Stage 2 Disinfectants and Disinfection 

Byproducts Rule

Consecutive Systems Guidance Manual

 
Office of Water (4607M) 

EPA 815-R-09-017 

March 2010 

www.epa.gov/safewater
Purpose: 

The purpose of this guidance manual is solely to help consecutive systems understand 

and meet the requirements of the Stage 2 Disinfectants and Disinfection Byproducts Rule 

(DBPR). 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. 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 

U.S. Environmental Protection Agency 

Mail Code 4607M 

1200 Pennsylvania Avenue NW
 

Washington, DC 20460 

Tel: (202) 564-5262 

Fax: (202) 564-3767 

Email: grubbs.thomas@epa.gov 

Acknowledgements: 

Steve Lohman – Denver Water 

James Parsons – Cobb County-Marietta Water Authority 

Consecutive Systems Guidance Manual iii March 2010 
CONTENTS 

Exhibits .........................................................................................................................vi 

Acronyms ......................................................................................................................vii 

 Glossary ........................................................................................................................ix 

1.0 Introduction ................................................................................................................1-1 

 1.1 Purpose of this Manual ......................................................................................1-1 

 1.2 Manual Organization .........................................................................................1-2 

2.0 Overview of Existing Regulatory Requirements for Consecutive Systems ............2-1 

 2.1 Public Notification Rule ....................................................................................2-1 

 2.2 Consumer Confidence Report (CCR) Rule........................................................2-2 

 2.3 Consecutive Systems Monitoring Requirements (40 CFR 141.29) ...................2-3 

3.0 Stage 2 DBPR Requirements for Consecutive Systems ............................................3-1 

 3.1 Disinfection Byproduct Maximum Contaminant Levels ...................................3-1 

 3.2 Initial Distribution System Evaluation...............................................................3-2 

 3.3 Stage 2 (subpart V) Compliance Monitoring Requirements ..............................3-4 

 3.3.1 Stage 2 DBPR Monitoring Plan .............................................................3-4 

 3.3.2 Stage 2 DBPR Compliance Monitoring .................................................3-5 

 3.3.3 Reporting and Recordkeeping Requirements ........................................3-8 

 3.4 Disinfectant Residual Monitoring ......................................................................3-8 

 3.5 Operational Evaluations .....................................................................................3-9 

 3.6 Simultaneous Compliance .................................................................................3-10 

4.0 Compliance Options for Consecutive Systems ..........................................................4-1 

 4.1 DBP Control in Consecutive Systems ...............................................................4-1 

 4.2 Water Age Management ....................................................................................4-3 

 4.2.1 Pipe Looping ..........................................................................................4-4 

 4.2.2 Managing Valves ...................................................................................4-4 

 4.2.3 Bypassing Oversized Pipes ....................................................................4-4 

 4.2.4 Installing Dedicated Transmission Main ...............................................4-4 

 4.2.5 Improving Tank Mixing and Turnover ..................................................4-5 

 4.2.6 Eliminating Excess Storage and Tanks in Series ...................................4-9 

 4.3 Reduction of Disinfectant Demand ....................................................................4-10 

 4.3.1 Replacing or Cleaning and Lining Unlined Cast Iron Pipes ..................4-10 

 4.3.2 Distribution System Flushing ................................................................4-10 

 4.4 Chloramination ..................................................................................................4-12 

 4.4.1 Water Quality Issues for Chloramines ...................................................4-12 

 4.4.2 Options for Chloramine Conversion ......................................................4-13 

 4.4.3 Cost, Handling, and Safety Issues..........................................................4-14 

 4.4.4 Public Education ....................................................................................4-15 

5.0 Other Alternatives for Consecutive Systems .............................................................5-1 

 5.1 Improved Water Quality from the Wholesale System .......................................5-1 

 5.2 Alternative Sources and Blending Strategies .....................................................5-3 

Consecutive Systems Guidance Manual iv March 2010
6.0 Communication Strategies for Consecutive and Wholesale Systems......................6-1 

 6.1 Communication Strategies for Stage 2 DBPR Compliance Monitoring ...........6-1 

 6.2 Communication Strategies for Operational Evaluations ....................................6-4 

 6.3 Agreements between Consecutive and Wholesale Systems ..............................6-5 

7.0 Developing Consecutive System Compliance Strategies ..........................................7-1 

 7.1 Data Acquisition ................................................................................................7-1 

 7.1.1 Monitoring Parameters...........................................................................7-1 

 7.1.2 Monitoring Frequency ...........................................................................7-3 

 7.1.3 Monitoring Locations.............................................................................7-3 

 7.2 Communication of Needs to the Wholesale System ..........................................7-6 

8.0 Frequently Asked Questions .......................................................................................8-1

9.0 References .....................................................................................................................9-1 

Appendices

Appendix A. Example of a Formal Agreement between Consecutive and Wholesale Systems

Consecutive Systems Guidance Manual v March 2010
EXHIBITS 

Exhibit 2.1 Tiers of Public Notice ........................................................................................2-2 

Exhibit 3.1 DBP MCLs ....................................................................................................3-1 

Exhibit 3.2 Stage 2 DBPR Compliance Schedule for Wholesale and ................................. 

 Consecutive Systems .........................................................................................3-2 

Exhibit 3.3 Stage 2 (subpart V) Routine Monitoring Requirements ....................................3-6 

Exhibit 4.1 Effect of Temperature Differential Between Inflow and Tank Bulk ................ 

 Water on Mixing Characteristics .......................................................................4-7 

Exhibit 4.2 Effect of Inlet Pipe Orientation on Mixing Characteristics ...............................4-9 

Exhibit 6.1 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - .................. 

 Consecutive System Receiving Water Directly from Wholesale System .........6-2 

Exhibit 6.2 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - .................. 

 Consecutive System Receiving Water Through Another ................................. 

 Consecutive System ...........................................................................................6-3 

Exhibit 6.3 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - .................. 

 Consecutive System Receiving Water from Wholesale System with No ......... 

 Customers ....................................................................................................6-3 

Exhibit 6.4 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - .................. 

 Approximate Water Age of Monitoring Locations is Known ...........................6-4 

Exhibit 6.5 Case Study of Formal Agreements between Consecutive and ......................... 

 Wholesale Systems ............................................................................................6-6 

Exhibit 6.6 Case Study of Informal Agreements between Consecutive and ....................... 

 Wholesale Systems ............................................................................................6-7 

Exhibit 7.1 DBP Formation from Wholesale to Consecutive System Example...................7-4 

Exhibit 7.2 Variation in DBP Formation with Chlorination and Chloramination ................7-5 

Consecutive Systems Guidance Manual vi March 2010
 

ACRONYMS 

40 CFR Code of Federal Regulations, Title 40 

AWWA American Water Works Association 

AwwaRF American Water Works Association Research Foundation 

BATs Best available technologies 

CCR Consumer Confidence Report 

CFD Computational fluid dynamics 

CNBr Cyanobromides 

CNCl Cyanochlorides 

CNX Cyanohalides 

CT Disinfectant residual concentration × contact time 

DBP Disinfection byproduct 

DBPR Disinfectants and Disinfection Byproducts Rule 

DPD N, N-diethyl-p-phenylenediamine 

EPA United States Environmental Protection Agency 

IDSE Initial Distribution System Evaluation 

GAC Granular activated carbon 

GWUDI Ground water under the direct influence of surface water 

HAA Haloacetic acid 

HAA5 The sum of five HAA species 

HPC Heterotrophic plate count 

IDSE Initial distribution system evaluation 

LCR Lead and Copper Rule 

LRAA Locational running annual average 

LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule 

MCL Maximum contaminant level 

M-DBP Microbial-disinfection byproducts 

mg/L Milligrams per liter 

mL Milliliter 

MRDL Maximum residual disinfectant level 

N.d. No date (for publication) 

NDMA N-nitrosodimethylamine 

NPDWR National Primary Drinking Water Regulation 

NOM Natural organic matter 

NTNCWS Nontransient noncommunity water system 

PAC Powdered activated carbon 

PWS Public water system 

RAA Running annual average 

SCADA Supervisory control and data acquisition 

SDWA Safe Drinking Water Act 

SSS System specific study 

SWTR Surface Water Treatment Rule 

TCR Total Coliform Rule 

THM Trihalomethane 

TOC Total organic carbon 

TTHM Total trihalomethanes 

UV Ultraviolet 

Consecutive Systems Guidance Manual vii March 2010 
 

VSS Very small system 

WTP Water treatment plant 

Consecutive Systems Guidance Manual viii March 2010 
 

 

GLOSSARY 

Best available technology (BAT): the best technology, treatment techniques, or other means 

which the Administrator finds, after examination for efficacy under field conditions and not 

solely under laboratory conditions, are available (taking cost into consideration). For the 

purposes of setting MCLs for synthetic organic chemicals, any BAT must be at least as effective 

as granular activated carbon. (40 CFR 141.2) 

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

disinfectant residual concentration throughout the distribution system. 

Combined distribution system: the interconnected distribution system consisting of the 

distribution systems of wholesale systems and of the consecutive systems that receive some or all 

of their finished water from those wholesale system(s). (40 CFR 141.2) 

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

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

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

finished water from one or more wholesale systems. Delivery may be through a direct 

connection or through the distribution system of one or more consecutive systems. (40 CFR 

141.2) 

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) 

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 and hypochlorite acid) or combined chlorine (chloramines). It is used in the 

Surface Water Treatment Rule as a measure for determining CT. 

Disinfection: a process that 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: a set of two samples collected at the same time and same location, with one 

sample analyzed for TTHM and the other sample analyzed for HAA5. Dual sample sets are 

collected for the purposes of conducting an IDSE under subpart U of 40 CFR 141.2 and 

determining compliance with the TTHM and HAA5 MCLs under subpart V of 40 CFR 141.2. 

Finished water: water that is introduced into the distribution system of a public water system and 

is intended for distribution and consumption without further treatment, except that treatment 

necessary to maintain water quality in the distribution system (e.g., booster disinfection, addition 

of corrosion control chemicals). (40 CFR 141.2) 

Consecutive Systems Guidance Manual ix March 2010 
 

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 large-diameter pathogens such as Giardia lamblia, or (2) significant and relatively rapid shifts 

in water characteristics such as turbidity, temperature, conductivity, or pH that 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 (e.g., 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) 

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. 

Locational running annual average (LRAA): the average of sample analytical results for 

samples taken at a particular monitoring location during the previous four calendar quarters. (40 

CFR 141.2) 

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

that is delivered to any user of a public water system. (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. 

Nitrification: a two-step process in which nitrifying bacteria convert ammonia to nitrite and then 

convert nitrite to nitrate. Nitrification can occur in water distribution systems in which naturally 

occurring ammonia is present, or in systems that add ammonia to the water as part of the 

chloramine disinfection process. 

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

(40 CFR 141.2) 

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

community water system and that regularly serves at least twenty-five of the same persons over 

six months per year. (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 

Consecutive Systems Guidance Manual x March 2010 
 

operator of such system and used primarily in connection with such system, and (2) any 

collection or pretreatment storage facilities not under such control that 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 the time when it reaches 

a particular point in the distribution system. Also referred to as water age. 

Running annual average: the average of monthly or quarterly averages of all analytical results of 

samples taken throughout the distribution system, as averaged over the preceding four quarters. 

Secondary disinfection: The process whereby a disinfectant (typically chlorine or chloramine) is 

added to finished water in order to maintain a disinfection residual in the distribution system. 

Also referred to as “residual disinfection.” 

State: the agency of the State or Tribal government that 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) 

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

141.2) 

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

residual. 

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. Note: Some publications may use “THM4” instead of “TTHM.” 

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 as necessary to produce finished 

water and then sells or otherwise delivers finished water to another public water system. 

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

consecutive systems. (40 CFR 141.2) 

Consecutive Systems Guidance Manual xi March 2010 
 

1.0 Introduction 

1.1 Purpose of this Manual 

The intent of this manual is to help consecutive systems understand and meet the 

requirements of the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). The Stage 

2 DBPR defines a consecutive system as a public water system (PWS) that receives some or all 

of its finished water from one or more wholesale systems. Delivery may be through a direct 

connection or through the distribution system of one or more consecutive systems. Consecutive 

systems that use a disinfectant other than ultraviolet (UV) light or that deliver water from 

another system that has been treated with a disinfectant other than UV light are subject to the 

Stage 2 DBPR. 

Most Safe Drinking Water Act (SDWA) regulations promulgated to date have not 

specifically addressed consecutive system requirements. Under the provisions of 40 CFR 

141.29, a State may, with concurrence of the United States Environmental Protection Agency 

(EPA), have modified monitoring requirements for a consecutive system to the extent that the 

interconnection of a wholesale and a consecutive system justifies treating them as a single 

system for monitoring purposes. Therefore, a consecutive system may not have been required by 

the State to conduct monitoring for certain contaminants if the wholesale system has already 

monitored for those contaminants. 

The Stage 2 DBPR does not change 40 CFR 141.29, so a State may still modify 

monitoring requirements (but not compliance determinations), with EPA’s concurrence, for 

consecutive systems as described above. However, absent EPA concurrence with a modification 

under 40 CFR 141.29, State flexibility to allow a consecutive system to modify its own 

distribution system monitoring for disinfection byproducts (DBP), depending on factors such as 

the size of the consecutive system’s distribution system, the amount of distribution system 

storage, and the quality of the source water, is available under 40 CFR 142.16(m). 

The Stage 2 DBPR may present certain challenges for consecutive systems. For 

example, a consecutive system may receive water that has been disinfected and already contains 

elevated levels of DBP. A consecutive system usually has no treatment facilities to control 

DBPs already present in the water from the wholesale system, and limited ability to control the 

continued formation of DBP in its own distribution system. For this reason, EPA has established 

Best Available Technologies (BATs) specifically for consecutive systems in the Stage 2 DBPR. 

EPA is aware of the difficulty in implementing consecutive system regulations because 

the relationships between wholesale and consecutive systems are complex and varied. EPA is 

also aware that there are a variety of State approaches to addressing regulatory requirements for 

consecutive systems. The Stage 2 DBPR presents an opportunity for consecutive systems to 

better define roles and responsibilities through discussions with their wholesaler and the State. 

Some States have taken a very active role in establishing relationships between wholesale and 

consecutive systems. 

As discussed later in this document, some of the deadlines imposed by the Stage 2 DBPR 

(deadlines related to the Initial Distribution System Evaluation (IDSE)) fall within six months of 

Consecutive Systems Guidance Manual 1-1 March 2010 
 

rule promulgation. Although EPA has already provided guidance for consecutive systems to 

comply with IDSE requirements, all consecutive systems, including those not previously 

required to comply with the Stage 1 DBPR, are encouraged to contact their wholesaler and their 

State to confirm their responsibilities for Stage 2 maximum contaminant level (MCL) 

compliance. EPA has also provided other guidance, where appropriate, to assist PWSs and 

States in implementing the Stage 2 DBPR. 

1.2 Manual Organization 

This guidance manual is organized as follows: 

•	 Chapter 1 - Introduction: Explains the purpose of this manual. 

•	 Chapter 2 - Overview of Existing Regulatory Requirements for Consecutive Systems: 

Provides an overview of the provisions of existing regulations that apply to 

consecutive systems. 

•	 Chapter 3 - Stage 2 DBPR Requirements for Consecutive Systems: Provides an 

overview of the Stage 2 DBPR requirements that apply to consecutive systems. 

•	 Chapter 4 - Compliance Options for Consecutive Systems: Discusses BATs 

identified by EPA for consecutive systems to decrease DBP formation in their 

systems. 

•	 Chapter 5 - Other Alternatives for Consecutive Systems: Discusses alternatives other 

than BATs for consecutive systems to reduce DBP formation in their systems. 

•	 Chapter 6 - Communication Strategies for Consecutive and Wholesale Systems: 

Describes communication strategies for consecutive systems needing to coordinate 

with wholesale systems to meet Stage 2 DBPR requirements. 

•	 Chapter 7 - Developing Consecutive System Compliance Strategies: Suggests 

approaches for consecutive systems to characterize DBP formation in their system 

and how to coordinate with the wholesaler on control strategies. 

•	 Chapter 8 - Frequently Asked Questions: Provides answers to questions frequently 

asked by systems and States. 

•	 Chapter 9 – References: Provides a bibliographic list of references cited in this 

manual. 

•	 Appendix A – Example of Formal Agreement between Consecutive and Wholesale 

Systems: Provides an example of a formal agreement between consecutive and 

wholesale systems that meets the requirements of the State of Colorado. Other States 

may have specific requirements that must be met in preparing these agreements. 

Consecutive Systems Guidance Manual 1-2 March 2010 
 

	 

	 

	 

	 

•

•

•

•

Contacting the appropriate State office. 

Calling the Safe Drinking Water Hotline at 1-800-426-4791. 

Downloading from EPA’s Web site at http://www.epa.gov/safewater. 

Calling the National Service Center for Environmental Publications at 1-800-490-

9198 or visiting their Web site at http://www.epa.gov/nscep/. 

 

This guidance manual is intended to address consecutive system-specific issues and 

contains many references to rules other than the Stage 2 DBPR that may apply to consecutive 

systems. References to appropriate guidance manuals are provided throughout this document. 

Copies of these manuals can be obtained by: 

Consecutive Systems Guidance Manual 1-3 March 2010 
 

 

2.0 Overview of Existing Regulatory Requirements for Consecutive Systems 

There are several existing drinking water regulations that contain general provisions that 

consecutive systems must meet for any rule (including Stage 2 DBPR). This chapter reviews the 

following regulations that address consecutive system requirements: 

• Public Notification Rule 

• Consumer Confidence Report (CCR) Rule 

• Consecutive System Monitoring Requirements Under 40 CFR 141.29 

In addition, other drinking water rules (e.g., Lead and Copper Rule, Ground Water Rule) 

have specific consecutive system requirements unrelated to the Stage 2 DBPR. 

2.1 Public Notification Rule 

The Public Notification Rule requires the owner or operator of any PWS to notify its 

customers any time it incurs a violation of a national primary drinking water regulation 

(NPDWR) and in other specific situations. The type of notification required varies depending on 

the violation. Exhibit 2.1 shows the tier of notification required for certain types of violations or 

situations as well as the notification frequency and method for each tier. 

PWSs that sell or provide water to another public water system must give public notice to 

its own customers as well as the owner or operator of the consecutive system (40 CFR 

141.201(c)(1)). The consecutive system is then responsible for providing public notice to its 

own customers. If the violation occurs in a portion of the distribution system that is physically 

or hydraulically isolated from other parts of the distribution system, the State may allow the 

system to limit public notification only to customers in that area of the distribution system. This 

could occur in a consecutive system if the system receives water from more than one wholesale 

system or has multiple entry points from a single wholesale system. However, the system must 

receive permission from the State in writing to limit distribution of the public notice (40 CFR 

141.201(c)(2)). 

Consecutive Systems Guidance Manual 2-1 March 2010 
 

 

 

 

Exhibit 2.1 Tiers of Public Notice 

Tier Types of Situations When Notice is Required Examples of Appropriate 

Notification Methods1 

1 NPDWR violations and 

situations with significant 

potential to have serious 

adverse effects on human 

health as a result of shortterm exposure. 

• As soon as practical but no 

later than 24 hours after the 

system learns of violation. 

• Consult with State as soon 

as practical but no later than 

24 hours after learning of 

the violation to determine 

additional public notification 

requirements. 

• Broadcast media 

• Posting in conspicuous 

location 

• Hand delivery 

• Other method approved by 

State 

2 All other NPDWR 

violations and situations 

with potential to have 

serious adverse effects on 

human health. 

• As soon as practical but no 

later than 30 days after the 

system learns of violation. 

• Repeat notice required 

every 3 months or as 

determined by State for as 

long as violation or situation 

persists. 

• Mail or other direct delivery 

• Newspaper notice 

• Posting in public places 

• Posting on the Internet 

• Delivery to community 

organizations 

3 All other NPDWR 

violations and situations 

not included in Tier 1 and 

Tier 2. 

• No later than 1 year after 

system learns of violation. 

• Repeat notice required 

annually. 

• Mail or other direct delivery 

• Newspaper notice 

• Posting in public places 

• Posting on the Internet 

• Delivery to community 

organizations 

• Inclusion in consumer 

confidence report 1 Note that some notification methods are only available to certain types of systems. 

For more information on Public Notification Rule requirements, refer to: 

• Public Notification Handbook (USEPA, 2000a) 

• The Public Notification Rule: A Quick Reference Guide (USEPA, 2000b) 

2.2 Consumer Confidence Report (CCR) Rule 

The CCR Rule requires community water systems to provide an annual report to their 

customers that provides information on the quality of the water delivered by the system and any 

risks from exposure to contaminants detected in the water. The report must be distributed by 

July 1 of each year and must contain data collected during or prior to the previous calendar year. 

 Consecutive systems should include information about all purchased water in their CCRs, in 

addition to information on their own total coliform and lead and copper monitoring. Wholesale 

systems are required to deliver the applicable water quality information to consecutive systems 

no later than April 1 of each year or by a date mutually agreed upon and included in a contract 

between the consecutive and wholesale system (40 CFR 141.152(d)). 

Consecutive Systems Guidance Manual 2-2 March 2010 
 

 

For more information on CCR requirements refer to: 

• Preparing Your Consumer Confidence Report: Revised Guidance for Water Suppliers

 (USEPA, 2005) 

• Consumer Confidence Report Rule: A Quick Reference Guide (USEPA, 2004b) 

2.3 Consecutive Systems Monitoring Requirements (40 CFR 141.29) 

The provisions for consecutive systems under 40 CFR 141.29 allow the State to modify 

the monitoring requirements for combined distribution systems. When justified, the State may 

treat the combined distribution system as a single system for monitoring purposes. Such systems 

must follow a monitoring schedule specified by the State and concurred with by the 

Administrator of the EPA. States may not modify compliance requirements. 

Consecutive Systems Guidance Manual 2-3 March 2010 
3.0 Stage 2 DBPR Requirements for Consecutive Systems 

Many consecutive systems deliver water that has been treated with a disinfectant other 

than UV light and which may therefore contain DBPs. Prior to promulgation of the Stage 2 

DBPR, monitoring of consecutive systems for DBPs was not specifically addressed by the Safe 

Drinking Water Act (SDWA) regulations. The intent of the Stage 2 DPBR with respect to 

consecutive systems is to present an effective approach for identifying and resolving DBP 

problems, keeping in mind that relationships between wholesale systems and consecutive 

systems are often complex and varied. Depending upon the specific nature of these 

relationships, States have some flexibility in their approach to the implementation of the Stage 2 

DBPR requirements. Consecutive systems are encouraged to contact their wholesale systems 

and their States as soon as possible after rule promulgation to discuss applicable requirements 

and responsibilities. 

This chapter describes the requirements of the Stage 2 DBPR that apply to consecutive 

systems. The following rule requirements are discussed: 

• Disinfection Byproduct MCLs; 

• IDSEs; 

• Stage 2 (subpart V) Compliance Monitoring Requirements; 

• Disinfectant Residual Monitoring; and 

• Operational Evaluations. 

3.1 Disinfection Byproduct Maximum Contaminant Levels 

The MCLs for total trihalomethanes (TTHM), haloacetic acid (five) (HAA5), bromate, 

and chlorite have not changed from the Stage 1 DBPR; however, the method of calculating 

compliance for TTHM and HAA5 has changed from a running annual average in Stage 1 to a 

locational running annual average in Stage 2. For more information on Stage 2 DBPR 

compliance calculations, refer to Section 3.4. The MCLs for DBPs are shown in Exhibit 3.1. 

The dates for complying with the Stage 2 DBPR MCLs for TTHM and HAA5 are shown in 

Exhibit 3.2. 

Exhibit 3.1 DBP MCLs 

Disinfection Byproduct MCL (mg/L) 

Bromate 

Chlorite 

TTHM 

HAA5 

0

0

.

1

.

0

.

0

10

0

80

0 0. 60

Consecutive Systems Guidance Manual 3-1 March 2010 
Consecutive Systems Guidance Manual 3-2 March 2010 

 

 

Exhibit 3.2 Stage 2 DBPR Compliance Schedule for Wholesale and Consecutive 

Systems 

Population Served by the Largest 

System in the Combined 

Distribution System1 

Date for Compliance with Stage 2 DBPR (subpart V) 

Monitoring Requirements2 

> 100,000 people April 1, 2012 

50,000 - 99,999 people October 1, 2012 

10,000 - 49,999 people October 1, 2013 

< 10,000 people October 1, 2013 if no Cryptosporidium monitoring is required 

under LT2ESWTR 

OR 

October 1, 2014 if Cryptosporidium monitoring is required under 

LT2ESWTR 

1 A combined distribution system consists of the distribution systems of wholesale systems and of the consecutive 

systems that receive some or all of their finished water from those wholesale system(s) (40 CFR 141.2). 

2

 If you are required to conduct quarterly monitoring, you must begin monitoring in the first full calendar quarter that 

includes the compliance date in Exhibit 3.2. If you are required to conduct monitoring at a frequency that is less than 

quarterly, you must begin monitoring in the calendar month recommended in the IDSE report (40 CFR 141.601 or 

141.602) or the calendar month identified in the subpart V monitoring plan (141.622) no later than 12 months after the 

date listed in Exhibit 3.2. The State may grant up to an additional 24 months for compliance if you require capital 

improvements to comply with an MCL. 

3.2 Initial Distribution System Evaluation 

This section briefly summarizes the Stage 2 DBPR IDSE requirements. For more 

information on Stage 2 IDSE requirements, refer to the Initial Distribution System Evaluation 

(IDSE) Guidance Manual for the Final Stage 2 Disinfectants and Disinfection Byproducts Rule 

(USEPA, 2006a). A separate guide has also been developed to briefly summarize the 

requirements for systems serving fewer than 10,000 people (USEPA, 2006b). 

Community water systems of any size and nontransient, noncommunity water systems 

(NTNCWS) serving at least 10,000 people are subject to the IDSE requirements if they use a 

primary or residual disinfectant other than UV light or deliver water that has been treated with a 

primary or residual disinfectant other than UV light. The purpose of the IDSE requirements is to 

help systems select representative high TTHM and HAA5 compliance monitoring locations. 

These sites are then used for compliance monitoring under the Stage 2 DBPR. 

There are four options available for systems to meet IDSE requirements, depending on 

their historical sampling data, size, and preference: 

•	 Receive a Very Small System (VSS) Waiver. Systems serving fewer than 500 

people with DBP sample results may be eligible for a waiver from the State. Systems 

receiving the waiver have no further IDSE requirements. 
•	 Receive 40/30 certification. A 

system has no further IDSE 

requirements if the system can 

certify to the State that all TTHM 

and HAA5 compliance data are 

less than or equal to 0.040 mg/L 

for TTHM and less than or equal 

to 0.030 mg/L for HAA5 during 

a specified two year period. In 

addition, the system must not 

have had any TTHM or HAA5 

monitoring violations during the 

same period. 

•	 Conduct a System Specific 

Study (SSS). A system may 

conduct an IDSE study based on 

existing monitoring results or a 

hydraulic model instead of 

conducting IDSE standard 

monitoring. A system’s model 

or existing monitoring results 

must meet specific criteria to be 

used in an SSS. 

•	 Conduct Standard Monitoring. 

Compliance Schedule for the IDSE 

The State sent a letter to each system 

with a determination of the system’s IDSE 

schedule based on system characteristics. The 

compliance schedule for consecutive and 

wholesale systems was based on the population 

of the largest system in the combined 

distribution system. For purposes of complying 

with the IDSE schedule, the State may have 

determined that the combined distribution 

system does not include certain consecutive 

systems based on factors such as receiving 

water from a wholesale system only on an 

emergency basis or receiving only a small 

percentage and small volume of water from a 

wholesale system. The State may also have 

determined that the combined distribution 

system does not include certain wholesale 

systems based on factors such as delivering 

water to a consecutive system only on an 

emergency basis or delivering only a small 

percentage and small volume of water to a 

consecutive system. 

IDSE standard monitoring entails one year of distribution system monitoring. The 

sampling frequency and minimum number of sample locations required depend on 

system characteristics such as size, source water type, and whether the system is part 

of a combined distribution system. 

A combined distribution system consists of 

the distribution systems of wholesale systems 

and of the consecutive systems that receive 

some or all of their finished water from those 

wholesale system(s) (40 CFR 141.2). For 

example, if a Town purchases water from a 

City to supplement its own groundwater 

supplies, the combined distribution system 

includes the City’s and the Town’s distribution 

systems. 

Town System City System 

Consecutive systems that do not apply a 

chemical disinfectant were not specifically 

addressed by Stage 1 DBPR requirements. 

Therefore, these systems may not have historical 

TTHM and HAA5 data unless the wholesale 

system collected samples within the consecutive 

system. In the absence of historic TTHM and 

HAA5 data, systems must either conduct 

standard monitoring or an SSS to comply with 

the IDSE requirements. Consecutive systems 

should consider obtaining Stage 1 data from the 

wholesaler to assist in IDSE site selection if no 

historical data exists. 

Consecutive Systems Guidance Manual 3-3 March 2010 
 

3.3 Stage 2 (subpart V) Compliance Monitoring Requirements 

This section provides a brief summary of the Stage 2 (subpart V) compliance monitoring 

requirements. For more information on Stage 2 DBPR monitoring, reporting, and recordkeeping 

requirements, refer to: 

•	 Stage 2 DBPR Operational Evaluation Guidance Manual (USEPA, 2008) 

•	 Initial Distribution System Evaluation Guidance Manual for the Final Stage 2 

Disinfectants and Disinfection Byproducts Rule (USEPA, 2006) 

•	 Complying with the Stage 2 Disinfectant and Disinfection Byproducts Rule: Small 

Entity Compliance Guide (USEPA, 2007c). 

A system is subject to the Stage 2 (subpart V) requirements if it is a community water 

system or a NTNCWS and it uses a primary or residual disinfectant other than UV light or 

delivers water that has been treated with a primary or residual disinfectant other than UV light. 

Therefore, consecutive systems that do not apply a disinfectant but purchase water that has been 

treated with a disinfectant must comply with these requirements. In addition, these consecutive 

systems must now comply with the Stage 1 DBPR analytical, monitoring, and maximum residual 

disinfectant level (MRDL) requirements for chlorine and chloramines. The chlorine and 

chloramine requirements are discussed further in Section 3.4. 

The MCLs for TTHM and HAA5 have not changed from the Stage 1 DBPR. However, 

the method of calculating compliance has changed. Stage 2 DBPR compliance determination is 

based on locational running annual averages (LRAAs) of TTHM and HAA5 concentrations. 

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

annual average (RAA) required under the Stage 1 DBPR. 

3.3.1 Stage 2 DBPR Monitoring Plan 

Systems must develop a monitoring plan to be used for Stage 2 monitoring and 

compliance determination (40 CFR 141.622). The monitoring plan must include: 

•	 Monitoring locations; 

•	 Monitoring dates; 

•	 Compliance calculation procedures; and 

•	 Monitoring plans for any other systems in the combined distribution system if the 

State has reduced monitoring requirements. 

Note that systems will recommend Stage 2 DBPR compliance monitoring locations and 

dates as part of their IDSE report. 

Systems using surface water, ground water under the direct influence of surface water 

(GWUDI), or purchased surface water and serving more than 3,300 people must submit a copy 

Consecutive Systems Guidance Manual 3-4 March 2010 
 

of the monitoring plan to the State prior to the date they are scheduled to collect their first Stage 

2 DBPR compliance samples. All systems must keep the plan on file for State and public 

review. A system that has been granted a VSS waiver must comply by updating its Stage 1 

monitoring plan or creating a new monitoring plan. 

Systems should make modifications to their monitoring plan as needed to reflect changes 

in treatment, distribution system operations and layout (including new service areas), or other 

factors that may affect TTHM or HAA5 formation. The State may also require modifications to 

the monitoring plan. 

3.3.2 Stage 2 DBPR Compliance Monitoring 

Routine Monitoring 

The Stage 2 DBPR routine monitoring requirements are shown in Exhibit 3.3. Systems 

must comply with Stage 2 DBPR monitoring requirements by the deadlines shown in Exhibit 3.2 

according to their Stage 2 DBPR monitoring plan. Consecutive and wholesale systems must 

determine their compliance schedules based on the population of the largest system in the 

combined distribution system. 

Modified Monitoring for Combined Distribution Systems 

In addition to modifying monitoring under 40 CFR 141.29 on a case-by-case basis with 

EPA concurrence each time (see Section 2.3), the State is allowed to modify the Stage 2 DBPR 

monitoring requirements of wholesale and consecutive systems on a case-by-case basis (40 CFR 

142.16(m)) without EPA concurrence each time. These modifications would allow the State to 

account for complex combined distribution systems, such as the following cases (USEPA, 

2007b): 

•	 Neighboring systems that buy and sell to each other regularly throughout the year; 

•	 Situations where water passes through multiple consecutive systems before it reaches the 

user; and 

•	 A large group of interconnected systems. 

The modified monitoring program must not undermine public health protection (USEPA, 

2007b). The State may reduce the number of monitoring sites required for individual wholesale 

and consecutive systems if the reduced number adequately represents DBP levels throughout the 

individual system’s distribution system. The combined distribution system must have at least the 

minimum number of Stage 2 DBPR monitoring sites and monitoring frequency shown in Exhibit 

3.3 based on the source water type and total population of the combined distribution system. In 

addition, each consecutive or wholesale system must have at least one compliance monitoring 

location. 

Systems should note that regulatory requirements present the minimum acceptable 

monitoring program. Monitoring above and beyond regulatory requirements is advised if the 

system has adequate resources. The additional monitoring data can help the system to be 

Consecutive Systems Guidance Manual 3-5 March 2010 
proactive in identifying areas of the distribution system with potentially high DBP levels, and to 

optimize operating practices to minimize DBP levels. 

There is a primacy requirement for States to decide how they will handle monitoring in 

consecutive systems. States can satisfy this special primacy condition regarding consecutive 

system monitoring by including a copy of the procedure they will use for addressing consecutive 

systems outside the provisions of 40 CFR 141.29, as provided for in 40 CFR 142.16(m). 

Alternatively, States can simply attest that they will not address consecutive system monitoring 

outside of 40 CFR 141.29 (including EPA concurrence). 

Consecutive systems are responsible for ensuring that required monitoring is completed 

and the system is in compliance. Each consecutive system must base compliance on samples 

collected within its distribution system. The consecutive system may conduct the monitoring 

itself or arrange for the monitoring to be done by the wholesale system or another outside party. 

Whatever approach it chooses, the consecutive system must document its monitoring strategy as 

part of its DBP monitoring plan. 

Exhibit 3.3 Stage 2 (subpart V) Routine Monitoring Requirements 

Source 

Water Type 

Population Size 

Category 

Monitoring 

Frequency 1 

Number of Distribution System 

Monitoring Sites 

subpart H 

< 500 per year 2 2 

500 - 3,300 per quarter 2 2 

3,301 - 9,999 per quarter 2 

10,000 - 49,999 per quarter 4 

50,000 - 249,999 per quarter 8 

250,000 - 999,999 per quarter 12 

1,000,000 - 4,999,999 per quarter 16 

> 5,000,000 per quarter 20 

Ground 

Water 

< 500 per year 2 2 

500 - 9,999 per year 2 

10,000 - 99,999 per quarter 4 

100,000 - 499,999 per quarter 6 

> 500,000 per quarter 8 

Source: 40 CFR 40 CFR 141.621 (a) 

1

 All systems must take at least one dual sample set during the month of highest DBP concentrations. Systems on 

quarterly monitoring (except for subpart H systems serving 500-3,300 people) must take dual sample sets every 90 

days. 

2

 A system is required to take individual TTHM and HAA5 samples (instead of a dual sample set) at the locations with 

the highest TTHM and HAA5 concentrations, respectively. Only one location with a dual sample set per monitoring 

period is needed if highest TTHM and HAA5 concentrations occur at the same location. 

Consecutive Systems Guidance Manual 3-6 March 2010 
Reduced Monitoring 

Systems may reduce the number or frequency of samples taken if all of the following 

occur: 

•	 The LRAA is less than or equal to 0.040 mg/L for TTHM and 0.030 mg/L for HAA5 

at each monitoring location. 

•	 Only data collected under the Stage 2 DBPR (or under Stage 1 DBPR if you monitor 

at the same locations for Stage 2) may be used to qualify for reduced monitoring. 

•	 The source water annual average total organic carbon (TOC) level, before any 

treatment, is less than or equal to 4.0 mg/L at each treatment plant treating surface 

water or GWUDI based on monitoring conducted under the Stage 1 DBPR. 

Consecutive systems should contact the wholesaler system to see if data are available. 

See 40 CFR 141.623 for specific reduced monitoring provisions for different categories 

of systems. 

Systems that were on reduced TTHM and HAA5 monitoring under the Stage 1 DBPR 

may remain on reduced monitoring under the Stage 2 DBPR if all of the above criteria are met 

and the system qualified for 40/30 certification or received a VSS waiver. 

Systems may remain on reduced monitoring for as long as the following occur: 

•	 For systems on quarterly monitoring: the LRAA is less than or equal to 0.040 mg/L 

for TTHM and 0.030 mg/L for HAA5 at each monitoring location 

•	 For systems on annual or less frequent monitoring: each TTHM sample is less than 

or equal to 0.060 mg/L and each HAA5 sample is less than or equal to 0.045 mg/L. 

•	 For systems using surface water or GWUDI: the source water annual average TOC 

level, before any treatment, is less than or equal to 4.0 mg/L at each treatment plant 

treating surface water or GWUDI based on monitoring conducted under the Stage 1 

DBPR. 

However, States may require systems to return to routine monitoring at their discretion. 

For example, if a system makes significant changes to its treatment or distribution system, or if a 

system changes monitoring locations, the State may require the system to return to routine 

monitoring. 

Increased Monitoring 

Systems that are required to monitor at a particular location yearly or less frequently 

under routine or reduced monitoring must begin increased monitoring at all locations if a TTHM 

sample is greater than 0.080 mg/L or an HAA5 sample is greater than 0.060 mg/L at any 

location. Increased monitoring consists of dual sample sets once per quarter at each monitoring 

location. The system may return to routine monitoring after it conducts increased monitoring for 

at least four consecutive quarters and the LRAA for every monitoring location is less than or 

Consecutive Systems Guidance Manual 3-7 March 2010 
equal to 0.060 mg/L for TTHM and 0.045 mg/L for HAA5. Systems that were on increased 

monitoring under the Stage 1 DBPR must remain on increased monitoring under the Stage 2 

DBPR until the criteria for returning to routine monitoring are met. 

3.3.3 Reporting and Recordkeeping Requirements 

Systems must report the results of Stage 2 (subpart V) TTHM and HAA5 monitoring to 

the State within 10 days of the end of any quarter in which monitoring is required. Systems 

conducting quarterly monitoring must calculate the LRAAs for TTHM and HAA5 by averaging 

the data from the most recent four quarters of monitoring. For systems that conduct monitoring 

yearly or less frequently, each sample is considered the LRAA for that monitoring location. 

However, if any single sample has a TTHM or HAA5 concentration greater than the MCL, the 

system does not incur a violation immediately. Instead, the system must begin increased 

monitoring. 

Systems that are seeking to remain on reduced monitoring must also submit the results of 

source water TOC monitoring for each surface water or GWUDI source. Note that source water 

samples must be taken prior to treatment and would probably have to be taken by the wholesaler. 

Systems must retain all monitoring results for ten years. 

3.4 Disinfectant Residual Monitoring 

Consecutive systems that do not add a chemical disinfectant to the water may not have 

previously monitored to determine compliance with the MRDLs for chlorine and chloramines. 

The Stage 2 DBPR (40 CFR 141.624) now specifically requires consecutive systems that deliver 

water that has been treated with a disinfectant other than UV light to comply with the following 

requirements for chlorine and chloramines: 

•	 Analytical requirements in 40 CFR 141.131(c). This section lists approved methods 

for chlorine and chloramine residual monitoring. The rule allows systems to use N, 

N-diethyl-p-phenylenediamine (DPD) kits, among other methods, for measuring these 

residuals. Only a party approved by EPA or the State may measure the residual 

disinfectant concentration for compliance. 

•	 Monitoring requirements in 40 CFR 141.132(c)(1). Systems must measure the 

residual disinfectant concentration at the same time and location as total coliforms are 

sampled. Reduced monitoring of disinfectant residuals is not allowed. 

•	 Compliance requirements in 40 CFR 141.133(c)(1). Systems must determine MRDL 

compliance using a running annual average (RAA), computed quarterly, of monthly 

averages of residual disinfectant samples collected for compliance. If the RAA 

exceeds the MRDL, the system is in violation of the MRDL and must report to the 

State and notify the public. Systems that switch between chlorine and chloramines 

must calculate compliance using results of both chlorine and chloramine residual 

monitoring together. The MRDL for chlorine is 4.0 mg/L and the MRDL for 

chloramines is 4.0 mg/L (40 CFR 141.65). 

Consecutive Systems Guidance Manual 3-8 March 2010 
 

•	 Reporting requirements in 40 CFR 141.134(c). Systems must report the results of 

chlorine and chloramine monitoring to the State by the tenth day of the month 

following the end of each quarter. Systems must report the number of samples taken 

during each month of the last quarter, the monthly average for samples taken in each 

of the last twelve months, the average of all monthly averages for the last twelve 

months, and whether the MRDL was exceeded. The State may instead choose to 

perform the calculations and determine compliance for the system. 

Systems must comply with these requirements beginning April 1, 2009, unless required 

to do so earlier by the State. Also, the state may modify monitoring provisions under 40 CFR 

141.29 (with EPA concurrence). 

For more information on Stage 1 DBPR requirements, refer to: 

•	 The Stage 1 Disinfectants and Disinfection Byproducts Rule: What Does it Mean to 

you? (USEPA, 2001) 

•	 Alternative Disinfectants and Oxidants Guidance Manual (USEPA, 1999a) 

3.5 Operational Evaluations 

The Stage 2 Microbial-Disinfection Byproducts (M-DBP) Agreement in Principle 

acknowledges that DBP peaks will sometimes occur, even when systems are in full compliance 

with the enforceable MCL. The operational evaluation requirements of the Stage 2 DBPR help 

systems to identify and reduce these peaks. The rule establishes operational evaluation levels of 

0.080 mg/L for TTHM and 0.060 mg/L for HAA5. A system exceeds the operational evaluation 

level at any monitoring location where one of the following occurs: 

•	 The two previous quarters’ TTHM results plus twice the current quarter’s TTHM 

result, divided by four, exceeds 0.080 mg/L, or 

•	 The two previous quarters’ HAA5 results plus twice the current quarter’s HAA5 

result, divided by four, exceeds 0.060 mg/L. 

A system that exceeds the operational evaluation level must conduct an operational 

evaluation and submit a written report of the evaluation to the State no later than 90 days after 

being notified of the analytical result that caused it to exceed the operational evaluation level. 

The operational evaluation must include an examination of system treatment and distribution 

operational practices. However, the system may request that the State allow it to limit the scope 

of the operational evaluation if it is able to identify the cause of the operational evaluation level 

exceedance to the State’s satisfaction. The operational evaluation must also include steps that 

could be considered to minimize the possibility of future operational evaluation level 

exceedances. Also, see Chapter 6 (section 6.2) for additional information about consecutive 

system operational evaluations and the possible need for the coordination with the wholesale 

system. 

An operational evaluation level exceedance is not a violation of the Stage 2 DBPR. 

However, failure to conduct an operational evaluation and submit the report to the State in the 

Consecutive Systems Guidance Manual 3-9 March 2010 
required time frame is a violation and requires Tier 3 public notice (as required by the Public 

Notification Rule). 

For more information on operational evaluations refer to EPA’s Stage 2 DBPR 

Operational Evaluation Guidance Manual (USEPA, 2008). 

3.6 Simultaneous Compliance 

Systems may encounter compliance issues with the Long Term 2 Enhanced Surface 

Water Treatment Rule (LT2ESWTR) when making changes to comply with the Stage 2 DBPR, 

and vice versa. In addition to the challenges of complying with the suite of M-DBP rules 

simultaneously, water system operators must also ensure that changes in treatment do not 

adversely affect compliance with other drinking water regulations, such as the Lead and Copper 

Rule (LCR) and Total Coliform Rule (TCR). Guidance on how to address these potential 

conflicts can be found in EPA’s Simultaneous Compliance Guidance Manual (USEPA, 2007a). 

Consecutive Systems Guidance Manual 3-10 March 2010 
 

4.0 Compliance Options for Consecutive Systems 

Consecutive systems purchase finished water from wholesale systems and may have 

limited control over the quality of water entering the distribution system. Many purchasing 

agreements specify the quantity of water available to a consecutive system from a wholesale 

system, but may not include specific water quality requirements. When water quality is 

included, purchasing agreements may stipulate only that water quality at the consecutive system 

entry point will meet all State and Federal regulations. However, because DBP concentrations 

can increase, sometimes significantly, from the consecutive system entry point through the 

distribution system, consecutive systems may at times have difficulty meeting the Stage 2 DBPR 

MCLs for TTHM and HAA5. As a result, there will be instances in which it is necessary for 

consecutive systems to implement treatment and/or operational changes to comply with the Stage 

2 DBPR. 

This chapter discusses the treatment and operational alternatives most likely to be 

available to consecutive systems to control DBP levels in treated water and comply with Stage 2 

DBPR. This chapter includes the following sections: 

4.1 DBP Control in Consecutive Systems 

4.2 Water Age Management 

4.3 Reduction of Disinfectant Demand 

4.4 Chloramination 

In addition, Chapters 5 and 6 provide information on approaches that may also help in 

maintaining compliance, either by themselves or as part of a plan that includes multiple 

approaches. 

4.1 DBP Control in Consecutive Systems 

Depending on the wholesale system-consecutive system physical arrangement and 

hydraulic characteristics, DBP concentrations may be higher in the consecutive system than in 

the wholesale system. This is particularly true when consecutive systems receive water through 

a distribution grid rather than dedicated transmission mains. In such cases, the water entering the 

purchasing system may already be several days old. Increased water age generally results in 

increased distribution system DBP concentrations. Under the Stage 2 DBPR, wholesale systems 

are not required to make treatment or operational modifications necessary to reduce DBP 

concentrations in their consecutive systems as long as the wholesale system meets the MCLs 

within its own distribution system. In such cases it may be necessary for the consecutive system 

to implement treatment or operational changes to reduce distribution system DBP concentrations 

and comply with the Stage 2 DBPR. 

Consecutive Systems Guidance Manual 4-1 March 2010 
The treatment or operational changes considered and ultimately implemented by a 

consecutive system to reduce DBP concentrations depend on the factor(s) causing the high DBP 

levels. The factors that most significantly impact DBP formation are: 

•	 Disinfectant type and dose. The type and dose of a disinfectant has a significant 

impact on DBP formation. Chlorine is the most common primary disinfectant used in 

water treatment, but it reacts with natural organic matter (NOM) to form chlorinated 

DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs). Some of the 

alternative primary disinfectants to chlorine are chlorine dioxide, ozone, and UV 

light. While these alternative disinfectants can help to reduce levels of regulated and 

unregulated chlorinated DBPs, they form other types of byproducts. Secondary 

disinfectants used to maintain a residual in the distribution system include chlorine 

and chloramines. 

•	 Inorganic DBP precursor concentrations. Bromide reacts with chlorine to form 

hypobromous acid, which is more aggressive in forming DBPs than chlorine 

(hypochlorous acid). Bromide cannot be cost-effectively removed at this time. 

•	 Organic DBP precursor concentration. NOM reacts with disinfectants to form DBPs. 

Treatment processes that may help to reduce levels of organic DBP precursors 

include enhanced coagulation, powdered activated carbon (PAC), granular activated 

carbon (GAC), ozone and biological filtration, and nanofiltration. 

•	 pH. DBP formation is affected by the pH of the water. Chlorination at higher pH 

forms a higher amount of THMs, while the opposite is true for HAAs. Water at a 

higher pH may also require a higher chlorine dose to maintain a consistent level of 

microbial inactivation before entering the distribution system to comply with the 

Surface Water Treatment Rule (SWTR). However, changes to pH to control DBPs 

should be carefully considered to prevent a decrease in corrosion control 

effectiveness in the distribution system and to avoid possible lead and copper 

corrosion problems. 

•	 Temperature. Seasonal variations in water temperature during treatment and in the 

distribution system can have an effect on the reaction rate. Higher temperatures 

increase reaction rates between DBP precursors and disinfectants to produce higher 

levels of DBPs. 

•	 Water age. The contact time between disinfectants and DBP precursors has a 

significant effect on DBP formation. As the reaction time with the disinfectant 

increases, so does DBP formation. However, biodegradation may actually reduce 

HAA5 levels if adequate disinfectant residuals are not maintained. 

These factors are discussed in greater detail in the Stage 2 DBPR Initial Distribution 

System Evaluation (IDSE) Guidance Manual (USEPA, 2006), Operational Evaluation Guidance 

Manual (USEPA, 2008), and Stage 2 M-DBP Simultaneous Compliance Guidance Manual 

(USEPA, 2007). 

Among the major factors identified above, the removal of DBP precursors and pH 

adjustment are typically achieved at the treatment plant of the wholesale system. Controlling the 

Consecutive Systems Guidance Manual 4-2	 March 2010 
 

water temperature is not a practical option for DBP control. Accordingly, the Stage 2 DBPR 

identifies two BATs for consecutive systems to reduce DBP formation: 

•	 For systems serving fewer than 10,000 people: hydraulic flow and storage 

management to control and reduce water age. 

•	 For systems serving at least 10,000 people: chloramination with hydraulic flow and 

storage management. 

These options are discussed further in sections 4.2 and 4.3. 

Consecutive systems should consult their purchasing agreement with their wholesaler 

before making modifications to reduce distribution system DBP concentrations. Purchasing 

agreements may prevent the consecutive system from adding treatment chemicals or making 

other system modifications. If so, the consecutive system may need to renegotiate its purchasing 

agreement to add ammonia to convert free chlorine to chloramines. Purchasing agreements may 

also assign responsibility for such modifications to the wholesaler. 

4.2 Water Age Management 

Water age is a significant factor in DBP formation. As water travels through the 

distribution system, chlorine continues to react with NOM to form DBPs. The longer the travel 

time or water age, the more likely it is that water quality will degrade and exhibit higher TTHM 

and HAA5 concentrations, reduced levels of residual chlorine, reduced effectiveness of chlorine 

residual through formation of organochlorine compounds, increased microbial activity, 

nitrification, and/or taste and odor problems. Where high water age is considered to be a 

contributing factor to elevated DBP concentrations, consecutive systems might consider adoption 

of operational practices to reduce water age in finished water storage facilities and distribution 

system piping. 

Some of the methods to reduce water age by hydraulic flow and storage management 

include: 

•	 Pipe looping, 

•	 Managing valves, 

•	 Bypassing oversized pipes, 

•	 Installing dedicated transmission main, 

•	 Improving tank mixing and turnover, and 

•	 Eliminating excess storage and tanks in series. 

These methods to reduce water age are discussed below. Additional information about 

reducing water age in a distribution system can be found in the Operational Evaluation 

Guidance Manual (USEPA, 2008). 

Consecutive Systems Guidance Manual 4-3	 March 2010 
4.2.1 Pipe Looping 

The highest DBP concentrations in a distribution system are most often observed at deadends (although this may not be true for HAAs because of biodegradation). Water at dead-ends is 

often stagnant and therefore provides long contact times for DBP formation. Excessive 

hydraulic residence time at dead ends can be reduced with pipe looping, which involves 

constructing new pipe sections to make appropriate hydraulic connections among existing pipes. 

Pipe looping may not always eliminate water age problems. For example, if two distribution 

pipes with low demand are looped together and there is insufficient demand to cause water to 

circulate, then an even larger hydraulic dead-end may result. This may create an even larger area 

in the system that is subject to water quality problems resulting from high water age, such as 

high DBP concentrations. Therefore, the specific hydraulic response of a system to looping 

should be assessed to make sure that looping does not negatively impact the residence time of 

other parts of the system. Further information on pipe looping can be found in the book 

Comprehensive Water Distribution Systems Analysis Handbook published by AWWA (Boulos et 

al., 2006). 

4.2.2 Managing Valves 

Intentional or unintentional closed valves in a distribution system may create stagnant 

water leading to high DBP levels in those locations. The presence of unintentional closed valves 

could be due to some valves being inadvertently turned in the wrong direction or being broken. 

These valves may remain undetected due to poor record keeping or because the valve boxes are 

buried or paved-over. A comprehensive valve inventory and maintenance program can help 

systems locate valves, determine their status, and find improperly positioned and broken valves. 

4.2.3 Bypassing Oversized Pipes 

In portions of a distribution system where pipes are oversized, the water velocity is lower 

and therefore hydraulic residence times are longer than necessary, causing high DBP levels. 

Areas of a distribution system that have been abandoned or have experienced negative demand 

growth over many years may contain oversized pipes, causing excessive hydraulic residence 

time. Where appropriate, the pipe sizes in these areas can be reduced or sections of pipes can be 

valved off if they are no longer needed to reduce the residence time of water. However, the 

effect of bypassing or valving oversized pipes on downstream areas should be evaluated to make 

sure that such modifications will not cause hydraulic constrictions for the downstream areas. 

4.2.4 Installing Dedicated Transmission Main 

When water travels through low demand areas and finished water storage facilities in a 

distribution system before reaching a consecutive system, the water at the entry point to the 

consecutive system may have high DBP levels due to high water age. In such cases, the 

installation of a dedicated transmission main to supply water to the consecutive system can be 

Consecutive Systems Guidance Manual 4-4 March 2010
 

 

 

considered to reduce water age but its effects on water age in the wholesale system should be 

estimated. 

4.2.5 Improving Tank Mixing and Turnover 

Excessive hydraulic residence time in distribution storage tanks results in high water age, 

which can cause high DBP levels in the tank and at downstream locations in the distribution 

system. The average hydraulic residence time in a tank can be estimated by the following 

equation: 

Theoretical average hydraulic residence time = [Vmax/(Vmax - Vmin)]/N 

where Vmin = average minimum daily volume 

Vmax = average maximum daily volume 

N = number of drain/fill cycles per day 

(Units for Vmax and Vmin must be consistent) 

It is important to recognize that the above equation provides information about the 

average amount of time spent by water inside a tank. In poorly mixed storage tanks, water age 

may actually be much higher (or lower) than the average hydraulic residence time in some 

portions of the tank. The Vmax and Vmin values are numbers that are averaged from data collected 

over several days or weeks to represent the typical operational characteristics of the tank. If tank 

operations are changed from one season to another, then the Vmax and Vmin values may be 

different during different seasons. Typically, the average hydraulic residence time for a storage 

tank should not exceed 5 days (Kirmeyer et al., 1999). However, some systems may need much 

lower hydraulic residence times due to site-specific water quality constraints. 

The average hydraulic residence time in a storage tank can be reduced by increasing the 

volume turnover. The volume turnover can be increased by increasing the volume of water that 

flows in and out of a tank during a given fill/drain cycle (the drawdown), or by increasing the 

number of fill/drain cycles per day. When possible, the recommended approach is to increase 

the drawdown between fill cycles. Increasing the number of fill/drain cycles is only effective 

when 1) the tank is well-mixed at the end of each fill cycle and 2) the drawdown between each 

fill/drain cycle is equal to the original drawdown. Increasing turnover by either of these 

strategies may be limited by system hydraulic (pressure) constraints. It may be necessary to 

adjust tank water level controls or the control settings for altitude valves to increase turnover. 

 Improving storage tank mixing characteristics can reduce average water age and 

minimize stagnant zones in the tank. These stagnant zones often have higher water age and thus 

tend to have higher DBP concentrations. Several tools can be employed to predict water mixing 

characteristics of a tank: 

• Desktop evaluations of hydraulic residence time, fill time, and inlet momentum. 

• Computational fluid dynamic (CFD) modeling. 

• Temperature measurements. 

Consecutive Systems Guidance Manual 4-5	 March 2010 
 

• Disinfectant residual measurements. 

The mixing predictions from desktop evaluations, CFD modeling, temperature 

measurements, and disinfectant residual measurements can be used to identify a storage tank 

with inadequate mixing and, therefore, a potential for high DBP formation in some regions in the 

tank. A method to estimate hydraulic residence time in a tank was presented previously in this 

section. Fill time and inlet momentum can be estimated from operational records and 

supervisory control and data acquisition (SCADA) data. Generally, longer fill times and greater 

inlet momentum result in better tank mixing. The minimum acceptable hydraulic residence time 

and inlet momentum is tank- and situation- specific, and depends on a number of system factors, 

including water quality, tank geometry, inflow rate, and inlet/outlet pipe configuration. 

CFD modeling provides a qualitative description of mixing characteristics by providing 

visual images of mixing inside a tank. It can be used to determine the effects of fill time and 

inlet momentum on mixing characteristics. 

Poor mixing conditions can cause thermal stratification in a tank. Thermal stratification 

in turn can exacerbate the poor mixing condition. Depending on the location and orientation of 

the inlet pipe and tank geometry, the water entering a tank from buried pipes may be cooler than 

the bulk water in the tank during the summer or warmer than the bulk water in the tank during 

the winter. In a tank with poor mixing characteristics, colder, denser water remains in the lower 

portion of the tank, whereas the warmer, less dense water has a tendency to rise to the top of the 

tank. Water temperature profiles can be used to determine the existence of thermal stratification 

inside a tank. The temperature profiles can be obtained from the collection of continuous water 

temperature measurements at various locations in the tank over the course of several days. 

Temperature differences as low as 1°C between the top and bottom of a tank may indicate a 

thermally stratified tank with poor mixing. 

Exhibit 4.1 shows cross-section views of water mixing characteristics observed in a 

standpipe tank under slightly different temperature conditions. In this test, a solution containing 

a one milligram per liter concentration of dye was added to water flowing into the tank. The dye 

concentrations in the tank were then monitored for a one-hour period. The left-hand profile 

shows the tank with a bulk water temperature 1o C warmer than the temperature of incoming 

water. Note that the incoming, colder water remains in the lower portion of the tank. This water 

will be the first to exit as demand draws water from the tank. The right-hand profile shows 

much improved mixing when the inflow water and the tank water were at the same temperature. 

Consecutive Systems Guidance Manual 4-6 March 2010 
Exhibit 4.1 Effect of Temperature Differential Between Inflow and Tank Bulk 

Water on Mixing Characteristics 

(3D) ⏐ 30 Nov 2000 ⏐HydroTank default ctl fil (3D) ⏐ 27 Sep 2000 ⏐HydroTank default ctl fil 

36” vertical inlet 

1 mg/L tracer after 60 mins 

140 140 

120 120 

100 100 

Conc 

36 inch inlet 0.8 Conc 80 80 2000 gpm inflow 0.6 0.8

60 mins run time 0.4 0.6 Tank temp 1 C > Inflow temp 60 0.36 inch inlet 2 0.4 60 2000 gpm inflow 0.1 Y Z Y Z 

0.2 60 mins run time
 Isothermal condition 0.01 0.1 

40 40 0.01

20 20 

0 0 

-20 

-25 -20 025 -20 0 20 -25 025 -20 0 20 

X 

Tank temp 1 C > Inlet Temp X

Isothermal condition (20 C) 

Source: Mahmood et al., 2005 

Disinfectant residual measurements, collected either as grab samples or from continuous 

online monitoring at various locations in the tank, can also be used to evaluate mixing and 

identify water quality stratification. Residual levels in thermally stratified portions of the tank 

representing older water will be less than residual levels in well mixed portions of the tank. In 

one study, researchers observed an average difference of 0.4 mg/L between the chlorine residual 

at the bottom of a standpipe compared to the top of the same standpipe based on samples 

collected at different residence times (Mahmood et al., 2005). Authors note that differences in 

chlorine residuals were consistent with differences in temperature (i.e., higher temperature 

tracked with the lower residual readings). 

 Additional information about the use of desktop evaluations, CFD modeling, temperature 

measurements, and disinfectant residual measurements to evaluate water mixing characteristics 

in storage tanks, and operational and/or physical modifications to improve mixing characteristics 

is presented in Water Quality Modeling of Distribution System Storage Facilities (Grayman et 

al., 2000) and Evaluation of Water Mixing Characteristics in Distribution System Storage Tanks

(Mahmood et al., 2005). 

 Once the water mixing characteristics of a storage tank have been evaluated, appropriate 

operational and/or physical modifications can then be recommended to improve water mixing in 

the tank. The mixing characteristics can be improved by operational changes, which include 

filling a tank for a longer time period and increasing inlet momentum. If operational changes are 

not possible, then the mixing characteristics can also be improved by design modifications, such 

as changing the location, orientation, and/or diameter of inlet/outlet pipes. 

 Inlet momentum (defined as velocity × flow rate) is a key factor for mixing water in a 

storage tank. As the inlet momentum increases, the mixing characteristics in the tank improve. 

The inlet momentum can be increased by increasing the flow rate (which also has the desirable 

Consecutive Systems Guidance Manual 4-7 March 2010
hit

r 

th

tal

re 

in 

ge

in 

he

ua

 be

in 

e 

r 

l 

effect of increasing the velocity) through installation of booster pumps near the tank, or other 

means. However, increasing the flow rate may not be practical due to the limitations of system 

hydraulics. For example, distribution system pressure may not be adequate to achieve desirable 

increases in flow rates, or a pump may not be available at the tank location to increase the 

pumping rate into the tanks. In such cases, the inlet velocity can be increased by reducing the 

inlet diameter. 

The location and orientation of the inlet pipe relative to the tank walls can have a 

significant impact on mixing characteristics. The optimum inlet pipe location and orientation to 

obtain good mixing in a tank depends on a number of site-specific factors including tank 

geometry, inflow rate, and temperature differences between the inflow and the bulk water in the 

tank. As water enters a tank through an inlet pipe, a jet is formed and the water present in the 

tank is drawn into the jet. This forms circulation patterns that result in mixing. The path of the 

jet must be long enough to allow the mixing process to develop, and therefore should not be 

pointed directly towards nearby impediments such as a wall or deflector. For example, in a tall, 

narrow tank, a horizontal inlet pipe at the bottom of the tank is likely to cause the water jet to 

the vertical wall of the tank, resulting in loss of inlet momentum and poor mixing near the top

portion of the tank. In general, outlet pipes are located near the bottom of tank, and relocating

the inlet pipe near the top of tank may improve mixing characteristics. However, the system 

hydraulics should be evaluated to ensure there would be adequate pressure to allow the tank to

fill to the desired level. Inlet pipes located near the bottom of a tank can be angled upwards, o

multiple inlet pipes can be used to improve mixing conditions in a tank. Exhibit 4.2 shows 

predicted mixing characteristics in tanks with two different inlet pipe orientations based upon 

results of CFD modeling. The left-hand profile shows limited mixing in a tank with a horizon

inlet. The right-hand profile shows much improved mixing in a tank with a vertical inlet. 

In water treatment plant basins, where contact time is required for disinfection and the

is generally simultaneous inflow and outflow, internal baffles are sometimes placed inside the

basins to encourage plug flow conditions. Since, chlorine contact time is usually not an issue 

distribution system tanks and reservoirs, baffles should generally be avoided. Baffles encoura

plug flow conditions and can result in poor mixing zones (dead zones) and greater variability 

DBP levels since dead zones within baffled tanks can have higher water age and therefore hig

DBP concentrations. Baffled tanks are likely to experience more significant disinfectant resid

decay than tanks with mixed flow conditions. There may be special circumstances, such as 

separate inlet and outlet pipes in close proximity to each other, under which a baffle wall may

desirable to force water into other parts of the tank. However, because of the wide variations 

tank geometry and inlet/outlet piping configurations for storage tanks, the use of baffles should 

be carefully evaluated for each specific situation to determine if baffles have any beneficial 

impact. Tracer testing, CFD modeling, and disinfectant residual monitoring are useful tools to 

determine the effects of baffles, and to optimize the location, and orientation of the inlet/outlet 

pipes. 

Consecutive Systems Guidance Manual 4-8 March 2010 
Exhibit 4.2 Effect of Inlet Pipe Orientation on Mixing Characteristics 

(3D) ⏐ 19 Jul 2000 ⏐HydroTank default ctl fil 

(3(3DD) ) ⏐⏐ 0303JJuunn2 20

(3D) ⏐ 19 Jul 2000 ⏐HydroTankdefault ctl fil 

1mg/Ltracerafter30 mins 

140 

1mg/Ltracerafter30mins Isothermal condition (20 C) 

1 mg/Ltracer after 30 mins 

140 

120 

120 

100 

Conc 

0.8 

0.6 

0.4 

80 

100 

80 

Conc 

0.8 

0.6 

0.4 

0.2 0.2 60 Y Z Y Z 

60 0.1 0.1 

0.01 0.01 40 

40 

20 

20 

0 

0 

-25 025 -20 0 20 40 

-20 

X -20 0 20 -25 025 

36” horizontal inlet X 

36” vertical inlet 

Source: Mahmood et al., 2005 

4.2.6 Eliminating Excess Storage and Tanks in Series 

Historically, distribution system storage tanks have generally been built to provide 

adequate pressures, fire flows, and to meet peak demands. Tanks are also often designed to 

accommodate future growth and long-term water system needs. Therefore, some distribution 

system storage tanks may be oversized. Storage tanks may also be hydraulically isolated from 

the distribution system due to high system pressures, low system demands, or inadequate tank 

height. Oversized tanks and/or tanks that are hydraulically locked out (due to system pressure 

being higher than the maximum water level in the tank most of the time) may not have adequate 

volume turnover, resulting in high water age and high DBP formation potential. When events 

such as main breaks, fire flows, or other unexpected peak demand conditions occur in a system, 

water from these tanks may be drawn into the distribution system. Areas receiving water from 

these tanks may have higher than normal DBP levels. 

 There are limited options to improve mixing characteristics and reduce water age for a 

tank that is oversized or hydraulically isolated under normal system operating conditions. It may 

be possible to increase volume turnover in a tank that is hydraulically isolated if the operational 

hydraulic grade in the vicinity of that tank can be lowered. This may be accomplished by 

valving off pipe sections during certain hours so that water demand in the vicinity of the tank is 

supplied primarily by the tank rather than from other parts of the distribution system. More 

water can be forced in and out of an oversized tank on a daily basis by installing pumps, 

adjusting pumping schedules (if pumps already exist), or adjusting the control settings for 

altitude valves. However these modifications may not be feasible due to system hydraulic 

Consecutive Systems Guidance Manual 4-9 March 2010
 

limitations. In such cases, decommissioning of the tank can be considered. If a consecutive 

system has such a tank, and the wholesale system has another tank in the vicinity with adequate 

storage, then the consecutive system may be able to decommission its tank. However, 

coordination with the wholesale system is necessary to ensure that when the consecutive 

system’s tank is decommissioned, the wholesale system’s tank has adequate hydraulic capacity 

(both storage and piping) for equalization storage, fire flow, or emergency conditions such as 

main breaks. Refer to Chapter 6 for additional information about communicating with the 

wholesale system. 

Tanks in series can also lead to high DBP levels in areas downstream of the tanks if there 

is inadequate mixing and volume turnover in the tanks. If the mixing and volume turnover issues 

cannot be addressed, consideration should be given to whether water can be re-routed to the 

distribution system pipe network directly rather than through other tank(s). Re-routing the water 

flow involves adjusting valve positions in the pipe network and pumping set points and 

schedules. A system operational analysis (generally using a hydraulic model) will allow the 

system to determine the pressure and flow impacts caused by re-routing the water flow. Since 

elimination of tanks in series may reduce the volume turnover in these tanks due to associated 

changes in frequency and magnitude of the drain/fill cycles, the system should evaluate these 

impacts. 

4.3 Reduction of Disinfectant Demand 

Aging pipes such as unlined cast iron pipes exert high disinfectant demand because of the 

presence of corrosion byproducts, biofilms, and sediment deposits. Consecutive systems can 

reduce localized chlorine decay and thus reduce the overall disinfectant demand by replacing or 

cleaning and lining pipes, and/or by conducting periodic flushing. Consecutive systems may see 

improved results if they coordinate their efforts with their wholesale systems. See Chapter 6 for 

more information. 

4.3.1 Replacing or Cleaning and Lining Unlined Cast Iron Pipes 

Pipe replacement may be the preferred option for reducing disinfectant demand if a 

pipeline has structural problems or if there is a need to increase hydraulic capacity with a larger 

diameter pipe. If a pipeline is structurally sound, then pipe cleaning is a less expensive option. 

For unlined cast iron pipes, pipe lining may also be necessary to achieve a permanent 

improvement and prevent a recurrence of the disinfectant demand problem. The AWWA 

Standard, Rehabilitation of Water Mains (M28), 2nd Ed. (AWWA, 2001), provides information 

and guidance on cleaning and lining technologies. 

4.3.2 Distribution System Flushing 

Periodic flushing can be an effective tool to control TTHM and HAA5 peaks to remove 

pipe sediments and biofilms, thereby reducing disinfectant demand. There are several 

approaches to conduct distribution system flushing depending on system configuration and water 

quality goals. The AwwARF report, Guidance Manual for Maintaining Distribution System 

Water Quality (Kirmeyer et al., 2000) provides detailed information on various flushing 

Consecutive Systems Guidance Manual 4-10 March 2010 
approaches. Regardless of the flushing method implemented, utilities should use water quality 

data to identify periods when DBPs have historically been high. However, utilities cannot 

simply flush in the area where DBP samples are collected prior to sampling dates for the 

purposes of reducing DBP compliance monitoring results. This practice is not allowed because 

such intermittent flushing is not considered normal operation. 

Conventional flushing is considered routine distribution system maintenance and is 

conducted by opening hydrants without directing the flow through the distribution system with 

isolation valves. Fire hydrants are usually opened and allowed to run until the water clears. 

While utilities often move through the system sequentially when practicing conventional 

flushing, this should not be confused with directional flushing. The velocities used for 

conventional flushing may be inadequate (less than 5 feet/second) for removing sediment, 

corrosion byproducts, and other debris that can contribute to high DBP levels. It is also possible 

to draw poor quality water from other areas into the areas being flushed. Additional information 

on flushing practices and selection of flushing velocities can be found in the AwwaRF report, 

Establishing Site-Specific Flushing Velocities (Friedman et al., 2003). 

Directional flushing involves the flushing of water in one direction through systematic 

operation of distribution system valves. Utilities practicing directional flushing typically begin 

at a source of high quality water (e.g., a large transmission main) and systematically move 

through the system opening hydrants and manipulating system valves to assure water moves in 

only one direction through the system. Because water travels toward a hydrant in a single 

direction, higher flushing velocities can be achieved. A properly designed and implemented 

directional flushing program can achieve water velocities higher than 5 feet/second to scour the 

pipe. In addition to increasing water flow in the selected main, directional flushing can reduce 

the impact of other factors contributing to the formation of high DBP concentrations including 

the accumulation of sediments and the build-up of corrosion byproducts. (Joseph and Pimblett, 

2000) 

“Blow-offs” can be used to eliminate dead-ends and stagnant water zones that have high 

water age and therefore contribute to high DBP levels. Blow-offs can operate in an automatic 

intermittent mode or continuous mode to remove old water from dead-end or stagnant zones and 

pull fresher water into these locations from other areas. The velocities for a blow-off are 

generally insufficient (< 2.5 feet/second) to remove sediments or biofilm. Blow-offs can be used 

on a seasonal basis when DBP peaks are more likely to occur, such as during high water 

temperature periods. The need for and appropriate locations for blow-offs can be determined 

from distribution system flow models or distribution system historical records. Low disinfectant 

residuals, high DBP concentrations, high heterotrophic plate counts (HPCs), coliform-positive 

samples, or nuisance bacteria are often associated with high water age locations. 

Whenever flushing is used, it may be necessary to dechlorinate or dechloraminate 

flushing water to prevent adverse impacts on nearby streams. Both chlorine and chloramines can 

have negative impacts on aquatic environments. Depending on where flushed water is 

discharged, it may end up in nearby streams or other bodies of water. In such cases, a 

dechlorinating agent (e.g., sodium bisulfite or sodium thiosulfate) can be used to prevent fish 

kills or other adverse effects. Consult your State or local regulatory agency to determine if it is 

necessary to dechlorinate or dechloraminate flushing discharges. Also consider discharging the 

flushed water to the sewer system. 

Consecutive Systems Guidance Manual 4-11 March 2010 
4.4 Chloramination 

As identified in Section 4.1, the disinfectant type can be a significant factor in DBP 

formation. Where the use of free chlorine is considered to be a contributing factor to elevated 

DBP concentrations, consecutive systems might consider switching to chloramines for secondary 

disinfection. THM and HAA formation is generally significantly lower for chloramines than for 

free chlorine. However, consecutive systems should consider the following issues before 

switching from free chlorine to chloramines: 

•	 Water quality issues for chloramines such as the formation of other currently 

unregulated DBPs, nitrification, corrosion, and taste and odor issues. 

•	 Whether to switch all or only a portion of the distribution system to chloramines. 

•	 Cost, handling, and safety issues. 

These issues are discussed further in the following sections. Additional information on 

chloramination can be found in EPA’s Simultaneous Compliance Guidance Manual for the Long 

Term 2 and Stage 2 DBP Rules (USEPA, 2007a) 

4.4.1 Water Quality Issues for Chloramines 

Chloramines are an effective secondary disinfectant because they are generally less 

reactive than free chlorine causing them to be more persistent in the distribution system, and they 

are able to better penetrate biofilms than chlorine. This greater persistence allows some utilities 

(e.g., large systems in warm water climates) otherwise unable to maintain a disinfectant residual 

using free chlorine to maintain a residual in the distribution system. In addition, the 

concentrations of TTHM and HAA5 usually decrease when switching from free chlorine to 

chloramines. Chloramines can react with organic precursor material to form THMs, but the 

reaction rates are very slow compared to free chlorine. Chloramines are highly effective at 

reducing THM formation levels in the distribution system and the reduction in THM levels is 

generally 40 to 80 percent compared to free chlorine. Chloramines also produce lower levels of 

HAAs than free chlorine, but may not be effective in controlling all types of HAAs. Some 

brominated HAAs are formed with chloramines. Chloramines generally produce lower levels of 

total chlorinated byproducts than free chlorine. 

Potential operational and simultaneous compliance issues when using chloramines 

(which may be greater in a complex combined distribution system) include the following: 

•	 Nitrification, 

•	 Increased corrosion and metal release if corrosion control is not evaluated and 

modified as necessary, 

•	 Taste and odor issues, 

•	 Weaker disinfectant, 

Consecutive Systems Guidance Manual 4-12 March 2010 
•	 Blending issues – chloraminated and chlorinated waters, 

•	 Issues with ozonation and GAC filtration, and 

•	 Issues for dialysis patients, fish owners and industrial customers. 

The reader is referred to EPA’s Simultaneous Compliance Guidance Manual for the Long 

Term 2 and Stage 2 DBP Rules (USEPA, 2007a) for more detailed information on these issues. 

4.4.2 Options for Chloramine Conversion 

When the wholesaler uses free chlorine for secondary disinfection and the consecutive 

system switches to chloramines for secondary disinfection of the water it provides, the 

consecutive system has two options for managing its water with disinfectants: 

•	 Option 1: Convert part of the consecutive system’s distribution system to chloramine 

and physically separate that area from the wholesaler’s and other areas of the 

consecutive system’s distribution systems. 

•	 Option 2: Convert the consecutive system’s entire distribution system to chloramine 

and physically separate the system from the wholesaler’s system. 

Option 1 

The first option may be considered if the consecutive system only needs to reduce high 

DBP levels in specific areas. Depending on the hydraulic characteristics of the distribution 

system, it may be feasible to isolate the chlorinated water from the chloraminated water in the 

same way that different pressure zones are isolated. The separation of the waters in the 

distribution system can be an inexpensive solution if it only involves closing a few existing 

valves or if it requires the installation of only a few new valves. If the chloraminated portion of 

the distribution system is connected to the chlorinated portion of the system with only a few 

major pipes, rather than a maze of small mains, then the physical separation of the waters may be 

an attractive solution. 

Caution should be exercised when considering conversion of only a portion of the system 

to chloramines. The physical separation of areas of the distribution system may reduce the 

reliability of the water supply to some service areas. The separation could lead to reduced 

fire-flow capacity and reduced pressure in some areas. The dynamics of water flow may also 

change to prevent adequate turnover in storage tanks. Flow reversal might also occur and could 

lead to water quality problems. 

Option 2 

The second option is more appropriate if the consecutive system desires reduction of 

DBP levels throughout its distribution system. Depending on the wholesale system-consecutive 

system interconnections, converting the entire distribution system to chloramines might 

minimize the hydraulic separation issues. It may also prevent potential water quality problems 

that would have resulted had the chlorinated and chloraminated water blended in the consecutive 

Consecutive Systems Guidance Manual 4-13 March 2010 
 

distribution system due to valve failure between pressure zones. Conversion of the entire 

distribution system from free chlorine to chloramines will require larger or additional ammonia 

and chlorine storage and feed systems. The ammonia feed system would have to be installed at 

the point-of-entry to the consecutive system such that the chlorine is converted to chloramines 

prior to entering the distribution system. Systems should consider installing backflow prevention 

devices or other control features at the interconnections between the wholesaler and consecutive 

systems to ensure that chloraminated water from the consecutive system does not backflow into 

the wholesaler’s system and mix with the wholesaler’s chlorinated water. Finally, systems must 

account for and address simultaneous compliance issues. 

Prior to conversion of all or a portion of the consecutive system to chloramines, the 

consecutive system should contact the State to determine what additional permitting, operational, 

or other requirements apply. Many States require review and approval of treatment changes 

through their permitting process. While many consecutive systems may not employ certified 

water treatment plant operators, the addition of chemical feed facilities may constitute treatment 

and the State may require the system to employ full- or part-time certified water treatment plant 

operators. 

4.4.3 Cost, Handling, and Safety Issues 

Conversion of chlorinated water to chloraminated water requires the addition of 

ammonia. Ammonia can be added in the form of anhydrous ammonia, aqueous ammonia, or 

ammonium sulfate. Each system should determine the most appropriate type of chemical to use 

by evaluating factors such as chemical cost, safety, storage requirements, and ease of handling. 

Ammonia costs in the United States vary considerably. Anhydrous ammonia is generally the 

least expensive option, followed by aqueous ammonia, and then ammonium sulfate. 

Considerations related to the use of these chemicals are discussed in Optimizing Chloramine 

Treatment, First and Second Editions (Kirmeyer et al., 1993 and 2004). 

The chemical feed systems for chlorine and ammonia must be capable of injecting the 

prescribed chemical doses into the water. Accurate feed control is necessary to ensure that a 

consistent desired chlorine to ammonia ratio (generally in the range of 4.5:1 to 5:1) is 

maintained. Immediate adjustments to chlorine or ammonia feed rates are necessary in response 

to changes in flow rates or other variables. These adjustments can be made automatically with 

feedback systems such as flow pacing or compound loop control. In a flow pacing system, the 

dose depends on the flow rate, which can be measured by a flow meter. This type of feed control 

can work if the chlorine residual entering the consecutive system is consistent. When both the 

flow rate and the chlorine residual vary, a compound loop control system is used to adjust the 

chemical doses based on the flow rate and the chlorine residual. In this case, a flow meter 

measures the flow rate and a chlorine analyzer measures the chlorine residual, and both signals 

are sent to a controller. The controller integrates the two signals and sends a signal to adjust the 

chemical doses. Many variations of the compound loop control system are available 

commercially. 

Consecutive Systems Guidance Manual 4-14 March 2010 
4.4.4 Public Education 

Before converting from free chlorine to chloramines as the secondary disinfectant, 

customer concerns should be addressed through public education and notification. Customer 

concerns generally fall into one of two categories: 

•	 Human health concerns. Chloramines are toxic when not removed prior to using 

water in the kidney dialysis process. Each hospital and dialysis treatment center 

should be advised before a conversion is made so they can provide adequate testing 

and treatment. 

•	 Miscellaneous household concerns. Chloramines (and chlorine) are generally toxic to 

fish, so homeowners, pet stores, and related businesses should be contacted. 

Each PWS should prepare a public education plan prior to a conversion to chloramines. 

Public education information, including examples of public education materials, can be obtained 

from A Guide for the Implementation and Use of Chloramines (Harms and Owen, 2004). PWSs 

may also want to add relevant language to their CCRs to keep customers advised of the presence 

of chloramines in their drinking water. Also, EPA has information about chloramine use on its 

website at www.epa.gov/safewater. 

Consecutive Systems Guidance Manual 4-15 March 2010 
 

 

5.0 Other Alternatives for Consecutive Systems 

Treatment and operational options for consecutive systems to reduce DBP levels are 

presented in Chapter 4. This chapter presents some of the other alternatives available for 

consecutive systems to reduce distribution system DBPs and achieve compliance with the 

requirements of the Stage 2 DBPR. The alternatives discussed in this chapter are (1) improving 

water quality from a wholesale system by methods such as treatment changes, reducing hydraulic 

residence time, and booster disinfection; and (2) finding alternative sources of water with higher 

quality and blending with wholesaler’s water either at the treatment plant or in the distribution 

system. This chapter is divided as follows: 

5.1 Improved Water Quality from the Wholesale System 

5.2 Alternative Sources and Blending Strategies 

5.1 Improved Water Quality from the Wholesale System 

The finished water leaving a wholesale system’s treatment plant can spend a considerable 

amount of time in the distribution system pipes before reaching a consecutive system. High 

hydraulic residence time combined with a sufficient disinfectant dose to maintain adequate 

disinfectant residual throughout the distribution systems can lead to high DBP formation in the 

consecutive system. For a consecutive system that uses free chlorine for secondary disinfection, 

the increase in DBP concentrations in the distribution system may be significant. If a 

consecutive system is unable to effectively reduce DBPs in its system because of the levels in the 

purchased water, the consecutive system should consider discussing control strategies with the 

wholesale system. Refer to Chapter 6 for additional information about communicating with the 

wholesale system. 

 Some DBP control strategies that a wholesale system can implement include: 

•	 Achieving better DBP precursor removal at the treatment plant by optimizing 

coagulation and/or clarification processes, or by adding a new treatment step such as 

GAC filtration or nanofiltration. 

•	 Moving the point of primary disinfectant addition downstream after removal of more 

DBP precursors. 

•	 Using an alternative primary disinfectant (e.g., ozone, chlorine dioxide) and/or 

secondary disinfectant. 

•	 Reducing disinfectant demand. 

•	 Reducing disinfectant dose. 

•	 Reducing the hydraulic residence time between the wholesale system’s treatment 

plant and the consecutive system. 

Consecutive Systems Guidance Manual 5-1	 March 2010 
 

 

 

Chapter 4 discusses options to reduce water age in greater detail. More information on 

these DBP control strategies can also be found in the following sources: 

•	 Stage 2 DBPR Operational Evaluation Guidance Manual (USEPA, 2008) 

•	 Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual 

(USEPA, 1999b) 

•	 Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2 DBP 

Rules (USEPA, 2007a) 

If it is not feasible for the wholesale system to implement some of the DBP control 

strategies identified above, then the use of booster disinfection systems can help reduce DBP 

levels. Booster disinfection systems could be installed in areas within the wholesale or 

consecutive system where it is difficult to maintain disinfectant residuals, thereby allowing the 

wholesale system to reduce the disinfectant residual leaving the treatment plant. Optimizing the 

location and operation of booster disinfection facilities in the distribution system is important to 

obtain desired results. The results from hydraulic models, disinfectant residual data, disinfectant 

decay data, and other water quality data are used to determine appropriate booster disinfection 

locations. 

The advantages of using booster disinfection facilities include: 

•	 Increasing the disinfectant residual only in areas that require it without increasing the 

disinfectant residual in other parts of the system beyond acceptable levels. 

•	 Maintaining a more consistent disinfectant residual throughout the distribution 

system. 

•	 Reducing the disinfectant dose and DBP formation at the treatment plant and prior to 

the point of booster disinfectant addition. 

The disadvantages of using booster disinfection facilities include: 

•	 Difficulty in controlling the required disinfectant dose at multiple booster stations due 

to the dynamic nature of chlorine demand in the system. 

•	 Regulatory concern with the degradation byproducts if hypochlorite is used or safety 

issues if chlorine gas is used. 

•	 Booster operation in chloraminated distribution systems can be challenging. 

For a chlorinated system, the primary controlling factor for chlorine dose is the difference 

between the measured and desired free chlorine residual. For the chlorine and ammonia dose in 

a chloraminated system, there are additional controlling factors besides the difference between 

the measured and desired total chlorine residual, such as excess free ammonia in the system due 

to chloramine decay. It is important to note that while booster disinfection can lead to lower 

DBP concentrations entering the consecutive system, it may do little to reduce DBP 

Consecutive Systems Guidance Manual 5-2	 March 2010 
 

concentrations at the extremities of the distribution system, particularly where water age is 

excessive. 

5.2 Alternative Sources and Blending Strategies 

A consecutive system may consider the use of an alternative water source with higher 

quality for reducing high DBP levels in the system. If high DBP levels in a consecutive system 

are due to the wholesaler’s use of a surface water supply, then the consecutive system can 

consider using a new groundwater source or increase the use of an existing groundwater source 

(if available) to supplement the surface water supply from the wholesaler. Groundwater tends to 

have lower TOC concentrations than surface water and is also less subject to rapid fluctuations in 

TOC levels that may occur with surface water during periods of heavy runoff. Lower TOC 

levels can significantly reduce DBP formation at the treatment plant, and for systems that use 

free chlorine for secondary disinfection, the DBP reduction may also be significant in the 

distribution system. During the summer, groundwater has lower temperatures than surface 

water. If a disinfectant is added at the treatment plant shortly after groundwater is withdrawn 

from the ground, then lower temperatures can reduce DBP formation at the treatment plant. 

Increasing groundwater use or finding new groundwater sources may be difficult because 

excessive groundwater withdrawal can reduce the groundwater table below desirable levels. 

This may result in degraded groundwater quality and may affect stream flow levels. Sustainable 

use of groundwater as an alternative source requires careful planning to allow adequate time for 

groundwater recharge. 

Another option for a consecutive system to reduce high DBP levels is to obtain an 

alternative water source by purchasing water from another adjacent utility if the utility can offer 

higher quality water. This option may be economically feasible if the water supply from the 

other utility is in close proximity to the consecutive system. Generally, when the availability of 

higher quality water is limited, the consecutive system may deliver the higher quality water only 

to parts of the distribution system that have high DBP levels. Interconnections between the two 

systems, and new pipelines, valves, and pumps may be required to deliver the higher quality 

water to the desired areas. 

When two or more alternative water sources are mixed, the final characteristics of the 

blended water depends on the water quality characteristics of the individual sources and the 

blending ratios. For DBP control, the primary water quality characteristics of concern are the 

types and concentrations of disinfectants and DBP precursor concentrations (such as TOC) 

present in each source. In many cases, blending may minimize the formation of high DBP 

levels, but other water quality problems may actually increase. Therefore, other water quality 

characteristics such as corrosion potential, pH, taste, loss of disinfectant residual, and hardness 

also need to be considered. Examples of water quality problems due to improper blending ratios 

of alternative sources include: 

• Loss of disinfectant residual when blending chlorinated and chloraminated water; 

• Increases in taste and odor; 

Consecutive Systems Guidance Manual 5-3 March 2010
 

•	 Increased corrosivity or increased calcium carbonate precipitation due to changes in 

pH, alkalinity, and hardness; 

•	 Iron and manganese precipitation due to water in a reduced state (groundwater) 

mixing with water in a higher oxidized state (surface water); and 

•	 Continual changes in chemical reactions between pipe walls and blended water due to 

intermittent flow reversals when the mixing zone of alternative water sources moves 

in relation to variable water demands in the system. 

Systems considering blending or making changes to their blending ratios should consider 

first performing a blending analysis to determine the effects of blending the different water 

sources. Blending analyses can be performed with hydraulic models, water quality models, or 

bench scale tests. Hydraulic modeling can be used to predict the areas of the system primarily 

supplied by each source and the areas where mixing of two or more sources takes place. Mixing 

zones and the relative contribution of each source at a given location can be predicted. The 

changes in the locations of mixing zones due to varying water demands can also be predicted. 

Water quality modeling can be used to predict water age, disinfectant residual, and DBP levels. 

Even if changes in water quality can be predicted from water quality models and spreadsheets, 

water quality monitoring is necessary to verify the effects of blending. 

It is generally easier to blend alternative sources before they enter the distribution system, 

especially if the blended water can be treated to the desired quality. However, if a wholesale 

system’s treatment plant is far from the alternative water source, and the high DBP areas of a 

consecutive system are in close proximity to the alternative source, then it may be more feasible 

to introduce the alternative source to the affected part of the system directly through 

interconnections. 

 

If water quality problems arise when water is blended in the distribution system, systems 

may consider physical or hydraulic separation of the different waters in the distribution system 

using valves and additional piping. The physical separation of portions of a distribution system 

may reduce water supply reliability, fire-flow capacity, and pressure in some areas. Detailed 

distribution system studies are helpful to determine the impacts of physical separation. 

Consecutive Systems Guidance Manual 5-4	 March 2010 
6.0 Communication Strategies for Consecutive and Wholesale Systems 

Consecutive systems and wholesale/consecutive system interactions and contractual 

relationships can be complex. To improve compliance with the requirements of the Stage 2 

DBPR, consecutive systems can utilize effective communication strategies with the wholesale 

system. It is important to establish a communication process for the consecutive systems to be 

aware of water quality and operational issues in the wholesale systems. Communication 

approaches could include: 

• Dedicated phone lines with afterhours forwarding or recorded message capacity; 

• Web-based information pages and message posting; 

• Pager and cell phone message transmission; 

• E-mail notification; and 

• Laboratory notification to both the consecutive and wholesale system. 

For information on communication strategies for IDSEs, refer to Appendix A of the Stage 2 

DBPR Initial Distribution System Evaluation Guidance Manual (USEPA, 2006). 

This chapter is organized as follows: 

6.1 Communication Strategies for Stage 2 DBPR Compliance Monitoring 

6.2 Communication Strategies for Operational Evaluations 

6.3 Agreements Between Consecutive and Wholesale Systems 

6.1 Communication Strategies for Stage 2 DBPR Compliance Monitoring 

This section provides possible communication strategies for consecutive and wholesale 

systems related to Stage 2 DBPR compliance monitoring. Stage 2 DBPR compliance monitoring 

requirements for consecutive systems vary by source water type and system size. Chapter 3 

discusses Stage 2 DBPR compliance monitoring requirements in greater detail. 

Before beginning Stage 2 DBPR compliance monitoring, each system must prepare a 

subpart V monitoring plan. Consecutive and wholesale systems should work together to 

coordinate their Stage 2 DBPR compliance monitoring schedules and should provide copies of 

their final subpart V monitoring plans to one another. It is not necessary for each consecutive 

system in a combined distribution system to provide copies of their monitoring plans to each 

other, but each consecutive system should provide a copy to the wholesale system, and each 

consecutive system should request a copy of the wholesale system’s monitoring plan. Where a 

consecutive system receives water through another consecutive system, the second consecutive 

system should request a copy of both the first consecutive system’s and the wholesale system’s 

monitoring plan. 

Consecutive Systems Guidance Manual 6-1 March 2010 
Exhibit 6.1 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - 

Consecutive System Receiving Water Directly from Wholesale System 

Wholesale System Consecutive System
 

Monitoring Date Monitoring Date
 

WTP Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 

Typical Consecutive System
 

Water Age
 

Note: WTP = water treatment plant. 

Although not required by the Stage 2 DBPR, coordination of compliance monitoring will 

allow both the wholesale and consecutive system to better understand DBP formation across the 

combined distribution system and help to formulate an appropriate compliance strategy, when 

necessary. Similarly, coordinating sampling schedules will better enable wholesale and 

consecutive systems to identify changes in source, treatment, or operation that impact DBP 

formation in the distribution system. More specifically, coordination of Stage 2 DBPR 

compliance monitoring schedules will help consecutive and wholesale systems conduct 

operational evaluations, when required. Recommended communication strategies for operational 

evaluations are discussed in greater detail in Section 6.2. 

To coordinate Stage 2 DBPR compliance monitoring for the wholesale and consecutive 

systems, their sampling schedules should account for the approximate system water age. For 

example, if it takes three or four days for water to pass through the consecutive system, the 

consecutive system might consider sampling three or four days after the wholesale system. 

When one consecutive system receives water through another consecutive system, the second 

system should account for the approximate water age in the first system when scheduling 

monitoring. Exhibits 6.1 and 6.2 show these concepts graphically. Exhibit 6.3 shows an 

example where a consecutive system receives water from a wholesale system transmission main 

with a known approximate water age. If approximate water ages at individual sample locations 

are known more precisely, the consecutive system may schedule monitoring at those locations 

based on individual location water ages. An example of this approach is provided in Exhibit 6.4. 

Again, the Stage 2 DBPR does not require wholesale and consecutive systems to coordinate 

monitoring schedules, and it does not require that monitoring schedules account for water age 

differences between wholesale and consecutive systems. In fact, in complex distribution systems 

and systems with limited understanding of hydraulic patterns and water age, such an approach 

can be difficult to implement. Also, this monitoring approach presented in Exhibit 6.4 may 

result in higher sampling costs since the consecutive system would be sampling on multiple 

days. 

Consecutive Systems Guidance Manual 6-2 March 2010 
Exhibit 6.2 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - 

Consecutive System Receiving Water Through Another Consecutive System 

Wholesale System Consecutive System 1 Consecutive System 2 

Monitoring Date Monitoring Date Monitoring Date 

WTP Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8

Typical Consecutive Typical Consecutive 

System 1 Water Age System 2 Water Age 

Note: WTP = water treatment plant. 

Exhibit 6.3 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - 

Consecutive System Receiving Water from Wholesale System with No Customers 

Consecutive System 

Monitoring Date 

WTP Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 

Typical Consecutive Typical Water Age in Wholesale System Water Age System Transmission Main 

Note: WTP = water treatment plant. 

Consecutive Systems Guidance Manual 6-3 March 2010
 

Exhibit 6.4 Coordinating Stage 2 DBPR Compliance Monitoring Schedules - 

Approximate Water Age of Monitoring Locations is Known 

Note: WTP = water treatment plant. 

As part of a general communications strategy to address operational, infrastructure, and 

water quality issues, consecutive and wholesale systems should share compliance monitoring 

data with each other as results are gathered. This will help all parties understand their status 

relative to Stage 2 DBPR compliance and, hopefully, prevent future surprises in the form of 

elevated DBP concentrations or LRAAs near the MCLs. Consecutive systems are also 

encouraged to ask the wholesale system to notify them in the event of source, treatment, or 

operational upsets that might impact DBP formation. Similarly, consecutive systems should 

notify the wholesale system immediately if they encounter unusual water quality data (e.g., 

changes in chlorine residual or DBP concentrations). 

6.2 Communication Strategies for Operational Evaluations 

This section discusses how communication between consecutive and wholesale systems 

can be enhanced to either prevent or, when necessary, conduct an operational evaluation. As 

described in Chapter 3, consecutive systems and wholesale systems are required to conduct an 

operational evaluation for their individual system when a routine DBP sample result, if repeated, 

would result in an exceedance of either the TTHM or HAA5 operational evaluation level (OEL). 

For example, consider the TTHM concentrations for the past three quarters at one of a 

utility’s Stage 2 DBPR monitoring locations were 0.065, 0.07, and 0.095 mg/L. The 0.095 mg/L 

concentration would trigger an operational evaluation, since a repeat value of 0.095 mg/L, 

Consecutive Systems Guidance Manual 6-4 March 2010 
resulting in values of 0.065, 0.07, 0.095 and 0.095 mg/L (operational evaluation value = 0.081 

mg/L), would result in an exceedance of the TTHM OEL at this location. The Stage 2 DBPR 

Operational Evaluation Guidance Manual (USEPA, 2008) provides much greater detail 

regarding identification of an operational evaluation level exceedance and conducting an 

operational evaluation. 

For consecutive systems, conducting an operational evaluation requires communication 

with the wholesale provider. Where water is received through another consecutive system, 

communication between consecutive systems may also be necessary. The wholesale system is 

most likely to have data regarding source and finished water TOC, disinfectant residual, pH, 

temperature, and other water quality parameters that impact distribution system DBP 

concentrations. Further, a comparison of wholesale and consecutive system DBP concentrations 

may help to identify the cause of the operational evaluation level exceedance. For example, if 

finished water quality was normal and wholesale system DBP concentrations were in their 

expected range, the cause of the operational evaluation level exceedance might be attributed to 

distribution system operations in the consecutive system (e.g., reduced demand contributing to 

higher water age). 

The need for communication between consecutive and wholesale systems when 

conducting an operational evaluation also underscores the value of coordinating Stage 2 DBPR 

compliance monitoring schedules. While finished water quality (e.g., TOC, temperature, etc.) 

may help to identify the cause of an operational evaluation level exceedance, a comparison of 

consecutive and wholesale system DBP concentrations may also be helpful in terms of how DBP 

levels change as water moves further from the treated water source. 

6.3 Agreements between Consecutive and Wholesale Systems 

Agreements between consecutive and wholesale systems, both formal and informal, can 

significantly improve coordination between consecutive and wholesale systems. These 

agreements establish lines of communication and assign responsibility for water quality in each 

of the systems. Such agreements can help to create cooperative, working relationships where no 

prior relationship exists. Where prior relationships exist, such agreements can clarify or enhance 

existing relationships. In either case, the agreement represents a commitment to protect public 

health by both the consecutive and wholesale system. When developing agreements, discussions 

between wholesale and consecutive systems may include evaluations of storage needs (including 

firefighting) and where that storage is located to ensure operational reliability while controlling 

water age, evaluation of different compliance and operational approaches (including who does 

what and how costs are divided), and other issues of joint interest (such as research or pilot 

studies). As necessary, systems should involve the State. 

Exhibits 6.5 and 6.6 provide case studies of formal and informal agreements, 

respectively. 

Consecutive Systems Guidance Manual 6-5 March 2010
Exhibit 6.5 Case Study of A Formal Agreement between Consecutive and 

Wholesale Systems 

Denver Water Department in Colorado serves more than 1 million customers in the City 

of Denver, Denver County, and surrounding suburban areas. This includes nearly 80 water 

service contracts with consecutive systems. The Denver system is very complex. In some cases, 

water passes from one consecutive system to another. In other cases, water may pass through a 

consecutive system and return to Denver’s distribution system. 

Under the Colorado Department of Public Health and Environment provisions for 

integrated systems, Denver Water has executed formal agreements with each of these 

consecutive systems. Under these agreements, Denver Water assumes responsibility for all 

regulatory compliance monitoring and sample analysis. However, the consecutive system is 

responsible for maintaining compliance with regulatory requirements. These requirements 

dictate that the consecutive systems essentially operate in the same manner as Denver Water, 

including flushing, storage tank cleaning, backflow prevention, and utilization of certified 

operators. 

Sources: Lohman, Steve. (303) 628-6000, Manager of Water Quality at Denver Water 

Department. 2007. Phone conversation with Chris Hill, Associate, Malcolm Pirnie, Inc. (813) 

242-7204. 

Consecutive Systems Guidance Manual 6-6 March 2010 
 

Exhibit 6.6 Case Study of Informal Agreements between Consecutive and 

Wholesale Systems 

The Cobb County-Marietta Water Authority (the Authority) provides water to 13 

consecutive systems in northwestern metropolitan Atlanta, Georgia. These systems include 

municipal and county water systems, as well as one industrial and one institutional customer. Of 

these customers, nine are sole-source customers buying their water only from the Authority. The 

Authority provides water service to its consecutive systems under long-term service contracts up 

to 50 years in length. These contracts stipulate that the Authority will provide the customer with 

water at mutually agreeable locations (connections). The contracts include no mention of water 

quality. 

The Authority has no retail customers of its own, and has no contractual obligation other 

than to "provide water" to its consecutive systems. The contracts also make no mention of sales 

volume. 

The Georgia Environmental Protection Division (EPD) has worked with the Authority 

and its sole source customers to address water quality on a rule-by-rule basis. The Total 

Coliform Rule is addressed by each consecutive system individually. The Lead and Copper Rule 

is administered to the Authority and its sole source customers as a single entity. Under this 

approach, if one system violates an MCL, then every consecutive system must respond as 

directed by EPD. A consecutive system can unilaterally withdraw from this arrangement, but 

must then conduct the monitoring and reporting to EPD individually. The Authority staff meets 

regularly with its consecutive systems to discuss and address water quality and regulatory issues, 

and all parties are involved in a cooperative working relationship. 

For the Stage 1 DBPR, the Authority and its sole-source customers are considered by the 

Georgia EPD as a combined distribution system. EPD worked with the Authority to develop the 

combined system DBP monitoring plan. Under this arrangement, the Authority has 

responsibility for all DBP monitoring in the combined sole-source distribution system. 

In preparation for the IDSE required under the Stage 2 DBPR, the Authority and its 

sole-source customers jointly conducted a fluoride tracer study to determine the areas of oldest 

water in the system. The information gathered under this study was used individually by the 

consecutive systems to develop their IDSE monitoring plans. 

Source: Parsons, James. (770) 426-8788, Director of Engineering, Cobb County-Marietta Water 

Authority. 2005. June 9, 2005. 

Consecutive Systems Guidance Manual 6-7 March 2010 
 

Exhibit 6.5 is an example of how Denver has applied a program developed by the State. 

The Colorado Department of Public Health and Environment (the Department) has established 

requirements for integrated systems - which consider the consecutive and wholesale systems as a 

single regulated entity (5 Colorado Code of Regulations 1003-1). The Department requires that 

the wholesale and consecutive systems included in the integrated system execute a “...contract, 

memorandum of agreement, or other enforceable mechanism.” The application for consideration 

as an integrated system includes the following: 

•	 A contact person, address, and phone number for each participating system, and each 

regulatory requirement for which an integrated system is being created. 

•	 The number of persons served by the wholesale and each consecutive system and 

whether the consecutive system is providing further disinfection. 

•	 A map showing the supply system and each consecutive system including the relevant 

elements of the distribution system such as meters, piping, pump stations, storage 

tanks, and finished water reservoirs. 

•	 A sampling plan for each regulatory provision covered by the integrated system (e.g., 

DBPs or disinfectant residual monitoring). The sampling plan shall meet all of the 

requirements of the respective provision and shall also identify the responsibilities of 

each party, including that each individual system is responsible for maintaining 

compliance with MCLs and other regulatory requirements. 

•	 A copy of each agreement between the consecutive and wholesale systems, including 

a common set of operations and maintenance standards that the wholesale system has 

established for each regulatory requirement for which an integrated system is being 

created. 

•	 A statement that clearly assigns legal responsibility to one of the participating 

systems for compliance with each individual regulatory provision in the integrated 

system. Under Stage 2, each system determines compliance based on samples taken 

in its own distribution system. 

An example of a formal agreement meeting the requirements of the State of Colorado is 

provided in Appendix A. Other States may have specific requirements that must be met in 

preparing these agreements. Water systems should contact their State to determine how specific 

requirements apply to wholesale and consecutive systems. 

Regularly scheduled communication between consecutive and wholesale systems can be 

an effective tool for managing water quality. Regular meetings between a consecutive system 

and its wholesale provider may be an appropriate forum to discuss and address water quality 

concerns with the frequency determined by parties. Where multiple consecutive systems 

purchase water from a wholesale system, meetings that involve all of the consecutive systems in 

the combined distribution system may be useful. Systems that are part of more complex 

combined distribution systems will generally need to make a greater effort to ensure effective 

communication among multiple wholesale and consecutive systems, as will combined 

distribution systems containing non-utility systems such as homeowners associations. 

Consecutive Systems Guidance Manual 6-8	 March 2010 
 

 

 

 

7.0 Developing Consecutive System Compliance Strategies 

The Stage 2 DBPR specifically requires consecutive systems to comply with the same 

MCLs for DBPs as wholesale systems and extends the disinfectant residual and MRDL 

requirements of the Stage 1 DBPR to consecutive systems. Chapter 3 discusses these 

requirements and their impacts on consecutive systems in greater detail. This chapter discusses a 

methodology that can be employed by consecutive systems to develop a compliance strategy to 

meet these requirements. It discusses the use of water quality monitoring data to identify 

potential compliance issues and develop, in concert with the wholesale system, effective 

compliance strategies. This chapter is organized into the following sections: 

7.1 Data Acquisition 

7.2 Communication of Needs to the Wholesale System 

7.1 Data Acquisition 

As part of normal system operations or as required by drinking water regulations, 

consecutive systems should routinely monitor distribution system water quality. Parameters such 

as DBP concentrations (TTHM and HAA5), pH, temperature, disinfectant residual (free chlorine, 

total chlorine, or chloramine),TOC and microbiological parameters (total and fecal coliform, 

HPC), can be used to characterize distribution system water quality and can be extremely useful 

in developing a compliance strategy. A historical record of water quality data combined with 

new data can be particularly useful in isolating and identifying DBP-related issues in the 

distribution system. The remainder of this section discusses: 1) what parameters a consecutive 

system might find useful in developing a compliance strategy; 2) when to monitor; and 3) where 

to monitor. The importance of these routine water quality parameters and their relation to overall 

DBP formation are further discussed below. In addition, systems should consider whether 

changes could lead to simultaneous compliance issues. 

7.1.1 Monitoring Parameters 

TTHM and HAA5 

Non-compliance operational monitoring of TTHM and HAA5 throughout the consecutive 

system after the IDSE may be a useful tool in determining if continuing compliance with the 

Stage 2 DBPR will be a concern. TTHM and HAA5 monitoring also help to determine the 

requirements necessary to achieve and maintain compliance. A comparison of DBP 

concentrations entering the system to concentrations throughout the distribution system will help 

to determine if the DBP concentrations entering the consecutive system are too high to achieve 

compliance with the Stage 2 DBPR, or if the consecutive system is able to employ some strategy 

to achieve compliance. High DBP locations may need further monitoring and evaluation 

because they likely correspond with longer residence time, lower disinfectant residuals, and 

higher bioactivity. Some of the strategies a consecutive system can implement to control DBP 

levels in the distribution system include water age management, using alternative disinfectants 

such as chloramine, managing the chlorine dosages effectively to avoid under- or over-dosing, 

Consecutive Systems Guidance Manual 7-1 March 2010 
 

 

blending with sources that have low DBP precursor levels, and/or purchasing water from a 

different wholesaler. These strategies are discussed in more detail in Chapters 4 and 5. In 

evaluating these strategies, systems should consider simultaneous compliance issues. 

pH and Temperature 

Water quality parameters such as pH and temperature can be used to identify seasonal 

trends and irregularities in distribution system water quality. Seasonal variations in water 

temperature can affect DBP formation in the distribution system. For instance, higher 

temperatures increase the reaction rate of DBP formation. Therefore, warmer water temperatures 

result in higher levels of TTHM and HAA5 unless better removal of precursors is achieved 

during treatment, alternative disinfection is practiced, or other DBP-minimizing strategies are 

implemented. Changes in pH can lead to different DBP levels and mixes and can also affect 

coagulation and disinfection conditions. 

Disinfectant Residual Data 

Disinfectant residual data should be routinely gathered and monitored throughout the 

distribution system. A measurable disinfectant residual should be maintained throughout the 

distribution system, as required by the SWTR, to provide adequate protection against the 

possible entry of pathogens or untreated water, and to maintain the microbial water quality 

achieved by primary disinfection. 

A low disinfectant residual at consecutive system entry points may indicate increased 

water age in the wholesale system. However, accumulation of sediments in a pipe, corrosion 

conditions, biofilm growth, pipe materials, and the pipe lining in either system can also 

contribute to disinfectant demand. Comparing historical data for a particular site may be helpful 

in isolating the contributing factors. Strategies to minimize water age are discussed in greater 

detail in Chapter 4. 

Conversely, excessive disinfectant residual concentrations at the consecutive system 

entry point may also contribute to higher DBP concentrations. In some instances, a high residual 

entering the system may be necessary for the consecutive system to maintain a residual at the 

ends of the system, or may be the result of the wholesale system needing to maintain a residual at 

the end of their own system. Strategies to minimize the disinfectant residual dose, such as 

optimizing the use of enhanced coagulation (to further reduce DBP precursor concentrations and 

disinfectant demand) by the wholesale system at its water treatment plant, moderation of chlorine 

residual levels through strategic placement of booster chlorination stations, chloramination, or 

water age management may help to reduce DBP concentrations in the distribution system. 

Microbial Data 

Microbial data, such as total and fecal coliforms or HPCs, may be useful in identifying 

potential DBP compliance strategies. Low disinfectant residual and increased microbial activity 

are most likely to occur at locations with high water age. In such cases, increased disinfectant 

doses might be considered necessary to maintain the residual and reduce microbiological 

activity. However, increasing the dose may also lead to higher DBP concentrations. 

Consequently, a strategy to reduce water age may be more appropriate to prevent increased 

formation of DBPs. Chapter 4 discusses operational strategies to reduce system water age. 

Consecutive Systems Guidance Manual 7-2 March 2010 
 

 

7.1.2 Monitoring Frequency 

Consecutive systems should consider collecting routine non-compliance samples for the 

various parameters discussed above at a regular frequency to better understand DBP formation in 

the distribution system, in addition to compliance monitoring. To the extent possible, 

consecutive systems may want to coordinate their monitoring schedule with the wholesale 

system to provide the most complete analysis of DBP formation. Coordination of sampling 

schedules allows for more accurate interpretation of data, as it is possible to see the change in 

water as it moves from one system to the next over the same time period. Coordination of 

monitoring with the wholesale system is discussed in greater detail in Chapter 6. 

Collecting samples at regular frequencies helps identify short and long term DBP trends, 

including seasonal impacts of water quality on distribution system DBP concentrations. 

Requirements for many parameters, such as disinfectant residual and DBP concentrations, are 

established by the Stage 2 DBPR. Chapter 3 provides a more thorough discussion of consecutive 

system monitoring requirements. 

7.1.3 Monitoring Locations 

Samples should be collected throughout the consecutive system distribution system, 

taking into account the population served and hydraulic profile. Sample locations should include 

locations such as the master meter connection, middle of the distribution system, and near the 

ends or other areas of the distribution system where the highest water age and DBP levels are 

expected. Monitoring at many of these locations is already required by the Stage 2 DBPR. If 

additional sites could be incorporated for monitoring, sampling locations should be spread 

throughout the distribution system. Samples collected from only one location or region within 

the distribution system may skew the DBP, disinfectant residual, or microbial data. 

Understanding how DBP formation varies across the entire system is critical to developing an 

effective DBP control strategy. Thus, it is important to collect and use data that represent the 

entire distribution system. 

Exhibits 7.1 and 7.2 provide case studies characterizing the differences in wholesale and 

consecutive system DBP formation. These examples show how TTHM, HAA5 and disinfectant 

residual concentrations are impacted by differences in disinfection practices from the wholesale 

system to the consecutive system. 

Consecutive Systems Guidance Manual 7-3 March 2010 
 

System B

System A Distribution

 

 

Exhibit 7.1 DBP Formation from Wholesale to Consecutive System Example 

Note: WTP = water treatment plant; THMs = trihalomethanes; HAAs = haloacetic acids; Cl2 = chlorine. 

System A

WTP

System D System C

25/22/1.0

32/25/0.8

40/30/1.0

55/15/0.3 50/27/0.5

TTHM/HAA5/Cl2 Residuals

System A 

WTP 

System B 

System A Distribution 

System D System C

25/22/1.0 

32/25/0.8 

40/30/1.0 

55/15/0.3 50/27/0.5 

TTHM/HAA5/Cl2 Residuals 

In Exhibit 7.1, System A is a wholesale system that provides drinking water to more than 

100,000 people. Water is treated using an advanced filtration process followed by disinfection 

using chlorine. The finished water then travels through large transmission lines from the water 

treatment plant to the distribution system. Finished water is distributed to three consecutive 

systems. System A supplies water to System B and System C, and System C supplies water to 

System D. 

Exhibit 7.1 illustrates the complex nature of wholesale and consecutive system 

relationships. This figure shows average TTHM and HAA5 concentrations, and chlorine 

residuals in the wholesale and consecutive systems. Only wholesale system A and consecutive 

system B practice booster chlorination to maintain chlorine residuals at acceptable levels. 

Consecutive systems C and D are smaller systems and do not practice booster chlorination. The 

chlorine residual in System A’s distribution system averages about 1.0 mg/L. An equal or lower 

chlorine residual is observed in the consecutive systems. 

The DBP formation as the water travels from the treatment plant to the distribution 

systems is also depicted in Exhibit 7.1. Within System A’s distribution system, a 40 percent 

increase in TTHM and a 25 percent increase in HAA5 occurs because it is a large system with 

booster chlorination systems at various locations. Although consecutive system B receives water 

directly from the same treatment plant and practices booster chlorination, DBP formation is 

lower than that of System A because it is a smaller system with lower overall water age. The 

average TTHM level in consecutive system C is 25 percent higher than System A because of a 

long transmission main between the two cities. Also, the use of booster chlorination by System 

A causes TTHM levels to be fairly high in System C. The increase in TTHM levels from 

consecutive system C to system D is minimal because these are both small systems with low 

Consecutive Systems Guidance Manual 7-4 March 2010 
water age in close proximity to one another. However, the TTHM levels in the consecutive 

systems are still fairly high because of the impact of System A. A small decrease in HAA5 

concentration is noted in the consecutive systems due to biodegradation of some HAA5 species 

in the distribution system. 

 

Exhibit 7.2 Variation in DBP Formation with Chlorination and Chloramination

Note: CS = Consecutive System; TTHM = total trihalomethane; HAA5 = sum of five HAA species; Cl2 = chlorine; 

NH2Cl = chloramines.

 Exhibit 7.2 compares DBP formation in City X (chlorinated system) and City Y 

(chloraminated system) which are both large wholesalers. City X uses free chlorine for 

secondary disinfection. City Y uses chloramine for secondary disinfection and also practices 

booster disinfection. Exhibit 7.2 shows the increase in DBP concentrations from the wholesale 

to the consecutive system. As would be expected, the overall TTHM and HAA5 concentrations 

are significantly higher in City X. However, the percentage increases in TTHM and HAA5 

concentrations are greater in the chloraminated system (City Y) than in the chlorinated system 

(City X). This reflects the fact that while chloramines may result in lower DBP concentrations, 

significant growth can still occur in the wholesale or consecutive system’s distribution system. 

Monitoring can be an effective tool to identify these relationships in your system. It is worth 

noting that these results are site/system-specific and may not be typical of results seen in other 

systems. 

Consecutive Systems Guidance Manual 7-5 March 2010
 

7.2 Communication of Needs to the Wholesale System 

Consecutive systems should meet with the wholesale system to discuss options and 

develop a mutually agreed-upon compliance strategy if possible. In developing the strategy, 

systems should consider a variety of options, including those identified in Chapters 4, 5, and 6. 

The strategy should clearly lay out responsibilities, including how costs will be apportioned. 

Chapter 6 discusses communication strategies and agreements between consecutive and 

wholesale systems in greater detail. 

Consecutive Systems Guidance Manual 7-6 March 2010 
 

8.0 Frequently Asked Questions 

Can I be both a consecutive system and a wholesale system? 

Yes. If you sell water and you purchase water, you are both a wholesale system and a 

consecutive system. 

I buy all of my water. Do I follow the requirements for subpart H systems or ground water 

systems? 

If you purchase all of your water and any of it is surface water or GWUDI, you must follow the 

requirements for subpart H systems. If you purchase all of your water and it is all ground water, 

you should follow the requirements for ground water systems. 

What if my wholesaler only serves groundwater? 

If your system does not have any surface water or GWUDI sources and your wholesaler serves 

only ground water, you should follow the requirements for ground water systems for Stage 2 

compliance. 

What if I purchase water but I also have my own sources? 

If your system purchases water, it is considered a consecutive system even if your system has its 

own sources. Your compliance schedule is based on the population of the largest system in the 

combined distribution system. However, for purposes of the compliance schedule, the State may 

determine that the combined distribution system does not include certain consecutive or 

wholesale systems if water is purchased or sold only on an emergency basis or if only a small 

percentage and small volume of water is purchased or sold by a system. While your compliance 

schedule is based on the population of the largest system, your monitoring requirements are 

based on your own retail population. 

I have my own ground water wells and buy water from a subpart H system. Do I follow the 

requirements for subpart H systems or ground water systems? 

If you purchase any surface water or GWUDI, you must follow the requirements for subpart H 

systems. 

Consecutive Systems Guidance Manual 8-1 March 2010 
 

What if I buy water from more than one wholesale system? 

If you buy water from more than one wholesale system, you are considered to be part of a 

combined distribution system that includes all of your wholesalers, all other systems served by 

your wholesalers, and any systems to which you sell water. If your system is part of a combined 

distribution system, your compliance schedule is based on the population of the largest system in 

the combined distribution system. However, for purposes of the compliance schedule, the State 

may determine that the combined distribution system does not include certain consecutive or 

wholesale systems if water is purchased or sold only on an emergency basis or if only a small 

percentage and small volume of water is purchased or sold by a system. While your compliance 

schedule is based on the population of the largest system, your monitoring requirements are 

based on your own retail population. 

My system has only undisinfected groundwater sources. I only buy disinfected water in July 

and August or when my supplies can’t meet demand. Do I still have to comply with the Stage 

2 DBP Rule? 

Yes, your system is subject to the Stage 2 DBPR, but Stage 2 DBPR monitoring is only required 

during the period when you are buying water. You should contact your State to confirm 

monitoring requirements. 

Why didn’t EPA just use 40 CFR 141.29 for consecutive system monitoring requirements? 

The Stage 2 M-DBP Federal Advisory Committee Agreement in Principle that was signed in 

September 2000 recommended that the monitoring provisions of the Stage 2 DBPR provide 

protection for customers in consecutive systems that is equivalent to that provided in wholesale 

systems. EPA concurred with this recommendation and followed this principle in development 

of the Stage 2 DBPR. 

EPA believes that providing equivalent public health protection in consecutive systems by 

assigning appropriate compliance monitoring locations throughout the combined distribution 

system requires case-by-case modification of appropriate monitoring. These modifications 

should be based on factors such as the amount and percentage of finished water provided; 

whether finished water is provided seasonally, intermittently, or full-time; and improved DBP 

occurrence information. In order to provide systems and States with improved DBP occurrence 

information, the Stage 2 DBPR requires consecutive systems to address IDSE requirements. 

Since the IDSE provides improved DBP occurrence information, States may consider 

modifications to Stage 2 compliance monitoring requirements for consecutive systems on a caseby-case basis as allowed by 40 CFR 141.29 or under the special primacy condition at 40 CFR 

142.16(m) by taking all these factors into consideration. Note that 40 CFR 141.29 requires caseby-case approval by EPA, but the Stage 2 rule has a special primacy condition that does not 

require case-by-case approval by EPA. In making these case-by-case determinations, the State 

can use its system-specific knowledge, along with the IDSE results, to develop an appropriate 

monitoring plan for each system within the combined distribution system. 

Consecutive Systems Guidance Manual 8-2 March 2010 
 

What are the minimum monitoring requirements for combined distribution systems if the 

State modifies monitoring? 

For combined distribution systems for which the State modifies monitoring requirements, the 

minimum number of Stage 2 DBPR monitoring sites and monitoring frequency is based on the 

total population of the combined distribution system. In addition, each consecutive and 

wholesale system must have at least one compliance monitoring location. Also, each wholesale 

or consecutive system must conduct its own IDSE. The schedule for your IDSE was based on 

the population of the largest system in the combined distribution system. The rest of your IDSE 

requirements were based on your individual system’s population. You cannot conduct one IDSE 

for the entire combined distribution system based on the combined service population. However, 

an IDSE coordinated among systems in a combined distribution system, with each system 

monitoring based on its retail population and submitting its own IDSE report, may result in 

improved information (but requires a high level of coordination). 

Why can’t my consecutive system forego DBP monitoring and base my compliance status on 

my wholesaler’s compliance status? 

Your consecutive system may not base your compliance status on your wholesaler’s compliance 

status because DBPs will continue to form in your consecutive system and may be significantly 

higher than in your wholesaler’s system. Therefore, DBP levels in your consecutive system may 

exceed the MCL even though your wholesaler is in compliance. Conversely, your DBP levels 

may be lower than the wholesale system’s DBP levels and you should not be in violation if the 

wholesale system exceeds the MCL. EPA believes that distribution systems and DBP formation 

are too complex to base compliance determinations on another system’s compliance monitoring 

results. 

Do I have to monitor at the same time as my wholesale system? 

You are not required to monitor at the same time as your wholesaler. However, you may wish to 

coordinate your monitoring schedule with your wholesaler to better understand DBP formation 

in your combined distribution system. See Chapter 6 of this guidance manual for details. 

If my wholesaler has a TTHM or HAA5 violation, is my consecutive system in violation? 

Your consecutive system is only in violation if TTHM or HAA5 levels in your distribution 

system exceed the MCL. However, your State may require additional follow-up monitoring or 

public notification if your wholesaler has a TTHM or HAA5 violation. If you receive water 

from the area of your wholesaler’s system where the TTHM or HAA5 violation occurred, you 

may also detect TTHM or HAA5 levels above the MCL in your consecutive system. 

Consecutive Systems Guidance Manual 8-3 March 2010 
 

If the lab with whom I have a contract does not collect DBP samples, am I in violation? What 

if my contract is with my wholesale system? 

Even if you have a contract with your laboratory or your wholesale system, you retain 

responsibility for the collection of DBP samples. If your laboratory or wholesale system fails to 

collect your DBP samples, your system incurs a monitoring violation. 

Can I use my wholesale system’s system-specific study or DBP data instead of monitoring my 

own system? 

Each wholesale and consecutive system must conduct its own IDSE. The schedule for your 

IDSE must be based on the population of the largest system in the combined distribution system. 

The rest of your IDSE requirements must be based on your individual system’s population. You 

cannot conduct one IDSE for the entire combined distribution system based on the combined 

service population. However, an IDSE coordinated among systems in a combined distribution 

system, with each system monitoring based on its retail population and submitting its own IDSE 

report, may result in improved information (but requires a high level of coordination). The 

individual IDSE reports may include analyses supporting a broader understanding of combined 

distribution system hydraulics, DBP formation, etc. that leads to recommendations for more 

effective compliance monitoring. 

What if my wholesaler will not conduct the monitoring in my consecutive system? 

As a public water system, you are responsible for ensuring that your monitoring is conducted. If 

your wholesaler does not conduct monitoring in your consecutive system and you do not have a 

contract with a laboratory to conduct monitoring in your system, you are responsible for 

collecting all of your compliance samples in your system, ensuring that the samples are analyzed 

in a certified laboratory, and reporting results to the State. 

How do consecutive systems qualify for reduced monitoring? 

There are no differences in how consecutive and non-consecutive systems qualify for reduced 

monitoring. Consecutive systems qualify for reduced monitoring if the LRAA is less than or 

equal to 0.040 mg/L for TTHM and less than or equal to 0.030 mg/L for HAA5 at all compliance 

monitoring locations. In addition, before any treatment, the source water average annual TOC 

level must be less than or equal to 4.0 mg/L at each treatment plant treating surface water or 

GWUDI, based on monitoring conducted under the Stage 1 DBPR. Consecutive systems will 

need to obtain source water TOC monitoring results from all surface water and GWUDI sources 

used by their wholesaler(s) in addition to their own sources to qualify. In addition, the State may 

modify monitoring requirements using either 40 CFR 141.29 or the special primacy condition in 

40 CFR 142.16(m). 

Consecutive Systems Guidance Manual 8-4 March 2010 
 

How is compliance determined for a consecutive system? 

A consecutive system’s compliance is based on the LRAA calculated using the sample results 

collected only in that system’s distribution system. However, the State may require the 

consecutive system to give public notice if the wholesaler has a violation, even if the consecutive 

system does not incur a violation. 

If my consecutive system is in danger of exceeding the TTHM or HAA5 MCLs, who is 

responsible for making changes to ensure compliance with the MCLs? 

Even though some agreements between wholesale and consecutive systems may indicate that the 

wholesale system is responsible for making changes, you are ultimately responsible for 

providing water that meets the MCLs within your consecutive system. You should consider 

discussing treatment changes with your wholesaler to reduce DBP levels prior to your entry 

point. See Chapter 5 for more information. However, if your wholesaler is in compliance with 

the MCLs, your wholesaler is not required by the Stage 2 DBPR to make any treatment changes 

to meet the MCLs in your consecutive system. Therefore, you should also consider changes to 

your distribution system to reduce DBP levels. See Chapter 4 for more information. If you are 

still unable to meet the MCLs, you should consider an alternate source of water or blending 

sources. See Chapter 5 for more information. 

What if my wholesaler will not be making treatment changes to meet the Stage 2 DBPR? 

If your system is in danger of exceeding the MCLs for TTHM or HAA5 and your wholesaler 

will not be making treatment changes to meet the Stage 2 DBPR, you should consider making 

distribution system changes to reduce DBP levels. Refer to Chapter 4 for more information. If 

you are still unable to meet the MCLs, you should consider alternate sources of water or 

blending sources. See Chapter 5 for more information. 

Consecutive Systems Guidance Manual 8-5 March 2010 
 

9.0 References 

American Water Works Association (AWWA). 2005a. Fundamentals and Control of 

Nitrification in Drinking Water Distribution Systems. Denver: AWWA. 

AWWA. 2005b. Managing Change and Unintended Consequences: Lead and Copper Rule 

Corrosion Control Treatment. Denver: AWWA. 

AWWA. 2001. The AWWA Standard, Rehabilitation of Water Mains (M28), 2nd Ed. Denver: 

AWWA. 

Boulos, P.F., K. E. Lansey, B.W. Karney. 2006. Comprehensive Water Distribution Systems 

Analysis Handbook. Denver: AWWA. 

Chowdhury, Z.K., C.P. Hill, M.J. Sclimenti, S.W. Krasner, R.S. Summers, C. Valenti, and J.G. 

Uber. 2009. Evaluation of Disinfection Practices for DBP and Precursor Occurrence in 

Distribution Systems. Denver: AwwaRF. 

Friedman, M.J., K. Martel, A. Hill, D. Holt, S. Smith, T. Ta, C. Sherwin, D. Hiltebrand, P. 

Pommerenk, Z. Hinedi, and A. Camper. 2003. Establishing Site-Specific Flushing Velocities. 

Denver: AwwaRF. 

Grayman, W. M., L. A. Rossman, C. Arnold, R. A. Deininger, C. Smith, J. F. Smith, and R. 

Schnipke. 2000. Water Quality Modeling of Distribution System Storage Facilities. Denver: 

AwwaRF. 

Harms, L. L., and C. Owen. 2004. A Guide for the Implementation and Use of Chloramines. 

Denver: AwwaRF. 

Harrington, G. W., D. R. Noguera, C. C. Bone, A. I. Kandou, P. S. Oldenburg, J. M. Regan, and 

D. V. Hoven. 2003. Ammonia From Chloramine Decay: Effects on Distribution System 

Nitrification. Denver: AwwaRF. 

Joseph, S. and J. G. Pimblett. 2000. Flushed with Success - Unidirectional Flushing Program is 

Clean Sweep. AWWA Opflow, Vol.26, No. 1. 

Kirmeyer, G.J., G.W. Foust, G.L. Pierson, J.J. Simmler, M.W. LeChevallier. 1993. Optimizing 

Chloramine Treatment. First Edition. Denver: AwwaRF and AWWA. 

Kirmeyer, G.J., M. Friedman, J. Clement, A. Sandvig, P.F. Noran, K.D. Martel, D. Smith, M. 

LeChevallier, C. Volk, E. Antoun, D. Hiltebrand, J. Dykesen, and R. Cushing. 2000. Guidance 

Manual for Maintaining Distribution System Water Quality. AwwaRF Report 90798. Project 

#357. Denver: AwwaRF. 

Kirmeyer, G.J., L. Kirby, B.M. Murphy, P.F. Noran, K. Martel, T.W. Lund, J.L. Anderson, and R. 

Medhurst. 1999. Maintaining and Operating Finished Water Storage Facilities to Prevent Water 

Quality Deterioration. Denver: AwwaRF and AWWA. 

Consecutive Systems Guidance Manual 9-1 March 2010 
  

 

Kirmeyer G., Martel K., Thompson G., Radder L., Klement W., LeChevallier M., Baribeau H., 

Flores A. 2004. Optimizing Chloramine Treatment, Second Edition. Denver: AwwaRF. 

Mahmood, F., Pimblett J. G., Grace N. O., and Grayman W. M. 2005. Evaluation of Water 

Mixing Characteristics in Distribution System Storage Tanks. Journal AWWA, 97:3:74-88. 

USEPA. 2008. Stage 2 Disinfectants and Disinfection Byproducts Rule Operational Evaluation 

Guidance Manual. EPA 815-R-08-018. Available at: http://www.epa.gov/nscep/. 

USEPA. 2007a. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2 

DBP Rules. EPA 815-R-07-017. Available at: http://www.epa.gov/nscep/. 

USEPA. 2007b. The Stage 2 Disinfectants and Disinfection Byproducts Rule Implementation 

Guidance. EPA 816-R-07-007. Available at: http://www.epa.gov/nscep/. 

USEPA. 2007c. Complying with the Stage 2 Disinfectant and Disinfection Byproducts Rule: 

Small Entity Compliance Guide. EPA 815-R-07-014. Available at: http://www.epa.gov/nscep/. 

USEPA. 2007d. Consecutive System Guide for the Ground Water Rule. EPA 815-R-07-020. 

Available at: http://www.epa.gov/nscep/. 

USEPA. 2006a. Initial Distribution System Evaluation Guidance Manual for the Final Stage 2 

Disinfectants and Disinfection Byproducts Rule. EPA 815-B-06-002. Available at: 

http://www.epa.gov/nscep/. 

USEPA. 2006b. Initial Distribution System Evaluation Guide for Systems Serving Fewer than 

10,000 People for the Final Stage 2 Disinfectants and Disinfection Byproducts Rule. EPA 815-

B-06-001. Available at: http://www.epa.gov/nscep/. 

USEPA. 2005. Preparing Your Consumer Confidence Report: Revised Guidance for Water 

Suppliers. EPA 816-R-05-002. Available at: http://www.epa.gov/nscep/. 

USEPA. 2004a. Code of Federal Regulations, Title 40 Section 141.2, Definitions. 

USEPA. 2004b. Consumer Confidence Report Rule: A Quick Reference Guide. EPA 816-F-02-

026. Available at: http://www.epa.gov/nscep/. 

USEPA. 2001. The Stage 1 Disinfectants and Disinfection Byproducts Rule: What Does it Mean 

to you? EPA 816-R-01-014. Available at : http://www.epa.gov/nscep/. 

USEPA. 2000a. Public Notification Handbook. EPA 816R-00-010. Washington, D.C.: USEPA. 

USEPA. 2000b. The Public Notification Rule: A Quick Reference Guide. EPA 

816-F-00-023. Available at: http://www.epa.gov/nscep/.
 

USEPA. 1999a. Alternative Disinfectants and Oxidants Guidance Manual. Office of Water. 

EPA 815-R-99-014. Available at: http://www.epa.gov/nscep/. 

Consecutive Systems Guidance Manual 9-2 March 2010 
 

USEPA. 1999b. Enhanced Coagulation and Enhanced Precipitative Softening Guidance 

Manual. EPA 815-R-99-012. Available at: http://www.epa.gov/nscep/. 

Consecutive Systems Guidance Manual 9-3 March 2010 
Appendix A 

Example of Formal Agreement between Consecutive and Wholesale Systems 

[NOTE: Stage 2 DBPR or other rules may contain requirements that will result in a need to 

modify or update existing agreements] 

Date: __________ __ 

To the Denver Board of Water Commissioners: 

The Board of (hereafter Distributor) 

requests to be included in Denver Water's Integrated System under the Colorado 

Primary Drinking Water Regulations (CPDWR). This Board acknowledges that it is 

legally and enforceably obligated to comply with Denver Water's Operating Rules and 

Engineering Standards through its distributor agreement with Denver Water. It further 

acknowledges that such rules and standards include the standard operating procedures

adopted by the reference in Chapter 12 of the Engineering Standards. 

Distributor's contact person: 

Address: 

Phone: No. of people served: 

The responsibilities of the parties are set forth as follows: 

Denver Water is responsible for: 

() all monitoring and MCl requirements related to. microbiological 

contaminants (Article 3, CDPWR) 

() all monitoring, reporting and MCl requirements related to 

disinfection byproducts (Art. 5 CPDWR) unless a distributor adds 

disinfectant in the distribution system 

( ) all tap monitoring, reporting, corrosion control and public education 

requirements of the lead and copper rule (Art. 7, CDPWR) 

() all collection , reporting and compl iance with residual disinfectant 
Distributor is responsible for all other requirements for consecutive systems enumerated 

by Article 1.6 of the CPDWR, specifically including but not limited to: 

() distribution system operator certification 

() hydrant inspection program () valve inspection program () lead service line replacement requirements (Art. 7, CPDWR) () operation of treated water storage (check if distributor has 

treated water storage) 

() water quality customer complaints, communication and initial 

response 

() leak repair and main disinfection () distribution system discharges () maintenance of treated water storage (cleaning can be 

contracted to Denver Water if checked above) 

() Instead of having Denver Water responsible, the Distributor prefers 

to be responsible for its own cross-connection control program, 

including all reporting, record-keeping and enforcement of 

hazardous cross-connection requirements and backflow prevention 

(Art. 12, CPDWR) (if checked, cross out and initial the last 

responsibility under Denver Water) 

Distributor further certifies that it (does/does not) provide further disinfection to the water it receives from Denver Water. 

ATTEST: 

[NAME OF DISTRIBUTOR] 

By __________________ __ By __________________ __ 

Title 
Date: Date: __________ _____ _ __ 

Date: __________________ _________ _ _ 

Manager of Water Quality