EPA

United States Office of Water EPA 815-R-99-011

Environmental Protection (4607) April 1999

Agency

Uncovered Finished

Water Reservoirs

Guidance Manual

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.

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

EPA Guidance Manual i April 1999

Uncovered Finished Water Reservoirs

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
CONTENTS

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

ii

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-1

A.1 UNCOVERED FINISHED WATER RESERVOIRS IN NEW JERSEY ........................................................ A-1

A.1.1 Pathogens.......................................................................................................................... A-1

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
CONTENTS

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

iii

FIGURES

Figure 1-1. Types of Finished Water Reservoirs........................................................1-2

Figure 3-1. LADWP’s Open Reservoirs Subject to 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 14-17

Table 5-1. Utility Survey Water Quality Monitoring Parameters....................................5-5
CONTENTS

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

iv

 ACRONYMS

APHA American Public Health Association

AWWA American Water Works Association

ASU Aerial Standard Unit

CDC Centers for Disease Control

CDHS California Department of Health

CFU Colony Forming Unit

CMU Concrete Masonry Unit

CSPE-R Reinforced Chlorosulfonated Polyethylene

CT Pathogen inactivation: disinfectant residual concentration (C, in mg/L) multiplied

by contact time (T, in minutes)

CWC Culp/Wesner/Culp

D/DBP Disinfectants/Disinfection By Product

DEP Department of Environmental Protection

ECP Extra Cellular Product

EPA U.S. Environmental Protection Agency

ESWTR Enhanced Surface Water Treatment Rule

GWUDI Ground Water Under the Direct Influence of Surface Water

HDPE High-Density Polyethylene

HPC Heterotrophic Plate Count

IESWTR Interim Enhanced Surface Water Treatment Rule

LADWP Los Angeles Department of Water and Power

LCR Lead and Copper Rule

MCL Maximum Contaminant Level

MG Million Gallons

MPH Miles per Hour

MPN Most Probable Number

MSDS Materials Safety Data Sheet

MTP Maximum TTHMFP

MWD Metropolitan Water District of Southern California

NEWWA New England Water Works Association

NOM Natural Organic Matter

NPDES National Pollution Discharge Elimination System

NTU Nephelometric Turbidity Unit

ppb parts per billion

PP-R Reinforced Polypropylene

psi pounds per square inch

PVC Polyvinyl Chloride

SMCL Secondary Maximum Contaminant Level

SOP Standard Operating Procedure

SDWA Safe Drinking Water Act

SWTR Surface Water Treatment Rule

TCR Total Coliform Rule

THM Trihalomethane

TOC Total Organic Carbon

TTHMs Total Trihalomethanes

TTHMFP Total Trihalomethane Formation Potential

USPHS U.S. Public Health Service

WIDB Water Industry Data Base
EPA Guidance Manual 1-1 April 1999

Uncovered Finished Water Reservoirs

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
1. INTRODUCTION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

1-2

Á 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
1. INTRODUCTION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

1-3

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 (WIDB) identifies more than 10,000 finished water storage facilities in the

United States. Approximately 3 percent, or 300 of the reservoirs identified in the WIDB,

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
1. INTRODUCTION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

1-4

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
1. INTRODUCTION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

1-5

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:
1. INTRODUCTION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

1-6

“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”(SPHEM,

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.
1. INTRODUCTION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

1-7

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.
1. INTRODUCTION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

1-8

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 μg/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 μg/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.
1. INTRODUCTION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

1-9

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 DBP occurrence in

the distribution system. The

DBPR replaces the current

TTHM rule. It reduced the

Maximum Contaminant Level

(MCL) for TTHMs to 80 μg/L

and established MCLs of 60

μg/L, 10 μg/L, and 0.8 μg/L

for HAA5, bromate, and

chlorite, respectively.

Uncovered reservoirs may provide conditions

that lead to increases in DBP levels. Higher

disinfection doses may be required to maintain

effective disinfectant residuals. Some studies

have shown DBP 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.
1. INTRODUCTION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

1-10

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual 2-1 April 1999

Uncovered Finished Water Reservoirs

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
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-2

• 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.
2. RESERVOIR MANAGEMENT PLAN

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

2-3

• Emergency Planning and Response – Resolves to respond promptly and

effectively to all emergencies with special regard to threats to public health or

safety.

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.
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-4

• 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)
2. RESERVOIR MANAGEMENT PLAN

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

2-5

• 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
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-6

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.
2. RESERVOIR MANAGEMENT PLAN

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

2-7

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,
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-8

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.
2. RESERVOIR MANAGEMENT PLAN

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

2-9

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.
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-10

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
2. RESERVOIR MANAGEMENT PLAN

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

2-11

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.
2. RESERVOIR MANAGEMENT PLAN

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

2-12

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual 3-1 April 1999

Uncovered Finished Water Reservoirs

3. SOURCES OF CONTAMINATION AND

ASSOCIATED CONTROL MEASURES

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
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-2

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)(1); 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)(1)).

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
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-3

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
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-4

ÁEncino 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.

ÁUpper 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.

Figure 3-1. LADWP’s Open Reservoirs Subject to SWTR

Source: LADWP, 1988
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-5

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).
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-6

Table 3-1. 1997 Nutrient Loadings by Bird Groups

in Seattle’s Open Reservoirs

Soluble Nutrient Loadings by Bird Groups

Geese Gulls Ducks Overall Nutrient

Reservoir Nitr. Phos. Nitr. Phos. Nitr. Phos. Total Conc.

kg/yr kg/yr kg/yr kg/yr kg/yr kg/yr kg/yr (μg/L)

Beacon Hill* 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Bitter Lake 0.82 0.24 0.01 0.00 0.06 0.02 1.15 14.09

Green Lake 1.78 0.52 0.03 0.01 0.53 0.16 3.04 16.05

Lake Forest 2.23 0.65 0.36 0.11 0.07 0.02 3.43 15.09

Lincoln 0.00 0.00 0.24 0.07 0.01 0.00 0.31 3.96

Maple Leaf 2.16 0.63 0.13 0.04 0.35 0.10 3.42 15.43

Myrtle 0.00 0.00 0.08 0.02 0.01 0.00 0.12 4.35

Volunteer 0.00 0.00 0.01 0.00 0.01 0.00 0.03 0.42

West Seattle 0.40 0.12 0.38 0.11 0.02 0.01 1.03 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) = D × F × N × S × P

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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-7

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,
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-8

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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-9

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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-10

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 DBPs

(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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-11

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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-12

3.4.2 Increase in Disinfection Byproducts

DBPs 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 DBPs, significantly degrading water

quality in finished water reservoirs and the distribution system (Karimi, 1988; Karimi and

Singer, 1991). DBP 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

μg/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.

30

40

50

60

70

80

90

100

September

1986

November

1986

January

1987

March

1987

May

1987

July

1987

September

1987

Maximum THM Levels across Silver Lake Reservoir

MTP Concentration- ug/L

Inlet

Blended Outlet

Source: Karimi and Singer, 1991

Figure 3-2. Maximum TTHMFP (MTP) in LADWP’s

Silver Lake Reservoir

It should be noted, however, that DBP levels do not necessarily increase in all open

reservoirs. Although the high TTHMFP values correlated with peak algal levels at
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-13

LADWP’s Silver Lake Reservoir, studies conducted at an open reservoir in Seattle

indicated that algae are not causative agents contributing to DBP formation. Other types

of organic substrate also have the potential to affect DBP formation.

Some utilities have observed no significant changes and some have actually experienced

decreases in DBP levels across their open reservoirs (AWWA, 1983). One utility has

conjectured that DBP 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
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-14

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 of fish 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 DBP 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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

3-15

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)(1)). 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 particulate

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.
3. SOURCES OF CONTAMINATION AND ASSOCIATED CONTROL MEASURES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

3-16

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual 4-1 April 1999

Uncovered Finished Water Reservoirs

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 DBP levels and increased DBP 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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-2

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 preestablished 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 shortcircuiting can be located by monitoring at multiple locations and depths to characterize

chlorine residual dynamics throughout the reservoir. The chlorine residual monitoring
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-3

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 waterlevel 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 waterlevel 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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-4

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 (NH3) to nitrite (NO2) and nitrate (NO3). 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.
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-5

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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-6

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 = G2μV

where G = velocity gradient, sec-1

P = power input, ft-lb/sec

μ = dynamic viscosity, lbf-sec/ft2

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-1

μ = 2.39 × 10-5 lbf-sec/ft2

V = 1.34 × 105 ft3 (1 million gallons)

P

Vμ
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-7

Determine mixing power requirements:

P = G2μV = (102)( 2.39 × 10-5)(1.34 × 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
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-8

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.
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-9

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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-10

The effective contact time of the reservoir, T10, is obtained from the test data. T10 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 T10/T, where T

is the theoretical detention time. A T10/T of 1.0 represents ideal plug flow conditions. A

reservoir with a high hydraulic efficiency has a T10/T in the range of 0.5 to 0.8. A T10/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 T10. 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 T10 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 T10.

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.
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-11

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

DBPs. 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 sitespecific 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
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-12

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.
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-13

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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-14

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
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-15

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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-16

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 Costs

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
4. MITIGATING WATER QUALITY DEGRADATION

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

4-17

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

Estimated Cost, 1998,

$ per Sq. Ft.

Estimated Service Life,

Years

Air Supported Fabric $2.00 to $5.50 25 to 25

Floating, Polypropylene $1.50 to $2.50 315 to 30

Wooden $13.00 to $23.00 25 to 50

Steel $14.00 to $22.00 30 to 60

Concrete $21.00 to $29.00 50 to 100

Aluminum Dome $14.00 to $32.00 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.
4. MITIGATING WATER QUALITY DEGRADATION

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

4-18

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual 5-1 April 1999

Uncovered Finished Water Reservoirs

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
5. WATER QUALITY MONITORING

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

5-2

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
5. WATER QUALITY MONITORING

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

5-3

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
5. WATER QUALITY MONITORING

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

5-4

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.
April 1999 5-5 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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.
April 1999 5-6 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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 inreservoir 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/100mL 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.
EPA Guidance Manual 5-7 April 1999

Uncovered Finished Water Reservoirs

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 inreservoir 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.
April 1999 5-8 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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 DBP

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.
EPA Guidance Manual 5-9 April 1999

Uncovered Finished Water Reservoirs

Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)

Parameter Monitoring Rationale Utility Survey Response

Algal populations/

type

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.

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.

Nitrates, nitrites,

phosphorous

Comply with MCLs. Avoid conditions that

lead to “blue baby syndrome.” Identification

of the availability of nutrients is required for

algal growth.

C monitors nitrates/nitrites biweekly and total

phosphorous monthly.

Ammonia Indicates nitrification potential. C monitors biweekly.

Note: Utilities surveyed are differentiated by letters A–F.
April 1999 5-10 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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.
EPA Guidance Manual 5-11 April 1999

Uncovered Finished Water Reservoirs

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.
April 1999 5-12 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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 followup 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.
EPA Guidance Manual 5-13 April 1999

Uncovered Finished Water Reservoirs

Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)

Parameter Monitoring Rationale Utility Survey Response

Giardia and

Cryptosporidium

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.

C monitors occasionally. F monitors Giardia

annually, Cryptosporidium biannually.

Total organic carbon

(TOC)

Indicates presence of organic compounds. B monitors monthly at the reservoir influent and

effluent. E monitors TOC.

Redox Characterizes water chemistry. A continuously monitors at one depth to track

chlorine dynamics. B monitors biweekly and samples

at intervals throughout water column.

Dissolved oxygen Characterizes water chemistry. 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).

Total plankton Characterizes biological activity. Meets taste

and odor requirements.

B monitors biweekly and sometimes analyzes species

population counts.

Midge fly larvae Meet aesthetic requirements. B monitors biweekly using vertical tow methods.

Note: Utilities surveyed are differentiated by letters A–F.
April 1999 5-14 EPA Guidance Manual

Uncovered Finished Water Reservoirs

Table 5-1. Utility Survey Water Quality Monitoring Parameters (continued)

Parameter Monitoring Rationale Utility Survey Response

Secchi disk Measures water transparency. A monitors weekly. B monitors biweekly.

Amorphous matter Characterizes potential for biological activity. B monitors biweekly.

Bird counts Potential sources of coliform and human

pathogens.

A monitors weekly. B conducts weekly surveys at

night. D monitors daily, recording species and

population data.

Zooplankton Monitors biological activity. A monitors weekly. B monitors biweekly as part of

its in-reservoir limnology program.

Debris/sediment Indicates impact of external contamination

sources.

D monitors annually when reservoir is cleaned.

Phytoplankton Indicates chlorine demand, DBP formation

potential, and biological activity.

B monitors biweekly as part of its in-reservoir

limnology program. D monitors bimonthly inreservoir (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.
5. WATER QUALITY MONITORING

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

5-15

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.
5. WATER QUALITY MONITORING

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

5-16

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual 6-1 April 1999

Uncovered Finished Water Reservoirs

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 Manual M25 - 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.

Mantus. 1997. “Watershed Protection for New York City’s Supply.” J. AWWA.

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

System.” J. American Mosquito Control Association. 9(3):283.

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.
6. REFERENCES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

6-2

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.” Opflow. 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 T10 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.
6. REFERENCES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

6-3

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(1):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 R.J. 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.
6. REFERENCES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

6-4

Morra, J.J. 1980. “A Review of Water Quality Problems Caused by Various Open

Distribution Storage Reservoirs.” J. New England Water Works Assoc. 94(4):316-

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

Standards”).

Standard Methods. 1995. Standard Methods for the Examination of Water and

Wastewater (Standard Methods). Nineteenth Edition. Franson, M.H., Eaton,

A.D., Clesceri, L.S., and Greenberg, A.E., Editors. American Public Health

Association, American Water Works Association, and Water Environment

Federation, Washington D.C.

Stolarik, G. and J. Miller. 1998. Personal communication. Gary Stolarik and John Miller

of the LADWP. July 27.

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.

USEPA. 1991b. Manual of Small Public Water Supply Systems. Washington, D.C.

USEPA. 1989a. “Drinking Water; National Primary Drinking Water Regulations;

Filtration, Disinfection, Turbidity, Giardia Lamblia, Viruses, Legionella, and
6. REFERENCES

EPA Guidance Manual April 1999

Uncovered Finished Water Reservoirs

6-5

Heterotrophic Bacteria (“Surface Water Treatment Rule”); Final Rule. 54 FR

27486. June 29.

USEPA. 1989b. “Drinking Water; National Primary Drinking Water Regulations; Total

Coliforms (Including Fecal Coliforms and E. Coli) (“Total Coliform Rule”); Final

Rule. 54 FR 27544. June 29.

USEPA. 1979. “National Interim Primary Drinking Water Regulations; Control of

Trihalomethanes in Drinking Water (“Total Trihalomethane Rule”); Final Rule).

44 FR 68624. November 29.

U.S. Public Health Services. 1946. Manual of Recommended Water Sanitation Practice.

Waller, K., S. Swan, B. Hopkins, G. Windham, L. Fenster, C. Schaefer, and R. Neutra.

1998. “Trihalomethanes in Drinking Water and Spontaneous Abortion.”

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.”

Conference proceedings, AWWA Conference, San Antonio, TX.

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.
6. REFERENCES

April 1999 EPA Guidance Manual

Uncovered Finished Water Reservoirs

6-6

THIS PAGE INTENTIONALLY LEFT BLANK
EPA Guidance Manual A-1 April 1999

Uncovered Finished Water Reservoirs

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 and 8.1 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; LeChevallier et al., 1997).
APPENDIX A. STUDIES PERFORMED

April 1999 A-2 EPA Guidance Manual

Uncovered Finished Water Reservoirs

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 μg/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 μg/L, whereas the average inlet concentration is 16.3 μg/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
APPENDIX A. STUDIES PERFORMED

EPA Guidance Manual A-3 February 1999

 Uncovered Finished Water Reservoirs

(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.
APPENDIX A. STUDIES PERFORMED

April 1999 A-4 EPA Guidance Manual

Uncovered Finished Water Reservoirs

THIS PAGE INTENTIONALLY LEFT BLANK