EPA
United States
Environmental Protection
Agency
GROUND WATER RULE
TRIGGERED AND REPRESENTATIVE SOURCE
WATER MONITORING GUIDANCE MANUAL
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Office of Water (4606) EPA 815-R-09-003 http ://www.epa. gov/safewater April 2009
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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.j eremy@epa.gov
202-564-2775
202-564-3767 (facsimile)
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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.
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CONTENTS
Exhibits Hi
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-l
Appendix B: Example Triggered Source Water Monitoring Plan (Template) B-l
Appendix C: Summary of Considerations for Representative Monitoring C-l
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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
AWWARF
ASTM
CDC
CCR
CFR
CT
CWS
OEMs
DLGs
DMA
EPA
EROS
ESICs
FR
GPS
GWR
GWS
GWUDI
HSA
HPC
LCR
NAPP
NCGMP
NCWS
NRC
NRCS
PWS
QA
QC
RASA
SDWA
Stage 1 DBPR
Stage 2 DBPR
SWAP
TC
TCR
IDS
UCMR
USDA
USGS
UV
WHPAs
WHPP
American Water Works Association
American Water Works Association Research Foundation
American Society of Testing Materials
Centers for Disease Control and Prevention
Consumer Confidence Report
Code of Federal Regulations
The Residual Concentration of Disinfectant (mg/L) Multiplied by the
Contact Time (in minutes)
Community Water System
Digital Elevation Models
Digital Line Graphs
Defense Mapping Agency
United States Environmental Protection Agency
Earth Resources Observation Systems
Earth Science Information Centers
Federal Register
Global Positioning System
Ground Water Rule (40 CFR Part 141 Subpart S)
Ground Water System
Ground Water Under the Direct Influence of Surface Water
Hydrogeologic Sensitivity Assessment
Heterotrophic Plate Count
Lead and Copper Rule (40 CFR Part 141 Subpart I)
National Aerial Photography Program
National Cooperative Geologic Mapping Program
Non-Community Water System
National Research Council
National Resources Conservation Service
Public Water System
Quality Assurance
Quality Control
Regional Aquifer-System Analysis
Safe Drinking Water Act
Stage 1 Disinfectants and Disinfection Byproducts Rule
Stage 2 Disinfectants and Disinfection Byproducts Rule
Source Water Assessment Program
Total Coliform
Total Coliform Rule (40 CFR Part 141 Subpart C)
Total Dissolved Solids
Unregulated Contaminant Monitoring Rule
United States Department of Agriculture
United States Geological Survey
Ultraviolet
Wellhead Protection Areas
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
repre sentati vene ss.
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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-or-
nothing 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
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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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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/Dav-08/w8763.pdf
• http://www.epa.gov/fedrgstr/EPA-WATER/2006/November/Dav-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
ia! and periodic sanitary surveys performed by the State
Community water systems (GWSs); every 3-5 years
Non-community water systems (NCWSs) every 5 years
..•-" Does the \
Stale require
assessment
source water
^monitoring? X
No
Conduct rapine sampling
under the Total Conform Rule
(TOR)
Does system
provide treatment
Was TCR
sample totaf
coifform-pc^itlve?
.-' Did the
State identify any
significant
•••,...deficiencies?'41 ,. ••
Yes
T
Consult Stats within 30 days of notification regarding
appropriate corrective action, if necessary
Implement State-approved or -specified corrective actions,
Options include*
* Eliminate source of contamination
» Correct significant deficiency
* Provide an alternate water source
* Provide treatment to achieve 4-log reduction of viruses
Complete correction or be in
accordance with a State-
approved schedule within 120
days of notice of fecal indicator
positive or significant deficiency
No
Conduct triggered
source water
$$a|S$Biertt! fi$ofiitorirtj|i- f* *?"*
^ _, / , 1 ^\ "* i «1' ,.''
Was
a sample fecal
indicator-
x positive? /
Perfoum public notification
and consult State within 24
hours
•''' Does the State
require corrective
action?
Yes
?
Consult State
within 30 days
regarding appropriate
corrective action, if
necessary
A
Perform pubhc notification
arid consult State within 24
hours
Was
9 sample fecal
indicator-
positive?
Perform pubSic notification
- and consult State within 24
hours
Per State
direction, take corrective
action or
5 additional
samples
Were any of the 5
repeat samples
positive?
Compliance monitoring - options include
Alternative \
Treatment i
T
j Chemical
Disinfection
Membrane
Filtration
(1) The GWR applies to all public water systems {PWSs} thai use graynd water,
except pubic water systems that combine all of ttieir ground water wfth surface
water or wrth ground water under the direct influence of surface water prior Jo
f
Monitor the
alternative
treatment
process In
with State-
specified
requirements ,
f
Serving
s3,300 j
people: j
Monitor j
residual j
disinfectant j
daily via grab ]
sample at j
peak flew j
f
Serving
>3,300
people:
Continuously
morstlor
residual
disinfectant
w
Monitor the
filtration
process in
accordance
with State-
specified
requirements
(2) Treatment using inacUvafcn, removal, or State-approved combination to achieve
a 4-log reduction of viruses before or at the flrat customer. Compliance monitoring
required,
(3) If the State determines that the distribution system is deficient or causes total
colifbrm-posrlwe samples, the system may be exempted from triggered source
water monitoring-
(4) The State must provide the GWS with written notice describing any significant
deficiencies within 30 days of identifying the significant deficiency.
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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. co//', 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 indicator-
positive 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 State-
required 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/disinfecti on/tcr/pdfs/issuepaper_invalidati on.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 coliform-
positive 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 (non-
regulated 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
Key
well
pressure zone boundary
pipes
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
Site ID
1H-1
1H-18
1H-2
1H-3
Primary Location
Name
FH#9,
1617 U St. NW
Bread for the City,
1525 7th St. NW
FH#16,
101 8 13th St. NW
FH#1,
2225 M St. NW
Tap location
Bathroom in
Officer's room
Hose bib
Bathroom sink
Kitchen sink
Upstream Location
Name
V Best Supermarket
1507UStNW
Dollar Plus Savings
Store
1541 7th St. NW
Stoney's Beef and
Beer 1 307 L St NW
Federal Market 1215
23rd St NW
Downstream
Location
Name
Keren Restaurant
1780 Florida Ave NW
Kennedy Recreation
Center
1401 7th St. NW
Roy Rogers
1275KStNW
Medical Society of
DC2215MStNW
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
West Side Well
West Pressure Zone
DiehlWell
South Pressure Zone
South Ave Well 1
South Ave Wei I 2
<'.'-;,) Storage tank
TCR Site
1
2
3
4
Pressure Zone
South
North Central
West Side
West Side
Contributing Wells
South Ave Well 1
South Ave Well 2
Diehl Drive Well
Main Well 1
Main Well 2
Main Well 3
West Side Well
Main Well 1
Main Well 2
Main Well 3
Main Well 1
Main Well 2
Main Well 3
West Side Well
Main Well 1
Main Well 2
Main Well 3
West Side Well
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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%20Qualitv.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 source-
specific.
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
Sand
Clay
Gravel
50 Feet
Exhibit 6.2: Inappropriate Candidates for Representative Sampling
Sand
Clay
Gravel
50 Feet
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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 non-
point 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 (HCCV) and carbonate (COs2")
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 (Giiler, 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 HCCV + COs2", 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"+ CO32", 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-of-
evidence 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
Sand
Clay
Limestone
Exhibit 6.5: Wells Screened in a Karst Aquifer Overlain by a Discontinuous Layer
Sand
Clay
Limestone
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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 (SOWA), 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/disinfecti on/gwr/pdfs/guide_gwr_sourcewaterassessments.pdf
State Geologic Survey, VSGS, 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
North
Plane View
Surface
Cross Section
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
Lake Wobegone
Map A Map B
1:25,000 1:250,000
Sand
• Clay
o Gravel
& Bedrock
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 (OEMs). DLGs are vector data files that
represent linear and areal features commonly found on topographic maps, including contour
lines. OEMs are data files that store point elevations spaced at regular intervals in a matrix.
Detailed OEMs have 10- and 30- meter resolutions. Because national coverage is incomplete for
both DLGs and OEMs, 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 USD A and from the USGS.
The NRCS and the Forest Service, both under the USD A, 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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UCMR2
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.
Giiler, C., G.D. Thyne, I.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. 1993 a. Ground Water Resource Assessment. Office of Water, EPA. EPA Report 813/R-
93-003 166 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
Ground Water Rule 7-4
Triggered and Representative Source
Water Monitoring Guidance Manual
-------
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.
Ground Water Rule 7-5
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This Page Left Intentionally Blank
Ground Water Rule 7-6
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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-l
Triggered and Representative Source
Water Monitoring Guidance Manual
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Ground Water Rule A-2
Triggered and Representative Source
Water Monitoring Guidance Manual
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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
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Ground Water Rule A-4
Triggered and Representative Source
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A. System Information
(Enter the following information about the water system.)
Our Town Water System
Water System Name:
PWSID #:
County or District:
Ground Water
Sources:
Storage:
Treatment:
Booster Stations:
Pressure Reducing
Stations:
Pressure Zones:
TCR sample sites:
AA7654321
Clark County
Source Name
Wettl
Source ID Number
Well Depth
200ft
Well 2
W1003
800ft
2 hydropneumatic tanks — each 100 gallons
None
None
One
There are 2 pressure zones. Well 1 serves the western
pressure zone (zone 1). Well 2 can serve both pressure
zones (zones I or 2).
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
Pressure Zone 1 — Western
Population
Connections
750
302
Pressure Zone 2 - Eastern
1,085
452
Total Population and Connections Served
754
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-5
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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.)
Two Pressure Zone Water System
Western Zone (1)
Well!
Well 2
! (; 4:$' Storage Tank
X) TCR Monitoring Site
Ground Water Rule
Triggered and Representative Source
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A-6
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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 contribute to TCR sites
Distribution system maps:
Coliform Monitoring Plan:
Distribution system hydraulic
models:
Water quality parameters:
Other:
Explanation of how tool was used for identification
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.
Our plan identifies primary TCR sampling sites
as well as upstream and downstream sites that
are sampled in the event of a TC+ sample.
Not used.
Not used.
Under normal operating conditions Well I 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 I drop to 35psi, 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
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Water Monitoring Guidance Manual
A-7
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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 JVo
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
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive sample taken at a TCR site. Attach additional sheets if
necessary.)
TCR Site
1
2
Zone
Western
(Zone 1)
Eastern
(Zone 2)
Sources
Contributing
to this TCR
Site
Wells 1&2
Well 2
Contributing
Sources
Representative
of Each Other
Representative
Source to
Sample
(Triggered)
Wells 1&2
Well 2
Seasonal
Considerations
Well 2 onfy serves
this site during high
demand (when
pressures drop below
35psi). This
is typically in
the months of
May through
September
n/a
Ground Water Rule
Triggered and Representative Source
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Ground Water Rule A-10
Triggered and Representative Source
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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
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Ground Water Rule A-12
Triggered and Representative Source
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A. System Information
(Enter the following information about the water system.)
Lakeview Water System
Water System Name:
AA3434343
PWSID #:
County or District:
Ground Water
Sources:
Trout County
Source Name
Wettl
Source ID Number
Well Depth
250ft
Well 2
W1003
250ft
Storage:
Treatment:
Booster Stations:
Pressure Reducing
Stations:
Pressure Zones:
TCR sample sites:
2 hydropneumatic tanks — each 100 gallons
None
None
None
There is a single pressure zone.
There is one site.
Population and Connections by Pressure Zone
Single Pressure Zone
Population
Connections
511
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-13
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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.)
Single Pressure Zone Water System
Well 1
Well 2
:; j= Storage Tank
X ) TCR Monitoring Site
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-14
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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:
Coliform Monitoring Plan:
Distribution system hydraulic
models:
Water quality parameters:
Other:
Both wells serve the entire distribution system.
We have 1 TCR site. Both wells contribute
to this site.
Not used.
Not used.
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-15
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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 I of the 2 sources for E. coli.
Ground Water Rule A-16
Triggered and Representative Source
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive sample taken at a TCR site. Attach additional sheets if
necessary.)
TCR Site
1
Zone
1
Sources
Contributing
to this TCR
Site
Wells 1&2
Contributing
Sources
Representative
of Each Other
Wettsl&2
Representative
Source to
Sample
(Triggered)
Well lor 2
Special
Operating
Conditions
n/fl
Ground Water Rule
Triggered and Representative Source
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A-17
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Ground Water Rule A-18
Triggered and Representative Source
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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
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Ground Water Rule A-20
Triggered and Representative Source
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A. System Information
(Enter the following information about the water system.)
Water System Name: Hydropolis Water System
PWSID #:
County or District:
Ground Water
Sources:
Storage:
Treatment:
Booster Stations:
Pressure Reducing
Stations:
Pressure Zones:
AA1234567
Beaverhead County
Source Name
WettX
Source ID Number
WellY
WellZ
WL004
Well A
WL005
WellB
WL006
Two ground level storage tanks - each 50,000 gallons.
The Blueberry Tank is located in the Blueberry Hills
zone (zone 2). The Eill Tank is located in the Eydropolis
zone (zone 3).
None
None
None
There are 3 pressure zones. Wells I, Y, and Zpump 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 I (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).
Well Depth
200ft
200ft
350ft
150ft
800ft
Population and Connections by Pressure Zone
Pressure Zone I - Montgomery Estates
Population
Connections
980
412
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-21
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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
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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.)
WellX
WellY
Multi Pressure Zone Water System
Zone 2: Blueberry Hills ^^^^^^^^^^^^B Zone 3: Hydropolis
\l Storage Tank
(X) TCR Monitoring Site we||
X) •< Well A
WellB
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-23
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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:
Coliform Monitoring Plan:
Distribution system hydraulic
models:
Water quality parameters:
Other:
Zone 1 (Montgomery) is at an elevation 0/2000
ft, Zone 2 (Blueberry) is at an elevation of
2500ft, and Zone 3 (Hydropolis) is at
an elevation of 2700 ft.
Our plan identifies the wells that serve each
zone and each TCR site. We made this
determination based on our map and a hydraulic
model prepared for us by our consultant.
The hydraulic model indicates that Wells X, If,
and Zfeed the Blueberry Hills zone. Similarly,
Wells A and B, located at the eastern end of
town, feed the Eydropolis zone. The lower
elevation Montgomery Estates zone is fed by
both sets of wells. The model also shows that
Eydropolis zone and the Blueberry Hills zone
are not hydraulically connected.
Not used.
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-24
-------
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 I and Y
Justification:
The Western well field includes Wells I, Y, and Z. Well Z is our oldest
well. It was drilled in 1968 and is onfy 40 feet deep. This well is onfy
used when required by very high demand. Wells I 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 lithologyfor 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 I 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
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive sample taken at a TCR site. Attach additional sheets if
necessary.)
TCR
Site
1
2
3
4
Zone
Montgomery
(Zone 1)
Blueberry Hills
(Zone 2)
Hydropolis (Zone
Hydropolis (Zone
Sources
Contributing
to this TCR
Site
Wells X,Y,&Z
Wells X,Y,Z,
A,&B
Wells A &B
Wells A &B
Contributing
Sources
Representative
of Each Other
WettsX&Y
Wells X&Y
N/A
N/A
Representative
Source to
Sample
(Triggered)
Wells X or Y,Z
Wells X or Y,Z
A,&B
Wells A &B
Wells A &B
Seasonal
Considerations
Well Z — operational
from May through
September
Well Z - operational
from May through
September
N/A
N/A
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-26
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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
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Ground Water Rule A-28
Triggered and Representative Source
Water Monitoring Guidance Manual
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A. System Information
(Enter the following information about the water system.)
Town of Paradise Water System
Water System Name:
PWSID #:
County or District:
Ground Water
Sources:
Storage:
Treatment:
Booster Stations:
Pressure Reducing
Stations:
Pressure Zones:
TCR sample sites:
M1207992
Jefferson County
Source Name
Paradise Well
ID Number
WL001
Village of
PWSIDAA1209851
Paradise
One 80,000-gallon elevated storage tank
No treatment on WLOOl. Village of Paradise water is
treated with potassium permanganate and green sand
filtration for manganese removal.
None
None
There is a single pressure zone.
There are three coliform sampling locations.
Well Depth
410ft
2 wells
Population and Connections by Pressure Zone
Single Pressure Zone
Population
2,630
Connections
957
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-29
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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.)
Wholesale Source and One Consecutive System
Town of Paradise Water System
1
Village of Paradise Water System
Paradise
WellWLOOl
Storage Tank
(X) TCR Monitoring Site
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-30
-------
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:
Coliform Monitoring Plan:
Distribution system hydraulic
models:
Water quality parameters:
Other:
Justification:
Most of the distribution system is served by
Village of Paradise Water. On average, we
purchase 500,000 gpdfrom the Village and we
pump approximately 30,000 gpdfrom our own
WLOOl. Since the amount of water entering the
distribution system from WLOOl is small
compared to the amount entering from our
connection with the Village, water from
WLOOl does not reach all parts of the
distribution system.
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 WLOOl water enters
the distribution system.
Not used.
Not used.
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
Triggered and Representative Source
Water Monitoring Guidance Manual
A-31
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(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
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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 JVo
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
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive sample taken at a TCR site. Attach additional sheets if
necessary.)
TCR Site
1
2
3
Zone
I/I
I/I
I/I
Sources
Contributing
to this TCR
Site
V. Paradise
V. Paradise MS
WL001
WL001
Contributing
Sources
Representative
of Each Other
I/I
I/I
I/I
Representative
Source to
Sample
(Triggered)
Notify V. of Paradise
WL001 and Notify V.
ofParadise
WL001
Seasonal
Considerations
I/I
I/I
I/I
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-34
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Ground Water Rule A-35
Triggered and Representative Source
Water Monitoring Guidance Manual
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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
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Ground Water Rule A-37
Triggered and Representative Source
Water Monitoring Guidance Manual
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A. System Information
(Enter the following information about the water system.)
Water System Name: Mley View Water System
PWSID #:
County or District:
AA7654321
Ground Water
Sources:
Storage:
Treatment:
Booster Stations:
Pressure Reducing
Stations:
Pressure Zones:
Greene County
Source Name
Mley View Well
Source ID Number
WL001
Emergency Well
We have one 200,000-gallon ground level storage tank
located adjacent to our upland reservoir and its
treatment plant. The storage tank onfy contains treated
surface water and feeds the distribution system by
gravityflow.
None (for ground water); Surface water receives
conventional treatment.
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.
TCR sample sites: 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
Well Depth
125ft
65ft
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-38
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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 Population Connections
Valley View Water System 2,420 980
Ground Water Rule A-39
Triggered and Representative Source
Water Monitoring Guidance Manual
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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.)
( Reservoir
Valley View Water System
III Storage Tank
X) TCR Monitoring Site
^ Valley View
^ Well
^ Emergency
^ ^^
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-40
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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:
Coliform Monitoring Plan:
Distribution system hydraulic
models:
Water quality parameters:
Justification:
The attached distribution system map shows the
locations of the coliform sampling sites relative
to our water sources and storage tank.
Not used
Not used.
Chlorine residual, pressure
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 daify 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
Triggered and Representative Source
Water Monitoring Guidance Manual
A-41
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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 JVo
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 500ft. 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
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive sample taken at a TCR site. Attach additional sheets if
necessary.)
TCR Site
1
2
Zone
N/A
N/A
Sources
Contributing
to this TCR
Site
Valley View
Reservoir
Valley View
Reservoir, Valley
View Well,
Emergency
Backup Well
(if in service)
Contributing
Sources
Representative
of Each Other
N/A
N/A
Representative
Source to
Sample
(Triggered)
None
Valley View Well,
Emergency Backup
Well (if in service)
Special
Operating
Considerations
N/A
Will only sample
Emergency Backup
Well if it was in
service at the time of
the coliform-positive
result.
Ground Water Rule
Triggered and Representative Source
Water Monitoring Guidance Manual
A-43
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Ground Water Rule A-44
Triggered and Representative Source
Water Monitoring Guidance Manual
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APPENDIX B
Example Triggered Source Water Monitoring Plan (Template)
Ground Water Rule B-l
Triggered and Representative Source
Water Monitoring Guidance Manual
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Ground Water Rule B-2
Triggered and Representative Source
Water Monitoring Guidance Manual
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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
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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:
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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.)
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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:
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E. Representative Triggered Monitoring Plan
(Complete the following information to indicate the ground water sources to be sampled based
on a routine total coliformpositive 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
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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?
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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.
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