United States
Environmental Protection
Agency
Office Of Water
(4204)
EPA 832-B-97-001
Draft
?/EPA Combined Sewer Overflows
Guidance For Monitoring
And Modeling
-------
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
-------
intended as guidance only and does not modify or superset the CWAor Agency icgnlations.
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and various tevdsof moang an nong r o
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situation. Mednmandlageconiiiniiiite
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nxHntomgandmodelmgneeds. It is essential that ^ document prodeg^^
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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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External Review Draft
December 6, 1996
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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
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December 6,1996
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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
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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
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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
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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
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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
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1-vii
December 6,1996
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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
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1-viii
December 6,1996
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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,
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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
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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
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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
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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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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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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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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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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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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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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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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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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
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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
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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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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
-------
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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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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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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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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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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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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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
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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
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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
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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
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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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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
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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
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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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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.
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December 6, 1996
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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
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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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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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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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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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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
-------
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
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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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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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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.
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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
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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
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•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
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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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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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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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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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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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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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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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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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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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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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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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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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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.
External Review Draft 6-9 December 6, 1996
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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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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.
External Review Draft 6-11 December 6, 1996
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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.
External Review Draft
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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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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.
External Review Draft 6-14 December 6, 1996
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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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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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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
External Review Draft 7-2 December 6, 1996
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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
External Review Draft 7-4 December 6, 1996
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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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7-5
December 6, 1996
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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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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)
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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
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December 6, 1996
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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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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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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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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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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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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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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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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
-------
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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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)
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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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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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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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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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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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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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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
-------
w
1
EL
CD
0
I
O\
(—»
I
Raingage
4 CSO Outfall Drainage
Area
Not to Scale
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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
-------
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
-------
!
!
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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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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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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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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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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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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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.
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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
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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
o\
VO
g
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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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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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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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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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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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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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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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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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Boat Launch
^upstream ~ "
7Q10 = 313.3 cfs
?*>
cso"
Outfall
River Flow
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Beach
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1
1,200,000
1,000,000
^ 800,000
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2 600,000
O 400,000 -
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200,000 •
.:
0
CSO Events for Example
•*
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, .*_••• ._J ' • • • .
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• • ^s ^— !*•*•§ ••** ii j •*•
5 10 15 20 25 30 3£
Year
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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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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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' 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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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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2
1
Design Flow Analysis
Bacterial Loads to a River
1
Standard
Exceeded
=fcft=
234
CSO flow (cfs)
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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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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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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
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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*
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Monte Carlo Analysis
April Excursions of 1000 MPN Standard
140
O
1 23456789 10 11 12 13 14'l5'l6'17
Number of Events
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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
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u
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.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
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Receiving Water Flow During CSOs
1200000
1 fcUww W
1000000 •
1 UUUUUU
CO?
5f"^* ftnonnn
V i** OUUUUU
0)
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
2
j
i
I
Q
&
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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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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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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.
5 Open-File Report 82-344. USGS, Denver, CO.
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
9
10 Ambrose, R.B., J.P. Connolly, E. Southerland, T.O. Barnwell and LL. Schnoor. 1988. "Waste
11 allocation simulation models." Journal WPCF. 60:1646-1655.
12
13 Ambrose, R.B., J.L. Martin and J.F. Paul. 1990a. Technical Guidance Manual for Performing
14 Waste Load Allocations. Book III: Estuaries. Part 1: Estuaries and Waste Load
15 Allocation Models. EPA 823/R-92-002. U.S. EPA Office of Water.
16
17 Ambrose, R.B. et al. 1990b. Technical Guidance Manual for Performing Waste Load
18 Allocations, Book III: Estuaries, Part 2: Application ofEstuarine Waste Load
19 Allocation Models. U.S. EPA Office of Water.
20
21 Ambrose, R.B., T.A. Wool, J.P. Connolly and R.W. Schanz. 1988b. WASP4, A
22 Hydrodynamic and Water Quality Model - Model Theory, User's Manual, and
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24 Athens, GA.
25
26 American Public Health Association (APHA). 1992. Standard Methods for the Analysis of
27 Water and Wastewater, IS? Edition. Washington, DC.
28
29 American Society for Testing and Materials (ASTM). 1991. Standard Guide for Conducting
30 Sediment Toxicity Tests with Freshwater Invertebrates. ASTM E-1383-94.
31 Philadelphia, PA.
32
33 Association of Metropolitan Sewerage Agencies (AMSA). 1996. Performance Measures for
34 the National CSO Control Program. Washington, DC.
35
36 Bedient, P.B. and W.C. Huber. 1992. Hydrology and Floodplain Analysis. Second Edition.
37 Addison-Wesley Publishing Company, New York.
38
39 Bowie, G.L. et al. 1985. Rates, Constants, and Kinetic Formulations in Surface Water Quality
40 Modeling (2d Edition). EPA 600/3-85/040. Environmental Research Laboratory,
41 Athens, GA
42 .
43 Brown, D.S. and JD. Allison. 1987. MINTEQA1, An Equilibrium Metal Speciation Model:
44 User's Manual. EPA 600/3-87/012.
45
External Review Draft R-l December 6, 1996
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WORKING DRAFT: Do NOT CITE OR QUOTE
1 Brown, L.C. and T.O. Barnwell. 1987. The Enhanced Stream Water Quality Model QUAL2E
2 and QUAL2E-UNCAS: Documentation and User's Manual. EPA 600/3-87/007
3
4 Crowder, L.B. 1990. "Community Ecology." in C.B. Schreck and P.B. Moyle (editors).
5 1990. -Methods for Fish Biology. American Fisheries Society, Bethesda, MD. pp 609-
6 632.
7
8 Delos, C.G. et al. 1984. Technical Guidance Manual for Performing Waste Load
9 Allocations, Book II: Streams and Rivers, Chapter 3: Toxic Substances.
10 EPA-440/4-84-022.
11
12 Dennis, W.M. and B.C. Isom (editors). 1984. Ecological Assessment of Macrophyton:
13 Collection, Use, and Meaning of Data. ASTM Special Technical Publication 843.
14 American Society for Testing and Materials, Philadelphia, PA.
15
16 Doneker, RX. and G.H. Jirka. 1990. Expert System for Hydrodynamic Mixing Zone Analysis
17 of Conventional and Toxic Submerged Single Port Discharges (CORMIX1). EPA
18 600/3-90/012.
19
20 Donigian, A.S. Jr. and W.C. Huber. 1991. Modeling ofNonpoint Source Water Quality in
21 Urban and Non-urban Areas. EPA 600/3-91/039. Environmental Research
22 Laboratory, Athens, GA
23
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.
27
28 Driscoll, EX)., T.W. Gallagher, J.L. Mancini, P.A. Mangarella, J.A. Mueller and R. Winfield.
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.
38
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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WORKINGDRAFT: Do NOT CITE OR QUOTE
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.
6 Cornell University Press, Ithaca, NY.
7
8 Fischer, H.B. 1972. "Mass Transport Mechanisms in Partially Stratified Estuaries." Journal
9 of Fluid Mechanics. 53:671-687.
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.
13
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.
16
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
26 Stream Flow Nutrients." Water Resources Bulletin. 23(3): 471-478.
27
28 HEC. 1977. Storage, Treatment, Overflow, Runoff Model "STORM", Users Manual.
29 Computer Program 723-S8-L7520. The Hydrologic Engineering Center, Corps of
30 Engineers, U.S. Army, Davis, CA
31
32 Hinson, M.O. and D. J. Basta. 1982. "Analyzing Surface Receiving Water Bodies." In D.J.
33 Basta and B.T. Bower, eds. Analyzing Natural Systems, Analysis for Regional
34 Residuals - Environmental Quality Management. Resources for the Future,
35 Washington, DC. pp. 249-388.
36
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
2 Loads-Impacts-Controls. EPA-440/3-79-023 (NTIS PB-299185/9).
3
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.
10 Lewis Publishers, Boca Raton, FL. pp. 215-242.
11
12 Jewell, T.K., T.J. Nunno and D.D. Adrian. 1978. "Methodology for Calibrating Stormwater
13 Models." Journal of the Environmental Engineering Division, ASCE. 104:485-501.
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.
21 EPA-600/3-84-066. Environmental Research Laboratory, Athens, GA
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.
26
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
34 Diatoms. EPA 670/4-74-005. National Environmental Research Center, U.S. EPA,
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
3 Assessment Group, Office of Health and Environmental Assessment, U.S. EPA, July
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
13 Quality Models. Technical Bulletin No. 367. National Council of the Paper Industry
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."
24 Water Resources Bulletin. 27(2): 189-200.
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.
External Review Draft R-6 December 6, 1996
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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.
External Review Draft R-9 December 6, 1996
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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
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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
External Review Draft
B-l
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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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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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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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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