EPA-600/2-77-083
April 1977
Environmental Protection Technology Series
STORM WATER MANAGEMENT MODEL:
LEVEL I • COMPARATIVE EVALUATION OF
STORAGE-TREATMENT AND OTHER
MANAGEMENT PRACTICES
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-600/2-77-083
April 1977
STORM WATER MANAGEMENT MODEL:
LEVEL I—COMPARATIVE EVALUATION OF STORAGE-TREATMENT
AND OTHER MANAGEMENT PRACTICES
by
James P- Heaney
Stephan J. Nix
Department of Environmental Engineering Sciences
University of Florida
Gainesville, Florida 32611
Grant No. R-802411
Project Officers
Richard Field Dennis Athayde
Storm and Combined Sewer Section Urban Runoff Program
Wastewater Research Division Non-Point Source Branch
Municipal Environmental Research Laboratory(Cinti.) Water Planning Division
Edison, New Jersey 08817 Washington, D.C. 20460
WATER PLANNING DIVISION
OFFICE OF WATER AND HAZARDOUS MATERIALS
US ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
and
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
US ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research Labora-
tory and the Water Planning Division, Office of Water and Hazardous Materi-
als, US Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views
and policies of the US Environmental Protection Agency, nor does any mention
of trade names or commercial products constitute endorsement or recommenda-
tion for use.
XI
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FOREWORD
The US Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solving and
it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from munici-
pal and community sources, for the preservation and treatment of public
drinking water supplies and to minimize the adverse economic, social, health,
and aesthetic effects of pollution. This publication is one of the products
of that research; a most vital communication link between the researcher and
the user community.
Combined sewer overflows and urban stormwater discharges are a significant
pollution source. This report describes simplified procedures to enable
decision makers to obtain a preliminary estimate of the magnitude of this
pollution source and the associated costs of control.
Francis T. Mayo, Director
Municipal Environmental Research Laboratory
Ned Notzen, Acting Director
Water Planning Division
111
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PREFACE
This report is part of a series of documents on urban stormwater management
which provides analysts with a wide variety of tools for evaluating alterna-
tives ranging from simple desktop procedures as outlined in this report
(Level I analysis) to sophisticated computer-based simulation using the
original Storm Water Management Model (Level IV analysis). The companion
document to this simplified procedure for comparing other management practices
with storage-treatment options would be very useful in supplementing this
report. The other report is titled:
Heaney, J.P., W.C. Huber, and S.J. Nix, Storm Water Management
Model: Level I—Preliminary Screening Procedures, EPA-600/2-76-
275, Environmental Protection Technology Series, USEPA, 1976.
IV
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ABSTRACT
The original USEPA Storm Water Management Model (SWMM) provides a detailed
simulation of the quantity and quality of stormwater during a specified
precipitation event lasting a few hours. This model is widely used. How-
ever, it is too detailed for many purposes. Indeed, a wide range of evalu-
ation techniques ranging from simple to complex procedures are needed. In
particular, the 208 planning effort needs simplified procedures to permit
preliminary screening of alternatives. In response to this need, four
levels of stormwater management models are being prepared. This volume
presents a "desktop" procedure to compare selected alternative control
technologies.
A graphical procedure is described which permits the analyst to examine a
wide variety of control options operating in series with one another or in
parallel. The final result is presented as a control cost function for
the entire study area which is the optimal (least costly) way of attaining
any desired level of control. Given a specification regarding the desired
overall level of control the user can determine the appropriate amount of
each control to apply.
This methodology is applied to Anytown, U.S.A., a hypothetical community
of 1,000,000 people. The results indicate the mix of treatment, storage,
street sweeping, and sewer flushing which attains the specified pollution
control level at a minimum cost.
This report is submitted as part of Grant No. R-802411 by the University of
Florida under sponsorship of the US Environmental Protection Agency. Work
was completed in December 1976.
v
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TABLE OF CONTENTS
Page
FOREWORD iii
PREFACE iv
ABSTRACT v
LIST OF FIGURES ix
LIST OF TABLES xi
LIST OF SYMBOLS xii
ACKNOWLEDGMENTS xv
SECTION
I SUMMARY 1
General Theory and Methodology 1
Control Technologies 2
Application to Anytown, U.S.A 2
II RECOMMENDATIONS 6
III INTRODUCTION 7
IV 208 PLANNING AREAS 9
V GENERAL THEORY AND METHODOLOGY 12
Theory 12
Marginal Analysis 12
Production Theory 13
Methodology 13
VI CONTROL TECHNOLOGIES 26
Street Sweeping 26
Combined Sewer Flushing 36
Catch-basin Cleaning 41
Storage-Treatment 41
VII
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TABLE OF CONTENTS (CONCLUDED)
SECTION
VII APPLICATION TO ANYTOWN, U.S.A 46
Problem Statement 46
Application 48
REFERENCES 65
GLOSSARY 67
APPENDICES
A. Quantity and Quality Analysis 69
B. Working Curves for Application to Anytown, U.S.A. 73
viii
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LIST OF FIGURES
FIGURE Page
1 PRODUCTION FUNCTIONS 14
2 GENERALIZED STORMWATER POLLUTION CONTROL NETWORK 16
3 GRAPHICAL PROCEDURE FOR DETERMINING OPTIMAL CONTROL
STRATEGIES, STEPS 1 AND 2 17
4 GRAPHICAL PROCEDURE FOR DETERMINING OPTIMAL CONTROL
STRATEGIES, STEP 3 20
5 GRAPHICAL PROCEDURE FOR DETERMINING OPTIMAL CONTROL
STRATEGIES, STEPS 4 AND 5 22
6 GRAPHICAL PROCEDURE FOR DETERMINING OPTIMAL CONTROL
STRATEGIES, STEPS 5 (CONCLUDED), 6 AND 7 24
7 STORMWATER POLLUTION CONTROL TECHNOLOGIES - AVAILABILITY
FACTORS EQUAL 1.0 27
8 IMPERVIOUSNESS ASA FUNCTION OF DEVELOPED POPULATION
DENSITY 33
9 SWEEPING AVAILABILITY FACTOR AS A FUNCTION OF DEVELOPED
POPULATION DENSITY 33
10 PRODUCTION FUNCTIONS FOR STREET SWEEPING 34
11 PRODUCTION FUNCTION FOR COMBINED SEWER FLUSHING 38
12 PRODUCTION FUNCTION (ISOQUANTS) FOR STORAGE-TREATMENT,
ATLANTA, GEORGIA 44
13 TOTAL COST CURVE FOR STORAGE-TREATMENT, STORM SEWERED
AREAS, ATLANTA, GEORGIA 45
14 STORMWATER POLLUTION CONTROL NETWORK FOR ANYTOWN, U.S.A.-
AVAILABILITY FACTORS EQUAL 1.0 49
15 MARGINAL COST CURVES FOR THE PARALLEL OPTIONS, STORM
AREAS MEDIUM AVAILABILITY FACTORS 51
IX
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LIST OF FIGURES ( CONCLUDED )
FIGURE
16 TOTAL COST CURVES FOR THE PARALLEL OPTIONS, STORM AREAS ... 52
17 TOTAL COST CURVE FOR STORAGE-TREATMENT, STORM AREAS 54
18 ISOQUANTS OF THE OVERALL FRACTION OF BOD REMOVED, STORM
AREAS - - HIGH AVAILABILITY FACTORS 55
19 ISOQUANTS OF THE OVERALL FRACTION OF BOD REMOVED, STORM
AREAS - - MEDIUM AVAILABILITY FACTORS 56
20 ISOQUANTS OF THE OVERALL FRACTION OF BOD REMOVED, STORM
AREAS LOW AVAILABILITY FACTORS 57
21 TOTAL COST CURVE FOR ALL OPTIONS, STORM AREAS HIGH
AVAILABILITY FACTORS 58
22 TOTAL COST CURVE FOR ALL OPTIONS, STORM AREAS MEDIUM
AVAILABILITY FACTORS ... 59
23 TOTAL COST CURVE FOR ALL OPTIONS, STORM AREAS LOW
AVAILABILITY FACTORS 60
24 TOTAL COST CURVES FOR ALL DRAINAGE SYSTEM SERVICE AREAS . . 64
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LIST OF TABLES
TABLE Page
1 ANNUAL COST OF OPTIMAL STRATEGY FOR ANYTOWN, U.S .A. , PRESENTED
BY TYPE OF SEWERAGE SYSTEM - MEDIUM AVAILABILITY FACTORS . . 4
2 ANNUAL COST OF OPTIMAL CONTROL STRATEGY FOR ANYTOWN,
U.S.A., PRESENTED BY TYPE OF CONTROL TECHNOLOGY FOR DIFFERENT
ASSUMED AVAILABILITY FACTORS 5
3 COMPARISON OF ANNUAL COST OF OPTIMAL CONTROL STRATEGY FOR
ANYTOWN, U.S.A. USING STORAGE-TREATMENT ALONE AND IN
COMBINATION WITH OTHER MANAGEMENT PRACTICES 5
4 PERCENT OF STREET POLLUTANTS IN VARIOUS PARTICLE SIZE
RANGES 29
5 BRUSH-TYPE SWEEPER EFFICIENCY FOR VARIOUS PARTICLE SIZE
RANGES 30
6 AVERAGE VALUES OF GUTTER LENGTH 37
7 UNIT COSTS OF STREET SWEEPING 37
8 EXAMPLE PROBLEM EVALUATING CATCH-BASIN PERFORMANCE .... 42
9 LAND USE AND POPULATION CHARACTERISTICS OF ANYTOWN, U.S.A. 47
10 ANNUAL WET- AND DRY-WEATHER FLOWS AND BOD LOADS FOR ANYTOWN,
U.S.A 50
11 OPTIMAL STRATEGY FOR 25, 50, 75, AND 85 PERCENT OVERALL BOD
REMOVAL, ANYTOWN, U.S.A. - HIGH AVAILABILITY FACTORS .... 61
12 OPTIMAL STRATEGY FOR 25, 50, 75, AND 85 PERCENT OVERALL BOD
REMOVAL, ANYTOWN, U.S.A. - MEDIUM AVAILABILITY FACTORS ... 62
13 OPTIMAL STRATEGY FOR 25, 50, 75, AND 85 PERCENT OVERALL BOD
REMOVAL, ANYTOWN, U.S.A. - LOW AVAILABILITY FACTORS .... 63
XI
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LIST OF SYMBOLS
A Area served by option p, ac
A Area served by combined sewers to be flushed, ac
SF
A Area to be swept, ac
Sw
AR Annual runoff, in/yr
a(i,j) Coefficient for storm and unsewered areas for pollutant j on
land use i, Ib/ac-yr-in
3(i,j) Coefficient for combined areas for pollutant j on land use i,
Ib/ac-yr-in
C Cost per unit of effort, $/X -yr
C Cost per mile of sewer flushed, $/mile
SF
C Cost per curb mile swept, $/curb-mile
o W
CF Total cost function for option p
DD Daily dust and dirt accumulation rate, Ib/day
DS Annual depression storage, in/yr
DWF Dry-weather flow, in/yr
e "Pick-up" efficiency of the street sweeping equipment
F Pounds of pollutant per pound of dust and dirt
f.(PD,) Population density function for land use i
G Gutter density, curb-miles/ac
I Total imperviousness, percent
Ig Imperviousness due to streets only, percent
Mpg Combined sewer deposition pollutant (BOD) load, Ib/yr
XII
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LIST OF SYMBOLS (CONTINUED)
M_ Pollutant load in area served by option p, Ib/yr
M" Pollutant load available to option p, Ib/yr
Pollutant load available to all parallel options , Ib/yr
MW Wet-weather pollutant (BOD) load, Ib/yr
MC Marginal cost per pound of pollutant removed by option p, $/lb
MC Composite marginal cost per pound of pollutant removed by the
parallel options , $/lb
MF Marginal cost function for option p
MF Composite marginal cost function for the parallel options
HL Annual dry-weather BOD load, Ib/ac-yr
TIL BOD load of combined sewer deposition, Ib/ac-yr
m Unit pollutant load in area served by option p, Ib/acre-yr
P
m^ Annual wet-weather pollutant (BOD) load, Ib/ac-yr
N_ Number of dry days since the last storm
N Number of days between street sweepings
O
n Number of times the streets were swept since the last storm
P Annual precipitation, in
P Total pollutant at the beginning of the storm, Ib
P Pollutant remaining at the end of the last storm, Ib
o
PD, Population density in the developed area, persons/ac
PF Production function for option p
4> Fraction of pollutant load available to option p (0 < (j> < 1.0)
4> Fraction of wet-weather BOD load available for flushing
SF (0£4>SFii.o)
Fraction of wet-weather BOD load available for sweeping
SW
Kill
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LIST OF SYMBOLS (CONCLUDED)
W Net pollutant (BOD) discharge, Ib/yr
EJ
W Pollutant removal by option p, Ib/yr
W Pollutant removal by the parallel options , Ib/yr
II
W BOD load in deposition removed by daily sewer flushing, Ib/yr
SF
W Wet-weather BOD removed by sweeping, Ib/yr
o -L
X Input vector
X Level of effort for process p (0 < X < 1.0)
p — P -
X Fraction of combined sewerage system components flushed daily
SF (o < XSF < i.o)
X Input vector to storage-treatment option (0 <_ X £ 1.0)
o 1 £> -I
X Fraction of days per year an area is swept (0 £ X £ 1.0)
Y Output vector
Y Fraction of available pollutant load removed by option p
P (0 < Y < 1.0)
— p —
Y Fraction of pollutant removed by the parallel options
(o i YIZ £ i.o)
Y, Fraction of pollutant removed by the serial operation
^ (0 < Y, < 1.0)
— ^ —
Y Fraction of available BOD removed by flushing (0 < Y < 1.0)
Y Fraction of BOD removed by storage-treatment (0 < Y < 1.0)
o -L
YSW Fraction of available BOD removed by sweeping (0 £ Y < 1.0)
r" o W
Z Total cost for process p, $/yr
Z^ Composite total cost of the parallel options , $/yr
zty Composite total cost of the serial operation, $/yr
ZSF Total cost of combined sewer flushing, $/yr
ZST Total cost of storage-treatment, $/yr
ZSW Total cost of sweeping, $/yr
xiv
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ACKNOWLEDGMENTS
Numerous individuals were very helpful in formulating and conducting
specific phases of this study. Dennis Athayde, Richard Field, and Pat
Waldo of USEPA provided many valuable suggestions and overall review. Dr.
William Pisano of Energy and Environmental Analysis, Inc. provided informa-
tion regarding their sewer flushing studies in Boston. George Hinkle and
Richard Sullivan of the American Public Works Association provided data
on street sweeping. John Lager of Metcalf and Eddy, Inc. provided informa-
tion regarding catch-basin cleaning. Dr. Wayne C. Huber, -University of
Florida, reviewed an earlier draft of this document.
xv
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SECTION I
SUMMARY
Analysis of wet-weather pollution control alternatives is much more compli-
cated than the traditional dry-weather sewage problem due to the highly
variable flow and the much broader range of options to be evaluated. The
highly variable nature of the flows requires statistical characterization
of the properties of the runoff hydrographs and pollutographs using averaging
times ranging from a single storm event to an annual series. The range of
control options has been extended from examining only storage and treatment
devices to inclusion of other management practices, e.g., street sweeping,
sewer flushing, catch-basin cleaning. These units operate in series and/or
in parallel with one another.
This report provides a simplified methodology for evaluating these other
management practices in conjunction with storage-treatment options. A
graphical solution technique is used to evaluate wet-weather control alter-
natives for Anytown, U.S.A., a typical U.S. city of 1,000,000 people. The
results demonstrate the technique and provide a preliminary indication
regarding the relative competitiveness of the various control options.
GENERAL THEORY AND METHODOLOGY
The optimal combination of storage-treatment devices and other management
practices for wet-weather pollution control can be determined using marginal
analysis from economic theory, and a graphical solution procedure. Marginal
analysis indicates that more intensive use should be made of control alter-
natives with lower marginal costs, measured in dollars per pound of pollu-
tant removed. As these activities are expanded, marginal costs increase to
the point where other options become competitive. The entire analysis can
be viewed as determining, at any specified marginal cost, the quantity of
pollution which the various control options, in parallel, would offer to
control. These results, for all options in parallel, are combined to yield
a composite control cost curve. Then this composite option is evaluated
with the downstream option(s) in series with it to yield the final result.
The solution is guaranteed to be optimal because every option produces a
diminishing marginal value of pollution control as its level of effort is
expanded. For example, if sewer flushing is to be used as a control alter-
native the initial monies will be spent where it is most effective, e.g.,
cleaning the pipes with the heaviest deposition rate. As more money is
spent, controls would be used on progressively cleaner sections of pipe.
Thus, the pollution control effectiveness, per dollar invested, would
1
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decrease. Also, constant unit control costs are assumed. As a consequence,
marginal costs Increase thereby guaranteeing that the control cost functions
are convex and the resulting graphical solution is the optimal one.
CONTROL TECHNOLOGIES
For the purposes of this study, four technologies were considered: street
sweeping combined sewer flushing, catch-basin cleaning, and storage-
treatment Only combined sewered areas utilize all four technologies.
Storm sewered areas do not require sewer flushing. In addition to flush-
ing, unsewered areas do not use catch-basin cleaning or street sweeping
if it is assumed that there are no gutters.
For street sweeping, an overall BOD removal efficiency of 0.5 is assumed.
The assumed unit cost is $7.00/curb-mile swept ($4.35/curb-km). The per-
formance of sweepers was estimated, for varying sweeping intervals and
removal efficiencies, using a continuous simulation of one year of data
for Minneapolis. A modified version of the street sweeping procedure
described in SWMM was used.
Data on combined sewer flushing were obtained from studies in Boston, Mass.
The results of these efforts indicated that a relatively small percentage
of the pipes retain a substantial amount of the total deposition. The
assumed annual costs of flushing per unit length of sewer line is $11.78/ft
($38.64/m). Daily flushing is assumed to remove 100 percent of the BOD
deposited in the affected pipes.
Catch basins were found to be relatively ineffective as a wet-weather pollu-
tion control device due to their relatively small size in relation to the
contributing drainage area. Thus, they were not investigated further.
The procedure for evaluating storage-treatment technologies was presented
in our earlier work. Thus, this control technology was not discussed in
detail.
APPLICATION TO ANYTOWN, USA
The methodology was applied to a hypothetical urbanized area, called Any-
town, which has characteristics typical of the 248 urbanized areas in the
US as listed below:
(1) Population Density (urbanized area): 5.14 persons/ac
(12.70 persons/ha)
(2) Mean Annual Precipitation: 33.4 in (84.8 cm)
(3) Land Use Percentage (urbanized area): residential, 31.4%;
commercial, 4.6%; industrial, 8.0%; other developed, 9.8%;
undeveloped, 46.2%.
2
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(4) Land Use Percentage (developed areas only): residential,
58.4%; commercial, 14.8%; industrial, 8.6%; other
developed, 18.2%.
(5) Percent of Developed Area Served by Type of Drainage
System: combined sewers, 14.4%; storm sewers, 38.3%;
unsewered, 47.3%.
(6) Population Density of the Developed Area by Type of
Drainage System—person/ac (persons/ha): combined,
16.7 (41.3); storm, 13.0 (32.1); unsewered, 4.6 (11.4);
all developed areas, 9.6 (23.7).
The results of this analysis, presented by type of sewerage system, are
shown in Table 1. Although the combined sewered area comprises less than
15 percent of the land area, about 40 percent of the total costs are
incurred for this area because the loadings are higher and it is more cost-
effective to control this portion of the total load.
A breakdown of total control costs, by type of technology and assumed
availablility factors, is presented in Table 2. For the medium availability
factors, storage-treatment is used for about 80 percent of total control.
As expected, sweeping and flushing gain in relative importance as the
availability factors increase. This effect is most pronounced for street
sweeping. This type of sensitivity analysis is quite helpful in providing
an indication of the importance of reliable estimates of the availability
factors.
Lastly, the significance of the savings resulting from using management
practices other than storage-treatment are evaluated in Table 3. The
results indicate savings (relative to using storage-treatment only) of 6
percent, 21 percent, or 37 percent for 50 percent control for low, medium,
and high availability factors, respectively. These results definitely
indicate the need to evaluate all available control options in area-wide
wastewater management planning.
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TABLE 1. ANNUAL COST OF OPTIMAL STRATEGY FOR ANYTOWN, U.S.A., PRESENTED
BY TYPE OF SEWERAGE SYSTEM - MEDIUM AVAILABILITY FACTORS
Type
of
System
Combined
Storm
Unsewered
Total
Acreage
ac(ha)
15,100
(6,110)
40,100
(16,230)
49,500
(20,030)
104,700
(42,370)
Total Annual Cost ($ x 10 /yr)
for Indicated % BOD Control
25% 50% 75% 85%
0.48 1.65 4.50 7.86
0.12 0.82 3.56 7.43
0.56 1.42 2.82 2.82
1.16 3.89 10.88 18.11
Q
Anytown has a population = 1,000,000
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TABLE 2. ANNUAL COST OF OPTIMAL CONTROL STRATEGY FOR ANYTOWN, U.S.A., PRESENTED BY TYPE OF
CONTROL TECHNOLOGY FOR DIFFERENT ASSUMED AVAILABILITY FACTORS.
Total Annual Cost ($ x 10 /yr) for Indicated % BOD Control and Assumed Availability Factors
Type of
Control
Technology Low
25%
Med
High
50%
Low Med High
Low
75%
Med
High
85%
Low Med High
Sweeping
Flushing
Storage-
Treatment
0 0.16 0.24
0.14 0.14 0.18
1.18 0.86 0.43
0.21 0.59 0.88
0.17 0.21 0.28
4.25 3.09 1.95
0.56 1.45 2.84
0.26 0.57 0.60
11.50 8.86 5.25
0.94 2.58 3.80
1.01 0.69 0.82
19.31 14.84 9.72
TOTAL
1.32 1.16 0.85
4.63 3.89 3.11
12.32 10.88 8.69
21.26 18.11 14.34
TABLE 3. COMPARISON OF ANNUAL COST OF OPTIMAL CONTROL STRATEGY FOR ANYTOWN, U.S.A., USING
STORAGE-TREATMENT ALONE AND IN COMBINATION WITH OTHER MANAGEMENT PRACTICES.
Annual Cost ($ x 10 /yr)
%BOD Storage-
Control Treatment(S-T)Only
Storage-Treatment and
" Other Options
Low
Medium
High
% Savings Over Storage-
Treatment Only
Low
Medium
High
25
50
75
85
1.47
4.95
13.39
22.42
1.32
4.63
12.32
21.26
1.16
3.89
10.88
18.11
0.85
3.11
8.69
14.34
10
6
21
21
19
19
42
37
35
36
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SECTION II
RECOMMENDATIONS
This simplified methodology for evaluating urban stormwater pollution con-
trol alternatives is intended to serve as a preliminary screening device.
It requires neither a computer nor an understanding of more refined analyti-
cal solution procedures. After the user understands the concepts and pro-
cedures, he may wish to substitute the appropriate analytical procedures
using derived functions.
The results indicate significant savings if other management options are
combined with storage-treatment options. Further savings can be realized
by recognizing that a significant portion of the control costs can be
assigned to other purposes.
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SECTION III
INTRODUCTION
In recent years there has been the realization that stormwater from urban
areas is a serious water pollution source. Abatement of this source will
require a monumental effort in research, development, and implementation.
In this study, a simple methodology is developed which provides a "first-
cut" evaluation of the problem and the optimal control strategy.
Several technologies are available to control stormwater pollution. At
present, emphasis is placed on storage-treatment control techniques [1].
However, other techniques are available, e.g., street sweeping, sewer
flushing. These methods, used in conjunction with storage-treatment, may
provide a more cost-effective pollution management package [2, 3, 4, 5, 6].
The resultant optimal mix of all control options is often referred to as
"Best Management Practice" or BMP's.
With the potential control effectiveness of options other than storage-
treatment established, the need has arisen for a methodology capable of
determining, on a "first-cut" basis, the most cost-effective usage of
these other options in conjunction with (or exclusive of) storage-treatment
in the urbanized area. "First-cut" or preliminary analyses establish the
magnitude of the problem and rapidly evaluate alternatives. This study
derives a relatively simple methodology to obtain this "first-cut."
Several analytical techniques which can provide an optimal "mix" of control
alternatives are available. Many require the use of computerized algorithms
which defeat the need for simplicity. Nearly all require an accurate knowl-
edge of the functional form of empirically derived relationships. A simple
methodology was developed by Heaney, Huber, and Nix [7] but was limited to
storage-treatment as a control alternative.
A graphical technique is chosen to provide a preliminary estimate of an
optimal stormwater pollution control strategy. Graphical solution tech-
niques do have drawbacks. They are relatively time consuming and more
susceptible to human error. Nevertheless, there are definite advantages.
Computational aides are not necessary and complex analytical procedures are
avoided.
The next section presents a generalized description of a typical 208 plan-
ning area. Section V describes the procedure used to obtain an optimal
strategy along with the economic theories used to derive the methodology.
This procedure is applicable to a wide variety of stormwater pollution
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control networks. Section VI discusses the various control technologies and
develops the production functions and cost equations necessary for the
methodology of Section V. Section VII is an application of the methodology
to a hypothetical urban area known as Anytown, USA. Anytown is given the
characteristics found for urbanized areas around the nation [1]. The opti-
mal integrated control package is determined for this hypothetical situation.
Appendix A presents a simplified method for estimating wet-weather quantity
and quality. Equations to estimate dry-weather quantity and quality are
also given for comparative purposes. Lastly, working curves for the applica-
tion to Anytown are placed in Appendix B.
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SECTION IV
208 PLANNING AREAS
The Federal Water Pollution Control Act Amendments of 1972 (PL92-500) are a
comprehensive piece of legislation designed to implement a procedure by
which virtually all sources of pollution to the nation's waters are to be
eliminated and the purity of these waters restored [8]. The pollutants are
discharged from both urban and rural areas and from point and nonpoint
sources. Several goals were set forth by the Act:
(1) that the discharge of pollutants into navigable waters
be eliminated by 1985;
(2) that a level of water quality be attained by July 1,
1983, that provides for the protection of aquatic
life, wildlife, and recreation; and
(3) that areawide water quality management planning
processes be developed and utilized.
Other provisions include funding for the necessary research and to aid in
the implementation of management plans.
Section 208 of the Act sets overall guidelines for the development of area-
wide planning processes. The US Environmental Protection Agency, designated
to carry out the intent of the Act, has published specific guidelines to aid
local authorities in attaining the overall goals [9]. These guidelines
state that the 208 planning procedure should proceed along the following
lines:
(1) Identify the problems in meeting the 1983 goals of
the Act.
(2) Identify all constraints and priorities pertaining to
the 208 planning area.
(3) Identify all possible solutions to the problems.
(4) Develop alternative plans to meet the statutory
requirements.
(5) Analyze the alternative plans for technologic and
economic feasibility.
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(6) Select an areawide plan.
(7) Seek approval for the plan.
(8) Periodically update the plan.
The selection of a specific plan should be based on cost effectiveness,
feasibility, and public acceptance.
An important portion of the selected plan should be involved with the con-
trol of stormwater pollutant discharges. EPA guidelines specifically state
the need for "an analysis of the magnitude of existing and anticipated urban
stormwater problems" [9]. Additionally, techniques to better manage the
existing drainage systems, thus preventing discharges at the source, and/or
improved methods for the storage and treatment of urban runoff, should be
developed.
Areawide management is conducted at the local level. In general, areawide
plans should be developed for a region relatively homogeneous in its waste-
water problems and ultimate discharge locations. Such an area will include
one or several urbanized areas which are of primary concern to this study.
In order to conduct an analysis of stormwater discharges from these areas
and potential control strategies, a comprehensive inventory of the charac-
teristics of each should be available. For the preliminary or "first-cut"
analysis conducted in this study, these characteristics should include
land use, sewerage system service areas and population served by each, and
the mean annual precipitation.
A definition of an urbanized area is needed to properly delineate the areas
of potential urban stormwater discharge. The U.S. Census describes an
urbanized area as follows [10]:
(1) A central city (or adjacent cities) of 50,000 or more
inhabitants.
(2) Settled areas in close proximity to the central city,
including the following:
a. Incorporated areas of 2,500 or more inhabitants
or less than 2,500 if the area includes 100 or
more closely settled housing units.
b. Small parcels of land with a population density
greater than 1,000 (386) inhabitants per square mile (km).
c. Other small parcels of unincorporated land with
less than the required population density that
eliminate enclaves.
With this definition, the local planner can divide the urbanized acreage
among five land use categories: residential, commercial, industrial, other
developed (parks, institutions, etc.), and undeveloped. The definition of
10
-------
an urbanized area allows for the inclusion of large areas of undeveloped
lands not likely to be developed in the planning future. These areas should
not be included in the following analysis. Additionally, the planner should
delineate the area and population served by combined and storm drainage
systems and unsewered areas within the remaining developed (or developing)
area. With these data, the following graphical procedures may be applied
to provide a "first-cut" evaluation of the urbanized area's stormwater
problem and optimal control strategy.
11
-------
SECTION V
GENERAL THEORY AND METHODOLOGY
This section presents the economic theories and general methodology neces-
sary to determine an optimal stormwater pollution control strategy. The
discussion is based heavily on production theory and marginal analysis from
economics.
THEORY
Marginal Analysis
In its simplest ternis, marginal may be defined as "extra." In economic
terms, for example, marginal cost is defined as the extra cost associated
with an additional unit of some commodity. In economic decision making
marginal analysis determines whether an action results in a sufficient
additional benefit to justify the additional cost.
Two basic rules governing the concept of marginal analysis are [11] :
(1) The scale of an activity should, if possible, be
expanded so long as its marginal net yield (taking
into account both benefits and costs) is a positive
value; and the activity should therefore be carried
to a point where this marginal net yield is zero.
(2) For optimal results, activities should, whenever
possible, be carried to levels where they all yield
the same marginal returns per unit of effort
(cost).
As an example of rule (2), assume that product A, at a specific production
level, is yielding $1.50 per $1.00 spent and product B is returning $2.00
per $1.00 spent. In this situation the firm is missing the opportunity to
gain $0.50 by not transferring the $1.00 spent to manufacture product A to
product B. Therefore, to assure the maximum return, both products should
be manufactured at levels of equivalent marginal return or yield.
In stormwater pollution control these same concepts apply. Analysts should
seek, in such cases, to utilize various control procedures at levels yield-
ing an equivalent marginal cost.
12
-------
Production Theory
A production process seeks to increase the utility of a commodity or com-
modities. In any such process certain technological relationships restrict
the decision maker's options on input a.nd output levels [12]. Consider an
input vector to a production process, X, defined as
x = (xr x2,..., x±J..., xn). (i)
Similarly, the output vector, Y, is defined as
Y = (Y1, Y2,..., Y .... Ym). (2)
The technological relationship between the input and output vectors, known
as the production function, is
Y = PF (X) (3)
where Y is the maximum output attainable with input vector X. In other
words, any output Y-j may not be increased without a reduction in some other
output Y or an increase in some input X^. Examples of production functions
are shown in Figure 1. The single-input, single-output production function
shown may be viewed as a two-input, single-output function with one input
held constant.
The shape of the production function is governed by the "law" of diminishing
returns which states that, as an input to a production process is increased,
with all other inputs held constant, a point will be reached beyond which
any additional input will yield diminishing marginal output. For example,
if a treatment plant experiences increases in raw sewage flow and no al-
terations are made to the facility, a flow will be reached where an incre-
ment in flow will result in a diminishing increase of pollutant removed.
METHODOLOGY
In this study, a stormwater pollution control option is defined as a unique
set of conditions and control technologies. For example, although a par-
ticular control technology, such as street sweeping, may be used in several
different subareas within an urbanized area, those subareas may have varying
pollutant loading rates which affect the cost-effectiveness of the common
technology. Also, within a particular subarea there may be several distinct
pollutant sources requiring different control technologies.
Knowing the production function for each stormwater pollution control tech-
nology (production process) and with the control options defined, it is
possible to graphically determine an optimal strategy. In the discussion
that follows all production functions have been transformed into a single-
input, single-output form and expressed in terms of the fraction of available
pollutant removed, Y, as a function of the fraction of the level of effort,
X. The definition of level of effort is dependent on the particular tech-
nology. For example, the level of effort for street sweeping is defined
as the fraction of days during a year when sweeping occurs. All production
functions and later functions or graphs are derived on an annual basis.
13
-------
Two-input, single-output
production process
*Y
INPUT I TO PRODUCTION PROCESS, X,
Single-input, single-output
production process
INPUT TO PRODUCTION PROCESS, X,
Figure 1. Production Functions
14
-------
Before delving into the methodology a few more definitions are required.
In stormwater pollution control, options may operate in parallel, series,
or a combination of both. A parallel operation is defined as one in which
the effluent (untreated portion) of any one option does not act as the
influent to any other parallel option. A serial operation is defined as
one in which options are sequential with the effluent from one option acting
as the influent to the next.
A network of series/parallel pollution control options is shown in Figure 2.
In this example four options (p = 1, 2, 3, and 4) operate in parallel
followed by one option (p = 5) operating in series with the parallel group.
The pollutant flows through this network are shown in terms of the pollutant
load in the area served by the parallel options, M^, the fraction of the
pollutant load available to option p, <£>„, and the pounds removed by each
option p, W . The pollutant load available to each option, Mp, is the
product of cf)p and Mp. The pollutant load M^ is shown as the influent to
an imaginary option (p = 4) that has zero pollutant removal capacity. This
simply allows the residual pollutant loads to be routed to option 5 without
passing through the other parallel options. For example, street sweeping
does not reach the entire surface pollutant load of an area. Therefore,
some portion may be washed off by runoff events and routed to a storage-
treatment facility without having the opportunity to be removed by sweeping.
The influent to option 5 is the pollutant load not removed by the parallel
group. This network will serve as an example and reference throughout the
remainder of this section.
Once the production functions are established, the first step is to construct
the total cost curve for each option (see Step 1, Figure 3). Production
functions for several specific pollution control technologies and methods to
develop the total cost curves are discussed in Section VI. However, for
the purposes of generalization, a total cost curve is defined as a function
of the fraction of pollutant removed, i.e.,
Z = CF (Y ) (4)
P P P
where Z = total cost for option p, $/yr;
P
Y = fraction of available pollutant load removed by option p
P (0 < Y < 1.0); and
— p —
CF (Y ) = total cost function in terms of Y .
P P P
Recall that the fraction of available pollutant removed is the dependent
variable of the production function. Thus, to derive the total cost curve,
one only needs to reverse the axes of the production function and develop
the relationship between the level of effort for option p, and the total
cost. Mathematically, this may be stated as
X = PF-1(Y ) (5)
P P P
15
-------
M4' =
M3 =03M3 ? (l' 0P)MP+ M«
W,
M +M + M +M - W -W -W -W
I t O T" I ^ O
LEGEND
M
M
W
= CONTROL PROCESS
= AVAILABLE POLLUTANT LOAD, Ib/yr
= AVAILABILITY FACTOR
= POLLUTANT LOAD , Ib/yr
= POLLUTANT REMOVAL, Ib/yr
Figure 2. Generalized Stormwater Pollution Control Network
16
-------
STEP I : FIND TOTAL COST CURVE FOR EACH OPTION (p = 1,2, 3,4, and 5)
PRODUCTION FUNCTION
m -
aro
u.0-
'max
LEVEL OF EFFORT, Xp
1.0
TOTAL COST CURVE
CO
o
o
Zp - Cp-Xp
0 1.0
FRACTION OF AVAILABLE
POLLUTANT REMOVED , Yp
STEP 2 .- FIND MARGINAL COST CURVE FOR EACH PARALLEL
OPTION (p= 1,2,3, and 4)
TOTAL COST CURVE MARGINAL COST CURVE
a.
rw
tn
O
o
Wp=0p-Mp-Yp /I
a.
o
O
O
<
z
cc
POLLUTANT REMOVED ,Wp , Ib /yr
0 wPmax
POLLUTANT REMOVED,Wp, Ib/yr
Figure 3. Graphical Procedure for Determining Optimal Control
Strategies, Steps 1 and 2
17
-------
where X = level of effort for option p (0 <_ X < 1.0);
Y = fraction of available pollutant load removed by option p
P (0 < Y £ 1.0) ; and
~~ P
PF (Y ) = inverse of the production function for option p.
P P
If total cost is assumed to be a linear function of the level of effort,
then
Z = C • X (6)
P P P
where C = annual cost of option p per unit of effort, $/X .
P P
Substituting equation (5) into equation (6) yields
Z = C • PF~1(Y ). (7)
P P P P
Equation (7) is the desired form of the total cost function (equation 4) .
The next step is to generate the marginal cost curve for each parallel
option (see Step 2, Figure 3). This curve gives the relationship between
the marginal cost per pound of pollutant removed at any level of pollutant
removed. The marginal cost curve is the first derivative of the total cost
curve. However, the total cost curves for the parallel options must be
converted from the fraction of pollutant removed to pounds removed. This
is accomplished using the following equation,
W = M' • Y (8)
P P P
where W = pollutant removal by option p, Ib/yr;
M" = pollutant load available to option p, Ib/yr; and
Y = fraction of available pollutant load removed by option p
P (0 < Y < 1.0).
— p —
The maximum value of W , Wpmax, depend
of option p, Y . The equation used
s on the maximum removal efficiency
p . se to find M^ is
M" = cf ' M (9)
P P P
where A = fraction of pollutant load (M ) available to option p
(0 1
-------
where m = unit pollutant load in area served by option p, lb/ac-yr;
P and
A = area contributing pollutants to option p, ac.
The pollutant load per acre, m^, can be found using methods described in
Appendix A. The normalized version of the total cost curve (equation 4) may
now be written as
Z = CF (W ) (10)
P P P
since only the units of the abscissa of the total cost curve are being
changed. Utilizing equation (10), the marginal cost curve is described
by the following equation,
d(CFp(Wp))
MCP --aw; - = MFP(V (11)
where MC = marginal cost per pound of pollutant removed by
parallel option p, $/lb; and
MF (W ) = the marginal cost function in terms of W .
P P P
Graphically, the marginal cost curve is determined by finding the slope,
AZp/AWp, of the total cost curve at several values of W . These values,
plotted against the values of W , give an approximation of the marginal
cost curve. The marginal cost curves are increasing functions of pounds
of pollutant removed. This result necessarily follows from the earlier
assumptions of a concave production function and constant unit costs.
Once the marginal cost curves are developed for the parallel options, a
composite marginal cost curve may be constructed (see Step 3, Figure 4).
This single curve summarizes the effect of the entire parallel group (p =
1, 2, 3, and 4). This is accomplished by adding the marginal cost curves
with respect to the ordinate of the marginal cost curves. In other words,
at several equivalent values of MCp for the parallel options, the corre-
sponding W ' s are summed. The composite marginal cost curve is
= MF(W) (12)
II
II
where MC = composite marginal cost per pound of pollutant
removed by the parallel options, $/lb;
W = pollutant removal by the parallel options, Ib/yr,
(= W1 + W? + W,,, in the example network); and
MF (W ) = the composite marginal cost function in terms of W .
19
-------
ho
O
STEP 3 : FIND COMPOSITE MARGINAL COST CURVE FOR ALL PARALLEL OPTIONS
(NOTE: OPTION 4 IS IMAGINARY)
MARGINAL COST CURVE ( p; I ) MARGINAL COST CURVE (p = 2) MARGINAL COST CURVE (p=3)
o
o
ac.
eg
o
o
o
z
o
a:
MC
ro
O
CO
o
o
a:
W
'o
W
W
W
max
POLLUTANT REMOVED,W( , Ib/yr
POLLUTANT REMOVED , W2 , Ib/yr
POLLUTANT, REMOVED,
COMPOSITE MARGINAL COST CURVE FOR ALL PARALLEL OPTIONS ( p = 1, 2,3 and 4 )
Figure 4.
POLLUTANT REMOVED BY PARALLEL OPTIONS , W- , Ib/yr
Graphical Procedure for Determining Optimal Control Strategies, Step 3
'3m£3m3
s. ib/yr
-------
The composite total cost curve for the parallel options is constructed
by integrating the composite marginal cost curve (see Step 4, Figure 5),
i.e. ,
max
where Z^ = composite total cost of the parallel options, $/yr;
and
W = maximum pollutant removal by the parallel options
max (W + W + W in the example network), Ib/yr.
max max max
At this point the economic behavior of the parallel group has been condensed
into a single equivalent "option." Therefore, the problem has been reduced
to one with two options in series. Next, the two-option serial operation
is aggregated into a single equivalent "option" representing the entire
example network. Although the procedure will be unique to a two-option
serial operation, this will not limit the number of options in series that
may be analyzed. Any number of options may be aggregated by simply working
with pairs until condensed to one equivalent "option." The previous pro-
cedure for the parallel case may be applied to any number of options.
A two-option serial operation may be viewed as a production "process" with
two inputs and one output. The production function can be described using
isoquants (see Figure 1), i.e., lines of input combinations capable of
producing a constant output and having the following characteristics [12]:
(1) Isoquants cannot intersect. Intersection would
imply that the same input levels are capable of
producing different output levels.
(2) Isoquants slope downward to the right because
increased use of one input requires the lessened
use of the other input.
(3) Isoquants are convex to the origin due to the
inability of one input to be substituted for
another at a specific level of output.
The inputs are the total costs of each option in series and the output is
the fraction of pollutant removed by the serial operation. In this par-
ticular case, the inputs are the composite total costs for the parallel
group, Z , and the total costs for the subsequent option, Z .
Before constructing the isoquants of the fraction removed by the serial
operation, both total cost curves must be in terms of the fraction of
pollutant removed. The curve for option 5 was constructed earlier (see
21
-------
STEP 4 : INTEGRATE COMPOSITE MARGINAL COST CURVE TO OBTAIN
COMPOSITE TOTAL COST CURVE FOR ALL PARALLEL OPTIONS
COMPOSITE MARGINAL COST
CURVE FOR ALL PARALLEL OPTIONS
W.
W
Io "H mox
POLLUTANT REMOVED, W,
MH
, »>/yr
COMPOSITE TOTAL COST CURVE
FOR ALL PARALLEL OPTIONS
>>
\
-w-
<
o
0 WJIo WJTmox Mn
POLLUTANT REMOVED,W , Ib/yr
STEP 5 .- FIND ISOQUANTS OF THE FRACTION OF POLLUTANT
REMOVED BY OPTIONS IN SERIES,
FOR ALL PARALLEL OPTIONS
TOTAL COST CURVE FOR OPTION 5
1=4
M
O
O
<
o
'•max
1.0
FRACTION OF POLLUTANT REMOVED
BY ALL PARALLEL OPTIONS .Y-
FRACTION OF POLLUTANT REMOVED
BY OPTION 5 , Y5
Figure 5. Graphical Procedure for Determining Optimal Control Strategies,
Steps 4 and 5
22
-------
Step 1, Figure 3) and is already in the proper form. The composite total
cost curve for the parallel group was left in terms of the pounds of
pollutant removed (equation 13). The following equation is used to con-
vert to the fraction removed:
where M = pollutant load available to all parallel processes
(= MI + M2 + M3 + M4), Ib/yr.
These curves must be in terms of the fraction removed due to the nature of
the serial operation. Essentially, one input is passing through two op-
tions, as opposed to a parallel operation where each input is independent.
Therefore, the action of one affects the other and it becomes necessary to
optimize the fraction removed by each option and then determine what
quantity of pollutant was removed by each, rather than the reverse.
Constructing the isoquants of the overall fraction of pollutant removed
requires several combinations of Y and Y capable of providing the desired
overall fraction. This is determined by the following equation,
^ II 5 II
where Y, = fraction of pollutant removed by the serial
operation.
Equation (15) states^that the fraction of pollutants removed by the serial
operation is the sum of the removal from the first option, Y , and the
incremental removal due to the second option, Y5(l-Yjj). By noting the Z
and Zr corresponding to the various combinations of YJJ and Y5 from each
of the total cost curves, the isoquants may be drawn (see Step 5, Figures 5
and 6) .
The next step is to develop the optimal expansion path from the isoquants
by constructing points of tangency between the isoquants and isocost lines.
As the name suggests, isocost lines are lines of equal cost. The isocost
lines are given as
Z = Z + Z5 (16)
where Z. = composite total cost of the serial operation, $/yr.
The slope of this linear equation is -1. Therefore, to find the point of
tangency simply requires that the point on the isoquant tangent to a line
of a negative unit slope be located. These points determine the optimal
or least-cost combination of costs from each option. The optimal solution
may fall at a corner point. Connecting these points gives the optimal ex-
pansion path (see Step 6, Figure 6)- The final step is to construct a com-
posite total cost curve for the serial operation. This may be done by
plotting the values of Z, against the corresponding values of Y^ found on
the optimal expansion path (see Step 7, Figure 6). This curve, for the
23
-------
STEP 5
(CONTINUED)
ISOQUANTS OF Yfc/
STEP 6
TOTAL COST , Zg , $
FIND OPTIMAL EXPANSION PATH
ISOQUANTS OF
TOTAL COST, 2g , $/yr
STEP 7 : FfND TOTAL COST CURVE FOR ALL OPTIONS
(p= 1,2,3,4, and 5)
Yfcin
-------
example network shown in Figure 2, represents the final total cost for the
entire network as a function of the overall fraction of pollutant removed.
If there were subsequent options the curve would merely represent a com-
posite of two options in series that could next be combined with the
following process.
The methodology for establishing optimal strategies has been developed. At
this point, a planner could select an overall removal fraction and proceed,
in reverse, through the seven steps shown in Figures 3 through 6 and deter-
mine the optimal operating levels of each option. This is demonstrated by
the example application found in Section VII.
25
-------
SECTION VI
CONTROL TECHNOLOGIES
Section V set up a methodology by which engineers and planners could deter-
mine an optimal strategy with any number of control options. For the
purposes of this study, four technologies will be considered: street
sweeping, combined sewer flushing, catch-basin cleaning, and storage-
treatment. Typically, these technologies operate as shown in Figure 7.
Only combined sewered areas may utilize all four technologies. Storm
sewered areas do not require sewer flushing to remove sanitary sewage
deposition. In addition to flushing, unsewered areas do not have catch
basins or street sweeping since materials are transported to adjacent
pervious areas. (It is assumed that there are no gutters.) For combined
sewered areas the network operates in the following manner. A portion of
the street solids are removed by sweeping and a portion are washed off during
runoff events and partially captured by catch basins which are subsequently
cleaned by artificial means or flushed by a storm surge. The sanitary
sewage deposited in the sewer lines is also flushed artificially or by
storm surges. The pollutants flushed from the catch basins and sewer lines
during storm surges are sent to the wet-weather storage-treatment facility.
The material removed from the catch basins is normally sent to a sanitary
landfill. The material flushed from the sewers is sent to the dry-weather
treatment plant.
This section develops the production function for each technology. Addi-
tionally, the relationships to construct the total cost curves are given.
With this information, the methodology of Section III may be applied to any
urbanized area.
The term "pollutant" has been used almost exclusively up to this point.
However, the pollutant BOD will be the parameter of concern in this and
remaining sections. BOD is the most commonly used indicator of general
water pollution levels. The same method could be used for any other single
pollutant.
STREET SWEEPING
The sweeping of roadways is a long-established practice in American cities.
However, the primary purpose of this activity is the removal of unsightly
debris. Recent studies indicate that a portion of the material found on
the streets (and therefore a potential pollution source during runoff
events) may be removed by .a conscientious sweeping program [4, 5], The
particle size and pollutant distribution of street contaminants are shown
26
-------
COMBINED SEWER AREAS
DEP
W,
CB
w,
ST
DEP WW
SF
2. STORM SEWER AREAS
M
W
ca
WE = Mw - wsw- wca -
Ni
3. UNSEWERED AREAS
W
LEGEND
ITEM
SOURCES
I ) WET-WEATHER POLLUTANT LOAD
2) DEPOSITION POLLUTANT LOAD
CONTROLS
I ) STREET SWEEPING (SW) REMOVAL
2) CATCH BASIN (CB)
3) SEWER FLUSHING (SF)
4) STORAGE-TREATMENT (ST) "
EFFLUENT
NET POLLUTANT DISCHARGE
ALL UNITS ARE IN POUNDS (Ibs).
SYMBOL
M
M
w
DEP
WSW
WCB
WSF
W
Figure 7. Stormwater Pollution Control Technologies - Availability Factors Equal 1.0
-------
in Table 4.
Street sweeping may be performed manually or mechanically, with the latter
enjoying more widespread usage. Mechanical sweepers are divided into two
categories: brush-type and vacuum-type. Removal efficiencies with brush-
type sweepers for various particle sizes are shown in Table 5. The overall
efficiency is 0.50 with the coarser materials enjoying higher efficiencies
than fine particles. APWA reports that vacuum type sweepers have achieved
efficiencies of greater than 0.95 [5]. Of course, the increased efficiency
of vacuum sweepers results in a substantially higher cost over brush-types.
Street sweeping has several advantages and disadvantages as a pollution
control technique. Some favorable characteristics are the
(1) control of pollutants at the source; and
(2) dual purpose of sweeping for pollution control
and esthetics.
Unfavorable traits include
(1) relatively low efficiency as a pollution control
measure;
(2) sweeper's history as a traffic hazard;
(3) removal of only the portion of the load located near
the gutter; and
(4) problems of vehicular parking along the streets.
Although sweeping has a relatively low removal efficiency, in a coordinated
system of storage-treatment and other management practices, it may prove
to be a viable alternative.
Street sweeping may be considered a production process (as described
earlier). Indeed, all pollution control techniques may be described as
such. Therefore, it is possible to describe the technological relationship
between the input and output of street sweeping in terms of a production
function. In this case, the input is the fraction of the days on which
sweeping occurs during a year and the output is the fraction of BOD removed.
In order to generate the production function a model was developed to
simulate the conditions within an urbanized area and the effect of street
sweeping. Hourly rainfall is converted to runoff using a simple runoff
coefficient, and subsequently accumulated BOD is removed by scheduled
sweeping or a runoff event. The model makes use of the following assump-
tions :
(1) The average removal efficiency for BOD is equivalent
to that of all particle sizes. This is assumed because
of the apparent consistency of the portion of BOD
28
-------
TABLE 4. PERCENT OF STREET POLLUTANTS IN VARIOUS PARTICLE SIZE RANGES
Pollutant
Total Solids
Volatile Solids
BOD5
COD
Kjeldahl Nitrogen
Nitrates
Phosphates
Percent of Pollutant Associated with Each Particle Size Range
Particle Size (microns)
>2,000 840 -> 2,000 246 -»- 840 104 -»• 246 43 -»• 104 <
24.
11.
7.
2.
9.
8.
0
4
0
4
4
9
6
7
17
20
4
11
6
0
.6
.4
.1
.5
.6
.5
.9
24.
12.
15.
13.
20.
7.
6.
6
0
7
0
0
9
9
27
16
15
12
20
16
6
.8
.1
.2
.4
.2
.7
.4
9
17
17
45
19
28
29
.7
.9
.3
.0
.6
.4
.6
5
25
24
22
18
31
56
43
.9
.6
.3
.7
.7
.9
.2
Source: Sartor, J.D., and Boyd, G.B., "Water Pollution Aspects of Street Surface Contaminants,'
USEPA Report EPA-22-72-081, November 1972, p. 7.
-------
TABLE 5. BRUSH-TYPE SWEEPER EFFICIENCY FOR
VARIOUS PARTICLE SIZE RANGES
Particle Size
(microns)
2000
840+2000
246+ 840
104+ 246
43+ 104
<43
Overall
Sweeper Efficiency
(%)
79
66
60
48
20
15
50
Source: Sartor, J.D., and Boyd, G. B., "Water Pollution Aspects of Street
Surface Contaminants," USEPA Report EPA-22-72-081, November 1972,
p. 10.
30
-------
contained within the particle size ranges (see
Table 4).
(2) A runoff event encompasses consecutive hourly
runoff occurrences and intermittent dry periods
not to exceed twelve hours. For example, an
intermittent dry period of twelve hours will
start a new event; a period of eleven hours or less
will not [1].
(3) No sweeping occurs during an event. If an event
and a scheduled sweeping coincide the streets are
simply not swept until the next scheduled time.
(4) Only one pass is made per sweep.
The pollutant washoff functions incorporated in the model were identical
to the functions found in the SWMM and STORM models [13, 14]. However, the
methods of pollutant build-up and removal by street sweeping are somewhat
different. SWMM and STORM allow the linear build-up of pollutants as
long as the elapsed time from the previous runoff event is less than the
street sweeping interval. The relationship is
P = F • DD • N+ P (17)
1 Do
where P, = total pollutant load at the beginning of the storm, Ib;
F = pounds of pollutant per pound of dust and dirt;
DD = daily dust and dirt accumulation rate, Ib/day;
N = number of dry days since the last storm; and
P = pounds of pollutant remaining at the end of the last
storm (event).
If the number of days since the last runoff event is greater than the
sweeping interval, the following equation is employed by SWMM and STORM.
P = P (i-e)n + N • DD - F • [(l-e)n + (l-e)1""1 + ... + (!-£)] (18)
1 o j
+ DD • F • (N - nN )
JJ J
where N = number of days between street sweepings;
O
n = number of times the streets were swept since the
last storm; and
£ = "pick up" efficiency of the street sweeping equipment.
31
-------
The major flaw in this procedure is that the street sweeping "counter" is
set to zero at the end of every runoff event. In other words, after the end
of an event, N days must pass before sweeping occurs. Therefore, it is
conceivable that the streets will never be swept according to this procedure.
For example, assume that N is 20 days. If the longest dry period during
a year is 15 days, STORM and SWMM will fail to simulate any sweeping — even
though an interval of 20 days was specified.
To correct this deficiency, the model developed for this study merely
establishes a sweeping schedule from which no deviation is allowed except
in the case of a coincident runoff event. This is not an entirely accurate
assumption, for public works departments certainly have the flexibility to
alter their sweeping schedule. However, this is not considered to be a
serious error. When sweeping does occur, the amount of pollutant removed
is taken as the product of the accumulated pollutants available and the
"pick-up" efficiency.
Not all of the accumulated pollutants are available for removal by sweeping.
There are considerable amounts on parking lots, driveways, and other im-
pervious areas not subject to sweeping by municipal units. Total and
street imperviousness as a function of developed population density is
shown in Figure 8 [1]. If pollutants are assumed to be uniformly distributed
over the impervious area and that only the pollutants in the street are
sweepable, then
sw = -f « 0.6 PD~°'2 for PDd >_ 0.1 (19)
where = sweeping availability factor, i.e., proportion of
pollutant load which is sweepable (0 < ty^u < 1-0)5
I = imperviousness due to streets only, percent; and
s
I = total imperviousness, percent.
A plot of equation (19) (Figure 9) shows that (}> ranges from about 0.43
at PDd = 5 persons/ac (12.4 persons/ha) to about .35 at PDd = 15 persons/ac
(37.1 persons/ha). In actuality, a disproportionate amount of the pollu-
tion is located on the streets or is delivered to the streets prior to
entering the final drainage canals. To test the sensitivity of the result
t0 ^SW evaluations will be made with cf>sw =0.40 representing a lower bound
SW = 1.0 representing the upper bound, and 4>sw=0.70 representing an
average value.
Running the model with several different efficiencies (ranging from 0.1 to
0.9) and sweeping intervals (ranging from 1 to 42 days) generated the family
of production functions shown in Figure 10. The model was run using data
for the developed areas of Minneapolis, Minnesota (including hourly pre-
cipitation for 1971). The production function for a "pick-up" efficiency
of ^0.50 is used to describe the typical mechanical sweeping operation.
This corresponds to the efficiency shown in Table 5 for brush-type sweepers.
The efficiency could be any value suitable to local conditions. For
32
-------
100
person*/ hectors
30 40
TOTAL IMPERVIOUSNESS
IMPERVIOUSNESS DUE TO STREETS ONLY
05 IO IS 20
DEVELOPED POPULATION DENSITY, PDd , persons/aero
Figure 8. Imperviousness as a Function of Developed Population
Density
20
persons / hectare
30 40
50
6O
70
05 10 13 20
DEVELOPED POPULATION DENSITY , PDd , person*/acre
Figure 9. Sweeping Availability Factor as a Function of
Developed Population Density
33
-------
1.0
STREET SWEEPING SIMULATION,
MINNEAPOLIS, MINN. - F97I
e = efficiency
0.
^ np
UJ O.o
CQ
Q
UJ
>
O
2
UJ
tr
Q
O
m
UJ
_i
m
u,
O
O
h-
o
_
0 0.2 0.4 0.6 0.8
FRACTION OF DAYS STREETS ARE SWEPT , Xsw
Figure 10. Production Functions for Street Sweeping
1.0
34
-------
example, the use of vacuum sweepers would dictate the use of a higher
efficiency.
The production function generated by the model is in terms of the fraction
of BOD removed annually. In order to generate the total cost curve the
fraction removed must be converted to the pounds of BOD removed (as
described in Section V). Therefore,
WSW = (mW - "DBF) ' ASW ' *SW ' YSW (20)
where W = wet-weather BOD removed by sweeping, Ib/yr;
IIL, = annual wet-weather BOD load, Ib/ac-yr;
= annual wet-weather BOD load due to combined sewer
deposition, Ib/ac-yr;
A = area to be swept, ac;
(j> = sweeping availability factor, i.e., proportion of
BOD load which is sweepable (0 < <|> T < 1.0); and
— bw —
Y = fraction of available BOD removed by sweeping
(0
-------
Also, some average values for gutter length are shown in Table 6. The
sweeping cost per curb mile, Cg, is more difficult to determine. APWA
reports a wide range of values for several street sweeping cost parameters
from over 160 municipalities [16]. The median and mean for each
parameter are given in Table 7. The median value of $7.00/curb mile
($4.35/curb-km) swept will be used because of the large variance in the
data.
COMBINED SEWER FLUSHING
Combined sewers often experience dry-weather sewage deposition. These
solids accumulate in the sewers until removed by a storm surge or by
artificial flushing. The deposition carried away by runoff discharges
directly to the receiving water if the dry-weather treatment plant is
bypassed. Controlled flushing allows the sewers to be cleaned without
adding pollutants to the water body. Instead, these pollutants are routed
to the dry-weather plant for treatment.
As with street sweeping, sewer flushing is not a new idea; its primary
purpose has been to improve hydraulic capacity and self-scouring ability.
However, several reports indicate the ability of a flushing program to
remove a substantial portion of the pollutants associated with deposition
[2, 3, 6]. Several systems are available for sewer flushing, e.g., flush-
ing stations, in-line storage, and portable tankers. Flushing stations
are tanks placed at strategic locations that release the required flushing
volumes. Varying degrees of automation are utilized [3]. In-line storage
involves a system of internal dams used to block the sewage flow at upstream
points for rapid release to scour downstream elements [2]. The use of
tankers merely requires that the trucks be dispatched to the system com-
ponents requiring flushing.
Pisano has investigated the deposition problem in two Boston systems—
Dorchester and South Boston [2]. The two systems have a total of 2666
sewer elements with an average length between manholes of 191 ft (58.2m) per
segment. Through a simulation model it was estimated that 10.3 percent
of the daily dry-weather solids in the Dorchester system was deposited in
the lines. The South Boston system retained 6.6 percent. Also, the
Dorchester system retains 75 percent of the total deposition in only 18
percent of the system components. South Boston retains 63 percent in 22
percent of the components. Therefore, a relatively small portion of the
combined sewer elements retain a substantial amount of the total deposition.
As expected, pipe slope was reported to be the major factor in determining
potential deposition problems.
Pisano provided the data used to develop the sewer flushing production
function [2]. The input to this process is the fraction of the combined
sewer segments flushed daily. The output is the fraction of available BOD
removed annually by flushing. The production function is based on informa-
tion regarding the relative concentration of deposition within the two
systems of Boston (e.g., 75 percent of the deposition is found in 18 percent
of the Dorchester system elements). The function, shown in Figure 11,
36
-------
TABLE 6. AVERAGE VALUES OF GUTTER LENGTH
Curb or Gutter Length
Land Use
miles/ac
(km/ha)
ft/ac
(m/ha)
Residential
Commercial
Industrial
Other
0.059
(0.235)
0.070
(0.279)
0.034
(0.136)
0.023
(0.091)
312
(235)
370
(279)
180
(136)
121
(91)
Source: Heaney, J.P., Huber, W.C., Medina, M.A., Murphy, M.P., Nix, S.J.,
and Hasan, S.M., "Nationwide Evaluation of Combined Sewer Overflows
and Urban Stormwater Discharges, Volume II: Cost Assessment,"
USEPA Report EPA-600/2-77-064B, March 1977-
TABLE 7. UNIT COSTS OF STREET SWEEPING
Street Sweeping Costs
Mean
Median
$/curb-mile
($/curb-km)
86.61
(53.82)
7.00
( 4.35)
($/m3)
22.14
(28.96)
13.79
(18.04)
$/ton
($/metric ton)
31.31
(34.51)
14.28
(15.74)
$/ cap it a/year
1.54
1.23
Source: Unpublished data from American Public Works Association, 1976.
37
-------
LJ
O
5
UJ
DC
O
O
m
ui
QQ
_J
>
2
O
or
u.
0.2
p o.U
o
0
CURVE BASED ON DATA FOR S. BOSTON
AND DORCHESTER, MASS. ( PISANO , [ 2 ])
0 O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
FRACTION OF SEWER COMPONENTS FLUSHED DAILY, X SF
Figure 11. Production Function for Combined Sewer Flushing
38
-------
is based on several assumptions:
(1) A flushing program cleanses a designated portion
of the system elements daily.
(2) Daily flushing will remove virtually 100 percent
of the available daily deposition. This assumes
that the sewers have been properly maintained and
do not contain beds of debris. Of course, not all
of the annual deposition will be available for
flushing, i.e., some portion will be removed
by runoff events.
(3) Pisano reports deposition in terms of suspended
solids. BOD, the pollutant of concern here,
is assumed to be deposited in a similar manner
[2].
(4) All components or pipe sections are ranked,
according to the severity of the deposition
problem, for flushing priority.
(5) The BOD flushed daily is routed to the dry-
weather treatment facility. The flushing
volumes are small enough to prevent an
artificial combined sewer overflow.
Inspection of the production function reveals that sewer flushing also ex-
hibits decreasing marginal output as the input is increased. In fact, the
effect is dramatic after approximately 10 or 20 percent of the sewers are
flushed daily.
To develop a total cost function for any urbanized area, it is necessary
to convert the production function in terms of the fraction of BOD removed
to the pounds of BOD removed annually. This is accomplished by the follow-
ing equation,
WSF = *SF "DEP * ASF * YSF (23)
where W = BOD in deposition removed by daily sewer flushing,
SF .,, /
lb/yr;
<£ = sewer flushing availability factor, i.e., proportion
of pollutant load that is flushable (0 £ £ 1.0)5
ni = annual BOD load of combined sewer deposition,
Ib/ac-yr;
A = area served by combined sewers to be flushed, ac; and
or
YqF = fraction of available BOD removed by flushing (0 £ YSF < 1.0)
39
-------
A method of estimating the combined sewer deposition BOD load, mDEp, is
found in Appendix A. A more refined procedure is being developed. Results
should be available later this year [17].
Assuming that the total annual costs of sewer flushing, ZgF, are a linear
function of the system footage to be flushed, the total cost curve for
any area is given by the following equation,
ZSF ' CSF ' (°'40G) ' V ' XSF (24)
where C „ = cost per mile of sewer flushed, $/mile;
or
0.40G = sewer length in A , miles/ac = 40 percent of
gutter length;
X = fraction of combined sewerage system components
flushed daily (0 < Xc_ < 1.0); and
— br —
X = PF (W ) , the inverse sewer flushing production function
in terms of pounds of BOD removed.
This equation and the construction of the total cost curve require several
assumptions :
(1) Flushing will be performed by the in-line storage
and sudden release of dry-weather flow at upstream
locations [2] .
(2) The redeposition of BOD at the trailing edge of the
resulting flush wave is assumed to be negligible [2].
(3) The cost per unit length of flushed sewer line is
constant; regardless of pipe size, type, slope, or
Manning ' s n .
(4) The length of combined sewers per acre is assumed to
be 40 percent of the gutter length. Equation 22 or
Table 6 may be used to estimate the gutter length, G.
Pisano indicates that the total present worth of the cost (capital and
operation/maintenance) per in-line flushing module (inflatable dam) and
the initial cleaning is $22,500. It is assumed that one module is needed
per segment requiring flushing. The annual cost per module is $2,250
(8% interest, 20 year service life). The Boston system segments have an
average length of 191 feet. Therefore, the annual cost of flushing per
unit length of sewer line is $11.78/ft ($38.64/m) or $62,200/mile
($38,600/km).
40
-------
CATCH-BASIN CLEANING
In a study dealing with overall catch-basin performance, Metcalf and Eddy,
Inc. define a catch basin as [18]:
a chamber or well, usually built at the curb line of
a street, for the admission of surface water to a
sewer or subdrain, having at its base a sediment sump
designed to retain grit and detritus below the point
of overflow.
This definition implies that catch-basins are not intended to remove BOD or
suspended solids, but act primarily as grit chambers designed to prevent
the clogging of sewer lines. However, the catch basin does act as a
sedimentation tank capable of removing some portion of the BOD. Unfor-
tunately, the small portion of BOD removed may be flushed from the sump
during runoff events. Catch basins act much as septic tanks, but are
subject to highly variable and, often, overwhelming flows. Lager and
Smith estimate the typical pollution control effectiveness in an example
shown in Table 8 [18]. The efficiency of BOD removal, calculated below using
data from Table 8, i.e.,
. = removal -loss = (345,800 -262,500) 100
ciency input 25,000 basins (50 storms)(1.04 Ib)
= 6.4%
indicates that the expected removal level is not significant. For this
reason, catch-basin cleaning will not be analyzed further.
STORAGE-TREATMENT
The remaining method of controlling stormwater pollution involves storage
and/or treatment of the collected runoff. Storage-treatment facilities
operate in series with the management practices.
A variety of storage and treatment technologies are available. Examples of
storage include
(1) in-line storage,
(2) tanks,
(3) lagoons, and
(4) tunnels.
Treatment methods include
(1) sedimentation,
41
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TABLE 8. EXAMPLE PROBLEM EVALUATING CATCH-BASIN PERFORMANCE
EXAMPLE PROBLEM 7-3: ANNUAL POLLUTION ASSESSMENT OF CATCHBASIN PERFORMANCE
Given the conditions expressed in the preceding problems, determine the aggre-
gate effectiveness of the catchbasins over a period of years in terms of BOD^
removed.
Specified Conditions
1. Total number of catchbasins = 25,000.
2. Curb length per catch basin = 0.10 curb mile (0.16 curb-km).
3. Annual precipitation = 35.1 in (89.2 cm).
4. Catchbasins are cleaned twice a year.
5. The pollution load displaced from each basin is 0.21 Ib (.10 kg)
BOD5 for each of 50 storms occurring in a year.
6. The runoff coefficient = 50%.
Assumptions
1. The annual rainfall can be characterized as 50 equal 5-h storms.
2. BODc; removal by sedimentation will total 26.6% of the applied load.
Solution
1. Determine the annual loss of BOD,, by liquid volume displacement.
BOD5 loss = 25,000 basins x 50 storms x 0.21 Ib (.10 kg)
= 262,500 Ib/yr (125,000 kg/yr)
2. Compute the BOD^ entering a catchbasin each storm (following pro-
cedures of earlier example)-
BOD,- entering = 1.3 Ib (.59 kg) available x 0.80 removed from streets
= 1.04 Ib (.47 kg)
3. Determine the annual removal of BOD,- by sedimentation.
BOD removed = 25,000 basins x 50 storms x [1.04 Ib (.47 kg) x 0.266]
= 345,800 Ib/yr (156,800 kg/yr)
4. Compare the net benefit ratio
Benefit = 345,800 Ib (156,800 kg) removed ~ 262,500 Ib (119,000 kg)
lost
= 1.32:1.
Comment
The problem illustrates that from a pollution abatement standpoint the bene-
fits of catchbasins are marginal at best. Of course, with the cleaning fre-
quency of twice per year, the liquid fraction pollution might average half the
specified value, thereby doubling the benefit ratio; however, the gross impact
is still small. This example is based on grossly synthesized data and real,
long-term removal data from a few catchbasins are required for an actual assess-
ment of catchbasins.
Reference: Lager, J.A., and Smith, W.G., "Catchbasin Technology Overview and
Assessment," USEPA Report (draft), 1977.
42
-------
(2) swirl concentrators,
(3) microstrainers,
(4) dissolved air flotation,
(5) contact stabilization, and
(6) physical-chemical treatment.
The operation of a storage-treatment facility is a production process
involving two inputs and one output. The inputs are the storage capacity
and the maximum treatment rate and represent the input vector to the
storage-treatment process, Xg^. The output is the fraction of available
BOD removed annually, Y .
o -L
A methodology to derive the production function and total cost curve for
storage-treatment in any urbanized area is discussed in an EPA publication
by Heaney, Huber, and Nix [7]. Rather than summarize this methodology
here, the reader is referred to this report for details. With relatively
little data, the production function and total cost curve may be derived
for any city in the U.S. As an example, a production function (in the two-
dimensional isoquant form) for Atlanta, Georgia, is shown in Figure 12.
Additionally, a total cost curve for the storm sewered areas of that city
is shown in Figure 13.
43
-------
0,90
0.80
0.10 -I
T , cm/hr
0.01 0.02 0
T, cm/hr
0.004 0.008 0.012 0.016 0.020
_L
hO.40
0.002 0.004 0.006 0.008
T , in/hr
0.010 0.020
TREATMENT , T, in. / hr
0.030
Figure 12. Production Function (Isoquants) for Storage-Treatment,
Atlanta, Georgia [Heaney, Huber and Nix, 1976]
44
-------
14.0
13.0 -
12.0 -
II.0 -
^ 10.0 -
O 9.0-1
x
8.0 -
7.0 -
6.0 -
S 5.0 ^
o
, 4.0 A
-w-
z
2
<
_J
3.0-
2.0 -
1.0 -
0
0 -10 .20 .30 .40 .50 .60 .70 .80
FRACTION OF BOD REMOVED BY STORAGE-TREATMENT ,
.90
1.0
Figure 13. Total Cost Curve for Storage-Treatment, Storm Sewered Areas, Atlanta,
Georgia
-------
SECTION VII
APPLICATION TO ANYTOWN, U.S.A.
PROBLEM STATEMENT
In this section, the methodology presented in Section V is applied to a
hypothetical urbanized area. The characteristics of this area, called Any-
town, necessary to utilize this methodology are derived from average charac-
teristics of the 248 urbanized areas in the U.S. [1]. These averages are:
(1) Population Density (urbanized area): 5.14 persons/ac
(12.70 persons/ha).
(2) Mean Annual Precipitation: 33.4 in (84.8 cm).
(3) Land Use Percentage (urbanized area): residential,
31.4%; commercial, 4.6%; industrial, 8.0%; other
developed, 9.8%; undeveloped, 46.2%.
(4) Land Use Percentage (developed areas only): residential,
58.4%; commercial, 14.8%; industrial, 8.6%; other
developed, 18.2%.
(5) Percent of Developed Area Served by Type of Drainage
System: combined sewers, 14.4%; storm sewers, 38.3%;
unsewered, 47.3%.
(6) Population Density of the Developed Area by Type of
Drainage System—persons/ac (persons/ha): combined,
16.7 (41.3); storm, 13.0 (32.1); unsewered, 4.6 (11.4);
all developed areas, 9.6 (23.7).
Assuming a population of 1,000,000 persons and using the above values, the
necessary land use, drainage system, and population characteristics for the
developed areas in Anytown are derived and shown in Table 9. The land use
percentages are assumed to be constant regardless of the drainage system
(e.g., combined, storm, and unsewered areas each have 58.4 percent of the
service area as residential). Additionally,it is assumed that the popula-
tion density for each drainage system service area is constant regardless
of the land use [e.g., residential, commercial, industrial, and other
developed areas in the combined sewered areas all have a population density
of 16.7 persons/ac (41.3 persons/ha)].
46
-------
TABLE 9. LAND USE AND POPULATION CHARACTERISTICS OF ANYTOWN, U.S.A.
Drainage
System
Combined
Storm
Unsewered
TOTAL OR AVG.
Land Use
Residential
Commercial
Industrial
Other
TOTAL or AVG.
Residential
Commercial
Industrial
Other
TQTAL or AVG.
Residential
Commercial
Industrial
Other
TOTAL or AVG.
Area,
ac
(ha)
8800
(3560)
1300
( 530)
2200
( 890)
2800
(1130)
15100
(6110)
23500
(9510)
3400
(1380)
5900
(2390)
7300
(2950)
40100
(16230)
29000
(11740)
4200
(1700)
7300
(2950)
9000
(3640)
49500
(20030)
104700
(42370)
Population Density,
persons/ac
(persons/ha)
16.7
(41.3)
16.7
(41.3)
16.7
(41.3)
16.7
(41.3)
16.7
(41.3)
13.0
(32.1)
13.0
(32.1)
13.0
(32.1)
13.0
(32.1)
13.0
(32.1)
4.6
(11.4)
4.6
(11.4)
4.6
(11.4)
4.6
(11.4)
4.6
(11.4)
9.6
(23.7)
47
-------
The methodology is applied to the control network shown in Figure 14. In
effect, the entire procedure is carried out for each drainage system area
as though it were a separate entity. Within each system area, a specific
control technique applied to one land use is regarded as a separate option.
This is primarily due to the fact that the wet-weather BOD load is differ-
ent for each land use. Therefore, in combined areas, the control network
consists of eight options (four for street sweeping and four for sewer
flushing) in parallel followed by storage-treatment in series. In the
storm sewered areas, the control network consists of the four street sweep-
ing options followed by storage-treatment in series. In the unsewered
areas, the only control option is storage-treatment. The notation repre-
senting the various land uses and drainage systems found in Figure 14 will
be used throughout the remainder of this section.
Before application of the methodology can begin, the wet-weather BOD loads
(the pollutant of interest here), for each land use within each drainage
system service area, must be estimated. Using the information provided
on Table 9 and the relationships found in Appendix A, these values are
computed and shown in Table 10. For comparative purposes, the annual wet-
weather and dry-weather flows and the dry-weather BOD loads are also shown.
APPLICATION
Following the seven steps discussed and shown in Figures3, 4, 5 and 6 of
Section V for each drainage system service area will give an optimal
operating strategy applicable to that area. The production functions and
total cost curves for the individual parallel options are derived from
the information provided in Section VI and Table 9. The gutter length
necessary to develop total cost curves for sweeping and flushing was
computed from Equation 22 for residential areas and taken from Table 6 for
other land uses. The production function and total cost curve for storage-
treatment for each drainage system are found by applying the data found in
Table 9 and the mean annual precipitation to the simplified assessment pro-
cedure discussed by Heaney, Huber, and Nix [7]. Anytown is assumed to be
located in Region III [7]. The total cost curves for the fifteen options
are presented in Appendix B.
Much uncertainty exists regarding the appropriate values to use for the
availability factors for street sweeping (sw) and sewer flushing ($„„).
Thus, three different cases will be analyzed: (1) high availability
(4>SF = ^SW = -L-0)* medium availability (SF = 0.8, 4>sw = 0.7), and low
availability (sw = 0.4).
Street sweeping in the storm sewered areas will be used to illustrate how
these four options shown in Figure 14 are combined into one equivalent
option. The marginal cost curves for these four options and the composite
marginal cost curve are shown in Figure 15. Recall that, for a given
marginal cost, the pollutant removal by the four options is simply the
sum of the individual removals. The removal by option SW4 is insignificant
because the pollutant loading per acre is so small. The derived total cost
curves for the three cases in the storm sewered area are shown in Figure 16
48
-------
COMBINED SEWERED AREA
I
STORM SEWERED AREA UNSEWERED AREA
I
STREET SWEEPING
SEWER FLUSHING
i
STREET SWEEPING
LEGEND
a = combined
b = storm
c = unsewered
I
2
3
4
W
"ST
= residential
= commercial
= industrial
= other developed
TOTAL EFFLUENT , W
Figure 14. Stormwater Pollution Control Network for Anytown, U.S.A. - Availability Factors Equal 1.0
-------
TABLE 10. ANNUAL WET- AND DRY-WEATHER FLOWS AND BOD LOADS FOR ANYTOWN, U.S.A.
Ul
o
Drainage
System
Combined
Storm
Unseuered
TOTAL
Land Use
Residential
Commercial
Industrial
Other
TOTAL
Residential
Commercial
Industrial
Other
TOTAL
Residential
Cooanercial
Industrial
Other
TOTAL
Wet-
Weather
Flow
in (cm)
13.7
(34.8)
13.7
(34.8)
13.7
(34.8)
13.7
(34.8)
-
12.5
(31.8)
12.5
(31.8)
12.5
(31.8)
12.5
(31.8)
-
8.5
(21.6)
8.5
(21.6)
8.5
(21.6)
8.5
(21.6)
Dry-
Weather
Flow
in (cm)
22.4
(56.9)
22.4
(56.9)
22.4
(56.9)
22.4
(56.9)
-
17.4
(44.2)
17.4
(44.2)
17.4
(44.2)
17.4
(44.2)
-
6.2
(15.7)
6.2
(15.7)
6.2
(15.7)
6.2
(15.7)
Dry-
Weather
BOD Load
Ib/ac
(kR/ha)
942
(1057)
703
(789)
910
(1021)
1035
(1161)
-
807
(905)
807
(905)
807
(905)
807
(905)
-
286
(321)
286
(321)
286
(321)
286
(321)
Wet-Weather BOD Loads
Street Sewer
Solids Deposition
Ib/ac Ib/ac
(kg/ha) (ks/ha)
30 95
(34) (107)
107 334
(120) (375)
40 127
(45) (142)
0.5 1.7
(0.6) (1.9)
-
27
(30)
107
(120)
40
(45)
0.5
(0.6)
-
17
(19)
107
(120)
40
(45)
0.5
(0.6)
TOTAL (all wet-weather i
Street
Solids
lO^lb
(106kg)
0.264
(0.120)
0.139
(0.063)
0.088
(0.040)
0.001
(0.0005)
0.492
(0.223)
0.634
(0.288)
0.364
(0.165)
0.236
(0.107)
0.004
(0.002)
1.238
(0.562)
0.493
(0.224)
0.449
(0.204)
0.292
(0.133)
0.004-
(0.002)
1.238
(fr.563)
2.968
(1.347)
sources) 4,
(2.
Sewer
Deposition
106lb
(106kg)
0.836
(0.380)
0.434
(0.197)
0.279
(0.127)
0.005
(0.002)
1.554
(0.706)
-
-
-
-
-
-
-
-
-
1.554
(0.706)
.522
,053)
-------
MEDIUM AVAILABILITY
0.2 0.4 as
BOD REMOVED BY PARALLEL OPTIONS
.0
, I06!b/yr
I
0.3
I
0.4
i
0.5
I
0.6
I
0.8
O.I 0.2 0.3 0.4 0.5 0.6 0.7
FRACTION OF BOD REMOVED BY PARALLEL OPTIONS , Y
0.9
b
n
1.2 1.238
1.0
Figure 15. Marginal Cost Curves for the Parallel Options, Storm Areas - Medium Availability Factors
-------
AVAILABILITY
FACTOR, 08W CURVE
0.2 0.4 0.6 0.8
BOD REMOVED BY PARALLEL OPTIONS, w£
.0
I0eib/yr
0.5
0.7
O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8
FRACTION OF BOD REMOVED BY PARALLEL OPTIONS,
1.236
0.9
1.0
Figure 16. Total Cost Curves for the Parallel Options, Storm Areas
-------
As expected, the total costs increase as the availability factor, cf'sW'
decreases.
For the storm sewer area, the problem is now reduced to evaluating the
optimal combination of the composite cost curve for the parallel options
and the downstream total cost curve for storage-treatment shown in Figure 17,
The resultant optimal solutions for the three assumed availability factors
are shown in Figure 18 (sw = 1.0), Figure 19 (c}>sw = 0.7), and Figure 20
(<)>gy =0.4). In each figure the ordinate and abscissa are scaled so that
the maximum cost is used as the upper bound. Thus, the maximum overall
pollutant removal is a point in the northwest corner of each figure, e.g.,
97 percent in Figure 18. Lastly, the final results for the storm sewered
area are shown in Figures 21 (sw = 1.0), 22 (sw = 0.4).
Identical procedures are used to determine the optimal solutions for the
combined sewered area and unsewered area. The result is now simply a case
of three options in parallel. These three options are combined to obtain
the final results which are presented, by availability factors, in Tables 11
(high), 12 (medium), and 13 (low). Lastly, the final total costs using
storage-treatment only, and in conjunction with other management practices,
are presented in Figure 24. If the availability factors are high, then
the savings from using an integrated program are quite substantial.
53
-------
Ul
14.0
12.0 -I
u>
O
x 10.0 -I
8.0 -I
CO
O 6.0 A
r>
2 4.0 -
20 -
0 •
I
O.I
0.2
0.3 0.4
0.5 0.6
r
0.7
0.8
FRACTION OF BOD REMOVED BY STORAGE - TREATMENT , Y
0.9 1.0
ST
Figure 17. Total Cost Curve for Storage-Treatment, Storm Areas
-------
5.84
10.0 11.0 11.46
TOTAL ANNUAL COST ,2^., $ X I06/yr
Figure 18. Isoquants of the Overall Fraction of BOD Removed, Storm Areas - High Availability Factors
-------
5.84
1.0
£0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
TOTAL ANNUAL COST , zj!T , $ X I06/yr
10.0 11.0 11.46
Figure 19, Isoquants of the Overall Fraction of BOD Removed, Storm Areas - Medium Availability Factors
-------
3.84
2.0 3.0 4.0 5.0
TOTAL ANNUAL COST
6.0 7.0
, $ X I06/yr
T
8.0
-r
9.0
10.0 11.0 11.46
Figure 20. Isoquants of the Overall Fraction of BOD Removed, Storm Areas - Low Availability Factors
-------
Ul
00
15.0 -
<£>
O
MJ
10.0-
co
O
O
<
r>
5.0 -;
_i
<
r
0
HIGH AVAILABILITY
0sw =1-0
0.2 0.4 0.6
BOD REMOVED BY ALL OPTIONS
1.0
I0 !b / yr
O.I
0.2
0.3
0.4
0.5
0.6
0.7
0.8
FRACTION OF BOD REMOVED BY ALL OPTIONS ,
0.9
1.2 1.238
1.0
Figure 21. Total Cost Curve for All Options, Storm Areas - High Availability Factors
-------
MEDIUM AVAILABILITY
0.2 0.4 0.6
BOD REMOVED BY ALL OPTIONS
0.8
, I0 Ib/yr
O.I 0.2 0.3 0.4 0.5 0.6 0.7
FRACTION OF BOD REMOVED BY ALL OPTIONS
0.8
1.2 1.238
0.9
1.0
Figure 22, Total Cost Curve for All Options, Storm Areas - Medium Availability Factors
-------
15.0 -
O
X
rw
10.0-
co
O
O
5.0 -,
i
0
LOW AVAILABILITY
0sw=
.0
BOD REMOVED BY ALL OPTIONS , w£ , I06 Ib / yr
O.I
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
FRACTION OF BOD REMOVED BY ALL OPTIONS , Y^
Figure 23. Total Cost Curve for All Options, Storm Areas - Low Availability Factors
1.2 1.238
1.0
-------
TABLE 11. OPTIMAL STRATEGY FOR 25, 50, 75 AND 85 PERCENT OVERALL BOD REMOVAL, ANYTOWN, U.S.A., -
HIGH AVAILABILITY FACTORS
Drainage
System Alternatives
Combined Street
Sweeping
Sever
Flushing
Storage-
Treatment
TOTAL/AVG.
Storm Street
Sweeping
Storage-
Treacment
TOTAL/AVG.
Jo»ewered TOTAL/AVG.
rnriT /i\ir. .
BOD Removed By
Each Process
(106 Ib/yr)
Land Use 252
Residential 0
Commercial 0.07
Industrial 0.03
Other 0
Residential 0.22
Commercial 0.18
Industrial 0.10
Other 0
0
0.60
Residential 0
Commercial 0.14
Industrial 0.01
Other 0
0
0.15
0.36
1.11
SOX
0
0.08
0.04
0
0.25
0.19
0.12
0
0.40
1.08
0.09
0.23
0.14
0
0
0.46
0.70
2.24
751
0.06
0.09
0.05
0
0.30
0.24
0.14
0
0.65
1.53
0.35
0.29
0.18
0
0
0.82
1.05
3.40
85%
0.11
0.09
0.06
0
0.32
0.26
0.16
0
0.78
j.73
0.41
0.2:)
0.19
0
C.12
1.0.L
1.05
3.84
Fraction of Influent
BOD Renoved By
Each Process
25%
0
0.50
0.36
0
0.27
0.41
0.37
0
0
0.30
0
0.39
0.02
0
0
0.12
0.29
0.25
50%
0
0.56
0.49
0
0.29
0.45
0.42
0
0.29
0.53
0.14
0.63
0.59
0
0
0.37
0.57
0.50
75%
0.22
0.64
0.61
0
0.36
0.54
0.51
0
0.56
0.75
0.56
0.79
0.75
0
0
0.66
0.85
0.75
85Z
0.43
0.68
0.65
0
0.38
0.59
0.56
0
0.75
0.87
0.64
0.30
0.80
0
0,33
0.82
0.85
0.85
25%
0
0.07
0.04
0
0.08
0.06
0.04
0
0
0.29
0
0.12
0.01
0
0
0.13
0.43
0.85
Total Cost of
Each Process
(S y. 106/yr)
50%
0
0.08
0.05
0
0.13
0.09
0.06
0
0.85
1.26
0.28
0.27
0.20
0
0
0.75
1.10
3.11
751
0.18
0.11
0.08
0
0.27
0.20
0.1?
0
2.43
3.40
1.43
0.59
0.40
0
0
2.47
2.82
8.69
85Z
0.39
0.13
0.09
0
0.35
0.29
0.1S
0
5.35
6.78
2.07
0.61
0.51
0
1.55
4.74
2.82
14.34
-------
TABLE 12. OPTIMAL STRATEGY FOR 25, 50, 75 AND 85 PERCENT OVERALL BOD REMOVAL, ANYTOWN, U.S.A. -
MEDIUM AVAILABILITY FACTORS
Drainage
System Alternatives
Combined Street
Sweeping
Sewer
Flushing
Storage-
Treatment
TOTAL/AVG.
Storr. Street
Sveeping
Storage-
Treatment
TOTAL/AVG.
Bnsevered TOTAL/AVG.
BOD Removed By
Each Process
(10° Ib/yr)
Land Use 25%
Residential 0
Commercial 0,03
Industrial 0
Other 0
Residential 0,16
Commercial 0.13
Industrial 0,03
Other 0
0.18
0.58
Residential 0
Commercial 0,08
Industrial 0,01
Other 0
0
0,09
0,45
5 OX
0
0,05
0.02
0
0.18
0.15
0.09
0
0,65
1.14
0.01
0,16
0,10
0
0,07
0,34
0.80
757,
0
0,06
0.04
0
0,24
0.19
0.11
0
0.93
1.57
0.14
0.17
0.10
0
0,36
0,77
1.05
85Z
0.04
0,06
0,04
0
0.25
0.20
0,12
0
.1.08
1.79
0,24
0,19
0,12
0
0.45
1,00
1.05
Fraction of Influent
BOD Removed By
Each Process
257.
0
0,32
0
0
0.24
0.38
0.35
0
0.11
0.29
0
0,31
0.07
0
0
0.07
0.36
50%
0
0,48
0,33
0
0,27
0.42
0.38
0
0.41
0.55
0.02
0,62
0.59
0
0.08
0,28
0.65
75X
0
0,63
0,58
0
0.35
0.54
0.51
0
0,66
0.77
0.33
0.67
0.62
0
0,43
0,63
0,85
85*
0,22
0,65
0,60
0
0.37
0.57
0.52
0
0.80
0.87
0.54
0.76
0.71
0
0.65
0.81
0.85
251
0
0.04
0
0
0,06
0,05
0,03
0
0.30
0.48
0
0.10
0,02
0
0
0,12
0.56
Total Cost of
Each Process
(S x 10°/yr)
50*
0
0.06
0.03
0
0.09
0.08
0.04
0
1,35
1.65
0.04
0,26
0.20
0
0.32
0.82
1.42
751
0
0.11
0.07
0
0.25
0.20
0.12
0
3.75
4.50
0.71
0.33
0.23
0
2,29
3.56
2.82
857.
0.18
0.11
0.08
0
0.30
0,25
0.14
0
6.80
7.86
1.39
0.49
0,33
0
5.22
7.43
2.82
TOTAL/AVG.
1.12
2.28
3.39
3.84
0.25
0.50
0.75
0.85
1.16
3.89 10.88 18.11
-------
TABLE 13. OPTIMAL STRATEGY FOR 25, 50, 75 AND 85 PERCENT OVERALL BOD REMOVAL, ANYTOWN, U.S.A. -
LOW AVAILABILITY FACTORS
Drainage
System Alternatives
Combined Street
Sweeping
Sewer
Flushing
Storage-
Treatment
TOTAL /AVG.
Store Street
Sweeping
Storage-
Treatment
TOTAL /AVG.
Jnsewered TOTAL/AVG.
BOD Removed By
Each Process
(106 Ib/yr)
Land toe 25Z
Residential 0
Commercial 0
Industrial 0
Other 0
Residential 0.12
Commercial 0.10
Industrial 0.06
Other 0
0.37
0.65
Residential "
Commercial 0
Industrial °
Other °
0
0
0.49
507.
0
0.01
0
0
0.13
0.11
0.06
0
0.82
1.13
0
0.06
0.02
0
0.2A
0.32
0.83
0.
0.
0.
0.
0.
1.
1.
0.
0.
0.
0.
1.
752
0
02
01
0
14
12
07
0
23
59
0
09
06
0
61
76
05
85%
0.02
0.04
0.02
0
0.20
0.16
0.09
0
1.29
1.82
0.02
0,09
0.06
0
0.82
0.99
1.05
Fraction of Influent
BOD Removed By
Each Process
257.
0
0
0
0
0.24
0.38
0.36
0
0.21
0.32
0
0
0
0
0
0
0.39
50;:
0
0.22
0
0
0.26
0.40
0.39
0
0.47
0.55
0
0.39
0.23
0
0,21
0.26
0.67
75?:
0
0.43
0.23
0
0.28
0.45
0.42
0
0.73
0.78
0
0.64
0.59
0
0.56
0.61
0.85
857.
0.16
0.65
0.57
0
0.40
0.61
0.57
0
0.85
0.89
0.06
0.65
0.60
0
0.77
0.80
0.85
25:
0
0
0
0
0.06
0.05
0.03
0
0.57
0.71
0
0
0
0
0
0
0.61
Total Cost of
Each Process
($ x 106/yr)
502
0
0.02
0
0
0.07
0.06
0.04
0
1.80
1.99
0
0.13
0.06
0
0.89
1.08
1.56
75:
0
0.05
0.02
0
0.11
0.08
0.07
0
4.97
5.30
0
0.29
0.20
0
3.71
4.20
2.82
B5£
0.14
0.11
0.07
0
0.47
0.34
0.20
0
8.14
9.47
0.12
0.29
0.21
0
8.35
8.97
2.82
TOTAL/AVG.
1.14
9 ^ft
t.. *.D
3.40
3.86
0,25
0.50
0.75
0.85
1.32
4,63 12.32 21.26
-------
HIGH AVAILABILITY
MEDIUM AVAILABILITY
LOW AVAILABILITY
STORAGE - TREATMENT
ONLY
0.5 1.0 1-5 2.0 2.5 3.0 3.5
BOD REMOVED BY TOTAL NETWORK, Wjbc , I06lb/yr
O.I 0.2 0.3 0.4 0.5 0.6 0.7
FRACTION OF BOD REMOVED BY TOTAL NETWORK,
0.8
xsdbC
0.9
4.522
1.0
Figure 24. Total Cost Curves for All Drainage System Service Areas
-------
REFERENCES
1. Heaney, J.P., Huber, W.C., Medina, M.A., Murphy, M.P., Nix, S.J., and
Hasan, S.M., "Nationwide Evaluation of Combined Sewer Overflows and
Urban Stormwater Discharges, Volume II: Cost Assessment," USEPA
Report EPA-600/2-77-064B, March 1977.
2. Pisano, W.A., "Cost Effective Approach for Combined and Storm Sewer
Cleanup," in Proc. Urban Stormwater Management Seminars, USEPA Report
WPD-03-76-04, Jan. 1976.
3. FMC Corporation, "A Flushing System for Combined Sewer Cleansing,"
USEPA Report 11020 DNO, March 1972.
4. Sartor, J.D. and Boyd, G.B., "Water Pollution Aspects of Street Surface
Contaminants," USEPA Report EPA-22-72-081, November 1972.
5. American Public Works Association, "Water Pollution Aspects of Urban
Runoff," USEPA Report 11030 DNS 01/69, January 1969.
6. Metcalf and Eddy, Inc., "Urban Stormwater Management and Technology:
An Assessment," USEPA Report EPA-670/2-74-040, December 1974.
7. Heaney, J.P., Huber, W.C., and Nix, S.J., "Stormwater Management Model:
Level I—Preliminary Screening Procedures," USEPA Report EPA-600/2-76-
275, October 1976.
8. Federal Water Pollution Control Act Amendments of 1972, PL 92-500.
9. Guidelines for Areawide Waste Treatment Management Planning, USEPA,
1975.
10. U.S. Bureau of the Census, County and City Data Book, 1972 (A Statisti-
cal Abstract Supplement), Social and Economic Statistic Administration,
U.S. Department of Commerce, 1973.
11. Baumol, W.J., Economic Theory and Operations Analysis, Prentice-Hall,
Inc., Englewood Clifs, New Jersey, 1965.
12. James, L.D., and Lee, R.R., Economics of Water Resources Planning,
McGraw-Hill, Inc., New York, 1971.
13. Huber, W.C., Heaney, J.P., Medina, M.A., Peltz, W.A., Hasan, S.M., and
Smith, G.F., "Storm Water Management Model; User's Manual—Version II,"
USEPA Report EPA-670/2-75-017, March 1975.
65
-------
14. Hydrologic Engineering Center, Corps of Engineers, "Urban Storm Water
Runoff: STORM," Generalized Computer Program 723-58-L2520, May 1975.
15. Graham, R.H., Costello, L.S., and Mallon, H.J., "Estimation of Impervi-
ousness and Specific Curb Length for Forecasting Stormwater Quality and
Quantity," Journal of the Water Pollution Control Federation, Vol. 46,
No. 4, April 1974, pp. 717-725.
16. Unpublished data from American Public Works Association, 1976.
17. Northeastern U., "Characterization of Solids Behavior in and Variabil-
ity Testing of Selected Control Techniques for Combined Sewer Systems,"
EPA Grant No. R-804578, R. Field, Project Officer, Edison, N.J., 1977.
18. Metcalf and Eddy, Inc., "Catchbasin Technology: Overview and Assess-
ment," USEPA Contract No. 68-03-0274 (Draft), September 1976.
66
-------
GLOSSARY
Combined sewage: Sewage containing both domestic sewage and surface water or
stormwater, with or without industrial wastes. Includes flow in heavily
infiltrated sanitary sewer systems as well as combined sewer systems.
Combined sewer: A sewer receiving both intercepted surface runoff and muni-
cipal sewage.
Combined sewer overflow: Flow from a combined sewer in excess of the inter-
ceptor capacity that is discharged into a receiving water.
Depression storage: Amount of precipitation which can fall on an area with-
out causing runoff.
Detention: The slowing,dampening, or attenuating of flows either entering
the sewer system or within the sewer system by temporarily holding the water
on a surface area, in a storage basin, or within the sewer itself.
Domestic sewage: Sewage derived principally from dwellings, business build-
ings, institutions, and the like. It may or may not contain groundwater.
Isocost lines: Lines of equal cost.
Isoquants: Curves representing combinations of the inputs yielding the same
amount of output.
Marginal cost: The rate of change of total cost.
Precipitation event: A precipitation event terminates if zero rainfall has
been recorded for the previous specified time interval.
Production function: Locus of technologically efficient combinations of
inputs and outputs.
Runoff coefficient: Fraction of rainfall that appears as runoff after sub-
tracting depression storage and interception. Typically accounts for infil-
tration into ground and evaporation.
Storm flow: Overland flow, sewer flow, or receiving stream flow caused
totally or partially by surface runoff or snowmelt.
Storm sewer: A sewer that carries intercepted surface runoff, street wash
and other wash waters, or drainage, but excludes domestic sewage and indus-
trial wastes.
67
-------
Storm sewer discharge: Flow from a storm sewer that is discharged into a
receiving water.
Stormwater: Water resulting from precipitation which either percolates into
the soil, runs off freely from the surface, or is captured by storm sewer,
combined sewer, and to a limited degree sanitary sewer facilities.
Surface runoff: Precipitation that falls onto the surfaces of roofs, streets,
ground, etc., and is not absorbed or retained by that surface, thereby col-
lecting and running off.
68
-------
APPENDIX A
QUANTITY AND QUALITY ANALYSIS
In order to develop an optimal stormwater pollution control strategy, the
magnitude of the problem must be estimated. Several methods are available
to estimate the quantity and quality of urban runoff. A simplied method
to assess stormwater pollution loads and control costs by Heaney, Huber,
and Nix can be used to compute these parameters for any urbanized area
[Al]. In addition to the runoff estimations, equations are presented to
determine the corresponding dry-weather (sanitary sewage) flows and quality.
This methodology is briefly described below. The following equations may
be applied to any land use or sewerage system service area.
Annual runoff may be estimated by the following equation:
AR = (0.15 + 0.75 (1/100)) P - 5.234 DS°'5957
\AJ-J
where AR = annual runoff, in;
I = total imperviousness, percent;
P = annual precipitation, in; and
DS = annual depression storage, in.
The annual depression storage is an index of the available areas capable
of retaining precipitation. This parameter is determined by the following
relationship,
DS = 0.25 - 0.1875 (1/100). (A2)
The equation used to estimate imperviousness is
(0.573-0.0391 log PD )
I = 9.6 PD, 1U (A3)
d
where PD, = population density in the developed area, persons/ac.
Knowing the population density of the area allows the annual runoff to be
quickly determined.
The dry-weather flow may be estimated by the following equation,
69
-------
DWF =1.34 PDd (A4)
where DWF = dry weather flow, in/hr.
This relationship is based on an assumed dry-weather flow of 100 gallons/
capita-day (3785,/capita-day) .
Estimating the quality of urban runoff presents a more difficult task.
Available data indicate wide variation in estimated pollutant loads. If
annual pollutant loads are assumed to vary as a function of population
density, precipitation, land use and type of sewerage system, the following
relationships may be used:
ITL = 3(i, j) *P*f . (PD,) for combined sewered areas, (A5)
and
m^ = a(i,j) *P*f . (PD ,) for storm and unsewered areas, (A6)
where m^ = annual wet weather pollutant load, Ib/ac-yr;
P = annual precipitation, in/yr;
f.(PD,) = population density function for land use i;
a(i,j) = coefficient for storm and unsewered areas for pollutant
j on land use i, Ib/ac-yr-in; and
3(i,j) = coefficient for combined sewered areas for pollutant
j on land use i, Ib/ac-yr-in.
Values of oi(i,j), 3(i,j) and f.(PD) are shown in Table AI.
The equation used to estimate dry-weather quality, in terms of BOD,
is
m^ = 62.1 PDd - mDEp (A7)
where m = annual dry-weather BOD load, Ib/ac-yr; and
HL = annual BOD load of combined sewer deposition,
Ib/ac-yr.
This estimate assumes a per capita BOD discharge of 0.17 Ibs (77 gm)/day.
Combined sewer deposition is defined as that portion of the dry-weather
pollutant load that is deposited in the combined sewers, usually due to
inadequate carrying velocities. Often, this load is flushed from the sewers
during runoff periods and becomes part of the stormwater discharge. The
deposition may be estimated by computing the difference between combined and
storm sewered area BOD loadings derived for the combined area of concern.
70
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TABLE Al. POLLUTANT LOADING FACTORS
Land Uses:
i
i
i
i
1 Residential
2 Commercial
3 Industrial
4 Other (assume PD,= 0)
Pollutants: j
j
j
j
j
1 BOD5, Total
2 Suspended Solids (SS)
3 Volatile Solids, Total (VS)
4 Total PO, (as PO,)
5 Total N
Population Function:
i = 1 f.(PD,) = 0.142 + 0.218
i = 2,3 f^"(PDd) = 1.0
1=4 f (PDd) = 0.142
PD
0.54
a and 3 Factors for Equations: Storm factors, a, and combined factors, 3,
have units Ib/ac-yr-in.
Storm
Areas, a
Pollutant, j
1. BOD 2. SS
1.
2 .
3.
4.
Residential
Commercial
Industrial
Other
0.799
3.20
1.21
0.113
3. VS 4. PO,
5. N
16.3
22.2
29.1
2.70
9.45
14.0
14.3
2.6
0.0336
0.0757
0.0705
0.00994
0.131
0.296
0.277
0.0605
Combined
Areas, 3
1. Residential
2. Commercial
3. Industrial
4. Other
3.29
13.2
5.00
0.467
67.2
91.8
120.0
11.1
38.9
57.9
59.2
10.8
0.139
0.312
0.291
0.0411
0.540
1.22
1.14
0.250
Source: Heaney, J.P., Huber, W.C., and Nix, S.J., "Storm Water Management
Model: Level I—Preliminary Screening Procedures," USEPA Report
EPA-600/2-76-275, October 1976, p. 17.
71
-------
This assumes that the greater loads experienced by combined areas are due
to the deposition of dry-weather solids. Thus, combined sewer deposition
is estimated by the following equation:
m.
'DEP
fi(PDd).
(A8)
Of course, for storm sewered and unsewered areas, deposition from dry-
weather sources is not computed unless there are illicit connections of
sewage to the storm sewers.
REFERENCE
Al. Heaney, J. P., Huber, W. C., and S. J. Nix, "Storm-Water Management
Model: Level I—Preliminary Screening Procedures," EPA-600/2-76-
275, Cincinnati, Ohio, Oct. 1976.
72
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APPENDIX B
WORKING CURVES FOR GRAPHICAL SOLUTION
The basic curves for the analysis consist of one curve for each option
showing total cost as a function of pounds of pollutant removed, and level
of pollutant control. The scaling of each curve is set by the total cost as a
a function of the level of pollution control which ranges from 0 to 1. The
actual pounds removed differ as a function of the availability factor, ,
and the total load, M. Thus, the scaling on this abscissa is set up as a
function of <£. The curves are arranged as follows:
Figures
B1-B4 Total Cost Curves for Combined Sewered Areas, by Land
Use, Street Sweeping
B5-B8 Total Cost Curves for Combined Sewered Areas, by Land
Use, Sewer Flushing
B9-B12 Total Cost Curves for Storm Sewered Areas, by Land Use,
Street Sweeping
B13-B15 Total Cost Curves for Storage-Treatment, by Type of
Sewerage System
78-81
82-85
86-88
73
-------
2.Q
MJ
CO
o
O 1.5
1.0
f- 05 -I
0.05
0.10
sw
0.15
sw
BOD REMOVED BY SWEEPING , Wsw JO6 Ib/yr
O.I
0-2
\
0.3
r
0.4
0.5
0.6
0.7
0.8
I
0.9
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING , Y
SW,
I
1.0
Figure Bl. Total Cost Curve for Residential Portion of Combined Sewered Areas, Street Sweeping
-------
VJ
Ui
(O
O
0.35
0.30 •
0.25 -
0.20 -
MJ
CO
O
0.15
o./o -I
<
O
I- 0.05 -
0.025 0SW 0.05
'sw
0.075 0SW 0.10
BOD REMOVED BY SWEEPING , W
SW,
I06lb/yr
0.125
0.139 0,
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING , Y°
SW r.
Figure B2. Total Cost Curve for Commercial Portion of Combined Sewered Areas, Street Sweeping
-------
0.35
0.30 -
(D
O
X 0.25
ro
o ^ 0.20
MJ
CO
8
o.io -
_i
<
h- 0.05 -
0.02
0.04
0.06
BOD REMOVED BY SWEEPING , w|w , I06 Ib/yr
0.08 0.088
O.I
0.2
0.4
05
0.6
0.7
0.8 0.9
a
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING , Y
SW,
1.0
Figure B3. Total Cost Curve for Industrial Portion of Combined Sewered Areas, Street Sweeping
-------
0.35
0.30
>>
\
(O
O
X 0.25
O.ZO -
0.15
0.10 -
0.05
O
O
<
O
I
0
/s
sw
BOD REMOVED BY SWEEPING , Wsw , 10 Ib/yr
i
0.6
0.8
0.001
sw
O.I 0.2 0.3 0.4 0.5 O.S 0.7 0.8 0.9
. a
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING , Y
SW4
Figure B4. Total Cost Curve for Other Portion of Combined Sewered Areas, Street Sweeping
-------
35.0
0.800 0.836
BOD REMOVED BY FLUSHING, W|p , 10° Ib/yr
i
0
O.I
0.2
0.3
0.4
1
0.5
I
0.6
i
0.7
0.8
0-9
1.0
FRACTION OF AVAILABLE BOD REMOVED BY FLUSHING , Y
SF,
Figure B5. Total Cost Curve for Residential Portion of Combined Sewered Areas, Sewer Flushing
-------
•4ft-
<
>-
o
3.5 -r
3.0
2.5
2.0 -
8 1.5
(.0
0.5
0-06
w 0.05
\
°0 0.04
X
0.03
0.02 -
0.01
0
i
0
0.10
0.05
W«artIOblb/yr
0.15
O.I
0.2
0.3
0.4
SFC
0.20
'ST
0.30
BOD REMOVED BY FLUSHING, W° , I06 Ib/yr
I
0.2
0.40^0.434^,
O.I 0.2 0.3 0.4 05 0.6 0.7 0-8 0-9
FRACTION OF AVALABLE BOD REMOVED BY FLUSHING , Y°
5 i f\
1.0
Figure B6. Total Cost Curve for Commercial Portion of Combined Sewered Areas, Sewer Flushing
-------
oo
o
3.5
3.0 -
:=: 2.5
x
8 1.5
1.0 -
I- 0.5 -
0 -
r
o
BOD REMOVED BY FLUSHING , WgF , I06 Ib/yr
FRACTION OF AVAILABLE BOD REMOVED BY FLUSHING , Y
0.279
O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
o
SF.
Figure B7. Total Cost Curve for Industrial Portion of Combined Sewered Areas, Sewer Flushing
-------
I
0
0.001 0
ST
O.OO2
BOD REMOVED BY FLUSHING , W
SF,
0.003 (5SF
, I06 Ib/yr
0.004
SF
I
O.J
T
0.2
F
0.3
I
0.4
0.6
0.5 0.6 0.7 0.8
FRACTION OF AVAILABLE BOD REMOVED BY FLUSHING , '
i
0.9
0.005
'ST
i
1.0
Figure B8. Total Cost Curve for Other Portion of Combined Sewered Areas, Sewer Flushing
-------
00
7.0
6.0
(D
2 5.0
$ 4.0 .
o v>
M
CO
8 3-
2.0 -
_l
<
H- 1.0 -
0.10
'SW
0.20
'SW
0.30 0
sw
0.40 0
SW
0.50
BOD REMOVED BY SWEEPING , W , 10 Ib/yr
1
0.60 flLw0.634
O.I
0.2
0.3
0.4
i
0.5
0.6
0.7
I
0.8
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING, Y
SW,
0.9
1.0
Figure B9. Total Cost Curve for Residential Portion of Storm Sewered Areas, Street Sweeping
-------
oo
0.7
0.6 -
O
X 0.5 -I
CM
0.4 •
NJ
8 0.3 J
0.2 J
O, J
0.05 $SVI 0.10 0SW O.I5 0SW 0.20 0^ 0.25
BOD REMOVED BY SWEEPING, WgW , I06 Ib'/yr
0-30 $sw 0.35 0SY/X364 0SW
O.I 0.2 0.3 0.4 0.5 0.6 07
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING , Y
0.8 0.9
b
1.0
SW,
Figure BIO. Total Cost Curve for Commercial Portion of Storm Sewered Areas, Street Sweeping
-------
00
-P-
0.7
0.6 -
><
£
0.5 -
0.4 -
.0 CO
MJ
C/3
o
o
0.3 -
5 0.2 -
cw
0.15
'sw
BOD REMOVED BY SWEEPING , Wgyy , I06 Ib/yr
3
0.20
O.I
0.2
0.3
0.4
0.5
0.6
0.7
i
0.8
0.9
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING ,
'
0.236
sw
1.0
Figure Bll. Total Cost Curve for Industrial Portion of Storm Sewered Areas, Street Sweeping
-------
00
0.7
0.6 -
- 0.5 -
X
it 0.4 -
§ 0.3
o
0.2 -
O.I
I
0-001
0002
°
0.003
'sv»
BOD REMOVED BY SWEEPING, W ,10 Ib/yr
0-1 0 -2 0.3 0 .4 0.5 0 .6 0.7
FRACTION OF AVAILABLE BOD REMOVED BY SWEEPING, Y
0.8
b
SW4
0.9
0.004
sw
1.0
Figure B12. Total Cost Curve for Other Portion of Storm Sewered Areas, Street Sweeping
-------
14.0
do
O.I 0.2 0.3 0.4 0.5 0.6 0.7
FRACTION OF BOD REMOVED BY STORAGE - TREATMENT ,
0.8 0.9
a
1.0
Figure B13. Total Cost Curve for Storage-Treatment, Combined Areas
-------
00
14.0
12.0 4
O.
x 10-0 -I
CO
8
4.0 -|
2.0 ^
r^
O.I
0.3
0.2 0.3 0.4 0.5 0.6 0.7 0.8
FRACTION OF BOD REMOVED BY STORAGE - TREATMENT
0.9 1.0
Figure B14. Total Cost Curve for Storage-Treatment, Storm Areas
-------
oo
00
14.0
«> 12.0 -
X
-w-
_: io-0' -
o w
ru
n
rw
8.0 -
6.0 -
1.2 1.238
BOD REMOVED BY STORAGE- TREATMENT , W,? ( = W° ),IQ6|b/yr
it ol
i
0.2
O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FRACTION OF BOD REMOVED BY STORAGE - TREATMENT , Y£ ( = Yl.
1.0
Figure B15. Total Cost Curve for all Options (Storage-Treatment), Unsewered Areas
-------
TECHNICAL REPORT DATA
fPlease read Instructions on the reverse before completing)
1 . REPORT NO.
EPA-600/2-77-083
3. RECIPIENT'S ACCESSIOf*NO.
4. TITLE AND SUBTITLE
STORM WATER MANAGEMENT MODEL: LEVEL I - COMPARATIVE
EVALUATION OF STORAGE-TREATMENT AND OTHER MANAGEMENT
PRACTICES
5. REPORT DATE
April 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
James P. Heaney
8. PERFORMING ORGANIZATION REPORT NO.
Stephan J. Nix
. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Environmental Engineering Sciences
University of Florida
Gainesville, FL 32611
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
R-802411
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: Richard Field, Phone: 201/548-3347 x503 (8-342-7503)
See also EPA-600/2-76-275, Storm Water Management Model: Level I - Preliminary
Screening
16. ABSTRACT
The original USEPA Storm Water Management Model (SWMM) provides a detailed simulation
of the quantity and quality of stormwater during a specified precipitation event last-
ing a few hours. This model is widely used. However, it is too detailed for many
purposes. Indeed, a wide range of evaluation techniques ranging from simple to complex
procedures are needed. In particular, the 208 planning effort needs simplified proce-
dures to permit preliminary screening of alternatives. In response to this need, four
levels of stormwater management models are being prepared. This volume presents a
"desktop" procedure to compare selected alternative control technologies.
A graphical procedure is described which permits the analyst to examine a wide variety
of control options operating in series with one another or in parallel. The final
result is presented as a control cost function for the entire study area which is the
optimal (least costly) way of attaining any desired level of control. Given a speci-
fication regarding the desired overall level of control the user can determine the
appropriate amount of each control to apply.
This methodology is applied to Anytown, U.S.A., a hypothetical community of 1,000,000
people. The results indicate the mix of treatment, storage, street sweeping, and
flnsh-mg whirh arfains the specified pollution control level at minimum cost.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
*Storm sewers, *Water pollution, Control
simulation, *Cost effectiveness, *Waste
treatment, ^Sewage treatment, ^Surface
/rater runoff, *Runoff, ^Combined sewers,
^Mathematical models, Storage tanks,
Methodology, Economics, Flushing,
Catch basins
Simplified evaluation,
Sewer flushing, Street
sweeping, Catch-basin
cleaning
13B
IS. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
105
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
89
U. S. GOVERNMENT PRINTING OFFICE: 1977-757-056/55't8 Region No. 5-II
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