EPA
United States
Environmental Protection
Agency
Office Of Water
(4204)
EPA 832-B-95-002
September 1995
Combined Sewer Overflows
Guidance For
Long-Term Control Plan
-------
EPA/832-B-95-002
August 1995
Combined Sewer Overflows
Guidance for Long-Term Control Plan
U.S. Environmental Protection Agency
Office of Wastewater Management
Washington, DC 20460
Recycled/Recyclable • Printed with Vegetable Based Inks on Recycled Paper (20% Postconsumer)
-------
NOTICE
The statements in this document are intended solely as guidance. This document
is not intended, nor can it be relied on, to create any rights enforceable by any
party hi litigation with the United States. EPA and State officials may decide to
follow the guidance provided in this document, or to act at variance with the
guidance, based on an analysis of specific site circumstances. This guidance may
be revised without public notice to reflect changes hi EPA's strategy for
implementation of the Clean Water Act and its implementing regulations, or to
clarify and update the text.
Mention of trade names or commercial products in this document does not
constitute an endorsement or recommendation for use.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
31 rags
OFFICE Of
MEMORANDUM WATER
SUBJECT: Guidance for Long Term Central 'Plan
FROM: Michael B. Cook,
Office of Wastewater Management (4201)
TO: Interested Parties
I am pleased to provide you with the Environmental
Protection Agency's (EPA's) guidance document on the development
and implementation of a long-term control plan for combined sewer
overflows (CSOs). This document is one of several being prepared
to foster implementation of EPA's CSO Control Policy. The CSO
Control Policy, issued on April 11, 1994, establishes a national
approach under the National Pollutant Discharge Elimination
System (NPDES) permit program for controlling discharges into the
nation's waters from combined sewer systems.
To facilitate implementation of the CSO Control Policy, EPA
is preparing guidance documents that can be used by NPDES
permitting authorities, affected municipalities, and their
consulting engineers in planning and implementing CSO controls
that will ultimately comply with the requirements of the Clean
Water Act.
This document has been prepared to provide guidance to
municipalities on how to develop a comprehensive long-term
control plan that recognizes the site specific nature of CSOs and
their impacts on receiving water bodies. The final plan should
include water quality based control measures that are technically
feasible, affordable, and consistent with the CSO Control Policy.
This guidance has been reviewed extensively within the
Agency as well as by municipal groups, environmental groups, and
other CSO stakeholders. I am grateful to all who participated in
its preparation and review, and believe that it will further the
implementation of the CSO Control Policy.
If you have any questions regarding the manual or its
distribution, please call Joseph Mauro in the Office of
Wastewater Management, at (202) 260-1140.
Recyctod/Racyctobte
Printed with Soy/Canol* Ink on paper *tt
contains at \aast 50% recycled fiber
-------
TABLE OF CONTENTS
Page
CHAPTER 1 INTRODUCTION 1-1
1.1 BACKGROUND 1-1
1.2 HISTORY OF THE CSO CONTROL POLICY 1-1
1.3 KEY ELEMENTS OF THE CSO CONTROL POLICY 1-3
1.4 GUIDANCE TO SUPPORT IMPLEMENTATION OF THE CSO
CONTROL POLICY 1-6
1.5 GOAL OF THIS GUIDANCE DOCUMENT 1-6
1.5.1 Target Audience 1-6
1.5.2 Document Organization 1-7
1.6 LONG-TERM PLANNING APPROACH SUMMARY 1-7
1.6.1 Initial Activities 1-10
1.6.2 Public Participation and Agency Interaction 1-12
1.6.3 Coordination with State Water Quality Standards Authority .... 1-13
1.6.4 Integration of Current CSO Control Efforts 1-15
1.6.5 Watershed Approach to CSO Control Planning 1-17
1.6.6 Small System Considerations 1-20
1.6.7 Sensitive Areas 1-21
1.6.8 Measures of Success 1-22
CHAPTER 2 SYSTEM CHARACTERIZATION 2-1
2.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION 2-1
2.2 OBJECTIVE OF SYSTEM CHARACTERIZATION 2-2
2.3 IMPLEMENTATION OF THE NINE MINIMUM CONTROLS 2-3
2.3.1 Existing Baseline Conditions 2-4
2.3.2 Summary of Minimum Controls 2-4
2.4 COMPILATION AND ANALYSIS OF EXISTING DATA 2-4
2.4.1 Watershed Mapping 2-7
2.4.2 Collection System Understanding 2-9
2.4.3 CSO and Non-CSO Source Characterization 2-9
2.4.4 Field Inspections 2-10
2.4.5 Receiving Water 2-11
2.5 COMBINED SEWER SYSTEM AND RECEIVING WATER
MONITORING 2-20
2.5.1 Monitoring Plan Development 2-20
2.5.2 Combined Sewer System Monitoring 2-21
2.5.2.1 Selection of Monitoring Stations 2-22
2.5.2.2 Frequency of Monitoring 2-24
2.5.2.3 Pollutant Parameters 2-25
2.5.2.4 Rainfall Monitoring and Analysis 2-26
2.5.2.5 CSO Flow Monitoring and Analysis 2-27
2.5.2.6 CSO Quality Sampling and Analysis 2-28
August 1995
-------
TABLE OF CONTENTS (Continued)
Page
2.5.3 Receiving Water Monitoring 2-29
2.5.3.1 Selection of Monitoring Stations 2-30
2.5.3.2 Extent of Monitoring 2-31
2.5.3.3 Pollutant Parameters 2-32
2.5.3.4 Hydraulic Monitoring and Analysis 2-32
2.5.3.5 Receiving Water Quality Monitoring and Analysis . . . 2-33
2.5.3.6 Sediment and Biological Monitoring and Analysis .... 2-34
2.6 COMBINED SEWER SYSTEM AND RECEIVING WATER
MODELING 2-48
2.6.1 Combined Sewer System Modeling 2-48
2.6.1.1 CSS Modeling Objectives 2-48
2.6.1.2 CSS Model Selection 2-50
2.6.1.3 CSS Model Application 2-53
2.6.2 Receiving Water Modeling 2-55
2.6.2.1 Receiving Water Modeling Objectives 2-55
2.6.2.2 Receiving Water Model Selection 2-56
2.6.2.3 Receiving Water Model Application 2-57
CHAPTER 3 DEVELOPMENT AND EVALUATION OF ALTERNATIVES
FOR CSO CONTROL 3-1
3.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION 3-1
3.2 LONG-TERM CONTROL PLAN APPROACH 3-3
3.2.1 Demonstration Versus Presumption Approach 3-3
3.2.1.1 Demonstration Approach 3-5
3.2.1.2 Presumption Approach 3-7
3.2.2 Small System Considerations 3-18
3.3 DEVELOPMENT OF ALTERNATIVES FOR CSO CONTROL 3-18
3.3.1 General Considerations 3-19
3.3.1.1 Interaction with Nine Minimum Controls 3-19
3.3.1.2 Interactions with Other Collection and Treatment
System Objectives 3-19
3.3.1.3 Creative Thinking 3-20
3.3.2 Definition of Water Quality and CSO Control Goals 3-21
3.3.3 Approaches to Structuring CSO Control Alternatives 3-24
3.3.3.1 Projects Common to All Alternatives 3-25
3.3.3.2 Outfall-Specific Solutions 3-25
3.3.3.3 Localized Consolidation of Outfalls 3-25
3.3.3.4 Regional Consolidation 3-26
3.3.3.5 Utilization of POTW Capacity and CSO-Related
Bypass 3-26
3.3.3.6 Consideration of Sensitive Areas 3-28
3.3.4 Goals of Initial Alternatives Development 3-29
ii August 1995
-------
TABLE OF CONTENTS (Continued)
Page
3.3.5 Identification of Control Alternatives 3-29
3.3.5.1 Source Controls 3-31
3.3.5.2 Collection System Controls 3-33
3.3.5.3 Storage Technologies 3-37
3.3.5.4 Treatment Technologies 3-38
3.3.6 Preliminary Sizing Considerations 3-39
3.3.7 Cost/Performance Considerations 3-41
3.3.8 Preliminary Siting Issues 3-47
3.3.9 Preliminary Operating Strategies 3-49
3.4 Evaluation of Alternatives for CSO Control 3-49
3.4.1 Project Costs 3-49
3.4.2 Performance 3-51
3.4.3 Cost/Performance Evaluations 3-55
3.4.4 Non-Monetary Factors 3-59
3.4.4.1 Environmental Issues/Impacts 3-59
3.4.4.2 Technical Issues 3-61
3.4.4.3 Implementation Issues 3-62
3.4.5 Rating and Ranking of Alternatives 3-63
3.5 Financial Capability 3-66
CHAPTER 4 SELECTION AND IMPLEMENTATION OF THE
LONG-TERM PLAN 4-1
4.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION 4-1
4.2 FINAL SELECTION AND DEVELOPMENT OF RECOMMENDED
PLAN 4-4
4.3 FINANCING PLAN 4-6
4.3.1 Capital Funding Options 4-6
4.3.1.1 Bonds 4-7
4.3.1.2 Loans 4-7
4.3.1.3 Grants 4-7
4.3.1.4 Privatization 4-8
4.3.1.5 Other Capital Funding Options 4-8
4.3.2 Annual Funding Options 4-8
4.3.3 Selection of Financing Method 4-9
4.4 IMPLEMENTATION SCHEDULE 4-9
4.5 OPERATIONAL PLAN 4-13
4.6 POST-CONSTRUCTION COMPLIANCE MONITORING 4-15
4.7 RE-EVALUATION AND UPDATE 4-16
REFERENCES R-l
GLOSSARY G-l
iii August 1995
-------
LIST OF EXHIBITS
Page
Exhibit 1-1. Roles and Responsibilities 1-5
Exhibit 1-2. Long-Term CSO Control Planning Approach 1-9
Exhibit 1-3. Example of a CSO Control Policy Implementation Timeline 1-11
Exhibit 1-4. Impact of CSO Program Improvements on System-Wide CSOs 1-16
Exhibit 1-5. Watershed-Based CSO Control Planning Approach for a Receiving
Water Segment 1-19
Exhibit 2-1. Summary of the Nine Minimum Controls 2-5
Exhibit 2-2. Data Types For CSO Planning 2-8
Exhibit 2-3. Lewiston-Auburn Location Plan 2-14
Exhibit 2-4. Watershed Characteristics in the City of Lewiston 2-15
Exhibit 2-5. Initial Water Resource Goals for Lewiston 2-16
Exhibit 2-6. Lewiston Watershed Data 2-18
Exhibit 2-7. Lewiston Source Input and Receiving Water Data 2-19
Exhibit 2-8. Screening of Final CSO Sampling and Monitoring Stations for the City
of Lewiston 2-39
Exhibit 2-9. Screening of Final CSO Sampling and Monitoring Stations for the
Auburn Sewerage District 2-40
Exhibit 2-10. Lewiston-Auburn CSO and Separate Storm Dram Monitoring and
Sampling Locations 2-41
Exhibit 2-11. Lewiston-Auburn Receiving Water Sampling Stations 2-43
Exhibit 2-12. Lewiston-Auburn CSO Quality Data 2-45
Exhibit 2-13. Lewiston-Auburn CSO Metals Data 2-45
Exhibit 2-14. Lewiston-Auburn Receiving Water E. Coli Data 2-47
Exhibit 2-15. Relevant CSS Hydraulic and Contaminant Transport Modeling for the
CSO Control Policy 2-51
Exhibit 3-1. An Example of Overflow Rates Versus Pollutant Removal During a Rainfall
Event 3-15
Exhibit 3-2. Typical Mass Diagram 3-44
Exhibit 3-3. Typical Representation of Interaction Between Storage and Treatment
Needs 3-45
Exhibit 3-4. Example Calculating Total Present Worth 3-52
Exhibit 3-5. Example of Cost-Performance Curves Indicating Impacts on Critical
Uses 3-56
Exhibit 3-6. Example of Cost-Performance Curve Indicating Removal of a Specific
Pollutant (fecal coliform bacteria) 3-57
Exhibit 3-7. Example Criteria for Rating Values 3-64
Exhibit 3-8. Example Matrix for Evaluating CSO Control Alternatives 3-65
Exhibit 3-9. Ranking CSO Technologies 3-76
Exhibit 3-10. Control Technologies Screening Summary 3-77
IV
August 1995
-------
LIST OF EXHIBITS (Continued)
Page
Exhibit 4-1. Example of Public Participation Program for Portland, Oregon, CSO
Management Program 4-2
Exhibit 4-2. Example of Phased Implementation Approach 4-12
Exhibit 4-3. Potential Implementation Responsibilities 4-14
August 1995
-------
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Combined sewer systems (CSSs) are wastewater collection systems designed to carry
sanitary sewage (consisting of domestic, commercial, and industrial wastewater) and storm water
(surface drainage from rainfall or snowmelt) in a single pipe to a treatment facility. CSSs serve
about 43 million people in approximately 1,100 communities nationwide. Most of these
communities are located in the Northeast and Great Lakes regions. During dry weather, CSSs
convey domestic, commercial, and industrial wastewater. In periods of rainfall or snowmelt,
total wastewater flows can exceed the capacity of the CSS and/or treatment facilities. When this
occurs, the CSS is designed to overflow directly to surface water bodies, such as lakes, rivers,
estuaries, or coastal waters. These overflows—called combined sewer overflows (CSOs)—can
be a major source of water pollution in communities served by CSSs.
Because CSOs contain untreated domestic, commercial, and industrial wastes, as well as
surface runoff, many different types of contaminants can be present. Contaminants may include
pathogens, oxygen-demanding pollutants, suspended solids, nutrients, toxics, and floatable
matter. Because of these contaminants and the volume of the flows, CSOs can cause a variety
of adverse impacts on the physical characteristics of surface water, impair the viability of aquatic
habitats, and pose a potential threat to drinking water supplies. CSOs have been shown to be
a major contributor to use impairment and aesthetic degradation of many receiving waters and
have contributed to shellfish harvesting restrictions, beach closures, and even occasional fish
kills.
1.2 HISTORY OF THE CSO CONTROL POLICY
Historically, the control of CSOs has proven to be extremely complex. This complexity
stems partly from the difficulty in quantifying CSO impacts on receiving water quality and the
site-specific variability in the volume, frequency, and characteristics of CSOs. In addition, the
financial considerations for communities with CSOs can be significant. The U.S. Environmental
1-1 August 1995
-------
Chapter 1 Introduction
Protection Agency (EPA) estimates the CSO abatement costs for the 1,100 communities served
by CSSs to be approximately $41.2 billion.
To address these challenges, EPA's Office of Water issued a National Combined Sewer
Overflow Control Strategy on August 10, 1989 (54 Federal Register 37370). This Strategy
reaffirmed that CSOs are point source discharges subject to National Pollutant Discharge
Elimination System (NPDES) permit requirements and to Clean Water Act (CWA) requirements.
The CSO Strategy recommended that all CSOs be identified and categorized according to their
status of compliance with these requirements. It also set forth three objectives:
• Ensure that if CSOs occur, they are only as a result of wet weather
• Bring all wet weather CSO discharge points into compliance with the technology-
based and water quality-based requirements of the CWA
• Minimize the impacts of CSOs on water quality, aquatic biota, and human health.
In addition, the CSO Strategy charged all States with developing state-wide permitting strategies
designed to reduce, eliminate, or control CSOs.
Although the CSO Strategy was successful in focusing increased attention on CSOs, it
fell short in resolving many fundamental issues. In mid-1991, EPA initiated a process to
accelerate implementation of the Strategy. The process included negotiations with
representatives of the regulated community, State regulatory agencies, and environmental groups.
These negotiations were conducted through the Office of Water Management Advisory Group.
The initiative resulted in the development of a CSO Control Policy, which was published in the
Federal Register on April 19, 1994 (59 Federal Register 18688). The intent of the CSO Control
Policy is to:
• Provide guidance to permittees with CSOs, NPDES permitting and enforcement
authorities, and State water quality standards (WQS) authorities
1-2 August 1995
-------
Chapter 1 Introduction
• Ensure coordination among the appropriate parties in planning, selecting, designing,
and implementing CSO management practices and controls to meet the requirements
of the CWA
• Ensure public involvement during the decision-making process.
The CSO Control Policy contains provisions for developing appropriate, site-specific
NPDES permit requirements for all CSSs that overflow due to wet weather events. It also
announces an enforcement initiative that requires the immediate elimination of overflows that
occur during dry weather and ensures that the remaining CWA requirements are complied with
as soon as possible.
1.3 KEY ELEMENTS OF THE CSO CONTROL POLICY
The CSO Control Policy contains four key principles to ensure that CSO controls are
cost-effective and meet the requirements of the CWA:
• Provide clear levels of control that would be presumed to meet appropriate health and
environmental objectives
• Provide sufficient flexibility to municipalities, especially those that are financially
disadvantaged, to consider the site-specific nature of CSOs and to determine the most
cost-effective means of reducing pollutants and meeting CWA objectives and
requirements
• Allow a phased approach for implementation of CSO controls considering a
community's financial capability
• Review and revise, as appropriate, WQS and their implementation procedures when
developing long-term CSO control plans to reflect the site-specific wet weather
impacts of CSOs.
1-3 August 1995
-------
Chapter 1 Introduction
In addition, the CSO Control Policy clearly defines expectations for permittees, State
WQS authorities, and NPDES permitting and enforcement authorities. These expectations
include the following:
• Permittees should immediately implement the nine minimum controls (NMC), which
are technology-based actions or measures designed to reduce CSOs and then* effects
on receiving water quality, as soon as practicable but no later than January 1, 1997.
• Permittees should give priority to environmentally sensitive areas.
• Permittees should develop long-term control plans (LTCPs) for controlling CSOs.
A permittee may use one of two approaches: 1) demonstrate that its plan is adequate
to meet the water quality-based requirements of the CWA ("demonstration
approach"), or 2) implement a minimum level of treatment (e.g., primary
clarification of at least 85 percent of the collected combined sewage flows) that is
presumed to meet the water quality-based requirements of the CWA, unless data
indicate otherwise ("presumption approach").
• WQS authorities should review and revise, as appropriate, State WQS during the
CSO long-term planning process.
• NPDES permitting authorities should consider the financial capability of permittees
when reviewing CSO control plans.
Exhibit 1-1 illustrates the roles and responsibilities of permittees, NPDES permitting and
enforcement authorities, and State WQS authorities.
In addition to these key elements and expectations, the CSO Control Policy also addresses
important issues such as ongoing or completed CSO control projects, public participation, small
communities, and watershed planning.
1-4 August 1995
-------
Chapter 1
Introduction
Exhibit 1-1. Roles and Responsibilities
Permittee
NPDES Permitting Authority
NPDES Enforcement Authority
State WQS Authorities
• Evaluate and implement NMC
• Submit documentation of NMC
implementation by January 1, 1997
• Develop LTCP and submit for
review to NPDES permitting
authority
• Support the review of WQS in
CSO-impacted receiving water
bodies
• Comply with permit conditions
based on narrative WQS
• Implement selected CSO controls
from LTCP
• Perform post-construction
compliance monitoring
• Reassess overflows to sensitive
areas
• Coordinate all activities with
NPDES permitting authority, State
WQS authority, and State
watershed personnel
• Reassess/revise CSO permitting
strategy
• Incorporate into Phase I permits
CSO-related conditions (e.g.,
NMC implementation and
documentation and LTCP
development)
• Review documentation of NMC
implementation
• Coordinate review of LTCP
components throughout the LTCP
development process and
accept/approve permittee's LTCP
• Coordinate the review and revision
of WQS as appropriate
• Incorporate into Phase n permits
CSO-related conditions (e.g.,
continued NMC implementation
and LTCP implementation)
• Incorporate implementation
schedule into an appropriate
enforceable mechanism
• Review implementation activity
reports (e.g., compliance schedule
progress reports)
Ensure that CSO requirements and
schedules for compliance are
incorporated into appropriate
enforceable mechanisms
Monitor adherence to January 1,
1997, deadline for NMC
implementation and documentation
Take appropriate enforcement
action against dry weather
overflows
Monitor compliance with Phase I,
Phase n, and post-Phase n permits
and take enforcement action as
appropriate
• Review WQS in CSO-impacted
receiving water bodies
• Coordinate review with LTCP
development
• Revise WQS as appropriate:
Development of site-specific
criteria
Modification of designated use to
- Create partial use reflecting
specific situations
- Define use more explicitly
Temporary variance from WQS
1-5
August 1995
-------
Chapter 1 Introduction
1.4 GUIDANCE TO SUPPORT IMPLEMENTATION OF THE CSO CONTROL
POLICY
To help permittees and NPDES permitting and WQS authorities implement the provisions
of the CSO Control Policy, EPA is developing the following guidance documents:
• Combined Sewer Overflows—Guidance for Long-Term Control Plan (EPA, 1995a)
• Combined Sewer Overflows—Guidance for Nine Minimum Controls (EPA, 1995b)
• Combined Sewer Overflows—Guidance for Screening and Ranking (EPA, 1995c)
• Combined Sewer Overflows—Guidance for Monitoring and Modeling (EPA, 1995d)
• Combined Sewer Overflows—Guidance for Financial Capability Assessment (EPA,
1995e)
• Combined Sewer Overflows—Guidance for Funding Options (EPA, 1995f)
• Combined Sewer Overflows—Guidance for Permit Writers (EPA, 1995g)
• Combined Sewer Overflows—Questions and Answers on Water Quality Standards and
the CSO Program (EPA, 1995h).
1.5 GOAL OF THIS GUIDANCE DOCUMENT
The main goal of this document is to provide technical support to assist municipalities
hi the development of technically feasible, affordable, and comprehensive LTCPs consistent with
the objectives of the CSO Control Policy.
1.5.1 Target Audience
The primary audience of this document is municipal officials who are developing LTCPs.
This document might be of particular benefit to small and medium-sized municipalities, which
might not have access to the resources and expertise available to larger municipalities. A
secondary audience is EPA and State officials, as well as NPDES permit writers, who can refer
to this document when reviewing and evaluating LTCPs. Although the document presents the
engineering concepts required for the preparation of certain aspects of the LTCPs, it has been
written for the non-engineer.
1-6 August 1995
-------
Chapter 1 Introduction
Certain aspects of EPA's CSO Control Policy are explained in more detail in other
guidance documents. This LTCP guidance document summarizes information from those
documents, where appropriate. It emphasizes the role of public participation and agency
interaction, the use of monitoring and modeling data to develop and evaluate CSO control
strategies, and the role of financial capability in the selection and implementation of CSO
controls.
1.5.2 Document Organization
Chapter 2 describes the characterization of the CSS, including the analysis of existing
data and system monitoring and modeling, establishment of the existing baseline conditions, and
integration of the NMC with the LTCP. Chapter 2 also includes a case study that documents
how a CSO community characterized its system. Chapter 3 presents methodologies for the
development and evaluation of CSO control alternatives. It discusses the role of public
participation, the "presumption" and "demonstration" approaches to developing alternatives,
identification of CSO control goals and alternatives to achieve those goals, and other aspects of
alternatives development, such as preliminary sizing, cost/performance considerations, siting
issues, and operating strategies. The chapter concludes with two case studies describing the
development and evaluation of CSO control alternatives. Chapter 4 discusses the final step of
the LTCP: the selection and implementation of the long-term controls. This step includes
development of an operational plan, identification of financing options and funding sources,
development of the implementation schedule and post-construction compliance monitoring
program, and re-evaluation and update of the final plan.
1.6 LONG-TERM PLANNING APPROACH SUMMARY
The overall planning approach consists of three major steps: system characterization,
development and evaluation of alternatives, and selection and implementation of the controls.
Each of these steps is discussed separately and in detail in subsequent chapters. The remainder
of this section provides general guidance on developing the program structure, which
municipalities usually need to proceed with the various aspects of the LTCP. Section 1.6 also
1-7 August 1995
-------
Chapter 1 Introduction
introduces several key topics that EPA feels are critical in developing an LTCP consistent with
the CSO Control Policy.
The CSO Control Policy lists nine elements that should be addressed as appropriate in
either one, or all three steps of the overall planning approach. Public participation should be
addressed in all three steps, for example, while an implementation schedule might be addressed
in two of the steps.
As listed in the Policy, the nine elements of the LTCP are:
1. Characterization, monitoring, and modeling activities as the basis for selection
and design of effective CSO controls
2. A public participation process that actively involves the affected public in the
decision-making to select long-term CSO controls
3. Consideration of sensitive areas as the highest priority for controlling overflows
4. Evaluation of alternatives that will enable the permittee, in consultation with the
NPDES permitting authority, WQS authority, and the public, to select CSO
controls that will meet CWA requirements
5. Cost/performance considerations to demonstrate the relationships among a
comprehensive set of reasonable control alternatives
6. Operational plan revisions to include agreed-upon long-term CSO controls
7. Maximization of treatment at the existing POTW treatment plant for wet
weather flows
8. An implementation schedule for CSO controls
9. A post-construction compliance monitoring program adequate to verify
compliance with water quality-based CWA requirements and ascertain the
effectiveness of CSO controls.
Exhibit 1-2 presents the recommended planning approach described in this document,
along with cross-references to the appropriate chapters of this document and sections of the CSO
Control Policy. The planning approach is generally intended to be followed sequentially;
1-8 August 1995
-------
Program Activities
I
Initiate Interaction
with Permitting
Authorities
I
Create Public
Review Committee
I
Refine Site-Specific
Program Goals
I
Conduct Public
Review
Interact
with Permitting
Authorities
Develop
Implementation
Schedule
I
Develop
Post-Construction
Compliance Monitoring
Program
Technical Activities
CSO Policy Sections
Final CSO Policy
Issued
Initiate Program
i
o
i
1. Introduction
II C.2. Public Participation
II.C.3. Consideration of Sensitive Areas
, III.B. Coordination with WQS
L
Conduct System
Characterization
• Analysis of Existing Data
• Monitoring
• Modeling
Assess, Implement,
and Evaluate Nine
Minimum Controls
Develop Long-Term
Control Plan Approach
Identify Water
Quality Goals and
CSO Control Goals
\tity Me
Identify Measures
to Meet CSO
Control Goals
I
Develop Alternatives
I
Evaluate Alternatives
Select and
Develop Long-term
Control Plan
I
Develop
Operational Plan
I
Determine
Financing
Re-Evaluate and
Update Plan
Conduct Post-
Construction
Compliance Monitoring
II.C.1. Characterization, Monitoring, and
Modeling of the CSS
II.B. Implementation of Nine
Minimum Controls
o
II.C. 4.a. Presumption Approach
II. C.4. b. Demonstration Approach
II. C.3. Consideration of Sensitive Areas
II. C. 4. Evaluation of Alternatives
III. B. WQS Reviews
II.C.7. Maximizing Treatment at POTW
II.C.4. Evaluation of Alternatives
II.C.5. Cost/Performance Considerations
o
II.C.6. Operational Plan
II.C.8. Implementation Schedule
II.C.9. Post-Construction
Compliance Monitoring Program
Exhibit 1-2. Long-Term CSO Control Planning Approach
1-9
-------
Chapter 1 Introduction
however, it can be altered depending on specific circumstances (e.g., municipalities with limited
combined systems or municipalities that have already conducted efforts to control CSOs may
select a different approach). Exhibit 1-2 distinguishes program activities from technical
activities. Program activities are tasks that will provide overall program structure, coordination,
and management; technical activities are the specific engineering tasks necessary to develop the
LTCP. Although the planning approach described in this document is intended to address CSOs,
it might also include information needed to address other pollution sources, such as storm water
and nonpoint sources.
The CSO Control Policy encourages municipalities to develop, and permit writers to
evaluate, LTCPs on a watershed management basis (see Section 1.6.5). Municipalities should
try to evaluate all sources of pollution (e.g., point sources, CSOs, storm water, CSOs) during
system characterization (Chapter 2) and, wherever possible, develop control strategies on a
watershed basis in coordination with the NPDES permitting authority.
Exhibit 1-3 provides an example of a typical CSO Control Policy implementation
timeline. As noted in the CSO Control Policy, municipalities should develop and submit their
LTCPs "...as soon as practicable, but generally within two years after the date of the NPDES
permit provision, Section 308 information request, or enforcement action requiring the permittee
to develop the plan" (II.C). As illustrated in Exhibit 1-3, however, "NPDES authorities may
establish a longer timetable for completion of the long-term CSO control plan on a case-by-case
basis to account for site-specific factors which may influence the complexity of the planning
process" (II.C).
1.6.1 Initial Activities
An important first step is development of an administrative structure for CSO control
planning. This involves organizing a CSO program team; establishing communication,
coordination, and control procedures for team members and other participants; identifying tasks
and associated resource needs; and scheduling tasks.
1-10 August 1995
-------
ACTIVITY
TIME
National CSO Control Policy Issued
Re-Evaluation of State Strategies
and CSO Permitting Priorities
Permit Issuance/Reissuance,
308 Issuance, Administrative Order to.
Require LTCP and Documentation
of Nine Minimum Controls
CSO System Characterization
and Monitoring
Documentation of Nine Minimum
Controls
Implementation of Nine Minimum
Controls
Development of LTCP
Selection of LTCP/Development of
Operational Plan
Review of LTCP and WQS
Review/Revision
Review of LTCP and Development
of Draft Phase II Permit
Final Phase II Permit Issued
Enforcement Order Issued
(if applicable)
iiiiiiiiiiiiiiiniii
LEGEND
niiiiiiiii NPDES Permitting Authority
——— Municipality Activity
• •—• — Ongoing Throughout Project
Extension Considered by
NPDES Permitting
Authorities on Case-by-Case
Basis
iiiiiiiiiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiii
X
X
Exhibit 1-3. Example of a CSO Control Policy Implementation Timeline
1-11
-------
Chapter 1 Introduction
The program team should include all entities who have a stake in the program outcome,
and it should be sufficiently multidisciplinary to address the myriad of engineering, economic,
environmental, and institutional issues that will be raised during the development of the LTCP.
The team generally will have to prepare a plan for funding the program and will develop a
program for public information, education, and involvement.
The team should contain municipal personnel such as public works, wastewater treatment
plant operations, and engineering personnel, as well as parks, conservation, and other officials
involved in such issues as utilities, land use and zoning, development review, and environmental
issues. It should include Federal and State regulatory officials, local political officials, and the
general public, including rate payers and environmental interests. Depending on the size and
complexity of the program, private consulting resources might also be necessary.
The municipality also should establish management tasks such as estimating, forecasting,
budgeting, and controlling costs; planning, estimating, and scheduling program activities;
developing and evaluating quality control practices; and developing and controlling the program
scope. Some municipalities already have project management and control procedures in place;
in other cases, particularly where several agencies are involved, it is appropriate to develop
management tasks specifically for the CSO control program.
1.6.2 Public Participation and Agency Interaction
Establishing early communication with both the public and regulatory agencies is an
important first step in the long-term planning approach and crucial to the success of a CSO
control program. The importance of public participation is stressed in the CSO Control Policy:
"In developing its long-term CSO control plan, the permittee will employ a public participation
process that actively involves the affected public in the decision-making to select the long-term
CSO controls" (II.C.2). Given the potential for significant expenditures of public funds for CSO
control, public support is key to CSO program success. By informing the public early in the
planning process about the scope and goals of the program and continuing public involvement
during development, evaluation, and selection of the control strategy, issues and potential
1-12 August 1995
-------
Chapter 1 Introduction
conflicts can be identified and addressed more expeditiously, minimizing the potential for
prolonged delay or additional cost.
Citizen Advisory Committees (CACs) can serve as liaisons among municipal officials,
NPDES permitting agencies, and the general public. Public meetings and public hearings can
provide an effective forum to present technical information and obtain input from interested
individuals and organizations. It is worthwhile to gage public acceptance of potential CSO
alternatives before completing the engineering evaluation of each alternative and to incorporate
input from the public meetings into the selection of a recommended plan. Impacts on user fees
and tax rates are also important to communicate as early as possible in the LTCP development.
After the municipality has selected a recommended plan, public involvement will continue to be
useful. Particular attention should be given to informing residents and businesses that would be
affected by any construction associated with project implementation.
If Federal or State funding is involved, the municipality might be required to submit a
work plan to the regulatory agency. The work plan should include an approach for public
participation. Public participation requirements for Federal- or State-funded projects are given
in 40 CFR Part 25.
The CSO Control Policy emphasizes that "State WQS authorities, NPDES authorities,
EPA regional offices and permittees should meet early and frequently throughout the long-term
planning process" (III.A). It also describes several issues involving regulatory agencies that
could affect the development of the LTCP, including the review and appropriate revision of
water quality standards (WQS) and agreement on the data, analyses, monitoring, and modeling
necessary to support the development of the LTCP.
1.6.3 Coordination with State Water Quality Standards Authority
A primary objective of the LTCP is to develop and evaluate a range of CSO control
alternatives sufficient to meet WQS, including attainment and protection of designated uses on
CSO-impacted receiving waters. To ensure that the LTCP meets this objective, State WQS
1-13 August 1995
-------
Chapter 1 Introduction
authorities should be involved early in the LTCP development process. This will give
participants an opportunity to review the proposed nature and extent of data and information to
be collected during LTCP development. Such data and information can be used in assessing the
attainability of the designated uses (through a use attainability analysis) and possibly revisiting
designated use classifications for the CSO-impacted waters (e.g., by defining uses more
precisely).
The CSO Control Policy recognizes that the review and appropriate revision of WQS is
an integral part of LTCP development, and describes the options available to States ". . . to
adapt their WQS, and implementation procedures to reflect site-specific conditions including
those related to CSOs" (III.B). Such options include:
Adopting partial uses to reflect situations where a significant storm event precludes
the use from occurring
Adopting seasonal uses to reflect that certain uses do not occur during certain seasons
(e.g., swimming does not occur in winter)
Defining a use with greater specificity (e.g., warm-water fishery in place of aquatic
life protection); or
Granting a temporary variance to a specific discharger in cases where maintaining
existing standards for other dischargers is preferable to downgrading WQS.
Whenever such changes are proposed, the State must ensure downstream uses are protected, and
other uses not affected by the storm or season are protected. The State must also ensure that
the quality of the water is improved or protected.
EPA encourages States with CSOs to work within their current regulatory framework,
using existing flexibility to consider wet weather conditions in reviewing then" WQS.
Early in the process, the municipality should identify data needs, monitoring protocols,
and models for system characterization, as well as develop a compliance monitoring program.
The water quality impacts of the existing CSOs can then be evaluated to establish the existing
1-14 August 1995
-------
Chapter 1 Introduction
baseline condition against which the effectiveness of the selected CSO controls can be measured,
and to predict whether or not WQS will be attained after LTCP implementation. If this
information indicates that WQS are not likely to be attained after LTCP implementation, it can
be used to identify additional CSO control alternatives necessary to attain WQS or to determine
whether non-CSO sources of pollution are contributing to nonattainment. A TMDL could be
used to evaluate more stringent controls on non-CSO dischargers for the receiving water and
pollutant(s) of concern.
Municipalities and States should share and coordinate information with other
municipalities within the same watershed. This information, along with storm water and other
point and nonpoint source data, provides an opportunity for NPDES permitting authorities and
permittees to implement a comprehensive watershed management approach, including TMDLs.
This same information also provides an opportunity for municipalities to coordinate the
development and implementation of their individual LTCPs with one another.
1.6.4 Integration of Current CSO Control Efforts
Some municipalities have already begun, and perhaps completed, CSO abatement
activities. In these cases, "...portions o/[the] Policy may not apply, as determined on a case
by case basis..." (I.C). The CSO Control Policy outlines three such scenarios: (1) municipalities
that have completed or substantially completed construction of CSO facilities, (2) municipalities
that have developed or are implementing a CSO control program pursuant to an existing permit
or enforcement order, and (3) municipalities that have constructed CSO facilities but have failed
to meet applicable WQS. Municipalities that fall under these scenarios should coordinate with
their NPDES permitting authorities to determine the scope of the required long-term planning
activities.
In cases where significant work has been conducted, municipalities would present an
overview of their programs to illustrate the impact of CSO improvements on a system-wide
basis. Exhibit 1-4 presents an example of an assessment of existing and future CSO controls.
In this example, system characterization was completed in 1989 and the system improvements
1-15 August 1995
-------
4.0-
(D
E
I?
3.0-
2 (0
•c o>
5 c
1.0-
Historical
System Improvements
Initiate Implementation
of 6 Minimum Controls
Complete
Implementation of
9 Minimum Controls
Actual
Predicted
Implement/Construct
Long-Term Controls
1989
1994
1999
2020
Exhibit 1-4. Impact of CSO Program Improvements on System- Wide CSOs
1-16
-------
Chapter 1 Introduction
shown as taking place between 1989 and 1999 include both minimum controls and other actions,
such as collection system and POTW improvements and upgrades, that will result in CSO
control.
1.6.5 Watershed Approach to CSO Control Planning
The CSO Control Policy acknowledges the importance of watershed planning in the long-
term control of CSOs by encouraging the permit writer "...to evaluate water pollution control
needs on a watershed management basis and coordinate CSO control efforts with other point and
nonpoint source control activities" (I.B). The watershed approach is also discussed in the section
of the CSO Control Policy addressing the demonstration approach to CSO control (II.B.4.b; see
also Chapter 3 of this document), which, in recommending that NPDES permitting authorities
allow a demonstration of attainment of WQS, provides for consideration of natural background
conditions and pollution sources other than CSOs, promoting the development of total maximum
daily loads (TMDLs).
EPA's Office of Water is committed to supporting States that want to implement a
comprehensive statewide watershed management approach. EPA has convened a Watershed
Management Policy Committee, consisting of senior managers, to oversee the reorientation of
all EPA water programs to support watershed approaches.
Of particular importance to CSO control planning and management is the NPDES
Watershed Strategy (EPA, 1994b). This strategy outlines national objectives and implementation
activities to integrate the NPDES program into the broader watershed protection approach. The
Strategy also supports the development of statewide basin management as part of an overall
watershed management approach. Statewide basin management is an overall framework for
integrating and coordinating water resource management efforts basin-by-basin throughout an
entire State. This will result in development and implementation of basin management plans that
meet stated environmental goals.
1-17 August 1995
-------
Chapter 1 Introduction
The sources of watershed pollution and impairment, in addition to CSOs, are varied and
include other point source discharges; discharges from storm drains; overland runoff; habitat
destruction; land use activities, such as agriculture and construction; erosion; and septic systems
and landfills. The benefits to implementing a watershed approach are significant and include:
• Consideration of all important sources of pollution or impairment
• Closer ties to receiving water benefits
• Greater flexibility
• Greater cost effectiveness (through coordination of monitoring programs, for
example)
• Fostering of prevention as well as control
• Fairer allocation of resources and responsibilities.
The major advantage in using a watershed-based approach to develop an LTCP is that
it allows the site-specific determination of the relative impacts of CSOs and non-CSO sources
of pollution on water quality. For some receiving water reaches within a watershed, CSOs could
well be less significant contributors to nonattainment than storm water or upstream sources. In
such cases, a large expenditure on CSO control could result in negligible improvement in water
quality.
Exhibit 1-5 outlines a conceptual framework for conducting CSO planning in a watershed
context. This approach can be used to identify CSO controls for each receiving water segment
based on the concepts of watershed management and use attainability.
The first activity in the process is to define baseline conditions, including WQS and
receiving water quality, and to delineate the watershed. The receiving water assessment includes
consideration of the major sources of pollutant loads in the watershed: CSOs, storm water
discharges, agricultural loads, and other point sources. Using information from an assessment
of baseline receiving water conditions, a range of water quality goals for each receiving water
1-18 August 1995
-------
fi
0>
Q.
0)
DC
,
O
Define baseline (WQS, source flows/
loads, receiving water quality) and
delineate watershed
Identify and notify stakeholders
Develop water quality goals
Identify areas of nonattainment and
other water quality concerns
Identify CSO and non-CSO sources
of pollution causing concerns
Develop corrective action plan
and/or TMDL
Evaluate, select, and implement CSO
and non-CSO controls
Assess effectiveness
Exhibit 1-5. Watershed-Based CSO Control Planning Approach for a Receiving Water Segment
1-19
-------
Chapter 1 Introduction
segment is established. At this stage of the planning approach, all affected stakeholders should
be notified.
The next step in this approach is to first identify the overall watershed concerns, and then
prioritize the cause or causes for each specific problem. The flows and loads from the pollutant
sources are estimated from modeled flows generated for various hydrologic conditions and from
pollutant concentrations generated from statistical analyses of available site-specific data. In the
approach illustrated in Exhibit 1-5, a receiving water model would be used to assess the impact
of CSOs and storm water on selected receiving water segments and to quantify the impacts of
CSO sources only, storm water and upstream sources only, and a combination of CSO, storm
water, and upstream sources on the attainment of WQS for each segment. It is possible that in
several receiving water segments, pollution contributed by CSOs will be only a fraction of the
total pollutant loads from other sources. In these segments, even complete elimination of CSOs
would not achieve the water quality goals because the other sources prevent the attainment of
beneficial uses. The CSO control goals are developed under the assumption that if the other
sources were remediated by the appropriate responsible parties, then the CSO control goals
would be stringent enough for water quality goals to be met.
Once CSO control goals to achieve the water quality goals in each receiving water
segment are established, engineering and hydraulic analyses are conducted to develop, evaluate,
and select a corrective action plan. Following the implementation of the CSO and non-CSO
controls, their effectiveness must be assessed. In some cases, implementation of CSO and non-
CSO controls might require a phased approach, whereby the process illustrated in Exhibit 1-5
could repeat itself over several cycles.
1.6.6 Small System Considerations
As EPA acknowledged in the CSO Control Policy, compliance with the scope of the
LTCP may be difficult for some small combined sewer systems. For this reason, "At the
discretion of the NPDES Authority, jurisdictions with populations under 75,000 may not need to
complete each of the formal steps outlined in Section II.C. of the Policy...." (I.D). At a
1-20 August 1995
-------
Chapter 1 Introduction
minimum, however, all small municipalities should be required to develop LTCPs that will
provide for the attainment of WQS and that include the following elements:
• Implementation of the NMC (II.B)
• Public participation (II.C.2)
• Consideration of sensitive areas (II.C.3)
• Post-construction compliance monitoring program (II.C.9).
A municipality with a population less than 75,000 should consult with both the NPDES
permitting and WQS authorities to ensure that its LTCP addresses the elements noted above and
can show that the CSO control program will meet the objectives of the CWA.
1.6.7 Sensitive Areas
In accordance with the CSO Control Policy, municipalities should give highest priority
to controlling overflows to receiving waters considered sensitive. As part of developing the
LTCP, municipalities should be required to identify all sensitive water bodies and the CSO
outfalls that discharge to them. The designated beneficial uses of the receiving water bodies will
help identify sensitive areas (EPA, 1995g). Sensitive areas are identified by the NPDES
authority, in coordination with other State and Federal agencies as appropriate. According to
the CSO Control Policy, sensitive areas include:
• Outstanding National Resource Waters
• National Marine Sanctuaries
• Waters with threatened or endangered species or their designated critical habitat
• Primary contact recreation waters, such as bathing beaches
• Public drinking water intakes or their designated protection areas
• Shellfish beds.
In accordance with the CSO Control Policy, the LTCP should give highest priority to the
prohibition of new or significantly increased overflows (whether treated or untreated) to
1-21 August 1995
-------
Chapter 1 Introduction
designated sensitive areas. If physically possible and economically achievable, existing
overflows to sensitive areas should be eliminated or relocated unless elimination or relocation
creates more environmental impact than continued discharge (with additional treatment necessary
to meet WQS) to the sensitive area.
1.6.8 Measures of Success
As municipalities, NPDES permitting authorities, and the public embark on a coordinated
effort to address CSOs, serious consideration should be given to "measures of success." For
purposes of this discussion, measures of success are objective, measurable, and quantifiable
indicators that illustrate trends and results over time. Measures of success generally fall into
four categories:
• Administrative measures that track programmatic activities;
• End-of-pipe measures that show trends in the discharge of CSS flows to the receiving
water body, such as reduction of pollutant loadings, the frequency of CSOs, and the
duration of CSOs;
• Receiving water body measures that show trends of the conditions in the water body
to which the CSO occurs, such as trends in dissolved oxygen levels and sediment
oxygen demand; and
• Ecological, human health, and use measures that show trends in conditions relating
to the use of the water body, its effect on the health of the population that uses the
water body, and the health of the organisms that reside in the water body, including
beach closures, attainment of designated uses, habitat improvements, and fish
consumption advisories. Such measures would be coordinated on a watershed basis
as appropriate.
EPA's experience has shown that measures of success should include a balanced mix of
measures from each of the four categories.
As municipalities begin to collect data and information on CSOs and CSO impacts, they
have an important opportunity to establish a solid understanding of the "baseline" conditions and
to consider what information and data are necessary to evaluate and demonstrate the results of
1-22 August 1995
-------
Chapter 1 ^^ Introduction
CSO control. Municipalities and NPDES permitting authorities should agree early in the
planning stages on the data and information that will be used to measure success.
The following list presents examples of potential measures of success for CSO control,
organized by the four categories discussed above:
• Administrative measures:
Number of NPDES permits or other enforceable mechanisms requiring
implementation of the NMC
- Number of NPDES permits or other enforceable mechanisms issued requiring
development of LTCPs
Number of municipalities meeting technology-based requirements in permits
- Number of municipalities meeting water quality-based requirements in permits
- Compliance rates with CSO requirements in permits
- Dollars spent/committed for CSO control measures
- Nature and extent of CSO controls constructed/implemented.
• End-of-pipe measures:
- Number of dry weather overflows eliminated
- Number of CSO outfalls eliminated
- Reduction in frequency of CSOs
- Reduction in volume of CSOs
- Reduction in pollutant loadings (conventional and toxics) in CSOs.
• Receiving water body measures:
- Reduced in-stream concentrations of pollutants
- Attainment of narrative or numeric water quality criteria.
• Ecological, human health, and use measures:
- Improved access to water resources
- Reduced flooding and drainage problems
- Reduced costs and treatment of drinking water
- Economic benefits (e.g., value of increased tourism, value of shellfish harvested
from beds previously closed)
Restored habitat
- Improved biodiversity indices
- Reduction in beach closures
Reduction in fish consumption advisories.
1-23 August 1995
-------
Chapter 1 Introduction
(Note: These measures are included as examples only; EPA is supporting the
development of national measures of success for CSOs through a cooperative agreement
with the Association of Metropolitan Sewerage Agencies (AMSA). The results of
AMSA's efforts are expected to be available in late 1995.)
When establishing CSO measures of success, municipalities and NPDES permitting
authorities should consider a number of important factors:
• Data quality and reproducibility—Can consistent and comparable data be collected
that allow for comparison over time (e.g., trend analysis) and from different sources
(e.g., watershed analysis)? Do standard data collection procedures exist?
• Costs—What is the cost of collecting and analyzing the information?
• Comprehensibility to the public—Will the public understand and agree with the
measures?
• Availability—Is it reasonably feasible for the data to be collected?
• Objectivity—Would different individuals evaluate the data or information similarly,
free from bias or subjectivity?
• Other uses in wet-weather and watershed planning and management—Can the
data be used by State agencies as support for other CSO and watershed planning
efforts?
Careful selection, collection, analysis, and presentation of information related to measures
of success should allow municipalities, States, and EPA to demonstrate the benefits and long-
term successes of CSO control efforts. Notwithstanding the effort to develop national measures
of success, municipalities should identify measures, document baseline conditions, and collect
appropriate information that demonstrates the cause and effect of CSO impacts and the benefits
and success of CSO control. It is likely that measures of success will vary from municipality
to municipality and will be determined by the environmental impacts of CSOs on site-specific
basis.
1-24 August 1995
-------
CHAPTER!
SYSTEM CHARACTERIZATION
Once the administrative structure for long-term combined sewer overflow (CSO) control
planning has been established, characterization of the combined sewer system (CSS) and
receiving water should begin. System characterization includes analysis of existing data and
monitoring and modeling of the CSS and receiving water.
Chapter 2 focuses on the establishment of existing baseline conditions. The objective of
this chapter is to provide an overview of how the components of the system characterization
contribute to LTCP development. As a prelude to the description of the technical activities that
make up the system characterization, this chapter discusses the importance of input from the
public and the appropriate regulatory agencies during LTCP development and integration of the
nine minimum controls (NMC) with the LTCP. The chapter includes a case study documenting
the watershed approach to system characterization used by a small CSO municipality. Combined
Sewer Overflows—Guidance for Monitoring and Modeling (EPA, 1995d) contains a more
comprehensive description of these components.
2.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION
Public participation and agency interaction facilitate system characterization. The public
participation effort might involve public meetings at key points during the system
characterization phase of the control plan development process. For example, meetings could
be held to discuss the scope of the various technical activities that make up the system
characterization, identification and consideration of the different watershed systems in the
analysis of existing data and development of the monitoring and modeling programs,
identification and status of implementation of the NMC, and the process for evaluating
alternative CSO controls. The municipality could present the following information to the public
as it is developed during system characterization:
• Scope of monitoring and assessment programs for system characterization
2-1 August 1995
-------
Chapter 2 System Characterization
• The watershed approach to CSO control planning
• Identification of watersheds in the CSO area
• Identification and quantification of non-CSO sources
• Existing sewer system conditions and problems (e.g., flooding, basement backups)
• Quantification of CSO flows and loads and impacts of CSOs on receiving waters
• Results of CSS and receiving water monitoring programs
• Development and calibration of the CSS and receiving water models
• Identification and implementation status of the NMC
• Process for evaluating alternatives.
Input from the public, obtained during the early phases of the planning process, will
enable a municipality to better develop an outreach program that reaches a broad base of
citizens. In addition to public meetings, municipalities can obtain input in a number of ways,
including telephone surveys, community leader interviews, and workshops. Each of these
activities can give the municipality a better understanding of the public perspective on local
water quality issues and sewer system problems, the amount of public concern about CSOs in
particular, and public willingness to participate in efforts to eliminate CSOs.
As noted in Exhibit 1-2 (Chapter 1), interaction between the municipality and the
regulatory agencies, including State WQS and National Pollutant Discharge Elimination System
(NPDES) permitting authorities, should be initiated in the early stages of CSO control planning
and continue through the development of the LTCP and the CSO plan re-evaluation and update.
An important outcome of this interaction during system characterization should be agreement
between all parties "...on the data, information and analysis needed to support the development
of the long-term CSO control plan and the review of applicable WQS, and implementation
procedures, if appropriate" (III. A).
2.2 OBJECTIVE OF SYSTEM CHARACTERIZATION
The primary objective of system characterization is to develop a detailed understanding
of the current conditions of the CSS and receiving waters. This assessment, a crucial component
2-2 August 1995
-------
Chapter 2 System Characterization
of the planning process, establishes the existing baseline conditions and provides the basis for
determining receiving water goals and priorities and identifying specific CSO controls in the
LTCP. In the context of the CSO Control Policy: "The purpose of the system characterization,
monitoring and modeling program initially is to assist the permittee in developing appropriate
measures to implement the nine minimum controls and, if necessary, to support development of
the long-term CSO control plan. The monitoring and modeling data also will be used to evaluate
the expected effectiveness of both the nine minimum controls and, if necessary, the long-term
CSO controls, to meet WQS" (II.C.l).
As discussed in Section 1.6.6, the municipality should characterize the system in the
context of entire watersheds. By characterizing both CSO and non-CSO sources of pollution
within each watershed, the causes of WQS nonattainment can be addressed more effectively, and
receiving water body goals can be established. Coordination of data collection and analysis
efforts throughout each watershed will also provide greater consistency with the LTCP
objectives.
System characterization and implementation of the NMC, described in this chapter, can
follow the sequential order shown in Exhibit 1-2. In practice, however, this sequential approach
might not always be possible or necessary, and the CSO Control Policy recognizes the need for
flexibility. In some cases, municipalities will not need to include every step in this process.
For example, some systems are already well understood by system engineers and planners
through ongoing monitoring, O&M, or other efforts and, therefore, need not revisit their current
approaches to monitoring and modeling. In other cases, because of time constraints, some
municipalities might be characterizing their combined systems and receiving waters,
implementing the NMC, and conducting monitoring programs concurrently.
2.3 IMPLEMENTATION OF THE NINE MINIMUM CONTROLS
One of the goals of the CSO Control Policy is to achieve an early level of CSO control,
even as the municipality is involved in developing the LTCP. Although the CSO Control Policy
recommends flexibility for municipalities to plan and implement the LTCP on a phased, iterative
2-3 August 1995
-------
Chapter 2 System Characterization
basis, it recommends that the NMC be implemented no later than January 1, 1997. Following
an assessment of NMC effectiveness, municipalities should ultimately integrate the NMC into
their LTCPs (EPA, 1995g).
2.3.1 Existing Baseline Conditions
The validated CSS and receiving water models can be used to predict the existing baseline
conditions, which are used to evaluate the effectiveness of the NMC and the performance of the
long-term CSO controls.
2.3.2 Summary of Minimum Controls
Exhibit 2-1 summarizes the NMC, based on the detailed discussion presented in
Combined Sewer Overflows—Guidance for Nine Minimum Controls (EPA, 1995b). The NMC
were developed to provide low-cost technology-based controls that can be implemented by
January 1, 1997, to reduce the magnitude, frequency, and duration of CSOs.
In practice, the implementation of NMC and their integration with the LTCP will be an
iterative process. For example, several of these minimum controls might already be ongoing
as part of regular operation and maintenance procedures. In some cases, others could be
implemented early in the process, before completion of system characterization. However, to
effectively maximize the use of the collection system for storage and maximize flow to the
POTW for treatment, an adequate understanding of the conveyance system and its hydraulic
characteristics is essential.
Although the NMC will generally not significantly reduce runoff entering the CSS, the
overflow volume to be addressed by the LTCP can be reduced by maximizing NMC
effectiveness, thus reducing potential program costs for the municipality.
2.4 COMPILATION AND ANALYSIS OF EXISTING DATA
As indicated in Exhibit 1-2, one of the first technical activities within system
characterization is the compilation and analysis of existing data. This section discusses
2-4 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-1. Summary of the Nine Minimum Controls
Minimum Control
Proper Operation
and Maintenance
Maximum Use of
Collection System
for Storage
Review and Modify
Pretreatment
Requirements
Maximum Flow to
the POTW for
Treatment
Eliminate Dry
Weather Overflows
Examples of Control Measures
Maintain/repair regulators
Maintain/repair tidegates
Remove sediment/debris
Repair pump stations
Develop inspection program
Inspect collection system
Maintain/repair tidegates
Adjust regulators
Remove small system bottlenecks
Prevent surface runoff
Remove flow obstructions
Upgrade/adjust pumping operations
Volume Control
• Diversion storage
• Flow restrictions
• Reduced runoff
• Curbs/dikes
Pollutant Control
• Process modifications
• Storm water treatment
• Improved
housekeeping
• BMP Plan
Analyze flows
Analyze unit processes
Analyze headless
Evaluate design capacity
Modify internal piping
Use abandoned facilities
Analyze sewer system
Perform routine inspections
Remove illicit connections
Adjust/repair regulators
Repair tidegates
Clean/repair CSS
Eliminate bottlenecks
Minimum Control
Control of Solid
and Floatable
Materials in CSOs
Pollution
Prevention
Public Notification
Monitoring
Examples of Control Measures
Screening - Baffles, trash racks, screens (static and
mechanical), netting, catch basin modifications
Skimming - booms, skimmer boats, flow balancing
Source controls - street cleaning, anti-litter, public
education, solid waste collection, recycling
• Source controls (see above)
• Water conservation
Posting (at outfalls, use areas, public places)
TV/newspaper notification
Direct mail notification
Identify all CSO outfalls
Record total number of CSO events and frequency
and duration of CSOs for a representative number
of events
Summarize locations and designated uses of
receiving waters
Summarize water quality data for receiving waters
Summarize CSO impacts/incidents
2-5
August 1995
-------
Chapter 2 System Characterization
watershed mapping, analysis of existing collection system information, CSO and non-CSO source
characterization, field inspections, and receiving water characterization. It concludes with a case
study.
Data collection activities are often the most expensive aspect of the CSO planning
process; therefore, it is important to maximize the use of available data, as well as to coordinate
efforts with other Federal, State, and local water quality agencies. By using existing
information, data gaps can be identified and efforts to collect new data can be more focused.
Investigating and describing existing conditions is generally a prerequisite to monitoring
and modeling, problem assessment, and evaluation of controls. Extensive applicable information
can usually be obtained from municipal government departments, State and Federal agencies,
and searches of maps, files, and data bases of environmental data. An investigation of existing
data should include gathering, reviewing, analyzing, and summarizing hydrological, water
quality, and other environmental data, as well as maps and municipal planning information for
the watershed. A description of existing conditions has two major components:
• Watershed characterization, which describes the sources of runoff and the causes of
water quality problems. The watershed characterization defines the watershed area
and its subwatersheds and further identifies relevant geographic and environmental
features (e.g., land use, geology, topography, wetlands), infrastructure features (e.g.,
sewerage and drainage systems), municipal data (e.g., population, zoning,
regulations, ordinances), and potential pollution source data (e.g., landfills,
underground tanks, point source discharges). This description can also include
historic, social, and cultural characterizations.
• A receiving water body characterization, which describes the receptors of the
pollutant sources within the watershed and the effects of those sources. The
receiving water body characterization provides water quality and flow information for
water bodies (e.g., rivers, streams, lakes, estuaries and their sediment and biota) in
the watershed.
These data collection efforts will provide support for future phases of CSO control
planning by:
• Providing a basis for establishing and reassessing water quality goals
2-6 August 1995
-------
Chapter 2 System Characterization
• Identifying pollutants of concern and their effects on water resources
• Identifying sensitive areas where pollutant loadings pose a high environmental or
public health risk and where control efforts should be focused
• Providing watershed base maps for locating pollution sources and controls.
2.4.1 Watershed Mapping
A watershed includes a water body and the entire land area that drains into that water
body. A single study area might include several watersheds because many wet weather and CSO
control programs are based upon political rather than watershed boundaries.
The first step is to delineate the watershed and its sub watersheds, using base maps or
digital mapping resources (if available) or topographic maps. The map should include the
municipalities and other entities with jurisdiction, as well as land use categories that could
contribute significantly to receiving water impacts. Additional information should then be added
as necessary to aid in CSO control planning; this includes topography, soils, infrastructure,
natural resources, recreational areas, special fish and habitat areas, and existing pollution control
structures. If this information is several years old, field validation might be necessary.
Exhibit 2-2 summarizes the types of data typically used in CSO planning.
Watershed maps can be generated by computer. One way of organizing and analyzing
data is in a Geographic Information System (GIS). The data in a GIS are organized into
thematic layers, such as infrastructure, land use, water bodies, watersheds, topography, or
transportation, which can be overlaid and plotted in any combination. In addition, a GIS
includes a data management system that can organize and store text and numerical descriptive
information. A well-developed GIS can contain most of the data needed. This descriptive
information can be very basic, such as land use type (e.g., residential or industrial), or very
sophisticated with multiple tables of related data, such as land ownership records, sewer system
physical configuration, discharge monitoring report data, soils information, and water quality
data.
2-7 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-2. Data Types For CSO Planning
Watershed Data
Source Input/Receiving Water Data
Environmental
Land use
Recreational and open areas
Soil and surface/bedrock geology
Natural resources
Temperature
Precipitation
Hydrology
Infrastructure
Roads and highways
Storm drainage system
Sanitary sewer (and combined sewer) system
Treatment facilities
Municipal
Population
Zoning
Land ownership
Regulations and ordinances
Potential Sources/BMPs
Municipal source controls
Direct (NPDES) and indirect dischargers
Pollution control facilities
Storm water control structures
Source Inputs (Flow and Quality)
CSO
Storm water
Other point source and nonpoint source
Receiving Water
Physiographic and bathymetric data
Flow characteristics
Sediment data
Water quality data
Fisheries data
Benthos data
Biomonitoring results
Federal standards and criteria
State standards and criteria
Source: EPA, 1993b
The use of a GIS might not be feasible for all municipalities undertaking CSO control
programs, because of the technical expertise required and the capital expenditures for computer
hardware (e.g., an appropriate personal or mainframe computer and a graphics plotter) and
software. Although full GIS capabilities can require expensive hardware and advanced training,
recently developed software, such as PC-based GIS and "view" systems, are making many GIS
functions more accessible to average PC users.
2-8
August 1995
-------
Chapter 2 System Characterization
2.4.2 Collection System Understanding
Understanding the physical and hydraulic characteristics of the existing collection system
is crucial to any CSO control program. The CSO Control Policy recommends that the
municipality ".. .evaluate the nature and extent of its combined sewer system through evaluation
of available sewer system records, field inspections and other activities necessary to understand
the number, location and frequency of overflows and their location relative to sensitive areas and
to pollution sources in the collection system, such as indirect significant industrial users"
(Il.C.l.b).
The municipality should compile existing information on the collection system. Drawings
and records are usually kept by the local public works department, city and county planning
offices, and municipal archives. Available information can provide an understanding of the
existing system and can also be used to identify areas where plans need to be verified or updated
during field inspections. Information should be compiled for sewers, regulators, diversion
chambers, pump stations, interceptors, outfalls, and any other key hydraulic control points.
Separate sewers, industrial connections, and other related information can be added as
appropriate. The municipality will need to know which drainage areas are combined and which
are separate or the location of partially separated or combined sewers. The CSO program team
can use these data for subsequent monitoring, modeling, and LTCP development.
2.4.3 CSO and Non-CSO Source Characterization
As noted in Section 1.6.6, an advantage in developing an LTCP using a watershed-based
approach is that it allows the site-specific determination of the relative impacts of CSOs and non-
CSO sources of pollution on water quality. The municipality should identify areas that contain
probable sources of significant loadings, such as industrial areas with significant indirect
industrial users (i.e., industrial users discharging to the POTW rather than directly to the
receiving water body). For many of these sources, the municipality can use existing data
collected through the pretreatment program. If the monitoring data are not available, the
municipality should consider the collection of such data in the monitoring plan.
2-9 August 1995
-------
Chapter 2 System Characterization
2.4.4 Field Inspections
The most effective method for accurately determining the operational status and condition
of a CSS is to conduct field investigations. Whereas watershed mapping and review of the
collection system information verify a system's design, field inspections help to determine actual
operation. Municipalities should inspect their CSSs for many reasons, including the following:
• To characterize areas of the watershed not adequately described by available
information
• To identify locations to conduct water quality sampling and install flow measurement
equipment
• To determine the structural integrity of the system
• To assess the mechanical condition and operational performance of the system
components
• To check for problems, including illegal connections, dry weather overflows, or
sediment buildup.
Field inspections can also provide the information necessary to begin assessing and
implementing the NMC. The complete implementation of certain minimum controls, such as
maximizing the use of the collection system for storage and maximizing flow to the POTW for
treatment, will be enhanced greatly by the hydraulic analysis conducted during system
characterization. This analysis must proceed from a correct and current understanding of the
system.
The extent of the inspection effort necessary will be a function of the adequacy of the
municipality's current records and inspection activities. In some cases, the CSS will be large
and available funds will dictate the investigation schedule. The municipality should develop a
list of inspection priorities related to the project objectives. A first priority might be to inspect
elements of the collection system where conflicting information exists, field modifications have
been made, or information is missing. A review of the existing drawings, maintenance crew
inspection reports, public complaint files, infiltration/inflow (I/I) reports, a sewer system
2-10 August 1995
-------
Chapter 2 System Characterization
evaluation survey (SSES), or treatment plant upgrade studies might reveal areas of inconsistency
or undocumented modifications.
2.4.5 Receiving Water
The main impetus for CSO control is attainment of WQS, including designated uses. To
this end, the review of existing information should include characterizing the receptors of CSOs
and other watershed pollutant sources and their effects as completely as possible. In many cases,
multiple receiving waters will exist, such as tributaries, larger rivers, estuaries, or lakes.
Identification and use of existing receiving water data can shorten the LTCP schedule and
reduce cost, particularly sampling and analysis cost. The municipality should review the types
of historical receiving water data and information summarized in Exhibit 2-2. These data should
be gathered to assist in developing a profile of the conditions in the CSO-impacted receiving
water. Often, pollutant source discharge, hydraulic, chemical, sediment, and biological data will
exist because of past studies conducted in the watershed. By gathering this information, the
municipality can describe existing conditions, as well as data gaps that need to be addressed with
the monitoring program. In addition, this effort is important to LTCP development because it
provides a basis for:
Establishing and reassessing priorities for improvements to receiving water quality
by water body
Documenting the type and extent of receiving water impacts caused by CSOs and
other point and nonpoint sources
Identifying sensitive areas
Quantifying pollutant loads
Documenting impairment or loss of beneficial uses and water quality criteria
exceedances
Identifying areas with good water quality that might be threatened or that should be
protected.
2-11 August 1995
-------
Chapter 2 System Characterization
Various agencies at the local, State, and Federal levels might have receiving water data.
The municipality should contact each agency that might have been involved in the study area,
obtain any existing data, and inquire about other potential data sources. The following list
provides possible sources at each level:
• Local—Municipal departments, including water, health, and public works, can be
useful sources of data and information generated as part of previous studies, wetland
or other permit applications, or routine receiving water monitoring. Data will be
available from NPDES monitoring records. Municipal departments responsible for
reviewing construction and wetlands permit applications can track local water quality
conditions as part of local water resource regulations designed to prevent cumulative
degradation of sensitive resources. Local permit applications can contain recent and
historical water quality, source discharge, and hydrologic data used to demonstrate
compliance with local or State wetlands and water quality regulations. Data might
also be available for water bodies in special drinking water or flood control districts.
• State—Most States have several agencies that deal directly or indirectly with water
quality issues: water resources, pollution control, clean lakes, transportation,
fisheries, environmental review, wetlands, and coastal zone management. States
periodically monitor important water resources and record affected receiving water
segments as part of CWA Section 305(b) requirements.
• Federal—The Federal Government is an excellent source of hydrology and water
resources data through a number of agencies, including EPA, Soil Conservation
Service (SCS), U.S. Geological Survey (USGS), and U.S. Fish and Wildlife Service.
A number of major Government agencies have water data, including water quality,
hydrology, meteorology, biomonitoring, and sediment quality data. In some cases,
information can be obtained through the mail; in other cases, such as the USGS
National Water Data Exchange and the National Weather Service, the information can
be accessed using a computer modem. Many of these agencies also have regional or
field offices that are additional sources of data.
An important objective of the initial receiving water investigation is the identification and
classification of areas potentially affected by CSOs. A more complete description of the possible
impacts to these receiving waters can be developed during monitoring, which is conducted as
part of the LTCP. When defining the wet weather receiving water impacts, the municipality
should consider the applicable WQS, as well as the existing and desired uses of the receiving
water. In developing the LTCP, a "use attainability" approach (40 CFR 131.10) can be an
effective method to ensure that recommended improvements in receiving water quality result in
the attainment of actual desired uses and that these desired uses are reasonably related to costs.
Chapter 3 addresses this issue under the discussion of the demonstration approach.
2-12 August 1995
-------
Chapter 2 System Characterization
CASE STUDY: LEWISTON-AUBURN, MAINE-CSO PLANNING
Lewiston and Auburn are located on opposite sides of the Androscoggin River in southwestern Maine.
Together, the communities serve as the industrial, commercial, and service center for the south-central-
western region of Maine. Lewiston, with a population of approximately 40,000, occupies about 35 square
miles of land along the east bank of the Androscoggin River. The city of Auburn has a population of
20,000 and occupies about 65 square miles on the west bank. Combined wastewater flows from both cities
are conveyed to the Lewiston-Auburn Water Pollution Control Facility (LAWPCF), located in Lewiston.
The LAWPCF provides secondary treatment (conventional activated sludge) with effluent wastewater
discharged to the Androscoggin River.
During wet weather conditions, excess flows within the Lewiston CSS and Auburn Sewer District (ASD)
CSS discharge directly to the Androscoggin River and its tributaries. On the east side of the river, CSOs
from the Lewiston CSS occur along the bank of the Androscoggin River and along drainage courses
tributary to the river, including Gully Brook, Jepson Brook, Stetson Brook, and Goff Brook. As indicated
in Exhibit 2-3, CSOs from the ASD sewer system on the west side occur along the banks of the
Androscoggin and Little Androscoggin Rivers.
In 1991, the cities embarked on a planning program to address a number of issues, including CSO impacts,
storm water management, and nonpoint source control. They decided to incorporate these considerations
into an overall planning effort. This case study, which is divided into three separate sections within
Chapter 2, outlines CSO planning efforts in Lewiston and Auburn. The first portion of the case study
focuses on Lewiston for the early steps in the planning process. The second section describes the CSO and
receiving water monitoring efforts, and the third section summarizes the CSO and receiving water
modeling.
PUBLIC PARTICIPATION AND AGENCY INTERACTION
The Department of Public Works (DPW) assumed responsibility for the program in Lewiston. The DPW
formed a team of representatives from the planning department, LAWPCF, highway department, and the
general public who would meet periodically and guide and provide input to the planning process. In
addition, the DPW secured funding (100 percent from city funds), developed a scope of services, and hired
an engineering consultant to perform technical tasks beyond the capability or available resources of the city.
One of the first tasks undertaken by the program team was to compile information on current Federal and
State regulations that were potentially pertinent to the planning effort. The team made a series of contacts,
especially with the State regulatory personnel, to determine the status of regulatory activities. They
gathered information on Federal and State policies and programs for CSO control, storm water NPDES
permitting, Safe Drinking Water Act compliance, nonpoint source pollution control, coastal zone nonpoint
source pollution control, and agricultural nonpoint source controls. Changes were occurring in several
areas, especially in CSOs and storm water, that needed to be monitored and incorporated into the program.
The team developed initial goals for the program in conjunction with an assessment of existing conditions
using available data. Initially, the overall area was divided into watersheds representing the land draining
to each of the water bodies in the city, and goals were set for each of these watersheds and receiving water
bodies. Exhibit 2-4 lists the characteristics of the watersheds in the city of Lewiston. Because the program
was initiated prior to the release of the CSO Control Policy, the team established a basic goal that the
program should result in an understanding of and compliance with current and upcoming regulations related
to CSO, storm water, and nonpoint source (NPS) control.
2-13 August 1995
-------
Source: USGS Topographic Maps
Lewiston, Maine 1979
Minot, Maine 1981
Lake Auburn East, Maine 1979
Lake Auburn West, Maine 1981
2000
2000
SCALE IN FEET
Exhibit 2-3. Lewiston-Auburn Location Plan
2-14
-------
Chapter 2
System Characterization
Exhibit 2-4. Watershed Characteristics in the City of Lewiston
Watershed Name
Size
(acres)
Land Use Description
No Name Pond
No Name Brook
Stetson Brook
Hart and Goff Brooks
Salmon/Moody Brooks
Jepson Brook
Androscoggin River
750
10,000
3,000
1,600
1,900
1,500
2,300
Rural/residential - shore line cottages
Mainly undeveloped - some residential
Ranges from rural to residential to
commercial/industrial
Residential, commercial, and industrial
Primarily undeveloped, minor agriculture
Residential and institutional
Urban in central core, undeveloped or industrial in
outlying area
The program team held a workshop to facilitate discussion and obtain input on the city's water resources
and initial goals for the program. The workshop included discussion of each watershed and the water
quality classifications, current uses, known problems, desired uses, and goals completed. A qualitative
assessment or "ranking" of the individual watersheds was included to indicate the relative importance of
the water resources to the city. The results indicated that CSOs exist mostly in water resources used
primarily for non-contact recreation, as shown in Exhibit 2-5.
In some cases, the desired uses of the water resource were being met. For these, maintaining and
protecting the uses was set as an initial goal. For some of the brooks, aesthetics was the only use of
concern, even though the Class B standard allows fishing and swimming. For these, the initial goal of
meeting Class B standards was set. For Jepson Brook, which is a channelized drainage ditch, there was
no desire to meet Class B standards. For No Name Brook, there was a desire to upgrade the standard from
Class C to Class B. The range of initial goals reflects the variety of watersheds and water resources being
addressed.
ANALYSIS OF EXISTING DATA
The program team assessed existing information and data and made the following conclusions pertaining
to the initial goals of the planning program:
• The city has an aggressive and extensive regulatory control system that addresses many NPS
and storm water control issues. With minor improvements, this system could fulfill the goals
of maintaining and protecting existing uses.
• There were virtually no water quality data or information on any of the brooks in the city.
More information is needed to better assess the existing conditions and establish goals for
these systems.
• There are extensive data on the Androscoggin River, which does not meet the Class C
standards. Most pollution appears to be from upstream sources, but the contribution of CSOs
needs to be defined better.
2-15
August 1995
-------
Chapter 2
System Characterization
Exhibit 2-5. Initial Water Resource Goals for Lewiston
Watershed
Name
No Name Pond
No Name Brook
Stetson Brook
Hart and Goff
Brooks
Salmon/Moody
Brooks
Jepson Brook
Androscoggin
River
Groundwater
Water
Quality
Class
GPA
C
B
B
B
B
C
GWA
Current Uses
Aesthetics
Recreation— fishing, boating
Aesthetics
Aesthetics
Aesthetics
Aesthetics
Drainage
Aesthetics
Recreation— fishing, boating
Drinking water supply (for
town of Lisbon)
Known Problems
Algal blooms
Septic tank discharges
Erosion from use of all terrain
vehicles
Debris
Erosion
CSOs
Erosion
Industrial areas
Interceptor sewer surcharging
Agriculture
CSOs (no visual/odor)
Debris
Point sources (paper mills)
Erosion (gravel pits)
CSOs
None
Qualitative
Assessment of
Importance
Most important town
water resource
Second most
important town water
resource
Third most important
town water resource
Fourth most
important town water
resource
Small watercourses
of minor importance
Channelized drainage
ditch
Large regional water
resource
Of limited current
importance to town
Desired
Uses
Same as
current
Same as
current
Same as
current
plus
fishing
Same as
current
Same as
current
Same as
current
Same as
current
Same as
current
Goals
Maintain and protect
existing uses
Maintain and protect
existing uses
Upgrade to Class B
Meet Class B
Meet Class B
Meet Class B
Maintain current use
Meet Class C
Maintain and protect
existing uses
2-16
August 1995
-------
Chapter 2 System Characterization
Proceeding from these conclusions, the program team made numerous contacts and held meetings with
individuals who might have pertinent data. Exhibit 2-6 lists the data compiled.
Potential Pollution Sources
In addition to CSOs, a number of possible pollution sources existed within the city's watersheds; however,
these had never been mapped. The city compiled extensive information on underground and above-ground
storage tanks, landfills, vehicle maintenance areas, salt storage and snow dumping areas, CSOs, and storm
drain cross-connections. These were plotted on a base map, along with watershed boundaries, receiving
waters, and other important features, such as gaging stations, recreational areas, and flood control
structures, to provide a convenient way of reviewing watersheds and potential pollution sources within
them, possible threats to receiving waters, and the underlying zoning districts.
The mapping showed that most of the potential pollution sources exist within the Jepson Brook, Hart
Brook, and Androscoggin River watershed areas, because these are the most developed watersheds.
Stetson Brook watershed has several potential sources, and Salmon/Moody Brook has almost none. The
No Name Brook and No Name Pond watersheds did not have many source areas. One area of medium
density residential development on Sabattus Street with a concentration of underground tanks was noted.
This area is of concern because it is located in the downstream portion of No Name Brook near No Name
Pond.
Nonstructural Controls
Nonstructural controls include regulatory controls that prevent pollution problems by controlling land
development and land use. They also include source controls that reduce pollutant buildup or lessen its
availability for washoff during rainfall. The program team reviewed the city's land use and zoning code
and other development guides to determine the status of nonstructural controls. It was determined that the
city has a comprehensive set of nonstructural controls. These were analyzed and presented in a series of
matrices, which were used to assess the strengths and weaknesses of the regulations. The major areas of
existing regulatory authority included conservation districts, performance standards, and development
review standards. These controls provide pollution control by reducing the amount of storm water runoff
and improving the runoff quality as new development and redevelopment occurs.
Municipal Source Controls
The team also conducted interviews to summarize the city's current source control activities. Most of the
activities appeared to correspond to standard practices of similar size municipalities. Areas that appeared
to need further consideration included sewer cross-connection removal, road salting, and household
hazardous waste pickup. The city identified some cross-connections and plans to implement a removal
program. Many communities are involved in household hazardous waste pickup programs. Such a
program could prove beneficial, and it would be consistent with the other aggressive solid waste programs
of the city. Such programs also can be expensive, however. The team plans further evaluation of
municipal BMP/source control activities after collection of data and evaluation of various possible BMP
programs.
Receiving Water Data
The program team located limited data on receiving waters and on the major pollution sources to the
receiving waters, as listed in Exhibit 2-7. Data were available for the Androscoggin and Little
Androscoggin (which feeds into the Androscoggin River in Lewiston) Rivers only. The USGS maintains
monitoring stations on both rivers, and published data on dissolved oxygen, temperature, pH, and
conductivity are available. Maine DEP collected grab samples on a weekly basis during summer months,
2-17 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-6. Lewiston Watershed Data
Description
Source
Environmental
Topography
Land Use
Recreational Areas
Soil and Surface/Bedrock Geology
Vegetation
Natural Resources
Temperature
Precipitation
Hydrology
USGS topographical maps; city's 100 and 200 scale maps
"Zoning Map Lewiston, Maine" revised 11-7-91;
Comprehensive Land Use Plan (1987)
Parks Department inventory
USDA Soil Conservation Service soil survey
USGS quadrangle sheets & Maine DOT aerial photos
Comprehensive Land Use Plan (1987)
NOAA
National Climatic Data Center; four rainfall gages owned and
operated by Lewiston
FEMA flood mapping
Infrastructure
Roads and Highways
Storm Drainage System
Sanitary Sewer and Combined
Sewer System
Treatment Facilities
Other Utilities
Various maps of the city exist
Record drawings provided by the city
Record drawings provided by the city
Record drawings provided by the city
Gas, New England Telephone maps
Municipal
Population
Zoning
Land Ownership
Regulations and Ordinances
Municipal Source Control BMPs
U.S. Census data; Maine Department of Data Research and Vital
Statistics; Comprehensive Land Use Plan (1987)
Zoning regulations; city zoning map; Comprehensive Land Use Plan
(1987)
City Assessor's maps
"Draft. Development Permit" provided by the city;
Comprehensive Land Use Plan (1987)
Interviews with various city departments and staff
Potential Sources/BMPs
Landfills
Waste Handling Areas
Salt Storage Facilities
Vehicle Maintenance Facilities
Underground Tanks
NPDES Discharges
Pollution Control Facilities
Retention/Detention Ponds
Flood Control Structures
Locations developed by city
Locations developed by city
Locations developed by city
Locations developed by city
Maine DEP list supplemented by the city
Locations developed by city
Lewiston Area Water Pollution Control Authority
Public Works Department inventory
Public Works Department inventory
2-18
August 1995
-------
Chapter 2
System Characterization
Exhibit 2-7. Lewiston Source Input and Receiving Water Data
Description
Source
Source Inputs (Flow and Quality)
CSO
Storm Water
Other NFS
None
None
None
Receiving Water
Physiographic and Bathymetric Data
Flow Characteristics
Sediment Data
Water Quality Data
Fisheries Data
Benthos Data
Biomonitoring Results
Federal Standards and Criteria
State Standards and Criteria
Some available - see water quality data below
USGS flow data
International Paper - Androscoggin River
Maine DEP, USGS, CMP, Union Water Power Co.
(Note: all water quality data in Androscoggin River
only)
International Paper - Androscoggin River
International Paper - Androscoggin River
None
EPA
Maine DEP
and data on dissolved oxygen, E. coli or fecal coliform bacteria, phosphorus, TKN, NO3, NH3, and
conductivity are available for several years. The most comprehensive set of data available was collected
by International Paper Company relative to its wastewater discharge upstream of Lewiston. Although the
available data do not cover the entire reach of the Androscoggin River in Lewiston, significant data on
fisheries and sediment exist. None of the existing data were oriented toward definition of wet weather
impacts in the receiving water. Some of the Maine DEP grab samples were taken during or after storm
events, and the bacteria data indicate elevated bacteria levels during these periods.
Due to the limitations in the available data, the program team identified two major areas for new data
collection: (1) CSO flows, loads, and impacts, which were required as part of CSO planning efforts by
the State and (2) water resources where no data currently exist. These programs are described in the next
section of the case study, following Section 2.5.3.6.
2-19
August 1995
-------
Chapter 2 System Characterization
2.5 COMBINED SEWER SYSTEM AND RECEIVING WATER MONITORING
In many cases, existing data will not be sufficient to establish existing baseline dry
weather or wet weather conditions. Thus, the next step in the long-term planning process
generally will be to develop and conduct a monitoring program to adequately characterize
existing conditions, as well as provide the necessary calibration and verification data for system
modeling. As stated in the CSO Control Policy, "The permittee should develop a
comprehensive, representative monitoring program that measures the frequency, duration, flow
rate, volume and pollutant concentration of CSO discharges and assesses the impact of the CSOs
on the receiving waters. The monitoring program should include necessary CSO effluent and
ambient in-stream monitoring and, where appropriate, other monitoring protocols such as
biological assessment, toxicity testing and sediment sampling" (II.C.l.c).
This section summarizes the main considerations in the development of a monitoring
program and the elements that make up the CSS and receiving water monitoring plans. Because
CSO data collection programs are site-specific and varied, providing detailed guidance on
"typical" activities is a difficult task. EPA's guidance on monitoring and modeling (EPA,
1995d) addresses these issues in greater detail and provides additional references.
2.5.1 Monitoring Plan Development
The monitoring plan plays a significant role in the CSO planning process. Because CSO
control decisions are based largely on system characterization (a major element of which is
monitoring data), the data obtained must represent the conditions throughout the CSS and
receiving water accurately. A well-developed monitoring plan is essential whether the collection
of monitoring data is for NMC implementation, LTCP development and implementation, or post-
construction monitoring. The municipality should continue to coordinate its efforts with the
regulatory authorities (State WQS and watershed personnel, and EPA Regional staff), as well
as with other municipalities in the same watershed, throughout the development of the
monitoring plan.
2-20 August 1995
-------
Chapter 2 System Characterization
The primary goal of any CSO control program is to implement the most cost-effective
controls to reduce water quality impacts from CSOs. The monitoring plan will generate data
to support decisions for selecting appropriate CSO controls. The monitoring plan might have
numerous data collection objectives, depending on local site-specific conditions, some of which
are given below:
• Define the CSS's hydraulic response to rainfall.
• Determine CSO flows and pollutant concentrations/loadings.
• Evaluate the impacts of CSOs on receiving water quality.
• Support the review and revision of WQS.
• Support implementation and documentation of the NMC.
• Support the evaluation and selection of long-term CSO controls.
Monitoring is expensive. By tailoring the monitoring program to the CSS, water quality
problems and priorities, pollutants of concern, and needs and resources of a community, a
balance can be achieved between obtaining sufficient data for system understanding and keeping
data collection costs under control. This balance can be achieved and maintained provided that
activities between the data collectors and model developers are well coordinated.
To meet the objectives listed above, the data collection program should identify sampling
stations, frequency of data collection, and parameters to be monitored. Section 2.5.2 briefly
discusses these components for CSS monitoring, as well as techniques and equipment for
obtaining rainfall, flow, and pollutant data. Section 2.5.3 follows the same approach for
receiving water monitoring.
2.5.2 Combined Sewer System Monitoring
The CSO Control Policy outlines several possible objectives of a CSS monitoring plan:
• Gain a thorough understanding of the CSS
2-21 August 1995
-------
Chapter 2 System Characterization
• Adequately characterize the CSS response to wet weather events, such as the number,
location, and frequency of the CSOs and the volume, concentration, and mass of
pollutants discharged
• Support a mathematical model to characterize the CSS
• Support the development of appropriate measures to implement the NMC
• Support LTCP development
• Evaluate the expected effectiveness of the NMCs and, if necessary, the long-term
CSO controls.
The CSS monitoring program should be conducted to satisfy the above objectives as
appropriate. For example, the CSO Control Policy specifies that permittees should immediately
begin characterizing their CSS and CSOs, demonstrating implementation of the NMC and
developing an LTCP. Implementation of the NMC is affected directly by the results of the CSS
monitoring program. Monitoring can be performed to support various aspects of the NMC,
including maximizing use of the collection system for storage, maximizing flow to the POTW
for treatment, and control of solids and floatable materials in CSOs.
2.5.2.1 Selection of Monitoring Stations
An accurate determination of CSO flow, pollutant loadings, and resulting water quality
impacts depends on the appropriate and efficient selection of sampling stations. The
municipality should select sampling stations strategically so that data collected from a limited
number of stations can be used to satisfy multiple monitoring objectives. As mentioned earlier,
a thorough examination of the available information on the CSS, its overflow points, field
investigation reports, and flow measurements will help in this exercise.
Wet weather discharges can contribute large pulses of pollutant load and might constitute
a significant percentage of long-term pollutant loads from combined sewer areas. Wet weather
sampling can be used to characterize runoff from these discharges, determine individual pollutant
source and total watershed loadings, and assess the impact to receiving waters. The municipality
2-22 August 1995
-------
Chapter 2 System Characterization
should consider the following criteria when selecting the actual location for CSO sampling (EPA,
1993b):
• Discharge Volume—Select sites that constitute a significant portion of the flow from
a watershed.
• Hydraulic Stations—Spread stations out in interceptors and sewers to define flows;
locate at key hydraulic control points, such as pump stations and diversions. Storm
water or other source flow data might be required; I/I in the system and entering
upstream might need to be defined.
• Pollutant Stations—Either based on historical information or deduced from an
analysis of land use or population density, select sampling sites to quantify
representative or varying pollutant loads (dry versus wet weather quality), sources
that affect sensitive areas, and, possibly, non-CSO sources.
• Geographic Location—Select sites that permit sampling of flows from major
subwatersheds or tributaries to permit isolation of pollutant sources.
• Accessibility—Select sites that allow safe access and sample collection.
If possible, the monitoring plan should include some type of flow and pollutant
concentration information at every CSO location. Municipalities with small systems and a
limited number of overflow points might be able to monitor all locations for each storm event
studied. Other municipalities, however, might have budget constraints or a large number of
discharge points that make this approach impossible. In such cases, an approach that includes
monitoring high priority or critical sites (e.g., the possible criteria outlined previously) with
techniques, such as continuous depth and velocity flow monitoring and the use of sampling for
chemical analyses, might be appropriate. According to the CSO Control Policy, a
"...representative sample of overflow points can be selected that is sufficient to allow
characterization of CSO discharges and their water quality impacts and to facilitate evaluation
of control plan alternatives" (II.C.I). Both the case study, presented after Section 2.5.3.6, and
EPA's guidance on monitoring and modeling (EPA, 1995d) present approaches for selecting
CSO monitoring sites.
2-23 August 1995
-------
Chapter 2 System Characterization
2.5.2.2 Frequency of Monitoring
Municipalities should monitor a sufficient number of storms to support development of
hydraulic models or prediction of the CSS response to rainfall events and CSO impacts. The
frequency of monitoring should be based on the need to collect data for the development of
models or predictions. The data to be collected should be based on model parameters and site-
specific considerations, such as the overflow rate, which depends on the rainfall pattern,
antecedent dry period, ambient tide or stage of river or stream, and base flow (wastewater and
infiltration) to the treatment plant. Monitoring frequency can reflect:
• A certain size precipitation event (e.g., 3-month, 24-hour storm)
• Precipitation events that result in overflows (e.g., more than 0.4 inches of rainfall)
• A certain number of precipitation events (e.g., monitor until five storms are collected
of a certain minimum size).
When determining the monitoring frequency, municipalities should consider the following
criteria:
• Frequency of Rainfall/Discharge—Facilities located in areas where rainfall is more
frequent might have more frequent CSOs.
• Sensitivity of Receiving Waters—If facilities discharge to sensitive areas or high
quality waters, more frequent monitoring might be desirable or warranted. For
example, in an area where human contact occurs through swimming, boating, and
other recreational activities or where there are intakes for drinking water, more
accurate estimates might be needed.
• Variability of Discharge—CSOs with variable characteristics should be monitored
more frequently than CSOs with relatively consistent characteristics.
The frequency of monitoring should change when the data are used for model verification and
later during the post-construction monitoring phase. Information on determining appropriate
sampling frequencies can be found in EPA, 1995d, and EPA, 1983.
2-24 August 1995
-------
Chapter 2 System Characterization
2.5.2.3 Pollutant Parameters
Chemical analyses generate information about the concentration of pollutants carried in
the combined sewage and the variability of these concentrations from outfall to outfall and from
storm to storm. Chemical analysis data are used with flow data to compute pollutant loadings
to receiving waters. In some cases, such data can also be used to detect the sources of pollutants
in the system.
The selection of parameters to be measured during the sampling program should be based
on problems identified during the review of existing conditions; the overall goals of the program;
the specific objectives of the data collection program; and the requirements of local, State, and
Federal regulations. For example, most State WQS have numeric limits for indicator bacteria
levels in waters intended for swimming and boating. If local beaches are threatened by bacterial
contamination from CSOs or storm water, the program needs to include bacteria sampling.
CSSs need to be monitored for the identified parameters of concern. Parameters of
concern should include the pollutants with water quality criteria for the specific designated use(s)
of the receiving water and pollutants key to the attainment of the designated water use(s). The
CSO Control Policy states: "Monitoring parameters should include, for example, oxygen
demanding pollutants, nutrients, toxic pollutants, sediment contaminants, pathogens,
bacteriological indicators (e.g., Enterococcus, E. coli), and toxicity" (II.C.l.c).
The monitoring plan should also include any other pollutants for which water quality
criteria are being exceeded, as well as pollutants suspected to be present in the combined
sewage. CSS monitoring should include identified pollutants of concern that are known or
thought to be discharged by industrial users in amounts that could affect CSO pollutant
concentrations and/or the receiving water. If the water quality criterion for zinc is being
exceeded, for example, CSS monitoring for zinc should be conducted in the portions of the CSS
associated with significant industrial users that discharge zinc. POTW monitoring data and
industrial pretreatment program data on nondomestic discharges can help identify other pollutants
expected to be present. In coastal systems, measurements of sodium, chloride, TDS, or
2-25 August 1995
-------
Chapter 2 System Characterization
conductivity can be used to detect the presence of sea water in the CSS, which can occur
because of intrusion through failed tide gates (EPA, 1995d).
2.5.2.4 Rainfall Monitoring and Analysis
Rainfall data are necessary to estimate the amount of runoff generated during a single wet
weather event or long-term series of events and for successful hydraulic modeling of the CSS.
CSS performance can be predicted by entering rainfall data into a hydrologic/hydraulic model,
observing the resulting simulated overflows, and correlating these predicted overflows with
measured overflow volumes. There are two general types of rainfall data: (1) continuous
rainfall records, obtained either from existing weather stations (often maintained at airports) or
from stations set up within the CSS watershed of interest and (2) rainfall frequency data (depth-
duration-intensity-frequency analyses of historic rainfall).
For rainfall data collection, the variability hi the possible distribution of rainfall over a
relatively small area might necessitate a network of ram gages. The number of gages necessary
depends on the size of the program, the area, topography, season, and typical characteristics of
local rainfall events. EPA has provided guidance for determining rain-gage network density
(EPA, 1976a). In addition, the sampling interval is important. The 1-hour data commonly
gathered at NOAA gages might underestimate CSO flows by averaging larger peak intensities
that occur over shorter tune intervals (5- or 15-minute rainfall data might be more appropriate).
Rainfall data can be analyzed using the EPA SYNOP program to develop long-term
rainfall statistics, such as depth, intensity, duration, and number of storms. In addition, it might
be necessary to develop synthetic rainfall hyetographs for particular design conditions of interest
to the program. (Hyetographs are graphs of rainfall intensity versus tune, and standard
hydrology textbooks contain methods for developing them.) More discussion of rainfall
monitoring and analysis can be found in Combined Sewer Overflows—Guidance for Monitoring
and Modeling (EPA, 1995d).
2-26 August 1995
-------
Chapter 2 System Characterization
2.5.2.5 CSO Flow Monitoring and Analysis
Accurate flow monitoring is needed to confirm the hydraulic characteristics of the CSS,
provide the necessary calibration and verification data for characterizing rainfall runoff and
conveyance, and predict CSO volumes. Selecting the most appropriate monitoring technique
often depends on a combination of site characteristics, budgetary constraints, and personnel
availability.
Flow measurements are generally made using automatic devices that can be installed in
channels, storm drains, or CSO structures. These devices use a variety of sensor types,
including pressure/depth sensors and acoustic measurements of stage height or Doppler effects
from flow velocity. Data are stored in a computer chip that can be accessed and downloaded
by portable computer. Data are processed based on the appropriate pipe, flume, or weir
hydraulic equations. Field calibration of data using such equations is important because these
types of data can be influenced by surcharging, backwater, tidal flows, and other complex
hydraulic conditions typical of wet weather flows. EPA's guidance on CSO monitoring and
modeling (EPA, 1995d) provides a matrix and description of the various CSO monitoring
methods, including manual methods, primary flow, depth sensing, and velocity meters, as well
as advantages and disadvantages of their use in CSS monitoring.
The CSS flow monitoring data can be evaluated to develop an understanding of the
hydraulic response of the system. Using this evaluation, the following questions can be
answered for the monitored outfalls based on the monitored storms (EPA, 1995d):
• Which CSOs contribute the majority of the flow volume?
• What size storm can be contained by the regulator serving each outfall?
• Does this capacity vary from storm to storm?
• Approximately how many overflows would occur and what would be their volume,
based on a rainfall record from a different year? How many occur per year, on
average, based on the long-term rainfall record?
2-27 August 1995
-------
Chapter 2 System Characterization
Extrapolating from the monitored period to other periods, such as a rainfall record for
a year with more storms or larger volumes, requires professional judgment and familiarity with
the data. In addition to analyzing total overflow volumes for the CSOs, flow data can be used
to develop various graphical and tabular presentations. These could include plots of flow and/or
head for a selected conduit during a storm event, as well as tables comparing the relative
volumes and activation frequencies from different monitoring sites in the CSS.
2.5.2.5 CSO Quality Sampling and Analysis
Characterization of the CSS requires information on the quality, as well as the quantity,
of the overflows. The objective of CSO pollution abatement is to prevent the degradation of
receiving water quality from short- and long-term effects of pollutant discharges during wet
weather events. It is necessary, therefore, to know the constituents of the overflows and their
pollutant loadings.
In general, water sampling methods fall into three categories: grab sampling, flow-
weighted sampling, and automated sampling. Grab samples are collected by hand using a
container to collect water from the sewer. This method requires minimal equipment and allows
field personnel to record additional observations while collecting the sample. Because of their
special characteristics, oil and grease, volatile compounds, and bacteria, must be analyzed from
a sample collected by manual methods according to standard procedures (APHA, 1992).
Data can be obtained by combining multiple grab samples collected throughout a storm
event to create a flow-weighted or composite sample. These samples provide data that are
representative of the overall quality of combined sewage averaged throughout a storm event.
Typically, samples are combined in relation to the amount of flow observed in the period
between the samples.
Automated samplers have features that are useful for CSS sampling, such as the ability
to collect multiple discrete samples, as well as single or multiple composited samples. They can
collect samples on a tuned basis or in proportion to flow measurement signals from a flow
2-28 August 1995
-------
Chapter 2 System Characterization
meter. Although these samplers require a large investment, they can decrease the labor required
in a sampling program and increase the reliability of flow-weighted compositing.
In addition, toxicity testing can be used to directly measure, prior to discharge, the acute
and chronic impacts of combined sewage on aquatic life. Procedures for toxicity testing are
described in Technical Support Document for Water Quality-based Toxics Control (EPA, 1991);
these procedures can also be used, with caution, for wet weather discharges.
Other important components of any CSO quality sampling effort include sample
preservation, handling, and shipping; chain of custody documentation; and quality assurance and
quality control (QA/QC) procedures. The QA/QC procedures are essential to ensure that data
collected in environmental monitoring programs are useful and reliable. QA refers to program-
related efforts to ensure the quality of monitoring and measurement data. QC, which is a subset
of QA, refers to the routine application of procedures designed to obtain prescribed standards
of performance in monitoring and measurement.
Because data collection programs generate large amounts of information, management
and analysis of the data are critical to a successful program. Even small-scale programs, such
as those involving only a few CSO and receiving water monitoring locations, can generate an
extensive amount of data. EPA's guidance on CSO monitoring and modeling provides examples
of data analysis methods (EPA, 1995d).
2.5.3 Receiving Water Monitoring
The objectives of receiving water monitoring generally include the following:
• Assess the attainment of WQS, including designated uses
• Establish the baseline conditions in the receiving water
• Evaluate the impacts of CSOs
• Gain sufficient understanding of the receiving water to support evaluation of proposed
CSO control alternatives, including any receiving water modeling that may be needed
2-29 August 1995
-------
Chapter 2 System Characterization
• Support the review and revision of WQS.
2.5.3.1 Selection of Monitoring Stations
Municipalities should select monitoring stations for receiving water quality sampling
considering the following factors (WPCF, 1989; EPA, 1993b):
• Proximity to discharge sampling locations
• Accessibility
• Safety of personnel and equipment
• Proper location upstream or downstream of incoming sources or tributaries
• Adequate mixing of sources or tributaries at the sampling site.
In addition, municipalities should coordinate the locations with sites that might already have an
existing monitoring data base.
To identify sampling locations as part of a receiving water monitoring program, some
knowledge of the dynamics of the receiving water is important. In addition to the general
criteria listed above, the selection of appropriate locations depends on the characteristics of the
receiving water, the pollutants of concern (e.g., bacteria, dissolved oxygen, toxic material), and
the location of sensitive areas. The number and placement of sampling locations also depends
on the size of the water body, the horizontal and vertical variability in the water body, and the
degree of resolution necessary to assess attainment of WQS.
Individual monitoring stations can be located to characterize:
• Pollutant concentrations and loadings from an individual source
• Concentrations and impacts at specific locations, including sensitive areas such as
shellfishing beds
• Variations in concentrations between upstream and downstream sampling sites for
rivers or between inflow and outflows for lakes, reservoirs, or estuaries
2-30 August 1995
-------
Chapter 2 System Characterization
• Changing conditions through time at individual sampling stations
• Differing water bodies or segments that receive CSOs, such as lakes, ponds, rivers,
tributaries, bays, or channels
• Effects of other pollution sources within the watershed.
2.5.3.2 Extent of Monitoring
Monitoring studies for receiving water characterization should target seasons, flow
regimes, and other critical environmental conditions where CSOs have the greatest potential for
impacts, as identified in the data investigation (Section 2.4). Based on initial sampling results,
the number of stations may be able to be reduced. For example, if initial sampling results show
that one of a series of streams within a watershed is of high quality, sampling coverage of this
stream could be reduced. Conversely, additional monitoring might be necessary to fill data
needs and to support receiving water modeling or to distinguish the relative contribution of other
sources to the water quality impairment.
In assessing or demonstrating compliance with WQS, monitoring should provide data
designed to answer relevant questions. For instance, to establish a maximum or geometric mean
coliform concentration at the point of discharge into a river (or mixing zone boundary, if
allowed), grab samples should be taken during and immediately after discharge events in
sufficient number (usually specified in the standards) to obtain a reasonable approximation of
actual in-stream conditions. On the other hand, assessing attainment of narrative standards to
control nutrient load to prevent eutrophication might require the collection of samples through
the water body and timed to examine long-term average conditions over the growing seasons.
Finally, assessing attainment of narrative standards for the support of aquatic life might require
biological assessment in potentially impacted locations and a comparison of the data to reference
sites. EPA's guidance on monitoring and modeling describes several examples of receiving
water sampling designs, including point-in-time, short-term, long-term, reference site, near-field,
and far-field designs (EPA, 1995d).
2-31 August 1995
-------
Chapter 2 System Characterization
2.5.3.3 Pollutant Parameters
To assess the impact of wet weather runoff, the water quality of receiving waters during
normal dry weather periods should be known. Water quality data collected during dry weather
conditions provide a basis of comparison to data collected during wet weather conditions.
Sampling several events with varying antecedent dry periods will help define the variations in
pollutant loading for the system.
Receiving water monitoring should include identified parameters of concern. These
parameters typically include those previously identified for combined sewage and CSO
monitoring.
• pH
• BOD
• TDS
• TSS
• Nutrients
• Metals
• Indicator bacteria.
Knowledge of the site-specific water quality concerns could expand the list to include dissolved
oxygen, toxics, biological assessment, and sediment.
2.5.3.4 Hydraulic Monitoring and Analysis
Establishing the hydraulic characteristics of the receiving water is an important first step
in a receiving water study, since the physical dynamics of the receiving water determine the
dilution of pollutants contained in CSOs. Large-scale water movement largely determines the
overall transport and transformation of pollutants. Small-scale hydraulics, such as water
movement near a discharge point (often called near-field), determine the initial dilution and
mixing of the discharge. For example, a discharge into a wide, fast-flowing river might not mix
2-32 August 1995
-------
Chapter 2 System Characterization
across the river for a long distance. This information can help identify sampling locations hi
the river to determine CSO effects (EPA, 1995d).
Hydraulic monitoring hi receiving waters consists of assessment of transport
characteristics (water depth and velocity) and physical characteristics (elevation, bathymetry,
cross-section) of the receiving water body. Hydraulic monitoring methods are determined hi part
based on the type of receiving water being assessed. Generally, gages can be installed on a
temporary or long-term basis to determine depth and velocity variations during wet weather.
Analysis of hydraulic data hi receiving waters can consist of developing stage-discharge
or other rating curves for specific monitoring locations, plotting and reviewing the hydraulic
data, pre-processing the data for input into hydraulic models, and evaluating the data to define
hydraulic characteristics, such as initial dilution, mixing, travel tune, and residence tune.
Methods for developing rating curves for various types of flow monitoring stations are presented
in Measurement and Computation of Streamflow (USGS, 1982) and Water Measurement Manual
(USDI, 1984). The general purpose of these analyses is to allow estimation of the flow rate
based on a depth measurement. Calibration of the stage-discharge relationship using measured
velocities is necessary.
2.5.3.5 Receiving Water Quality Monitoring and Analysis
The collection and analysis of receiving water quality data are necessary when available
data are not sufficient to describe water quality impacts that result from the CSOs. The initial
steps in conducting a receiving water sampling program involve selecting sampling locations and
determining sampling frequency and parameters (Sections 2.5.3.1-2.5.3.3).
Sampling receiving waters to provide background water quality data and to assess CSO
impacts can range from manual collection of bacterial samples from a stream to a full-scale
oceanographic investigation of a harbor using a sizable vessel and requiring considerable
logistics (EPA, 1993b). The use of proper sampling techniques is crucial (USDI, 1984; EPA,
1982; Plumb, 1981; APHA, 1992).
2-33 August 1995
-------
Chapter 2 System Characterization
Chemical receiving water quality data are analyzed by plotting and reviewing the raw
data to define water quality characteristics and by processing the data for input to water quality
models. Data can be analyzed and displayed using various types of spreadsheets, graphics
software, and statistical packages. One basic analysis is to compare the receiving water quality
data with applicable water quality criteria to determine whether criteria are being exceeded in
the receiving water body. Sampling before, during, and after a wet weather event can indicate
whether water quality problems occur during dry and/or wet weather and if they are likely due
to CSOs or other sources. Sampling data in areas thought to be affected by CSOs can be
compared with data from areas upstream of or away from CSO outfalls to try to distinguish CSO
impacts. In addition, water quality data are used to calibrate receiving water models usually by
plotting the data versus time and/or distance to compare with model simulations (Section 2.6.2).
In some cases, special studies might be necessary to identify rate constants, such as bacteria die-
off rates or suspended solids settling rates.
2.5.3,6 Sediment and Biological Monitoring and Analysis
It is often difficult and expensive to identify CSO impacts during wet weather using
hydraulic and water quality sampling (EPA, 1995d). In some cases, sediment and biological
monitoring can serve as cost-effective supplements or even as alternatives to water quality
sampling. For example, the long-term effect of CSOs can be represented by comparing grab
samples of bottom sediments or biota to data from reference sampling points.
Sediment Sampling
Receiving water sediments serve as sinks for a wide variety of materials. Nutrients,
metals, and organic compounds bind to suspended solids and settle to the bottom of a water body
when flow velocity is insufficient to keep them in suspension. However, it should be noted that
sediments affected by wet weather runoff usually exhibit the long-term effects of both dry and
wet weather discharges because of their relative immobility. Grab samples can be taken to
indicate historical accumulation patterns. Sampling sites can be located at points of impact,
upstream (or downstream) reference sites, areas of future expected changes, or other areas of
2-34 August 1995
-------
Chapter 2 System Characterization
particular interest, based on an awareness of possible impact sites, accessibility, and hydraulic
conditions.
Sediment sampling results are useful for assessment of physical characteristics (grain size,
distribution, type of sediment) of the deposited sediments, chemical analysis of sediments
deposited by CSOs, and examination of benthic communities that might be affected. Sediments
from upstream reference stations, and possibly from areas affected by non-CSO sources, should
be sampled for comparison with sediments near the CSO. (It should be noted that sediments
affected by CSOs and other wet weather sources may be considerably downstream of the
sources, particularly in waters whose velocities increase greatly during rainfall. In general,
sediments tend not to settle in streams with velocities greater than 0.5 feet/second.)
Biological Sampling
Evaluating aquatic populations and communities can provide information not available
through water and sediment testing. Because resident populations and communities of aquatic
organisms integrate over time all the environmental changes that affect them, the biological
community can reveal the cumulative impact of pollutant sources or short-term toxic discharges
not represented in discrete water and sediment samples. EPA's guidance on monitoring and
modeling provides a comprehensive summary of biological collection methods, as well as the
information potentially available through the monitoring of aquatic organisms (EPA, 1995d).
Benthic (bottom-dwelling) organisms are affected by contaminants in the water column
and through contact with or ingestion of contaminated sediments. Therefore, the type,
abundance, and diversity of benthic organisms can be used to investigate the presence, nature,
and extent of pollution problems. Comparing areas upstream and downstream of a suspected
pollution source requires sampling locations with similar bottom types, because physical
characteristics affect the habitat requirements of organisms.
Community structure, described in terms of species diversity, richness, and species
evenness, is commonly used to evaluate the environment. The use of biological organisms as
2-35 August 1995
-------
Chapter 2 System Characterization
indicators of aquatic environmental health is based on the understanding that a natural
environment is normally characterized by a balanced biological community comprised of a large
number of species with no one species dominating. The presence of certain species that are
known to be intolerant of polluted or disturbed conditions may also be used as an indicator of
an unstressed environment, and conversely, other species may serve as indicators of
environmental stress. Species diversity is affected by such factors as colonization rates,
extinction rates, competition, predation, physical disturbance, and pollution, and it is often
difficult to determine which factors have caused measured variation in species diversity (i.e.,
pollution or other conditions). A qualitative data assessment whereby the benthic species
collected and their relative population sizes are compared with their known sensitivities to
contaminants present, can help with this determination. Various documents describe these
assessment techniques (EPA, 1995d; Plafkin et al., 1989).
2-36 August 1995
-------
Chapter 2 System Characterization
CASE STUDY: LEWISTON-AUBURN, MAINE—CSO
AND RECEIVING WATER MONITORING
Because of the limited CSO and receiving water data available, a full monitoring program was undertaken.
The objective of the monitoring program was to collect dry weather (baseline condition) and wet weather
data on CSOs, sanitary and separate storm sewer flows, and the rivers and brooks receiving CSOs. These
data were then used to quantify pollutant loadings to receiving waters and to assess impacts of those
loadings on receiving water quality. The sampling and monitoring data were also used to calibrate and
verify computer models of the CSSs in both Lewiston and Auburn (see the case study following Section
2.6.2.3). The different elements of the sampling and monitoring program are summarized below:
• Wastewater flows within each sewer system were measured, sampled, and analyzed for
various water quality parameters during dry weather, high ground water (spring time)
conditions to determine base wastewater flows, infiltration rates, and baseline pollutant
loadings.
• CSOs from four storm events at selected CSO regulators within each CSS were measured,
sampled, and analyzed for various water quality parameters during two 6-week periods to
determine CSO flows and loads to receiving waters.
• Storm water runoff from four storm events at selected locations within the separate storm
drain systems of each city were measured, sampled, and analyzed for various water quality
parameters during two 6-week periods to determine pollutant loadings hi storm water runoff
to receiving waters.
• Receiving waters were sampled and analyzed during dry weather and during two storm
events. The collected samples were analyzed for various water quality parameters and
priority pollutants to define baseline receiving water quality and to determine the impacts of
CSOs on receiving water quality.
• Continuous release dye studies were conducted to assess the rate of mixing and dispersion of
CSOs from each city in the receiving waters.
Each of these sampling activities occurred during the same storm events to ensure consistency among the
data. The discussions in this case study focus only on the CSO and receiving water sampling.
SELECTION OF CSO MONITORING STATIONS
A review of existing information coupled with a field inspection of the CSSs in Lewiston and Auburn
identified a total of 29 CSO regulators and 17 cross-connections between the combined sewer and separate
storm drain systems. Because it was not economically feasible to sample and monitor each CSO outfall,
site-selection criteria for CSO sampling and monitoring stations were used to select representative CSOs
in the study area that were significant contributors of CSO flows to receiving waters.
Initially, the location of each CSO regulator and cross connection hi Lewiston was ranked as having a low,
moderate, or high frequency of activity. The ranking was determined as follows:
• Low frequency of activity, rainfall greater than 0.75 inches
• Moderate frequency of activity, rainfall between 0.25 and 0.75 inches
• High frequency of activity, rainfall less than 0.25 inches.
2-37 August 1995
-------
Chapter 2 System Characterization
Because the CSOs in Auburn were not inspected during all storm events, the data were limited. As a
result, a ranking of the frequency of activity during specific rainfall volumes (similar to ranking performed
for Lewiston) was not possible. Instead, the frequency of activity between the CSOs for the period that
data were available was compared. The criteria used to rank the frequency were as follows:
• Low frequency of activity, 0 to 3 overflows recorded
• Moderate frequency of activity, 4 to 7 overflows recorded
• High frequency of activity, 8 to 10 overflows recorded.
The following final monitoring station selection criteria were developed:
• Land Use—The tributary area land uses must be representative of the study area in order to
define meaningful rainfall/runoff relationships and pollutant loadings for use in analyzing
other tributary areas in the study area.
• Tributary Area—An important selection criterion for monitoring CSOs is the ability to define
the tributary area boundaries. Tributary areas free of external diversions or transfers were
sought to ensure that the flows and pollutants measured at the monitoring site were actually
produced within the subbasin being monitored rather than being imported from adjacent
service areas or exported out of the subbasin. The tributary areas were identified through
detailed study of the sewer systems and topographical maps of the study areas.
• Hydraulic Compatibility—The hydraulic control sections at the monitoring stations must be
stable and compatible with the proposed monitoring equipment.
• Accessibility—The sites should be readily accessible from public rights-of-way and during
adverse weather conditions and should be located away from high traffic areas.
• Receiving Water—The ecological, social, scenic, or recreational importance of the receiving
water where the discharge occurs was considered.
Based on field inspection of CSO regulators and cross-connections, a preliminary screening of potential
sampling and monitoring stations was performed using the site-selection criteria. Preliminary screening
identified a total of 12 potential locations: 9 in Lewiston and 3 in Auburn (see Exhibits 2-8 and 2-9,
respectively).
Subsequent to this preliminary screening, field inspections of the potential sampling and monitoring stations
were conducted. The purpose of these inspections was to ensure that each location was easily accessible,
hydraulically compatible with the equipment to be used, and had a clearly defined tributary area. The eight
most advantageous locations were then selected as the final sampling and monitoring stations for CSOs.
Exhibit 2-10 shows the locations of the monitoring and sampling locations. As indicated in Exhibit 2-10,
these included six CSO regulators in Lewiston (30 percent of the total) and two in Auburn (25 percent of
the total). This approach yielded sufficient wet weather data to quantify CSOs in the study area at a
reasonable cost.
2-38 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-8. Screening of Final CSO Sampling and Monitoring Stations for the City of Lewiston
CSOor
Cross-
connection
003
004
005
007
012
013
015
Structure 'B'
@ LAWPCF
X-2
Advantages
Overflows frequently, easy accessibility.
Overflows frequently, one of few that serves
predominantly commercial/industrial area.
Overflows to small, stagnant receiving water,
potentially large volume of overflow,
overflows frequently.
Moderate frequency of overflows, serves
predominantly residential area, easy
accessibility, medium size service area.
Moderate frequency of overflows.
Overflows frequently.
Overflows frequently, represents only CSO
discharging directly to Goff Brook, serves
predominantly residential neighborhood.
Easy accessibility, potentially large volume of
bypassed flows, can bypass flow during some
plant maintenance procedures.
Moderate frequency of overflows, serves
predominantly residential neighborhood,
discharges to Jepson Brook.
Disadvantages
Represents mixed land use, small tributary
area.
Moderate accessibility due to traffic and
ventilation concerns.
Difficult to monitor CSO flows accurately
due to configuration of regulator, potential
recreational use of Gully Brook is very
limited.
Regulator manhole is shallow making it
difficult to install sampling and monitoring
equipment.
Represents mixed land use, limited record
information on CSO regulator.
Represents mixed land use, difficult to
monitor CSO flows accurately due to having
two tributary regulators.
Dry weather flow in Goff Brook is nearly
nonexistent, no potential for recreational use.
Represents mixed land use, all CSO
regulators in the system are tributary,
bypassed flows controlled manually.
Difficult to monitor CSO flows due to
configuration of regulator.
Selected
X
X
X
X
X
X
Not
Selected
X
X
X
Reason Not Selected
Represents small
tributary area.
Not hydraulically
compatible to monitor
because it would
require at least three
flow metering locations.
Two flow meters would
be required to
determine flows and
pollutant loads tributary
to each regulator.
2-39
August 1995
-------
Chapter 2
System Characterization
Exhibit 2-9. Screening of Final CSO Sampling and Monitoring Stations for the Auburn Sewerage District
CSO or
Cross-
Connection
002
003
005
Advantages
Easy accessibility, discharges to Little
Androscoggin River, high frequency of
overflows.
Representative of large land area, easy
accessibility, discharges to Little
Androscoggin River. Moderate frequency
of overflow due to plugging of siphon.
Easy accessibility, high frequency of
overflows.
Disadvantages
Represents mixed land use.
Represents mixed land use, overflows
infrequently when both siphons operating.
Represents mixed land use.
Selected
X
X
Not
Selected
X
Reason Not Selected
Infrequent overflows,
difficult to access
remote location during
off-hours.
2-40
August 1995
-------
Source: USGS Topographic Maps
Lewiston, Maine 1979
Minot, Maine 1981
Lake Auburn East, Maine 1979
Lake Auburn West, Maine 1981
SCALE IN FEET
LEGEND
CSO Monitoring and Sampling Station
Storm Drain Monitoring and Sampling Station
Rainfall Gauge
Exhibit 2-10. Lewiston-Auburn CSO and Separate Storm Drain
Monitoring and Sampling Locations
2-41
-------
Chapter 2 System Characterization
EXTENT OF CSO MONITORING AND PARAMETERS ANALYZED
The elements of the CSO monitoring program in each community are summarized below:
• Conducted flow metering for two 6-week periods at six CSOs in Lewiston and two CSOs in
Auburn.
• Sampled the CSO monitoring locations during four significant storm events (at least 0.5 inches
of rainfall with high rainfall intensity). For each storm event, a maximum of 12 discrete
samples were collected during first flush and sustained flow. Initially, samples were taken
at 15-minute intervals. Samples for sustained flow were collected in progressively longer
time intervals (e.g., 15-, 30-, 60-, 90-minutes) depending on the anticipated duration of the
overflow event. Each discrete sample was analyzed for BOD5, suspended solids, pH, and E.
coli bacteria. A single flow-weighted composite, prepared from the discrete samples collected
with an automatic sampler for one storm event, was analyzed for lead, chromium, zinc,
copper, nickel, mercury, silver, cadmium, arsenic, and TKN.
• Collected a grab sample at the CSO monitoring locations during the first flush for one storm
event and was analyzed for hydrocarbons, polyaromatic hydrocarbons, PCBs, and herbicides.
Specific toxic pollutants, herbicides, and hydrocarbons were selected for analyses based on
available analysis methods, experience on other previous similar projects, the probability of
their existence within the geographic region, and on water quality analysis industry standards.
• Conducted block testing for all CSO regulators and cross-connections in each community
during the two 6-week periods that temporary flow metering was conducted to identify the
frequency of CSOs to study area receiving waters.
• Conducted coordinated sampling of Lewiston's and Auburn's influent flow at the treatment
plant during the four monitored events. Plant personnel collected and analyzed influent
samples for BOD5, suspended solids, and E. coli bacteria.
The CSS was monitored using a combination of automatic samplers and hand-operated manual samplers.
Continuous flow and velocity measurements in the collection system were also recorded.
SELECTION OF RECEIVING WATER MONITORING STATIONS
To assess the impacts of CSOs on the receiving waters in the study area, water quality data were collected
during wet weather periods. CSOs originating from the Lewiston and Auburn sewer systems occur along
the banks of the Androscoggin River and the Little Androscoggin River, as well as along drainage brooks
tributary to the Androscoggin River, including Goff Brook, Gully Brook, Jepson Brook, and Stetson Brook.
Sampling and monitoring were conducted at eight stations to obtain data on CSO-related water quality
impacts. The receiving water sampling and monitoring stations were selected based on an examination of
the receiving water use, location, importance, and the number, frequency, and relative size of the CSOs
compared to that of the receiving water. Field inspections of the area receiving waters were conducted in
conjunction with the field inspections of CSO regulators and cross-connections within the Lewiston and
Auburn sewer systems. The purpose of these inspections was to determine the locations for sampling and
monitoring of receiving waters to assess CSO-related water quality impacts.
Exhibit 2-11 shows the locations of the eight final sampling and monitoring stations for receiving waters
in the study area. Four sampling and monitoring stations were selected for the Androscoggin River
(stations numbered R-l through R-4) to assess water quality impacts resulting from CSOs by both Lewiston
and
2-42 August 1995
-------
LEGEND
A Flow Sampling Station
SOURCE: USGS Topographic Maps
Lake Auburn East, Maine 1979
Lewiston, Maine 1979
SCALE IN FEET
Exhibit 2-11. Lewiston-Auburn Receiving Water Sampling Stations
2-43
-------
Chapter 2 System Characterization
Auburn. Two sampling and monitoring stations were selected for the Little Androscoggin River (stations
numbered R-5 and R-6) to assess water quality impacts resulting from Auburn's CSOs to the river. Two
sampling and monitoring stations were selected for Jepson Brook (stations numbered R-7 and R-8) to assess
water quality impacts resulting from Lewiston's CSOs to the brook.
RECEIVING WATER MONITORING FREQUENCY AND PARAMETERS
The elements of the monitoring program for receiving waters are summarized below:
• A dry weather sampling survey was conducted, with samples collected at three lateral
locations at each of the stations in the Androscoggin and Little Androscoggin Rivers.
Samples were collected at only one location at each of the stations along Jepson Brook
because it is relatively narrow. Samples were analyzed for E. coli bacteria. In-situ
measurements were made of pH, dissolved oxygen (DO), and temperature. In-situ
measurements for pH, DO, and temperature in the Androscoggin River and Little
Androscoggin River were collected in 1-meter vertical profiles at each location. The sample
for E. coli bacteria was collected near the water surface. In-situ measurements in Jepson
Brook were not taken in 1-meter vertical profiles because the channel is relatively shallow.
• Two wet weather receiving water surveys were conducted during the same storm events that
CSO sampling and monitoring were performed. Samples were collected during the two storm
events at the eight stations in 4- to 6-hour intervals over a 2-day period. pH, DO, and
temperature were measured in-situ. The collected samples were analyzed for E. coli bacteria.
• As part of the receiving water sampling and monitoring program, a continuous release dye
study was conducted on one CSO from each community. The purpose of the dye studies was
to evaluate the mixing and dispersion characteristics of the CSOs entering the Androscoggin
River. This was accomplished by injecting dyed-water into a CSO conduit to create a
simulated CSO and tracking the dye in the river using a fluorometer.
• Temporary flow monitoring at the Jepson Brook drainage channel was conducted for the
duration of the sampling and monitoring program to determine the quantity of CSOs conveyed
by the channel. The flow monitoring was located where the flow enters a circular conduit,
and most CSOs occur upstream.
CSO AND RECEIVING WATER DATA
The collected data illustrate the quality of wastewater flow during dry weather, CSO and storm water flows
during wet weather, and receiving water quality during both dry and wet weather. The data indicate
impacts on receiving water quality from storm-induced CSOs and storm water discharges. Violations of
the E. coli bacteria standards in the area receiving water are widespread during wet weather conditions and,
to a limited extent, during dry weather.
CSO Data
Wet weather flow and quality data were collected during three storm events and, as indicated Exhibit 2-12,
were analyzed for BOD5, TSS, and E. coli bacteria. The data are within typical ranges for CSO quality
and generally show a "first-flush" phenomenon. In addition, the collected samples from one storm event
were composited and analyzed for selected metals, nutrients, PCBs, herbicides, and hydrocarbons. No
PCBs or herbicides were detected in any of the CSO samples. The composite samples were also analyzed
for a series of metals (see Exhibit 2-13), which are often present in runoff and CSOs.
2-44 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-12. Lewiston-Auburn CSO Quality Data
Location
Auburn
CSO 002
CSO 005
Lewiston
CSO 004
CSO 007
CSO 012
CSO 015
X-2
LAWPCF
Structure B
Typical CSO
Characteristics'"'
BOD,, mg/l
Range
41 - 139
13 - 110
5 - 151
12 - 139
5-50
4-6
4 -21
31 - 195
60 - 220
Average
43
43
59
52
25
5
12
25
-
TSS, mg/l
Range
40 - 200
38 - 276
4 -230
28 - 310
55 - 144
21 -28
14-48
72-200
270 - 550
Average
111
108
101
123
98
25
34
129
-
E. cott Range
Colonies/100 ml
9.0xl04-2.1xlO*
l.lxlO5- 2.7x10*
S.OxlO3 - 1.3x10*
0 - 7.0x10*
2.0xl04 - S.SxlO5
6-OxlO4
1.2X105- 1.1x10*
3.7xl03- 1.2x10*
2-OxlO5- 1.1x10*
(a) Source: Metcalf & Eddy, Inc., 1991
Exhibit 2-13. Lewiston-Auburn CSO Metals Data
Parameter
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Silver
Zinc
Data Range
(mg/l)
.0011 - .0022
.0002 - .0019
.0040 - .0085
.07 - .15
.0213 - .0810
< .0002 - < .0004
.002 - .006
.0008 - .002
.09- .13
EPA Freshwater
Acute Criteria
(mg/l)
.36
.0039
.016
.018
.0830
.0024
1.400
.0041
.12
2-45
August 1995
-------
Chapter 2 System Characterization
Receiving Water Data
Wet weather data were collected during two storm events where CSO and storm water sampling were also
conducted (Exhibit 2-14). E. coli bacteria levels increased significantly in the Androscoggin River during
both events. At Station R-l, the upstream station at Gulf Island Pond, little to no bacteria were detected
in the samples during either storm event, indicating negligible bacterial contamination entering the study
area from upstream areas. During the course of both storm events, bacterial concentrations at the
downstream stations on the Androscoggin River were elevated in response to the storm-induced CSOs and
storm water discharges.
DO and pH also exhibited a measurable response to the storm-related discharges. In general, when the
peak levels of bacteria were observed, the DO levels declined to the lowest values and then rebounded.
The variation in DO was generally less than 2 mg/1 and, even at the lowest levels, DO was well above the
Class C standard of 5.0 mg/1. By contrast, pH exhibited the opposite trend from the dissolved oxygen
data. The pH levels generally climbed in response to the storm event.
At the downstream station of the Little Androscoggin River, significant levels of bacteria were measured
during the peak periods of the September storm. These levels exceeded the Class C criterion, reaching
concentrations of 8,000 colonies/100 ml. The high levels did not persist for an extended period of time.
In the October storm, the bacterial levels increased as a result of the storm-induced CSOs, but not to a
level that exceeded the Class C criterion.
DO at both stations on the Little Androscoggin indicated a noticeable sag in response to the storm-induced
CSOs. Oxygen levels at both stations are normally elevated due to aeration as a result of the dams
immediately upstream of each sampling site. DO concentrations declined by approximately 1 to 2 mg/1
in the September storm, while less sag was observed during the October storm. During both storm events,
the DO sag was temporary, with the oxygen concentrations returning to pre-storm conditions relatively
quickly. Because both upstream and downstream stations exhibited the DO sag and increase, upstream
influences appear to have a significant impact on oxygen levels.
The highest E. coli counts measured in the receiving water sampling program were detected in Jepson
Brook. Bacteria levels at both sampling stations exceeded the Class B criterion of 427 colonies/100 ml
during the two storm events. Levels of E. coli rose significantly in response to the storms. This was
expected for the downstream sampling station, Station R-8, due to the number of CSO outfalls and storm
drains discharging to the brook. The elevated E. coli levels at the upstream end of the brook were not
anticipated, however. Similar levels were observed in both storm events.
DO levels exhibited a decrease in response to the storm events. The dissolved oxygen sag was significant,
as the lowest value for oxygen measured was 5.0 mg/1, well below the Class B criterion of 7.0 mg/1.
The wet weather receiving water data clearly indicated the impacts of CSOs and storm drain discharges
on the local receiving waters during storm events. These data, together with the background dry weather
water quality data, CSO and storm drain flow and load data, and the continuous dye study, provided the
basis for the CSO and receiving water modeling effort described in the next case study, following Section
2.6.2.3.
2-46 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-14. Lewiston-Auburn Receiving Water E. Coli Data
Station
Androscoggin River
R-l
R-2
R-3
R-4
Little Androscoggin
River
R-5
R-6
Jepson Brook
R-7
R-8
Dry Weather
Range
(colonies/lOOml)
0
480 - 2,280
100 - 135
280 - 355
5- 115
35-80
60
115
% of Samples
Above
Standards
0
67
0
0
0
0
0
0
Wet Weather
September 26-28, 1993
Range
(colonies/100 ml)
0-20
0 - 1,440
160 - 6,800
60 - TNTC
0-810
0-8,000
20 - 2,400
40 - 30,000
% of Samples
Above Standards
5
8
58
71
0
17
33
83
October 12-14, 1993
Range (colonies/
100ml)
0
0-980
10 - 3,500
90 - TNTC
0-210
0-280
40 - 2,500
140 - TNTC
% of Samples
Above Standards
0
4
25
29
0
0
31
62
Note: Class C Standard: Instantaneous level of 949 colonies/100 ml
TNTC = Too numerous to count
2-47
August 1995
-------
Chapter 2 System Characterization
2.6 COMBINED SEWER SYSTEM AND RECEIVING WATER MODELING
Section 2.6 summarizes the use of mathematical models to characterize CSSs and evaluate
CSO control alternatives and CSO impacts to receiving waters. This section discusses modeling
objectives, as well as model selection and application, for the CSS and receiving water. As with
other sections of this chapter, the intent is to provide an introduction to the information
presented in greater detail in EPA's guidance on monitoring and modeling (1995d).
2.6.1 Combined Sewer System Modeling
This section briefly summarizes CSS modeling objectives, model selection strategy, and
model development and application, including model calibration and validation and the different
types of model simulations (e.g., long-term continuous versus storm event simulations).
2.6.1.1 CSS Modeling Objectives
The primary objective of CSS modeling is to understand the hydraulic response of the
CSS to a variety of precipitation and drainage area inputs. CSS modeling can also be used to
predict pollutant loadings to receiving waters. Once the model is calibrated and verified, it can
be used for numerous applications that support CSO planning efforts, including (EPA, 1995d):
• To predict overflow occurrence, volume, and, in some cases, quality for rain events
other than those which occurred during the monitoring phase. These can include a
storm event of large magnitude (long recurrence period) or numerous storm events
over an extended period of time.
• To predict the performance of portions of the CSS that have not been extensively
monitored.
• To develop CSO statistics, such as annual number of overflows and percent of
combined sewage captured in response to the presumption approach of the CSO
Control Policy.
• To optimize CSS performance as part of NMC implementation. In particular,
modeling can assist in locating storage opportunities and hydraulic bottlenecks and
demonstrate that system storage and flow to the POTW are maximized.
2-48 August 1995
-------
Chapter 2 System Characterization
• To evaluate and optimize control alternatives, from simple controls described under
the NMC to more complex controls proposed in a municipality's LTCP. An example
of a simple control would be to raise weir heights to increase in-line storage. The
model can be used to evaluate the resulting reductions in CSO volume and frequency.
CSS Modeling and the CSO Control Policy
The CSO Control Policy ".. .supports the proper and effective use of models, where
appropriate, in the evaluation of the nine minimum controls and the development of the long-term
CSO control plan" (II. C. 1 .d). Every CSS does not need to be analyzed using complex computer
models. In simple systems, computation of hydraulic profiles using basic equations (e.g.,
Manning's equation) and spreadsheet programming might be sufficient for identifying areas
where certain measures can be implemented and for evaluating their hydraulic effect.
Mathematical simulation can play an important role in credibly predicting the performance of
any CSS, however. In many cases, especially in complex CSSs that have looped networks or
sections that surcharge, a hydraulic computer model will be a useful tool to assess both NMC
and LTCP options.
As discussed in the CSO Control Policy, continuous simulation refers to the use of
long-term rainfall records (from several months to several years) rather than rainfall records for
individual storms (design storms). Continuous simulation has several advantages:
(1) simulations are based on a sequence of storms so that the additive effect of storms occurring
close together can be examined, (2) storms with a range of characteristics are included, and
(3) in cases where the municipality intends to use the presumption approach to WQS attainment,
long-term simulations enable the development of performance criteria based on long-term
averages, which are not readily determined from design storm simulations. Continuous
simulation need not involve the application of extremely complex models. Models that simulate
runoff without complex simulation of sewer system hydraulics (e.g., STORM, SWMM
RUNOFF) might be appropriate if rough estimates are acceptable or for CSSs with simple basic
hydraulics.
2-49 August 1995
-------
Chapter 2 System Characterization
Modeling can support either the demonstration or presumption approach of the CSO
Control Policy. The demonstration approach requires demonstration that a control plan is
adequate to meet CWA requirements. Meeting this requirement can necessitate detailed CSS
modeling to define inputs to receiving water impact analyses. The presumption approach,
however, involves numeric limits on the number or volumes of CSOs. This approach may
require less modeling of receiving water impacts. However, the presumption approach is
acceptable only if "...the permitting authority determines that such presumption is reasonable
in light of the data and analysis conducted in the characterization, monitoring and modeling of
the system and the consideration of sensitive areas..." (II.C.4.a).
2.6.1.2 CSS Model Selection
Several guidance documents present strategies for selecting the appropriate CSS model
(EPA, 1995d; Shoemaker et al., 1992; Donigian and Huber, 1991; WPCF, 1989). This section
briefly summarizes the model selection process.
CSS modeling involves two distinct elements—hydraulics and water quality:
• Hydraulic modeling consists of predicting flow characteristics in the CSS. These
characteristics include the different flow rate components (i.e., sanitary, infiltration,
and runoff), the flow velocity and depth in the interceptors and sewers, and the CSO
flow rate and duration.
• CSS water quality modeling consists of predicting the quality of the combined sewage
in the system, particularly at CSOs and at the treatment plant. Water quality is
measured in terms of critical parameters, such as bacterial counts, and concentrations
of constituents, such as BOD, suspended solids, nutrients, and toxic contaminants.
Some models include both hydraulic (e.g., number and magnitude of overflows) and
water quality components, while others are limited to one or the other. The type and complexity
of modeling depends on the aspect of the CSO Control Policy being evaluated. Exhibit 2-15
shows the different combinations of hydraulic and contaminant simulation that might be
appropriate under different circumstances.
2-50 August 1995
-------
Chapter 2
System Characterization
Exhibit 2-15. Relevant CSS Hydraulic and Contaminant Transport Modeling
for the CSO Control Policy
CSS Hydraulic Modeling
CSS Contaminant Transport
Modeling
Nine Minimum Controls
Demonstrate implementation of the
nine minimum controls
Simple to complex models of
duration and peak flows
Limited - Not usually performed
Presumption Approach
Limit number of overflow events
per year
Capture at least 85 % of wet weather
combined sewage volume per year
Eliminate or reduce mass of
pollutants equivalent to 85% capture
requirement
Long-term continuous simulations
(preferred) or design storm
simulation
Same
Same
Limited - Not usually performed
Limited - Not usually performed
Use measured concentrations
or
simplified transport modeling
Demonstration Approach
Demonstrate that a selected control
program is adequate to meet the
water quality-based requirements of
theCWA
Design storm simulations
or
long-term continuous simulations
Use measured concentrations
or
contaminant transport simulations
Source: EPA, 1995d
Hydraulic Models
The hydraulic models appropriate for CSS simulations can be divided into three main
categories (EPA, 1995d):
• Water-budget models based on Soil Conservation Service (SCS) curve numbers,
runoff coefficients, or other similar method for the generation of flow. These models
can estimate runoff flows influent to the sewer system and, to a lesser degree, flows
at different points hi the system. However, these models do not actually simulate
flow hi the CSS and, therefore, do not predict such parameters as the flow depth,
which frequently control CSO occurrence.
• Models based on the kinematic wave approximation of the hydrodynamic
equations. These models can predict flow depths and, therefore, overflows in
systems not subject to surcharging or backups (backwater curves).
• Complete, dynamic models are based on the full hydrodynamic equations and can
simulate surcharging, backwaters, or looped systems.
2-51
August 1995
-------
Chapter 2 System Characterization
Examples of these three classes of models are the RUNOFF, TRANSPORT and EXTRAN
blocks, respectively, of the EPA Storm Water Management Model (SWMM). EPA's guidance
on monitoring and modeling lists the capabilities and limitations of these models (1995d). The
following list provides criteria for selecting a CSS hydraulic model:
• Ability to accurately represent the physical characteristics and flow processes relevant
to CSS performance
• Extent of monitoring activity underway
• Need for long-term simulations
• Needs for CSS water quality simulations
• Needs for receiving water quality analysis
• Ability to assess the effects of control alternatives
• Use of the presumption or demonstration approach
• Ease of use and cost.
Water Quality Models. CSS water quality models can be divided into the following categories:
• Land Use Loading Models—These models provide pollutant loadings as a function
of the distribution of land uses in the watershed. Although there are variations, the
basic approach is to attribute to each land use a concentration for each water quality
parameter. The overall runoff quality is then calculated as a weighted sum of these
concentrations. Pollutant concentrations for the different land uses can be derived
from local data bases or the NURP studies, if local data are not available (local data
are strongly recommended).
• Statistical Methods—A more sophisticated version of the previous method is based
on a derived frequency distribution for Event Mean Concentrations (EMCs), usually
based on lognormality assumptions. Documents on NURP discuss the use of
statistical methods to characterize CSO quality in detail (Hydroscience, Inc., 1979)
and in summary form (EPA, 1983).
• Buildup/Washoff Models—These models attempt to deterministically simulate the
basic processes that control the quality of runoff. This approach can consider such
factors as time periods between events, rainfall intensity and best management
practices. Calibration is required, however.
2-52 August 1995
-------
Chapter 2 System Characterization
For some pollutants, chemical reactions and transformations within the CSS might be
important. Few models address this topic, and calibration is difficult because loading into the
CSS is never exactly known. If a CSS water quality model is warranted, criteria for the
selection of a model for the LTCP include the following (EPA, 1995d):
• Needs of the receiving water quality simulation
• Ability to assess control and best management practice (BMP) alternatives
• Ability to accurately represent significant characteristics of pollutants of concern
• Capability for pollutant routing
• Expense and ease of use.
EPA and Army Corps of Engineers have developed numerous hydraulic and water quality
models, ranging from simple to complex, which are available for use. A description of these
models and their characteristics is beyond the scope of this guidance. EPA's guidance on
monitoring and modeling provides detailed information (EPA, 1995d).
2.6.1.3 CSS Model Application
In modeling terminology, the model's level of discretization (i.e., coarse versus fine
scale) determines the accuracy with which it will represent the geometry of the CSS or the land
characteristics of the drainage basin. In determining the appropriate level of discretization, the
modeler must ask the following questions. What is the benefit of a finer level of detail? What
is the penalty (in accuracy) in not modeling a portion of the system? For systems controlled
hydraulically at their downstream ends, modeling only the larger downstream portions of the
CSS might be successful. This strategy would not be wise, however, if it is known that
surcharging in upstream areas of the CSS (in small pipes) occurs, limiting flows. In this case,
a simulation neglecting the upstream portion of the CSS would overestimate flows in the system.
2-53 August 1995
-------
Chapter 2 System Characterization
In some cases, it is difficult to determine ahead of time the appropriate level of detail.
In these cases, the modeler can take a phased approach, determining the value of additional
complexity or data added in the previous step.
A model general enough to fit a variety of situations typically should be adjusted to the
characteristics of a particular site and situation. Modelers use model calibration and verification
first to perform this adjustment and then to demonstrate the credibility of the model simulation
results. Using an uncalibrated model might be acceptable for screening purposes. Without
supporting evidence, however, the uncalibrated result might not be accurate. To use model
simulation results for evaluating control alternatives, the modeler should supply evidence
demonstrating the model's reliability.
Model Calibration
Calibration is the process of using a set of input data and then comparing the results to
measurements of the system. For example, a CSS hydraulic model used to simulate overflows
is calibrated by running the model using measured rainfall data to simulate attributes of CSOs,
such as volume, depth, and timing. The model results are then compared to actual
measurements of the overflows. The modeler then adjusts parameters, such as the Manning
roughness coefficient or the percent imperviousness of subcatchments, and runs the model a
second time, again comparing the results to observations. Initial calibration runs often point to
features of the system, such as a connection or bypass, that might not have been evident based
on the available maps. The modeler repeats this procedure until satisfied that the model
produces reasonable simulations of the overflows.
Verification
Verification is the process of testing the calibrated model using one or more independent
data sets. Verification is important to modeling because it assesses whether the model retains
its generality (i.e., a model that has been adjusted extensively to match a particular storm exactly
might lose its ability to predict the effects of other storms). In the case of the hydraulic
simulation, the model is run without any further adjustment using an independent set of rainfall
2-54 August 1995
-------
Chapter 2 System Characterization
data. Then, the results are compared to the field measurements collected concurrently with these
rainfall data. If the results are suitably close, the model is considered to be verified. The
modeler can then use the model with other sets of rainfall data or at other outfalls. If
verification fails, the modeler must recalibrate the model and verify it again using a third
independent data set. If the model fails a verification test, the next test must use a new data set.
Re-using a data set from a previous verification test does not constitute a fair test, because the
modeler has already adjusted model parameters to ensure compliance.
2.6.2 Receiving Water Modeling
This section describes the use of models in evaluating CSO impacts on receiving waters.
2.6.2.1 Receiving Water Modeling Objectives
The goal of the receiving water analysis (which may include modeling) is to characterize
CSO impacts on receiving water quality and to predict the improvements from different CSO
controls.
Receiving Water Quality Modeling and the CSO Policy
Under the CSO Control Policy, a municipality should develop an LTCP that adopts either
the demonstration or the presumption approach to attainment of WQS. The demonstration
approach is based on adequately demonstrating that the selected CSOs will provide for the
attainment of WQS, including designated uses in the receiving water. The presumption approach
does not explicitly call for analysis of receiving water impacts. The presumption approach
usually involves at least screening-level models of receiving water impacts, however, because
the approach will not apply if the NPDES permitting authority determines that the LTCP will
not result in attainment of CWA requirements.
2-55 August 1995
-------
Chapter 2 System Characterization
2.6.2.2 Receiving Water Model Selection
Three factors need to be considered when selecting a receiving water model:
• The type and physical characteristics of the receiving water body. Rivers, estuaries,
coastal areas, and lakes typically require different models.
• The water quality parameters that need to be modeled, which include bacteria,
dissolved oxygen, suspended solids, toxics, and nutrients. These parameters are
affected by hydrodynamics and by other processes (e.g., die-off for bacteria, settling
of solids, biodegradation for DO, adsorption for metals), which have different time
scales (e.g., hours for bacterial die-off, days for biodegradation) and different
kinetics. The time scale in turn affects the extent of the receiving water modeled
(e.g., a few hundred feet for bacteria to a few miles for dissolved oxygen).
• The number and geographical distribution of discharge points and the need to
simulate sources other than CSOs.
Receiving water modeling may consist of hydrodynamic modeling (to assess flow
conditions) and/or water quality modeling. Both hydrodynamic and water quality receiving
water models can be steady-state or transient. Steady-state models assume that conditions do
not change over time, while transient models can simulate time varying conditions. Depending
on the application, various combinations of steady-state and transient models can be used for
receiving water models.
Hydrodynamic Models
For simple cases, hydrodynamic conditions can be determined from the receiving water
monitoring program; otherwise, flow conditions are calculated using a hydrodynamic model.
The main purpose of a hydrodynamic model is to provide the flow conditions, characterized by
the water depth and velocity, for which water quality must be predicted. Because the same basic
transport equations apply, the major models for receiving waters can generally simulate more
than one type of receiving water body (i.e., rivers, estuaries, coastal areas, lakes). Whether a
model can be used with a particular hydraulic regime depends upon several factors: whether the
model is a one-, two-, or three-dimensional simulation; the ability of the model to handle
specific boundary conditions, such as tidal boundaries; whether the model assumes steady-state
2-56 August 1995
-------
Chapter 2 System Characterization
conditions or allows for time varying pollutant loading. In general, steady-state loading models
cannot accurately model CSO problems that require analysis of far-field effects.
Water Quality Models
Because CSO loads are typically delivered in short pulses during storm events, the
selection of appropriate time scales for receiving water modeling depends upon the time and
space scales necessary to evaluate the WQS. If analysis requires determining the concentration
of a toxic at the edge of a relatively small mixing zone, a steady-state mixing zone model might
be satisfactory. When using a steady-state mixing zone model in this way, the modeler should
apply appropriately conservative assumptions about instream flows during CSO events. For
pollutants such as oxygen demand, which could result in an impact over a period of several days
and often several miles downstream of the CSO, incorporating the pulsed nature of the loading
might be warranted. Assuming a constant loading is much simpler (and less costly) to model,
however, it is conservative (i.e., leads to impacts larger than expected). For pollutants such as
nutrients where the response time of the receiving water body might be slow, simulating only
the average loading rate might suffice.
Detailed receiving water simulation models do not need to be implemented in all
situations (EPA, 1995d). In some cases, the use of dilution and mixing zone calculations or
simulation with simple spreadsheet models is sufficient to assess the magnitude of potential
impacts or to evaluate the relative merit of various control options. EPA's guidance on
monitoring and modeling discusses the simulation of different water quality parameters in rivers,
lakes, and estuaries and summarizes available water quality models (EPA, 1995c).
2.6.2.3 Receiving Water Model Application
The application of receiving water models for CSO programs includes the following
steps:
• Development of the model
• Model calibration and verification
2-57 August 1995
-------
Chapter 2 System Characterization
• Model analysis
• Interpretation of results.
Although the general principles of establishing the data needs for receiving water models
are similar to those discussed for CSS models, the specific requirements depend upon the
hydraulic regime and model employed (EPA, 1995d). For specific input data requirements, the
municipality should refer to the documentation for individual models, the relevant sections of
the Guidance for State Water Monitoring and Wasteload Allocation Programs (EPA, 1985), or
to texts such as Principles of Surface Water Quality Modeling and Control (Thomann and
Mueller, 1987).
Model Calibration and Verification
Like CSS models, receiving water models need to be calibrated and verified. This is
accomplished by running the model to simulate events for which receiving water hydraulic and
quality monitoring was conducted and comparing the model results with the measurements.
Calibration and verification are often conducted in two steps: first for receiving water
hydrodynamics and then for water quality. Calibration of a receiving water quality model
typically cannot be achieved with the same degree of accuracy as that of a CSS model for the
following reasons:
• Pollutant loadings, which are required input to the receiving water quality model, are
typically not known accurately, whether they are determined by monitoring or
modeling of the CSS system.
• Because three-dimensional receiving water models are still not commonly available
and used in CSO control efforts, receiving water models involve spatial averaging
(over the depth, width, or cross-section). Thus, model results are not directly
comparable with measurements, unless the results have sufficient spatial resolution
to allow comparable averaging.
• Loadings from non-CSO sources (such as storm water), upstream boundaries, other
point sources, and atmospheric deposition, are frequently not known.
• Receiving water hydrodynamics are affected by numerous factors which are difficult
to account for, including fluctuating winds, large-scale eddies, and density effects.
2-58 August 1995
-------
Chapter 2 System Characterization
These uncertainties, however, make calibration all the more important to ensure that the model
reasonably reflects receiving water characterization data. Measures of Verification, Workshop
on Verification of Water Quality Models presents a detailed discussion of the validation procedure
for water quality models (Thomann, 1980).
Model Analysis
Analyses can be conducted using single events or long-term simulations. Single event
simulations are usually favored when using complex models, although advances in computer
technology keep extending the limits of what can practically be achieved. Long-term simulations
can provide predictions of water quality impacts on an annual basis.
While a general goal might be to determine the number of WQS exceedances, models
allow evaluation of these exceedances using different measures, such as duration of exceedance
at critical points (e.g., beaches), acre-hours of exceedance, and mile-hours of exceedance along
a shore. These provide a more refined measure of CSO impacts on water quality and of the
improvements that would result from implementation of different CSO controls. A frequently
used approach is to conduct separate simulations for CSO loadings alone to gage the CSO
impacts relative to other sources. Chapter 3 discusses the application of this approach. This
procedure is appropriate because the equations governing receiving water quality are linear and,
consequently, the effects are additive.
It is useful to assess the sensitivity of modeling results due to variations and changes in
parameters, rate constants, and coefficients. Results of such sensitivity analyses determine the
key parameters, rate constants, and coefficients that merit particular attention in evaluating CSO
control alternatives. The modeling approach should accurately represent features that are fully
understood and also be supported by sensitivity analyses to develop an understanding of the
significance of other factors or features that are not as clearly defined. Sensitivity or uncertainty
analyses can define the extent of variation in predicted future water quality conditions due to a
variation of water quality parameters or factors that are not well defined or well established.
2-59 August 1995
-------
Chapter 2 System Characterization
Interpretation of Results
Using averages over space and time, simulation models predict CSO volumes, pollutant
concentrations, and other variables of interest. The extent of this averaging is a function of the
model structure, model implementation, and resolution of the input data. The purpose of
modeling generally includes assessing the attainment of WQS, the number or volume of overflow
events, or other conditions proposed by the permit writer. The model's space and time
resolution should match that of the necessary analysis. For instance, the applicable WQS can
be expressed as a 1-hour average concentration not to exceed a given concentration more than
once every 3 years on average. Spatial averaging can be represented by a concentration
averaged over a receiving water mixing zone or implicitly by the specification of monitoring
locations to compare results with in-stream criteria. In any case, the municipality should note
whether the model predictions use the same averaging scales required in the permit or relevant
WQS.
The key output of the receiving water modeling is the prediction of expected conditions
due to CSO control alternatives and their associated reductions of pollutant loads. In most cases,
the municipality will use the modeling results to determine which load reductions are necessary
for achieving WQS.
2-60 August 1995
-------
Chapter 2 System Characterization
CASE STUDY: LEWISTON-AUBURN, MAINE-CSO
AND RECEIVING WATER MODELING
The CSSs in Auburn and Lewiston were analyzed to determine the flow quantities and pollutant loads
discharged to area receiving waters from CSSs within each community. The CSO analysis was
accomplished using the Storm Water Management Model (SWMM), which mathematically simulates the
time varying nature of CSOs, including both quantity and quality variation over time, under various
hydrologic conditions. As part of the analysis, the CSO response to short-term rainfall, including a range
of design storm events, and the effects of long-term rainfall, using annual precipitation records, were
evaluated for existing and future no-action conditions.
In addition, the Androscoggin and Little Androscoggin Rivers were analyzed to assess the impacts of CSOs
on receiving waters. This analysis focused on E. coli bacteria levels in the two rivers because the wet
weather monitoring program indicated that only this criterion was exceeded.
CSO MODEL DEVELOPMENT
To use SWMM to determine the CSO flows and loads discharged by each community, the physical
characteristics of each CSS and their combined sewer tributary areas were discretized into individual
elements for model input. For this study, a coarse level of discretization was used to characterize the
CSOs. The level of discretization involved modeling the main trunk sewers, interceptors, and CSO
regulators in detail and modeling the area tributary to each CSO as a single drainage area, or subcatchment,
depending on land use. The discretization provided the necessary degree of accuracy for the hydraulics
controlling CSOs, while maintaining an economical analysis effort for the study area.
SWMM was used to predict the quantity and quality of CSOs from both the Auburn and Lewiston CSSs
under various conditions, which were not directly measured, and under proposed future conditions. First,
however, the model's ability to predict such conditions was demonstrated through the following steps:
• Flow monitoring, block testing, rainfall monitoring, and quality sampling during dry weather
and wet weather storm events were conducted, as described in the case study following
Section 2.5.3.6.
• Necessary input data for SWMM were established by reviewing existing record information
and field measurements.
• SWMM was run with data collected during one storm event, and the model results were
compared to the observed field results. Physical parameters were adjusted within acceptable
limits to obtain the "best fit" between observed and computed data.
• A second storm event was then run using SWMM with the same physical parameters used to
model the first storm. Model results were compared with observed data, thereby establishing
confidence in the model's results.
• Flow and pollutant concentration data from monitored CSOs were extrapolated to the
remainder of the study area in order to model the entire area.
• Overall study area simulations were compared with block testing data from non-monitored
locations to confirm accurate predictions.
2-61 August 1995
-------
Chapter 2 System Characterization
CSO MODEL CALIBRATION AND VERIFICATION
The SWMM models were calibrated using the flow and quality data collected at the eight monitored CSOs
and the treatment plant during September 26-28, 1993. Several parameters were used to assess the
accuracy of the calibration process, including:
• Duration, peak flow, and volume of CSOs
• Hydrographs of measured flows versus predicted model results
• Magnitude and timing of peak flow and quality values.
To achieve agreement between measured values and predicted modeling results, adjustments were made
to the hydraulic and hydrologic input data developed for each system. The major factor affecting the
magnitude of runoff peaks and volumes was the percent of impervious area of the individual subcatchments.
The initial values for percent imperviousness were based on the review of existing sewer record plans and
topographical maps, which show the study area drainage patterns. Consequently, these values were
considered likely candidates for adjustment during calibration. A second parameter that affected the
magnitude and timing of peak flows is the subcatchment width. Other factors that could alter the timing
and magnitude of peak flows included ground slope and surface storage, as well as resistance parameters.
These factors were also used during calibration, although their impact on runoff peaks and volumes is
significantly less than the percent of impervious area and the subcatchment width.
For the calibration of CSO quality, pollutant washoff coefficients and constituent fractions of dust and dirt
were the major adjustment parameters. The pollutant washoff coefficients and constituent fractions affect
the magnitude of surface runoff pollutant concentrations, while the washoff coefficients alter the distribution
of the pollutant concentration over time during a storm. Once a generally close match was obtained
between actual and model results, the models were verified. Verification involved running additional
storms without adjusting model parameters. The models were verified using the October 12-13, 1993
storm event, which yielded 1.22 inches of rainfall over a 13-hour period, activating all of the monitored
CSOs for a sustained period of time.
CSO MODEL RESULTS
Once the model was calibrated and verified, CSO flow and pollutant loads were simulated for a range of
developed design storms. Design storms with return periods of 1 week, 1 month, 3 months, 6 months,
1 year, 2 years, 5 years, and 10 years were selected for analysis. The design storms were run in SWMM
to determine the storm size required to trigger CSOs under existing and future no-action conditions.
Total CSO volume and pollutant loads were estimated for the 1-week through 10-year design storms for
existing conditions. These served as the basis for sizing and evaluating CSO control alternatives. Once
the baseline existing conditions had been developed, the future no-action conditions were analyzed. These
conditions changed from the existing condition as a result of increases in population or major projects
scheduled in the study area that would affect the quantity and quality of CSOs. For the purposes of this
study, the CSO analysis for future conditions was based on estimates of wastewater flows and pollutant
loads for a 20-year planning period, or until the year 2015.
Values were estimated for annual population growth, domestic wastewater contribution rates, annual
increase in commercial/industrial flows, and pollutant loadings for domestic and commercial/industrial
wastewater. The projected incremental growth, together with the flow and load values for the baseline
year, were then totaled to provide flow and load estimates for the year 2015 and project incremental growth
in wastewater flow and pollutants loads between the baseline year (1992) and the planning year (2015).
2-62 August 1995
-------
Chapter 2 System Characterization
In comparison, the results for this future no-action condition showed a slight increase in CSO volumes and
pollutant loads over existing conditions.
In addition to the design storm study outlined, the continuous simulation mode of SWMM was used to
develop annual CSO flows and loads for the study area. Hourly precipitation data for a long-term period
were used to generate CSO flows and loads during wet weather periods, while pollutant buildup on
subcatchment areas was calculated during dry weather periods. A historical rainfall analysis identified 1974
as the most representative year for the period of record, in which 95 storms occurred totaling 43.3 inches
of rainfall. The hourly precipitation data recorded for 1974 were then input to the SWMM models for a
continuous simulation of annual CSO flows and loads in the study area under existing and future no-action
conditions.
RECEIVING WATER MODEL DEVELOPMENT
To assess CSO impacts on area receiving waters, the Androscoggin and Little Androscoggin Rivers were
analyzed. The wet weather monitoring data indicated that the existing CSOs only result in exceedance of
the criterion for E. coli bacteria. For this reason, the receiving water analysis conducted in this study only
considered E. coli bacteria levels within the Androscoggin and Little Androscoggin Rivers under existing
and future no-action conditions.
After reviewing available approaches to conducting the receiving water analysis, a simplified modeling
effort was selected to provide a useful definition of the duration of impacts from wet weather discharges
at a relatively low cost. The simplified modeling approach was used, therefore, for the analysis of the two
major rivers in the study area. In addition, CSOs in Lewiston affect several small receiving waters,
including Goff Brook, Gully Brook, Jepson Brook, and Stetson Brook. With the exception of Gully Brook,
there is very little or, in some cases, no flow in these brooks during dry weather. Any CSO to these
receiving waters causes significant exceedances of bacterial standards. Gully Brook, an extension of the
Upper Canal from the Androscoggin River, flows within and normally is contained within the CSS, only
discharging to the canal during a CSO event. Consequently, Gully Brook was not considered as a separate
receiving water, but as pan of the Androscoggin River.
Jepson Brook is also somewhat unique in the study area. Once a natural drainage brook tributary to the
Androscoggin River, Jepson is now a concrete-lined trapezoidal drainage channel that receives discharges
from 15 CSOs and many separate storm drains. Although designated as a Class B receiving water suitable
for swimming and aquatic life, there is no evidence that either use exists in Jepson Brook. The base flow
in the brook is quite low, less than 0.5 cfs, and similar to the other brooks, any CSO will cause
exceedances of the water quality criteria for bacteria.
An adaptation of the CHARLESA model was used to simulate CSO and storm water impacts on the
Androscoggin and Little Androscoggin Rivers. The CHARLESA model, developed by the Massachusetts
Institute of Technology, is a simplified version of the one-dimensional, time-dependent QUAL2EXP water
quality model. This modified version of the QUAL2EXP model only simulates the transport and first-order
decay (bacterial die-off) of E. coli bacteria.
The receiving water model requires discretization of the river into a number of model "elements," each
representing a short length of the river. The model determines the volume of water and pollutant load
passed from one element to the next over short-time intervals. Pollutant loads from CSOs are added to
elements that correspond to outfall locations along the river banks. Water quality is assumed to be fully
mixed laterally. The hydraulic portion of the model is semi-transient with constant model element volumes
but varying flows. Conservation of mass (continuity) is ensured by increased river discharge downstream
of inflows. A completely transient hydraulic model was determined not to be necessary for the scope of
the modeling effort in this project.
2-63 August 1995
-------
Chapter 2 System Characterization
Model inputs included river segment volumes (river geometry), upstream flows and pollutant loads, and
source flows and pollutant loads. River geometry was determined using cross-sections from previous
hydraulic modeling efforts performed by the USGS to delineate flood zones along the river. Using these
cross-sections and river discharge information recorded by the USGS gaging station in Auburn, river
surface elevations were estimated for both monitored rainfall events (September 26-27 and October 12-13)
and used to determine river segment volumes. Upstream flows were set equal to the measured river
discharges. Upstream bacterial loads were assumed to be negligible.
CSO loads from both communities were estimated using SWMM results, discussed previously. Other
source loadings included the flow and pollutant load contributions from the Little Androscoggin River and
Jepson Brook, as well as dry weather overflows in Auburn during the time of the sampling and monitoring
period. Pollutant loadings from the Little Androscoggin River were simulated using the receiving water
model, while the dry weather overflows were estimated based on the monitoring data collected on the rivers
during dry weather conditions.
RECEIVING WATER MODEL CALIBRATION AND VERIFICATION
The model was calibrated and verified to determine the optimum dispersion and decay coefficients for use
in simulations of future conditions and to ensure that the model could reasonably reproduce river quality
for a known rainfall event. The two storms during which water quality sampling was performed were used
for calibration and verification of the model. The calibration runs were performed with a decay coefficient
of 1.0 (/day) and a longitudinal dispersion coefficient of 5.0 (m2/sec). Additional runs of the model with
varied coefficients did not change model results in any significant manner. It was observed that, due to
the huge variations in loadings and the relatively large volume of clean upstream flow, the modeled
pollutant concentrations were dominated by advection effects (the transport of pollutants due to movement
of the river water) with relatively little decay occurring within the model bounds. Simulations of the
verification storm that occurred on October 12-13, 1993, confirmed the reasonable accuracy of the water
quality models.
RECEIVING WATER MODEL RESULTS
Once the receiving water models were calibrated and verified, water quality simulations for the full range
of design storms were performed for existing and future no-action conditions under the worst case scenario
of 7-day, 10-year low flow (7Q10) conditions. Because the stages of both the Androscoggin and Little
Androscoggin Rivers are regulated extensively by the various dams in the Lewiston-Aubura area, however,
a true quantification of the 7Q10 flow condition was not possible. For the purpose of these simulations,
therefore, the design flows for the Androscoggin and Little Androscoggin Rivers were assumed to be the
minimum release requirements for the Lewiston Falls Dam on the Androscoggin River and the lower
Barker Mills Dam on the Little Androscoggin River.
CSO pollutant loads, developed in the CSS analyses, were input to the water quality model for each design
storm simulation. In general, water quality criteria exceedances in the Androscoggin River occurred for
a longer period of time for the future condition simulations than the calibration and verification runs with
similar rainfall. This indicated that water quality conditions depend greatly upon the flushing capabilities
of the Androscoggin River. Whereas the design flow was only 1,000 cfs, the average flows for the
calibration and verification storm events were 2,590 and 3,370 cfs, respectively. A similar trend was also
observed in the modeling of the Little Androscoggin River. The design storm simulations also indicated
that storms in excess of the 1-month storm do not increase significantly the period of water quality criteria
exceedances. Thus, larger quantities of pollutants would be expected to increase the magnitude of
exceedances, but not the duration. The analysis demonstrated that wet weather discharges cause
exceedances of the WQS for bacteria in all area receiving waters.
2-64 August 1995
-------
CHAPTER 3
DEVELOPMENT AND EVALUATION OF ALTERNATIVES FOR CSO CONTROL
This chapter provides guidance on the development and evaluation of alternatives for
long-term control of combined sewer overflows (CSOs). The information presented includes the
following:
• The role of public participation and the need to coordinate with the National Pollutant
Discharge Elimination System (NPDES) permitting and State water quality standards
(WQS) authorities
• An overview of general approaches for developing the long-term control plan
(LTCP), including the demonstration and presumption approaches for showing
compliance with CWA requirements, as well as small system considerations
• Specific approaches to and aspects of developing alternatives, including definition of
CSO control goals, identification of control measures, sizing, cost, and siting issues
• Approaches for evaluating alternatives, including cost/performance evaluations, non-
monetary factors, and financial capability.
The chapter concludes with two case studies.
3.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION
It is important to develop and maintain avenues for public involvement throughout LTCP
development. Opportunities for public involvement in the assessment of existing conditions and
the development of system monitoring information were presented in Chapter 2. During the
development and evaluation of alternatives, the goal of the public participation program should
be to involve citizens in the development of alternative solutions that protect the local waterways
and consider the financial impacts to the community as a whole.
3-1 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
During development and evaluation of CSO control alternatives, the following key
information can be presented to the public as it is developed:
• Water quality goals for each receiving water segment
• CSO control goals for each receiving water segment as developed under the
presumption and/or demonstration approach options
• Types of control alternatives available to meet CSO control goals
• CSO control alternatives identified to meet the control goals
• The process of evaluating and comparing various alternatives for CSO control.
These issues can be technically complex and require effort and imagination to present in
a manner that will be understandable to the public. Technical jargon and complex charts and
figures might be useful to and understandable by engineers but might not be clear or
understandable to the lay person. Public confusion or lack of understanding can lead to
skepticism, hostility, and the inability or unwillingness to participate. These reactions can be
avoided by understanding the audience and taking the time to arrange and present the
information in an appropriate format. A well-designed public participation program will involve
the public in the decision-making process as it proceeds.
Citizen advisory committees can serve as liaisons between municipal officials, the general
public, the NPDES permitting agency, and the State WQS agency. Public meetings, public
hearings, workshops, and discussion panels provide effective forums to explain the alternatives
and to obtain input from as many neighborhood, business, environmental, and civic organizations
as possible. These meetings should be well advertised in local papers and on local radio
stations. Interested parties should be encouraged not only to speak but also to provide written
comment and input. The public participation program can include activities designed to educate
children about the CSO program, informational material distributed through general mailing lists
or inserted into monthly utility bills, and media briefings concerning specific projects or issues.
3-2 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Interaction with the NPDES permitting authority and State WQS authority should
continue during development and evaluation of CSO control alternatives with a sharing of the
technical information noted previously. It is important to gain ongoing agency input during this
phase for many reasons. Expectations for CSO control measure performance and interpretations
of wet weather data are often subject to debate, due to such factors as the relative shortage of
historical data and the inherent variability of wet weather flows. The community and the
regulatory agency should agree on such fundamental issues early in the project to avoid costly
misunderstandings later. States have also developed their own CSO strategies, which might
differ from the EPA CSO Control Policy. In these cases, a municipality should ensure through
agency coordination that its LTCP addresses the appropriate State and Federal policy
requirements. In addition, if CSOs occur to sensitive areas, the municipality should consult with
the NPDES permitting authority, as well as other appropriate State and Federal agencies, to
ensure consistency with CSO Control Policy provisions regarding sensitive areas (II. C. 3).
Ultimately, the NPDES permitting authority should be satisfied that the municipality has studied
all reasonable options in developing a list of final alternatives for evaluation and that the
evaluation process incorporates all identified concerns.
3.2 LONG-TERM CONTROL PLAN APPROACH
The LTCP should provide site-specific, cost-effective CSO controls that will provide for
attainment of WQS. It should provide flexibility to municipalities in recognition of the variable
impacts of CSOs on water quality and the ability of different municipalities to afford varying
levels of CSO control. EPA expects that the LTCP will consider a reasonable range of
alternatives and varying control levels within those alternatives, using cost-effectiveness as a
consideration to help guide consideration of the controls.
3.2.1 Demonstration Versus Presumption Approach
The CSO Control Policy identifies two general approaches to attainment of WQS: the
demonstration approach and the presumption approach. The demonstration and presumption
approaches provide municipalities with targets for CSO controls that achieve compliance with
the Clean Water Act, particularly protection of designated uses. As described in Chapter 2, all
3-3 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
municipalities should characterize their CSSs in order to establish a baseline and provide a basis
for implementing and evaluating the effectiveness of the nine minimum controls (NMC).
Characterization will likely include monitoring and modeling to characterize CSO flow and
pollutant loads, impacts on receiving water quality from CSO and non-CSO sources, and efficacy
of CSO controls. This characterization will enable the NPDES permitting authority, in
conjunction with the municipality and with input from the public and appropriate review
committees, to determine whether the demonstration or presumption approach is the most
suitable.
Generally, if sufficient data are available to demonstrate that the proposed plan would
result in an appropriate level of CSO control, then the demonstration approach will be selected.
The demonstration approach is particularly appropriate where attainment of WQS cannot be
achieved through CSO control alone, due to the impacts of non-CSO sources of pollution. In
such cases, an appropriate level of CSO control cannot be dictated directly by existing WQS but
must be defined based on water quality data, system performance modeling, and economic
factors. These factors might ultimately support the revision of existing WQS. If the data
collected by a community do not provide "...a dear picture of the level of CSO controls
necessary to protect WQS" (II.C.4.a.), the presumption approach may be considered. Use of
the presumption approach is contingent, however, on the municipality presenting sufficient data
to the NPDES permitting authority to allow the agency to make a reasonable judgment that WQS
will probably be met with a control plan that meets one of the three presumption criteria (see
Section 3.2.1.2).
The CSO Control Policy recommends flexibility in allowing a municipality to select
controls that are cost-effective and tailored to local conditions. For this reason, the choice
between the demonstration approach and presumption approach does not necessarily have to be
made before a municipality commences work on its LTCP. In some cases, it might be prudent
for a municipality to assess alternatives under both approaches. In addition, if a municipality
has CSOs that occur to two different water bodies, a control plan that includes the demonstration
approach for one receiving water and the presumption approach for the other may be
appropriate. Because of the flexibility in selecting an approach, it is imperative that the
3-4 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
municipality coordinate closely with the NPDES permitting authority. Involving the public and
other stakeholders will also provide a foundation for subsequent LTCP acceptance.
3.2.1.1 Demonstration Approach
Under the demonstration approach, the municipality would be required to successfully
demonstrate compliance with each of the following criteria (II.C.4.b):
/. the planned control program is adequate to meet WQS and protect designated
uses, unless WQS or uses cannot be met as a result of natural background
conditions or pollution sources other than CSOs;
ii. the CSO discharges remaining after implementation of the planned control
program will not preclude the attainment of WQS or the receiving waters'
designated uses or contribute to their impairment. Where WQS and
designated uses are not met in part because of natural background conditions
or pollution sources other than CSOs, a total maximum daily load, including
a wasteload allocation, a load allocation or other means should be used to
apportion pollutant loads;
in. the planned control program will provide the maximum pollution reduction
benefits reasonably attainable; and
iv. the planned control program is designed to allow cost-effective expansion or
cost-effective retrofitting if additional controls are subsequently determined to
be necessary to meet WQS or designated uses.
Under Criterion i, the CSO Control Policy reiterates that NPDES permits must require
attainment of WQS, but recognizes that in many receiving water segments, sources other than
CSOs might be contributing substantially to nonattainment of WQS. In these cases, even
complete elimination of CSOs might not result in attainment of WQS. Criterion ii is intended
to ensure that the selected level of CSO control would be sufficient to allow attainment of WQS
if other sources causing nonattainment were controlled. Criterion iii reiterates the emphasis on
developing cost-effective levels of control, while Criterion iv ensures that sufficient flexibility
is incorporated into the LTCP to allow upgrading to higher levels of control if necessary.
3-5 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
The demonstration approach encourages the development of total maximum daily loads
(TMDLs) and/or the use of a watershed approach throughout the LTCP process. In conducting
the existing baseline water quality assessments as part of the system characterization, for
example, the specific pollutants causing nonattainment of WQS, including existing or designated
uses, would be identified, and then the sources of these pollutants could be identified and loads
apportioned and quantified. Assessments would be made of the relative contribution of CSOs
and other sources to the total pollutant loads to the receiving waters, and then a range of controls
could be identified to target the CSO contribution. Controls for the non-CSO sources of
pollutants could also be assessed at the same time, depending on the overall scope of the LTCP,
jurisdictional issues within the municipality, and other issues.
The statutory basis for defining the relative contributions of different sources of pollution
is the CWA, under Section 303(d), which requires the identification of "water quality limited"
stream segments still requiring TMDLs. These are areas where water quality does not meet
applicable WQS and/or is not expected to meet applicable WQS even after the application of
required controls, such as the technology-based control measures (40 CFR 131.3(h)). A TMDL
is defined as the sum of the individual wasteload allocations (WLA) for point sources; load
allocations (LA) for nonpoint sources of pollution and natural background sources, tributaries,
or adjacent segments; and a margin of safety. The objective of the TMDL is attainment of
WQS. The process uses water quality analyses to predict water quality conditions and pollutant
concentrations. The establishment of a TMDL for a particular water body depends on the
location of point sources, available dilution, WQS, nonpoint source contributions, background
conditions, and in-stream pollutant reactions and effluent toxicity. A TMDL can be expressed
in terms of chemical mass per unit time, by toxicity, or by other appropriate measures.
In cases where the natural background conditions, or pollution sources other than CSOs,
are contributing to exceedances of WQS, the State is responsible for the development of a
TMDL and the WLA for any CSOs. The municipality must then demonstrate compliance with
the effluent limitation derived from the WLA established as part of the TMDL (EPA, 1995g).
The NPDES permitting authority will also specify what constitutes a reasonable effort by the
municipality to demonstrate the maximum pollution reduction benefits reasonably attainable.
3-6 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
The term "reasonably attainable" generally refers to the cost of implementing the planned control
program in relation to the pollution reduction benefit achieved (EPA, 1995g).
3.2.1.2 Presumption Approach
The CSO Control Policy recognizes that "...data and modeling of wet weather events
often do not give a clear picture of the level of CSO controls necessary to protect WQS"
(II.C.4.a). For this reason, the presumption approach was included in the CSO Control Policy
as an alternative to the demonstration approach. The presumption approach is based on the
assumption that an LTCP that meets certain minimum defined performance criteria "...would
be presumed to provide an adequate level of control to meet the water quality-based requirements
of the CWA, provided the permitting authority determines that such presumption is reasonable
in light of the data and analysis conducted in the characterization, monitoring, and modeling of
the system and the consideration of sensitive areas..." (II.C.4.a).
Under the presumption approach, controls adopted in the LTCP should be required to
meet one of the following criteria (II.C.4.a):
i. No more than an average of four overflow events per year, provided that the
permitting authority may allow up to two additional overflow events per year.
For the purpose of this criterion, an overflow event is one or more overflows
from a CSS as the result of a precipitation event that does not receive the
minimum treatment specified... [see definition of minimum treatment, below];
or
ii. The elimination or the capture for treatment of no less than 85% by volume
of the combined sewage collected in the CSS during precipitation events on
a system-wide annual average basis; or
Hi. The elimination or removal of no less than the mass of the pollutants
identified as causing water quality impairment through the sewer system
characterization, monitoring, and modeling effort for the volumes that would
be eliminated or captured for treatment under paragraph ii above.
3-7 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
The minimum level of treatment applicable to Criteria i and ii is defined in the CSO
Control Policy as follows (II.C.4.a):
• Primary clarification; removal of floatable and settleable solids may be
achieved by any combination of treatment technologies or methods that are
shown to be equivalent to primary clarification;
• Solids and floatables disposal; and
• Disinfection of effluent, if necessary, to meet WQS, protect designated uses
and protect human health, including removal of harmful disinfection chemical
residuals, where necessary.
Use of the presumption approach does not release municipalities from the overall
requirement that WQS be attained. If data collected during system characterization suggest that
use of the presumption approach cannot be reasonably expected to result in attainment of WQS,
the municipality should be required to use the demonstration approach instead. Furthermore,
if implementation of the presumption approach does not result in attainment of WQS, additional
controls beyond those already implemented might be required. This is why the CSO Policy
recommends "The selected controls should be designed to allow cost-effective expansion or cost-
effective retrofitting if additional controls are subsequently determined to be necessary to meet
WQS, including existing and designated uses" (II.C).
As noted in Chapter 2, the existing baseline should be established following the system
characterization. This is the point at which one of the presumption approach criteria is applied.
Implementation of the NMC following system characterization could reduce the number of
overflows and/or the amount of flow subject to 85-percent capture, therefore potentially reducing
the costs associated with LTCP implementation.
Criterion i. The CSO Control Policy defines an overflow event under Criterion i as
"... one or more overflows from a CSS as the result of a precipitation event that does not receive
the minimum treatment specified..." (II. C. 4. a. i). In a CSS with three outfalls, therefore, if one,
two, or three of the outfalls discharge untreated or inadequately treated combined sewage during
3-8 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
a rain event, then a single overflow event has occurred. Furthermore, in terms of defining an
overflow event, a "CSS" is not necessarily the entire set of combined sewers within a municipal
or regional boundary. In some cases, a municipality or regional sewer authority might be
considered to have more than one CSS if the systems are not hydraulically related. In such a
case, the calculation of four overflow events per year would apply for each system individually
and not to the entire set of combined sewers within the municipality or regional jurisdiction (this
concept would apply to Criteria ii and iii, as well). In addition, the prohibition of more than
four overflow events per year (with up to two more if the NPDES permitting authority approves)
applies to overflows not receiving the minimum treatment of primary clarification, solids and
floatables disposal, and disinfection, if necessary. Outfalls may overflow more frequently if
they receive the minimum specified treatment.
Criterion ii. Under Criterion ii, the "85 percent by volume of the combined sewage"
refers to 85 percent of the total volume of flow collected in the CSS during precipitation events
on a system-wide, annual average basis (not 85 percent of the volume being discharged). In
other words, no more than 15 percent of the total flow collected in the CSS during storm events
should be discharged without receiving the minimum specified treatment. The total volume of
flow collected during wet weather on a system-wide annual average basis would be most readily
computed using a model of the CSS, such as SWMM. Similarly, the total volume of flow
discharged without receiving the minimum treatment can also be computed using an annual
simulation with a CSS model, such as SWMM. Comparing these two volumes under existing
conditions will indicate the extent of additional controls necessary to meet the criterion for 85
percent elimination or capture. Sizing facilities to meet a performance criterion based on annual
average performance, however, will probably require iterative evaluations of annual simulations.
Depending on the size and complexity of the system being modeled, as well as the speed of the
hardware used for the simulation, this process can require a great deal of computer tune and
follow-up analysis.
Analysis performed in conjunction with EPA's 1992 CSO Control Policy dialogue has
shown that criteria i and ii are approximately equal. Based on regional rainfall patterns, and
primary clarification provided by an appropriately designed sedimentation/storage basin, the
3-9 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
number of annual overflows corresponding to primary clarification of 85 percent of the
combined sewage was determined. On a nationwide basis, the number of overflows not
receiving primary treatment and corresponding to 85 percent capture for treatment, ranged from
four to six depending on location. In practice, a CSO control facility that captures for treatment
85 percent of the combined sewage collected in the system may experience more than six
overflows on an annual average basis, although a significant deviation from this range of
overflows would not be expected. In cases where a significant deviation due to local conditions
is encountered, the permit writer's judgment should be used to determine whether use of the 85
percent capture criterion is appropriate. Also, as previously stated, use of either of the
presumption approach options should be based on reasonable assumption that implementation of
controls meeting these criteria will be sufficient to prevent violations of WQS.
Criterion iii. Criterion iii, meanwhile, makes the distinction between the control of CSO
volume and the control of the specific pollutants within that volume that cause water quality
impairment. As noted earlier, CSS modeling could provide the total volume of flow collected
during wet weather in the CSS on an annual average basis. The volume needed to be captured
to meet Criterion ii would then be 85 percent of that total. Using average pollutant
concentrations and removal efficiencies associated with the equivalent of primary treatment, one
could compute the mass of the pollutants that would be removed if 85 percent of the wet weather
flow received the equivalent of primary treatment. Comparing this value with the mass of
pollutants that is currently removed during wet weather would yield the additional mass of
pollutants needed to be removed to meet Criterion iii.
For example, suppose a municipality's CSS had the following characteristics, based on
the system characterization:
• Total volume of combined sewage collected in the CSS on an annual average basis
during wet weather—100 MG
• Total volume of combined sewage receiving secondary treatment at the municipality's
POTW during wet weather—10 MG
• Pollutant causing water quality impairment in receiving water body—BOD
3-10 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Average concentration of BOD in CSO from the municipality's CSS—80 mg/1
• Wet weather BOD removal efficiency for primary clarification as determined for the
municipality based on review of local POTW performance and historical data—20
percent
• Wet weather BOD removal efficiency from municipality's secondary POTW—80
percent.
The mass of BOD removed by providing the equivalent of primary clarification for 85
percent of the combined sewage collected during wet weather on an annual average basis would
be computed as follows:
100 MG x 85% x 80 mg/1 x 8.34 x 20% = 11,342 Ibs.
Since 10 MG of combined flow receives secondary treatment at the municipality's POTW
during wet weather, the remaining load of BOD to be captured from CSOs to meet Criterion iii
would be:
11,342 Ibs - (10 MG x 80 mg/1 x 80% x 8.34) = 6,005 Ibs.
Criterion iii also considers pollution prevention measures. Activities such as street
sweeping, litter control, and erosion control programs would reduce the load of certain pollutants
carried to the receiving water, without affecting overflow volumes. Similarly, if more
sophisticated modeling and monitoring programs support the use of time varying concentrations
to compute pollutant loads, it might be possible to demonstrate that capture of the appropriate
load of pollutants could be achieved with capture of a lower volume of flow.
The specific pollutants causing WQS nonattainment may vary from water body to water
body. The pollutants of concern to a given municipality will, therefore, depend on the specific
water resources affected by CSOs and their desired uses. The intent of the minimum level of
treatment recommended in the presumption approach is to control floatables, pathogens, and
solids. The primary impact of floatable material on receiving waters is aesthetic. Pathogens are
3-11 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
bacteria, protozoa, and viruses that can cause disease in humans through ingestion, inhalation,
and skin contact. These potential health risks are associated with uses of receiving waters for
water supplies, primary contact recreation, such as swimming; secondary contact recreation,
such as boating; and with the consumption of contaminated fish and shellfish. Although not
pathogenic themselves, the presence of coliform bacteria is used as an indicator of the potential
presence of pathogens and of potential risk to human health. Solids can cause problems in either
the suspended or deposited state and their removal is important for several reasons. Suspended
solids can make the water look cloudy or turbid, diminishing the aesthetic and recreational
qualities of the water body. Turbidity limits light penetration into the water column and reduces
the growth of microscopic algae and submerged aquatic vegetation. Suspended solids can also
impede feeding by filter-feeding organisms, such as shellfish and small aquatic invertebrates.
In addition, deposited sediments can change the physical nature of the bottom, altering
hydrology and habitat and affecting navigation. Sedentary bottom-dwelling species can be
smothered by accumulating sediment, and the change in habitat can preclude the continued
success of many species that use the bottom habitat to feed, spawn, or live. Sediments are also
a sink for adsorbed pollutants, such as nutrients (e.g., nitrogen, phosphorus), toxic metals, and
organics, which can affect both water-column and bottom-dwelling organisms. These toxic
pollutants can be remobilized if sediments are disturbed and can pose a health hazard to humans
consuming fish and shellfish.
Defining "minimum treatment" and "primary clarification." As stated above, the
minimum level of treatment applicable to Criteria i and ii of the presumption approach consists
of:
• Primary clarification or equivalent;
• Solids and floatables disposal; and
• Disinfection, as necessary, and removal of disinfection residuals, as necessary.
The definition of "primary clarification" is one of the key implementation issues
underlying the presumption approach and has generated considerable debate among regulators,
3-12 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
municipalities, consultants, and equipment suppliers. The intent of primary clarification is
removal of settleable solids from the wastestream, which will result in the environmental benefits
outlined above.
The CSO Control Policy does not define specific design criteria or performance criteria
for primary clarification, however. This guidance document does not provide a definition either;
instead, it discusses general considerations for primary clarification under the presumption
approach, recognizing the variable nature of CSOs and general lack of historical data on CSO
treatment facility performance. EPA recognizes the need for flexibility and urges municipalities
and NPDES permitting authorities to coordinate to develop a site-specific definition of CSO
primary clarification as "minimum treatment" under the presumption approach.
This definition should take the form of target ranges for design criteria (overflow rate,
sidewall depth, residence time) and/or performance (removal rates), rather than a specific
number or limit and should be based on several factors, including:
• Wet weather performance of primary treatment facilities at the municipality's POTW
• Historic data (e.g., literature values, existing POTW primary treatment data, existing
CSO facility performance data).
The following documents provide additional information on defining primary clarification
for a specific application:
• Water and Wastewater Engineering (Fair et al, 1968)
• Recommended Standards for Wastewater Facilities (Ten States Standards) (Great
Lakes-Upper Mississippi River Board of State Public Health and Environmental
Managers, 1990)
• Wastewater Engineering: Treatment, Disposal, Reuse (Metcalf & Eddy, Inc., 199la)
• Design of Municipal Wastewater Treatment Plants, WEF Manual of Practice No. 8:
ASCE Manual and Report on Engineering Practice No. 76. (WEF, 1992)
3-13 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
These documents describe performance and design parameters commonly associated with POTW
primary treatment facilities.
In determining an equivalent of primary clarification for CSO flows, the following
differences between CSO control facilities and POTWs should be considered:
• Influent hydrographs for CSO control facilities tend to exhibit more sharply defined
peaks, not typical of POTW influent hydrographs, as well as periods of no flow.
Therefore, the concept of "average" flow is less significant for a CSO control facility
than a POTW. For example, the peak influent flow rate can occur before the
sedimentation/storage tank is full; therefore, the maximum overflow rate would occur
on the falling leg of the influent hydrograph, and the actual maximum overflow rate
would be less than a calculated overflow rate associated with the actual peak influent
flow.
• Compared to relatively constant influent pollutant concentrations at POTWs, influent
pollution loads and concentrations to CSO treatment facilities can be highly variable
within a single storm event and between different events.
• CSO flows generally have a higher fraction of heavier solids than separate sanitary
flows.
Exhibit 3-1 illustrates how a CSO storage/sedimentation facility might perform during
a rainfall event. The lower vertical axis represents the total flow rate of the combined sewage
collected upstream of the storage/sedimentation facility, while the upper vertical axis indicates
rainfall intensity. The horizontal dashed lines represent surface loading rates within the
storage/sedimentation facility. The capacity of the CSS corresponds to the "0 gpd/ft2" line, and
thus the volume of flow above that line is diverted into the storage/sedimentation facility.
Between hours 0 and 4, the conveyance system carries the entire combined sewage
volume to the POTW treatment plant. At hour 4, the capacity of the conveyance system is
exceeded, and the excess flow is diverted to the storage/sedimentation facility. Between hours
4 and 7.25, the facility tanks are filling, and no overflow is discharged. At hour 7.25, the
tanks are completely filled, and excess flow is discharged at an overflow rate of between 1,000
and 2,000 gpd/ft2. Overflow rates within this range are assumed to provide at least 40 percent
TSS removal, based on typical sedimentation system design criteria. Between hours 8 and 10,
the overflow rate exceeds 2,500 gpd/ft2, and the volume of overflow occurring during this period
3-14 August 1995
-------
Overflow Rate >2,500 gpd/ft
Assume ~ 30% SS Removal
Storage
Volume
Available -% 43 m'm
Overflow Rate <2,000 gpd/ft
Assume ~ 40% SS Removal
Volume Stored tor
Pumpback
85% SS Removal
Overflow Rate <1,000 gpd/ft
Assume ~ 60% SS Removal
Full Volume
toWWTP
85% SS Removal
8 10
Time (hours)
12
14
16
Exhibit 3-1. An Example of Overflow Rates Versus Pollutant Removal During a Rainfall Event
3-15
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
is assumed to receive 30 percent TSS removal. At hour 10, the overflow rate drops to less than
1,000 gpd/ft2 as the storm begins to subside. Overflow volumes in this range are assumed to
receive 60 percent TSS removal. After hour 11, flows have dropped back below the capacity
of the conveyance system, and flow into the facility ceases. At hour 16, dewatering of the
facility begins, thus restoring the available storage volume. The dewatered volume is assumed
to be returned to the POTW for full secondary treatment, with 85 percent TSS removal.
Thus, a CSO treatment facility designed for storage and sedimentation would typically
provide the following levels of control:
Full secondary treatment (85 percent TSS and BOD5 removal) for small rainfall
events where the total CSO volume diverted to the storage/sedimentation facility is
less than the volume of the storage/sedimentation basin, and all of the CSO flow is
stored and directed back to the POTW. While providing secondary treatment of
overflows from small storms is not specifically included as part of the presumption
approach, it would be an additional benefit of using the storage/sedimentation tank
technology.
A combination of primary and secondary treatment for storms that exceed the volume
of the storage/sedimentation tanks, but where the overflow rates are within the
determined range for primary treatment. The flow discharged from the facility would
receive the equivalent of primary treatment, while the volume of the tanks would be
returned to the POTW for secondary treatment.
Lower levels of treatment for major storm events where the peak overflow rate
exceeds the design range for primary treatment. Under the presumption approach,
the CSO Control Policy recommends that NPDES permitting agencies allow the
exceedance of the design overflow rates four times per year or, alternatively, 15
percent of total annual combined sewage flow to be discharged without receiving the
equivalent of primary treatment.
Because storage/sedimentation is only one potential CSO control alternative, the
municipality and the NPDES permitting agency might also have to determine the effectiveness
of other types of CSO control alternatives to meet the performance criteria of the presumption
approach. This task can be challenging, given the shortage of published CSO performance data.
In many cases, published data are site-specific and cannot necessarily be generalized for other
locations due to differences in CSO quality and flow characteristics. For further discussions
3-16 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
of related CSO control technologies, refer to the Manual on Control of CSO Discharges (EPA,
1993a).
In summary, the municipality should consider the following points when selecting the
presumption approach:
• The NPDES permitting authority must be able to judge that the system
characterization data submitted by the municipality provide a reasonable assurance
that WQS would be met with the presumption approach. Based on the available data,
the NPDES permitting authority may disallow use of the presumption approach or
may restrict the selection of the criterion (i, ii, or iii) to be adopted in the LTCP.
Close coordination between the municipality and the NPDES permitting and WQS
authorities is necessary at all times to ensure appropriate data development to support
selection of the presumption approach.
• The NPDES permitting authority has the ultimate authority to determine the number
of allowable overflow events.
• The four overflows per year criterion is only one option available to municipalities
in choosing an approach to comply with the CWA. A municipality may prefer to
consider the demonstration approach, or the 85 percent capture or pollutant mass
options under the presumption approach where appropriate.
• Selection of the presumption approach does not relieve the municipality from the need
to characterize the CSS. This characterization should provide the basis for the
NPDES permitting authority to determine whether the presumption approach would
likely result in attainment of WQS.
• The selected LTCP option to be included in an NPDES permit must "...ultimately
result in compliance with the requirements of the CWA" (II. C). For this reason, if
post-construction compliance monitoring indicates WQS nonattainment due to CSO
impacts, a greater level of control should be required than was originally
contemplated under the selected presumption approach criterion.
• The decision to choose either the presumption or the demonstration approach is
important because it will affect the development of alternatives for the LTCP. It
might be appropriate to evaluate a range of alternatives under both approaches so that
the level of control, costs, and benefits can be compared in making a decision.
3-17 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
3.2.2 Small System Considerations
The CSO Control Policy acknowledges that "...the scope of the long-term CSO control
plan, including the characterization, monitoring and modeling, and evaluation of
alternatives...may be difficult for some small CSSs" (I.D). EPA recognizes that smaller
communities with limited resources might benefit more than investment in CSO controls than
from these aspects of LTCP development (EPA, 1995g). For this reason, at the discretion of
the NPDES permitting authority, municipalities with populations of less than 75,000 need not
be required to complete each of the formal steps outlined in the CSO Control Policy.
At a minimum, however, the permit requirements for developing an LTCP should include
compliance with the NMC, consideration of sensitive areas, a post-construction compliance
monitoring program sufficient to determine whether WQS are attained, and public participation
in the selection of the CSO controls (EPA, 1995g). In developing a small system LTCP,
municipalities should consult with both the NPDES permitting and WQS authorities to ensure
that the plan includes enough information to allow the NPDES permitting authority to approve
the proposed CSO controls.
3.3 DEVELOPMENT OF ALTERNATIVES FOR CSO CONTROL
Development of alternatives for CSO control is generally based on the following sequence
of events:
1. Definition of water quality goals
2. Definition of a range of CSO control goals to meet the CSO component of the water
quality goals
3. Development of alternatives to meet the CSO control goals.
Within this general context, this section is organized as follows. Section 3.3.1 presents
some general considerations, primarily regarding the relationships between the LTCP and other
related aspects of a municipality's collection and treatment system, including the NMC. Section
3.3.2 discusses and highlights an example of possible definitions for water quality goals and
3-18 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
corresponding CSO control goals. Section 3.3.3 provides a series of approaches to structuring
CSO control alternatives. These approaches are intended to provide a means for focusing or
organizing CSO control alternatives and include such categories as evaluation of outfall-specific
solutions, local or regional consolidation of outfalls, utilization of POTW capacity (including
CSO-related bypass), and special considerations for sensitive areas. Depending on the size of
the CSS, different approaches might be appropriate in different parts of the CSS. Having
discussed the goals of CSO control and general approaches to structuring alternatives to meet
those goals, Sections 3.3.4 to 3.3.9 provide guidance on the scope of initial alternatives
development. Section 3.3.4 introduces this topic, while Sections 3.3.5 to 3.3.9 present specific
aspects of initial alternatives development, such as identification of control measures or
technologies, preliminary sizing considerations, cost/performance considerations, preliminary
siting issues, and preliminary operating strategies.
3.3.1 General Considerations
This section presents general concepts that should be considered when developing CSO
control alternatives.
3.3.1.1 Interaction with Nine Minimum Controls
Certain minimum control measures developed in conjunction with the CSO system
characterization might affect baseline flows and loads. In particular, measures associated with
maximizing collection system storage and flows to the POTW might reduce the volume and/or
frequency of predicted overflows at specific locations. Minimum control measures associated
with the control of solid and floatable material in CSOs might be sufficient in scope to be
considered as long-term alternatives. Because minimum controls would be implemented before
the completion of the LTCP, the LTCP should incorporate the expected benefits of the minimum
controls.
3.3.1.2 Interactions with Other Collection and Treatment System Objectives
Implementation of CSO controls is likely to affect other point and nonpoint source control
activities occurring within the same watershed. The CSO Control Policy encourages
3-19 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
municipalities to evaluate water pollution control needs on a watershed management basis, and
to coordinate CSO control efforts with other point and nonpoint source control activities (see
Section 1.6.6). For example, if a municipality evaluates sewer separation as an alternative, it
should consider the impact of increased storm water loads on receiving waters. Similarly, the
system characterization model should explore the interrelationships between inflow/infiltration
removal, interceptor capacity, CSO control alternatives, and POTW capacity. The LTCP
provides an opportunity to optimize the operation of new and already-planned components of the
treatment system, and to explore new system modifications that affect the operation of these
components.
3.3.1.3 Creative Thinking
The initial identification of alternatives should involve some degree of brainstorming and
free thinking. CSO control can be a challenging problem, where lack of available sites, potential
impacts on sensitive receptors, and stringent water quality goals are common issues. The CSO
Control Policy encourages "Permittees and permitting authorities...to consider innovative and
alternative approaches and technologies that achieve the objectives of this policy and the CWA"
(I.F). Some of the more successful urban CSO projects have incorporated original ideas for
multiple use facilities and for mitigating impacts on neighboring areas. For example:
• Rochester, NY—A tunnel system was designed to cross the Genesee River by way
of a conduit suspended across the Genesee Gorge. Crossing the gorge above rather
than below the river surface eliminated the need for downstream pumping to the
POTW and also allowed the construction of a pedestrian walkway along the
suspended conduit, providing access between parks located on either side of the
gorge.
• Newport, RI—Below-grade, covered storage/sedimentation tanks located on a
commercial block were designed to allow parking on the roof slab. Architectural
features of the facility were designed to blend in with historic homes in an adjacent
neighborhood.
3-20 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
3.3.2 Definition of Water Quality and CSO Control Goals
This section discusses the first two aspects of development of alternatives: identifying
water quality goals and identifying CSO control goals to meet the water quality goals.
The CSO Control Policy clearly states that the ultimate goal of the LTCP is "compliance
with the requirements of the CWA" (II.C). The CSO Control Policy also recommends that a
range of control levels be evaluated as part of the LTCP (II.C.4), while State CSO policies
sometimes identify specific control goals for evaluation. The initial definition of CSO control
goals, however, should be based on an identification of watershed-specific or receiving water
segment-specific water quality goals. Water Quality goals are defined without regard to sources
of pollution. Examples of water quality goals might include meeting WQS at all times, or
meeting WQS except for four times per year. CSO control goals refer to specific levels of
pollution control from CSO sources only. Defining a CSO control goal based on a water quality
goal means identifying a level of CSO control which will allow attainment of the water quality
goal, assuming non-CSO sources of pollution are also controlled to an appropriate level. Once
a CSO control goal is defined, CSO control alternatives, comprised of technologies or other
control measures, can then be developed to meet the CSO control goal.
For example, a water quality goal of meeting existing WQS at all times might correspond
to a CSO control goal of eliminating the CSO impacts on a given receiving water. CSO control
alternatives to meet this goal might include sewer separation or CSO relocation. A water quality
goal of meeting existing WQS except for four times per year might correspond to a CSO control
goal of eliminating the CSO impacts except for four times per year. CSO control alternatives
to meet this goal might include, storage or treatment of overflows from storms with a recurrence
interval of four times per year. In this second case, the existing WQS would not be attained at
all times. The CSO Control Policy recognizes, however, that existing WQS might not be
appropriate in all cases for a given receiving water: ".. .this Policy allows consideration of... WQS
review..." (II.E). In order for a water quality goal that does not fully support existing WQS to
conform with the CWA, either a variance, a partial use designation, or a revision to WQS would
have to be obtained, as outlined in Part III of the CSO Control Policy. A review of WQS might
3-21 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
also be appropriate if non-CSO sources of pollution are contributing substantially to
nonattainment, making the definition of an appropriate water quality goal for an LTCP less
clear.
Through the evaluation process, a specific water quality goal might ultimately drive the
selection of the recommended plan. For example, a goal of meeting a bacteria criterion that
allows unrestricted shellfishing could require a CSO control goal of eliminating CSOs to a
particular receiving water containing shellfish beds. While less aggressive CSO control goals
might be more cost effectively attained, if stakeholders agree that the goal of unrestricted
shellfishing is desired and appropriate, then that goal should govern the selection of a
recommended plan. Alternatively, cost-effective analysis in conjunction with a use attainability
analysis might identify instances where attainment of an existing WQS is not an appropriate goal.
For example, suppose an industrial shipping channel is currently rated for primary contact
recreation. The cost of the CSO controls required to achieve that goal might be excessive
compared with the benefit gained (e.g., even if the bacteria criterion for swimming were met,
swimming would not be allowed in the channel for safety reasons due to ship traffic).
Coordination with State WQS authorities regarding the possible revision of the existing WQS
(consistent with 40 CFR 131.10) to allow a limited number of wet weather excursions from the
standard for primary contact recreation might be an appropriate part of the recommended plan.
In this case, determination of the ultimate water quality goal would have been driven by the
alternatives development and evaluation process.
Under the demonstration approach, the initial system characterization should identify the
specific pollutants causing nonattainment of WQS and, where possible, their sources. The CSO
Control Policy recognizes that total elimination of the CSO sources of these pollutants might not
be technically or economically feasible, nor might it be required to meet the appropriate water
quality goals. Determining the appropriate level of control of these pollutants from the point
of view of WQS, available technology, cost, and non-monetary factors is one of the goals of the
CSO control alternative development and evaluation process. By evaluating a range of control
levels, the municipality, NPDES permitting agency, and other stakeholders will be sure that the
most cost-effective solution has been developed to address the appropriate level of CSO control.
3-22 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
As an example of one way to derive CSO control goals, consider the following scenario
for a particular receiving water segment. System characterization indicates wet weather fecal
coliform bacteria counts and floatables are causing nonattainment of WQS, while wet weather
dissolved oxygen, TSS, nutrients, metals, and other constituents are within acceptable ranges.
In addition, the fecal coliform contributions from storm water alone would continue to cause
WQS violations. In this case, elimination of CSOs would not result in attainment of existing
WQS. Under the demonstration approach, the appropriate water quality goal would be a level
where remaining CSO pollutant loads "...will not preclude the attainment of WQS or the
receiving waters' designated uses or contribute to their impairment" (Il.C.b.ii).
To determine an appropriate level of CSO control, a municipality can start by identifying
a "reasonable range" of control goals, such as the following:
• Level I: Eliminate the impact of CSOs on receiving water quality.
• Level II: Reduce the CSO fecal coliform load and control floatables to a level that
would not alone cause nonattainment of existing WQS and reduce the
impact of other CSO constituents on the receiving water segment.
• Level III: Reduce the CSO fecal coliform load and control floatables to a level that
would not alone cause nonattainment of existing WQS.
With this range of controls, the constituents contributing to nonattainment of WQS are
in all cases targeted for control, while varying levels of control are identified for other
constituents that do not directly affect attainment of WQS. General categories of CSO control
technologies could be identified that would achieve each particular level of control. Within
Levels II and III, controls could be evaluated over a range of design conditions, such as 1 to 3,
4 to 7, and 8 to 12 overflow events per year, as suggested in the CSO Control Policy. Level
I would be equivalent to zero overflow events per year.
While this approach is intended to provide flexibility and facilitate cost/benefit analysis,
it is clear that even with a fairly simple CSS, the number of possible alternatives can become
very large. For example, five outfalls discharge to a receiving water segment and, at each
3-23 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
outfall, three technologies are identified as potentially feasible, and each technology could be
sized for three different design conditions (i.e., 1-month, 3-month, and 1-year storm).
Therefore, cost and performance data would have to be generated for 45 facilities. This point
emphasizes the need for iterative screening of alternatives, particularly where multiple CSOs
occur to a single receiving water segment. Where a CSS discharges CSOs to receiving water
segments in different watersheds, it would be appropriate to at least initially evaluate the
alternatives within the different watersheds separately.
This example of developing a range of CSO control goals is intended to be just that—an
example. Individual municipalities should develop an approach that is best suited to their own
CSS, receiving waters, and control needs. Smaller communities in particular might be able to
simplify this process to some degree, but the general concept of defining goals and evaluating
a range of controls should be maintained. In all cases, early coordination with appropriate
regulatory agencies in the development of the LTCP approach is necessary. Consensus among
stakeholders, including the public, on the methodology for developing the LTCP is desirable and
contributes to achieving consensus on the recommended plan.
3.3.3 Approaches to Structuring CSO Control Alternatives
A first step in identifying CSO control alternatives to meet the initial range of CSO
control goals is to identify ways to structure the alternatives, given the geographic layout of the
CSS, as well as hydraulic and other constraints. In other words, how will the alternatives
developed for each outfall be related to alternatives developed for other outfalls. This evaluation
can be conducted somewhat independently of the specific technologies to be applied to the
overflows. For example, the municipality can determine whether local or regional consolidation
of outfalls appear to be feasible or whether outfall-specific solutions appear more practical. At
this stage, it is not necessary to identify the specific control technologies to be applied. Rather,
general categories of projects such as "storage," "treatment," or "in-system controls" would
suffice. This "brainstorming" can help focus the initial identification of alternatives, particularly
with regard to identifying opportunities for consolidation of outfalls and regional solutions. A
given LTCP could ultimately include various combinations of approaches to structuring
3-24 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
alternatives. For example, an LTCP featuring regional consolidation of outfalls might also
include a number of outfall-specific facilities to control remote outfalls that would not be part
of the consolidation system. The following subsections discuss typical approaches to structuring
CSO control alternatives. Each of the following approaches should be considered in developing
the LTCP. It is possible, however, that for a given collection system, a particular approach
might yield no feasible alternatives.
3.3.3.1 Projects Common to All Alternatives
Projects common to all alternatives would be part of the LTCP regardless of the
recommendations for other alternatives. These projects might be associated with the NMC or
be specific fast-track projects for which the need and the expected benefit have already been
defined (perhaps as part of an earlier study). For example, if a previous study recommended
modifying the operation of a pumping station to relieve upstream surcharging in a particular
interceptor, the project can be incorporated into each alternative for long-term control, whether
the alternative be for end-of-pipe treatment or for local or regional consolidation. Subsequent
alternatives development should consider the effect of these common projects on predicted
system performance and implementation schedules.
3.3.3.2 Outfall-Specific Solutions
These alternatives are intended to control CSOs at individual outfalls. This approach
might be appropriate for outfalls that are located remotely from other outfalls. Typical
alternatives for single-outfall abatement include localized sewer separation, off-line storage, and
end-of-pipe treatment.
3.3.3.3 Localized Consolidation of Outfalls
Where several outfalls are near each other, municipalities should investigate whether to
consolidate them to a single location for storage and/or treatment. Consolidation can provide
more cost-effective control of CSOs, minimizing the number of sites necessary for abatement
facilities, and the institutional benefit of reducing the number of permitted outfalls.
3-25 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Consolidation conduits between outfalls may present opportunities for in-line storage, which may
reduce the required size of the abatement facilities.
3.3.3.4 Regional Consolidation
Municipalities with multiple outfalls and limited available space for near-surface facilities
should consider consolidation of outfalls on a regional basis using deep tunnels or other
appropriate technologies. Depending on the geographic distribution of outfalls, subsurface
geological conditions, and other factors, a deep tunnel alternative can include near-surface
consolidation conduits or satellite near-surface storage/treatment facilities for remotely located
outfalls. Alternatives involving deep tunnels should consider whether the tunnels will serve
primarily as storage facilities to be pumped out to the POTW at the end of a storm event or
whether they will also serve to convey wet weather flows to the POTW for treatment during a
storm event.
3.3.3.5 Utilization of POTW Capacity and CSO-Related Bypass
The CSO Control Policy encourages municipalities to consider the use of POTW capacity
for CSO control as part of the LTCP. The use of POTW capacity is presented in the CSO
Control Policy within three general contexts. First, as a minimum control, maximizing flow to
the POTW is intended to ensure that optimum use is made of existing POTW capacity. Second,
the CSO Control Policy states that ".. .the long-term control plan should also consider expansion
of POTW secondary and primary capacity in the CSO abatement alternative analysis" (II.C.4).
In some cases, it might be more cost-effective to expand existing POTW facilities than to site
separate facilities for CSO control. Third, the CSO Control Policy addresses the specific case
where existing primary treatment capacity at a POTW exceeds secondary treatment capacity and
it is not possible to utilize the full primary treatment capacity without overloading the secondary
facilities. For such cases, the CSO Control Policy states that at the request of the municipality,
EPA may allow an NPDES permit "...to authorize a CSO-related bypass of the secondary
treatment portion of the POTW treatment plant for combined sewer flows in certain identified
circumstances" (II.C.7). Under this provision, flows to the POTW within the capacity of
primary treatment facilities but in excess of the capacity of secondary treatment facilities may
3-26 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
be diverted around the secondary facilities, provided that "...all wet weather flows passing the
headworks of the POTW treatment plant will receive at least primary clarification and solids and
floatables removal and disposal, and disinfection, where necessary, and any other treatment that
can reasonably be provided" (II.C.7). In addition, the CSO-related bypass should not cause
exceedance of WQS.
The regulatory basis for permitting a CSO-related bypass is included at 40 CFR
122.41(m), which defines a bypass as "...the intentional diversion of waste streams from any
portion of a treatment facility." At 40 CFR 122.41(m)(4), bypasses are prohibited except where
unavoidable to prevent loss of life, personal injury, or severe property damage and where there
were no feasible alternatives to the bypass. "Severe property damage" is defined at 40 CFR
122.41(m)(l) to include "...damage to treatment facilities which causes them to become
inoperable...." Under the CSO Control Policy, severe property damage could "...include
situations where flows above a certain level wash out the POTW's secondary treatment system"
(II.C.7).
Thus, the CSO-related bypass provision applies only in situations where the POTW meets
the requirements of 40 CFR 122.41(m), as evaluated on a case-by-case basis. The municipality
is responsible for developing and submitting the technical justification supporting the request for
a CSO-related bypass. As with other aspects of the long-term plan development, coordination
between the municipality and the permitting agency on this issue is very important. For the
purpose of applying the requirements of 40 CFR 122.41(m) to the CSO-related bypass, the
municipality must demonstrate that the following criteria are met:
• The bypass was unavoidable to prevent severe property damage, the definition of
which includes damage to the treatment facilities that causes them to become
inoperable (i.e., washout of the secondary treatment system)
• There was no feasible alternative to the bypass, such as the use of auxiliary treatment
facilities, retention of untreated wastes, or maintenance during normal periods of
equipment downtime.
3-27 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
To satisfy the first criterion, ".. .the long-term control plan, at a minimum, should provide
justification for the cut-off point at which the flow will be diverted from the secondary treatment
portion of the treatment plant" (II. C. 7). Examples of the types of information that support the
"no feasible alternative" criterion include:
Records demonstrating that the secondary treatment system is properly operated and
maintained
A demonstration that the system has been designed to meet secondary limits for flows
greater than the peak dry weather flow plus an appropriate quantity of wet weather
flow
A demonstration that it is either technically or financially infeasible to provide
secondary treatment for greater amounts of wet weather flow.
In presenting alternatives incorporating the CSO-related bypass in the context of the
LTCP, the municipality should also provide "...a benefit-cost analysis demonstrating that
conveyance of wet weather flow to the POTWfor primary treatment is more beneficial than other
CSO abatement alternatives such as storage and pump back for secondary treatment, sewer
separation, or satellite treatment" (II.C.7).
The permit can include the conditions under which a CSO-related bypass would be
approved and can specify appropriate treatment, monitoring, or effluent limitation requirements
related to the bypass event. An example of permit language for the CSO-related bypass
requirement is included in the permit writer's guidance document (EPA, 1995g).
3.3.3.6 Consideration of Sensitive Areas
The CSO Control Policy states that "EPA expects a permittee's long-term CSO control
plan to give the highest priority to controlling overflows to sensitive areas, as determined by the
NPDES authority in coordination with State and Federal Agencies, as appropriate..." (II.C.3).
Examples of sensitive areas presented in the CSO Control Policy include designated Outstanding
National Resource Waters, National Marine Sanctuaries, waters with threatened or endangered
species and their habitat, waters supporting primary contact recreation (e.g., bathing beaches),
3-28 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
public drinking water intakes or their designated protection areas, and shellfish beds. As
described in Chapter 1, the CSO Control Policy (II.C.3) provides a hierarchy of approaches for
controlling overflows to sensitive areas. Each of the approaches to developing alternatives could
be applied to controlling overflows to sensitive areas, and an awareness of the locations of
sensitive areas might guide the development and selection of control alternatives, as well as the
identification of priorities for project implementation.
3.3.4 Goals of Initial Alternatives Development
Once a range of CSO control goals has been developed and approaches to structuring
CSO control alternatives have been identified, the next step is to develop specific alternatives
to achieve the various CSO control goals. As noted previously, in the initial alternatives
development steps, the number of alternatives necessary to cover the range of control levels for
each CSO can be very large. Judgment is necessary to develop a manageable array of
alternatives. It is important to remember that the iterative screening of alternatives is flexible
and not a rigid process. Alternatives initially rejected might become more feasible as more
information is developed. Similarly, agency interaction and public participation throughout the
process might contribute additional alternatives.
Municipalities should generally include the following steps during the initial development
of alternatives to meet CSO control goals:
1. Identification of control alternatives (Section 3.3.5)
2. Preliminary sizing of control alternatives (Section 3.3.6)
3. Preliminary development of cost/performance relationships (Section 3.3.7)
4. Identification of preliminary site options and issues (Section 3.3.8)
5. Identification of preliminary operating strategies (Section 3.3.9).
3.3.5 Identification of Control Alternatives
A municipality's LTCP should contain one or a combination of CSO control alternatives
to achieve receiving water segment-specific CSO control goals. Each alternative, in turn, will
3-29 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
likely consist of one or more control measures. Control measures can include technologies,
operating strategies, public policies and regulations, or other measures that would contribute to
some aspect of CSO control. Control measures can generally be classified under one of the
following categories:
• Source controls
• Collection system controls
• Storage technologies
• Treatment technologies.
Given the number of specific control measures within each of these categories and the
range of sizing options for specific measures, initially it might be practical to consider general
categories, such as storage or treatment, rather than specific storage or treatment technologies.
Alternatively, it might be appropriate to identify "representative" technologies, with the
understanding that specific technologies would be considered as part of more detailed
evaluations. For example, if the consolidation of three outfalls appears to be feasible, the
general categories of alternatives for these outfalls would include consolidation to storage or
treatment. Representative technologies could include storage in the consolidation conduit, a
storage tank downstream of the conduit, or a storage/sedimentation facility downstream of the
conduit. The storage/sedimentation tank could be representative of or a "place-holder" for other
treatment technologies, which could be evaluated in more detail once the general feasibility of
achieving CSO control goals with the representative technology is established. In general,
receiving water-specific CSO control goals will provide a basis for initial screening of CSO
control measures. As the feasibility of the general categories of controls is resolved, the
concepts will be developed gradually to higher levels of detail, allowing further screening of
specific measures within the general categories.
The following discussion briefly introduces some common control measures under the
above categories. The list is for general information only and is not intended to be
comprehensive or imply EPA endorsement. Municipalities should also be open to evaluating
new and emerging control measures. More detailed discussions of specific CSO control
3-30 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
measures are given in the Manual—Combined Sewer Overflow Control (EPA, 1993a) and
Combined Sewer Overflow Pollution Abatement (WPCF, 1989).
3.3.5.1 Source Controls
Source controls affect the quantity or quality of runoff that enters the collection system.
Since source controls reduce the volumes, peak flows, or pollutant loads entering the collection
system, the size of more capital-intensive downstream control measures can be reduced or, in
some cases, the need for downstream facilities eliminated. The source controls discussed below
include both quantity control and quality control measures:
Porous Pavements—Porous pavements reduce runoff by allowing storm water to
drain through the pavement to the underlying soil. Porous pavements, most
commonly used in parking lots, require skill and care in installation and maintenance
to ensure that the pores in the pavement do not become plugged. The benefits of
porous pavements in cold climates might be limited.
Flow Detention—Detention ponds in upland areas and roof-top storage can store
storm water runoff temporarily, delaying its introduction into the collection system,
and thereby helping to attenuate peak wet weather flows in the collection system.
The detention facilities drain back to the collection system when peak wet weather
flows subside.
Area Drain and Roof Leader Disconnection—In highly developed areas with
relatively little open, pervious space, roof leaders and area drains are commonly
connected directly to the combined drainage system. Rerouting of these connections
to separate storm drains or available pervious areas can help reduce peak wet weather
flows and volumes.
Use of Pervious Areas for Infiltration—Detention of storm flow in pervious areas
not only helps attenuate peak wet weather flow in the collection system but also
reduces runoff volume through infiltration into the soil. Grassed swales, infiltration
basins, and subsurface leaching facilities can be used to promote infiltration of runoff.
Infiltration sumps can be used in areas with well draining soils. This type of control
might be more appropriate as a requirement for future development or redevelopment
and could be implemented through sewer use ordinances and through strict review of
proposed development plans.
Air Pollution Reduction—One way to control pollutant loadings from combined
sewer areas is to limit the amount of pollutants contributed to local air. Paniculate
and gaseous pollutants in air are carried to the ground by rainfall and airborne
3-31 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
particulates also settle to the ground during dry weather. It is extremely difficult,
however, to quantify the potential reduction in storm water pollution associated with
air quality improvement.
• Solid Waste Management—Although littering is generally prohibited everywhere,
it is a common problem in many communities. Street litter typically includes
metallic, glass, and paper containers; cigarettes; newspapers; and food wrappers. If
not removed from the street surfaces by cleaning equipment, some of these items
often end up in combined sewer overflows, creating visible pollution due to their
floatable nature.
Enforcement of anti-litter ordinances is generally given a relatively low priority by
law enforcement agencies due to the limited availability of personnel and funds, as
well as the difficulty of identification and conviction of violators. Both public
education programs and conveniently placed waste disposal containers might be
effective, low-cost alternatives, especially in urban business areas. The proper
disposal of leaves, grass clippings, crankcase oil, paints, chemicals, and other such
wastes can be addressed in a public education program. Because the results of such
a program depend on voluntary cooperation, the level of effectiveness can be difficult
to predict.
• Street Sweeping—Street sweeping may be evaluated as a best management practice
(BMP) for CSO pollution control. Frequent street sweeping can prevent the
accumulation of dirt, debris, and associated pollutants, which may wash off streets
and other tributary areas to a combined collection system during a storm event.
Current sweeping practices can be analyzed to determine whether more frequent
cleaning will yield CSO control benefit. The overall effectiveness of street sweeping
as a CSO control measure has been debated and depends on a number of factors,
including frequency of sweeping, size of particles captured by sweeping, street
parking regulations, and climatic conditions, such as rainfall frequency and season.
• Fertilizer and Pesticide Control—Fertilizers and pesticides washed off the ground
during storms contribute to the pollutant loads in storm water runoff. The municipal
parks department is probably the user easiest to control. It is important, therefore,
that these departments follow proper handling and application procedures. The use
of less toxic formulations should also be encouraged. In highly urbanized areas, the
use of these chemicals by the general public is not likely to be a major source of
pollution. Because most of the problems associated with these chemicals are a result
of improper or excessive usage, however, a public education program might be
beneficial.
• Snow Removal and De-Icing Control—This abatement measure involves limiting the
use of chemicals for snow and ice control to the minimum necessary for public
safety. This, in turn, would limit the amount of chemicals (normally salt) and sand
washed into the collection system and ultimately contained in CSOs. Proper storage
3-32 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
and handling measures for these materials might also reduce the impacts of runoff
from material storage sites.
• Soil Erosion Control—Properly vegetated and/or stabilized soils are not as
susceptible to erosion and, thus, will not be washed off into combined sewers during
wet weather. Controlling soil erosion is important in relation to CSOs and water
quality for a number of reasons: soil particles create turbidity in the receiving water,
blocking sunlight and causing poor aesthetics; soil particles carry nutrients, metals,
and other toxics which may be released in the receiving water, contributing to algal
blooms and bioaccumulation of toxics; and eroded soil can contribute to
sedimentation problems in the collection system, potentially reducing hydraulic
capacity. Like fertilizer and pesticide control, an educational program may be useful
in controlling soil erosion, and implementation and enforcement of erosion control
regulations at construction sites can also be effective.
• Commercial/Industrial Runoff Control—Commercial and industrial lands, including
gasoline stations, railroad yards, freight loading areas, and parking lots, contribute
grit, oils, grease, and other pollutants to CSSs. Such contaminants can run off into
CSSs. Installing and maintaining oil and grease separators in catch basins and area
drains can help control runoff from these areas, while pretreatment requirements can
be identified as part of the community's sewer use regulations.
• Animal Waste Removal—This measure refers to removing animal excrement from
areas tributary to CSSs. As with air pollution control, the impact of this control
measure is difficult to quantify; however, it might be possible to achieve a minor
reduction in bacterial load and oxygen demand. This BMP can be addressed by a
public information program and "pooper-scooper" ordinances.
• Catch Basin Cleaning—The regular cleaning of catch basins can remove
accumulated sediment and debris that could ultimately be contained in CSOs. In
many communities, catch basin cleaning is targeted more toward maintaining proper
drainage system performance than pollution control.
3.3.5.2 Collection System Controls
Collection system controls and modifications affect CSO flows and loads once the runoff
has entered the collection system. This category of control measures can reduce CSO volume
and frequency by removing or diverting runoff, maximizing the volume of flow stored in the
collection system, or maximizing the capacity of the system to convey flow to a POTW and
includes the following control alternatives:
3-33 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Sewer Line Flushing—Sediments that accumulate in sewers during dry weather can
be a source of CSO contaminants during storm events. Periodically flushing sewers
during dry weather will convey settled materials to the POTW. A 2-year study
conducted in Boston, Massachusetts, addressed the cost-effectiveness and feasibility
of sewer line flushing as part of a CSO management program (EPA, 1976a). The
study determined that flushing combined sewer laterals removed pollutant
accumulations. The cost effectiveness of such a program, however, depends on
treatment, labor costs, physical sewer characteristics, and productivity.
Sewer cleaning usually requires the use of a hydraulic, mechanical, or manual device
to resuspend solids into the waste flow and carry them out of the collection system.
This practice might be more effective for sewers with very flat slopes. Cleaning
costs increase substantially for larger interceptors due to occasional accumulations of
thick sludge blankets in inverts.
• Maximizing Use of Existing System—This control measure involves maximization
of the quantity of flow collected and treated, thereby minimizing overflows. It
involves ongoing maintenance and inspection of the collection system, particularly
flow regulators and tidegates. In addition, minor modifications or repairs can
sometimes result in significant increases in the volume of storm flow retained in the
system. Strict adherence to a well-planned preventive maintenance program can be
a key factor in controlling dry and wet weather overflows.
• Sewer Separation—Separation is the conversion of a CSS into separate storm water
and sanitary sewage collection systems. This method has historically been used by
many communities as a way to eliminate CSOs and their effects altogether.
Separation has been reconsidered in recent years because it typically results in
increased loads of storm water runoff pollutants (e.g., sediments, bacteria, metals,
oils) being discharged to the receiving waters, is relatively expensive, and can disrupt
traffic and other community activities during construction. Sewer separation is a
positive means of eliminating CSOs and preventing sanitary flow from entering the
receiving waters during wet weather periods, however, and might still be applicable
and cost-effective. It also can be considered in conjunction with the evaluation of
sensitive areas in accordance with the CSO Control Policy, although storm drain
discharges will likely still remain. In some cases, municipalities that separate their
combined sewers might be required to file for NPDES storm water permit coverage.
• Infiltration/Inflow Control—Excessive infiltration and inflow (I/I) can increase
operations and maintenance costs and can consume hydraulic capacity, both in the
collection system and at the treatment plant. In CSSs, surface drainage is by design
the primary source of inflow. Other sources of inflow in CSSs might be appropriate
to control, including tidal inflow through leaking or missing tidegates and inflow in
separate upstream areas, which might be tributary to a downstream combined system.
Infiltration is ground water that enters the collection system through defective pipe
joints, cracked or broken pipes, manholes, footing drains, and other similar sources.
3-34 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Infiltration flow tends to be more constant but of lower volume than inflow. The
control of infiltration is difficult and often expensive, since infiltration problems are
usually difficult to isolate and reflect a more general sewer system deterioration.
Significant lengths of sewers usually must be rehabilitated to effectively remove
infiltration, and the rehabilitation effort often must include house laterals.
Controlling infiltration might have minimal impact on CSO volume due to its small
magnitude compared to inflow.
• Polymer Injection—Polymers can increase the hydraulic capacity of pipelines by
correcting specific capacity deficiencies in a transport system. The injection of
polymer slurries into sewers is intended to increase pipe capacity by reducing pipe
friction. In certain cases, this increase can be significant and might reduce system
surcharging and backups during wet weather. This method has mostly been tested
in relatively small sanitary sewers during dry weather.
• Regulating Devices and Backwater Gates—Flow regulating devices have been used
for many years in CSSs to direct dry weather flow to interceptors and to divert wet
weather combined flows in excess of interceptor capacity to receiving waters. The
following discussion of regulators was adapted from the Manual—Combined Sewer
Overflow Control (EPA, 1993a).
In general, regulators fall into two categories: static and mechanical. Static
regulators have no moving parts and, once set, are usually not readily adjustable.
They include side weirs, transverse weirs, restricted outlets, swirl concentrators (flow
regulators/solids concentrators), and vortex valves. Mechanical regulators are
adjustable and might respond to variations in local flow conditions or be controlled
through a remote telemetry system. They include inflatable dams, tilting plate
regulators, reverse-tainter gates, float-controlled gates, and motor-operated or
hydraulic gates.
Many of the older float-operated mechanical regulators have proven to be erratic in
operation and require constant maintenance. In Saginaw, Michigan, many existing
float-operated regulators were replaced by vortex valves, due to the unreliability and
excessive maintenance associated with the mechanical regulators. In Boston,
Massachusetts, many float-operated regulators have been replaced over the years with
static regulators.
The following types of regulators and gates have been installed in more recent CSO
control projects or have been used to replace older, less reliable types:
- Vortex Valves—Vortex valves are static regulators that allow dry weather flow
to pass without restriction but control higher flows by a vortex throttling action.
Vortex valves have been used to divert flows to CSO treatment facilities, control
flow out of storage facilities, and replace failed mechanical regulators. They
have the following advantages over standard orifices:
3-35 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
- The discharge opening on the vortex valve is larger than the opening on a
standard orifice sized for the same discharge rate, thereby reducing the risk
of blockage.
— The discharge from the vortex valve is less sensitive to variations in upstream
head than a standard orifice (Urbonas and Stahre, 1993).
- Inflatable Dams—An inflatable dam is a reinforced rubberized fabric device that,
when fully inflated, forms a broad-crested transverse weir. When deflated, the
dam collapses to take the form of the conduit in which it is installed. Inflatable
dams can be positioned to restrict flow in an outfall conduit or combined sewer
trunk. The dams, when fully inflated, can act as regulators by directing flow into
an interceptor and preventing the diversion of flow to an outfall until the depth
of flow exceeds the crest of the dam. Alternatively, when installed upstream of
a regulator, dams can be inflated during wet weather to create in-system storage.
Inflatable dams are controlled by local or remote flow or level sensing devices,
which regulate the height of the dam to optimize in-line storage and prevent
upstream flooding. The dam height is controlled by the air pressure in the dam.
Because inflatable dams are typically constructed of rubber or strong fabric, they
are subject to puncturing by sharp objects. These devices generally require
relatively little maintenance, although the air supply should be inspected regularly
(WPCF, 1989).
- Motor- or Hydraulically Operated Sluice Gates—Similar to the inflatable dams,
motor- or hydraulically operated gates typically respond to local or remote flow
or level sensing devices. Normally closed gates can be located on overflow pipes
to prevent overflows except under conditions when upstream flooding is
imminent. Normally open gates can be positioned to throttle flows to the
interceptor to prevent interceptor surcharging or to store flow upstream of
regulators. Controls can be configured to fully open or close gates, or to
modulate gate position. The level of control and general reliability of
motor-operated gates make them well suited for use with real-time control
systems.
- Elastomeric Tidegates—While not actually regulators, tidegates are intended to
prevent the receiving water from flowing back through the outfall and regulator
and into the conveyance system. Inflow from leaking tidegates takes up hydraulic
capacity in the downstream interceptors and increases the hydraulic load on
downstream treatment facilities. Elastomeric tidegates provide an alternative to
the more traditional flap-gate style tidegates, which are prevalent in many CSO
communities. Tidegates have historically required constant inspection and
maintenance to ensure that the flaps are seated correctly and that no objects or
debris are preventing the gate from closing. Warpage, corrosion, and a tendency
to become stuck in one position are also characteristic of flap-gate style tidegates.
Elastomeric tidegates are designed to avoid the maintenance problems associated
with the flap gates. In particular, the elastomeric gates are designed to close
3-36 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
tightly around objects which might otherwise prevent a flap gate from closing
(Field, 1982).
Several documents provide detailed descriptions of other regulator types (WPCF,
1989; Metcalf & Eddy, 1991; and Urbonas and Stahre, 1993).
• Real-Time Control—System-wide real-time control (RTC) programs can provide
integrated control of regulators, outfall gates, and pump station operations based on
anticipated flows from individual rainfall events, with feed-back control adjustments
based on actual flow conditions within the system. Computer models associated with
the RTC system allow an evaluation of expected system response to control
commands before execution. Localized RTC might also be provided to individual
dynamic regulators, based on feedback control from upstream and/or downstream
flow monitoring elements. As with any plan for improving in-line storage, to take
the greatest advantage of RTC, a CSS should have relatively flat upstream slopes and
sufficient upstream storage and downstream interceptor capacity (EPA, 1993a).
• Flow Diversion—Flow diversion is the diversion or relocation of dry weather flow,
wet weather flow, or both from one drainage basin to another through new or
existing drainage basin interconnections. Flow diversion can relieve an overloaded
regulator or interceptor reach, resulting in a more optimized operation of the
collection system. Flow diversion can also be used to relocate combined sewer flow
from an outfall located in a more sensitive receiving water area to an outfall located
in a less sensitive one.
3.3.5.3 Storage Technologies
Wet weather flows can be stored for subsequent treatment at the POTW treatment plant
once treatment and conveyance capacity have been restored. Technologies include the following:
• In-Line Storage—In-line storage is storage in series with the sewer (Urbonas and
Stahre, 1993). In-line storage can be developed in two ways: (1) construction of
new tanks or oversized conduits to provide storage capacity or (2) construction of a
flow regulator to optimize storage capacity in existing conduits. The new tanks or
oversized conduits are designed to allow dry weather flow to pass through, while
flows above a design peak are restricted, causing the tank or oversized conduit to fill.
A flow regulator on an existing conduit functions under the same principle, with the
existing conduit providing the storage volume. Developing in-line storage in existing
conduits is typically less costly than other, more capital-intensive technologies, such
as off-line storage/sedimentation, and is attractive because it provides the most
effective utilization of existing facilities. The applicability of in-line storage,
particularly the use of existing conduits for storage, is very site-specific, depending
on existing conduit sizes and the risk of flooding due to an elevated hydraulic grade
3-37 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
line. Examples of flow regulating technologies used to develop in-line storage were
discussed previously.
• Off-Line Near Surface Storage—This technology reduces overflow quantity and
frequency by storing all or a portion of diverted wet weather combined flows in
off-line storage tanks. The storage arrangement is considered to be parallel with the
sewer. Stored flows are returned to the interceptor for conveyance to the POTW
treatment plant once system capacity is available. In some cases, flows are conveyed
to a CSO treatment facility.
• Deep Tunnel Storage—This technology provides storage and conveyance of storm
flows in large tunnels constructed well below the ground surface. Tunnels can
provide large storage volumes with relatively minimal disturbance to the ground
surface, which can be very beneficial in congested urban areas. Flows are introduced
into the tunnels through dropshafts, and pumping facilities are usually required at the
downstream ends for dewatering.
3.3.5.4 Treatment Technologies
Treatment technologies are intended to reduce the pollutant load in the CSO to receiving
waters. Specific technologies can address different pollutant constituents, such as settleable
solids, floatables, or bacteria. Where treatment facilities are to be considered, the LTCP should
contain provisions for the handling, treatment, and ultimate disposal of sludges and other
treatment residuals. The following list highlights selected treatment technologies:
• Off-Line Near Surface Storage/Sedimentation—These facilities are similar to
off-line storage tanks, except that sedimentation is provided for flows in excess of the
tank volume. Coarse screening, floatable control, and disinfection are commonly
provided as part of these facilities.
• Coarse Screening—This technology removes coarse solids and some floatables.
Coarse screening is typically provided upstream of other control technologies, such
as storage facilities or vortex units, and is also used in end-of-pipe treatment
applications.
• Swirl/Vortex Technologies—These devices provide flow regulation and solids
separation by inducing a swirling motion within a vessel. Solids are concentrated and
removed through an underdrain, while clarified effluent passes over a weir at the top
of the vessel. Types of swirl/vortex devices include the EPA swirl concentrator and
commercial vortex separators. Conceptually, the EPA swirl concentrator is designed
to act as an in-line regulator device. In addition to flow routing or diversion, it
removes heavy solids and floatables from the overflow. The commercial vortex
3-38 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
separators are based on the same general concept as the EPA swirl concentrator but
include a number of design modifications intended to improve solids separation. The
commercial designs have been applied as off-line treatment units. Each type of
swirl/vortex unit has a different configuration of depth/diameter ratio, baffles, pipe
arrangements, and other details designed to maximize performance.
• Disinfection—This process destroys or inactivates microorganisms in overflows, most
commonly through contact with forms of chlorine. Various disinfection technologies
are available both with and without chlorine compounds. Some of the more common
technologies include gaseous chlorine, liquid sodium hypochlorite, chlorine dioxide,
ultraviolet radiation, and ozone. For disinfection of CSOs, liquid sodium
hypochlorite is the most common of the above technologies.
• Dechlorination—A major disadvantage of chlorine-based disinfection systems is that
the residual chlorine concentration can have a toxic effect on the receiving waters,
due either to the free chlorine residual itself or to the reaction of the chlorine with
organic compounds present in the effluent. With the relatively short contact times
available at many CSO control facilities, disinfection residuals can be of particular
concern and can require consideration of dechlorination alternatives. Two of the
more common means for dechlorinating treated effluent are application of gaseous
sulfur dioxide or liquid sodium bisulfite solution.
• Other Treatment Technologies—A number of other treatment technologies have
been identified as applicable to CSOs and have been studied in pilot tests, but have
not been widely implemented in operating facilities. These technologies include
dissolved air floatation, high-rate filtration, fine screens and microstrainers, and
biological treatment. Fine screens and microstrainers have been used in full-scale
facilities but, in some cases, have been unreliable due to mechanical complexity and
blinding of the screens. Biological treatment at a POTW treatment plant of pump
back flows from a CSO storage facility is a common practice, but a biological
treatment facility dedicated solely to CSO treatment would not likely be successful
due to the impact of prolonged dry periods on the biological media.
3.3.6 Preliminary Sizing Considerations
The preliminary sizing of CSO control alternatives will likely depend on the following
factors:
Predicted CSO flow rates, volumes, and pollutant loads under selected hydraulic
conditions
Level of abatement of predicted CSO volumes and pollutant loads necessary to meet
CSO control goals
3-39 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Design criteria for achieving the desired level of abatement with the selected control
measure or technology.
The collection system hydraulic model developed for system characterization is an
appropriate tool for predicting CSO flow rates and volumes (EPA, 1995d). The design
hydrologic conditions can include historical storms of specified recurrence intervals, a continuous
simulation based on a statistical year or multiple years of rainfall data, or both. The system
model should be used to define a baseline condition, which will serve as a basis for evaluating
reductions in CSO impacts resulting from the implementation of minimum technologies or other
currently planned, short-term projects that are likely to be implemented before the major
components of the LTCP. A "future planned conditions" baseline, incorporating short-term
projects as well as design year base flows, would provide the basis for evaluating the impacts
of the CSO control alternatives proposed as part of the LTCP. The future planned conditions
baseline would be equivalent to a "future no-action condition" in facilities planning, although,
in the case of CSOs, this nomenclature is misleading because near-term actions, such as
implementation of minimum controls, are generally required and would be incorporated into the
model.
The level of abatement of predicted flows necessary to meet CSO control goals depends
on the definition of the specific goals. A goal of CSO elimination means that discharges from
a given CSO location would be eliminated under all possible hydraulic and hydrologic
conditions. This goal essentially dictates either sewer separation or CSO relocation, in which
the relocation conduit is sized for the absolute peak flow from the CSO outfall. This peak flow
can be determined by analyzing increasingly larger storm events (e.g., 5-year, 10-year, 20-year
storms) until a storm is reached above which the peak flow from the CSO outfall does not
increase. At this point, the collection system is at absolute capacity, and additional runoff
cannot enter the collection system.
Sizing to meet goals of providing storage for 1 to 3, 4 to 7, and 8 to 12 overflows per
year can be estimated initially by capturing the volumes from the 1-year, 3-month, and 1-month
storms, respectively. Similarly, sizing to provide treatment over that range can be estimated
3-40 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
using the peak flow rates from the range of storms, in conjunction with sizing criteria for
treatment, which are usually based on flow rates. As CSO control alternatives are further
developed, the basis for sizing should be evaluated against a long-term simulation, which would
incorporate the impacts of dewatering rates and antecedent storms, particularly if the CSO
control goals are tied to average annual overflow frequencies.
It is also important to evaluate the impact of remaining overflows on the receiving
waters. A receiving water model might be required, for example, to evaluate whether the
remaining overflow from the 6-month or 1-year storm would cause exceedances of WQS if a
storage tank is sized to capture the volume from a 3-month storm. This evaluation might
indicate whether flow hi excess of the capacity of the tank should continue to pass through the
tank receiving a level of treatment or whether excess flows should be diverted upstream of the
tank.
As is evident from this discussion, the issues of sizing and performance are closely
related. The relationships between sizing criteria and expected performance might not be as
clearly defined for CSO treatment as they are for sizing of POTW treatment plant unit processes.
This latter issue was addressed earlier hi the discussion of the definition of equivalent primary
treatment under the presumption approach. For the purposes of initial alternatives development,
reasonable assumptions regarding design criteria should be made to allow a preliminary sizing
and estimate of performance. These assumptions can then be revisited during further steps or
refinements hi the alternatives development and evaluation process, as more information becomes
available and as the general feasibility of alternatives becomes better defined.
3.3.7 Cost/Performance Considerations
The CSO Control Policy states that cost/performance evaluations should be "...among
the other considerations used to help guide selection of controls" (II.C.5). These analyses
typically involve estimating costs for a range of control levels, then comparing performance
versus cost and identifying the point of diminishing returns, referred to as the "knee" of the
curve. Cost/performance analyses, used for the evaluation of alternatives, are discussed in more
3-41 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
detail in Section 3.4. For the development of alternatives, it is likely that more than one
alternative will be identified to achieve each level of control. During the alternatives
development, a simpler cost/performance approach might be appropriate to eliminate non-cost-
effective alternatives. For example, a computation of capital cost per gallon controlled might
provide a reasonable basis for screening certain alternatives. During the more detailed
alternatives evaluation process described later, present worth costs, incorporating annual O&M
costs, would be developed for the remaining alternatives.
During alternatives development, non-monetary factors can also be defined and
compared. For example, siting and environmental impacts and construction-related issues can
be identified and used as a basis for the preliminary screening of alternatives. While at a more
detailed level of alternatives development and evaluation, it might be appropriate to assign dollar
values to some of these factors, in the initial development phase, qualitative assessments might
be sufficient to eliminate certain alternatives from further consideration.
Thus, more formal cost/benefit analyses are appropriate during the detailed alternatives
evaluation phase. For municipalities with larger or more complex CSSs where more initial
screening of alternatives is necessary to make the alternatives evaluation analyses more
manageable, simpler cost/benefit relationships provide an appropriate basis for that screening.
Another approach to cost-performance evaluations is the optimization of combinations of
storage and treatment facilities. Given a design condition, the desired level of control could be
achieved by providing storage of the entire CSO volume, sedimentation/treatment based on a
maximum overflow rate for the peak CSO flow, or a combination of storage and treatment.
Providing sufficient storage volume to capture all of the CSO or sufficient surface area to meet
the maximum overflow rate at peak flow might not be feasible due to site or cost constraints.
A more feasible alternative might be to size a sedimentation tank for a maximum flow that is
less than the peak and provide storage for flows between the design maximum and the actual
peak flows.
3-42 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
A mass diagram for the selected design storm (Exhibit 3-2) can be used to determine the
range of combinations of storage and treatment to meet a given control goal. The mass diagram
consists of a plot of cumulative volume of overflow versus tune, based on a hydrograph
developed by a collection system hydrologic/hydraulic model, such as SWMM. The slope at
any given point on the curve represents the flow rate (change in volume with respect to tune)
at that point in time, and the end of the storm is indicated where the slope of the curve
approaches zero (flow equals zero). The total volume at the end of the storm represents the
storage volume required if no treatment is provided. The inflection point on the curve, where
the slope is at a maximum, represents the peak flow rate to be treated if no storage is provided.
The intermediate combinations of storage and treatment required to achieve a level of control
between all-storage and all-treatment can be determined from the mass diagram. The changing
slope of the curve represents the increase then decrease in CSO flow rate during the storm event.
If a given flow rate (less than the peak) is selected as the maximum design flow rate for
treatment, then flows above this maximum rate must be stored. Graphically, the selected
maximum flow rate can be identified as two points on the curve, one above and one below the
inflection point. All points between these two points on the curve represent flow rates greater
than the design maximum. The vertical distance between the tangents at these two points,
therefore, represents the volume of flow occurring while the flow rate is greater than the
maximum design flow rate and, thus, represents the necessary storage volume.
Exhibit 3-3 is an alternative representation of this approach. In this figure, the predicted
CSO flow rate to a facility is plotted against tune. A horizontal line is drawn at the selected
maximum flow rate for treatment, corresponding to a peak hydraulic loading rate. The volume
of flow associated with flow rates in excess of the design maximum, which is to be captured for
storage, is represented by the area of the curve above the maximum treatment rate. To optimize
the storage/treatment combinations, cost estimates are developed for the all-storage, all-
treatment, and selected intermediate combinations, and then the points are plotted and the
minimum cost alternatives identified. Alternatives for the intermediate combinations of storage
and treatment would require separate tankage for treated flows and for stored flows, with a
regulator to limit peak flows to the treatment tanks. Flow would be introduced into the
treatment tanks first. When the influent flow exceeded the design maximum, flow to the
3-43 August 1995
-------
CO
o
75
o>
1
O
"o
0>
O
Maximum Storage Volume
(no treatment)
Inflection Point
-Maximum Treatment Rate
(no storage)
Cumulative
Overflow
Volume
Storage Volume
Required at
Specified
Treatment Rate
Source: Camp, Dresser & McKee, 1989
Time (hours)
Exhibit 3-2. Typical Mass Diagram
3-44
-------
Volume of storage
required for flows
above maximum
treatment rate
Time (hours)
Exhibit 3-3. Typical Representation of Interaction Between Storage and Treatment Needs
3-45
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
treatment tanks would be throttled, with flows in excess of the design maximum diverted to the
storage tanks. Once flows subsided to below the design maximum, the diversion of flow to the
storage tanks would cease, and all flows would again be diverted to the treatment tanks. A
vortex valve with an upstream overflow weir is an example of the type of regulator device that
could be used to achieve the necessary flow control. The vortex valve would limit flow into the
treatment tanks to a design maximum, with the excess flows diverted over the upstream weir to
the storage tanks.
The mass diagram approach might be most applicable where an existing tank is available
for CSO sedimentation. If the tank is not big enough to meet the maximum allowable overflow
rate at peak flow, the size of a new storage facility to work in conjunction with the existing tank
can be readily determined from the mass diagram, using the procedure described above.
One drawback to the mass diagram analysis is that the level of CSO control provided by
each alternative is not equal. Storage of the full volume of CSO from a given storm for
subsequent pumpback to a POTW treatment plant will likely provide a higher level of control
than providing the equivalent of primary treatment at a satellite facility, particularly if pumpback
occurs once secondary treatment capacity is available at the POTW treatment plant. A second
drawback is that this analysis does not consider the storage volume available in the sedimentation
tank. Depending on the total volume, peak flow, and hydrograph shapes for the selected design
storm, the volume of the sedimentation tank might have more or less of an impact on
performance. It is possible that the peak influent flow to a sedimentation facility will occur
before the tank volume is full, so that the actual peak overflow rate occurs on the falling leg of
the influent hydrograph, at a value less than the peak influent flow. The mass diagram could
be used to estimate the total CSO volume associated with the point of maximum flow for
comparison with the volume of the sedimentation tank.
In general, the evaluation of storage/treatment optimization can provide an additional
level of information from which to identify potential alternatives. The analysis does not predict
the performance or impact on water quality, other than that the performance will be between the
boundary conditions of all-storage and all-treatment. In addition, questions of reliability,
3-46 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
operability, and increased maintenance needs associated with maintaining separate tankage for
storage and treatment should be considered in evaluating such alternatives.
3.3.8 Preliminary Siting Issues
One of the key considerations in assessing the overall feasibility of a CSO control
alternative is the identification of an appropriate site. Siting issues can overshadow technical and
even financial issues in the process of gaining public acceptance of a CSO control program. As
with other aspects of the alternatives development process, identifying and evaluating potential
sites calls for iterative screening. The objective of preliminary site development is to identify
potential locations for the range of facilities identified based on the sizing procedures. Common
sense and engineering judgement are used at the preliminary siting level to identify possible
locations for facilities.
Initial criteria for screening potential sites can include:
• Availability of sufficient space for the facility on the site
• Distance of the site from CSO regulator(s) or outfall(s) that will be controlled
• Environmental, political, or institutional issues related to locating the facility on the
site.
Recent aerial photographs or relatively small-scale maps, such as USGS topographic
maps, are useful for the initial identification of potential sites. To assess whether sufficient
space is available on a site, however, larger-scale maps, such as 100-scale sewer maps, are more
useful. It is helpful to develop an estimate of the footprint of the proposed facility, then lay the
footprint over an assessor's map, or other larger-scale plan view of the site. Consolidation or
connecting conduits, where required, should also be located on the preliminary site plans. Site
inspections are extremely valuable to confirm geographic information and to identify obvious
features that might not appear on the available maps or aerial photographs.
3-47 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
If possible, it is usually beneficial to identify more than one potential site for each
facility. Later evaluation of alternate sites may involve tradeoffs and comparisons between sites.
Public participation through public meetings and workshops provides key input for the evaluation
of these trade-offs, as well as to other aspects of preliminary site development.
Deciding whether a site is within a reasonable distance of the required point of control
requires engineering judgment, particularly if an apparently ideal site is located further from the
point of control than an apparently less-ideal site. The tradeoffs between distance and other
factors can be evaluated during the detailed alternative evaluation process described in the next
section. During alternatives development, however, initial comparisons might eliminate some
options from further consideration.
Detailed analysis of the environmental, political, and socioeconomic impacts of locating
a facility at a particular site is also part of the detailed alternative evaluation process. In some
areas, however, a municipality might have specific knowledge of the history or existing plans
for a particular site, which would preclude that site for consideration as a location for a CSO
control facility. For example, a vacant lot might be known to contain contaminated soil or might
to be already committed to commercial development. In such a case, a more detailed analysis
of the site would not be worthwhile, unless perhaps no other feasible sites were available.
The municipality also needs to consider issues of "environmental justice" at the
preliminary siting level. If the initially identified sites for CSO control facilities are all in low-
income neighborhoods, the municipality should attempt to identify alternative sites in other areas
to balance perceived inequities in project siting. If no other sites are technically feasible, then
the municipality should recognize the need for additional effort in public participation, such as
public meetings with concerned members of the community or multilingual fact sheets about the
proposed facility. Development of multiple-use facilities with special architectural considerations
or linkage with neighborhood improvement projects can also foster public acceptance of the
proposed plan.
3-48 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
3.3.9 Preliminary Operating Strategies
Once a preliminary size and location have been identified for an alternative, the
municipality should develop conceptual operating considerations to ensure that the alternative
can function reasonably in the context of its geographic location and relationship to the collection
system. For an off-line storage/treatment facility, the preliminary operating considerations might
include the location of regulators and conduits for diverting flow into the facility, identification
of influent or effluent pumping needs, route of a dewatering force main and facility outfall,
identification of solids handling needs, and coordination of dewatering rates with POTW
capacity. For a deep tunnel, the alternative development process might include preliminary
identification of diversion structures, consolidation conduits, dropshaft, access and work shaft
locations, screening facilities, and pumping requirements.
3.4 Evaluation of Alternatives for CSO Control
The evaluation of CSO control alternatives can be a complex process, and no one
methodology is appropriate for all CSO control programs. Certain general considerations,
however, apply to most evaluation approaches. In general, evaluations focus on cost,
performance, and non-monetary factors. Cost evaluations are quantitative, performance
evaluations can be both quantitative and qualitative, and non-monetary factor evaluations are
generally qualitative. One of the challenges to alternatives evaluation is how to assess the
relative importance of cost, performance, and non-monetary factors in selecting a preferred
alternative. The following sections present discussions and examples of ways to evaluate these
issues.
3.4.1 Project Costs
Project costs include capital costs, annual O&M costs, and life-cycle costs. Capital cost,
the cost to build a particular project, includes construction cost, engineering costs for design and
services during construction, legal and administrative costs, and typically a contingency. The
contingency is usually developed as a percentage of the construction cost, and the engineering,
legal, and administrative costs are usually combined as a percentage of the construction plus
contingency. Annual O&M costs reflect the annual costs for labor, utilities, chemicals, spare
3-49 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
parts, and other supplies required to operate and maintain the facilities proposed as part of the
project.
At the facilities planning level, published cost curves are usually acceptable for estimating
capital and O&M costs. Care should be taken to determine whether the cost curves to be used
are for a specific technology or for a complete facility. For example, a capital cost curve for
a storage/sedimentation facility might not include costs for coarse screening, disinfection,
pumping, or other unit operations, which are often included in such a facility. Most curves also
do not include allowances for land acquisition, utility relocation, engineering and contingencies,
and special site considerations, such as removal of contaminated material or difficult permitting.
Cost curves should also be indexed to account for inflation, using an index such as the
Engineering News Record Cost Correction Index (ENR CCI). The ENR CCI allows a cost
estimate based on, for example, 1990 costs to be adjusted to current costs by multiplying the
1990 cost by the ratio of the current ENR CCI to the 1990 ENR CCI. The ENR CCI varies
with geographic location, so local ENR CCI information needs to be used.
Life-cycle costs refer to the total capital and O&M costs projected to be incurred over
the design life of the project. Life-cycle costs can be conveniently expressed hi terms of total
present worth (TPW), which is the sum of money that, if invested now, would provide the funds
necessary to cover all present and future costs of a project over the design life of the project.
Life-cycle costs can also be expressed as an equivalent annual cost (EAC), which converts a
non-uniform tune-series of costs (such as 2 years of construction costs followed by 20 years of
annual O&M costs) into a uniform annual cost over the design life of the project. One benefit
of these analyses is that they allow for direct comparison of projects with high capital costs and
relatively low annual O&M costs against projects with lower up-front capital costs but higher
annual O&M costs. The TPW can also be expressed as a cost per volume of CSO controlled
to indicate the relative cost-effectiveness of an alternative.
The TPW of a project is calculated by adding the initial capital cost to the present worth
of annual O&M costs and then subtracting the present worth of the salvage value of the project
3-50 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
(i.e., the depreciated value of the project at the end of its design life). The present worth of
annual O&M costs is computed by multiplying the average annual O&M cost by the appropriate
uniform series present worth factor, based on the given discount rate and design life. The
discount rate to be used in the TPW analysis for facilities planning is set each year by EPA; the
uniform series present worth factor can be obtained from tables in standard engineering
economics textbooks. The present worth of the salvage value is computed by multiplying the
salvage value by the appropriate single payment present worth factor, based on the given
discount rate and design life. The value of land generally should not be depreciated and might
even be assumed to increase in value over the course of the project design life. The value of
the land should then be added to the depreciated value of the facility to obtain the total salvage
value. Exhibit 3-4 presents an example using this procedure.
3.4.2 Performance
The expected performance of CSO control alternatives can be evaluated in a number of
ways, depending in part on the technologies under consideration. The benefits of source controls
are generally the hardest to quantify, particularly management practices such as street sweeping
and catch basin cleaning. Although some studies have been conducted to quantify the benefits
of BMPs, their performance is variable, site-specific, and difficult to quantify. Thus, the
performance of source controls might need to be described qualitatively, such as "reduces
floatables." Collection system controls, such as sewer separation or I/I removal, are more
readily quantified and can be simulated hi models such as SWMM. The performance of
collection system controls can be expressed hi terms of reduction in overflow volume and/or
frequency as predicted by SWMM. If pollutant concentrations are known or can be predicted,
then the overflow volumes can be converted into pollutant loads. These flows and loads, hi
turn, can be used as input to a receiving water model to assess the impact of load reduction on
beneficial use criteria. The benefits of certain collection system controls, such as interceptor
relief, can also be evaluated using a hydraulic model to assess the reduction hi flooding or
surcharging.
3-51 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Exhibit 3-4. Example Calculating Total Present Worth
Two alternatives for CSO control are proposed, with the following estimated costs.
Alternative A Alternative B
Capital Cost $5.200,000 $4,300,000
Annual O&M Cost $50,000 $150,000
Salvage Value $500,000 $400,000
Land Value $150,000 $100,000
Assume that the following conditions apply:
• Design life = 20 years
• Discount rate = 8 percent
• Annual rate of increase in land value = 3 percent.
Based on these conditions, the following factors are obtained from tables:
• Uniform series present worth factor = 9.8181
• Single payment present worth factor = 0.2145.
The total present worth of each alternative is computed as follows.
Alternative A:
Present Worth, Capital Cost = $5,200,000
Present Worth, Annual O&M Cost
$50,000x9.8181 = $491,000
Present Worth, Salvage Value
Land: $150,000 x 1.0320 = $271,000
Facility: 500.000
771,000 x 0.2145 = (-) 165,000
Total Present Worth $5,526,000
Alternative B:
Present Worth, Capital Cost = $4,300,000
Present Worth, Annual O&M Cost
$150,000x9.8181= 1,473,000
Present Worth, Salvage Value
Land: $100,000 x 1.0320 = $181,000
Facility: 400.000
581,000 x 0.2145 = (-) 125,000
Total Present Worth $5,648,000
Over the design life of the project, the lower annual O&M cost of Alternative A compensates for the
higher capital cost, making it the lower cost alternative on a TPW basis.
3-52 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Similarly, the performance of storage alternatives can be evaluated in terms of reduction
in overflow volume and/or frequency, based on the volume to be stored. Storage facilities can
be sized to capture the volume from statistical design storms, such as a 3-month, 6-hour storm,
or a 1-year, 24-hour storm. SWMM can be used to develop the volumes to be captured from
the selected design storm event(s). The volume reduction can then be translated into pollutant
load reduction, based on estimated or simulated pollutant concentrations. Performance can also
be evaluated on an annual basis, using a statistically average year or multiple years of rainfall
data. For storage alternatives, a means of simulating the dewatering of the storage facilities is
necessary in order to evaluate the impact of antecedent storms on facility performance.
The evaluation of treatment alternatives is less straightforward because pollutant removal
performance criteria should be assigned to the treatment technology. The selected pollutant
removal criterion is then applied to the volume predicted to be discharged from the treatment
facility. For example, if a tank was sized to provide primary treatment for the 3-month, 24-hour
storm, SWMM would predict the volume of flow tributary to the treatment facility. The
resultant pollutant load to the receiving water would be calculated by subtracting the volume of
the tank from the influent volume, multiplying by the assumed pollutant removal efficiency, and
then multiplying by the appropriate conversion factor for units of measure. For time-varying
performance assessments, a model that includes the treatment process can be considered.
The measures of performance used will depend on the water quality goals to be achieved,
as well as the level of sophistication of the evaluation tools available to the municipality. If
receiving water modeling is not available, the reduction in pollutant loads compared with future
planned conditions or other appropriate baseline condition is another measure of performance.
Changes in pollutant loads to receiving waters can be computed in a number of ways. For
example, the reduction in pollutant load from a CSO can be determined as a percent of baseline
load from a CSO, or the reduction in pollutant load from all sources (CSO, storm water,
upstream sources) can be calculated as a percentage of baseline load from all sources.
The reduction in overflow frequency is also a useful measure of performance. If a
municipality does not have the capability to perform long-term model simulations, overflow
3-53 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
frequencies can be estimated from the recurrence interval of the storm serving as the basis of
design. If receiving water modeling is available, isopleths (maps indicating areas of similar
concentration) of in-stream pollutant concentrations can be developed. Other statistics can also
be generated, such as hours of exceedances of water quality criteria, acre-days of exceedances,
and changes in concentrations of pollutants at given locations over time.
All of these factors can be valid measures of performance, depending on the
circumstances. One of the challenges to alternatives evaluation is to determine ways to use such
performance factors to make rational decisions on the relative merits of various CSO control
alternatives. One method is to look at cost/performance relationships, while another is to apply
qualitative rating and ranking methodologies to the performance data. These methods are
discussed in following sections.
Performance can also be evaluated in terms of conformance with general objectives.
Criteria under this category include the control of major discharges, impact on sensitive areas,
and elimination of problem areas. The degree to which a particular alternative incorporates
control of the larger CSOs is important because the majority of the pollutant load from a
community, in most cases, originates from the largest CSOs. Continuous modeling analyses
have shown that a municipality's minor CSOs often contribute a smaller percentage of overflow
volume and pollutant load on an annual basis than they do during a design event. Mitigating
impacts on sensitive areas is a significant concern, as expressed in the CSO Control Policy
(Section II.C.3). Sensitive areas are often the focus for public access and use of the receiving
water and are identified by the NPDES permitting authority in coordination with State and
Federal agencies, as appropriate. Eliminating existing problem areas identified in the CSS
potentially can improve system performance in many ways. Existing problem areas can include
locations of repeated sewer backups and flooding, as well as recurring system maintenance
problems, including grit deposition, pumping station flooding, and river or tidal inflow. The
effectiveness of each alternative in addressing each of these general objectives can be rated
qualitatively (e.g., good, fair, poor) or quantitatively (e.g., number of large CSOs, sensitive
areas, or problem areas abated).
3-54 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
3.4.3 Cost/Performance Evaluations
Having developed present worth costs and measures of performance, one of the
traditional methods for evaluating engineering alternatives is by constructing cost/performance
curves. Two common methods are to compare similar alternatives over a range of design
conditions (such as 1-month, 3-month, 6-month, and 1-year storms) and to compare a range of
control alternatives for a given design condition. Ideally, these comparisons would indicate that
for lower levels of control, small increments of increased cost would result in large increments
of improved performance, and for high levels of control, large increments of increased cost
would result in small increments of unproved performance. The optimal point, or "knee of the
curve," is identified as the point where the incremental change in cost per change in performance
changes most rapidly, indicating that the slope of the curve is changing from shallow to steep,
or vice versa. Theoretically, if a smooth curve were fit through the data points, the knee of the
curve would be the point where the second derivative of the function describing the curve is at
a maximum. In practice, four or five points are plotted, then the point of the knee is determined
from the shape of the curve. Because the points reflect planning-level estimates, a rigorous
mathematical determination of the knee is generally not warranted and might imply false
precision.
Exhibits 3-5 and 3-6 are examples of knee-of-the-curve analyses. In Exhibit 3-5, a
proposed storage facility was sized to control CSOs from each of six design storm conditions,
and the costs for each facility size were estimated. The impact of the various levels of control
on critical uses (shellfishing and beach usage) was then determined. The resulting plot indicates
the most cost-effective level of control using storage in terms of critical use impacts. In this
example, the knee of the curve for shellfish area restrictions is clearly at the 3-month storm.
For the other two criteria, shellfish area and beach closings, the location of the knee is less
obvious. These curves are typical of the ambiguity often associated with knee-of-the-curve
evaluations.
3-55 August 1995
-------
1 Mo. 3 Mo.
I i
Design Storm Event
6 Mo. 1 Yr.
2Yr.
5Yr.
60
50-
40-
1
S.
"5
3
30-
20-
10 -
n i i i
7 8 9 10
Ir^ I I | i l
11 12 13 14 15 16 17 18
Source: Metcalf & Eddy, 1991
Present Worth ($ millions)
Exhibit 3-5. Example of Cost-Performance Curves Indicating Impacts on Critical Uses
3-56
-------
200
180
160
140
•«• 120
r 100
80
60
40
20
It
+
*
+
»
A
I
k
+ UIH Sewer Separation
• UIH2 1 -Yr Storage at MWR203, BOS019; Consol. to
Storage BOS009-0133; Consol/Storage Conduit
BOS057/060; Screens BOS 050, 052
A UIH3 1 -Yr Primary Tr. MWR203, BOS01 9; Consol. to
Primary Tr. BOS009-013; Consol/Storage Conduit
BOS057-060; Screens BOS050, 052
* UIH4 3-Mo Storage MWRA203, BOS019; Int. Relief
BOS009-013; Screens BOS050-060
1 UIH4 3-Mo Storage MWRA203, BOS01 9; Int. Relief
BOS009013; Screens BOS050-060
• UIH5 3-Mo Primary Tr. MWR203, BOS1 09; Consol. to
Primary Tr. BOS009-013, BOS050-060
+ UIH61-Yr Less Than primary Tr.MWR203; Coarse
Screens BOS019, BOS009-013, BOS050-060
# UIH7 Detention/Treatment MWR203; Screen & Disinf.
BOS019; Int. Relief BOS009-013; Screens at 8 Outfalls
Note: Total load is from CSO,
storm water, and upstream
sources
10
20
30
40
50
60
70
80
90
Fecal Coliform Total Load Reduction as a Percent of Baseline Total Load for Upper Inner Harbor,
1-Year Storm
SOURCE: Metcalf & Eddy, 1994
Exhibit 3-6. Example of Cost-Performance Curve Indicating Removal of a Specific Pollutant
(fecal coliform bacteria)
3-57
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Exhibit 3-6 is an example of the second method of using cost/performance evaluations.
In this figure, alternatives were compared for controlling fecal coliform bacteria loads into a
coastal receiving water during a 1-year, 24-hour storm. Ten CSO outfalls discharge to this
receiving water segment, and the alternatives evaluated included a range of control technologies
for individual outfalls and groups of outfalls. Performance is measured as the reduction in total
fecal coliform loads (from CSO, storm water, and upstream sources) as a percent of baseline
total load. In this case, the knee of the curve corresponded to alternative "UIH7." This
alternative included continuing treatment at an existing detention/treatment facility, providing
a screening and disinfection facility at outfall BOS019, reducing overflow frequencies and
volumes at outfalls BOS009 to BOS013 through interceptor relief, and installing screens at the
remaining outfalls, which activate approximately four times per year or less. Two other
observations from Exhibit 3-6 are noteworthy. First, the most expensive alternative, which
involves complete capture for storage of all CSOs active during the 1-year storm, only results
in approximately 80-percent removal of bacterial loads to the receiving water. The remaining
20 percent of the baseline load is contributed by storm water, which is not affected by the CSO
control technologies. This example demonstrates the importance of considering sources of
pollutants other than CSOs.
The second point demonstrated by this example is the need to screen alternatives before
reaching this level of evaluation. This receiving water segment was just one of fourteen
receiving water segments evaluated as part of an LTCP. Within that one receiving water
segment, the 10 outfalls were divided into four groups, based on system hydraulic relationships.
For each of those four groups of outfalls, alternatives were initially developed to address a range
of control levels. In order to evaluate cost/performance on a receiving water basis, alternatives
for each group of outfalls had to be combined. In addition, other design conditions (e.g., annual
rainfall series and other design storm events) were used during this project. Using this
approach, the number of possible combinations of alternatives for this receiving water segment
could become very large, very quickly. To obtain a reasonable number of alternatives,
preliminary screening was necessary, along with reasonable judgment on possible combinations
of alternatives for the various groups of outfalls. This concept applies both to large systems and
3-58 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
smaller systems. Even for a municipality with only one receiving water segment and a total of
10 CSOs, the number of possible combinations of alternatives could be similar to this example.
3.4.4 Non-Monetary Factors
Non-monetary factors that can influence the selection of a recommended alternative
generally fall into three categories: environmental issues and impacts, technical issues, and
implementation issues. These factors are more qualitative than cost and performance
evaluations, but they address decision factors critical in alternative evaluation and provide a
necessary "reality check" on the overall implementability of CSO control alternatives, which
cannot be obtained from cost and performance numbers alone.
3.4.4.1 Environmental Issues/Impacts
The evaluation of environmental issues and impacts involves site inspection, with
reference to zoning, soils, floodway, and similar types of maps, as well as coordination with
local and State agencies. Depending on the potential cost of the alternatives and scope of the
planning effort, more detailed field surveys and/or geotechnical or hazardous waste
investigations might be necessary. During this evaluation process, it may be appropriate to
identify the various permits that would be required to implement the proposed CSO control
alternatives, because the permit application process can require significant effort to support the
implementation of certain types of projects. The specific environmental impacts to be evaluated
vary from municipality to municipality, but the following general categories of impacts should
typically be covered:
• Land Use—This category includes existing or planned land use of the proposed site;
difficulty of property, easement, and right-of-way acquisition; zoning; and
surrounding land use issues. Each of these issues could be considered a separate
category for evaluation, if appropriate.
• Traffic and Site Access—Traffic impacts can include disruptions of traffic patterns
or increases in truck traffic during construction, potential effects of traffic disruptions
on local businesses, availability of alternate routes, changes to long-term traffic
patterns following facility start-up, and impacts on residential areas. Site access
considerations also include feasibility and/or impacts of new access roads.
3-59 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Utilities Relocation—Potential impacts on existing utilities can be rated qualitatively
(e.g., high, medium, or low potential for impact) or, in some cases, included as an
allowance on the estimated cost. Detailed investigation of utilities locations is usually
performed during the design phase.
• Noise and Vibration—The impact of noise and vibration from construction and
facility operation can be evaluated by comparing ambient and predicted noise and
vibration levels and by determining the number, type, and proximity of sensitive
receptors—i.e., land uses or facilities that might be particularly sensitive to project
impacts, especially increased noise and traffic. Sensitive receptors typically include
open space areas (including cemeteries), picnic areas, playgrounds, recreation and
sports areas, parks, residences, hotels and motels, schools, churches, libraries, and
hospitals.
• Historic and Archaeologic Resources—A project's effects on historic and
archaeological resources can be determined by consulting with the local or State
historic preservation commission or similar agency.
• Soils/Rock—The suitability of the soils at a proposed site to provide a foundation for
CSO facilities is considered in this evaluation. In addition, ground-water table and
bedrock depths should be considered with respect to constructibility and to effects on
adjacent structures.
• Wetlands—The existence and location of wetlands on a site is a major factor in
determining a site's suitability for a proposed facility. Depending on local or State
wetlands regulations, the potential for indirect impact due to activities within
specified buffer zones around coastal or riverine wetlands should also be considered.
Upland sites are generally considered more favorable than sites with wetlands, within
wetland buffer zones, or within regulated coastal resources areas.
• Floodplains—The extent to which proposed facilities would encroach upon the 100-
year floodplain and the potential for mitigation by providing compensatory storage
should be identified.
• Water Quality—Construction of the CSO facilities is intended to improve receiving
water quality. Construction activities, however, can temporarily degrade water
quality, and this should be considered in the evaluation process.
• Air Quality—Construction-related dust and odors from operating facilities can create
significant air quality impacts, which could cause concern at sites located close to
residential areas, hospitals, or other sensitive receptors.
• Threatened and Endangered Species—The presence of Federal- or State-listed
threatened or endangered species or critical habitat for these species would likely
eliminate a potential site from further consideration.
3-60 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
* Hazardous Materials—The potential for encountering hazardous materials at a
proposed site should be evaluated carefully. A review of previous land use records
can provide insight on the existence of hazardous wastes or contaminated soils.
State agencies should maintain records of known hazardous waste spill locations.
Detailed and rigorous onsite investigations are typically not undertaken in the
planning phase of a project; however, a planning level review of existing
documentation can reveal whether a proposed location was previously a site of
commercial or industrial use or the location of routine use, storage, or disposal of
hazardous materials. Some field testing might be necessary.
3.4.4.2 Technical Issues
Various technical issues require qualitative evaluation in addition to financial
considerations. These include the following:
• Constructibility—While it is recognized that costs can be associated with anticipated
requirements for rock excavation, sheeting, or dewatering at a proposed site, these
and other constructibility issues can also be considered on a more qualitative level.
For example, an alternative involving deep tunnels will generally involve more
specialized or complex construction techniques than a near-surface
storage/sedimentation facility. Similarly, an alternative that requires a river crossing
for a consolidation conduit will likely be more challenging in terms of constructibility
than an alternative that does not require a river crossing. The overall size and
location of a proposed alternative are also relevant to the constructibility analysis.
• Reliability—The operating history of similar installations is a good basis for
predicting the reliability of a proposed facility. Contacting and/or visiting similar
existing facilities can provide useful information on operations and reliability,
especially since the availability of published information on operating facilities is
limited. The evaluation of reliability should also include expected operating
conditions, particularly for CSO facilities that are commonly unstaffed, rely on
automatic activation, and operate only on an intermittent basis. Generally,
alternatives that rely on simpler or less extensive mechanical equipment are more
reliable than alternatives that rely on more complex equipment. The extent of
reliance on existing facilities also affects reliability. For example, if the operation
of a new CSO treatment facility relies on the operation of an aging upstream pumping
station, the overall reliability of the alternative might be limited by the reliability of
the pumping station. This aspect might be very important in areas where the existing
collection system is known to be in poor condition.
• Operability—Issues of operability involve both process considerations and personnel-
related considerations. Process considerations include the methods of solids handling
3-61 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
and potential flexibility of response to various loading conditions; personnel-related
considerations include the degree of automation and level of operator skill necessary
to fully optimize use of available process features, as well as the need for confined
space entry and for increased staff levels.
3.4.4.3 Implementation Issues
In addition to the cost, performance, environmental impacts, and technical issues, several
other issues, which pertain to the political and institutional aspects of a project, affect the
decision to implement a potential alternative. The following list discusses these implementation
issues:
• Adaptability to Phased Implementation—The CSO Control Policy provides that
".. .schedules for implementation of the CSO controls may be phased based on the
relative importance of adverse impacts upon WQS and designated uses, priority
projects identified in the long-term plan, and on a permittee's financial capability"
(II.C.8). Given the cost of CSO control facilities, municipalities might determine
that projects that can be implemented in smaller parts over a period of time are more
affordable than a single, large, one-time project. Phased implementation also allows
time for evaluating completed portions of the overall project and the opportunity to
modify later parts of the project due to unanticipated changes in conditions. The
initial stages of phased projects often can be implemented sooner than a single, more
massive project, bringing more immediate relief to a CSO problem.
• Institutional Constraints—Political and institutional forces can affect proposed CSO
control programs in a number of ways. Because most CSO programs are funded by
tax payers or sewer rate payers, elected officials generally must be able to convince
the general public that the proposed CSO control program is cost-effective and for
the public good. Public rejection of a proposed project can jeopardize the chances
of raising the funds needed for project implementation. The best way to ensure public
acceptance of a project is through an ongoing public participation program, as
stressed throughout this guidance document.
In addition to cost, siting issues are commonly the subject of most public debate on
CSO control projects. Issues involving facility location, land takings, and easements
in both public and private lands can lead to disagreements among Federal, State, and
local officials, public utilities, private companies, and private citizens. Involvement,
coordination, and negotiation among politicians, institutions, and other stakeholders
and interested parties are necessary to ensure that a technically feasible project is also
politically feasible.
3-62 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Regional CSO controls call for coordination among the regional authority and the
individual municipalities within the region, particularly where individual
municipalities have already expended funds for planning and/or implementation of
local projects. Intermunicipal agreements might be necessary if a CSO control
project affects the collection systems of bordering municipalities.
The CSO Control Policy encourages permittees to ".. .evaluate water pollution control
needs on a watershed management basis and coordinate CSO control efforts with
other point and nonpoint source control activities" (I.B). The overall goals of a CSO
control plan and the steps for achieving those goals can be affected or influenced by
the goals of storm water or nonpoint source control programs. Therefore, these
programs should be considered in evaluating CSO control program options.
• Multiple Use Considerations—One means for gaining public and institutional
acceptance of CSO projects is through the development of multiple-use facilities.
Locating parking facilities over storage/treatment tanks, constructing bike paths over
the routes of consolidation conduits, and improving river access are possible
enhancements to CSO control projects that have been shown to provide additional
public benefit.
3.4.5 Rating and Ranking of Alternatives
Because most of the non-monetary factors described are qualitative in nature, evaluation
of these factors necessarily entails a degree of subjectivity. To make reasonable comparisons
among multiple alternatives, the qualitative judgments should be standardized to the extent
possible. While cost and performance criteria are generally quantitative, judgment should still
be made as to the relative importance of specific cost and performance data both with respect
to the range of cost and performance criteria identified for each alternative and with respect to
the non-monetary factors. For example, performance criteria can include predicted duration of
exceedance of fecal coliform bacteria standards, reduction in fecal coliform loading during a
given design storm, and reduction in overflow frequency during a typical year. Each of these
performance criteria is quantitative; the municipality must determine whether they are equally
important, whether any criteria are more important than the others, and their importance
compared with siting or constructability issues. Developing a methodology to evaluate the data
compiled for each alternative in such a way that the appropriate weight is given to the
appropriate evaluation criterion is a difficult, yet important, step in the evaluation process.
3-63 August 1995
-------
Chapter 3
Development and Evaluation of Alternatives for CSO Control
One approach for evaluating the information developed for each alternative is to construct
a matrix listing each factor or criterion on the vertical axis and each alternative on the horizontal
axis. A rating system is then established for each factor, defining the relative magnitude of the
factor, the degree of impact each alternative has on that factor, or vice versa, as appropriate.
Rating systems can be descriptive (e.g., high, medium, low impact), symbolic ( + , 0, -), or
numeric (1 to 5, with 1 = low impact, 5 = high impact). Using a numerical scale facilitates
summing the individual ratings to produce an overall rating. A numerical scale is also most
amenable to weighting factors. For example, if the annual overflow frequency is determined
to be more important than the TSS load during a specific design storm, then the rating for annual
overflow frequency can be multiplied by a weighting factor. This weighting increases the
relative impact of that specific rating when all of the ratings for a given alternative are summed.
To provide as much consistency as possible, criteria must be defined for each rating
value. Exhibit 3-7 provides examples of criteria for rating values.
Exhibit 3-7. Example Criteria for Rating Values
Category
Rating
Criteria
Constructibility
1
2
Standard construction techniques
Standard techniques, but with restraints (such as limited
staging area, difficult site access)
Special techniques or more severe restraints on
construction
TSS Load
1
2
Substantial improvement over existing conditions
Limited improvement or no change compared with
existing conditions
Load increases compared with existing conditions
In this exhibit, for Constructibility, certain construction activities, such as tunneling with
tunnel boring machines (TBMs), can be defined as being "special techniques." For TSS load,
"substantial improvement over existing conditions" can be defined further as a minimum percent
reduction in load. In general, the greater the degree of definition of the ratings, the less
subjective the rating process.
3-64
August 1995
-------
Chapter 3
Development and Evaluation of Alternatives for CSO Control
Exhibit 3-8 presents an example of a matrix for evaluating CSO control alternatives. In
this example, non-monetary factors, such as conformance with objectives, operability, and
constructibility, have been rated qualitatively. As a next step, numerical values can be assigned
to the ratings of "good," "fair," "poor," "medium," and "low," as well as to the relative values
of the monetary factors. If appropriate, the numerical values can be weighted, then the values
in each column can be summed to create an overall rating for each alternative.
Exhibit 3-8. Example Matrix for Evaluating CSO Control Alternatives
Selection Criteria
Monetary Factors:
Capital Costs
Annual O£r\A f^nct
/YUIiUal VvOCiVl V^Ual
Present Worth
P.W. $/Design Storm CSO Gallons Abated
Conformance with Objectives:
Control of Major Discharges
Elimination of Identified Problem Areas
Impact on Priority Areas
Operability:
Number of Facilities
Reliability
Level of O&M
Reliance on Existing Facilities
Impacts on Downstream Facilities
Constructibility:
Site Requirements
Extent of Disruption
Degree of Difficulty
Adaptability to Phased Implementation
Conformance with Current Plans
Sewer
Separation
$2,690,000
$2,470,000
$8.40
Good
Fair
N/A
0
Good
Low
Low
Low
Low
Medium
Medium
Good
Good
Storage
$3,450,000
t'2^ 000
tjtjj j\J\J\S
$3,570,000
$12.15
Good
Poor
N/A
2
Fair
Medium
Medium
Medium
Medium
Low
Low
Fair
Poor
Screening
and
Disinfection
$3,740,000
«47 000
JTT / ,\^W
$3,920,000
$13.35
Good
Poor
N/A
2
Fair
Medium
Medium
Medium
Medium
Low
Low
Fair
Poor
N/A - Not Applicable
Source: Metcalf & Eddy, 1988
Rating and ranking systems should be viewed as a tool in the evaluation process and not
necessarily as the final determinant of a recommended plan. Once a series of alternatives has
3-65
August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
been rated and/or ranked, it is sometimes necessary to "step back" from the evaluation process
to ensure that the recommendations make sense and that program goals are being met. Public
input, through workshops, public meetings, and written comments, can also reshape the
recommended plan. These and other issues associated with the final selection of the
recommended plan are addressed in Chapter 4. Additional guidance on rating and ranking
procedures is provided in (EPA, 1995d).
3.5 Financial Capability
As part of LTCP development, the ability of the municipality to finance the final
recommendations should be considered. The CSO Control Policy "...recognizes that financial
considerations are a major factor affecting the implementation of CSO controls... [and]... allows
consideration of a permittee's financial capability in connection with the long-term CSO control
planning effort, WQS review, and negotiation of enforceable schedules" (I.E). The CSO Control
Policy also specifically states that"...schedules for implementation of the CSO controls may be
phased based on...a permittee's financial capability" (II. C. 8). In considering the implementation
costs of CSO controls, the municipality should investigate both the total cost of the various
alternatives and its ability to absorb the costs. To this end, EPA is developing guidance on
financial capability assessment (EPA, 1995e).
EPA's assessment process to determine a municipality's financial capability is a two-step
process involving an initial screening followed by an investigation of overall financial condition.
In the initial screening step, financial parameters are identified and the financial implications of
the proposed wastewater treatment and CSO controls evaluated. In this step, the municipality
determines the total wastewater and CSO capital and operating cost per household (CPH) to
implement the proposed control plan and the median household income (MHI) in the service
area. With these two numbers, the municipality can assess the financial impact of each CSO
control alternative on residential users.
3-66 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
The second step is an assessment of the following selected indicators to evaluate the
municipality's financial capability:
• Debt Indicators—These give an indication of the debt burden on the municipality and
include the bond rating and overall net debt as a percent of full market property
value.
• Socioeconomic Indicators—These give an indication of the long-term trends in the
municipality and include the unemployment rate and the median household income.
• Financial Management Indicators—These give an indication of the municipality's
ability to manage financial operations and include the property tax revenue collection
rate and property tax revenue as a percent of full market property value.
Although the financial analysis can influence the selection of a recommended plan, the
financial capability assessment is primarily intended to serve as a guide for developing an
implementation schedule for the recommended plan. For example, a municipality might not be
able to implement multiple CSO controls simultaneously, but the financial capability analysis
would provide guidance on an approach to phasing the implementation of the controls so that
the financial impacts are attenuated over a period of years. Chapter 4 provides additional details
on project financing and other implementation issues.
3-67 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
CASE STUDY: MASSACHUSETTS WATER RESOURCES AUTHORITY
(MWRA) - CSO CONCEPTUAL PLAN AND SYSTEM MASTER PLAN
The Massachusetts Water Resources Authority (MWRA) provides wastewater services to 43
communities in the greater Boston area. Within this service area, four communities—Boston, Cambridge,
Somerville, and Chelsea—have CSSs with a total of 80 CSO outfalls in Boston Harbor and six tributary
rivers. The MWRA's CSO Conceptual Plan and System Master Plan (CCP/SMP), December 1994,
presented an LTCP for CSO control, as well as an evaluation of the impacts of sizing and selection of CSO
control alternatives of other aspects of the MWRA system, such as interceptor performance, secondary
treatment at Deer Island, and system-wide I/I.
The MWRA's CSO program involved three major components:
• Reduction in the overall CSO volume and increase in the percentage of flow receiving
treatment as results of recent improvements to the conveyance system, POTW, and CSO
treatment capability
• Further reduction in CSO volumes through system optimization
• Development of long-term CSO control recommendations.
The demonstration approach was selected for the development of long-term CSO control facilities.
This approach featured a combination of detailed modeling and a watershed approach to evaluate causes
of current nonattainment of WQS, to define appropriate water quality goals and associated CSO control
goals, and to develop cost-effective alternatives to meet the CSO control goals. For the purpose of this
. study, the receiving waters affected by CSOs were divided into 14 separate receiving water segments. The
receiving water segment boundaries were generally defined by physical features, such as dams, river
influences, and embayments. In many cases, these boundaries also correlated with changes in water uses,
level uses, hydrology, and/or pollution sources. Solutions were developed for each receiving water
segment, while considering the interrelationships among segments.
The MWRA invested in a detailed system characterization, which provided a solid foundation for
developing a detailed system model (SWMM EXTRAN). The model then allowed for comprehensive
engineering evaluations, through which a recommended plan was developed. This plan will lower expected
project costs by approximately $900 million over a previous CSO control plan. The approximately $2
million spent on the system characterization not only substantially reduced the expected project costs, but
also provided stakeholders with a high level of confidence in the results of the engineering evaluations.
Although the four communities, 80 outfalls, and multiple receiving waters included in the
MWRA's CCP/SMP would clearly constitute a large and complex system, the approach taken by the
MWRA would generally be applicable to smaller systems as well. In effect, the MWRA applied its
methodology to 14 smaller systems representing the 14 receiving water segments. Much of the complexity
in this project derived from the interrelationships among the segments. A smaller municipality could apply
the same principles in its approach to the LTCP; however, with fewer outfalls and receiving waters, the
scope of the work could be reduced appropriately.
3-68 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
PUBLIC PARTICIPATION
The MWRA established the following goals for its public participation program:
• Provide education on CSO issues
• Provide opportunities for public review and comment on the CSO program during
development
• Respond to questions and comments in a timely fashion
• Ensure stakeholder input at key project milestones.
Specific aspects of the MWRA's public participation program included the following:
• Working with a citizens advisory committee, which included representatives of environmental,
business, and neighborhood associations, citizen activists, and municipal and elected officials.
• Working with agency and regulatory representatives, including EPA and the State WQS
authority.
• Publication of the CSO Bulletin to explain key CSO issues and planning decisions, notify
municipal officials and working group members of upcoming events, and provide information
on how CSOs fit into other MWRA planning efforts.
• Presenting two series of interactive workshops at key junctures in the development of the
CCP/SMP: one series to present baseline receiving water data, initial water quality and CSO
control goals, and initial alternatives for CSO control and another series to present the results
of more detailed evaluations of CSO control alternatives. Attendees included MWRA and
CSO community staff, representatives from regulatory agencies, environmental groups and
other stakeholders. Each series consisted of a number of individual workshop sessions to
present information pertaining to individual receiving water segments.
• Conducting two series of neighborhood meetings (one addressing water quality evaluations
and one addressing control technology alternatives) to present the results from the above
workshop series. Neighborhood meetings were arranged to generally correspond with
groupings of receiving water segments.
• Conducting individual presentations upon request to groups having particular technical and/or
local area interests.
LONG-TERM CONTROL PLAN APPROACH
As an initial step in developing its LTCP, the MWRA conducted an extensive system
characterization program, followed by a receiving water quality evaluation program. Key features of the
system characterization program included:
• Collecting flow data from approximately 250 metering locations, including CSO outfalls,
interceptors, system headworks, and existing CSO treatment facilities
• Conducting numerous inspections of CSO regulators and other system features
• Developing detailed piping schematics for each regulator
• Developing a detailed hydraulic/hydrologic model (SWMM) for the four CSO communities.
3-69 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Key features of the receiving water quality evaluation program included:
• Defining existing water quality standards
• Defining existing water quality through wet and dry weather sampling
• Characterizing watersheds, waterbody hydrodynamics, CSO sources, and storm water sources
• Developing a receiving water quality model
• Defining causes of nonattainment of WQS.
Data from the MWRA's receiving water and combined sewer system characterization program
indicated that non-CSO pollution sources contributed substantially to nonattainment of WQS in most
receiving water segments. The MWRA considered both the presumption and demonstration approaches
and determined that, for the impacted receiving water segments, the demonstration approach was necessary
to fully evaluate attainment of WQS. Thus, the MWRA selected the demonstration approach for its LTCP.
The demonstration approach allowed for the development of appropriate levels of CSO control for each
receiving water segment and coordination of CSO control with appropriate water quality goals. Ranges
of control were evaluated for each receiving water segment, with an emphasis on higher levels of control
in critical use areas. Regulatory agency participation in the workshop series provided the opportunity for
early coordination and presentation of the data, as well as the development of a mutual understanding of
water quality issues.
DEVELOPMENT OF ALTERNATIVES FOR CSO CONTROL
Definition of CSO Control Goals
The MWRA developed a long-term conceptual plan for CSO control using a watershed-based
approach, so that site-specific water quality conditions and impacts from CSOs relative to non-CSO sources
of pollution could be determined. The process for selecting the recommended CSO control alternative for
each receiving water segment integrated the concepts of watershed management and use attainability. A
range of water quality goals was initially established for each receiving water segment, using information
from an assessment of baseline receiving water conditions. The receiving water assessment included
consideration of the major sources of pollutant loads in the watershed: CSOs, storm water discharges, and
boundary or upstream sources. The flows and loads from these sources were estimated from modeled
flows generated for various hydrologic conditions (design storm events and a design annual rainfall series)
and from pollutant concentrations generated from statistical analyses of available site-specific data.
Receiving water models were used to assess the impacts of CSOs and storm water on selected
riverine and coastal receiving water segments. These models were used to quantify the impacts of CSO
sources only, storm water and upstream sources only, and a combination of CSO, storm water, and
upstream sources on the attainment of bacteria standards for each segment.
In general terms, the range of water quality goals defined for each receiving water segment was
as follows:
• Level I: Full attainment of designated uses
• Level II: Attainment of designated uses for most of the year (i.e., except for four or less
overflows per year)
• Level III: Improvement over existing conditions (until other, more prominent sources of
pollution are addressed).
3-70 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
A range of CSO control goals was then defined that would contribute to achievement of the water
quality goals for each receiving water segment. The CSO control goals addressed only the CSO-related
conditions that contributed to nonattainment of beneficial uses. In several receiving water segments, it was
determined that pollution contributed by CSOs was only a small fraction of the total pollutant loads from
other sources. In these segments, even complete elimination of CSO outfalls would not achieve the water
quality goals because the other sources prevented the attainment of beneficial uses. The CSO control goals
were developed with the assumption that if the other sources were remediated by the appropriate
responsible parties, then the CSO controls would be stringent enough for water quality goals to be met.
Examples of a range of CSO control goals for a receiving water segment included the following:
• Level I: Eliminate all CSOs by sewer separation or relocation of the outfall(s)
• Level II: Reduce untreated CSOs to approximately four overflows per year by transport
improvements, storage, or treatment
• Level III: Control floatables and meet other aesthetic criteria.
Initial Alternatives Development and Screening
Once CSO control goals were established to achieve the water quality goals in each receiving water
segment, engineering and hydraulic analyses were conducted to develop and screen initial CSO control
alternatives. The use of GIS and comprehensive system modeling allowed development and evaluation of
alternatives where receiving water segment boundaries did not match collection and transport system
hydraulic boundaries. While the impact of solutions focused on receiving water segments, hydraulic
feasibility depended on the collection and transport system configuration. In some cases, structural
modifications in one receiving water basin affected system performance in another receiving water basin.
GIS maps provided an excellent backdrop for initial development of control alternatives, particularly with
regard to identifying opportunities for consolidation of outfalls and geographic relationships among the most
active outfalls and regulators.
The types of alternatives developed generally included elimination of CSOs through sewer
separation or CSO relocation; near-surface storage, storage/sedimentation, or floatables control with
disinfection; consolidation of outfalls to a regional storage or treatment facility, and use of consolidation
conduits for storage; in-system storage; deep tunnel storage; interceptor or trunk sewer relief; upgrade of
existing CSO control facilities; sewer separation upstream of selected regulators; and end-of-pipe floatables
controls. Alternatives were generally sized for both a 3-month and 1-year design storms and were
evaluated using continuous simulation for a 1-year period.
Hydraulically feasible alternatives were initially screened based on a range of criteria, including
hydraulic performance, water quality improvement, cost, construction risks, mitigation concerns, and short-
and long-term environmental impacts. The screening was conducted in a matrix format, with alternatives
organized by receiving water segment or subarea. For each alternative, the criteria were rated
qualitatively, and the ratings for each alternative were summed to create a total score for each alternative.
The performance, construction risks, and other criteria associated with each alternative were rated in a
similar manner. Alternatives within a given receiving water segment that scored substantially lower than
others within that segment were not evaluated further. Compatible alternatives for the receiving water
segments were combined to form regional and system-wide CSO control strategies. The screening process
was conducted during the first series of workshops, mentioned previously, which incorporated stakeholder
viewpoints and concerns and served to educate all parties regarding the system and possible solutions. The
result was a relatively short list of alternatives for each receiving water segment that then underwent a more
detailed evaluation.
3-71 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
Evaluation of Alternatives for CSO Control
CSO control alternatives remaining after the initial screening process were evaluated in more detail
using a variety of tools, including SWMM EXTRAN simulations using a design annual rainfall series and
design storm evaluations using one- and two-dimensional receiving water quality models. More detailed
evaluation criteria were established, organized into the following categories:
• Cost—Capital, O&M, and net present worth
• Performance—Reduction in CSO frequency/volume and percent reduction in pollutant loads
• Cost/Performance Relationships—Knee of the curve analyses based on pollutant load
reductions for selected design storms
• Water Quality—Duration of WQS exceedances, number and frequency of untreated
overflows remaining, and relative impact of non-CSO sources of pollution
• Siting Constraints—Qualitative evaluations of site availability and constraints.
A numerical rating system was established for these criteria to rate and rank the alternatives for
each receiving water segment. For example, for performance and water quality impacts, receiving water-
specific criteria were identified, based on an assessment of the current status of attainment of water quality
criteria and designated uses. If a given water quality criterion, such as a fecal coliform standard to support
primary contact recreation, was not currently attained during wet weather, then an evaluation criterion,
such as predicted hours of exceedance of the fecal coliform standard for primary contact recreation, was
defined for that receiving water segment. An alternative would be assigned a rating of one to three for that
criterion, based on whether the alternative resulted in a reduction, no change, or increase in the predicted
hours of exceedance as compared with the baseline condition. The ratings for each alternative would be
summed, then the alternatives would be ranked on an overall scale of one to three, based on the ratings.
Other examples of the water quality and performance criteria used to evaluate alternatives included fecal
coliform bacteria load, BOD and TSS loads, volume of untreated overflows, and annual frequency of
untreated overflows. A similar rating and ranking process was conducted for cost. Rating and ranking
of alternatives based on the more detailed evaluation were conducted in the second series of workshops,
referenced previously.
Various combinations of alternatives for the 14 receiving water segments were developed into
system-wide control strategies to allow the evaluation of a range of control levels, in accordance with
provisions in the CSO Control Policy. For example, one strategy included the most preferred control
alternative for each of the individual segments, one strategy consisted of system-wide sewer separation,
and one strategy consisted of system-wide control of overflows to a frequency of one overflow per year.
By developing the system-wide strategies, it was possible to compare total CSO plan costs for different
levels of control and review combinations of alternatives for consistency and compatibility. A summary
matrix of the system-wide strategies was developed, which served as a useful tool in presenting the results
of the evaluations to the various stakeholders. The preferred system-wide CSO control plan consisted of
a mixed level of control alternatives. The range of control alternatives that comprised the recommended
plan included sewer separation, CSO outfall relocation, interceptor relief, end-of-pipe screening and
disinfection, in-line storage, detention/treatment, upgrading of existing CSO treatment facilities, and end-of-
pipe floatables control (for relatively inactive outfalls). The plan will eliminate CSOs from critical use
areas (beaches and shellfish beds), while providing cost-effective levels of control in other receiving water
segments with consideration of existing uses and impacts of non-CSO sources of pollution.
3-72 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
CASE STUDY: PORTLAND, OREGON - CSO MANAGEMENT PLAN
Portland's existing CSS captures and treats approximately 96 percent of the sewage from homes
and businesses. The remaining 4 percent becomes part of the untreated overflow discharged at 42 outfalls
on the Willamette River and 13 outfalls on the Columbia Slough. During a typical year, there are
approximately 150 days of rainfall in Portland. The magnitude and frequency of overflow varies from one
outfall to another, however. Some outfalls overflow virtually every time it rains, whereas others overflow
as few as 30 days in a typical year. During an average year, the city's CSS discharges an estimated total
of 6 billion gallons of urban storm water mixed with sewage, representing approximately 1,600 hours when
bacterial standards are exceeded because of CSOs.
In 1990, the city began an engineering study to evaluate CSO control alternatives. The following
year, the State of Oregon established requirements for CSO abatement, based on currently available
information, that were enumerated in an agreement called the Stipulation and Final Order (SFO). This
agreement, between the city and the State, called for the virtual elimination of CSO outfalls. The Draft
Facility Plan for the CSO Management Program (CH2MHILL, 1993) presented a CSO control alternative
that satisfies the CSO Control Policy and evaluates two levels of CSO control between the CSO Control
Policy and the SFO.
The SFO was amended in August 1994 to require that untreated overflows to the Willamette River
be reduced to the 3-year return summer storm and the four in 1-year return winter storm, or a reduction
of 94 percent of the CSO volume currently discharged to the Willamette River. The level of control for
the CSOs to the Columbia Slough was kept at the original SFO control level of 1 in 10-year storm in the
summer and the 1 in 5-year storm in the winter (AMSA, 1994).
PUBLIC PARTICIPATION
The objective of the public education and involvement process was to reach as many residents as
possible during LTCP development. The components of the public participation process for the Portland
CSO management program are summarized in Chapter 4 (Exhibit 4-1). The key components included the
River Alert Program, public education, and public involvement.
LONG-TERM CONTROL PLAN APPROACH
The objective of the CSO Management Study was to develop a planning approach to establish
water quality goals and associated system performance criteria, in addition to integrating with other
collection and treatment system needs. To examine the wide range of possible solutions to CSOs, the city
adopted three simultaneous planning approaches: (1) results-based, (2) statistics-based, and (3) technology-
based:
• Results-Based Approach—This begins with the reduction of storm water flow and pollutants
at the source through inflow reduction and urban BMPs. Next, CSO control is reviewed as
part of meeting larger water quality goals, including strengthened watershed protection
elements.
• Statistics-Based Approach—This approach focuses on identifying a specific frequency of
CSOs and developing control strategies to achieve that frequency. For example, the SFO
designated the statistical frequency of CSOs to the Columbia Slough as once in 10 summers
and once in 5 winters. This approach provided a clear, numerical goal that can be achieved
without correlating that statistical yardstick with the benefit achieved.
3-73 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Technology-Based Approach—This approach generates the sewer separation alternative. A
second sewer system would be constructed throughout the combined area to convey storm
water, and the existing system would be rededicated to transporting only sanitary wastewater.
A single alternative was evaluated in which a completely new system was assumed and costs developed.
DEVELOPMENT OF ALTERNATIVES FOR CSO CONTROL
To lay the foundation for the development of the CSO Management Plan, control options or
technologies were examined for their applicability in the city's sewer service area. These technologies
represent the "building blocks" for the development of comprehensive alternatives that meet target levels
of CSO control. Once a list of control alternatives to be considered for the program was compiled, each
of the individual alternatives was evaluated for its ability to meet the needs of the program. This process
began with a comprehensive list of CSO control alternatives. Then the list was narrowed to include only
control alternatives that were appropriate or desirable to be considered further. Typically, a number of
control alternatives will be inappropriate for the circumstances encountered in a given community, such
as siting restrictions, financial constraints, nonconformance with WQS, or public or institutional opposition.
These control alternatives can be eliminated from the list of potential controls by using an initial screening
process. This initial screening makes it easier to develop realistic and appropriate control alternatives by
reducing the number of possible controls to be considered, thus focusing effort on more viable alternatives.
A set of performance, implementation, and environmental criteria were developed (in conjunction
with Bureau of Environmental Services staff) to evaluate the various CSO control technologies available
for use in Portland.
PERFORMANCE FACTORS
The criteria grouped under the category of performance factors are related to pollutant removal,
as well as overflow frequency and volume control. These criteria described the ability of the control
alternative to meet an acceptable level of pollutant control and included the following:
• CSO Volume/Frequency—The control alternatives should be screened based on their ability
to reduce the frequency of overflows and the overall volume discharged.
• Pollutant Control—Control alternatives more effective at controlling the primary pollutants
of concern (e.g., bacteria, floatables, or suspended solids) in the municipality will generally
be favored over measures that control other pollutants of lesser concern.
Implementation and Operation Factors
In addition to the performance factors, control measures are often assessed for their relative ease
of implementation and operation according to the following criteria:
• Complexity—The more complex a control measure, the more likely there is to be a problem
during implementation or operation.
• Reliability—Some control measures might be difficult to maintain and, therefore, should be
eliminated from further consideration.
• Flexibility—Control measures that can be implemented in a number of configurations and
across a wide range of circumstances will be preferred over more restrictive controls.
3-74 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
• Land Required—If a control technology has large land requirements, it might not be possible
to implement in a highly developed watershed.
• Public Acceptance—In order for some control measures to be implemented, a high degree
of public involvement is required. Public acceptance, therefore, can be important to the
success of the control.
• Development Time—Controls that can be implemented immediately will generally be
preferred over controls that must be developed over a number of years.
• Cost—The use of cost as a screening criterion at this early stage in the development of
alternatives is not always appropriate, because the proposed control measures have not yet
been sized. In certain cases, however, such as for treatment technologies that would provide
a greater level of control than required to meet WQS, the higher level of control might not
be justified by the cost of these technologies, allowing them to be eliminated from further
consideration. More detailed cost evaluation is described under the Evaluation of Alternatives
for CSO Control section of this case study.
Environmental Impacts
The following criteria are generally related to the potential negative side-effects resulting from
constructing structural controls:
• Construction Period—Some control technologies require extensive construction activities that
could adversely affect the surrounding environment. These would be ranked lower than
corresponding controls that are less intrusive.
• Operating Considerations—The operation of some major structural controls can cause
environmental impacts, such as noise or odor problems.
• Siting Restrictions—The implementation of some control technologies can be discouraged
because of surrounding land use impacts that are more significant than the improvements
provided by the control of CSOs.
The technologies were evaluated during meetings and workshops held in 1991 and 1992. Exhibit
3-9 summarizes the results of the evaluation, listing the range of rankings from excellent to adverse for
each technology considered. The technologies were evaluated further in later phases of the project when
additional information was obtained and during the development of the CSO Management Plan. The basic
tenets of the screening methodology, including the basis of evaluation given above, were retained
throughout plan development.
The selection of system components for inclusion in control alternatives was based on the
screening results and input from BBS staff. Technologies were either eliminated from further consideration
or selected for one or more applications: widespread use throughout the system, localized use, or interim
use. Exhibit 3-10 summarizes the selected components. Through this initial screening process, 12 of the
original 31 potential control measures were eliminated from further consideration. Control technologies
considered appropriate for widespread use were incorporated into the program elements for the alternatives
development. Local solutions were included in specific applications when appropriate.
3-75 August 1995
-------
Exhibit 3-9. Ranking CSO Technologies
Performance
Factors
Implementation and
Operation Factors
Environmental
Impacts
00
1
o
O
o
03
|c
S.Q
oT.y
II
S 0.
C
|l
cc
0>
O)
S
o
55
00
c
o , .
11
r|
||
/ JJ
•
•
0
a
•
0
a
a
a
©
0
®
©
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
* /
3 /
5 £
/ ®
a
a
a
a
a
a
0
•
•
a
a
•
•
0
©
0
0
0
0
0
0
0
0
0
e
0
0
a
•
/
V
A
/ i
•
•
a
•
•
©
a
a
a
©
0
®
©
(^
®
0
0
0
0
0
0
©
©
©
0
0
0
•
0
• Excellent a Very Good
SOURCE: CH2MHILL, 1993
gGood
3-76
© Poor
® Adverse
-------
Chapter 3
Development and Evaluation of Alternatives for CSO Control
Exhibit 3-10. Control Technologies Screening Summary
CSO Control Technology
Source Controls
Street Sweeping
Construction Site Erosion
Catch Basin Cleaning
Industrial Pretreatment
Garbage Disposal Ban
Onsite Domestic Wastewater
Combined Sewer Flushing
Sewer System Optimization
Static Flow Control
Variable Flow Control
Real-Time Flow Control
Inflow Reduction Techniques
Upland Storm Water Storage
Storm Water Sumps
Sewer Separation
Stream Diversion
Storage
Earthen Basins
Open Concrete Tanks
Closed Concrete Tanks
Storage Conduits
Storage Tunnels
Physical/Chemical
Swirl Concentrator
Vortex Separator
Coarse Screening
Primary Sedimentation
Flocculation/Sedimentation
Dissolved Air Flotation (DAF)
DAF with Polymer Addition
High Rate Filtration (HRF)
Flocculation/HRF
Chlorination/Dechlorination
Biological Treatment
Columbia Boulevard WWTP
Wetlands
Consider for
Widespread
Use
X
X
X
X
X
X
X
X
X
Consider for
Localized
Use
X
X
X
X
X
X
X
Consider for
Interim Use
X
X
X
X
X
X
X
Eliminate
from Further
Consideration
X
X
X
X
X
X
X
X
X
X
X
X
Source: CH2MHILL, 1993
3-77
August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
EVALUATION OF ALTERNATIVES FOR CSO CONTROL
SWMMs were developed for each of the 43 combined sewer basins and for the major interceptors,
and calibrated and verified based on extensive rainfall and flow data. Both long-term (15 years) and single-
storm simulations were performed using the calibrated models. In addition to the CSS hydraulic modeling,
CSS pollutant and receiving water quality models were developed to assess CSO impacts to the Willamette
River.
The first step in the CSO control approach for Portland was to focus on technically simpler and
lower cost methods that could be implemented on a neighborhood scale to reduce the size of the CSO
problem. It is anticipated that the following projects, called Cornerstone Projects, will reduce the annual
average volume of overflow by 47 percent (AMSA, 1994):
• Storm Water Sump Construction—Much of the combined sewer area has highly permeable
soils with a high hydraulic capacity. Street inlets are currently being disconnected from the
CSS and connected to sumps, which are designed to infiltrate the storm water into the ground.
The sumps are designed to settle suspended solids and reduce pollutant loads.
• Roof Drain Disconnections—Most of the roof drains in the combined sewer service area are
connected to the CSS. A program is currently underway to disconnect these roof drains from
the CSS and dispose of the drainage on site. Roof drain disconnection is particularly effective
in areas to be sumped, because any roof drainage leaving the property would be kept out of
the CSS.
• Street Diversion—As Portland grew, several streams in Portland were channelized and routed
into pipes to allow property development in the downtown area. These streams discharge into
the CSS and reduce the collection system capacity available for sewage. The city will be
disconnecting these streams from the CSS.
• Local Sewer Separation Projects—Sewer separation is planned in areas where the CSS is
undersized, in remote basins where conveyance costs are high, and where the outfalls
discharge to sensitive areas, such as parks. Several of these separation projects are being
designed and built.
The next step was to analyze the amount of remaining overflow that would occur in the Columbia
Slough. The Slough is shallow and slow moving and can be dominated by CSOs during large storm events.
It has been identified as water quality limited for bacteria, pH, aesthetics, and some toxics. The facility
plan concluded that the presumption approach identified in the CSO Control Policy would not provide
adequate treatment for the Slough. The recommended control plan is to capture overflows to the Slough
to the once in 10-year summer storm and the once in 5-year winter storm. All combined sewage flow
resulting from storms smaller than these design storms will be conveyed to a wet weather treatment facility
at the Columbia Boulevard Treatment Plant Site. It is anticipated that CSOs from storms larger than these
design storms will continue to overflow without treatment. This represents a 99.6-percent capture of the
existing CSO volume to the Columbia Slough.
The final step was to analyze the amount of remaining overflow that would occur in the Willamette
River. Because of the swifter-flowing nature of the river, the large volume of water it contains, and the
river's own ecology, the facility plan examined options to protect the beneficial uses of the Willamette
River with facilities that capture and treat less CSO volume than required by the SFO. The approach was
to compare the methods, benefits, and costs of alternative levels of control ranging between the two key
benchmarks—the SFO and the CSO Control Policy. The resulting recommended plan is to capture
3-78 August 1995
-------
Chapter 3 Development and Evaluation of Alternatives for CSO Control
overflows to the Willamette to the one in 3-year summer storm and the three in 1-year winter storm. All
combined sewage overflow resulting from storms smaller than these design storms will be conveyed to a
wet weather facility located on the Willamette River. A fallback option determined to be technically
feasible but more costly is to convey the Willamette River overflows to the Columbia Boulevard
Wastewater Treatment Plant. Overflows from storms larger than these design storms will continue to
overflow without treatment. This represents a 94-percent capture of the existing overflow volume to the
Willamette River.
To capture and treat the overflow, the city will rely on a combination of storage and wet weather
treatment. A number of storage and treatment options were considered in the facilities plan for their ability
to cost effectively store and treat overflows, for their operational simplicity, for their implementability
within Portland, and for their ability to protect water quality and beneficial uses. Wet weather storage will
be provided by oversizing the tunnels that convey overflows to the new wet weather treatment plants. This
will provide in-line storage. Off-line storage will not be a major component of the CSO solution for
Portland. Wet weather treatment will include screening, sedimentation basins, and disinfection. The
planning assumption was that disinfection will be accomplished with hypochlorite injection followed by
dechlorination. It is anticipated that the discharges from the treatment plants will allow in-stream WQS
to be met at the edge of the mixing zone.
3-79 August 1995
-------
CHAPTER 4
SELECTION AND IMPLEMENTATION OF THE LONG-TERM PLAN
This chapter recommends procedures for selecting, adopting, and implementing combined
sewer overflow (CSO) controls under the long-term control plan (LTCP). The procedures
include the role of public participation and agency interaction, selection and development of a
recommended plan, adoption, financing, implementation scheduling, preparation of an
operational plan, post-construction compliance monitoring, and re-evaluation and update of the
LTCP.
4.1 PUBLIC PARTICIPATION AND AGENCY INTERACTION
After detailed evaluation, but prior to the selection of specific CSO controls under the
LTCP, the public should be informed about each alternative. The detailed evaluation and
ranking of alternatives is typically compiled in a draft report. Because long-term CSO abatement
planning usually involves a significant amount of data collection and analysis, it is often prudent
to summarize the results of the evaluation in an executive summary. Copies of the draft report
should be distributed to the repositories established at the initiation of the public participation
program. Control plan alternatives can include control alternatives involving both the
construction of facilities and the adoption of new management practices. The extent to which
each type of control measure is utilized within each alternative can be based on public input.
The implementation schedule and method of financing can also be selected or modified based
on public input.
Informing the public about potential alternatives is one part of the public participation
process. The extent of the public participation program generally depends on the amount of
resources available and the size of the municipality. Exhibit 4-1 presents component programs
and their elements for a comprehensive public education and involvement process in Portland,
Oregon.
4-1 August 1995
-------
Chapter 4
Selection and Implementation of the Long Term Plan
Exhibit 4-1. Example of Public Participation Program
for Portland, Oregon, CSO Management Program
Component Programs
Program Elements
River Alert Program
Public Education
Public Involvement
Placement of informational and warning signs
Media advisories
Media coverage
Speaker's bureau
Clean River Review newsletter
CSO Update newsletter
Direct mailers
Billing inserts
Videotape production
Issue and choices booklet
Educational theater presentations
Interactive educational software
Public meetings
Creative Alternatives Workshop
Clean River Funding task force
Clean River committee
Community leader interviews
General public telephone survey
Focus groups
Source: CH2MHILL, 1993
Typically, public meetings are the forum for describing and explaining alternatives. The
municipality and its agents should discuss each alternative thoroughly. Technical solutions
should be presented in a simple, concise manner, understandable to diverse groups. The
discussion should include, to the greatest level of detail possible, background on the project, a
description of proposed facilities, the level of control to be achieved, temporary and permanent
impacts, possible mitigating measures, and cost and financial information. Graphics can be used
to compare each alternative with regard to site layouts, resource requirements, and cost. The
benefits of each alternative should be articulated clearly so that public support can be generated.
Public hearings are usually formal proceedings in which the agenda, including comments,
questions, and responses, are recorded. One or more public hearings are generally held so that
public interest groups, business and civic organizations, and members of the general public can
officially comment and/or pose questions to the municipality. The municipality should consult
4-2
August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
with local, State, and Federal regulatory agencies to identify any public participation
requirements. In some cases, municipalities might consult the public participation conditions and
program elements set forth in 40 CFR Part 25. These regulations provide for:
• Well-publicized notice of the hearing mailed to interested and affected parties at least
45 days prior to the date of the hearing
• Location and time of the hearing chosen to facilitate attendance by the public
• Presentations scheduled in advance to ensure maximum participation
• Conduct of the hearing in a manner that allows for informing the audience and
soliciting information from the public
• Record of the hearing procedures prepared and made available by transcript or
recording.
To improve communications at public meetings or hearings held during this phase, the
municipality can summarize technical information that will be presented at meetings. The
municipality should also generally designate an agent to attend the meetings, take notes, and
distribute and collect public comment sheets so that participants' views are recorded. If the
municipality has retained a consultant to prepare the plan, the consultant will typically present
the findings and recommendations of the alternative evaluations. In larger municipalities, an
experienced public participation consultant can be used as a facilitator or moderator. A number
of public meetings (held prior to formal public hearings) might be necessary for larger
municipalities; however, smaller municipalities should consider at least two meetings prior to
a formal public hearing.
Presentations to the public should explain the benefits of CSO control. For example,
improvements in water quality can significantly improve aesthetics, recreational areas,
opportunities for increased use of beaches, or fishing and shellfishing. These benefits might
offset construction, environmental, and financial impacts associated with each alternative and,
therefore, should be communicated in order to reach a consensus. A key objective of the public
education process is to build support for increases in user charges and taxes that might be
4-3 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
required to finance CSO control projects. By demonstrating the importance of improved water
quality and the cost-effectiveness of proposed control alternatives, rate payers and taxpayers will
be assured that environmental protection is being provided at the lowest reasonable cost.
In order to proceed with adoption of an LTCP, the regulatory community should be part
of the consensus. Presumably, Federal, State, county, and other regulatory groups will have
been involved throughout the long-term CSO control planning process. Early and consistent
coordination with the regulatory authorities during the development and implementation of the
LTCP and WQS review provides "...greater assurance that the long-term control plan selected
and the limits and requirements included in the NPDES permit will be sufficient to meet WQS
and to comply with Sections 301(b)(l)(C) and 402(a)(2) of the CWA" (III.A). Typically, the
municipality submits to the regulatory authority technical memoranda, interim reports, minutes
of public meetings, and responsiveness summaries. The regulatory agencies then submit their
comments to the municipality. The municipality is responsible for responding to each agency.
4.2 FINAL SELECTION AND DEVELOPMENT OF RECOMMENDED PLAN
After appropriate public input (e.g., one or more public hearings) and receipt of
comments from interested parties, the municipality should proceed to selecting and adopting an
LTCP. If the public information program has been strong and continual during the course of
the planning effort, the highest-ranked alternative from the alternatives evaluation will probably
be adopted. If a consensus to select a different alternative has developed as a result of the final
public meetings, public hearings, and comments, however, a different option might be selected.
The responsible legal entity takes action to select and officially adopt the LTCP. For example,
a large metropolitan water management authority would adopt the plan by a vote of its board of
directors. Cities might require a vote by the city council or, in smaller communities, its
counterpart.
In some cases, multiple agencies or jurisdictions might have to adopt the plan. If more
than one entity is responsible, intermunicipal agreements might be necessary. The final
4-4 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
published plan should incorporate adopted resolutions of plan acceptance and proposed or
executed intermunicipal agreements.
The municipality should develop the LTCP to enable implementation by the CSO
program team. The information obtained through the earlier tasks of assessing existing baseline
conditions and alternatives evaluation can be used as a basis for fully developing the selected
plan.
The first part of the LTCP should describe the controls selected for implementation. This
includes both management and operational controls, as well as controls that require constructed
facilities. For controls that do not include the construction of facilities, the selected plan should
identify the frequency of conducting each practice, where the practice takes place, a schedule
of activities, the necessary staffing, and the cost. Initial program start-up costs can include
training staff and purchasing equipment. Ongoing costs typically include labor for maintenance
efforts. A record system should also be designed to track activities and pertinent data.
Controls that require constructed facilities eventually necessitate engineering design and
construction. At this stage of plan development, the LTCP should include a description and
diagrams, concept sketches, or architectural renderings of each facility. Design information,
including assumptions and design criteria, should be tabulated. Site-specific information such
as known site conditions, including existing structures, topography, and use, as well as soil
conditions, utility locations, and wetlands and other resource areas, should be documented.
Final detailed design plans and specifications should be prepared in accordance with the
implementation schedule.
For each selected control, the municipality should develop a cost estimate. Although the
cost is initially estimated during the alternatives development step, it can be refined for the
implementation plan. Accuracy is important because the cost estimates might provide a basis
for fund allocation. Project cost estimates should include costs for engineering, construction,
site acquisition, and legal and financing fees. Because uncertainty still exists at this stage (site
survey and engineering work is still normally necessary), contingencies should be included in
4-5 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
the estimate, and a range of values might be appropriate. Operation and maintenance (O&M)
costs can also be refined at this stage to assess the impact on user fees or tax rates. Cost
estimates can be tied to an applicable cost index, such as the ENR/CCI for construction costs
or the PPI (Producer Price Index) and the CPI (Consumer Price Index) for O&M costs. Using
these indices, costs can be adjusted in the future to account for inflation.
Because proper O&M is particularly important to the long-term functioning of constructed
controls, it is necessary to ensure that maintenance requirements are included in the selected
plan. Specifically, the implementation plan can identify the number of and time period that
additional staff might be needed or reassigned. A more detailed review of resource inputs, such
as chemical deliveries, can be included.
4.3 FINANCING PLAN
The key element for implementation of an LTCP is the ability to obtain funding for the
selected controls. Most LTCPs include construction of abatement facilities. For some
municipalities, the LTCP includes relatively costly, capital-intensive projects, such as deep
tunnel storage. Chapter 3 describes the importance of cost-effectiveness in alternatives selection.
The financial capability of the municipality is a major factor in determining the implementation
schedule. The financing method is also important. The CSO Control Policy states that each
municipality ".. .is ultimately responsible for aggressively pursuing financial arrangements" (I.E)
for implementation. For this reason, some municipalities might engage a financial consultant
familiar with municipal finance as part of the planning and/or implementation team. The
municipality should review and select both a capital funding approach and a method of collecting
annual funding needs.
4.3.1 Capital Funding Options
Capital funding options include bonds, loans, grants, and privatization (EPA, 1995f).
4-6 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
4.3.1.1 Bonds
Bonds are promissory notes issued (sold) by local governments to raise funds to pay for
projects that require a large amount of capital. A bond has a fixed payment schedule that is
often 20 years for municipal or local utility bonds. Revenue bonds, sometimes referred to as
water/sewer bonds, are generally backed by user fees or service charges paid by system users.
General obligation (GO) bonds are issued by a municipal or county government to fund capital
projects of the jurisdiction. GO bonds are secured by the general taxing power of the local
jurisdiction. GO bonds are viewed as the most secure type of local debt. Many municipalities
require voter approval to issue these bonds. Statutory limits can apply to the amount of GO
debt.
4.3.1.2 Loans
Loans from private, State, and Federal sources can be used to finance CSO control
projects. The loan interest rates vary, depending on the program. The ability of a municipality
to secure a loan depends, in part, on its "creditworthiness," or ability to repay the funds
borrowed. Loans are available from a variety of sources, including State Revolving Fund (SRF)
programs, other State loan programs, the Rural Development Administration, CoBank (the
National Bank of Cooperatives), and commercial lending institutions. Each source has different
requirements, advantages, and limitations.
4.3.1.3 Grants
Many municipalities have experience with wastewater construction grants. Grants are
expected to play only a limited role in future CSO program funding, however. Direct Federal
grants have been replaced with SRFs and other local funding options. Individual States might
have different SRF program elements. For example, some might include partial grants and
subsidized loans, while others have only subsidized loans. EPA offers a variety of State and
local grants for program research and development, administration, demonstration, and planning.
These grants can provide funding for CSO-related activities indirectly. The availability of grant
funds usually varies annually, reflecting congressional mandates and EPA policies. Also, for
small and economically disadvantaged communities, the Rural Development Administration
4-7 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
offers up to 75-percent grants for the construction of environmental infrastructure facilities. The
Economic Development Administration (EDA), U.S. Department of Commerce, also awards
grants to economically disadvantaged communities for construction of public works.
4.3.1.4 Privatization
Private investment in wastewater treatment facilities can provide an additional option for
funding CSO facilities. In response to a recent Executive Order, EPA is developing policy and
regulatory changes to encourage private investment in EPA-funded municipal wastewater
treatment facilities. The final outcome of these changes is unknown at this time, but for some
municipalities, privatization might be a viable option.
4.3.1.5 Other Capital Funding Options
Other options include special reserves, special assessments, and "pay-as-you-go." Special
reserves are usually funds established by municipalities to fund capital equipment repair or
replacement. In some cases, these reserves can be used to fund CSO controls. Special
assessments are used to provide and fund projects for a specific geographical area. Special
assessment districts provide the legal arrangement to charge those receiving the service for the
capital and/or operating cost of the project. For smaller, less expensive projects that are more
common to smaller municipalities, a "pay-as-you-go" approach can be used where projects are
funded with annual tax and other revenues.
4.3.2 Annual Funding Options
Annual CSO costs include:
• O&M costs for CSO controls
• Annual loan payments for SRF or other loans used to fund CSO controls
• Debt service on local bonds used to fund CSO controls
• Reserves for future equipment replacement.
4-8 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
Annual funding options include different types of fees and taxes. Both the Federal
construction grant program and the SRF program require sewer user fee systems. Federal law
requires such systems only on SRF loans and aid from the Federal Government to the SRF.
Loans made from State funds in the SRF do not require user fee systems except pursuant to State
law. User fees are widely accepted as an equitable source of revenues for water pollution
control. Some municipalities have implemented storm water utilities that assess user fees based
on impervious area or runoff. In general, sales, property, or income taxes cannot be used to
pay annual operating costs of projects funded under EPA construction grant funding or SRF
funding but can be used to repay bonds used for capital outlays. A number of communities use
an ad valorem (i.e., general property) tax levy to collect operating costs. These exceptions
require EPA approval.
4.3.3 Selection of Financing Method
The method of financing will be determined by several factors, including:
• The availability of each option. For example, some municipalities might have
difficulty in obtaining long-term bond financing. Some States might have applicable
grant or loan assistance programs, while other States might not.
• The advantages and limitations of a specific type of financing.
The LTCP should identify a specific capital and annual cost funding approach. EPA's
guidance on funding options presents a detailed description of financing options and their
benefits and limitations, as well as case studies sharing different approaches municipalities took
to fund CSO control projects (EPA, 1995f). Most municipalities will continue to depend on
local revenue bonds or SRF loans for capital to fund CSO controls. Annual costs will most
likely be paid for by user fees.
4.4 IMPLEMENTATION SCHEDULE
A common characteristic of an LTCP is that CSO controls will be implemented over a
long time period. The municipality is expected to consider a number of factors in preparing a
4-9 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
schedule of activities. According to the CSO Control Policy, the nine minimum controls (NMC)
should be implemented prior to adoption of the LTCP.
The CSO Control Policy recommends a phased implementation schedule based on the
relative importance of adverse impacts upon water quality standards (WQS) and designated uses.
The municipality is expected to consider eliminating overflows that discharge to sensitive areas
and cause use impairment.
In addition, the CSO Policy recommends consideration of financial capability in
developing the implementation schedule. As described in Section 3.5, the financial capability
assessment should include an evaluation of the following:
• Median household income
• Total annual wastewater and CSO control costs per household as a percent of median
household income
• Overall net debt as a percent of full market property value
• Property tax revenues as a percent of full market property value
• Property tax collection rate
• Unemployment
• Bond rating.
In addition to financial capability, the CSO Control Policy recommends that the
municipality consider sources of funding in determining the phasing of construction projects.
The municipality can consider the availability of grants and loans; previous and current
residential, commercial, and industrial sewer user fees and rate structures; and other viable
funding mechanisms.
Other considerations include the need for pilot-scale testing, time necessary for obtaining
necessary permits, and the need to observe timing constraints for obtaining funding (e.g., SRF
4-10 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
grant/loan application deadlines, local referenda). These considerations are incorporated into
a schedule with start and finish dates for major tasks and milestones. The schedule should also
include interim dates for reporting CSO control results and monitoring program results.
Depending on the size of the LTCP, the schedule could be shown by means of a simple
bar chart or a more complex Critical Path Method (CPM) system using project scheduling/
management computer software. The decision on the type of schedule to develop should be
determined by the level of program complexity. This can be assessed by the number of tasks
and subtasks (activities) required, the number of entities involved, the length of time over which
the LTCP will extend, and the available management resources. Tasks associated with financing
should be included in the implementation schedule.
Implicit in developing an implementation schedule is the need to set priorities. The CSO
program team should review the recommended CSO controls and determine an order of
implementation (or phasing), taking into account extenuating circumstances in any particular
case. If funding is a major issue, for example, the least expensive controls can be implemented
early in the process. Individual projects should be phased in accordance with available funding.
In general, priorities and, thus, the schedule of program implementation, should be tailored to
each situation.
If the development of public support for the LTCP is a critical issue, the CSO program
team should consider addressing first any control with the potential for significant pollution
reduction. In this case, controls that could improve the water quality of widely used water
bodies should be implemented, if possible, before other steps are taken. These decisions should
be reflected in the implementation schedule.
Exhibit 4-2 provides an example of a phased implementation. After implementation of
the NMC and development of the LTCP, this particular municipality will proceed with six
construction projects. The first three construction contracts—contracts 1,2, and 3—will address
sensitive areas by protecting a designated National Marine Sanctuary, eliminating beach closings,
preventing fish kills, and opening shellfish beds. They will address overflows that include
4-11 August 1995
-------
NPDES Phase 1 Permit Issued
NPDES Phase 2 Permit Issued
Implement NMC
Develop Long-Term Control Plan
Implement LTCP
Contract 1
Contract 2
Contracts 1,2, & 3 - Abatement
Projects:
• Protect Designated National
Marine Sanctuary
• Eliminate Beach Closings
• Prevent Fish Kills
• Protect Shellfish Beds
• Reduce Industrial Source Influents
• Favorable Cost/Performance Ratio
Contracts 4,5, & 6 - Abatement Projects
• Eliminate Fishery Advisories
• Receiving Water - Large River
• CSO Flow Volume to Receiving Water
Flow Volume <25%
• Reduce Low Percentage on Industrial
Source Influents
• Higher Cost/Performance Ratio
Contract 3
Contract 4
Contract 5
Contract 6
TIME
Exhibit 4-2. Example of Phased Implementation Approach
4-12
-------
Chapter 4 Selection and Implementation of the Long Term Plan
significant discharges from industrial sources with potentially toxic materials. The projects also
have favorable cost/performance ratios, and the financial impact on the municipality will not be
excessive. The subsequent three projects, Contracts 4 through 6, address overflows to a less
sensitive area, a large river. They have a relatively low flow volume compared to the flow of
the receiving water and have little influent contributed by industrial sources. Their cost/
performance ratio is not as favorable as the initial three projects. As shown on the schedule,
the three contracts are staggered to allow for funding availability in successive years.
It is important that the individuals and entities responsible for implementing each aspect
of the program be identified in the LTCP. Much of the effort for implementing plans should
come from either local or regional governments. At the State and Federal levels, enforcement
and oversight probably will occur, and technical and financial assistance might be available. To
develop a plan, municipal officials should coordinate and initiate activities, as well as motivate
others in the municipality or other agencies to get involved. Firm commitments from these
agencies prior to program implementation is important to the final success of the program.
Exhibit 4-3 identifies groups, agencies, and individuals that can support aspects of the
management plan, including monitoring, design, permitting, regulations, public education,
maintenance, and enforcement.
4.5 OPERATIONAL PLAN
As part of the implementation of the NMC, municipalities should be required to develop
and document programs for operating and maintaining the components of their CSSs. Once an
LTCP has been approved, however, the municipality's O&M program should be modified to
incorporate the facilities and operating strategies associated with the LTCP controls.
Typically, each facility constructed as part of the LTCP will have its own O&M manual
detailing the equipment and features of the facility, including operating instructions,
troubleshooting guides, and safety considerations. If the LTCP features multiple facilities,
however, a master operating strategy should be developed to optimize the operation of the
various LTCP components. Optimization might involve coordination of pump back timing,
4-13 August 1995
-------
Chapter 4
Selection and Implementation of the Long Term Plan
Exhibit 4-3. Potential Implementation Responsibilities
Program
Component
Responsible Organization
Other Potentially Involved
Parties
Monitoring
Engineering
Design
Permitting and
Regulatory
Controls
Public Education
Maintenance
Enforcement
Local Water Pollution Control Agency
Local Boards of Health
State Water Pollution Control Agency
State Marine Fisheries Department
Local Water Pollution Control Agency
Local Engineering Department
State Department of Public Works
Local Water Pollution Control Agency
Local Boards of Health
Local Conservation Office
Local Planning Board
EPA
State Water Resources Agency
Federal Coastal Zone Management Office
U.S. Army Corps of Engineers
Local Water Pollution Control Agency
Regional Environmental Agency
Local Environmental Groups
Watershed Associations
State Environmental Agency
EPA
Local Water Pollution Control Agency
Local Department of Public Works
Local Conservation Agency
Local Board of Health
Planning Board
Local Code Enforcement Officer
Coastal Zone Management
U.S. Army Corps of Engineers
State Environmental Agency
EPA
Local Environmental Groups
University Students
Volunteer Organizations
Environmental Consultants
University Engineering
Departments
Engineering Consultants
Local Environmental Groups
Environmental Consultants
Local Environmental Groups
Local Civic Groups
Private Organizations
Cable TV/Newspapers
Public Participation Consultants
Contract Maintenance Providers
Local Environmental (watchdog)
Groups
dynamic regulator operation, or other real-time operating strategies. Interim operating strategies
might be required for phased projects and for construction-period operations and flow transitions.
Maintenance programs should consider the unique operating conditions of CSO facilities,
particularly with regard to schedules for inspecting and exercising idle equipment. Aspects of
4-14
August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
the post-construction monitoring program might also be incorporated into the operational plan,
as regular schedules for sampling and maintaining sampling equipment are developed.
If not addressed in the individual facility O&M manuals, the operational plan should
identify staffing needs for CSO control facilities, both in terms of numbers of staff and specific
positions necessary, with appropriate descriptions of responsibilities and minimum qualifications.
4.6 POST-CONSTRUCTION COMPLIANCE MONITORING
The municipality should conduct a monitoring program during and after LTCP
implementation to help determine the effectiveness of the overall program in meeting CWA
requirements and achieving local water quality goals. Monitoring during LTCP implementation
should include data collection to measure the overall effects of the program on water quality and
to determine the effectiveness of CSO controls. Because existing water quality conditions should
have been determined during the planning process, receiving water quality will probably be well
understood before LTCP implementation. A monitoring plan to assess water quality conditions
during and after program implementation will allow evaluation of the improvements through
comparison to baseline conditions.
Sampling data can also be used to educate the public on the effects of CSOs on receiving
water quality and the need for CSO control. To increase public awareness, information that
identifies the effects of CSO abatement can be disseminated in newsletters, at public meetings,
or by other means. Trend analyses are helpful in understanding the changes in receiving water
quality and can provide important feedback to assessments of the success of CSO controls.
Long-term data can be used to demonstrate the influence of control plan activities on water
quality.
Overall plan effectiveness can usually be determined more easily than the effectiveness
of individual controls. The long-term monitoring plan should be designed to measure
effectiveness and provide accountability. The plan should use existing monitoring stations (both
those used in previous studies and those used for collecting data during system characterization,
4-15 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
as outlined in Chapter 2) to collect long-term data for comparisons. Using this approach,
program progress in addressing pollution problems and preventing further water quality
degradation can be determined. Monitoring plan components (e.g., a map of monitoring
stations, a record of the frequency of sampling at each station, a parameter list, a QA/QC
project work plan) should be identified in a work plan similar to that outlined for sampling in
Chapter 2.
Collecting sufficient data to clearly define the effectiveness of CSO controls is
challenging sometimes for various reasons, including the variability of rainfall and CSOs and
the difficulty in specifically identifying the effect of a particular control on a receiving water.
This type of monitoring program should be developed with caution because of the importance
associated with demonstrating the effectiveness of CSO controls on receiving water quality.
4.7 RE-EVALUATION AND UPDATE
The post-construction compliance monitoring program is intended to "... verify compliance
with water quality standards and protection of designated uses as well as to ascertain the
effectiveness of CSO controls" (II. C. 9). The CSO Control Policy provides that "... the selected
controls should be designed to allow cost effective expansion or cost effective retrofitting if
additional controls are subsequently determined to be necessary to meet WQS, including existing
and designated uses" (II.C). If the implemented controls do not result in attainment of WQS,
including designated use, a municipality should evaluate the current system's operating practices
before considering structural modifications. If correct operating practices are confirmed, the re-
evaluation might indicate that a different operating strategy should be considered, such as
bypassing flow at a different flow rate. In some cases, real-time control system operating
software might have to be modified or weir elevations changed.
If post-construction compliance monitoring indicates that existing WQS are not being met,
the data generated can be used to identify the additional CSO controls necessary to achieve
WQS. This can include a repeat of the WQS review conducted earlier in the planning process.
The CSO Control Policy provides that "...if adequately supported with data and analyses,
4-16 August 1995
-------
Chapter 4 Selection and Implementation of the Long Term Plan
Agency regulations and guidance provide states with the flexibility to adapt their WQS, and
implementation procedures to reflect site-specific conditions including those related to CSOs. ...In
addition, the regulations.. .specify when and how a designated use may be modified" (III.B). In
accordance with the CSO Control Policy, however, expansion or retrofitting of a CSO control
facility might ultimately be required.
4-17 August 1995
-------
REFERENCES
American Public Health Association (APHA). 1992. Standard Methods for the Analysis of
Water and Wastewater, 18th Edition.
Camp, Dresser & McKee, Inc. 1989. Combined Sewer Overflow Mitigation Study CSO Area
C - Upper Woonsquatucket River Interceptor Drainage Basin for the Narragansett Bay
Commission.
CH2MHILL, 1993. City of Portland Bureau of Environmental Services Combined Sewer
Overflow Management Plan.
Donigan, A.S., Jr. and W.C. Huber. 1991. Modeling of Nonpoint Source Water Quality in
Urban and Non-Urban Areas. Environmental Research Laboratory, Athens, GA.
EPA/600/3-91/039.
Fair, G.M., J.C. Geyer, and D.A. Okun. 1968. Water and Wastewater Engineering. New
York, NY: John Wiley and Sons, Inc.
Field, R. 1982. Storm and Combined Sewers: Part of the Treatment Process, Water Engineering
and Management.
Great Lakes-Upper Mississippi River Board of State Public Health and Environmental
Managers. 1990. Recommended Standards for Wastewater Facilities (Ten States
Standards). Albany, NY: Health Education Services, Inc.
Hydroscience, Inc. 1979. A Statistical Method for Assessment of Urban Storm Water Loads-
Impacts-Controls. EPA-440/3-79-023 (NTIS PB-299185/9).
Metcalf & Eddy, Inc. 1994. Final CSO Conceptual Plan and System Master Plan. Prepared
for the Massachusetts Water Resources Authority.
Metcalf & Eddy, Inc. 1991a. Wastewater Engineering: Treatment, Disposal, Reuse. 3rded.,
McGraw-Hill, Inc. New York.
Metcalf & Eddy, Inc. 1991b. Combined Sewer Overflow Facilities Plan Draft Report to the
City of Gloucester, Massachusetts.
Metcalf & Eddy, Inc. 1988. Lower Connecticut River Phase II Combined Sewer Overflow
Study.
Plafkin, J.L., M.T. Barbour, K.D. Porter, S.K. Gross, and R.M. Hughes. 1989. Rapid
Bioassessment Protocols for Use in Streams and Rivers - Benthic Macroinvertebrates and
Fish. Office of Water, U.S. EPA, Washington, DC. EPA/440/4-89/001.
R_l August 1995
-------
References
Plumb, 1981. Procedures for Handling and Chemical Analysis of Sediment and Water Samples.
Technical Report EPA/CE-81-1. U.S. Environmental Protection Agency/U.S. Army
Corps of Engineers Technical Committee on Criteria for Dredged and Fill Material.
Vicksburg, MS: U.S. Army Waterways Exp. Station.
Shoemaker, L.L. et al. 1992. Compendium of Watershed-Scale Models for TMDL Development.
U.S. EPA Office of Wetlands, Oceans and Watersheds, and Office of Science and
Technology. EPA/84l-R-92-002.
Thomann, R.V. 1980. Measures of Verification, Workshop on Verification of Water Quality
Models, EPA-600/9-80-016.
Thomann, R.V. and J.A. Mueller. 1987. Principles of Surface Water Quality Modeling and
Control. New York, NY: Harper and Row Publishers.
Urbonas, B. and P. Stahre. 1993. Stormwater: Best Management Practices and Detention for
Water Quality, Drainage, and CSO Management. Englewood Cliffs, NJ: PTR Prentice
Hall.
U.S. Department of the Interior. 1984. Water Measurement Manual. Bureau of Reclamation
Water Resources Technical Publication. Washington, DC: U.S. Govt. Printing Office.
U.S. Environmental Protection Agency (EPA). 1995a. Combined Sewer Overflows—Guidance
for Long-Term Control Plan. EPA 832-B-95-002.
U.S. Environmental Protection Agency (EPA). 1995b. Combined Sewer Overflows—Guidance
for Nine Minimum Controls. EPA 832-B-95-003.
U.S. Environmental Protection Agency (EPA). 1995c. Combined Sewer Overflows—Guidance
for Screening and Ranking. EPA 832-B-95-004.
U.S. Environmental Protection Agency (EPA). 1995d. Combined Sewer Overflows—Guidance
for Monitoring and Modeling. EPA 832-B-95-005.
U.S. Environmental Protection Agency (EPA). 1995e. Combined Sewer Overflows—Guidance
for Financial Capability Assessment. EPA 832-B-95-006.
U.S. Environmental Protection Agency (EPA). 1995f. Combined Sewer Overflows—Guidance
for Funding Options. EPA 832-B-95-007.
U.S. Environmental Protection Agency (EPA). 1995g. Combined Sewer Overflows—Guidance
for Permit Writers. EPA 832-B-95-008.
U.S. Environmental Protection Agency (EPA). 1995h. Combined Sewer Overflows—Questions
and Answers on Water Quality Standards and the CSO Program. EPA 832-B-95-009.
R-2 August 1995
-------
References
U.S. Environmental Protection Agency (EPA). 1994a. Combined Sewer Overflow Control
Policy.
U.S. Environmental Protection Agency (EPA). 1994b. NPDES Watershed Strategy.
U.S. Environmental Protection Agency (EPA). 1993a. Manual—Combined Sewer Overflow
Control. EPA/625/R-93/007.
U.S. Environmental Protection Agency (EPA). 1993b. Handbook—Urban Runoff Pollution
Prevention and Control Planning. EPA/625/R-93/004.
U.S. Environmental Protection Agency (EPA). 1991. Technical Support Document for Water
Quality-based Toxics Control. EPA/505/2-90-001, PB91-127415.
U.S. Environmental Protection Agency (EPA). 1985. Guidance for State Water Monitoring and
Wasteload Allocation Programs.
U.S. Environmental Protection Agency (EPA). 1984. Construction Grants - 1985, Municipal
Wastewater Treatment.
U.S. Environmental Protection Agency (EPA). 1983. Guidelines for the Monitoring of Urban
Runoff Quality. EPA/600/2-83/124.
U.S. Environmental Protection Agency (EPA). 1982. United States Environmental Protection
Agency. Handbook for Sampling and Sample Preservation of Water and Wastewater.
EPA-600/4-82-029.
U.S. Environmental Protection Agency (EPA). 1976a. Methodology for the Study of Urban
Storm Generated Pollution and Control. EPA/600/2-76/145.
U.S. Environmental Protection Agency (EPA). 1976b. Areawide Assessment Procedures
Manual, Volumes I, II and III. EPA-600/9-76-014.
U.S. Geological Survey (USGS). 1982. Measurement and Computation of Streamflow: Vol.
1—Measurement of State and Discharge: Vol. 2—Computation of Discharge. Water-
Supply Paper 1275.
Water Environment Federation (WEF). 1992. Design of Municipal Wastewater Treatment
Plants, WEF Manual of Practice No. 8: ASCE Manual and Report on Engineering
Practice No. 76, 2nd ed. Alexandria, VA: WEF, and New York, NY: American Society
of Civil Engineers.
Water Pollution Control Federation. 1989. Combined Sewer Overflow Pollution Abatement.
Manual of Practice FD-17. WPCF, Alexandria, VA.
R_3 August 1995
-------
GLOSSARY1
BOD5
catch basin
collector sewer
combined sewage
combined sewer
combined sewer
overflow (CSO)
designated use
infiltration
infiltration/inflow (I/I)
inflow
Five-day biochemical oxygen demand; a standard measure of the
organic content of wastewater, expressed in mg/1.
A chamber usually built at the curbline of a street, which admits
surface water for discharge into a storm drain.
The first element of a wastewater collection system used to collect
and carry wastewater from one or more building sewers to a main
sewer. Also called a lateral sewer.
Wastewater and storm drainage carried in the same pipe.
A sewer designed to carry wastewater and stormwater runoff.
1) The portion of flow from a combined sewer system (CSS)
which discharges into a water body from an outfall located
upstream of the headworks of a POTW, usually during a rainfall
event.
2) The outfall pipe which carries this discharge.
Use specified in WQS for each water body or segment whether or
not it is being attained.
Water other than wastewater that enters a wastewater system and
building sewers from the ground through such means as defective
pipes, pipe joints, connections, or manholes. (Infiltration does not
include inflow.)
The total quantity of water from both infiltration and inflow.
Water other than wastewater that enters a wastewater system and
building sewer from sources such as roof leaders, cellar drains,
yard drains, area drains, foundation drains, drains from springs
and swampy areas, manhole covers, cross connections between
storm drains and sanitary sewers, catch basins, cooling towers,
stormwaters, surface runoff, street wash waters, or drainage.
(Inflow does not include infiltration.)
'These definitions were developed solely for the purposes of this guidance document.
G-l
August 1995
-------
Glossary
interceptor sewer
load allocation (LA)
overflow rate
peak flow
rainfall duration
rainfall intensity
regulator
TSS
A sewer without building sewer connections which is used to
collect and carry flows from main and trunk sewers to a central
point for treatment and discharge.
The portion of a receiving water's loading capacity that is
attributed to one of its existing or future nonpoint sources of
pollution, or to natural background sources.
Detention basin release rate divided by the surface area of the
basin. It can be thought of as an average flow rate through the
basin. Generally expressed as gallons per day per sq. ft.
(gpd/sq.ft.)
The maximum flow that occurs over a specific length of time
(e.g., daily, hourly, instantaneous).
The length of time of a rainfall event.
The amount of rainfall occurring in a unit of time, usually
expressed in inches per hour.
A device in combined sewer systems for diverting wet weather
flows which exceed downstream capacity to an overflow.
Total suspended solids; a standard measure of the concentration of
particulate matter in wastewater, expressed in mg/1.
wasteload allocation(WLA) The portion of a receiving water's loading capacity that is allocated
to one of its existing or future point sources of pollution. WLAs
can be the basis for water quality-based effluent limitations.
wet weather flow
Dry weather flow combined with stormwater introduced into a
combined sewer, and dry weather flow combined with inflow in a
separate sewer.
•ft U.S. GOVERNMENT PRINTING OFFICE: 1996-612-844
G-2
August 1995
-------
In order for the Municipal Technology Branch to be effective in meeting your needs,
we need to understand what your needs are and how effectively we are meeting them. Please
take a few minutes to tell us if this document was helpful in meeting your needs, and what
other needs you have concerning wastewater treatment, water use efficiency, or reuse.
Indicate how you are best described:
[ ] concerned citizen [ ] local official [ ] researcher
[ ] consultant [ ] state official [ ] student
[ ] other
Name and Phone No. (optional)
[ ] This document is what I was looking for.
[ ] I would like a workshop/seminar based on this document.
[ ] I had trouble [ ]finding [ ]ordering [ ]receiving this document.
[ ] The document was especially helpful in the following ways:
[ ] The document could be improved as follows:
[ ] I was unable to meet my need with this document. What I really need is:
[ ] I found the following things in this document which I believe are wrong:
[ ] What other types of technical assistance do you need?
We thank you for helping us serve you better. To return this questionnaire, tear it out, fold it,
staple it, put a stamp on it and mail it. Otherwise, it may be faxed to 202-260-0116.
COMBINED SEWER OVERFLOWS
Guidance for Long-Term
Control Plan
Office of Wastewater Management
MUNICIPAL TECHNOLOGY BRANCH
-------
STAPLE HERE
FOLD HERE
Municipal Technology Branch 4204
United States Environmental Protection Agency
401 M Street SW
Washington, DC 20460
FOLD HERE
-------
United States
Environmental Protection Agency
(4204)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
------- |