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**DISCLAIMER**

This manual provides a basic understanding of the potential sources of
external contamination in uncovered finished water reservoirs and
provides guidance to water treatment operators for evaluation and
maintaining water quality in these reservoirs.

This document is EPA guidance only. It does not establish or affect
legal rights or obligation. EPA decisions in any particular case will be
made applying the laws and regulation on the basis of specific facts
when permits are issued or regulations promulgated.

Mention of trade names or commercial products does not constitute an EPA
endorsement or recommendation for use.

**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

CONTENTS

1\. Introduction [1-1](#introduction)

1.1 Water Quality Degradation Concerns
[1-3](#water-quality-degradation-concerns)

1.2 Policies and Regulatory Background
[1-5](#policies-and-regulatory-background)

1.2.1 USPHS Standard [1-5](#usphs-standard)

1.2.2 Ten States Standards [1-6](#ten-states-standards)

1.2.3 AWWA Policy [1-6](#awwa-policy)

1.2.4 EPA Policy [1-6](#epa-policy)

1.2.5 New EPA Regulations [1-7](#new-epa-regulations)

2\. Finished Water Reservoir Management Plan
[2-1](#finished-water-reservoir-management-plan)

2.1 General Information [2-1](#general-information)

2.1.1 Purpose [2-1](#purpose)

2.1.2 Background [2-1](#background)

2.1.3 Policies [2-2](#policies)

2.1.4 Roles and Responsibilities [2-3](#roles-and-responsibilities)

2.2 Reservoir-Specific Information
[2-4](#reservoir-specific-information)

2.2.1 Background Information [2-4](#background-information)

2.2.2 Policies and Ordinances [2-5](#policies-and-ordinances)

2.2.3 Operations [2-5](#operations)

2.2.4 Maintenance [2-6](#maintenance)

2.2.5 Water Quality Monitoring [2-7](#water-quality-monitoring)

2.2.6 Staffing and Training [2-9](#staffing-and-training)

2.2.7 Safety [2-9](#safety)

2.2.8 Construction [2-9](#construction)

2.2.9 Recordkeeping and Reporting [2-10](#recordkeeping-and-reporting)

2.2.10 Reservoir Security [2-10](#reservoir-security)

2.2.11 Emergency Response Plans [2-10](#emergency-response-plans)

3\. Sources of Contamination and Associated Control Measures
[3-1](#sources-of-contamination-and-associated-control-measures)

3.1 Surface Water Runoff [3-2](#surface-water-runoff)

3.2 Bird and Animal Wastes and Control
[3-3](#bird-and-animal-wastes-and-control)

3.2.1 Bird Waste [3-3](#bird-waste)

3.2.2 Bird Control [3-5](#bird-control)

3.2.3 Animal Waste [3-7](#animal-waste)

3.2.4 Animal Control [3-7](#animal-control)

3.3 Human Activity [3-8](#human-activity)

3.3.1 Pesticides and Fertilizers [3-8](#pesticides-and-fertilizers)

3.3.2 Swimming [3-8](#swimming)

3.3.3 Discarded Debris [3-9](#discarded-debris)

3.3.4 Deliberate Contamination [3-9](#deliberate-contamination)

3.3.5 Human Activity Measures [3-9](#human-activity-measures)

3.4 Algal Growth [3-10](#algal-growth)

3.4.1 Increase in Bacteria Populations
[3-11](#increase-in-bacteria-populations)

3.4.2 Increase in Disinfection Byproducts
[3-12](#increase-in-disinfection-byproducts)

3.4.3 Increase in Taste, Odor, and Sediment Problems
[3-13](#increase-in-taste-odor-and-sediment-problems)

3.5 Insects and Fish [3-13](#insects-and-fish)

3.5.1 Insect Larvae [3-13](#insect-larvae)

3.5.2 Fish [3-14](#fish)

3.6 Ground Water Intrusion [3-14](#ground-water-intrusion)

3.7 Airborne Deposition [3-15](#airborne-deposition)

4\. Mitigating Water Quality Degradation
[4-1](#mitigating-water-quality-degradation)

4.1 Reservoir Turnover [4-2](#reservoir-turnover)

4.2 Disinfectant Residual [4-3](#disinfectant-residual)

4.3 Hydraulic Effects [4-5](#hydraulic-effects)

4.3.1 Flow Short-Circuiting [4-5](#flow-short-circuiting)

4.3.2 Hydraulic Circulation System [4-6](#hydraulic-circulation-system)

4.3.3 Reservoir Baffling [4-7](#reservoir-baffling)

4.3.4 Submerged Mixer [4-8](#submerged-mixer)

4.3.5 Relocating Inlets and Outlets
[4-8](#relocating-inlets-and-outlets)

4.3.6 Altering Flow Patterns at the Inlet and Outlet
[4-9](#altering-flow-patterns-at-the-inlet-and-outlet)

4.3.7 Aerators [4-9](#aerators)

4.3.8 Analyzing Reservoir Hydraulics
[4-9](#analyzing-reservoir-hydraulics)

4.4 Reservoir Cleaning [4-11](#reservoir-cleaning-1)

4.5 Water Quality Effects on the Distribution System
[4-12](#water-quality-effects-on-the-distribution-system)

4.6 Covers [4-13](#covers)

4.6.1 Floating Covers [4-14](#floating-covers)

4.6.2 Fixed Covers [4-15](#fixed-covers)

4.6.3 Air-Supported Roofs [4-16](#air-supported-roofs)

4.6.4 Costs [4-16](#costs)

5\. Water Quality Monitoring [5-1](#water-quality-monitoring-1)

5.1 Introduction [5-1](#introduction-1)

5.2 Types of Monitoring [5-1](#types-of-monitoring)

5.2.1 Sampling and Analysis [5-1](#sampling-and-analysis)

5.2.2 Visual Inspection [5-2](#visual-inspection)

5.3 Parameters to Monitor [5-3](#parameters-to-monitor)

5.4 Frequency of Monitoring [5-4](#frequency-of-monitoring)

5.5 Issues Related to Water Quality Monitoring
[5-15](#issues-related-to-water-quality-monitoring)

5.5.1 Laboratory Testing [5-15](#laboratory-testing)

5.5.2 Recordkeeping and Reporting [5-15](#recordkeeping-and-reporting-1)

5.5.3 Training [5-15](#training)

5.5.4 Water Quality Monitoring Equipment
[5-15](#water-quality-monitoring-equipment)

6\. References [6-1](#references)

Appendix A. Studies Performed A-[1](#appendix-a.-studies-performed)

A.1 Uncovered Finished Water Reservoirs in New Jersey
A-[1](#a.1-uncovered-finished-water-reservoirs-in-new-jersey)

A.1.1 Pathogens A-[1](#a.1.1-pathogens)

A.1.2 Other Contaminants A-[2](#a.1.2-other-contaminants)

A.2 Uncovered Finished Water Reservoirs in California
A-[2](#a.2-uncovered-finished-water-reservoirs-in-california)

A.2.1 Los Angeles Department of Water and Power
A-[2](#a.2.1-los-angeles-department-of-water-and-power)

A.2.2 Metropolitan Water District of Southern California
A-[2](#a.2.2-metropolitan-water-district-of-southern-california)

FIGURES

Figure 1-1. Types of Finished Water Reservoirs
[1-2](#__RefHeading___Toc428457718)

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](#refheading___toc428457720)

TABLES

Table 1-1. Uncovered Reservoirs and Implication for Compliance with
Drinking Water Regulations [1-7](#__RefHeading___Toc448712595)

Table 3-1. 1997 Nutrient Loadings by Bird Groups
in Seattle's Open Reservoirs [3-6](#__RefHeading___Toc448712596)

Table 4-1. Estimated Cost Ranges to Cover Existing Reservoirs at 1998
Cost Levels ^1^ [4-17](#__RefHeading___Toc448712597)

Table 5-1. Utility Survey Water Quality Monitoring Parameters
[5-5](#__RefHeading___Toc448712598)

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

# 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 []{#__RefHeading___Toc428457718 .anchor}

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height="2.3229166666666665in"}

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.

## 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 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*

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-   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
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.

## 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.

### USPHS Standard

The USPHS published its first *Manual of Recommended Water Sanitation
Practice* in 1946 (Pluntze, 1974). This manual states:

> *"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."*

### 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).

### 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.

### 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.

### 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.

[]{#__RefHeading___Toc448712595 .anchor}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 | Control of         | The SWTR requires all public   |
| Treatment     | turbidity and      | water systems supplied by      |
| Rule (SWTR)   | pathogens in       | surface water sources to       |
|               | drinking water     | implement disinfection and     |
| (54 *FR*      | through filtration | filtration treatment           |
| 27486, June   | and disinfection.  | practices. If certain source   |
| 19, 1989)     |                    | 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         | Prevent waterborne | Open reservoirs increase       |
| Coliform Rule | microbial disease  | opportunities for the          |
| (TCR)         | through monitoring | introduction of coliform       |
|               | total coliform     | bacteria and microbial         |
| (54 *FR*      | bacteria in the    | pathogens to the system,       |
| 27544, June   | distribution       | increasing the possibility of  |
| 29, 1989)     | system as          | noncompliance with the TCR.    |
|               | an indicator of    |                                |
|               | overall microbial  |                                |
|               | contamination.     |                                |
+---------------+--------------------+--------------------------------+

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         | Reduce cancer risk | The use of uncovered           |
| T             | from exposure to   | reservoirs in a public water   |
| rihalomethane | THMs. Requires     | system tends to increase the   |
| (TTHM) Rule   | that public water  | potential for TTHM formation.  |
|               | systems serving at | If the TTHM level in the       |
| (44 *FR*      | least 10,000       | treated water entering the     |
| 68624,        | people analyze     | reservoir is high (greater     |
| November 29,  | water in the       | than approximately 80 μg/L),   |
| 1979)         | distribution       | the potential contamination    |
|               | system for TTHM    | sources in the reservoir water |
|               | concentrations and | could increase TTHM            |
|               | maintain an annual | concentrations in the          |
|               | average of less    | distribution system to         |
|               | than 100 μg/L. The | unacceptable levels.           |
|               | 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.             |                                |
+---------------+--------------------+--------------------------------+
| Lead and      | Reduce consumer    | The primary effects of open    |
| Copper Rule   | exposure to lead   | reservoirs is that it is more  |
| (LCR)         | and copper by      | difficult to control basic     |
|               | developing and     | water chemistry that impacts   |
| (56 *FR*      | implementing a     | the efficacy of corrosion      |
| 26460, June   | corrosion control  | control strategies (i.e., pH,  |
| 7, 1991)      | program. LCR       | alkalinity, temperature, etc.) |
|               | revisions are      | due to the fact that the       |
|               | expected to be     | reservoir is an open system.   |
|               | promulgated in     | Copper sulfate applications    |
|               | 1999.              | 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.      |
+---------------+--------------------+--------------------------------+

**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       | Reduces health     | Uncovered reservoirs may       |
| Disinfectants | risks through      | provide conditions that lead   |
| and           | control of DBP     | to increases in DBP levels.    |
| Disinfection  | occurrence in the  | Higher disinfection doses may  |
| Byproducts    | distribution       | be required to maintain        |
| Rule (DBPR)   | system. The DBPR   | effective disinfectant         |
|               | replaces the       | residuals. Some studies have   |
| (63 *FR*      | current TTHM rule. | shown DBP levels to increase   |
| 69390,        | It reduced the     | in open reservoirs due to      |
| December 16,  | Maximum            | factors such as long detention |
| 1998)         | Contaminant Level  | times, algal growth, seasonal  |
|               | (MCL) for TTHMs    | temperature variations, and    |
|               | to 80 μg/L and     | heavy in-reservoir             |
|               | established MCLs   | chlorination (Karimi, 1988;    |
|               | of 60 μg/L, 10     | Karimi and Singer, 1991).      |
|               | μg/L, and 0.8 μg/L |                                |
|               | for HAA5, bromate, |                                |
|               | and chlorite,      |                                |
|               | respectively.      |                                |
+---------------+--------------------+--------------------------------+
| Interim       | The IESWTR revises | This rule requires all         |
| Enhanced      | the SWTR to        | finished water reservoirs      |
| Surface Water | further protect    | built after February 16, 1999, |
| Treatment     | against disease    | to be covered. Uncovered       |
| Rule (IESWTR) | causing pathogens  | reservoirs, particularly those |
|               | -- viruses,        | that are strongly influenced   |
| (63 *FR*      | *Giardia lamblia*, | by waterfowl and other sources |
| 69477,        | and                | of external contamination,     |
| December 16,  | *Cryptosporidium*  | increase a system's exposure   |
| 1998)         | -- in drinking     | to pathogens controlled by the |
|               | water for surface  | rule.                          |
|               | water and GWUDI    |                                |
|               | systems serving at |                                |
|               | least 10,000       |                                |
|               | people.            |                                |
+---------------+--------------------+--------------------------------+

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# 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.

## 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.

### 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.

### Background

The plan should discuss background information that establishes the
basis for its development. This may include the following elements:

-   A description of the events that lead to the utility's decision to
    develop the plan

-   Any applicable statutory and regulatory requirements

-   Historic perspective of water quality issues for the system and its
    open reservoirs

-   Narrative and schematic exhibits that describe the system

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-   General description of system operations with emphasis on the
    uncovered finished water reservoirs.

### 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.

-   Emergency Planning and Response -- Resolves to respond promptly and
    effectively to all emergencies with special regard to threats to
    public health or safety.

### 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.

-   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.

## 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.

### 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

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-   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)

-   Reservoir Operations (Drawdown, Refill, Turnover Rate,
    Short-Circuiting)

-   Treatment methods

-   Surrounding area and land use

-   Known water quality problems

-   Known sources of contamination

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-   Previous problems with reservoir and solutions.

### 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.

### 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 {#reservoir-operations .unnumbered}

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 .unnumbered}

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 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 {#other-equipment .unnumbered}

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.

### 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 {#reservoir-cleaning .unnumbered}

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.

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 {#facilities-maintenance .unnumbered}

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 {#equipment-maintenance .unnumbered}

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.

### 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 .unnumbered}

Monitoring parameters should be identified for each reservoir. The *SWTR
Guidance Manual* is a good reference for identifying parameters for a
monitoring program (AWWA, 1991). Additional parameters will depend upon
specific reservoir and downstream quality requirements. Chapter 5
discusses water quality monitoring in greater detail.

##### Monitoring Criteria {#monitoring-criteria .unnumbered}

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 {#monitoring-program .unnumbered}

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 .unnumbered}

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.

##### Contamination Control {#contamination-control .unnumbered}

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.

### 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.

### 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.

### 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.

### 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.

### 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.

### 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 needs to be developed for the
operation of the dam as well as an emergency action plan addressing how
the utility will respond to a dam failure.

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# 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

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-   Airborne deposition

Each of these sources of contamination and methods to mitigate their
impact are discussed below.

## 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 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.

## 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.

### 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

![](media/image7.png){width="3.4298611111111112in" height="2.34375in"}

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.

### 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).

[]{#__RefHeading___Toc448712596 .anchor}Table 3-1. 1997 Nutrient
Loadings by Bird Groups in Seattle's Open Reservoirs

+----------+------+------+------+------+-----+------+------+-------+
| Soluble  |      |      |      |      |     |      |      |       |
| Nutrient |      |      |      |      |     |      |      |       |
| Loadings |      |      |      |      |     |      |      |       |
| by Bird  |      |      |      |      |     |      |      |       |
| Groups   |      |      |      |      |     |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > **Res  | *    |      | *    |      | **D |      | **O  | **    |
| ervoir** | *Gee |      | *Gul |      | uck |      | vera | Nutri |
|          | se** |      | ls** |      | s** |      | ll** | ent** |
+----------+------+------+------+------+-----+------+------+-------+
|          | N    | P    | N    | P    | Ni  | P    | *    | **Co  |
|          | itr. | hos. | itr. | hos. | tr. | hos. | *Tot | nc.** |
|          |      |      |      |      |     |      | al** |       |
+----------+------+------+------+------+-----+------+------+-------+
|          | k    | k    | k    | k    | kg  | k    | k    | (     |
|          | g/yr | g/yr | g/yr | g/yr | /yr | g/yr | g/yr | μg/L) |
+----------+------+------+------+------+-----+------+------+-------+
| > Beacon | 0.00 | 0.00 | 0.00 | 0.00 | 0   | 0.00 | 0.00 | 0.00  |
| > Hill\* |      |      |      |      | .00 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > Bitter | 0.82 | 0.24 | 0.01 | 0.00 | 0   | 0.02 | 1.15 | 14.09 |
| > Lake   |      |      |      |      | .06 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > Green  | 1.78 | 0.52 | 0.03 | 0.01 | 0   | 0.16 | 3.04 | 16.05 |
| > Lake   |      |      |      |      | .53 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > Lake   | 2.23 | 0.65 | 0.36 | 0.11 | 0   | 0.02 | 3.43 | 15.09 |
| > Forest |      |      |      |      | .07 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| >        | 0.00 | 0.00 | 0.24 | 0.07 | 0   | 0.00 | 0.31 | 3.96  |
|  Lincoln |      |      |      |      | .01 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > Maple  | 2.16 | 0.63 | 0.13 | 0.04 | 0   | 0.10 | 3.42 | 15.43 |
| > Leaf   |      |      |      |      | .35 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > Myrtle | 0.00 | 0.00 | 0.08 | 0.02 | 0   | 0.00 | 0.12 | 4.35  |
|          |      |      |      |      | .01 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > V      | 0.00 | 0.00 | 0.01 | 0.00 | 0   | 0.00 | 0.03 | 0.42  |
| olunteer |      |      |      |      | .01 |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+
| > West   | 0.40 | 0.12 | 0.38 | 0.11 | 0   | 0.01 | 1.03 | 4.00  |
| >        |      |      |      |      | .02 |      |      |       |
|  Seattle |      |      |      |      |     |      |      |       |
+----------+------+------+------+------+-----+------+------+-------+

\*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:]{.underline}

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.

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.

### 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).

### 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, altering the nearby habitat to discourage animal
entry, and trapping and removing or exterminating nuisance animals.

## 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.

### 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.

### 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 10^9^ protozoa
and 10^14^ 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.

### 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.

### 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.

### 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.

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.

## 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.

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.

### 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.

### 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.

![](media/image11.wmf)

Source: Karimi and Singer, 1991

[]{#refheading___toc428457720 .anchor}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 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.

### 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.

## Insects and Fish

### 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 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).

### 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.

## 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.

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.

## 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.

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# 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.

## Reservoir Turnover

Reservoir flow-through rate, or turnover rate, is a measure of the
frequency with which water is replaced in the reservoir. Excessive
detention time will occur if a reservoir's turnover rate is too slow, or
if there is hydraulic short-circuiting. Water degradation results when
the chlorine residual decreases as detention time increases. The loss of
chlorine residual is a typical problem in open reservoirs and is of
concern because it allows bacteria and other microorganisms that pose a
threat to public health to multiply.

In developing an effective turnover rate for its reservoirs, a utility
should consider all reservoir functions to achieve a proper balance in
system operations. Some traditional reservoir management practices that
are used to achieve non-water quality related functions tend to result
in turnover rates that are too slow. The constant maintenance of
sufficient reservoir water storage to meet system pressure and emergency
requirements, for example, may have to be balanced against the water
level drawdown/refilling operations needed to obtain an adequate
turnover rate.

The maintenance of an adequate turnover rate is an effective and
economic tool for controlling water quality degradation problems
(Silverman et al., 1983). Proper reservoir management dictates that
utilities actively identify and maintain the best practicable turnover
rates in their open reservoirs. The optimal average turnover rate is
determined by site-specific factors and will therefore be specific to
each reservoir within a system. The desired turnover rate also may vary
over time for a given reservoir in response to seasonal or other
periodic changes in controlling factors. To determine the desired
turnover rate for a reservoir, a utility should define and evaluate at
least two primary factors: (1) the chlorine decay rate in the reservoir
and (2) the configuration of the reservoir.

Based on the chlorine residual at the reservoir inlet and chlorine decay
rate in the reservoir, the utility can determine the theoretical
turnover rate needed to achieve a pre-established chlorine residual
goal. This method of calculating the turnover rate is most applicable to
reservoirs in which the water-flow regime most closely approximates
ideal plug flow. Ideal plug flow, a flow regime in which a well-mixed
volume of water will proceed at a steady rate from an inlet at one end
to an outlet at the opposite end, is best suited to rectangular-shaped
reservoirs with smooth and even surfaces.

Open reservoirs, which are often circular or irregularly shaped and not
well mixed, typically do not exhibit ideal plug flow. Hydraulic "dead
spots" of stagnant water, for example, are frequently found in
reservoirs having an inlet and outlet in close proximity of one another.
In this type of reservoir, the water that is hydraulically
short-circuited near the inlet and outlet may have an adequate chlorine
residual, but significant water quality degradation can occur in the
dead spots that may form outside of the inlet/outlet area of influence.
The water in these dead spot areas may have a detention time as high as
several weeks and will therefore not have a chlorine residual. These
dead spots and short-circuiting can be located by monitoring at multiple
locations and depths to characterize chlorine residual dynamics
throughout the reservoir. The chlorine residual monitoring data can be
used to determine an optimal average turnover rate for the reservoir
that will result in an adequate chlorine residual throughout the
reservoir.

To ensure that the optimal turnover rate for each reservoir is actually
achieved during day‑to-day operations, the utility should develop and
implement a water-level fluctuation strategy. The objective of this
strategy is to force most of a reservoir's water to turn over in one
continuous cyclical operation of water drawdown and refilling. A cycle
consists of draining a large percentage of the reservoir and allowing a
pre-determined period of time to pass before refilling. Another, but
less desirable method, involves periodic flushing of the reservoir by
overflowing. Turnover rate management programs that include water-level
fluctuation strategies will avoid the long detention times that might
occur in dead spots, or poorly circulating areas. The frequency and
amount of water fluctuation necessary will depend on the flow
characteristics of the reservoir. This type of strategy is critically
important for reservoirs that have common inlets and outlets such as
standpipes.

Some utilities have developed turnover rate management programs that
include water-level fluctuation strategy as an important tool for the
correction of water quality degradation, preventing conditions from
worsening. One large utility, faced with a water quality problem such as
taste and odor, will increase the turnover rate using any of the
following water-level fluctuation methods: (1) flushing out the affected
reservoir by overflowing at high rates, (2) adjusting distribution
system valves to increase flows from the affected reservoirs, and (3)
using auxiliary pump stations to draw down the reservoir at an
accelerated rate. This utility's open reservoir management plan includes
a turnover rate goal of 5 days and a minimum chlorine residual goal of
0.6 mg/L at the reservoir outlet.

If a system chooses to incorporate a water level fluctuation strategy,
it should address potential algal growth problems. Algae growth can
cause problems because it tends to colonize on the surface of the sides
of the reservoir. As a water-level fluctuation strategy is implemented
and the water level is decreased, the algae on the sides of the
reservoir may perish. Once the water level is increased, the water will
come in contact with these dead organisms, which may result in water
quality degradation. It is important to address this possibility while
deciding whether to implement a water fluctuation strategy.

Although turnover rate can be used to effectively decrease water quality
degradation, only one State has regulations that address turnover. Ohio
requires that at least 20 percent of the reservoir volume turns over
daily. Internationally, Germany limits maximum detention time to between
5- to 7-days for concrete-lined reservoirs, while Switzerland limits a
1- to 3-day maximum, based on the lower chlorine residuals maintained at
Swiss facilities. Kirmeyer and Noran (1997) indicated that an average
turnover rate should range from 3-to 7-days.

## 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. 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 (NH~3~) to nitrite
(NO~2~) and nitrate (NO~3~). 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.

## 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.

### 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. 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.

### 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:

^2^µV

where G = velocity gradient, sec^-1^

P = power input, ft-lb/sec

µ = dynamic viscosity, lbf-sec/ft^2^

V = Volume, ft^3^

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]{.underline}
>
> Given G = 10 sec-^1^
>
> µ = 2.39 × 10^-5^ lbf-sec/ft^2^

V = 1.34 × 10^5^ ft^3^ (1 million gallons)

> Determine mixing power requirements:
>
> P = G^2^µV = (10^2^)( 2.39 × 10^-5^)(1.34 × 10^5^) = 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.

### 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 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.

### 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.

### 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.

### 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.

### 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.

### 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 {#tracer-study .unnumbered}

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.

The effective contact time of the reservoir, T~10~, is obtained from the
test data. T~10~ 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 T~10~/T, where T is the theoretical
detention time. A T~10~/T of 1.0 represents ideal plug flow conditions.
A reservoir with a high hydraulic efficiency has a T~10~/T in the range
of 0.5 to 0.8. A T~10~/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 T~10~. 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 T~10~ 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 T~10~.

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.

As noted previously, chlorine residual monitoring also can be used to
roughly characterize reservoir hydraulics.

##### Finite Element Modeling {#finite-element-modeling .unnumbered}

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.

## 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
    site-specific and best for the particular facility (e.g., every six
    months, once per year, every two years). This time-frame depends on
    the monitoring of water quality parameters such as pH, temperature,
    nutrient loadings, quality of the influent, etc. that will have an
    affect on algal growth in the reservoir. This cleaning should
    coincide with draining the reservoir and inspecting the integrity 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.

## 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.

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.

## 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

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-   The capital and maintenance costs and other economic factors
    involved.

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.

### 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

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-   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 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.

### 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.

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.

### 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.

### 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 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)

[]{#__RefHeading___Toc448712597 .anchor}Table 4-1. Estimated Cost Ranges
to Cover\
Existing Reservoirs at 1998 Cost Levels ^1^

  ------------------------ ----------------------- -----------------------
  Type of Cover            Estimated Cost, 1998,\  Estimated Service
                           \$ per Sq. Ft.          Life,\
                                                   Years

  Air Supported Fabric     \$2.00 to \$5.50 ^2^    5 to 25

  Floating, Polypropylene  \$1.50 to \$2.50 ^3^    15 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.

THIS PAGE INTENTIONALLY LEFT BLANK

# Water Quality Monitoring

## 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.

## 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.

### 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 .unnumbered}

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 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 .unnumbered}

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 .unnumbered}

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.

### 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 .unnumbered}

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 trespassing may be made daily or weekly, while inspection of overflows might be appropriate on a weekly or monthly basis. {#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-trespassing-may-be-made-daily-or-weekly-while-inspection-of-overflows-might-be-appropriate-on-a-weekly-or-monthly-basis. .unnumbered}

##### Follow-Up Observation {#follow-up-observation .unnumbered}

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 {#special-study-observation .unnumbered}

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.

## 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]{.underline} 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 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.

## 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.

+------------+-------------------------+------------------------------+
| [          |                         |                              |
| ]{#__RefHe |                         |                              |
| ading___To |                         |                              |
| c448712598 |                         |                              |
| .an        |                         |                              |
| chor}Table |                         |                              |
| 5-1.       |                         |                              |
| Utility    |                         |                              |
| Survey     |                         |                              |
| Water      |                         |                              |
| Quality    |                         |                              |
| Monitoring |                         |                              |
| Parameters |                         |                              |
+------------+-------------------------+------------------------------+
| Parameter  | Monitoring Rationale    | Utility Survey Response      |
+------------+-------------------------+------------------------------+
| > *E       | > Indicates fecal       | > **A** has set follow-up    |
| scherichia | > contamination and     | > action levels at greater   |
| > coli*    | > likelihood of         | > than 40 Most Probable      |
|            | > pathogens of          | > Number (MPN)/100 mL. **B** |
|            | > intestinal origin.    | > monitors **biweekly** as   |
|            | > Some species are      | > part of its in‑reservoir   |
|            | > human pathogens. Also | > limnology program and      |
|            | > monitors              | > collects one influent      |
|            | > effectiveness of bird | > sample and eight effluent  |
|            | > and animal control    | > samples **daily**. Each of |
|            | > program.              | > the effluent samples is a  |
|            |                         | > composite of samples       |
|            |                         | > collected at six different |
|            |                         | > times and three grab       |
|            |                         | > samples.                   |
+------------+-------------------------+------------------------------+
| > Fecal    | > Similar to *E. Coli*. | > **B** does not monitor     |
| >          |                         | > fecal coliforms. **D**     |
|  coliforms |                         | > 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.**

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

  ------------- -------------------------- -------------------------------
  Parameter     Monitoring Rationale       Utility Survey Response

  Total         Determines effectiveness   **A** monitors **daily**
  coliforms     of treatment and           in-reservoir and **weekly** at
                distribution system        outlets of reservoirs impacted
                integrity. Indicates a     by surface runoff. For other
                system's vulnerability to  reservoirs, **weekly**
                fecal contamination, not   in-reservoir monitoring is
                whether fecal              done. Follow up action
                contamination actually     threshold level is greater than
                exists.                    500 MPN/100 mL. **B** monitors
                                           **biweekly** as part of its
                                           in-reservoir limnology program
                                           collects one influent sample
                                           and eight effluent samples
                                           **daily**. Each of the effluent
                                           samples is a composite of
                                           samples collected at six
                                           different times and three grab
                                           samples. **C** collects
                                           **daily** in-reservoir samples.
                                           **D** samples **weekly** at
                                           both in-reservoir and reservoir
                                           checkpoint locations, and
                                           conducts follow-up sampling and
                                           response action when levels
                                           reach greater than 100
                                           colonies/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.**

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

  ------------- -------------------------- -------------------------------
  Parameter     Monitoring Rationale       Utility Survey Response

  HPC           Indicates bacterial growth **B** monitors **biweekly** as
                and overall water quality. part of its in-reservoir
                A few types of HPC may     limnology program**. D**
                cause gastrointestinal     samples **weekly** at both
                illness.                   in-reservoir and reservoir
                                           checkpoint locations, and
                                           conducts follow-up sampling
                                           when levels reach greater than
                                           500 colonies/100 mL in 2
                                           consecutive samples. Follow up
                                           action consists of increasing
                                           the turnover rate and, if no
                                           improvement occurs, adding
                                           calcium hypochlorite tablets to
                                           the reservoir.
  ------------- -------------------------- -------------------------------

Note: Utilities surveyed are differentiated by letters A--F.

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

  --------------------- -------------------------- -------------------------------
  Parameter             Monitoring Rationale       Utility Survey Response

  Chlorine/chloramine   Ensures adequate           **A** monitors free and total
  residual (free and    disinfection through       residual **continuously** at
  total)                maintenance of target      outlets, and **daily** before
                        residual goals. Avoids     and after the point of
                        over-chlorination that may chlorination at reservoirs
                        contribute to DBP          impacted by surface runoff.
                        formation and pipe         **B** monitors **biweekly**
                        corrosion.                 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.

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

  -------------- -------------------------- -------------------------------
  Parameter      Monitoring Rationale       Utility Survey Response

  Algal          Avoids problems associated **A** monitors **continuously**
  populations/   with algal blooms,         in reservoirs impacted by
  type           including color, taste and surface runoff, **weekly** in
                 odor, bacterial growth,    other reservoirs (chlorophyll
                 THM formation, and         grab sample). For one reservoir
                 turbidity. Some blue-green that is subject to
                 species produce toxins     surface runoff, follow-up
                 that may be harmful or     action levels have been set:
                 fatal to humans and        (1) chlorination is initiated
                 animals. Blooms may clog   when chlorophyll is greater
                 filters. Monitoring should than 1 parts per billion (ppb)
                 identify algal species     and growth rate is greater than
                 and/or toxins present at   0.1 ppb/day, and (2)
                 "high" levels.             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,      Comply with MCLs. Avoid    **C** monitors
  nitrites,      conditions that lead to    nitrates/nitrites **biweekly**
  phosphorous    "blue baby syndrome."      and total phosphorous
                 Identification of the      **monthly**.
                 availability of nutrients  
                 is required for algal      
                 growth.                    

  Ammonia        Indicates nitrification    **C** monitors **biweekly.**
                 potential.                 
  -------------- -------------------------- -------------------------------

**Note: Utilities surveyed are differentiated by letters A--F.**

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

  ------------- -------------------------- -------------------------------
  Parameter     Monitoring Rationale       Utility Survey Response

  Specific      Identifies water source    **A** monitors **daily,**
  conductance   when a reservoir may be    before and after point of
                supplied by multiple       chlorination at reservoirs
                source waters.             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   **A** monitors **continuously**
                problems. Measures water   at outlets and **daily** before
                corrosivity. Maintains     and after points of
                optimal corrosion control  chlorination at reservoirs
                in distribution system.    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.**

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

  ------------- -------------------------- -------------------------------
  Parameter     Monitoring Rationale       Utility Survey Response

  Temperature   Identifies mixing problems **A** monitors **continuously**
                (thermoclines). Avoids     at three different depths at
                conditions conducive to    outlets and **daily** before
                algal and bacterial        and after points of
                growth.                    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 **A** monitors **daily,**
                suspended colloidal        before and after chlorination
                particles. Identifies      points of reservoirs impacted
                chlorine demand and        by surface runoff and
                disinfection interference. **weekly** for other
                Meets aesthetic water      reservoirs. **B** monitors
                quality requirements.      **daily** at the reservoir
                Evaluates                  effluent and **biweekly** in
                erosion/sedimentation      reservoir. **B** Conducts
                control programs.          follow-up monitoring **when
                Indicates presence of      greater than a 0.7
                other contaminants, such   nephelometric turbidity units
                as heavy metals and        (NTU)**. **C** monitors
                synthetic organic          **weekly**. **D** monitors
                compounds, that may bind   **weekly** at in-reservoir (5
                to turbidity particles.    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.**

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

  --------------- -------------------------- -------------------------------
  Parameter       Monitoring Rationale       Utility Survey Response

  Taste and odor  Meet aesthetic             **B** monitors **daily** at the
                  requirements.              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  **B** monitors **biweekly** and
                  and aesthetic quality.     **daily** at the reservoir
                                             effluent.

  *Pseudomonas*   May act as a human         **B** speciates all atypical
                  pathogen, particularly for growths greater than 25 Colony
                  immuno-compromised         Forming Units (CFU) identified
                  individuals (e.g., has     during its coliform monitoring.
                  been found to cause fevers **D** samples **weekly** and
                  in hospital dialysis       conducts follow-up
                  patients, and also may     sampling/action when levels
                  cause pneumonia and        reach greater than 100
                  secondary infections).     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.**

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

  ------------------- -------------------------- -------------------------------
  Parameter           Monitoring Rationale       Utility Survey Response

  *Giardia* and       Cause giardiasis and       **C** monitors **occasionally.
  *Cryptosporidium*   cryptosporidiosis, which   F** monitors *Giardia*
                      are associated with        **annually**, *Cryptosporidium*
                      surface runoff. Monitoring **biannually.**
                      for these pathogens        
                      verifies that a finished   
                      water reservoir is not     
                      receiving surface runoff   
                      and fecal contamination.   

  Total organic       Indicates presence of      **B** monitors **monthly** at
  carbon (TOC)        organic compounds.         the reservoir influent and
                                                 effluent**. E** monitors TOC.

  Redox               Characterizes water        **A continuously** monitors at
                      chemistry.                 one depth to track chlorine
                                                 dynamics. **B** monitors
                                                 **biweekly** and samples at
                                                 intervals throughout water
                                                 column.

  Dissolved oxygen    Characterizes water        **A** monitors **weekly** from
                      chemistry.                 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   **B** monitors **biweekly** and
                      activity. Meets taste and  sometimes analyzes species
                      odor requirements.         population counts.

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

**Note: Utilities surveyed are differentiated by letters A--F.**

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

  ----------------- -------------------------- -------------------------------
  Parameter         Monitoring Rationale       Utility Survey Response

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

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

  Bird counts       Potential sources of       **A** monitors **weekly. B**
                    coliform and human         conducts weekly surveys at
                    pathogens.                 night. **D** monitors
                                               **daily**, recording species
                                               and population data.

  Zooplankton       Monitors biological        **A** monitors **weekly. B**
                    activity.                  monitors **biweekly** as part
                                               of its in-reservoir limnology
                                               program.

  Debris/sediment   Indicates impact of        **D** monitors **annually**
                    external contamination     when reservoir is cleaned.
                    sources.                   

  Phytoplankton     Indicates chlorine demand, **B** monitors **biweekly** as
                    DBP formation potential,   part of its in-reservoir
                    and biological activity.   limnology program. **D**
                                               monitors **bimonthly**
                                               in-reservoir (at a location 5
                                               feet from sides and 15 feet
                                               below the surface) and
                                               **weekly** at a reservoir
                                               checkpoint after chlorination.
                                               In-reservoir monitoring
                                               includes species identification
                                               and enumeration.
  ----------------- -------------------------- -------------------------------

**Note: Utilities surveyed are differentiated by letters A--F.**

## Issues Related to Water Quality Monitoring

### 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.

### 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.

### 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.

### Water Quality Monitoring Equipment

Water utilities should consider online continuous monitoring equipment,
especially at reservoir inlets and outlets. Data from continuous
monitoring will help establish a correlation between reservoir and
distribution system water quality. Utilities also should consider the
use of permanently installed sampling lines to facilitate sample
collection.

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# Appendix A. Studies Performed {#appendix-a.-studies-performed .unnumbered}

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 {#a.1.1-pathogens .unnumbered}

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).

### A.1.2 Other Contaminants {#a.1.2-other-contaminants .unnumbered}

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-uncovered-finished-water-reservoirs-in-california .unnumbered}

### A.2.1 Los Angeles Department of Water and Power {#a.2.1-los-angeles-department-of-water-and-power .unnumbered}

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 {#a.2.2-metropolitan-water-district-of-southern-california .unnumbered}

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 (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.

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