STAGE 2 DISINFECTANTS AND DISINFECTION 

BYPRODUCTS RULE

United States

Environmental 

Protection Agency

Office of Water

(4601)

EPA [No. TBD]

July 2003 

Draft

This text is a draft provided for public comment. It has not had a final review for 

technical accuracy or adherence to EPA policy; do not quote or cite except as a 

public comment.

INITIAL DISTRIBUTION SYSTEM EVALUATION
Note on the Stage 2 Disinfectants and Disinfection Byproducts 

Initial Distribution System Evaluation Guidance Manual, July 2003 Draft

Purpose:

The purpose of this guidance manual, when finalized, is solely to provide technical 

information for water systems and States to use for compliance with the Initial Distribution 

System Evaluation (IDSE), a component of the Stage 2 Disinfectants and Disinfection 

Byproducts Rule (Stage 2 DBPR). EPA is developing the Stage 2 DBPR to reduce DBP 

occurrence peaks in the distribution system based on changes to compliance monitoring 

provisions. Chapter 1 of this manual contains additional information about this regulation.

This guidance is not a substitute for applicable legal requirements, nor is it a regulation 

itself. Thus, it does not impose legally-binding requirements on any party, including EPA, 

states, or the regulated community. Interested parties are free to raise questions and objections to 

the guidance and the appropriateness of using it in a particular situation. Although this manual 

describes many methods for complying with IDSE requirements, the guidance presented here 

may not be appropriate for all situations, and alternative approaches may provide satisfactory 

performance. The mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. 

Authorship: 

This manual was developed under the direction of EPA’s Office of Water, and was 

prepared by The Cadmus Group, Inc. and Malcolm Pirnie, Inc. Questions concerning this 

document should be addressed to:

Thomas Grubbs and Elin Warn

U.S. Environmental Protection Agency

Mail Code 4607M

1200 Pennsylvania Avenue NW

Washington, DC 20460-0001

Tel: (202) 564-5262 (Thomas Grubbs)

 (202) 564-1807 (Elin Warn)

Fax: (202) 564-3767

Email: Grubbs.Thomas@epamail.epa.gov and Warn.Elin@epamail.epa.gov

Request for comments: 

EPA is releasing this manual in draft form in order to solicit public review and comment. 

The Agency would appreciate comments on the content and organization of technical 

information presented in this manual. Please submit any comments no later than 90 days after 

publication of the Stage 2 Disinfectants and Disinfection Byproducts Rule proposal in the 

Federal Register. Detailed procedures for submitting comments are stated below. 
Acknowledgements:

American Water Works Association

Association of Metropolitan Water Agencies

Andrew DeGraca—San Francisco Water

Walter Grayman—W.M. Grayman Consulting 

Mike Grimm—Oregon Health Department

Rich Haberman—California Department of Health Services

Mike Hotaling—City of Newport News

Alexa Obolensky—Philadelphia Water Department

David Reckhow—University of Massachusetts Amherst

Tom Schaeffer—Association of Metropolitan Water Agencies

Charlotte Smith—Charlotte Smith & Associates

Vanessa Speight—University of North Carolina

Scott Summers—Colorado University

Jim Uber—University of Cincinnati

Marguerite Young—Clean Water Action

Procedures for submitting comments: 

Comments on this draft guidance manual should be submitted to EPA’s Water Docket. 

You may submit comments electronically, by mail, or through hand delivery/courier. 

• To submit comments using EPA’s electronic public docket, go directly to EPA Dockets at 

http://www.epa.gov/edocket, and follow the online instructions for submitting comments. 

Once in the system, select “search,” and then key in Docket ID No. OW-2002-0039. 

• To submit comments by e-mail, send comments to OW_Docket@epa.gov, Attention Docket 

ID No. OW-2002-0043. If you send an e-mail comment directly to the Docket without going 

through EPA’s electronic public docket, EPA’s e-mail system automatically captures your email address, which is included as part of the comment that is placed in the official public 

docket.

• To submit comments on a disk or CD ROM, mail it to the address identified below. These 

electronic submissions will be accepted in WordPerfect or ASCII file format. Avoid the use 

of special characters and any form of encryption. 

• To submit comments by mail, send three copies of your comments and any enclosures to: 

Water Docket, Environmental Protection Agency, Mail Code 4101T, 1200 Pennsylvania 

Ave., NW, Washington, DC, 20460, Attention Docket ID No. OW-2002-0043. 

• To submit comments by hand delivery or courier, deliver your comments to: Water Docket, 

EPA Docket Center, Environmental Protection Agency, Room B102, 1301 Constitution 

Ave., NW, Washington, DC, Attention Docket ID No. OW-2002-0043. 
Please identify the appropriate docket identification number in the subject line on the first page 

of your comment. If you submit an electronic comment, please include your name, mailing 

address, and an e-mail address or other contact information in the body of your comment. Also 

include this contact information on the outside of any disk or CD ROM you submit, and in any 

cover letter accompanying the disk or CD ROM. 

For public commenting, please note that EPA’s policy is that public comments, whether 

submitted electronically or in paper, will be made available for public viewing in EPA’s 

electronic public docket as EPA receives them and without change, unless the comment contains 

copyrighted material, confidential business information, or other information whose disclosure is 

restricted by statute. 
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft i

Contents

Acronyms .................................................................. viii

Definitions ................................................................... ix

1.0 Introduction

1.1 Classifying Systems for the Purposes of the IDSE ............................... 1-2

1.1.1 Determining Source Water Classification ................................ 1-3

1.1.2 Determining When an IDSE Report is Due to the State ..................... 1-3

1.1.3 Buying or Treating Water ........................................... 1-7

1.1.4 Number of “Plants”—Producing Systems Only ........................... 1-8

1.2 Summary of the Stage 2 DBPR ........................................... 1-13

1.3 Overview of IDSE Requirements .......................................... 1-17

1.3.1 Purpose ....................................................... 1-17

1.3.2 Applicability .................................................... 1-17

1.3.3 IDSE Options .................................................. 1-17

1.3.4 IDSE Reporting and Recordkeeping .................................. 1-18

1.3.5 IDSE Standard Monitoring Program Requirements ....................... 1-19

1.4 Guidance Manual Navigation Charts ........................................ 1-22

2.0 Requirements for Systems NOT Conducting an IDSE SMP or SSS

2.1 Introduction ........................................................... 2-1

2.2 Criteria for Receiving a Very Small System Waiver .............................. 2-2

2.3 Criteria for Qualifying for the 40/30 Certification ................................ 2-3

2.4 Selecting Stage 2B Compliance Monitoring Sites ............................... 2-4

2.4.1 Protocol for Adding Stage 2B Compliance Monitoring Sites ................. 2-5

2.4.2 Protocol for Dropping Stage 1 Compliance Monitoring Locations ............ 2-6

2.5 Reporting Requirements .................................................. 2-7

3.0 System-Specific Studies

3.1 Introduction ........................................................... 3-1

3.2 Schedule for an SSS .................................................... 3-2

3.3 SSS Using Historical Data ................................................ 3-2
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3.3.1 Sample Site and Frequency ......................................... 3-3

3.3.2 Analytical Data Quality ............................................. 3-4

3.3.3 Historical Sampling Period .......................................... 3-4

3.3.4 Treatment and Source Conditions ..................................... 3-5

3.3.5 Distribution System Conditions ....................................... 3-6

3.4 SSS Using a Water Distribution System Model ................................. 3-7

3.4.1 Minimum Model Requirements ....................................... 3-9

3.4.1.1 Model Details ............................................. 3-9

3.4.1.2 Accurate Simulation of Water Consumption ...................... 3-10

3.4.1.3 Model Calibration ......................................... 3-11

3.4.2 Identifying Preliminary Sites Using Model Results ........................ 3-12

3.4.2.1 EPS Modeling to Estimate Residence Time, Influence Zones, and Mixing Zones 3-12

3.4.2.2 Preliminary Sample Site Selection to Meet SMP Criteria ............. 3-13

3.4.3 Performing At Least One Round of Sampling ........................... 3-15

3.5 Alternative SSSs ...................................................... 3-16

3.5.1 Evaluation of Alternative SSSs ...................................... 3-16

3.5.2 Historical Data Combined with New Data ............................. 3-17

3.5.3 Historical or New DBP Data Combined with a Distribution System Tracer Study

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

3.6 Selecting Stage 2B Compliance Monitoring Sites Using SSS Results ................ 3-20

3.6.1 Selecting High TTHM and HAA5 Sites ............................... 3-23

3.6.2 Selecting Average Residence Time Sites ............................... 3-25

3.6.3 Examples of Stage 2B Site Selection .................................. 3-26

3.7 Reporting Results to the State ............................................. 3-29

4.0 Standard Monitoring Program Requirements for 100 Percent Purchasing Systems

4.1 Introduction ........................................................... 4-1

4.2 Schedule for Conducting the SMP .......................................... 4-1

4.3 SMP Monitoring Requirements ............................................. 4-4

4.4 Timing of Sample Collection ............................................... 4-6

4.5 Sampling Protocol ...................................................... 4-8
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5.0 Standard Monitoring Program Requirements for: Producing Surface Water Systems

Serving at Least 10,000 People

5.1 Introduction ........................................................... 5-1

5.2 Schedule for Conducting the SMP .......................................... 5-1

5.2.1 Consecutive Water Systems and Wholesalers ............................ 5-3

5.3 Number of Samples Required .............................................. 5-3

5.4 Sample Site Requirements ................................................ 5-5

5.4.1 Changing Disinfectants During the SMP Period ........................... 5-5

5.5 Timing of SMP Sample Collection .......................................... 5-6

5.6 Sampling Protocol ...................................................... 5-9

6.0 Standard Monitoring Program Requirements for: Producing Surface Water Systems

Serving 500 to 9,999 People or Producing Ground Water Systems Serving at Least

10,000 People

6.1 Introduction ........................................................... 6-1

6.2 Schedule for Conducting the SMP .......................................... 6-2

6.3 SMP Monitoring Requirements ............................................. 6-3

6.4 Timing of Sample Collection ............................................... 6-6

6.5 Sampling Protocol ...................................................... 6-9

7.0 Standard Monitoring Program Requirements for: Producing Surface Water Systems

Serving Less Than 500 People or Producing Ground Water Systems Serving Less

Than 10,000 People

7.1 Introduction ........................................................... 7-1

7.2 Schedule for Conducting the SMP .......................................... 7-2

7.3 Number of Samples Required .............................................. 7-4

7.4 Sample Site Requirements ................................................ 7-5

7.5 Timing of Sample Collection ............................................... 7-6

7.6 Sampling Protocol ...................................................... 7-6

8.0 Standard Monitoring Program Site Selection and Reporting

8.1 Introduction ........................................................... 8-1

8.2 Description of SMP Sample Site Types ...................................... 8-2

8.2.1 Near-Entry Point SMP Sites ........................................ 8-5
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8.2.1.1 Near-Entry Point SMP Sites for 100 Percent Purchasing Systems ....... 8-5

8.2.1.2 Near-Entry Point SMP Sites for Producing Systems ................. 8-7

8.2.2 Average Residence Time SMP Sites ................................... 8-8

8.2.3 High TTHM and High HAA5 Sites .................................... 8-8

8.3 Considerations for Systems with More than One Plant or Entry Point ................ 8-9

8.3.1 100 Percent Purchasing Systems with More Than One Consecutive System Entry Point 8-9

8.3.2 Producing Systems with More than One Plant ........................... 8-12

8.4 Data Sources and Tools for Identifying Preliminary SMP Sites .................... 8-19

8.4.1 Maps ......................................................... 8-20

8.4.1.1 High TTHM and High HAA5 Sites ............................. 8-20

8.4.1.2 Average Residence Time Sites ................................ 8-21

8.4.2 Distribution System Water Quality Data ............................... 8-21

8.4.2.1 Disinfectant Residual Data ................................... 8-21

8.4.2.2 DBP Data ............................................... 8-26

8.4.3 Simulated Distribution System Laboratory Test .......................... 8-26

8.4.4 Models ....................................................... 8-30

8.4.4.1 High TTHM Sites .......................................... 8-31

8.4.4.2 High HAA5 Sites .......................................... 8-32

8.4.4.3 Average Residence Time Sites ................................ 8-33

8.4.5 Tracer Studies .................................................. 8-33

8.4.6 System Operating Data ........................................... 8-35

8.4.7 Geographic Information System (GIS) ................................ 8-36

8.5 Methodology for Selecting Final SMP Sites .................................. 8-38

8.5.1 Identifying Preliminary Sites Using Combinations of Tools and Data Sources

............................................................. 8-38

8.5.2 Selecting Final SMP Sites from Preliminary Sites ......................... 8-43

8.5.2.1 Selecting High TTHM and HAA5 SMP Sites (All Systems) .......... 8-43

8.5.2.2 Selecting Average Residence Time Sites ......................... 8-45

8.6 Stage 2B DBPR Site Selection and IDSE Reporting Requirements ................. 8-45

8.6.1 100 Percent Purchasing Systems .................................... 8-48

8.6.2 Producing Systems ............................................... 8-49

8.6.3 Examples of Stage 2B DBPR Site Selection ............................ 8-50

8.7 Reporting Results to the State ............................................. 8-53
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Appendices

Appendix A Impacts of an Alternative Population-Based Monitoring Approach

Appendix B Formation and Control of Disinfection Byproducts

Appendix C TTHM and HAA5 Sampling Protocol

Appendix D Simulated Distribution System Test

Appendix E IDSE SMP Report for Producing Surface Water Systems Serving $ 10,000 People

Appendix F IDSE SMP Report for Producing Ground Water Systems Serving $ 10,000 People

Appendix G IDSE SMP Report for Producing Surface Water Systems Serving 500-9,999 People

Appendix H IDSE Report for Producing Ground Water Systems Serving < 10,000 People

Appendix I IDSE SMP Report for Producing Surface Water Systems Serving < 500 People

Appendix J IDSE SMP Report for a 100 Percent Purchasing Surface Water Systems

Appendix K IDSE System Specific Study Using a Hydraulic Model

Appendix L IDSE System-Specific Study Using Historical Data
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Tables and Figures

Tables

Table 1.1 Summary of IDSE Reporting Schedules ............................... 1-13

Table 1.2 Stage 2B Plant-based DBPR Monitoring Requirements for Producing

Systems ....................................................... 1-15

Table 1.3 Stage 2B Population-based Compliance Monitoring Requirements for

100 Percent Purchasing Systems .................................... 1-16

Table 1.4 IDSE SMP Requirements for Producing Systems ........................ 1-20

Table 1.5 IDSE SMP Requirements for 100 Percent Purchasing Systems .............. 1-21

Table 2.1 Compliance Monitoring Data Requirements for the 40/30 Certification ............. 2-4

Table 3.1 Stage 2B Plant-based Compliance Monitoring Requirements for

Producing Systems ........................................................... 3-21

Table 3.2 Stage 2B Population-based Compliance Monitoring Requirements for 100 Percent

Purchasing Systems .................................................... 3-22

Table 3.3 Example IDSE Reports ............................................... 3-30

Table 4.1 Consecutive System IDSE Report Schedule ................................. 4-2

Table 4.2 SMP Sampling Requirements for 100 Percent Purchasing Systems ................ 4-5

Table 4.3 Example of Historic DBP and Temperature Data ............................. 4-7

Table 5.1 SMP Sample Sites for Producing Surface Water Systems

Serving at Least 10,000 People .................................................. 5-5

Table 5.2 Example of Historic DBP and Temperature Data ............................. 5-8

Table 6.1 Summary of SMP Sampling Requirements .................................. 6-4

Table 6.2 Example of Historic TTHM and Temperature Data ............................ 6-8

Table 7.1 IDSE Report Schedule ................................................ 7-2

Table 8.1 SMP Sampling Requirements for 100 Percent Purchasing Systems1,2.............. 8-3

Table 8.2 SMP Sampling Requirements for Producing Systems .......................... 8-4

Table 8.3 Summary of Characteristics of High TTHM and High HAA5 Areas ............... 8-9

Table 8.4 Summary of GIS Data Storage Capabilities ................................ 8-37

Table 8.5 Stage 2B Compliance Monitoring Requirements for

100 Percent Purchasing Systems1,2......................................... 8-47

Table 8.6 Summary of Stage 2B Compliance Monitoring Requirements for Producing Systems

................................................................... 8-48

Table 8.7 Example IDSE Reports ............................................... 8-54
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Figures

Figure 1.1 Decision Tree for Determining IDSE Reporting Schedule ................... 1-5

Figure 3.1 Allowable SSS Historical Sampling Period for Systems on the Large System Schedule3-4

Figure 3.2 SSS Historical Sampling Period for Systems on the Small System Schedule ...... 3-5

Figure 3.3 Example of Historical Data Limitations for System on Large System Schedule With a

Significant Change in Distribution System Hydraulics ....................... 3-7

Figure 4.1 Early Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates) ........................................ 4-3

Figure 4.2 Late Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates) .................................. 4-3

Figure 4.3 Example Historic DBP and Temperature Data ............................... 4-6

Figure 5.1 Large System Schedule for Conducting the SMP

(Showing Latest Recommended Start Dates) ........................................ 5-2

Figure 5.2 Planned Conversion to Chloramines ...................................... 5-6

Figure 5.3 Example Historic DBP and Temperature Data ............................... 5-7

Figure 6.1 Large System Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates) ........................................ 6-2

Figure 6.2 Small System Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates) .................................. 6-3

Figure 6.3 Example Historic DBP and Temperature Data ............................... 6-7

Figure 7.1 Large System Schedule for Conducting the IDSE SMP 

(Showing Latest Recommended Start Dates) ........................................ 7-3

Figure 7.2 Small System Schedule for Conducting the IDSE SMP ........................ 7-4

Figure 8.1 Data Sources and Tools for Selecting SMP Sites ............................ 8-19

Figure 8.2 Conceptual Diagram of GIS ........................................... 8-36

Figure 8.3 Starting Point for Preliminary Site Selection ................................ 8-39
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Acronyms

CWS Community water system

CT Residual disinfectant concentration (in mg/L) multiplied by the contact time (in min)—a

measure of inactivation

DBP Disinfection byproduct

DBPR Disinfectants and Disinfection Byproducts Rule

EPS Extended period simulation

HAA Haloacetic acid

HAA5 The sum of five HAA species

HPC Heterotrophic plate count

ICR Information Collection Rule 

IDSE Initial distribution system evaluation

LRAA Locational running annual average

LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule

MCAA Monochloroacetic acid 

MCL Maximum contaminant level

M-DBP Microbial and disinfection byproduct

NPDWR National Primary Drinking Water Regulation

NTNCWS Nontransient noncommunity water system

PWS Public water system

RAA Running annual average

SDS Simulated distribution system

SDWA Safe Drinking Water Act

SMP Standard monitoring program

SSS System-specific study 

SWTR Surface Water Treatment Rule

TCAA Trichloroacetic acid

TCR Total Coliform Rule

THM Trihalomethane

TOC Total organic carbon

TNCWS Transient noncommunity water system

TTHM Total trihalomethanes

UV Ultraviolet light
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Definitions

Aquifer: a geological formation composed of rock, gravel, sand, or other porous material that yields

water to wells or springs.

Best professional judgement: using knowledge and experience to make a decision on an issue that

does not have a clear direction or answer, or deciding to take an alternative path to the one

recommended based on knowledge and experience. 

Booster disinfection: the practice of adding disinfectant in the distribution system to increase

disinfectant residual concentration.

Combined distribution system: the interconnected distribution system consisting of the distribution

systems of wholesale systems and of the consecutive systems that receive finished water from those

wholesale system(s). 40 CFR 141.2

Community water system: a public water system which serves at least 15 service connections used by

year-round residents or regularly serves at least 25 year-round residents. 40 CFR 141.2

Conductivity: a measurement of the ability of a solution to carry an electrical current.

Consecutive system: a public water system that buys or otherwise receives some or all of its finished

water from one or more wholesale systems for at least 60 days per year. 40 CFR 141.2

Consecutive system entry point: a location at which finished water is delivered at least 60 days per

year from a wholesale system to a consecutive system. 40 CFR 141.2

Controlling month: the month of historical peak DBP levels, or, in the absence of DBP data, the

month of highest water temperature by which the IDSE sampling schedule is set.

Disinfectant: any oxidant, including but not limited to chlorine, chlorine dioxide, chloramines, and

ozone added to water in any part of the treatment or distribution process, that is intended to kill or

inactivate pathogenic microorganisms. 40 CFR 141.2
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Disinfectant residual concentration: the concentration of disinfectant that is maintained in a

distribution system. Disinfectant could be free chlorine (the sum of the concentrations of hypochlorous

acid (HOCl) and hypochlorite acid (OCl-)) or combined chlorine (chloramines). It is used in Surface

Water Treatment Rule as a measure for determining CT. 

Disinfection: a process which inactivates pathogenic organisms in water by chemical oxidants or

equivalent agents. 40 CFR 141.2

Disinfection byproduct (DBP): compound formed from the reaction of a disinfectant with organic and

inorganic compounds in the source or treated water during the disinfection process.

Dual Sample set: TTHM and HAA5 samples that are taken at the same time and location for the

purpose of conducting an IDSE evaluation and determining compliance with the TTHM and HAA5

MCLs.

Finished Water: water that has been introduced into the distribution system of a public water system

and is intended for distribution without further treatment, except that necessary to maintain water quality

(such as booster disinfection). 40 CFR 141.2 

Ground water under the direct influence of surface water (GWUDI): any water beneath the surface

of the ground with (1) significant occurrence of insects or other macroorganisms, algae, or largediameter pathogens such as Giardia lamblia, or (2) significant and relatively rapid shifts in water

characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to

climatological or surface water conditions. Direct influence must be determined for individual sources in

accordance with criteria established by the State. The State determination of direct influence may be

based on site-specific measurements of water quality and/or documentation of well construction

characteristics and geology with field evaluation. 40 CFR 141.2

Haloacetic acid (HAA): one of the family of organic compounds named as a derivative of acetic acid,

wherein one to three hydrogen atoms in the methyl group in acetic acid are each substituted by a

halogen atom (namely, chlorine and bromine) in the molecular structure.

Haloacetic acids (five) (HAA5): the sum of the concentrations in milligrams per liter of the haloacetic

acid compounds (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic

acid, and dibromoacetic acid), rounded to two significant figures after addition. 40 CFR 141.2
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Heterotrophic plate count (HPC): a procedure for estimating the number of heterotrophic bacteria in

water, measured as the number of colony forming units per 100 mL. 

Influence zone: the portions of the distribution system supplied with water from a particular source of

supply.

Locational running annual average (LRAA): the average of samples taken at a particular monitoring

site during the previous four calendar quarters. 

Maximum contaminant level (MCL): the maximum permissable level of a contaminant in water which

is delivered to any user of a public water system. 40 CFR 141.2

Maximum contaminant level goal (MCLG): the maximum level of a contaminant in drinking water at

which no known or anticipated adverse effect on the health of persons would occur, and which allows

an adequate margin of safety. Maximum contaminant level goals are non-enforceable health goals. 40

CFR 141.2

Mixing Zone: an area in the distribution system where water flowing from two or more different

sources blend.

Monitoring site: the location where samples are collected.

Nontransient noncommunity water system (NTNCWS): a public water system that is not a

community water system and that regularly serves at least 25 of the same persons over 6 months per

year. 40 CFR 141.2

Noncommunity water system: a public water system that is not a community water system. 40 CFR

141.2

Public water system (PWS): a system for the provision to the public of piped water for human

consumption, if such system has at least fifteen service connections or regularly serves an average of at

least twenty-five individuals daily at least 60 days out of the year. Such term includes (1) any

collection, treatment, storage, and distribution facilities under control of the operator of such system and

used primarily in connection with such system, and (2) any collection or pretreatment storage facilities
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

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not under such control which are used primarily in connection with such system. A public water system

is either a “community water system” or a “noncommunity water system.” 40 CFR 141.2

Residence time: the time period lasting from when the water is treated to a particular point in the

distribution system. Also referred to as water age. 

Residual disinfection: also referred to as “secondary disinfection.” The process whereby a disinfectant

(typically CL or CLM) is added to finished water in order to maintain a disinfection residual in the

distribution system. 

Running annual average: the average of monthly or quarterly averages of all samples taken throughout

the distribution system, as averaged over the preceding four quarters. 

Service connection: as used in the definition of public water system, does not include a connection to a

system that delivers water by a constructed conveyance other than a pipe if:

(1) The water is used exclusively for purposes other than residential uses (consisting of drinking,

bathing, and cooking, or other similar uses);

(2) The State determines that alternative water to achieve the equivalent level of public health protection

provided by the applicable national primary drinking water regulation is provided for residential or

similar uses for drinking and cooking; or

(3) The State determines that the water provided for residential or similar uses for drinking, cooking,

and bathing is centrally treated or treated at the point of entry by the provider, a pass-through entity, or

the user to achieve the equivalent level of protection provided by the applicable national primary

drinking water regulations. (From the National Primary Drinking Water Regulations, 40 CFR Ch.1,

7/1/00 Edition.) 

Stage 2A: the period beginning [3 years after rule promulgation] until the dates specified for compliance

with Stage 2B, during which systems must comply with Stage 2A MCLs.

Stage 2B: the period beginning [6 years after rule promulgation] for systems serving at least 10,000

people; [8.5 years after rule promulgation] for systems serving fewer than 10,000 people that are

required to do Cryptosporidium monitoring under the Long Term 2 Enhanced Surface Water

Treatment Rule (LT2ESWTR); [7.5 years after rule promulgation] for all other systems serving fewer

than 10,000 people, during which systems must comply with Stage 2B MCLs. 
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State: the agency of the State or Tribal government which has jurisdiction over public water systems.

During any period when a State or Tribal government does not have primary enforcement responsibility

pursuant to section 1413 of the Act, the term “State” means the Regional Administrator, U.S.

Environmental Protection Agency. 40 CFR 141.2

Subpart H systems: public water systems using surface water or ground water under the direct

influence of surface water as a source that are subject to the requirements of 40 CFR 141.2 (h). 40

CFR 141.2

Surface water: all water which is open to the atmosphere and subject to surface runoff. 40 CFR

141.2

Total trihalomethanes (TTHM): the sum of the concentration in milligrams per liter of the

trihalomethane compounds (trichloromethane, [chloroform], dibromochloromethane,

bromodichloromethane, and tribromomethane [bromoform]), rounded to two significant figures. 40

CFR 141.2

Total chlorine residual: the sum of combined chlorine (chloramine) and free available chlorine residual.

Tracer study: a procedure for estimating hydraulic properties of the distribution system, such as

residence time. Where more than one water source feeds the distribution system, tracer studies can be

used to determine the zone of influence of each source.

Trihalomethane (THM): one of the family of organic compounds named as derivatives of methane,

wherein three of the four hydrogen atoms in methane are each substituted by a halogen atom in the

molecular structure. 40 CFR 141.2

Water distribution system model: a computer program that can simulate the hydraulic, and in some

cases, water quality behavior of water in a distribution system.

Wholesale system: a public water system that treats source water and then sells or otherwise delivers

finished water to another public water system for at least 60 days per year. Delivery may be through a

direct connection or through the distribution system of another consecutive system. 40 CFR 141.2 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

 A CWS is public water system that has at least 15 service connections used by year-round residents or

regularly serves at least 25 year-round residents (40 CFR 141.2).

2

 A NTNCWS is a public water system that has at least 15 service connections or regularly serves an

average of at least 25 of the same individuals for at least 6 months per year (40 CFR 141.2).

3

Throughout this document, the terms “State” or “States” are used to refer to all types of primacy

agencies, including U.S. Territories, Indian Tribes, and EPA Regions.

July 2003- Proposal Draft 1-1 All Systems

Subsequent chapters of

this manual apply to

different IDSE options

and system sizes and

types.

1.0 Introduction

Initial Distribution System Evaluations (IDSEs), required by the Stage 2 Disinfectants and

Disinfection Byproducts Rule (DBPR), are studies conducted by water systems to identify compliance

monitoring sites that represent high disinfection byproduct (DBP) levels in distribution systems (40 CFR

141.600). IDSEs are based on either 1 year of monitoring or other system-specific data that provide

equivalent or better information than monitoring. Systems serving fewer than 500 people can receive

waivers from IDSE requirements, and systems that demonstrate historically low distribution system

DBP concentrations may not have to perform an IDSE.

The Stage 2 DBPR (also referred to as “the rule”) applies to all community water systems1

(CWSs) and nontransient noncommunity water systems2 (NTNCWSs) that add a primary or residual

disinfect other than ultraviolet light (UV), or deliver water that has been treated with a primary or

residual disinfectant other than UV (40 CFR 141.620(b)). IDSEs are a key part of the rule and the

focus of this guidance manual. The purposes of this manual are two-fold—to provide guidance to

systems so that they can meet IDSE requirements and provide guidance to States3 in evaluating the

adequacy of IDSEs.

This introductory chapter is organized as follows:

1.1 Classifying Systems for the Purposes of the IDSE

1.2 Summary of the Stage 2 DBPR

1.3 Overview of IDSE Requirements

1.4 Guidance Manual Navigation Charts

Chapters 2 through 8 of this manual describe IDSE requirements for

different IDSE options and system sizes and types.

Systems will not need to read every chapter of this

manual—the manual is organized such that systems can refer to one

or more stand-alone chapters depending on their systems’

characteristics and IDSE option.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-2 All Systems

The manual contains the following features to guide systems to the appropriate chapters:

• The worksheet on page 1-13 will help systems classify themselves for the purposes of

determining their IDSE requirements (all systems should fill out this worksheet).

• The flow chart and examples in section 1.1 will help systems determine their IDSE

schedule.

• The Guidance Manual Navigation charts in section 1.4 are provided to help systems

determine which IDSE option they can use to meet requirements and which chapter(s)

provides more information on each option.

• Additional flow charts at the end of Chapters 4 through 7 are for those systems that

conduct monitoring for an IDSE.

• Notes on the bottom of every page indicate the type and size of system to which that

chapter applies.

1.1 Classifying Systems for the Purposes of the IDSE

Requirements for the IDSE (as well as requirements for Stage 2 DBPR compliance monitoring)

differ by system size and type (40 CFR 141.602). For example, systems using only ground water will

have different monitoring requirements than systems using surface water. Small systems may have

different IDSE schedules than large systems. Before reading the rest of this manual, it is important for

systems to first determine their classification so that they will understand which rule requirements apply

to them. 

In general, there are four main system characteristics that drive IDSE requirements:

• Source water classification (surface vs. ground)

• Buying and selling relationships with other systems (consecutive vs. wholesale)

• Size (population served)

• Number of treatment plants

Source water classification is discussed in section 1.1.1. Section 1.1.2 describes how to

determine when the IDSE report is due to the State. This is important in the classification process

because the IDSE schedule determines which operating year must be reviewed to determine further
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-3 All Systems

rule requirements (for systems that buy at least some of their water). Section 1.1.3 provides additional

rule clarifications for systems that buy some or all of their water. Section 1.1.4 follows with guidance

for determining the number of plants in a water system (e.g., if you buy finished water from another

water system, the rule may require that interconnection to be considered a “plant”). A worksheet is

provided at the end of this section to help systems determine their classifications. 

1.1.1 Determining Source Water Classification

For the purposes of the IDSE and Stage 2 DBPR, systems must determine if they are a surface

or ground water system.

• Surface water systems are the same as subpart H systems—they use surface water or

ground water under the direct influence of surface water (GWUDI). Surface water systems

include those that treat surface water (or GWUDI) themselves or purchase finished surface

water from other systems. Surface water systems include all mixed systems that have both

surface and ground water sources.

 

• Ground water systems are those systems that use only disinfected ground water (or

purchased disinfected ground water).

1.1.2 Determining When an IDSE Report is Due to the State

For the purposes of this guidance manual, the early schedule means that systems must submit

their IDSE report no later than [2 years after rule promulgation], while the late schedule means that

systems must submit their report no later than [4 years after rule promulgation]. Table 1.1 shows which

systems must conform to each schedule type.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-4 All Systems

Table 1.1 Summary of IDSE Reporting Schedules1

Schedule Type Report Due Date Applicable Systems

Early schedule [2 years after rule

promulgation]

Systems serving at least 10,000 people

Systems serving less than 10,000 people that are part of

a combined distribution system with at least one system

serving 10,000 or more people

Late schedule [4 years after rule

promulgation]

Systems serving less than 10,000 people that are not

part of a combined distribution system with at least one

system serving 10,000 or more people

1

(40 CFR 141.600(c))

As indicated in the table, an IDSE report schedule is based on the population served by the

largest system in the combined distribution system. Note that the schedule is based on the largest

population served by a single system (not the sum of all system populations) in the combined

distribution system. The Stage 2 DBPR defines the following terms for systems buying and selling

finished water (40 CFR 141.2):

Consecutive system - public water system that buys or otherwise receives some or all of their

finished water from one or more systems for at least 60 days per year.

Wholesale systems - public water system that treats source water and then sells or otherwise

delivers finished water to another public water system for at least 60 days per year. Delivery

may be through a direct connection or through the distribution system of one or more

consecutive systems.

Combined distribution system - the totality of the distribution systems of wholesale systems

and of the consecutive systems that receive finished water from those wholesale systems.

Delivery of water from a wholesale system can be through a direct connection(s) or through the

distribution system of another system. For example, in a situation where system A buys water from

system B who buys all their water from system C, all three systems are considered to be in the same

combined distribution system.

To determine which systems are included in a combined distribution system, include only those

that buy for at least 60 days per year during year 2004. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-5 All Systems

The flow chart in Figure 1.1 can be used to determine the IDSE report schedule required for

systems. Examples 1.1 through 1.3 show how the guidance is applied in specific situations. Systems

that are still unclear on their IDSE report schedule after reading this section should contact their State

for guidance. A worksheet for systems to complete is provided at the end of the section that also

assists in determining report schedule.

EPA recommends that systems share information about their IDSE report schedule with all

wholesale purchasers. Coordination with purchasing systems is not required, but is strongly

recommended.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-6 All Systems

No

Does your system serve 

>10,000 people?

Early 

Schedule

Did your system 

purchase water 

from or sell water to 

another system for 

more than 60 days 

in 2004?

Yes

Yes

You are part of a combined 

distribution system

No

Late 

Schedule

Is there a system 

that serves >10,000 

people in the 

combined distribution 

system?

No Yes

No

Does your system serve 

>10,000 people?

Early 

Schedule

Did your system 

purchase water 

from or sell water to 

another system for 

more than 60 days 

in 2004?

Yes

Yes

You are part of a combined 

distribution system

No

Late 

Schedule

Is there a system 

that serves >10,000 

people in the 

combined distribution 

system?

No Yes

Figure 1.1 Decision Tree for Determining IDSE Reporting Schedule
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-8 All Systems

Bloomville Water 

System

Population Served = 

3,000

Red Hill Water 

System

Population Served = 

8,000

Elm Grove Water 

System

Population Served = 

12,000

Bloomville Water 

System

Population Served = 

3,000

Red Hill Water 

System

Population Served = 

8,000

Elm Grove Water 

System

Population Served = 

12,000

Apple Burg System

Population Served = 

5,000

Greenville System

Population Served = 

14,000

Your City System

Population Served = 

7,500

Apple Burg System

Population Served = 

5,000

Greenville System

Population Served = 

14,000

Your City System

Population Served = 

7,500

***Examples for Determining IDSE Report Schedule***

Example 1.1—One Seller with Two Buyers 

Red Hill water system sells water to both Elm Grove and Bloomville systems year- round.

Bloomville, Red Hill, and Elm Grove are all part of one combined distribution system. Because Elm

Grove serves greater than 10,000 people, all three systems are on the early schedule.

Example 1.2— Systems with Temporary Sources

Your City purchases all of its water from nearby Apple Burg. A

pple Burg purchased water on an emergency basis from Greenville for less th

an 60 days in 2004. Because Greenville is considered a temporary (not a p

ermanent) source for Apple Burg, it is not considered to be part of the s

ame combined distribution system as Apple Burg and Your City. T

herefore, Your City and Apple Burg are on the late schedule.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-10 All Systems

Newington System

Population Served = 

4,000

Seaside System

Population Served = 

16,000

Dellwood System

Population Served = 

8,000

Groveland System

Population Served = 

3,000

Newington System

Population Served = 

4,000

Seaside System

Population Served = 

16,000

Dellwood System

Population Served = 

8,000

Groveland System

Population Served = 

3,000

Example 1.3—Systems with Permanent, Seasonal Sources

Seaside system sells water for

approximately 90 consecutive days in

the summer to Dellwood. Dellwood buys

the remainder of its water from

Newington. Groveland buys a portion of

its water year-round from Dellwood.

All four systems shown are part of

the same combined distribution system. 

Because the largest system serves 16,000

people, all systems are on the early

schedule.

1.1.3 Buying or Treating Water

IDSE requirements differ between those system that treat some or all of their water and those

that buy all of their finished water. Because the use of seasonal or emergency water can differ from

year to year, the Stage 2 DBPR requires that systems evaluate operating data from the year 2004 if

they are on the early IDSE schedule and from year 2006 if on the late IDSE schedule (40 CFR

141.602(d)). 

Throughout this guidance manual, the terms “100 percent purchasing systems” and “producing

systems” are used to differentiate between the two system types when describing IDSE requirements.

• 100 percent purchasing systems - consecutive systems that buy or otherwise receive all of

their finished water from one or more systems year-round. Systems that buy all of their

finished water, but also use booster disinfection, are still considered a 100 percent

purchasing systems.

• Producing systems- systems that do not purchase 100 percent of their finished water from

other systems year-round (i.e., they have one or more non-purchased sources and produce

some or all of their own finished water).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

4 A consecutive system entry point is a site at which finished water is delivered from a wholesale system to

a consecutive system that buys some or all of its water, at least 60 days per year. To be considered a “plant,” water

must be delivered for 60 consecutive days per year.

July 2003- Proposal Draft 1-11 All Systems

1.1.4 Number of “Plants”—Producing Systems Only

If you are a 100 percent purchasing system, you can skip this section and go directly to

next section (1.2 Summary of the Stage 2 DBPR).

Monitoring requirements of the Stage 2 DBPR depend on the number of “plants” in a system

for those systems that produce some or all of their own water. The rule specifies that consecutive

system entry points4 receiving water treated by a disinfectant other than UV, for at least 60 consecutive

days a year, must be considered as a plant (40 CFR 141.601(d)). For the purposes of guidance the

following should also be considered as a “plant”:

• A facility treating a surface water source in the system.

• A facility treating (at minimum, adding a disinfectant, not including UV) a ground water

source in the system. 

Note, a system may be defined as a consecutive system (receiving water for at least 60 days

per year) while the consecutive entry point is not considered as a plant because they do not receive

water for 60 consecutive days. 

The rule allows States to consider multiple entry points or treatment facilities as one “plant” in

the following situations (40 CFR 141.601(d)):

• Multiple Wells Drawing from the Same Aquifer. With State approval, systems with

multiple wells drawing from a single aquifer may consider those wells as one plant.

• Multiple Consecutive Entry Points Delivering Water from One Wholesaler. Systems

with multiple consecutive entry points from the same wholesale system may consider those

entry points one plant, with State approval. In these cases, the system must demonstrate

that factors such as relative locations of entry points, residence times, sources, and the

presence of treatment (such as corrosion control or booster disinfection) are similar and will

not have a significant effect on TTHM and HAA5 formation between the entry points. 

The following are instances in which treatment facilities and entry points should not considered

a plant. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-12 All Systems

• Booster disinfection or other satellite treatment facilities that may add disinfection to

finished water. 

• Individuals wells that feed into one entry point or treatment facility (only the one entry point

would be considered a plant).

• Consecutive entry points that are used for less than 60 consecutive days per year (e.g.,

emergency connections).

• Interconnections that deliver untreated water.

Examples 1.4 through 1.6 show how these guidelines can be used to determine the number of plants for

the purposes of an IDSE.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-13 All Systems

Purchased surface water

Well #2 

(Chlorinated)

Well #1 

(Chlorinated)

Well #3 

(Chlorinated)

Purchased surface water

Well #2 

(Chlorinated)

Well #1 

(Chlorinated)

Well #3 

(Chlorinated)

Wholesaler, 

Ground 

Water 

Source

Well 

#1

Well 

#2

Chlorine Feed

Wholesaler, 

Ground 

Water 

Source

Well 

#1

Well 

#2

Chlorine Feed

***Examples for Determining Number of Plants***

Example 1.4—Multiple Wells and Purchasing Treated Water

A system purchases treated surface water year-round through one entry point, and has

three wells. Chlorine is added at each well site. The State determined that two of the wells draw

from the same aquifer and that the third well draws from a different aquifer.

Total plants: 3 (one for the

purchased water entry

point, the second for the

two wells drawing from the

same aquifer, and the third

for the well drawing from

another aquifer).

Example 1.5—Multiple Consecutive Entry Points and Multiple Wells

A system purchases treated ground water from one wholesaler through five entry points

and has two wells. The State has approved multiple consecutive entry points to be considered as

one plant. The two wells feed into one pumphouse where chlorine is added; this is considered one

treatment plant.

Total plants: 2 (one plant for the

consecutive entry points and one

ground water plant)
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-14 All Systems

***Examples for Determining Number of Plants (continued)***

Example 1.6—Connections Not Used Year-Round

Your City’s system purchases disinfected ground water from City A year-round and has an

emergency connection with City B. In the summer of 2004, City A’s water supply was low, so

Your City’s system had to use City B intermittently from July to September. Your City reviewed its

purchasing records from year 2004 and determined that you received water from City B for 72 days

that year, but at most, only 45 days were consecutive.

Total plants: 1 (City A) (Although the City B connection is considered a consecutive system entry

point, it is not considered a plant since Your City’s system did not receive water for 60 consecutive

days in year 2004). 

1.1.5 System Classification Worksheet

A system classification worksheet is provided on the next page to help systems determine

their IDSE schedule and buying/selling relationships for the purposes of determining IDSE requirements

and navigating this guidance manual. Before using this manual, it is very important that all

systems complete this worksheet.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-15 All Systems

System Classification Worksheet

Determine System Size and Schedule

1. What is the population served by your water system?

>10,000 o You are a Large System on the Late Schedule. Go to #3.

<10,000 o You are a Small System. Go to #2.

2. Small systems (serving <10,000): Did your system buy or sell finished water for at least 60

days in the year 2004?

No o You are on the Late Schedule.

Yes o Is there a system that serves over 10,000 people in your combined distribution

system?

No o You are on the Late Schedule.

Yes o You are on the Early Schedule. 

Determine Consecutive System Status

3. Did you buy finished water for at least 60 days in 2004 (if on the Early Schedule) or 2006 (if on

the Late Schedule)?

No o You are a Producing System (you are done with this worksheet).

Yes o You are a Consecutive System. Go to #4.

4. Consecutive systems: Did you buy all of your finished water in 2004 (if on the Early Schedule)

or 2006 (if on the Late Schedule)?

No o You are a Producing System. Go to #5.

Yes o You are a 100 Percent Purchaser (you are done with this worksheet).

5. Consecutive, producing systems: If you purchase any finished water from a wholesale system

for at least 60 consecutive days during 2004 (if on the Early Schedule) or 2006 (if on the Late

Schedule), you must treat these entry points as “plants” for the purposes of determining IDSE and

Stage 2B monitoring requirements. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

5

 U.S. Environmental Protection Agency. 2000. Stage 2 M-DBP Agreement in Principle.

Microbial/Disinfection Byproducts (M-DBP) Federal Advisory Committee. Signed September 12, 2000. Federal

Register 65(251):83015-83024.

6

 Actual compliance dates to be provided in future drafts.

7 Although MCLs are Stated in milligrams per liter (mg/L) in the Stage 2 DBPR rule language, they are

presented as :g/L to be consistent with terminology in the rest of this guidance manual.

July 2003- Proposal Draft 1-16 All Systems

1.2 Summary of the Stage 2 DBPR (40 CFR 141, Subpart Q, Appendix A,

141.600, and 141.626)

The Stage 2 DBPR applies to all CWSs and NTNCWSs that add a primary or residual

disinfectant other than UV, or deliver water that has been treated with a disinfectant other than UV. 

The compliance determination and schedule, compliance monitoring, and significant excursion

requirements for the Stage 2 DBPR are discussed below. Section 1.3 provides a more detailed

description of IDSE provisions.

Purpose

As Stated in the Stage 2 Microbial and DBP Agreement in Principle, “The Stage 2 DBPR is

designed to reduce DBP occurrence peaks in the distribution system based on changes to compliance

monitoring provisions. Compliance monitoring will be preceded by an IDSE study to select sitespecific optimal sample points for capturing peaks.”5

Compliance Determination and Schedule

Compliance determination for the Stage 2 DBPR is based on a locational running annual

average (LRAA) of total trihalomethanes (TTHM) and five haloacetic acids (HAA5) concentrations. 

Compliance must be met at each monitoring location, instead of system-wide using the running annual

average (RAA) used under the Stage 1 DBPR.

The rule will be implemented in two stages:

Stage 2A: Starting [3 years after rule promulgation],6 all systems must comply with TTHM/HAA5

maximum contaminant levels (MCLs) of 120/100 micrograms per liter (μg/L)7, measured as

LRAAs at each Stage 1 DBPR compliance monitoring site and continue to comply with the

Stage 1 DBPR MCLs of 80/60 μg/L measured as RAAs.

Stage 2B: Beginning in [6 years after rule promulgation], systems serving at least 10,000 people must

comply with TTHM/HAA5 MCLs of 80/60 μg/L measured as LRAAs at the monitoring

sites identified in the IDSE report. For systems serving fewer than 10,000 people that are
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-17 All Systems

required to do Cryptosporidium monitoring under the Long Term 2 Enhanced Surface

Water Treatment Rule (LT2ESWTR), compliance with the 80/60 μg/L MCLs measured as

LRAAs will begin [8.5 years after rule promulgation]. For all other systems serving fewer

than 10,000 people, compliance with the 80/60 μg/L MCLs measured as LRAAs will begin

[7.5 years after rule promulgation]. States may grant up to a 2-year extension if capital

improvements are required by a system to comply with the MCLs.

Compliance Monitoring

Systems will continue to monitor at their Stage 1 DBPR compliance monitoring locations during

Stage 2A. For Stage 2B, EPA has developed different compliance monitoring approaches depending

on the system’s buying and selling relationships with other systems:

• A plant-based approach for producing systems that is dependent on population served,

source water, AND the number of plants in a system (as with Stage 1 DBPR compliance

monitoring) and applies to systems that produce some or all of their own finished water. 

For the purpose of the Stage 2 DBPR, a plant can be either a treatment plant (that

provides, at a minimum, disinfection using a disinfectant other than UV) or a consecutive

system entry point that operates for at least 60 consecutive days per year.

• A population-based approach for 100 percent purchasing systems that is dependent

on population served and source water and applies to only those systems that purchase 100

percent of their finished water from other systems.

Tables 1.2 and 1.3 summarize Stage 2B compliance monitoring requirements for producing systems

(plant-based approach) and 100 percent purchasing systems (population-based approach),

respectively.

Changes in the total number of samples collected per year from the Stage 1 to the Stage 2

DBPR will be minor for most producing systems. The type of samples, however, will change for most

systems. For 100 percent purchasing systems, the change in monitoring from the Stage 1 to the Stage

2 DBPR will vary from system to system depending on the number of plants.

Significant Excursion Evaluations

Because Stage 2 DBPR MCL compliance is based on an annual average of DBP

measurements at a given location, a system could from time to time have DBP levels significantly higher

than the MCL while still being in compliance. This is because high concentrations could be averaged

with lower concentrations at a given location. The Stage 2 DBPR requires States to develop a

procedure for identifying significant DBP excursions as a special primacy condition. If a significant

excursion occurs, a system must conduct a significant excursion evaluation and discuss the evaluation
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-18 All Systems

The number of compliance monitoring sites presented in Table 1.2 are per plant.

with the State no later than the next sanitary survey. Significant excursion evaluations are not covered

in this manual. EPA is developing a separate guidance manual to address significant excursion

evaluations.

Table 1.2 Stage 2B Plant-based Compliance Monitoring Requirements for

Producing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by location type) per Plant4

Total

Number of 

Sites per

Plant

Monitoring

Frequency5

Stage 1

Average

Residence Time

Site

Highest

TTHM 

Highest

HAA5

Surface Water Systems6

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 90 days

> 10,000 1 2 1 4 Every 90 days

Ground Water Systems

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

> 10,000 - 1 1 2 Every 90 days

1

(40 CFR 141.605 (a))

2 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water).

3 Population served is typically a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 For the purposes of the Stage 2 DBPR compliance monitoring, a consecutive system entry point that operates

for at least 60 consecutive days per year must be considered a plant (40 CFR 141.601(d)).

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample

that is taken at the same time and location. 

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

7 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different location, then only one sample is collected at each location. If they occur at the

same location, then a dual sample set is collected at that location.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-20 All Systems

The number of compliance monitoring sites presented in Table 1.3 are per system.

Table 1.3 Stage 2B Population-based Compliance Monitoring Requirements for

100 Percent Purchasing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by location type) per System

Total

Number of 

Sites per

System

Monitoring

Frequency4

Stage 1

Average

Residence Time

Site

Highest

TTHM 

Highest

HAA5

Surface Water Systems5

< 500 - 1 1 2

6 Every 365 days

500 - 4,999 - 1 1 2

6 Every 90 days

5,000 - 9,999 - 1 1 2 Every 90 days

10,000 - 24,999 1 2 1 4 Every 90 days

25,000 - 49,999 1 3 2 6 Every 90 days

50,000 - 99,999 2 4 2 8 Every 90 days

100,000 - 499,999 3 6 3 12 Every 90 days

500,000 - 1,499,999 4 8 4 16 Every 90 days

1.5 million - < 5 million 5 10 5 20 Every 90 days

> 5 million 6 12 6 24 Every 90 days

Ground Water Systems

< 500 - 1 1 2

6 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

10,000 - 99,999 1 2 1 4 Every 90 days

100,000 - 499,999 1 3 2 6 Every 90 days

> 500,000 2 4 2 8 Every 90 days

1

(40 CFR 141.605 (e))

2 For the purpose of this guidance manual, 100 percent purchasing systems are those systems that buy or

otherwise receive all of their finished water from one or more wholesale systems year-round.

3 Population served is typically a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample

that is taken at the same time and location.

5 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

6 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different location, then only one sample is collected at each location. If they occur at the

same location, then a dual sample set is collected at that location.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-21 All Systems

1.3 Overview of IDSE Requirements (40 CFR 141.600-604)

This section provides a brief overview of IDSE requirements. Other sections of this manual

that provide more detailed information and guidance are referenced.

1.3.1 Purpose

The Stage 2 DBPR requires monitoring at sites that represent the areas of high DBP levels in

the distribution system, which differs from Stage 1 DBPR site requirements. The existing Stage 1

DBPR monitoring site requirements are based on residence time only. Other factors contribute to DBP

formation, particularly for HAAs, that can cause higher DBP concentrations in areas not represented by

Stage 1 sites. Additionally, for surface water systems, the Stage 1 DBPR requires only one of four

monitoring sites per plant at a maximum residence time location and three sites at average residence

time locations. Generally, high DBPs occur in areas of higher residence time and a well-maintained

residual disinfectant.

The purpose of the IDSE is to identify areas in the distribution system with 

representative high DBP concentrations. The purpose of the IDSE is not to identify the peak daily or

hourly DBP concentrations that occur in a distribution system, but instead, to find areas with routinely

higher DBP concentrations than other locations. As discussed later in this manual, systems will select

compliance monitoring sites based on annual averages of DBP data at selected sites, not the results of

individual sampling events.

1.3.2 Applicability

IDSE requirements of the Stage 2 DBPR apply to all CWSs that add a primary or residual

disinfectant other than UV to their water and consecutive CWSs that deliver water that has been

treated with a primary or residual disinfectant other than UV. The same requirements apply to

NTNCWSs except those that serve fewer than 10,000 people—these systems are not required to

perform an IDSE.

1.3.3 IDSE Options

This section provides a brief summary of waivers and certifications for systems not performing

an IDSE, as well as options available for systems that must perform an IDSE. The first guidance

manual navigation chart in section 1.6 directs readers to other chapters of this manual for guidance on

determining the appropriate IDSE option for a specific system.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-22 All Systems

The systems that do not have to perform an IDSE are described below.

• NTNCWSs serving fewer than 10,000 people do not have to meet the IDSE provisions

of the Stage 2 DBPR and do not have to perform an IDSE.

• States can grant very small system waivers to systems serving fewer than 500 people if

the State determines that the Stage 1 DBPR compliance monitoring site represents both

high TTHM and high HAA5 concentrations.

• Systems can qualify for the 40/30 certification. Systems that can certify all TTHM and

HAA5 compliance data are less than or equal to 40 μg/L for TTHM and 30 μg/L for

HAA5 are not required to perform an IDSE.

Systems not performing an IDSE may still need to add a monitoring site to meet the requirements of the

Stage 2B (selecting Stage 2B monitoring sites are addressed in other chapters of this manual - see

section1.6 for the guidance manual navigation chart for IDSE options).

For systems performing an IDSE, there are two options:

• Conduct a System-Specific Study (SSS). The purpose of an SSS is to evaluate DBP

concentrations throughout the distribution system using an existing data source or

combinations of data sources. Possible data sources include: historical DBP and

disinfectant residual data, water distribution system modeling, and tracer studies.

• Complete the Standard Monitoring Program (SMP). The SMP entails 1 year of

distribution system monitoring. The minimum number of sample locations required and

sampling frequency depend on system characteristics such as size, source water type, and

number of plants (for some systems).

The SMP option for an IDSE is the default—if a system does not qualify for a waiver and does

not meet the requirements for or choose to complete an SSS, they must conduct monitoring under the

SMP.

1.3.4 IDSE Reporting and Recordkeeping

IDSE reporting requirements depend on the IDSE option used by the system. The following

options require an IDSE report to be submitted to the State:

• 40/30 certification
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

8

EPA is considering an alternative to the Stage 2 DBPR whereby the population-based approach would

apply to ALL systems for IDSE and Stage 2B monitoring. Appendix A describes the possible impacts on systems

and implications for this guidance manual of this alternative 

July 2003- Proposal Draft 1-23 All Systems

• SSS

• SMP

Systems receiving a very small system waiver do not need to submit an IDSE report. 

Minimum report contents for each option are addressed later in this manual (see section1.6 for

guidance manual navigation charts for IDSE options). The schedule for submitting reports to the State

does not depend on the IDSE option, but is based on system size and buying and selling relationships

with other systems as follows:

• Large systems (serving at least 10,000 people) or systems with a large system in their

combined distribution system must submit their report [2 years after rule promulgation].

• All other systems must submit their report [4 years after rule promulgation].

Section 1.4 provides detailed guidance for identifying systems in a combined distribution system and

determining an IDSE report due date.

Systems must keep a complete copy of the submitted IDSE report for 10 years after the initial

submission date. The reports must also be available for review by the State or public during this time.

1.3.5 IDSE Standard Monitoring Program Requirements

As with Stage 2B compliance monitoring, there are two regulatory approaches to an IDSE

SMP8:

• A plant-based approach for producing systems that is dependent on source water type,

population served, AND number of plants in a system (consistent with Stage 1 DBPR

compliance monitoring). This approach applies to systems that produce some or all of their

own finished water.

• A population-based approach for 100 percent purchasing systems that is dependent

on source water type, population served, and applies to only those systems that purchase

100 percent of their finished water from other systems.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-24 All Systems

The number of SMP sites presented in Table 1.4 are per plant.

Tables 1.4 and 1.5 summarize an IDSE SMP compliance requirements for producing systems and 100

percent purchasing systems, respectively. Note that the TTHM and HAA5 results from the IDSE

SMP are not to be used in compliance calculations for the Stage 1 or Stage 2A.

Table 1.4 IDSE SMP Requirements for Producing Systems1,2

System Size

(Population

Served3)

Residual

Disinfectant

Number of Distribution System Sites (by

location type) per Plant Total

Number of

Sites per

Plant 

Monitoring

Frequency4

Near Entry

Point

Average

Residence

Time

High

TTHM 

High

HAA5 

Surface Water Systems5

< 500 Chlorine or

Chloramines - - 1 1 2 Every 180 days

500 - 9,999 Chlorine or

Chloramines - - 1 1 2 Every 90 days

> 10,000

Chlorine 1 2 3 2 8

Every 60 days

Chloramines 2 2 2 2 8

Ground Water Systems

< 10,000 Chlorine or

Chloramines - - 1 1 2 Every 180 days

> 10,000 Chlorine or

Chloramines - - 1 1 2 Every 90 days

1

(40 CFR 141.602(a))

2 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water).

3 Population served is usually a system’s residential population. It does not include populations served by

consecutive systems that purchase water from that system.

4 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location. A dual sample set is one TTHM and one HAA5 sample that is taken at the same

time and location.

5 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-25 All Systems

The number of SMP sites presented in Table 1.5 are per system.

Table 1.5 IDSE SMP Requirements for 100 Percent Purchasing Systems1,2

System Size 

(Population Served3)

Number of Distribution System

Sites (by location type) per System

Total

Number of

Sites per

System 

Monitoring

Frequency for

the 1-year IDSE

Period5

Near

Entry

Point4

Average

Residence

Time

High

TTHM

 High

HAA5

Surface Water Systems6

< 500 - - 1 1 2 Every 180 days

500 - 4,999 - - 1 1 2 Every 90 days

5,000 - 9,999 - 1 2 1 4 Every 90 days

10,000 - 24,999 1 2 3 2 8 Every 60 days

25,000 - 49,999 2 3 4 3 12 Every 60 days

50,000 - 99,999 3 4 5 4 16 Every 60 days

100,000 - 499,999 4 6 8 6 24 Every 60 days

500,000 - < 1.5 million 6 8 10 8 32 Every 60 days

1.5 million - < 5 million 8 10 12 10 40 Every 60 days

> 5 million 10 12 14 12 48 Every 60 days

Ground Water Systems

< 500 - - 1 1 2 Every 180 days

500 - 9,999 - - 1 1 2 Every 90 days

10,000 - 99,999 1 1 2 2 6 Every 90 days

100,000 - 499,999 1 1 3 3 8 Every 90 days

> 500,000 2 2 4 4 12 Every 90 days

1

(40 CFR 141.602 (b)) 

2 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

3 Population served is usually a system’s residential population. It does not include populations served by

consecutive systems that purchase water from that system.

4 See section 8.2 for requirements when the number of entry points in a system is different from the number of

required near-entry point sites in this table.

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location. A dual sample set is one TTHM and one HAA5 sample that is taken at the same

time and location.

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-26 All Systems

1.4 Guidance Manual Navigation Charts

The guidance manual navigation flow charts in this section will help guide readers to the

appropriate section or chapter(s).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-27 All Systems

Could your system 

be eligible for a very 

small system waiver or 

a 40/30 certification?

Yes

Verify eligibility.

Go to Chapter 2 − Requirements 

for Systems NOT Performing an 

IDSE SMP or SSS

No

Understand SMP 

Requirements.

Continue to Guidance Manual 

Navigation for SMPs. 

Does your system have 

extensive water quality or 

hydraulic data?

Yes Determine if data can be used for 

an SSS.

Go to Chapter 3 − System 

Specific Studies

No

Are you a 

NTNCWS serving 

< 10,000 people? 

Yes

N o

Go to Chapter 2 − Requirements 

for Systems NOT Performing an 

IDSE SMP or SSS

Eligible?

Comply with 

requirements 

in Chapter 2

Comply with 

requirements 

in Chapter 3

Conducting an 

SSS?

Yes

Yes

N o

No

Could your system 

be eligible for a very 

small system waiver or 

a 40/30 certification?

Yes

Verify eligibility.

Go to Chapter 2 − Requirements 

for Systems NOT Performing an 

IDSE SMP or SSS

No

Understand SMP 

Requirements.

Continue to Guidance Manual 

Navigation for SMPs. 

Does your system have 

extensive water quality or 

hydraulic data?

Yes Determine if data can be used for 

an SSS.

Go to Chapter 3 − System 

Specific Studies

No

Are you a 

NTNCWS serving 

< 10,000 people? 

Yes

N o

Go to Chapter 2 − Requirements 

for Systems NOT Performing an 

IDSE SMP or SSS

Eligible?

Comply with 

requirements 

in Chapter 2

Comply with 

requirements 

in Chapter 3

Conducting an 

SSS?

Yes

Yes

N o

No
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003- Proposal Draft 1-28 All Systems

-Surface water systems 

serving 500–9,999 people 

-Ground water systems

serving >10,000 people 

-Surface water systems

serving >10,000 people 

Go to Chapter 5 - SMP 

Requirements for Producing 

Systems: SW serving > 10,000 

people

Go to Chapter 6 - SMP 

Requirements for Producing 

Systems: SW serving 500–9,999 

people and GW serving > 10,000 

people

Go to Chapter 7 - SMP 

Requirements for Producing 

Systems: SW serving < 500 

people and GW serving 

< 10,000 people

Go to Chapter 8 – SMP 

Site Selection and 

Reporting

Are you a 100 

Percent 

Purchasing 

System?

No

Yes Go to Chapter 4 –

SMP Requirements 

for 100 Percent Purchasing 

Systems

Find the source water type and 

size of your Producing System

-Surface water systems 

serving <500 people 

-Ground water systems 

serving < 10,000 people 

-Surface water systems 

serving 500–9,999 people 

-Ground water systems

serving >10,000 people 

-Surface water systems

serving >10,000 people 

Go to Chapter 5 - SMP 

Requirements for Producing 

Systems: SW serving > 10,000 

people

Go to Chapter 6 - SMP 

Requirements for Producing 

Systems: SW serving 500–9,999 

people and GW serving > 10,000 

people

Go to Chapter 7 - SMP 

Requirements for Producing 

Systems: SW serving < 500 

people and GW serving 

< 10,000 people

Go to Chapter 8 – SMP 

Site Selection and 

Reporting

Are you a 100 

Percent 

Purchasing 

System?

No

Yes Go to Chapter 4 –

SMP Requirements 

for 100 Percent Purchasing 

Systems

Find the source water type and 

size of your Producing System

-Surface water systems 

serving <500 people 

-Ground water systems 

serving < 10,000 people 

1

1

 Use System Classification Worksheet to determine whether you are a 100% purchasing or producing system and

whether you are a ground or surface water system.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round. Producing systems are those that

do not buy 100 percent of their water year-round (i.e., they produce some or all of their own finished water). See

Chapter 1 for additional guidance on classifying systems.

July 2003 - Proposal Draft 2-1 All Systems

2.0 Requirements for Systems NOT Conducting an

IDSE SMP or SSS

2.1 Introduction

Systems are NOT required to conduct the IDSE system-specific study (SSS) or standard

monitoring program (SMP) if (40 CFR 141.600(b)):

1) They are a nontransient noncommunity water system (NTNCWS) serving less than 10,000

people.

2) They receive a very small system waiver from the State. States can grant very small system

waivers to systems serving less than 500 people if they determine that the Stage 1

Disinfectants and Disinfection Byproducts Rule (DBPR) compliance monitoring site

represents both high total trihalomethane (TTHM) and high five haloacetic acids (HAA5)

concentrations.

3) They qualify for the 40/30 certification. Any system can “opt out” of the IDSE if they

certify that all compliance monitoring data are less than or equal to 40 μg/L for TTHM and

30 μg/L for HAA5.

Even if they do not perform the IDSE, systems that purchase 100 percent of their finished water1 may

have to add or be able to remove compliance monitoring sites from their existing Stage 1 DBPR

compliance locations to meet the requirements of the Stage 2 DBPR.

This chapter addresses requirements for those systems not conducting an IDSE SSS or SMP

and is organized as follows:

2.2 Criteria for Receiving a Very Small System Waiver

2.3 Criteria for Qualifying for the 40/30 Certification

2.4 Selecting Stage 2B Compliance Monitoring Sites

2.5 Reporting Requirements
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

2

 This rule of thumb is based on analysis of TTHM and HAA5 data collected under the Information

Collection Rule (ICR).

July 2003 - Proposal Draft 2-2 All Systems

2.2 Criteria for Receiving a Very Small System Waiver

Systems serving fewer than 500 people are eligible for an IDSE waiver if the State determines

that the Stage 1 DBPR monitoring site (the location of maximum residence time in the distribution

system) represents the highest concentration for both TTHM and HAA5 (40 CFR 141.603). This will

often be the case—both TTHM and HAA5 tend to continue to form in drinking water as long as

disinfectant residuals and DBP precursors are present. Unlike TTHM, however, HAA5 is known to

biodegrade when disinfectant residuals are low (see Appendix B for additional information of HAA5

formation and biodegredation). Below are some system conditions that indicate that the highest

TTHM and HAA5 concentrations may not occur at the same location:

• Inability to maintain a disinfectant residual in all parts of the system. Areas with very low or

no disinfectant residual can have long residence times and may have some biological

activity. These areas may have high TTHM concentrations due to long residence time, but

have less-than-maximum HAA5 concentrations due to biodegradation in the distribution

system.

• High levels of heterotrophic bacteria (if data are available). Elevated levels of 

heterotrophic bacteria in the distribution system (especially if they occur repeatedly) may

reflect environmental conditions that promote biofilm growth and, thus, have the potential

for HAA5 biodegradation. 

• TTHM concentration much greater than HAA5 concentration at the Stage 1 DBPR

monitoring site (possibly indicating degradation of HAA5 in the sample location area). As a

rule of thumb, EPA recommends that systems consider selecting a different monitoring site

to represent high HAA5 if their Stage 1 DBPR TTHM data are, on average, more than 4

times greater than Stage 1 DBPR HAA5 data.2

These guidelines are not all-inclusive—TTHM and HAA5 formation depends on many system-specific

factors.

States should notify systems serving less than 500 people as to their waiver status. If the

highest TTHM and HAA5 concentrations do not occur at the same location and the State does not

grant the waiver, systems must perform an IDSE. See Chapter 4 for SMP requirements for 100

percent purchasing systems and Chapter 7 for SMP requirements for producing systems serving less

than 500 people.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 2-3 All Systems

2.3 Criteria for Qualifying for the 40/30 Certification

Systems demonstrating low historic TTHM and HAA5 distribution system concentrations in

accordance with the Stage 2 DBPR requirements may qualify for the 40/30 certification. Systems must

meet the following to qualify (40 CFR 141.603(b)):

• All individual TTHM compliance data must be less than or equal to 40 μg/L and all

individual HAA5 compliance data must be less than or equal to 30 μg/L during the periods

specified in Table 2.1. 

• No TTHM or HAA5 monitoring violations during the period specified in Table 2.1

• All monitoring data must have been analyzed by a certified laboratory (per Stage 1 DBPR

compliance monitoring requirements).

Consecutive systems that did not take the number of samples required of its size and source

water type under the Stage 1 DBPR, are not eligible for the 40/30 certification (40 CFR 141.601(a)). 

The Stage 1 DBPR allowed the State to allocate sample sites across a combined distribution system at

their discretion. As a result, some systems may have few or no sample sites and thus insufficient data to

support a 40/30 certification.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 2-4 All Systems

Table 2.1 Compliance Monitoring Data Requirements for the 40/30 Certification1

Source Water

Type Population Served2 Regulation and Monitoring Period3

Surface water4 >10,000 people Stage 1 DBPR compliance data from January

2002 to December 2003

< 10,000 people that have a system

serving > 10,000 people in their

combined distribution system5

Stage 1 DBPR compliance data collected in

2004

<10,000 people that do not have a

system serving > 10,000 people in

their combined distribution system5

Stage 1 DBPR compliance data from January

2004 to December 2005

Ground water >10,000 people TTHM Rule compliance data from 2003 and

Stage 1 DBPR compliance collected in 2004

< 10,000 people that have a system

serving > 10,000 people in their

combined distribution system5

Stage 1 DBPR compliance data collected in

2004 

< 10,000 people that do not have a

system serving > 10,000 people in

their combined distribution system5

Stage 1 DBPR compliance data from January

2004 to December 2005

1 40 CFR 141.603(b).

2 Population served is usually a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

3 All data must have been analyzed by a certified laboratory and done by approved methods (as required by the

Stage 1 DBPR). In addition, systems must not have had any TTHM or HAA5 monitoring violations during the

period specified.

4 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

5 A combined distribution system is the totality of the distribution system of all wholesale systems and the

consecutive systems that receive finished water from the wholesale systems. See section 1.1 for guidance in

identifying the largest system in a combined distribution system.

2.4 Selecting Stage 2B Compliance Monitoring Sites

NTNCWSs Serving < 10,000 People and CWSs Receiving Very Small System Waivers (40 CFR

141.601(a))

All NTNCWSs serving less than 10,000 people and CWSs receiving a very small system waiver

must continue to use their Stage 1 DBPR monitoring location for the Stage 2B. In addition, samples

must be collected during the same month as used for compliance under the Stage 1 DBPR.

Systems Qualifying for the 40/30 Certification (40 CFR 141.605(c))
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 2-5 All Systems

Producing systems that qualify for the 40/30 certification may continue using their Stage 1 DBPR

monitoring locations or may select different Stage 2B monitoring sites that better represent high TTHM

and HAA5 concentrations. New sites should represent water with long residence times and detectable

disinfectant residual concentrations. Systems must always retain the Stage 1 DBPR monitoring

locations with the highest TTHM and HAA5 annual average concentrations. If there are site changes,

the rationale must be included in the IDSE report (see section 2.5 for reporting requirements for

systems that qualify for the 40/30 certification).

For 100 percent purchasing systems that qualify for the 40/30 certification, there may be a change in

the required number of monitoring sites as these systems move from a plant-based (under Stage 1

DBPR) to a population-based monitoring approach under the Stage 2 DBPR. These systems may be

required to select more Stage 2B monitoring locations if more sites are required under Stage 2B than

were required under Stage 1. Similarly, if fewer monitoring sites are required under Stage 2B

compared to Stage 1, then systems are permitted to “drop” monitoring locations.

Sections 2.4.1 and 2.4.2 describe the protocol for adding and dropping sites, respectively. Examples

2.1 and 2.2 that follow illustrate this protocol.

2.4.1 Protocol for Adding Stage 2B Compliance Monitoring Sites

When additional Stage 2B 

sites are required, they should be selected in

the following order: maximum residence time

site followed by an average residence time site. 

If a system is required to add more than two

sites, additional sites should be added in the

same order. Chapter 8 provides guidance for

identifying maximum and average residence

time locations.

100% Purchasing Systems

Add Stage 2B sites in the following order:

1) Maximum residence time

2) Average residence time

Repeat if more than two sites are required.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 2-6 All Systems

2.4.2 Protocol for Dropping Stage 1 Compliance Monitoring Locations

When fewer sites are required for Stage 2B than are required for Stage 1 DBPR, compliance

monitoring locations may be dropped based on Stage 1 DBPR monitoring results. Sites should be

dropped according to the lowest annual average TTHM concentration (provided these locations are

not the highest HAA5 sites).

***Examples for Adding and Dropping Compliance Monitoring Sites***

Example 2.1–Adding Sites

A 100 percent purchasing surface water system serving 85,000 people can qualify for the

40/30 certification. This system has one consecutive system entry point and was required to have 4

compliance monitoring sites for the Stage 1 DBPR. For the Stage 2 DBPR, this system must have 8

compliance monitoring sites. This system must ADD 4 sites to its existing Stage 1 DBPR monitoring

sites to meet the Stage 2 DBPR requirements. The 4 sites must be as follows: 2 maximum residence

time sites and 2 average residence time sites.

Example 2.2–Dropping Sites

A 100 percent purchasing surface water system serving 12,000 people can qualify for the

40/30 certification. This system has 2 consecutive system entry points from 2 different wholesale

systems and was required to have 8 sites under the Stage 1 DBPR. For the Stage 2 DBPR, this

system is required to have a total of 6 compliance monitoring sites. Thus, this system can DROP 2

sites from its existing Stage 1 DBPR compliance monitoring sites to meet the Stage 2 DBPR

requirements. The 2 sites must be as follows: 2 sites with lowest annual average TTHM

concentration (as long as these sites do not have the maximum annual average HAA5
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 2-7 All Systems

2.5 Reporting Requirements

The following systems DO NOT have to submit IDSE reports to their States:

1) NTNCWS serving less than 10,000 people.

2) Systems receiving a very small system waiver from the State.

Systems qualifying for the 40/30 certification, however, MUST complete an IDSE report and submit it

to their State (40 CFR 141.604(b)). See section 1.1 to determine if your system is on the Early

Schedule and must submit your report by [2 years after rule promulgation] or the Late Schedule and

must submit your report by [4 years after rule promulgation].

At minimum, the IDSE report for the 40/30 certification must include (40 CFR 141.604(b) and

(c)):

• All TTHM and HAA5 analytical results from compliance monitoring used to qualify for the

40/30 certification

• A schematic of the distribution system with results, location, and date of all compliance

samples noted

• Proposed month(s) of monitoring for Stage 2B—schedule must include peak historical

month for TTHM and HAA5 concentrations, unless the State approves another month (40

CFR 141.605(f))

• For systems that decide NOT to use one or more of their Stage 1 DBPR sites for Stage 2B

compliance monitoring, the location(s) of and rationale for selecting the new site(s)

• For 100 percent purchasing systems that must add a site, the location of additional Stage

2B compliance monitoring sites
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 3-1 All Systems

The SSS must provide

equivalent or superior

data for selection of Stage

2B sites compared to

selection of sites resulting

from an SMP (40 CFR

141.603).

3.0 System-Specific Studies

3.1 Introduction

A System-Specific Study (SSS), like the Standard Monitoring Program (SMP) described in

Chapters 4 through 7, evaluates total trihalomethane (TTHM) and five haloacetic acid (HAA5) levels

throughout the distribution system. An SSS uses historical data, distribution system models, or other

analyses as the basis to select Stage 2B compliance monitoring sites.

To ensure an SSS evaluates and characterizes TTHM and HAA5 formation throughout the

distribution system to the extent required for the IDSE, the study must provide equivalent or superior

data for the selection of new Stage 2B compliance monitoring sites compared to an SMP (40 CFR

141.603). The SSS option allows systems with extensive

historical disinfection byproduct (DBP) and other water quality

data, previous pertinent studies, or other detailed knowledge of

the distribution system operations to use these resources as the

basis for choosing new monitoring sites. Conducting an SSS

can also allow a system to avoid the duplication of DBP field

monitoring efforts if significant TTHM and HAA5 monitoring, in

addition to the Stage 1 DBPR requirements, has been

performed in the past. The development of new detailed and

expensive studies is neither intended nor required.

This chapter describes two approaches to completing an SSS:

1) The use of historical TTHM and HAA5 data that are equivalent or superior to data that

would be obtained under the IDSE SMP.

2) The use of a calibrated water distribution system hydraulic model and at least one round of

new sampling conducted during the month of peak historical TTHM levels (or the month of

peak distribution system water temperature if peak TTHM data are not available).

EPA recognizes that there are other combinations of data and system analyses that may provide

equivalent or superior selection of Stage 2B compliance sites (a few alternative SSSs are discussed

later in this chapter). Final approval of an SSS is dependent on the State—the approaches described

here are only guidance.

This chapter focuses on requirements and general guidelines for completing an SSS using

historical data or a water distribution system model. It also describes how systems can use results of
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

EPA defines a combined distribution system as the totality of the distribution systems of wholesale

systems and of the consecutive systems that receive finished water from those wholesale systems (40 CFR 141.2).

July 2003 - Proposal Draft 3-2 All Systems

their SSSs to select final Stage 2B monitoring sites and report results and final site selection to their

States.

The remainder of this chapter is organized as follows:

3.2 Schedule for an SSS

3.3 SSS Using Historical Data

3.4 SSS Using a Water Distribution System Model

3.5 Alternative SSSs

3.6 Selecting Stage 2B Compliance Monitoring Sites Using SSS Results

3.7 Reporting Results to the State

3.2 Schedule for an SSS

The rule requires systems to submit their IDSE report [2 years after rule promulgation] if they

are on the early schedule, or [4 years after rule promulgation] if they are on the late schedule (40

CFR 141.600(c)). The schedule is based on the population of the largest system in the combined

distribution system.1 See section 1.4 for guidance on determining whether a system is on the large or

small system schedule.

Systems on the early schedule will have to decide whether to conduct an SSS or SMP before

States are expected to receive primacy for the Stage 2 DBPR. Therefore, States will generally not be

able to formally approve or accept the use of an SSS prior to the time when SMP field sampling should

begin. This guidance manual contains criteria that States may use to evaluate the system-specific study. 

Systems should carefully consider the data and information sources available for completing an SSS. If

there are doubts about the completeness of data for an SSS, systems should consider completing an

SMP instead of an SSS. Systems are encouraged to contact their State for an opinion if there are

questions about the adequacy of an SSS. If a system decides not to conduct the SMP and completes

an SSS that, after the State review process, is ultimately not approved by the State, that system would

be in violation of the Stage 2 DBPR.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 3-3 All Systems

3.3 SSS Using Historical Data

This section describes an SSS that uses historical TTHM and HAA5 data to select Stage 2B

monitoring sites. It provides guidelines for determining whether historical data are appropriate for use in

an SSS (e.g., DBP sampling location and frequency, sampling periods, analytical quality, and

correlation with existing system conditions). Sections 3.6 and 3.7 build on this section by showing how

final Stage 2B compliance monitoring sites are selected based on SSS results and by listing minimum

IDSE SSS reporting requirements.

3.3.1 Sample Site and Frequency

Historical data should be representative of your entire distribution system. At a minimum these

data should meet the overall SMP requirements with respect to:

• Number of sites

• Location of sites

• Number of dual sample sets per site

Tables 1.4 and 1.5 summarize the SMP sample site requirements for various system sizes,

source waters, and residual disinfectant types (Chapters 4 through 7 provide additional details). 

Historical sites that are generally equivalent to each of the required SMP sites should be specifically

identified (e.g., near entry point, average residence time, representative high TTHM concentration). 

Using historical data from more sites than required for the SMP is acceptable and encouraged.

Consistent with SMP requirements, TTHM and HAA5 data should have been collected at each

site. The interval for historical data collection (e.g., quarterly, biannually) should generally reflect SMP

requirements for monitoring frequency. At a minimum, at least one set of historical TTHM and HAA5

samples should represent the month of peak distribution system temperature or peak historical TTHM

levels. The collection period for historical data should be at least one full year, and sampling should

have been conducted at evenly spaced intervals throughout the collection period.

Specific sampling requirements of the SMP do not have to be mirrored precisely in a historical

data set, but the overall intent of the SMP should be satisfied. For example:

• If more sites per plant were sampled than are required by the SMP, fewer sample sets

(e.g., quarterly instead of bimonthly) may be acceptable for the SSS, as long as the sample

sets were collected at evenly spaced time intervals.
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ALL Historical Data

> 50% of Historical Data

IDSE Report 

Due

Stage 2 DBPR 

Promulgation

[Year 1] [Year 1] [Year 2] [Year 2] [Year 3] [Year 3] [Year 4] [Year 4] [Year 5] [Year 5] [Year 6] [Year 6] [Year 7] [Year 7] [Year 8] [Year 8] [Year 9] [Year 9] [Year 10] [Year 10]

• If samples were collected quarterly (rather than bimonthly) for multiple years (rather than 1

year) at an appropriate number of sites, the data may be acceptable for an SSS, as long as

the sample sets were collected at evenly spaced time intervals.

If historical data equivalent to the requirements of an SMP are not available, the completion of

an alternative SSS using a combination of historical and newly collected TTHM and HAA5 data may

be appropriate (see section 3.5).

3.3.2 Analytical Data Quality

Historical TTHM and HAA5 samples should have been analyzed using approved methods by a

laboratory certified to perform these measurements under the Drinking Water Certification Program. 

Systems should contact their laboratory or State to confirm certification status. Appendix C describes

the approved analytical methods for TTHM and HAA5. Note, HAA5 data collected before 2002

were likely not to have been analyzed by certified laboratories.

3.3.3 Historical Sampling Period

To ensure historical data represents current water treatment and distribution conditions, only

data collected within the 10 years preceding the due date of the IDSE report should be used for an

SSS. Also, at least 50 percent of the historical samples should have been collected within 5 years

prior to your system’s IDSE report due date. Figures 3.1 and 3.2 depict recommended limits on

historical sampling periods according the early and late schedules.

Figure 3.1 Recommended Limits of Historical Sampling Period 

for Systems on the Early Schedule
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ALL Historical Data

> 50% of Historical Data

IDSE Report 

Due

Stage 2 DBPR 

Promulgation

[Year 1] [Year 1] [Year 2] [Year 2] [Year 3] [Year 3] [Year 4] [Year 4] [Year 5] [Year 5] [Year 6] [Year 6] [Year 7] [Year 7] [Year 8] [Year 8] [Year 9] [Year 9] [Year 10] [Year 10]

Figure 3.2 Recommended Limits of Historical Sampling Period 

for Systems on the Late Schedule

3.3.4 Treatment and Source Conditions

Historical data should reflect the source water(s) and treatment configuration in place at the

time that your IDSE report is due (see Figures 3.1 and 3.2 for IDSE report schedules). Within the

historical period, temporary changes, such as regular maintenance, rehabilitation, and upgrades of plant

processes are generally acceptable. Temporary changes to disinfection practices (e.g., short duration

switches to free chlorine for secondary disinfection to control nitrification in a chloraminated system and

short duration emergency and special disinfection operations) are also generally acceptable within the

historical sampling period. Data from short duration periods of unusual (not routine seasonal) system

conditions could be excluded from the analysis of the historical data set, with appropriate justification to

the State. Routine, repeating, and seasonal changes in supply or treatment should be allowable during

the historical data period.

If a system made permanent changes that significantly affected DBP formation, plant production

rates, and/or distribution systems, only historical data representing conditions after the change

should be used for an SSS. Significant permanent treatment process or source changes that should

be considered “cutoff points” for use of historical data include:

• Permanent changes in primary or secondary disinfection type or practice, such as:

– Using a different disinfectant for primary disinfection

– Switching to chloramines for secondary disinfection

– Adding booster chlorination in the distribution system

• Major, permanent changes in raw water sources that significantly affected DBP

concentrations in water produced by the plant (e.g., addition of a new water source)
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• Major, permanent changes to plant configuration that affect disinfectant contact time (e.g.,

increasing clearwell volume with same flow rate of water through the clearwell)

• Major, permanent changes in treatment that affected DBP concentration in water produced

by the plant (e.g., addition of granular activated carbon (GAC) or membranes)

Minor treatment changes that affected the magnitude of TTHM and HAA5 levels in the

distribution system, but that are unlikely to have changed the DBP formation kinetics and relative levels

of TTHMs and HAA5s in different parts of the system, are acceptable. For example, improved control

of an existing coagulation process or minor changes in coagulation pH that reduce average levels of

DBP precursors is acceptable, but switching from chlorine to ozone for primary disinfection is not. If

treatment process or source changes have occurred and data collected prior to the change are utilized

in an SSS, then the use of the data should be justified with an explanation of the change and a

demonstration that it is unlikely to have significantly affected the relative TTHM and HAA5 levels in the

distribution system.

3.3.5 Distribution System Conditions

The historical data set should also reflect the overall distribution system hydraulic operation and

large scale movement of water through the system at the time an IDSE report is due (see Figures 3.1

and 3.2 for IDSE report schedules). Normal daily and seasonal changes in system operation during

your historical sampling period should be acceptable. Supply points, pressure zones, large transmission

mains, pump stations, storage tanks, and large wholesale and retail customers should generally be

consistent throughout the historical sampling period, but do not have to remain exactly the same. A

steady increase in water demand during the historical sampling period due to population growth should

be acceptable if it did not result in major changes in water flow pattern and age within the distribution

system.

Significant distribution system changes that should be considered as “cutoff points” for use of

historical data include:

• Major, permanent changes in plant production rates, high service or booster pump station

pumping rates, or pump operation schemes that significantly change the influence zones of

treatment plants

• Major, permanent changes in water use patterns or system hydraulics, such as:

– addition or removal of a very high water use industrial, institutional, or wholesale

customer

– addition, deletion, or replacement of mains, pump stations, or storage tanks that

significantly change water flow patterns 
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Usable Historical Data

> 50% of Historical Data

IDSE Report 

Due

Stage 2 DBPR 

Promulgation

[Year 1] [Year 1] [Year 2] [Year 2] [Year 3] [Year 3] [Year 4] [Year 4] [Year 5] [Year 5] [Year 6] [Year 6] [Year 7] [Year 7] [Year 8] [Year 8] [Year 9] [Year 9] [Year 10] [Year 10]

Installed New 

Transmission Line from 

the Treatment Plant to 

an Area to Improve Fire 

Flow

Data prior to change 

is not useful

– looping of mains

This list is not inclusive—systems should always use best professional judgement to determine if a

distribution system modification affected the location of TTHM and HAA5 peaks.

Figure 3.3 provides an example of the acceptable historical sampling period for a surface water

plant serving at least 10,000 people that placed a new large finished water transmission main into

service within the last 10 years, changing distribution system hydraulics (e.g., flow rates, directions, and

patterns).

Figure 3.3 Example of Historical Data Limitations for a System on the Early

Schedule With a Significant Change in Distribution System Hydraulics

3.4 SSS Using a Water Distribution System Model

This section describes an SSS that uses a detailed, comprehensive, and well-calibrated water

distribution system model to help select Stage 2B monitoring sites. There are two types of water

distribution system models that can be used for the SSS—hydraulic models and water quality models. 

Because the complexity and accuracy of the models differ, section 3.4.1 recommends minimum

requirements that should be met by the model.
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Hydraulic models can predict water age, but they do not predict changes in water quality

parameters, such as chlorine or TTHM concentrations. Water quality models can reasonably predict

disinfectant residuals and, in some cases TTHM concentrations, in addition to hydraulic patterns in

distribution systems. A well-calibrated water quality model may provide more data that could lead to

superior selections of Stage 2B compliance sites compared to hydraulic models. However, proper

calibration of the water quality component can be a difficult task and is typically done with much less

accuracy than calibration of the hydraulic component. Thus, the minimum requirements for the

predefined SSS are focused only on the hydraulic component of water distribution system models. If a

system decides to use a water quality model, they are encouraged to provide information on the water

quality calibration to the State.

Operation of a water distribution system should be simulated over extended periods to reflect

maximum residence time in the system under conditions of high TTHM and HAA5 formation potential. 

The period of high TTHM and HAA5 formation potential for many systems will occur during the

summer months (although this is not the case for all systems). The operation and behavior of treated

water storage facilities must also be well-characterized in the model. The results should then be used to

determine:

• The spatial and temporal patterns of water movement from all plants (if there are multiple

sources of supply)

• The typical pattern of residence time in the system during the period of high TTHM and

HAA5 formation potential

Model results should be combined with at least one round of TTHM and HAA5 sampling at sites that,

at a minimum, meet SMP requirements for number and type of site. These results will be used in

selecting final Stage 2B compliance monitoring sites.

This section provides detailed guidance for the following topics:

• Minimum model requirements (including modeled components, simulation of water

consumption, and model calibration)

• Selecting preliminary sites that meet SMP requirements based on model outputs

• Performing at least one round of TTHM and HAA5 monitoring during the month of peak

TTHM concentrations or peak temperature (additional sampling beyond one round or at

additional sites is allowed and encouraged)

Section 3.7 shows how modeled results, one round of monitoring data, and TTHM and HAA5

compliance monitoring results are used to select final Stage 2B compliance monitoring sites.
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The option of using a water distribution system model is intended to allow systems that have

models to use their existing technical resources to perform the IDSE. For many systems, developing a

detailed and well-calibrated water distribution system model from scratch and training staff to use it will

cost more than conducting an SMP. If the model will be used for other purposes after the completion

of the SSS, such as optimizing system operations and prioritizing capital improvements, then the cost of

the model development may be justified.

If your model does not meet the criteria described in this section, you may be able to upgrade

the model or use it in combination with other data and/or analyses for your SSS. These alternative

SSSs might involve the use of less robust models, supplemented with data from tracer studies or more

extensive historical or new TTHM and HAA5 monitoring data (see Section 3.5 for alternative SSSs). 

3.4.1 Minimum Model Requirements

In general, your water distribution system model should be more comprehensive for the

purpose of an SSS than models typically used for long-range capital improvement program analysis

(e.g., master planning). A calibrated hydraulic model intended for detailed distribution system design

(e.g., for system improvements) or operational studies is likely to be adequate. A well-calibrated water

quality model is likely to be acceptable.

Because systems are always changing (e.g., population growth, new industries, aging of mains),

it is important that your model generally reflect system conditions and demand at the time of the IDSE

SSS. A model that has not been updated or calibrated in the last 10 years is unlikely to be adequate

for the SSS.

Note that the guidelines in this section are not comprehensive—every distribution system is

unique. Systems and States should always use their best professional judgement when determining

model adequacy for the SSS.

3.4.1.1 Model Details

Most water distribution system models do not include every pipe in a distribution system. 

Typically, small pipes near the periphery of the system and other pipes that affect relatively few

customers are excluded to a greater or lesser extent depending on the intended use of the model. This

process is called skeletonization.

It is a generally accepted practice to skeletonize models to a certain extent depending on the

model’s intended use. To be used for the purposes of this predefined SSS, the model should be
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relatively detailed and include the majority of pipes in the distribution system. EPA recommends that a

model used for an SSS generally include the following:

• At least 50 percent of total pipe length in the distribution system

• At least 75 percent of the pipe volume in the distribution system

• All 12-inch diameter and larger pipes

• All 8-inch and larger pipes that connect pressure zones, influence zones from different

sources, storage facilities, major demand areas, pumps, and control valves, or are known

or expected to be significant conveyors of water

• All 6-inch and larger pipes that connect remote areas of a distribution system to the main

portion of the system

• All storage facilities, with controls or settings applied to govern the open/closed status of the

facility that reflect standard operations

• All active pump stations, with realistic controls or settings applied to govern their on/off

status that reflect standard operations

• All active control valves or other system features that could significantly affect the flow of

water through the distribution system (e.g., interconnections with other systems, valving

between pressure zones)

If a model used to conduct an SSS does not generally meet these criteria, additional justification

of the suitability of the model for use in an SSS should be provided to the State in the IDSE report.
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3.4.1.2 Accurate Simulation of Water Consumption

Water consumption (demand) should be accurately simulated in the model:

• Water demand should be allocated among the nodes of the model in a manner that reflects

the actual spatial distribution of such demand throughout the system and with fineness of

detail appropriate for the system size, in order to assure the model will provide a realistic

simulation of water flow throughout the system.

• As the level of detail (percentage of pipe modeled compared to actual total length of pipe in

the system) of a model increases, the percentage of nodes with demand assignments can

sometimes be less than that would be needed in a less detailed model, without significantly

impacting the overall accuracy of the model.

• Water demand should generally be assigned to all end nodes so that the flow of water is

simulated in dead-end pipes and remote areas of a system.

• Demand data should reflect, at a minimum,

S domestic water use

S large commercial and industrial users

S unaccounted for system water losses

S seasonal trends

• A system-specific, diurnal (24-hour) demand pattern should be applied to the overall

system demand. Demand patterns can be derived from a review of master meter flows,

tank levels, pumping rates, or other similar operational data.

• The model should accurately simulate seasonal system configuration and operational

changes to meet changes in demand, such as a reservoir that is taken out of service during

winter months, or a large seasonal user (e.g., a campground).

3.4.1.3 Model Calibration

Generally, calibration is the process of:

• Compiling field data on pressures, flows, and tank water levels in the system under known

conditions

• Comparing model results with field data
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• Adjusting the model (e.g., pipe roughness factors, tank/pump operational settings, etc.) to

agree with field data

Calibration is never exact, and there are no official calibration standards or guidelines in the

United States. There is general agreement in the modeling profession that the extent of calibration

should reflect the intended uses of the model. For example, a more rigorous model calibration is

expected when the model is used for design work compared to master planning. For the purposes of

the SSS, a slightly less rigorous calibration compared to design work is most likely to be adequate. 

Calibration performed several years ago for the purposes of general master planning may not be

acceptable. For more information regarding the calibration of distribution system hydraulic models,

refer to Modeling Water Quality in Drinking Water Distribution Systems (Clark and Grayman

1998, AWWA) or Advanced Water Distribution Modeling and Management (Beckwith et al.

2002, Haested Methods), or other reference books.

It is recommended that systems verify the reasonableness of their model calibration by

comparing residence time estimates with disinfectant residual data. To do this, plot (electronically or by

hand) the residence time estimates obtained from your model and disinfectant residual monitoring results

on a map of the distribution system. A system should generally find that average disinfectant residuals

are similar for locations with equivalent residence times (disregarding pipe tuberculation, biofilm, etc.). 

If actual disinfectant residuals are not similar in areas with similar modeled residence times, it is possible

your calibration is insufficient or differences in tuberculation and biofilm between the areas being

compared have affected the disinfectant residuals. If systems encounter this situation, but believe their

model calibration is accurate, they should provide a justification for the data inconsistency in the IDSE

report.

3.4.2 Identifying Preliminary Sites Using Model Results

To select preliminary monitoring sites using a water distribution system model, systems should:

• Run the model in extended period simulation (EPS) mode until a consistent, repeating

temporal pattern of water age is established at all nodes of the model. Generally, the model

should be run under high DBP formation conditions (typically summer months).

• Choose preliminary sites satisfying the SMP sample site requirements based on water age

results. (See section 1.3.5 for a summary of SMP requirements.)

The rule requires an SSS include an analysis demonstrating that the SSS characterized

expected TTHM and HAA5 levels throughout the distribution system (40 CFR 141.604(a)). This

approach recommends systems, at a minimum, conduct one round of sampling (collecting dual sample

sets) at the preliminary sites during the month of peak TTHM levels or water temperature in the

distribution system (one round of monitoring is addressed in section 3.4.3).
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Model results and all available TTHM and HAA5 data monitoring results are combined to

select Stage 2B compliance monitoring sites (see section 3.6). The use of a water quality model would

be similar, but instead of choosing preliminary sites based on water age results, chlorine residual or

TTHM results would be used. The following sections describe a pre-defined SSS option that involves

the use of a water distribution system model for identifying preliminary monitoring sites.

3.4.2.1 EPS Modeling to Estimate Residence Time, Influence Zones, and

Mixing Zones

When a water distribution system model is used to estimate residence times, influence zones,

and mixing zones, the modeling must be performed in EPS mode instead of the steady-State simulation

mode. In EPS modeling, variables such as water demands and tank water levels are allowed to change

over time (in steady-State modeling, all variables remain constant over time). EPS models should be

run until a consistent or consistently repeating pattern of residence time is established at all nodes of the

model. Typically, a repeating 24-hour pattern of water use (demand) and system operations are

assumed in EPS modeling. Depending on particular system characteristics and the specific starting

conditions imposed on the model, an EPS model may require a simulation time of 7 to 21 days or more

for a consistent pattern of residence time to develop. An EPS model usually needs to be run much

longer than the actual maximum residence time of water in a particular distribution system before a

consistent pattern of residence time is attained at the system extremities.

The model should be run under conditions of high DBP formation potential. In most areas of

the United States, water demand and system operation vary seasonally. Seasonal variations can

generally be classified into summer conditions (high usage), winter conditions (low usage), springautumn conditions (medium usage), or wet and dry period conditions. In applying a model to select

preliminary Stage 2B monitoring sites, the examination of summer usage will generally suffice if summer

conditions represent the period of peak TTHM formation potential. The consideration of additional

usage conditions is acceptable.

In systems with multiple plants, source tracing should be used to determine zones of influence

and mixing zones. Most models have a “source tracing” option in which the percentage of water

coming from a single source can be traced over the course of several days. By tracing each source

separately, a map can be generated showing areas that predominantly receive water from a single

source and areas with mixing zones where, either on a diurnal or a seasonal basis, water is received

from multiple sources. This information is used to make informed selections of sampling sites that are

representative of a single source or a mixing zone.
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3.4.2.2 Preliminary Sample Site Selection to Meet SMP Criteria

The residence time, influence zone, and mixing zone information developed through modeling

should be used to select preliminary sites. The number of preliminary sites should equal or exceed the

required number of SMP sites. Stage 1 monitoring sites should not be selected as preliminary sites for

one round of monitoring. The type of preliminary sites (near entry point, high TTHM, high HAA5, and

average residence time) should also generally mirror SMP sites for your system size and source water

type. See section 1.3.5 for a summary of SMP site criteria according to system size and source water

type; see Chapters 4 through 7 for more details.

The next three sections provide detailed guidance on selecting high TTHM, high HAA5, and

average residence time sites. Appendix B provides additional information regarding TTHM and HAA5

formation that could be useful in selecting these sets. Because hydraulic models usually are somewhat

skeletonized and have varying degrees of calibration and accuracy of demand allocation, best

professional judgement should always be used when analyzing the results and using model outputs to

assist in the selection of preliminary sites.

High TTHM Sites

High residence time locations (most often high TTHM sites) can be identified by reviewing the

modeled water age at each node in the model. When the run time of an EPS model is long enough to

produce a consistent pattern of water age values at all nodes, sometimes with repeating fluctuations due

to diurnal variations in water demands, then the water age values at the model nodes can be used for

the purposes of identifying high residence time locations. 

One way to show high residence time sites is by color coding each model node according to its

residence time. High TTHM sites should be chosen from the area or areas of the distribution system

where the high residence time model nodes are located. The sites do not have to be chosen at the

exact location of a model node, just in the general area identified by the model results.

Precautions in using model data to select high TTHM sites include:

• If no water demand is applied to dead-end nodes in a model or if the water demand in a

dead-end is highly uncertain, the water age results for those nodes can be unrealistic and

meaningless.

• The accuracy of water age estimates from a model generally decreases as the model moves

from large diameter mains to small diameter mains to subdivision piping and dead-ends. 

This is due to the increasing uncertainty in water usage rates as the system moves away

from large, aggregate demands to smaller demands exerted by a few customers or a single

customer.
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• If the model is skeletonized, the model results for high residence time areas should be

compared to maps of the actual distribution system piping and to actual customer locations

in those areas before sample sites are finalized in order to assure that the sample site is

representative of the actual distribution system and not just the skeletonized model in the

high residence time areas.

• Residence time is just one factor for identifying high TTHM sites and should be compared

with other distribution system data (e.g., disinfectant residual data) before making

preliminary site selections.

In some cases, there can be zones in the distribution system where water flowing from opposite

directions meet. This can occur in:

• Long, looping mains

• The interface of the influence zones of two or more different supply points

• Areas where different pressure zones meet within one system

This type of area is sometimes called a “mixing zone” and may act as a hydraulic dead-end. 

Mixing zones can occur anywhere in the distribution system, but occur more often in the central portion

of a distribution system. If the water demand in the mixing zone is low, then the water age and TTHM

concentrations could be high. Water distribution system models can be useful in locating mixing zones

and identifying high TTHM sites within the mixing zone.

High HAA5 Sites

The criteria and procedure for selecting high HAA5 sites using a hydraulic model is generally

the same as that described above for selecting high TTHM sites with one important difference: the sites

chosen to represent high HAA5 should have a detectable disinfectant residual. HAA5 concentrations

typically increase in distribution systems as water age increases but can also decrease if disinfectant

residuals are not present and biological activity is high. It is generally recommended that high HAA5

sites be selected in areas with a minimum chlorine residual of 0.2 mg/L or a minimum chlorine residual

or 0.5 mg/L.

Average Residence Time Sites

Average residence time sites can be selected from sites with residence times close to the flowweighted mean of all nodal residence times (or system average). As with selecting high TTHM/HAA5

sites, color coding nodes by nodal residence time can be helpful. Preliminary sample sites should be

chosen from the area or areas of the distribution system where the nodal residence time is close to the

system average. The preliminary sites do not have to be chosen at the exact location of a model node,
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just in the general area identified by the model results. Selected sites should represent the entire

distribution system and should not be clustered.

3.4.3 Performing At Least One Round of Sampling

Although hydraulic models can be used to reasonably predict residence times, the behavior of

HAA5 cannot be directly predicted based on residence time in a distribution system. Therefore, to

meet the rule requirement of demonstrating model accurately characterized expected TTHM and

HAA5 levels (40 CFR 141.604(a)), this approach recommends systems perform at least one round of

sampling at preliminary sites (i.e., collecting dual sample sets at each site). Generally, the TTHM

concentrations from this sampling should confirm the model predictions of residence time and verify the

selection of preliminary sites.

If only one round of sampling is performed, it should occur in the month of peak TTHM levels

or water temperature in the distribution system. Additional rounds of sampling are allowed and

encouraged. All results should be considered in the selection of Stage 2B compliance monitoring sites

and included in the IDSE report. Stage 1 DBPR compliance monitoring and other historical TTHM

and HAA5 data should be considered, if available, and included in the IDSE report.

If the results from Stage 1 DBPR compliance monitoring and the single round of sampling are

not reasonably consistent with modeled residence times, the potential reason for the discrepancy should

be explained in the IDSE report. If factors such as demand variations, distribution system operations,

tank operations, tank cleaning, or new construction are thought to have impacted the sampling results,

then the specifics of these factors should be included in the IDSE report. One or more additional

rounds of sampling may also be performed and are encouraged. Modeling revisions might be needed if

actual conditions during the sampling were found to be different than modeled conditions. In this case,

select new preliminary sites and repeat the monitoring.

 It is recognized that distribution system modeling results usually do not completely reflect the

true range and variability of hydraulic and water quality conditions that exist in distribution systems. 

This limitation of modeling allows for some amount of variability between sampling and modeling results. 

However, if significant inconsistencies exist between modeling results and the required one round of

sampling, then additional explanation would need to be provided in the IDSE report.

3.5 Alternative SSSs

EPA recognizes that there are many combinations of data and analyses that can be used for an

SSS. Potential combinations include, but are not limited to:

• Historical data supplemented with new data
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• Historical data and tracer study results

• New TTHM and HAA5 data, distribution system modeling, and tracer study results

In general, any alternative SSS should be representative of the majority of the distribution system,

including the extremities, and provide equivalent or superior data for the selection of Stage 2B

monitoring sites compared to an IDSE SMP.

Section 3.5.1 lists questions that States should consider when evaluating an alternative SSS. 

Sections 3.5.2 and 3.5.3 provide guidelines for two alternative SSSs: historical DBP data

supplemented with new DBP data, and historical or new DBP data combined with a tracer study. The

guidelines listed in this section are NOT definitive—SSSs will always be evaluated on a case-by-case

basis by the State.

3.5.1 Evaluation of Alternative SSSs

The following is a list of questions that States should consider when evaluating an SSS:

1) Does the study adequately evaluate the extremities? Does the study target other potential

areas with long water residence times?

2) Do the historical data meet the specified criteria for analytical quality and represent existing

distribution system conditions (see section 3.3)?

3) Does the study cover at least 1 continuous year?

4) Are there data representing the month of peak TTHM or highest temperature?

3.5.2 Historical Data Combined with New Data

The total number of samples analyzed should be equal to or greater than the total number of

samples required for the IDSE SMP (see Tables 1.4 and 1.5). The type of monitoring site should also

satisfy the SMP requirements.
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Historical data should meet the requirements and general guidelines in section 3.3. New

sampling should be performed to fill in “gaps” in historical data as needed to meet the minimum number

of samples and coverage of the distribution system. Treatment, source water, and distribution system

conditions should be similar during the historical and new sampling periods, in accordance with the

requirements and guidelines in sections 3.3.4 and 3.3.5. In cases where all historical data are used for

some locations and all new data for other locations, there should be no permanent changes to

treatment, source water, and distribution system conditions that affect the overall magnitude of TTHM

and HAA5 concentrations between the historical and new data sampling periods. The selected sites

should adequately represent the entire distribution system.

3.5.3 Historical or New DBP Data Combined with a Distribution System Tracer

Study

Time-of-travel tracer studies can be used to determine actual water residence times in a

distribution system under specific conditions, and are sometimes used to calibrate water distribution

system models. They are particularly useful for predicting water residence time in areas of a system

where there is uncertainty about true pipe diameters due to poor records or the buildup of corrosion

deposits. When pipe diameters in a model are inaccurate, model predictions can be very different than

the actual hydraulic conditions in a distribution system.

Although tracer studies often provide very good information, they can be time consuming and

costly. Conducting a tracer study solely for the IDSE SSS may not be cost effective. However, if your

system is considering a tracer study for some other purpose (e.g., calibrating a hydraulic model),

Example 3.1 Monitoring Requirements for a Surface Water System Serving More Than

10,000 People

If your system is a producing surface water system serving more than 10,000 people using free chlorine for

residual disinfection, your combined historical and new TTHM and HAA5 data should represent, at

minimum:

1) At least eight sample sites per treatment plant, with at least one representing a near entry

point, two representing average residence time areas, three representing high TTHM areas,

and two representing high HAA5 areas.

1) At least six TTHM and HAA5 sample results from each site (equivalent to requirements for

SMP monitoring), with at least one group of samples collected during the month of

historical peak TTHM levels or high water temperature.
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July 2003 - Proposal Draft 3-19 All Systems

consideration should be given to using the tracer study as a tool for the IDSE SSS. Also, results from

previously conducted tracer studies may be very useful in identifying areas in the distribution system

with high and average residence times.

Tracer studies can be performed by monitoring the concentration of a conservative constituent

(i.e., a chemical that does not degrade over time) through the distribution system. Chemicals used for

tracers must not be harmful to people or the environment. Tracer chemicals can be substances that are:

• Specially injected or normally injected in the water for treatment purposes (e.g.,

hydrofluorosilic acid or sodium fluoride)

• Characteristic of the finished water (e.g., hardness, conductivity)

Before injecting any tracer, a baseline concentration of the tracer in the distribution system

water should be determined (fluoride, the most common tracer, may be normally present in trace

amounts). If your system adds fluoride, you can turn off the fluoride feed for a period of time, and

monitor the resulting decrease of its concentration throughout the distribution system.

If you do not routinely add fluoride to the finished water, you can conduct tracer tests by

injecting a small dose of fluoride (about 1 mg/L) into the water entering the distribution system. 

However, flouride can interact with the material deposited inside pipes and storage facilities which

reduces the accuracy of the calculated residence times. As a result, you must inject sufficient fluoride to

meet the “fluoride demand” of your distribution system while assuring that fluoride concentrations in the

distribution system do not exceed allowable concentrations of 4 mg/L (the primary MCL for fluoride is

4 mg/L and the secondary MCL which is non-enforceable is 2 mg/L). If other tracers are used such as

calcium chloride or sodium chloride, State environmental agencies may require that food grade

chemicals are used or that other assurances are made concerning the safety of the tracer. With some

tracer chemicals, systems may want to consider notifying sensitive users.

When selecting tracer monitoring locations, you should consider the following:

• Major intersections or branches in large transmission mains

• Branches in minor mains where flow is split between two or more groups of customers

• Storage tanks

• Entry points to large commercial or industrial users

• Sites prior to the last fire hydrant in remote areas with few customers
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

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To adequately characterize distribution system residence time, tracer concentrations must be

measured frequently and in relatively close proximity to one another. The frequency of sampling will

determine the accuracy of the study results. For example, if sampling is conducted every 8 hours, the

water age at a given site will only be accurate to within 8 hours. Furthermore, the proximity of sample

sites to one another will also affect the accuracy of the study results. It may be appropriate to space

samples far apart on large transmission mains, but within the distribution system (which contains many

piping and hydraulic interactions), samples should be located more closely together.

The following are general guidelines for using a tracer study as part of a SSS:

• In general, the tracer study should reflect the existing distribution system configuration and

should have been conducted within the last 10 years. If permanent and significant changes

to demand, piping, pumping, or storage have occurred since the tracer study was

completed, the study may not be suitable for an SSS.

• The tracer study should generally represent conditions of high DBP formation potential and

high water age (typically summer months and low demand periods for most systems).

• The tracer study should be detailed enough to provide good characterization of water

residence time for the entire distribution system. Not all extremities must be covered by the

study, but the data should be complete enough to allow for a reasonable extrapolation of

the results to cover the entire distribution system.

• If the tracer study does not provide residence time information for the extremities of the

distribution system, then historical TTHM and HAA5 data should be reviewed if available,

or new data should be collected at expected representative high TTHM and HAA5 sites.

• Regardless of the level of detail of the tracer study, systems should have historical data for

at least one complete round of sampling at the preliminary sites or should perform at least

one new round of sampling at the preliminary sites (see section 3.4.3 for guidance on

conducting one round of sampling). At a minimum, one round of sampling should occur

during the month of historical peak TTHM levels or highest water temperature, if the

historical peak TTHM month is unknown.
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3.6 Selecting Stage 2B Compliance Monitoring Sites Using SSS Results

This section describes procedures for using results of an SSS to select Stage 2B compliance

monitoring sites. Tables 3.1 and 3.2 summarize the Stage 2B monitoring requirements for producing

and 100 percent purchasing systems, respectively (Chapter 1 also provides this information).

Section 3.6.1 addresses selection of high TTHM and high HAA5 sites, while Section 3.6.2

addresses selection of average residence time Stage 2B sites using SSS results (note that only a subset

of systems need to select average residence time sites, as addressed in Section 3.6.2). Section 3.6.3

provides examples of site selection. Appendix K contains an example IDSE report where a hydraulic

model was used to select Stage 2B compliance sites, and Appendix J contains an example IDSE report

where historical data were used to select Stage 2B compliance sites.
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July 2003 - Proposal Draft 3-22 All Systems

Table 3.1 Stage 2B Plant-based Compliance Monitoring Requirements for

Producing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by type of site) per Plant4

Total

Number of 

Sites per

Plant

Monitoring

Frequency5

Stage 1

Average

Residence Time 

Highest

TTHM 

Highest

HAA5

Surface Water Systems6

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 90 days

> 10,000 1 2 1 4 Every 90 days

Ground Water Systems

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

> 10,000 - 1 1 2 Every 90 days

1

(40 CFR 141.605 (a))

2 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water).

3 Population served is typically a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 For the purposes of the Stage 2 DBPR compliance monitoring, a consecutive system entry point that operates

for at least 60 consecutive days per year must be considered a plant (40 CFR 141.601(d)).

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each site, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample that

is taken at the same time and site. 

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

7 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different site, then only one sample is collected at each site. If they occur at the same

site, then a dual sample set is collected at that site.
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Table 3.2 Stage 2B Population-based Compliance Monitoring Requirements for

100 Percent Purchasing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by type of site) per System

Total

Number of 

Sites per

System

Monitoring

Frequency4

Stage 1

Average

Residence Time 

Highest

TTHM 

Highest

HAA5

Surface Water Systems5

< 500 - 1 1 2

6 Every 365 days

500 - 4,999 - 1 1 2

6 Every 90 days

5,000 - 9,999 - 1 1 2 Every 90 days

10,000 - 24,999 1 2 1 4 Every 90 days

25,000 - 49,999 1 3 2 6 Every 90 days

50,000 - 99,999 2 4 2 8 Every 90 days

100,000 - 499,999 3 6 3 12 Every 90 days

500,000 - 1,499,999 4 8 4 16 Every 90 days

1.5 million - < 5 million 5 10 5 20 Every 90 days

> 5 million 6 12 6 24 Every 90 days

Ground Water Systems

< 500 - 1 1 2

6 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

10,000 - 99,999 1 2 1 4 Every 90 days

100,000 - 499,999 1 3 2 6 Every 90 days

> 500,000 2 4 2 8 Every 90 days

1

(40 CFR 141.605 (e))

2 For the purpose of this guidance manual, 100 percent purchasing systems are those systems that buy or

otherwise receive all of their finished water from one or more wholesale systems year-round.

3 Population served is typically a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each site, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample that

is taken at the same time and site.

5 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

6 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different site, then only one sample is collected at each site. If they occur at the same

site, then a dual sample set is collected at that site.
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3.6.1 Selecting High TTHM and HAA5 Sites

Selection Using a Historical Data SSS

The following steps detail how Stage 2B sites should generally be selected based on historical

TTHM and HAA5 data. These steps also apply to systems using a combination of historical and new

data.

1) Calculate the Locational Running Annual Average (LRAA) for TTHM and HAA5

concentrations at each historical data site. Historical data should cover at least 1 full year. 

If your data covers a longer period, calculate separate annual averages for each full year. 

Select the data for the year with highest average for each site (see the example in Appendix

L for sample calculations).

2) Calculate the LRAA for TTHM and HAA5 concentrations at the Stage 1 DBPR maximum

residence time site(s). If your data covers more than 1 year, calculate separate averages

for each full year. Select the data for the year with highest average for each site.

3) Select high TTHM and high HAA5 sites starting with the highest TTHM and HAA5

LRAAs from both the Stage 1 DBPR compliance monitoring sites and historical data sites.

TTHM and HAA5 LRAAs are the most important factors to consider when selecting Stage 2B

monitoring sites. However, the Stage 2 DBPR allows for some flexibility in selecting Stage 2B

compliance sites. Other factors should be considered and may lead to selecting a site with a slightly

lower LRAA over another site. The following conditions are possible reasons why you may select a

site with a lower LRAA over another site:

• The site provides for more complete geographic coverage of the entire distribution system

• The site allows you to maintain an historical record

• Sampling at that site provides the opportunity to collect other water quality or operational

data (e.g., chloramine systems may want to collect nitrate data at that site)
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

2

The Stage 2 DBPR does not specify a difference between two LRAAs that allows selection of a site with

the lower LRAA for Stage 2B. EPA recognizes there is uncertainty and variability associated with the TTHM and

HAA5 data quality. While the LRAA calculation reduces the impact of these to some extent, they can cause a small

difference between two LRAAs to be statistically insignificant and thus, making the selection of the Stage 2B site

dependent on other factors. The intent of the Stage 2 DBPR is to reduce peak DBP concentrations in the distribution

system. You should use best professional judgment to select Stage 2B sites with consideration to the intent of the

rule and demonstrate to the State the reason for the selection.

.

July 2003 - Proposal Draft 3-25 All Systems

If you do not use your highest TTHM and HAA5 LRAAs to select your Stage 2B sites, you

must provide justification for your selection in your IDSE report (40 CFR 141.605).2

Selection Using a Water Distribution System Model SSS

The first step in selecting Stage 2B sites is to compare the model-predicted residence times for

your preliminary sites with the TTHM and HAA5 concentrations from the one round of sampling, Stage

1 compliance monitoring results, and any other historical TTHM and HAA5 data. Are the results

consistent? In other words, do those sites with the highest residence time also represent those sites

with the highest TTHM concentrations?

Ideally, the preliminary or Stage 1 DBPR sites with the highest TTHM and HAA5 sampling

results should be selected as the Stage 2B high TTHM and high HAA5 sites. However, TTHM and

HAA5 data collected during the one round of sampling at preliminary sites may not represent typical

levels. Distribution conditions at the time of sampling should be taken into account. EPA recognizes

that one round of samples reflects only a snapshot of the distribution system. Modeled data represent a

more comprehensive picture of the distribution system, and therefore, may not agree with the sampling

results. If your modeled data and sampling results do not agree and you select a site based on modeled

results, you should explain your rationale for selecting that site in your IDSE report.

For example, say that a model predicts that “Site A” normally receives water from the West

Tank during the daytime hours. The TTHM and HAA5 results from Site A were much lower than

expected, compared to other sites. Upon reviewing the tank operating data from the day of sampling, it

is likely that the site was not receiving water from the West Tank during the time of sampling due to low

system demand that day. In this situation, the system may want to select Site A as a Stage 2B

compliance monitoring site based on the modeled data and noting in the IDSE report the discrepancy

between modeled data and sample results.

You should also consider other factors such as geographic coverage when selecting sites. It is

acceptable to pick a site with a slightly lower TTHM or HAA5 result over another if the selected site

provides better geographic coverage; however, you must provide your rationale for selection in the

IDSE report.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

3

 100 percent purchasing ground water systems serving at least 10,000 people were not required to have

average residence time sites for Stage 1 DBPR. 100 percent purchasing surface water systems may have an average

residence time Stage 1 DBPR site, depending on the monitoring plan for their combined distribution system.

July 2003 - Proposal Draft 3-26 All Systems

3.6.2 Selecting Average Residence Time Sites

The following systems are required to select average residence time site(s) for the Stage 2B (40

CFR 141.605):

• 100 percent purchasing surface water or ground water systems serving at least 10,000

people

• Producing surface water systems serving at least 10,000 people.

One of the purposes of the Stage 2B average residence time site is to ensure that a historical

data record of system DBP levels is maintained (i.e., systems keep one site the same from Stage 1 to

Stage 2 DBPR). Producing systems can meet this goal by selecting their Stage 2B average residence

time site from their three Stage 1 DBPR average residence time sites (guidelines for selecting from

Stage 1 DBPR compliance monitoring sites are provided below). 100 percent purchasing systems may

not have average residence time sites under the Stage 1 DBPR requirements.3 In these situations, they

must alternate between high HAA5 and high TTHM sites to fill the required number of Stage 1 average

residence time sites. 

Producing Systems

Systems must select their Stage 2B average residence time site (one per plant) from the three

existing Stage 1 DBPR average residence time sites. Stage 2B average residence time sites should

have the highest TTHM or highest HAA5 LRAA among the Stage 1 DBPR average residence time

sites, considering the most recent year of data. If the high TTHM and high HAA5 LRAAs do not

occur at the same site, consider other factors such as geographical coverage and how close LRAAs are

to the MCLs, in order to decide between the two sites. Considering the second situation, if the high

TTHM LRAA is 70 μg/L and high HAA5 LRAA is 35 μg/L, then the site with the high TTHM LRAA

is the better choice.
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3.6.3 Examples of Stage 2B Site Selection

This section provides examples of Stage 2B site selection:

Example 3.2 Selecting Stage 2B Sites from Historical Data

Example 3.3 Maintaining an Historical Record

Example 3.4 Providing Geographical Coverage When Choosing Stage 2B Sites
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 3-28 All Systems

Example 3.2 Selecting Stage 2B Sites from Historical Data

A producing water system serves 90,000 people and has one surface water treatment plant. 

This system must select 4 Stage 2B compliance sites: 2 high-TTHM sites; 1 high-HAA5 site; and 1

from the 3 existing Stage 1 DBPR average residence time compliance sites. The table below lists the

TTHM and HAA5 LRAAs for all Stage 1 DBPR compliance monitoring sites and three of the eight

historical sites (these data represent the seven highest TTHM and HAA5 LRAAs).

Site TTHM LRAAs HAA5 LRAAs

A (Stage 1 max. residence time) 70 (1st year) , 69 (2nd year) 51 (1st year), 49 (2nd year)

B (historical high TTHM site) 66 (1st year), 64( 2nd year) 40 (1st year), 38 (2nd year)

C (historical high HAA5 site) 72 (1st year), 71 (2nd year) 53 (1st year), 50 (2nd year)

D (historical high TTHM site) 76 (1st year), 72 (2nd year) 50 (1st year), 49 (2nd year)

E (Stage 1 avg. residence time) 57 48

F (Stage 1 avg. residence time) 42 30

G (Stage 1 avg. residence time) 55 50

Selecting the Average Residence Time Site

The average residence time site should have either the highest TTHM or highest HAA5 LRAA

of the Stage 1 DBPR average residence time sites. The water system may choose either Site E

(highest TTHM LRAA) or Site G (highest HAA5 LRAA). With two valid options, the site providing

the best geographic coverage is preferred. Site G is located downstream of an elevated tank and is the

only site that receives water from that tank; therefore, the water system selects Site G.
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July 2003 - Proposal Draft 3-29 All Systems

Example 3.2 Selecting Stage 2B Sites from Historical Data (cont.)

Selecting the High-TTHM Sites

Site D has the highest TTHM LRAA. Therefore, this site is chosen as the first of the high-TTHM

sites. Site C has the next highest TTHM LRAA, and Site A has a slightly lower TTHM LRAA than Site

C. The difference in the TTHM values between Site A and Site C is minimal, and Site A is a Stage 1

DBPR “maximum compliance” site. Because the difference between the TTHM LRAAs of Site A and C

are minimal, and Site A would maintain a historic record of sampling, Site A is chosen as the second highTTHM site.

Selecting the High-HAA5 Site

Site C has the highest HAA5 LRAA. Sites A and D have almost as high HAA5 LRAAs. 

However, because Sites A and D have already been chosen as the high-TTHM sites, Site C is chosen as

the high-HAA5 site.

A

Water Treatment Plant

B

C

Example 3.4 Providing Geographic Coverage when Choosing Stage 2B Sites

In general, the two representative highest TTHM sites (per plant) should not be from the same area

of the distribution system. Consider the following

example— 

The two highest TTHM LRAAs in the distribution

system are from adjacent historical sample sites (sites A and

B). The site with the third highest TTHM LRAA is on the

far side of the distribution system (site C). In this case,

consider selecting sites A and C or B and C as Stage 2B

sites for a broader geographical coverage of the distribution

system.
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July 2003 - Proposal Draft 3-30 All Systems

3.7 Reporting Results to the State

You are required to include your proposed Stage 2B compliance monitoring sites in your IDSE

report. At a minimum, your IDSE report must include:

• A schematic of the distribution system

• All studies, reports, data, analytical results, and modeling to support your SSS

• All TTHM and HAA5 analytical results from Stage 1 DBPR compliance samples collected

during the period of the IDSE

• Proposed Stage 2B compliance monitoring sites with justification for selection of each

proposed site

• Proposed month(s) during which Stage 2B monitoring is to be conducted

Example 3.3 Maintaining an Historical Record

A 100% purchasing system serves 4,000 people and purchases all of its water. This system must

select two Stage 2B compliance sites: one high-TTHM and one high-HAA5 site. The table below lists

historical and Stage 1 DBPR compliance monitoring results for this system.

Sample Sites

LRAA

TTHM (μg/L) HAA5 (μg/L)

Historical #1 (High TTHM) 71 51

Historical #2 (High TTHM) 65 45

Historical # 3 (High HAA5) 60 53

Stage 1 DBPR max residence

time site

69 51

Because the TTHM LRAA for the Stage 1 DBPR site is only slightly lower than the maximum

TTHM LRAA (Historical #1), the system chooses the Stage 1 DBPR site over Historical #1 for the

Stage 2B high TTHM site to maintain the historic DBP record at that site. Historical #3 is selected as the

high HAA5 site because this site has the highest HAA5 LRAA. 
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Example reports for SSSs are in appendices to this manual, as listed in Table 3.3.

Table 3.3 Example IDSE Reports

Appendix System Characteristics

Appendix K SSS for a System Using a Hydraulic Model

Appendix L SSS for a System Using Historical Data
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

2

 The Stage 2 DBPR defines a combined distribution system as the totality of the distribution systems of

wholesale systems and of the consecutive systems that receive finished water from those wholesale systems (40

CFR 141.2).

July 2003 - Proposal Draft 4-1 100 Percent Purchasing Systems

4.0 Standard Monitoring Program Requirements for

100 Percent Purchasing Systems

4.1 Introduction

This chapter describes the Initial Distribution System Evaluation (IDSE) Standard Monitoring

Program (SMP) requirements for 100 percent purchasing systems.1 IDSE and Stage 2B Disinfectants

and Disinfection Byproducts Rule (DBPR) monitoring requirements for 100 percent purchasing systems

are based on population served and source water type, not on the number of plants as under the Stage

1 DBPR. Since these systems do not have treatment plants, a population-based monitoring program is

more practical than the alternative method of determining the number of plants by the number of entry

points. 

The SMP requirements presented in this chapter include monitoring frequency, sample sites,

and schedules. Chapter 8 builds on this chapter by describing how to select SMP monitoring sites. 

Chapter 8 also describes how SMP results are used to select Stage 2B DBPR compliance monitoring

sites and lists the minimum requirements for the IDSE SMP report. The remainder of this chapter is

organized as follows:

4.2 Schedule for Conducting the SMP

4.3 SMP Monitoring Requirements

4.4 Timing of Sample Collection

4.5 Sampling Protocol

Although some guidance in this chapter is appropriate for other system types, this chapter solely

addresses 100 percent purchasing systems. Refer to Chapters 5 through 7 for guidance directed

towards systems that produce some or all of their finished water.

4.2 Schedule for Conducting the SMP

All systems conducting the SMP must prepare an IDSE report. Systems must either submit

their report [2 years after rule promulgation] if they are on the early schedule, or [4 years after rule

promulgation] if they are on the late schedule. The schedule is based on population of the largest

system in the combined distribution system.2 Section 1.1 describes how systems determine when their

IDSE report is due (i.e., if they are on the large or small system schedule).
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-2 100 Percent Purchasing Systems

It is recommended that systems begin SMP planning no later than 18 months before their IDSE

report is due to the State. The 18 months allows for 3 months of planning, 12 months of SMP

sampling, and 3 months for analyzing the final round of samples, reviewing the results, choosing the new

compliance sites, and completing the IDSE report. Table 4.1 shows IDSE report due dates and the

latest recommended SMP sampling start dates for systems on the early and late schedules.

Table 4.1 Consecutive System IDSE Report Schedule

Schedule Type1

IDSE Report Due

Date2

Recommended SMP

Sampling Start Date

Figure of

Schedule

(on next page)

Early Schedule [2 years after rule

promulgation]

No later than [9 months

after rule promulgation]

Figure 4.1

Early System

Late Schedule [4 years after rule

promulgation]

No later than [2 years

and 9 months after rule

promulgation]

Figure 4.2

Late System

1 See section 1.1 to determine your schedule type.

2 40 CFR 141.600(c).

To ensure smooth execution of an SMP, systems should begin planning several months (at least

three months is recommended) before the first sample date. A written SMP sample plan must be

prepared before systems begin sampling. An SMP plan must be submitted with the IDSE report and

include, at a minimum:

• The number of required sample sites

• The specific site of all selected SMP sample sites

• The rationale for selection of SMP sample sites (not required, but recommended)

• A sampling schedule

Figures 4.1 and 4.2 show the latest dates by which systems should begin planning, sampling,

and preparing the report for an IDSE SMP. Figure 4.1 presents the early schedule and Figure 4.2

presents the late schedule.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-3 100 Percent Purchasing Systems

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Submit IDSE 

Report to 

State/Primacy 

Agency

Rule 

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

[Year 1] [Year 2]

[Year 1 and 2] [Year 3] [Year 4]

Submit IDSE 

Report to 

State/Primacy 

Rule Agency

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Figure 4.1 Early Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates)

Figure 4.2 Late Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates)
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

3

 For the purposes of this guidance manual, surface water systems are the same as subpart H

systems—they use surface water or ground water under the direct influence of surface water (GWUDI) as a source. 

Surface water systems include all mixed systems (i.e., those that use surface and ground water). Ground water

systems are those that use only ground water as a source.

July 2003 - Proposal Draft 4-4 100 Percent Purchasing Systems

Stage 1 DBPR

compliance monitoring

sites cannot be used

as SMP sites.

4.3 SMP Monitoring Requirements

Table 4.2 summarizes the number of sites, sampling

frequency, and total number of samples that must be collected

for 100 percent purchasing surface and ground water systems3

(40 CFR 141.602(a) and (b)). The number of sites and

samples is based on the population of the system. All of a

system’s IDSE SMP samples must be dual samples sets,

meaning one total trihalomethane (TTHM) and one five

haloacetic acids (HAA5) sample that is taken at the same time and location. Chapter 8 provides

guidance for selecting SMP sites to meet the requirements of the IDSE.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-5 100 Percent Purchasing Systems

Table 4.2 SMP Sampling Requirements for 100 Percent Purchasing Systems1

System Size 

(Population Served3)

Number of Distribution System

Sites (by location type) per System

Total

Number of

Sites per

System 

Monitoring

Frequency for

the 1-year IDSE

Period5

Near

Entry

Point4

Average

Residence

Time

High

TTHM

 High

HAA5

Surface Water Systems6

< 500 - - 1 1 2 Every 180 days

500 - 4,999 - - 1 1 2 Every 90 days

5,000 - 9,999 - 1 2 1 4 Every 90 days

10,000 - 24,999 1 2 3 2 8 Every 60 days

25,000 - 49,999 2 3 4 3 12 Every 60 days

50,000 - 99,999 3 4 5 4 16 Every 60 days

100,000 - 499,999 4 6 8 6 24 Every 60 days

500,000 - < 1.5 million 6 8 10 8 32 Every 60 days

1.5 million - < 5 million 8 10 12 10 40 Every 60 days

> 5 million 10 12 14 12 48 Every 60 days

Ground Water Systems

< 500 - - 1 1 2 Every 180 days

500 - 9,999 - - 1 1 2 Every 90 days

10,000 - 99,999 1 1 2 2 6 Every 90 days

100,000 - 499,999 1 1 3 3 8 Every 90 days

> 500,000 2 2 4 4 12 Every 90 days

1

(40 CFR 141.602 (b)) 

2 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

3 Population served is typically a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 See section 8.2 for requirements when the number of entry points in a system is different from the number of

required near-entry point sites in this table.

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location. A dual sample set is one TTHM and one HAA5 sample that is taken at the same

time and location.

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-6 100 Percent Purchasing Systems

0

10

20

30

40

50

60

70

80

90

Jan-01

Feb-01Mar-01

Apr-01

May-01

Jun-01

Jul-01

Aug-01Sep-01

Oct-01

Nov-01Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Month

Highest Distribution System DBP Concentration (ug/L)

0

10

20

30

40

50

60

70

80

TTHM

HAA5

Temperature (F)

Average Distribution System Temperature (degrees 

Fahrenheit)

Highest DBP value 

occurred in June

4.4 Timing of Sample Collection

A system’s monitoring schedule must be determined using historical disinfection

byproduct (DBP) data or temperature data (40 CFR 141.602(a)). DBP data should be used as the

primary indicator, and then temperature data if DBP data are not sufficient. The month with the highest

TTHM or HAA5 concentration (whichever of the two is highest) or maximum temperature is referred

to as the controlling month. 

Systems may select any date in the controlling month to sample and should consider dates when

staff are available to collect samples. The other rounds of sampling must be scheduled around the

controlling month at the required sampling frequency listed in Table 4.2. The sampling dates for the

entire year must be scheduled and documented in the system’s sampling plan before collecting the first

sample. Systems can select a start date prior to the controlling month provided the controlling month is

included in their schedule. Figure 4.3 and Table 4.3 provides an example of how to select the

controlling month using hypothetical distribution system data.

Figure 4.3 Example Historic DBP and Temperature Data
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-7 100 Percent Purchasing Systems

Table 4.3 Example of Historic DBP and Temperature Data

Month TTHM (μg/L) HAA5 (μg/L)

Average Distribution

System Temp. (F)

Mar. 2001 41 15 48

Apr. 2001 52

May 2001 55

June 2001 82 31 65

July 2001 73

Aug. 2001 71

Sept. 2001 64 36 70

Oct. 2001 60

Nov. 2001 53

Dec. 2001 40 32 50

Jan. 2002 48

Feb. 2002 46

Mar. 2002 45 50 50

Apr. 2002 52

May 2002 56

June 2002 67 23 60

In this example, the highest DBP level was the TTHM value from June 2001. Therefore the

controlling month is June and the IDSE SMP sampling must be scheduled to include that month. If no

DBP data were available, July would have been selected as the controlling month because it has the

highest average distribution system temperature.

In the example, if the system must monitor quarterly, using the data in Figure 4.3 and Table 4.3

the four sampling dates should be scheduled approximately every 90 days considering June as the

controlling month as follows:

• First Tuesday in March 2003 

• First Tuesday in June 2003 (controlling month)
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-8 100 Percent Purchasing Systems

• First Tuesday in September 2003

• First Tuesday in December 2003

Chloramine systems that routinely convert to free chlorine for a “burnout period” must still set

their schedules according to the highest DBP (or temperature) month (40 CFR 141.602(a)), regardless

of whether chloramine or free chlorine is used during the controlling month. 

SMP samples should be collected as scheduled. EPA recognizes extenuating circumstances

can occur that may delay sampling (e.g., an ice storm). Any deviations from the scheduled sampling

days must be noted in the IDSE report (40 CFR 141.604(a)).

4.5 Sampling Protocol

Generally, it is best to collect samples in the morning to allow the samples to be packed and

shipped the same day if systems are sending them to a contract laboratory. Samples should be

collected in a manner that ensures they are representative of the water in the distribution system at that

sampling point. If sampling from indoor plumbing, samples should be collected from the cold water

line. The line between the sample tap or faucet and the distribution system should be flushed. This can

usually be accomplished by opening the faucet where the sample is collected and allowing the water to

run for a few minutes. When the water temperature stabilizes, this indicates fresh water from the

distribution system is being obtained.

The sample bottles should contain appropriate dechlorinating agents/preservatives prior to

filling. Sampling and storage protocols outlined in the approved analytical methods must be followed. 

Contact the laboratory analyzing the samples for their recommended sampling and preservation

protocols. Appendix C provides more detailed information on sampling procedures and approved

sampling methods. Samples must be analyzed by laboratories that have received certification by EPA

or the State.

If a sample is lost or broken, take a replacement sample as soon as possible. Systems only

need to resample for the lost sample bottle; they do not need to resample the entire set. For example, if

a TTHM sample is broken during shipping, the system would resample only for TTHM as soon as

possible at the given site. Make sure to note the deviation in sampling schedule for this sample in the

IDSE report.

Sampling near Fire Hydrants

Fire hydrants or blow-offs in locations that could impact the water reaching a sampling point

should not be flushed prior to the collection of the DBP samples, because that could significantly change

the “age” of the water being sampled. The intent of the DBP sampling effort is to obtain water that is

representative of what the customers normally receive.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 4-10 100 Percent Purchasing Systems

Continue to Chapter 8—SMP Site Selection
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water). See Chapter 1 for additional guidance

on classifying systems.

2

 For the purposes of this guidance manual, surface water systems are the same as “subpart H”

systems—they use surface water or ground water under the direct influence of surface water (GWUDI) as a source. 

Surface water systems include all mixed systems (i.e., those that use surface and ground water). Ground water

systems are those that use only ground water as a source.

July 2003 - Proposal Draft 5-1 Producing Surface Water Systems (> 10,000)

5.0 Standard Monitoring Program Requirements for:

Producing Surface Water Systems

Serving at Least 10,000 People

5.1 Introduction

This chapter describes the Initial Distribution System Evaluation (IDSE) Standard Monitoring

Program (SMP) requirements for producing surface water systems1, 2 serving at least 10,000 people. 

These requirements include monitoring frequency, sample sites, and scheduling. Chapter 8 builds on

this chapter by describing how final SMP monitoring sites should be selected using various sources and

tools. Chapter 8 also describes how SMP results are used to select Stage 2B Disinfectants and

Disinfection Byproducts Rule (DBPR) compliance monitoring sites and lists the minimum requirements

for the IDSE SMP report. The remainder of this section is organized as follows:

5.2 Schedule for Conducting the SMP 

5.3 Number of Samples Required 

5.4 Sample Site Requirements

5.5 Timing of SMP Sample Collection

5.6 Sampling Protocol

Although some guidance in this chapter is appropriate for other system types and sizes, this

chapter specifically addresses producing surface water systems serving at least 10,000

people. Refer to Chapters 6 and 7 for guidance directed towards other producing system types. 

Refer to Chapter 4 for guidance directed towards 100 percent purchasing systems.

5.2 Schedule for Conducting the SMP

All surface water systems serving at least 10,000 people are on the large system schedule

and must submit their IDSE report [2 years after rule promulgation]. It is recommended that systems

begin planning their SMP no later than [6 months after rule promulgation]. The 18 months includes 3

months for planning, 12 months of SMP sampling, and 3 months to analyze the final round of samples,

review the results, choose the new compliance sites, and complete the IDSE report.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-2 Producing Surface Water Systems (> 10,000)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Submit IDSE 

Report to 

State/Primacy 

Agency

Rule 

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

[Year 1] [Year 2]

To ensure smooth execution of an SMP, systems should begin planning several months (at least

three months is recommended) before the first sample date. A written SMP sample plan must be

prepared before beginning sampling. The plan must be submitted with the IDSE report and include, at

a minimum:

• The number of required sample sites

• The specific site of all selected SMP sample sites

• The rationale for selection of SMP sample sites (not required but recommended)

• A sampling schedule

Figure 5.1 shows the latest recommended dates by which systems should begin planning, sampling,

and preparing the report for an SMP to meet regulatory requirements.

Figure 5.1 Large System Schedule for Conducting the SMP

(Showing Latest Recommended Start Dates)
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-3 Producing Surface Water Systems (> 10,000)

Approximately

Every 60 Days

for 1 Year HAA5

TTHM

5.2.1 Consecutive Water Systems and Wholesalers

The IDSE SMP report is due at the same time as that of the largest system in the combined

distribution system. Therefore, if a small system serving less than 10,000 people buys water from a

system serving at least 10,000 people, they must submit their report on the large system schedule, or [2

years after rule promulgation]. EPA recommends that systems share information about their IDSE

report schedule with all wholesale purchasers of their water. Coordination with systems that purchase

water from systems serving at least 10,000 people is not required, but is strongly recommended.

5.3 Number of Samples Required

Producing surface water systems serving at least 10,000 people must collect samples every 2

months over a 1 year period. Samples must be collected at eight sites per plant and analyzed for

total trihalomethanes (TTHM) and five haloacetic acids (HAA5). These sites must be different than the

Stage 1 DBPR compliance monitoring sites. All systems’ IDSE SMP samples must be dual samples

sets, meaning one TTHM and one HAA5 sample that is taken at the same time and location. For a

system with one plant, a total of 48 dual sample sets are required during the 1-year monitoring period

(see the illustration below).

8 Sites per plant × 6 Sample Periods = 48 Dual Samples Sets

Section 1.1 provides guidelines for estimating the number or plants in a system.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-4 Producing Surface Water Systems (> 10,000)

***Examples for Determining Number of Plants, Sites, and Samples***

Example 5.1

A system serving 100,000 people operates one surface water treatment plant and receives

water from two disinfecting ground water systems, at separate entry points, for more than60

consecutive days per year.

Total plants: 3 (one surface water and two ground water)

Total SMP sites: 8 sites per plant × 3 plants = 24 sites

Total Samples: 24 sties × 6 sample periods = 144 dual samples

Example 5.2

A system serving 35,000 people purchases treated surface water through one entry 

point and has three wells. Chlorine is added at each well site. The State determined that two of the

wells draw from the same aquifer and that the third well draws from a different aquifer.

Total plants: 3 (one for the purchased water entry point, the second for the two wells drawing from

the same aquifer, and the third for the well drawing from another aquifer)

Total sites: 8 sites per plant × 3 plants = 24 sites

Total Samples: 24 sites × 6 sample periods = 144 dual samples

Example 5.3

A system serves 90,000 people, purchases treated water from one wholesaler, through five

entry points, and has two wells which they use on a daily basis. The wholesaler has three surface

water treatment plants. Three of the entry points receive water from plant A and two of the entry

points receive water from plant B. The State-approved multiple consecutive entry points to be

considered as one plant—the three entry points receiving water from plant A are one plant and the

two entry points receiving water from plant B are a second plant. The two wells feed into one

pumphouse where chlorine is added; this is considered one treatment plant.

Total plants: 3 (two plants for the consecutive entry points and one ground water)

Total SMP sites: 8 sites per plant × 3 plants = 24 sites

Total Samples: 24 sites × 6 sample periods = 144 dual samples
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-5 Producing Surface Water Systems (> 10,000)

Stage 1 DBPR

compliance monitoring

sites cannot be used

as SMP sites.

Purchased E n try Point #1 W ater Purchased Entry Point #2 W ater T Surface reat ment Plant W ater Purchased E n try Point #1 W ater Purchased Entry Point #2 W ater T Surface reat ment Plant W ater Purchased E n try Point #1 W ater Purchased Entry Point #2 W ater T Surface reat ment Plant W ater 

5.4 Sample Site Requirements

Sample site requirements depend on a system’s residual

disinfectant type. Table 5.1 summarizes the SMP site requirements

for producing surface water systems serving at least 10,000 people. 

The required SMP sample sites listed in Table 5.1 are in addition to

Stage 1 DBPR compliance monitoring sites. Chapter 8 describes

how real entry point sites are selected for chlorine and chloramine

systems and provides guidance for selecting all other SMP sites to meet the requirements of the IDSE.

Table 5.1 SMP Sample Sites for Producing Surface Water Systems

Serving at Least 10,000 People

Residual

Disinfectant

Type

 Number of SMP Sample Sites Required per Plant

Near Entry Point 

Average

Residence Time

High

TTHM High HAA5

Total Dual

Samples

per Plant

Chlorine 1 2 3 2 8

Chloramines 2 2 2 2 8

5.4.1 Changing Disinfectants During the SMP Period

If systems anticipate a change in residual disinfectant during the 1-year SMP sampling period,

selection of SMP sites should be based on the disinfectant expected to be in use at the end of the

sampling period. Figure 5.2 shows an example timeline where a system uses free chlorine at the start of

the SMP, but changes to chloramines before the end of the SMP sampling period. In this case, sample

site selection should be performed as required for chloraminated systems. Thus, two sample sites

(instead of one) near the entry point and four sites (instead of five) representative of highest TTHM and

HAA5 should be selected. In both cases, two average residence time sites are required.

If systems are unsure as to whether their disinfectant conversion will take place during the SMP

sampling period, they should select sites based on SMP requirements for a chlorine system.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-6 Producing Surface Water Systems (> 10,000)

SMP Sampling Period

Months

Planned 

Conversion to 

Chloramines

SMP must be based on chloramine requirements.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Rule 

Promulgation

Figure 5.2 Planned Conversion to Chloramines

5.5 Timing of SMP Sample Collection

A system’s monitoring schedule must be determined using historical disinfection

byproduct (DBP) data or temperature data (40 CFR 141.602(a)). DBP data should be used as the

primary indicator, and then temperature data if DBP data are not sufficient. The month with the highest

TTHM or HAA5 concentration (whichever of the two is highest) or maximum temperature is referred

to as the controlling month. 

Systems may select any date in the controlling month to sample and should consider dates when

staff are available to collect samples. The other rounds of sampling must be scheduled around the

controlling month at two month intervals. The sampling dates for the entire year must be scheduled and

documented in the system’s sampling plan before collecting the first sample. Systems can select a start

date prior to the controlling month provided the controlling month is included in their schedule. Figure

5.3 and Table 5.2 provides an example of how to select the controlling month using hypothetical

distribution system data.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-7 Producing Surface Water Systems (> 10,000)

0

10

20

30

40

50

60

70

80

90

Sep-00

Oct-00Nov-00

Dec-00

Jan-01

Feb-01Mar-01

Apr-01

May-01

Jun-01

Jul-01

Aug-01Sep-01

Oct-01Nov-01

Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Month

Highest Distribution System DBP Concentration (ug/L)

0

10

20

30

40

50

60

70

80

90

Average Distribution System Temperature (degrees F)

TTHM

HAA5

Temperature (F)

Highest DBP value

occurred in July

Figure 5.3 Example Historic DBP and Temperature Data
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-8 Producing Surface Water Systems (> 10,000)

Table 5.2 Example of Historic DBP and Temperature Data

Month TTHM (μg/L) HAA5 (μg/L)

Average Distribution

System Temp. (F)

Nov. 2000 50

Dec. 2000 43

Jan 2001 43 29 40

Feb 2001 43

Mar. 2001 45

Apr. 2001 62 45 50

May 2001 60

June 2001 70

July 2001 85 42 74

Aug. 2001 78

Sept.2001 70

Oct. 2001 55 38 60

Nov. 2001 49

Dec. 2001 42

Jan. 2002 48 32 40

Feb. 2002 41

Mar. 2002 44

Apr. 2002 50 53 48

May 2002 62

In this example, the highest DBP level was the TTHM value from July 2001. Therefore, the

controlling month is July and the SMP sampling must be scheduled considering that month. If no DBP

data were available, August would have been selected as the controlling month because it has the

highest average distribution system temperature.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-9 Producing Surface Water Systems (> 10,000)

For the example in Figure 5.3 and Table 5.2, the six sampling dates should be scheduled

approximately every 60 days with July as the controlling month as follows:

• First Thursday in March 2003

• First Thursday in May 2003

• First Thursday in July 2003 (controlling month)

• First Thursday in September 2003

• First Thursday in November 2003

• First Thursday in January 2004

Chloramine systems that routinely convert to free chlorine for a “burnout period” must still set

their schedules according to the highest DBP (or temperature) month (40 CFR 141.602(a)), regardless

of whether chloramine or free chlorine is used during the controlling month. 

SMP samples should be collected as scheduled. EPA recognizes extenuating circumstances

can occur that may delay sampling (e.g., an ice storm). Any deviations from the scheduled sampling

days must be noted in the IDSE report (40 CFR 141.604(a)).

5.6 Sampling Protocol

Generally, it is best to collect samples in the morning to allow the samples to be packed and

shipped the same day if systems are sending them to a contract laboratory. Samples should be

collected in a manner that ensures they are representative of the water in the distribution system at that

sampling point. If sampling from indoor plumbing, samples should be collected from the cold water

line. The line between the sample tap or faucet and the distribution system should be flushed. This can

usually be accomplished by opening the faucet where the sample is collected and allowing the water to

run for a few minutes. When the water temperature stabilizes, this indicates fresh water from the

distribution system is being obtained.

The sample bottles should contain appropriate dechlorinating agents/preservatives prior to

filling. Sampling and storage protocols outlined in the approved analytical methods must be followed. 

Contact the laboratory analyzing the samples for their recommended sampling and preservation

protocols. Appendix C provides more detailed information on sampling procedures and approved

sampling methods. Samples must be analyzed by laboratories that have received certification by EPA

or the State.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft 5-10 Producing Surface Water Systems (> 10,000)

Continue to Chapter 8—SMP Site Selection

If a sample is lost or broken, take a replacement sample as soon as possible. Systems need to

resample only for the lost sample bottle; they do not need to resample the entire set. For example, if a

TTHM sample is broken during shipping, systems would resample only for TTHM as soon as possible

at the given site. Make sure to note the deviation in sampling schedule for this sample in the IDSE

report.

Sampling near Fire Hydrants

Fire hydrants or blow-offs in locations that could impact the water reaching a sampling point

should not be flushed prior to the collection of the DBP samples, because that could significantly change

the “age” of the water being sampled. The intent of the DBP sampling effort is to obtain water that is

representative of what the customers normally receive.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water). See Chapter 1 for additional guidance

on classifying systems.

2

For the purposes of this guidance manual, surface water systems are the same as “subpart H”

systems—they use surface water or ground water under the direct influence of surface water (GWUDI) as a source. 

Surface water systems include all mixed systems (i.e., those that use surface and ground water). Ground water

systems are those that use only ground water as a source.

July 2003 - Proposal Draft Producing Systems

6-1 SW (500-9,999) and GW (>10,000)

6.0 Standard Monitoring Program Requirements for:

Producing Surface Water Systems Serving 500 to 9,999 People

or

Producing Ground Water Systems Serving at Least 10,000 People

6.1 Introduction

This chapter describes the Initial Distribution System Evaluation (IDSE) Standard Monitoring

Program (SMP) requirements for producing surface water systems 1, 2 serving 500 to 9,999 people and

producing ground water systems serving at least 10,000. These requirements include monitoring

frequency, sample sites, and schedules. Chapter 8 builds on this chapter by describing how to select

SMP monitoring sites. Chapter 8 also describes how SMP results are used to select Stage 2B

Disinfectants and Disinfection Byproducts Rule (DBPR) compliance monitoring sites and lists the

minimum requirements for the IDSE SMP report. The remainder of this chapter is organized as

follows:

6.2 Schedule for Conducting the SMP

6.3 SMP Monitoring Requirements

6.4 Timing of Sample Collection

6.5 Sampling Protocol

Although some guidance in this chapter is appropriate for other system types and sizes, this

chapter specifically addresses producing surface water systems serving 500 to 9,999 people and

producing ground water systems serving at least 10,000 people. 100 percent purchasing systems

should refer to Chapter 4, and producing systems of other source water types and system sizes should

refer to Chapters 5 and 7.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

3

 The Environmental Protection Agency (EPA) defines a combined distribution system as the

totality of the distribution systems of wholesale systems and of the consecutive systems that receive

finished water from those wholesale systems.

July 2003 - Proposal Draft Producing Systems

6-2 SW (500-9,999) and GW (>10,000)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Submit IDSE 

Report to 

State/Primacy 

Agency

Rule 

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

[Year 1] [Year 2]

6.2 Schedule for Conducting the SMP

All systems conducting the SMP must prepare an IDSE report. Systems must either submit

their report [2 years after rule promulgation] if they are on the large system schedule, or [4 years

after rule promulgation] if they are on the small system schedule. The schedule is based on

population of the largest system in the combined distribution system.3 Section 1.4 describes how

systems determine when their IDSE report is due (i.e., if they are on the large or small system

schedule).

It is recommended that systems begin planning the SMP no later than 18 months before the

IDSE report is due to the State. The 18 months includes 3 months of planning, 12 months of SMP

sampling, and 3 months for analyzing the final round of samples, reviewing the results, choosing the new

compliance sites, and completing the IDSE report. Figures 6.1 and 6.2 show the latest recommended

dates by which systems should begin planning, sampling, and preparing the report for an SMP to meet

regulatory requirements. Figure 6.1 represents the large system schedule and Figure 6.2 represents the

small system schedule.

Figure 6.1 Large System Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates)
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft Producing Systems

6-3 SW (500-9,999) and GW (>10,000)

[Year 1 and 2] [Year 3] [Year 4]

Submit IDSE 

Report to 

State/Primacy 

Rule Agency

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Stage 1 DBPR

compliance monitoring

sites cannot be used as

SMP sites.

Figure 6.2 Small System Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates)

A written SMP sample plan must be prepared before systems begin sampling. The plan must

be submitted with the IDSE report and include, at a minimum:

• The number of required sample sites

• The specific site of each selected SMP sample site

• The rationale for selection of SMP sample sites (not required, but recommended)

• A sampling schedule

6.3 SMP Monitoring Requirements

Table 6.1 summarizes the number of sites,

sampling frequency, and total number of samples that

must be collected per plant in a system (this sampling

requirement is in addition to the Stage 1 DBPR

compliance monitoring). All of a system’s IDSE SMP

samples must be dual sample sets, meaning one total

trihalomethane (TTHM) and one five haloacetic acids

(HAA5) sample that is taken at the same time and location. The SMP sample sites are in addition to
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft Producing Systems

6-4 SW (500-9,999) and GW (>10,000)

TTHM

Approximately

Every 90 Days

HAA5

Stage 1 DBPR compliance monitoring sites (40 CFR 141.602(a)). Chapter 8 provides guidance for

selecting SMP sites to meet the requirements of the IDSE.

Table 6.1 Summary of SMP Sampling Requirements1

Source Type and

Population Served Number of Sites Sampling Frequency

Total Dual

Samples per

Plant

Surface Water (500 - 9,999)

and

Ground Water (> 10,000)

2 per plant—1 high TTHM

and 1 high HAA5

every 3 months for 

1 year

8

1

 40 CFR 141.602(a))

For producing surface water systems serving 500 to 9,999 people and ground water systems

serving at least 10,000 people and having one plant, a total of 8 dual sample sets is required, and each

must be analyzed for TTHM and HAA5 (see the illustration below).

 2 Sites per Plant × 4 Sample Periods = 8 Dual Samples Sets

Section 1.1 provides guidelines for estimating the number or plants in a system.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft Producing Systems

6-5 SW (500-9,999) and GW (>10,000)

***Examples for Determining Number of Plants, Sites, and Samples***

Example 6.1

A system serving 6,000 people operates one surface water treatment plant and receives

water from two other surface water systems, at separate entry points, for more than 60 consecutive

days per year. 

Total plants: 3 (one surface water and two consecutive entry points)

Total SMP sites: 2 sites per plant × 3 plants = 6 sites

Total samples: 6 sites × 4 monitoring periods = 24 dual sample sets

Example 6.2

A system serves 5,000 people, purchases treated surface water through one entry point, 

and has three wells. Chlorine is added at each well site. The State determined that two of the wells

draw from the same aquifer and that the third well draws from a different aquifer. 

Total plants: 3 (one for the purchased water entry point, the second for the two wells drawing from

the same aquifer, and the third for the well drawing from another aquifer)

Total sites: 2 sites per plant × 3 plants = 6 sites

Total samples: 6 sites × 4 monitoring periods = 24 dual sample sets

Example 6.3

A system serves 25,000 people, purchases treated ground water from one wholesaler,

through five entry points, and has two wells. The State approved multiple consecutive entry points

to be considered as one plant—the three entry points receiving water from plant A are one plant and

the two entry points receiving water from plant B are a second plant. The two wells feed into one

pumphouse where chlorine is added; this is considered one treatment plant. 

Total plants: 3 (two plants for the consecutive entry points and one ground water)

Total SMP sites: 2 sites per plant × 3 plants = 6 sites

Total samples: 6 sites × 4 monitoring periods = 24 dual sample sets
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft Producing Systems

6-6 SW (500-9,999) and GW (>10,000)

6.4 Timing of Sample Collection

A system’s monitoring schedule must be determined using historical disinfection

byproduct (DBP) data or temperature data (40 CFR 141.602(a)). DBP data should be used as the

primary indicator, and then temperature data if DBP data are not sufficient. The month with the highest

TTHM or HAA5 concentration (whichever of the two is highest) or maximum temperature is referred

to as the controlling month. 

Systems may select any date in the controlling month to sample and should consider dates when

staff are available to collect samples. The other rounds of sampling must be scheduled around the

controlling month at three month intervals. The sampling dates for the entire year must be scheduled

and documented in a system’s sampling plan before collecting the first sample. Systems can select a

start date prior to the controlling month provided the controlling month is included in their schedule. 

Figure 6.3 and Table 6.2 provide an example of how to select the controlling month using hypothetical

distribution system data.
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0

10

20

30

40

50

60

70

80

90

Jan-01

Feb-01Mar-01

Apr-01

May-01

Jun-01

Jul-01

Aug-01Sep-01

Oct-01

Nov-01Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Month

Highest Distribution System DBP Concentration (ug/L)

0

10

20

30

40

50

60

70

80

TTHM

HAA5

Temperature (F)

Average Distribution System Temperature 

(degrees Fahrenheit)

Highest DBP value 

occurred in June

Figure 6.3 Example Historic DBP and Temperature Data
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Table 6.2 Example of Historic TTHM and Temperature Data

Month TTHM (μg/L) HAA5 (μg/L)

Average Distribution

System Temp. (F)

Mar. 2001 41 15 48

Apr. 2001 52

May 2001 55

June 2001 82 31 65

July 2001 73

Aug. 2001 71

Sept. 2001 64 36 70

Oct. 2001 60

Nov. 2001 53

Dec. 2001 40 32 50

Jan. 2002 48

Feb. 2002 46

Mar. 2002 45 50 50

Apr. 2002 52

May 2002 56

June 2002 67 23 60

In this example, the highest DBP level was the TTHM value from June 2001. Therefore, the

controlling month is June and the SMP sampling must be scheduled to include that month. If no DBP

data were available, July would have been selected as the controlling month because it has the highest

average distribution system temperature.

In the example, if the system must monitor quarterly, using the data in Figure 6.3 and Table 6.2,

the four sampling dates should be scheduled approximately every 90 days considering June as the

controlling month as follows:

• First Monday in March 2003

• First Monday in June 2003 (controlling month)
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• First Monday in September 2003

• First Monday in December 2003

Chloramine systems that routinely convert to free chlorine for a “burnout period” must still set

their schedules according to the highest DBP (or temperature) month (40 CFR 141.602(a)), regardless

of whether chloramine or free chlorine is used during the controlling month. 

SMP samples should be collected as scheduled. EPA recognizes extenuating circumstances

can occur that may delay sampling (e.g., an ice storm). Any deviations from the scheduled sampling

days must be noted in the IDSE report (40 CFR 141.604(a)).

6.5 Sampling Protocol

Generally, it is best to collect samples in the morning to allow the samples to be packed and

shipped the same day if systems are sending them to a contract laboratory. Samples should be

collected in a manner that ensures they are representative of the water in the distribution system at that

sampling point. If sampling from indoor plumbing, samples should be collected from the cold water

line. The line between the sample tap or faucet and the distribution system should be flushed. This can

usually be accomplished by opening the faucet where the sample is collected and allowing the water to

run for a few minutes. When the water temperature stabilizes, this indicates fresh water from the

distribution system is being obtained.

The sample bottles should contain appropriate dechlorinating agents/preservatives prior to

filling. Sampling and storage protocols outlined in the approved analytical methods must be followed. 

Contact the laboratory analyzing the samples for their recommended sampling and preservation

protocols. Appendix C provides more detailed information on sampling procedures and approved

sampling methods. Samples must be analyzed by laboratories that have received certification by EPA

or the State.

If a sample is lost or broken, take a replacement sample as soon as possible. Systems need to

resample only for the lost sample bottle; they do not need to resample the entire set. For example, if a

TTHM sample is broken during shipping, the system would resample only for TTHM as soon as

possible at the given site. Make sure to note the deviation in sampling schedule for this sample in the

IDSE report.

Sampling near Fire Hydrants

Fire hydrants or blow-offs in sites that could impact the water reaching a sampling point should

not be flushed prior to the collection of the DBP samples, because that could significantly change the
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Continue to Chapter 8—SMP Site Selection

“age” of the water being sampled. The intent of the DBP sampling effort is to obtain water that is

representative of what the customers normally receive.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

1

 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water). See Chapter 1 for additional guidance

on classifying systems.

2

 For the purposes of this guidance manual, surface water systems are the same as “subpart H”

systems—they use surface water or ground water under the direct influence of surface water (GWUDI) as a source. 

Surface water systems include all mixed systems (i.e., those that use surface and ground water). Ground water

systems are those that use only ground water as a source.

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7.0 Standard Monitoring Program Requirements for:

Producing Surface Water Systems Serving Less Than 500 People

or

Producing Ground Water Systems Serving Less Than 10,000

People

7.1 Introduction

This chapter describes the Initial Distribution System Evaluation (IDSE) Standard Monitoring

Program (SMP) requirements for producing surface water systems1, 2 serving less than 500 people and

producing ground water systems serving less than 10,000 people. These requirements include

monitoring frequency, sample sites, and schedules. Chapter 8 builds on this chapter by describing how

to select SMP monitoring sites. Chapter 8 also describes how SMP results are used to select Stage 2B 

Disinfectants and Disinfection Byproducts Rule (DBPR) compliance monitoring sites and lists the

minimum requirements for the IDSE SMP report. The remainder of this chapter is organized as follows: 

7.2 Schedule for Conducting the SMP

7.3 Number of Samples Required

7.4 Sample Site Requirements

7.5 Timing of Sample Collection

7.6 Sampling Protocol

Although some guidance in this chapter is appropriate for other system types and sizes, 

this chapter specifically addresses producing surface water systems serving less than 500 people

and producing ground water systems serving less than 10,000 people. 100 percent purchasing

systems should refer to Chapter 4, and producing systems of other source water types and system sizes

should refer to Chapters 5 and 6.
The Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

3

 The Environmental Protection Agency (EPA) defines a combined distribution system as the totality of the

distribution systems of wholesale systems and of the consecutive systems that receive finished water from those

wholesale systems.

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7.2 Schedule for Conducting the SMP

All systems conducting the SMP must prepare an IDSE report. Systems must either submit

their report [2 years after rule promulgation] if they are on the large system schedule, or [4 years

after rule promulgation] if they are on the small system schedule. The schedule is based on

population of the largest system in the combined distribution system.3 Section 1.4 describes how

systems determine when their IDSE report is due (i.e., if they are on the large or small system

schedule).

It is recommended that systems begin planning the SMP no later than 18 months before the

IDSE report is due to the State. The 18 months includes 3 months of planning, 12 months of SMP

sampling, and 3 months for analyzing the final round of samples, reviewing the results, choosing the new

compliance sites, and completing the IDSE report. Table 7.1 shows IDSE report due dates and the

latest recommended SMP sampling start dates for systems on the small and large system schedules.

Table 7.1 IDSE Report Schedule

Schedule Type 

IDSE Report Due

Date

Recommended SMP

Sampling Start Date

Figure of

Schedule

(on next page)

Large System Schedules [2 years after rule

promulgation]

No later than [9 months

after rule promulgation]

Figure 7.1

Large System

Small System Schedule [4 years after rule

promulgation]

No later than [2 years

and 9 months after rule

promulgation]

Figure 7.2

Small System

Note: See section 1.4 to determine the schedule type.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Submit IDSE 

Report to 

State/Primacy 

Agency

Rule 

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

[Year 1] [Year 2]

To ensure smooth execution of an SMP, systems should begin planning several months (at least

three months is recommended) before the first sample date. A written SMP sample plan must be

prepared before systems begin sampling. The plan must be submitted with the IDSE report and

include, at a minimum:

• The number of required sample sites

• The specific site of all selected SMP sample sites

• The rationale for selection of SMP sample sites (not required, but recommended)

• A sampling schedule

Figures 7.1 and 7.2 show the latest dates by which systems should begin planning,

sampling, and preparing the report for an SMP to meet regulatory requirements. Figure 7.1 represents

the schedule for consecutive systems with a large system in the combined distribution system and Figure

7.2 represents the small system schedule.

Figure 7.1 Large System Schedule for Conducting the IDSE SMP 

(Showing Latest Recommended Start Dates)
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[Year 1 and 2] [Year 3] [Year 4]

Submit IDSE 

Report to 

State/Primacy 

Rule Agency

Promulgation

[Actual Timeline to be provided]

Start SMP 

Monitoring

1 Year of Monitoring

Begin 

Planning for 

IDSE SMP

Start Preparing 

Report

25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

TTHM

Once every 6

months for 1 year

HAA5

Figure 7.2 Small System Schedule for Conducting the IDSE SMP

(Showing Latest Recommended Start Dates)

7.3 Number of Samples Required

Producing surface water systems serving fewer than 500 people and ground water systems

serving fewer than 10,000 people must collect samples every 6 months over a 1-year period (this

sampling requirement is in addition to Stage 1 DBPR monitoring). Samples must be collected at two

sites per plant and analyzed for total trihalomethane (TTHM) and five haloacetic acids (HAA5). All of

a system’s IDSE SMP samples must be dual sample sets, meaning one TTHM and one HAA5 sample

that is taken at the same time and location. For systems with one plant, a total of 4 dual sample sets are

required, and each should be analyzed for TTHM and HAA5 (see the illustration below).

2 Sites per Plant × 2 Sample Periods = 4 Dual Sample Sets
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***Examples for Determining Number of Plants, Sites, and Samples***

Example 7.1

A system serves 450 people, purchases treated surface water through one entry point, 

and has two wells. Chlorine is added at each well site. The State determined that the two wells

draw from the same aquifer. 

Total plants: 2 (one for the purchased water entry point and one for the two wells drawing from the

same aquifer)

Total sites: 2 sites per plant × 2 plants = 4 sites

Total samples: 8 samples

Example 7.2

A system serves 300 people, purchases treated surface water from one wholesaler through

two entry points. The State allowed the multiple consecutive entry points to be considered as one

plant. 

Total plants: 1 (one plant for both consecutive entry points)

Total SMP sites: 2 sites per plant × 1 plant = 2 sites

Section 1.1.4 provides guidelines for estimating the number or plants in a system.

7.4 Sample Site Requirements

Systems must select two SMP sample sites per plant, meeting the following criteria:

• One site representative of the highest TTHM concentration in the system

• One site representative of the highest HAA5 concentration in the system

• Sites must be different than the Stage 1 DBPR monitoring sites
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Stage 1 DBPR

compliance monitoring

sites cannot be used as

SMP sites.

In many small systems, the highest HAA5 concentration

would be expected to occur at the same site as the highest TTHM

concentration. However, in some systems (often those with low

disinfectant residual levels and high maximum water age) the

HAA5 concentration can decrease in some parts of the distribution

system, because HAA5 can biodegrade when no residual

disinfectant is present. The highest HAA5 site will not be the same

as the highest TTHM site. As a result, this situation is described and help is provided. Chapter 8

provides guidance for selecting SMP sites to meet the requirements of the IDSE.

7.5 Timing of Sample Collection

One of the system’s sampling dates must occur in the month with the highest water temperature

in their distribution system (systems should already be taking the Stage 1 DBPR compliance samples

during this month). The system’s other sampling date must be 6 months before or after the high

distribution system water temperature month. The 6-month interval should be maintained as closely as

possible (40 CFR 141.602(a)). 

SMP samples should be collected as scheduled. EPA recognizes extenuating circumstances

can occur that may delay sampling (e.g., an ice storm). Any deviations from the scheduled sampling

days must be noted in the IDSE report (40 CFR 141.604(a)).

This regimen is expected to typically result in one sample date occurring in the summer (July

through September), and the second in the winter (January-March).

7.6 Sampling Protocol

Generally, it is best to collect samples in the morning to allow the samples to be packed and

shipped the same day if systems are sending them to a contract laboratory. Samples should be

collected in a manner that ensures they are representative of the water in the distribution system at that

sampling point. If sampling from indoor plumbing, samples should be collected from the cold water

line. The line between the sample tap or faucet and the distribution system should be flushed. This can

usually be accomplished by opening the faucet where the sample is collected and allowing the water to

run for a few minutes. When the water temperature stabilizes, this indicates fresh water from the

distribution system is being obtained.

The sample bottles should contain appropriate dechlorinating agents/preservatives prior to

filling. Sampling and storage protocols outlined in the approved analytical methods must be followed. 

Contact the laboratory analyzing the samples for their recommended sampling and preservation
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Continue to Chapter 8—SMP Site Selection

protocols. Appendix C provides more detailed information on sampling procedures and approved

sampling methods. Samples must be analyzed by laboratories that have received certification by EPA

or the State.

If a sample is lost or broken, take a replacement sample as soon as possible. Systems only

need to resample for the lost sample bottle; they do not need to resample the entire set. For example, if

a TTHM sample is broken during shipping, the system would resample only for TTHM as soon as

possible at the given site. Make sure to note the deviation in sampling schedule for this sample in the

IDSE report.

Sampling near Fire Hydrants

Fire hydrants or blow-offs in locations that could impact the water reaching a sampling point

should not be flushed prior to the collection of the disinfection byproduct (DBP) samples, because that

could significantly change the “age” of the water being sampled. The intent of the DBP sampling effort

is to obtain water that is representative of what the customers normally receive.
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Data Sources and Tools

Disinfectant residual, 

maps, models, etc.

Select Preliminary Sites

Narrow Down 

Selection

Select Final Sites

General Approach to 

SMP Site Selection

8.0 Standard Monitoring Program Site Selection and Reporting

8.1 Introduction

Chapters 4 through 7 of this manual provided detailed requirements for conducting an Initial

Distribution System Evaluation (IDSE) Standard Monitoring Program (SMP). This chapter, which

applies to all system types, system sizes, and source water types, expands on those chapters by

providing technical guidance for selecting SMP monitoring sites using various tools.

The general approach for selecting SMP sites is to use available data sources and analysis tools

to select a large number of potential sites (referred to as preliminary sites). From that group of sites,

systems should consider geographic coverage and other distribution system factors to narrow down

preliminary sites to final SMP sites.

This chapter is organized as follows:

Background Information

8.2 Description of SMP Site Types

8.3 Considerations for Systems with More than One Plant or Entry Point

8.4 Data Sources and Tools for Identifying Preliminary SMP Sites
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SMP Site Selection

8.5 Methodology for Selecting Final SMP Sites

Stage 2B Site Selection Based on SMP Results and Reporting

8.6 Stage 2B DBPR Site Selection and IDSE Reporting Requirements

8.7 Reporting Results to the State

8.2 Description of SMP Sample Site Types

Tables 8.1 and 8.2 summarize the SMP sample site requirements according to system type,

system size, and source water type (Chapter 1 also provides this information). As shown in the tables,

there are four types of sampling locations defined for the SMP: near-entry point, average residence

time, high total trihalomethane (TTHM), and high five haloacetic acids (HAA5). Sections 8.2.1 through

8.2.3 provide descriptions of each type of sample site. Note that all sample site types are not required

for all systems and, as stated in Chapters 4 through 7, the Stage 1 DBPR compliance monitoring sites

cannot be used as SMP sites.
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Table 8.1 SMP Sampling Requirements for 100 Percent Purchasing Systems1,2

System Size 

(Population Served3)

Number of Distribution System

Sites (by location type) per System

Total

Number of

Sites per

System 

Monitoring

Frequency for

the 1-year IDSE

Period5

Near

Entry

Point4

Average

Residence

Time

High

TTHM

 High

HAA5

Surface Water Systems6

< 500 - - 1 1 2 Every 180 days

500 - 4,999 - - 1 1 2 Every 90 days

5,000 - 9,999 - 1 2 1 4 Every 90 days

10,000 - 24,999 1 2 3 2 8 Every 60 days

25,000 - 49,999 2 3 4 3 12 Every 60 days

50,000 - 99,999 3 4 5 4 16 Every 60 days

100,000 - 499,999 4 6 8 6 24 Every 60 days

500,000 - < 1.5 million 6 8 10 8 32 Every 60 days

1.5 million - < 5 million 8 10 12 10 40 Every 60 days

> 5 million 10 12 14 12 48 Every 60 days

Ground Water Systems

< 500 - - 1 1 2 Every 180 days

500 - 9,999 - - 1 1 2 Every 90 days

10,000 - 99,999 1 1 2 2 6 Every 90 days

100,000 - 499,999 1 1 3 3 8 Every 90 days

> 500,000 2 2 4 4 12 Every 90 days

1

(40 CFR 141.602 (b)) 

2 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

3 Population served is usually a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 See section 8.2 for requirements when the number of entry points in a system is different from the number of

required near-entry point sites in this table.

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location. 

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).
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Table 8.2 SMP Sampling Requirements for Producing Systems1,2

System Size

(Population

Served3)

Residual

Disinfectant

Number of Distribution System Sites

(by location type) for each Plant Total

Number of

Sites per

Plant 

Monitoring

Frequency4

Near-Entry

Point

Average

Residence

Time

High

TTHM 

High

HAA5 

Surface Water Systems5

< 500 Chlorine or

Chloramines - - 1 1 2 Every 180 days

500 - 9,999 Chlorine or

Chloramines - - 1 1 2 Every 90 days

> 10,000

Chlorine 1 2 3 2 8

Every 60 days

Chloramines 2 2 2 2 8

Ground Water Systems

< 10,000 Chlorine or

Chloramines - - 1 1 2 Every 180 days

> 10,000 Chlorine or

Chloramines - - 1 1 2 Every 90 days

1

(40 CFR 141.602(a))

2 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water).

3 Population served is usually a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location. A dual sample set is one TTHM and one HAA5 sample that is taken at the same

time and location.

5 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

As described in previous chapters, the monitoring requirements for producing systems are

based on the number of plants. The Stage 2 DBPR does not define a plant, but does specify the

following:

• Consecutive system entry points receiving disinfected water for at least 60 consecutive

days must be considered a plant (40 CFR 141.602(a))

• Multiple entry points or multiple wells drawing from the same aquifer may be considered as

one plant (40 CFR 141.601(d)) 
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Example 8.1 Less Required than Entry Points in the Systems

A 100 percent purchasing system receives ground water from two wholesalers and serves

300,000 people. Approximately 70 percent of the system’s water is purchased from Wholesaler A, the

remaining 30 percent from Wholesaler B. The IDSE SMP requirements for this system include one

near-entry point site (see Table 8.1). This system should locate its near-entry point site near the

Wholesaler A consecutive system entry point.

For guidance purposes, any location where disinfected water enters the distribution system should be

considered a “plant”. See Chapter 1, section 1.1 for guidance on determining number of plants in a

system.

8.2.1 Near-Entry Point SMP Sites

The rule does not have specific location requirements for near entry point sites. EPA

recommends locating these sites between the treatment facility or consecutive system entry point and

before or near the first customer. Data from this site represent the minimum residence time and can be

used as a baseline for interpreting changes in water quality as water travels through the distribution

system. DBP data from near-entry point sites can also be used to identify opportunities for

improvements at the treatment plant. 

The next two sections provide additional guidance for selecting near-entry point SMP sites.

8.2.1.1 Near-Entry Point SMP Sites for 100 Percent Purchasing Systems

As indicated in Table 8.1, the number of near-entry point sites required for 100 percent

purchasing systems depends only on the source water type and population served. As a result, a

situation may exist where a system has more or less actual consecutive system entry points than the

number of near-entry points sites required by Table 8.1 or Table 8.2. If this occurs, the rule requires

the following adjustments (40 CFR 141.6022(b)):

• If the required number of near-entry point SMP sites is less than the actual number of

consecutive system entry points, first select sites at the entry points delivering surface water

in order from the highest to lowest flow, then select sites at the entry points delivering

ground water, in order from the highest to lowest flow, until the required number of SMP

sites have been identified. (See Example 8.1.)

• If the required number of near-entry point SMP sites is more than the actual number of

consecutive system entry points, the “excess” near-entry point sites must be distributed
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A

B

C

D

From Big City WTP Your City Distribution System

A

B

C

D

From Big City WTP Your City Distribution System

Example 8.3 Multiple Entry Points on One Transmission Line

Your City receives water from

Big City through a single transmission

main with multiple consecutive system

entry points (A, B, C, and D) and little

difference in average flows. The State

has determined these entry points are

a single source and the estimated

water age at each entry point is

similar. In this case, A, B, C, or D

would be acceptable and should be

among high TTHM and high HAA5 sites so that the total number of SMP sites is met. 

These excess sites must be distributed in the order of high TTHM, high HAA5 . (see

Example 8.2.)

Multiple Entry Points Considered as One Plant

Multiple consecutive entry points may be considered a single plant with approval from the State

(40 CFR 141.601(d)). There is no provision in the rule designating which entry point must be used to

locate the near-entry point site. A location near any entry point or prior to the first group of customers

for any one entry point should be acceptable. However, if the average flow differs significantly between

the entry points, you should consider using the entry point with the greatest flow to locate your nearentry point SMP site. (See Examples 8.3 and 8.4.)

Example 8.2 Excess Near-entry Point Site Requirements

A 100 percent purchasing system receives surface water from three wholesalers and serves

550,000 people. The IDSE SMP requirements for this system include six near-entry point sites (see

Table 8.1), but the system has only 3 consecutive system entry points. This system must select 3

near-entry point sites. According to the rule stated above, the remaining 3 near-entry point sites

would be distributed as follows: 2 high TTHM sites and 1 high HAA5 site.
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A

B

C

Your City Distribution System

From Big City WTP

Example 8.4 Multiple Entry Points with Different Flows

Your City receives water from Big City at three consecutive system entry points (A, B and C). 

Entry points A and B are branches of a common main; entry point C is off a separate main. The State

has determined these entry points are a single source and the estimated water age at each entry point is

similar. 50 percent of Your City’s water enters through A, 20 percent through B, and 30 percent

through C. Your city selects a near-entry point SMP site near A because the majority of water enters

through this entry point.

8.2.1.2 Near-Entry Point SMP Sites for Producing Systems

The rule requires producing surface water systems that serve at least 10,000 people to select

near-entry point sites depending on the total number of plants in the system and the residual disinfectant

type (40 CFR 141.602 (a)) (see Table 8.2). 

• Chlorinated systems must select one near-entry point SMP site per plant

• Chloraminated systems must select two near-entry point SMP sites per plant

The requirements differ between chlorinated systems and chloraminated systems because DBP

formation differs under chloraminated and chlorinated conditions. Chloramine residuals are more stable

than chlorine residuals and, therefore, do not react as readily with organic compounds in the water. 

Based on evaluation of Information Collection Rule (ICR) data, DBP concentrations in chloraminated

systems vary less throughout the distribution system than in chlorinated systems. HAA5, in particular,

can peak at or near the entry point to the distribution system in a chloraminated system. (Appendix B

describes DBP formation in more detail.) As recommended in the beginning of section 8.2.1, any sites

between the treatment facility (or entry point) and a first group of customers should be acceptable for

chloraminated systems.
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Well #1

A

B

First group of 

customers for 

Well # 1

Well #2

First group of 

customers for Well # 2

Example 8.5 Multiple Entry Points

The system has two wells which the State

determined were drawing from the same aquifer and

could be considered as one plant. Site A or Site B

would be acceptable for their near-entry point site.

Ground Water Wells or Multiple Entry Points Considered as One Plant

Multiple ground water wells drawing from one aquifer and delivering disinfected water directly

to the distribution system may be considered a single plant with approval from the State. Locations

prior to the first group of customers of any well are an acceptable near-entry point SMP site. Similarly,

for multiple consecutive entry points considered as a single plant, any entry point would be acceptable

for a near-entry point SMP site. (See Example 8.5.)

8.2.2 Average Residence Time SMP Sites

Sites with average residence time should represent the average water age that is delivered to

the majority of customers in the distribution system. In most distribution systems, average residence

time is not simply one-half the maximum residence time. Ideally, it should be a flow-weighted or

population-weighted average residence time. EPA recognizes that determining this value is very

complex and, at best, most systems can only make a rough estimate. Section 8.4 provides

methodologies for estimating average residence time with various types of data and tools.

8.2.3 High TTHM and High HAA5 Sites

It is not the intent of the SMP to identify peak daily or hourly DBP concentrations. Instead,

high TTHM and high HAA5 sites should be chosen to represent areas in the distribution system with

the highest annual average DBP concentrations. Higher temperatures and increased residence time

typically lead to higher TTHM and HAA5 concentrations. However, HAA5 can biodegrade when

disinfectant residual levels are low or non-existent and, therefore, a high HAA5 site may not be the site

with the longest residence time. These principles are the basis of the guidance provided for selecting

high TTHM and high HAA5 SMP sites. Table 8.3 summarizes the typical characteristics of distribution
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July 2003 - Proposal Draft 8-9 All Systems

system areas with high TTHM and high HAA5 levels. Section 8.4 further describes how data sources

and analysis tools can be used to identify these areas in the distribution system.

Table 8.3 Summary of Characteristics of High TTHM and High HAA5 Areas

Area Characteristics

High TTHM S Long residence time (e.g. remote areas with few customers or low water

demand)

S Low or no disinfectant residual, also high heterotrophic plant count (HPC) or

history of positive coliform

S Downstream of storage facilities

S Areas with historical data showing high TTHM

High HAA5 S Residence time can vary

S Low but existing disinfectant residual (to prevent biodegradation)

S May be downstream of storage facilities

S Areas with historical data showing high HAA5

Note: These are only general characteristics; DBP formation in distribution systems is system-specific.

8.3 Considerations for Systems with More than One Plant or Entry Point

This section describes how systems with multiple plants or entry points should distribute the

sites with respect to the influence zone of each plant or entry point. 

8.3.1 100 Percent Purchasing Systems with More Than One Consecutive System

Entry Point

The 100 percent purchasing systems are not required to assign SMP sample sites to the

influence zone of a particular entry point. When selecting average residence time and high TTHM/high

HAA5 SMP sites, 100 percent purchasing systems should consider the quantity and quality of water

received at each consecutive system entry point. For example, if one entry point supplies 75 percent of

the water then more SMP sites should be located in the influence zone of that supply. Geographic

distribution of SMP locations should also be considered. Examples 8.6 and 8.7 illustrate how sites

could be distributed with respect to multiple entry points.
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LEGEND

SMP Sample Site

Storage Tank 

Oakville WTP 

Entry Point 

(25%)

Mapleton WTP 

Influence Zone Oakville WTP 

Influence Zone

Mapleton WTP 

Entry Point

(75%)

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

A

A

A

H H

H

T

T

T

T

LEGEND

SMP Sample Site

Storage Tank 

Oakville WTP 

Entry Point 

(25%)

Mapleton WTP 

Influence Zone Oakville WTP 

Influence Zone

Mapleton WTP 

Entry Point

(75%)

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

A

A

A

H H

H

T

T

T

T

Example 8.6 Large and Small Surface Water Entry Points

Your City is a 100 percent purchasing system serving 30,000 people and purchases

chlorinated water from two surface water wholesalers (Mapleton and Oakville). Your City is

required to identify 12 SMP sites (from Table 8.1—2 near-entry points, 3 average, 4 high TTHM,

and 3 high HAA5 sites). On average, Mapleton supplies Your City with 75 percent of its water;

while Oakville provides only 25 percent. The water quality from each is similar. 

Site selection rationale:

Based on the average flow split and similar water quality, approximately 75 percent (9) of

the sites should be in the influence zone of the Mapleton supply and the remaining 25 percent (3)

should be in the influence zone of the Oakville source. As shown in the schematic, in order to

achieve a good geographic coverage of the distribution system, 2 of the Mapleton sites are located in
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Deep Rock Well 

Entry Point 

(60%)

Lory RiverWTP

Influence Zone Deep Rock Well 

Influence Zone

Lory River WTP 

Entry Point

(40%)

LEGEND

SMP Sample Site

Storage Tank 

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

LEGEND

SMP Sample Site

Storage Tank 

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

A

A

A

H

H

H

T

T

T

T

Example 8.7 Surface Water and Ground Water Entry Points

Your City is a 100 percent purchasing system serving 48,000 people with purchased water

from two water wholesalers. The Lory River WTP supplies 40 percent of the demand with surface

water. The Deep Rock well supplies 60 percent of the demand with ground water. Your City is

required to identify 12 SMP sites as follows: 2 near-entry point, 3 average residence time, 4 high

TTHM, and 3 high HAA5.

SMP selection rational:

More sites are placed within the influence area of the Lory River WTP because it is a

surface water source and thus, more likely to have higher DBP levels.
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8.3.2 Producing Systems with More than One Plant

As indicated in Table 8.2, the rule specifies the number of SMP sites for each plant. For most

systems, the distribution areas of the plants are not distinctly separate. However, systems can usually

identify the primary influence zones of each plant and should use these zones to assign SMP sites. 

Recognizing that the boundaries of influence zones can overlap and change on a daily, hourly, and

seasonal basis, SMP sites should be chosen within the typical (during normal operating mode) influence

zone boundaries, as best can be determined.

Once sample sites have been selected based on the typical influence zone boundaries, the

samples must be collected as scheduled, regardless of the actual source of water serving the site at

the time of sampling (40 CFR 141.602(c)). If it is suspected or known that the source of water

supplying a particular SMP site is different during sample collection, then this should be noted and taken

into consideration when evaluating the results of the SMP. However, identification of the source of

supply to each sample site during each sampling event is not required.

Where overlap exists between two or more influence zones, the water quality, quantity, and

operating characteristics should be considered when locating SMP sites. There are numerous scenarios

that could exist when a distribution system is supplied with water from more than one plant. The

following sections provide general guidance and examples for four specific scenarios:

• One plant produces the majority of the water (Example 8.8)

• One plant supplies water with much higher TTHM/HAA5 concentrations than the other

plant(s) (Example 8.9)

• The system purchases water for less than 60 consecutive days per year (Example 8.10)

• The system has a seasonal source of water (used at least 60 consecutive days per year, but

less than 100 percent of the time) (Example 8.11)

The guidelines for these four scenarios are general and will not apply to all systems and all

situations; you should always use best professional judgement when selecting SMP sites.

One Plant Supplies the Majority of the Water

In systems where one plant delivers substantially more water than another, an equal distribution

of sites within influence zones may result in disproportionate coverage of the distribution system. That

is, the sites representing a large treatment plant must cover a wider geographic area than the sites

representing a smaller plant. Example 8.8 illustrates this situation and provides an SMP selection

approach that maximizes coverage of the distribution system while still locating SMP sites for each plant

in the appropriate zone of influence. In the example, SMP sites required for the smaller plant are used
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Red SW 

treatment plant Well #1

Well #2

Red Plant 

Influence Zone

Legend

Red plant SMP Site

Green plant SMP site

 ̈ Well 

Green Plant 

Influence Zone

 ̈

 ̈

E- Entry Point

A – Average

T – High TTHMs

H – High HAA5

H

H

H

H

E E

A

A

A

A

T

T

T

T

T

T

Example 8.8 Producing System with One Large and One Small Plant

A system supplying 12,000 people has 2 chlorinated plants, Red and Green. The Red plant

is a surface water treatment plant that provides 8 MGD. The Green plant is supplied by 2 wells

drawing from the same aquifer, produces 1 MGD, and has been approved by the State as drawing

from a common aquifer. Generally, the Green plant supplies the east area of the distribution system

and the Red plant supplies all other areas. From Table 8.2, a total of 8 SMP sites for each plant are

required for mixed surface and ground water systems.

Site selection rationale:

For both plants, the 8 required SMP sites are located in the influence zone of the respective

plant. Because the Green plant has a much smaller influence area, Green’s sites are selected to cover

the overlapping mixing zone, thus allowing the 8 Red sites to cover the larger Red influence zone. 

This arrangement of sites respects the requirement to locate sites within individual plant influence

to cover the entire area of the overlapping influence zones; SMP sites for the large plant are located

exclusively in the influence zone of the large plant.
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One Plant Supplies Water with Much Higher DBP Concentrations Than the Others

Systems should also consider quality of water when locating SMP sites. The overall objective

of the IDSE SMP is to identify sites in the distribution system where water with representative high

TTHM and HAA5 concentrations is delivered to customers. If you suspect that the high TTHM and/or

high HAA5 sites will be in the influence zone of a particular plant on more than a seasonal basis, you

should locate SMP sites to maximize coverage in that influence zone. Example 8.10 shows how SMP

sites can be located when one source is suspected of having high TTHM/HAA5 concentrations.
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Riverdale WTP 

Influence Zone

LEGEND

Riverdale SMP Sample Sites

Spring Hills Sample Site 

Riverdale WTP 

(60%)

Spring Hills WTP 

Influence Zone

Spring Hills WTP 

(40%)

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

T

T

T T

T

T

H

H

H

H

A

A

A

A

Riverdale WTP 

Influence Zone

LEGEND

Riverdale SMP Sample Sites

Spring Hills Sample Site 

Riverdale WTP 

(60%)

Spring Hills WTP 

Influence Zone

Spring Hills WTP 

(40%)

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

T

T

T T

T

T

H

H

H

H

A

A

A

A

Example 8.9 Producing System with One High- and One Low-DBP Plant

Your City is a producing system serving 85,000 people. Your City operates 2 plants—

Riverdale (a surface water plant with moderate to high source water TOC levels) and Spring Hills (a

low-TOC ground water plant). Riverdale provides approximately 60 percent of your daily demand

and Spring Hills the remaining 40 percent. Both plants use free chlorine for primary and secondary

disinfection.

From Table 8.2, Your City is required to select 8 SMP sample locations for each treatment

plant (a total of 16 sites). Since the Spring Hills supply is likely to have lower DBP concentrations

than the Riverdale supply, locate the Riverdale SMP sites exclusively in the Riverdale influence zone

and use the Spring Hills SMP sites to cover the mixing zone.
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Emergency Connections (Used Less Than 60 Consecutive Days per Year)

Consecutive entry points used on a temporary basis that provide water for less than 60

consecutive days per year are not considered to be “plants” under the IDSE SMP requirements

(141.602 (d)(2)). In other words, systems do not have to identify near-entry point, average residence

time, or high TTHM/HAA5 SMP sites for these entry points. However, typical water demand patterns

in the area of the distribution system supplied by the temporary source (influence zone) should be

considered when locating SMP sites (see Example 8.10).

Example 8.10 Producing Systems with Temporary Sources

• A large surface water system buys water during the highest temperature month(s) from a

system with a low-TOC ground water source. In this case, SMP sites should not be

located in the influence zone of the temporary source; focus should be on other areas of

the distribution system. The reason for this is the influence zone of the temporary source is

likely to have lower DBP concentrations than areas served by the surface water supply.

• A large surface water system buys water that is low-TOC ground water source, but not

during the highest temperature month(s). In this case, you should consider locating SMP

sites in the influence zone of your temporary source because the zone will be more

representative of your surface water source during the highest temperature month. This is

particularly applicable if you believe the area has high TTHM or high HAA5 levels when it is

supplied by your normal surface water supply. You should be cognizant, however, of which

source is providing the water that you are collecting during your SMP. If you collect a

sample that is not representative of your surface water source, you should note this

information in your IDSE report and consider that when selecting final Stage 2B DBPR

compliance monitoring sites (see sections 8.6 and 8.7 for guidelines for selecting Stage 2B

DBPR compliance monitoring sites and completing your IDSE report).
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Purchasing Water on a Part-time Basis (Used at Least 60 Consecutive Days per Year)

If a system buys water from a wholesale system on a part-time or seasonal basis, for more than

60 consecutive days of the year, the source is considered to be a “plant” under the IDSE SMP

requirements (141.602 (d)(2)). As with plants operating year-round, the SMP sites for a seasonal

plant should be located in the influence zone of that plant. Although the seasonal plant would not be

providing water to the SMP sites all the time, the SMP sampling sites should not be modified once

sampling has begun (SMP sites should remain fixed for the 1-year monitoring period).

Even if water from a seasonal plant is known to have low DBP concentrations relative to water

provided by other plants (e.g., a seasonal ground water supply in a surface water system), the eight

sites for the seasonal plant should still be selected within the influence zone of that plant. DBP data of

all plants are important in evaluating the entire distribution system.

Example 8.11 illustrates the SMP site selection for a large producing system that operates two

surface water plants and purchases water during the summer to meet increased seasonal demands. 
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Purchased Water 

Influence Zone

Elm Plant 

Influence Zone

Maple Plant 

Influence Zone

Legend

Maple plant SMP Site 

Purchased water entry 

point SMP site 

Elm plant SMP site

Maple SW 

treatment plant

Elm SW 

treatment plant

Entry point for 

purchased water

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

E

H

H H

H

H

T

T

T

T

T

T

T

T

T

H

A

A

A

A

A

A

Purchased Water 

Influence Zone

Elm Plant 

Influence Zone

Maple Plant 

Influence Zone

Legend

Maple plant SMP Site 

Purchased water entry 

point SMP site 

Elm plant SMP site

Purchased Water 

Influence Zone

Elm Plant 

Influence Zone

Maple Plant 

Influence Zone

Legend

Maple plant SMP Site 

Purchased water entry 

point SMP site 

Elm plant SMP site

Legend

Maple plant SMP Site 

Purchased water entry 

point SMP site 

Elm plant SMP site

Maple SW 

treatment plant

Elm SW 

treatment plant

Entry point for 

purchased water

E – Entry Point

A – Average

T – High TTHMs

H – High HAA5

E

E

E

H

H H

H

H

T

T

T

T

T

T

T

T

T

H

A

A

A

A

A

A

Example 8.11 Producing System with Seasonal Plants

A system serving chlorinated water to 55,000 people has three plants: Maple plant (6 MGD

surface water), Elm plant (3 MGD surface water), and purchased water from a neighboring city (2

MGD in summer only—for more than 60 consecutive days).

Site selection rationale:

The Maple plant and Elm plant influence zones mostly overlap; together, their sites cover the

entire area except the influence zone of the purchased water. Although the system only purchases

during the summer, those sites will be sampled during the entire 1-year SMP sampling period and will

represent the surface water plants’ water quality for a majority of the year.
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Tracer Studies

System 

Operating Data

Hydraulic Model

Maps 

Geographic 

Information 

System (GIS)

SDS Tests

Water Quality 

Data

Tracer Studies

System 

Operating Data

Hydraulic Model

Maps 

Geographic 

Information 

System (GIS)

SDS Tests

Water Quality 

Data

8.4 Data Sources and Tools for Identifying Preliminary SMP Sites

Several sources of information can be used to help select SMP sites that represent average

residence time, high TTHM, and high HAA5 concentrations (see Figure 8.1 below).

Figure 8.1 Data Sources and Tools for Selecting SMP Sites

These data sources and tools are best applied in combination with each other. For example, a

map is critical in assessing geographic and population coverage; however, it is of limited use when used

alone to identify average residence time or high HAA5 sites.

Generally, data used to identify SMP sites should be less than 10 years old and represent the

current distribution system and treatment plant(s) configuration. Chapter 3 discusses the quality of data

recommended for use in a historical data-based SSS. 

This section describes how each data source can be used to identify preliminary SMP sites

representing high TTHM, high HAA5, and average residence time. Section 8.5 presents step-by-step

methodologies for using combinations of these data sources to select final SMP sites.
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8.4.1 Maps

Map features that may be helpful in selecting SMP sites include:

• Length and diameter of pipes

• Age of pipes

• Pressure zone delineations with

valving identified

• Location of distribution system

pumping stations

• Location and configuration of

storage facilities

• Location of fire hydrants and flush valves

• Existing land use

• Population density

• Location of booster disinfection stations

• Entry points with source type noted

• System boundary lines

8.4.1.1 High TTHM and High HAA5 Sites

Generally, areas with light development, with low residential population density, or between

pressure zones that are furthest away from the treatment plant(s) are likely to have the longest residence

times. Therefore, these areas have potentially high TTHM concentrations and, provided there is a

detectable disinfectant residual, high HAA5 concentrations.

In general, sites at the very end of a distribution system main with no customers should not be

selected:

• In many distribution systems, there may be no customers at the actual physical end of some

dead-end sections of a water main. Water quality at this type of location is not truly

“representative” of water in the distribution system that is delivered to customers.

High TTHM (and in some cases HAA5) SMP sites should be generally located near the ends of the

distribution system at or before the last group of customers or in mixing zones.

Sample sites should be located prior to the last fire hydrant.

Sample sites should not be located at a dead-end where there are no customers.
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• High TTHM and, in some cases, high HAA5 SMP sites should generally be chosen near

the end of the distribution system at the last group of customers or in mixing zones where

“hydraulic dead-ends” might occur. Samples should always be collected at locations prior

to (upstream of) the last fire hydrant.

Storage facilities in a distribution system increase water age. During tank drain cycles, water

age immediately downstream of a storage facility may be significantly (e.g., several days or more) older

than “fresh” water upstream of the storage facility. As a result, areas of a distribution system receiving

water that has been stored may have higher TTHM and HAA5 concentrations than areas that do not

receive any stored water. Therefore, you should generally locate your high TTHM sites and, in some

cases, high HAA5 sites downstream of storage facilities.

8.4.1.2 Average Residence Time Sites

Average residence time is the average age of water delivered to the majority of customers in a

distribution system. Estimating average distribution system residence time based solely on maps can be

difficult and requires a thorough understanding of your distribution system. Under ideal circumstances,

maps are just one tool that can be combined with other data and tools (e.g., disinfectant residual data,

hydraulic modeling) to identify areas that are representative of average water age. These other data

and tools are discussed further in sections 8.4.2 through 8.4.7. 

Approximate average residence time areas can be identified by looking for service areas with

the most development. If a few large customers exist in a system, then their location should be

identified and the effect of water flowing to them taken into consideration. In many systems that do not

have large individual customers, highly developed areas in the approximate geographic center of the

distribution system are potential average residence time sites.

8.4.2 Distribution System Water Quality Data

Systems routinely sample for various water quality parameters as required by regulations or for

operational purposes. A review of recent historical DBP and/or disinfectant residual data (free chlorine

or chloramine) can be very useful in the selection of SMP sample sites.

8.4.2.1 Disinfectant Residual Data

Because chlorine and chloramines decay over time, low disinfectant residuals relative to those

leaving the treatment facility (or entering through a consecutive system entry point) can generally be
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Sources of disinfectant residual data:

- TCR data

- Stage 1 DBPR data (for some systems)

- Operational sample sites

- Sampling in response to customer complaints

considered an indicator of increased water

age. A review of disinfectant residual data

from existing distribution system monitoring

sites can help identify the areas of your

system with the highest residence time and

those with average residence time. Sources

of disinfectant residual data may include

regular compliance monitoring sites (e.g.,

Total Coliform Rule (TCR) or Stage 1 DBPR monitoring sites), operational sample sites, or special

sites sampled in response to customer complaints. Combining the data from these various sample sites

may help you better understand the change in disinfectant residual as water flows through your

distribution system and, consequently, help you choose the required SMP sample sites.

There are cases, however, where lower disinfectant residuals do not necessarily indicate greater

water age. Common factors that can influence disinfectant residual decay and affect the relationship

between residual levels and water age are:

• Pipe material and internal lining

• Corrosion condition in the pipe

• Biofilm growth in the pipe

• Accumulation of sediment in the pipe

• Booster disinfection

In particular, use of disinfectant residual data becomes difficult when booster disinfection is

applied. Booster disinfection is the practice of adding a disinfectant in the distribution system to raise

the disinfectant residual concentration and is commonly used in peripheral zones of the distribution

system or near storage tanks where water age may be high and disinfectant residuals are low. TTHM

and HAA5 levels are likely to increase after a booster disinfectant is applied. Additional TTHM and

HAA5 may be formed due to the greater concentration of disinfectant available for reaction with DBPs

precursors. Furthermore, the additional disinfectant prevents the biological degradation of HAA5, thus

favoring their accumulation in the areas of the distribution system affected by booster chlorination.

If your system does not have much disinfectant residual data, or if you are not able to identify

sites with average or high residence times based on your existing data, you may want to collect

additional disinfectant residual data from your system to better characterize your system and provide a

better basis for selecting SMP sites.
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1) High TTHM and High HAA5 Sites

Booster Disinfection

If your system uses booster disinfection continuously or intermittently, the high TTHM and

HAA5 sites should not be located before a booster disinfection station.

Low Disinfectant Residual Relative to System Average

Low disinfectant residuals relative to the system average generally indicate longer residence

times, and may correlate with higher TTHM and HAA5 concentrations. Very low or no disinfectant

residual, however, could also indicate biological decay of HAA5, and should generally not be chosen

as your high HAA5 site.

• When selecting preliminary high HAA5 sites, locations with free chlorine residuals less than

0.2 mg/L or chloramine residuals less than 0.5 mg/L should not be selected because of the

potential for biodegradation of HAA5.

• High HAA5 sites should have no significant increase in recorded HPCs to ensure a low

potential for HAA5 biodegradation. If you have HPC data, a comparison of disinfectant

residual and HPC data can help you more precisely determine the threshold disinfectant

residual below which HPC levels begin to increase. However, HPC testing is not required

as a part of the IDSE.

Review Disinfectant Residual Data from the Warmer Months

Because disinfectant residuals typically decay faster during the summer, a review of data from

the summer months may be more useful in identifying areas with consistently low residuals. During the

winter, disinfectants are usually more persistent, and residuals can often be maintained in relatively old

water within a distribution system. The correlation between residence time and residual decay is less

pronounced in the colder months.

2) Average Residence Time Sites

One of the best ways to calculate average residence time is by using a hydraulic model (see

Chapter 3 for information on hydraulic modeling). However, if this tool is not available, calculating the

average disinfectant residual in your distribution system can help you identify locations with average

water residence time (this method is not valid for areas in the influence of booster disinfection). When

calculating average disinfectant residual, it is important that you use data from sites that are

representative of your entire distribution system. One way to do this is to limit data to those collected at

your TCR monitoring sites (the TCR requires that all monitoring sites combined represent the
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distribution system). Use of historical data or other data (e.g., data from customer complaints) could

skew the results if a large portion of the data are from a single area.

Assuming your disinfectant residual data are representative of your distribution system, the

following analysis of TCR monitoring data can be used to help identify sites with average residence

time:

1) Calculate an average disinfectant residual at each of your TCR sites using data from your

warmest months (chlorine decay is more pronounced in warmer temperatures so you are

more likely to see larger changes in chlorine residual from one point to the next).

2) Using averages from the individual sites, calculate an overall distribution system average

residual concentration. 

3) Those sites with an average residual close to the distribution system average can be

considered representative of average residence time in the distribution system.

Note, if your system has booster disinfection, then residual data collected after those locations

will skew this analysis. You should either omit that data or estimate what the residual would be without

the added disinfectant. 
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 Monthly Average (mg/L)

Jun Jul Aug

#1 1.4 1.3 1.6 1.4

#2 0.7 0.9 0.7 0.8

#3 1.0 0.9 1.2 1.0

#4 0.6 0.6 0.7 0.6

#5 0.9 1.2 1.4 1.2

#6 0.4 0.5 0.4 0.4

#7 0.2 0.3 0.6 0.4

#8 1.5 1.7 1.7 1.6

#9 0.9 0.7 0.8 0.8

#10 0.5 0.3 0.8 0.5

Distribution 

System Ave

0.8 0.8 1.0 0.9

Site Average 

(mg/L) Site ID

Example 8.12 System Average Disinfectant Residual Calculation

A system with June, July, and August as their warmest months has the residual data below. 

The averages for the system and each site are calculated as shown. Note that sites #2, #3, and #9

have average chlorine residual concentrations close to the system average.
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8.4.2.2 DBP Data

Non-compliance DBP (TTHM and HAA5) data, collected in addition to your Stage 1 DBPR

compliance monitoring data, can be useful in selecting high TTHM and high HAA5 SMP sites. 

Remember, however, that Stage 1 DBPR compliance monitoring sites cannot be used as SMP sites

(141.602(b)). For surface water systems, historical DBP data should be evaluated with respect to raw

water quality conditions before and during the sampling period (e.g., changes in TOC concentration

from year to year can significantly affect DBP levels). DBP data should not be used for the purpose of

estimating average residence time because DBP formation is complex and dependent on many factors. 

(See Appendix B for a discussion of DBP formation.)

If your system has extensive non-compliance TTHM and HAA5 data at a variety of sites

throughout your distribution system, you may wish to consider completing an SSS based on your

historical data, possibly with a limited amount of new monitoring. See Chapter 3 if you think you may

be able to use historical data alone or in combination with other data for an SSS.

High TTHM and High HAA5 Sites

Regulatory compliance data (including all data collected under the Stage 1 DBPR) are not a

definitive source for identifying the representative high TTHM and HAA5 concentrations. There may

now be other areas with higher TTHM and HAA5 concentrations that have not been sampled or do

not have high historical results due to differences in flow or water quality at the time of sampling. 

Therefore, historical data should always be used in conjunction with other data sources and tools. 

Results from a Simulated Distribution System (SDS) test can also be helpful in evaluating TTHM and

HAA5 data. (Section 8.4.3 describes the SDS test and how it can be used in conjunction with DBP

data to select SMP sites and Appendix D describes the recommended procedure for conducting the

SDS test.)

Good candidates for high TTHM and HAA5 sites include:

• Historic sample sites with high TTHM concentrations in areas with long residence times.

• Historic sample sites with high HAA5 concentrations in areas that consistently maintain a

disinfectant residual.

• Historic sample sites with TTHM/HAA5 concentrations that are close to the TTHM/HAA5

concentration from an SDS test for maximum residence time.
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8.4.3 Simulated Distribution System Laboratory Test

An SDS laboratory test is another tool that can be used in conjunction with Stage 1 DBPR

compliance monitoring or other DBP data to select SMP sites. In the SDS test, finished water samples

are collected (generally at system entry points) and stored for selected periods of time at chemical and

environmental conditions simulating those occurring in the distribution system (e.g., temperature and

pH). These samples are analyzed for TTHM and HAA5 concentrations at the end of the selected

holding time. Appendix D describes the recommended procedures for conducting an SDS test. Note

that this procedure would have to be modified if a system has a booster disinfection station.

One use of an SDS test is to confirm that existing Stage 1 DBPR or other DBP monitoring sites

represent the maximum water residence time. For this purpose, SDS samples should be collected in

conjunction with (preferably on the same day or 1 to 3 days before) the DBP samples collected from

the distribution system. At least one SDS sample should be stored for a period of time approximately

equal to the maximum residence time, then analyzed for TTHM and HAA5 concentrations. (Note: an

SDS sample must have a detectable disinfectant residual at the end of the holding time.) It would

also be useful in evaluating results to hold an SDS sample for a period of time equal to your average

system residence time. If your maximum residence time is more than 5 days, a third SDS test, at a

residence time between the average and maximum residence time, is recommended. All SDS samples

should be stored at the same temperature as the distribution system water (see Appendix D for

suggested procedures).

If distribution system TTHM of HAA5 results are equivalent to or higher than the SDS

maximum residence time TTHM or HAA5 results, you can infer that the site is likely representative of

high TTHM or HAA5 levels. Remember that you cannot use Stage 1 DBPR sites for the SMP;

however, you may wish to investigate other locations with similar hydraulic and disinfectant residual

characteristics for your high TTHM SMP sites (and high HAA5 sites if they meet other criteria). 

Examples 8.13 and 8.14 demonstrate how SDS test results and data from Stage 1 DBPR and

operational monitoring sites can be used to select SMP sites.
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Example 8.13 Using the SDS Test to Evaluate Operational Monitoring

Locations (Big City Water)

Big City Water has collected the following distribution system data and SDS test results. 

Sample Location/Type TTHM (μg/L) HAA5 (μg/L)

SDS at Maximum Residence Time178 46

Stage 1DBPR Max Residence Time #1 75 45

Stage 1DBPR Max Residence Time #2 71 35

Operational Location #1 79 43

Operational Location #2 40 50

Operational Location #3 80 45

Operational Location #4 61 50

Note: In this example, the SDS sample was collected on a Monday; distribution system samples were

collected during that week.

1 Maximum residence time determined using the results of a previously conducted tracer study.

Based upon the SDS results for Big City presented above, the following conclusions can be drawn:

• Stage 1 DBPR max residence time #1 most likely represents high TTHM and

HAA5 concentrations.

• Stage 1 DBPR max residence time #2 may represent high TTHM, but not HAA5

(possible biodegradation).

• Operational locations #1 and #3 most likely represent high TTHM and HAA5

concentrations.

• Operational locations #2 and #4 represent only high HAA5 concentrations.

For this example, high TTHM SMP sites should be located in areas with similar characteristics to

Stage 1 DBPR max residence time #1 and #2, or operational locations #1 and #3. High HAA5

sites should be located in areas with similar characteristics to operational locations #2 and #4 (as

long as there is a disinfectant residual concentration).
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Example 8.14 Using the SDS Test to Evaluate Operational Monitoring

Locations (Blue Ridge Water)

Blue Ridge Water has the following SDS and distribution system data.

Sample Location/Type TTHM (μg/L) HAA5 (μg/L)

SDS at Maximum Residence Time1100 67

Stage 1DBPR Max Residence Time #1 98 55

Stage 1DBPR Max Residence Time #2 72 58

Operational Location #1 65 45

Operational Location #2 95 62

Operational Location #3 91 72

Operational Location #4 80 62

Note: In this example, the SDS sample was collected on a Monday; distribution system samples were

collected during that week.

1 Maximum residence time calculated using an hydraulic model.

Based upon the SDS results for Blue Ridge presented above, the following conclusions can be

drawn:

• Stage 1 DBPR max residence time #2 may not be representative of high TTHM

concentrations.

• Operational locations #2 and #3 most likely represent high TTHM and HAA5

concentrations.

• Operational location #4 represents only high HAA5 concentrations.

For this example, high TTHM SMP sites should be located in areas with similar characteristics to

Stage 1 DBPR max residence time #1 or operational locations #2 and #3. High HAA5 sites

should be located in areas with characteristics similar to operational location #4 (as long as there

is a disinfectant residual concentration and no evidence of bacteriological activity).
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SDS results must viewed with caution. Distribution system conditions are complex and cannot

be perfectly replicated in the laboratory, so some error is expected. Also, if you do not have a good

idea as to your true maximum distribution system residence time, your SDS results may indicate your

Stage 1 DBPR sites are inadequate when, in fact, they are representative of maximum residence time. 

Similarly, if the SDS test conditions are not representative to the treatment (i.e., source and finished

water quality) and distribution system conditions, the test results can be misinterpreted. If your system

uses booster chlorination, the SDS test should be run for a finished water sample and a sample taken

after the addition of the booster disinfectant dose.

Another use of an SDS test is to help describe DBP formation in the distribution system and, in

conjunction with Stage 1 DBPR compliance monitoring and other data, determine average and

maximum residence time. Appendix D describes how SDS tests can be used to estimate average and

maximum residence time using DBP and chlorine residual data.

8.4.4 Models

A water distribution system model is a computer program that simulates the hydraulic behavior

of water in a distribution system. Water distribution system models are widely used in the water

industry for planning and operations. Several public domain and commercial software modeling

packages are available. For instance, EPA developed a water quality modeling software package,

EPANET, that is available without charge via the internet. Your water distribution system model should

be adequately calibrated when selecting SMP sample sites (see Chapter 3 for a discussion of model

calibration).

A water distribution system hydraulic model can predict water age in a distribution system when

it is run under extended period simulation conditions (i.e., water production, demand, etc., are allowed

to change over time). In addition, most models can track the movement of water from each plant or

supply point through the distribution system. Model results can provide a picture of the influence zone

of each entry point and identify blending zones.

The size of your system and the degree of skeletonization of your hydraulic model will

determine how useful the model can be for selecting SMP sites. Skeletonization refers to the degree of

detail relating to distribution system piping in your model. Highly skeletonized models may only show

large distribution mains and omit much of the smaller piping in individual subdivisions or other areas of

the distribution system. In such cases, highly skeletonized models may be of limited use in large systems

To obtain a free copy of EPANET go to:

http://www.epa.gov/ordntrnt/ORD/NRMRL/wswrd/epanet.html
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where small pipes account for significant localized increases in system residence time. Because

hydraulic models usually are somewhat skeletonized and have varying degrees of calibration and

accuracy of demand allocation, best professional judgement should always be used when analyzing the

results and using model outputs to assist in the selection of preliminary sites.

It is highly recommended that existing, calibrated water distribution and water quality models be

used to estimate water age, identify influence zones, and identify mixing zones to help select SMP

sample sites. If a model does not already exist, the time and expense to create a new model and train

staff solely for use in selecting IDSE SMP sample sites may not be justified. Model development or

enhancement may be justified if you intend to employ the model for other uses in addition to the

selection of SMP sample sites.

If you have an existing, detailed, well calibrated distribution system model, as well as

appropriately trained staff to operate the model and evaluate results, you may wish to consider

completing an SSS based on the use of your model and a limited amount of new testing. Chapter 3

describes the requirements for an SSS using a water distribution system model.

8.4.4.1 High TTHM Sites

Water distribution system modeling software can be used to identify high residence time

locations (most often your high TTHM sites) when used in the Extended Period Simulation (EPS)

mode. When the run time of an EPS model is long enough to produce a consistent pattern of water age

values at all nodes, sometimes with repeating fluctuations due to diurnal variations in water demands,

then the water age values at the model nodes can be used for the purpose of identifying high residence

time locations.

One way to show high residence time locations is by color coding each model node according

to its residence time. High TTHM sites should be chosen from the area or areas of the distribution

system where the high residence time model nodes are located. The sample sites do not have to be

chosen at the exact location of a model node, just in the general area identified by the model results.

Precautions in using model data to select high TTHM/HAA5 sites include:

• If no water demand is applied to dead-end nodes in a model or if the water demand in a

dead-end is highly uncertain, the water age results for those nodes can be unrealistic and

meaningless.

• The accuracy of water age estimates from a model generally decreases as the model moves

from large diameter mains to small diameter mains to subdivision piping and dead-ends. 

This is due to the increasing uncertainty in water usage rates as one moves from large,

aggregate demands to smaller demands exerted by a few customers or a single customer.
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• If the model is skeletonized, the model results for high residence time areas should be

compared to maps of the actual distribution system piping and to actual customer locations

in those areas before sample sites are finalized in order to assure that the sample site is

representative of the actual distribution system and not just the skeletonized model in the

high residence time areas.

• Residence time is just one factor for identifying high TTHM sites and should be compared

with other distribution system data (e.g., disinfectant residual data) before making your

preliminary SMP site selections. 

Because water distribution system models usually are somewhat skeletonized and have varying degrees

of calibration and accuracy of demand allocation, best professional judgement should always be used

when analyzing the results and using model outputs to assist in the selection of preliminary SMP sample

sites.

Blending Zones

In some cases, there may be zones in the distribution system where water flowing from opposite

directions meet. This can occur in:

• Long, looping mains

• The interface of the influence zones of two or more different supply points

• Areas where different pressure zones meet within one system

This type of area is sometimes called a “blending zone” and may act as a hydraulic dead-end. 

Blending zones can occur anywhere in the distribution system, but they more often occur in the central

portion of a distribution system. If the water demand around the blending zone is low, then the water

age and TTHM and HAA5 concentrations could be high. Hydraulic models can be useful in locating

blending zones and identifying high TTHM or HAA5 locations within the blending zone.

8.4.4.2 High HAA5 Sites

The criteria and procedure for selecting preliminary high HAA5 SMP sites using a water

distribution system model is generally the same as that described for selecting high TTHM sites with one

important difference: the locations chosen to represent high HAA5 must have a detectable disinfectant

residual. HAA5 concentrations typically increase in distribution systems as water age increases but can

also decrease if disinfectant residuals are not present and biological activity is high. High HAA5 sites

should be chosen from locations with a high residence time and a detectable disinfectant residual.
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8.4.4.3 Average Residence Time Sites

Average residence time SMP sites can be selected from locations with residence times close to

the flow-weighted mean of all nodal residence times (or system average). As with selecting high

TTHM/HAA5 sites, color coding nodes by nodal residence time can be helpful. SMP sample sites

should be chosen from the area or areas of the distribution system where the nodal residence time is

close to the system average. The SMP sample sites do not have to be chosen at the exact location of a

model node, just in the general area identified by the model results.

8.4.5 Tracer Studies

Tracer studies can be used to determine actual water residence times in a distribution system

under specific conditions and are sometimes used to calibrate water distribution system models. They

are particularly useful for predicting water residence time in areas of a system where there is uncertainty

about true pipe diameters due to poor records or the buildup of corrosion deposits affecting system

hydraulics. When pipe diameters in a model are inaccurate, model predictions can be very different

from the actual hydraulic conditions in a distribution system.

You can perform a tracer study by monitoring the concentration of a conservative constituent

(i.e., a chemical that does not degrade over time) through the distribution system. Chemicals used for

tracers must not be harmful to people or the environment. Tracer chemicals can be substances that are:

• Specially injected or normally injected in the water for treatment purposes (e.g., 

hydrofluorosilic acid or sodium fluoride)

• Characteristic of the finished water (e.g., hardness, conductivity)

Before injecting any tracer, a baseline concentration of the tracer in the distribution system

water should be determined (fluoride, the most common tracer, may be normally present in trace

amounts). If your system adds fluoride, you can turn off the fluoride feed for a period of time, and

monitor the resulting decrease of its concentration throughout the distribution system.

If you do not routinely add fluoride to the finished water, you can conduct tracer tests by

injecting a small dose of fluoride (about 1 mg/L) into the water entering the distribution system. 

However, flouride can interact with the material deposited inside pipes and storage facilities, reducing

the accuracy of the calculated residence times. As a result, you must inject sufficient fluoride to meet

the “fluoride demand” of your distribution system while assuring that fluoride concentrations in the

distribution system do not exceed allowable concentrations of 4 mg/L (the primary maximum

contaminant limit (MCL) for fluoride is 4 mg/L and the secondary MCL which is non-enforceable is 2

mg/L). If other tracers are used such as calcium chloride or sodium chloride, State environmental

agencies may require that food grade chemicals are used or that other assurances are made concerning
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the safety of the tracer. With some tracer chemicals, systems may want to consider notifying sensitive

users.

When selecting tracer monitoring locations, you should consider the following:

• Major intersections or branches in large transmission mains

• Branches in minor mains where flow is split between two or more groups of customers

• Storage tanks

• Entry points to large commercial or industrial users

• Prior to the last fire hydrant in remote areas with few customers

To adequately characterize distribution system residence time, tracer concentrations should be

measured frequently and in relatively close proximity to one another. The frequency of sampling will

determine the accuracy of the study results. For example, if sampling is conducted every 8 hours the

water age at a given location will only be accurate to within 8 hours. Furthermore, the proximity of

sample locations to one another will also affect the accuracy of the study results. It may be appropriate

to space samples far apart on large transmission mains, but within the distribution system (which

contains many piping and hydraulic interactions) samples should be located closer together.

Optimally, tracer studies should be conducted under conditions that represent high DBP

formation (typically summer months). Also, the study should be detailed enough to provide good

characterization of the entire distribution system. Not all extremities must be covered by the study, but

the data must be complete enough to allow for a reasonable extrapolation of the results to cover the

entire distribution system.

Although tracer studies often provide very good information, they can be time consuming and

costly. Conducting a tracer study solely for the IDSE SMP may not be cost effective. However, if you

are considering a tracer study for some other purpose (e.g. calibration of a water distribution system

model), consideration should be given to using the tracer study as a tool for the IDSE SMP.

Results from previously conducted tracer studies may be very useful in identifying areas in the

distribution system with high and average residence times. Typically, the study should have been

conducted within the past 10 years and represent the existing distribution system configuration. 

However, if your system has implemented operational changes that permanently and significantly

changed the flow of water through your distribution system (i.e., new transmission mains, addition of

large industrial users, significant development in formerly unpopulated or remote areas, etc.) since your

tracer study, the study will be of limited use in selecting SMP sample locations.
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If you have recently conducted or are planning to conduct a detailed tracer study of your

system, you may want to consider completing an alternative SSS (see Chapter 3).

1) High TTHM and High HAA5 Sites

High residence time locations should be identified on a map of the system based on the tracer

study field results. SMP sample sites should be chosen from the area or areas of the distribution system

where these high residence time tracer study sites are located. The SMP sample sites do not have to

be chosen at the exact location of the tracer study monitoring sites, just in the general area identified by

the study.

When selecting high TTHM and high HAA5 sites based on tracer study results it is important to

remember that residence time is just one factor in identifying high TTHM and high HAA5 sites. 

Residence time estimates should be compared with other distribution system data (e.g., disinfectant

residual data) before making your final sample site selections. Areas with high residence time but low

or no disinfectant residual may have microbiological activity which can degrade HAA5. Consequently,

high HAA5 sites may not necessarily be located at areas with high residence times.

2) Average Residence Time

The residence time at all sites sampled during the tracer test field effort should be plotted on a

map of the system. The overall system average age should be calculated by determining the median

residence time results obtained during the field test. Sites with residence times approximately equal to

the median of tracer study results should be identified on the map and the required SMP sample sites

chosen from within these areas.

8.4.6 System Operating Data

System operating data, such as pump run times, pumping rates, tank level data or flow rates,

metered flows between pressure zones, and demand data for large users may be helpful in

understanding overall water flow patterns in your distribution system. For example, storage tank

configuration and operation can have a significant impact on maximum and average residence times in

the areas of a system “downstream” of the storage tank. Pumping rates and flow metering between

pressure zones can provide a direct indication of the movement of water through your system. A

review of billing records can identify your largest customers. Areas of your system “upstream” of your

largest customers are likely to have fresher water than areas downstream of these customers.
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Distribution System 

Map

Residence Time 

(Days)

Residual Data 

(mg/L)

DBP Data (:g/L)

0.5

2.1

1.4

1.5

0.8

1.9

2.5

3.0

1.1

1.9

1.3

1.0

0.9

0.7

0.5

0.3

15

44

24

18

31

63

85

77

1.7

1.0

0.4

0.5

0.1

1.1

1.4

1.5

8.4.7 Geographic Information System (GIS)

Geographic information system (GIS) software is capable of assembling, storing, manipulating,

and displaying geographically referenced data. ArcView and Intergraph are examples of two packages

currently available. GIS allows large amounts of distribution system data to be compiled and users to

query those data to identify areas in a distribution system meeting specified criteria. It is equivalent to

plotting various data on individual see-through maps and laying those maps on top of each other so all

data can be viewed together (Figure 8.2 depicts this concept).

Figure 8.2 Conceptual Diagram of GIS
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Table 8.4 summarizes the data storage capabilities of a typical GIS application.

Table 8.4 Summary of GIS Data Storage Capabilities

General System Data Structural Data Operational Data Water Quality Data

Land uses and zoning

Population density

Pipe diameter and

length

Valves and fittings

Pumps

Pipe age

Pipe material

Pipe maintenance

history

Pipe velocities

System pressure

Pressure zones

Residence time

Temperature

Residual disinfectant

Total coliforms

HPC

DBPs

While GIS applications can be a valuable tool for evaluating many types of distribution system

data geographically, they are not hydraulic models and cannot predict system conditions. GIS

applications are a framework for displaying information related to your distribution system. This means

residence times, system pressures, pipe velocities, and other operational data should be collected by

some other method (e.g., hydraulic model or field measurements) and entered into the GIS database.

After hydraulic and water quality data are integrated into a GIS application, users can query the

data to locate areas which meet several criteria for SMP sites. For example, a user may request

locations where the residence time exceeds 4 days, the free chlorine residual is between 0.2 and 0.5

mg/L, and the HPC count is less than 500 cfu/mL. Most GIS applications can highlight those locations

on a map of the distribution system. The user can then select geographically diverse locations from

these areas for the purposes of IDSE SMP monitoring.

The procedure by which GIS identifies preliminary SMP sample locations is similar to the

process an individual might use if they were doing the analysis by hand. However, GIS is capable of

looking at a larger amount of data in an integrated manner, without the excess time of plotting the data

manually. Purchasing a GIS application solely for the purpose of conducting the IDSE may not be

efficient because there will be a considerable effort involved in getting the system up and running. 

However, if your system currently utilizes or is planning to purchase a GIS application, consideration

should be given to using the application as a tool for identifying SMP sites.
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8.5 Methodology for Selecting Final SMP Sites

As described in the previous section, various data sources and tools can be used to identify

SMP sites, but some may provide more accurate estimates of high TTHM and HAA5 locations or

average residence time locations than others. How do you prioritize the data and combine data sources

and tools to select final SMP sites? This section addresses this question by providing general guidelines

for (1) identifying all possible preliminary SMP sites and (2) narrowing down the preliminary sites to

final SMP sites. Detailed guidance for identifying preliminary sites using each data source or tool was

provided in section 8.4—this section focuses on combining tools to select preliminary and final sites.

A key to selecting final SMP sites is the ability to plot preliminary sites on a detailed map of

your distribution system. You should always visually confirm that SMP sites provide geographic

coverage of the distribution system and are in expected areas of high and average residence time (as

predicted by a hydraulic model or other data source) and that you are not missing key areas that may

not have been sampled in the past. If you have GIS capabilities, queries can be extremely useful in

automating the site selection process. In particular, GIS queries can be used to evaluate multiple data

sources for you rather than having you perform the time consuming process of evaluating multiple

parameters by hand or in a spreadsheet.

The information and considerations presented in this section are not intended to be limiting or

prescriptive. EPA recognizes DBP formation is system-specific and the guidance provided in this

manual will not apply to every system. The operational experience and knowledge of system personnel

and all available information should be considered in selecting SMP sample sites. Best professional

judgement should be exercised in the specific application of guidelines in this manual.

8.5.1 Identifying Preliminary Sites Using Combinations of Tools and Data

Sources

This section contains a multi-step process that allows you to use any combination of the

following data sources with maps to select preliminary sites:

• Water distribution system model outputs

• Tracer study results

• Disinfectant residual data

• DBP data

All steps involve plotting preliminary sites on a map of your distribution system. Figure 8.3 is flow-chart

that indicates at which step you should start, depending on your available data sources.
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Do you have a water model

or tracer study? Start at Step 1

Do you DBP Data? Start at Step 2

Yes

No

Do you Disinfection 

Residual Data?

Start at Step 3 Yes

No

Start at Step 4

No

Yes

Figure 8.3 Starting Point for Preliminary Site Selection

The steps in this section focus on identifying preliminary high TTHM and high HAA5 sites at

locations of high residence time. Guidance for selecting average residence time sites (for 100 percent
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purchasing systems serving at least 10,000 people and for producing surface water serving at least

10,000) is presented separately at the end of each step.

Step 1 - Using Modeling and Tracer Study Results

Identifying Preliminary High TTHM and High HAA5 Sites Residence Time Sites

Use output from your water distribution system model or tracer study results to identify areas

with the highest residence times. You should identify at least twice as many preliminary SMP sites as

required. For example, from Table 8.1 producing ground water systems serving 500 to 9,999 people

must have one high TTHM and one high HAA5 site per plant for the SMP; therefore, they should

select at least two preliminary high TTHM sites and two preliminary high HAA5 sites per plant using

model or tracer study data. Plot all preliminary sites on a map of your distribution system.

Identifying Preliminary Average Residence Time Sites

Use output from your water distribution system model or tracer study results to identify areas

with average residence times. You should identify at least twice as many preliminary SMP sites as

required.

C For 100 percent purchasing systems serving at least 10,000 people, see Table 8.1 for the

number of average residence time sites that are required for the SMP. (100 percent

purchasing systems serving less than 10,000 people do not have to select average residence

time sites). 

C For producing systems providing surface water in whole or in part, at least four preliminary

sites per plant should be identified (two SMP sites per plant are required). 

Plot all preliminary average residence time sites on a map of your distribution system.

Step 2 - Using TTHM and HAA5 Data

Note: DBP data are generally not useful in identifying average residence time sites. 

Only preliminary high TTHM and high HAA5 sites are covered in this step.

If you completed Step 1:

Determine if the high TTHM and HAA5 locations correspond to areas with high water

residence time. It is possible that the water distribution system model or tracer study did not capture

mixing effects or other factors leading to higher residence times than predicted. If the high TTHM and
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HAA5 data occur outside predicted areas of high residence time, you should select additional

preliminary sites to cover these areas.

If you did not complete Step 1:

Review TTHM and HAA5 data and identify areas with the highest TTHM and HAA5

concentrations (and/or areas with similar characteristics to sites with high TTHM and HAA5

concentrations). Plot these areas on your distribution system map.

Step 3 - Using Disinfectant Residual Data

If you completed Step 1:

Identifying preliminary high TTHM and high HAA5 sites residence time sites:

On a map of your system, identify areas with low disinfectant residual concentration compared

to finished water. (It may be helpful to record the average concentration for the summer months or the

minimum monthly concentration on a map of you system). Determine if the areas with high residence

times identified in Step 1 correspond to areas with low disinfectant residuals. (Note, the use of booster

disinfection will affect this correlation.) It is not unusual for disinfectant residual data to show different

trends compared to hydraulic model outputs. It is possible that a hydraulic model or tracer study did

not capture mixing effects or other factors leading to higher residence times than predicted. Disinfectant

residual can be influenced by other factors, such as internal corrosion, biological activity, etc. (refer to

section 8.4.2.1 for a more complete description of other factors affecting disinfectant residual decay). 

Thus, low disinfectant residual is not a definitive indication of long residence time. 

If areas with low disinfectant residuals are identified outside predicted areas of high residence

time, you may wish to select additional preliminary SMP sites to cover these areas. For preliminary

high HAA5 sites, a minimum residual of 0.2 mg/L chlorine or 0.5 mg/L chloramine should be present.

Identifying preliminary average residence time sites:

On a map of your system, identify areas of average residence time based on disinfectant

residual data. (See section 8.4.2.1 for guidance on identifying areas of average residence time using

disinfectant residual data.) Do average residence time sites identified by your water distribution system

model or tracer study in Step 1 correspond with average residence time sites identified by evaluating

disinfectant residual data? Identify additional preliminary SMP sites for average residence times if your

residual data show different locations than results from your model or tracer study.
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If you did not complete Step 1:

Identifying preliminary high TTHM and high HAA5 sites residence time sites

Evaluate your disinfectant residual data from warmer months and identify areas with the lowest

or no residual concentrations. These locations are likely those with the highest residence time, and

represent potential locations for high TTHM and HAA5 SMP sites. (High HAA5 sites should be

limited to those sites with a free chlorine residual of at least 0.2 mg/L or a chloramine residual of at least

0.5 mg/L.) Identify at least twice as many SMP sites as required. Plot these areas on your distribution

system map.

Identifying preliminary average residence time sites

Using disinfectant residual data from your TCR monitoring locations (and flow data, if

available), calculate the average system and locational average disinfectant residuals. Section 8.4.2.1

discusses these methodologies. Identify those locations with average disinfectant residuals

approximately equal to the system average. Identify at least twice as many preliminary SMP sites as

required. Plot these areas on your distribution system map.

Step 4 - Map Review

Review your water distribution system map to identify additional preliminary SMP locations

representative of high TTHMs and high HAA5 not identified in Steps 1 through 3 where:

• There is light development or low residential population far away from a treatment plant

• An area is served by one or more distribution system storage facilities, especially if the

storage facility(s) have high water residence times

• An area is served by booster disinfection stations

You should not select preliminary sites at the very end of a water main past the last customer. 

A better location would be at the last group of customers.

8.5.2 Selecting Final SMP Sites from Preliminary Sites

The following are general guidelines for choosing final SMP sites from your list of 
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preliminary sites identified in accordance with section 8.5.1. Specific guidelines for very small systems

serving less than 500 people are at the end of section 8.5.2.1. EPA recognizes there are systemspecific factors that may lead you to select final sites that do not specifically meet these guidelines. If

you deviate from the guidelines, provide justification to your State in your IDSE Report.

8.5.2.1 Selecting High TTHM and HAA5 SMP Sites (All Systems)

1) Select SMP sites in hydraulically different areas (i.e., do not select two sites close to one

another).

2) Select SMP sites in geographically different areas and separated from existing Stage 1

DBPR sites.

3) Prioritize sites that meet the most siting criteria and those identified based on more than one

data source. For example, a preliminary high TTHM site that has low disinfectant residual,

is near the edge of the distribution system and is downstream of a tank would be a likely

SMP site.

4) Select high TTHM sites located after storage facilities and booster disinfection stations.

5) Select high TTHM sites in areas with the lowest or no residual disinfectant (unless your

system uses booster disinfection).

6) Generally, select high HAA5 sites with a minimum of 0.2 mg/L chlorine residual or 0.5

mg/L chloramine residual for all observations.

7) Locate at least one of your high TTHM sites in a remote area of your distribution system. If

you are only required to select one high TTHM site, it is strongly recommended that you

locate this site away from the treatment plant, near the last group of customers (but prior to

the last fire hydrant).

8) DBP data are important as long as they represent your current system configuration. If you

have a historical TTHM or HAA5 data in an area, these data can be used to prioritize sites

(or select one over another) when other data shows no difference between the sties. For

example, if disinfectant residual data are the same for three sites over the same periods,

then the DBP data can be used to select a high TTHM/HAA5 site.
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Special Considerations for Storage Tanks

9) Understanding the impact of storage tanks on water movement and water age in a

distribution system is complicated by a variety of specific physical and operational

characteristics. The mixing characteristics of storage tanks are impacted by the inlet/outlet

piping configuration, inlet momentum, temperature, and duration of drain/fill cycles. For

example, horizontal inlets at the base of storage tanks, oversized inlet piping which results in

low inlet momentum, and short drain/fill cycles are all potential causes of poor mixing in

storage tanks. A methodology for evaluating storage tank mixing characteristics is

presented in Water Quality Modeling of Distribution System Storage Facilities

(Grayman et al. 2000). 

Tanks with poor mixing characteristics and common inlet/outlet piping may operate in a

“last in–first out” mode, meaning that the freshest water in the tank is the first to be

discharged during a drain cycle. During periods of higher than normal demand, when drain

periods may be extended, these tanks may discharge water from the upper regions of the

tank where water age is substantially (e.g., several days or weeks) higher than water in the

lower regions of the tank. If you suspect poor mixing in one or more of your storage tanks,

areas receiving the stored water from those tanks may occasionally have high DBP

concentrations.

Tank level data can be used to assess the theoretical average residence time of water in a

tank; however, the mixing characteristics of the tank must be thoroughly understood to

adequately estimate the true average water age in a storage tank (Uber et al. 2002). It is

important to understand that distribution system storage facilities can have significant but

variable impacts on water age. As a result, high TTHM and HAA5 sites should typically be

located downstream of distribution system storage facilities.

Specific Guidance for Systems Serving Less Than 500 People

10) Select a high TTHM site in a high residence time area that is not near your Stage 1 DBPR

site. (Your Stage 1 DBPR site should be located in an area of your distribution system that

represents your maximum residence time.) 

11) Locate your high HAA5 site in a location other than near your high TTHM and Stage 1

DBPR sites. If those two sites cover the high residence time areas of your distribution

system, then select a site in an area with average residence time (see section 8.4.2.1 for

determining average residence time based on disinfectant residual data) for your high

HAA5. The highest HAA5 concentrations may not occur at the highest residence time

locations. There may be system-specific factors that cause HAA5 to biodegrade and,

therefore, areas with average residence time may have the highest HAA5 concentrations.
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8.5.2.2 Selecting Average Residence Time Sites

SMP sites representing average residence time are required for:

C 100 percent purchasing systems serving at least 10,000 people

C Producing surface water systems serving at least 10,000 people 

From the preliminary average residence time sites, select final average residence time sites that are

geographically diverse from the other SMP sites and existing Stage 1 DBPR average residence time

compliance sampling sites.

8.6 Stage 2B DBPR Site Selection and IDSE Reporting Requirements (40 CFR

141.605)

Once the SMP monitoring period has ended, the Stage 2B compliance monitoring sites can be

selected from the SMP and Stage 1 DBPR results (or Stage 2A DBPR for systems on the late IDSE

schedule). Selection must be based on the average TTHM and HAA5 concentrations measured over

the SMP monitoring period at each site, or locational running annual averages (LRAAs). Tables 8.5

and 8.6 summarize the Stage 2B site requirements for 100 percent purchasing and producing systems,

respectively.

TTHM and HAA5 LRAAs are the most important factors to consider when selecting Stage 2B

DBPR monitoring locations. However, the rule allows for some flexibility in selecting Stage 2B

compliance sites. Other factors should be considered and may lead to selecting a site with a slightly

lower LRAA over another site. The following conditions are possible reasons why you may select a

site with a lower LRAA over another site:

• The site provides for more complete geographic coverage of the entire distribution system

• The site allows you to maintain an historical record

• Sampling at that site provides the opportunity to collect other water quality or operational

data (e.g., chloramine systems may want to collect nitrate data at that location)
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1

The Stage 2 DBPR does not specify a difference between two LRAAs that allows selection of a site with

the lower LRAA for Stage 2B. EPA recognizes there is uncertainty and variability associated with the TTHM and

HAA5 data quality. While the LRAA calculation reduces the impact of these to some extent, they can cause a small

difference between two LRAAs to be statistically insignificant and thus, making the selection of the Stage 2B site

dependent on other factors. The intent of the Stage 2 DBPR is to reduce peak DBP concentrations in the distribution

system. You should use best professional judgment to select Stage 2B sites with consideration to the intent of the

rule and demonstrate to the State the reason for the selection.

July 2003 - Proposal Draft 8-46 All Systems

If you do not use your highest TTHM and HAA5 LRAAs to select your Stage 2B DBPR sites,

you must provide justification for your selection in your IDSE report.1
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Table 8.5 Stage 2B Compliance Monitoring Requirements for

100 Percent Purchasing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by location type) per System

Total

Number of 

Sites per

System

Monitoring

Frequency4

Stage 1

Average

Residence Time

Site

Highest

TTHM 

Highest

HAA5

Surface Water Systems5

< 500 - 1 1 2

5 Every 365 days

500 - 4,999 - 1 1 2

5 Every 90 days

5,000 - 9,999 - 1 1 2 Every 90 days

10,000 - 24,999 1 2 1 4 Every 90 days

25,000 - 49,999 1 3 2 6 Every 90 days

50,000 - 99,999 2 4 2 8 Every 90 days

100,000 - 499,999 3 6 3 12 Every 90 days

500,000 - 1,499,999 4 8 4 16 Every 90 days

1.5 million - < 5 million 5 10 5 20 Every 90 days

> 5 million 6 12 6 24 Every 90 days

Ground Water Systems

< 500 - 1 1 2

6 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

10,000 - 99,999 1 2 1 4 Every 90 days

100,000 - 499,999 1 3 2 6 Every 90 days

> 500,000 2 4 2 8 Every 90 days

1

(40 CFR 141.605 (e))

2 For the purpose of this guidance manual, 100 percent purchasing systems are those systems that buy or

otherwise receive all of their finished water from one or more wholesale systems year-round.

3 Population served is usually a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample

that is taken at the same time and location.

5 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

6 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different locations, then only one sample is collected at each location. If they occur at the

same location, then a dual sample set is collected at that location.
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Table 8.6 Summary of Stage 2B Compliance Monitoring Requirements for

Producing Systems1,2

System Size

(Population Served3)

Number of Distribution System Sites

(by location type) per Plant4

Total

Number of 

Sites per

Plant

Monitoring

Frequency5

Stage 1

Average

Residence Time

Site

Highest

TTHM 

Highest

HAA5

Surface Water Systems6

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 90 days

> 10,000 1 2 1 4 Every 90 days

Ground Water Systems

< 500 - 1 1 2

7 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

> 10,000 - 1 1 2 Every 90 days

1

(40 CFR 141.605 (a))

2 For the purpose of this guidance manual, producing systems are those that do not buy 100 percent of their

water year-round (i.e., they produce some or all of their own finished water).

3 Population served is usually a system’s retail population. It should not include populations served by

consecutive systems that purchase water from that system.

4 For the purpose of the Stage 2 DBPR compliance monitoring, a plant can be either a treatment plant (that

provides, at a minimum, disinfection using a disinfectant other than UV) or a consecutive system entry point that

operates for at least 60 consecutive days per year.

5 Monitoring frequency is the approximate number of days between monitoring events. A dual sample set must

be collected at each location, unless otherwise noted. A dual sample set is one TTHM and one HAA5 sample

that is taken at the same time and location. 

6 For the purpose of this guidance manual, “surface water systems” are equivalent to subpart H systems (i.e., any

system that uses surface water or GWUDI as a source, including all mixed systems that use some surface

water or GWUDI and some ground water).

7 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different locations, then only one sample is collected at each location. If they occur at the

same location, then a dual sample set is collected at that location.

8.6.1 100 Percent Purchasing Systems

The rule requires 100 percent purchasing systems to use the following protocol for selecting

Stage 2B sites from IDSE and Stage 1 compliance monitoring data.

1) Site with the highest TTHM LRAA
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2) Site with the highest HAA5 LRAA (not previously selected)

3) Existing Stage 1 DBPR compliance monitoring site

4) Site with the highest TTHM LRAA (not previously selected)

Repeat the protocol, selecting from the remaining sites, until the required number has been

selected. For #3, alternate between highest HAA5 and highest TTHM of Stage 1 DBPR average

residence time sites, not previously selected.

8.6.2 Producing Systems

The rule requires producing systems to select the required amount of sites for each plant using

the following protocols:

Large surface water systems

For each plant, select sites with following:

1) Highest TTHM LRAA

2) Highest TTHM LRAA

3) Highest HAA5 LRAA

4) Existing Stage 1 DBPR Average Residence Time site with the highest TTHM or HAA5

LRAA. If you do not have a Stage 1 Average Residence Time site, then you must choose the

next highest HAA5 site.

Small surface water systems and all ground water systems

Select sites with the highest TTHM LRAA and HAA5 LRAA for each plant. 

• Systems serving 500 to less than 10,000 people—if the highest TTHM and HAA5 occur at

the same site for a given plant, then your system may monitor at only that site for that plant. 

• Systems serving less than 500—you are required to take one TTHM and one HAA5

sample per year per plant. If the high TTHM and HAA5 for a given plant occurred at

different sites, then you only need to collect a TTHM sample at the high TTHM site and a

HAA5 sample at the high HAA5 site.
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8.6.3 Examples of Stage 2B DBPR Site Selection

This section provides examples of Stage 2B DBPR site selection:

Example 8.15 Selecting Stage 2B DBPR Sites from SMP Data

Example 8.16 Maintaining an Historical Record

Example 8.17 Providing Geographical Coverage When Choosing Stage 2B DBPR Sites
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Example 8.15 Selecting Stage 2B DBPR Sites from SMP Data

A producing system serves 90,000 people and has one surface water treatment plant. This

system must select four Stage 2B DBPR compliance sites (from Table 8.9): two high-TTHM sites; one

high-HAA5 site; and one from the three existing Stage 1 DBPR average residence time compliance

sites. The table below lists the TTHM and HAA5 LRAAs for all Stage 1 DBPR compliance

monitoring sites and three of the eight SMP sites (these data represent the seven highest TTHM and

HAA5 LRAAs).

Site TTHM LRAAs HAA5 LRAAs

A (Stage 1 max. residence time) 64 39

B (SMP high TTHM site) 66 40

C (SMP high HAA5 site) 72 52

D (SMP high TTHM site) 76 50

E (Stage 1 avg. residence time) 57 48

F (Stage 1 avg. residence time) 42 30

G (Stage 1 avg. residence time) 55 50

Selecting the Average Residence Time Site

The average residence time site should have either the highest TTHM or highest HAA5 LRAA

of the Stage 1 DBPR average residence time sites. The water system may choose either Site E

(highest TTHM LRAA) or Site G (highest HAA5 LRAA). With two valid options, the site providing

the best geographic coverage is preferred. Site G is located downstream of an elevated tank and is the

only site that receives water from that tank; therefore, the water system selects Site G.

Selecting High-TTHM and High-HAA5 Sites

Sites C and D have both the highest TTHM and HAA5 LRAAs (they can represent the two

high-TTHM sites or one high-TTHM site and one high-HAA5). One more high TTHM or high HAA5

site must be chosen between Sites A and B. The differences in LRAAs between Site A and Site B are

minimal. Site A was first selected as a THM Rule “maximum” compliance site and is now a Stage 1

site DBPR. To maintain the historic record of sampling, Site A is chosen.
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Example 8.16 Maintaining an Historical Record

A producing system serves 4,000 people and has one ground water treatment plant. This system

must select two Stage 2B compliance sites (from Table 8.9): one high-TTHM and one high-HAA5 site. A

comparison of SMP and Stage 1 DBPR compliance monitoring results are presented in the table below.

Sample Locations with Highest

LRAAs

LRAA

TTHM (μg/L) HAA5 (μg/L)

SMP #1 High TTHM 72 51

SMP #2 High TTHM 65 56

SMP # 3 High HAA5 60 51

Stage 1 DBPR max residence

time site

70 51

Because the TTHM LRAA for the Stage 1 DBPR site is only slightly lower than the maximum

TTHM LRAA (SMP #1), the system chooses the Stage 1 DBPR site over SMP #1 for the Stage 2B

DBPR high TTHM site to maintain the historic DBP record at that site. SMP #2 is selected as the high

HAA5 site.
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8.7 Reporting Results to the State

The rule requires the following data and information be included in your IDSE report to the

State (40 CFR 141.604):

• The original SMP plan and an explanation of any deviations from that plan

• All TTHM and HAA5 analytical results from the SMP

• All TTHM and HAA5 analytical results from Stage 1 DBPR compliance samples collected

during the period of the IDSE

• A schematic of your distribution system with the results, location, and date of all IDSE

SMP and compliance samples noted

• Data used to justify IDSE SMP site selections

• Proposed Stage 2B compliance monitoring sites with justification for selection of each

proposed site

• Proposed month(s) during which Stage 2B monitoring is to be conducted

Water Treatment 

Plant

A

B

C

Example 8.17 Providing Geographic Coverage When Choosing Stage 2B DBPR Sites

In general, the two representative high TTHM sites (per

plant) should not be from the same area of the distribution system. 

The two highest TTHM LRAAs in the distribution system

are from adjacent SMP sample sites (Sites A and B). The site with

the third highest TTHM LRAA is on the far side of the distribution

system (site C). In this case, consider selecting sites A and C or B

and C as Stage 2B DBPR sites for a broader geographical

coverage of the distribution system.
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 Refer to Appendices E through J for example IDSE reports based on source water and system

size (see Table 8.10).

Remember that TTHM and HAA5 data collected for the SMP are not to be included in

compliance calculations for the Stage 1 or Stage 2A DBPR. Also, results from the SMP should not be

reported in your Consumer Confidence Report.

If you do not receive notification that your Stage 2B site selection was acceptable by [3 years

after rule promulgation] for systems on the early schedule or [6 years after rule promulgation] for

systems on the late schedule, you should contact your State to verify your Stage 2B sites meet

compliance requirements.

Table 8.7 Example IDSE Reports

Appendix System Characteristics

Appendix E SMP for Producing Surface Water System (> 10,000)

Appendix F SMP for Producing Ground Water System (> 10,000)

Appendix G SMP for Producing Surface Water System (500 - 9,999)

Appendix H SMP for Producing Ground Water System (< 10,000)

Appendix I SMP for Producing Surface Water System (< 500)

Appendix J SMP for 100 Percent Purchasing Surface Water System
Appendix A

Impacts of an Alternative Population-Based Monitoring Approach
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Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

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A.1 Introduction

The Stage 2 DBPR includes monitoring requirements that were recommended by the Stage 2

M-DBP Federal Advisory Committee (Stage 2 FACA) in the Agreement in Principle (USEPA 2000). 

Many of these monitoring requirements were based on those in the 1979 TTHM Rule and Stage 1

DBPR. For example, the frequency of monitoring under the Stage 1 DBPR is a function of source

water type (ground or surface water), size of system, and the number of plants per system. For the

Stage 2 DBPR, as under the Stage 1 DBPR, the Stage 2 FACA recommended that compliance

sampling be required on a per-plant basis. This recommendation is based on the assumption that as

systems increase in size, they will tend to have more plants and increased complexity of water treatment

and distribution, thereby warranting increased monitoring to represent DBP occurrence in the

distribution system. The Stage 2 FACA also recommended higher frequency monitoring for systems

using surface water than those using ground water because ground water tends to have lower and more

stable concentrations of organic DBP precursors than surface water. Furthermore, since many ground

water systems have multiple wells/entry points drawing water from the same aquifer, the Stage 2 FACA

recommended that these wells be considered as a single plant with the same monitoring requirements

prescribed for one plant, if approved by the State.

Upon further analysis of the Stage 2 FACA recommendations, EPA has identified the following

issues related to the monitoring requirements of the Stage 2 DBPR:

• Basing increased monitoring on numbers of water treatment plants per system, as opposed

to population alone, may result in either excessive or insufficient samples to represent DBP

occurrence in the distribution system.

• The proposed sampling requirements for mixed systems (i.e., those receiving surface water

and disinfecting ground water in their distribution system) may be excessive, depending

upon the system's characteristics. 

• The proposed monitoring requirements, based on additional samples per water treatment

plant, pose unique implementation issues for systems with temporary supplies during the

year.

To address these issues, the Stage 2 DBPR uses two approaches to monitoring for two

different groups of systems:

1) The plant-based approach is dependent on population served, source water, AND the

number of plants in a system (as with Stage 1 DBPR compliance monitoring) and applies to

systems that produce some or all of their own finished water (called producing systems in
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft A-2

this manual). For the purpose of the Stage 2 DBPR, a plant can be either a treatment plant

(that provides, at a minimum, disinfection using a disinfectant other than UV) or a

consecutive system entry point that operates for at least 60 consecutive days per year.

• The population-based approach that is dependent on population served and source

water and applies to only those systems that purchase 100 percent of their finished water

from other systems (called 100 percent purchasing systems in this manual).

Section V(F)(2) of the Stage 2 DBPR preamble describes the monitoring issues in detail and

requests comment on them, particularly the significance of a plant-based (the proposed monitoring

scheme) versus a population-based monitoring approach (monitoring requirements based on population

and source type only). 

The purpose of this Appendix is to describe how this guidance manual would be revised if the

Stage 2 monitoring scheme were changed to a population-based approach. First, section A.2 presents

EPA’s proposed framework for an alternative population-based monitoring scheme. Section A.3 then

discusses a revised organization and consolidation of chapters for this guidance manual to reflect a

population-based approach monitoring scheme for all systems. 

A.2 Summary of Alternative Population-Based Approach

The Stage 2 DBPR requires monitoring for (1) the IDSE and (2) Stage 2A and Stage 2B

compliance. Currently, monitoring requirements are based on population and source water only for

100 percent purchasing systems, and based on population, source water, and number of plants for

producing systems. Under the alternative population-based approach, the proposed monitoring

requirements for 100 percent purchasing systems would be applied to all systems. The following

exhibits summarize the IDSE and Stage 2B monitoring requirements for the population based approach. 

(These requirements are identical to those presented in Chapters 1, 4, and 8 for 100 percent

purchasing.)

• Table A.1 – IDSE SMP monitoring requirements for Population-based Approach

• Table A.2 – Stage 2B routine samples required for Population-based Approach
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft A-3

Table A.1 IDSE SMP Sampling Requirements for Population-based Approach

System Size

(Population Served)

Number of Distribution System

Sites2 (by location type) per System

Total

Number of

Sites per

System

Monitoring

Frequency for

the 1-year IDSE

period4

Near

Entry

Point3

Average

Residence

Time

High

TTHM

High

HAA5

Surface Water Systems5

< 500 - - 1 1 2 Every 180 days

500 - 4,999 - - 1 1 2 Every 90 days

5,000 - 9,999 - 1 2 1 4 Every 90 days

10,000 - 24,999 1 2 3 2 8 Every 60 days

25,000 - 49,999 2 3 4 3 12 Every 60 days

50,000 - 99,999 3 4 5 4 16 Every 60 days

100,000 - 499,999 4 6 8 6 24 Every 60 days

500,000 - < 1.5 million 6 8 10 8 32 Every 60 days

1.5 million - < 5 million 8 10 12 10 40 Every 60 days

> 5 million 10 12 14 12 48 Every 60 days

Ground Water Systems

< 500 - - 1 1 2 Every 180 days

500 - 9,999 - - 1 1 2 Every 90 days

10,000 - 99,999 1 1 2 2 6 Every 90 days

100,000 - 499,999 1 1 3 3 8 Every 90 days

> 500,000 2 2 4 4 12 Every 90 days

1 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

2 A dual sample set must be collected at each location. A dual sample set is one TTHM and one HAA5 sample

that is taken at the same time and location.

3 See section 8.2 for requirements when the number of entry points in a system is different from the number of

required near-entry point sites in this table.

4 Monitoring frequency is the approximate number of days between monitoring events.

5 For the purposes of this guidance manual, “surface water” systems are equivalent to “subpart H” systems and

include systems that provide GWUDI.
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Table A.2 Stage 2B Compliance Monitoring Requirements for Population-based

Approach

System Size

(Population Served)

Number of Distribution System Sites2

(by location type) per System

Total

Number of 

Sites per

System

Monitoring

Frequency3

Existing Stage 1

Compliance

Sites

Highest

TTHM 

Highest

HAA5

Surface Water Systems4

< 500 - 1 1 2

5 Every 365 days

500 - 4,999 - 1 1 2

5 Every 90 days

5,000 - 9,999 - 1 1 2 Every 90 days

10,000 - 24,999 1 2 1 4 Every 90 days

25,000 - 49,999 1 3 2 6 Every 90 days

50,000 - 99,999 2 4 2 8 Every 90 days

100,000 - 499,999 3 6 3 12 Every 90 days

500,000 - 1,499,999 4 8 4 16 Every 90 days

1.5 million - < 5 million 5 10 5 20 Every 90 days

> 5 million 6 12 6 24 Every 90 days

Ground Water Systems

< 500 - 1 1 2

5 Every 365 days

500 - 9,999 - 1 1 2 Every 365 days

10,000 - 99,999 1 2 1 4 Every 90 days

100,000 - 499,999 1 3 2 6 Every 90 days

> 500,000 2 4 2 8 Every 90 days

1 For the purposes of this manual, 100 percent purchasing systems are those systems that buy or otherwise

receive all of their finished water from one or more wholesale systems year-round.

2 A dual sample set must be collected at each location, unless otherwise noted. A dual sample set is one TTHM

and one HAA5 sample that is taken at the same time and location.

3 Monitoring frequency is the approximate number of days between monitoring events.

4 For the purposes of this guidance manual, “surface water” systems are equivalent to “subpart H” systems and

include systems that provide GWUDI.

5 Dual sample sets are not required at both the high TTHM and the high HAA5 site—if the highest TTHM and

HAA5 levels occur at a different locations, then only one sample is collected at each location. If they occur at the

same location, then a dual sample set is collected at that location.
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A.3 Revised Guidance Manual Organization

The IDSE and Stage 2B requirements are less complex with a monitoring scheme that is based

only on population served and source water type (the population-based approach) compared to plantbased requirements. Table A.3 hypothesizes how this manual might be revised if the monitoring

requirements were to change. Note two chapters will be deleted and no additional chapters will be

necessary.

Table A.3 Revised Chapter Organization and Content

Reflecting a Population-Based Monitoring Approach for All Systems

Current Chapter Chapter Revisions

1 - Introduction Revised. (Remove distinctions between producing and 100

percent purchasing system).

2 - Criteria for IDSE Waiver and

Reporting Requirements

Same

3 - System Specific Study Same

4 - SMP Requirements for 100

Percent Purchasing Systems

Revised to present SMP requirements for all systems, SW and

GW.

5 - SMP Requirements for Producing

Systems, SW serving > 10,000 people

Deleted. Revised Chapter 4 will cover all systems.

6 - SMP Requirements for Producing

Systems, SW serving 500 - 9,999

people and GW serving > 10,000

people

Deleted. Revised Chapter 4 will cover all systems.

7 - SMP Requirements for Producing

Systems, SW serving < 500 people

and GW serving < 10,000 people

Revised to address only systems serving less than 500 people. 

Becomes Chapter 5.

8 - SMP Site Selection and Reporting Same, becomes Chapter 6.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft A-6

References

EPA, 2000. Stage 2 M-DBP Agreement in Principle. Microbial/Disinfection Byproducts (M-DBP)

Federal Advisory Committee. September 12, 2000.
Appendix B

Factors Affecting Disinfection Byproduct Formation
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B.1 Introduction

The purpose of this appendix is to identify and discuss the factors that affect formation of

disinfection byproducts (DBPs) in water treatment processes and distribution systems. This appendix is

intended to serve as a tool for systems for the purpose of identifying IDSE sample locations and Stage

2B monitoring locations. It is divided into the following sections: 

B.2 Factors Affecting DBP Formation

B.3 Disinfectant Type

B.4 Disinfectant Dose

B.5 Time Dependency of DBP Formation

B.6 Concentration and Characteristics of DBP Precursors

B.7 Water Temperature

B.8 Water pH

B.2 Factors Affecting DBP Formation

Organic DBPs (and oxidation byproducts) are formed by the reaction between organic

substances and oxidizing agents (e.g., chlorine and ozone) that are added to water during treatment. In

most water sources, natural organic matter (NOM) is the most significant constituent of organic

substances and DBP precursors. NOM is often measured as total organic carbon (TOC) and as such

the two terms are used interchangeably in much of the discussion presented in this appendix. Major

factors affecting the type and amount of DBPs formed include:

• Type of disinfectant, dose, and residual concentration

• Contact time and mixing conditions between disinfectant (oxidant) and precursors

• Concentration and characteristics of precursors

• Water temperature

• Water chemistry (including pH, bromide ion concentration, organic nitrogen concentration,

and presence of other reducing agents such as iron and manganese)

B.3 Disinfectant Type

Organic DBPs can be subdivided into halogenated and non-halogenated byproducts.

Halogenated organic disinfection byproducts are formed when organic compounds found in water react

with free chlorine, free bromine, or free iodine. The formation reactions take place in both the

treatment plant and the distribution system. Free chlorine can be introduced to water directly as a
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primary or secondary disinfectant, as a byproduct of the manufacturing of chlorine dioxide, or as a

component in the formation of chloramines for secondary disinfection. Reactions between NOM and

chlorine lead to the formation of a variety of halogenated DBPs including THMs and HAAs. 

Free chlorine and ozone oxidize bromide ion to hypobromite ion/hypobromous acid, which in

turn can react with NOM to form brominated DBPs (e.g., bromoform). The presence of bromide

affects both the rate and yield of DBPs. As the ratio of bromide to NOM (measured as total organic

carbon) increases, the percentage of brominated DBPs increases. For example, Krasner (1999)

reported the rate of THM formation is higher in waters with increased concentrations of bromide. 

Oxidation of organic nitrogen can lead to the formation of DBPs containing nitrogen, such as

haloacetonitriles, halopicrins, and cyanogen halide (Reckhow et al. 1990; Hoigné and Bader 1988). 

Brominated DBPs can also form by bromine substitution in the chlorinated byproducts. Hypobromous

acid is a more effective substituting agent, while hypochlorous acid is a better oxidant (Krasner 1999).

Non-halogenated DBPs may form when precursors react with strong oxidants. For example,

the reaction of organics with ozone and hydrogen peroxide results in the formation of aldehydes, aldoand keto-acids, and organic acids (Singer 1999). Chlorine can also trigger the formation of some nonhalogenated DBPs (Singer and Harrington 1993). Many of the non-halogenated DBPs are

biodegradable.

Studies have documented that chloramines produce significantly lower DBP levels than free

chlorine, and there is no clear evidence that the reaction of NOM and chloramine leads to the formation

of THMs (Singer and Reckhow 1999; EPA 1999). Predictions of an empirical DBP formation model

calibrated using ICR data indicated that THMs and HAAs are formed in full-scale plants and

distribution systems under chloraminated conditions at a fraction of the amount that would be expected

based on observations of DBP formation under free chlorine conditions. The amount of formation with

chloramines varied from 5 percent to 35 percent of that calculated for free chlorine, depending on the

individual DBP species (Swanson et al. 2001). 

It is possible that DBPs might form during the mixing of chlorine and ammonia, when free

chlorine might react with NOM before the complete formation of chloramines. In addition,

monochloramine slowly hydrolyzes to release free chlorine in water. This free chlorine may contribute

to the formation of small amounts of additional DBPs in the distribution system. The benefits of low

DBP formation with chloramines are especially important at the extremities of the distribution system

where high DBP levels can found. 

The application of chlorine dioxide does not produce significant amounts of organic halogenated

DBPs. Only small amounts of total organic halides (TOXs, the class of halogenated organic byproducts that includes THMs and HAAs) are formed. However, THMs and HAAs will form if excess

chlorine is added to water to ensure complete reaction with sodium chlorite during the production of

chlorine dioxide.

To date, there is no evidence to suggest that ultraviolet irradiation (UV) results in the formation
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of any disinfection byproducts; however, little research has been performed in this area. Most of the

research regarding application of UV and DBP formation has focused on chlorinated DBP formation as

a result of UV application prior to the addition of chlorine or chloramines. The evidence suggests UV

does not affect chlorinated DBP formation.

Ozone does not produce chlorinated DBPs; however, ozone can alter the reactions between

chlorine and NOM and affect the speciation of chlorinated DBPs when chlorine is added downstream. 

In waters with sufficient bromide concentrations, ozonation can lead to the formation of bromate and

other brominated DBPs. Bromate, like THMs and HAAs, is a regulated DBP. Ozonation of natural

waters also produces aldehydes, haloketones, ketoacids, carboxylic acids, and other types of

biodegradable organic material. The biodegradable fraction of organic material can serve as a nutrient

source for microorganisms, and should be removed to prevent microbial regrowth in the distribution

system. 

B.4 Disinfectant Dose

The concentration of disinfectant can affect the formation of DBPs. In general, changes in the

disinfectant dose have a great impact on DBP formation during primary disinfection. This is because

the amount of disinfectant added during primary disinfection is usually less than the long-term demand

and the disinfectant is the limiting reactant in DBP formation reactions. Although disinfectant dose can

affect DBP formation during secondary disinfection, the effect is less significant than in primary

disinfection. During secondary disinfection DBP formation reactions may be precursor limited since an

excess of disinfectant is added to the water. In the distribution system, DBP formation reactions

become disinfectant-limited when the free chlorine residual drops to low levels. Singer and Reckhow

(1999) suggested a chlorine concentration of 0.3 mg/L as a rule of thumb.

In many systems booster disinfection is applied to raise disinfectant residual concentration,

especially in remote areas of the distribution system or near storage tanks where water age may be high

and disinfectant residuals can be low. The additional chlorine dose applied to the water at these

booster facilities can increase THM and HAA levels when sufficient precursors remain in the water. 

Booster chlorination can also maintain high HAA concentrations because the increased free chlorine

residual can prevent the biodegradation of HAAs.

B.5 Time Dependency of DBP Formation

In general, DBPs continue to form in drinking water as long as disinfectant residuals and

reactive DBP precursors are present. Therefore, the longer the contact time between the

disinfectant/oxidant and NOM, the greater the amount of DBPs that can be formed. This accumulation

is a consequence of the formation of THMs and HAAs and their associated chemical stabilities, which

are generally quite high in the disinfected drinking water as long as a significant disinfectant residual is

still present (Singer and Reckhow 1999).
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High TTHM values usually occur where the water age is the oldest. Unlike THMs, HAAs

cannot be consistently related to water age because HAAs are known to biodegrade over time when

the disinfectant residual is low. This might result in relatively low HAA concentrations in areas of the

distribution system where disinfectant residuals are depleted.

In contrast to chlorination byproducts, ozonation byproducts form more rapidly, but their

period of formation is much lower than that of chlorination byproducts(Singer and Reckhow 1999). 

This is the result of the quick dissipation of ozone residuals in drinking water treatment plants.

B.6 Concentration and Characteristics of DBP Precursors

The formation of halogenated DBPs is related to the concentration of NOM at the point of

chlorination. Greater DBP levels are formed in waters with high concentrations of precursors. Studies

conducted with different fractions of NOM have indicated the reaction between chlorine and NOM

with high aromatic content tends to form higher DBP levels than NOM with low aromatic content. For

this reason, UV absorbance (typically indicated by UV absorbance at 254 nm [UV-254]), which is

generally attributed to the aromatic and unsaturated components of NOM, is considered a good

predictor of the tendency of a source water to form THMs and HAAs (Owen et al. 1998; Singer and

Reckhow 1999). It should be noted, however, that the more highly aromatic precursors, characterized

by high UV-254, in source waters are more easily removed by coagulation. Thus, it is the UV-254

measurement immediately upstream of the point(s) of chlorination within a treatment plant that is more

directly related to THM and HAA formation potential.

B.7 Water Temperature

The rate of formation of THMs increases with increasing temperature. HAA formation rates

may also increase with temperature, though the effects are less pronounced. Consequentially, the

highest THM and HAA levels may occur in the warm summer months. However, water demands are

often higher in warmer months, resulting in lower water age within the distribution system and helping to

control DBP formation. Furthermore, high temperature conditions in the distribution system promote

the accelerated depletion of residual chlorine, which can mitigate DBP formation and promote

biodegradation of HAAs (unless chlorine dosages are increased to maintain high residuals). (Singer and

Reckhow 1999). For these reasons, depending on the specific system, the highest THM and HAA

levels may be observed during months which are warm, but not necessarily the warmest.

Seasonal trends affect differently where high THM and HAA concentrations might be found. 

For example, when water is colder, microbial activity is typically lower and DBP formation kinetics are

slower. Under these conditions, the highest THM and HAA concentrations might appear coincident

with the oldest water in the system. In warmer water, the highest HAA concentrations might appear in
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fresher water, which is likely to contain higher disinfectant residuals that can prevent the biodegradation

of HAAs.

B.8 Water pH

In the presence of NOM and chlorine, THM formation increases with increasing pH, whereas

the formation of HAAs and other DBPs increase with decreasing pH. The increase of THMs at higher

pH values is likely due to base catalyzed reactions that lead to THM formation. HAA formation

pathway can be altered at high pH since their precursors can hydrolyze (Singer and Reckhow 1999).

The major byproducts of ozonation are not affected by base hydrolysis. However, the rate of

decomposition of ozone to hydroxyl radical is accelerated as pH increases. This occurrence is thought

to be responsible for the decrease of some byproducts (e.g., aldeydes) and the increase of others (e.g.,

carbonyl byproduct and total organic halides; Singer and Reckhow 1999). The application of ozone to

bromide containing waters leads to the formation of hypobromite and hypobromous acid. At low pH,

the equilibrium shifts to hypobromous acid which can react with NOM to form halogenated byproducts

such as bromoform and dibromoacetic acid (Singer and Reckhow 1999). 
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References

EPA, 1999. Alternative Disinfectants and Oxidants Guidance Manual. EPA 815-R-99-014.

Hoigne J., and H. Bader. 1988. “The formation of Trichloronitromethane (chloropicrin) and

Chloroform in a Combined Ozonation/Chlorination Treatment of Drinking Water.” Water Resources.

22 (3):313.

Krasner S. W., 1999. “Chemistry of Disinfection By-Product Formation”, in Formation and Control

of Disinfection By-Products in Drinking Water, Singer P.C. editor, American Water Works

Association, Denver CO. 

Reckhow, D.A., P.C. Singer, and R.L. Malcom. 1990. “Chlorination of Humic Mateials: Byproduct

Formation and Chemical Interpretations.” Environ. Sci. Technol. 24(11):1655.

Singer, P.C. and D.A. Reckhow. 1999. “Chemical Oxidation.” Water Quality and Treatment, 5

th

edition. Letterman R.D. technical editor, American Water Works Association, McGraw-Hill, New

York, NY.

Singer, P.C. (editor) 1999. Formation and Control of Disinfection Byproducts in Drinking Water.

American Water Works Association, Denver, CO.

Singer, P.C., and G.W. Harrington. 1993. “Coagulation of DBP Precursors: Theoretical and Practical

Considerations.” Conference proceedings, AWWA Water Quality Technology Conference, Miami,

FL.

Swanson, W.J., Z. Chowdhury, R. Summers, and G. Solarik. 2001. “Predicting DBPs at Full-Scale:

Calibration and Validation of the Water Treatment Plant Model Using ICR Data” Conference

proceedings, 2001 AWWA Annual Conference and Exhibition, Washington, DC.
Appendix C

TTHM and HAA5 Sampling Protocol
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C.1 Introduction

TTHM and HAA5 samples must be properly collected and analyzed to ensure accurate

analytical results. For example, THMs are volatile chemicals, meaning they can move from the liquid

phase to the gas phase under ambient conditions. Therefore, care must be taken to make sure that no

air bubbles are present in the filled sample vial. This appendix summarizes information on proper

sample collection, handling, and laboratory analytical techniques.

C.2 Analytical Methods

Table C.1 lists the analytes that are included in TTHM and HAA analyses. 

Table C.1 TTHM and HAA Analytes

Analyte Group Code

Analytes in Group

(Abbreviation for Analyte)

HAA5 Haloacetic acids:

 Dibromoacetic acid (DBAA)

 Dichloroacetic acid (DCAA)

 Monobromoacetic acid (MBAA)

 Monochloroacetic acid (MCAA)

 Trichloroacetic acid (TCAA)

HAA9 HAA5 plus four additional analytes

 Bromochloroacetic acid (BCAA)

 Bromodichloroacetic acid (BDCAA)

 Chlorodibromoacetic acid (CDBAA)

 Tribromoacetic acid (TBAA)

TTHM Trihalomethanes:

 Bromodichloromethane (BDCM)

 Bromoform (CHBr3) 

 Chloroform (CHCl3)

 Dibromochloromethane (DBCM)

Table C.2 lists the approved laboratory analytical methods for TTHM and HAA5 along with

guidelines for sample collection and storage. These guidelines include type of sample container,

preservative and dechlorinating agents, pH, and sample collection. 
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Table C.2 Sampling Requirements of TTHM and HAA5 Analyses

Analyte

Group

Analytical

Method

Sample Container

Material2

Preservative/Dechlorinating Agent 

(Recommended amount)

Storage

Guidelines 

Sample Collection

Guidelines

TTHM EPA 502.2 40 ml -120 ml screw

cap glass vials with

PTFE-faced silicone

septum

Options:

(1) 3 mg Na2S2O3/40 mL sample or 

(2) 3 mg Na2S2O3/40 mL sample and immediate

acidification using HCl to pH < 2 or

(3) 25 mg ascorbic acid/40 mL sample and

immediate acidification using HCl to pH < 2.

Option 1 may be used if THMs are the only

compounds being determined in the sample.

Options 2 & 3 require the sample to be

dechlorinated prior to the addition of acid.

Keep at

4°C.

14 days

maximum

hold time3.

Fill bottle to just overflowing

but do not flush out

preservatives. 

No air bubbles. 

Do not overfill. 

Seal sample vials with no

head space.

If ascorbic acid is used to

dechlorinate TTHM samples,

then the samples MUST be

acidified. Acidification of

TTHM samples containing

Na2S2O3 is required if the

samples will also be analyzed

for VOCs. In both cases, the

pH must be adjusted at the

time of sample collection, not

later at the laboratory. 

EPA 524.2 40 ml -120 ml screw

cap glass vials with

Teflon-faced silicone

septum

EPA 551.1 60 ml screw cap

glass vials with

PTFE-faced silicone

septum

1 g phosphate buffer & NH4Cl or Na2SO3 mixture

per 60 mL sample (mixture consists of 1 part

Na2HPO4, 99 parts KH2PO4 , and 0.6 parts NH4Cl

or Na2SO3. 1g per 60 mL results in a pH of

4.5-5.5 and 0.1 mg NH4Cl or Na2SO3 per mL of

sample.)

HAA5 EPA 552.1 250 ml (approx.)

amber glass bottles 

fitted with Teflonlined screw caps

0.1 mg NH4Cl per mL of sample 

EPA 552.2 50 ml (approx.)

amber glass bottles

fitted with Teflonlined screw caps

EPA

552.34

50 ml (approx.)

amber glass bottles

fitted with Teflonlined screw caps

SM 6251 B 40 ml or 60 ml screw

cap glass

65 mg NH4Cl

1 (40 CFR 141.131 (b))

2 Selection of container should be coordinated with the laboratory.

3

 The holding time has been changed to 14 days for all HAA5 samples as a part of the Stage 2 DBPR. 

4

 EPA Method 552.3 has been added as an approved HAA5 method as part of the Stage 2 DBPR.
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C.2.1 Sampling Procedure

It is important to follow sampling procedures provided by your certified laboratory. Sampling

procedures may vary slightly among individual laboratories; you should contact your laboratory to learn

their procedures. The following is common procedure for collecting samples for TTHM and HAA5

analyses.

You will need:

1) Sample vials provided by laboratory (most laboratories will provide sample vials with

proper preservative and dechlorinating agents) 

2) Small bottle of 1:1 hydrochloric acid and eye dropper or pasteur pippettes (pH adjustment

is necessary for some TTHM methods)

3) Water proof labels and permanent (indelible ink) marker

4) Ice/coolant and cooler

Procedure:

1) Label each sample vial. Use waterproof labels and indelible ink. Each label should include:

• Unique sample ID

• System name

• Sample location

• Sample date and time

• Analysis required, if not already on label

2) Remove the aerator from the tap, if there is one present.

3) Open the water tap and allow the system to flush until the water temperature has stabilized

(usually about 3-5 minutes). The purpose of this step is to ensure the sample does not

represent stagnant water that has sat for a long time in the water line between the street and

the faucet. The sample should be representative of the water flowing through the

distribution system at the chosen sampling point. 

4) Adjust the flow so that no air bubbles are visually detected in the flowing stream.
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5) Slowly fill the sample vial almost to the top without overflowing. Use the bottle cap to add

a small amount of additional sample water while simultaneously capping the vial to achieve a

headspace-free sample. Be careful not to rinse out any of the preservative/dechlorinating

agent during this process. After the bottle is filled, invert three or four times.

6) If collecting TTHM samples that require acidification, let the sample set for about 1 minute,

allowing the dechlorinating chemical to take effect. Carefully open the vial and adjust the

pH of TTHM sample to < 2 by adding approximately 4 drops of hydrochloric acid for

every 40 mL of sample (amount of acid needed will depend on buffering capacity of

sample). Recap the vial, and invert three or four times.

7) Invert the vial and tap it to check for air bubbles. If bubbles are detected, carefully open

the vial and add more sample water using the cap to achieve a headspace-free sample.

8) Immediately cool the samples to 4oC by placing them in a cooler with frozen refrigerant

packs or ice, or in a refrigerator. Samples should be maintained at this temperature during

shipping to the laboratory.

9) Complete the Sample Chain of Custody provided by the laboratory and include it with the

sample shipment.

C.2.2 Regarding Loss of Samples

Samples may be “lost” due to a number of reasons:

• Bottle broken during shipment from the water system to the laboratory

• Sample improperly collected (e.g., sample bottle not completely filled)

• Sample improperly shipped (e.g., not kept cold during shipment)

• Sample improperly preserved (e.g., not dechlorinated)

• Bottle is broken or lost at the laboratory

• Quality control doesn’t meet method specifications when sample is analyzed

Resampling for the lost sample should be conducted as soon as possible after the loss is

determined. Only the lost sample needs to be recollected, not the entire sample set that was collected

together. Make sure to note the loss of sample and resample date as a deviation in your IDSE report. 
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C.3 Analytical Method Descriptions

The following are brief summaries of the approved TTHM and HAA5 methods.

C.3.1 EPA Method 502.2

Highly volatile organic compounds with low water solubility are extracted (purged) from the

sample matrix by bubbling an inert gas through a 5 mL aqueous sample. Purged sample components

are trapped in a tube containing suitable sorbent materials. When purging is complete, the sorbent tube

is heated and back flushed with helium to thermally desorb trapped sample components onto a capillary

gas chromatography (GC) column. The column is temperature programmed to separate the method

analytes which are then detected with a photoionization detector (PID) and an electrolytic conductivity

detector (ELCD) placed in series. Analytes are quantitated by procedural standard calibration. The

PID is not required, if only TTHMs are being determined.

Identifications are made by comparison of the retention times of unknown peaks to the retention

times of standards analyzed under the same conditions used for samples. Additional confirmatory

information can be gained by comparing the relative response from the two detectors. For absolute

confirmation, a gas chromatography/mass spectrometry (GC/MS) determination according to USEPA

Method 524.2.

Highly volatile compounds with low water solubility, including TTHMs, are extracted from the

water sample by bubbling an inert gas through 5 mL of the sample. The chemical compounds that are

extracted from the water sample are then trapped in a tube that contains material to which the chemicals

attach, or sorb. Once the extraction process has been completed, the tube containing the extracted

chemicals is treated with helium, and the mixture of helium and chemicals enters a capillary gas

chromatography (GC) column. The column is temperature programmed to separate the chemicals

extracted from the water, which are then detected with a photoionization detector (PID) and an

electrolytic conductivity detector (ELCD) placed in series. The amount of each chemical is determined

using procedural standard calibration. The PID is not required if only TTHMs are being measured. 

Chemical compounds are identified by comparing the retention times of unknown GC peaks

with retention times for chemical standards analyzed under the same conditions. Confirmation can be

made by comparing the relative response from the two detectors. For absolute confirmation of results,

a gas chromatography/mass spectrometry (GC/MS) determination can be made using U.S. EPA

Method 524.2.

For a complete description of this method see EPA publication: EPA/600/R-95/131 Methods

for the Determination of Organic Compounds in Drinking Water: Supplement III. 
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C.3.2 EPA Method 524.2

Volatile organic compounds, including TTHMs, are extracted from the water sample by

bubbling an inert gas through the sample. Extracted compounds are trapped in a tube that contains

material to which the chemicals attach, or sorb. When the extraction process is complete, the tube is

heated and flushed with helium to de-sorb the trapped chemicals into a capillary gas chromatography

(GC) column interfaced with a mass spectrometer (MS). The GC column is temperature programmed

to allow for the separation of different chemicals, which are then detected with the MS. Compounds

detected by the GC are identified by comparing their measured mass spectra and retention times with

reference mass spectra and retention times in a database. Reference mass spectra and retention times

for different compounds are obtained by measuring calibration standards under the same conditions that

are used for the water samples. The concentration of each compound is measured by comparing the

MS response of the compound with the MS response of another compound used as an internal

standard. Surrogate chemicals, whose concentrations are known in every sample, are measured using

the same internal standard calibration procedure.

For a complete description of this method see EPA publication: EPA/600/R-95/131 Methods

for the Determination of Organic Compounds in Drinking Water: Supplement III. 

C.3.3 EPA Method 551.1

A 50 mL volume of the sample is extracted using either 3 mL of methyl-tert-butyl ether

(MTBE) or 5 mL of pentane. A small sub-sample of the extract (2 μL) is then injected into a GC

equipped with a fused silica column for separation, and a linearized electron capture detector for

analysis. Concentrations of different chemical compounds are determined by comparing their measured

amounts to standard calibration curves.

A typical sample can be extracted and analyzed using this method in 50 minutes for chlorinated

byproducts (e.g., HAA5) and chlorinated solvents, and in two hours for all of the compounds analyzed

by this method. Results can be confirmed by using a second, different GC column, by using primary

confirmation columns installed in a single injection port, or by a separate confirmation analysis.

For a complete description of this method see EPA publication: EPA/600/R-95/131 Methods

for the Determination of Organic Compounds in Drinking Water: Supplement III. 

C.3.4 EPA Method 552.1

A 100 mL volume of the sample is adjusted to pH 5.0 and extracted using a pre-conditioned

miniature anion exchange column. The chemical compounds to be analyzed are first eluted using small

amounts of acidic methanol, and are then esterified directly in this medium after adding a small volume
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of methyl-tert-butyl ether (MTBE) as a co-solvent. The methyl esters are partitioned into the MTBE

phase, and are identified and measured using capillary column gas chromatography with an electron

capture detector (GC/ECD).

For a complete description of this method see EPA publication: EPA/600/R-92/129 Methods

for the Determination of Organic Compounds in Drinking Water: Supplement II. 

C.3.5 EPA Method 552.2

The pH of a 40 mL volume of sample is adjusted to less than 0.5, and the sample is extracted

using 4 mL of methyl-tert-butyl ether (MTBE). The haloacetic acids that have been partitioned are then

converted to their methyl esters by adding acidic methanol and heating them slightly. The acidic extract

is then returned to neutral pH using a saturated solution of sodium bicarbonate. The chemical

compounds of interest are identified and measured using capillary column gas chromatography with an

electron capture detector (GC/ECD). Chemical concentrations are determined using standard

calibration procedures.

For a complete description of this method see EPA publication: EPA/600/R-95/131 Methods

for the Determination of Organic Compounds in Drinking Water: Supplement III. 

C.3.6 EPA Method 552.3

[to be developed]

C.3.7 Standard Method 6251 B

The sample is extracted using methyl-tert-butyl ether (MTBE) at an acidic pH. A salting agent

is added during the extraction process to increase the extraction’s efficiency. Once extracted,

compounds are methylated using diazomethane solution to produce methyl ester or other ether

derivatives that can be separated in a gas chromatograph. A gas chromatograph equipped with a fused

silica capillary column and an electron capture detector (GC/ECD) is used for analysis. Alternative

detectors can be used if quality control criteria are met. Calibration standards are extracted,

methylated, and analyzed in the same manner as the water samples to compensate for less than 100%

recoveries during sample preparation.

For a complete description of this method see Standard Methods for the Examination of

Water and Wastewater: 21st Edition published jointly by the APHA, AWWA, and WEF. 
Appendix D

Simulated Distribution System Test
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D.1 Introduction

An SDS test involves storing a sample of disinfected finished water in a manner that reflects the

conditions (pH, temperature, and residence time) of the distribution system. The purpose of an SDS

test is to evaluate the potential of the finished water to form TTHM and HAA5 in the distribution system

conditions at different residence times. An SDS test is site-specific and therefore, there is no universal

set of conditions that applies to all systems.

Section D.2 provides the recommended procedure for conducting an SDS laboratory test. 

Section D.3 describes how SDS tests can be used in conjunction with Stage 1 DBPR and other DBP

monitoring data to estimate average and maximum residence times.

D.2 Recommended SDS Test Procedure

A separate SDS sample should be collected for each distribution system residence

time to be evaluated. The following protocol is recommended for collecting, storing, and analyzing an

SDS sample: 

Test Conditions

• The pH of the sample should be that of the distribution system water (± 0.2). No pH

adjustments should be made after collecting the finished water samples for any of the SDS

tests.

• The sample should be held at a temperature comparable to the distribution system

temperature between the treatment plant and the TTHM sampling points in the distribution

system for the corresponding time period. The goal should be a temperature within ± 2°C

of either the water entering the distribution system or the water at the DBP sampling point

being evaluated. If major temperature fluctuations occur in the distribution system during

the SDS tests, these should be taken into account when analyzing the data.

• The holding time of an SDS test begins when an SDS sample is collected, and ends when

the sample is transferred into sample bottles (with appropriate preserving and dechlorinating

agents) for TTHM and HAA5 analysis. The total reaction time actually begins with the

addition of chlorine-based oxidants at the treatment plant.

• A disinfectant residual should be present at the end of the holding time.
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Sample Collection

• SDS samples should be collected at the entry point to the distribution system, after the final

addition of chlorine and/or ammonia or any chemicals added for corrosion control or pH

adjustment are completely mixed in treated water. (In cases where systems use

chloramines for secondary disinfection, SDS sample collection will typically be at the

location where the system measures free ammonia to control the dosing of ammonia). If

systems employ booster disinfection, then a second SDS sample collected after

booster disinfectant addition and a separate SDS analysis are recommended.

• SDS samples should be collected in 250 mL amber glass bottles (or larger) with TFE-lined

screw caps, and should be collected head space-free, with no addition of any preservatives

or dechlorinating agents. (The sample should be of sufficient volume for all the analyses

needed for SDS sample analyses, i.e., DBPs, disinfectant residual, pH, etc.) Prior to

collecting the samples, the bottles should be pre-treated with concentrated chlorine solution

and copiously rinsed with deionized water, then oven dried at 180 /C for an hour, to ensure

that the glassware is chlorine demand free.

Holding Time

The holding time represents a residence time pre-determined by the system. The system could

conduct several SDS tests at a range of residence times to develop a kinetic curve (see section D.3). 

The system could also use estimated residence times of DBP sampling sites in the distribution system

and compare the SDS results to its DBP results. 

Sample Storage

The bottle containing an SDS sample is best stored in the treatment plant where it is collected.

 

• It can be suspended in the plant clearwell to maintain it at the finished water temperature, or

in a container in a sink with a constant flow of finished or distributed water running through

the container. 

• The collected sample may be transported to an off-site laboratory, provided it is maintained

at the desired storage temperature during transport and for the duration of the test. During

the holding time at the laboratory, an SDS sample can be placed in an incubator (set at the

selected distribution system temperature ± 2 /C) or in a container in a sink with a constant

flow of finished or distributed water running through the container (if the laboratory receives

water from the same distribution system being tested). 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft D-3

Sample Analysis

At the end of a specified residence time, an SDS sample is analyzed for several parameters

(disinfectant residual, TTHM, and HAA5, pH, temperature). 

• The SDS sample should be divided by pouring it into sample bottles containing the

appropriate dechlorinating agents/preservatives for each analysis. The TTHM sample

bottle should be filled first, followed by the HAA5 sample bottle. Care must be taken to

not aerate the sample during this splitting process, in order to prevent the loss of volatile

THMs. 

• Immediately after the TTHM and HAA5 sample bottles are filled, the pH, temperature, and

disinfectant residual concentration should be determined in the remaining aliquot of the SDS

sample. If no disinfectant residual is detected, then the result of this SDS test should be

thrown out. 

• The TTHM and HAA5 samples should be analyzed within the holding time specified by the

method. 

• The TTHM and HAA5 analyses should be conducted by a laboratory certified under the

drinking water certification program to perform those analyses. Appendix C describes

TTHM and HAA5 laboratory analyses.

D.3 Using SDS Tests to Determine Average and Maximum Residence Time

For systems that do not have good information about their residence time, a number of 

SDS tests can be conducted and compared to Stage 1 compliance monitoring data to help estimate

average and maximum residence time. It should be noted that the SDS tests should be conducted in

conjunction (preferably done on the same day or a couple of days before) with the Stage 1 DBP

compliance monitoring sampling. 

Because DBP formation is not linear, it is recommended that a kinetic curve be developed to

describe the system specific DBP formation. To create a useful curve, a minimum of four SDS samples

should be collected at the finished water sampling location. Analysis should begin immediately for the

first sample (aliquots should be transferred to sample vials with appropriate preservation and

dechlorinating agents for TTHM and HAA5 anlaysis, and chlorine residual, pH, and temperature should

be analyzed immediately thereafter). This represents time zero. A second sample should be stored at

the finished or distribution system temperature (see section D.2 for details) for an estimated maximum

distribution system residence time (this selected time interval will be a best guess estimate). The other

two SDS samples are stored for two intermediate time intervals that equally subdivide the maximum
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft D-4

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7 8 9 10

Residence Time (days)

DBP Concentration (ug/L)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Free Chlorine Residual (mg/L)

TTHM

HAA5

Chlorine

residence time (e.g., if you estimate that your maximum residence time is 6 days, store your other two

SDS samples for 2 days and 4 days). At the end of the selected storage times, transfer the sample

aliquots to appropriate TTHM and HAA5 sample bottles (with preservation and dechlorinating agents)

for analysis. Plot the the resultant TTHM and HAA5 data (:g/L) on the y-axis and corresponding

holding times (days) on the x-axis. An example kinetic curve with disinfectant residual data is presented

in Figure D.1.

Figure D.1 SDS Test Kinetic Curve

To estimate the residence time of monitoring sites in the distribution system, use the DBP results

from the monitoring sites and the kinetic curve developed from the SDS tests. For example, the TTHM

result from a Stage 1 compliance monitoring sample was 40 μg/L. Using Figure D.1, 40 μg/L of

TTHM corresponds to a residence time of 2 days. Combining these data with disinfectant residual data

from each of the four SDS samples may also be useful. 

When designing SDS studies, systems using booster disinfection must consider the application
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft D-5

of disinfectants in the distribution system. For systems that employ booster chlorination in the

distribution system, another SDS sample should be taken after the re-chlorination station and the

residence time should simulate the distribution system conditions downstream of the re-chlorination

station.
Appendix E

IDSE SMP Report for

Producing Surface Water Systems Serving $ 10,000 People

This appendix is provided as an example IDSE report for producing surface water

systems serving at least 10,000 people and opting to complete the Standard Monitoring Program

(SMP). 

Chapter 5 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not 

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Elm City

PWSID Number: US1111111 

Address: 1234 Main Street 

Elm City, US 99999 

Contact Person: Mr. Ronald Doe, P.E. 

 

Phone Number: 123-555-0000 

Fax Number: 123-555-0001 

Email Address: Rdoe@ci.elmcity.us 

System Type: Community, surface water 

Population Served: 160,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data should also be in

this section, including a brief description of the water treatment process train. 

General system characteristics:

Service area: Elm City plus surrounding suburban areas

Production: Annual average daily production = 15 MGD

Source Water Information: 

Hardwood Lake (surface water)

pH: from 6.9 to 7.5

Alkalinity: from 82 to 98 mg/L as CaCO3

TOC: from 2.1 to 4.0 mg/L as C

Softwood River (surface water)

pH: from 6.8 to 7.9

Alkalinity: from 77 to 94 mg/L as CaCO3

TOC: from 1.6 to 4.4 mg/L as C

Entry points and service areas under the influence of each entry point:

(Entry points should be tied to source(s) and typical flows noted) 

Entry points: Hardwood Plant: Design Capacity = 20 mgd

Average Daily Production = 7.5 mgd

Softwood River Plant: Design Capacity = 20 mgd

Average Daily Production = 7.5 mgd

Customers located in the Industrial Park area, Oakville, Pineville, and south downtown areas

generally receive water from the Hardwood Plant

Customers located in the Cypressville, Cedarville, Poplarville, and north downtown areas

generally receive water from the Softwood Plant

Customers located in the Weeping Willow Community, Appleville, and central downtown areas

generally receive a mixture of water from both plants
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-2

Treatment Provided:

Hardwood – ferric chloride coagulation, flocculation, sedimentation, dual-media filtration

Softwood River – ferric chloride coagulation, flocculation, sedimentation, dual-media filtration,

followed by GAC

Primary and residual disinfection: Chlorine/chlorine at both plants

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 400 miles, 4" - 56" (approximately 6 MG total pipe volume)

5 storage tanks of 10 MG total capacity

1 ground tank 4 MG capacity 

4 elevated tanks 6 MG capacity

Following recent customer complaints in areas downstream of the Cherry Hill tank, the city

evaluated mixing conditions in each distribution system tank. As a result, the city made some

inlet/outlet modifications at both the Cherry Hill and Apple Drive tanks to improve tank mixing. 

The average residence time of water in the distribution system is six to eight days.

Pump stations:

Station #1 is located at the ground storage tank (in Pineville). This pump is primarily used

during peak demands and low pressure situations. The pump is timed to turn on in the morning

and evening during peak demand and when the pressure drops below 40 psi at a point

downstream of the pump station.

Stations #2 and #3. These pumps are used to boost system pressure when the pressure in the

areas downstream of these pumps (Weeping Willow and Poplarville) drops below 40 psi. 

Booster chlorination facilities:

Facility #1 is located on Cherry Hill Ave. (downstream of the Cherry Hill storage tank at pump

station #3). This facility is occasionally used during the summer when remote locations

downstream of the booster chlorination facility lose residual.

Facility #2 is located at the intersection of Second Ave. and 11th St. (in a mixing zone) in an

area of the distribution system where chlorine residuals are frequently low. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-3

Poplarville

Softwood River WTP

Hardwood WTP

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

Elm City Water Distribution System

Apple

Drive EST

Jackson

EST

Cherry

Hill EST

Pineville

GST

East

EST

2. Schematic of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-4

3. SMP monitoring requirements:

The Elm City system serves approximately 160,000 people and has two surface water plants. 

Therefore, a total of 16 SMP sample sites (8 per plant) are required to be sampled approximately

every 60 days for one year (6 dual sample sets per site) for TTHM and HAA5. Because it uses

chlorine as a disinfectant in the distribution system, three sites representative of high TTHM are

required, but only one site near the entry point is required.

Required SMP Sample Sites

SMP Site Type

Number of Sites in

the Hardwood Plant

Influence Zone

Number of Sites in

the Softwood River

Plant

Influence Zone

Near entry to the distribution system 1 1

Average residence time 2 2

Representative of high TTHM 3 3

Representative of high HAA5 2 2

Available Data:

Report all data that helped in sample site selection. If you have bromide, TOC, or HPC data,

these may be helpful for justifying Stage 2B site selection. For this example, only tables with

limited data are presented for Stage 1 DBPR sample sites and the sites chosen as SMP sample

sites. Your report should include data for all sites that were considered for SMP sites. 

Chlorine residual and HPC data were available for Total Coliform Rule sample sites and the 8

Stage 1 DBPR sample sites. The chlorine data for the summer months of June, July, August, and

September were reviewed, and monthly averages and an overall average were calculated. Table E.1

presents these data and shows which sites were chosen as SMP sites. 

Quarterly HPC data was also available for the same year and at the same sites as the free

chlorine data. The four results for each site were averaged. The quarterly results and yearly average

values are presented in Table E.2. The results are ordered based on the Stage 1 DBPR and SMP site

numbers.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-5

Table E.1 Elm City Distribution System—Free Chlorine Residual (Cl2) Data

Sample

Site

ID #

Source/

Plant

Stg. 1

Site

Type

SMP 

Site #

SMP

Site

Type

Free Chlorine Residual (mg/L)

June July Aug. Sept. Avg.

Stg. 1 #1 SRP Avg. 0.6 0.9 1.1 0.8 0.9

Stg. 1 #2 SRP Avg. 0.6 0.7 0.8 1.2 0.8

Stg. 1 #3 SRP Avg. 0.3 0.6 0.3 0.2 0.4

Stg. 1 #4 SRP Max. 0.2 0.3 0.5 0.3 0.6

Stg. 1 #5 HP Avg. 0.9 0.7 1.0 1.2 1.0

Stg. 1 #6 HP Avg. 0.2 0.8 0.8 0.5 0.6

Stg. 1 #7 HP Avg. 0.8 0.9 0.3 0.8 0.7

Stg. 1 #8 HP Max. 0.2 1.0 0.7 0.1 0.6

TCR #5 HP 1 E 1.6 1.4 1.6 1.5 1.5

TCR #4 HP 2 A 0.8 0.6 0.9 0.8 0.8

TCR #15 HP 3 A 0.6 0.4 0.4 0.4 0.5

TCR #16 HP 4 H 0.6 0.2 0.5 0.4 0.4

TCR #8 HP 5 H 0.4 0.3 0.3 0.5 0.4

TCR #2 HP 6 T 0.3 0.4 0.2 0.2 0.3

TCR #9 HP 7 T 0.3 0.2 0.2 0.4 0.3

TCR #12 HP 8 T ND 0.1 0.1 0.3 0.1 

TCR #10 SRP 9 E 1.4 1.2 0.9 1.7 1.3

TCR #11 SRP 10 A 0.6 0.6 0.5 0.9 0.7

TCR #13 SRP 11 A 0.5 0.3 0.4 0.5 0.6

TCR #6 Mix/SRP 12 H 0.7 0.4 0.8 1.0 0.7

TCR #1 SRP 13 H 0.5 0.8 0.9 0.4 0.7

TCR #7 Mix/SRP 14 T 0.3 0.4 0.7 0.6 0.5

TCR #3 SRP 15 T 0.2 0.6 0.3 0.2 0.3

TCR #14 Mix/SRP 16 T 0.6 0.7 0.6 0.6 0.6

Distribution System Warm Months Average 0.6

Mix - Mixing Zone TCR - Total Coliform Rule E - Near Entry Point

HP - Hardwood Plant Stg. 1 - Stage 1 DBPR A - Average Residence Time

SRP - Softwood River Plant ND - Non-Detection T - Representative High TTHM

H - Representative High HAA5
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-6

Table E.2 Elm City Distribution System—Heterotrophic Plate Counts (HPC) Data

Sample

Site

ID #

Source/

Plant

Stg. 1

Site

Type

SMP 

Site #

SMP

Site

Type

HPC (cfu/mL)

4

th Qtr. 1st Qtr. 2nd Qtr. 3rd Qtr. Avg.

Stg. 1 #1 SRP Avg. 56 42 276 345 180

Stg. 1 #2 SRP Avg. 82 136 246 146 152

Stg. 1 #3 SRP Avg 140 215 615 557 382

Stg. 1 #4 SRP Max 280 163 263 446 288

Stg. 1 #5 HP Avg. 140 66 236 364 201

Stg. 1 #6 HP Avg. 50 42 222 223 134

Stg. 1 #7 HP Avg 53 42 72 84 63

Stg. 1 #8 HP Max 196 45 425 653 330

TCR #5 HP 1 E 12 8 12 34 17

TCR #4 HP 2 A 78 86 364 384 228

TCR #15 HP 3 A 35 62 92 147 84

TCR #16 HP 4 H 34 76 89 97 74

TCR #8 HP 5 H 68 43 57 79 62

TCR #2 HP 6 T 35 43 45 64 47

TCR #9 HP 7 T 156 278 359 169 240

TCR #12 HP 8 T 233 214 546 456 362

TCR #10 SRP 9 E 67 14 42 35 40

TCR #11 SRP 10 A 43 34 224 156 114

TCR #13 SRP 11 A 54 65 65 573 189

TCR #6 Mix/SRP 12 H 53 64 123 94 83

TCR #1 SRP 13 H 50 34 63 113 65

TCR #7 Mix/SRP 14 T 69 43 43 37 48

TCR #3 SRP 15 T 70 212 332 356 242

TCR #14 Mix/SRP 16 T 66 53 53 153 81

Mix - Mixing Zone TCR - Total Coliform Rule E - Near Entry Point

HP - Hardwood Plant Stg. 1 - Stage 1 DBPR A - Average Residence Time

SRP - Softwood River Plant T - Representative High TTHM

H - Representative High HAA5
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-7

4. Summary of selected SMP sample sites:

Present the rationale for the selection of the SMP sample sites in your system, as well as a

schematic showing their location within the distribution system. 

Sample sites were chosen to represent diverse geographical areas of the distribution system. 

Each site is shown on the map of the distribution system in section I.6. Water quality data obtained

from residual chlorine (Table E.1) and HPC (Table E.2) monitoring were considered in the selection of

the SMP monitoring sites. 

SMP Site #1 – Entry point to the distribution system for Hardwood Water Treatment Plant. This site is

where the first group of customers receives water.

SMP Site #2 – Represents average residence time of water leaving the Hardwood Plant. Based on

chlorine monitoring results at TCR sample sites, we identified the areas within the system where chlorine

levels equaled approximately 50 percent of the initial residual concentration at the high service pumps

and chose this site from within those areas. There are no storage facilities between the treatment plant

and this site. 

SMP Site #3 – Represents average residence time of water leaving the Hardwood Plant. Water at this

site does not go through a storage facility, but the chlorine residual is generally 35 to 40 percent of the

Hardwood Plant finished water concentration. We attribute this loss of chlorine to the fact that the

transmission and distribution lines serving this area are older unlined cast iron and have been observed

to show significant build-up of corrosion by-products (tubercles). We believe that these corrosion

by-products exert a chlorine demand that results in lower than typical chlorine residual at this site,

although we believe it has a lower average water age than SMP #2.

SMP Site #4 – Represents high HAA5 levels. Sample site is in an area approaching the perimeter of

the distribution system. Water in this area is primarily from the Hardwood Plant. Chlorine residual at

this site ranges between 0.2 and 0.6 mg/L, and the heterotrophic plate count is consistently below 100

cfu per mL year round. 

SMP Site #5 – Represents high HAA5 levels. We have over 7 years of data from this site. Water at

this site is from the Hardwood Plant. Chlorine residual levels are between 0.3 and 0.5 mg/L, and

heterotrophic plate count is below 100 cfu/mL.

SMP Site #6 – Represents high TTHM levels. This sampling site is believed to receive water from a 4

MG ground tank located in the Appleville region of the distribution system during high demand periods

and is at the entrance to a small subdivision cul-de-sac in the Oakville community. This site is near the

predicted edge of the mixing zone, and chlorine residuals at this site are generally very low, indicating

this may be a hydraulic dead end. The sample site is near the first house on the cul-de-sac (which has

12 homes total).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-8

SMP Site #7 – Represents high TTHM levels. This site is near the edge of the mixing zone between

the Softwood River and Hardwood plant influence areas, but within the an area of the system believed

to receive all of its water from the Hardwood Plant. Chlorine residual levels ranged between 0.2 and

0.4 mg/L at this site. 

SMP Site #8 – Represents high TTHM levels. This site has been problematic in the past due to

positive total coliform test results, non-detectable chlorine residuals, high heterotrophic plate count

results, and odor complaints. A 4-inch blow-off was installed downstream of this site, but it continues

to have periodic poor water quality. Water in this area is from the Hardwood Plant. 

SMP Site #9 – Entry point to the distribution system for the Softwood River Water Treatment Plant. 

This site is just after the high service pumps at the Water Treatment Plant. 

SMP Site #10 – Represents average residence time. Chlorine residual is generally 50 to 60 percent of

the plant finished water concentration.

SMP Site #11 – Represents average residence time. Water does not go through a storage facility but

the chlorine residual is generally 35 to 40 percent of the plant finished water concentrations. The

transmission and distribution lines serving this area are older unlined cast iron with build-up of corrosion

by-products (tubercles) in several areas. We believe these corrosion by-products exert a chlorine

demand, lowering chlorine residual, even though residence time is less than in areas with similar chlorine

residual concentrations.

SMP Site #12 – Represents high HAA5 levels. At this site, the water age is believed to be greater than

average because it is within the mixing zone, but the chlorine residual is never below 0.4 mg/L and the

heterotrophic count plate is usually low (below 100 cfu/mL).

SMP Site #13 – Represents high HAA5 levels. Our Stage 1 DBPR monitoring results indicate that the

high HAA5 concentrations move around our system depending on the season and production of the

Hardwood and Softwood River Plants, especially in the areas served by the Softwood River Plant.

SMP Site #14 – Represents high TTHM levels. This sample site is located in a zone of the distribution

system that has been recently developed. This connection is located downstream from a chlorine

booster station. Chlorine residuals are normally in the 0.3 to 0.7 mg/L range. Water in this area is

generally a mix of water from the Hardwood and Softwood River Plants.

SMP Site #15 – Represents high TTHM levels. This site is downstream from the Cypressville Storage

Tank, a 1.5 million gallon elevated storage tank. There are often low chlorine residuals in the areas

downstream of this tank.

SMP Site #16 – Represents high TTHM levels. This sampling site is in the mixed zone before the last

group of connections near the end of the distribution system. This area receives water from the
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-9

Jackson Storage Tank and water that bypasses the tank. Water from this area can vary greatly in the

percentages of Softwood River and Hardwood Plant water.

5. SMP Sample Schedule:

Because the quarterly Stage 1 DBPR monitoring is the only DBP monitoring that has been

performed in the Elm City system, historic DBP data is available for only the months of January, April,

July, and October. July has regularly had the highest DBP levels, but no DBP data is available for the

other summer months. As a result, we also reviewed finished water temperature from two years of

TCR sampling records and determined that our peak month for distribution system water temperature is

August. However, we also found that July’s average distribution system water temperature for the two

years reviewed was only 0.5o C less than August’s. Based on the historic DBP data and minimal

difference in average water temperature, we concluded that July is the controlling month for the Elm

City distribution system. The following table summarizes our planned SMP sample dates and is based

on collection of our samples on the second Monday of the month.

Proposed SMP Sample Schedule

Planned Sample Date

November 8, 2005

January 10, 2006

March 7, 2006

May 9, 2006

July 11, 2006

September 12, 2006

Dual sample sets will be collected from each of the 16 SMP sample sites on or close to the

listed dates and analyzed for TTHM and HAA5 by a State-certified laboratory.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-10

Poplarville

MIXING

ZONE

Softwood River WTP

Hardwood WTP

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

8

7

5 6

4

3

2

1

8

7 6

5

4

3 2

1

9

16

15

14

13

12

11

10

Stage 1 DBPR site

TCR / Selected SMP site

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

Elm City Influence Zones

And Sample Sites

6. Map of the distribution system showing major transmission mains, numbered Stage 1

DBPR compliance sites, and numbered SMP sample sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-11

II. SMP RESULTS

1. Introduction:.

The SMP was conducted between November 2004 and September 2005. The following table

summarizes our planned SMP sample dates, the actual dates when samples were collected, and the

reasons for deviations from the plan.

Actual SMP Sample Schedule

Planned Sample Date Actual Sample Date Explanation

November 8, 2005 November 8, 2005 On schedule.

January 10, 2006 January 10, 2006 On schedule.

March 7, 2006 March 11, 2006 Major snowstorm created

hazardous road conditions and

limited access to sample sites

May 9, 2006 May 9, 2006 On schedule.

July 11, 2006 July 11, 2006 On schedule.

September 12, 2006 September 12, 2006 On schedule

2. Summary of IDSE SMP and Stage 1 DBPR compliance data:

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in this section. Table E.3 presents the DBP results for the SMP sample sites, organized by

plant, then in order of highest to lowest TTHM average. Table E.4 presents the DBP results for the

Stage 1 DBPR compliance sample sites for the period from November 2004 to August 2005. Sites

proposed as Stage 2B compliance sites are shaded within the tables.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-12

Table E.3. Elm City—IDSE SMP Monitoring Results

SMP Site

# Plant Site Type

TTHM (μg/L) HAA5 (μg/L)

Data1 LRAA Data1 LRAA

1 Hardwood entry point 36, 42, 30,

25, 38, 28

33 50, 44, 43,

47, 48, 38

45

2 Hardwood average residence

time

54, 39, 42,

56, 60, 42

49 22, 29, 36,

40, 41, 30

33

3 Hardwood average residence

time

47, 40, 52,

43, 51, 41

46 20, 25, 25,

29, 27, 19

24

4 Hardwood high HAA5 33, 29, 41,

42, 44, 22

35 36, 43, 52,

51, 48, 38

45

5 Hardwood high HAA5 35, 40, 41, 37

46, 43

40 60, 59, 64,

55, 66, 54

60

6 Hardwood high TTHM 62, 60, 60,

64, 68, 70

64 42, 40, 33,

38, 46, 30

38

7 Hardwood high TTHM 68, 62, 54,

52, 72, 70

63 39, 45, 28,

33, 40, 32

36

8 Hardwood high TTHM 65, 61, 73,

71, 72, 64

68 41, 39, 46,

45, 39, 47

43

9 Softwood River entry point 40, 42, 49,

38, 38, 46

42 43, 47, 40,

48, 

45

10 Softwood River average residence

time

42, 20, 58,

62, 62, 30

46 23, 56, 40,

52, 40, 28

40

11 Softwood River average residence

time

47, 50, 41,

54, 48, 40 

47 14, 20, 21,

23, 29, 19

21

12 Mix/Softwood

River

high HAA5 35, 29, 47,

37, 47, 27 

37 36, 40, 46,

48, 40, 34 

41

13 Softwood River high HAA5 52, 35, 46,

42, 50, 38

44 56, 44, 65,

50, 50, 58

54

14 Mix/Softwood

River

 high TTHM 56, 50, 55,

51, 61, 45

53 42, 30, 43,

38, 34, 42

38

15 Softwood River high TTHM 48, 56, 70,

52, 65, 49

57 28, 40, 33,

38, 34, 42

35

16 Mix/Softwood

River

 high TTHM 72, 49, 68,

55, 69, 53

61 20, 21, 38,

28, 19, 35

27

1Data obtained from sampling every 60 days are listed in order for November, January, March, May, July, and

September (as required for a surface water supply $10,000).

Note: Bold text and shading identify proposed Stage 2 DBPR compliance sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-13

Table E.4. Elm City—Stage 1 DBPR Compliance Monitoring Results

Site ID # Plant Site Type

TTHM (μg/L) HAA5 (μg/L)

Data1 LRAA Data1 LRAA

Stg. 1 #1 Softwood River Average 45, 34, 56, 62 49 24, 32, 43, 45 36

Stg. 1 #2 Softwood River Average 36, 42, 45, 45 42 47, 50, 55, 56 52

Stg. 1 #3 Softwood River Average 32, 34, 48, 67 45 50, 62, 64, 65 59 

Stg. 1 #4 Softwood River Maximum 64, 68, 83, 74 72 21, 25, 26, 28 25

Stg. 1 #5 Hardwood Average 44, 20, 62, 42 42 34, 45, 33, 41 38

Stg. 1 #6 Hardwood Average 46, 49, 39, 50 46 22, 30, 39, 41 33

Stg. 1 #7 Hardwood Average 41, 22, 50, 59 43 4, 46, 64, 58 54

Stg. 1 #8 Hardwood Maximum 65, 50, 60, 73 62 19, 22, 37, 30 27

1Data listed in order for October, January, April, and July quarterly sampling.

Note: Bold text and shading identify proposed Stage 2B compliance sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-14

III. PROPOSED STAGE 2B COMPLIANCE MONITORING SITES

1. Site Summary:

A total of eight Stage 2B compliance monitoring sites (four per plant) were selected from the

Stage 1 DBPR and SMP sites, as shown in the previous tables and as summarized in the following

table. A schematic of the monitoring sites is presented in section III.4.

Stage 2B Proposed Compliance Monitoring Sites

Stage 2B Compliance Sites Previous Site ID #

Site #

Source/

Plant Type

SMP 

Site #

Stage 1

DBPR

Site #

1 Softwood River Average Stg. 1 #3

2 Softwood River High HAA5 Stg. 1 #21

3 Softwood River High TTHM 16

4 Softwood River High TTHM Stg. 1 #4

5 Hardwood Average Stg. 1 # 7

6 Hardwood High HAA5 5

7 Hardwood High TTHM 8

8 Hardwood High TTHM Stg. 1 # 8

1

 This site was an average residence time site under Stage 1 DBPR, but represented high HAA5

concentrations in the distribution system.

2. Justification of Site Selections:

1. Softwood River Plant Average Site – Although Stage 1 DBPR site #1 had the highest

TTHM LRAA of the Stage 1 average residence time sites, Stage 1 DBPR site #3 was

chosen because the TTHM LRAAs at these two sites were similar, but the HAA5 LRAA

at Stage 1 DBPR site #3 was considerably higher. Therefore, Stage 1 DBPR site #3 was

chosen as Elm City’s Stage 2B site #1.

2. Softwood River Plant Representative High HAA5 Site – Stage 1 DBPR site #2 and

SMP site #13 had similar HAA5 LRAAs. However, Stage 1 site #2 was chosen as the

Stage 2B #2 because we have multiple years of data at this site, and this will allow us to

maintain an historical record at this site. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-15

3. Softwood River Plant Representative High TTHM Sites – SMP site #16 and Stage 1

DBPR site # 4 were chosen as Elm City’s Stage 2B sites #3 and #4, respectively, because

they had the highest TTHM averages over the SMP sampling period among all Softwood

River Plant sample sites.

4. Hardwood Plant Average Site – Stage 1 DBPR site #7 had the highest HAA5 LRAA

for the SMP sampling period, much higher than the other two Stage 1 DBPR average

residence time sites, and a TTHM LRAA that was second highest among the Stage 1

DBPR average residence time sites. Therefore, Stage 1 DBPR site # 7 was chosen as Elm

City’s Stage 2B site #5.

5. Hardwood Plant Representative High HAA5 Site – SMP site #5 was chosen as Elm

City’s Stage 2B site #6 because it has the highest HAA5 LRAA of all the Hardwood Plant

sample sites.

6. Hardwood Plant Representative High TTHM Sites – SMP site #8 and Stage 1 DBPR

site #8 were chosen as Elm City’s Stage 2B sites #7 and #8, respectively. SMP site #8

was chosen because it had the highest TTHM LRAA of all the Hardwood Plant sample

sites during the SMP period. Stage 1 DBPR site #8 was chosen for several reasons. It is

in an area of the system not represented by other Stage 2B sites. It is downstream of a

storage tank. It will provide historical continuity in DBP sampling. It had a single sample

TTHM result higher than the highest single sample result of the two sites that had higher

averages (73 vs. 72 and 70). It had a TTHM LRAA only slightly lower than the two SMP

sites that had higher averages (62 vs. 63 and 64) and achieved this average with a warm

weather sample being taken in only one month (July), versus the three warm weather

samples (May, July, and September) taken at the SMP sites.

3. Proposed Stage 2B Compliance Monitoring Schedule 

Stage 2B compliance monitoring will be scheduled for January, April, July, and October, the

same as Stage 1 DBPR and Stage 2A DBPR sampling, for consistency and because the difference in

distribution system water temperature between July and August is minimal (average 0.5o C higher in

August, based on a review of 2 years of TCR sampling records).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft E-16

Poplarville

MIXING

ZONE

Softwood River WTP

Hardwood WTP

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

Elm City Stage 2B DBPR

Compliance Sample Sites

Stage 2B DBPR Highest TTHM

Stage 2B DBPR Highest HAA5

Stage 2B DBPR Average 

Residence Time

#

#

#

1

5

3 4

8

7

2

6

4. Map of Proposed Stage 2B Compliance Monitoring Sites:
Appendix F

IDSE SMP Report for

Producing Ground Water Systems Serving $ 10,000 People

This appendix is provided as an example IDSE report for producing ground water

systems serving at least 10,000 people and opting to complete the Standard Monitoring Program

(SMP).

Chapter 6 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Oak City

PWSID Number: US5555555 

Address: 124 Oak Drive 

Oak City, US 11111-1234 

 

Contact Person: Mr. Joseph Smith, P.E. 

Phone Number: 123-555-1111 

Fax Number: 123-555-2222 

Email Address: Jsmith@ci.oakcity.us 

System Type: Community, ground water 

Population Served: 200,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data should also be in

this section, including a brief description of the water treatment process train. 

General system characteristics:

Service area: Oak City plus surrounding suburban areas

Production: Annual average daily demand = 20 MGD

Source Water Information:

Silver Springs Wellfield (Silver Aquifer)

pH: from 7.0 to 7.5

Alkalinity: from 125 to 175 mg/L as CaCO3

TOC: from 1.4 to 2.7 mg/L as C

Blue Springs Wellfield (Blue Aquifer)

pH: from 6.9 to 7.3

Alkalinity: from 82 to 198 mg/L as CaCO3

TOC: from 2.1 to 3.7 mg/L as C

Entry points and service areas under the influence of each entry point:

(Entry points should be tied to source(s) and typical flows noted.)

Entry points: Silver Plant (Silver Springs Wellfield), 25 MGD production capacity 

Winter Average Production = 18 MGD

Summer Average Production =20 MGD

Blue Pumping Station (Blue Springs Wellfield), 10 MGD production capacity

Winter Average Production = 0 MGD

Summer Average Production = 6 MGD

The second supply source (Blue Springs Wellfield) is necessary to cope with higher demand

during the summer. The two wellfields draw from two different aquifers. 

When the Blue Pumping Station is in service, customers located in the Cypressville, Cedarville,

Poplarville, and north downtown generally receive water from the Blue Springs Wellfield.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-2

Customers located in the Elmville, Oakville, Pineville, and south downtown generally receive

water from the Silver Plant year round.

Customers located in the Weeping Willow Community, Appleville, and central downtown

generally receive a mixture of water from both plants when both the Silver Plant and Blue

Pumping Station are in service.

Treatment Provided: 

Silver Plant: Direct filtration, chlorination, in service 12 months per year.

Blue Pumping Station: Chlorination, in service approximately three months per year, during

the summer (over 60 consecutive days of operation).

Primary and residual disinfection: Chlorine/chloramines at both plants. 

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 600 miles, 4" - 56"

The estimated range of residence time of water in the distribution system is 0 to 6 days.

5 storage tanks

1 ground tank 4 MG capacity 

4 elevated tanks 6 MG total capacity (1.5 MG each)

Pump stations:

Station #1 is located at the ground storage tank. This pump is primarily used during peak

demands and low pressure situations. The pump is timed to turn on in the morning and evening

during peak demand, and when the pressure drops below 40 psi downstream of the station.

Stations #2 and #3. These pumps are used to boost system pressure when the pressure in the

areas downstream of these pumps (Poplarville and Weeping Willow) drops below 40 psi.

Booster facilities:

Both facilities are total chlorine paced, and the target dose after boosting is 3.0 to 3.5 mg/L. 

Ammonia is added (residual ammonia before boosting is accounted for) to target a Cl2:NH3-N

ratio of 4.5 to 4.0. 

Facility #1 is located on Industrial Park Ave. (downstream from the Courthouse storage tank at

pump station #3). This facility is occasionally used during the summer when low total chlorine

residual (below 1.0 mg/L) are measured at remote locations downstream of the booster facility. 

Facility #2 is located at the intersection of First Ave. and 13th St. (in a mixing zone) in an area

of the distribution system where total chlorine residuals are frequently low. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-3

Pineville

Oakville

Elmville

Weeping Willow

Downtown Appleville

Poplarville

Cedarville

Cypressville

MIXING

ZONE

Blue Pumping Station

(seasonal source)

Silver Plant

Elevated Storage Tank

Ground storage tank

Pump station

Booster disinfection station

2

1

3

P

P

P

P

Stage 1 DBPR site

SMP site

1

4

2

Oak City Distribution System

Pineville

Oakville

Elmville

Weeping Willow

Downtown Appleville

Poplarville

Cedarville

Cypressville

MIXING

ZONE

Blue Pumping Station

(seasonal source)

Silver Plant

Elevated Storage Tank

Ground storage tank

Pump station

Booster disinfection station

2

1

3

P

P

P

P

Stage 1 DBPR site

SMP site

1

4

2

Pineville

Oakville

Elmville

Weeping Willow

Downtown Appleville

Poplarville

Cedarville

Cypressville

MIXING

ZONE

Blue Pumping Station

(seasonal source)

Silver Plant

Elevated Storage Tank

Ground storage tank

Pump station

Booster disinfection station

2

1

3

P

P

P

P

Stage 1 DBPR site

SMP site

1

4

2

Oak City Distribution System

2. Schematic of the distribution system with SMP and Stage 1 DBPR sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-4

3. SMP monitoring requirements:

The system serves approximately 200,000 people and uses two ground water sources. 

Therefore, a total of 4 SMP sample sites (2 per plant) must be sampled approximately every 90 days

(4 dual sample sets per quarter) for the IDSE.

Required SMP Sample Sites

SMP Site Type

Number of Sites in

the Silver Plant

Influence Zone

Number of Sites 

in the Blue Station

Influence Zone

Representative of high TTHM 1 1

Representative of high HAA5 1 1

Available Data:

Report all data that helped in site selection. If you have bromide, TOC, or HPC data,

these may be helpful for justifying Stage 2B site selection. For this example, tables with data

from Stage 1 DBPR, Total Coliform Rule, and operational sample sites are presented. The sites

chosen as SMP sample sites should also be noted for reference. Your report should include data

for all sites that were considered as candidates for SMP sites.

Total chlorine and HPC data were available from Total Coliform Rule sample sites and the two

Stage 1 DBPR sample sites. Distribution system water temperature varies over a small range

between winter and summer, so chlorine data for November, February, May, and August were

reviewed, and monthly averages and an overall average were calculated. The typical average

water age at each site was also estimated based on results from the distribution system

hydraulic model. Table F.1 presents this data, with sites grouped by summer time plant service

area and then ordered from low to high by the yearly average total chlorine concentration. The

selected SMP sample sites are numbered and their type identified for reference.

Quarterly HPC data were available for the same year and at the same sites as the chlorine data. 

The four results for each site were averaged. The quarterly results and yearly average values are

presented in Table F.2. The results are presented following the order based on the yearly average

HPC values.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-5

Table F.1 Oak City Distribution System—Total Chlorine Data

Sample

Site

ID #

Source/

Plant

Stage 1

Site

Type

SMP

Site

 #

SMP

Site

Type

Total Chlorine (mg/L)

Nov. Feb. May Aug. Mean

Oper #9 SP 1 T 0.4 0.3 0.5 0.9 0.5

TCR #9 SP 3 H 0.9 1.2 1.0 0.9 1.0

TCR #4 SP 0.9 1.6 0.8 0.6 1.0

Stg. 1 #2 SP Avg. 0.6 3.0 2.1 0.8 1.6

TCR #3 SP 1.8 1.8 1.5 2.7 2.0

TCR #6 SP 2.4 2.7 0.9 2.4 2.1

Oper #10 SP 1.8 1.3 2.4 3.6 2.3

Oper #20 SP 4.0 3.6 2.7 4.0 2.6

TCR #2 BP 2 T 0.6 1.2 0.9 1.0 0.9

TCR #5 BP 0.6 0.9 1.5 0.9 1.0

TCR #8 BP 4 H 1.8 1.3 1.6 0.9 1.4

TCR #1 BP 1.8 2.1 1.8 1.7 1.9

Stg. 1 #1 BP Avg. 0.6 2.4 2.4 1.5 1.7

Oper #1 BP 1.8 2.7 3.3 2.4 2.6

TCR # 7 BP 2.7 2.1 3.0 3.6 2.9

Oper #30 BP 4.0 3.8 4.2 2.9 3.7

SP - Silver Plant TCR - Total Coliform Rule T - Representative High TTHM

BP - Blue Plant Stg. 1 - Stage 1 DBPR H - Representative High HAA5

Oper. - Operational sample
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-6

Table F.2 Oak City Distribution System—Heterotrophic Plate Counts (HPC) 

Sample

Site

ID #

Source/

Plant

Stage 1

Site

Type

SMP

Site

 #

SMP

Site

Type

HPC (cfu/mL)

Nov. Feb. May Aug. Mean

Oper #9 SP 1 T 56 42 176 245 130

TCR #9 SP 3 H 54 65 65 82 67

TCR #4 SP 43 34 224 156 114

Stg. 1 #2 SP Avg. 55 60 85 125 81

TCR #3 SP 53 42 72 84 63

TCR #6 SP 35 62 92 80 67

Oper #10 SP 0 0 0 5 1

Oper #20 SP 0 0 0 0 0

TCR #2 BP 2 T 70 212 132 356 242

Oper #30 BP 0 0 4 1 1

TCR #5 BP 280 163 263 96 201

TCR #8 BP 4 H 57 72 37 77 68

TCR #1 BP 56 43 43 143 71

Stg. 1 #1 BP Avg. 25 52 82 70 57

Oper #1 BP 15 42 72 60 47

TCR # 7 BP 2 1 12 25 10

SP - Silver Plant TCR - Total Coliform Rule T - Representative High TTHM

BP - Blue Plant Stg. 1 - Stage 1 DBPR H - Representative High HAA5

Oper. - Operational sample
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-7

4. Summary of selected SMP sample sites

Present the rationale for the selection of the SMP sample sites.

Sample sites were chosen to represent diverse geographic areas of the distribution system. A

description of the four SMP sites for the Oak City metro area distribution system is given below. The

distribution system map in section I.2 shows these sites.

SMP Site #1 – Chosen to represent high TTHM levels in the Silver Plant influence zone and the mixing

zone. This monitoring site is located before the last group of connections in proximity to the end of the

distribution system in the mixing zone. At this site, water demand tends to be low, total chlorine levels

are always low (ranging between 0.3 and 0.9 mg/L) and heterotrophic plate counts are often greater

than 200 cfu/mL.

SMP Site #2 – Chosen to represent high TTHM levels in the Blue Pumping Station influence zone. 

This monitoring site is located after the first group of connections (approximately 0.5 miles) downstream

of the Courthouse Reservoir (1.5 MG elevated storage facility) in the influence zone of the Blue

Pumping Station.

SMP Site #3 – Chosen to represent high HAA5 levels in the Silver Plant influence zone. Sample tap is

a hose bib at an elementary school located in a zone of the distribution system with water age greater

than average. Total chlorine levels at this site range between 0.9 and 1.2 mg/L, and the heterotrophic

plate count is consistently below 100 cfu/mL throughout the year.

SMP Site #4 – Chosen to represent high HAA5 levels in the Blue Pumping Station influence zone and

the mixing zone. This site is a dedicated sampling site routinely used for monitoring water quality in

downtown Oak City. In this area, the water age is greater than the average, the total chlorine is never

below 0.9 mg/L and the heterotrophic count plate is usually low (below 100 cfu/mL). This area is

believed to be in the mixing zone, receiving water from both the Blue Pumping Station and Silver Plant.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-8

5. SMP Sample Schedule

Because the quarterly Stage 1 DBPR monitoring is the only DBP monitoring that has been

performed in the Oak City system, historic DBP data is available for only the months of February,

May, August, and November. August has regularly had the highest DBP levels. No other DBP data is

available for any other months of the year, so water temperature data was also reviewed to see which

month of the year had the warmest water temperature. Our review of three years of finished water

temperature data from TCR sample sites showed that distribution system water was warmest in August. 

Therefore, based on the agreement of the water temperature and TTHM and HAA5 monitoring results,

we concluded August is the controlling month for the Oak City distribution system. The following table

summarizes our planned SMP sample dates and is based on sampling on the second Monday of the

month.

Proposed SMP Sample Schedule

Planned Sample Date

November 8, 2005

February 14, 2006

May 9, 2006

August 8, 2006

Dual sample sets will be collected from each of the four SMP sample sites on or close to the

listed dates and analyzed for TTHM and HAA5 by a State-certified laboratory. Stage 1 DBPR

compliance samples will be collected on the same days.

6. Map of the distribution system showing major transmission mains, numbered Stage 1

DBPR compliance sites, and numbered SMP sample sites:

For this example, the map in Section I.2 was used to show SMP sample sites. The system

in this example has only four SMP sites and two Stage 1 DBPR monitoring sites. Depending on

the size of your system and the number of sample sites. It may be more appropriate (for clarity)

to show SMP sites on a separate schematic in this section.

See map in section I.2.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-9

II. SMP RESULTS

1. Introduction:

The SMP was conducted between November 2005 and August 2006. The following table

presents the planned SMP sample dates, the actual dates when samples were collected, and the reason

for the one deviation from the plan.

Actual SMP Sample Dates

Planned Sample Date Actual Sample Date Explanation

November 8, 2005 November 8, 2005 On schedule.

February 14, 2006 February 14, 2006 On schedule.

May 9, 2006 May 9, 2006 On schedule.

August 8, 2006 August 5, 2006 System maintenance was planned in the area

of SMP site #1 for the week of August 8 and

was expected to require extensive system

flushing, so SMP sampling was performed on

the prior Friday.

2. Summary of IDSE SMP data and Stage 1 DBPR compliance data:

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in the following tables. The first table presents the TTHM and HAA5 results for the SMP

sample sites and the second table presents the results for the Stage 1 DBPR compliance sampling for

the period from February 2005 to August 2006. 

Oak City IDSE SMP Monitoring Results

SMP Sample Site

TTHM (μg/L) HAA5 (μg/L)

Monitoring

Results1 LRAA

Monitoring

Results1 LRAA

#1 - Representative high TTHM (Silver) 62, 71, 82, 85 75 21, 25, 26, 28 25

#2 - Representative high TTHM (Blue) 49, 68, 72, 69 65 20, 21, 38, 28 27

#3 - Representative high HAA5 (Silver) 33, 29, 41, 42 36 43, 52, 48, 38 45

#4 - Representative high HAA5 (Blue) 35, 29, 37, 47 37 36, 40, 46, 40 41

1

 Data obtained from sampling every 90 days are listed in order for November, February, May, and August (as

required for a ground water supply serving $10,000 people).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-10

Oak City Stage 1 DBPR Monitoring Results

Stage 1 DBPR Monitoring Site

TTHM (μg/L) HAA5 (μg/L)

Monitoring

Results1 LRAA

Monitoring

Results1 LRAA

Maximum residence time #1 45, 34, 56, 62 49 24, 32, 43, 45 36

Maximum residence time #2 60, 68, 68, 98 74 42, 33, 30, 38 36

1

 Data obtained from sampling every 90 days are listed in order for November, February, May, and August (as

required for a ground water supply serving $10,000 people).

III. PROPOSED STAGE 2B COMPLIANCE MONITORING SITES

1. Site Selection:

Two Stage 2B compliance sample sites were selected for each plant from the one Stage 1

DBPR site and two SMP sample sites per plant. The selections were based on the TTHM and HAA5

LRAAs. The sites with the highest LRAAs were selected, with one exception. The following tables

rank the sites based on their TTHM and HAA5 LRAAs. The sites proposed as Stage 2B compliance

sites are shaded in the tables. A schematic of the sites is presented in section III.4.

Proposed Stage 2B Compliance Monitoring Sites

Silver Plant Blue Pumping Station

TTHM HAA5 TTHM HAA5

Site

LRAA

(μg/L) Site

 LRAA

(μg/L) Site

LRAA

(μg/L) Site

 LRAA

(μg/L)

SMP #1 75 SMP #3 45 SMP #2 65 SMP #4 41

Stg. 1#2 74 Stg. 1#2 36 Stg. 1#1 49 Stg. 1#1 36

SMP #3 36 SMP #1 25 SMP #4 37 SMP #2 27

Note: Bold text and shading identify proposed Stage 2 DBPR compliance sites.

2. Justification of Site Selections:

For the Silver Plant, the proposed site for highest TTHM is Stage 1 DBPR site #2. This site

had a LRAA nearly equal to the highest LRAA (74 vs. 75 μg/L at SMP #1), had the highest single test

result for TTHM (98 vs. 85 μg/L at SMP #1), and had a higher HAA5 average than SMP #1 (36 vs

25 μg/L). Continuing the use of the Stage 1 DBPR site will also allow the city to maintain a longer

continuous historical record of TTHM concentrations at a single location. The proposed site for highest

HAA5 is SMP #3, which had the highest HAA5 LRAA of the three Silver Plant sample sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-11

For the Blue Pumping Station, the proposed site for highest TTHM is SMP #2, since it had the

highest TTHM average. The proposed site for highest HAA5 is SMP #4, which had the highest HAA5

average. 

3. Summary of Proposed Compliance Sites and Sampling Schedule:

Stage 2B Sample Site Site Description

1. Silver Plant Highest TTHM Old Stage 1 DBPR Site #2

2. Silver Plant Highest HAA5 SMP Site #3

3. Blue Pumping Station Highest TTHM SMP Site #2

4. Blue Pumping Station Highest HAA5 SMP Site #4

Dual sample set Stage 2B sampling is proposed to occur in March, June, August (peak

historical month for TTHM concentrations), and December.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft F-12

Pineville

Oakville

Elmville

Weeping Willow

Downtown Appleville

Poplarville

Cedarville

Cypressville

MIXING

ZONE

Blue Pumping Station

(seasonal source)

Silver Plant

1

2

2

Elevated Storage Tank

Ground storage tank

Pump station

Booster disinfection station

P

P

P

P

4

3

Stage 2B highest HAA5 site

Stage 2B highest TTHM site #

#

Oak City Distribution System

Pineville

Oakville

Elmville

Weeping Willow

Downtown Appleville

Poplarville

Cedarville

Cypressville

MIXING

ZONE

Blue Pumping Station

(seasonal source)

Silver Plant

1

2

2

Elevated Storage Tank

Ground storage tank

Pump station

Booster disinfection station

P

P

P

P

4

3

Stage 2B highest HAA5 site

Stage 2B highest TTHM site #

#

Oak City Distribution System

4. Map of Proposed Stage 2B Compliance Monitoring Sites:
Appendix G

IDSE SMP Report for

Producing Surface Water Systems Serving 500 - 9,999 People

This appendix is provided as an example IDSE report for producing surface water

systems serving 500 to 9,999 people and opting to complete the Standard Monitoring Program

(SMP).

Chapter 6 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2 B compliance monitoring site selection is

shown in this example, along with several instances of the use of best professional judgement

being applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Lakeside City

PWSID Number: US0000000 

Address: P.O. Box 1234 

Lakeside City, US 22222-1234 

Contact Person: Ms. Mary Smith, P.E. 

Phone Number: 123-555-1111 

Fax Number: 123-555-2222 

Email Address: Msmith@ci.lakeside.us 

System Type: Community, surface water 

Population Served: 3,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data should also be in

this section, including a brief description of the water treatment process train. 

General System Characteristics:

Service area: Lakeside City – the system serves an area within a three-mile radius

Production: Annual average daily demand 1 MGD

Source Water Information:

Deep Lake water quality data:

pH: from 6.8 to 7.9

Alkalinity: from 77 to 94 mg/L as CaCO3

TOC: from 1.6 to 4.4 mg/L as C

Entry points (tied to source(s)) and identification of service area(s) under the influence of each entry

point:

(Entry points should be tied to source(s) and typical flows noted) 

Entry points: Deep Lake Plant Design Capacity = 2.5 mgd

Average Daily Production = 1.0 mgd

Treatment Provided:

Deep Lake Plant: alum coagulation, flocculation, sedimentation, and dual media filters.

Disinfection: chlorine for both primary and secondary disinfection.

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 20 miles, 4" - 12"

2 elevated tanks with total capacity of 0.5 MG
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-2

A pump station is located near the western storage tank (most distant from the plant). This

pump is primarily used during peak demands and low pressure situations. The pump is timed to

turn on in the morning and evening during peak demand and when the pressure drops below 40

psi at a point downstream of the pump station.

The residence time of water in the distribution system is believed to average approximately 2

days, and ranges up to nearly 5 days.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-3

Deep Lake WTP

1 P

Elevated Storage Tank

P Pump Station

1

Stage 1 DBPR site

SMP TTHM site

SMP HAA5 site

#

#

2

Big 

Industrial 

Park

2. Schematic drawing of the distribution system with SMP and Stage 1 DBPR sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-4

3. SMP monitoring requirements:

The Lakeside City system serves approximately 3,000 people and has one surface water plant. 

Therefore, a total of 2 SMP sample sites are required by the Stage 2 DBPR to be sampled

approximately every 90 days (2 dual sample sets per quarter).

Required SMP Sample Sites

SMP Site Type Number of Sites

Representative of high TTHM 1

Representative of high HAA5 1

Available Data:

Report all data that helped in sample site selection. If you have bromide, TOC, or HPC

data, these may be helpful for justifying Stage 2B site selection. For this example, only limited

tables are presented with data for Stage 1 DBPR sample sites and the sites chosen as SMP

sample locations. Your report should include data for all sites that were considered as candidates

for SMP sites. 

Chlorine residual information was available for Total Coliform Rule sample sites, the Stage 1

DBPR sample site, and the operational sample site. In addition, HPC data was available for Total

Coliform Rule sample sites. The following table presents these data, with the selected SMP sample

sites numbered and their type identified for reference.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-5

Table G.1 Lakeside Distribution System—Free Chlorine Residual Data

Sample 

Site 

ID #

SMP 

Site #

SMP

Site

Type

Free Chlorine Residual (mg/L)

7/ 04 8/ 04 9/ 04 10/ 04 11/ 04 12/ 04 1/ 05 2/ 05 3/ 05 4/ 05 5/ 05 6/ 05 7/ 05 8/ 05 9/ 05 10/ 05

Stg. 1 0.14 0.32 0.68 0.63 0.20 0.45

Oper. #1 1.5 1.5 1.4 1.2 1.1 1.2 1.1 1.1 1.2 1.2 1.4 1.4 1.4 1.5 1.3 1.2

TCR #3 1 T 0.12 0.10 0.22 0.34 0.44 0.48 0.65 0.62 0.59 0.65 0.62 0.24 0.23 0.25 0.39 0.44

TCR #2 2 H 0.41 0.42 0.46 0.51 0.58 0.48 0.70 0.60 0.72 0.61 0.54 0.42 0.42 0.40 0.47 0.51

TCR #1 0.32 0.35 0.42 0.54 0.75 0.66 0.82 0.70 0.70 0.91 0.55 0.46 0.36 0.35 0.40 0.64

TCR - Total Coliform Rule T - Representative High TTHM

Stg. 1 - Stage 1 DBPR H - Representative High HAA5

Oper. - Operational sample

Table G.2 Lakeside Distribution System—Heterotrophic Plate Counts (HPC)

Sample

Site 

ID#

SMP 

Site #

SMP Site

Type

HPC (cfu/mL)

7/04 10/ 04 1/05 4/05 7/05 10/05

Stg. 1 468 223 76 72 423 98

Oper. #1 0 0 0 0 0 0

TCR #3 1 T 540 202 85 67 342 102

TCR #2 2 H 97 75 23 31 98 59

TCR #1 95 53 15 19 76 48

TCR - Total Coliform Rule T - Representative High TTHM

Stg. 1 - Stage 1 DBPR H - Representative High HAA5

Oper. - Operational sample
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-6

4. Summary of the selected SMP sample sites:

Present the rationale for the selection of the SMP sample sites in your system, as well as

a schematic showing their locations within the distribution system. 

The system has only one source. Therefore, a total of two SMP monitoring sites are 

required by the Stage 2 DBPR. Each monitoring site is marked on the map of the distribution system

(see section I.2). Residual chlorine and HPC data from the TCR and operational monitoring sites (see

Tables G.1 and G.2) were considered in the selection of the SMP monitoring sites. 

SMP Site #1 – Chosen to represent high TTHM levels. This monitoring site is located in the vicinity of

TCR sample site # 3, and before the last group of connections in proximity to the end of the distribution

system. At this site, water demand tends to be low, chlorine residuals are often very low (less than 0.5

mg/L) and heterotrophic plate counts are often higher than 100 cfu/mL.

SMP Site #2 – Chosen to represent high HAA5 levels. Sample tap is a hose bib at an elementary

school located in a zone of the distribution system with water age greater than average. Chlorine

residual at this site is never below 0.4 mg/L (range is between 0.4 and 0.7 mg/L), and the heterotrophic

plate count is consistently below 100 cfu/mL throughout the year.

5. SMP sample schedule:

Because the quarterly Stage 1 DBPR monitoring is the only DBP monitoring that has been

performed in the Lakeside City system, historic DBP data are available for only the months of

February, May, August, and November. August has regularly had the highest DBP levels. No other

DBP data are available for any other months of the year, so water temperature data from TCR sample

sites were also reviewed to see which month of the year had the warmest water temperature. Our

review of 3 years of temperature data showed that distribution system water was warmest in August. 

Therefore, based on the agreement of the water temperature and TTHM and HAA5 monitoring results,

we concluded that August is the controlling month for the Lakeside City distribution system. The

following table summarizes our planned SMP sample dates, which are based on sampling on the

second Monday of the month.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-7

Proposed SMP Sample Schedule

Planned Sample Date

November 13, 2007

February 12, 2008

May 14, 2008

August 13, 2008

Dual sample sets will be collected from each of the 2 SMP sample sites on or close to the listed

dates and analyzed for TTHM and HAA5 by a State-certified laboratory. Stage 1 DBPR compliance

samples will be collected on the same days.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-8

II. SMP Results

1. Introduction

The SMP was conducted between November 2007 and August 2008. The following table

presents the planned SMP sample dates, the actual dates when samples were collected, and the reason

for the one deviation from the plan.

Actual SMP Sample Schedule

Planned Sample Date Actual Sample Date Explanation

November 13, 2007 November 13, 2007 On schedule.

February 12, 2008 February 12, 2008 On schedule.

May 14, 2008 May 14, 2008 On schedule

August 13, 2008 August 17, 2008 One of the sample bottles broke from the

August 10 sampling, so re-sample was

performed 4 days later.

2. Summary of IDSE SMP data and Stage 1 DBPR compliance data.

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in the following two tables. The first table presents the TTHM and HAA5 results for the

SMP sample sites and the second table presents the results for the Stage 1 DBPR compliance sampling

for the period from November 2007 to August 2008. 

Lakeside City IDSE SMP Monitoring Results

SMP Sample Site

TTHM (μg/L) HAA5 (μg/L)

Monitoring

Results1 LRAA

Monitoring

Results1 LRAA

#1 - Representative high TTHM 63, 53, 78, 89 71 21, 25, 32, 41 30

#2 - Representative high HAA5 38, 32, 48, 56 44 43, 49, 53, 63 52

1 Data obtained from sampling every 90 days (as required for surface water supplies serving 500-9,999 people)

are listed in order for November, February, May, and August.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-9

Lakeside City Stage 1 DBPR Monitoring Results

SMP Sample Site

TTHM (μg/L) HAA5 (μg/L)

Monitoring Results1 Avg Monitoring Results1 Avg

Maximum residence time 56, 49, 79, 95 70 25, 30, 36, 51 36

3. Proposed Stage 2B Compliance Sites and Schedule:

Two Stage 2B compliance sample sites were selected from among the one Stage 1 DBPR and

two SMP sample sites. The selections were based on the TTHM and HAA5 LRAAs. The following

table ranks the sites based on their TTHM and HAA5 LRAAs. The sites proposed as Stage 2B

compliance locations are shaded in the table.

Proposed Stage 2 B Compliance Sites

TTHM HAA5

Site LRAA (μg/L) Site LRAA (μg/L)

SMP #1 71 SMP #2 52

Stage 1 70 Stage 1 36

SMP #2 44 SMP #1 30

Note: Bold text and shading identify proposed Stage 2B compliance sites.

The proposed highest HAA5 site is SMP #2, which had the highest LRAA of the three sample

locations. The proposed highest TTHM site is the Stage 1 DBPR site. This site had an LRAA nearly

equal to the highest LRAA (70 vs. 71 μg/L at SMP #1), and had the highest single test result for TTHM

(95 vs. 89 μg/L at SMP #1). It also had a higher HAA5 LRAA than SMP #1 (36 vs. 30 μg/L). 

Continuing to use the Stage 1 DBPR site will also allow the city to maintain a continuous historical

record of TTHM concentrations at a single location.

Dual sample set Stage 2 B sampling is proposed to occur in March, June, August (peak

historical month for TTHM concentrations), and December.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft G-10

Elevated Storage Tank

P Pump Station

Stage 2 high HAA5 site

Deep Lake WTP Stage 2 high TTHM site

P

Big 

Industrial 

Park

4. Schematic drawing of the distribution system with Stage 2B sites:
Appendix H

IDSE Report for

Producing Ground Water Systems Serving < 10,000 People

This appendix is provided as an example IDSE report for producing ground water 

systems serving less than 10,000 people and opting to complete the Standard Monitoring

Program (SMP).

Chapter 7 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Greenspring City

PWSID Number: US0000000 

Address: P.O. Box 1234 

Greenspring City, US 11111-1234 

Contact Person: Ms. Jennifer Smith, P.E. 

Phone Number: 123-555-9876 

Fax Number: 123-555-9877 

Email Address: Jsmith@ci.greenspring.us 

System Type: Community, ground water 

Population Served: 1,500 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data should also be in

this section, including a brief description of the water treatment process train. 

General system characteristics:

Service area: All of Greenspring City—an area of approximately 4 square miles

Production: Annual average daily demand - 250,000 gpd

Source water information:

Greenspring Wellfield water quality data:

pH typically ranges from 6.8 - 7.5

Alkalinity averages 185 mg/L as CaCO 3

TOC averages 1.5 mg/L as C

Entry points (tied to source and identification of service area under influence of each):

(Entry points should be tied to source(s) and typical flows noted) 

Green Hill Water Plant located at Greenspring Wellfield—the only entry point, feeds entire

distribution system

Design Capacity = 1.0 mgd

Average Daily Production = 0.25 mgd

Treatment provided:

Green Hill Water Plant adds chlorine for primary and secondary disinfection

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 7 miles, 4" - 12"

Number of storage tanks and total storage capacity: 

1 ground tank at the Green Hill water plant (0.05 MG) and 1 elevated tank (0.25 MG)

The average residence time of water in the distribution system is believed to be 1 day, and may

range up to nearly 3 days at the ends of the system.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-2

Elevated Storage Tank

Stage 1 DBPR site

SMP TTHM site

SMP HAA5 site

#

#

Green Hill Water Plant

1

1

2

2. Schematic of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-3

3. SMP monitoring requirements:

The Greenspring City system serves approximately 1,500 people. This is a ground water

system, served by one aquifer. Therefore, for the IDSE, a total of 2 SMP sample sites must be

sampled approximately every six months (2 dual sample sets every six months). 

SMP Site Requirements

Site Criteria Number of Sample Sites

Representative high TTHM 1

Representative high HAA5 1

Available Data:

Report all data that helped in sample site selection. For this example, only tables with limited

data are presented for Stage 1 DBPR sample sites and the sites chosen as SMP sample locations.

If you have bromide, TOC and/or HPC data, these may be helpful for justifying Stage 2B site

selection. Your report should include data for all sites that were considered as SMP sites. 

Chlorine residual was available for the system’s two Total Coliform Rule sample sites, the

Stage 1 DBPR sample site, and the operational sample site. The following table presents these data,

with SMP site numbers and types provided for those sites chosen for SMP monitoring.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-4

Table H.1 Greenspring Distribution System—Chlorine Residual Data

Sample 

Site 

ID #

SMP 

Site #

SMP

Site

Type

Free Chlorine Residual (mg/L)

1/03 2/03 3/03 4/02 5/03 6/03 7/03 8/03 9/03 10/03 11/03 12/03 1/04 2/04 3/03 4/04 5/04 6/04 7/04 8/04 9/04 10/04 11/04 12/04

Stg 1 0.25 0.28

TCR #2 1 TTHM 0.61 0.63 0.59 0.38 0.37 0.25 0.21 0.23 0.22 0.34 0.44 0.48 0.65 0.62 0.59 0.61 0.62 0.24 0.23 0.25 0.39 0.44 0.49 0.53

Avg. 2 HAA5 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

TCR #1 0.73 0.68 0.55 0.42 0.42 0.40 0.41 0.42 0.46 0.51 0.58 0.48 0.70 0.60 0.72 0.61 0.54 0.42 0.42 0.40 0.47 0.51 0.56 0.48

FW 1.3 1.0 1.2 1.2 1.4 1.5 1.5 1.6 1.4 1.2 1.1 1.1 1.2 1.1 1.3 1.4 1.4 1.4 1.5 1.5 1.4 1.2 1.1 1.0

TCR - Total Coliform Rule

Stg. 1 - Stage 1 DBPR

FW - Finished Water (operational sample site)

Avg - Average Residence Time (operational sample site)
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-5

4. Summary of selected SMP sample sites:

Present the rationale for the selection of the SMP sample sites in your system, as well as

a schematic showing their locations within the distribution system. 

SMP Site #1 – Chosen to represent high TTHM levels. This is TCR site #2. This site is at the end of

the distribution system, before the last significant group of connections, at a hose bib at the town library. 

It is located near TCR monitoring site #1, downstream of the storage tank, and before the last group of

connections in proximity to the end of the distribution system. At this site, chlorine residuals are often

very low (less than 0.5 mg/L). This site also represents high residence time within the distribution

system.

SMP Site #2 – Chosen to represent high HAA5 levels. This site is a hose bib at an elementary school

located in a zone of the distribution system with water age greater than average (based on operators’

knowledge of the distribution system) but less than that of SMP #1. Free chlorine is not routinely

monitored at this site. However, this site is expected to have higher chlorine residual than the TTHM

SMP site, and therefore less potential for biodegradation. This site was also chosen to provide good

geographical representation of the distribution system (although TCR #1 had free chlorine data, it was

physically too close to SMP #1 to be considered).

5. SMP sample schedule:

Because the yearly Stage 1 DBPR monitoring is the only DBP monitoring that has been

performed in the Greenspring system, historic DBP data are available for only the month of August. 

No other DBP data are available for any other months of the year, so water temperature data were

also reviewed to see which month of the year had the warmest water temperature. Our review of 3

years of finished water temperature data from TCR sample sites showed that distribution system water

was warmest in August. Therefore, based on the agreement of the water temperature and TTHM and

HAA5 monitoring results, we concluded that August is the controlling month for the Greenspring City

distribution system. The following table summarizes our planned SMP sample dates and is based on

sampling on the second Monday of the month.

Proposed SMP Sample Schedule

Planned Sample Date

February 12, 2008

August 13, 2008

Dual sample sets will be collected from each of the 2 SMP sample sites on or close to the 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-6

listed dates and analyzed for TTHM and HAA5 by a State-certified laboratory. Stage 1 DBPR

compliance samples will be collected on the same days.

II. SMP RESULTS

1. Introduction:

The SMP was conducted in February and August 2008. The following table presents the

planned SMP sample dates, the actual dates when samples were collected, and the reason for the one

deviation from the plan.

Actual SMP Sample Schedule

Planned Sample Date Actual Sample Date Explanation

February 12, 2008 February 13, 2008 Sampler was sick on 2/12/08

August 13, 2008 August 13, 2008 On schedule

2. Summary of IDSE SMP data and Stage 1 DBPR compliance data.

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in the following two tables. The first table presents the TTHM and HAA5 results for the

SMP sample sites and the second table presents the results for the Stage 1 DBPR compliance sampling

for the period from February 2008 to August 2008. 

Greenspring City SMP Monitoring Results

SMP Sample Site

TTHM (μg/L) HAA5 (μg/L)

2/08 8/08 LRAA 2/08 8/08 LRAA

#1 - Representative high TTHM 35 73 54 22 50 36

#2 - Representative high HAA5 25 55 40 23 49 36

Note: Bold text and shading identify proposed Stage 2B compliance sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-7

Greenspring City Stage 1 DBPR Monitoring Results

Stage 1 DBPR Sample Site

TTHM (μg/L) HAA5 (μg/L)

2/08 8/08 LRAA 2/08 8/08 LRAA

Maximum Residence Time 47 63 55 22 44 33

Note: Bold text and shading identify proposed Stage 2B compliance sites.

3. Proposed Stage 2B Compliance Sites and Schedule:

Stage 2B compliance sample sites were selected from among the two SMP sample sites and

one Stage 1 DBPR site. The selections were based on the LRAAs for TTHM and HAA5. 

Proposed Stage 2B Compliance Sites

Stage 2B

Site Number

Site Type Location Description

1 Highest TTHM Stage 1 DBPR #1

2 Highest HAA5 SMP #1

The proposed site for high TTHM is the Stage 1 DBPR site, which had an LRAA of 55 μg/L. 

The highest HAA5 LRAA occurred at both SMP #1 and SMP #2. The HAA5 values during the peak

temperature months were similar for these two sites. Because SMP #1 has a higher TTHM LRAA

than SMP #2, it was chosen as the second Stage 2B compliance monitoring site. 

Dual sample set Stage 2B sampling is proposed to occur in February and August (the peak

historical month for TTHM concentrations).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-8

Elevated Storage Tank

Stage 2 high TTHM site

Green Hill Water Plant

#

# Stage 2 high HAA5 site

1

2

4. Schematic of the distribution system with Stage 2B sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft H-9

This page intentionally left blank.
Appendix I

IDSE SMP Report for

Producing Surface Water Systems Serving < 500 People

This appendix is provided as an example IDSE report for producing surface water

systems serving less than 500 people and opting to complete the Standard Monitoring Program

(SMP).

Chapter 7 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Riverdale

PWSID Number: US0000000 

Address: P.O. Box 1234 

Riverdale, US 22222-1234 

Contact Person: Mr. John Jones, P.E. 

Phone Number: 123-555-1111 

Fax Number: 123-555-2222 

Email Address: JJones@ci.riverdale.us 

System Type: Community ground water under direct 

influence

Population Served: 300 
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Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data is also part

of this section, including a description of water treatment trains. General information about

residence times within the distribution system should also be included, if available.

General System Characteristics:

Service area: Riverdale

Production: Annual average daily demand 40,000 gpd

Source Water Information:

Green Meadows spring:

pH: from 6.8 to 7.9

Alkalinity: from 77 to 94 mg/L as CaCO3

TOC: from 1.6 to 2.4 mg/L as C

Entry points (tied to source(s)) and identification of service area(s) under the influence of each entry

point:

Entry points: Green Meadows well field

Treatment Provided: 

Green Meadows well field: Direct filtration

Primary and residual disinfection: Chlorine/chlorine

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 1 mile, 4" - 6"

1 standpipe with total capacity of 50,000 gallons

Riverdale did not receive a very small system waiver from the State because the standpipe,

which is used to maintain system pressure in the western half of the system, was considered

oversized and may contribute to excessive residence times in the tank. Chlorine residual

measurements in the tank show that it may be operating in a last-in/first-out mode, and water at
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-2

Green Meadows Well Field

1

1

2

Elevated Storage Tank

Stage 1 DBPR site

SMP TTHM site

SMP HAA5 site

#

#

the top of the tank may be much older than water in the bottom of the tank. Furthermore, the

Green Meadows spring is situated in the center of the Riverdale system, while the Stage 1

DBPR monitoring site is located on the east side of the system. The State suggested that the

western half of the system be monitored, upstream and downstream of the storage tank. 

The residence time of water in the distribution system is thought to average approximately 1

day, but is probably higher near the standpipe.

2. Schematic drawing of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-3

3. SMP monitoring requirements:

The Riverdale system serves approximately 300 people. This is a system using ground water

under the direct influence of surface water and is served by one plant. Therefore, a total of 2 SMP

sample sites are required by the Stage 2 DBPR to be sampled approximately every six months (2 dual

sample sets every six months).

SMP Site Requirements

Site Criteria Number of Sample Sites

Representative high TTHM 1

Representative high HAA5 1

Available Data:

Provide all data that helped in site selection. You can include are data from Stage 1 DBPR,

Total Coliform Rule, and operational sample sites (any site not used for rule compliance). You

should also provide residence times in the distribution system, if known. If you have bromide,

TOC, or HPC data, these may be helpful for justifying your Stage 2B site selection. Your report

should include data for all sites that were considered as candidates for SMP locations.

Chlorine residual information was available at Total Coliform Rule and operational sample sites. 

A summary of chlorine residual data in the distribution system is presented in Table I.1. The chlorine

residual results from a study of water flow through the storage tank are shown in Table I.2.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-4

Table I.1 Riverdale Distribution System—Chlorine Residual Data

Sample

Site ID

Chlorine Residual (mg/L)

1/05 2/05 3/05 4/05 5/05 6/05 7/05 8/05 9/05 10/

05

11/

05

12/

05

1/06 2/06 3/06 4/06 5/06 6/06 7/06 8/06 9/06 10/

06

11/

06

12/

06

WF #1 1.3 1.0 1.2 1.2 1.4 1.5 1.5 1.6 1.4 1.2 1.1 1.1 1.2 1.1 1.3 1.4 1.4 1.4 1.5 1.5 1.4 1.2 1.1 1.0

TCR #1 0.71 0.62 0.59 0.41 0.37 0.27 0.23 0.21 0.23 0.35 0.43 0.48 0.63 0.62 0.58 0.62 0.61 0.31 0.25 0.24 0.41 0.44 0.51 0.62

WF - Wellfield finished water

TCR - Total Coliform Rule

Table I.2 Riverdale Distribution System—Chlorine Residual Data at Storage Tank

Water Depth1 Test 1 Test 2 Test 3 Average

1 ft from top ND ND ND ND

3 ft from top ND 0.1 0.1 0.10

5 feet from top/bottom 0.2 0.3 0.2 0.23

3 ft from bottom 0.7 0.9 0.8 0.80

1 ft from bottom 1.1 1.0 1.1 1.07

1

 This is a 50 ft tall standpipe.

Note: Data collected in July 2004.

ND - Non Detect
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-5

4. Summary of selected IDSE SMP sites:

Present the rationale for the selection of SMP sample sites in your system, as well as a

schematic showing their location within the distribution system.

A description of the two SMP sites proposed for the Riverdale distribution system is given

here. Each site is shown on a map of the distribution system in section I.2. 

SMP Site #1 – Chosen to represent high TTHM levels. This site is located downstream of the

standpipe on the western edge of town. It is located before the last group of connections in proximity

to the end of the distribution system. Because water with high residence time from the upper portions

of the tank is thought to be occasionally drawn into the distribution system during peak demand periods,

this site has the potential for high TTHM levels.

SMP Site #2 – Chosen to represent high HAA5 levels. This site is a hose bib located upstream (prior

to) of the storage tank on the western edge of the system. This site has average residence time within

the distribution system, and chlorine residual is expected to be adequate (greater than 0.5 mg/L) to

prevent biodegradation. 

5. SMP Sample Schedule:

Annual Stage 1 DBPR monitoring is the only DBP monitoring that has been performed in the

Riverdale system. As a result historic DBP data are available for only the month of August. DBP data

is not available for any other months of the year, so water temperature data were reviewed to see

which month of the year had the warmest water temperature. Our review of three years of finished

water temperature data from the TCR sample site showed that distribution system water was warmest

in August. Therefore, we concluded that August is the controlling month for the Riverdale distribution

system. The following table summarizes our planned SMP sample dates and is based on sampling on

the second Monday of the required month.

Proposed SMP Sample Schedule

Planned Sample Date

February 12, 2008

August 13, 2008

Dual sample sets will be collected from each of the 2 SMP sample sites on or close to the listed

dates and analyzed for TTHM and HAA5 by a State-certified laboratory. Stage 1 DBPR compliance

samples will be collected on the same day in August.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-6

II. SMP RESULTS

1. Introduction:

The SMP was conducted in February and August 2008. The following table presents the

planned SMP sample dates, the actual dates when samples were collected, and the reason for the one

deviation from the plan.

Actual SMP Sample Schedule

Planned Sample Date Actual Sample Date Explanation

February 12, 2008 February 13, 2008 A blizzard prevented the operator from getting

to the monitoring sites on February 12.

August 13, 2008 August 13, 2008 On schedule.

2. Summary of IDSE SMP data and Stage 1 DBPR compliance data:

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in the following table. The table presents the TTHM and HAA5 results for the SMP sample

sites and the Stage 1 DBPR compliance site. 

Riverdale SMP and Stage 1 DBPR Monitoring Results

Monitoring Site

TTHM (μg/L) HAA5 (μg/L)

2/08 8/08 LRAA 2/08 8/08 LRAA

SMP Site #1 - Representative high TTHM 45 82 64 18 32 25

SMP Site #2 - Representative high HAA5 33 65 49 20 35 28

Stage 1 Maximum residence time N/A 78 N/A N/A 45 N/A
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-7

III. PROPOSED STAGE 2B COMPLIANCE MONITORING SITES

This section of the report should include a summary of your proposed Stage 2B

monitoring sites including a schematic of the distribution system showing their locations, a

discussion of the rationale for your selection of those sites, and a proposed monitoring schedule.

Stage 2B compliance sample sites were selected from the two SMP sample sites and the Stage

1 DBPR site. The selections were based on a comparison of the average TTHM and HAA5 values at

the SMP sites and the August results for all three sites (two SMP and one Stage 1 DBPR sites). The

following tables rank the sites based on their average TTHM and HAA5 values. The sites proposed as

Stage 2B compliance sites are in bold text and shaded in the table. A schematic of the monitoring sites

is presented in section III.2.

Proposed Stage 2B Compliance Monitoring Sites

TTHM HAA5

Site

LRAA

(μg/L)

August

results

(μg/L) Site

 LRAA

(μg/L)

 August

results

(μg/L

SMP #1 64 82 Stage 1 N/A 45

Stage 1 N/A 78 SMP #2 28 35

SMP #2 49 65 SMP #1 25 32

Bold text and shading identifies proposed Stage 2B compliance monitoring sites.

The proposed highest TTHM site is SMP #1. Of the three locations, SMP #1 has the highest

average TTHM value as well as highest TTHM value during the peak temperature month (August).

The proposed highest HAA5 site is the Stage 1 DBPR site. This site has the highest August

HAA5 value of the three sites.

Stage 2B sampling is proposed to occur in August (peak historical month for TTHM

concentrations). TTHM samples will be collected at SMP #1 only, and HAA5 will be collected at the

Stage 1 site only.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft I-8

Elevated Storage Tank

Stage 2B High HAA5

Stage 2B High TTHM

Green Meadows Well Field

2. Schematic drawing of the distribution system with Stage 2 DBPR sites:
Appendix J

IDSE SMP Report for a

100 Percent Purchasing Surface Water System

This appendix is provided as an example IDSE report for surface water systems

purchasing 100 percent of their water, serving 100,000 - 499,999 people, and opting to complete

the Standard Monitoring Program (SMP).

Chapter 5 presents the detailed SMP requirements for these systems, and Chapter 8

provides guidance on selecting SMP sites and Stage 2B compliance monitoring sites based on

SMP results. Chapter 8 also presents the IDSE reporting requirements. The application of the

basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not 

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Grove City

PWSID Number: US1111111 

Address: 1234 Main Street 

Grove City, US 99999 

Contact Person: Ms. Margaret Doe, P.E. 

 

Phone Number: 123-555-0000 

Fax Number: 123-555-0001 

Email Address: MDoe@ci.grovecity.us 

System Type: Community, 100 % purchased SW 

Population Served: 160,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-1

I. SMP PLAN

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system.

General system characteristics:

Service area: Grove City plus surrounding suburban areas

Production: Annual average daily demand 15 MGD

Source Water Information: 

The wholesalers do not provide us with raw water quality data, but our purchasing agreements

require water quality at our city’s entry points to meet State and federal drinking water quality

standards.

Entry points and service areas under the influence of each entry point:

(Entry points should be tied to source(s) and typical flows noted)

Entry points: Purchase approximately 50 percent (7.5 mgd average) from Big City

Purchase remaining 50 percent (7.5 mgd average) from New City

Both sources provide treated surface water and are used year round.

Customers located in the Cypressville, Cedarville, Poplarville, and north downtown generally

receive water from Big City

Customers located in the Industrial Park area, Oakville, Pineville, and south downtown

generally receive water from New City

Customers located in the Weeping Willow Community, Appleville, and central downtown

generally receive a mixture of water from both plants

Treatment Provided:

Big City – conventional treatment followed by UF

New City – conventional treatment

Primary and residual disinfection: chlorine/chloramines at both sources.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-2

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 400 miles, 4" - 56" (approximately 20 MG carrying capacity)

5 storage tanks of 10 MG total capacity

1 ground tank 4 MG capacity 

4 elevated tanks 6 MG total capacity (1.5 MG each)

The average residence time of water in the distribution system is six to eight days.

Pump stations:

Station #1 is located at the ground storage tank (in Pineville). This pump is primarily used

during peak demands and low pressure situations. The pump is timed to turn on in the morning

and evening during peak demand, and when the pressure drops below 40 psi at a point

downstream of the pump station.

Stations #2 and #3. These pumps are used to boost system pressure when the pressure in the

areas downstream of these pumps (Poplarville and Weeping Willow, respectively) drops below

40 psi.

Booster chloramination facilities:

Facility #1 is located on Cherry Hill Ave. (downstream of the Cherry Hill storage tank at pump

station #3 in Weeping Willow). This facility is occasionally used during the summer when

remote locations downstream of the booster chloramination facility lose total chlorine residual.

Facility #2 is located at the intersection of Second Ave. and 11th St. (in a mixing zone) in an

area of the distribution system where total chlorine residuals are frequently low. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-3

Poplarville

Big City Purchased 

Water Entry Point

New City Purchased 

Water Entry Point

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

Grove City Water Distribution System

Apple

Drive EST

Jackson

EST

Cherry

Hill EST

Pineville

GST

East

EST

2. Schematic drawing of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-4

3. SMP monitoring requirements:

The Grove City system serves 160,000 people and purchases only surface water. Therefore, a

total of 24 SMP sample sites are required to be sampled approximately every 60 days for one year (6

dual sample sets per site) for TTHM and HAA5.

Required SMP Sample Sites

Site Criteria Number of Sample Sites

Near entry to the distribution system 2

1

Average residence time 6

Representative of high HAA5 7

Representative of high TTHM 9

1

 The Stage 2 rule requires 4 near-entry point SMP sites for our size of system. However,

because we only have two consecutive entry points, the other two were divided among

high TTHM and HAA5 sites.

Available Data:

Report all data that helped in site selection. For this example, tables are presented with

limited data for Stage 1 DBPR sample sites and the sites chosen as SMP sample locations. Your

report should include data for all sites that were considered as candidates for SMP sites. If you

have bromide, TOC, or HPC data, these may be helpful for justifying Stage 2B site selections.

Total chlorine residual and HPC data were available at our Total Coliform Rule and Stage 1

DBPR sample sites. The chlorine data for the summer months of June, July, August, and September

were reviewed, and monthly averages and an overall average were calculated. These data are

presented in Table J.1. The SMP sample site numbering and type are also provided for reference.

Quarterly HPC data were available for the same year and at the same sites as the total chlorine

data. The four results for each site were averaged. The monthly results and overall average values are

presented in Table J.2. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-5

Table J.1 Grove City Distribution System—Total Chlorine Residual Data

Sample Site

ID #

Source/

Plant

Stage 1

Type

SMP

 Site #

SMP

Type

Total Chlorine Residual (mg/L)

June July Aug. Sept. Mean

TCR #9 NC 1 E 3.6 3.4 3.5 3.6 3.5

TCR #11 NC 2 A 2.9 2.7 3.2 2.4 2.5

TCR #22 NC 3 A 2.3 2.1 2.3 2.4 2.3

TCR #3 NC 4 A 2.4 2.7 2.3 2.5 2.5

TCR #46 NC 5 H 2.1 1.7 1.9 2.0 1.9

TCR #5 NC 6 H 1.0 1.2 1.1 1.0 1.1

TCR #6 NC 7 H 1.8 1.6 1.6 1.6 1.7

TCR #78 NC 8 T 0.9 0.9 1.2 0.9 1.0

TCR #81 NC 9 T 1.0 1.1 1.3 1.1 1.1

TCR #39 NC 10 T 1.7 1.8 1.7 1.7 1.7

TCR #10 NC 11 T 0.6 0.6 0.9 0.6 0.7

TCR #1 BC 12 E 3.4 3.2 3.7 2.9 3.3

TCR #86 BC 13 A 2.1 2.1 2.4 2.0 2.2

TCR #21 BC 14 A 2.0 1.8 2.0 1.9 1.9

TCR #35 BC 15 A 2.2 1.9 2.5 2.3 2.2

TCR #13 BC 16 H 2.0 2.3 1.9 2.4 2.2

TCR #49 BC 17 H 1.5 1.2 1.8 1.6 1.5

TCR #65 BC 18 H 1.9 2.2 1.8 2.3 2.1

TCR #16 MIX 19 T 2.5 2.6 2.8 2.9 2.7

TCR #51 BC 20 T 0.9 1.3 0.9 1.0 1.0

TCR #72 MIX 21 T 1.9 2.0 1.9 1.9 1.9

TCR #71 MIX 22 H 2.0 1.8 1.6 1.7 1.8

TCR #20 MIX 23 T 0.7 1.1 0.7 0.8 0.8

TCR #58 MIX 24 T 0.5 0.6 0.8 0.6 0.6

Stg. 1 #1 BC Avg 2.2 2.5 2.4 2.7 2.5

Stg. 1 #2 BC Avg 2.1 2.2 2.7 2.3 2.3

Stg. 1 #3 MIX Avg 1.6 1.7 1.7 1.9 1.7

Stg. 1 #4 BC Max 0.8 1.1 0.7 0.8 0.9

Stg. 1 #5 NC Avg 2.5 2.6 2.5 2.0 2.4

Stg. 1 #6 NC Avg 2.4 2.2 2.7 2.5 2.5

Stg. 1 #7 MIX Avg 1.4 2.0 1.7 2.0 1.8

Stg. 1 #8 NC Max 0.7 1.7 0.8 1.4 1.0

MIX - Mixing Zone TCR - Total Coliform Rule E - Near Entry Point

NC - New City Source Stg. 1 - Stage 1 DBPR A - Average Residence Time

BC - Big City Source T - Representative High TTHM

H - Representative High HAA5
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-6

Table J.2 Grove City Distribution System—Heterotrophic Plate Count (HPC) Data

Sample Site

ID #

Source/

Plant

Stage 1

Type

SMP

Site #

SMP

Type

HPC (cfu/mL)

June July Aug. Sept. Mean

TCR #9 NC 1 E 12 8 34 12 17

TCR #11 NC 2 A 78 86 384 364 228

TCR #22 NC 3 A 35 62 147 92 84

TCR #3 NC 4 A 43 34 156 224 114

TCR #46 NC 5 H 34 76 97 89 74

TCR #5 NC 6 H 54 65 87 97 76

TCR #6 NC 7 H 35 43 64 45 47

TCR #78 NC 8 T 68 175 399 375 254

TCR #81 NC 9 T 151 273 164 354 235

TCR #39 NC 10 T 43 67 125 102 84

TCR #10 NC 11 T 156 278 169 359 240

TCR #1 BC 12 E 67 14 35 42 40

TCR #86 BC 13 A 43 34 156 224 114

TCR #21 BC 14 A 54 65 573 65 189

TCR #35 BC 15 A 56 72 202 147 119

TCR #13 BC 16 H 53 64 94 123 83

TCR #49 BC 17 H 50 34 113 63 65

TCR #65 BC 18 H 35 43 64 45 47

TCR #16 MIX 19 T 34 76 97 89 74

TCR #51 BC 20 T 69 43 37 43 48

TCR #72 MIX 21 T 54 65 573 65 189

TCR #71 MIX 22 H 66 53 153 53 81

TCR #20 MIX 23 T 70 212 356 332 242

TCR #58 MIX 24 T 233 214 456 546 362

Stg. 1 #1 BC Avg 56 42 345 276 180

Stg. 1 #2 BC Avg 82 136 146 246 152

Stg. 1 #3 MIX Avg 280 163 446 263 288

Stg. 1 #4 BC Max 140 215 557 615 382

Stg. 1 #5 NC Avg 50 42 223 522 209

Stg. 1 #6 NC Avg 53 42 84 72 63

Stg. 1 #7 MIX Avg 140 66 364 236 201

Stg. 1 #8 NC Max 196 45 653 425 330

MIX - Mixing Zone TCR - Total Coliform Rule E - Near Entry Point

NC - New City Source Stg. 1 - Stage 1 DBPR A - Average Residence Time

BC - Big City Source T - Representative High TTHM

H - Representative High HAA5
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-7

4. Summary of selected SMP sample sites:

Present the rationale for the selection of the IDSE sampling sites, as well as a schematic

showing their location within the distribution system.

Sampling sites were chosen to represent diverse geographical areas of the distribution system. 

Each site is shown on the map of the distribution system in section I.6. Residual total chlorine (Table

J.1) and HPC data (Table J.2) were considered in the selection of SMP monitoring sites.

SMP Site #1 – Entry point to the distribution system for New City supply. This site is located where

the first group of customers receives water.

SMP Site #2 – Represents average residence time of water leaving New City. Based on total chlorine

monitoring results at TCR sample sites, we identified the areas within the system where total chlorine

levels dropped by approximately 50 percent of the total drop in residual seen in the area supplied by

New City. The average initial concentration (at SMP #1) was 3.5 mg/L. The average residual at SMP

#11 (the site with the lowest residual and solely under the influence of New City) is 0.7 mg/L. 

Therefore, the average drop in residual across the system is approximately 2.8 mg/L; half of that drop is

1.4 mg/L. Sites with residual concentrations near 2.1 mg/L were considered to be approximate

average residence time sites. The average residual at this site is 2.5 mg/L. There are no storage

facilities between the entry point and this site. 

SMP Site #3 – Represents average residence time of water received from New City. Water at this site

has an average total chlorine residual of 2.3 mg/L. Based on the rationale presented in the discussion of

site #2, this site was determined to be an approximate average residence time site.

SMP Site #4 – Represents average residence time of water entering from New City. Water at this site

has an average total chlorine residual of 2.5 mg/L. Based on the rationale presented in the discussion of

site #2, this site was determined to be an approximate average residence time site.

SMP Site #5 – Represents high HAA5 levels. Sample site is in an area approaching the perimeter of

the distribution system. Water in this area is primarily from the New City. Total chlorine residual at this

site ranges between 1.7 and 2.1 mg/L, and the heterotrophic plate count is consistently below 100 cfu

per mL year round. 

SMP Site #6 – Represents high HAA5 levels. This site is at the edge of the mixing zone between the

New City and Big City influence areas. Total chlorine residual levels ranged between 1.0 and 1.2 mg/L

at this site, and the heterotrophic plate count never exceeded 100 cfu per mL. 

SMP Site #7 – Represents high HAA5 levels. This site is a hose bib located at a convenience store. 

Total chlorine residual levels ranged between 1.6 and 1.8 mg/L at this site, and the heterotrophic plate

count never exceeded 100 cfu per mL. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-8

SMP Site #8 – Represents high TTHM levels. This sampling site is the western edge of the city. Total

chlorine residuals at this site are generally very low.

SMP Site #9 – Represents high TTHM levels. This sampling site is believed to receive water from the

Pineville Storage tank (a 4 MG ground tank) during high demand periods and is at the entrance to a

small subdivision cul-de-sac in the Oakville community. Chlorine residuals at this site are generally low. 

The sample site is near the first house on the cul-de-sac (which has 12 homes total).

SMP Site #10 – Represents high TTHM levels. This site is located upstream of the Stage 1 DBPR

monitoring site #7. Both are used for routine Total Coliform Rule and chlorine residual monitoring. We

have over 7 years of data from this site. This site is located near the predicted edge of the mixing zone

where chlorine residual measurements indicate there may be a hydraulic dead end. Water at this site is

generally from the New City supply, although specific conductivity data show that some mixed zone

water may also influence this site. 

SMP Site #11 – Represents high TTHM levels. This site has been problematic in the past due to

positive total coliform test results, very low total chlorine residuals, high heterotrophic plate count

results, and odor complaints. A 4-inch blow-off was installed downstream of this site, but it continues

to have periodic poor water quality. Water in this area is from the New City supply. 

SMP Site #12 – Entry point to the distribution system for the Big City supply. This site is located near

the first group of customers that receive water from the Big City supply. 

SMP Site #13 – Represents average residence time of water entering from Big City. Based on total

chlorine monitoring results at TCR sample sites, we identified the areas within the system where total

chlorine levels dropped by approximately 50 percent of the total drop in residual seen in the area

supplied by Big City. The average initial concentration (at SMP #1) was 3.3 mg/L. The average

residual at site #24 (the site with the lowest residual and solely under the influence of New City) is 0.6

mg/L. Therefore, the average drop in residual across the system is approximately 2.7 mg/L; half of that

drop is 1.3 to 1.4 mg/L. Sites with residual concentrations near 2.0 mg/L were considered to be

approximate average residence time sites. The average total chlorine residual at this site is 2.2

SMP Site #14 – Represents average residence time of water entering from Big City. Water at this site

has an average total chlorine residual of 1.9 mg/L. Based on the rationale presented in the discussion of

site #13, this site was determined to be an approximate average residence time site.

SMP Site # 15 – Represents average residence time for the Big City water supply. This sampling site

is in the southern edge of Cedarville subdivision. Water at this site has an average total chlorine residual

of 2.2 mg/L. Based on the rationale presented in the discussion of site #13, this site was determined to

be an approximate average residence time site.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-9

SMP Site #16 – Represents high HAA5 levels. Our Stage 1 DBPR results indicate the high HAA5

concentrations move around our system depending on the season and proportion of water supplies

from New City and Big City, especially in the areas served by the Big City.

SMP Site #17 – Represents high HAA5 levels for the Big City supply. At this site, the water age is

greater than average (evidenced by average total chlorine residual of 1.5), the total chlorine residual

was never below 1.8 mg/L and the heterotrophic count plate is usually low (below 100 with one

exception in August).

SMP Site #18 – Represents high HAA5 levels for the Big City supply. At this site, the water age is

approximately equal to the system average (evidenced by average total chlorine residual of 2.1), the

total chlorine residual was never below 1.9 mg/L and the heterotrophic count plate is usually low

(below 100). 

SMP Site #19 – Represents high TTHM levels. This sample site is located in a zone of the distribution

system that has been recently developed. This connection is located downstream from a chlorine

booster station. Total chlorine residuals are normally in the 2.5 to 2.9 mg/L range. Water in this area is

generally a mix of water from the New City and Big City supplies.

SMP Site #20 – Represents high TTHM levels. This site is downstream from the Jackson Storage

Tank in Cypressville, a 1.5 million gallon elevated storage tank. There are often low chlorine residuals

in the areas downstream of this tank.

SMP Site #21 – Represents high TTHM levels. This sampling site is in the mixed zone before the last

group of connections near the end of the distribution system. This area receives water from the Cherry

Hill Storage Tank and water that bypasses the tank. Water from this area can vary greatly in the

percentages of New City and Big City water.

SMP Site #22 – Represents high HAA5 levels. At this site, the water age is believed to be greater than

average because it is within the mixing zone, but the total chlorine residual is never below 1.6 mg/L and

the heterotrophic count plate is usually low (below 100 cfu/mL with one exception in August). 

SMP Site #23 – Represents high TTHM levels. This sampling site is in the mixed zone. Total chlorine

residuals range from 0.7 to 1.1 mg/L which is well below the system average. This area receives water

from the Pineville ground storage tank.

SMP Site #24 – Represents high TTHM levels. This sampling site is in the mixed zone. It has total

chlorine residuals that range from 0.5 to 0.8 mg/L which is well below the system average.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-10

5. SMP Sample Schedule:

Because the quarterly Stage 1 DBPR monitoring is the only DBP monitoring that has been

performed in the Grove City system, historic DBP data is available for only the months of January,

April, July, and October. July has regularly had the highest DBP levels, but no DBP data is available

for the other summer months. As a result, we also reviewed finished water temperature in two years of

TCR sampling records and determined our peak month for distribution system water temperature is

August. But, we also found that July’s average distribution system water temperature for the two years

reviewed was only 0.5o C less. Based on the historic DBP data and minimal difference in average

water temperature, we concluded July is the controlling month for the Elm City distribution system. The

following table summarizes our planned SMP sample dates and is based on collection of our samples

on the second Monday of the month.

Proposed SMP Sample Schedule

Planned Sample Date

November 8, 2005

January 10, 2006

March 14, 2006

May 9, 2006

July 11, 2006

September 12, 2006

Dual sample sets will be collected from each of the 24 SMP sample sites on or close to the

listed dates and analyzed for TTHM and HAA5 by a State-certified laboratory.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-11

Poplarville

MIXING

ZONE

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

8

7

5 6

4

3

2

1

11

10

4

6

3

2

1

12

21

20

19

16

22

14 13

Stage 1 DBPR site

TCR / Selected SMP site

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

New City Purchased 

Water Entry Point

Big City Purchased 

Water Entry Point

Grove City Water Distribution System

18

17

15

23

24

5

9

8

7

6. Map of the distribution system showing major transmission mains, numbered Stage 1

DBPR compliance sites, and numbered SMP sample sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-12

II. SMP RESULTS

1. Introduction:

The SMP was conducted between November 2005 and September 2006. The following table

summarizes our planned SMP sample dates, the actual dates when samples were collected, and the

reasons for deviations from the plan.

Actual SMP Sample Schedule

Planned Sample Date Actual Sample Date Explanation

November 8, 2005 November 8, 2005 On schedule

January 10, 2006 January 10, 2006 On schedule

March 14, 2006 March 14, 2006 On schedule

May 9, 2006 May 9, 2006 On schedule

July 11, 2006 July 11, 2006 On schedule

September 12, 2006 September 14, 2006 Flooding closed many of the

roads in Grove City, making many

sample sites inaccesible until

September 14.

2. Summary of IDSE SMP data and Stage 1 DBPR compliance data:

All DBP results from the SMP and concurrent Stage 1 DBPR compliance monitoring are

presented in this section. The first table presents the DBP results for the SMP sample sites, organized

by plant, then in order of highest to lowest TTHM LRAA. The second table presents the DBP results

for the Stage 1 DBPR compliance sample sites for the period from November 2005 to August 2006. 

Sites proposed as Stage 2B compliance monitoring locations are shaded within the tables.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-13

Grove City—IDSE SMP Monitoring Results

SMP

Site # Site Type

TTHM (ug/L) HAA5 (ug/L)

Data1 LRAA Data1 LRAA

1 entry point 36, 42, 30, 25, 38, 28 33 50, 44, 43, 47, 48, 38 45

12 entry point 30, 32, 39, 40, 32, 28 29 31, 29, 38, 48, 51, 45 43

13 average residence time 42, 34, 52, 57, 62, 51 50 23, 56, 40, 52, 40, 28 40

2 average residence time 54, 39, 42, 56, 60, 42 49 22, 29, 36, 40, 41, 30 33

4 average residence time 51, 42, 50, 39, 50, 42 47 19, 26, 28, 31, 26, 22 25

14 average residence time 47, 40, 52, 43, 51, 41 46 14, 20, 21, 23, 29, 19 21

15 average residence time 40, 45, 45, 48, 52, 46 46 41, 32, 45, 40, 35, 43 39

3 average residence time 42, 39, 53, 43, 49, 40 44 20, 25, 25, 29, 27, 19 24

6 high HAA5 36, 41, 43, 39 49, 45 42 60, 58, 68, 57, 68, 55 61

16 high HAA5 52, 35, 46, 42, 50, 38 44 56, 44, 65, 50, 50, 58 54

17 high HAA5 50, 33, 44, 40, 48, 36 42 53, 42, 64, 48, 49, 55 52

7 high HAA5 35, 30, 42, 44, 44, 25 37 37, 43, 55, 57, 50, 42 47

5 high HAA5 33, 29, 41, 42, 44, 22 35 36, 43, 52, 51, 48, 38 45

18 high HAA5 35, 31, 47, 38, 49, 30 39 37, 42, 48, 50, 41, 35 42

22 high HAA5 35, 29, 47, 37, 47, 27 37 36, 40, 46, 48, 40, 34 41

11 high TTHM 68, 59, 78, 76, 75, 65 70 42, 39, 47, 46, 40, 49 44

8 high TTHM 62, 60, 65, 71, 74, 72 67 42, 40, 33, 38, 46, 30 38

10 high TTHM 68, 62, 54, 65, 72, 70 65 39, 45, 28, 33, 40, 32 36

23 high TTHM 67, 59, 58, 49, 71, 75 63 32, 35, 27, 30, 39, 29 32

21 high TTHM 69, 56, 72, 59, 71, 55 63 19, 25, 39, 29, 21, 38 29

20 high TTHM 65, 61, 54, 50, 69, 71 62 37, 41, 29, 30, 41, 29 35

9 high TTHM 51, 56, 69, 58, 67, 52 59 31, 38, 37,40, 32, 45 37

24 high TTHM 50, 51, 55, 53, 62, 65 56 37, 39, 29, 28, 39, 27 33

19 high TTHM 56, 50, 55, 51, 61, 45 53 42, 30, 43, 38, 34, 42 38

1Data obtained from sampling every 60 days are listed in order for November, January, March, May, July, and

September (as required for a surface water supply $10,000).

Note: Bold text and shading identifies proposed Stage 2 DBPR compliance sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-14

Grove City—Stage 1 DBPR Compliance Monitoring Results

Stage 1

Site # Site Type

TTHM (ug/L) HAA5 (ug/L)

Data1 LRAA Data1 LRAA

Stg. 1 #4 Maximum 64, 68, 83, 74 72 21, 25, 26, 28 25

Stg. 1 #8 Maximum 61, 48, 56, 71 59 19, 22, 37, 30 27

Stg. 1 #2 Average 38, 42, 52, 62 49 50, 62, 64, 65 59

Stg. 1 #1 Average 45, 34, 56, 62 49 24, 32, 43, 45 36

Stg. 1 #6 Average 47, 49, 39, 52 47 22, 30, 39, 41 33

Stg. 1 #3 Average 36, 42, 45, 45 42 47, 50, 55, 56 52 

Stg. 1 #5 Average 44, 20, 62, 42 42 34, 45, 33, 41 38

Stg. 1 #7 Average 41, 22, 50, 59 43 32, 46, 59, 52 47

1Data listed in order for October, January, April, and July quarterly sampling.

Note: Bold text and shading identifies proposed Stage 2B compliance sites.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-15

III. PROPOSED STAGE 2B COMPLIANCE MONITORING SITES

1. Site Summary:

A total of 12 Stage 2B compliance monitoring sites were selected from the Stage 1 DBPR and

SMP sites, as shown in the previous tables and as summarized in the following table.

Stage 2B Proposed Compliance Monitoring Sites

Stage 2B Compliance Sites

Site # Type Previous Sample Site ID

1 Average Stg. 1 #2

2 Average Stg. 1 #3

3 Average Stg. 1 #1

4 High HAA5 SMP #6

5 High HAA5 SMP #16

6 High HAA5 SMP #17

7 High TTHM Stg. 1 #4

8 High TTHM SMP #11

9 High TTHM SMP #8

10 High TTHM SMP #10

11 High TTHM SMP #23

12 High TTHM SMP #20
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-16

2. Justification of Site Selections:

The reasons for the selection of the 12 sites for Stage 2B monitoring are:

1. Average Residence Time Sites – The Stage 2 DBPR required us to select three

average residence time sites from among our existing Stage 1 DBPR monitoring sites. 

The sites were required to be selected based on alternating highest TTHM LRAA and

HAA5 LRAA. Because we have three average residence time sites, we ultimately

ended up selecting two based on highest TTHM LRAA and one based on highest

HAA5 LRAA. Stage 1 DBPR average residence time sites #2 and #1 had the highest

TTHM LRAA among Stage 1 DBPR average residence time sites. Stage 1 DBPR site

#3 had the highest HAA5 LRAA among the Stage 1 average residence time sites.

2. Representative High HAA5 Site – The three highest HAA5 LRAA values occur at

SMP site #6 and #16, and #17. Therefore, these three sites were designated as Stage

2B sites (numbers 4, 5, and 6). 

3. Representative High TTHM Sites – The six highest TTHM LRAA values occur at

SMP Site #11, #8, #10, #23, and #20, and Stage 1 DBPR Site #4. Therefore, these

six sites were designated as Stage 2B sites. SMP site #20 and #21 actually had the

same TTHM LRAA, but site #20 provided better geographic coverage and was

selected as a proposed Stage 2B monitoring site. 

3. Proposed Stage 2B Compliance Monitoring Schedule:

Stage 2B compliance monitoring will be scheduled for January, April, July, and October, the

same as Stage 1 DBPR and Stage 2A DBPR sampling, for consistency and because the difference in

distribution system water temperature between July and August is minimal (average 0.5o C higher in

August, based on a review of 2 years of TCR sampling records).
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-17

Poplarville

MIXING

ZONE

Elevated Storage Tank

Ground storage tank

Pump station

Chlorine Booster Station

Appleville

Weeping Willow

Oakville

Pineville

Cedarville

Cypressville

Downtown

Industrial

Park

PS2

CB2

PS3

CB1

PS1

Grove City Stage 2B DBPR

Compliance Sample Sites

Stage 2B Representative High TTHM

Stage 2B Representative High HAA5

Stage 2B Average Residence Time

#

#

#

New City Purchased 

Water Entry Point

Big City Purchased 

Water Entry Point

1

4

2

3 6

5

7

10

11

12

8

9

4. Map of Proposed Stage 2B Compliance Monitoring Sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft J-18

This page intentionally left blank.
Appendix K

IDSE System Specific Study Using a Hydraulic Model

This appendix is provided as an example IDSE report for producing surface water

systems serving least 10,000 people and opting to complete a System Specific Study (SSS) using a

water distribution system model.

Chapter 3 presents detailed guidance on the requirements for performing an SSS with a

water distribution system model. Chapter 5 presents the detailed SMP requirements for these

systems. Chapter 3 also provides guidance on selecting SMP sites and Stage 2B compliance

monitoring sites based on SSS data, as well as IDSE reporting requirements. The application of

the basic guidance on SMP site selection and Stage 2B compliance monitoring site selection is

shown in this example, along with several instances of the use of best professional judgement

being applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Big City

PWSID Number: US1111111 

Address: 1234 Main Street 

Big City, US 99999 

Contact Person: Mr. John Smith, P.E. 

 

Phone Number: 123-555-0000 

Fax Number: 123-555-0001 

Email Address: jsmith@ci.bigcity.us 

System Type: Community, surface water 

Population Served: 55,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-1

1. System Description:

This section of the report includes a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system. 

Information about water treatment processes and source water quality data should also be part

of this section, including a description of water treatment, actual residence times within the

water treatment plant and the distribution system. 

General system characteristics:

Service area: Big City plus surrounding suburban areas

Production: Annual average daily demand 7 MGD

Source Water Information: 

Adams Reservoir (surface water) water quality:

pH: from 7.0 to 8.0

Alkalinity: from 62 to 88 mg/L as CaCO3

TOC: from 3.2 to 6.8 mg/L as C

Lincoln River (surface water) water quality:

pH: from 6.8 to 7.9

Alkalinity: from 77 to 94 mg/L as CaCO3

TOC: from 1.6 to 4.4 mg/L as C

Entry points and service areas under the influence of each entry point:

(Entry points should be tied to source(s) and typical flows noted) 

Entry points: Adams Plant – serves the northern half of the city

Lincoln Plant – serves the southern half of the city

Treatment Provided: 

Adams Plant is a 6 MGD plant located on the northern edge of the city. It draws water from

Adams Reservoir. The plant utilizes coagulation (with ferric chloride), flocculation,

sedimentation, and dual media filters (filter loading rates are approximately 4 gpm/sf). 

Lincoln Plant is an 8 MGD plant located in the southern part of the system and draws water

from Lincoln River. The treatment process is identical to that of the Adams Plant, except that

the Lincoln Plant also includes GAC filters following dual media filtration to enhance TOC

removal. The Lincoln River is prone to rapid changes in TOC, and the GAC was installed as

an extra barrier to prevent significant DBP formation in the distribution system. 

Primary and residual disinfection: Chlorine/chloramines at both plants.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-2

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 300 miles, 4" - 36"

Lined and unlined cast iron pipe, ductile iron pipe, and plastic pipe

4 storage tanks of 9 MG total capacity

1 ground tank 4 MG capacity 

2 elevated tanks each with 2 MG capacity

1 elevated tank with 1 MG capacity

The average residence time of water in the distribution system is approximately two days.

Pump stations:

A pump station is located at the north tank (4 MG ground storage tank). This pump is primarily

used during peak demands and low pressure situations. The pump is timed to turn on in the

morning and evening during peak demand, and when the pressure drops below 40 psi at a point

downstream of the pump station.

Booster chloramination facilities:

Booster Facility A is located in the northwestern part of the city. This facility is occasionally

used during the summer when total chlorine residuals at remote locations downstream of the

booster facility cannot be maintained.

Booster Facility B is located in the southeastern part of the city, where total chloramine

residuals have historically been low. 

A schematic of the distribution system is presented in the following section.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-3

Booster chloramination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

Booster chloramination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

2. Schematic of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-4

3. Summary of SSS requirements:

Big City has extensive experience with water distribution system modeling. To select Stage 2B

compliance monitoring sites, the city has performed a System Specific Study (SSS) based on its water

distribution system model, data from one round of new DBP sampling, and data from Stage 1 DBPR

compliance monitoring.

To confirm model results, we conducted one round of DBP sampling at sites equivalent to those

that would be selected under the SMP requirements for large, subpart H systems. A summary of these

requirements is presented in the following table. The methodology by which these sites were chosen is

presented in section 5.

Additional DBP Sampling Site Criteria1

Site Criteria

Number of Sample Sites

Adams WTP

Influence Zone

Lincoln WTP

Influence Zone

Near entry to the distribution system 2 2

Average residence time 2 2

Representative of high TTHM 2 2

Representative of high HAA5 2 2

1 These sites were allocated based on SMP requirements for a system of our size and

source water type and practicing similar disinfection methods.

4. Description of Hydraulic Model

The hydraulic model for Big City includes all 8-inch and larger pipes and also includes 6-inch

pipes for the remote areas of the distribution system. Approximately 60 percent of the total pipe length

in the distribution system is included in the model. The open/closed status of all four storage tanks and

the on/off status of the pump station at the North Tank have been modeled. There are two control

valves in the distribution system, but these do not significantly affect the water flow through the

distribution system. Therefore, these control valves have not been modeled.

Water demand has been assigned to approximately 60 percent of the nodes in the model. In

areas where there are no water users at the dead-end of a pipe segment, a very small nominal demand

was assigned to the end nodes so that water ages at the dead ends could be calculated by the modeling

software. Summer and winter average demand data were available for residential customers and large

commercial and industrial customers. The estimated water loss in the system is about 10 percent and

this was accounted for in the model. Based on the master meter flows, tank levels, and customer meter

readings, a diurnal (24-hour) demand pattern was derived and was applied to the residential,
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-5

commercial, and industrial customers. The inclusion of diurnal demand patterns allows the hydraulic

model to be run in the extended period simulation (EPS) mode.

A major calibration effort was performed when the model was developed in 1998. At that time

the model was calibrated for average summer and maximum day conditions. Since the last calibration,

no significant changes have been made to the distribution system that could change the system

hydraulics. The calibration program included extensive C-factor tests conducted over the previous 10

years and comparisons of modeled and measured pressures throughout the system. The model

predicted pressures were within ± 3 psi of the field measured pressures at 70 percent of the readings. 

This is consistent with calibration guidelines for hydraulic models to be used for water quality purposes

(Walski, et al., “Perspectives in Calibration,” Current Methods, 1:1:21, Haested Press, 2001).

5. Summary of the SSS methodology:

Summarize the methodology used to conduct the SSS, including the rationale for the

selection of sites equivalent to the sample sites required for the Standard Monitoring Program

(SMP). 

The hydraulic model was applied in a variety of ways to understand the flow of water 

through the distribution system and guide the selection of monitoring sites that reflected the selection

criteria outlined in Chapter 3 of the IDSE guidance manual. For this SSS, 16 sites were selected that

meet the criteria required for the SMP of a system of a similar size and source water type providing

similar disinfection (see section 3). 

The model was run in the extended period simulation (EPS) mode under average summer

conditions for 14 days, and showed a consistent, repeating pattern of water age at all nodes after

approximately 10 days. This indicates the maximum residence time in the distribution system under

average summer conditions is approximately 10 days. The water age option was used in the model to

obtain residence time throughout the distribution system. In addition to residence time calculations, the

model was used to define influence zones of the two source waters. The source tracing option was

used in the model to determine the average contribution of the two water sources to each node in the

model. 

Three zones were defined based on the two water sources: 

• The area served primarily by the Adams WTP

• The area served primarily by the Lincoln WTP

• The area that generally received water from both treatment plants 

over the course of the day, either as a mixture or on an alternating basis 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-6

Because the Stage 1 DBPR compliance data indicates that DBP levels are highest in the Big

City distribution system during the summer months, average day demands for the summer were used to

determine residence times and mixing zones. Average day demands during winter conditions were also

examined and the mixing zone was found to be very similar to the summer conditions.

The residence time data obtained from the model for the summer conditions were compared

with the total chlorine residual data at the TCR monitoring sites for May and August (Table K.1). In

general, there is a direct correlation between model-predicted residence times and total chlorine

residuals. Sites on the periphery of the distribution system have longer residence times and lower total

chlorine residuals, except for areas where booster chloramination is used. Sites which are under the

influence of the booster facilities maintain relatively high total chlorine residuals. However, these sites

also have high residence times. Table K.1 also summarizes model-predicted residence times at each of

the TCR monitoring sites. 

The residence times from the model were used to select 16 of the 20 TCR monitoring sites for

DBP monitoring. These sites are described in further detail in the following section. After the selection

of 16 sites, one round of DBP dual samples was taken at these sites during August, which is the month

of historically high DBP levels. The residence time data, Stage 1 DBPR compliance data (Table K.2),

and DBP data from this new round of sampling were then used to select Stage 2B compliance

monitoring sites.

Available Data:

Report all data that helped in site selection. If you have bromide, TOC, and or HPC

data, these may be helpful for justifying Stage 2B site selection.

Total chlorine residual data for the months of February, May, August, and November, and

residence time data for summer demand conditions obtained from the water distribution system model,

at TCR monitoring sites is presented in Table K.1. Quarterly Stage 1 DBPR compliance monitoring

data is presented in Table K.2.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-7

Table K.1 Big City Distribution System—Total Chlorine Residual at TCR

Monitoring Sites

Monitoring

Site

Free Chlorine Residual

(mg/L)

Residence Time During

Summer Demand

Conditions (days)

Nov. 2004 Feb. 2005 May 2005

Aug.

2005 Residence Time

TCR #1 3.2 3.4 3.5 3.6 0.1

TCR #2 3.0 3.2 3.3 3.4 0.2

TCR #3 2.4 2.3 1.9 1.8 4.1

TCR #4 2.3 2.5 1.8 2.0 3.9

TCR # 5 3.0 2.9 2.6 2.5 2.1

TCR # 6 2.9 3.0 2.7 2.4 1.8

TCR # 7* 2.9 3.1 1.8 2.0 5.5

TCR # 8 1.8 1.4 1.1 1.0 6.6

TCR # 9 3.3 3.4 3.4 3.5 0.1

TCR # 10 3.4 3.3 3.5 3.4 0.1

TCR # 11 2.5 2.6 2.0 1.8 1.9

TCR # 12 2.7 2.4 1.9 1.7 2.2

TCR # 13 2.5 2.2 1.7 1.9 3.2

TCR # 14 2.4 2.2 2.0 1.8 4.1

TCR # 15 1.4 1.5 1.2 1.3 6.7

TCR # 16 1.6 1.6 1.3 1.1 7.0

TCR # 17 1.9 2.2 2.0 1.8 3.4

TCR # 18 2.6 2.4 2.6 2.5 1.3

TCR #19 3.0 3.1 1.9 2.2 5.3

TCR # 20 2.0 1.9 1.5 1.6 4.4

Note: Site 7 is located downstream of Booster Station A.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-8

Table K.2 Big City Distribution System—Stage 1 DBPR Monitoring Results

Monitoring Site

TTHM

(μg/L)

HAA5

(μg/L)

Last 4

Quarters

Data1

Aug.

2005

LRAA

Last 4

Quarters

Data1

Aug.

2005

LRAA

Adams Plant average residence time 

Site Number 1

45, 34, 56, 62 49 24, 32, 43, 45 36

Adams Plant average residence time

Site Number 2

32, 34, 48, 67 45 42, 47, 55, 56 50

Adams Plant average residence time

Site Number 3

36, 42, 45, 45 42 50, 62, 67, 68 62

Adams Plant maximum residence time

Site Number 4

64, 68, 83, 74 72 21, 25, 26, 28 25

Lincoln Plant average residence time

Site Number 5

44, 20, 62, 42 42 34, 45, 33, 41 38

Lincoln Plant average residence time

Site Number 6

46, 49, 39, 50 46 22, 30, 39, 41 33

Lincoln Plant average residence time

Site Number 7

41, 22, 50, 59 43 4, 46, 64, 58 54

Lincoln Plant maximum residence time

Site Number 8

73, 50, 67, 58 62 19, 22, 37, 30 27

1

 Data listed in order for November 2004 and February, May, and August 2005 quarterly sampling.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-9

6. Description of SSS monitoring sites:

Present the rationale for selection of the SSS monitoring sites, as well as a schematic

showing their location within the distribution system.

SSS monitoring sites were selected based on modeling results and available total chlorine

residual data. The sites represent diverse geographical areas of the distribution system and are shown

on the map of the distribution system in section 7. 

Sites #1 and #2 represent the entry point to the distribution system from Adams Plant. The

residence time at these sites is about 2 to 4 hours.

Sites #3 and #4 are representative of predicted high HAA5 concentrations in the zone served

by the Adams WTP. These sites are located on 6-inch dead-end lines near the extremities of the

system. As a result, travel time (and thus water age) to these sites is long, approximately 4 days, based

on the water age modeling. However, the modeling indicates that these sites are always fed directly

from the treatment plant (the water does not go through a storage tank) and routine sampling has shown

that there are adequate chlorine residuals at these sites. As a result, biodegradation is not expected to

occur, and high HAA5 concentrations are expected.

Sites #5 and #6 were selected to represent average conditions in the zone fed by Adams WTP. 

Monitoring results indicated an average total chlorine residual at these sites of 2.8 mg/L during the

summer. Modeling shows that typical water age at these sites is approximately 2 days.

Site #7 was selected to represent high TTHM levels in the Adams WTP zone. This site is

downstream of the Chlorine Booster Station A; thus, the chlorine residuals are relatively high. The

model indicated that the water age is high (around 5 days).

Site #8 is representative of high TTHM levels in the mixing zone and is counted as one of the

eight sites required for the Adams WTP. Modeling shows that water age at this site is generally high (>

6 days) throughout the day, representing water that has traveled a significant distance and that has

usually been through one of the storage tanks.

Sites #9 and #10 represent the entry point to the distribution system from the Lincoln Plant. 

The residence time of these sites is about 2 hours.

Sites #11 and #12 were selected to represent average conditions in the area served by Lincoln

WTP. Water age modeling indicated the residence times for these sites are approximately 2 days.

Sites #13 and #14 represent expected high HAA5 concentrations in the zone served by the

Lincoln WTP. These sites are located on 12-inch looped lines with low water demand near the

extremities of the system. As a result, travel time (and thus water age) to these sites is approximately 3

to 4 days, based on the water age modeling. However, the modeling indicates that the sites are always
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-10

fed directly from the Lincoln WTP and routine sampling has shown that the total chlorine residual at

these sites is usually about 2.3 mg/L during the summer. As a result, biodegradation is not expected to

occur, and high HAA5 concentrations are expected.

Site #15 is located on the eastern extremity of the system beyond the South Tank. Based on

modeling, it was determined that, due to the travel time from the plant to this site and the effects of

South Tank, the water age at this site typically exceeds 5 days. This site represents high TTHM.

Site #16 is representative of high TTHM levels in the mixing zone and is counted as one of the

eight sites required for the Lincoln WTP. Modeling shows that water age at this site is generally high (>

6 days) throughout the day, representing water that has traveled a significant distance and that has

usually been through one of the storage tanks.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-11

Booster chloramination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

1

3

4

5

11

6

7

8

10

12

15

16

13 14

20

19

18

17

1

2

3

4

5

6

7

8

TCR Site used for SSS

TCR Site not used for SSS

Stage 1 DBPR Compliance Site

##

##

#

2

9

Booster chloramination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

1

3

4

5

11

6

7

8

10

12

15

16

13 14

20

19

18

17

1

2

3

4

5

6

7

8

TCR Site used for SSS

TCR Site not used for SSS

Stage 1 DBPR Compliance Site

##

##

#

2

9

7. Map of the distribution system showing major transmission mains, Stage 1 DBPR

compliance sites, and SSS sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-12

8. Summary of SSS monitoring results:

One round of DBP samples was collected in August 2005 at the SSS sites listed in section 6. 

August is historically the high DBP month for Big City. The results from this sampling are presented in

the following tables, with separate sections for each plant and the sites in order according to TTHM

results, from highest to lowest. For comparison, Stage 1 DBPR sampling results for the month of

August 2005 and the LRAAs as of August 2005 (shown in parentheses) are also presented in the table

ranked by individual TTHM sample results.

Adams Plant TTHM and HAA5 Test Results

Site # Type TTHM Result (μg/L) HAA5 Result (μg/L)

Adams Plant SSS Sites - August 2005

SSS #7 High TTHM 83 48

SSS #8 High TTHM 62 45

SSS #3 High HAA5 50 50

SSS #5 Average Residence Time 48 45

SSS #4 High HAA5 48 32

SSS #6 Average Residence Time 45 30

SSS #2 Near Entry Point 34 28

SSS #1 Near Entry Point 32 30

Site # Type

TTHM Result

(LRAA)

(μg/L)

HAA5 Result

(LRAA)

(μg/L)

Adams Plant Stage 1 DBPR Sites - August 2005

Stage 1 #4 Max. Residence Time 74 (72) 28 (25)

Stage 1 #2 Avg. Residence Time 67 (45) 56 (50)

Stage 1 #1 Avg. Residence Time 62 (49) 45 (36)

Stage 1 #3 Avg. Residence Time 45 (42) 68 (62)
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-13

Lincoln Plant TTHM and HAA5 Test Results

Site # Type

TTHM Result

(μg/L) HAA5 Result (μg/L)

Lincoln Plant SSS Sites - August 2005

SSS #16 High TTHM 76 48

SSS #15 High TTHM 73 36

SSS #13 High HAA5 66 35

SSS #14 High HAA5 62 58

SSS #11 Average Residence Time 52 40

SSS #12 Average Residence Time 50 42

SSS #9 Near Entry Point 40 34

SSS #10 Near Entry Point 44 32

Lincoln Plant Stage 1 DBPR Sites - August 2005

Site # Type

TTHM Result

(LRAA)

(μg/L)

HAA5

Result (LRAA)

(μg/L)

Stage 1 #7 Avg. Residence Time 59 (43) 58 (54)

Stage 1 #8 Max. Residence Time 58 (62) 30 (27)

Stage 1 #6 Avg. Residence Time 50 (46) 41 (33)

Stage 1 #5 Avg. Residence Time 42 (42) 41 (38)

9. Proposed Stage 2B monitoring sites:

Big City is a system serving 55,000 people that uses two surface water sources. Therefore, Big

City is required to designate four (4) Stage 2B compliance monitoring sites for each plant resulting in a

total of eight (8) Stage 2B compliance monitoring sites. A summary of these requirements is presented

in the following table. 

Stage 2B Compliance Monitoring Requirements

Site Criteria

Number of Sample Sites

Adams WTP

Influence Zone

Lincoln WTP

Influence Zone

Stage 1 average residence time sites 1 1

Representative of high HAA5 1 1

Representative of high TTHM 2 2
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-14

Based on the modeling results, Stage 1 DBPR data, and additional DBP sampling results at the

SSS monitoring sites, we are proposing the Stage 2B compliance monitoring sites listed in the following

table. The rationale for their selection follows.

Stage 2B Proposed Compliance Sample Sites

Stage 2B Sites

No. Plant Type Site Description (Previous Site ID)

1 Adams Average Stage 1 DBPR average residence time (Stage 1 #3)

2 Adams Highest HAA5 Stage 1 DBPR average residence time (Stage 1 #2)

3 Adams Highest TTHM High TTHM from Adams Plant (SSS #7)

4 Adams Highest TTHM Stage 1 DBPR maximum residence time (Stage 1 #4)

5 Lincoln Average Stage 1 DBPR average residence time (Stage 1 #7)

6 Lincoln Highest HAA5 High HAA5 from Lincoln Plant (SSS #14)

7 Lincoln Highest TTHM High TTHM from Lincoln Plant (SSS #16)

8 Lincoln Highest TTHM High TTHM from mixing zone (SSS #15)

• Stage 2B Site #1: This is the average residence time site for the Adams WTP influence

area. It had the highest HAA5 test result in the August round of

sampling of all the sites, both SSS and Stage 1 DBPR. It also had the

highest HAA5 LRAA (62 μg/L) of the Stage 1 DBPR sites, and this

LRAA exceeds the MCL. The other two Stage 1 DBPR average

residence time sites had higher individual TTHM results and TTHM

LRAAs, but their HAA5 results and LRAAs were significantly less. 

This site (the old Stage 1 DBPR #3) is also in the geographic center of

the Adams Plant influence area.

• Stage 2B Site #2: This is the representative high HAA5 site for the Adams WTP influence

area. It had the second highest (after Stage 2B #1) HAA5 result of the

12 sites. It is located on the south central region of the distribution

system.

• Stage 2B Site #3: This is one of two representative high TTHM sites for the Adams WTP

influence area. It had the highest TTHM result of the 12 Adams WTP

sites. It is on the western periphery of the Adams WTP influence area

and downstream of Booster Station A, which is used intermittently

during the summer.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-15

• Stage 2B Site #4: This is the second of the representative high TTHM sites for the Adams

WTP influence area. It had the second highest TTHM result of the 12

Adams sites, and because it was the Stage 1 DBPR maximum

residence time location, its continued use will maintain an uninterrupted

historic record of DBP levels at the site. It is in the mixing zone in the

center of the city.

• Stage 2B Site #5: This is the average residence time site for the Lincoln WTP influence

area. It had the highest TTHM and HAA5 test results in the August

round of sampling of the Stage 1 DBPR average sites. Its TTHM

LRAA was not as high as one of the other two Stage 1 DBPR average

sites (old Stage 1 DBPR #6), but its HAA5 LRAA was the highest

HAA5 LRAA of the Stage 1 sites by a large margin. This site (the old

Stage 1 DBPR #7) is also in the geographic center of the Lincoln Plant

influence area. 

• Stage 2B Site #6: This is the representative highest HAA5 site for the Lincoln WTP

influence area. It had the highest HAA5 result of the 8 Lincoln SSS

sites. It is located on the eastern periphery of the Lincoln WTP

influence area and has historically always had a measurable total

chlorine residual, which is most likely due to the effect of the frequent

operation of Booster Station B.

• Stage 2B Site #7: This is the first of two representative highest TTHM sites for the Lincoln

WTP influence area. It had the highest TTHM result of the 12 Lincoln

WTP sites, and is located in the mixing zone in the central portion of the

city.

• Stage 2B Site #8: This is the second of the representative highest TTHM sites for the

Lincoln WTP influence area. It had the second highest TTHM result of

the 12 Lincoln sites. It is on the eastern edge of the city. 

The map on the following page shows the proposed Stage 2B compliance monitoring sites.

10. Proposed Stage 2B Compliance Monitoring Schedule:

Stage 2B compliance monitoring will be scheduled for the first week of February, May, August,

and November. This is the same as the Stage 1 DBPR and Stage 2A DBPR sampling, because August

is the historic month of maximum DBP levels and water temperature in the distribution system.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-16

Booster chlorination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

3

8

7

1

5

Stage 2B Representative High TTHM

Stage 2B Representative High HAA5

Stage 2B Average Residence Time

#

#

#

6

2

4

Booster chlorination facility

Ground storage tank

Elevated storage tank

MIXING

ZONE

Adams WTP

Lincoln WTP

North Tank 

(w/pump station)

South Tank

West Tank

Central Tank

Booster Station B

Booster Station A

3

8

7

1

5

Stage 2B Representative High TTHM

Stage 2B Representative High HAA5

Stage 2B Average Residence Time

#

#

#

Stage 2B Representative High TTHM

Stage 2B Representative High HAA5

Stage 2B Average Residence Time

#

#

#

6

2

4

11. Proposed Stage 2B compliance monitoring sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft K-17

This page intentionally left blank.
Appendix L

IDSE System-Specific Study Using Historical Data

This appendix is provided as an example IDSE report for a producing system opting to

complete a System-Specific Study (SSS) using historical DBP data.

Chapter 3 presents detailed guidance on the requirements for performing an SSS with

historical data and guidance on the selection of Stage 2B compliance monitoring sites using SSS

data. Chapter 3 also presents the IDSE reporting requirements for systems conducting an SSS. 

The application of the basic guidance on the use of historical data to select sites meeting the

SMP site criteria and the use of the data to select Stage 2B compliance monitoring sites is shown

in this example, along with several instances of the use of best professional judgement being

applied.

The italicized text within the appendix consists of comments and explanations and is not

intended to represent the recommended content of an actual IDSE Report.
This page intentionally left blank.
Initial Distribution System

Evaluation Report for

Magnolia City

PWSID Number: US0000000 

Address: P.O. Box 1234 

Magnolia City, US 11111-1234 

Contact Person: Ms. Mary Flower, P.E. 

Phone Number: 234-555-1111 

Fax Number: 234-555-2222 

Email Address: Mflower@ci.magnolia.us 

System Type:Community, surface water 

 

Population Served: 125,000 
This page intentionally left blank.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-1

1. System Description:

This section of the report should include a summary of typical system operating 

characteristics (and how they change on a seasonal basis if appropriate) explaining how sources

are used to meet system demands, where high water age is expected to occur, and any special

aspects of operation that could affect DBP concentrations in the distribution system.

Information about water treatment processes and source water quality data is also part of this

section, including a description of actual residence times within the water treatment plant and

the distribution system. 

General system characteristics:

Service Area: Magnolia City plus surrounding suburban areas

Production: Annual average daily demand 35 MGD

Source Water Information:

Grand Falls River

pH: from 6.7 to 7.7

Alkalinity: from 73 to 104 mg/L as CaCO3

TOC: from 1.8 to 5.4 mg/L as C

Entry points (tied to source(s) and identification of service area(s) under the influence of each entry

point:

Entry points: River Run Plant, serves the entire service area

Treatment Provided:

River Run Plant, coagulation (with ferric chloride), flocculation, sedimentation, and dual media

filtration (filter loading rates are approximately 4 gpm/sf). Chlorine is used for both primary and residual

disinfection.

Description of distribution system:

Distribution system (estimated length of lines and range of diameter):

About 800 miles, 4" - 56"

11storage tanks with a total of 19 MG capacity

4 elevated tanks 2.0 MG each (8 MG)

2 elevated tanks, 1.5 MG (3 MG)

2 elevated tanks, 0.5 MG (1 MG)

3 ground tanks (two 2 MG and one 3 MG, 7 MG total capacity)

The average residence time of water in the distribution system is estimated as two days.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-2

Pump stations:

Station #1 is located at the ground storage tank on North Boulevard. This station is primarily

used during peak demands and low pressure situations. The pump is timed to turn on in the

morning and evening during peak demand, and when the pressure drops below 40 psi at a point

downstream of the pump station.

Stations #2 and #3. These pumps are used to boost system pressure when the pressure in the

areas downstream of these pumps (Flower Village and Friendship Heights) drops below 40 psi.

Booster chlorination facilities:

Facility #1 is located in proximity to Freedom Square (downstream of the Columbus St.

storage tank). This facility is occasionally used during the summer when remote locations

downstream of the booster chlorination facility lose residual.

Facility #2 is located at the Flower Village elevated tank, in an area of the distribution system

where chlorine residuals are frequently low. 

Facility #3 is located near the North Village (downstream of the north storage tank) in an area

of the distribution system where chlorine residuals are frequently low. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-3

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

2. Schematic of the distribution system:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-4

3. SMP monitoring requirements:

Magnolia City is a system serving 125,000 people that uses one surface water source. 

Instead of an IDSE SMP, an IDSE SSS has been performed based on historical system-specific

monitoring data that are comparable or superior to data that would be collected at monitoring sites

required by the Standard Monitoring Program. A comparison of SMP monitoring site requirements

and sites used as a part of this SSS is presented in the following table.

Comparison of SMP and SSS Monitoring Sites

Site Criteria

Number of Sample Sites

Required by

SMP Provided in SSS

Near-entry to the distribution system 1 1

Average residence time 2 4

Representative of high TTHM 3 5

Representative of high HAA5 2 2

Total 8 12

4. Description of Historical Data:

The selected SSS sites have been monitored three times a year for a period of five years

(1999-2003). This monitoring was conducted separately from Stage 1 DBPR compliance monitoring. 

TTHM testing for the entire 5- year period was performed by certified labs. HAA5 testing was

performed by certified labs beginning in 2002, so HAA5 data provided by non-certified labs in the

previous years were not considered and have not been included in this report.

During the 5-year period of DBP monitoring, there were no significant, 

long-term changes made at the water treatment plant or in the operation of the distribution system. 

There have been no process changes at the plant, and no new tanks, pump stations, or significant water

mains added to the distribution system. A small booster chlorination facility was added to the North

EST in the spring of 2003, which allows chlorine to be added to water flowing out of the tank. This

helped increase the chlorine residual levels in the area around and past the tank in the summer of 2003. 

The area affected by this new chlorine booster facility is limited to the area that receives water from this

0.5 MG tank, so the area is relatively small.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-5

Available Data:

Report all data that helped in site selection. If you have bromide, TOC, or HPC data,

these may be helpful for justifying selection of Stage 2B sites.

Table L.1 summarizes free chlorine residual data at each of the city’s 24 TCR monitoring sites. 

Of these 24 sites, 12 have been monitored for DBP’s over the last 5 years and were selected as SSS

monitoring sites. Table L.2 presents HPC data for the 24 TCR monitoring sites

The historical sampling stations were chosen in 1999 to represent diverse geographical areas of

the distribution system, using water quality data collected in 1997 and 1998 for free residual chlorine

(Table L.1) and heterotrophic plate counts (HPC) (Table L.2). The extent of this network of 12

monitoring stations is, in our opinion, superior to the eight monitoring stations required by the IDSE

SMP for a system under the influence of one surface water source. 

Table L.3 in section 7 presents TTHM and HAA5 test results for the 12 TCR monitoring sites

where TTHM and HAA5 testing has been conducted on a regularly scheduled basis for the last 5

years.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-6

Table L.1 Magnolia City—Free Chlorine Residual Data (mg/L)

TCR

Site # Location SSS # 11/97 02/98 05/98 08/98 Average

1 Lakeshore Dr 7 0.5 0.8 0.9 0.4 0.7

2 Dogwood Dr 5 0.7 0.6 0.8 1.0 0.8

3 Brown Pike 6 0.6 0.9 1.1 0.8 0.9

4 Near Heights 8 0.7 0.7 0.4 0.2 0.5

5 Museum Rd 2 0.6 0.7 0.6 0.8 0.7

6 Country Club Rd 9 0.2 0.6 0.3 0.2 0.3

7 Logan Pl 12 0.5 0.3 0.2 0.5 0.4

8 Langley Ave 0.8 0.9 1.2 1.1 1.0

9 Grant Hill Pl 0.6 0.6 0.5 0.9 0.7

10 River Run entry point 1 1.4 1.2 1.3 1.7 1.3

11 Gray Sq 10 0.3 0.6 0.1 0.0 0.1

12 Pink Ln 0.2 0.3 0.5 0.3 0.6

13 Oak Dr 0.8 0.9 0.3 0.8 0.7

14 Sea Dr 0.2 0.8 0.8 0.5 0.6

15 River Rd 0.2 1.0 0.7 0.1 0.6

16 Lake Ave 0.9 0.7 1.0 1.2 1.0

17 Hardwood Sq 0.9 1.2 1.0 0.8 1.0

18 Long Dr 1.6 1.4 1.6 1.5 1.5

19 Colonial Plaza 0.8 0.6 0.9 0.8 0.8

20 Butler Pl 4 0.6 0.2 0.5 0.4 0.4

21 Sunset Rd 11 ND 0.1 0.1 0.3 0.1

22 Gatewood Ln 0.2 0.2 0.2 0.5 0.3

23 Morgan Ave 3 0.6 0.4 0.4 0.6 0.5

24 Central Street ND 0.2 ND 0.1 0.1

ND - Non Detect
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-7

Table L.2 Magnolia City—Heterotrophic Plate Counts (cfu/mL)

TCR

Site # Location SSS # 11/97 02/98 05/98 08/98 Average

1 Lakeshore Dr 7 50 34 63 113 65

2 Dogwood Dr 5 53 64 123 94 83

3 Brown Pike 6 56 42 276 345 180

4 Near Heights 8 82 136 246 146 152

5 Museum Rd 2 66 53 53 153 81

6 Country Club Rd 9 70 212 332 356 242

7 Logan Pl 12 54 65 65 93 69

8 Langley Ave 69 43 43 37 48

9 Grant Hill Pl 43 34 224 156 114

10 River Run entry point 1 67 14 42 35 40

11 Gray Sq 10 140 215 615 857 456

12 Pink Ln 280 163 263 746 363

13 Oak Dr 50 42 522 223 209

14 Sea Dr 140 66 236 364 201

15 River Rd 196 45 425 853 380

16 Lake Ave 53 42 72 84 63

17 Hardwood Sq 35 43 45 64 47

18 Long Dr 12 8 12 34 17

19 Colonial Plaza 78 86 364 384 228

20 Butler Pl 4 34 76 89 97 74

21 Sunset Rd 11 156 278 359 469 315

22 Gatewood Ln 233 214 546 656 412

23 Morgan Ave 3 35 62 92 147 84

24 Central Street 68 175 375 399 254
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-8

5. Description historical sample sites:

A description of the characteristics used to select the twelve historical sites used for DBP

monitoring in the distribution system is given here. These sites are presented graphically in section 3. 

Historical DBP data for these sites is presented in section 8.

Historical Site #1 – Entry point to the distribution system for River Run Water Treatment Plant. This

site is located just after the first significant group of connections downstream of the plant.

Historical Site #2 – Represents average residence time of water leaving the plant. We estimated the

point where the chlorine decays to about 50 percent of its original residual concentration (at the high

service pumps). There are no storage facilities between the plant and this site. 

Historical Site #3 – Represents average residence time. Water at this site does not go through a

storage facility, and the chlorine residual is generally 35 to 40 percent of the River Run Plant effluent

concentration. We attribute this additional loss of chlorine to the fact that the transmission and

distribution lines serving this area are older unlined cast iron and have significant build-up of corrosion

by-products (tubercles). We believe that these corrosion by-products exert a chlorine demand which

results in lower chlorine residual at this site, although it is probably lower in water age than Site #2.

Historical Site #4 – Represents average residence time. The site is used as an alternative site for our

coliform and chlorine residual monitoring.

Historical Site #5 – Represents average residence time. The chlorine residual at this site is generally 45

to 50 percent of the plant effluent concentration.

Historical Site #6 – Represents high TTHM levels. This sampling site is downstream of the Brown Pike

Storage Tank (a 1.5 MG elevated tank). The sampling station is located downstream of the tank

before the last group of connections (approximately 0.5 miles) to be representative of water delivered

to customers.

Historical Site #7 – Represents high TTHM levels. This site is the last dedicated sampling site

downstream of the Flower Village EST and is used for routine Total Coliform Rule and chlorine

residual monitoring. We have over 7 years of data from this site. This site is located before the last

group of connections near the end of the system, where the water demand tends to be relatively low.

Historical Site #8 – Represents high TTHM levels. This sample site is a faucet at a connection located

in a zone of the distribution system that has been recently developed. Chlorine residuals are normally in

the 0.2 to 0.7 mg/L range.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-9

Historical Site #9 – Represents high TTHM levels. This site is downstream of the North Storage Tank,

a 0.5 MG elevated tank with a booster chlorination facility that was recently added to aid in maintaining

a chlorine residual.

Historical Site #10 – Represents high TTHM levels. This site has been problematic in the past, with the

occurrence of coliform bacteria, non-detectable chlorine residuals, high heterotrophic plate count, and

odor complaints. A 4-inch blow-off was installed downstream of this site, but the site continues to have

poor water quality. 

Historical Site #11 – Represents high HAA5 levels. Although chlorine residual levels are often low at

this site, there has never been an occurrence of a heterotrophic plate count greater than 500 cfu/mL or

a positive coliform bacteria test.

Historical Site #12 – Represents high HAA5 levels. Sample tap is a hose bib at a building located in a

zone of the distribution system with water age greater than average. Chlorine residual at this site ranges

from 0.2 to 0.5 mg/L, and the heterotrophic plate count is consistently below 100 per mL all year

round. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-10

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

3

Historical DBP monitoring site

Stage 1 DBPR site

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

8

6

2

7

4

5

1

12

9

11

10

1

2

3 4

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

3

Historical DBP monitoring site

Stage 1 DBPR site

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

8

6

2

7

4

5

1

12

9

11

10

1

2

3 4

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

3

Historical DBP monitoring site

Stage 1 DBPR site

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

8

6

2

7

4

5

1

12

9

11

10

1

2

3 4

6. Map of the distribution system showing major transmission mains, numbered Stage 1

DBPR compliance sites, and numbered historical sample sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-11

7. Summary of historical DBP data and Stage 1 DBPR compliance data:

Data for five years of TTHM monitoring and two years of HAA5 monitoring are presented in

Table L.3. Data were collected three times a year, during April, July, and October. No winter samples

were taken. The historical monitoring did not include sampling during August—the peak historical

month for water temperature and DBPs (based on Stage 1 DBPR compliance monitoring provided

below). Therefore, a single set of additional samples was collected at the 12 historical sites in August

2003 and the results included as part of the 2003 monitoring data in the following table. The August

value is included in the table to allow for a comparison between the individual sampling results. 

However, the August 2003 results were not included in the calculation of the 2003 yearly averages

because this would have prevented a direct comparison of the 2003 averages to the averages from

previous years that do not include an August sample result.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-12

Table L.3 Magnolia City Historical DBP Monitoring Results (1999-2003)

SSS Sample Site Year

TTHM (μg/L) HAA5 (μg/L)

Monitoring

Data1 08/03 Avg

Monitoring

Data1 08/03 Avg

#1 - Plant entry point 1999 36, 92, 89 72

2000 24, 78, 93 65

2001 33, 15, 24 24

2002 24, 35, 46 35 21, 15, 68 35

2003 37, 45, 58 69 47 38, 58, 53 46 50

#2 - Average residence time 1999 66, 82, 80 76

2000 76, 94, 83 84

2001 72, 98, 79 83

2002 51, 75, 80 69 29, 35, 41 35

2003 44, 68, 71 78 61 45, 50, 48 56 48

#3 - Average residence time 1999 56, 71, 63 63

2000 36, 84, 103 74

2001 62, 68, 54 61

2002 41, 58 , 69 70 24, 23, 74 40

2003 41, 65, 70 74 59 47, 63, 59 48, 56

#4 - Average residence time 1999 61, 77, 75 71

2000 68, 86, 75 79

2001 67, 88, 79 78

2002 56, 75, 75 69 34, 33, 54 40

2003 47, 71, 74 85 66 43, 68, 63 59 58

#5 - Average residence time 1999 55, 70, 62 62

2000 35, 83, 82 67

2001 60, 66, 52 59

2002 43, 60 , 71 72 22, 21, 64 37

2003 39, 63, 69 92 57 48, 62, 58 36 56

#6 - High TTHM 1999 85, 71, 93 83

2000 82, 92, 102 92

2001 70, 72, 95 79

2002 61, 81, 85 76 40, 56, 68 55

2003 68, 76, 80 123 75 50, 50, 58 23 53
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

SSS Sample Site Year

TTHM (μg/L) HAA5 (μg/L)

Monitoring

Data1 08/03 Avg

Monitoring

Data1 08/03 Avg

July 2003 - Proposal Draft L-13

#7 - High TTHM 1999 82, 69, 83 78

2000 92, 102, 112 102

2001 90, 92, 105 96

2002 71, 91, 95 86 45, 33, 25 34

2003 88, 96, 100 98 95 30, 60, 68 63 53

#8 - High TTHM 1999 75, 80, 82 79

2000 65, 103, 112 93

2001 60, 106, 152 106

2002 53, 80, 91 75 32, 31, 23 29

2003 89, 55, 99 152 81 28, 33, 49 44 37

#9 - High TTHM 1999 80, 85, 87 84

2000 75, 93, 109 92

2001 70, 110, 98 93

2002 73, 100 , 101 95 35, 36, 28 34

2003 84, 90, 94 132 89 31, 39, 59 47 45

#10 - High TTHM 1999 78, 87, 89 85

2000 85, 103, 119 102

2001 60, 120, 108 96

2002 75, 102 , 103 98 34, 36, 30 33

2003 54, 70,114 92 79 45, 19, 29 26 31

#11 - High HAA5 1999 56, 71, 63 63

2000 37, 85, 84 69

2001 63, 69, 55 62

2002 42, 58 , 69 69 42, 71, 55 56

2003 41, 65, 71 83 59 50, 65, 79 82 65

#12 - High HAA5 1999 56, 72, 70 66

2000 63, 81, 70 74

2001 62, 83, 74 73

2002 51, 70, 70 64 44, 43, 25 37

2003 42, 66, 69 90 61 53, 68, 83 78 68

1

 Data obtained from sampling at approximate 90 day intervals each year are listed in order for April, July, and

October. Bold values are August 2003 results and are not included in the calculated averages.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-14

Stage 1 DBPR sampling occurred as scheduled from November 2002 through August 2003. 

These data are presented in the following table.

Magnolia City—Stage 1 DBPR Monitoring Results for 2003

Monitoring Site

TTHM (μg/L) HAA5 (μg/L)

Individual

Results1 LRAA

Individual

Results1 LRAA

Average residence time #1 45, 34, 51, 67 49 24, 27, 43, 50 36

Average residence time #2 36, 42, 41, 49 42 42, 47, 50, 61 50

Average residence time #3 32, 34, 43, 72 45 50, 62, 62, 73 62

Maximum residence time #4 64, 68, 74, 83 72 21, 25, 26, 28 25

1

 Data listed in order for November, February, May, and August quarterly sampling.

8. Proposed Stage 2B monitoring sites:

Magnolia City is a system serving 125,000 people and uses one surface water source.

Therefore, Big City is required to propose a total of four Stage 2B compliance monitoring sites. A

summary of these requirements is presented in the following table. 

Stage 2B Compliance Monitoring Requirements

Site Criteria Number of Sites

Stage 1 average residence time sites 1

Representative of high HAA5 1

Representative of high TTHM 2

Based on historical DBP data, Stage 1 compliance data, and other available water quality data

(free chlorine residual and HPC), we are proposing the Stage 2B monitoring sites listed in the following

table. The rationale for their selection follows. A schematic of the sites is presented in section 9. 
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-15

Proposed Stage 2B Compliance Monitoring Sites

Sample Site Site Description

Stage 2B Site #1 Stage 1 DBPR #3

Stage 2B Site #2 SSS #11 - High HAA5

Stage 2B Site #3 SSS #7 - High TTHMs

Stage 2B Site #4 SSS #9 - High TTHMs

1. One Stage 2B monitoring site representative of average residence time must be selected

from the three Stage 1 DBPR average residence time sites. Stage 1 DBPR #3 was

retained as the Stage 2B monitoring site representative of average residence time. This

site had the highest individual TTHM concentration and the highest HAA5 LRAA. 

Because Stage 1 #3's HAA5 LRAA was much greater than the HAA5 LRAAs of the

other two Stage 1 sites and the TTHM LRAAs of all three sites were relatively close,

the decision was made to retain Stage 1 #3 as the Stage 2B average residence time

compliance site.

2. One Stage 2B monitoring site must be representative of the highest HAA5 levels in the

distribution system. Among all the SSS and Stage 1 DBPR sites, SSS #12 had the

highest average HAA5 value during the 2003 sampling period (68 μg/L) but had a

much lower average (37 μg/L) in 2002. SSS #11 had the highest average HAA5

values when considered together for 2002 and 2003, the only site to have such

consistently high values. It is believed that the startup of Booster Chlorination Facility

#2 in June 2003 resulted in an increase in HAA5 values at SSS #12, compared to the

values seen the previous summer. Operation of Booster Chlorination Facility #2 is on

an as needed basis, so it appears that if the booster facility is not operating, the HAA5

levels at SSS #12 will be much lower. Also, SSS #12 is geographically and

hydraulically a little too close to Stage 2B #3. Therefore, based on our professional

judgement of these factors, SSS #11 is proposed as the Stage 2B compliance

monitoring site representative of highest HAA5.

3. Two Stage 2 DBPR monitoring sites must be representative of highest TTHM levels. 

Among all the SSS and Stage 1 DBPR sites, SSS #7 and #9 consistently had the

highest average TTHM values during 1999-2003. Therefore, we propose SSS sites

#7 and #9 as the Stage 2B compliance monitoring sites representative of highest

TTHM.
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-16

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

Stage 2B representative high HAA5 location

Stage 2B representative high TTHM location #

#

# Stage 2B average residence time location

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

1

3

4

2

River Run WTP

P

Elevated Storage Tank

Pump station

Booster chlorination station

P

Ground Storage Tank

P#1

Stage 2B representative high HAA5 location

Stage 2B representative high TTHM location #

#

# Stage 2B average residence time location

Flower Village

Friendship Heights

P#3

P#2

1

2

3

North EST

Flower

Village

EST

Brown

Pike

EST

Columbus

Street

EST

1

3

4

2

9. Proposed Stage 2B compliance sample sites:
Stage 2 DBPR Initial Distribution System Evaluation Guidance Manual

July 2003 - Proposal Draft L-17

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