United States
           Environmental Protection
           Agency
Office Of Water
(4204)
EPA 832-B-97-001
Draft
?/EPA     Combined Sewer Overflows
           Guidance For Monitoring
           And Modeling

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                    UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                                  WASHINGTON, D.C. 20460
                                      Offi 16896
                                                                          OFFICE OF
                                                                           WATER
 SUBJECT: Combined Scwa Overflows-Guidance for Monitoring andModdmg
 FROM:    James F.Pendergast, Acting Director *^Ow*^ -7.  K^^ec^^^
           Pomits Division (MC: 4203)                                   °
 TO:       Interested Parties
       lam pleased to provide, foryonr review and comment, an external review draft of EPA's
 document Combined Sewer Overflows - Guidance for Monitoring andModeting:

       CtaAr^ 11,1994,EPAissuedtte&ial Combing
 Policy eghthKshftg a nnnsishait natinnal flppmaeJTfiir cnnfmllmg At^ffg^ fain ctmbmcd SFfftT 5y3tCm3 to
 the Nation's waters through the National PoflutarrtDischaiseElimriiatian^

       EPA^e rSO rrmfnJ PrJtidmwf^liii^
       4.     Combined Sewer Overflows-Guidance for Long-Tenn Control Plan
       S.
EPA has released a sbah guidance document (Combined Sewer Overflow -Guidance for Financial
Cattily Assessment auTSdiedide Developing                 EPA plans to issue this document as
final in th^yqy pffffl* fatBTP.


       The attached dnraimnnt, Combined Sewer Overflows - Guidance for Monitoring andModeUng, is the
final guidance document that EPA vriH develop in support of the National CSO Control PoKcy. We are
tetpesting that ynn remear this manual atvi mhrni* ynnr ., .imi^im t» ne
draft and assure you that EPA will give serious consideration to aflcooniicnts and information received Please
note that this guidance is currently in draft fora and shcvkl net be used as teAgencys final guidance. It is

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intended as guidance only and does not modify or superset the CWAor Agency icgnlations.


       Tfoffoffrri«rtpt>.Q.ntginApm
andvak^levebrfinomtoriiujandmode^
                     » _  .  •  •      •• __?__	uj ... • j»i»^^ a^^MK^MfliMflMkAt MBOV oM Bnn^¥^^wnv* n^r iiiEir
and various tevdsof moang an  nong  r o
body. EPA*atecomnimifetDdgv^
situation. Mednmandlageconiiiniiiite
needmorc sophisticated moo^
Many usego^docaneat, however, a^
nxHntomgandmodelmgneeds. It is essential that ^ document prodeg^^
regaidles7ofsi«,ondevdo^
                             OHiffl^
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              WORKING DRAFT: Do Nor CITE OR QUOTE
                   COMBINED SEWER OVERFLOWS

             GUIDANCE FOR MONITORING AND MODELING
                    Office of Wastewater
                  U.S. Environmental Protection Agency
                         401M Street, S.W.
                        Washington, DC 20460
                          December 1996
External Review Draft                                    December 6, 1996

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              WORKING DRAFT:  Do NOT CITE OR QUOTE


External Review Draft
                                                   December 6, 1996

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               WORKING DRAFT:  Do NOT CITE OR QUOTE
BMP
BOD
BPJ
CAD
CSO
CSS
CWA
EMC
EPA
I/I
LA
LTCP
NCDC
NGO
NMC
NOAA
NPDES
NURP
O&M
POTW
RBP
QA
QC
scs
SSES  .
STORE!
SWMM
IDS
TMDL
TSS
USGS
VOC
WBS
WLA
WQS
                 LIST OF ACRONYMS

Best Management Practice
Biochemical Oxygen Demand
Best Professional Judgment
Computer Aided Design
Combined Sewer Overflow
Combined Sewer System
Clean Water Act
Event Mean Concentration
U.S. Environmental Protection Agency
Geographic Information System
Infiltration/Inflow
Load Allocation
Long-Term Control Plan
National Climatic Data Center
Nongovernmental Organization
Nine Minimum Controls -
National Oceanic and Atmospheric Administration
National Pollutant Discharge/Elimination System
National Urban Runoff Program .
Operations and Maintenance  '
Publicly Owned Treatment Works
Rapid Bioassessment Protocol.
Quality As
 -^.   *
Quality Control
Soil Conservation Service
Sewer-System Evaluation Studies
Storage and Retrieval of U.S. Waterways Parametric Data
Storm Water Management Model '
Total Dissolved Solids
Total Maximum Daily Load
Total Suspended Solids
U.S. Geological Survey
Volatile Organic Compounds
Water Body System
Wasteload Allocation
Water Quality Standards
 External Review Draft
                                                    December 6,1996

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             WORKING DRAFT: Do Nor CITE OR QUOTE
                      T^BLE OF CONTENTS

                                                              Page

1.   INTRODUCTION	  1-1

    1.1  BACKGROUND	  1-1
    1.2  HISTORY OF THE CSO CONTROL POLICY	  1-1
    1.3  KEY ELEMENTS OF THE CSO CONTROL POLICY	  1-3
    1.4  GUIDANCE TO SUPPORT IMPLEMENTATION OF THE CSO
        CONTROL POLICY	  1-6
    1.5  PURPOSE OF GUIDANCE	  1-6
    1.6  MANUAL ORGANIZATION	  1-7

2.   INTRODUCTION TO MONITORING AND MODELING	  2-1
                              »  •
    2.1  MONITORING AND MODELING FOR NINE MINIMUM CONTROLS
        AND LONG TERM CONTROL PLAN	  2-1
        2.1.1  Nine Minimum Controls  	  2-2
        2.1.2  Long-Tom Control Plan Development	  2-4
        2.1.3  Monitoring and Modeling During Phase I 	  2-9
        2.1.4  Monitoring and Modeling During Phase H	2-10
    2.2  MONITORING AND MODELING AND THE WATERSHED
        APPROACH	2-11
    2.3  MEASURES OF SUCCESS	2-13
    2.4  COORDINATION WITH OTHER WET WEATHER MONITORING AND
        MODELING PROGRAMS	2-14
    2-J  REVIEW AND REVISION OF WATER QUALITY STANDARDS	2-14
    2.6  OTHER ENTITIES INVOLVED IN DEVELOPING AND
        IMPLEMENTING THE MONITORING AND MODELING PROGRAM .. 2-15

3.   INITIAL SYSTEM CHARACTERIZATION - EXISTING DATA ANALYSES
    AND FIELD INVESTIGATIONS  	  3-1

    3.1  PHYSICAL CHARACTERIZATION OF CSS 	  3-2
        3.1.1  Review Historical Information	  3-2
        3.1.2  Study Area Mapping	  3^5
        3.1.3  System Held Investigations 	  3-6
        3.1.4  Preliminary CSS Hydraulic Analysis	  3-8
    32  CHARACTERIZATION OF COMBINED SEWAGE AND CSOS  	3-10
        3.2.1  Historical Data Review	3-10
        3.2.2  Mapping	3-11
    3.3  CHARACTERIZATION OF RECEIVING WATERS 	3-12
        3.3.1  Historical Data Review  	3-12
        3.3.2  Mapping  	3-15
    3.4  IDENTIFY DATA GAPS'	3-15
External Review Draft                1-iii                   December 6, 1996

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               WORKING DRAFT: Do NOT CITE OR QUOTE
                   TABLE OF CONTENTS (Continued)

                                                                    Page

     MONITORING AND MODELING PLAN	, 4-1

     4.1   DEVELOPMENT OF A MONITORING AND MODELING FLAN	 4-2
          4.1.1   Goals and Objectives	 4-3
          4.1.2   Modeling Strategy	 4-5
          4.1.3   Monitoring Data Needs	4-7
     4.2   ELEMENTS OF A MONITORING'AND MODELING PLAN 	 4-8
          4.2.1   Duration of Monitoring Program	 4-10
          4.2.2   Sampling Protocols and Analytical Methods	-	4-11
     4.3   CSS AND CSO MONITORING	4-12
          4.3.1   CSS and CSO Monitoring Locations		,	\.	4-12
          4.3.2   Monitoring Frequency	4-18
          43.3   Combined Sewage and CSO Pollutant Parameters	4-19
     4.4   SEPARATE STORM SEWERS  	.'	4-21
     4.5   RECEIVING WATER MONITORING.	;	4-22
          4.5.1   Monitoring Locations			.4-23-
          4.5.2   Monitoring Frequency, Duration* and Timing;««-.....	4-26
          4.5.3   Pollutant-Parameters •....-.......'..,.:...«...»	 4-27
     4.6   CASE STUDY		'. _.,	 .-.-„.*	4-28
     4.7   DATA MANAGEMENT AND ANALYSE-..	....;. J. i,	4-30
         4.7.1   Quality Assurance Programs....... —	,	4-30
         4.7.2   Data Management	-.	 4-33
     4.8  IMPLEMENTATION OF MONITORING AND MODELING PLAN	4-35
         4.8.1   Recordkeeping and Reporting	-.	—.		4-35
         4.8.2   Personnel Responsible for Implementation	.- J	4-35
         4.8.3   Scheduling	;		4-35
         4.8.4   Resources —	.... T	 4-36

5.   CSS  MONITORING	"...	........;...,.. 5-1

     5.1  THE CSO POLICY AND CSS MONITORING  	 5-1
     5.2  RAINFALL DATA FOR CSS CHARACTERIZATION	 5-2
         5.2.1   Rainfall Monitoring	 5-2
         522   Rainfall Data Analysis	".	 5-3
     5.3  FLOW MONITORING IN THE CSS  	5-10
         5.3.1   Flow Monitoring Techniques	5-10
         5.3.2   Conducting die Flow Monitoring Program	 5-17
         5.33   Analysis of CSS Flow Data	5-18
     5.4  WATER QUALITY MONITORING IN THE CSS	:	5-22
         5.4.1   Quality Sampling 	5-22
         5.4.2   Analysis of Wastewater Monitoring Data	5-29
External Review Draft                 1-iv                    December 6, 1996

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                  TABLE OF CONTENTS (Continued)
 6.   RECEIVING WATER MONITORING	.-	  6-1

     6.1  THE CSO CONTROL POLICY AND RECEIVING WATER
         MONITORING	             6-1
     6.2  RECEIVING WATER HYDRAULICS ;	'.',"  6-2
         6.2.1   Hydraulic Monitoring  ...,	  6-3
         6.22   Analysis of Hydraulic Data	         6-5
     6.3  RECEIVING WATER QUALITY	t	;	\  6-6
         63.1   Water Quality Monitoring	"  6-7
         6.32   Analysis of Water Quality Data	....	  6-8
     6.4  RECEIVING WATER SEDIMENT AND BIOLOGICAL MONITORING..  6-9
         6.4.1   Sediment Sampling Techniques*........... ^...:. .._'.;,.;	  6-9
         6.4^   Analysis of Sediment Data <-„	6-11
         6.43   Biological Sampling Techniques.-..-.	_ A	;	6-11
         6.4.4   Analysis of Biological Data ....-.,... 4	.-.-	6-14

7.   COMBINED SEWER SYSTEM MODELING.'.	•-..,		  7-1

     7.1  THE CSO CONTROL POLICY AND CSS MODELING c.	,- 7-1.
     72  MODELSELECTION	^	  7-3
         7.2.1  Model Selection ,..-...;	.; .. .^1.....;:	  7-6
         7.22  Selecting Hydraulic Model*  .;... ".„...... ..;•„-	  7-10
     73  AVAILABLE MODELS	.-. .J..:..,.:	7-12
     7.4  MODEL APPLICATION .-	7-12
         7.4.1  Model Development.'.	7-12
         7.42  Model Calibration and Verification.	7-16
         7.4.3  Performing me Modeling Analysis	»".........•	7-20
         7.4.4  Interpretation, of Results	V.	7-21
     7.5  EXAMPLE SWMM MODEL APPLICATION	7-24
         7.5.1  Data Requirements	7-25
         7.5.2  SWMMBlock*...	".	'...7-28
         .733  Model Calibration and Application  ......:	7-31
         73.4  SWMM Quality Modeling	7-33
External Review Draft                 1-v                    December 6, 1996

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               WORKING DRAFT:  Do Nor CITE OR QUOTE
                  TABLE OF CONTENTS (Continued)
 8.   RECEIVING WATER QUALITY MODELING	 g-i

     8.1  THE CSO POLICY AND RECEIVING WATER MODELING  	 8-1
     8.2  MODEL SELECTION STRATEGY	 8-2
               Hydrodynamic Models	 8-3
               Water Quality Models	 8-5
     8.3  AVAILABLE MODELS 	 8-6
         8J.1  Simplified Analyses	 8-6
         8.32  Model Types	 8-6
         8.3.3  EPA-Supported Models	8-15
         83.4  Other Models	8-18
     8.4  USING A RECEIVING WATER MODEL	8-19
         8.4.1  Developing the Model	'.	8-19
         8.42  Calibrating and Validating the Model	8-19
         8.4.3  Performing the Modeling Analysis	8-20
         8.4.4  Modeling Results	8-20

9.   ASSESSING RECEIVING WATER IMPACTS AND ATTAINMENT OF
     WATER QUALITY STANDARDS	  9-1

     9.1  IDENTIFYING RELEVANT WATER QUALITY STANDARDS	  9-2
     9.2  OPTIONS FOR DEMONSTRATING COMPLIANCE	  9-4
     9.3  EXAMPLES OF RECEIVING WATER ANALYSIS  	:..  9-5
         9.3.1   Example 1: Bacterial Loads to a River	  9-6
         9.3.2   Example 2: Bacterial Loads to an Estuary	9-23
         93.3   Example 3: BOD Loads	9-28
     9.4  SUMMARY	9-34

REFERENCES	R-l

APPENDIX A	A-l
APPENDIX B	B-l
External Review Draft                 1-vi                    December 6, 1996

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                 WORKING DRAFT:  Do Nor CITE OR QUOTE
                                LIST OF EXHIBITS

                                                                              Page

Exhibit 1-1.       Roles and Responsibilities	  1-5

Exhibit 3-1.       Flow Balance Diagram  	  3.9

Exhibit 4-1.       Data for Example 4-1	4-17
Exhibit 4-2.       Monitoring Location Example  	'.:... 4-25

Exhibit 5-1.       Ranking of Yearly Runoff Characteristics as Simulated by the
                  Storm Model  	  5.5
Exhibit 5-2.       Rainfall and Runoff Parameters for Typical and Extreme Years ...  5-6
Exhibit 5-3.       1993 Rainfall Data for a 5,305 Acre Drainage Area	  5-8
Exhibit 5-4.       Rain Gage Map for Example 5-1  	  5-9
Exhibit 5-5.       CSO Flow Monitoring Devices			5-H
Exhibit 5-6.       Illustration of a Bottle Board Installation		5-14
Exhibit 5-7.       Example Outfall Bottle Rack Readings  	5-15
Exhibit 5-8.       Total Overflow Volume	5-19
Exhibit 5-9.       Example CSS Plots of Flow and Head versus Time  	5-21
Exhibit 5-10.       Composite Sampling Data (mg/1)  	5-30
Exhibit 5-11.       Pollutant Concentration Summary Statistics (mg/1)  	5-30
Exhibit 5-12.       Pollutant Loading Summary	5-32
Exhibit 5-13.       Fecal Coliform Data Outfall 1, Example Storm	5-33

Exhibit 6-1.       Overview of Field Biological Sampling Methods  	6-12

Exhibit 7-1.       Relevant CSS Hydraulic and  Contaminant Transport Modeling for
                  EPA's CSO Control Policy   	  7-5
Exhibit 7-2.       Characteristics of RUNOFF, TRANSPORT, and EXTRAN Blocks
                  of the EPA Storm Water Management Model (SWMM)  	  7-8
Exhibit 7-3.       Characteristics of CSS Hydraulic Public Domain Models	7-13
Exhibit 7-4.       Water Quality Simulation Model Characteristics	'.. 7-14
Exhibit 7-5.       Commercial CSS Models	7-15
Exhibit 7-6.       Levels of Discretization	7-17
Exhibit 7-7.       Drainage Area Map	7-26
Exhibit 7-8.       Sewer Network and Subareas	7-27
Exhibit 7-9.       SWMM Runoff Block Input Parameters (SWMM HI Card)	7-29
Exhibit 7-10.       SWMM transport Block Input Parameters (SWMM EF Card)	7-30
Exhibit 7-11.       Flow Hydrograph	7-32
Exhibit 7-12.       Pollutographs	7-34
Exhibit 7-13.       Predicted and Observed Pollutant Concentrations*	7-34
                                             V

Exhibit 8-1.       Dissolved Oxygen Superposition Analysis ...	8-10
Exhibit 8-2.       EPA CEAM Supported Receiving Water Models  	8-16
External Review Draft
1-vii
December 6,1996

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                WORKING DRAFT:  Do Nor CITE OR QUOTE
                         LIST OF EXHIBITS (Continued)
Exhibit 9-1.       Map For Example 1	9-7
Exhibit 9-2.       CSO Events for Example 1  	 9-8
Exhibit 9-3.       Design Flow Analysis	9-13
Exhibit 9-4.       Flow Duration Curve	9-17
Exhibit 9-5.       Expected Exceedances of Water Quality Criterion	9-19
Exhibit 9-6.       Excursions of Water Quality Criterion by Month  	9-21
Exhibit 9-7.       Receiving  Water Flow During CSOs	•	9-22
Exhibit 9-8.       Map for Example 2	9-24
Exhibit 9-9.       Steady State Predictions of Fecal Coliform Count (MPN/lOOml)... 9-27
Exhibit 9-10.      Design Condition Prediction of DO Sag;.:	9-31
Exhibit 9-11.      Relationship Between DO Concentration and Upstream Flow	9-33
External Review Draft
1-viii
December 6,1996

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                        WORKING DRAFT:  ,Do Nor CUE OR QUOTE
  i                                        CHAPTER l
  2
  3                                      INTRODUCTION

       1.1    BACKGROUND
  6\
  7 \           Combined sewer systems '(CSSs) are wastewater collection systems designed to cany
  8  \   sanitary sewage (consisting of domestic, commercial, and industrial wastewater) and storm water
    \
  9   ,  (surface drainage from rainfall or snowmelt) in a single pipe to a treatment facility. CSSs serve
10     about 43 million people in approximately 1,100  communities nationwide.  Most of these
11     communities are located in the Northeast and Great Lakes regions. During dry weather, CSSs
12     convey domestic, commercial/ and industrial wastewater to a publicly owned treatment works
13     (POTW). In periods of rainfall or snowmelt, total wastewater flows can exceed the capacity of
14     the CSS or the treatment facilities. When this occurs, the CSS is designed to overflow directly
15     to surface water bodies,, such as lakes, rivers, estuaries, or coastal waters. These overflows—
16     called combined sewer, overflows (CSOs)—can be  a  major source, of water pollution hi
17     communities served by CSSs.
18
19           Because CSOs contain untreated domestic, commercial, and industrial wastes, as well as
20     surface runoff, many different types of contaminants can b£ present Contaminants may include
21     pamogens, oxygen-demanding pollutants, suspended solids, nutrients, toxics, and floatable matter.
22     Because of these contaminants and the volume of the flows, CSOs can cause a variety of adverse
23     impacts on the physical characteristics of surface water, impair the viability of aquatic habitats,
24     and pose a potential threat to drinking water .supplies. CSOs have been shown to be a major
25     contributor to use impairment and aesthetic degradation of many receiving waters  and have
26     contributed to shellfish harvesting restrictions, beach closures, and even occasional fish kills.
27
28     L2   HISTORY OF THE CSO CONTROL POLICY
29
30           Historically, the control of CSOs has proven to be extremely complex. This complexity
31     stems partly from the difficulty in quantifying CSO impacts on receiving water quality and from
32     the site-specific variability in the volume, frequency, and characteristics of CSOs. In addition,

       External Review Draft                    1-1                       December 6, 1996

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                       WORKING DRAFT:  Do Nor CITE OR QUOTE
 r     the financial considerations  for communities with CSOs can be  significant  (1994-'.
 2     Survey). The U.S. Environmental Protection Agency (EPA) estimates the CSO abatement costs
 3     for the  1,100  communities  served  by CSSs  to  be approximately $50.0 billion based on
 4     preliminary modeling results  from the 1990 Clean Water Needs Survey.
 5                        '
 6           To address these challenges, EPA's Office of Water issued a National Combined Sewer
 7     Overflow Control Strategy on August 10, 1989 (54 Federal Register 37370).  This  Strategy
 8     reaffirmed that CSOs  are point source  discharges, subject  to National Pollutant Discharge
 9     Elimination System (NPDES) penmt requirements and to Clean Water Act (CWA) requirements^
10     The CSO Strategy recommended mat all CSOs.be identified and categorized according to their
11     status of compliance with these requirements.  It also set forth three objectives;
12                             ^       -
13           •  Ensure that if CSOs occur, they are only as- a result of wet weather-
14      -
15           •  tiring  all  wet weather CSO discharge points into compliance with the technology-
16              based and water quality-based requirements of the CWA:•.-
17                        •  '                                      -        -.
18           •  Minimi™ the water qualify, aqnaric biota, and human health impacts from CSOs.
  \                        «
19                                                                         .
20     In addition, the CSO Strategy charged all States with developing state-wide permitting strategies
                              •     ^
21.     designed to reduce, eliminate, or control CSOs.
22
23           Although the  CSO Strategy was successMmfocushigmcieased attention on CSOs, it fell
24     short in resolving many fundamental issues, m mid-1991, EPA initiated a process to accelerate
25     implementation of the Strategy;  The process included negotiations with representatives of the
26     regulated conununity, State regulatory agencies, and environmental groups. These negotiations
27     were conducted through the Office of Water Management Advisory  Group.  The initiative
28     resulted in  the development of a CSO Control Policy, which was published hi the Federal
29     Register on April 19,1994 (59 Federal Register 18688). The intent of the CSO Control Policy
30     is to:
31
        External Review Draft                     1-2                        December 6, 1996

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                        WORKING DRAFT: Do Nor CITE OR QUOTE
  1            •  Provide  guidance to permittees  with CSOs, NPDES permitting and enforcement
  2               authorities, and State water quality standards (WQS) authorities
  3
  4            •  Ensure coordination among the appropriate parties in planning, selecting, designing,
  5               and implementing CSO management practices and controls to meet the requirements
  6               oftheCWA
  7
  8            •  Ensure public involvement during the decision-making process.
  9                                                             '

 10            The CSO Control Policy contains provisions for developing appropriate, site-specific
 11     NPDES permit requirements for all CSSs that overflow due to wet weather events:  It also
 12     announces an enforcement initiative that requires the immediate elimination of overflows that
 13     occur during dry weather and ensures that the- remaining CWA requirements are complied with
 14     as soon as possible.
 15

 16     13    KEY ELEMENTS OF THE CSO CONTROL POLICY
 17
 18      •      The CSO Control Policy contains four key principles to ensure mat CSO controls are cost-
 19     effective and meet the requirements of the CWA:
20

21            •   Provide clear levels of control that would be presumed to meet appropriate health and
22               environmental objectives
23
24            •   Provide sufficient flexibility to municipalities, especially those mat are financially
25               disadvantaged, to consider the site-specific nature of CSOs and to determine the most
26               cost-effective  means of  reducing pollutants  and meeting  CWA objectives and
27               requirements
28
29            •   Allow  a  phased approach for  implementation of CSO controls  considering  a
30               community's financial capability
31
32            •   Review and revise, as appropriate. WQS and thek implementation procedures when
33               developing  long-term GSO control plans  to reflect the site-specific wet weather
34               impacts of CSOs.
35
       External Review Draft                    1-3                       December 6, 1996

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                        WORKING DRAFT:  Do NOT CITE OR QUOTE
 1           In addition, the CSO. Control Policy clearly defines expectations for permittees, State
 2     WQS authorities, and NPDES permitting and enforcement authorities. These expectations include
,3     the following:
 4
 5           •  Permittees should immediately implement the nine minimum controls (NMQ, which
 6              ate technology-based actions or measures designed to reduce CSOs and their effects
 7              on receiving water quality, as soon as practicable but no later than January 1, 1997.
 8
 9           •  Permittees should give priority to environmentally sensitive areas.
10
11           •  Permittees should develop long-term control plans (LTCPs) for controlling CSOs. A
12              permittee may use one of two approaches:  1) demonstrate that its plan is adequate
13              to meet the water qiiakty4>ased requirements of m^
14              or 2) implement a minimnm level of treatment (e.g., primary clarification of at feast
15              85 percent of the collected combined sewage flows) mat is presumed to meet the
16              water quality-based requirements of the CWA,  unless data indicate otherwise
17              ("presumption approach").
18
19           •  WQS authorities should review and revise, as appropriate, State WQS during me CSO
20              long-term planning process,
21
22           •  NPDES permitting authorities should consider the financial capability of permittees
23              when reviewing CSO control plans.
24                              -                                  -
25.           Exhibit 1-1 illustrates the roles and responsibilities of permittees, NPDES permitting and
26     enforcement authorities, and State WQS authorities.
27
28           In addition to these key elements and expectations, the CSO Control Policy also addresses
29     important issues such as ongoing or completed CSO control projects, public participation, small
30     communities, and watershed planning.
31
32
        External Review Draft                    1-4                       December 6, 1996

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                                                         Exhibit 1-1.  Roles and Responsibilities
            Evaluate and implement NMC
          • Submit documentation of NMC
            implementation by January 1,1997

          • Develop LTCP and submit for
            review to NPDES permitting
            authority

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

          • Comply with permit conditions
            based on narrative WQS

          • Implement selected CSO controls
            from LTCP

          • Perform post-construction
            compliance monitoring

          • Reassess overflows to sensitive
            areas

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

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

•  Review documentation of NMC
   implementation

•  Coordinate review of LTCP
   components throughout the LTCP
   development process and
   accept/approve permittee's LTCP

•  Coordinate the review and revision
   of WQS as appropriate

•  Incorporate Into Phase II permits
   CSO-related conditions (e.g.,
   continued NMC implementation
   and LTCP Implementation)

•  Incorporate implementation
   schedule into an appropriate
   enforceable mechanism

•  Review implementation activity
   reports (e.g.. compliance schedule
   progress reports)
• Ensure that CSO requirements and
  schedules for compliance are
  incorporated into appropriate
  enforceable mechanisms

  Monitor adherence to January 1,
  1997, deadline for NMC
  implementation and documentation

  Take appropriate enforcement
  action against dry weather
  overflows

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

Coordinate review with LTCP
development

Revise WQS as appropriate:

Development of site-specific
criteria
                     i

Modification of designated use to

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

Temporary variance from WQS
Os

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  1     1A    GUIDANCE TO SUPPORT IMPLEMENTATION OF THE CSO  CONTROL
  2            POLICY
  3
  4            To help permittees and NPDES pennitting and WQS authorities implement the provisions
  5     of the CSO Control Policy, EPA has developed the following guidance documents:
                                                              »
  6
  7            •  Combined Sewer Overflows - Guidance for Long-Term Control Plan (EPA, 1995a)
  8              (EPA 832-B-95-OQ2)
  9
 10            •  Combined Sewer Overflows - Guidance for Nine Minimum Controls (EPA, 1995b)
 11              (EPA 832-B-95-003)
 12                                              .
 13           '•  Combined Sewer Overflows - Guidance for Screening and Ranking (EPA, 1995c>
 14       .       (EPA 832-B-95-004)
 15                                        '
 16           •  Combined Sewer Overflows - Guidance for Funding Options (EPA, 1995d) (EPA 832-
 17              B-95-007)
 18              .                     '           -             .
 19           •  Combined Sewer Overflows - Guidance for Permit Writers (EPA, 1995e) (EPA 832-
20              B-95-008).
21                   -                          .                .
22     1.5   PURPOSE OF GUIDANCE
23.
24           This manual explains the. role .of monitoring  and modeling in the development and
25     implementation of a CSO control program. It expands discussions of monitoring and modeling
26     introduced hi the  CSO Control Policy and presents examples of data collection and CSS
27     simulation.
28
29           This manual is not a "how-to" manual defining how many samples to collect or which
30     flow metering technologies-to use. The CSO Control Policy is not a regulation. Rather, it is a
31     set of guidelines that provides flexibility for a municipality to develop a site-specific strategy for
32     characterizing  its  CSS operation and impacts and for  developing  and  implementing a
33     comprehensive CSO control plan.  CSSs vary greatly in their size, structure, operation, and
34     receiving water impacts. A monitoring and modeling strategy appropriate for a large city such
35     as New York or San Francisco would generally not apply to a small CSS with only one or two
36     flow regulators and outfalls. In addition, communities have varying degrees of knowledge about
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  1     how their CSSs react hydraulically to wet weather and how their CSOs affect receiving water
        quality.  A municipality that  does not know the location  of its CSO outfalls has different
  j.    information collection needs from a municipality that has already conducted CSS flow and water
        quality studies.
  5-
              this manual provides  guidance for communities of all sizes,  ft presents  low-cost
  7     monitoring  and  modeling techniques, which  should prove particularly helpful to  small
        communities. However, communities with large CSSs should note that inexpensive technique^
  9     often prove useful in extending monitoring resources and in verifying the performance of more
        sophisticated techniques and equipment
 11
              To use mfc mfl^'"»l, a municipality should already be familiar with the basic functioning
 13     of its CSS, basic monitoring procedures, and the general purpose of modeling.  Since basic
        monitoring and modeling techniques are already covered extensively in other technical literature,
 i<     this manual focuses mainly on  die process of characterization as described in the CSO Control
  i     Policy,  referring to other literature for more in-depth explanations of specific techniques or
 «     procedures.
  {
 10     1.6    MANUAL ORGANIZATION
  3
 *1           This manual begins with-an overview of monitoring and modeling under the CSO Control
  2     Policy,  and then provides a detailed discussion of me monitoring and modeling activities that
1^3     should be conducted for NMC implementation  and LTCP development and implementation.
 14     These activities (and the chapters in which they are discussed) are as follows:
 25
 26           2.0   Introduction To Monitoring and Modeling
 27           3.0   Initial System Characterization—Existing Data Analyses and Field Investigation
 28           4.0   Monitoring and Modeling Plan
 29           5.0   Combined Sewer System Monitoring
 30           6.0   Receiving Water Monitoring
 31           7.0   Combined Sewer System Modeling
 32           8.0   Receiving Water Quality Modeling
 33  '         9.0   Assessing Receiving Water Impacts and Attainment of Water Quality Standards.
 34

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  i                                       CHAPTER 2
  2
  3                   INTRODUCTION TO MONITORING AND MODELING
  4
  5           Monitoring and modeling activities are central to implementation of the Combined Sewer
  6     Overflow (CSO) Policy.  Thoughtful development and implementation of a monitoring and
  7     modeling plan will support the selection and implementation of cost-effective CSO controls and
  8     assessment of their impacts on receiving water quality.
  9
 10           This chapter describes general expectations for monitoring and modeling activities as part
 11      of a permittee's CSO control program.  It also describes how monitoring and modeling efforts
 12     conducted as part of CSO control program implementation can be coordinated with other key
 13      EPA and State programs and efforts (e.g., watershed approach, other wet weather programs).
 14
 15            While this chapter will describe general expectations, EPA encourages the permittee to
 16      take advantage  of the flexibility in the CSO Control Policy by developing a monitoring and
 17      modeling program that is cost-effective and tailored to local conditions, providing adequate but
 18      not duplicative or unnecessary information.
 19
20     2.1    MONITORING AND MODELING FOR NINE MINIMUM CONTROLS AND
21            LONG TERM CONTROL PLAN
22
23            The CSO Control Policy urges permittees to develop a thorough understanding of the
24     hydraulic responses of their CSSs to wet weather events. Permittees may also need to estimate
25     pollutant loadings from CSOs  and the fate of pollutants in receiving water both for existing
26     conditions and for various CSO control options. The CSO Control Policy states that permittees
27     should  "immediately undertake a process to accurately characterize their CSSs, to demonstrate
28     implementation  of the nine minimum controls, and to develop a long-term CSO control plan."
29     Characterizing the CSS and its hydraulic response to wet weather events, implementing the NMC
30     and producing related documentation, and  developing an LTCP will involve gathering and
31     reviewing existing data, and, in most cases, conducting some field inspections, monitoring, and
32     modeling.  Since flexibility  is a key  principle in CSO Control Policy implementation, these

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  1     activities will be carried out to different degrees based on each permittee's  situation.  In

  2     particular, the type and complexity of necessary modeling will vary from permittee to permittee.
  3

  4     2.1.1  Nine Minimum Controls
  5
  6           The CSO Control Policy recommends that a Phase I permit require the permittee to

  7     immediately implement technology-based requirements, which in most cases will be the NMC,

  8     as determined on a best professional judgment (BPJ) basis by the NPDES permitting authority.

  9     The NMC are:

 10

 11            1. Proper operation and regular maintenance programs for the sewer system
 12
 13           2. Maximum use of the collection system for storage
 14
 15            3. Review  and modification of pretreatment requirements to assure CSO impacts are
 16               minimized
 17
 18            4. Maximization of flow to the publicly owned treatment works (POTW) for treatment
 19
20            5. Prohibition of CSOs during dry weather
21
22            6. Control of solids and floatable materials in CSOs
23
24            7. Pollution prevention
25
26            8. Public notification to ensure that the public receives adequate notification of CSO
27               occurrences and CSO impacts
28
29            9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls.
30

31            The NMC are technology-based controls, applied on a site-specific basis, to reduce the

32     magnitude, frequency, and duration of CSOs and their impacts on receiving water bodies. NMC
                               \
33     measures typically do not require significant engineering studies or major construction and thus

34     implementation is expected by January 1, 1997.  EPA's guidance document Combined Sewer

35     Overflows - Guidance for Nine Minimum Controls (EPA, 1995b) provides a detailed description

36     of the NMC, including example control measures and their advantages and limitations.
37
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  1            Monitoring is specifically included as the ninth minimum control. Implementation of this

  2     control would typically involve the following activities:

  3

  4  .          •   Mapping the drainage  area for the combined sewer system (CSS), including the
  5               locations of all CSO outfalls and receiving waters
  6\
  7            •   Identifying, for each receiving water body, designated and existing uses, applicable
  8               water quality criteria, and whether WQS are currently being attained
  9
10            •   Developing a record of overflow occurrences
11
12            •   Compiling existing information on water quality impacts associated with CSOs (e.g.,
13               beach closings, evidence of floatables wash-up, fish kills, and sediment accumulation).

14
15           Monitoring as part of the NMC is not intended to be extensive or costly. Implementation
16     is expected to entail collection of  existing information from relevant agencies about the  CSS,

17     CSOs, and.the receiving water body, as well as preliminary investigation activities, such as field
18      inspections and simple measurements using chalk boards, bottle boards, and block tests.   The

19     information and data collected will be used to establish a baseline of existing conditions for
20     evaluating the efficacy of the technology-based controls and to develop the LTCP (as described
21      in the Section 2.12}.
22

23            Data analysis and field inspection activities also support implementation of several other
24      NMC:

25
26            •  Proper  operation-   and  regular  maintenance  programs   for  the  sewer
27               system—Characterization of the CSS will support the evaluation of the effectiveness
28               of current operation and maintenance (O&M) programs and help identify areas within
29               the CSS that need repair.
30
31            •  Maximum use of the collection system for storage—Information gained during field
32               inspections, such as the system topography (e.g., location of any steep slopes) and the
33               .need for regulator or pump adjustments, can assist in identifying locations where
34               minor modifications to the CSS can increase in-system storage.
35
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                 Review and modification ofpretreatment requirements to assure CSO impacts an
                 minimized—Preticalanejti. program information and existing monitoring data will
                 support assessment of the impacts of nondomestic discharges on CSOs.
                 Control of solids and floatable materials in CSOs—Existing  information about
                 receiving water impacts and observations made during field inspections of the CSS
                 will help  determine the extent of solid and  floatable materials present and  the
                 effectiveness of any controls installed.
                 Dry weather overflows—Field inspections will assess the presence of dry weather
                 overflows, the conditions under which they occur, and the effectiveness of any control
                 measures in place.
  I-            Because specific NMC implementation requirements will be embodied hi a permit or other
  5     enforceable mechanism that is developed on a site-specific basis, the permittee should coordinate
  6     NMC implementation with the NPDES permitting authority on an ongoing basis.
 7
 8     2.1.2  Long-Term Control Plan Development
 .9  '
 !Q            The CSO Control  Policy recommends that a Phase I permit require the permittee to
 21     develop and submit an LTCP mat, when implemented, win ultimately result hi compliance with
22     CWA  requirements.   The  permittee  should use either the presumption approach or the
23     demonstration approach hi developing an LTCP that will provide for WQS attainment The
24     permittee  should  evaluate the data and  information  obtained  through  the. initial system
25     characterization to determine which approach  is more  appropriate based on site-specific
26     conditions. Generally, the demonstration approach would be selected when me permittee thinks
27     sufficient data are available to "demonstrate" mat a proposed LTCP is adequate to meet the water
28     quality-based requirements of the CWA.  If sufficient  data are not  available and cannot be
29     developed to allow use of the demonstration approach, and the permit writer believes it is likely
30     that implementation of a control program mat meets certain performance criteria will result in
31     attainment of CWA requirements, me permittee would use the presumption approach.  The two
32     approaches are discussed hi more detail below and in Chapters 7 and 8.
33
34   .         Demonstration  Approach.    Under  the demonstration approach,  the permittee
35     demonstrates the  adequacy  of its CSO control program to meet  the water quality-based

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   1      requirements of the CWA.   As  stated in the  CSO Control Policy, the permittee should
   2      demonstrate each of the following:
   3

  4            "i.    The planned control program is adequate to meet WQS and protect designated
  5                  uses, unless WQS or uses cannot be met as a result  of natural background
  6                  conditions or pollution sources other than CSOs;
  7
  8            iL     The CSO  discharges remaining after implementation of the planned control
  9                  program will not preclude the attainment  of WQS or the receiving waters'
 10                  designated uses or contribute to their impairment.  Where WQJS and designated
 11                  uses are not met in part because of natural background  conditions or pollution
 12                  source? other than CSOs, a total maximum daily load,  including a wasteload
 13                  allocation  and a load allocation, or other means, should be used to apportion
 14                  pollutant loads:           •  '     '                •                  •   '
 15                    •                                                  '
 16            «••    The planned control program will provide the maximum pollution reduction
 17        •      •    benefits reasonably attainable; and
 18
 19            iv.     The planned control program, is designed to. allow cost effective expansion or cost
 20                  effective retrofitting if additional controls are subsequently determined to be-
 21                  necessary 10 meet WQS or designated uses.
22

23     Generally, monitoring and modeling activities will be integral to successfully demonstrating that
24     these criteria have been met
25           .'

26           Presumption Approach This approach is based on the presumption that WQS will be
27     attained with implementation of an LTCP mat provides for certain performance-based controls.
28     For die presumption approach, die CSO Control Policy states mat:
29                              .
                                                                   •.                     •
30           "A programihat meets any of the criteria listed below would be presumed to provide an
31            adequate level of control  to meet Out water quality-based requirements of the CWA.
32           provided Out permitting authority determines that such presumption is reasonable in light
33            of the data and analysis conducted in the characterization, monitoring, and modeling of
34           the system and the consideration of sensitive areas described above.  These criteria are
35            provided because data and modeling  of wet weather events often do not give a clear
36            picture of the level of CSO controls necessary to protect WQS.
37
38            L      No more than an average of four overflow events per year...
39
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 1            U.     The elimination or the capture for treatment of no kss than 85% by volume of the
1 2                  combined sewage collected in the CSS during precipitation events on a system-
 's                  -wide annual average basis...
 4
 S            Hi.    The elimination or removal of no less then the mass of pollutants, identified as
 6                  causing water quality impairment.., for the volumes that would be eliminated or
 1                  captured for treatment under paragraph «..." (ILCAa.)

 8

 9     Monitoring and modeling activities  are also  likely to be necessary in order to obtain the

10     permitting authority's approval for using the presumption approach.

11
12            Whether the  LTCP ultimately reflects the demonstration approach or the presumption

13     approach, it should contain the same elements, as identified in the CSO Control Policy:

14

IS            •   Characterization, monitoring, and modeling of the combined sewer system
16
17            •   Public participation
18
19            •   Consideration of sensitive areas
20
21            •   Evaluation of alternatives
22
23            •   Cost/performance considerations
24
25            •   Operational plan
26
27            •*  Maximization of treatment at the POTW treatment plant
28
29            •   Implementation schedule
30
31            •   Post-construction compliance monitoring program.

32
33            Of these elements, the first and last are directly linked to monitoring and modeling. •

34
35            Characterization, monitoring, and modeling of the combined sewer system
36            The first step in developing an LTCP involves characterization, monitoring, and modeling
      *                             »
37     of the combined sewer system.  The CSO Control Policy states:

38


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  1            "In order to design a CSO control plan adequate to meet the requirements of the
  2            CWA, a permittee should have a thorough understanding of its sewer system, the
  3            response of the system to various precipitation events, the characteristics of the
  4            overflows, and the water quality impacts that result from CSOs.  The permittee
  5            should adequately characterize through monitoring, modeling, and other means
  6            as appropriate, for a range of storm events, the response of its sewer system to
  7            wet weather events including  the number, location and frequency  of CSOs,
  8            volume, concentration and mass of pollutants discharged and the impacts of the
  9            CSOs on the receiving waters and their designated uses.  The permittee may need
 10            to consider information on  the contribution and importance of other pollution
 11             sources in order to develop a final plan designed to meet water quality standards.
 12            The purpose of the system characterization, monitoring and modeling program
 13             initially is to assist the permittee in developing appropriate measures to implement
 14            the nine minimum controls and, $ necessary, to support development of the
 IS             long-term CSO control plan. The monitoring and modeling data also wUI be used
 16             to evaluate the expected effectiveness ofbotii die nine minimum controls and, if
 17             necessary, the long-term CSO controls, to meet WQS." (ILC.1)
 18

 19             Characterization, monitoring, and modeling of the combined sewer system can be broken
 20      into the following elements:
 21
                                     i
 22             1.  Examination of rainfall records and other existing data
 23     .        2.  Characterization of the CSS
                                   *               t
 24             3..  Monitoring-of CSOs and receiving water
 25            4.  Modeling of the CSS and receiving water.
 26

 27            Analysis of existing data should include an examination of rainfall records. This analysis,
 28      as well as information from field[inspections and simple measurements using chalk boards, bottle
29      boards, and block testsT provide the basis for the preliminary gysteni eha.raetgriza*iq'n This initial

30      characterization of die system (described in more detail in Chapter 3) should identify die number,
31      location, and frequency  of overflows and clarify their relationship to  sensitive areas, pollution
32      sources within  die collection system (e.g., indirect discharges from nondomestic sources), and
33      other pollution sources  discharging to  the receiving water (e.g., direct industrial discharges,
34      POTWs, storm water discharges).
35
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 1            Since some of these activities are also conducted as part of NMC implementation, the
 2      LTCP should be developed in coordination with NMC implementation efforts.  Ultimately,
 3      because the LTCP is based on more detailed knowledge of the CSS and receiving waters than
 4      is necessary to implement the NMC, the extent of monitoring and  modeling for LTCP
 5      development is expected to be more sophisticated.
 6
 7            Examination of rainfall data, field inspections and  simple measurements, and other
 8      preliminary characterization activities will serve as the basis for the development of a cost-
 9      effective monitoring and modeling plan (discussed in Chapter 4). The monitoring and modeling
10      plan should be designed to provide the information and data needed to develop and evaluate CSO
11      control alternatives and to select the most cost-effective CSO controls.
12
13            Chapter 4 provides an overview of the development of a monitoring and modeling plan.
14     Chapters 5 and 7 discuss CSS monitoring and modeling, and Chapters 6 and 8 discuss receiving
15      water monitoring and modeling, respectively, ft is important to remember that the monitoring
16     and modeling plan should be based on the site-specific conditions of. the CSS and receiving
17     water. Therefore the permittee should, on an ongoing basis, consult and coordinate these efforts
18     with the NPDES permitting authority.
19
20            Implementation of the monitoring and modeling plan should enable the permittee to
21     predict the CSS's response to various wet weather events and evaluate CSO impacts on receiving
22     waters for alternative control strategies.  Evaluation of CSO  control alternatives is discussed in
23     Combined Sewer Overflows - Guidance for Long Term Control Plan (EPA, 1995a).
 24
 25            Based on the evaluation of control strategies, the permittee, in  coordination  with the
 26     public, the NPDES permitting authority, and the State WQS authority, should select the most
 27     cost-effective CSO controls needed to provide for the attainment of WQS. Specific conditions
 28     relating to implementation of these CSO controls will be incorporated into the NPDES permit
 29      as described in Section 2.1.4.
 30
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  1            Post-construction compliance monitoring program
  2            Not only should the LTCP contain a characterization, monitoring, and modeling plan
  3     adequate to evaluate CSO controls, but it should also contain a post-construction compliance
  4     monitoring plan to ascertain the effectiveness of long-term CSO controls in achieving compliance
  5     with CWA requirements. Generally, post-construction compliance monitoring will not occur until
  6     after development and at least partial implementation of the LTCP.  Nevertheless, the permittee
  7     should consider its needs for post-construction monitoring as its, monitoring and modeling plan
  8     develops. The development of a post-construction compliance monitoring program is discussed
  9     in Section 2.1.4 and Chapter 4.
10   .
11     243   Monitoring and Modeling During Phase I
12
13            The CSO Control Policy recommends that the Phase I permit require permittees to:
14
IS            • - Immediately implement  BAT/BCT, which at a mmmnim should include the nine
16              minimum controls, as determined on a BPJ basis by the.NPDES permitting authority
17
18            •  Submit appropriate.docnmentation on NMC implementation activities within two years
19              of permit issuance/modification but no later man January 1,1997
20
21            •  Comply with applicable WQS expressed as narrative limitations
22                                       -           .
23            •  Develop and submit an LTCP as soon as practicable, but generally within 2 years
24              after permit issuance/modification.
25                                  .                   ...
26            The permittee should not  view  NMC  implementation  and LTCP development  as
27     independent activities, but rattier as related components in the CSO control planning process.
28     Implementation of the NMC establishes the baseline conditions upon which the LTCP will  be
29     developed.
30                                                            .
31            In many cases, the LTCP will be developed concurrent with NMC implementation.  As
32     described in Sections 2.1.1 and 2.1.2, both efforts require the permittee to develop a thorough
33     understanding of the CSS.  For example, monitoring done  as part of the NMC  to effectively
34     characterize CSO impacts and the efficacy of CSO controls should provide a base of information

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  1     and data that the permittee can use in conducting more thorough characterization, monitoring, and

  2     modeling activities for LTCP implementation.

  3

  4           Therefore, the characterization activities needed to implement the NMC and develop the

  5     LTCP should be a single coordinated effort

  6

  7     2.1.4  Monitoring and Modeling During Phase n
  8                                                       .
  9           The CSO Control Policy recommends that a Phase n permit include:

10

11           *-  Requirements to implement technology-based controls including the NMC on a BPJ,
12          •     basis      .       '                '              .
13
14           •   A narrative requirement that selected CSO controls be implemented, operated,  and
IS               maintained as described in the LTCP
16                                           -               -              -
17 .          •   Water quality-based effluent limits expressed in the form of numeric performance
18               standards
19
20           •   Requirements to implement the post-construction compliance .monitoring program
21
22           • ~ Requirements to reassess CSOs to sensitive areas
23
24           •   Requirements for maximizing the treatment of wet weather flows at the  treatment
25               plant
26
27           •   A reopener clause authorizing permit modifications if CSO controls fail to meet WQS
28               or protect designated uses.
29
30     The post-construction compliance monitoring program should provide sufficient data to determine
31     the effectiveness of CSO controls in attaining WQS. The frequency and type of monitoring in
32     the program will be site-specific. In most cases, some monitoring will be conducted during the
33     constructionAmplementation period to evaluate the effectiveness of the long-term CSO controls.
34     In some cases, however, it may be appropriate to delay implementation of the post-construction
35     monitoring program until construction is  well underway or completed
36
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   1            The post-construction compliance monitoring program may  also include appropriate
   2      measures for determining the success of the CSO control program. Measures of success, which
   3      are also discussed in Section 2.3, can address both CSO flow and quality issues. For example,
   4      flow-related measures could include the number of dry weather overflows or CSO outfalls
   5      eliminated, and reductions in the frequency and volume of CSOs. Quality-related measures could
   6      include decreases hi loadings of conventional and toxic pollutants in CSOs.  Environmental
   7      measures focus on human and ecosystem health trends such as reduced beach, closures or fish
   8      kills, improved biological integrity indices, and the full support of designated uses in receiving
   9      water bodies.
 10                                                      .             v   -.  .
                                 •         it  •                               .
 II     22    MONITORING AND MODELING AND THE WATERSHED APPROACH
 12                                                      ..
 13            The watershed approach represents EPA's  holistic approach to understanding and
 14     addressing all surface water, ground water, and habitat strcssors within a geographically defined
 15     area, instead of addressing individual pollutant sources in isolation,.  It serves as the basis for
 16     place-based solutions, to ecosystem protection.                           ,'   '•'
 17                               ;                               .
 18            EPA's watershed approach is based on a few mam principles:
 19
 20            •  Geographic Focus—Activities are focused on specific drainage areas   - •
 21                                .                                ...
 22            •  Environmental Objectives and Strong Science/Data—Using  strong scientific tools
 23              and sound data, the priority problems are characterized; environmental objectives are
• 24              determined, action-plans- anr developed  and implemented, and effectiveness  is
 25              evaluated
 26
 27            •  Establishment of Partnerships—Management teams representing various interests
 28              (e.g., regulatory agencies, industry, concerned citizens) are formed to jointly evaluate
 29              watershed management decisions
 30                   .
 31            •  Coordinated Priority Setting and Integrated Solutions—Using a coordinated approach
 32              across  relevant organizations, priorities can be set and integrated actions taken that
 33              consider all environmental issues hi the  context of various water programs and
 34              resource limitations.
 35
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 1            Point and nonpoint source programs, the drinking water program, and other surface and.
 2      ground water programs are all integrated into the watershed approach.  Under the watershed
 3      approach, these programs address watershed problems in an effective and cooperative fashion.
 4      The CSO Policy encourages NPDES permitting authorities to evaluate CSO control needs on a
 5      watershed basis and coordinate CSO control program efforts with the efforts of other point and
 6      nonpoint source control activities .within the watershed.
 7   •
 8            The application of the watershed approach to a CSO control program is particularly timely
 9      and appropriate since the ultimate goal of the CSO Control Policy is the development of long-
10      term CSO controls that will provide for toe-attainment of WQS.  Since pollution sources other
11      than CSOs are likely to be discharging to the receiving water and affecting whether WQS are
12      attained, the permittee needs to consider and understand these sources in developing its LTCP.
13      The permittee should compile existing information and monitoring data on these sources, from
14     the NPDES permitting authority,  Stale  watershed personnel or  even other permittees or
IS      dischargers within the watershed. If other permittees within the watershed are also developing
16     long-term CSO control plans, an opportunity exists for these permittees to pursue a coordinated
17     and cooperative approach to CSO control planning.
18                   ..                                      .
19            If the  permittee determines during-its. LTCP development  that WQS cannot be met
20     because of other pollution sources within the watershed, a total maximum daily load (TMDL),
21     including wasteload allocation (WLA) and load allocation (LA), may be necessary to apportion
22     loads  among dischargers. Several EPA publications provide TMDL guidance (see References).
23     In many cases a TMDL may  not have been developed for the permittee's watershed.  In these
24     cases, the monitoring and modeling conducted as part of the development and implementation
25     of long-term CSO controls will support an assessment of water quality and could support me
26     development of a TMDL.
27
28            Use of the comprehensive watershed approach during long-term CSO planning will result
 29     in a more cost-effective program for achieving WQS in a watershed.
 30
 31
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  1     23    MEASURES OF SUCCESS
  2
  3            Before developing a monitoring plan for characterizing the CSS and determining post-

  4     construction compliance,  the permittee should determine appropriate measures of success based

  5     on site-specific conditions.  Measures of success are objective, measurable, and quantifiable

  6     indicators that illustrate trends and results over time. Measures of success generally fall into four

  7     categories:

  8            •  Administrative measures that track programmatic activities;
  9
 10            •  End-of-pipe measures that show trends in the discharge of CSS flows to the receiving
 11               water body, such as reduction of pollutant loadings, the frequency of CSOs, and the
 12              duration of CSOs;
 13
 14            •  Receiving water body measures that show trends of the conditions in the water body
 15               which receives the CSOs, such as trends in dissolved oxygen levels and sediment
 16               oxygen  demand;
'17
 18             •  Ecological, human health, and use measures that show trends in conditions relating
 19               to the use of the water body, its effect on the health of the population that uses the
 20               water body, and the health of the organisms that reside in the water body, including
 21               beach closures, attainment of designated  uses, habitat  improvements,  and fish
 22               consumption advisories. Such measures would be coordinated on a watershed basis
 23               as appropriate.
 24

 25      EPA's experience has shown that measures of success should include a balanced mix of measures
 26      from each of the four categories.
 27

 28            As municipalities begin to collect data and information on CSOs and CSO impacts, they
 29      have an important opportunity to establish a solid understanding of the "baseline" conditions and
 30      to consider what information and data are necessary to evaluate and demonstrate the results of
 31      CSO control.  The permittee should choose measures of success that can be used to indicate
 32      reductions in CSOs and their effects.  Municipalities and NPDES permitting authorities should

 33      agree early in the  planning  stages on the data  and information that will  be used to measure
 34      success.  (Measures of success  for the CSO program  are  discussed in Combined Sewer
 35      Overflows-Guidance for Long-Term Control Plan. (EPA, 1995a) and Performance Measures for
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  1     the National CSO Control Program (AMSA, 1996)).  The permittee should consider these
  2     measures of success when determining which parameters to include in its monitoring plan.
  3                                             '                     •
  4     2.4    COORDINATION WITH OTHER WET WEATHER MONITORING AND
  5           MODELING PROGRAMS
  6
  7           The permittee may be subject to monitoring requirements for other regulated wet weather
  8     discharges, such as storm water, in addition to monitoring activities for a CSO control program.
  9     Due to the unpredictability of wet weather discharges, monitoring of such discharges presents
 10     challenges  similar to those for monitoring  CSOs.  The permittee should  coordinate all wet
 11      weather monitoring  efforts.  Developing one monitoring and modeling  program for all wet
 12     weather programs will enable the permittee  to establish a clear set of priorities for monitoring
 13      and modeling activities.
 14
 15      15   REVIEW AND REVISION OF WATER QUALITY STANDARDS
 16   -
 17           A key principle of the CSO Control Policy is the review and revision, as appropriate, of
 18      WQS and  their implementation procedures to reflect the site-specific wet weather impacts of
 19      CSOs. Review and revision of WQS should be conducted concurrent with the development of
20      the LTCP to ensure that the long-term CSO controls will be sufficient to provide for the
21      attainment of applicable WQS.
22
23           The WQS program contains several types of mechanisms that could potentially be used
24     to address site-specific factors such as wet weather conditions.  These include the following:
25
26           •  Adopting partial uses to reflect situations where a significant storm event precludes
27              the use from occurring
28
29           •  Adopting seasonal uses to reflect that certain uses do not occur during certain seasons
30              (e.g., swimming does not occur in winter)
31
32           •  Defining a use with greater specificity (e.g., warm-water fishery in place of aquatic
33              life protection)
34
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  1           •  Granting a temporary variance to a specific discharger in cases where maintaining
  2              existing standards for other dischargers is preferable to downgrading WQS.
  3
  4           These potential  revisions  are described in detail in the  Water Quality  Standards
  5     Handbook, Second Edition (EPA, 1994).
                                                       «
  6
  7           Reviewing and revising WQS requires the collection of information and data to support
  8     the proposed revision. In general, a use attainability analysis (UAA) is required to support a
  9     proposed WQS revision.  The process for conducting UAAs for receiving waters has been
 10     described in various EPA publications (see References).
 11
 12           The information and data collected during LTCP development could potentially be used
 13      to support a UAA for a proposed revision to WQS to reflect wet weather conditions. Thus, it
 14      is important for the permittee, NPDES permitting authority, State WQS authority, and EPA
 15      Regional offices to agree on the data, information and analyses that are necessary to support the
 16      development of the long-term CSO controls as well as  the review of applicable WQS and
 17      implementation procedures, if appropriate.
 18
 19      2.6    OTHER ENTITIES INVOLVED IN DEVELOPING AND IMPLEMENTING
20            THE MONITORING AND MODELING PROGRAM
21
22            Development and implementation of a CSO monitoring and modeling program should not
23      be solely  the permittee's responsibility.   Development  of a  successful and cost-effective
24      monitoring and modeling program should  reflect the coordinated efforts of a team that includes
25      the NPDES permitting authority, State WQS authority, State watershed personnel, EPA or State
26      monitoring personnel, and any other appropriate entities.
27
28            NPDES Permitting Authority
29            The NPDES permitting authority should:
30
              •  Develop appropriate system characterization, monitoring, and modeling requirements
                 for NMC implementation and LTCP development (in a Phase I permit),  LTCP
33               implementation (in a Phase n permit) and post-construction (Phase n and ongoing)
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  1            •   Coordinate with the permittee to ensure that the monitoring requirements in the permit
  2               are appropriately site-specific
  3
  4            •   Assist in compiling relevant existing information, monitoring data, and studies at the
  5               State and/or EPA Regional level
  6
  7            •   Coordinate the permittee's CSO monitoring and modeling efforts with monitoring and
  8               modeling efforts of other permittees within the watershed
  9
 10            *   Coordinate the team review of the monitoring and modeling plan, monitoring and
 11               modeling data  and results, and other components of the LTCP. To ensure team
 12               review  of the monitoring  and  modeling  plan, the  permitting  authority could
 13               recommend that the plan include a signature page for endorsement by all the team
 14               members after their review.

 15

 16           State WQS Authority

 17           The State WQS authority should:

 18

 19           •   Provide input on the review and possible revision of WQS including conduct of a use
20               attainability analysis
21
22           •   Assist in compiling existing State information, monitoring data, and studies for the
23                receiving water body
24
25            •   Ensure that the permittee's monitoring and  modeling efforts  are coordinated and
26                integrated with  ongoing State monitoring programs
27
28            •   Evaluate any special monitoring activities such as biological testing, sediment testing,
29                and whole effluent toxicity testing.
30

31            State Watershed Personnel

32            State watershed personnel should:
33

34            •  Ensure that the permittee's monitoring  activities  are  coordinated with ongoing
35               watershed monitoring programs
36
37            •  Assist in compiling existing State information, monitoring data, and studies for the
38               receiving water body
39
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  1            •  Ensure the permittee's monitoring and modeling efforts are integrated with TMDL
  2               application or development.
  3
  4            EPA/State Monitoring Personnel
  5            EPA and State monitoring personnel should:
  6
  7            •  Provide  technical support and  reference material on monitoring  techniques and
  8               equipment
  9
 10            •  Assist in compiling relevant existing monitoring data and studies for the receiving
 11               water body
 12
 13            • - Provide information on available models and the monitoring data needed as model
 14               inputs
 15
 16            •  Assist in the evaluation and selection of appropriate models.
 17
 18            The public should also participate in development and implementation of the system
 19     characterization activities and the monitoring and modeling program. Throughout the LTCP
20     development process, the public should have the opportunity to review and provide comments
21     on the results of the system characterization, monitoring, and modeling activities that are leading
22     up to the selection of long-term CSO controls.
23
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  i                                        CHAPTERS
  2
  3        INITIAL SYSTEM CHARACTERIZATION - EXISTING DATA ANALYSES AND
  4                                 FIELD INVESTIGATIONS
  5
  6            As explained in Chapter 2, implementation of the nine minimum controls (NMC) and
  7     development of a long-term control plan (LTCP) requires a thorough characterization of the CSS.
  8     Accurate information on CSS design, CSS responses to changing flows, chemical characteristics
  9     of CSOs, and biological and chemical characteristics of receiving waters is critical in identifying
10   .  CSO impacts and the projected efficacy of proposed CSO controls. Before in-depth monitoring
11     and modeling efforts begin, however,  the permittee should assemble as much information as
12     possible from existing data sources and preliminary field investigations.   Such preliminary
13     activities will contribute to a baseline characterization of the CSS and its receiving water and
14     help focus the monitoring and modeling plan.
15
16             The primary objectives of the  existing data analyses and field investigations are:
17
18           •   To determine the current level of understanding and knowledge of the  CSS and
19               receiving water
20
21           •   To assess the design and current operating condition of the CSS
22
23           •   To identify CSO impacts on receiving waters
24
25           •   To identify the data that need to be collected through the monitoring and  modeling
26               program
27
28 ^          •   To assist in NMC implementation and documentation.
29
30           The activities required to meet these objectives will vary widely from system to system.
31     Many permittees have  already  made significant progress in conducting  initial system
32     characterizations under the 1989 CSO Strategy or through other efforts. For example, permittees
33     that have  begun NMC implementation probably have compiled  a substantial amount of
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  1     information on their CSSs. Studies by EPA, State agencies, or other organizations may provide
  2     substantial information and data for the receiving water characterization.
  3

  4            This chapter generally describes the following types of activities conducted during the
  5     initial system characterization:
  6

  7            •  Physical Characterization of CSS—identification and description of all functional
  8              elements  of the CSS, including sources discharging into the CSS, as well as the
  9              delineation of the CSS drainage areas, analysis of rainfall data throughout the drainage
 10              area, identification of all CSO outfalls, and preliminary CSS hydraulic analyses.

 12            •  Characterization  of Combined  Sewage and CSOs—analysis of existing data to
 13               determine volume, chemical characteristics, and pollutant loadings of CSOs
 14                                             ^
 15             •  Characterization of Receiving Waters—identification  of the designated uses and
 16               current status of the receiving waters affected by CSOs, chemical characterization of
 17               those receiving waters, and identification of biological receptors potentially impacted
 18               by CSOs.
 19

 20            The permittee should consult with the NPDES permitting authority and the review team
 21      (see Section 2.6)  while  reviewing the results from the initial system characterization and in
 22      preparation for development of the monitoring and modeling plan (Chapter 4).  Performing and
 23      documenting initial characterization activities may help satisfy certain requirements for NMC
 24      implementation and documentation. Thus, it is essential that the permittee coordinate with the
 25      NPDES permitting authority on an ongoing basis throughout the initial characterization process.
 26

 27      3.1    PHYSICAL  CHARACTERIZATION OF CSS
 28
 29      3.1.1   Review Historical Information
 30
 31            For the first part of the physical characterization, the permittee should compile, catalogue,
 32      and review existing information on the design and construction of the CSS to clarify and evaluate
 33      how the CSS operates, particularly in response to wet weather events.  The permittee should
34      compile, for the entire CSS, information  on the contributing drainage areas, the location and
35      capacity of the POTW and interceptor network, the location and operation of flow regulating
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  1     structures,  the location  of all known or suspected CSO outfalls,  and the general hydraulic

  2     characteristics of the system.  Historical information is often available from the following

  3     sources:
  4

  5            •   Sewer Maps  of Suitable Scale—Sewer maps  define the  pipe network of the sewer
  6               system and may  indicate  the  drainage areas  that contribute to each CSO outfall.
  7               Ideally, they should include the combined, separate sanitary, and separate storm sewer
  8               systems.  Data provided from these maps, such as the invert elevations, can be used
  9               to calculate individual pipe capacities and to develop detailed hydraulic  models.
 10               Sewer maps should be field checked because field conditions may differ significantly
 11               from the plans (see System Field Investigations, Section 3.1.3).
 12
 13            •   Topographic Maps—The U.S. Geological Survey (USGS) provides topographic maps,
 14               usually with  10-foot contour intervals.  The local municipality or planning agency
 15               may have prepared topographic maps with finer contour intervals, which may be more
 16               useful in identifying drainage areas contributing to CSOs.
 17
 18            •   Aerial Photographs—When overlaid with sewer maps and topographic maps, aerial
 19               photos may aid in identifying land uses  in  the drainage areas.  Local  planning
20               agencies, past land use  studies, or State Departments of Transportation may have
21                aerial  photographs suitable for the initial characterization.
22
23             •   Diversion  Structure  Drawings—Drawings of CSS structures, in plan and section
24               view,  indicate how the structures operate, how they should be monitored, and how
25                they could be altered to facilitate monitoring or improve flow control.
26
27             •   Rainfall Data—Rainfall  data are one of the most important and useful types of data
28                collected  during  the initial  system characterization.   Reliable  rainfall data are
29                necessary to understand the hydraulic response of the CSS and, where applicable, to
30               model this response.  Sources of data  may  include long-term precipitation data
31                collected from a weather station within or outside the CSS drainage basin, or  short-
32                term, site-specific precipitation data from stations within  the drainage basin or sub-
33                basins.
34
35              ,  Long-term rainfall data collected within the drainage basin provide the best record of
36                precipitation within the  system and hence have the greatest value  in correlating
37                historic overflow events with precipitation events and in predicting the likelihood of
38                wet weather events of varying  intensities.  If such data are not available, however,
39                both long-term regional and short-term local data may be used.
40
41                National rainfall data are  available from the National Weather Service, which operates
42              .  thousands  of weather  monitoring stations throughout  the  country.   The  local
43                municipality, airports, universities, or other State or Federal facilities can also provide
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i
2
3
                  rainfall  data.  The National  Oceanic  and Atmospheric Administration's  (NOAA)
                  National Climatic Data Center (NCDQ's Climate Services Branch is responsible for
                  collecting precipitation data. Data on hourly, daily, and monthly precipitation for each
  4               monitoring station (with latitude and longitude) can be obtained on computer diskette,
  5               microfiche, or hard copy by calling (704) 259-0682, or by writing to NCDC, Climate
  6               Services Branch, The Federal Building, Asheville,NC 28071-2733. The NCDC also
  7               provides a computer program  called SYNOP  for  data analysis.  Additionally,
  8               permittees with few or no rain gages located within the system drainage basin may
  9               want to  install  one or more gages early in the CSO control planning process. The
 10               collection and analysis of rainfall data are discussed in Chapters 4 and 5.

 12            Other Sources of Data

 13            A variety of other historical data  sources may  be used in completing the  physical
 14     characterization of a CSS. As-built plans and documentation of system modifications can provide
 15     reliable information on  structure location and dimensions.   Similarly, any recent surveys and
 16     studies conducted on the  system can verify  or enhance sewer map information.  Additional
 17     information may be available from:
 18

 19           •  As-built  plans

 20           •  Documentation of system modifications
 21            •  Treatment plant upgrade reports
 22            •  Other related  surveys and reports
 23            •  Design specifications
 24            •  Infiltration/inflow (W) studies

 25            •  Sewer system evaluation studies  (SSES)
 26            •  Storm water master plans
 27            •  Section 208 areawide waste treatment plans
 28            •  Section 201 facility plans.
 29

 30     The availability of these sources of information varies widely among permittees.  Collection
 31     system operations and maintenance personnel can be invaluable in determining the existence and
32     location of such data, as  well as providing system knowledge and insight.
33
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  1     3.1.2   Study Area Mapping
  2
  3            Using the historical data, the permittee should develop a map of the CSS, including the

  4     drainage basin of combined sewer areas and separate storm sewer areas.  Larger systems will find

  5     it useful to map sub-basins for each regulating structure and discharge point. This map will be

  6     used for analyzing system flow directions and interconnections, analyzing land use and runoff

  7     parameters, locating monitoring networks, and developing model inputs.  The map can  also be

  8     a valuable planning tool in identifying areas of special concern in the CSS and  coordinating

  9     further investigation efforts and logistics.  The map should  be modified as necessary to reflect

 10     additional CSS and receiving water information and data (such as the  locations of other point
 11      source  discharges to receiving- water, the location of sensitive areas, and planned or existing
 12     monitoring locations), when it becomes available.

 13

 14            The completed map should include the following information:
 15
 16            •  Delineation of contributing drainage areas
 17
 18            •  General land uses
 19
20            •  POTW and interceptor network
21
22            •  Main line locations and sizes
23
24            •  Diversion structures
25
26            •  CSO outfalls
27
28            •  Access points (e.g., manholes;  flat, open areas accessible for sampling)
29
30            •  Pump stations
31
32            •  Rain gages
33
34            •  Existing monitoring locations
35
36            •  USGS gage stations
37
38            •  Receiving water bodies
39
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                         WORKING DRAFT; Do NOT CITE OR QUOTE
   1            •  Sensitive areas  (including drinking water intakes, downstream beaches, and other
   2               public access areas)
   3
   4            •  Soil types
   5
   6            •  Ground water flow
   7
   8            •  Other point source discharges such as industrial discharges and separate storm water
   9               system discharges
 10
 11            •  Existing treatment facilities.
 12
 13           II may te useful to generate two or more maps with different scales, such as a coarse-

 14     scale map (e.g., 7.5-minute USGS map) for land uses and other watershed scale information and

 15     a finer-scale map (e.g., 1" = 200' or 1" = 400') for sewer system details.  In some cases, a

 16     Computer -Aided Design (CAD) or Geographic Information System (GIS) approach can be used.

 17     Some advanced sewer models can draw information directly from CAD files, eliminating the

 18     duplication  of entering data into the model.   A municipality's planning department may be

 19     another useful source for the hardware, software, and data needed for such mapping efforts.

 20

 21      3.13  System Field Investigations
 22
 23            Before a monitoring and modeling program is developed, historical information on a CSS

 24      will generally need to be supplemented with field observations of the system to verify findings

 25      or fill data gaps.  For example, visual inspection of regulator chambers and overflow structures

 26      during dry  and wet weather verifies information included in drawings and provides data on

 27      current conditions.  Further, it is necessary to verify that gates or flow diversion structures

 28      operate correctly so that ensuing monitoring programs collect information representative of the

 29      expected behavior of the system.

 30

 31             In general, field inspection activities may be used to:

 32

 33            •  Verify the design and as-built drawings

34            •  • Locate and clarify portions of the system not shown on as-built drawings

35            •  Identify dry weather overflows


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  1            •   Identify locations of CSO outfalls
  2            •   Identify non-standard engineering or construction practices
  3            •   Examine the function of flow regulating equipment
  4            •   Identify areas in need of maintenance, repair, or replacement.
  5
  6     Several references provide useful descriptions of system evaluations (WPCF, 1989).
  7
  8             Although generally beyond  the scope of a small system characterization effort, in-line
  9     TV cameras can be used to survey the system, locate connections, and identify needed repairs.
 10     Such surveys may have been done as part of an infiltration/inflow study.  In-line inspection
 11      methods are also described in detail in WPCF (1989).
 12
 13            The field investigation may also involve preliminary collection of flow and depth data,
 14      which can support the CSS' flow monitoring and modeling activities later in the CSO planning
 15      process. Preliminary CSS flow and depth estimates can help answer the following questions:
 16
 17            •  How much rain causes an overflow at each outfall?
 18
 19            •  How many dry weather overflows occur? How frequently and at which outfall(s)?
20
21            •  Do surcharging or backwater effects occur in intercepting devices or flow diversion
22               structures?
23
24            •  How deep are the maximum flows at the flow diversion  structures for investigated
25               storms (i.e., are the maximum flows at a depth that, if slightly altered, would affect
26               whether a CSO occurs)?
27
28            A variety of simple  flow measurement techniques may be employed to  answer these
29     questions prior to development and implementation of monitoring and modeling plans. These
30     include:
31
32            •  Chalk Board—A chalk board is a simple depth-measuring device, generally placed
33               in a manhole. It consists of a vertical board  with a vertical chalk line drawn on it.
34               Sewer flow passing by the board washes away a portion  of the chalk line,  roughly

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1                indicating the maximum flow depth that occurred since the board was placed in the
  2                sewer.
  3
  4            •   Bottle Boards—A bottle board is a vertical board with a series of attached open
  5                bottles. As flow rises the bottles with openings below the maximum flow are filled.
  6                When the flow recedes the bottles remain full indicating the height of maximum flow
  7                (see Exhibit 5-6).
  8
  9      .      •   Block Tests—Block tests do not measure depth, but are used to detect the presence
 10                of an overflow. A block of wood or ottier float is placed atop the overflow weir. If
 11                an overflow occurs, it is washed off the weir indicating that the event took place.  The
 12                block can be tethered to the weir for retrieval.
 13

 14            These simple flow measurement techniques could also be considered as NMC measures
 15      for monitoring to characterize CSO impacts and  the efficacy of CSO controls. The permittee

 16      may wish  to discuss  this  with the permitting authority.   In some limited cases, automated
 17      continuous flow monitoring may be used.  These techniques are discussed with other CSS
 18      monitoring techniques in Chapter 5.
 19

20      3.1.4  Preliminary CSS Hydraulic Analysis
21
22            The physical characterization of the CSS should include a flow balance, using a schematic
23      diagram of the collection system like that in Exhibit 3-1. The schematic diagram, together with
24      the historical data review and supplemental field study, should enable the permittee to assign

25      typical flows and maximum capacities to various interceptors for non-surcharged flow conditions.
26      Flow capacities can be approximated from sewer maps or calculated from invert elevations. The
27      resulting values provide a preliminary estimate of system flows at peak capacity.  Calculations
28      of flow within intercepting devices  or flow diversion structures and flow .records  from the
29      treatment plant help in locating sections of the CSS. that limit the overall hydraulic capacity.
30
31
                      Note to reviewers:  If you do not think Exhibit 3-1 is useful,
                      please comment on how it can be improved.  If you find
                      another type of diagram more useful, submitting an example
                      with your comments would be helpful.
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      27.50
                            Exhibit 3-1. Flow Balance Diagram
                                  River
             — Outlet Sewer Hydraulic Capacity (MGD)

             — Sewer Service Area

             — Cumulative Dry Weather Row (MGD)

             — Cumulative Wet Weather Flow (MGD)

             —Total Row (MGD)


             — Inlet Sewer Hydraulic Capacity (MGD)
  * Cumulative flows » flows from the service area and service areas
  upstream in the collection system. Wet weather flow values are for
  the average of several sampled storm events.
                                         21.5
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  1            The preliminary hydraulic analysis, together with other physical characterization activities,
  2     will be useful in designing the CSS monitoring program. This preliminary analysis can help in
  3     determining likely CSO locations, the magnitude of rainfall events that result in CSOs, estimated
  4     CSO volumes, and potential control points.  Application of a hydraulic model may be useful in
  5     conducting the analysis.
  6
  7     3.2   CHARACTERIZATION OF COMBINED SEWAGE AND CSOS
  8
  9     3.2.1  Historical Data Review
 10
 11            As part of the initial system characterization, the permittee should review existing data
 12      to determine the pollutant characteristics of combined sewage during both dry and wet weather
 13      conditions, and, if possible, CSO pollutant loadings, to the receiving water. The purpose of this
 14      effort is to identify pollutants of concern in CSOs, their concentrations, and where possible, likely
 15      sources of such pollutants.  Together, these data will support decisions on what constituents
 16      should be monitored and where.  This is discussed in detail in Chapter 4.
 17
 18             The POTW's records can provide influent chemical and flow data for both dry weather
 19      and wet weather conditions.  Such data can be analyzed to address important questions, such as:
20
21            '   How do the influent volume, loads, and concentrations at the plant change during wet
22               weather?
23
24            •   What is the average concentration of parameters such as solids and BOD at the plant
25               during wet weather flow?
26
27            •   Which portions of the  CSS are contributing significant pollutant loadings?
28
29            •   Which pollutants are discharged by industrial users, particularly significant industrial
30               users?
31
32     For example,  data analysis could include plotting a plant inflow  time  series by storm  and
33     comparing it to a rainfall  time series plot for the same storm(s).
34
35

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  1            Potential sources of information for this analysis include:
  2
  3            •   General treatment plant operating data
  4            •   POTW discharge monitoring reports (DMRs)
  5            •   Treatment plant optimization studies
  6            •   Special'studies done as part of NPDES permit application
  7            •   Pretreatment program data
  8            •   Existing wet weather CSS sampling and analyses.
  9
 10            The permittee can potentially use National or Regional storm water data (e.g., NURP data)
 11     (U.S. EPA, 1983a) to  supplement its available data, although more recent localized data are
 12     preferred.  If approximate CSS flow volumes are known, approximate CSS pollutant loads can
 13     be estimated using POTW data, CSS flow volume, and assumed storm water concentration
 14     values.  However, assumed constant or event mean  concentration  values for storm water
 15     concentrations should be used with  reservation for  CSOs  since concentrations vary during a
 16     storm.
 17
 IS           In order to obtain recent and reliable characterization data, the permittee may need to
 19     conduct limited sampling at locations within the CSS as well as at CSO outfalls as part of the
20     initial system characterization.  Since this limited sampling is usually less cost-effective than
21      sampling done as part of the overall monitoring program, the permittee  should fully evaluate the
22     need for data before sampling for the initial characterization. Chapter 5 provides details on CSS
23     monitoring procedures.
24
25      322  Mapping
26
27            The permittee should plot existing characterization data for points within the CSS as well
28      as for CSO outfalls on the study map as appropriate. This will enable  the permittee to identify
29      areas where no data exist and areas with high concentrations of pollutants.
30
31

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   1     33    CHARACTERIZATION OF RECEIVING WATERS
  2
  3     33.1   Historical Data Review
  4
  5            The third part of the initial system characterization is to establish the status of each
  6     receiving water body impacted by CSOs. Using existing data and information, the permittee
  7     should attempt to answer the following types of questions:
  8
  9            •  Does the receiving water body contain sensitive areas (as defined by the CSO Control
 10              Policy)?
 11
 12           *  What  are the  applicable WQS  and is the receiving water body currently  attaining
 13              those WQS?
 14
 15           -Are there particular problems in the receiving water body attributable wholly or in
 16              part to CSOs?
 17
 18 .          •  What  are the  hydraulic characteristics 6f the receiving water body (e.g.,  average/
 19              maximum flow)?
 20
 21            •  What other sources of pollutants in the watershed are discharging to the receiving
 22              water body?
 23
 24            •  What is the receiving water quality upstream of the CSO outfalls?
 25
 26            •  What are die ecologic conditions and aesthetics of the receiving water body?
 27
 28     The following types of receiving water data will  help answer these questions:
 29
 30            •  Applicable State  WQS
 31            •   Flow characteristics
 32            •   Physiographic and bathymetric data
 33            •   Water quality data
 34            •   Sediment data
 35            •   Fisheries data
36            •   Benthos data
37            •   Biomonitoring results
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  1            •   Ecologic data (habitat, species diversity).
  2
  3            Permittees may already have collected receiving water data as part of other programs or
  4     studies. For example, the NPDES permit may require receiving water sampling upstream and
  5     downstream of the treatment plant outfall or the permittee may have performed special receiving
  6     water studies as part of its NPDES permit reissuance process. Receiving water data may also
  7     be obtained through consultation with the NPDES permitting authority, EPA Regional staff, State
  8     WQS personnel, and State watershed personnel, since the Clean Water Act requires States, and
  9     EPA (when States fail to do so), to generate and maintain data on certain water bodies within
 10     their jurisdictions.
 11
 12           The following reports may provide information useful for, characterizing a receiving water
 13     body:
 14
 15           •   Section 303(d) Lists—Under CWA section 303(d), EPA or delegated States identify
 16               and  establish total maximum daily  loads (TMDLs), for all waters that  have  not
 17               achieved water quality criteria for  designated  uses even after  implementation  of
 18               technology-based  and water quality-based controls.
 19
20           •   State 304(1) Lists—Under CWA section  3040), EPA or States  identified surface
21                waters adversely affected by toxic and conventional pollutants from point  and non-
22               point sources, with priority given to those surface waters adversely affected by point
23                sources of toxic pollutants.  This one-time effort was completed in 1990.
24
25            •   State 305(b) Reports—Under CWA section 305(b), States must report biennially on
26                the status of waters of the State with respect to water quality, including designated
27                beneficial uses, aquatic life, and causes/sources of nonattainment.
28
29       •     •   Section 319 State Assessment Reports—Under  CWA section  319,  States were
30                required to identify surface waters adversely affected by nonpoint sources of pollution,
31                in a one time effort following enactment of the 1987 CWA Amendments.
32
33            Generally, these information sources may be obtained from EPA or State offices or may
34     be accessed through EPA's Storage and Retrieval of  U.S. Waterways Parametric Data (STORET)
35     system, EPA's Water Quality System resident within STORET, or EPA's Water Body System
36     (WBS). Access to EPA mainframe data bases such as STORET and WBS, however, requires

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  1     user accounts and familiarity with SAS and other data base systems.  Further, these data bases
  2     might not include the particular water bodies being evaluated.  Therefore, the permittee should
  3     contact State officials prior to attempting to locate data on specific water bodies.
  4
  5           In addition, studies conducted under special programs and initiatives, enforcement actions,
  6     new permitting actions, and for other purposes may provide relevant data on receiving water
  7     flow, quality, and uses.  EPA and State personnel may also generally be  aware of studies
  8     conducted by other Federal organizations, such as the U.S. Fish and Wildlife Service,  the U.S.
  9     Army Corps of Engineers, the U.S. Geological Survey, and the National Biological Service, and
 10     other organizations such as The Nature Conservancy and formalized  volunteer groups.  Thus,
 11      permittees may save considerable time  and expense by consulting directly with these entities
 12      during the initial system characterization.
 13
 14            The  receiving water characterization should also  include evaluation of whether CSOs
 15      discharge to sensitive areas, which are a high priority for CSO elimination or control under the
 16      CSO Control Policy.  The  long-term CSO control plan  should prohibit new or significantly
 17      increased overflows  to sensitive areas and eliminate or relocate such'overflows wherever
 18      physically possible and economically achievable. (This is discussed in  more detail in Combined
 19      Sewer Overflows - Guidance for Long-Term Control Plan, EPA,  1995a).  Therefore, the
20      permittee should work with the NPDES permitting authority, the U.S. Fish and Wildlife Service,
21      and relevant State  agencies  to determine whether particular receiving water segments  may be
22      considered sensitive under the CSO Control Policy.
23
24           In addition to reviewing existing data, the permittee may wish to  conduct an observational
25      study of the receiving water body, noting differences in depth or width, tributaries, circulation
26      (for estuaries), point sources,  suspected nonpoint sources, plant growth, and other noticeable
27      features.  This information can be used later to define segments for a receiving water model.
28
29           To supplement the observational study, the permittee may consider limited chemical or
30      biological sampling of the receiving water.  Biocriteria or indices may be used in States  such as
31      Ohio that have systems  in place.   Biocriteria describe the biological integrity of  aquatic

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  1     communities in unimpaired waters for a particular designated aquatic life use. Biocriteria can

  2     be numerical values or narrative conditions and serve as a reference point since biological

  3     communities in the unimpaired waters represent the best attainable conditions (U.S. EPA, 1991 a).

  4

  5     3.3.2  Mapping
  6
  7           The permittee should include existing receiving water  characterization data on the study
                                                                                  •v.
  8     map as appropriate. This will permit visual identification of  areas for which no data exist,

  9     potential areas  of concern, and potential monitoring locations. GIS mapping can be used as an

 10     aid in this process. The map could include the following:

 11

 12           •  WQS classifications for receiving waters at discharge locations and for upstream and
 13               downstream reaches
 14
 15            •  Location of sensitive areas such as  contact recreation,  drinking water intakes,
 16               endangered species habitats, sensitive biological populations or habitats
 17
 18            •  Locations of  structures,  such  as weirs  and dams,  that can  affect pollutant
 19               concentrations in the receiving water
20
21            •  Locations of access points, such as bridges, that make convenient sampling sites.

22

23      3.4    IDENTIFY DATA GAPS
24
25            The final task of the initial system characterization consists  of identifying gaps in

26      information and data that  are essential to a basic understanding of the CSS response to rain

27      events and the  impact of CSOs  on the receiving water.  The  following questions may help to

28      identify data gaps that need to be addressed in the monitoring and modeling plan:

29

30            CSS Physical Characterization

31            •  Have all CSO outfalls been identified?
32
33            •  Are the drainage sub-areas delineated for each CSO outfall?
34
35            •  Is  sufficient information  on  the  location, size, and characteristics of the sewers
36               available to support more complex analysis, including hydraulic modeling?
37


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  1           •  Is sufficient information on  the location, operation, and  condition of regulating
  2              structures available to construct at least a basic hydraulic  simulation?  (Even if a
  3              hydraulic computer model is not used,  this  level  of knowledge  is critical  to
  4              understanding how the system works and for implementing  the NMC.)

  6           •  Are the amount of rainfall and rainfall intensity that cause CSOs at various outfalls
  7              known?
  8
  9           •  Are areas of surcharging in the CSS known?
 10
 11           •  Have potential monitoring locations in the  CSS been identified?
 12
 13           •  Are there differences between POTW wet weamer and dry weather operations? If so,
 14              are these clearly understood?  (Enhanced POTW wet weather operation can improve
 IS             • capture of CSS flows significantly.)

 16

 17           CSS Characterization

 18           •   Are the flow and quality of CSOs known?
 19
 20           •   Are sources of pollutant loadings known?
 21
 22           •   Is sufficient information available on the pollutant loadings of CSOs and other sources
 23               to support an evaluation of long-term CSO control alternatives?

 24

 25            Receiving Water Body Characterization

 26            •   Are the  hydraulic  characteristics' of receiving waters known, such as the average/
 27               maximum flow  of rivers and streams  or the freshwater  component,  circulation
 28               patterns, and mixing characteristics of estuaries?
 29
 30            -Are locations of sensitive areas and the use classifications (e.g., A, B, SA, SB)
 31               identified on a study map?
 32
 33            •   Have existing monitoring locations in the  receiving water been identified?  Have
 34               potential monitoring locations (e.g., safe, accessible points) in  the receiving water
 35               been identified for  areas of concern and areas where no data exist?
 36
 37            •   Are sufficient data  available to assess existing water quality problems including:
 38
 39               -   Erosion
40               -   Sediment accumulation
41               -   Dissolved oxygen levels
42               -   Bacteria] .problems, such as those leading to beach closures
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 1               -  Nuisance algal or aquatic plant growths
 2               -  Damage to a fishery (e.g., shellfish beds)
 3               -  Damage to a biological community (e.g., benthic organisms)?
 4
 5           •   Is sufficient information available on natural background conditions that may preclude
 6               the attainment of WQS? (For example, a stream segment with a high natural organic
 7               load may have a naturally low dissolved oxygen level.)
 8
 9           •   Is sufficient information available on other pollutant sources that may  preclude the
10               attainment of WQS?
11

12     The answers to these types of questions will support the development of goals and objectives for
13      the monitoring plan, as described in Chapter 4.
14
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  i                                         CHAPTER 4
  2
  3                           MONITORING AND MODELING PLAN
  4
  5            The CSO Control Policy specifies that permittees should immediately begin a process of
  6     characterizing their CSS, demonstrating implementation of the nine minimum controls (NMC),
  7     and developing a long-term control plan (LTCP). The NMC and the LTCP both contain elements
  8     that involve monitoring and modeling activities.  The NMC include monitoring to characterize
  9     CSO  impacts  and the efficacy of CSO controls, while  the  LTCP includes  elements for
10     characterization,  monitoring, and modeling of the  CSS and receiving waters, evaluation and
11     selection of CSO control alternatives, and development of a post-construction  monitoring
12     program. As discussed in Chapters 2 and 3, "monitoring" as part of the NMC involves gathering
13     and analyzing existing data and performing field investigations, but does not generally involve
14     sample collection and analysis or the use of complex models.  Thus, the monitoring and modeling
                                                              \
15     elements discussed  in this chapter and subsequent chapters primarily pertain to LTCP
16     development and implementation.
17
18           Monitoring requirements associated with  LTCP development and implementation will
19     likely be incorporated into the NPDES permit.  In many cases, the permit will first require the
20     permittee to submit a monitoring and modeling plan before conducting monitoring and modeling
21     activities. For example, the Phase I permit may require submission of a monitoring and modeling
22     plan as an interim deliverable during LTCP development.
23
24           For many reasons, accurate monitoring data  and modeling results are important factors
25     in making CSO control decisions.  A well-developed monitoring and modeling plan is essential
26     throughout  the   CSO  planning process  to provide useful monitoring data  for  system
27     characterization, evaluation and selection of control alternatives, and post-construction compliance
28     monitoring. Development of the plan is likely to be an iterative process, with changes made as
29     more knowledge about the CSS and CSOs is  gained. The NPDES permitting authority and the
30     rest of the CSO planning team (i.e., State WQS personnel, State watershed personnel and EPA
31     Regional staff) should be involved throughout this process.

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  1            This chapter describes how the permittee can develop a monitoring and modeling plan that
  2     will provide essential and accurate information about the CSS and CSOs, and the impact of CSOs
  3     on the receiving water.  The chapter discusses the identification of monitoring and modeling
  4     goals and objectives and the development of a monitoring and modeling plan to ensure that those
  5     goals and objectives are met. It provides detailed discussions and examples on identifying
  6     sampling locations, frequencies, and parameters to be assessed in the CSS, CSOs, and receiving
  7     water body. In addition, it briefly discusses certain monitoring and modeling plan elements that
  8     are common to all system components being monitored.  Readers should consult the appropriate
  9     EPA guidance documents (see References) for further information on monitoring topics such as
 10     chain-of-custody, sample handling, equipment, resources, and quality assurance/quality control
 11      (QA/QC) procedures.
 12
 13      4.1    DEVELOPMENT OF A MONITORING AND MODELING PLAN
 14
 15            A monitoring and modeling plan can be developed with the following steps:
 16
 17            Step 1:  Define the short- and long-term objectives — In order to identify appropriate
 18      model inputs and facilitate well-informed decisions on CSO controls, the permittee should first
 19      formulate the short- and long-term objectives of  the monitoring and modeling effort. Every
20      activity proposed in me plan should contribute to attaining those objectives.  (Section 4.1.1)
21
22            Step 2:  Determine whether to use a model — The permittee should decide whether to
23      use a model during LTCP development (and, if so, which model might be appropriate).  This
24      decision should be based on site-specific considerations (e.g., CSS characteristics and complexity,
25      type of receiving water) and the information compiled in the initial system characterization. If
26      a permittee decides to use a model, a modeling strategy should be developed.  (Section 4.1.2)
27
28            Step 3:  Identify data needed — The next step in plan development is to identify the
29      monitoring data that are needed to meet the goals and objectives.  If modeling is planned, the
30      monitoring plan should include any additional data needed for model inputs. (Section  4.1.3)
31
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  1           Step 4: Identify sampling criteria (e.g., locations, frequency) — The permittee needs
  2     to evaluate and select monitoring  locations within the, CSS (flow monitoring and chemical
  3     analyses), CSOs (flow monitoring, chemical analyses, and potentially whole effluent toxicity
  4     testing), as well as points within the receiving water body (chemical and, potentially, biological
  5     and sediment  monitoring).  The permittee should also identify the frequency and duration of
  6     sampling, parameters to be sampled, sample types to be collected  (e.g.,  grab, composite), and
  7     sample handling and preservation procedures.  If modeling will be done, the monitoring plan
  8     should include any additional sampling locations, sample types, and parameters necessary to use
  9     the proposed model.  If this is not feasible, the  permittee may need to reevaluate the model
 10     choice and select a different or less-complex model. (Sections 4.2  to 4.6)
 11
 12           Step 5: Develop data management and analysis procedures — A monitoring  and
 13      modeling plan also needs to specify QA/QC procedures to ensure that the collected data are
 14      reliable and a data management program to facilitate storage,  use, and analysis of the data.
 15      (Section 4.7)
 16
 17            Step 6: Address implementation issues — Finally, the  monitoring and modeling plan
 18      should  address implementation issues,  such as record keeping  and  reporting,  responsible
 19      personnel, scheduling, and the equipment and resources necessary to accomplish  the monitoring
20      and modeling.  (Section 4.8)
21
22            These steps are described in  detail in the remainder of this chapter.
23
24      4.1.1  Goals and Objectives
25
26            The ultimate goal of a CSO control program is to implement the most cost-effective
27      controls  to reduce  water  quality impacts from CSOs.  Monitoring and modeling will foster
28      attainment of this goal by generating data to support decisions for selecting CSO controls.  The
29      monitoring and modeling  plan should identify how data will be collected and used to meet the
30      following goals:
31

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  1           •   Define the CSS's hydraulic response to rainfall.
  2
  3               -  What level of rainfall causes CSOs?
  4               -  Where do the CSOs occur?
  5               -  How long do CSOs last?
  6               -  Which structures or facilities limit the hydraulic capacity of the CSS?
  7
  8           •   Determine CSO flows and pollutant concentrations/loadings.
  9
 10               -  What volume of flow is discharged?
 11               -  What pollutants are discharged?
 12               -  Do the flows and concentrations of pollutants vary greatly from event to event and
 13                  outfall to outfall?
 14               -  How do pollutant  concentrations and loadings vary within a storm event?
 15
 16           •   Evaluate the impacts of CSOs on receiving water quality.
 17
 18               -  What is the baseline quality of the receiving water?
 19               -  What are the upstream background pollutant concentrations?
20               -  What are the impacts of CSOs?  Are applicable WQS being met?
21                -  What is the contribution of pollutant loadings from other sources?
22              -  Is biological, sediment, or whole effluent toxicity testing necessary?
23
24           •    Support model input, calibration, and verification.,
25
26           •    Support the review and revision, as appropriate, of WQS.
27
28               -  What data are needed to support potential revision of WQS to reflect wet weather
29                  conditions?
30              -  What data are needed to support a use attainability analysis?
31
32            •   Support implementation and documentation of the NMC.
33
34              -  Are there dry weather overflows?
35               - ,  How can available storage in the system be maximized?
36              -  How can flow to the POTW be maximized?
37               -  How can system problem areas and bottle necks be relieved?
38
39           •   Evaluate the effectiveness of the NMC.
40
41            •   Evaluate and select long-term CSO control alternatives.
42
43               -  What improvements in water quality  will result from proposed CSO control
44                  alternatives in the  LTCP?
45               -  How will the CSS hydraulics and CSOs change under various control alternatives?
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  1.               -  How can CSO flows be relocated to less sensitive areas?
  2
  3
  4
  5
  6
          —  now tau \*,&\j uuws DC relocated 10 less sensitive areas:

       In addition to selecting and implementing long-term CSO controls, the permittee will also
be required to develop and implement a post-construction compliance monitoring program. For
this type of monitoring program, the goal will typically be to:
                                       *
 7            •   Evaluate the effectiveness of the long-term CSO controls.
 8
 9                -  Are applicable WQS being met?
 10                -  How much water quality improvement do environmental indicators show?
 11
 12            Besides the broad goals, a municipality may have some site-specific objectives for its
 13      monitoring program. For example, when monitoring to define the CSS's hydraulic response to
 14      rainfall, the permittee may wish to determine whether portions of the trunk lines are under-sized
 15      and whether specific portions of the combined sewer trunk lines can provide in-line storage.
 16
 17      4.1.2  Modeling Strategy
 18
 19            In developing a monitoring and modeling plan, the permittee should consider up front
20      whether to use modeling. Modeling aids in characterizing and predicting:
21
22            •   Sewer system  response to storm events,
23            •   Pollutant loading to receiving waters, and
24            •   Impacts within the receiving waters.
25
26      Modeling also assists.in  formulating and  testing the cause-effect relationships between storm
27      events and receiving water impacts.  This knowledge can help the permittee evaluate control
28      alternatives and formulate an acceptable LTCP. Through the use of modeling, the permittee has
29      a tool for predicting the effectiveness of a range of potential control alternatives.  By assessing
30      the expected outcomes of control alternatives before then: implementation, the permittee can make
31      decisions  more cost efficiently. Modeling results may  also be relevant to potential revisions of
32      State WQS. The use of a model and its level of complexity affect the need for monitoring data.
33      Thus, early in the development of a  monitoring and  modeling  plan, the permittee should
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                         WORKING DRAFT;  Do NOT CUE OR QUOTE
  1     determine if modeling is needed to provide sufficient information for making CSO control
  2     decisions.

  3

  4           Once the model is calibrated and verified, it can be used for the following activities:
  5

  6           •   To predict overflow occurrence, volume, and in some cases, quality, for rain events
  7               other than those which occurred during the monitoring phase. These can include a
  8               storm event of large magnitude (with a long recurrence period) or numerous storm
  9               events over an extended period of time.
 10
 11            •   To predict the performance of portions of the CSS that  have not been monitored
 12               extensively.
 13
 14            •   To develop CSO  statistics such as  annual number of overflows and percent of
 15                combined  sewage captured  (particularly  useful  for municipalities pursuing the
 16                presumption approach under the CSO Control Policy).
 17
 18            •   To optimize the sewer system  performance as part of the nine minimum controls
 19                (NMC).  In particular, modeling can assist  in locating storage opportunities and
 20                hydraulic bottlenecks and demonstrate that system storage and flow to the POTW are
 21               maximized.
 22
 23            •  To evaluate and optimize control alternatives, from simple controls described under
 24               the NMC (e.g., raising weir heights  to increase in-line storage), to more complex
 25               controls proposed hi a municipality's LTCP. The model can be used to evaluate the
 26               resulting reductions in CSO volume and frequency.
 27

 28            If the permittee decides to perform  modeling, a modeling strategy should be developed.

 29     There are several considerations in developing an appropriate modeling strategy:
 30

 31            •   Meeting the expectations of the CSO Policy—Models should adequately meet the
 32               needs of the presumption or demonstration approach chosen by the permittee, in
 33               conjunction with the NPDES permitting authority, in LTCP development.  The focus
 34               of modeling depends hi part  on which  approach  the  permittee adopts.   The
 35               demonstration approach can necessitate detailed simulation of receiving water impacts
 36               to show that CWA requirements will  be met under selected CSO control measures.
 37               The presumption approach may involve less emphasis on receiving water modeling
 38               since it presumes that CWA requirements are met based on certain performance
 39               criteria, such as the maximum number of CSO events.
40
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  1            •  Successfully simulating the physical characteristics of the CSS, pollutants, and
  2               receiving waters under study—Models should be chosen to simulate the physical and
  3               hydraulic characteristics of the sewer system and the receiving water body, chemical
  4               and biological characteristics of the pollutants of concern, and the time and distance
  5               scales necessary to evaluate attainment of WQS.  A model's governing equations and
  6               boundary conditions should match the characteristics of the water body,  the pollutants
  7               of concern, and the pollutant fate and transport processes under study. A model does
  8               not necessarily need to describe the system completely in order to analyze CSO events
  9               satisfactorily. Different modeling strategies will be necessary for the different physical
 10               domains  being  modeled:   overland storm flow,  pollutant  buildup/washoff, and
 11               transport  to the collection system; transport within the  CSS  to POTW, storage or
 12               oVerflow; and dilution and transport hi receiving waters. In most cases, simulation
 13               models appropriate for the sewer system also address pollutant buildup/washoff and
 14               overland flow.  Receiving water models are  typically separate from the storm water/
 15               sewer models, although in some cases compatible interfaces are available.
 16
 17           •   Meeting information needs at optimal cost—The modeling strategy should provide
 18               answers as detailed and accurate as needed at the lowest corresponding expense and
 19               effort Since more detailed, accurate models require greater expense and effort to use,
 20               the permittee needs to identify the point at which  an increased modeling effort would
 21                provide diminishing returns.  The permittee may use an incremental  approach, in
 22               which simple screening models are used with initial, and usually limited, data. These
 23                results may then lead to refinements in the monitoring and modeling plan so that the
 24               appropriate data are generated for more detailed modeling.
 25

 26            More detailed discussions on modeling, including model selection,  development, and
 27      application, are included in Chapters 7 (CSS Modeling) and 8 (Receiving Water Modeling).
 28

 29      4.1 J  Monitoring Data Needs
 30
 31            The monitoring effort necessary to address each  of the identified goals will  depend on a
 32'     number of factors: the layout of the collection system; the quantity, quality, and variability of
33      existing historical data; the quantity, quality, and variability of the necessary additional  data;

 34      whether modeling will be done and the complexity of the model;  and the available budget.  In
35      some cases, the initial characterization will yield sufficient historical data so that  only limited
36      additional monitoring will be necessary.  In other cases,  considerable effort may be  necessary to
37      fully investigate the characteristics of the CSS, CSOs, and receiving water. Some municipalities
38      may choose to allocate a relatively large portion of the available budget to  monitoring, while
39      others may allocate a smaller portion. Because decisions on data needs may change  as additional


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  1     knowledge is obtained, the monitoring program must be a dynamic program that changes to
  2     reflect any changes in data needs.
  3
  4           In identifying goals and objectives, a modeling strategy, and monitoring data needs, the
  5     permittee should work with the team that will be reviewing NMC implementation and LTCP
  6     development and implementation (e.g., NPDES permitting authorities, State WQS authorities, and
  7     State watershed personnel).  This coordination should begin in the initial planning stages so that
  8     appropriate goals and objectives are identified and effective monitoring and modeling approaches
  9     to meet these goals and objectives are developed.  Concurrence  among the review team
 10     participants during the planning stages should ensure design of a monitoring and modeling plan
 11      that  is able to support sound CSO control program decisions.  The proposed monitoring and
 12     modeling plan should be submitted to  the review team and modified according to reviewer
 13      comments. The permittee should also coordinate the monitoring and modeling plan with other
 14      Federal and State agencies,  and with other point source dischargers, especially for effects on
 IS      watersheds and ambient receiving waters.
 16
 17     42    ELEMENTS  OF A MONITORING AND MODELING PLAN
 18
 19            In addition to identifying the goals and objectives, monitoring and modeling plans should
20     generally contain the  following major elements:
21
22            •   Review of Existing Data and Information (discussed in detail in Chapter 3)
23
24               -  Summary of existing data and information
25               -  Determination of how existing data address  goals and objectives
26               -  Identification of data needs
27
28            •   Development of Sampling Program to Address Data Needs (discussed in detail in
29               Chapters 5 and 6)
30
31               -  Duration of monitoring program
32               -  Monitoring locations
33               -  Frequency of sampling and/or  number of precipitation events to be sampled
34               -  Criteria for when the samples will be taken (e.g., greater than x days between
35                  precipitation events, rainfall events greater than 0.4 inches to be sampled)
36               -  Sampling protocols (e.g., sample types, sample containers, preservation methods)

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1               -  Flow measurement protocols
  2               -  Pollutants or parameters to be analyzed and/or recorded
  3               -  Sampling and safety equipment and personnel
  4               -  QA/QC procedures for sampling and analysis
  5
  6           •   Discussion of Methods for Data Management and Analyses
  7
  8               -  Data management (e.g., type of data base)
  9               -  Statistical methods for data analysis
 10               -  Modeling strategy, including model(s) selected (discussed in detail in Chapters 7
 11                  and 8)
 12               -  Use of data to support NMC implementation and LTCP development
 13
 14           •   Implementation Plan
 15                    '  '
 16               -  Recordkeeping and reporting
 17               -  Personnel responsible  for implementation
 18               -  Scheduling
 19               -  Resources (funding, personnel and equipment)
20               -  Health and safety issues.
21
22           The checklists in Appendix A Tables A-l and A-2 list items that should be addressed in
23     formulating a monitoring  program.   Elements  in the first checklist should  be pan of any
24     monitoring program and cover seven major areas:  sample and field data collection, laboratory
25     analysis, data management, data analysis, reporting, information use, and general. The second
26     checklist applies specifically to CSO monitoring and covers three areas: mapping of the CSS and
27     identification of monitoring locations, monitoring of CSO quantity,  and monitoring of CSO
28     quality.
29
30            Because each permittee's CSS, CSOs, and receiving water body are unique, it is not
31     possible  to recommend  a generic,  "one-size-fits-all" monitoring and modeling plan in this
32     document.  Rather, each permittee should design a cost-effective monitoring and modeling plan
33     tailored to local conditions and reflecting the size of the CSS, the impacts of CSOs, and whether
34     modeling will be performed. It should balance the costs of monitoring against the amount of data
35     and information needed to develop, implement, and verify the effectiveness of CSO controls.
36
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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            While the monitoring budget may appear large, it is often a small percentage of the total
  2     cost of controlling CSOs. Each municipality should balance the cost of monitoring against the
  3     risk of developing CSO controls based on insufficient or inaccurate data.   By using  the
  4     information obtained through additional  monitoring or modeling, some  municipalities have
  5     achieved a larger reduction in total CSO control costs than the costs for the additional monitoring
  6     or modeling.
  7
  8     4.2.1   Duration of Monitoring Program
  9
 10            The duration of the monitoring program will vary from location to location and reflect
 11      the number of storm events  needed to provide the data for calibrating and validating the CSS
 12     hydraulic model (if a model is used), and evaluating CSO control alternatives and receiving water
"13      impacts. During that period (which generally may be a season or several months), storms of
 14      varying intensity, antecedent dry days, and total  volume should be monitored to ensure that
     \
 15      calculations and models represent the range of conditions experienced by the CSS.
 16
 17            The monitoring program should span enough storm events to develop a full understanding
 18      of pollutant loads from CSOs, including the means and variations of pollutant concentrations and
 19      the resulting effects on receiving water quality,  ff only a few storm events are monitored, the
 20      analysis should  include  appropriately conservative assumptions because of the uncertainty
 21      associated with small  sample sizes. For example, if monitoring data are collected from a few
 22      storms  during spring, when CSOs are generally larger and more frequent, mean pollutant
 23      concentrations may be lower due to  flow dilution and diminished  first flush effects. When
 24      monitoring data are collected for additional storms, including those in the summer and fall when
 25      CSOs are less frequent, the mean pollution concentrations may increase significantly.  Additional
 26      samples should reduce the level of uncertainty, and allow the use of a smaller margin of safety
 27      in the analysis.
 28
 29            The value of additional monitoring diminishes when additional data would result in a
 30      limited  change in the estimated mean and  variance of a data set.  The permittee should assess
 31      the value of additional data as they are collected by reviewing the change in the estimated mean

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     and variance of contaminant concentrations. If estimated values stabilize, the need for additional
  2     data should be reassessed.
  3
  4           Pollutant loadings vary according to the number of days since the last storm and the
  5     intensity of previous rainfalls. Therefore, to better represent the variability of actual conditions,
  6     the  monitoring program  should be designed to sample storms with a variety of pre-storm
  7     conditions.
  8
  9     4.2.2  Sampling Protocols and Analytical Methods
 10
 11           The monitoring and modeling plan should describe the sampling and analytical procedures
 12     that will be used. Sample types depend on the parameter, site conditions, and the intended use
 13     of the data.   Flow-weighted composites may be most appropriate for determining average
 14     loadings of pollutants to the receiving stream.  Grab samples may suffice if only approximate
 IS     levels  of pollutants are needed or if worst-case .conditions (e.g., first  15 or 30 minutes of
 16     overflow) are being assessed.  In addition, grab samples should be collected, for pollutant
 17     parameters that cannot be composited, such as oil and grease, pH, and bacteria. The monitoring
 18     plan should follow the sampling and analytical procedures in 40 CFR Part 136, including the use
 19   .  of appropriate sample containers, sample preservation methods, maximum allowable holding
20     times, and analytical methods referencing one or more of the following:
21
22           •   Test methods in Appendix A to 40 CFR Part 136 (Methods for Organic Chemical
23               Analysis of Municipal and Industrial Wastewater)
24
25            •   Standard Methods for the Analysis of Water and Wastewater (use the most current,
26               EPA-approved edition)
27
28            •   Methods for the Chemical Analysis of Water and Wastes (EPA, 1979.  EPA-600/
29               4-79-020).
30
31            In some cases, other well-documented analytical protocols may be more appropriate for
32      assessing in-stream parameters.  For example, in estuarine areas, a protocol from NOAA's Status
33      and  Trends  Program  may  provide better accuracy and precision if it  reduces  saltwater
34      interferences.

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                         WORKING DRAFT:  Do NOT CUE OR QUOTE
  1            For details on sampling or analysis of specific parameters, the permittee should refer to
  2     these publications.  In addition, these issues are discussed in further detail in Section 5.4.1.
  3
  4     43    CSS AND CSO MONITORING
  5
  6            To satisfy the objectives of the CSO Control Policy, the monitoring and modeling plan
  7     should specify how the CSS  and CSOs will be monitored, detailing  monitoring locations,
  8     frequencies, and pollutant parameters. The plan should be coordinated  with other concurrent
  9     sampling efforts (e.g., ongoing State water quality monitoring programs) to reduce sampling and
 10     monitoring costs and maximize use of available resources.
 11
 12     43.1  CSS and CSO Monitoring Locations
 13
 14          . The monitoring and modeling plan should specify how rainfall data, flow data,  and
 15      pollutant data will be collected to define the CSS's hydraulic response to rainfall and to measure
 16      CSO flows and pollutant loadings. The monitoring program should also provide background data
 17      on conditions  in the  CSS during dry weather conditions, if this information is not already
 18      available (see Chapter 3):  Dry weather monitoring of the CSS may help identify pollutants of
 19      concern in CSOs during wet weather.
20
21            Rainfall Gage Locations
22            The permittee should ascertain whether additional  rainfall  data are necessary  to
23      supplement existing data.  If so, the monitoring and modeling plan should identify where rain
24      gages will be placed to provide data representative of the entire CSS drainage area. Gages
25      should be spaced closely enough that location variation in storm tracking and storm intensity does
26      not result in large errors in estimation of the rainfall within the CSS area. Recommended spacing
27      is the subject of a variety of research papers. The CSO Pollution Abatement Manual of Practice
28      (WPCF, 1989) provides the following summary of recommendations  on rain gage spacing:
29
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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            "In Canada, rainfall and collection system modelers recommend one gauge every
  2            1 or 2 kilometers.  In Britain, the Water Research Center has recommended only
  3            half that density, or one gauge every 2 to 5 kilometers.  In the United States
  4            current spacing recommendations are related to thunderstorm size.  The average
  5            thunderstorm  is 6 to  8 kilometers  in diameter...Therefore rain  gauges  are
  6           frequently spaced every 6 to 8 kilometers..."
  7
  8     For small watersheds, rain gages may need to be placed  more closely  than every 6 to 8
  9     kilometers so that sufficient data are available for analysis and calibration of any models that may
 10     be used. The monitoring and modeling plan should document the rationale for rain gage spacing.
 11
 12            CSS Monitoring Locations
 13            The monitoring and modeling plan will need to identify locations within the collection
 14     system where flow and pollutant loading data will be collected. To predict the likelihood and
 IS     locations of CSOs during wet weather, it is necessary to assess general flow patterns and volume
 16     in the CSS and which structures tend to limit the hydraulic capacity. This may require sampling
 17     along various trunk lines of the collection system.   Flow data from existing  monitors and at
 18     hydraulic controls such as pump stations and POTW headworks can also be used.
 19
20           To obtain complete flow and pollutant loading data, the plan should  also target portions
21      of the collection system that are likely to receive significant pollutant loadings.  The plan should
22     identify locations where industrial users discharge into  the collection system,  and specify any
23     additional monitoring that  will be conducted to  supplement  data collected through the
24     pretreatment program. Special consideration should be  given to these areas if  they are located
25     near CSOs.  See Section 4.3.3 for a discussion of the types of pollutants to  be  monitored.
26
27           CSO Monitoring Locations
28            The monitoring and modeling plan should provide for collection of flow and pollutant
29     concentration information at as many CSO locations as possible.  Small systems may be able to
30     monitor all outfalls for each storm event studied. Others may require a tiered approach, in which
31      only outfalls  with higher flows or pollutant loadings, or discharges to sensitive areas, would
32      warrant continuous depth and velocity flow monitoring and the use of composite samples for

        External Review Draft                    4-13                        December 6,  1996

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                          WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     chemical  analyses.  Lower-priority outfalls,  meanwhile, would  be monitored with simpler
  2     techniques such as visual observation, block tests, depth measurement, overflow timers, or chalk
  3     boards (discussed in section 3.1.3) and limited chemical analyses.  When multiple outfalls are
  4     located along the  same interceptor, flow monitoring of selected outfalls and  at  one or two
  5     locations in the interceptor should suffice.
  6
  7            Even if a monitoring program accounts for most of the total land area or estimated runoff,
  8     monitoring other outfall locations, even with simple techniques, can provide information about
  9     problem areas. For example, at an overflow point with only 10 percent of the contributing
 10     drainage area, a malfunctioning regulator may result in discharges during dry weather or during
 11      small storms when the interceptor has remaining  capacity. As a result, this overflow point may
 12     become a major contributor of flows. A simple technique such as a block test could identify this
 13     problem.
 14
. 15            Alternatively, flow measurement equipment can be rotated between locations so that some
 16     locations are monitored for a subset of the storms studied. For example, during one storm critical
 17     outfalls could be monitored with automated flow monitoring equipment, two less-important
 18      outfalls could be monitored with portable flow meters, and the rest could be monitored using
 19      chalk boards. During a second storm, the critical outfalls could still be monitored with automated
 20     flow equipment, but the portable flow meters could be rotated to two other outfalls of secondary
 21      importance.
 22
 23             If it is not feasible to monitor all outfalls, the permittee  should identify a  specific
 24      percentage of the outfalls to be monitored based on the size of the collection system, the total
 25      number of outfalls, the number of different receiving water bodies, and potential  and known
 26     impacts. The selected locations should represent the system as a whole or represent the worst-
 27      case scenario (for- example,  where overflows occur most frequently, have the largest pollutant
 28      loading or flow volume, or discharge to sensitive areas).
 29
 30            In general,  monitoring locations should be distributed to achieve optimal coverage  of
 31      actual overflows with a minimum number of stations. The initial system characterization should

        External Review Draft                    4-14                        December 6, 1996

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                          WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     have already provided information useful in selecting and prioritizing monitoring locations, such

  2     as:

  3

  4            •   Drainage Area Flow Contribution—-The relative flow contributions from different
  5               drainage areas can be used to prioritize flow monitoring and chemical analysis efforts.
  6               There are several methods for estimating relative flow contributions. The land area
  7               of each outfall's sub-basin provides only an approximate estimate of the relative flow
  8               contribution because regulator operation and land use characteristics affect overflow
  9               volume.  Other estimation methods, such as the rational method, account for the
 10               runoff characteristics of the upstream land area and produce relative peak flows of
 11               individual drainage areas.  Flow estimation using Manning's equation (see Section
 12               5.3.1) may produce a better estimate of the relative flow contribution by the drainage
 13               area.
 14
 15            •   Upstream Land Use—During the initial sampling effort, the permittee should estimate
 16               the relative contribution of pollutant loadings from individual drainage areas.  Maps
 17               developed during  the  initial system characterization  should  provide land  use
 18               information that can be used to derive pollutant concentrations for the different land
 19               uses from localized data bases (based on measurements in the CSS).  If local data are
20               not available,  the permittee may use regional land-use based National Urban Runoff
21                Program (NURP) studies, although NURP data reflect only storm water and must be
22               adjusted for the presence of sanitary sewage flows.  Pollutant concentration and
23               drainage  area flow data can then be used to estimate  loadings.   Since pollutant
24               concentrations can vary greatly for different land uses, monitoring locations should
25               represent subdivisions of the drainage area which have differing land uses.
26
27            •   Location of Sensitive Areas—Since  the permittee's LTCP should give the highest
28               priority to controlling overflows to sensitive areas, the monitoring and modeling plan
29               should identify locations where CSOs to sensitive areas, and their impacts, will be
30               monitored.
31
32            •   Feasibility and Safety of Using the location—After using the criteria above to
33                identify which outfalls will provide the most appropriate data, the permittee should
34               determine whether the locations  are  safe and accessible and identify which safety
35                precautions are necessary.  If it is not feasible or practical to monitor at the point of
36               discharge, the permittee should select the  closest downstream location that is still
37                representative  of the overflow.
38

39             Example 4-1 illustrates one approach  to selecting discharge  monitoring sites  for a
40     hypothetical CSS with ten outfalls. The selected outfalls—1,4,5,7, and 9—discharge flow from
41      approximately 60 percent of the total drainage area and 80 percent of the industrial area. In
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                     WORKING DRAFT;  Do NOT CITE OR QUOTE
  Example 4-1.  One Approach to Selecting Discharge Monitoring Sites for a Hypothetical
                                       CSS with 10 Outfalls
     A municipality has a combined sewer^reawfth-4,800 acres and 10 individual outfalls discharging into
     a large river. Exhibit 4-1/shows the characteristics'of the discharge points that are potentially useful in
     choosing which intercepting devices to monitor.  Investigators used sewer and topographic maps to
     determine the size of the drainage areas.  Aerial photographs and information .from a previous .study
     indicated land use. Sewer maps, spot checked in-the field; verified the type of regulatingstructute. Both
     the sewer map and discussions with CSS persormehprovaded information about safety and«ase of access.

     Outfalls 7 and 9 account for 33 percent .of-the .total .drainage area, and outfall 7 provides data on
     commercial and industrial -land uses that may have relatively higher pollutant loadings.  These sites pose
     no safety/accessibility concerns, making them desirable sampling locations.

     Outfall 5 discharges mpark has many recreational uses, including swimming-during the warmermonths.
     Since areas used for primary •.contact-recreation are considered sensitive areas, they -are given highest
     priority in the permittee's LTCP under the CSO Control Policy. -This outra&^wtricb. accounts.forvabout
     lO.percentof -the drainag&.area, should he-monitored.             .   -

     Outfall 4, which is served .by a pump station, accounts:fbr
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r
EL
I
Exhibit 4-1.  Data for Example 4-1
Outfall
#
1
2
3
4
5
6
7
8
9
10
Total
Drainage
Area
(acres)
69S
ISO
560
430
500
800
690
120
1.060
300
5.305
Land Use
Residential
% '
80
50
75
60
90
90
20
40
80
90
71%
Industrial
%

20

10


60
50


11%
Coinniercial
. %
20
30
5
30

10
20
10


10%
Open/Park
%


20

10



20
10
8%
Flow Regulation Device
Welt
' Gravity
/

S

S

S

S


Weir '
.Backflow





/

/•



Orifice
Backwater

/







S

Punip
Station



/







Access/
{Safety

S



S

S

S

Sensitive
Area
^










Potential
bfonliorlog
Location
Possible
No
Possible
Yes
Possible
No
Yes
No
Yes
No

o\

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     addition, outfalls 1 and 5 are adjacent to sensitive areas. Consequently, these five outfalls should
  2     provide sufficient in-depth coverage for the city's monitoring program. Using simplified flow
  3     and modeling techniques at outfalls 2, 3, 6, 8, and 10 can supplement the collected monitoring
  4     data and allow estimation of total system flow.
  5
  6           For additional  guidance in prioritizing  monitoring locations, permittees can  consult
  7     Combined Sewer Overflows - Guidance for Screening and Ranking (EPA, 1995c).  Although
  8     generally intended for ranking CSSs with respect to one another, the techniques in this reference
  9     may prove useful for ranking outfalls within a single system.
 10
 11      4.3.2  Monitoring Frequency
 12
 13            The permittee should monitor a sufficient number of storms  to accurately predict the
 14      CSS's response to  rainfall events and the characteristics of resulting CSOs. The frequency of
 IS      monitoring should be based on site-specific considerations such as the overflow frequency and
 16      duration, which depend on the rainfall pattern, antecedent dry period, type of receiving water and
 17      circulation pattern  or flow,  ambient  tide  or stage of river or stream, and diurnal flow to the
 18      treatment plant  Monitoring frequency may be targeted to such factors as:
 19
20            •   A certain size precipitation event (e.g., 3-month, 24-hour)
21
22            •   Precipitation events that result in overflows, or
23
24            •   A certain number of precipitation events (e.g., monitor until five storms of a certain
25               minimum size are sampled).
26
27            Overall, the monitoring and modeling plan should usually  provide for more frequent
28      monitoring where:
29
30            •   Facilities discharge to sensitive or high-quality areas, such as waters with drinking
31               water  intakes or swimming, boating, and other recreational activities
32
33            •   CSO flow volumes vary significantly  from storm event to storm event
34
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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            The number of samples collected will also reflect the type of sample collected. Where
  2     possible, flow-weighted composite samples should be collected to determine the average pollutant
  3     concentration over a storm event (also known as the event mean concentration or EMC). This
  4     approach decreases  the  analytical cost of a program  based  on  discrete  samples.   Certain
  5     parameters, such as oil and grease and bacteria, however, need to be collected by grab sample.
  6     Additionally, when the permittee needs to determine whether a pattern of pollutant concentration,
  7     such as a first-flush phenomenon, occurs during storms, the monitoring program should collect
  8     multiple samples from locations throughout a storm.
  9
 10           Because the pollutant loads in CSOs, the sensitivity of the receiving water to which they
 11      discharge, and the resources of permittees vary significantly,  this manual does not recommend
 12     a minimum number of samples or suggest a specific expenditure level for sample collection. The
 13      permittee should carefully consider the tradeoffs involved in committing resources to a sampling
 14      program.  A small  number of samples may necessitate overly conservative assumptions because
 15      of high sample variability, while a larger data set might better determine pollutant concentrations
 16      and result in a more detailed analysis, enabling the permittee to optimize any investment in  long-
 17      term CSO controls. On the other hand, a permittee should avoid spending large sums of money
 18      on  monitoring when the  additional  data  will not  significantly enhance the  permittee's
 19      understanding of CSOs and their impacts.  The permittee should work closely with the NPDES
20      permitting authority and the review team to design a monitoring program that will adequately
21      characterize the CSS, CSO impacts on the receiving water body, and effectiveness of proposed
22      CSO control alternatives.
23
24      4 J3  Combined  Sewage and CSO Pollutant Parameters
25
26            Chemical analyses provide information about the concentrations of pollutants carried in
27      the combined sewage and the variability of these concentrations from outfall to outfall and storm
28      to storm.  Chemical analysis data should be used with flow data to  compute pollutant loadings
29      to receiving waters. In some cases chemical analysis data can also be used to detect the sources
30      of pollutants in the system.
31

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1            The monitoring and modeling plan should identify which parameters will be monitored.
  2     These should include pollutants with water quality criteria for the specific designated use(s) of
  3     the receiving water and pollutants key to the attainment of the designated water use(s). The
  4     NPDES permitting authority may have specific  guidance  regarding parameters for  CSO
  5     monitoring.  Parameters of concern may include:
  6
  7            •   Indicator bacteria
  8
  9            •   Total suspended solids (TSS)
 10
 11             •   Biochemical oxygen demand (BOD) and dissolved oxygen (DO)
 12
 13             •   pH
 14
 IS             •   Settleable solids
 16
 17            •   Nutrients
 18
 19            •   Toxic pollutants reasonably expected to be present in the CSO based on an industrial
20                survey or tributary land use, including metals.
21
22            The* monitoring and modeling plan should also include monitoring for any other pollutants
23      for which water quality criteria are being exceeded, as well as pollutants suspected to be present
24      in the combined sewage and those discharged in significant quantities by industrial users. For
25      example, if the water quality criterion for zinc is  being exceeded in the receiving water, zinc
26      monitoring should be conducted in the portions of the CSS where significant industrial users
27      discharge zinc to the collection system. POTW monitoring data and pretreatment program data
28      on nondomestic discharges can help identify other pollutants that should be monitored. In coastal
29      systems, measurements of sodium, chloride, total dissolved solids, or conductivity can be used
30      to detect the presence of sea water hi the CSS, which can  occur because of intrusion through
31      failed tide gates.
32
33            Not all pollutants need to be analyzed for each location sampled. For example:
34
35            •  A larger list of pollutants should be analyzed for  an industrial area suspected to have
36               contaminated storm water or a large load of pollutants in its sanitary sewer.   •

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                          WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            •  Bacteria should be analyzed in a CSO upstream of a beach with past bacteriological
  2               problems.
  3
  4            The permittee should also ensure that monitored parameters correspond to the downstream
  5     problem as well as the water quality criteria that apply in the receiving water body at the
  6     discharge pipe.  For example, the downstream beach may have an Enterococcus standard while
  7     the water quality criterion at the discharge point might be expressed in fecal coliforms.  In this
  8-     case, samples should be analyzed for both parameters.
  9
 10            The permittee should consider collecting composite data for  certain parameters on as
 11      many overflows as possible during the monitoring program.  This  can help establish mean
 12     pollutant concentrations for computing pollutant loads.  For instance, TSS concentrations are
 13      generally important both because of potential habitat impacts and because they are associated
 14      with adsorbed toxics.
 15
 16'           The permittee should consider initial screening-level sampling for a wide range  of
 17      pollutants, and then should analyze subsequent samples only for the subset of pollutants identified
 18      in the screening.  However, because  pollutant concentrations in CSO discharges are highly
 19      variable, the permittee should exercise caution in removing pollutants  from the analysis list.
20
21      4.4    SEPARATE STORM SEWERS
22
23            If separate storm sewers discharge to the same receiving water as CSOs, the permittee
24      should determine pollutant loads from storm sewers as well as CSOs in order to understand
25      relative loadings from different wet weather sources and target CSO and storm water controls
26      appropriately. If sufficient storm water data are not available, the permittee may need to conduct
27      separate storm sewer sampling and the monitoring and modeling plan should include storm water
28      sampling for the pollutants being sampled in the CSS.  Storm water discharges from areas
29      suspected of having high loadings, such as high-density commercial areas or industrial parks,
30      should have priority.
31
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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1           The monitoring and modeling plan  should  reflect storm water  and other  sampling
  2     programs occurring concurrently and provide for coordination with them.  This will ensure that
  3     wet weather discharges and impacts are monitored and addressed in the most cost-effective,
  4     targeted manner possible.
  5
  6     4.5   RECEIVING WATER MONITORING
  7
  8           The goals of receiving water monitoring should include the following:
  9
 10           •   Assess attainment of WQS (including designated uses)
 11
 12           •   Establish the baseline conditions in the receiving water (chemical, biological, and
 13               physical parameters)
 14
 15           •   Evaluate the impacts of CSOs
 16
 17           •   Gain sufficient understanding of the receiving water to support evaluation of proposed
 18               CSO control alternatives, including any receiving water modeling that may be needed
 19
20           •   Support review and revision, as appropriate, of WQS.
21
22           The monitoring program should also provide background data on conditions  in the
23      receiving waters during dry weather conditions, if this information is not already available (see
24     Chapter 3). Dry weather monitoring of the receiving  water body will establish the background
25      water quality and will determine whether water quality criteria are being met or exceeded during
26      dry weather.
27
28            Where  a permittee intends to eliminate CSOs entirely (i.e., separate its system), only
29      limited or  short-term receiving water monitoring may be necessary (depending on how long
30     elimination of CSOs will take).  It may be in the permittee's interest, however, to collect samples
31      before separation to establish the baseline as well as after separation to evaluate the impacts of
32      CSO elimination.
33
34            The permittee should coordinate monitoring activities closely with the NPDES permitting
35      authority. In many cases, it may be appropriate to use a phased approach in which the receiving

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     water monitoring program focuses initially on determining the pollutant loads from CSOs and
  2     identifying short-term water quality impacts.  The information obtained from the first phase can
  3     then be used to identify additional data and analytical needs in an efficient manner.  Monitoring
  4     efforts can be expanded as circumstances dictate to provide additional levels of detail, including
  5     evaluation of downstream effects and longer term effects.
  6 .
  7           The scope of the receiving water monitoring program will depend on several factors, such
  8     as the identity of the pollutants of concern, whether the receiving water will be modeled, and the
  9     relative size of the discharge. For example:
 10
 11           •  To study dissolved oxygen (DO) dynamics, depth and flow velocity data must be
 12              collected well  downstream of the CSO outfalls. DO modeling may necessitate data
 13              on the plant and algae community, the temperature, the sediment oxygen demand, and
 14              the shading of the river.  Therefore, DO monitoring locations would likely span a
 15              larger area than for some other pollutants of concern.
 16
 17           •  When the volume of the overflow is small relative to the receiving water body, as in
 18              the case  of a small CSO into a large, well mixed river, the overflow may have little
 19              impact. Such a situation generally would not require extensive downstream sampling.
20
21            In developing  the monitoring and modeling plan, the permittee should consider the
22     location and impacts of non-CSO sources of pollutant loadings. As mentioned in Chapter 3, data
23     and  information  regarding non-CSO sources are generally compiled and reviewed during the
24     initial system characterization.  To evaluate the impacts of CSOs on the receiving water body,
25     the permittee should try to select monitoring locations  that have limited or known effects from
26     non-CSO sources. If the initial system characterization did not provide sufficient information to
27     adequately determine the location of non-CSO sources, the permittee may need to conduct some
28     monitoring to better characterize these sources.
29
30     4.5.1  Monitoring  Locations
31
32           In planning where to sample, it is important to understand land uses in the drainage basin
33      (which affect what pollutants are likely to be present) and characteristics of the receiving water
34     body such as:

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  1            •  Pollutants of concern (e.g., bacteria, dissolved oxygen, metals)
  2            •  Locations of sensitive areas
  3            •  The size of the water body
  4            •  Horizontal and vertical variability in the water body
  5            •  Degree of resolution necessary to assess attainment of WQS.
  6
  7            Individual monitoring stations may be located to characterize:
  8
  9            •   Flow patterns
 10
 11             •   Pollutant concentrations and loadings from individual sources
 12
 13             •   Concentrations and impacts at specific locations, including sensitive areas where
 14               potential CSO impacts are of most concern, such as shellfishing zones
 15
 16             •   Differences.in concentrations between upstream and downstream sampling sites for
 17                rivers, or between inflows and outflows for lakes, reservoirs, or estuaries
 18
 19             •   Changing conditions over time at individual sampling stations (i.e., before, during, and
 20                after a storm event)
 21
 22             •   Differences between baseline and current conditions in CSO-impacted water bodies
 23                such as a lake, river, tributary, or bay
 24
 25            •   Locations of non-CSO as well as  CSO pollution sources.
 26
 27            Exhibit 4-2 illustrates how sampling locations  might be  distributed in  a watershed to
 28      assess the effect of other sources  of pollution.
 29
 30            The permittee  should also consider making cooperative sampling arrangements where
 31      pollutants from multiple sources enter a receiving water or where several agencies share the cost
 32      of the collection system and the POTW. The identification of new monitoring locations should
 33      account for sites that may already be part of an existing monitoring system used by local or state
34      government agencies or research organizations.
35
36.

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                      Exhibit 4-2.  Monitoring Location Example
        Upstream of Study Area
  Q    Downstream of Industrial Point Sources
  Q    Upstream of Tributary
  Q    Mouth of Tributary
  0    Downstream at CSO
  O    Downstream End of Study Area
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               Monitoring Frequency, Duration, and Timing
  2
  3            In general, the monitoring and modeling plan should target receiving water monitoring
  4     to those seasons,  flow regimes, and other critical conditions where CSOs have the greatest
  5     potential for impacts, as identified in an initial system characterization (see Chapter 3).  It should
  6     specify additional monitoring as necessary to fill data gaps and to support receiving water
  7     modeling and analysis (see Tables B-2  through B-5 in Appendix B for suggested modeling
  8     parameters), or to distinguish the  relative  contribution of other sources to water quality
  9     impairment.
 10
 11           In establishing the frequency, duration, and timing of receiving water monitoring in the
 12     monitoring  and modeling plan, the permittee should consider seasonal variations to determine
 13     whether measurable and significant changes occur in the receiving water body during different
 14     times of year. The monitoring and modeling plan should also enable the permittee to address
 15     issues regarding attainment of WQS, such as:
 16
 17           •  Establishing a maximum or geometric mean coliform concentration at the point of
 18              discharge into a river or mixing zone boundary—to do this, grab  samples should be
 19              taken during and immediately after discharge events in sufficient number (possibly
20              specified in the standards) to reasonably approximate actual in-stream conditions
21
22           •  Assessing attainment of narrative standards to control nutrient load—this may call for
23               samples collected throughout the water body and timed to examine long-term average
24              conditions over the growing season.
25
26            •  Assessing attainment of narrative standards for support of aquatic life—this may call
27               for biological assessment in potentially impacted locations and a comparison of the
28               data to reference sites.
29
30            Receiving water sampling designs include the following:
31
32            •   Point-in-time single-event samples  to obtain estimates where variation in time is not
33               a large concern.
34
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  1            •  Short-term intensive sampling for a predetermined period of time in order to detail
  2               patterns of change during particular events, such as CSOs. Sample collections for
  3               such studies may occur at such intervals as five minutes, one hour, or daily.
  4
  5            •  Long-term less-intensive samples collected at regular intervals—such as weekly,
  6               monthly, quarterly, or annually—to establish ambient or background conditions or to
  7               assess seasonal patterns or general trends occurring over years.
  8
  9            •  Reference site samples collected at separate locations for comparison with the CSO
 10               study site to determine relative changes between the locations.
 11
 12            •  Near-field studies to sample and assess receiving waters within the immediate mixing
 13               zone of discharges.  These studies can examine possible short-term toxicity impacts
 14               or long-term habitat alterations near the discharge.
 15
 16            •  Far-field studies to sample and assess receiving waters outside the immediate vicinity
 17               of the discharge.  These studies typically examine delayed impacts, including oxygen
 18                demand,  nutrient-induced  eutrophication,  and changes in  macroinvertebrate
 19               assemblages.
20                  I.
21      4.53   Pollutant Parameters
22
23             The monitoring and modeling plan should identify parameters of concern in the receiving
24      water, including pollutants with water quality criteria for  the specific designated use(s) of the
25      receiving water and pollutants key to the attainment of the designated water use(s). The NPDES
26      permitting authority may have  specific  requirements or guidance regarding parameters for
27      CSO-related  receiving water monitoring. These parameters may include  the ones previously
28      identified for combined sewage:
29
30             •   Indicator bacteria
31             •   TSS
32             •   BOD and DO
33             •   pH
34             •   Settleable solids
35             •   Nutrients
36             •   Metals.
37
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  1      In addition,  the permittee should consider  the following types of monitoring prior to or
  2      concurrently  with the chemical parameter analyses:
  3
  4            •  Biological assessment (including habitat assessment)
  5            •  Sediment monitoring
  6            •  Monitoring other pollutants known or expected to be present.
  7
  8            Depending on the complexity of the receiving water and the analyses to be performed,
  9      the monitoring and modeling plan may need to reflect a larger list of parameters. Measuring
10      temperature, flow, depth, and velocity, and more complex parameters such as solar radiation, light
11      extinction, and sediment oxygen demand, can enable investigators to simulate the dynamics of
12      the receiving  water that affect basic parameters  such as bacteria, BOD, and TSS (for example,
13      a Streeter-Phelps DO analysis requires temperature, flow rate, reach length, and sediment oxygen
14      demand). Table B-l in the Appendix lists the data needed to perform the calculations for several
15      dissolved oxygen, ammonia, and algal studies.
16
17      4.6    CASE STUDY
18
19            The case study in Example 4-2 outlines the monitoring aspects of a comprehensive effort
20      to determine  CSO impacts on a river and evaluate possible control alternatives.  The city of
21      South Bend, Indiana developed and implemented a monitoring program to characterize flows and
22      pollutant loads in the CSOs and receiving water.  The city then used a model to evaluate possible
23      control alternatives.
24
25            In developing its monitoring plan, South Bend carefully selected monitoring locations that
26      included roughly 74 percent of the area within the CSS and represented the most characteristic
27      land uses.  The city conducted its complete monitoring program at 6 of the 42 CSO outfalls and
28      performed simpler chalk board  measurements at  the  remaining outfalls to  give some basic
29      information on the occurrence of CSOs across the system.  By using existing flow monitoring
30      stations in the CSS, the city was able to limit the need to establish new monitoring stations.
31

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                             Example 4-2.  Monitoring Case Study
                                        South Bend, Indiana

     The City of South Bend, population of 109,000, has 42 combined sewer service areas covering over
     14,000 acres.

     Monitoring Goals

     The ultimate goal of the CSO control effort was'to reduce or eliminate impacts to beneficial uses of the
     receiving water, including recreation. The more immediate goal consisted of quantifying-CSO impacts
     to .-the St. Joseph River and evaluating  alternatives for cost-effective ^management of wet -weather
     overflows. In order to achieve these goals, the City reviewed its existing data to determine what additional
     data were jieeded to characterize.CSO impacts. The City.then developed.and implemented a monitoring
     plan .to fiD in these data. gaps. Objectives of the monitoring plan included quantifying overflow .volumes
     andpdllutant loads in the overflows and flows and pollutant loads in the receiving-water. After evaluating
     various analytical and modeling tools, the City decide to use the SWMM model to assist in predicting the
     benefits of alternative control strategies and definmgnproblems caused by storm-related CSO discharges.

     Monitoring Flan Deslfp^d Implementation

     The mom'toringplan was designed to focus on die 6'largest dramage areas, whiclrwere most characteristic
     of land uses within .the-:CSS area .and included 74 percent x>f thatarea. .Monitoring all 42 outfalls was
     judged to.be unnecessarily costly. The monitoring plan-specified 8 temporary and 9 pennanent,flow
     monitoring locations along the main/interceptor and.in the influent and.out£all structures of the 6 largest
     GSOs. The remaining CSO sites had chalk boards 'installed to.determine which stonns caused overflows
     and to help verify correct operation of monitoring equipment Although/monitoring only 15 percent of
     the outfalls, this plan measured-flow and .water quality-for most of .the CSS area.        -  .

     The .monitoring plan stipulated collecting water quality samples for both dry weatherand wet weather
     periods.  The plan specified sample collection from four CSO structures during at least five storm events.
     Monitored water quality parameters included nine metals, total suspended solids (TSS); BOD, CBOD
     (carbonaceous biochemical oxygen demand), total Kjeldahl.nitrogen (TKN), ammonia, total phosphorus,
     total and fecal colifbnn bacteria; conductivity, andhardness. Periodic.dry-weather grab sample collections •
     at the interceptors were also, planned.

     During storm, events, water quality samples wer&collected using 24-bottle automatic samplers at four CSO
     points. To quantify "fust-flush" concentrations, ue-automatic samplers began sample collection at the start
     of an overflow and continued collecting  samples every -five  minutes for the first two hours of the
     monitored events.   A two-person crew drove between sites during  each .monitored event to  check
     equipment operation and the adequacy of sample collection.
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  1     4.7    DATA MANAGEMENT AND ANALYSIS
  2
  3     4.7.1   Quality Assurance Programs
  4
  5            Since inaccurate or unreliable data may lead to faulty decisions in evaluating, selecting,
  6     and implementing CSO controls, the monitoring and modeling plan must provide for quality
  7     assurance and quality control to ensure that the data collected are precise and accurate. Quality
  8     assurance and quality control (QA/QC) procedures are necessary both in the field (during
  9     sampling) and in the laboratory to ensure that data collected in environmental monitoring
 10     programs are of known quality, useful, and reliable.  Quality assurance refers to programmatic
 11      efforts  to ensure  the quality of monitoring and measurement data.  QA  programs increase
 12      confidence in the validity of the reported analytical data.  Quality control, which is a subset of
 13      quality assurance, refers to the application of procedures designed to obtain prescribed standards
 14      of performance in monitoring and measurement. For example, a program describing a calibration
 15      schedule is QA, while the calibration procedures are QC.
 16
 17            QA/QC procedures can be divided into two categories, field procedures and laboratory
 18      procedures.  Both types of QA/QC are described in the following subsections.
 19
20           Field QA/QC  QA  programs for sampling  equipment and for field measurement
21      procedures (for such parameters  as temperature, dissolved oxygen, and pH) are necessary to
22      ensure data of the highest quality.  A field QA program should contain the following documented
23      elements:
24
25           •  The sampling and analytical methodology; special sample handling procedures; and
26       '       the precision, accuracy, and detection limits of all analytical methods used
27
28           •  The basis for selection of sampling and analytical methods.  Where methods do not
29              exist, the QA plan  should state how the new method will be documented, justified,
30              and approved for use.
31
32           •  Procedures for  calibration  and maintenance  of field instruments  and  automatic
33              samplers.
34
35           •  Training of all personnel involved in any function affecting the data quality.
36

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  1            •  A performance evaluation  system assessing the performance  of field sampling
  2               personnel in the following areas:
  3
  4               -  Qualifications  of field personnel for a particular sampling situation

  6               -  Determination of the best representative sampling site
  7
  8               -  Sampling technique including  monitoring  locations, the choice  of grab or
  9                  composite sampling, the type of automatic sampler, special handling procedures,
 10                  sample preservation, and sample identification
 11
 12               -  Row measurement
 13
 14               -  Completeness of data, data recording, processing, and reporting
 15
 16               -  Calibration and maintenance of field instruments and equipment
 17
 18               -  The use of QC samples such as duplicate, split, or spiked samples and blanks as
 19                  appropriate to assess the validity of data.
 20
 21            •   Procedures for the recording, processing, and reporting of data; procedures for review
 22               of data and invalidation of data based upon QC results.
 23
 24           •   The amount of analyses for QC, expressed as a'percentage of overall analyses, to
 25                assess the validity  of data.

 26

 27            Sampling QC includes calibration and preventative maintenance procedures for sampling

 28      equipment, training of sampling personnel,  and collection and analysis of QC samples.  QC

 29      samples  are used to determine the performance of sample collection techniques and should be

 30      collected when the other sampling is performed. The following sample types should be part of

 31      field QC:

 32

 33            •   Duplicate Samples (Field)—Duplicate field samples collected at selected locations
 34                provide a check for precision in sampling equipment and techniques.
 35
 36            •   Equipment Blank—An aliquot of distilled water which is taken to and opened in the
 37                field, its contents poured over or through the sample collection device, collected in
 38                a sample container, and returned to the laboratory for analysis to check sampling
 39                device cleanliness.
40
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  1            •  Field/nip Blank—An aliquot of distilled water or solvent that is brought to the field
  2               in a sealed container and transported back to the laboratory with the sample containers
  3               for  analysis in order to check  for contamination from transport, shipping, or site
  4               conditions.
  5
  6            •  Preservation  Blank—Adding a known amount of preservative  to  an aliquot of
  7               distilled water and analyzing the substance to  determine the effectiveness of the
  8               preservative (i.e., whether the aliquot is contaminated).
  9

 10            Laboratory QA/QC. Laboratory QA/QC procedures ensure high-quality analyses through

 11      instrument calibration and the processing of control samples. Precision of laboratory findings

 12     refers to the reproducibility of results.  In a laboratory QC program, a sample  is analyzed

 13      independently, more than once using the same methods and set of conditions. The precision is

 14      estimated by comparing the measurements.  Accuracy refers to the degree of difference between

 15      observed values and known or actual values.  The accuracy of a method may be determined by

 16      analyses of samples to which known amounts of reference standards have been added.
 17

 18            The following techniques are useful in determining confidence hi the validity of analytical
 19      data:

20

21            •  Duplicate Samples (Laboratory)—Samples received  by  the laboratory and divided
22               into  two or more portions at  the laboratory, with each portion then separately and
23               identically prepared and analyzed.  These samples  determine precision to assess
24               sampling techniques and equipment.
25
26            •  Split Samples (Field)—Single samples split in the field and analyzed separately check
27               for variation hi laboratory method or between laboratories. Samples can be split and
28               submitted to a single laboratory or to several laboratories.
29
30            •  Spiked Samples (Laboratory)—Introducing a known quantity of a substance into
31               separate aliquots of the sample or into a volume of distilled water and analyzing for
32               that substance provides a check of the accuracy of laboratory and analytic procedures.
33
34            •  Reagent Blanks—Preserving and analyzing a quantity of distilled water in the same
35               manner as environmental water samples  can  indicate  contamination  caused by
36               sampling and laboratory  procedures.
37
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  1     QA/QC programs are discussed in greater detail in EPA Requirements for Quality Assurance
  2     Project Plans for Environmental Data Operations (EPA, 1994d) and Industrial User Inspection
  3     And Sampling Manual For POTWs (EPA, 1994c).
  4
  5     4.72   Data Management
  6
  7            Although a permittee may collect accurate and representative data through its monitoring
  8     efforts and verity the reliability of the data through QA/QC procedures, these data are of limited
  9     usefulness if they are not stored in an organized manner and analyzed properly.  The permittee
 10     should develop a data management program to provide ready access to data, prevent data loss,
 11      prevent introduction of data errors, and facilitate data review and analysis.  Even if a permittee
 12     intends to use a "complex" model to evaluate the impacts of CSOs and proposed CSO control
 13      alternatives,  the model  still requires appropriate data for  input  parameters, as  a basis for
 14      assumptions made in the modeling process, and for model calibration and verification. Thus, the
 15     . permittee needs to properly manage monitoring data and perform some review and analysis of
 16      the data regardless of the analytical tools selected.
 17
 18            All monitoring data should be organized and stored in a form that allows for ready access.
 19      Effective data management is necessary because the voluminous and diverse nature of the data,
20      and the variety of individuals who can be involved in collecting, recording and entering data, can
21      easily lead to data loss or error and severely damage the quality of  monitoring programs.
22
23            Data management systems must address both  managerial and  technical issues.  The
24      managerial issues include data storage, data validation and verification, and data access.  First,
25      the permittee should determine if a computerized data management system will be used.  The
26      permittee should consider factors such as the volume of monitoring data (number of sampling
27      stations, samples taken at each station, and pollutant parameters), complexity of data analysis,
28      resources available (personnel, computer equipment, and software),  and  whether modeling will
29      be performed. To enable efficient and accurate data analysis,  a computerized system  may be
30      necessary for effective data management in all but the smallest watersheds.  Computerized data
31      management systems may also facilitate modeling if the data can be uploaded directly  into the

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  1     model rather than being reentercd.  Thus, if modeling will be performed, the permittee should
  2     consider compatibility with the model when selecting any computerized data management system.
  3     Technical issues related  to data management systems involve the selection of appropriate
  4     computer equipment and software and the design of the data system, including data definition,
  5     data standardization, and a data dictionary.
  6
  7           Data quality must be rigidly controlled from the point of collection to the point of entry
  8     into the data management system. Field and laboratory personnel must carefully enter data into
  9     proper spaces on data sheets and avoid transposing numbers.  To avoid transcription errors when
 10     using  a computerized data management system, entries into a preliminary data base should be
 11      made from original data sheets or photocopies. As a preliminary screen for data quality, the data
 12     base/spreadsheet design should include automatic range-checking of all parameters, where values
 13      outside defined ranges are flagged and either immediately corrected or included in a follow-up
 14     review.  For some parameters, it might be appropriate to include automatic checks to disallow
 IS      duplicate values. Preliminary data base/spreadsheet files should be printed and verified against
 16      the original data to identify errors.
 17
 18            Additional  data validation can include  expert  review of the verified data to identify
 19      possible  suspicious values.  In some  cases, consultation with the individuals responsible for
20      collecting or entering original  data may be necessary to resolve problems.  After all data are
21      verified and validated, they can be merged into the monitoring program's master data files. For
22      computerized systems, to prevent loss of data from computer failure at least one set of duplicate
23      (backup) data files should be maintained.
24
25            Data analysis is discussed in Chapters 5 (CSS Monitoring) and  6  (Receiving  Water
26      Monitoring). The use of models for more complex data analysis and simulation is discussed in
27      Chapters 7 (CSS Modeling) and 8 (Receiving Water Modeling).
28
29
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  1     4.8   IMPLEMENTATION OF MONITORING AND MODELING PLAN
  2
  3           During development of the monitoring and modeling plan, the permittee needs to consider
  4     implementation issues such as recordkeeping and reporting requirements, personnel responsible
  5     for carrying out each  element  of the plan, scheduling, and resources.   Although  some
  6     implementation issues cannot be fully addressed in the monitoring and modeling plan until other
  7     plan elements have evolved, they  should be considered on a preliminary basis in order to ensure
  8     that the resulting plan will satisfy reporting requirements and be feasible with available resources.
  9
 10     4.8.1  Recordkeeping and Reporting
 11
 12           The monitoring and modeling plan should include a recordkeeping and reporting plan,
 13      since future permits will contain recordkeeping and reporting requirements such as progress
 14      reports on NMC and LTCP implementation and submittal of monitoring and modeling results.
 15      The recordkeeping and reporting plan should address the post-compliance monitoring program
 16      the permittee will develop as part of the LTCP.
 17
 18      4.8.2  Personnel Responsible for Implementation
 19
20            The monitoring and modeling plan should identify the personnel that will implement the
21      plan. In some cases, particularly in a city with a small CSS, the appropriately trained personnel
22      available for performing  the tasks specified in the monitoring and modeling plan may be very
23      limited. By reviewing personnel and assigning tasks, the permittee will be prepared to develop
24      an  implementation schedule that will  be attainable  and will  be able  to  identify resource
25      limitations and needs (including training) early hi the process.
26
27      4.83  Scheduling
28
29            The permittee should develop a tentative implementation schedule for the monitoring and
30      modeling plan to ensure that elements of the plan are implemented continuously and efficiently.
31      The schedule should be revised as necessary to reflect the review team's assessment of the plan
32      and the evaluation of monitoring and modeling results.  The schedule should  address:
33
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  1            •   Reporting and compliance dates included in the NPDES permit
  2            •   Monitoring frequencies
  3            r   Seasonal sampling schedules and dependency on rainfall patterns
  4            •   Implementation schedule for the NMC
  5            •   Coordination with other ongoing sampling programs
  6            •   Availability of resources (equipment and personnel).
  7
  8     4.8.4   Resources
  9
 10            During development of the monitoring and modeling plan, the permittee should identify
 11      equipment, personnel, and other resource needs, and may need to modify the plan after assessing
 12      the availability of these resources. For example, if the monitoring and modeling plan identifies
 13      complex modeling strategies, the permittee may need to consider modeling techniques that have
 14      more moderate data requirements. Alternatively, if the permittee does not have the resources to
 15      purchase the hardware or software needed to run  a detailed model, the permittee may be able to
 16      make arrangements to use the equipment at another facility (e.g., another municipality developing
 17      a CSO control program) or at a State or Federal agency. However, if such arrangements are not
 18      possible, the permittee may  need to choose a less detailed model which could lead  to reduced
 19      monitoring costs.
20
21            Through a review of resources, the permittee may identify monitoring equipment needed
22      to implement the monitoring and modeling plan.   By obtaining needed equipment, such as
23      automatic samplers, flow measuring equipment, rain gages, and safety equipment before the date
24      when monitoring is scheduled to begin, the permittee can prevent some potential  delays. The
25      permittee may also be able to spread the costs of implementing the monitoring and modeling plan
26      across several budget years.
27
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  i                                       CHAPTERS
  2
  3                                   CSS MONITORING

  4

  5           This chapter describes techniques and equipment for monitoring rainfall and CSS flow

  6     and  quality, and describes procedures for organizing and analyzing the data  collected.   It

  7   '  discusses a range of monitoring and analysis options and provides criteria for identifying

  8     appropriate options for a particular system.

  9

 10     5.1    THE CSO POLICY AND CSS MONITORING
 11
 12           The CSO Control Policy  identifies several possible objectives of a CSS monitoring

 13      program:

 14

 IS            •   To gain a thorough understanding of the sewer system
 16
 17            •   To adequately characterize the system's response to wet weather events, such as the
 18               magnitude, frequency, and duration of CSOs and the volume, concentration, and mass
 19               of pollutants discharged
20
21            •  To support a mathematical model to characterize the CSS
22
23            •  To support development of appropriate measures to implement the nine minimum
24              controls (NMC)
25
26            •  To support development of the long-term control plan (LTCP)
27
28            •  To evaluate the expected effectiveness of the NMC and the long-term CSO controls
29              to meet WQS.

30

31            CSS monitoring also directly supports implementation of the following NMC:

32

33            •  Maximum use of the collection system for storage

34            •  Maximization of flow to the POTW for treatment

35            •  Control of solids and floatable materials in CSOs

36            •  Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls.


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  1            CSS  monitoring  will also support the  in-depth system characterization  and post-
  2     construction compliance monitoring that are central elements in the LTCP.
  3
  4            This chapter outlines the steps that are critical to collection and analysis of rainfall, flow,
  5     and quality data in accordance with the CSO Control Policy.
  6
  7     52    RAINFALL DATA FOR CSS CHARACTERIZATION
  8
  9            Rainfall data, including both long-term rainfall records and data gathered at specific sites
 10     in  the CSS, are a vital part of a CSS monitoring program.  This information is necessary to
 11      analyze the CSS, calibrate and validate CSO models, and develop design conditions for predicting
 12     current and future CSOs.
 13
 14            This section describes  how to install and  use rainfall monitoring equipment to collect
 15      rainfall data and how to analyze the data gathered.
 16
 17      5.2.1  Rainfall Monitoring
 18
 19            National rainfall data are available from a number of federal and local sources, including
20      the National  Weather  Service, the National Climatic  Data Center (NCDC), airports, and
21      universities (see Chapter 3). However, because rainfall conditions vary significantly over short
22      distances, it is generally necessary to  supplement national data with data from local rainfall
23      monitoring stations.
24
25            Equipment
26            Two types of gages are  used to measure the amount and intensity of rainfall.  A standard
27      rain gage collects the rainfall directly in a marked container and the amount of rain is measured
28      visually. Although inexpensive, standard gages do  not provide a way to record changes in storm
29      intensity without making frequent observations during the storm.
30
       External Review Draft                    5-2                        December 6, 1996

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                          WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            Because  wet weather flows vary with rainfall' intensity, CSS monitoring programs
  2     typically use recording gages, which provide a permanent record of the rainfall amount over time.
  3     The three most common types of recording gages are:
  4
                                                                                         i
  5            .•  Tipping  Bucket Gage—Water caught in  a  collector is  tunneled into  a two-
  6               compartment bucket. Once a known quantity of rain is collected, it is emptied into
  7               a reservoir, and the event is recorded electronically.
  8
  9            •  Weighing Type Gage—Water is weighed when it falls  into a bucket placed on the
 10               platform  of a spring or lever balance.  The weight of the contents is recorded on a
 11                chan, showing the accumulation of precipitation.
 12
 13             •  Float Recording Goge—Rainfall is measured by the rise of a float that is placed in
 14                the collector.
 15
 16             A combination of standard and recording  gages can be  used to collect representative
 17      rainfall data more economically. If recording gages are strategically  placed amid standard gages,
 18      the permittee can compare spatial variations in total  rainfall at each recording gage with  the
 19      surrounding standard gages. Since fewer recording gages may then be needed, money can be
20      saved.
21
22            Equipment Installation and Operation
23            Rain gages are fairly easy to operate and will provide accurate data when installed and
24      used properly. They  should be located in open spaces away from the immediate shielding effects
25      of trees or buildings.   Ground installations are preferable (if vandalism is not a significant
26      problem), although roof installations are also an option. Public buildings, such as  police, fire,
27      or public works buildings, are often used.
28
29      5.22  Rainfall Data Analysis
30
31            Rainfall monitoring should be  synchronized with  CSS  flow  monitoring, so rainfall
32      characteristics can be related to the amount of runoff and CSO volume during a wet weather
33      event and so a CSS model can be calibrated and validated.  In addition, long-term rainfall data
34      gathered from  existing gages are necessary to develop  appropriate  design  conditions for

        External Review Draft                    5-3                         December 6, 1996

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                          WORKING DRAFT;  bo NOT CITE OR QUOTE
  1     determining existing and future CSO impacts on receiving water bodies.  Because precipitation
  2     can vary considerably within short distances, it is usually necessary to use data from several rain
  3     gages to estimate the average precipitation for an area.
  4
  5            Development of Design Conditions
  6            The first step in rainfall characterization is to look at multiple storm events in order to
  7     develop a "design storm," which  is a precipitation event with a specific characteristic used to
  8     estimate a volume of runoff or discharge of specific recurrence interval.  Historic rainfall data
  9     (such as data from NOAA's National Climatic Data Center) can be used to characterize area
 10     rainfall and to estimate design conditions, as long as the data were collected close enough to the
 11      CSS's service area to reflect site conditions. Long-term rainfall data (usually extending over 30
 12      years or more although  10 years of data are usually sufficient) from existing NCDC rain gages
 13      can be analyzed in a number of different ways to develop design storms.  Common methods for
 14      characterizing rainfall include total volumes, event statistics, return period/volume curves, and
 15      intensity-duration-frequency curves.  Each of these methods is described below:
 16
 17            Total Volumes.  The  National Weather  Service publishes annual  totals  as well as
 18      deviations from the average for each rain gage in its network.  Wet- and dry-year rainfalls can
 19      be defined by comparing a particular year's rainfall to the long-term average.  Monthly totals and
20      averages also can be computed in  the same way to examine seasonal differences. This review
21      of seasonal and annual rainfall totals is used to select the time period for detailed simulation
22      modeling.
23
24            For example, 38  years of rainfall records, 1955-1992, were collected at a NOAA gage
25      near (but not within) a CSS drainage area. These records indicate an average of 44 storm events
26      per year, with a wide variation from year to year.  To generate runoff predictions for the CSS
27      drainage area, the STORM runoff model was calibrated and run using the 38 years of hourly
28      rainfall data. The model predicted  the number of runoff events per year, the total  annual runoff,
29      and the average overflow volume  per event in inches/land area.  Exhibit 5-1 ranks the years
30      based on the number of events, inches of runoff, and average runoff per event predicted by the •
31      model.  Results showed  the year 1969 with both the highest number of runoff events (68) and

        External Review Draft                     5-4                        December 6, 1996

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                WORKING DRAFT:  Do NOT CITE OR QUOTE
               Exhibit 5-1.  Ranking of Yearly Runoff Characteristics
                        as Simulated by the Storm Model
Rank
l
2
3
4
5
6
7
8
9
10
11
12
13
14
IS
16
17
18
.19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
Mean
Median
Tear
1969
1984
1987
1983
1976
1989
1974
1966
1980
1956
1988
1975
1972
1957
1.960
1962
1971
1970
1955
1985
1979
1968
1959
1992
1982
1965
1964
1991
1990
1978
1967
1958
1981
1977
1963
1986
1973
1961

No. of Events
68
58
57
56
56
54
54
54
53
53
52
52
52
52
50
49
47
47
47
45
43
43
43
41
40
40
40
34
34
33
33
32
31
30
30
29
29
28
44
46
Tear
1969 '
1987
1984
1975
1974
1956 -
1960
1980
1983
1955
1966
1962
1992
1976
1965
1957
1970
1967
1988
1971
1979
1991
1985
1989
1982
1959
1990
1968
1981
1972
1973
1964
1977
1963
1978
1986
1961
1958

Total Runoff (in)
15.1
14.9
14.7
14.2
13.1
13.1
118
12.6
12.5
115
114
111
111
110
110
11.9
11.7
11.0
10.9
10.9
10.7
10.6
10.4
9.7
9.1
82
8.1
7.9
7.6
73
72.
7.1
6.7
63
6.0
5.8
4.8
4.6
10.3
10.9
Year
1967
1991
1992
1965
1975
1955
1987
1960
1984
1979
1973
1970
1962
1956
1989
1981
1980
1974
1985
1982
1971
1966
1957
1983
1977
1969
1988
1976
1963
1986
1959
1989
1978
1968
1964
1961
1972
1958

Avg Overflow
(hv/event)
033
031 •
0.30
030
027
027
026
026
025
025
025
025
025
025
024
024
024
024
023
023
023
023
023
022
022
022
021
021
021
020
0.19
0.18
0.18
0.18
0.18
0.17
0.14
0.14
023
023
           Extreme Year = 1969
Typical Year = 1970
External Review Draft
       5-5
December 6, 1996

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                         WORKING DRAFT; Do NOT CUE OR QUOTE
  i
  2
  3
  4
  5
  6
  7
  8
  9
10
11
12
13
14
15
16
 largest total runoff volume (15.1 inches).  The year 1967 had the highest predicted average
 overflow per event (0.33 inches).

        Exhibit 5-2 lists minimum, maximum, mean, and median values for  annual runoff
 statistics. These statistics identify typical and extreme years to select for modeling or evaluating
 the frequency of overflows under various control alternatives. Long-term computer simulations
 of the CSS using a multi-year continuous rainfall record or one-year simulations using typical
 or wet years are useful for assessing alternative long-term control strategies.

      Exhibit 5-2.  Rainfall and Runoff Parameters for Typical and Extreme Years
•
Maximum (all years)
1969
1956
1970
Mean (all years)
Median (all years)
1971
1988
1985
1979
Minimum (all years)
No. 
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                          WORKING DRAFT:  Do Nor CITE OR QUOTE
  1            Event Statistics. Information may also be developed on the characteristics of individual
  2     storm events for a site.  If the sequence of hourly rainfall volumes from the existing gages is
  3     grouped into separate events (i.e., each period of volume greater than zero that is preceded and
  4     followed by at least one period of zero volume would mark a separate event), then each storm
  5     event may be characterized  by  its duration,  volume, average  intensity, and the time interval
  6     between successive events. The event data can be analyzed using standard statistical procedures
  7     to determine the  mean and  standard deviation for each storm event, as well  as probability
  8     distributions and recurrence intervals. The computer program SYNOP can be used  to group the
  9     hourly rainfall values into independent rainfall events and calculate the storm characteristics and
 10     interval since the preceding storm.
 11
 12           Return Period/Volume Curves. The "return period" is the frequency of occurrence for
 13      a parameter (such  as rainfall volume) of a given magnitude.  The return period for a storm  with
 14      a specific rainfall  volume may be plotted as a probability distribution indicating  the percent of
 15      storms with a total volume less than or equal to a given volume. For example, if approximately
 16      ten percent of the  storm events historically deposit 1.5 inches of rain or more,  and  there are an
 17      average of 60 storm events per year, an average of 6 storm events per year would  have a  total
 18      volume of 1.5 inches or more, and the 1.5-inch rain event could be characterized as the "two-
 19      month storm."
20
21            Intensity-Duration-Frequency Curves. Duration can be plotted against average intensity
22      for several constant storm return frequencies, in order to design hydraulic structures  where short
23      duration peak flows must be considered to avoid local flooding. For example, when  maximizing
24      in-system storage (under the NMC), the selected design event should ensure that backups in the
25      collection system,  which cause flooding, are avoided.  Intensity-duration-frequency curves are
26      developed by analyzing an hourly rainfall record in such a way as to compute a running sum of
27      volumes for consecutive  hours equal to the duration of interest  The set of volumes for  that
28      duration are then ranked, and based on the length in years of the record, the recurrence interval
29      for any rank is determined. This rainfall analysis procedure is used to calculate the local value
30      for design storms such as a 1-year, 6-hour design condition.
31

        External Review Draft                     5-7                         December 6, 1996

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                         WORKING DRAFT;  Do NOT CITE OR QUOTE
  i
  2
  3
  4
  5
  6
  7
  8
  9
10
11
        Local Rain Gage Data
        In order to calibrate and verify .runoff and water quality models, it is also necessary to
 analyze rainfall data for specific storm events in which CSO quality and flow sampling is
 occurring.

        Local rain gage data can be used to assess the applicability of the long-term record of the
 site.  For example, Exhibit 5-3 presents two months of local rainfall data from three tipping
 bucket gages flabelled A, B, and C in Exhibit 5-4). Comparison with NOAA data indicates that
 the average value of the three gages was close to the regional record with only slight variations
 among gages. Three events were  selected for detailed water quality sampling and analysis.
                                    \

            Exhibit 5-3. 1993 Rainfall Data for a 5,305 Acre Drainage Area
Storm .
Event
1
2
3
4
5
6
7
8
9

-Date
4/6
4/14 M
4/21
4/28 M
5/5
5/8
5/11
5/13 M
5/14
Total
Gage A
(inches)
0.58
0.22
0.11
0.87
0.12
0.47
0.50
0.44
0.48
3.79
GageB
(inches)
0.58
0.17
0.12
1.20
0.18
0.40
0.45
0.31
0.43
3.84
GageC
(inches)
0.62
0.19
0.08
1.05
0.12
0.42
0.45
0.22
0.52
3.67
1K£pVAMSn KAAAl^n1
1 OI ^A&UIE&II *
(inches)
0.59
0.19
"0.10
1.04
0.14
0.43
0.47
0.32
0.48
3.70
Duration'
(hours) .
4.8
1.5
1.4
2.5
1.5
9.4
4.5
0.8
4.3
30.7
Intensity
- -{in/or)
0.12
0.13
0.07
0.42
0.09
0.05
0.10
0.40
0.11
0.12
12
13
14
15
16
17
M = event selected for detailed water quality monitoring

       As indicated by Exhibit 5-3, storm #4 (April 28) would be particularly useful for model
calibration or verification because a large amount of rain fell over a relatively short period.

       In cases where local rain gages are placed near but not exactly at the locations where CSS
flow and quality is being monitored, rainfall data from several nearby rain gage locations can be
       External Review Draft
                                         5-8
December 6,  1996

-------
I
EL
                                          Exhibit 5-4. Rain Gage Map for Example 5-1
VO
^o
ON
                                                                                                  4   CSO Outfall Drainage
                                                                                                      Area

                                                                                                                                    I
                                                                                                                                    o
                                                                                                                                    o
                                                                                                                                    n
                                                                                                                                   o
                                                                                                                                    I
Not to Scale

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                           WORKING DRAFT:  Do NOT CITE OR QUOTE
  i
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 It
 16
 17
 18
 19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
 interpolated to estimate the rainfall at the sampling location.  The inverse distance weighting
 method can be used to calculate the rainfall over a CSS sampling location in watershed 4 in
 Exhibit 5-4.
                           In verse Distance Weighting Method

    Using this method, tte.estimated.pretiprtation.at the sampling location is determined as a. weighted
    average.of the .precipitation at the surrounding rain gages. Jhe. weights are die .reciprocals of th& squares
    of die distances between die,sampling,location,vand:lhe rain;gages. JThe estimated rainfall at the sampling
    Incatifwis calmlnteH hv milllllling"rtlP'rnwinrtatifvn tiiinae^ttia oraurht tnr aa/Oi-«« •«>•«».«-"J *-
   the sum of the weights: \Forexampley if the distance between the .sampling location m-watershed'4>and'
   rain gage Ads X, iamgageCBasT,andiain gage;Cis Z^and^eprec^toticmat^acfriain'ga^e is'P^P,
   and- Pc, men the precipitation at the sampling location in watershed 4-can be estimated by:   .  ...
                                                          .        •    •         •
  . If P*. PB, anff-Pc.are 0.87, 130, andJLOS inches, respectively, and X, Y, and Z-are..kO, 1.5, and 3K),feet
   respectively, men .   -  ".   ',              •           .       '•'•'.

It may also vbe possible to use radar imaging data to estimate rainfall intensities at multiple
locations throughout the rainfall event.

53    FLOW MONITORING IN THE CSS
       Accurate flow monitoring is critical to understanding the hydraulic characteristics of a
CSS and predicting the magnitude, frequency, and duration of CSOs.  Monitoring flows in CSSs
can be difficult because of surcharging, backflow, tidal flows, and the intermittent nature of
overflows.   Selecting  the most appropriate flow  monitoring technique  depends  on  site
characteristics, budget constraints, and availability of personnel.  This section outlines options
for measuring CSS flow and discusses how to organize and analyze the data collected.

53.1   Row Monitoring Techniques
       Flow measurement techniques vary greatly in complexity, expense, and accuracy.  This
section describes a range of manual and automated flow monitoring techniques.  Exhibit 5-5
summarizes their advantages and disadvantages.
        External Review Draft
                                          5-10
December 6, 1996

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              WORKING DRAFT: Do NOT CITE OR QUOTE
                  Exhibit 5-5.  CSO Flow Monitoring Devices
Monjtoring Method,
Manual Methods
Timed Flow
Dilution Method

Direct Measurement
Chalking Boards
Bottle Boards
Primary Flow
Weir
Flume
Orifice Plate

Depth Sensing
Ultrasonic Sensor
Pressure Sensor



Float Sensor
Velocity Meters
Ultrasonic
Electromagnetic
[-" ,., * - ^Description- \ ;.*.•. . ;

Timing how long it takes to fill a
container of a known size
Injection of dye or saline solution in
the system and measuring me
dilution
Use of a flow meter and surveying
rod to manually measure flow and
depth
Installation of a board with a chalk
line which is erased to the level of
highest flow
Installation of multiple bottles of
different size where the tallest filled
bottle indicates the depth of flow

Devices placed across the flow such
that overflow occurs through a
notch. Flow is determined by the
depth behind the weir
Chute-like structure thaT allows for
controlled flow
A plate with a circular or oval
opening designed to control flow


Sensor mounted above the flow that
measures depth with an ultrasonic
signal
Sensor mounted below the flow
which measures the pressure exerted
by the flow

and measuring the resistance to
bubble formation
Sensors using a mechanical float to

Meter designed to measure velocity
through a continuous pulse
Meter designed to measure velocity
through an electromagnetic process
;v^?;^YaiSages< -<-•*.:.*

* Dimple to iiiiiiimHftiit
• Little equipment needed
• Accurate for instantaneous
flows
• Easy to collect data
• Easy to implement
• Easy to implement

• Many CSOs have existing
weirs
• More accurate than other
• Accurate estimate of flow
• Less prone to clogging man
weirs ,
• Can measure flow in full
nines
• Portable and inexpensive to
operate

• Generally provide accurate
measures
• Generally provide accurate



• Generally provide accurate

• Instrument does not interfere
with flow
• Can be used in full pipes
• Instrument does not interfere
with flow
• Can be used in full pipes
|&>:V4*£Ma4Bryf v<;\

• Labor intensive
• Suitable only for low
flows

continuous flow
• Outside contaminants
could impact results
• Labor intensive
• Multiple measurements
may be needed at a single
location
• Only rough estimate of
depth measured
• Only rough estimate of
depth measured

• Cannot be used in full or
nearly full pipes
• Somewhat prone to.
clogging and silting
• Not appropriate for
backflow conditions
• More expensive than
wens
• Prone to solids
accumulation


• May be impacted by
solids or foam on flow
surface
• Require frequent cleaning
and calibration

to prevent clogging
• Must be accurately
calibrated prior to use and
regularly checked

• More expensive than
other1 eQUipment
• More expensive man
other equipment
External Review Draft
5-11
December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1           Manual Methods
  2           The simplest flow monitoring techniques involve manual measurement of velocity and
  3     depth, use of bottle boards and chalking (see Example 5-1), and dye testing. Manual methods
  4     are difficult during wet weather, however, since they rely extensively on labor-intensive field
  5     efforts during storm events and do not provide an accurate, continuous flow record. Manual
  6     methods are most useful  for instantaneous flow measurement, calibration  of other flow
  7     measurements, and flow measurements in small systems.  They are difficult to use for measuring
  8     rapidly changing  flows .because numerous instantaneous measurements must be taken  at the
  9     proper position to correctly  estimate the total flow.
 10
 11            Measuring Flow Depth
 12           Primary flow devices, such as weirs, flumes, and orifice plates, control flow in a portion
 13      of pipe such that the flow's depth is proportional to its flow rate. They enable flow rate to be
 14     determined by manually or automatically measuring the depth of flow.  Measurements taken with
 IS      these devices are accurate in the appropriate hydraulic conditions but are not where surcharging
 16      or backflow occur.  Also, the accuracy of flow calculations depends on the reliability of depth-
 17      sensing equipment, since small errors in depth measurement can result in large errors in flow rate
 18      calculation.
 19
20            Depth-sensing devices can be used with pipe equations or primary flow and velocity-
21      sensing devices to determine flow rates. They include:
22
23            •   Ultrasonic Sensors, which are typically mounted above the flow in  a pipe or open
24               channel and send an ultrasonic signal toward the flow.  Depth computations are based
25               on the time the reflected signal takes to return to the sensor.  These sensors provide
26               accurate depth measurements but can be affected by high  suspended solid loads or
27               foaming on the water surface.
28
29            •   Pressure sensors, which use transducers to sense the pressure of the water  above
30               them.  They are used with a flow monitor that converts the pressure value to a depth
31               measurement.
32
33            •   Bubbler Sensors, which emit  a  continuous stream of  fine bubbles.  A pressure
34               transducer senses resistance to bubble formation, converting it  to  a depth value.

       External Review Draft                    5-12                        December 6, 1996

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                            WORKING DRAFT:  Do NOT CITE OR QUOTE
                                                  ^Example 5-1,

              A bottle rack is used to determine Ae approximate depth of overflows from a 36-inch combined sewer
              in an overflow manhole (Exhibit;5-6)^ Tie overflow-weir fortbirbutfall isd2dnches,above^the invert
              of the'sewer, and .Hows -below ibis level' are routed out the bottbnvof the structnre to the interceptor
              and mewastewater,treatmentplant (WWTP). Anyflow-overflowingThe 12-inch weirds routed .to the
              42-Inch outfall .sewer. AttacheoVto the manhole steps, the tottle^k.approximates the flow Jevel in
              •me manhole by the .-height ;ofithe bottles'fhatVare fiUed^This^outfallJias. potential for surcharging
              because <)fflowiestriMons leading to the interceptor. Consequently;rthe bottle lack extends well above
              the crown (of the outfall sewer.  After each rainfall,; ar-member ofcthe monitoring team pulls :the rack
              from the manhole, records theJiighesti>ptde filled, andoeturns the rack to the manhole.  Exhibit 5-7
              presents dep>m data for the ;nme^nris-listed;inExfiibit-5-3.   *     •                 ...

              Storm-3; winch had'B.l indroFrain in 85,rnmutes,;Tvas contained-aWhe outfall with no .overflow,
              although it did overflowed: other loca'tionsi ~, Storm 5,:wHh£aa-ayerageottle boan£anaicatesjcqjproximate maximum flpw^depm,
             . not duration w flow volume, it, is not ;sufficient:tocaiibrate'rnqstinodels:               x  :

              Storms 4 and 8 caused flow depthrto surcharge, orincrease-above1he,crown of the pipe. Bom-stoons.x
             . occurred during late afternoon when°sanitary&ewer flows are typically iighest, potentially exacerbating
              the overflow. .The snrchargmg pipe indicates thatilow measurements ^wifl be difficult for large stonns
              at'thislocation. Purthetfi^ld investigations wfll be necessary to define the hydraulics of this.particular
              outfaU andinterceptmg device.- Because;of safety considera6ons>m gaining access to this location;the-
              monitoring team used only the bottle :board during the early monitoring period.   Later, "the *«^""
              instaTIed,a velocity ^rneter and a series of. depth .probes to determine a surface profile.
 1
 2
 3
 4
 5
 6

 7

 8

 9

10

11
           These devices provide accurate measurements.  The bubble tube can clog, however,
           and the device itself requires frequent calibration.

           Float Sensors, which sense depth using a mechanical float, often within a chamber
           designed to damp out  surface waves.  Floats can clog with grease and solid materials
           and are, therefore, not commonly used to sense flow in sewers.
        Using depth measurement data, pipe equations can be applied to develop flow estimates.
The Hazen-Williams  equation, Manning equation, and  similar equations  can  be useful  for

estimating flow capacity of the system and performing a preliminary flow analysis of the CSS.
        External Review Draft
                                              5-13
December 6, 1996

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
                        Exhibit 5-6.  Illustration of a Bottle Board Installation

                                                  Section
 i
 2
 3

 4

 5
 6
 7
 8
 9
10
11
12

13
              42" CSO
               to River
                                                                                36"
                                           To Wastewater
                                           Treatment Plant
The Hazen-Williams equation is generally used for pressure conduits, while the Manning equation
is usually used in open-channel situations (Viessman, 1993).  The Hazen-Williams equation is:
V = 1.318 C(R)°-63 (S)0-54
where:

      V = mean flow velocity
      C = Hazen-Williams coefficient, based on material and age of the conduit
      R = hydraulic radius
      S = slope of energy gradeline (foot rise/foot run).
       External Review Draft
                                       5-14
December 6, 1996

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                        WORKING DRAFT:  Do NOT CUE OR QUOTE
                         Exhibit 5-7.  Example Outfall Bottle Rack Readings
Storm Event
1
2
3
4
5
6
7
8
9
Manhole J1ow Level
(inches)
21
18
12
48
18
18
30
42
24
Height of Overflow
(inches)
9
6
none
36 (surcharge)
6
6
18
30 (surcharge)
12
       The Manning Equation is:
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

18

19
20

21

22
V = (1.49/n) (R)a<66 (S)0-5
where:

      V = mean flow velocity
      n  = • Manning roughness coefficient, based on type and condition of conduit
      R = hydraulic radius
      S  = slope of energy gradeline (foot rise/foot run).

The volumetric flow rate (Q) is computed by:  Q = VA where:

      V = mean flow velocity
      A = cross-sectional area.

      Since the calculations are based on the average upstream characteristics  of the pipe,
personnel should measure depth at a point in the sewer where there are no bends or sudden

changes in invert elevation immediately upstream. These features can introduce large errors into
the flow estimate. Anomalies in sewer slope, shape, or roughness also can cause large errors (SO

percent and greater) in flow measurement.  However, in uniform pipes, a careful application of

the formula can measure flows with an error as low as 10 to 20 percent (ISCO,  1989).  The
       External Review Draft
                                       5-15
December 6,. 1996

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                         WORKING DRAFT;  Do NOT CITE OR QUOTE
  1     permittee can improve the accuracy of the equation somewhat by calibrating it initially, using
  2     measurements of velocity and depth to adjust slope and roughness values.
  3
  4           Velocity Meters
  5           Velocity meters use ultrasonic or electromagnetic technology to sense flow velocity at a
  6     point, or in a cross section of the flow.  The velocity measurement is combined with a depth
  7     value (from a depth sensor attached to the velocity meter) to compute flow volume. Velocity
  8     meters can measure flows in a wider range of locations and flow regimes than  depth-sensing
  9     devices  used with  primary  flow  devices, and they are  less prone to clogging.  They are
 10     comparatively expensive, however, and can be inaccurate at low flows and when suspended-solid
 11  .    loads vary rapidly. (One type of meter combines an electromagnetic velocity sensor with a depth
 12      sensing pressure transducer in a single probe. It is useful  for CSO applications because it can
 13      sense flow in surcharging, and backflow conditions. This device is available as a portable model
 14      or for permanent installation.)
 15
 16            Measuring Pressurized Flow
 17            Although sewage typically flows by gravity, many combined sewer systems use pumping
 18      stations or other means to pressurize their flow. Monitoring pressurized flow requires different
 19      techniques from those used to monitor gravity flows.  If a station is designed to pump  at a
20      constant  rate, the flow rate through the station can be estimated from the length of time the
21      pumps are on. If a pump empties a wet well or cavern, the pumping rate can be determined by
22      measuring the change in water level in the wet well.  If  the pump rate is variable, or pump
23      monitoring time is insufficient to measure flow, then full-pipe metering is required.
24
25            Measuring Flow in Full Pipes
26            Full pipes can be monitored using orifices, Venturis, flow nozzles, turbines, and ultrasonic,
27      electromagnetic,  and vortex shedding meters.  Although  most of these technologies require
28      disassembling the piping and  inserting a meter, several types of meters strap to the outside of a
29      pipe and  can be moved easily to different locations.  Another measurement technique involves
30      using two pressure transducers, one at the bottom of the pipe, and one at the  top of the pipe or


        External Review Draft                    5-16                        December 6, 1996

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                         WORKING DRAFT: Do NOT CUE OR QUOTE
  1      in the manhole just above the pipe crown. Closed pipe metering principles are discussed fully
  2      in The Flow Measurement Engineering Handbook (Miller, 1983).   Manufacturers' literature
  3      should be consulted for installation requirements.
  4
  5
 6
 7
Note to reviewers: Some of these measurement techniques may not be
feasible in many systems or applications. If other techniques are more
appropriate/feasible, please note diem in your comments.
 8
 9      53.2  Conducting the Flow Monitoring Program
10
11            Most flow monitoring involves the use of portable, battery-operated depth and velocity
12      sensors, which are left hi place for several storm events and then moved elsewhere. For some
13      systems, particularly small CSSs, the program may involve manual methods. In such cases, it
14      is important to allocate the available personnel and prepare  in advance for the wet weather
15      events.
16
17            Although temporary metering installations are designed to operate automatically, they are
18      subject to clogging in combined sewer systems and should be checked as often as possible for
19      debris.
20
21            Some systems use permanent flow monitoring installations to collect data continuously
22      at critical points. Permanent installations also can allow centralized control of transport system
23      facilities to maximize storage of wastewater in the system and maximize flow to the treatment
24      plant.  The flow data recorded at the site may be recovered manually or telemetered to a central
25      location.
26
27            To be of use in monitoring CSSs, flow metering installations should be able to measure
28      all possible flow situations, based on local conditions.  In a pipe with smooth flow characteristics,
29      a weir or flume in combination with a depth sensor or a calibrated Manning equation may  be
30      sufficient. Difficult locations might warrant redundant metering and frequent calibration.  The
       External Review Draft                    5-17                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     key to successful monitoring is combining good design and judgment with field observations, the
  2     appropriate metering technology, and a thorough meter maintenance and calibration schedule.
  3
  4     53.3  Analysis of CSS Flow Data
  5
  6           The CSS flow data can be evaluated to develop an understanding of the hydraulic
  7    , response of the system to wet weather events and to answer the following questions for the
  8     monitored outfalls:
  9
 10           •   Which CSO outfalls contribute the majority of the overflow volume?
 11
 12           •   What size storm can be contained by the regulator serving each outfall?  Does this
 13               containment capacity vary from storm to storm?
 14
 IS            •  Approximately how many overflows would occur and what would be their volume,
 16               based on a rainfall record from  a  different year?'How many occur per year, on
 17                average,  based on the long-term rainfall record?
 18
 19            Extrapolating from the monitored period to other periods, such as a rainfall record for a
20     year with more storms or larger volumes, requires professional judgment and familiarity with the
21     data.  For  example, as shown in Exhibit 5-8,  the flow regulator serving Outfall 4 prevented
22     overflows during Storm 3, which had 0.10 inch of rain in 1.4 hours.  However, approximately
23     half of the rainfall volume overflowed from Storm 5, which had 0.14 inch in 1.5 hours.  From
24     these data, the investigator might conclude that, depending on  the short-term intensity of the
25     storm or the antecedent moisture  conditions, Outfall 4  would contain a future storm of 0.10
26     inches but that even slightly larger storms would cause an overflow. Also, Exhibit 5-8 indicates
27     that a storm even as small as Storm 3 can cause overflows at the other outfalls.
28
29            Comparing the overflow volumes of different outfalls indicates which outfalls contribute
30     the bulk of the overflow volume and, depending on loading measurements, may contribute most
31     heavily to water quality problems. To compare the hydraulic performance-of different outfalls,
32     flows should be normalized against the drainage area and rainfall. Provided that rainfall data are
33     representative of the area's rainfall, inches of overflow (spread over the discharge subarea) per
       External Review Draft                    5-18                        December 6, 1996

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                                                   Exhibit 5-8.  Total Overflow Volume
so
Storm
1
2
3
4
5
6
7
8
9
Average
Rainfall
Depth (ft)
(inches)
0.59
0.19
0.10
1.04
0.14
0.43
0.47
, 0.32
0.48
0.42 .
Duration
(hours)
4.8
1.5
1.4
2.5
1.5
9.4
4.5
0.8
4.3
3.41
Outfall (and service area size, in acres)
#1 (659 acres)
V
0.24
0.07
na
0.62
0.06
0.19
0.26
na
0.26
0.24
V/R
0.41
0.37
na
0.60
0.43
0.44
0.55
na
0.54
0.48
#4 (430 acres)
V
0.39
0.085
0.00
0.832
0.071
0.195
0.32
0.252
0.32
0.27
v/k
0.65
0.45
0.00
0.80
0.51
0.45
0.68
0.79
0.66
0.55
#5(500 acres)
V
0.27
na
0.04
0.39
0.05
0.18
0.16
0.15
0.14
0.17
V/R
0.46
na
0.41
0.73
0.37
0.43
0.34
0.46
0.29
0.43
#7 (690 acres)
. V
0.50
0.14
0.06
0.81
0.102
0.361
0.334
0.25
0.29
0.32
V/R
0.85
0.72
0.56
0.77
0.73
0.84
0.71
0.78
0.60
0.73
#9 (1,060 acres)
V
na
0.072
0.045
0.44
0.051
0.23
0.2
0.141
0.17
0.17
V/R
na
0.38
0.45
0.67
0.36
0.53
0.42
0.44
0.35
0.45
             V   = overflow volume (inches depth when inches of overflow is spread over drainage area)
             R   = rainfall depth (inches)
             na   = no measurement available
                                                                                                                                                I
                                                                                                                                                !
!
f
S
o\

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     inch of rainfall constitutes a useful statistic. Exhibit 5-8 presents the overflow volumes in inches
  2     and the ratio of depth of overflow to depth of rain (V/R).
                                                                i
  3  '
  4           For each outfall, V/R varies with the storm depending on antecedent dry days, the time
  5     of the storm, and the maximum rainfall intensity. V/R also varies with the outfall depending on
  6     land  characteristics  such as its impervious portion, the hydraulic capacity  upstream and
  7     downstream of the flow regulator, the operation of the flow regulator, and features that limit the
  8     rate at which water can enter the system draining to that overflow point.  Because of the large
  9     number  of  factors affecting variations in V/R, small  differences  generally provide little
 10     information about overflow patterns.  However, certain patterns, such as an increase in V/R over
 11      time or large differences in V/R between storms or between outfalls, may indicate design flaws,
 12      operational problems, maintenance problems, or erroneous flow measurements, or a rainfall gauge
 13      that does not represent  the average depth of rain falling on the discharge subarea.
 14
 15            Li addition to analyzing total  overflow volumes for the CSOs, flow data can be used to
 16      create  a plot of flow and head for a selected conduit during a storm event, as  shown in Exhibit
 17      5-9. These plots can be used to illustrate the  conditions under which overflows occur at a
 18      specific outfall.  They  can also be used during CSS model calibration and verification (see
 19      Chapter 7).
20
21            Exhibits '5-8 and 5-9 (representing" different CSS monitoring programs) illustrate some of
22      the numerous methods available for analyzing CSO flow monitoring data. Flow data can also
23      be used to tabulate CSO volumes and frequencies of overflows during the monitored time period
24      and to  compare the relative volumes and frequencies from different monitoring sites in the CSS.
25      Such plotting, tabulating, and analysis of data are conducted prior to a modeling assessment as
26      described in Chapter 7.
27
       External Review Draft                    5-20                        December 6, 1996

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w
oT
6L

§f
i'
                           MAY  31   -  JUNE  1,  1992  STORM
                  Hytlognp^       gilran Horn       LUltt 81IA
                                  II    II    10    2<

                                     Time, Hours
                                                         21    37     31
 K>
I
              110


              its

              11*
             101



             102



             100
                           MAY  31   -  JUNE   1,   1992  STORM
                                     Hd t072t   ualtr Qai019l.REOI9-
                                        i     i
                                  <2     II    I.     24    21    32     II

                                     Time, Hours •
                                                                                                              SEPTEMBER 26  -   27,   1992  STORM
                                                                                                                    e«tr«n flow       M«l«r m«
                                                                                                                   	HH
                                                                                                                                   V
                                                                                                                         Time, Hours
                                                                                                                                                                        ¥
                                                                                                                                                                         O


III
III
114
J 112
• 110
Y
f
-
-

/^^-v
; A \
i i i i i i i
0 4 • 12 11 20 24 2. 1
Time, Hours
a
f
i
i
&
i ^
in CQ
c Q
c N-t

2


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                         WORKING DRAFT;  Do NOT CITE OR QUOTE
  1     5.4   WATER QUALITY MONITORING IN THE CSS
  2
  3           Collecting and analyzing  CSS wastewater samples  is essential to characterizing an
  4     overflow and determining its  impact on a receiving water body.  Water quality monitoring
  5     information can be used to:
  6
  7           •  Indicate potential exceedances of water quality criteria
  8           •  Indicate potential human health and aquatic life impacts
  9           •  Develop CSO quality models
 10           •  Assess pretreatment and pollution prevention programs as part of the NMC.
 11
 12      This section outlines various methods for collecting, organizing, and analyzing CSS wastewater
 13      data.
 14
 15      5.4.1   Quality Sampling
 16
 17            There are two basic aspects of wastewater quality sampling:
 18
 19            •   Sample type (i.e., grab versus composite)
20            •   Sample technique (i.e., manual versus automatic).
21
22      Sample type refers to the kind of sample collected—either grab or composite. Sample technique
23      refers to the method by which a grab or composite sample is actually collected—either manually
24      or by  automatic sampler.  Each of these sample types and techniques is discussed below.
25
26            Sample Types
27            In general, wastewater sample types fall into the following two categories:
28
29            •   Grab samples
30            •   Composite samples.
31
       External Review Draft                    5-22                       December 6, 1996

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                        WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            Grab Sampling.  A grab sample is a discrete, individual sample collected over a period
  2      of time not greater than 15 minutes.  Grab samples represent the conditions at the time the
  3      sample is taken and may not be representative of conditions at other times.  Therefore, data from
  4      grab samples indicate the quality of CSS flow at a distinct point in time and do not account for
  5      variations in quality throughout a storm event. Multiple grab samples can be gathered at a station
  6      to define such variations, although costs increase due to additional labor and laboratory expenses.
  7
  8            Composite Sampling.  A composite sample is a mixed  or combined  sample  that is
  9      formed by combining a series of individual and discrete  samples collected over a period of time,
10      or representing more than one specific location or depth.  Composite sampling provides data
11      representing the  overall  quality of combined sewage averaged over a storm event.   The
12      composited sample can be collected by continuous filling of a container throughout the time
13      period, a series of separate aliquots, or by combining  individual grab samples from separate
14      times, depths, or locations.  Common types of composite samples  include:
15
16            •   Time composite samples - Composed  of constant volume discrete sample aliquots
17               collected at constant time intervals.
18
19            •   Flow-weighted composite samples - Composed of samples combined in relation to the
20               amount of flow observed in the period between the samples.
21
22            Flow-weighted compositing can be done in two ways:
23
24            •   Collect samples at equal time intervals at a volume proportional to the flow rate (e.g.,
25               collect 100 ml of sample for every 100 gallons of flow that passed during a 10-minute
26               interval).
27
28            •   Collect samples of equal volume at varying times proportional to the flow (e.g.,
29               collect a 100 ml sample for each 100 gallons of flow irrespective of time).
30
       External Review Draft                    5-23                       December 6, 1996

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                         WORKING DRAFT:  Do NOT CUE OR QUOTE
  1           The second method'is preferable for sampling wet weather flows, since it results in the
  2     greatest number of samples when the flow rate is the highest  More detailed information on
  3     methods of flow weighting is presented  in the NPDES Storm Water Sampling  Guidance
  4     Document (U.S. EPA, 1992).
  5
  6           Sampling Methods
  7     -      There are two methods of sample collection:
  8
  9           •   Manual—Each sample (whether grab  or composite) or aliquot is obtained by an
 10              individual, either using equipment or by direct collection into the sample container or
 11               intermediate collection vessel.
 12
 13            •  Automatic—Sampling equipment (usually powered by battery or 120-volt power
 14              supply) is programmed to collect individual grab samples or composite samples based
 15               upon set time intervals or flow rates.
 16
 17     Manual and automatic sampling methods can be used to collect both grab and composite samples.
 18
 19            Manual Sampling.  Manual samples are usually collected using a hand-held container.
20     This method  requires minimal equipment and allows field personnel to record  additional
21     observations while the sample is collected.  Because  of their special characteristics,  certain
22     pollutants shouid be collected manually.  For example,  fecal streptococcus, fecal coliform, and
23     chlorine have very short holding times (i.e., 6 hours), pH and temperature need to be analyzed
24     immediately, and oil and grease requires teflon-coated  equipment to prevent adherence to the
25     sampling equipment. Volatile compounds must be collected manually into the sample container
26     according to standard procedures since these compounds will likely volatilize as a result of
27     agitation during automatic sampler collection (APHA, 1992).
28
29            Manual sampling caff be labor-intensive and expensive when the sampling program is
30     long-term and involves many locations. Personnel must be available around the clock to sample
31     storm events.  Safety issues or hazardous  conditions may affect sampling at certain locations.
32
       External Review Draft                   5-24                       December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            Automated Sampling.  Automated samplers are useful for CSS sampling because they

  2      can be pre-programmed to collect multiple discrete samples  as well as single  or  multiple

  3      composited samples.  They can  collect samples on a timed basis or in proportion to flow

  4      measurement signals from a flow meter.  Although these samplers require a large investment,

  5      they can reduce the amount of labor required in a sampling program and increase the reliability

  6      of flow-weighted compositing.

  7

  8            Automated samplers consist of a lower compartment, which holds glass or plastic sample

  9      containers and an ice well to cool samples, and an upper part, containing a microprocessor-based

10      controller, a pump assembly, and a filling mechanism.  The samplers can operate off of a battery,

11      power pack, or electrical supply.  More-expensive samplers have refrigeration equipment and

12      require a 120-volt power supply.  Many samplers can be connected to flow meters that will

13      activate flow-weighted compositing programs, and some samplers are activated by inputs from

14      rain gages.

15

16            Automated samplers also have limitations:

17

18            •   Some pollutants cannot be sampled by automated equipment unless only approximate
19               results are desired (e.g., oil and grease as mentioned above).
20
21            •   The self-cleaning capability of most samplers provides reasonably separate samples,
22               but some cross-contamination is unavoidable because water droplets usually remain
23               in the tubing.
24
25            •   Batteries may run down or the power supply may fail.
26
27            •   Debris in the sewer, such as'rags and plastic bags, can block the end of the sampling
28               line, preventing  sample collection. When  the sampling line is located near a flow
29               meter, this clogging can also cause  erroneous flow measurements.  Samplers and
30              ' meters should be checked during storms and must be tested and serviced regularly.
31               If no field checks are made during a storm event, data for the entire event may be
32               lost.

33
       External Review Draft                    5-25                        December 6, 1996

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                          WORKING DRAFT; Do NOT CITE OR QUOTE
   1            Sampling Strategies

   2            Since pollutant concentrations can vary widely during a storm event, the peimittee should

   3      consider sampling strategies that include pre-storm, first flush, peak flows, recovery, and post-

   4      storm samples. For example, individual grab samples could be taken at each site during the

   5      different storm stages  and analyzed.  Another  sampling  regime the permittee can use is

   6      combining samples collected during the stages at each site:
  7

  8           •  Pre-storm grab sample

  9           •  Composite grab samples collected during first flush

 10           •  Composite samples collected during peak flow

 11           •  Composite samples collected after peak flows
 12           •  Post-storm sample.

 13

 14     A third possible sampling regime could include a first flush composite taken over the .first 30

 15     minutes of discharge, followed by a second composite over the next hour of discharge, followed

 16     by a third composite for the remainder of the storm. These types of sampling regimes can better

 17     capture the varying concentrations  (i.e., higher concentrations during first flush followed by

 18     declining concentrations for later discharges) that are often found in combined sewer systems.
 19

 20           Contaminants Requiring Special Collection Techniques

 21           The above discussion focuses  on CSS sampling for contaminants  with  no special

 22     collection requirements.   The following contaminants have special handling requirements (as
 23     identified in 40 CFR Part 136).
 24'

 25           •   Bacteria—Samples collected for bacteria analysis cannot be held for more than six
 26              hours, and most laboratories  recommend that the sample be returned the same day it
 27              is collected. Automatic samplers are not appropriate for collecting bacterial samples,
 28              so  they must  be collected manually. Bacteria are collected directly into a sterile
 29              container or plastic bag, and care must be taken not to contaminate  the sample by
 30              touching it. Often the samples are preserved with sodium thiosulfate
 31
32            •   Volatile Organic Compounds (VOC)—VOC& are collected directly into special glass
33               vials. Each vial must be filled so that there is no air space into which the VOCs can
34               volatilize and be lost.


       External Review Draft                    5-26                       December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            •  Oil and Grease—Oil and grease must be collected by grab sample using a glass jar
  2               with a teflon-coated lid.  Samples are preserved by lowering the pH below 2.0 using
  3               a strong acid.
  4
  5            The monitoring program may also include toxicity testing, in which the acute and chronic
  6      impacts to aquatic life are determined. Procedures for toxicity testing for wet weather discharges
  7      may be found in Technical Support Document for Water Quality-based Toxics Control (U.S.
  8      EPA, 1991a).
  9
10            Sample Preparation and Handling
11            Sample bottles are typically supplied by the laboratory that will perform the analysis.
12      Laboratories may provide properly cleaned sampling containers with appropriate preservatives.
13      For most parameters, preservatives should be added to the container after the sample.  To avoid
14      hazards from fumes and spills, acids and bases should not be in containers  without a sample.
15      If preservation is by  adjusting sample pH, the preserved sample  should always be checked to
16      make sure it is at the proper pH level. The laboratory will usually indicate the maximum allowed
17      holding period for each analysis. Acceptable procedures for cleaning sample bottles, preserving
18      their contents, and analyzing for appropriate chemicals are detailed in various methods manuals,
19      including APHA (1992) and U.S. EPA (1979).
20
21            Water samplers, sampling hoses,  and sample storage bottles should always be made of
22      materials compatible  with the pollutants being sampled.  For example, when metals are the
23      concern, bottles should not have metal components that can contaminate the samples.  Similarly,
24      when organic contaminants are the concern, bottles and caps should be made of materials not
25      likely to leach into the sample.
26
27            Sample Volume, Preservation, and Storage. Sample volumes, preservation techniques,
28      and maximum holding times for most parameters are specified in 40 CFR Part 136. Refrigeration
29      of samples during and after collection at a temperature of 4°C is required for most analyses.
30      Manual samples are  usually placed in  a cooler containing ice  or an ice  substitute.   Most
31      automated samplers have a well next to the sample bottles to hold either ice or ice substitutes.

        External Review Draft                    5-27                        December 6, 1996

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1      Some expensive samplers have  mechanical  refrigeration equipment.   Other preservation
  2      techniques include pH adjustment and chemical fixation. pH adjustment usually requires strong
  3      acids and bases, which should be handled with extreme caution.
  4
  5            Sample Labeling. Samples should be identified by waterproof labels containing enough
  6      information to ensure that each is unique. The information on the label should also be recorded
  7      in a sampling notebook. The label typically includes the following information:
  8
  9            •  Name of project
10            •  Date and time of sample collection
11            •  Name or initials of sampler
12            •  Analysis to be performed
13            •  Sample ID number
14            •  Preservative used
15            •  Type of sample (grab, composite).
16
17            Sample Packaging and  Shipping. Sometimes it is necessary to ship samples to the
18     laboratory. Holding times should be  checked prior to shipment to ensure that they will not be
19     exceeded. While wastewater samples generally are not considered hazardous, some samples, such
20     as those with extreme pH, will require special procedures. If the sample is  shipped through a
21     common carrier or the U.S. Postal Service, it must comply with Department of Transportation
22     Hazardous Material Regulations (49 CFR Parts 171-177). Air shipment of samples classified as
23     hazardous may also be covered by the Dangerous Goods Regulations (International Air Transport
24     Association, 1996).
25
26            Samples should be sealed with  chain-of-custody form seals in leak-proof bags and padded
27     against jarring and breakage.  Samples must be packed with  an ice substitute to maintain a
28     temperature of 4°C during shipment.  Plastic or metal coolers make ideal shipping containers
29     because they protect and insulate the  samples. Accompanying paperwork such as the chain of
30     custody documentation should be sealed in a waterproof bag in the shipping container.
31

       External Review Draft                    5-28                       December 6, 1996

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1           Chain of Custody. The chain of custody form documents the changes of possession of
  2     a sample between time of collection and time of analysis.  At each transfer of possession, both
  3     the relinquisher and the receiver sign and date the form in order to document transfer of the
  4     samples and to minimize opportunities for tampering. The container holding the samples can also
  5     be sealed with a signed tape or seal to document that the samples are uncompromised.
  6
  7           Copies of the  chain of custody  form should be retained by the sampler and by the
  8     laboratory.  Often contract laboratories supply chain of custody forms with sample containers.
  9     The form is also useful for documenting which analyses will be performed on the samples.
 10     Forms typically contain the following information:
 11
 12           •   Name of project and sampling locations
 13            •   Date and time that each sample is collected
 14            •   Names of sampling personnel
 IS            •   Sample identification names and numbers
 16            •   Types of sample containers
 17            •   Analyses to be performed on each sample
 18            •   Additional comments on each sample
 19            •   Names of all personnel transporting the samples.
20
21      5.4.2   Analysis of Wastewater Monitoring Data
22
23            Since  monitoring programs can generate large amounts  of  information,  effective
24      management and analysis of the data are essential. Even small-scale programs, such as those
25      involving only a few CSS and receiving  water monitoring locations, can generate an extensive
26      amount of data. This section discusses tools for data analysis including spreadsheets, graphical
27      presentations, and statistical analysis.  (Data management is discussed in Section 4.7.2.  Chapters
28      7 and 8 discuss more detailed data  analysis during modeling.)
29                                     .
30            This section outlines an example  analysis of data collected during three storms, where
31      flow-weighted  composite samples were collected and analyzed for BOD and TSS. Exhibit 5-10

        External Review Draft                    5-29                       December 6, 1996

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                         WORKING DRAFT;  Do NOT CITE OR QUOTE
 •i
 2
 3
 4
 5
 6
 7
 8
 9
10
                            Exhibit 5-10. Composite Sampling Data (mg/1)

Outfall
1
4
5
7
9
Average
Storm #2
BOD
us
96
128
92
110
108
TSS
340
442
356
552 -
402
418
Storm #4
BOD
80
94
88
82
120
93
TSS
200
324
274
410
96
261
Storm #8
BOD
110
120
92
71
55
90
TSS
240
350
288
383
522
357
Average
BOD
102
103
103
82
95
97
TSS
260
372
306
448
340
345
shows average concentrations for each storm at the monitored outfalls; the small sample size does
not provide statistically reliable information on the expected variability of these concentrations
for other events.  Exhibit 5-11 shows that the mean and median for the data are similar.  To
determine expected values over a large sample size (i.e., more storm events), the projected mean,
median, and 90th-percentile value for the data were computed assuming a lognormal distribution.
(The lognormal distribution has been shown to be applicable to CSO quality (Driscoll, 1986).)
If used as a basis for estimating impacts, the 90th percentile values would be more conservative
than the means for BOD and TSS since only 10 percent of the actual concentrations for these
pollutants should exceed the 90th-percentile values.

           Exhibit 5-11. Pollutant Concentration Summary Statistics (mg/1)

Mean
Median
Projected Mean*
Projected Median*
Projected 90th Percentile Value*
BOD
96.87
94.00
97.16
94.70
126.64
TSS
345.27
350.00
352.53
321.29
558.03
                    'Projected statistic from sampling population (i.e., very large data set)
11
       External Review Draft
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                        "WORkmcDRAFT:  DO NOT ClTE OR QUOTE
  1           Multiplying flow measurements (or estimates) by pollutant concentration values drawn
  2     from monitoring data gives the total pollutant load discharged during each storm at each outfall.
  3     Exhibit 5-12 lists pollutant loads for the three storms at each monitored outfall.  As with flow
  4     data, these brief statistical summaries provide insight into the response of the system before
  5     performing more involved computer modeling. For example, the load in pounds of BOD and
  6     TSS  discharged by each outfall, normalized by rainfall depth or land area,  helps to identify
  7     differences in loading rates between outfalls over the long term.  These loading  factors can
  8     provide rough estimates of the loads from unmonitored outfalls that have land uses or impervious
  9     areas similar to the monitored area. Finally, the total load per storm helps in comparing storms
10     and projecting storm characteristics that would produce higher or lower loads. The number of
11      dry days and the number of days without a flushing storm affect pollutant loads, because these
12     factors represent a period when no severe scour activity occurred in the sewer system.
13
14            Three storms can indicate trends but do not provide enough data to characterize the load
15      of the CSS or its individual source areas.  As additional data are collected during the monitoring
16      program, estimates based on the data set become statistically more reliable because the size of
17      the data sets increases. The additional information allows continual refinement of the permittee's
18      knowledge of the system.
19
20            The following example, involving bacteria sampling, illustrates some additional important
21      issues. Because automated samplers are not appropriate for collecting bacterial samples, manual
                 -\
22      grab samples were collected and analyzed for fecal colifonn bacteria.  During a single storm
23      event, samples were collected from Outfall 1 at 30-minute intervals, beginning shortly after the
24      storm started and ending with sample #6 approximately 2Vt hours later (Exhibit 5-13). Peak flow
25      occurred within the first 90 minutes. The fecal colifonn concentration peaked in the first half
26      hour and declined more than one-hundredfold to the last sample, exhibiting a "first flush" pattern.
27      The geometric mean for these samples was  1.79 x 10* MPN/100 ml.  To calculate total fecal
28      conform loading,  flow  measurements were multiplied by the corresponding  grab sample
29      concentrations at each half-hour interval. The geometric mean concentration was also multiplied
30      by the total flow for comparative purposes. This calculation underestimates the total by a factor
31

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                 •WORKING DRAFT;  Do NOT CITE OR QUOTE
                       Exhibit 5-12. Pollutant Loading Summary

STORM 2
composite
composite
load
load
STORM 4
composite
composite
load
load
STORMS
composite
composite
load
oad
Total Load*

Area Load**
Ib/acre/storm)
Loading Rate
(lb/inch rain)

Flow (MG)
BOD (mg/1)
TSS(mg/l)
BOD (Ibs)
TSS Qbs)
Flow (MG)
BOD (mg/1)
TSS (mg/1)
BOD (Ibs)
TSS (Ibs)
How (MG)
BOD (mg/1)
TSS (mg/1)
BOD (Ibs)
TSS (Ibs)
BOD (Ibs)
TSS (Ibs)
BOD
TSS
BOD
TSS
OUTFALL
1
1.39
us
340
1,333
3,941
11.67
80
200
7,786
19,466
na
110
240
0
0
9,119
23,407
7
18
7,417
19,038
4
0.99
96
442
793
3,649
9.72
94
324
7,620
26,265
2.95
120
350
2,952
8,611
11365
38,525
9
30
7,329
24,843
5
na
128
356
. 0
0
5.31
88
274
3,897
12.134
2.00
92
288
1,535
4,804
5,432
16,938
5
17
3,997
12,465
7
2.55
92
552
1,957
11,739
15.09
82
410
10,320
51,599
4.68
71
686
2,771
26,775
15,048
90,113
7
44
9,709
58,144
9
2.07
110
402
1,899
6,940
12.64
120
96
12,650
10,120
4.07
55
522
1,867
17,719
16,416
34,779
5
11
10,595
22,440
TOTAL
7.00
_
_
5,982
26,269
54.43
_
_
42,273
119,584
13.70
—
—
9,125
57,909
57380 •
203,762
7
24
7,809
27,386
na = No flow data available. MG = millions of gallons.
load (Ibs) = composite concentration (mg/1) x flow (MG) x 8.34 (conversion factor)
* For monitored storms
** Acreage data taken from Exhibit 5-8; for monitored storms (i.e., either 2 or 3)
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December 6, 1996

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                         WORKING DRAFT: Do NOT CUE OR QUOTE
                     Exhibit 5-13. Fecal Coliform Data Outfall 1, Example Storm
Sample
I
2
3
4
5
6
Fecal Coliform Concentration
. (NoJlOO ml)
2.00 E+07
1.40 E+07
6.40 E+06
3.10 E+06
5.00 E+04
1.20 E+05

CSO How 30'Minate.Avg
(ds) . .
9.1
20.4
29.8
25.4
10.6
6.5
Total Load
Load*
(No. of Fecal Gdlifonns) '
9.27 E+13
1.45 E+14
9.72 E+13
4.01 E+13
2.70 E+ll
3.97 E+ll '
3.76 E+14
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
Geometric Mean
1.79 E+06
Mean:Flow
17.0
Estimated Total.Load**
9 JO E+13
       * Load = [Concentration (NoJlOO ml) x Total How (ml)] / 100 (since concentration is for 100 ml)
         Total Flow (in ml) = cfe x 1800 (# of seconds in one 30-minute interval) x 28321 (# of ml in one cf)
       ** Load estimated by multiplying geometric mean bacteria by the total flow
of three, primarily because it fails to correlate the high bacteria level to the high flows.  This
example illustrates the value of correlating flow and concentration.

       In many cases background conditions or  upstream wet weather sources may provide
significant pollutant loads. It is also common to have discharges from separate storm sewer
systems entering  the same receiving water segment as CSOs.  In such cases estimation of
pollutant loads from non-CSO sources is important so that loadings from these sources can be
taken into account when assessing receiving water impacts from CSOs.  The permittee should
consider monitoring these  and other non-CSO wet weather sources so that pollutant loads may
be calculated. The data analysis techniques discussed in this section apply equally well to other
wet  weather sources,  although the pollutant concentrations  in  such sources  may  differ
significantly.
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                       WORKING DRAFT; Do NOT CITE OR QUOTE
 1            Single composite samples or average data may be sufficient for a preliminary estimate of
 2      pollutant loadings.  Establishing an upper bound estimate for CSS pollutant  loads may be
 3      necessary in order to analyze short-term impacts based on short-term pollutant concentrations in
 4      the receiving water and to develop estimates for rare events, which have not been measured. A
 5      statistical distribution, such as normal or'lognormal, can be developed for the data and mean
 6      values and variations can be estimated.  These concentrations can be multiplied by measured
7      flows or an assumed design flow to generate storm loads  in order to predict rare or extreme
8      impacts.  Chapters 8 and 9 discusses further how to predict receiving water impacts.
9
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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  i                                         CHAPTER 6
  2
  3                             RECEIVING WATER MONITORING

  4

  5            This chapter discusses techniques and equipment for receiving water monitoring, including

  6      hydraulic, water quality, sediment, and biological sampling procedures. The techniques vary hi

  7      applicability and complexity, but all are generally applicable to CSO-impacted receiving waters.

  8      In collecting and analyzing receiving water monitoring data, the permittee needs to implement

  9      a quality assurance and quality control (QA/QC) program to ensure that accurate and reliable data
10      are used for CSO planning decisions (see Section 4.7.1).

11

12      6.1    THE CSO CONTROL POLICY AND RECEIVING WATER MONITORING
13
14            The CSO Control Policy discusses characterization and monitoring of receiving water

15      impacts as follows:
16

17            •  In order to design a CSO control plan adequate to meet the requirements of the CWA,
18               a permittee should have a thorough understanding of its sewer system, the response
19               of the system to various precipitation events, the characteristics of the overflows, and
20               the water quality impacts that result from CSOs.
21
22            •  The permittee should  adequately characterize...the impacts of the  CSOs on the
23               receiving waters and their designated uses.  The permittee may  need to consider
24               information on the contribution and importance of other pollution sources in order
25               to develop a final plan designed to meet water quality standards.
26
27            •  The permittee should develop a comprehensive,  representative monitoring program
28               that...  assesses the impact of the CSOs on the receiving waters.  The monitoring
29              program should include necessary CSO effluent and ambient in-stream monitoring
30               and,  where appropriate, other monitoring protocols such  as biological assessment,
31               toxicity testing and sediment sampling.  Monitoring parameters should include, for
32               example,  oxygen  .demanding pollutants,  nutrients,  toxic  pollutants,  sediment
33               contaminants, pathogens, bacteriological indicators (e.g., Enterococcus, E. Coli), and
34          t     toxicity. A representative sample of overflow points can be selected that is sufficient
35               to allow characterization of CSO discharges and their water quality impacts and to
36              facilitate evaluation of control plan alternatives.  (II.C.l)
37
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                        "WORKINGT)RAFT; "DO NOT ClTE OR QUOTE
  1            As discussed in Chapter 2, the permittee will use either the presumption approach or the
  2     demonstration approach in assessing attainment of WQS. Under the demonstration approach, the
  3     municipality demonstrates the adequacy of its CSO control program to attain WQS.  Generally,
  4     municipalities selecting the demonstration approach will need to monitor receiving waters to
  5     show that their control programs are adequate.
  6
  7           The presumption approach is so named because it is based on the presumption that WQS
  8     will be met when certain performance-based criteria identified in the CSO Policy are achieved,
  9     as  shown by the permittee in its LTCP.  The regulatory agency is likely,to-request some
 10     validation of the presumption, such as receiving water quality sampling or end-of-pipe sampling
 11      of  overflows combined with flow information and dilution  calculations.  Discussion of the
 12     different modeling considerations related to the demonstration and presumption approaches is
 13      included in Chapters 7 (CSS Modeling) and 8 (Receiving Water Quality Modeling).
 14
 15      62    RECEIVING WATER HYDRAULICS
 16
 17            When a CSO enters a receiving water body, it is subject to fate and transport processes
 18      that modify pollutant  concentrations in the  receiving water  body.  The impact of CSOs to
 19      receiving waters is largely determined  by the hydraulics  of the  receiving water body and the
20      relative magnitude of the CSO loading. Assessing receiving water hydraulics is an important first
21      step in a receiving water study, since an understanding of how CSOs are transported and diluted
22      is essential to characterizing their impacts on receiving waters.  Awareness of large-scale and
23      small-scale hydrodynamics can help in determining where to sample in the receiving water for
24      the effects of CSOs. Large-scale water movement largely determines the overall  transport and
25      transformation of pollutants. Small-scale hydraulics, such as water movement near a discharge
26      point (often called near-field), determine the  initial dilution and  mixing of the discharge.  For
27      example, a discharge into a wide, fast-flowing river might not mix across the river for a long
28      distance since it will quickly be transported downstream.
29
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                          WORKING DRAFT:  DO^NOT CITE OR QUOTE
  1     6.2.1  Hydraulic Monitoring
  2
  3   .         Hydraulic monitoring involves measuring the depth and velocity of the receiving water,
  4     body and its other physical characteristics (e.g., elevation, bathymetry, cross section), in order to
  5     assess transport and dilution characteristics. This may include installation of gages on either a
  6     temporary or long-term basis to determine depth and velocity variations during wet weather
  7     events.  In all cases, existing mapping or  a new  survey of the physical characteristics of the
  8     receiving water is necessary for interpretation of the hydraulic data and understanding of the
  9     hydraulic dynamics of the receiving water.  (Section 4.5 discusses receiving water sampling
 10     designs and the selection of monitoring locations.)
 11
 12           Identifying a suitable hydraulic monitoring  method depends largely on the type and
 13     characteristics of receiving water.
 14
 IS           Rivers and Streams
 16
 17           In rivers and streams, flow rate is generally a factor of the depth, width, cross-sectional
 18     area, and hydraulic  geometry of the river  or stream channel.  Flow in rivers and streams  is
 19     usually determined by  measuring the stage  (elevation of water above a certain base level) and
20     relating stage to discharge with a rating curve. This relationship is developed by measuring flow
21      velocity in the stream or river at different stages, and using velocity and the  area of the stream
22     or river channel to determine the total discharge for each  stage (Bedient and Huber, 1992).  For
23      large rivers and streams, long-term flow and geometry data are often available for specific gaging
24     stations from the USGS and the U.S. Army Corps of Engineers.
25
26            For a CSO  outfall located near a USGS gage, the monitoring team can use relative
27      watershed areas to estimate flow at the discharge site.1 Flow information may also be available
28      from stage measurements at bridge crossings and  dams,  and from studies performed by other
29      State and Federal agencies. In the absence of such flow data, the permittee may need to install
30      stage indicators or use current meters to collect flow measurements.  Many of the CSO flow
31         'For example, the 5,000-square mile Menimack River watershed in New Hampshire and Massachusetts has 46
32     USGS gages that monitor most of the larger tributaries and the main stem in several locations.

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1      monitoring devices described in Exhibit 5-5 of Chapter 5 may apply to open channel flow in
  2      rivers and streams.  The USGS (1982) and USDI (1984) have published detailed manuals on
  3      stream gaging techniques.
  4
  5            Estuaries and Coastal Areas
  6
  7            Estuaries and coastal areas are regions connecting rivers and oceans and thus represent
  8      a complex system of tides, salinity from the ocean, and upstream drainage from the river.  Tidal
  9      variations and density effects from the varying levels of salinity need to be defined to determine
10      how pollutants from CSOS are transported.
11
12            Tidal variations affect estuarine circulation patterns which, along with salinity patterns,
13      determine how pollutant loadings entering the estuary or coastal area are dispersed.  Based on
                                                                                      i
14      velocity and salinity patterns, estuaries can be classified as one of the following types:
15
16            •   Stratified estuaries have large fresh water  inflows over a salt water layer.  Tidal
17                currents  are not sufficient  to mix the separate layers.  Transport of pollutants is
18                largely dependent on the difference in the densities of the pollutants and the receiving
19                water.
20
21            •   Well-mixed estuaries have a tidal flow much greater than the river outflow, with
22                mixing and flow reversal sufficient to create a well-mixed water column at all depths.
23                Pollutants tend to move with the motion of the tides and are slowly carried seaward.
24
25            •  Partially-mixed estuaries have flow and stratification characteristics between the other
26                two types and have tide-related flows much greater than river  flows.  Pollutant
27                transport depends somewhat on density, but also involves significant vertical mixing.
28
29      Classification depends on the river outflow at the given time, with large river flows leading to
30      more stratified estuaries (EPA, 1985b).
31
32            Tidal height data and current predictions, published annually by NOAA, may  provide
33      sufficient information,  or it may be necessary  to install a new tide gage (stage monitor) to
34      develop data closer to the CSO-impacted area. Due to the variation of tides and winds; estuarine
35      and coastal currents often change rapidly. It is necessary, therefore, to measure tides and currents

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                         WORKING DRAFT:  Do NOT CITE OR" QUOTE
  1      simultaneously using continuous recording depth and velocity meters.  Tidal currents can be
  2      measured with meters similar to those used for measurement of river currents, but the direction
  3      of the currents must also be recorded.  Information on monitoring methods for such areas may
  4      also be found in USGS (1982) and USDI (1984).
  5
  6            Lakes
  7
  8            .The hydraulic characteristics of lakes depend on several factors, including the depth,
  9      length, width, surface area, volume, basin material, surrounding ground cover, typical wind
10      patterns, and surface inflows and outflows (including CSOs). Lakes tend to have relatively low
11      flow-through velocities and significant vertical temperature gradients, and thus are usually not
12      well-mixed (Thomann and Mueller, 1987). To determine how quickly pollutants are likely to be
13      removed from a lake, it is necessary to define the flushing rate.  The flushing rate depends on
14      water inputs  (inflows and precipitation) and outputs (outflows, evaporation, transpiration, and
15      withdrawal), pollutants and  their characteristics, and the degree of mixing in the lake.  Mixing
16      in lakes is primarily from the  wind, temperature changes, and atmospheric pressure.
17
18            Analysis of pollutant fate and transport in lakes is often complex and generally requires
19      the use of detailed simulation models. Some less-complex analysis can be done when simplifying
20      assumptions,  such as complete mixing in  the lake, are made. To perform these analyses,
21      parameters that need to be  defined include lake  volume, surface area, mean depth, and mean
22      outflow and inflow rates.  Analytical and modeling methods for lakes and the data necessary to
23      use the methods are  discussed in greater detail in Section 8.3.2 and in Thomann and Mueller
24      (1987) and Viessman, et al. (1977).
25
26      6.2.2     Analysis of Hydraulic Data
27
28            Analysis of hydraulic data in receiving waters will allow estimation of the flow rate based
29      on depth measurement. This analysis may involve:
30
31            •  Developing stage-discharge,  area-depth,  or volume-depth  curves  for  specific
32               monitoring locations, using measured velocities to calibrate the stage-discharge

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                         WORKING DRAFT:  Do Nor CTTE
  1               relationship (methods for various types of flow monitoring stations are presented in
  2               USGS (1982) and USDI (1984))
  3
  4            •   Pre-processing the data for input into hydraulic models

  6            •   Plotting and review of the hydraulic data
  7
  8            •   Evaluating the data to define hydraulic characteristics, such as initial dilution, mixing,
  9               travel time, and residence time.
 10
 11
 12            Plotting programs such as spreadsheets and graphics programs are useful for presenting

 13      hydraulic data. A data base, supplemented with a plotting and statistical analysis package, will

 14      typically be necessary to analyze the data and generate such information as:

 15

 16            •  Plots of depth, velocity and flow vs. time
 17
 18            •  Plots of depth, velocity and flow vs. distance from the outfall
 19
 20            •  Frequency distributions of velocities and flows
 21
 22            •  Vector components of velocities and flows
 23
 24            •  Means,  standard deviations,  and other  important statistical measures for depth,
 25               velocity, and flow data.

 26

 27            As presented  later  in  Chapter 8, receiving water models need physical system and

 28     hydraulic data as input  Processing of input data is specific to each model. In general, however,

29     the physical characteristics of the receiving water (slopes, locations, and temperatures) are used

 30     to develop the model  computational grid.  The measured hydraulic data (depths, velocities, and

 31     flows) are used to compare with model calculations  for purposes of model validation.

 32

 33     6.3    RECEIVING WATER QUALITY
 34
 35            Collection and analysis of receiving water quality data are necessary when available data

36     are not sufficient to describe water quality impacts from CSOs.  This section discusses how to

37     conduct a receiving water sampling program and analyze data for chemical quality.  (Chapters
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                         WORKING DRAFrrDo'NoT CUE OR QUOTE
  1      3 and  4 discuss how to identify sampling  locations, sampling parameters,  and sampling
  2      frequency. Section 6.4 discusses biological and sediment sampling and analysis.)
  3
  4      63.1     Water Quality Monitoring
  5
  6            Receiving water monitoring involves many techniques similar to CSS monitoring (see
  7      Section 5.4.1) and many of the same decisions, such as whether to collect grab or composite
  8      samples and whether to use manual or automated methods.  Receiving water quality monitoring
  9      involves the parameters discussed in Section 4.5.3 as well as field measurement of parameters
 10      such as temperature and conductivity.
 11
 12            Sample Program Organization
 13
 14            Sampling receiving waters, especially large water bodies, requires careful planning and
 15      a sizable resource commitment.  For example, a dye study of a large river requires careful
 16      planning regarding travel time, placement of sampling crews, points of access, and use of boats.
 17      Sampling of  wet weather  events is  typically  more complicated than for dry weather, often
 18      requiring rapid mobilization of several sampling teams on short notice, sampling throughout the
 19      night, and sampling in rainy conditions with higher-than-normal flows in the receiving water
20      body. Time of travel between the various sampling stations may necessitate the use of additional
21      crews if sample collection must occur at predetermined times.
22
23            Wet weather sampling requires specific and accurate  weather information. Local offices
24      of the American Meteorological Society can provide a list of Certified Consulting Meteorologists
25      who can provide forecasting services specific to the needs of a sampling program.  Radar contact
26      can also be established for real-time observation of conditions. While these efforts represent an
27      additional cost to the program, they may result in significant savings in costs associated with
28      false starts and unnecessary laboratory charges.
29
30            The rainfall, darkness, and cold temperatures that often accompany  wet weather  field
31      investigations can  make even small tasks difficult.   Contingency planning and extensive
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                         "WORKING DRAFT;  Do Nor CITE OR QUOTE
        preparation can, however, minimize mishaps and help to ensure safety.  Prior to field sampling,
        the permittee should ensure that:
  4            •   Sampling personnel are well trained and familiar with their responsibilities, as defined
  5               in the sampling plan
  6
  7            •   Personnel use proper safety procedures
  8
  9            •   A health and safety plan identifies the necessary emergency procedures and safety
 10               equipment
 11
 12            •   Sample containers are assembled and bottle labels are filled out to the extent possible
 13
 14            •   All necessary equipment is inventoried, field monitoring equipment is calibrated and
 15               tested, and equipment such as boats, motors, automobiles, and batteries are checked.
 16
 17            Sample Preparation and Handling
 18                                      '
 19           As discussed in Section 5.4.1, sample collection, preparation and handling, preservation,
20     and storage should minimize  changes in the condition of sample constituents.  The standard
21      procedures for collecting, preserving, and storing receiving water samples are the same as those
22     for combined sewage samples and are described in 40 CFR Part 136. Procedures for cleaning
23      sample bottles, preserving water quality samples, and analyzing for appropriate chemicals are
24      detailed in  various methods manuals, including APHA  (1992) and U.S. EPA (1979).  Samples
25      should be labeled with unique identifying information and should have chain of custody forms
26      documenting the changes of possession of the samples  between time of collection and time of
27      analysis (see Section 5.4.1).
28
29      6.3.2     Analysis of Water Quality Data
30
31 .           As was the case for hydraulic data,  water quality data for receiving waters are analyzed
32      by plotting  and reviewing the raw data to define water quality characteristics and by processing
33      the data for input to water  quality models.   Data can be  analyzed and displayed using
34      spreadsheets, databases, graphics software,  and statistical packages, such as Statistical Analysis
35      Software (SAS) and Statistical Package for Social Sciences (SPSS).
36

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                         WORKING DRAFT:  Do Nor CITE OR QUOTE
  1            Simple receiving water analyses could include:
  2
  3            •   Comparing receiving water quality with applicable water quality criteria to determine
  4               whether criteria are being exceeded
  5
  6            •   Comparing sampling results from before, during, and after a wet weather event to
  7               indicate whether  water quality problems are attributable to CSOs and other wet
  8               weather events
  9
 10            •   Comparing data upstream from CSOs with data from downstream to distinguish CSO
 11                impacts.
 12
 13             Water quality data are also used to calibrate receiving water models (see Chapter 8). This
 14     is generally facilitated by plotting the data vs. time and/or distance to compare with model
 IS      simulations. Special studies may be required to determine rate constants, such as bacteria die-off
 16      rates or suspended solids  settling rates, if these values are used in the model.
 17
 18      6.4    RECEIVING WATER SEDIMENT AND BIOLOGICAL MONITORING
 19
20            It is often difficult and expensive to identify CSO impacts during wet weather using only
21      hydraulic and water quality sampling. As acknowledged in the CSO Control Policy, "... data and
22      modeling of wet weather events often do not give a clear picture of the levels of CSO controls
23      necessary to protect  WQS."  Sediment and biological monitoring may serve as cost-effective
24      supplements or even as alternatives to water quality sampling.  The following sections discuss
25      sediment and biological sampling techniques and data analysis.
26
27      6.4.1  Sediment Sampling Techniques
28
29            Receiving water sediments are sinks for a wide variety  of materials.  Nutrients, metals,
30      and organic compounds bind  to suspended solids and settle to the bottom of a water body when
31      flow velocity is insufficient  to keep them in suspension.  Once re-suspended through flood
32      scouring, bioturbation, desorption, or biological uptake, free contaminants can dissolve in the
33      water column, enter sediment-dwelling organisms, or accumulate or concentrate in fish and other
34      aquatic organisms and subsequently be ingested by humans and other terrestrial animals.
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                         WORKING DRAFT: 1)0 NOT CITE X>R QUOTE
  1            Typically, CSOs contain suspended material that can settle out in slower-moving sections
  2     of receiving waters. Sediments can release accumulated contaminants for years after overflows
  3     have been eliminated.
  4
  5            Sediment samples are collected using hand or winch-operated dredges as follows:
  6
  7            •   The device is lowered through the water column by a hand line or a winch.
  o
  9            -The device is then activated either by the attached line or by a weighted messenger
 10               sent .down the line.
 11
 12            •   The scoops or jaws of the device close either by weight or spring action.
 13
 14            •   The device is retrieved to the surface.
 15
 16             Ideally, dredging should disturb the bottom as little as possible and collect  all fine
 17      particles.2
 18
 19             Sediments  can  also be collected by core sampling to determine how pollutant types,
20      concentrations, and accumulation rates have varied over time.  Sediments must be physically
21      amenable to coring, however.
22
23             To avoid sample contamination, sediments should be removed from the dredge or core
24      sampler by scraping back layers in contact with the device and extracting sediments from the
25      central  mass of the sample.  In  many cases the upper-most layer of sediment will be the most
26      contaminated and,  therefore, of most interest. Sediment samples for lexicological and chemical
27      examination should  be collected following method  E 1391 detailed  in  Standard Guide for
28      Conducting Sediment Toxicity Tests with Freshwater Invertebrates (ASTM, 1991).
29
30        Commonly used sediment samplers include the Ponar, Eckman, Peterson, Orange-peel, and Van Veen dredges.
31     Macroirtvertebrate Field and Laboratory Methods for Evaluating the Biological Integrity of Surface Waters (Klemm,
32     1990) has detailed descriptions of such devices.

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                         WORKING DRAFT: Do NOT'CITE OR QUOTE
  1     6.4.2  Analysis of Sediment Data
  2
  3            CSO investigations will benefit from analysis of a range of sediment characteristics,
  4     including physical characteristics  (grain  size, distribution,  type of  sediment),  chemical
  5     composition, and benthic makeup (discussed in Section 6.4.3). These characteristics should also
  6     be evaluated in sediments from upstream reference stations and sediments from non-CSO sources
  7     to facilitate comparison with sediments near the CSO outfall.
  8
  9            Sediment data are typically analyzed by developing grain size distributions and plotting
 10     concentrations of chemicals vs. distance. If the area of interest is two-dimensional horizontally,
                   *x
 11      isopleths can be plotted showing contours of constant concentration from the CSO outfall.  If
 12      vertical variations from core samples are available, concentration contours can also be plotted vs.
 13      depth.  Sediment chemistry data may be statistically analyzed to  compare areas that are affected
 14      by CSOs, non-CSO sources, and unaffected (background) areas.  These analyses  can give a
 15      longer-term view of CSO impacts than  water quality monitoring.
 16
 17      6.4.3  Biological Sampling Techniques
 18
 19      '      Evaluation of aquatic organisms is another way to obtain information on cumulative
20      impacts of CSOs, since resident communities of aquatic organisms integrate over time all the
21      environmental changes that affect them.
22
23            Collection and Handling of Biological Samples
24            This section describes collection techniques for fish, phytoplankton, zooplankton, and
25      benthic macroinvertebrates. Additional  information is in Exhibit 6-1.
26
27            Fish.  Although other aquatic organisms may be more sensitive to pollutants, fish generate
28      the greatest public  concern.  Observable adverse effects from  pollutants include declines of
29      populations and tumor growth on individuals. Fish monitoring programs can identify the relative
30      and absolute numbers of individuals of each species; the size distributions within species; growth
31      rates; reproduction  or recruitment success; the incidence of disease, parasitism, and tumors;
32      changes in behavior; and the  bioaccumulation of toxic constituents.

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            Exhibit 6-1.  Overview of Field Biological Sampling Methods
Sample Parameter
Phytoplankton
Algae
Limitations:
Riparian and aquatic
macrophytes
Limitations:

Zooplankton
I .imitations:
Benthic invertebrates
Limitations:
Fish
Limitations:
Information Gained
• Chlorophyll a
* Community
structure
• Primary
productivity
• Biomass
• Density
Memod«f, Collection
• Plankton buckets attached
to a vertical or horizontal
tow net (e.g., Wisconsin
style net)
• Discreet depth samples
using VanDom or Kemmer
bottles
• Periphytometer
References
American Public Health
Association-(APHA), 1992;
American Society for Testing and
Materials-(ASTM), 1991; Lind,
1985;
Vollenwedder, 1969;
Weber, 1989;
Wetzel and Likens, 1979
Small organisms can pass through the net, and periphytometers are only good for algae mat
attach to a substrate.
structure
• Distributions, depth
& basin wide
• Biomass
- Density
• Tissue analysis
• Usually qualitative visual
• Quantitative assessments '
use quadrant or line point
methods
APHA, 1992; ASTM, 1991; Dennis
and Isom, 1984; Vollenweider,
1969; Weber, 1989; Wetzel and
Likens, 1979; Plafkin et al., 1989
Limited to the growing season for many species.
• Community
structure
• Distributions
• Biomass
• Sensitivity
• Density
• Plankton buckets attached
to a vertical or horizontal
tow net (e.g., Wisconsin
style net)
• Discreet depth samples
using VanDom or Kemmer
bottles
APHA, 1992; ASTM, 1991; Lind,
1985; Pennak, 1989; Weber, 1989;
Wetzel and Likens, 1979
Small organisms can pass through the net; some zooplankton migrate vertically in the water
column, therefore it is possible to miss some species.
> Community
structure
• Biomass
• Density
• Distribution
• Tissue analysis
• Ponar grab sampler
• Eckman dredge sampler
• Surber
• Hess
• Kick net or D-ring net
• Artificial substrates
APHA, 1992; ASTM, 1991; Lind,
1985;
Merritt and Cummins. 1984;
Pennak. 1989; Weber, 1989;
Klemm et al.. 1990; Wetzel and
Likens, 1979; Plafkin et al.. 1989
Some methods are time consuming and labor intensive; some methods are depth restrictive (&g.,
can only be used in shallow waters).
. Community
structure
• Distributions, depth
& basin wide
• Biomass
• Density
• Bioconcentration
• Fecundity
Each method is biased to
are designed for use in re
• Hectroshocking
• Seines
• Gill nets
• Trawls
• Angling
• Traps
APHA, 1992; ASTM, 1991;
Everhart et al., 1975; Nielsen and
Johnson, 1983; Plafkin et aL, 1989;
Schreck and Movie, 1990; Ricker,
1975; Weber, 1989
some degree as to the kind and size of fish collected. Some methods
latively shallow water.
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  i
  2            Common methods of sampling fish include  angling, seines, gill and trap nets, and
  3     electrofishing.  The references  shown in Exhibit 6-1 provide guidance on methods used for
  4     collection, measurement, preservation, and analysis of fish samples.3
  5
  6            Phytoplankton.  Phytoplankton are free-floating, one-celled algae. They are useful in
  7     monitoring receiving  water quality  because  many  species  are highly sensitive to  specific
  8     chemicals. Because phytoplankton have relatively rapid rates of growth and population-turnover
  9     (approximately 3 to 5 days during the summer season), only short-term CSO impacts can be
 10     analyzed.  Laboratory analyses  can provide information on the abundance of each taxon, the
 11      presence of,  or changes  in, populations  of indicator species,  and the  total  biomass of
 12     phytoplankton present.  Lowe (1974) and VanLandingham (1982) provide useful guides to the
 13      environmental requirements  and  pollution tolerances  of diatoms  and blue-green algae,
 14      respectively.
 15
 16            Zooplankton. Zooplankton are free-floating aquatic protozoa and small animals. Many
 17      species are sensitive indicators of pollution. Particularly in lakes and reservoirs, Zooplankton can
 18      provide  information on the presence of specific  toxics.  Zooplankton are often collected by
 19      towing a plankton net through a measured or estimated volume of water. To calculate population
20      density it is necessary to determine the volume of the sampling area, using a flow meter set in
21      the mouth of the net or calculations based on the area of the net opening and the distance towed.
22      Laboratory analyses can provide information similar to that for phytoplankton.
23
24            Benthic  Macroinvertebrates.  Benthic  macroinvertebrates  are  organisms  such as
25      plecoptera (stoneflies), ephemeroptera (mayflies), and trichoptera (caddisflies) that live in and on
26      sediments. Like plankton, benthic macroinvertebrates  include useful indicator species that can
27         'Two reference works published by the American Fisheries Society are especially informative.  Fisheries
28      Techniques (Nielsen and Johnson, 1983) focuses mainly on field  work considerations, discussing most of the
29      sampling techniques currently practiced. The companion volume, Methods for Fish Biology (Schreck and Moyle,
30      1990), focuses primarily on methods used to analyze and assess collected fish samples. It includes material on fish
31      growth, stress and acclimation, reproduction, behavior, population ecology, and community ecology.

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                           WORKING DRAFT;  DO"NOT CITE OR QUOTE
  1      provide valuable information about the presence and nature of toxics in the sediments of lakes
  2      and reservoirs.
  3
  4             Monitoring teams generally use dredges to sample benthic macroinvertebrates. Samples
  5      are either preserved in their entirety in polyethylene bags or other suitable containers or are
  6      washed through a fine sieve and then preserved in a suitable container (Klemm et al., 1990). The
  7      sample can be analyzed for taxa present, the total density of each taxon, relative abundance by
  8      numbers or biomass of these taxa, changes in major and indicator species populations, and the
  9      total biomass of benthic macroinvertebrates present.4
.10
11       6.4.4  Analysis of Biological Data
12
13             Community  structure can be described in  terms  of species diversity,  richness, and
                                              *
14       evenness.  Diversity is affected by colonization rates, extinction rates, competition, predation,
15       physical disturbance, pollution, and other factors (see Crowder, 1990).
16
17             A qualitative data assessment can help determine which factors have caused measured
18       variation in species diversity.  In such an assessment, the species  collected and their relative
19      population sizes are compared  with their known sensitivities to contaminants present   The
20      tendency of species to be abundant, present, or absent relative to their tolerances or sensitivities
21      to sediments, temperature regimes, or various chemical pollutants can indicate the most likely
22   •   cause of variation in species diversity at the sampled sites.
23
24             Two cautions should be noted regarding qualitative analysis. First, different strains of the
25      same species can sometimes have differing sensitivities to a stressor, particularly where species
26      have undergone extensive hatchery breeding programs.  Second, because listed characteristics of
27      organisms can vary from region to region, when using lists of indicator species, it is important
28         'Three manuals (U.S. EPA, 1983b, 1984a, 1984b) discuss the interpretation of biological monitoring data for
29      larger bottom-living invertebrates.  The Rapid Bioassessment Protocols (Plafltin et al., 1989) manual discusses the
30      use of fish and macroinvertebrates as a screening method in assessing environmental integrity. Macroinvertebrate
31      Field and Laboratory Methods for Evaluating the Biological Integrity of Surface Waters (Klemm et al., 1990)
32      discusses analysis of qualitative and quantitative data, community metrics and pollution indicators, pollution tolerance
33      of selected macroinvertebrates, and Hilsenhoff s family-level pollution tolerance values for aquatic arthropods.
                                                                          		
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  1     to note whether the data were collected in the same region as the CSO study.  Investigators
  2     should generally limit the use of diversity indices as general indicators of environmental effects
  3     to comparisons within the study where sampling  and sample analysis methods are consistent.
  4     Investigators should contact local authorities to determine whether biological reference data can
  5     be obtained to use in the CSO study.
  6
  7           Rapid Bioassessment Protocols
  8
  9           Rapid biological assessments, using techniques  such as rapid bioassessment protocols
 10     (RBPs), are a valuable and cost-effective approach to evaluating the status of aquatic systems
 11      (Plafkin et al., 1989). RBPs integrate information on biological communities  with information
 12     on physical and chemical characteristics of aquatic habitats.  RBPs have been successfully used
 13      to:
 14
 15            •  Evaluate whether a'stream supports designated aquatic life uses;
 16            •  Characterize the existence and severity  of use impairments;
 17            •  Identify sources and causes of any use impairments;
 18            •  Evaluate the effectiveness of implemented control actions;
 19            •  Support use attainability analyses; and
20            •  Characterize regional biotic components within ecosystems. .
21
22            Typically, RBPs provide integrated evaluations that compare habitat and biological
23      measures for studied systems to empirically-defined reference conditions (see Plafkin et al.,
24      1989).  Reference conditions are defined through  systematic monitoring of one or more sites
25      selected to represent the natural range of variation in  "least disturbed" water chemistry, physical
26      habitat, and biological conditions. A percent similarity is computed for each biological, chemical,
27      or physical parameter measured at the study sites relative to the conditions found at the reference
28      site(s). These percentages may be computed based on the total number of taxa found, dissolved
29      oxygen saturation, or the embeddedness of bottom material.
30
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  1            Generally, where the computed percent similarity is greater than 75-80 percent of the
  2      corresponding reference condition (depending on the parameter  compared),  the results can
  3      indicate  that conditions at the  study sites are sufficiently similar to those occurring at the
  4      reference site(s). For such cases it is reasonable to conclude that the study sites' conditions are
  5      "non-impaired."  In contrast, where the computed percent similarity of conditions at the study
  6      sites is less than 50 percent of the reference conditions (depending on the parameter compared),
 7      it is reasonable to conclude that  conditions at those study sites are "severely impaired," relative
 8      to the reference site(s). For those sites with a percent similarity falling between these ranges, the
 9      results can indicate that conditions at the study sites are "moderately impaired" (Plafkin et al.,
10      1989). An application of the use of RBPs in two case studies is presented in Combined Sewer
11      Overflows and the Multimetric Evaluation of Their Biological Effects: Case Studies in Ohio and
12     New York (EPA, 1996).
13
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                         WORKING DRAFT:  Do NOT CUE OR QUOTE
  i                                          CHAPTER?
  2
  3                          COMBINED SEWER SYSTEM MODELING

  4

  5            This chapter discusses the use of modeling in characterizing the CSS and evaluating CSO

  6     control alternatives. It discusses how to identify the appropriate level of modeling, based on site-

  7    'specific considerations, and describes the various types of available  models.  Because of the

  8     site-specific  nature of CSSs, the  varying needs  for information by municipalities,  and the

  9     numerous available models, it does not recommend a specific model or modeling approach.

 10

 11      7.1     THE CSO  CONTROL POLICY AND CSS MODELING
 12
 13             The CSO Control Policy refers to modeling as a tool for characterizing a CSS and its

 14      impacts on receiving waters.  It does not intend that every CSS be  analyzed using complex

 15      computer models.

 16

 17   .          The CSO Control Policy describes the use of modeling as follows:

 18            Modeling - Modeling of a sewer system is recognized as a valuable tool for predicting sewer
 19            system response to  various wet weather events  and assessing water quality impacts when
20            evaluating different control strategies and alternatives. EPA supports the proper and effective use
21            of models, where appropriate, in the evaluation of the nine minimum controls and the development
22            of the  long-term CSO control plan. It is also recognized that there are many models which may
23            be used to do this. These models range from simple to complex.  Having decided to use a model,
24            the permittee should base its choice of a model on the characteristics of its sewer system, the
25            number and location of overflow points, and the sensitivity of the receiving water body to the CSO
26            discharges...  The sophistication of the model should relate to the complexity of the system to be
27            modeled and to the information needs associated with evaluation of CSO control options and
28            water  quality impacts. (n.C.l.d)

29

30            The Policy also states that:

31            The permittee should adequately characterize through monitoring, modeling, and other means as
32            appropriate, for a range of storm events, the response of its sewer system to wet weather events
33            including the number, location and frequency of CSOs,  volume, concentration and mass of
34            pollutants discharged, and the impacts of the CSOs on the receiving waters and their designated
35            uses.  (H.C.1)

36
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                          WORKING DRAFT;  Do NOT CITE OR QUOTE
  1            Finally, the CSO Control Policy also states:
  2            EPA believes that continuous simulation models, using historical rainfall data, may be the best
  3            way to model sewer systems,  CSOs, and their impacts.  Because of the iterative nature of
  4            modeling sewer systems, CSOs,  and their impacts, monitoring and modeling efforts  are
  5            complementary and should be coordinated.  (II.C.l.d)
  6
  7            The CSO Policy supports continuous simulation modeling (use of long-term  rainfall
  8     records rather than records for individual storms) for several reasons.  Long-term continuous
  9     rainfall records enable simulations to be based on a sequence of storms so that the additive effect
 10     of storms occurring close together can be examined.  They also enable storms with a range of
 11      characteristics to be included.  When a municipality uses the presumption approach, long-term
 12     simulations are appropriate because the performance criteria are based on long-term averages,
 13      which are not readily determined from design storm simulations. Continuous simulations do not
 14      require highly complex models. Models that simulate runoff without complex simulation of
 15      sewer hydraulics (e.g., STORM, SWMM RUNOFF)  may  be appropriate where the basic
 16      hydraulics of the system are simple.
 17
 18            The CSO Control Policy also states that after instituting the NMC, the permittee should
 19      assess their effectiveness and should
20                                •
21            submit any information or data on the degree to which the nine minimum  controls achieve
22            compliance with water quality standards. These data and information should include results made
23            available through monitoring and modeling activities done in  conjunction with the development
24            of the long-term CSO control plan.  (E.B)
25
26            The purpose of the system characterization, monitoring and modeling program initially is to assist
27            the permittee in developing appropriate measures to implement the nine minimum  controls and,
28            if necessary,  to support development of the long-term CSO control plan.  The monitoring and
29            modeling data also will be used to evaluate the expected effectiveness of both the nine minimum
30            controls, and, if necessary, the long-term CSO controls, to meet WQS.  (ILC.1)
31
32            The LTCP should be based on more detailed knowledge of the CSS and its receiving
33      waters than is necessary to implement the NMC.  The LTCP should consider a reasonable range
34      of alternatives, including  various levels  of controls.  Hydraulic modeling may be necessary to
35      predict how a CSS will respond to various control scenarios. A computerized model may be
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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1      necessary for a complex CSS, especially one with looped networks or sections that surcharge.
  2      In simpler systems, however, basic equations (e.g., Hazen-Williams or Manning equation - see
  3      Section 5.3.1) and spreadsheet programs can be used to compute hydraulic profiles and predict
  4      the hydraulic effects of different control measures. (Verification using monitoring data becomes
  5      more important in these latter situations.)
  6
  7            Finally, modeling can support either the presumption or demonstration approaches of the
  8      CSO Control Policy. The demonstration approach requires demonstration that a control plan is
  9      adequate to meet CWA requirements.  Meeting this requirement can necessitate detailed CSS
 10      modeling as an input to receiving water impact analyses.  On the other hand, the presumption
 11      approach involves performance-based limits on the number or volumes of CSOs. This approach
 12      may require less modeling of receiving water impacts, but is acceptable only if  "the permitting
 13      authority determines that such presumption is reasonable in light of the data and analysis
 14      conducted in the characterization, monitoring, and modeling of the system and the consideration
 15      of sensitive areas . . . ." (n.C.4.a)  Therefore, the presumption approach does not eliminate the
 16      need to consider receiving water impacts.
 17
 18      7.2    MODEL SELECTION STRATEGY
 19
20            This section discusses how to select a CSS model. This section does  not describe all of
21      the available CSS-related models, since other documents provide this information (see Shoemaker
22      et al., 1992; Donigian and Huber, 1991; WPCF, 1989).
23  •
24            CSS modeling involves two distinct elements:  hydraulics and  water quality.
25
26            •   Hydraulic modeling consists of predicting the flow characteristics in the CSS. These
27               include the different flow rate components (sanitary, infiltration, and runoff), the flow
28               velocity and depth in the interceptors, and the CSO flow rate and  duration.
29
30            •   Water  quality modeling consists  of predicting the pollutant characteristics of the
31               combined sewage in the system, particularly at CSO outfalls and at the treatment
32               plant.  Water quality is measured in terms of bacterial counts, and concentrations  of
33               important constituents  such as  BOD,  suspended  solids, nutrients, and  toxic
34               contaminants.

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                                                                                            *
  1            Some models include both hydraulic and water quality components, while others are
  2     limited to one or the other.  Although CSO projects typically involve hydraulic modeling, water
  3     quality modeling is less common, and  a  community may decide to rely on  water quality
  4     monitoring data instead.
  5
  6              Several factors will dictate whether water quality modeling is appropriate. WPCF
  7     (1989) concludes that "simulation of quality parameters should only be performed when necessary
  8     and only when requisite calibration and verification data are availablef...] Another option is to
  9     couple modeled hydrologic and hydraulic processes with measured quality data to simulate time
 10     series of loads and overflows.11 Modeling might not be justified in cases where measured  water
 11      quality  variations are difficult to relate to parameters such as land use,  rainfall intensity, and
 12      pollutant accumulation rates. For these cases, using statistics (e.g., mean, standard deviation, etc.)
 13      of water quality parameters measured in the system can be a valid approach.  One limitation of
 14      this approach, however, is that it cannot account for the implementation of best management
 IS      practices such as street  sweeping or the use  of detention basins.
 16
 17            Exhibit  7-1  shows  how model selection can be affected by  the  status of NMC
 18      implementation and LTCP  development, and  by whether the  LTCP will  be based on the
 19      presumption or demonstration approach.  To avoid duplication of effort, the permittee should
20      always consider modeling needs that will arise during later stages of LTCP development or
21      implementation.
22
23            Nine Minimum  Controls (NMC)
24            In this initial phase of CSO control, hydraulic modeling can be used to estimate existing
25      CSO volume and frequency and the impacts of implementing alternative controls under the NMC.
26      Typically, in this stage of analysis, modeling would focus more on reductions in CSO magnitude,
27      frequency, and duration than on contaminant transport.
28
29            Long-Term Control Plan (LTCP)
30      •     EPA  anticipates  that  hydraulic modeling will be necessary for most CSSs regardless of
31      whether the community  uses the presumption approach or demonstration approach to show that

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                        WORKING DRAFT:  Do Not CUE OR QUOTE
             Exhibit 7-1. Relevant CSS Hydraulic and Contaminant Transport Modeling
                                  for EPA's CSO Control Policy

CSS Hydraulic Modeling
CSS Contaminant
Transport Modeling
Nine Minimum Controls
Demonstrate implementation of the
nine minimum controls
Simple to complex models
of duration and peak flows
Limited - Not usually
performed
LTCP "Presumption Approach"
Limit average number of overflows
per year
Capture at least 85% of wet weather
CS volume per year
Eliminate or reduce mass of
pollutants equivalent to 85%
capture requirement
LTCP "Demonstration ApproacK"
Demonstrate that a selected control
program ... is adequate to meet the
water quality based requirements of
theCWA
Long-term continuous
simulations (preferred) or
design storm simulation
Same
Same
Limited - Not usually
performed
Limited - Not usually
performed
Use measured concentrations
or simplified transport
modeling
.
Design storm simulations
or
Long-term continuous
simulations
Use measured concentrations
or
contaminant transport
simulations
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
its LTCP will provide for WQS attainment. Both approaches require accurate predictions of the
number and volume of CSO events; under the demonstration approach, this information will help
determine the amount and timing of pollutant loadings to the receiving water.

       Presumption Approach.   The presumption  approach is likely  to  require  hydraulic
modeling to develop accurate predictions of the number and volume of CSOs. Some level of
contaminant transport modeling may also be necessary to ensure that the presumption approach
will not result in exceedances of water quality criteria in light of available data (loading estimates
can be developed using measured concentrations or simplified screening methods, coupled with
hydraulic modeling).
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  1            Demonstration Approach.  Under the demonstration approach, the permittee is held to
  2     a higher level of proof, and should show that the planned controls will attain WQS unless WQS
  3     cannot be attained as a result of natural background conditions or pollution sources other than
  4     CSOs.
  5
  6            Therefore, CSS modeling under the demonstration approach  should describe pollutant
  7     loadings to the receiving water body. Since water quality modeling in the CSS is directly linked
  8     to water quality modeling in  the receiving water, the CSS model must generate sufficient data
  9     to drive the receiving water model. Further, the resolution needed for the CSS pollutant transport
 10     estimates will depend on the time resolution called for in the receiving water model, which  is in
 11      turn driven by WQS.  For pollutants with long response times in the receiving water (e.g., BOD
 12     and nutrients), the appropriate level  of loading information is usually the total load introduced
 13      by the CSO event.   For pollutants with shorter response times (e.g., bacteria, acute toxic
 14     contaminants), it may be necessary to consider the timing of the pollutant load within the course
 15      of the CSO event.
 16
 17      7.2.1  Selecting Hydraulic Models
 18
 19            Hydraulic models  used for CSS simulations can be divided into three main categories:
20
21            •  Water-budget  models based on Soil Conservation Service (SCS) runoff curve
22               numbers,1 runoff coefficients, or other similar method for the generation of flow.
23               These models can estimate runoff flows influent to the sewer system and, to a lesser
24               degree, flows at different  points in the system. Water-budget models  do not actually
25               simulate flow in the CSS, however, and therefore do not predict such parameters as
26               the flow depth, which  frequently control the occurrence of CSOs.  (The RUNOFF
27               block of EPA's Storm Water Management Model (SWMM) is an example of a water-
28               budget model.)
29
30
31         'SCS runoff curves were developed based on field studies measuring runoff amounts from different soil cover
32     combinations. The appropriate runoff curve is determined from antecedent moisture condition and the type of soil.
33     (Viessman, et al., 1977)

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                         WORKING DRAFT:" "Do NOT CITE OR QUOTE
  1            •  Models based on the kinematic wave approximation of the full hydrodynamic
  2               equations.2  These models can predict flow depths, and therefore overflows, in
  3               systems which are not subject to surcharging or back-ups (backwater effects).  (The
  4               TRANSPORT block of SWMM is an example.)
  5
  6            •  Complete, dynamic models are based on the full hydrodynamic equations and can
  7               simulate surcharging, backwaters or looped systems. (The EXTRAN block of SWMM
  8               is an example.)
  9

 10     Exhibit 7-2 summarizes the strengths and limitations of these three classes of models.  Section
 11     7.3 discusses available hydraulic models.
 12

 13            The simpler models were developed to support rapid evaluations of CSSs.  They require
 14     little input data, are relatively easy to use, and require less computer time than complete models.

 IS     These features, however, are becoming less relevant as complete models with user-friendly pre-
 16     and post-processors are now widely available. Advances in computer technology render run time
 17     a secondary issue for all but the largest of applications. Thus, complete and complex models can
 18     often be used with as much ease and as little data as  simple models.
 19
20            Criteria for the selection of a CSS hydraulic model include:
21

22            1.  Ability to accurately represent CSS's hydraulic behavior. The hydraulic model
23               should be  selected with  the above limitations in mind.  For example,  a complete
24               dynamic model  may be  appropriate  if CSOs are due to back-ups or surcharging.
25               Since models differ in their ability to deal with such factors as conduit cross-section
26               shapes, special structures,, pump station controls, tides simulation, and automatic
27               regulators, these features in a CSS may guide the choice of one model over another.
28
29            2.  Extent of Monitoring.  Monitoring usually cannot cover an entire CSS, particularly
30               a large CSS.  A dynamic model is more reliable for predicting the behavior of
31                unmonitored overflows, since all the hydraulic features controlling the overflow can
.32         2Flow, which is caused by the motion of waves, can be described by the hydraulic routing technique.  This
33     technique is based on the simultaneous solution of the continuity equation and the momentum equation for varying
34     flow.  Under certain conditions, these hydrodynamic equations can be simplified to a one-dimensional continuity
35     equation and a uniform flow equation (in place of the full momentum equation). This is referred to as the kinematic
36     wave approximation (discharge is simply a function of depth).  (Bedient arid Huber, 1992)


       External Review Draft                     7-7                        December 6, 1996

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                WORKING DRAFT; Do NOT CUE OR QUOTE
   Exhibit 7-2.  Characteristics of RUNOFF, TRANSPORT, and EXTRAN Blocks of the
                  EPA Storm Water Management Model (SWMM)1

Characteristics
1. Hydraulic simulation method
2. Relative computational expense
for identical network
schematizations
3. Attenuation of hydrograph peaks
4. Time displacement of hydrograph
peaks
5. In-conduit storage
6. Backwater or downstream control
effects
7. Flow reversal
8O,— .— U*.— <••••
ourcnarge
9. Pressure flow
10. Branching tree network
11. Network with looped connections
12. Number of preprogrammed
conduit shapes
13. Alternative hydraulic elements
(e.g., pumps, weirs, regulators)
14. Dry-weather flow and infiltration
generation (base flow)
15. Pollution simulation method
16. Solids scour-deposition
17. User input of hydrographs/
pollutographs
Blocks
RUNOFF .
Nonlinear reservoir,
cascade of conduits
Low
Yes
Weak
Yes
No
No
Weak
No
Yes
No
3
No
No
Yes
No
No
TRANSPORT
Kinematic wave,
cascade of conduits
Moderate
Yes
Yes
.Yes
No2
No
Weak
No
Yes
No
16
Yes
Yes
Yes
Yes
Yes
EXTRAN
Complete equations,
conduit networks
High
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
8
Yes
Yes
No
No
Yes
1 After Huber and Dickinson, 1988.
2 Backwater may be simulated as a horizontal water surface behind
         a storage element
External Review Draft
7-8
December 6, 1996

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1               be simulated.  In some cases, however, estimates of overflow at unmonitored locations
  2               can be made based on  monitoring in comparable areas (i.e., areas with similar
  3               geographic features  like elevation), based on  V/R ratios (see Section 5.3.3) and
  4               drainage basin characteristics.
  5
  6         •   3.  Need for long-term simulations.  Long-term simulations are desirable to predict the
  7               average annual number of CSOs, volumes, and loadings upon which the presumption
  8               approach is based. For large systems, long-term  simulations using a detailed dynamic
  9               model often require lengthy computer run times.
 10
 11            4.  Need to assess water quality in CSS.  If CSS water quality simulations are needed,
 12               the hydraulic model should also be capable of simulating water quality.
 13
 14            5.  Need to assess water quality in receiving waters. The pollutants of concern and the
 15               nature of the receiving water affect the resolution of the CSO data needed for the
 16               water quality analyses. For example, analyses of bacteria will typically require hourly
 17               rather man daily loading data, and the hydraulic  model must be capable of providing
 18               this resolution.
 19
 20            6.  Ability to assess the effects of control alternatives.  If control alternatives involve
 21                relieving downstream back-ups or surcharging, correct simulation may require use of
 22               a dynamic model.
 23
 24             7.  Use of the presumption or demonstration approach. Some permittees using the
 25                first presumption approach option—no more than four overflow events per year—can
 26                estimate the number of overflow events fairly accurately by calculating the probability
 27                of exceeding storage and treatment capacity. Other permittees may need to  account
 28                for transient flow peaks, requiring accurate flow  routing. The other two presumption
 29                approach options—percent volume capture  and pollutant  load  capture—generally
 30                require some  analysis of the timing and peaking of flows, so that a hydraulic
 31                simulation  approach may be needed.
 32
 33                If a permittee is using the demonstration approach, receiving  water modeling is
 34                necessary,  and the pollutant transport time step for receiving water modeling  may
 35                influence the time step for CSS quality modeling. This hi turn will constrain the  time
 36                resolution for  CSS hydraulic  modeling.   If the permittee uses the demonstration
 37                approach, more sophisticated modeling  approaches will probably be necessary.
 38
 39            8.  Ease of use and cost As mentioned above, simple models tend to be easier to use
40                than complete dynamic models, although user-friendly dynamic models now exist.
41                These, however, are generally commercial models and cost more than public domain
42                models.  Another option  is  to use commercial pre- and post-processors (or shells)
43                designed to facilitate the use of public  domain models such as SWMM.  They can
44                provide graphically-oriented, menu-driven data  entry and extensive results plotting
45                capabilities at a cost lower than that of complete dynamic models.
       External Review Draft                     7-9                         December 6, 1996

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                         WORKING DRAFT:" Do NOT CITE OR QUOTE
  1               Another issue related to ease of use is robustness—i.e., a model's lack of propensity
  2               to become unstable.  Instabilities are uncontrolled oscillations of the model results
  3               which are due to the approximations made in the numerical solution of the basic
  4               differential equations. Instabilities tend to occur primarily in fully dynamic models,
  5               and are caused  by many factors, including attempts to simulate short conduits.
  6               Resolving model instabilities  can be time-consuming and may require extensive
  7               experience with the model.  Commercial models tend to be more robust than public
  8               domain models.
 10     1.22     Selecting Water Quality Models
 11
 12           CSS water quality models can be divided into the following categories:

 13

 14           •  Land Use Loading Models—These models .provide pollutant loadings as a function
 15               of the distribution of land uses in the watershed. Generally, these models attribute to
 16               each land use a concentration for each water quality parameter, and calculate overall
 17               runoff quality as a weighted sum of these concentrations. Pollutant concentrations for
 18               the different land uses can be derived from  localized data bases or the Nationwide
 19       .        Urban Runoff Program (NURP) studies.  Local data are usually preferable to NURP
20               data since local data are generally more recent and site-specific.
21
22            •  Statistical Methods—A more sophisticated version of the previous method, statistical
23               methods  attempt to formulate a derived frequency distribution for Event Mean
24               Concentrations (EMCs). EMCs are defined as the total mass of a pollutant discharged
25               during an event divided by the total discharge volume. NURP documents discuss the
26               use of statistical methods to characterize CSO quality in detail (Hydroscience, Inc.,
27               1979) and in summary form (U.S. EPA, 1983a).
28
29            •  Build-Up/Washoff Models—These models simulate the basic processes that control
30               runoff quality, accounting for such factors as time periods between events, rainfall
31               intensity, and best management practices. They require calibration.
32                                                                                 -

33            Few  models  address  the  potentially  important  role of  chemical  reactions  and
34     transformations within the CSS.  Calibration is difficult because pollutant loading into the CSS
35     is never known exactly.
36
37
       External Review Draft                    7-10                        December 6, 1996

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                          WORKING DRAFT: Do NOT CITE ORTQUOTE
   1            The permittee should consider the following criteria when selecting a CSS water quality
   2      model:
  4            1.  Needs of the receiving water quality simulation.  The time scale of the water
  5                quality simulation in the CSS, and the degree of sophistication of the model, depends
  6                partly on the needs of the receiving water quality simulation (if implemented) and,
  7                ultimately, on the level of detail required to demonstrate compliance with the CWA.
  8                If it is only necessary to estimate average annual loading to the receiving water, then
  9                detailed hourly or sub-hourly simulation of combined sewage quality generally will
 10                not be necessary.  As noted above, there are many  cases where it is  appropriate to
 11                combine sophisticated hydraulic modeling with approximate quality modeling.
 12
 13            2.  Ability to assess  control  and best management practice (BMP) alternatives.
 14                When the  control alternatives under assessment include specific BMPs or control
 15                technologies, the quality model should be sophisticated enough to estimate the effects
 16                of these alternatives.
 17
 18            3.  Ability to accurately represent significant characteristics of pollutants of concern.
 19                The pollutants involved in CSS quality simulation can be roughly grouped as bacteria,
 20                BOD, nutrients, sediments and sediment-associated pollutants, and toxic contaminants.
 21                Most water quality models are designed to handle sediments and nutrients, but not all
 22                can model additional pollutants. In some cases and for some pollutants, this limitation
 23                can be circumvented by using a sediment  potency factor, which relates mass of a
' 24                given pollutant to sediment transport.
 25
 26            4.  Capability for  Pollutant Routing.  Another concern is the  model's  capability for
 27                pollutant  routing—i.e.,  its  capacity  to  account  for variability   in  pollutant
 28                concentrations during storm events-.  Many models translate  source availability and
 29                CSO  quantity to pollutant loading without  taking  separate account of the timing of
 30                pollutant delivery due to transport through the CSS. Many systems deliver the highest
 31                concentrations of pollutants in the rising limb of the storm  flow (the "first flush"
 32                effect). If the CSO loading for such systems is modeled using overflow quantity and
 33                average concentrations, inaccuracies will result, particularly if the "first flush" is
 34                effectively  captured by the POTW or storage.
 35
 36            5. Expense and Ease of Use.  Sophisticated water quality models can be expensive to
 37                calibrate and will generally be more difficult to use.  If a simpler model is applicable
 38               to the situation and can be  properly calibrated, it may be sufficient.
 39
 40
        External Review Draft                     7-11                        December 6, 1996

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                         WORKING "DRAFT: D6 NOT ClTE OR QUOTE
  1     73    AVAILABLE MODELS
  2
  3            Exhibits 7-3 and 7-4 summarize several hydraulic and water quality models, respectively,
  4     that have been developed by EPA and the Army Corps of Engineers and are available in the
  5     public domain. An increasing number of high-quality commercial models and pre/post-processors
  6     is also available, either as custom-developed software or as more user-friendly, enhanced models
  7     based on popular public  domain software.3 Several of the available commercial models and
  8     pre/post processors are listed in Exhibit 7-5. This listing is provided to assist potential users; it
  9     is not meant to endorse any particular model or imply that models not listed are not acceptable.
 10
  1            These  exhibits summarize some important technical criteria, and can  be used as a
  2      preliminary guide. However, to evaluate the use of a specific model in a particular situation the
  3      permittee should refer to the more detailed reviews and major references listed in Exhibits 7-3
  4      and 7-4.  Both Shoemaker et al. (1992) and Donigian and Huber (1991) provide preliminary
  5      evaluations of the functional criteria, including an indication of  the cost of implementation and
  6      data requirements.
  7
  8      7.4    USING A CSS MODEL
 9
10      7.4.1  Developing the Model
11
12            Until recently the modeler had to compromise between the level of detail in a model, the
13      mode in which it was run (complex vs. simple), and the time period for the simulation (event vs.
14      continuous). As computer technology continues to improve, limitations in computing power are
IS      becoming less of a factor in determining the appropriate level of modeling complexity.  In some
16      cases, where detail is not required, a simplified model may save time spent filling the data
17      requirements of the model, preparing files, and doing the model runs.  Shoemaker et al. (1992,
18
19        'The commercial packages have not been reviewed by EPA and they are subject to continued evolution and
20     change, like all commercial software.  A recent listing of some available models is found in Mao (1992).  Other
21     recent developments in sewer and runoff models include models linked to geographic information systems (GIS),
22     computer-aided design (CAD) systems, and receiving water models such as WASP.

       External Review Draft                    7-12                       December 6,  1996

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                'WORKING DRAFT: Do NOT CITE OR QUOTE
                 Exhibit 7-3. CSS Hydraulic Models (Public Domain)
Model Name
EPA Statistical1
The Simple Method
USGS Regression .
Method
SLAMM
P8-UCM
Auto-Q-ILLUDAS
STORM
DR3M-QUAL
HSPF
SWMM
Characteristics
Hydranlic
Time Scales
Annual,
Event
Annual,
Event
Annual,
Event
Continuous
-Daily
Continuous
-Hourly
Continuous
-Hourly
Continuous
-Hourly
Continuous
-Sub-hourly
Continuous
-Sub-hourly
Continuous
-Sub-hourly
Hydraulic
Simulation Type
Runoff
Coefficient
Runoff
Coefficient
Regression
Water Balance
Curve Number
• Water Balance
Runoff Coeff 7
Curve Number
Kinematic Wave
Kinematic Wave
Kinematic &
Dynamic Wave
Assess Control
No
No
No
Limited
Advanced
Limited
Limited
Advanced
Moderate2
Advanced
Key to
Reviews
1A3
1
1,2
1
1
1,3
1,2,3
U.3
1,2,3
1,23
Major
Hydroscience, 1979
Driscoll et al., 1990
Schueler, 1987
Driver & Tasker,
1988
Pitt, 1986
Palmstrom &
Walker, 1990
Terstriep et al.,
1990
HEC, 1977
Alley & Smith,
1982a & 1982b
Johanson et al.,
1984
Huber & Dickinson,
1988; Roesner et
al., 1988
   Notes:
   Key to Reviews:
1 Reviewed as "FHWA" by Shoemaker et al., 1992
2 Can be used for assessment of control alternatives, but not designed to readily
  implement that function.

1 Shoemaker et al., 1992.
2 Donigian and Huber, 1991.
3 WPCF, 1989.
External Review Draft
                     7-13
December 6, 1996

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                  WOWONGDRAPT:  "D6 NOT ClTE OR QUOTE
                 Exhibit 7-4. CSS Water Quality Models (Public Domain)
Model Name
EPA Statistical1
The Simple Method
USGS Regression Method
Watershed
GWLF
SLAMM
P8-UCM '
Auto-Q-ELLUDAS
STORM
DR3M-QUAL
HSPF
SWMM

Quality
Time Scales
Annual
Annual
Annual
Annual
Continuous -
Daily
Continuous -
Daily
Event
Continuous •
Hourly
Continuous -
Hourly
Continuous -
Sub-hourly
Continuous -
Sub-hourly
Continuous -
Sub-hourly
Characteristics
Pollutant
Types
S.N.O
S.N.O
S.N.O
S.N.O
S,N
S.N.O
N,0
S.N.O
S.N.O
S.N2
S.N.O
S.N2
Pollutant
•Routing-
Tnrasport
no
no
no
no
low
medium
low
medium
no
high
high
low3
Pollutant
Routing -
Transformation
no
no
no
no
no
no
no
no
no
no
high
low
BMP
Evaluation
low
low
no
medium
low
medium
high
medium
medium
medium
high
high
       Notes:  1  Reviewed as "FHWA" by Shoemaker et al. 1992
              2  Other constituents can be modeled by assumption of a sediment potency fraction.
              3  Low rating from Shoemaker et al. for "weak" quality simulations may not be fully justified
                relative to the strength of other models.

       Key to Pollutant Type:  S - Sediment N - Nutrients O -. Other
External Review Draft
7-14
December 6, 1996

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                        WORKING DRAFT:  Do Nor CITE OR QUOTE
                               Exhibit 7-5. Commercial CSS Models
Package Name*
XP-SWMM
Hydra
Eagle Point
Hydrology Series
Mouse
HydroWorks
PC-SWMM
MTVE
SWMMDuet
Capabilities *
"Pre/Post*
Processor.
Graphical User
Interface and
Post-processor
forSWMM
Yes
Yes
Yes
Yes
Menu-driven
interface for
SWMM
ForSWMM
EXTRAN&
RUNOFF .
SWMM/GIS
Interface
Hydraulic
Dynamic
Dynamic
Dynamic
Dynamic
Dynamic
No
No
No
Water Quality
In Development*
No
No
Yes
In Development
No
No
No

* ^^ODtSICt
XP Software
Tampa, Florida
8 13-886-7724/800-883-3487
Pizer, Inc.
Seattle, Wash.
206-634-2808/800-222-5332
Eagle Point
800-678-6565
Danish Hydraulic Institute
011-45-42867951
Wallingford Software, England
011-4401491 824777
Computational Hydraulics
Guelph, ON
(519) 767-0197
lOBrooks Software
(313) 761-1511
Delaware Dept of Natural
Resources
(302) 739-3451
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
    * as of April 1995

Tables 7-9) provides a tabular summary of the main input data and output information for each
of the models presented hi Exhibits 7-3 and 7-4.

      The level of discretization (i.e., coarse vs. fine scale) determines how accurately the
geometry of the CSS and the land characteristics of the drainage basin are described.  At a very
coarse level of discretization, the CSS is a black box with lumped parameters and primarily CSOs
are simulated (e.g., using the STORM model). A more complex approach might be to simulate
the larger pipes of the CSS, but to lump the characteristics of the smaller portions of the CSS.
Another intermediate level of complexity is to simulate the interceptor since it is the limiting
component in the CSS for controlling overflows. Much can be learned about system behavior
       External Review Draft
                                       7-15
December 6, 1996

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                          WORKING DRAFT:  Do NOT CITE OR~QUOTE
  1     by simulating interceptor hydraulics in response to surface runoff. More complex simulations
  2     would include increasing levels of detail about the system.
  3
  4            In determining the appropriate level of discretization, the modeler must ask:
  5
  6            •   What is the benefit of a finer level of detail?
  7            •   What is the penalty  (in accuracy) in not modeling a portion of the system?
  8
  9     For systems that are controlled hydraulically at their downstream ends, it may only be necessary
 10     to model the larger downstream portion of the CSS.  If flows are limited due to surcharging in
 11      upstream areas,  however, a simulation neglecting the upstream portion  of  the CSS  would
. 12     over-estimate flows in the system. In some cases it is difficult to determine ahead of time what
 13      the appropriate level of detail is.  In these cases, the modeler can take an incremental approach,
 14     determining the value of additional complexity or data added at each step.  Exhibit 7-6,  for
 15      example, compares  a simulation based on  5 subcatchments  (coarse  discretization)  and a
 16      simulation based on 12 subcatchments (finer discretization) with observed values. Only marginal
 17      improvement is observable when subcatchments are increased from 5 to 12. The modeler should
 18      probably  conclude that even finer discretization (say, 15 subcatchments) would provide little
 19      additional value.
 20
 21      7A2  Calibrating and Validating the Model
 22
 23            A model general enough to fit a variety of situations typically needs to be adjusted to  the
 24      characteristics of a particular site and situation. Model calibration and validation are used to
 25      "fine-tune" a model to a specific need and then to  demonstrate the credibility of the simulation
 26    •  results.  Using an uncalibrated model may be acceptable for screening purposes, but without
 27      supporting evidence the uncalibrated result may not be accurate.  To use model simulation results
 28      for evaluating control alternatives, the model must be  reliable.
 29
 3Q               Calibration is the process of using a set of input data and then comparing the results
 31      to actual  measurements of the system.  For example,  a CSS hydraulic model used to simulate

        External Review Draft                    7-16                         December 6, 1996

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EL
           60
I
D
I
OS
       _
      O
           50
           40
           30
           20
           10
                                                                        ~ ~ 12 Subcatchment System


                                                                        1	5 - Subcatchment System


                                                                        "^~ Observed
                                                                                       •••«,
10      20      30        40      50

                      Time (Min.)
                                                                  60
70
80
90

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                         WORKING DRAFT:  Do NOT CUE OR QUOTE
  1      overflows is calibrated by running the model using measured rainfall data to simulate attributes
  2      of CSO overflows, such as volume, depth, and timing. The model results are then compared to
  3      actual measurements of the overflows. The modeler then adjusts parameters such as the Manning
  4      roughness coefficient or the percent imperviousness of subcatchments and runs the model a
  5      second time, again comparing the results to observations.  Initial calibration runs often point to
  6      features of the system which may not have been evident based on the available maps.  For
  7      example, a connection or bypass may have been installed without being reflected on available
  8      maps. The modeler repeats this procedure until satisfied that the  model produces reasonable
  9      simulations of the overflows. Calibration is usually performed on more than one storm, to ensure
10      appropriate performance for a range of conditions. Example model calibration plots of flow and
11      depth during storm events are shown in Exhibit 5-9.
12
13              Validation is the process of testing the calibrated model using one or more independent
14      data sets.  In the case of the hydraulic simulation, the model is run without any further
15      adjustment using independent set(s) of rainfall data.  Then the results are compared to the field
16      measurements collected concurrently with these rainfall data.  If the results are suitably close, the
17      model is considered to be validated. The modeler can then use the model with  other sets of
18      rainfall data or at other outfalls. If validation fails, the modeler must recalibrate the model and
19      validate it again using a third independent data set If the model fails a validation  test, the next
20      test must use a new data set.  (Re-using a data set from a previous validation test does not
21      constitute a fair test, because the modeler has already adjusted model parameters to better the fit
22      of the model to the data.) Validation is important because it assesses whether the model retains
23      its generality: that is,  a model-that has been adjusted extensively to match a particular storm
24      might lose its ability to predict the effects of other storms.
25
26           The availability of adequate calibration  data  places  constraints on which models are
27      appropriate.  Simplified  models in which many system features are aggregated require more
28      calibration than detailed models which simulate  every component of the system.
29
30           When identifying  the time period for  conducting CSS flow monitoring, the permittee
31      should consider the effect of using larger data sets. The CSO Control Manual (U.S. EPA, 1993)

        External Review Draft                   7-18                       December 6, 1996

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                          WORKING MAFT:  Do NOT CITE OR QUOTE
  1      states that "an adequate number of storm events (usually 5 to 10) should be monitored and used

  2      in the calibration."  The monitoring period should indeed cover at least that many storms, but

  3      calibration and validation are frequently done with 2 to 3 storms each.

  4

  5        '    EPA's Compendium of Watershed-Scale Models for TMDL Development (Shoemaker et

  6      al., 1992)  includes the following comments on calibration and validation:

  7

  8            Most models are more accurate when applied in a relative rather than an absolute manner.
  9            Model output data concerning the relative contribution...^ overall pollutant loads is more reliable
10            than an absolute prediction of the impacts of one control alternative viewed  alone.  When
11            examining model output. . . it is important to note three factors that may influence the model
12            output and produce  unreasonable data.  First, suspect data may result from  calibration or
13            verification data that are  insufficient or inappropriately applied.  Second,  any.given model,.
14            including detailed models, may not  represent enough detail to adequately describe existing
15            conditions and generate reliable output. Finally, modelers should remember that all models have
16            limitations and the selected model may not be capable of simulating desired conditions. Model
17            results must therefore be'interpreted within the limitations of their testing and  their range of
18            application.  Inadequate model calibration and verification can result in spurious model results,
19            particularly when used for absolute predictions. Data limitations may require that model results
20            be used only for relative comparisons.

21

22            Common practice employs both judgment and graphical analysis to assess a model's

23      adequacy.   However, statistical evaluation can provide a more rigorous and less subjective

24      approach to validation (see Reckhow et al., 1990, for a discussion of statistical evaluation of

25      water-quality models).

26

27            Nix (1990) suggests the following  general sequence for the calibration of CSS  models:

28

29            1.  Identify the important model  algorithms  and parameters.  A combination of
30                sensitivity analysis and study of model algorithms can determine which parameters
31                are most important for calibration of a given model-site pairing.
32
33            2.  Classify model parameters to determine the degree to which they can be directly
34                measured, or,  alternatively,  are conceptual parameters  not  susceptible to direct
35                measurement. For instance, a parameter such as area is usually easily defined, and
36                thus not varied in calibration, while parameters that are both important to model
37                performance and not susceptible to direct measurement (e.g., percent imperviousness)
38                will be the primary adjustment factors  for calibration.
       External Review Draft                     7-19                         December 6, 1996

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                         WORKING DRAFT:" DcTNoT CITE OR'QUOTE
  1            3.  Calibrate the model(s) first for the representation of overflow volume.
  2
  3            4.  After obtaining a reasonable representation of event overflow volume, calibrate to
  4                reproduce the timing and peak flow (hydrograph shape) of overflows.
  5
  6            5.  Finally, calibrate the quality parameters only after an acceptable quantity simulation
  7                has been obtained.
  8

  9             Section 7.5 describes an example of CSS modeling, including commentary on calibration

 10      and simulation accuracy.

 11

 12      7.4 J  Performing the Modeling Analysis
 13
 14            Once a model  has been  calibrated and validated, it can be run for either long-term

 15      simulations (i.e., continuous simulation) or for single events (usually a set of design storms).
 16

 17            •   Long-term simulations can account for the sequencing of the rainfall in the record,
 IS                and the effect of having storms immediately follow each other. Such simulations are
 19                therefore useful for assessing the long-term performance of the system under the
20                presumption approach. If possible, continuous simulation models should be calibrated
21                using continuous data. Calibration with single events is also possible, but antecedent
22                conditions must be taken into account.  As the speed of desktop computers increases,
23                modelers will be able  to perform long-term continuous simulations with higher and
24                higher levels of detail.
25
26            •    Single event simulations are useful for developing  an understanding of the system
27                (including the causes of CSOs) and for the formulation of control measures, and can
28                be used for calibrating models.
29
30            Although increased computer capabilities enable continuous simulations with greater levels
31      of detail, continuous simulation of very large systems can have some drawbacks:
32
33            •    The  model  may generate  such  a  large amount of data, that data analysis and
34                interpretation are difficult, and
35
36            •    Limitations in the accuracy  of hydrologic input data (due to the inability to perform
37                a continuous simulation of spatially variable rainfall over a large catchment area) may
38                lead to an inaccurate time series of hydraulic conditions within the interceptor.
       External Review Draft                    7-20                        December 6, 1996

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                         WORKING DRAFT: Do Not CUE OR QUOTE
  1     7.4.4  Modeling Results
  2
  3            Model Output
  4            The most basic type of model output is text files in which the model input is repeated and
  5     the results are tabulated.  These can include flow and depth versus time in selected conduits and
  6     junctions, as well as other information such as which conduits are surcharging. The model output
  7     may  include an overall system mass balance with such measures as the runoff volume entering
  8     the system, the volume leaving the system at the downstream boundaries, the volume lost due
  9     to flooding, and the change of volume in storage.  The model output can also measure the mass
 10     balance accuracy of the model run, which may provide indications that problems, such as
 11      instabilities (see Section 7.2.1), occurred.
 12
 13             Most models also produce plot files, which are easier to evaluate than text files.  Output
 14     data from plot files can be plotted using spreadsheet software or commercial post-processors,
 15      which are available for several public-domain models (particularly SWMM). Commercial models
 16      typically include extensive post-processing capabilities, allowing the user to plot flow or depth
 17      versus time at any point in the system or to plot hydraulic profiles versus time along any set of
 18      conduits.
 19
20      Interpretation of Results
21            Simulation models predict CSO volumes, pollutant concentrations, and other variables at
22      a resolution that depends on the model structure, model implementation, and the resolution of the
23      input data.   Because the ultimate purpose of modeling is generally to assess the CSO controls
24      needed  to provide for the attainment of WQS, the model's space and time resolution  should
25      match mat  of the applicable WQS. (For instance, the State WQS may include a criterion that
26      a one-hour  average concentration not exceed a given concentration more than once every 3 years
27      on average.) Spatial averaging may be represented by a concentration averaged over a receiving
28      water mixing zone, or implicitly by the specification of monitoring locations to establish whether
29      die instream criteria can  be met.  In any case, the permittee should  note whether the model
30      predictions use the same averaging scales as the relevant water quality criteria.  When used for
31      continuous  rather than event simulation, as suggested by the CSO  Control Policy, simulation

        External Review Draft                    7-21                         December 6, 1996

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                         WORKING DRAFT: ~Do NOT CITE OR QUOTE
  1     models provide output that can be analyzed to predict water quality criteria exceedances and the
  2     frequency of such exceedances.
  3
  4           In interpreting model results, the permittee needs to be aware that modeling usually will
  5     not provide exact predictions of system performance measures such as overflow volumes or
  6     exceedances of water quality criteria. With sufficient effort, permittees often can obtain a high
  7     degree of accuracy in modeling  the hydraulic response of a CSS,  but results of modeling
  8     pollutant buildup/washoff, transport in the CSS, and fate in receiving waters are considerably less
  9     accurate.  Achieving  a high degree of accuracy is  more difficult in a continuous simulation
 10     because of the  difficulty of specifying continually changing boundary conditions for the model
 11      parameters.
 12
 13            In model interpretation, the permittee should  remember the following:
 14
 15            •   Model predictions are only as accurate as  the user's understanding and knowledge of
 16               the system being modeled and the  model  being used,
 17
 18      •      •   Model predictions are no better than the quality  of the calibration and validation
 19               exercise and the quality of the data used in the exercise, and
20
21            •   Model predictions are only estimates of the response of the system to rainfall events.
22
23     .       Model Accuracy and Reliability
24            Since decisions are based on model  predictions, permittees  need to understand the
25     uncertainty associated with the model prediction.  For instance, a model for a CSO event of a
26     given volume may predict a colifonn count of 350 MPN/100 ml in the overflow, well below the
27     hypothetical water quality criterion of 400 MPN/100 ml.  However, the model prediction is not
28     exact, as observation of an event of that volume would readily show. Consequently, additional
29     information specifying how much variability to expect around the "most likely" prediction of 350
30     is  useful.  Obviously, the interpretation of this prediction  differs, depending on whether the
31     answer is "likely between 340 and 360" or "likely between 200 and  2000."
32
       External Review Draft                    7-22                        December 6,  1996

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                         WORKING DRAFT:  Do "Not CITE OR QUOTE
  1            Evaluating these issues involves the closely related concepts of model accuracy and
  2      reliability.  "Accuracy" is a measure of the agreement between the model predictions and
  3      observations.  "Reliability" is a measure of confidence in model predictions for a specific set of
  4      conditions and for a specified confidence level.  For example, for a simple mean estimation, the
  5      accuracy  could  be measured by the sample standard  deviation,  while the reliability of the
  6      prediction (the sample mean in this case) could be evaluated at the 95 percent confidence level
  7      as plus or minus approximately two standard deviations around the mean.
  8
  9            Modeling as part of LTCP development enables the permittee to demonstrate that a given
10      control option is  "likely" to result in  compliance with the  requirements of the  CWA and
11      attainment of applicable  WQS, including protection  of designated uses.   During  LTCP
12      development,  the permittee will justify that a proposed level of control will be adequate  to
13      provide for the attainment of WQS.  Therefore, the permittee should be prepared to estimate and
14      document the accuracy and reliability of model predictions.
15                                      '                '               •
16            An evaluation of model accuracy and reliability is particularly important for the analysis
17      of wet-weather episodic loading, such as CSOs. Whether water quality criteria involve a defined
18      duration (averaging period) and frequency of excursion, as average monthly and maximum daily
19      values, or as a maximum concentration for a given design stream flow (e.g., 7Q10), duration and
20      frequency are included either  directly or implicitly. .Estimating  duration and frequency of
21      excursion requires  knowledge of model reliability, and the duration and frequency of the storm
22      events serving as a basis for the model.
23
24            Available techniques for quantifying uncertainties in modeling studies include sensitivity
25      analysis, first-order error analysis,  and  Monte Carlo simulations.  Sensitivity analysis is the
26      simplest and most commonly used technique in water quality modeling (U.S. EPA, 1995g).
27      Sensitivity analysis is used to assess the impact of the uncertainty of one or more input variables
28      on the simulated output variables. First-order analysis is used in a manner similar to sensitivity
29      analysis where input variables are assumed to be independent, and the model is assumed to
30      respond linearly to the input variables. In addition to estimating the change of an output variable
31      with respect to an input variable, first-order error analysis also provides an estimate of the output

        External Review Draft                     7-23                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CHE OR QUOTE
  1     variance. Monte Carlo simulation, a more complex technique, is a numerical procedure where
•  2     an input variable is defined to have a certain probability density function (pdf).  Before each
  3     model run, an input variable is randomly selected from each predefined pdf. By combining the
1  4     results of several model runs, a pdf can be developed for the output variable which is useful in
  5     predicting overall model results.  The number of model runs is extremely large  as compared to
  6     the number of runs typically done for sensitivity or first-order error analysis.
  7
  8           The main input variables for simulating the impact of CSO loadings are properties of the
  9     mean rainfall event (storm event depth, duration, intensity, and interval between events), CSO
10     concentrations of specific pollutants, design flow of the receiving water body, and its background
11      concentrations. The output consists of an assessment of the water quality impact in terms of
12      duration and frequency of exceedances of water quality criteria. Pollutant concentrations are the
13      main "uncertain" (sensitive) input variables and can be varied over a range of reasonable values
14      to asses their impact  on  the resulting  water  quality.  Uncertainty  analysis can improve
IS      management decisions and provide insight into the need for any additional data collection to
16      refine the estimated loads. For instance, if a small change in a pollutant concentration results in
17      an extremely large variation in the prediction of water quality, it may be appropriate to allocate
18      resources to more accurately estimate the CSO pollutant concentration used in the model.
19
20      7.5  -  EXAMPLE SWMM MODEL APPLICATION
21
22            This section applies the Storm Water Management Model (SWMM) to a single drainage
23      area from the example CSS drainage area presented in  Chapters  4 and 5.  While some of the
24      details of the  application are particular to the SWMM  model, most of the  explanation is
25      applicable to a range of hydraulic models. The TRANSPORT block of the SWMM model was
26      chosen for the flow routing because the  hydraulics in the  system did not include extensive
27      surcharging, and the system engineers felt that a dynamic hydraulic model such as SWMM
28      EXTRAN was not needed to accurately predict the number and volume of CSOs.
29
       External Review Draft                    7-24                        December 6, 1996

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                         TVORKING DRAFT:  Do NOT CTTE OR QUOTE
  1      7.5.1   Data Requirements
  2
  3             The first step in model application is defining the limits of the combined sewer service
  4      area, and delineating  subareas  draining to  each outfall (see Exhibit 7-7).   This can be
  5      accomplished using a sewer system map, a topographic map, and aerial photographs as necessary.
  6      The modeler next must decide what portions of the system to model based on their contributions
  7    .  to CSOs (as illustrated in Example 4-1). The next step is to divide selected portions of the CSS
  8      and drainage area into segments and translate drainage area and sewer data into model
  9      parameters. This process, referred to as discretization, begins with the identification of drainage
10      boundaries, the location of major sewer inlets using sewer maps, and the selection of channels
11      and pipes to be represented in the model. The drainage area is then further divided into subareas,
12      each of which contributes to the nodes of the simulated network. The modeler must consider the
13      tradeoff between a coarse model that simulates only the largest structures in the CSS, and  a
14      fine-scale model that considers nearly every portion of the CSS. A coarse model requires less
15      detailed knowledge of the system, less model development time, and less computer time.  The
16      coarse model, however, leaves out details of the system such as small pipes and structures in the
17      upstream  end of the CSS.  Flow in systems that are limited by upstream structures and  flow
18      capacities will not be simulated accurately.
19
20            Where pipe capacities limit the amount of flow leaving a drainage area or delivered to
21      the wastewater treatment plant, the flow routing features of the model should be used to simulate
22      channels and pipes in those areas of concern.  The level of detail should be consistent with the
23      minimum desired level of flow routing resolution. For example, information cannot be obtained
24      about upstream storage when the upstream conduits and their subcatchments are not simulated.
25      Further, sufficient  detail needs to be provided to allow control options within the system to be
26      evaluated for different areas.
27
28            In this example, the modeled network is carried to points where the sewers branch into
29      pipes smaller than 21 inches. From these points upstream, the system isn't directly modeled.
30      Instead, runoff from the upstream area is estimated and routed into the 21-inch pipes.  Exhibit
31      7-8 presents the modeled sewer lines and the subareas tributary to those lines for service area 1.

        External Review Draft                     7-25                         December 6, 1996

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w

1
EL
CD




0
I
O\
(—»

I
                                                      Raingage
                                                                                                                     4    CSO Outfall Drainage
                                                                                                                          Area
Not to Scale

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               WORKING DRAFT:  Do "NOT CITE OR QUOTE
                   Exhibit 7-8. Sewer Network and Subareas
       Combined Sewer
       Service Area #1
  0°y SewerSubarea

   24"  Pipe Size (inches)
External Review Draft
7-27
December 6, 1996

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                       "WORKING DRAFT:  Do NOT CITE OR QUOTE
 2     7.5.2  SWMM Blocks
 3
 4            RUNOFF block. The RUNOFF block of SWMM generates surface runoff and pollutant
 5'     loads in response to precipitation input and modeled surface pollutant accumulations.  The main
 6     data inputs for the RUNOFF block are:
 7
 8            •   subcatchment width
 9            •   subcatchment area
10            •   subcatchment imperviousness
11            •   subcatchment ground slope
12            •   Manning's roughness coefficient for impervious and pervious areas
13            •   impervious and pervious area depression storage
14            •   infiltration parameters.
15
16     The main RUNOFF block data inputs (by subcatchment area number) for the example are shown
17     in Exhibit 7-9. The subcatchment area is measured directly from maps and the width is generally
18     taken as the physical width of overland flow.  Selection of subcatchment width is more subjective
19     when the subcatchment is not roughly rectangular, symmetrical and uniform.  Slopes are taken
20     from topographic maps, and determinations  of imperviousness, infiltration parameters, ground
21     slope, Manning's roughness coefficients, and depression storage parameters are based on field
22     observations and aerial photographs.
23
24            The RUNOFF block data file  is  set up to generate an  interface file that transfers
25     hydrographs  generated by  the RUNOFF block to  subsequent SWMM blocks for further
26     processing. In this example, the data generated in the RUNOFF block are processed by the
27     TRANSPORT block.
28
29            TRANSPORT block. The TRANSPORT Block  is typically used to route flows and
30     pollutant loads through the sewer system.  TRANSPORT also allows for the introduction of dry
31     weather sanitary and infiltration flow to the system. The  main TRANSPORT block inputs by

       External Review Draft                    7-28                       December 6, 1996

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f
I
Exhibit 7-9.  SWMM Runoff Block Input Parameters
               (SWMM HI Card)
Sub
Area
No.
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
Inlet No.
(manhole)
125
126
126
127
128
129
130
130
131
132
133
133
134
135
136
Width
(ft.) .
3216
4114
3468
4080
5140
3407
7596
5614
8581
5026
5445
2505
7504
5610
10069
Area
(DC.)
25.1
34.0
20.7
28.1
47.2
21.9
27.9
23.2
39.4
20.0
35.0
29.9
37.9
74.7
220.0
Imperv
%
55
35
28
55
22
31
46
38
35
75
17
59
39
29
37
Slope
(ft/ft.)
.0060
.0060
.0125
.0100
.0001
.0040
.0001
.0001
.0170
.0100
.0200
.0140
.0125
.0001
.0100
Manning (it) .
Imperv.
0.015
0.015
0.015
0.015
0.015
0.015
.0150
0.015
0.015
0.015
0.015
0.015
0.015
0.015
0.015
Perv«
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
... Degression Stbr.
Imperv.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
I*e*v.
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
Infiltration
Max Rate
(in./hr.)
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
Min Rate
(in^hr.)
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Decay Rate
(I/sec.)
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
vo
g

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!
!
71
SEWER ELEMENT DATA
ELEMENT
NO.
125
175
126
177
150
178
127
179
128
176
129 '
160
130
181
131
182
132
183
133
184
134
185
135
UPSTREAM
ELEMENT
NO.1
175
126
176
150
178
127
0
128
0
129
180
130
181
131
182
132
183
133
184
134
185
135
0
UPSTREAM
ELEMENT
NO. 2
0
0
177
0
179
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
UPSTREAM
ELEMENT
NO. 3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ELEMENT
TYPE
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
sewer pipe
manhole
LENGTH (ft)
[for pipe element]
INFLOW (cfs)
[for manhole]
0.087
1000
0.188
840
0
390
0.097
651
0.163
733
0.076
841
0.176
'620
0.136
727
0.103
771
0.221
1110
0.256
1007
0.131
PIPE
DIMENSION
(ft)
0
0.45
0
2.75
0
1.75
0
2.0
0
4.5
0
4.0
0
4.0
0
3.5
0
3
0
2.75
0
1.75
0
PIPE
SLOPE
(ft/100 ft)
0
0.5
0
0.28
0
0.39
0
0.34
0
0.07
0
0.16
0
0.09
0
0.12
0
0.16
0
0.13
0
0.4
0
MANNING
PIPE
ROUGHNESS
(n)
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
0.014
0
                                                                                                                                                              o
                                                                                                                                                              a
                                                                                                                                                c»
g
ON

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     element number are presented in Exhibit 7-10. The exhibit specifies the number and type of each
  2    . element (including upstream elements), the element length (for pipe elements), and inflow (for
  3     manholes).
  4
  5           The inflow parameter allows for introduction of dry-weather (sanitary) flow to the system.
  6     Dry-weather flow is typically distributed proportional to area served. Here it is set to 0.0035 cfs
  7     per acre. If the records are available, this parameter can be refined by multiplying the per-capita
  8     wastewater flow (typically available from the wastewater treatment plant or latest facilities plan)
  9     by the average population density calculated from census figures and sewer service area maps.
 10
 11      7.53  Model Calibration and Application
 12
 13            The  output hydrograph for element (manhole) 125 from the TRANSPORT  block is
 14      presented as Exhibit 7-11, with the measured flow for the event plotted for comparison. The
 15      peak flow, shape of the hydrograph, and the total volume of overflow for this calibration run  are
 16      very close to the measured values.
 17
 18          ,  The SWMM model is applied to monitored drainage areas within the CSS using available
 19      monitoring data to calibrate the  hydraulic portions of the program to monitored areas. For
20      outfalls that  are not monitored, parameters are adjusted based on similar monitored areas and on
21      flow depths or flow determinations obtained from the initial system characterization (see Chapter
22      3). Once the entire CSS drainage area is modeled and the  SWMM model calibrated, the model
23      then needs to be validated.  It can then be used to predict the performance of the system for
24      either single events (actual or design) or for a continuous rainfall record.  Recall that it is
25      desirable to  calibrate the model to a continuous sequence of storms if is to be applied to a
26      continuous rainfall record. Individual storms related to monitored events can be run to calculate
27      the total volume of overflow for the system. Peak flow values from the SWMM hydrographs
28      can be used for preliminary sizing of conveyance facilities  that may be needed to alleviate
29      restrictions.
30
       External Review Draft                    7-31                        December 6, 1996

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                      WORKING DRAFT:  Do NOT CITE OR QUOTE
                                Exhibit 7-11. Flow Hydrograph
           90-
           80--
           70--
        ^60-
        J2
        3.50--
        §40-
        OL30--
           20-
           10-
ooooooooooooooo
qcoocooooqcoqcoocoocoo
                                o
                                oo
                                                                                o
                                                                                o
                                   TIME OF DAY (hours)
                                       Predicted
            Measured
1           To predict the number of overflows that will occur per year, the calibrated model can
2     either be run in a continuous mode or for design storm events.  In the continuous mode the
3     model can be run using the long-term rainfall record (preferable where the data are available),
4     or for a shorter period of time (say, for a typical or extreme year from the example discussed
5     throughout Chapter 5). While the event mode is useful for some design tasks and for estimating
6     hourly loading for a fine-scale receiving water model, the continuous mode is preferable for
7     evaluating the number of overflows under the  presumption  approach.  In this example, a
8     continuous simulation based on the 38-year rainfall record predicted between 12 and 32 overflow
      External Review Draft
7-32
                                                         December 6, 1996

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                         WORKING DRAFT:  Do NOT CTTE OR QUOTE
  1     events per year.  The average—22 overflow events per year—is used for comparison with the
  2     4-event-per-year criterion in the presumption approach. (Note that only one outfall in the system
  3     needs to overflow to trigger the definition of "CSO event" under the presumption approach.)
  4
  5            Based on model  results, system modifications were recommended as part of NMC
  6     implementation. After the NMC are in place, the model will be rerun to assess improvement and
  7     the need for additional controls.
  8
  9     7.5.4   SWMM Quality Modeling
 10
 11             Once the SWMM model has been hydraulically calibrated, it can be used to predict
 12     pollutant concentrations in the overflow.  The summary of the flow-weighted concentrations
 13      output by the model can then be compared to composite values of actual samples taken during
 14      the course of the overflow.  Plots of individual concentrations versus  time (pollutographs) can
 IS      also be used to match the variation in concentration of a pollutant during the course of the
 16      overflow. First flush effects can also be observed from the model output if buildup/washoff is
 17      used.
 18
 19            Model Results
20            Exhibit  7-12 presents the BOD and total solids output of the SWMM model for the
21      example storm. Note that the modeled concentrations of both pollutants follow a similar pattern
22      throughout the overflow with little if any first flush concentration predicted in the early part of
23      the overflow.  The initial loads assigned within the model for this calibrated example were 70
24      pounds per acre for BOD and 1,000 pounds per acre for total solids.  This model was previously
25      calibrated using monitoring data.
26
27            Predicted and observed values for BOD and total solids concentrations are presented in
28      Exhibit 7-13. The observed concentrations are from analyses of composite samples collected in
29      an automated field sampler for this storm.  The modeled values give  an  approximate, but not
30      precise, estimate of the parameters. While some studies have resulted in closer predictions, this
31      discrepancy between predicted and observed pollutant values is not uncommon.

        External Review Draft                    7-33                       December 6, 1996

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                       WORKING DRAFT: Do Ntfr CITE OR QUOTE
                                  Exhibit 7-12.  Pollutographs
                 Exhibit 7-13. Predicted and Observed Pollutant Concentrations

Flow-weighted concentration (mg/1)
Predicted
BOD
31.4
TS
420
Observed .
BOD
94
TS
300
2
3
4
5
6
      The modeling in this example would be useful for evaluating the CSS performance against
the four-overflow-event-per-year criterion in the presumption approach.  It could also be used to
evaluate the performance of simple controls.  If further analysis is required, more complex
modeling may be necessary.
      External Review Draft
                                      7-34
December 6, 1996

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                        WORKING DRAFT:  Do NOT CUE OR QUOTE
  i                                         CHAPTERS
  2
  3                              RECEIVING WATER MODELING
  4
  5            This chapter discusses the use of receiving water modeling in evaluating CSO impacts to
  6     receiving waters. It introduces simplified techniques, such as dilution and decay equations, and
  7     more complex computer models, such as QUAL2EU  and WASP.  This chapter uses the term
  8     "modeling" broadly to refer to  a range of receiving water simulation techniques.
  9
10     8.1    THE CSO POLICY AND RECEIVING WATER MODELING
11
12            Under the CSO Control Policy a permittee should develop an LTCP that provides for
13     attainment of WQS using either the demonstration approach or presumption approach. Under the
14     demonstration approach, the permittee documents that the selected CSO control measures will
15     provide for the attainment of WQS, including designated uses in the receiving water.  Receiving
16     water modeling may be necessary to characterize the impact of CSOs on receiving water quality
17     and to predict the improvements which would result from different CSO control measures. The
18     presumption approach does not explicitly call for analysis of receiving water impacts. However,
19     because the presumption approach may not be used when the permitting authority determines that
20     it  will not result  in  compliance with CWA requirements,  the permittee may  need to use
21     screening-level models to show receiving water impacts.
22
23            In many cases, CSOs discharge to receiving waters that are water quality-limited and
24     receive pollutant loadings from other  sources, including nonpoint sources and other permitted
25     point sources. The CSO Control Policy states that the permittee should characterize "the impacts
26     of the CSOs and other pollution sources on the receiving waters and their designated uses."
27     Under the demonstration approach, "where WQS and designated uses are not met in part because
28     of natural background conditions or pollution sources other than CSOs, a total maximum daily
29     load, including a wasteload allocation and a load allocation, or other means should be used to
30     apportion pollutant loads."
31
       External Review Draft                    8-1                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            Established under Section 303(d) of the CWA, the TMDL process assesses point and
  2     nonpoint pollution sources that together may contribute to a water body's impairment. This
  3     process relies on receiving water models.
  4
  5            An important initial decision—which water quality parameters should be modeled—should
  6     be based on data from receiving water monitoring. CSOs affect several receiving water quality
  7     parameters.  Since the impact on one parameter is frequently much greater than on  others,
  8     relieving this main impact will likely also relieve the others.  For example, if a CSO  causes
  9     exceedances of bacteria standards by several hundred-fold, as well as moderate dissolved oxygen
 10     depressions, solving the bacterial problem will likely solve the dissolved oxygen problem  and so
 11      it may be sufficient to monitor bacteria only. Reducing the scope of modeling in this fashion
. 12     may substantially reduce its cost.
 13
 14      8.2    MODEL SELECTION STRATEGY
 15
 16             A receiving water model should be selected according to the following factors:
 17
 18             •  The type and physical characteristics of the receiving water body.  Rivers, estuaries,
 19               coastal areas, and lakes typically require different models.
20
21             •  The water quality parameters to be modeled.  These may include bacteria, dissolved
22               oxygen,  suspended solids, toxics,  and nutrients.  These parameters are affected by
23               different processes  (e.g., die-off for bacteria, settling for solids, biodegradation for
24               DO, adsorption for metals) with different time scales (e.g., hours for bacterial die-off,
25        .       days for biodegradation) and different kinetics.  The time scale in turn affects the
26               distance  over  which the receiving water is modeled (e.g., a few hundred feet for
27               bacteria to a few miles for dissolved oxygen).
28
29             •  The number and geographical distribution of discharge points and the need to simulate
30               sources other than CSOs.
31
32             The rest of Section 8.2 discusses some important considerations for hydrodynamic and
33      water quality modeling, and how they affect the selection and use of a model.
34
       External Review Draft                     8-2                 .        December 6, 1996

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                          WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            The main purpose of a receiving water model for-CSO analyses is to predict receiving

  2     water quality under different receiving water conditions and loadings.  The flow conditions, or

  3     hydrodynamics, of the receiving water are an important factor in determining the effects of CSOs

  4     on receiving water quality. For simple cases, hydrodynamic conditions can be determined from

  5     the receiving water monitoring program; otherwise a hydrodynamic model may be necessary to
  6     characterize flow conditions.

  7

  8            Hydrodynamic and water quality models are etio&i steady-state or transient. Steady-state

  9     models assume that conditions do not change over time, while transient models can simulate

 10     time-varying conditions.  Flexibility exists in the choice of model types;  generally, either a

 11      steady-state or transient water quality simulation can be done regardless of  whether  flow
 12     conditions are steady-state or transient.

 13

 14      8.2.1  Hydrodynamic Models
 15
 16            A hydrodynamic model provides the flow conditions, characterized by the water depth and

 17      velocity, for which water quality must be predicted. The following factors should be considered
 18      for different water body types:

 19

20            •  Rivers—The flow in rivers is generally unidirectional (except for  localized eddies or
21               other flow features) and the stream velocity and depth are a function of the flow rate.
22               For relatively  large rivers, the flow rate may not increase  significantly due to wet
23               weather discharges, and a constant flow can be used as a first  approximation.   This
24               constant flow  can be a specified low flow or a flow typical of a season or month.
25               When the increase of river flow is important, it can be estimated by adding together
26               all upstream flow  inputs or by doing a transient flow simulation.  The degree of
27               refinement required also depends on the time scale of the water  quality parameters of
28               interest.  For  example, a constant river flow may suffice for  bacterial simulations
29               since die-off is relatively rapid.  For  dissolved oxygen,  the time variations in river
30               flow rate may be important and need  to be considered.
31
32            •  Estuaries—CSO impacts in estuaries  are affected by tidal variations of velocity and
33               depth (including possible reversal of current  direction) and  by possible salinity
34               stratification.  Tidal fluctuations can  be assessed by measuring velocity and depth
35               variations over a tide cycle or by using a one- or two-dimensional model.  Toxics
36               with  relatively  small  mixing zones  can  be analyzed  using  steady  currents
       External Review Draft                     8-3                        December 6, 1996

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                         WORKING DRAFT: DO^NOT CITE OR QUOTE
  1                corresponding to different times during the tidal cycle, but this may require using a
  2                computed circulation pattern 'from a model.
  3
  4            •   Coastal Areas—CSO impacts in coastal areas are also affected by tidal fluctuations.
  5                The discussion on estuaries generally applies to coastal areas, but, because the areas
  6                are not channelized,  two-dimensional  or even  three-dimensional models may be
  7                necessary.
  8
  9            •   Lakes—CSO impacts in lakes are affected by wind (which usually accompanies wet
10                weather) and thermal stratification. Wind-driven currents can be monitored directly
11                or simulated using a hydrodynamic model (to properly simulate wind-driven currents,
12                the model may need to cover the entire lake). Thermal stratification can generally be
13                measured directly.
14
15            Because the same basic hydrodynamic equations apply (momentum and continuity)1, the
16      major models for receiving waters can typically simulate more than one type of receiving water
17      body. Ultimately, three factors dictate whether a model can be used for a particular hydraulic
18      regime.  One factor is whether it provides a one-, two-, or three-dimensional simulation.  A
19      second is the model's ability to handle specific boundary conditions, such as tidal boundaries.
20
21            A third factor  is whether the model assumes  steady-state  conditions or allows for
22      time-varying pollutant loading. In general, steady-state loading models cannot accurately model
23      CSO problems that require analysis of far-field effects.  However, in  some instances  a
24      steady-load model can estimate the maximum potential effect, particularly in systems where the
25      transport of constituents is dominated by the main flow of the water body, rather than  local
26      velocity gradients. For example, by assuming a constant source and following the peak discharge
27      plug  of water downstream, the steady-load model QUAL2EU can determine the maximum
28      downstream effects of conventional pollutants. The result is a compromise that approximates the
29      expected  impact  but  neglects  the  effects  of  longitudinal  dispersion  in  moderating the
30      concentration peak as it moves downstream.  However, QUAL2EU cannot give an accurate
31      estimate of the duration of excursions above WQS.
32
33         'The momentum equation describes the motion of the receiving water, while the continuity equation is a flow
34      balance relationship (i.e., total inflows to the receiving water less total outflows is equal to the change in receiving
35      water volume).

        External Review Draft                    8-4                         December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1      82.2  Water Quality Models
  2
  3            The frequency  and duration of CSOs are important determinants of receiving  water
  4      impacts and need to be considered in determining appropriate time scales for modeling.  CSO
  5      loads are typically delivered in short pulses during storm events. Selection of appropriate time
  6      scales for modeling receiving water impacts resulting from a pulsed CSO loading depends upon
  7      the time and space scales necessary to evaluate the WQS. If analysis requires determining the
  8      concentration of a toxic at the edge of a relatively small mixing zone, a steady-state mixing zone
  9      model may be satisfactory.  When using a steady-state mixing zone model in this way,  the
10      modeler should apply appropriately conservative assumptions about instream flows during CSO
11      events.  For pollutants such as oxygen demand, which can have impacts lasting several days and
12      extending several miles downstream of the discharge point, it may be warranted to incorporate
13      the pulsed nature of the loading. Assuming a constant loading is much simpler (and less costly)
14      to model; however, it is conservative (i.e., leads to impacts larger than expected).  For pollutants
15      such as nutrients where the response time of the receiving water body may be slow, simulating
16      only the average loading rate may suffice.
17
18            Receiving water models vary from simple estimations to complex software packages. The
19      choice of  model should reflect site  conditions.  If the  pulsed  load and receiving  water
                                                     ;
20      characteristics are adequately represented, simple estimations may be appropriate for the analysis
21      of CSO impacts.  To demonstrate compliance with the CWA, the permittee may not need to
22      know precisely where in the receiving water excursions above WQS will occur.  Rather,  the
23      permittee needs to know the maximum pollutant concentrations and the likelihood that excursions
24      above the WQS can occur at any point within the water body. However, since CSOs impacting
25      sensitive areas are given a higher priority under the CSO policy, simulation models for receiving
26      waters with sensitive areas may need to use short time scales (e.g., hourly pollutant loads), and
27      have high  resolution (e.g., several hundred yards or  less)  to specifically  assess impacts to
28      sensitive areas.
29
30
       External Review Draft                     8-5                        December 6, 1996

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                                            i  Do NOT€ITE on QUOTE
  1     8.3   AVAILABLE MODELS
  2
  3           Receiving water mpdels cover a wide variety of physical and chemical situations, and, like
  4     CSS models, vary in complexity.  EPA has produced extensive guidance  on receiving water
  5     modeling as part of the Waste Load Allocation (WLA) guidance series. These models, however,
  6     tend to concentrate on continuous sources and thus may not be the most suitable for CSOs. A
  7     recent summary of EPA-supported models including receiving water models is  provided in
  8     Ambrose et al. (1988).   This guidance does not provide a complete catalogue  of available
  9     receiving water models. Rather, it describes simplified techniques and provides a brief overview
 10     of relevant EPA-supported receiving water models.
 11
 12      83.1  Simplified Analyses
 13
 14            In many cases, detailed receiving water simulation may not be necessary.  Use of dilution
 15      and mixing zone calculations or simulation with simple spreadsheet models will be  sufficient to
 16      assess the magnitude of potential impacts or evaluate the relative merits  of various control
 17      options.
 18
 19            Many of the simpler approaches to receiving water evaluation make assumptions of steady
20      flow and steady or gradually varying loading. These assumptions may be appropriate if an-order-
21      of-magnitude estimate or an upper bound of the impacts are required. The latter is  obtained by
22      using conservative parameters such as peak loading and low current speed.  If WQS attainment
23      is predicted under realistic worst case assumptions, more complex simulations may not be
24      needed.
25
26      83.2  Model Types
27
28            The following sections discuss the simulation of different water quality parameters in
29     rivers, lakes and estuaries.
30
31            RIVERS
32            Bacteria and Toxics. Bacteria and toxic contaminants are primarily a concern in the
33     immediate vicinity of CSO outfalls. They are controlled by lateral mixing, advection, and decay

       External Review Draft                    8-6                        December 6, 1996

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                         WORKINGDRAFT: DO NOT CUE OR QUOTE
  1     processes such as die-off (for bacteria) and settling or vaporization (for toxics).  When stream
  2     flow is small relative to CSO flow, lateral mixing may occur rapidly and a one-dimensional
  3     model may be appropriate.  Initial estimates can be made using a steady-state  approach that
  4     neglects the time-varying nature of the CSO. In this case, concentrations downstream of a CSO
  5     are given by:
                                          '      Q,
 6
 7            where:       Cx     =     max pollutant concentration at distance X from the outfall
 8                         Ce     =     pollutant concentration in effluent
 9                         Cu     =  ,   pollutant concentration upstream from discharge
10                         Qe     =     effluent flow
11                         Qtt     =     stream flow upstream of discharge
12                         Q,     =     stream flow downstream of discharge (Qu + Qe)
13                         X     =     distance from outfall
14                         u      =     stream flow velocity
15                         K     =     decay rate (die-off rate for bacteria, settling velocity divided
16                                      by stream depth for settling, vaporization rate divided by
17                                      stream depth for vaporization)
18
19     For CSOs in large rivers, lateral mixing may occur over large distances and bacterial counts or
20     toxics concentrations on the same shore as the discharge can be calculated using the following
21     expression, as a conservative estimate (U.S. EPA, 1991a):
                                           ^_   C&W
                                                   TlDyX
22
23            where:       £>„    =     lateral dispersion coefficient
24                         W    =     stream width
25
26            This equation is conservative  because it  neglects any discharge-induced mixing.
27     Simulating over the correlated probability  distributions of Ce,  Qe, Q and Q, can provide an
28     estimate of the frequency of WQS exceedances at a specific distance from the outfall.  The
29     method requires the estimation of a lateral dispersion coefficient, which can be measured in dye
       External Review Draft                     8-7                         December 6, 1996

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              WORKING DRAFT: DO~NOT CITE OR QUOTE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
studies or by methods described in Mixing in Inland and Coastal Waters (Fischer et aL, 1979).
Fischer's methods calculate the lateral dispersion coefficient Dy as follows:











Dy = 0.6du*±50%
where: d = water depth at the specified flow
u* = shear velocity

In turn, the following equation estimates shear velocity:

«* = (gas)*
where: g = acceleration due to gravity
s = slope of channel
d - water depth

EPA (1991a) advocates the use of three modeling techniques for assessing toxic
discharges: continuous simulation, Monte Carlo simulation, and lognormal probability modeling.
These methods approximate the complete probability distributions of receiving water
concentrations, in accordance with the recommended frequency-duration format for water quality.
The model DYNTOX (LimnoTech, 1985) is specially designed for lognormal probability analysis
of toxics in rivers. The WLA series by Delos et al. (1984) and U.S. EPA (1991a) address the
transport of toxics and heavy metals in rivers.





Note to reviewers: Would it be helpful to add a description here of continuous 1
and Monte Carlo simulations and logononnal probability modeling, or should that I
be left to the referenced documents? I
_^H^^^^^^HHBHHH|||^^|^^^|H^^^H||^^J

Oxygen Demand/Dissolved Oxygen. The time scales and distances affecting DO
processes are greater than for bacteria and toxics. Lateral mixing therefore results in
approximately uniform conditions over the river cross section and one-dimensional models are
usually appropriate for simulation. The WLA guidance (U.S. EPA, 1994) discusses the effects
External Review Draft
8-8
December 6, 1996

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                        "WORKING DRAFT: Do NOT CITE OR QUOTE
  1     of steady and dynamic DO loads, and provides guidelines for modeling impacts of steady-state
  2     sources.  Simple spreadsheet models such as STREAMDO IV (Zander and Love, 1990) have
  3     recently become available for DO analysis.
                   /
  4                     '
  5           In general,  screening analyses using classical steady-state equations can  examine DO
  6     impacts to rivers as a result of episodic loads.  This approach assumes plug flow, which in turn
  7     allows an assumption of constant loading averaged over the volume of the plug (Freedman and
  8     Marr, 1990). This approach does not consider longitudinal diffusion from the plug, making it
  9     a conservative approach. The plug flow analysis should correlate with the duration of the CSO.
10     For example, a plug flow simulation of a 2-hour CSO event would result  in a downstream DO
11      sag that would also last for 2 hours. Given the plug flow assumption, the classic Streeter-Phelps
12     equation can estimate the DO concentration downstream:
13
14            where:       D     =     dissolved oxygen deficit downstream (MAO
15                         Dg    =     initial dissolved oxygen deficit (MAO
16                         Ka    =     atmospheric re-aeration rate (1/T)
17                         t      =     time of passage from source to downstream location (T)
18                         W    =     total pollutant loading rate (M/T)
19                         Q     =     total river flow (V/T)
20                         Kd    =     BOD deoxygenation rate (1/T)
21                         Kr    =     BOD loss rate (1/T)
22
23            This method can address the joint effects of multiple steady sources through the technique
24     of superposition (Exhibit 8-1). However, it cannot address multiple sources that change over
25     time, nor can it address the effects of river morphology. When such issues are important, more
26     sophisticated modeling techniques are necessary.
27
28            Nutrients/Eutrophication.  Nutrient discharges  affect river eutrophication over time
29     scales  of several days to  several weeks.  Nutrient/eutrophication analysis considers the
30     relationship between nutrients and algal growth. Analysis of nutrient impacts in rivers is complex
       External Review Draft                    8-9                        December 6, 1996

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oo
(—«
o
        6 -•
     0)
Other Sources of BOD



Point Sources of BOD
                       CSOBOD
                                                                                           I
ON
        1



        0
                                     10
                            15
                                         River Mile
20
H

 25

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                         WORKING DRAFT; Do NOT CITE OR QUOTE
   1      because nutrients and planktonic algae2, which are free-floating one-celled algae, usually move
   2      through the system rapidly.
   3
   4            The current WLA guidance (U.S. EPA, 1995g) considers only planktonic algae (rather
   5      than all aquatic plants) and discusses nutrient/eutrophication in rivers primarily as a component
   6      in computing DO. The guidance applies to narrative criteria that limit nuisance plant growth in
   7      large, slowly flowing rivers.
   8
  9            LAKES
 10            Bacteria and Toxics. Mixing zone analysis can often be used to assess attainment of
 11     WQS for bacteria and toxics in lakes. For a small lake in which the effluent mixes rapidly, the
 12     concentration response is given by (Freedman andMarr, 1990):
 13
 14           where:       M    = mass loading (M)
 15                        Q     =flow(L3/T)
 16                        K     = decay rate (1/T)
 17                        V     = lake volume (L3)
 18                        t      = time (T)
 19                        C     = concentration (MIL3)
 20
 21            For an incompletely-mixed lake, however, a complex  simulation  model is generally
 22    necessary to estimate transient impacts from slug loads. The EPA WLA guidance series contains
 23     a  manual (Hydroqual, Inc., 1986) on chemical models for lakes and impoundments.  This
                                                                    m                 •
 24     guidance, which is also applicable to bacteria, describes simple and complex models and presents
 25     criteria for selecting models and model parameters.
 26
 27           Oxygen Demand/Dissolved Oxygen.   Simple analytical approximations can  model
 28     oxygen demand and DO in cases where DO  mixing occurs quickly relative to depletion by
29        2Aquatic plants can be divided into those that move freely with the water (planktonic aquatic plants)' and those
30     that are attached or rooted in place.

 External Review Draft                          8-11                        December 6, 1996

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                        WORKING"DRAFT:  DO~NOT CUE OR QUOTE
  1      COD/BOD. Where lateral mixing occurs rapidly but vertical temperature stratification exists, DO
                          •
  2      concentration can be addressed for a two-layer stratified lake under the following simplifying
  3      assumptions (from Thomann and Mueller, 1987):
  4
  5            •  The horizontal area is constant with depth
  6            •  Inflow occurs only to the surface layer
  7            •  Photosynthesis occurs only in the surface layer
  8            •  Respiration occurs at the same rate throughout the lake
  9            •  The'lake is at steady-state.
10
11            With these severe restrictions, the solution is given by:
                                                 V*          KL+«
12
13     and
14
15     where the subscripts 1 and 2 refer to the epilimnion (top layer) and hypolimnion (lower layer)
16     respectively, and variables without subscripts refer to the whole lake, and where:
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
q
KL
c
C0> Cs
P
H
H,
R
SB
Kj
L

=
=
=
—
=
=
=
=
=
=
=

Outflow rate (L/T)
DO transfer rate at lake surface (L/T)
DO concentration (M/L3)
Initial and saturation dissolved oxygen concentrations (M/L3)
Gross photosynthetic production of DO (m/L3-T)
Depth (L)
H/2 when H, = H2 and H, when H2 » H, (L)
Phytoplankton DO respiration (M/L3-T)
Sediment oxygen demand (M/L2-T)
Deoxygenation coefficient (1/T)
Steady-state CBOD concentration in water column (M/L3),
W/fQ+KjV), where W is the mass loading rate, Q is the rate










~
of
flow through the lake, V is the volume, and K, is the net loss rate.
E
=
Dispersion coefficient (L/T)

       External Review Draft                   8-12                        December 6, 1996

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                         "WORKING "DRAFT:  DO NOT CITE OR QUOTE
  1             Because this analysis assumes steady-state loading and because measuring some of the

  2      parameters proves difficult, the method may only have limited application to CSOs.

  3

  4             In many cases, complex simulation models are necessary to analyze DO in lakes. These

  5      are either specialized lake models or flexible models, such as EUTROWASP, that are designed

  6      to address issues specific to lakes.  Some modelers have been successful in modeling thermally

  7      stratified lakes with one or two dimensional river models (e.g., QUAL2EU) that assume the river

  8      bottom is the thermocline.

  9
                                                                                          1
10             Nutrient/Eutrophication Impacts. For lakes, simple analytic equations often can analyze

11      end-of-pipe impacts and whole-lake impacts. However, evaluating mixing phenomena in a lake

12      frequently requires a complex computer model (Freedman and Man, 1990).  Simple analytical

13      methods can  be applied to lake nutrient/eutrophication impacts in situations where the CSOs mix

14      across the lake area within the time scale required to obtain a significant response in the algal

IS      population. In most lakes, phosphorus is considered to be the limiting nutrient for nuisance algal

16      impacts and  eutrophication:   Mancini et al. (1983) and Thomann and Mueller (1987) have

17      developed a  procedure for calculating the allowable surface loading rate.  The following steps

18      are drawn from this procedure:

19

20  .          Step 1.    Estimate the lake volume, surface area, and mean depth.
21
22            Step 2.    Estimate the mean annual outflow rate. Where urban areas draining to the
23                      lake constitute a significant fraction of the total drainage area, flow estimates
24                      from urban runoff and CSOs should be included in the hydrologic balance
25                      around the lake.  For lakes with large surface areas, the estimate should
26                      include surface precipitation and evaporation.
27
28            Step 3.    Determine the average annual total phosphorus loading due  to  all sources,
29                      including all tributary inflows, municipal and industrial sources, distributed
30                      urban and rural runoff, and atmospheric inputs. Technical Guidance Manual
31                      for Performing  Waste  Load Allocation (Mancini et al., 1983)  discusses
32                      techniques for estimating these loadings.
33
34            Step 4.    For total phosphorus, assign a net sedimentation loss rate that is consistent
35                      with a local data base.
36


        External Review Draft                    8-13                        December 6, 1996

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                         ~WORKINGT)RAFT: "DO NOT CITE OR QUOTE
  1            Step 5.    Select  trophic state objectives of either total phosphorus  or  chlorophyll-*
  2                      consistent with local experience.   Calculate the  value of the allowable
  3                      phosphorus areal loading, W, from:
  4                  where:        W    is the allowable areal surface loading rate (M/L2-T)
  5                                a     is  the  trophic  state  objective  concentration . of total
  6                                      phosphorus or chlorophyll-a (M/L3),
  7                                Q     is outflow (L3/T),
  8                                V     is lake volume (L3),
  9                                z     is mean depth (L), and
 10                                v,     is the net sedimentation velocity (L/T).
 12            Step 6.     Compare the total  areal loading determined in Step 3 to the value of W
 13                      obtained in Step 5.
 14
 15            Additional approaches are discussed in Rechkow and Chapra (1983b).
 16
 17            ESTUARIES
 18          -  Unlike rivers, estuaries are tidal. When averaged on the basis of tidal cycles, pollutant
 19     transport in narrow, vertically mixed estuaries with dominant longitudinal flow is similar to that
20     in rivers.  However, due to tidal  reversals of flow, a narrow estuary may have a much larger
21      effective dispersion coefficient since shifting tides may cause greater lateral dispersion. In such
22     a system, the modeler can apply approximate or screening models used for rivers, provided that
23      an appropriate tidal  dispersion coefficient has been calculated.   In wider estuaries, tides and
24     winds often result in complex flow patterns and  river-based models  would be inappropriate.
25      WLA' guidance  for  estuaries is provided in several EPA manuals (Ambrose et al., 199.0a;
26      Ambrose et al., 1990b; Jirka, 1992;  Freedman et al., 1992).
27
28            In addition to their tidal component, many estuaries are characterized by salinity-based
29      stratification. Stratified estuaries have the horizontal mixing due to advection and dispersion that
30      is associated with rivers and the vertical stratification characteristic of lakes.
31
       External Review Draft                    8-14                         December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1            In  complex estuaries, accurate analysis of far-field CSO impacts—such as nutrients/
  2     eutrophication, DO, and  impacts  on particular sensitive areas—typically requires  complex
  3     simulation models. Simpler analyses are sometimes possible by treating the averaged effects of
  4     tidal and wind-induced circulation and mixing as temporally constant parameters.  This approach
  5     may require extensive site-specific calibration.
  6
  7            Near-field mixing zone analysis in estuaries also presents special problems, because of
  8     the role of buoyancy differences in mixing. Jirka  (1992) discusses mixing-zone modeling for
  9     estuaries.
 10
 11      8.33   EPA-Supported Models
 12
 13            EPA's Center for Exposure Assessment Modeling (CEAM) maintains a distribution center
 14     for water quality models and related data bases (Exhibit 8-2). CEAM-supported models relevant
 15      to modeling impacts to receiving water include QUAL2EU, WASP, HSPF, EXAMSH, CORMIX,
 16      and MINTEQ.
 17
 18            QUAL2EU is  a one-dimensional model for rivers.  It assumes steady-state flow and
 19      loading but allows simulation of diurnal variations  in temperature or algal photosynthesis and
 20      respiration.  QUAL2EU simulates temperature, bacteria, BOD, DO, ammonia, nitrate, nitrite,
 21      organic nitrogen, phosphate, organic phosphorus, algae, and additional conservative substances.3
 22      Because it assumes steady flow and pollutant loading, its applicability to CSOs is limited.
 23      However, the model can use steady loading rates to generate worst-case projections for CSOs to
 24      rivers.   The model has pre and post-processors for  performing uncertainty and sensitivity
 25      analyses.
 26
 27            Additionally, in certain cases, experienced users may be able to use the model to simulate
 28      non-steady pollutant loadings  under steady flow  conditions by establishing certain initial
29      conditions or by dynamically varying climatic conditions.  If used in this way, the QUAL2EU
30        3A conservative substance is one that does not undergo any chemical or biological transformation or degradation
31     in a given ecosystem. (EPA, 1995g)

       External Review Draft                    8-15                        December 6, 1996

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                               Exhibit 8-2. EPA CEAM Supported Receiving Water Models
Applicability to Hydraulic Regimes and Pollutant Type

Model
QUAL2EU
WASPS
HSPF
EXAMSH
DYNTOX
CORMIX
MINTEQ
Rivers & Streams
Nutrients Oxygen Other
/ / /
/ / S
s s s
s
s
Lakes
Nutrients

/



& Impoundments
Oxygen Other

/ S

S

Estuaries
Nutrients

/



Oxygen

/



Other

/

S

Near-Held mixing model for all water body types
Equilibrium metal speciation model
Near Field
Mixing






^

Key Characteristics and References
Model
QUAL2EU
WASPS
HSPF
EXAMSH
CORMIX
MINTEQ
Pollutant Loading Type
Steady
Dynamic
Dynamic (Integrated)
Dynamic
Steady (near field)
Steady
Transport Dimensionality
1-D
Quasi-2/3-D (link-node)
1-D
User input (quasi 3-D)
Quasi-3-D (zonal)
None
Current
Version
3.22
S.10
10.11
2.96
2.10
3.11
Key References
Brown & Barnwell, 1987
Ambrose, et al., 1988
Johanson, et al., 1984
Burns, et al , 1982
Doneker & Jirka, 1990
Brown & Allison, 1987
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                         WORKING DRAFT:  DO^NOT'CITE OR QUOTE
  1     model should be considered a screening tool since the model was not designed to simulate
  2     dynamic quality conditions.
  3
  4           WASPS is  a quasi-two-dimensional  or  quasi-three-dimensional water quality  model
  5     applicable to rivers, estuaries, and many lakes. It has a link-node formulation, which simulates
  6     storage at the nodes and transport along the links.  The links represent a one-dimensional solution
  7     of the advection dispersion equation, although quasi-two-dimensional or quasi-three-dimensional
  8     simulations are possible if nodes  are connected  to multiple links.  The model also simulates
  9     limited sediment processes. It includes the time-varying processes of advection, dispersion, point
 10     and nonpoint mass loading, and boundary exchanges.   WASPS can be used in two modes:
 11      EUTRO5 for nutrient and eutrophication analysis and TOXI5 for analysis of toxic pollutants and
 12     metals. WASP is essentially a pollutant fate and transport model; transport can be driven by the
 13      WASP companion hydrodynamic model, DYNHYD, which simulates transient hydrodynamics
 14      (including tidal estuaries) or  by using it with another hydrodynamic model.
 15
 16            HSPF is a comprehensive  hydrologic  and water quality simulation  package  which can
 17      simulate both  CSSs and receiving waters for conventional and toxic  organic pollutants.  It
 18      simulates  channels (such as  rivers) on a one-dimensional basis and completely-mixed waters
 19      (such as reservoirs) as zero-dimensional.  HSPF simulates three sediment types: sand, silt and
20      clay. It can also simulate an organic pollutant and transformation products  of that pollutant.
21
22            EXAMSII can rapidly evaluate the fate, transport,  and exposure concentrations of steady
23      discharges of synthetic organic chemicals to aquatic systems.  A recent upgrade of the model
24      considers  seasonal  variations  in  transport and  time-varying chemical loadings,  making it
25      quasi-dynamic.  The user must specify transport fields to the model.
26
27            CORMEX is an expert system for mixing zone analysis. It can simulate submerged or
28      surface, buoyant or non-buoyant discharges into stratified or unstratified receiving waters, with
29      emphasis on the geometry and dilution characteristics of the initial mixing zone. The model uses
30      a zone approach, in which a flow classification  scheme determines which near-field mixing
31      processes to model.

        External Review Draft                    8-17                        December 6, 1996

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                         WORKING DRAFT: 'Do NOT €TTE OR QUOTE
  1            MINTEQ  detennines geochemical equilibrium for  priority pollutant metals.  Not  a
  2     transport model, MINTEQ provides a means for modeling metal partitioning in discharges. The
  3     model usually must be ran in connection with another fate and transport model, such as those
  4     described above. It provides only steady-state predictions.
  5
  6     8.3.4   Other Models
  7
  8           EPA CEAM or other government agencies also support the following additional models:4
  9
 10           MICHRTV (Richardson et al.,  1983) is  a one-dimensional  steady-state model  for
 11      simulating the transport of contaminants in the water column and bed sediments in streams and
 12      non-tidal rivers.
 13
 14            SERATRA (Onishi and Wise, 1982) is a two-dimensional vertical plane model for the
 IS      transport of contaminants and sediments in rivers.
 16
 17            CE-QUAL-W2 is a reservoir and narrow estuary hydrodynamics and water quality model
 18      developed by the Waterways Experiment Station of the U.S. Army  Corps  of Engineers in
 19      Vicksburg, Mississippi. The model provides dynamic two-dimensional (longitudinal and vertical)
20      simulations.  It accounts for density effects on flow  as a function of the water temperature,
21      salinity and suspended solids concentration.  CE-QUAL-W2 can simulate up to 21 water quality
22      parameters hi addition to temperature, including one passive tracer (e.g., dye), total dissolved
23      solids (TDS), coliform  bacteria, inorganic suspended solids, algal/nutriemVDO dynamics (11
24      parameters), alkalinity, pH and carbonate species (4 parameters).
25
26           Another model relevant to assessing impacts to receiving water is DYNTOX.  DYNTOX
27      is a one-dimensional, probabilistic toxicity dilution model for transport in rivers.  It provides
28      continuous Monte Carlo or lognormal probability simulations that can  be used to analyze the
29        'McKeon and Segna (1987), Ambrose et al. (1988) and Hinson and Basta (1982) have reviewed some of these
30     models.

       External Review Draft                    8-18                       December 6, 1996

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                         WORKING DRAFT: DO~NOT CITE OR QUOTE
  1     frequency and duration of ambient toxic concentrations resulting from a waste discharge.  The
  2     model considers dilution and net first-order loss, but not sorption and benthic exchange.
  3
  4     8.4    USING A RECEIVING WATER MODEL
  5                 •  •
  6            As was the case for CSS models (see Section 7.4), receiving water modeling involves
  7     development of the model, calibration and validation, performing the simulation, and interpreting
  8     the results.
  9
 10     8.4.1  Developing the Model
 11
 12           Specific data needs for receiving water models depend upon the hydraulic regime and
 13      model employed.   For specific input data requirements,  the permittee  should  refer to the
 14      documentation for individual models, the relevant sections of the WLA guidance, or to texts such
 15      as Principles of Surface Water Quality Modeling and Control (Thomann  and Mueller, 1987).
 16      Tables B-2 through B-5 in Appendix B contain general tables of data inputs to receiving water
 17      models.
 18      '
 19      8.4.2  Calibrating and Validating the Model
 20
 21            Like CSS models, receiving water models need to be calibrated and validated. The model
 22      should be run to simulate events for which receiving water hydraulic and quality monitoring were
 23      actually conducted, and the model results should be compared to the measurements. Generally,
 24      receiving water models are calibrated and validated first for receiving  water hydraulics and then
 25      for water quality.  Receiving water models typically cannot be calibrated to the same degree of
 26      accuracy as CSS models because:
 27
 28            •  Pollutant loading inputs typically are estimates rather than precisely known values.
 29
 30            •  Since three-dimensional receiving water models are still not commonly used for CSO
 31               projects, receiving water models involve spatial averaging (over the depth, width or
32               crossrsection).  Thus, model results are not directly comparable  with measurements,
33               unless the measurements also have sufficient spacial resolution to allow comparable
34               averaging.
35

        External Review Draft                     8-19                        December 6, 1996

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                         WORKING DRAFT:  Do NOTICITE OR QUOTE
  1            •   Loadings from non-CSO sources, such as storm water, upstream boundaries, point
  2               sources, and atmospheric deposition often are not accurately known.
  4            •   Receiving water hydrodynamics are affected by numerous factors which are difficult
  5               to account for.  Those  include fluctuating winds, large scale  eddies, and density
  6               effects.
  7
  8            Although these factors make model calibration challenging, they also underscore the need
  9     for calibration to ensure that the model reasonably reflects receiving water data.
 10
 11      8.43   Performing the Modeling Analysis
 12
 13             Receiving water modeling can involve single events or long-term simulations.  Single
 14      event simulations are usually favored when  using complex models, since these model  require
 15      larger amounts of input data and  take significantly longer to run.  However, advances in
 16      computer technology keep pushing  the limits of what can practically be achieved. Long-term
 17      simulations can predict water quality impacts on an annual basis.
 18
 19            Although a general goal is to predict the number  of water quality criteria exceedances,
20      models can evaluate exceedances using different measures, such as hours of exceedance at
21      beaches or other critical points, acre-hours of exceedance, and mile-hours of exceedance along
22      a shore. These provide a more refined measure of the water quality impacts of CSOs and of the
23      expected effectiveness of different control measures.
24
25            Commonly, CSO loadings are simulated separately in order to gage CSO impacts relative
26      to other sources. This procedure is appropriate because the  equations which govern receiving
27      water quality are linear and, consequently, effects are additive.
28
29      8.4.4  Modeling Results
30
31            By means of averages over  space and time,  simulation models predict CSO volumes,
32      pollutant concentrations, and  other variables  of interest. The extent  of this averaging depends
33      on the model structure, how  the model is applied, and the resolution of the input data.  The
34      model's space and time resolution should match that of the necessary analysis.  For instance, the

        External Review Draft                     8-20                        December 6, 1996

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                       "^WORKING DRAFT: IDo Nor
  1     applicable WQS may be expressed as a 1-hour average concentration not to exceed a given
  2     concentration more than once every 3 years on average.  Spatial averaging may be represented
  3     by a concentration averaged over a receiving water mixing zone, or implicitly by the specification
  4     of monitoring locations to establish compliance with instream criteria. In any case, the permittee
  5     should note whether the model predictions use the same averaging scales required in the permit
  6     or relevant WQS.
  7
  8           When used for continuous rather than event simulation, as suggested by the CSO Control
  9     Policy, simulation model results can predict the frequency of exceedances of water quality
 10     criteria.   Probabilistic models, such as the Monte  Carlo  simulation, also can  make  such
 11      predictions.  In probabilistic models the simulation is made over the probability distribution of
 12     precipitation and other forcing functions (e.g., temperature, point sources, flow).  In either case,
 13      modelers can analyze the output for water quality criteria exceedances and the frequency .of such
 14      exceedances.
 15
 16            The key result of receiving water modeling is the prediction of future conditions, due to
 17      implementation of CSO control alternatives. In most cases, CSO control decisions will have to
 18      be supported by model predictions of the pollutant load reductions necessary to achieve water
 19      quality standards. In the receiving waters, critical or design water quality conditions might be
20      periods of low flows and high temperature that are impacted by  wet weather events.  These
21      periods are  established based on a  review  of  available  data.  Flow,  temperature, and other
22      variables for these periods then form the basis of future condition analysis.
23
24            It  is useful  to assess the  sensitivity of model results  to variations and  changes in
25      parameters, rate constants, and coefficients.  Such a sensitivity analysis can determine the  key
26      parameters, rate constants, and coefficients which merit particular  attention in evaluating CSO
27      control alternatives.  The modeling approach should accurately represent features that are fully
28      understood, and sensitivity analysis should be used to evaluate the significance of factors that are
29      not as clearly defined. (See Section  7.4.4 for additional discussion of sensitivity analysis.)
       External Review Draft                     8-21                         December 6, 1996

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  i                                         CHAPTER 9
  2
  3        ASSESSING RECEIVING WATER IMPACTS AND ATTAINMENT OF WATER
  4                                   QUALITY STANDARDS
  5
  6            This chapter focuses on the link between CSOs and the attainment of WQS in a water
  7     body. As discussed in previous chapters, permittees can consider a variety of methods to analyze
  8     the performance of the CSS and the response of a water body to pollutant loads. Permittees can
  9     use these methods to estimate the water quality impacts of a proposed CSO control program and
10     evaluate whether it is adequate to meet CWA requirements.
11
12            Under the CSO Control Policy, permittees  need  to develop a long-term control plan
13     (LTCP) that  provides for WQS attainment using  either the presumption approach or the
14     demonstration approach.  This  chapter focuses primarily on issues related to the demonstration
15     approach since this approach requires the permittee to adequately demonstrate that the selected
16     CSO controls will provide  for the attainment of  WQS.  As  mentioned  in  Chapter 8, the
17     presumption approach does not explicitly call for analysis of receiving water impacts and thus
18     generally involves less complex modeling.
19
20            Modeling time-varying wet weather sources such as CSOs is more complex than modeling
21     more traditional point sources. Typically, point-source modeling assumes constant pollutant
22     loading to a receiving water body under critical, steady-state conditions—such  as minimum
23     seven-consecutive-day average stream flow occurring once every ten years (i.e., 7Q10).  Wet
24     weather loads occur in pulses, however, and often have their peak impacts under conditions other
25     than low-flow situations.  A receiving water model must therefore accommodate the short-term
26     variability of pollutant concentrations and flow volume in the discharge as well  as the dynamic
27     conditions in the receiving water body.
28
                                                                                    i
29            CSO loads can be incorporated into receiving water models using either a steady-state or
30     a dynamic approach. A steady-state model can be used to obtain an approximate solution using,
31     for example,  average loads  for  a design storm.  A dynamic approach, on the other hand,

       External Review Draft             .       9-1                        December 6, 1996

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                        WORKING DRAFT:  Do *NOT CITE OR QUOTE
  1      incorporates time-varying loads and simulates the time-varying response of the water body. The
  2      steady-state approximation uses conservative assumptions and sacrifices accuracy but typically
  3      requires less cost and effort  A dynamic model requires greater resources but may result in a
  4      more cost-effective CSO control plan, since it avoids conservative assumptions.
  5
  6            Generally, the modeler should use the simplest approach that is appropriate for local
  7      conditions. For example, a steady-state model may be appropriate in a receiving water that is
  8      relatively insensitive to short-term variations in load rate.  (For instance, the response time of
  9      lakes and coastal embayments to some pollutant loadings may be measured in weeks to  years,
10      and the response time of large rivers to oxygen demand may be measured in days (Donigian and
11      Huber, 1991).) Steady-state models are also useful for estimating the dilution of pollutants, such
12      as acute toxins or bacteria,  close to the point of release.
                                /
13
14      9.1    IDENTIFYING RELEVANT WATER QUALITY STANDARDS
15
16            If a permittee uses the demonstration approach, the permittee should prove that its selected
17      CSO controls will ensure that WQS are met.  The CSO Control Policy states that:
18
19            The permittee  should demonstrate...
20
21               i. the planned control program is adequate to meet WQS and protect designated uses,
22               unless WQS or uses cannot be met as a result of natural background conditions or
23               pollution sources other than CSOs;
24
25               H.   the CSO discharges remaining after implementation of the planned control
26               program will not preclude the attainment of WQS or the receiving waters' designated
27               uses, or contribute to their impairment.  Where WQS and designated uses are not met
28               in part because  of natural background conditions or pollution sources other than
29               CSOs... (DLCAb)
30
31            The first step  in analyzing CSO  impacts on receiving water consists of defining  the
32     pollutants or stressors of concern and any corresponding WQS applicable to the receiving water.
33      CSOs are distinguished from storm water loadings by the increased levels of such pollutants as
       External Review Draft                    9-2                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1     bacteria,  oxygen-demanding  wastes, and certain nutrients.   In some  cases, toxic pollutants
  2     entering the CSS from industrial sources may be pollutants of concern in CSOs.
  3
  4           State WQS include designated uses and numerical and narrative criteria.  Since CSO
  5     controls must ultimately provide for attainment of WQS,. the analysis of CSO control alternatives
  6     should be tailored to the applicable WQS.  For example, if the WQS specifies daily average
  7     concentrations, the analysis should address daily averages.  Many water bodies have narrative
  8     criteria such  as a requirement to limit nutrient loads to an amount that does not produce a
  9     "nuisance" growth of algae, or the prevention of solids and floatables build-up. In such cases,
 10     the permittee could consider developing a site-specific, interim numeric performance standard that
 11      would result in meeting the narrative criterion.
 12
 13            EPA has developed water quality criteria to assist States in developing their numerical
 14      standards and to assist in interpreting narrative standards (EPA, 199la).  EPA recommends that
 15      water quality criteria for the protection of aquatic  life have a magnitude-duration-frequency
 16      format, which requires  that the concentration of a given constituent not exceed a critical value
 17      more than once in a given return period:
 18
 19            •   Magnitude—The concentration of a pollutant, or pollutant parameter such as toxicity,
20               that is allowable.
21
22            •   Duration—The averaging period, which  is the period  of time over which  the in-
23               stream concentration is averaged for comparison with criteria concentrations.  This
24               specification limits the duration of concentrations above the criteria.
25
26            •   Frequency—How often criteria can be exceeded.
27
28            A  magnitude-duration-frequency criteria statement directly addresses protection of the
29      water body by expressing the acceptable likelihood of excursions above the WQS. Although this
30      approach appears useful, it requires  estimation of long-term average rates of excursion above
31      WQS.
32
33            Many  States rely instead on the concept of  design flows, such as 7Q10.  Evaluating
34      compliance at a design low flow of specified recurrence is a simple way to approximate the

        External Review Draft                      9-3                         December 6, 1996

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                         WORKING DRAFT;  Do NOT CITE OR QUOTE
  1     average duration and frequency of excursions above the WQS. A single design flow, however,

  2     is not necessarily the best choice for wet-weather flows, which are unlikely  to  occur

  3     simultaneously with critical low-flow conditions.  Consequently, a design flow-based control
  4     strategy may be overly conservative.
  5

  6           The statistical form of the relevant WQS is important in determining an appropriate model

  7     framework. Does the permittee need to calculate a long-term average, a worst case maximum,

  8     or an actual time sequence of the number of water quality excursions? An approach that gives

  9     a reasonable estimate of the average may not prove useful for estimating an upper bound. In

 10     some cases, such as State standards for indicator bacteria, water quality criteria will be expressed

 11      as both a short-term maximum (or upper percentile) and a long-term average component.
 12

 13      92    OPTIONS FOR DEMONSTRATING COMPLIANCE
 14
 15            Receiving water impacts  can be analyzed at varying levels of complexity, but all

 16      approaches attempt to answer the same question: Using a prediction of the frequency and volume

 17      of CSO events and the pollutant loads delivered by these events, can WQS in the receiving water
 18      body be attained with a reasonable level of assurance?
 19

20            Any of the following types of analyses, arranged in order of  increasing complexity, can
21      be used to answer this question:
22

23            •   Design Flow Analysis—This approach  analyzes  the impacts of CSOs under the
24               assumption that.they occur at a  design condition (e.g., 7Q10 low flow prior to
25               addition of the flow from the CSS). The CSO is added as a steady-state load: If
26               WQS can be attained under such a design condition, with the CSO treated as a steady
27               source, WQS are likely to be attained  for the actual wet weather conditions.  This
28               approach is conservative in two respects: (1) it does not  account for the short-term
29               pulsed nature of CSOs, and (2) it does not account for increased receiving water flow
30               during  wet weather.
31
32            •   Design Flow Frequency  Analysis—Where the WQS  is  expressed in  terms of
33               frequency and duration, the frequency of occurrence of CSOs can be included in the
34               analysis. The design flow approach can then be refined by determining critical design
35               conditions that can reasonably be expected to take place concurrently with CSOs.  For


       External Review Draft                     9-4                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  1                instance, if CSO events occur primarily in one season, the analysis can include critical
  2                flows and other conditions appropriate to that season, rather than the 7Q10.
  3
  4            •   Statistical Analysis—Whereas the previous two approaches rely  on conservative
  5                design conditions, a statistical analysis can be used to consider the range of flows that
  6                may occur together with CSO events.  This  analysis  more accurately reflects the
  7                frequency of excursions of WQS.
  8
  9            •   Watershed  Simulation—A  statistical analysis does  not consider  the dynamic
 10                relationship  between CSOs and receiving water flows.  For example, both the CSO
 11                and receiving water flows increase during wet weather,  providing additional dilution
 12                capacity. Demonstrating the availability of this additional capacity, however, requires
 13                a model that includes the responses of both the sewershed and its receiving water to
 14                the rainfall events.  Dynamic watershed simulations may  be carried out for single
 IS                storm events or continuously for multiple storm events.
 16
 17            The permittee should consider the tradeoffs between simpler and more complex types of
 18     receiving water analysis. A more complex approach, although more costly, can generally provide
 19     more precise analysis using less conservative assumptions. This may result in a more tailored,
20     cost-effective CSO control strategy.
21
22            Additional discussion on data assessment for determining support of WQS can be found
23     in Guidelines for the Preparation of-the 1996 State Water Quality Assessments (305(b) Reports)
24     (EPA, 1995f).
25
26     93    EXAMPLES OF RECEIVING WATER ANALYSIS
27
28            This section presents three examples to  illustrate key points for CSO receiving water
29     impact analysis.  The examples focus on (1) establishing the link between model results and
30     demonstrating the attainment of WQS, and (2) the uses of receiving water models at different
31     levels of complexity, from design flow analysis to dynamic continuous simulation.
32
33            The first example shows how design flow analysis or more sophisticated methods can be
34     used to analyze bacteria loads  to a river from a single CSO event.  The second example, which
35     is more complex, involves bacterial loads to an estuary.  The third example illustrates how BOD
36     loads from a CSS contribute to dissolved oxygen depletion.

       External  Review Draft                     9-5                        December 6,  1996

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                         WORKING DRAFT;  "Do NOT CUE OR QUOTE
  1     93.1   Example 1:  Bacterial Loads to a River
  2
  3            This  example involves a  CSS in a small northeastern city that overflows  relatively
  4     frequently and contributes to WQS excursions.  CSOs are the only pollutant source, and only a
  5     single  water quality criterion—for fecal coliform-^applies.   The use classification for this
  6     receiving water body is primary and secondary contact recreation. The city has planned several
  7     engineering improvements to its CSS and wishes to assess the water quality impacts of those
  8     improvements.
  9
 10            Exhibit 9-1 is a map of key features in this example.
 11
 12             In this example, dilution calculations may suffice to predict whether the water quality
 13      criterion is likely to be attained during a given CSO event. This is because:
 14
 15     .        (1)    Mixing zones are allowed in this State, so the water quality criterion must be met
 16                   at the edge of the mixing zone.  If the criterion is met at that point, it will also be
 17                   met at points farther away.
 18
 19             (2)    Die-off will reduce the numbers of bacteria as distance from the discharge/mixing
20                   zone increases.
21
22            (3)    Since the river flows constantly in one direction, bacterial concentrations do not
23                   accumulate or combine loads from several days of release.
24
25            To illustrate the various levels of receiving water analysis, this example assumes that the
26     magnitude and timing of CSOs, based on controls instituted to date, can be predicted  precisely
27     and that the long-term average characteristics of the CSS will remain constant. The predictions
28     for the next 31  years include the following (Exhibit 9-2):
29
30            (1)   The system should experience a total of 238 overflow events, an average of 7.7
31                  per year.
32
33            (2)   The largest discharge is approximately  1.1 million cubic feet, but most of the
34                  CSOs are less than 200,000 cubic feet
35
36            (3)   The maximum number of CSOs in any one-month is 18.

       External Review Draft                     9-6                         December 6, 1996

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                                     Exhibit 9-1. Map for Example 1
I
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                                        River Flow
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^ 800,000
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CSO Events for Example


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                         WORKING DRAFT:  Do NOT CITE OR QUOTE
  i
  2            (4)    During that month, the maximum receiving water concentration resulting from
  3                   CSOs exceeds 6,000 MPN/100 ml. Even in this "worst-case" month, however, the
  4                   geometric mean is 400 MPN/100 ml, based on 30 daily samples and assuming a
  5                   background concentration of 100.
  6
  7            At least one CSO event occurs in each calendar month, although 69 percent of the events
  8     occur in March' and April when snowmelt increases flow in the CSS.  Because river flow is lower
  9     in summer and fall, the rarer summer and fall CSOs may cause greater impact in the receiving
10     water. For simplicity, assume that background fecal coliform levels are close to zero, and that
11     CSOs are the only significant source of fecal coliforms in the river.
12
13            Water Quality Standards
14            Water quality criteria for fecal coliforms differ from State to State, but typically specify
IS     a 30-day geometric mean or median and a certain small percentage of tests performed within a
16     30-day period that are not to exceed a particular upper value.  In this case, the applicable water
17     quality criterion for fecal  coliforms specifies that:
18
19            (1)     The geometric mean for any 30-day period not exceed 400 MPN ("most probable
20                   number") per 100 ml, and
21
22            (2)     Not more than 10 percent of samples taken during any 30-day period exceed 1,000
23                   MPN per 100 ml.1
24
25     The water quality criterion does  not specify an instantaneous maximum count for this use
26     classification.
27
28            It is comparatively simple to assess how the first component—the geometric mean of 400
29     MPN/100 ml—applies.2  In this case, CSOs occur only occasionally.  In the worst-case month,
30     which had 18 CSOs, the  geometric mean is still only 400 MPN/100 ml based on 30  daily
31         'Most Probable Number (MPN) of organisms present is an estimate of the average density of fecal coliforms
32     in a sample, based on certain probability formulas.
33        ^e geometric mean, which is defined as the antilog of the average of the logs of the data, typically
34     approximates the median or midpoint of the data.

       External Review Draft                     9-9                        December 6, 1996

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                         WORKING DRAFT;  Do TCOT CITE on QUOTE
  1     samples.  It is therefore extremely unlikely that the geometric mean concentration standard of
  2     400 MPN/100 ml will be violated in any other month.
  3
  4           In general,  the second  component of the water quality criterion— a  percentile  (or
  5     maximum) standard— will prove more restrictive for CSOs.  A CSS that overflows less than
  6     1 0 percent of the time (fewer than 3 days per month) could be expected to meet a not-more-than-
  7     10-percent requirement, on average.  This CSS could meet such a requirement if loads from other
  8     sources were well below 1000 MPN/100 ml and the CSS discharged to a flowing river system,
  9     where bacteria do not accumulate from day to day. Further, an actual overflow event may not
 10     result in an excursion above the 1000 MPN/100 ml criterion if the flow in the receiving water
 1 1      is sufficiently large. The permittee, however, must demonstrate that the occurrence of a 30-day
 12     period when CSOs  result in non-attainment of the WQS more than  10-percent of the time is
 13      extremely unlikely. This means that the analysis must consider both the likelihood of occurrence
 14      of overflow events and the dilution capacity of the1 receiving water at the time of an overflow.
 15      The following sections demonstrate various ways to make this determination.
 16
 17            Design Flow Analysis
 18            Design flow  analysis is the simplest but not necessarily the most appropriate approach.
 19      This approach uses conservatively low receiving water flow to represent the minimum reasonable
20      dilution capacity.  If the effects of all CSO events would  not prevent the attainment of the
21      standard under these stringent conditions, the  permittee has clearly  demonstrated that  the
22      applicable WQS should be attained.  In cases where nonattainment is indicated, however, the
23      necessary reductions to reach attainment may be unreasonably  high since CSOs are unlikely to
24      occur at the same time as design low flows.
25
26            The CSO outfall in this example  is at  a bend in  the river where  mixing is rapid.
27      Therefore, the loads are  considered fully  mixed through  the  cross-section of flow.   The
28      concentration in the  receiving water is determined by a simple mass balance equation,
29
                                      c  .
       External Review Draft                    9-10                        December 6, 1996

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                        WORKING DRAFT: DO*NOT CITE OR QUOTE
                                                  '              i
  1      where C represents concentration and Q flow (in any consistent units). The subscripts RW, CSO,
  2      and U refer to "receiving water," "combined sewer overflow," and "upstream," respectively.
  3
  4            For the  design flow analysis, upstream volume QD is set to a low flow of specified
  5      recurrence and receiving water concentration CRW is set equal to the water quality criterion.  In
  6      this example, upstream volume Qv is set at the 7Q10 flow.  The 7Q10 flow is commonly used
  7      for steady-state wasteload  analyses; although it has a 10-year recurrence and is much more
  8      stringent than the not-more-than- 1 0-percent requirement of the standard, this conservatism ensures
  9      that excursions of the standard will indeed occur only rarely.
 10
 1 1            The 7Q10 flow in this river is 313.3 cfs, so upstream volume Q0 is set to 313.3.  Since
 12      background (upstream) fecal coliform concentrations are negligible, Qj is set to 0. The WQS
 13      stipulates that not more than 10 percent of samples taken during any 30-day period exceed 1,000
 14      MPN/100 ml; thus receiving water concentration CRW is set at 1000.  Given 7Q10 flow in the
 IS      receiving water (and assuming a negligible fecal coliform contribution from upstream), the mass
 16      balance equation may be rearranged to express the CSO concentration that just meets the
 17      standard, in terms of the CSO flow volume:
 18
                             CR«(Qcso+QJ-c
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                         WORKING DRAFT: Do Nor CITE OR QUOTE
  1           Exhibit 9-3 displays a line that represents combinations of CSO concentration and CSO
  2     flow that just meet the WQS at 7Q10 flow. The region below the line represents potential
  3     control strategies. For instance, for CSO flows below 0.05 cfs (0.03 MOD), the WQS would be
  4     met at design low flow provided that the concentration hi the CSO remained below 6.3 x 10*
  5     MPN/100 ml. At a CSO flow of 6 cfs, however, the concentration would need to be below 0.053
  6     x 106 MPN/100 ml.
  7
 X
  8           The typical concentration of fecal coliforms in CSOs is approximately 2 x 106 MPN/100
  9     ml.  With upstream concentration C0 equal to zero, the mass  balance equation is:
 10
                                                  v. 1000(
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•a
2

1
                Design Flow Analysis
               Bacterial Loads to a River
                1
Standard

Exceeded
                                        =fcft=
   234

    CSO flow (cfs)
                                                      VO
                                                      ON
                                                      ON
                                   vo

                                   t-c
                                                      1

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                         WORKING DRAFT: Do NOT CTTE OR QUOTE
  1      days in a 30-day period experience CSOs, or—more precisely—not more than 3 days have CSOs
  2      with a pollutant loading above a critical amount.
  3
  4            The Poisson distribution is the'statistical distribution commonly used to describe the
  5      number of discrete random events, such as precipitation or CSOs, occurring within a given time
  6      period.3  To meet the not-more-than-10-percent criterion, the probability of four or more CSO
  7      events occurring within a 30-day period needs to be acceptably low, such as less than 5 percent
  8      (i.e., the probability that exactly zero, one, two, or three events occur within 30 days must be
  9      greater than 95 percent). Achieving this result entails setting the cumulative Poisson distribution
10      for z = 0 to 3 events to 0.95, as follows:
11

                                                   I e-V
                                                   ^ —-=0.95
                                                        z\
                                                  «.—v        ..                      r

12
13      where the parameter v is the average number of events in 30 days. Solving this, equation yields
14      a value of v that is predicted to result in a less than 5-percent chance of experiencing more than
15      3 events in a month. The resulting estimate is v = 1.37 events per month, equivalent to 16.62
16      events per  year.  At a 99-percent confidence level (1% probability of more than 3 events), v =
17      0.822, or 9.86 events per year.
18
19            Over the 31  years,  238 CSO events occur, giving an average of 0.64 events per month.
20    . Although this number is less than the value of v determined above, the permittee has not actually
21      demonstrated  that the  WQS will be  attained.  This is because CSO events  are  unevenly
22      distributed throughout the  year  over 31 years, only one CSO has occurred in August but 96
23      have occurred in April. Box 9-1 shows the average numbers by month.
24
25        'More information on the use of Poisson distributions may be found in Environmental Statistics and Data
26     Analysis (Ott, 1995).

       External Review Draft                    9-14                        December 6, 1996

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                         WORKING DRAFT:  Do NOT CITE oft QUOTE
  i
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Box 9-1.
of CSOs
Example
Jan
Feb
Mar
Apr
May
Jun
- Jul
Aug
Sep
Get
Nov
Dec
Average Number
per Month m

0.32
0.16
2^3-
3.10
OJ2
0.13
0.19
0.03
0.13
0.13
0.32 *
"0.42
       Since most CSOs occur in spring, the probability of
a water quality criterion exceedance needs to be calculated on
a month-by-month rather than annual average basis.  Here,
reducing the relatively high number of overflows in April
should result in attainment of the criterion in other months.
A control plan that reduces the April average from 3.1  (the
current number) to 1.37 (as calculated above) should result
in the attainment of  the water  quality  criterion in other
months as well.

       Additional refinements can focus more specifically on
eliminating only those CSO events predicted to exceed WQS
at actual  receiving water flow.  Not all of the April events result in such excursions; many are
very small.  Further, the dilution capacity of the receiving water tends to be high during the
spring. Therefore, the analysis can be refined by considering a design flow appropriate to the
month in question and then counting only those CSO events predicted to result in excursions
above WQS at this flow.

       Box 9-1 indicates that only March and April exceed the number of overflows per month
indicated by the Poisson analysis (v = 1.37 at 95% confidence level).  The 7Q10 flow for these
months is 440 cfs. Using this higher receiving water flow, almost 10 percent of the March-April
CSO events would not cause exceedance of the 1,000 MPN/100 ml standard, leaving art  April
recurrence of 2.87 per month (almost 10 percent less than 3.1). More importantly, the resulting
table of predicted receiving water concentrations can be analyzed to  determine the percentage
reduction in CSO volume needed to meet  the standard. Engineering improvements that result in
a reduction  to approximately 11 percent of current CSO volume would  be predicted  to limit
CSO-caused WQS excursions to the desired Poisson frequency.

       The design flow frequency analysis gives results that are doubly conservative, because the
analysis assumes low flow at the same time that it imposes a low probability of exceeding the
standard at that low flow.  This approach, then, pays a price for its simplicity, by requiring highly
       External Review Draft
                                         9-15
December 6, 1996

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                          WORKING DRAFT:  Do "NOT CITE IOR QUOTE
  1     conservative assumptions.  A less restrictive analysis would need information on the probability
  2     distribution of receiving water flows likely to occur during CSO events.
  3
  4            Statistical Analysis
  5            The next level  considers not only design low flows, but  the whole  range  of flows
'  6     experienced during a month. Although CSOs are more likely when receiving water flow is high,
  7     CSO events do not always have increased dilution capacity available. Clearly, however, CSOs
  8     will experience at least the typical range of dilution capacities.  Therefore, holding the probability
  9     of excursions to a specified low frequency entails analyzing the impacts of CSOs across the
10     possible range of receiving water flows, and not only design low flows.
11
12            This example assumes that the permittee has a predictive model of CSO volumes and
13     concentrations and adequate knowledge of the expected distribution of flows based on 20 or more
14     years of daily gage data.   In short, the permittee knows the loads  and the range of  available
IS     dilution capacity but not the frequency with  which a particular load will correspond to  a
16     particular dilution capacity. A Monte Carlo simulation can readily address this type of problem,
17     and is used with the April CSO series.4
18
19             The April receiving  water flows are summarized by  a flow-duration curve,  which
20     indicates the percent of time a given flow is exceeded (Exhibit 9-4). The distribution of flows
21      is asymmetrical, with a few large outliers.  Daily flows typically are lognormally distributed.
22     April's flows are lognormal with mean natural log of 7.09 (1,200 cfs)5, and standard deviation
23     of 0.46.
24
25         4The Monte Carlo approach describes statistically the components of the calculation procedure or model that are
26      subject to uncertainty. The model (in this case, the simple dilution calculation) is run repeatedly, and each time the
27      uncertain parameter, such as the receiving water flow, is randomly drawn from an appropriate statistical distribution.
28      As more and more random trials are run, the resulting  predictions build up an empirical approximation of the
29      distribution of receiving water concentrations that would result if the CSO series were repeated over a very long
30      series of natural  flows.  The  Monte Carlo analysis can  often be performed using a spreadsheet  The resulting
31      distribution can then be used for analyzing control strategies.
32         5For a lognormal distribution, the mean is equal to the natural log of the median of the data (7.09 = In (median)).
33      Therefore, the median April flow = e ""* = 1200 cfs.

        External  Review Draft                     9-16                         December  6, 1996

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               Flow Durations: April
i
2
       12000
       10000
                  20     40     60      80

                   Percent of Time Exceeded
100
I
                                                      13

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                         WORKING DRAFT: Do NOT CITE OR QUOTE
  1            The 31 years of CSS data include 96 April overflow events.  In the Monte  Carlo
  2     simulation these 96 events were matched with randomly selected receiving water flows from the
  3     April flow distribution, for a total of 342 Aprils of simulated data.  The number of events in
  4     which the 1,000 MPN/100 ml standard would be exceeded was then calculated, and the  count
  5     for the month tabulated.
  6
  7           Exhibit 9-5 shows the results. Of the 342 Aprils simulated, 122 had zero excursions of
  8     the standard attributable to the CSS.  The maximum number of predicted excursions in any April
  9     was 17. The average number for the month was 2.45, which, as expected, is less than the 2.87
 10     average determined in the  design  flow frequency  analysis since that analysis assumed a
 11      conservatively low receiving water flow.  However, this average still exceeds the desired Poisson
 12     frequency of 1.37.
 13
 14            This analysis more closely approaches the actual pattern of water quality excursions
 15      caused by the CSS. The objective implied by the WQS is three or fewer excursions per month.
 16      In Exhibit 9-5, the right-hand axis gives the cumulative frequency of excursions, expressed on
 17      a zero-to-one scale. Of the 342 simulated Aprils, over 75 percent were predicted to have  three
 18      or  fewer  excursions, leaving 25 percent predicted to have four or more.   Note  that the  11
 19      simulated Aprils with either  16 or 17 excursions all result from the same month of CSS  data,
20      corresponding to an abnormally wet period.  The permittee may wish to explore whether  these
21      data are representative of expected future conditions.
22
23            Once set up, the Monte Carlo simulation readily evaluates potential control strategies.
24      For instance, a control strategy with the goal of a 20-percent reduction in CSO flow and a 30-
25      percent reduction in coliform levels would raise to 82 the percentage predicted to meet the water
26      quality criterion. Although the Monte Carlo analysis introduces a realistic distribution of flows,
27      it may still result in an overly conservative analysis for how CSOs correlate with receiving water
28      flows, since it involves using a distribution, such as lognormal, which at best approximates the
29      true distribution of flows.   A more  exact analysis  needs  accurate information about the
30      relationship between CSO flows and loads and receiving  water dilution capacity.
31

        External Review Draft                    9-18                        December 6,  1996

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0*
I
              Monte Carlo Analysis
      April Excursions of 1000 MPN Standard
     140
                                           O
          1 23456789 10 11 12 13 14'l5'l6'17
                 Number of Events
VO
§
vd
                                                 ON
I


I






I

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                         WORKING DRATT:  Do NOT CTTE OR QUOTE
  1            Watershed Simulation
  2            The most precise approach may be a dynamic simulation of both the CSS and the
  3      receiving water.  This approach uses the same time series, of precipitation to drive both the
  4      CSS/CSO model and the receiving water model.  In cases where a dynamic simulation of the
  5      entire watershed would be prohibitively expensive, and where sufficient flow and precipitation
  6      records are available, the permittee may combine measured upstream flows and a simulation of
  7      local rainfall-runoff to represent the receiving water portion of the simulation.
  8
  9            As above, receiving water modeling entails an extremely simple dilution calculation.
10      Determining the data for the dilution calculation by simulating dilution capacity or flows, and
11      the analysis of the data, introduce complexity. This analysis uses a model that accurately predicts
12      the available dilution capacity corresponding to each CSO event.  Such  a-model accurately
13      represents the actual coliform counts in the  receiving  water and enables  the permittee to
14      determine which events exceed the standard of 1,000 MPN/100 ml.
15
16            Exhibit 9-6 presents the  results as the count of CSO events by month which result hi
17      receiving water concentrations greater than or equal to 1,000 MPN/100 ml. For 31 years of data,
18      only three individual months are predicted to have more than three (greater than 10%) days hi
19      excess of the standard.  Consequently, excursions above the monthly percentile goal occur only
20      about 0.8 percent of the time.  Further, the return period for years with exceedances of this
21      standard is 31/3 = 10.3 years. Although the CSS produces relatively frequent overflows, the rate
22      of actual water quality problems is quite low.  Exhibit 9-7, which plots CSO volumes versus
23      receiving water flow volume, illustrates why water quality problems remain rare.  This figure
24      shows that all the CSO events have occurred when the receiving water is at flow above 7Q10.
25      Furthermore, most of the large CSO discharges are associated with receiving water flows well
26      above low flow.  Although this excess dilution capacity reduces the effect of the CSO pollutant
27      loads, demonstrating compliance  also necessitates careful documentation of the degree  of
28      correlation.
29
30            Of course, no simulation  represents reality perfectly. Further, the precipitation series or
31      rainfall-runoff relations on which the model is based are likely to change with time. Therefore,

        External Review Draft                     9-20                        December 6, 1996

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1
i
u
I
•8
.2

£
1
       Water Quality Excursions by Month
             Full Dynamic Simulation
       10
       8
     o
     O 4
         1  3  4  6  8 10 12 14 16 18 20 22 24 26 28 30
                        Year

                                                I
                                                1
                                                73
                                                I

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B
I
OS
O
I
§
• •
^^
§
i
1
«
Receiving Water Flow During CSOs
1200000
1 fcUww W
1000000 •
1 UUUUUU
CO?
5f"^* ftnonnn
V i** OUUUUU
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13 600000 -
____ \J\J\J\J\J\/
O 400000 -
JTJL twUUUV
O
2OOOOO -


•
•

'
^ •
• • •
• •
• • • • •
• •
i:l^^^^*iVi- JL^ i*
u m*^^*^*i"i ^ t^i* i •> «f 1 P*i i | E f i *i <* i i i t | i i > i i i i i i |
^ 10000 20000 30000 400
7Q10FIow RWFIOW(cfs)
00


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                         WORKING DRAFT:  Do "Nor CITE OR QUOTE
  1      an analysis of the uncertainty present in predictions should accompany any predictions based on
  2      continuous simulation modeling.   A  long-term control plan justified  by the demonstration
  3      approach should include a margin of safety that reflects the degree of uncertainty in the modeling
  4      effort.
  5
  6      9.3.2  Example 2: Bacterial Loads to an Estuary
  7
  8            In the previous example, a simple dilution calculation sufficed to calculate impact in the
  9      receiving water body,  since compliance  was evaluated at the point of mixing  and the
10      concentration of pollutants decreased as they moved away from the source area.
11
12            The second example, involving bacterial WQS in a tidal estuary, is more complex.  Like
13      the previous example, it evaluates the frequency of excursions of WQS, but modeling the fate
14      of bacteria in the receiving water is more complicated.  This is because estuaries are typically
IS      both advective  and dispersive in nature (that is,  contaminants are dispersed as a result of
16      freshwater flow-through as well  as tidal mixing). The tidal component can move contaminants
17      both up- and down-estuary from the source.  As  a result, observed bacterial concentrations
18      depend not only on current releases but also on previous days' releases. This example introduces
19      another complication: the receiving water includes shellfish beds and public beaches with more
20      restrictive bacterial standards. Exhibit 9-8 is a map of the estuary, indicating direction of tidal
21      flow, mixing zone, and location  of sensitive areas.
22
23            As in the previous example, WQS for fecal coliform are expressed as a geometric mean
24      of 400 MPN/100 ml and not more than 10 percent  of samples in a 30-day period above 1,000
25      MPN/100 ml. The shellfishing and bathing areas have more restrictive WQS, specifying that the
26      30-day geometric mean of fecal coliform counts not exceed 200 MPN/100 ml on a minimum of
27      five samples and that not more than 20 percent of samples exceed 400 MPN/100 ml.
28
29            Design Condition Analysis
30            As-in the previous example, the simplest level of analysis considers conservative design
31      conditions.  For an estuary, however, other processes need to be considered:

        External Review Draft                   9-23                        December 6, 1996

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tn

I
EL

f
I
O
I
Exhibit 9-8. Map for Example 2
         Upstrearf

         inflow
         7Q10 = 900cfs
         30Q10=1,500cfs
  Mixing Zone

  (	1 mi
Shellfishing
                                 1.5 mi
                                          CSO
                                         Outfall
                                                  JE*2 -3 midday

                                             Estuary

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                         WORKING DRAFT:  DoTCof CITE OR QUOTE
  i
  2
  3
  4
  5
  6
  7
  8
  9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
       (1)    This estuary is not strongly stratified near the source, so unstratified critical
              dilution conditions apply.6
       (2)    Further from the CSO discharge, it is necessary to evaluate the combination of
              reasonable flows and diffusion coefficients that produces the maximum impact by
              combining relatively high dispersion rates and relatively low dilution rates.
       (3)    Design conditions should also include temperature and salinity, both of which
              influence the colifonn die-off rate.
        ; Box 9-2.. Assumptions for
          Estnarme CSO Example
Upstream Flows
    - 7Q10      = 900 cfs
     IL(7Q10)  = L5 mi/day
     30Q10     =• 1,500 .cfs
     U (30Q10) = 2.5 mi/day
                = KMJQOft2
       This example uses an analytical
model  for  one-dimensional  estuarine
advection and dispersion .  Selected data
are presented in Box 9-2. This solution is
based on the assumption of an infinitely
long estuary of constant area and is useful
for estuaries that are sufficiently long to
approach  steady  state near  the outfall.
The ratio KE/U2, referred to as the estuary
number, strongly controls the character of
the solution.  The estuary number reflects
the relative importance of dispersive and
advective  fluxes.    As  this  number
approaches zero,  advection predominates
and transport in  the  estuary  becomes
increasingly similar to river transport. In this estuary, the ratio is approximately 1.5, indicating
relatively strong tidal mixing with significant transport up-estuary.
Estuary
   1  A
     E
     T
     K
                = 27°C
                =.l.ll/day .
     Unstratified
CSO
     c
     Qe
                = 1 x 10* coliforms/100 ml
                = 0.1 -MGD  .as  maximum
                   average per month, 2 MGD
                   as-daily maximum
30
31
32
33
34
35
36
   ""Recommendations for design ("critical dilution") conditions in estuaries are provided in U.S. EPA (1991b):
       In estuaries without stratification, the critical dilution condition includes a combination of low-water slack
       at spring tide for the estuary and design low flow for river inflow.  In estuaries with stratification, a
       site-specific analysis of a period of minimum stratification and a period of maximum stratification, both at
       low-water slack, should be made to evaluate which one results in the lowest dilution....
        External Review Draft
                                         9-25
                            December 6, 1996

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                         WORKING DRAFT;  Do NOT CTIE OR QUOTE
  1            The geometric mean requirement of the water quality criterion is taken as an average
  2     condition over time for scoping; that is, the 30-day time frame for this analysis is assumed to be
  3     sufficiently long to allow the variability in the load, as well as tidal cycles, to be averaged out.
  4     The scoping thus assumes a steady load in terms of an  average over time.  An advection-
  5     dispersion solution can again be used in this case. Results of the scoping analysis based on the
  6     one-dimensional advection-dispersion solution are shown in Exhibit 9-9.  A mixing zone of 0.5
  7     mile up-estuary and down-estuary of  the outfall is allowed.  The beach location, 1.5 miles
  8     up-estuary of the  outfall,  is of particular concern.  The model was applied for  a variety of
  9     conditions, including freshwater flows at 7Q10 and 30Q10 levels and loads at the estimated event
 10     maximum daily average load and expected maximum 30-day average load. Because the answer
 11      depends on the value assigned to the dispersion coefficient, sensitivity of the answer to dispersion
 12     coefficients ranging from 2 miVday to 3 mi2/day, representing the expected range for the part of
 13     .the estuary near the outfall, was examined.
 14
 15            It is most appropriate to compare the geometric mean criteria to the 30Q10 upstream flow
 16      and average load (as the standard is written as a 30-day average), and the percentile standards
 17      to the  7Q10 upstream flow and event  maximum load.  Scoping indicates that the CSOs may
 18      cause the short-term criterion to be exceeded at the mixing zone boundaries and are likely to
 19      cause impairment at the up-estuary beach.  Increasing the estimate of the dispersion coefficient
20      increases the estimated concentration at the beach, reflecting increased up-estuary "smearing" of
21      the contaminant plume, which illustrates that the minimum  mixing power may not be a
22      reasonable design condition for evaluating maximum impacts at points away from the outfall.
23      WQS excursions  at the beach  are likely to occur only at low  upstream flows, while the
24      combination of average loads and 30Q10 freshwater flows is not predicted to cause impairment.
25      In evaluating impacts'at the beach, recall that scoping was  conducted using a one-dimensional
26      model, which averages a cross-section. If the average is correctly estimated, impacts at a specific
27      point (e.g., the beach) may still  differ from the average. Concentrations at the beach may be
28      higher or lower than the cross-sectional average, depending on tidal circulation patterns.
29
30            The design condition analysis identifies instantaneous concentrations at the down-estuary
31      boundary of'the mixing zone and the beach as potential compliance problems. It also predicts

        External Review Draft                    9-26                        December 6, 1996

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                        WORKING DRAFT:  Do NOT CITE OR QUOTE
             Exhibit 9-9. Steady State Predictions of Fecal Coliform Count (MPN/lOOml)
vHow.
Load:
Dispersion:
Mixing Zone,
Upstream
Mixing Zone,
Downstream
Beach
Upstream: 900 eft
(TQlb)
Upstream: 1,500 cfs <30Q10)
"Event Maxiirnnn Load
E = 2
mi2/day
838
1212
252
E = 3
miVday
821
1050
333
E = 2
miVday
596
1102
123
E = 3
miz/day
651
981
207
Average Load
E = 2
miz/day
30
35
6
E = 2
miVday
33
49
10
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
excursions  at average flow  conditions and  suggests that  additional  controls are needed.
Numerical experiments with the design condition scoping model suggest that a target 25-percent
reduction in CSO flow volume would provide for the attainment of WQS.

      Design Flow Frequency Analysis
      The design condition analysis addresses the question of whether there is a potential for
excursions  of WQS.  It does not address  the frequency of excursions.   The frequency of
excursions depends on (1)  the frequency and  magnitude  of CSO events, and (2) the dilution
capacity of the receiving water body at the time of discharge (note that, in the estuary, the range
of dilution capacities (on a daily basis) is  less extreme  than in the river, because the tidal
influence is always present,  regardless of the level of upstream flows). To  obtain an upper-bound
(conservative) estimate of the frequency of excursions, an analysis of the monthly or seasonal
frequency of CSO events should be combined with a design dilution capacity appropriate to that
month.  A  simple analysis  of the frequency of CSO events on a monthly  or seasonal basis is
combined with a design dilution capacity appropriate  to that month to obtain an upper-bound
(conservative) estimate of the frequency of excursions of the WQS.

      Statistical Analysis
      The design flow analyses of the previous two sections contain a number of conservative
simplifying assumptions:
       External Review Draft
                                        9-27
December 6, 1996

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                         WORKING PRATT;  Do NOT CITE OR QUOTE
   1            (1)    They assume a steady (rather than intermittent) source
  2
  3            (2)    They assume a design minimum dilution capability for the estuary
  5            (3)    They do not account for many of the real-world complexities of estuarine mixing
  6
  7            (4)    They do not account for the effects of temperature and salinity on bacterial die-
  8                  off.
  9
                   scoping analysis can be improved by considering a full distribution of probable
 1 1     upstream flows in a Monte Carlo simulation. The expected range of hydrodynamic dispersion
 12     coefficients could also be incorporated into the analysis.
 13
 14           Watershed Simulation
 15           Building a realistic model  of  contaminant distribution and transport in estuaries is
 16     typically resource-intensive and demanding.  A watershed simulation may, however, be needed
 17     to demonstrate compliance for some systems where the results of conservative design flow
 1 8     analyses are unclear. Detailed guidance on the selection and use of estuarine models is provided
 19     in EPA's Wasteload Allocation series, Book m, Parts 1-4.
20                               ,
21      9.33  Example3: BOD Loads
22
23           The third example concerns BOD and depletion of DO, another important water quality
24     concern for many CSSs. Unlike bacterial loads, BOD impacts are usually highest downstream
25      of the discharge and occur some time after the discharge has occurred.
26
27            The CSS in an older industrial city has experienced frequent overflow events.  The CSOs
28      discharge  to a moderate-sized coastal plain river, which also receives point-source loads
29      upstream.  In the reach below the CSS discharge, the river's  7Q10 flow is 194 cfs, with a depth
30      of 5 feet and a velocity of 0.17 ft/s. Above the city, velocities range from 0.2 to 0.3 ft/s at 7Q10
31      flow. A major industrial point source of BOD lies 18 miles upstream (Box 9-3).  Other minor
32      BOD loads enter via tributaries.
33
       External Review Draft                    9-28                       December 6, 1996

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                        WORKING DRAFT:  Do NOT CITE OR QUOTE
  i
  2
  3
  4
  5
  6
  7
  8
  9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
       The river reach below the city has
 a  designated use of supporting a warm
 water fishery. For this designation, State
 criteria for DO are a 30-day mean of 7.0
 mg/1 and a 1-day minimum of 5.0 mg/1.
 The State also  requires that WLAs for
 BOD be calculated on the basis  of the
 1-day minimum DO standard calculated at
 7Q10 flow and the  maximum average
 monthly  temperature.   The   5.0 mg/1
 criterion   is   not    expressed   in    a
 frequency-duration  format;  the   1-day
 minimum is a fixed value, but evaluation
 in  terms of an extreme  low flow of
 specified recurrence implicitly assigns an
 acceptable frequency of recurrence to DO
 1-day average concentrations less than 5.0
mg/1.  (The State criterion for DO is thus
hydrologically  based  and  is  roughly
  Box 9-3. Assumptions for BOD Example
CSO Discharge (atmaximum load)
    BODj = 200.mg/l
    CB0DU/BODS =
    NBOD=Omg/l
Point-Source Effluent Upstream
    .Distance Upstream = .18 mi
    GB0DU/BOD5=2J
    NB0D=Oing/l
  ••.-<&« 5.MGD
Reaction Parameters
                        .(1.024) <**»
    where U = avg stream velocity (fl/s)
    and; H,= average depth r (ft)
    K* -= 1^ =03. x (1.047) •(r-20)
    SOD (below-CSS) ='0.3 mg/l-day  •
    SOD (elsewhere) =0
Upstream Background'
    BODU>= 1 mg/1 -
    DOD=lingyi
equivalent to maintaining an acceptable frequency of biologically based excursions of the water
quality criteria for ambient DO).

      Design Condition Analysis
      A conservative assessment of impacts from the CSS can be established by combining a
reasonable worst-case load (the maximum design storm with a 10-year recurrence interval) with
extreme receiving water design conditions.  Limited monitoring data and studies of other CSO
problems suggested'that a reasonable worst-case estimate was a 1-day CSO volume of 4 MGD,
with an average BOD5 concentration of 200 mg/1.
       External Review Draft
                                      9-29
                          December 6, 1996

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                         WORKING DRAFT: "Do"NoT €ITE XHTQUOTE
  1            As described in Chapter 8, initial scoping was carried out using a simple, steady-state DO
  2      model (see Section 8.3.2, Rivers Oxygen Demand/Dissolved Oxygen subsection)7. The initial
  3      scoping  assumes the presence of the upstream point source and the estimated wprst-case CSO
  4      load.  All BODS was initially assumed to be CBOD and fully available to the dissolved phase.
  5      Sediment oxygen demand (SOD),  known to play a role in the reach below the CSS, was
  6      estimated at 0.3 mg/l-day . No SOD was assumed for other reaches as a qualitative balance to
  7      the assumption that no BOD load is lost to settling.
  8
  9            Results of the scoping model application are shown in Exhibit 9-10, which shows the
10      interaction  of the point source, CSO, and minor steady  sources to the, river.  The exhibit
11      combines two worst-case conditions: high flow from the episodic source and low  (7Q10) flow
12      in the receiving water.  Under these conditions, the maximum DO deficit is expected to occur
13      7.5 miles downstream of the CSO, with predicted DO concentrations as low as 3.9 mg/1.  Under
14      such conditions, the  CSO flow is approximately 25 percent of total flow in the river.
15
16            Design Flow Frequency Analysis
17            The State criterion called for a one-day minimum DO concentration of 5 mg/1, calculated'
18      at design low flow conditions for steady sources. Use of the 7Q10 design flow was interpreted
19      as implying that an approximately once-in-three year excursion of the standard, on average, was
20      acceptable (U.S.  EPA, 199la).8  As in the previous examples, the rate of occurrence  of CSOs
21      provides an upper bound on the frequency of WQS excursions attributable to CSOs.  In this case,
22      however, the once-in-three-years excursion frequency cannot be attained through CSO control
23      alone. Instead, the co-occurrence of CSOs and receiving water flows must be examined.
24
25            To accommodate this relationship, the design flow model can be  modified to assess the
26      dependence of DO concentrations on upstream flow during maximum likely loading  from the
27         7   Similar DO analysis is discussed in Thomann and Mueller (1987).
28         8The average frequency of excursions is intended to provide an average period of time during which aquatic
29      communities recover from the effects of the excursion and function normally before another excursion.  Based on
30      case studies, a three year return internal was determined to be appropriate. The three year return internal was linked
31      to the 7Q10 flow since this flow is generally used as a critical low flow condition.

        External Review  Draft      .               9-30                         December 6, 1996

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o

a
I
S>
3
utt
       Design Condition Prediction of DO Sag

Minimum DO

Standard
                                         en
                           River Mile

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                        WORKING DRAFT: Do NOT CITE OR QUOTE
  1      CSO.  Design flow was simulated using the worst-case CSO flow over a variety of concurrent
  2      upstream flows, since upstream flows affect both the dilution  capacity of the river and the
  3      velocity of flow and reaeration rate.  As shown in Exhibit 9-11, the estimated DO concentrations
  4      depend strongly on upstream flow. Note that WQS are predicted to be attained if the upstream
  5      flow is greater than about 510 cfs.  A flow less than 510 cfs occurs about five times per year,
  6      on average, in this segment of the river.
  7
  8            The target rate of WQS excursions is one in three years. An upper bound for the actual
  9      long-term average rate of excursions can be established as the probability that flow is less than
10      510 cfs in the river multiplied by the probability that a CSO occurs:
11
12
13     where P^ is the probability of a WQS excursion on any given day and f^ is the fraction of days
14     in the year on which CSO discharges occur, on average.  Since the goal for excursions is once
15     every three years, P^ is set at l/(3 x 365), or .000913.  Since a flow less than 510 cfs occurs
16     five times per year, p(Q<510) is 5/365, or .0137.  Substituting these values into the equation
17     yields f^ = .000913/.0137 = 0.067.  This implies  that up to 24 CSOs per year will meet the
18     long-term average goal for DO WQS excursions, even under the highly conservative assumption
19     that all CSOs provide the reasonable maximum BOD load.
20
21           An important caveat, however, is that no  other significant wet  weather sources  are
22     assumed to be present in the river.  In most real rivers, major precipitation events also produce
23     BOD loads from urban storm water, agriculture, etc. Where such loads are present, conservative
24     assumptions regarding  these additional sources need to be incorporated into the scoping level
25     frequency analysis.
26
27           As with the other examples, further refinement in the analysis- can be attained by
28     examining the statistical behavior of the CSO and receiving water flows in more detail.  Finally,


       External Review Draft                    9-32                       December 6, 1996

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1
I
o
Q
!
M
Q-
o\
.ts
W
        DO Minimum Dependence on Upstream Flow
100
                                                                CO
              200
                   300
400   500   600   700
   Upstream Flow (cfs)
                                         000
1000

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                        WORKING DRAFT:  Do "NOT CITE OR QUOTE
 1     dynamic continuous simulation models could be used to provide a more realistic estimate of the
 2     actual time series of DO concentrations resulting from CSOs.
 3
 4     9.4    SUMMARY
 5
 6            As illustrated in the preceding examples, no one method is appropriate for a particular
 7   _  CSS or for all CSSs:  the method should be appropriate for the receiving water problem, and a
 8     complex dynamic simulation is not always necessary. The municipality (in cooperation with the
 9     NPDES authority) needs to balance effort spent in analysis with the level of accuracy required.
10     However, as the first example illustrated, as additional effort is invested assumptions can usually
11      be refined to better reflect the actual situation.
12
      External Review Draft                    9-34                       December 6, 1996

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                       "WORKING DRAFT: DO~NOT~CITE OR QUOTE
 i                                       REFERENCES
 2
 3
 4     Alley, W.M. and P.E. Smith.  1982a.  Distributed Routing Rainfall-Runoff Model, Version II.
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 6
 7     Alley, W.M. and P.E. Smith. 1982b. Multi-Event Urban Runoff Quality Model. Open-File
 8           Report 82-764. USGS, Denver, CO
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10     Ambrose, R.B., J.P. Connolly, E. Southerland, T.O. Barnwell and LL. Schnoor. 1988. "Waste
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17     Ambrose, R.B. et al. 1990b. Technical Guidance Manual for Performing Waste Load
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20
21     Ambrose, R.B., T.A. Wool, J.P. Connolly and R.W. Schanz. 1988b. WASP4, A
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25
26     American Public Health Association (APHA). 1992.  Standard Methods for the Analysis of
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29     American Society for Testing and Materials (ASTM).  1991.  Standard  Guide for Conducting
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32
33     Association of Metropolitan Sewerage Agencies (AMSA).  1996. Performance Measures for
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35
36     Bedient, P.B. and W.C. Huber.  1992. Hydrology and Floodplain Analysis.  Second Edition.
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38
39     Bowie, G.L. et al.  1985. Rates,  Constants, and Kinetic Formulations in  Surface Water Quality
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42 .
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45
       External Review Draft                   R-l                       December 6, 1996

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  1     Brown, L.C. and T.O. Barnwell.  1987.  The Enhanced Stream Water Quality Model QUAL2E
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 24     Driscoll, E.D., J.L. Mancini and P. A. Mangarella. 1983a. Technical Guidance Manual for
 25           Performing Waste Load Allocations, Book II: Streams and Rivers, Chapter 1:
 26           Biochemical Oxygen Demand/Dissolved Oxygen. EPA 440/4-84-020.
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 29           1983b. Technical Guidance Manual for Performing Waste Load Allocations, Book II:
 30           Streams and Rivers, Chapter 2: Nutrient/Eutrophication Impacts. EPA 440/4-84-021.
 31
 32      Driscoll, E.D. and D.M. DiToro/ 1984. Technical Guidance Manual for Performing Waste
 33            Load Allocations, Book VII: Permit Averaging Periods. EPA 440/4-84-023.  OWRS.
 34
 35      Driscoll, E.D. 1986.  "Lognormality of Point and Nonpoint Source Pollutant Concentrations."
 36            Proceedings ofStormwater and Water Quality Model Users Group Meeting, Orlando,
 37            FL.  EPA 600/9-86/023, pp. 157-176, US EPA, Athens, GA.
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 39     Driscoll, E.D., P.E. Shelley and E.W. Strecker.  1990. Pollutant Loadings and Impacts from
 40           Highway Stormwater Runoff. Volume I: Design Procedure.  FHWA-RD-88-006 (NTIS
 41  -          PB90-257551). Turner-Fairbank Highway Research Center, McLean, VA
42
43      Driver, NJ5. and GX>. Tasker.   1988. Techniques for Estimation of Storm-Runoff Loads,
44            Volumes,  and  Selected Constituent Concentrations in Urban Watersheds in the United
45            States. Open-File Report 88-191.  USGS, Denver, CO
       External Review Draft                    R-2                       December 6, 1996

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  1     Eschenroeder, A. 1983.  "The Role of Multimedia Fate Models in Chemical Risk Analysis."
  2            In Fate of Chemicals in the Environment.  ACS Symposium Series 225. American
  3            Chemical Society, Washington, DC
  4
  5     Everhart, W.H., A.W. Hipper and W.D. Youngs.  1975.  Principles of Fishery Science.
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  7
  8     Fischer, H.B.  1972. "Mass Transport Mechanisms in Partially Stratified Estuaries." Journal
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 10
 11     Fischer, H.B., E.J. List, R.C.Y. Koh, J. Imberger & N.H. Brooks.  1979. Mixing in Inland
 12            and Coastal Waters.  Academic Press, Orlando.
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 14     Flavelle, P.  1992.  "A Quantitative Measure of Model Validation and its Potential Use for
 15            Regulatory Purposes." Advances in Water Resources.  15: 5-13.
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 17     Freedman, P.L., D.W. Dilks and B.A. Monson. 1992. Technical Guidance Manual for
 18            Performing Waste Load Allocations, Book HI: Estuaries, Part 4: Critical Review of
 19            Coastal Embayment and Estuarine Waste Load Allocation Monitoring.
 20            EPA-823-R-92-005.
 21
,22     Freedman, P.L. and J.K. Marr. 1990. "Receiving-water Impacts." In Control and Treatment
 23            of Combined Sewer Overflows.  Van Nostrand Reinhold, New York. pp. 79-117.
 24
 25     Haith, D.A. and L.L. Shoemaker. 1987.  "Generalized Watershed Loading Functions for
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 33            Basta and B.T. Bower, eds.  Analyzing Natural Systems, Analysis for Regional
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 35            Washington, DC.  pp. 249-388.
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 37     Huber, W.C. and R.E. Dickinson. 1988. Storm Water Management Model Version 4, User's
 38            Manual.  EPA 600/3-^88/OOla (NTIS PB88-236641/AS).  Environmental Research
 39            Laboratory, Athens, GA
 40
 41      Hydroqual, Inc.  1986.  Technical Guidance Manual for Performing Wasteload Allocations,
 42           Book TV: Lakes, Reservoirs and Impoundments, Chapter 3: Toxic Substances Impact.
 43            EPA-440/4-87-002.
 44
        External Review Draft                    R-3                        December 6, 1996

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                        WORKING'DRAFT:  Do NOT CITE OR QUOTE
  1     Hydroscience, Inc. 1979. A Statistical Method for Assessment of Urban Storm Water
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  4     International Air Transport Association (IATA).  1996. Dangerous Goods Regulations, 37th
  5           Edition. Montreal, Quebec.
  6
  7     Irvine, K.N., E.G. Loganathan, EJ. Pratt and H.C. Sikka. 1993. "Calibration of PCSWMM to
  8           estimate metals, PCBs and HCB in CSOs from an industrial sewershed.  In W. James,
  9           ed. New Techniques for Modelling the Management ofStormwater Quality Impacts.
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 14
 15      Jirka, G.H. 1992.  Technical Guidance Manual for Performing Waste Load Allocations, Book
 16            ///: Estuaries, Part 3: Use of Mixing Zone Models in Estuarine Waste Load
 17            Allocations. EPA-823-R-92-004.
 18
 19      Johanson, R.C., J.C. Jmhoff, JJL Kittle, Jr. and A.S. Donigian.  1984.  Hydrological
 20            Simulation Program - FORTRAN (HSPF), Users Manual for Release 8.0.
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 22
 23      Klemm.  1990.  Macroinvertebrate Field and Laboratory Methods for Evaluating the
 24            Biological Integrity of Surface  Waters.  U.S. EPA. Office of Research and
 25            Development.  EPA 600/4-90/030.
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 27      LimnoTech, Inc. 1985. Dynamic Toxics Waste Load Allocation Model (DYNTOX):  User's
 28            Manual.
 29
 30      Lind, O.T.  1985.  Handbook of Common Methods in Limnology. Kendall/Hunt Publishing
 31          . Company, Dubuque, IA.
 32
 33      Lowe, RX. 1974. Environmental Requirements and Pollution Tolerance of Freshwater
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 35            Cincinnati, OH.
 36
 37      Mancini, J.L., G.G. Kaufman, P.A. Mangarella and ED. Driscoll.  1983.  Technical Guidance
 38           Manual for Performing Waste Load Allocations, Book TV, Lakes and Impoundments,
 39            Chapter 2, Nutrient/Eutrophication Impacts. EPA-440/4/-84-019.  Office of Water
40            Regulations and Standards, Monitoring and Data Support Division.
41
42      Mao, K.  1992.  "How to Select a Computer Model for Storm Water Management." Pollution
43           Engineering.  Oct. 1, 1992: 60-63.
44
       External Review Draft                   R-4                        December 6, 1996

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                        WORKING DRAFT:  Do NOT CITE OR QUOTE
 1     McKeon, T.J. and JJ. Segna. 1987. Selection Criteria for Mathematical Models Used in
 2            Exposure Assessments: Surface Water Models. EPA 600/8-87/042. Exposure
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 4            1987.
 5
 6     Merritt, R.W. and K.W. Cummins.  1984.  An Introduction to the Aquatic Insects of North
 7            America, 2nd Edition.  Kendall/Hunt Publishing Company, Dubuque, IA.
 8
 9     Miller, R.W.  1983.  The Flow Measurement Engineering Handbook.  McGraw Hill, New
10            York.
11
12     NCASI. 1982. A Study of the Selection, Calibration and Verification of Mathematical Water
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14            for Air and Stream Improvement, New York.
15
16     Nielsen, L.A. and D.L. Johnson (editors).  1983.  Fisheries Techniques. American Fisheries
17            Society, Bethesda, MD.
18
19     Nix, SJ.  1990. "Mathematical. Modeling of the  Combined Sewer System." In Control and
20            Treatment of Combined Sewer Overflow.  Van Nostrand Reinhold, New York,  pp.
21            23-78.
22
23     Nix, S.J., PJE. Moffa and D.P.  Davis.  1991.  "The Practice of Combined Sewer Modeling."
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25
26     O'Connell, R.L. and N.A. Thomas. 1965.  "Effect of Benthic Algae on Stream Dissolved
27            Oxygen." Journal of the Sanitary Engineering Division, ASCE. 91(SA3):  1-16.
28
29     Onishi, Y. and S.E. Wise.  1982.  User's Manual for the Instream Sediment-Contaminant
30            Transport Model SERATRA. EPA-600/3-82-055.
31
32     Ott, W.R. 1995. Environmental Statistics and Data Analysis. Lewis Publishers, Boca Raton,
33            FL.
34
35     Palmstrom, M. and W.W. Walker Jr. 1990.  P8  Urban Catchment Model: User's Guide,
36            Program Documentation, and Evaluation  of Existing Models, Design Concepts, and
37            Hunt-Potowomut Data Inventory. Report No. NBP-90-50. The Narragansett Bay
38            Project, Providence, RI.
39
40     Pennak,R.W.  1989.  Freshwater Invertebrates of the United States, 3rd Edition. John Wiley
41            and Sons, Inc., New York.
42
43     Pitt, R. 1986. "Runoff Controls in Wisconsin's  Priority Watersheds." In: Urban Runoff
44            Quality - Impact and Quality Enhancement Technology, Proceedings of an
       External Review Draft      .              R-5                       December 6, 1996

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                        WORKING DRAFT:  "Do NOT CITE OR QUOTE
 1            Engineering Foundation Conference. Henniker, NH, June 23-27, 1986. ASCE, New
 2            York.  pp. 290-313.
 3
 4     Plafkin, J.L., M.T. Barbour, K.D. Porter, S.K. Gross, and R.M. Hughes. 1989. Rapid
 5            Bioassessment Protocols for Use in Streams and Rivers—Benthic Macroinvertebrates
 6            and Fish. Office of Water, U.S. EPA, Washington, DC. EPA 440/4-89/001.
 7  .
 8     Reckhow, K.H. and S.C. Chapra. 1983a.  "Confirmation of Water Quality Models."
 9            Ecological Modelling.  20: 113-133.
10
11     Reckhow, K.H. and S.C. Chapra. 1983b.  Engineering Approaches for Lake Management,
12            Vol. 1 and Vol. 2.  Butterworth Publishers, Woburn, MA.
13
14     Reckhow, K.H., J.T. Clements and R.C. Dodd.  1990.  "Statistical Evaluation of Mechanistic
IS            Water-quality'Models." Journal of Environmental Engineering, ASCE.  116(2):
16            250-268.
17
18     Richardson, W.L. et al. 1983. User's Manual for the Transport and Fate Model M1CHKJV.
19            U.S. EPA Large Lakes Research Station, Grosse He, MI.
20
21     Ricker, W.E.  1975.  Computation and Interpretation of Biological Statistics of Fish
22            Populations. Bulletin of Fish. Res. Board Can. 191.
23
24     Roesner, L.A., J.A. Aldrich and RJE. Dickinson.  1988.  Storm Water Management Model.
25            User's Manual, Version 4, EXTRAN Addendum. EPA 600/3-88/OOlb (NTIS
26            PB84-198431). Environmental Research Laboratory, Athens, GA
27
28     Saunders, J.F. m, W.M. Lewis Jr. and A.  Sjodin.  1993. Ammonia Toxicity Model AMMTOX
29            Version 1.0,  Operator's Manual. Center for Limnology, University of Colorado,
30            Boulder, CO
31
32     Schnoor, J.L.  1985. "Modeling Chemical Transport in Lakes, Rivers, and Estuarine
33            Systems." InNeely, W.B. andGJE. Blau, eds., Environmental Exposure from
34            Chemicals, vol 2.  CRC Press, Boca Raton, FL.
35
36     Schreck, C.B. and P.B. Moyle (editors). 1990. Methods for Fish Biology.  American
37            Fisheries Society, Bethesda, MD.
38
39     Schueler, T.R,  1987.  Controlling Urban  Runoff: A Practical Manual for Planning and
40            Designing Urban BMPs.  Document No. 87703.  Metropolitan Washington Council of
41            Governments, Washington, DC.
42
43     Shoemaker, L.L. et al.  1992.  Compendium of Watershed-Scale Models for TMDL
44            Development. EPA 841-R-92-002.  U.S. EPA Office of Wetlands, Oceans and
45            Watersheds and Office of Science and Technology.
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                        WORKING DRAFT: DO*NOT CITE OR QUOTE
  i
  2     Sonnen, M.B.  1980.  "Urban Runoff Quality: Information Needs."  Journal of the Technical
  3            Councils, ASCE. 106(TC1): 29-40.
  4
  5     Terstriep, M.L., M.T. Lee, E.P. Mills, A.V. Greene and M.R. Rahman.  1990. Simulation of
  6            Urban Runoff and Pollutant Loading from the Greater Lake  Calumet Area. Prepared
  7            by the Illinois State Water Survey for the U.S. Environmental Protection Agency,
  8            Region V, Water Division, Watershed Management Unit, Chicago, EL.
  9
 10     Thomann, R.V., and J. A. Mueller. 1987. Principles of Surface Water Quality Modeling and
 11            Control  Harper and Row Publishers, New York.
 12
 13     U.S. Environmental Protection Agency (EPA).  1996. Combined Sewer Overflows and the
 14            Multimetric Evaluation of Their Biological Effects: Case Studies in Ohio and New
 15            York. EPA 823-R-96-002.
 16
 17     U.S. Environmental Protection Agency (EPA).  1995a.  Combined Sewer
 18            Overflows—Guidance for Long-Term Control Plan. EPA 832-B-95-002.
 19
20     U.S. Environmental Protection Agency (EPA).  1995b.  Combined Sewer
21            Overflows—Guidance for Nine Minimum Controls.  EPA 832-B-95-003.
22
23     U.S. Environmental Protection Agency (EPA).  199Sc.  Combined Sewer
24            Overflows—Guidance for Screening and Ranking.  EPA 832-B-95-004.
25
26     U.S. Environmental Protection Agency (EPA).  1995d.  Combined Sewer
27            Overflows—Guidance for Funding Options. EPA 832-B-95-007.
28
29     U.S. Environmental Protection Agency (EPA).  1995e.  Combined Sewer
30            Overflows—Guidance for Permit Writers.  EPA 832-B-95-008.
31
32     U.S. EPA.   1995f.  Guidelines for the Preparation of the 1996 State Water Quality
33           Assessments (305(b) Reports).  EPA 841-B-95-001.
34
35     U.S. Environmental Protection Agency (EPA).  1995g.  Technical Guidance Manual for
36           Developing Total Maximum Daily Loads, Book II: Streams  and Rivers, Parr 1:
37           Biochemical Oxygen Demand/Dissolved Oxygen and Nutrients/Eutrophication.  EPA
38            823-B-95-007.
39
40     U.S. Environmental Protection Agency (EPA).  1994. Water Quality Standards Handbook,
41           Second Edition. EPA 823-B-94-006.
42
43     U.S. Environmental Protection Agency (EPA).  1994a.  Combined Sewer Overflow Control
44           Policy.
45
       External Review Draft                    R-7                       December 6, 1996

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                       "WORKING DRAFT: Do NOT CITE OR QUOTE
  1      U.S. Environmental Protection Agency (EPA). 1994b. NEEDS Survey.
  2
  3      U.S. Environmental Protection Agency (EPA). 1994c. Industrial User Inspection and
  4            Sampling Manual for POTWs. EPA 831-B-94-001.
  5
  6      U.S. Environmental Protection Agency (EPA). 1994d. EPA Requirements for Quality
  7            Assurance Project Plans for Environmental Data Operations.  EPA QA-R-5.
  8
  9      U.S. Environmental Protection Agency (EPA). 1993.  Combined Sewer Overflow Control
 10            Manual. EPA 625-R-93-007.
 11
 12      U.S. Environmental Protection Agency (EPA). 1992.  NPDES Storm Water Sampling
 13            Guidance Document. EPA 833-B-92-001.
 14
 15      U.S. EPA.  1991a.  Technical Support Document for Water Quality-based Toxics Control.
 16            EPA 505/2-90-001.  OWEP/OWRS.
 17
 18      U.S. EPA.  1991b.  Guidance for Water Quality-based Decisions: The TMDL Process. EPA
 19            440/4-91-001. Assessment and Watershed Protection Division, OWRS.
 20
 21      U.S. EPA. 1988. Technical Guidance on Supplementary Stream Design Conditions for
 22            Steady-State Modeling.  Assessment and Watershed Protection Division, OWRS.
 23
 24      U.S. EPA.  1985a,  Guidelines for Deriving Numerical National Water Quality Criteria for
 25            the Protection of Aquatic Organisms.  NTIS PB85-227049.
 26
 27      U.S. EPA.  1985b.  Water Quality Assessment: A Screening Procedure for Toxic and
 28            Conventional Pollutants in Surface and Ground Water.  EPA 600/6-85/002.
 29            Environmental Research Laboratory, ORD.
 30
 31      U.S. EPA.  1984a.  Technical Support Manual: Waterbody Surveys and Assessments for
 32            Conducting Use Attainability Analyses, Volume II: Estuarine Systems. Office  of
 33            Water, U.S. EPA, Washington, DC. '
 34
 35      U.S. EPA.  1984b.  Technical Support Manual: Waterbody Surveys and Assessments for  '
 36            Conducting Use Attainability Analyses, Volume III: Lake Systems.  Office of Water,
 37            U.S. EPA, Washington,  DC.
38
 39  ,    U.S. EPA.  1983a.  Results of the Nationwide  Urban Runoff Program, Volume I, Final
40            Report. NTIS PB84-185552.
41
42      U.S. EPA.  1983b.  Technical Support Manual: Waterbody Surveys and Assessments for
43            Conducting Use Attainability Analyses. Office  of Water, U.S. EPA, Washington, DC.
44
       External Review Draft                    R-8                        December 6, 1996

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                       WORKING DRAFT:  Do NOT CITE OR QUOTE
 1     U.S. EPA.  1979. Methods for the Chemical Analysis of Water and Wastes.  EPA 600/4-79-
 2           020.
 3
 4     USGS, 1982.  United States Geological Survey. Measurement and computation of
 5           streamflow: volume 1: measurement of stage and discharge.  Washington, DC.
 6
 7     USDI, 1984. United States Department of the Interior. Water measurement manual, 2nd
 8           edition. Bureau of Reclamation.  Denver, CO.
 9
10     VanLandingham, S.L.  1982. Guide to the Identification, Environmental Requirements and
11           Pollution Tolerance of Freshwater Blue-Green Algae (Cyanophyta). EPA  600/3-82-
12           073. Environmental Monitoring and Support Laboratory, U.S. EPA, Cincinnati, OH.
13
14     Viessman, Jr., W. and M. Hammer. 1993, Water Supply and Pollution Control.  Fifth
15           Edition.  Harper Collins College Publishers.
16
17     Viessman, Jr., W., J.W.,Knapp, GJL Lewis, and T.E. Harbaugh.  1977. Introduction to
18           Hydrology. Second Edition. Harper and Row Publishers, New York.
19
20     Vollenweider, R.A.  1969. A Manual on Methods for Measuring Primary Production in
21           Aquatic Environments.  Blackwell Scientific Punlications,  Oxford and Edinburgh,
22           England.
23
24     Walker, J.F., S:A. Pickard and W.C. Sonzogni. 1989.  "Spreadsheet Watershed Modeling for
25           Nonpoint-source Pollution Management in a Wisconsin Basin."  Water Resources
26           Bulletin. 25(1): 139-147.
27
28     Weber, C.L. et al.  1989. Short-Term Methods for Estimating the Chronic Toxicity of
29           Effluents and Receiving Waters to Freshwater Organisms. U.S. EPA. Environmental
30           Systems Laboratory. Cincinnati, OH. EPA 600/4-89-001.
31
32     Welch, E.B., R.R. Homer and C.R. Patmont..  1989. "Prediction of Nuisance Periphytic
33           Biomass: A Management Approach."  Water Research. 23(4): 401-405.
34
35     Wetzel, R.G. and G.E. Likens.  1979.  Umnological Analyses. W.B. Saunders Company.
36
37     WPCF.  1989. Combined Sewer Overflow Pollution Abatement.  Manual of Practice No.
38           FD-17. Water Pollution Control Federation, Alexandria, VA.
39
40     Yotsukura. 1968.  As Referenced  in Thomann, R.V., and J. A. Mueller, Principles of Surface
41            Water Quality  Modeling and Control. Harper and Row Publishers, New York (page
42           50).
43
44     Zander, B. and J. Love.  1990. STREAMDOIV and Supplemental Ammonia Toxicity Models.
45           EPA Region Vm, Water Management  Division, Denver, CO.
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                         WORKING'DRAFT:" "DO NOT CITE OR QUOTE
  1     A.     Annotated References on Monitoring
  2
  3           In addition to the monitoring guidance provided in the above sections, many documents
  4     contain information useful in designing a monitoring program for CSO controls.  This section
  5     briefly highlights information from these documents.
  6
  7           •  The Water Environment Federation's Combined Sewer Overflow Pollution
  8              Abatement Manual of Practice No. FD-17 (WPCF 1989) includes discussions on
  9              establishing planning objectives for characterizing receiving waters, their aquatic
 10              life, and meteorologic conditions; identifying critical events; evaluating system load
 11              characteristics; selecting analytic methods; mapping the system; developing the
 12              sampling plan; selecting field sampling procedures; monitoring CSS and
 13              environmental flow; and modeling.
 14                                                                             '
 15           •   Design of Water-Quality Monitoring Systems (Ward et al. 1990) includes insightful
 16              discussions on the design of monitoring plans, the essential role of statistics,
 17              frameworks for designing water-quality information systems, quantification of
 18              information, data analysis, and the documentation of monitoring plans. This
 19              reference also includes four case studies of large-scale and long-term monitoring
20              programs.
21
22           •   NPDES Storm Water Sampling Guidance Document, EPA 833-B-92-001, (EPA
23               1992) details EPA's requirements for monitoring storm water discharges. When
24              such monitoring is required as a condition of a CSS's NPDES permit, monitoring
25               efforts for CSO control  should be coordinated with this required monitoring effort
26               in order to maximize data collection efficiencies and minimize monitoring costs.
27
28            •   A Statistical Method for Assessment of Urban Stormwater Loads, Impacts, and
29               Controls, EPA 440/3-79-023, (Driscoll et al. 1979) discusses approaches for
30               defining the purpose of  monitoring programs; monitoring rainfall; using rainfall
31               data to project and evaluate impacts; selecting monitoring sites; characterizing
32               drainage basins; determining study periods, sampling frequencies, and sampling
33               intervals during storms;  selecting sampling procedures  and sampling parameters;
34               understanding special considerations for monitoring receiving waters; and using
35               continuous monitoring.  It also provides an extensive literature compilation
36           ~    regarding storm water and CSO monitoring.
37
38            •   Data Collection and Instrumentation in Urban Stormwater Hydrology (Jennings
39               1982)  reviews data and instrumentation needs for urban storm water hydrology.
40               This reference considers monitoring strategy design and the collection and use of
41               data to characterize rainfall, other meteorological characteristics, streamflows,
42               receiving water biologies and chemistries,  and land use.
43
       External Review Draft                    R-10                       December 6, 1996

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                         WORKING "DRAFT: "Do NOT CUE OR QUOTE
  1           •   Use of Field Data in Urban Drainage Planning (Geiger 1986) describes rainfall-
  2               runoff processes and data collection constraints, the need to match data collection
  3               to study objectives, the use of data in urban drainage planning, the application and
  4               verification of models used in urban drainage planning, the validity of the design
  5               storm concept, the reliability of storm water simulations, and the real-time use of
  6               monitoring'data in control and sewer system operation.
  7
  8           •   "Water Body  Survey and Assessment Guidance For Conducting Use Attainability
  9               Analyses (UAA)" (EPA.  1983a. In Water Quality Standards Handbook.).  The
10               UAA concepts discussed in this Handbook include useful field sampling methods,
11               modeling, and interpretation approaches in three Technical Support Documents for
12               flowing waters, estuaries, and  lakes (EPA 19835, 1984a, and 1984b).
13
14           •   Several guidance documents that discuss or pertain to EPA's Waste Load
15               Allocation (WLA) process also provide useful information on a wide range of
16               topics that are potentially valuable when planning monitoring programs for CSO
17               control:
18
19               - Guidance for State Water Monitoring  and Waste Load Allocation Programs
20                 (EPA, 1985) includes a chapter on monitoring for water-quality-based controls.
21                 It discusses the process of collecting and  analyzing effluent and ambient
22                 monitoring data in establishing water-quality standards and EPA's
23                 responsibilities in this process. .
24
25               - Handbook—Stream Sampling for Waste Load Allocation Applications (Mills et
26                 al.  1986) addresses sampling considerations for acquiring data on stream
27                 geometry, hydrology, meteorology, water quality, and plug flows.  It also
28                 reviews sampling considerations for gathering data to meet various modeling
29               '  needs.
30
31               - "Nutrient/Eutrophication Impacts," Chapter 2 of Technical Guidance Manual for
32                 Performing Waste Load Allocations, Book IV: Lakes and Impoundments,
33                 (Mancini et al. 1983) primarily emphasizes modeling considerations. However,
34                 this chapter also provides useful introductions to approaches for estimating
35                 loading rates to standing water systems and needs for monitoring data to support
36                 modeling efforts.
37
38               - Technical Guidance Manual for Performing Waste Load Allocations, Book III:
39                 Estuaries, Part 2:  Application ofEstuarine Waste Load Allocation Models
40                 (Martin et al. 1990) includes a chapter on monitoring protocols for calibrating
41                 and validating estuarine WLA models. It reviews the types of data needed,
42                 frequency of collection, spatial coverage,  and quality assurance.
43
44               - Water Quality Assessment:  A Screening Procedure for Toxic and Conventional
45                 Pollutants in Surface and Ground Water (Mills et al. 1985a, b) presents a broad
46                 array of modeling and data management approaches for assessing aquatic fates
47                 of toxic organic substances, waste-load calculations, rivers and streams,
48                 impoundments, estuaries,  and ground waters.


       External Review Draft                    R-ll                       December 6, 1996

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                            WORKING DRAFT:  Do NOT CUE OR QUOTE
  i                                             APPENDIX A
  2
  3
  4                                                Table A-l
  5                       Checklist of Considerations for Documenting Monitoring
  6              Program Designs and Implementation (expanded from Ward et al., 1990);
  7
  8
  9     Sample and Field Data Collection
 10
 11             Pre-Sampling Preparations
 12             	   Selecting personnel and identifying responsibilities
 13             	   Training personnel in safety, confined space entry, and verifying health-care (first-aid and wet-
 14                  weather training, CPR, safety guides,, currency of vaccinations etc.)
 IS             	   Preparing site access and obtaining legal consents
 16             	   Acquiring necessary scientific sampling or collecting permits
 17             _i   Developing formats for field sampling logs and diaries
 18             	   Training personnel in pre-sampling procedures (e.g., purging sample lines, instrument calibration)
 19             	   Checking equipment  availability, acquisition, and maintenance
20             	   Scheduling sample collection  (random? regular? same-time-of-day?)
21             	   Preparing pre-sampling checklist
22
23             Sampling Procedures
24             	   Procedures documentation
25             	   Staff qualifications and training
26             	   Sampling protocols
27             	   Quality-control procedures (equipment checks, replicates, splits, etc.)
28             	   Required sample containers
29             	   Sample numbers and labeling
30             	   Sample preservation (e.g, "on ice" or chemical preservative)
31             	   Sample transport (delivery to laboratory)
32             	   Sample storage requirements
33             	   Sample tracking and chain-of-custody procedures
34             	   Quality control or quality assurance
35             	   Held measurements
36             	   Held log and diary entries
37            	   Sample custody and audit records
38
39             Post-Sample Follow Up
40             	   Filing sample logs and diaries
41             _   Cleaning and maintaining equipment
42             	   Disposing chemical wastes properly
43             	   Reviewing documentation and audit reports
        External Review Draft                       A-l                            December 6, 1996

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                            WORKING DRAFT:  Do Nor CUE OR QUOTE
  1                                          Table A-l (continued)
  2                        Checklist of Considerations for Documenting Monitoring
  3              Program Designs and Implementation (expanded from Ward et ah, 1990);
  4
  5      Laboratory Analysis
  6
  7             Pre-Sample Analysis Preparations
  8             	   Verifying use of proper analytical methods
  9             	   Scheduling analyses
 10             	   Verifying sample number
 11             	   Defining a recording system for sample results
 12             	   Applying a system to track each sample through the lab
 13             	   Maintaining and calibrating equipment
 14             	   Preparing quality control solutions
 15
 16             Sample Analysis
 17             	   Sample analysis methods and protocols
 18             	'  Use of reference samples, duplicates, blanks, etc.
 19             	   Quality control and quality assurance compliance
 20             	   Sample archiving
 21              	   Proper disposal of chemical wastes
 22             	   Full documentation in bench sheets
 23
 24             Data Record Verification
 25              	   Coding sheets, data loggers
 26              	   Data verification procedures and compliance with project plan
 27              	   Verifying analysis of splits within data quality objectives
 28              	   Assigning data-quality indicators and explanations
 29
 30      Data Management
 31
 32              	   Selecting appropriate hardware and software
 33              	   Documenting data-entry practices and data validation (e.g., entry-range limits, duplicate entry
 34                   checking)
 35              	   Data tracking
 36              	   Defining characteristics of data achieving system
 37              	   Developing data-exchange protocols
 38              	   Formatting data for general availability
 39
40      Data Analysis
41
42              	   Selecting software
43              	   Handling missing data and non-detects
44              	   Identifying and using data outliers
45              	   Planning graphical procedures (e.g., scatter plots, notched-box and whisker)
46              	   Parametric statistical  procedures
47              	   Non-parametric statistical procedures
48              	   Trend analysis procedures
49              	   Multivariate procedures
50              	   Quality-control checks on statistical analyses
        External Review Draft                       A-2                           December 6, 1996

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                          "WORKING DRAFT:  Do NOT CITE OR "QUOTE
  1                                        Table A-l (continued)
  2                       Checklist of Considerations for Documenting Monitoring
  3              Program Designs-and Implementation (expanded from Ward et al., 1990);
  4
  5      Reporting
  6
  7             	   Scheduling reports—timing, frequency, and lag times following sampling
  8             	   Designing report contents and formats
  9             	   Designing planned tables and graphics
10             	   Assigning report sign-off responsibility (ies)
11'         	   Determining report distribution recipients and availability
12             	   Planning use of paper and electronic formats
13             	   Presentations
14
15      Information Use
16
17             	   Identifying and applying decision or trigger values, resulting-action
18             	   Implementing construction, control, and/or monitoring design alternatives
19             	   Planning public-release procedures
20
21      General
22
23             	   Contingencies
24             	   Follow-up procedures
25             	   Data management
26             	   Data analysis.
27             	   Reporting.
28             	   Information use.
29
30
31
        External Review Draft                      A-3                          December 6, 1996

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                            WORKING DRAFT;  Do NOT CITE OR QUOTE
  1                                                Table A-2
  2                        Checklist for Reviewing CSO Control Monitoring Plans

  4
  5      CSO Drainage and Sewer System Map
  6
  7              	    up-to-date
  8              	    shows "as-built" sewer system
  9              	    drainage areas with land use information indicated
 10              	    location of major industrial sewer users indicated
 11              _    location of all direct discharge points indicated, including all related CSO, POTW, storm water,
 12                     and industrial discharges into the receiving water
 13v             _    bypass points distinguished from CSOs points with locations indicated
 14              	    locations of CSO quantity and quality monitoring sites indicated
 15              	    receiving waters identified
 16              	    designated and existing uses of receiving waters indicated
 17              	    areas of historical use impairment indicated
 18
 19      CSO Overflow Quantity
 20
 21               	    number of storms to be monitored
 22              	    number of CSO outfalls to be monitored
 23               	    sampling points include major CSOs
 24              _    POTW influent flow to be monitored
 25               	   method of flow measurement adequate
 26               	   frequency of flow measurement during each storm event
 27               	   storm statistics to be reported—mean, maximum, duration
 28               	   storm statistics to be reported for all storms during the study period

 30       CSO Overflow Quality
 31
 32               	   number of storms to be monitored
 33               	    number of CSO outfalls to be monitored
 34               	    sampling points include major CSOs
 35               	    POTW influent quality to be monitored
 36               	    drainage areas representative of entire drainage area for land use and sewer users
 37               	    number of storm events to be monitored
 38               	    method and frequency of sampling  •
 39               	    parameters to be analyzed
40               	    detection limits adequate
41               	    toxicity test conducted
42               	    receiving waters) to be sampled
43               	    aesthetics monitored
        External Review Draft                       A-4                           December 6, 1996

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1
2
3
4
5
6




7
8
9
10
11
12
13'
14
15
\l
18
19
20
21 .
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
APPENDIX B

Table B-l



Data Requirements for Hand-Calculation Techniques Described in WLA Guidance
Documents and Screening Manual (Mills et al.) For Analysis of Conventional

Algal
Predictions AM
Stneter- Without Predictions Algal Effects
PhelpsDO NH3Toricity Nutrient With Nutrient on Daily
Data Requirements Analyses-' Calculations-" Limitations-' Limitations-5 Average DO-C
Hydraulic and Geometric
Data
Flow Rates "X x x x x
Velocity x x x x x
Depth x x x x x
Cross-sectional area x x x x x
Reach length x x x x x



DO x
CBOD, NBOD x
NH3 x
Temperature x x x x x
Inorganic P x x x
Inorganic N x x x
Chlorophyll a x x x
pH x

DO/BOD Parameters
Restoration rate coefficient x *
Sediment Oxygen Demand x
CBOD decay rate x
CBOD removal rate x
NBOD decay rate x
NH3 oxidation rate x *
Oxygen per unit
chlorophyll a
Algal oxygen production x
rate
Algal oxygen respiration x
rate

Pollutants



Algal Effects
on Diurnal
DO-«


x
x
X
X
X






X
X
X
X



X




X







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December 6, 1996

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1
2
3
4
5




6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
26
27
28
29
30
31
32
33
34
35
36
37
38
Table B-l (Continued)

Data Requirements for Hand-Calculation Techniques Described in WLA Guidance
Documents and Screening Manual (Mills et al.) For Analysis of Conventional


Algal
Predictions Algal
Streeter- Without Predictions Algal Effects
PhelpsDO NH3Toxicity Nutrient With Nutrient on Daily
Data Requirements Analyses-' Calculations-11 Limitations-' Limitations-' Average DO-'
Phytoplankton Parameters
Maximum growth rate x x x
Respiration rate x x x
Settling velocity x x x
Saturated light intensity x x x
Phosphorous half-saturation constant x x
Nitrogen half-saturation x x
constant
Phosphorous to chlorophyll x x x
ratio
Nitrogen to chlorophyll x x x
ratio

Light Parameters
Daily solar radiation x x x x
Photo period x x x x
Lieht extinction coefficient x x x x
v CiwMfpr.PH^Inc TVI calnilntiMic &n* jfacnrihml in fhaiw^r 1 nf Rrvtlr Tl t\f tlw V/T A oniiflan**^ jliti'iniimiiL fTaM* 1_1^
and the Screening Manual (Mills et aL).

" Ammonia torichy calculations are described in Chapter 1 of Book Eof the WLA guidance documents. •

Pollutants




Algal Effects
on Diurnal
DO-'

x
x
X
x
X
X

X

X











c> Algal predictions and their effects on DO are discussed in Chapter 2 of Book n of the WLA guidance
documents.
.
* Flow rates are needed for the river and all point sources at various points to define nonpoint flow.

e) Constituent concentrations are needed at the upstream boundary and all point sources.







, ° Chlorophyll a concentrations are also needed at the downstream end if the reach to estimate net growth rates.
External Review Draft
B-2
December 6, 1996

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                      WORKING DRAFT: "Do NOT CITE OR QUOTE
  i
  2
  3

  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 IS
 19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
                          Table B-2
              Model Input Parameters for Qual-2E
Input Parameter
Variable
by Reach
Input Parameter
Variable Variable
by Reach with Time
Dissolved Oxygen Parameters
Reservation rate coefficients
O2 consumption per unit of NH3 oxidation
02 consumption per unit of NO2 oxidation
02 production per unit photosynthesis
O2 consumption per unit respiration
Sediment oxygen demand

Carbonaceous BOD Parameters
CBOD decay rate
CBOD settling rate

Organic Nitrogen
Hydrolize to ammonia

Ammonia Parameters
Ammonia oxidation rate
Benthic source rate

Nitrite Parameters
Nitrite oxidation rate

Nitrate Parameters
None

Organic Phosphorous
Transformed to diss. p

Phosphate Parameters
Benthic source rate

Phytoplankton Parameters

Yes




Yes


Yes
Yes


Yes


Yes
Yes


Yes





Yes


Yes

•
Nonconservattve Constituent Parameters
Decay rate

Meteorological Data
Solar radiation
Cloud cover
Dry bulb* temperature
Wet bulb temperature
Wind speed
Barometric pressure
Elevation
Dust attenuation coefficient
Evaporation coefficient

Stream Geometry Data
Iross-sectional area vs. depth
Reach length

Hydraulic Data (Stage-flow Curve Option)
Coefficient for stage-flow equation
Exponent for stage-flow equation
Coefficient for velocity-flow equation
Exponent for velocity-flow equation

'iydraulic Data (Manning's Equation Option)
tanning's n
Jottom width of channel
Side slopes of channel
Thflnn*?! slope

Flow Data
Jpstream boundaries















Yes
Yes


Yes
Yes
Yes
Yes


Yes
Yes
Yes
Yes


Yes




Yes
Yes
Yes
Yes
Yes
Yes






















      External Review Draft
                            B-3
                                 December 6, 1996

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                       WORKING DRAFT:  Do NOT CITE OR QUOTE
  i
  2
  3
  4

  5
  6
  7
  8
  9
10
11
12
13
14
15
16
17
18
19
                     Table B-2 (continued)
              Model Input Parameters for QuaI-2£
Input Parameter
Variable
by Reach
Input Parameter
Variable Variable
by Reach with Time
Maximum growth rate
Respiration rate
Settling rate
Nitrogen half-saturation constant
Phosphorous half-saturation constant
Light half-saturation constant
Light extinction coefficient
Ratio of chlorophyll a to algal biomass
Nitrogen fraction of algal biomass
Phosphorous fraction of algal biomass

Covjom rorofneters
Die-off rate


Yes



Yes
Yes




Yes
Tributary inflows
Point sources
Nonpoint sources
Diversions

Constituent Concentrations
Initial conditions
Upstream boundaries
Tributary inflows
Point sources
Nonpoint sources


Yes
Yes
Yes
Yes


Yes
Yes
Yes
Yes









Yes





      External Review Draft
                                                     December 6, 1996

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m                                                              Table B-3
       Comparison of Qual-II With Other Conventional Pollutant Models Used in Waste Load Allocations [Adapted from (11)]
                  Temporal Variability
                 Water
        Model    Quality    Hydraulics
                                                                         Process Simulated
  Variable                    Spatial
Loading Rated  Types of Loads  Dimensions    Water Body
Water Quality
 Parameters
   Model
Chemical/Biological    Physical
DOSAG-I
SNS1M
QUAL-II
RECEIV-II
Steady-
state
Steady-
state
Steady-
state or
dynamic
Dynamic
Steady-state
Steady-state
Steady-state
Dynamic
No
No
No
Yes
multiple point
source
Multiple point
sources &
nonpoint sources
multiple point
sources &
nonpoint sources
multiple point
sources
1-D
1-D
I-D
1-D or 2-D
stream network
stream network
stream network
stream network
or well-mixed
estuary
DO. CBOD.
NBOD,
conservative
DO, CBOD.
NBOD,
conservative
DO, CBOD,
temperature,
ammonia, nitrate,
nitrite, algae,
phosphate,
coliforms, non-
conservative
substances, three
conservative
substances
DO. CBOC,
ammonia, nitrate,
nitrite, total
nitrogen,
phosphate,
coliforms, algae,
salinity, one
metal ion
Ist-order decay of
NBOD, CBOD,
coupled DO
Ist-order decay of
NBOD, CBOD.
coupled DO, benthic
demand (s),
photosynthesis (s)
Ist-order decay of
NBOD, CBOD.
coupled DO, benthic
demand (s), CBOD
settling (s), nutrient-
algal cycle
Ist-order decay of
NBOD, CBOD.
coupled DO, benthic
demand (s), CBOD
settling (s), nutrient-
algal cycle
dilution,
advection,
reservation
dilution,
advection,
reservation
dilution
advection,
reservation,
heat balance
dilution,
advection,
reservation
w
      (s) = specified

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                       Table B-4
Methods for Determining Coefficient Values in Dissolved Oxygen
                and Eutrophication Models
Model Parameter
Symbol
                                          Method Determination
Dissolved Oxygen Parameters
Reaeration rate coefficient
O2 consumption per unit of NH3 oxidation
O2 consumption per unit NO2 oxidation
O2 production per unit photosynthesis
(^consumption per unit respiration
Sediment oxygen demand
Carbonaceous BOD Parameters
CBOD decay rate
CBOD settling rate
Ammonia Parameters
Ammonia oxidation rate .
Benthic source rate
Nitrite Parameters
Nitrite oxidation rate
Phosphate Parameters
Benthic source rate

K,
al
a2
a3
a4
KSOD

Kd
K,

KNI
KBEN

K«

KBEP
•
Compute as a function of depth and velocity using an
appropriate formula, or measure in field using tracer techniques.
Constant fixed by biochemical stoichiometry
Constant fixed by biochemical stoichiometry
Literature values, model calibration and measurement by light to
dark bottles and chambers.
Literature values and model calibration .
In situ measurement and model calibration.

'lot CBOD measurements on semi-log paper or measure in
aboratory.
Plot CBOD measurements on semi-log paper and estimate from
steep part of curve.

lot TKN measurements and N03+N03 measurements on semi-
og paper.'
Model calibration.

Jse literature values and calibration, since this rate is much
aster than the ammonia oxidation rate.

dodel calibration.
      External Review Draft
                         B-6
                           December 6, 1996

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                      ^WORKING DRAFT:  Do NOT CITE OR QUOTE
                                    Table B-4 (Continued)
                 Methods for Determining Coefficient Values in Dissolved Oxygen
                                  and Eutrophication Models
                 Model Parameter
                                  Symbol
Method Determination
Phytoplankton Parameters
Growth rate .
Respiration rate
settling rate
Nitrogen fraction of algal biomass
Phosphorous fraction of algal biomass
Half-saturation constants for nutrients
Saturating light intensity or half-saturation '
constant for light

H
r
v,
a5, a6,
a?
as, a9
K..K,
L.OTK,.

Literature values and model calibration, or measure in
using light-dark bottle techniques.
Literature values and model calibration, or measure in
using light-dark bottle techniques.
Literature and model calibration.
Literature values and model calibration or laboratory
determinations from field samples.
Literature values and model calibration or laboratory
determinations from field samples.
Literature values and model calibration.
Literature values and model calibration.

field
field



 5

 6

 7
 8
 9
1?
Note: Literature values for model coefficients are available in ref. (18,19, 20)
       External Review Draft
                                      B-7
        December 6, 1996

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27
28
29
ir\
31)

Table B-5
Summary of Data Requirements for Screening Approach for Metals in Rivers



Data
Hydraulic Data
1. Rivers:
• River flow rate, Q

• Cross-sectional area, A
• Water depth, h

• Reach lengths, x
• Stream velocity, U


2. Lakes:
• Hydraulic residence time,
T
• Mean depth, H
Source data
1. Background
• Metal concentrations, C,

• Boundary flow rates, Q,
• Boundary suspended
solids, Su


• Silt, clay fraction of
suspended solids
• Locations
2. Point Sources
• Locations
• Flow rate, Qw
• Metal concentration, Q,
• Suspended solids, Sw

Calculation
Methodology
Where Data
are Used* Remarks


D, R, S, L An accurate estimation of flow rate is very important because of
dilution considerations. Measure or obtain from USGS gage.
D,R,S
D, R, S, L The average water depth is cross-sectional area divided by the surface
width.
R,S
R, S The required velocity is distance divided by travel time. It can be
approximated by Q/A only when A is representative of the reach being
studied.

L Hydraulic residence times of lakes can vary seasonally as the flow rates
through the lakes change.
L Lake residence times and depths are used to predict settling of
absorbed metals in lakes.
-

D, R, S, L Background concentrations should generally not be set to zero without
justification.
D, R, S, L
D, R, S, L One important reason for determining suspended solids concentrations
is to determine the dissolved concentration, C, of metals based on Cp
S, and Kp. However, if C is known along with C,. and S, this
information can be used to find K,,.
L

D, R, S, L •

D, R, S, L
D, R, S, L
D, R, S, L
D, R, S, L

External Review Draft
B-8
December 6, 1996

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                                      Table B-5 (continued)
       Summary of Data Requirements for Screening Approach for Metals in Rivers
 Bed Data
 •   Depth of contamination
             For the screening analysis, the depth of contamination is most useful
             during a period of prolonged scour when metal is being input into the
             water column from the bed.
    Porosity of sediments, n
    Density of solids in sediments (e.g.,2.7 for sand) u,
    Metal concentration in bed during prolonged scour period, Q
Derived Parameters
•   Partition coefficient, K,     All
    Settling velocity, w,
SJL
•   Resuspension velocity, WB' R
The partition coefficient is a very important parameter. Site-specific
determination is preferable.
This parameter is derived based on suspended solids vs. distance
profile.
This parameter is derived based on suspended solids vs. distance
profile.
Equilibrium Modeling
•   Water quality              E
    characterization of river
•   pH
•   Suspended solids
•   Conductivity
•   Temperature
•   Hardness

•   Total organic carbon
•   Other major cations  and anions
             Equilibrium modeling is required only if predominant metal species
             and estimated solubility controls are needed.
             Water quality criteria for many metals are keyed to hardness, and
             allowable concentrations increase with increasing hardness.
*D- motion (includes total dissolved and adsorbed phi
R~ dilution and vcsuspension
S-dilution an<^ ^•«»i«*»p
L-lake
               ntration predictions)
        External Review Draft
                                               B-9
                                                  December 6, 1996

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