GROUND WATER RULE 

TRIGGERED AND REPRESENTATIVE SOURCE 

WATER MONITORING GUIDANCE MANUAL 
______________________________________________________________________________ 

Office of Water (4606) EPA 815-R-09-003 http://www.epa.gov/safewater April 2009 
DISCLAIMER 

The statutory provisions and U.S. Environmental Protection Agency (EPA) regulations 

described in this document contain legally binding requirements. 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. 

While EPA has made every effort to ensure the accuracy of the discussion in this guidance, the 

obligations of the regulated community are determined by statutes, regulations, or other legally 

binding requirements. In the event of a conflict between the discussion in this document and any 

statute or regulation, the statute and regulation, not this document, would be controlling. 

Interested parties are free to raise questions and objections to the guidance and the 

appropriateness of using it in a particular situation. 

Although this manual describes suggestions for complying with Ground Water Rule 

(GWR) requirements, the guidance presented here may not be appropriate for all situations, and 

alternative approaches may provide satisfactory performance. 

Mention of trade names or commercial products does not constitute an EPA endorsement 

or recommendation for use. 

Please direct questions on this document to: 

 Jeremy Bauer 

U.S. EPA 

2218B, EPA East: MC-4607M 

1201 Constitution Ave, N.W. 

Washington, DC 20460-0001 

 bauer.jeremy@epa.gov 

202-564-2775 

 202-564-3767 (facsimile) 

Ground Water Rule 

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ACKNOWLEDGEMENTS 

American Water Works Association; 

Association of State Drinking Water Administrators; 

Association of Metropolitan Water Agencies; 

Michael Finn, U.S. EPA, HQ; 

Bob Moore, Ohio EPA. 

Ground Water Rule 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
CONTENTS 

Exhibits .......................................................................................................................................... iii
 

Acronyms ....................................................................................................................................... iv
 

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

1.1 Purpose of this Document ................................................................................................ 1-2
 

1.2 Relevant Data Considerations for Representative Monitoring Decisions ....................... 1-2
 

1.3 Organization of this Guidance Manual............................................................................ 1-3
 

2. Ground Water Rule Requirements ...................................................................................... 2-1
 

2.1 Sanitary Surveys .............................................................................................................. 2-3
 

2.2 Source Water Monitoring ................................................................................................ 2-3
 

2.2.1 Triggered Source Water Monitoring .................................................................... 2-3
 

2.2.2 Additional Source Water Monitoring .................................................................. 2-3
 

2.2.3 Assessment Source Water Monitoring ................................................................. 2-4
 

2.3 Corrective Action............................................................................................................. 2-4
 

2.4 Compliance Monitoring ................................................................................................... 2-4
 

3. Triggered Monitoring ........................................................................................................... 3-1
 

3.1 Overview.......................................................................................................................... 3-1
 

3.2 Consecutive and Wholesale Systems............................................................................... 3-2
 

3.3 Exceptions to the Triggered Source Water Monitoring Requirements ............................ 3-2
 

3.3.1	 Invalidation of Total Coliform Rule Samples ...................................................... 3-2
 

3.3.2	 Determining Whether the Cause of a Total Coliform-Positive is Directly Related 

to the Distribution System. .................................................................................. 3-3
 

3.4 Invalidation of Triggered Source Water Samples ............................................................ 3-4
 

4. Representative Source Water Monitoring........................................................................... 4-1
 

4.1	 Ground Water Sources Representing Coliform Monitoring Locations in the Distribution 

System.............................................................................................................................. 4-2
 

4.2	 Wells Representative of Other Wells in the Same Hydrogeologic Setting ..................... 4-3
 

4.3	 Triggered Source Water Monitoring Plan........................................................................ 4-3
 

5. Ground Water Sources Representing Coliform Monitoring Locations in the Distribution 

System ......................................................................................................................................... 5-1
 

5.1 Linking Sources to TCR Sites.......................................................................................... 5-1
 

5.2 Tools ................................................................................................................................ 5-2
 

5.2.1 Distribution System Maps ................................................................................... 5-2
 

5.2.2 Coliform Sample Siting Plan ............................................................................... 5-4
 

5.2.3 Operating Conditions and Operations Records .................................................... 5-5
 

5.2.4 Distribution System Hydraulic Models ............................................................... 5-5
 

5.2.5 Distribution System Tracer Studies ..................................................................... 5-6
 

5.2.6 Customer Complaint Records .............................................................................. 5-6
 

5.2.7 Water Quality Parameters .................................................................................... 5-7
 

5.3 Consideration While Preparing a Plan ............................................................................. 5-8
 

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6. Wells Representative of Other Wells in the Same Hydrogeologic Setting ....................... 6-1
 

6.1 Physical Properties........................................................................................................... 6-1
 

6.1.1	 Well Proximity to other Wells ............................................................................. 6-1
 

6.1.2	 Well Construction ................................................................................................ 6-2
 

6.1.3	 Water Chemistry .................................................................................................. 6-4
 

6.1.3.1	 Total Dissolved Solids ................................................................................ 6-5
 

6.1.3.2	 Nitrates and Ammonia ................................................................................ 6-5
 

6.1.3.3	 Hardness and Alkalinity.............................................................................. 6-6
 

6.2 Hydrogeological Representativeness ............................................................................... 6-7
 

6.2.1 Aquifer Type and Driller’s Logs .............................................................................. 6-7
 

6.2.2	 Additional Data.................................................................................................... 6-9
 

6.2.2.1	 Hydrogeologic Data Sources ...................................................................... 6-9
 

6.2.3 Capture Zone Models......................................................................................... 6-16
 

7. Additional Useful Considerations for Representative Monitoring Proposals .................. 7-1
 

7.1 Reviewing the Proposal ................................................................................................... 7-1
 

7.1.1	 Technical Considerations when Reviewing Proposals for Representative 

Monitoring ........................................................................................................... 7-1
 

7.1.2 Ensuring the Proposal is Complete ...................................................................... 7-2
 

7.1.2.1	 Ground Water Sources Representing Coliform Monitoring Locations in the 

Distribution System .................................................................................... 7-3
 

7.1.2.2	 Wells Representative of Other Wells in the Same Hydrogeologic Setting 7-4
 

7.2 Notifying the System and Recordkeeping Associated with a Representative Monitoring 

Decision ........................................................................................................................... 7-5
 

Appendix A: Examples of Five Triggered Source Water Monitoring Plans ............................. A-1 

Appendix B: Example Triggered Source Water Monitoring Plan (Template) ...........................B-1 

Appendix C: Summary of Considerations for Representative Monitoring ................................C-1 

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EXHIBITS 

Exhibit 2.1: Summary of GWR Requirements ............................................................................ 2-2 

Exhibit 4.1: Simplified Representative Monitoring Scenarios .................................................... 4-2 

Exhibit 5.1: Example Distribution System Map .......................................................................... 5-4 

Exhibit 5.2: Total Coliform Sample Site Locations ..................................................................... 5-5 

Exhibit 5.3: Example Triggered Source Water Map and Table ................................................... 5-9 

Exhibit 6.1: Potentially Good Candidates for Representative Sampling ..................................... 6-3 

Exhibit 6.2: Inappropriate Candidates for Representative Sampling ........................................... 6-3 

Exhibit 6.3: Wells in Close Proximity Not Representative Due to Fractured Bedrock ............... 6-4 

Exhibit 6.4: Wells Screened in a Karst Aquifer Overlain by a Continuous Layer ...................... 6-8 

Exhibit 6.5: Wells Screened in a Karst Aquifer Overlain by a Discontinuous Layer ................. 6-8 

Exhibit 6.6: Strike and Dip ........................................................................................................ 6-12 

Exhibit 6.7: The Importance of Map Scale for Determining Aquifer Type .............................. 6-14 

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ACRONYMS 

AWWA American Water Works Association 

AWWARF American Water Works Association Research Foundation 

ASTM American Society of Testing Materials 

CDC Centers for Disease Control and Prevention 

CCR Consumer Confidence Report 

CFR Code of Federal Regulations 

CT The Residual Concentration of Disinfectant (mg/L) Multiplied by the 

Contact Time (in minutes) 

CWS Community Water System 

DEMs Digital Elevation Models 

DLGs Digital Line Graphs 

DMA Defense Mapping Agency 

EPA United States Environmental Protection Agency 

EROS Earth Resources Observation Systems 

ESICs Earth Science Information Centers 

FR Federal Register 

GPS Global Positioning System 

GWR Ground Water Rule (40 CFR Part 141 Subpart S) 

GWS Ground Water System 

GWUDI	 Ground Water Under the Direct Influence of Surface Water 

HSA Hydrogeologic Sensitivity Assessment 

HPC Heterotrophic Plate Count 

LCR Lead and Copper Rule (40 CFR Part 141 Subpart I) 

NAPP National Aerial Photography Program 

NCGMP National Cooperative Geologic Mapping Program 

NCWS Non-Community Water System 

NRC National Research Council 

NRCS National Resources Conservation Service 

PWS Public Water System 

QA Quality Assurance 

QC Quality Control 

RASA Regional Aquifer-System Analysis 

SDWA Safe Drinking Water Act 

Stage 1 DBPR Stage 1 Disinfectants and Disinfection Byproducts Rule 

Stage 2 DBPR Stage 2 Disinfectants and Disinfection Byproducts Rule 

SWAP Source Water Assessment Program 

TC Total Coliform 

TCR Total Coliform Rule (40 CFR Part 141 Subpart C) 

TDS Total Dissolved Solids 

UCMR Unregulated Contaminant Monitoring Rule 

USDA United States Department of Agriculture 

USGS United States Geological Survey 

UV Ultraviolet 

WHPAs Wellhead Protection Areas 

WHPP Wellhead Protection Program 

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Additional Information 

For more information, contact EPA’s Safe Drinking Water Hotline at 1-800-426-4791, or 

see the Office of Ground Water and Drinking Water Web page at http://www.epa.gov/safewater. 

This guidance manual is available electronically at: 

http://www.epa.gov/safewater/disinfection/gwr/compliancehelp.html. 

To order a paper copy of guidance manuals, you may contact the US EPA Water 

Resource Center at 202-566-1729 or by mail at: 

US Environmental Protection Agency 

Water Resource Center (RC-4100) 

1200 Pennsylvania Ave NW 

Washington, DC 20460 

E-mail: center.water-resource@epa.gov
 

Guidance Manuals and Materials for the Ground Water Rule 

EPA is developing a series of guidance documents to help public water systems 

implement requirements associated with the Ground Water Rule. Electronic versions of the 

guidance documents are, or will be, available on the Ground Water Rule Compliance Help page 

at http://www.epa.gov/safewater/disinfection/gwr/compliancehelp.html. 

Complying with the Ground Water Rule: Small Entity Compliance Guide (EPA 

815-R-07-018) – This guide is designed for owners and operators of public water systems 

serving 10,000 or fewer persons that are required to comply with the Ground Water Rule. 

Ground Water Rule Corrective Actions Guidance Manual (EPA 815-R-08-011) – 

This manual provides information for ground water systems that must provide corrective 

action as a result of significant deficiencies or fecally-contaminated source water. The 

guidance includes technical information on selecting appropriate disinfection 

technologies to enable primacy agencies and public water systems to select the treatment 

most appropriate for a given system. It also provides technical information to States and 

systems on eliminating sources of contamination, utilizing alternate sources, and 

correcting significant deficiencies for situations in which disinfection is not the selected 

corrective action. 

Sanitary Survey Guidance Manual for Ground Water Systems (EPA 815-R-08-015) 

– This guidance provides information to assist States and other primacy programs in 

conducting sanitary surveys of ground water systems. 

Ground Water Rule Source Water Monitoring Methods Guidance Manual (EPA 

815-R-07-019) – This manual provides guidance on triggered and optional assessment 

source water monitoring issues such as: selection of fecal indicators, sample collection 

and shipping, source water monitoring methods, laboratory quality assurance (QA) and 

quality control (QC), and evaluation of fecal indicator data. This manual also provides an 

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overview of Ground Water Rule requirements and includes frequently asked questions 

regarding source water monitoring. 

Ground Water Rule Source Assessment Guidance (EPA 815-R-07-023) – This 

manual provides information on procedures for identifying ground water sources at risk 

for fecal contamination. Risk factors are discussed with emphasis on identifying readily 

available factors suitable for desk-top rather than field evaluation of individual public 

water system wells. The guidance also lists sources of information for making a risk 

determination, and includes field methods for determining the presence of a 

hydrogeologic barrier. 

Consecutive System Guide for the Ground Water Rule (EPA 815-R-07-020) – This 

guidance describes the regulatory requirements of the Ground Water Rule that apply to 

wholesale ground water systems and their consecutive systems. 

Other Guidance Manuals and Materials 

EPA has developed other guidance manuals to aid EPA, State agencies, and water 

systems in implementing the Ground Water Rule and other rules, and to help to ensure consistent 

implementation. 

Consider the Source: A Pocket Guide to Protecting Your Drinking Water Pocket 

Guide #3 (EPA 816-K-02-002) – An electronic version is available at 

http://www.epa.gov/safewater/sourcewater. 

Revised Public Notification Handbook (EPA 816-R-07-003) – An electronic version is 

available at http://www.epa.gov/safewater/publicnotification/compliancehelp.html. 

Preparing Your Drinking Water Consumer Confidence Report (CCR), Revised 

Guidance for Water Suppliers (EPA 816-R-002) – This document provides 

information to assist drinking water systems with preparing and distributing Consumer 

Confidence Reports. An electronic version is available at 

http://www.epa.gov/safewater/ccr/compliancehelp.html. 

Consumer Confidence Report Rule: A Quick Reference Guide (EPA 816-F-02-026) 

– A condensed guide that provides a brief overview of the Consumer Confidence Report 

Rule. An electronic version is available at 

http://www.epa.gov/safewater/ccr/compliancehelp.html. 

Surface Water Treatment Rule Guidance Manual – The Appendices include CT 

tables for the inactivation of Giardia and viruses for chlorine, chlorine dioxide and 

ozone. An electronic version is available at 

http://www.epa.gov/safewater/mdbp/guidsws.pdf. 

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1. Introduction 

EPA developed the Ground Water Rule (GWR) to provide for increased public health 

protection for consumers of water from public water systems that use ground water. A key 

element of the GWR is to identify public ground water sources that are susceptible to fecal 

contamination. The GWR also ensures that these systems take corrective action to eliminate the 

source of contamination or to remove or inactivate pathogens in the drinking water they provide 

to the public. Fecal contamination is a broad term that refers to microbial contaminants from 

human or animal feces. It is a likely source of microbial pathogens in drinking water. These 

microbial pathogens are a significant threat to public health because they can cause serious 

illness and even death when consumed. 

Fecal contamination may be introduced into finished ground water via inadequately 

treated or inadequately protected source water or from problems in the distribution system. 

Common sources of ground water contamination include septic systems, leaking sewer pipes, 

landfills, sewage lagoons, and improperly abandoned wells. Microbial contamination in an 

aquifer can be localized or may be transported as water moves through the aquifer. 

The GWR requires ground water systems (GWSs) that provide less than 4-log removal, 

inactivation, or State-approved combination of these or that do not perform compliance 

monitoring of treatment to sample their source water for the presence of a fecal indicator when 

total coliform bacteria are detected in the distribution system. This monitoring requirement is 

triggered by the results of routine coliform sampling performed for compliance with the Total 

Coliform Rule (TCR). The triggered monitoring requirement is designed to allow systems and 

States to identify and to correct public health risks from fecal contamination found at the source. 

Additionally, assessment source water monitoring may be required for specific systems at the 

State’s discretion. Assessment source water monitoring is routine monitoring of the system’s 

specified ground water source(s) for a fecal indicator at the frequency and duration determined 

by the State. 

If approved by the State, systems with more than one ground water source may conduct 

triggered source water monitoring at a representative ground water source or sources. The State 

may require systems with more than one ground water source to submit for approval a triggered 

source water monitoring plan that the system will use for representative sampling. A triggered 

source water monitoring plan must identify ground water sources that are representative of each 

monitoring site in the system’s TCR sample siting plan. Systems should consider the relative 

value of using representative sampling versus the cost of evaluating individual sources and 

developing a representative monitoring plan. It may be more cost effective for systems, 

especially small systems, to conduct triggered monitoring when necessary rather than to make an 

up-front investment in developing a plan. Systems should discuss these options with the State. 

EPA believes that this alternative can be as protective of public health as monitoring all 

wellheads, provided that the chosen wells are truly representative of all wellheads. In addition, 

for situations where a particular sample site is inaccessible, the State may identify an alternate 

sampling site that is representative of the water quality of the ground water at the inaccessible 

sample site. 

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Representative source water monitoring for the GWR, also called representative 

monitoring, falls within one of two categories: 

1. Ground Water Sources Representing Coliform Monitoring Locations in the 

Distribution System. This relates to situations in which a system has more than one 

ground water source but not all sources provide water to each total coliform sample 

collection site in the distribution system. In this case, if approved by the State, only those 

sources that hydraulically represent (or provide water to) a specific total coliform sample 

site would need to be sampled under the triggered monitoring provision of the GWR if a 

routine sample from that site were total coliform-positive. 

2. Wells Representative of Other Wells in the same Hydrogeologic Setting. This 

relates to situations in which a system has multiple sources and some are so similar (e.g., 

physically and hydrogeologically) that a reasonable case could be made that one source 

may be representative of another or of others with regard to the risk of fecal 

contamination. In this case, one or more of the sources would be sampled to indicate the 

source water quality of all of the representative sources. If approved by the State, 

representative sources based on physical and hydrogeological properties could be used 

for triggered monitoring and for assessment source water monitoring. 

1.1 Purpose of this Document 

The purpose of this guidance manual is to provide GWSs and States with 

recommendations and examples of the types of information, data, and tools that might be used to 

demonstrate the appropriateness of representative source water monitoring. Because every 

system has unique well locations, distribution system hydraulics, and aquifer hydrogeologic 

characteristics, a decision of whether representative monitoring adequately protects public health 

should be made on a case-by-case basis by the State or primacy agency. 

Although some GWSs may have a wealth of information on which to base representative 

monitoring requests, many, if not most, GWSs likely have little data but might still be able to 

make a good case for representative monitoring. This guidance is designed to show the various 

ways that systems, working with their primacy agency, might use the information at their 

disposal to demonstrate whether representative monitoring is an appropriate option. 

1.2 Relevant Data Considerations for Representative Monitoring Decisions 

The type and amount of evidence systems will utilize to make their case for 

representative monitoring is likely to vary depending on the characteristics of the specific 

system. For example, a large system with multiple, interconnected pressure zones might utilize a 

complicated distribution system model to identify sources that are hydraulically representative of 

each routine total coliform sample site. In contrast, a less complex system might be able to make 

the same point with a simple map of the distribution system, which includes locations of the 

system’s wells, critical valves, and pressure zones. Similarly, existing information on each 

well’s zone of influence, construction details, source water chemistry, and aquifer characteristics 

may provide sufficient information to support evaluation of source physical and hydrogeological 

representativeness. 

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As discussed in Chapter 4, the suggested steps for identifying representative sources 

begins by initially grouping those that appear similar to each other using the most readily 

available information. The grouped wells are then compared using sequentially more complex 

information. The overall recommended process is one of elimination – removing wells from 

consideration that would not be representative of other wells with regard to the risk of fecal 

contamination. It is recommended that water system operators work deliberately through the 

suggestions addressed in this guidance, gather any information at their disposal, and exercise and 

document their conclusions based on their best professional judgment. 

Ultimately, each State will decide if the specifics of a particular system warrant 

representative monitoring and should give approval for representative monitoring accordingly. 

The GWR has granted States flexibility on representative monitoring in that it is not an all-ornothing approval process. For systems that are interested in sampling at representative well(s), 

State approval of representative monitoring is required before it can be applied by a system; 

therefore, a GWS must conduct triggered monitoring at each source prior to State approval. 

Systems that are interested in sampling at representative source(s) must have prior approval from 

the State to do so. 

1.3 Organization of this Guidance Manual 

The remaining six chapters and the two appendices of this guidance manual are organized 

as follows: 

•	 Chapter 2 – Ground Water Rule Requirements: Provides a brief overview of the 

GWR and how source water monitoring fits into the other regulatory requirements. 

•	 Chapter 3 – Triggered Monitoring: Discusses the triggered monitoring provisions of 

the Ground Water Rule in greater detail. 

•	 Chapter 4 – Representative Source Water Monitoring: Provides an overview of the 

different types of representative monitoring applicable to the GWR. The types include 

wells representing coliform monitoring locations in the distribution system and wells 

representative of other wells. This chapter also describes the critical elements of a 

triggered source water monitoring plan, which some States may require from systems in 

order to qualify for representative source water monitoring. The chapter also includes a 

general outline of steps that may be followed to determine whether representative 

monitoring is appropriate for a GWS. Details of the outlined steps are discussed in 

subsequent chapters. 

•	 Chapter 5 – Ground Water Sources Representing Coliform Monitoring Locations in 

the Distribution System: Examines what information on distribution system hydraulics 

may be useful and how it may be applied when considering whether some but not all 

sources are representative of specific routine total coliform sampling sites. 

•	 Chapter 6 – Wells Representative of other Wells in the Same Hydrogeologic Setting: 

Discusses various source water chemistry, well construction details, and hydrogeological 

data useful when considering whether a well is representative of the fecal contamination 

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Water Monitoring Guidance Manual 
health risk of multiple wells. This chapter is applicable to both triggered source water 

monitoring and assessment source water monitoring. 

•	 Chapter 7 – Additional Useful Considerations for Representative Monitoring 

Proposals: Examines information systems might consider when finalizing and States 

might consider when reviewing representative monitoring proposals. 

•	 Appendix A – Examples of Five Triggered Source Water Monitoring Plans: Presents 

five example case studies of hypothetical systems pursuing representative monitoring. 

•	 Appendix B – Example Triggered Source Water Monitoring Plan (Template): 

Provides a blank template to help water systems develop a Triggered Source Water 

Monitoring Plan. 

•	 Appendix C – Summary of Considerations for Representative Monitoring: Provides 

a summary of major points discussed in the Ground Water Rule Triggered and 

Representative Source Water Monitoring Guidance Manual. 

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Water Monitoring Guidance Manual 
2. Ground Water Rule Requirements 

EPA published the Ground Water Rule (GWR) in the Federal Register on November 8, 

2006 (Federal Register Volume 71, Number 216, 65574) and a rule correction on November 21, 

2006 (Federal Register Volume 71, Number 224, 67427). Copies of the Federal Register are 

available at: 

•	 http://www.epa.gov/fedrgstr/EPA-WATER/2006/November/Day-08/w8763.pdf 

•	 http://www.epa.gov/fedrgstr/EPA-WATER/2006/November/Day-21/w8763.pdf 

The GWR addresses source water fecal contamination in systems that use wells or other 

ground water sources. The rule applies to all public water systems (PWSs) including community 

and non-community systems regardless of size that: 

•	 Rely entirely on one or more ground water sources; 

•	 Are consecutive systems that receive finished ground water; or 

•	 Mix surface and ground water, where ground water is added directly to the distribution 

system and provided to consumers without treatment equivalent to the treatment required 

for surface water. 

The GWR does not apply to PWSs that combine all of their ground water with surface 

water before treatment. The GWR also does not apply to systems using ground water sources 

that have been determined by the State to be ground water under the direct influence of surface 

water (GWUDI). A GWUDI source refers to any water beneath the surface of the ground with 

significant occurrence of insects or other macroorganisms, algae, or large-diameter pathogens 

such as Giardia lamblia or Cryptosporidium, or significant and relatively rapid shifts in water 

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

climatological or surface water conditions (40 CFR 141.2). Direct influence must be determined 

for individual sources in accordance with criteria established by the State. GWUDI sources are 

subject to the treatment requirements of surface water systems. 

For the purposes of this document, the term “ground water system” (or GWS) will be 

used to refer to a system to which the GWR applies. Key provisions of the GWR include: 

•	 Periodic sanitary surveys of GWSs addressing eight specific sanitary survey elements to 

evaluate the system for the presence of significant deficiencies. 

•	 Source water monitoring either through triggered monitoring or State-directed assessment 

monitoring to test for the presence of one of three fecal indicators (E. coli, enterococci, or 

coliphage). 

•	 Requirements to correct significant deficiencies and eliminate or treat for fecal 

contamination through specified actions. 

•	 Compliance monitoring to ensure that treatment technologies, installed to treat drinking 

water, reliably achieve at least 99.99 percent (4-log) treatment of viruses (via 

inactivation, removal, or a combination of these). 

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GWSs must comply, unless otherwise noted, with the GWR beginning December 1, 

2009. The flow chart provided in Exhibit 2.1 includes a summary of the GWR requirements. 

Exhibit 2.1: Summary of GWR Requirements 

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Water Monitoring Guidance Manual 
2.1 Sanitary Surveys 

Under the GWR, States are required to conduct regular comprehensive sanitary surveys. 

GWSs must provide, at the State’s request, any existing information that would allow the State to 

perform a sanitary survey. If a significant deficiency is identified, either during a sanitary survey 

or at any other time, the GWS is required to take corrective action. Failure to complete the 

required corrective action will result in a treatment technique violation. “Significant 

deficiencies” include, but are not limited to, defects in design, operation, or maintenance, or a 

failure or malfunction of the sources, treatment, storage, or distribution system that the State 

determines to be causing, or have the potential for causing, the introduction of contamination 

into the water delivered to consumers. 

The sanitary surveys must be conducted, at a minimum, every three years for community 

GWSs and every five years for noncommunity GWSs and must include a review of eight critical 

elements, as applicable to the system. The eight elements are: 

• Source (protection, physical components, and condition) 

• Treatment 

• Distribution System 

• Finished Water Storage 

• Pumps, Pump Facilities, and Controls 

• Monitoring, Reporting, and Data Verification 

• Water System Management and Operations 

• Operator Compliance with State Requirements 

The State may reduce the frequency of sanitary surveys for community GWSs to at least 

once every five years if the community GWS has an outstanding performance record as 

determined by the State, or the community GWS is providing 4-log treatment of viruses and 

conducting compliance monitoring of the treatment system under the GWR. 

2.2 Source Water Monitoring 

The GWR has three general categories of ground water source microbial monitoring 

requirements: 1) triggered source water monitoring, 2) additional source water sampling, and 3) 

assessment source water monitoring. GWSs conducting source water monitoring under the 

GWR must collect and analyze at least 100 mL of source water for one of three fecal indicators 

(E. coli, enterococci, or coliphage) using one of the analytical methods specified in the GWR. 

2.2.1 Triggered Source Water Monitoring 

The triggered source water provisions of the Ground Water Rule are described in Chapter 

3 of this guidance manual. 

2.2.2 Additional Source Water Monitoring 

If the State does not require corrective action in response to a fecal indicator-positive 

triggered source water sample, the GWS must collect five additional source water samples from 

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each fecal indicator-positive source within 24 hours of being notified of the fecal indicatorpositive result. All five of the additional samples must be analyzed for the presence of a fecal 

indicator. If any of the five additional source water samples is fecal indicator-positive, the GWS 

must take corrective action. 

2.2.3 Assessment Source Water Monitoring 

As a complement to the triggered source water monitoring provision, States may require 

GWSs to conduct assessment source water monitoring, as needed. The purpose of optional 

assessment monitoring is to allow States to target monitoring of GWSs that the State believes are 

at higher risk for fecal contamination. As discussed in the preamble of the GWR, EPA 

recommends that States require systems that are conducting assessment source water monitoring 

to collect a total of 12 ground water source samples that represent each month the system 

provides ground water to the public. However, the State determines the requirements for 

assessment source water monitoring, including the number of samples and their sampling 

interval and whether one or more wells within the GWS could be sampled to physically and 

hydrogeologically represent multiple wells. 

2.3 Corrective Action 

GWSs must take corrective action if any one of the three situations applies: 

•	 A significant deficiency is identified, 

•	 A triggered source sample has tested positive for a fecal indicator and corrective action is 

required by the State, or 

•	 At least one of the five additional source water samples collected in response to a fecal 

indicator-positive triggered sample has also tested positive for a fecal indicator. 

If corrective action is required, the GWS must consult with the State regarding the 

necessary action or implement at least one of the following, as directed by the State: 

•	 Correct all significant deficiencies 

•	 Provide an alternate source of water 

•	 Eliminate the source(s) of contamination 

•	 Provide treatment that reliably achieves at least 4-log treatment of viruses at or before the 

first customer (using inactivation, removal, or a State-approved combination of 4-log 

virus inactivation and removal) and conduct compliance monitoring. 

2.4 Compliance Monitoring 

Compliance monitoring for the GWR refers to monitoring the effectiveness or reliability 

of the treatment system installed to ensure 4-log removal or inactivation, or a combination of 

removal and inactivation, of viruses. Only wells that provide 4-log treatment of viruses and that 

perform compliance monitoring are excluded from the triggered source water monitoring 

requirements of GWR. 

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 To not be subject to triggered source water monitoring, by December 1, 2009, a GWS 

must notify the State that it provides at least 4-log treatment of viruses before or at the first 

customer. The GWS must then begin compliance monitoring by December 1, 2009. In addition, 

any GWS that is required to provide 4-log treatment of viruses as a corrective action must also 

conduct compliance monitoring to ensure that the 4-log treatment is functioning properly. 

One of the compliance monitoring requirements is that GWSs that use chemical 

disinfection and that serve more than 3,300 people must continuously monitor their disinfectant 

residual concentration. GWSs must maintain the minimum disinfectant residual concentration 

determined by the State. GWSs that use chemical disinfection and serve 3,300 people or fewer 

must take daily grab samples for disinfectant residual concentration or meet the continuous 

monitoring requirements. If any daily grab sample measurement falls below the minimum Staterequired residual disinfectant concentration, the GWS must take follow-up samples every 4 

hours until the residual is restored to the required level. 

GWSs using membrane filtration for 4-log treatment of viruses must monitor the 

membrane filtration process according to State-specified monitoring requirements and must 

operate the membrane filtration according to all State-specified compliance requirements. 

GWSs may use alternative treatment technologies (e.g., ultraviolet radiation [UV]) 

approved by the State, if the alternative treatment technology, alone or in combination (e.g., 

membrane filtration with UV) can reliably provide at least 4-log treatment of viruses. GWSs 

must monitor the alternative treatment according to State-specified monitoring requirements and 

must operate the alternative treatment according to compliance requirements established by the 

State. 

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3. Triggered Monitoring 

3.1 Overview 

Under the triggered monitoring provision of the GWR, undisinfected ground water 

systems are triggered into taking source water samples as a result of a total coliform-positive 

sample in the distribution system. Any GWS that does not provide at least 4-log treatment of 

viruses before or at the first customer (including both treating to 4-log and demonstrating 4-log 

treatment by conducting compliance monitoring) must comply with the triggered source water 

monitoring requirement as described in 40 CFR 141.402(a). When a GWS is notified of a total 

coliform-positive routine sample, the GWS must collect, within 24 hours of notification, at least 

one sample from each ground water source in use at the time the total coliform-positive routine 

sample was collected, unless the system has approval from the State to do otherwise. The 

triggered source water sample(s) must be analyzed for the presence of a State-approved fecal 

indicator. If the triggered source water sample is fecal indicator-positive and the sample is not 

invalidated by the State, the GWS must either take corrective action, if required by the State, or 

collect five additional source water samples from that source and analyze them for the presence 

of a State-approved fecal indicator. 

The triggered monitoring provision enhances the existing Total Coliform Rule (TCR). 

The TCR requires all public water systems (PWSs) to monitor for the presence of total coliforms 

in the distribution system at a frequency proportional to the number of people served. Total 

coliforms are a group of closely related bacteria that are (with few exceptions) not harmful to 

humans. Because total coliforms are common inhabitants of ambient water and may be injured 

(i.e., not irreparably harmed) or inactivated by environmental stresses (e.g., lack of nutrients) and 

water treatment (e.g., chlorine disinfection) in a manner similar to most bacterial pathogens and 

many viral enteric pathogens, EPA considers them a useful indicator of these pathogens. More 

important, for drinking water, total coliforms are used to determine the adequacy of water 

treatment and the integrity of the distribution system. The absence of total coliforms in the 

distribution system minimizes the likelihood that fecal pathogens are present, whereas the 

presence of total coliforms may suggest that a pathway to contamination exists. As discussed 

above, a GWS with a distribution system TCR sample that tests positive for total coliform is 

required to conduct triggered source water monitoring to evaluate whether the total coliform 

presence in the distribution system is due to fecal contamination in the ground water source. 

Triggered source water monitoring provides a critical ongoing evaluation of GWSs. 

If approved by the State, systems with more than one ground water source may conduct 

triggered source water monitoring at a representative ground water source or sources. The State 

may require systems with more than one ground water source to submit for approval a triggered 

source water monitoring plan that the system will use for representative sampling. When it is 

required by the State, a triggered source water monitoring plan must identify ground water 

sources that are representative of each monitoring site in the system’s TCR sample siting plan 

(40 CFR 141.402(a)(2)(ii)). If a system has a representative monitoring plan in place and 

encounters a fecal indicator-positive sample at representative source, the system should discuss 

with the State the implications for the other sources that are represented by that source. See 

Chapter 4 for more information about representative source water monitoring. 

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Source water samples should be taken from the source water well(s) for the drinking 

water system when possible rather than later in the distribution system, so that treatment and/or 

the distribution system environment do not change the character of the source water sample. 

This is especially true for systems that have multiple wells. The rationale is that fecal 

contamination among nearby wells is likely to be non-uniform in its distribution (i.e., in a group 

of wells drawing water from a single aquifer, it is possible that only a single well is fecally 

contaminated). If a system draws water from more than one well, but only a single well is 

fecally contaminated, the dilution of fecally contaminated water with water from other wells 

makes it likely that the fecal contamination would be more difficult to detect at subsequent 

locations downstream within the distribution system. 

Because the focus of source water monitoring under the final GWR is to determine 

whether the source water is fecally contaminated, source water monitoring samples should not 

come from test, injection or monitoring wells (or well types other than production wells) because 

these wells may not reflect the water from the system’s source water production well. 

The final GWR provides States and systems with flexibility such that if a system’s 

configuration does not allow for sampling at the well itself, the system may collect source water 

samples at a State-approved location, before any treatment, provided that the sample is 

representative of the water quality of that well as determined by the State. 

3.2 Consecutive and Wholesale Systems 

The GWR has additional triggered source water monitoring requirements that apply to 

consecutive systems and their wholesale GWSs. If a consecutive system is notified that a sample 

it collected for compliance with the TCR is total-coliform positive, that consecutive system is 

required to notify its wholesale system of the positive sample. The wholesale system is then 

required to perform triggered source water monitoring as described above. If a triggered source 

water sample collected by the wholesale system is positive for a fecal indicator, the wholesale 

system must notify all consecutive systems served by that ground water source of the fecal 

indicator source water positive result. For more information and guidance on the GWR 

requirements for consecutive systems, refer to EPA’s Consecutive System Guide for the Ground 

Water Rule (EPA 815-R-07-020, July 2007) available at 

http://www.epa.gov/safewater/disinfection/gwr/pdfs/guide_gwr_consecutive-guidance.pdf. 

3.3 Exceptions to the Triggered Source Water Monitoring Requirements 

As indicated in 40 CFR 141.402(a)(5), a ground water system is not required to take 

triggered source water samples if the total coliform-positive sample is invalidated, caused by a 

distribution system deficiency, or collected at a location that meets State criteria for distribution 

system conditions that will cause total coliform-positive samples. See the next two sections for 

more resources and details related to these exceptions. 

3.3.1 Invalidation of Total Coliform Rule Samples 

Triggered source water monitoring samples are not required if the coliform sample is 

invalidated by the State. Under the TCR, the State may invalidate total coliform-positive 

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samples only if (1) the laboratory establishes that improper sample analysis led to the positive 

result, (2) the State, based on repeat sample results, determines that the problem resulted from 

domestic or other non-distribution system plumbing problems, or (3) the State has substantial 

reason to believe that the positive result does not reflect the water quality in the distribution 

system. The state must invalidate a total coliform-negative sample if a laboratory observes 

interference with the test by other organisms. For a complete discussion on invalidation of 

samples under the Total Coliform Rule, please see the EPA whitepaper Invalidation of Total 

Coliform Positive Samples available at: 

http://www.epa.gov/safewater/disinfection/tcr/pdfs/issuepaper_invalidation.pdf. 

3.3.2 Determining whether the Cause of a Total Coliform-Positive is directly related to the 

Distribution System 

Under 40 CFR 141.402(a)(5)(i) and 141.402 (a)(5)(ii), the GWR allows States to 

determine that the cause of a total coliform-positive sample collected in compliance with the 

TCR is directly related to the distribution system and should therefore not trigger fecal indicator 

source water monitoring. Triggered source water monitoring is required after a total coliformpositive sample is collected from the distribution system in compliance with the TCR. A GWS 

may not be required to comply with the triggered source water monitoring requirement if the 

GWS provides documentation to the State within 30 days of the total coliform-positive sample 

that it met the State criteria for distribution system conditions that cause total coliform-positive 

samples. In addition, the State can determine that a total coliform-positive sample collected 

under the TCR was caused by a distribution system deficiency. To meet this Special Primacy 

Requirement, States must describe the criteria that will be used to determine whether a total 

coliform-positive sample taken under the TCR is directly related to the distribution system. 

States may consider that samples constitute documentation of a distribution system deficiency. 

For example, follow-up distribution sampling or system repair records may be useful. 

Some examples are: 

•	 If the water system is known to have recurring documented biofilm problems and the 

total coliform-positive sample is convincingly related to biofilm growth in the 

distribution system; 

•	 After a storage tank inspection where contamination is evident; 

•	 After main repair or repair of a storage tank; 

•	 In a zone of the distribution system where water pressure is negative or low (e.g., less 

than 20 psi); or, 

•	 When it is likely that contamination is the result of cross connection in the distribution 

system. 

The reasons for triggered source water samples not being taken should be valid and 

defensible, and past distribution system problems supporting the total coliform-positive result 

should have been documented before the positive coliform sample result was received. For 

example, if a system attributes a positive total coliform result to a cross connection, the cross 

connection should have been previously identified and documented in writing before the positive 

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total coliform sample was collected. In such a case, EPA recommends that a plan be put in place 

to address cross connecting problems. 

3.4 Invalidation of Triggered Source Water Samples 

If the State provides written documentation that a fecal-indicator positive sample does not 

reflect source water quality, or if a GWS provides the State with written notice from the 

laboratory that improper analysis of a sample occurred, the State may invalidate the fecal 

indicator-positive sample as described in the GWR (40 CFR 141.402(d) Invalidation of a fecal 

indicator-positive ground water source sample.). Within 24 hours of receiving the State sample 

invalidation notification, a GWS is required to take another sample and have it analyzed for the 

same fecal indicator. 

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4. Representative Source Water Monitoring 

The GWR establishes a risk-targeted approach to identify and address ground water 

sources that are susceptible to fecal contamination. A key provision of the GWR is monitoring 

sources of ground water systems providing less than 4-log treatment of viruses to determine if 

they are fecally contaminated, as indicated by the presence of fecal indicator organisms. 

Systems that provide 4-log treatment of viruses and the related compliance monitoring 

are not subject to the triggered source water monitoring requirements of the GWR. However, 

ground water sources of systems that do not provide 4-log treatment of viruses must be 

monitored for fecal indicators if triggered by a TCR-related total coliform-positive routine 

sample in the distribution system. For triggered monitoring, a GWS must collect, within 24 

hours of notification of the total coliform-positive sample, at least one sample from each ground 

water source in use at the time the total coliform-positive routine sample was collected under the 

TCR, unless the system has approval from the State to conduct triggered source water 

monitoring at a representative ground water source or sources. 

The State may require systems with more than one ground water source to submit for 

approval a triggered source water monitoring plan that the system will use for representative 

sampling. A triggered source water monitoring plan must identify ground water sources that are 

representative of each monitoring site in the system’s TCR sample siting plan. EPA believes that 

this alternative can be as protective of public health as monitoring all wellheads, provided that 

the chosen wells are truly representative of all wellheads. In addition, for situations where a 

particular sample site is inaccessible, the State may identify an alternate sampling site that is 

representative of the water quality of the ground water at the inaccessible sample site. When 

considering representative sampling, EPA encourages water systems to consult the State or 

primacy agency early to determine if representative sampling is applicable for the system and the 

level of efforts and information that may be needed to ensure equivalent public health protection 

as monitoring all sources or wellheads. 

In addition, a GWS may be directed by the State to conduct assessment source water 

monitoring of ground water sources that are at risk for fecal contamination. The GWR allows 

representative monitoring if a State requires a system to perform assessment source water 

monitoring and gives the GWS approval to use representative monitoring. 

This chapter describes the two types of representative monitoring and presents the basic 

elements that GWSs should present to States when requesting permission to conduct 

representative monitoring. The first type of representative monitoring is based on the distribution 

system’s water flow characteristics or hydraulics and is discussed in section 4.1 and in Chapter 5. 

This is applicable to triggered source water monitoring. The second type is based on the 

systems’ sources and their physical and hydrogeologic similarity. This type of representative 

monitoring is discussed in more detail in section 4.2 and in Chapter 6, and applies to triggered 

monitoring and assessment source water monitoring. In all cases, representative source water 

monitoring must be approved by the State before it is implemented, and a written plan may be 

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required to be submitted for State approval. Section 4.3 briefly addresses these plans; example 

plans and templates are included in Appendix A and B, respectively. 

4.1 Ground Water Sources Representing Coliform Monitoring Locations in the 

Distribution System 

A system may be able to demonstrate that a given ground water source or sources do not 

supply water to a section of the distribution system in which a specific TCR routine sample site 

is located to show that it is not likely to have contributed water to the site. In such cases, the 

ground water sources would not be "representative" of that TCR monitoring site, and would not 

have been the source of the total coliform found at that site. The State has the discretion to 

determine whether to require the system to take samples at such ground water source(s) when a 

total coliform positive is encountered in the indicated section of the distribution system. 

GWSs that have hydraulically separate or distinct zones in their distribution system can 

request State approval of representative triggered monitoring based on an identification of which 

sources supply each section of the distribution system, and therefore which source(s) could 

potentially contribute water to each TCR routine sample site. If the system can demonstrate that 

the water at a TCR sampling site can only come from a subset of its sources, State-approved 

representative monitoring would limit triggered sampling to only those sources that could have 

been the source of the contamination. 

Exhibit 4.1 provides an example of a system schematic that could be used to determine 

representative sources and develop a triggered source water monitoring plan based on where in 

the distribution system the total coliform-positive sample is found. If approved by the State, the 

system could sample wells 1 and 2 after a total coliform-positive at Site 1 since Site 1 is in the 

zone served by those sources. A total coliform-positive at Site 2 would require source sampling 

from all three wells since this area is served by all sources. If approved by the State, a total 

coliform-positive at Site 3 would require source sampling only from well 3. 

Exhibit 4.1: Simplified Representative Monitoring Scenarios 

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Two additional possibilities with Exhibit 4.1 include: 1) Well 1 goes in and out of service 

to supplement Well 2 as needed; and 2) Well 1 is seasonal and is only used during the summer 

months. The GWR requires triggered monitoring at those sources “in use at the time the total 

coliform-positive sample was collected” (40 CFR 141.402(a)(2)). Thus, if Well 1 is not in use at 

the time that a total coliform positive sample is collected at Site 1, triggered monitoring would 

only be required at Well 2. 

4.2 Wells Representative of other Wells in the same Hydrogeologic Setting 

 This type of representative monitoring is based on the assumption that if multiple wells 

feed a given TCR sample site, and they are similar enough (e.g., construction, well completion, 

water chemistry, etc.) and draw from the same hydrogeologic setting, the State may allow the 

system to sample one or more wells to represent multiple wells. This type of representative 

monitoring applies to both triggered and assessment source water monitoring. 

As an example, the system shown in Exhibit 4.1 may provide information indicating that 

wells 1 and 2 are located geographically near each other, have similar well construction, and are 

drilled to the same depth and in the same aquifer to demonstrate that they are physically and 

hydrogeologically similar. In addition, the system may provide a general chemical (nonregulated constituents) screening analysis from each well demonstrating that they are also 

chemically similar. Based on these characteristics, the system may make a case to the State that 

these two wells are representative of each other, and if the State approves and if source sampling 

is triggered or assessment monitoring is required, the system would be able to use a sample at 

one well to represent both wells. 

4.3 Triggered Source Water Monitoring Plan 

The GWR does not require every GWS that proposes to conduct representative triggered 

source water monitoring to complete or submit a triggered source water monitoring plan. The 

State may require that a plan be developed and submitted for approval. However, even if the 

State does not require that the GWS prepare a plan, the GWS may wish to develop one and 

include the plan in its operations manual. A triggered source water monitoring plan helps to 

ensure that the correct source(s) is sampled without collecting unnecessary samples. The 

purpose of the triggered source water monitoring plan is for the GWS to have a step-by-step plan 

in place that identifies which sources must be sampled in response to a total coliform-positive 

sample at any given TCR site. It is important that the plan be readily available to water system 

personnel responsible for sample collection, since triggered source water samples must be 

collected within 24 hours of learning of the TCR routine sample result. A written triggered 

source water monitoring plan may be helpful to GWSs for any of the following reasons: 

•	 If a GWS is part of a network of wholesale and consecutive systems, the triggered source 

water monitoring plan would provide direction as to whom should be notified and who 

should collect fecal indicator source water samples under different total coliform-positive 

scenarios. 

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•	 If the operation of the GWS is divided so that the distribution system is operated and 

maintained by different staff than those who operate and maintain the sources and their 

related treatment. 

•	 If sample collection for the GWS is conducted by staff other than the operators (e.g., a 

commercial laboratory), a written plan would help the GWS and laboratory staff ensure 

that the proper locations are sampled. 

•	 A written, accessible sampling plan will prevent in-house communication errors and the 

chance of inadequate or inaccurate sampling. 

•	 A written plan could help assure communication among staff and delineate roles for 

conducting distribution system and source water sampling. 

A triggered source water monitoring plan should include the following minimum 

elements: 

1.	 Map or schematic of the system with sources and/or points of entry and TCR sample 

siting plan monitoring locations identified. The distribution system map or schematic 

should not contain information that poses a security risk to the system. EPA recommends 

that the schematic include either a distribution system schematic with no landmarks or 

addresses or a city map without locations of pipes indicated. 

2.	 The source type and level of treatment provided for each source/point of entry and 

whether it is seasonal, emergency, ground water, surface water, a wholesale supply, etc. 

3.	 The source(s) serving each TCR routine monitoring location and the basis for the 

determination (e.g., system hydraulics, operation, water quality data, etc.) 

4.	 Any representativeness among sources based on the physical and hydrogeological 

properties of sources and the basis for the determination (e.g., well construction, water 

chemistry, aquifer type, well log, etc.) 

5.	 For wholesale systems, the consecutive systems served and, if applicable, the sources 

serving each consecutive system. See Consecutive System Guide for the Ground Water 

Rule for more information on triggered monitoring as it relates to consecutive and 

wholesale systems. The guidance is available at: 

http://www.epa.gov/safewater/disinfection/gwr/pdfs/guide_gwr_consecutive-guidance.pdf 

6.	 Any changes or variations expected in the monitoring plan such as the use of seasonal 

sources, rotating sources, etc. 

The triggered source water monitoring plan can be a stand-alone, independent document 

or the system may incorporate it as part of its TCR sample siting plan. Incorporating it as part of 

the TCR sample siting plan may be useful because of the direct relationship that exists between 

TCR and GWR. In addition, many systems might need to create a multi-scenario monitoring 

plan to reflect the variety of ways in which their systems are operated throughout the year. For 

example, a GWS that uses a well field only during certain months to meet high demand may 

need to have one monitoring plan for those months and another monitoring plan for the others. 

However, where there is uncertainty of which wells are in use, a conservative approach should 

be used in which all potential sources are included. 

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Appendix A provides three examples of triggered source water monitoring plans for 

hypothetical systems. These examples vary in complexity and information used to justify the 

plan. Appendix B provides a blank template for the example plans used in Appendix A. This 

template is only a suggested format; each State agency may develop their own source water 

monitoring plan requirements. 

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5. Ground Water Sources Representing Coliform Monitoring Locations in the 

Distribution System 

Some ground water sources may be representative of certain coliform monitoring 

locations in the distribution system based on system hydraulics. In such cases, ground water 

source(s) are capable of providing water to specific TCR routine sample sites based on the 

hydraulics of the distribution system. Triggered monitoring requires that samples be collected 

from each ground water source following a total coliform-positive routine TCR sample unless 

the system has approval from the State to conduct triggered source water monitoring at a 

representative ground water source or sources. 

Identifying sources that could not have provided water to specific sites is a recommended 

first step in determining whether reducing the number of source water samples that must be 

collected is appropriate for the GWS. The distribution system should be analyzed from a 

hydraulic perspective. This chapter outlines step-by-step procedures and tools that can be used 

to evaluate system hydraulics and provides guidance on determining whether a source is 

hydraulically connected to a particular TCR sampling site. 

5.1 Linking Sources to TCR Sites 

System design and operational practices impact the direction and velocity of flow in the 

distribution system. The water’s hydraulic path is affected by source entry point locations, pump 

station operations, finished water storage tank locations, valve settings, elevations throughout the 

system, consumer demand, and operational settings of all tanks and pumps. Systems will 

typically be knowledgeable of their distribution system configuration and will generally have a 

good understanding of water movement in their system. However, for the purposes of 

representative sampling, it is important to definitively determine which ground water source or 

sources could provide water to each routine total coliform sample site and which sources could 

not have provided water. 

Those sources that are unlikely to have provided water to a sampling site may be 

excluded from being a representative location for triggered monitoring, if approved by the State. 

All other sources that could provide water to the coliform sample site are thereby linked to that 

site. In some instances, water flow from one zone to another is possible but generally unlikely 

during normal operating conditions. To ensure that the appropriate sources are sampled if 

monitoring is triggered, systems should eliminate only those sources that clearly cannot provide 

water to the coliform sampling site. 

This kind of knowledge is helpful in preparing a satisfactory plan. If the system does not 

understand the issues well, it should not consider a representative monitoring plan or should 

consider hiring experts to help to prepare it. Simple water systems with uncomplicated 

distribution systems will likely be straight-forward to evaluate, while those that are more 

hydraulically complicated will likely require more advanced analysis of water movement, 

especially in cases with very extensive delineation of hydraulic zones and separation of sources 

from zones. In either case, when considering representative sampling, EPA encourages water 

systems to consult the State or primacy agency early to determine if representative sampling is 

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applicable for the system and the level of efforts and information that may be needed to ensure 

equivalent public health protection as that achieved by monitoring all sources or wellheads. The 

following is a general step-by step process for linking sources to TCR routine sample collection 

sites: 

1.	 Map what is already known. Water systems should work with the State or primacy 

agency to determine the amount of effort to invest in additional studies of their 

distribution systems and sources. The various maps of system water quality, pressure 

zones, etc. that are applicable are discussed in section 5.2.1. 

2.	 Superimpose the routine sample collection sites for the TCR-related sample siting plan on 

the distribution system map. For many systems, this step will have already been 

completed as part of developing the initial sample siting plan. Coliform sample siting 

plans are discussed in section 5.2.2. 

3.	 Review operations records. Historical operations records, such as well pumping 

compared to tank levels and controls, may provide insight into water flow patterns under 

typical operating conditions. See section 5.2.3. 

4.	 Apply information from a hydraulic model, if available. The modeled results may be 

useful when gathering data to make a case for representative source water monitoring. 

See section 5.2.4 for more on hydraulic models. 

5.	 Review water quality parameter data. Distribution system water quality parameter data 

may be helpful if the system’s water sources are of differing water quality. This 

information may help to identify sources that serve specific coliform sample sites and is 

discussed in section 5.2.5. 

5.2 Tools 

Ground water systems should have a wide variety of tools available to evaluate the 

distribution system to determine which sources contribute to each TCR site. In some instances, 

States may determine that information from simply locating sources, entry points, and TCR sites 

on the distribution system map is adequate. In other cases, States may require that additional 

information from hydraulic models or tracer studies be used to confirm whether sections of the 

distribution system are hydraulically separated. 

5.2.1 Distribution System Maps 

The most critical tool available to begin analyzing how water moves in a water system 

and identifying hydraulically separated pressure zones is a distribution system map. 

Many distribution systems have distinct zones that allow water movement to be managed. 

Zones can be created and managed to maintain a constant range of pressures in a distribution 

system with different elevations. Valves, pumps, and storage facilities all provide ways for a 

distribution system to maintain different zones and, as a result, reliable water system pressure. 

Control valves, such as pressure reducing valves and gate valves, are used to regulate 

flow or pressure in a distribution system. Locations of valves and how they are operated 

influence whether water in different parts of the distribution system mixes significantly. Valves 

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that are improperly maintained and exercised may leak and not serve as reliable tools for 

isolating different zones. Valve condition, therefore, should also be considered, as should records 

of regular valve exercising and inspections. 

Pumps are often used in distribution systems to boost water to higher elevations or 

increase pressure. Another way to satisfy the need for adequate capacity and pressure is to use 

standpipes, elevated tanks, and large storage reservoirs. Knowing the locations, specifications, 

and condition of the valves, booster pumps, and storage facilities that comprise the distribution 

system is important for personnel who are trying to characterize its water movement. 

A system map may be as simple as a schematic or a street map or may be quite detailed 

and based on as-built drawings and system surveys. Any distribution system map or schematic 

that is shared outside of the water system should not contain information that poses a security 

risk to the system. EPA recommends that such schematic include either a distribution system 

schematic with no landmarks or addresses or a city map without locations of pipes indicated. 

The following locations should be indicated on the map or included with the map: 

•	 All water source entry points including any interties (i.e., interconnections) with other 

water systems. 

•	 Treatment facilities and the extent of treatment provided. 

•	 All routine total coliform sampling sites with an identifying number. 

•	 Storage tanks / reservoirs. 

•	 Pressure regulation facilities (reducing stations). 

•	 Other infrastructure that may affect pressure and/or flow in the distribution system. 

•	 Booster pump stations. 

•	 Pressure zone boundaries. 

•	 Transmission lines (the pipeline or aqueduct used for water transmission of water from 

the source to the treatment plant and from the plant to the distribution system [AWWA, 

2003]). 

•	 Critical valves (those valves whose function is vital to the successful operation of the 

system or whose failure can lead to serious consequences [Dorf, 2005]). 

The system map should reflect operational changes that have altered the hydraulic zones 

linked to each TCR site. It may be helpful to prepare a summary table listing each source and 

the pressure zone(s) it serves. 

Exhibit 5.1 illustrates a simple multi-pressure zone distribution system map. Assume that 

all pressure zones are hydraulically separated as demonstrated by evidence presented by the 

system (e.g., significant differences of elevations among pressure zones, presence of closed 

valves among zones, other supporting data, etc.) and source sampling has been triggered by a 

total coliform positive result in Zone 1. Representative monitoring based on system hydraulics 

could specify that only the wells in Zone 1 must be sampled (because wells in Zones 2 and 3 do 

not contribute to Zone 1 and are therefore not representative of Zone 1). 

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Chapter 6 explains how the case for representative monitoring can be further developed 

to include wells representative of other wells within the same hydrogeologic setting. For 

example, consider a system that is required by the State to develop a triggered source water 

monitoring plan to qualify for representative source water monitoring. If the system presents 

supporting information, and the State agrees, that two or more of the wells in pressure Zone 1 are 

representative of each other, then the triggered source water monitoring plan could specify that 

fewer than all 4 wells would need to be sampled. In this case, the water quality of the sampled 

wells would be representative of that of the unsampled wells. However, if the wells in pressure 

Zone 1 are not shown to be similar enough based on their physical and hydrogeological 

properties then all of the wells in pressure Zone 1 would need to be sampled. 

Exhibit 5.1: Example Distribution System Map 

5.2.2 Coliform Sample Siting Plan 

Each ground water system should have a coliform sample siting plan as required by 40 

CFR 141.21(a). The purpose of this sample siting plan is to identify sites throughout the 

distribution system that are representative of the water quality of the entire distribution system. 

An analysis of which sources feed each section of the distribution system may have been 

completed in developing the coliform sample siting plan since it is necessary to identify 

sampling sites that are hydraulically upstream and downstream from the routine total coliform 

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monitoring sites. If available, this analysis could be useful during the development of the 

triggered source water monitoring plan. 

The coliform sample siting plan typically includes a map and an address list of routine, 

upstream, and downstream sample sites with descriptions of tap locations. Example information 

is listed in Exhibit 5.2. 

Exhibit 5.2: Total Coliform Sample Site Locations 

Primary Location Upstream Location Downstream 

Location 

Site ID Name Tap location Name Name 

1H-1 FH #9, 

1617 U St. NW 

Bathroom in 

Officer's room 

V Best Supermarket 

1507 U St NW 

Keren Restaurant 

1780 Florida Ave NW 

1H-18 Bread for the City, 

1525 7th St. NW 

Hose bib Dollar Plus Savings 

Store 

1541 7th St. NW 

Kennedy Recreation 

Center 

1401 7th St. NW 

1H-2 FH #16, 

1018 13th St. NW 

Bathroom sink Stoney's Beef and 

Beer 1307 L St NW 

Roy Rogers 

1275 K St NW 

1H-3 FH #1, 

2225 M St. NW 

Kitchen sink Federal Market 1215 

23rd St NW 

Medical Society of 

DC 2215 M St NW 

5.2.3 Operating Conditions and Operations Records 

Another resource may be historical operations records such as tank levels and pumping 

data and interviews with system operators. For example, a review of well pump status (whether 

the well pump is operating) and tank level data (whether the tank is filling) for the same time 

period can indicate which area is served by each well, after taking consumer demand into 

consideration. System operators generally have an understanding of which sources serve which 

parts of the distribution system based on their experience with pump controls and related 

telemetry. System operators should use available records and/or observations to support this 

understanding. When operations records and operator experience indicate that the areas served 

by ground water sources are not clearly delineated, additional information is likely required to 

determine whether hydraulically representative monitoring is feasible. 

In situations where sources go in and out of service or where other operating conditions 

regularly change, systems should discuss with the State the appropriateness of having different 

representative monitoring plans under different operating conditions, what measurable criteria 

should be included to define when the conditions change and new representative sources apply, 

and how many variations might be acceptable. 

5.2.4 Distribution System Hydraulic Models 

Hydraulic modeling can be used to determine the flow path from one point to another in a 

distribution system. For example, it can be used to determine the upstream hydraulic path from 

the routine total coliform sampling site to the source(s) of supply. In order to give accurate 

results, the hydraulic model should meet these criteria (Martel et al. 2005): 

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•	 The model is calibrated. 

•	 Demand patterns are accurately detailed. 

•	 The model is regularly updated to reflect changes in the hydraulic configuration of the 

system. 

•	 The model provides more than a “skeleton” view of the distribution system. 

Some utilities have used hydraulic models to meet the requirements of the Stage 2 

Disinfection Byproducts Rule (Stage 2 DBPR) Initial Distribution System Evaluation. In this 

evaluation, the hydraulic model estimates water age throughout the distribution system. Systems 

may be able to utilize the work completed for Stage 2 DBPR to confirm which source or sources 

contribute to a routine total coliform sampling site. 

Hydraulic modeling may not be available to most small groundwater systems, but it may 

not be necessary for some ground water systems with simple distribution systems. However, the 

benefits of using a hydraulic model in order to justify representative monitoring may be clearer 

to other systems such as very complex systems with numerous pressure zones. 

5.2.5 Distribution System Tracer Studies 

A tracer study may help a system to better understand the paths and destinations that 

water takes from a source to various points throughout the system and the proportion of that 

water taking a particular path. These studies involve adding a chemical such as fluoride to the 

distribution system at one point, and measuring the chemical concentration at 

downstream points to estimate the travel time between the two points. After the tracer is added, 

the operator should sample in the distribution system to determine how levels of the tracer 

appear and then diminish over time, providing an indication of the water’s age and the area 

served by the source. If the system already adds fluoride to the water, it is possible for the tracer 

study to be conducted by stopping the fluoride feed in one source at a time and measuring the 

decreasing fluoride concentration at downstream points. 

For the purposes of a triggered source water monitoring plan, one recommended 

approach is to add the tracer at one source and not at others, with monitoring throughout the 

distribution system to identify areas where the tracer appears. Tracer studies should be done with 

some care, however, to consider consumer demand, finished water storage influences, and other 

source water pumping, so that a valid assessment of the area served by the investigated source 

can be made with confidence. Systems considering a tracer study should contact their State prior 

to beginning the study and the tracer used should be approved for use in potable water supplies. 

5.2.6 Customer Complaint Records 

Customer complaints records sometimes function as a sentinel for water utility personnel. 

These records can reveal water quality issues overlooked by sampling and other barriers that are 

in place to protect public health. The TCR white papers (available at 

http://www.epa.gov/OGWDW/disinfection/tcr/regulation_revisions.html) include several 

examples in which water quality issues correlate with customer complaints. Customer 

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complaints may supplement other tools mentioned above to help the States or primacy agency to 

determine if representative monitoring sampling is appropriate for a system. For instance, if the 

utility is receiving the same types of customer complaints from two areas, this may be an 

indication that the areas may be connected or are receiving water from the same source. In this 

case, the system should utilize other tools to investigate the problem and confirm whether the 

areas are actually hydraulically linked. 

Customer complaint records may also be helpful in identifying areas in which different 

sources are mixing. If the distribution system is fed by multiple sources with varying water 

quality, the release of biofilms, scales, or sediments may occur where different sources blend. 

For example, the City of Tulsa, Oklahoma, found that the majority of positive coliform samples 

that were detected over a two-year period occurred at the interface between two treated waters in 

the distribution system (Kirmeyer et al. 2000). Customers in this area of blended water 

complained of red or brownish water that may have been caused by loosening or dissolution of 

scale material due to changing water quality. In such areas where mixing occurs, water is 

coming from more than one source. This should be considered when determining which wells to 

sample when triggered source water monitoring is required. 

5.2.7 Water Quality Parameters 

Water quality varies with each source of supply. The source water may or may not 

contain dissolved minerals, dissolved gases, organic matter, or combinations of these 

constituents that can be used to distinguish one source from another, or to link the source to a 

particular routine total coliform sample site. For example, ground water from wells tends to 

contain more dissolved minerals than either lake or river water since the groundwater seeps 

through minerals in the earth. 

If available, the following water quality parameters may be used to help to characterize a 

ground water source and link it to coliform sites if the same parameters are also monitored at the 

sample collection sites: 

• Total hardness as calcium carbonate 

• Alkalinity as calcium carbonate 

• Conductivity 

• Chlorides 

• Fluoride 

• Nitrates 

• Phosphate 

• Sulfate 

• pH 

• Total dissolved solids 

• Aesthetic quality of water (e.g., taste, color, or odor) 

• Water temperature 

If the system is unsure whether a source feeds a certain area of the distribution system, 

and they have a well or well field with water quality characteristics that are unique to that site, 

they may conduct monitoring in the distribution system to determine where in the distribution 

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system those same characteristics are found. For instance, if a system has one set of wells with 

relatively high sulfate levels and the other sources have low levels, sulfate sampling in the 

distribution system may help clarify whether that source contributes water to that part of the 

distribution system. 

5.3 Considerations While Preparing a Plan 

This section discusses considerations that may be useful when developing a triggered 

source water monitoring plan. As discussed previously, the State may require systems with more 

than one ground water source to submit for approval a triggered source water monitoring plan 

that the system will use for representative sampling. If a plan is not required, the system may 

still wish to consider the same criteria described here in determining whether representative 

monitoring is appropriate. In either case, EPA encourages water systems to consult the State or 

primacy agency early to determine if representative sampling is applicable for the system and the 

level of effort and information that may be needed to ensure equivalent public health protection 

as that achieved by monitoring all sources or wellheads. 

Once the system has pulled together the tools available to help determine which sources 

feed each routine total coliform sampling site, the next step is to begin to prepare the triggered 

source water monitoring plan. The system should start by reviewing the system map to identify 

any areas of the distribution system that are clearly and defensibly hydraulically separated. 

The plan should include a distribution system map that identifies all sources, critical 

infrastructure such as tanks and pump stations, delineation of pressure zones, identification of 

system elevations, and all routine total coliform sampling sites. The plan should also provide a 

discussion of how the link from each source to each site was determined. 

When determining which sources do not require sampling after a total coliform-positive 

sample, the system should take a conservative approach. For example, sources should only be 

excluded if there is very little or no likelihood that water from that well can contribute to the mix 

of water at the sample location. 

The example in Exhibit 5.3 provides a simple schematic of a distribution system along 

with a table identifying each routine total coliform sampling site and identifying sources that can 

supply water to each site. In this example, the South Pressure Zone is at a lower elevation than 

both the West Pressure Zone and the North Pressure Zone, and the West Pressure Zone is at a 

lower elevation than the North Pressure Zone. Using their understanding of hydraulics, the 

operators reasoned that water flows from the North Pressure Zone to both the West and South 

Pressure Zones and that water flows from the West Pressure Zone to the South Pressure Zone. 

This assertion can be further supported by conducting tracer studies. The case for hydraulic 

separation is strengthened if (1) a tracer is introduced into the South Pressure Zone, and it is not 

detected in either the West Pressure Zone or the North Pressure Zone and (2) a tracer is 

introduced into the West Pressure Zone, and it is not detected in the North Pressure Zone. 

The next section of this manual will build on this example by discussing criteria for 

identifying whether wells are representative of each other based on physical and hydrogeological 

properties. 

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Exhibit 5.3: Example Triggered Source Water Map and Table 

TCR Site Pressure Zone Contributing Wells 

1 South South Ave Well 1 

South Ave Well 2 

Diehl Drive Well 

Main Well 1 

Main Well 2 

Main Well 3 

West Side Well 

2 North Central Main Well 1 

Main Well 2 

Main Well 3 

3 West Side Main Well 1 

Main Well 2 

Main Well 3 

West Side Well 

4 West Side Main Well 1 

Main Well 2 

Main Well 3 

West Side Well 

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Water Monitoring Guidance Manual 
References 

AWWA. 2003. Water Transmission and Distribution (Water Supply Operations Training), 3rd 

Edition. American Water Works Association. 

Dorf, Richard C. 2005. The Engineering Handbook. Boca Raton, Florida. CRC Press. 

Iowa Department of Natural Resources. Groundwater Basics Occurrence, Movement, and 

Quality. Available at: 

http://www.igsb.uiowa.edu/GWBASICS/Chapters/Groundwater%20Basics%20Occur 

rence%20Movement%20and%20Quality.pdf 

Kirmeyer, G., M. Friedman, J. Clement, A. Sandvig, P. Noran, K. Martel, D. Smith, M. 

LeChevallier, C. Volk, E. Antoun, D. Hiltebrand, J. Dyksen, and R. Cushing. 2000. 

Guidance Manual for Maintaining Distribution System Water Quality: CD-ROM. 

AWWA Research Foundation. Denver, CO. 

Martel et al. 2005. Data Integration for Water Quality Management. Denver, Colo.: AwwaRF. 

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6. Wells Representative of Other Wells in the Same Hydrogeologic Setting 

A public water system may request that one or more wells be considered representative of 

multiple wells’ risk for fecal contamination based on physical and hydrogeological evidence. If 

approved by the State, the system may not need to sample all of the wells that serve a TCR site 

when triggered source water monitoring is required. This representativeness based on physical 

and hydrogeological properties may also reduce the source water monitoring burden that applies 

to assessment source water monitoring directed by the State. When considering representative 

sampling, EPA encourages water systems to consult the State or primacy agency early to 

determine if representative sampling is applicable for the system and the level of effort and 

information that may be needed to ensure equivalent public health protection as that achieved by 

monitoring all sources or wellheads. 

Wells that are determined to be representative of each other based on physical and 

hydrogeological properties should have similar well construction, draw water from the same 

hydrogeological setting, and have the same vulnerability to fecal contamination. It is important 

to emphasize that even wells that appear nearly identical in location, construction, and water 

chemistry (their physical representativeness), and that tap the same aquifer (their 

hydrogeological representativeness), may have different vulnerabilities to fecal contamination 

based on their distance to source(s) of fecal contaminants and the wells’ recharge zones. Any 

one of these items may provide information that indicates wells under evaluation are not 

representative of each other. The State or primacy agency may determine that wells are not 

representative of each other based on any one of these criteria. This chapter discusses the 

information that systems could use to determine whether wells are representative of other wells, 

and presents a decision-making approach that removes from further consideration sources that do 

not meet any one of these suggested criteria. 

Total coliform monitoring data and heterotrophic plate count bacteria (HPC) data are not 

included as information useful to decision makers of representative monitoring programs since 

an absence of these microbes is generally expected for ground water sources. Wells with a 

history of total coliform organisms or elevated HPC levels should be monitored for fecal 

indicator organisms. In addition, an absence of total coliforms should not be interpreted to mean 

a fecal indicator would also be absent. A viral pathogen may be present even though bacterial 

indicators are not detected. 

6.1 Physical Properties 

To begin to inform whether wells have the same risk for fecal contamination, physical 

properties of the wells should be evaluated. Physical similarities described in this chapter 

address the proximity of the wells, their construction, and the water chemistry of the wells. 

6.1.1 Well Proximity to other Wells 

Because fecal contamination in an aquifer can be localized, a relatively easy aspect for a 

system to consider would be the physical proximity of the wells. Although any representative 

scheme will be at the discretion of the State and based on the professional judgment of State and 

system personnel, a general rule of thumb is that the farther the geographical/physical distance 

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between two sources, the less likely that one source can represent the fecal contamination risk or 

water quality at the other. The consideration of well separation distances are system and sourcespecific. 

Some systems may have supply wells located intermittently throughout a community. 

Wells spaced intermittently throughout a community are unlikely to be good candidates for 

representative sampling if there are great distances between them. The assumption that wells 

that are relatively distant from one another are not representative of one another may generally 

be true for shallow wells or hard rock wells common in the Eastern U.S. However, this may not 

be true for the large, deep wells commonly found in the Western U.S. 

Systems having well fields or clusters of wells are likely to have wells located relatively 

close to one another. These wells may be excellent candidates for representative sampling if 

they are able to meet the other physical and hydrogeological criteria. 

6.1.2 Well Construction 

Well construction information is vital to the process of designating representative wells. 

Well construction refers to many aspects including the drilling method, depth of the well, 

grouting depth, the screened interval, and the condition of the sanitary well seal. Cracks in well 

casings, failure of a subterranean vent or other construction problem may occur in one well and 

not others and not be observed from the ground surface. Therefore, determining that a particular 

well is representative of other wells should reflect an understanding of well construction or 

condition. Differences in these physical characteristics of a well would render some wells more 

susceptible to contamination than others, particularly if contaminants could enter the well 

through means other than via the aquifer. Poorly constructed wells have higher probability or 

risk to contaminate. For example, surface runoff may enter the well down the casing of a poorly 

constructed well. Representative sampling would be inappropriate for wells with different 

construction. 

Drillers’ logs provide important information not only on the location of the well, geologic 

descriptions that aid in determining the aquifer type from which the well draws water, and the 

depths of screened intervals, but also information on the casing and grouting, which can help 

States and systems evaluate well integrity. If drillers’ logs are not available for each of the wells, 

it will be difficult for primacy agencies to approve representative sampling for those wells. 

The importance of considering information from drillers’ logs on the depths of screened 

intervals is demonstrated in Exhibits 6.1 and 6.2, below, which show a cluster of three wells at 

an airport that are very close to each other at the surface. In Exhibit 6.1, the wells are likely to be 

good candidates for representative sampling because the wells are similarly constructed and 

screened at the same depth. Drillers’ logs would be the primary way of identifying the problem 

in Exhibit 6.2, where although the wells are close at the surface, they are drawing water from 

different depths in the aquifer, and, in the case of one well, from a different aquifer altogether. 

Such wells would not be good candidates for representative sampling. 

 States may require information in addition to well location, construction, and drillers’ 

logs to approve representative sampling. 

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Exhibit 6.1: Potentially Good Candidates for Representative Sampling 

Exhibit 6.2: Inappropriate Candidates for Representative Sampling 

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6.1.3 Water Chemistry 

Source water chemistry data can be an excellent tool in providing evidence that two or 

more wells are or are not representative of each other. Water chemistry comparisons may be as 

simple as evaluating basic chemical screens that capture total dissolved solids, hardness, and 

sodium, or may include more elaborate monitoring data information. Wells located close to each 

other, even those that are screened at the same depths, but that have significantly different source 

water chemistries, may be drawing water from different subsurface sources, given that 

subsurface hydrogeology may be very complex. 

For example, in fractured bedrock, one of the most complex of subsurface environments, 

two subsurface fractures that are very close to each other (even only feet or inches away from 

each other) may be hydraulically disconnected, with each fracture containing water from one of 

two near-surface sources that are very far apart (see Exhibit 5.3). In this case, two wells that are 

near to each other and screened at the same depth (but, unbeknownst to the system, drawing 

water from the two hydraulically disparate fractures), could have remarkably different source 

water chemistries and vulnerability to fecal contamination, and thus could not be considered 

representative of each other. 

Exhibit 6.3: Wells in Close Proximity Not Representative Due to Fractured 

Bedrock 

Three particular types of source water chemistry data are discussed below. A State or 

system may have one, all, or some of these indicators on which to base a decision about 

representativeness. Additional types of source water chemistry data may be available to assist in 

determining if wells are representative of each other. Significant differences in TDS or nitrate 

levels among wells suggest that wells are not representative of each other. The State may 

determine that because all wells have certain levels and types of TDS or nitrates (whether those 

levels are similar or dissimilar among wells) that all wells should be sampled under the triggered 

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source water monitoring requirement of GWR because the State may determine that the TDS and 

nitrates in the wells are tied to pathways or potential sources of fecal contamination. 

Because considering multiple chemical indicators (as opposed to one) provides a greater 

degree of confidence regarding a decision about wells being representative of each other, States 

may require additional information during the approval process. 

6.1.3.1 Total Dissolved Solids 

Total Dissolved Solids (TDS) is a measure of the amount of solid material that has been 

dissolved in water. TDS can include carbonate, bicarbonate, chloride, sulfate, phosphate, nitrate, 

calcium, magnesium, sodium, organic ions, and other ions. 

Sources of TDS in ground water include the solid material of the aquifer itself and nonpoint source pollutants such as road salt, lawn fertilizer, and septic system effluent. Much of the 

TDS found in ground water samples may also be used to indicate proximity to a surface water 

source. This may be important if fecal contamination in the surface water could reach the 

ground water source. 

Wells with significantly dissimilar TDS contents should not be treated as representative 

of each other. However, caution should be applied in using similar TDS data to determine 

whether wells are representative of each other. Water samples with similar TDS values may in 

some cases have different major ion contents that happen to add up to similar TDS values (in 

which case the wells from which the samples were taken would not be representative of each 

other). 

6.1.3.2 Nitrates and Ammonia 

Because excessive levels of nitrate in drinking water have caused serious illness and 

sometimes death, it is a regulated contaminant for all public water systems and is commonly 

monitored at the source water entry point to the distribution system. Nitrate is also fairly easy to 

test for. Thus, nitrate data may be one piece of evidence in an investigation of whether two or 

more wells should be considered representative of one another, particularly if wells have 

comparable and low levels of nitrate. 

Nitrate is derived from nitrogen, which is present in fertilizers and animal manure. 

Airborne nitrogen compounds from automobile and industrial emissions can also contribute to 

nitrate in ground water. (In general, nitrogen is converted to nitrate in natural waters.) In 

residential areas, lawn fertilizers, septic systems, and pets are common sources of nitrates, 

whereas in agricultural areas nitrates are even more common due to frequent application of 

fertilizers. Nitrates generally persist in ground water for decades (USGS, 1988). 

In many rural areas in the U.S. in which wastewater is treated through individual on-site 

septic systems, elevated nitrate levels can be used as an indicator of possible wastewater 

influence. If two or more wells have elevated levels of nitrate, this may be an indication that 

wastewater has contaminated the aquifer and pathogens may be present. Because pathogens tend 

to be less uniformly distributed in an aquifer than nitrates, elevated nitrates in two or more wells 

is not a good reason to consider the wells representative of each other. Thus, except in those 

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cases where fertilizer or other background concentrations of nitrate are the cause of the elevated 

concentrations in samples, elevated nitrates in samples from wells indicates a need for more 

sampling of the aquifer, not less. In summary, if the source of the nitrate is wastewater or animal 

manure, it would not be prudent to rely on representative monitoring to eliminate one or more of 

the high nitrate wells from sampling for fecal indicators. 

Comparisons of ammonia data between two wells may be a better indicator of whether 

the wells are representative of one another than comparisons of total nitrate concentrations. This 

is because ammonia converts to nitrate after a short time, so the presence of ammonia indicates a 

recent influx of ammonia. Nitrates, being longer-lived and also attributable to a variety of 

sources, are commonly found in many wells. Thus, when available, ammonia data is preferred to 

nitrate data for determining representativeness. Information on typical nitrate levels for the 

aquifer may not be readily available to the operator. The system should consult with the State 

drinking water office, State geologist, or local USGS office for more information and possible 

assistance with interpreting results. 

6.1.3.3 Hardness and Alkalinity 

Ground water samples from wells being considered for representative sampling can be 

analyzed for parameters such as hardness, alkalinity, major cations, and major anions. As 

discussed above, additional source water chemistry data provide a greater degree of confidence 

regarding a decision about representative source water sampling. Hardness and alkalinity are 

both commonly (and easily) measured when characterizing water chemistry and can provide 

additional evidence when evaluating samples for similar chemistry. Hardness indicates the 

mineral content of the water and is determined primarily by the concentrations of calcium and 

magnesium ions. It is expressed in terms of mg/L of calcium carbonate. Groundwater that has 

flowed through limestone commonly has high concentrations of these ions, and thus is very hard 

(Freeze and Cherry, 1979). Alkalinity is calculated as the sum of the bases in water and provides 

an indication of the ability of the water to buffer acidity. In most natural waters, alkalinity is 

approximated by the sum of the concentrations of bicarbonate (HCO3

-

) and carbonate (CO3

2-) 

ions (Drever, 1988). These constituents are represented on both Piper and Stiff diagrams. 

Piper diagrams (Piper, 1944) and the Stiff diagrams (Stiff, 1951) are graphical methods 

for displaying the chemical composition of water samples. Multiple samples can be plotted on 

each type of diagram, allowing for quick visual comparison of water chemistry from different 

sources. As such, Piper and Stiff diagrams are useful tools for evaluating the degree of similarity 

among water samples. Samples from wells being considered for representative sampling should 

have very similar results when ion concentrations are plotted on the Piper and Stiff diagrams. 

The Piper diagram is the most widely used graphical method of representing the relative 

proportions of the major ionic species (Güler, et al., 2002). The diagram consists of two ternary 

plots, one for the major cations (with Ca2+, Mg2+, and Na+ + K+

 on the axes) and one for the 

major anions (with HCO3

-

+ CO3

2-, SO42-, and Cl- on the axes). The points from the two ternary 

diagrams are then projected onto a third, diamond-shaped plot, which displays the overall 

chemical character of the sample. Samples with similar chemical compositions will result in 

points that are clustered together on the final diagram. The Stiff diagram also displays 

concentrations of the major ionic species, but the values are displayed along a horizontal axis. 

Concentrations of the major cations are plotted on the left side of the axis, and concentrations of 

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the major anions are plotted on the right side of the axis. Pairs of ions or ion groups are plotted 

opposite each other (i.e. Na+ + K+

 vs. Cl-, Ca2+ vs. HCO3

-

+ CO3

2-, and Mg2+ vs. SO42-) and the 

points are connected to create a polygon. Samples with similar chemical compositions will 

result in similarly-shaped polygons. Figure 1 from Hands-on laboratory exercises for an 

undergraduate hydrogeology course (Lee, 1998) provides an example Piper and Stiff diagram. 

6.2 Hydrogeological Representativeness 

The following sections discuss desktop sources and types of hydrogeologic information 

that is available for helping to make decisions on the representativeness of wells. These sources 

can provide information on aquifer type as well as confining layer information. Other factors, 

such as heterogeneity and anisotropy (directional dependence) of the aquifer from which the well 

produces water, may affect the capture zones of individual wells such that wells within a well 

cluster are not very representative of one another. Thus, it is important to use a weight-ofevidence approach to determining which wells are good candidates for representative sampling. 

States and systems should make use of all available data, including well location, depth 

of the screened intervals, well construction, aquifer properties, water chemistry data, etc. The 

additional information on more complex hydrogeological analyses provided in section 6.2.2 may 

not be useful or necessary for most systems but is provided here to accommodate those that will 

find it beneficial. 

6.2.1 Aquifer Type and Driller’s Logs 

Data on aquifer type can be useful when determining if two or more wells can be 

considered representative of one another. States should consider the information along with the 

hydrogeology of the site as a whole, including the type of confining layer overlying the aquifer 

in question. 

For example, two wells screened in a karst aquifer overlain by a continuous confining 

layer (Exhibit 6.4) are more likely to be representative of each other than two wells screened in a 

karst aquifer overlain by a discontinuous confining layer (Exhibit 6.5). This is the case even if in 

both scenarios the two wells are fairly close to each other, both in horizontal distance and in the 

vertical separation of the screened interval of each well. This is because the discontinuous 

confining layer may not be providing the same level of protection to all wells because it is 

discontinuous. A continuous barrier protects all wells equally while a discontinuous layer may 

allow contamination to enter one well more easily than another. 

When wells draw water from fractured bedrock aquifers, it is difficult to determine the 

direction of ground water flow and vulnerability to sources of contamination. It is also very 

likely that nearby wells (both drawing from fractured bedrock aquifers) are producing water of 

markedly different quality, or at least markedly different vulnerability to contamination. Thus, 

wells in fractured bedrock aquifers are among the worst candidates for representative sampling, 

and only in rare cases where systems have fairly detailed knowledge of subsurface conditions 

should representative sampling be considered in fractured bedrock aquifers. Operators who need 

assistance should consult with the State drinking water office, State geologist, or the local USGS 

office for possible assistance with interpreting results. 

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Exhibit 6.4: Wells Screened in a Karst Aquifer Overlain by a Continuous Layer 

Exhibit 6.5: Wells Screened in a Karst Aquifer Overlain by a Discontinuous Layer 

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Drillers’ logs are often a good way of identifying aquifer type. A driller’s log typically 

records changes in lithology with depth, although local terminology may be used and may need 

deciphering. For example, in much of the United States the term “artesian well” is used by 

drillers as a lay term to indicate a producing bedrock well. This contrasts with the 

hydrogeologist’s definition - a confined aquifer where the water in a well rises above the top of 

the aquifer, sometimes flowing to the land surface. Another example is the use of the term 

“hardpan” by drillers to describe what may be a dense glacial till, a cemented soil, or a hard clay. 

A driller’s log may also include information on the drilling method employed, which may give 

clues to the type of materials the drillers encountered. 

6.2.2 Additional Data 

This section discusses in detail a wide spectrum of data that States and systems may 

consider useful. Some information may not be readily available to systems. Before expending 

significant resources to gather additional data, systems should consult with the State or primacy 

agency and consider the trade-offs for investing so heavily in a pursuit of representative 

monitoring because they may not need to conduct significant amounts of triggered monitoring. 

On the other hand, some systems may have one or more of these helpful pieces of information 

available that can aid them with their representative monitoring analysis and justification. 

6.2.2.1 Hydrogeologic Data Sources 

A number of EPA publications provide detailed discussions of hydrogeologic data 

sources. An EPA workgroup was convened in 1993 to develop a guidance document on ground 

water resource assessment. The guidance describes sources of hydrogeologic data and how this 

data may be used to evaluate aquifer sensitivity (USEPA 1993a). EPA also published the 

Ground Water Information Systems Roadmap, A Directory of EPA Systems Containing Ground 

Water Data (USEPA 1994a). Another reference that summarizes hydrogeologic data sources is 

an EPA Handbook entitled Ground Water and Wellhead Protection (USEPA 1994b). 

State and Federal Hydrogeologic Investigations 

These data sources are electronic or hard copy reports or data produced through previous 

desktop analyses or field investigations. Such information may have been generated to meet the 

requirements of Source Water Assessment Plans (SWAPs), or through water quality or water 

supply investigations initiated at the local, State, or federal level. Existing data for a given PWS 

well may be used. For example, if an existing report or appropriate scale map indicates whether 

two wells are screened in a particular aquifer, then that information can be used to help 

determine if the wells should be considered representative of each other. Generally, spatial data 

at the scale of 1:100,000 or larger (e.g., 1:24,000) are sufficiently detailed for most purposes 

[Note: large scale maps provide detailed information of small geographic areas.] 

Wellhead Protection and Source Water Assessment Studies 

The Safe Drinking Water Act (SDWA), as amended in 1986, created the Wellhead 

Protection Program (WHPP). Each State is required to adopt a program to protect wellhead 

areas within its jurisdiction from contaminants that may have adverse health effects and to 

submit the program plan to the EPA Administrator. Currently, 49 States and two territories have 

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WHPPs in place. In their WHPPs, States address all program elements including how to 

delineate wellhead protection areas (WHPAs) and how to identify and inventory all potential 

sources of contamination. 

Section 1453 of the 1996 SDWA Amendments required all States to establish SWAPs 

and to submit plans to EPA for approval by February 6, 1999. These SWAPs address both 

surface water and ground water protection, and their SWAP plans detail how States will: (1) 

delineate source water protection areas; (2) inventory significant contaminants in these areas; and 

(3) determine the susceptibility of each public water supply to contamination. States may use 

any available information to carry out the SWAP, including data generated through the WHPP. 

After plan approval, the States must have completed susceptibility determinations for all PWSs 

by November 6, 2001, unless the State was granted an 18-month extension until May 6, 2003. 

EPA encourages States and systems to build upon previous SWAP or WHPP efforts to 

help determine if two or more wells are representative of one another. A review of selected, 

approved State SWAP plans across EPA regions indicates that many States intend to evaluate 

hydrogeologic information that may enable them to determine a PWS well’s aquifer type. Data 

in approved SWAP plans may include the aquifer types in which PWS plans are screened as well 

as information on the continuity of confining layers (e.g., WIDNR 1999). Other approaches to 

fulfilling SWAP requirements are also likely to result in data that will be useful for determining 

representativeness of wells. Case studies # 2 and # 4, presented in sections 3.2.2 and 3.3.2, 

respectively, of the Ground Water Rule Source Assessment Guidance Manual, illustrate just two 

ways in which data can be extracted from SWAP investigations. This guidance manual is 

available at 

http://www.epa.gov/safewater/disinfection/gwr/pdfs/guide_gwr_sourcewaterassessments.pdf 

State Geologic Survey, USGS, and Other Hydrogeologic Investigations 

Many State geologic surveys or agencies of natural resources have significant experience 

studying local and regional aquifer systems and investigating ground water quality and quantity 

issues. Although many of these studies may have directly supported, or continue to support, 

SWAP or WHPP work, many more studies have been conducted independent of these efforts. In 

addition to State geologic surveys, the United States Geological Survey (USGS) has district 

offices that perform similar work in each State, sometimes in cooperation with State agencies. 

Universities, local governments, and non-governmental organizations also conduct pertinent 

hydrogeologic research. 

Hydrogeologic and Geologic Maps 

Hydrogeologic or aquifer maps generally show the location, spatial extent, and depth of 

aquifers in a region. Such maps typically include information on aquifer type as well. 

Hydrogeologic maps will often be the most direct means to evaluating aquifer type and presence 

of continuity of confining layers. 

Geologic maps may depict a region’s surficial geology, which would include the 

locations and extent of distinct unconsolidated deposits and bedrock units exposed at the earth’s 

surface, or, alternatively, the bedrock geology of an area. Surficial geologic maps are available 

for many areas from the USGS and often include a key to interpret the results of various test 

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holes shown on the map. Using geologic maps is a less direct means to identifying aquifer type 

than using hydrogeologic maps, but by using analytical techniques such as projection (described 

below) and using information such as well depth, these data can help determine aquifer type. 

The availability of hydrogeologic maps at an appropriate scale varies among States and 

among regions. The following sources may be useful to States and systems in obtaining 

appropriate maps for use in determining representativeness of wells. As part of its Regional 

Aquifer-System Analysis (RASA) program, the USGS produced a large variety of hydrogeologic 

maps at various scales. Some of these maps are at scales that may be useful for determining 

representativeness. The RASA program completed studies of 25 major U.S. aquifer systems in 

1995. The Ground Water Atlas of the United States was developed as part of the RASA 

program, and provides small-scale (i.e., less detailed coverage of large geographic areas) 

hydrogeologic data for the country both as a printed atlas and as a digital dataset (available on 

the Internet (accessed 6/30/08) at: http://pubs.usgs.gov/ha/ha730/). The printed atlas has 13 

individual chapters that cover specific U.S. regions. The Ground Water Atlas data, however, are 

compiled at scales that may not be suitable for evaluating representativeness of wells at PWSs 

(e.g., at the relatively small 1:5,000,000 and 1:2,500,000 scales). 

In areas where hydrogeologic maps are not available, it is possible to use a geologic map 

along with the projection method to determine the aquifer type for a well of a given depth. 

Projection is a structural geologic technique which can be used to determine aquifer depth, or the 

depth of any local geologic unit at a well, using the strike and dip of the aquifer as measured at 

nearby outcrops. Typically, bedding (layering) can be described in terms of its strike and dip. 

Bedding also occurs but may be indistinct in some sedimentary rocks, in metamorphic rocks 

called metasediments, and in some igneous rocks such as volcanic flows (e.g., basalts). Outcrop 

mapping of the bedrock is shown on many geologic maps with the values of the strike and dip of 

the bedding. The strike is the compass direction or azimuth of the line formed by the intersection 

of the bed with its horizontal (planar) surface. The dip is the angle in degrees between the 

bedding and a horizontal surface, measured at right angle to the strike (see Exhibit 6.6). If the 

bedrock is a known aquifer, the depth to that aquifer can be determined by projecting the dip 

over the distance to the well location. Using simple trigonometry, the depth to the aquifer is then 

equal to the tangent of the angle multiplied by the distance. This method can be used in areas of 

simple geology. 

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Exhibit 6.6: Strike and Dip 

More detailed hydrogeologic and geologic maps are available from a variety of public 

and private entities. The USGS, as well as State geologic surveys or natural resources agencies, 

are the most prolific sources. However, coverage is highly variable from State to State. The 

National Research Council (NRC) estimated in 1988 that less than 20 percent of the United 

States has been geologically mapped at a scale of 1:24,000 or larger (NRC 1993). In response to 

this situation, Congress enacted the National Geologic Mapping Act of 1992. This act 

established the National Cooperative Geologic Mapping Program (NCGMP) to implement 

expanded geologic mapping efforts through a consortium of geologic mappers. As part of this 

program, the USGS conducts federal mapping projects through its FEDMAP program; 

STATEMAP, run by State geological surveys, is a matching-funds grant program; and 

universities participate in another matching-funds program - EDMAP. The USGS coordinates 

the NCGMP, which has a long term goal of producing 1:24,000 scale geologic maps for high 

priority areas of the States, and national coverage at the 1:100,000 scale. 

The NCGMP also maintains an exceptionally useful database for locating existing 

geologic maps produced by a wide variety of entities. The database includes mapping currently 

in progress through the consortium and is searchable by location, scale, and other parameters. 

The database, as well as general information on the program, is available on the Internet at 

http://ngmdb.usgs.gov/. A geologic map index is also available for many States showing 

boundaries for compiled map projects and references. 

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Topographic Data 

Well coordinates, depth to the screened interval of a well, and topographic maps 

(described below) can be used to determine whether particular wells are drawing water from a 

given aquifer. Imprecise plotting of a well’s location could lead to an erroneous assessment of 

the aquifer type from which the well is drawing water (and thus possibly an incorrect evaluation 

of whether the well is representative of a nearby well). Accurate determinations of well 

locations are critical for determining representativeness using a desktop analysis; thus, it is 

important to use large scale topographic maps (e.g., 1:24,000 topographic quadrangles) for 

plotting the well’s location (see Exhibit 6.7). In the absence of a detailed topographic map (e.g., 

1:24,000), a base map of comparable scale is needed to accurately locate the well. Such a map 

might be available from the local community (e.g., Assessor’s Office, Engineering Department, 

Department of Public Works, Water Board, Board of Health, Planning Board, and Conservation 

Commission) or from State, federal, or regional natural resource agencies and planning 

departments. 

Accurate well coordinates may be sought first from the PWS’s records. Well registration 

information collected by federal, State, and local regulatory programs also usually include 

coordinates, or they may be available from the well drilling company records. If necessary, well 

coordinates can also be obtained in the field using Global Positioning System (GPS) technology. 

Exhibit 6.7 below shows the importance of map scale for determining aquifer type. In 

Exhibit 6.7, X indicates the location of a well with known areal coordinates and depth. Use of 

the larger scale map, Map A, allows for more precise plotting of the well's location, while use of 

the smaller scale map, Map B, introduces much more error into the plotting of the well’s 

location. The cross-section shows a correct identification, based on Map A, of the well's aquifer 

as gravel and an incorrect identification, based on Map B, of the well's aquifer as sand. The 

exhibit shows how the error introduced by imprecise plotting translates into erroneous 

determination of aquifer type. 

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Exhibit 6.7: The Importance of Map Scale for Determining Aquifer Type 

Topography can be represented in two dimensions with contours, continuous lines that 

join points of equal value (equal elevation in this case). The contour interval, which is the 

change in elevation between each successive contour line (e.g., 20 feet), is chosen depending 

upon the scale of the map and the topographic relief. The USGS and the Defense Mapping 

Agency (DMA) have produced most of the topographic maps for the United States (NRC 1993). 

The USGS produces maps at a variety of scales, but the most common scales for topographic 

maps are 1:24,000/1:25,000, 1:100,000, and 1:250,000. The 1:250,000 scale maps are available 

for the entire United States. The much more detailed topographic quadrangles (1:24,000 or 

1:25,000) are available for most of the country. Index maps for each State showing available 

topographic maps are provided by the USGS without charge. Each 1:24,000 topographic map 

covers approximately 58 square miles, where 1 inch corresponds to 2,000 feet. 

Digital topographic data for the United States are also available from the USGS as Digital 

Line Graphs (DLGs) and Digital Elevation Models (DEMs). DLGs are vector data files that 

represent linear and areal features commonly found on topographic maps, including contour 

lines. DEMs are data files that store point elevations spaced at regular intervals in a matrix. 

Detailed DEMs have 10- and 30- meter resolutions. Because national coverage is incomplete for 

both DLGs and DEMs, and State-wide coverage varies considerably by State, the remainder of 

this section will focus on paper topographic quadrangles. 

Stereoscopic Aerial Photography 

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Aerial photographs taken with approximately 30 percent overlap allow three dimensional 

imaging of land surface features with the aid of stereoscopes. In regions with limited geologic or 

topographic data, stereoscopic air photos may help locate wells. In most cases, however, such 

photos will be most useful for determining aquifer types when used in conjunction with other 

data sources. For example, if low resolution geologic maps or well log data indicate that a given 

PWS well may be screened in a karst aquifer, stereoscopic air photos could be used to determine 

the presence or absence of sinkholes or other characteristic karst landform features. Aerial 

photographs are available from several entities within the USDA and from the USGS. 

The NRCS and the Forest Service, both under the USDA, have extensive U.S. coverage 

at scales appropriate for hydrogeologic sensitivity assessments. The NRCS uses high resolution 

aerial photography to compile their county level soil surveys at scales ranging from 1:12,000 to 

1:63,360. The USDA Aerial Photography Field Office, Farm Service Agency acts as the 

clearinghouse for all USDA aerial imagery, archiving over 10,000,000 images dating to 1955. 

USDA aerial photo coverage, availability, and ordering information are available through their 

Website at: http://www.apfo.usda.gov/. 

The USGS National Mapping Division administers the National Aerial Photography 

Program (NAPP). The NAPP coordinates the collection of cloud-free coverage of the 

conterminous United States and Hawaii at a uniform scale (approximately 1:40,000) about every 

five years. NAPP photographs are available in black-and-white, and in many cases, color 

infrared. The imagery is available from the USGS’s Earth Resources Observation Systems 

(EROS) data center (http://edc.usgs.gov/) or Earth Science Information Centers (ESICs; 

http://edc.usgs.gov/guides/napp.html). NAPP photos are also available from the USDA Aerial 

Photography Field Office, Farm Service Agency (see link above). 

Well Registration Information, Well Logs, and other Information 

Well registration information and well logs collected by local, State, and federal 

regulatory programs may be very useful for determining aquifer type. Well registrations usually 

indicate well locations, which is information necessary to determine if wells may be considered 

representative of one another. A sufficiently detailed driller’s log for a PWS well could itself, or 

in combination with other data sources, adequately characterize the subsurface stratigraphy and 

aquifer type. For example, based upon a regional bedrock geology map that is of moderately low 

resolution (e.g., 1:700,000), a State may identify that two PWS wells are located in an area 

underlain primarily by limestone. The State may review the driller’s logs (if available) to 

confirm that, in fact, the wells are screened in the same limestone aquifer. Certain States such as 

New Jersey and New Hampshire require drillers to file a log for each well with the appropriate 

State agency, such as a water well board or the State Environmental Protection Agency. 

Additional desktop sources include consultant reports and database searches for property 

site assessments conducted by private search companies. These searches of federal, State, and 

local agency databases are conducted as part of due diligence investigations for property site 

assessments and are usually in accordance with the standards of the American Society of Testing 

Materials (ASTM). These database searches include a description of the bedrock and surficial 

geology, a well inventory, and usually air photo coverage for the area in question. The well 

inventory summarizes well locations, construction, soil and bedrock type, water quality, and 

other pertinent data. 

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UCMR 2 

Some systems may have already gathered information about their wells to select 

representative wells under EPA Unregulated Contaminant Monitoring Rule 2 (UCMR 2). This 

information may help to inform the appropriateness of representative monitoring under GWR. 

6.2.3 Capture Zone Models 

EPA’s Source Assessment Guidance Manual (USEPA, 2008) provides a detailed 

discussion of capture zone models that are very appropriate for helping to determine whether two 

or more wells can be considered as possibly representative of one another. Many systems 

conduct such modeling as part of their wellhead protection efforts. Models in use include 

Wellhead Protection Area Model (WHPA) and Wellhead Analytic Element Model (WHAEM). 

Systems and States are encouraged to make full use of information that may be easily available 

and appropriate in determining representativeness. In cases where capture zone modeling has 

already been conducted, the results of such modeling likely fall in this category. Where 

resources permit, EPA recommends that States or systems conduct capture zone modeling for the 

express purpose of determining whether two or more wells are drawing water from the same 

areas of the same aquifer, and thus can be considered representative of one another. 

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References 

Barlow, Paul. 1995. Particle Tracking Analysis of Contributing Areas of Public-Supply Wells in 

Simple and Complex Flow Systems, Cape Cod, Massachusetts. United States Geological 

Survey Water-Supply Paper 2434. 

Drever, J., 1988. The Geochemistry of Natural Waters. 2nd edition. Prentice Hall, NJ. 

Freeze, R.A., and Cherry, J.A., 1979. Groundwater. Prentice Hall, NJ. 

Güler, C., G.D. Thyne, J.E. McCray, and A.K. Turner, 2002. Evaluation of graphical and 

multivariate statistical methods for classification of water chemistry data. Hydrogeology 

Journal 10:455-474. 

Lee, M., 1998. Hands-on laboratory exercises for an undergraduate hydrogeology course. 

Journal of Geoscience Education 6:433-483. 

NRC. 1993. Ground Water Vulnerability Assessment: Predicting Relative Contamination 

Potential under Conditions of Uncertainty. Washington, D.C.: National Academy Press. 

204 pp. 

Piper, A.M., 1944. A graphic procedure in the geochemical interpretation of water-analyses. 

Transactions of the American Geophysical Union 25:914–923. 

Stiff, H.A. Jr., 1951. The interpretation of chemical water analysis by means of patterns. Journal 

of Petroleum Technology 3:15-17. 

USGS. 1988. A national look at nitrate contamination of ground water, By Bernard T. Nolan, 

Barbara C. Ruddy, Kerie J. Hitt, and Dennis R. Helsel. Available on the Internet at 

http://water.usgs.gov/nawqa/wcp/. 

USEPA, 2008. Ground Water Rule Source Assessment Guidance Manual, Office of Water, EPA, 

EPA document 815-R-07-023. 

USEPA. 1993a. Ground Water Resource Assessment. Office of Water, EPA. EPA Report 813/R93-003 166 pp and 4 appendices. 

USEPA. 1994a. Ground Water Information Systems Roadmap, A Directory of EPA Systems 

Containing Ground Water Data. EPA Report 813-B-94-001. 

USEPA. 1994b. Handbook, Ground Water and Wellhead Protection. EPA Report 625/R-94/001. 

269 pp. 

Wisconsin Department of Natural Resources (WIDNR). 1999. Wisconsin’s Source Water 

Assessment Program Plan. Available on the Internet at: 

http://www.dnr.State.wi.us/org/water/dwg/gw/SWP.HTM. Accessed August 20, 2008, 

last updated November 18, 2004. 

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7. Additional Useful Considerations for Representative Monitoring Proposals 

The GWR includes flexibility for representative source water monitoring to reduce the 

burden of sampling ground water sources. Ultimately, each State decides if the specifics of a 

particular system warrant representative monitoring and whether to require a written triggered 

source water monitoring plan. As noted in section 1.2 of this manual, the GWR has granted 

States flexibility on representative monitoring in that it is not an all-or-nothing approval process. 

That is, not all systems need to participate, and not all sources in a given system warrant 

representative monitoring. 

The GWR is clear in requiring State approval of all representative monitoring – whether 

it is requested for triggered monitoring or as part of a State-mandated assessment source water 

monitoring program. The GWR is also specific in requiring that representative monitoring be 

approved before it can be applied by a system; therefore, a GWS cannot conduct monitoring only 

at representative sources without prior State approval. When considering representative 

sampling, EPA encourages water systems to consult the State or primacy agency early to 

determine if representative sampling is applicable for the system and the level of effort and 

information that may be needed to ensure equivalent public health protection as that achieved by 

monitoring all sources or wellheads. 

This chapter describes the information EPA recommends States require and/or review 

prior to approving representative monitoring of ground water wells. All of these items have been 

discussed previously in this manual; this information is presented here to serve as a checklist of 

the elements EPA considers essential to making an informed decision. Appendix C summarizes 

the points included in this chapter. 

7.1 Reviewing the Proposal 

States are responsible for reviewing requests from water systems to conduct 

representative source water monitoring. EPA believes that representative source water 

monitoring can be as protective of public health as monitoring all wellheads, provided that the 

chosen wells are truly representative of all wellheads. 

As they review requests from utilities, States should consider the goal of public health 

protection by approving representative monitoring only when it is appropriate. This section 

discusses what information States should consider requesting from systems, and provides 

guidance on how to evaluate a system’s request for representative monitoring. 

7.1.1 Technical Considerations when Reviewing Proposals for Representative Monitoring 

There are two general reasons why a system would propose conducting representative 

monitoring: 1) to sample certain ground water sources that represent certain TCR sampling sites 

in the distribution system (and not sample other ground water sources that do not provide water 

to the particular TCR sampling site; or 2) to sample one or more wells that represent multiple 

wells in the same hydrogeologic setting. States may allow a ground water system to address 

either or both of these circumstances in their proposal to conduct representative monitoring. 

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Some criteria that States may use during a technical review of both these categories of 

representative monitoring are provided below. 

7.1.2 Ensuring the Proposal is Complete 

Systems should consult with the State before submitting proposals to be sure that they are 

familiar with State expectations. The first step in a State’s review may be to ensure that the 

proposal provided by the system has considered all of the information needed for a complete 

review. Depending on the nature of the system’s request, different materials may be submitted. 

These may include a written plan (if required by the State), which should include: 

For one or more representative sources serving a TCR sampling site: 

•	 Map or schematic of the system. The distribution system map or schematic should not 

contain information that poses a security risk to the system, but should include the 

following: 

o	 Pressure zone boundaries in the distribution system. 

o	 TCR routine monitoring locations, distinctly labeled. 

o	 Entry points of all sources, distinctly labeled, with the contributing sources clearly 

identified. 

o	 Entry points and status of any interconnections to other systems. 

o	 Storage tanks / reservoirs. 

o	 Pressure regulation facilities (reducing stations). 

o	 Other infrastructure that may affect pressure and/or flow in the distribution 

system. 

o	 Booster pump stations. 

o	 Critical valves. 

•	 The source type and level of treatment provided for each source/point of entry such as 

whether it is seasonal, emergency, ground water, surface water, a wholesale supply, etc. 

•	 The source(s) serving each TCR compliance monitoring location and the basis for the 

determination such as system hydraulics, operation, water quality data, etc. 

For one or more representative wells in the same hydrogeologic setting: 

•	 Physically and hydrogeologically representative ground water sources that will be used to 

satisfy the triggered monitoring requirements or State required assessment or additional 

monitoring requirements of the GWR and the basis for the selection. 

•	 Any changes or variations expected in the triggered source water monitoring plan such as 

the use of seasonal sources, rotating sources, etc. 

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The triggered source water monitoring plan can be a stand-alone, independent document 

or it can incorporate the TCR sample siting plan. In addition, many systems might need to create 

a multi-scenario triggered source water monitoring plan to reflect the variety of ways their 

system is operated over the year. The system should not only submit the appropriate supporting 

study results and other information, but should also include a narrative explaining how the 

information supports the system’s case for representative monitoring. 

7.1.2.1 Ground Water Sources Representing Coliform Monitoring Locations in the 

Distribution System 

Groundwater systems have a wide variety of tools available for evaluating the 

distribution system and determining which sources contribute to each TCR site. Simple water 

systems with uncomplicated distribution systems should be straightforward to evaluate. For 

some systems, locating sources, entry points, pressure zones, and TCR sites on the distribution 

system map may suffice. Systems that are more hydraulically complex will require a more 

advanced analysis of water movement. Hydraulic models or tracer studies help to inform 

whether sections of the distribution system are hydraulically separated. To provide maximum 

public health protection, States should take a conservative approach when considering reducing 

the number of sources that have to be sampled when source sampling is triggered. Sources that 

have very little likelihood that water from that well was the cause of the coliform sample may be 

eliminated from triggered source water monitoring. 

Expert judgments will be made by appropriately trained State staff. The following 

relevant considerations may be helpful to the States as they consider requests from systems. In 

addition, the considerations may be helpful to systems as they prepare requests for the States: 

•	 Does the system identify each TCR sampling site as well as each source / entry point into 

the distribution system? 

•	 Does the system demonstrate that areas of the distribution system are consistently 

hydraulically disconnected due to elevation, pressure gradients, tank locations, or through 

valving? 

•	 Do historical operating records of the system’s wells and distribution system support the 

system’s proposal for representative monitoring? 

•	 Is water flow possible from one zone to another but generally unlikely during normal 

operating conditions? If so, is this enough to justify representative monitoring? 

•	 Do all sources of information available, including water quality data, match certain wells 

to certain sampling sites in the distribution system? Does the water quality differ enough 

among the various distribution system locations to distinguish the sources of water? 

•	 If a distribution system hydraulic model is used: 

o	 Is the model calibrated? 

o	 Are demand patterns accurately detailed? 

o	 Does the model characterize the current hydraulic configuration of the distribution 

system? 

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o Does the model provide a sufficiently detailed view of the distribution system? 

7.1.2.2 Wells Representative of Other Wells in the same Hydrogeologic Setting 

Determining whether one or more wells are representative of the risk of fecal 

contamination of multiple wells should be based on a single-elimination approach. That is, if a 

ground water source fails to meet any one of several details, it should be eliminated from further 

consideration of representative monitoring. 

Helpful data or information used to determine if wells should be considered 

representative of one another includes proximity to other wells, well construction, water 

chemistry, the aquifer type tapped by the well and the overall hydrogeology of the site. Example 

sources of information that might be submitted include: 

•	 Well locations plotted using GPS or other means to denote proximity to other wells. 

•	 Well construction details for each well, including depth, grouting, sanitary seal, and 

screened interval. 

•	 Water chemistry analysis results demonstrating similarities or differences among wells or 

vulnerabilities of wells to contamination. 

•	 Aquifer information and other hydrogeologic studies, as appropriate. Hydrogeologic 

studies may include: 

o	 Wellhead protection or source water assessment studies (may inform location and 

proximity to potential sources of contamination). 

o	 State Geologic Survey, USGS, and other hydrogeologic investigations. 

o	 Hydrogeologic and geologic maps. 

o	 Topographic data. 

o	 Stereoscopic aerial photography. 

o	 Capture zone models. 

An important consideration when evaluating whether a system can conduct representative 

monitoring is the sanitary condition of the wells themselves. Wells being considered for 

representative monitoring should be structurally sound (e.g., raised casing, sanitary seal) and 

similar in design to one another. The State should be careful not to approve representative 

monitoring resulting in a well not being sampled that is in poor sanitary condition. If such a 

situation were approved, the well that was in poor sanitary condition and not sampled could be a 

source of fecal contamination that would not be identified under triggered source water 

monitoring. 

While source water chemistry data can be an excellent tool for identifying wells that are 

representative of each other, States should ensure that water chemistry results submitted are 

representative of the wells under all operating conditions. Results submitted for TDS, chloride, 

nitrate, or other chemical parameters should be accompanied by a narrative explaining why the 

data should be considered representative of the wells under all conditions, and how the water 

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chemistry data collected reflects the spectra of flows and seasonal variability that may impact 

each well’s water quality. 

Submittals to the State of hydrogeologic studies should provide information on aquifer 

type as well as confining layer information. Systems should include in their submittals a 

narrative that interprets the findings of any submitted hydrogeologic studies in the context of the 

wells being addressed by the proposed representative monitoring. 

The following relevant considerations may be helpful to States as they consider requests 

from systems. In addition, they may be helpful to systems as they prepare requests for States: 

•	 Is each well’s structure and condition sufficiently characterized? Are the structural 

conditions of the wells being grouped similar? 

•	 Did the system provide third party information about the structure and condition of its 

wells (e.g., driller’s log or well completion report) to support the characterization of the 

wells? 

•	 Are flows from the wells being addressed similar to one another? 

•	 If a hydrogeologic study is included, does it provide information on the aquifer type and 

the confining layer? 

•	 If water quality data are included and integral to defining the representative monitoring 

locations, do the data characterize all wells in use under the full ranges of seasonal and 

flow conditions? 

•	 If multiple wells are determined to be representative of each other, how many wells will 

be sampled? Will the sampled wells be alternated? 

7.2 Notifying the System and Recordkeeping Associated with a Representative 

Monitoring Decision 

States are required to keep records of approvals of triggered source water monitoring 

plans (40 CFR 142.14(d)(17)(vi)). These records include all supporting information and an 

explanation of the technical basis of each decision. This recordkeeping requirement of States is 

another reason that may compel States to require systems to submit written triggered source 

water monitoring plans. 

States should notify the system with the status of their applications, and GWSs should 

confirm with their State or primacy agency that they have approval before implementing 

representative source water monitoring. If the State approves representative monitoring for a 

system but does not require the system to prepare a written triggered source water monitoring 

plan, the State may want to include in the written record of its decision the conditions of the 

approved representative monitoring. 

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APPENDIX A 

Examples of Five Triggered Source Water Monitoring Plans 

•	 Example 1 – Demonstrates ground water sources representing coliform monitoring 

locations in the distribution system 

•	 Example 2 – Demonstrates wells representing other wells in the same hydrogeologic 

setting 

•	 Example 3 – Demonstrates ground water sources representing coliform monitoring 

locations and wells representing other wells in the same hydrogeologic setting 

•	 Example 4 – Demonstrates a combination system of one wholesale system and one 

consecutive system 

•	 Example 5 – Demonstrates a system with one SWTR-compliant surface water source, 

one regularly-used ground water source, and an emergency backup ground water source 

 Ground Water Rule A-1 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-2 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
EXAMPLE 1 

Triggered Source Water Monitoring Plan for Our Town Water System 

Ground water sources representing coliform monitoring locations in the distribution system. 

 Ground Water Rule A-3 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-4 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
A. System Information 

(Enter the following information about the water system.) 

Our Town Water System

Water System Name: 

AA7654321 

PWSID #: 

Clark County 

County or District: 

Ground Water Source Name Source ID Number Well Depth 

Sources: Well 1 WL002 200 ft 

Well 2 WL003 800 ft 

Storage: 2 hydropneumatic tanks – each 100 gallons 

Treatment: None 

Booster Stations: None 

Pressure Reducing One 

Stations: 

Pressure Zones: There are 2 pressure zones. Well 1 serves the western 

pressure zone (zone 1). Well 2 can serve both pressure 

zones (zones 1 or 2). 

TCR sample sites: We have two TCR sites. One site is in the western zone 

(zone 1) and the other is in eastern zone (zone 2). (See 

map attached). 

Population and Connections by Pressure Zone Population Connections 

Pressure Zone 1 – Western 750 302 

Pressure Zone 2 – Eastern 1,085 452 

Total Population and Connections Served 1,835 754 

 Ground Water Rule A-5 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, pressure zones, 

distribution system, storage tanks, and TCR sites.) 

 Ground Water Rule A-6 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Wells Representative of Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells Explanation of how tool was used for identification 

that contribute to TCR sites 

Distribution system maps: Our system has two pressure zones. The 

western zone is at a lower elevation and is 

generally fed by Well 1 although during high 

demand, it is also fed by Well 2. The eastern 

zone is higher and is fed by well 2 only. 

Coliform Monitoring Plan: Our plan identifies primary TCR sampling sites 

as well as upstream and downstream sites that 

are sampled in the event of a TC+ sample. 

Distribution system hydraulic Not used. 

models: 

Water quality parameters: Not used. 

Other: Under normal operating conditions Well 1 is 

sufficient to serve the western pressure zone 

(zone 1), and Well 2 serves the eastern zone 

(zone 2). However, during the high demand 

experienced during summer months (May through 

September), Well 1 does not have enough 

capacity to meet the demand in Zone 1. When 

pressures in zone 1 drop to 35 psi, water is 

fed from the eastern zone into the western zone 

through a pressure reducing valve located at a 

valve vault near the intersection of Main and 

Elm Streets. 

 Ground Water Rule A-7 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Wells Representative of Each Other 

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be No 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: 

Justification: 

 Ground Water Rule A-8 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR Site Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Seasonal 

Considerations 

1 Western 

(Zone 1) 

Wells 1 & 2 Wells 1 & 2 Well 2 only serves 

this site during high 

demand (when 

pressures drop below 

35 psi). This 

is typically in 

the months of 

May through 

September 

2 

Eastern 

(Zone 2) Well 2 Well 2 n/a 

 Ground Water Rule A-9 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-10 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
EXAMPLE 2 

Triggered Source Water Monitoring Plan for Lakeview Water System 

Wells representing other wells in the same hydrogeologic setting. 

 Ground Water Rule A-11 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-12 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
A. System Information 

(Enter the following information about the water system.) 

Lakeview Water System

Water System Name: 

AA3434343 

PWSID #: 

Trout County 

County or District: 

Ground Water Source Name Source ID Number Well Depth 

Sources: Well 1 WL002 250 ft 

Well 2 WL003 250 ft 

Storage: 2 hydropneumatic tanks – each 100 gallons 

Treatment: None 

Booster Stations: None 

Pressure Reducing None 

Stations: 

Pressure Zones: There is a single pressure zone. 

TCR sample sites: There is one site. 

Population and Connections by Pressure Zone Population Connections 

Single Pressure Zone 511 204 

 Ground Water Rule A-13 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, transmission 

mains and primary distribution mains, pressure zones, distribution system, storage tanks, TCR 

sites and a scale.) 

 Ground Water Rule A-14 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Wells Representative of Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells that Explanation of how tool was used for identification 

contribute to TCR sites 

Distribution system maps: Both wells serve the entire distribution system. 

Coliform Monitoring Plan: We have 1 TCR site. Both wells contribute 

to this site. 

Distribution system hydraulic Not used. 

models: 

Water quality parameters: Not used. 

Other: 

 Ground Water Rule A-15 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Wells Representative of Each Other 

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be Yes 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: Wells 1 and 2 

Justification: 

The town is served by a small well field of 2 wells, both within a 2 

acre site at the west side of town. The attached well logs show that all 

wells were completed in the same aquifer and drilled to approximately 

250 feet. In 2007 our engineering consultant prepared a wellhead 

protection plan (also attached) which shows that the wells all have a 

common recharge area which is free of any obvious sources of nearby 

fecal contamination. 

We feel that each of these wells are representative of the water quality 

drawn from this site, and are therefore appropriate for representative 

monitoring. If source monitoring is triggered by a TCR positive sample, 

we propose to sample only 1 of the 2 sources for E. coli. 

 Ground Water Rule A-16 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR Site Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Special 

Operating 

Conditions 

1 1 Wells 1 & 2 Wells 1 & 2 Well 1 or 2 n/a 

 Ground Water Rule A-17 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-18 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
EXAMPLE 3 

Triggered Source Water Monitoring Plan for Hydropolis Water System 

Ground water sources representing coliform monitoring locations and wells representing other 

wells in the same hydrogeologic setting. 

 Ground Water Rule A-19 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-20 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
A. System Information 

(Enter the following information about the water system.) 

Water System Name: Hydropolis Water System 

PWSID #: AA1234567 

County or District: 

Ground Water 

Sources: 

Beaverhead County 

Source Name 

Well X 

Source ID Number 

WL002 

Well Depth 

200 ft 

Well Y WL003 200 ft 

Well Z WL004 350 ft 

Well A WL005 150 ft 

Well B WL006 800 ft 

Storage: 

Treatment: 

Two ground level storage tanks – each 50,000 gallons. 

The Blueberry Tank is located in the Blueberry Hills 

zone (zone 2). The Hill Tank is located in the Hydropolis 

zone (zone 3). 

None 

Booster Stations: None 

Pressure Reducing 

Stations: 

None 

Pressure Zones: There are 3 pressure zones. Wells X, Y, and Z pump to 

the Blueberry Tank in zone 2 (Blueberry Hills zone). 

Well Z is a seasonal well that operates in the summer 

months only. Wells A and B pump to the Hydropolis 

Tank in zone 3 (Hydropolis zone). Zone 1 (Montgomery 

zone) is fed by all of the wells. 

TCR sample sites: We have four TCR sites. One site is in the Blueberry 

Hill zone, one site is in Montgomery zone, and two sites 

are in the Hydropolis zone. (See map attached). 

Population and Connections by Pressure Zone Population 

Pressure Zone 1 – Montgomery Estates 980 

Connections 

412 

 Ground Water Rule A-21 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
Pressure Zone 2 – Blueberry Hills 1,200 542 

Pressure Zone 3 – Hydropolis 1,525 784 

Total Population and Connections Served 3,705 1,738 

 Ground Water Rule A-22 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, pressure zones, 

distribution system, storage tanks, and TCR sites.) 

 Ground Water Rule A-23 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Wells Representative of Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells Explanation of how tool was used for identification 

that contribute to TCR sites 

Distribution system maps: Zone 1 (Montgomery) is at an elevation of 2000 

ft, Zone 2 (Blueberry) is at an elevation of 

2500 ft, and Zone 3 (Hydropolis) is at 

an elevation of 2700 ft. 

Coliform Monitoring Plan: Our plan identifies the wells that serve each 

zone and each TCR site. We made this 

Distribution system hydraulic 

models: 

determination based on our map and a hydraulic 

model prepared for us by our consultant. 

The hydraulic model indicates that Wells X, Y, 

and Z feed the Blueberry Hills zone. Similarly, 

Wells A and B, located at the eastern end of 

town, feed the Hydropolis zone. The lower 

elevation Montgomery Estates zone is fed by 

both sets of wells. The model also shows that 

Water quality parameters: 

Hydropolis zone and the Blueberry Hills zone 

are not hydraulically connected. 

Not used. 

Other: 

 Ground Water Rule A-24 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Wells Representative of Each Other 

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be Yes 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: Wells X and Y 

Justification: 

The Western well field includes Wells X, Y, and Z. Well Z is our oldest 

well. It was drilled in 1968 and is only 40 feet deep. This well is only 

used when required by very high demand. Wells X and Y were drilled in 

2004 and 2007. They are approximately 400 feet apart, and each is 

drilled past the perched aquifer at 40 feet and into the deeper more 

confined aquifer at 130 feet. The logs show a common lithology for each 

of these wells, and a comparison of water chemistry shows similar TDS 

levels and no detects on nitrate or nitrite. In addition, the recharge areas 

for these two wells overlap considerably, and neither has a potential 

source of contamination unique to that well. 

We believe that Wells X and Y are similar enough both physically and 

chemically that they can be considered representative of each other. Well 

Z however is not representative of the other wells at this site and 

should be sampled if it is in use when a TCR sample is total coliform 

positive in the Blueberry Hills or Montgomery zones. 

 Ground Water Rule A-25 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR 

Site 

Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Seasonal 

Considerations 

1 Montgomery 

(Zone 1) 

Wells X, Y, & Z Wells X & Y Wells X or Y, Z Well Z – operational 

from May through 

September 

2 Blueberry Hills 

(Zone 2) 

Wells X, Y, Z, 

A, & B 

Wells X & Y Wells X or Y, Z 

A,& B 

Well Z – operational 

from May through 

September 

3 Hydropolis (Zone 

3) 

Wells A & B N/A Wells A & B N/A 

4 Hydropolis (Zone 

3) 

Wells A & B N/A Wells A & B N/A 

 Ground Water Rule A-26 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
EXAMPLE 4 

Triggered Source Water Monitoring Plan for Town of Paradise Water System 

Demonstrates a combination system of one wholesale system and one consecutive system. 

 Ground Water Rule A-27 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-28 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
A. System Information 

(Enter the following information about the water system.) 

Town of Paradise Water System

Water System Name: 

AA1207992 

PWSID #: 

Jefferson County 

County or District: 

Ground Water Source Name ID Number Well Depth 

Sources: Paradise Well WL001 410 ft 

Village of PWS ID AA1209851 2 wells 

Paradise 

Storage: One 80,000-gallon elevated storage tank 

Treatment: No treatment on WL001. Village of Paradise water is 

treated with potassium permanganate and green sand 

filtration for manganese removal. 

Booster Stations: None 

Pressure Reducing None 

Stations: 

Pressure Zones: There is a single pressure zone. 

TCR sample sites: There are three coliform sampling locations. 

Population and Connections by Pressure Zone Population Connections 

Single Pressure Zone 2,630 957 

 Ground Water Rule A-29 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, transmission 

mains and primary distribution mains, pressure zones, distribution system, storage tanks, TCR 

sites and a scale.) 

 Ground Water Rule A-30 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Wells Representative of Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells that Explanation of how tool was used for identification 

contribute to TCR sites 

Distribution system maps: Most of the distribution system is served by 

Village of Paradise Water. On average, we 

purchase 500,000 gpd from the Village and we 

pump approximately 30,000 gpd from our own 

WL001. Since the amount of water entering the 

distribution system from WL001 is small 

compared to the amount entering from our 

connection with the Village, water from 

WL001 does not reach all parts of the 

distribution system. 

Coliform Monitoring Plan: We have 3 TCR sampling sites: Sample Site 1 

is located near the entry point where the Village 

of Paradise water enters the distribution 

system; Sample Site 2 is located downstream of 

the storage tank; and Sample Site 3 is located 

near the entry point where WL001 water enters 

the distribution system. 

Distribution system hydraulic Not used. 

models: 

Water quality parameters: Not used. 

Other: 

Justification: 

Pressure readings in the distribution system. 

Based on pressure readings at different 

locations in our distribution system, we know 

that our storage tank is filled only by the 

Village of Paradise’s water, and service 

connections upstream of the storage tank 

 Ground Water Rule A-31 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
(between the point where Village of Paradise 

water enters our distribution system and the 

storage tank) are also served only by Village of 

Paradise water. Sample Site 1 was established 

at its location with the intention that it would 

represent Village of Paradise water. Sample 

Site 3 is intended to test water from WL001; 

again, we picked the sample site location 

because we wanted to have a sample we knew 

was representing WL001 water. We can also 

support this with pressure readings. The source 

of water at Sample Site 2 is less clear and 

where the water at that location comes from 

depends on the demand in the system at that 

time. 

 Ground Water Rule A-32 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Wells Representative of Each Other 

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be No 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: 

Justification: 

 Ground Water Rule A-33 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR Site Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Seasonal 

Considerations 

1 N/A V. Paradise N/A Notify V. of Paradise N/A 

2 N/A V. Paradise AND 

WL001 

N/A WL001 and Notify V. 

of Paradise 

N/A 

3 N/A WL001 N/A WL001 N/A 

 Ground Water Rule A-34 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-35 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
EXAMPLE 5 

Triggered Source Water Monitoring Plan for the Valley View Water System 

A representation of a system with one SWTR-compliant surface water source, one regularly-used 

ground water source, and an emergency backup ground water source. 

 Ground Water Rule A-36 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-37 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
A. System Information 

(Enter the following information about the water system.) 

Water System Name: Valley View Water System 

PWSID #: AA7654321 

County or District: 

Ground Water 

Sources: 

Storage: 

Treatment: 

Greene County 

Source Name Source ID Number 

Valley View Well WL001 

Emergency Well WL002 

We have one 200,000-gallon ground level storage tank 

located adjacent to our upland reservoir and its 

treatment plant. The storage tank only contains treated 

surface water and feeds the distribution system by 

gravity flow. 

None (for ground water); Surface water receives 

conventional treatment. 

Well Depth 

125 ft 

65 ft 

Booster Stations: 

Pressure Reducing 

Stations: 

Pressure Zones: 

TCR sample sites: 

None but chlorine is injected into water leaving the 

storage tank. 

None 

There is one pressure zone. High pressure water flows 

from the storage tank, but it does not maintain enough 

pressure to safely supply the easternmost part of the 

system. Our well (WL001) in the valley provides 

approximately 12,000 gpd to the eastern part of the 

distribution system. 

2 coliform samples are collected each month: Sample Site 

1 is located in the northwest quadrant of the distribution 

system, which is served exclusively by water leaving the 

storage tank; Sample Site 2 is located in the 

northeastern corner of the distribution system where we 

 Ground Water Rule A-38 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
have had some issues maintaining sufficient pressure. 

Sample Site 2 receives water from both the surface 

water treatment plant and the well. 

Population and Connections 

Valley View Water System 

Population 

2,420 

Connections 

980 

 Ground Water Rule A-39 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, pressure zones, 

distribution system, storage tanks, and TCR sites.) 

 Ground Water Rule A-40 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Wells Representative of Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells Explanation of how tool was used for identification 

that contribute to TCR sites 

Distribution system maps: The attached distribution system map shows the 

locations of the coliform sampling sites relative 

to our water sources and storage tank. 

Coliform Monitoring Plan: Not used 

Distribution system hydraulic Not used. 

models: 

Water quality parameters: Chlorine residual, pressure 

Justification: The free chlorine residual in the water entering 

the distribution system from the storage tank 

is maintained at 1.0 mg/L +/- 0.2 mg/L. Based 

on daily measurements at the Department of 

Public Works building, where Sample Site 1 

coliform samples are collected, the chlorine 

residual consistently measures at or near 0.8 

mg/L. Water at the location where Sample Site 

2 coliform samples are collected only has a 

detectable residual (about 0.1-0.2 mg/L). The 

higher pressure and higher chlorine residual at 

Sample Site 1, as well as its location near the 

storage tank entry point, demonstrate that 

water at the Sample Site 1 location is provided 

by the surface water source and not the ground 

water source. 

 Ground Water Rule A-41 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Wells Representative of Each Other 

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be No 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: Valley View Well and Emergency Backup Well 

Justification: 

The emergency backup well is located within 500 ft. of the Valley View 

Well. It is turned on for less than one week a year while we are doing 

maintenance work on the Valley View Well. The emergency backup well 

is a much shallower well and its water quality is different. If the 

emergency backup well is in service at the time of a positive coliform 

result at Sample Site 2, we will sample both the emergency backup 

well and the Valley View Well. 

 Ground Water Rule A-42 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR Site Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Special 

Operating 

Considerations 

1 N/A Valley View 

Reservoir 

N/A None N/A 

2 N/A Valley View 

Reservoir, Valley 

View Well, 

Emergency 

Backup Well 

(if in service) 

N/A Valley View Well, 

Emergency Backup 

Well (if in service) 

Will only sample 

Emergency Backup 

Well if it was in 

service at the time of 

the coliform-positive 

result. 

 Ground Water Rule A-43 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule A

-44 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
APPENDIX B 

Example Triggered Source Water Monitoring Plan (Template)
 

 Ground Water Rule B-1 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule

Triggered and Representative Source 

Water Monitoring Guidance Manual 

 B-2 
A. System Information 

(Enter the following information about the water system.) 

Water System Name: 

PWSID #: 

County or District: 

Ground Water Source Name Source ID Number Well Depth 

Sources: 

Storage: 

Treatment: 

Booster Stations: 

Pressure Reducing 

Stations: 

Pressure Zones: 

TCR sample sites: 

Population and Connections by Pressure Zone Population Connections 

 Ground Water Rule B-3 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
B. Identification of Which Wells Contribute to Each TCR Site 

(Provide the following information on the system’s TCR sites and how it was determined 

which source provides the water to that site.) 

Tools used to identify wells Explanation of how tool was used for identification 

that contribute to TCR sites 

Distribution system maps: 

Coliform Monitoring Plan: 

Distribution system hydraulic 

models: 

Water quality parameters: 

Other: 

 Ground Water Rule B-4 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
C. Map of the Water System 

(Provide a map either below or attached that shows the location of the sources, pressure zones, 

distribution system, storage tanks, and TCR sites.) 

 Ground Water Rule B-5 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
D. Representative Ground Water Sources

(Provide information about sources and justification for representativeness.) 

Are there ground water sources in your system that can be 

representative of each other: 

If Yes, list sources and provide justification: 

Ground water sources: 

Justification: 

 Ground Water Rule B-6 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
E. Representative Triggered Monitoring Plan 

(Complete the following information to indicate the ground water sources to be sampled based 

on a routine total coliform positive sample taken at a TCR site. Attach additional sheets if 

necessary.) 

TCR Site Zone Sources 

Contributing 

to this TCR 

Site 

Contributing 

Sources 

Representative 

of Each Other 

Representative 

Source to 

Sample 

(Triggered) 

Seasonal 

Considerations 

 Ground Water Rule B-7 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
 Ground Water Rule

Triggered and Representative Source 

Water Monitoring Guidance Manual 

 B-8 
APPENDIX C - Summary of Considerations for Representative Monitoring 

There are two general reasons why a system would propose conducting representative 

monitoring: 1) to sample certain ground water sources that represent certain TCR sampling sites 

in the distribution system (and not sample other ground water sources that do not provide water 

to the particular TCR sampling site; or 2) to sample one or more wells that represent multiple 

wells in the same hydrogeologic setting. States may allow a ground water system to address 

either or both of these circumstances in their proposal to conduct representative monitoring. A 

summary of considerations that systems and States may find helpful during development and 

review of representative monitoring, respectively, are provided below. 

For Ground Water Sources Representing Coliform Monitoring Locations 

•	 Ground Map or schematic of the system 

•	 Identification of each source/entry point, its type (e.g., seasonal, emergency), and its level 

of treatment, if any 

•	 Identification of each TCR monitoring location 

•	 Data correlating TCR monitoring locations to particular ground water source(s) (e.g., 

hydraulic, operational, water quality, etc.) 

•	 The following relevant considerations may be helpful to States as they consider requests 

from systems. In addition, they may be helpful to systems as they prepare requests for 

States: 

o	 Does the system demonstrate that areas of the distribution system are consistently 

hydraulically disconnected due to elevation, pressure gradients, tank locations, or 

through valving? 

o	 Do historical operating records of the system’s wells and distribution system 

support the system’s proposal for representative monitoring? 

o	 Is water flow possible from one zone to another but generally unlikely during 

normal operating conditions? If so, is this enough to justify representative 

monitoring? 

o	 Do all sources of information available, including water quality data, match 

certain wells to certain sampling sites in the distribution system? Does the water 

quality differ enough among the various distribution system locations to 

distinguish the sources of water? 

o	 If a distribution system hydraulic model is used: 

	 Is the model calibrated? 

	 Are demand patterns accurately detailed? 

	 Does the model characterize the current hydraulic configuration of the 

distribution system? 

o Does the model provide a sufficiently detailed view of the distribution system? 

 Ground Water Rule C-1 

Triggered and Representative Source 

Water Monitoring Guidance Manual 
For Wells Representing Other Wells in the Same Hydrogeologic Setting 

•	 Well locations plotted using GPS or other means to denote proximity to other wells 

•	 Well construction details for each well, including depth, grouting, sanitary seal, and 

screened interval 

•	 Water chemistry analysis results demonstrating similarities or differences among wells or 

vulnerability of wells to contamination 

•	 Aquifer information and other hydrogeologic studies, as appropriate 

•	 The following relevant considerations may be helpful to States as they consider requests 

from systems. In addition, they may be helpful to systems as they prepare requests for 

States: 

o	 Is each well’s structure and condition sufficiently characterized? Are the 

structural conditions of the wells being grouped similar? 

o	 Did the system provide third party information about the structure and condition 

of its wells (e.g., driller’s log or well completion report) to support the 

characterization of the wells? 

o	 Are flows from the wells being addressed similar to one another? 

o	 If a hydrogeologic study is included, does it provide information on the aquifer 

type and the confining layer? 

o	 If water quality data are included and integral to defining the representative 

monitoring locations, do the data characterize all wells in use under the full ranges 

of seasonal and flow conditions? 

o	 If multiple wells are determined to be representative of each other, how many 

wells will be sampled? Will the sampled wells be alternated? 

This appendix provides a summary of major points discussed in the Ground Water Rule 

Triggered and Representative Source Water Monitoring Guidance Manual. Please consult the 

full guidance for a more complete discussion on each major point. The guidance is available 

electronically at http://www.epa.gov/safewater/disinfection/gwr/compliancehelp.html. 

 Ground Water Rule C-2 

Triggered and Representative Source 

Water Monitoring Guidance Manual