MEMBRANE CONCENTRATE DISPOSAL: 

PRACTICES AND REGULATION 

FINAL REPORT 

By: 

Michael C. Mickley 

Mickley & Associates 

Boulder, CO 

Agreement No. 98-FC-81-0054 

Desalination and Water Purification Research and Development 

Program Report No. 69 

 

September 2001 

U.S. DEPARTMENT OF THE INTERIOR 

Bureau of Reclamation 

Technical Service Center 

Water Treatment Engineering and Research Group
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and 

maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including 

suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suit 1204, Arlington VA 22202-4302, 

and to the Office of Management and Budget, Paperwork Reduction Report (0704-0188), Washington DC 20503.

1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE

September 2001 

3. REPORT TYPE AND DATES COVERED

 Final 

4. TITLE AND SUBTITLE

Membrane Concentrate Disposal: Practices and Regulation 

5. FUNDING NUMBERS

Agreement No. 98-FC-81-0054 

6. AUTHOR(S)

Michael C. Mickley, P.E., Ph.D. 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Mickley & Associates 

752 Gapter Road 

Boulder, CO 80303

8. PERFORMING ORGANIZATION 

 

REPORT NUMBER

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Bureau of Reclamation 

Denver Federal Center 

PO Box 25007 

Denver CO 80225-0007

10. SPONSORING/MONITORING 

 

AGENCY REPORT NUMBER

DWPR Program Report No. 69 

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Available from the National Technical Information Service, Operations Division, 

5285 Port Royal Road, Springfield, Virginia 22161

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The project objective was to provide the membrane utility industry with a valuable and useful reference source focusing on 

characterizing and documenting membrane concentrate and backwash disposal practices and regulations. The project objective was 

accomplished though the following tasks: 

Survey Task: A detailed survey of 149 membrane plants provided a characterization of the membrane utility industry, in general, 

and the concentrate and backwash disposal practices, in particular. 

Regulatory task: Federal regulations were documented to provide the framework for a subsequent state-by-state review of disposal 

regulations. 

Cost model task: Design and cost issues associated with the various concentrate disposal options were discussed and for four 

disposal options (deep well injection, spray irrigation, evaporation pond, and zero liquid discharge), preliminary level cost models 

were developed. 

Database development task: A stand-alone executable database was developed to permit viewing, manipulation, and printing of the 

survey information. 

CD deliverable task: The stand-alone database, the project final report, and the preliminary cost models were made available in an 

easy to use, menu-driven CD format.

14. SUBJECT TERMS-- 

Membranes, drinking water, concentrate, backwash, disposal, cost, regulations, survey 

15. NUMBER OF PAGES

 266 

16. PRICE CODE

17. SECURITY CLASSIFICATION 

 OF REPORT

 UL 

18. SECURITY CLASSIFICATION 

 

OF THIS PAGE

 UL 

19. SECURITY CLASSIFICATION 

 

OF ABSTRACT

 UL 

20. LIMITATION OF ABSTRACT

 UL 

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. 239-18 

298-102
MEMBRANE CONCENTRATE DISPOSAL: 

PRACTICES AND REGULATION 

FINAL REPORT 

By: 

Michael C. Mickley 

Mickley & Associates 

Boulder, CO 

Agreement No. 98-FC-81-0054 

Desalination and Water Purification Research and Development 

Program Report No. 69 

 

September 2001 

U.S. DEPARTMENT OF THE INTERIOR 

Bureau of Reclamation 

Technical Service Center 

Water Treatment Engineering and Research Group
 

 i 

ACKNOWLEDGMENTS 

 

The author of this report is indebted to the research and development tasks undertaken by 

the following individuals: 

• Jorge Briceno, Ph.D. (Database survey, state regulations, general support of other 

tasks) 

• Jeffrey Truesdall (Database survey, general support of other tasks) 

• Patrick Fitzgerald (Database development and programming) 

• Gary Fehr (Final database packaging and production of CDs) 

In addition, the author wishes to thank the many individuals from over 150 utilities, many 

membrane and membrane equipment OEMs who provided information about individual 

membrane plants. Dick Smith, editor of Water Desalination Report was especially 

helpful in identifying the status and contacts for several membrane plants. Ed Geishecker 

of Ionics and Paul Johnson of Memcor were especially helpful in identifying plants using 

their membrane technologies. 

The project benefited from conversations with Scott Irvine, Project Manager for The 

Bureau of Reclamation and Kevin Price, manager of the DeSal Program under which this 

project was funded. 
 

 ii 

Bureau of Reclamation 

Mission Statement 

The Mission of the Bureau of Reclamation is to manage, develop, and protect waters and 

related resources in an environmentally and economically sound manner in the interest of 

the American public. 

U.S. Department of Interior Mission Statement 

As the Nation’s principal conservation agency, the Department of the Interior has 

responsibility for most of our nationally owned public lands and natural resources. This 

includes fostering wise use of our land and water resources; protecting our fish, wildlife, 

and biological diversity; preserving the environmental and cultural values of our national 

parks and historical places; and providing for the enjoyment of life through outdoor 

recreation. The Department assesses our energy and mineral resources and works to 

ensure that their development is in the best interests of all our people by encouraging 

stewardship and citizen participation in their care. The Department also has a major 

responsibility for American Indian reservation communities and for people who live in 

island territories under US. Administration. 

Disclaimer 

The information contained in this report regarding commercial products or firms may not 

be used for advertising or promotional purposes and is not to be construed as an 

endorsement of any product or firm by the Bureau of Reclamation. 

The information contained in this report was developed for the Bureau of Reclamation: 

no warranty as to the accuracy, usefulness, or completeness is expressed or implied. 
 iii 

TABLE OF CONTENTS 

 page 

Table of Contents..................................................................... iii 

 

List of Tables........................................................................... vi 

 

List of Figures.......................................................................... vii 

Glossary and Abbreviations.......................................................... ix 

1. Executive Summary................................................................ 1 

2. Conclusions and Recommendations............................................. 3 

2.1 Conclusions.......................................................... 3 

2.2 Recommendations................................................... 6 

3. Background Information........................................................... 9 

3.1 Background........................................................... 9 

3.2 Purpose of the Project Work....................................... 11 

3.3 Research Objectives................................................. 12 

3.4 Report Content....................................................... 13 

4. Research Conducted................................................................ 15 

4.1 Introduction........................................................... 15 

4.2 Survey Task .......................................................... 15 

4.3 Database Program Task.............................................. 19 

4.4 Regulatory Task....................................................... 20 

4.5 Issue-Related Task................................................... 21 

4.6 Cost Modeling Task................................................... 21 

5. Plant Survey Results.................................................................. 33 

5.1 Introduction............................................................. 33 

5.2 Total Number of Membrane Plants in the U.S..................... 33 

5.3 Results of the Project Survey......................................... 35 

5.4 Desalting Plant Results................................................ 43 

5.5 MF and UF Results..................................................... 48 

6. Regulation - Federal Perspective.................................................... 51 

6.1 Introduction.............................................................. 51 

6.2 Overview................................................................. 53 

6.3 Surface Water Discharge............................................... 59 

6.4 Disposal to Sewer....................................................... 69 

6.5 Disposal to Deep Well.................................................. 70 

6.6 Disposal by Other Methods............................................ 72 

6.7 Special Topics: Radionuclides, MF/U Backwash, 

Contaminated Concentrate, Toxic and Hazardous Waste.......... 72 
 iv 

7. Regulation - State Perspective......................................................... 75 

7.1 Background................................................................ 75 

7.2 Survey of WTP Disposal Options...................................... 75 

7.3 Survey of NPDES-Related State Regulations......................... 78 

7.4 Summary of Regulatory Requirements for Selected States......... 83 

8. Surface Water and Sewer Disposal..................................................... 91 

8.1 Background................................................................. 91 

8.2 Design Considerations for Disposal to Surface Water................ 91 

8.3 Cost Considerations for Disposal to Surface Water................... 95 

8.4 Disposal to Sewer........................................................... 97 

9. Deep Well Disposal ..................................................................... 99 

9.1 Background............................................................... 99 

9.2 Design Considerations.................................................... 102 

9.3 Cost Factors................................................................ 106 

9.4 Design Approach for the Deep Well Disposal Cost Model.......... 118 

9.5 Deep Well Disposal Worksheet and Example......................... 119 

9.6 Deep Well Disposal Regression Model................................. 119 

10. Evaporation Pond Disposal............................................................ 121 

10.1 Background................................................................ 121 

10.2 Design considerations................................................... 122 

10.3 Cost Parameters............................................................ 125 

10.4 Design Approach for the Evaporation Pond Cost Model............. 141 

10.5 Evaporation Pond Worksheet and Example............................ 142 

10.6 Evaporation Pond Regression Model................................. 144 

11. Spray Irrigation Disposal............................................................ 145 

11.1 Background............................................................ 145 

11.2 Design Considerations................................................ 146 

11.3 Cost Factors............................................................ 150 

11.4 Design Approach for Spray Irrigation Model..................... 159 

11.5 Spray Irrigation Model Worksheet and Example.................. 164 

11.6 Spray Irrigation Regression Model.................................... 166 

12. Zero Discharge Disposal ............................................................ 167 

12.1 Background............................................................ 167 

12.2 Model for Interaction of Membrane and Thermal Systems...... 175 

12.3 Design Considerations................................................ 177 

12.4 Cost Parameters...................................................... 178 

12.5 Design Approach for the Zero Liquid Discharge Cost Model... 182 

12.6 Zero Liquid Discharge Worksheet and Example.................. 188 

12.7 Zero Liquid Discharge Regression Model........................... 190 

13. Analysis of Cost Models............................................................ 191 
 v 

13.1 Introduction............................................................... 191 

13.2 Sensitivity Analysis...................................................... 191 

13.3 Model Comparison...................................................... 194 

14. Instructions for Using CD............................................................. 197 

14.1 Format of the CD......................................................... 197 

14.2 Installation of the CD.................................................... 199 

References.................................................................................... 203 

APPENDICES.............................................................................. 205 

Appendix 1 - SI Metric Conversion Table................................................ 205 

Appendix 2 - Plant Survey Tabulations................................................... 207 

Appendix 3 – State NPDES-Related Regulations....................................... 235 
 vi 

LIST OF TABLES 

Table 4.1 Arrangement of Data in Database.................................... 16 

Table 4.2 1992 Survey of 140 Plants............................................. 17 

Table 4.3 Data Analysis Categories............................................... 22 

Table 4.4 Worksheet for Evaporation Pond Capital Costs..................... 26 

Table 5.1. Estimated Number of Membrane WTPs and WWTPs in the 50 

States of the U.S.................................................... 34 

Table 5.2 Plants included in the 1999 Survey.................................... 37 

Table 5.3 Distribution of Plants Surveyed....................................... 43 

Table 5.4 Present Survey: Distribution of 102 Desalting Plants by Size..... 43 

Table 5.5 1992 Survey: Distribution of 140 Desalting Plants by Size....... 44 

Table 5.6 Desalting Plant Size by Year of Startup.............................. 45 

Table 5.7 Selected Survey Results – Number of Desalting Plants by Category; 

Built 1993 – 1999................................................... 46 

Table 5.8 Memcor MF Plants in the 50 States of the US Through 1999 

(>0.5 mgd)......................................................... 50 

Table 5.9 MF Plants at WWTP Sites: Plant Size by Year of Startup......... 49 

Table 6.1 Characteristics of Concentrate and Backwash Streams............ 52 

Table 6.2 Delegation Status of States for Federal Programs................... 57 

Table 7.1 Description of Specific Legislative Rules in the Porter-Cologne Water 

Quality Control Act................................................ 79 

Table 7.2. List of Specific Regulations (Title 62 FAC) that Cover the Currently 

Accepted Disposal Options in the State of Florida............... 80 

Table 7.3. Description of Regulations and Corresponding Legislative Sections of 

the Texas Administrative Code Applicable to Membrane Disposal 

Options............................................................... 82 

Table 7.4 Comments on Waste Disposal Options for Selected States......... 84 

Table 9.1 Relationship between Pipe Diameter and Flow Rate......... 106 

Table 9.2 Logging, Surveying, and Testing Events from Florida 3400 ft Well... 107 

Table 9.3 Worksheet for Deep Well Disposal Capital Costs..................... 120 

Table 10.1 Worksheet for Evaporation Pond Disposal Capital Costs............ 143 

Table 11.1 Site Selection Factors and Criteria....................................... 148 

Table 11.2 Worksheet for Spray Irrigation Disposal Capital Costs............... 165 

Table 12.1 Schematic of Membrane/Thermal System and Mathematical Relations 

to Calculate System Flows.......................................... 176 

Table 12.2 Flows for Membrane and Membrane/Thermal Systems........... 175 

Table 12.3 Worksheet for Zero Liquid Discharge Disposal Cost............... 189 
 vii 

LIST OF FIGURES 

Figure 4.1 Regression Estimates as Function of Input Values............... 29 

Figure 4.2 Regression Residuals as Function of Estimated Value........... 31 

Figure 5.1 Cumulative Number of Utility Membrane Plants by Two-Year 

Period............................................................... 36 

Figure 6.1 NPDES Implementation Procedure for Whole Effluent Toxics Control 

Program.............................................................. 64 

Figure 6.2 Diagram of a Stream Mixing Zone.................................... 67 

Figure 9.1 Schematic Diagram of a Three-Transition Injection Well with Packer 104 

Figure 9.2 Logging, Testing, and Survey Costs as Function of Tubing Diameter 108 

Figure 9.3 Drilling and Reaming Cost as Function of Tubing Diameter.... 110 

Figure 9.4 Installed Tubing Cost as Function of Tubing Diameter............ 111 

Figure 9.5 Installed Packer Cost as Function of Tubing Diameter............. 112 

Figure 9.6 Installed Casing Cost as Function of Tubing Diameter............. 113 

Figure 9.7 Installed Grouting Cost as Function of Tubing Diameter............ 114 

Figure 9.8 Monitoring Well Cost as Function of Well Depth...................... 116 

Figure 9.9 Mobilization & Demobilization Cost as a Function of Well Depth... 117 

Figure 10.1 Rate of Precipitation in Evaporation Pond (after USDI, Office of 

Saline Water, 1970)................................................... 126 

Figure 10.2 Area Correction Factor as Function of Evaporative Area (1 to 10 

Acres)..................................................................... 128 

Figure 10.3 Area Correction Factor as Function of Evaporative Area (10 to 100 

Acres).................................................................. 129 

Figure 10.4 Dike Cost as Function of Evaporative Area (1 to 10 Acres)...... 130 

Figure 10.5 Dike Cost as Function of Evaporative Area (10 to 100 Acres)... 131 

Figure 10.6 Schematic Diagram of a Baffled Evaporation Pond............... 133 

Figure 10.7 Liner Cost as Function of Evaporative Area (1 to 10 Acres).... 134 

Figure 10.8 Liner Cost as Function of Evaporative Area (10 to 100 Acres)... 135 

Figure 10.9 Fence Cost as Function of Evaporative Area (1 to 10 Acres)... 137 

Figure 10.10 Fence Cost as Function of Evaporative Area (10 to 100 Acres)... 138 

Figure 10.11 Road Cost as Function of Evaporative Area (1 to 10 Acres)...... 139 

Figure 10.12 Road Cost as Function of Evaporative Area (10 to 100 Acres)... 140 

Figure 11.1 Land Requirements as a Function of Flow and Loading (Flows up 

to 1.2 mgd)............................................................... 152 

Figure 11.2 Land Requirements as a Function of Flow and Loading (Flows up 

to 3.5 mgd)............................................................... 153 

Figure 11.3 Schematic Diagram of a Typical Spray Irrigation Distribution 

System.................................................................. 154 

Figure 11.4 Distribution System Piping Cost as Function of Area (up to 50 acres) 156 

Figure 11.5 Distribution System Piping Cost as Function of Area (up to 200 

acres)................................................................... 157 

Figure 11.6 Sprinkler, Valves, and Control System Cost as Function of Area 158 

Figure 11.7 Cost of Low-Head Pumps as Function of Flow Rate............ 160 

Figure 11.8 Storage Tank Cost as Function of Flow Rate (up to 0.5 mgd)...... 161 

Figure 11.9 Storage Tank Cost as Function of Flow Rate (up to 5 mgd)...... 162 
 viii 

Figure 12.1 Schematic Diagram of Brine Concentrator Process Flow – 

Pumps Not Shown (after RCC, 2001)........................ 171 

Figure 12.2 Schematic Diagram of Forced-Circulation, Vapor Compression 

Crystallizer Process Flow (after RCC, 2001).................. 173 

Figure 12.3 Schematic Diagram of a Typical Spray Dryer (after RCC, 2001)... 173 

Figure 12.4 Capital Cost of Skid-Mounted Brine Concentrator as Function of 

Flow Rate (0 to 200 gpm).......................................... 179 

Figure 12.5 Capital Cost of Non-skidded Brine Concentrator as Function of 

Flow Rate (0 to 1.2 mgd)............................................. 180 

Figure 12.6 Capital Cost of Non-skidded Brine Concentrator as a Function 

of Flow Rate (1 to 2.5 mgd)....................................... 181 

Figure 12.7 Capital Cost of Crystallizer as a Function of Flow Rate (5 to 

50 gpm)............................................................... 183 

Figure 12.8 Capital Cost of Spray Dryer as a Function of Flow Rate (1 to 

12 gpm)............................................................... 184 

Figure 12.9 Energy Requirements for the Brine Concentrator as Function of 

Flow Rate (up to 1 mgd).......................................... 185 

Figure 12.10 Energy Requirements for the Brine Concentrator as a Function 

of Flow Rate (1 to 3 mgd).......................................... 186 

Figure 12.11 Energy Requirements for the Crystallizer as a Function of Flow 

Rate..................................................................... 187 

Figure 14.1 Menu for Accessing CD files........................................ 198
 ix 

GLOSSARY AND ABBREVIATIONS 

A irrigation area, acre 

ADA American Desalting Association 

ALR annual hydraulic loading rate (ft./yr.) 

AWWA American Water Works Association 

AWWARF American Water Works Association Research Foundation 

BOD biological oxygen demand 

BRO brackish reverse osmosis 

BTU British thermal unit 

C concentration of constituent (mg/L) 

Ca calcium 

CAA Clean Air Act 

CD compact disk 

CERCLA Comprehensive Environmental Response, Compensation and Liability Act 

CFR Code of Federal Regulation 

CRWQCB California Regional Water Quality Control Board 

CWA Clean Water Act 

d day 

DO dissolved oxygen 

DOE Department of Energy 

DOT Department of Transportation 

ED/EDR electrodialysis/electrodialysis reversal 

EPA Environmental Protection Agency 

EPCRA Emergency and Community Right-To-Know Act 

EPRI-CEC Electric Power Research Institute – Community Environmental Center 

ESA Endangered Species Act 

ET evapotranspiration 

F fetch (straight line distance the wind can blow without obstruction) 

FAC Florida Administrative Code 

FDEP Florida Department of Environmental Protection 

FFDCA Federal Food, Drug, and Cosmetic Act 

FIFRA Federal Insecticide, Fungicide and Rodenticide Act 

Fl Florida 

FOIA Freedom of Information Act 

FQPA Food Quality Protection Act 

ft feet 

ft2

 square feet 

ft3 cubic feet 

gal gallon 

gpd gallons per day 

gpm gallons per minute 

GPO Government Printing Office 

HDPE high density polyethylene 

HLR hydraulic loading rate 

hr hour 
 x 

Hw wave height (ft) 

IMS integrated membrane system 

in. inch 

Ivi ith independent variable 

KW kilowatt 

LAS land application system 

lb pound 

Lc loading rate of constituent (lb/acre-yr) 

LOEL lowest observed effects level 

MCL maximum contaminant level 

MF microfiltration 

Mg magnesium 

mg/L milligram per liter 

mgd million gallons per day 

mils thousandths of an inch 

mph miles per hour 

Na sodium 

NEPA National Environmental Policy Act of 1969 

NF nanofiltration 

NOI notification of intent 

NPDES National Pollutant Discharge Elimination System 

NWRI National Water Research Institute 

OEM original equipment manufacturer 

ONRW Outstanding National Resource Waters 

OPA Oil Pollution Act of 1990 

OSHA Occupational Safety and Health Administration 

PER percolation 

POTW publicly owned treatment work 

PPA Pollution Prevention Act 

ppm parts per million 

PPT precipitation 

Q concentrate flow (gpd) 

RCRA Resource Conservation and Recovery Act 

RO reverse osmosis 

SAR sodium adsorption ratio 

SARA Superfund Amendments and Reauthorization Act 

SDWA Safe Drinking Water Act 

SRO seawater reverse osmosis 

TCC total capital cost 

TDS total dissolved solids 

THMFP trihalomethane formation precursor 

TMDL total maximum daily load 

TPDES Texas Pollutant Discharge Elimination System 

TRC total residual chlorine 

TRE toxicity reduction evaluation 

TSCA Toxic Substance Control Act 
 xi 

TSS Total suspended solids 

UF ultrafiltration 

UIC Underground Injection Control 

USDW underground source of drinking water 

USEPA United States Environmental Protection Agency 

W wind velocity (mph) 

WET whole effluent toxicity 

WETC whole effluent toxics control 

WQ water quality 

WQS water quality standards 

WTP water treatment plant 

WWTP wastewater treatment plant 

yd3 cubic yard 

yr year 

 
 1 

CHAPTER 1. 

EXECUTIVE SUMMARY 

The major objective of the project was to provide the membrane utility industry with a 

valuable and useful reference source focusing on characterizing and documenting 

concentrate (from membrane desalting processes) and backwash (from low pressure 

membrane processes) disposal practices and regulations. 

The project objective was accomplished through the following tasks: 

• Survey task: A detailed survey of 149 membrane plants was made that included 

84 percent of the utility desalting (reverse osmosis, nanofiltration, and 

electrodialysis) plants built in the US from 1993 through 1999 above a size of 

50,000 gpd. It also included 44 percent of the utility low-pressure membrane 

(microfiltration and ultrafiltration) plants built in the US of size greater than 

50,000 gpd. The survey provided a detailed characterization of the membrane 

utility industry, in general, and the concentrate and backwash disposal practices, 

in particular. 

• Regulatory task: Federal regulations were documented to provide the 

framework for a subsequent state-by-state review of disposal regulations. 

• Cost model task: Design and cost issues associated with the various concentrate 

disposal options were discussed and for four disposal options (deep well injection, 

spray irrigation, evaporation pond, and zero liquid discharge), preliminary level 

cost models were developed. 

• Database development task: A stand-alone executable database was developed 

to permit viewing, manipulation, and printing of the survey information. 

• CD deliverable task: The stand-alone database, the project final report, and the 

preliminary cost models were made available in an easy to use menu-driven CD 

format. 

In addition to the detailed survey of 149 plants, the research identified an estimated 95+ 

percent of all membrane utility plants ever built in the US above a size of 25,000 gpd. 

This identification allowed additional statistics to be developed on the numbers of 

different types of plants with time. A total of 372 plants through the year 2000 (303 

through the year 1999) were identified. Of these about 25 plants operate at wastewater 

plants in water reuse situations. The other plants produce drinking water 

The identification of utility plants and the survey provide statistics to characterize the 

water and wastewater utility’s use of membrane processes by startup date, size, location, 

type of process, and several other parameters. The dramatic growth of the use of 

membranes in the utility industry is documented along with the equally dramatic increase 

I 

n size of the membrane plants and the increase number of states now having membrane 

plants. Statistics are also provided about concentrate and backwash disposal practices 
 2 

and results of the survey are compared with the results of a 1992 survey (Mickley et al, 

1993). 

A review of the Federal and state-by-state regulations affecting concentrate and 

backwash disposal is presented. Major ion toxicity (Mickley, 2000) that has occurred in 

several groundwater membrane systems in Florida appears not to have occurred 

elsewhere. This seems due to the fact that whole effluent toxicity tests are not routinely 

part of surface discharge (NPDES) permits in states other than Florida and where they are 

used, the mysid shrimp used in the Florida WET tests is not necessarily used. Backwash 

from low-pressure membrane systems frequently (depending on the application) has 

elevated levels of microorganisms. Presently there are no water quality criteria for 

microorganisms that might hinder discharge to receiving waters. Such regulation is only 

a matter of time, however. 

The design parameters and costs factors associated with several concentrate (and 

backwash) disposal methods are discussed in detail. The disposal methods (listed in 

order of decreasing frequency of use) include: 

• Surface water discharge 

• Discharge to sewer 

• Deep well injection 

• Evaporation ponds 

• Spray irrigation 

• Zero liquid discharge 

 

Preliminary level capital cost models are presented for the final four disposal methods in 

both worksheet form and closed form equation. In the case of discharge to surface water 

the large number of site-specific variables makes it difficult to formulate a meaningful 

general model. In the case of disposal to the sewer, the only cost other than pipeline 

conveyance to the disposal site is a negotiated fee payable to the wastewater plant. These 

fees can range from zero to very high. 

The survey results are stored in a ‘run-time’ version of Microsoft Access. This is a standalone version that does not require the user to have Access to run. This database is made 

available in CD form along with a pdf file containing the entire project report, the capital 

cost worksheets, and the closed form equations that can also be used to calculate 

preliminary level capital costs for the disposal options. Upon installation, a convenient 

menu provides several options for interfacing with the database and for accessing the 

other items. 

The project CD provides the user with a broad and valuable resource that characterizes 

the membrane utility industry, its concentrate and backwash disposal practices, the 

regulations that govern disposal, and the costs associated with disposal options. 
 3 

CHAPTER 2. 

CONCLUSIONS AND RECOMMENDATIONS 

2.1 CONCLUSIONS 

2.1.1 About the Membrane Plant Survey (General Aspects): 

• Approximately 85% of the utility desalting plants built in the US between 1992 

and 2000 of size greater than 50,000 gpd were included in the survey. About 

48% of the low-pressure utility membrane plants built in this same time in the US 

were surveyed. 

• Desalting plants (RO, NF, ED/EDR) are used in WTPs to provide new sources of 

potable water via the treatment of lower quality water resources. 

• Low-pressure membrane plants (MF and UF) are used in WTPs to help meet 

SDWA Amendment requirements for higher quality, and in WWTPs to provide a 

polishing treatment step in water reuse situations. 

• Several aspects of the use of membrane technology in the drinking water and 

wastewater utilities have changed significantly since the last (1992) survey. 

• With regard to the number of plants: 

o The number of operating utility desalting plants in the US of size 25,000 

gpd and higher has increased from approximately 133 in 1992 to 203 in 

1999. 

o The number of utility low-pressure MF and UF plants in the US of size 

25,000 and higher has increased from 1 in 1992 (operating at a state park) 

to 104 in 1999. 

o Based on the yearly increases in the different plants of this size and larger, 

the number of MF and UF plants should surpass the number of desalting 

plants by the end of 2001. 

• With regard to the location of plants: 

o A higher percentage of plants are being built in states other than Florida. 

About 26% of the desalting plants built between 1992 and 2000 are in 

Florida with the remainder scattered through 19 states, with 17% in 

California and 9% in Texas. This is in contrast to the results of the 1992 

survey, when about 61% of the desalting plants were in the state of Florida 

and the rest of the plants were scattered about 13 states, with 9 % in 

California and 9% in Texas. 

o The distribution of low-pressure MF plants is considerably different from 

that of desalting plants. For Memcor MF plants the leading states are 

California (with 32% of the plants as of 1999) and Virginia (with 17% of 

the plants). The rest of the Memcor plants are scattered in 14 other states. 

[Until 1999 nearly all of the MF plants were Memcor systems.] 

• With regard to size: 

o Although dependent on the particular plants surveyed, an increase in the 

size of desalting plants is striking. In the 1999 survey, 18% of the plants 

were of size greater than 6 mgd (compared to 3% for the 1992 survey). 
 4 

Also only 9% of the plants in the 1999 survey were of size less than 0.1 

mgd, as opposed to 33% in the 1992 survey.

o From 1993 through 1997, 27% of the desalting plants (10 of 36) built were 

of size 3 mgd or greater. In 1998 and 1999 the percentage doubled to 56% 

(15 of 27). 

o Many of the larger desalting plants are being built in Florida. About 50% 

of the desalting plants built in Florida since 1992 are of size greater than 3 

mgd, whereas about 23% of desalting plants built elsewhere in this same 

time frame were greater than 3 mgd.

o The size and number of MF plants has increased dramatically since 1995. 

Prior to 1996, 1 of 19 Memcor plants built were of size 1 mgd or larger. 

Since 1996 and through 1999, 25 of 66 Memcor plants were of size greater 

than 1 mgd with 10 being greater than 3 mgd. 

• With regard to the types of plants: 

o The relative number of plants of different types built since 1992 is roughly 

the same as plants operating in 1992. Brackish water RO plants account 

for about 72% of all plants, with NF plants (11%), ED/EDR (15%), and 

seawater RO (2%) making up the rest. 

o In spite of the large numbers of plants in Florida, most ED/EDR plants are 

not in Florida (as in 1992). 

• With regard to membrane systems providers: 

o Until 1999 nearly all of the MF plants were Memcor systems. Since then 

Pall has made a significant entry into the marketplace. 

o Since 1999 three strong companies have emerged to provide UF systems 

(Aquasource, Koch, and Zenon) 

2.1.2 About the Survey (Concentrate Disposal Aspects): 

• The relative use of different means of concentrate disposal has changed somewhat 

since the previous survey (comparison of plants built between 1992 and 2000 

• to plants operating in 1992): 

o A similar percentage dispose to surface water: 48% to 45% 

o A significantly higher percentage dispose concentrate to sewer: 42% to 

23% 

o A lower percentage dispose concentrate to deep wells: 9% to 12 % 

o A lower percentage dispose concentrate by evaporation pond and spray 

irrigation: for evaporation pond the percentages are 2% as opposed to 6%, 

and for spray irrigation the percentages are 2% compared to 12%. 

• The relative use of different concentrate disposal options shows similar trends, 

with plant size as in the previous survey: 

o Disposal to surface water is an option used at approximately the same 

relative frequency regardless of plant size 

o Disposal to sewer is used somewhat more frequently for smaller sized 

plants (< 1 mgd product); however, the percentage of plants disposing to 

sewer increased in every size category (<0.3, 0.3-<1, 1-<3, >3 mgd) 

relative to 1992 results. 
 5 

o Disposal to deep well injection is primarily used for larger plants (>1 

mgd) 

o Disposal via evaporation pond and spray irrigation are used primarily with 

smaller plants (< 1 mgd). 

• As in the previous survey, deep well disposal of concentrate has been practiced 

only in the State of Florida 

2.1.3 About Backwash Disposal Options: 

• Disposal of backwash from MF and UF plants does not follow any trends with 

plant size (likely because backwash is of considerably smaller volume than 

concentrate - due to much greater recoveries). 

• Disposal to sewer (48%) and surface water (36%) are the most widely used 

disposal options. 

• Unlike concentrate disposal, deep well injection has not been used for backwash 

disposal. This is due to the small number of low pressure membrane systems in 

Florida, the only state presently using deep well disposal for concentrate, as well 

as the small volume of backwash relative to concentrate. 

2.1.4 About the Regulations: 

• Many more states have membrane system sites and must regulate disposal of 

membrane concentrate and backwash (25 as of 1999 versus 14 as of 1992) 

• The most widely regulated disposal options are disposal to surface water and 

sewer. They both involve NPDES permits either for the WTP discharging the 

concentrate or backwash or the WWTP plant receiving the concentrate or 

backwash. 

• There have been no major changes in Federal regulations over the past 8 years; 

TMDLs, which may come into play in NPDES permits, are more of a burden for 

states than for individual surface water dischargers. 

• A major surface water disposal issue in the State of Florida since 1992 has been 

the occurrence of major ion toxicity (Mickley, 2000) in several concentrates from 

desalting plants using groundwater sources. 

• Very few states require whole effluent tests on membrane concentrate discharged 

to surface waters. This explains in part why major ion toxicity problems 

associated with brackish RO concentrate appear to have occurred only in Florida. 

• Some regulatory distinction has been given to drinking water membrane 

concentrate in the State of Florida. Although it is still regulated as an industrial 

waste, it is called ‘potable water byproduct’ where produced by plants of size 

50,000 gpd or less. Pending legislation may extend this to plants of larger size. 

• Deep well disposal of industrial wastes (including membrane concentrate and 

backwash) is not permitted in many states. 

2.1.5 About the Disposal Methods and Cost Models: 

• The costs of different disposal methods for concentrate disposal are very site 

dependent; consequently the cost models developed are to be considered for 

preliminary level estimates only. 
 6 

• The major factors influencing deep injection well costs are the depth of the well 

and the diameter of the well tubing and casing strings. The diameter has 

surprisingly low influence on the cost; drilling, reaming, cementing, and testing 

costs are much more significant than material costs. The minimal cost of a well is 

high enough that these wells are typically used only with large concentrate flow 

rates. 

• Spray irrigation of concentrate usually requires blending to decrease the salinity 

to an acceptable range. The method is also land intensive, although the irrigation 

need may exist and the land need not be purchased. This disposal method is 

limited by the climate and the soil uptake rates. The major cost elements include 

the distribution system material cost, the cost of installation, and the storage tank 

cost. This method is usually used only for small concentrate flow rates. 

• Evaporation ponds are also land intensive, and land may need to be purchased for 

use. In general, net evaporation rates are lower than soil uptake rates; thus 

evaporation ponds require more land than spray irrigation for a given volume 

flow. This disposal method is limited by climate and evaporation rate. The major 

capital cost element is usually the liner material. 

• Zero liquid discharge is not typically an economical disposal option. It has not 

yet been used for disposal of concentrate from a drinking water membrane plant. 

The major capital cost elements are the installed equipment costs of the brine 

concentrator and crystallizer. However, the high annual energy cost is usually 

equal to a sizable portion of the capital cost and thus on an annualized cost basis 

(assuming an equipment life of 20 to 30 years) the energy cost is by far the major 

element. 

2.1.6 About the Differing Nature of Low-Pressure Membrane Systems: 

• Low-pressure membrane systems offered by different system suppliers differ 

significantly from each other. For instance, the systems may have different 

membrane configurations (spiral wound, hollow fiber, tubular). The hollow fiber 

systems can differ in whether the high-pressure side is inside or outside the fiber, 

and the means of backwashing the membranes (with air, with water, other 

variables) can also differ considerably. There is also a lack of standards for 

system components. Much of this is due to the relative youth of the application 

and there being a variety of successful system designs. 

• This is in sharp contrast to equipment used in desalting membrane systems where 

components made by different manufacturers must meet various industry 

standards. Most of the components are thus, to a high degree, interchangeable. 

For a given system, several OEMs may be involved in providing the system 

components. 

2.2 RECOMMENDATIONS 

2.2.1 About Plant Surveys... 

• Surveys such as this one should be conducted periodically as a means to: 

o Monitor and document the trends and changes within the utility membrane 

industry, particularly concentrate disposal. 
 7 

o Identify industry challenges and needs. 

o Provide information and understanding to existing and future utility 

membrane plants that can result in the improved use of the technology and 

associated cost savings. 

o Provide information and understanding to regulators, legislators, decision 

makers, and the public to facilitate and support the growing use of 

membrane technology in meeting drinking water and water reuse 

challenges. 

• Future surveys of the type presented here might be conducted in the following 

manner: 

o Minimum size cutoff for desalting plants be set at 50,000 gpd to avoid 

small systems serving truck stops, mobile home parks, etc. 

o Minimum size cutoff for low pressure membrane plants be set at 1 mgd to 

make the survey manageable given the rapidly growing numbers and sizes 

of these plants. 

o Include plant operation date so that information trends can be followed 

with time. 

o For low pressure membrane plants obtain plant lists from the major system 

suppliers as a means of gathering general statistics on numbers, locations, 

and sizes of plants. [This cannot be done for desalting plants as the 

systems are supplied in parts from many different suppliers.] 

o Attempt to get more than the minimum sampling of plants typical of 

mailed surveys. The reasons for doing this include: 1) the population of 

plants contains several subpopulations, making it difficult to get a 

meaningful representative sampling; and 2) the relatively small total 

number of these plants still makes it possible to take the more accurate 

approach to obtain survey information. 

2.2.2 About Regulations: 

• To avoid future problems, utilities in other states should be made aware of the 

major ion toxicity issues and the resolution of those issues that are affecting many 

brackish RO plants in Florida (Mickley, 2000). 

• Utilities should be aware of forthcoming regulations that may affect their 

concentrate of backwash disposal. It is anticipated that water quality standards 

will tighten as a result of increased drinking water standards. Although the 

relation is not a direct one, as the water quality requirements for certain 

parameters of potable water increase, further efforts will be made to limit 

contamination of water resources for these same parameters. A case in point is 

that of microorganisms. The SDWA amendments require increased removal 

levels of microorganisms (among other things) from drinking water. The 

dramatic increase in use of low-pressure membrane systems in WTPs is, in part, 

in response to this requirement. Microorganism removal by MF and UF 

processes results in concentration of the microorganisms in the backwash from 

these processes. There are, however, no water quality standards prohibiting or 

limiting discharge of such backwash to surface waters. Such standards, however, 
 8 

are inevitable. Other water quality standards may follow future changes in 

drinking water standards.

2.2.3 About the Preliminary Level Disposal Cost Models: 

• Actual disposal costs for new membrane plants should be gathered as the plants 

come into operation. It is difficult to obtain historical costs, and more recent costs 

are the pertinent ones. This information can be used to further test and validate 

the usefulness of the preliminary level disposal cost models presented. 

• Parties interested in the presented preliminary disposal cost models should 

carefully read the supporting text chapters to understand the limitations, 

assumptions, and general basis for these cost models. The chapters together with 

the models are best used to provide an understanding of the issues, design 

parameters, and cost factors involved with each of the disposal options. From this 

understanding site-specific cost models can be more easily developed. Care is 

taken to not to use the models beyond the purpose for which they were intended. 

• As with all models, feedback on their usefulness and general validity should be 

used to refine and improve the models. 

2.2.4 About General Aspects: 

• The work should be made as visible and available as reasonably possible so it can 

benefit the utility community for which it is intended. 
 9 

CHAPTER 3. 

BACKGROUND INFORMATION 

3.1 BACKGROUND 

3.1.1 Membrane Drinking Water Industry: The relatively young membrane drinking 

water industry has grown dramatically, particularly since the late 1980’s. Membrane 

processes are the technology of choice where lower quality water sources need to be 

desalted, and for several application areas where specialized treatment is required by the 

Safe Drinking Water Act Amendments of 1986. 

An earlier work (Mickley et al, 1993) provided a unique opportunity to see the membrane 

drinking water industry from several different perspectives. Interactions and interviews 

took place with several groups involved in matters concerning membrane drinking water 

plants. This included utilities, regulators, legislators, engineering design firms, original 

equipment manufacturers (OEMs), decision makers (city councils, etc.), and the public. 

From such a broad or all-encompassing viewpoint, it becomes evident that matters such 

as providing the best technology to meet a treatment need are not simply ones of 

technology and economics. All of the above-mentioned groups play some role in the 

consideration of and feasibility of various treatment options. 

The membrane drinking water industry and the complexity of technical, economic, 

environmental, political, and social interplay involved with bringing a new membrane 

plant into operation have grown dramatically. In spite of this growth and the reality of 

the cost-effective, environmentally safe, technically sound capabilities of the technology, 

many of the above groups (regulators, legislators, decision makers, public) carry 

misconceptions and mistaken perceptions about the technology. 

This situation has affected how the tremendous potential of membrane technology to 

provide drinking water has unfolded. It acts as a block or limiting constriction to the 

realization of this potential. 

The previous work (Mickley et al, 1993) provided definition of and recommendations for 

addressing disposal issues and challenges. It also provided useful design, cost, 

regulatory, and statistical information for utilities to use in their planning, design, and 

operation. 

3.1.2 Changes Since 1992: Since the previous report (Mickley et al, 1993), concentrate 

disposal has become an accepted and routine session topic at the AWWA Membrane 

Conference, the American Desalting Association (ADA) conference, and international 

conferences. The role and importance of concentrate disposal in membrane plant 

considerations have been recognized. However, the subject is not static and in the time 

since the original information-gathering effort, the industry has grown and changed, 

bringing new disposal challenges to be addressed. These changes include: 
 10 

• The impact of the Safe Drinking Water Act amendments 

o the commercialization (in the US) of ultrafiltration and microfiltration 

plants 

o the consideration of integrated membrane systems (employing two or 

more different types of membrane processes) 

o the resultant increased focus on surface water applications 

• increased awareness, relevance, and importance of European efforts 

o as leaders in surface water membrane applications 

o reflected in increased mutual participation in US and European 

membrane-related conferences 

o reflected in increased joint projects and research studies 

o reflected in the appearance of European and Canadian membrane 

technologies in the US plants. 

• increased number of nanofiltration (NF), reverse osmosis (RO), and 

electrodialysis/electrodialysis reversal (ED/EDR) plants 

• the increased number of states becoming aware of membrane applications and 

beginning to form disposal regulatory policies 

• increased degree of regulation (example: more stringent monitoring requirements) 

• significant research undertaken particularly in areas of surface water discharge of 

concentrate 

o investigation of major ion toxicity (Mickley et al, 2000) 

o development of new mixing zone models for surface water discharge 

(EPRI-CEC, 1994) 

• the increased pro-active involvement by many groups in addressing important 

issues (Reclamation, AWWARF, NWRI, EPRI-CEC, FDEP, etc.) 

The needs highlighted by the above situation include: 

• communication and education (based on gathering and analysis of information). 

• appropriate technical research to provide new information 

The present work focuses on the first of these needs. One project goal is to document the 

latest understanding and practice involved with concentrate disposal, including state-bystate regulation of the various disposal options. 

3.1.2.1 Appearance of MF and UF Plants in the US: In 1992, the time of the last 

extensive membrane drinking water plant survey, there were no utilities using 

ultrafiltration (UF) or microfiltration (MF) technology in the US. Since then there have 

been many MF installations, several UF installations, and a great number of plants in the 

planning stages; all reflecting the promise and success of these processes in meeting Safe 

Drinking Water Act Amendment water quality requirements. It is likely that the number 

of these plants will increase at a dramatic rate - a rate greater than the increase in NF, RO, 

and ED/EDR plants. Whereas concentrate from NF, RO and ED/EDR processes is 

characterized by some degree of concentration of TDS, which limits recovery to 

generally less than 85 to 90%, the concentrate (or the backwash) from UF and MF 
 11 

processes does not concentrate TDS and the recovery is frequently greater than 90%. 

The differing nature of this concentrate/backwash from ‘conventional’ concentrate raises 

new disposal issues. There is also new interest in integrated membrane systems (IMS) 

that employ more than one type of membrane process. These systems result in multiple 

concentrates to be disposed. 

3.2 PURPOSE OF THE PROJECT WORK 

New issues evolve out of the changing nature of industry and thus it is important to 

periodically redefine and document the nature of the industry and its issues. The product 

of such research is primarily knowledge leading to understanding. The project report is 

will also include a CD containing the project report and in particular 1) the membrane 

drinking water plant survey database in a user-friendly form suitable for sorting and 

manipulating the data records but not allowing for data entry and 2) the state-by-state 

review of disposal regulations. 

The membrane plant survey and documentation of each state’s disposal regulations are 

the direct means of gathering information that will allow definition and documentation of 

concentrate and backwash disposal issues. The survey that is necessary to allow for full 

characterization of disposal practices and correlation of practices with plant type and size, 

for instance, will also provide valuable information for other purposes. The survey and 

regulatory documentation will present a broad and full characterization of the membrane 

plants that will provide several benefits discussed below. 

More specifically, the purpose of the project effort is to provide a means and a tool for: 

• Determining, documenting, and representing the status of the membrane drinking 

water industry 

o to document industry growth 

o to define industry trends 

o to define industry problems and needs 

• Communicating such information to interested parties 

o to highlight the viability and feasibility of membrane-produced drinking 

water 

o to represent the size, growth, and strength of the industry 

o to reflect the importance of the industry and consequently the importance 

of addressing and settling issues surrounding membrane-produced 

drinking water 

• Enabling utilities to set up a network of similar membrane plants that can result in 

cost reductions and savings during planning, design, and operation 

• (more generally) Use in the evaluation, planning, design, and operation of 

membrane facilities - to avoid past shortcomings and capitalize on successes of 

existing facilities 

The survey provides the industry with a detailed self-portrait; a quantitative description of 

existing practices that reflects patterns and trends not only of the entire industry but by 
 12 

geographical area, plant size, membrane process, year of startup, etc. Since the survey 

will be the second one done in this expansive manner, a comparison can be made of 

changes in practices, patterns, and trends with those found in the original survey 

(Mickley et al, 1993). The survey provides a detailed portrait, not just a 'representative' 

one. While the Bureau of Reclamation, NWRI, AWWA, AWWARF, and other 

organizations and groups refer to the membrane drinking water utility industry and 

characteristics about it such as its practices, its growth, etc., this survey is the only means 

of documenting and thereby portraying these aspects in a statistical sense. The survey 

and its results then become a firm basis from which to better represent issues, concerns, 

and needs. There is a need for educating many groups about the existing benefits and the 

great potential of membrane drinking water plants to provide new sources of drinking 

water and improved treatment necessary to meet SDWA requirements. The survey 

provides a factual, quantitative basis for describing and explaining the growing industry. 

It is thus a tool to help frame communication and educational efforts and energies. The 

survey can also provide a basis for defining industry research needs. 

The survey and documentation of regulatory practices can also help individual utilities to 

see and appreciate the 'big picture' of membrane drinking water plants; providing a 

degree of confidence in the technology. And finally, the survey can provide the 

individual utilities with a means of establishing a network of similar-situation plants as a 

cost-savings tool at the planning, design, and operation stages. 

3.3 RESEARCH OBJECTIVES 

The project objectives were: 

• To develop a detailed characterization and representation of the membrane 

drinking water industry in general and the concentrate disposal practices in 

particular [through a plant survey and subsequent analysis of survey results] 

• To provide a complete documentation and characterization of the regulation of 

membrane concentrate disposal [through a review of Federal and state 

regulations] 

• To provide preliminary level cost models for the various concentrate disposal 

options 

• To make this information readily available through putting research results in a 

CD format that includes: 

o Report text 

o Membrane plant database 

o Worksheets for developing preliminary level cost estimates of disposal 

option costs 

o Mathematical relations for directly calculating preliminary level cost 

estimates 

These objectives led to five general areas of effort: 
 13 

• Conducting survey tasks 

• Conducting regulatory tasks 

• Conducting issue-related tasks (analysis of survey and other information) 

• Conducting cost modeling tasks 

• Conducting routine project administrative and management tasks 

3.4 REPORT CONTENT 

Chapter 4 presents the project methodology information through a discussion of the 

research conducted. It describes the technical approach taken to accomplish the project 

tasks. Chapter 5 presents the results of the detailed membrane plant survey that covers 

over 150 plants. In Chapter 6 the regulation of membrane concentrate is documented 

from a Federal perspective. This is followed by the State’s perspective in Chapter 7. 

Chapter 8 begins the first of several chapters devoted to modeling the capital cost of 

different concentrate disposal options. Chapter 8 focuses on disposal to surface water 

and to sewer. Chapter 9 looks at disposal by deep well injection. Disposal by 

evaporation pond is discussed in Chapter 10 followed by disposal by spray irrigation in 

Chapter 11. Disposal by thermal zero liquid discharge is the subject of Chapter 12. 

Chapter 13 provides an analysis of the cost models and Chapter 14 contains instructions 

for using the stand-alone CD containing the membrane plant database, the full report text, 

worksheets for calculating disposal costs, and closed-form equations for calculating these 

disposal costs. Appendices contain an SI Metric conversion table and state-by-state 

discussions of concentrate regulation with state contacts provided. 
 14 
 15 

CHAPTER 4. 

RESEARCH CONDUCTED 

4.1 INTRODUCTION 

The project research effort was divided into several tasks: 

 

• Survey task 

• Database program task 

• Regulatory task 

• Issue-related task (analysis of survey and other information) 

• Cost modeling task 

The present chapter discusses the technical approach taken to accomplish these tasks. 

4.2 SURVEY TASK 

The general technical approach was to efficiently and effectively gather, analyze, and 

report information using methods and procedures that the researchers have successfully 

used in past project work. The intended technical approach was to contact each and 

every membrane drinking water plant above a size of 25,000 gpd. While statistically 

representative surveys that use blanket mailings serve a purpose, the degree of detail 

sought in this project was high and it was felt that personal contact and repeated 

interactions with plants were necessary for obtaining the information. All interactions 

with the membrane drinking water plants were done by telephone or fax. The 

information sought is listed in Table 4.1. The items marked by an asterisk (*) are the 

new items that were not included in the 1992 survey and database. 

4.2.1 Identifying Plants: The initial and significant challenge was to locate and contact 

the plants. The previous survey (Mickley et al, 1993) listed contact names and telephone 

numbers. There was a surprising number of changes in both area codes and local 

numbers, such that the list was much less useful than anticipated. Individual membrane 

manufacturers and membrane system suppliers were contacted. In contrast to the 

considerable help and assistance given in the previous survey, most of these groups were 

not forthcoming with information. This was taken to be an indication of the high level of 

competitiveness that exists in the industry. This also was not anticipated. Attempts were 

also made through the state regulatory agencies to obtain lists and contacts of plants. In 

most instances membrane drinking water plants were not culled out as a separate group 

within these agencies, and lists were not available. The most effective source of 

information was the Water Desalination Report published by Maria Carmen Smith. 

Issues of this weekly newsletter, going back to 1990, were reviewed for plant names and 

locations. 
 16 

Table 4.1 Arrangement of data in database 

Plant Identification Information Contact

- State - Date of contact 

- County - Name 

- Plant name - Title 

- Address - Telephone number 

General Plant * Fax number 

- Type of plant Membrane 

- Reason for plant - Material 

- Plant status - Manufacturer 

- Initial capacity - Type 

* Present capacity * model 

- Build-out capacity * Configuration 

* Basis for capacity (include blending?) Membrane Process

- Start-up date - Feed operating pressure 

Feedwater - System recovery 

- Source * Number of process trains 

* TDS * Train capacity 

* Removal requirements Permeate Post-Treatment

Pretreatment * Process steps 

- Process steps * Blending? ratio 

Concentrate Membrane cleaning solutions

- Treatment - Cleaning solutions used 

- Method of disposal - Method of disposing of cleaning 

Engineering Design, Contractor wastes 

- Other disposal, and options considered OEMs

- Disposal permits obtained - Engineering design firm 

* Disposal permit conditions (mixing - Contact name 

 zones, etc.) - Contact address 

* Disposal permit monitoring * General contractor 

 requirements * OEM's 

- Difficulties obtaining permits 

Other Information

* Operating, equipment, permitting changes within last three years 

* Reason for changes 

* Date of last major membrane replacement 

* Problems encountered within last three years 

* Most frustrating operating aspect 

* Information they would use network for (needs basis) 

* Information they would be willing to network with (advice basis) 

- other comments including identification of issues that plants feel the industry 

should address 
 17 

From the outset the plan was to contact only plants larger than 25,000 gpd (0.025 mgd), 

the same cutoff size used in the previous survey. Plants smaller than this tend to be for 

trailer home parks and other small and non-municipal sites. Table 4.2 details the size 

distribution of plants from the 1992 survey. 

Table 4.2 1992 Survey of 140 plants 

Size number cumulative cumulative 

Range (mgd) of plants number percent

0.025 - 0.05 26 26 19 

0.05 8 34 24 

0.06 5 39 28 

0.07 - < 0.10 7 46 33 

0.10 - < 0.20 19 65 46 

0.20 - < 0.50 24 89 64 

0.50 – <1.0 10 99 71 

1.0 - <3.0 20 119 85 

3.0 - < 6.0 17 136 97 

>6.0 4 140 100 

 TOTAL 140 

What constitutes a ‘small’ plant is arbitrary; however, a size of 0.05 mgd (50,000 gpd or 

37 gpm) has been used by the Florida State Government in legislation to allow special 

provisions for plants of this size or smaller in terms of concentrate disposal. 

4.2.2 Contacting Plants: The initial telephone call established the purpose of the call. 

The project objectives and backing of the Bureau of Reclamation, the usefulness of the 

data, and the existing database were mentioned. This initial telephone conversation was 

very important in setting the tone and energy of the remaining interactions. Once a 

contact saw the non-threatening nature of the project, and beyond that the usefulness to 

him of the study, the level of cooperation was good. Since the utility contacts are 

frequently busy with their routine and non-routine responsibilities, the first question was 

'when would it be convenient to ask you questions for the survey?’ Prior to the first 

detailed discussion, any known information was filled into the data form. This was 

information from the previous survey or information obtained from any other source. 

During the conversation other entries were made into the database form. In some 

instances a second telephone call was made to obtain missing and confusing or unclear 

information. When the initial contact did not have all of the information sought, another 

contact was sought. After information for a given plant was obtained, it was entered into 

the formal database. The entire process for a given utility typically stretched over an 

elapsed time of several weeks. After many plants were contacted, the database 

information was printed out in a concise form. This form was faxed to the plant for their 

verification and modification if necessary. Frequently the returned form contained 

additional information. Perhaps 20 percent of the faxed forms were returned with 

comments, new information or corrected information. 
 18 

It should be noted that no attempt was made to gather cost information from the survey. 

This was not an objective in large part due to the difficulties and challenges associated 

with obtaining this type of information, particularly when several different types of plants 

are involved. While utilities are willing to describe their process, they are much less 

willing to share cost information. Not only is the reliability of such information in 

question, but also it is also difficult to get cost data from different plants on the same 

basis - fitting pre-defined cost categories. In addition, much of the capital cost 

information is not recent and not well documented. In a separate project task, cost 

models of different disposal options were developed. The information needed for these 

models was not addressed in the interactions with the individual utilities. 

During the course of the survey task, some changes were made in the data-gathering 

effort. First, the size of the minimum plant surveyed was increased from 0.025 mgd to 

0.05 mgd. As can be seen in Table 4.2 plants in this size range constituted almost 20 

percent of the 1992 survey. Most of these plants were from Florida, and several of these 

plants are no longer in existence. Several small plants operating in 1992 are no longer 

operating, having been shut down in favor of more economical options for providing 

drinking water and because of problems with obsolescence and concentrate disposal. 

Furthermore, most plants of this size have a part-time operator who is typically not easily 

contacted, and when reached not very interested in participating in the survey. In some 

instances these smaller systems were found to have become part of larger systems. 

Because of the general trend in new membrane plants becoming larger, it was decided to 

focus the data-gathering efforts on larger utilities. As explained in the data analysis 

discussion of Chapter 4, the effect of this change on the concentrate disposal statistics 

was both definite and predictable. 

Another change involved limiting the number of microfiltration plants contacted. The 

primary reason for this was that nearly all of the microfiltration plants used Memcor 

microfiltration systems (the survey cutoff date for MF plants was 1999). Microfiltration 

systems are much more similar from site to site than are reverse osmosis (RO), 

nanofiltration (NF), or electrodialysis (ED/EDR) systems, and many sites were producing 

similar data. It was assumed that the data obtained were representative of many plants 

not contacted. Similarly, it was decided to set the minimum size cutoff for MF plants at 

0.50 mgd as MF plants tend to be larger than other membrane plants and, like other 

plants, their typical size is increasing. 

A handful of plants in Florida declined to participate in the survey, saying that they did 

not want to jeopardize their ongoing permit-related challenges with the Florida 

Department of Environmental Protection. 

The net result of these changes on the plants surveyed was that several plants are not 

included in the survey. In the 1992 survey that included 140 plants, it was estimated that 

as many as 95 percent of the candidate plants were contacted and included in the survey. 

In the present case, it is estimated that the number of candidate RO, NF, and ED/EDR 

systems surveyed was about 70 percent and the number of candidate MF plants surveyed 

was about 50 percent. The 1999 survey includes 150 plants. 
 19 

4.3 DATABASE PROGRAM TASK 

The 1992 survey information was summarized in an EXCEL spreadsheet. This form was 

convenient at the time for tabular display of the information. The 1999 survey contains 

considerably more information, thus requiring a change in format away from displaying 

all data from several plants on a single page. More important, the EXCEL format is not 

convenient for sorting and searching for information, and in, general, for data analysis. 

4.3.1 Database Software: Various relational databases were reviewed to determine 

which most closely suits the intended purposes. Development of the database software 

for different platforms (Windows 32-bit, Windows 16-bit, Mac, UNIX, etc.) involves 

somewhat separate efforts. Because of this, it was decided to develop the database 

software only for the Windows 32-bit platform, as this platform is the most widely used 

one and the one whose usage is increasing. The database software may be considered to 

have a ‘front end’ that the user sees and a ‘back end’ which is the database itself. It was 

decided to use a Microsoft back end so that others on the research team can interact with 

it or visit this using the popular Microsoft program Access. It was also decided to use 

Access, itself, for the backend. With purchase of the Access 97 Developers Toolkit, 

distribution of the resulting program can be done without paying a royalty fee to 

Microsoft. This product easily handles the relatively small size of the database (a 

maximum of 200 plants and 150 pieces of information per plant). 

4.3.2 Programming: Programming of the database included customizing (defining 

input and output formats and forms) and manipulation (how information is retrieved and 

sorted). Programming aspects included: 

• Designing the tables where the data will be held 

• Designing the input form and the front end interface 

• Designing a report (output form) so the input information can be printed out for 

immediate use 

• Designing the reports and query mechanisms for the final product 

• Modifying this to make an executable product which does not have input 

• Creating a menu-driven user interface 

The initial step was to develop a listing of information to be included in the database. 

Table 4.1 was developed for this purpose. Next, the nature and format of possible entries 

for each of these data were identified. After a dozen or so plants were contacted and the 

information from the plants was reviewed, database tables were constructed to house the 

individual data entries. A means of linking the data for each plant to that plant was 

developed. The end result was a series of interlinked tables. 

To facilitate easy entry of data into these tables, an input form was created as the userprogram interface. Data obtained from the survey were then entered into the database 

using this form. Creation of an output form allowed a hardcopy printout of the input data 

such that it could be sent to the individual plant for their review of accuracy and 

completeness. 
 20 

A simple demonstration database software program was developed to demonstrate all the 

functions and capabilities of the final project database software program, albeit in a 

limited form. The intent of the demonstration effort was to encounter each of the 

different program design and CD formatting steps and challenges early in the project. A 

very simple database of limited information was thus developed that allowed data input, 

data query, data manipulation, report generation, and printing just as the project database 

software program would later do. 

The database program to this point was all done in Microsoft Access. The creation of a 

stand-alone executable program that did not require Access software to run requires 

further programming. Microsoft Office products allow for some code to be written in 

Visual Basic. No separate software is required as the Visual Basic is accessed from 

within the Office product software. The stand-alone version of the database was created 

using these Microsoft Access capabilities. 

The next priority was to program the query mechanism. The programming step involved 

defining what types of queries would be made, how the queries would be made, and how 

the results of the queries would be displayed. Since the user creates the queries some 

programming was required to provide this interface. An installation program, using the 

software INSTALLSHIELD, was created for this purpose. 

4.3.3 Final User Interface: The database is included along with other project products 

in a CD format. The contents of the CD include: 

• A front-end menu providing choices to the user. 

• The stand-alone database program 

• The full project text report 

• The preliminary level disposal cost model worksheets 

• The preliminary level disposal cost regression models 

The front-end menu was created using Visual Basic. The stand-alone database program 

was simply written onto the CD. The report text was converted into a pdf files for 

inclusion into the CD format. The worksheets were also provided as pdf files. The 

regression models allow for some calculation to be done by the user. These files were 

written in Visual Basic also. 

 

4.4 REGULATORY TASK 

The regulation of concentrate and backwash disposal from membrane systems is an 

important consideration in the planning and design of a membrane drinking water system. 

Fifteen years ago, however, the meeting of regulatory requirements was a relatively 

minor challenge, as requirements were minimal. Since then regulatory requirements have 

evolved considerably, as reflected in NPDES permit requirements in Florida. These have 

gone from the 1985 consideration of about 6 parameters to 1) an increase in the number 

of specific chemical parameters considered, 2) more stringent limits for many of these 

specific chemical parameters, and 3) use of whole effluent toxicity tests. While much of 
 21 

the historical membrane activity has been in the State of Florida, this situation has been 

changing. In addition to documenting the federal regulatory structure and framework for 

concentrate disposal, the goal of the present work was to document state-by-state 

regulation. This was accomplished through contact with regulatory agencies from each 

state and discussing with them the regulatory requirements for the different types of 

concentrate disposal options. Many of the states now have Internet web sites that 

facilitate information gathering. 

4.5 ISSUE-RELATED TASK 

There are several levels of data analysis. The first level of analysis was the compiling of 

lists such as plants by type of membrane process, plants by reason for treatment, and 

plants by disposal method. The second level of analysis was the breakdown of these lists 

by other parameters, such as plant size, year of startup, etc. The number of possible 

different responses was limited, and the analyses at these levels were a simple matter of 

adding up plant responses. 

The third level of analysis involves responses that required interpretation to fit them into 

categories. Examples included descriptions of disposal difficulties, of permit changes, of 

areas where networking advice would be given or sought, etc. Where feasible, data 

entries were categorized to facilitate searching and sorting, as opposed to entering a 

myriad of comments that could not be easily compared. 

Table 4.3 lists more specific data analysis summaries that have been prepared. An 

important goal of data analysis was to identify trends and patterns in the data. 

In addition to using the survey results to identify trends and thus issues affecting the 

membrane drinking water industry, discussions with various utility, regulatory, and other 

industry people frequently provided insights into issues that were affecting them. 

4.6 COST MODELING TASK 

4.6.1 Cost Estimates: In general, the approach taken to develop cost estimates depends 

on the degree of accuracy desired and the amount of information available, including 

whether cost estimation programs are available. Cost estimates may be made at several 

stages of process design ranging from conceptual or preliminary stage to a final detailed 

stage. In this sequence the accuracy desired may range from 50 percent at the 

preliminary stage to 10 to 15% at the design stage. 

The most accurate cost estimates are developed using a ‘ground up’ approach where costs 

for individual items are determined and then summed to arrive at the total cost. This 

approach is absolutely necessary to obtain the most accurate and meaningful cost 

projections. It takes into account regional and site-specific factors and all details required 

for vendors to issue quotes. For some well established technologies and applications 
 22 

Table 4.3 Data Analysis Categories 

• Plants by type of membrane process with entries under 

-- seawater reverse osmosis (SRO) -- BRO plus ED-EDR 

-- electrodialysis-electrodialysis reversal (ED-EDR) -- NF plus BRO 

-- membrane softening (MS) -- ultrafiltration (UF) 

-- nanofiltration (NF) -- microfiltration (MF) 

-- integrated membrane systems -- brackish RO 

-- brackish RO (BRO) plus ion exchange (IX) 

• Plants by reason for why treatment was needed with entries under 

-- bacteriologicals -- manganese 

-- bicarbonate -- nitrates 

-- calcium, hardness -- organics 

-- chloride -- radium 

-- color -- sodium 

-- fluoride -- sulfate 

-- iron -- TDS 

-- magnesium -- THMFP 

-- many others -- turbidity 

• Plants by disposal method with entries under 

-- discharge to sewer -- deep well injection 

-- evaporation ponds -- surface water discharge 

-- spray irrigation (many categories) 

-- percolation pond -- other 

Another aspect involves preparation of tables and statistics such as: 

• types of plants by location 

• operating plant capacity (total and average) by type of plant; by location 

• means of disposal by location 

• means of disposal by size of plant 

• means of disposal by year of startup 

• others including combinations of these (example: means of disposal by 

location and size of plant) 

Still another aspect involves tallying of other responses made such as: 

• disposal difficulties 

• plant problems occurring within last three years 

• operating, equipment, permit changes occurring within last three years 

• most frustrating aspect of plant operation 

• areas of networking advice and corresponding plants 
 23 

there are cost estimation programs available, such as for a brackish reverse osmosis 

system (Bureau of Reclamation, 1999). The accuracy of these programs may approach 

that of a final design estimate depending on the sophistication of the model and the 

quality of the input data. This is particularly true of technologies that are equipment 

oriented and whose equipment is substantially the same regardless of site location. 

Although membrane processes themselves fit this category, disposal options in general do 

not. For instance, whereas membrane processes can be used almost anywhere, most 

disposal options are location- and climate-dependent AND these site-dependent features 

must be considered for accurate disposal cost estimates. As a result, disposal cost 

estimation programs similar to those available for membrane processes do not exist. 

Another approach to developing cost estimates involves studies undertaken to determine 

the range of costs encountered in the field. Cost information is gathered from existing 

facilities, typically new facilities where cost information is available. This approach has 

been used (Adham et al, 1996; Leitner et al, 1997) to determine rough costs and cost 

trends with plant size, etc. This approach must deal with the challenge of fitting cost 

information from different sources into a standard and usually arbitrary format, and is not 

appropriate for meeting the present objectives. 

4.5.2 Cost model objectives: The objectives of the modeling effort are two-fold: 

1) To provide a simple means of developing preliminary cost estimates for different 

disposal options; this also allows the user to compare relative costs between 

different disposal options. 

2) To do so in a manner that illustrates the different individual cost elements. 

This allows the user to explore the influence of different design parameters on the total 

cost and to understand the equipment and operational aspects of the disposal options. 

The descriptive model can serve as a template for the user to develop more precise sitespecific cost estimates. 

These objectives have led to the development of two different types of cost-estimation 

models: worksheet models and simple closed-form regression models. The worksheet 

approach requires the user to choose design parameter values, to look up the individual 

cost factor values from figures, and to enter the values in a worksheet. The worksheet 

and the associated figures make the design parameters and cost factors explicit and 

provide a means of understanding the technical and economic aspects of the disposal 

option. The relative importance of the different cost factors can be seen easily. This 

calculation framework also allows the user a basis from which to develop more exacting 

cost estimates. The calculation process is, however, labor intensive. The regression 

models are closed-form mathematical relations developed from the worksheet models, 

and thus represent approximations to them. They require the user to choose design 

parameter values and to make a simple calculation of the total capital cost. The 

regression models are much easier to use. They do, however, obscure any understanding 

of individual cost factors and their relative importance in determining the total cost. 
 24 

4.5.3 Recommendations for use of the models: User understanding is best served by 

reading about the individual model cost factors to appreciate the nature of the disposal 

option and also to appreciate the assumptions and limitations of the model. When some 

level of understanding is at hand, the regression models offer a means of developing 

quick relative comparison of costs for the different disposal options and analyzing cost 

sensitivities and trends with design parameter values. The worksheet calculations should 

be used when more accurate estimates are required. 

4.5.4 Development of worksheet models: The following worksheet models are 

developed for six disposal options and for the transport of concentrate from the 

membrane plant to the disposal site. 

• Deep well disposal 

• Evaporation pond 

• Spray irrigation 

• Surface water disposal 

• Discharge to sewer 

• Zero liquid discharge 

• Transport 

The worksheet models, especially for the first three items, borrow heavily from a 

previous work the author participated in (Mickley et al., 1993). More specifically this 

includes the cost factor approach and some of the descriptive text from that work. Cost 

factor values have been updated from the previous work. 

The worksheet models were developed in several steps as described below. 

4.5.4.1 Step 1: Identification of Cost factors: Cost factors are the independent cost items 

that, in sum, make up the total capital cost for each disposal option (Mickley, 1996). As 

an example, the cost factors for the evaporation pond disposal option include: 

• Land 

• Land clearing 

• Dike 

• Pond liner 

• Perimeter fence 

• Road 

• Engineering 

• Contingency 

4.5.4.2 Step 2: Identification of Design Parameters: The capital cost of each cost factor 

is dependent on the design parameters necessary to characterize the cost factor. For 

instance, in the case of a pipeline the design factors might include the pipe material, wall 

thickness, length of the pipe, and diameter of the pipe. Not all combinations of these 

parameters are considered in the models; in some cases parameters are restricted, for 

instance in setting values of pipe material and wall thickness. Values are chosen to be 
 25 

most representative and typical of field use. In situations where other values are required 

at a site, the model user will need to adjust the calculations accordingly. The choice of 

design parameters is dependent on the design approach taken in the model. The design 

parameters that determine the independent cost factors for the evaporation pond model 

are: 

• Land acreage 

• Land type 

• Dike height 

• Total pond liner thickness 

4.5.4.3 Step 3: Identification of Values for Cost Factors: Costs were developed through 

interaction with equipment vendors in various parts of the country to assure that costs 

were not biased by regional differences. The assignment of values or curves to the 

resulting data was somewhat arbitrary given differences in cost values found from 

different sources. Values were chosen which were judged to be representative. 

4.5.4.4 Step 4: Development of Worksheet: Table 4.4 presents the worksheet for the 

evaporation pond disposal model. There are five design parameters called variables in 

the worksheet. In the example provided, values are chosen of 10 acres for the 

evaporative surface, 8 ft for the dike height, 60 mil for the total liner thickness, 

$5,000/acre for the land purchase cost, and $4,000/acre for the clearing of medium 

wooded land. From these five variable values, the values of several cost factors are 

determined from the appropriate figures listed in the worksheet. The worksheet contains 

room for additional calculations. Similar worksheets are developed for the other disposal 

options. 

4.5.5 Development of Regression Models: The total capital cost (TCC) for a disposal 

method is equal to the sum of several individual cost factors. Each of these cost factors 

(such as pipe, pump, pond liner, land, etc.) may be represented by the size or amount of 

the cost element times its unit cost factor. The cost factor for land, for instance, is 

determined by the acres of land required times the cost per acre of the land. The cost 

curves presented in figures represent these individual cost factors as a function of design 

parameters (number of acres, for example) for set values of the unit cost factors. 

For the cost models, the TCC (a dependent variable) is thus dependent on design 

parameters (independent variables). A closed form mathematical relationship expressing 

this dependency is of the form: 

 TCC = function(independent variables) (1) 

In a multilinear regression model with three independent variables, this function is linear 

in the independent variables such as: 

 TCC = a + b*IV1 + c*IV2 + d*IV3 + ... (2)
 26 

Table 4.4 Worksheet for Evaporation Pond Capital Costs 

WORKSHEET for Evaporation Pond Disposal Capital Costs For preliminary level costs only ENTER variable values Variable Range example case 1 casA - evaporative surface (acres) 0 to 100 10 B - dike height (ft) 4, 8, 12 8 C - total liner thickness (mils) 20 to 120 60 D - land unit cost ($/acre) 0 - 10,000 5000 E - land type (see note 1 below) 1,2, 3, 4 3 CALCULATION of total acreage Action F - ratio: total acreage to evaporative acreage use Figures 10.2, 10.3 1.36 G - total acreage = A*F 13.6 FIND unit area costs from figures using total acreage, G Action cost, $ H - land, $/acre same as E 5000 I - land clearing (see note 1 below), $/acre 4000 J - dike, $/acre use Figures 10.4, 10.5 8600 K - nominal liner, $/acre use Figures 10.7, 10.8 22680 L - liner, $/acre =K*D/60 22680 M - fence, $/acre use Figures 10.9, 10.10 4500 N - road, $/acre use Figures 10.11, 10.12 770 

TOTAL Unit Cost add H, I, J, L, M & N 45550 

TOTAL above times G 619480 

 add engineering at 10% 61948  add contingency at 10% 61948 

GRAND TOTAL 743376 

COMMENTS: note 1: clearing cost ($/acre) 1-brush $1,000 2-sparsely wooded 

3-medium wooded $4,000 4-heavily wooded 
 27 

Where a, b, c, and d are constants determined by the regression algorithm and IV1, IV2, 

and IV3 are the three independent variables. 

Once values of the four constants are determined, the total capital cost, TCC, may be 

calculated by inserting particular values for the three independent variables, IV1, IV2, 

and IV3, into this relationship. 

It is obvious from the figures of cost factor values as a function of the independent 

variables that the relationships are not always linear. However, there is no reason to 

assume that a linear regression model for the total capital cost will not be adequate and in 

any case this needs to be evaluated as a first step in developing the regression relation. 

The regression algorithms require several sets of data comprised of values for each of the 

independent variables and the corresponding value for the dependent variable. From 

statistical considerations, 30 sets of data are sufficient to estimate regression relation 

constants with high confidence, providing a meaningful linear relation exists. This is the 

first of several steps in the development of a regression model. 

4.5.5.1 Step 1: Calculation of 30 Sets of Values for the Independent Variables: To 

guarantee that the 30 sets of data cover the full range of independent variable values 

(ranges of the design parameters) and are randomly distributed over these ranges, values 

of the independent variables are chosen using the following approach: 

• Thirty (30) sets of random numbers, between the values of zero and one, are 

developed for each independent variable. 

• These random numbers are then used to calculate values for the independent 

variables. For example, if the flow rate variable is assumed to go from 0 to 5 

mgd, then the flow rate is determined from multiplying the random number times 

the full range of the variable, which in this case is 5. A random number of 0.48 

gives a flow rate of 0.48 * 5 or 2.40. For a variable such as the number of casing 

transitions that can take on a value of 3 or 4, the value of 3 is used if the random 

number is 0 to 0.5 and a value of 4 is used if the random number is >0.5 to 1.0. 

Problematic cases are thrown out, such as flow rates below 0.1 mgd. 

• The resulting sets of independent variable values are then checked for 

autocorrelation; that is, to see if the values for one variable are correlated, through 

chance, to the values of another variable. The variable values are also checked to 

make sure the range of possible values is adequately represented. If there are 

problems with the values, either from autocorrelation or from value bias, a new 

set of random numbers is generated until 30 suitable sets of data are obtained. 

4.5.5.2 Step 2: Calculation of the Total Capital Costs: The worksheets previously 

discussed are used to calculate 30 total capital costs using the 30 sets of parameter values. 

4.5.5.3 Step 3: Multiple Regression on the 30 Data Sets: The software used to perform 

the regression calculations is SYSTAT 9, a powerful statistical and graphical analysis 

system marketed by SPSS, Inc. The program calculates the constant and coefficient 
 28 

values, such as a, b, c, and d, in the above relation and various indicators of degree of 

regression success such as regression coefficients, confidence intervals in the 

coefficients, and residuals (the difference between data values for total capital cost and 

calculated or predicted values for total capital cost using the regression relation). 

The primary indicator of regression success is taken as the adjusted squared multiple R, 

where R2 is the familiar regression coefficient that expresses the fraction of the total 

variability in the data that is explained by the regression relation. The adjusted value 

takes into consideration the number of data sets considered. When a regression model is 

based on relatively few cases, the multiple squared R tends to be an optimistic estimate of 

how well the model fits the population from which the data are assumed to come from. 

At this point in the procedure, a closed form mathematical relation such as equation (2) 

exists. A standard procedure in determining the adequacy of the model is an analysis of 

residuals. This will indicate the presence of outliers, curvature, or other forms of nonlinearity are present in the data. 

4.5.5.4 Step 4: Analysis of Model Residuals: The residual for a given set of data, i.e. for 

a given set of independent variable values, is the difference between the total capital cost 

used in the regression and the total capital cost predicted by the regression equation. A 

comparison between each of the 30 sets of values (the worksheet calculated total capital 

costs and the regression equation total capital costs) yields 30 residual values. Patterns in 

residuals are studied to determine if there is a consistent trend of residual values with 

high or low or certain combinations of design variable values. Ideally, the magnitude of 

the residuals would be fairly constant and normally distributed without any outlier values. 

Where residual patterns deviate from this ideal it may mean that 1) a worksheet 

calculation mistake was made in certain values (particularly where outliers exist), 2) 

outliers exist for some other reason, 3) the linear model is not necessarily the best to use 

to fit the data. 

As an illustration of these considerations, the regression model for the evaporation pond 

(total cost per unit area) is considered. The model coefficients, a, b, c, and d were 

determined to be: 

a = 5406 

b = 465 

c = 1.07 

d = 0.931 

e = 217.5 

The squared multiple R value is 0.997 and the adjusted square multiple R value is 0.996. 

These are high and good regression coefficients, suggesting that the regression model fits 

the data quite well. Figure 4.1 shows a plot of calculated total unit area cost values using 

the regression equation versus input data for the regression, the calculated total unit area 

cost values from the worksheet calculation. Visually the agreement is quite good. The 
 29 

Figure 4.1 Regression Estimates as Function of Input Values 

20000

30000

40000

50000

60000

70000

80000

20000 30000 40000 50000 60000 70000 80000

Input Data Value

Regression Estimated Value
 30 

regression residuals are plotted in Figure 4.2. The residual appear to be fairly randomly 

distributed with positive and negative values and there is no apparent trend with the 

estimate or predicted value. 

This type of analysis was performed for each of the models and used to guide the 

modeling effort. 
 31 

Figure 4.2 Regression Residuals as Function of Estimated Value 

-2000

-1500

-1000

-500

0

500

1000

1500

2000

20000 30000 40000 50000 60000 70000 80000

Regression Estimated Value

Residual Value
 32 
 33 

CHAPTER 5. 

PLANT SURVEY RESULTS 

5.1 INTRODUCTION 

The purpose of the membrane plant survey was to document the growth and trends of the 

industry, particularly in regard to concentrate disposal practices. The survey, conducted 

mostly in 2000, provides information that can directly be compared to that from a 

previous survey conducted in 1992 (Mickley et al, 1993). While such surveys are 

necessary to provide detailed information about the individual plants, it is possible to 

gather statistics on numbers and sizes of plants from information readily available from 

membrane system manufacturers. Information about total number and size of plants is 

provided in section 5.2. This is followed by a discussion of the surveyed plants. 

MF and UF plants are considered separately from the other plants because of their natural 

differences. Foremost is the fact that MF and UF plants do not concentrate TDS and 

consequently the disposal of backwash from MF and UF plants is considerably different 

than disposal of concentrate from the desalting (RO, NF, and ED/EDR) plants. An 

additional reason is that at the time of the previous survey (Mickley et al, 1993), which 

focused on membrane drinking water plants, there were no MF or UF plants operating at 

drinking water plants. Separation in the present survey allows direct comparison of the 

present results with the 1992 survey results. 

5.2 TOTAL NUMBER OF MEMBRANE PLANTS IN THE U.S. 

There were several reasons for estimating and identifying (not surveying) the total 

number of membrane plants in water and wastewater facilities in the U.S. The first was 

the desire to determine how representative the survey results were relative to the larger 

population of all plants. The second was to better document the growing number of 

plants. The third was to estimate the number of new plants built in the year 2000. While 

these plants were not in the survey scope of work (the project started in 1999), it became 

apparent during the information gathering that several membrane industry milestones 

occurred in the year 2000. These milestones are discussed below. An accurate picture of 

the state of membrane technology in the year 2001 needs to include these important 

events. Thus while the plants included in the detailed survey are restricted to plants built 

prior to 2000, an effort was made to document the number of plants of different types that 

were in operation by the end of the year 2000. 

5.2.1 Tabulation of Plants in the U.S. through 2000: Table 5.1 is a tabulation of 

operating membrane plants by 2-year period and by membrane technology. It was 

developed based on data from the 1992 survey (Mickley et al. 1993), the present 1999 

survey, estimates of the number and type of plants not contacted in the years up to 2000, 

and estimates of the membrane plants built during 2000. This and all such plant tallies 

have minimum size cutoffs that influence the numbers of plants listed. For this 
 34 

 Table 5.1. Estimated Number of Membrane WTPs and WWTPs in the 50 States 

Year BRO SRO NF EDR MF UF DESALTING MF/UF to

< 1971 0 0 0 1 0 0 1 0 

1971/72 4 0 0 0 0 0 4 0 4 1973/74 8 0 0 4 0 0 12 0 11975/76 8 0 0 0 0 0 8 0 8 1977/78 10 1 0 1 0 0 12 0 11979/80 5 1 0 0 0 0 6 0 6 1981/82 9 0 0 0 0 0 9 0 9 1983/84 14 0 0 0 0 0 14 0 11985/86 3 0 0 3 0 0 6 0 6 1987/88 4 1 3 0 0 0 8 0 8 1989/90 16 0 1 3 0 0 20 0 21991/92 18 3 8 3 1 0 32 1 31993/94 17 0 3 2 14 2 22 16 31995/96 9 0 2 2 14 0 13 14 21997/98 11 1 3 2 43 2 17 45 61999/00 27 2 6 2 63 12 37 75 1

Totals 163 9 26 23 135 16 221 151 37

Comments: 1. Only plants greater than 25,000 gpd were considered 2. The tabulation includes an estimated 22 WWTPs 3. The tabulation is a combination of hard data (from the 1992 and 1999 surveys conducted by Mickley & Assoc4. The tabulation also contains estimates - mostly for the 1999/00 time frame Where: BRO = brackish reverse osmosis SRO = seawater reverse osmosis  NF = nanofiltration EDR = electrodialysis/electrodialysis reversal  MF = microfiltration UF = ultrafiltration 
 35 

tabulation a size cutoff of 25,000 gpd was used for both desalting plants and low pressure 

UF and MF plants. This cutoff eliminates most smaller plants that serve truck stops, 

mobile home parks, hospitals, campgrounds and the like. In the final four columns of 

Table 5.1 the number of desalting plants and MF/UF plants is tallied for each two-year 

period as well as the total number of plants and the cumulative number of plants. 

Figure 5.1 shows the cumulative number of plants by two year period beginning in 1971. 

The total number of all types of plants, the number of MF/UF plants and the number of 

desalting plants are shown separately. 

Several important events are evident from Table 5.1 and Figure 5.1. These include: 

• Most (163, or 74%) of the 221 desalting plants are brackish water RO plants with 

few (9, or 4%) seawater RO plants and about an equal number of NF and 

ED/EDR plants (26, or 12% and 23, or 10% respectively). 

• The early plants were BRO and ED/EDR plants with the first NF plant coming on 

line in 1987. 

• The number of desalting plants being built per period has been in double digits 

since 1989. 

• MF plants begin appearing in large numbers in 1994 and these numbers have 

steadily increased in each two-year period since that time. 

• UF plants first appear in large numbers in the year 2000. 

• If these trends continue, the number of MF/UF plants will outnumber the 

desalting plants in the period 2001/02 or soon thereafter. 

In the remaining sections of the chapter, data will also show the following: 

• Most of these early plants were in Florida, with as many as 61% of the plants in 

1993 being in Florida 

• Until about 1998 perhaps 95+% of the MF plants were Memcor systems 

• In the year 2000 especially, several other MF and UF companies have introduced 

their membrane systems. 

• The size of both desalting and MF/UF plants has been increasing dramatically in 

recent years. 

5.3 RESULTS FROM THE PROJECT SURVEY 

Table 5.2 is a list of the 149 membrane plants contacted. The survey was limited to 

plants built prior to the year 2000. The number of different types of membrane 

processes surveyed is: 
 36 

Figure 5.1 Cumulative Number of Utility Membrane Plants by Two-Year Period 

All Plants 

All Plants 

Desalting Plants

MF/UF Plants 

0

50

100150200250300350400

< 1971

1971/72

1973/74

1975/76

1977/78

1979/80

1981/82

1983/84

1985/86

1987/88

1989/90

1991/92

1993/94

1995/96

19

Two-Year Period

Cumulative Number of Plants

All Plants 

Desaltin

g Pla
 37 

Table 5.2 Plants Included in the 1999 Survey 

 Size Water Disposal Startup Feed TDS Treatme

Name State Category (mgd) Source Method Year (mg/L) ConcerBrackish Reverse Osmosis Plants Dauphin Island AL DW 0.22 GW sewer 1997 West Basin Desalter CA DW 1.3 GW sewer 1993 3600 17th Street Desalter CA DW 2.3 GW sewer 1996 1500 TDS, silChino Basin CA DW 8 GW surface 2000 2000 TDS,siliMorrow Bay CA DW 0.6 GW 1991 (emergeSan Luis Desalter CA DW 2 GW sewer 1994 1700 TDS, FePort Hueneme Water Agency CA DW 0.73 GW sewer 1999 1000 TDS, haCity of Tustin CA DW 0.5 GW sewer 1990 750 TDS, nitSweetwater Authority CA DW 4 GW sewer 1999 2000 TDS, bioCity of Los Angeles CA WW 5 tertiary surface 2001 4050 Water Factory 21 CA other 6 secondary surface 1977 935 Arlington Desalter CA other 4 GW surface 1990 1050 TDS, nitCity of Brighton CO DW 4 GW surface 1993 550 TDS, nitCity of Las Animas CO DW 1.18 GW surface 1997 3500 TDS, haVA Medical Center, Ft. Lyon CO DW 0.24 GW lagoon 1990 800 TDS, haSpruce Creek WTP FL DW 0.5 GW surface 1995 650 TDS, taGasparilla Island WTP FL DW 0.75 GW surface 1990 8500 TDS North Collier County FL DW 20 GW DWI 1993 600 TDS Melbourne WTP FL DW 6.5 GW surface 1996 1800 TDS, haVillage of Tequesta FL DW 1.2 GW surface 1999 4075 TDS Charlotte Harbor RO Plant FL DW 0.5 GW surface 1998 1700 TDS Hollywood RO WTP FL DW 36 GW surface 1996 5000 TDS City of Plantation FL DW 6 GW DWI 1997 325 South County RO Plant FL DW 8.57 GW surface 1983 900 TDS Sanibel Island WTP FL DW 4.7 GW DWI 1981 3000 TDS, raKnight Island Utilities Inc. FL DW 0.9 GW DWI 1985 4000 TDS Town of Jupiter FL DW 12 GW surface 1990 5000 TDS 
 38 

Table 5.2 - continued 

 Size Water Disposal Startup Feed TDS Treatme

Name State Category (mgd) Source Method Year (mg/L) ConcerCity of Vero Beach WTP FL DW 3.4 GW surface 1992 TDS City of Venice FL DW 4 GW surface 1989 3000 TDS Burnt Store RO Plant FL DW 0.56 GW DWI 1994 2120 TDS Halifax Plantation RO Plant FL DW 0.25 GW surface 1998 692 TDS City of Sarasota FL DW 4.5 GW surface 1982 2050 TDS, suCity of Cape Coral FL DW 15 GW surface 1976 1800 TDS Gasparilla Pines RO WTP FL DW 0.1 GW surface 1977 5000 TDS Greater Pine Island RO Plant FL DW 1.5 GW land 1993 1650 TDS, haMarco Island RO Plant FL DW 6 GW surface 1992 6665 TDS Englewood Water District RO Plant FL DW 3 GW 1982 7000 TDS City of Laurens IA DW 0.346 GW surface 1989 1478 TDS, haCity of Manson IA DW 0.2 GW surface 1992 760 TDS, fluCity of Wenona IL DW 0.2 GW 1991 1150 TDS, raCity of Elmwood IL DW 0.4 GW 1993 2000 TDS, raDupage County RO IL DW 1.152 GW 1989 800 TDS, haCity of Toluca IL DW 0.4 GW 1992 1500 TDS, raCity of Minonk IL DW 0.23 GW 1993 1600 TDS, fluCity of Abilene KS DW 3.2 GW surface 1998 TDS, nitCity of Nevada MO DW 1.3 GW surface 1984 1200 TDS, raCity of Circle MT DW 0.33 GW surface 1997 1150 TDS, fluTown of Froid MT DW 0.072 GW 1996 2072 TDS, suTown of Richey MT DW 0.864 GW 1999 1450 TDS, fluCity of Ocracoke NC DW 0.432 GW surface 1977 3600 TDS Hyde County - Fairfield NC DW 0.288 GW surface 1995 1000 TDS, fluHyde County - Ponzer NC DW 0.43 GW surface 1992 500 TDS, fluHyde County - Rodanthe NC DW 1 GW surface 1996 1300 TDS, nitVillages at Ocean Hill NC DW 0.08 GW surface 1990 TDS, Fe Dare County - North NC DW 3 GW surface 1989 3800 TDS 
 39 

Table 5.2 - continued 

 Size Water Disposal Startup Feed TDS Treatme

Name State Category (mgd) Source Method Year (mg/L) ConcerHatteras Island NC DW 3 GW surface 2000 9000 TDS City of Alexander ND DW 0.1 GW lagoon 1995 1370 TDS, fluRolla ND DW 0.2 GW 1993 1465 TDS, suCity of Gwinner ND DW 0.316 GW 1990 TDS City of Creighton NE DW 0.576 GW surface 1993 520 TDS, nitCity of Elmwood NE DW 0.2 GW surface 1995 350 nitrate City of Cape May NJ DW 2 GW surface 1998 2100 TDS, FeMt. Pleasant RO Plant #1 SC DW 1.19 GW surface 1991 1200 TDS, fluMt. Pleasant RO Plant #2 SC DW 3.22 GW surface 1991 1200 TDS, fluIsle of Palms SC DW 1.1 GW surface 1993 2000 TDS, fluHarlingen Waterworks System TX WW 4 secondary surface 1999 1200 TDS, silCity of Ft. Stockton TX DW 3 GW lagoon 1997 1400 TDS, haHaciendas Del Norte TX DW 0.08 GW evap 1983 1500 TDS, haBig Bend Motor Inn, Terlingua TX DW 0.05 GW evap 1989 2900 TDS, suEsperanza TX DW 0.058 GW evap 1994 1100 TDS, suRiver Oaks Ranch TX DW 0.076 GW surface 1989 1500 TDS, suSportsmans World TX DW 0.144 lake surface 1982 2500 TDS City of Chesapeake, system 1 VA DW 5 GW surface 1998 7000 TDS, FeCity of Chesapeake, system 2 VA DW 8 river surface 1999 1500 TDS, THCity of Newport News VA DW 5.7 GW surface 1998 2900 TDS, fluSeawater Reverse Osmosis Plants Marina Coast Water District CA DW 0.3 beach well beach well 1997 TDS Morrow Bay CA DW 0.6 beach well surface 1991 TDS Santa Catalina Island CA DW 0.17 creek surface 1980 TDS 
 40 

Table 5.2 - continued 

 Size Water Disposal Startup Feed TDS Treatmen

Name State Category (mgd) Source Method Year (mg/L) Concerns Nanofiltration Plants Port Hueneme Water Agency CA DW 0.77 GW sewer 1999 1000 TDS, hardHollywood NF WTP FL DW 36 GW sewer 1995 500 color, turbDunedin FL DW 9.5 GW sewer 1992 500 hardness, Plantation WTP FL DW 12 GW DWI 1991 TDS, Fe, Miramar West Plant FL DW 4.5 GW DWI 1995 420 Cooper City FL DW 3 GW DWI 1998 500 color, TOCCity of Fort Myers WTP FL DW 12 river spray 1992 THMFP City of Chenoa IL DW 0.35 GE 1992 TDS, fluorDupage County IL DW 1.535 GE sewer 1998 800 hardness, City of Itasca IL DW 0.144 GE 1997 hardness, Nevada Lake Mead Echo Bay WTP NV DW 0.21 lake pond 2000 TDS, hardNevada Lake Mead Overton Beach NV DW 0.11 lake pond 2000 TDS, hardElectrodialysis (& EDR) Plants Arizona State Prison Complex AZ DW 1.5 GW evap 1998 1700 TDS, fluorCity of Buckeye AZ DW 0.9 GW surface 1989 1850 TDS, nitraCity of Tolleson AZ DW 1 GW 1993 900 TDS, bariuT. Mabry Carlton EDR Facility FL DW 12 GW DWI 1995 1100 TDS, sulfaCity of Washington IA DW 1.8 GW surface 1992 1200 TDS, hardCity of Mt. Pleasant IA DW 3.4 GW surface 1999 1800 TDS, radiuCity of Alta IA DW 0.432 GW sewer 1997 1400 TDS, hardCity of Foss OK DW 2.9 reservoir surface 1974 1200 TDS, hardLake Granbury TX DW 7.5 lake lake 1989 1200 TDS, sulfaDell City TX DW 0.1 GW spray 1996 1450 TDS, hardCity of Sherman TX DW 6 lake 1993 1200 TDS, THMOak Trail Shores TX DW 0.144 lake lake 1985 TDS, bioloCity of Granbury TX DW 0.62 lake lake 1984 1800 TDS, sulfaCity of Suffolk VA DW 3.75 GW surface 1990 475 fluoride 
 41 

Table 5.2 - continued 

 Size Water Disposal Startup Feed TDS Treatmen

Name State Category (mgd) Source Method Year (mg/L) Concerns Microfiltration Plants Barrow WTP AK DW 0.36 reservoir lagoon 1999 380 THMFP, tAnthem Community WWTP AZ WW 0.5 secondary sewer 1999 Anthem Community WTP AZ DW 1 mixed 1999 620 Rancho Cucamonga WTP CA DW 4 creek spray 1997 biologicalsCarson Regional Water Recycling CA WW 5 tertiary sewer 1999 turbidity Sarasota filter Plant CA DW 5 creek sewer 1994 240 turbidity, bGene Pumping Station WWTP CA WW 0.019 river sewer 1994 turbidity, bStrawberry WTP CA DW 0.132 river river 1994 biologicals van Damme State Park CA DW 0.03 stream leach field 1999 turbidity Westside School CA DW 0.019 river spray 1993 turbidity El Segundo WWTP CA WW 3.2 tertiary sewer 1980 biologicals Bolinas WTP CA DW 0.16 creek/res. 1996 turbidity Livermore WWTP CA WW 1 tertiary sewer 1997 Dublin San Ramon WWTP CA WW 2.94 secondary sewer 1998 turbidity, aWater Factory 21 CA WW 0.5 secondary sewer 1994 turbidity, bInverness First Valley WTP CA DW 0.12 creek perc pond 1996 turbidity, bPine Brook Water District CO DW 0.24 creek sewer 1996 turbidity, cLahaina WTP HI DW 2.7 river perc pond 1997 turbidity, bNuuanu Lower Aerator HI DW 2 GW sewer 1999 turbidity, bLinwood Metropolitan WTP MI DW 0.225 lake surface 1999 turbidity Algonac Water Filtration Plant MI DW 2 river surface 1999 turbidity, bFayette State Park WTP MI DW 0.03 GW septic 1997 biologicals Mackinac Island WTP MI DW 2.7 lake lake 1997 turbidity, bMarquette WTP MI DW 7 lake lake 1997 60 biologicals West Jefferson WTP NC DW 0.12 GW 1998 turbidity, bNevada Lake Mead Echo Bay WTP NV DW 0.21 lake settling pond 2000 TOC, bioloCity of Minden NV DW 1.25 lake sewer 1997 turbidity, b
 42 

Table 5.2 - continued 

 Size Water Disposal Startup Feed TDS Treatment 

Name State Category (mgd) Source Method Year (mg/L) Concerns Nevada Lake Mead Overton Beach NV DW 0.11 lake settling pond 2000 biologicals, THPine Hill WWTP NY WW 1.29 tertiary surface 1998 biologicals White Plains WTP NY DW 1.6 reservoir 1999 turbidity, biologMargaretville Surface Treatment NY WW 0.48 tertiary surface 1999 biologicals Grand Gorge WWTP NY WW 0.5 tertiary sewer 1998 biologicals Tannersville WWTP NY WW 0.8 tertiary surface 1998 biologicals Lucien WTP OK DW 0.12 reservoir lagoon 1997 turbidity, biologCastle Dale WTP UT DW 1.2 reservoir surface 1999 250 turbidity, biologRocco Farm Food WTP VA DW 1.5 GW 1996 turbidity, biologRural Retreat WTP VA DW 0.5 GW surface 1998 turbidity, biologHigh Point WTP VA DW 0.06 GW+ res. perc pond 1998 turbidity, biologDayton WTP VA DW 3.3 lake surface 1999 turbidity Vista Corporation Park WTP VA DW 0.06 GW 1999 turbidity, biologTown of New Market VA DW 1.18 GW surface 1998 turbidity, biologSchuyler WTP VA DW 0.08 GW surface 1994 turbidity, biologColes Run WTP VA DW 1 reservoir perc pond 1998 turbidity, biologCity of Aberdeen WA DW 7.5 reservoir spray 1999 turbidity, biologKenosha WTP WI DW 16 lake sewer 1998 turbidity, biologManitowoc WTP WI DW 14 lake lake 1999 turbidity, biolog

KEY DW = drinking water evap = evaporation pond 

 WW = wastewater spray = spray irrigation  GW = groundwater perc pond = percolation pond  DWI = deep well injection res = reservoir  biologicals = bacteria, viruses, cysts 
 43 

Table 5.3 Distribution of Plants Surveyed 

 Total Number of Number of 

Membrane process Number plants >1992 WWTP 

Desalting (RO, NF, EDR, SRO) 102 59 0

MF 46 46 11 

UF 1 1 0 

Comparison of these numbers with those of the total number of plants from Table 5.1 

provides an indication of how complete the survey is with regard to contacting every 

plant. From Table 5.1 it can be seen that at the end of 1992 there were an estimated 133 

operating plants of size greater than 25,000 gpd. The 1992 survey included 141 plants, 

with some not fully operational. Thus the 1992 survey was judged to be substantially 

complete with over 95 percent of the existing plants being included. Also from Table 

5.1 it may be seen that the number of desalting plants built since 1992 and through 1998 

was estimated to be 52, with another 18 plants built in 1999 for a total of 70 plants. The 

1999 survey included 59 of these plants, which represents about 84 percent of the total. 

While these numbers can certainly be off by 5 and even 10 percent, they do give an 

indication of the level of completeness represented by the surveys. 

For the MF and UF plants, Table 5.1 estimates 71 MF and 4 UF plants at the end of 1998 

and an additional 75 MF plants at the end of 2000. We estimate that 100 MF plants were 

in operation at the end of 1999. The survey includes 47, or 47 percent of these plants. 

5.4 DESALTING PLANT RESULTS 

Table 5.4 focuses on desalting plants. Due to the high number of membrane plants in 

Florida, statistics for Florida are highlighted. The numbers of plants in Florida and plants 

not in Florida are listed by size. 

Table 5.4 Present Survey: Distribution of 102 Desalting Plants by Size 

Plants not from Fl. Plants from Florida Total 

Size cum. Cum. Cum. Cum. Cum. cum 

Range num. num. % num. num. % num num %

< 0.05 mgd 2 2 3 0 0 0 2 2 2 

0.05 1 3 4 0 0 0 1 3 3 

0.06 1 4 5 0 0 0 1 4 4 

0.07- <0.10 5 9 12 0 0 0 5 9 9 

0.10 - <0.20 4 13 18 1 1 3 5 14 14 

0.20 - < 0.50 18 31 42 1 2 7 19 33 32 

0.50 - < 1.0 11 42 58 5 7 24 16 49 48 

1.0 - <3.0 17 59 81 2 9 31 19 68 67 

3.0 - < 6.0 9 68 93 7 16 55 16 84 82 

> 6.0 5 73 100 13 29 100 18 102 100 

TOTAL 73 29 102 
 44 

From Table 5.4 it may be seen that only 9 percent of the plants are of size less than 0.1 

mgd, but 18 percent of the plants are of size greater than 6.0 mgd. This is in sharp 

contrast to the results of the 1992 survey shown in Table 5.5: 

Table 5.5 1992 Survey: Distribution of 140 Desalting Plants by Size 

Plants not from Fl. Plants from Fl. total 

Size cum. cum cum. cum cum cum 

Range num. Num. % num. num. % num num %

< 0.05 mgd 7 7 13 19 19 22 26 26 19 

0.05 0 7 13 8 27 32 8 34 24 

0.06 1 8 15 4 31 36 5 39 28 

0.07 - < 0.10 5 13 24 2 33 39 7 46 33 

0.10 - < 0.20 6 19 35 13 46 54 19 65 46 

0.20 - < 0.50 14 33 60 10 56 66 24 89 64 

0.50 – <1.0 6 39 71 4 60 71 10 99 71 

1.0 - <3.0 7 46 84 13 73 86 20 119 85 

3.0 - < 6.0 5 51 93 12 85 100 17 136 97 

>6.0 4 51 100 0 85 100 4 140 100 

 TOTAL 55 85 140 

Here, 33 percent of the plants are of size less than 0.1 mgd and only 3 percent of the 

plants are of size greater than 6.0 mgd. A comparison of the size-related results from the 

1999 and 1992 surveys shows: 

 1992 1999 

 Survey Survey

 % plants < 0.1 mgd 33 9 

 % plants > 6.0 mgd 3 18 

Another indication of the increase in size of desalting plants can be seen from Table 5.6 

which was developed based on both surveyed and un-surveyed plants (for which data 

could be obtained). Of the estimated 70 plants built in the time frame of 1993 through 

1999 63 of the plants are represented in the data. The size of the plant is indicated by 

year of starting operation. 
 45 

Table 5.6 Desalting Plant Size by Year of Startup 

 

 Size range in mgd 

Year <0.3 0.3 - < 1 1 - < 3 3 - 6 >6

1993 2 2 4 2 1 

1994 1 1 1 1 0 

1995 3 1 0 1 3 

1996 2 0 2 0 1 

1997 2 3 2 0 1 

1998 1 1 4 3 0 

1999 0 3 3 8 4 

Prior to 1998 28 percent (10 of the 36) of the plants built were of size greater than 3 mgd. 

However, in 1998 and 1999 55 percent (15 of the 27) of the plants built were of this size 

or greater. 

Table 5.7 contains selected survey results on the number of desalting plants built during 

the period 1993 to 1999. 

The results from Table 5.7a may be compared with those from the 1992 survey. The 

entries in the following table are percentages. 

Disposal option 1992 1999 (post-1992 data) 

Surface discharge 48% 45% 

Discharge to sewer 23 42 

Deep well 12 9 

Evaporation pond 6 2 

Spray irrigation 12 2 

 Total 100% 100% 

Data taken in these two surveys were different in one aspect: The 1992 survey used a 

plant size cutoff of 25,000 gpd, whereas the 1999 survey used a value of 50,000 gpd. 

The 1992 survey revealed that land-intensive disposal options are more typically 

restricted to smaller-sized plants having smaller volume concentrates. Thus the low 

number of evaporation pond and spray irrigation disposal sites in the 1999 survey for 

post-1992 plants may be, in part, attributable to this difference. An alternative 

interpretation, however, is that more of the recent plants dispose to the sewer than in 

previous times and that fewer dispose by evaporation pond and spray irrigation. 
 46 

Table 5.7 Selected Survey Results – Number of Desalting Plants 

by Category; Built 1993 - 1999

a. Discharge type by 

location 

 

 FL CA rest total % 

Surface 3 3 18 24 45.3 

Sewer 4 5 13 22 41.5 

deep well 5 0 0 5 9.4 

evaporation pond 1 0 0 1 1.9 

spray irrigation 1 0 0 1 1.9 

 totals 14 8 31 53 100.0 

 % 26.4 15.1 58.5 100.0 

 

b. Plant type by location 

 FL CA rest total % 

BRO 10 5 23 38 71.7 

ED 1 1 6 8 15.1 

SRO 0 1 0 1 1.9 

NF 3 1 2 6 11.3 

 totals 14 8 31 53 100.0 

 % 26.4 15.1 58.5 100.0 

 

c. Plant type by size (mgd) 

 

 <0.3 0.3-1 1-3 >3 total % 

BRO 9 9 9 11 38 71.7 

ED 1 3 1 3 8 15.1 

SRO 1 0 0 0 1 1.9 

NF 1 1 2 2 6 11.3 

 totals 12 13 12 16 53 100.0 

 % 22.6 24.5 22.6 30.2 100.0 

 

d. Size (mgd) by location 

 <0.3 0.3- 1 1-3 >3 total % 

FL 2 2 3 7 14 26.4 

CA 1 3 3 1 8 15.1 

rest of US 9 8 6 8 31 58.5 

 totals 12 13 12 16 53 100.0 

 % 22.6 24.5 22.6 30.2 100.0 

 

e. Disposal type by size 

(mgd) 

 

 <0.3 0.3- 1 1-3 >3 total % 

surface 5 4 6 9 24 45.3 

sewer 6 8 5 3 22 41.5 

deep well 0 1 0 4 5 9.4 

evaporation pond 0 0 1 0 1 1.9 

spray irrigation 1 0 0 0 1 1.9 

 totals 12 13 12 16 53 100.0 

 % 22.6 24.5 22.6 30.2 100.0 
 47 

For plant type by location, the comparison of Table 5.7b results with 1992 survey results, 

again in percentages, is: 

Plant Type 1992 1999 (post-1992 data) 

BRO 73% 72% 

SRO 5 2 

ED/EDR 11 15 

NF 11 11 

 Total 100% 100% 

Minor differences include the decrease in SRO plants and increase in ED/EDR plants. 

Table 5.7b data may be used to compare the more specific location of different type 

plants. Here data are again cast into percentages and compared with similar data from the 

1992 survey. 

 1992 1999 (post-1992 data) 

Plant Type FL CA Rest FL CA Rest

BRO 81% 58% 61% 71% 63% 74% 

SRO 2 42 0 0 13 0 

ED/EDR 2 0 32 7 12 19 

NF 15 0 7 22 12 7 

 Total 100% 100% 100% 100% 100% 100% 

The older trends still appear. Florida has a high percentage of BRO plants, no SRO 

plants, very few ED/EDR plants, and the highest percentage of NF plants. California has 

most of the SRO plants and few ED/EDR plants. Most of the ED/EDR plants continue to 

be in sites other than Florida and California. 

Skipping to Table 5.7d, the percentage data show that location of membrane plants has 

shifted since 1992. 

Plant Type 1992 1999 (post-1992 data) 

Florida 61% 26% 

California 9 15 

Other States 30 59 

 Total 100% 100% 

The result shows the large increase in plants in locations other than Florida. 

From data of Table 5.7c, 5.7d, and 5.7e the size of plants may be compared with those 

from the 1992 survey. These data are again in terms of percentages. 

 
 48 

Plant size 1992 1999 (post-1992 data)

< 0.3 mgd 56% 22% 

0.3 – < 1.0 17 25 

1.0 - <3.0 12 23 

>3.0 15 30 

 Total 100% 100% 

The clear trend is the building of larger plants. As part of the 1999 survey several pre1993 plants were contacted, plants that were previously contacted in the 1992 survey. 

Several small drinking water membrane plants in Florida were no longer in operation as 

the local utility found other more attractive means of obtaining potable water. Several 

small membrane utilities in Florida were bought out by larger utilities and subsequently 

closed down. Two reasons for this include population growth masking of former 

residential boundaries and challenges the plants were having in dealing with major ion 

toxicity issues (Mickley, 2000). For these same reasons this suggests that in addition to 

larger plants being built, fewer small plants are being built. The above numbers also 

show that plants built since 1992 are spread fairly evenly over the size ranges shown. 

From Table 5.7c it may be seen that there is a fairly even spread of plants over the size 

ranges for the different plant types as well. 

In the following table data from Table 5.7e, disposal method data as a function of plant 

size are recalculated in terms of percentages and compared with similar data from the 

1992 survey. 

1992 1999 (post-1992 data) 

Disposal option <0.3 0.3-<1 1-<3 >3 <0.3 0.3-<1 1-<3 >3

Surface disposal 44% 52% 53% 55% 42% 23% 50% 56% 

Disposal to sewer 23 35 18 15 50 69 42 19 

Deep well 4 4 29 25 0 8 0 25 

Evaporation pond 10 0 0 0 0 0 8 0 

Spray irrigation 18 9 0 5 8 0 0 0 

 Total 100% 100% 100% 100% 100% 100% 100% 100% 

Roughly similar trends with size are apparent in the 1992 and post-1992 survey results. 

Surface disposal appears to be a well used disposal option for all sized plants. While 

disposal to sewer is also widely used, its use falls off somewhat with larger sized plants. 

Deep well disposal is used primarily for larger plants. 

5.5 MF AND UF RESULTS 

At the time of the 1992 survey there was only 1 MF plant and no UF plants operating in 

WTPs and WWTPs. At the end of 1999 there were only 7 UF plants. There were, 

however, a total of 100 MF plants identified (operating as of 1999), that were of size 
 49 

25,000 gpd or greater. A total of 44 plants were surveyed. Out of the 100 plants 85 were 

Memcor systems. 

From the 44 surveyed plants, Table 5.8a shows that 48 percent of the plants dispose MF 

backwash to the sewer. For WWTP membrane systems this means recycling the 

backwash to some part of the wastewater treatment process. Approximately 36 percent 

of the surveyed plants dispose to surface waters. The remaining 16 percent of plants 

dispose to evaporation ponds, percolation ponds, septic tanks, and by irrigation, with no 

single method accounting for over 7 percent. There are no obvious trends with size of 

plant for any of the disposal methods. This is not unexpected since the backwash from 

MF processes is a small percentage of the feed flow to the process. Thus even for a 3 

mgd MF plant, the backwash stream might be only 60,000 gpd, a relatively small volume 

which can be disposed of by many different options. 

Table 5.8b lists the 85 Memcor plants by location and size. Almost one third of the 

plants are in California and one sixth are in Virginia. None of the MF plants are located 

in Florida, in sharp contrast to the membrane desalting plants. Three quarters of the 13 

membrane WWTPs are located in California and New York, with an equal number in 

each of these states. 

Table 5.8c shows that prior to 1996 only 1 of 19 plants was of size greater than 1 mgd. 

Since 1996, however, 25 of the next 66 plants built were larger than 1 mgd. 

Table 5.9 tallies the Memcor plants as of 1999 that were operating at WWTP and the 

dates of their starting operation. 

Table 5.9 shows the year and size of MF plant startups at WWTP sites. These data are 

not from the survey but from a tabulation of all known plants that formed the basis for 

Table 5.1. 

Table 5.9 MF Plants at WWTP Sites: Plant Size by Year of Startup 

 

 Size range in mgd 

Year <0.3 0.3 - < 1 1 - < 3 3 - 6 >6 Total

1994 0 2 0 0 0 2 

1995 0 0 0 0 0 0 

1996 0 0 0 0 0 0 

1997 0 2 1 0 0 3 

1998 1 2 2 1 0 6 

1999 1 3 1 1 1 7 

While the application of MF technology for reuse of WWTP effluent is relatively new, 

these figures suggest that this application will likely continue to grow.
 50 

Table 5.8 Memcor MF Plants in the 50 States of the US Through 1999 (>0

a. Disposal options by plant size (mgd) – survey data  0.3 0.3-<1 1-3 >3 total % 

surface 4 4 5 3 16 36.4 

sewer/recycle 5 4 7 5 21 47.7 

evaporation pond 1 0 0 0 1 2.3 

percolation pond 2 0 1 0 3 6.8 

Septic tank 1 0 0 0 1 2.3 

irrigation 0 0 1 1 2 4.5 

 13 8 14 9 44 100.0 b. Plant size (mgd) by location – Memcor plants  WTPs WWTPs G

state < 0.3 0.3-<1 1-3 >3 total % <0.3 0.3-<1 1-3 >3 total % T

California 21 0 0 2 23 31.9 0 2 2 1 5 38.5 

Virginia 7 3 4 0 14 19.4 0 0 0 0 0 0.0 

Hawaii 2 1 3 1 7 9.7 0 0 0 0 0 0.0 

Colorado 3 1 1 1 6 8.3 0 0 0 0 0 0.0 

New York 0 0 1 0 1 1.4 0 4 1 0 5 38.5 

Michigan 2 0 2 1 5 6.9 0 0 0 0 0 0.0 

Nevada 3 1 0 0 4 5.6 0 0 0 0 0 0.0 

Other 9 states 4 3 2 3 12 16.7 0 2 0 1 3 23.1 

 42 9 13 8 72 100.0 0 8 3 2 13 100.0 

c. Plant size (mgd) by year – Memcor plants 

< 0.3 0.3-<1 1-3 >3 total % 

1991 1 0 0 0 1 1.2 1992 0 0 0 0 0 0 1993 2 0 0 0 2 2.4 1994 9 2 0 1 12 14.1 1995 4 0 0 0 4 4.6 1996 6 0 2 0 8 9.4 1997 10 3 4 2 19 22.4 1998 8 6 4 4 22 25.9 1999 3 5 5 4 17 20.0 

 43 16 15 11 85 100.0 
 

 51 

CHAPTER 6. 

REGULATION – FEDERAL PERSPECTIVE 

6.1 INTRODUCTION 

6.1.1 Membrane Wastes: Membrane systems separate feedwater into a cleaner product 

water and a more concentrated stream that is called concentrate in RO, NF, and EDR 

systems and backwash in UF and MF systems. In the former systems TDS and most 

constituents of the feed stream are concentrated, and in the latter systems TDS is not 

concentrated but larger-sized species may be concentrated depending on size. The 

portion of the feedstream which ends up as concentrate or backwash varies considerably 

among the membrane processes ranging from as much as 70 percent in some seawater 

systems to as little as one percent in some MF and UF systems. Table 6.1 summarizes 

the characteristics of the different concentrates and backwash streams. 

Because of these different characteristics, and as seen in the survey results of Chapter 4, 

the disposal options used for the various concentrate and backwash streams also vary 

with membrane process. Consequently, the regulations that come into play with the 

different membrane processes vary. 

Cleaning wastes represent another membrane system waste. They are usually much 

lower in volume and generated only periodically. Most often cleaning wastes are either 

blended into the concentrate or backwash streams or are handled separately such as 

through bleeding to the sewer. The present study focuses on the concentrate and 

backwash streams generated in membrane processes. 

6.1.2 General Classification and Regulation of Membrane Concentrate and 

Backwash: In federal regulations, wastes are either industrial or municipal. The 

designation ‘municipal’ is restricted to wastewater treatment plant (WWTP) effluents that 

may contain bacteria and other microorganisms. Thus, membrane concentrate and 

backwash are, by definition, industrial wastes. 

For small plants of size 50,000 gpd or less, the State of Florida classifies membrane 

concentrate as ‘potable water byproduct’ instead of industrial wastewater. Present 

proposed legislation will extend this classification to larger plants. In addition the 

proposed legislation will create a technical advisory committee to assist in rule 

development regarding permit applications for concentrate disposal, specific options and 

requirements for concentrate disposal, requirements for evaluating mixing of effluents in 

receiving waters, and permitting requirements relating to the occurrence of major ion 

toxicity in concentrate (Mickley, 2000). This effort recognizes the nature and 

characteristics of membrane concentrate which stand in contrast to those of most 

industrial effluents that are characterized primarily by process added contaminants. 
 52 

Table 6.1 Characteristics of Concentrate and Backwash Streams 

 Typical Typical 

Membrane Feedwater Operating System System Ion What is 

Process TDS (mg/L) Pressure (psi) Recovery Rejection (%) Concentrated 

PROCESSES HAVING CONCENTRATES Seawater RO (SRO) 10,000 - 45,000 800 - 1,200 20 - 60 99+ (TDS) Salt, Dissolved organics

 Colloids, Bacteria, Cysts Particulates 

Brackish RO (BRO) 500 - 3,500 100 - 600 60 - 85 85-96 (TDS) Salt (lesser extent than 

 (low pressure) 95 - 98 (hardness) Most dissolved organics 3,500 - 10,000 Colloids, Bacteria, Cysts (high pressure) 

Nanofiltration Up to 600 50 - 150 75 - 90 80 - 90 (hardness) Salt (lesser extent than 

 Dissolved organics, Viru Colloids, Bacteria, Cysts

Electrodialysis Up to 7,500 Not applicable 70 - 90+ Effective monovalent Salt, Some polar organi

 ion removal can be >95 

PROCESSES HAVING BACKWASHES Ultrafiltration < 500 (not used Below 100 95+ Zero rejection of TDS Some organics, Some v

 to remove TDS) Some colloids, Bacteria Cysts, Particulates 

Microfiltration < 500 (not used Below 100 95+ Zero rejection of TDS Some bacteria, Cysts, P

 to remove TDS) 
 

 53 

The regulations covering disposal of concentrate or backwash depend on the particular 

disposal option utilized. In following sections, the federal and state regulations will be 

reviewed. 

The USEPA has not established any regulations that are specifically directed at disposal 

of water treatment plant residuals (which include membrane wastes). There are federal 

regulations associated with various acts, discussed below, that are applicable to 

membrane wastes. In some cases the federal regulations are only guidelines for the 

states, whereas in others the federal regulations are mandatory. Most states have been 

delegated by USEPA to take responsibility for establishing and administering regulations 

that will meet the requirements of the federal acts. The regulation of membrane wastes, 

therefore, is primarily the responsibility of the states. 

The next discussion is of the general framework for federal regulation, the USEPA, and 

federal acts forming the basis for USEPA programs. The discussion then highlights the 

specific federal acts that affect the different disposal methods for membrane wastes. 

Finally, the relation between federal, state, and local regulation of wastes is presented 

prior to discussion of the regulatory issues associated with each of the disposal methods. 

Both federal and state regulatory aspects are brought into this discussion. 

6.2 OVERVIEW 

6.2.1 Laws and Regulation: Laws and regulations are a major tool in protecting the 

environment. Congress passes laws that govern the United States. Once an act is passed, 

the House of Representatives standardizes the text of the law and publishes in the United 

States Code. The US Code is the official record of all federal laws. Laws often do not 

include all necessary details, and to put those laws into effect, to make the laws work on a 

day-to-day basis, Congress authorizes certain government agencies to create and enforce 

regulations. The authorized agency typically decides a regulation may be needed, 

researches it, proposes it, considers public comment, revises the regulation, and issues a 

final rule. Twice a year each agency publishes a comprehensive report that describes all 

the regulations it is working on or has recently finished. These are published in the 

Federal Register and the Unified Agenda of Federal Regulatory and Deregulatory 

Actions. Once a regulation is completed and has been printed in the Federal Register as a 

final rule, it is ‘codified’ by publication in the Code of Federal Regulations (CFR). The 

CFR is the official record of all regulations created by the federal government. It is 

divided into 50 volumes, called titles, each of which focuses on a particular area. Almost 

all environmental regulations appear in Title 40. The CFR is revised yearly. The full text 

of CFR Title 40, known as the Protection of Environment, is available via the internet in 

portable document format (pdf). Text is available from a Government Printing Office 

website (www.access.gpo.gov/su_docs/aces/aaces002.html) and a Cornell University site 

(www4.law.cornell.edu/uscode/index.html). 

6.2.2 Federal Acts Affecting Disposal of Membrane Wastes: In 1914 the US 

government issued very basic water quality standards, and in 1925 the US Public Health 

Service was given the lead role in addressing water quality issues. This situation 
 

 54 

remained until the formation of the Environmental Protection Agency (USEPA) in 1970. 

Since then, the federal government, through the USEPA, sets water quality standards, 

carries out appropriate studies and research, coordinates the work of other federal 

regulatory agencies, and supports the states in enforcing the standards. In a similar 

fashion the USEPA has come to oversee the protection of air, soil, and groundwater. 

More than a dozen major statutes or laws form the legal basis for the programs of the 

USEPA. These include: 

• NEPA (National Environmental Policy Act of 1969) 

• CAA (Clean Air Act) 

• CWA (Clean Water Act) 

• CERCLA (Comprehensive Environmental Response, Compensation and Liability 

Act) 

• EPCRA (Emergency and Community Right-To-Know Act) 

• ESA (Endangered Species Act) 

• FIFRA (Federal Insecticide, Fungicide and Rodenticide Act) 

• FFDCA (Federal Food, Drug, and Cosmetic Act) 

• FQPA (Food Quality Protection Act) 

• FOIA (Freedom of Information Act) 

• OSHA (Occupational Safety and Health Administration) 

• OPA (Oil Pollution Act of 1990) 

• PPA (Pollution Prevention Act) 

• RCRA (Resource Conservation and Recovery Act) 

• SDWA (Safe Drinking Water Act) 

• SARA (Superfund Amendments and Reauthorization Act) 

• TSCA (Toxic Substances Control Act) 

Only a portion of these acts and the resulting regulations apply to the disposal of water 

treatment plant (WTP) residuals. The waste disposal method and the corresponding 

applicable regulations (USEPA et al., 1996) are: 

Disposal method Applicable regulations

Surface disposal RCRA, NPDES (CWA), state and local regulations 

Disposal to WWTP State and local regulations 

Land application RCRA, DOT, state and local regulations 

Deep well injection RCRA, NPDES, state and local regulations 

Landfilling RCRA, CERCLA, state and local regulations 

Radioactive storage RCRA, DOT, DOE 

Evaporation ponds RCRA, NPDES, state and local regulations 

Incineration State and local air quality regulations (CAA) 

NPDES stands for the National Discharge Pollutant Elimination System. Note the 

inclusion of two non-USEPA agencies in this table: the Department of Transportation 

(DOT) and the Department of Energy (DOE). 
 

 55 

This table applies to all WTP residuals. Membrane wastes (concentrate, backwash, 

cleaning solutions, etc.) represent a subset of the WTP residuals that, in general, does not 

involve radionuclides or the disposal of solid waste material (such as via landfilling and 

incineration). Exceptions to this statement are discussed at the end of this chapter. 

Thus, for the vast majority of the cases for membrane waste disposal the above 

representation may be simplified considerably to: 

Disposal method Applicable regulations

Surface discharge NPDES (CWA), state and local regulations 

Disposal to WWTP State and local regulations 

Land application State and local regulations 

Deep well injection NPDES (CWA), SDWA (UIC), state and local regulations 

Evaporation ponds NPDES (CWA), state and local regulations 

UIC stands for Underground Injection Control. 

6.2.3 Impact of Drinking Water Requirements on Discharge Regulations: The 

reason membrane technology has made such an impact on the production of drinking 

water is twofold. First, where fresh water resources are not sufficient to meet demands 

such as due to population growth, membrane technology has become the technology of 

choice to produce drinking water from lower quality water sources. Second, as drinking 

water standards and requirements have tightened it has become more difficult for most 

conventional drinking water technology to achieve these treatment levels. Membrane 

technology, however, is well suited to attain most of these requirements, many of them 

with a single membrane system. 

Regulation of effluents is primarily under the federal Clean Water Act (CWA) and state 

regulations. Regulation of drinking water quality is primarily under the Safe Drinking 

Water Act (SDWA) and state regulations. There is a connection, however, between the 

increasing requirements for higher quality drinking water and the increasingly more 

stringent effluent discharge regulations. 

The SDWA also calls for protection of the source waters used for drinking water. Thus 

while membrane technologies are well suited to meet the treatment needs, at the same 

time it is becoming more difficult to dispose of the concentrate and backwash generated 

by the membrane processes – due to the possibility of concentrate disposal having a 

negative impact on the source water (surface water and groundwater) quality. 

Another relationship between drinking water standards (via SDWA) and water quality 

standards (via CWA) is that for certain water body classifications some states use the 

drinking water standards as the water quality standards. As the drinking water standards 

tighten the water quality standards also tighten for these waters. 

6.2.4 Federal and State Regulatory Interface: All states must conform to the federal 

regulations. States may elect to oversee some of the federal regulatory programs 
 

 56 

themselves, in which case they must meet federal regulatory program guidelines and 

become ‘delegated’ by the USEPA. The states, once delegated, continue to interact with 

the USEPA in terms of reporting and communicating status and other items; however, in 

these primacy states the regulatory decisions are made at the state level. Since there are 

separate federal programs that must be adhered to, a state may become delegated with 

respect to one program and not another. Three federal programs, the NPDES program 

(under CWA) for surface water protection, the UIC program (under SDWA) for control 

of well injections and more generally for groundwater protection, and the pretreatment 

program (under CWA) for discharge to the sewer apply for the discharge of membrane 

wastes. Table 6.2 is a list of the delegation status of states for these federal programs. 

States that have not been granted complete authority are not excluded from the permitting 

process, but generally work closely with the regional administrator in the application and 

evaluation process. For example, the USEPA must obtain state certification prior to 

issuing an NPDES permit. This process allows non-delegated states to have a voice in if, 

when and where a permittee can discharge to a surface water (Mickley et al., 1993). 

6.2.5 State and Local Programs: Regulatory protection of public water supply sources 

is more directly provided through state and local laws and ordinances. In addition to the 

implementation of federal laws and regulations, individual states, supported as necessary 

by the USEPA, may provide comprehensive protection through the adoption of statewide 

water quality standards and criteria. These state programs generally establish quality 

standards for surface and groundwater, and may include goals, best-use determinations, 

and a classification system for the water sources. These reflect regional circumstances, 

but must be at least as strict as federal standards. States are charged with enforcement of 

standards and development of their own certification and training programs. 

 

In addition, individual state programs exist that provide source protection through 

sanitary regulations, regulations of inland wetland areas, and other means of watercourse 

and aquifer protection. 

Local governments work within the federal and state guidelines to build and operate 

facilities, implement land use plans and local regulations to protect water supplies, and 

carry out other relevant activities. The individual water supply utility can best integrate 

these protective mechanisms into its own source water quality management program by 

working cooperatively and providing effective enforcement to mutual advantage. Such 

participation by the water utility should be directed toward the adoption of practical laws 

and regulations that provide tangible benefits in terms of enhanced protection of source 

waters (Pontius, 1990). 

Local public programs are also available to public water supply utilities for the 

enhancement of source water protection. A public education approach, both in schools 

and at large, can be used to increase awareness and to avoid indiscriminant disposal of 

harmful contaminants. This can result in enhanced protection and improved community 

relations. Concerned individuals and groups propose additional standards through 

initiative processes. Such standards usually rely on public referenda, often at the state 

level, for adoption. 
 

 57 

Table 6.2 Delegation status of states for Federal programs 

States by 

USEPA 

Regions 

Approved 

NPDES 

Program 

Approved 

States 

Pretreatment 

Program 

Approved 

States 

General 

Permit 

Approved 

States UIC 

Program 

Region I 

Connecticut 09/26/73 06/03/81 03/10/92 03/26/84 

Maine --- --- --- 09/26/83 

Massachusetts --- --- --- 12/23/82 

N. Hampshire --- --- --- 10/21/82 

Rhode Island 09/17/84 09/17/84 09/17/84 08/15/84 

Vermont 03/11/74 03/16/82 08/26/93 07/06/84 

Region II 

New Jersey 04/13/82 04/13/82 04/13/82 08/15/83 

New York 10/28/75 --- 10/15/92 --- 

Virgin Islands 06/30/76 --- --- --- 

Puerto Rico --- --- --- 07/29/92 

Region III 

Delaware 04/01/74 --- 10/23/92 05/07/84 

Maryland 09/05/74 09/30/85 09/30/91 06/04/84 

Pennsylvania 06/30/78 --- 08/02/91 --- 

Virginia 03/31/75 04/14/89 04/20/91 --- 

West Virginia 05/10/82 05/10/82 05/10/82 --- 

Region IV 

Alabama 10/19/79 10/19/79 06/26/91 08/25/83 

Florida 05/01/95 05/01/95 05/01/95 03/09/83 

Georgia 06/28/74 03/12/81 01/28/91 05/21/84 

Kentucky 09/30/83 09/30/83 09/30/83 --- 

Mississippi 05/01/74 05/13/82 09/27/91 09/26/83 

North Carolina 10/19/75 06/14/82 09/06/91 04/19/84 

South Carolina 06/10/75 04/09/82 09/03/92 07/24/84 

Tennessee 12/28/77 08/10/83 04/18/91 --- 

Region V 

Illinois 10/23/77 --- 01/04/84 03/03/84 

Indiana 01/01/75 --- 04/02/91 08/19/91 

Michigan 10/17/73 04/16/85 11/29/93 --- 

Minnesota 06/30/74 07/16/85 11/29/93 --- 

Ohio 03/11/74 07/27/83 08/17/92 01/14/85 

Wisconsin 02/02/74 12/24/80 08/17/92 1/14/85 

Region VI 

Arkansas 11/01/86 11/01/86 11/01/86 07/06/82 

Louisiana 08/27/96 08/27/96 08/27/96 03/23/82 

New Mexico --- --- --- 08/10/83 

Oklahoma 11/19/96 11/19/96 09/11/97 07/24/82 
 

 58 

Texas 09/14/98 09/14/98 09/14/98 02/07/82 

Region VII 

Iowa 08/10/78 06/03/81 08/12/92 --- 

Kansas 06/28/74 --- 11/24/93 12/02/83 

Missouri 10/30/74 06/03/81 12/12/85 12/02/83 

Nebraska 06/12/74 09/07/84 07/20/89 06/12/84 

Region VIII 

Colorado 03/27/75 --- 03/04/82 04/02/84 

Montana 06/10/74 --- 04/29/83 11/19/96 

Nevada 09/19/75 --- 07/27/92 10/05/88 

North Dakota 06/13/75 --- 01/22/90 10/05/84 

South Dakota 12/30/93 12/30/93 12/30/93 12/07/84 

Utah 07/07/87 07/07/87 07/07/87 07/20/90 

Wyoming 01/30/75 --- 09/24/91 08/17/83 

Region IX 

Hawaii 11/28/74 08/12/83 09/30/91 --- 

California 05/14/73 09/22/89 09/22/89 05/11/84 

Region X 

Alaska --- --- --- 06/19/86 

Idaho --- --- --- 07/22/85 

Oregon 09/26/73 03/12/81 02/23/82 10/09/84 

Washington 11/14/73 09/30/86 09/26/89 09/24/84 
 

 59 

6.3 SURFACE WATER DISCHARGE 

6.3.1 General Considerations: Membrane wastes may be discharged to surface waters 

either directly or following passage over the soil. Ultimate disposal is by dilution in a 

receiving water. Such disposal by dilution in large bodies of water is by far the most 

common method of wastewater disposal (including membrane wastes) in the United 

States today (Mickley et al., 1993). 

In natural streams there is a balance between plant and animal life. Waters of good 

quality are characterized by a multiplicity of species with no dominance. Organic matter 

that enters the stream is broken down by bacteria to ammonia, nitrates, sulfates, carbon 

dioxide, and the like, which are utilized by plants and algae to produce carbohydrates and 

oxygen. Introduction of excessive quantities of waste material can upset this natural 

cycle. Historically this fundamental approach of letting nature finalize the treatment of 

wastes was taken. However, nature can only do so much, and the assimilative capacity of 

the receiving waters was exceeded and pollution resulted (Metcalf & Eddy 1979). 

The amount of natural or self-purification capacity in the receiving water depends on its 

flow or volume, its oxygen content and ability to reoxygenate itself, currents, 

sedimentation, bottom deposits, sunlight, and temperature. The proportion of the 

assimilative capacity that can be safely utilized in rivers, lakes, and the like, depends on 

how the water is used elsewhere, the desires of the people, and the self-purification 

capacity of the receiving water system (Metcalf & Eddy 1979). 

Water pollution control is concerned with the protection of the aquatic environment and 

the maintenance of water quality in lakes, reservoirs, streams, rivers, estuaries, and the 

oceans. The desired or required water quality that must be maintained depends on the 

uses to be made of the water. Therefore, water quality criteria must be available for 

alternative beneficial uses if the adequacy of various pollution control measures is to be 

assessed properly. Domestic water supply, industrial water supply, agricultural water 

supply, water for recreational uses, and water for fish, other aquatic life, and wildlife are 

well established beneficial uses. Once the criteria necessary for the protection of the 

various beneficial uses have been established, it is possible to set standards for surface 

waters with the stipulation that no discharge shall create conditions that violate them 

(Metcalf & Eddy 1979). 

6.3.2 Federal Programs: The federal program to protect the quality of the nation’s 

water bodies is authorized under the Federal Water Pollution Control Act (FWPCA) of 

1972. The statute has been amended several times and renamed the Clean Water Act 

(CWA). The CWA was the first of a series of national environmental laws; it directly 

regulates the introduction of contaminants into surface waters and groundwaters. 

The act and associated regulations attempt to ensure that water bodies maintain the 

appropriate quality for their intended uses, such as swimming, fishing, navigation, 

agriculture, and public water supplies (USEPA et al., 1996). 

 
 

 60 

The national regulatory program includes the Effluent Guidelines Program to develop 

limitations and standards for all facilities that discharge or may discharge directly into 

waterways of the United States or that indirectly discharge or may discharge into publicly 

owned treatment works (POTWs). 

The national regulatory program also created the National Pollutant Discharge 

Elimination System (NPDES), which sets minimum treatment standards for surface water 

dischargers and also establishes the framework for setting additional discharge standards. 

Under Section 402 of the CWA, any direct discharge to waters of the United States must 

have an NPDES permit. The permit specifies the permissible concentration or level of 

contaminants in a facility’s effluent. 

Under the NPDES the administrator of the USEPA may issue permits for the discharge of 

any pollutant or combination of pollutants upon condition that such discharge will meet 

all applicable requirements of the CWA relating to effluent limitation, water quality 

standards and implementation plans, new source performance standards, toxic and 

pretreatment effluent standards, inspections, monitoring and entry provisions, and 

guidelines establishing ocean discharge criteria. Permit holders (point sources, except for 

POTWs) were required to achieve, not later than July 1, 1977, effluent limitations that 

require the application of the best practical control technology currently available. 

POTWs were required to achieve secondary treatment by the same date, and all point 

source dischargers must comply with applicable water quality standards requirements. 

Point sources in this definition means any discernible, confined, and discrete conveyance, 

including but not limited to any pipe, ditch, change, tunnel, conduit, well, discrete fissure, 

container, rolling stock, concentrated animal feeding operation, vessel, or other floating 

craft, from which pollutants may be discharged. NPDES is the system by which the 

administrator can issue, condition, and deny permits for the discharge of pollutant from 

point sources into the navigable waters, the contiguous zone, and the ocean. Dischargers 

required to obtain permits include, among other point sources, municipal and other 

POTWs, industries discharging directly to navigable waters, and concentrated animal 

feeding operations. 

States are authorized to act as the primary agent for the NPDES program, provided they 

meet all USEPA requirements. States meeting such requirements become ‘delegated’ 

states. A list of the delegated states was given in Table 6.2. For states not granted 

primacy, USEPA regional offices issue NPDES permits. State regulations controlling the 

discharge of membrane wastes can vary from state to state. 

In general, without regard to membrane drinking water plants or water treatment plants, 

the NPDES permit specifies effluent levels dependent on technology-based effluent 

limitations, water quality standards, or both. These water quality standards may be both 

numeric and narrative. Under Sections 301 and 304 of the CWA, USEPA is required to 

establish national effluent limitations for major categories of industrial dischargers. 

These limitations take into consideration the best available technology that can 

economically be used to treat industrial effluent for surface water discharge. While 
 

 61 

technology-based limitations have been developed for many different industries, they 

have not yet been issued for water treatment plant residuals. Federal guidelines for 

controlling WTP discharges were drafted but never fully implemented (USEPA, ASCE, 

AWWA, 1996). Because of this, NPDES permits issued for WTP discharges are based 

only on water quality standards (numeric and narrative). 

6.3.3 Federal Guidelines - General: To assist the states in this requirement, the CWA 

requires USEPA to publish (and update) ambient surface water quality criteria. The 

criteria are not legally enforceable but are intended as guidance towards the development 

of discharge standards and in determining potential environmental impact of a given 

discharge on surface water. The Water Quality Criteria include aquatic life values (fresh 

acute, fresh chronic, marine acute, and marine chronic LOEL - lowest observed effects 

level - values) and human health values (water and fish ingestion and fish consumptiononly values). 

 

The CWA lists a number of water uses for the states to consider. Those used by a given 

state vary, but most include: aquatic life, drinking water supply, agricultural, and 

recreational. Recreational standards are typically based on bacteriological values and in 

some states dissolved oxygen values. Some agricultural criteria were developed in the 

early 1970’s. Many states use aquatic life criteria. Drinking water supply standards 

consider both drinking water standards developed under the SDWA and the human health 

part of the CWA WQ criteria. 

 

Every water is classified by the state as having a designated use, and the standards that 

apply are dictated by the use classifications. For example, one water may have aquatic 

life use only, while another may be classified as having aquatic life use, drinking water 

use, and human health exposure. In the first case aquatic life standards apply, whereas in 

the second case several standards apply. In all cases the most stringent value of all those 

state standards appropriate for the particular use designation applies. For carcinogens, 

the human standards are generally tighter. Part of the reason for this is that for humans 

the carcinogen level protects against one in a million occurrence and this level of concern 

is not applied to fish. For non-carcinogens, with a few exceptions such as nitrates, 

perhaps 90 percent of the water quality standards are tighter than drinking water 

standards. This is because aquatic life is more sensitive mainly from dosage 

considerations. For metals, the aquatic life values are generally the tightest; for organics, 

it is usually the human values. There are also differences among aquatic life. For 

example, coho and trout streams have tighter standards than streams with other aquatic 

life because these fish are more sensitive. 

States thus require that certain concentration levels be met in surface waters. The values 

vary from state to state, but are at least as stringent as the federal recommendations. 

These are ambient criteria; that is, they relate to the concentration of a pollutant in the 

surface water and not in the discharge itself. The correlation between the concentration 

of a particular constituent in a discharge and its effect on receiving water will depend on 

a number of variables, including the dilution and mixing capacity of the receiving water. 

Generally, the more the concentration of a particular constituent is above its criteria level 
 

 62 

(in the discharge), the higher the likelihood of environmental damage in the receiving 

water. More specifically, certain in-stream water quality standards must be met at the 

edge of a mixing zone to allow direct discharge of the effluent. 

The states use the water quality criteria documents published by USEPA, as well as other 

advisory information, as guidance in setting maximum pollutant limits. USEPA reviews 

and approves the state standards. The state standards can be more stringent than the 

allowable discharge that will meet the USEPA in-stream water quality criteria. 

In addition to the numeric criteria there are narrative criteria as developed by the USEPA 

Whole Effluent Toxicity (WET) Program. 

6.3.4 Federal Guidelines – Specific: Under Section 303 of the CWA, each state is 

required to establish ambient Water Quality Standards (WQS) for its water bodies. These 

standards define the type of use and the maximum permissible concentrations of 

pollutants for specific types of water bodies. In addition, the WQS further defines the 

water quality goals of a water body, or portion thereof, by establishing anti-degradation 

policies and implementation procedures that serve to maintain and protect water quality. 

The WQS regulations, Section 131.1, also encourage states to adopt both numeric and 

narrative criteria. Aquatic life criteria should protect against both short-term (acute) and 

long-term (chronic) effects. 

As specified in 40 CFR 131.10, each state must identify the designated use of the 

individual water body for which they are set. In the case where a water body has multiple 

designated uses, the criteria must protect the most sensitive designated use. In the 

numerical criteria the states are recommended to establish values based on 304(a) 

guidance adapted for site-specific conditions, or use scientifically defensible methods. 

For narrative toxicity criteria the stats are recommended to establish criteria based on 

toxicity test methods where numeric criteria are not established or to supplement numeric 

criteria. Antidegradation Policy 40 CFR 131.12 ensures that once a use is achieved, it 

will be maintained. As part of their WQS each state must develop and adopt an Antidegradation Policy and identify methods for implementing the policy. The policy should 

at a minimum delineate how the state shall maintain water quality in water bodies where 

existing uses are being met, how the state shall maintain water quality in cases where 

uses are exceeded, whether they will allow lower water quality in cases where it is 

necessary to accommodate important economic or social development in the areas, and 

how the state will protect Outstanding National Resource Waters. Finally the policy must 

be consistent with the CWA Section 316 for thermal discharge. A new antidegradation 

requirement was recently added and the NPDES permitting regulations were revised to 

implement the requirement. The changes affect discharges into water bodies that are not 

attaining water quality standards. These changes include revisions of the Total 

Maximum Daily Load (TMDL) regulations so that TMDLs can more effectively 

contribute to improving the nation’s water quality. 

6.3.5 USEPA WET Program: Whole Effluent Toxicity tests (exposure of various test 

species to 100 percent effluent and various dilutions of it) have been in use as a 
 

 63 

regulatory tool in the NPDES program since the mid-1970s when USEPA Region IV 

conducted and required on-site flow-through acute toxicity testing at selected industries 

as part of a Section 308 (a)(4)(iii) permittee’s monitoring requirement. During the 1980s 

chronic test methods were developed and included as permit requirements along with 

acute limits as a regulatory tool. The 1984 USEPA policy addresses the technical 

approach for assessing and controlling the discharge of toxic substance to the Nation’s 

waters through the NPDES permit program. During the 1990s the program gained 

experience and led State and Federal agencies to build upon successes and adjust the 

program as warranted. USEPA manuals provide guidance for the states in using WET 

tests. 

Previously, pollutant limits in the NPDES permits were based on treatment technology 

and chemical-specific standards. Overall, however, toxicity is not simply the sum of the 

individual pollutants. Synergistic effects can increase or decrease the toxicity of an 

individual pollutant. In 1984 the USEPA issued a new policy under which pollutant 

limits are based also on the quality of the receiving water. To assess the toxicity of an 

effluent to receiving water, bioassay tests are conducted that directly expose selected test 

organisms to various effluent dilutions for a specified period of time. The requirement to 

perform bioassays has been written into many NPDES permits and is being incorporated 

into virtually all new permits. 

WET testing is one aspect of an integrated toxics control strategy using both chemicalspecific numerical limits and biologically based whole effluent procedures. Chemicalspecific and whole effluent testing approaches have different advantages and limitations. 

An effective toxics control program therefore will have to include both. This integrated 

approach is emphasized in the new Section 303(C)(2)(B) of the CWA, as amended by the 

Water Quality Act of 1987. 

Bioassays and biomonitoring are carried out using species that occur in the receiving 

waters or closely related species. Fish, invertebrates, and plants may all be considered 

for biomonitoring. The toxicity endpoints or measurements may be acute, chronic, or 

both. The acute toxicity test is a measure of the organism’s survival rate. Chronic 

toxicity occurs when the survival, growth, or reproduction rates of the test species 

exposed to the effluent are significantly less than those of the control specimens. The 

bioassay tests are conducted at certified laboratories and can be time consuming and 

expensive to run. The type of toxicity test, species used, and frequency of testing vary 

widely. 

The general NPDES implementation procedures for whole effluent toxics control 

(WETC) testing are described in Figure 6.1. The procedures may vary slightly from state 

to state, but are expected to be similar for all. Flexibility exists in the type of species 

selected (they must be of equivalent sensitivity), monitoring frequency, and exact dates 

for implementation by the permittee. However, any deviation from the diagram must be 

justified in the “statement of basis” accompanying the permit. Also, major permits must 

require two-species testing, completions of a toxicity reduction evaluation (TRE) if 

toxicity is determined, and an appropriate limitation of WET after approximately 3 years. 
 

 64 

This process may be accelerated for any discharger singled out of control. A more 

stringent definition than is provided by the NPDES program of when chronic or acute 

toxicity has been demonstrated is left to the discrepancy of the state regulatory authority. 

A specific definition can be incorporated into the permit or it can be left to the judgment 

of the regulatory authorizing agency, much as it is now for all other permit limitations. In 

this latter case, it would be up to the permit-issuing authorizing 

agency to notify the permittee that the WET results had demonstrated toxicity and that 

the required TRE should be immediately implemented. 

Actual procedures to be followed in a TRE are expected to be different for each 

individual site. In addition, the discharger will always be more familiar with his 

operation than the regulatory agency, and an excessive amount of procedural detail may 

inhibit an innovative approach. In any event, a TRE in most cases should include the 

following elements, most of which are self-evident (Martin 1992). 

Figure 6.1 NPDES Implementation Procedure for Whole Effluent Toxics Control 

Program 

Receiving water of 

No low flow dilution Yes

Chronic tests 

Two species

Acute tests 

Two species

Discharge exceeds 20 mgd for a 

POTW or 10 mgd for an industry?

Discharge exceeds 20 mgd for a 

POTW or 10 mgd for an industry?

No Yes No Yes

Quarterly 

testing

Monthly 

testing

Quarterly 

testing

Monthly 

testing

Acute toxicity demonstrated 

during the first year

Acute toxicity demonstrated 

during the first year

No Yes No Yes

Reduce testing 

to single species 

only; once every 

quarter

Conduct a TRE 

during next year; 

Continue testing 

as before

Reduce testing 

to single species 

only; once every 

quarter

Conduct a TRE 

during next year; 

continue testing 

as before

Effective 3 years after permit 

issuance, apply an effluent limit of 

no chronic toxicity

Effective 3 years after permit 

issuance, apply an effluent limit of 

no acute toxicity – all dilutions
 

 65 

If toxicity has been established, initial efforts should focus on characterization and 

identification of the toxicant(s). Procedures exist for rapidly narrowing the possibilities 

to certain groups of pollutants such as metals, nonpolar organics, and so forth. It is 

anticipated that in many cases the TRE may essentially terminate at this point if it is 

conclusively shown that the problem is due to one distinct pollutant whose source and 

method of correction are both known. The pollutant may already be controlled through a 

compliance schedule linked to a numerical limit. Alternatively a numerical limit or 

compliance schedule or both may be imposed on the permittee following negotiation. 

Once the toxicant has been identified, the objective is its elimination by process controls, 

pretreatment, combined water stream treatment, or other means. 

If the toxicity problem cannot be readily identified even with diligent effort on the part of 

the permittee, the authorizing agency may be persuaded to grant additional time for 

compliance. However, the discharger must convince the regulatory agency that a diligent 

and thorough TRE has been done and that more time is needed to address the problem. 

Only then is permit relief likely to be granted. 

In some instances concentrate dischargers have encountered discharge permit problems 

based on WET testing. For instance, discharge permits for new RO facilities are 

generally issued on a temporary basis prior to facility completion. Estimates are required 

of the quantity and quality of the concentrate eventually to be discharged. This 

estimation can be difficult and inexact. If available, pilot plant data are a much better 

source of discharge information. A temporary discharge permit is issued and 

construction of the facility goes forward on the assumption that a permanent permit will 

eventually be issued on this basis. The tests require an actual concentrate; therefore, 

when the plant initiates operation, a full toxicity analysis is conducted. In at least one 

instance, a new plant was built based on a preliminary discharge permit and was then 

denied a permanent permit because it failed the WET test. Although the WETC program 

allowed a grace period for the effluent to be brought within standards, the extra time and 

expense were not anticipated or budgeted. 

6.3.6 Surface Water Discharge Permitting Process: The process is to look at all use 

classifications for the potential receiving water, then look at all the standards that apply. 

The most stringent standard for a given pollutant applies. The calculation of the permit 

limit begins with the appropriate standard. A waste load calculation is made, which takes 

into account concentration and flow of discharge, and the flow, concentration and 

standard of the receiving body. A mixing zone calculation is one aspect of the waste load 

calculation. A chronic permit limit is the value to be met at the edge of the mixing zone. 

The acute value is the value met at the end of the discharge pipe. If the background 

concentration is greater than the standard, an ambient standard can be used, but the 

effluent must not be worse than the ambient standard. 

6.3.6.1 Implementation Policy: The WQS regulation allows the states to include in their 

standards state policies and provisions regarding WQS implementation. Often these 

address issues such as mixing zones, variances, and low flow exemptions. It is 

recommended that the policy also include information on the implementation of WET 
 

 66 

criteria, such as the use of mixing zones, test species and methods. All policies related to 

criteria development should include reference to the three criteria components 

(magnitude, duration, and frequency). Magnitude established how much of a pollutant 

(or pollutant parameter such as toxicity) expressed as concentration is allowable. 

Duration establishes the period of time (averaging period) over which the receiving water 

concentration is averaged for comparison with criteria concentrations. Frequency 

establishes how often criteria may be exceeded; USEPA uses a 3-year return period. 

Magnitude, duration, and return frequency provisions of WET criteria are used in the 

development of waste load allocations and effluent limitations to control the WET of the 

discharge. 

6.3.6.2 Definition of Effluent Limitations: Effluent limitations for each permit will, at a 

minimum, meet the applicable federal effluent limitations. More stringent limitations 

may be set at the state or local level. Technology-based effluent limitations do not apply 

to concentrate or backwash because it does not fall under the requirements of Section 301 

of the federal CWA (point source industrial category). 

Where effluent limitations will not provide treatment sufficient to meet water quality 

standards for the receiving waters, more stringent effluent limitations standards will be 

based on application of appropriate physical, chemical, and biological factors reasonably 

necessary to achieve the levels of protection required by the standards. Such 

determinations shall be made on a case-by-case basis. When this scenario is applicable, 

the permit will be written with effluent limitations that respect the methods by which 

water quality standards were derived and the degree of variation of water quality that 

exists in the relevant stream segment on a seasonal basis, or otherwise. A mass balance 

analysis is used to define the effluent limitations such that the combined concentrations 

of pollutants contributed by the discharger and the receiving waters upstream for the 

point of discharge do not exceed the water quality standards for the receiving waters 

downstream of any established mixing zone. Figure 6.2 and the accompanying equation 

are used for the analysis. 

For most pollutants the authorizing agency will assign effluent limitations defined from 

the mass balance analysis described above as the 30-day average value in the permit. If 

the pollutant has a relatively acute toxic effect, the resultant concentration will be 

assigned to a shorter-term average, such as a 7-day or daily maximum. 

The authorizing agency will exercise its best engineering judgment in writing effluent 

limitations based on water quality standards and will give consideration to other 

regulations, as well as other factors such as mixing zone studies, seasonal low flows, 

bioassays, and biosurveys. 

Once the discharge limits are known, they can be used to develop the design of the 

discharge system. Useful discharge limitations data include: 

• Which constituents will be limited 

• Concentrations of the limited constituent 
 

 67 

• Seasonal variations allowed for the constituents 

• Hazardous or toxic limitations for any constituents 

• Monitoring requirements for any constituents 

• Receiving-stream data such as flow rate, existing quality, and stream 

specifications 

With the raw water quality data it is possible to accurately predict the concentration of 

constituents in the concentrate before installation by using various methods, including 

computer programs and vendor data. 

6.3.6.3 Monitoring, Recording, and Reporting: Any discharge authorized by a discharge 

permit may be subject to such monitoring, record keeping, and reporting requirements as 

may reasonably be required in writing by the authorizing agency.. All permits specify 

required types, intervals, and frequencies of monitoring sufficient to yield data 

representative of the monitored activity including, when appropriate, continuous 

monitoring. To assure compliance with permit limitations, at least the following will be 

required of the permittee: 

• Monitoring of the mass (or other specified measurement) for each pollutant 

limited in the permit and of the volume of effluent discharged from each outfall 

• The provision of access to the authorizing agency (with the appropriate 

credentials) to sample the discharge at a point after the final treatment process (if 

applicable) but prior to the discharge mixing with the receiving waters 

• Records of monitoring activities and results, which will include for all samples: 

o The data, type, exact place, and time of sampling or measurements 

o The individual(s) who performed the sampling or measurements 

o The data the analyses were performed 

o The individual(s) who performed the analyses 

o The analytical techniques or methods used 

o The results of such analyses 

Figure 6.2 Diagram of a Stream Mixing Zone 

 Receiving Stream 

 Mixing Zone

Discharge Concentration (Y) (ppm) 

Flow rate (Q1) (mgd)

Upstream 

Concentration (X) (ppm) 

Flow rate (Q0) (mgd)

Downstream 

Concentration (Z) (ppm) 

Flow rate (Q0 + Q1) (mgd) X * (Q0) + Y * (Q1) = Z * (Q0 + Q1) 
 

 68 

• Retention, for a minimum of 3 years, of records of all monitoring information 

including all original strip chart recordings for continuous monitoring 

instrumentation, all calibration and maintenance records, copies of all reports, and 

records of all data used to complete the application for the permit 

• Reporting at whatever time interval the authorizing agency reasonably determines 

to be necessary 

6.3.6.4 Permit Duration: The duration of an NPDES permit is for a fixed term and will 

not exceed 5 years. A permit may be transferred to an new permittee, if both: 

• The current permittee notifies the authorizing agency in writing 30 days in 

advance of the proposed transfer data 

• The notice includes a written agreement between the existing and new permittees 

giving a specific date of the transfer of permit responsibility, coverage, and 

liability 

The permit duration is important for the applicant whose facility or process may change 

in less than 5 years. A decision must be made as to how the original permit will be 

written. For instance, the concentrate for the first 2 years of facility operation may be 25 

to 30 gpm; however, the owner or operator knows that the concentrate stream will 

increase after 2 years to between 75 and 100 gpm. The original permit may be written for 

25 to 30 gpm and then be amended when the discharge increases; or the original permit 

may be written for between 75 and 100 gpm form the very start. Flow rate is a simple 

example. More complications arise if there will be changes in the raw water quality or 

pretreatment, both of which affect the constituent of the concentrate, or in operation of 

the system that affects concentrations of rejected constituents. 

6.3.6.5 Generalities about NPDES Permits: Dischargers from point sources (individual 

discrete facilities) into surface water must obtain an NPDES discharge permit from the 

appropriate state regulatory agency (dependent on state delegation status). The NPDES 

permit application process in most states requires 180 days before any discharge takes 

place, or to renovate their permit, or the discharger will make significant changes to the 

existent permit. A set of forms is involved. USEPA form 1, the application, is the 

standard form to initiate the process. Form 1 requires general facility information such as 

name, address, telephone, contact person, standard industrial classification codes, and 

nature of the business, operator information, existing environmental permit, and a 

topographic map that covers at least one mile beyond property lines. 

Form 2C provides wastewater discharge information. This form requires information 

concerning flows, source of pollution, and treatment technologies, production and 

improvement to reduce pollutants in the discharge point, effluent characteristics, 

biological toxicity data, and analytical contractor information. 

Facilities that do not discharge process water will fill out EPA form 2E. This form 

requires information concerning the receiving waters, discharged dates, type of waste, 
 

 69 

effluent characteristics, indication if the discharge will be intermittent or seasonal, and 

the treatment systems. 

Each state will include additional forms depending on the different programs associated 

with the NPDES program. For example, there are forms for Discharge of Storm Water, 

Combined Sewer Overflow, Land Irrigation, and injection wells that are regulated under 

the UIC program. 

Once a draft permit is generated, the state issues notice for a public hearing providing 

stakeholders a copy of the draft permit. The public hearing length is subject to the level 

of response received by the state. In some states this step is conditional to the level of 

controversy associated with the permit. After considering the public comments and a 

final review, the permit is either granted or denied. A site inspection is typical before the 

start of a new operation. The permit is valid for a maximum of five years. After 

approval the state agency in charge of the permit has the right to inspect the facility 

annually or as deemed necessary, reserving the authority to revoke or suspend a permit 

for noncompliance of any standard, limitations or other permit requirements. Civil 

penalties may also be imposed for noncompliance. 

6.4 DISPOSAL TO SEWER 

6.4.1 Disposal to Sewer: An NPDES permit is not required for a discharge to a POTW. 

Each direct discharger must have an NPDES permit specifying, among other things, the 

required waste quality, and must submit regular reports to the regulatory agency. Under 

these regulations, a membrane treatment facility must obtain an NPDES permit to 

discharge directly to a surface water. 

The NPDES permit requires compliance with all federal standards and may also require 

additional controls based on local conditions. A POTW may have trouble meeting the 

NPDES permit conditions if the concentration of pollutants flowing into the treatment 

plant is too high. One way to control the concentration of these pollutants is to require 

pretreatment by the individual industrial dischargers prior to discharge. This control was 

provided by the implementation of the National Pretreatment Program in 1981. 

The CWA also called for the USEPA to develop national pretreatment standards to 

control industrial discharges into sewage systems. The standards are uniform national 

requirements that restrict the level of certain industrial wastewater pollutants discharged 

into the sewage system. All POTWS must enforce the federal standards. The standards in 

effect today consist of two sets of rules: categorical pretreatment standards and prohibited 

discharge standards. 

Categorical pretreatment standards are organized by type of industry, and different 

requirements are mandated for each specific industry as part of the CWA Effluent 

Guidelines Program. For example, a categorical standard for the iron and steel industry 

limits the concentrations of ammonia, cyanide, and other specific pollutants that may be 

present in the wastewater discharged. 
 

 70 

Prohibited discharge standards forbid any discharge to sewer systems of certain types of 

waste from all sources. For example, the release of any wastewaters with pH lower than 

5.0 is prohibited because such wastes may corrode the sewer system. 

Membrane treatment facilities are classified “industrial” by default because they are not 

considered POTWs (for municipal wastewater treatment) and therefore must abide by the 

prohibited discharge standards when discharging into the local sewage system. Also no 

point source category (e.g., steel mills) exists for membrane treatment facilities. The 

categorical pretreatment guidelines pertain to the primary industrial point sources. 

Concentrate and backwash are not regulated as a primary industrial point source. 

6.5 DISPOSAL TO DEEP WELL 

As a result of the growing concern over contamination of the nation’s groundwater 

resources from the estimated 300,000 injection wells in the United States, Congress 

included in the Drinking Water Act of 1979 a statutory mandate to establish minimum 

requirements for state programs designed to protect underground sources of drinking 

water from contamination by subsurface injection. The Underground Injection Control 

(UIC) regulations were intended to strengthen state regulations as well as establish 

minimum federal standards reflecting good engineering practices. As in the NPDES and 

Pretreatment programs, the delegation of authority for the UIC program has in certain 

cases been made at the state level. Currently 40 states have primacy with regard to the 

UIC program (see Table 6.2) for a listing of state programs and their status). 

During formulation of the regulations, it became clear that many differences existed 

between states, including injection applications and geological conditions. For this 

reason the regulations were worded to allow states maximum flexibility in preventing 

contamination of drinking water sources. 

6.5.1 Classification of Injection Wells: Injection wells are divided into five classes 

(CFR 1989a, b). Class I wells include: 

• Wells used by generators of hazardous wastes or by owners or operators of 

hazardous waste management facilities to inject hazardous wastes beneath the 

lowermost formation containing, within 0.25 mi of the well bore, an underground 

source of drinking water 

• Other industrial and domestic disposal wells that inject fluids beneath the 

lowermost formation containing, within 0.25 mi of the well bore, an underground 

source of drinking water 

Classes II through V include wells for many specific uses and different fluids. Only 

Class I wells are pertinent to the disposal of membrane concentrate. 

6.5.2 Municipal Class I injection Wells: Class I injection wells include both industrial 

and municipal disposal wells that inject fluid beneath the lowermost formation containing 

an underground source of drinking water. Industrial disposal wells include those
 

 71 

facilities that inject industrial wastes regardless of their corrosivity, toxicity, or hazard to 

health. Municipal waste disposal wells are not nearly as numerous as industrial waste 

disposal wells. Increasingly stringent controls on discharges of sewage effluents into 

surface water bodies have forced municipalities to seek more effective means of waste 

treatment and disposal. Currently the largest, most numerous, and most sophisticated 

municipal Class I injection wells are in southern Florida, where the favorable 

hydrogeology makes the use of wells for subsurface injection of wastes possible. 

Municipal wastewater, a category not rigidly defined in the federal regulations, is 

primarily sewage effluent that has received a minimum of secondary treatment. 

Municipal wastewater may contain minor contributions from non-municipal or industrial 

sources. These sources must ensure that their wastes have received the required 

pretreatment and are compatible with the municipal wastewater. For purposes of the UIC 

program in Florida, municipal sewage effluent that contains less than 5 percent (of its 

current operating capacity) contribution from non-municipal sources is considered 

municipal wastewater. 

Of particular importance to the classification of municipal wells is an exclusion that 

eliminates the tubing and packer requirement. A packer is a device that is placed inside 

the innermost casing string and holds the base of the tubing through which the fluid is 

injected in place. The annular space between the tubing and casing string is filled with 

fluid, most commonly water mixed with a corrosion-inhibitor. The packer in conjunction 

with the tubing protects the casing from injection pressures, isolates the casing from the 

injection fluid, and provides an additional opportunity for monitoring through the tubingand-casing annulus. Under the UIC regulations, “All Class I injection wells, except those 

municipal wells injecting non-corrosive wastes, shall inject fluids through tubing with a 

packer set immediately above the injection zone, or tubing with an approved fluid seal as 

an alternative. The tubing, packer, and fluid seal shall be designed for the expected 

service” (CFR 1989b, p 734). 

The tubing and packer represent additional capital costs, the largest by far being that of 

the tubing string. The well casings will be somewhat larger diameter to accommodate the 

tubing. This represents some additional cost, however, most of the capital cost of a deep 

well is in labor and testing and not in materials. Solution in annular area between the 

tubing and the final casing is monitored 24 hours per day for pressure. Either a surface 

air compressor or source of nitrogen is used to keep the annulus at a pressure higher than 

the working pressure. In general the tubing and packer wells required more maintenance 

that typical injection wells. 

The UIC program responsibilities go beyond that of permitting deep well injection of 

wastes. All injection wells are not waste disposal wells. Some Class V wells, for 

instance, inject surface water to replenish depleted aquifers or to prevent salt water 

intrusion. In addition some Class II wells inject fluids for enhanced recovery of oil and 

natural gas, and other inject liquid hydrocarbons that constitute our Nation’s strategic fuel 

reserves in times of crisis (USEPA, 2001). Thus the situation exists where states have 
 

 72 

UIC programs but do not allow underground injection of industrial wastes including 

membrane concentrate. 

6.6 DISPOSAL BY OTHER METHODS 

Permits for disposal by methods other than to surface water, to POTWs, and to deep 

wells, are site specific (Mickley et al, 1993). 

Permits for evaporation ponds are not specifically required under either the NPDES or 

UIC programs. Permits may be prudent (or even required) if the potential exists for 

leakage to either surface water or a drinking water aquifer and no secondary containment 

method exists. A permit is recommended because it is very difficult to prove that a leak 

will not contaminate a potential source water. 

An NPDES permit may be required for spray irrigation if the potential exists for runoff to 

reach a receiving water. To avoid this requirement, the facility must prove beyond 

reasonable doubt that no runoff can possibly travel to a receiving water, or it must 

provide secondary containment. Proving that runoff will never reach a receiving water is 

generally more costly and time consuming than obtaining a permit. 

In the zero liquid discharge scenario such as through the use of brine concentrators and 

crystallizers, the waste produced is a sludge-like material or dry salts. Solids disposal 

methods are required including final disposal in an impervious area to eliminate the 

potential for contamination of surface and groundwater. 

6.7 SPECIAL TOPICS: RADIONUCLIDES, MF/UF BACKWASH, 

CONTAMINATED CONCENTRATE, TOXIC AND HAZARDOUS WASTE 

There can be site-specific disposal challenges such as when the concentrate or backwash 

contain some material that will not meet disposal requirements. 

6.7.1 Groundwater based Membrane Processes: Groundwater typically contains high 

levels of dissolved gases that include CO2, H2S, and possibly NH3. In addition, 

groundwater is typically low in dissolved oxygen. Concentrate resulting from such 

groundwater sources cannot be disposed to surface waters due to the aquatic toxicity that 

results from high H2S or NH3 and low DO. Consequently, it is routine to post-treat 

concentrate using steps that might include chlorination (followed by dechlorination), 

degasification, and aeration. In addition, it is routine to make pH adjustments on 

concentrate prior to discharge to surface water. These situations are regularly occurring 

ones and do not present final disposal problems. 

6.7.2 Regional Problems Occurring with Groundwater: Membrane concentrate is 

essentially concentrated raw water. The constituents that are concentrated and the extent 

to which they are concentrate depend on the type of membrane process and the operating 

conditions. Typically, there are few process-added chemicals (acid and antiscalant) and 
 

 73 

thus the nature of the concentrate reflects the makeup and nature of the raw water from 

which it came. A detailed characterization of membrane concentrate (Mickley et al, 

1993) highlights how concentrate differs in this regard from nearly all other industrial 

wastewaters. 

Historically, most membrane concentrates have been free from the presence of 

problematic levels of contaminants because of the low occurrence of contaminants in the 

raw water. 

Sometimes, however, local raw waters will contain relatively high levels of certain 

constituents that become spikes of ‘contaminants’ in the resulting concentrate. One such 

site-specific situation is presence of radionuclides in a raw water. In a previous survey 

(Mickley et al, 1993) 16 plants were identified (in Florida, Illinois, Iowa, and Missouri) 

that cited radium removal as one of the reasons for the membrane plant. In Southwest 

Florida this has frequently meant that the only viable disposal option was deep well 

injection. 

6.7.3 MF and UF backwash: Backwash presents an emerging disposal challenge. 

While these processes do not concentrate salts (including radionuclides) they concentrate 

to varying extents suspended solids, organics, and microorganisms. The backwash may 

contain elevated levels of microorganisms such as giardia and cryptosporidium which 

common sense suggests should not be routinely disposed to surface water or sewer. At 

present, however, there are no water quality criteria for receiving waters with regards to 

surface water disposal of effluents containing these microorganisms. 

6.7.4 Future Concentrate Challenges: In section 6.6.2, the presence of radionuclides 

in concentrate is a natural occurrence due to the local raw water makeup. It is also 

possible, however, to have raw waters that are contaminated by human activity. Such 

examples will increasingly include raw waters with high levels of nitrates (from fertilizer 

use), pesticides (also from agricultural activity), arsenic (from mining area waters), and 

possibly endocrine blockers (from several sources). The concentrate resulting from 

treatment of these waters will have spikes of these ‘contaminants’ that will complicate or 

prevent their disposal by most methods. Treatment of concentrate for pesticide and 

arsenic removal has occurred in Europe. 

6.7.5 Toxicity and Hazardous Labels: Unless the concentrate is contaminated with a 

toxic of hazardous substance it is not generally toxic or hazardous (Mickley et al, 1993). 

Historically, the only reasons that the author is aware of for failed toxicity tests from 

membrane drinking water plant concentrate include: 

• metal leaching from pump parts 

• high levels of H2S and NH3 resulting from groundwater 

• low levels of dissolved oxygen resulting from groundwater 

• high levels of fluoride and or calcium resulting from groundwater 
 

 74 

The first case was addressed by changing pump parts. The second and third situations 

routinely occur and are addressed by removal of H2S and NH3 and aeration of 

concentrate to increase the level of dissolved oxygen. The fourth case refers to major ion 

toxicity, which has recently been extensively studied (Mickley, 2000). This type of 

toxicity is different from that resulting from heavy metals or pesticides in that it is not 

bioaccumulative and has a threshold nature that results in the toxicity disappearing at low 

dilution levels. Perhaps even more important is the fact that the toxicity has occurred 

almost exclusively (there are exceptions) as a result of conducting the whole effluent 

toxicity tests using the mysid shrimp as the test organism. The mysid shrimp appears to 

be the most sensitive test organism routinely used for these tests. 

As a result of the unusual nature of the major ion toxicity, the State of Florida is 

considering legislation to regulate concentrate shown to have this toxicity (in the absence 

of other causes of toxicity) differently than concentrate with other types of toxicity. 
 

 75 

CHAPTER 7. 

REGULATION – STATE PERSPECTIVE 

7.1 BACKGROUND 

As explained in Chapter 5, the states play in important role in the regulation of 

concentrate disposal. Federal (USEPA) guidelines, directives, and framework provide 

starting points for state regulation. While starting with this common framework, state 

regulations can differ in the details of how the guidelines and directives are implemented. 

They can also differ in how stringent the regulatory requirements are providing they are 

at least as stringent as the federal guidelines. 

Many states do not have membrane plants producing potable water. In addition, many 

other states that do have membrane plants have only limited experience with either very 

small plants or with a small number of plants. 

Two different surveys were conducted to document State’s regulation of membrane 

concentrate disposal. Because of this limited experience of most States with membrane 

technology the first survey focused on options available for disposal of WTP residuals, in 

general. The second survey, which was also of a similar more general nature, focused 

on disposal of residuals to surface waters and the NPDES-related State regulations. 

Some terminology comments are in order. There are some similar terms used to describe 

residuals in both conventional water treatment plants and membrane water treatment 

plants. This can be confusing unless understood. The term ‘concentrate’ unless referred 

to as ‘membrane concentrate’ means a liquid waste/sludge prior to dewatering. Similarly, 

unless the term ‘backwash’ is in the context of membrane plants and membrane 

backwash, it refers to filter backwash. 

7.2 SURVEY OF WTP DISPOSAL OPTIONS

The first of the two surveys conducted was undertaken to document disposal options 

available to WTPs in different states. The more detailed results of the survey are 

included as Appendix A. This survey is not restricted to membrane concentrate but 

includes information about how various WTP residuals are disposed. 

Information was obtained from the Internet through checking the State environmental 

agency websites in order to list and document the relevant programs dealing with water 

quality issues for the drinking water utilities. The corresponding agency was contacted 

by phone an interviewed accordingly. In some instances due to the division of authority 

within the State more than one agency was involved in the survey. 
 

 76 

The questions addressed in the survey concerning the Water Treatment Plant’s waste 

disposal options concerned: 

• Options of liquid waste disposal 

• Options of residue or sludge disposal 

• Raw water source and overall quality 

• Chemicals or technical treatment problems faced by the utilities 

• Groundwater reinjection as a waste disposal option 

• Membrane technology use by the operating WTP 

• Programs involved dealing with disposal options 

Appendix A presents this information in a narrative form as was hand recorded during the 

interviews. Further technical details as well as the legal requirements for the permits or 

policies listed can be obtained directly from the contact person phone number or 

checking the agency corresponding website. 

Results for the states for California, Florida, and Texas are presented here. Appendix A 

has results for all 50 states. 

7.2.1 California: 

California Environmental Protection Agency 

State Water Control Board 

SWRCB Division of Water Quality 

Los Angeles Region 4 

101 Center Plaza Dr 

Monterrey Park CA 91754-2156 

Ph: (323) 266-7557 

Fx: (323) 266-7600 

Website: www.dwr.water.ca.gov/ 

Contact Person: Shirley Birosik Division of Water Quality; Abdell Shrudaji Department 

of Health Services ph: (213) 977-6808 

Currently there is no special regulation for disposal of wastes from drinking water plants; 

the waste generated will fall within existent programs such as NPDES permit for surface 

discharge. This is the most common option of disposal for liquid waste and permit 

requirements are managed by the Division of Water Quality. Disposal of the concentrate 

or sludge to a sanitary landfill as solid waste is also allowed and the solid waste group in 

the Department of Health Services handles the necessary requirements. In the State some 

utilities dispose their sludge as road construction material and no permit is involved in 

this process, with the exception of notification to the solid waste group. Source water is a 

combination of surface and groundwater, the northern part of the State use primarily 

surface whereas in the southern portion there is more use of groundwater. In the region 

(Los Angeles) source water quality is acceptable, but there are frequent problems with 
 

 77 

salinity, nitrates, and VOCs. There are utilities using membrane technology such as RO 

and Microfiltration. Santa Catalina Island has an RO plant to treat salt water. There are 

some cases of re-injection occurring as an option for treating drinking water disposal 

specially to control salt intrusion. The State has an UIC program to oversee any reinjection into groundwater. 

7.2.2 Florida: 

Florida Department of Environmental Protection 

Division of Water Facilities 

Drinking Water Section 

2600 Blair Stone Rd, MS 3520 

Tallahassee, FL 32399-2400 

Ph: (850) 487-1762 

Fx: (850) 414- 9031 

Website: www.dep.state.fl.us/ 

Contact: Richard Drew, Bureau Chief (850) 487-0563; Elsa Potts, office of Wastewater 

Management ph:(850) 921-9495; fax: (850) 414-9031 

The State of Florida issued in 1996 a set of guidelines for RO membrane utilities. This 

document does not elaborate on waste disposal options but describes current trends and 

present case studies of these membrane facilities. Currently, the State allows surface 

water disposal and blending is a common practice. The concentrate is mixed with clean 

treated effluent to reduce saline concentration before discharge; all water quality 

standards must be met. The sludge or concentrate also can be land filled, but few utilities 

chose this options due to the high chloride of the sludge that render it unsuitable for land 

application, areas with high lime concentrations may qualify for this type of disposal. 

The State requires a UIC permit for deep well injection of brine or concentrate.

7.2.3 Texas: 

Texas Natural Resource and Conservation Commission 

Water Utilities 

Water Quality Division 

TNRCC, P.O.Box 13087 

Austin, TX 78711-3087 

Ph: (512) 239-6020 

Fx: (512) 239 6050 

Website: www.tnrcc.texas.gov/ 

Contact: Jack Schulze, Public Drinking Water Section 

Drinking water utilities are allowed to discharge their liquid waste to a receiving stream 

only under an NPDES permit. They also can discharge to an existing sewer system and 
 

 78 

in this case no permit is required. A third practice in the State for liquid waste disposal is 

recycling of the waste to the head of the plant. Typically the supernatant of the settling 

lagoon is recycled, reducing the volume of liquid discharge. Any sludge or residue 

generated after dewatering can be disposed in a permitted sanitary landfill. There is a 

beneficial use program that the utilities can apply for, but most utilities prefer the first 

option. No use of the sludge for road construction is known at this moment. The utilities 

also have the option of re-injection of the stream waste, but most of them do not choose 

this option due to the stringent UIC program requirements. There are some concerns 

regarding quality of raw water. Utilities located east of highway I-35 face some color, 

alkalinity, iron, and manganese problems. West of I-35 the situation is different 

involving mainly high salt content in the surface and groundwater. Also in this area, 

there is evidence of high fluoride concentration that requires attention. Surface water 

presents some sporadic problems with BTEX, and Atrazine and the utilities have 

problems meeting MCLs. Along the Rio Grande the problem is TDS, salinity, and urban 

pollution coming from Mexico. Around Austin, the South section has excellent water 

quality and no major problems occur. There are some RO systems in the State serving 

small communities. In West Texas there are about 5 ultrafiltration and microfiltration 

utilities; 2 are under construction and the rest (3) are approved and in final design phase. 

7.3 SURVEY OF NPDES-RELATED STATE REGULATION 

A second survey was undertaken to focus on the disposal of effluents to surface waters 

and the NPDES-related State regulations that govern this. As mentioned in Chapter 6, 

about 87 percent of the surveyed desalting plants dispose membrane concentrate either 

directly to surface water or indirectly to surface water through disposal to the sewer. For 

low-pressure membrane systems and membrane backwash, the figure is 84 percent. 

Survey results for the states for California, Florida, and Texas are presented here. 

Appendix B has results for all 50 states. 

7.3.1 California: There are three main pieces of legislation for the regulation of 

concentrate disposal in the State: 

• Porter-Cologne Water Quality Control Act 

• California Regional Water Quality Control Board Basin Plans 

• Water Recycling Criteria 

The Porter-Cologne Water Quality Control is listed as Division 7 Water Quality in the 

California Water Code. A summary of the main sections of the rule is presented in Table 

2. 
 

 79 

Table 7.1. Description of specific legislative rules in the Porter-Cologne Water 

Quality Control Act* 

Chapter* Article Subject Covered in the Legislation 

 

3 3 California State policies for water quality control 

4 3 Addresses Regional Water Quality Control Plans and 

outlines water qualities objectives, plan 

implementation and compliance 

4 4 Waste discharge requirements indicating who is 

required to report discharges and requirements for 

groundwater discharges, treatment facilities and 

injection wells 

5.6 - Guidelines for protection of beneficial uses of bay and 

estuarine waters 

7 6 Waste well regulations and wastewater reuse 

including reuse in landscaping, industrial cooling 

processes, toilet, flushing water, and dual delivering 

systems for recycled water distribution. 

7.5 - Water recycling act of 1991 

*Information abstracted from: Kenna E. N., and A.K. Zander. 2000. Current 

Management of Membrane Plant Concentrate, AWWA Research Foundation Publication. 

The permitting procedures regarding the NPDES program in the State are as follows: The 

Regions of the California Regional Water Quality Control Board (CRWQCB) receive the 

request from interested parties for surface discharge of liquid waste. There are three 

general categories that include Waste Water, Industrial, and General. WTP utilities will 

fall under the industrial group category. The permit is valid for 5 years and it is very 

similar to the USEPA permit, in some instances depending the plant location it could be 

more stringent. Any WET test requirement is tailored to the receiving water ecosystem: 

freshwater will have the corresponding species (C. dubia and P. promelas) and saltwater 

typically includes the Mysids and the Silverside. A third species (Selenastrum 

capricornotun) is frequently added as part of the WET requirement to check for nutrient 

overload in fresh and saltwater conditions (a marine algae for salt water). 

In most instances the WET test is not included in the permit, but is considered n a caseby-case basis. The State runs an executive authorized program for the sporadic 

discharger although they must meet drinking water criteria; some WTPs choose this 

option. There are no special requirements for the WTP facilities using membrane 

technology. Concentrate and sludge disposal is not regulated, but must be described in 

the permit. 

7.3.2 Florida: The State of Florida has six regulatory districts in charge of issuing 

permits (NPDES) for discharge of wastewater into waters of the State including 

groundwater. The districts are distributed in six different geographical regions of the 

State including the Norwest, Northeast, Central, Southwest, Southeast, and the South 

districts. Florida is a USEPA delegated State since 1995 for the application of the 

NPDES permits and has over 20 years of experience issuing discharge permits. When 

the State became delegated they combined USEPA guidelines with the State 

requirements, therefore USEPA guidelines are included in the current Florida regulation 

pertaining (Chapter 62 of the Florida Administrative Code). In some cases requirements 
 

 80 

in the State are more stringent than the federal requirements. Each facility’s permit is 

defined by specific constituents or conditions of the discharge and the receiving stream. 

The Districts do not make any difference regarding the requirements for other industrial 

facilities and the drinking water utilities (WTPs). All requirements are tailored to the 

operational and waste type of the applicant to ensure that the discharge will not impact 

water quality standards or cause or contribute to pollution. 

Table 7.2. List of specific regulations (Title 62 FAC) that cover the currently 

accepted disposal options in the State of Florida* 

Regulation* Main Topic Covered Disposal Option 

 

62-4.240 Permit for water pollution sources Surface Water 

62-4.242 Antidegradation permit requirements Surface Water 

62-4.244 Mixing zones requirements Surface Water 

62-620 Wastewater facility permitting Discharge to wastewater 

treatment plants (WWTP) 

62-302 State surface water standards Surface Water 

62-302.400 County by county surface water 

classification including listing of the 

classes 

Surface Water 

62-302.500 Numerical criteria for parameter of 

each Florida water class 

Surface Water 

62-302.700 Outstanding Florida Waters 

protection requirement 

Surface Water 

62-500 Groundwater protection Groundwater 

62-520 Groundwater classification 

standards 

62-522 Groundwater permitting and 

monitoring requirement 

Groundwater 

62-528 Groundwater injection Groundwater 

62-528.300 Well classification and general 

provisions 

Groundwater 

62-528.305 Well permitting process Groundwater 

62-528.605 Description of Class I and II well 

operation and monitoring 

Groundwater 

62-528.630 Class V well permitting Groundwater 

62-610 Re-use of reclaimed water and land 

application 

Groundwater 

62-610.200 Definition of demineralization 

concentrate 

Groundwater 

62-610.865 Blending of concentrate, regulations 

and requirement 

Groundwater 

*Information abstracted from: Kenna E. N., and A.K. Zander. 2000. Current 

Management of Membrane Plant Concentrate, AWWA Research Foundation Publication. 

Regarding WET test requirement for the NPDES permit: FDEP emphasizes that every 

permit is unique and technical considerations for disposal of RO Membrane Plant 

concentrate are taken into account when writing the permit and the biomonitoring 

requirements. Typically, marine species are considered for WET testing, i.e., Menidia 

beryllina and Mysidopsis bahia. If the TDS of the concentrate is primarily determined by 

ions other than chloride and sodium, and thus the concentrate is of lower salinity, fresh 

water species are considered. Any surface discharge must comply with biomonitoring 

and chemical standards before discharge. Utilities can request variance of discharge 
 

 81 

standards filing a state form if they consider that permit constituents do not apply to their 

current situation (a copy of the form application can be obtained from the Florida DEP 

website). 

The complexity of the individual permit for membrane utilities is defined by the 

receiving Florida water, which follows a designation system. Several of the standards 

and requirements are based on which type of Florida water is receiving the discharge. 

Waters in Class III, for example, include all recreational waters; Class II describes waters 

dedicated to fisheries activities and will have more requirements on pollutants than the 

previous one. The permit process typically takes between 6 months to a year. However 

it can get lengthy if sensitive environments in the State are involved. Currently, there are 

some legislative initiatives to resolve the issue of WET testing requirements for the 

membrane utilities. In some cases the demonstration of absence of other pollutants has 

been required by FDEP, although it is up to the districts to get satisfaction on this 

requirements since they are the ones issuing the NPDES permit. 

There are no special requirements for utilities discharging to a marine environment with 

the caveat that they must meet all standards established for the specific environment 

where they plan to discharge. It is obvious that discharging to a Florida Outstanding 

Water system will make a difference in permitting requirements. 

7.3.2.1. Deep Well injection: Current deep well injection permits in Florida are issued 

under provisions of Chapter 403, Florida Statutes (F.S.) And Florida Administrative Code 

(FAC) Rules 62-4, 62-550, 62-660, and 62-528. The permit describes all technical 

requirements for Class I injection wells to dispose of non-hazardous reverse osmosis 

concentrate. The permit specifies well I.D., depth, casing, volume (mgd) allowed to be 

disposed, injection pressure, and required monitor wells. 

In addition, the permit narrative indicates the General Conditions that are required from 

the permittee such as record keeping, compliance with monitoring requirements, 

emergency procedures etc. The Specific Conditions of the permit describe the operating 

requirements for the injection well such as which type of waste is allowed in the well, 

daily monitoring, abandonment procedures, testing and reporting requirements etc. A 

certification of financial responsibility is required as part of the permit to ensure that the 

facility has the necessary resources to close, plug, and abandon the injection and 

associated monitor wells, at all times. 

7.3.2.2. Spray Irrigation/Land Application: This type of permit is issued under the 

provision of Chapter 403 of the Florida Statutes and applicable rules of the Florida 

Administrative Code (See Table 1). The permit covers holding pond facilities for 

concentrate waste prior to the irrigation stage. Typically the concentrate is blended with 

other raw water to meet TDS standards before irrigation in most cases to golf course 

facilities. The permit specifies monitoring parameters which for the Land Application 

such as Flow, TDS, Sodium, Chloride, Sulfate and pH. Ground water protection is also 

specified in the permit. DMR reporting and blending ratios of concentrate with raw water 

(4:1) are detailed in the permit. 
 

 82 

7.3.2.3. Surface Discharge: The outfall discharge point is specified in the permit as well 

as the type of waste allowed to be discharged. Monitoring parameters at the mixing zone 

and the dimension of the zone are detailed in the permit. The permittee must comply 

with the applicable FAC Rules 62-4.244 and 63-302.500 (Table 1) related to the subject 

of mixing zones. Land Application, Emergency Surface Discharge, other methods of 

disposal or recycling and further limitations of monitoring reporting are defined in the 

permit. A WET testing Program is also described in the permit and is mandatory for 

surface dischargers. 

7.3.3 Texas: The disposal options for membrane concentrate and their regulatory 

requirements are specified in Title 30 of the Texas Administrative Code. Table 3 list the 

main topics included in this piece of legislation indicating the appropriate disposal option 

allowed by TNRCC (Texas Natural Resources Conservation Commission). 

Table 7.3. Description of regulations and corresponding legislative sections of the 

Texas Administrative Code applicable to membrane disposal options* 

Chapter/Sub-Chapter* Section Subject Covered in the Legislation 

 

307 307.5 Description of the anti-degradation policy in 

the State 

 307.6 Prohibition of toxic substances that can cause 

acute toxicity to aquatic life in waters of the 

State 

 307.7 Site specific uses and criteria for different 

classes of water 

 307.9 Standard application 

319 - Discuss pre and post treatment issues and 

surface water discharges 

309 - Addresses evaporation ponds and land 

application of concentrate. It sets 

requirements for waste ponds and lagoons. 

309 Sub-Chapter C - Expand on land application of effluents 

through an irrigation system or percolation 

pond 

335 - Refers to handling and disposal of industrial 

solid waste, including permitting procedures, 

land disposal restriction and waste 

classification 

331 - Regulates underground injection wells. 

331 Sub-Chapter A - Establish classification of injection wells and 

waste associated with each class 

331 Sub-Chapter C - Discuss corrective actions standards and well 

closure requirements 

331 Sub-Chapter G - Describe permitting process for underground 

injection wells 

*Information abstracted from: Kenna E. N., and A.K. Zander. 2000. Current 

Management of Membrane Plant Concentrate, AWWA Research Foundation Publication. 

Current disposal options in the State are: recycle to the head of the plant, land irrigation, 

discharge to a sanitary sewer system, evaporation pond, surface discharge to Texas 

Waters, discharge of brines or concentrate, and disposal of waste sludge. Few of these 
 

 83 

options involve State or Federal permitting. Discharge to surface water, i.e., water of the 

State or USA waters, requires a TPDES (Texas NPDES) permit that will have all Federal 

and State requirements. It is clear that the permit narrative is dictated by type and 

volume of discharge, receiving water conditions, frequency of the discharge etc. all of 

these factors are site specific. Sludge disposal requires a State permit for disposal to a 

sanitary landfill or registration with TNRCC for land application of the sludge near the 

surface as it is indicated in 30 TAC Section 312.121. Re-injection is always an option for 

concentrate disposal, but not a preferred one since it must require meeting UIC 

requirements. In the case of land irrigation, it will only require a permit if the discharge 

is above 5000 gallons/day in which case it will require a TPDES permit. Volumes below 

5000 gallons do not require permits according to current rules. The on-site disposal 

option of sludge or concentrate (within the WTP property) also is an accepted practice 

and it will be covered by the TPDES permit. 

The TPDES permit is currently being implemented and there is no indication that the 

WTPs are treated any different from other industrial dischargers. The drinking water 

utilities will fall under the category of industrial dischargers and will follow the same 

protocol for getting a permit. The existing process will take approximately 180 days in 

length, from the day of a declaration of administrative completeness. Due to the 

extensive review it is recommended that the process should start a year in advance. 

7.4 SUMMARY OF REGULATORY REQUIREMENTS FOR SELECTED 

STATES 

Table 7.4 presents information about the waste disposal options for WTPs from states 

that provided detail NPDES-related information. Information is presented about 1) the 

NPDES-related requirements associated with surface water disposal of wastes, 2) about 

the various disposal options available for disposal of WTP residuals, and 3) about 

membrane concentrate disposal in particular. 
 84 

Table 7.4 Comments on Waste Disposal Options for Selected States 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

CONNECTICUT General; 

Includes RO brines discharge

Chemical s including inorganic, organic, and pesticides in excess of MCL’s shall be included 

Included as a monitoring requirement but in most cases not necessary 

Allowed, lagoon berm must be above the 100 year flood elevation 

Not included as an disposal option 

Groundwater disposal not allowed 

Under POTW authority 

Allowed as Water Treatment Wastewater. 

Onexopto 

COLORADO General; 

authorize discharge of WTP waste to State waters. Brines not included 

TSS, TDS, Total Phosphorous TRC, Flow 

It is optional depending on individual cases, some concern with metals. 

Allowed, but emphasize controls for TSS. Recycling and supernantant discharge are practiced 

Only processed water (blowdown cooling water, no chlorinated water) 

Under UIC program, typically more stringent monitoring requirements 

Allowed option. Not common in the state due to location of WTPs 

Allowed, but must comply with sludge disposal regulations. The State runs a biosolid program 

Muwiregtheprohigdisindma

CALIFORNIA Individual; 

WTP fall within Industrial sector 

TSS, TDS, Total Residual Chlorine, EC, pH, flow, Temp. Ammonia 

Three species testing if required. WTP discharge does not require toxicity testing 

Not a common practice, but available. Must comply with MCLs. 

Available in some regions as a disposal option, but requires meeting water quality requirements 

Must comply with UIC program 

Available option. The receiving utility monitors effluent load 

Sludge program available. Annual sludge production, and disposal method must be described. 

Conobumuadpe

WEST VIRGINIA General; 

Industrial NPDES 

Flow, TSS, Fluoride, Mn, Fe, Al, and 

TRC

Not required for industrial WTP discharges 

Not allowed as a disposal option 

Not allowed as a disposal 

i b

Available option to dispose WTP 

Accumulated solids from the 

di

No bricoRO 
 85 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

TRC option, but 

the permit should include a Ground water Protection Plan 

waste sedimentation basin 

should be disposed in a sanitary landfill 

RO 

WASHINGTON General 

permit for WTP with production > 0.05 mgd, only covers backwash waste 

Settleable Solids, TRC, pH. For new and existing facilities. WTP using groundwater fall within Group I parameters, surface water users will meet Group II list 

Optional, but required in the General Permit 

Not a common option, but available for some utilities. BMP must ensure safety of groundwater in highly permeable soils. 

Does not require any type of permit since the State has determined that as long as it is contained to land there is not major problem with WTP waste. 

Must follow UIC guidelines and protocols 

Is an acceptable option although is not cover by the general permit. Discharger must ensure that POTW is not affected by toxic waste. 

WTPs must submit a sludge or solid waste control plan 

Thwiof coStaBeMPraenpecoof apcobe 

PENNSYLVANIA Individual 

NPDES permit is required by the State for WTPs discharging into waters of the commonwe

Technologybased effluent control include: TSS, Fe, Al, Mn, and pH. 

Not a requirement as part of the WTP’s NPDES permits process. 

It is a common practice to handle and dispose sludge and backwash water. These lagoons are 

Allowed in the Commonwealth. An approved landfill must be used to dispose sludge, ion exchange 

Not allowed as a disposal option for WTPs in the commonwealth. Any groundwater 

Available option to dispose filter backwash or waste sludge, no permit required. Some pretreatment may be 

Only to an approved sanitary landfill. Some land application allowed 

It hadveprocowaregapion co
 86 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

alth periodically 

drained and the sludge dewatered. 

cartridge and dewatered solids from settling basin 

reinjection must comply with UIC requirements. 

necessary. Pre

disof to lonhavohig

WISCONSIN General 

Permit, allows disposal of WTP waste to surface and groundwater 

TSS, Flow, pH, KMnO4, Al, Metals. There is special care to avoid discharge to wetlands and outstanding and exceptional resource waters of the State 

Not required as part of the general permit 

Not a common practice, doesn’t require a permit 

Valid option to dispose WTPs waste. Solid removal is enforce to avoid altering draining capacity of the soil 

Groundwater disposal is allowed after fulfilling monitoring requirements for flow at each outfall of the plant 

Allowed under current guidelines, there is no permit involved 

Only to an approved sanitary landfill 

Is the pewaMCpereqbe

S. CAROLINA General 

Permit. Includes WTP discharge based on TRC levels 

Parameters defined around TRC levels, also includes: TSS, Phosphorous, pH, Total Fe, Flow 

Toxicity testing is not required for WTP discharges 

Covered under the Land Application Program. A permit is required to dispose filter backwash, or other residual generated during the process 

No groundwater waste disposal allowed 

Allowed under current guidelines, there is no permit involved 

Separate permit for sludge disposal, also there is a beneficial use program for generated solids. 

No regcothibe resfrotrecohabe 
 87 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

MICHIGAN General 

permit for potable water treatment and conditioning. It will cover most current technologies 

Parameters include Flow, pH. For Iron removal facilities Fe, and TSS. If chlorinating is used TRC will be monitor 

No WET test is required under the general permit 

Not a common practice in the State 

Must comply with solid waste disposal. Facilities must have an approved Management Plan 

Discouraged as a waste disposal method 

Allowed under current guidelines, there is no permit involved 

The residual handling management plan should address disposal or use of generated sludge. 

SpgedoRO Fathefor NP

MINNESOTA General 

permit for discharge of filter backwash. The permit includes a State Disposal System permit 

Flow, pH, TSS, no visible sheen on the receiving water 

No WET test required 

Available option must comply with permit requirements 

This option is only available to Landspreading Facilities which are permitted under State rules 

Not available as a waste disposal option 

Available option, no permit involved 

Covered under the SDS permit 

Nothe peFaapindNP

TEXAS WTPs are 

considered industrial dischargers and subject to individual TPDES. 

Flow, pH, TSS, TRC 

Typically not required for WTPs 

Available option, requires Sewage Sludge permit and technical reporting 

Available as a disposal option. Also requires Sewage Sludge Permit and Texas Land Permit 

Available, but is not a common practice. Requires UIC permit. 

Is an available option. 

Requires Sewage Sludge Permit 

CodisdisStareqpe
 88 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

(TLAP) 

FLORIDA WTPs 

using membrane technology are required individual FDEP/ NPDES permit 

TDS, pH, TRC, Flow, Chloride, Conductivity 

WET test required for surface discharger 

Available as a disposal option for small volume discharger 

Available in combination with deep well injection for backwash and low Chloride reject water 

Most RO utilities use deep well injection. FDEP issues Class I UIC permit 

Is an available option within the system, most WTPs do not have a POTW nearby. Some municipalities use their own, no permit required 

Sludge disposal and dewatered solids are disposed in a sanitary landfill. Requires solid waste permit 

Exregrequtimetec

NEVADA Individual 

NPDES permits are issued for any surface discharge in the State 

TSS, TRC, Flow, Turbidity 

No required for WTP discharge only for POTW permits 

Available option subject to permit requirements for water quality standards 

Does not required additional permit 

NA Available, 

does not require permit 

No State permit involved 

No proreqNPreq

KENTUCKY Surface 

discharge requires a KPDES permit (401 KAR). WTPs are covered under a General Permit 

TSS, TRC, Flow, pH 

No WET test required for WTP 

Available, must meet water quality standards 

Available, requires State permit 

Under UIC program. Typically not an option for WTPs 

Available Requires 

State permit under the Sludge program. The State follows EPA sludge classification 

Curegnocodis
 89 

(FOR STATES THAT SENT NPDES PERMITS TO BUREC SURVEY)

STATES NPDES PERMIT REQUIREMENTS DISPOSAL OPTIONS

Type of NPDES Permit 

Monitoring Parameters 

WET Test requirement 

Evaporation/Percolation Pond 

Land Irrigation/Application 

Well injection 

Discharge to POTW 

Sludge Disposal 

MCDi

MARYLAND Individual 

NPDES and State permits are required for WPTs discharging to surface water 

TSS, Total Iron, TRC, pH, and Flow 

No WET test required 

Available typically as settling pond before surface discharge 

Available requires permit and monitoring 

Only under UIC program 

Available, must report volume and quality to POTW 

Requires meeting sludge program requirements 

No protyp

VERMONT Individual 

NPDES permit for any surface discharge to State water 

Flow, TSS, pH, Turbidity, TRC 

Not required for WTP discharge 

No permit required if surface discharge is not involved 

NA NA Available, no 

permit required 

WTP sludge does not qualify for beneficial use 

No spefor discostareqNP
 

 90 
 

 91 

CHAPTER 8. 

SURFACE WATER AND SEWER DISPOSAL 

8.1 BACKGROUND 

Disposal of concentrate to surface water and sewer are the two most widely used disposal 

options for both desalting and MF/UF membrane processes. Data from the present 

survey (post 1992 data only) provide the following statistics: 

 Desalting MF/UF 

Disposal Option Plants Plants

Surface Water Disposal 45% 36% 

Disposal to Sewer 42% 48% 

TOTAL 87% 84% 

These two disposal options, though not always available, are the simplest options in 

terms of equipment involved and frequently the lowest cost options. As will be seen, 

however, the design of an outfall structure for surface water disposal can be complex. 

Disposal to surface water involves conveyance of the concentrate or backwash to the site 

of disposal and an outfall structure that typically involves a diffuser and outlet ports or 

valves mounted on the diffuser pipe. Factors involved in the outfall design are discussed 

in this chapter and cost factors are presented. However, due to the large number of cost 

factors and the large variability in design conditions associated with surface water 

disposal, a relatively simple cost model cannot be developed. As discussed in Chapter 6, 

disposal to surface waters requires an NPDES permit. 

Disposal to the sewer involves conveyance to the sewer site and typically a negotiated fee 

to be paid to the WWTP. Because the negotiated fees can range from zero to substantial, 

there is no model that can be presented. No disposal permits are required for this 

disposal option. Disposal of concentrate or backwash to the sewer, however, affects the 

WWTP’s effluent that requires an NPDES permit. 

8.2 DESIGN CONSIDERATIONS FOR DISPOSAL TO SURFACE WATER 

8.2.1 Ambient conditions: Because receiving waters can include rivers, lakes, estuaries, 

canals, oceans, and other bodies of water, the range of ambient conditions can vary 

greatly. Ambient conditions include the geometry of the receiving water bottom, and the 

receiving water salinity, density, and velocity. Receiving water salinity, density, and 

velocity may vary with water depth, distance from the discharge point and time of day 

and time of year. 

8.2.2 Discharge conditions: Discharge conditions include the discharge geometry and 

the discharge flow conditions. The discharge geometry can vary from the end of the pipe 

to a lengthy multi-port diffuser. The discharge can be at the water surface or submerged. 
 

 92 

The submerged outfall can be buried (except for ports), or not. Much of the historical 

outfall design work deals with discharges from WWTPs. These discharges can be very 

large, up to several hundred mgds in flow. In ocean outfalls and in many inland outfalls 

these discharges are of lower salinity than the receiving water and the discharge has 

positive buoyancy. The less dense effluent rises in the more dense receiving water after it 

is discharged. 

The volume flow of membrane concentrates is on the lower side of the range of WWTP 

effluent volumes, extending up to perhaps 15 mgd at present. Membrane concentrate, as 

opposed to WWTP effluent, tends to be of higher salinity than most receiving waters, 

resulting in a condition of negative buoyancy where the effluent sinks after it is 

discharged. This presents a concern of the potential impact of the concentrate on the 

benthic community at the receiving water bottom. Any possible effect on the benthic 

community is a function of the local ecosystem, the composition of the discharge, and the 

degree of dilution present at the point of contact. The chance of an adverse impact is 

reduced by increasing the amount of dilution at the point of bottom contact through 

diffuser design. 

8.2.3 Regulations: Receiving waters can differ substantially in their volume, flow, 

depth, temperature, composition, and degree of variability in these parameters. The 

effect of discharge of a concentrate or backwash to a receiving water can vary widely 

depending on these factors. As described in Chapter 6 the regulation of effluent disposal 

to receiving water involves several considerations, some of which are the end-of-pipe 

characteristics of the concentrate or backwash. Comparison is made between receiving 

water quality standards (dependent on the classification of the receiving water) and the 

water quality of the effluent to determine disposal feasibility. In addition, in states such 

as Florida the effluent must also pass whole effluent toxicity (WET) tests where test 

species chosen based on the receiving water characteristics are exposed to various 

dilution of the effluent. Because the nature of the concentrate or backwash is different 

than that of the receiving water, there is a region near the discharge area where mixing 

and subsequent dilution of the concentrate or backwash occurs. 

Where conditions cannot be met at the end of the discharge pipe, a mixing zone may be 

granted by the regulatory agency. The mixing zone is an administrative construct that 

defines a limited area or volume of the receiving water where this initial dilution of the 

discharge is allowed to occur. The definition of an allowable mixing zone is based on 

receiving water modeling as discussed in Chapter 6. The regulations require that certain 

conditions be met at the edge of the mixing zones in terms of concentration and toxicity 

(via the WET test). 

8.2.4 The Outfall Structure: The purpose of the outfall structure is to assure that 

mixing conditions can be met and that discharge of the effluent, in general, will not 

produce any damaging effect on the receiving water, its lifeforms, wildlife, and the 

surrounding area. 
 

 93 

In a highly turbulent and moving receiving water with large volume relative to the 

effluent discharge, simple discharge from the end of a pipe may be sufficient to assure 

rapid dilution and mixing of the effluent. For most situations, however, the mixing can 

be improved substantially through the use of a carefully designed outfall structure. Such 

design may be necessary to meet regulatory constraints. 

The most typical outfall structure for this purpose consists of a pipe of limited length 

mounted perpendicular to the end of the delivery pipe. This pipe, called a diffuser, has 

one or more discharge ports along its length. 

8.2.5 Dilution Levels: Some examples will serve to illustrate the dilution levels sought 

in the use of diffusers. It has been estimated that in seawater most organisms can 

tolerate a departure of +/- 1 ppt from the normal salinity, which represents a 3% deviation 

from the ambient (EPRI-CEC, 1994). For seawaters where the membrane concentrate is 

of 70 ppt salinity, a dilution of approximately 35 times would be required to achieve an 

effluent stream salinity of 1 ppt above ambient. This can be shown as follows: 

Let x = receiving water salinity and y = effluent salinity. After 1 dilution (equal 

volumes) the resulting salinity is (y + x)/2. After the 2nd dilution where another volume 

of the receiving water is added, salinity is (y + 2x)/3. After the ith dilution the salinity is 

(y + i*x)/(i+1). For the case where x = 35 and y = 70, at the 35th dilution the final 

salinity is 35.97 and thus within 1 ppt of the receiving water salinity. 

This same formula may be used to determine the effects on salinity of blending 

concentrate with other effluents. For instance, if membrane seawater concentrate is 

blended with WWTP effluent of a salinity of 1 ppt (very high), the 2nd dilution of the 

seawater concentrate by the WWTP effluent will result in a combined effluent of 24 ppt. 

For ocean discharge, such a dilution changes the discharge from one of negative 

buoyancy to one of positive buoyancy. This discharge will rise rather than sink in the 

receiving water and thus avoid (minimize) any effect on the benthic community. 

8.2.3 Diffuser Characteristics and Design Variables: There are several parameters 

that characterize diffuser design. These include: 

• Diameter of the diffuser pipe 

• Length of the diffuser pipe 

• Pipe material 

• Length of risers (if any) between pipe and ports/valves 

• Riser material 

• Port or valve materials 

• Number of diffuser ports or valves 

• Size of the diffuser ports or valves 

• Distance between diffuser ports or valves 

• Angles of diffuser ports with respect to the diffuser pipe 
 

 94 

Other characteristics of the diffuser include its orientation in relation to the receiving 

water boundaries and surface. This orientation may be described in terms of: 

• Distance from shore 

• Depth from surface 

• Angles with respect to receiving water boundaries and flow 

• Trenched or not 

Many outfall structures are designed using software packages that take into consideration 

design variables such as: 

• Effluent flow rate 

• Hydrodynamics of the receiving water 

o Currents 

o Turbulence 

o Tidal influences 

o Velocity 

• Shape of the receiving water boundaries (sides and bottom) including bottom 

slope 

• Temperature of effluent 

• Temperature profile of receiving water 

• Density of the effluent relative to that of the receiving water (buoyancy) 

8.2.4 COREMIX and Other Software: This software development began at Cornell 

University in 1986 under contract from the USEPA. Following the development of 

COREMIX1 subsystem (Doneker and Jirka, 1990) other systems were added in the 

ensuing years. COREMIX1 applies to single port discharges and COREMIX2 to 

multiport discharges. COREMIX 3 deals with surface level discharges. D-COREMIX 

extends the capabilities of CORMIX to negatively buoyant discharges. Software has also 

been developed for visualization of outfall design and mixing zone properties 

(http://steens.ese.ogi.edu). 

Other modeling software includes the USEPA PLUMES (Visual Plumes) models that 

were developed primarily for wastewater discharges from WWTPs. A discussion of the 

differences between the COREMIX and PLUMES software may be found on the 

webpage: http://steens.ese.ogi.edu/faq.html. 

 

The COREMIX simulations are for steady-state constant source systems. For transient 

simulations more sophisticated software is required such as various CFD (computational 

fluid dynamics) packages. These software packages are much more expensive (many 

systems are $15,000 or more) than the COREMIX system (about $500 for a single user 

plus $900 for the visualization tools). Several companies also offer services in 

providing CFD simulations. 

8.2.5 General Design Approach for Diffusers: The reason for diffusers is to meet 

dilution requirements. Sometimes dilution is not required, as when conditions at end of 
 

 95 

pipe can be met. If the diffuser cannot be designed to meet the mixing zone 

requirements, then there needs to be more treatment prior to discharge. For the 

intermediate cases where a design is needed and possible, there are options as to the 

general nature of the diffuser. One alternative is to lay the diffuser pipe on bottom 

surface with holes drilled in the side; this is the cheapest alternative if it can be supported 

and maintained in its bottom position. Another option is a buried pipeline with protection 

from scouring or damage (such as from a dragging anchor) with a protruding vertical 

riser and gooseneck elbow that would discharge horizontally. In cases where flow is 

intermittent, it may be prudent and even necessary to install a valve at each discharge port 

to prevent backflow of seawater (for instance) or to prevent organisms and even wildlife 

from entering the diffuser. One company (Red Valve) makes rubber valves that have no 

moving parts but will open and close depending on the discharge flow/pressure. 

Software packages may be used to develop conceptual designs by exploring the various 

design variables within the constraints of the ambient conditions and the dilution 

requirements. Sometimes several different designs can meet the dilution requirement, in 

which case usually a design with a shorter diffuser and smaller ports will offer the less 

expensive option. 

One design constraint is the maximum discharge velocity of about 12 fps. Discharge 

velocities range from 5 to 12 fps, but most typically designs strive for a 10 fps discharge 

velocity. Most designs have the ports far enough apart so the plumes just barely touch. 

This spacing, as well as smaller port diameters, leads to increased dilution. Dilution also 

increases with smaller density differences between the discharge and receiving water 

(another advantage of blending prior to discharge). 

In general, the diameter of the diffuser is sized just like that of any pipe being based on 

velocity and pressure drop considerations. In the case of long diffusers (which for 

WWTP outfalls can be several thousand ft in length), sometimes the diffuser pipe is 

tapered to maintain flow velocities, as flow is lost through the ports. The design length of 

the pipe typically would increase with flow but this is dependent on the site-specific 

dilution requirements and ambient flow conditions. The size of the ports may be targeted 

to be a certain percentage of the diffuser diameter. The port size typically increases with 

the magnitude of the total flow being discharged. 

8.3 COST CONSIDERATIONS FOR DISPOSAL TO SURFACE WATER 

The design of the outfall system is influenced by more variables and larger variability in 

conditions than the design of any of the other concentrate disposal methods. 

Consequently outfall design is much more site-specific and more difficult to describe in 

terms of a cost model. Unlike other disposal options presented in following chapters, a 

cost model is not presented. Cost factors, however, are discussed in this section. 

The various cost elements in disposal of concentrate to surface water include: 

! Conveyance of concentrate to shoreline: 
 

 96 

o pump 

o pipeline 

o fabrication 

o trenching of pipeline 

! Pipe from shore to outfall 

o Pipeline 

o Possible underwater fabrication 

o Dredging/trenching 

! Outfall structure 

o Pipe (diffuser) 

o Risers 

o Ports 

o Fabrication 

o Possible trenching 

 

The conveyance of the concentrate from membrane plant to the disposal site is an 

element common to all disposal options. It may be considerably more complex for 

surface water disposal, however, due to the portion of the conveyance pipe that is 

underwater. Underwater dredging and trenching can be more expensive by a factor of 

perhaps three or four than trenching on land. In an extreme case of an ocean outfall 

where the water depth is greater than 60 feet, divers may be required for the pipeline 

work and costs may approach $1,000 per liner ft of pipe. In most situations, however, 

this will not be the case. The amount and depth of underwater work is highly variable 

and the major cost in most outfall systems above a relatively small size is the 

construction and installation of the underwater pipeline. 

The cost of the actual diffuser on smaller systems is not much more than standard pipe 

length. Where valves are used for situations of intermittent flow, the valve costs may 

range from about $600 for a 3 in. valve to $1,500 for a 12 in. valve. 

In the simplest of situations, the surface disposal might consist of concentrate discharged 

from an unsubmerged pipe extending over the receiving water. The costs in this case are 

simply the cost of the pipe. In the other extreme, outfall system design may result in a 

submerged pipeline and outfall structure at a considerable distance from shore in water 

perhaps more than 60 ft in depth. In this case the outfall costs are considerable. 

8.3.1 Consideration of shared outfall structures: Where possible, one option that 

should be considered is co-disposal of concentrate along with another effluent in an 

existing outfall. The advantages of this co-siting option include the dilution possible 

through mixing of the effluents, the savings of outfall costs, and the time and effort saved 

in modifying an existing discharge permit rather than applying for a new permit. 

Assuming the concentrate to be of higher salinity than the receiving water, mixing of 

concentrate with wastewater of salinity less than that of the receiving water can, provided 

the relative volumes allow enough dilution, lead to a positively buoyant discharge. 
 

 97 

Mixing of concentrate with wastewaters with densities greater than ambient but less than 

the concentrate will result in an effluent still having negative buoyancy, but modeling has 

shown that the mixing will also result in greater dilution at the point of contact with the 

benthic zone, and the point of contact will be further from the discharge point. 

8.7 DISPOSAL TO SEWER 

Where possible this means of disposal is simple and usually cost-effective. Disposal to 

sewer does not require a permit but does require permission from the wastewater 

treatment plant. The impact of both the flow volume and composition of the concentrate 

will be considered by the WWTP, as it will affect their capacity buffer and their NPDES 

permit. The high volume of some concentrates prohibits their discharge to the local 

WWTP. In other cases concerns are focused on the increased TDS level of the WWTP 

effluent that results from the concentrate discharge. 

The possibility of disposal to sewer is highly site dependent. In addition to the factors 

mentioned, the possibility is influenced by the distance between the two facilities, by 

whether the two facilities are owned by the same entity, and by future capacity increases 

anticipated. Where disposal to the sewer is allowed, the WTP may be required to pay 

fees based on volume and or composition. 
 98 
 99 

CHAPTER 9. 

DEEP WELL DISPOSAL 

9.1 BACKGROUND 

Injection wells are a disposal option in which liquid wastes are injected into porous 

subsurface rock formations. Depths of the wells typically range from 1,000 to 8,000 ft. 

The rock formation receiving the waste must possess the natural ability to contain and 

isolate it. Paramount in the design and operation of an injection well is the ability to 

prevent movement of wastes into or between underground sources of drinking water. 

Historically this disposal option has been referred to as deep well injection or disposal to 

waste disposal wells. Because of the very slow fluid movement in the injection zone, 

injection wells may be considered a storage method rather than a disposal method; the 

wastes remain there indefinitely if the injection program has been properly planned and 

carried out. 

Because of their ability to isolate hazardous wastes from the environment, injection wells 

have evolved as the predominant form of hazardous waste disposal in the United States. 

According to a 1984 study by the USEPA, almost 60 percent of all hazardous waste 

disposed of in 1981, or approximately 10 billion gallons, was injected into deep wells. 

By contrast, only 35 percent of this waste was disposed of in surface impoundments, and 

less than 5 percent in landfills. The USEPA study also found that a still smaller volume 

of hazardous waste, under 500 million gallons, was incinerated in 1981 (Gordon 1984). 

Although RO concentrate is not classified as hazardous, injection wells are widely used 

for concentrate disposal in the State of Florida. 

A study prepared for the Underground Injection Practices Council showed that relatively 

few injection well malfunctions have resulted in contamination of water supplies 

(Strycker and Collins 1987). However, other studies document instances of injection 

well failure resulting in contamination of drinking water supplies and groundwater 

resources (Gordon 1984). 

Injection of hazardous waste can be considered safe if the waste never migrates out of the 

injection zone. However, there are at least five ways a waste material may migrate and 

contaminate potable groundwater (Strycker and Collins 1987). Wastes may: 

• Escape through the well bore into an underground source of drinking water 

because of insufficient casing or failure of the injection well casing due to 

corrosion or excessive injection pressure 

• Escape vertically outside of the well casing from the injection zone into an 

underground source of drinking water (USWD) aquifer 

• Escape vertically from the injection zone through confining beds that are 

inadequate because of high primary permeability, solution channels, joints, faults, 

or induced fractures 
 100 

• Escape vertically from the injection zone through nearby wells that are 

improperly cemented or plugged, or that have inadequate or leaky casing 

• Contaminate groundwater directly by lateral travel of the injected wastewater 

from a region of saline water to a region of fresh water in the same aquifer 

9.1.3 Deep Well Disposal in Southern Florida: Southern Florida receives abundant 

rainfall of over 60 in./yr; however, 45 to 50 of those inches are lost very quickly to 

evaporation. There are additional losses through runoff to the ocean and percolation into 

the sandy Florida soil. The problem is further complicated by limited storage capacity. 

The majority of the rainfall occurs during a 6-month period, and the ability of lakes and 

reservoirs to store this water is limited by the flat topography of the state. 

The rapid population growth of southern Florida, which has been second only to that of 

California, has stretched the existing freshwater supplies to the limit in many areas and 

forced many municipalities to turn to treatment of brackish sources as a supplement. 

Florida is exceeded only by New Mexico in dependence on groundwater, with 91 percent 

of the total population relying on that source (Miller 1989). Southern Florida also leads 

the nation in operating municipal Class I disposal wells and has more membrane drinking 

water plants than any other state in the nation. Florida also has some of the best geologic 

formations to support deep well injection. This unique combination of characteristics has 

placed Florida at the center of a controversy over disposal of membrane concentrate, the 

resolution of which will most likely establish precedents for the nation as a whole. 

Brackish water of varying quality is available in aquifers underlying all of southern 

Florida. The main aquifer, in southeastern Florida, is a confined one known as the 

Florida aquifer; it ranges in depth from approximately 500 to 2,000 ft below sea level. 

The water quality of this aquifer is between 2,000 and 8,000 mg/L TDS, depending on 

exact locations and depths. 

In southwestern Florida, the geology is much more complex; there are up to 10 separate, 

confined water-bearing zones. Each has a different production rate and quality of water. 

Feedwater for desalination is commonly withdrawn from the Hawthorn Formation of the 

Suwannee Limestone at depths between 250 and 900 ft. The salinity of the water from 

these aquifers generally ranges from 1,000 to 3,500 mg/L (Morin 1987). 

Currently in Florida over 100 membrane plants are in operation. The majority of these 

plants use surface water discharge to dispose of the concentrate generated during plant 

operation. Many of the early plants were small, producing less than 100,000 gpd of 

product water. These plants served mobile home parks or small communities or 

municipalities, or they produced water for irrigation purposes. These small facilities 

generated concentrate for disposal in amounts proportionate to their size. The plants 

being proposed today are much larger in scope. Projects currently in development will 

serve larger communities, producing upwards of 20 mgd of product water and a 

correspondingly larger amount of concentrate for disposal. It is the disposal of these 

larger volumes of concentrate that presents the biggest obstacle to the use of membrane 

technology. Deep well injection is an option for concentrate disposal, but the designation 
 101 

of concentrate as an industrial waste requires that the wells include the more expensive 

tubing and packer, which are not required of municipal disposal wells. 

Municipal wells were excluded from the tubing and packer requirement because, at the 

time the regulations were published, several Florida wells then in operation were 

disposing of typical municipal wastewater (treated sewage effluent) and were not 

constructed with tubing and packer. The regulations allowed the continued operation of 

these wells to dispose of typical municipal wastewater and allowed future construction of 

similar wells (i.e., for typical municipal wastewater). The USEPA has pointed out that 

the intent of the exemption was to limit the construction of Class I wells without tubing 

and packer to typical municipal wastewater effluents (treated sewage plant effluent). The 

5 percent limit allows for minor contributors to municipal systems, but prohibits the large 

non-municipal wastewater contributors from using municipal wells as a means of 

disposal. The USEPA has emphasized that municipal wells should not serve as a 

disposal method for large non-municipal contributors. 

9.1.4 Geology of Southern Florida: Southern Florida is underlain by a series of 

groundwater-bearing strata of cavernous limestone and dolomites separated by thick and 

impervious layers of marls and dense limestone. Groundwater in the deeper strata, 

generally at depths grater than 1,500 ft, is highly mineralized. At a depth of 

approximately 3,000 ft cavernous dolomite exists. This zone is called the Boulder Zone 

of the Oldsmar Formation because oil well drillers have reported fractured dolomite 

fragments (boulders) falling into bore holes during drilling. Water quality is poor at this 

depth, and the zone has extremely high permeability and the capacity to receive large 

amounts of waste under low injection pressures. The Boulder Zone is isolated from 

overlying aquifers by thick, dense layers that act as barriers to fluid exchange, thus 

protecting the water quality of the overlying aquifers. Consequently, a number of Class I 

municipal injection wells have been developed in the area in the past decade. The water 

quality of this zone is similar to seawater, or about 35,000 mg/L TDS (Muniz and Skehan 

1988). 

At West Palm Beach, the Boulder Zone is approximately 3,150 ft deep and 350 ft thick, 

and accommodates injection rates of 20 to 22 mgd (14,000 to 15,000 gpm) of sewage 

effluent; with peak injection rates as much as 25,000 gpm. The inner casings of injection 

wells in Florida typically range from 12 to 30 in. in diameter, with outer casings being 

progressively larger. Casings are typically 0.5 in thick steel. Each different diameter 

casing is cemented after its full string is positioned. The casings are generally cemented 

from the bottom up to the land surface. In southeastern Florida, the final casing depth 

settings are around 2,700 ft with most wells drilled to a total depth of 3,300 ft (Muniz and 

Skehan 1988). 

In the Tampa area, several wells have been drilled for injection into the Avon Park 

Formation with total depths in the range of 1300 to 2000 ft. 
 102 

9.2 DESIGN CONSIDERATIONS 

9.2.1 Siting: Site selection is the first step, and one of the most important steps, in 

developing an injection well. The UIC regulations state, “all Class I wells shall be sited in 

such a fashion that they inject into a formation which is beneath the lowermost formation 

containing, within 1⁄4 mile of the well bore, an underground source of drinking water” 

(CFR 1989b, p. 729). 

Site selection is dependent upon geologic and hydrogeologic conditions, and only certain 

areas are suitable for construction of Class I wells. Suitable underground strata capable 

of receiving the waste must be present and separated from any underground sources of 

drinking water by impermeable strata. Most favorable locations are generally in the 

midcontinental, Gulf Coast, and Great Lakes regions of the country. Site selection 

involves evaluation of many conditions; most important is the determination that the 

underground formations possess the natural ability to contain and confine the injected 

waste. The ability of properly designed and operated injection wells to provide long-term 

confinement makes deep well disposal an environmentally acceptable option. This 

characteristic has allowed the entrapment and containment of naturally occurring oil and 

gas deposits, which have been held in place, moving little if at all, for millions of years. 

Rock formations such as sandstone are highly porous and are able to take in large 

volumes of liquid. Other rock formations such as shales and clays are essentially 

impermeable, and act as confining layers that make it possible to dispose of liquids 

underground into porous strata, and prevent migration of the wastewater into potable 

water aquifers. 

Groundwater quality usually deteriorates with increased depth. Although high-purity 

deep aquifers do exist, water sources with low salinity and mineral content (fresh water) 

are typically located near the surface. Deep aquifers, which are used for deep well 

disposal, typically have very poor water quality, and are not considered potential sources 

of drinking water. 

In addition to the existence of the necessary types of underground formation, it is 

essential that the well not be located in areas subject to earthquakes or in regions 

containing recoverable mineral resources such as ores, oil, coal, or gas. Any wells in the 

area in question, both operating and abandoned, must be investigated to assure that they 

are properly plugged to prevent migration of the waste to other aquifers. 

9.2.2 Construction: The UIC regulations require that all Class I wells be cased and 

cemented to prevent the movement of fluids into or between underground sources of 

drinking water. The casing and cement used in the construction of each well are to be 

designed for the life expectancy of the well. In determining and specifying casing and 

cementing requirements, the following factors should be considered (CFR 1989b): 

• Depth to the injection zone 

• Injection pressure, external pressure, internal pressure, and axial loading 
 103 

A Class I injection well is constructed in successive stages of drilling (or reaming), 

casing, and cementing until a well of the required depth (to reach the disposal formation) 

and diameter (to accommodate the required flow rate) is completed (see Figure 9.1). The 

first step is the drilling of a pilot hole of perhaps 12 in. diameter to either the final depth 

or to the setting depth of the first casing string. Next the hole is reamed to a much larger 

diameter to this same depth, typically a depth of between 20 and 200 ft. The initial 

casing is set to this depth and the void between the reamed borehole and the outside of 

the initial casing if filled with cement. Well construction service companies indicate that 

the single most important factor in ensuring well integrity is obtaining a satisfactory 

primary cementing job. Primary cementing involves placing cement in the annulus 

between the bore hole and the outermost casing and between the concentric strings of 

casing, to restrict fluid movement between formations as well as to support and to bond 

the casing and protect the casing pipe material from external corrosion by subsurface 

water. 

If the original drilling did not go to final depth, then drilling is conducted to the depth 

where the nest casing string is set. In either case with the hole now drilled to at least this 

depth, the hole is reamed to this depth. This procedure is repeated, using successively 

smaller diameter drilling tools and casing, until the depth of disposal is reached. Casing 

and cementing the well as the drilling proceeds stabilizes and seals the upper strata while 

allowing drilling to proceed to the required depth. 

The first and largest-diameter casing to be installed is called the conductor casing and is 

used to stabilize the top of the bore hole and prevent soil from washing out around the 

base of the drilling rig during construction. The next casing string is called the surface 

casing. It protects the well from unconsolidated sediments caving in, and seals shallow 

freshwater aquifers from injection fluid contamination. The surface casing may extend as 

little as 200 ft or as far as 4,500 ft, depending on the well design and geologic conditions. 

At a minimum, the surface casing must be deep enough to reach solid formations that will 

not fracture or break down under the pressures imposed by the drilling fluid needed to 

reach the ultimate depth of the well. One or more intermediate casing strings are used to 

protect the bore hole at the lower depths by sealing off weak formations that could 

fracture under the drilling stresses. The final casing is the injection casing, which 

protects other formations from the injection fluid and houses the tubing and packer. 

Casing is distinguished from tubing with respect to its function and location in the well. 

Casing refers to the outer pipe string cemented in place to maintain structural integrity in 

the borehole and to seal upper aquifers. Tubing refers to the innermost pipe string 

through which injection takes place. A mechanical device called a packer seals the 

annular space between the tubing and casing. 

Once the casing, tubing, and packer are in place, the annulus between the tubing and 

innermost casing is filled with a noncorrosive fluid, and positive pressure is maintained in 

the annulus. The presence of the tubing and packer isolates the injection fluid from the 

casing and thus provides corrosion protection to the casing. Although corrosion-resistant 

coating or liners may be applied to the casing, the integrity cannot be guaranteed, and 

these additions increase the cost of the well significantly. The annular fluid can also be 
 104 

Packer 

Casing

Cement 

Injection tube 

Ground surface 

Figure 9.1 Schematic Diagram of a Three-Transition Injection Well with Packer 
 105 

monitored for pressure, and analyzed periodically to detect failure of the tubing and allow 

corrective action to be taken before the failure is transmitted to the casing and 

contamination of groundwater occurs. 

The design of the deep well disposal system requires specification of 1) the flow rate of 

the concentrate or backwash stream in units of mgd, 2) the depth of the well in feet, and 

3) the number of casing transitions (usually 3 or 4). There are several independent cost 

factors such as the pump, the drilling and reaming, the casing, and others that are 

dependent on the values of these design parameters. Since the cost of the well is 

primarily labor and testing, the material costs and thus the diameter of the well are not 

major cost factors. Because of this, to allow for future increases in use many wells are 

made of much larger diameter than required. 

Depending on site conditions, deep well disposal can be an economical option. Costs of 

developing a disposal well are difficult to estimate for a generic site. Site-specific 

geological characteristics will vary, requiring different drilling depths and construction 

techniques (Mickley et al, 1993). 

9.2.3 Design Basis - Flow Versus Tubing Diameter: For most of the cost models, the 

size of the disposal option is based on flow rate of concentrate. For the deep well 

disposal this is not always the case. Because the material costs are not the major cost 

factor for the deep injection wells, there is relatively little penalty or additional cost for 

designing and building a well capable of receiving larger flows. This might be done to 

allow for future plant expansion or for future shared use of the well. It should be noted 

that if the tubing and packer requirements were not necessary for disposal of membrane 

concentrate, the tubing could be removed, resulting in effect in a much larger capacity 

deep injection well – limited by the diameter of the final casing string. Some wells in 

Florida are being designed and built with a larger than necessary final casing diameter for 

this future possibility. Because of lack of correlation between design flows and tubing 

size in the Florida deep wells, the cost basis was chosen to be the tubing diameter instead 

of the concentrate flow rate. 

Correlations between flow and diameter are based on assumption of a flow formula such 

as the Hazen and Williams formula with a constant in the equation chosen to represent 

the flow-friction characteristics of different pipe materials. Specification of a maximum 

flow velocity then sets the correlation. For new steel pipe, Table 9.1 gives the 

relationship between nominal internal pipe diameter and flow rate. 

Although the design basis chosen for the following model is based on nominal tubing 

diameter, the above tabulation may be used to determine a correlation with allowable 

concentrate flow rate. For downhole injection, a velocity of 10 fps is recommended. 
 106 

Table 9.1 Relationship between Pipe Diameter and Flow Rate 

Flow Rates (mgd) for Different Flow Velocities (fps) 

Diameter (in) 5 fps 8 fps 10 fps

2 0.07 0.11 0.14 

3 0.16 0.25 0.32 

4 0.28 0.45 0.56 

6 0.63 1.02 1.27 

10 1.76 2.82 3.52 

12 2.54 4.06 5.08 

16 4.51 7.22 9.02 

20 7.05 11.28 14.10 

24 10.15 16.24 20.30 

9.3 COST FACTORS 

9.3.1 Pretreatment: The wastewater to be injected may require pretreatment in an 

above-surface facility to prevent plugging in the receiving formation. When significant 

suspended solids are present, such as when concentrate is mixed with membrane prefilter 

backwash and periodic cleaning waste, typical pretreatment consists of TSS removal. 

Cartridge filters to remove 5 micron and larger particles may be required. Depending 

upon the specific characteristics of the wastewater and receiving formation water, pH 

adjustment may also be necessary. When pH is adjusted, scale formation can be 

minimized with two incompatible waters. The cost of pretreatment cannot be estimated 

with general guidelines; a site-specific evaluation is necessary. 

9.3.2 Pumps: Pumps are used in above-surface facilities to inject the concentrate. The 

flow and pressure requirements are site specific. The discharge head will vary depending 

upon the geologic conditions and depth of the injection zone. Some municipal disposal 

wells operate at pressures as low as 3 to 6 psig. More typical discharge pressures are in 

the range of 30 to 50 psig; however, much higher pressures are often required. Discharge 

as high as 2,000 to 5,000 psi can be encountered. To attain discharge pressures in this 

range, reciprocating pumps are typically used, and the pump cost increases drastically. 

At a 1992 installation the cost of a reciprocating pump rated for 150 gpm at 3,180 psig 

was $150,000 (1992 costs). For low-head pumps, the cost would be approximately 

$10,000. Estimates of pumping costs for low-head pumps (less than 50 psig) can be 

obtained from Figure 10.7. If higher-head pumps are required, a site-specific evaluation 

is necessary. 

9.3.3 Site Tests – Logging, Surveying, and Testing: Site tests are conducted following 

the initial drilling and throughout the repeated sequence of drilling (or reaming), setting 

casing, and setting cement. A final injection test is conducted before the drilling rig is 

disassembled. Early site tests include core samples obtained to determine the soil 

conditions, which indicate the most effective type of drilling. Water tests are also 

conducted to predict the compatibility of the formation water and the injected 
 107 

wastewater. Based on the water tests, the required pretreatment can be established. As 

an example of how involved the logging and testing can be, Table 9.2 lists events that 

took place at a disposal well in Florida. 

Table 9.2 Logging, Surveying, and Testing Events from Florida 3400 ft Well 

• Geophysical logging to 220’ 

• Caliper survey to 220’ 

• Geophysical logging from 220’ to 1000’ 

• Caliper survey to 1000’ 

• Flow Test to 2100’ 

• Geophysical logging from 1000’ to 2100’ 

• Downhole video survey from 1000’ to 2100’ 

• Straddle packer pumping test between 1000’ and 2100’ 

• Caliper survey to 2100’ 

• Flow test to 3000’ 

• Geophysical logging from 2100’ to 3000’ 

• Downhole video survey from 2100’ to 3000’ 

• Straddle packer pumping test between 2100’ and 3000’ 

• Caliper survey to 3000’ 

• Pressure test of final casing 

• Geophysical logging from 3000’ to 3400’ 

• Collect water samples from the injection zone and analyze 

• Perform video survey in the final casing to the total depth 

• Temperature and gamma ray log entire well 

• Perform hydrostatic pressure test on the annulus of tubing 

• Video survey injection tubing from land surface to total depth of well 

• Conduct radioactive tracer survey 

• Conduct injection test 

Many of these tests are fairly independent of the well size and well depth. The total cost 

of logging, surveying, and testing is summarized in Figure 9.2. 

9.3.4 Injection Well Formation: Deep injection wells are normally multicased. The 

use of more than one casing provides transition zones and isolates deep contaminated 

aquifers from the purer water contained in shallower aquifers. The injection tube is run 

from the surface to the deep aquifer where the water will be injected. The tube is encased 

in cement at least 5 in. thick to comply with environmental regulations. Intermediate 

depths of casing are selected based on the geological conditions at each site. Figure 9.1

illustrates the well arrangement for three transitions. The costs presented in the following 

sections are based on this general arrangement. 

It should be noted that the grout surrounding the intermediate casing is always a 

minimum of 3 in. thick and may be as high as 10 in. The grouting thickness is dictated to 

some extent by the allowable standard casing sizes. 
 108 

Figure 9.2 Logging, Testing, and Survey Costs as Function of Tubing Diameter 

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600

0 5 10 15 20 25

Tubing Diameter (inches)

Loggin and Testing Costs (2001 $ in thousands)

2500 ft 

5000 ft 

7500 ft 

10000 ft 
 109 

One of the cost-related characteristics of deep wells is that the cost of materials is not the 

major cost factor involved. The labor costs of drilling, testing (logging, surveying and 

testing), and installing casing and tubing are high relative to the material costs, and vary 

in a minor way with diameter. Over the several month on-site drilling operation, the 

drilling of a 16 in. well rather than a 24 in. well may speed up the project by less than a 

week. 

9.3.4.1 Drilling: Where a pilot hole to the final depth is drilled first, the subsequent 

drillings may be called reamings. Several factors influence the cost of drilling (reaming), 

including soil conditions, materials, labor rates, rig rental costs, and drilling waste 

disposal costs. 

As discussed above, the soil conditions are identified from the core samples. The depth of 

the formation and the type of soil (sandy, rocky, and so forth) will impact the final 

drilling cost. During the drilling operation several materials are required, including 

cement, mud, and drill bits. None of these add greatly to the overall costs. The 

significant drilling costs are labor and drill rig rental. 

Water is utilized to cool the drill bit during drilling. This cooling water and water 

produced from the formation sometimes require treatment before disposal. Settling of 

suspended matter in basins is normally the only required treatment. 

The final drilling cost is also dependent on the quantity of the disposal waste, which will 

establish the diameter required for the well casing and tubing. Waste flows vary widely, 

ranging from 50 to 3,000 gpm. 

As explained in the previous section, the number of holes to be drilled depends upon the 

number of transitions required. The cost of drilling is summarized in Figure 9.3. The 

costs are summarized for depths of 2,500, 5,000, 7,500, and 10,000 ft. Note the relatively 

small change in cost with flow (diameter). 

9.3.4.2 Tubing and Packer: The disposal well uses tubing and packer to isolate the well 

casing from the wastewater. The cost of the tubing is a function of material, length, and 

diameter. The most frequently used material is carbon steel or stainless steel. Figure 9.4 

illustrates the cost of installed tubing. Limiting the maximum velocity through the tubing 

to 8 fps sets the required diameter of the tubing. The cost of the packer depends upon the 

well diameter and the operating pressure of the well. Packer costs are summarized in 

Figure 9.5 for various well sizes. 

9.3.4.3 Casing and Grout: Because the casing is isolated from the waste, it can be 

fabricated from steel. Typically steel is used for the inner casing, with concrete on the 

outside of the steel. Casing steel costs have been estimated and summarized in Figure 

9.6. 

Costs of the grout are graphed in Figure 9.7. The thickness of the initial grout (cement 

with possible additives) outside the initial casing string depends on the choice of reaming 
 110 

Figure 9.3 Drilling and Reaming Cost as Function of Tubing Diameter 

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Drilling/Reaming Cost (in thousands 2001 $)

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 111 

Figure 9.4 Installed Tubing Cost as Function of Tubing Diameter 

0

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Installed Tubing Cost (2001 $ in thousands)

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 112 

60

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0 5 10 15 20 25 30

Tubing Diameter (inch)

Installed Packer Cost (2001 $ in thousands

Figure 9.5 Installed Packer Cost as Function of Tubing Diameter 
 113 

Figure 9.6 Installed Casing Cost as Function of Tubing Diameter 

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s

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 114 

Figure 9.7 Installed Grouting Cost as Function of Tubing Diameter 

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 115 

diameter and the initial casing string diameter. Subsequent thickness of grout between 

the various casing diameters depends on the choice of casing diameters. These grout 

thickness may range form 3 to 10 in. 

 

9.3.5 Monitoring: To ensure compliance with environmental regulations, some 

regulatory agencies require monitoring wells. From these wells periodic samples can be 

taken and analyzed to determine if there has been any leakage of the waste to the 

surrounding aquifers. In general the most critical areas are the upper freshwater aquifers. 

The model assumes either a dual zone single monitoring well or a deep and a shallow 

monitoring well. The wells monitor conditions in the overlying aquifers that are 

structurally isolated from the confining, injection aquifer. The shallow well or upper 

monitoring zone of the dual zone well is to detect any changes in the upper freshwater 

aquifer. A deep monitoring well is also required to detect any changes in the deeper 

formation. The depth of the monitoring wells depends on the depths of the aquifers to be 

monitored, which, of course, is site specific. In Florida most of the monitoring wells are 

approximately 2000 ft in depth for deeper Boulder Zone deep injection wells and about 

900 ft in depth for the Avon Park Formation shallower injection wells. Estimated 

monitoring costs are presented in Figure 9.8. 

9.3.6 Other Considerations: Mobilization and demobilization will also constitute part 

of the total cost. The drilling rig must be assembled and then disassembled. These costs 

are represented in Figure 9.9. 

Systems handling wastewater must take corrosion into account as a design consideration. 

Special materials can be used to minimize corrosion, but the cost of special alloys may be 

prohibitive. Utilization of a corrosion inhibitor is often more feasible. The corrosion 

inhibitors add to the operating cost but can be cost effective for flows of 200 gpm or less. 

The interaction between the water and the formation water can form precipitates that plug 

the formation. To control this commingling, a buffer zone may need to be established. 

Injecting a quantity of neutral water before injecting the waste forms this buffer. This 

procedure has little impact on cost. 

9.3.7 Operating Costs: The operating costs for disposal wells are generally low. Well 

maintenance consists of periodically checking the casing and repairing it if required. 

Thus a large capital cost (of $1,000,000 or more) can be offset by economical operating 

costs. 

The operating costs encountered are for pumping power, chemical costs, and operating 

labor. Of these the pumping power is the most significant. For the 150 gpm pump at 

3,150 psig, a 350-hp motor is required, resulting in a cost of more than $50,000/yr. 

Chemical costs are normally much lower than this. For example, treating a waste flow of 

150 gpm with a corrosion inhibitor would cost approximately as much as $7,000/year. 

Thus, unless elaborate pretreatment is required, the chemical costs are not excessive. 
 116 

Figure 9.8 Monitoring Well Cost as Function of Well Depth 

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Monitoring Well Depth (feet)

Monitoring Well Cost (2001 $ in thousands)

900 ft – Rough 

depth of 

2000 ft – Rough depth 

of monitoring wells for 

deeper injection wells in 

Florida
 117 

Figure 9.9 Mobilization & Demobilization Cost as a Function of Well Depth 

200

300

400

500

600

700

800

900

1000

0 2000 4000 6000 8000 10000 12000

Well Depth (feet)

Mobilization/Demobilization Cost (2001 $ in thousands
 118 

9.4 DESIGN APPROACH FOR THE DEEP WELL DISPOSAL COST MODEL 

The costs of disposal by deep well injection are subject to many site-specific 

circumstances - perhaps more so than those of any other disposal method. The site 

terrain may vary considerably from site to site and may require substantial clearing, 

grading and road-building. The site may be close to a water source that can provide 

injection test water. Sometimes the site can use city pumps and flow lines; other times a 

series of pumps and lines might need to be set up. The costs are affected also by how 

many different groups are involved. The work may involve a general contractor, well 

driller, a group to do the packer tests, a group to do the logging, etc. Or it may involve 

one company tightly controlling all these elements. The work is also significantly 

affected by the geology of the area that determines aspects from the difficulty of drilling 

and reaming to the depths at which the casing strings are set. 

The reader is cautioned to use the models provided only to obtain a preliminary level cost 

estimate. The supporting text should give the user an understanding from which to better 

determine, from a site-specific approach, more accurate costs involved in a deep well 

disposal system. 

The design approach taken in the following worksheet model is straightforward but based 

on conditions in Florida, where nearly all of the deep well disposal of concentrate has 

occurred. 

• The design approach chosen for the worksheet model is as follows: 

o The number of casing transitions (normally three or four in Florida) is not 

broken out as a cost factor, but its influence is embedded in the other cost 

curves. 

o The total well depth and the injection tubing diameter determine the 

following costs: 

• Logging, testing, and survey 

• Drilling and reaming 

• Installed casing 

• Installed grouting 

• Installed injection tubing 

o The diameter of the injection tubing determines the packer cost 

o The injection well cost is the sum of these costs. 

o The mobilization and demobilization cost is taken as 20 percent of the 

injection well cost. 

o The monitoring well cost is determined from the monitoring well depth. 

• The design variables thus include: 

o Total depth of the well 

o Diameter of the injection tubing 

• Costs included in the capital cost model: 

o Drilling and reaming 

o Logging, testing, and survey 

o Installed casing 
 119 

o Installed grouting 

o Installed injection tubing 

o Installed packer 

o Mobilization and demobilization 

o Monitoring well 

• Costs not included in the capital cost model: 

o Pretreatment 

o Pump 

9.5 DEEP WELL DISPOSAL WORKSHEET AND EXAMPLE 

Based on the cost data provided in the figures, a preliminary capital cost estimate can be 

developed for a specific site. Such an estimate can provide an order-of-magnitude cost, 

but a specific site evaluation would be required to provide an accurate estimate. 

The worksheet for deep well disposal is provided in Table 9.3. An example calculation is 

provided in the column marked ‘example.’ For this example, the assumption is made that 

an injection tube of 16 in. nominal diameter is required. The well depth is 3,400 ft. The 

figures previously presented can now be applied to develop an estimated cost. From 

Figure 9.2, a cost of $350,000 is obtained for logging of the injection well. The drilling 

and reaming costs, estimated from Figure 9.3, are $790,000. Referring to Figure 9.4, the 

cost is $430,000 for injection tubing in a 3,400 ft well. Based on the tubing diameter and 

well depth, the cost of packer, casing, and grouting are obtained from Figures 9.5, 9.6, 

and 9.7 respectively. These costs are estimated at $97,000, $920,000, and $600,000, 

respectively. The monitoring well cost for a dual zone monitoring well is taken from 

Figure 9.8 with an estimated cost of $600,000. Finally, the rig mobilization and 

demobilization cost is estimated from Figure 9.9 to be $710,000. The total estimated cost 

is shown in Table 9.3 to be $4,497,000. 

9.6 DEEP WELL DISPOSAL REGRESSION MODEL 

Based on about 35 cases from the worksheet, a closed form mathematical relation was 

developed to approximate the worksheet model. The user is reminded that the cost 

projections from both the worksheet model and the regression model that approximates 

the worksheet model are for preliminary level cost estimates only. The model developed 

below is linear in the various cost factors. The mathematical expression is: 

Total Capital Cost ($) = -288 + 145.9 * TUBEDIAMETER + 0.754 * DEPTH 

For the worksheet example conditions of: 

 

 TUBE DIAMETER = 16 in. 

 DEPTH = 3,400 ft 

the calculated total capital cost is $4,610,000, which compares to the worksheet result of 

$4,497,000. 
 120 

Table 9.3 Worksheet for Deep Well Disposal Capital Costs 

WORKSHEET for Deep Well Disposal Capital Costs 

Preliminary Level Cost 

Variable 

ENTER variable values range example case 1 case 2 case 3 A - tubing diameter (in) 5 - 24 16 B - depth (ft) 0 - 10,000 3,400 FIND costs from figures Action C - Cost of logging, testing & survey use A & B, Figure 8.2 350,000 D - Cost of drilling & reaming use A & B, Figure 8.3 790,000 E - Cost of installed casing use A & B, Figure 8.6 920,000 F - Cost of installed grouting use A & B, Figure 8.7 600,000 G - Cost of installed injection tube use A & B, Figure 8.4 430,000 H - Cost of installed packer use A, Figure 8.5 97,000 I - TOTAL INJECTION WELL COST =C+D+E+F+G+H 3,187,000 J - Mobilization/demobilization cost use B, Figure 8.9 710,000 K - Monitoring well cost use B, Figure 8.8 600,000 

TOTAL COST =I+J+K 4,497,000 
 

 121 

CHAPTER 10. 

EVAPORATION POND COST MODEL 

10.1 BACKGROUND 

Solar evaporation, a well established method for removing water from a concentrate 

solution, has been used for centuries to recover salt (sodium chloride) from seawater. 

There are also installations that are used for the recovery of sodium chloride and other 

chemicals from strong brines, such as the Great Salt Lake and the Dead Sea, and for the 

disposal of brines resulting from oil well operations (USDI, Office of Saline Water 

1971). 

Evaporation ponds for membrane concentrate disposal are most appropriate for smaller 

volume flows and for regions having a relatively warm, dry climate with high 

evaporation rates, level terrain, and low land costs. These criteria apply predominantly in 

the western half of the United States – in particular, the southwestern portion. 

Advantages associated with evaporation ponds are described in the following list: 

• They are relatively easy and straightforward to construct. 

• Properly constructed evaporation ponds are low maintenance and require little 

operator attention compared to mechanical equipment. 

• Except for pumps to convey the wastewater to the pond, no mechanical 

equipment is required. 

• For smaller volume flows, evaporation ponds are frequently the least costly means 

of disposal, especially in areas with high evaporation rates and low land costs. 

Despite the inherent advantages of evaporation ponds, they are not without disadvantages 

that can limit their application, as described in the following list: 

• They can require large tracts of land if they are located where the evaporation rate 

is low or the disposal rate is high. 

• Most states require impervious liners of clay or synthetic membranes such as PVC 

or Hypalon. This requirement substantially increases the costs of evaporation 

ponds. 

• Seepage from poorly constructed evaporation ponds can contaminate underlying 

potable water aquifers. 

• There is little economy of scale for this land-intensive disposal option. 

Consequently disposal costs can be large for all but small-sized membrane plants. 

In addition to the potential for contamination of groundwater, evaporation ponds have 

been criticized because they do not recover the water evaporated from the pond. 

However, the water evaporated is not “lost;” it remains in the atmosphere for about 10 

days and then returns to the surface of the earth as rain or snow. This hydrologic cycle of 
 

 122 

evaporation and condensation is essential to life on land and is largely responsible for 

weather and climate. 

10.2 DESIGN CONSIDERATIONS 

10.2.1 Sizing of Evaporation Ponds: Evaporation ponds function by transferring liquid 

water in the pond to water vapor in the atmosphere above the pond. The rate at which an 

evaporation pond can transfer this water governs the size of the pond. Selection of pond 

size requires determination of both the surface area and the depth needed. The surface 

area required is dependent primarily on the evaporation rate. The pond must have 

adequate depth for surge capacity and water storage, storage capacity for precipitated 

salts, and freeboard for precipitation (rainfall) and wave action. 

10.2.1.1 Determining the Evaporation Rate: Proper sizing of an evaporation pond 

depends on accurate calculation of the annual evaporation rate. Evaporation from a 

freshwater body, such as a lake, is dependent on local climatological conditions, which 

are very site specific. In order to develop accurate evaporation data throughout the 

United States, meteorological stations have been established at which special pans 

simulate evaporation from large bodies of water such as lakes, reservoirs, and 

evaporation ponds. The pans are fabricated to standard dimensions and are situated to be 

as representative of a natural body of water as possible. A standard evaporation pan is 

referred to as a Class A pan. The standardized dimensions of the pans and the consistent 

methods for collecting the evaporation data allow comparatively and reasonably accurate 

data to be developed for the United States. The data collection must cover several years 

to be reasonably accurate and representative of site-specific variations in climatic 

conditions. Published evaporation rate databases typically cover a 10-year period or 

more and are expressed in inches per year. 

The pan evaporation data from each site can be compiled into a map of pan evaporation 

rates. Because of the small heat capacity of evaporation ponds, they tend to heat and cool 

more rapidly than adjacent lakes and to evaporate at a higher rate than an adjacent natural 

pond of water. In general, experience has shown the evaporation rate from large bodies 

of water to be approximately 70 percent of that measured in a Class A pan (USDI, 

Bureau of Reclamation 1969). This percentage is referred to as the Class A pan 

coefficient and must be applied to measured pan evaporation in order to arrive at actual 

lake evaporation. Over the years site-specific Class A pan coefficients have been 

developed for the entire area of the United States. Multiplying the pan evaporation rate 

by the pan coefficient results in a mean annual lake evaporation rate for a specific area. 

Maps are also available that depict annual average precipitation across the United States. 

Subtracting the mean annual evaporation from the mean annual precipitation gives the net 

lake surface evaporation in inches per year. This is the amount of water that will 

evaporate from a freshwater pond (or the amount the surface level will drop) over a year 

if no water other than natural precipitation enters the pond. All these maps assume an 

impervious pond that allows no seepage. Note that for some parts of the country the 

results of this calculation give a negative number and in other parts of the country it is a 
 

 123 

positive number. A negative number indicates a net loss of water from a pond over a 

year, or a drop in the pond surface level. A positive number indicates more precipitation 

than evaporation at a particular site. A freshwater pond at one of these sites would 

actually gain water over a year, even if no water other than natural precipitation were 

added. Thus such a site would not be a candidate for an evaporation pond. 

It is important to realize that data of this type are representative only of the particular 

sites of the individual meterological stations, which may be separated by many miles. 

Climatic data specific to the exact site should be obtained if at all possible prior to actual 

construction of an evaporation pond. 

The evaporation data described above are for freshwater pond evaporation. However, 

brine density has a marked effect on the rate of solar evaporation. Most procedures for 

calculating evaporation rate indicate evaporation is directly proportional to vapor 

pressure. Salinity reduces evaporation primarily because the vapor pressure of the saline 

water is lower than that of fresh water, and because dissolved salts lower the free energy 

of the water molecules. Cohesive forces acting between the dissolved ions and the water 

molecules may also be responsible for inhibiting evaporation, making it more difficult for 

the water to escape as vapor (Miller 1989). 

The lower vapor pressure and lower evaporation rate of saline water result in a lower 

energy loss and thus a higher equilibrium temperature than that of fresh water under the 

same exposure conditions. The increase in temperature of the saline water would tend to 

increase evaporation, but the water is less efficient in converting radiant energy into 

latent heat due to the exchange of sensible heat and long-wave radiation with the 

atmosphere. The net result is that, with the same input of energy, the evaporation rate of 

saline water is lower than that of fresh water. 

For water saturated with sodium chloride salt (26.4 percent), the solar evaporation rate is 

generally about 70 percent of the rate for fresh water (USDI, Office of Saline Water 

1971). Studies have shown that the evaporation rate from the Great Salt Lake, which has 

a TDS level of between 240,000 and 280,000 mg/L, is about 80 to 82 percent of the rate 

for fresh water. Other studies indicate that evaporation rates of 2, 5, 10, and 20 percent 

sodium chloride solutions are 97, 98, 93, and 78 percent, respectively, of the rates of 

fresh water (USDI, Bureau of Reclamation 1969). These ratios are determined from both 

experiment and theory. However, there is no simple relationship between salinity and 

evaporation, for there are always complex interactions among site-specific variables such 

as air temperature, wind velocity, relative humidity, barometric pressure, water surface 

temperature, heat exchange rate with the atmosphere, incident solar absorption and 

reflection, thermal currents in the pond, and depth of the pond. As a result these ratios 

should be used only as guidelines and with discretion. It is important to recognize that 

salinity can significantly reduce evaporation rate and to allow for this effect in sizing the 

evaporation pond’s surface area. In lieu of site-specific data, an evaporation ratio of 0.70 

is a reasonable allowance for long-term evaporation reduction. This ratio is also 

considered to be an appropriate factor for evaporation ponds that are expected to reach 

salt saturation over their anticipated service life. 
 

 124 

10.2.1.2 Pond Depth: Studies indicate that pond depths ranging from 1 to 18 in. are 

optimal for maximizing evaporation rate. However, similar studies indicate only a 4 

percent reduction in the evaporation rate as the pond depth is increased from 1 to 40 in. 

(USDI, Bureau of Reclamation 1969). Very shallow evaporation ponds are subject to 

drying and cracking of the liners and are not functional in long-term service for 

concentrate disposal. From a practical operating standpoint, an evaporation pond must 

not only evaporate wastewater but also provide 

• Surge capacity or contingency water storage 

• Storage capacity for precipitated salts 

• Freeboard for precipitation and wave action 

For an evaporation pond to be a viable disposal alternative for membrane concentrate, it 

must be able to accept concentrate at all times and under all conditions so as not to 

restrict operation of the desalination plant. The pond must be able to accommodate 

variations in the weather and upsets in desalination plant. The desalination plant cannot 

be shut down because the evaporation pond level is rising faster than anticipated. 

In order to allow for unpredictable circumstances, it is important that design 

contingencies be applied to the calculated pond area and depth. Experience from the 

design of industrial evaporation ponds has shown that discharges are largest during the 

first year of plant operation, are reduced during the second year, and are relatively 

constant thereafter. A long-term 20 percent contingency may be applied to the surface 

areas of the pond or its capacity to continuously evaporate water. The additional 

contingencies above the 20 percent (up to 50 percent) during the first and second years of 

operation are applied to the depth holding capacity of the pond. 

Freeboard for precipitation should be estimated on the basis of precipitation intensity and 

duration for the specific site. There may also be local codes governing freeboard 

requirements. In lieu of site-specific data, an allowance of 6 in. for precipitation is 

generally adequate where evaporation ponds are most likely to be located in the US 

(USDI, Office of Saline Water 1970). 

Freeboard for wave action can be estimated as follows (USDI, Office of Saline Water 

1970): 

Hw = 0.047 * W * √(F) 

Where Hw = wave height (ft) 

 W = wind velocity (mph) 

 F = fetch, or straight-line distance the wind can blow without obstruction (mi) 

The run-up of waves on the face of the dike approaches the velocity head of the waves 

and can be approximated as 1.5 * Hw. Hw is the freeboard allowance for wave action 

and typically ranges from 2 to 4 ft. The minimum recommended combined freeboard 
 

 125 

(for precipitation and wave action) is 2 ft. This minimum applies primarily to small 

ponds. 

Over the life of the pond (which should be sized for the same duration as the projected 

life of the desalination facility), the water will likely reach saturation and precipitate salts. 

The type and quantity of salts is highly variable and very site-specific. Allowance in the 

pond depth for precipitate salts can be made using Figure 10.1, which provides an 

estimate for the depth of precipitate produced as a function of the salinity of the 

wastewater discharged to the pond (USDI, Office of Saline Water 1970). For a given 

salinity, Figure 10.1 provides an estimate of precipitate produced (in feet per year) for 

each foot of wastewater discharged to the pond. Multiplying the annual deposition depth 

times the depth of water discharged to the pond each year and then by the life of the pond 

will result in the necessary allowance for the life of the pond. 

10.3 COST PARAMETERS 

Although sizing of an evaporation pond is a relatively straightforward procedure once 

appropriate net evaporation data are available, the costs associated with pond 

construction are highly site-specific and quite variable. Therefore generic cost estimating 

of evaporation ponds from typical handbook-type data is very difficult and subject to a 

wide range of accuracy. However, by gathering site-specific data a reasonably accurate 

cost estimate can be made. 

The following section sets forth the steps necessary to accurately determine the cost of an 

evaporation pond. Typical cost data are used. Graphs of the various costs for an 

evaporation pond can be used as the bases for determining site-specific costs. For some 

applications an evaporation pond can be a cost-effective disposal alternative; in other 

locations the cost can be prohibitive. 

In general it is anticipated that evaporation ponds will most likely be competitive for 

relatively small plants in remote, inland locations with high evaporation rates. Large 

membrane treatment plants are typically located near large population centers, where the 

availability of large tracts of inexpensive land will generally be limited. The major 

factors contributing to the cost of an evaporation pond are: 

• Land costs 

• Earthwork 

• Lining 

• Miscellaneous cost 

• Operation and maintenance 
 

 126 

Figure 10.1 Rate of Precipitation in Evaporation Pond (after USDI, Office of 

Saline Water, 1970) 

0

0.005

0.01

0.015

0.02

0.025

0 10 20 30 40 50 60

Salinity of Concentrate (ppm/1000)

Depth of Precipitate per Year (ft/yr)
 

 127 

10.3.1 Land Costs: The cost of land can vary greatly from site to site. In general, 

however, the cost of land at locations appropriate for evaporation ponds is a small 

percentage of the total cost. Costs vary not only from city to city but also in the vicinity 

of a particular municipality itself. Land costs can easily vary by a factor of 10 or more, 

depending on the exact location near the city. 

10.3.2 Earthwork: Like the cost of land itself, the cost of earthwork is very sitespecific, depending on whether the terrain is flat or hilly, rocky or sandy, forested or 

clear, and so forth. In selecting a site for an evaporation pond, such factors must be 

considered in making the final selection. Of course, in some cases there are only limited 

choices. If the desalination plant location is fixed by the proximity of the water source or 

the locus of the demand for the desalted water, the evaporation pond must be located 

reasonably close by. Certain aspects are generic, however; typical construction features 

for an evaporation pond include the following: 

• Land clearing 

• Perimeter dikes 

• Baffle dikes (optional) 

• Dike covers 

Land is required for the evaporative surface area and for the perimeter area that includes 

the dike, road, and fence. This distinction between evaporative area and total area is 

important in determining land requirements. Figures 10.2 and 10.3 provide an area 

correction factor to multiply times the evaporative area to calculate the total area. The 

correction factor value depends on the evaporative area and the dike height. This 

correction factor will be applied in determining land and land clearing costs. 

10.3.2.1 Land Clearing: The initial step in the construction of the pond consists of 

clearing the land. Land clearing can be labor intensive, and the cost is dependent upon 

the specific characteristics of each site. Costs can be categorized based on the type of 

vegetation at the site. The typical cost for clearing brush is $1,000/acre; for sparsely 

wooded areas, $2,000/acre; for medium-wooded areas, $4,000/acre; and for heavily 

wooded areas, $7,000/acre. 

10.3.2.2 Dikes: Dike construction, which is also labor intensive, involves excavating 

part of the soil and using it for the dike. Evaporation pond dikes are typically constructed 

with a 2:1 to 4:1 slope and a 12-ft top width that provides for a maintenance roadway. 

Generally the excavated earth is sufficient for the dike’s construction. The configuration 

of the pond determines the dike perimeter. To minimize the perimeter and the associated 

costs, the pond should be square. 

The major variable in dike design is the required height. The pond depth is set by the 

volume required to accumulate sludge and the height required to prevent overflow due to 

wave action. Dike heights of 4 to 12 ft are typical. Figures 10.4 and 10.5 summarize the 

cost of dikes with 4-ft, 8-ft, and 12-ft heights and acreages of 1 to 10 and 10 to 100 acres. 

These costs include material and labor for dike construction. 
 

 128 

Figure 10.2 Area Correction Factor as Function of Evaporative Area (1 to 10 

Acres) 

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 12

Evaporative Area (acres)

Area Correction Factor

12 ft. dike

8 ft. dike

4 ft. dike 
 

 129 

Figure 10.3 Area Correction Factor as Function of Evaporative Area (10 to 100 

acres) 

1

1.1

1.2

1.3

1.4

1.5

1.6

0 20 40 60 80 100 120

Evaporative Area (Acres)

Area Correction Factor

12 ft dike

8 ft dike 

4 ft dike
 

 130 

Figure 10.4 Dike Cost as Function of Evaporative Area (1 to 10 Acres) 

0

5

10

15

20

25

30

0 2 4 6 8 10 12

Evaporative Area (Acres)

Dike Cost (in 2001 $/Acre * 1,000)

12 ft dike

8 ft dike

4 ft dike 
 

 131 

Figure 10.5 Dike cost as Function of Evaporative Area (10 to 100 Acres) 

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100 120

Evaporative Area (acres)

Dike Cost (in 2001 $/Area * 1,000)

12 ft dike

8 ft dike

4 ft dike
 

 132 

Dike heights can be lower if the evaporation pond solids are periodically cleaned out. 

For cleanout, either a baffled single pond or multiple ponds are provided. A single pond 

designed for cleanout is baffled to allow sections of the pond to operate while other 

sections are cleaned. Figure 10.6 illustrates this arrangement. This scheme provides for 

a pond of smaller acreage as well as lower dike height. The water level can be lower, 

thus increasing the temperature, which will increase the evaporation rate and reduce the 

area required. The baffling will also help to settle the precipitates in a relatively uniform 

pattern, helping to minimize the required pond depth. Often one section is dried, and silt 

is placed over the salt precipitates to prevent the salts from redissolving as new 

wastewater is introduced. This practice also increases the net evaporation rate. The 

disposal costs for periodic cleaning of a baffled pond can be substantial and frequently 

rule out this option. 

10.2.2.3 Liners: Evaporation ponds have been used for decades for the disposal of liquid 

wastes. Historically numerous unlined evaporation ponds have been used as catchall 

disposal sites for a variety of wastes. Dumping in unlined evaporation ponds has 

frequently contributed to contamination of groundwater supplies with hazardous 

chemicals. Once contaminated, groundwater supplies are very difficult and expensive to 

clean up. 

Because the potential for groundwater contamination exists with any evaporation pond, 

most states require impervious liners of clay or synthetic membranes, which substantially 

increase the cost. Where the waste discharged to the pond can be verified as 

nonhazardous and the groundwater in the area is of poor quality or substantially distant 

from the pond, or both, a single liner may be acceptable. However, if the water has the 

potential to contain even trace amounts of hazardous substances or high-quality 

groundwater exists in shallow aquifers, double-lined ponds with leak detection systems 

are frequently required. These liners must be impervious to any seepage of water. 

Several types of liners are available, including polyvinyl chloride, high-density 

polyethylene, butyl rubber, and Hypalon. 

The costs of installing liners include those for material, hand dressing for raking rocks, 

ditching for liner anchoring, and installation. The total quantity of liner required is based 

on the areas of the pond bottom, the dike slope area, and an additional 6 to 10 ft for 

anchoring around the berm perimeter. On this basis, costs were developed for the liner 

assuming the use of a high-density polyethylene (HDPE) liner. These costs are presented 

in Figures 10.7 and 10.8. The reason for both the increasing liner unit cost with area and 

the dependency on dike height is an artifact of the way the curves are presented. The 

liner cost per acre is cost per total acre as opposed to evaporative surface acre. Although 

costs vary for alternative liner materials a rule of thumb that has been used in the 

calculations is $0.01 per mil thickness per ft2

. Given the many factors that can influence 

the actual liner cost, this rule is a reasonable compromise value for the preliminary level 

cost analysis. 
 

 133 

Figure 10.6 Schematic Diagram of a Baffled Evaporation Pond 

Baffle 

 Wastewater 
 

 134 

Figure 10.7 Liner Cost as Function of Evaporative Area (1 to 10 Acres) 

5

10

15

20

25

30

0 2 4 6 8 10 12

Evaporative Area (Acres)

Liner Cost (in 2001 $/Area * 1,000

4 ft dike

8 ft dike

12 ft dike
 

 135 

Figure 10.8 Liner Cost as Function of Evaporative Area (10 to 100 Acres) 

19

21

23

25

27

29

31

0 20 40 60 80 100 120

Evaporative Area (Acres)

Liner Cost (in 2001 $/Acre * 1,000)

4 ft dike 

8 ft dike

12 ft dike
 

 136 

10.3.3 Miscellaneous Costs: The following costs depend upon the needs of the specific 

installation; they may constitute a significant percentage of the total cost of the 

evaporation pond installation. Some of these possible costs include: 

• Fencing 

• Maintenance roadways 

• Disposal 

• Seepage monitoring 

• Contaminated ground cleanup 

10.3.3.1 Fencing: If the evaporation pond is not part of the main plant property, the cost 

of fencing should be applied to the cost of pond development. Fencing is required for 

several reasons. The membrane-lined sides of evaporation ponds are relatively steep and 

slick and pose a very real hazard for people and animals that might wander into the area. 

Fencing is also required for security purposes, to preclude acts of vandalism and 

unauthorized dumping. Installed fence costs are relatively standard and are estimated at 

$15/linear ft. Figures 10.9 and 10.10 provide estimates for the cost of fencing. The 

height of the dike impacts the size of the perimeter slightly, and thus the length of fence. 

This factor, however, is negligible in the context of the present model. 

10.3.3.2 Maintenance Roadways: For large evaporation ponds, maintenance roadways 

facilitate security patrols and routine inspection of the pond, and provide access for 

maintenance vehicles. In some bids the labor for constructing a roadway may be 

considered as part of the dike construction. In the following, however, this cost has been 

separated as the labor and material for construction a gravel roadbed. Figures 10.11 and 

10.12 illustrate the cost of the roadbed for various sizes of ponds based on $15/yd3

. 

10.3.3.3 Disposal: The solid precipitates collected in the pond may require periodic 

disposal if the pond is not large enough to hold the total volume of sludge produced 

during the life of the plant. This may occur either because the solids contribution to the 

pond is especially high (high suspended solids in the water stream, large amounts of 

windblown dirt, and the like), or because the pond has a shallow depth to enhance the 

evaporation rate or to avoid the local water table. 

The cost for solids disposal include dredging the solids from the pond, transporting the 

solids, and landfill disposal costs. In isolated cases the solids may require stabilization if 

hazardous materials (e.g., heavy metals) are present in the pond. 

10.3.3.4 Seepage Monitoring: Seepage monitoring or leak detection may be required, 

depending on the pond construction, the proximity and quality of nearby aquifers, or 

both. Single-lined ponds allow for no direct means of detecting seepage until the water 

has left the pond. However, for relatively clean wastes such as most membrane 

concentrates, a single-lined pond used in conjunction with monitoring wells may satisfy 
 

 137 

Figure 10.9 Fence Cost as Function of Evaporative Area (1 to 10 Acres) 

4

5

6

7

8

9

10

11

12

13

14

0 2 4 6 8 10 12

Evaporative Area (Acres)

Fence Cost (in 2001 $/Acre * 1,000)

12 ft dike

8 ft dike

4 ft dike
 

 138 

Figure 10.10 Fence Cost as Function of Evaporative Area (10 to 100 Acres) 

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 20 40 60 80 100 120

Evaporative Area (Acres)

Fence Cost (in 2001 $/Area * 1,000)

12 ft dike

4 ft dike

8 ft dike
 

 139 

Figure 10.11 Road Cost as Function of Evaporative Area (1 to 10 Acres) 

500

700

900

1100

1300

1500

1700

1900

2100

2300

0 2 4 6 8 10 12

Evaporative Area (acres)

Road Cost (in 2001 $/acre)

4 ft dike

8 ft dike

12 ft dike
 

 140 

Figure 10.12 Road Cost as Function of Evaporative Area (10 to 100 Acres) 

200

300

400

500

600

700

800

900

0 20 40 60 80 100 120

Evaporative Area (acres)

Road Cost (in 2001 $/Acre)

4 ft dike

12 ft dike

8 ft dike
 

 141 

local regulatory requirements. For contaminated wastes or in locations where highquality aquifers are present, a double-lined pond may be required to assure the integrity 

of the disposal site. In double-lined ponds a porous layer is provided between the two 

liners. Should the first liner leak, the wastewater will pass into the porous layer and drain 

to a monitoring sump, where it will be detected. Until draining or repair of the pond, or 

both, is affected, the second liner prevents groundwater contamination. For large ponds 

where draining of the porous layer to a sump is not practical because of the distances 

involved, electronic moisture detectors or lysimeters can be embedded in the porous 

layers at regular intervals to detect primary liner leaks. 

Where evaporation ponds are located in an area of known precious groundwater 

contamination, the owner may install monitoring wells around the pond, not to detect 

pond leaks but to establish a historical record of the existing groundwater contamination 

in the area. Then if additional contamination should occur in the area, the owner of the 

pond can provide water quality monitoring data from the wells, along with periodic 

samples of the wastewater in the pond, to assure the regulatory agencies that any 

additional groundwater contamination did not originate from the pond. 

To detect seepage around the pond, several methods may be used: bore holes, monitoring 

wells, or moisture detectors. The costs of these depend upon the required monitoring 

depth. 

10.3.3.5 Contaminated Ground Cleanup: The earth surrounding the evaporation pond 

may become contaminated through contact with the wastewater. The contamination 

could be the result of seepage or upset overflows from the pond. Cleanup of 

contaminated soils is becoming a cost factor in many states, but the requirements for 

cleanup are too varied at this time to reasonably predict the costs. Site-specific 

evaluations are required. 

10.3.4 Operating Costs: Once it has been constructed, the pond operates essentially 

maintenance-free. Periodic maintenance is required only for the repair of the dike or 

liner, pipe, flow control devices, etc. Operating costs also include security and damage 

inspection. The annual operating costs can be estimated at 0.5 percent of the total 

installation costs. 

10.4 DESIGN APPROACH FOR THE EVAPORATION POND COST MODEL 

• The climatic variables are key in the determination of the effective evaporation 

rate. This is not a simple matter and is perhaps the most critical design variable. 

• The model assumes that the effective evaporation rate is known. 

• Once known, this determines the total evaporation surface required. A 

contingency factor of 20 percent is included in the evaporation surface required. 

• The design challenge is to determine the suitable evaporation pond depth or 

conversely the dike height. This depends on the nature of the solution to be 

evaporated. 
 

 142 

• Standard tables exist for calculating the sludge buildup with time as a function of 

solution salinity. 

• The dike design variables include dike height (pond depth plus freeboard), dike 

slope ratio, and dike width at top. 

• Typically only enough earth will be excavated to build the dikes. 

• The total earth to be moved depends on the amount of dike, and this depends on 

pond size. The entire evaporative surface can be from one or many ponds. 

Typically the largest possible pond size is used, as this minimizes costs associated 

with earth moving, liner installation, road construction, and other costs. 

• Pond size, however, depends on the wind level and the possibility of dike erosion. 

• Dike height has a similar effect on dike cost as total system size, and both have a 

much greater effect on dike cost than the number of ponds 

• As the total pond size decreases, the dike physically makes up more of the total 

area of the system 

• The ratio of dike costs for different dike heights holds for any size system, as it is 

a function only of the relative sizes (volumes) of the different dikes 

• The design approach chosen for the worksheet model is as follows: 

o Excess evaporation surface of 20 percent is assumed as a design 

contingency 

o The dike slope is set at 3:1 

o The design is based on a single pond 

o The road width is set at 12 ft. 

o Excess liner for sealing and overlap is set at 2% 

• The remaining design variables include 

o Dike height (pond depth plus freeboard) 

o Evaporation surface determined by net evaporation rate and total 

concentrate flow) 

• Other input variables include: land type, total thickness of liner material, and unit 

land cost 

• Costs included in the capital cost model: 

o Land 

o Land clearing 

o Dike 

o Liner 

o Fencing 

o Roadway 

• Costs not included in the capital cost model: 

o Disposal of sludge 

o Seepage monitoring 

o Cleanup of contaminated soil 

o Cost of pipeline to the evaporation pond site 

10.5 EVAPORATION POND WORKSHEET AND EXAMPLE 

With the information provided above, the total cost of an evaporation pond can be 

determined. The worksheet for evaporation pond is provided in Table 10.1. An example 
 143 

Table 10.1 Worksheet for Evaporation Pond Disposal Capital Costs 

WORKSHEET for Evaporation Pond Disposal Capital Costs Preliminary Level Cost ONLY ENTER variable values Variable Range example case 1 A - evaporative surface (acres) 0 to 100 10 B - dike height (ft) 4, 8, 12 8 C - total liner thickness (mils) 20 to 120 60 D - land unit cost ($/acre) 0 - 10,000 5000 E - land type (see note 1 below) 1,2, 3, 4 3 CALCULATION of total acreage Action F - ratio: total acreage to evaporative acreage use Figures 10.2, 10.3 1.36 G - total acreage = A*F 13.6 FIND unit area costs from figures using total acreage, G Action cost, $ H - land, $/acre same as E 5000 I - land clearing (see note 1 below), $/acre 4000 J - dike, $/acre use Figures 10.4, 10.5 8600 K - nominal liner, $/acre use Figures 10.7, 10.8 22680 L - liner, $/acre =K*D/60 22680 M - fence, $/acre use Figures 10.9, 10.10 4500 N - road, $/acre use Figures 10.11, 10.12 770 

TOTAL Unit Cost add H, I, J, L, M & N 45550 

TOTAL above times G 619480 

 add engineering at 10% 61948  add contingency at 10% 61948 

GRAND TOTAL 743376 

COMMENTS: note 1: clearing cost ($/acre) 1-brush $1,000 2-sparsely woode

3-medium wooded $4,000 4-heavily wooded 
 

 144 

calculation is provided in the column marked ‘example.’ The land available is assumed 

to be 10 medium-wooded acres. A single liner material of thickness 60 mils is assumed 

along with a dike height of 8 ft and a unit land cost of $5,000/acre. The land and land 

clearing costs are entered into the worksheet. From Figure 10.2 an area correction factor 

of 1.36 is determined which multiplied times the evaporative surface area required gives 

the total land area required as 13.6 acres. The unit dike cost is $8,600/acre as found from 

Figure 10.4. From Figure 10.7 the liner cost is determined to be $22,680/acre. Perimeter 

fence cost is determined from Figure 10.9 to be $4500/acre. The Roadbed cost is 

$770/acre as per Figure 10.11. These unit costs are entered into the worksheet and added 

to give the total unit cost of $45,500/acre. For 13.6 acres this amounts to $619,480. 

With engineering and contingency fees both set at 10 percent, the grand total capital cost 

becomes $743,376. 

10.6 EVAPORATION POND REGRESSION MODEL 

For convenience, it is helpful to have a simplified closed-form mathematical expression 

to calculate preliminary capital cost. Cautions on using the worksheet model to develop 

capital cost for the evaporation pond apply to the regression model. By definition, the 

regression model is less accurate being based on a best fit of the results from the 

worksheet calculations. A linear regression model is used to develop the equation for 

total unit area capital cost. This model is valid from 10 to 100 acres. To obtain the total 

capital cost this expression is then multiplied times the total area required as well as by a 

20 percent contingency factor (1.2). The expression for the total area is non-linear taking 

into account the area adjustment factor as well as the evaporative surface area. 

Total Unit Area Capital Cost ($/acre) = 5406 + 465 * LINER THICKNESS 

+ 1.07 * LAND COST 

+ 0.931 * LAND CLEARING COST 

+ 217.5 * DIKE HEIGHT 

Total Area (plus contingency factor) = 1.2 * EVAP AREA * [1 + 

0.155 * DIKE HEIGHT/ 

(SQRT(EVAP AREA)) 

When multiplied together these two expressions yield the Total Capital Cost. 

For the worksheet example conditions of : 

LINER THICKNESS = 60 mil 

 LAND COST = $5000/acre 

LAND CLEARING COST = $4,000/acre 

DIKE HEIGHT = 8 ft 

 EVAP AREA = 10 acres 

The calculated total capital cost is $737,045, which compares to the worksheet result of 

$743,376. 
 

 145 

CHAPTER 11. 

SPRAY IRRIGATION WORKSHEET MODEL 

11.1 BACKGROUND 

Land application methods include irrigation systems, rapid infiltration, and overland flow 

systems (Crites et al, 2000). These methods, and in particular irrigation, were originally 

used to take advantage of sewage effluent as a nutrient or fertilizer source as well as to 

reuse the water. Membrane concentrate has been used for land application in the spray 

irrigation mode. Using the concentrate in lieu of fresh irrigation water helps conserve 

natural resources, and in areas where water conservation is of great importance, spray 

irrigation is especially attractive. Because of the higher TDS concentration of RO and 

EDR concentrate, unless it is diluted, concentrate is less likely than NF concentrate to be 

used for spray irrigation purposes. 

Concentrate can be applied to cropland or vegetation by sprinkling or surface techniques 

for water conservation by exchange when lawns, parks, or golf courses are irrigated; and 

for preservation and enlargement of greenbelts and open spaces. 

Where the nutrient concentration of the wastewater for irrigation is of little value, 

hydraulic loading can be maximized to the extent possible, and system costs can be 

minimized. Crops such as water-tolerant grasses with low potential for economic return 

but with high salinity tolerance are generally chosen for this type of requirement. 

Fundamental considerations in land application systems include knowledge of 

wastewater characteristics, vegetation, and public health requirements for successful 

design and operation. Environmental regulations at each site must be closely examined 

to determine if spray irrigation is feasible. Contamination of the groundwater and runoff 

into surface water are key concerns. Also, the quality of the concentrate – its salinity and 

toxicity, and the soil permeability – must be acceptable. 

The principal objective in spray irrigation systems for concentrate discharge is ultimate 

disposal of the applied wastewater. With this objective the hydraulic loading is usually 

limited by the infiltration capacity of the soil. If the site has a relatively impermeable 

subsurface layer or a high groundwater table, underdrains can be installed to increase the 

allowable loading. Grasses are usually selected for the vegetation because of their high 

nutrient requirements and water tolerance. 

Other conditions must be met before concentrate irrigation can be considered as a 

practical disposal option. First there must be a need for irrigation water in the vicinity of 

the membrane plant. If the need exists, a contract between the operating plant and the 

irrigation user would be required. Second, a backup disposal or storage method must be 

available during periods of heavy rainfall. Third, monitor wells must be drilled before an 

operating permit is obtained (Conlon 1989). 
 

 146 

11.2 DESIGN CONSIDERATIONS 

The following design considerations are applicable to spray irrigation of concentrate for 

ultimate disposal: 

• Salt, trace metals, and salinity 

• Site selection 

• Preapplication treatment 

• Hydraulic loading rates 

• Land requirements 

• Vegetation selection 

• Distribution techniques 

• Surface runoff control 

11.2.1 Salt, Trace Metals, and Salinity: Three factors that affect an irrigation source’s 

long term influence on soil permeability are the sodium content relative to calcium and 

magnesium, the carbonate and bicarbonate content, and the total salt concentration of the 

irrigation water. Sodium salts remain in the soil and may adversely affect its structure. 

High sodium concentrations in clay-bearing soils disperse soil particles and decrease soil 

permeability, thus reducing the rate at which water moves into the soil and reducing 

aeration. If the soil permeability, or infiltration rate, is greatly reduced, then the 

vegetation on the irrigation site cannot survive. The hardness level (calcium and 

magnesium) will form insoluble precipitates with carbonates when the water is 

concentrated. This buildup of solids can eventually block the migration of water through 

the soil. 

The U.S. Department of Agriculture’s Salinity Laboratory developed a sodium adsorption 

ratio (SAR) to determine the sodium limit. It is defined as follows: 

SAR = Na/[(Ca + Mg)/2]1/2

Where Na = sodium, meq/L 

 Ca = calcium, meq/L 

 Mg = magnesium, meq/L 

High SAR values (>9) may adversely affect the permeability of fine-textured soils and 

can sometimes be toxic to plants. 

Trace elements are essential for plant growth; however, at higher levels some become 

toxic to both plants and microorganisms. The retention capacity for most metals in most 

soils is generally high, especially for pH above 7. Under low pH conditions some metals 

can leach out of soils and may adversely affect the surface waters in the area. 

Salinity is the most important parameter in determining the impact of the concentrate on 

the soil. High concentrations of salts whose accumulation is potentially harmful will be 

continually added to the soil with irrigation water. The rate of salt accumulation depends 
 

 147 

upon the quantity applied and the rate at which it is removed from the soil by leaching. 

The salt levels in many brackish reverse osmosis concentrates can be between 5,000 and 

10,000 ppm, a range that normally rules out spray irrigation. 

In addition to the effects of total salinity on vegetation and soil, individual ions can cause 

reduction in plant growth. Toxicity occurs when a specific ion is taken up and 

accumulated by the vegetation, ultimately resulting in damage to it. The ions of most 

concern in wastewater effluent irrigation are sodium, chloride, and boron. Other heavy 

metals can be very harmful, even if present only in small quantities. These include 

copper, iron, barium, lead, and manganese. These all have strict environmental 

regulations in many states. 

In addition to the influence on the soil, the effect of the salt concentrations on the 

groundwater must be considered. The possible impact on groundwater sources may be a 

difficult obstacle where soil saturation is high and the water table is close to the surface. 

The chances of increasing background TDS levels of the groundwater are high with the 

concentrate. Due to this consideration, spray irrigation requires a runoff control system. 

An underdrain or piping distribution system may have to be installed under the full areas 

of irrigation to collect excess seepage through the soil, and thus to protect the 

groundwater sources. If high-salinity concentrate is being used, scaling of the underdrain 

may become a problem. The piping perforations used to collect the water can be easily 

scaled because the openings are generally small. Vulnerability to scaling must be 

carefully evaluated before a project is undertaken. 

11.2.2 Site Selection: Site selection factors and criteria for effluent irrigation are 

presented in Table 11.1. A moderately permeable soil capable of infiltration up to 2 

in./day on an intermittent basis is preferable. The total amount of land required for land 

application is highly variable but primarily depends on application rates. 

11.2.3 Preapplication Treatment: Factors that should be considered in assessing the 

need for preapplication treatment include whether the concentrate is mixed with 

additional wastewaters prior to application, the type of vegetation grown, the degree of 

contact with the wastewater by the public, and the method of application. In four Florida 

sites concentrate is aerated prior to discharge, because each plant discharges to a retention 

pond or ponds prior to irrigation. Aeration by increasing DO prevents stagnation and 

algae growth in the ponds, and also supports fish populations. The ponds are required for 

flow equalization and mixing. Concentrate is typically blended with biologically treated 

wastewater. 

11.2.4 Hydraulic Loading Rates: Determining the hydraulic loading rate is the most 

critical step in designing a spray irrigation system. The loading rate is used to calculate 

the required irrigation area and is a function of precipitation, evapotranspiration, and 

percolation. The following equation represents the general water balance for hydraulic 

loading based upon a monthly time period and assuming zero runoff: 
 

 148 

Table 11.1 Site Selection Factors and Criteria 

Factor Criterion 

Soil 

 Type Loamy soils are preferred, but most soils from sands to clays are 

 acceptable 

 Drainability Well-drained soil is preferred. 

 Depth Uniformly 5 to 6 ft or more throughout sites is preferred. 

Groundwater 

 Depth to groundwater A minimum of 5 ft is preferred. 

Groundwater control Control may be necessary to ensure renovation if the water table is 

 less than 10 ft. from the surface. 

 Groundwater movement Velocity and direction of movement must be determined. 

 

Slopes Slopes of up to 20 percent are acceptable with or without terracing. 

Underground formations Formations should be mapped and analyzed with respect to 

 interference with groundwater or percolating water movements. 

 

 

Isolation Moderate isolation from public is preferred; the degree of isolation 

depends on wastewater characteristics, method of application, and 

crop. 

Distance from source of wastewater An appropriate distance is a matter of economics 

HLR = ET + PER - PPT 

Where HLR = hydraulic loading rate 

 ET = evapotranspiration 

 PER = percolation 

 PPT = precipitation 

In most cases surface runoff from fields irrigated with wastewater is not allowed without 

a permit or at least must be controlled; it is usually controlled just so that a permit does 

not have to be obtained. 

Seasonal variations in each of these values should be taken into account by evaluating the 

water balance for each month as well as the annual balance. For precipitation the wettest 

year in 10 is suggested as reasonable in most cases. Evapotranspiration will also vary 

from month to month, but the total for the year should be relatively constant. Percolation 

includes that portion of the water that, after infiltration into the soil, flows through the 

root zone and eventually becomes part of the groundwater. The percolation rate used in 

the calculation should be determined on the basis of a number of factors, including soil 

characteristics underlying geologic conditions, groundwater conditions, and the length of 

drying period required for satisfactory vegetation growth. The principal factor is the 

permeability or hydraulic conductivity of the least permeable layer in the soil profile. 
 

 149 

Resting periods, standard in most irrigation techniques, allow the water to drain from the 

top few inches of soil. Aerobic conditions are thus restored, and air penetrates the soil. 

Resting periods may range from a portion of each day to 14 days and depend on the 

vegetation, the number of individual plots in the rotation cycle, and the availability of 

backup storage capacity. 

To properly calculate an annual hydraulic loading rate, monthly evapotranspiration, 

precipitation, and percolation rates must be obtained. The annual hydraulic loading rate 

represents the sum of the monthly loading rates. Recommended loading rates range from 

2 to 20 ft/yr (Goigel 1991). 

11.2.5 Land Requirements: Once a hydraulic loading rate has been determined, the 

required irrigation area can be calculated using the following equation: 

 A = Q * K1/ALR 

Where A = irrigation area (acre) 

 Q = concentrate flow (gpd) 

 ALR = annual hydraulic loading rate (ft/yr) 

 K1 = 0.00112 d * ft3

 * acres/(hr * gal * ft2) 

The total land area required for spray irrigation includes allowances for buffer zones and 

storage and, if necessary, land for emergencies or future expansion. 

For loadings of constituents such as nitrogen, which may be of interest to golf course 

managers who need fertilizer for the grasses, the field area requirement is calculated as 

follows: 

Field area (acres) = 3,040 * C * Q/Lc 

Where C = concentration of constituent (mg/L) 

 Q = flow rate (mgd) 

 Lc = loading rate of constituent (lb/acre-yr) 

11.2.6 Vegetation Selection: The important aspects of vegetation for irrigation systems 

are water needs and tolerances, sensitivity to waste water constituents, public health 

regulations, and vegetation management considerations. 

The vegetation selection depends highly on the location of the irrigation site and natural 

conditions such as temperature, precipitation, and topsoil condition. Automated watering 

alone cannot always ensure vegetation propagation. 

Vegetation selection is the responsibility of the property owners. Woodland irrigation for 

growing trees is being conducted in some areas. The principal limitations on this use of 

wastewater include low water tolerances of certain trees and the necessity to use fixed 

sprinklers, which are expensive. 
 

 150 

Membrane concentrate disposal will generally be to landscape vegetation. Such 

application, for example to highway median and border strips, airport strips, golf courses, 

parks and recreational areas, and wildlife areas, has several advantages. Problems 

associated with crops for consumption are avoided and the irrigated land is already 

owned, so land acquisition costs are saved. 

11.2.7 Distribution Techniques: Many different distribution techniques are available 

for engineered wastewater effluent applications. For irrigation, two main groups, 

sprinkling and surface application, are used. Sprinkling systems used for spray irrigation 

are of two types, fixed and moving. Fixed systems, often called solid set systems, may be 

either on the ground surface or buried. Both types usually consist of impact sprinklers 

mounted on risers that are spaced along lateral pipelines, which are in turn connected to 

main pipelines. These systems are adaptable to a wide variety of terrains and may be 

used for irrigation of either cultivated land or woodlands. Portable aluminum pipe is 

normally used for above ground systems. This pipe has the advantage of relatively low 

capital cost, but is easily damaged, has a short expected life because of corrosion, and 

must be removed during cultivation and harvesting operations. 

Pipe used for buried systems may be buried as deep as 1.5 ft below the ground surface. 

Buried systems usually have the greatest capital cost; however they are probably the most 

dependable and are well suited to automatic control. 

There are a number of different moving sprinkler systems, including center-pivot, sideroll, wheel-move, rotating-boom, and winch-propelled systems. 

11.2.8 Surface Runoff Control: Surface runoff control depends mainly on the 

proximity of surface water. If runoff drains to a surface water, an NPDES permit may be 

required. This situation should be avoided if possible due to the complication of 

quantifying overland runoff. Berms can be built around the irrigation field to prevent 

runoff. Another alternative although expensive is for a surrounding collection system. It 

is best to use precautions and backup systems to ensure that overwatering and subsequent 

runoff do not occur in the first place. 

11.3 COST FACTORS 

The model presented is for a fixed and buried spray system for landscape irrigation. The 

major parameters that will determine the cost of a spray irrigation system include 

concentrate flow rate, transport pipeline, irrigation land purchase and preparation, 

distribution piping and sprinklers, pumping pressure, facilities for wet weather storage, 

and subsurface underdrain system. 

11.3.1 Land: The spray irrigation of concentrate is more land intensive than other 

disposal methods, including evaporation ponds, as loading rates that determine the 

irrigation area are generally lower than net evaporation rates that determine evaporation 

pond area. If an existing area requiring irrigation is not available, then areas surrounding 
 

 151 

the plant must be purchased or leased for concentrate disposal. Land costs fluctuate with

the location and characteristics of the site. Several options exist for the purchase or 

control of land used for a concentrate disposal system. The land may be purchased 

outright, leased on a long-term basis, or purchased and leased back to another party (i.e., 

to a farmer for irrigation). Purchasing land allows for complete control over it, and 

makes future expansion of the disposal site easier to accomplish. 

The area required for irrigation has been estimated for waste flow rates between 0 and 5 

mgd. The necessary area has been calculated for hydraulic loadings of 5 to 20 ft/yr. The 

results are illustrated in Figures 11.1 and 11.2. With these figures the area can be 

approximated for each specific site. 

Preparation of the irrigation land, such as clearing or grubbing, will add to overall 

disposal site costs and should be considered when selecting the potential irrigation site. 

Spray irrigation systems also require land for service roads, buffer zones, storage 

lagoons, and equipment storage in addition to the area needed for the irrigation field. 

These additional land requirements are small compared to the large irrigation area and are 

not taken into account in the estimates provided in this section. The unit costs of land 

clearing are similar to those for an evaporation pond, but are much larger due to the 

expanded area. However, the same criteria can be applied: cost for clearing bushes, 

$1,000/acre; sparsely wooded areas, $2,000/acre; medium-wooded areas, $4,000/acre; 

and heavily wooded areas, $7,000/acre. 

11.3.2 Distribution: The cost of the distribution system includes the cost of the piping 

(main header, subheaders, and laterals), the cost of the sprinklers, and the cost of valves 

placed on the subheaders to segregate portions of the system for isolation. Figure 11.3 

illustrates a distribution system with four submain headers. The size and length of the 

main header pipe are set by the area of land to be irrigated and the flow rate required. As 

the size of the area to be irrigated relative to the available flow increases, it no longer 

becomes feasible to irrigate the entire system at the same time, due to minimum flow 

requirements for the individual sprinkler. The entire distribution system is segmented 

into several subsystems, each of which is operated in a sequential pattern. A minimum 

number of subsystems is required to meet the minimum flow requirements per sprinkler. 

The number of submain headers and the number of sprinklers per lateral are determined 

by the number of subsystems. Setting of the number of submain headers uniquely 

determines the number of sprinklers per lateral. The more submain headers, the fewer 

sprinklers per lateral. 

Sprinklers are characterized by the wetted diameters of their coverage and their 

pressure/flow characteristics. The water delivered (in/hr) by a sprinkler is greatest near 

the sprinkler head and decreases in a bell-shaped curve to the edge of the wetted 

diameter. In order to deliver more uniform coverage, sprinklers are typically spaced with 

as much as a 30 to 50 percent overlap in coverage. Thus the spacing of the sprinklers is 

less than the wetted diameter of the sprinkler. 
 

 152 

Figure 11.1 Land Requirements as a Function of Flow and Loading (Flows up to 

1.2 mgd) 

0

20

40

60

80

100

120

140

0 0.2 0.4 0.6 0.8 1 1.2

Flow Rate (mgd)

Area (acres)

20 ft/yr 

15 ft/yr 

10 ft/yr 

5 ft/yr 

2 ft/yr 
 

 153 

Figure 11.2 Land Requirements as a Function of Flow and Loading (Flows up to 

3.5 mgd) 

0

50

100

150

200

250

300

350

400

450

500

0 0.5 1 1.5 2 2.5 3 3.5

Flow Rate (mgd)

Area (acres) 

2 ft/yr

5 ft/yr 

10 ft/yr 

15 ft/yr 

20 ft/yr 
 

 154 

Figure 11.3 Schematic Diagram of a Typical Spray Irrigation Distribution System 

In designing the distribution system, one first determines the area of land that is required 

based on the concentrate flow and the loading rate of the land. This sets the length of the 

main header. Setting of the sprinkler spacing determines the total number of sprinklers 

required. The subsystem design may be based on meeting a minimum flow rate per 

sprinkler. The lengths of main header, submain header, and laterals are set at this point. 

The size of the piping is chosen to meet pressure drop limitations dictated by delivering a 

certain pressure to the sprinkler head consistent with its pressure/flow characteristics. 

Typically lower acceptable diameter piping is specified to minimize pipe cost. There are 

choices and options in sprinkler and distribution design that may be made based on 

minimizing overall system cost and providing system flexibility. 

The present model is for preliminary design purposes only. Because the more final 

design requires site-specific information and costs to be considered, the present model 

makes several design assumptions that are listed in the design approach section. 

Submain 

Lateral 

Main Header 
 

 155 

Piping costs include the cost of the main header, the submain headers, and the laterals. 

Also included in the distribution system costs are the cost of sprinkler heads and 

mountings, the cost of valves mounted on each submain half, and the cost of the control 

system that operates these valves. 

An assumption is made that the piping header will run the length of the land. The length 

is estimated by assuming the land will be in the form of a square. After the length of pipe 

is calculated, the final cost is estimated by using the appropriate unit piping length cost. 

First the pipe size is calculated on the assumption that the maximum velocity of 5 fps will 

not be exceeded. The standard pipe diameter will bracket a range of flows. For example, 

a 2 in. pipe can handle flows up to 0.07 mgd before exceeding the 5 fps criterion. Then a 

3 in. pipe can handle flows between 0.07 and 0.16 mgd. The normal step changes this 

causes in cost curves have been eliminated in the cost figures due to the preliminary 

nature of the cost estimates. The costs presented are based on the costs of PVC piping. 

The costs of the submains are estimated by a similar procedure. Again, the submain 

length is assumed to be the total length of the land. The lateral cost is a function of how 

many sprinklers are on each lateral and the distance the sprinklers can cover. 

The single main header is sized for the total flow and is the largest diameter pipe in the 

system. Flow in the main header goes into the submain headers mounted perpendicular 

to it. Valves are located on each submain half near the main header to control flow into 

the submain halves. The valves are either fully open or closed according to which 

subsystem of the distribution system is operating. For example, perhaps a system has 8 

submain headers and thus 16 half submains. If each subsystem involves 2 submain 

halves, then the total flow in the main header flows into these 2 submain halves and on to 

the laterals and sprinkler heads associated with these submain halves. The submain 

header halves are sized according to the flow and velocity constraints. After this 

subsystem has operated for a period of time, valve closures and openings shunt the flow 

to another subsystem. Typically the major piping cost is for the submain headers. 

Figures 11.4 and 11.5 provide piping costs (header, submain headers, and laterals) as a 

function of area to be irrigated. For a given area, land with greater hydraulic loadings 

will receive more flow and the piping system will be of larger diameter to accommodate 

the greater flows. Thus the greater piping cost for the larger loading systems is reflected 

in these figures. 

The cost of the sprinklers, valves, and control system are combined and presented in 

Figure 11.6. The sprinkler cost is typically the largest of these cost items. The cost is 

dependent upon the land area. 

The installed costs, which include labor and trenching for the distribution system, are 

taken as 1.8 times the material cost obtained from Figures 11.4 through 11.6. 
 

 156 

Figure 11.4 Distribution System Piping Cost as Function of Area (up to 50 acres) 

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Area (acres)

Pipe Cost ($/1000)

20 ft/yr 

10 ft/yr 

5 ft/yr 
 

 157 

Figure 11.5 Distribution System Piping Cost as Function of Area (up to 

200 acres) 

0

50

100

150

200

250

300

0 50 100 150 200 250

Area (acres)

Pipe Cost ($/1000)

20 ft/yr 

10 ft/yr 

5 ft/yr 
 

 158 

Figure 11.6 Sprinkler, Valves, and Control System Cost as Function of Area 

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250

Area (acres)

Sprinkler, Valves, Control Ssytem Cost ($/1000)
 

 159 

11.3.3 Pumping: The concentrate stream is first stored in a storage facility and then 

pumped to the irrigation system. The head requirement of the pump is established by the 

pumping distance and the pressure loss through the sprinklers. Based on the flow rate 

and pump head, the size of the pump and estimated cost can be established. For this 

study, the pump heads are assumed to be less than 100 psig and would be similar in cost 

to the low-head pumps for deep well injection (see Figure 11.7). 

11.3.4 Storage: Temporary storage facilities are necessary to retain concentrate during 

heavy rainfall periods or other circumstances when irrigation is not necessary. The need 

for retention facilities is particularly important in areas with large average yearly rainfall. 

Storage tanks or lined ponds can be utilized. The volume of storage required is set by the 

amount of rainfall expected at the site. Historical rainfall data must be reviewed to 

determine the maximum number of consecutive days on which irrigation would not be 

necessary. Storage tank costs have been estimated based on using retention and circular 

tanks designed for 1-day capacity. These costs are summarized in Figures 11.8 and 11.9. 

11.3.5 Underdrains: Irrigation systems may be required to include underdrainage to 

protect groundwater sources. Subsurface drainage systems consist of a network of buried 

drainage pipes with open holes or perforations that recover the waste stream effluent that 

has percolated through the soil. A collection basin is used to recover the water collected 

by the underdrains. This water can then be reused by the irrigation system. The 

contribution of this water to the total flow is minor. 

The cost of an underdrain system will add significantly to the overall cost of the system. 

The underdrain system will consist of header and subheader pipes arranged similarly to 

the distribution piping. For a cost estimate, use 80 percent of the piping cost as 

determined from Figures 11.4 and 11.5. 

11.3.6 Operational Costs: Costs associated with the labor requirements for spray 

irrigation must be addressed, because the operation and maintenance of a concentrate 

spray irrigation system is more labor intensive than the disposal methods previously 

discussed. Labor requirements include sprinkler system repair and vegetative surface 

maintenance. The energy costs for pump operation also add to the system’s total 

operational costs. 

11.4 DESIGN APPROACH FOR SPRAY IRRIGATION MODEL 

NOTE: in a site-specific design various options for the sprinkler (sprinkler size, spacing, 

overlap) and distribution system (submain header, laterals, sprinklers per lateral) would 

be investigated. The design constraints include cost, pressure drop, available sizes, etc. 

In this way the most appropriate and effective system can be defined. In addition the 

variability of loading and application rates with time of day and month of the year would 

be examined to ensure that the design meets minimum and maximum flow, temperature, 
 

 160 

Figure 11.7 Cost of Low-head Pumps as Function of Flow Rate 

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8 9 10

Flow Rate (mgd)

Pump Costs (in 1992 $ * 1,000)
 

 161 

Figure 11.8 Storage Tank Cost as Function of Flow Rate (up to 0.5 mgd) 

0

20

40

60

80

100

120

0 0.1 0.2 0.3 0.4 0.5

Flow Rate (mgd)

Storage Tank Costs (in 1992 $ * 1,000)
 

 162 

Figure 11.9 Storage Tank Cost as Function of Flow Rate (up to 5 mgd) 

0

200

400

600

800

1000

1200

012345

Flow Rate (mgd)

Storage Tank Costs (in 1992 $ * 1,000)
 

 163 

and other conditions. In the following approach to preliminary cost estimation, various 

assumptions are made to simplify the design process and enable cost estimates to be 

developed more easily. 

• The system is a solid set buried spray irrigation system comprised of PVC piping. 

• The total flow (mgd) and loading factor (ft/yr) determine the total number of acres 

needed to take up the water. 

• The main header is sized to handle the total flow. 

• The entire distribution system (main header, submain headers, laterals, sprinklers) 

that covers the acreage cannot be active at one time because of minimum flow 

requirements for the individual sprinkler. 

• Consequently only a portion of the system is active at any given time. 

• Gate valves on each submain half control which submain halves are active at a 

given time. 

• The hydraulics for the subsystem (portion active at any one time) determine the 

pipe sizing for the headers and laterals. Considerations include flow, pressure, 

velocity, irrigation rate (in./hr), etc. 

• The length of time any part of the system is on is limited by the allowable 

application rate (in/hr). 

• The entire irrigation system is chosen to be in the shape of a square. 

• The main header flows the entire length of the square (minus a portion of the 

wetted radius of the sprinkler at the distal end). 

• The submain headers are perpendicular to the main header and span the entire 

length of the square (minus portions of the wetted radius of the sprinkler at each 

end). 

• The laterals are perpendicular to the submain headers and may contain one to 

several sprinklers per lateral. 

• The length of each lateral is a function of how many sprinklers are on each lateral. 

• There is an inverse relation between the number of submain headers and the 

number of sprinklers per lateral. The more submain headers, the fewer sprinklers 

per lateral. 

• A certain number of submain headers is necessary to allow division of the entire 

system into subsystems, only one of which operates at a time. This permits a 

minimum sprinkler flow to be met. 

• The ground coverage from the sprinklers is highest nearest the sprinkler, having a 

bell curve-type distribution with distance from the sprinkler. 

• To assure some coverage of all ground and to provide more uniformity of 

coverage, the spacing between sprinklers is chosen to provide an overlap in 

ground coverage. This overlap is typically from 30 to 50% of the wetted 

diameter. 

• The most economical and efficient design needs be investigated for each sitespecific situation. 

• The specific design approach chosen for this model is as follows: 

o Number of submain headers is a variable that ranges from 1 to 16 
 

 164 

o This allows for up to 32 identical subsystems as there are 32 independent 

halves to the submain system, each of which can be active or inactive 

o Each subsystem is identical 

o The system is active for 20 hours per day 

o Each subsystem is active for an identical period of time each day. 

o It is assumed that an impact sprinkler will be used that has a flow of from 

10 to 35 gpm per sprinkler and a wet radius in the range of 55 to 85 ft; the 

wet radius increasing with the flow 

o The actual design is a trial and error process that involves choice of 

number of submain headers, and number of active subsystems. These 

variables are exercised until a solution is found where a sprinkler roughly 

matching the performance characteristics of the impact sprinkler just 

mentioned, is found. Very few combinations of the variables result in 

conditions matching sprinkler performance specifications. 

o It is assumed that the pressure to the distribution system is 100 psi and that 

the pressure drop through the piping is not greater than 25 psi. 

o Where design constraints dictate changes in pipe diameter from one 

nominal size to another, there would be step changes in the cost curves. 

These step changes are eliminated from the figures due to the preliminary 

nature of the cost estimate and to enforce the recommendation that a sitespecific cost workup be done whenever any cost estimate other than a 

preliminary one is sought. 

• Costs included in the capital cost model: 

o Land 

o Land clearing 

o Distribution systems (header, submain header, laterals, sprinklers, valves) 

o Pump 

o Storage tank 

o Underdrain 

• Costs not included in the capital cost model: 

o Cost of blending, modifying, or pretreating concentrate to meet water 

quality requirements 

o Cost of pipeline to the spray irrigation site 

o Cost of monitoring wells 

11.5 SPRAY IRRIGATION MODEL WORKSHEET AND EXAMPLE 

The total capital cost of a spray irrigation system, based on the assumptions made above, 

can now be determined. The worksheet for the calculation is given in Table 11.2. The 

flow rate is taken to be 1 mgd. The land is capable of taking an annual loading of 10 ft/yr 

and is initially a sparsely wooded area requiring a clearing cost of $2,000 per acre. One 

day’s storage of concentrate is assumed to be required. The land sells for $5,000 per 

acre. From figure 11.1 the area required is determined to be 110 acres. The cost of the 

land and of clearing the land is calculated to be $550,000 and $220,000 respectively. 

The distribution system piping cost is determined from Figure 11.5 to be $112,000 and 

the sprinkler, valve, and control system cost is determined from Figure 11.6 to be 
 165 

Table 11.2 Worksheet for Spray Irrigation Disposal Capital Costs

WORKSHEET for Spray Irrigation Disposal Capital Costs 

Variable 

ENTER variable values range example case 1 case 2 cA - flow rate (mgd) 1 to 5 1 B - loading (ft/yr) 5 to 20 10 C - land type (see note 1) 2 D - storage time (days) 1 or 2 1 E - land unit cost ($/acre) 0 - 10,000 5000 DETERMINE land parameters Action F - land requirement (acres) use A, Figures 10.1 & 10.2 110 G - land clearing unit cost ($/acre) see note below 2000 FIND costs from figures and calculations Action H - land cost (acres * land unit cost), $ = F * E 550000 I - land clearing cost (acres * unit cost), $ = F * G 220000 J - piping cost, $ use F, Figures 10.4 & 10.5 112000 K - sprinkler, valves, control system cost, $ use F, Figure 10.6 60000 L - distribution system material cost, $ = J + K 172000 M - installed distribution system cost, $ = 1.8 * L 309600 N - pump cost, $ use A, Figure 10.7 25000 O - storage tank cost, $ use A * D, Figure 10.8 & 10.9 230000 P - underdrain cost, $ = 1.44 * J 161280 

TOTAL =H+I+M+N+O+P 1495880 

COMMENTS: note 1: clearing costs ($/acre): 1-brush 1000 

 2-sparsely wooded 2000 

 3-medium wooded 4000 

 4-heavily wooded 7000 
 

 166 

$60,000. Together, the last two costs determine the distribution system material cost of 

$172,000. The installed distribution system is 1.8 times this, or $309,600. From Figure 

11.7 the pump cost is set at $25,000 and from Figure 11.9 the storage tank cost is 

determined to be $230,000. The underdrain system is taken at 80 percent of the piping 

cost, or at 1.44 times the installed piping cost, which equals $161,280. The sum of the 

various costs is $1,495,880. 

11.6 SPRAY IRRIGATION REGRESSION MODEL 

Based on about 30 cases from the worksheet, a closed form mathematical relation was 

developed to approximate the worksheet model. The user is reminded that the cautions 

that apply to the worksheet model apply even more for the less accurate regression 

model. The costs developed are for preliminary design levels only. The model 

developed below is linear in the various cost factors. The mathematical expression is: 

Total Capital Cost ($) = 89,961 + 1,163,000 * FLOW 

- 27,080 * LOADING 

 + 33,133 * STOREDAYS 

 + 57.6 * LANDCOST 

 + 70.3 * CLEARCOST 

For the worksheet example conditions of: 

 

 FLOW = 1 mgd 

 LOADING = 10 ft/yr 

 STOREDAYS = 1 day 

 LANDCOST = 5,000 $/acre 

 CLEARCOST = 2,000 $/acre 

The calculated total capital cost is $1,443,776, which compares to the worksheet result of 

$1,495,880. 
 

 167 

CHAPTER 12. 

ZERO LIQUID DISCHARGE MODEL 

12.1 BACKGROUND 

In this approach evaporation is used to further concentrate the membrane concentrate. In 

the extreme limit of processing concentrate to dry salts, the method becomes a zero 

discharge option. Evaporation requires major capital investment, and the high energy 

consumption together with the final salt or brine disposal can result in significant disposal 

costs. 

Because of this, disposal of municipal membrane concentrate by mechanical evaporation 

would typically be considered only under the special circumstance where no other 

disposal option is feasible. Cost aside, however, there are some advantages to zero 

liquid discharge. These include: 

• It may avoid a lengthy and tedious permitting process. 

• It may gain quick community acceptance. 

• It can be located virtually anywhere. 

• It represents a positive extreme in recycling, in efficient use of the water source. 

When this thermal process is used following an RO system, for example, it produces 

additional product water by recovering high-purity distillate from the concentrate 

wastewater stream. The distillate can be used to help meet the system product water 

volume requirement. This reduces the size of the membrane system and thus the size of 

the membrane concentrate to be treated by the thermal process. In addition, because the 

product purity of the thermal process is so high (TDS in the range of 10 mg/L), some of 

the product water volume requirement of the system may be met by blending the thermal 

product with untreated source water. The usual concerns and considerations of using 

untreated water for blending need to be addressed. The end result may be a system where 

the system product requirement is met by three streams: 1) membrane product, 2) thermal 

process product, and 3) bypass water. 

12.1.1 Single- and Multiple-Effect Evaporators: Using steam as the energy source, it 

takes about 1000 BTU to evaporate a pound of water. In a single-effect evaporator, heat 

released by the condensing steam is transferred across a heat exchange surface to an 

aqueous solution boiling at a temperature lower than that of the condensing stream. The 

solution absorbs heat and part of the solution water vaporizes, causing the remaining 

solution to become richer in solute. The water vapor flows to a barometric or surface 

condenser, where it condenses as its latent heat is released to cooling water at a lower 

temperature. The finite temperature differences between the steam, the boiling liquid, and 

the condenser are the driving forces required for the heat transfer surface area to be less 

than infinite. Practically all the heat removed from the condensing stream (which had 
 

 168 

been generated initially by burning fuel) is rejected to cooling water and is often 

dissipated to the environment without being of further use. 

The water vapor that flows to the condenser in a single-effect evaporator is at a lower 

temperature and pressure than the heating stream, but has almost as much enthalpy. 

Instead of releasing its latent heat to cooling water, the water vapor may be used as 

heating steam in another evaporator effect operating at a lower temperature and pressure 

than the first effect. 

Additional effects may be added in a similar manner, each generating additional vapor, 

which may be used to heat a lower-temperature effect. The vapor generated in the 

lowest-temperature effect finally is condensed by releasing its latent heat to cooling water 

in a condenser. The economy of a single- or multiple-effect evaporator may be expressed 

as the ratio of kilograms of total evaporation to kilograms of heating steam. As effects 

are added, the economy increases representing more efficient energy utilization. 

Eventually added effects result in marginal added benefits and the number of effects is 

thus limited by both practical and economic considerations. Multiple effect evaporators 

increase the efficiency (economy), but add capital cost in the form of additional 

evaporator bodies. 

More specifically, the number of effects, and thus the economy achieved, is limited by 

the total temperature difference between the saturation temperature of the heating steam 

(or other heat source) and the temperature of the cooling water (or other heat sink). The 

available temperature difference may also be constrained by the temperature sensitivity 

of the solution to be evaporated. The total temperature difference, less any losses, 

becomes allocated between effects in proportion to their resistance to heat transfer, the 

effects being thermal resistances in series. 

The heat transfer surface area for each effect is inversely proportional to the net 

temperature difference available for that effect. Increasing the number of effects reduces 

the temperature difference and evaporation duty per effect, which increases the total area 

of the evaporator in rough proportion to the number of effects. 

The temperature difference available to each effect is reduced by boiling point elevation 

and by the decrease in vapor saturation temperature due to pressure drop. The boiling 

point elevation of a solution is the increase in boiling point of the solution compared to 

the boiling point of pure water at the same pressure; it depends on the nature of the solute 

and increases with increasing solute concentration. In a multiple-effect evaporator, the 

boiling point elevation and vapor pressure drop losses for all the effects must be summed 

and subtracted from the overall temperature difference between heat source and sink to 

determine the net driving force available for heat transfer. 

12.1.2 Vapor Compression Evaporator Systems (Brine Concentrators): A vapor 

compression evaporator system, or brine concentrator, is similar to a conventional singleeffect evaporator, except that the vapor released from the boiling solution is compressed 

in a compressor. Compression raises the pressure and saturation temperature of the vapor 

so that it may be returned to the evaporator steam chest to be used as heating steam. The 
 

 169 

latent heat of the vapor is used to evaporate more water instead of being rejected to 

cooling water. 

The compressor adds energy to the vapor to raise its saturation temperature above the 

boiling temperature of the solution by whatever net temperature difference is desired. 

The compressor is not completely efficient, having small losses due to mechanical 

friction and larger losses due to nonisentropic compression. The additional energy 

required because of nonisentropic compression is not lost from the evaporator system, 

however; it serves to superheat the compressed vapor. The compression energy added to 

the vapor is of the same magnitude as energy required to raise feed to the boiling point 

and make up for radiation and venting losses. By exchanging heat between the 

condensed vapors (distillate) and the product with the feed, it is usually possible to 

operate with little or no makeup heat in addition to the energy necessary to drive the 

compressor. The compressor power is proportional to the increase in saturation 

temperature produced by the compressor. The evaporator design must trade off 

compressor power consumption versus heat transfer surface area. 

Using the vapor compression approach to evaporate water requires only about 100 BTU 

to evaporate a pound of water. Thus one evaporator body driven by mechanical vapor 

compression is equivalent to 10 effects or a 10-body system driven by steam. 

While most brine concentrators have been used to process cooling water, concentrators 

have also been used to concentrate reject from RO plants. Perhaps 90 percent of these 

concentrators operate with a seeded slurry process that allows the reject to be 

concentrated as much as 40 to 1 without scaling problems developing in the evaporator. 

Brine concentrators also produce a distilled product water that can be used for high-purity 

purposes or for blending with other water supplies. Because of their ability to achieve 

such high levels of concentration, brine concentrators can reduce or eliminate the need 

for alternative disposal methods such as deep well injection or solar evaporation ponds. 

When operated in conjunction with crystallizers or spray dryers, brine concentrators can 

achieve zero liquid discharge of RO concentrate under all climatic conditions. 

Individual brine concentrator units range in capacity from approximately 10 to 700 gpm 

of feedwater flow. Units below 150 gpm of capacity are usually skid mounted, and larger 

units are field fabricated. A majority of operating brine concentrators are single-effect, 

vertical tube, falling film evaporators that use a calcium sulfate-seeded slurry process. 

Energy input to the brine concentrator can be provided by an electric-driven vapor 

compressor or by process steam from a host industrial facility. Steam-driven systems can 

be configured with multiple effects to minimize energy consumption. 

Product water quality is normally less than 10 mg/L TDS. Brine reject from the 

concentrator typically ranges between 2 and 10 percent of the feedwater flow, with TDS 

concentrations as high as 250,000 mg/L. 

Because of the corrosive nature of many wastewater brines, brine concentrators are 

usually constructed of high-quality materials, including titanium evaporator tubes and 
 

 170 

stainless steel vessels suitable for 30-year evaporator life. For conditions of high chloride 

concentrations or other more corrosive environments, brine concentrators can be 

constructed of materials such as AL6XN, Inconal 825, or other exotic metals to meet 

performance and reliability requirements. 

A schematic diagram of a typical single-effect vertical tube brine concentrator is shown 

in Figure 12.1. Wastewater, such as RO concentrate, enters a tank where the pH is 

adjusted in preparation for deaeration. The wastewater then passes through a heat 

exchanger and enters a deaerator, where noncondensable gases are removed. From the 

deaerator the wastewater enters the evaporator sump, where it mixes with the brine 

slurry. The slurry is constantly recirculated from the sump to a floodbox at the top of the 

evaporator tube bundle. Water from the floodbox flows through brine distributors and 

moves as a thin film down the interior walls of the evaporator tubes. 

Some of the brine evaporates and flows through mist eliminators before entering the 

vapor compressor, where additional heat is added. Vapor from the compressor then 

flows to the outside of the evaporator tubes, where its heat is transferred to the cooler 

brine falling inside the tubes. As the compressed vapor gives up heat, it condenses as 

product water and is collected and pumped through the feedwater heat exchanger, where 

it transfers its heat to the incoming feedwater. 

Scaling of the evaporator tubes is prevented by the seeded slurry process. Calcium 

sulfate and silica precipitates build on calcium sulfate seed crystals in the recirculation 

brine instead of scaling on heat transfer surfaces. With the seeded slurry system, 

concentrations of up to 30 percent total solids can be reached in the recirculating water 

without scaling. 

Brine concentrator technology was developed in the early 1970s to help thermal power 

stations achieve zero discharge of wastewater. At present approximately 75 brine 

concentrators are in operation in the United States and overseas. Of these, about a dozen 

are being used to concentrate reject streams (RO concentrate) from industrial RO plants. 

The operating experiences of these plants have shown that the use of brine concentrator 

evaporators for concentration of RO concentrate is a viable application and that the 

systems are highly reliable. Many operating systems have achieved on-stream operating 

availabilities greater than 90 percent over an extended period of years. 

The specific design features and performance of brine concentrator systems are usually 

developed in conjunction with the equipment suppliers, based on the flow, chemistry, and 

economic factors involved in each case. The suppliers use proprietary methods to 

determine concentration factors in order to minimize brine concentrator blowdown rates 

while controlling scaling in the evaporator tubes.
 171 

Figure 12.1 Schematic Diagram of Brine Concentrator Process Flow – Pumps Not Shown (after RCC

Brine 

Concentrator

Heat 

Exchanger 

Wast

Deaerator 

Concentrate 

Product Water 

Co
 

 172 

Process water recovery is typically limited by the formation of a double salt that is a 

combination of sodium and calcium sulfate. Thus recovery is dependent on the sitespecific feed water quality, but is usually in the 90 to 98 percent range. 

Brine concentrators can be applied to a majority of RO concentrate streams. For such 

streams that are already saturated in calcium sulfate, brine concentrators operate without 

calcium sulfate addition. If concentrations of calcium sulfate in the concentrate stream 

are insufficient, calcium sulfate is added as required to support the seeded slurry process. 

Blowdown from brine concentrators is high in dissolved and suspended solids and 

saturated in calcium sulfate. Disposal can be handled in several ways. In areas where 

evaporation ponds are feasible and cost-effective, brine concentrator blowdown can be 

settled in a decant basin and then pumped to an evaporation pond. Settled solids are then 

removed by a front-end loader, clamshell, or other device, and transported to a land 

disposal facility. Blowdown can also be sent directly to a disposal pond, where the solids 

can be periodically removed, or to a pond constructed deep enough so that solids removal 

will not be required during the design life of the facility. 

In areas with negative net evaporation rates, or with expensive construction requirements 

for evaporation ponds, brine concentrator blowdown can be concentrated to a wet cake or 

dry powder using crystallizers or spray dryers. These technologies will be discussed in 

the next two sections. 

The method of evaporation will be selected based on the characteristics of the RO 

membrane concentrate and the type of energy source to be utilized. 

12.1.3 Crystallizers: Crystallizer technology has been used for many years to 

concentrate feed streams in industrial processes. More recently, as the need to 

concentrate wastewaters has increased, this technology has been applied to reject from 

desalination processes, such as brine concentrate evaporators, to reduce wastewater to a 

transportable solid. Crystallizer technology is especially applicable in areas where solar 

evaporation pond construction cost is high, solar evaporation rates are negative, or deep 

well disposal is costly, geologically not feasible, or not permitted. 

Crystallizers used for wastewater disposal range in capacity from about 2 to 50 gpm. 

These units have vertical cylindrical vessels with heat input from vapor compressors or 

an available stream supply. For small systems in the range of 2 to 6 gpm, steam-driven 

crystallizers are more economical. Steam can be supplied by a package boiler or from a 

process source, if one is available. For larger systems, electrically driven vapor 

compressors are normally used to supply heat for evaporation. 

A schematic of a forced-circulation vapor compression crystallizer is shown in Figure 

12.2. Wastewater, in the form of brine concentrator blowdown or from another source, is 

fed to the sump of the crystallizer. The incoming wastewater joins the recirculating brine 

and is pumped to a shell-and-tube heat exchanger, where it is heated by vapor from the 

vapor compressor. Because the tubes in the heat exchanger are submerged, the brine is 
 

 173 

Figure 12.2 Schematic Diagram of Forced-Circulation, Vapor Compression 

Crystallizer Process Flow (after RCC, 2001) 

Figure 12.3 Schematic Diagram of a Typical Spray Dryer (after RCC, 2001) 

Heater 

Vapor 

Compressor Mist 

Eliminator

Vapor Body

Feed 

Recirculation Pump 

Crystals to 

Centrifuge 

or Filter 

Condensate

Atomizer 

Feed 

Gas

Air Inlet 

Atomizer

Spray 

Drying 

Chamber

Bag 

Filter

Rotary Air 

Valve 

Product Outlet 

Exhaust Fan 

Air Outlet 
 

 174 

under pressure and will not boil. This arrangement prevents scaling in the tubes. The 

recirculating brine enters the crystallizer vapor body at an angle and swirls in a vortex. A 

small amount of the brine evaporates. As water is evaporated from the brine, crystals 

form. Most of the brine is recirculated to the heater. A small stream from the 

recirculating loop is sent to a centrifuge or filter to separate remaining water from the 

crystals. The vapor is compressed in a vapor compressor. Vapor from the compressor 

heats the recirculating brine as it condenses on the shell side of the heat exchanger. 

Condensate is collected and may be recycled to other processes requiring high-quality 

water. The crystallizer system produces a wet solid that can readily be transported for 

land disposal. 

The crystallizer typically requires a purge stream of about 2 percent of the feed to the 

crystallizer. This is necessary in preventing extremely soluble species (such as calcium 

chloride) from building up in the vapor body and preventing production of dry cake 

solids. The suggested disposal of this stream is to a small evaporation pond. 

Considerable solids are produced in the crystallizer that can be disposed of to commercial 

landfill. 

The first crystallizers, applied to power plant wastewater disposal, experienced problems 

related to materials selection and process stability, but subsequent design changes and 

operating experience have produced reliable technology. 

For RO concentrate disposal, crystallizers would normally be operated in conjunction 

with a brine concentrator evaporator to reduce brine concentrator blowdown to a 

transportable solid. Crystallizers can be used to concentrate RO reject directly, but their 

capital cost and energy usage is much higher than for a brine concentrator of equivalent 

capacity. 

12.1.4 Spray Dryers: Spray dryers provide an alternative to crystallizers for 

concentration of wastewater brines to dryness. Spray dryers are generally more costeffective for smaller feed flows of less than 10 gpm. 

A schematic of a spray dryer is shown in Figure 12.3. The system includes a feed tank, 

vertical spray drying chamber, and dried brine separator (bag filter) to collect dried 

solids. Concentrate from the desalination plant is routed to the feed tank, where it is 

recirculated and mixed to keep solids in suspension. From the feed tank, brine is pumped 

to the top of the drying chamber, where it is distributed into the chamber through a 

centrifugal brine atomizer. The atomizer consists of a shaft and rotating disc that 

protrudes into the hot gas stream. 

Air, heated by a gas, oil, or electric-powered heater, is also introduced at the top of the 

drying chamber. Hot air is pulled into the chamber and through the bag filter by the 

suction of an exhaust fan. The bag filter separates dry powder from the drying chamber 

from the hot air stream. Powder in the drying chamber is collected in a hopper and the 

air exits to the atmosphere. Dry powder is discharged from the hopper to a pneumatic 

conveyor that transports it to a storage silo for transfer to a disposal site. 
 

 175 

Spray dryer technology for wastewater concentration was developed in the early 1980s. 

Like crystallizers, spray dryers offer an alternative to evaporation ponds, percolation 

ponds, and deep well disposal for RO concentrate disposal. For such applications, spray 

dryers are usually operated in conjunction with brine concentrator evaporators for 

feedwater flows up to 10 gpm. If the RO concentrate stream is in the range of 1 to 10 

gpm, spray dryers can be cost-effective when applied directly to the stream, thus 

eliminating the brine concentrator evaporator. 

12.2 MODEL FOR INTERACTION OF MEMBRANE AND THERMAL 

SYSTEMS 

As briefly discussed in the opening paragraph, the use of a thermal brine concentrator to 

further treat membrane concentrate provides additional product water that can be used to 

meet the system product water requirements. Thus instead of relying on the membrane 

system to alone provide product water, the combined membrane/thermal system will 

together provide the product water with the result that the membrane system itself can be 

reduced in size. A schematic of the combined membrane/thermal system is shown in 

Table 12.1. In addition to both the membrane and thermal systems providing product 

water, due to the high quality (low TDS) of the thermal product water, some feed water 

may bypass the processing system and mix with the two product streams to meet product 

TDS requirements. As an example, Table 12.2 shows the size of feed and product 

streams for a membrane (RO) system alone and the combined membrane/thermal system 

for a system producing 5 mgd product water. The following parameters were assumed: 

• Membrane system recovery 0.70 

• Thermal system recovery 0.997 

• Feed TDS 3000 mg/L 

• Membrane product TDS 60 mg/L 

• Thermal product TDS 10 mg/L 

• Product TDS requirement 500 mg/L 

Table 12.2 Flows for Membrane and Membrane/Thermal Systems 

Membrane Membrane/ 

 Only Thermal

Total Product (mgd) 5 5 

Membrane Feed (mgd) 6.08 4.23 

Membrane bypass (mgd) 0.75 0.77 

Total feed (mgd) 6.82 5.004 

Membrane product 4.25 2.96 

Membrane concentrate (mgd) 1.82 1.27 

Final liquid waste (mgd) 1.82 0.004 

System recovery (%) 70 99.9+ 
 176 

RO or EDR 

System 

Thermal + 

crystallizer 

System 

Combined 

product water 

P, PTDS

Feed 

A, ATDS

B, ATDS 

Product water from 

membrane system 

F, FTDS C, CTDS 

bypass Product water 

from bypass 

E, ATDS 

Product water from 

thermal system 

D, DTDS

wastewater 

Substituting relations (5), (6), and (7) into (5) and rearranging to solve for E gives: E = P – B * [R1 + R2 * (1 – R1)] (10) Substituting relations (5), (6), and (7) into (9) and rearranging to solve for E gives: E = (PTDS * P – B * [FTDS * R1 + R2 * (1 – R1)])/ATDS (11) Now have 2 equations [(10) and (11)] in 2 unknowns, E and B Specify ATDS, FTDS, DTDS, PTDS, R1, R2 and solve Then use other relations to calculate other flows

RELATIONS Mass (flow) balances: A = B + E (B = C + F (2C = D + G (3P = E + F + D (4F = R1 * B (5C = (1 – R1) * B (6D = R2 * C (7G = (1 – R2) * C (8Where R1 = recovery of membraR2 = recovery of thermal A, B, C, D, E, F, G, and P Overall solids balance: ATDS * E + FTDS * F + DWhere ATDS, FTDS, DTDlevels in mg/L for streams 

Table 12.1 Schematic of Membrane/Thermal System and Mathematical Relations to Calcula
 

 177 

The equations for the model are given in Table 12.1. Through substitution, the equations 

can be reduced to two equations in two unknowns and easily solved. The results of 

Table 12.2 illustrate the effect of combining thermal and membrane technologies. Since 

the combined system has such a high recovery (>99.9%), the total feed to the system, 

5.004 mgd, is only slightly greater than the product requirement, 5.0 mgd. The 

membrane system is much smaller in the combined system, sized to produce 2.96 mgd as 

opposed to 4.25 mgd, a reduction of 30%. In this example, the amount of bypass flow is 

about the same in both cases. 

12.3 DESIGN CONSIDERATIONS 

Costs aside, most desalting membrane sites are potential candidates for a zero liquid 

discharge system. The site must be able to meet the large electrical power requirement as 

well as provide adequate space for the sizable footprint of the thermal processing system. 

The electricity cost can be as much as 95 percent of the non-labor operating cost. A 

single brine concentrator able to treat up to about 1 mgd of concentrate might have a 

footprint of 140 ft by 100 ft, with a height of 100 ft. The height is for the brine 

concentrator itself. The height of the rest of the footprinted area is considerably less than 

this. Equipment includes vessels, tanks, condensers, heat exchangers, pumps, 

compressors, motors, control valves, major diameter piping, and instruments and 

controls. Typically, the vessels are outside in the ambient air and a building structure 

houses the rotating equipment, the controls, the electrical system, the heat exchanger, 

dewatering equipment, the crystallizer, and produced solids. 

A life of 20 years is generally considered a minimum. Units in the Southwest U.S. have 

been operating for 28 years. 

Piloting of the thermal processes is not necessary. Design and scale-up information is 

obtainable from bench-scale glassware testing. The testing for the first feed (to the 

thermal unit), chemistry, which includes analytical results of feed, distillate, and 

concentrate, is usually available for less than $10,000. Elapsed time for such testing is 

typically less than a month. 

Design considerations primarily concern the sizing of the thermal system. 

12.3.1 Sizing of Zero Discharge Systems Evaporation: The relationship between the 

desalting membrane system and the brine concentrator, as just described, needs to be 

considered when determining the size of both the membrane system and the brine 

concentrator. The model presented above can be used for this purpose. 

The preliminary level cost estimate for the brine concentrator can be determined using 

the calculated concentrate flow rate resulting from the model. The costs can be obtained 

from using the cost figures that follow in this chapter. While in all likelihood a desalting 

membrane concentrate will be a viable candidate for a combined membrane - brine 

concentrator system, the general feasibility of the use of a brine concentrator and possible 

follow-on thermal devices such as a crystallizer or spray dryer can be confirmed by 
 

 178 

exchanging information with manufacturers of brine concentrators. A detailed water 

quality analysis of the membrane concentrate is helpful for the manufacturers to 

determine what degree of further concentration is possible with the brine concentrator. 

Levels of sparingly soluble salts will be analyzed to determine these limits. 

12.4 COST PARAMETERS 

12.4.1 Brine Concentrators: The cost of brine concentrator evaporators can vary 

widely depending on the chemistry of the feedwater stream to it, in this case the 

concentrate. Feed water chemistry affects the concentration factor, energy usage, 

evaporator surface area, construction materials, need for chemical additives, and other 

design and operating parameters. 

Typical capital costs for the brine concentrators are shown in Figures 12.4, 12.5, and 

12.6. These costs are based on titanium evaporator tube bundles and stainless steel 

construction, which have been used in a majority of installations. The cost curves 

represent skid-mounted units with capacities up to 200 gpm and units fabricated on site 

with capacities up to 700 gpm. Larger systems involved multiple units. The nature of 

the cost curves reflects this. In Figures 12.4 the break in the curve represents the shift 

from one to two of the skid-mounted units. Only one non-skidded unit is reflected in 

Figure 12.5. The jump in Figure 12.6 represents a shift from two to three units. 

Most brine concentrators are powered by electrically driven vapor compressors that 

constitute a major portion of the operating cost. Electric power consumption can range 

from about 60 to 100 kW*hr/1,000 gal of feedwater. In the design of the brine 

concentrator, the cost of the evaporator surface area can be traded off against the vapor 

compressor energy cost to optimize total system cost. In most cases, the evaporator 

surface area is selected to produce a power demand of 80 to 90 kW*hr/1,000 gal of 

feedwater flow.

Where brine concentrators are installed in conjunction with RO plants, the added labor 

required to operate the brine concentrator is in the range of 2 to 4 hours per 8 hr shift, 

depending on the overall quality of facility operation and maintenance. Brine 

concentrators require laboratory support similar to that of RO plants, where it is 

advantageous to have operators perform basic lab analyses, such as those for TDS and 

suspended solids. 

Maintenance, other than normal instrumentation, controls, and equipment requirements, 

is usually limited to chemical cleaning of the evaporator tubes, normally once or twice a 

year. 

12.4.2 Crystallizers: Crystallizer costs can vary widely depending on the chemistry of 

the feedwater, in this case the concentrate stream from the brine concentrator. When 

operating on brine concentrator blowdown, crystallizers can be exposed to corrosive 
 

 179 

Figure 12.4 Capital Cost of Skid-mounted Brine Concentrator as Function of 

Flow Rate (0 to 200 gpm) 

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250

Flow Rate (gpm)

Typical Capital Costs of Skid-mounted Brine Crystallizer ($ in millions)

Equipment only 

Equipment only 

Installed 

Installed 
 

 180 

Figure 12.5 Capital Cost of Non-skidded Brine Concentrator as Function of Flow 

Rate (0 to 1.2 mgd) 

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 0.2 0.4 0.6 0.8 1 1.2

Flow Rate (mgd)

Typical Capital Costs for a Non-skidded Brine Concentrator ($ in million

s

Installed

Equipment only 
 

 181 

Figure 12.6 Capital Cost of Non-skidded Brine Concentrator as a Function 

of Flow Rate (1 to 2.5 mgd) 

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5 3 3.5

Flow Rate (mgd)

Capital Cost of Non-skidded Brin Concentrator ($ in millions)

Installed 

Equipment only 
 

 182 

environments that often require expensive materials such as AL6XN, Inconel 825, or 

Hastelloy. 

Typical capital costs for crystallizers applied to the concentration of brine concentrator 

blowdown are shown in Figure 12.7. Power consumption for vapor compression 

crystallizers falls in the range of 200 to 250 kW*hr/1,000 gal of feedwater. Crystallizers 

are generally more cost-effective than spray dryers for feedwater streams above 10 gpm. 

When crystallizers are operated in conjunction with a brine concentrator or RO plant, 2 to 

4 additional man-hours per 8 hr shift are normally required if the crystallizer is designed 

properly and the facility is well organized. 

12.4.3 Spray Dryers: Spray dryer costs can be significantly affected by the chemistry 

of the feedwater, in this case the blowdown from the brine concentrator. This determines 

the construction materials that will be required. Typical capital costs for spray dryers, in 

the range of 2 to 12 gpm of feedwater capacity, are shown in Figure 12.8. 

Energy usage for spray dryers operated with natural gas or oil as heating fuels averages 

about 0.70 BTU/gpm of feedwater flow. Operating labor requirements for spray dryers 

are similar to those for crystallizers, adding about 2 to 4 man-hours per 8 hr shift to an 

RO facility, provided sound design methods and operating philosophy are applied. 

12.4.4 Energy: The energy requirements for these thermal processes are significant and 

are much greater than for any other disposal method and each of the thermal processes 

produces a waste stream for disposal. In any cost comparisons between different 

membrane disposal methods, the cost of the thermal processing must be adjusted for the 

energy consumption and for either additional treatment or disposal of the reject. The 

reject can be disposed of by other options, such as evaporation pond or deep well. 

Figures 12.9 and 12.10 show the energy requirements for the brine concentrator and 

Figure 12.11 for the crystallizer. 

12.5 DESIGN APPROACH FOR THE ZERO LIQUID DISCHARGE COST 

MODEL 

For the preliminary cost model, it is assumed that the water quality of the membrane 

concentrate poses no unusual problem for the thermal process. The equipment cost for 

the brine concentrator is based on the concentrate flow rate. There are step changes in 

cost as the number of modular units required increases. This is reflected in the Figures 

12.4 and 12.6. 

• The design approach chosen for the worksheet model is as follows: 

o The feed rate determines the size of the brine concentrator and thus the 

capital cost and the energy usage 

o The percent rejection level of the brine concentrator determines the feed 

rate to the crystallizer and consequently its size 
 

 183 

Figure 12.7 Capital Cost of Crystallizer as Function of Flow Rate (5 to 50 gpm) 

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60

Flow Rate (gpm)

Typical Capital Cost of Crystallizer ($ in millions)

Installed 

Equipment only 
 

 184 

Figure 12.8 Capital Cost of Spray Dryer as a Function of Flow Rate (1 to 12 

gpm) 

Equipment only 

Equipment only 

Installed 

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

Flow Rate (gpm)

Capital Costs (2001 $ in thousands)

Installed 

Equipment only 
 

 185 

Figure 12.9 Energy Requirements for the Brine Concentrator as Function of 

Flow Rate (up to 1 mgd) 

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.2 0.4 0.6 0.8 1 1.2

Flow Rate (mgd)

Energy Requirement (kW)
 

 186 

Figure 12.10 Energy Requirements for the Brine Concentrator as a Function of 

Flow Rate (1 to 3 mgd) 

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

0 0.5 1 1.5 2 2.5 3 3.5

Flow Rate (mgd)

Energy Requirement (kW)
 

 187 

Figure 12.11 Energy Requirements for the Crystallizer ax a Function of Flow 

Rate 

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60

Flow Rate (gpm)

Energy Requirements (kW)
 

 188 

o This in turn determines the capital cost of the crystallizer and its energy 

usage 

o The actual energy cost depends on the cost of electricity applied to the 

energy usage 

o Unlike other concentrate disposal options, the high energy usage of the 

thermal concentration system results in a very high operating cost. 

Because of this, the annualized cost of operation (annualized capital cost 

plus annual operating cost) is used to provide a more accurate indication 

of the system cost. 

• The design variables thus include: 

o Feed flow rate 

o Rejection level of the brine concentrator 

• Costs included in the capital cost model: 

o Brine concentrator 

o Crystallizer 

o Spray dryer 

o Energy 

o Construction and installation 

• Costs not included in the capital cost model: 

o Disposal of final waste 

12.6 ZERO LIQUID DISCHARGE WORKSHEET AND EXAMPLE 

With the information provided above, the total annualized cost of a brine 

concentrator/crystallizer thermal evaporation system can be determined. The worksheet 

for this zero liquid discharge system provided in Table 12.2. An example calculation is 

provided in the column marked ‘example.’ The concentrate flow from the membrane 

system to the brine concentrator is set as 1 mgd. The reject level of the brine 

concentrator is 5 percent, which for the 1 mgd feed represents 34.7 gpm. This is the feed 

flow to the crystallizer. The installed capital cost of the brine concentrator is determined 

to be $5.3 million from Figure 12.5. Similarly, the installed capital cost of the 

crystallizer is determined to be $2.65 million from Figure 12.7. The energy usage for the 

brine concentrator and crystallizer are determined from Figures 12.9. and 12.11 

respectively to be 3,750 kW and 525 kW. At an assumed cost of electricity of 

$0.10/kW-hr and operation of the yearly energy cost is determined to be $3.285 million 

for the brine concentrator and $459,900 for the crystallizer. When the concentrator and 

crystallizer capital costs are spread over 20 years, the annual capital costs are $265,000 

and $132,500 respectively. The total annual cost is the sum of the energy and capital 

costs, and amounts to $4,142,400. 
 189 

Table 12.3 Worksheet for Zero Liquid Discharge Disposal Cost 

WORKSHEET for Zero Liquid Discharge Disposal Costs 

Variable 

ENTER variable values range example case 1 case 2 A - flow rate (mgd) 0 - 5 1 B - reject level of unit 2 to 10% 5 MAKE calculation Action C - Concentrator reject/feed to crystallizer (mgd) = A*B/100 0.05 D - Feed to Crystallizer (gpm) = C * 694 34.7 FIND costs and energies from figures Action E - Capital cost of installed concentrator ($) use A, Figures 11.5 - 11.7 5,300,000 F - Capital cost of installed crystallizer ($) use D, Figure 11.8 2,650,000 G - Energy usage for concentrator (kW) use D, Figures 11.10 & 11.11 3750 H - Energy usage for crystallizer (kW) use A, Figure 11.12 525 ESTIMATE energy cost Action I - Cost of electricity ($/kwh) estimate 0.1 MAKE calculations Action J - Annualized capital cost of concentrator = E/20 265,000 K - Annualized capital cost of crystallizer = F/20 132,500 L - Annual energy cost of concentrator = G*I*8760 3,285,000 M - Annual energy cost of crystallizer = H*I*8760 459,900 TOTAL ANNUAL COST = J+K+L+M 4,142,400 COMMENTS: The cost of disposal of the solid waste produced is not included in 
 

 190 

12.7 ZERO LIQUID DISCHARGE REGRESSION MODEL 

A simplified model for the preliminary level annualized cost is provided below. All the 

cautions mentioned for using the worksheet model apply to this closed form model. The 

regression equation below is by definition less accurate than the worksheet model that it 

is based on. It is, however, more convenient and is useful for obtaining an understanding 

of how the various cost factors influence the final cost. As always, the user is advised to 

examine the assumptions on which the models are based to determine their applicability 

to the situation at hand, and to develop costs from an understanding of the various cost 

factors and from applying site-specific quotes to these factors. The model is valid for 

flows ranging from 0.4 mgd to 2.0 mgd. The closed form equation obtained from multilinear regression on data generated from 30 random worksheet cases is: 

Annualized Cost ($) = -2,722,800 

+ 4,035,700 * FLOW 

+ 37,720 * REJECT 

+ 285,900 * ELECTRIC 

For the worksheet case where: 

 FLOW = 1 mgd 

 REJECT = 5 % 

 ELECTRIC = 0.10 $/kWhr 

 

The calculated annualized cost is $4,360,565. This compares to the worksheet result of 

$4,142,400. 
 

 191 

CHAPTER 13. 

ANALYSIS OF COST MODELS 

13.1 INTRODUCTION 

Four cost models (deep well disposal, evaporation pond, spray irrigation, and zero liquid 

discharge) are discussed individually and then compared. In this way the sensitivity of 

each model to the various design parameters included in the cost models is reviewed, and 

the relative magnitude of costs associated with each concentrate disposal method is 

illustrated. 

As pointed out in the chapters discussing the individual models, (Chapters 9 through 12), 

care must be taken in interpreting and applying the model results. These models are 

limited in their applicability. The models make many assumptions that may not apply to 

a site-specific situation. Assumptions, discussed in each disposal method chapter, need 

to be reviewed for the user to better understand how the models apply to the situation of 

their concern. The models were developed to provide preliminary cost estimates only; 

they do not take into account regional differences in material and labor costs and the 

applicability of the concentrate disposal options. There may be site-specific costs that are 

not included in the model. 

It is recommended that the model user read the chapter discussing the model in question 

to understand the assumptions made, the design parameters involved, and the cost factors 

associated with each model. By understanding the design approach and the model 

limitations, other costs not included in the model may be added to provide a more 

accurate site-specific cost estimate. The worksheet model provides a blueprint for 

developing more accurate, site-specific cost estimates. 

The regression models provide a more rapid, but less accurate, cost estimate for these 

same disposal options. The range of applicability of the regressions is less than that of 

the worksheet models and this further limits their applicability beyond the concerns 

expressed above. 

13.2 SENSITIVITY ANALYSIS 

 

13.2.1 Relative Importance of Design Parameters: In following sections design 

parameters that appear directly in the four regression models are listed along with the 

Standardized Coefficient for that parameter from the regression model. The absolute 

magnitude of the Standardized Coefficient provides an indicator of the relative 

importance of the individual design parameters in the regression model. The more 

important the parameter, the more it affects the total cost. This indicator takes into 

account the full range of values each design parameter may take on, and more correctly 

considers the entire ‘solution space’ covered by the individual data sets used to develop 

the regression equation. The Standardized Coefficient is in this sense an averaged value 

that applies to the entire solution space. The relative importance of a parameter at a 
 

 192 

specific point in the solution space may be different from that provided by this ‘averaged’ 

indicator. The Coefficients, however, provide a single number indication of the 

sensitivity to the model (the regression equation) to that design parameter. 

The relative magnitude of the Standardized Coefficients is meaningful only for the 

solution space for which the regression model was developed. They are thus influenced 

by the ranges of the individual design parameters used in the development of the model. 

13.2.2 Spray Irrigation: The five design parameters included in the spray irrigation 

model and the corresponding Standardized Coefficients are: 

 Regression Model 

Design Parameter Standardized Coefficient

Flow 0.866 

Loading -0.227 

Storage Days 0.024 

Land Cost 0.243 

Land Clearing Cost 0.160 

From this listing it may be seen that, in the averaged sense discussed above, flow has the 

strongest influence on the total capital cost, and the number of storage days has the least 

impact. For a given flow the loading rate directly determines the required acreage. The 

negative sign on the loading Standardized Coefficient reflects that, as the loading rate 

increases, the required acreage decreases, and thus the total cost decreases. 

13.2.3 Zero Liquid Discharge: For the zero liquid discharge model the cost factors and 

Standardized Coefficients are: 

 Regression Model 

Design Parameter Standardized Coefficient

Flow 0.818 

Cost of Electricity 0.446 

Rejection Level 0.034 

For this annualized cost model the two primary design variables are the flow rate and the 

cost of electricity. 

13.2.3.1 Annualized Costs: The high operating cost for the zero liquid discharge option is 

much greater than for any of the other disposal options. It can be as high as 60 percent or 

more of the capital cost. For other disposal options annual operating costs are, in general, 

less than five percent of the capital cost. 

If the system lifetime is taken as 20 years and the capital cost is considered to be 

amortized over this time frame, then the annual costs for the system (not taking into 

account the time value of money) is simply the capital cost divided by 20 (or five percent 

of the capital cost) plus the annual operating cost. For a system where the operating cost 
 

 193 

would be five percent of the capital cost, the annual cost would have equal contributions 

from the yearly amortized capital cost and the operating cost. For the zero liquid 

discharge system where the operating cost might be 60 percent of the capital cost, the 

annual operating cost would be 12 times the yearly amortized capital cost. The cost of 

the zero discharge option is misleading if the high operating cost is not considered. 

It is for this reason that the regression model for zero liquid discharge is developed in 

terms of the annualized cost. 

13.2.4 Evaporation Pond: There are four cost factors and Standardized Coefficients for 

the evaporation pond model. They are: 

 Regression Model 

Design Parameter Standardized Coefficient

Liner Thickness 0.980 

Land Cost 0.245 

Land Clearing Cost 0.189 

Dike Height 0.061 

In the model these parameters determine the unit area cost. This cost is multiplied times 

the required area to determine the total capital cost. The liner thickness has the highest 

Standardized Coefficient of any parameter in these four models. In practice, the liner 

material can frequently cost 50 percent of the total capital cost. 

It is to be noted that flow did not explicitly appear in the regression model for the 

evaporation pond. As discussed in Chapter 10, the evaporation area is determined by the 

flow and the net evaporation rate. 

13.2.5 Deep Well Injection: The two cost factors and their Standardized Coefficients 

are: 

 Regression Model 

Design Parameter Standardized Coefficient

Tubing Diameter 0.378 

Depth 0.871 

The depth has by far the largest influence on the capital cost of the deep wells. It is to be 

noted again that flow does not explicitly appear in the regression model used. Many of 

the deep injection wells are built with future expansion in mind, and thus the tubing 

diameter, which is flow limiting as well as cost influencing, does not reflect the 

concentrate flow level. For this reason the tubing diameter was used in the regression 

model for cost. 
 

 194 

13.2.6 Summary: In all cases the size of a concentrate disposal system is most directly 

dependent on the magnitude of the concentrate flow. 

Capital costs for the land intensive disposal options of spray irrigation and evaporation 

are dependent on the land area required. The land area, in turn, is determined by the 

concentrate flow and the loading rate (for the spray irrigation case) or the net evaporation 

rate (for the evaporation pond). The highest loading rates (in the range of 20 ft/yr) are 

higher than the highest net evaporation rates (in the range of 8 ft/yr). Consequently, in 

general, evaporation ponds are more land intensive than spray irrigation systems. 

The zero liquid discharge system cost is heavily dependent on the cost of electricity as 

well as the concentrate flow rate. 

The deep well injection cost is strongly dependent on the depth of the well. Since 

injection wells are costly and less suitable to be expanded once built, they are frequently 

designed for much larger capacity than immediately required. Thus, in practice, the well 

costs do not necessarily correlate with the concentrate flow level. In the deep well 

model the tubing diameter is used as the sizing parameter in place of concentrate. 

13.3 MODEL COMPARISON 

Costs for the evaporation pond and spray irrigation disposal options associated with land 

purchase and clearing can be substantial. The land costs for the deep well disposal and 

zero liquid discharge options are minimal. In the following model comparison the cost 

of land and clearing of the land have been eliminated from consideration. This allows a 

more meaningful comparison of the equipment and construction/development involved 

with the disposal options. A comparison of models also requires a common basis, and 

concentrate flow is the logical choice. Since the cost models for the spray irrigation and 

the deep well disposal options do not have the concentrate flow rate as a direct variable, 

the relationship to flow needs to be developed for these models. For the evaporation 

pond model this is quite simple. Figures 11.1 and 11.2 of the spray irrigation chapter, 

used to determine area based on concentrate flow and loading, can be used to determine 

area based on concentrate flow and net evaporation rate. For the deep well disposal 

model the relation between tubing diameter and concentrate flow needs to be developed. 

For this purpose a maximum flow velocity of ten feet per second provides a reasonable 

estimate of tubing required for a given flow. The Hazen-Williams formula for new steel 

pipe is used to predict the maximum flow for a given tubing diameter. In the following 

sections, capital costs are estimated for concentrate flows of 0.5, 1.0 and 2.0 mgd. 

13.3.1 Spray Irrigation: 

Concentrate Cost at 5 ft/yr Cost at 20 ft/yr 

Flow (mgd) Loading ($) Loading ($) 

0.5 569,000 163,000 

1.0 1,151,000 744,000 

2.0 2,313,400 1,907,100 
 

 195 

Capital costs are provided for two different loading values of 5 and 20 ft/yr. As predicted 

by the Standardized Coefficients, both flow and loading have a significant effect on the 

cost. The costs of land and land clearing can significantly increase the capital cost 

beyond the values listed. 

13.3.2 Zero Liquid Discharge: 

Concentrate Cost of Cost at 2% Cost at 10% 

Flow (mgd) Electricity ($/kW/h) Rejection ($) Rejection ($)

0.5 5 800,000 1,102,000 

1.0 5 2,818,000 3,120,000 

2.0 5 6,854,000 7,155,000 

0.5 20 5,089,000 5,390,000 

1.0 20 7,107,000 7,408,000 

2.0 20 11,142,000 11,444,000 

Annualized costs are provided as a function of both cost of electricity and the brine 

concentrator rejection level. Consistent with the Standardized Coefficients, the rejection 

level has only a small effect on the cost, while both flow and cost of electricity have 

major effects. 

13.3.3 Deep Well Injection:

Concentrate Cost at depth Cost at Depth Cost at Depth 

Flow (mgd) of 500 ft ($) of 5,000 ft ($) of 10,000 ft ($)

0.5 819,000 4,212,000 7,982,000 

1.0 964,000 4,359,000 8,127,000 

2.0 1,256,000 4,650,000 8,419,000 

The tubing diameters suggested by concentrate flows are 5, 6, and 8 in respectively. The 

effect of flow is small because it represents only a limited portion of the range of tubing 

diameter sizes covered in the model development. The substantial effect of depth is seen. 

13.3.5 Evaporation Pond: 

 Cost at 8 ft/yr Net Cost at 8 ft/yr Net 

 Evaporation Rate, Evaporation Rate, 

Concentrate 4 ft Dike Height, 12 ft Dike Height, 

Flow (mgd) 20 mil Thickness ($) 120 mil Thickness ($)

0.5 1,419,000 6,578,000 

1.0 area is greater than 100 acres; outside limits of model 

2.0 area is greater than 100 acres; outside limits of model 

The evaporation pond model was developed only for areas of 100 acres or less. The 

acreage required for flows of 1.0 mgd even at this maximum net evaporation rate are 

greater than 100 acres. The large combined effect of greater dike height and increased 
 

 196 

liner thickness are evident. As with the spray irrigation model, the cost of land and land 

clearing can significantly increase the capital cost. 

13.3.6 Summary: From the model results presented, it may be seen that in the absence 

of land-related costs, the spray irrigation cost appears to be the lowest cost disposal 

method. This can be misleading, however, due to 1) the absence of land related costs and 

2) the likely need to dilute the concentrate prior to irrigation. The dilution will increase 

the volume to be disposed and the cost associated with disposal. The zero liquid 

discharge cost is somewhat inflated because of the interaction between the thermal 

treatment system and the membrane system, as discussed in section 12.2 that results in a 

smaller membrane system needed to produce the required product volume. Similar 

statements can be made for the other models. These statements exemplify why care 

should be taken in using the model results. 

It should be kept in mind that not all disposal options are possible at a given plant. This 

may be for reasons of climate (limiting land applications), geology (limiting deep well 

injection), chemistry (limiting surface water disposal), volume (for disposal to sewer), or 

several other reasons. Further, where different options are possible, they may be at 

different distances from the membrane plant and require different amounts of conveyance 

to the disposal site. In an idealized situation where all options are possible, require 

minimal treatment prior to disposal, and are located at similar distances from the 

membrane plant, disposal to sewer should be the least expensive disposal option – 

provided disposal fees are not high. Disposal to surface waters or by land application 

would in most cases be less expensive than disposal to deep well. Typically zero liquid 

discharge would be the most expensive disposal option. 

The inevitable exceptions to this idealized situation underscore the need to develop sitespecific disposal costs. The cost models presented may be used as a means of providing 

preliminary cost estimates and insights into developing more accurate disposal costs.
 

 197 

CHAPTER 14. 

INSTRUCTIONS FOR USING CD 

14.1 FORMAT OF THE CD 

The CD contains the following items: 

• The complete survey database 

• The complete report 

• Worksheets for use in developing cost estimates of disposal options 

• 

• Calculation pages for capital costs of disposal options 

• A front-end menu for accessing these individual parts of the CD 

Each of these items is discussed in turn prior to a review of the installation procedure for 

loading and using the CD. 

There are two requirements that must be installed on the user computer system: 

1. The user must have at least one printer defined on the computer, as Microsoft 

Access requires a printer definition in order to display certain reports. The user, 

however, does not need Microsoft Access software. 

2. The user must have Adobe Acrobat Reader version 4.0 or higher installed on the 

computer. Adobe Acrobat Reader is a free software application that is needed to 

view certain reports in the CD. You can download a free copy from 

http://www.adobe.com/prodcuts/acrobat/readstep2.html. 

14.1.1 A Front-end Menu for Accessing These Individual Parts of the CD: A userfriendly menu is the starting point for use of the CD. It provides several buttons that are 

used to access different parts of the CD. The menu is shown in Figure 14.1. 

14.1.2 The Stand-alone Database: The database contains the survey results from 

approximately 150 membrane plants in summary form of three (sometimes four) pages of 

information for each plant. There are several ways of accessing these summaries. The 

first is by viewing a list of all the plants and by first clicking on the PLANT LIST button 

and then clicking on a particular plant name on the list that appears. The second is by 

clicking on the FULL PLANT REPORT button and then by scrolling through a large 

single file that appears which contains summary pages for all the plants. The final way is 

by clicking on the SEARCH button and by specifying search parameters on the resulting 

screen and then clicking on the Search Now button. A list of plants will appear and when 

a particular plant name in a list is clicked, the summary pages for that plant will appear. 

The SEARCH function can be used to provide a listing of plants matching any 

combination of search parameters. 
 

 198 

Figure 14.1 Menu for accessing CD files 

The database, developed using Microsoft Access, is provided as a ‘run-time’ version that 

does not require Microsoft Access for it to run. 

14.1.3 The complete text report: The hardcopy final report is fully reproduced as a pdf 

file that requires Adobe Acrobat Reader software to read it. This file can be accessed 

directly from the initial menu by clicking on the FULL TEXT REPORT button. The 

report is presented as a single file. Different parts of the report are found by scrolling. 

Parts may be printed out by specifying pages for printout in the print menu. 

14.1.4 Worksheets for use in developing cost estimates of disposal options: 

Worksheets are provided that can be used together with cost curves presented in the 

report text to develop estimates of preliminary level capital costs for the different 

disposal options. The worksheets may be accessed by first clicking on the 

CONCENTRATE DISPOSAL COST WORKSHEETS button. The particular worksheet 

corresponding to a disposal option can then be chosen from specifying it on the 

dropdown list that appears. The worksheet that appears may be printed out and used for 

manually calculating the capital cost for that disposal option. The user specifies certain 

design parameters, uses various cost curves in the text report to determine individual cost 

values, enters these costs on the worksheet, and performs the simple calculations 
 

 199 

described on the worksheet to develop a total cost. The text report contains separate 

chapters for each of the disposal options. The worksheets are discussed in these text 

report chapters along with design considerations and a discussion of the cost model 

assumptions and limitations. An example calculation is provided on each worksheet. 

14.1.5 Calculation pages for capital costs of disposal options: Closed form equations 

were developed from regressing on 30 to 35 sets of data generated from worksheet 

calculations for each disposal option cost model. These calculation sheets may be 

accessed by first clicking on the SIMPLIFIED CALCULATION OF DISPOSAL COSTS 

button. A specific disposal option can then be chosen on the resulting screen by clicking 

on the disposal option name. The calculation page for that disposal option then appears. 

When the user declares values for the input variables specified on the calculation page, 

and then clicks on the 'calculate cost' button, the total capital cost for the disposal option 

is calculated and displayed. 

Use of the calculation page provides a simple and quick method of generating 

preliminary level cost estimates. The user, however, is cautioned to study the text report 

chapter and to work with the cost worksheets to develop an understanding of the 

assumptions and limitations of the cost models. 

14.1.6 Glossary: By clicking on the GLOSSARY button, the user can access a glossary 

of abbreviations and terms used in the report. 

14.2 INSTALLATION OF THE CD 

The following installation instructions are enclosed with each CD: 

Installation Instructions for Membrane Concentrate Disposal 

Database

Version 1.0 

1. Before beginning installation of the database, two items must already be installed 

on your system: 

a) You must have at least one printer defined on your computer (local or 

network). Microsoft Access requires a printer definition in order to 

display certain reports. 

b) You must have Adobe Acrobat Reader version 4.0 or higher installed on 

your computer. Adobe Acrobat Reader is a free software application that 

is needed to view certain reports in the database. You can download a free 

copy from http://www.adobe.com/products/acrobat/readstep2.html. 

2. Insert the CD into the CD-ROM drive. After a few seconds the following screen 

will appear while several files are copied. 
 

 200 

3. After this you may see a message appear that says “Setup cannot continue because 

some system files are out of date on your system.” Click the OK button to update 

the files. 

After the update, a second message will appear saying “Do you want to restart 

Windows now?” Click the Yes button and let the computer reboot. 

4. After rebooting, remove the CD and then insert it again to kick off the 

continuation of the installation. 

5. If you don’t have Access 2000 already installed on your system, you’ll see a 

message saying “The application you are installing requires Microsoft Access 

2000. Setup will now close and launch the Microsoft Access 2000 Runtime setup 

program.” Click OK to allow this to happen. 

Note: The Access 2000 Runtime is not a full version of Access, only the 

necessary portions to allow the database to execute on your system. 

6. Follow instructions on the screen to install the Access 2000 Runtime. 

7. At the end you will be prompted to reboot. Click OK or Yes. 

8. After rebooting, the Membrane Database setup should automatically start, 

displaying the screen below. Click OK. 
 

 201 

9. The window below will appear. Click on the computer icon to begin installation. 

For the current version of the database, do not modify any defaults such as 

installation directory or program group names. Use all defaults as supplied. 

10. Follow the prompts until installation is completed. Dismiss the final window 

shown below. 

11. To run the database, go to Start/Programs/MickleyAssoc/Membrane Concentrate 

Disposal Database. 
 

 202 
 

 203 

REFERENCE LIST 

Adham, Samer S., J. Jackangelo, and J-M Laine. 1996. Characteristics and Costs of MF 

and UF Plants, AWWA Journal. 88 (5), 22-31. AWWA. Denver. 

CFR. 1989a. Protection of Environment-Underground Injection Control Program. 40 

CFR, Part 144. 

------. 1989b. Protection of Environment – Underground Injection Control Program. 40 

CFR, Part 146 

Conlon, W.J. 1989. Disposal of Concentrate from Membrane Process Plants. Waterworld 

News, Jan./Feb.:18-19. 

Crites, R.W., S.C. Reed, and R.K. Bastian, 2000. Land Treatment Systems for Municipal 

and Industrial Wastes, McGraw-Hill, New York. 

EPRI-CEC 1994. Modeling of Brine Disposal in Oceans. EPRI-CEC. St. Louis. 

Goigel, J. F. 1991. Regulatory Investigation and Cost Analysis of Concentrate Disposal 

From Membrane Plants. M.S. Thesis, University of Central Florida, Orlando, Florida. 

Gordon, W. 1984. A Citizen’s Handbook on Groundwater Protection. New York: Natural 

Resources Defense Council. 

Leitner, Gordon F. and F. L. Murray. 1997. U.S. Desalination & Membrane Softening 

Potable Water Costs. The International `Desalination & Water Reuse Quarterly. 7(2) 

Aug./Sep.44-50. 

Martin, A.M. 1992. Use of Biomonitoring Data to Reduce Effluent Toxicity. Chemical 

Engineering Progress, 88(9): 43-49). 

Metcalf & Eddy, 1979. Wastewater Engineering: Treatment/Disposal/Reuse. 2nd ed. 

Revised by George Tehobanoglous. New York: McGraw-Hill. 

Mickley, M.C., R. Hamilton, L. Gallegos, and J. Truesdall. 1993. Membrane Concentrate 

Disposal, Denver, Colo. AwwaRF and AWWA. 

Mickley, M.C. 1996. Environmental Considerations for the Disposal of Desalination 

Concentrates. The International `Desalination & Water Reuse Quarterly. 5(4) 

Feb./Mar.:56-61. 

Mickley, M.C. 2000. Major Ion Toxicity in Membrane Concentrate, Denver, Colo. 

AwwaRF and AWWA. 
 

 204 

Miller, W. 1989. Estimating Evaporation from Utah’s Great Salt Lake Using Thermal 

Infrared Satellite Imagery. Water Res. Bull., 25:541-542. 

Morin, O.J. 1987. Assessing Desalting Needs of South Florida. In Desalination in South 

Florida, Proc. of NWSIA and SFWMD Seminar. Edited by O.K. Buros. 

Muniz, A. and S.T. Skehan. 1988. Disposal of Concentrate from Brackish Water 

Desalting Plants, In Disposal of Concentrates From Brackish Water Desalting Plants, 

Proc. of NWSIA and SFWMD Seminar. Edited by O.K. Buros. 

NWSIA,, CAREW, 1989. Setting Water Quality Standards: A Complex Issue – A White 

Paper. 

Pontius, F.W., ed. 1990. AWWA Water Quality and Treatment Handbook. New York: 

McGraw-Hill. 

Strycker, A., and A.G. Collins. 1987. State-of-the–Art Report: Injection of Hazardous 

Wastes Into Deep Wells. Ada, Okla.: Robert S. Kerr Environmental Research Laboratory. 

USDI (U.S. Department of the Interior). Bureau of Reclamation. 1969. Disposal of Brine 

Effluents from Desalting Plants. Washington, D.C.: Government Printing Office. 

USDI. Office of Saline Water. 1970. Disposal of Brine by Solar Evaporation: Field 

Experiments. Washington, D.C.: Government Printing Office. 

USDI. Office of Saline Water. 1971. Summary of Desalination Plant Brine Disposal 

Methods for Inland Locations. Washington, D.C.: Government Printing Office. 

USEPA, ASCE, AWWA. 1996. Technology Transfer Handbook: Management of Water 

Treatment Plant Residuals. EPA/625/R-95/008. 

Wilbert, M.C., J. Pellegrino, J. Scott, C.Kramer, M. Lewis. 1999. Water Treatment Cost 

Estimation User Manual. Bureau of Reclamation. 
 

 205 

APPENDIX 1 

METRIC CONVERSIONS 

 

 

From To Multiply by

ft m 0.3048 

in m 0.0254 

ft2

 m2 0.09290304 

gal (U.S.) L 3.785412 

Acre-ft m3

 1,233.489 

lb/in2 kPa 6.894 

F C C=(F-32)/1.8
 

 206 
 

 207 

APPENDIX 2 

SURVEY OF STATE REGULATIONS REGARDING 

DRINKING WATER WASTE DISPOSAL

BACKGROUND 

Most of the survey was conducted from December 1998 to early 2000 with periodic 

checks with States that had membrane plants. Relevant information was obtained from 

the Internet and checking the State’s environmental agencies’ website in order to list and 

document the relevant programs dealing with water quality issues for the drinking water 

utilities. The corresponding agency was contacted by phone an interviewed accordingly. 

In some instances due to the division of authority within the State more than one agency 

was involved in the survey. 

The key topics addressed in the survey concerning the Water Treatment Plant’s waste 

disposal options were the following: 

• Options of liquid waste disposal 

• Options of residue or sludge disposal 

• Raw water source and overall quality 

• Chemicals or technical treatment problems faced by the utilities 

• Groundwater reinjection as a waste disposal option 

• Membrane technology use by the operating WTP 

• Programs involved dealing with disposal options 

The report that follows is presented in a narrative form as was hand recorded during the 

interviews, further technical details as well as the legal requirements for the permits or 

policies listed can be obtained directly from the contact person phone number or 

checking the agency corresponding website. 

COMMENTS 

Most states do not have membrane plants producing potable water. Several states have 

only small systems operating or have very few membrane plants. Consequently, the 

survey conducted and highlighted in this appendix refers mostly to disposal options for 

WTP residuals other than membrane concentrate or membrane backwash. 

There are some similar terms used to describe residuals in conventional water treatment 

plants and membrane water treatment plants. This can be confusing unless directly 

addressed. In what follows, the term ‘concentrate’ unless referred to as ‘membrane 

concentrate’ means a liquid waste/sludge prior to dewatering. The term ‘backwash’ does 

not refer to ‘membrane backwash’ as from a UF or MF process but means filter 

backwash. 
 

 208 

ALABAMA 

Alabama Department of Environmental Management (ADEM) 

ADEM Montgomery Office 

1751 Cong. W. L. Dickinson Dr 

Montgomery AL 36109-2608 

Ph: (334) 271-7823 

Fx: (334) 271-3051 

Web site: www.adem.state.al.us/h2owebpg.htlm 

Drinking Water contact: Steve Williams ph: (334) 271-7788 Water Supply Branch. 

Industrial facilities of all types including drinking water utilities that discharge storm water and/or 

wastewater to surface water must apply for an NPDES permit. In Alabama the preferred option is 

to discharge backwash waste into a retaining pond. Most utilities do not discharge since they 

have enough surface area to allow evaporation to occur and their waste volume is minimal. The 

few that discharge must have an NPDES permit. The State also has a permitting procedure for 

industrial discharger to POTW’s under the State Indirect Discharge (SID) permit. There is no 

ground water re-injection option for waste disposal and the UIC program has been cancelled in 

Alabama. The northern section of the State relies on surface water and the southern portion on 

groundwater as the main drinking water source. Only one RO system is currently operating in the 

State in Dolphin Island, this is a small unit treating water for high chloride since groundwater in 

the Gulf Coast is affected by saltwater intrusion. 

ALASKA 

Alaska Department of Environmental Conservation 

Division of Air and Water Quality 

Section of Water Quality Protection 

410 Willoughby Ave. Suite 105 

Juneau, AK 99801-1795 

Ph: (907) 465-5308 

Fx: (907) 465-5274 

Website: www.state.ak.us/local/akpages/ENV.CONSERV/dawq/wqhome.htm 

Contacts: Susan Braley, Section Chief 

Joe Cottingham; Drinking Water Program 

The State maintains and supervises the NPDES program ensuring that water quality standards are 

met by industrial dischargers including the water treatment plants. Other disposal options such as 

indirect discharge to a sewer system are available to the utilities. Residue is typically disposed 

either on-site or sent to a sanitary landfill. Raw water is mainly surface water for the large 

utilities and several smaller communities use groundwater. Very few membrane plants in the 

state with the exception of drilling rigs in Cook Bay which use RO system to treat drinking water 

for small facilities. They submit regular monitoring analytical data to the State. 
 

 209 

ARIZONA 

Arizona Department of Environmental Quality (ADEQ) 

Water Permits 

3033 North Central Ave. 

Phoenix, AZ 85012 

Ph: (602) 207-4677 

Fx: (602) 207-4634 

Website: adeq.state.az.us/water/index.htm 

Contact Person: John Coleman Ph: (602) 506-6935 Maricopa County 

The State does not have additional regulations or permitting requirements for Drinking Water 

Plant waste disposal. The Engineering Department of ADEQ authorizes the construction and 

operation of the new facilities and the Water Permits section monitors compliance with the 

NPDES program in the event of discharges to surface water. New facilities must submit an 

Effluent Disposal Plan that can be incorporated in the design report for residual liquid disposition. 

Other options available in Maricopa County and the State are dewatering of the concentrate and 

landfilling; indirect discharge to POTWs; recycling of backwash; and in some cases treated 

wastewater is permitted for agriculture irrigation. Currently Arizona does not have a sludge 

classification program, but there is concern about sludge quality regarding cryptosporidium and 

giardia cysts. A new Nuclear Plant facility in Palo Verde will be using RO technology for 

treating drinking water. A new Phoenix utility will also be implementing microfiltration 

technology. There is concern about arsenic and pesticide in membrane concentrates of these new 

membrane facilities and the ADEQ Water Quality Division will be monitoring their waste 

streams closely. 

ARKANSAS 

Arkansas Department of Pollution Control and Ecology 

Water Division 

8001 National Dr 

Little Rock, AR 72209 

Ph:(501) 682-0656 

Fx: (501) 682-0910 

Arkansas Health Department 

Drinking Water Program 

Division of Engineering 

4815 Markan St. 

Little Rock, AR 72205 

Ph: (501)661- 2623 

Fx:(501) 661-2032 
 

 210 

Website: www.adeq.state.ar.us/water/main.htm 

Contacts: Ted Schlurter, Health Department. 

Dischargers must meet State regulations for water quality standards ( APCE Regulation 2) and all 

regulations related to the administration of the NPDES program (APCE Regulation 6). Drinking 

water utilities currently dispose backwash to a retaining settling pond. In some cases they require 

an NPDES permit for surface discharge. The WTP residual or concentrate can be dewatered and 

disposed in a sanitary landfill. Land application is also a viable option. In both cases the utility 

must fulfill the required documentation for sludge disposal. The State does not have a 

classification or sludge program for the drinking water waste, which is considered in most cases 

non hazardous. Land irrigation using backwash water is also allowed by the State. The source of 

water for the WTP is mixed, surface and groundwater, in western Arkansas is primarily surface 

water whereas in the eastern section of the State is groundwater. Source water is considered of 

good quality with minor metal or organic concentration problems i.e., due to the treatment 

process. The use of alum is common and is considered the only additive necessary for treatment 

in most of the WTP utilities. Only one RO system is being proposed in the State to treat deep 

well water for a small community in Northern Arkansas. 

The Water Quality Planning Branch of APCE is in charge of groundwater protection monitoring 

landfills and other industrial facilities that store wastewater or solid waste that could potentially 

impact groundwater; they run the UIC program. Currently the State does not have a formal set of 

groundwater standards, the Water Division uses Federal standards and health advisory limits to 

determine status of the aquifers. 

CALIFORNIA 

California Environmental Protection Agency 

State Water Control Board 

SWRCB Division of Water Quality 

Los Angeles Region 4 

101 Center Plaza Dr 

Monterrey Park CA 91754-2156 

Ph: (323) 266-7557 

Fx: (323) 266-7600 

Website: www.dwr.water.ca.gov/ 

Contact Person: Shirley Birosik Division of Water Quality; Abdell Shrudaji Department of Health 

Services ph: (213) 977-6808 

Currently there is no special regulation for disposal of wastes from drinking water plants; the 

waste generated will fall within existent programs such as NPDES permit for surface discharge. 

This is the most common option of disposal for liquid waste and permit requirements are 

managed by the Division of Water Quality. Disposal of the concentrate or sludge to a sanitary 

landfill as solid waste is also allowed and the solid waste group in the Department of Health 

Services handles the necessary requirements. In the State some utilities dispose their sludge as 

road construction material and no permit is involved in this process, with the exception of 

notification to the solid waste group. Source water is a combination of surface and groundwater, 
 

 211 

the northern part of the State use primarily surface whereas in the southern portion there is more 

use of groundwater. In the region (Los Angeles) source water quality is acceptable, but there are 

frequent problems with salinity, nitrates, and VOCs. There are utilities using membrane 

technology such as RO and Microfiltration. Santa Catalina Island has an RO plant to treat salt 

water. There are some cases of re-injection occurring as an option for treating drinking water 

disposal specially to control salt intrusion. The State has an UIC program to oversee any reinjection into groundwater. 

COLORADO 

Colorado Department of Health and Environment 

Water Quality Control Division 

4300 Cherry Creek Drive South 

Denver, CO 80222-1530

Ph: 303 692-3546 

Fx: 303 692-0390 

Website:http://governor.state.co.us/gov_dir/cdphe_dir/ 

Contacts: Jerry Biberstaine and Glen Butner, Primary Drinking Water Regulation Division. Also 

Phil Hegeman Ext. 3598 contribute to the survey. 

The State of Colorado has not developed any new policies concerning disposal of drinking water 

plant waste. The Division currently has issued 79 permits for filtered backwash and other 

concentrate disposal, which include some membrane concentrate from RO treatment units (there 

is no record by technology used). The recommended procedure is to dispose the high TDS brine 

into lined settling ponds and allow for evaporation. The residue is disposed in a landfill or land 

applied after compliance with sludge classification criteria and meeting State regulations for solid 

waste disposal. Other disposal options such as discharge to Wastewater Treatment Plants, surface 

discharge, or use of non-membrane concentrate for road base material are currently considered 

and permitted in a case by case basis. 

CONNECTICUT 

Department of Environmental Protection 

79 Elm St. 

Hartford, CT 06106-5127 

Ph: (860) 424-3837 

Fx: (860) 424-4074 

Website: www.state.ct.us/dep 

Contact: Dave Cherico 

The State has currently about 169 towns with municipal drinking water facilities. The main water 

source is groundwater, which is of excellent water quality requiring minimum treatment. The 

drinking water utilities can apply to the Waste Management Bureau for a General Disposal Permit 

that will mirror EPA waste disposal regulation and will cover surface discharge situations. 
 

 212 

Disposal options in clued discharge to an existing sewer system, landfilling after dewatering, and 

surface discharge. There is current concern about excess iron and some heavy metals and 

hardness. 

DELAWARE 

Delaware Department of Natural Resources and Environmental Control 

Division of Water Resources 

Surface Water Discharge Section 

89 King Highway 

Dover, DE 19901 

 

Ph: (302) 739-4731 

Fx: (302) 739-3591 

Website: www.dnrec.state.de.us/ 

Contact: Peter Hansen groundwater discharge section (302) 739-5731 

The State runs a sludge disposal program under the Department of Public Health. Backwash, 

concentrate, and other high TDS (brines) as drinking water waste are currently regulated under 

the sludge disposal program with all other sludge from wastewater treatment plants. All options 

are allowed for disposal of drinking water treatment plant waste. These include surface discharge 

which will go through the NPDES section under the division of Water Resources and discharge to 

a wastewater plant. In most cases the backwash is allowed to settle in the sump with enough 

retention time to separate the solids. As with all effluents, the liquid must meet the 30 mg/l TDS 

State limit before surface discharge. The solids can be landfilled or land spread (reporting how 

many pounds per acre will be spread.) The State issues permits on a case-by-case basis for land 

application of concentrate. There is no groundwater discharge of concentrate allowed in the State. 

There is an aquifer recharge project in the State where the aquifer is filled during the wet season 

for demand later in the summer, but no waste goes into it. 

FLORIDA 

Florida Department of Environmental Protection 

Division of Water Facilities 

Drinking Water Section 

2600 Blair Stone Rd, MS 3520 

Tallahassee, FL 32399-2400 

Ph: (850) 487-1762 

Fx: (850) 414- 9031 

Website: www.dep.state.fl.us/ 

Contact: Richard Drew, Bureau Chief (850) 487-0563; Elsa Potts, office of Wastewater 

Management ph:(850) 921-9495; fax: (850) 414-9031 

The State of Florida issued in 1996 a set of guidelines for RO membrane utilities. This document 

does not elaborate on waste disposal options but describes current trends and present case studies 
 

 213 

of these membrane facilities. Currently, the State allows surface water disposal and blending is a 

common practice. The concentrate is mixed with clean treated effluent to reduce saline 

concentration before discharge; all water quality standards must be met. The sludge or 

concentrate also can be land filled, but few utilities chose this options due to the high chloride of 

the sludge that render it unsuitable for land application, areas with high lime concentrations may 

qualify for this type of disposal. The State requires a UIC permit for deep well injection of brine 

or concentrate.

GEORGIA 

Department of Natural Resources 

Environmental Protection Division 

Drinking Water Program 

205 Butter St, SE Suite 1362 

Atlanta, GA 30334 

Ph: (404) 656-2750 

Fx: (404) 651-9590 

Website: www.dnr.state.ga.us/ 

Contact: Bill Moaries ph: (404) 651-5158 

The majority of the drinking water utilities (conventional alum precipitation plants) in the State 

have NPDES permits since the preferred option is surface water discharge for the supernatant 

after settling in a lined pond or lagoon. Raw water source is mainly surface, but wells are also 

used especially for the smaller utilities. There is no groundwater re-injection allowed in the State. 

Very few utilities use membrane technology. The common practice includes the use of sand 

filters, and plate and press filters. Residual generated can be dewatered and sent to a landfill. 

Some utilities may choose to negotiate with farmers to arrange land application of the sludge; 

currently this is not a common practice. 

HAWAII 

Department of Environmental Health 

Safe Drinking Water Branch 

919 Ala Moana Blvd 

Honolulu, HI 96814 

Ph: (808) 586-4258 

Fx: (808) 586-4370 

Website: hawaii.gov./doh/eh/eiemdw00.htm 

Contact: Lawrence Whang 

There are very few utilities in the State (about 8) using membrane technology. Options for waste 

disposal fall within the NPDES program if the utility is discharging directly to surface water. 

Other options available to the industry have been landfill application after dewatering. No 

groundwater re-injection is allowed in the State. Indirect discharge to a sewer system is also 

allowed, but no permit is required. Surface water is the main source of raw water and in general 
 

 214 

quality is good requiring minimum treatment. Technology use in the larger utilities includes 

conventional sand filters combined with a clarifier and chlorination process. Small utilities 

serving campground or resort areas use membrane technology such as RO systems. 

IDAHO 

Division of Environmental Quality 

Water Quality 

1410 North Hilton 

Boise, ID 83706 

Ph: (208) 373 0265 

Fx:(208) 373 0576 

Website: www2.state.id.us/deq 

Contacts: Steve Tanner (208) 769-1422 Twin Falls Regional Office, Dick Rogers (208) 373-0265 

Boise DEQ. 

Drinking water facilities in the northern section of the State do not generate significant waste. 

Source water comes from reservoirs with excellent water quality. The water is chlorinated to 

meet health standards but no further process is usually required. In the Southern portion utilities 

using surface and groundwater generate some residuals that is permitted for land application since 

it has alkaline properties and helps to maintain soil pH. Direct discharge of backwash wastes to 

surface water, falls within the NPDES permitting program. Most utilities discharge to an existing 

sewer system and do not require further permits. In some cases, the utility is allowed to discharge 

backwash water to an infiltration basin as long it meets water quality standards. There are few 

utilities (1 or 2) using micro and ultra filtration in the State. 

ILLINOIS 

Illinois EPA 

Bureau of Water 

Division of Public Water Supply 

1021 North Grand Ave. East 

Springfield, IL 62702 

Ph: (217) 782-3397 

Fx: (217) 782-0075 

Website: www.epa.state.il.us/ 

Contacts: Derek Rompot at (217) 782-0610 

Drinking water utilities must have an NPDES permit for surface water discharge. In other 

instances the utility can discharge to a wastewater treatment system previous reporting to the 

permitting office for clearance. More often direct agreement with the wastewater treatment 

facility suffices to avoid affecting water quality in the receiving plant. Source of raw water for 

the WTPs in the State is surface water. Other options such as sludge disposal directly to a landfill 

are available once the utility meets solid waste requirements, for example sludge water content. 
 

 215 

For a complete list of treatment plants in the State and technology used in each one, it is possible 

to submit a formal request through the Freedom of Information office to the following address: 

Division of Water Pollution Control 

P.O.Box 19276 

Springfield, IL 62794-9276 

The letter should be mark FOI request. 

INDIANA 

Indiana Department of Environmental Management 

Drinking Water Branch 

100 N. Senate 

P.O. Box 6015 

Indianapolis, IN 46206-6015 

Ph: (317) 308-3308 

Fx: (317) 308-3339 

Website: www.state.in.us/idem/ 

Contact: Steve Roush ph: (317) 232-8706 

Lagoon settling and further discharge of the supernatant is the preferred option for drinking water 

plants in the State to discharge their backwash or liquid waste. Any surface discharge will 

require an NPDES permit, but very few utilities have a permit since most of them discharge to an 

existing sewer system. Residual land application is allowed once the sludge meets the required 

standards to ensure that no hazardous material is involved. Landfill application is also an option 

for residual disposal. Very few RO systems are currently in operation in the State of Indiana. No 

re-injection to groundwater is allowed as a method of waste disposal. About 95% of the public 

drinking water plants use groundwater as their primary water source. 

IOWA 

Iowa Department of Natural Resources 

Public Water Supply 

Henry Wallace Bldg. 

502 E. 9th St. 

Des Moines, IA 50319-0034 

Ph: (515) 281-6599 

Fx:(515) 281- 8895 

Website: www.state.ia.us/government/dnr/organiza/ 

Contact: Roy Ney ph: (515) 281-8945 

Drinking water plants dispose their waste stream into a holding pond or lagoon. In the event of 

surface discharge an NPDES permit is required. The most common disposal option is to 

discharge into an existing sewer system for which no permit is required. Groundwater re-
 

 216 

injection is not a disposal option for liquid waste in the State. Residual disposal to a landfill is a 

common option; again no permit is required with the exception of the normal landfill paperwork. 

Most of the utilities use surface water as the main source of raw water. In the State there are 6 

RO systems currently operating: 3 electrodialysis and probably 1 microfiltration. Most plants are 

traditional alum settling plants that follow AWWA guidance for treating drinking water. 

KANSAS 

Kansas Department of Health and the Environment 

Division of Environment 

Bureau of Water 

Forbes Field Bldg. #283 

Topeka, KS 66620-0001 

Ph: (785) 296-5500 

Fx: (785) 296-5509 

Website: www.kdhe.state.ks.us/ 

Contact: Iragh Pourmirza 

Drinking water plants must have an NPDES permit for surface discharge to streams or other 

surface water. For drinking water utilities it is mandatory that they meet a TDS limit between 20 

to 81 mg/l TDS (required for all effluents) and also a pH range between biological acceptable 

limits (6.5 to 9.0). Most of the utilities have a settling lagoon and in few cases they dispose their 

concentrate to a sanitary landfill. None of the State utilities use membrane technology in Kansas. 

There is no groundwater discharge option available for drinking water plants. 

KENTUCKY 

Kentucky Department of Environmental Protection 

Frankfort Office Park 

Division of Water 

14 Reilly Rd 

Frankfort KY 40601 

Ph: (502) 564-2150 

Fx: (502) 564-4245 

Website: www.state.ky.us/agencies/nrepc/dep2.htm 

Contact: Tom Skaggs, ph: (502) 564-2225 

The State allows surface water disposal of backwash or any liquid waste stream, but requires 

permitting by the NPDES program. Use of lagoons and holding ponds are common. The indirect 

discharge to POTWs is practiced by municipal drinking water plants. The State conducts 

supervision of sludge quality for hazardous material through the Municipal Waste branch, which 

permits land farming of the sludge after quality control is performed. Main source of raw water is 

surface, but use of groundwater is common. About 250 utilities are on surface water. The State 

conducts a UIC program, but groundwater re-injection is not allowed as a disposal option. 
 

 217 

LOUISIANA 

Department of Environmental Quality 

Office of Water Resources 

Drinking Water Program 

P.O. Box 82215 

Baton Rouge, LA 70884 -2215 

Ph: (225) 342-9500 

Fx: (225) 765-0635 

Website: www.deq.state.la.us/ 

Contact: Clay Bowes Drinking Water Program Engineer 

The State allows surface water discharge from retaining ponds; the overflow discharge requires 

an NPDES permit. Recycling of backwash is common practice as well as indirect discharge to a 

sewer system. Some WTPs generate sludge that is dewatered and landfilled without further 

requirement. Most of the utilities operate basic technology using clarifiers, sand filters, etc. There 

is no RO or other membrane technology currently being used by drinking water utilities in the 

State. 

MAINE 

Maine Department of Environmental Protection 

17 State House Station 

Augusta, Maine 04333-0017 

Ph: (207) 287-7688 

Fx: (207) 287-7191 

Website: www.state.me.us/dep/mdephome.htm 

Contact: Charles Brown 

Liquid waste generated in the process by WTPs is retained in a lagoon or holding pond and can 

be discharged to a surface stream as long as the plant has a valid NPDES permit. Indirect 

discharge to a sewer system is a valid option for liquid waste disposal. The concentrate residue is 

typically disposed in a sanitary landfill after dewatering, in this case it classifies as a solid waste 

and can be disposed as such. Source water is mainly surface water from streams and reservoirs; 

few groundwater wells are also a source of raw water. Iron and manganese are the main 

chemicals of concern. Liquid waste re-injection is not allowed by the current regulations for 

waste disposal. The State has a UIC program that addresses other aspects of groundwater 

protection. There are a few small membrane systems in the State. 

MARYLAND 

Maryland Department of the Environment 
 

 218 

2500 Broening Highway 

Baltimore, MD 21224 

Ph: (410) 631-3706 

Fx: (410) 631-3157 

Website: www.mde.state.md.us/ 

Contact: Barry O’Brian, Water Supply Program 

The drinking water utilities are allowed to dispose their liquid waste directly to a surface stream 

providing previous clearance with the State has been obtained through an NPDES type of permit. 

Although indirect discharge to a sewer system is allowed very few utilities choose this option. 

No groundwater re-injection is currently allowed. The sludge or residual generated is commonly 

disposed in a sanitary landfill. There are very few utilities applying to the State for land 

application of backwash waste. In the State most of the sludge is mixed with the municipal 

wastewater sludge as the preferred way to handle residual concentrate. Raw water source is of 

acceptable quality, and with most of the large cities relying on surface water and the rest on 

groundwater. There are about 500 drinking water utilities in the State. 25 of them (the larger 

ones) use surface water from reservoirs or streams. Iron and Manganese are typical problems in 

surface and ground water. In some communities wells have arsenic and low radioactive 

contamination (mainly radium and radon). There is only one RO system in the State dealing with 

a high sodium concentration. 

MASSACHUSETTS 

Massachusetts Department of Environmental Protection 

1 Winter St. 2nd Floor 

Boston, MA 02108 

Ph: (617) 574-6871 

Fx: (617) 292-5696 

Website: www.state.ma.us/ 

Contact: Frank Niels 

All traditional disposal options are currently available to drinking water utilities in the State. 

Surface discharge will require an NPDES permit. Groundwater re-injection will be regulated by 

the groundwater program (UIC) and must report water quality before re-injecting; currently 

reinjection is not a preferred practice. Drinking water utilities prefer to discharge into an existing 

sewer system. Sludge generated can be landfilled. In 1996 the State issued a document 

containing guidelines for residual disposal from drinking water utilities. 

 

MICHIGAN 

Michigan Department of Environmental Quality 

Field Operation Section 

350 Ottawa NW 

Grand Rapid, MI 49503 
 

 219 

Ph: (616) 356-0277 

Fx: (616) 356-0298 

Website: www.deq.state.mi.us/dwr/ 

Contact: Dave Timm Field Operation Section Grand Rapid District 

Surface discharge under an NPDES permit is the common practice to dispose liquid waste in the 

State, but indirect discharge and recycling within the plant are available options. Most residue is 

dewatered and disposed in a landfill; some land application occurs, but it is not common. The 

Michigan DEQ has a sludge program that oversees any land application. Surface and ground 

water are used as source water for public water utilities, but surface water coming from the Grand 

Lakes is the main source of raw water in the State. In general the water quality is good requiring 

minimal treatment. In groundwater, iron and in few cases arsenic are chemicals of concerns. The 

State does not allow groundwater re-injection. There are a few utilities using membrane 

technology in the State, mainly reverse osmosis systems. 

MINNESOTA 

Minnesota Pollution Control Agency 

Municipal and Industrial Water Quality 

520 Lafayette Rd. 

St. Paul, MN 55155-4194 

Ph: (651) 296-6300 

Fx: (615) 296-8717 

Department of Health 

Public Water Program 

121 East 7th Place 

P.O. Box 64975 

Saint Paul, MN 55164-0975 

Ph: (651) 215-0770 

Fx: (651) 215-0775 

Website: www. pca.state.mn.us/water/ 

Contact: Dick Clark at (651) 215-0747 

Drinking water utilities in the State can dispose wastewater or backwash directly to surface water 

after complying with NPDES regulations. Indirect discharge to sewer systems is also common 

practice. The State does not allow any underground waste disposal. Sludge generated is 

dewatered and sent to a sanitary landfill. No land application is allowed. Few membrane utilities 

currently operate in the State dealing with high TDS water source. Source of water quality in the 

State is good and no major issues regarding concentration of pollutants occur. 

MISSISSIPPI 

Mississippi Department of Environmental Quality 
 

 220 

Office of Pollution Control 

Division of Water Supply (Department of Health) 

P.O.Box 10385 

Jackson, MS 39289-0385 

Ph: (601) 961-5171 

Fx: (601) 354- 6612 

Website: www.deq.state.ms.us/ 

Contact: James McClellen, ph: (601) 961-5061 fx: (601) 961-5187 

Drinking water plants can apply for DEQ NPDES permits for surface discharge. Most of the 

utilities discharge to a retaining pond or lagoon, allowing for settling time and eventual surface 

discharge under a DEQ permit. Indirect discharge is also common and utilities negotiate directly 

with the sewer utilities about volumes and quality of the effluent. Overall the State enforces a 

total TDS < 45 mg/l in any surface discharge from drinking water utilities (and from other 

industries). DEQ does not allow underground water re-injection since almost all utilities draw 

groundwater for drinking purposes. Recycling of backwash is encouraged and practiced by most 

utilities. Only the City of Jackson is currently permitted by DEQ under the NPDES program, but 

it is currently under a Consent Order since they have an alum problem with their sludge. The rest 

of the State utilities do not require permits due to reduced amounts of waste generated. No RO 

utilities currently exist in the State. 

MISSOURI 

Missouri Department of Natural Resources 

Division of Environmental Quality 

Public Drinking Water Program 

P.O.Box 176 

Jefferson City, MO 65102 

Ph: (573) 751-7428 

Fx: (573) 526-5797 

Website: www.dnr.state.mo.us/deq/ 

Contact: Terry Timmons (573) 751-1188 Public Drinking Water Program 

Drinking water utilities in Missouri have two options for waste disposal under the current NPDES 

program. The first is to surface discharge to main rivers such as the Missouri or the Mississippi 

Rivers. This option is being currently reviewed because of increasing concern regarding 

additives such as alum or softener used by the utilities. The second option is to discharge to a 

retaining pond and discarding the supernatant and concentrating the sludge that is later removed, 

dewatered, and landfilled. Currently the State has over 2000 public water treatment plants, only 

100 of them use surface water as the raw water source, the rest depend on groundwater. There 

are no extensive uses of membrane technology among the utilities, only the City of Nevada is 

currently using this technology. Due to the extensive use of groundwater as water source there is 

no groundwater re-injection program for waste disposal. 
 

 221 

MONTANA 

Montana Department of Environmental Quality 

1520 E. Six Ave. 

Helena, MT 59620 

Ph: (406) 444-2544 

Fx: (406) 444-4386 

Website: www.deq.state.mt.us/ 

Contact: Terry Campbell ph: (406) 444-5311 

In most cases drinking water plants discharge to an existing sewer system or surface discharge 

under an NPDES permit which requires the applicant to meet water quality standards. Residue 

generated at the plant is sent to a sanitary landfill after being dewatered. Some land application 

occurs, but is authorized in a case-by-case basis. There are no RO plants currently in the State/ 

Some utilities are using different types of cartridge such as 3M bag filters in some cases with 

granular pre-filtering, These plants serve small communities (<50K) and resort areas. Source of 

raw water is a combination of surface and groundwater. In general source water quality is good 

with few exceptions dealing with nitrate intrusion mainly in utilities relying on groundwater. 

NEBRASKA 

Nebraska Department of Environmental Quality 

1200 N. Street, Suite 400 

P.O.Box 98922 

Lincoln, NE 68509 

Ph: (402) 471-2186 

Fx: (402) 471-2909 

Website: www.deq.state.ne.us/ 

Contact: Jack Daniels, Department of Health, Drinking Water Program ph: (402) 471-0510 

Drinking water utilities in the State discharge their liquid waste to a pond or lagoon to allow 

settling of the solids and the overflow can be discharged directly to a receiving body of water 

under an NPDES permit. Indirect discharge to a sewer system is also a common option. Raw 

water source for the drinking water utilities is surface and groundwater. In general water quality 

is good, but some iron and manganese occur and need treatment. There are very few utilities 

using membrane technology; at least one is using an RO system to treat a nitrate problem. There 

is no underground re-injection allowed in the State as an option for waste disposal, but the State 

has an UIC program. 

NEVADA 

Department of Conservation and Natural Resources 

Division of Environmental Protection 

Bureau of Water 
 

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1550 East College Pkwy, Suite 142 

Carson City, NV 89706-7921 

Ph: (775) 687-6353 

Fx: (775) 687-5856 

Website: www.state.nv.us/cnr/ndwp/home/htm 

Contact: Dana Penny 

The State allows surface water discharge under an NPDES permit. Indirect discharge to an 

existing sewer system is also allowed. Landfill disposal of concentrate generated by the drinking 

water utilities is also allowed. In some cases deep well injection is permitted under the UIC 

program, but is not a common practice among the drinking water utilities. Source raw water is 

mainly surface and groundwater requiring treatment to deal with high TDS. Membrane 

technology is used in the State on a small scale mainly by utilities dealing with sodium and 

chloride problems. 

NEW HAMPSHIRE 

New Hampshire Department of Environmental Services 

6 Hazen Drive 

Concord, NH 03302 

Ph: (603) 271-3139 

Fx: (603) 271-5171 

Website: www. state.nh.us/des/descover.htm 

Contact: Richard Skarinka 

The State allows drinking water utilities several waste disposal options. The most common 

options are discharge to a holding lagoon and surface water (under the NPDES program), and 

direct discharge to a sewer treatment system. Reports to the sewer utility are in most cases 

required. The residue must be dewatered and dried before land disposal. The State reviews alum 

content to allow this option. Iron and manganese are metals of concern. Sludge with low 

radioactive levels of radon is also a potential problem. 

NEW JERSEY 

New Jersey Department of Environmental Protection 

401 East State St. 

P.O.Box 029 

Trenton, NJ 08625-0029 

Ph: (609) 292-4543 

Fx: (609) 984-7938 

Website: www.state.nj.us/dep/dwq/ 

Contact: Jeffrey Reading and Mary Jo Aiello 
 

 223 

The State allows different options for waste disposal from the drinking water plants. Surface 

water discharge falls within the NPDES program. Currently, a set of guidelines for the drinking 

water industry is scheduled for 1999 implementation of a general permit. Sludge generated can 

be landfilled or used for land application once approved by the Sludge Quality Assurance 

program where the utility must report quantity and quality of the sludge to be applied or disposed. 

There is concern in some cases with the amount of chlorine left in the residual, therefore the level 

of trihalomethane is closely monitored. Heavy metal concentration is also monitored in some 

cities arsenic is a major concern especially among utilities using groundwater as the raw water 

source. In one case a utility is disposing sludge as construction material in a dam project. The 

State offer what is called Determination Program for Beneficial Use of Waste, if the utility can 

support any beneficial use of its waste it can apply for a permit under this program. 

NEW MEXICO 

New Mexico Environmental Department 

Surface Water Quality Bureau 

Harold Runnels Bldg, N 2050 

1190 St. Francis Dr 

Santa Fe, NM 87502 

Ph: (505) 827-0187 

Fx: (505) 827-0160 

Website: www.nmenv.state.nm.us/ 

Contact: Steve Baumgarth ph: (505) 827-2803 

Drinking water utilities in New Mexico can discharge liquid waste to surface water if they have a 

current NPDES permit. Holding pond or settling lagoons are common among the drinking water 

industry because they generate small waste volume. The State also allows the landfill option for 

disposal of concentrate or sludge; no land application is practiced or permitted. Indirect 

discharge to a sewer system is also a valid disposal option and no permit is involved, but the 

utilities negotiate the terms of the disposal to maintain quality of effluent discharge. The main 

source of raw water for the utilities is groundwater and therefore no re-injection of any industrial 

liquid waste is allowed in the State. The groundwater bureau manages the UIC program. 

NEW YORK 

New York State Department of Environmental Conservation 

Division of Water 

Bureau of Water Permit 

50 Wolf Rd 

Albany, NY 12233-8010 

Ph: (518) 457-7464 

Fx: (518) 485-7786 

Website: www.dec.state.ny.us/ 

Contact: Joe Callaghen ph: (518) 457-0663 
 

 224 

Drinking water utilities in the State discharge preferably to an existing sewer system and no 

permit is required. Other utilities discharge to surface water after settling the solids and this 

option will require an NYNPDES permit. Currently there is no groundwater disposal option 

available in the State since most of the plants obtain their source water from wells. Sludge 

generated by drinking water plants is typically high in alum and therefore must be landfilled. 

This option does not require special permit. Minimum land application is known to occur with 

the sludge generated by the drinking water utilities. 

NORTH CAROLINA 

North Carolina Department of Environmental and Natural Resources 

Division of Water Quality 

Raleigh, NC 27626-0535 

Ph: (919) 733-7015 

Fx: (919) 733-2496 

Website: www.ehnr.state.nc.us/ 

Contact: Harold Seylor ph: (828) 251-6786, fx: (828) 251-6770 

Surface discharge of backwash water is a disposal option in the State, but requires a NPDES 

permit. Indirect discharge to a sewer system is available as well as recycling the waste to the 

front end of the plant. Sludge generated in the plant is typically landfilled, and in some instances 

used for land application and supervised by the solid waste group. Utilities using groundwater as 

source water are not allowed to dispose waste into the wells. The State has an UIC program that 

will be involved if a utility choose this option. So far this situation has not occurred in the State. 

Public utilities use surface and groundwater as their main source water. In the coast there is 

problem with saltwater intrusion in the aquifers because some of them have geological fractures. 

This salt intrusion is aggravated by poor well design and construction. There are no major 

chemicals of concern in the raw water used by the industry. There are several, about a dozen, 

utilities using membrane technology (RO and MF) and about 10 more on line to be permitted. 

NORTH DAKOTA 

North Dakota Department of Health 

Environmental Health Section 

Division of Water Quality 

1200 Missouri Ave. 

Bismark, ND 58506-5520 

Ph: (701) 328-5150 

Fx:(701) 328-5200 

Website: www.health.state.nd.us/ndhd/environ/wq/ 

Contact: Gerry Bracht ph: (701) 328-5227, Dave Bergsagel 

Discharge to a settling lagoon is the preferred option in the State by drinking water utilities to 

dispose backwash waste. For surface discharge an NPDES permit is required, and it is issued by 
 

 225 

the Department of Health. Most utilities discharge to an existent sewer treatment system. The 

sludge once dewatered is allowed to be disposed into a sanitary landfill. In the State land 

application is not an option due to poor sludge quality for such purpose. Only 1 or 2 small RO 

plants are currently operating in the State. 

OHIO 

Ohio Environmental Protection Agency 

Division of Surface Water 

Lazarus Government Center 

122 South Front St 

Columbus, OH 43215 

Ph: (614) 644-2001 

Fx: (614) 644-2329 

Website: www.epa.ohio.gov/ 

Contact: Sangee Prakash ph: (614) 644-2752, drinking and groundwater engineering and 

operating facilities; fx:(614) 644-2909. 

In the State there is a high percentage (> 90%) of drinking water plants recycling backwash to the 

front end of the plant. In some cases surface discharge permits are issued under the NPDES 

program, but the preferred method of liquid waste disposal is indirect discharge to a sewer 

system. Underground injection is not allowed by the State. The common technology to treat 

drinking water in the State is flocculation and the use of clarifiers to remove iron and manganese. 

There are about 3 to 5 utilities using membrane technology (RO and MF). 

OKLAHOMA 

Oklahoma Department of Environmental Quality 

P.O.Box 1677 

Oklahoma City, OK 73101-1677 

Ph: (405) 702-8100 

Fx: (405) 702-8101 

Website: www.deq.state.ok.us/ 

Contact: Pratap Ganti 

Water treatment plants can discharge their liquid waste from their holding ponds directly to a 

receiving body once they fulfill the requirements of the NPDES program. Few utilities choose 

this option and the majority recycle to the front of the plant. Indirect discharge to a sewer system 

is also an option valid in the State and does not require a permit from DEQ. The residue or 

sludge is disposed on-site and in some cases sent to a sanitary landfill. The State has a sludge 

quality program for the POTWs. Source of raw water is groundwater in the southwestern portion 

of the State and surface water in the eastern part. In general, the water is of good quality with few 

instances of iron, manganese, and nitrates. Underground waste disposal is discouraged but there 

are few WTPs that re-inject their waste. The State conducts an UIC program to ensure 
 

 226 

groundwater protection. There are few utilities using membrane technology, but none of the large 

WTPs have membrane systems. 

OREGON 

Oregon Department of Environmental Quality 

Water Quality Division 

Environmental Engineering 

2020 S.W. 4th Ave. Suite 400 

Portland, OR 97201 

Ph: (503) 229-5279 

Fx: (503) 229-6957 

Website: www.deq.state.or.us/ 

Contact: Jim Sheelz ph: (503) 229-5310 

Liquid waste generated in the WTP is typically sent to a retaining lagoon for settling of the solids 

and posterior overflow discharge to a stream. The State requires an NPDES permit for this 

option. Indirect discharge to a sewer district is another valid option in the State. Residue or 

sludge generated is disposed in a sanitary landfill and in some cases used for land application. 

Any land application is supervised by the wastewater sludge program. Some re-injection of 

liquid waste is still practiced by the existing plants. The State is working to discourage this 

practice, but some wells come with high salt content and the utilities choose to re-inject specially 

in Central Oregon. The UIC program oversees this practice. Raw water quality is good in the 

State and very few utilities have problems. Recently high nitrates have originated some concern. 

No membrane technology is currently operating in the State or if so, only serving small 

campground locations. 

PENNSYLVANIA 

Department of Environmental Protection 

P.O.Box 2063 

Harrisburg, PA 17105-2063 

Ph: (717) 783-2300 

Fx: (717) 783-8926 

Website: www.dep.state.pa.us/ 

Contacts: Ed Rosky, Division of Drinking Water ph: (717) 783-9037 

Surface discharge of liquid waste (backwash, clarifier blowdown etc.) to a receiving stream is 

allowed in the State under the NPDES program. Indirect discharge to a sewer system is also a 

valid option for waste disposal. Sludge generated by the utilities is typically disposed in a 

sanitary landfill. There is a sludge program and other disposal options may be available such as 

land application or as filling material, but these latter options are negotiated by DEP in a case-bycase basis. The utilities use both sources of raw water, surface and groundwater, with most of 

the utilities (about 75%) on groundwater. In terms of population served the use is almost even 
 

 227 

between the two sources. Most of the utilities use traditional filtration, coagulation, and 

flocculation to treat the raw water. There is one microfiltration and one ultrafiltration utility in 

the State, but no RO systems currently operating. In general, raw water quality is good and no 

major concerns beside some iron and manganese occur. 

RHODE ISLAND 

Rhode Island Department of Environmental Management 

Bureau of Environmental Protection 

235 Promenade Rd. 

Providence, RI 02908 

Ph: (401) 222-6605 

Fx: (401) 222-3162 

Website:www.deq.state.or.us/ 

Contact: Jim Scheetz ph: (503) 229-5310 

The State issues General NPDES permits for drinking water utilities that discharge to a surface 

water stream or creek. In Rhode Island general permits are issued to an industrial sector instead 

of an individual facility and the permit will cover intermittent or continuous effluent discharges. 

Utilities must meet the corresponding water requirements described in the permit. Residual 

disposal after dewatering is accomplished in a sanitary landfill. This is the preferred disposal 

option. Land application is also allowed and the State has a program for this option, but since the 

requirements are more stringent there are not many applicants. The State does not allow 

groundwater injection for the new facilities, however existing facilities in high saline areas still 

use this option. The State maintains a UIC program to monitor these facilities. The goal is to 

phase out this option in the near future. There are some chemicals of concern such as nitrates in 

some areas and the Health Department monitors this sector of the drinking water utilities. Also 

the sludge program is managed by the Health Department. 

SOUTH CAROLINA 

South Carolina Department of Health and Environmental Control 

Bureau of Water 

Water Facilities 

2600 Bull Street 

Columbia, SC 29201 

Ph: (803) 898-4300 

Fx: (803) 898-4215 

Website: www.state.sc.us/dhec/eqchome.htm 

Contact: Coy Waritts, water facilities ph:(803) 898-4257 

In the State over 90% of the WTPs choose surface discharge as needed under a General discharge 

permit, although some paperwork is involved is less stringent on the monitoring side than an 

individual NPDES permit. Waste streams from holding ponds or lagoons can also be discharged 
 

 228 

to a sewer system. The residue or concentrate is typically sent to a POTW and in some cases 

landfilled. The preferred option is to dispose the sludge on-site. Some WTPs sell their sludge to 

cement plants. Source water comes from both surface and groundwater. The larger utilities use 

more surface water. The State allows some utilities to store excess treated water underground for 

future use. The UIC program is involved in these cases and the program is called capacity use, 

but there are very few of these in the State. Raw water is of good quality with some specific 

communities dealing with natural occurrence of radioactive material, chlorides, and salts in 

general. Groundwater is typically treated for iron and manganese. Membrane technology is used 

in the State on a very limited scale. 

SOUTH DAKOTA 

South Dakota Department of Environment and Natural Resources 

Office of Drinking Water 

Joe Foss Bldg. 

523 E. Capitol 

Pierre, SD 57501 

Ph: (605) 773-3754 

Fx: (605) 394-2229 

Website: www.state.sd.us/state/executive/denr/denr.html 

Contact: Gerry Stephanson 

Direct discharge to surface water in the State is regulated under the NPDES program. This 

requirement applies to any industrial or drinking water utility discharge. Indirect discharge to a 

sewer system is also an option and no permit is involved, but the utilities should discuss the terms 

to keep within the required standards. No groundwater re-injection is allowed for disposal of 

liquid waste. The State has an UIC program to monitor groundwater quality and use by utilities. 

Most of the utilities use surface water, but the smaller ones rely on wells. There is some concern 

in the State for low radioactive contaminants such as radium 228. 

TENNESSEE 

Department of Environment and Conservation 

Division of Water Supply 

6th Floor, L&C Tower 

401 Church St 

Nashville, TN 37243-1549 

Ph: (615) 532-0191 

Fx: (615) 532-0503 

Website: www.state.tn.us/environment 

Contact: Bill Hench ph: (615) 532-0165 

Direct discharge of liquid waste is allowed in the State under an NPDES permit, but is not the 

preferred option of the drinking water utilities. The option of choice is to recycle the decanted 
 

 229 

water to the front end of the process. Discharge to a POTW is also practiced on a lesser scale. 

The sludge generated is in most cases stored on-site, landfilled, or used in a beneficial use 

program for land application. If the utility applies to this program it must meet quality criteria for 

health and hazardous requirements before releasing the sludge. Source of raw water in the State 

is both ground and surface water. The middle and East part of the State rely more on 

groundwater. The water is of good quality and only very few problems are known, among them 

iron and manganese. Some utilities are facing VOC pollution that requires air stripping. No reinjection is allowed and the State has an UIC program. There few membrane technology plants 

in the State are mainly in small communities or suburbs. 

TEXAS 

Texas Natural Resource and Conservation Commission 

Water Utilities 

Water Quality Division 

TNRCC, P.O.Box 13087 

Austin, TX 78711-3087 

Ph: (512) 239-6020 

Fx: (512) 239 6050 

Website: www.tnrcc.texas.gov/ 

Contact: Jack Schulze, Public Drinking Water Section 

Drinking water utilities are allowed to discharge their liquid waste to a receiving stream only 

under an NPDES permit. They also can discharge to an existing sewer system and in this case no 

permit is required. A third practice in the State for liquid waste disposal is recycling of the waste 

to the head of the plant. Typically the supernatant of the settling lagoon is recycled, reducing the 

volume of liquid discharge. Any sludge or residue generated after dewatering can be disposed in 

a permitted sanitary landfill. There is a beneficial use program that the utilities can apply for, but 

most utilities prefer the first option. No use of the sludge for road construction is known at this 

moment. The utilities also have the option of re-injection of the stream waste, but most of them 

do not choose this option due to the stringent UIC program requirements. There are some 

concerns regarding quality of raw water. Utilities located east of highway I-35 face some color, 

alkalinity, iron, and manganese problems. West of I-35 the situation is different involving mainly 

high salt content in the surface and groundwater. Also in this area, there is evidence of high 

fluoride concentration that requires attention. Surface water presents some sporadic problems 

with BTEX, and Atrazine and the utilities have problems meeting MCLs. Along the Rio Grande 

the problem is TDS, salinity, and urban pollution coming from Mexico. Around Austin, the 

South section has excellent water quality and no major problems occur. There are some RO 

systems in the State serving small communities. In West Texas there are about 5 ultrafiltration 

and microfiltration utilities; 2 are under construction and the rest (3) are approved and in final 

design phase. 

UTAH 

Utah Department of Environmental Quality 

Division of Drinking Water 
 

 230 

Utah State Office Park 

1950 W. North Temple 

Salt Lake City, UT 84114-4830 

Ph: (801) 536-4200 

Fx: (801) 536-4211 

Website: www.deq.state.ut.us/ 

Contact: Michael Georgenson ph: (801) 536-4197 

The State runs a General Permit program that covers the situation for WTPs discharging 

supernatant to surface water. Typically this discharge is intermittent and in small volumes. 

Indirect discharge to a sewer system is not a common option in the State. The sludge generated is 

disposed in a sanitary landfill or combined with POTW sludge. Source of raw water for the 

WTPs is a combination of surface and groundwater, but the utilities depend more on 

groundwater. Chemicals of concern in the State are iron and manganese, and TDS specifically 

sulfates. No re-injection of liquid waste is allowed and the State has an UIC program. In the 

State there are some utilities using membrane technology, one is and ultrafiltration plant and there 

are several small units on-line using RO systems. 

VERMONT 

Vermont Department of Environmental Conservation 

Water Quality Division 

Agency of Natural Resources 

103 S. Main 10 N 

Waterbury, VT 05671-0408 

Ph: (802) 241-3777 

Fx: (802) 241-3287 

Website: www.anr.state.vt.us/ 

Contact: Gregg Bostock 

Surface discharge of a holding pond or lagoon supernatant to a receiving stream needs to be 

permitted (NPDES) by the State. Indirect discharge to a sewer system is also an option. Source 

of raw water is a combination of surface and groundwater. The water quality in the State is good 

and the utilities do minimum treatment with sandbag filtration in some cases coagulation and 

flocculation to handle iron and manganese. No liquid waste re-injection is permitted to 

groundwater, but the State has an UIC program. The sludge is dewatered and disposed in a 

landfill. No land application is practiced since the sludge quality is poor for this purpose. In the 

state, utilities can dispose sludge as filling material. There is no knowledge of membrane 

technology being used by existing or upcoming utilities. 

VIRGINIA 

Virginia Department of Environmental Quality 

Water Program 

Pollution Prevention 
 

 231 

629 East Main St 

Richmond, VA 23240 

Ph: (804) 698-4108 

Fx: (804) 698-4032 

Website: www.deq.state.va.us/ 

Contact: Martin Bergenson ph:(804) 698-4374 

Drinking water utilities have the option to discharge directly any liquid waste (i.e., supernatant 

from a retaining pond) to a receiving stream only if they have a current NPDES permit. The 

residue once dried can be disposed in a sanitary landfill. There is also the option of land 

application for the solids under the State pollution abatement program. The program requires 

quality control of any permitted sludge. Surface water is the main source of raw water, but there 

are some small WTPs on ground water. One utility is permitted to re-inject treated water under 

the UIC program. There is only one RO plant in the State dealing with brackish water. 

WASHINGTON 

Washington Department of Health 

Division of Drinking Water 

Air Industrial Center, Bldg. 3 

P.O. Box 478222 

Olympia, WA 98504 

Ph:(360) 236-3153 

Fx:(360) 236-2522 

Website: www.wa.gov/ 

Contact: Jim Rio 

All surface dischargers must comply with State and Federal regulations and have an NPDES 

permit to discharge to a surface stream. WTPs hold the liquid waste in a lagoon for settling and 

the supernatant is discharged as needed. The plant can also recycle to the front end of the process 

as an option to reuse the supernatant. Indirect discharge to a sewer system is also a valid option 

in the State. Surface water is the most common raw water source in the State. Groundwater is 

also used as source water especially by smaller utilities. In general source water quality is good 

and only nitrate has been reported as a problem by a few utilities. The concentrate generated is 

typically dewatered and disposed in a sanitary landfill or onsite. The State does not allow liquid 

waste re-injection and just started the UIC program that will supervise any re-injection request for 

water reclamation. There is no information about RO or other membrane systems in the State. 

WEST VIRGINIA 

West Virginia Department of Environmental Health 

Office of Environmental Engineering 

815 Quarrier St 
 

 232 

Charleston, WV 25301 

Ph: (304) 558-2981 

Fx: (304) 558-0691 

Website: www.dep.state.wv.us/ 

Contact: William Harold Assistant Director of Environmental Engineering 

Drinking utilities in the State discharge supernatant after settling in a lagoon to surface streams 

only under an NPDES permit. The most common disposal option is recycling the backwash by 

sending the liquid waste to the front-end of the plant. Indirect discharge to a sewer system is also 

practiced, but in a minor proportion of the plants. The residue or sludge is mainly land applied or 

landfilled; this option is handled by the solid waste program. Source water for the utilities is 

mainly surface (70%) with few springs and wells used by small utilities. Raw water quality is 

good with mainly iron and manganese to be treated. In most cases only chlorination and aeration 

is required to meet drinking water standards. Only 1 or 2 plants are currently using membrane 

technology. No groundwater re-injection of liquid waste is allowed. 

WISCONSIN 

Wisconsin Department of Natural Resources 

Environmental Protection 

Bureau of Drinking Water and Groundwater 

Ph: (608) 266-9265 

Fx:(608) 267-7650 

Website: www.dnr.state.wi.us/org/water 

Contact: Steve Lendorff 

Discharge to a surface stream under an NPDES permit is one of the options available to WTPs in 

the State. The utility’s backwash is retained in a holding pond or is recycled to the front of the 

process. This is a common practice among the utilities. In few instances they have the option of 

indirect discharge to a sewer system. The sludge or residue is commonly sent to a POTW as 

liquid waste for disposal; some WTPs choose to dewater and send their sludge to a landfill. Half 

of the population in the State is served by utilities using surface water and the rest by 

groundwater. There are 20 large utilities using surface water and about 200 small plants on 

groundwater. The State does not allow waste re-injection and closely monitors all well operation 

under the UIC program. Source water quality is good with few exceptions where the plants have 

to deal with VOC leaching from nearby landfills. There are two plants under construction with 

microfiltration technology. 

 

WYOMING 

Wyoming Department of Environmental Protection 

Water Quality Division 

122 West 25th St., Herschler Bldg. 

Cheyenne, WY 82002 
 

 233 

Ph: (307) 777-7981 

Fx: (307) 777-5973 

Website: www.deq.state.wy.us/ 

Contact: Larry Robertson ph: (307) 777-7075 

EPA region VIII runs from Denver several programs related to Wyoming’s water issues. At this 

time EPA sets the water quality standards for the NPDES program, including the monitoring, 

capacity development, drinking water reporting, and confirmation of permits to the waste and 

drinking water utilities. The officer in charge of Wyoming in the region is Maureen Dauddy 

(ph:303 312-6262). 

There are only nine WTPs currently operating in the State, in most cases they send the backwash 

and other liquid waste to a lagoon and after the solids have settled the decant could be discharged 

to a surface stream or recycled to the front of the process within the plant. This latter option is 

common practice among the utilities. Sludge or concentrate residue can be disposed to a sanitary 

landfill once it passes the “paint filter test” to measure the level of water content. There are some 

land applications of the concentrate, but it is not a popular option since the sludge must meet 

quality criteria (e.g., Federal sludge criteria). Source water is a combination of surface and 

groundwater. There is no re-injection of liquid waste and the State conducts a UIC program to 

monitor groundwater quality. Groundwater is good requiring very minimum treatment such as 

chlorination to control coliforms. No membrane technology is currently in use among the State’s 

WTPs. 
 

 234 
 

 235 

APPENDIX 3 

STATE NPDES-RELATED REGULATIONS 

COMMENTS 

Most states do not have membrane plants producing potable water. Several states have 

only small membrane systems operating or have very few membrane plants. The words 

‘concentrate’ and backwash’ have different meanings in non-membrane treatment plants 

and care must be taken when using these terms to denote the intended meaning. In what 

follows, the term ‘concentrate’ unless referred to as ‘membrane concentrate’ means a 

liquid waste/sludge prior to dewatering. Similarly, the term ‘backwash’ means filter 

backwash unless specifically referred to as ‘membrane backwash’ (from a UF or MF 

process). The context of the paragraph should also help to make the distinction clear. 

Regulations for the states of California, Florida, and Texas are highlighted due to the high 

level of membrane activity there. Information about regulation in the other states 

follows. 

CALIFORNIA 

There are three main pieces of legislation for the regulation of concentrate disposal in the 

State: 

• Porter-Cologne Water Quality Control Act 

• California Regional Water Quality Control Board Basin Plans 

• Water Recycling Criteria 

The Porter-Cologne Water Quality Control is listed as Division 7 Water Quality in the 

California Water Code. A summary of the main sections of the rule is presented in Table 

2. 

The permitting procedures regarding the NPDES program in the State are as follows: The 

Regions of the California Regional Water Quality Control Board (CRWQCB) receive the 

request from interested parties for surface discharge of liquid waste. There are three 

general categories that include Waste Water, Industrial, and General. WTP utilities will 

fall under the industrial group category. The permit is valid for 5 years and it is very 

similar to the EPA permit, in some instances depending the plant location it could be 

more stringent. Any WET test requirement is tailored to the receiving water ecosystem: 

freshwater will have the corresponding species (C. dubia and P. promelas) and saltwater 

typically includes the Mysids and the Silverside. A third species (Selenastrum 

capricornotun) is frequently added as part of the WET requirement to check for nutrient 

overload in fresh and saltwater conditions (a marine algae for salt water). 
 

 236 

Table 2. Description of specific legislative rules in the Porter-Cologne Water Quality 

Control Act. 

Chapter* Article Subject Covered in the Legislation 

 

3 3 California State policies for water quality control 

4 3 Addresses Regional Water Quality Control Plans and 

outlines water qualities objectives, plan 

implementation and compliance 

4 4 Waste discharge requirements indicating who is 

required to report discharges and requirements for 

groundwater discharges, treatment facilities and 

injection wells 

5.6 - Guidelines for protection of beneficial uses of bay and 

estuarine waters 

7 6 Waste well regulations and wastewater reuse 

including reuse in landscaping, industrial cooling 

processes, toilet, flushing water, and dual-delivering 

systems for recycled water distribution. 

7.5 - Water recycling act of 1991 

*Source: Kenna E. N., and A.K. Zander. 2000. Current Management of Membrane 

Plant Concentrate, AWWA Research Foundation Publication. 

In most instances the WET test is not included in the permit, but is considered n a caseby-case basis. The State runs an executive authorized program for the sporadic 

discharger although they must meet drinking water criteria; some WTPs choose this 

option. There are no special requirements for the WTP facilities using membrane 

technology. Concentrate and sludge disposal is not regulated, but must be described in 

the permit. 

FLORIDA 

The State of Florida has six regulatory districts in charge of issuing permits (NPDES) for 

discharge of wastewater into waters of the State including groundwater. The districts are 

distributed in six different geographical regions of the State including the Norwest, 

Northeast, Central, Southwest, Southeast, and the South districts. Florida is a USEPA 

delegated State since 1995 for the application of the NPDES permits and has over 20 

years of experience issuing discharge permits. When the State became delegated they 

combined EPA guidelines with the State requirements, therefore USEPA guidelines are 

included in the current Florida regulation pertaining (Chapter 62 of the Florida 

Administrative Code). In some cases requirements in the State are more stringent than 

the federal requirements. Each facility’s permit is defined by specific constituents or 

conditions of the discharge and the receiving stream. The Districts do not make any 

difference regarding the requirements for other industrial facilities and the drinking water 

utilities (WTPs). All requirements are tailored to the operational and waste type of the 

applicant to ensure that the discharge will not impact water quality standards or cause or 

contribute to pollution. 

Regarding WET test requirement for the NPDES permit: FDEP emphasizes that every 

permit is unique and technical considerations for disposal of RO Membrane Plant
 

 237 

Table 1. List of Specific Regulations (Title 62 FAC) that Cover the Currently 

Accepted Disposal Options in the State of Florida. 

Regulation* Main Topic Covered Disposal Option 

 

62-4.240 Permit for water pollution sources Surface Water 

62-4.242 Antidegradation permit requirements Surface Water 

62-4.244 Mixing zones requirements Surface Water 

62-620 Wastewater facility permitting Discharge to wastewater 

treatment plants (WWTP) 

62-302 State surface water standards Surface Water 

62-302.400 County by county surface water 

classification including listing of the 

classes 

Surface Water 

62-302.500 Numerical criteria for parameter of 

each Florida water class 

Surface Water 

62-302.700 Outstanding Florida Waters 

protection requirement 

Surface Water 

62-500 Groundwater protection Groundwater 

62-520 Groundwater classification 

standards 

62-522 Groundwater permitting and 

monitoring requirement 

Groundwater 

62-528 Groundwater injection Groundwater 

62-528.300 Well classification and general 

provisions 

Groundwater 

62-528.305 Well permitting process Groundwater 

62-528.605 Description of Class I and II well 

operation and monitoring 

Groundwater 

62-528.630 Class V well permitting Groundwater 

62-610 Re-use of reclaimed water and land 

application 

Groundwater 

62-610.200 Definition of demineralization 

concentrate 

Groundwater 

62-610.865 Blending of concentrate, regulations 

and requirement 

Groundwater 

*Source: Kenna E. N., and A.K. Zander. 2000. Current Management of Membrane 

Plant Concentrate, AWWA Research Foundation Publication. 

concentrate are taken into account when writing the permit and the biomonitoring 

requirements. Typically, marine species are considered for WET testing, i.e., Menidia 

beryllina and Mysidopsis bahia. If the TDS of the concentrate is primarily determined by 

ions other than chloride and sodium, and thus the concentrate is of lower salinity, fresh 

water species are considered. Any surface discharge must comply with biomonitoring 

and chemical standards before discharge. The utilities can request variance of discharge 

standards filing a state form if they consider that permit constituents do not apply to their 

current situation (a copy of the form application can be obtained from the Florida DEP 

website). 

The complexity of the individual permit for membrane utilities is defined by the 

receiving Florida water, which follows a designation system. Several of the standards 

and requirements are based on which type of Florida water is receiving the discharge. 

Waters in Class III, for example, include all recreational waters; Class II describes waters 

dedicated to fisheries activities and will have more requirements on pollutants than the 
 

 238 

previous one. The permit process typically takes between 6 months to a year. However 

it can get lengthy if sensitive environments in the State are involved. Currently, there are 

some legislative initiatives to resolve the issue of WET testing requirements for the 

membrane utilities. In some cases the demonstration of absence of other pollutants has 

been required by FDEP, although it is up to the districts to get satisfaction on this 

requirements since they are the ones issuing the NPDES permit. 

There are no special requirements for utilities discharging to a marine environment with 

the caveat that they must meet all standards established for the specific environment 

where they plan to discharge. It is obvious that discharging to a Florida Outstanding 

Water system will make a difference in permitting requirements. 

A summary of accepted disposal options in the State for WTP (RO or conventional) 

includes the following: 

1. Deep Well injection 

Current deep well injection permits in Florida are issued under provisions of Chapter 403, 

Florida Statutes (F.S.) And Florida Administrative Code (FAC) Rules 62-4, 62-550, 62-

660, and 62-528. The permit describes all technical requirements for Class I injection 

wells to dispose of non-hazardous reverse osmosis concentrate. The permit specifies well 

I.D., depth, casing, volume (mgd) allowed to be disposed, injection pressure, and 

required monitor wells. 

In addition, the permit narrative indicates the General Conditions that are required from 

the permittee such as record keeping, compliance with monitoring requirements, 

emergency procedures etc. The Specific Conditions of the permit describe the operating 

requirements for the injection well such as which type of waste is allowed in the well, 

daily monitoring, abandonment procedures, testing and reporting requirements etc. A 

certification of financial responsibility is required as part of the permit to ensure that the 

facility has the necessary resources to close, plug, and abandon the injection and 

associated monitor wells, at all times. 

2. Spray Irrigation/Land Application 

This type of permit is issued under the provision of Chapter 403 of the Florida Statutes 

and applicable rules of the Florida Administrative Code (See Table 1). The permit covers 

holding pond facilities for concentrate waste prior to the irrigation stage. Typically the 

concentrate is blended with other raw water to meet TDS standards before irrigation in 

most cases to golf course facilities. The permit specifies monitoring parameters which for 

the Land Application such as Flow, TDS, Sodium, Chloride, Sulfate and pH. Ground 

water protection is also specified in the permit. DMR reporting and blending ratios of 

concentrate with raw water (4:1) are detailed in the permit. 
 

 239 

3. Surface Discharge 

The outfall discharge point is specified in the permit as well as the type of waste allowed 

to be discharged. Monitoring parameters at the mixing zone and the dimension of the 

zone are detailed in the permit. The permittee must comply with the applicable FAC 

Rules 62-4.244 and 63-302.500 (Table 1) related to the subject of mixing zones. Land 

Application, Emergency Surface Discharge, other methods of disposal or recycling and 

further limitations of monitoring reporting are defined in the permit. A WET testing 

Program is also described in the permit and is mandatory for surface dischargers. 

TEXAS 

The disposal options for membrane concentrate and their regulatory requirements are 

specified in Title 30 of the Texas Administrative Code. Table 3 list the main topics 

included in this piece of legislation indicating the appropriate disposal option allowed by 

TNRCC (Texas Natural Resources Conservation Commission). 

Table 3. Description of regulations and corresponding legislative sections of the 

Texas Administrative Code applicable to membrane disposal options. 

Chapter/SubChapter* Section Subject Covered in the Legislation 

 

307 307.5 Description of the anti-degradation policy in 

the State 

 307.6 Prohibition of toxic substances that can cause 

acute toxicity to aquatic life in waters of the 

State 

 307.7 Site specific uses and criteria for different 

classes of water 

 307.9 Standard application 

319 - Discuss pre and post treatment issues and 

surface water discharges 

309 - Addresses evaporation ponds and land 

application of concentrate. It sets 

requirements for waste ponds and lagoons. 

309 Sub-Chapter C - Expand on land application of effluents 

through an irrigation system or percolation 

pond 

335 - Refers to handling and disposal of industrial 

solid waste, including permitting procedures, 

land disposal restriction and waste 

classification 

331 - Regulates underground injection wells. 

331 Sub-Chapter A - Establish classification of injection wells and 

waste associated with each class 

331 Sub-Chapter C - Discuss corrective actions standards and well 

closure requirements 

331 Sub-Chapter G - Describe permitting process for underground 

injection wells 

*Source: Kenna E. N., and A.K. Zander. 2000. Current Management of Membrane 

Plant Concentrate, AWWA Research Foundation Publication. 
 

 240 

Current disposal options in the State are: recycle to the head of the plant, land irrigation, 

discharge to a sanitary sewer system, evaporation pond, surface discharge to Texas 

Waters, discharge of brines or concentrate, and disposal of waste sludge. Few of these 

options involve State or Federal permitting. Discharge to surface water, i.e., water of the 

State or USA waters, requires a TPDES (Texas NPDES) permit that will have all Federal 

and State requirements. It is clear that the permit narrative is dictated by type and 

volume of discharge, receiving water conditions, frequency of the discharge etc. all of 

these factors are site specific. Sludge disposal requires a State permit for disposal to a 

sanitary landfill or registration with TNRCC for land application of the sludge near the 

surface as it is indicated in 30 TAC Section 312.121. Re-injection is always an option for 

concentrate disposal, but not a preferred one since it must require meeting UIC 

requirements. In the case of land irrigation, it will only require a permit if the discharge 

is above 5000 gallons/day in which case it will require a TPDES permit. Volumes below 

5000 gallons do not require permits according to current rules. The on-site disposal 

option of sludge or concentrate (within the WTP property) also is an accepted practice 

and it will be covered by the TPDES permit. 

The TPDES permit is currently being implemented and there is no indication that the 

WTPs are treated any different from other industrial dischargers. The drinking water 

utilities will fall under the category of industrial dischargers and will follow the same 

protocol for getting a permit. The existing process will take approximately 180 days in 

length, from the day of a declaration of administrative completeness. Due to the 

extensive review it is recommended that the process should start a year in advance. 

IOWA 

The State issues NPDES permits for surface discharge regardless of which industry 

discharges the waste. WTPs are not typical permittees since they have other options such 

as discharge to a POTW. Groundwater reinjection is not a disposal option for liquid 

waste in the State. Residual disposal to a landfill is a common option; again no permit is 

required with the exception of the normal landfill paperwork. The Municipal Solid 

Waste office runs this program. Evaporation pond is not a disposal option due to weather 

conditions. 

The NPDES program is similar to the Federal with water quality standards and biological 

requirements tailored to the type of waste and receiving water conditions. For WTPs 

there is no WET test requirement. The normal processing time for an NPDES permit is 

180 days. 

 

ALABAMA 

Surface discharge of liquid waste generated by WTPs in the State will require an 

individual NPDES permit issued by the Permit and Compliance section of ADEM. 

Currently, there are not many of these permits issued since in the State there are only 
 

 241 

about 25 WTPs that serve mostly small communities. The permit process takes about 6 

months to complete and follows EPA guidelines. Constituents monitored include metals 

such as aluminum, and Iron. Other parameters such as pH, TSS, Total residual chlorine, 

turbidity are also included. The permit does not require WET testing. In general, few 

utilities are issued a permit since there are other disposal options available such as 

indirect discharge to a POTW. 

ARKANSAS 

The State offers individual NPDES permits for WTPs that have been issued a 

construction permit by the State. The process requires submission of a notice of intent 

(NOI) form, a fee of $200.00, and corresponding maps indicating the discharge points. 

The process can take up to 3 months to complete including the comment period and draft 

review. Each utility is analyzed in a case-by-case basis. A partial priority pollutant scan 

must be submitted and from the data, constituents for monitoring are defined. A WET 

test may be required based on the analytical report, but in most cases it is not required. 

The State permit has similar requirements as the federal NPDES and the water quality 

standards are on line with CWA specifications. 

Sludge disposal of concentrate and residual generated by the utilities are included in the 

permit. Landfill disposal and discharge to a POTW utility do not require a State permit. 

CONNECTICUT 

WTP waste disposal in the State does not require an NPDES permit for surface discharge 

of liquid waste. The State runs a general permit for the WTP utilities that covers disposal 

of residue or liquid backwash, filter rinse water, brines and other waste generated during 

the process. 

The permit describes in detail activities authorized and type of wastes covered such as 

clarifier tank sludge blowdown, filter media backwash, infiltration bed and settling 

lagoon overflows etc. The permit also specifies that the applying utility must submit in 

the event of indirect discharge to a POTW all pertinent information about the volumes 

and characterization of sludge and effluent. 

The extent of requirements and constituents are defined after reviewing the presented 

information such as DMRs, process chemicals etc. In general WET test requirements are 

not required. 

 

COLORADO 

The Colorado River Salinity Standards are listed in Regulation 39 and administered by 

the Colorado Department of Health. These standards are established to ensure that any 
 

 242 

discharge to surface water will not increase salt content (Reg. 61.8(2) (1)) in the Colorado 

River. 

The State issues a General Permit (GP 60040000) for the WTP disposal of backwash and 

other liquid waste from retaining ponds. This permit will establish limits for pH, TSS, 

residual chlorine, flow and other general constituents. Each utility must report their 

process chemicals and other treatments use in order to set the discharge requirements. 

WET testing is not typically included, but is always an option based on specific 

constituents (chemical use in the process). The permit follows NPDES guidelines and is 

on line with federal CWA requirements regarding water quality standards. The permit is 

issued to utilities that have completed construction permit requirements and it takes about 

30 days to be completed. The most common disposal option currently used by the local 

utilities is natural percolation to the ground, which does not require a State permit. 

Disposal options that require a State permit include land application of concentrate, 

which is regulated under the bio-solid program. Landfill disposal requires clearance with 

the landfill operator. No other options involve permitting. 

DELAWARE 

Disposal options for the WTP in the State are: discharge to a POTW sewer system, 

landfill, on-site disposal, and in some instances spray or land irrigation of backwash 

reject. The only option that is covered under a State program is Land Irrigation. The 

others are not currently regulated. Concerning surface discharge only one plant in the 

State has requested an individual NPDES permit. 

The State NPDES program does not included any special regulation for WTPs. The 

program is on line with EPA requirements and in some cases there has been disagreement 

on MCLs for metals since the utilities may concentrate these during the process to high 

levels for those constituents already existing in the source water. The State allows for a 

pollutant credit program, which accounts for initial level concentrations and credits the 

utilities at the moment of disposal of the particular constituent. The State would like to 

provide waivers to the utilities in these situations, but the EPA region is reluctant to open 

this venue and it demands the meeting of water quality standards. 

There is no difference in the NPDES program for WTPs, but overall few utilities request 

an individual permit (only one facility has initiated the permitting process). Regarding 

WET tests: only industrial dischargers with complex mixtures in their waste are required 

to submit biomonitoring data. WTPs are not required to do WET testing. The State has a 

set of guidelines for discharge to the marine environment and it is site specific in the 

standards that the discharger has to meet including definition of mixing zones, sensitive 

environment, seashell fisheries etc. 

In the event a WTP initiates the process for a NPDES permit, the time it takes from 

application to issuing the permit could be 6 months to 1 year. Location of the facility is 
 

 243 

the key decisive factor that might lengthen the process; in the simplest case it can be fast 

(6 months). 

GEORGIA

Disposal options for the WTPs in the State are centered in surface discharge, land 

irrigation, land application of concentrate, and indirect discharge to POTW sewer system. 

The State permits through the NPDES program any surface discharge to State or US 

surface waters, the State also runs a Land Application System (LAS) permit program that 

covers both land irrigation and sludge application for the municipal treated effluent and 

bio-solids. WTPs can apply to dispose backwash or blowdown waters, but it is not a 

common choice. The NPDES permit is posted in the web and is relatively simple for the 

WTP to apply for it and comply with basic requirements such as TSS, Turbidity, pH, and 

in some cases heavy metals such as Fe++, and Mn++. The individual permit is process in 

120 days. 

HAWAII 

Few utilities are issued NPDES permits since the main option to dispose liquid waste is 

the evaporation pond. In the island of Maui the WTP utility has been issued an 

individual permit for supernatant discharge. The permit includes typical constituents 

such as pH, TSS, and Total residual Chlorine, which is the major concern to protect 

aquatic biota. One important aspect of the permit is that there is no marine discharge 

allowed, only discharge to fresh water streams. 

ILLINOIS 

Disposal options covered by State regulations include landfill and surface discharge to 

State waters. All other options do not require State permits, but WTPs must comply with 

general guidelines, i.e., indirect discharge to a sewer system implies agreement between 

utilities. 

It is common that WTPs request and obtain an NPDES permit for surface discharge. In 

the State they are considered within the industrial sector and must meet all water quality 

standards before effluent discharging. The process is the same for all industrial facilities. 

WTPs using advance technology such as RO systems or other advance filtration systems 

must report in detail their waste composition providing analytical data on constituents. 

The permit process in Illinois typically takes 180 days from the moment of submission of 

all pertinent documentation. There is high priority in the State for new WTP utilities. In 

general the Illinois NPDES permit is in-line with the EPA permit and follows to the letter 

CWA standards and requirements. It is evident that the permit is tailored to individual 

conditions and variations exist due to the uniqueness of each case. 
 

 244 

The NPDES permits in the State for WTPs typically do not require WET tests, but it is 

possible to add this requirement based on the specific situation. The State used to have a 

general permit for WTPs, but it has been phased out and the current policy is to allow old 

permits to expire and to issue a new individual permit that in general resembles quite 

close the old permit. Requirements such as pH, TSS, flow, and metals are common. 

After reviewing analytical data of typical constituents other MCLs may be established. 

INDIANA 

Disposal options currently available in the State include indirect discharge to a POTW for 

which there is no permit involved and surface discharge of liquid waste that does require 

an individual NPDES permit that follows EPA guidelines. For drinking water utilities 

there are only secondary water quality standards on their key constituents, but no 

biomonitoring or WET testing since this utilities are considered low flow and low 

pollutant contributors. The permit process is direct and by statute the State must finish 

the process in 180 days from submission. 

Currently WTPs are facing problems meeting chloride standards and although there is no 

membrane technology treating drinking water in the State it is expected that as the 

chloride problem becomes more critical some of the utilities will be considering 

advanced technology.

KANSAS 

Public utilities typically use retaining lagoons as a disposal option of their liquid waste 

and for this the State will issue a General Water Supply permit. There is no further 

requirement. The lagoon is allowed to evaporate or trickle underground. Since the water 

is considered relatively clean, further requirements are not necessary. 

The NPDES permit for those WTPs that will need to go to surface discharge proceeds as 

it would for any other industrial discharger, although the process is less complex and 

within six to eight months the WTP can obtain a permit. The State will establish the 

water quality standards according to process constituents. Currently the permitting office 

requires TSS, pH, residual chlorine, and polymers as the main chemicals to monitor in 

the WTP utilities. Biomonitoring requirements with two species are only requested once 

at the onset of the permit to confirm no deleterious effect on aquatic biota. 

KENTUCKY 

The State issues a general permit for surface discharge of industrial facilities. WTPs are 

considered within this latter category. The permit is specifically for backwash or process 

water from a drinking water utility and requirements listed include: TSS, pH, Residual 

Chlorine, and in some cases metals such as Iron and Manganese. 
 

 245 

The permitting process is direct and streamlined taking only from 30 to 60 days. All 

water quality standards and constituents follow CWA and EPA guidelines. 

Disposal options that require a State permit include Land Application, which is regulated 

by the sludge program and the solid waste program. The permittee must meet EPA 

sludge criteria. 

MARYLAND 

WTPs in the State are classified as Municipal Wastewater plants for waste disposal 

regulation. For surface discharge of backwash or other liquid waste the utility is required 

to apply for an individual NPDES permit. The permit defines basic constituents such as 

pH, TSS, Coagulants used, Aluminum, Iron, and Total Residual Chlorine. WET testing 

requirements are not included in the permit since the utility effluent is considered to be a 

low pollutant contributor. There is no special requirement for discharging to State marine 

waters once all standards specified in the permit have been met. 

The State does not allow land application of residual or concentrate from WTPs. 

Landfill disposal of sludge is dealt directly with the landfill operator. The permit process 

takes between 6 months to a year depending on the backlog in the permitting office. 

MICHIGAN 

Currently the State is implementing a General Permit for waste disposal of WTP 

residuals, specifically backwash and reject water from the drinking water treatment 

process. A new permit application will take between 2 to 6 six months. The constituents 

currently monitored include TSS, pH, Residual Chlorine, Settleable solids, and in few 

cases some metals. There are no WET test requirements involved as of this date. The 

metro area plants (Detroit) discharge to existing sewer systems and therefore avoid the 

NPDES permit. In the State there are about 70 WTPs and few of the medium to small 

size have chosen the General Permit route. 

MISSISSIPPI 

In the State the largest WTP is in the city of Jackson and currently is under a Consent 

Order to stop surface discharge due to frequent violation of State standard for Aluminum 

and TDS. None of the other smaller utilities have requested an NPDES permit. Although 

in the event of surface discharge they will be requested to comply with DEQ regulations. 

Most of the WTPs avoid surface discharge by negotiating with POTWs for sewer 

disposal and conducting on-site disposal of liquid and solid waste. The State does issue 

individual permits for other industrial dischargers. The process of applying and issuing a 

permit could take from 90 days to 6 months depending on data submitted in the 
 

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application. All permit specifications mirror EPA guidelines and the utilities must 

comply with State standards. WET testing is frequently included in these permits. 

MISSOURI 

Disposal options for the WTP facilities include discharge to a POTW, landfill of the 

concentrate, and sludge disposal generally on-site. None of these options require a State 

permit. Only surface discharges to State waters require an NPDES permit. The State 

manages two types of permits: a general permit for small utilities and individual permits 

for larger WTPs. The key characteristic that the permitting office considers as a criterion 

to sort out whether a utility qualifies as a small or large facility is how the WTP handles 

and disposes the concentrate. Discharge of liquid waste and sludge to the Mississippi or 

Missouri river must have an individual permit (large facility), which will include WET 

testing with two species. Constituents such as pH, TSS, Settleable and Suspended Solids, 

Residual Chlorine are typically included. The WET test requirement in the individual 

permit is being contested by the public utilities and there is ongoing litigation concerning 

this issue. The general permit is more flexible and does not include WET testing. 

Utilities that qualify for the general permit do not dispose any sludge or residual to the 

rivers. The general permit can be processed in 60 days; an individual NPDES permit can 

take as long as 3 years. There is no difference of these permits from the EPA guidelines. 

MINNESOTA 

The State issues a General NPDES Permit for surface discharge of WTP effluent 

including backwash, blowdown, and holding pond overflow. This general permit is 

issued only to utilities already in the system i.e., already with construction and operation 

permits and in that sense it is a straightforward procedure that only takes 30 days. 

Constituents monitored in this permit are: TSS, flow, pH, Iron, Manganese, and in some 

cases Total Residual Chlorine. The permit, also includes concentrate waste management 

within the facility. There is no WET testing included in the permit. 

MONTANA 

Requirements for WTP surface discharge of their settling pond or backwash and liquid 

waste involve an NPDES individual permit. Typical constituents that are listed in the 

permit are TSS, Turbidity, dissolved Aluminum, chlorine. The permit process takes 

about 6 months but depending on the site location of discharge it can be issued in 90 

days. The write up of the permit is on line with EPA guidelines. WTP are low pollutant 

generators and therefore will not require WET testing. 
 

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NEBRASKA

The State is currently reviewing the policies concerning surface discharge of liquid waste 

for the WTP sector. Utilities that discharge into the Missouri river are monitored for 

TSS, pH, flow, and residual chlorine. At this time no WET test requirements are 

included in the permit. EPA guidelines are followed and the required water quality 

standards meet CWA specifications. In the State the utilities undergoing permit renewal 

must obtain an individual NPDES permit. The process from application to issuing the 

permit could take from 30 to 60 days for utilities that have completed the construction 

and permitting phase. The permit also covers sludge disposal and requires submission of 

a solid management plan. Although the State does not have a Beneficial Use Program for 

concentrate, it encourages use of sludge as soil amendment in agricultural land. 

NEVADA 

Discharge of backwash and process wastewater to State waters by WTPs requires an 

individual NPDES permit. In most instances pond and water tank overflow requires a 

permit. Typical constituents monitored in the permit are: TSS, Total Residual Chlorine, 

pH, settleable solids, and turbidity. The permit follows EPA guidelines and is at least as 

stringent as the Federal requirements. 

Landfill disposal of generated sludge and indirect discharge to POTW do not require 

State permits. Underground wastewater disposal will require a UIC permit. This latter 

option is not common among the utilities. 

NEW JERSEY 

WTPs in the State are covered under a General NJPDES permit for surface discharge of 

filter backwash, cleaning operation of clarifiers, or other liquid wastes generated in the 

process of bringing the raw water supply to drinking water standards. In the State most 

of the WTPs discharge their effluent to an outdoor infiltration-percolation lagoon that 

ultimately discharges to groundwater. Based on the water source, either groundwater or 

surface water, the permit constituents are defined. Whether or not the pond is lined plays 

a key role in writing the permit. The permit requires sampling of the accumulated sludge 

to characterize metal content in the sediment. The State is more concerned with 

problematic parameters such as dissolved metals that can impact aquatic life or in the 

case of surface water trihalomethanes or other reactive chlorinated compounds. WET 

tests are not included in the permit. Sludge generated must be handled in a safe and legal 

manner. The permit has a section for reporting and describing sludge disposal 

procedures. The State manages a beneficial use of sludge program for which the utilities 

need to apply and submit qualifications. 

Process time of the permit is typically 30 to 60 days. This implies that the WTP is 

already permitted to operate and it will only be issued a discharge permit. 
 

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NEW YORK 

In the State the WTPs are classified as industrial facilities and issued an individual permit 

that is tailored to the discharge composition. The chemical composition of the discharge 

and the flow and category of the receiving waters dictate the constituents to be regulated. 

The permit process can take from 4 to 6 months. 

The preferred disposal option, however for most of the State utilities, is discharge to an 

existing sewer system. The State does not issue any permit for the above disposal option. 

There is no groundwater reinjection allowed for waste disposal. 

OREGON 

Waste disposal options for WTPs include land application under the wastewater sludge 

State program. Some utilities still have the option of groundwater disposal; this option is 

only available to existent facilities prior to implementation of a UIC program. The 

ODEQ is phasing out this practice. Surface discharge of liquid waste is covered under a 

General NPDES industry permit to dispose backwash waste to surface water. Currently 

the State issue two types of general permits the first one for utilities only discharging 

backwash and other liquid waste (100 G) where requirements for constituents are only 

TSS, pH, Flow, Total Residual Chlorine, and any other process chemical reported by the 

utility such as biocide, antiscalant, polymers, etc. The other permit (200 G) is issued for 

utilities disposing concentrate, and other sludge as well as liquid waste. Neither permit 

requires WET testing or other biomonitoring requirement. 

PENNSYLVANIA 

The State issues individual NPDES permits for disposal of backwash and overflow 

lagoons. WTPs applying for the permit must submit a series of requirements including 

DMRs and process stream composition, which are used to judge which monitoring 

requirements will be included in the permit. Typically the process takes around 180 days 

and the permit is valid for 5 yrs. The permit follows EPA guidelines. 

The permit mentions waste disposal of concentrate and specifies that it must be handled 

and disposed of in a safe manner, but does not enforce the utility to follow a specific way 

of disposal. The State runs some other programs that deal directly with sludge disposal 

(solid waste, beneficial use of sludge). 

Constituents to be monitored include TSS, pH, Total Residual Chlorine, and Al, Fe, Mn. 

There are no WET test requirements in the permit. 
 

 249 

NORTH CAROLINA 

Regulations pertaining to surface and sewer discharges are listed sections 2B and 2H of 

Title 15A of the North Carolina Administrative Code. Sections 2B.0201 and 2B.0204 

present the antidegradation policies in the State, and mixing zones for surface discharges. 

Section 2H.0100 governs the issue of NPDES permits for point source discharge. 

Water utilities discharging to State waters require an individual NPDES permit in which 

constituents are specified for monitoring. In the case of membrane utilities the State is 

issuing a new set of discharge policies and regulation to address the disposal of 

concentrate or residual waste. Utilities treating over 50,000 gallons per day are required 

to comply with WET testing. There are several membrane utilities in the State (approx. 

20 to 50) with a few large R.O. systems in the coast over 1 MGD. An individual permit 

takes about 180 days after application. For membrane utilities it may be longer due to 

some environmental issues related to the source water quality. 

The State has a water classification system (Section 2B0101), which determines the 

permit requirements in the event of discharging to receiving bodies of water that could 

impact sensitive fisheries areas. 

NORTH DAKOTA 

The State issues individual NPDES permits for WTP surface discharge of backwash, and 

supernatant or overflow from retaining lagoons. The permit includes basic parameters 

depending the type of process used by the utilities. For iron and manganese removal 

plants constituents include TSS, pH, and the metals Fe, Mn. Plants that use limesoftening processes are required to monitor TSS, pH, TDS, and Total Residual Chlorine. 

There is no WET testing involved in either permit. The State does not have primacy on 

sludge issues, which are handled by EPA region VIII. The permit process takes about 

180 days. 

OHIO

The State will issue NPDES individual permits for any WTP waste stream disposed by 

surface discharge. Similar requirements apply to disposal of lagoon overflow or 

backwash waste. The permit follows EPA guidelines, and defines the water quality 

standards based on State regulation. For this type of discharge basic secondary treatment 

parameters are monitored among them TSS, TDS, pH, flow, Chloride, Total Residual 

Chlorine, and depending on the treatment process, metals such as Fe, and Mn. A new 

facility is issued the construction and NPDES permits at the same time and it can take 

from 3 to 9 months if the comments received from the Notification of Intent (NOI) are 

not complex. 
 

 250 

The sludge or concentrate generated is also included in the permit and the facility must 

present a solid or sludge management program to address this type of waste. 

RHODE ISLAND 

Few WTP utilities in the State request a discharge permit. In the event that they require a 

RIPES (the NPDES version in the State) permit this will fall within the industrial sector 

permit. The constituents to be monitored are: TSS, pH, and Residual Chlorine. The main 

disposal option in the State is indirect discharge to an existing sewer system or on-site 

disposal of dry sludge. 

SOUTH CAROLINA 

There are several types of permits depending on the constituents in the wastewater. 

According to the interviewed officer the permit documents address all current policies in 

the State concerning waste disposal for the WTP utilities. 

TENNESSEE 

The State issues an NPDES individual permit for all discharge into State waters. The 

permit follows EPA guidelines on discharge requirements such as water quality 

standards. The draft for a General Permit will be posted in the State website for public 

comments. This proposal includes the secondary treatment constituents that will be 

monitored as well as which type of liquid discharge and process will be covered under 

this permit. There is no special reference to a particular process or WET test 

requirement. The State is simplifying the permitting process. 

VERMONT 

The State issues individual NPDES permits for WTP surface discharge of liquid waste. 

The permit is a simple one with few constituents to monitor such as flow, pH, TSS, and 

few metals depending on the treatment process. As of this date there is no WET testing 

involved in the permit, however the State closely monitors plant additives to ensure 

safety for aquatic organisms. The permit process starts with filling an application and 

submitting all required data to the permitting office. In a period of about 180 days the 

permit is processed including notification of intent and public review. If there is no 

public comment the permit is issued within the above period. 

Concentrate generated by the WTP is disposed in a sanitary landfill or on-site. Although 

the State runs a sludge program drinking water utility sludge does not qualify for 

beneficial use. 
 

 251 

VIRGINIA 

WTPs discharging to State surface water must have an individual NPDES permit. The 

permit is very basic with few constituents to monitor such as pH, TSS, Total Residual 

Chlorine, and flow. This type of individual permit typically does not include WET 

testing. However, depending on the DMR results, chemicals used in the process as well 

as the volume of the discharge, WET tests may be required. 

There is no special requirement for discharge to seawater environments except the ones 

specified in the State water quality standards for marine environments. The State has a 

surface water (fresh and saltwater) classification system. 

The permit also requires concentrate and sludge management information which must 

presented by the permittee to address disposal of process byproducts. The permit process 

can take from 4 to 6 months. 

WEST VIRGINIA 

The State considers discharge to surface water by WTP utilities a matter requiring an 

individual NPDES permit. Although most of the State utilities do not discharge to 

surface water there are few that do no have an option and need to obtain a permit. In the 

State only individual permits are issued. As in other states the WTP utilities will comply 

with few parameters. Parameters monitored are flow, pH, Residual Chlorine, and in 

some cases metals such as Fe, Mg, Mn, Al. Metals are more common in facilities using 

groundwater as source water. 

The permit process can take from 90 to 180 days depending on comments received 

during the notification of intention phase. 

WASHINGTON 

Chapter 173-220 of the Washington Administrative Code provides information on 

discharge limitations, monitoring, and reporting for NPDES permits in the State. Chapter 

173-221 presents discharge standards and limits for wastewater facilities. 

WTPs with a maximum production capacity of 50,000 gallons in a 24 hour period qualify 

for the General Permit issued by the State to dispose backwash, lagoon overflow, and 

other specific liquid waste described in the rule which applies to any concentrate. There 

is specific language in the permit to indicate which types of liquid waste are covered. 

These permits have been applied mostly to traditional pants and a few filtration processes 

that remove TDS. These situations include filter rinse, backwash, and concentrates that 

resemble sludge produced in the filtration/coagulation process. Parameter monitored 

under the General Permit follow secondary treatment criteria (TSS, TRC, pH, flow). 
 

 252 

Although sludge disposal is mentioned in the permit this issue is left to the permittee and 

the State does not enforce submission of a waste disposal management plan. 

UTAH 

Public drinking water utilities in the State discharging overflow, backwash, blowdown or 

any other liquid waste are covered under a General Permit. This permit follows NPDES 

and EPA guidelines that establish constituent requirements such as pH, TDS, TSS, and 

Total Residual Chlorine. Depending on the characteristics of the receiving waters the 

above requirements can be expanded. The State has a surface water classification system 

that identifies outstanding areas to ensure special protection. There is no WET test 

requirement in the permit, but each facility must submit their DMR results. The permit 

process takes about 180 days for a new facility. 

Other disposal options such as recycling at the head of the plant, landfill, or on-site 

disposal of residual sludge do not require State or Federal permits. 

WISCONSIN 

Surface discharge of overflows, backwash, blowdown and column exchange waste will 

require a general NPDES discharge permit. In order to qualify for this type of permit the 

utilities must fulfill some requirements. These include: submitting DMRs reports, 

documentation for the process for treating the raw water, waste management plans, and 

description of the receiving water and outfall location. 

The State has in the past issued two general permits for WTP facilities. One, for the 

traditional filtration/coagulation process and the second one for plants using sodium 

cycling anion/cation exchange columns. This second permit is being eliminated since 

high chloride resulting from the process has proven toxic to aquatic life. In the State 

there are about 12 plants using this cation/anion process. The General Permit currently 

available has typical secondary treatment facility parameters and does not include WET 

testing. 

WYOMING 

The State issues individual NPDES permits to dispose backwash, filter rinse water, 

overflow, and other liquid waste. The permit is a standard NPDES surface discharge 

requirement that monitors TSS, pH, Total Residual Chlorine, and in some cases 

Ammonia, flow, and BOD which according to EPA correspond to secondary treatment 

parameters. In some instances the permit may include sludge disposal. Typically the 

WET test is not included but depending the nature and classification of the receiving 

waters it may be included. The volume of the discharge can also require verifying 

aquatic toxicity impacts in streams with small flow. The permit takes approximately 180 

days to be processed.