United States
Environmental Protection
Agency
Office of Water (4601M)
Office of Ground Water and Drinking Water
Total Colform Rule (TCR) and Distribution System Issue Papers Overview
Total Colform Rule (TCR) and Distribution System
Issue Papers Overview
DECEMBER 2006

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PREPARED FOR:
U.S. Environmental Protection Agency
Office of Ground Water and Drinking Water
Standards and Risk Management Division
1200 Pennsylvania Ave., NW
Washington DC 20004
Background and Disclaimer
The USEPA is revising the Total Coliform Rule (TCR) and is considering new possible
distribution system requirements as part of these revisions. As part of this process, the
USEPA is publishing a series of issue papers to present available information on topics
relevant to possible TCR revisions. This paper was developed as part of that effort.
The objective of the "white papers" is to review the available data, information and
research regarding the potential public health risks associated with the distribution
system issues, and where relevant, identify areas in which additional research may be
warranted. The white papers will serve as background material for EPA, expert and
stakeholder discussions. The papers only present available information and do not
represent Agency policy. Some of the papers were prepared by parties outside of EPA;
EPA does not endorse those papers, but is providing them for information and review.
Additional Information
The paper is available at the TCR web site at:
http://www.epa.gov/safewater/disinfection/tcr/requlation revisions.html
Questions or comments regarding this paper may be directed to TCR@epa.gov.

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Total Coliform Rule (TCR) and Distribution System Issue Papers Overview
The purpose of this paper is to: 1) provide an overview of current Federal and
State Distribution System (DS) requirements; 2) provide background information on
EPA's decision to revise the TCR and consider additional distribution system (DS)
requirements; 3) provide an overview of how the 19 issue papers inform DS risk and the
need for potential TCR revisions, and 4) summarize the content of the different TCR and
DS issue papers that are available from EPA's website.
1) Overview of current Federal and State DS requirements
Federal Requirements
Total Coliform Rule (TCR)
Routine sampling requirements
Community Water Systems (CWS) and Non-community Water Systems (NCWS) using
surface water or ground water must monitor for total coliforms from one (<1000 people)
to 480 samples per month depending on population served. For CWS using ground water
(GW) serving 1000 or fewer people, the State may reduce the monitoring frequency to
once per quarter if the source is deemed protected and is free of sanitary survey defects.
NCWS using GW and serving 1000 or fewer must monitor at least each calendar quarter
of operation but may monitor as little as once per year if the State determines the system
is free of sanitary survey defects. Sampling locations, identified in the sample siting plan,
are required to be representative of water throughout the distribution system, including all
pressure zones and areas supplied by each water source and distribution reservoir.
Follow-up sampling for initial total coliform positives
Each sample tested to be total coliform positive must also be tested for either E.coli or
fecal coliform presence. In addition, systems must collect a set of repeat samples for each
total coliform positive. Systems with 1 or fewer routine samples per month must collect 4
repeat samples (one at same tap, one downstream within 5 service connections, one
upstream within 5 service connections, and one elsewhere in the DS). Systems with 2 or
more routine samples per month must collect 3 repeat samples (one at same tap, one
downstream within 5 service connections, one upstream within 5 service connections).
Also, during the month following a total coliform positive, systems taking fewer than 5
routine samples per month must take a total of 5 DS samples.

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MCL determinations:
•	For a system serving more than 33,000 people and collecting more than 40 samples per
month, a monthly maximum contaminant level (MCL) violation occurs when more than
5.0 percent of the samples collected during the calendar month are total coliform positive.
•	For systems serving 33,000 people or fewer and collecting less than 40 samples per
month, a monthly MCL violation occurs when more than one sample is total coliform
(TC) positive in a given calendar month.
•	For any system, an acute MCL violation occurs when it finds a TC sample positive
followed by a repeat sample positive, with at least one of these also being positive for E.
coli or fecal coliform.
See Figure 1 for an illustration of how MCL determinations are made.
Figure 1 Determining
Coliform Maximum
Contaminant Level
Violations
Fecal Cot form
Present
>1 positive sample for PWSs taking <40 samptesftwi# i
>6% pocttv* stmplss for PWSs taxing **0 mmptw/mc • i ;
(u/-) 		(/ST)
for PWSs
Stop
Total Coliform
Pfesent (only)
Original Sampie
FECAL NEGATIVI

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Surface Water Treatment Rule (SWTR)
The SWTR pertains to all CWS using surface water (SW) or ground water under the
direct influence of surface water (GWUDI), sets treatment technique requirements for
pathogens originating at the source (Giardia, viruses, Legionella), and includes specific
requirements for the DS. The residual disinfectant concentration in the DS, measured as
total chlorine, combined chlorine, or chlorine dioxide cannot be undetectable in more
than 5 percent of samples each month, for any two consecutive months that the system
serves water to the public. Water in the distribution system with a heterotrophic bacteria
plate count (HPC) of less than or equal to 500 colony forming units/milliliter is deemed
equivalent to having a detectable disinfectant residual for the purpose of determining
compliance with this requirement. Samples for measuring residual disinfectant
concentrations or heterotrophic bacteria must be taken at the same locations in the
distribution system and at the same time as samples collected for total coliforms.
Lead and Copper Rule (LCR)
The LCR requires corrosion control treatment, lead service line replacement, and public
education. The LCR has "action levels" for lead and copper. An action level is exceeded
when greater than 10 percent of samples collected from the sample pool contain lead
levels above 0.015 mg/L or copper levels above 1.3 mg/L. Water systems exceeding the
respective action level are required to install corrosion control treatment and conduct lead
service line replacement and mandatory lead education. Worst case condition sampling is
required twice a year at 5 to 100 within home distribution system sites depending on
system size, with allowance for reduced frequency and sites depending upon levels
found.
Stage 1 Disinfection Byproducts Rule (Stage 1DBPR)
The Stage 1 DBPR applies to all public water systems (PWS) that disinfect, and requires
systems to meet MCLs for total trihalomenthanes (TTHMs) at 0.080 mg/L, five
haloacetic acids (HAA5) at 0.060 mg/L, bromate at 0.010 mg/L, and chlorite at 1.0 mg/L.
Compliance with the TTHM and HAA5 MCLs is computed as a running annual average
and is based on monitoring in the distribution system. Compliance with the bromate MCL
is computed as a running annual average and is based on monitoring prior to the first
customer. Compliance with the chlorite MCL is based on individual measurements
determined each month, based on screening monitoring at plant and follow-up monitoring
in the DS.
The Stage 1 DBPR sets Maximum Residual Disinfectant Levels (MRDLs) for chlorine,
chloramines (measured as total chlorine), and chlorine dioxide. For chlorine and
chloramines, samples for measuring residual disinfectant must be taken at the same
locations in the distribution system and at the same time as samples collected for total
coliforms. For chlorine dioxide, samples must be taken daily at the entrance to the
distribution system. Compliance with the MRDLs for chlorine and chloramines (4 mg/1)
is based on the annual running average of all monthly samples collected, while

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compliance with the MRDL for chlorine dioxide (1.0 mg/1) is based on each daily
sample.
Interim Enhanced Surface Water Treatment Rule (IESWTR) and Long Term 1 Enhanced
Surface water Treatment Rule (LT1)
The IESWTR (for large systems) and LT1 (for small systems) pertain to all CWS using
SW or GWUDI and set treatment technique requirements for Cryptosporidium
originating in the source water. The IESWTR requires States to conduct sanitary surveys
(including inspection of DS) for all SW systems and GWUDI within every 3 years for
CWS and within every 5 years for NCWS. Systems must report to States how they are
addressing significant deficiencies identified by the State. The IESWTR also requires that
all finished water storage facilities, for which construction began after February 16, 1999,
be covered.
Long Term 2 Enhanced Surface Water Treatment Rule (LT2)
The LT2 Rule pertains to all CWS using SW or GWUDI sets treatment technique
requirements for Cryptosporidium originating at the source. The LT2 requires PWS with
uncovered finished water storage reservoirs to cover the reservoir or treat the reservoir
discharge to the distribution system to achieve inactivation and/or removal of at least 2-
log Cryptosporidium, 3-log Giardia, and 4-log virus.
Stage 2 DBPR
The Stage 2 DBPR requires that water systems meet the MCLs for TTHM and HAA5 at
each sampling location based on the running annual average of any four consecutive
quarterly sample results at that location. To determine the locations within the
distribution system where the highest levels of TTHM and HAA5 are expected to occur,
the Rule requires water systems to conduct an Initial Distribution System Evaluation
(IDSE). IDSEs are studies that evaluate THM and HAA5 levels at various points within
the distribution system. The results from these studies along with existing compliance
monitoring information will be used to determine future compliance monitoring
locations.
Ground Water Rule (GWR)
The GWR sets treatment technique requirements for systems using ground water (i.e.,
ground water not GWUDI) for pathogens originating in the source water. The GWR
requires States to conduct sanitary surveys (including inspection of DS) for all GW
systems within every 3 years for CWS and within every 5 years for NCWS. For a CWS,
the State may allow the sanitary survey to be conducted every 5 years, if the system
provides 4-log inactivation or removal of viruses or has a history of reliable operation and
no TCR MCL or reporting violations, as determined by the State. Systems must correct
for significant deficiencies identified by the State, including DS deficiencies.

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State Requirements
Most states have set requirements for the design, construction, operation, and
maintenance of distribution systems. Some states have established mechanisms and
delegate resources for implementation while others only encourage certain prevention
activities and some states do not address certain contamination issues in distribution
systems at all. For example, while 50 states have some requirements for the control of
cross-connection and/or backflow prevention, many states do not require an authority to
implement a pertained local ordinance or rule and only three states conduct periodic
reviews of cross-connection control programs. There appears to be substantial lack of
consistency of distribution system requirements set by States.

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2) Background on EPA's decision to revise the TCR and consider additional DS
requirements
The 1996 amendments to the Safe Drinking Water Act (SDWA) [Section 1412(b) (9)]
require EPA to review and revise, as appropriate, each national primary drinking water
regulation no less often than every six years.
On April 17, 2002, EPA presented and requested comment on its intent to revise the TCR
(67FR19029). The basis for this decision was to consider how to reduce the
implementation burden of the existing TCR with possible new requirements for ensuring
the integrity of distribution systems. On July 18, 2003 EPA confirmed its decision to
revise the TCR including consideration of new requirements for ensuring the integrity of
distribution systems (68FR42907). The July Federal Register Notice also stated, in
response to public comments, that any consideration for reducing the implementation
burden of the TCR should not lead to a reduction in public health protection (SDWA
anti-backsliding provision 1412(b)(9)).
In 2000, as part of its recommendations concerning the LT2 and the Stage 2 DBPR, the
Stage 2 Microbial/Disinfection Byproducts (M/DBP) Federal Advisory Committee
recognized the following points in its Agreement in Principle:
"Finished water storage and distribution systems may have an impact on
water quality and may pose risks to public health."
"Cross-connections and backflow in distribution systems represent a
significant public health risk."
"Water quality problems can be related to infrastructure problems and that
aging of distribution systems may increase risks of infrastructure problems."
"Distribution systems are highly complex and that there is a significant
need for additional information and analysis on the nature and magnitude of
risk associated with them."
The M/DBP Federal Advisory Committee concluded from these points that EPA should
review and evaluate available data and research on those aspects of distribution systems
that may create or pose risks to public health as a part of the Six-Year Review of the
Total Coliform Rule. The Advisory Committee also specifically recommended that EPA
initiate a process for addressing cross connection control and backflow prevention
requirements.
The current TCR requires utilities to take total coliform samples in the distribution
system. This monitoring constitutes the majority of distribution system monitoring.
While this monitoring may capture and identify several microbial contamination event
pathways in the distribution system, it was not designed to capture the range of risks that
were identified by the M/DBP Federal Advisory Committee. EPA plans to assess the
effectiveness of the current TCR and determine what alternative and/or additional risk
reduction strategies are available, and to consider revisions to the TCR with new
requirements for ensuring the integrity of the distribution system. To help achieve these
goals, it is important to understand 1) DS contamination mechanisms and pathways, 2)
how water quality conditions can impact public health, and 3) tools available for, and

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issues related to, identifying and assessing potential distribution system public health
risks. EPA has developed issue papers that pertain to these categories of interest.
3) Issues Related to Distribution Risk and the TCR revision
Following is a brief summary of the content of the issue papers pertaining to the above
three categories. Also, briefly discussed is how the categories relate to each other.
1)	Contamination mechanisms and pathways issue papers in this category describe
mechanisms and pathways for how contaminants can enter the distribution system.
Contaminants can enter the distribution system via intrusion, cross-connections and
backflow, permeation and leaching, during main repair or replacement, and unintended
access through finished water storage facilities. Five papers elaborate on our current
understanding of these respective risk factors.
2)	Distribution system water quality conditions that impact public health risk issue papers
in this category describe how the water quality within the distribution system can be
affected by contamination mechanisms and pathways, and/or underlying water quality
and distribution system operations. Areas of focus include microbial growth and biofilm
development and release; nitrification; aging infrastructure and corrosion; water age;
effects of treatment on nutrient availability (and influence on microbial growth and
biofilm); DS infrastructure inventory and integrity; and inorganic contaminant
accumulation in the distribution system.
3)	Distribution system tools and issues related to identifying and assessing potential
public health risk issue papers in this category describe different strategies for monitoring
and identifying contamination and deficiencies, and also include tools that assess the
effectiveness and reliability of water quality indicators. Overall these tools are a way to
look at water quality and public health risk factors that are a result of contamination
pathways and/or underlying water quality and distribution system operations. Areas of
focus include papers on various aspects of TCR compliance and implementation, DS
indicators of water quality, how hazard analysis can inform monitoring and contaminant
control strategies, and use of disinfectant residuals as an indicator and contaminant
control strategy.
Overall the 19 issue papers categories are interrelated. Contaminants can enter the DS
through a variety of pathways and affect water quality, and a variety of tools can be used
to assess such impacts. As an example of this interrelationship, Figure 2 illustrates how
aging infrastructure impacts main repair and replacement, which in turn impacts
microbial water quality. As listed on the figure, the tools that can help to identify and
assess public health risk may include indicators of water quality, Hazard Analysis and
Critical Control Point (HACCP), effectiveness of distribution system residuals, and
distribution system integrity.

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Example:

Z	Contamination Z
*	Mechanisms ¦
¦	m
Z	and Pathways Z
| DS Tools and	.
issues Related to	¦
I Identifying and	I
| Assessing	.
, Potential Public	"
' Health Risk	|
¦ Tools:	I
Indicators of	¦
I WQ, HAACP,
| Effectiveness of ¦'
Distribution	|
1 Residuals,
| Distribution	'
. System Integrity	I
i	¦
WQ Condition:
Microbial contamination
Mechanism:
Aging Infrastructure
Pathways:
Main repair/ replacement
Underlying Finished
Water Quality and
Distribution System
Operations
Distribution System Water Quality
Conditions that Impact Public
Health Risk
Figure 2. Example of Interrelationships between Distribution System Issues
4) Summaries of Issue Papers
Contamination Mechanism and Pathways
The Potential for Health Risks from Intrusion of Contaminants into the Distribution
System from Pressure Transients
This paper describes how pressure transients cause intrusion of contaminants into the
distribution system, potential public health risk associated with intrusion, and existing
control measures. Pressure transients (which can also lead to backflow) in
distribution systems resulting from activities such as valve closures, pipe fractures, or
pump stoppage coupled with pipe leaks can provide a pathway for untreated, possibly
contaminated groundwater or contaminated water from other sources (e.g. nearby
leaking sewer lines) to enter the finished water in the distribution system. Pressure
transients are caused by an abrupt change in the velocity of water, which results in an
exchange of energy between flow and pressure. This pressure change is exhibited as
a wave of increased and decreased pressures. Pathogens or chemicals in close
proximity to the pipe can be drawn into the pipes and be a potential contamination
source even though they are originated external to the distribution system. Existing
control measures for intrusion that are covered by the paper include engineering
standards for pipeline and pump design, valve selection and installation, surge tanks,
and distribution system network analysis considering pressure transients.

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Potential Contamination Due to Cross-Connections and Backflow and the Associated
Health Risks
This paper describes cross-connections and backflow and the causes of backflow
contamination through cross-connections, as well as strategies for mitigation
including discussion of state programs. A cross-connection is a point in a plumbing
system where it is possible for a nonpotable substance to come into contact with the
potable drinking water supply. Backflow is any unwanted flow of used or nonpotable
water, or other substances from any domestic, industrial, or institutional piping
system back into the potable water distribution system. The paper also reports on
actual contamination events that led to illness. From 1981 to 1998, the CDC
documented 57 waterborne disease outbreaks related to cross-connections, resulting
in 9,734 illnesses. These include 20 outbreaks (6,333 cases of illness) caused by
microbiological contamination, 15 outbreaks (679 cases of illness) caused by
chemical contamination, and 22 outbreaks (2,722 cases of illness) where the
contaminant was not reported or unknown. Mitigation of backflow contamination
covered by this paper includes installing and maintaining backflow prevention
devices and assemblies.
Permeation and Leaching
This paper describes permeation and leaching in the distribution system, characterizes
contamination due to permeation and leaching, examines the factors that lead to
leaching and permeation risk, the indications of these conditions, and mitigation
methods. Distribution system infrastructure and appurtenances can react with both
water within the pipe and external water, potentially allowing contaminants into the
drinking water. Leaching is the dissolution of metals, chemicals, and other materials
of the piping and appurtenances into water. Permeation is the movement of
chemicals from outside the pipe, through the pipe or appurtenance materials
themselves (as opposed to through orifices or leaks, as in intrusion), and into water.
Mitigation methods examined in the paper include meeting acceptable pipe material
as specified in ANSI/AWWA standards.
New or Repaired Water Mains
This brief paper reviews situations under which microbes and chemicals may
contaminate the distribution system as the result of installation of new pipes and/ or
repair of existing pipes. The paper provides an overview of information on
procedures to prevent contamination during construction and repair from AWWA
manuals and the scientific literature. A brief discussion of the risk of waterborne
disease associated with contamination of mains and some examples of contamination
events that occurred as a result of poor construction or repair practices are presented.

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Finished Water Storage Facilities
The paper presents a description of risk due to microbes and chemicals that originate
in finished water storage facilities or enter through defects in the finished water
storage facilities, and discusses a range of prevention and mitigation measures and
indicators of potential problems. Contamination mechanisms and examples of
contamination of both external and internal origin are discussed, including
contamination from tank materials and coatings, contamination due to faulty design,
poor operational practices that allow water to stagnate over long periods of time and
inadequate maintenance. Prevention and mitigation measures are the major focus of
the paper, including a discussion of tank inspection practices and maintenance and
operational activities, and discussion of design of storage facilities. Water quality
indicators, water quality monitoring, and modeling are also discussed. Sections on
maintenance activities and design of storage include references to standard practices
(e.g. AWWA standards for disinfection procedures, ANSI/NSF standards for
coatings, and Ten States Standards).
Distribution System Water Quality Conditions that Impact Public Health Risk
Health Risks from Microbial Growth and Biofilms in Drinking Water Distribution
Systems
This paper reviews information from the scientific literature relevant to assessing and
controlling potential risks associated with growth of bacteria and the presence of
biofilms in the distribution system. Biofilms are a complex mixture of microbes,
organic and inorganic material accumulated amidst a microbially-produced organic
polymer matrix attached to the inner surfaces of distribution systems. The paper
includes a discussion of the opportunistic pathogenic bacteria that grow in the
distribution system as well as survival of frank pathogens in biofilms and factors that
affect associated health risks. The paper discusses factors that affect the presence of
microbes in the distribution system, including routes of entry, factors that influence
growth, measures to prevent or control microbial growth and entry of microbes into
the distribution system. Indicators of potential problems are also discussed.
Nitrification
This paper describes the condition of nitrification, its causes, the potential risk to the
public, and how to prevent the condition. Nitrification is a microbial process by
which nitrogen compounds (primarily ammonia) are sequentially oxidized to nitrite
and nitrate. Ammonia is present in drinking water through either naturally-occurring
processes or through ammonia addition during secondary disinfection to form
chloramines. While nitrification can degrade water quality, the formation of nitrite,
nitrate and disinfection byproducts are the only water quality issues associated with
nitrification. Other effects of nitrification, such as reductions in pH and alkalinity,
may impact public health less directly, perhaps by resulting in elevated lead or copper

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levels. The prevention and mitigation strategies for nitrification are discussed.
Deteriorating Buried Infrastructure
This paper describes why deteriorating water distribution system infrastructure
experiences increased leakage; main breaks; taste, odor and color complaints; reduced
hydraulic capacity and greater disinfectant demands due to corrosion products and
biofilms. The paper examines primary mechanisms of pipe failure: hydraulic
transients, internal corrosion, leadite, and material fatigue and includes decision
making matrices. How infrastructure deterioration causes contamination to occur is
also discussed along with strategies for mitigation such as surge control, operator
training, cathodic protection, and joint replacement, depending on the type of pipe
failure problem identified in the paper.
Effects of Water Age on Distribution System Water Quality
This paper reviews water quality problems associated with water age that may pose a
public health problem. Water age is a major factor that may contribute to water
quality deterioration within the distribution system by several mechanisms including:
disinfection byproduct formation, nitrification, microbial growth, and corrosion. The
prevention and mitigation discussion includes tools for determining water age
including tracer studies and models, references of standard design guidelines for
hydraulic considerations, and methods to reduce water age by modifying operations,
maintenance and source water treatment. The review of indicators of high age
discusses different aesthetic indicators and monitoring indicators.
Effect of Treatment on Nutrient Availability
This paper examines the degree to which various types of water treatment may
increase nutrient levels and have an affect on water quality in the DS. Some treatment
processes can increase nutrients in the distribution systems to a level that may
contribute to microbial growth in distribution system biofilms. Ozonation, for
example, degrades complex humic substances to small, easily metabolized organic
substances that are used for growth and energy by many biofilm organisms.
Distribution System Inventory, Integrity and Water Quality
This paper provides a national picture of the susceptibility of distribution system
infrastructure by providing information on different materials used for infrastructure,
and an assessment of their conditions (e.g., age, degree of corrosion). Different types
of pipe and other infrastructure materials have different susceptibilities to unexpected
contamination, and to various infrastructure degradation processes. The paper
examines information from multiple surveys, databases, studies, and publications, and
identifies data gaps relative to certain types of infrastructure and materials. While the
intent of the paper is to address distribution system integrity many of the surveys do
not include information on the conditions of the infrastructure.

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Inorganic Contaminant Accumulation in Distribution Systems
This paper discusses factors that may lead to contaminant accumulation and
subsequent release back into drinking water, and methods for detecting and
controlling contaminant release. Inorganic contaminants entering the distribution
system either through the treatment process or through other mechanisms can adhere
to pipe scales and accumulate within the scales or pipe and storage tank sediments.
Biofilms are discussed also. Under some circumstances these inorganic contaminants
may be released during times of water chemistry change (e.g. initiation of residual
disinfection), or during hydraulic disturbances (e.g., pressure fluctuations). There are
documented instances of inorganic contaminants being released from scales or
sediments at levels above the Maximum Contaminant Level (MCL), where levels
below the MCL existed at entry to the distribution system. By and large, these events
likely go undetected due to a lack of sampling in the distribution system.
Distribution System tools and issues related to identifying and assessing
potential public health risk
Analysis of Compliance and Characterization of Violations of the Total Coliform
Rule
This paper analyzes compliance with the TCR from 1997 to 2005. The paper
identifies, on a National, State and EPA Regional basis, the annual MCL and
monitoring/reporting violations. Variables include the type of MCL violation (acute
versus non-acute), system size category, system type (e.g., non-transient
noncommunity water system), and water source. Statistically significant relationships
are determined.
Total Coliform Sample Invalidation
This paper identifies the invalidation requirements of the TCR and their rationale,
feedback from some states on the approximate number of positive samples being
invalidated (and due to what causes), and the approximate percentage of samples
being invalidated by laboratories (along with the analytical methods associated with
the interference). When promulgating the TCR, EPA recognized that there would be
instances where there would be the need to invalidate certain total coliform-positive
samples and total coliform-negative samples. At the same time, the Agency was
concerned about the potential for systems to regard any positive sample as a sample
collection error if repeat samples were negative, and thus, ignore the original sample.
Thus, the Agency included constraints in the final TCR for invalidating a positive
sample.

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Causes of Total Coliform Positive Samples and Contamination Events in Distribution
Systems
This paper identifies the factors that can lead to the occurrence of total coliform
positives and unexpected contamination events in distribution systems. The factors
that are examined include water treatment failures, accidental events (e.g., main
breaks), natural events (e.g., significant weather events), operations and maintenance
events (e.g., pressure fluctuations), and a host of other events. The paper links these
contamination events to documented cases of distribution system contamination,
including contaminants such as undesirable chemicals, hazardous substances,
pathogens, and total coliform-positive samples, or TCR MCL violations (as identified
in EPA's Safe Drinking Water (SDWIS) database, where possible).
Distribution System Indicators of Water Quality
This paper identifies and characterizes potential indicators of distribution system
contamination, particularly those related to unexpected contamination of the
distribution system. Microbial indicators discussed include total coliforms, fecal
coliforms, E. coli, enterococci, fecal streptococci, somatic coliphage, f-specific
coliphage and heterotrophic bacteria. Various chemical (e.g., sterols, turbidity, AOC)
and physical indicators (e.g., water loss, pressure drops) are examined. Data
indicating a potential relationship between public health risk and the indicators are
discussed.
Evaluating HACCP Strategies for Distribution System Monitoring, Hazard
Assessment and Control
This paper reviews information and data regarding the use of HACCP in the U.S. and
other countries for identifying locations in the distribution system that are most
susceptible to contamination and thus critical for safeguarding public health. The
paper discusses how monitoring and contamination prevention and control strategies
can be developed through HACCP. It has been used in drinking water distribution
systems in some European countries, Australia, New Zealand, and in some locations
in the U.S.
A Review of Distribution System Monitoring Strategies under the Total Coliform Rule
This paper examines potential monitoring strategies with a focus on those strategies
that are independent of the HACCP approach. The paper reviews current TCR
approaches (e.g., State-approved sampling plans) and a range of existing sampling
criteria (e.g., sample volumes used, disinfectant residual sampling at the point of TCR
sampling). The paper explores alternative monitoring approaches to the existing
strategies, such as the number of samples being based on a statistical determination of
number of samples needed. This information can be used to identify monitoring

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strategies that may provide the same level of public health protection as the current
TCR at potentially less cost and resource burden.
The Effectiveness of Disinfectant Residuals in the Distribution System
This paper reviews the existing literature, research and information to inform the
effectiveness of disinfectant residuals in the distribution system. The paper focuses
on the effectiveness of residuals to control biofilm, indicate distribution system
upsets, and inactivate contaminants that may enter the distribution system. The paper
reviews disinfection CT (concentration and contact time) for a range of pathogens
under conditions that may mimic those in distribution systems.

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