United States
Environmental Protection
Agency
Technology Transfer
Seminar Publication

Benefit  Analysis for
Combined Sewer
Overflow Control

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Technology Transfer	EPA-625/4-79-013
Seminar Publication

Benefit Analysis
for Combined
Sewer Overflow
Control
 April 1979
 Environmental Research Information Center
 Cincinnati, OH 45268

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Acknowledgements
This seminar publication contains material prepared for the U.S. Environmental Protection Agency Technology
Transfer Program and has been presented at Technology Transfer seminars on combined sewer overflow assess-
ment and control procedures throughout the United States during 1978.
The majority of topics presented at the seminars were the result of research projects managed by Richard Field and
Staff of the Storm and Combined Sewer Section, Wastewater Research Division. M unicipal Environmental Research
Laboratory, Office of Research and Development, U.S. Environmental Protection Agency.
This publication was prepared by Thomas E. Walton and Virginia R. Hathaway of JACA Corporation, Fort
Washington, Pennsylvania from papers presented by Eugene D. Driscoll, Hydroscience Inc., Westwood, New Jer-
sey; James P. Heaney, University of Florida, Gainseville, Florida; John A. Lager, Metcalf and Eddy, Inc., Palo
Alto, California; John L. Mancini, Manhattan College, Bronx, New York; Myron A. Tiemons, Facility Require-
inents Branch, Municipal Construction Division, U.S. EPA, Washington, DC; and Jack Warburton, Brown and
Caidwell. Seattle, Washington.
Notice
The mention of trade names or commercial products in this publication is for illustration purposes. and does not constitute endorsement or
recommendation for use by the U.S. Environmental Protection Agency.

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Contents
Page
List of Figures V
List of Tables V
Chapter I — INTRODUCTION
Nature of Combined Sewer Overflows
Distribution of Combined Sewer Systems 3
Regulations Governing Combined Sewer Overflow Control Projects 3
Cost of Combined Sewer Overflow Control 4
Chapter II— LEGISLATION AND REGULATIONS 5
Chapter III — BENEFICIAL USES AS OBJECTIVES 9
Requirements and Limitations 9
Mandated Goals 10
Compatibility with Social and Economic Objectives 10
Mutual Compatibility of Multiple Uses of the Receiving Water 11
Limitations Imposed by Natural Characteristics 11
Seasonal Limitations 11
Public Interest or Demand 11
Design Conditions and the Concept of Acceptable Risk 11
Technological and Financial Feasibility 12
Selection and Ranking 13
Chapter IV — RELATING POLLUTANT SOURCES TO BENEFICIAL USES 15
Water Quality Problems Associated with Water Uses 15
Water Pollution Sources Identified with Beneficial Uses 15
Models 20
Monitoring and Sampling 21
Summary 23
Chapter V — ALTERNATIVES FOR CONTROLLING COMBINED SEWER OVERFLOWS 25
Control Strategy Development 25
Control Alternatives 27
Source Controls 27
Street Cleaning 27
Combined Sewer Flushing 28
Catch Basin Cleaning 28
Collection System Controls 28
Existing System Management 28
Flow Reduction Techniques 28
Sewer Separation 28
In-Line Storage 28
Storage Treatment 28
Off-Line Storage 28
Treatment 28
Selection of Control Alternatives 29

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Chapter VI— COSTS OF COMBINED SEWER OVERFLOW CONTROL ALTERNATIVES 31
Cost Allocation in Multi-Purpose Projects 34
Alternative Justifiable Expenditure Method 36
Chapter VII— BACK TO BENEFITS 39
Estimating Benefits 39
Comparing Costs and Benefits 40
Selection of Design Storm 41
Chapter VIII — CASE STUDIES 43
Seattle 43
Collection System Analysis 43
CSO Characteristics 44
Identification of Beneficial Uses and Sensitivity of Receiving Waters 44
Cost Control Relationship 44
Water Body Beneficial Use 49
CSO Control Levels and Beneficial Uses 49
Swimming 49
Fish Rearing/Spawning 50
Recreational Boating/Shoreline Parks 50
Conclusions of Seattle Case 50
New York City 50
BIBLIOGRAPHY 53
iv

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List of Tables
Table 1. Water Quality Problems Associated with Beneficial Uses 16
Table 2. Pollutants Contributed by Various Non-Point Sources 17
Table 3. Pollutants Removed by Structural Alternatives 29
Table 4. Estimated Construction Costs 32
Table 5. Cost Ranges for Selected Source and Collection Control Alternatives 34
Table 6. Relation Between Design Basis and Benefits 40
Table 7. Average CSO Pollutant Levels — Seattle 44
Table 8. Beneficial Uses and CSO Pollutants — Seattle 49
List of Figures
Figure 1. Representative Stormwater Discharge Quality 2
Figure 2. Geographic Distribution of Population Served by Combined Sewer Systems 3
Figure 3. Time Scales for Storm Runoff Water Quality Problems 18
Figure 4. Space Scales for Storm Runoff Water Quality Problems 19
Figure 5. Various Levels of Detail in Stormwater Load Characterization 22
Figure 6. Methodology for Determining Load Reduction Requirements 26
Figure 7. Optimum Combination of Control Alternatives for Various Levels of
Pollutant Reduction and Budgetary Limits 27
Figure 8. Storage Reservoir Labor and Cost of Supplies 33
Figure 9. Capital Cost Ranges for Selected Treatment Processes 34
Figure 10. Overflow Volumes and Incremental Levels of Control 35
Figure 11. Identifying Specific-Purpose Costs Within the Costs of a Multi-Purpose Project 36
Figure 12. Allocating Joint Costs in a Multi-Purpose Project 37
Figure 13. Relation Between Costs and Benefits 41
Figure 14. Water Contact Recreation: Risk of Degradation from Combined Sewer Overflows 45
Figure 15. Biotic Life Zones and Critical Habitats: Risk of Degradation from Combined Sewer Overflows 46
Figure 16. Water Quality: Relative Sensitivity to Pollutant Loading 47
Figure 17. Relative Priority in Terms of Pollution Risk from Combined Sewer Overflows 48
Figure 18. Cost-Overflow Control Curve — Priority 5 Overflow Area: Lake Union (South and
East Shores) and Portage Bay 49
Figure 19. Facilities for Areawide Swimming: New York City 51
V

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Chapter I
Introduction
With each passing year, the number of publicly owned
sewage treatment plants and industrial dischargers of
waste water that are not in compliance with the na-
tional effluent guidelines set by the Federal Water Pol-
lution Control Act Amendments of 1972 grows
smaller. At the same time, there have been noticeable,
often dramatic improvements in the quality of our
streams and lakes. Fish kills caused by discharges of
inadequately treated sewage were once common sum-
mer events in urban or industrialized areas; they have
become infrequent. Waters that were once unappeal-
ing aesthetically are now attractive components of the
urban landscape.
However, as the most obvious water pollution prob-
lems are abated, others become visible. In some urban
areas, providing the required treatment for continuous
point source discharges has not yielded the desired or
mandated improvements in water quality. Attention
has naturally turned to storm-related pollution in the
form of storm sewer discharges and especially com-
bined sewer overflows.
This publication is intended for the use of elected
officials of municipalities served by combined sewers,
their technical staff members, and their consultants.
The report concerns an analysis of the benefits antici-
pated from control of combined sewer overflows. A
number of references are available on combined sewer
problems, their assessment and control technologies.
They are cited in this publication, and some discussion
of those topics is necessarily included here. But the
subject of benefit analysis is uniquely important to
anyone contemplating combined sewer overflow con-
trols because of the nature of the overflows them-
selves, the distribution of combined sewer systems in
the nation, the regulations governing the use of U.S.
Environmental Protection Agency (EPA) construction
grant moneys for this purpose, and the potentially
high cost of corrective measures.
A clear understanding of the material in this publi-
cation will help any municipality, small or large. to
avoid numerous and costly pitfalls and to take full ad-
vantage of opportunities for assistance in planning
and implementing a combined sewer overflow control
program.
The Nature of Combined Sewer
Overflows
Combined sewers are, by definition, collection sys
tems that convey both sanitary sewage and stormwa-
ter. They are typically found in older cities. Regulators
in the sewers channel dry-weather flows (primarily
sanitary sewage) into interceptors and thence to the
sewage treatment plant. These regulators are set so
that the excessive flows that enter the system through
street inlets during storms are allowed to overflow to
some receiving stream or lake rather than overloading
the plant or the collection system with stormwater or
backing up in sewers and causing localized flooding.
Combined sewer overflows can be characterized in
several ways. First, they occur during or after storm
events (unless regulators malfunction and allow con-
tinuous discharges), and their volumes and frequency
are thus related to the rainfall patterns in the locality.
Second, they occur at discrete overflow points. Third,
they contain the constituents found in urban stormwa-
ter as well as those in sanitary sewage, often in higher
concentrations as shown in Figure 1.
The result of an overflow can be a significant dis-
charge of organic material, nutrients, sediment, micro-
organisms, oil and grease. and metals and other
potentially toxic substances into the receiving water.
In some cases, concentrations are higher at the begin-
ning of the overflow — the so-called first flush of ma-
terial accumulated in the sewer. Depending on the
characteristics and sensitivity of the receiving water,
the overflow can have a variety of effects, ranging
from serious to negligible. Benefit analysis is in part
concerned with identifying those effects and the antici-
pated results of effecting changes in them.
1

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TSS BOD Lead Fecal Coliforms
1000 Organisms! 100 ml
Legend
Stormwater Runoff from Dec. 1 973 Assessment
Stormwater Runoff from this Update
Combined Sewer Overflows from Dec. 1 973 Assessment
Combined Sewer Overflows from this Update
Figure 1. Representative Stormwater Discharge Quality.
Source: Lager. A.. W. G. Smith. W. G. Lynard. R. M. Finn. and E. J. Fnnemore, Urban Stormwater Management and Technology. Update
and Users Guide, U.S. EPA Report, EPA 6OO!8 77-014. p. 10. September 1977.
2
COD Total Nitrogen Total
Phosphorus
Parameter

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Distribution of Combined Sewer
Systems
Approximately 40 million people (one-fifth of the
nation’s population) are served by combined sewers.
There are between 1,100 and 1,300 combined sewer
systems, covering an area of more than 2 and one half
million acres. Seventy-seven major cities, including 10
of the country’s 14 largest have combined sewer over-
flow control needs of $50 million or more. They ac-
count for 96 percent of urbanized area combined
sewer overflow control needs and 64 percent of na-
tional needs. The remaining control needs are shown
in Figure 2.2
0%-i 0%
51%-75%
26%-50% Overl5%
Regulations Governing Combined Sewer
Overflow Control Projects
Combined sewer overflow control projects are eli-
gible for federal assistance covering 75 percent of costs
for feasibility studies, design and construction. How-
ever, the requirements for approval and funding are
very different from those that apply to sewage treat-
ment facilities. In the case of the latter, federal law re-
quires at least secondary treatment. Facilities that
have not adiieved that level must do so, and when
they are high enough on the state priority list, they can
receive federal funding.
Figure 2. Geographic Distñbution of Population Served by Combined Sewer Sy.t.ms.
Source: U.S. Environmental Protection Agency, Report to Congress on Control of Combined Sewer Overflows in the United States, MCD-50,
p.6-2 .19 78 .
These statistics reveal another important character-
istic of combined sewers: They are concentrated in
some of our most heavily populated urban centers. In
fact, the average population density of combined
sewer service areas is 16.7 persons per acre. Conse-
quently, when overflows occur, they affect relatively
short reaches of surface waters, but millions of people
feel the impact on water quality.. 3
There is no such technology-based treatment re-
quirement for combined sewer overflows. Benefit anal-
ysis must be performed to demonstrate that the
proposed level of overflow control or treatment will re-
suit in some tangible improvement in water-quality-
related benefits. This is the same kind of requirement
faced by states wishing to set water quality standards
which require higher than secondary treatment; the
Ratio of projected population served by
combined sewers to total sewered popul
3

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state must show the connection between the water
quality criterion and some beneficial use to be
protected.
Other regulations governing combined sewer over-
flows require permits for each outfall. However, they
differ from the National Pollutant Discharge Elimina-
tion System (NPDES) permits for treatment plants,
which specify effluent limitations based on technology
or water quality standards. NPDES permits for com-
bined sewer overflows contain no effluent limitations,
though they do usually require monitoring and data
collection.
The Cost of Combined Sewer Overflow
Control
Some of the options for controlling combined sewer
overflows, especially those involving the division of the
combined sewers into separate storm and sanitary sys-
tems. necessitate monumental expenditures that se-
verely strain local budgets and state construstion grant
allocations. On a nationwide basis, the EPA 1976
Needs Survey 4 estimated that more than $18 billion
($21 billion in 1978 dollars) would be needed for con-
trol of pollution from combined sewer overflow, com-
pared to $13 billion for secondary treatment and $21
billion for more stringent treatment of sanitary sew-
age. The 1978 Needs Surve/ contains a revised esti-
mate of $25.7 billion for combined sewer overflow
control. This estimate is based on optimum or least-
cost alternative to provide certain minimum benefits.
If sewer separation were arbitrarily carried out for all
combined systems, the cost w;uld be an estimated
$104 billion.
As a tool to relate proposed expenditure to antici-
pated benefit, a properly executed benefit analysis
helps a municipality, and thus the U.S. government,
avoid unnecessary costs. A benefit analysis provides
justification for funding requested from the state and
EPA, and it demonstrates to the taxpayers that their
tax dollars are being used to achieve desirable
objectives.
References
1 Federal Water Pollution Control Act Amendment of
1972,33 U.S.C. 1251, etseq., P.L. 92-500.
2 U.S. Environmental Protection Agency, Report to
Congress on Control of Combined Sewer Overflows
in the United States (MCD-50), 1978.
3 lbid., p. 6-9.
4 Turner, B., R. Holbrook, R. Corbitt, and R. Wysoff,
1976 Needs Survey: Summary of Technical Data
for Combined Sewer Overflow and Storm water Dis-
charge, U.S. EPA Report, EPA 430/9-76-012,
February 1977.
sWycoff R. J.. J. Scholl, and S. Kissoon, 1978 Needs
Survey: Cost Methodology of Control of Combined
Sewer Overflows and Stormwater Discharge, U.S.
EPA Report, EPA-430/9-79-003, February,
1979.
4

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Chapter II
Legislation and Regulations
To succeed in obtaining approval and funding assist-
ance for a combined sewer overflow (CSO) project, it
is necessary to know the regulations and policies that
have an impact on ultimate grant application approv-
als. A clear understanding should be developed at the
beginning of the process. because the plans must pro-
vide special outputs and must meet a number of cri-
teria peculiar to combined sewer overflow control
planning. Thus, this chapter will review briefly the leg-
islation under which combined sewer overflow control
planning and construction may be funded, the regu-
lations promulgated by EPA in response to that legis-
lation, other laws and regulations having an impact on
combined sewer overflow, and the policies developed
to guide not only the planners, engineers and at-
torneys, but also the elected officials, state environ-
mental agencies, and EPA itself.
Under Section 208 of the Clean Water Act of 1977
(P.L. 95-2 17)’ which ammended the Federal Water
Pollution Control Act Amendments of 1972 (P.L. 92-
Soo),2 funds are provided for areawide waste treatment
management planning. This planning must include:
The identification of treatment works necessary to meet the
anticipated municipal and industrial waste treatment needs
of the area over a twenty-year period, annually updated
[ and] the necessary wastewater collection and urban Storm
water runoff systems. [ Section 208(b)(2)(A)]
The rules and regulations for 208 planning (promul-
gated by the EPA in 1975) specifically require as a
component of the areawide plan the identification of
required improvements to existing urban and indus-
trial stormwater systems (including combined sewer
overflows) necessary to attain and maintain applicable
water quality standards [ 40 CFR 131.1 l(l)(1)].
For simplicity, all Act citations are from P.L. 95-217 to ensure
that no amendments are omitted, although in many cases the lan-
guage of P.L. 92-500 remained unchanged.
The EPA guidelines for completing this element of
208 planning spelled out the steps to be followed:
• Inventory existing combined sewer systems, includ-
ing locations of intakes, bypasses, pipes, regulators,
and outfalls;
• Assess system performance;
• Measure or estimate waste constituents and loads
and wastewater flows;
• Project wasteloads and flows; and
• Develop and evaluate alternatives.
As a practical matter, few 208 agencies have been able
to accomplish all of this work.
One of the greatest difficulties faced by 208 planners
was determining the relative contribution of combined
sewer overflow pollution to existing water quality
problems. The necessary data and analytical tools
were not available and could not be assembled within
the limitations imposed by time or budget. This prob-
lem definition function remains an appropriate task
for the areawide planning process. Ongoing initial 208
programs, as well as those in the continuing planning
stage, should incorporate it to provide a general
framework for more detailed planning and engineer-
ing studies, including benefit analysis, which must pre-
cede implementation of combined sewer overflow
controls.
What has in fact happened to date is that whatever
combined sewer overflow problem definition has been
accomplished in specific areas has been done in con-
nection with the more detailed planning process for
sanitary sewer treatment facilities under Section 201 of
the Clean Water Act. This has weakened the areawide
and comprehensive emphasis of the Act. Section 201
authorizes the Administrator of EPA to make grants
for the planning and construction of publicly owned
wastewater treatment works. For the purpose of Sec-
tion 201, the term “treatment works” is defined rather
broadly and includes (Section 212):
• Liquid waste storage, treatment, recycling and recla-
mation systems and devices;
5

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• Interceptor and outfall sewers, collection systems,
and related equipment;
• Extensions, improvements, or alterations to existing
systems; and
• Any other method or system for preventing, abating,
reducing, storing, treating. separating or disposing
of municipal waste (including storm water runoff) or
industrial waste (including waste in combined storm
water and sanitary sewer systems).
The grants are generally for 75 percent of the cost of
construction of the most cost effective alternative that
provides the necessary treatment.
Part 35 of Title 40 of the Code of Federal Regu-
lations 3 covers EPA’s treatment works construction
grant program. Section 35.915 establishes the state
priority system used to allocate federal grant moneys.
It specifies that projects are to be rated by the states on
the basis of:
• Severity of the pollution problem;
• Population affected;
• Need for preservation of high quality waters; and
• At the state’s option. the category of need addressed.
The categories of need are particularly significant;
they consist of the following:
• Secondary treatment of wastewater under dry
weather conditions;
• More stringent treatment under dry weather
conditions;
• Correction of problems causing infiltration and in-
flow into sewers during storms;
• Sewer system replacement or major rehabilitation;
• New collectors and appurtenances;
• New interceptors and appurtenances: and
• Correction of combined sewer overflows.
Each state is given both the sole authority to deter-
mine the priority of the categories of need and the au-
thority to determine the relative weight given to each
criterion. Whether a given combined sewer overflow
control project falls in the fundable part of the list is
thus dependent on state policy as well as the nature of
the combined sewer overflow problem. It is easy to en-
vision, for instance, a situation in which secondary
treatment is being achieved at most locations in the
state even though water quality is still below standards
in a populous urban area served by combined sewers.
In such a case, acombined sewer overflow control proj-
ect might rank high on the priority list. In another state,
however, where secondary treatment has not
been achieved in a number of plants and where exten-
sive unsewered areas with septic tank malfunctions
continue to exist, the combined sewer overflow control
category would likely be given a lower priority, and
such projects would be unfundable.
Although the state sets priorities, the federal EPA
has provided specific policy guidance on the support-
ing justification and cost allocation approaches it will
allow when approving a combined sewer overflow proj-
ect for federal construction grant assistance. The first
of two program requirements memoranda, PRM No.
75_344 has as its stated purpose the assurance that
projects be funded only when careful planning has
demonstrated that they are cost effective. The memo-
randum makes clear that the combined sewer overflow
planning must include, for a 20-year period, a thorough
analysis of the following aspects of the proposed project:
• Alternative control techniques that might be utilized
to attain various levels of pollution control (related
to alternative beneficial uses, if appropriate);
• The costs of achieving the various levels of pollution
control by each of the techniques appearing to be
the most feasible and cost effective after the prelimi-
nary analysis;
• The benefits to the receiving waters of a range of
levels of pollution control dui ing wet weather condi-
tions; and
• The costs and benefits of treating combined sewer
overflows as compared to the costs and benefits of
advanced treatment of municipal dry weather flows
in the area, i.e., treatment beyond the required sec-
ondary treatment.
The alternative finally selected will qualify for funding
only if the following criteria have been met:
• Analysis has demonstrated that the level of pollu-
tion control provided will be necessary to protect a
beneficial use of the receiving water even after tech-
nology based standards are achieved by industrial
point sources and at least secondary treatment is
achieved for dry weather municipal flows in the
area;
• Provision has already been made for funding of sec-
ondary treatment of dry weather flows in the area;
• The pollution control technique proposed for com-
bined sewer overflows is a more cost effective means
of protecting the beneficial use of the receiving wa-
ters than other combined sewer pollution control
techniques and the addition of treatment higher
than secondary treatment for dry-weather municipal
flows in the area;
• The marginal costs are not substantial compared to
marginal benefits.
PRM 75-34 recommends graphic displays of margi-
nal costs and benefits. Monetary. social, and environ-
mental costs should be compared to pollution
reduction, water quality improvements, and improve-
ments in beneficial uses, in quantitative or qualitative
terms, as appropriate. The significance of the benefi-
cial uses to be protected also should be explained.
6

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PRM 75-34 also states that multipurpose projects
(combining flood control, recreation, and pollution
abatement, for example) will be eligible for construc-
tion grant assistance only after an equitable allocation
of cost savings has been made among the several pro-
jects: funding will not be allowed for an amount which
exceeds the most cost effective single-purpose project
for pollution control. The details of how this eligibility
is to be determined, and how any cost savings arising
from combining multiple purposes are to be dealt
with, are the subjects of the second major EPA com-
bined sewer overflow policy guidance document. PRM
77-4.’ The cost allocation approach discussed in these
memoranda is referred to as the alternative justifiable
expenditure method.
The alternative justifiable expenditure method is fundamen-
tally based on the justified investment for each function. That
justified investment is taken to be the cost of the most eco-
nomical alternative single-purpose project which will achieve
substantially the same benefits as does that function in the
multiple-purpose project. That investment, sometimes called
the alternative justifiable investment, represents the largest
amount which could justifiably be expended on the function
in the multiple-purpose project, for, in most instances, no
more should be spent on a purpose than the Cost of produc-
ing those benefits from the least expensive alternative
source.
Further discussion of this allocation approach can be
found in Chapter IV of this publication.
References
‘Clean Water Act of 1 977, 33 U.S.C. 1 251 et seq.
P.L. 95-217.
2 Federal Water Pollution Control Act Ammendments
of 1972,33 U.S.C. 1251 etseq. P.L. 92-500.
40 CFR 35, 37 FR 11650, June 9, 1972, effective
July 1, 1972.
4 Rhett, J. T., Water Programs Operations, U.S. Envi-
ronmental Protection Agency, “Program Require-
ments Memorandum, No. PRM 75-34”, received
December3, 1976.
“Program Requirements Memorandum,
No. PRM 77-4”, received December 16, 1976.
7

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Chapter III
Beneficial Uses as Objectives
In any well executed planning process in the public
realm, there are two general principles regarding the
preparation of objectives. First, the effort to define
them should begin early in the project. Definition may
not be completed immediately. In fact, it may be im-
possible to arrive at a complete set of objectives until
more information becomes available, but it is essential
that all who will participate in the various aspects of
the planning process be introduced to the work of
identifying objectives. The refinement and final selec-
tion of objectives can occur as the work proceeds. Sec-
ond, though decisions on objectives can be facilitated
by the technicians and consultants who can suggest al-
ternatives and indicate the range of choices, the actual
choices must be made by elected officials. Moreover,
the public must be allowed and encouraged to
participate.
A third principle has applicability to many types of
projects but is of critical importance to planning for
control of pollution from combined sewer overflows.
The tasks of developing a combined sewer overflow
control program that will qualify for EPA approval
and funding and then obtaining the funding as well as
local support for the proposal will be immensely easier
if the combined sewer overflow control objectives are
related to benefits and expressed in such a way that
measurement of benefit is made possible.
PRM 75-34’ requires a measurement of benefits.
Abating pollution is not, in itself, sufficient benefit in
this context. It is the benefits that are the results of
pollution abatement — the improvements expected in
receiving water uses — that must be demonstrated. Be-
cause this is the case, it makes sense to select as pollu-
tion control objectives the maintenance of or
improvement in specific beneficial uses. There is good
precedent for this; water quality standards are already
based on beneficial uses to be protected.
Requirements and Limitations
The first step in this examination is to sort out what
uses the community wants, or is required, to provide
and what uses are, in fact, possible. Subsequent chap-
ters of this publication will discuss the relationship of
these beneficial uses to water quality and pollution,
the determination of polluting sources and their con-
tribution to the pollution affecting beneficial uses
(Chapter IV), the estimation of the costs of control
(Chapter VI), and the assessment of the benefits
(Chapter VII).
This whole sequence may appear rather simple and
straightforward as it is set down in print, but this is
anything but true, even in the early stages. The selec-
tion of specific water use objectives can be a highly po-
litical and complex activity. For instance, the
realization of a particular benefit may conflict with the
attainment of other desired objectives. In addition,
citizens may agree in principle with the goals of the
project but be unwilling to pay the costs that they per-
ceive to outweigh the benefit.
Though some of the inputs into the decision making
process regarding objectives, particularly those that re-
late to cost, cannot come until fairly far into the plan-
ning process, much can be contributed early in the
process to narrow the number and scope of the al-
ternatives that must eventually be evaluated in detail.
Certain rules of thumb can also be used at early stages
of the analysis to indicate the general magnitude of
probable costs to achieve certain beneficial uses.
Beneficial uses may be uses new to the community,
uses that were lost and now are to be restored, or uses
that presently exist and are to be maintained. To de-
termine the uses for a given body of water, one could
consider the following possibilities:
1. Near shore land uses:
• Recreational
• Residential
• Commercial
• Industrial
2. Near shore water uses:
• Swimming
• Skindiving
9

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• Boating — recreational or commercial
• Sheilfishing
• Fish spawning
• Fish rearing
• Fish habitat
• Crustacean habitat
• Wildfowl food chain
3. Receiving water uses:
• Water supply
• Boating — recreational or commercial
• Fish habitat
• Wildfowl food chain
The list could be extended. However, the choices to
be made are not unconstrained. A realistic choice
among uses for a given body of water, or portion of it,
must take into account the following:
• Federal, state, and regional government mandates;
• Compatibility with other objectives, including eco-
nomic and social goals;
• Mutual compatibility of multiple uses of the receiv-
ing water;
• Limitations imposed by natural characteristics;
• Seasonal limitations;
• Public interest in or demand for certain uses;
• Design conditions and the concept of acceptable
risk; and
• Technological and financial feasibility.
Each of these considerations are discussed briefly in
the following sections.
Mandated Goals
The language of Section 10 1(a) of the Clean Water
Act of 1977,2 which amended the Federal Water Pollu-
tion Control Act of I 972, is familiar:
The objective of this Act is to restore and maintain the
chemical, physical, and biological integrity of the Nations
waters, In order to achieve this objective it is hereby declared
that, consistent with the provisions of this Act —
(1) it is the national goal that the discharge of pollutants into
the navigable waters be eliminated by 1985;
(2) it is the national goal that wherever attainable, an interim
goal of water quality which provides for the protection
and propagation of fish, shellfish, and wildlife and pro-
vides for recreation in and on the water be achieved by
July 1. 1983;
(3) it is the national policy that the discharge of toxic pollu-
tants in toxic amounts be prohibited;
(4) it is the national policy that federal financial assistance
be provided to construct publicly owned waste treatment
works;
(5) it is the national policy that areawide waste treatment
management planning processes be developed and im-
plemented to assure adequate control of sources of pol-
lutants in each state; and
(6) it is the national policy that a major research and demon-
stration effort be made to develop technology necessary
to elimate the discharge of pollutants into the navigable
waters, waters of the contiguous zone, and the oceans.
Because this is national policy, any local water quality
goals must be consistent with it.
The Act establishes certain technology-based re-
quirements to be met by point source dischargers; ef-
fluent limitations based on secondary treatment for all
publicly owned treatment works are an example [ Sec-
tion 301(b)].
It also directs the states to promulgate water quality
standards consisting of statements of the uses desig-
nated for the waters involved and the water quality
criteria which must be met to protect those uses.
Such standards shall be such as to protect the public health
or welfare, enhance the quality of water and serve the pur-
poses of this Act taking into consideration [ the waters’]
use and value for public water supplies, propagation of fish
and wildlife, recreational purposes, and agricultural, indus-
trial, and other purposes, and also taking into consideration
their use and value for navigation [ Section 301 (c)(1)J.
As a result, there are already designated uses and re-
lated water quality criteria for most waters, with some
variation from stream to stream and state to state.
Moreover, the Act recognizes that the technology-
based effluent limitations required of all point source
discharges may be insufficient for the protection of the
designated uses of the states or the attainment of the
Act’s overall objectives in certain waters. It provides
that states may establish more stringent effluent limi-
tations in these cases [ Section 302(a)]. Therefore the
selection of local beneficial uses is further constrained
in that not only must the local objectives for water
quality be consistent with federal policy but also they
cannot be less stringent than state standards.
Compatibility With Social and Economic
Objectives
Though Section 302(a) of the Clean Water Act per-
mits the imposition of effluent limitations more strin-
gent than the national requirements for certain waters,
it also requires that, where this is proposed. there be
public hearing to determine the relationship of the eco-
nomic and social costs of achieving any such limitation
including any economic or social dislocation in the affected
community. . - to the social benefits to be obtained (includ-
ing the attainment of the objective of this Act) . . [ Section
302(b)(1 )].
Congress recognized that there may be circumstances
when proceeding beyond nationally required min-
imum levels of pollution control, even if necessary to
attain the’act’s objectives. may exact costs, both eco-
nomic and social, that are out of proportion to the ex-
pected benefits. If “there is no reasonable relationship
between the economic and social costs and the benefits
10

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to be obtained.” the more stringent limitations will not
become effective.
This policy applies to the states as well as to EPA,
and it should be embodied in any local planning proc-
ess when water quality uses or benefits are being de-
termined. The application of this policy, for instance,
would prevent the objective of increasing trout fishing
opportunities from being implemented if it is seriously
incompatible with other goals such as maintaining
high employment in a particular area.
Any such incompatibility of goals should be consid-
ered carefully by the decision makers involved and
should be resolved long before elaborate plans and
control alternatives are developed.
Mutual Compatibility of Muttiple Uses of the
Receiving Water
A related question to be considered in determining
desired uses is whether or not any uses of particular
segments of the receiving water are mutually incompa-
tible. While swimming and fishing opportunities may
not be impaired by recreational boating. for example.
commercial ship navigation and bulk cargo handling
may greatly restrict those activities. A reach of river
that is a busy seaport should not also be designated for
swimming and fishing since efforts to protect the latter
uses would, in all likelihood, simply waste the tax-pay-
ers’ money. Similarly, swimming is dangerous near
large hydroelectric facilities and is therefore incompa-
tible with such a use. Likewise, the use of the receiving
water for irrigating agricultural lands may lead to fluc-
tuating water levels, making boating impossible. A list
of beneficial uses should not include two or more
which are mutually incompatible.
Limitations Imposed by Natural Characteristics
No matter how clean the water may become, a
warm-water stream will not become a self-sustaining
trout fishery. any more than a white-water river is suit-
able for racing sailboats. Naturally acid rivers and
lakes have a characteristic flora and fauna that cannot
be replaced by plants and animals adapted to neutral
or alkaline waters, regardless of public policy. There
are other, more subtle natural limitations than these,
and they should be taken into account when selecting
desired water quality uses. For instance, when a cer-
tain use, such as swimming. is precluded by the ab-
sence of necessary conditions such as a beach, the cost
of pollution control beyond the national minimum
may be unwarranted.
Seasonal Limitations
Swimming and, to a great extent, boating. are not
possible in many of the nation’s waters during the win-
ter months. Fishing, too, has seasonal aspects, espe-
cially in fresh water. Substantial savings in pollution
control may be realized by including seasonal require-
ments in the objectives.
Public Interest or Demand
Water uses should not be selected on the basis of as-
sumptions about public desires. Demand for a given
beneficial use should be ascertained through public
hearings, surveys, opinion polls, statistics on use of fa-
cilities, and any other available information sources.
This is especially important, of course, when two in-
compatible uses are being considered or when protec-
tion of the use in question would involve large
expenditures of public moneys. For example, rivers in
the arid Southwest that are intensively managed as
sources of irrigation water offer only limited opportu-
nity for recreation. Most planners assume that water-
based recreation is universally desired, but that as-
sumption would have to be tested locally. It would
take a strong expression of public demand to support
changes in stream management that might adversely
affect agricultural productivity and thus the economies
of farming communities.
A second issue, also implicit in this example, is the
question of distribution of costs and benefits. Recrea-
tional development is likely to attract users (benefi-
ciaries) from outside the immediate area, but the local
share of the costs of the necessary pollution control is
borne by area residents. There may be non-financial
costs as well. Greater recreational use can lead to traf-
fic congestion on local roads, for example. These
points, and others, such as the issue of economic bene-
fits to area shops and restaurants, are certain to
emerge in any public discussion of water uses, and
they need to be carefully considered.
Design Conditions and the Concept of
Acceptable Risk
Selecting the storm conditions (frequency and inten-
sity of storms in a year) around which a control system
or facility will be developed is intimately involved in
the whole process of determining water use objectives
to be achieved through combined sewer overflow con-
trols. The size of control facilities and therefore capital
and operating costs can be directly related to the de-
sign condition. Financial and technological feasibility,
achievable levels of benefits, and public acceptability
of the local financial portion of the costs all depend on
the design condition selected.
Therefore, early in the benefit selection process, the
idea of acceptable risk should be introduced since it
will be important when design conditions are set and if
any adjustment of the package of desired benefits is
made necessary by unacceptably high estimates of
11

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cost. Here the aim is to determine the level or range of
levels of acceptable beneficial use. Though ideal goals
often cannot be reached because of limited funds, it is
not always essential that they be achieved anyway.
Consider a situation in which swimming has been
selected as a desired use at a given beach but each
combined sewer overflow results in a 2-day beach clos-
ing because of high fecal coliform counts. If rain nor-
mally causes a combined sewer overflow once every 3
days. regardless of season. the beach will be closed an
average of 20 days per month. The community is en-
joying the use of its swimming beach for only one-
third of the season, clearly an unacceptable level of
benefits. Let us assume that a decision is made to pre-
vent or treat overflows for not only these frequent.
small storms, but for all storms up to ones expected to
occur only once in 10 years. This 10-year event be-
comes the design storm for combined sewer overflow
controls. An effective control system would reduce
overflows to one every 3.650 days. essentially eliminat-
ing all beach closings during swimming season. How-
ever. the cost of this much protection. or this amount
of benefit, can be quite large. If a community is willing
to accept a somewhat higher risk of loss of benefit —
beach closings, in this case — one could use a smaller.
more frequent design storm and reduce the cost. In
fact, if a 1-year storm were selected as the design
storm, there would be only one overflow every 365
days on the average. If this large storm were typically
in the non-swimming season, the beach would not be
closed at all for swimming. Allowing overflows from
all storms of a size likely to occur once every 3 months
(and therefore, of course including even larger storms)
would result in 0.7 days of closed beach each month.
The decision maker should obviously seriously con-
sider accepting the risk of a few days of closed beaches
each season if it results in significant savings.
A note of caution should be added here. Public out-
cry over 0.7 days of lost benefits is likely to be much
louder than the expressions of appreciation for the
29.3 days of benefits received unless the public is
aware of the financial consequences of greater control.
Such situations underscore the need for full public
participation in the process of determining pollution
control objectives, as well as clear graphic presenta-
tions of control alternatives and costs.*
Technological and Financial Feasibility
Questions of technological and financial feasibility
become most clear when one begins to estimate the
‘An alternative to the single event, or design storm, as the basis
for determining pollution control needs is continuous simulation. It
is more complex but, in many ways, conceptually more realistic,
and it may be appropriate in certain circumstances. See Chapter IV
for a discussion of this approach.
costs involved n providing the selected benefits. It is
then that one sees the need for feedback in this plan-
fling process. from the evaluation of costs back to the
selection or refinement of desired benefits. The objec-
tives may have to be modified when the technological
or financial resources available fall short of what
would be required to meet them. This will be dis-
cussed further in Chapter ‘VI. For the moment, it is
sufficient to say that some concern for technical and fi-
nancial feasibility should be included in the process of
selecting desired uses of the receiving water. Rules of
thumb and general information on control alternatives
and approximate costs can be used.
Selection and Ranking
The public (defined as broadly as possible) must par-
ticipate in the selection of a set of beneficial uses to
serve as objectives. The question. after all, is one which
only the public can properly answer: “What beneficial
uses are important to you?” As already pointed out.
protection of some uses is mandated by state or federal
regulations. whereas other uses are made either pos-
sible or impossible (or impractical) by natural limita-
tions or established conflicting uses. However, a range
of choice remains, and each interest group is likely to
have its own position. Environmental groups. sports-
men. industry, and commercial interests should con-
tribute to the selection. Government agencies other
than those directly concerned with water quality man-
agement — park and recreation, fish and wildlife, or
transportation. for instance — should also be consulted
to identify and resolve any conflicts in goals. Obtaining
and utilizing these inputs require great effort, espe-
cially because it is sometimes difficult both to draw at-
tention to the project and to provide potential
participants with enough information for them to
make meaningful contributions. Somewhat easier is
the job of analyzing the results for use by the decision
makers. Finally, participants must be given feedback
to enable them to see how their inputs were used.
In preparing the list, one should be alert for situations
in which provisions for protection of one group of uses
meets or exceeds requirement for protection of an-
other group. For example. EPA’s Continuous
Stormwater Pollution Simulation System has shown
that when water quality objectives for swimming are
met, fish and wildlife objectives, in most cases. will
also have been achieved. 4
When the objective selection process is complete.
the list should:
• Be expressed in terms of specific beneficial uses,
• Include mandated uses.
• Be sensitive to natural and seasonal constraints and
opportunities.
12

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References
• Be geographically specific to protect uses where they
can occur, and
• Insofar as possible, be stated in such a way that
achievement is measurable.
One final step, also the task of the elected officials, is
to rank the beneficial uses. Technical or financial limi-
tations may make it impossible to provide protection
for all desired uses immediately or for certain uses at
all possible times or locations. Consequently, they
should be ordered from the most critical or important
to the least critical. This is by no means an easy task,
because interest groups again may conflict, and politi-
cal pressures and technical recommendations may dif-
fer. However, this ranking will be extremely useful
when budgeting local capital, preparing the justifica-
tion portion of the construction grant application, and
demonstrating that the planning process has been a
reasonable one.
1 Rhett, J. T. “Programs Requirements Memorandum,
No. 75-34”, Water Programs Operations, U.S. En-
vironmental Protection Agency December 3,
1976.
2 Clean Water Act of 1 977, 33 U.S.C. 1 251 et seq.
P.L. 95-217.
3 Federal Water Pollution Control Act Amendments of
1972 33 U.S.C. 1251 etseq. P.L. 92-500.
4 Wycoff, R. and M. Mara, 1978 Needs Survey: Con-
tinuous Stormwater Pollution Simulation System
User’s Manual, US. EPA Report, EPA-430/9-79-
004, February, 1979.
13

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Chapter IV
Relating Pollutant Sources to Beneficial Uses
The determination of both required and desired uses
of local receiving water is only the beginning of the
analysis necessary to plan for combined sewer over-
flow control projects that are to be funded by the fed-
eral government. As discussed in Chapter II. PRM 75-
34’ states that one criterion for federal approval of
combined sewer overflow projects is that the analysis
must have
demonstrated that the level of pollution control provided
will be necessary to protect a beneficial use of the receiving
water even after technology-based standards - . are
achieved by industrial point sources and at least secondary
treatment is achieved for dry weather mun ,cipal flows in the
area.
Combined sewer overflow control must also be shown
to be more cost effective than “the addition of treat-
ment higher than secondary treatment for dry weather
municipal flows in the area.”
Taken together. these criteria mean among other
things that, in order for a CSO project to qualify for
federal funding, the pollutants to be controlled must
be identified with a specific beneficial use, and that a
primary contributor of that pollutant must be demon-
strated to be combined sewer overflows. A comprehen-
sive control program that has as its single objective the
upgrading of all water quality parameters of the re-
ceiving water will not be supported with grant funds
there must be well documented justification relating
the program to specific benefits. A municipality and its
consultants cannot assume, furthermore. that benefi-
cial uses will automatically be achieved by a combined
sewer overflow control program. The federal govern-
ment requires a demonstration that combined sewer
overflows, and not some other source, are a significant
source of the offending pollutants and that control of
the overflows, and not some other source, will not only
bring about the desired improvement but will do so
more cost effectively.
Water Quality Problems Associated with
Water Uses
The first step in the effort to achieve the selected
beneficial uses is to determine what variables in fact
are restricting the specific uses at the sites that are ap-
propriate for them. Table I illustrates water quality
problems that are generally associated with specific
water uses.
In many areas, facility planners will be fortunate to
have the problem variables in their particular receiv-
ing waters already identified in the water quality in-
ventories prepared as a part of a 208 areawide water
quality management planning study. However, addi-
tional detail may be necessary to be sure that the in-
ventory contains information related to the specifically
designated sites and their selected uses. Existing files
of water quality monitoring data may be sufficient to
supplement the inventories but, in some cases. sam-
pling to determine the concentrations of those vari-
ables affecting the desired uses will be needed.
One note of caution is appropriate here. As water
quality problems become better understood, changes
in standards and in lists of human pollutants occur. As
just one example, several recent publications have
questioned the appropriateness of bacteria count lim-
its for contact recreation noting that the same path-
ogens are also present in reservoirs.- 3 While the issue
is unresolved, it leads to obvious questions about the
justification of large expenditures for disinfection of
overflows. It is important to keep up to date on such
developments.
Water Pollution Sources Identified With
Beneficial Uses
Most of the urban areas with combined sewers will
already have pollution source inventories. Such an in-
ventory should cover four major categories:
• Continuous point sources
— Municipal sewage treatment plant discharges
— Industrial waste discharges
• Intermittent point sources
— Storm sewer outfalls
— Combined sewer overflow points
15

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• Nonpoint sources
— Surface runoff
— Groundwater discharge
— Atmospheric pollutants
• Background loadings
— Natural concentrations
— Upstream pollutant loadings.
Table 1. Water Quality Problems Associated with
Beneficial Uses.
Beneficial water uses Type of impact Water quality problems
Bacteria
Virus
Toxics
Metals
Total dissolved solids
Aesthetics Color, taste, odor
Plankton
Health Bacteria
Virus
Aesthetics Solids and color
Floatables
Plankton
Turbidity
Health Bacteria
Virus
Toxics
Metals
Survival Dissolved oxygen
Total dissolved solids
Toxics
Metals
Health Toxics
Metals
Bacteria and virus
Survival Dissolved oxygen
Plankton
Toxics
Metals
Eutrophication Nutrients
Plankton
Rooted plants
Other Floatables
Solids
Odor and color
Source: Driscoll, E. D. and J. L. Mancini, ‘Assessment of
Benefits Resulting from Control of Combined Sewer Overflows•
p. 7, presented at EPA Technology Transfer Seminars on Combined
Sewer Overflow Assessment and Control Procedures. 1 978
The inventory should include the location of all
sources. It should also state whether effluent standards
have been met or programs to bring about compliance
have been funded for each municipal and industrial
discharger. One important use of this aspect of the in-
ventory will be to document the status of industrial
and municipal sources, as required by PRM 75-34.
The inventory should also include information on
the constituents and volume of each continuous point
source. This information may be obtained also from
NPDES permit files but usually will not be available
for intermittent point and nonpoint sources or for
background loadings. Background quality resulting
from upstream conditions and activities can be deter-
mined in a relatively straightforward manner by mea-
surement of the stream flow and quality immediately
upstream of the area; information on background
loadings can also be found in water quality monitoring
records. Actual measurement to determine quantities
of pollutants from non-point sources is often impracti-
cal, but estimates of flows and wasteloads can be pro-
duced using literature values. The variety of pollutants
which can be expected from various non-point sources
is indicated in Table 2.
Because these inventories include the location as
well as the volume and constituents of each municipal
and industrial pollution source, it may be easy in some
cases to determine directly the source producing the
pollutants that are restricting beneficial uses.
Other cases may be more complex. but the appli-
cation of a basic knowledge of the time and space rela-
tionships of water quality problems and sources may
help focus the analysis and eliminate much unneces-
sary work and expense. This takes into account the
fact that pollutants in one section of a river or in one
period of time. for example. may not have adverse af-
fects at another place or at a later time. For instance,
Figure 3 shows that, because of a high die-off rate,
bacteria that enter the receiving water typically have
water quality impacts that do not persist for more than
a few days. Similarly. Figure 4 shows that typically
only a few miles of stream would be affected by float-
ables discharged at a given location. On the other
hand, a dissolved oxygen sag caused by the discharge
of oxygen-demanding material at the same point may
exert its maximum impact dozens of miles down-
stream. Distribution of toxic effects generally can be
expected to extend for some distance downstream be-
cause of extremely slow rates of decay.
Consider the case in which swimming is restricted at
a given site because of high coliform counts for long
periods of time during wet and dry weather. Com-
bined sewer overflows would not be the most probable
source. because the effects of these intermittent storms
should not persist for more than a few days after an
Health
Water supply
(public, private,
agricultural)
Swimming
Shell fishing
Fishing
Aesthetic enjoyment
16

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overflow (Figure 3). A continuous discharge (which
could include a combined sewer with a malfunctioning
regulator) should be sought as the cause. If, on the
other hand, the bacteria counts exceed health stan-
dards in a pattern that does seem related to storm
events, attention should be focused on storm sewers
and combined sewers between the affected point and a
point roughly 10 miles upstream (Figure 4). Nutrients
and toxic substances, on the other hand, are long-
term, regional problems. and unfavorable conditions
for swimming or fishing caused by eutrophication or
acute or chronic toxicity are not likely to be alleviated
by control of local combined sewer overflows alone.
Such simplified analysis can be very helpful for
many communities. However, in some cases, the num-
ber of point and, particularly. nonpoint sources and
the complex mixing. settling and resuspension of the
materials during a storm, for example. may make it
difficult to identify combined sewer overflows specifi-
cally and with confidence as the significant contributor
to the reduction in the desired use of the water. The
Table 2. Pollutants Contributed by Various Non-Point Sources.
Pollutants
Non-point source Organic
Micro- Trace Toxic Acid
categories matter Sediment Nutrients organisms metals organics Salts wastes
Urban sources
a. Runoff
b. Storm sewers + +
c. Combined sewer overflows + +
d. Separate sanitary sewer overflows + +
Construction 0 + +
++ + ++
++ ++ ++
++ ++ 0
+
+ ++ 0
+ ++
÷ 4+
O 0
+ 0 0
Residual wastes disposal
a. Rural sanitation
b. Landfills
c. Sludge disposal
d. Dredge Spoils disposal
Hydrographic modifications
a. Dredging
b. Maintenance facilities
c. Channel modification
d Dams
Ground water
a. Brine
b. Deicing salts
Agricul%ure
a. Livestock production
b. Crop production
c. Manure disposal
d. Windborne loadings
e. Tile drainage
Silviculture
a. Forestry management
b. Forest harvesting
c. Recreation
Mining
a. Surface
b. Subsurface
Miscellaneous
a. Atmospheric
b. Spills
c. Benthic loads
O ++ 0
O ++ 0
0
+
+
+4-
-1-
+
+4-
4+
++
O ++
o ++
O + ++
O ++ ++
+ + +4
o ++ 0
+ ++ 0
O 0
O 0
O 0
o + -
++ ++
O +
o ++
O 0
Key + + Severe; + = Moderate; 0 = Slight or None
Source Delaware Valley Regional Planning Commission, Pennsylvania Department of
Engineers COWAMP 208 Water Quality Management Plan. Southeastern, PA, April, 1 978.
Environmental Resources and Chester- Bets
++ +4 ++ + ++
++
++
++
+
+
0
0
0
0
0
0
0
0
0
0
0
+
+
+
4
4+
+4
+
0
0
0
++
+
+4
0
++
++
+
0
++
++
++
0
++
+
0
0
+
++
4-
0
-i-+
++
0
0
+1-
4 +-
+
0
++
++
0
0
++
0
++
+
0
0
0
0
0
±+
0
0
0
0
0
0
+
+
+
0
0
0
0
0
++
+4
++
++
0
4-
+
0
+
+4-
+4-
0
+
++
0
0
-4--f
-1-- I-
++
++
0
0
+
0
0
+
0
+
+
+
0
0
+4
+
+4
+
0
++
+
0
+
0
4+
0
0
+
++
++
++
0
0
+
+
++
0
4-
0
0
0
17

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Seconds
10 i0 10 106 10’ 108 1O
Floatables
Bacteria
Dissolved Oxygen
Suspended Solids
Nutrients
Dissolved Solids
Acute Toxic Effects Long Term Toxic Effect
Day Month Year
Hour Week Season Decade
Figur. 3. Tim. Scale. for Storm Runoff Water Quality Problem..
Source: Driscoll. E. 0. and J. L. Mancini. “Assessment of Benefits Resulting from Control of Combined Sewer Overflows, p. 9, presented
at EPA TEchnology Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures, 1 978.
18

-------
Miles
0-’ 10-3 10-2 10° 10’ 102 10°
(5 Ft.) (50 Ft.) (500 Ft.)
________ _____________________ _____________________ 1. —
Hydraulic Design
Floatables
I I
Bacteria
Suspended Solids
Dissolved Oxygen
_______________ _______ — I
Nutrients
I I ___ _
Toxic Effects
Dissolved Solids
Local
L . Region
Basin
Figure 4. Space Scales for Storm Runoff Water Quality Problems.
Source: Driscoll, E. D. and J. L. Mancini, “Assessment of Benefits Resulting from Control of Combined Sewer Overflows ‘, p. 10, presented
at EPA Technology Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures, 1978.
19

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waste loads which result from storms are difficult to
characterize because of the intermittent nature of rain-
fall, the number and wide spatial distribution of com-
bined sewer overflow points, the variability in size of
storm events, and the variety of pollutants and their
concentrations found in the runoff.
In addition, the nature of water quality problems as-
sociated with the receiving waters and around metro-
politan areas is quite varied. Local factors have a
predominant influence in determining the specific
source or sources that contribute to a problem and to
its severity. Factors that affect water quality include, in
addition to the amount of rainfall and its frequency
and intensity, local geography, population concentra-
tion, the character and degree of industrialization in
the area, the extent of paved surfaces, and the receiv-
ing water system (including its nature, size, hydrology.
and upstream and downstream characteristics).
To determine which of several potential sources of
particular pollutants is a critical source, and particu-
larly whether or not combined sewer overflows are a
significant source. may require extensive monitoring
and sampling and perhaps the use of mathematical
models. Sophisticated models requiring subtantial
data inputs are available; there are also simpler desk-
top models that are frequently just as useful. (Just as
with the planning component of municipal wastewater
pollution control projects. the costs for these assess-
ments are eligible for federal 75 percent grants under
the construction grants program.)
Models
There are two types of mathematical models useful in
combined sewer overflow control planning —stormwater
models and receiving water quality models.
The stormwater models are tools to estimate or pre-
dict the volume of stormwater discharge and the load-
ings of its constituent pollutants. They typically consist
of two elements — a runoff element that simulates the
washoff of pollutants by rain falling on the watershed.
and a transport element that simulates the movement
of those pollutants in the sewer system and their even-
tual discharge from it. Such models serve two primary
purposes:
• To describe stormwater discharges. including com-
bined sewer overflows, in terms of volume and pol-
lutant concentration and loading, and
• To evaluate the effectiveness of various control al-
ternatives and to identify optimum solutions.
Both applications are complex tasks, except in simple
sewer systems. The first use can sometimes be accom-
plished manually, but the second is much better han-
dled by a computer model of the system.
Receiving stream models, often called water quality
models, predict or simulate the effects of pollutant
sources on the quality of the body of water into which
they are discharged. They are used in the following
ways:
• To assess the effects of known sources on water
quality,
• To predict the impacts of future discharges,
• To compare the effects of different sources, and
• To determine the reductions in pollutant loadings
that will bring about desired water quality
improvements.
There are a number of receiving water and
stormwater models available for various applications
and with differing input data requirements. An excel-
lent discussion on the selection of stormwater models,
including a brief description of the common ones, is
presented in Urban Stormwater Management and
Technology: Update and User’s Guide. 4 Stormwater
Management Model: Level I — Preliminary Screening
Procedures 5 explains a simplified model that requires a
minimum of data collection and is useful in the pre-
liminary assessment of combined sewer overflow prob-
lems. More detail on the whole process of stormwater
loading estimation, including discussion on data col-
lection and models, may be found in the EPA Areaw-
ide Assessment Procedures Manual (July 1976).
Further details on receiving water quality models are
available in Evaluation of Water Quality Models: A
Management Guide for Planners. 7 It explains modeling
approaches. describes existing models, and provides
guidance for selection of the proper model.
Most of the models are run for particular design
conditions — storm events for the runoff-and-transport
models and stream flow for the water quality models.
In other words, a decision is reached concerning the
conditions to which the results are to apply. That deci-
sion may be a policy choice made in the course of de-
fining desired benefits. For example, it may be decided
that dissolved oxygen should not fall below a concen-
tration of 4.0 milligrams per liter even during the 7-
day, 10-year low flow. The water quality model is then
run for that flow, and the results can be used to deter-
mine the load reductions needed to achieve that goal.
Likewise, a corresponding design condition for the
stormwater model might be a particular rainfall dura-
tion and intensity, perhaps that of a thunderstorm
which typically occurs during that low flow period.
(Note that some models are dynamic. The variations
in flow that would occur during storms can be simu-
lated. However, antecedent conditions still must be
specified and are, in essence, design conditions.)
There are models that do not require a prior selec-
tion of design conditions. One of these, the Contin-
uous Stormwater Pollution Simulation System alluded
20

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to in Chapter III and newly developed for use in the
1978 Needs Survey, 9 combines the functions of runoff!
transport and receiving stream models in a single
package that has three main applicaitons:
• To determine whether a given urban area/receiving
water system is experiencing a water quality
problem,
• To determine how much of the problem is caused by
combined sewer overflows and urban stormwater,
and
• To determine the level of pollutant removal re-
quired to achieve selected water quality goals.
The model is designed for long-term rather than single
event simulation. Instead of a set of design conditions,
it accepts historical rainfall and streamfiow statistics. It
generates a representative array of rainfall depths for
a period of 1 year and converts these to runoff arrays,
one for separate storm sewers and one for combined,
on the basis of watershed characteristics. Pollutant
washoff is then computed, using calculated or esti-
mated pollutant accumulation as well as decay rates
and washoff coefficients. 9 Overflows are simulated by a
sewer infiltration module, and a storage and treatment
module permits simulation of the effects of those con-
trol techniques on pollutant discharge.
A separate module generates an annual array of dry
weather wastewater treatment plant flows and loads.
Another uses up to 5 years of flow values to simulate
streamfiow. These results, plus background water
quality data, are used in the receiving water response
module, along with the simulated stormwater and
combined sewer overflows, to simulate receiving water
response. The simulation is long-term and continuous.
In other words, the outputs are an array of concentra-
tions of various pollutants that are likely to occur dur-
ing the course of a typical year under the rainfall, dry
weather flow, background. and pollutant washoff con-
ditions originally entered into the system. This is in
contrast to the single event model that provides simu-
lated receiving stream response for one design storm.
Before leaving the subject of models, i few observa-
tions on their appropriateness and some associated
drawbacks may be useful. First, for all but the simplest
sewer system, a runoff and transport model is neces-
sary to assist in defining the CSO discharges and per-
mit development and comparison of pollutant
reduction alternatives. Fortunately. calibrating such a
model for a given system is a rather straightforward
process. The system specifications themselves provide
most of the needed information.
The selection and calibration of receiving stream or
water quality models is a more complicated process.
Large amounts of reliable data on waste discharges
and in-stream pollutant concentrations may be
needed, necessitating expensive and time consuming
sampling programs. Without these inputs, the water
quality model cannot be expected to produce realistic
results. On the other hand, these sophisticated models
are not always necessary. If localized public health or
gross aesthetic problems are the cause of impaired
beneficial use, and if the surface water system is not
unduly complicated (as it would be in a major estuary.
for example), simple observation and discharge sam-
pling may be adequate to determine the source of the
offending pollutants. When a water quality model is
needed, the design storm approach will usually be suf-
ficient for public health or dissolved oxygen problems.
If eutrophication or other long-term problems are of
concern, the continuous, probabilistic model may be
the better alternative.
Monitoring and Sampling
When dealing with combined sewer overflows.
monitoring and sampling will usually be necessary to
meet three goals:
• To determine combined sewer overflow pollutant
characteristics,
• To learn the fate of those pollutants, and
• To determine the effects of those pollutants on water
quality.
Sampling of the overflow is necessary to meet the
first goal. When sufficient data are collected, analysis
will permit:
• Determination of pollutant loads discharged,
• Identification of first-flush effect,
• Determination of benefits of best management prac-
tices currently in use.
• Development of relationship to tributary land use
characteristics, and
• Comparison of antecedent and storm characteristics.
Data to meet the other goals must be obtained from
receiving water samples. The actual extent of pollutant
effect, in terms of time and distance, is one deter-
mination to be made. Other questions concern the na-
ture of the effect. Is benthic life eliminated around the
outfall, and if so, how far from it? Do trash and scum
accumulate on beaches or boats? Is there a dissolved
oxygen sag? How severe is it? How far does it extend?
At what time of year is it most evident? Does it coin-
cide with fish migrations? These and other such ques-
tions can only be answered definitively by sampling.
When the monitoring and sampling program is de-
signed. careful attention should be paid to the nature
of the information being sought. For example. health
problems related to combined sewer overflows may be
one subject explored. Since, as Figure 3 shows, bac-
teria that enter the receiving water during a storm
21

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event do not have water quality impacts for more than
a few days. average bacteria counts or samples taken
at regular intervals independent of weather will nor-
mally not be useful. Therefore daily or more frequent
sampling during and after storms will be necessary.
On the other hand. short term daily measurements of
instream nutrient concentrations are not usually ap-
propriate in studying eutrophication. since it is a long-
term phenomenon with seasonal water quality im-
pacts. Each water quality variable involved in an iden-
tified problem must be examined in an appropriate
way (see Figure 5).
For a quick appraisal of the effects of combined
sewer overflows, data on the total annual or seasonal
stormwater quantities and pollutant loadings may be
sufficient. This level of analysis is particularly appro-
priate for an evaluation of pollutants with predomi-
nantly long-term effects on lakes and large estuary
systems such as nutrients, toxics, settleable solids, and
heavy metals. In addition, it gives a rough estimate of
storm related waste loads that can be compared to
point source waste loads. The data required for this
Level 1: Total yearly storm load
LB
type of analysis can be generated fairly easily, in part
by using estimates of loads, runoff, and reaction
coefficients extrapolated from other studies or projec-
ted from data secured from limited areas over short
time periods.
To identify with some accuracy the specific time pe-
riods in which storm-related pollutants would affect
certain locations, data on the number of storms, their
frequency. and the pollutant loadings of each storm
would be required. This information would be needed,
for instance, if bacterial contamination or dissolved
oxygen deficits were the problems being analyzed.
Very detailed information and, therefore, data in-
puts are usually only necessary when exploring the ef-
fectiveness of a specific control strategy. For example,
a best management practice may have been proposed
to overcome the problems associated with first flush,
the concentration of pollutants discharged in the first
hour or two of a storm. To evaluate this strategy. data
on the variation in the intensity and loading rates
within each storm would be necessary.
Total Yearly Storm Load I
I s One Year •11
Level 2: Actual distribution of loads by storm
LB
LB/HR —
One Year
Level 3: Actual distribution of load within each storm (first flush. etc.)
Avg. Loading Rate per Event
--
N n
One Year
Figure 5. Various Levels of Detail in Stormwater Load Characterization.
Source: Driscoll. E. D. and J. L. Martcini. Assessment of Benefits Resulting from Control of Combined Sewer Overflows p. 22, presented
at EPA Technology Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures, 1978
Avg Load per Event
1
22

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Summary
By this point in the process of planning for a com-
bined sewer overflow project. a number of significant
decisions have been made and data assembled. All of
this is essential so that a municipality will be able to
determine — and, what is more, provide justification
and obtain support for — an overall control strategy
for combined sewer overflows, as well as specific con-
trol alternatives.
Desired benefits have been identified. The receiving
waters have been evaluated, not in terms of all water
quality parameters but in terms of the specifically
identified beneficial uses and of those pollutants and
pollutant sources that are adversely affecting the par-
ticular uses. This is necessary because it must be con-
vincingly demonstrated that combined sewer
overflows adversely affect the uses to a significant ex-
tent. Finally, it will have been shown that the tech-
nology-based effluent limitations have been met by
industry and municipalities, or it must be evident that
meeting them will still not result in the achievement of
water quality objectives.
In Seattle. all of these factors were evaluated as
Metropolitan Seattle prepared for selecting pollution
control alternatives. Seattle determined the following:
• Specific receiving water areas where desired benefi-
cial uses were impaired because of water quality.
• The water quality variables having the adverse
impacts.
• The significant sources of pollutants that unfavor-
ably affected the water quality variables.
• The relative contribution of each source to the im-
pairment of use.
• The significant contribution of combined sewer
overflow to the impairment of use, and
• The pollution control status of the various sources.
Seattle had also developed an initial list of nine pos-
sible beneficial uses for Seattle’s waters:
• Residential use
• Swimming
• Shellfishing
• Fish spawning/rearing
• Juvenile fish migration
• Recreational boating
• Shoreline parks
• Commerce
• Industry.
Commercial and industrial uses were determined to be
little affected by CSO and were eliminated from con-
sideration. Though fish were assumed to undergo
stress as a result of toxics in CSOs. there were not suf-
ficient data to allow a determination of the degree of
stress. Control of overflows to protect fish therefore
could not be judged eligible for federal funding. Pro-
tection of shoreline parks and recreational boating
would neither justify nor, in all likelihood, necessitate
controls stricter than those necessary for swimming.
Ultimately. the package of beneficial uses selected as
the objectives of combined sewer overflow control was
reduced to human uses with public health implications
— swimming. shellfish harvesting, and residential oc-
cupancy. The other uses were eliminated either be-
cause they were unaffected by combined sewer
overflows (or could not be demonstrated to be affected
by them) or because more extensive protection neces-
sitated by other uses would protect them as well.
As a result of this process. Seattle was ultimately
successful in demonstrating to the federal government
the relationship of its combined sewer overflows to the
reduction in the beneficial uses of Seattle’s numerous
receiving waters.
References
Rhett, J. T., ‘Programs Requirements Memo-
randum. No. 75-34”, Water Programs Operations,
U.S. Environmental Protection Agency, December
3, 1976.
Lager, J. A., W. G. Smith, W. G. Lynard, R.M. Finn
and E. J. Finnemore, Urban Stormwater Manage-
ment and Technology: Update and User’s Guide,
U.S. EPA Report, EPA-600/8-77-014, September
1977.
3 Olivieri, V., C. Kruse, K. Kawata, and J. E. Smith,
Microorganisms in Urban Stormwater, U.S. EPA
Report, EPA 600/2-77-087, July 1977,
4 Field, R., V. Olivieri, E. Davis, J. E. Smith, and E.
Tuft, Jr., Proceedings of Workshops on Micro-
organisms in Urban Stormwater, U.S. EPA Report,
EPA 600/2-76-244, November 1976.
5 Heaney, J. P., W. C. Huber, and S. J. Nix, Storm-
water Management Model: Level / — Preliminary
Screening Procedures, U.S. EPA Report, EPA-
600/2-76-275, October 1976.
6 Municipal Environmental Research Laboratory, Office
of Research and Development, U.S. Environmental
Protection Agency, Areawide Assessment Proce-
dures Manual, Vol.1,11, and Ill, U.S. EPA Report,
EPA-600/9-76-014, July 1976.
7 Grimsrud, G. P., E. J. Fennemore, and H. J. Owens,
Evaluation of Water Quality Models: A Manage-
ment Guide for Planners, U.S. EPA Report, EPA
600/5-76-004, July 1976.
23

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8 Wycoff, R. and M. Mara, 1978 Needs Survey: Con-
tinuous Storm water Pollution Simulation System —
User’s Manual. U.S. EPA Report, EPA 430/9-79-
004, February 1979.
9 Warburton, J., Seattle’s Approach to Evaluating
Costs and Benefits of Combined Sewer Overflow
Control per PGM-6 1. Presented at U.S. EPA Tech-
nology Transfer Seminar Series on Combined
Sewer Overflow Assessment and Control Proce-
dures, 1 978.
24

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Chapter V
Alternatives for Controlling Combined Sewer
Overflows
Selecting from among the alternatives available for
controlling combined sewer overflows does not enter
the planning process until many decisions about de-
sired benefits have been made and data gathering is
quite far advanced. The water quality parameters as-
sociated with the desired beneficial uses provide the
link between objectives and control alternatives. The
objectives must first be translated into the water qual-
ity criteria necessary to protect the uses. Then the re-
ductions in specific pollutant inputs required to meet
the criteria can be calculated. With this work com-
pleted. two tasks remain: the development of a control
strategy and the selection of control alternatives.
Control Strategy Development
Figure 6 illustrates the steps to be taken to deter-
mine the control strategy — that is. the combination of
pollutant source reductions that yield the required to-
tal reduction. The upper half of the chart applies to
dry weather conditions. The process it outlines must
be completed before or as part of combined sewer
overflow control planning, since PRM 75-34 requests
convincing evidence that achievement of the national
minimum levels of point source treatment for munici-
pal and industrial wastewater will be insufficient to
protect beneficial uses before funding for combined
sewer overflow control can be considered. The lower
half of the chart begins with the question. “Will the
dry weather controls selected also meet required re-
ductions during storm periods?” If the answer is “no”.
two strategies must be investigated (a PRM 75-34 re-
quirement): 1) further reductions in continuous point
source loadings, and 2) control of intermittent sources
including combined sewers. Combinations are, of
course, possible. All alternatives produced are checked
for technological feasibility, and the one that costs
least is selected and rechecked to be sure it provides
the necessary reductions. The process is iterative, al-
lowing for the consideration of various levels of con-
trol and benefit required by PRM 75-34.
In some cases. the process of developing a control
strategy will be quite straightforward. In a stream or
lake if fecal coliform standards are met during dry
weather but swimming beaches are nevertheless closed
because of high bacteria counts after rainfall, a sophis-
ticated model is not needed to show that a stormre-
lated intermittent discharge is the likely cause. Further
treatment of dry weather flows will not increase bene-
fits (swimming opportunities), but a reduction in the
amounts of bacteria from the intermittent sources will.
The strategy is obvious, and consideration can imme-
diately be given to the various alternative techniques
for implementing it.
There are other cases, however, when developing
the strategy is more complicated. For example, in a
stream in which minimum dissolved oxygen standards
are being met during dry weather by compliance with
continuous point source effluent limitations, the addi-
tional influx of organic material from overflowing
combined sewers may drive dissolved oxygen below
the minimum for some period of time after a storm. If
the concentration is low enough for a long enough pe-
riod to affect fish, some benefit is possible through or-
ganic load reduction. Here, two strategies are possible.
Additional treatment of continuous point sources to
raise the general dissolved oxygen level may prevent
violation of the fish-protecting standard even after a
storm though the combined sewer overflow loadings
remain the same. Alternatively, if the combined sewer
overflow inputs can be reduced to the point at which
the oxygen demand they cause is not large enough to
carry concentrations below the minimum, the same
benefit can be realized. A rather complex receiving
water quality model may be necessary to determine
the required reductions under each strategy or under a
combination of both strategies.
Inherent in both strategy determination and in the
more specific selection of control alternative is the con-
cept of optimization. The goal is to eventually arrive at
the optimal. or least costly, combination of control al-
ternatives that will result in the necessary level of pol-
lutant reduction to achieve desired beneficial uses. The
economic theory and methodology for optimization
are discussed in the 1978 Needs Survey 2 and by
25

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For Each Relevant Water Quality Constituent
Identify Combinations of Source Reductions that Give
Required Total Reductions in Receiving Water
J Meet Required Reductions
During Summer Low Flow?
* *
(a) C
Technologically
Feasible _________
Alternative?
Emphasize Reduction of One Component of
Response (i.e., Nitrogenous for DO Def)
Look at Combination of Location and
Component Reductions
Meet Required Reductions
During Storm Periods? I .iiii i: ——
No
$
I
[ Emphasize Reductions to Intermittent Sources
Continuous Non-Point Combined Sewer
i Source Reductions __________________
- — —
*
Emphasize Further Continuous Point or
Non-Point Source Reductions
Look at Combinations of Intermittent and Continuous
Point or Non-Point Source Reductions
Meet Required Reduction Over Long Term
r Yes—
Figure 6. Methodology for Determining Load Reduction Requirements.
Source: Municipal Environmental Research Laboratory. Office of Research and Development, U.S. Environmental Protection Agency,
AreawideAssessment Procedures Menu l Vol. I, p. 6-10. U.S. EPA Report EPA 600/9-76-014, July 1976.
Yes
Continuous Non-Point
Source Reduction
Pick Least
Cost Alternative
Yes [
Continuous Point
Source Reduction
*
No
4
-I
Emphasize Reductions at One Location
I
Pick
Least Cost
Alternative
(b) _____
Continuous Point
Source Reductions
1
+
I
Intermittent
Source Control
No
a 1
II !
Storm Sewerl
I Technologically j 4 [
Feasible?
26

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>
C
0,
> .
Ofl
Figure 7. Optimum Combination of Control Alternatives for Various Levels of Pollutant Reduction
and Budgetary Limits.
Source: Heaney. J. P.. “A Strategy for Integrating Storage Treatment Options with Management Practices’, presented at EPA Technology
Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures. 1978.
Heaney and Nix. 3 The essense of the process is the de-
termination, for each possible level of pollutant reduc-
tion, of all possible combinations of alternatives that
will achieve that level. To do this it is necessary to
know, for each alternative, the specific relationship be-
tween cost and pollutant removal. From this, a graph-
ical presentation of the sort shown in Figure 7 can be
developed. The curved isoquants represent combina-
tion expenditures on alternatives A and B to achieve
specific removals, while the straight isocost lines show
combinations of spending on the two alternatives that
are possible within a fixed budget. The points of tan-
gency between the two show optimum combinations.
Control Alternatives
Technologies to control pollution from combined
sewer overflow, many of which are also applicable to
urban stormwater runoff, can be grouped in three
main categories: source controls to reduce the
amounts of pollutants entering the sewer system, col-
lection system control to improve the system’s effec-
tiveness in storing and handling the flows, and off-line
storage and treatment to remove pollutants from com-
bined sewer flows. The control alternative selected for
any given situation may include techniques from one
or more of these groups.
Source Controls
Most source controls are non-structural in nature,
and are often referred to as best management prac.-
tices or BMP in 208 planning projects. The principle
common to all of them is reduction of pollutant accu-
mulation on impervious surfaces in the drainage basin
or in portions of the collection system itself, so that
pollutant loadings in combined sewer flows during
storm events are lowered.
Street cleaning. Originally intended to prevent
dust and dirt accumulation in urban streets, street
cleaning can be accomplished by manual labor, me-
chanical broom sweepers, vacuum sweepers, or street
flushing. The first three result in removal of some p oi-
lutants from streets, typically to landfills, while the last
method merely causes pollutants to be transported
into sewers during dry weather. The practices are most
applicable to highly developed urban and suburban
areas. Street sweeping, as opposed to flushing, effec-
tively removes some pollutants from the streets. The
degree of effectiveness depends on efficiency of the
equipment, frequency of sweeping, method of oper-
ation, and coordination with parking regulations and
litter control programs. Whether or not any of the var-
ious sweeping techniques will preserve or increase de-
sired beneficial uses of waters affected by combined
sewer overflows, however, depends not only on effec-
tiveness but also on the pollutants that are impairing
those uses. If toxicity from lead is an identified prob-
lem, for instance, street sweeping may be helpful, be-
cause lead from vehicle exhaust accumulates on street
surfaces. On the other hand, if the combined sewer
40%
$1 yr Alternative B
27

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overflow problems are nutrients. BOD. or bacteria.
street sweeping ma not result in sufficient improve-
ment. 4 The next technique may be more helpful.
Combined Sewer Flushing. A major source of
pollutants in combined sewer overflows is the accumu-
lation of sanitary sewage solids that have settled in the
sewers. The purpose of combined sewer flushing is to
resuspend this material and transport it to the sewage
treatment plant before a storm event carries it to the
receiving water in an overflow. Flushing can be ac-
complished using tank trucks or water detained in the
sewer system and probably should be carried out by
flushing small sections of the system in sequence in a
downstream direction. Effectiveness depends on sewer
system characteristics, flush volume and discharge
rate. frequency of flushing. and efficiency of the treat-
ment plant. Implementation of a sewer flushing pro-
gram requires detailed knowledge of the functioning
of the sewer system:
Catch Basin Cleaning. Catch basin cleaning to re-
move accumulated solids at the inlets is intended to re-
duce the first flush pollutant load, It can be
accomplished manually or b ’ eductor. bucket, or vac-
uum. However, the 1978 Needs Survey cites evidence
that it is probably not effective as a pollution control
measure. The normal range of combined sewer over-
flow BOD. removal that can be accomplished by street
sweeping is 2 to Il percent. Sewer flushing may result
in 18 to 32 percent removals. Catch basin cleaning
yields neglible results.
Collection System Controls
Techniques of collection system controls are in-
tended to ensure that the sewer system operates as ef-
ficiently as possible and that maximum advantage is
taken of any opportunities it offers for combined sewer
overflow pollution reduction. All of these measures re-
quire detailed knowledge of the sewer system. Some
are structural and some are non-structural.
Existing System Management. Correcting ma!-
functions. unbiocking clogged lines, optimizing regu-
lator functions, and locating unused in-line storage
capacity are all part of existing system management.
comprising continuing repair and maintenance. It be-
gins with a complete sewer system inventory and per-
formance survey, both of which should be the initial
phase of any combined sewer overflow control pro-
ject. The goals of these measures are maximum sewer
system efficiency and minimum overflows.
Flow Reduction Techniques. The demands on
existing conveyance and treatment capacities are re-
duced by flow reduction techniques that reduce the
volume of water entering the system. In a sanitary
sewer system. infiltration and inflow reduction are fa-
miliar concepts. A combined sewer is designed by defi-
nition to experience inflow. However, when new
development occurs in combined sewer service areas.
there may be opportunities to employ roof-top or
parking-lot storage, detention basins, or infiltration to
groundwater to mininiize increases in the rates of run-
off to the sewer. The frequency and magnitude of
overflow would thus not be unnecessarily increased.
Sewer Separation. Sewer separation is the conver-
sion of a combined sewer system into separate sanitary
and storm sewer systems. Either a new storm sewer or
a new sanitary sewer may be constructed. using the old
combined sewer for the other purpose. Some type of
pollution control may be necessary for the stormwater
after seçaration. since pollutant loads from that source
may continue to impair beneficial uses. Sewer separa-
tion can be enormously expensive but may be the cost
effective approach in relatively small watersheds (100
acres or less). BOD., reductions of 54 to 65 percent are
typical. 9
In-Line Storage. When the collection system is
large and has the potential for regulation of flow. in-
line storage may be an effective combined sewer over-
flow control alternative. Static or dynamic regulators
(the latter may be manual or computer-operated) are
employed to distribute storm flows within the system.
essentially storing stormwater to minimize the peak
flows at any given points that will cause overflows. The
1978 Needs Survey points out that this approach may
not entirely eliminate overflows. If the predicted re-
sults are not sufficient to provide the desired beneficial
uses, other measures will have to be combined with in-
line storage.’°
Storage and Treatment
Off-Line Storage. Off-line storage in earthen ba-
sins. caverns, or covered or uncovered concrete basins
detains storm flows for controlled discharge to treat-
ment facilities. Overflows may he reduced or elimi-
nated and. because flows are more uniform. treatment
facilities can be smaller and can operate more effi-
ciently. Storage can be located at overflow points or
near dry weather or wet weather treatment facilities.
Land availability may constrain the applicability of
this alternative.
Treatment. Treatment options are very numerous.
The list includes the following, some of which are still
in the research or demonstration stage with respect to
combined sewer overflow control:
• Sedimentation, with or without air flotation:
• Screens for removal of coarse materials:
• Microscreens for suspended solids and ROD
removal:
28

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• High-rate granular filtration which is more efficient
than screening;
• Swirl and helical concentrators for solids removal, a
treatment that can be used to regulate the volume
and quality of overflow;
• Chemical additives to enhance pollutant removal in
sedimentation, dissolved air flotation, and high-rate
filtration processes through coagulation, floccula-
tion, etc.;
• Disinfection to control micro-organisms using chlo-
rine oxidants — chlorine, calcium or sodium hy-
pochiorite, chlorine dioxide, or ozone;
• Biological treatment to remove nutrients and or-
ganic matter;
• High-gradient magnetic separation. a treatment that
can provide removal of metals and nutrient as well
as solids; and
• Carbon adsorption to remove soluble organics.
Removal efficiencies (BOD 5 ) of from 10 to 95 percent
are possible with storage/treatment options. depending
on drainage basin size and level of control desired.”
Selection of Control Alternatives
More details and bibliography are available in the
1978 Needs Survey. Analysis of a wide range of control
alternatives can be found in the Areawide Assessment
Procedures Manual’ 2 and Urban Storm waler Manage-
ment and Technology: Update and User’s Guide,’ cited
in Chapter IV.
Many of the structural alternatives are quite selec-
tive in terms of the pollutants removed (Table 3). It is,
therefore, very important that alternatives selected be
appropriate to the identified beneficial use being pro-
tected or enhanced.
A second consideration to keep in mind when struc-
tural alternatives are concerned is the concept of stag-
ing. Facilities that can be constructed in stages provide
future flexibility to deal with water quality problems
and allow some control to be achieved even when
funds ard limited.
When the list of control alternatives has been nar-
rowed down to those that look most promising, each
should be tested again for effectiveness in providing
the desired benefit — that is, in meeting the criteria to
protect that benefit. Furthermore, a range of control
levels to provide a range of levels of benefits must be
examined for each alternative (PRM 75-34) and re-
lated to costs. Once the cost-beneficial relationship has
been determined, the optimal solution can be selected.
References
‘Rhett, J. T., “Program Requirements Memorandum,
No. PRM 75-34”, Water Programs Operations,
U.S. Environmental Protection Agency, December
3,1976.
2 Wycoff, R., J. Scholl, and S. Kissoon, /978 Needs
Survey: Cost Methodology for Control of Combined
Sewer Overflow and Stormwater Discharge, U.S.
EPA Report, EPA 430 / 9-79-003, February 1979.
3 Heaney, J. P. and S. J. Nix, Stormwater Manage-
ment Model: Level / — Comparative Evaluation of
Storage Treatment and Best Management Pi’ac-
tices, U.S. EPA Report, EPA 600/2-77-083, April
1977.
4 Wycoff, R., J. Scholl, and S. Kissoon, p. 3-2.
5 Wycoff, R., J. Scholl, and S. Kissoon, p. 3-3.
6 Heaney, J. P. and S. J. Nix.
Wycoff, R., J. Scholl, and S.Kissoon, pp. 3-3 and 4.
Table 3. Pollutants Rei oved by Structural Alternatives.
Control method
Pollutant removed
Disinfection
Swirl concentration
Screens
Increased sewer transfer/holding
Local treatment-sedimentation
Physical/chemical
Col forms
Floatables, greases, oils, and heavier solids
Floatables and solids larger than mesh size
All pollutants
Settleable pollulants
Settleable and suspended pollutants
Source: Letter from Jack Warburton. Brown and Caidwell Consulting Engineers.
Seattle. WA. received December 29. 1978.
29

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9 Wycoff, R., J. Scholl, and S. Kissoon, p. 3-4.
9 Heaney, J. P. and S. J. Nix, p. 7-1 1.
°Wycoff, R., J. Scholl, and S. Kissoon, pp. 3-4and 5.
1 Heaney, J. P. and S. J. Nix, pp. 7-11 and 12.
2 M unicipal Environmental Research Laboratory, Of-
fice of Research and Development, U.S. Environ-
mental Protection Agency, Areawide Assessment
Procedures Manual, Vol. I, II, and Ill, U.S. EPA Re-
port, EPA 600/9-76-014, July 1976.
3 Lager, J. A., W. A. Smith, W. A. Lynard, R. M.
Finn, and E. J. Fennemore, Urban Stormwater
Management and Technology: Update and User’s
Guide, U.S. EPA Report, EPA 600/8-77-014,
September 1977.
30

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Chapter VI
Costs of Combined Sewer Overflow Control
Alternatives
The significance of different aspects of combined
sewer overflow control costs varies depending on the
needs of the persons reviewing them. Total cost (the
discounted present value of capital plus operation and
maintenance costs) should be related to benefits or wa-
ter quality objectives when deciding on the level of
control and should be used when selecting the most
cost effective alternative and justifying the project to
funding agencies. However, since only capital costs are
eligible for 75 percent EPA construction grant assist-
ance. they must be used to arrive at the costs to be
borne by the local and federal (and, in some cases,
state) governments. Once the local share of capital
costs is determined, it and the operating and main-
tenance costs comprise the expense to the municipality
(except that some operating and maintenance assist-
ance is available in some states). This is most mean-
ingful when expressed as an annual expenditure (the
sum of debt service and operating and maintenance
expenses for each year) since it enables municipal offi-
cials and taxpayers to see a project’s budget and tax
implications.
The capital costs of a combined sewer overflow con-
trol project consist of costs for construction, planning
and engineering, legal services, land acquisition and
administration, and interest during construction. Op-
eration and maintenance costs include expenses for la-
bor. power, chemicals, other supplies, laboratory and
sampling, and administration. Capital costs, with the
exception of land acquisition. can be predicted with
reasonable accuracy based on the type and size of the
facilities being considered. Land acquisition — both
finding a suitable site and paying for it — is of course
quite site specific. In an urban area with scarce avail-
able land it may be virtually impossible to find a large
storage site without expensive tunneling; the cost ef-
fectiveness of a storage alternative may thus be more
influenced by this variable than any other in many
cases. Operation and maintenance expenses are vari-
able but can be estimated in general. EPA Cost Esti-
mating Manual — Combined Sewer Overflow Storage
and Treatment contains tables of capital costs for a va-
riety of storage and treatment facilities and guidelines
for estimating operating and maintenance costs.
Though it contains 1976 figures, it should be a useful
document in the planning and alternative selection
stages of a CSO project, primarily as a source of rela-
tive cost information (Table 4 and Figure 8). Table 5
summarizes costs for various source and collection
control alternatives, and Figure 9 shows the cost
ranges experienced with several treatment processes.
This iterative examination of the cost/benefit rela-
tionship is a feature that distinguishes combined sewer
overflow control planning from municipal sewage
treatment planning. In the latter, once calculations
and estimates of present and projected waste flows and
loads have been developed and effluent limits as-
signed, the task is to select the most cost effective sys-
tem of a size sufficient to treat the projected flows. For
combined sewer overflows, the size and, therefore, the
cost component is intimately linked to the levels of
beneficial uses determined to be necessary. The initial
list of desired beneficial uses entails a required facility
storage or treatment capacity, for which costs can be
estimated. The costs may cause the locality to revise
the levels of beneficial uses, and the process can con-
tinue until a final alternative is selected. To facilitate
this ongoing process and as a requirement of PRM 75-
34,2 the costs associated with various levels of control
must be developed and presented graphically in this
part of the analysis.
Availability of funds must play a role here too. The
construction grant moneys allocated to each region
and state have never been sufficient to cover every
proposed project, nor are they likely to be. Thus, since
few sewage facilities projects can be constructed with-
out federal assistance, any proposed combined sewer
overflow control project will be competing for limited
funds and will be taking its place on a state priority
list. Realistic proposals (in terms of design storm) and
persuasive presentations are essential, especially true
when justiflying anticipated costs. A presentation such
as Figure 10 would be helpful because it shows clearly
the increased levels of control of stormwater that are
possible with increased levels of investment beyond a
base level.
31

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Table 4. Estimated Construction Costs.
Earthen Storage Reservo4rs
Cost component
Volume (million gallons)
0.57 1.95 4.90 9.20 14.80 50.85
108.50
187.80
Earthwork
Liner
Paving
Seeding
Fencing
Miscellaneousitems
Contingency
2540 6,670 14,900 24,700 36,940 93,330
7,730 14,350 32,780 53,720 79,650 233,400
2,180 3,140 4,340 5,540 6,740 11,540
870 1,750 3,150 4,960 6.540 13,800
5,650 7,940 10,720 13,500 16,100 26,300
2,850 5,100 9,900 15,360 21,900 56,700
3,270 5,790 11,350 17,650 25,210 65,150
156,320
467,150
16,340
20,600
26,300
103,000
118,290
229,530
780,900
21,140
28,000
45,900
165,820
190,430
TotalEstimatedCost
25,090 44,740 87.140 135,430 193,080 500,220
908,000
1,461,720
Concrete Storage Reservoirs—Concrete Reservoirs Without Covers
Cost component
Volume (million gallons)
1.0
2.0 4.0 7.5 15.0 30.0 60.0
120.0
240.0
Concrete and
forms 80,370
Steel 110,400
Labor 99,140
Miscellaneous
items 43.490
Contingency 50,010
109,030 166,360 230.390 358,450 513,270 822.940
149.600 277,200 313,600 486,400 692.000 1,104,000
135,850 208.610 294.060 465.840 686.800 1,129,260
59,170 97.830 125,710 196,600 283,810 458,430
68,050 112,500 144,560 226,090 326,380 527,190
1.239,770
1,648,800
1,771,140
698,960
803,800
2,073,370
2,739,200
3.055.330
1,180,190
1,357,210
Total Estimated
Cost 383,410
521,700 862.500 1.108,320 1,733.380 2,502,260 4,041,820
6,162,470
10,405.300
Cost component
Concrete Storage Reservoirs—Additional Costs for Concrete Reservoirs With Covers
Volume (million gallons)
1.0
2 0 4.0 7.5 15.0 30.0 60.0
120.0
240.0
Concrete
andforms 5.150
Steel 2.650
Labor 10.150
Precast
concrete 20,000
Roofing
material 2,000
Miscellaneous
items 6.000
Contingency 6.890
15,450 30.900 72.100 144,200 309.000 618,000
7,950 15.900 37,100 74,200 159,000 318,000
23.450 46.900 100,100 200.200 413.000 826,000
40.000 160.000 320.000 640.000 1,280.000 2,560,000
4.000 16,000 32,000 64,000 128,000 256,000
13.600 40.500 84,200 168,390 343,350 686.700
15,660 46.460 96.690 193,390 394,310 788,630
1,277,200
657,200
1,677,200
5,120,000
512.000
1,386,540
1,592,350
2,544,400
1,314,000
3.354.400
10,240,000
1,024,000
2.773,080
3,184,680
Cost for
Cover 52,840 120.110 356.660 742.190 1.484.380 3.026,660 6.053.330 12,222.490 24,434,960
Total Estimated Cost
withCover 436.250 641.810 1.219,160 1,950,510 3,217.760 5.528.920 10,095,150 18,384,960 34,840.260
Source: Berijes. Jr. H. H., Cost Estimating Manual — Combined Sewer Overflow Storage and Treatment, U.S. EPA Report. EPA 600/ 2.76-
286 p. 28. 29.
32

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10,000
Numberof Overflow
Events per year
PIII!III!II
30
720
710
lifl liii
100 ______________________
10,000
Cu
0
C
U)
0.
0.
1.000
0
U,
0
C-)
C
100
1,000
Figure 8. Storage Reservoir Labor and Cost of Supplies.
Source: Benjes, Jr. H. H., Cost Estimating Manual — Combined Sewer Overflows Storage and Treatment, U.S.
EPA Report, EPA 600/2-76- 286, p. 102, December 1976.
10 100
Volume of Storage Reservoir (Million Gallons)
1,000
U)
0
I
Cu
1,000
0
Cu
C
C
1 10 100
Volume of Storage Reservoir (Million Gallons)
33

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Table 5. Cost Rang.s for Selected Source and
Collection Control Alternatives.
Control Range of costs
($1 lb BOOS)
Source controls:
Street sweeping
Catch basin cleaning
Sewer flushing
Collection system controls:
Sewer separation
Swirl concentor
Remote control in-line storage
Roof drain disconnection
Source: U.S. Environmental Protection Agency ,‘ Report to
Congress on Control of Combined Sewer Overflows in the United
States (MCD-50)” p. 7-12. 1978.
An additional complication in the cost analysis re-
sults from the fact that combined sewer overflow con-
trol options include some structural approaches that
are capital intensive and some non-structural manage-
ment techniques that utilize labor and materials more
heavily. For instance, peak flow storage and sub-
sequent treatment at an existing plant with adequate
capacity requires significant capital investment and,
by comparison, little maintenance and operating labor
or materials. Increasing the frequency of street sweep-
ing or sewer flushing, on the other hand, has propor-
tionally higher manpower requirements. In a situation
where either approach would provide the needed wa-
ter quality improvement, the eventual budgetary bur-
den on the community might be lower in the more
capital intensive alternative because of the federal
grant assistance. However, one of the more labor in-
tensive approaches may be somewhat less expensive
overall. The community might wish to select the to-
tally structural alternative in that case. However fed-
eral regulations require (PRM 75-34) that the project
that has least cost overall be chosen.
Cost Allocation in Multi-Purpose Projects
Because combined sewers are multiple-purpose sys-
tems, it is not uncommon that combined sewer over-
flow control projects have multiple benefits. An
undersized combined system may back up as well as
overflow during storms, causing street flooding with its
related traffic and aesthetic problems. Parking lots as
well as other public and private lands and, in extreme
cases, basements may flood because storm drainage is
inadequate. At the other end of the system, smaller
streams may be flooded as well as polluted by dis-
3.00—7.50
>50.00
0.94—4.00
24.00
2.30—4.00
1.25—4.00
>50.00
charges from combined sewers. Bank erosion and sedi-
ment deposition may increase the expense of channel
maintenance. Consequently, a project that improves
the efficiency of the sewer system’s operation — sepa-
rating the combined system. for example, or utilizing
in-line storage — may provide benefits by reducing
street flooding while improving water quality. Any
storage alternative may reduce stream flooding and
bank erosion as well as pollutant discharge. These are
considered multiple purpose projects.
70 —
60 —
c
0
cc
U-
a,
cc
5 -
I
- 0
,4O
‘I,
o -
o
o
cc
U)
— U)
30 — c c
c
0
cc
-
—
00. cc
cc
tU)
cc
cc
u 2
C ,,
O
cc
10—
0 I I I
Unit Process (Complete Systems)
Figure 9. Capital Cost Ranges for Selected
Treatment Processes.
Source: Lager, J. A., “CSO Treatment Potential and Information
Source for Small to Medium Sized Communities, p 18,
presented at EPA Technology Transfer Seminars on Combined
Sewer Overflow Assessment and Control Procedures, 1978.
34

-------
80
i 60
C)
0
40
0
0
5,
E
20.
>
60
0
5,
0
0
5
E
o 20
>
Base Condition
I-i
0
80
)ncrements of Investment
rI I lit - i
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
CO N C) C) 0 N 0) ‘ U) CO N C)C5 0 N 0) U) CO N C) C) 0’- N C’) U) CON C) C) 0
0 0 0 0 N N N N N N N N N N C ’) C’) C’) 0) C’) C’) C’) C’) C’) C’) ‘
C) 0) C) C) 0) C) C) C) C) C) C) C) C) C) C) C) C) C) 0) 0) C) C) C) C) C) C) C) 0) C) C) C) C) C) C) C)
Water Year
- 1 -tF
‘ii’
4jI
0• I I I I I I I I I T I I I I I I I I I I I I I I I I I I I I 11 I
— N C’) IS) CON C) 0)0 ‘- N C’) Lt ) CON C) C) 0 — N C’) U) (ON C) 0)0 .- 04 C’) U)
‘ ‘4’ ‘ U) U) U) U) IS) U) I L) U) U) U) (0 C D CO CO CL) CO (0 (0 CD CO N N N N N N
C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) C) 0) C) C) C) C) C) C) C) C) C) C) C) 0) C) C)
Water Year
Figure 10. Overflow Volumes and Incremental Levels of Control.
Source. John A. Lager. “CSO Facilities Planning Using a Macroscopic Model” (A Case Study), presented at EPA Technology Transfer Seminars on Combined
Sewer Overflow Assessment and Control Procedures, 1978.

-------
EPA policy on pollution control facilities construc-
tion grants for multiple-purpose projects is that they
“may be eligible for an amount not to exceed the cost
of the most cost effective single-purpose pollution
abatement system” (PRM 75-34). since the agency is
not permitted to fund construction of storm drainage
facilities. Therefore, when application is made for an
EPA construction grant. it is necessary first to differ-
entiate project costs in such a way that EPA does not
fund any non-pollution control elements (PRM 75-34).
Second. the costs must be allocated so that an ’ savings
resulting from multiple-purpose construction are
shared equitably among the various purposes.
Alternative Justifiable Expenditure Method
In PRM 77-43. EPA expands on how costs should
be allocated. It requires the use of the alternative justi-
fiable expenditure method (AJE) to make the neces-
sary cost allocation, except under unusual
circumstances, with the provision that construction
grant-eligible costs shall “in no case, exceed the cost of
the least cost single-purpose pollution control alterna-
tive”. To apply it. one needs to know the following:
• Total cost of the multipurpose project.
• Costs that can be specifically attributed to each pur-
pose in the project. and
• Costs of the most cost effective single-purpose pro-
ject to achieve the same objectives as the multipur-
pose project.
The unknown quantities are the fractions ofjoint costs
those which cannot be attributed solely to one pur-
pose or the other — to be added to the specific costs for
each purpose. One way of determining these is use of
the AJE method.
The method is based on the assumption that it is
possible to develop cost estimates for a set of most cost
effective, single-purpose projects that would accom-
plish the same objectives as the multipurpose project.
(When this cannot be done. the “unusual circum-
stances” mentioned above can be assumed to exist.) In
the case of an off-line storage project as in Figure II.
for instance, the two single-purpose projects might be
construction of a storm sewer to relieve street flooding
and enlargement of a municipal sewage treatment
plant to avoid the necessity for overflows. Construc-
tion of off-line storage facilities, in this example. solves
the flooding problem by eliminating local system over-
loads and reduces the rate of wet weather flow to the
treatment plant to the point that overflows no longer
occur.
Within this hypothetical multipurpose project. there
are certain costs. referred to as specific costs, attribut-
able to one purpose or the other. Constructing new
stormwater inlets, for example. is solely an urban
drainage cost, but rehabilitating or replacing inter-
ceptors may be considered pollution control costs.
When all such specific costs have been identified and
subtracted, the remaining amount is the joint cost.
Multi-Purpose
1 and 2 Costs
Single Purpose
2 Costs
Figure 11. Identifying Specific-Purpose Costs Within the Costs of a Multi-Purpose Project.
Joint Costs
1 and 2
Sing’e Purpose
1 Costs
Specific
Remaining
Costs 1
4 Specific
Costs 1
Construct Storm Sewer Off Line Storage
Rera i ii i
Costs 2
Enlarge Treatment Plant
36

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Figure 12. Allocatin9 Joint Costs in a Multi-Purpose Project.
Much of the storage basin construction would be joint
cost in this case. Clearly the capital costs specific to
pollution control are eligible for construction grant as-
sistance, and those specific to urban storm drainage
improvement are not. To determine what fraction of
the jomt costs can also be included in the grant appli-
cation to EPA, first, the specific costs for each purpose
in the multipurpose project are subtracted from the
corresponding single-purpose costs. The remainders
(two in this case), or the remaining costs, provide the
basis for allocating the joint costs. Dividing the re-
maining cost for pollution control by the sum of the
remaining costs yields a fraction by which the joint
cost is multiplied, as in Figure 12. The result is the pol-
lution control share ofjoint cost; this amount is added
to the specific costs for pollution control, and the sum
is eligible for EPA construction grant assistance. The
specific costs for storm drainage and the remainder of
the joint cost are not grant eligible.
This procedure can be expressed in simple equation
form, where:
TC = total multipurpose project cost
JC = joint costs within multipurpose project
SC = specific costs for purpose i within multipur-
pose project
SPC 1 = cost of single purpose project that would ac-
complish purpose i
RC 1 = remaining cost of purpose i
AC 1 = portion of multipurpose project cost allo-
cated to purpose i
Joint costs are then determined by:
JC = TC-(SC, + SC. + ÷ SC, )
In order to allocate joint costs, remaining costs must
be calculated for each purpose:
RC, = SPCI - SC,
RC, = SPC 2 - SC.
RC = SPC , - SC,,
Assuming the pollution control purpose is purpose 1,
the share of total project costs eligible for construction
grant assistance becomes:
AC, = SC 1 ± JC( RC ,
KU, + KU 2 + + RC ,,
Costs can be allocated to other purposes in the same
way, but these are not EPA grant-eligible.
AC 1 =SC 1 +JC( RC
RC , ± RC 2 + + RC,,
It should be noted that in no case will the costs allo-
cated to a given purpose exceed the cost of the most
cost effective single-purpose equivalent or be less than
the specific costs for that purpose.
SC, 
-------
One unusual situation which may arise occurs when References
no specific costs can be identified for the pollution
control component of the multipurpose project (pur-
pose 1 in this example). However, this can be handled
in the same manner as above; nothing is subtracted
from the single-purpose pollution control cost, and the ‘Benles, Jr. H. M., Cost Estimating Manual — Corn-
pollution control share ofjomt cost is proportional to bined Sewer Overflow Storage and Treatment, U.S.
the unreduced single purpose cost. EPA Report, EPA-600/2-76-286, December,
1976.
Sc 1 = 0
JC = TC —(0 + SC 2 + + SCM) 2 Rhett, J. T.. ‘Program Requirements Memorandum,
RC, = spc, -o No. PRM 75-34”, Water Programs Operations,
U.S. EPA, December 3, 1976.
Therefore:
3 “Program Requirements Memorandum,
AC = .Jc ( SPC 1 No. PRM 77-4”, Water Programs Operations,
1 SPC, + RC. + •• + RC,, U.S. EPA, December 16, 1976.
38

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Chapter VII
Back to Benefits
The analysis and planning for combined sewer over-
flow correction has rested solidly on a determination
of desired or required beneficial uses of a receiving
water body and the most cost effective controls that
will result in these beneficial uses. The culmination of
this process in a decision to proceed depends on the
presentation of the answers to three basic questions:
• What are the benefits?
• How costly is the project?
• Do the benefits expected justify the commitment of
public funds and other resources?
The key to a successful outcome of this stage is that
the questions be answered in a clear, logical, and real-
istic manner. No elected officials — and they are the
ones who make the decisions that will begin the imple-
mentation process — can proceed further without
being satisfied on these points. The dollar amounts in-
volved in combined sewer overflow control projects
are invariably large enough to attract more than ca-
sual interest. If it is not possible to demonstrate to the
taxpayers a favorable relationship of benefits to costs.
it is not likely that they will lend their support to the
undertaking. Furthermore, EPA requires evidence
that the proposed project is necessary to “protect a
beneficial use” before it will provide a construction
grant.
Estimating Benefits
There are four general methods for estimating bene-
fits of water quality management projects:
• Apply available technology with no explicit estimat-
ing analysis.
• Control water quality standards,
• Estimate increased water use potential. or
• Use classical cost benefit analysis.
The first is the simplest. It assumes that benefits will
automatically be realized from the proposed activity
and that they are so large that they justify the alloca-
tion of required resources. It completely avoids the
benefit measurement problem. An example of this
method is the federal requirement for secondary treat-
ment at all publicly owned treatment works. This ap-
proach is appropriate under certain circumstances —
when water quality is very poor and public demands
for it is high, for instance.
In the second method, it is assumed that certain wa-
ter quality standards are associated with the protection
of water uses. This is generally felt to be the case, al-
though the connection may not always he scientifically
defensible. Once standards to protect desired benefi-
cial uses have been established, the comparison of pro-
jected water quality with the standards provides an
estimate of benefit. When the level of pollutant reduc-
tion required to meet water quality standards can be
determined, then pollutant reduction can also serve as
a surrogate measure of benefit. This is particularly
convenient, since pollutant reduction can also be re-
lated rather directly to control cost.
Estimates of increased water use potential are devel-
oped by translating improvements in water quality
into numerical increases in usable length of beaches.
swimming days, fishing days. or water-front property
values, to name a few possibilities. This is, in effect. a
refinement of the water quality standards approach.
allowing benefits to be estimated directly.
The best known method is classical cost benefit
analysis. In this method each anticipated water usage
has a dollar value assigned as a measure of unit worth
or willingness to pay. The actual project usages are
multiplied by the corresponding unit values, and the
sum is compared directly to total project costs.
The first approach is unacceptable for combined
sewer overflow control planning, because a demon-
stration of anticipated benefit is necessary. The public.
local officials, and EPA must be shown that there will
be an improvement in water quality producing bene-
fits which are consistent with the costs. The third and
fourth methods suffer from great subjectivity that can
only be overcome at considerable expense by detailed
studies of demand, use, and willingness to pay. The
water quality standards approach seems most appro-
39

-------
priate for combined sewer overflow control planning
at this time. Of course, when information on increased
water use potential is available and can be related to
the standards, it will strengthen the analysis, and it
should, therefore, be employed.
Comparing Costs and Benefits
How the relationship between costs and benefits for
various levels of combined sewer overflow control is
developed and presented is as critical as the initial de-
termination of desired beneficial uses. PRM 75-34’
specifically recommends graphical displays of this in-
formation, relating quantified pollutant reduction and
water quality improvements to dollar costs. supporting
descriptive material should compare monetary, social,
and environmental costs to benefits. The decision
makers will focus most of their attention on this part
of the report.
The presentation must meet the needs of three
groups: local elected officials, citizens, and funding and
regulatory agencies. The most important users of the
analysis results, the public and its elected officials, are
for the most part not specialists in water quality man-
agement. Moreover, they have other demands on their
time. They will appreciate material that they can under-
stand without technical consultants and that they can
read and digest in a reasonable amount of time.
All of the report should therefore follow these
recommendations:
Table 6. Relation Between Design Basis and Benefits.
• Be presented in non-technical language,
• Be concisely written, with well-conceived graphics,
• Set for its arguments completely and logically,
• Be expressed in terms relevant to beneficial use and
cost interests of the reader, and
• Be responsive to EPA requirements.
The way the results are displayed is critical. Tables
should be uncomplicated and informative. Graphics
should be designed to highlight key findings. Details
should be placed in an appendix or in supporting
documents. The explantory text should help the reader
follow the analyst’s reasoning, briefly describing meth-
odology and stating any assumptions.
Table 6 contains information on design storm al-
ternatives when controlling bacterial contamination
from combined sewer overflow to increase the usabi-
lity of bathing beaches in a hypothetical urban area in
the northeastern United States. Figure 13 is a graphic
presentation of the cost benefit relationship of Table 6,
showing expected increases in swimming availability
as a function of dollars invested in the construction of
covered concrete retention basins. Note the character-
istic knee of the curve, the point at which the amount
of additional benefit obtained for each additional do!-
lar spent declines sharply. Expressed in the language
of PRM 75-34, marginal costs become substantial
compared to marginal benefits in this range. That is.
the cost for each additional unit of pollution control
becomes large enough, and/or the amount of benefit
anticipated from that unit of control small enough, to
Design Storm
Days Between
Average Days! Month
Retention Tank Required
to Achieve Control
Return Frequency
Overflow Events
Beach Closed
mg/sq mi 1975 S/sq mi
3 20 0
0.33 Month
10
6
3.5
1,000.000
70.5
3 Month
90
0.7
16
2.500,000
96.7
1 Year
365
0.2
28
3,500,000
99.18
10 Year
3650
0.02
45
5,000.000
99.92
0
% Storms Smaller Than
Desiqn Storm
Assumptions:
Each overflow event closes beach for 2 days.
Storm characteristics typical of N. Eastern U.S.: 122 storms/year; mean Unit rain volume = 0.4 inches; coefficient of variation of
storm volume = 1 .5; runoff/rainfall ratio for area = 0.5.
Retention tank is concrete basin with cover.
Aereal coverage provided by 1 basin/sq. mi. drainage area.
Source: Driscoll, E.D. and J.L Mancini “Assessment of Benefits Resulting from Control of Combined Sewer Overflows”, presented at EPA
Technology Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures, p 21, 1 978
40

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Figure 13. Relation Between Costs and Benefits.
(Data from Example in Table 6)
20 . .
18 —
16 —
-c
C
c 12
>-
0 ’) =
W c 1
Co,
— I
—
I
I
— I
I
1
—I
I
7
call the advisability of purchasing that additional unit
into question. These are familiar tools in economic
analysis. when the theoretical optimum level of pro-
duction (i.e.. pollution control) is the point at which
marginal cost equals marginal revenue (i.e.. benefit).
Selection of Design Storm
During the early phases of the planning process.
rough costs were used to assist in selecting desired lev-
els of benefit. Now, with more detailed information
available, the design storm can be selected more pre-
cisely and, moreover, the selection can be explained
and justified. it may be that the initial choice has
proven to require expenditures beyond the knee of the
curve, and a more modest objective should be consid-
ered. On the other hand. if the first selection proves to
be considerably below the knee. the objective should
he reexamined to determine if a higher level of control
would produce additional usable benefit.
Reference
0 I Rhett. J. T., Program Requirement Memorandum.
1 2 3 4 No. PRM 75-34”. Water Programs Operations,
CostinSmitions.Sq.Mi U.S. EPA, December 3, 1976.
41

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Chapter VIII
Case Studies
Seattle
Metropolitan Seattle (Metro) has 110 sewer overflow
locations. Overflow averages 40 occurrences per year,
with approximately 6 during the summer recreation
season. Planning for control of pollution from over-
flows, conducted under Section 201 of the Clean Wa-
ter Act, involved two major technical phases —
evaluation and optimization of control alternatives
and quantification of benefit or effects of proposed fa-
cilities. Optimizing control alternatives was a straight-
forward process of comparing appropriate alternatives
and establishing the overall least cost facility configu-
ration. Quantification of benefits was complicated by
the existence of multiple receiving waters with a wide
range of beneficial uses and sensitivities to pollution.
The seven distinct steps in the study were:
• Development of a collection system model with flex-
ibility to allow optimization at successive levels of
control.
• Application of a collection system model to establish
optimum controls as a function of a storm recur-
rence interval.
• Application of a collection system model to establish
effectiveness of controls as a function of recurrence.
• Determination of combined sewer overflow quality
parameters.
• Measurement of impacts on receiving waters.
• Identification of beneficial uses for all receiving wa-
ters and determination of sensitivity to pollution by
CSOs.
• Relating CSO impacts to beneficial uses.
Collection System Analysis
Several hundred storm sewer network simulation
models are available in the current literature; how-
ever, none could handle the complexities inherent in
the Seattle system without extensive modifications.
Those models that did have the basic sophistication to
handle the flood routing aspects were too detailed and
thus too time consuming for the planning effort. Con-
sequently. at the start of the planning it was decided to
custom-build a model that would not only address the
needs of the study but would also, with minimum re-
finement, be suitable for subsequent detailed design
and be a useful tool for future Metro planning.
The adopted two-part model consists of a runoff
model based on the unit hydrograph technique that
provided the input to the transport model that simu-
lates the flow of the runoff through the system.
Once the model was built and calibrated, the tool
was available to evaluate and optimize control al-
ternatives and to determine CSO volume reductions
for specific control levels.
CSO control alternatives evaluated included the
following:
• Full separation in partially separated areas,
• Full and partial separation in combined areas.
• Roof-top storage.
• In-line storage of existing system (CATAD. or Com-
puter Augmented Treatment and Disposal).
• In-line storage with new pipe/tunnels.
• Off-line storage.
• Localized storage/transfer and centralized storage.
• Local off-shore discharge.
• Local treatment, and
• Transfer and centralized treatment.
Controls were optimized for 114 sub-basins, consider-
ing overall cost based on a range of permitted over-
flow frequencies from the present 40 per year to tO per
year. I per year. and I in ten years.
In basins tributary to the fresh inland waters of
Lake Washington and the ship canal downstream to
the outlet of Lake Union. control alternatives were
limited to storage. transport. and source control. In
other drainage basins. additional alternatives of local-
ized treatment or upgraded outfalls were evaluated.
Once the range of alternatives was established, the
analysis was conducted for each drainage basin by de-
tailing the size of physical facilities required and es-
tablishing their cost.
43

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*
Systemwide cost optimization was accomplished by
matching flows at drainage boundaries and apportion-
ing the cost for downstream facilities based on their
proportion of total facility required. Selected facilities
were based on flexibility for area! emphasis and stage-
able controls within specific areas.
The facility arrangements that yielded most eco-
nomical control at the three selected storm frequency
control levels were identified. In general, localized
and/or centralized holding was found to be the most
cost effective in the areas remote from the treatment
plants. A combination of holding, transport. and in-
creased treatment capacity was found to be the most
economical for controlling overflows closer to the
plants.
At the conclusion of this phase, the tools were avail-
able to find the least cost for controlling any combina-
tion of overflows, and incremental control level and
corresponding reduction in overflows could be
determined.
CSO Characteristics
Of the 110 overflow points, 5 were selected from
representative runoff areas and subjected to detailed
analysis. Investigation included analysis of the over-
flows, dye studies. coliform die-off studies. and benthic
studies. Grab and composite site sampling was con-
ducted at each point through a representative range of
storms. A large range of values was obtained from the
analyses (Table 7), but some general conclusions could
be made: Tributary land use did not significantly af-
fect conventional pollutant concentrations; the phe-
nomenon of the first flush was not evident; season was
not significant; and the size of the storm was not sig-
nificant. Average pollutant concentrations could there-
fore be used for determination of pollutant loadings
throughout the area and for various sizes of storms.
Dye studies indicated that the impact of overflows
was typically localized within one-half mile for specific
wind and localized current conditions. Coliform levels
exceeded local public health water contact quality
standards for up to 3 days. Benthic analysis at the
overflow indicated significant dead areas overlain by
sludge deposits.
Identification of Beneficial Uses and Sensitivity
of Receiving Waters
Recognizing that the impact of overflows differs de-
pending on the sensitivity of the receiving water and
their attendant uses, Seattle’s consultants prepared a
geographical inventory of water use areas, aquatic life
habitats, and ranking of relative risk to pollutant load-
ings based on physical characteristics (e.g., water cir-
culation. dilution factors. and flushing) to assist in
ROD
15
82
60
COD
100
330
236
SS
141
296
217
NH 4 -N
0.5
1.5
0.9
P
1.2
1.7
1.4
Cu
0.1
0.3
0.2
Pb
0.5
0.9
0.6
Hg
0.01
0.01
0.01
Cr
0.02
0.20
0.10
Cd
0.01
0.02
0.01
Total coliforms 8 X 1O 7000 x 1O
Fecal coliforms 3.6 x 10 780 x 1O
‘All values in mg/I except for coliform units, which are in
colonies/i 00 ml.
Source: Warburton, J., “Seattle’s Approach to Evaluating Costs
and Benefits of Combined Sewer Overflow Control per PGM-6 1
p. 8, presented at U.S. EPA Technology Transfer Seminars on
Combined Sewer Overflow Assessment and Control Procedures,
1978.
ranking overall sensitivity of the various water bodies
to degradation from pollution loads.
Individual environmental risk maps, depicting rec-
reational use (Figure 14), biotic life zones (Figure 15),
and water quality sensitivity (Figure 16) were com-
bined utilizing the overlay technique developed by Ian
McHarg, and three levels of risk were identified for lo-
cations with combined sewer overflow (Figure 17).
This prioritization does not constitute a cost effective
analysis for abatement techniques but simply groups
the overflows relative to their degree of environmental
risk. It is the first step in grouping overflows with spe-
cific beneficial uses. The more localized the analysis,
the easier it is to identify the relationships between
beneficial use and CSO impact.
The next step was an evaluation of the commonality
of collection subsystem, CSO impact overlaps, water
body physical characteristics and dominant beneficial
uses. This evaluation resulted in defining nine separate
overflow areas that were then prioritized utilizing the
initial risk analysis concept.
Cost Control Relationship
For each of the overflow areas, a plot of cost versus
control level was made utilizing data developed in the
control level optimization (Figure 18). In all cases, a
pronounced “knee” (indicating a dramatic increase in
control costs) was indicated in the one-per-year to one-
per-ten-year overflow limit range. This knee of the
curve is significant because it represents a point where
marginal costs begin to increase quite rapidly. In other
Pollutant
Table 7. Average CSO Pollutant Levels — Seattle.
Minimum Maximum Average
44

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Figure 14. Water Contact Recreation: Risk ot Uegraclatuon Trom tomo.nea ewer UVUIUOW5.
Source: Brown and Caldwell. Consulting Engineers for Municipality of Metropolitan Seattle, Combined Sewer Overflow Control Program.
p. 6-23, January 1979.
45
0
Legend
High Risk
: : Moderate Risk

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Legend
High Risk
Moderate Risk
Figure 15. Biotic Life Zones and Critical Habitats: Risk of Degradation from Combined Sewer
Overflows.
Source: Brown and Caldwell. Consulting Engineers for Municipality of Metropolitan Seattle, Combined Sewer Overflow Control Program.
p. 6-24. January 1 979.
46

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Figure 16. Water Quality: Relative Sensitivity to Pollutant Loading.
Source: Brown and CaIdwell. Consulting Engineers for Municipality of Metropolitan Seattle, Combined Sewer Overflow Control Program,
p. 6-25, January 1979.
47
Legend
High Risk
Moderate Risk

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Legend
:‘:‘!iI High Risk
Moderate Risk
Low Risk
• CSO locations
Figure 17. Relative Priority in Terms of Pollution Risk from Combined Sewer Overflows.
Source: Brown and CaIdwell. Consulting Engineers for Municipality of Metropolitan Seattle. Combined Sewer Overflow Control Program.
p. 6-26, January 1979.
48

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Million Gallons
42 22
25
20
0
15
0
0
C
0
0
0
C.)
Annual Overflow Volume Reduction
Figure 18. Cost-Overflow Control Curve —
Priority 5 Overflow Area: Lake Union (South
and East Shores) and Portage Bay.
Source: Warburton, J. ‘Seattle’s Approach to Evaluating Costs
and Benefits of Combined Sewer Overflow Control per PGM 61
p. 11 presented at U.S. EPA Technology Transfer Seminars on
Combined Sewer Overflow Assessment and Control Procedures, 1978.
words, the cost for each additional unit of pollution
control above the knee is much greater than the cost
for a comparable increment below it. EPA examines
this relationship critically in deciding whether margi-
nal costs are substantial in comparison to marginal
benefits.
The next step was to relate the reduction in pollu-
tant to increase in benefit.
Water Body Beneficial Use
A list of all existing beneficial uses and potential
beneficial uses lost because of the existing CSOs was
prepared for each of the overflow areas. Use informa-
tion was based on field observations, state environ-
mental and wildlife departments. local universities
and colleges, the county health department. the city
parks department, local community groups, and corn-
4.1 0.5 ments made during the public hearing. The beneficial
uses were then listed in order of importance, based on
a combination of factors including public risk. biota
sensitivity, and city zoning/planning policies for the
area. A list of identified beneficial uses is shown in
Table 8.
CSO Control Levels and Beneficial Uses
For each of the nine overflow areas and for each
beneficial use within each area, the relationship of
CSO control to beneficial use was evaluated, assessing
existing conditions and projecting the benefits that
would accrue by increased reductions in overflow
events.
For illustrative purposes, priority 2 area. Lake
Washington South is shown. The prioritized beneficial
uses were:
• Swimming,
• Fish rearing.
• Fish spawning.
• Recreational boating, and
• Shoreline parks.
Swimming. Up to 20 overflows per year were dis-
charging near the shore, resulting in up to 3 days of
health standard coliform count violations for each oc-
currence. Up to 5 overflows occurred durmg the sum-
mer recreation season. CSOs diu not preclude
swimming activity, because beach closing procedures
were not in effect, but participants were subjected to
risk when swimming during the effects of CSOs. Thus.
on a strict use definition basis, elimination of CSOs
would not increase swimming activity, only reduce a
potential health risk. However, the reduction in risk
was a sufficient argument to meet EPA guidelines. Le-
Table 8. Beneficial Uses and CSO Pollutants —
Seattle.
Use CSO Pollutants
Source. Warburton. J., “Seattle’s Approach to Evaluating Costs
and Benefits of Combined Sewer Overflow Control per PGM-61
p 8, presented at U.S. EPA Technology Transfer Seminars on
Combined Sewer Overflow Assessment and Control Procedures. 1978.
Residential
Swimming
Shell fishing
Fish spawning/rearing
Juvenile fish migration
Recreational boating
Shoreline parks
Commerce
Industry
Coliforms /floatables
Coliforms/floatables
Coliforms /virus
Toxicity/suspended solids
Toxicity
F loatables
Floatables
Minimal
Negligible
50
Percent
49

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gal substantiation for this approach has recently been
provided in a court case involving the State of Illinois
versus the City of Milwaukee, Wisconsin. The judge
stated that “exposure to a hazard is itself actionable.
whether or not that exposure results in the actual con-
traction of a disease.”
Other factors taken into consideration were prior
community commitment to CSO control, local politi-
cal policy to reduce overflows to 1 per year, the large
percentage of the shoreline accessible by public park,
and the number of swimming areas operated by the
city within the CSOs areas of influence. For swimming
use, funding of facilities to control overflows to 1 event
per year was agreed upon: this is equivalent to 1 sum-
mer overflow every 2 years.
Fish Rearing/Spawning. Combined sewer over-
flows are potentially toxic to fish, particularly during
spawning and early development. It was the opinion
of fishery experts as well as the regulatory agencies
that overflows do affect these processes adversely, but
available information on the degree of CSO stress was
lacking. Until a closer definition of stress can be deter-
mined, the funding agencies would not participate in
CSO controls to protect fish rearing/spawning.
Recreational Boating/Shoreline Parks. Control
levels beyond those developed for swimming would
not be necessary to protect recreational boating or
shoreline park use.
Similar analyses were conducted for each water
body. and in each case it was only the human health-
related beneficial uses that could meet the EPA bene-
fit requirements — namely, residential areas subjected
to CSOs, swimming, and shellfish harvesting. The case
for CSO control to protect fishery related uses could
not be made sufficiently strong to meet the rigors of
PRM 75-34.’
Conclusions of Seattle Case
Success of technical aspects of planning. facilities
optimization and control effectiveness estimation is
highly dependent on the collection system model used.
In this case, the model used was highly flexible and
readily adaptable to various control alternatives.
Available data on actual effects of CSO discharge to
local receiving waters were sufficient only to justify
control of overflows to receiving water segments where
human contact recreation is the controlling beneficial
use. Receiving water effects considered did not include
those from the comprehensive list of EPA priority pol-
lutants. Further studies to identify specific effects of
overflows on the biological community are currently
being developed by Metro.
The results of the planning process demonstrate that
EPA will consider favorably funding CSO controls
when benefits are demonstrated and when reduction
of CSO is one element in an overall comprehensive
201/208 solution approach to addressing a water qual-
ity problem.
New York City
The combined sewer overflow control planning ac-
complished as part of the New York City 208 project
illustrates the intimate connections among water qual-
ity problems. desired benefical uses, objectives, and
control alternatives.
Even before the 208 grant application was sub-
mitted, the city of New York Set, as one water quality
objective, the opening swimming beaches along the
Hudson River and in the South Bronx and the open-
ing of additional beaches on Staten Island. This would
be of direct benefit to lower income people concen-
trated in the South Bronx and Manhattan. for whom
access to the usable beaches in Brooklyn. Rockway,
and Staten Island was difficult. A desired beneficial
use had thus been specified and the locations at which
it was to be provided pinpointed.
Analyzing the relationship of overflows to water
quality at the beaches involved the development of a
rainfall simulator that could provide estimated pollu-
tant loads from overflow events. This information for
80 distinct drainage lines, together with continuous
point source loads, could be fed into a complex time-
variable hydrodynamic model of the Hudson River es-
tuary. These analytical tools were used to first screen
and then evaluate the many alternatives that could
conceivably be pursued to open the beaches.
The first conclusion drawn from the m9deling anal-
ysis was that once secondary treatment of dry weather
flows had been achieved, control of combined sewer
overflows did not have to he accomplished throughout
the city to attain the stated objective. The water qual-
ity problem preventing the use of the beaches in ques-
tion, high fecal coliform concentrations, could be
traced to overflows in the vicinity of the beaches them-
selves. Some of these overflows occurred in dry
weather, indicating that repair and maintenance of
regulators should be a part of any control alternative.
The areas in which this was necessary were delineated.
Further analysis showed that after elimination of these
dry weather overflows, disinfection would be necessary
at 240 major overflow points and at about 12 separate
storm sewer outfalls, all clustered near the beaches
(Figure 19).
Up to this point, the analysis had concentrated on
health problems. A new dimension was added to the
50

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problem when health department officials pointed out
that floatable solids and other visible signs of pollution
would make beaches aesthetically unattractive even if
they were safe from the fecal coliform standpoint. Af-
ter simple observations from a small boat, it was de-
cided that skimmers at 10 overflows would solve this
problem.
Significantly. it was by precise definition and loca-
tion of desired beneficial uses, by use of analytical
tools suited to the problem, and by careful matching
of control alternatives to both problem and beneficial
use, that the solution ultimately recommended was a
substantially more practical and less costly approach
than might otherwise have been developed. The esti-
mated capital cost to provide the desired beneficial
uses was $280 million. Of this, $40 million was for re-
habilitation of interceptors. Expenditure of $120 mil-
lion would cover the 10 skimming basins and $120
million would provide disinfection at 240 points.
There are more than 850 overflow points in the metro-
politan area; if the recommendation been to provide
skimming and disinfection at all of them, the cost
would have approached $10 billion.
Although this CSO project is obviously larger than
most others in the country. savings of similarly large
proportions are often within the reach of municipal-
ities through similar well-conceived planning as the
municipalities seek to provide enhanced use of local
water bodies through the control of combined sewer
overflows.
Reference
‘Rhett, J. T. ‘Program Requirements Memorandum,
No. PRM 75-34”, Water Programs Operations,
U.S. EPA, December 3, 1976.
Source: Mancini, J., “Assessment of Benefits Resulting from Control of Combined Sewer Overflows, presented at U.S. EPA Technology
Transfer Seminars on Combined Sewer Overflow Assessment and Control Procedures. 1 978.
No Dry Weather Leakage
CSO Disinfection
• SWO Disinfection
T Disinfection and Skimming
• Beaches
New Jersey
Queens
Figure 19. Facilities for Areawide Swimming: New York City.
51

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Bibliography
The following publications about combined sewer
overflows are available free and provide comprehen-
sive lists of reports and other publications on plan-
ning, assessment and monitoring procedures.
modeling, control alternatives, and case studies.
Bibliography of Research Development, Demonstra-
tion Grant, Contract and In-House Project Reports,
Storm and Combined Sewer Section, Wastewater
Research Division, Municipal Environmental Re-
search Laboratory — Cincinnati, U.S. EPA, April,
1978.
• Annotated Partial Bibliography of User Assistance
Tools in Combined Sewer Pollution Abatemeni,
Wastewater Systems Control Technology, Office of
Research and Development, U.S. EPA, Washington,
DC, April, 1978.
The following were referenced in this publication:
1. Benjes, Jr. H. H., Cost Estimating Manual — Com-
bined Sewer Overflow Storage and Treatment, U.S.
EPA Report, EPA 600/2-76-286. December 1976
(NTIS: PB-266-359).
2. Clean Water Act of 1977,33 U.S.C. 1251 etseq.
P.L. 952-17.
3. Delaware Valley Regional Planning Commission,
Pennsylvania Department of Environmental Re-
sources, and Betz Engineers, COWAMP 208 Wa-
ter Quality Management Plan, Southeastern
Pennsylvania, April 1978.
4. Driscoll, E. D. and J. L. Mancini, “Assessment of
Benefits Resulting from Control of Combined
Sewer Overflows”, presented at EPA Technology
Transfer Seminars on Combined Sewer Overflow
Assessment and Control Procedures, 1978.
5. Federal Water Pollution Control Act Ammend-
ments, 33 U.S.C. 1251, et seq., P.L. 92-500.
6. Grimsrud, G. P., E. J. Finnemore, and H. J.
Owens, Evaluation of Water Quality Models.’ A
Management Guide for Planners, U.S. EPA Re-
port, EPA 600/5-76-004, July 1976 (NTIS: PB-
256-412).
7. Heaney, J. P., “A Strategy’ for Integrating Storage
Treatment Options with Management Practices”,
presented at EPA Technology Transfer Seminars
on Combined Sewer Overflow Assessment and
Control Procedures, 1978.
8. Heaney. J. P., W. C. Huber. and S. J. Nix,
Stormwater Management Model: Level I — Prelim-
inar ,v Screening Procedures, U.S. EPA Report.
EPA 600/ 2-76-275. October 1976 (NTIS: PB-259-
916).
9. Heaney. J. P.. and S. J. Nix, Stormwater Manage-
ment Model: Level I — Comparative Evaluation of
Storage Treatment and Best Management Prac-
tices, U.S. EPA Report. EPA 600/2-77-083. April
1977.
10. Lager. J. A.. “CSO Treatment Potential and Infor-
mation Source for Small to Medium Sized Com-
munities”, presented at EPA Technology Transfer
Seminars on Combined Sewer Overflow Asess-
ment and Control Procedures, 1978.
11. Lager. J. A.. W. G. Smith. W. G. Lynard. R. M.
Finn and E. J. Finnemore. Urban Stormwater
Management and Technology: Update and User’s
Guide, U.S. EPA Report. EPA 600/8-77-014, Sep-
tember 1977 (NTIS: PB-275-654).
12. Municipal Environmental Research Laboratory.
Office of Research and Development, U.S. EPA,
A reawide Assessment Procedures Manual, Vol. I,
II, and III, U.S. EPA Report. EPA 600/9-76-0 14,
July 1976.
53

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13. Rhett, J. T., “Program Requirements Memo-
randum, No. PRM 75-34”, Water Programs Oper-
ations, U.S. Environmental Protection Agency,
December 3, 1976.
14. “Program Requirements Memorandum,
No. PRM 77-4”, Water Programs Operations.
U.S. Environmental Protection Agency, December
16, 1976.
15. Turner, B., R. Holbrook, R. Corbitt. and R. Wy-
coff, 1976 Needs Survey: Summary of Technical
Data for Combined Sewer Overflow and Stormwa-
ler Discharge, U.S. EPA Report, EPA 430/9-76-
012, February 1977.
16. U.S. Environmental Protection Agency, “Report
to Congress on Control of Combined Sewer Over-
flows in the United States (MCD-50)”, 1978.
17. Warburton. J., “Seattle’s Approach to Evaluating
Costs and Benefits of Combined Sewer Overflow
Control per PGM 61”, presented at U.S. EPA
Technology Transfer Seminars on Combined
Sewer Overflow Assessment and Control Proce-
dures, 1978.
18. Wycoff, R. and M. Mara. 1978 Needs Survey: Con-
tinuous Stormwater Pollution Simulation System
User’s Manual, U.S. EPA Report. EPA 430/9-79-
004, February 1979.
19. Wycoff, R., J. Scholl, and S. Kissoon, 1978 Needs
Survey: Cost Met hodology for Control of Com-
bined Sewer Overflow and Storm water Discharge.
U.S. EPA Report. EPA 430/9-79-003. February.
1979.
20. 40 CFR 35. 37 FR 11650, June 9, 1972, effective
July 1. 1972.
54
* (IS. GOVERN*BtT PIIIITING OffK : 1979 -657-060/1673 Region No. 5-fl

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