United States
Environmental Protection
Agency
Office of Water
(4607)
Uncovered Finished
Water Reservoirs
Guidance Manual
EPA815-R-99-011
April 1999
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DISCLAIMER
This manual provides a basic understanding of the potential sources of external
contamination in uncovered finished water reservoirs and provides guidance to water
treatment operators for evaluation and maintaining water quality in these reservoirs.
This document is EPA guidance only. It does not establish or affect legal rights or
obligation. EPA decisions in any particular case will be made applying the laws and
regulation on the basis of specific facts when permits are issued or regulations
promulgated.
Mention of trade names or commercial products does not constitute an EPA endorsement
or recommendation for use.
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ACKNOWLEDGMENTS
The Environmental Protection Agency gratefully acknowledges the assistance of the
members of the Microbial and Disinfection Byproducts Federal Advisory Committee and
Technical Work Group for their comments and suggestions to improve this document.
EPA also wishes to thank the representatives of drinking water utilities, researchers, and
the American Water Works Association for their review and comment. In particular, the
Agency would like to recognize the following individuals for their contributions:
Cheryl Capron, Seattle Public Utilities
Julie Hutchins, Seattle Public Utilities
Joe Glicker, Montgomery Watson
Mark Knudson, City of Portland Bureau of Water Works
John Miller, Los Angeles Department of Water and Power
Gary Stolarik, Los Angeles Department of Water and Power
Salome Freud, New York City Department of Environmental Protection
Mark LeChevallier, American Water Works Service Company, Inc.
Mark Stein, EPA Region I
Kevin Reilly, EPA Region I
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CONTENTS
1. INTRODUCTION 1-1
1.1 WATER QUALITY DEGRADATION CONCERNS 1-3
1.2 POLICIES AND REGULATORY BACKGROUND 1-5
1.2.1 USPHS Standard 1-5
1.2.2 Ten States Standards 1-6
1.2.3 AWWA Policy 1-6
1.2.4 EPA Policy 1-6
1.2.5 New EPA Regulations 1-7
2. FINISHED WATER RESERVOIR MANAGEMENT PLAN 2-1
2.1 GENERAL INFORMATION 2-1
2.1.1 Purpose 2-1
2.1.2 Background 2-1
2.1.3 Policies 2-2
2.1.4 Roles and Responsibilities 2-3
2.2 RESERVOIR-SPECIFIC INFORMATION 2-4
2.2.1 Background Information 2-4
2.2.2 Policies and Ordinances 2-5
2.2.3 Operations 2-5
2.2.4 Maintenance 2-6
2.2.5 Water Quality Monitoring 2-7
2.2.6 Staffing and Training 2-9
2.2.7 Safety 2-9
2.2.8 Construction 2-9
2.2.9 Recordkeeping and Reporting 2-10
2.2.10 Reservoir Security 2-10
2.2.11 Emergency Response Plans 2-10
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES 3-1
3.1 SURFACE WATER RUNOFF 3-2
3.2 BIRD AND ANIMAL WASTES AND CONTROL 3-3
3.2.1 Bird Waste 3-3
3.2.2 Bird Control 3-5
3.2.3 Animal Waste 3-7
3.2.4 Animal Control 3-7
3.3 HUMAN ACTIVITY 3-8
3.3.1 Pesticides and Fertilizers 3-8
3.3.2 Swimming 3-8
3.3.3 Discarded Debris 3-9
3.3.4 Deliberate Contamination 3-9
3.3.5 Human Activity Measures 3-9
3.4 ALGAL GROWTH 3-10
3.4.1 Increase in Bacteria Populations 3-11
3.4.2 Increase in Disinfection Byproducts 3-12
3.4.3 Increase in Taste, Odor, and Sediment Problems 3-13
3.5 INSECTS AND FISH 3-13
3.5.1 Insect Larvae 3-13
3.5.2 Fish 3-14
3.6 GROUND WATER INTRUSION 3-14
3.7 AIRBORNE DEPOSITION 3-15
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CONTENTS
4. MITIGATING WATER QUALITY DEGRADATION 4-1
4.1 RESERVOIR TURNOVER 4-2
4.2 DISINFECTANT RESIDUAL 4-3
4.3 HYDRAULIC EFFECTS 4-5
4.3.1 Flow Short-Circuiting 4-5
4.3.2 Hydraulic Circulation System 4-6
4.3.3 Reservoir Baffling 4-7
4.3.4 Submerged Mixer 4-8
4.3.5 Relocating Inlets and Outlets 4-8
4.3.6 Altering Flow Patterns at the Inlet and Outlet 4-9
4.3.7 Aerators 4-9
4.3.8 Analyzing Reservoir Hydraulics 4-9
4.4 RESERVOIR CLEANING 4-11
4.5 WATER QUALITY EFFECTS ON THE DISTRIBUTION SYSTEM 4-12
4.6 COVERS 4-13
4.6.1 Floating Covers 4-14
4.6.2 Fixed Covers 4-15
4.6.3 Air-Supported Roofs 4-16
4.6.4 Costs 4-16
5. WATER QUALITY MONITORING 5-1
5.1 INTRODUCTION 5-1
5.2 TYPES OF MONITORING 5-1
5.2.1 Sampling and Analysis 5-1
5.2.2 Visual Inspection 5-2
5.3 PARAMETERS TO MONITOR 5-3
5.4 FREQUENCY OF MONITORING 5-4
5.5 ISSUES RELATED TO WATER QUALITY MONITORING 5-15
5.5.1 Laboratory Testing 5-15
5.5.2 Recordkeeping and Reporting 5-15
5.5.3 Training 5-15
5.5.4 Water Quality Monitoring Equipment 5-15
6. REFERENCES 6-1
APPENDIX A. STUDIES PERFORMED A-l
A.I UNCOVERED FINISHED WATER RESERVOIRS IN NEW JERSEY A-l
A. 1.1 Pathogens A-l
A. 1.2 Other Contaminants A-2
A.2 UNCOVERED FINISHED WATER RESERVOIRS IN CALIFORNIA A-2
A.2.1 Los Angeles Department of Water and Power A-2
A.2.2 Metropolitan Water District of Southern California A-2
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CONTENTS
FIGURES
Figure 1 -1. Types of Finished Water Reservoirs 1-2
Figure 3-1. LAD WP's Open Reservoirs Subjectto SWTR 3-4
Figure 3-2. Maximum TTHMFP (MTP) in LADWP's Silver Lake Reservoir 3-12
TABLES
Table 1-1. Uncovered Reservoirs and Implication for Compliance with Drinking Water
Regulations 1-7
Table 3-1. 1997 Nutrient Loadings by Bird Groups in Seattle's Open Reservoirs 3-6
Table 4-1. Estimated Cost Ranges to Cover Existing Reservoirs at 1998 Cost Levels M-17
Table 5-1. Utility Survey Water Quality Monitoring Parameters 5-5
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CONTENTS
APHA
AWWA
ASU
CDC
CDHS
CPU
CMU
CSPE-R
CT
CWC
D/DBP
DEP
ECP
EPA
ESWTR
GWUDI
HOPE
HPC
IESWTR
LADWP
LCR
MCL
MG
MPH
MPN
MSDS
MTP
MWD
NEWWA
NOM
NPDES
NTU
ppb
PP-R
psi
PVC
SMCL
SOP
SDWA
SWTR
TCR
THM
TOC
TTHMs
TTHMFP
USPHS
WIDE
ACRONYMS
American Public Health Association
American Water Works Association
Aerial Standard Unit
Centers for Disease Control
California Department of Health
Colony Forming Unit
Concrete Masonry Unit
Reinforced Chlorosulfonated Polyethylene
Pathogen inactivation: disinfectant residual concentration (C, in mg/L) multiplied
by contact time (T, in minutes)
Culp/Wesner/Culp
Disinfectants/Disinfection By Product
Department of Environmental Protection
Extra Cellular Product
U.S. Environmental Protection Agency
Enhanced Surface Water Treatment Rule
Ground Water Under the Direct Influence of Surface Water
High-Density Polyethylene
Heterotrophic Plate Count
Interim Enhanced Surface Water Treatment Rule
Los Angeles Department of Water and Power
Lead and Copper Rule
Maximum Contaminant Level
Million Gallons
Miles per Hour
Most Probable Number
Materials Safety Data Sheet
Maximum TTHMFP
Metropolitan Water District of Southern California
New England Water Works Association
Natural Organic Matter
National Pollution Discharge Elimination System
Nephelometric Turbidity Unit
parts per billion
Reinforced Polypropylene
pounds per square inch
Polyvinyl Chloride
Secondary Maximum Contaminant Level
Standard Operating Procedure
Safe Drinking Water Act
Surface Water Treatment Rule
Total Coliform Rule
Trihalomethane
Total Organic Carbon
Total Trihalomethanes
Total Trihalomethane Formation Potential
U.S. Public Health Service
Water Industry Data Base
April 1999
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1. INTRODUCTION
The purpose of this document is to provide a basic understanding of the potential sources
of external contamination in uncovered finished water reservoirs and to provide guidance
to water treatment operators for evaluating and maintaining water quality in these
reservoirs. To achieve these objectives, this document discusses:
. Existing regulations and policies pertaining to uncovered reservoirs
. Developing a reservoir management plan
. Potential sources of water quality degradation and contamination
Operation and maintenance of reservoirs to maintain water quality
. Mitigating potential water quality degradation.
This guidance document is based on a review of current literature and includes case
studies of four large potable water utilities in the United States.
The term "finished water reservoir," as used in this document, refers to any holding facility
that stores potable water prior to its distribution for consumption in a public water system.
Figure 1-1 presents examples of various types of finished water reservoirs used in the
United States. Water is considered "finished" when it has received all treatment necessary
to meet the requirements of the 1989 Surface Water Treatment Rule (SWTR) and is
therefore suitable for human consumption. Almost all potable water systems in the United
States include one or more finished water storage reservoirs in advance of or in the
distribution system. These finished water storage reservoirs should not be confused with
raw water supply reservoirs. Raw water supply reservoirs typically consist of a large
surface water impoundment, such as a dammed river, and store thousands or even millions
of acre-feet of untreated raw water. Finished water reservoirs are typically much smaller
in volume and vary considerably with regard to design function, materials of construction,
and capacity. A small system may have an elevated steel storage tank that stores several
hundred gallons of finished water, while a large system may have a concrete-walled basin
that stores on the order of 150 acre-feet (50-million gallons) of water for distribution and
firefighting purposes.
Uncovered reservoirs that receive surface water runoff and/or ground water intrusion
(particularly ground water under the influence of surface water) are subject to the
regulatory provisions of the SWTR and are considered source water reservoirs. This
guidance manual specifically addresses open reservoirs that have adequate protection
measures and/or are adequately lined to prevent any surface water runoff or ground water
intrusion, and therefore qualify as "finished water" reservoirs.
Finished water reservoirs are typically designed and constructed to meet peak demand,
equalize distribution system pressure, or provide water for emergencies such as
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1. INTRODUCTION
<• Elevated tank
Source: Babbit et al. 1967
Covered finished water reservoir
Source: Los Angeles Department of Water and
Power (LADWP), 1988
Uncovered finished water reservoir
Source: Montgomery Watson, 1998
Standpipe
Source: Babbit et al., 1967
Figure 1-1. Types of Finished Water Reservoirs
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1. INTRODUCTION
firefighting. Finished water reservoirs may be designed to provide gravity outflow,
depending on topographical and water distribution system constraints, thereby ensuring
adequate water supply during power outages.
Finished water reservoirs may be constructed of various materials. Steel is commonly
used for tanks, although wood has been used for smaller tanks. Tanks may be elevated, at
ground level, or underground. Larger reservoirs are generally ground excavations
consisting of earthen or lined bottom and walls that may be lined with impermeable
materials. Lining materials include concrete, asphalt or asphaltic concrete, masonry, steel,
plastic, and rubber compounds.
Because finished water reservoirs store treated water suitable for human consumption,
care is generally taken to prevent contamination of the water and degradation of the water
quality. Therefore, most finished water reservoirs in the United States are covered to
provide substantial isolation from the external environment. Cover materials include
reinforced concrete, steel, aluminum, and wood for tanks, and fixed reinforced concrete
and floating flexible membranes for large surface reservoirs.
There are, however, finished water reservoirs still in use in the United States that are
uncovered and open to the atmosphere. These uncovered finished water reservoirs,
commonly referred to as "open reservoirs," were constructed primarily during the late
1800s through the early 1940s. Although new Federal regulations require that all
reservoirs for systems serving 10,000 or more people and using surface water or ground
water under the direct influence of surface water (GWUDI) constructed after February 16,
1999, be covered, reservoirs constructed prior to that date are not required to provide a
retrofit cover. Open reservoirs were once a common engineering design. The
construction of large open reservoirs adjacent to urban centers was considered to be a
cost-effective means of providing large quantities of water during emergencies. Water
professionals of that era did not have a complete understanding of waterborne diseases
and water quality degradation issues. Regulations to protect water quality were early in
their developmental phases during that time. The first national water quality standard was
not adopted until 1914 (McDermott, 1973).
In the mid-1970s, a nationwide survey found 750 open distribution water reservoirs in use
(Pluntze, 1974). The 1992 American Water Works Association (AWWA) Water Industry
Data Base (WIDE) identifies more than 10,000 finished water storage facilities in the
United States. Approximately 3 percent, or 300 of the reservoirs identified in the WIDE,
are classified as uncovered or open water reservoirs (Kirmeyer and Noran, 1997). Despite
their relatively small numbers, open reservoirs provide drinking water for a significant
portion of the population, including several large metropolitan areas.
1.1 Water Quality Degradation Concerns
The use of uncovered finished water reservoirs can lead to significant water quality
degradation and increase health risks to consumers. This finding is clearly supported by
literature on the subject, and several examples are summarized in Appendix A. Finished
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1. INTRODUCTION
water quality degradation has been attributed to contamination from both internal and
external sources and includes increases in the following:
• Algal growth
• Coliform bacteria growth
• Heterotrophic plate count (HPC) bacteria growth
• Turbidity
• Particulates
• Disinfection byproducts such as trihalomethanes (THMs)
• Metals
• Taste and odor
• Insect larvae
• Giardia and Cryptosporidium
• Nitrification of chloraminated waters.
Some of these water quality problems are exacerbated by the loss of a chlorine residual
and poor hydraulic circulation that are characteristic of large open reservoirs.
Water degradation in open reservoirs has been a recognized concern for many decades. In
his annual report of 1912, the City Engineer for Seattle, citing rapid urban growth and the
potential for an epidemic disease outbreak, recommended that a reinforced concrete cover
be considered for the Lincoln Reservoir (Pluntze, 1974). Reports published between 1929
and 1969, by the American Public Health Association (APHA), the U.S. Public Health
Service (USPHS), and the AWWA recommended that all finished water reservoirs be
covered (Pluntze, 1974). Many reservoirs remain uncovered, however, due to the capital
cost of covering them and the difficulty in clearly quantifying the public health benefits of
covering. Open reservoirs also are considered to have great aesthetic value by nearby
homeowners who have strongly opposed covering them. In some instances, open
reservoirs have been declared historic monuments, preventing utilities from implementing
any significant modifications (Erb, 1989).
Although the occurrence of water quality degradation in open reservoirs is well
documented, the literature also indicates that violations of drinking water standards are
not commonly traced to their use. This finding may be the result of insufficient data to
demonstrate clear cause-and-effect relationships. Bailey and Lippy (1978) found that
there were no definitive studies on water quality parameter dynamics, contaminant
introduction, or cause-and-effect. Bailey and Lippy concluded that there was a need for
additional studies that focus on the correlation between drinking water contamination and
the use of open reservoirs. Since then, numerous studies have documented the occurrence
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1. INTRODUCTION
of water quality degradation in open reservoirs (AWWA, 1983; Geldreich and Shaw,
1993; Karimi and Singer, 1991; LeChevallier et al., 1997; Silverman et al., 1983).
In 1983, the AWWA emphasized the importance of selecting appropriate monitoring
parameters based on suspected contamination sources, such as monitoring for Salmonella
in reservoirs that are frequented by known carriers such as gulls. In 1993, a Salmonella
outbreak in Gideon, Missouri, was attributed to pigeons roosting in a finished water tank.
Although the tank was covered, openings in the cover (i.e., unscreened vents) allowed
bird access. This waterborne disease outbreak resulted in seven deaths and caused illness
in 60 percent of the population (CDC, 1996).
Water quality degradation and increased potential for drinking water standard violations
and disease outbreaks resulting from the use of uncovered reservoirs requires serious
consideration. Appendix A contains a summary of two published case studies that discuss
the performance of eight open reservoirs in New Jersey and four open reservoirs in
Southern California.
1.2 Policies and Regulatory Background
Requirements for open reservoirs vary greatly across the United States due to the lack of a
Federal regulation that sets a uniform standard for existing reservoirs. The Interim
Enhanced Surface Water Treatment Rule (IESWTR) requires that new reservoirs operated
by systems serving at least 10,000 people and using surface water or GWUDI be covered,
but does not contain requirements for existing reservoirs. The Long-Term 1 Enhanced
Surface Water Treatment Rule, to be promulgated in November 2000, may contain a
similar requirement for systems serving less than 10,000 people and using surface water or
GWUDI. The fact that there has been no single, unified standard for existing open
reservoirs has forced other regulatory and industry groups to implement and recommend
procedures. Many State health departments, such as California, Oregon, Washington, and
Arizona, have crafted their own policies and regulations to address open reservoirs. For
example, Arizona requires that all finished water storage units be fitted with watertight
roofs to prevent contamination and quality deterioration of the finished water. Arizona
also requires that all existing open finished water storage units be eliminated or covered
(Arizona Department of Health Services, 1978). Professional drinking water
organizations also have developed policies and standards on open reservoir use. As a
result, utilities should rely on their State and industry organizations to identify applicable
standards and policies for use and operation.
Following is a sampling of existing standards and policies on the use and operation of
uncovered reservoirs.
1.2.1 USPHS Standard
The USPHS published its first Manual of Recommended Water Sanitation Practice in
1946 (Pluntze, 1974). This manual states:
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1. INTRODUCTION
"A suitable and substantial cover should be provided for any reservoir,
elevated tank, or other structure used for water storage. Covers should be
watertight, of permanent material, and constructed so as to provide
drainage away from the cover and prevent entrance of contamination into
the stored water. The surface of covers on storage reservoirs should not
be used for any purpose in connection with which contaminating matter is
likely to be produced. "
1.2.2 Ten States Standards
The latest edition of Recommended Standards for Water Works (Ten States
Standards) specifies in Section 7.0.2:
"All new finished water storage structures shall have suitable watertight
roofs which exclude birds, animals, insects, and excessive dust"(SPUEM,
1992).
1.2.3 AWWA Policy
In 1975, the AWWA adopted the following policy regarding potable water reservoirs:
"The AWWA strongly supports the practices of filtration of surface water
used as sources of public water supply, disinfection of public water
supplies, including the maintenance of residual disinfectant in the
distribution system, and the covering of reservoirs that store potable water
for direct delivery to consumers and adequate monitoring to assure
conformance with water quality standards (AWWA, 1997/1998). "
This policy was reaffirmed in 1984 and 1988. Clearly, the water industry supports and
encourages the covering of finished water reservoirs.
1.2.4 EPA Policy
The Safe Drinking Water Act (SDWA) is the primary law in the United States for
protecting the quality of drinking water. Congress enacted the SDWA in 1974 and
amended it in 1986 and 1996. The intent of the SDWA is to protect public health by
establishing standards and regulations for water treatment and to minimize or eliminate
water quality degradation in finished water distribution systems. The SDWA and its
amendments of 1986, and 1996 do not specifically address uncovered finished water
reservoirs. In 1991, EPA published two guidance documents entitled Guidance Manual
for Compliance with the Filtration and Disinfection Requirements for Public Water
Systems Using Surface Water Sources (AWWA, 1991) and Manual of Small Public
Water Supply Systems (USEPA, 1991b), both of which recommended that all finished
water reservoirs and storage tanks be covered.
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1. INTRODUCTION
1.2.5 New EPA Regulations
In March, 1994, EPA proposed the Interim Enhanced Surface Water Treatment Rule
(IESWTR) requesting comments on a "possible supplemental requirement" to cover
finished water reservoirs and storage tanks. Promulgated on December 16, 1998, the
IESWTR requires surface water and ground water under the direct influence (GWUDI)
systems that serve 10,000 or more people to cover all new reservoirs, holding tanks or
other storage facilities for finished water for which construction begins after the effective
date of this rule, February 16, 1999 (EPA, 1998). The IESWTR does not apply these
requirements to existing uncovered finished water reservoirs.
Table 1-1 provides a summary of existing and pending Federal drinking water regulations
and the potential compliance concerns for utilities that operate uncovered finished water
reservoirs.
Table 1-1. Uncovered Reservoirs and Implication for Compliance with
Drinking Water Regulations
Regulation
Goal of Regulation
Potential Effect on Uncovered Reservoir
Operations and Regulatory Compliance
Surface Water
Treatment Rule
(SWTR)
(54 FR 27486, June
19, 1989)
Control of turbidity and
pathogens in drinking water
through filtration and
disinfection.
The SWTR requires all public water systems
supplied by surface water sources to implement
disinfection and filtration treatment practices.
If certain source water quality requirements are
met, systems may avoid filtration. Failure to
meet requirements for detectable disinfectant
residual throughout the distribution system
violates SWTR requirements. Therefore,
uncovered reservoirs should be managed to
ensure the maintenance of a disinfectant
residual.
Total Coliform Rule
(TCR)
(54 FR 27544, June
29, 1989)
Prevent waterborne
microbial disease through
monitoring total coliform
bacteria in the distribution
system as an indicator of
overall microbial
contamination.
Open reservoirs increase opportunities for the
introduction of coliform bacteria and microbial
pathogens to the system, increasing the
possibility of noncompliance with the TCR.
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1. INTRODUCTION
Table 1-1. Uncovered Reservoirs and Implication for Compliance with
Drinking Water Regulations (continued)
Regulation
Goal of Regulation
Potential Effect on Uncovered Reservoir
Operations and Regulatory Compliance
Total Trihalomethane
(TTHM) Rule
(44 FR 68624,
November 29, 1979)
Reduce cancer risk from
exposure to THMs. Requires
that public water systems
serving at least 10,000 people
analyze water in the
distribution system for TTHM
concentrations and maintain
an annual average of less than
100 u,g/L. The Stage 1 DBPR
will replace the TTHM rule
and for compliance purposes
in 2001 for surface water and
GWUDI systems serving at
least 10,000 people and 2003
for surface water and GWUDI
systems serving less than
10,000 people and all ground
water systems. See summary
of Stage 1 DBPR in this table.
The use of uncovered reservoirs in a public
water system tends to increase the potential for
TTHM formation. If the TTHM level in the
treated water entering the reservoir is high
(greater than approximately 80 u,g/L), the
potential contamination sources in the reservoir
water could increase TTHM concentrations in
the distribution system to unacceptable levels.
Lead and Copper Rule
(LCR)
(56 FR 26460, June 7,
1991)
Reduce consumer exposure to
lead and copper by developing
and implementing a corrosion
control program. LCR
revisions are expected to be
promulgated in 1999.
The primary effects of open reservoirs is that it
is more difficult to control basic water
chemistry that impacts the efficacy of corrosion
control strategies (i.e., pH, alkalinity,
temperature, etc.) due to the fact that the
reservoir is an open system. Copper sulfate
applications for algae control, if used by the
utility, may increase copper levels in drinking
water. If the levels of lead or copper are too
high, the LCR may require the system to
implement some treatment options to ensure
that compliance is maintained.
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1. INTRODUCTION
Table 1-1. Uncovered Reservoirs and Implication for Compliance with
Drinking Water Regulations (continued)
Regulation
Goal of Regulation
Potential Effect on Uncovered Reservoir
Operations and Regulatory Compliance
Stage 1 Disinfectants
and Disinfection
Byproducts Rule
(DBPR)
(63 FR 69390,
December 16, 1998)
Reduces health risks through
control of DBF occurrence in
the distribution system. The
DBPR replaces the current
TTHMrule. It reduced the
Maximum Contaminant Level
(MCL) for TTHMs to 80 ug/L
and established MCLs of 60
ug/L, 10 ug/L, and 0.8 ug/L
for HAAS, bromate, and
chlorite, respectively.
Uncovered reservoirs may provide conditions
that lead to increases in DBF levels. Higher
disinfection doses may be required to maintain
effective disinfectant residuals. Some studies
have shown DBF levels to increase in open
reservoirs due to factors such as long detention
times, algal growth, seasonal temperature
variations, and heavy in-reservoir chlorination
(Karimi, 1988; Karimi and Singer, 1991).
Interim Enhanced
Surface Water
Treatment Rule
(IESWTR)
(63 FR 69477,
December 16, 1998)
The IESWTR revises the
SWTR to further protect
against disease causing
pathogens - viruses, Giardia
lamblia, and Cryptosporidium
- in drinking water for
surface water and GWUDI
systems serving at least
10,000 people.
This rule requires all finished water reservoirs
built after February 16, 1999, to be covered.
Uncovered reservoirs, particularly those that are
strongly influenced by waterfowl and other
sources of external contamination, increase a
system's exposure to pathogens controlled by
the rule.
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1. INTRODUCTION
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2. FINISHED WATER RESERVOIR
MANAGEMENT PLAN
As discussed in Chapter 1, the use of uncovered finished water reservoirs can lead to
water quality degradation and therefore increase health risks to consumers. Utilities that
have uncovered reservoirs should develop and implement a comprehensive reservoir
management plan to efficiently and effectively protect water quality. The plan should
unite all relevant information in a single document for use by all levels of utility staff, and
it should ensure the proper management of each reservoir, and the system as a whole.
This chapter provides general guidance for the preparation of a reservoir management
plan. It was created largely from information provided by two utilities that currently
operate uncovered finished water reservoirs (Knudson, 1998a, 1998b, 1998c; Capron,
1998). Because of the complexity of factors affecting the management of each reservoir
and system, each utility should develop a plan that addresses its own specific needs and
circumstances. The guidance offered in this chapter should be applied accordingly.
2.1 General Information
A utility may operate one or more uncovered reservoirs as part of its system. The first
section of the plan should provide general information addressing concerns that apply to
the management of all of a utility's open reservoirs in the context of the entire system.
This section outlines the topics that should be covered under general information.
2.1.1 Purpose
The goal of the management plan is to protect water quality in the utility's uncovered
finished water reservoirs. Achieving this goal involves attaining certain objectives, such as
the continued maintenance of regulatory compliance, water quality at the highest possible
standard, and prevention of waterborne disease outbreaks.
2.1.2 Background
The plan should discuss background information that establishes the basis for its
development. This may include the following elements:
• A description of the events that lead to the utility's decision to develop the plan
• Any applicable statutory and regulatory requirements
• Historic perspective of water quality issues for the system and its open
reservoirs
• Narrative and schematic exhibits that describe the system
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2. RESERVOIR MANAGEMENT PLAN
• General description of system operations with emphasis on the uncovered finished
water reservoirs.
2.1.3 Policies
The plan should clearly define all utility policies that pertain to the management of its
uncovered or open reservoirs. This may be a single policy that states that the system's
water quality goals and objectives will be met through a comprehensive management
program, or there may be multiple policies, each of which applies to a program element.
The following policies should be considered for inclusion in a management plan:
• General Policies and Ordinances - General utility policies and city ordinances
that govern the overall management of the utility.
• Operations - Defines the goals of open reservoir operations and the various
procedural options that are acceptable in achieving those goals such as
increased turnover, overflowing and flushing, by-passing the reservoir, runoff
prevention, waterfowl/other bird control, algae, etc.
• Maintenance - Describes the need for maintaining open reservoirs and related
facilities and establishes the minimal requirements for preventive maintenance
(e.g., each open reservoir will be drained and cleaned at least annually).
• Water Quality Monitoring - Requires the maintenance of a minimum chlorine
residual at the reservoir outlet, describes known contamination sources and
accepted control measures, or establishes water quality monitoring parameters
and frequencies.
• Staffing and Training - Establishes that adequate staffing will be maintained to
fulfill all open reservoir management requirements and that all staff receive
appropriate training at regular intervals.
• Safety - Establishes employee safety as a high priority and ensures that
employees will not be at risk in fulfilling their responsibilities. This includes
ensuring that all hazardous materials are stored and handled in accordance with
all applicable Federal, State and local requirements.
• Construction - Requires that all construction activities within or near open
reservoirs are conducted in a manner such that water quality impacts are
prevented or mitigated.
• Recordkeeping and Reporting - Requires the preparation of accurate and
complete records, minimum record retention time, preparation of routine
reports at regular intervals, and the prompt reporting of deficiencies and
discrepancies to the appropriate utility staff and external agencies.
• Reservoir Security - Defines the major security concerns for the system's open
reservoirs and establishes security methods and frequencies.
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• Emergency Planning and Response - Resolves to respond promptly and
effectively to all emergencies with special regard to threats to public health or
safely.
2.1.4 Roles and Responsibilities
For each of the major management program elements indicated below, there should be a
detailed description of the roles and responsibilities of specific individuals (by job title) or
organizational groups (by section or department name). The plan should clearly describe
the tasks that need to be accomplished, how and when the tasks will be performed, and
who will perform the tasks. The plan also should describe the process for review and
modification of the plan itself to account for changes in utility policies, treatment goals, or
treatment practices.
The major management program elements for which general roles and responsibilities
should be defined are as follows:
• General Policies and Ordinances -Develop and implement all general policies
and ordinances to provide necessary reservoir protection and to address any
changes that may impact reservoir management.
• Operations - Develop standard operating procedures (SOPs) and provisional
procedures considering turnover time, hydraulics, and water quality changes
across reservoirs.
• Maintenance - Identify requirements and develop schedules and procedures for
preventive maintenance of major equipment or of the reservoir itself, and
frequency for cleaning reservoirs.
• Water Quality Monitoring - Identify potential contamination sources,
regulatory requirements, water quality monitoring parameters, and monitoring
frequencies and procedures.
• Staffing and Training - For each staff position, identify commensurate training
requirements and implement a program that provides for all orientation
training, refresher training, and certifications.
• Safety - Identify dangerous situations that should be recognized and avoided
by personnel, develop procedures for reporting and responding to unsafe
conditions. This should include the identification of all hazardous materials in
use and applicable requirements for storage and handling including material
safety data sheets, risk management plans, and special personnel requirements.
• Construction -Develop procedures for performing construction activities that
can impact water quality and provide oversight responsibilities for ensuring
that construction activities are carried out in accordance with established
policies and procedures.
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• Recordkeeping and Reporting - Develop standard forms for all aspects of data
collection, develop a document control system, identify all required reports,
and develop standards for format and content.
• Reservoir Security - Describe roles and responsibilities for conducting regular
security inspections, identifying appropriate access control measures,
identifying trespassing routes, posting signage, and coordinating with the local
police department.
• Emergency Planning and Response - Develop emergency planning and
response procedures as a separate section in the plan.
2.2 Reservoir-Specific Information
This section of the reservoir management plan is intended to address reservoir-specific
issues and procedures. The plan should address elements that include background
information for each reservoir, operations criteria and procedures, and a program for
water quality maintenance that includes monitoring, visual inspections, and contamination
control. It should also include maintenance requirements, as well as security requirements
and staffing and training information.
2.2.1 Background Information
The reservoir management plan should include a section containing background
information for each reservoir. The information should include the following basic
information identifying the reservoir:
• Reservoir name
• Location
• Pressure level or zone
• Overflow elevation
• Storage volume rating curve (graph of reservoir level versus storage volume)
• Service area map
• Overflow point of discharge (e.g. sewer, storm drain, or creek)
• Contact name and telephone number
• Applicable regulations and policies.
It also may be helpful to compile other information about each reservoir that will provide a
quick understanding of the reservoir for use in analysis of problems. This information may
include a summary of the following:
• History (age, construction, materials used, level of maintenance performed)
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• Reservoir Operations (Drawdown, Refill, Turnover Rate, Short-Circuiting)
• Treatment methods
• Surrounding area and land use
• Known water quality problems
• Known sources of contamination
• Previous problems with reservoir and solutions.
2.2.2 Policies and Ordinances
Any policies and ordinances that are specific to particular reservoirs within the system
should be included in the reservoir management plan. This section also includes policies
that pertain to reservoirs of different construction types or different sizes. These could
include ordinances or policies regarding construction, pesticide or herbicide use, public
access, or other activities in the vicinity of the open reservoir. A utility may need to obtain
the authority to issue such ordinances, or may need to request the issuance of such
ordinances by the local government.
2.2.3 Operations
The reservoir management plan should include information concerning the overall
operation of the reservoir as part of the larger water system, as well as information related
to the reservoir disinfection system. It also should include information related to the
operation of any other equipment, such as a mixing system, that is used at a particular
reservoir.
Reservoir Operations
The plan should include a section identifying basic reservoir operation criteria, including
level operating targets and set points, level alarms and critical conditions, as well as
criteria for turnover rate. The section also should include SOPs for filling and draining the
reservoir, overflowing the reservoir, internal notification, and emergency shutdown of the
reservoir. The plan should refer to the utility's emergency response procedures, discussed
in greater detail later in this chapter. Procedures for disinfection of the reservoir and
dechlorination of water that is drained or overflowed should also be included (Knudson,
1998b). Utilities discharging directly or indirectly to water bodies of the United States
should consult with the National Pollution Discharge Elimination System (NPDES)
permitting authority regarding requirements for dechlorination.
Disinfection Operations
Disinfection operations are important to the proper functioning of the reservoir. A utility
should ensure that a minimum residual is maintained in the water that is entering the
distribution system and that an adequate pathogen inactivation is achieved. The
disinfection residual of a reservoir will vary seasonally, therefore, disinfectant dosages
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should be varied accordingly. Outlet disinfection is a high priority, especially in systems
that use unfiltered water sources. Responsibility for the maintenance of disinfection
equipment needs to be specifically outlined and assigned. The possibility of a failure in the
disinfection system should be considered and emergency response plans outlined (Capron,
1998).
The plan should include information about the type of disinfectant and disinfection
equipment used at the plant, as well as SOPs for the disinfection system. Disinfection
system data such as a system schematic, design criteria for the system, and chemical
supplier contact information should be included in the plan. SOPs should be included for
routine operations and treatment targets, chemical handling and delivery, as well as
procedures for chemical testing and quality assurance and quality control of the chemicals.
This section also might include a safety management and/or risk management plan for the
disinfection system along with emergency response information identifying responsibilities
and procedures.
Other Equipment
Information explaining the operation of any other equipment used in the operation of the
reservoir should be included in the management plan. This equipment includes pumps or
mixers used in a circulation system. Design criteria for these systems should be included
and responsibilities for these systems should be assigned.
2.2.4 Maintenance
This section of the reservoir management plan should address maintenance of the
reservoir, reservoir facilities, and equipment used to operate the reservoir. Maintenance of
the reservoir itself usually consists of cleaning the reservoir and repairing the liner and
sealing joints. Maintenance of the facilities includes maintaining security measures,
contamination control measures, and other facilities critical to maintaining water quality in
the reservoir. Equipment maintenance includes maintaining disinfection equipment or
other equipment such as pumps or mixers that impact the operation or water quality in the
reservoir.
Reservoir Cleaning
Cleaning strategies for reservoirs will vary. Some reservoirs can be cleaned easily once
emptied. Some must be cleaned while remaining full or in service. It may not be feasible
to clean some reservoirs due to the size or nature of the reservoir.
Reservoirs that can be removed from service and drained should be cleaned to prevent
accumulations of silt and algae on the sides and bottom of the reservoir. Utilities should
develop criteria used to initiate reservoir cleaning and plan the removal of a reservoir from
service to ensure that the reliability of the distribution system is not compromised. It is
critical not only to look at the other storage facilities that are out of service at the same
time, but also at projected construction schedules for adjacent water distribution pipelines
and feeder mains so that either the pipeline or reservoir remain in service.
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Weather may be a factor in planning a washing schedule. During freezing weather it may
be necessary to keep a reservoir full to prevent damage to the structure from ground
heaving, freeze-thaw cycling, and concrete contraction. Reservoirs also should be kept
wet in extremely hot weather because hot weather can melt joint sealant, which could
increase leakage from the reservoir (Capron, 1998).
The data collected during water quality monitoring can be used to plan or initiate a
cleaning schedule. Security reports and breaches in security also should be considered
when planning reservoir cleaning.
SOPs should be developed for all activities performed during reservoir cleaning. Cleaning
procedures should be developed along with procedures for the disposal of debris and
sediment. Cleaning SOPs also should incorporate routine cleaning activities as well as
spot-cleaning activities in and around the reservoir. These SOPs should address the
removal of any debris, garbage, or other objects near the reservoir or floating on the
surface.
Facilities Maintenance
The plan should include SOPs for the maintenance of the reservoir structures. This would
include paving repair and weed control. Typically, structural maintenance is performed on
structures in the reservoir whenever a reservoir is taken out of service.
Equipment Maintenance
The reservoir management plan should include preventative maintenance strategies for all
equipment necessary to properly operate the reservoir and control water quality. Routine
maintenance should be performed consistently, so as to keep reactive maintenance to a
minimum. It is a good idea to perform maintenance activities whenever a reservoir is
taken out of service.
2.2.5 Water Quality Monitoring
Water quality monitoring is an essential element of a reservoir management plan. A water
quality maintenance program should consist of water quality monitoring, visual
inspections, and control of contamination sources. Water quality monitoring not only aids
a utility in meeting regulatory requirements but also helps to identify normal or baseline
operational characteristics of the reservoir. Visual inspection is another method that
should be used to monitor problems since it can help to identify the causes of water quality
problems or even to prevent them. Both water quality monitoring and visual inspections
will give information that will identify contamination sources of particular concern to each
reservoir and will help to develop control strategies for mitigation.
Monitoring Parameters
Monitoring parameters should be identified for each reservoir. The SWTR Guidance
Manual is a good reference for identifying parameters for a monitoring program (AWWA,
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1991). Additional parameters will depend upon specific reservoir and downstream quality
requirements. Chapter 5 discusses water quality monitoring in greater detail.
Monitoring Criteria
Water quality monitoring criteria should be established for each reservoir. Operating
targets and operation limits should be established for water quality parameters such as
disinfectant residual, pH, and turbidity. Alarms should be activated when parameters
reach critical conditions. Samples should be collected downstream of the treatment
process and used to verify that the treatment process is working properly.
Monitoring Program
Once monitoring parameters have been defined for each reservoir, a monitoring program
can be developed to sample, analyze, and monitor the parameters. This information can be
used to develop specific strategies to control the parameter of interest. Data are necessary
to implement the strategies (i.e., to make control decisions). A consistent sampling
program will also help verify the effectiveness of control strategies. Additionally, this
information can be compiled in a database to establish a history of typical variations in the
reservoir water quality.
Some water quality parameters will be monitored using discrete sampling locations and
frequencies. These parameters may include bacteriological monitoring or disinfectant
residual monitoring at locations within the reservoir. Other parameters, such as pH and
chlorine residual, may be monitored continuously at key locations (e.g., at the outlet).
The sampling frequency of discretely monitored parameters will depend upon the amount
of risk associated with the parameter. If an elevated risk is associated with a specific
parameter, increasing the monitoring frequency of the parameter may be necessary. For
instance, if the disinfectant residual concentration drops below a specified level in a
storage tank, monitoring should be increased until disinfectant residual levels return to
normal.
Visual Inspections
Visual inspections of the reservoir should be performed on a routine basis. Inspections of
the water surface of the reservoir and the fence line should be performed daily.
Inspections should identify and monitor factors that are used to indicate that a reservoir
needs to be cleaned. The storm water drainage system should be inspected frequently
during the rainy season and monitored during a large rain event. Routine inspections of
the disinfection equipment, as well as other equipment, should be performed to verify that
the equipment and processes are working properly, to verify that there is adequate
disinfectant, and to adjust feed rates, if necessary.
Reservoir underdrains and other submerged structures should be inspected every time the
reservoir is taken out of service. Inspection of the drained reservoir also will help identify
the nature of contaminants that enter the reservoir. This includes the identification of
foreign objects, as well as the nature of sediments and algae. Consistent patterns of
foreign objects that are found can help identify security problems.
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Contamination Control
Potential contamination sources should be evaluated at each reservoir. Contamination
sources such as surface water runoff, bird and animal wastes, human activity, algal
growth, insects and fish, ground water intrusion, airborne deposition, and any other
identified sources should be considered as part of the evaluation. The reservoir
management plan should address these different sources of contamination and identify
control methods or strategies employed by the utility. As discussed previously, reservoirs
receiving surface water runoff or ground water intrusion are considered source water
reservoirs that are not compliant with provisions of the SWTR.
Control methods should be implemented to minimize the risk caused by exposure to a
contamination source. Routine observation of the water surface may reveal the type of
contaminants that are delivered to the reservoir, which in turn will help in determining
possible control and response strategies. Information regarding these specific potential
sources of contamination and their associated control measures are discussed further in
Chapter 3. In addition, general methods to protect and maintain water quality in
uncovered finished water reservoirs are presented in Chapter 4.
2.2.6 Staffing and Training
The plan should contain information concerning staffing and training that is unique to
specific reservoirs. Additional or unique types of training could be based on, for example,
the location of a reservoir, the construction of a reservoir, or the disinfection system used
in a reservoir. Training should be provided both for any new staff and periodically for
existing staff in order to enforce the goals of the reservoir management plan.
2.2.7 Safety
Safety issues that are specific to a reservoir should be included in the reservoir
management plan. Chemicals that are used at the different reservoirs should be identified.
Additionally, a Materials Safety Data Sheet (MSDS) should be maintained for each
chemical stored on-site to provide a reference for potential hazards. Safety issues related
to activities performed at specific reservoir sites also should be addressed.
2.2.8 Construction
The reservoir management plan should have procedures that will ensure that construction
activities do not affect the reservoir water quality. A procedure should be developed to
address onsite painting activities. If a reservoir has multiple basins and one of these basins
must be taken offline to perform construction activities, the utility should address the
problem of minimizing or eliminating the effect of the activities on the water quality in the
adjacent basins.
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2.2.9 Recordkeeping and Reporting
Recordkeeping and reporting requirements should be designed to meet any regulatory
requirements that are imposed upon the utility. Beyond the need to meet regulatory
requirements, accurate recordkeeping and reporting will help identify how a reservoir is
operating and will provide information that can be used to compare a present situation
with past experiences. It also can help to predict the effectiveness of potential reservoir
management strategies.
Data management, reporting, and tracking is important for a variety of reservoir
management functions such as reservoir operations, disinfection operations, water quality
monitoring, control of contamination sources, and reservoir cleaning activities. Records
for the operation and maintenance of the disinfection facilities should be maintained, and
any lapses in disinfection should be documented. Occurrences of security and equipment
breakdown should be documented. Records also should be kept of any debris found in the
reservoir, consumer complaints, algal control methods used, and water quality parameters
that are relevant to aquatic growth. Episodes of actual or threatened contamination
should be recorded and documented as well as any security violations, actual or
attempted. Example data sheets should be included in the document for each set of
information that a utility wants to collect, such as security information, water quality
information, or information derived from routine inspections.
2.2.10 Reservoir Security
Each reservoir needs to be evaluated to determine the level of protection that is required.
Major security problems should be defined and corrective responses identified. Specific
procedures need to be formulated to determine who corrects security problems and the
necessary time frame. A summary of the security measures employed at each reservoir
should include identifying fence height, setback distance, surveillance measures, and the
like.
2.2.11 Emergency Response Plans
The plan should provide policy and describe the roles and responsibilities with regard to
planning for and responding to emergencies at a utility's open reservoirs. In addition, the
plan should include emergency planning and response procedures for the different types of
emergency events that have a reasonable potential for occurring. As a minimum,
emergency procedures should be developed for each of the following scenarios: loss of
disinfection residual, breach of security, water quality contamination, hazardous chemical
release, and loss of structural integrity. Each type of emergency scenario should be
defined in the plan, including examples and subcategories as appropriate. Preventive
measures, warning measures, specific response procedures, persons/entities to be
contacted, recordkeeping and reporting requirements should be described for each type of
emergency.
If the reservoir is classified as a dam and regulated by either a Federal or State dam
agency, additional guidance should be developed. An operations and maintenance manual
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needs to be developed for the operation of the dam as well as an emergency action plan
addressing how the utility will respond to a dam failure.
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Utilities that operate open reservoirs should assess the water quality dynamics of their
facilities. The goal of the assessment is to characterize the potential sources of water
quality degradation and develop appropriate mitigation measures. The assessment should
consider all relevant environmental and operational factors, such as source water quality,
the watershed from which source water is drawn, adjacent land uses, ground water quality
in the surrounding watershed, and the presence or absence of a reservoir liner.
A thorough understanding of the potential sources of contamination is required for each
reservoir in the system so that mitigation measures can be implemented efficiently and
promptly at the first sign of contamination. The prevention of contamination should be
emphasized to the maximum extent possible. Utilities may want to consider the feasibility
of eliminating the open reservoir or implementing preventive controls such as reservoir
covers and liners, regular draining and washing, proper security and monitoring, and
drainage design to prevent surface runoff from entering the facility.
Failure to identify a potential water quality degradation problem, and control its
occurrence during initial developmental phases, can compound the problem and increase
the corrective effort required. An uncontrolled algal bloom, for example, will support
bacterial growth. Failing to prevent an algal bloom may significantly increase public health
risk, and increase the cost to control the problem using either additional chlorination,
other chemicals, or by removing the reservoir from service for cleaning.
Extracellular products from algae and algal biomass will contribute to the oxidant demand
of the reservoir; this is discussed later in the chapter. This oxidation may in turn result in
the formation of disinfection byproducts, such as THMs.
As discussed earlier, water works professionals have associated water quality issues and
threats to public health with open reservoirs for more than 80 years. Geldreich and Shaw
(1993) found that early studies of water contamination in open reservoirs identified the
following contamination sources: birds, animals, airborne deposition, plant growth, and
human activity (primarily swimming). More recent studies have expanded on the
traditional list of open reservoir contamination sources and include:
• Surface water runoff
• Bird and animal wastes
• Human activity
• Algal growth
• Insects and fish
• Ground water intrusion
• Airborne deposition
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Each of these sources of contamination and methods to mitigate their impact are discussed
below.
3.1 Surface Water Runoff
Any reservoir that receives surface water runoff is not in compliance with the SWTR, nor
is it a finished water reservoir but instead is a raw water storage reservoir (40 CFR
141.70(a)(l); 141.70(a)(2)). To maintain water quality and control risks, utilities must
completely eliminate all surface water runoff into their reservoirs. Any surface water
entering the reservoir is unacceptable for proper operation and regulatory compliance.
Surface runoff must never be allowed to enter the reservoir because contaminants may be
introduced to the treated water.
Contaminants that may be found in surface water runoff include soil, agricultural
fertilizers, pesticides, microbial pathogens, oil and other automotive fluids, vehicle tire and
brake wear residuals, and organic litter. Surface water runoff also can be a significant
source of turbidity, sediment, nutrients, natural organic matter (NOM), and some metals.
One study by Karimi and Ruiz (1991) of the Stone Canyon Reservoir complex of the Los
Angeles Department of Water and Power (LADWP) found a direct relationship between
heavy rainfall and high turbidity attributed to surface water runoff. Erb (1989) indicated
that Lower Stone Canyon Reservoir is one of three large open reservoirs operated by
LADWP that are essentially canyons with dams. As such, LADWP has indicated that it is
impossible to completely isolate these reservoirs from the effects of surface water runoff,
and it is not feasible to cover them. The California Department of Health (CDHS) has
declared four of LADWP's open finished water reservoirs to be untreated surface water
because of their exposure to surface runoff. The CDHS has mandated that these
reservoirs either be removed, covered, or their effluent treated by filtration. Figure 3-1
shows the LADWP reservoirs and indicates how LADWP intends to achieve compliance
with CDHS requirements.
Credit toward achieving the filtration and disinfection requirements of the SWTR begins
after the water is no longer subject to surface water runoff (40 CFR 141.70(a)(l)).
Disinfection that is applied prior to an open reservoir that is subject to surface water
runoff is not creditable under the SWTR. Adequate treatment is necessary after the point
in which the surface runoff enters the reservoir.
Several common methods exist to protect open reservoirs from surface runoff
contamination (AWWA, 1983; Bailey and Lippy, 1978). Observation of the reservoirs
can help determine where runoff is entering a reservoir and will help to determine how to
control it. If possible, samples of the runoff should be collected to determine the effect on
the reservoir and the steps needed to minimize the impact. The local drainage utility or
surface water management agency also may aid in identifying drainage basins and known
contaminants within the basins.
The fences surrounding many reservoirs are built upon a parapet wall to prevent runoff
from entering the reservoirs. Some facilities use a drainage system to channel runoff water
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to the closest storm sewer. Other reservoirs are built between earthen berms that are high
enough to eliminate runoff into the reservoirs. Drainage improvements generally employ a
multiple barrier approach and may include a combination of the above methods along with
gutters and pipe storm drainage systems. Surface runoff must be completely prevented
from entering an open reservoir system.
3.2 Bird and Animal Wastes and Control
Open reservoirs provide attractive habitats for birds and animals. Birds and animals may
carry microbial contaminants, including human pathogens. Contaminants may be carried
externally on the feathers, fur, and skin and transmitted to the reservoir through direct
body contact with the water. Contaminants also may be carried internally in the digestive
system, and may be transmitted to the reservoir through natural biological processes, such
as defecation occurring in or near the reservoir.
3.2.1 Bird Waste
Birds, particularly gulls and waterfowl, commonly visit or inhabit open reservoirs.
Identification of the type of birds that frequent a reservoir is important when deciding on
avian control measures, as well as determining how much of a problem is attributable to a
specific species. Birds are widely reported to be one of the most common and significant
sources of contamination at open reservoirs. Feces from these birds are a source of
coliform bacteria, viruses, and human pathogens, including vibrio cholera, Salmonella,
Mycobacteria, Typhoid, Giardia, and Cryptosporidium (Geldreich and Shaw, 1993).
Some Cryptosporidium species that are pathogenic to humans do not affect birds, but
birds may be carriers (Clement, 1997). Some of these carriers, such as gulls, are
scavengers and may ingest the pathogens while feeding at landfills or wastewater
treatment plants prior to visiting a reservoir. It is believed that these birds also carry
pathogens on their feet and feathers. It has been estimated that 5 to 20 percent of the bird
population is periodically infected with Salmonella and other intestinal organisms that are
pathogenic to humans.
As noted earlier, a 1993 waterborne Salmonella outbreak in Gideon, Missouri, that
resulted in seven fatalities, was traced to pigeons that had been roosting in a finished water
storage tank. Although the tank was provided with a cover, there were openings in the
cover that allowed birds access.
Several early studies found that the presence of waterfowl increased levels of coliform
bacteria in small recreational lakes by a factor of 20 times normal levels (Morra, 1980). In
1993, an Escherichea coli occurrence in the New York City system partially was
attributed to large numbers of seagulls frequenting the finished water reservoirs. Bird
carcasses have
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^Encino Reservoir. A filtration
plant has been proposed but must be
approved through the environmental
review process.
Lower Stone Canyon Reservoir. A
filtration plant has been proposed but
must be approved through the
environmental review process.
Clipper Hollywood Reservoir. This
reservoir will be replaced by covered
tanks.
Lower Hollywood Reservoir.
A small microfiltration plant has
been approved through the
environmental review process and is
currently in the design phase.
Source: LADWP, 1988
Figure 3-1. LADWP's Open Reservoirs Subject to SWTR
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been found within open reservoirs during cleaning, providing another source of bacteria
from the decomposition process.
As indicated in Table 3-1, bird feces may contribute nutrient loadings that can enhance
algal growth in the reservoir. Decaying carcasses of birds and animals that may be found
in open reservoirs also contribute to microbial growth. Reservoirs with large bird
populations also tend to have feathers and scavenged garbage carried into or nearby the
reservoir by the bird population.
3.2.2 Bird Control
Historically, many different methods of discouraging waterfowl from residing in or near
open treated water reservoirs have been practiced. Examples of methods to repel birds
include habitat modification, decoys, eagle kites, noisemakers, scarecrows, plastic owls,
dog hazing, and wires strung across the reservoir.
The installation of bird deterrent wires appears to be the most effective and economical
bird repellent method. Several utilities have had success using the wires, reporting
significant decreases in birds, coliform bacteria, and nutrients. The use of bird deterrent
wires at some large reservoirs, however, is not practical because of the extensive surface
areas to be covered. Some bird harassment methods may have adverse impacts associated
with their use. Noisemakers, such as cannon fire, may generate complaints from nearby
residents. Further, a bird harassment program may be more expensive than wires because
of the ongoing effort required of utility personnel responsible for performing harassment
activities; however, not all bird problems are continuous throughout the year. They are
generally dependent on seasonal activities, such as migration, nesting, and molting. Large
urbanized birds such as gulls and geese may become accustomed to noisemakers and
visual scaring devices within 2 to 3 weeks, necessitating frequent changes to the devices to
maintain effectiveness.
Observations at reservoirs where bird deterrent wires have been installed indicate that the
wires decrease the area available for the birds to land on the water surface. Upon sighting
the wires, birds that are approaching the reservoir have been observed to turn and fly
away. The wires are particularly effective against species that require relatively large
landing areas, such as waterfowl. Wires also have been installed on top of the parapet
walls that surround many open reservoirs to effectively prevent birds from perching on the
walls.
The City of Newport Beach, California, significantly reduced waterfowl landings by
stringing lengths of 0.015-inch stainless steel wire at 40-foot intervals over the 800-foot
length of a 20-acre open reservoir (Morra, 1980). Seagull activity at the Garvey
Reservoir operated by the Metropolitan Water District of Southern California also has
been significantly reduced by the installation of piano wire at 100-foot intervals (AWWA,
1983).
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Table 3-1. 1997 Nutrient Loadings by Bird Groups
in Seattle's Open Reservoirs
Soluble Nutrient Loadings by Bird Groups
Reservoir
Beacon Hill*
Bitter Lake
Green Lake
Lake Forest
Lincoln
Maple Leaf
Myrtle
Volunteer
West Seattle
Geese
Nitr. Phos.
kg/yr kg/yr
0.00 0.00
0.82 0.24
1.78 0.52
2.23 0.65
0.00 0.00
2.16 0.63
0.00 0.00
0.00 0.00
0.40 0.12
Gulls
Nitr. Phos.
kg/yr kg/yr
0.00 0.00
0.01 0.00
0.03 0.01
0.36 0.11
0.24 0.07
0.13 0.04
0.08 0.02
0.01 0.00
0.38 0.11
Ducks
Nitr. Phos.
kg/yr kg/yr
0.00 0.00
0.06 0.02
0.53 0.16
0.07 0.02
0.01 0.00
0.35 0.10
0.01 0.00
0.01 0.00
0.02 0.01
Overall
Total
kg/yr
0.00
1.15
3.04
3.43
0.31
3.42
0.12
0.03
1.03
Nutrient
Cone.
(MS/L)
0.00
14.09
16.05
15.09
3.96
15.43
4.35
0.42
4.00
*Beacon Hill has a chain-link fence around the water and a bird wire canopy, which excludes the
birds from the water. Birds counted on the site were outside the wire enclosure.
Notes:
Loadings (L) = DxFxNxSxP
Where:
L = Nitrogen or phosphorous loading
D = Number of days in consideration
F = Dry weight of feces produced per bird per day
N = Percent of nitrogen or phosphorous by dry weight feces
S = Solubility of nitrogen or phosphorous as percent of dry weight feces
P = Probability that feces enter the lake over a 24-hour period:
Geese 50%
Gulls 60%
Ducks 80%
Source: Seattle Public Utilities, 1997
Such wire systems are relatively inexpensive and have proven to have no serious adverse
affect on the birds. One of Seattle's open reservoirs had a severe problem caused by gulls
and waterfowl. This problem was completely eliminated through the installation of a wire
canopy and a chain-link fence. The City of New York's Department of Environmental
Protection (DEP) is a strong proponent of bird deterrent wires, reporting significant
decreases in both birds and coliforms following the installation of wires at their Hillview
Reservoir (Ashendorff et al., 1997). The city of Tacoma, WA has also installed bird
deterrent wires to combat this problem.
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The City of New York DEP has implemented an effective bird mitigation program at their
Kensico Reservoir, a source water reservoir considered too large for bird wires. The
program consists of habitat modification and bird harassment components. The City
constructed fences to inhibit the birds' access to the landscape areas. The harassment
program is implemented by a full-time manned patrol that scares birds away from the
reservoir by using guns, cannons, and other noisemakers. The DEP has reported that its
bird mitigation program at Kensico has been very effective. While this program is being
implemented on a source water reservoir, the techniques used there have practical value
for finished water reservoirs as well.
The City of Seattle experienced significant decreases in gulls and associated nutrient
loadings through the use of gull decoys and eagle kites. Seattle also has successfully
deterred geese by placing weighted plastic jugs on grassy areas.
3.2.3 Animal Waste
Animals known or suspected to contaminate open reservoirs include dogs, cats, deer, rats,
mice, opossums, squirrels, raccoons, beavers, and frogs. It is likely that some portion of
the animal population is infected with human pathogens that may be discharged to the
reservoirs in feces or transmitted by direct contact between animals and the water. Dogs
may cause contamination at reservoirs that are located in a park-like setting in residential
areas. In such environments, people tend to exercise their dogs in areas adjacent to the
reservoirs. This activity results in the deposition of waste products from the dogs that
may eventually reach the reservoirs in storm water runoff or by other means.
One major utility had a designated off-leash dog run area located adjacent to two of its
open reservoirs, although it did not have a problem with surface runoff. This area was
heavily used by pet owners, resulting in the deposition of fecal matter and significant
erosion of slopes adjacent to the reservoirs, thus increasing the potential for reservoir
contamination. Off-leash dogs also became more prevalent in other areas adjacent to the
reservoirs, resulting in feces deposition in all areas adjacent to the reservoirs and the
discovery of items such as dog toys and feces scoop bags in the reservoirs. Restricting
off-leash dogs to an area that was physically separated from the reservoirs solved this
contamination source.
Another concern with dog fecal matter is the risk of infection of other wildlife in the area
caused by organisms in dog fecal matter. If organisms in dog fecal matter infect other
animals in the vicinity of the reservoir, the risk of contamination to the reservoir is
increased, even if the dog fecal matter does not directly contaminate the reservoir
(Knudson, 1998c).
3.2.4 Animal Control
Utility owners should conduct surveys to characterize any animal contamination issues and
to aid in developing appropriate control measures. Such control measures may include the
following: modification of the perimeter security fence to reduce the risk of animal entry,
increasing fence setback distances, prohibiting pets within the vicinity of the reservoirs,
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
altering the nearby habitat to discourage animal entry, and trapping and removing or
exterminating nuisance animals.
3.3 Human Activity
While some open reservoirs are visited only rarely by persons other than operating
personnel, other reservoirs are visited frequently by the general public. Reservoirs that are
close to housing or are in a park setting may be exposed to significant human activities.
Some open reservoirs have become cultural centerpieces, the surrounding development
providing recreational and aesthetic amenities such that people and pets are drawn to the
very edge of the reservoirs. Although such reservoirs might have some controls, such as
decorative wrought-iron fences mounted on the reservoir's parapet walls, these may be
inadequate. For example, lack of sufficient fence setback and existence of an elevated
topography adjacent to the reservoir may leave a reservoir vulnerable to contamination.
Various activities, such as swimming and discarding of debris can directly contaminate
open reservoirs. Other human activities that occur outside of a reservoir's drainage area,
including some that may occur miles away, can create airborne deposition that may
degrade reservoir water quality. Airborne deposition is discussed further in Section 3.7.
3.3.1 Pesticides and Fertilizers
Pesticides and fertilizers may be applied to maintain landscaped areas adjacent to open
reservoirs. Airborne drifts from spray applications may carry these contaminants into the
reservoir. No-spray zones should be identified around open reservoirs to avoid surface
runoff and airborne deposition.
3.3.2 Swimming
In a 1998 water quality study of its system, Portland, Oregon found that bacteria and
viruses that cause disease in humans may be passed in the feces, shedded skin, and mucus
membranes of infected persons swimming in a reservoir. A single infected person can
shed a significant number of pathogenic fecal organisms in a single fecal event; up to 109
protozoa and 1014 virus. One open reservoir operated by a large utility was reported to be
a favorite swimming hole for the local high school students who repeatedly cut through
the security fence to gain access. Contamination from swimming is considered significant
in Portland, Oregon, where illegal swimming in the city's open reservoirs is reported
almost every year. The problem is aggravated by the inability to conduct primary
disinfection in the reservoirs and by hydraulic short-circuiting that could result in the
contamination rapidly reaching the reservoir outlet. Based on these factors, Portland,
Oregon was advised to develop an emergency protocol for the immediate shutdown and
disinfection of any reservoir in which swimming is observed.
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
3.3.3 Discarded Debris
When cleaning and inspecting open reservoirs, utilities routinely find a great variety of
items that have been thrown or otherwise deposited into the water. These items are a
potential source of pathogens and toxic substances. A study conducted in 1969 found
numerous items in an annual cleanup of Seattle's Volunteer Park Reservoir including a
dead cat, a plastic garbage can, beer cans, a pay phone, shoes, bottles, a shovel, and other
items. (Pluntze, 1974). These items were found in the reservoir despite the 8-foot high
chain-link fence topped with barbed wire and set back 10 feet from the reservoir. Even
though this study was conducted before open reservoir protection measures were
introduced in the 1970s, it underscores the importance of providing the maximum fence
setback possible and keeping humans away from a reservoir's immediate vicinity.
3.3.4 Deliberate Contamination
The susceptibility of open reservoirs to vandalism suggests that water quality sabotage is
possible. The City of Portland, Oregon initiated a risk potential study of the deliberate
contamination of the city's open reservoirs (Montgomery Watson, 1998). The study
concluded that deliberate contamination should be classified as "high hazard." No
incidents related to sabotage of open reservoirs have been documented as of this date.
Deliberate contamination can be avoided by implementing security measures such as
installing surveillance cameras or hiring security guards. Measures taken to provide
security at water treatment plants should also be used at reservoirs.
3.3.5 Human Activity Measures
Many water utilities maintain a perimeter security fence system around their open
reservoirs to minimize access by humans and animals to and near the water. Security
fences are considered to be an important and cost-effective measure to mitigate
contamination caused by human activity. Fences help secure the reservoir from illegal
swimming and the resultant contamination from body bacteria, fecal and urinary releases.
Utilities are strongly encouraged to install a security fence around each open reservoir
with a maximum possible setback distance from the reservoir as a standard preventative
measure. Impacts from human activity, such as debris discarded in the reservoir generally
decrease as fence-setback distance increase.
The Washington State Department of Health requires a 7-foot-high perimeter fence with a
100-foot setback from the edges of an open reservoir, or a 12-foot-high fence with a 50-
foot setback. In Washington, fences surrounding open reservoirs must be topped with
two strands of barbed wire and inspected at least daily. If site-specific constraints make
these requirements infeasible for a given facility, alternative security measures are
required, such as area lighting, fence motion alarms, closed-circuit television surveillance,
or a hired watchman who periodically inspects the premises. These types of security
measures are highly effective at discouraging trespassers. Several water utilities have
installed video cameras that feed to the central control room enabling the operator to
continually monitor the reservoir perimeter.
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
Public education programs also may be effective in preventing human contamination.
Some studies show that many people living near open reservoirs are unaware that they
contain finished drinking water. Utilities should identify whether such an awareness gap
exists and, if it does, consider developing a public education program. This educational
program should explain the use of the reservoir water as drinking water, the consequences
of contamination, and how to prevent contamination. The public education program may
include measures involving the posting of appropriate signs on the reservoir perimeter
security fence and distributing informational brochures at public counters and as
enclosures in water bills. Utilities may wish to discuss open finished water reservoirs in
their Consumer Confidence Report as well.
Open reservoir operations plans and monitoring programs should include provisions for
maintaining reservoir security. Responsibilities and procedures should be established for
identifying and responding to security breaches and for inspecting and repairing fences and
locks.
3.4 Algal Growth
Algal growth is a common source of water quality degradation in open and closed
reservoirs. A 1978 water quality survey of three public water systems serving customers
in California, Washington, and New Jersey found algae to be a major factor in water
quality degradation in all three systems (Montgomery Watson, 1998). A recent survey of
10 utilities in the United States and Canada indicated that algal growth is the most
common water quality problem in open reservoirs. Algal growth is a direct cause of
aesthetic degradation consisting of color, taste, and odor and can be evidenced in changes
in pH. In addition, algae play a fundamental role in the increase of other contaminants in
open reservoirs. These secondary contaminants, including pathogenic bacteria and DBFs
(such as THMs), may result in public health threats and waterborne disease if not
adequately controlled. Algae, especially blue-green algae, may contain toxins called
cyanobacterial toxins. These toxins are known to cause headaches, fever, diarrhea,
abdominal pain, nausea, and vomiting (Health Canada, 1998). Algal growth can increase
system maintenance requirements, such as more frequent reservoir cleaning and
distribution system flushing. It also may lead to consumer complaints.
Algal growth can be monitored. One utility monitors algal growth using a network of
sensors that identifies the prevalence of algae in the reservoir. This information is used to
identify locations for and timing of disinfectant application to curb the growth of algal
blooms (White et al., 1991).
Algal growth is stimulated in open reservoirs by the presence of sunlight and nutrients
provided by NOM. Algal growth increases biomass within reservoirs. The decomposition
of dead algal cells and other organic matter in the reservoir sediment can increase oxygen
loss and release iron, manganese, and nutrients, which in turn, supports further biological
growth.
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
Typically, algal growth in open reservoirs is controlled through the application of chlorine
or copper sulfate. Potassium permanganate and chlorine dioxide are also used to control
algal growth, but their use may be limited since these compounds are hazardous to
humans. Their potential health effects include skin and eye damage and these compounds
are potentially fatal if swallowed. Copper sulfate use is banned in several states and also
has similar health effects. LADWP controls algae in its Silver Lake Reservoir using batch
applications of dry copper sulfate and continuous applications of aqueous chlorine.
Copper sulfate is spread around the reservoir from a power boat or crop dusting plane,
while chlorine is injected through lengths of diffuser piping located near the reservoir
surface and bottom. Some utilities also may choose to drain and wash their open
reservoirs, however this is dependent on the character of the raw water, the climate of the
specific locale, and the treatment practices currently in place.
If copper sulfate and chlorine are applied to control intermittent algal growth, it is
important that they are applied while algal populations are low. Applying control
measures after the algal bloom has occurred makes the problem more difficult to control,
results in additional decaying biomass in the reservoirs, and poses a threat to water quality.
Killing mature algae also can cause the release of substantial amounts of absorbed
manganese.
Historically, LADWP has experienced chronic algal growth problems in several of their
large open reservoirs and has found that the prevention of algal blooms is the most
important aspect of maintaining water quality. In recent years, LADWP has developed
procedures to prevent algal blooms in these reservoirs through controlled chlorine
disinfection on an as-needed basis. These procedures are based on a type of reflectance
radiometer technology using electronic optical sensor equipment to monitor algal growth.
These procedures allow LADWP to chlorinate only when necessary and have reduced
chlorine use by approximately 30 percent.
3.4.1 Increase in Bacteria Populations
Several studies of natural waters have found correlations between algal growth and the
presence of bacteria. As part of a 1978 AWWA study, the Metropolitan Water District of
Southern California discovered that algal growth had resulted in the increase of the
number and types of bacteria in its open reservoirs, including a substantial population of
opportunistic pathogens. Furthermore, studies have shown that algae shield bacteria from
the effects of disinfection. LeChevallier et al. (1981) showed that bacteria are physically
protected within turbidity particles. Geldreich and Shaw (1993) determined that turbidity
particles greater than 1.2 microns are an optimal size for bacterial protection. Algae can
comprise a significant portion of the total turbidity in an open reservoir, including particles
of this optimal size. All these factors associated with algal growth (i.e., increases in algae,
bacteria, and turbidity) increase chlorine demand for disinfection of reservoir water.
EPA Guidance Manual 3-11 April 1999
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
3.4.2 Increase in Disinfection Byproducts
DBFs are water contaminants that may form as a result of the free chlorine disinfection
process. The combination of the presence of algae and free chlorine that often occurs in
open reservoirs contributes to the formation of DBFs, significantly degrading water
quality in finished water reservoirs and the distribution system (Karimi, 1988; Karimi and
Singer, 1991). DBF formation is enhanced in warmer water. Studies indicate that algae
release extracellular products (ECPs) during growth that are known to be THM
precursors (Karimi and Singer, 1991). During active photosynthesis, ECPs have a high
total trihalomethane formation potential (TTHMFP). In one instance, approximately 25
|j,g/L of TTHMFP was found to be produced per 1,000 aereal standard units (ASU) per
milliliter of algae cells. Figure 3-2 indicates that the maximum TTHMFP (MTP) in
LADWP's Silver Lake Reservoir was found to lag by approximately 1 month behind peak
algal growth periods. This study showed that bypassing the treated water around the
reservoir reduces THM formation by 40 percent. A direct correlation between THM
formation and chlorination was observed, with peak THM levels lagging approximately 1
month behind maximum chlorine application.
100
90
O)
D
C
O
e
+j
o 60
o
80
70
50
40
30
— Inlet
- -Blended Outlet
September November January March May
1986 1986 1987 1987 1987
July September
1987 1987
Maximum THM Levels across Silver Lake Reservoir
Source: Karimi and Singer, 1991
Figure 3-2. Maximum TTHMFP (MTP) in LADWP's
Silver Lake Reservoir
It should be noted, however, that DBF levels do not necessarily increase in all open
reservoirs. Although the high TTHMFP values correlated with peak algal levels at
April 1999
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
LADWP's Silver Lake Reservoir, studies conducted at an open reservoir in Seattle
indicated that algae are not causative agents contributing to DBF formation. Other types
of organic substrate also have the potential to affect DBF formation.
Some utilities have observed no significant changes and some have actually experienced
decreases in DBF levels across their open reservoirs (AWWA, 1983). One utility has
conjectured that DBF levels may decrease through volatilization or through oxidation of
precursors by heterotrophic bacteria. As there are many potential variables involved with
this subject, further study is necessary.
3.4.3 Increase in Taste, Odor, and Sediment Problems
Algae are a common cause of taste and odor problems in open reservoirs. High doses of
chlorine reacting with the algae during summer months has prompted numerous customer
complaints of foul taste and odor (Kittredge, 1994). Decaying microorganisms can form a
sediment layer at the bottom of the reservoir. When the reservoir level is low during dry
seasons or periods of high demand, these sediments can be drawn into the distribution
system. These sediments in the distribution system can severely compromise water quality
and appearance and increase health risks to consumers. Long-term deposition of
sediments in the distribution system can cause operational problems and harm the
hydraulic efficiency of the system.
One utility reported that severe taste and odor problems occurred in several of its open
reservoirs during 1997 to 1998. This water quality degradation was related to blue-green
algae and required removal of the reservoirs from service during peak demand season,
despite acceptable microbiological quality. The utility was unable to determine why this
problem occurred only in its lined reservoirs. Accumulation of sediment, including
organic matter and silt, also was observed in these reservoirs, although this is common in
both open and closed reservoirs. Sediment accumulations are due partially to the fact that
the source water is unfiltered. The affected reservoirs needed to be cleaned twice as
frequently as the other system reservoirs. Increased distribution system flushing was
required to alleviate taste and odor concerns.
Algal blooms occur regularly in the open reservoirs of one major utility, primarily during
spring as water temperature increases. These blooms are caused by green algae and have
contributed to taste and odor problems in the system. Blue-green algae, although present
in viable numbers, do not cause the blooms and are believed to be controlled by
environmental conditions within the reservoirs, such as cool water temperatures and
nutrient-deficient waters.
3.5 Insects and Fish
3.5.1 Insect Larvae
Uncovered reservoirs are occasionally infested with the larvae of insects such as midge
flies and water fleas (Moore, 1979; Atherholt, 1997). Infestations are typically discovered
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
at the customer's tap because the larvae and can be carried through the distribution system
from the reservoir. Several utilities experienced exacerbated infestations once or twice in
a 10-year period. Since chlorination is ineffective against midge fly larvae, one utility
employs seasonal malathion spraying to control the larvae. The spraying is conducted on
the trees and shrubs around the perimeter of the reservoir and only when winds are less
than 15 mph. Another midge fly control measure involves the temporary removal of the
affected reservoir from service for cleaning. A secondary impact of midge fly outbreaks
that may occur is the temporary increase in insect-eating birds, such as swallows, that
arrive at the affected reservoir to feed on the adult flies swarming above the water surface.
Because they are open to colonization by insects, the potential for infestation; may be
greater in an open reservoir. Covering a reservoir, however, is not a guarantee against
infestation if the reservoir is infested before covering (Bay, 1993).
3.5.2 Fish
Some open finished water reservoirs have been found to support fish populations. In one
instance, extensive chlorination killed approximately a thousand fish that had been living
undetected in a 120-foot-diameter open reservoir. Upon discovery of the fish, the
reservoir was cleaned and an accumulation of 2 feet offish droppings was found at the
bottom. This waste had been periodically drawn into the distribution system (Morra,
1980). Utilities can shock reservoirs to determine whether fish are present. If detected,
they should be removed or eliminated.
3.6 Ground Water Intrusion
Both open and closed reservoirs may experience problems with ground water intrusion.
Ground water can contaminate the water in a reservoir and may contain significant levels
of nitrogen and/or phosphorus, each of which can increase algal growth and aid in THM
formation. Bromide ion levels in the water also may affect DBF formation. Ground water
can be contaminated from a number of sources, including substances leaking from
underground storage tanks and municipal and industrial wastes entering an aquifer.
Utilities should line their reservoirs with impermeable substances to prevent the intrusion
of adjacent ground water. Effective reservoir liner materials include concrete, asphalt, and
chlorosulfonated polyethylene. Concrete and asphalt liners need to have sealers between
slabs. Several considerations should be accounted for when designing a liner for a finished
water reservoir. These considerations include material characteristics, cost and life
expectancy, climatic conditions, and the reservoir geotechnical characteristics. These
considerations are discussed in greater detail in the AWWA Manual M25 entitled
"Flexible-Membrane Covers and Linings for Potable-Water Reservoirs" (AWWA, 1996).
All liners should be inspected periodically to identify leaks and make necessary repairs. A
properly maintained liner typically lasts 25 to 30 years, while a poorly maintained liner
may last only 15 years.
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
Finished water reservoirs subject to intrusion of ground water under the direct influence of
surface water are in violation of the SWTR (40 CFR 141.70(a)(l)). These systems
require treatment (including disinfection) to meet the SWTR requirements.
3.7 Airborne Deposition
Open reservoirs also are subject to airborne deposition from contaminants, such as
industrial pollutants, volcanic ash, automobile emissions, pollen, dust, and paniculate
matter. Deposition occurs during all types of weather conditions, but is likely to be
accelerated during precipitation events as air pollutants are transported from the air
column above the reservoir by rain or snow. Furthermore, bacteria may enter open
reservoirs through airborne pathways. Studies have shown, however, that the impact of
dust and other airborne contaminants on reservoir water quality is minimal (AWWA,
1983).
The process of airborne deposition is well illustrated by the historical data on lead
contamination in the sediment of Portland, Oregon's reservoirs (Montgomery Watson,
1998). Based on a laboratory detection limit of 0.001 mg/L, lead was not detected in the
source water or in water leaving the reservoir.
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3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES
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April 1999 3-16 EPA Guidance Manual
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4. MITIGATING WATER QUALITY
DEGRADATION
This chapter focuses on general methods to protect and maintain water quality in
uncovered finished water reservoirs. Covering reservoirs with fixed or floating covers
may be the best way to protect water quality. Additional measures to protect and maintain
water quality can be accomplished through operational measures such as the adjustment of
detention time, turnover rate, disinfection, and hydraulic flow-through. The feasibility of
implementing a mitigation measure varies with individual site conditions. Detailed
feasibility analysis is required to identify the most technically and economically suitable
solution and determine whether the reservoir can be eliminated, replaced, or provided with
a fixed or floating cover.
Uncovered finished water reservoirs are susceptible to contamination from a variety of
sources, as described in Chapter 3, because they are open and exposed to external
influences. These contamination sources can include bird and animal wastes, human
activity, algal growth, insects and fish, surface water runoff, ground water intrusion, and
airborne deposition. This chapter describes control measures not necessarily associated
with a particular source of contamination.
Three primary types of water quality degradation problems may occur in open reservoirs:
• Microbiological - algal growth, HPC bacteria, coliform bacteria populations,
pathogens, animal contamination, taste and odor problems, nitrification when
chloramines are used as a disinfectant
• Chemical - elevated DBF levels and increased DBF formation potential
• Physical - increased particulate levels from airborne dust contamination and
animal contamination.
The single most important factor adversely influencing water quality degradation is
excessive detention time (Kirmeyer and Noran, 1997). Excessive detention time leads to
the loss of chlorine residual and contributes to all three types of water degradation
problems.
Finished water is a precious and perishable resource that cannot be stored for an indefinite
period of time without incurring serious risk of water quality degradation. The longer
water resides in a reservoir, the greater the opportunity for degradation by contaminants
and chemical processes. The adoption and reinforcement of this fundamental concept is
the crucial first step toward an understanding of the proper storage of potable water.
EPA Guidance Manual 4-1 April 1999
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4. MITIGATING WATER QUALITY DEGRADATION
4.1 Reservoir Turnover
Reservoir flow-through rate, or turnover rate, is a measure of the frequency with which
water is replaced in the reservoir. Excessive detention time will occur if a reservoir's
turnover rate is too slow, or if there is hydraulic short-circuiting. Water degradation
results when the chlorine residual decreases as detention time increases. The loss of
chlorine residual is a typical problem in open reservoirs and is of concern because it allows
bacteria and other microorganisms that pose a threat to public health to multiply.
In developing an effective turnover rate for its reservoirs, a utility should consider all
reservoir functions to achieve a proper balance in system operations. Some traditional
reservoir management practices that are used to achieve non-water quality related
functions tend to result in turnover rates that are too slow. The constant maintenance of
sufficient reservoir water storage to meet system pressure and emergency requirements,
for example, may have to be balanced against the water level drawdown/refilling
operations needed to obtain an adequate turnover rate.
The maintenance of an adequate turnover rate is an effective and economic tool for
controlling water quality degradation problems (Silverman et al., 1983). Proper reservoir
management dictates that utilities actively identify and maintain the best practicable
turnover rates in their open reservoirs. The optimal average turnover rate is determined
by site-specific factors and will therefore be specific to each reservoir within a system.
The desired turnover rate also may vary over time for a given reservoir in response to
seasonal or other periodic changes in controlling factors. To determine the desired
turnover rate for a reservoir, a utility should define and evaluate at least two primary
factors: (1) the chlorine decay rate in the reservoir and (2) the configuration of the
reservoir.
Based on the chlorine residual at the reservoir inlet and chlorine decay rate in the
reservoir, the utility can determine the theoretical turnover rate needed to achieve a pre-
established chlorine residual goal. This method of calculating the turnover rate is most
applicable to reservoirs in which the water-flow regime most closely approximates ideal
plug flow. Ideal plug flow, a flow regime in which a well-mixed volume of water will
proceed at a steady rate from an inlet at one end to an outlet at the opposite end, is best
suited to rectangular-shaped reservoirs with smooth and even surfaces.
Open reservoirs, which are often circular or irregularly shaped and not well mixed,
typically do not exhibit ideal plug flow. Hydraulic "dead spots" of stagnant water, for
example, are frequently found in reservoirs having an inlet and outlet in close proximity of
one another. In this type of reservoir, the water that is hydraulically short-circuited near
the inlet and outlet may have an adequate chlorine residual, but significant water quality
degradation can occur in the dead spots that may form outside of the inlet/outlet area of
influence. The water in these dead spot areas may have a detention time as high as several
weeks and will therefore not have a chlorine residual. These dead spots and short-
circuiting can be located by monitoring at multiple locations and depths to characterize
chlorine residual dynamics throughout the reservoir. The chlorine residual monitoring
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data can be used to determine an optimal average turnover rate for the reservoir that will
result in an adequate chlorine residual throughout the reservoir.
To ensure that the optimal turnover rate for each reservoir is actually achieved during
day-to-day operations, the utility should develop and implement a water-level fluctuation
strategy. The objective of this strategy is to force most of a reservoir's water to turn over
in one continuous cyclical operation of water drawdown and refilling. A cycle consists of
draining a large percentage of the reservoir and allowing a pre-determined period of time
to pass before refilling. Another, but less desirable method, involves periodic flushing of
the reservoir by overflowing. Turnover rate management programs that include water-
level fluctuation strategies will avoid the long detention times that might occur in dead
spots, or poorly circulating areas. The frequency and amount of water fluctuation
necessary will depend on the flow characteristics of the reservoir. This type of strategy is
critically important for reservoirs that have common inlets and outlets such as standpipes.
Some utilities have developed turnover rate management programs that include water-
level fluctuation strategy as an important tool for the correction of water quality
degradation, preventing conditions from worsening. One large utility, faced with a water
quality problem such as taste and odor, will increase the turnover rate using any of the
following water-level fluctuation methods: (1) flushing out the affected reservoir by
overflowing at high rates, (2) adjusting distribution system valves to increase flows from
the affected reservoirs, and (3) using auxiliary pump stations to draw down the reservoir
at an accelerated rate. This utility's open reservoir management plan includes a turnover
rate goal of 5 days and a minimum chlorine residual goal of 0.6 mg/L at the reservoir
outlet.
If a system chooses to incorporate a water level fluctuation strategy, it should address
potential algal growth problems. Algae growth can cause problems because it tends to
colonize on the surface of the sides of the reservoir. As a water-level fluctuation strategy
is implemented and the water level is decreased, the algae on the sides of the reservoir may
perish. Once the water level is increased, the water will come in contact with these dead
organisms, which may result in water quality degradation. It is important to address this
possibility while deciding whether to implement a water fluctuation strategy.
Although turnover rate can be used to effectively decrease water quality degradation, only
one State has regulations that address turnover. Ohio requires that at least 20 percent of
the reservoir volume turns over daily. Internationally, Germany limits maximum detention
time to between 5- to 7-days for concrete-lined reservoirs, while Switzerland limits a 1- to
3-day maximum, based on the lower chlorine residuals maintained at Swiss facilities.
Kirmeyer and Noran (1997) indicated that an average turnover rate should range from 3-
to 7-days.
4.2 Disinfectant Residual
As stated in the previous section, the maintenance of a chlorine residual within a reservoir
is an important measure for controlling the growth rate of bacteria and microorganisms.
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Long detention times that result from insufficient reservoir turnover cause a decline in
chlorine residual and degradation of water quality. Sunlight also will react with the
chlorine, making it especially difficult to maintain a residual.
The chlorine residual required to maintain water quality is unique to each reservoir. The
required chlorine residual is based on reservoir size, detention time, water quality, and
hydraulic characteristics. The initial chlorine dosage required to maintain the residual level
will vary with the season and the quality of the source water. However, other factors may
contribute to making it difficult to maintain a chlorine residual even during periods of
higher water use. For instance, the higher temperatures that lead to higher water use also
may promote greater biological growth in the reservoir, which will increase chlorine
demand. The chlorine demand also may increase because of the greater exposure of the
reservoir to sunlight during the warmer summer months, which will tend to degrade the
chlorine residual. These two factors alone may make it difficult to maintain a chlorine
residual even when the detention time is shortened due to high water usage.
Chlorine levels should be monitored frequently to ensure that proper disinfection and
water quality are maintained. The frequency of chlorine monitoring is specific to a
reservoir and to the quality of the source water. Utilities should monitor the residual
regularly for two reasons: (1) to ensure that a protective level of disinfection is
maintained, and (2) to detect a sudden loss in residual, or a sudden decrease in residual
that is indicative of deteriorating water quality in the reservoir, or of some other event
occurring that should be addressed (e.g., an algal event in the reservoir or a source water
problem).
Chlorine levels should be monitored in various locations in the reservoir to determine the
location of "dead spots" where water can reside for extended periods. These hydraulically
stagnant areas can be located by sampling for chlorine residual at different locations and
depths and identifying those areas having the lowest chlorine residual concentrations. The
subject of dead spots is discussed further in Section 4.3.
Chloraminated systems are subject to the threat of nitrification. During nitrification,
nitrifying bacteria convert ammonia (NHs) to nitrite (NCh) and nitrate (NOs). Nitrite and
nitrate are inorganic chemicals that are contaminants under the SDWA. The MCLs for
nitrite and nitrate are 1 mg/L-N and 10 mg/L-N, respectively, at the entry point to the
distribution system. Utilities should strive to maintain nitrite and nitrate levels as far
below their MCLs as possible because additional nitrification may occur in the distribution
system. Excess amounts of nitrate and nitrite are known to cause methemoglobinemia
(blue baby syndrome). Maintaining short detention times and frequent turnover will allow
utilities to minimize nitrification potential (Kirmeyer and Noran, 1997). This will ensure
that nitrifying bacteria populations cannot grow sufficiently large to produce an unsafe
amount of contaminants. The utility may need to adjust the chlorine:ammonia:nitrogen
ratio at the water treatment plant to control nitrification. Monitoring the chloramine
residual and levels of nitrifying bacteria is a site-specific activity that is vital for proper
management of a chloraminated system. Monitoring should be frequent enough to identify
problems before they become serious.
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4.3 Hydraulic Effects
A properly designed reservoir provides sufficient mixing within the reservoir to eliminate
any hydraulically stagnant areas and ideally has flow characteristics approaching ideal plug
flow. These design considerations will help to maintain uniform chlorine residual
concentrations throughout the reservoir. As stated in Section 4.1, long detention times
and low chlorine residual concentrations result in HPC and coliform bacteria growth, algal
growth, and nitrification of chloraminated waters. The chlorine demand is then increased
in these types of situations, especially in warmer waters.
In contemplating any potential remedial or mitigation improvements, it is appropriate to
conduct initial modeling to evaluate potential sources of the problems, conduct modeling
studies to evaluate alternative mitigation options, and conduct follow-up monitoring to
assess the potential effectiveness of improvements.
4.3.1 Flow Short-Circuiting
In an ideal reservoir all water molecules will spend an equal amount of time in the
reservoir. Inconsistencies in the physical configuration of a reservoir, however, can often
lead to dead spots and short-circuiting of water flows. The following reservoir
characteristics are common causes of flow short-circuiting:
• Common inlet and outlet location - Water is not allowed to flow throughout
the reservoir and displace water further away from the inlet/outlet location.
Therefore, the water that most recently has flowed into the reservoir can be the
first to flow out of the reservoir. Thus, the most likely location for dead spots
is the end of the reservoir opposite the inlet/outlet structure.
• Poor location of inlets and outlets - Water will naturally tend to flow in the
path of least resistance from reservoir inlet to outlet. Hydraulic dead spots and
short-circuiting will form in reservoirs with poor inlet and outlet locations and
no baffles to direct the water flow. Ideally, the reservoir outlets should be
located on the side opposite the inlets. Common inlets and outlets, and inlets
that are in close proximity of outlets, will result in undesirable flow patterns.
Water will short-circuit along the natural flow path between inlet and outlet,
and the dead spots will form in areas outside of that path.
• Uneven reservoir depths - If the reservoir has any spots that are significantly
deeper than adjacent areas, the water in the deeper areas will tend to stagnate.
Water in these stagnant zones will tend not to mix with the water flowing
above.
• Shape of the reservoir - The potential for flow short-circuiting and dead spots
increases if the shape of the reservoir has any irregularities, such as bays,
peninsulas, or uneven sides.
• Thermal stratification - Seasonal temperature changes and reservoir water
flow patterns can lead to the thermal stratification of the reservoir water.
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Thermal stratification results in the formation of distinct thermoclines that
separate into warm and cold water zones. This condition can be hydraulically
stable and can inhibit water movement between the thermally stratified water
zones. LADWP discovered that thermal stratification significantly decreased
disinfection efficiency in some of their reservoirs (White, 1998). In this
stratified environment, chlorine tended to accumulate at the bottom of warm
water thermoclines, forming a lens of chlorine concentration in those areas and
chlorine residual deficiencies in surrounding areas.
4.3.2 Hydraulic Circulation System
The reservoir characteristics described above often cannot be readily changed in an
existing reservoir. Therefore, systems may choose to install hydraulic circulation systems.
In a circulation system, water is pumped out of the reservoir and returned to another
location in the reservoir, to ensure homogeneous water quality throughout the entire
reservoir. Hydraulic circulation is optimized when the distance between the circulation
system inlet and outlet is maximized.
Kirmeyer and Noran (1997) proposed that the velocity gradient be used as a basis for
establishing the power needed to maintain adequate mixing in a reservoir. The equation is:
G= / or P = G2|iV
where G = velocity gradient, sec"1
P = power input, ft-lb/sec
|i = dynamic viscosity, Ibf-sec/ft
V = Volume, ft3
The velocity gradient is a widely accepted general design criterion for rapid mixing and
flocculation unit operations. However, the use of the velocity gradient in establishing
power requirements for reservoir mixing is a relatively new concept. A "G" factor of
10/sec has been suggested as an acceptable velocity gradient for reservoirs (Kirmeyer and
Noran, 1997). The following is an example of the use of this equation in determining the
required power input.
Example calculation
Given G = 10 sec-
\i = 2.39 x 10'5 Ibf-sec/ft2
V = 1.34 x 105 ft3 (1 million gallons)
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Determine mixing power requirements:
P = G2|iV = (102)(2.39x 10"5)(1.34x 105) = 320 ft-lb/sec
Since 1 ft-lb/sec = 550 hp
P = 0.58 hp
This calculation does not take into account the inefficiency of the pump motor, pump,
piping head losses, or discharge losses. The velocity gradient calculation estimates the
total power required to mix a reservoir but does not consider how this energy should be
distributed. The proper distribution of this energy is crucial in achieving adequate mixing.
Circulated water should be introduced into the reservoir as uniformly as possible to
promote mixing within the reservoir. This can be accomplished using diffusers. Diffusers,
in this application, are pipes with a series of strategically placed and sized orifices or ports.
The following procedure may be used as an approach for design of the circulation system
(Kirmeyer and Noran, 1997).
1. Select the velocity gradient goal
2. Determine diffuser port spacing and placement
3. Select diffuser port diameter and circulation system flow
4. Design piping system, compute head losses and check piping system for proper
distribution of flow between nozzles
5. Choose the orientation of jets
6. Select pump
7. Decide whether a rechlorination system is needed.
One additional benefit of a pumped circulation system is the possibility of introducing a
chemical feed system to adjust chlorine residual. The chemical feed pump in this system
could be automatically operated using feedback from a chlorine residual analyzer that tests
water entering the circulation system. This system could be designed to operate
continuously or intermittently with either timer control or residual pacer control.
4.3.3 Reservoir Baffling
Baffles that are properly designed to promote uniform plug flow inside the reservoir can
minimize short-circuiting. A properly designed baffle will not inhibit reservoir
maintenance or cleaning. All baffles should extend from the floor of the reservoir to above
the maximum water level. Small openings in the baffles at floor level can be provided to
facilitate drainage and cleaning. Preferably, any openings in the baffles should be sealed
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when not in use to prevent short-circuiting. Removable doors and walk-through openings
have been used in baffles to facilitate inspections and reservoir maintenance activities.
For a rectangular reservoir, baffling should be designed to provide a length-to-width ratio
of 20:1. The width is measured as the spacing, or channel width, between baffles. The
length is the total distance traveled through all channels. Length-to-width ratios of 20:1
are considered to be the optimal for rectangular reservoirs because greater ratios have not
been found to significantly improve the desired plug flow regime. Baffling may not be
appropriate if dead zones of stagnant water are not expected to be a problem.
For a circular reservoir, a baffling configuration of three to seven baffles is suggested.
The number of baffles and their placement are primarily determined by water quality
concerns and the occurrence of stagnant water areas.
Many construction materials and design configurations are available for a baffling system.
Materials of construction include cast-in-place concrete, concrete masonry units (CMUs),
and framing, such as stainless steel, aluminum, or fiber-reinforced plastic. If a floating
cover will be installed, there is a variation of baffling known as hanging baffles in which
weighted flexible baffles hang from the cover and are not attached to the reservoir floor.
All of these options should be weighed according to the needs of the site and the cost of
construction. Cast-in-place concrete and CMUs have a high capital cost but are durable
and long lasting.
4.3.4 Submerged Mixer
Submerged mixers can be installed in a few key locations in the reservoir to create
instability in the reservoir flow. The mixer accomplishes this by introducing a source of
kinetic energy that disturbs the equilibrium that normally evolves in the reservoir. Even
one small mixer in the center of the reservoir will create an unstable area that affects the
entire reservoir. Water surrounding the instability will be attracted toward the unstable
area in an effort to reach a stabilized condition. The energy required to create this
disturbance does not need to be substantial. As with the hydraulic circulation system
above, a "G" factor in the range of 10/sec has been suggested as an acceptable velocity
gradient for reservoir mixing.
4.3.5 Relocating Inlets and Outlets
Ideally, the reservoir inlet and outlet are positioned to maximize the length of the water
flow path. In a reservoir without baffling, it is best to maximize the distance between the
inlet and outlet. Separation of the inlet and outlet may reduce short-circuiting through the
reservoir and improve circulation. If a utility is considering relocating an inlet or outlet of
a reservoir, it should compare the costs to the cost of a baffle system that will increase
mixing and increase the length of the flow path.
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4.3.6 Altering Flow Patterns at the Inlet and Outlet
The design of the inlet and outlet also can have an affect on the flow in the reservoir. One
design that has been used successfully in circular shaped reservoirs involves realigning the
inlet pipe. For example, providing a 90-degree bend on the inlet oriented parallel to the
wall of a circular reservoir will promote water flow around the perimeter of the reservoir,
thereby increasing the flow distance between inlet and outlet.
4.3.7 Aerators
Aerators are mechanical mixing devices that can be used in reservoirs to prevent thermal
stratification. Two types of aerators normally used in reservoirs include bubble plume
aerators and deep draw aerators.
Bubble plume aerators, also known as air curtains, consist of low-pressure air lines
installed on the floor of the reservoir. The air lines have groupings of small-diameter holes
along their length, resulting in a curtain of air that flows from the reservoir bottom to the
water surface. The air bubbles move colder water from the reservoir bottom toward the
surface, resulting in the colder water mixing with the overlying layers of warmer water.
The mixing of warm and cold water creates instability as the water seeks thermal
equilibrium.
Deep draw aerators are similar to bubble plume aerators. An air line is extended to the
bottom of a reservoir. A draft tube may be used to guide the initial upward rise of
bubbles. The rising bubbles cause a roll-type blending of the warm and cold water layers.
4.3.8 Analyzing Reservoir Hydraulics
Reservoir hydraulics can be investigated and better understood by using tracer tests or
finite element modeling. Tracer testing involves introducing a tracer chemical into the
reservoir water stream and measuring the concentration of the tracer at the reservoir
effluent at various time intervals. The results provide insight on the hydraulic
characteristics of the reservoir. Finite element modeling is a powerful computer
simulation method that can model the dynamics of reservoir flow. The following sections
provide more detailed information on tracer testing and the benefits of finite element
modeling.
Tracer Study
As mentioned above, reservoir hydraulics can be analyzed using a tracer test. A tracer test
is performed by injecting a known amount of tracer into the inlet of the reservoir. The
concentration of the tracer is then measured at the effluent of the reservoir at various time
intervals. The test results are summarized graphically as tracer concentration versus time.
The resulting graph provides insight on the hydraulic characteristics of the reservoir. A
more detailed discussion of how to perform a tracer test provided in the SWTR Guidance
Manual, Appendix C (AWWA, 1991), is summarized below.
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The effective contact time of the reservoir, Tio, is obtained from the test data. Tio is
defined as the time at which a portion of the water has passed through the effluent
sampling point. The hydraulic efficiency of the reservoir is represented by Tio/T, where T
is the theoretical detention time. A Tio/T of 1.0 represents ideal plug flow conditions. A
reservoir with a high hydraulic efficiency has a Tio/T in the range of 0.5 to 0.8. A Tio/T
below 0.3 represents a low hydraulic efficiency, which indicates short-circuiting and dead
spots.
The two basic methods of tracer addition include the step-dose method and slug-dose
method. Both methods are theoretically equivalent for determining Tio. In the step-dose
method, the tracer is dosed at a constant rate until the concentration reaches a steady-state
level. An advantage of the step-dose method is that Tio can be determined directly from
test results. One of the disadvantages of the step-dose method is that it requires chemical
feed equipment. Another disadvantage of the step-dose method is that a concentrated
tracer is needed to adequately define concentration versus time.
In the slug-dose method, the tracer is dosed as a one-time application. The slug-dose
method does not require chemical feed equipment; however, intensive mixing of the
influent, following tracer addition, is required. Further, additional data manipulation is
required in the slug-dose method to determine Tio.
The selected tracer chemical should be readily available, nonreactive, easily monitored,
and approved for use in potable water supply. Commonly used tracers include fluoride,
Rhodamine WT, lithium, sodium, and chloride. Fluoride is the least expensive of these
tracers.
The tracer concentration should be sufficiently high to allow the tracer to be detected, but
should not exceed the Secondary Maximum Contaminant Level (SMCL) for the chemical.
With the step-dose method, the ideal tracer concentration is at least four times the
background concentration of the chemical. With the slug-dose method, the tracer
concentration depends on the anticipated hydraulic efficiency of the reservoir. A reservoir
with an anticipated low hydraulic efficiency would need a larger amount of tracer
compared with the reservoir with a high hydraulic efficiency because of a lower peak
concentration.
It is important to maintain a constant flow and a constant water level in the reservoir
during the tracer test. Since reservoir hydraulics will change depending on the level of the
reservoir, several tests should be conducted, each at different reservoir levels. At a low
reservoir level, the hydraulic efficiency may be high because of less dead volume due to
the lower depth. At a higher reservoir level, the dead volume may increase, leading to a
lower hydraulic efficiency.
Water temperature also may be an important variable in the tracer study. If a reservoir is
known to experience wide variation in temperature over a short period of time, it may be
useful to conduct additional tracer tests at different temperature conditions to determine if
temperature currents are causing short-circuiting problems.
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As noted previously, chlorine residual monitoring also can be used to roughly characterize
reservoir hydraulics.
Finite Element Modeling
Finite element modeling is another method to locate dead spots. Finite element modeling
is a method of computer simulation that simplifies complex systems, such as a reservoir
system, by dividing it into many small elements. The hydraulics within each of these
smaller, simpler elements can be modeled and the results used to estimate the overall
reservoir system hydraulic flow.
Finite element modeling can be used to model not only the existing reservoir hydraulic
characteristics, but also the characteristics of the reservoir hydraulics when influenced by a
mixer, other water circulation device, or baffles. Results provided from the modeling are
in two or three dimensions and include speed contour plots, velocity vector plots, kinetic
energy (turbulence) plots, and other parametric plots. In more complex modeling,
chemical feed applications such as chlorine can be modeled if chemical diffusivity, mass
flow rate, rate reaction constants, and injection points are described. Chemicals can
alternatively be modeled as particulates, with the trajectories plotted (Stolarik and Miller,
1998; Henry, 1996).
Finite element modeling does have limitations that result from the lack of detailed input
information or the inability of the program to simulate extremely complex phenomena.
These limitations include the inability to simulate thermally induced convection and wind
induced currents, and are derived from complex phenomena such as density variations and
chemical decay.
4.4 Reservoir Cleaning
To maintain water quality, a reservoir maintenance schedule should include cleaning to
remove floating debris, sediment, and algal growth that can enter the distribution system
or otherwise contribute to water quality degradation. The lining of reservoirs, whether it
is constructed of asphalt, concrete, or HDPE, provides a surface to which algae, slimes,
and other aquatic organisms can attach and accumulate. It is necessary to periodically
remove these organisms because they increase disinfectant demand and react to form
DBFs. Reservoir cleaning should include the following activities:
• Routine inspection for floating debris and for sources of contamination that
could affect water quality, with documentation and removal of any threats of
contamination.
• A thorough cleaning should be conducted on a time schedule that is site-
specific and best for the particular facility (e.g., every six months, once per
year, every two years). This time-frame depends on the monitoring of water
quality parameters such as pH, temperature, nutrient loadings, quality of the
influent, etc. that will have an affect on algal growth in the reservoir. This
cleaning should coincide with draining the reservoir and inspecting the integrity
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of all liners as well as other reservoir structures such as inlet flapper gates,
outlet piping, valves, detention chambers, and so on. A high-pressure hose or
equivalent should be used to remove accumulated sediment, debris, and aquatic
growth. One large utility uses a concrete scrubbing machine to clean the liner.
This machine has brushes and rotating jets driven by high-pressure water and is
designed to clean paved surfaces such as parking lots. This machine is
designated by the utility for reservoir cleaning only and has been adapted for
use in cleaning reservoir sidewalls of concrete or asphalt.
4.5 Water Quality Effects on the Distribution System
The water distribution system is a dynamic chemical and biological system. Open
reservoirs can cause significant changes to the quality of the water entering the distribution
system. Rates and severity of corrosion and biofilm growth within the distribution system
are heavily influenced by the chemistry of the water flowing through the system. Utilities
should maintain a certain level of water quality stability by maintaining parameters within
optimal concentration levels, to ensure pipes are protected and regulatory requirements
are met under rules such as the LCR and D/DBP Rule.
Utilities should maintain stable water quality in the reservoir for the following reasons:
• Determine water quality parameters such as pH, dissolved organic carbon,
phosphate, dissolved oxygen, total inorganic carbon, and the solubility of
solids, which can form passivating films that protect the pipe.
• Red and blue water can result from poor corrosion protection.
• A stable pH is necessary for corrosion control strategies to work effectively
and consistently (i.e., compliance with the LCR).
The stability of the distributed water (particularly pH) is critical in achieving any positive
corrosion control results. It is unlikely that any corrosion inhibitor program can be
effective on lead bearing surfaces unless there is stability in the distribution system pH.
Excursions that drop the distribution pH by greater than 0.5 units, even for brief periods,
appear to disrupt the effective passivation of the corrosion surfaces, especially on brass
and lead/tin solder surfaces. Fluctuations of pH in uncovered reservoirs easily can exceed
this.
The pH in the distribution system should remain in a certain range for a specific corrosion
control strategy to work. The pH can range from 7.2 to 7.8 for systems using
orthophosphate treatment and between a pH of 9 or 10 for those using pH/alkalinity
control. Shifts in pH can be caused by photosynthetic reactions. To maintain good
corrosion control, the water should have adequate buffering to resist diurnal changes in
pH and major cyclical shifts in the dissolved inorganic carbonate content.
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Stability also plays a role in the release of corrosion products from iron surfaces. It is
believed that many well-publicized distribution problems stem from the inability to
maintain a consistent water quality, resulting in severe and extended red water problems.
Many utilities that blend different water qualities in the distribution network have reported
adverse corrosion impacts attributed to chemical variability, the impact being especially
pronounced on lead-bearing surfaces. Adjusting the pH of the source waters before
blending has proven useful. Heavy dosages of phosphate-based inhibitors also have been
used with success.
Using corrosion inhibitors such as orthophosphate or blended ortho/polyphosphate can
aggravate the growth of algae and possibly other aquatic organisms when applied to or
before open reservoirs. Chemical methods of controlling algae that are widely accepted by
industry include applications of copper sulfate and aqueous chlorine as discussed in
Section 3.4. However, these chemicals also may attack plumbing materials and corrode
piping. Utilities should not maintain excessive chlorine residuals in the reservoir since
extreme levels in pH in the distribution system accelerate corrosion rates. Disinfectant
residual and bacterial monitoring will help utilities maintain adequate but not excessive
disinfectant residual.
4.6 Covers
Covers have been used successfully to protect treated water reservoirs from
contamination. Reservoir covers can eliminate water quality deterioration caused by
airborne deposition, bird and animal wastes, human activities such as swimming, and
deliberate contamination or sabotage. In addition to providing public health protection,
covers prevent algal growth and reduce the amount of chlorine lost during storage by
excluding sunlight (Griffith, 1988). Covers also have been shown to dramatically improve
the bacteriological quality of the reservoir water (Krasner, 1985).
Numerous types of covers exist. Covers may be designed as a flexible membrane floating
or as a fixed structure on the water surface. They can be made from a variety of materials
including reinforced concrete, steel, aluminum, wood, or polypropylene. The type of
cover that is best suited for a particular reservoir depends upon a number of factors:
• Location, size, and shape of the reservoir
• Materials used in the construction of the reservoir
• Footing and other support conditions (soil/geotechnical considerations)
• Estimated snow, wind, and seismic loads
• Aesthetics
• The length of time, if any, that the reservoir can be removed from service
• The capital and maintenance costs and other economic factors involved.
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The capital cost of covering existing open reservoirs with fixed covers has been a
deterrent in the past. Within the past 20 years, however, the advent and acceptance of
floating covers has substantially reduced the costs of covers. This has led to a large
increase in the number of covered finished water reservoirs (CWC-HDR, 1986). The
following sections discuss the two general options for covering finished water reservoirs,
floating covers, and fixed covers.
4.6.1 Floating Covers
A floating cover consists of a flexible-membrane that is designed to float on the surface of
the reservoir. Floating covers typically consist of relatively rigid flat sheets that cover the
majority of a reservoir. Floating covers also have strategically placed flexible areas that
create folds to allow the cover to compensate for changing reservoir levels. These flexible
areas also act as natural drainage channels to collect rainwater or washwater.
Several considerations should be taken into account when designing a floating cover for a
finished water reservoir. The primary considerations that should be evaluated include the
following:
• Construction materials
• Cost and life expectancy
• Climatic conditions
• Cleaning and maintenance.
Other design considerations include air vents, rainwater collection and drainage, reservoir
level fluctuation, piping, and seams. These considerations are discussed in greater detail in
the AWWA Manual M25, "Flexible-Membrane Covers and Linings for Potable Water
Reservoirs" (AWWA, 1996). Although the AWWA M25 document provides information
on the design of flexible-membrane covers and linings, it does not provide minimum
design standards. However, the AWWA California-Nevada Section Reservoir Floating
Cover Task Force is creating a summary of minimum design standards for reservoir
floating covers for the California Department of Health Services.
Many of the first-used floating covers were constructed of ethylene-propylene-diene
monomer (EPDM) rubber or polyvinyl chloride (PVC). Experience with these materials,
however, showed that they were not designed for harsh climatic conditions. For example,
field seams in the EPDM covers exhibited a low tolerance to the bending and twisting
action caused by ice movement and reservoir level fluctuation.
In recent years, flexible-membrane covers have been constructed of reinforced
chlorosulfonated polyethylene (CSPE-R) and polypropylene (PP-R). Each of these
flexible- membrane materials has unique physical characteristics and methods of
construction and repair that should be evaluated thoroughly before a particular product is
specified. For instance, potable grade PP-R is available in a variety of colors such as tan,
white, blue, black, and gray, while potable grade CSPE-R membrane is only available in
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black. Another difference between these different types of cover material is the method
used to bond pieces together. PP-R can be thermally welded, even after years of use and
exposure to sunlight. CSPE-R membrane can be thermally welded when only new. After
years of exposure to solar radiation the new membrane material becomes incompatible;
resulting in the need to use a solvent-welding process for most repairs.
Cover materials should be at least 45-milimeters thick and consist of multiple plies of
flexible-membrane material ensuring a pinhole-free sheet. Additional information on
choosing the appropriate floating cover material for a reservoir can be found in AWWA
D130-96, Standard for Flexible-Membrane Lining and Floating Cover Materials for
Potable Water Storage (AWWA, 1996).
Previous performances of floating cover materials should be evaluated and a conservative
economic life expectancy assigned before choosing an appropriate floating cover material.
A floating cover is normally warranted for 20 years. If a floating cover is well maintained
it may last as long as 25 or 30 years. Conversely, if a cover is not properly maintained it
may last for only 15 years. The cost to install a floating cover currently ranges from
approximately $1.50 to $2.50 per square foot of covered reservoir area.
Cleaning and properly maintaining a floating cover is very important to the quality of
protection that the cover will provide and to the life expectancy of the cover. Daily
inspections of the cover may be appropriate, but this frequency is dictated by site-specific
conditions. Regular inspections will identify any problems such as vandalism, wildlife, or
large tears. Maintenance and repair of the cover should be performed weekly and involves
two steps: inspection and identification of tears or breaks in the liner, and the repair of
these problems.
It may be appropriate to clean the cover four times per year, depending on site-specific
conditions and previous experience. Flushing and cleaning of the cover may prove more
labor intensive on covers that are not designed and constructed with adequate tension
across the cover membrane. The cost of a maintenance program for flexible-membrane
covers depends on the level of maintenance provided. One utility that performs the
suggested maintenance estimates that its maintenance program costs approximately
$50,000 per year for a 1-million-square-foot floating cover.
4.6.2 Fixed Covers
Fixed covers are permanent structures constructed to provide drainage away from the
reservoir and to prevent entrance of contamination into the stored water. These covers
are constructed from a variety of materials including reinforced concrete, steel, aluminum,
and wood. They can be designed as flat, conical, or dome-shaped. In general, fixed
covers are economically limited to fairly small-sized reservoirs, up to a maximum of 10- to
20-million gallons (MG) (approximately 100,000 square feet in surface area). Concrete
roofs constructed over an existing open reservoir can be a pre-cast T-beam/membrane
roof with concrete column supports, or a cast-in-place concrete roof with concrete column
supports.
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Reinforced concrete options include a completely new covered tank made of prestressed
concrete. This option may be considered for a size of about 1- to 10-MG. A prestressed
concrete tank is not an option when the existing finished water reservoir contains a water
storage volume much larger than 10 MG. Steel water storage tanks also should be
considered along with prestressed tanks since steel tanks have a lower capital cost than
prestressed tanks and can be used for reservoirs up to a maximum size of about 10- to 20-
MG.
The all-aluminum geodesic dome is another example of a fixed cover, although it is limited
to covering circular reservoirs. This dome consists of a skeleton of aluminum trusses and
a skin of aluminum panels. The advantages of the geodesic dome are its long life (50-to
100-years), no maintenance requirements, no painting requirements, its light weight, no
interior columns or supports, and fast construction. The dome can be installed while the
reservoir is in operation. Disadvantages of the geodesic dome include high initial cost and
its span and shape limitations. The largest dome installed, as of 1986, had a span of 230
feet. A dome this size could cover a 35-foot-deep 11 MG storage tank.
4.6.3 Air-Supported Roofs
The air-supported roof is another type of cover initially used for swimming pools,
greenhouses, and similar enclosures, but was eventually adapted for use on reservoirs.
The covers can be circular-, square-, or rectangular-shaped. Air-supported covers are
inflated and kept in place with blowers that operate continuously to maintain about 2
pounds per square inch (psi) (14 kPa) more pressure inside the cover than outside. Two
blowers, with one serving as a standby, and a standby emergency generator should be
included in this type of design to support the roof during emergencies. Materials for fabric
include polyester-reinforced vinyl, CSPE, and Teflon-coated fiberglass, with service lives
of 5 to 10, 10 to 20, and 25 or more years, respectively. Cost of the material used to
fabricate an air-supported roof increases proportionally with the desired service life.
4.6.4 Cosfs
Costs of four different types of fixed cover systems were compared to the costs of a CSPE
floating cover in an article published in the New England Waterworks Association
(NEWWA) Journal (Kittredge, 1984). Although these costs are outdated, they illustrate
the relative comparison of capital costs for the different types of cover designs. These
cost estimates show that the capital costs for fixed covers are up to 5 to 10 times the cost
of floating covers and air-supported fabric.
A summary of the estimated cost ranges for covering an existing reservoir at 1998 cost
levels is included in Table 4-1 (CWC-HDR, 1986). It should be noted that these costs do
not include design of the floating cover, which can be considerable depending on the
complexity of the design. Furthermore, these costs do not include other construction
costs that will be necessary when installing covers. These additional costs may include
rehabilitating the existing reservoir, upsizing the impacted storm water drainage facilities
surrounding the reservoir, and/or adding partition walls or baffles to the reservoir to allow
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4. MITIGATING WATER QUALITY DEGRADATION
the proper functioning of the reservoir with the cover. Storm water drainage facilities may
need to be upsized due to the creation of a significant additional surface area that will
cause the accumulation of runoff from rainfall. These costs will vary from application to
application depending on a variety of factors such as size, complexity, or even the time of
the year (Schader, 1998)
Table 4-1. Estimated Cost Ranges to Cover
Existing Reservoirs at 1998 Cost Levels 1
Type of Cover
Air Supported Fabric
Floating, Polypropylene
Wooden
Steel
Concrete
Aluminum Dome
Estimated Cost, 1998,
$ per Sq. Ft.
$2.00 to $5.50 2
$1.50 to $2.50 3
$13.00 to $23.00
$14.00 to $22.00
$2 1.00 to $29.00
$14.00 to $32.00
Estimated Service Life,
Years
5 to 25
15 to 30
25 to 50
30 to 60
50 to 100
50 to 100
1 - Costs were inflated to 1998 levels using Means cost indices.
2 - This cover would have an energy operation and maintenance cost also.
3 - Based on actual 1998 bid costs for floating covers.
As noted in Table 4-1, the current cost of installing a floating cover on a reservoir will
range from $1.50 to $2.50 per square foot. This cost includes only the cost of the cover
material, the rain collection system, and installation of the cover. A recent replacement of
a floating cover on the 2-million-square-foot Garvey Reservoir in California cost $3.5
million ($1.75 per square foot). Other costs also could significantly increase the cost of
implementing a cover. A recent New York study estimated that the total cost of covering
a 3.9 million-square-foot reservoir ranged from $42.6 million ($10.87 per square foot) for
a floating cover to $218 million ($55.60 per square foot) for a concrete cover (Freud,
1998). These estimates include the costs of the covers along with other associated costs
that pertain to the individual application.
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5. WATER QUALITY MONITORING
5.1 Introduction
The two primary objectives of water quality monitoring in uncovered finished water
reservoirs are: (1) to ensure that the quality of water exiting the reservoir complies with
applicable water quality requirements, and; (2) to identify reservoir contamination or
water quality degradation quickly so that swift remedial action can be taken.
An adequate monitoring program is essential for providing accurate and useful data.
Before a program is formulated, each utility should determine what is expected to be
accomplished, identified, or measured by the program. Based on analysis of the water
quality data, the utility can characterize the effects that an open reservoir has on the
downstream system water quality and develop an effective reservoir management plan.
Chapter 2 provides a general outline of the topics and issues that should be addressed in
an open reservoir management plan. Each utility should design a plan that specifically
addresses the issues that are encountered within its system of reservoirs.
The water quality monitoring program should be designed to alert responsible individuals
of the development, or potential development, of significant water quality degradation in a
reservoir, and should characterize both the short-term and long-term water qualities in the
reservoir. The plan should ensure that monitoring data are analyzed regularly by
personnel who have been trained to interpret the information and initiate any necessary
response action. All utility personnel in the monitoring program should be trained to a
level commensurate with their responsibilities. Training should include familiarity with
applicable portions of the reservoir management plan.
5.2 Types of Monitoring
The overall water quality monitoring program for an open reservoir system should consist
of subprograms that are designed to support a specific portion of the reservoir
management plan through sampling and analysis and visual inspection.
5.2.1 Sampling and Analysis
Water sampling and laboratory analyses are necessary to monitor the chemical and
biological status of the reservoir water. Monitoring of the water quality falls into three
categories: routine, follow-up, and special study monitoring.
Routine Monitoring
Routine monitoring of baseline parameters should be conducted on a regular, continuous
schedule. The routine monitoring program should include the establishment of threshold
levels for specific parameters such as chlorine/chloramine residuals and fecal and total
coliforms. When these threshold levels are exceeded, follow-up monitoring and a specific
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5. WA TER QUALITY MONITORING
response action for any necessary adjustment in system operations and management may
be required. Monitoring parameters and threshold levels may vary from utility to utility
and from reservoir to reservoir to reflect site-specific conditions.
The results of the analysis of these data provide a guide to day-to-day management of the
system for maintaining compliance with applicable water quality requirements. The results
also facilitate the rapid identification of any water quality degradation or contamination,
thereby enabling a timely and efficient response.
Follow-Up Monitoring
Follow-up monitoring is performed on specific parameters that present a potential or
actual water quality concern. In some instances, follow-up monitoring may consist of a
more frequent version of the routine monitoring program, or portion thereof. For
example, one large utility samples total coliforms biweekly and conducts follow-up
sampling when coliform bacteria are present in reservoir outlet samples. Procedures also
should be developed to initiate follow-up monitoring based on other criteria, such as
certain operator inspection observations and customer complaints.
Special Study Monitoring
Special study monitoring is a self-contained monitoring program designed to study a
specific issue, usually on a one-time or as-needed basis. Examples include developing
computer monitoring programs, assessing a new water treatment facility or procedure, and
characterizating a potential contamination source.
5.2.2 Visual Inspection
Visual inspection of the reservoir and grounds should be performed daily to identify and
prevent water contamination and water quality degradation caused by external factors
such as discarded trash, trespassing, and wildlife. Visual inspections can be routine,
follow-up, or conducted as part of a special study.
Routine Observation
Routine observation is conducted on a regular ongoing schedule to identify sources of
contamination affecting water quality. Routine visual observation should include
inspection of the fence line, the grounds between the fence and the reservoir, the surface
of the reservoir, and the color of the water in the reservoir. Any changes in water color
should be noted and followed by sampling and analysis. An inspection also should include
the storm water drainage system, curbs and gutters, parapet wall, and so on. Any trash
that is observed in the vicinity of or on the surface of the reservoir should be removed.
Bird control devices or structures and animal traps should be checked.
The type and frequency of inspection is driven by factors such as the type of reservoir,
susceptibility to vandalism, age, condition, time lapse between cleaning or maintenance,
and history of water quality. Exterior inspections for indications of vandalism or
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trespassing may be made daily or weekly, while inspection of overflows might be
appropriate on a weekly or monthly basis.
Follow-Up Observation
Follow-up observation is performed in specific locations identified as a source, or potential
source, of contamination. These locations may include areas in which trash is usually
found or areas in which the fence has been damaged. In some instances, this follow-up
observation may consist of a more frequent version of the routine observation program, or
of a portion thereof.
Special Study Observation
A special study observation program is designed to study a specific issue and usually is
conducted on an as-needed basis. Examples include the identification of a contamination
source, the study of wildlife to determine possible mitigation measures, and the
observation of continually trespassed areas.
5.3 Parameters to Monitor
The selection of monitoring parameters for a particular reservoir requires careful
consideration of the types of contamination sources present. The utility first should
identify potential contaminants of concern for each open reservoir. The assessment should
cover elements such as historical water quality data, potential sources of watershed
contamination, and system dynamics. The initial assessment should be followed
periodically with additional assessments to update information and identify trends. For
some systems, these trends, and therefore monitoring parameters, may vary seasonally. In
addition to identifying parameters based on the probable types of contamination sources,
the utility may monitor other parameters that would pose a significant hazard if present.
Table 5-1 summarizes information on water quality parameters that are monitored by
some large utilities currently operating uncovered finished water reservoirs.
The parameters monitored by individual utilities may be different than those listed in Table
5-1 to address any site-specific concerns and conditions. For example, if gulls are a
known concern, Salmonella and coliform bacteria monitoring are appropriate. If nearby
motor vehicle traffic is a potential contamination source, it may be necessary to monitor
for asbestos, metals, oil, and grease.
Table 5-1, on the following pages, provides examples of monitoring schemes some utilities
employ at their uncovered reservoirs. EPA does not endorse or recommend that systems
use these examples to develop their own monitoring scheme, nor is EPA judging the
adequacy of the schemes by providing them as examples. Systems should develop a
monitoring plan and response actions based upon site-specific conditions and needs. The
monitoring plan and response actions should be sufficiently robust to provide confidence
that water quality goals are being met and water quality degradation is identified in a
timely manner. With regard to the far right column in Table 5-1, "Utility Survey
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Response," EPA recommends that systems consider the reservoir water quality that should
be maintained in the reservoir to meet TCR and other regulatory requirements.
Special studies to investigate a particular concern may require monitoring a completely
different set of parameters than routine water quality monitoring. A study of
contamination in reservoir sediments, for example, should consider parameters that are
typically found in sediment. These may include heavy metals, synthetic organic pesticides,
and other non-biodegradable or slowly degrading parameters. It may be appropriate to
sample and analyze sediment each time the reservoir is drained.
Some studies may require a more detailed investigation. For example, to determine the
impact of turbidity on chlorine demand, monitoring should provide information on particle
size distribution. As such, the laboratory should be requested to provide information to
determine the proportion of particles in excess of 1.2 microns, the size above which
particles offer significant protection to bacteria from the effects of chlorination (Geldreich
and Shaw, 1993).
In addition to determining appropriate parameters, sampling locations that are indicative
of water quality should be selected. In-reservoir sampling locations may be appropriate
when performing a special study to evaluate reservoir hydraulics.
Pertinent information that may affect the interpretation of data should be collected during
water quality monitoring. These include water level elevations, hydraulic conditions, flow
conditions, flow directions, inlet and outlet configurations, and valve positions.
5.4 Frequency of Monitoring
Water systems typically have many continually fluctuating water parameters. Some
parameters are adjusted intentionally, such as orthophosphate for corrosion control and
chlorine residual for disinfection. Other parameters will vary according to environmental
factors, such as coliform bacteria and turbidity. Together, these continually changing
parameters result in a system water quality that is also in a continuous state of flux. As
noted in Section 5.2, monitoring should vary with actual or potential system variability.
When certain thresholds are exceeded for indicator parameters, increased monitoring
frequency for other parameters may be necessary. Thresholds that indicate a need for an
increase in chlorine residual include instances when the water has a pH greater than 8, a
color greater than 10 units, or if the chlorine residual is found to be less than 0.2 mg/L.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters
Parameter
Monitoring Rationale
Utility Survey Response
Escherichia coli
Indicates fecal contamination and
likelihood of pathogens of intestinal origin.
Some species are human pathogens. Also
monitors effectiveness of bird and animal
control program.
A has set follow-up action levels at greater than 40
Most Probable Number (MPN)/100 mL. B
monitors biweekly as part of its in-reservoir
limnology program and collects one influent sample
and eight effluent samples daily. Each of the
effluent samples is a composite of samples collected
at six different times and three grab samples.
Fecal coliforms
Similar to E. Coli.
B does not monitor fecal coliforms. D samples
weekly and discharges contaminated water to waste
when levels reach greater than 20 colonies/100 mL
in 2 consecutive samples collected from finished
water.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
Total coliforms
Determines effectiveness of treatment and
distribution system integrity. Indicates a
system's vulnerability to fecal contamination,
not whether fecal contamination actually
exists.
A monitors daily in-reservoir and weekly at outlets of
reservoirs impacted by surface runoff. For other
reservoirs, weekly in-reservoir monitoring is done.
Follow up action threshold level is greater than 500
MPN/100 mL. B monitors biweekly as part of its in-
reservoir limnology program collects one influent
sample and eight effluent samples daily. Each of the
effluent samples is a composite of samples collected at
six different times and three grab samples. C collects
daily in-reservoir samples. D samples weekly at both
in-reservoir and reservoir checkpoint locations, and
conducts follow-up sampling and response action when
levels reach greater than 100 colonies/lOOmL or when
coliform bacteria are present in reservoir outlet
samples. Follow-up action consists of adding calcium
hypochlorite tablets to the reservoir, and discharging
water to waste if no improvement occurs.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
HPC
Indicates bacterial growth and overall water
quality. A few types of HPC may cause
gastrointestinal illness.
B monitors biweekly as part of its in-reservoir
limnology program. D samples weekly at both in-
reservoir and reservoir checkpoint locations, and
conducts follow-up sampling when levels reach greater
than 500 colonies/100 mL in 2 consecutive samples.
Follow up action consists of increasing the turnover
rate and, if no improvement occurs, adding calcium
hypochlorite tablets to the reservoir.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
Chlorine/chloramine
residual (free and
total)
Ensures adequate disinfection through
maintenance of target residual goals. Avoids
over-chlorination that may contribute to DBF
formation and pipe corrosion.
A monitors free and total residual continuously at
outlets, and daily before and after the point of
chlorination at reservoirs impacted by surface runoff.
B monitors biweekly in-reservoir and continuously at
reservoir inlets/outlets. Increases chlorine residual
when < 0.2 mg/L is reached. C monitors chlorine
residual continuously at each of two open reservoir
system outlets and collects daily in-reservoir samples.
D monitors weekly at reservoir checkpoints and also
records data continuously. For any single reservoir,
when chlorine residual is < 0.2 mg/L in a downstream
distribution system, follow-up actions may include
flushing, revised operations, or increasing chlorine
dosage at reservoir outlet. For other reservoirs, when
residual is < 0.6 mg/L, the Water Treatment Section is
notified. E monitors its chlorine residual continuously
at one reservoir outlet.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Algal populations/
type
Nitrates, nitrites,
phosphorous
Ammonia
Monitoring Rationale
Avoids problems associated with algal
blooms, including color, taste and odor,
bacterial growth, THM formation, and
turbidity. Some blue-green species produce
toxins that may be harmful or fatal to humans
and animals. Blooms may clog filters.
Monitoring should identify algal species
and/or toxins present at "high" levels.
Comply with MCLs. Avoid conditions that
lead to "blue baby syndrome." Identification
of the availability of nutrients is required for
algal growth.
Indicates nitrification potential.
Utility Survey Response
A monitors continuously in reservoirs impacted by
surface runoff, weekly in other reservoirs (chlorophyll
grab sample). For one reservoir that is subject to
surface runoff, follow-up action levels have been set:
(1) chlorination is initiated when chlorophyll is greater
than 1 parts per billion (ppb) and growth rate is greater
than 0.1 ppb/day, and (2) chlorination is terminated
when chlorophyll is 0.5 ppb and growth rate is < 0.1
ppb for two consecutive days. B monitors biweekly.
C samples biweekly. D samples biweekly, conducts
follow-up sampling if nonsource water resident species
are found. E monitors algae.
C monitors nitrates/nitrites biweekly and total
phosphorous monthly.
C monitors biweekly.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
Specific conductance
Identifies water source when a reservoir may
be supplied by multiple source waters.
A monitors daily, before and after point of
chlorination at reservoirs impacted by surface runoff.
B monitors biweekly and samples are collected at
intervals throughout the water column. C monitors
weekly. D monitors weekly at in-reservoir (5 feet
from side and 15 feet below surface) and at the
reservoir checkpoint after chlorination.
pH
Identifies chemical feed problems. Measures
water corrosivity. Maintains optimal
corrosion control in distribution system.
A monitors continuously at outlets and daily before
and after points of chlorination at reservoirs impacted
by surface runoff. B monitors biweekly in-reservoir,
continuously at reservoir inlets/outlets, and increases
chlorine residual when pH is 8 or greater. D monitors
weekly at in-reservoir (5 feet from side and 15 feet
below surface) and at the reservoir checkpoint after
chlorination.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
Temperature
Identifies mixing problems (thermoclines).
Avoids conditions conducive to algal and
bacterial growth.
A monitors continuously at three different depths at
outlets and daily before and after points of chlorination
at reservoirs impacted by surface runoff. B monitors
daily at the reservoir effluent and biweekly at intervals
throughout the water column. C monitors daily.
D monitors weekly in-reservoir (5 feet from side and
15 feet below surface) and at the reservoir checkpoint
after chlorination.
Turbidity
Measures a wide variety of suspended
colloidal particles. Identifies chlorine demand
and disinfection interference. Meets aesthetic|
water quality requirements. Evaluates
erosion/sedimentation control programs.
Indicates presence of other contaminants,
such as heavy metals and synthetic organic
compounds, that may bind to turbidity
particles.
A monitors daily, before and after chlorination points
of reservoirs impacted by surface runoff and weekly
for other reservoirs. B monitors daily at the reservoir
effluent and biweekly in reservoir. B Conducts
follow-up monitoring when greater than a 0.7
nephelometric turbidity units (NTU). C monitors
weekly. D monitors weekly at in-reservoir (5 feet
from side and 15 feet below surface) and at the
reservoir checkpoint after chlorination. E monitors
continuously at one reservoir.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Monitoring Rationale
Utility Survey Response
Taste and odor
Meet aesthetic requirements.
B monitors daily at the reservoir effluent. D monitors
weekly at the reservoir checkpoint after chlorination
for one of its reservoirs. When the Flavor Rating
Assessment is greater than 6.5 and is 2 units greater
than the source water, and customer complaints reach
10 to 12 calls/day, follow-up action consists of dilution
with disinfected source water, overflow, or blending
reservoir outflow. When the Flavor Rating
Assessment reaches 8 or greater and customer
complaints are greater than 20, evaluation to remove
the reservoir from service is initiated.
Color
Indicates of algal growth and aesthetic
quality.
B monitors biweekly and daily at the reservoir
effluent.
Pseudomonas
May act as a human pathogen, particularly for
immuno-compromised individuals (e.g., has
been found to cause fevers in hospital dialysis
patients, and also may cause pneumonia and
secondary infections).
B speciates all atypical growths greater than 25 Colony
Forming Units (CFU) identified during its coliform
monitoring. D samples weekly and conducts follow-
up sampling/action when levels reach greater than 100
colonies/100 mL in 2 consecutive samples. Follow-up
action consists of adding calcium hypochlorite tablets
to the reservoir and discharging water to waste if no
improvement occurs.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Giardia and
Cryptosporidium
Total organic carbon
(TOC)
Redox
Dissolved oxygen
Total plankton
Midge fly larvae
Monitoring Rationale
Cause giardiasis and cryptosporidiosis, which
are associated with surface runoff.
Monitoring for these pathogens verifies that a
finished water reservoir is not receiving
surface runoff and fecal contamination.
Indicates presence of organic compounds.
Characterizes water chemistry.
Characterizes water chemistry.
Characterizes biological activity. Meets taste
and odor requirements.
Meet aesthetic requirements.
Utility Survey Response
C monitors occasionally. F monitors Giardia
annually, Cryptosporidium biannually.
B monitors monthly at the reservoir influent and
effluent. E monitors TOC.
A continuously monitors at one depth to track
chlorine dynamics. B monitors biweekly and samples
at intervals throughout water column.
A monitors weekly from locations near water surface
and reservoir bottom. B monitors biweekly and
samples at distance of 3.3 feet from water surface
and reservoir bottom (two locations).
B monitors biweekly and sometimes analyzes species
population counts.
B monitors biweekly using vertical tow methods.
Note: Utilities surveyed are differentiated by letters A-F.
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Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)
Parameter
Secchi disk
Amorphous matter
Bird counts
Zooplankton
Debris/sediment
Phytoplankton
Monitoring Rationale
Measures water transparency.
Characterizes potential for biological activity.
Potential sources of coliform and human
pathogens.
Monitors biological activity.
Indicates impact of external contamination
sources.
Indicates chlorine demand, DBF formation
potential, and biological activity.
Utility Survey Response
A monitors weekly. B monitors biweekly.
B monitors biweekly.
A monitors weekly. B conducts weekly surveys at
night. D monitors daily, recording species and
population data.
A monitors weekly. B monitors biweekly as part of
its in-reservoir limnology program.
D monitors annually when reservoir is cleaned.
B monitors biweekly as part of its in-reservoir
limnology program. D monitors bimonthly in-
reservoir (at a location 5 feet from sides and 15 feet
below the surface) and weekly at a reservoir
checkpoint after chlorination. In-reservoir monitoring
includes species identification and enumeration.
Note: Utilities surveyed are differentiated by letters A-F.
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5.5 Issues Related to Water Quality Monitoring
5.5.1 Laboratory Testing
Laboratory analysis of samples collected in compliance with monitoring requirements
should be conducted in accordance with the approved methods specified in the
regulations, and in some states the analysis must be performed by a state-approved
laboratory. Samples collected for operational purposes or to monitor unregulated
contaminants should be performed in accordance with Standard Methods (1995) to insure
consistency.
5.5.2 Recordkeeping and Reporting
Forms and checklists should be used for thoroughness and consistency in data collection.
Findings should be quantified and recorded as often as possible. Photographs, videotapes,
and audiotaped explanations should supplement written field notes. A comprehensive
report summarizing water quality issues should be prepared annually for the utility's
manager. Some utilities have developed an automated database and reporting capability.
5.5.3 Training
Laboratory technicians should receive onsite training at each reservoir. Technicians
should be trained to collect and analyze representative samples, maintain accurate and
complete records, perform water quality studies, and recognize algal blooms and other
sources of contamination.
5.5.4 Water Quality Monitoring Equipment
Water utilities should consider online continuous monitoring equipment, especially at
reservoir inlets and outlets. Data from continuous monitoring will help establish a
correlation between reservoir and distribution system water quality. Utilities also should
consider the use of permanently installed sampling lines to facilitate sample collection.
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6. REFERENCES
Atherholt, T., W. Norton, and M. LeChevallier. 1997. "Survey of Open Finished Water
Reservoirs for Giardia Cysts and Cryptosporidium Oocysts." New Jersey
Department of Environmental Protection, Division of Science and Research.
March.
AWWA (American Water Works Association). 1997/1998. "Statements of Policy on
Public Water Supply Matters."
AWWA. 1996. American Water Works Association ManualM25 - Flexible-Membrane
Covers and Linings for Potable-Water Reservoirs. Second Edition.
AWWA. 1991. Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources.
Washington, D.C.
AWWA. 1983. "Deterioration of Water Quality in Large Distribution Reservoirs (Open
Reservoirs)." Committee Report. J. AWWA. 75(6):313-18.
AWWA. 1975. "Statement of Policy on Water Supply Matters." Treatment of Public
Water Supplies and Quality Control in the Distribution System.
Arizona Department of Health Services. 1978. "Guidelines for the Construction of Water
Systems." Engineering Bulletin No. 10. May.
Ashendorff, A., M. Principe, A. Seely, J. LaDuca, L. Beckhardt, W. Faber Jr., and J.
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89(3):75-88.
Babbit, H.E., J.J. Doland, and J.L. Cleasby. 1967. Water Supply Engineering. Sixth
Edition. McGraw Hill Book Company, Inc., New York, NY.
Bailey, S.W., and E.C. Lippy. 1978. "Should All Finished Water Reservoirs Be
Covered?" Public Work. 109(4):66-70.
Bay, E.C. 1993. "Chironomid Larvae Occurrence and Transport in a Municipal Water
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Beuhler, M.D., D. Foust, and R. Mann. 1994. "Monitoring To Identify Causative Factors
of Degradation of Water Quality: What to Look For." Conference proceedings,
AWWA Conference, New York, NY.
Capron, C. 1998. Personal communication. Cheryl Capron of Seattle Public Utilities.
August 17.
CDC (Centers for Disease Control). 1996. "CDC Surveillance Summaries." Morbidity,
Mortality Weekly Report. 45(SS-1). April.
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Clement, B. 1997. Issue Paper Concerning Possible Regulatory Requirements for
Uncovered Finished Water Reservoirs and Cross-Connection Control. U.S.
Environmental Protection Agency, Office of Research and Development. July 2.
CWC-HDR (Culp/Wesner/Culp - HDR Engineering Inc.). 1986. Handbook of Public
Water Systems. New York, NY: Van Nostrand Reinhold Company.
Dial, H.S. 1975. "Floating Covers for Hydraulic Installations." Opflaw. 1(12): 1,7.
Erb, T.M. 1989. "Implementation of Environmental Regulations for Improvements to
Distribution Reservoirs in Los Angeles." Conference proceedings, AWWA
Annual Conference, Los Angeles, CA.
Ford, J. 1994. "Open Distribution Reservoir Disinfection, Security and Water Quality
Protection Enhancement Measures." Seattle Water Quality Program Technical
Memorandum. January 14.
Freud, S. 1998. Personal communication. Salome Freud of the New York City
Department of Environmental Protection. November 2.
Geldreich, E.E. 1996. Microbial Quality of Water Supply in Distribution Systems. Boca
Raton, FL: CRC Press, Inc.,
Geldreich, E.E., and S. Shaw. 1993. New York City Water Supply Microbial Crisis.
U.S. Environmental Protection Agency.
Griffith, C. 1988. "Floating Reservoir Cover Controls Algae Growth, Allows Lowered
THM's." J. AWWA. 80(10):66,68-69.
Health Canada. 1998. "Blue-Green Algae (Cyanobacteria) and Their Toxins." It's Your
Health."
Henry, D.J. 1996. Proposal: FEA Modeling of the Los Angeles Department of Water
and Power's Encino Reservoir. August.
Henry, D.J. and E.M. Freeman. Finite Element Analysis and Tio Optimization of Ozone
Contactors. MWD (Metropolitan Water District) of Southern California.
Hoehn, R, D. Barnes, B. Thompson, C. Randall, T. Grizzard, and P. Shaffer. 1980. "Algae
as Sources of Trihalomethane Precursors." J. AWWA. 72(6):344-350.
Karimi, A.A. 1988. "Water Quality Characterization of Silver Lake Reservoir." Los
Angeles Department of Water and Power, Water Engineering Design Division,
Planning Section. Water Quality Research and Development. Los Angeles, CA.
Karimi, A.A. and R.F. Ruiz. 1991. "Water Quality Characterization of Stone Canyon
Reservoir Complex." Los Angeles Department of Water and Power, Water
Engineering Design Division, Planning Section, Water Quality Research and
Development. Los Angeles, CA.
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Karimi, A.A., and P.C. Singer. 1991. "Trihalomethane Formation in Open Reservoirs."
J. AWWA. 83(3):84-88.
Kirmeyer, G.J., and P. Noran. 1997. Operating and Maintaining Finished Water Storage
Reservoirs to Maintain Water Quality. Conference proceedings, AWWA
Distribution System Symposium, Norfolk, VA.
Kittredge, D. 1994. "Experience With Floating Covers at the Manchester Water Works."
Conference proceedings, AWWA Annual Conference, New York, NY.
Kittredge, D. 1984. "Design and Operation of Flexible-Membrane Covers for Distribution
Storage Reservoirs." J. New England Water Works Assoc. 98(3):259-270.
Knudson, M. 1998a. Personal communication. Mark Knudson of the City of Portland
Bureau of Water Works.
Knudson, M. 1998b. Personal communication. Mark Knudson of the City of Portland
Bureau of Water Works. August 17.
Knudson, M. 1998c. Personal communication. Mark Knudson of the City of Portland
Bureau of Water Works. October 19.
Krasner, S.W. 1985. "Returning a Newly Hypalon-Covered Finished Water Reservoir to
Service: Health and Aesthetic Considerations." Conference proceedings, AWWA
Conference, Managing a Priceless Resource, Washington, D.C.
Kreft, P., M. Umphres, J. Hand, C. Tate, M. McGuire, and R. Trussel. 1985. "Converting
From Chlorine to Chloramines: A Case Study." J. AWWA. 77(l):38-45.
LADWP (Los Angeles Department of Water and Power). 1988. "Safeguarding a Vital
Asset." Los Angeles, CA.
LeChevallier, M.W., T.M. Evans, and RJ. Seidler. 1981. "Effect of Turbidity on
Chlorination Efficiency and Bacterial Persistence in Drinking Water." J. AWWA.
42(1):159-167.
LeChevallier, M.W., W.D. Norton, and T.B. Atherholt. 1997. "Protozoa in Open
Reservoir." J. AWWA. 89(9):84-96.
McDermott, J.H. 1973. "Federal Drinking Water Standards Past, Present, and Future."
J. Environmental Engineering. 99:EE4:469.
Montgomery Watson. 1998. "City of Portland Water Bureau Open, Reservoir Study."
Technical Memorandum 2.7, Water Quality Evaluation. Portland, Oregon.
Moore, L.L. 1979. "Viewpoint: Open Finished Water Reservoirs." J. AWWA. 71(8):11.
Moore, L.L. 1978. Monitoring Quality in Open Finished Water Reservoirs. Conference
proceedings, AWWA Conference, Louisville, KY.
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Uncovered Finished Water Reservoirs
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Morra, JJ. 1980. "A Review of Water Quality Problems Caused by Various Open
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21.
Pluntze, J.C. 1974. "Health Aspects of Uncovered Reservoirs." J. AWWA. 67(8):432-7.
Safe Drinking Water Act, 1996. U.S. Congress. Amended August 6.
Safe Drinking Water Act Advisor. 1994. AWWA Regulatory Update Service.
Schader, L.R. 1998. Personal communcation. Larry Schader of Steven Geomembranes.
June 12 and November 6.
Seattle Public Utilities. 1998. Open Distribution Reservoir Protection Program 1997
Annual Report for Seattle Public Utilities. Water Quality and Supply Division.
Seattle, WA.
Seattle Water Department. 1995. "A Plan To Cover Open Reservoirs." Seattle, WA.
Silverman, G.S., L.A Nagy, and B.H. Olson. 1983. "Variations in Particulate Matter,
Algae, and Bacteria in an Uncovered, Finished Drinking Water Reservoir."
J. AWWA. 75(4).
SPHEM (State Public Health and Environmental Managers). 1992. "Great Lakes Upper
Mississippi Board." Recommended Standards for Water Works ("Ten State
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Standard Methods. 1995. Standard Methods for the Examination of Water and
Wastewater (Standard Methods). Nineteenth Edition. Franson, M.H., Eaton,
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Stolarik, G. and J. Miller. 1998. Personal communication. Gary Stolarik and John Miller
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USEPA (U.S. Environmental Protection Agency). 1998a. "National Primary Drinking
Water Regulations: Disinfectants and Disinfection Byproducts; Final Rule." 63 FR
69390. December 16.
USEPA. 1998b. "National Primary Drinking Water Regulations: Interim Enhanced
Surface Water Treatment Rule; Final Rule." 63 FR 69477. December 16.
USEPA. 1991a. "Maximum Contaminant Level Goals and National Primary Drinking
Water Regulations for Lead and Copper; Final Rule." 56 FR 26460. June 7.
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USEPA. 1989a. "Drinking Water; National Primary Drinking Water Regulations;
Filtration, Disinfection, Turbidity, Giardia Lamblia, Viruses, Legionella, and
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Heterotrophic Bacteria ("Surface Water Treatment Rule"); Final Rule. 54 FR
27486. June 29.
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Trihalomethanes in Drinking Water ("Total Trihalomethane Rule"); Final Rule).
44 FR 68624. November 29.
U.S. Public Health Services. 1946. Manual oj'Recommended Water Sanitation Practice.
Waller, K., S. Swan, B. Hopkins, G. Windham, L. Fenster, C. Schaefer, and R. Neutra.
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Epidemiology. 9(2).
Weldon, C.K.T. 1993. "Enhancing Public Participation Through a Consensus Process:
Recent Experiences of the Los Angeles Department of Water and Power."
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White, B.N., D. Kiefer, J. Morrow, and G. Stolarik. 1991. Remote Biological Monitoring
in an Open Finished Water Reservoir. J. AWWA. 83(9): 107-12.
White, B.N. 1998. Personal communication. Brian White of Los Angeles Department of
Water and Power, Water Quality Section. April 2.
EPA Guidance Manual 6-5 April 1999
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6. REFERENCES
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APPENDIX A. STUDIES PERFORMED
Numerous studies and monitoring projects have been undertaken to evaluate the impacts
that uncovered finished water reservoirs have on water quality. These studies have shown
that drinking water quality deteriorates in open reservoirs (Pluntze, 1974; Morra, 1980;
Silverman et al., 1989; Erb, 1983; Atherholt et al., 1997). Because of the large number of
variables and site-specific issues associated with each open finished water reservoir, the
results vary widely from study to study. Generally, however, the larger open reservoirs
show greater water quality degradation than do the smaller reservoirs. This greater
deterioration of water quality in larger open reservoirs is due to the greater difficulty and
cost of implementing contamination control measures at a larger reservoir, such as lining
the reservoirs, and controlling the access of humans and animals.
The monitoring programs discussed in this appendix were conducted in New Jersey and
California, but studies were also performed in Washington, New York, Maryland, and
Pennsylvania (AWWA, 1983; Geldreich and Shaw, 1993; Bailey and Lippy, 1978). These
studies all suggest that water quality degradation in uncovered finished water reservoirs is
a common and widespread problem.
A.1 Uncovered Finished Water Reservoirs in New Jersey
A.1.1 Pathogens
The New Jersey Department of Environmental Protection conducted a study in 1997 in
which six uncovered finished water reservoirs were monitored for Giardia cysts and
Cryptosporidium oocysts at the inlets and outlets. These reservoirs range in capacity from
19-to 679-million gallons. Water entering and exiting each reservoir was sampled 10
times over 1 year, giving a total of 120 samples. The water samples were filtered through
a 1-micron polypropylene filter and the filters were analyzed using the methods specified
in the EPA's Information Collection Rule.
The results reported that: "Giardia cysts were detected in 8 (13%) inlet and 9 (15%)
outlet samples and average concentrations were 1.9 and 6.1 per 100 liters, respectively.
Cryptosporidium oocysts were observed in 3 (5%) inlet and 7 (12%) outlet samples at
average concentrations of 1.2 and8.1 per 100 liters, respectively" (Atherholt et al.,
1997). The researchers did not find the difference in the presence of Giardia in the outlet
samples as compared to the inlet samples to be statistically significant. However, the
study did find a statistically significant difference between Cryptosporidium in the samples
taken from the inlets and outlets. It was concluded that the increase in these pathogen
levels in the reservoirs most likely comes from the fecal wastes of animals (Atherholt et
al., 1997;LeChevallieretal., 1997).
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APPENDIX A. STUDIES PERFORMED
A.1.2 Other Contaminants
In addition to the increase in Giardia and Cryptosporidium, increases also were found in
turbidity levels, particle counts, chlorine residual, bacteria as measured by HPC, and total
coliform and fecal coliform bacteria levels (Atherholt, 1997). An additional concern exists
with the increase in total and fecal coliform levels because they are potentially pathogenic
organisms regulated under the TCR (Atherholt, 1997).
In a 1980 study, two open finished water reservoirs in New Jersey were monitored
weekly. The samples were analyzed in a laboratory certified by the States of New York
and New Jersey. The reported results were that "Turbidity levels increased in the
reservoirs, occasionally exceeding 1 NTU .... Color levels increased in the reservoirs,
occasionally exceeding the recommended limit of 10 units... " (AWWA, 1983). The
increases in turbidity and color appeared to be influenced mainly by algal growth in the
reservoirs; an increase in bacterial population also was observed. The nutrient
concentrations monitored were not significantly affected. Despite the observed changes in
water quality, the reservoir effluent quality met the standards of the New Jersey
Department of Environmental Protection at all times.
A.2 Uncovered Finished Water Reservoirs in California
A.2.1 Los Angeles Department of Water and Power
In 1991, the LADWP conducted studies of both the Stone Canyon Open Reservoirs and
the Silver Lake Reservoirs. The Stone Canyon Reservoir complex comprised two
separate reservoirs, upper and lower, in the Santa Monica Mountains. The studies
concluded that turbidity at the lower reservoir averaged slightly less than 1 NTU,
exceeding the 0.5 NTU standard set by the CDHS. However, the lower reservoir is not
protected from surface water runoff, therefore a filtration plant has been proposed and is
currently going through the approval process. High algae counts occurred seasonally
during the summer. The THM values measured in these reservoirs had an average of
about 24 (ig/L. Data suggested that coliform bacteria levels in the lower reservoir were
greater than those in the upper reservoir (Karimi and Ruiz, 1991). The information
confirmed that water quality was deteriorating in the Stone Canyon Open Reservoirs.
The investigation at Silver Lake Reservoir focused on THMs, turbidity, and coliforms.
The water samples indicated that the average THM concentration at the reservoir outlet is
25.4 |j,g/L, whereas the average inlet concentration is 16.3 |j,g/L. The turbidity samples
taken at various locations were inconsistent and inconclusive. Coliform sampling and
analysis indicated that in two cases the measured level of total coliform bacteria was
slightly higher than 100/100 mL (Karimi, 1988).
A.2.2 Metropolitan Water District of Southern California
The Metropolitan Water District (MWD) of Southern California studied water quality at
both the Garvey Reservoir and the Palos Verdes Reservoirs in 1979. The results
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APPENDIX A. STUDIES PERFORMED
(AWWA, 1983) indicate that turbidity occasionally increased to levels exceeding 1 NTU
and the total coliform bacteria count frequently was greater than 100/100 mL. Algal
populations grew to extensive proportions during the study and the bacterial population
was substantial. Although the water quality deterioration was evident, the measured water
quality met the 1977 standards of the CDHS at all locations and all times.
EPA Guidance Manual A-3 February 1999
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APPENDIX A. STUDIES PERFORMED
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