/L DMR Data

Bromoform (tribromomethane) 0 mg/L (a) 0.050 mg/L Transfer from 

Chloroform

Dibromochloromethane (CDBM; 

Chlorodibromomethane)

0 mg/L (a) 0.002 mg/L DMR Data

Haloacetic acids (5HAA’s) 0 mg/L (a) 0.060 mg/L MCL

Total residual chlorine (b) 0.144 mg/L 0.192 mg/L DMR Data

a – No DMR data were available. EPA assumed that, in WTPs that perform dechlorination, the effluent 

concentrations of these parameters are not present (i.e., are zero).

b – Percent of non-detect samples in DMR databases exceeds 10 percent.

9.3.3 DMR Data Limitations 

The DMR data received as part of the industry questionnaire includes limitations 

which affected the calculation of pollutant loadings estimates. In these cases, EPA used its best 

engineering judgment to calculate loadings. The primary data limitation is that there was no 

standard list of pollutants monitored by all WTPs. The DMR data submitted by each WTP 

includes data for only those pollutants listed in the plant’s NPDES permit. For example, a state 

may have a core set of pollutants that WTPs need to monitor; however, additional pollutant 

monitoring might be more random and dependent on the watershed characteristics of the source 

water. Furthermore, it is not known why pollutants are monitored at specific facilities, that is, 

whether the monitoring is due to suspected problems so that these facilities are more likely to be 

representative of high loading plants than not. On the other hand, it may be the case that facilities 

with lower loading levels were more likely to report their DMR data with the 2007 industry 

questionnaire In the absence of additional information, it’s not possible to describe the potential 

magnitude and direction of bias, if any. Where appropriate, EPA transferred pollutant 

concentrations from another model plant group. 

EPA also found that some model plants had more data than others. For example, 

EPA had DMR data for 24 precipitative softening plants and for 76 coagulation/filtration plants. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

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Whereas, EPA had a limited number of WTPs with DMR data for the three other source water 

treatment types: filtration only (5 WTPs), membrane desalination (2 WTPs), and ion 

exchange/adsorption (4 WTPs). For the filtration only WTPs, 4 WTPs represented discharges 

following solid/water separation and only one WTP represented untreated discharges. For the ion 

exchange/adsorption, 3 WTPs represented discharges following solid/water separation and only 

one WTP represented untreated discharges. Neither membrane desalination plants treated the 

discharge using solid/water separation prior to discharge. In some cases, only a single WTP had 

DMR data for a pollutant in a certain model plant group. EPA used these data to estimate the 

pollutant concentration, however, EPA does not have the data available to determine whether the 

concentration reported is representative of a majority of discharges for the model plant group. 

Membrane desalination plants typically do not treat the concentrate prior to 

discharge (Malmrose, et al., 2004). Therefore, EPA used the same pollutant concentration to 

represent WTPs treating residuals via solid/water separation as those WTPs not treating residuals 

prior to discharge. EPA's questionnaire database included only two membrane desalination 

plants that performed solid/water separation. Both of these WTPs are zero discharge plants (U.S. 

EPA, 2009a). 

Where appropriate, EPA transferred concentrations or modified the calculation of 

average pollutant concentrations to use for the pollutant loading estimates. The memorandum 

entitled, Pollutant Loadings Estimates for Drinking Water Treatment Plants (ERG, 2009), 

provides details. 

9.4 MODEL PLANT FLOW RATE ESTIMATION

As noted above, EPA determined that the effluent flow rate would vary based on 

three of the four model plant characteristics: 1) source water treatment; 2) population served size; 

and 3) discharge type. EPA did not distinguish flow rates by residuals treatment type; EPA 

assumed that the flow rate would not be significantly altered by solid/water separation or 

dechlorination. Solid/water separation results in removal of certain parameters from the 

wastewater (e.g., TSS, metals); however EPA does not believe this will result in a significant 

difference in the wastewater volume discharged. The dechlorination process is the addition of 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-18

sulfur chemicals (e.g., sodium metabisulfite) to react with chlorine in the wastewater and remove 

free chlorine and total combined chlorine residual. The addition of the sulfur chemicals is not 

expected to significantly impact the wastewater volume discharged. 

EPA estimated the model plant flow rates using reported flow data from DMRs 

submitted with the 2007 industry questionnaire and the responses to the survey (U.S. EPA, 2007; 

U.S. EPA, 2009a). As such, the loadings estimate will be reflective of actual flow rather than 

design flow. An additional data limitation for this analysis is that the flow rates from 2006 (either 

in response to the 2007 industry questionnaire or included with the 2006 DMR data) might not 

be typical. 

 

9.4.1 Review of DMR and Questionnaire Data

EPA categorized each of the 108 WTPs that submitted questionnaire responses 

and DMR data into a model plant type to calculate flow rate. EPA used the DMR data to 

estimate direct discharge flow rates and questionnaire responses to estimate indirect discharge 

flow rates and population served. EPA then used the DMR and questionnaire data to estimate 

model plant effluent flow rates. For direct discharging WTPs, EPA assumed continuous 

discharge (i.e., discharge occurs 365 days per year). 

For indirect dischargers, EPA reviewed responses to the questionnaire to 

determine whether the discharge was continuous, batch, or an emergency discharge. For 

continuous indirect discharges, EPA assumed the discharge occurred 365 days per year. For 

batch discharges, EPA multiplied the volume discharged by the number of batches per year and 

then normalized the flow rate to 365 days per year. For example, if a WTP discharged 1,000,000 

gallons (1 MG) for 20 days of the year, then the flow rate normalized for the year was calculated 

as follows: 

(1 MG × 20 DPY)/365 = 0.055 MGD (Eq. 9-4) 

If the number of batch discharges was greater than 365 days per year, EPA assumed the 

discharge occurred 365 days per year, for the purpose of estimating the average daily discharge 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-19

rate. For example, if a WTP reported 1,100 batch discharges annually and each batch was 1 MG, 

EPA calculated the discharge as follows:

(1 MG × 1,100 Batches)/365 = 3.0 MGD (Eq. 9-5) 

For indirect dischargers reporting both continuous and batch flow rates, EPA summed the two 

quantities to estimate total daily flow rate from the WTP. EPA excluded emergency discharge 

volumes unless no other discharges (i.e., continuous or batch) were reported. 

9.4.2 Model Plant Effluent Flow Rate Results

For each model plant group, EPA calculated an average effluent flow rate using 

the data from individual WTPs. Table 9-6 presents the model plant flow rates (range of 

individual WTP flow rates and average) estimated for each source water treatment type, 

population served, and discharge type. 

Table 9-6. Model Plant Effluent Flow Rates

Treatment Plant 

Type

Population 

Served

Direct 

Discharge 

Effluent Flow 

Rate Range 

(MGD)

Direct 

Discharge 

Average 

Effluent 

(MGD)

Indirect 

Discharge 

Effluent Flow 

Rate Range 

(MGD) (a)

Indirect 

Discharge 

Average Effluent 

(MGD) (a)

Precipitative 

Softening

10,001 to 50,000 0.04175 to 

0.432

0.235 0.00021 to 0.469 0.144

50,001 to 100,000 0.062 to 0.512 0.312 0.00082 to 0.830 0.297

100,001 to 

500,000

0.067 to 20.1 3.79 0.00091 to 1.057 0.339

>500,000 3.56 to 7.79 5.68 (b) 0.339

Coagulation & 

Filtration

10,001 to 50,000 0.0114 to 0.903 0.209 4.5E-7 to 0.61 0.089

50,001 to 100,000 0.003 to 1.26 0.376 4.5E-6 to 1.1 0.168

100,001 to 

500,000

0.0046 to 3.5 1.22 0.000146 to 3.13 0.276

>500,000 0.502 to 7.04 3.47 0.0142 to 0.985 0.291

Filtration Only 10,001 to 50,000 0.0656 to 0.337 0.179 8.6E-7 to 0.18 0.040

50,001 to 100,000 (b) 0.179 0.00063 to 

0.341(d)

0.171(d)

100,001 to 

500,000

0.734 to 1.36 1.05 0.00063 to 

0.341(d)

0.171(d)

>500,000 (b) 1.05 (b) 0.171
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-20

Table 9-6. Model Plant Effluent Flow Rates

Treatment Plant 

Type

Population 

Served

Direct 

Discharge 

Effluent Flow 

Rate Range 

(MGD)

Direct 

Discharge 

Average 

Effluent 

(MGD)

Indirect 

Discharge 

Effluent Flow 

Rate Range 

(MGD) (a)

Indirect 

Discharge 

Average Effluent 

(MGD) (a)

Membrane 

Desalination

10,001 to 50,000 (c) 0.627 1.5E-5 to 0.00274 0.002

50,001 to 100,000 (c) 1.15 (c) 0.26

100,001 to 

500,000

(b) 1.15 0.122 to 0.997 0.560

>500,000 (f) Not applicable (f) Not applicable

Ion Exchange & 

Adsorption 

10,001 to 50,000 0.0576 to 0.185 0.120 2.8E-6 to 0.7(e) 0.110(e)

50,001 to 100,000 (c) 1.15 2.8E-6 to 0.7(e) 0.110(e)

100,001 to 

500,000

(f) Not applicable (b) 0.110

>500,000 (f) Not applicable (f) Not applicable

Sources: U.S. EPA, 2007; U.S. EPA, 2009a 

MGD – Million Gallons per Day

a – EPA calculated annual normalized flow rates using indirect discharge data from the questionnaire response 

database for the 2006 industry questionnaire (U.S. EPA, 2008a). EPA multiplied the gallons per day by the number 

of days per year reported in the questionnaire; and then divided by 365 days per year.

b – No flow rate data were available for this population category. For pollutant loadings analysis, EPA transferred 

the average flow rate from the next smallest population group with the same treatment plant type.

c – Not applicable: only one WTP falls into this characteristic group.

d – For the indirect discharge effluent flow rate, EPA combined the flow rate averages for plants serving 50,001 to 

100,000 people with the flow rate averages for plants serving between 100,001 and 500,000. The average flow rate 

for the larger population group is smaller than the average flow rate for the smaller population group suggesting that 

this size distinction is not adequately represented or less meaningful. 

e – For the indirect discharge effluent flow rate, EPA combined the flow rate averages for plants serving 10,001 to 

50,000 people with the flow rate averages for plants serving between 50,001 and 100,000. The average flow rate for 

the larger population group is smaller than the average flow rate for the smaller population group suggesting that 

this size distinction is not adequately represented or less meaningful.

f – The national estimates do not include any WTPs in this population category.

9.5 RESULTS OF THE POLLUTANT LOADINGS ESTIMATE FOR MODEL 

PLANTS

EPA calculated the pollutant loadings and TWPE for each model plant as 

described above. EPA did not have data to quantify the pollutant discharges attributed to source 

water contaminants and those attributed to treatment chemical addition. The portion from source 

water contaminants would be site-specific; WTPs did not submit source water quality data to pair 

with the effluent discharge data. However, WTPs might collect source water quality data to help 

optimize addition of treatment chemicals. These data can be used by permit writers when 

developing best professional judgment (BPJ) permit limitations. From literature data, membrane 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-21

concentrate has very few process-added chemicals and the pollutants are primarily from the 

source water (U.S. EPA, ASCE, AWWA, 1996). 

Tables 9-7 through 9-10 each show the pollutant loading estimate for model 

plants by the five source water treatment types and by residuals treatment type (with or without 

solid/water separation) for direct and indirect dischargers. Each table is for a different population 

served size category.

Table 9-7. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 10,001 to 50,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Precipitative Softening

Bulk Parameters

BOD 1030 68.8 1030 68.8

Nitrogen, Total 2610 679 2610 679

TSS 4220 270 1030000 65600

Total Bulk Parameters 

(Precipitative Softening)

7860 1017.8 1033640 66347.8

Specific Parameters

Aluminum 127 8.2 6.98 0.452 127 8.2 6.98 0.452

Ammonia 345 0.383 129 0.143 345 0.383 129 0.143

Barium 7.16 0.0143 1.96 0.00391 7.16 0.0143 1.96 0.00391

Calcium 6250 0.175 3500 0.0979 6250 0.175 3500 0.0979

Copper 49.6 31.5 4.8 3.04 49.6 31.5 4.8 3.04

Fluoride 476 16.7 113 3.94 814 28.5 192 6.74

Iron 82.3 0.461 9.07 0.0508 82.3 0.461 9.07 0.0508

Lead 4.07 9.12 0.562 1.26 4.07 9.12 0.562 1.26

Magnesium 1840 1.6 968 0.838 1840 1.6 968 0.838

Manganese 248 17.5 90.1 6.34 248 17.5 90.1 6.34

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 303 57.4 303 57.4

Zinc 226 10.6 28.9 1.35 226 10.6 28.9 1.35

Total Specific Parameters 

(Precipitative Softening)

9,958 96 4,910 18 10,296 108 4,989 20
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-22

Table 9-7. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 10,001 to 50,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Coagulation & Filtration

Bulk Parameters

BOD 921 42.8 921 42.8

Nitrogen, Total 2320 422 2320 422

TSS 34700 1550 85800 3830

Total Bulk Parameters 

(Coagulation & Filtration)

37941 2014.8 89041 4294.8

Specific Parameters

Aluminum 1380 89 52.9 3.42 1380 89 52.9 3.42

Ammonia 308 0.341 80.2 0.089 308 0.341 80.2 0.089

Barium 6.38 0.0127 1.22 0.00243 6.38 0.0127 1.22 0.00243

Calcium 5570 0.156 2170 0.0609 5570 0.156 2170 0.0609

Copper 44.2 28.1 2.98 1.89 44.2 28.1 2.98 1.89

Fluoride 436 15.3 72.1 2.52 436 15.3 72.1 2.52

Iron 1740 9.76 134 0.751 2750 15.4 211 1.18

Lead 3.63 8.13 0.349 0.783 3.63 8.13 0.349 0.783

Magnesium 1640 1.42 602 0.521 1640 1.42 602 0.521

Manganese 282 19.8 71.5 5.03 282 19.8 71.5 5.03

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 270 35.7 270 35.7

Zinc 201 9.45 18 0.842 201 9.45 18 0.842

Total Specific Parameters 

(Coagulation & Filtration)

11,881 181 3,241 16 12,891 187 3,318 16

Filtration Only

Bulk Parameters

BOD 788 19.1 788 19.1

Nitrogen, Total 1990 188 1990 188

TSS 1430 33.2 12200 285

Total Bulk Parameters 

(Filtration Only)

4208 240.3 14978 492.1
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-23

Table 9-7. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 10,001 to 50,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Specific Parameters

Aluminum 501 32.4 10 0.649 501 32.4 10 0.649

Ammonia 263 0.292 35.7 0.0396 263 0.292 35.7 0.0396

Fluoride 100 3.5 8.59 0.301 100 3.5 8.59 0.301

Iron 69.9 0.392 2.8 0.0157 69.9 0.392 2.8 0.0157

Lead 3.1 6.95 0.156 0.348 3.1 6.95 0.156 0.348

Manganese 31.3 2.2 4.13 0.291 31.3 2.2 4.13 0.291

Phosphorus, Total 231 15.9 231 15.9

Total Specific Parameters 

(Filtration Only)

1,199 46 77 2 1,199 46 77 2

Membrane Desalination

Bulk Parameters

CBOD5 1910 0.52 1910 0.52

Nitrogen, Total 5640 6.01 5640 6.01

TSS 5460 1.43 5460 1.43

Total Bulk Parameters 

(Membrane Desalination)

13010 7.96 13010 7.96

Specific Parameters

Ammonia 2960 3.29 4.52 0.00501 2960 3.29 4.52 0.00501

Cadmium 1.98 45.7 0.000492 0.0114 1.98 45.7 0.000492 0.0114

Chlorides 13600000 331 14500 0.353 13600000 331 14500 0.353

Copper 1.7 1.08 0.000673 0.000427 1.7 1.08 0.000673 0.000427

Fluoride 4030 141 3.89 0.136 4030 141 3.89 0.136

Iron 2800 15.7 1.26 0.00705 2800 15.7 1.26 0.00705

Phosphorus, Total 129 0.1 129 0.1

Total Specific Parameters 

(Membrane Desalination)

13,609,923 538 14,510 1 13,609,923 538 14,510 1

Ion Exchange and Adsorption

Bulk Parameters

CBOD5 366 36.4 366 36.4

Nitrogen, Total 172 67.2 332 129

TDS 3130000 2640000 3130000 2640000

TSS 2330 223 2330 223

Total Bulk Parameters 

(Ion Exchange & 

Adsorption)

3132868 2640326.6 3133028 2640388.4
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-24

Table 9-7. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 10,001 to 50,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Specific Parameters

Ammonia 32.7 0.0363 18.2 0.0203 32.7 0.0363 18.2 0.0203

Cadmium 0.378 8.75 0.0345 0.797 0.378 8.75 0.0345 0.797

Chlorides 1070000 26 417000 10.2 2600000 63.3 1010000 24.7

Copper 0.544 0.345 0.0787 0.0499 0.544 0.345 0.0787 0.0499

Fluoride 771 27 273 9.55 771 27 273 9.55

Iron 132 0.74 21.8 0.122 132 0.74 21.8 0.122

Lead 0 0 0 0 0 0 0 0

Manganese 134 9.47 73.1 5.15 134 9.47 73.1 5.15

Phosphorus, Total 35.3 10 35.3 10

Zinc 1.73 0.081 0.33 0.0155 1.73 0.081 0.33 0.0155

Total Specific Parameters 

(Ion Exchange & 

Adsorption)

1,071,108 72 417,397 26 2,601,108 110 1,010,397 40

Source: U.S. EPA, 2008a; U.S. EPA, 2009b

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs 

for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr. 

Table 9-8. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 50,001 to 100,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr)

Precipitative Softening

Bulk Parameters

BOD 1370 142 1370 142

Nitrogen, Total 3460 1400 3460 1400

TSS 5610 556 1360000 135000

Total Bulk Parameters 

(Precipitative Softening)

10440 2098 1364830 136542
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-25

Table 9-8. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 50,001 to 100,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr)

Specific Parameters

Aluminum 168 10.9 14.4 0.932 168 10.9 14.4 0.932

Ammonia 459 0.509 266 0.295 459 0.509 266 0.295

Barium 9.52 0.0189 4.05 0.00807 9.52 0.0189 4.05 0.00807

Calcium 8300 0.232 7210 0.202 8300 0.232 7210 0.202

Copper 65.9 41.8 9.89 6.28 65.9 41.8 9.89 6.28

Fluoride 633 22.1 232 8.13 1080 37.9 397 13.9

Iron 109 0.613 18.7 0.105 109 0.613 18.7 0.105

Lead 5.41 12.1 1.16 2.6 5.41 12.1 1.16 2.6

Magnesium 2450 2.12 2000 1.73 2450 2.12 2000 1.73

Manganese 329 23.2 186 13.1 329 23.2 186 13.1

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 402 119 402 119

Zinc 301 14.1 59.5 2.79 301 14.1 59.5 2.79

Total Specific Parameters 

(Precipitative Softening)

13,232 128 10,121 36 13,679 143 10,286 42

Coagulation and Filtration

Bulk Parameters

BOD 1650 80.3 1650 80.3

Nitrogen, Total 4170 792 4170 792

TSS 62400 2910 154000 7180

Total Bulk Parameters 

(Coagulation and Filtration)

68220 3782.3 159820 8052.3

Specific Parameters

Aluminum 2470 160 99.2 6.41 2470 160 99.2 6.41

Ammonia 553 0.613 150 0.167 553 0.613 150 0.167

Barium 11.5 0.0228 2.29 0.00456 11.5 0.0228 2.29 0.00456

Calcium 10000 0.28 4080 0.114 10000 0.28 4080 0.114

Copper 79.4 50.4 5.59 3.55 79.4 50.4 5.59 3.55

Fluoride 784 27.4 135 4.73 784 27.4 135 4.73

Iron 3130 17.5 251 1.41 4940 27.6 396 2.22

Lead 6.52 14.6 0.655 1.47 6.52 14.6 0.655 1.47

Magnesium 2950 2.55 1130 0.978 2950 2.55 1130 0.978
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-26

Table 9-8. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 50,001 to 100,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr)

Manganese 506 35.6 134 9.44 506 35.6 134 9.44

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 485 67 485 67

Zinc 362 17 33.7 1.58 362 17 33.7 1.58

Total Specific Parameters 

(Coagulation & Filtration)

21,337 326 6,088 30 23,147 336 6,233 31

Filtration Only

Bulk Parameters

BOD 788 81.8 788 81.8

Nitrogen, Total 1990 807 1990 807

TSS 1430 142 12200 1220

Total Bulk Parameters 

(Filtration Only)

4208 1030.8 14978 2108.8

Specific Parameters

Aluminum 501 32.4 43 2.78 501 32.4 43 2.78

Ammonia 263 0.292 153 0.17 263 0.292 153 0.17

Fluoride 100 3.5 36.9 1.29 100 3.5 36.9 1.29

Iron 69.9 0.392 12 0.0673 69.9 0.392 12 0.0673

Lead 3.1 6.95 0.667 1.49 3.1 6.95 0.667 1.49

Manganese 31.3 2.2 17.7 1.25 31.3 2.2 17.7 1.25

Phosphorus, Total 231 68.2 231 68.2

Total Specific Parameters 

(Filtration Only)

1,199 46 331 7 1,199 46 331 7

Membrane Desalination

Bulk Parameters

CBOD5 3500 86.2 3500 86.2

Nitrogen, Total 10300 996 10300 996

TSS 10000 237 10000 237

Total Bulk Parameters 

(Membrane Desalination)

23800 1319.2 23800 1319.2
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-27

Table 9-8. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 50,001 to 100,000 People 

Source Water Treatment 

Type and Pollutant 

Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr)

Specific Parameters

Ammonia 5430 6.03 749 0.831 5430 6.03 749 0.831

Cadmium 3.63 83.8 0.0816 1.89 3.63 83.8 0.0816 1.89

Chlorides 24900000 607 2400000 58.4 24900000 607 2400000 58.4

Copper 3.12 1.98 0.111 0.0708 3.12 1.98 0.111 0.0708

Fluoride 7390 259 646 22.6 7390 259 646 22.6

Iron 5130 28.7 209 1.17 5130 28.7 209 1.17

Phosphorus, Total 237 16.6 237 16.6

Total Specific Parameters 

(Membrane Desalination)

24,918,194 987 2,401,621 85 24,918,194 987 2,401,621 85

Ion Exchange & Adsorption

Bulk Parameters

CBOD5 3500 36.4 3500 36.4

Nitrogen, Total 1650 67.2 3180 129

TDS 30000000 2640000 30000000 2640000

TSS 22300 223 22300 223

Total Bulk Parameters (Ion 

Exchange & Adsorption)

30027450 2640326.6 30028980 2640388.4

Specific Parameters

Ammonia 313 0.348 18.2 0.0203 313 0.348 18.2 0.0203

Cadmium 3.63 83.8 0.0345 0.797 3.63 83.8 0.0345 0.797

Chlorides 10200000 250 417000 10.2 24900000 607 1010000 24.7

Copper 5.21 3.31 0.0787 0.0499 5.21 3.31 0.0787 0.0499

Fluoride 7390 259 273 9.55 7390 259 273 9.55

Iron 1270 7.09 21.8 0.122 1270 7.09 21.8 0.122

Lead 0 0 0 0 0 0 0 0

Manganese 1290 90.7 73.1 5.15 1290 90.7 73.1 5.15

Phosphorus, Total 338 10 338 10

Zinc 16.6 0.777 0.33 0.0155 16.6 0.777 0.33 0.0155

Total Specific Parameters 

(Ion Exchange & 

Adsorption)

10,210,626 695 417,397 26 24,910,626 1,052 1,010,397 40

Source: U.S. EPA, 2008a; U.S. EPA, 2009b

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs

for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr. 

a – Excluded from total: chlorides is a constituent of TDS.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-28

Table 9-9. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 100,001 to 500,000 People 

Source Water Treatment 

Type and Pollutant

Pollutant Loadings for Model Plants Serving 100,001 to 500,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yrTWPE 

(lb-eq/yr)

Precipitative Softening

Bulk Parameters

BOD 16,700 162 16,700 162

Nitrogen, Total 42,100 1,600 42,100 1,600

TSS 68,100 636 16,600,000 155,000

Total Bulk Parameters 

(Precipitative Softening)

126,900 2,398 16,658,800 156,762

Specific Parameters

Aluminum 2,050 132 16.4 1.06 2,050 132 16.4 1.06

Ammonia 5,570 6.19 304 0.337 5,570 6.19 304 0.337

Barium 116 0.23 4.63 0.00922 116 0.23 4.63 0.00922

Calcium 101,000 2.82 8240 0.231 101,000 2.82 8,240 0.231

Copper 801 508 11.3 7.17 801 508 11.3 7.17

Fluoride 7,690 269 265 9.29 13,100 460 454 15.9

Iron 1,330 7.44 21.4 0.12 1,330 7.44 21.4 0.12

Lead 65.7 147 1.32 2.97 65.7 147 1.32 2.97

Magnesium 29,800 25.8 2280 1.98 29,800 25.8 2,280 1.98

Manganese 4,000 282 212 15 4,000 282 212 15

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 4,890 135 4,890 135

Zinc 3,650 171 68 3.19 3,650 171 68 3.19

Total Specific Parameters 

(Precipitative Softening)

160,963 1,551 11,559 41 166,373 1,742 11,748 48

Coagulation & Filtration

Bulk Parameters

BOD 5,350 132 5,350 132

Nitrogen, Total 13,500 1,300 13,500 1,300

TSS 202,000 4,790 498,000 11,800

Total Bulk Parameters 

(Coagulation & Filtration)

220,850 6,222 516,850 13,232
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-29

Table 9-9. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 100,001 to 500,000 People 

Source Water Treatment 

Type and Pollutant

Pollutant Loadings for Model Plants Serving 100,001 to 500,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yrTWPE 

(lb-eq/yr)

Specific Parameters

Aluminum 7,980 516 163 10.6 7,980 516 163 10.6

Ammonia 1,780 1.98 248 0.275 1,780 1.98 248 0.275

Barium 37 0.0737 3.77 0.00751 37 0.0737 3.77 0.00751

Calcium 32,300 0.904 6,720 0.188 32,300 0.904 6,720 0.188

Copper 256 163 9.21 5.85 256 163 9.21 5.85

Fluoride 2,530 88.6 223 7.79 2,530 88.6 223 7.79

Iron 10,100 56.6 414 2.32 15,900 89.3 653 3.66

Lead 21.1 47.2 1.08 2.42 21.1 47.2 1.08 2.42

Magnesium 9,530 8.25 1,860 1.61 9,530 8.25 1,860 1.61

Manganese 1,630 115 221 15.5 1,630 115 221 15.5

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 1,570 110 1,570 110

Zinc 1,170 54.8 55.5 2.6 1,170 54.8 55.5 2.6

Total Specific Parameters 

(Coagulation & Filtration)

68,904 1,052 10,029 49 74,704 1,085 10,268 51

Filtration Only

Bulk Parameters

BOD 4,610 81.8 4,610 81.8

Nitrogen, Total 11,600 807 11,600 807

TSS 8,360 142 71,700 1,220

Total Bulk Parameters 

(Filtration Only)

24,570 1,031 87,910 2,109

Specific Parameters

Aluminum 2,930 190 43 2.78 2,930 190 43 2.78

Ammonia 1,540 1.71 153 0.17 1,540 1.71 153 0.17

Fluoride 585 20.5 36.9 1.29 585 20.5 36.9 1.29

Iron 409 2.29 12 0.0673 409 2.29 12 0.0673

Lead 18.2 40.7 0.667 1.49 18.2 40.7 0.667 1.49

Manganese 183 12.9 17.7 1.25 183 12.9 17.7 1.25

Phosphorus, Total 1,350 68.2 1,350 68.2

Total Specific Parameters 

(Filtration Only)

7,015 268 331 7 7,015 268 331 7
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-30

Table 9-9. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of 100,001 to 500,000 People 

Source Water Treatment 

Type and Pollutant

Pollutant Loadings for Model Plants Serving 100,001 to 500,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yrTWPE 

(lb-eq/yr)

Membrane Desalination

Bulk Parameters

CBOD5 3,500 185 3,500 185

Nitrogen, Total 10,300 2,140 10,300 2,140

TSS 10,000 509 10,000 509

Total Bulk Parameters 

(Membrane Desalination)

23,800 2,834 23,800 2,834

Specific Parameters

Ammonia 5,430 6.03 1,610 1.79 5,430 6.03 1,610 1.79

Cadmium 3.63 83.8 0.176 4.06 3.63 83.8 0.176 4.06

Chlorides 24,900,000 607 5,170,000 126 24,900,000 607 5,170,000 126

Copper 3.12 1.98 0.24 0.152 3.12 1.98 0.24 0.152

Fluoride 7,390 259 1,390 48.6 7,390 259 1,390 48.6

Iron 5,130 28.7 449 2.52 5,130 28.7 449 2.52

Phosphorus, Total 237 35.8 237 35.8

Total Specific Parameters 

(Membrane Desalination)

24,918,194 987 5,173,485 183 24,918,194 987 5,173,485 183

Ion Exchange & Adsorption

Bulk Parameters

CBOD5 Not applicable. No 

plants in this model 

plant group.

36.4 Not applicable. No plants in this model plant 

group. Nitrogen, Total 67.2

TDS 2,640,000

TSS 223

Total Bulk Parameters (Ion 

Exchange & Adsorption)

2,640,327

Specific Parameters

Ammonia Not applicable. No 

plants in this model 

plant group.

18.2 0.0203 Not applicable. No plants in this model plant 

group. Cadmium 0.0345 0.797

Chlorides 417,000 10.2

Copper 0.0787 0.0499

Fluoride 273 9.55

Iron 21.8 0.122

Lead 0 0

Manganese 73.1 5.15

Phosphorus, Total 10

Zinc 0.33 0.0155

Total Specific Parameters 

(Ion Exchange & 

Adsorption)

417,397 26
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-31

Source: U.S. EPA, 2008a; U.S. EPA, 2009b 

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs

for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr.

Table 9-10. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of More than 500,000 People 

Source Water Treatment 

Type and Pollutant

Pollutant Loadings for Model Plants Serving >500,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yrTWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Precipitative Softening

Bulk Parameters

BOD 25,000 162 25,000 Not applicable. No 

plants in this model 

plant group. Nitrogen, Total 62,900 1,600 62,900

TSS 102,000 636 24,800,00

0

Total Bulk Parameters 

(Precipitative Softening)

189,900 2,398 24,887,90

0

Specific Parameters

Aluminum 3,060 198 16.4 1.06 3,060 198 Not applicable. No 

plants in this model 

plant group.

Ammonia 8,340 9.25 304 0.337 8,340 9.25

Barium 173 0.344 4.63 0.00922 173 0.344

Calcium 151,000 4.22 8240 0.231 151,000 4.22

Copper 1,200 760 11.3 7.17 1,200 760

Fluoride 11,500 402 265 9.29 19,600 688

Iron 1,990 11.1 21.4 0.12 1,990 11.1

Lead 98.3 220 1.32 2.97 98.3 220

Magnesium 44,500 38.5 2280 1.98 44,500 38.5

Manganese 5,980 421 212 15 5,980 421

Nickel 0 0 0 0 0 0

Phosphorus, Total 7,310 135 7,310

Zinc 5,460 256 68 3.19 5,460 256

Total Specific Parameters 

(Precipitative Softening)

240,611 2,320 11,559 41 248,711 2,606

Coagulation & Filtration

Bulk Parameters

BOD 15,200 139 15,200 139

Nitrogen, Total 38,400 1,370 38,400 1,370

TSS 575,000 5,040 1,420,000 12,400

Total Bulk Parameters 

(Coagulation & Filtration)

628,600 6,549 1,473,600 13,909
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-32

Table 9-10. Model Plant Pollutant Loadings by Source Water Treatment Type and 

Residuals Treatment Type (With and Without Solid/Water Separation) for Direct and 

Indirect (Pass Through) Discharges: Population Served of More than 500,000 People 

Source Water Treatment 

Type and Pollutant

Pollutant Loadings for Model Plants Serving >500,000 People

With Solid/Water Separation Without Solid/Water Separation

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yrTWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Specific Parameters

Aluminum 22,800 1470 172 11.1 22,800 1,470 172 11.1

Ammonia 5,090 5.65 260 0.289 5,090 5.65 260 0.289

Barium 106 0.21 4 0.0079 106 0.21 3.97 0.0079

Calcium 92,100 2.58 7,070 0.198 92,100 2.58 7,070 0.198

Copper 731 464 9.69 6.15 731 464 9.69 6.15

Fluoride 7,220 253 234 8.19 7,220 253 234 8.19

Iron 28,900 162 436 2.44 45,500 255 687 3.85

Lead 60 135 1.14 2.54 60 135 1.14 2.54

Magnesium 27,200 23.5 1,960 1.69 27,200 23.5 1,960 1.69

Manganese 4,660 328 232 16.4 4,660 328 232 16.4

Nickel 0 0 0 0 0 0 0 0

Phosphorus, Total 4,470 116 4,470 116

Zinc 3,330 156 58.3 2.73 3,330 156 58.3 2.73

Total Specific Parameters 

(Coagulation & Filtration)

196,667 3,000 10,553 52 213,267 3,093 10,804 53

Filtration Only

Bulk Parameters

BOD 4,610 81.8 4,610 Not applicable. No 

plants in this model 

plant group. Nitrogen, Total 11,600 807 11,600

TSS 8,360 142 71,700

Total Bulk Parameters 

(Filtration Only)

24,570 1,031 87,910

Specific Parameters

Aluminum 2,930 190 43 2.78 2,930 190 Not applicable. No 

plants in this model 

plant group. 

Ammonia 1,540 1.71 153 0.17 1,540 1.71

Fluoride 585 20.5 36.9 1.29 585 20.5

Iron 409 2.29 12 0.0673 409 2.29

Lead 18.2 40.7 0.667 1.49 18.2 40.7

Manganese 183 12.9 17.7 1.25 183 12.9

Phosphorus, Total 1,350 68.2 1,350

Total Specific Parameters 

(Filtration Only)

7,015 268 331 7 7,015 268

Membrane Desalination

Not applicable. No plants in this model plant group.

Ion Exchange & Adsorption

Not applicable. No plants in this model plant group.

Source: U.S. EPA, 2008a; U.S. EPA, 2009b 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-33

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs

for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr.

Tables 9-11 and 9-12 each show the pollutant loading estimate for model plants 

that disinfect using chlorine by the five source water treatment types and by residuals treatment 

type (with or without dechlorination) for direct and indirect dischargers. Table 9-12 shows the 

estimate for the population served size categories 10,001 to 50,000 and 50,001 to 100,000. Table 

9-13 shows the estimate for the population served size categories 100,001 to 500,000 and greater 

than 500,000. EPA did not include any bulk parameters (i.e., parameters that measure more than 

one chemical) in the list of pollutants in wastewaters from WTPs that disinfect using chlorine.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-34

Table 9-11. Model Plant Pollutant Loadings for WTPs Performing Chlorination by Source Water Treatment Type and Residuals 

Treatment Type (With and Without Dechlorination) for Direct and Indirect (Pass Through) Discharges: Population Served of 10,001 to 

100,000 People 

Source Water 

Treatment Type and

Pollutant

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Dechlorination Without Dechlorination With Dechlorination Without Dechlorination

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE (lbeq/yr) Lb/yrTWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Precipitative Softening

Total trihalomethanes 0 0 1.6 0.264 0 0 2.12 0.545

Chloroform 0 0 0 0 36.1 0.0751 5.96 0.0124 0 0 0 0 48 0.0997 12.3 0.0256

Bromodichloromethane 0 0 0 0 7.29 0.24 1.59 0.0525 0 0 0 0 9.69 0.319 3.29 0.108

Bromoform 0 0 36.1 5.96 0 0 48 12.3

Dibromochloromethane 0 0 0 0 1.57 0.0699 0.955 0.0425 0 0 0 0 2.09 0.0929 1.97 0.0876

Haloacetic acids 

(5HAA’s)

0 0 43 26.3 0 0 57.1 54.2

Total residual chlorine 103 52.6 0 0 137 70 0 0 137 69.9 0 0 183 93 0 0

Total (Precipitative 

Softening) (a)

103 52.6 0 0 261.06 70.385 40.765 0.1074 137 69.9 0 0 347.88 93.5116 84.06 0.2212

Coagulation and Filtration

Total trihalomethanes 0 0 1.42 0.164 0 0 2.56 0.308

Chloroform 0 0 0 0 32.2 0.0669 3.71 0.00771 0 0 0 0 57.8 0.12 6.95 0.0145

Bromodichloromethane 0 0 0 0 6.49 0.214 0.992 0.0327 0 0 0 0 11.7 0.384 1.86 0.0612

Bromoform 0 0 32.2 3.71 0 0 57.8 6.95

Dibromochloromethane 0 0 0 0 1.4 0.0623 0.594 0.0264 0 0 0 0 2.52 0.112 1.11 0.0495

Haloacetic acids 

(5HAA’s)

0 0 38.3 16.3 0 0 68.7 30.6

Total residual chlorine 92 46.9 0 0 122 62.3 0 0 165 84.2 0 0 220 112 0 0

Total (Coagulation & 

Filtration) (a)

92 46.9 0 0 232.59 62.6432 25.306 0.06681 165 84.2 0 0 418.52 112.616 47.47 0.1252
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-35

Table 9-11. Model Plant Pollutant Loadings for WTPs Performing Chlorination by Source Water Treatment Type and Residuals 

Treatment Type (With and Without Dechlorination) for Direct and Indirect (Pass Through) Discharges: Population Served of 10,001 to 

100,000 People 

Source Water 

Treatment Type and

Pollutant

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Dechlorination Without Dechlorination With Dechlorination Without Dechlorination

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE (lbeq/yr) Lb/yrTWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Filtration Only

Total trihalomethanes 0 0 1.22 0.0731 0 0 1.22 0.314

Chloroform 0 0 0 0 27.5 0.0572 1.65 0.00343 0 0 0 0 27.5 0.0572 7.08 0.0147

Bromodichloromethane 0 0 0 0 5.55 0.183 0.442 0.0145 0 0 0 0 5.55 0.183 1.89 0.0624

Bromoform 0 0 27.5 1.65 0 0 27.5 7.08

Dibromochloromethane 0 0 0 0 1.2 0.0533 0.264 0.0118 0 0 0 0 1.2 0.0533 1.13 0.0504

Haloacetic acids 

(5HAA’s)

0 0 32.7 7.28 0 0 32.7 31.2

Total residual chlorine 78.7 40.1 0 0 105 53.3 0 0 78.7 40.1 0 0 105 53.3 0 0

Total (Filtration 

Only) (a)

78.7 40.1 0 0 199.45 53.5935 11.286 0.02973 78.7 40.1 0 0 199.45 53.5935 48.38 0.1275

Membrane Desalination

Total trihalomethanes 0 0 4.26 0.00288 0 0 7.82 0.477

Chloroform 0 0 0 0 96.3 0.2 0.065 0.000135 0 0 0 0 177 0.367 10.8 0.0224

Bromodichloromethane 0 0 0 0 19.5 0.64 0.0174 0.000573 0 0 0 0 35.7 1.17 2.88 0.0949

Bromoform 0 0 96.3 0.065 0 0 177 10.8

Dibromochloromethane 0 0 0 0 4.19 0.187 0.0104 0.000463 0 0 0 0 7.69 0.342 1.73 0.0768

Haloacetic acids 

(5HAA’s)

0 0 115 0.287 0 0 210 47.5

Total residual chlorine 276 140 0 0 367 187 0 0 505 257 0 0 672 342 0 0

Total (Membrane 

Desalination) (a)

276 140 0 0 698.29 188.027 0.4448 0.001171 505 257 0 0 1279.39 343.879 73.71 0.1941
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-36

Table 9-11. Model Plant Pollutant Loadings for WTPs Performing Chlorination by Source Water Treatment Type and Residuals 

Treatment Type (With and Without Dechlorination) for Direct and Indirect (Pass Through) Discharges: Population Served of 10,001 to 

100,000 People 

Source Water 

Treatment Type and

Pollutant

Pollutant Loadings for Model Plants Serving 10,001 to 50,000 People Pollutant Loadings for Model Plants Serving 50,001 to 100,000 People

With Dechlorination Without Dechlorination With Dechlorination Without Dechlorination

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE (lbeq/yr) Lb/yrTWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Ion Exchange and Adsorption

Total trihalomethanes 0 0 0.816 0.202 0 0 7.82 0.202

Chloroform 0 0 0 0 18.4 0.0383 4.56 0.00947 0 0 0 0 177 0.367 4.56 0.00947

Bromodichloromethane 0 0 0 0 3.72 0.122 1.22 0.0401 0 0 0 0 35.7 1.17 1.22 0.0401

Bromoform 0 0 18.4 4.56 0 0 177 4.56

Dibromochloromethane 0 0 0 0 0.802 0.0357 0.729 0.0324 0 0 0 0 7.69 0.342 0.729 0.0324

Haloacetic acids 

(5HAA’s)

0 0 21.9 20.1 0 0 210 20.1

Total residual chlorine 52.7 26.8 0 0 70.1 35.7 0 0 505 257 0 0 672 342 0 0

Total (Ion Exchange & 

Adsorption) (a)

52.7 26.8 0 0 133.322 35.896 31.169 0.08197 505 257 0 0 1279.39 343.879 31.169 0.08197

Source: U.S. EPA, 2008a; U.S. EPA, 2009b. 

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr. 

a – Excluded total trihalomethanes from totals to prevent double counting; individual trihalomethane compounds are included in the total.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-37

Table 9-12. Model Plant Pollutant Loadings for WTPs Performing Chlorination by Source Water Treatment Type and Residuals 

Treatment Type (With and Without Dechlorination) for Direct and Indirect (Pass Through) Discharges: Population Served Greater than 

100,000 People 

Source Water 

Treatment Type and 

Pollutant

Pollutant Loadings for Model Plants Serving 100,001 to 500,000 People Pollutant Loadings for Model Plants Serving >500,000 People

With Dechlorination Without Dechlorination With Dechlorination Without Dechlorination

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Precipitative Softening

Total trihalomethanes 0 0 25.8 0.622 0 Not applicable. No 

plants in this model 

plant group (based on 

plant size).

38.6 0.622

Chloroform 0 0 0 0 583 1.21 14.1 0.0292 0 0 872 1.81 14.1 0.0292

Bromodichloromethane 0 0 0 0 118 3.87 3.76 0.124 0 0 176 5.79 3.76 0.124

Bromoform 0 0 583 14.1 0 872 14.1

Dibromochloromethane 0 0 0 0 25.4 1.13 2.25 0.1 0 0 37.9 1.69 2.25 0.1

Haloacetic acids 

(5HAA’s)

0 0 694 61.9 0 1040 61.9

Total residual chlorine 1,670 849 0 0 2,220 1,130 0 0 2,490 1,270 3,320 1,690 0 0

Total (Precipitative 

Softening) (a)

1,670 849 0 0 4,223 1,136 96 0 2,490 1,270 6,318 1,699 96 0

Coagulation & Filtration

Total trihalomethanes 0 0 8.26 0.507 0 0 23.6 0.534

Chloroform 0 0 0 0 187 0.388 11.5 0.0238 0 0 0 0 532 1.11 12.1 0.0251

Bromodichloromethane 0 0 0 0 37.7 1.24 3.06 0.101 0 0 0 0 107 3.54 3.22 0.106

Bromoform 0 0 187 11.5 0 0 532 12.1

Dibromochloromethane 0 0 0 0 8.13 0.361 1.83 0.0816 0 0 0 0 23.2 1.03 1.93 0.0858

Haloacetic acids 

(5HAA’s)

0 0 222 50.5 0 0 633 53.1

Total residual chlorine 534 272 0 0 710 362 0 0 1520 776 0 0 2,030 1,030 0 0

Total (Coagulation & 

Filtration) (a)

534 272 0 0 1,352 364 78 0 1,520 776 0 0 3,857 1,036 82 0.22
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-38

Table 9-12. Model Plant Pollutant Loadings for WTPs Performing Chlorination by Source Water Treatment Type and Residuals 

Treatment Type (With and Without Dechlorination) for Direct and Indirect (Pass Through) Discharges: Population Served Greater than 

100,000 People 

Source Water 

Treatment Type and 

Pollutant

Pollutant Loadings for Model Plants Serving 100,001 to 500,000 People Pollutant Loadings for Model Plants Serving >500,000 People

With Dechlorination Without Dechlorination With Dechlorination Without Dechlorination

Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge Direct Discharge Indirect Discharge

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Filtration Only

Total trihalomethanes 0 0 7.13 0.314 0 Not applicable. No 

plants in this model 

plant group (based on 

plant size).

7.13 0.314

Chloroform 0 0 0 0 161 0.335 7.08 0.0147 0 0 161 0.335 7.08 0.0147

Bromodichloromethane 0 0 0 0 32.5 1.07 1.89 0.0624 0 0 32.5 1.07 1.89 0.0624

Bromoform 0 0 161 7.08 0 161 7.08

Dibromochloromethane 0 0 0 0 7.01 0.312 1.13 0.0504 0 0 7.01 0.312 1.13 0.0504

Haloacetic acids 

(5HAA’s)

0 0 192 31.2 0 192 31.2

Total residual chlorine 461 235 0 0 613 312 0 0 461 235 613 312 0 0

Total (Filtration 

Only) (a)

461 235 0 0 1166.51 313.717 48.38 0.1275 461 235 1166.51 313.717 48.38 0.1275

Membrane Desalination

Total trihalomethanes 0 0 7.82 1.03 Not applicable. No plants in this model plant group (based on plant size).

Chloroform 0 0 0 0 177 0.367 23.2 0.0482

Bromodichloromethane 0 0 0 0 35.7 1.17 6.21 0.204

Bromoform 0 0 177 23.2

Dibromochloromethane 0 0 0 0 7.69 0.342 3.71 0.165

Haloacetic acids 

(5HAA’s)

0 0 210 102

Total residual chlorine 505 257 0 0 672 342 0 0

Total (Membrane 

Desalination) (a)

505 257 0 0 1,279 344 158 0

Ion Exchange & Adsorption

Not applicable. No plants in this model plant group (based on plant size).

Source: U.S. EPA, 2008a; U.S. EPA, 2009b. 

Blanks indicate that for this pollutant, no TWF is available and therefore, no TWPE were calculated. EPA does not derive TWFs for conventional pollutants.

Zero indicates that EPA estimates the load for this pollutant at zero lbs/yr. 

a – Excluded total trihalomethanes from totals to prevent double counting; individual trihalomethane compounds are included in the total.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-39

9.6 NATIONAL POLLUTANT DISCHARGE ESTIMATES 

EPA estimated the national discharges of pollutants from WTPs serving more 

than 10,000 people (all four size categories) using the model plant loadings presented in Section 

9.5 and national estimates of WTP counts (see Appendix E). For WTPs classified as both direct 

and indirect dischargers, EPA assumed that half would discharge pollutant loadings similar to 

direct dischargers and half would discharge pollutant loadings similar to indirect dischargers 

(i.e., pass through the POTW). For example, national estimates list a total of 49 coagulation and 

filtration plants, performing dechlorination, and serving between 10,001 and 50,000 people. Of 

these 49 plants, 39 are direct dischargers, 2 are indirect discharges, and eight discharge both 

directly and indirectly. For the pollutant loadings calculations, EPA used the following WTP 

counts: 

• 43 direct dischargers (39 direct + 4 both); and 

• 6 indirect dischargers (2 indirect + 4 both). 

EPA used Equation 9-6 and Equation 9-7 to estimate industry pollutant loadings.

Load Industry = Σ (Load Model Plant × WTP Count Model Plant) (Eq. 9-6) 

where:

Load Industry = Total industry loadings, in pounds per year (lb/year), for 

the model plant group. 

Load Model Plant = Pollutant loadings, in lb/year, taking into account any 

pollutant removals by the POTW for indirect dischargers. 

WTP Count Model Plant = National estimate of total number of WTPs for the 

corresponding model plant group. 

TWPE Industry = Σ (TWPE Model Plant × WTP Count Model Plant) (Eq. 9-7) 

where:

TWPE Industry = Total industry loadings, in toxic weighted pound 

equivalents per year (lb-eq/yr), for the model plant group. 

TWPE Model Plant = Pollutant loadings, in lb-eq/year, taking into account any 

pollutant removals by the POTW for indirect dischargers. 

WTP Count Model Plant = National estimate of total number of WTPs for the 

corresponding model plant group. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-40

Table 9-13 presents a summary of the industry pollutant discharges by source 

water treatment type and pollutant, including an estimate of pollutant loadings per facility for 

each of the five source water treatment types. 

Table 9-14 presents the industry pollutant discharges without pollutant detail by 

source water treatment type and WTP size category. The total discharges from the industry are 

352 million pounds per year (excluding bulk parameters to prevent double counting of pollutant 

loadings) and 415,000 toxic-weighted pound equivalents (TWPE) per year. Most of the TWPE 

(85 percent) is due to five pollutants: 

1. Total Residual Chlorine: 120,000 lb-eq/yr;

2. Aluminum: 88,600 lb-eq/yr;

3. Copper: 60,700 lb-eq/yr;

4. Manganese: 41,800 lb-eq/yr; and

5. Fluoride: 41,100 lb-eq/yr.

Discharges of Chloramines 

As discussed in Section 8, total residual chlorine (TRC) is the amount of chlorine 

remaining in the wastewater after chlorine demand. TRC is the summation of free chlorine and 

combined chlorine (chloramines). The industry discharges of TRC total 235,000 pounds per year 

and 120,000 toxic-weighted pound equivalents per year. EPA does not have data available to 

determine the portion of TRC that is chloramines versus free chlorine. Therefore, EPA cannot 

estimate the percent of TRC loadings attributed to chloramines. EPA did collect data in the 

industry questionnaire to estimate the number of WTPs using chloramines for primary 

disinfection. From national estimates, 318 of 2,002 WTPs performing primary disinfection and 

serving more than 10,000 people use chloramines as their primary disinfectant, or approximately 

16 percent of plants that perform primary disinfection. Most of the plants (192 of 318 WTPs) 

serve less than 50,000 people. For the larger plants 

• 83 are precipitative softening plants; 

• 37 are conventional filtration plants; and 

• 6 are membrane desalination, microfiltration, or ultrafiltration plants.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-41

Table 9-13. Pollutant Loadings a for WTPs: National Estimates by Source Water Treatment Type and Pollutant

Pollutants

Precipitative Softening

Coagulation and 

Filtration Filtration Only Membrane Desalination

Ion Exchange and 

Adsorption INDUSTRY TOTAL

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Bulk Parameters

BOD 1,160,000 885,000 31,200 2,070,000

CBOD 31,000 9,610 40,600

Nitrogen, Total 3,020,000 2,460,000 90,000 97,800 12,300 5,680,000

TDS 252,000,000 252,000,000

TSS 275,000,000 38,700,000 65,800 88,500 60,500 314,000,000

Total Bulk 

Parameters

280,000,000 42,100,000 187,000 217,000 252,000,000 574,000,000

Specific Parameters

Aluminum 142,000 9,130 1,320,000 78,200 19,700 1,270 1,480,000 88,600

Ammonia 408,000 453 344,000 356 12,800 14.2 53,300 59.2 1,950 2 820,000 884

Barium 8,330 16.5 6,810 12.6 15,100 29.1

Cadmium 32 740 9.7 224 41.8 964

Calcium 7,630,000 213 6,760,000 177 14,400,000 390

Chlorides 236,000,000 5,740 90,500,000 2,210 326,000,000 7,950

Copper 55,800 35,400 43,100 25,300 27.9 17.7 16.1 10.2 99,000 60,700

Fluoride 642,000 22,500 457,000 14,900 4,459 156 69,300 2,430 34,600 1,210 1,210,000 41,100

Iron 92,800 519 1,830,000 9,490 2,860 16 46,100 259 4,100 23 1,970,000 10,300

Lead 4,610 10,300 3,620 7,500 129 290 0 0 8,360 18,100

Magnesium 2,240,000 1,940 1,960,000 1,590 4,200,000 3,530

Manganese 292,000 20,600 313,000 20,600 1,511 106 7,880 556 615,000 41,800

Nickel 0 0 0 0 0 0

Phosphorus, Total 346,000 277,000 9,981 2,186 1,400 637,000 0

Zinc 256,000 12,000 200,000 8,660 57 2.67 456,000 20,600

Total Specific 

Parameters

12,100,000 113,000 13,500,000 167,000 51,400 1,860 236,000,000 9,240 90,600,000 4,240 352,000,000 295,000
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-42

Table 9-13. Pollutant Loadings a for WTPs: National Estimates by Source Water Treatment Type and Pollutant

Pollutants

Precipitative Softening

Coagulation and 

Filtration Filtration Only Membrane Desalination

Ion Exchange and 

Adsorption INDUSTRY TOTAL

Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr) Lb/yr

TWPE 

(lb-eq/yr)

Pollutants from Chlorination

Total 

trihalomethanes

1,510 0 830 0 27.5 0 12.8 0 11.5 0 2,390 0

Chloroform 34,000 70.7 18,800 39 621 1.29 290 0.601 260 0.54 54,000 112

Bromodichloromet

hane

6,950 228 3,950 130 132 4.34 58.7 1.93 69.5 2.29 11,200 367

Bromoform 34,000 0 18,800 0 621 0 290 0 260 0 54,000 0

Dibromochloromet

hane

1,610 71.4 1,090 48.7 38.5 1.72 12.7 0.566 41.6 1.85 2,790 124

Haloacetic acids 

(5HAA’s)

43,900 0 30,000 0 1,050 0 348 0 1,150 0 76,400 0

Total residual 

chlorine

139,000 70,600 91,600 46,700 2,620 1,330 1,100 561 1,000 509 235,000 120,000

Total From 

Chlorination (b)

259,000 71,000 164,000 46,900 5,090 1,340 2,100 564 2,780 514 433,000 120,000

Total Specific 

Pollutants plus 

Chlorination 

Pollutants

12,400,000 184,000 13,700,000 214,000 56,500 3,200 236,000,000 9,800 90,600,000 4,750 352,000,000 415,000

Number of WTPs 

(a)

349 1,010 97 41 92 1,620

Loads per WTP --

Bulk Parameters

801,000 41,800 1,930 5,300 2,740,000 354,000

Loads per WTP) --

Specific Pollutants

34,700 324 13,400 166 530 19.1 5,760,000 225 984,000 46.1 217,000 182

Loads per WTP --

Chlorination 

Pollutants

743 203 163 46.7 52.5 13.8 51.2 13.8 30.2 5.59 267 74.1

Loads per WTP –

Specific Pollutants 

plus Chlorination 

Pollutants

35,400 527 13,600 213 583 32.9 5,760,000 239 984,000 51.7 217,000 256

Source: U.S. EPA, 2009b. 

a – Loadings include only those pollutants included in the analysis (see Section 9.3). 

b – Excluded total trihalomethanes from totals to prevent double counting; individual trihalomethane compounds are included in the total.
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-43

Table 9-14. Pollutant Loadings a for WTPs Serving More than 10,000 People: National 

Estimate by Source Water Treatment Type and WTP Size (as Population Served)

Source Water 

Treatment Type

WTPs Serving 10,001 to 

50,000 People

WTPs Serving 50,001 

to 100,000 People

WTPs Serving 

100,001 to 500,000 

People

WTPs Serving 

>500,000 People

Lb/yr Total

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr) Lb/yr

TWPE 

(lbeq/yr)

Precipitative 

Softening

1,380,000 16,700 1,040,000 13,400 7,950,000 124,000 2,000,000 30,300 12,400,000 lb/yr 

(184,000 lb-eq/yr)

Coagulation and 

Filtration

5,150,000 66,500 2,250,000 37,300 5,020,000 87,600 1,250,000 22,200 13,700,000 lb/yr 

(214,000 lb-eq/yr)

Filtration Only 41,000 2,630 663 14.1 14,000 536 760 14.3 56,500 lb/yr 

(3,200 lb-eq/yr)

Membrane 

Desalination

191,000,000 8,100 4,800,000 170 40,400,000 1,540 0 0 236,000,000 lb/yr 

(9,800 lb-eq/yr)

Ion Exchange and 

Adsorption

86,000,000 4,520 2,020,000 80.8 2,500,000 155 0 0 90,600,000 lb/yr 

(4,800 lb-eq/yr)

Total by WTP Size 283,000,000 98,400 10,100,000 50,900 55,900,000 214,000 3,250,000 52,500 352,000,000 lb/yr 

(415,000 lbeq/yr)

Source: U.S. EPA, 2009b. 

a – Loadings include only those pollutants included in the analysis. Totals exclude total trihalomethanes (individual trihalomethanes are included 

in the total) and bulk parameters to prevent double counting of pollutant loadings. 

9.7 REFERENCES

Eastern Research Group (ERG), 2009. Memorandum: Pollutant Loadings Estimates for Drinking 

Water Treatment Plants: Model Plants and National Estimates, January 29, 2009. Chantilly, VA. 

DCN DW03777. 

Malmrose, et al., 2004. Paul Malmrose, Jim Lozier, Michael Mickley, Robert Reiss, Jerry 

Russell, James Schaefer, Sandeep Sethi, Jennifer Manuszak, Robert Bergman, and Khalil Z. 

Atasi, Residual Management Research Committee Subcommittee on Membrane Residual 

Management, “2004 Committee Report: Residuals Management for Desalting Membranes,” 

Jour. AWWA, 96:12:73. American Water Works Association (AWWA), December 2004. 

Document Control Number (DCN) DW00032. 

U.S. Environmental Protection Agency (U.S. EPA), 1982. Fate of Priority Pollutants in Publicly 

Owned Treatment Works (EPA 440/1-82/303, September 1982. 

U.S. EPA, 1994. National Risk Management Research Laboratory (NRMRL) Treatability 

Database Version 5.0, Cincinnati, OH. 

U.S. EPA. 2006. Toxic Weighting Factor Development in Support of CWA 304(m) Planning 

Process. Washington, DC. (June). EPA-HQ-OW-2004-0032-1634. 

U.S. EPA, 2007. Phase I Discharge Monitoring Report (DMR) Database, Office of Water, 

Washington, DC. DCN DW03703. 
Drinking Water Industry Report Section 9 – Water Treatment Plant Pollutant Discharge Estimates

9-44

U.S. EPA, 2008a. Drinking Water 2006 Baseline Pollutant Loadings Database, Office of Water, 

Washington, DC. DCN DW03741 

U.S. EPA, 2008b. National Primary Drinking Water Standards (List of Drinking Water 

Contaminants and MCLs) (original document published in 2003, DCN DW00657), Office of 

Ground Water and Drinking Water, Washington, DC. Retrieved from 

http://www.epa.gov/safewater/contaminants/index.html Accessed April 2008 for updates.

U.S. EPA, 2009a. Drinking Water Survey Response Database – Technical Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03790. 

U.S. EPA, 2009b. Drinking Water Treatment Industry Review: Estimated Discharge of 

Pollutants from Water Treatment Plants (WTPs) Serving More than 10,000 People(MS Excel 

spreadsheet), Office of Water, Washington, DC. DCN DW03776 

U.S. EPA, ASCE, and AWWA, 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals (EPA 625-R-95-008), Office of Research and Development, 

Washington, DC. DCN DW03736. 
10-1

SECTION 10

POTENTIAL SCOPE OF ENVIRONMENTAL IMPACTS OF 

POLLUTANT DISCHARGES

As part of its review of the drinking water treatment industry, EPA assessed the 

potential scope of environmental impacts from surface water discharges of water treatment plant 

(WTP) residuals. The purpose of the assessment was to better understand, at the national level, 

the degree to which discharges of residuals may be causing environmental harm. 

Due to incomplete data, EPA is unable to draw conclusions about the extent and 

magnitude of potential environmental impacts from WTP discharges. EPA did not conduct 

sampling of WTP discharges, so the analysis of environmental impacts typically performed for 

an effluent guidelines rulemaking was not performed. Instead, EPA reviewed publicly available 

information about potential environmental impacts. This section provides general environmental 

impact information on pollutants found in WTP residuals, but does not provide an environmental 

assessment of the WTP industry discharges.

10.1 REVIEW OF PUBLICLY AVAILABLE INFORMATION 

EPA reviewed literature obtained through major on-line research services, 

together with a search of the websites of 18 drinking water treatment utilities and industry 

organizations. The search yielded 197 references and EPA reviewed 106 articles published 

between 1984 and 2005, including articles from U.S. regional newspapers and trade journals. 

The articles identified only a few environmental impact issues associated with WTP discharges. 

The majority of articles (26 articles) concern the disposal of desalination concentrate, 

particularly in Tampa Bay, Florida, and discharges from the Washington Aqueduct WTP to the 

Potomac River in Washington, DC. Other articles about specific plants include reporting of a 

treatment chemical spill in North Carolina, an unpermitted WTP discharge in Massachusetts, 

alum discharge issues at a WTP in Arkansas, and a permit application in Virginia involving 

desalination concentrate discharges.
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-2

 Key points about potential environmental impacts found in studies and journal 

articles include:

• Alum and lime sludge discharges may pose a threat to aquatic life through 

benthic smothering downstream of outfalls. 

• Aluminum and other metals present in alum sludge may be toxic to 

aquatic organisms (AWWARF, 1987; George, 1995; Sotero-Santos et al., 

2005; Tumeo, 1992). 

• Periodic batch discharge of accumulated sludge in settling basins likely 

disrupts the ecosystem more than a continuous low-level discharge. 

• The flow and volume of the receiving waterbody is a factor in the degree 

of impacts from alum and lime sludge. If the flow is low, then sludge will 

more readily fall out of suspension in the water column and coat the 

bottom (U.S. EPA/ASCE/AWWA, 1996). 

10.2 SUMMARY OF ENVIRONMENTAL IMPACT OF WTP RESIDUALS BY 

POLLUTANT 

This section provides details on the pollutants highlighted in the review of readily 

available information for the environmental impacts and common pollutants found in WTP 

residuals (see Section 8). The information in this section is not specific to WTP discharges. 

10.2.1 Environmental Impact of Solids 

Suspended solids discharged by WTPs may settle to form bottom deposits in the 

receiving water, potentially causing benthic smothering. Suspended solids also increase turbidity 

in receiving waters and reduce light penetration through the water column, thereby limiting the 

growth of rooted aquatic vegetation that serves as a critical habitat for fish, shellfish, and other 

aquatic organisms. Suspended solids also provide a medium for the transport of other sorbed 

pollutants, including nutrients, pathogens, metals, and toxic organic compounds, which may 

accumulate in settled deposits. Settled suspended solids and other associated pollutants may have 

a long-term impact on the water column through cycles of resuspension. 
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-3

In addition, suspended solids in wastewater discharges can clog fish gills. In 

severe situations, clogging of fish gills can result in asphyxiation; in less severe situations, it can 

result in an increase in susceptibility to infection. 

Pollutants in dissolved solids can have a potential impact on the subsequent use of 

receiving waters that serve as source waters for public and industrial water supplies. Dissolved 

solids (e.g., hardness level of the water) also have the potential to alter the chemistry of natural 

waters to a degree that adversely affects indigenous aquatic biota, especially in the immediate 

vicinity of the effluent discharge. 

10.2.2 Environmental Impact of Metals 

Metals are potentially toxic to phytoplankton and zooplankton and to higher 

aquatic plant and animal species, including fish. They also have the potential for 

bioaccumulation and biomagnification in aquatic food chains and presence downstream in 

effluent receiving waters used as source waters for potable water supplies.

Aluminum is toxic in the aquatic environment. The direct effect of WTP residuals 

on the aquatic environment is difficult to isolate from the effect of naturally-occurring aluminum. 

The aluminum species concentration causing toxicity depends on water chemistry, aquatic 

organism affected, and the effect being monitored. Studies on the toxic effects of aluminum in 

the aquatic environment have shown that inorganic aluminum can be toxic to several fresh-water 

species of fish, invertebrates, bacteria, and algae at pH conditions less than 6 (U.S. EPA, ASCE, 

AWWA, 1996). 

10.2.3 Environmental Impact of Chlorine and Chloramines

WTPs commonly use chlorine and chloramines to disinfect drinking water. These 

chemicals may become part of residuals waste streams either by addition prior to residuals 

generation (primary disinfection) or by using finished drinking water as backwash (disinfection 

at the clear well is secondary disinfection). 
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-4

Free chlorine is directly toxic to aquatic organisms and can react with naturally 

occurring organic compounds in receiving waters to form toxic compounds such as 

trihalomethane. Chloramines can remain chemically stable in water from hours to days. They are 

highly toxic to fish and other organisms which live in water. These substances are not found to 

be bioaccumulative, or to transfer up the food chain (Environment Canada, 2002). 

10.2.4 Environmental Impact of Oxygen Demand 

When WTP wastewaters are discharged to surface waters, the microorganisms 

present in the naturally occurring microbial ecosystem decompose the organic matter contained 

in the wastewater. The decomposition process consumes oxygen and reduces the amount 

available for aquatic animals. Severe reductions in dissolved oxygen concentrations can lead to 

fish kills. Even moderate decreases in dissolved oxygen concentrations can adversely affect 

waterbodies through decreases in biodiversity, as manifested by the loss of some species of fish 

and other aquatic animals. Loss of biodiversity in aquatic plant communities due to anoxic (i.e., 

insufficient oxygen) conditions can also occur. 

10.2.5 Environmental Impact of Chlorides 

Chloride (Cl-) is a common anion in wastewaters and natural waters. For the 

protection of freshwater fish and aquatic life, EPA recommends the following for chloride: 

criteria maximum concentration of 860 mg/L (acute effects) and criterion continuous 

concentration of 230 mg/L (chronic effects) (U.S. EPA, 2006). Exceeding these chloride levels 

in wastewater discharges can be harmful to animals and plants in non-marine surface waters and 

can disrupt ecosystem structure. It can also adversely affect biological wastewater treatment 

processes. Furthermore, excessively high chloride concentrations in surface waters can impair 

their use as source waters for potable water supplies. If sodium is the predominant cation present, 

the water will have an unpleasant taste due to the corrosive action of chloride ions. 

10.2.6 Environmental Impact of Nitrogen 

Under both anaerobic and aerobic conditions, the readily biodegradable fraction 

of organic nitrogen is mineralized readily by microbial activity. The nitrogen not used for cell 
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-5

synthesis accumulates as ammonia nitrogen. The water quality impacts associated with organic 

nitrogen are related to this process of mineralization to ammonia nitrogen in natural waters and 

are discussed below.

Both ammonia nitrogen and ammonium nitrogen can be directly toxic to fish and 

other aquatic organisms; ammonia nitrogen is the more toxic. In addition, discharges of ammonia 

nitrogen can reduce ambient dissolved oxygen concentrations in receiving surface waters 

because of the microbially mediated oxidation of ammonia nitrogen to nitrite plus nitrate 

nitrogen. This demand is known as nitrogenous oxygen demand (NOD). 

Ammonia nitrogen in wastewater discharges can also be responsible for the 

development of eutrophic conditions in the receiving water. Eutrophic waters are rich in mineral 

and organic nutrients. These nutrients promote the growth of plant life, especially algae. Plants 

reduce the dissolved oxygen content. These adverse impacts on ambient dissolved oxygen 

concentrations occur if nitrogen is the nutrient limiting primary productivity. Although 

phosphorus is typically the nutrient limiting primary productivity in fresh surface waters, 

nitrogen is typically the limiting nutrient in marine waters and the more saline segments of 

estuaries. Algae blooms from eutrophic conditions cause shifts in ambient dissolved oxygen 

concentrations from supersaturation on sunny days to substantial deficits at night and on cloudy 

days, when photosynthesis does not occur. The decay of the biomass generated by excessive 

primary productivity also exerts a demand on ambient dissolved oxygen concentrations. With the 

depression of ambient dissolved oxygen concentrations, populations of fish and other aquatic 

organisms are adversely affected, possibly causing a change in ecosystem composition and a loss 

of biodiversity. 

Although nitrite plus nitrate nitrogen exerts an NOD in surface waters, the 

principal concern about oxidized forms of nitrogen in wastewater discharges is related to their 

role in the development of eutrophic conditions. The impacts of such conditions on fish 

populations, biodiversity, recreation, and potable water supply are discussed above. An 

additional concern is their potential for increasing ambient surface water nitrate (as nitrogen) and 

nitrite (as nitrogen) concentrations above the national maximum contaminant levels in source 

waters used for public drinking water supplies. 
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-6

10.2.7 Environmental Impact of pH Changes

The hydrogen-ion concentration in an aqueous solution is represented by the pH, 

which is defined as the negative logarithm of the hydrogen-ion concentration in a solution. On 

the pH scale ranging from zero to 14, a value of seven represents neutral conditions—the 

concentrations of hydrogen (H+) and hydroxyl ions (OH-) are equal. pH values less than seven 

indicate acidic conditions and values greater than seven represent basic conditions.

WTPs adjust the pH to optimize source water treatment, and the addition of lime 

for softening raises the pH of the water. pH varies in WTP wastewaters and can have negative 

impacts on receiving water. Wastewaters with pH values markedly different from the receiving 

stream pH can have a detrimental effect on the environment. Sudden pH changes can kill aquatic 

life. 

10.2.8 Environmental Impact of Phosphorus

Phosphorus is the nutrient typically limiting primary productivity in freshwater 

ecosystems. In such aquatic ecosystems, an increase in ambient phosphorus concentration due to 

wastewater discharges above naturally occurring levels results in the excessive growth of algae 

and other phytoplankton, with the development of eutrophic conditions as the consequence. In 

turn, eutrophic conditions can cause fish kills, disruption of natural aquatic ecosystem structure, 

and loss of biodiversity. In marine waters, phosphorus is not as much of a concern because of 

relatively high naturally occurring phosphorus concentrations. The impact of phosphorus in 

wastewater discharges into estuaries varies—in general, impacts decrease as salinity levels 

increase.

10.2.9 Environmental Impact of Radionuclides 

Radionuclides regulated in drinking water include combined radium -226/-228, 

(adjusted) gross alpha, beta particle and photon radioactivity, and uranium. Exposure to 

radionuclides from drinking water results in the increased risk of cancer. Exposure to elevated 
Drinking Water Industry Report Section 10 – Potential Environmental Impacts 

10-7

uranium levels in drinking water has been shown to lead to changes in kidney function that are 

indicators of potential future kidney failure (U.S. EPA, 2000). 

10.3 REFERENCES

American Public Health Association (APHA), 1995. Standard Methods for the Examination of 

Water and Wastewater, 19th edition, Washington, DC. 

American Water Works Association Research Foundation (AWWARF), 1987. Water Treatment 

Plant Waste Management. Prepared by Environmental Engineering and Technology, Newport 

News, VA for AWWARF, Denver, CO. Document Control Number (DCN) DW00186. 

Eastern Research Group (ERG), 2006. Memorandum: Literature Review Results for the Drinking 

Water Environmental Assessment and Summary of the Environmental Impacts of Water 

Treatment Residuals Discharged to Surface Waters (April 28, 2006). Chantilly, VA. DCN 

DW00626. 

Environment Canada, 2002. Backgrounder: Chloramines, Canadian Environmental Protection 

Act (CEPA) Environmental Registry, Retrieved from 

http://www.ec.gc.ca/CEPARegistry/subs_list/Chloramines_BG.cfm, last updated September 13, 

2002. DCN DW00423. 

George, 1995. Dennis B. George, et al. Alum Sludge in the Aquatic Environment [Project #319]. 

AWWARF, Denver, CO. DCN DW00449. 

Sotero-Santos, Rosana B., Odete Rocha, and Jurandyr Povinelli. 2005. Evaluation of water 

treatment sludges toxicity using the Daphnia bioassay. Water Research 39: 3909-3917. DCN 

DW00530. 

Sutherland, David, W. 1999. Washington Aqueduct Sediment Discharges: Report of Panel 

Recommendations. Chesapeake Bay Field Office. U.S. Fish and Wildlife Office. DCN DW00534 

Tumeo, Mark A, 1992. Effects of Lime-Sludge Discharge on an Arctic River [Paper Number 

92102]. American Water Resources Association. Issue Volume 28, Number 6, December 1992, 

pages 1083-1094. 

U.S. EPA, 2000. Technical Fact Sheet: Final Rule for (Non-Radon) Radionuclides in Drinking 

Water (EPA 815-F-00-013), Office of Ground Water and Drinking Water, Washington, DC. 

Retrieved from http://www.epa.gov/safewater/radionuclides/regulation_techfactsheet.html. 

U.S. EPA, 2006. National Recommended Water Quality Criteria, Office of Water, Washington, 

DC. DCN DW01149. 

U.S. EPA, ASCE, and AWWA, 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals (EPA 625-R-95-008), Office of Research and Development, 

Washington, DC. DCN DW03736. 
11-1

SECTION 11

TECHNOLOGIES AND PRACTICES FOR PREVENTING,

TREATING, DISPOSING OF, AND DISCHARGING SOURCE 

WATER TREATMENT RESIDUALS

Water treatment plants (WTPs) use control technologies and management 

practices to improve the prevention, treatment, disposal, and discharge of source water treatment 

residuals. Adoption of certain control technologies and management practices may significantly 

help WTPs meet permit limits. Other benefits of control technologies and management practices 

include improved water quality, reduced treatment system operation costs, avoidance of NPDES 

permitting costs, and energy savings. 

The Clean Water Act (CWA) authorizes EPA to require WTPs to implement best 

management practices (BMPs) as part of their National Pollutant Discharge Elimination System 

(NPDES) permits. EPA has the flexibility to include BMPs in addition to pollutant concentration 

limits or in lieu of pollutant limits. Examples of BMPs in permits include establishing schedules 

of activities; prohibitions of practices; maintenance procedures; treatment requirements; and 

operating procedures and practices to control plant site runoff, leaks and spills, sludge or waste 

disposal, and drainage from raw material storage areas.

 

When applied to WTPs, the Pollution Prevention Act of 1990 and EPA’s national 

pollution prevention policy24, provide a framework for determining BMPs, beginning with 

pollution prevention at the source, followed by recycling of filter backwash, efficient treatment 

of residuals, land disposal of solids and certain waste streams, and practices to minimize the 

potential aquatic impacts of the discharge of residuals. This chapter discusses a range of BMPs, 

organized according to their placement in the hierarchy: 

• Pollution prevention and waste reduction (Section 11.1);

• Residuals treatment (Section 11.2);

 

24 See http://www.epa.gov/p2/pubs/p2policy/definitions.htm#national for a description of EPA’s national pollution 

prevention policy. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-2

• Disposal of wastes (Section 11.3); and 

• Discharge of wastes (Section 11.4).

WTPs that do not discharge treatment residuals to surface water or to POTWs are 

not required to obtain a NPDES permit, and thus exemplify the most effective application of 

BMPs. Zero discharging WTPs that generate residuals but do not discharge, are not required to 

obtain a NPDES permit. Becoming a zero discharging WTP results in multiple benefits such as 

water conservation, environmental improvements, and cost reduction. Most plants achieve zero 

discharge status through a combination of pollution prevention/waste management and residuals 

treatment practices, such as recycling, evaporation, composting, landfill disposal, spray 

irrigation, underground injection, and land application. EPA’s 2006 survey found that 70 percent 

of WTPs perform one or more of these methods to reduce discharges to surface waters or 

POTWs and 25 percent have achieved zero discharge status (see Appendix A). 

Ground water plants use primarily underground injection control, recycling, and 

landfill disposal to achieve zero discharge. Surface water plants use recycling, landfill disposal, 

and land application (see Appendix A). 

11.1 POLLUTION PREVENTION AND WASTE REDUCTION

This section discusses pollution prevention (e.g., process modifications) and 

waste reduction (e.g., resource recovery) opportunities at WTPs to reduce the generation of 

residuals during source water treatment.25 Pollution prevention and waste reduction practices 

may also benefit WTPs by reducing operating costs, reducing risk of liability, and improving

system or plant image, without compromising the finished water quality. 

As part of the 2006 industry survey, EPA collected data on pollution prevention 

and waste reduction practices at WTPs. Figure 11-1 presents the distribution of pollution 

prevention and waste reduction practices commonly found at WTPs serving more than 10,000 

people. 

 

25 Pollution prevention is the use of materials, processes, or practices that reduce or eliminate the creation of 

pollutants or waste at the source (U.S. EPA, 1992).
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-3

TOTAL Optimizing

source water

intake

Recycling of

filter

backwash

Recycling of

filter-towaste

Recovery of

treatment

chemicals

Recycle of

softening

chemicals

Other

No pollution

prevention 

0

200

400

600

800

1000

1200

1400

1600

Number of WTPs

Ground Water Plants (637 WTPs)

Surface Water Plants (1,514 WTPs)

Figure 11-1. WTP Pollution Prevention and Waste Reduction Practices in the U.S. in 2006 

Source: Appendix A. 

WTP pollution prevention and waste reduction options discussed in this section 

include: 

• Optimizing source water intake conditions to reduce suspended solids and 

thereby reduce source water treatment requirements.

• Optimizing filter media for finished water and residuals.

• Optimizing pH to reduce coagulant chemicals used. 

• Reducing softening chemicals used by frequent monitoring of source 

water hardness. 

• Returning backwash water and filter-to-waste to the head of the source 

water treatment plant for reuse.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-4

• Reusing precipitative softening chemicals by recycling softening residuals.

• Recovering treatment chemicals. 

11.1.1 Optimize Intake Water Conditions

When properly designed, situated, and instrumented, intake structures can play an 

important role in regulating the quality, volume, and composition of the source water presented 

for treatment. Intake features must be flexible to meet the current and future demands, yet be 

durable enough to withstand the rigors of time and nature. Careful placement of the intake 

structure (particularly in lakes or reservoirs) allows the WTP to draw water that has lower levels 

of total suspended solids, which in turn requires less coagulant to be added and generates a 

smaller volume of solid residuals. 

An example of a facility that is currently optimizing intake water conditions is the 

James J. Corbalis Water Treatment Plant in Fairfax, Virginia. Fairfax Water constructed an

extension that moved the intake structure away from the edge of the river. The new intake 

location improved the quality of the source water by decreasing turbidity and total organic 

carbon levels, and provided a more consistent day-to-day source that is less influenced by local 

runoff. The new intake location resulted in approximately 30 percent lower consumption of 

treatment chemicals and a corresponding reduction in residuals generation (U.S. EPA, 2005).

The relocation of the intake pipe in the example above might be an option for 

WTPs with high total suspended solids (TSS) and turbidity levels in the source water. While 

relocating the intake pipe requires an investment of capital, plants might be able to recoup these 

costs over a reasonably cost-effective time frame through savings on operation and maintenance. 

11.1.2 Optimize Filter Media 

By optimizing filter media, WTPs might be able to maintain or improve finished 

water quality, while reducing the quantity of backwash residuals. For example, in 1996, the 

Philadelphia Suburban Water Company replaced the support gravel and media in four of the dual 

media filters at the Pickering West Water Treatment Plant in Phoenixville, Pennsylvania. The
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-5

Philadelphia Suburban Water Company replaced the support gravel and sand with the same size 

and quality media in all of the filters. The water company also replaced the anthracite with the 

same effective size and quality in all of the filters, but with different uniformity coefficients

(UC)26 (one at 1.6 UC, one at 1.5 UC, one at 1.4 UC, and one at 1.3 UC). Data gathered over a 

one-year period indicated substantial differences in the filter run times and water quality. The 

lower anthracite uniformity coefficient showed the following benefits: 

• Longer filter run times: up to 50 percent longer; 

• Fewer backwashes—up to 33 percent less; 

• Increased drinking water production—2 percent higher; and 

• Improved water quality—up to 38 percent lower 2-5 micron particle 

counts (Cryptosporidium falls into this particle size range) (Yohe, 2006). 

Reducing the volume of backwash water residuals can reduce the costs associated with residuals 

management, as long as finished water quality is not compromised. 

11.1.3 Optimize pH to Reduce Coagulant Chemicals

As water progresses through the source water treatment train at coagulation and 

filtration plants, operators add coagulants to enhance the efficiency of solids removal. The 

majority of coagulant chemicals settle, along with the removed contaminants, during source 

water treatment. The coagulant chemicals then become part of the residuals waste stream. When 

selecting a coagulant chemical, plants might consider waste generation along with their finished 

water quality goals.

Coagulants contain active ingredients (e.g., aluminum, iron) and impurities (e.g., 

chromium, mercury, nickel, zinc). By reducing the amount of coagulant needed to achieve solids 

removal, WTPs also reduce the amount of these coagulant chemicals in the residuals. To 

minimize the use of coagulants, WTPs can optimize solids settling using the pH in clarifiers and 

sedimentation tanks. The pH of the water affects the performance of alum and ferric coagulation 

 

26 Measure of the particle size variations (ratio).
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-6

salts. Alum has a minimum solubility at pH 6, while ferric salts have a minimum solubility at pH 

8 (Tchobanoglous, et al., 2003). Thus, the continuous adjusting of pH to keep optimal 

coagulation conditions might help to reduce waste products but still effectively treat the source 

water. 

11.1.4 Reduce Softening Chemicals by Monitoring Source Water Hardness

Similar to coagulation, softening operations add chemicals to adjust the pH, adjust 

the bicarbonate equilibrium, and precipitate the calcium hardness as calcium carbonate. WTPs 

remove calcium hardness to a level that meets the aesthetic requirements of the customer. By 

monitoring the calcium content of the influent, WTPs might reduce the amount of chemicals 

needed to precipitate the required fraction of calcium hardness, thus resulting in a minimized 

amount of residuals requiring additional treatment or disposal. 

11.1.5 Return Backwash Water and Filter-to-Waste to the Head of the Source 

Water Treatment Plant for Reuse 

Filter backwash water and filter-to-waste are good examples of residuals suitable 

for reuse, provided finished drinking water quality is maintained. Usually, finished drinking 

water is used as the filter scouring agent to backwash (or clean) the filter. Filter-to-waste is the 

initial permeate production when a filter is brought back online following backwashing, and is 

part of the backwash waste stream. 

The backwash process generates a significant volume of wastewater that can 

amount to 2 to 5 percent of plant capacity (U.S. EPA, ASCE, and AWWA, 1996). If allowed to 

settle for 24 hours, the majority of the suspended solids in the backwash separate and the effluent 

can be returned to the head of the treatment plant for reuse while the solids are managed as 

waste. This practice also helps WTPs supplement available source water, which might prove 

especially valuable during water shortages. WTPs can also use this approach for decanted 

effluents from sludge thickeners and other dewatering liquids, thereby reducing the amount of 

effluent discharged. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-7

In 2001, EPA’s Filter Backwash Recycle Rule (FBRR) established requirements 

to ensure that WTPs do not compromise the quality of finished drinking water when reusing 

water in this manner. The FBRR applies to WTPs that use surface water or ground water under 

the direct influence of surface water and operate conventional or direct filtration plants (i.e., 

perform coagulation, filtration, and possibly sedimentation of the intake water). The FBRR 

requires WTPs that reuse certain wastewater residuals (i.e., filter backwash, thickener 

supernatant, and dewatering process liquids) to return the water to a point in the source water 

treatment process where it will be treated by coagulation and filtration. Introduction of reused 

waters at any other location requires prior state approval. 

The purpose of the FBRR is to reduce the risk of illness from microbial pathogens 

in drinking water. During reuse, contaminants might be reintroduced into the source water 

treatment plant. The introduction of the contaminants can impair treatment process performance 

if not done properly. This can result in contaminants passing through source water treatment and 

into the drinking water. 

Depending on the source water quality and wastewater characteristics (i.e., 

contaminant levels), some plants might not be able to reuse water streams. For example, 

concentrate residuals from membrane systems can concentrate contaminants more than five 

times their original concentration in the source water. Returning concentrate to the head of the 

treatment plant without extensive pretreatment would put a significant strain on the efficiency of 

the membrane and reduce its effectiveness. If the concentrate volume is low, discharge to a 

sanitary sewer might be the more affordable alternative to pretreatment and reuse.

11.1.6 Reuse of Precipitative Softening Chemicals

WTPs might reuse precipitative softening chemicals (i.e., lime) to save costs on 

purchasing lime and disposing of softening residuals. Lime recovery from the residuals is 

accomplished using recalcination, in which the calcium carbonate in the lime softening sludge is 

converted to calcium oxide. WTPs perform dewatering and oxidation to complete the 

conversion. WTPs generally use centrifugal separators to dewater the calcium carbonate. The 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-8

calcium carbonate is then dried and oxidized, usually in a furnace. The recovered lime is 

returned back to the source water treatment plant (U.S. EPA, ASCE, and AWWA, 1996). 

11.1.7 Recovery of Treatment Chemicals

In addition to the lime recovery discussed above, WTPs might recover coagulants 

for reuse at the plant. Assuming recovered treatment chemicals meet purity standards, this 

process results in cost savings from reduced cost to dispose of solid waste residuals and reduced 

cost for purchasing new treatment chemicals. A second treatment recovery option available to 

WTPs is to recover salts from ion exchange concentrate residuals. The salt is a saleable resource. 

11.1.7.1 Coagulant Recovery 

Most coagulants are cationic (positively-charged) in nature and include the 

following chemicals: aluminum (alum), iron (ferric) salts, and a wide variety of organic 

polymers. The type and character of the source water, as well as plant choice, determines which 

chemicals are used and the degree of possible reuse. 

Solubility diagrams for aluminum and iron show that both metals approach their 

minimum solubility in the pH range of 6 to 8 (Tchobanoglous, et al., 2003). Because this is the 

normal operating range for most utilities, nearly all of the insoluble coagulant components added 

are expected to be incorporated in the precipitated solids and to be available for recovery. 

Solubility diagrams also show that the solubility for both metals increases as the pH is made 

more acidic (less than 6). 

The traditional approach for alum recovery has been acid extraction to convert the 

alum to a dissolved form for decanting and recycling. Aluminum recovery rates of 60 to 80 

percent have been reported at the pH 3 level (ASCE, 1997). However, this approach can also 

carry over “native” metals in the source water and the recycled coagulant might be of lesser

purity than American National Standards Institute (ANSI)/National Science Foundation (NSF) 

Standard 60. Ion exchange has also been successfully used to recover dissolved aluminum from 

acid extraction. Iron recovery can be accomplished in a way that is similar to alum recovery. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-9

Acid extraction at a pH between 1.5 and 2 has produced iron recoveries at 60 to 70 percent 

(ASCE, 1997), but dewatering difficulties with the sludge have limited its commercial 

application. 

Since aluminum and iron are amphoteric (i.e., exhibiting properties of both an 

acid and a base), a strong base can also dissolve the metal hydroxides. Treatment with sodium 

hydroxide produces a sodium aluminate compound that can be reused as a coagulant in water 

treatment. To date, few WTPs recover coagulants due to purity concerns and the low cost 

(market price)27 of purchasing of new chemicals. 

11.1.7.2 Salt Recovery Via Evaporation and Crystallization of Concentrate 

The use of membrane and ion exchange technologies produces a clean permeate 

stream and a reject stream (or concentrate) containing the source water contaminants. 

Concentrate generated by membrane water treatment technologies contains sodium and 

potassium salts of 36,000 milligrams per liter (mg/L) or more (Tchobanoglous, et al., 2003).

Concentrate generated by ion exchange plants contains sodium (Na+) at average concentrations 

between 2,000 and 5,000 mg/L (U.S. EPA, ASCE, and AWWA, 1996). By recovering these 

salts, plants can gain a saleable resource and prevent the discharge of the concentrate into surface 

waters. 

WTPs can use drying beds to recover salts by evaporating the water. Drying beds 

are particularly effective in the southern and southwestern parts of the country with moderate to 

hot temperatures. 

Crystallization of salts from concentrate involves removing enough water to 

exceed salt solubility limitations. Once the salt changes phase from dissolved to crystallized 

form, it can be readily removed. If the residuals contain mixtures of chemical components, then 

additional steps are required to refine the crystallized material prior to sale or reuse. 

 

27 The market price of the coagulant does not include the costs incurred to mitigate any potential environmental 

damage that pollutants in coagulants cause the environment when released in the effluent stream of the WTP. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-10

11.2 RESIDUALS TREATMENT

Residuals contain contaminants removed from the source water and treatment 

chemicals added by the WTP. Prior to final waste management (e.g., land application, disposal, 

or discharge), residuals from the source water treatment operations (e.g., filter backwash water, 

coagulation sludge) can be treated on site by the WTP. This subsection is organized by 

technologies used by WTPs to achieve the following: 

• Separation of solids from water (Section 11.2.1); 

• Precipitation of chemicals (Section 11.2.2); 

• Increase in oxygen content (Section 11.2.3); 

• Removal of chlorine (Section 11.2.4); and 

• Adjustment of pH (Section 11.2.5). 

Table 11-1 presents the distribution of residuals treatment practices commonly 

found at WTPs serving more than 10,000 people. Section 11.2.6 presents nonwater 

environmental quality impacts to consider when installing a residuals treatment system.

Table 11-1. Distribution of Residuals Treatment Technologies at Drinking Water 

Treatment Plants

Treatment Category Treatment Unit

Number and Percent of WTPs With the 

Treatment Unit in Place

(2,151 WTPs)

Solid/Water Separation Equalization only 159 (7%)

Clarification Included with non-mechanical dewatering

Lagoon Included with non-mechanical dewatering

Thickening Included with non-mechanical dewatering

Mechanical dewatering 195 (9%)

Non-mechanical dewatering a 1,413 (66%)

Drying or evaporation Included with non-mechanical dewatering

Other Residuals Treatment Chemical precipitation Not estimated

Aeration to increase oxygen content Not estimated

Dechlorination 230 (14% of 1,599 plants that disinfect 

with free chlorine)

pH Adjustment Not estimated

No Treatment No treatment 522 (24%)

Source: Appendix A. 

a – Might include equalization.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-11

11.2.1 Solids Removal (Separation of Solids and Water) 

The volume and characteristics of the residuals depend on the source water, 

drinking water production rate, efficiency of source water treatment, and type of source water 

treatment used. Treatment residuals contain naturally occurring suspended and dissolved solids, 

as well as precipitated solids generated by chemical treatment. Many WTPs treat residuals to 

separate solids from the wastewater.

WTPs can use one or more solids removal processes to treat WTP residuals. For 

example, WTPs can separate solids and water using an equalization basin, followed by a gravity 

thickener, and finally a centrifuge. At each process in the residual treatment train, additional 

separation occurs. 

Decreasing the volume of water while increasing solids content is the principle 

objective of solids removal systems. The decreased volume reduces landfill requirements and

reduces cost. (Landfills usually charge customers by weight.) “Thickening” and “dewatering” are 

solids removal terms that are often used interchangeably. Based on the applicable treatment 

techniques, these two practices have many common elements. The discussion that begins with 

Table 11-2 describes solid/water separation using the following terminology: 

• Thickening: Solids separation by physical means without the significant 

application of mechanical devices. Sedimentation (gravity settling) and 

dissolved air flotation are examples of drinking water residuals thickening 

technologies. 

• Mechanical Dewatering: Solids separation by mechanical means.

Pressure filtration and centrifugation are examples of mechanical 

dewatering technologies. 

• Non-Mechanical Dewatering: Solids concentration by evaporation of the 

water. Storage ponds, lagoons, and drying beds are examples of nonmechanical dewatering.

• Thermal Treatment: Solids concentration by evaporation of the water 

using mechanical drying processes.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-12

Table 11-2 presents the range of solids concentrations that typically results from 

using various solids removal processes (U.S. EPA, ASCE, and AWWA, 1996). 

Table 11-2. Comparison of Solids Removal Technologies: Solids Concentration After 

Treatment by Residuals Type

Solids Removal Treatment

Solids Concentration for Treated 

Lime Softening Residuals

Solids Concentration for Treated 

Coagulation Residuals

Thickening

Gravity Thickening 15–30% 1–3% (low TSS)

5–30% (high TSS)

Flotation Thickening Not available 2–4%

Gravity Belt Not available 2.5–4.5%

Mechanical Dewatering

Scroll Centrifuge 55–65% 20–30%

Belt Filter Press 50–60% 1 –20% (Alum)

4–50% (Alum, TSS)

Plate (or Pressure) Filter 55–70% 35–45%

Diaphragm Filter Press 50–70% 30–60% (Alum with lime conditioning)

Non-Mechanical Dewatering

Storage Lagoon 50–60% 7–15%

Sand Drying Bed 50% 20–25%

Source: U.S. EPA, ASCE, and AWWA, 1996. 

11.2.1.1 Thickening

The objective of thickening is to increase the solids content of the residuals by 

removing a portion of the water. Gravity settling, dissolved air flotation, and gravity belt are the 

most common thickening technologies. 

Thickening of residuals can take several paths, but the end result is to remove a 

portion of the influent water to concentrate the solids for resource recovery. The importance of 

having a higher concentration of solids progressing to the next treatment/recovery phase is 

reflected in the reduction of the capital and operating costs of the continuing treatment (e.g., an 

increase in solids from 3 to 6 percent results in a 50 percent volume reduction which in turn 

would reduce capital expenditures associated with the construction of greater wastewater 

handling capacity in this residuals treatment phase. An increase in solids concentration can also 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-13

facilitate the design and reduce per unit cost associated with wastewater treatment and solids 

disposal. 

Gravity settling is the term that describes using gravity to separate (thicken) solids 

from water. Initially, applications of this technology at WTPs consisted of long, narrow, and 

deep tanks with residence times of at least four hours. The industry has since shifted to use of 

circular units due to operational difficulties with removing residue from the long, narrow tanks 

and advances in engineering design. Figure 11-2 presents a diagram of a circular gravity 

thickener. New designs with the same thickening efficiencies have reduced the residence time to 

two hours or less (ASCE, 1997). Metal hydroxide (i.e., coagulation) residuals with low TSS 

concentrations can be thickened to up to 3 percent solids, while residuals with higher TSS 

concentrations can be thickened to as high as 30 percent solids. Lime softening residuals 

(carbonate residuals) can be thickened to the range of 15 to 30 percent solids (U.S. EPA, ASCE, 

and AWWA, 1996). The number of gravity settling tanks required for residuals treatment 

depends on the plant’s treatment volume and the amount of redundancy required. For example, if 

the influent solids content is in the 1 to 3 percent range, and a design solids loading rate of 4.0 

pounds/day/square foot is used (AWWARF, 1987), a sedimentation tank with a diameter of 30 

feet is needed for each million gallons of waste treated.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-14

Source: U.S. EPA, 1987. Design Manual: Dewatering Municipal Wastewater Sludges. 

Figure 11-2. Gravity Thickener (U.S. EPA, 2003) 

Dissolved air flotation (DAF) is the most common of several flotation separation 

technologies. Pressurized air is injected into recycled drinking water and added to the residuals 

feed. When the pressure on the injected water is released, it allows the super saturated air to 

escape into the residuals as small bubbles that cause turbulence. The small bubbles mix with the 

TSS in the residuals stream and adhere to the suspended particles, pushing them to the surface. 

The floating material (thickened solids) is then skimmed off. Flotation separation techniques for 

drinking water residuals are used more widely in Europe and can generate floating solid residuals 

with 3 to 4 percent solids reported (U.S. EPA, ASCE, and AWWA, 1996). 

If space is a constraint, or if gravity settling or flotation do not provide the desired 

solids thickening, then plants can use a gravity belt thickener as an alternative. Gravity belt 

thickeners are constructed from a porous belt (metal mesh) that allows water to drain through the 

belt while retaining the solids. The recirculating belt travels through solids removal and wash 

sections before returning to service. The design of the belt material and the loading applied 

influence separation efficiencies, with solids concentrations for treated metal hydroxides

residuals ranging from 2.5 to 4.5 percent (U.S. EPA, ASCE, and AWWA, 1996). Gravity belts 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-15

are simple designs with minimal operator oversight; however, they generate another residuals

stream (wash water), usually require use of a solids conditioner, and require maintenance. 

Following the thickening operation, the solids continue to the next solid/water 

separation step (i.e., mechanical dewatering). The supernatant from the thickening operation is 

recycled or discharged by the plant. 

11.2.1.2 Mechanical Dewatering

WTPs commonly follow residuals thickening with mechanical dewatering for 

additional volume reduction and concentration of solids. Common mechanical dewatering 

technologies used by the WTPs are belt filter presses, plate and frame filter presses, and 

centrifuges. 

Belt filter presses use pressure to force water out of the residuals through the 

porous belt while retaining the separated solids on the belt. Figure 11-3 shows the design of a 

belt filter press. Treatment residuals are placed on the dewatering belt and drained in the free 

drainage zone. The remaining solids/water are sandwiched between two porous belts and passed 

over/under a series of different diameter rollers. The different rollers impart low and high 

pressure on the belts, squeezing the additional water from the solids and through the porous belt. 

The more extensive the belt travel, the drier the filter cake. Lime softening residuals are good 

candidates for this system because their more granular structure can withstand higher pressures.

Using this technology, plants have reported lime filter cake with 50 to 60 percent solids (U.S. 

EPA, ASCE, and AWWA, 1996). 

Pressure filters (e.g., plate and frame filter press, diaphragm filter press) apply

high pressure to a solid/liquid suspension and force the liquid out while retaining the solids. Plate 

and frame filters have a recessed area that receives the pumped influent waste material at 

elevated pressures. The filter fabric covering the plates allows the water to escape while retaining

the solids. This is a continuous process until the pressure drop across the filter equals the 

pumping pressure and the unit is shut down. The filter is then broken down and manually 

cleaned and returned to service. A diaphragm filter press allows WTP operators to vary the 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-16

volume in the receiving area. It employs a two-stage filtering process in which the diaphragm is

expanded after initial filtering has been completed. Lime softening residuals have been 

dewatered to solids concentrations of 50 to 70 percent using this technique (U.S. EPA, ASCE, 

and AWWA, 1996). 

Source: U.S. EPA, 1987. Design Manual: Dewatering Municipal Wastewater Sludges. 

Figure 11-3. Belt Filter Press (U.S. EPA, 2000a) 

Centrifugal separators use centrifugal force to separate suspended solids from 

water. The amount of force applied to the waste stream solids depends on the centrifuge’s 

rotational speed. The force applied and the centrifuging time determine separation effectiveness.

As the industrial application of centrifuges increases in size, so do the operational problems and 

energy costs. The solid bowl centrifuge is the principal type of centrifugal separator used to 

dewater treatment residuals. The bowl centrifuge has two moving parts: the bowl and the scroll. 

As centrifugal force pushes the solids to the edge of the spinning bowl, a rotating scroll moves 

the dewatered solids along a horizontal axis to a collection point. Centrifuges perform better with 

the addition of a conditioning agent, thus they are rarely operated without the addition of a 

polymer to the residual suspension (U.S. EPA, ASCE, and AWWA, 1996). 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-17

Table 11-3 lists example cake solids concentrations that have been achieved by 

mechanical dewatering operations performed in a laboratory (U.S. EPA, ASCE, and AWWA, 

1996). 

Table 11-3. Laboratory Results for Mechanical Dewatering Operations for Various 

Drinking Water Treatment Residuals

Residuals

Specific Gravity 

of Particles

Solids Concentration 

After Gravity 

Thickening

Solids Concentration After 

Mechanical Dewatering

Centrifuge Pressure Filter

Lime Softening Sludge (low 

Magnesium [Mg])

1.19 28.5% 60.6% 69.5%

Iron Sludge 1.16 26.0% 55.6% 64.6%

Ferric Hydroxide 1.07 7.2% 28.2% 36.2%

Lime Sludge (high Mg) 1.05 5.6% 24.8% 34.6%

Aluminum Hydroxide 1.03 3.6% 19.0% 23.2%

Source: U.S. EPA, ASCE and AWWA, 1996. 

11.2.1.3 Non-Mechanical Dewatering

Two types of non-mechanical dewatering are discussed in this section: storage 

lagoons and drying bed operations. Both are often used at the end of the residuals treatment train. 

Storage Ponds and Lagoons 

WTPs can collect and hold treatment residuals in settling ponds, tanks, or lagoons 

to separate solids. Plants can allow solids settling prior to further solids separation (e.g., 

thickening or mechanical dewatering) or discharge. In addition, lagoons and ponds can serve as 

long-term waste disposal. Since the separation occurs without physical means, the use of 

lagoons, ponds, and settling tanks is considered a non-mechanical dewatering process. 

WTPs collect residuals in storage ponds and lagoons and allow long-term 

sedimentation and compaction to separate the solids from the water. For metal hydroxide 

residuals like aluminum and iron (from coagulation) that are retained in a pond or lagoon for a 

month, solids concentrations of 10 percent in the settled sludge are common. For lime softening 

sludges, solids concentrations of 20 percent in the settled sludge are common (ASCE, 1997). 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-18

Storage ponds and lagoons are long-term residuals treatment approaches that

require periodic draining, cleaning, and maintenance. In addition, application of this residuals 

treatment method depends on the land available, evaporation rates (if no further discharge or 

recycling), and any ground water contamination concerns. This use of storage ponds might result 

in no discharge from the WTP; however, some WTPs perform intermittent discharges of 

overflows from the tanks. 

Drying Beds

Drying bed technologies share a common design concept: the cover material (bed) 

is installed over an under-drain consisting of gravel and perforated pipe. Drying bed technologies 

differ in the type of supporting material used for the bed surface (e.g., sand) and in whether 

external forces such as vacuum are used to promote the separation of the solids (see Figure 11-

4). Initially, water percolates through the bed and is collected by the under-drain and discharged. 

Additional dewatering then occurs via evaporation. The rate of evaporation depends on the local 

climate, the solids characterization in the residuals, and the extent of external drainage 

enhancement. Thin layers dry faster than thick layers, but result in higher operating costs. 

The following non-thermal drying bed technologies are used to reduce the 

moisture content in WTP residual solids: 

• Sand drying beds dewater residuals by gravity drainage, followed by 

evaporation. Water drains through the sand and exits through the underdrain. 

• Freeze-assisted sand beds are sand drying beds where the residuals are 

applied and then allowed to freeze (either naturally or mechanically). By 

freezing and then thawing the residuals, the solids become compressed 

together, more granular, and easier to dewater. WTPs use this technique 

for alum residuals, which have a gelatinous consistency that makes them 

difficult to dewater without the added freezing step. 

• Vacuum-assisted systems apply negative pressure to promote the 

percolation of the free water through the bed, thus speeding the drying 

process. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-19

• Solar drying beds can be used in specific geographic locations where the 

climate is sufficiently hot and dry (e.g., southwestern United States) to 

quickly dry the residuals. “Greenhouse” solar drying beds can also be used 

in less sunny areas, but they are not currently widespread. 

Lime solids concentrations as high as 50 percent have been achieved using drying 

beds. Alum residuals might require the addition of a chemical conditioner prior to drying. The 

solids content after the drying bed has been reported as high as 25 percent (U.S. EPA, ASCE, 

and AWWA, 1996). 

Sand

Gravel

Splash 

Slab

Side 

Wall

Gate

Collection 

System

Drainage

Sludge

Figure 11-4. Sand Drying Bed Section (U.S. EPA, ASCE, and AWWA, 1996) 

11.2.1.4 Thermal Drying

The final step in a residuals treatment train might be thermal drying. Thermal 

drying is not widely used by the industry because the costs of the technology are more than the 

costs savings that result from reduced residuals volume. In general, WTPs employ this 

technology to solve problems with pathogen control, odor control, and storage problems rather 

than to achieve solids/water separation alone. Thermal drying operations include direct fired 

systems (rotary kiln, fluidized bed, low temperature desorption), indirect fired (heated coils), and 

infrared radiation.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-20

11.2.2 Chemical Precipitation

Chemical precipitation removes dissolved metals from wastewater by the addition 

of a precipitating reagent. The reagent reacts with the metal ions and creates insoluble forms of 

the metal. This type of residuals treatment is applicable to aqueous waste streams, such as filter 

ion exchange backwash and rinse and membrane desalination concentrates. The most common 

precipitating reagent is hydroxide; WTPs can add lime, quicklime, soda ash, or caustic soda to 

the residuals to introduce the hydroxide ions. Depending on the metals present in the residuals, 

sulfide and ferrous salt can also be used. Chemical precipitation of the residuals can be used to 

remove aluminum, antimony, arsenic, cadmium, chromium, copper, iron, lead, mercury, 

selenium, silver, thallium, or zinc. (U.S. EPA, 1993) 

Equipment needed to perform chemical precipitation includes a stirred vessel 

reactor and clarifier. WTPs can add coagulants to aid solid settling. This treatment process 

results in: 1) a clean supernatant stream that is recycled or discharged, and 2) clarifier sludge. 

The clarifier sludge can be dewatered prior to disposal. (U.S. EPA, 1993) 

11.2.3 Increased Oxygen Content by Aeration 

Drinking water plants use aeration to treat both the source water and residuals

streams. Aeration increases the oxygen content in the water. The dissolved oxygen concentration 

in the water indicates the amount of oxygen used by biological components and provides a 

qualitative measure to judge the relative purity of the residuals stream. To control biological 

oxygen demand discharges and increase dissolved oxygen levels, WTPs add oxygen to residuals 

prior to discharge. 

11.2.4 Dechlorination

Residual chlorine in WTP discharges is toxic to many kinds of aquatic life and 

can react with organic materials in the receiving water to form carcinogenic trihalomethanes and 

organochlorines, including chloramines. Chloramines are highly toxic to fish and other 

organisms that live in water. Dechlorination removes the free or total combined chlorine residual 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-21

remaining after disinfection through the addition of sulfur chemicals such as sulfur dioxide, 

sodium sulfite, sodium bisulfite, sodium metabisulfite, and sodium thiosulfite. Carbon adsorption 

can also be used for total dechlorination; however, this process is typically more expensive.

Dechlorination requires an adequate control system to reduce residual chlorine to 

near-zero levels of residual chlorine without overdosing with sulfite. Too much sulfite can result 

in sulfate formation, which suppresses oxygen content and lowers the pH of the treatment 

residuals (U.S. EPA, 2000b). 

As presented in Section 3.3.2.2, EPA’s survey found that 93 percent of WTPs in 

the target population perform primary disinfection (i.e., 2,002 of the 2,151 WTPs). Most WTPs

(1,917 of 2,002) use free chlorine or chloramines for primary disinfection (1,599 and 318 plants 

respectively). EPA’s survey found that only 230 WTPs perform dechlorination. 

Costs for a dechlorination system depend on the particular conditions at the WTP. 

Cost considerations include capital costs (equipment, installation, and labor), operation and 

maintenance costs, and type of dechlorination chemical (U.S. EPA, 2000b). 

11.2.5 pH Adjustment

As a result of treatment chemical addition, the source water pH is altered during 

treatment operations to improve treatment performance. Ecosystems are more vulnerable than 

humans to changes in pH—for example, small changes can affect reproductive patterns and 

longevity. NPDES permits typically require the pH of residuals discharges to range between 6 

and 9. To adjust the pH, WTPs add acids to lower the pH and bases to raise the pH. Chemicals 

used by WTPs meet certified purity standards.

11.2.6 Nonwater Quality Environmental Impact Considerations 

Eliminating or reducing one form of pollution may create or aggravate other 

environmental problems. When reviewing whether to install a residuals treatment system, WTPs 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-22

and permit writers must look at the nonwater quality environmental impacts to determine any 

adverse effects on the environment.

11.2.6.1 Air Pollution and Control 

The majority of impurities removed during source water treatment include 

suspended solids, metals, synthetic organic chemicals, and microbes. EPA does not expect 

suspended solids, metals, or microbes to escape and become air pollutants during residuals 

treatment. Air stripping of volatile organics is a residuals treatment option available to WTPs; 

however, the use of air stripping is infrequent. Materials handling operations may generate 

fugitive emissions, and these emissions can be managed by installing a proper ventilation system 

or dust suppression system. 

Any increased air emissions as a result of installing residuals treatment would be 

primarily from the electric power generation facilities providing any additional energy and 

increased truck traffic due to additional sludge hauling.

11.2.6.2 Solid Waste Generation and Disposal 

WTPs that treat large volumes of source water can generate large volumes of 

residuals. Plants have several options for handling the sludge/slurries produced by source water 

treatment. Options range from recycle/reuse to direct discharge. Recycling, discharging to a 

landfill, and performing land application are the most common approaches (U.S. EPA, 2008). 

Residuals from WTPs are typically not hazardous and can be accepted by landfills

or managed via land application. Treatment and disposal methods for residuals may vary among 

WTPs and are based on the characteristics of the waste. The volume and characteristics of the 

residuals generated by WTPs are discussed in Section 7 of this document. 

11.2.6.3 Energy Requirements

The operation of the residuals treatment technology and operation of pumps to 

recycle residual streams would require additional energy. Total energy requirements for residuals 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-23

treatment technologies are not expected to create a large impact. Incremental energy costs may 

be incurred by the installation of residuals treatment technology or other practices. 

11.3 DISPOSAL PRACTICES FOR TREATMENT RESIDUALS

This subsection summarizes the typical disposal practices for residuals, including 

land application (Section 11.3.1) and land disposal via landfilling or deep well injection (Section 

11.3.2). These disposal practices help reduce or eliminate discharges to surface water and 

POTWs. As such, they can be employed to help WTPs become zero discharging facilities. 

11.3.1 Land Application of Residuals

After separating the solids from the wastewater and recovering usable materials, 

WTPs typically manage residual solids by land application or disposal in landfills (see Section 

11.3.2). Land application involves spreading residuals on the land and cultivating it into the soil.

 

The application of residuals onto land depends on the crop being grown, 

chemistry of the soil, and sludge properties. Land application typically occurs with lime 

softening sludge, and to some extent coagulation sludge (e.g., alum sludge). Lime softening 

sludge can be used on farm land in place of commercial products to neutralize soil pH. Alum 

sludge does not benefit the soil and is used only for filler material. The ideal land application of 

WTP residuals occurs on non-food chain crops, mine reclamation areas, and forests (U.S. EPA, 

1993). 

Disadvantages of land application might exist depending on the properties of the 

residuals. For example, land application can result in increased concentration of metals in the soil 

(and possibly ground water). Application of aluminum and iron hydroxide sludge from 

coagulation can result in the adsorption of phosphorus from the soil to the applied residuals, 

resulting in less productive soil (U.S. EPA, 1993). 

Land application requires large tracts of land and additional supporting 

infrastructure (tractor, pipes, lagoon, etc.). Further, ground water protection must also be 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-24

addressed. If 1,000 (dry) pounds of residuals are produced daily, about 300 acres and about 

$50,000 in annual operating expenses are required (U.S. EPA, ASCE, and AWWA, 1996).

WTPs can transport the residuals for offsite land application via tanker or truck. 

Residuals managed by land application typically contain less than 15 percent 

solids. There must be sufficient liquid in the residuals to form pumpable slurry. Land application 

methods include spraying from trucks or a sprinkler system, injecting into the subsurface, or 

discharging the slurry onto a selected field. Dewatered residual sludge can be spread on the land 

(U.S. EPA, 1993). 

Land application of membrane desalination concentrates is not as common as 

application of residual sludge. However, if desalination concentrates are applied to land, WTPs 

use percolation ponds, rapid infiltration basins, or landscape/crop irrigation (Malmrose, et al., 

2004). 

11.3.2 Disposal of Residuals to Landfills or Deep Injection Wells

Landfills for residuals can be either monofills (which contain one kind of waste) 

or municipal sanitary landfills (which contain many different kinds of waste). Disposal fees are 

usually based on weight of material presented for disposal and vary with different locations 

around the country. EPA regulates landfill disposal under the Resource Conservation and 

Recovery Act (RCRA). 

In addition to landfills, WTPs can dispose of residuals using subsurface, or deep 

well, injection. Concentrates from membrane desalination can be disposed of through this 

practice, which is commonly performed by plants in Florida (Malmrose, et al., 2004). EPA 

regulates deep well injection disposal under its Underground Injection Control (UIC) program.

11.4 WASTEWATER DISCHARGES OF TREATMENT RESIDUALS

Wastewater from WTPs, such as filter backwash water, can be recycled to the 

head of the source water treatment plant or evaporated from residual solids. Solids (or slurries) 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-25

from WTPs, such as lime softening sludge and coagulation sludge, can be dewatered and 

disposed of in a landfill or managed by land application. In some cases, WTPs opt to discharge 

treatment residuals either directly to waters of the United States or indirectly through publicly 

owned treatment works (POTWs). 

Direct discharge to surface waters is the most common waste management 

method for conventional filtration and precipitative softening plants. Some of these WTPs are 

also able to achieve zero discharge using recycling, land application, and landfill disposal. 

Indirect discharge is common for WTPs co-located with POTWs (i.e., operated by 

a local municipality) (U.S. EPA, 1993). Most membrane desalination plants are indirect 

dischargers or zero dischargers. 

Some of the best discharge practices that might be included in NPDES permits or 

implemented by WTPs include the following:

• Limiting discharge flow rate. Rather than allowing batch discharges, 

NPDES permits can require WTPs to slowly discharge residuals into the 

receiving stream. Slowly discharging the residuals allows dilution in the 

receiving stream and minimizes the impacts of the pollutant discharge. 

• Prohibiting discharges of solid residuals unless land-based use/disposal 

options are not feasible and/or WTPs demonstrate discharge does not 

degrade receiving water quality.

• Requiring that solids disposal from periodic cleaning of settling basins be 

land-based to avoid large batch discharges to the receiving stream. 

• Prohibiting discharges of chlorinated backwash (or other waste streams) 

unless the WTP demonstrates that the receiving water-quality standards 

can be met at all times.

• Equalizing28 the residuals discharge to avoid large batch discharges of 

pollutants. The WTP collects residuals in a tank, basin, or other device and

discharges at a controlled flow rate over time. This practice can be used 

for filter backwash water (generated at very high flow rates for short 

 

28 Equalization is the practice of collecting residuals in a tank, basin, or other device for later treatment or discharge 

at a controlled flow rate.
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-26

periods of time) and ion exchange regeneration waste streams (also 

generated at intermittent times) (AWWARF, 1987).

11.5 REFERENCES

American Society of Civil Engineers (ASCE)/American Water Works Association (AWWA), 

1997. Water Treatment Plant Design, 3rd Edition, New York: McGraw-Hill. Document Control 

Number (DCN) DW00961. 

American Water Works Association Research Foundation (AWWARF), 1987. Water Treatment 

Plant Waste Management. Prepared by Environmental Engineering and Technology, Newport 

News, VA, for AWWARF, Denver, CO. DCN DW00186. 

Malmrose, et al., 2004. Paul Malmrose, Jim Lozier, Michael Mickley, Robert Reiss, Jerry 

Russell, James Schaefer, Sandeep Sethi, Jennifer Manuszak, Robert Bergman, and Khalil Z. 

Atasi, Residual Management Research Committee Subcommittee on Membrane Residual 

Management, “2004 Committee Report: Residuals Management for Desalting Membranes,” 

Jour. AWWA, 96:12:73. American Water Works Association (AWWA), December 2004. DCN 

DW00032. 

Tchobanoglous, et al., 2003. George Tchobanoglous, Franklin L. Burton, H. David Stensel,

Wastewater Engineering Treatment & Reuse, 4th edition. Metcalf & Eddy, Inc., New York: 

McGraw-Hill. DCN DW00871. 

U.S. Environmental Protection Agency (EPA), 1992. Facility Pollution Prevention Guide (EPA600-R-92-088). Office of Solid Waste, Washington, DC. DCN DW00885. 

U.S. EPA, 1993. Large Water System Byproducts Treatment and Disposal Cost Document (EPA 

811-D-93-002). Office of Water, Washington, DC. DCN DW00058. 

U.S. EPA, ASCE, and AWWA, 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals (EPA 625-R-95-008). Office of Research and Development, 

Washington, DC. DCN DW03736. 

U.S. EPA, 2000a. Biosolids Technology Fact Sheet: Belt Filter Press (EPA 832-F-00-057). 

Office of Water, Washington, DC. [Internal Reference: U.S. EPA, 1987. Design Manual: 

Dewatering Municipal Wastewater Sludges.] DCN DW00900. 

U.S. EPA, 2000b. Wastewater Technology Fact Sheet: Dechlorination (EPA 832-F-00-022). 

Office of Water, Washington, DC. DCN DW00678. 

U.S. EPA, 2002a. Filter Backwash Recycling Rule: Technical Guidance Manual (EPA 816-R02-014). Office of Ground Water and Drinking Water, Washington, DC. DCN DW00064. 

U.S. EPA, 2003. Biosolids Technology Fact Sheet: Gravity Thickener (EPA 832-F-03-022). 

Office of Water, Washington, DC. [Internal Reference: U.S. EPA, 1987. Design Manual: 

Dewatering Municipal Wastewater Sludges.] DCN DW00901. 
Drinking Water Industry Report Section 11 – Technologies & Practices for Residuals

11-27

U.S. EPA, 2005. Drinking Water Treatment Facility Site Visit Report: James J. Corbalis Water 

Treatment Plant. Office of Water, Washington, DC. DCN DW00178. 

U.S. EPA, 2009. Drinking Water Survey Response Database – Technical Data for the 2006 

Drinking Water Industry Questionnaire. Office of Water, Washington, DC. DCN DW03790. 

Yohe, Thomas L. et al., 2006. White Paper: The Effect of Low Uniformity Coefficient Anthracite 

on Dual Media Filtration. The F.B. Leopold Company, Inc., Bryn Mawr, PA, March 20, 2006. 

DCN DW03779. 
12-1

SECTION 12

TREATMENT TECHNOLOGY COST CONSIDERATIONS FOR 

RESIDUALS THICKENING AND DEWATERING

As part of the drinking water industry review, EPA investigated technologies

available to reduce residual discharges from the most common types of water treatment plants 

(WTPs) that discharge to surface waters. EPA evaluated the factors that affect the cost of 

installing and operating residuals treatment systems from conventional filtration (i.e., 

coagulation and filtration) and precipitative softening plants since these plants are the most 

prevalent across the country. EPA did not analyze options for treating residuals from other types 

of plants (e.g., ion exchange, adsorption, or membrane desalination). This section summarizes 

EPA’s findings on costs and provides references to assist permit writers in estimating the costs 

for technology options. An example of costing analysis performed for a conventional filtration 

WTP is contained in the report Technical Analysis for Determination of Technology-Based 

Permit Limits for the Guaynabo Drinking Water Treatment Facility NPDES No. PR0022438

(U.S EPA, 2009). 

Section 12.1 presents a typical residuals treatment system which EPA used as part 

of its costing review. Section 12.2 provides background on cost data sources including cost 

models reviewed by industry experts and recent data provided by an industry trade association. 

Sections 12.3 and 12.4 summarize the determination of system size requirements and estimation 

of approximate costs for specific elements of the residuals treatment system. 

12.1 RESIDUALS THICKENING AND DEWATERING TREATMENT TRAIN

Residuals from softening and conventional filtration plants include sedimentation 

basin underflow and spent filter backwash (see Figure 6-1). These residuals may be treated by 

various dewatering processes. As described in Section 11.2, WTPs can use one or more solids 

removal processes to dewater WTP residuals. At each process in the residual treatment train, 

additional separation occurs. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-2

This report identifies cost considerations for the typical residuals treatment train 

illustrated in Figure 12-1. The residuals treatment train includes the following processes: spent 

filter backwash (SFBW) equalization basins and clarifiers, thickeners that further dewater 

clarifier underflow and treat sedimentation basin underflow from the source water treatment 

plant, centrifuges to further dewater underflow from the thickener, and final sludge handling 

prior to disposal. The figure does not show the source water treatment operations, only the 

treatment of residuals.

WTPs produce finished drinking water and generate residuals during source water 

treatment. Residuals from lime softening, coagulation, and filtration processes include filter 

backwash and sedimentation basin sludge. In the typical residuals treatment train, SFBW is 

pumped to equalization basins followed by a clarifier. Clarifier overflow can be discharged or 

recycled, as shown by the dashed line. Clarifier underflow is pumped to a thickener. 

The thickener receives the SFBW clarifier underflow, sludge from the WTP’s 

sedimentation basin, and the water that is removed during the dewatering step. Thickener 

overflow can be either recycled or discharged, as shown by the dashed line. Thickener underflow 

is pumped to dewatering. 

In Figure 12-1, dewatering is accomplished using centrifuges. Centrate, the water 

that is removed from sludge in the centrifuge is shown returning to the thickener. Dewatered 

solids are stored and ultimately disposed. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-3

Figure 12-1. Residuals Treatment Technology Train 

Spent Filter 

Backwash 

Equalization 

Basins (2) Spent Filter 

Backwash

Holding 

Tank

Overflow

Recycle or Discharge

Polymer

Underflow from WTP 

Sedimentation Basins

Overflow

Polymer

Off-Site Disposal

Centrate Recycled from Dewatering

Spent Filter 

Backwash 

Clarifier

Thickener

Polymer

Biosolids 

Storage 

Lime Bins

Dewatering 

Centrifuges (2)

Dewatered 

Sludge Cake

Source 

Water 

Treatment 

Plant

Source 

Water 

Treatment 

Plant
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-4

12.2 COST DATA SOURCES IDENTIFIED 

EPA identified several primary sources of data to assess the cost of installing and 

operating residuals treatment systems. First, EPA sought the opinion of industry stakeholders and 

experts to review and characterize cost information (see Section 2.6). Second, EPA used data 

provided by the American Water Works Association (AWWA, 2008), an industry trade 

association. Third, EPA incorporated information on its forthcoming Work Breakdown Structure 

(WBS) cost models for drinking water treatment technologies.

12.2.1 Drinking Water Treatment Technology Review Group 

EPA sought the opinion of a broad range of stakeholders to review documents 

that summarize the major technical and engineering issues related to the management of drinking 

water treatment residuals. Goals for this review included the following: 

• Characterization of typical residuals; 

• Identification of pollutants of concern; 

• Identification of pollution prevention and treatment technologies for 

residuals;

• Evaluation of 1993 and 1987 cost estimates developed by EPA and 

AWWA, respectively, for these residuals treatment technologies; and

• Application of prevention and treatment technologies. 

From 2005 through 2007, EPA held several meetings and provided stakeholders 

with various technical papers to review. EPA developed the document entitled, Identification of 

Technology Options (U.S. EPA, 2006), which included possible technology options to control 

residuals discharges and cost considerations for these options. EPA received comments on the 

technology options document and developed an input summary document (U.S. EPA, 2007). 

The Identification of Technology Options document (U.S. EPA, 2006) included a 

comparison of costing data sources developed for WTP residuals. EPA reviewed the following 

costing data sources:
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-5

• EPA, 1993: EPA developed and presented drinking water residuals 

treatment costs in the Large Water System Byproduct Treatment and 

Disposal Cost Document (U.S. EPA, 1993). EPA also presented these 

costs in Chapter 11 of the Office of Research and Development (ORD) 

Technology Transfer Handbook: Management of Water Treatment 

Residuals (U.S. EPA, ASCE, AWWA, 1996). This source is referenced as 

EPA's 1993 costs. 

• ERG, 2006: ERG, 2006 included a summary of information from early 

drafts of EPA's WBS cost models. This source has been superseded by upto-date information provided directly by EPA (see Section 12.2.3). 

• AWWA 1987: AWWA developed and presented residuals treatment costs 

in the handbook Water Treatment Plant Waste Management (AWWA, 

1987). 

Both EPA and AWWA estimated costs for several treatment technologies for 

residuals. Table 12-1 references specific sections for the residuals management cost equations 

that are available from EPA’s 1993 document and AWWA’s 1987 document. AWWA and EPA 

have also estimated lagoon costs and costs for evaporation ponds/sand drying beds. However, 

their use as a treatment option is highly dependent on weather/climate and the availability of land 

and their cost curves are highly dependent on land costs. Therefore, those options were not 

included in the costing review summarized in the Identification of Technology Options

document. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-6

Table 12-1. Available Residuals Management Cost Equations

Management Options 1993 EPA Section 1987 AWWA Section

Gravity Thickening 4.4 4.3.3

Chemical Precipitation 5.5 Not Included

Sludge Conditioning Polymer feed system and feed included with 

filter press costs.

4.4.2

Sludge Pumping Thickened sludge pumping costs to the filter 

press are included in the filter press costs. 

Assumes waste streams flow by gravity 

from the treatment plant to the settling tank.

4.5.2

Mechanical Dewatering – Pressure Filter 

Press

6.5 4.7.3

Mechanical Dewatering –Centrifuge 

(Scroll / Decanter)

6.10 4.6.3

Mechanical Dewatering – Belt Filter 

Press

Not included 4.9.3

Non-Mechanical Dewatering – Lagoon 

(lime softening sludge)

7.5 4.11.3

Non- Mechanical Dewatering – Lagoon 

(alum sludge)

7.6 4.11.3

Evaporation Ponds / Sand Drying Beds 8.5 4.10.3

POTW Discharge 9.5 Not included

Direct Discharge 10.5 Not included

Land Application – liquid sludge 11.5 Not included

Land Application – dewatered sludge 11.7 Not included

Non-hazardous Waste Landfill – off site 12.4 Not included

Non-hazardous Waste Landfill – on site 12.6 Not included

Hazardous Waste Landfill 13.4 Not included

Radioactive Waste Disposal Not included Not included

Deep Well Injection Not included Not included

Chemical Recovery Not included 4.12

Source: U.S. EPA, 2006.

POTW—Publicly Owned Treatment Works.

12.2.2 AWWA 2008 Cost Estimates 

AWWA sponsored a report entitled Costing Analysis to Support National 

Drinking Water Treatment Plant Residuals Management Regulatory Options (AWWA, 2008). 

AWWA estimated costs to install and operate a typical residuals treatment system at model 

plants and reviewed its estimates compared with actual installations. The resulting report 

presents a series of cost curves showing cost relative to population served, WTP type 

(conventional filtration or lime softening), and solids loading. By developing several of these 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-7

cost estimates for a range of plant sizes, this study was able to capture the range of costs 

associated with implementing residuals management at WTPs plants across the country. 

12.2.3 EPA’s Work Breakdown Structure (WBS) Cost Models

EPA has developed its draft WBS cost estimating models for drinking water 

treatment technologies andanticipates public release of selected models in 2012.29 The WBS 

models are spreadsheet-based engineering models for individual treatment technologies, linked 

to a central database of component unit costs. Under the WBS approach, a treatment technology 

is broken down into discrete components that can be measured for the purpose of estimating 

costs. The components include capital equipment (e.g., tanks, vessels, pipes, and instruments) 

and operational expenditures (e.g., annual expenditures on labor, chemicals, and energy).

By adopting a WBS-based approach to identify the components that should be 

included in a cost analysis, the models produce a transparent and comprehensive assessment of 

the capital and operating costs for a treatment system.

Instead of presenting a series of total cost curves, the WBS models estimate the 

cost of an individual treatment plant, including residuals management, at the level of line-item 

detail for individual pieces of equipment (e.g., clarifiers, piping, valves, instrumentation and 

system controls). Although the models estimate total cost for the entire treatment process, critical 

components of residuals management can easily be identified in the line-item output list. There 

are separate models for several conventional and emerging water treatment technologies.. The 

residuals management options available in each model are specific to the technology being 

modeled, driven by the types of residuals generated, their quantity, the frequency of generation 

(e.g., intermittent versus continuous), and their characteristics. 

EPA subjected the individual models to a process of external peer review by 

nationally recognized technology experts. EPA also has conducted benchmarking, comparing the 

model results to actual capital and O&M costs for existing drinking water treatment systems. 

 

29 For updates on the status of the WBS models, please check the EPA webpage at: 

http://water.epa.gov/scitech/wastetech/guide/treatment/index.cfm.
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-8

12.3 TREATMENT UNITS: DESCRIPTION AND CAPACITY

Many variables affect the cost of installing and operating a residuals treatment 

system, but the variable driving cost is capacity. The capacity requirements for treatment units 

determine how large they are and how many are required, which is by far the determining factor 

in the cost of residuals treatment. The factors that affect the capacity requirements are solids 

content and residuals flow rate (AWWA, 2008; U.S. EPA, ASCE, AWWA, 1996). 

This section discusses how to estimate capacity requirements for the residuals 

treatment system shown in Figure 12-1, which includes the following treatment units: 

• SFBW equalization tanks; 

• SFBW clarifier(s);

• Gravity thickener(s);

• Dewatering holding tank(s);

• Dewatering centrifuges; and

• Ancillary equipment, including pumps, associated piping, control devices, 

and buildings to house equipment as necessary. 

By estimating the flow of residuals from source water sedimentation, source water 

filtration, and residuals dewatering, the capacity requirements of a residuals treatment system can 

be determined and costs can then be estimated. 

12.3.1 Typical Ranges of Solids Content and Flow in Residuals from Conventional 

Filtration and Softening Plants

As much as the capacity requirements of treatment units drive costs, it is the 

solids content and flow of residuals that drive the capacity requirements (AWWA, 2008; U.S. 

EPA, ASCE, AWWA, 1996). For example, if the source water for a treatment system is lake 

water, the residuals flow and solids content may be low. If the source water for a treatment 

system is from a river that receives large sediment loads, the residuals flow and solids content 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-9

will be higher. The residuals treatment system would be smaller in capacity and less expensive to 

build and operate for the lake water WTP than for the river WTP, assuming their finished water 

productions are similar. 

In its 2008 study, AWWA estimated a range of residuals production, based on 

population served. The study found that plant flow rate (finished drinking water) averages 150 

gallons per capita per day (gpcpd) (AWWA, 2008). This corresponds well with results from 

EPA’s data collection, as shown in Table 3-4 (on an annual basis). AWWA compiled ranges of 

residuals production for the various plant sizes using unit residuals production data from EPA’s 

Information Collection Rule (ICR) database, shown in Table 12-2. These ranges can be used to 

help estimate capacity requirements for treatment units.

Table 12-2. Ranges of Residuals Production Estimated for AWWA 2008 Study

Population

Average Flow Rate

for WTP

(MGD)

Unit Residuals Production

Design Daily Residuals Production

(dry)

Low a (lb/mg) High a (lb/mg) Low (lb/day) High (lb/day)

Coagulation and Filtration

13,000 2.0 120 539 351 1,577

30,000 4.5 810 3,638

70,000 10.5 1,890 8,489

110,000 16.5 2,970 13,340

175,000 26.3 4,725 21,223

265,000 39.8 7,155 32,138

400,000 60.0 10,800 48,510

650,000 97.5 17,550 78,829

1,000,000 150.0 27,000 121,275
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-10

Table 12-2. Ranges of Residuals Production Estimated for AWWA 2008 Study

Population

Average Flow Rate

for WTP

(MGD)

Unit Residuals Production

Design Daily Residuals Production

(dry)

Low a (lb/mg) High a (lb/mg) Low (lb/day) High (lb/day)

Precipitative Softening

13,000 2.0 1,278 3,151 3,738 9,217

30,000 4.5 8,627 21,269

70,000 10.5 20,129 49,628

110,000 16.5 31,631 77,987

175,000 26.3 50,321 124,071

265,000 39.8 76,201 187,878

400,000 60.0 115,020 283,590

650,000 97.5 186,908 460,834

1,000,000 150.0 287,550 708,975

Source: AWWA, 2008.

MGD—million gallons per day.

lb - pound.

mg - milligram.

a - The AWWA used the median solids concentration from lake sources in the ICR database for the “low” unit 

residuals production and the 90th percentile solids concentrations from river sources in the ICR database for the 

“high” residuals production.

12.3.2 Spent Filter Backwash Equalization and Clarifier Capacity 

As described in Section 7, WTPs typically backwash filters to clean them, 

generating SFBW, including filter-to-waste,

30 typically at a rate of 2 to 5 percent of the total 

plant production volume (U.S. EPA, ASCE, AWWA, 1996). For example, a WTP producing 1 

MGD of finished water would generate approximately 20,000 to 50,000 gallons per day (GPD) 

of SFBW. Typically, WTPs backwash one filter at a time, which results in spikes of SFBW sent

to residuals treatment. SFBW equalization tanks provide a consistent, lower flow through the 

residuals treatment system. The lower flow lowers the required treatment capacity, and the cost 

to install and operate the overall treatment system decreases (AWWA, 2008). 

In their 2008 study, the AWWA found that WTPs could estimate the optimal 

capacity required for SFBW equalization based on a SFBW recycle flow rate of 6 percent of the 

 

30 Filter-to-waste is the initial permeate production when a filter is brought back online following backwashing, and 

is part of the backwash waste stream.
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-11

total WTP flow rate (AWWA, 2008).31 Also, the AWWA found that WTPs should install at least 

two equalization basins to provide redundancy. For a smaller plant, a single tank may meet 

capacity requirements; however, the plant would require an additional tank to provide backup. 

Table 12-3 summarizes optimal capacities for SFBW equalization tanks from AWWA’s 2008 

study. The table presents both average and peak flow rates for the WTP, which are used when 

sizing equipment and determining required volume capacity.

Table 12-3. SFBW Equalization Basin Capacity

Population 

Served

Plant Flow Rate Optimal Capacity b

Number of 

Basins

Basin 

Diameter a Average (mgd) Peak (mgd) MGal ft3

13,000 2.0 3.9 0.22 28,845 2 38

30,000 4.5 9.0 0.44 58,151 2 53

70,000 10.5 21.0 0.97 129,336 2 79

110,000 16.5 33.0 1.45 194,365 2 97

175,000 26.3 52.5 2.03 272,027 2 94

265,000 39.8 79.5 2.44 326,830 2 102

400,000 60.0 120.0 2.88 385,001 2 111

650,000 97.5 195.0 2.16 288,390 2 96

1,000,000 150.0 300.0 1.43 190,896 2 96

Source: AWWA, 2008.

a - Basin height was limited to less than 20 feet, and basin diameter was limited to 150 feet. AWWA’s analysis was 

based on actual residuals treatment plant installations and standard assumptions used for engineering design.

b - Design capacity based on 6 percent of plant flow rate (peak capacity is used to set maximum size needed). As 

plant flow increases, required capacity decreases. That is, the backwash:plant flow ratio decreases as plant flow 

increases. AWWA’s analysis was based on actual residuals treatment plant installations and standard assumptions 

used for engineering design.

As shown in Figure 12-1, water from the SFBW equalization basins can be treated 

through clarifiers to initially remove solids. The optimal capacity of SFBW clarifiers can be 

derived from the same flow rates shown in Table 12-3. The cost data sources discussed in this 

section provide further details on clarifier sizing, polymer feed rates, and design assumptions. 

After equalization and clarification, the treated SFBW overflow is either recycled or discharged. 

SFBW clarifier underflow typically contains 1 to 3 percent solids, and further dewatering is 

necessary, hence the thickener (U.S. EPA, ASCE, AWWA, 1996; Bosgraaf, 2005). 

 

31 The general assumption of 6 percent is based on review of plant data that show recycle to be approximately 6 

percent of spent filter backwash water and recommendations by The Partnership for Safe Water and EPA’s Filter 

Backwash Recycling Rule (recycle no more than 5 to 10 percent of total plant flow).
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-12

12.3.3 Gravity Thickener Capacity 

As shown in Figure 12-1, the typical gravity thickener receives clarified SFBW 

and sedimentation tank underflow from the WTP. Gravity thickeners increase the solids content 

of sludge and further remove solids from the residuals wastewater stream. The thickened sludge 

is pumped to the dewatering portion of the residuals treatment train, and the thickener overflow 

is either recycled or discharged.

In thickened lime sludge, the solids content ranges from 15 to 30 percent (U.S. 

EPA, ASCE, AWWA, 1996; AWWA, 2008); thickened coagulant sludge tends to have a solids 

content between 2 to 10 percent (U.S. EPA, ASCE, AWWA, 1996; AWWA, 2008). 

Gravity thickener capacity requirements depend on many site specifics. Main 

design parameters include:

• Solids Loading Rate (SLR) – Thickener diameter and surface area are 

determined by the required SLR. Although generally recommended SLRs 

are available, WTPs can perform site-specific tests to determine the 

optimum design SLR. In general, the coagulant sludge SLR is between 2 

and 3 lb/day/ft2

, and the lime softening sludge SLR is between 20 and 40 

lb/day/ft2

 (U.S. EPA, ASCE, AWWA, 1996; AWWA, 2008). 

• Hydraulic Loading Rate (HLR) – For WTP sludges, the HLR is not 

typically the limiting factor for thickener design (U.S. EPA, ASCE, 

AWWA, 1996). However, if large volumes of water will be pumped to the 

thickener, equalization may be required. For example, if sedimentation 

tanks are emptied periodically, the increased HLR from such a batch 

discharge may lead to poor solids removal. HLR is measured in 

gal/day/ft2

. 

• Residuals flow – The flow of residuals to the gravity thickener can be 

calculated as the summation of the clarified SFBW, sedimentation tank 

underflow, and recycle from dewatering. 

The cost data sources discussed in this section provide further details on gravity thickener 

capacity, and design assumptions. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-13

12.3.4 Sludge Dewatering Centrifuges and Equalization Tanks

The most common type of WTP dewatering is evaporation through nonmechanical dewatering such as sludge drying beds, ponds, or lagoons, as shown in Table 3-11. 

However, these technologies are not universally available, and the feasibility and costs of 

lagoons and evaporation ponds depend on land availability. Therefore, EPA analyzed costs for 

mechanical dewatering. Specifically, EPA collected information on the costs to install and 

operate centrifuges, because this technology can be applied universally to precipitative softening 

and conventional filtration residuals treatment. For coagulation plants, WTPs may use belt filter 

presses for dewatering; however this application is not common for softening residuals. 

Precipitative softening plants may use plate and frame presses for dewatering; however this 

application is not commonly used for coagulation residuals due to high operation and 

maintenance costs (AWWA, 2008). 

As shown in Figure 12-1, thickener sludge is pumped to the dewatering process. 

The sludge solids content will fluctuate, and a holding tank for equalization is needed to simplify 

the design and operation of dewatering centrifuges. 

As with sludge thickening, the dewatering holding tank capacity requirements 

depend on SLR. However, these values are less complicated by site specifics than thickener 

SLR. The SLR can be calculated based on the influent solids load and holding tank dimensions. 

The solids load entering the centrifuges can be calculated as:

 Solids Load (lbs/day) = Thickener Sludge (gpd) × Sludge Density (lbs/gal) (Eq. 12-1) 

where:

Thickened Sludge = Volume of sludge pumped from the thickener; and 

Sludge Density = 65 lb/ft3, or 8.7 lb/gal (AWWA, 2008), by assumption. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-14

The holding tank size will vary based on WTP requirements, such as capacity

limitations. In its 2008 study, the AWWA estimated holding tank diameters between 10 to 100 

feet (AWWA, 2008). Once holding tank surface area is determined, the SLR can be calculated 

as:

SLR (lbs/day/ft2) = Solids Load (lbs/day) ÷ Tank Surface Area (ft2) (Eq. 12-2) 

The dewatering capacity of centrifuges can then be calculated from the solids 

loading rate and dewatering treatment duration. Treatment duration will vary by plant. Small 

WTPs may operate the centrifuges for less than eight hours per day, while larger plants may run 

multiple shifts daily. For example, treatment duration for a large plant operating two shifts will 

be 16 hours per day, or 112 hours per week. Treatment duration for a small plant operating one 

five-hour shift will be five hours per day, or only 35 hours per week for a seven-day work week. 

12.3.5 Ancillary Equipment 

Ancillary equipment includes pumps, piping, instrumentation, biosolids storage 

bins, and treatment system housing. In its 2008 study, AWWA estimated the costs for the 

ancillary equipment, except pumps, as indirect costs, using a percentage of the total direct capital 

cost (AWWA, 2008). Therefore, of the ancillary equipment, only pumps are not included in the 

AWWA cost estimate. When sizing and costing a pump, plants review the flow rate required, 

hydraulic properties (e.g., need to pump to a higher elevation vs. gravity flow, amount of solids 

in the waste stream), any potential corrosion issues, and the need for backup equipment. 

In comparison, the EPA WBS cost models estimate the cost of ancillary 

equipment, including residuals pumps, piping, instrumentation, storage, and buildings, as direct 

line items, based on engineering requirments. In the WBS framework, indirect costs that are not 

directly related to the treatment technology used or the amount or quality of the treated water 

produced, but that are associated with the construction and installation of a treatment process. 

Section 12.4.2 further discusses indirect costs. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-15

12.4 COSTS TO INSTALL AND OPERATE RESIDUALS TREATMENT 

SYSTEMS 

The cost to install and operate a residuals treatment system includes: 

• The capital costs to construct and install treatment units, such as an 

equalization tank and centrifuge; 

• The indirect capital costs associated with construction and installation, 

such as project management;

• Annual costs, such as operations and maintenance requirements; and

• Additional, site-specific costs that vary between WTPs.

Upgrades to or retrofitting of an existing residuals treatment system may require 

additional costs that are not included in this section. 

12.4.1 Capital Costs for Treatment Units

Estimates of capital costs to construct treatment units are available from sources 

including: 

• AWWA, 1987: AWWA-developed residuals treatment costs. 

• EPA-developed residuals treatment costs (U.S. EPA 1993 and U.S. EPA, 

 ASCE, and AWWA, 1996). 

• AWWA, 2008: AWWA-developed full cost estimates.

• EPA’s forthcoming draft WBS Cost Models. 

 For certain treatment units, EPA compared estimated treatment unit costs. In 

general, the studies are not directly comparable due to differences in methodologies. The 2008 

AWWA study built on the earlier two studies, and identified some additional costs that they did 

not include: the need for redundancy, differentiation by WTP type (coagulation versus 

softening), and trends in solids loads being higher than estimated in the earlier studies. Softening 

plants typically have higher costs than conventional filtration plants due to the larger amount of 

residuals generated (AWWA, 2008). 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-16

 The EPA WBS cost models also differentiate by WTP type (including coagulation, 

softening, and more than a dozen other technologies) and address the need for redundancy. The 

specific capital equipment costs included in a WBS model depend on the WTP technology and 

the residuals management option chosen for that technology. The line-item capital costs in the 

WBS models for coagulation and softening, however, cover all of the components shown in the 

typical treatment train in Figure 12-1. The WBS models also include more ancillary equipment 

components as direct line items, instead of indirect costs, and include costs not covered in some 

of the previous costing studies, such as land and permitting cost.

12.4.2 Indirect Capital Costs

The magnitude of indirect cost multipliers depends greatly on which cost 

components are defined as indirect costs rather than direct capital costs (AWWA, 2008). Table

12-4 compares the indirect cost factors from the studies. 

12.4.3 Annual Operating Costs

Annual operating costs for residuals treatment systems include chemical 

purchasing, labor to operate and maintain the treatment units, dewatered sludge disposal, 

electricity, and materials to maintain the treatment units. In the AWWA (2008) estimates, sludge 

disposal was the most expensive annual cost. AWWA estimated sludge disposal costs from 

previously published data. In 2007 dollars, the sludge disposal costs would be $0.37 per wet ton 

per mile for transportation and $36.32 per wet cubic ton for disposal (AWWA, 2008). In the 

EPA WBS models, the relative magnitude of various operating costs varies depending on a 

variety of factors. These factors include, but are not limited to: the WTP technology, the types of 

residuals generated, their quantity, the frequency of generation, residuals characteristics, the 

types of residuals treatment employed, the disposal or discharge options chosen, and the degree 

of automation of the process. Sludge transportation and disposal unit costs, however, are similar 

to those in the AWWA (2008) estimates. In 2010 dollars, the WBS unit costs are $0.468 per ton 

per mile for transportation and $59.99 per ton for non-hazardous waste disposal. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-17

12.4.4 Additional Costs that Vary Between WTPs 

Costs that differ by WTP were excluded from the costs presented in this section. 

These costs will vary because of WTP location, receiving stream, and other site-specific factors. 

However, they will affect the overall residuals management costs. Additional costs include the 

following: 

• Sample Collection and Laboratory Analysis. Costs for sample 

collection and analysis to determine solids content, free liquids (i.e., 

separate phase), toxicity characteristics, and other parameters. Depending 

on the residuals management method selected, sampling requirements 

could be minimal or extensive. 

• Permits and Other Regulatory Requirements. Costs for permits and 

other regulatory requirements. Requirements vary considerably from state 

to state and for given management option. Permitting costs vary based on 

the capacity and complexity of a unit and the local governing jurisdiction. 

Management methods that may require permits include landfills, land 

application, evaporation ponds, and storage lagoons. In addition, 

generators of hazardous waste are required to comply with EPA Resource 

Conservation and Recovery Act (RCRA) generator regulations. 
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-18

Table 12-4. Indirect Cost Factors and Selected Unit Costs for WTP Residuals Treatment System Planning

Component 

Factor

AWWA

(1986 Cost)c

EPA

(1992 Cost)d

AWWA

(2008 Cost)e

EPA’s Draft WBS Models (2010 Cost)f

Land Not estimated as 

part of study

$10,000/acre Not estimated as 

part of study

$13,000 to $115,000 per acre (based on system size)

Buildings $75/ft2 (1st floor); 

$50/ft2 (2nd floor)

$33.00/ft2 Included with 

treatment unit cost

$39 to $152/ ft2

(based on quality; size; and heating, ventilating, and air conditioning 

(HVAC))

Piping A percent of 

equipment costs 

and experience 

from authors

5% of installed 

equipment a

10% of installed 

equipment

Included in direct costs. Varies by material, diameter, length, process 

size; includes additional length to account for fittings cost

Pipe fittings 20% of piping 

costs b

Electrical Not estimated as 

part of study

1% of installed 

equipment

15% of installed 

equipment, piping, 

and general costs 

(see below)

10% of direct cost for outdoor lighting, yard wiring, switchgear, 

transformers, and miscellaneous wiring (General building electrical, 

such as building wiring and lighting fixtures, is included in the 

building cost. Certain other electrical costs are included in direct costs 

for system controls and pumps.)

Instrumentation Not estimated as 

part of study

1–2% of installed 

equipment

15% of installed 

equipment, piping, 

and general costs

Technology- and site-specific instrumentation and system controls are 

included in direct costs

Engineering fee Not estimated as 

part of study

15% of direct 

capital

Included as part of 

contractor’s 

overhead and 

profit

Direct cost multipliers: 

20% <1 mgd

12% 1–9.9 mgd

8% >= 10 mgd

Contingency, 

bonding, and 

mobilization

10% contingency 

applied to 

manufacturing 

furnished 

equipment costs. 

These costs cover 

site-specific 

requirements and 

extras normally 

encountered.

20% of direct 

capital

25% of installed 

equipment, piping, 

general costs, 

electrical, and 

instrumentation

Contingency: 0% to 13.4% of direct costs

Mobilization/demobilization: 2% to 5% of direct costs

Performance bonds: up to 2.5% of direct costs
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations

12-19

Table 12-4. Indirect Cost Factors and Selected Unit Costs for WTP Residuals Treatment System Planning

Component 

Factor

AWWA

(1986 Cost)c

EPA

(1992 Cost)d

AWWA

(2008 Cost)e

EPA’s Draft WBS Models (2010 Cost)f

Contractor’s 

overhead and 

profit (nonconstruction 

cost)

20% of 

construction cost 

subtotal

12% of direct 

capital

30% of total 

construction cost

General contractor overhead: 3.2% to 10% of direct costs

(Includes construction management fee and builder’s risk insurance. 

Installing contractor overhead and profit is included in direct costs for 

installed equipment.)

Additional addon costsNot estimated as 

part of study

Not estimated as 

part of study

Included as part of 

contractor’s 

overhead and 

profit (nonconstruction cost)

Pilot study: equipment rental, analytical costs, labor cost

Permits: vary by technology and site

Additional 

indirect cost 

categories

Not estimated as 

part of study

Not estimated as 

part of study

General costs: site 

work, yard piping, 

and final grading

30% of installed 

equipment and 

piping 

Indirect 

construction cost: 

30% of installed 

equipment, piping, 

general costs, 

electrical, 

instrumentation, 

and contingency 

(i.e., total direct 

construction costs)

Architectural fee: 4.5% to 9% of building costs

Sitework: $10.90/ ft2

Yard piping: varies by site

Geotechnical: varies by site

Standby power: varies by site

Miscellaneous allowance: 10% of direct costs

Financing during construction: 0% to 5% of direct costs

Legal, fiscal, administrative: 2% of direct costs

a - Piping costs are calculated directly when piping is a significant cost (e.g., for direct discharge).

b - Factor is used when piping costs are calculated directly.

c - AWWA, 1986. 

d - EPA, 1993. 

e - AWWA, 2008. 

f – For updates on the status of the WBS models, please check the EPA webpage at: 

http://water.epa.gov/scitech/wastetech/guide/treatment/index.cfm.
Drinking Water Industry Report Section 12 – Treatment Technology Cost Considerations 

12-20

• Additional Land Requirements. Some WTPs will require additional land 

or have no adequate land adjacent. If land is not available, a residuals 

treatment system may not be possible, and alternate scenarios, such as 

piping residuals, would be necessary. 

• Power Capacity. Depending on location, additional power capacity 

needed for residuals treatment may not be available or may require 

additional costs.

12.5 REFERENCES

American Water Works Association (AWWA), 1987. Water Treatment Plant Waste 

Management. Document Control Number (DCN) DW00186. 

AWWA, 2008. Costing Analysis to Support National Drinking Water Treatment Plant Residuals 

Management Regulatory Options. Submitted by Environmental Engineering & Technology, Inc. 

Newport News, VA. DCN DW03766. 

Bosgraaf, 2005. Bosgraaf, Bob (U.S. Filter). Water Treatment Residuals Products Presentation 

for EPA. Presentation to EPA on May 25, 2005. DCN DW00156. 

Eastern Research Group (ERG), 2006. Presentation: Work Breakdown Structure (WBS) 

Residuals Management Cost Model from EPA OGWDW. DCN DW00383. 

U.S. Environmental Protection Agency (EPA), 1993. Large Water System Byproducts Treatment 

and Disposal Cost Document (EPA 811-D-93-002). Office of Water, Washington, DC. DCN 

DW00058. 

U.S. EPA, 2006. Identification of Technology Options. Office of Water, Washington, DC. 

November 7, 2006. DCN DW03 

U.S. EPA, 2007. Review Input Summary: Identification of Technology Options. Office of Water, 

Washington, DC. September 2007. DCN DW03750. 

U.S EPA, 2009. Technical Analysis for Determination of Technology-Based Permit Limits for 

the Guaynabo Drinking Water Treatment Facility NPDES No. PR0022438 (EPA 821-R-11-006).

Office of Water, Washington, DC. March 23, 2009. 

U.S. EPA, ASCE, and AWWA, 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals (EPA 625-R-95-008). Office of Research and Development, 

Washington, DC. DCN DW03736. 
13-1

SECTION 13

ECONOMIC CONSIDERATIONS FOR PERMIT WRITERS

13.1 INTRODUCTION

This section outlines a methodology for determining whether a proposed residuals 

management technology is economically achievable for a public water system (PWS) under their 

NPDES permit. Because drinking water systems are usually regulated monopolies or publicly 

owned entities, the way to evaluate economic achievability of technological requirements is 

different than the methods that would normally be used when evaluating impacts in a 

competitive industry. 

In a competitive industry, the total cost of installing and operating pollution 

control technologies are often not passed on to the consumer. A firm that raises its price in a 

competitive industry risks losing sales or even customers. Therefore, companies operating in a 

competitive market will usually decide to raise their price by less than the amount of the 

additional production cost, lowering their operating profits as a result. In competition, it’s also 

possible that the price increase the market will bear would require a firm to lower its operating 

profits to the point where they are negative and the firm can’t stay in business. 

Because public water systems are regulated monopolies or publicly owned 

entities, the rates (prices) they charge their customers are not set in an unregulated competitive 

marketplace. Instead, the rates are based on the costs the PWS incurs in delivering water to their 

customers. These costs include residuals management expenditures that are incurred as a result 

of NPDES permitting, as well as costs associated with complying with Safe Drinking Water Act 

regulations. Unless a PWS has access to funds not derived from water services, they are likely to 

completely pass on residuals management compliance costs to customers in the form of higher 

water rates. Therefore, the ability of the PWS to pay for residuals management technology is 

only limited by its ability to raise the water rates it charges its customers. Of course, there is a 

limit to how much customers can and will pay for their water services.

 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-2

The economic analysis of improved residuals management for a PWS is focused

on the impact of water rate increases on customers and, in particular, on their residential 

customers. Pollution abatement measures would be deemed economically achievable if the 

PWS’s customer base is able to bear the impact of the water rate increases associated with the 

costs of the residuals management improvements. The analysis of customer impact could be 

extended to businesses; however, the impact to businesses of water rate increases is not likely to 

be substantial, except potentially in instances where effluent treatment costs for the PWS are 

very high and certain business customers rely heavily on publicly supplied water as an important 

factor in their production processes. But even these firms may be able to pass costs on to their 

customers.

13.2 A METHODOLOGY FOR DETERMINING THE ECONOMIC 

ACHIEVABILITY OF BEST PROFESSIONAL JUDGMENT EFFLUENT 

LIMITATIONS FOR A PUBLIC WATER SYSTEM

The approach to determining the economic achievability of residuals management 

technology improvements is conducted at the system or utility level, depending on whether the 

costs for a treatment technology would be spread amongst consumers at the system level or 

across all the customers of the larger utility. For the purpose of determining the financial strength 

of the larger corporate entity which owns the individual drinking water treatment plant 

implementing the NPDES residuals technology improvements and the impacts to the large 

corporate entity’s customer base, EPA must look to the level of the system (the PWS). It is at the 

system level that the costs of technology improvements are financed, and it is the system that can 

spread the costs of upgrades to a specific plant or plants across its total customer base. In some 

instances a larger utility may own more than one system and spreads the cost of technology 

improvements across those systems. In these cases the proper level of financial assessment is at 

the level of the utility.

The assessment of economic achievability for NPDES residuals management 

technology at the PWS level consists of four steps, once the annualized costs associated with the 

technology improvements have been determined: 

1. Estimate the increase in water rates for household customers.
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-3

2. Estimate the increase in the annual cost of water as a result of residuals 

management improvements for household customers by Census-based 

income class.

3. Based on the ratio of water cost increase as a result of additional residuals 

handling expenditures to household income by Census-based income 

class, estimate the number and percentage of households (total and within 

income classes) for which the estimated increase in household cost of 

water exceeds the chosen percent of median household income 

achievability threshold. 

4. For water systems in which the number and/or percentage of adversely 

affected households exceed the relevant threshold, assess the potential for 

using rate-structure-based methods to shift the potential water rate 

increase away from households for which the increase is determined to be 

too great. 

Embedded within these four steps are two important threshold criteria that are not 

prescribed here. The first criterion is the percent of median household income achievability 

threshold which represents the maximum acceptable portion of household income that could be 

expended on new residuals management treatment technologies without significantly affecting a 

household’s financial condition. It is important to remember that, this threshold value represents 

that fraction of income which can be spent by the household on the incremental cost of the new 

NPDES permitting requirements. The second criterion to be set is the number of households 

whose cost share is greater than the threshold percent of income that would cause the technology 

costs to be considered not economically achievable. Ultimately, which percent of income 

achievability threshold used, as well as the number of households for which rates exceed the 

percent of income threshold, are important policy decisions for the Director to consider. 

In order to provide a numerical example of this suggested NPDES residuals 

management economic achievability methodology, EPA selected a median annual household 

income threshold. This threshold is based on a review of the economic support documents from 

past Effluent Limitation Guideline (ELG) rulemakings. Particular attention was focused on the 

regulated entities that operate as a local monopoly much the same way as PWSs operate. 

Through this review, EPA found that the economic achievability analysis that most closely 

mirrored the proposed drinking water NPDES permit cost achievability methodology was 

conducted for the final “Effluent Limitations Guidelines, Pretreatment Standards, and New 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-4

Source Performance Standards for the Landfills Point Source Category” rulemaking. The 

Landfills ELG economic achievability analysis used a compliance cost share of household 

income test. This test was used to assess community level economic impacts when municipallyowned landfills would likely pass costs on to household customers. The ratio of the average per 

household share of compliance costs to median household income was calculated and if the ratio 

exceeded a 1.0 percent threshold EPA determined that the technology costs would likely have a 

“severe impact” to the community. Although the achievability methodology presented here is 

more refined, the 1.0 percent of median household income threshold value from the Landfills 

ELG will be utilized in the example analysis. Because the 1.0 percent threshold in the Landfills 

ELG signified a high probability of severe economic impacts to the community EPA 

recommends to the Director that the percent of median household income ultimately selected be 

lowered if moderate impacts are the measure of interest. 

EPA did not select a value for the maximum number of households being served 

by the PWS that would be allowed to receive a treatment cost share greater than the threshold 

percent of income in the following example. The Agency does want to note that: (1) a decrease 

in the allowed percentage of households whose share of costs exceeds the household income 

threshold (or a decrease in the income threshold) will make the economic achievability more 

stringent; and (2) increasing the number of households that can exceed the income threshold (or 

raising the income threshold value) will have the effect of making the achievability test less 

stringent. 

The remainder of this section demonstrates how to go about completing the four 

steps to determining the economic achievability of NPDES residuals management technology 

improvements at PWSs.

13.2.1 Estimate Increase in Water Rates to Household Customers

Regardless of the specific criteria used to determine economic achievability for 

PWSs, the analysis should begin with estimating the increase in total water costs to all

households in the water system service territory due to the proposed improvements. This figure 

represents the total revenue to be raised by the increase in water rates to household customers, 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-5

and the estimated quantity of water consumed by households. Estimating the change in water 

rates involves two main steps: 

1. Estimate the aggregate rate effect due to technological improvements; and

2. Estimate the change in water rates per unit of consumption, by customer 

class. 

13.2.1.1 Estimate Total Rate Effect of Compliance Costs

The estimated change in water rates, and resulting costs to households, should 

reflect how the cost to adopt technology improvements would actually be incorporated into a 

PWS’s rate structure. The change in a PWS’s revenue requirements is typically the basis for 

setting water rates. For annually recurring costs (e.g., operation and maintenance (O&M) costs), 

this analysis is straightforward: such costs are simply added to the system’s total revenue 

requirements. However, for capital or other non-annually recurring costs, completing this 

analysis will require several assumptions. 

The first assumption involves how these costs would be financed, including the 

cost and terms of the financing. Funds may be borrowed, taken from current operating revenue, 

or, if the company is privately owned, gained from issuing equity stakes in the company. The 

recommended assumption is to use the weighted average of the reported cost of capital and 

repayment periods for projects undertaken within the past five years to establish the cost and 

terms of the capital required.

The second assumption involves how costs would be incorporated into the PWS’s 

near-term rate structure. This issue includes the cost recovery and rate-making practices at the 

affected PWS. The cost recovery for capital outlays may be: 

• Fixed to a constant annual value over the cost recovery period, or 

• Based on a framework of depreciating rate base with an allowed rate of 

return. 
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13-6

Under the constant annual payment framework, the cost analysis is relatively 

straightforward. The annual charge for capital outlays is calculated as a constant annual payment, 

based on an interest rate32 and repayment term of the amount to be financed. This approach is 

appropriate if the average repayment period is approximately equal to the estimated useful life of 

the capital improvements. The annual charge would be calculated as follows: 

( )

( ) 1r1

r1r Capital Charge Capital Outlay N

N

−+

+× = × (Eqn. 13-1) 

where:

Capital charge = The constant annual rate increase to recover the new 

technology capital outlay over the N year capital recovery 

period at the interest rate r. 

Capital outlay = The capital outlay for implementing the new technology (or 

other non-annually occurring outlays associated with the 

new technology).

N = The number of years over which the Capital outlay is 

recovered in water system rates presumed to be equal to the 

estimated useful life of the new capital equipment.

r = The allowed interest rate for recovering capital outlay over 

the capital recovery period, presumed to be equal to the 

average of interest rates reported for recent borrowings by 

the water system.

The situation of a depreciating rate base with allowed rate of return follows the 

conventional regulated utility ratemaking framework, but the cost analysis is somewhat more 

complicated. The annual charge is based on the amount of capital outlay placed into “ratebase,”33 the depreciation period for the capital outlay, and the allowed rate of return on the ratebase. The capital charge in any year is typically calculated as the sum of the straight-line 

depreciation of the initial rate-base value and the product of the rate of return and the depreciated 

rate-base value. Under this approach, the annual capital charge would be calculated as follows: 

 

32 The interest rate should correspond to the credit ratings of the PWS. The bond yield for the appropriate credit 

rating can be found in sources such as S&P or Moody’s Investor Services.

33 “Rate-base” refers to the aggregate value of capital the PWS is entitled to recover through customer water rates, 

with a rate of return.
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-7

( ) ( )

( ) 1n

Capital Outlay/ rN Capital Outlay N/i-N

Capital Charge 

n

0i

+





 





×+ ×

=

∑= (Eq. 13-2) 

where:

Capital Charge = The average amount of the technology capital outlay 

recovered annually in the total water rate over the first 

(n+1) years of capital recovery. For this analysis, EPA

would propose to look at a relatively short period of initial 

rate effect – e.g., the first three years, in which case the 

value n would be 2. 

Capital Outlay = The capital outlay for implementing the new technology (or 

other non-annually recurring outlay associated with the 

new technology).

N = The number of years over which the Capital Outlay is 

depreciated for ratemaking purposes – presumed to be 

equal to the estimated useful life of the new capital 

equipment. 

i = The number of years since placing the Capital Outlay into 

rate base.

n+1 = The total number of years for which the annual charge is 

calculated. For this analysis, EPA would use something like 

n+1=3, or n=2. 

r = The allowed rate of return on rate base – presumed to be 

equal to the average of interest rates reported for recent 

borrowings by the water system.

Finally, the sum of the annual recurring costs and the charges for capital outlays 

for compliance with the proposed abatement technology yields the total increase in annual water 

rates resulting from the new technology: 

Total Rate Increase = Recurring Costs + Capital Charge (Eq. 13-3) 

where:

Total Rate increase = The annual increase in total water system rates resulting 

from implementing new technology. 

Recurring Costs = Technology costs that recur annually – e.g., recurring 

operating and maintenance expenses.

Capital Charge = Annual recovery of the capital outlay for new technology. 
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13-8

13.2.1.2 Estimate Rate Effect per Unit of Water Consumed 

The total rate increase must be allocated to the different types of customers the 

PWS serves. As above, this analysis may require different treatments for the recurring cost and 

capital cost components. 

The recurring cost component is assumed to be the same for all customer classes. 

(This would not be true if pretreatment contributed to technology costs, as pretreatment 

requirements are derived from certain customer classes). The recurring cost rate effect is 

calculated by dividing the annual recurring costs charge by the total volume of finished and 

partially treated34 water sold annually by the PWS. 

ΔRateRecurringCosts = Recurring Costs ÷ Treated Volume (Eq. 13-4) 

where:

ΔRateRecurringCosts = Increase in water system rates, per-unit-consumed, from the 

recurring cost component of new technology (assume rate 

structure is preserved and increase is across-the-board).

Recurring Costs = Total rate increase from costs the recur annually.

Treated Volume = Total volume of finished and partially treated water sold 

annually. 

As in subsection 13.2.1.1, the capital charge component presents a potentially 

more challenging case as the capital charge is more likely to be allocated differentially by 

customer class than the recurring cost component of the water rate charge. For example, if the 

amount of capital equipment required for compliance with the effluent limitation is determined 

by the peak water demand during a several-hour period of the day, then it would be reasonable to 

allocate capital costs according to the contribution of individual customer classes to demand 

levels during different periods (e.g., user profile during low-demand, medium-demand, and highdemand periods). Because PWS-specific rate structure information may not be available, and in 

order to be conservative in this achievability analysis, the capital charge should be allocated to 

the household rate class based on the greater of: 

 

34 The Agency suggests including water that is treated at any level – i.e., both finished water and partially treated 

water – in the denominator for calculating the unit rate increases. The logic for this definition of the denominator is 

that the treatment requirements, and thus cost, will apply to the residuals of water treatment, whether for finished 

water or partially treated water.
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13-9

1. The percentage of total water consumed by residential customers, or 

2. The percentage of total water sales revenue from residential customers. 

Once a component of capital costs has been allocated to the residential class, the 

average rate impact can be calculated based on the total water volume sold to residential 

customers.

[ ( ) ]

res

res res

Capital Charge Treated Volume

WaterMax ,Share Rev Share Capital Charge Rate×

∆ = (Eq. 13-5) 

where:

ΔRate Capital Charge = Increase in water system rates to residential customers, perunit-consumed, from the capital charge component of new 

technology costs

Water Share res = Residential customers’ share of total water consumption

Rev Share res = Residential customers’ share of total water sales revenue

Capital Charge = Total annual rate increase from the new technology capital 

outlay 

Treated Volume res = Total volume of finished water sold annually to residential 

customers, in same units as rate structure is expressed

Summing the Recurring Cost and Capital Charge rate components yields the total 

per-unit-consumed rate increase to residential customers:

ΔRateTotal = ΔRateRecurring Costs + ΔRateCapital Charge (Eq. 13-6) 

where:

Δ Rate Total = Total increase in water system rates to residential 

customers, per-unit-consumed, resulting from new 

technology 

Δ Rate Recurring Costs = Increase in water system rates, per-unit-consumed, from the 

recurring cost component of new technology costs 

Δ Rate Capital Charge = Increase in water system rates to residential customers, perunit-consumed, from the capital charge component of new 

technology costs
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-10

13.2.2 Estimate Increase in Annual Water Service Cost for Household Customers

The next step in the analysis is to calculate the increase in annual water service 

cost to households. This calculation involves multiplying the unit rate increase, from the 

preceding step, by the estimated average household water consumption. This general 

understanding can be more accurately described within the framework of the following two substeps:

1. Estimate the average quantity of water consumed per household; and, 

2. Estimate the annual increase in household water service cost. 

13.2.2.1 Estimate Average Household Water Consumption 

Average household water consumption is calculated by dividing total water 

quantity supplied to residential customers by the estimated number of households served.35 The 

number of households served by a PWS is estimated by dividing the reported number of people 

served by the system – available through EPA’s Safe Drinking Water Information System 

(SDWIS) – by the average number of persons per household within the service area of the PWS. 

The average number of persons per household is calculated from Census data36 for the ZIP codes 

reported as served by the PWS. Following is the calculation for the number of households served 

by a water system:37

 

35 The calculation of the number of households served is required because many PWSs do not know the number of 

households served, but rather, know the number of residential connections served. Since many multi-family 

dwellings (e.g., apartment buildings) do not have separate meters for each household, the number of residential 

connections will likely underestimate the number of households served. However, multi-family dwellings may not 

see 100% cost pass-through, due to some units being billed for water as part of rent, which is subject to market 

forces.

36 Based on the most recently available Census data. 37 In this equation, the average number of households is calculated by using the average household size by ZIP code 

(or county) and weighting by number of households reported in the ZIP code (or county), both as reported by the 

Census, instead of simply summing total population and households over the ZIP codes and dividing total 

population by total households. This calculation is necessary because the reported average household size for a ZIP 

code (or county) as reported in the Census frequently differs from the average household size that would be 

calculated for a ZIP code (or county) using the reported population and households for a ZIP code (or county).
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13-11

























×

=

∑

∑

=

=

Z

1z

z

Z

1z

z z

est

N HHS Census

(N HHS Census HHS Size Census )

N Households Persons (Eq. 13-7) 

where:

N Households est = Estimated number of households served currently by the 

PWS. 

Persons = Number of persons served by the PWS. 

Z = The total number of zip codes (or counties) served by the 

PWS.

z = Zip Code or county index. 

N HHS Census z = Number of households reported in Census data for zip code 

(or county), z.

HHS Size Census z = Average household size reported in Census data for zip 

code (or county), z.

To calculate annual water consumption per average household, divide the annual 

flow of water to residential customers (available from the PWSs) by the number of households 

served by the water system:

est

residential

av N Households

VolWater WaterHH Cons = (Eq. 13-8) 

where:

HH Water Cons av = Annual water consumption for the average household. 

Water Vol residential = Total water volume delivered annually to residential 

customers. 

N Households est = Estimated number of households served currently by the 

PWS. 

13.2.2.2 Estimate Increase in Annual Water Service Cost for Household Customers, 

Based on Estimated Household Water Consumption 

The water consumption quantity is then multiplied by the estimated change in per 

unit water rates to calculate the increase in annual water cost to household customers: 

ΔWater Costav hh = HH Water Consav + ΔRateTotal (Eq. 13-9) 
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13-12

where:

Δ Water Cost av hh = Increase in water service cost to the average household, 

resulting from new technology. 

HH Water Cons av = Annual water consumption for the average household. 

Δ Rate Total = Total increase in water system rates to residential 

customers, per-unit-consumed, resulting from new 

technology. 

13.2.3 Estimate Number and Percentage of Households, by Water System, for 

which the Annual Household Water Service Cost Increase Exceeds a Percent 

of Income Achievability Threshold

As the initial test of economic achievability for residuals treatment under the 

NPDES program, calculate the number of households for which the estimated increase in water 

service cost will exceed the chosen income achievability threshold. As noted previously, the 

income achievability threshold used, as well as the maximum number of households being 

served by the PWS that would be allowed to receive a treatment cost share greater than the 

percent of income threshold before the proposed new NPDES treatment technology would be 

considered not economically achievable, are important decisions for the Director. The example 

threshold presented is 1.0% of median household income. 

A household is counted as facing an achievability challenge at a given threshold if 

the ratio of the estimated water cost increase to household income exceeds the threshold. 

Implementing this achievability test concept requires several additional steps, as described 

below. 

13.2.3.1 Adjust for the Difference in the Reporting Year of the Household Income 

Information for the Most Recent Census

The difference in the reporting year of the household income information should 

be adjusted for the most recent Census and the year for which new technology costs will be

estimated. To compare the increase in water service cost with household income at current 

levels, the household counts by income range from the most recent Census need to be brought 

forward to the current year. Several issues arise in this adjustment:
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13-13

• General change in household income over time; 

• Shifts in household counts within the income distribution; and 

• Change in the aggregate number of persons and households over time. 

The decennial Census reports the number of households in specific income 

ranges. Below $50,000 household income, the household counts are reported in $5,000 ranges 

(with the exception of the first income range, which includes $0-$9,999). Above $50,000, the 

income ranges widen progressively, from $10,000 to $50,000, and finally ending at “greater than 

$200,000.” Although the Census publishes a variety of sample-based updates between the 

decennial census years, it does not publish an update of the data on household count by income 

range. Table 13-1 provides an example of the income distribution information provided from the 

2000 Census. 

Table 13-1. Example of Income Distribution from the 2000 U.S. Census

Income Range Number of Households

0 to 9,999 1,056

10,000 to 14,999 1,311

15,000 to 19,999 1,523

20,000 to 24,999 1,708

25,000 to 29,999 2,014

30,000 to 34,999 3,003

35,000 to 39,999 2,322

40,000 to 44,999 1,307

45,000 to 49,999 2,636

50,000 to 59,999 4,659

60,000 to 74,999 2,839

75,000 to 99,999 4,682

100,000 to 124,999 3,396

125,000 to 149,999 1,908

150,000 to 199,999 1,452

200,000 and Above 1,299

A two-step process is used to adjust the households-by-income-range data from 

the census year to the present (or as close to the present as is possible based on U.S. Census 

reporting). First, the income-range values from the census year are adjusted to the present year

based on the change in median household income by state (or possibly county) as reported in the 

non-decennial series published in the American Community Survey and the Annual Social and 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-14

Economic Supplement (U.S. Census). This adjustment holds as constant the household counts by 

income range from the census year data, but shifts upward (or downward) the definition of the 

ranges to which the household counts apply based on the change in income at the 50th percentile 

of the household income distribution (see calculation in the equation below). As an example, 

Table 13-2 shows the income range limits from Table 13-1 adjusted for a 10 percent increase in 

household income. All that is done is the low-end and high-end of each income range is 

multiplied by 1.10. The number of households in each range remains constant for now. 

Income Ranget,l = (1+ΔMHIl) × Income RangeCensus (Eq. 13-10) 

where:

Income Range t,l = Income range value after adjustment to the present (time t) 

for location l (state or county) 

Δ MHI l = Percent change in median household income from 

decennial census (e.g. 2000) to time t for location l (state or 

county) 

Income Range Census = Income range value used in Census household-by-income 

level reports – e.g., $10,000. 

Table 13-2. Example of Income Distribution Provided by the U.S. Census

With Ranges Updated to Current Year (10% increase in income)

Income Range Number of Households

0 to 10,999 1,056

11,000 to 16,499 1,311

16,500 to 21,999 1,523

22,000 to 27,499 1,708

27,500 to 32,999 2,014

33,000 to 38,499 3,003

38,500 to 43,999 2,322

44,000 to 49,499 1,307

49,500 to 54,999 2,636

55,000 to 65,999 4,659

66,000 to 82,499 2,839

82,500 to 109,999 4,682

110,000 to 137,499 3,396

137,500 to 164,999 1,908

165,000 to 219,999 1,452

220,000 and Above 1,299
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13-15

The second step is to adjust the number of households in the Census distribution – 

both in total and within the income ranges – according to the ratio of the total population 

currently served (again, as reported in SDWIS), to total population for the identified ZIP codes 

(or counties) as reported in the Census. This adjustment accounts for both the change in total 

population since the census year and for the population coverage differential resulting from only 

a part of the ZIP codes (or counties) reported by the drinking water system actually being served 

by the system (see calculation in equation below). As an example, Table 13-3 shows the number 

of households from Table 13-2 adjusted for a 3 percent increase in population. So, the number of 

households from Table 13-2 is multiplied by 1.03 for each income range. 

 N Householdsir,t = (Persons Servedt ÷ PopulationCensus ) × N Householdsir,Census (Eq. 13-11) 

where:

N Households ir,t = Number of households in Income Range ir at time t.

Persons Served t = Number of persons reported served by the PWS at time t. 

Population Census = Total population reported at time of Census data for zip 

codes or counties served by the PWS. 

N Households ir,Census = Number of households in Income Range ir as reported at 

time of Census data. 

Table 13-3. Example of Income Distribution Provided by the U.S. Census

With Ranges and Number of Households Updated to Current Year (10% 

increase in income and 3% increase in population) 

Income Range Number of Households

0 to 10,999 1,088

11,000 to 16,499 1,350

16,500 to 21,999 1,569

22,000 to 27,499 1,759

27,500 to 32,999 2,074

33,000 to 38,499 3,093

38,500 to 43,999 2,392

44,000 to 49,499 1,346

49,500 to 54,999 2,715

55,000 to 65,999 4,799

66,000 to 82,499 2,924

82,500 to 109,999 4,822

110,000 to 137,499 3,498

137,500 to 164,999 1,965

165,000 to 219,999 1,496

220,000 and Above 1,338
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-16

13.2.3.2 Accounting for the Lack of Information on How Household Income is 

Distributed within the Census-Reported Income Ranges 

The Census provides the number of households by the income ranges described 

above. In this analysis, the objective is to calculate the number of households for which the 

estimated increase in water service cost exceeds a threshold percentage of household income. For 

each PWS, the household income level at which the estimated increase in water service cost 

equals a threshold percentage is determined using on the equation below. 

Incthreshold level,i = ΔWater Costav hh ÷ Income Thresholdi (Eq. 13-12) 

where:

Inc threshold level, i = Threshold income level, based on income threshold i. 

Δ Water Cost av hh = Increase in water service cost to the average household, 

resulting from compliance.

Income Threshold = Threshold percentage of income the compliance costs 

cannot exceed i.

This step is followed by the estimation of the number of households served by the 

PWS with household income less than that threshold income level. In all likelihood, a threshold 

income level will fall within, and not at the edge of, a Census income range. Accordingly, the 

fraction of households within a Census income range that fall below a threshold income level 

must be estimated. For simplicity’s sake, assume that households are uniformly distributed over 

the income values within an income range. As a result, the fractional point at which the threshold 

income level lies within an income range will also be the fraction of households within that 

income range that fall below the threshold level. Of course, all households in an income range 

that is below the range in which the threshold income level falls will be below the threshold 

income level.

38

 

38 The assumption of a uniform distribution of income within each income range inevitably involves error and could 

overstate or understate the fraction of households within an income range that fall below an impact threshold. 

Nevertheless, the assumption of a uniform distribution within an income range is a reasonable approach. In applying 

the uniform-distribution assumption, the Agency warns about the potential for overestimation of adverse impact in 

the lowest income range segment – less than $10,000 (before adjusting for income change over time) – if that range 

includes a threshold impact income value. 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-17

The occurrence of households for which the water service cost increase exceeds a 

threshold income level is calculated as follows:

( )

( ) ir*

mxir*, mnir*,

threshold level mnir*,

incir*, Households N

Inc Inc

Inc Inc

Households N × −

− = (Eq. 13-13) 

where:

N Households ir*, inc = Number of households in Income Range ir *with income 

below threshold income level (inc), where Income Range 

ir* contains the threshold income level inc.

Inc threshold level = Threshold income level, calculated above. 

Inc ir*, mn = Minimum value of Income Range ir*.

Inc ir*, mx = Maximum value of Income Range ir*.

N Households ir = Total number of households in Income Range ir* estimated 

served by the PWS. 

Lastly, the total number of households with income below the threshold income 

level is aggregated over all income ranges. 

∑

−

=

= +

ir 1*

ir 1

N Householdsinc N Households incir*, N Householdsir (Eq. 13-14) 

where:

N Households inc = Number of households over all income ranges with income 

below threshold income level (inc). 

N Households ir*, inc = Number of households in Income Range ir* with income 

below threshold income level (inc), where Income Range 

ir* contains the threshold income level inc.

N Households ir = Number of households in Income Ranges ir below Income 

Range ir*. 

Table 13-4 follows from the examples above. This table shows the number of 

households (and the percentage of households) that are expected to realize an increase in water 

costs higher than the achievability income threshold (1.0 percent of household income). In this 

example, assume the cost of compliance is $6.69 million, or $175.00 per household. The 

threshold income level is then $17,500 which falls in the adjusted Census income range of 

$16,500 - $21,999 (the shaded row in Table 13-4). The number of households in the Census 

income range where the increase in water cost has an impact greater than the achievability 

income threshold is calculated to be 285. The number of households above the achievability 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-18

threshold in lower income ranges is always equal to the number of households in the range, 

while the number of households above the achievability threshold in higher income ranges is 

always equal to zero. The total number of households above the achievability income threshold 

is 2723, which equals 7 percent of the total households served by the PWS. 

Table 13-4. Example of the Calculation of Number and Percent of Households above an 

Achievability Threshold (1.0% of Median Household Income)

Income Range

Number of 

Households

Compliance 

Costs Per 

Household

Achievability

Threshold

Threshold 

Income 

Level

Number of 

Households 

above 

Achievability

Threshold

Percent of 

Households 

above 

Achievability

Threshold

0 to 10,999 1,088 $175.00 1.0% $17,500 1,088 100%

11,000 to 16,499 1,350 $175.00 1.0% $17,500 1,350 100%

16,500 to 21,999 1,569 $175.00 1.0% $17,500 285 18%

22,000 to 27,499 1,759 $175.00 1.0% $17,500 0 0%

27,500 to 32,999 2,074 $175.00 1.0% $17,500 0 0%

33,000 to 38,499 3,093 $175.00 1.0% $17,500 0 0%

38,500 to 43,999 2,392 $175.00 1.0% $17,500 0 0%

44,000 to 49,499 1,346 $175.00 1.0% $17,500 0 0%

49,500 to 54,999 2,715 $175.00 1.0% $17,500 0 0%

55,000 to 65,999 4,799 $175.00 1.0% $17,500 0 0%

66,000 to 82,499 2,924 $175.00 1.0% $17,500 0 0%

82,500 to 109,999 4,822 $175.00 1.0% $17,500 0 0%

110,000 to 137,499 3,498 $175.00 1.0% $17,500 0 0%

137,500 to 164,999 1,965 $175.00 1.0% $17,500 0 0%

165,000 to 219,999 1,496 $175.00 1.0% $17,500 0 0%

220,000 and above 1,338 $175.00 1.0% $17,500 0 0%

Total 38,228 2,723 7%

13.2.3.3 Determining Public Water System-Level Achievability Income Thresholds

Once the number (and percentage) of households in a service territory for which 

the estimated increase in water service cost would exceed an achievability income threshold is

calculated, the Director still has to determine if these numbers constitute an economically 

achievable solution for the PWS as a whole. As mentioned above, this important question is 

subjective and a policy decision that must be made by the permitting authority. 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-19

For example, if the permitting authority believes that 1.0 percent of household 

income is the correct achievability threshold, 2,723 or seven percent of the households served by 

the PWS would have difficulty paying for the higher cost of water associated with the 

compliance cost of the permit limitations. 

13.2.4 Assessing the Impact of Rate Structure on the Achievability Determination

The example above assumes that all households served by the PWS share equally 

in the additional costs associated with compliance, which is not necessarily the case. A

community and its PWS may be able to shift costs away from more economically vulnerable 

population segments via increasing block rates, lifeline rates or other income support 

mechanisms. These rate structures and programs should be considered when conducting an 

achievability analysis. Table 13-5 provides an example of how the achievability analysis can be 

modified to take into account a simplistic lifeline-type rate structure. In this case, the cost of 

compliance is the same as in the example above ($6.69 million). However, in this example, 

because of a lifeline rate structure, no household with annual income below $16,500 will incur 

any additional rate increase. Therefore, the cost of compliance is shared among the remaining 

households at a greater rate ($186.92 per household versus $175.00 in the earlier example). In 

this case, the threshold income level rises to $18,692, but at the same time, fewer households 

exceed the achievability threshold (two percent versus seven percent in the example above). The 

lifeline rate structure partially mitigates the achievability concerns of this effluent limitation. Of 

course, the permit authority still has to decide if the lifeline rate structure mitigates the 

achievability issue enough to determine that the effluent limitations are economically achievable.

If a PWS has an increasing block rate structure, they could choose to only 

increase the highest end of the block rates. This would pass the entire increase in cost to 

households that are consuming the largest quantities of water and are most likely those 

households that can best afford a rate increase. 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-20

Table 13-5. Example of the Calculation of Number and Percent of Households above an 

Achievability Threshold (1.0% of Median Household Income) assuming a Lifeline Rate 

Structure for Income Below $16,500

Income Range

Number of 

Households

Compliance 

Costs Per 

Household

Achievability

Threshold

Threshold 

Income 

Level

Number of 

Households 

above 

Achievability

Threshold

Percent of 

Households 

above 

Achievability

Threshold

0 to 10,999 1,088 $0 1.0% $0 0 0%

11,000 to 16,499 1,350 $0 1.0% $0 0 0%

16,500 to 21,999 1,569 $186.92 1.0% $18,692 628 40%

22,000 to 27,499 1,759 $186.92 1.0% $18,692 0 0%

27,500 to 32,999 2,074 $186.92 1.0% $18,692 0 0%

33,000 to 38,499 3,093 $186.92 1.0% $18,692 0 0%

38,500 to 43,999 2,392 $186.92 1.0% $18,692 0 0%

44,000 to 49,499 1,346 $186.92 1.0% $18,692 0 0%

49,500 to 54,999 2,715 $186.92 1.0% $18,692 0 0%

55,000 to 65,999 4,799 $186.92 1.0% $18,692 0 0%

66,000 to 82,499 2,924 $186.92 1.0% $18,692 0 0%

82,500 to 109,999 4,822 $186.92 1.0% $18,692 0 0%

110,000 to 137,499 3,498 $186.92 1.0% $18,692 0 0%

137,500 to 164,999 1,965 $186.92 1.0% $18,692 0 0%

165,000 to 219,999 1,496 $186.92 1.0% $18,692 0 0%

220,000 and Above 1,338 $186.92 1.0% $18,692 0 0%

Total 38,228 628 2%

13.3 REFERENCES

Dalhuisen, Jasper M., Raymond J. G. M. Florax, Henri L. F. de Groot, and Peter Nijamp. 2003. 

“Price and Income Elasticities of Residential Water Demand: A Meta-Analysis.” Land 

Economics 79(2): 292-308. 

Dalhuisen, Jasper M., Raymond J. G. M. Florax, Henri L. F. de Groot, and Peter Nijamp. 2001. 

“Price and Income Elasticities of Residential Water Demand: Why empirical estimates differ.” 

Tinbergen Institute Discussion Paper. Department of Spatial Economics, Vrije Universiteit and 

Tinbergen Institute, Amsterdam, The Netherlands. 

Environmental Finance Center. Rate Setting Analysis: Public Water Supply Financial Capacity, 

Developing Water Rates. No date. http://www.maxwell.syr.edu/efc/RateSettingAnalysis.htm. 

Environmental Finance Center, Syracuse, NY.

Environmental Finance Center at Boise State University. 2002. Drinking Water System 

Management Handbook: Administration of a drinking water system through financial, technical 

and managerial planning.
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-21

http://sspa.boisestate.edu/efc/Publications/Drinking%20Water%20System%20Management%20

Handbook.PDF. Environmental Finance Center at Boise State University, Boise, ID. February 

2002. 

Midwest Assistance Program, Inc. 1999. North Dakota Small Community Water System’s 

Handbook on Developing and Setting Water Rates. http://www.mapinc.org/Publications/Publications/WatrRate.pdf. Midwest Assistance Program, Inc. New Prague, 

MN. 

Rubin, Scott J. 2001. Criteria to Assess the Affordability of Water Service. National Rural Water 

Association, Rural Water Partnership Fund White Paper. October, 2001. 

Rubin, Scott J. 2002. Criteria to Assess the Affordability Concerns in Conference Report for 

H.R. 2620. National Rural Water Association, Rural Water Partnership Fund White Paper. 

January, 2002. 

U.S. Environmental Protection Agency. 1995a. Interim Economic Guidance for Water Quality 

Standards. Workbook, Office of Water. EPA-823-B-95-002, March 1995. 

U.S. Environmental Protection Agency. 1998a. National-Level Affordability Criteria Under the 

1996 Amendments to the Safe Drinking Water Act. Prepared by International Consultants, Inc., 

Hagler Bailly Services, Inc and Janice A. Beecher, Ph.D. for the EPA. August, 1998. 

U.S. Environmental Protection Agency. 1998b. Information for States on Developing 

Affordability Criteria for Drinking Water. Office of Water. EPA 816-R-98-002, February, 1998. 

U.S. Environmental Protection Agency. 1999a. Economic Analysis of Final Effluent Limitations 

Guidelines and Standards for the Landfills Point Source Category. Office of Water. EPA-821-B99-005, November 1999. 

U.S. Environmental Protection Agency. 1999b. Revised Interim Guidance for EPA Rulewriters: 

Regulatory Flexibility Act as Amended by the Small Business Regulatory Enforcement Fairness 

Act, Office of Regulatory Management and Information. March 29, 1999. 

U.S. Environmental Protection Agency. 2000a. Arsenic in Drinking Water Rule Economic 

Analysis. Prepared by Abt Associates Inc. for Office of Ground Water and Drinking Water, 

EPA-815-R-00-026, December. 

U.S. Environmental Protection Agency. 2000b. Economic Analysis of the Radionuclides 

National Primary Drinking Water Regulations. Prepared by Industrial Economics, Inc. for Office 

of Ground Water and Drinking Water. December, 2000. 

U.S. Environmental Protection Agency. 2000c. Guidelines for Preparing Economic Analyses, 

September, 2000. 

U.S. Environmental Protection Agency. 2002. Affordability Criteria for Small Drinking Water 

Systems: An EPA Science Advisory Board Report. EPA-SAB-EEAC-03-004, December 2002. 
Drinking Water Industry Report Section 13 – Economic Considerations for Permit Writers

13-22

U.S. Environmental Protection Agency. 2005. Economic Analysis for the Final Stage 2 

Disinfectants and Disinfection Byproducts Rule. Office of Water, EPA-815-R-05-010, December 

2005. 
14-1

SECTION 14

GLOSSARY, ACRONYMS, AND ABBREVIATIONS

A

Activated carbon – Carbon particles usually obtained by carbonization of cellulosic material in 

the absence of air and possessing a high adsorptive capacity. Process is to typically heat carbon 

to increase porosity surface area.

Administrator – The Administrator of the U.S. Environmental Protection Agency. 

Adsorption – The adherence of a gas, liquid, or dissolved material to the surface of a solid. 

Aeration – Process that mixes air and water, normally by injecting air into water, spraying water 

into the air, or allowing water to pass over an irregular surface, to release compounds from the 

water through oxidation, precipitation, or evaporation. 

Agency – The U.S. Environmental Protection Agency. 

Alkalinity – The capacity of water to neutralize acids, a property imparted by the water’s content 

of carbonates, bicarbonates, hydroxides, and occasionally borates, silicates, and phosphates. It is 

expressed in milligrams per liter of equivalent calcium carbonate.

Alum – A common name in water and wastewater treatment field for commercial-grade 

aluminum sulfate (Al2(SO4)3 · 14H2O).

Anion – The ion in an electrolyte solution that carries the negative charge and that migrates 

toward the anode under the influence of a potential difference. 

Anode – Positive pole of an electrolytic system, towards which anions (negatively charge ions) 

migrate.

Aquifer – A natural underground layer, often composed of sand or gravel, that contains water. 

B

Backwash – The process of reversing the flow of water back through the filter media to remove 

the entrapped solids. 

Basin – 1) A natural or artificially created space or structure, surface or underground, which has 

a shape and character of confining material that enable it to hold water. The term is sometimes 

used for a receptacle midway in size between a reservoir and a tank. 2) The surface area within a

given drainage system. 3) A shallow tank or depression through which liquids may be passed or 

in which they are detained for treatment or storage.
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-2

Batch (intermittent) discharge – A discrete volume or mass of liquid or solid residuals that are 

collected and discharged periodically. Equalization or slower discharge rate of batch discharges 

may decrease negative impacts on the receiving stream.

Biochemical Oxygen Demand (BOD) – The quantity of oxygen used in the biochemical 

oxidation of organic matter in a specified time, at a specified temperature, and under specified 

conditions. 

BOD5 – Biochemical oxygen demand measured over a 5-day period. 

Best professional judgment (BPJ) – The method used by permit writers to develop technologybased NPDES permit conditions on a case-by-case basis using all reasonably available and 

relevant data.

C

Cathode – Negative pole of an electrolytic system, towards which cations (positively charge 

ions) migrate.

Cation – The ion in an electrolyte solution that carries the positive charge and that migrates 

toward the cathode under the influence of a potential difference. 

Centrate – Water separated from the solids by a centrifuge.

Centrifuge – A mechanical device in which centrifugal force is used to separate solids from 

liquids and/or to separate liquids of different densities. 

CFR – Code of Federal Regulations.

Clarification – Separation and concentration of solids from liquid/solid mixtures that are mostly 

liquid (contrast with dewatering and thickening). 

Clarifier – A large circular or rectangular tank or basin in which water is held for a period of 

time, during which the heavier suspended solids settle to the bottom by gravity. 

Clay – 1) Soil consisting of inorganic material, the grains of which have diameters smaller than 

0.002 millimeters. 2) A mixture of earthy matter formed by the decay of certain minerals. The 

composition of clays varies widely and dictates its use. It is sometimes used in water treatment to 

aid coagulation and to remove tastes and odors. 

Clean Water Act (CWA) – Federal legislation enacted by Congress to “restore and maintain the 

chemical, physical, and biological integrity of the nation’s waters” (Federal Water Pollution 

Control Act of 1972, as amended, 33 U.S.C. 1251 et seq). 

Clear well – A reservoir for storage of finished water prior to distribution. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-3

Coagulant – A chemical added to water that has suspended and colloidal solids to destabilize 

particles, allowing subsequent floc formation and removal by sedimentation, filtration, or both. 

Coagulation – As defined in 40 CFR 141.2, a process in which colloidal and suspended 

materials are destabilized and agglomerated into flocs by using coagulant chemicals and mixing.

Colloids – Finely divided solids that will not settle but may be removed by coagulation of 

biochemical action or membrane filtration; they are intermediate between true solutions and 

suspensions. 

Community Water System (CWS) – A water system that supplies drinking water to 25 or more 

of the same people year-round. 

Contaminant – Anything found in water (including microorganisms, minerals, chemicals, 

radionuclides, etc.) that may be harmful to human health or the environment. 

Continuous discharge – A volume or mass of liquid or solid residuals that are discharged at 

constant flow without significant interruption. 

Conventional filtration – As defined in 40 CFR 141.2, a series of processes including 

coagulation, flocculation, sedimentation, and filtration resulting in substantial particulate 

removal.

Conventional pollutants – Constituents of wastewater as determined by Section 304(a)(4) of the 

CWA and EPA regulations. Conventional pollutants are classified as biochemical oxygen 

demand, total suspended solids, oil and grease, fecal coliform, and pH. 

D

Decant – To draw off the liquid from a basin or tank without stirring up the sediment in the 

bottom. 

Deep-well injection – Long-term or permanent disposal of untreated, partially treated, or treated 

wastewaters by pumping the wastewater into underground formations of suitable character 

through a bored, drilled, or driven well. Most commonly used for desalination plant concentrates. 

Dewatering – Separation of liquid from liquid/solid mixtures that are predominantly solids, 

often containing very low moisture content to start with (contrast with clarification and 

thickening). 

Dewatering processes – Mechanical and non-mechanical methods used to remove excess 

liquids from residual solids in order to concentrate the solids. These methods include belt 

presses, centrifuges, filter presses, vacuum presses, and lagoons. 

Diatomaceous earth filtration –filtration method in which the filter media, diatomaceous earth, 

is deposited on a support membrane or screen (called a septum) prior to each filter run (pre-coat). 

The filter media is washed and wasted at the end of each filter run. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-4

Direct discharge – The discernible, confined, and discrete conveyance of pollutants to United 

States surface waters such as rivers, lakes, and oceans. See 40 CFR 122.2. 

Direct discharger – A facility that discharges or may discharge treated or untreated wastewaters 

into waters of the United States.

Direct filtration – As defined in 40 CFR 141.2, a series of processes including coagulation and 

filtration, but excluding sedimentation, resulting in substantial particulate removal.

Direct recycle – The return of recycle flow within the treatment process without first passing 

through treatment or equalization. 

Discharge – The discernible, confined, and discrete conveyance of pollutants to: 1) United 

States surface waters such as rivers, lakes, and oceans (“direct discharge”), or 2) a publicly 

owned, privately owned, federally owned, combined, or other treatment works (“indirect 

discharge”). Note that the definition at 40 CFR 122.2 excludes indirect discharges to publicly 

owned treatment works; however, in this report, “discharge: refers to any direct or indirect 

discharge. 

Disinfectant – As defined in 40 CFR 141.2, any oxidant, including but not limited to chlorine, 

chlorine dioxide, chloramines, and ozone added to water in any part of the treatment or 

distribution process, that is intended to kill or inactivate pathogenic microorganisms. 

Disinfection – As defined in 40 CFR 141.2, a process that inactivates pathogenic 

microorganisms (such as bacteria, viruses, and protozoa) in water by chemical oxidants or 

equivalent agents. Disinfection may be a chemical (commonly chlorine, chloramine, or ozone) or 

physical process (e.g., ultraviolet light). 

Disinfection by-products (DBPs) – Organic compounds formed by the reaction of the 

disinfectant, natural organic matter, and the bromide ion. Regulated DBPs include 

trihalomethanes, haloacetic acids, bromate, and chlorite. 

Disposal – Intentional placement of residuals into or on any land, in either a permitted waste 

disposal facility (e.g., landfill) or land application for agricultural or other purposes. Does not 

include direct or indirect discharge of residuals. 

Dissolved-air flotation – A method of solids separation, whereby a side stream is saturated with 

air at high pressure and then injected into the flotation tank to mix with the incoming water 

stream. As the air bubbles rise to the surface they attach to floc particles and create a sludge layer 

at the surface of the tank, which is then removed for disposal. 

Distribution system – A network of pipes leading from a treatment plant to customers' 

plumbing systems. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-5

E

Electrodialysis – A method of water treatment that utilizes electric current applied to permeable 

membranes to remove minerals and salts from water.

Emergency discharge – A volume or mass of liquid or solid residuals that are discharged only 

during extenuating circumstances (i.e., a treatment process malfunction). Also referred to as 

upset or bypass discharge. 

Equalization – A method used to control the flow of water or residuals stream by providing 

storage and detention time between the point of origin and the return (or next) location of the 

water or residuals stream. The water or residuals stream is then removed from the storage unit at 

a controlled, uniform rate. 

Evaporation – The process by which water or other liquid becomes a gas. Water from land 

areas, bodies of water, and all other moist surfaces is absorbed into the atmosphere as a vapor. 

Evaporation ponds – Dewatering and concentration of concentrates using evaporation. 

F

Facility – All contiguous property and equipment owned, operated, leased, or under the control 

of the same person or entity. 

Filter press – A press operated mechanically for partially separating water from solid materials.

Filter-to-waste – Provision in a filtration process to allow the first filtered water, after 

backwashing a filter, to be washed or reclaimed. Cleans filter prior to being put back into service 

after backwashing.

Filtrate – The water separated from the solids by a filter press or the liquid that has passed 

through a filter. 

Filtration – As defined in 40 CFR 141.2, a process for removing particulate matter from water 

by passage through porous media. 

Finished water – As defined in 40 CFR 141.2, water that is introduced into the distribution 

system of a public water system and is intended for distribution and consumption without further 

treatment, except as treatment necessary to maintain water quality in the distribution system 

(e.g., booster disinfection, addition of corrosion control chemicals). 

Floc – Collections of smaller particles that have come together (agglomerated) into larger, more 

settleable particles as a result of the coagulation-flocculation process. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-6

Flocculation – As defined in 40 CFR 141.2, a process to enhance agglomeration or collection of 

smaller floc particles into larger, more easily settleable particles through gentle stirring by 

hydraulic or mechanical means.

Flow – 1) The movement of a stream of water or other mobile substance from place to place; a 

stream of water; movement of silt, water, sand, or other material. 2) The fluid that is in motion. 

3) The quantity or rate of movement of a fluid; discharge; total quantity carried by a stream. 4) 

To issue forth or discharge. 

Freeze-assisted sand beds – A structure used to freeze and thaw residuals to change the 

characteristics to a more granular consistency that is easier to dewater. Most commonly used 

with alum residuals.

G

Gravity filter – A rapid sand filter of the open type, the operating level of which is placed near 

the hydraulic grade line of the influent and through which the water flows by gravity. 

Ground water – Water in a saturated zone or stratum beneath the surface of land or water.

H

Haloacetic acids (HAA5) – The five haloacetic acid compounds include monochloroacetic acid, 

dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. All are 

disinfection by-products. 

Hardness – A characteristic of water, imparted by salts of calcium, magnesium, and iron such as 

bicarbonates, carbonates, sulfates, chlorides and nitrates, that cause curdling and increased 

consumption of soap, deposition of scale in boilers, damage in some industrial processes, and 

sometimes objectionable taste.

I

Impoundment – A pond, lake, tank, basin, or other space, either natural or man-made that is 

used for storage, regulation, and control of water.

Indirect discharge – The discernible, confined, and discrete conveyance of pollutants to a 

publicly owned treatment works. See 40 CFR 122.2. 

Indirect discharger – A facility that discharges or may discharge wastewaters to a publicly 

owned treatment works. 

Influent water – Raw water plus any recycle streams.
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-7

Inorganic contaminants – Mineral-based compounds such as metals, nitrates, and asbestos. 

These contaminants are naturally-occurring in some water, but can also arise through farming, 

chemical manufacturing, and other human activities. 

Ion – A charged atom, molecule, or radical, the migration of which affects the transport of 

electricity through an electrolyte solution or, to a certain extent, through a gas. An atom or 

molecule that has lost or gained one or more electrons. By such ionization it becomes electrically 

charged. An example is the alpha particle.

Ion exchange (IX) – Process using a resin formulated to have capability to adsorb cationic or 

anionic species, such as arsenate.

Ion-exchange regenerant – A chemical solution used to restore an exhausted bed of ion 

exchange resins to the fully ionic (regenerated) form necessary for the desired ion exchange to 

again take place effectively.

L

Lagoon – Basin or artificial impoundment containing solid or liquid material for purposes of 

storage, treatment, or disposal. 

Lime – Any of a family of chemicals consisting essentially of calcium hydroxide made from 

limestone (calcite) that is composed almost wholly of calcium carbonate or a mixture of calcium 

and magnesium carbonate. 

Long-term average (LTA) – Average pollutant levels achieved over a period of time (EPA 

recommends five years) by a plant or technology option. 

M

Maximum Contaminant Level (MCL) – The highest level of a contaminant that EPA allows in 

drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term 

health risk. EPA sets MCLs at levels that are economically and technologically feasible. States 

can set MCLs that are more stringent than EPA MCLs. 

Mechanical dewatering device – A device that operates mechanically to remove water from 

residuals and produce a non-flowing residual. Examples include centrifuges, filter presses, belt 

presses, plate press, and vacuum filters. Contrast with non-mechanical dewatering.

Median – In a statistical array, the value having as many cases larger in value as cases smaller in 

value, or 50th percentile. 

Membrane concentrate – The reject stream generated when the source water is passed through 

a membrane for treatment.

MGD – Million gallons per day. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-8

mg/L – Milligrams per liter.

Microfiltration – A method of water treatment that utilizes a membrane to separate micrometer 

or submicrometer particles from a solution. The method clarifies water by trapping particles and 

microorganisms in the membrane, while allowing dissolved substances to pass through with the 

permeate (i.e., clean water).

Micron – A unit of length equal to one micrometer (μm). One millionth of a meter or one 

thousandth of a millimeter. One micron equals 0.00004 of an inch. 

Microorganisms – Tiny living organisms that can be seen only with the aid of a microscope. 

Some microorganisms can cause acute health problems when consumed in drinking water. Also 

known as microbes. 

Monofill – An ultimate disposal technique for water treatment plant sludge in which the sludge 

is applied to a landfill designed for sludge only. 

N

North American Industry Classification System (NAICS) – NAICS was developed jointly by 

the United States, Canada, and Mexico to provide comparability in statistics about business 

activity across North America.

Nanofiltration – A method of water treatment that utilizes membranes and has the primary goal 

of removing hardness, bacteria, viruses, and organic-related color.

Nonconventional pollutants – Pollutants that are neither conventional pollutants (40 CFR 

401.16) nor priority pollutants (40 CFR 423 Appendix A). 

Non-mechanical dewatering process – Process to separate solids from liquids in liquid/solid 

mixtures without the use of mechanical devices, examples include sand or similar drying beds, 

dewatering lagoons (lagoons designed for routine solids clearing), and freeze-assisted sand beds. 

Contrast with mechanical dewatering and disposal, which includes long-term lagoons (i.e., 

lagoons that are cleaned of solids every 10 to 20 years or more). 

Non-Transient, Non-Community Water System (NTNCWS) – A water system that supplies 

water to 25 or more of the same people at least six months per year in places other than their 

residences. Some examples are schools, factories, office buildings, and hospitals that have their 

own water systems. 

Nonwater quality environmental impact – Deleterious aspects of control and treatment 

technologies applicable to point source category wastes, including, but not limited to air 

pollution, noise, radiation, sludge and solid waste generation, and energy use. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-9

National Pollutant Discharge Elimination System (NPDES) – As authorized by the Clean 

Water Act, the NPDES permit program controls water pollution by regulating point sources that 

discharge pollutants into waters of the United States. Point sources are discrete conveyances such 

as pipes or man-made ditches. Individual homes that are connected to a municipal system, use a 

septic system, or do not have a surface discharge do not need an NPDES permit; however, 

industrial, municipal, and other facilities must obtain permits if their discharges go directly to 

surface waters. In most cases, the NPDES permit program is administered by authorized states. 

O

Off site – Outside the boundaries of a facility. 

On site – The same or geographically contiguous property, which may be divided by a public or 

private right-of-way, provided the entrance and exit between the properties is at a crossroads 

intersection, and access is by crossing as opposed to going along the right-of-way. 

Noncontiguous properties owned by the same company or locality but connected by a right-ofway, which it controls, and to which the public does not have access, is also considered on-site 

property. 

Operating capacity – The maximum finished water production rate at a water treatment plant 

approved by the state drinking water program authority. 

Organic contaminants – Carbon-based chemicals such as solvents and pesticides that can get 

into water through runoff from cropland or discharge from factories. 

Outfall – The mouth of conduit drains and other conduits from which a facility discharges 

effluent into receiving waters.

P

Pathogen – A disease-causing organism. 

Permeability – The property of a material that permits appreciable movement of water through 

it when it is saturated and the movement is actuated by hydrostatic pressure of the magnitude 

normally encountered in natural subsurface water.

pH – An expression of the intensity of the basic or acid condition of a solution. Mathematically, 

pH is the negative logarithm (base 10) of the hydrogen ion concentration, [H+]. [pH = log 

(1/H+)]. The pH may range from 0 to 14, where 0 is most acidic, 14 most basic, and 7 neutral. 

Natural waters usually have a pH between 6.5 and 8.5. 

Pollutant – Under the Clean Water Act, a dredged spoil, solid waste, incinerator residue, filter 

backwash, sewage, garbage, sewage sludge, munitions, chemical waste, biological materials, 

certain radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and 

industrial, municipal, and agricultural waste discharged into water. This definition includes 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-10

residuals (including miscellaneous residuals) generated by water treatment plants. See 40 CFR 

122.2. 

Pollution prevention – The use of materials, processes, or practices that reduce or eliminate the 

creation of pollutants or residuals. 

Polymer – A synthetic organic compound with high molecular weight and composed of 

repeating chemical units (monomers). Polymers may be polyelectrolytes (such as water soluble 

flocculants), water-insoluble ion exchange resins, or insoluble uncharged materials (such as 

those used for plastic or plastic-lined pipe). 

Potable water – Water that does not contain objectionable pollution, contamination, minerals, or 

infective agents and is considered satisfactory for domestic consumption. 

Precipitative softening – A method of water treatment with the primary goal of reducing water 

hardness. The method may include lime softening, sedimentation/precipitation, filtration, and 

disinfection. 

Presedimentation – Water treatment operation that is at the head of the plant. Its primary 

purpose is to remove a significant percentage of suspended solids and other contaminants in the 

water prior to other water treatment operations (e.g., conventional filtration, precipitative 

softening). This water treatment operation may require a small addition of water treatment 

chemicals, such as polymer coagulants (e.g., 0.5 to 1 mg/L), to aid sedimentation. 

Priority pollutant – 126 compounds listed in 40 CFR Part 423 Appendix A that are a subset of 

the toxic pollutants and classes of pollutants outlined pursuant to Section 307 of the CWA. 

Process wastewater – Any water that, during source water treatment operations, comes into 

direct contact with or results from the storage, production, or use of any raw material, byproduct, or waste product. Wastewater from equipment cleaning, direct-contact air pollution 

control devices, rinse water, stormwater associated with industrial activity, and contaminated 

cooling water are considered to be process wastewater. Process wastewater may also include 

wastewater that is contract hauled for off-site disposal. Sanitary wastewater, uncontaminated 

noncontact cooling water, stormwater not associated with industrial activity, and finished 

drinking water are not considered to be process wastewater.

Public Water System (PWS) – Any water system that provides drinking water to at least 25 

people for at least 60 days annually. 

Publicly owned treatment works (POTW) – A treatment works as defined by Section 212 of 

the CWA, which is owned by a state or municipality (as defined by Section 502(4) of the CWA). 

This definition includes any devices and systems used in the storage, treatment, recycling and 

reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes sewers, 

pipes and other conveyances, only if they convey wastewater to a POTW treatment plant. The 

term also means the municipality, as defined in Section 502(4) of the CWA, that has jurisdiction 

over the indirect discharges to and the discharges from such a treatment works. 

Purchased water – Water obtained from a third-party vendor. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-11

R

Radionuclides – Any man-made or natural element that emits radiation; may cause cancer after 

many years of exposure through drinking water. 

Raw water – Water in its natural state, prior to any treatment for drinking. 

Recovery – The process of extracting some other useable constituent from one or more residuals 

streams, for example, recovery of alum from coagulation sludge, lime from precipitative 

softening sludge, and salt from concentrates. 

Recycle – Process of returning liquid or combined liquid/solid residuals streams back to the 

water treatment process (e.g., filter backwash recycling).

Regeneration – 1) In ion exchange, the process of restoring an ion exchange material to the state 

employed for adsorption. 2) The periodic restoration of exchange capacity of ion exchange 

media used in water treatment.

Reservoir – See “impoundment.” 

Residuals – The solid, liquid, or mixed solid/liquid materials generated during source water 

treatment. Examples of residuals include: sludges and wastewaters generated from 

presedimentation, coagulation, flocculation, sedimentation, clarification, precipitative softening, 

filter backwash operations, and filter-to waste; membrane reject wastewaters; ion exchange 

resins and concentrate wastewaters; activated carbon wastes; and other miscellaneous residuals. 

Residuals include those accumulated for batch discharge. 

Residuals treatment – Any activity designed to change the character or composition of liquid 

and solid residuals streams from water treatment processes as needed to render it amenable to 

recycle, recovery, reduce its volume, or prepare it for transportation, storage, disposal, or 

discharge. For example, this would include equalization, thickening, mechanical dewatering, 

non-mechanical dewatering, and other processes defined separately.

Reverse osmosis – A method of water treatment that involves the application of pressure to a 

concentrated solution that causes the passage of a liquid from the concentrated solution to a 

weaker solution across a semipermeable membrane. The membrane allows the passage of the 

solvent (water) but not the dissolved solids (solutes). This method is typically used, in 

combination with pretreatment, for desalination and the removal of ions, radionuclides, bacteria, 

and viruses. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-12

S

Sand drying beds – Similar to evaporation ponds; evaporation is used to dewater and 

concentrate liquid/solid residuals mixtures. One difference is that these structures are also 

engineered to filter out solids so that a portion of the liquid is removed via subsurface infiltration 

into ground water or the vadose zone. 

Screen – A device with openings, generally of uniform size, used to retain or remove suspended 

or floating solids in flowing water or wastewater and to prevent them from entering an intake or 

passing a given point in a conduit. The screening element may consist of parallel bars, rods, 

wires, grating wire mesh, or perforated plate. The openings may be of any shape, although they 

are usually circular or rectangular.

Safe Drinking Water Information System (SDWIS) – Database containing information about 

drinking water treatment systems and plants. There is a federal SDWIS and state SDWIS. 

SDWIS identification numbers (or PWS IDs) are nine characters in length, with the first two 

digits usually composed of the state abbreviation. 

Sedimentation – Separation of solids and liquids from mixtures. Discrete and hindered settling 

principally involves separation of solids from mixtures that are predominantly liquids, and these 

processes are referred to as “clarification.” Sedimentation refers to the physical separation 

process, in contrast to non-mechanical dewatering, which is a residuals treatment process, and 

disposal, which is a residuals destination.

Sedimentation basin – A basin or tank in which water or wastewater containing settleable solids 

is retained in order to remove by gravity a part of the suspended matter. Also called 

sedimentation tank, settling basin, and settling tank.

Sequestering – To render inactive, such as chelation (binding of metal ion to form an inactive 

metal compound). 

Settleable solids – That matter in wastewater that will not stay in suspension during a 

preselected settling period, such as one hour, but either settles to the bottom or floats to the top. 

Settling – See “sedimentation.”

Settling basin – See “sedimentation basin.” 

Site – See “facility.”

Slow sand filtration – As defined in 40 CFR 141.2, a process involving passage of raw water 

through a bed of sand at low velocity (generally less than 0.4 meters/hour) resulting in 

substantial particulate removal by physical and biological mechanisms.

Sludge – The accumulated solids separated from liquids during processing. 
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-13

Sludge thickener – A tank or other piece of equipment designed to concentrate water treatment 

sludges. 

Source reduction – Any practice prior to recycling, treatment, or disposal that reduces the 

amount of any hazardous substance, pollutant, or contaminant entering any residuals stream or 

otherwise released into the environment. Source reduction can include equipment or technology 

modifications, process or procedure modifications, substitution of raw materials, and 

improvements in housekeeping, maintenance, training, or inventory control.

Source water – Intake (raw) water treated and/or distributed by utilities.

Spent filter backwash water – A stream containing particles that are dislodged from filter 

media when water is forced back through a filter (backwashed) to clean the filter.

Standard Industrial Classification (SIC) – A numerical categorization system used by the U.S. 

Department of Commerce to catalogue economic activity. SIC codes refer to the products, or 

group of products, produced or distributed, or to services rendered by an operating establishment. 

SIC codes are used to group establishments by the economic activities in which they are 

engaged. SIC codes often denote a facility's primary, secondary, tertiary, etc. economic activities. 

This system predated NAICS. 

Supernatant – The water standing above a sediment or precipitate. 

Surface waters – Waters of the United States, as defined at 40 CFR 122.2, including, but not 

limited to, oceans and all interstate and intrastate lakes, rivers, streams, creeks, mudflats, sand 

flats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, and natural ponds. 

Suspended solids – Solid organic and inorganic particles that are held in suspension by the 

action of flowing water and are not dissolved. 

System – One or more water treatment facilities that produce and deliver finished water to 

customers over the same distribution network. 

T

Thickener supernatant – Thickener supernatant is the clarified water that exits the units after 

particles have been allowed to settle out. 

Thickening – Gravity separation and concentration of solids from liquid/solid mixtures that are 

mostly solids. 

Total suspended solids (TSS) – Solids in water that can be trapped by a filter. TSS can include 

a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes, and 

sewage.
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-14

Total trihalomethanes (TTHM) – The trihalomethane compounds include trichloromethane 

(chloroform), dibromochloromethane, bromodichloromethane and tribromomethane 

(bromoform).

Toxic pollutants – those pollutants listed by the Administrator under CWA Section 307(a) and 

listed at 40 CFR 401.15 

Transient, Non-Community Water System (TNCWS) – A water system that provides water in 

a places such as a gas station or campground where people do not remain for long periods of 

time. 

Treatment – Any method, technique, or process designed to change the physical, chemical, or 

biological character or composition of any metal-bearing, oily, or organic waste in order to 

neutralize such wastes, to render such wastes amenable to discharge, or to recover metal, oil, or 

organic content from the wastes. 

Trihalomethane (THM) – As defined in 40 CFR 141.2, one of the family of organic 

compounds, named as derivatives of methane, wherein three of the four hydrogen atoms in 

methane are each substituted by a halogen atom in the molecular structure.

Turbidity – The cloudy appearance of water caused by the presence of suspended and colloidal 

matter that cause the scattering and adsorption of light. In the drinking water industry, a turbidity 

measurement is used to indicate the clarity of water. Technically, turbidity is an optical property 

of the water based on the amount of light reflected by suspended particles. WTPs may be able to 

correlate turbidity to suspended solids. Because source water quality varies seasonally, weekly or 

monthly correlations may be necessary.

U

Ultrafiltration – A method of water treatment that uses membranes in a pressure-driven process 

for concentrating solutions containing colloids and higher molecular weight materials. The 

method typically removes viruses, colloids, clays, bacteria, humic acids, and fulvic acids. 

Underground injection – The technology of placing fluids underground, in porous formations 

of rocks, through wells or other similar conveyance systems.

Utility – The public or private entity managing the business aspects of the production and 

distribution of finished water from one or more water treatment systems (e.g., billing customers 

for water service, paying utility employees and third-party vendors for services and products 

provided to the utility, paying servicing fees for any outstanding debts). Customers are usually 

more familiar with utility as a water supplier than a system, in those utilities that operate multiple 

systems.
Drinking Water Industry Report Section 14 – Glossary, Acronyms, and Abbreviations

14-15

V

Vacuum-assisted drying beds – Dewatering technology in which a vacuum is applied to the 

underside of porous media plates to remove the water from residuals. 

Vadose zone – Area between the land surface and the water table. 

W

Wastewater – See “process wastewater.”

Wastewater treatment – The processing of wastewater by physical, chemical, biological, or 

other means to remove specific pollutants from the wastewater stream, or to alter the physical or 

chemical state of specific pollutants in the wastewater stream. Treatment is performed for direct 

or indirect discharge of treated wastewater, recycle of treated wastewater to the same process 

that generated the wastewater, or for reuse of the treated wastewater in another process.

Water treatment – Any activity associated with altering the character or composition of source 

water prior to storage, transmission, distribution, and consumption by public water utility 

consumers. This treatment takes place at a water treatment plant (see definition).

Water treatment plant (WTP) – A water treatment facility in which ground water, surface 

water, or other source water is processed to produce potable water for storage, transmission, 

distribution, or consumption by public water utility consumers. For the purposes of the industry 

review, this term does not encompass off-facility treatment stations (e.g., booster chlorination 

stations, fluoridation stations, corrosion control treatment stations) or off-site water transfer 

infrastructure (e.g., tunnel transferring turbid water from one watershed body to another 

waterbody upstream of the facility, water towers that are downstream of the facility).

Water treatment system – One or more water treatment plants that produce and deliver finished 

water to customers over the same distribution network. 

Water treatment utility – See “utility”.

Watershed – The land area from which water drains into a stream, river, or reservoir. 

Well – A bored, drilled or driven shaft whose depth is greater than the largest surface dimension; 

a dug hole whose depth is greater than the largest surface dimension; an improved sinkhole; or 

a subsurface fluid distribution system. 

Z

Zero discharge – Disposal of process residuals other than by direct discharge to a surface water 

or by indirect discharge to a publicly owned, privately owned, federally owned, combined, or 

other treatment works.
Drinking Water Industry Report Appendix A

APPENDIX A 

QUESTIONNAIRE DESIGN AND CALCULATION OF NATIONAL ESTIMATES
Drinking Water Industry Report Appendix A

A-1 

APPENDIX A

QUESTIONNAIRE DESIGN AND CALCULATION OF NATIONAL 

ESTIMATES

One of the data collection activities undertaken by EPA was a survey of drinking 

water treatment facilities, known as the Water Treatment Plant Questionnaire. This appendix 

provides detailed information about the statistical methods used in conducting the questionnaire. 

Section A.1 provides a discussion of the sample frame created for the questionnaire. Section A.2 

presents the statistical sample design used to select treatment systems for inclusion in the 

questionnaire. Section A.3 describes the response rates for Part A of the questionnaire (technical 

questions). Section A.4 presents the statistical methods used to calculate national estimates of 

various operating characteristics based upon the responses to Part A. The national estimates are 

provided in Section 3 of this report. Section A.5 provides references. 

A.1 SAMPLE FRAME

This section provides an overview of the sample frame used to select systems for 

the questionnaire. Further information about the sample frame and questionnaire design can be 

found in EPA’s Information Collection Request Supporting Documentation (U.S. EPA, 2006). 

For the questionnaire, EPA originally considered approximately 160,000 public 

water systems that collectively provide 90 percent of the nation’s drinking water. After 

examining existing data sources, EPA reduced the target population for the questionnaire to a 

relatively small subset to reduce industry’s burden and to obtain information from systems most 

likely to produce residuals. Specifically, the target population included all public water systems 

except those in the following groups: 

• Systems serving fewer than 10,000 people were excluded because, while 

they account for 93 percent of community water systems (CWSs), EPA 

estimates they contribute less than nine percent of the residuals from the 

industry (U.S. EPA, 2006). 
Drinking Water Industry Report Appendix A

A-2 

• CWSs that do not produce residuals were excluded either because they do 

not treat the source water, or they treat it in a manner that is unlikely to 

produce residuals. 

• About 10 non-community water systems (NCWS) serving populations 

greater than 10,000 were excluded because they do not serve permanent 

resident populations and, thus, may have different discharge practices and 

financial characteristics.

The sample frame from which the sample was drawn was derived from EPA’s 

Safe Drinking Water Information System (SDWIS), a database that stores routine data about the 

nation’s drinking water. The data in SDWIS were combined with additional data from other 

sources, such as the 2000 CWSS (Community Water System Survey) – which has operational 

and financial data not available in SDWIS – and the May 14, 1996 Information Collection Rule

to support future regulation of microbial contaminants, disinfectants, and disinfection byproducts 

– which has engineering and operations information not available in SDWIS. The database 

created from these sources provided a complete listing of all systems in the United States. The 

sample frame database also contained information about each treatment plant within a system. 

Information maintained in the sample frame database at the system level included:

• Public Water System identification number PWSID, name, owner, and 

contact information; 

• Primary water source;

• Population served; and 

• Community served. 

Information contained in the sample frame database at the treatment facility (plant) level 

included: 

• Facility Registration System identification number FRSID, name, and 

location; 

• Associated PWSID;

• Primary water source;

• Estimated population served; 
Drinking Water Industry Report Appendix A

A-3 

• Treatment method information; and

• Discharge information. 

The data associated with systems was considered to be of high quality. The quality of the 

information about individual plants, however, varied, with high-quality information about 

primary water source and treatment method but poor quality information about discharge and 

population served. 

The plants that met the criteria presented above formed the target population. 

However, data collected by the CWSS, as well as other data available in SDWIS, focused on 

information at the system level rather than information for each individual plant. Thus, EPA 

decided to create a sample frame of water treatment systems and to request information from 

each system about its member plants. Specifically, the questionnaire that was sent to each 

sampled system asked a series of qualifying questions to determine if the system had any plants 

within the target population. Systems were only required to complete the remaining questions if 

they had plants within the target population. 

EPA determined that the sample frame of treatment systems has a nearly 100 

percent coverage rate for the target population. The sample frame database provided a complete 

listing of all community water systems in the United States serving at least 10,000 people at the 

time it was finalized. Because no treatment plant in a system serving fewer than 10,000 people 

could serve more than 10,000 people, the sample frame should contain all systems that have 

members of the target population. There is, however, a small probability that between the times 

that the sample frame database was finalized and the sample was selected, the size of the 

population served by a single-facility system could have moved from fewer than 10,000 to over 

10,000. In such a case, the facility would be in the target population but its system would not be 

in the sample frame. EPA has judged the likelihood of such a case occurring as being very small. 
Drinking Water Industry Report Appendix A

A-4 

A.2 SAMPLE DESIGN

This section describes the sample design for the questionnaire. A sample design 

identifies the way in which the questionnaire data are to be collected. EPA chose to use a 

stratified sample design that required only some systems to respond. The systems and plants 

identified from the stratified sample are statistically representative of all systems and plants in 

the target population. 

A.2.1 Statistical Design and Strata

EPA used a stratified sample design to select treatment systems to receive a 

questionnaire. Stratification is performed by selecting one or more characteristics of interest and 

dividing the members of the population into “strata” that are defined by those characteristics. 

Generally, the sample frame identifies these characteristics or provides a basis to reasonably 

assign characteristics to each population member. Stratified sampling consists of selecting a 

probability-based sample from within each stratum, then combining them to constitute the total 

sample. There are several benefits that can result from a stratified sampling approach, including: 

• Ensuring that the sample contains representatives from every stratum;

• Improving the precision of parameter estimates (if the strata are defined 

appropriately); 

• Allowing important parameters to be estimated at the stratum level; and

• Allowing certain subpopulations of particular interest to be sampled at a 

greater rate than others. 

To select systems to receive questionnaires, EPA used the following stratification 

variables, which were available from the sample frame:

• Size of population served; 

• Primary water source (surface water or ground water); and

• Treatment type. 
Drinking Water Industry Report Appendix A

A-5 

Size of population served was selected for use in stratification because it served as a surrogate 

for the volume of water treated and the volume of residuals that are produced. EPA considered 

two population size groups. The chosen cut-point was 50,000, because a review of existing 

literature showed that this cut-point is commonly used in evaluating drinking water systems. 

Primary water source was selected as a stratification variable because substantial differences can 

exist in the amount and type of residuals that a plant produces between treating surface water and 

treating ground water. Surface water, which is taken from above-ground sources such as rivers, 

lakes, wetlands, or estuaries, is more vulnerable to contamination and usually needs treatment 

before it is safe to drink. Ground water, which is pumped from underground aquifers through 

drilled wells or from springs, is protected by layers of soils and other subsurface materials and 

often needs only minimal treatment.

EPA considered larger systems (i.e., those serving populations greater than 

50,000) to be more likely to have residual management (or treatment) than small systems. Thus, 

for larger systems, EPA considered treatment type as an additional stratification variable, 

because it can affect the volume and characteristics of the residuals generated. Treatment type 

often depends on the plant’s size, its source water quality, and other environmental factors, such 

as climate. It may also depend on the experience of the plant operator or engineer with the 

treatment technologies. In addition, state or federal regulatory requirements may affect 

technology choices. EPA considered the following four treatment types: 

• Softening or ion exchange (SOFT/IX); 

• Conventional and direct filtration, including coagulation/flocculation 

(CONV);

• Membrane technology, including reverse osmosis, ultrafiltration, and 

electrodialysis (MEM); and

• Other, including filtration without coagulation/flocculation, activated 

carbon, activated alumina, and aeration (OTHER).

In addition to these stratification variables, EPA also considered whether a 

system’s water quality region would be an appropriate stratification variable, because geographic 

differences in source water characteristics could affect treatment and residuals generation. 
Drinking Water Industry Report Appendix A

A-6 

However, EPA determined that use of water quality region in conjunction with the other 

stratification variables would have resulted in an extremely inefficient statistical sample design 

with large variance estimates. Instead, EPA incorporated water quality region into the sample 

selection mechanism in a manner that would not disproportionally affect variance. First, EPA 

sorted the plants by water quality region within each stratum defined by the four stratification 

variables. EPA then drew a systematic sample from each cell, which involves selecting every k

th

plant, where k is determined randomly according to the selection rate. In this manner, EPA 

ensured that the sample was reasonably diverse from a geographical perspective while achieving 

an efficient sample design.

A.2.2 Target Precision Expected from the Sample Design

For the final sample design, EPA selected a total of 616 systems to receive the 

questionnaire. The number of systems selected was based on requirements concerning the 

precision of the questionnaire estimates. The precision depends on both the sample design and 

the sample size. For the drinking water treatment (DWT) industry questionnaire, the precision 

requirement was defined in terms of the width of a 95 percent confidence interval for an 

estimated proportion. Because a proportion of 0.5 (or 50 percent) results in the largest possible 

variance for the binomial distribution, EPA used that case in defining the target precision. Based 

upon EPA’s simulation, the sample would be expected, with 95 percent confidence, to yield 

sufficient data to estimate the value of an unknown proportion to within ±0.05 of its true value 

for the target population. This precision target will hold when the proportion’s true (unknown) 

value is equal to 0.5, and even greater precision is expected when the true value of the proportion 

is not equal to 0.5. Furthermore, the simulation estimated that a statistical sample of 593 systems 

distributed among the sampling strata would result in a sample of 673 plants from the target 

population, which would then represent an estimated 2,402 plants in the total population. (After 

including additional systems into its sample frame, EPA slightly increased the sample size to 616 

systems.) 
Drinking Water Industry Report Appendix A

A-7 

A.2.3 Sample Selection Procedure

The statistical selection of systems to receive questionnaires, as noted above, was 

done systematically within each stratum after sorting by water quality region to ensure 

geographic diversity within the sample. In addition, EPA sampled at a higher rate among strata 

that were mostly likely to produce residuals. EPA sampled more large systems than small ones 

and more surface water systems than ground water systems. In summary, the sample design had 

the following characteristics:

• Systems for large populations (greater than 50,000) were four times more 

likely to be selected than systems serving small populations (between 

10,000 and 50,000); 

• Systems with surface water as the primary water source were three times 

more likely to be selected than systems with ground water; 

• Larger populations were selected on the basis of (i.e., stratified by) 

primary water source and treatment method, while smaller populations 

were stratified by primary water source only; and

• A minimum of five systems were selected from each cell. 

The specific strata, the number of systems within each stratum, the sampling 

fraction, and number of systems that were selected in each stratum for the DWT industry 

questionnaire as part of the statistical sample are shown in Table A-1. In the original sample 

design, EPA included an allotment for a judgment sample of 25 systems that would not have 

been part of the statistical estimates. However, EPA later chose to increase the statistical sample 

size and used the allotment from the judgment sample for this purpose. 
Drinking Water Industry Report Appendix A

A-8 

Table A-1. DWT Questionnaire Strata, Population Size, and Sample Size

Stratum Sample Information

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method

Sampling 

Fraction

(Percent) a

Number of 

Systems in 

Frame

Number of 

Systems in 

Statistical 

Sample

10,001-50,000

Ground Any 6 625 37

Surface Any 18 1,044 187

Total Sub-total 1,669 224

More than 50,000

Ground

Conventional Filtration 100 8 8 

Membrane 100 5 5 

Other 24 82 20

Softening 24 50 12

Ion Exchange 100 5 5

Sub-total 150 50

Surface

Conventional Filtration 72 288 208

Membrane 72 26 19

Other 72 86 62

Softening 72 67 49

Ion Exchange 100 4 4

Sub-total 471 342

Sub-total 621 392

Total 2,290 616

a – A minimum of five systems were sampled from each stratum. 

A.3 RESPONSE STATUS

This section describes the response rates, non-response evaluations, bias 

considerations, and unusual situations requiring adjustments to the Part A responses. 

A.3.1 Response Rates

Table A-2 shows the final disposition of Part A responses to the questionnaire by 

stratum. In the rest of the document, references to the “questionnaire” and “responses” pertain 

only to the Part A (technical) responses. Table A-2 addresses the number of non-responding 

systems but does not address non-responses to individual questions. Data were analyzed without 

any adjustments made for missing responses to individual questions. 
Drinking Water Industry Report Appendix A

A-9 

Despite EPA efforts to obtain the missing information through repeated phone 

calls and email communications with the questionnaire respondents, 46 questionnaires had one 

or more missing responses and/or responses needing clarification at the completion of the 

questionnaire. An additional 28 questionnaires had missing information; however, these 

questionnaires included 27 questionnaires from Puerto Rico and one questionnaire from New 

York. The next section describes EPA’s evaluation of potential patterns in the non-responses. 
Drinking Water Industry Report Appendix A

A-10 

Table A-2. DWT Questionnaire Part A: Strata, Population Size, and Sample Size, and Response Information for Systems

Stratum Sample Information Response/In-Scope Information For SYSTEMS

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Sampling 

Fraction

(Percent) a

Number 

of 

Systems 

in Frame

Number of

Systems in 

Sample

Number of 

Responses 

Received 

Number of 

NonRespondents 

Number 

In-Scope 

Respondents

Estimated 

Population 

In-Scope

10,001-

50,000

Ground Any 6 625 37 17 20 17 283

Surface Any 18 1,044 187 125 62 125 694

Sub-total 1,669 244 142 82 142 978

More than 

50,000

Ground

Conventional 

Filtration 100 8 8 5 3 5 5 

Membrane 100 5 5 3 2 3 3

Other 24 82 20 8 12 8 33

Softening 24 50 12 11 1 11 46

Ion Exchange 100 5 5 3 2 3 3

Sub-total 150 50 30 20 30 90

Surface

Conventional 

Filtration 72 288 208 175 33 174 242

Membrane 72 26 19 14 5 14 19

Other 72 86 62 43 19 42 58

Softening 72 67 49 37 12 37 51

Ion Exchange 100 4 4 2 2 2 2

Sub-total 471 342 271 71 269 373

Sub-total 621 392 301 91 299 463

Total 2,290 616 443 173 441 1,441

 a – A minimum of five systems were sampled from each stratum. 
Drinking Water Industry Report Appendix A

A-11 

A.3.2 Non-Response Evaluation 

This section describes EPA’s evaluation of potential non-response patterns to the 

questionnaire. Such patterns are evaluated as a function of known information about all systems 

that were included in the sample. Some information about the sampled systems is available in the 

sampling frame. Specifically, the sample frame includes (1) information that was used to define 

sampling strata, and (2) other system characteristics that were not used to create sampling strata. 

For the DWT questionnaire, EPA used the size of the population served, the primary water 

source, and the treatment method to create the sampling strata. Other information available in the 

DWT questionnaire sampling frame used to examine potential non-response patterns includes: 

• EPA Region, 

• Water Quality Region,

• State, and

• Type of owner. 

EPA combined the information from the sampling frame with the results of the 

DWT questionnaire to prepare summaries of non-response rates compared with system 

characteristics. Tables A-3 through A-7 provide summaries of non-response rate of the sampled 

systems in relation to several of the variables. In particular:

• Table A-3 shows the non-response information by stratum,

• Table A-4 shows the non-response information by EPA Region, 

• Table A-5 shows the non-response information by Water Quality Region, 

• Table A-6 shows the non-response information by state, and 

• Table A-7 shows the non-response information by type of owner. 

Each of the five tables contains the following information: 

• Variable level,

• Total number of systems in the DWT questionnaire sample,

• Number and percent of sampled systems whose responses indicated that 

they were unqualified for participation in the questionnaire, 

• Number of qualified systems responding to the questionnaire (and percent 

of all sampled systems not known to be unqualified), 
Drinking Water Industry Report Appendix A

A-12 

• Number of non-responding systems (which includes those systems that did 

not return the questionnaire and those systems that returned the 

questionnaire but only provided partial responses (response to Question 1, 

indicated they were qualified to participate in the questionnaire), and 

• Number of known in-scope non-respondents (i.e., only responded to 

Question 1 and indicated they were in-scope). 

As noted in the bullets above, there were two types of non-responding systems 

defined for the summaries: those for which no responses were received, and those that sent 

partial responses. The latter group comprises the “known in-scope non-respondents” systems. 

The percentages shown in Tables A-3 through A-7 are calculated differently for various 

columns. For the number of unqualified systems, the denominator of the percentage is the 

number of systems sampled. For the number of responding and non-responding systems that 

were not known to be unqualified, the denominator of the percentage subtracted the number of 

unqualified systems from the total number sampled, or equivalently, the sum of the numbers of 

systems that were known to be qualified and the systems for which there was no response at all. 

For example, in the first row of Table A-3, the percentage of unqualified systems is equal to 19 

divided by 37, and the percentage of non-responding systems is equal to 3 divided by 18 (37 – 

19). 

Upon examining Tables A-3 through A-7, EPA noted the following situations 

with increased rates of non-response: 

• In Table A-3, most strata have between 20 and 40 percent non-response 

rates. The two exceptions, at 50 and 75 percent, are the two ion exchange 

strata for populations greater than 50,000. Both of these strata have no 

more than five members. 

• In Table A-4, EPA Region 2 has a significantly higher non-response rate 

(62%) than the other regions, due in part to non-response by systems in 

Puerto Rico. 

• In Table A-5, systems with a Water Quality Region specification of “e” 

have a 95% non-response rate, while all other regions have non-response 

rates of less than 40%. The “None” category includes Puerto Rico and 

Guam.

• In Table A-6, the states that have a greater than 50% non-response rate 

include Maryland and Puerto Rico. Mississippi, Nebraska, and Utah have 

50% response rates, but there were only 2 qualified systems sampled in 

each.

• In Table A-7, non-response rates were similar for all types of owner.
Drinking Water Industry Report Appendix A

A-13 

In examining all five tables together, it is clear that the primary place where there 

is a significant non-response pattern is caused by the partial responses from the systems in Puerto 

Rico.

A.3.3 Bias Considerations 

Non-response bias occurs when the questionnaire responses that would have been 

received from a group of sampled subjects who do not respond to the questionnaire are 

systematically different than the actual responses received from the subjects who did complete 

the questionnaire. Thus, non-response bias can be present any time there are non-respondents, 

regardless of whether there are any obvious patterns in respondents and non-respondents. 

However, in the case of the DWT questionnaire, there is a clear pattern of non-response from the 

Puerto Rico systems that could have an associated non-response bias due to potential differences 

in characteristics between Puerto Rico systems and the responding systems. The presence of nonresponse bias related to partial responses from Puerto Rico systems may lead to inaccurate 

national estimates of variables measured by the questionnaire. This is due to the fact that the 

different values of questionnaire responses from Puerto Rico are not incorporated into the 

national estimate, causing under- or over-estimates of the variables of interest. As explained 

below, EPA considers that inaccurate national estimates are unlikely, even considering the nonresponses from Puerto Rico. 

There are three available options for addressing the issue of potential response 

bias due to the partial responses from the Puerto Rico systems that were included in the sample. 

Each of the options, with information about assumptions and consequences are presented below. 

(1) Assume that Puerto Rico systems are similar to others within strata.

The purpose of placing systems into strata for the sample selection (and into domains for 

the analysis) is to create sets of systems that should have similar questionnaire responses 

based on the fact that they have similar characteristics with regard to population size, 

primary water source, and treatment method. Because EPA placed the Puerto Rico 
Drinking Water Industry Report Appendix A

A-14 

systems into strata based on these characteristics, EPA would assume that all other 

systems in the strata would produce similar results to those that would be expected from 

the Puerto Rico systems. If it can be assumed that the strata are homogenous, EPA would 

expect no non-response bias because other similar systems are present. As a result, the 

methods that EPA have used to adjust for unit non-response will be adequate to account 

for the Puerto Rico systems, and no additional adjustments to the questionnaire analysis 

will be required. 

(2) Make additional efforts to obtain data from some of the Puerto Rico systems. 

The electronic/mailed questionnaire used with the DWT questionnaire failed to obtain all 

the necessary data from the Puerto Rico systems to include in the questionnaire response 

database. This may be due to one of two likely reasons: (a) the systems were unwilling to 

respond to a particular question in the questionnaire, or (2) the systems could not reliably 

respond to a questionnaire in English. To counter these reasons, EPA could choose one of 

two alternatives to collect data from the Puerto Rico systems. The first alternative is for 

EPA to follow up with several of the systems and attempt to collect some data. EPA did 

contact the system, but did not receive a response.. A second alternative is for EPA to 

translate the questionnaire into Spanish and resubmit it to the sampled Puerto Rico 

systems. If the Puerto Rico systems did not respond, EPA would then need to address 

non-response associated with these systems. If some responses were received from 

follow-up efforts, EPA can adjust the analyses to incorporate the new data, including a 

revision of the non-response adjustments to the questionnaire weights.

(3) Re-define the target population to represent the 50 states and DC.

Because the most significant non-response issue is that of partial responses from Puerto 

Rico, which is a territory rather than a state, EPA could choose to change the scope of the 

questionnaire results to apply to only the 50 United States and the District of Columbia. 

This would also result in the elimination of any data from systems from other territories, 

such as Guam and Saipan, as well as Puerto Rico. If this approach was taken, EPA would 
Drinking Water Industry Report Appendix A

A-15 

need to revise the questionnaire weights to account for changes in the probability of 

selection and redo the analysis incorporating the new questionnaire weights.

EPA considers Option 1 to be the most reasonable alternative for three reasons. First, the sample 

design was developed to place Puerto Rico systems within strata based on characteristics they 

shared with other systems. Thus, EPA expected Puerto Rico responses to be similar to those for 

other systems within the associated strata, and thus, it would not be appropriate to redefine the 

target population (i.e., Option 3). Second, a logistic regression analysis of the non-response rates 

in Table 1 shows that there are no statistically significant differences in the non-response rates 

among the various strata. Thus, the strata that contain the Puerto Rico systems (small surfacewater systems, large surface-water systems with conventional treatment, and large surface-water 

systems with “other” treatment) are similar to the other strata with regard to non-response rates. 

Third, during permit support activities, EPA visited and evaluated several Puerto Rico systems. 

The engineering team noted many similarities to systems operated elsewhere. While these 

observations are subjective, they support a finding that Option 1 is a reasonable assumption. 
Drinking Water Industry Report Appendix A

A-16 

Table A-3. Questionnaire Part A: Non-Response by Stratum

Stratum

Number in 

Sample

Number 

Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

Size of 

Population 

Served

Primary 

Water 

Source Treatment Method

10,001-50,000

Ground Any 37 19 (51) 15 (83) 3 (17) 1 

Surface Any 187 21 (11) 118 (71) 48 (29) 26

Sub-total 224 40 (18) 133 (72) 51 (28) 27

More than 

50,000

Ground

Conventional 

Filtration 8 1 (13) 6 (86) 1 (14) 1 

Membrane 5 0 (0) 3 (60) 2 (40) 0 

Other 20 10 (50) 8 (80) 2 (20) 1 

Softening 12 0 (0) 8 (67) 4 (33) 3 

Ion Exchange 5 1 (20) 1 (25) 3 (75) 3 

Sub-total 50 12 (24) 26 (68) 12 (32) 8 

Surface

Conventional 

Filtration 208 5 (2) 147 (72) 56 (28) 37

Membrane 19 1 (5) 11 (61) 7 (39) 3 

Other 62 13 (21) 27 (55) 22 (45) 18

Softening 49 1 (2) 32 (67) 16 (33) 9 

Ion Exchange 4 0 (0) 2 (50) 2 (50) 0 

Sub-total 342 20 (6) 219 (68) 103 (32) 67

Sub-total 392 32 (8) 245 (68) 115 (32) 75

Total 616 72 (12) 378 (69) 166 (31) 102
Drinking Water Industry Report Appendix A

A-17 

Table A-4. Questionnaire Part A: Non-Response by EPA Region

EPA 

Region

Number 

in Sample

Number Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

01 38 5 (13) 28 (85) 5 (15) 2 

02 62 10 (16) 20 (38) 32 (62) 24

03 65 4 (6) 37 (61) 24 (39) 14

04 147 16 (11) 93 (71) 38 (29) 25

05 82 3 (4) 68 (86) 11 (14) 7 

06 68 10 (15) 38 (66) 20 (34) 12

07 27 1 (4) 19 (73) 7 (27) 2 

08 26 3 (12) 17 (74) 6 (26) 2 

09 82 16 (20) 45 (68) 21 (32) 13

10 19 4 (21) 13 (87) 2 (13) 1 

Table A-5. Questionnaire Part A: Non-Response by Water Quality Region 

Water Quality 

Region

Number 

in 

Sample

Number 

Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

Appalachia 33 5 (15) 24 (86) 4 (14) 2 

Central North 24 2 (8) 18 (82) 4 (18) 2 

Central South 31 2 (6) 21 (72) 8 (28) 2 

Florida 31 9 (29) 13 (59) 9 (41) 3 

Great Lakes 74 3 (4) 60 (85) 11 (15) 7 

Mid Atlantic 72 3 (4) 47 (68) 22 (32) 17

North East 116 18 (16) 67 (68) 31 (32) 15

North Mountain 4 0 (0) 4 (100) 0 (0) 0 

North West 18 4 (22) 12 (86) 2 (14) 1 

South East 50 3 (6) 32 (68) 15 (32) 10

South Mountain 26 2 (8) 18 (75) 6 (25) 2 

South West 74 15 (20) 38 (64) 21 (36) 13

Texas 41 4 (10) 23 (62) 14 (38) 9 

None 22 2 (9) 1 (5) 19 (95) 19
Drinking Water Industry Report

A-18 

Table A-6. Questionnaire Part A: Non-Response by State/Territory

State

Number in 

Sample

Number 

Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

AL 15 1 (7) 12 (86) 2 (14) 2

AR 9 3 (33) 5 (83) 1 (17) 1

AZ 8 0 (0) 7 (88) 1 (13) 0

CA 68 14 (21) 36 (67) 18 (33) 11

CO 15 0 (0) 10 (67) 5 (33) 2

CT 8 0 (0) 7 (88) 1 (13) 1

FL 31 9 (29) 13 (59) 9 (41) 3

GA 21 0 (0) 13 (62) 8 (38) 4

GU 1 1 (100) 0 0 (NA) 0

HI 1 0 (0) 1 (100) 0 (0) 0

IA 9 0 (0) 6 (67) 3 (33) 1

ID 1 0 (0) 1 (100) 0 (0) 0

IL 20 1 (5) 16 (84) 3 (16) 2

IN 11 2 (18) 7 (78) 2 (22) 1

KS 7 1 (14) 4 (67) 2 (33) 0

KY 16 1 (6) 10 (67) 5 (33) 5

LA 4 0 (0) 3 (75) 1 (25) 0

MA 20 5 (25) 12 (80) 3 (20) 0

MD 7 0 (0) 3 (43) 4 (57) 1

ME 1 0 (0) 1 (100) 0 (0) 0

MI 8 0 (0) 8 (100) 0 (0) 0

MN 8 0 (0) 8 (100) 0 (0) 0

MO 9 0 (0) 8 (89) 1 (11) 0

MP 1 1 (100) 0 0 (NA) 0 

MS 3 1 (33) 1 (50) 1 (50) 0

MT 1 0 (0) 1 (100) 0 (0) 0

NC 29 1 (3) 21 (75) 7 (25) 6

ND 2 0 (0) 2 (100) 0 (0) 0

NE 2 0 (0) 1 (50) 1 (50) 1

NH 4 0 (0) 4 (100) 0 (0) 0

NJ 19 6 (32) 7 (54) 6 (46) 2

NM 3 2 (67) 1 (100) 0 (0) 0

NV 3 0 (0) 1 (33) 2 (0) 2

NY 24 4 (17) 13 (65) 7 (35) 3

OH 25 0 (0) 20 (80) 5 (20) 3

OK 11 1 (9) 6 (60) 4 (40) 2

OR 11 3 (27) 6 (75) 2 (25) 1

PA 35 3 (9) 19 (59) 13 (41) 8

PR 19 0 (0) 0 (0) 19 (100) 19

RI 3 0 (0) 2 (67) 1 (33) 1

SC 11 1 (9) 6 (60) 4 (40) 4

SD 3 2 (67) 1 (100) 0 (0) 0

TN 21 2 (10) 17 (89) 2 (11) 1

TX 41 4 (10) 23 (62) 14 (38) 9

UT 3 1 (33) 1 (50) 1 (50) 0

VA 20 1 (5) 13 (68) 6 (32) 5

VT 2 0 (0) 2 (100) 0 (0) 0

WA 7 1 (14) 6 (100) 0 (0) 0

WI 10 0 (0) 9 (90) 1 (10) 1
Drinking Water Industry Report Appendix A

A-19 

State

Number in 

Sample

Number 

Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

WV 3 0 (0) 2 (67) 1 (33) 0

WY 2 0 (0) 2 (100) 0 (0) 0

Table A-7. Questionnaire Part A: Non-Response by Type of Owner

Owner Type

Number in 

Sample

Number 

Unqualified

(%)

Number 

Respondents

(%)

Number NonRespondents

(%)

Number NonRespondents in 

Scope

Federal 

Government 8 2 (25) 4 (67) 2 (33) 2 

Local 

Government 503 56 (11) 307 (69) 140 (31) 85

Private 92 10 (11) 61 (74) 21 (26) 13

Public/Private 4 1 (25) 2 (67) 1 (33) 0 

State 

Government 5 2 (40) 2 (67) 1 (33) 1 

Unknown 4 1 (25) 2 (67) 1 (33) 1 
Drinking Water Industry Report Appendix A

A-20 

A.3.4 Assumptions Used to Modify Responses

While analyzing the questionnaire responses, it was necessary for EPA to make 

assumptions about the responses under certain circumstances. These circumstances, and EPA’s 

actions, were:

• If a system had multiple similar plants but a common residuals treatment 

system, EPA treated the multiple plants as a single plant having one 

residuals treatment system.

• If one plant discharged to another plant within the same system for 

residuals treatment but the finished water processes were significantly 

different (e.g., desalination and conventional), the process was recorded as 

multiple plant information. For the site without a residuals treatment 

system, the discharge was a zero or indirect discharge to the other site. For 

the site with the residuals treatment system, the discharges from both 

plants were influent to the residuals treatment system. 

Additionally, some treatment facilities provided unusual responses. These systems, their 

issues, and EPA’s resolution are noted below. 

• The cities of Phoenix and Mesa, AZ, co-owned the Val Vista plant 

(AZ0407025). As a result, separate sets of economic responses were 

submitted for each system, while only one set of technical responses was 

submitted for the plant. In this situation, two “pseudo-plants” were 

created, one within each system, and the technical responses were 

apportioned to each of the pseudo-plants proportionally to the percentage 

of operating costs paid by each system. 

• The Hillsboro and Joint Water Commission (JWC) plant is jointly owned 

by the cities of Hillsboro (PWS OR4100379), Tigard (OR4100878), 

Beaverton (OR4100081) Tualatin (OR4100665), and Forest Grove 

(OR4100305). Only Hillsboro was included in the sample, but they 

provided data for the jointly-owned plant. The plant information was 

scaled down to represent only the City of Hillsboro and not the other four 

cities that own and use water from the plant. 

• The sample included both the City of Poughkeepsie (NY1330291) and 

Town of Poughkeepsie (NY1302774). The data for the Town of 

Poughkeepsie was received first, so it was included in the analysis. The 

City of Poughkeepsie data was a duplicate of the Town of Poughkeepsie 
Drinking Water Industry Report Appendix A

A-21 

data. Thus, the City of Poughkeepsie was determined to be out-of-scope 

and was not included in the analysis. 

• The Lancaster County (SC) Water system (SC292001) and the Union 

County (NC) Water System (NC0190413) share ownership of a single 

plant. Only the SC system was included in the sample. It uses 40 percent 

of the total water production from the plant, while the NC system uses the 

other 60 percent. The questionnaire response includes complete technical 

information for the plant but economic data for only the SC system. The 

technical data was scaled down to represent only the SC system.

A.4 STATISTICAL METHODS FOR CALCULATING ESTIMATES

The following subsections discuss the methods that were used to calculate the 

national estimates of the technical and economic characteristics of DWT plants and systems. 

Section A.4.1 discusses the questionnaire weights that were calculated for the DWT 

questionnaire. Section A.4.2 discusses the methods used to organize the results for presentation 

in this report. Finally, Section A.4.3 presents the methods for calculating the national estimates. 

A complete discussion of the statistical methods can be found in Cochran (1977). 

A.4.1 Questionnaire Weights

Questionnaire weights are applied during the analysis of questionnaire data to 

obtain unbiased estimates of the population parameters of interest. Because a sample of DWT 

systems was selected, the results for any given respondent may represent more than one plant or 

system. The weight indicates the number of plants or systems that are represented by the 

respondent. These weights are used in calculating unbiased estimates of the national estimates. 

The questionnaire weights have been obtained in the manner prescribed by Office of 

Management and Budget (2006). 

The subsections that follow describe the calculation of the questionnaire weights 

for the DWT questionnaire. Section A.4.1.1 presents the method used for calculating the base 

questionnaire weights. Section A.4.1.2 presents the methods used for adjusting the weights for 

ineligible and non-responding systems. Section A.4.1.3 provides a table showing the actual 

weights that were calculated for the DWT questionnaire. 
Drinking Water Industry Report Appendix A

A-22 

A.4.1.1 Base Questionnaire Weight Calculation

The first step in obtaining the questionnaire weights required to ensure unbiased 

estimates of population parameters was to calculate base questionnaire weights. These base 

questionnaire weights are defined to be the inverse of the probability of selection. That is, for 

stratum h, 

h

h

h

n

N

w = , (Eq. A.1) 

where Nh is the number of systems in the stratum and nh is the number of systems. 

A.4.1.2 Eligibility and Non-Response Adjustments to Questionnaire Weights

Because not all systems responded to the questionnaire, and also because some of 

the systems included in the sample were not eligible to participate, the base questionnaire 

weights may inaccurately represent the systems within each stratum. To ensure that the weights 

are representative, the base weights are adjusted to account for ineligible systems that are in the 

sample and population and to account for systems that did not respond to the questionnaire. 

Potential respondents can be divided into four categories: 

1. Eligible respondents (r);

2. Eligible non-respondents (e);

3. Ineligible respondents (i); and

4. Systems with unknown eligibility (u).

For the DWT questionnaire, it was not possible to determine whether non-respondents were 

eligible or not eligible, so all non-respondents were placed into the category of unknown 

eligibility (i.e., e = 0).

The eligibility and non-response adjustments were made in two steps. In the first 

step, the base weight was adjusted for ineligibility. The specific equation for obtaining the 

eligibility-adjusted questionnaire weights was

hh

hhh

hh

ur

iur

ww

+

++  ⋅= , (Eq. A.2) 
Drinking Water Industry Report Appendix A

A-23 

where rh is the number of eligible respondents, uh is the number of systems with unknown 

eligibility, and ih is the number of ineligible respondents. In the second step, the eligibilityadjusted weight was adjusted for non-response using the following equation 

h

hh

hh

r

ur

ww

+  ⋅= . (Eq. A.3) 

In this case, the value of uh represents all non-respondents. 

A.4.1.3 Final Questionnaire Weights

Table A-8 contains the base and adjusted questionnaire weights that were used in 

the analysis of the DWT questionnaire data. These weights were calculated using Equations 

(A.1), (A.2), and (A.3). 

Table A-8. Questionnaire Part A: Calculated Questionnaire Weights 

Size of 

Population 

Served

Primary 

Water 

Source

Treatment 

Method

Base 

Questionnaire

Weights

Eligibility 

Adjustment

NonResponse 

Adjustment

Final

Questionnaire

Weights

10,001-50,000

Ground Any 16.89 2.31 1.07 41.67

Surface Any 5.58 1.30 1.22 8.85

More than 

50,000

Ground

Conventional 

Filtration

1.00 1.14 1.17 1.33

Membrane 1.00 1.67 1.00 1.67

Other 4.10 2.22 1.13 10.25

Softening 4.17 1.09 1.38 6.25

Ion Exchange 1.00 1.25 4.00 5.00

Surface

Conventional 

Filtration

1.38 1.13 1.25 1.96

Membrane 1.37 1.36 1.27 2.36

Other 1.39 1.38 1.67 3.19

Softening 1.37 1.20 1.28 2.09

Ion Exchange 1.00 2.00 1.00 2.00

A.4.2 Organization of Results using Analysis Domains

The sample design for the DWT survey defined the way in which the 

questionnaire participants were selected and data were to be collected. For this questionnaire, 
Drinking Water Industry Report Appendix A

A-24 

DWT systems were selected using a stratified sampling design, with the size of the population 

served, primary water source, and primary treatment method used as stratifying variables. 

Technical data were collected for qualifying treatment plants that were part of the selected 

systems, and economic data were collected for the systems themselves.

There were many cases observed where the characteristics of a particular plant 

differed from that of the system as a whole. For example, there were some systems that served 

over 50,000 people that had individual plants serving fewer than 50,000 people. Similarly, a 

system that used primarily surface water could have had a plant that used primarily ground 

water. Because EPA’s interest concerning the technical operational data is at the plant level, EPA 

chose to present the results of the technical data based on the characteristics of the plants rather 

than based on the questionnaire strata (which was based on system-level characteristics). EPA 

defined a set of “domains” of a plant for presenting the national estimates of the technical data. 

These domains correspond to the sampling strata; that is, the domains are based on the number of 

people served, the primary water source, and the treatment method used at the plant. 

For population served, the plant domain that was used in technical analyses 

presented in Section 3.2 was defined using the population served by the plant. Specifically, 

plants were divided into one of two groups: those that served between 10,000 and 50,000, and 

those that served more than 50,000. For the system-level economic analyses presented in Section 

3.3, system domains for population served were defined by summing the population counts 

served by each individual plant within the system (for which data were available). Systems were 

placed into one of two categories: those that served between 10,000 and 50,000 and those that 

served more than 50,000. 

For primary water source, the domain for each plant used in the technical analyses 

of Section 3.2 was defined as the water source with the largest percentage as reported in 

Question 2e of the questionnaire. The system domain used for the economic analyses of Section 

3.3 was defined to be the domain for the largest plant in the system, as defined by gallons of 

water produced from Question 2d of the questionnaire. There were several instances where this 

method for defining system domain may have produced inaccurate results. For example, consider 

a system that has three plants, one that produces 3 million gallons per day (MGD) using 100% 
Drinking Water Industry Report Appendix A

A-25 

surface water, and two others that each produce 2 MGD using 100% ground water. The system 

as a whole uses more ground water, but it is classified into the surface-water domain based on 

the use of the primary source from the largest plant. There are other similar scenarios that could 

result in misclassification of the primary water source. Despite the potential misclassifications, 

EPA chose to define system domains for primary water source using the characteristics of the 

plant with the largest water production. 

For treatment method, plant domains were defined using the treatment methods 

provided in their response to Question 2f of the questionnaire. If there was a single treatment 

method listed (or there were several different methods that fell under the same grouping as 

shown in Section A.2.1) the plant was assigned to that treatment method grouping. There were 

several cases where a plant indicated that it used more than one treatment method (in different 

groupings). Table A-9 shows the types of multiple-treatment-methods plants that responded to 

the questionnaire and the number of plants in each group. Based on an examination of the 

individual cases, each of these plants was assigned by an expert to one of the treatment methods. 

Table A-9 also shows the way the plants were assigned to treatment methods. 
Drinking Water Industry Report Appendix A

A-26 

Table A-7. Questionnaire Part A: Assignment of Multiple-Treatment Plants to Treatment 

Types

Treatment Types

Treatment Type for 

Analyses Number of Cases

Conventional Filtration plus some other method of treatment Conventional 451

Dechlorination, Primary Disinfection, and Ultrafiltration Membrane 1

Other, Primary Disinfection, and Reverse osmosis Membrane 1

Nanofiltration and Primary Disinfection Membrane 3

Primary Disinfection and Reverse osmosis Membrane 1

Precipitative and Primary Disinfection Softening 4

Ion exchange and Primary Disinfection Softening 2

Dechlorination, Microfiltration, Presedimentation, and 

Primary Disinfection Other 1 

Microfiltration, Presedimentation, and Primary Disinfection Other 1

Dechlorination, Other, and Primary Disinfection Other 2

Other, Presedimentation, and Disinfection Other 1

Microfiltration and Primary Disinfection Other 2

Other and Primary Disinfection Other 11

A.4.3 National Estimates Based Upon Part A Responses 

National estimates were calculated directly from Part A of the questionnaire 

results for each of the questions, except Question 2j and the questions requesting contact 

information. EPA presents the methods used to calculate the national estimates in the report. 

Section A.4.3.3 contains a discussion of the methods used to obtain baseline estimates for 

pollutant loadings. 

A.4.3.1 Estimates and Standard Errors

Several types of population estimates were calculated from the DWT 

questionnaire data. For numeric data (e.g., flow volume, number of connections), these estimates 

included minima, maxima, medians, means, and totals. The category of numeric variables also 

included several cases where two or more numeric variables were combined. For example, cost 

per connection was a numeric variable that was calculated by dividing the total cost for a plant 

by the total number of connections for the plant. For “characteristic” data (i.e., categorical 

responses to questions asking whether plants or systems had certain characteristics), the types of 

estimates calculated included proportions/percentages and counts. Although the DWT 

questionnaire was designed as a stratified sample, stratified sampling estimators were not 

directly relevant because the results are reported for domains rather than for the strata.
Drinking Water Industry Report Appendix A

A-27 

The formulas used to calculate the estimates are provided in the subsections 

below. Several terms are common to these formulas, including: 

• H is the total number of strata;

• nh is the number of sampled plants or systems in stratum h; 

• fh is the sampling rate for stratum h; 

•

•

•

•

 yhi = the measurement of interest collected from the ith sampled member 

of stratum h; 

whi = the questionnaire weight associated with the ith sampled member of 

stratum h, which is equal to wh from Equation (A.3); 

yhi if ( h,i ) belongs to Domain D

zhi =  ; and

 0 otherwise

whi if ( h,i ) belongs to Domain D

vhi =  . 

 0 otherwise

All of the formulas discussed below are implemented in SAS® using the procedures 

UNIVARIATE for minima, maxima, and median, and SURVEYMEANS for means, totals, 

counts, and proportions (SAS Institute Inc., 2008). 

Minima and Maxima 

The population minimum value of a continuous variable was estimated using the 

smallest observed value of the variable among all strata. Similarly, the population maximum was 

estimated using the largest observed value of the variable among all strata. Minimum and 

maximum values within strata were estimated using the smallest and largest observed value 

within the stratum.
Drinking Water Industry Report Appendix A

A-28 

Medians

The population median, or 50th percentile, was estimated using the following 

formula:















<⋅<

+⋅ ⋅=

=

∑∑∑

∑ ∑

+

= = =

+

= =

+

1

1 1 1

1

1 1

1

50

50

50 50

i

j

j

n

j

j

i

j

i j

i

j

n

j

ii j j

y if w ww

yy if w w

y

.

(. ) .

ˆ

)(

)()(

. , (Eq. A.4) 

where y(i) indicates the ith smallest value within the domain or stratum and wi is the weight 

associated with that value.

Means

The formula that was used to calculate estimates of population means for domains 

can be written as

∑∑

∑∑

= =

= =

⋅

= H

h

n

i

hi

H

h

n

i

hihi

D h

h

v

zv

y

1 1

1 1 . (Eq. A.5) 

The variance of this estimated mean is calculated as

∑ ∑( ) = =





 



 −⋅ −

−⋅ =

H

h

n

i

hhi

h

h h

D

h

rr

n

fn yV

1 1

2

1

1 )( )( , (Eq. A.6) 

where 

( )

∑∑= =

−⋅ = H

h

n

i

hi

Dhihi

ij h

v

yzv

r

1 1

(Eq. A.7) 

and 

h

n

i

hi

h

n

r

r

h

∑= = 1 . (Eq. A.8)

The standard error of the estimated mean is the square root of the variance shown in Equation 

(A.6).
Drinking Water Industry Report Appendix A

A-29 

Totals 

The formula for estimates of population totals, YD, for domains can be written as 

∑∑= =

⋅=

H

h

n

i

D hihi

h

Y zv

1 1

. (Eq. A.9) 

The variance of this estimated total is 

∑ ∑( ) = =





 



 −⋅⋅ −

−⋅ =

H

h

n

i

hhihi

h

h h

D

h

azv

n

fn YV

1 1

2

1

1 )( )( , (Eq. A.10) 

where 

h

n

i

hihi

h

n

zv

a

h

∑=

⋅

= 1 . (Eq. A.11) 

The standard error of the estimated total is the square root of the variance.

Ratios 

There were several cases where new variables were defined as ratios of two 

measured variables. For example, in Table 3-35, the estimated sales revenue per volume was 

defined using the total sales and the total water volume. For these types of estimates, EPA 

defined a new variable as the ratio of the two component variables, calculated this ratio for each 

responding plant or system, and used Equations (A.5) through (A.8) to calculate the estimates of 

the mean ratio and its standard error. 

Plant Counts

Estimates for the number of plants or systems within domains are obtained using 

the equations presented for domain totals. In this case, the values of the continuous variable for 

which totals are calculated are replaced with indicator variables corresponding to whether the 

plant or system possesses the characteristic of interest. For example, if we define yhi = 1 if the i

th

plant in stratum h uses conventional filtration and 0 if it does not for all sampled plants, equation 

(A.9) can be used to estimate the total number of plants within each domain that use 
Drinking Water Industry Report Appendix A

A-30 

conventional filtration. Equation (A.10) can also be used to calculate the variability of the plant 

counts as well as its standard error.

Proportions/Percentages 

Estimates of population proportions for domains are calculated in a similar 

manner to plant counts using Equations (A.5) through (A.8) applied to the indicator variables 

defined for plant counts. The overall national estimates of proportions (using the strata rather 

than domains) are calculated as

∑=

=

12

h 1

st pwp hh ˆˆ , (Eq. A.12) 

where

h

h

h

n

a

pˆ = . (Eq. A.13) 

The variance of the estimated population proportion is 

( )( ) h

h h

h h

st h f

n

pp wpV − −− = ∑=

1

1

1 12

1

2 ˆˆ ( ˆ ) (Eq. A.14) 

and its standard error is the square root of the variance. 

A.4.3.2 Confidence Intervals

In many cases, there will be interest in obtaining confidence intervals for the 

national parameters rather than “point” estimates of the parameters. Confidence intervals provide 

a range of probable values that the population parameter could be. The following formula is used 

to calculate a confidence interval for a domain mean:

)( D 2/ D ⋅+= ySEzyCI α , (Eq. A.15) 

where zα/2 is the upper 100(α/2) percentile of a standard normal distribution and is the 

standard error for . For other population parameters, confidence intervals are obtained using 

the associated estimates and their standard errors in Equation (A.15). 

D y

)( D ySE
Drinking Water Industry Report Appendix A

A-31 

A.4.3.3 Baseline Pollutant Loading Estimates

In addition to providing basic estimates using the specific questions on the DWT 

questionnaire, EPA examined the source of pollutant loadings. For this analysis, plants were 

divided into domains based on five parameters: treatment plant type, separation of residuals 

employed, discharge status, population served (as a surrogate for flow volume), and use of 

chlorination. Treatment method was defined as in Section A.2.1. For the other parameters, EPA 

classified plants in the following manner:

• Separation of residuals was “Yes” if the plant used thickening, drying, 

mechanical dewatering, non-mechanical dewatering, evaporation ponds, 

equalization, or sediment tank ponds to treat residuals. 

• Discharge status was direct, indirect, or both, based on the plant’s 

response to Question 2k of the questionnaire. 

• Four size categories were defined based on the population they served: 

10,000 to 50,000, 50,001 to 100,000, 100,001 to 500,000, and more than 

500,000. 

• Chlorination plants included those that used some form of calcium 

hypochlorite, chloramination, free chlorine, gaseous chlorine, or sodium 

hypochlorite as their primary disinfection. 

EPA prepared separate tables for chlorination and non-chlorination plants. 

A.5 REFERENCES

Cochran, W.G., 1977. Sampling Techniques. Wiley & Sons, New York. 

Office of Management and Budget, 2006. Guidance on Agency Survey and Statistical 

Information Collections. Office of Information and Regulatory Affair.

SAS Institute, Inc., 2008. SAS/STAT 9.2 User's Guide. SAS Institute, Inc., Cary, North Carolina. 

U.S. Environmental Protection Agency (EPA), 2006. Supporting Statement: Survey of Drinking 

Water Treatment Facilities. Office of Water.
Drinking Water Industry Report Appendix B

APPENDIX B 

COMPOSITION OF COMMON DRINKING WATER TREATMENT CHEMICALS ILLUSTRATING 

PRODUCTION IMPURITIES

(Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. 

Macphee and Richard Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA 

Research Foundation)
Drinking Water Industry Report Appendix B

B-1

Table B-1. Composition of Aluminum-Based Coagulants Illustrating Production 

Impurities

Pollutant

Median Concentration (mg/kg dry weight) a

Standard Alum Low-iron Alum

Polyaluminum Chloride 

(PACl)

Aluminum 90,000 89,400 153,911

Antimony <0.8 <0.8 <1.2

Arsenic <2.06 <2.00 <2.6

Barium <0.10 <0.10 0.21

Cadmium <0.1 <0.1 <0.2

Calcium 62 62 149

Chromium 66 0.6 0.6

Cobalt <0.20 <0.15 <0.41

Copper 1.86 0.21 1.34

Iron 1,300 39 91

Lead <4.1 <4.1 <4.1

Magnesium 33 14 41

Manganese 2.5 0.8 3.2

Mercury <0.82 1.03 1.44

Molybdenum <1.7 <1.7 <1.4

Nickel 0.90 0.41 1.65

Phosphorus 89 <4 <9

Potassium 7.5 7.7 10.7

Selenium <4.1 <5.1 <2.1

Silicon 52 14 56

Silver <0.82 <0.82 <1.65

Sodium 247 577 546

Strontium 1.03 0.41 0.41

Sulfur Not analyzed Not analyzed Not analyzed

Tin <2.1 <2.1 <2.7

Titanium 27 1.2 3.0

Vanadium 39 0.20 6

Yttrium <0.41 <0.30 <0.52

Zinc 3 16 14

Zirconium 12 0.4 0.9

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a – The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 
Drinking Water Industry Report Appendix B

B-2

Table B-2. Composition of Iron-Based Coagulants Illustrating Production Impurities

Pollutant

Single Sample Concentration (mg/kg dry weight) a

Ferric Chloride

SPL#1 SPL#2 TiO2#1 Ferric Sulfate

Aluminum 1,289 19,737 3,158 82

Antimony 9 6 7 <4

Arsenic <5 <3 <3 <4

Barium 0.3 1 18 1

Cadmium 1.0 1.0 1.0 1.4

Calcium 158 974 153 371

Chromium 124 111 100 <1

Cobalt 17 8 22 8

Copper 95 82 6 <0.4

Iron 355,263 305,263 315,789 228,866

Lead 53 <5 <13 41

Magnesium 55 316 316 173

Manganese 1,868 1,079 2,553 169

Mercury <5 <3 5 No data

Molybdenum <1 3 18 <0.8

Nickel 58 39 11 23

Phosphorus 29 263 42 163

Potassium 26 23 50 56

Selenium No data <3 <3 No data

Silicon 12 <1 15 8

Silver <5 <2 <2 <4

Sodium 211 395 895 47

Specific Gravity 1.4 1.4 1.4 No data

Strontium 2 4 9 2

Sulfur 158 2,579 63 206,186

Tin <5 <3 14 <4

Titanium 2 24 10,789 13

Vanadium 95 79 1,553 227

Yttrium <1 <0.5 <0.5 <0.8

Zinc 45 53 258 37

Zirconium 10 8 4,474 6

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a – The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 

SPL – Steel pickle liquor derived.

TiO2 – Derived during manufacture of titanium oxide.
Drinking Water Industry Report Appendix B

B-3

Table B-3. Composition of Potassium Permanganate in Samples from One Study 

Illustrating Production Impurities

Pollutant

Single Sample Concentration (mg/kg dry weight) a

Product #1 Product #2

Aluminum 560 610

Antimony <10 <10

Arsenic <10 <10

Barium 11 100

Cadmium <1 <1

Calcium 39 230

Chromium 44 72

Cobalt <2 <2

Copper <1 <1

Iron 320 520

Lead <49 <400

Magnesium <0.3 <0.3

Manganese 333,000 336,000

Mercury 79 <10

Molybdenum 24 12

Nickel 26 31

Potassium 238,000 234,000

Selenium 73 80

Silicon 750 1,000

Silver 82 79

Sodium 370 3,300

Strontium 1 7

Tin <10 <10

Titanium 4 9

Vanadium <2 <2

Yttrium 2 <2

Zinc 2 3

Zirconium 3 <2

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a – The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 
Drinking Water Industry Report Appendix B

B-4

Table B-4. Composition Data for Organic Polymers Illustrating Production Impurities

Pollutant

Concentrations for 12 Organic Polymers (mg/kg wet weight) a

Minimum Maximum Median

Aluminum <0.50 2,200 <40

Antimony <1 <240 <76

Arsenic <1 <240 <76

Barium <0.01 <3 <1

Cadmium <0.10 <25 <8

Calcium 0.50 120 73

Chromium <0.20 <49 <16

Cobalt <0.20 <49 <16

Copper <0.10 <25 <8

Iron <0.20 <340 <17

Lead <1 <460 <78

Magnesium <0.30 54 7

Manganese <0.02 8 3

Mercury <1 <240 <76

Molybdenum <0.20 <49 <16

Nickel <0.04 <49 <16

pH (standard units) 4.2 6.8 5.7

Potassium <4.00 <970 <324

Selenium <1 <240 <160

Silicon <1 130 <52

Silver <0.80 <190 <61

Sodium 85 27,000 940

Specific Gravity (no units) 0.99 1.14 1.04

Strontium <0.02 <3 <1

Sulfur 13 4,100 695

Tin <1 <240 <76

Titanium <0.10 490 <8

Total organic carbon (TOC) 4,178 (one sample) No data No data

Vanadium <0.20 <49 <16

Yttrium <0.20 <49 <16

Zinc <0.10 230 <12

Zirconium <0.20 140 <17

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a – The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 
Drinking Water Industry Report Appendix B

B-5

Table B-5. Composition Data for Lime Products Illustrating Production Impurities

Pollutant

Single Sample Concentration (mg/kg as Ca(OH)2 dry weight)a

Hydrated lime #1 Hydrated lime #2 Hydrated lime #3 Pebble lime

Aluminum 2,154 2,700 2,267 1,135

Antimony <15 <2 <67 <2

Arsenic <15 <2 <67 <2

Barium 77 13 27 5

Cadmium <1.5 0.2 <6.7 <0.2

Calcium 507,692 495,000 493,733 495,676

Chromium <3.1 2 <13.3 1

Cobalt <3.1 0.4 <13.3 <0.3

Copper 1.5 2 <6.7 0.5

Iron 846 1,600 1,067 560

Lead <15 <4 <333 <3

Magnesium 7,231 7,700 16,667 4,465

Manganese 35 23 73 16

Mercury <15 <2 <6.7 <2

Molybdenum 4.6 <0.4 <13.3 <0.3

Nickel <3.1 1 <13.3 0.5

Potassium 785 860 1,067 832

Selenium <15 <2 <67 <2

Silicon 4,154 4,600 6,467 1,665

Silver <12 <2 <53 <2

Sodium 1,277 49 3,000 22

Strontium 338 240 307 212

Tin <15 <2 <67 <2

Titanium 74 66 87 26

Vanadium 3.1 3 <13.3 2

Yttrium <3.1 1 <13.3 1

Zinc 9 4 6.7 2

Zirconium 3.1 3 <13.3 2

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a –The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 
Drinking Water Industry Report Appendix B

B-6

Table B-6. Composition Data for Caustic Soda Illustrating Production Impurities

Pollutant

Single Sample Concentration (mg/kg dry weight)

a

50% 50% 25% 50%

Aluminum 8 5 <2 <1

Antimony <2 <2.0 <4 <2

Arsenic <2 <2.0 <4 <2

Barium <0.02 <0.02 0.2 0.6

Cadmium <0.2 <0.2 <0.4 <0.2

Calcium <1 1 24 6

Chromium <0.4 <0.4 <0.8 1

Cobalt <0.4 <0.4 <0.8 <0.4

Copper 0.2 <0.2 <0.4 <0.2

Iron 1 2.0 6 36

Lead <2 <2.0 <20 <20

Magnesium 0.2 0.4 4 2

Manganese <0.04 <0.04 <0.08 0.6

Mercury <2 <2.0 <4 <2

Molybdenum <0.4 <0.4 <0.8 0.6

Nickel <0.4 <0.4 <0.8 1

pH (standard units) 9.94 11.10 12.80 10.70

Phosphorus 112 <8 <4 7

Potassium 320 1,180 560 980

Selenium <2.0 <2.0 <4 <2

Silicon 340 480 44 166

Silver <2 <1.6 <3 <2

Sodium 508,000 510,000 444,000 508,000

Specific gravity (no units) 1.53 1.53 1.22 1.52

Strontium 0.4 0.2 4 2.4

Sulfur 18 36 60 168

Tin <2 <2 <4 <2

Titanium <0.2 <0.4 0.8 <0.2

Vanadium <0.4 <0.4 <0.8 <0.4

Yttrium <0.4 <0.4 <0.8 <0.4

Zinc 0.4 <0.2 1.2 0.4

Zirconium <0.4 <0.4 <0.8 <0.4

Source: American Water Works Association (AWWA), David A. Cornwell, Michael J. Macphee and Richard 

Brown, 2002. Trace Contaminants in Drinking Water Chemicals, AWWA Research Foundation.

a – The less than sign denotes that the value was below sample-specific method detection limits (MDL); the value 

listed is the MDL. 
Drinking Water Industry Report Appendix C

APPENDIX C 

POTW PERCENT REMOVALS

(Sources: U.S. Environmental Protection Agency (U.S. EPA), 1982. Fate of Priority Pollutants 

in Publicly Owned Treatment Works (EPA 440/1-82/303, September 1982 and U.S. EPA, 1994. 

National Risk Management Research Laboratory (NRMRL) Treatability Database Version 5.0, 

Cincinnati, OH) 
Drinking Water Industry Report Appendix C

C-1

Table C-1. POTW Removals

DWT Parameter Name POTW Removal (fraction)

Aluminum, Dissolved 0.91

Aluminum, Total 0.91

Aluminum, Unknown 0.91

Ammonia, Total 0.39

Ammonia, Unionized 0.39

Ammonia, Unknown 0.39

Arsenic 0.6577

Barium, Unknown 0.5515

Benzene 0.95

Cadmium, Total 0.9005

Chlorine, Free 1

Chlorine, Total Residual 1

Chloroform 0.73

Chromium 0.8033

Copper, Dissolved 0.842

Copper, Total 0.842

Copper, Unknown 0.842

Dichloroboromomethane 0.6424

Lead, Total 0.7745

Lead, Unknown 0.7745

Manganese, Total 0.406

Manganese, Unknown 0.406

Manganese, Dissolved 0.406

Mercury, Unknown 0.9016

Nickel, Unknown 0.5144

Zinc, Total 0.7914

Selenium 0.3433

Zinc, Unknown 0.7914

Aluminum 0.91

Ammonia 0.39

Barium 0.5515

Cadmium 0.9005

Copper 0.842

Lead 0.7745

Manganese 0.406

Mercury 0.9016

Nickel 0.5144

Zinc 0.7914

Phosphorus, Total 0.69

Phosphorus as P 0.69
Drinking Water Industry Report Appendix C

C-2

Table C-1. POTW Removals

DWT Parameter Name POTW Removal (fraction)

Trihalomethane 0.73

Trihalomethane, Total 0.73

Trihalomethane, Unknown 0.73

Mercury, Total 0.9016

Boron 0.3042

Fluoride 0.6135

Iron 0.8199

Oil & Grease 0.8608

Chlorodibromomethane 0.0073

Magnesium 0.1414

Nitrogen, Total 0.5741

TKN 0.5741

Hydrogen Sulfide 0.5741

TSS 0.8955

Turbidity 0.8955

BOD 0.8912

Calcium 0.0854

Chlorides 0.5741

Nitrates 0.5741

Nitrites 0.5741

Phosphates 0.3252

Settleable Solids 0.8955

SS 0.8955

CBOD5 0.8912

Sulfate 0.8461

Total Organic Carbon 0.7028

TDS 0.08

Bromoform 0.73

Haloacetic Acids 0.73

DWT – Drinking Water Treatment. 
Drinking Water Industry Report Appendix D

APPENDIX D 

TOXIC WEIGHTING FACTORS (TWFS) 

(Source: U.S. EPA. 2006. Toxic Weighting Factor Development in Support of CWA 304(m) 

Planning Process. Washington, DC. (June). EPA-HQ-OW-2004-0032-1634) 
Drinking Water Industry Report Appendix D

D-1

Table D-1. Toxic Weighting Factors

DWT Parameter Name

TWF (toxic weighted pounds per pound of 

pollutant)

Aluminum, Dissolved 0.064691216

Aluminum, Total 0.064691216

Aluminum, Unknown 0.064691216

Ammonia, Total 0.00111

Ammonia, Unionized 0.00111

Ammonia, Unknown 0.00111

Arsenic 4.041333333

Barium, Unknown 0.001990757

Benzene 0.031678038

Boron, Total 0.17721519

Cadmium, Total 23.1168

Calcium, Unknown 0.000028

Chlorides 2.43478E-05

Chlorine, Free 0.509162182

Chlorine, Total Residual 0.509162182

Chlorine, Unknown 0.509162182

Chlorodibromomethane 0.044483378

Chloroform 0.002078389

Chromium 0.075696709

Copper, Dissolved 0.634822222

Copper, Total 0.634822222

Copper, Unknown 0.634822222

Dichloroboromomethane 0.032918058

Fluoride, Total 0.035

Fluoride, Unknown 0.035

Hydrogen Sulfide 2.801446667

Iron, Dissolved 0.0056

Iron, Total 0.0056

Iron, Unknown 0.0056

Lead, Total 2.24

Lead, Unknown 2.24

Magnesium 0.000865533

Manganese, Dissolved 0.07043299

Manganese, Total 0.07043299

Manganese, Unknown 0.07043299

Mercury, Total 117.1180233

Mercury, Unknown 117.1180233

Nickel, Unknown 0.108914308

Nitrogen, Total

Phosphate, Total
Drinking Water Industry Report Appendix D

D-2

Table D-1. Toxic Weighting Factors

DWT Parameter Name

TWF (toxic weighted pounds per pound of 

pollutant)

Sulfate 0.0000056

Zinc, Total 0.046886

Nitrates 0.000746667

Nitrites 0.0032

BOD

Oil and Grease

Phosphorus, Total

Radium, Combined

Salinity

Selenium 1.121344

Settleable Solids

TDS

Total Organic Carbon

Trihalomethane, Total

TSS

Zinc, Unknown 0.046886

Aluminum 0.064691216

Ammonia 0.00111

Barium 0.001990757

Cadmium 23.1168

Calcium 0.000028

Copper 0.634822222

Fluoride 0.035

Iron 0.0056

Lead 2.24

Manganese 0.07043299

Mercury 117.1180233

Nickel 0.108914308

Zinc 0.046886

DWT – Drinking Water Treatment. 

Blanks indicate that EPA has not derived TWFs for these chemicals. EPA does not assign toxicity values to

conventional pollutants or bulk parameters; therefore, these chemicals do not have TWFs.
Drinking Water Industry Report Appendix E

APPENDIX E 

NATIONAL ESTIMATES: WATER TREATMENT PLANT COUNTS FOR POLLUTANT LOADINGS 

ESTIMATES
Drinking Water Industry Report Appendix E

E-1

Table E-1. WTP Counts for Pollutant Loadings Excluding Chlorination Pollutants

Treatment Plant 

Type

Solid/Water 

Separation of 

Residuals

Population Served 

(Corresponds to 

Discharge Flow Rate)

National Estimates

(Number of WTPs)

Direct Indirect Both

Lime Softening

Yes

10,000 to 50,000 46 41 23

50,000 to 100,000 55 8 7

100,000 to 500,000 33 19 4

More than 500,000 6 2 0

No

10,000 to 50,000 31 42 0

50,000 to 100,000 2 10 0

100,000 to 500,000 8 2 6

More than 500,000 2 0 0

Coagulation & 

Filtration

Yes

10,000 to 50,000 257 181 40

50,000 to 100,000 63 34 28

100,000 to 500,000 48 46 14

More than 500,000 4 4 4

No

10,000 to 50,000 36 203 0

50,000 to 100,000 4 22 4

100,000 to 500,000 8 4 0

More than 500,000 0 0 0

Filtration only

Yes

10,000 to 50,000 22 31 8

50,000 to 100,000 0 0 0

100,000 to 500,000 2 0 0

More than 500,000 0 2 0

No

10,000 to 50,000 0 28 0

50,000 to 100,000 0 2 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

Desalting 

Membrane

Yes

10,000 to 50,000 2 8 8

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 4 4 8

50,000 to 100,000 0 2 0

100,000 to 500,000 0 2 2

More than 500,000 0 0 0

Ion Exchange & 

Adsorption

Yes

10,000 to 50,000 19 0 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 6 0

More than 500,000 0 0 0

No

10,000 to 50,000 0 65 0

50,000 to 100,000 0 2 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0
Drinking Water Industry Report Appendix E

E-2

Table E-1. WTP Counts for Pollutant Loadings Excluding Chlorination Pollutants

Treatment Plant 

Type

Solid/Water 

Separation of 

Residuals

Population Served 

(Corresponds to 

Discharge Flow Rate)

National Estimates

(Number of WTPs)

Direct Indirect Both

None

Yes

10,000 to 50,000 0 19 0

50,000 to 100,000 0 0 0

100,000 to 500,000 2 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 19 0 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0
Drinking Water Industry Report Appendix E

E-3

Table E-2. WTP Counts for Pollutant Loadings Chlorination Pollutants

Treatment 

Plant Type Chlorination

Dechlorination of 

Residuals

(in 2f and/or 2h)

Population Served 

(Corresponds to 

Discharge Flow Rate)

National Estimates

(Number of WTPs)

Direct Indirect Both

Lime 

Softening

Yes

Yes

10,000 to 50,000 12 0 8

50,000 to 100,000 8 0 5

100,000 to 500,000 2 2 2

More than 500,000 2 0 0

No

10,000 to 50,000 66 83 15

50,000 to 100,000 42 17 2

100,000 to 500,000 37 15 8

More than 500,000 5 2 0

No a NA NA 16

Coagulation 

& Filtration

Yes

Yes

10,000 to 50,000 39 2 8

50,000 to 100,000 14 0 12

100,000 to 500,000 25 0 4

More than 500,000 4 0 2

No

10,000 to 50,000 221 356 28

50,000 to 100,000 48 49 16

100,000 to 500,000 27 48 6

More than 500,000 0 2 0

No a NA NA 94

Filtration only

Yes

Yes

10,000 to 50,000 8 10 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 15 47 8

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 2 0

No a NA NA 7

Desalting 

Membrane

Yes

Yes

10,000 to 50,000 0 0 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 0 8 6

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No a NA NA 27
Drinking Water Industry Report Appendix E

E-4

Table E-2. WTP Counts for Pollutant Loadings Chlorination Pollutants

Treatment 

Plant Type Chlorination

Dechlorination of 

Residuals

(in 2f and/or 2h)

Population Served 

(Corresponds to 

Discharge Flow Rate)

National Estimates

(Number of WTPs)

Direct Indirect Both

Ion Exchange 

& Adsorption

Yes

Yes

10,000 to 50,000 19 0 0

500,00 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 0 57 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No a NA NA 16

None

Yes

Yes

10,000 to 50,000 0 0 0

50,000 to 100,000 0 0 0

100,000 to 500,000 0 0 0

More than 500,000 0 0 0

No

10,000 to 50,000 19 19 0

50,000 to 100,000 0 0 0

100,000 to 500,000 2 0 0

More than 500,000 0 0 0

No a NA NA 0

a – For plants that do not add chlorine, EP A assumes that pollutant loadings of chemicals from chlorination, such as 

disinfection by-products, are zero.