United States
          Environmental Protection
            Office Of Water
EPA 832-B-95-002
September 1995
Combined Sewer Overflows

Guidance For
Long-Term Control Plan

                                                 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)


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.

                        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.
                                                     Printed with Soy/Canol* Ink on paper *tt
                                                     contains at \aast 50% recycled fiber

                           TABLE OF CONTENTS



      1.1    BACKGROUND	1-1
            CONTROL POLICY  	1-6
            1.5.1   Target Audience	1-6
            1.5.2   Document Organization  	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


            2.3.1   Existing Baseline Conditions   	2-4
            2.3.2   Summary of Minimum Controls  	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
            MONITORING	  2-20
            2.5.1   Monitoring Plan Development  	  2-20
            2.5.2   Combined Sewer System Monitoring  	  2-21
          Selection of Monitoring Stations  	  2-22
          Frequency of Monitoring	  2-24
          Pollutant Parameters  	  2-25
          Rainfall Monitoring and Analysis	  2-26
          CSO Flow Monitoring and Analysis	  2-27
          CSO Quality  Sampling and Analysis	  2-28
                                                                August 1995

                       TABLE OF CONTENTS (Continued)


            2.5.3 Receiving Water Monitoring   	  2-29
           Selection of Monitoring Stations  	  2-30
           Extent of Monitoring	  2-31
           Pollutant Parameters  	  2-32
           Hydraulic Monitoring and Analysis	  2-32
           Receiving Water Quality Monitoring and Analysis   . .  .  2-33
           Sediment and Biological Monitoring and Analysis ....  2-34
            MODELING  	  2-48
            2.6.1 Combined Sewer System Modeling  	  2-48
           CSS Modeling Objectives  	  2-48
           CSS Model Selection	  2-50
           CSS Model Application	  2-53
            2.6.2 Receiving Water Modeling  	  2-55
           Receiving Water Modeling Objectives	  2-55
           Receiving Water Model Selection	  2-56
           Receiving Water Model Application	  2-57

             FOR CSO CONTROL	3-1

            3.2.1 Demonstration Versus Presumption Approach	3-3
           Demonstration Approach	3-5
           Presumption Approach	3-7
            3.2.2 Small System Considerations  	  3-18
            3.3.1 General Considerations	  3-19
           Interaction with Nine Minimum Controls	  3-19
           Interactions with Other Collection and Treatment
                           System Objectives	  3-19
           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
           Projects Common to All Alternatives  	  3-25
           Outfall-Specific Solutions  	  3-25
           Localized Consolidation of Outfalls  	  3-25
           Regional Consolidation	  3-26
           Utilization of POTW Capacity and CSO-Related
                           Bypass	  3-26
           Consideration of Sensitive Areas	  3-28
            3.3.4 Goals of Initial Alternatives Development  	  3-29
                                       ii                             August 1995

                       TABLE OF CONTENTS (Continued)


            3.3.5  Identification of Control Alternatives  	  3-29
          Source Controls  	  3-31
          Collection System Controls  	  3-33
          Storage Technologies	  3-37
          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
          Environmental Issues/Impacts	  3-59
          Technical Issues	  3-61
          Implementation Issues	  3-62
            3.4.5  Rating and Ranking of Alternatives  	  3-63
      3.5   Financial Capability	  3-66

             LONG-TERM PLAN	4-1

            PLAN  	4-4
      4.3   FINANCING PLAN	4-6
            4.3.1  Capital Funding Options	4-6
          Bonds  	4-7
          Loans  	4-7
          Grants	4-7
          Privatization  	4-8
          Other Capital  Funding Options  	4-8
            4.3.2  Annual Funding Options	4-8
            4.3.3  Selection of Financing Method	4-9
      4.5   OPERATIONAL PLAN  	  4-13
      4.7   RE-EVALUATION AND UPDATE	  4-16


                                      iii                           August 1995

                                LIST OF EXHIBITS
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
August 1995

                          LIST OF EXHIBITS (Continued)


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

       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

       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.


       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

       •   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
                                                Exhibit 1-1.  Roles and Responsibilities
   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

• Support the review of WQS in
  CSO-impacted receiving water

• Comply with permit conditions
  based on narrative WQS

• Implement selected CSO controls
  from LTCP

• Perform post-construction
  compliance monitoring

• Reassess overflows to sensitive

• Coordinate all activities with
  NPDES permitting authority, State
  WQS  authority, and State
  watershed personnel
• Reassess/revise CSO permitting

• Incorporate into Phase I permits
  CSO-related conditions (e.g.,
  NMC implementation and
  documentation and LTCP

• Review documentation of NMC

• 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

Monitor compliance with Phase I,
Phase n, and post-Phase n permits
and take enforcement action as
• Review WQS in CSO-impacted
  receiving water bodies

• Coordinate review with LTCP

• Revise WQS as appropriate:

  Development of site-specific

  Modification of designated use to

  -  Create partial use reflecting
     specific situations
  -  Define use more explicitly

  Temporary variance from WQS
                                                                         August 1995

Chapter 1                                                               Introduction

      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,
      •   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).

      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

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.

       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
   Initiate Interaction
    with Permitting
    Create Public
  Review Committee
  Refine Site-Specific
   Program Goals
   Conduct Public
    with Permitting
Compliance Monitoring
  Technical Activities
     CSO Policy Sections

Final CSO Policy

Initiate Program
1. Introduction
II C.2. Public Participation
II.C.3. Consideration of Sensitive Areas
, III.B. Coordination with WQS
    Conduct System
• 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
                                              Develop Alternatives
                                              Evaluate Alternatives
                                                  Select and
                                              Develop Long-term
                                                  Control Plan
                                               Operational Plan
   Re-Evaluate and
     Update Plan
                                                Conduct Post-
                                             Compliance Monitoring
II.C.1.  Characterization, Monitoring, and
Modeling of the CSS
II.B.  Implementation of Nine
Minimum Controls
                            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
                            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


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

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
Implementation of Nine Minimum
Development of LTCP
Selection of LTCP/Development of
Operational Plan
Review of LTCP and WQS
Review of LTCP and Development
of Draft Phase II  Permit
Final Phase II Permit Issued
Enforcement Order Issued
(if applicable)
niiiiiiiii NPDES Permitting Authority
——— Municipality Activity
• •—• — Ongoing Throughout Project
                                                                       Extension Considered by
                                                                       NPDES Permitting
                                                                       Authorities on Case-by-Case
                                     Exhibit 1-3. Example of a CSO Control Policy Implementation Timeline

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

       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

       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


2 (0
•c o>
5 c
                                                    System Improvements
Initiate Implementation
of 6 Minimum Controls
 Implementation of
9 Minimum Controls
Long-Term Controls
                                Exhibit 1-4. Impact of CSO Program Improvements on System- Wide CSOs

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

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
       •  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

       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

                        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

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
       •  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
       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
                                          1-24                              August 1995

                          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.

       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).

       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

       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.

       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.

       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
Maximum Flow to
the POTW for
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
• 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
Public Notification
                             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
                                                                                       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

       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
                                           2-7                               August 1995

Chapter 2
                     System Characterization
                        Exhibit 2-2.  Data Types For CSO Planning
                  Watershed Data
     Source Input/Receiving Water Data
 Land use
 Recreational and open areas
 Soil and surface/bedrock geology
 Natural resources
 Roads and highways
 Storm drainage system
 Sanitary sewer (and combined sewer) system
 Treatment facilities
 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)
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.
                               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"
       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
       •  To identify locations to conduct water quality sampling and install flow measurement
       •  To determine the structural integrity of the system
       •  To assess the mechanical condition and  operational performance of the system
       •  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

       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
          Identifying areas with good water quality that might be threatened or that should be
                                          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

    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


    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
         SCALE IN FEET
                                                Exhibit 2-3. Lewiston-Auburn Location Plan


Chapter 2
                                         System Characterization
               Exhibit 2-4.  Watershed Characteristics in the City of Lewiston
     Watershed Name
              Land Use Description
     No Name Pond

     No Name Brook
     Stetson Brook

     Hart and Goff Brooks
     Salmon/Moody Brooks
     Jepson Brook

     Androscoggin River


Rural/residential - shore line cottages
Mainly undeveloped - some residential
Ranges from rural to residential to

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


    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.
                                                    August 1995

Chapter 2
System Characterization

Exhibit 2-5. Initial Water Resource Goals for Lewiston
No Name Pond
No Name Brook
Stetson Brook
Hart and Goff
Jepson Brook
Current Uses
Recreation— fishing, boating
Recreation— fishing, boating
Drinking water supply (for
town of Lisbon)
Known Problems
Algal blooms
Septic tank discharges
Erosion from use of all terrain
Industrial areas
Interceptor sewer surcharging
CSOs (no visual/odor)
Point sources (paper mills)
Erosion (gravel pits)
Assessment of
Most important town
water resource
Second most
important town water
Third most important
town water resource
Fourth most
important town water
Small watercourses
of minor importance
Channelized drainage
Large regional water
Of limited current
importance to town
Same as
Same as
Same as
Same as
Same as
Same as
Same as
Same as
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

       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

    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

    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
Land Use
Recreational Areas
Soil and Surface/Bedrock Geology
Natural Resources
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)
National Climatic Data Center; four rainfall gages owned and
operated by Lewiston
FEMA flood mapping
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
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
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
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

         August  1995

Chapter 2
System Characterization
               Exhibit 2-7.  Lewiston Source Input and Receiving Water Data
Source Inputs (Flow and Quality)
Storm Water
Other NFS
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
International Paper - Androscoggin River
International Paper - Androscoggin River
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
          August 1995

Chapter 2                                                           System Characterization

       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.   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,
       •  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, 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   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
       •  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   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).   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   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

       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.   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.   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.   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   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

       •  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.   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.   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

       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

       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
                         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  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

           •   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.


    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,

    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
Structure 'B'

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.

Represents mixed land use, small tributary
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
Regulator manhole is shallow making it
difficult to install sampling and monitoring
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.








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.

        August 1995

            Chapter 2
System Characterization
Exhibit 2-9. Screening of Final CSO Sampling and Monitoring Stations for the Auburn Sewerage District
CSO or

Easy accessibility, discharges to Little
Androscoggin River, high frequency of
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

Represents mixed land use.
Represents mixed land use, overflows
infrequently when both siphons operating.
Represents mixed land use.





Reason Not Selected

Infrequent overflows,
difficult to access
remote location during

     August 1995

Source: USGS Topographic Maps
      Lewiston, Maine 1979
      Minot, Maine 1981
      Lake Auburn East, Maine 1979
      Lake Auburn West, Maine 1981

                               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

Chapter 2                                                                   System Characterization

    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

            •   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.


    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
                                                2-42                                   August 1995


     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


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.


    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.


    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
CSO 002
CSO 005
CSO 004
CSO 007
CSO 012
CSO 015
Structure B
Typical CSO
BOD,, mg/l

41 - 139
13 - 110

5 - 151
12 - 139
4 -21

31 - 195
60 - 220



TSS, mg/l

40 - 200
38 - 276

4 -230
28 - 310
55 - 144
21 -28

270 - 550



E. cott Range
Colonies/100 ml

l.lxlO5- 2.7x10*

S.OxlO3 - 1.3x10*
0 - 7.0x10*
2.0xl04 - S.SxlO5
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
Data Range
.0011 - .0022
.0002 - .0019
.0040 - .0085
.07 - .15
.0213 - .0810
< .0002 - < .0004
.002 - .006
.0008 - .002
.09- .13
EPA Freshwater
Acute Criteria
         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
                                                  2-46                                    August 1995

Chapter 2
System Characterization
Exhibit 2-14. Lewiston-Auburn Receiving Water E. Coli Data

Androscoggin River
Little Androscoggin
Jepson Brook
Dry Weather


480 - 2,280
100 - 135
280 - 355

5- 115

% of Samples



Wet Weather
September 26-28, 1993
(colonies/100 ml)

0 - 1,440
160 - 6,800
60 - TNTC


20 - 2,400
40 - 30,000
% of Samples
Above Standards



October 12-14, 1993
Range (colonies/

10 - 3,500
90 - TNTC


40 - 2,500
140 - TNTC
% of Samples
Above Standards




Note: Class C Standard: Instantaneous level of 949 colonies/100 ml
TNTC = Too numerous to count
         August 1995

Chapter 2                                                         System Characterization


       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).   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

       •  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
                                         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).   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
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
Long-term continuous simulations
(preferred) or design storm
Limited - Not usually performed
Limited - Not usually performed
Use measured concentrations
simplified transport modeling
Demonstration Approach
Demonstrate that a selected control
program is adequate to meet the
water quality-based requirements of
Design storm simulations
long-term continuous simulations
Use measured concentrations
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.
         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).   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 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.   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

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   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).   Receiving Water  Model Application
       The  application  of receiving  water models for  CSO programs includes the following

       •  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

       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
                           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.


    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

           •   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

    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.


    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


    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.


    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.


    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

       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
       •   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.

      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.

       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

       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

       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.   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).   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];
       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
       •   Wet weather BOD removal efficiency from municipality's secondary POTW—80

       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
       •   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
       •  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
       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
                                                                                    Available -%   43 m'm
Overflow Rate <2,000 gpd/ft
Assume ~ 40% SS Removal
    Volume Stored tor
    85% SS Removal
                                                              Overflow Rate <1,000 gpd/ft
                                                              Assume ~ 60% SS Removal
                                                                              Full Volume
                                                                              85% SS Removal
                                       8            10

                                        Time (hours)
Exhibit 3-1. An Example of Overflow Rates Versus Pollutant Removal During a Rainfall Event


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

          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,


       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.

       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.   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.   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.    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
       •  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
                                          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

       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.   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.   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.   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.   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.   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"

       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
           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
           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).    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).   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

       •  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.   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

          -   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.   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.    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

       •  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

          Predicted CSO  flow rates,  volumes, and pollutant loads under selected  hydraulic

          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

       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

       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



                     Maximum Storage Volume
                          (no treatment)
                                                    Inflection Point
                                                        -Maximum Treatment Rate
                                                        (no storage)
Storage Volume
Required at
Treatment Rate
      Source: Camp, Dresser & McKee, 1989
                                            Time (hours)
                             Exhibit 3-2. Typical Mass Diagram

                                               Volume of storage
                                               required for flows
                                               above maximum
                                               treatment rate
                                      Time (hours)
Exhibit 3-3. Typical Representation of Interaction Between Storage and Treatment Needs

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

       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

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

       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
                                          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

       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
                                          3-55                              August 1995

               1 Mo.   3 Mo.
                I        i
                                              Design Storm Event

                                                   6 Mo.     1 Yr.

     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

•«•   120
r   100








+ 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
          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)

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.   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

       •  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.    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.   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

       •  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
Standard construction techniques
Standard techniques, but with restraints (such as limited
staging area, difficult site access)
Special techniques or more severe restraints on
  TSS Load
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.
                                                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
Number of Facilities
Level of O&M
Reliance on Existing Facilities
Impacts on Downstream Facilities
Site Requirements
Extent of Disruption
Degree of Difficulty
Adaptability to Phased Implementation
Conformance with Current Plans





t'2^ 000
tjtjj j\J\J\S




«47 000
JTT / ,\^W



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
                                         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
       •  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

           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

            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

            •   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

            •   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.


            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.


    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

            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).


            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.


            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-

            •    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

            •    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.


            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.


            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
                  Implementation and
                   Operation Factors



S 0.



o , 	 .
 / JJ






* /
3 /
5 £
/ ®





/ i





• Excellent               a Very Good


© 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
Earthen Basins
Open Concrete Tanks
Closed Concrete Tanks
Storage Conduits
Storage Tunnels
Swirl Concentrator
Vortex Separator
Coarse Screening
Primary Sedimentation
Dissolved Air Flotation (DAF)
DAF with Polymer Addition
High Rate Filtration (HRF)
Biological Treatment
Columbia Boulevard WWTP
Consider for






Consider for




Consider for
Interim Use





from Further







Source: CH2MHILL, 1993

                                          August 1995

Chapter 3                              Development and 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

            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

       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

       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,
                                         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
                                           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

       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.

       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

       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

       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.

       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   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.   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.   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.   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.   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.

       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
  •  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
                               Exhibit 4-2. Example of Phased Implementation Approach

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.

       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
           Responsible Organization
  Other Potentially Involved
 Permitting and
 Public Education

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
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
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
Local Environmental Groups
University Students
Volunteer Organizations
Environmental Consultants

University Engineering
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)
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
                                                               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.

       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

       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.

       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

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

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.

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

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


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

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


U.S. Environmental Protection Agency (EPA).  1994a.   Combined Sewer Overflow Control

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.

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


catch basin

collector sewer

combined sewage

combined sewer

combined sewer
overflow (CSO)
designated use

infiltration/inflow (I/I)

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
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.
                                                August 1995

interceptor sewer
load allocation (LA)
overflow rate
peak flow

rainfall duration

rainfall intensity


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.

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.
                                                  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  4204
United States Environmental Protection Agency
401 M Street SW
Washington, DC  20460

United States
Environmental Protection Agency
Washington, DC  20460

Official Business
Penalty for Private Use