United States
                  Environmental Protection
                  Agency       	
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
                  Research and Development
EPA-600/S2-83-086 Nov. 1983
AER&        Project Summary
                  EPA Macroscopic  Planning
                  Model (EPAMAC)for Stormwater
                  and  Combined  Sewer  Overflow
                  Control:  Application Guide
                  and  User's  Manual

                  William G. Smith and Marianne E. Strickfaden
                    A simplified stormwater management
                  model known as EPAMAC (EPA Macro-
                  scopic Planning Model) has been
                  developed to provide an inexpensive.
                  flexible tool for planning and preliminary
                  sizing of stormwater facilities. The
                  purposes of this project were (1) to
                  describe the application of the model to
                  San Francisco (SFMAC), which lead to
                  the generalized EPAMAC  and (2) to
                  write a user's guide. Documentation of
                  the model and instructions for  data
                  preparation and application are included
                  in the user's guide portion of the report.
                    The model was effectively used to
                  compare a large number of alternative
                  storage and treatment facilities and to
                  optimize their sizing. The SFMAC was
                  then generalized for use at any location
                  as EPAMAC.
                    EPAMAC is a special purpose, con-
                  tinuous simulation model for  surface
                  runoff. The model has  minimal input
                  data requirements, broad areal and
                  temporal coverage, and both flexibility
                  and ease of application.
                    EPAMAC was developed as part of a
                  methodology for managing stormwater
                  that uses both simple computer programs
                  and hand  computations. The model
                  consists of three uncomplicated but
                  interrelated programs that can be used
                  singularly or together: EPAMAC, HISTO.
                  and VDAY. In addition to quantity and
                  quality analyses for stormwater flows,
                  model capabilities include dry-weather
                  flow, hourly simulation of  flows,
                  overflow event analysis, determination
of pollutant removals as a result of
sedimentation in storage, and addition
of dry-weather flow and lateral inflows
from adjacent areas. .Postprocessor
programs can also provide histogram
plots of flow and quality (HISTO) and
analyses of violation days for coliform
limits in receiving water for several
coliform standards (VDAY).
  The model proved to be useful to
planners and engineers as well as public
enforcement agencies. Information
developed from application of the
model in San Francisco (SFMAC) was
used by the regional  water quality
enforcement agency in an evaluation of
appropriate stormwater overflow fre-
quency levels to be included in NPDES
permits. Pollutant loadings developed
from SFMAC application and coliform
violation day data from VDAY were
used in cost/benefit analyses to deter-
mine an allowable overflow frequency
consistent  with beneficial uses of the
shoreline, ocean, and bay waters.
  This Project Summary was developed
by EPA's  Municipal Environmental
Research Laboratory. Cincinnati. OH.
to announce key findings of the research
project  that is fully documented in a
separate report of the same  title (see
Project Report ordering information at
back).

Introduction
Complex stormwater models provide
valuable data for  the design and final
sizing of stormwater facilities. But the

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detailed models generally require compre-
hensive,  detailed input data and large
blocks of time on relatively large computers
for execution. In an attempt to provide an
intermediate step between the large,
complex models and the traditional
desktop analysis used in facilities planning
projects, the U.S. Environmental Protec-
tion Agency (EPA) has participated in the
development of several simplified comput-
er models for planning and preliminary
sizing of facilities. These simplified
models require very moderate expenditures
for data preparation and execution, and
they provide a flexible tool for analyzing
a variety of system configurations.
  The application guide and  user's
manual presented in the  full  report
summarize the mathematical modeling
work performed in support of the storm-
water and  combined sewage treatment
master plan for  the City and County of
San  Francisco and provide  a  compact
reference base for applying the model to
future locations. The model consists of
three  uncomplicated but  interrelated
programs that can be used singularly or
together (EPAMAC, HISTO, and VDAY).
This design allows the user to build on his
individual data strengths and to focus on
individual study objectives.

Background
  San Francisco has a unique physical
setting that must be considered in the
development of wastewater facilities.
The City is located on a peninsula, which
allows for the option of effluent discharge
to either the bay or ocean. The planning
area contains 23 watersheds comprising
11,554 ha (28,550 acres) with numerous
hills and peaks. Much of the land slopes
steeply to the water, but a  flat  coastal
strip exists along the east side of the City.
Rainfall occurs mainly  from October
through May, and average annual rainfall
is about 51 cm (20 in.).
  The San  Francisco combined sewer
system conveys both dry- and wet-
weather flows. To advance the planning
concepts and to  meet  water  quality
requirements,  a  citywide computer
modeling  approach was necessary.
During dry weather, major concerns are
transportation  and treatment of the
flows, and  the  resulting quality of the
effluent. Wet-weather concerns also
include minimizing overflow volume and
frequency through storage and pumping
balance, and maximizing quality of
overflow and effluent. Since flows from
different sections  of the city  influence
one another, the reaction of the whole
system to one or a series of storm events
must be examined. Runoff volumes from
all 23 watersheds need identification and
integration to obtain guidance on facilities
necessary  to  process  the flows cost
effectively.  Rainfall data for 70 years of
record are available for analysis. Such an
analysis needs to be accurate enough to
be reliable but not so involved that it
would hinder the planning process.
Computer simulation using an appropriate
model would achieve analysis of a large
number of alternatives reasonably short
time.
  The types of alternatives to be analyzed
involve major regrouping of watersheds
and routing of flows to multiple locations.
Four alternative concepts are presented
in the rnaster plan (Figure 1). Some of the
                          NSPS
SWOO
             Dual Crossing.
                         : Outfall
                          NPWPCP
                           NSPS
swoo
        Modified Ocean Discharge.
           Legend
      •• « Wet - Weather Flow Routes
        • Pump Station
        • Treatment Plant
      	 Outfall
      alternative routes pass through politically
      sensitive areas. The ultimate planning
      goal is to determine for each alternative
      the ability to  meet effluent discharge
      requirements, overflow frequency limita-
      tions, and the minimum cost for  an
      optimized system.
        Existing computer models were either
      too detailed  to quickly survey multiple
      alternatives  or too broad to examine
      storage and treatment interactions. Thus
      SFMAC  (later generalized as EPAMAC)
      was developed to meet the needs of the
      San  Francisco planning process. The
      relationship of the computer modeling to
      the overall planning process is shown in
      Figure 2.
                 Low Level Bay side.
                             •.Outfall

                             NPWPCP
                               NSPS
                                       swoo\SWWPCP
           Bay and Ocean Discharge.
   NSPS  North Shore Pumping Station
     IPS  Islais Pumping Station
   WSPS  Westside Pumping Station
SWWPCP  Southwest Water Pollution Control Plant
  SWOO  Southwest Ocean Outfall
 Figure 1.    Alternative concepts for wet-weather master plan.

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     Initial Preparation
      Data Gathering
      Input Preparation
 EPA MA C and Post Processor
       Computer Runs
       Result Analysis
  Selection of New Values or
 Selection of New Alternatives
   Narrowed Set of Possible
        Alternatives
   Evaluation and Ultimate
   Selection of Alternatives
 Using Social, Environmental
      and Cost Factors
  Rainfall input data were developed
from two sources. The first source was a
network of 30 gages that the City of San
Francisco established in December 1971.
The second  source  was  the National
Weather Service (NWS), which has
maintained  a recording gage  in  San
Francisco since January 1907. The NWS
gage record for the 69-year period (1907-
76) was compared with the 4-year (1972-
76) data set. The storm duration, intensity,
and magnitude characteristics  of both
sets of data showed very close agreement.
  Water  quality also was determined in
the preparatory phase. Dry-weather data
were  obtained from influent records for
the three existing  sewage treatment
plants. Projected per  capita dry-weather
loadings were used as input to the model.
  Treatment plant influent data for storm
days  were analyzed to obtain  a wet-
weather  quality characterization. Since
the plant records were based on daily
composite samples, a sampling program
was developed to obtain additional wet-
weather characterization data.

Watershed Data Analysis
  After input preparation was completed,
EPAMAC was run for each subarea. The
hourly runoff volume and quality were
established for each subarea and water-
shed in the initial EPAMAC runs. Pollutant
loads from each watershed were obtained
from the model. The next phase of the
application was to route the subarea and
watershed flows to storage/treatment
facilities. A flow-routing diagram  was
developed for each system configuration.
EPAMAC was then run again to model
the system flow routes for the alterna-
tives.

Balance of Storage and
Treatment Requirements
  In addition to routing the flows, the
second series of EPAMAC runs was used
to determine the optimal sizes of storage
and treatment  facilities.  During  this
stage, storage and pumping requirements
along with treatment plant capacity were
balanced to obtain the desired overflow
frequency during wet weather.
  The relationship  between pumping  or
treatment rates and overflows is illustrated
in Figure 3. Since several  storage and
treatment size combinations can produce
a given overflow frequency, a separate
hand cost  computation optimized the
selection for each system configuration.

Effect of Sedimentation in
Storage Facilities
  One feature of EPAMAC is the ability to
model  the  pollutant removal effect  of
storage (sedimentation) on overflows
from  storage. A  constant pollutant
removal efficiency factor is applied only to
the overflow  volume to determine the
effect of storage on  improvements  in
overflow water quality. Additional EPAMAC
Figure 2.    Relationship of EPAMAC appli-
            cation to the planning process.


Model Application

Input Preparation
  The first step in applying SFMAC was
the  preparation of input data,  which
involved  identification and gathering of
watershed and collection system charac-
teristic data.
  The  population,  area, and general
character of each watershed  were
determined. Information on watershed
characteristics, potential sites for future
storage facilities, and storage available in
the  existing system  were  identified.
Watershed data were reviewed and
regrouped because systemwide alterna-
tives modified  individual  watershed
configurations.
  The a reas a nd ru noff coeff ici ents for six
different land use types were determined
for each subarea. Runoff coefficients
were determined from actual rainfall and
sewer flow records.
 o
u.

I
                                                  r
             WW &DW Max Pumping Rate
             (Includes Effects of Storage)
             DW Max Pumping (Treatment
             Rate)
                             Time-
       Overflow Portion

       Treatment Portion


            WW Treatment


            DW Treatment
Figure 3.    Overflow and dry- and wet- weather flow relationships to pumping rates.

                                        3

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runs compared the effects of pollutant
removal during storage on receiving
water quality.

Analysis of Receiving
Water Quality
  After EPAMAC runs established water-
shed characteristics and system treatment
and storage interactions, the postprocessor
programs were used on EPAMAC output to
glean information about water quality im-
pacts on receiving waters. The violation day
postprocessor program (VDAY)was used to
determine the effect of the overflows for va-
rious storage/treatment capacity options on
the receiving water coliform concentra-
tion limits.
  The postprocessor program HISTO, which
produces histogram plots of flow, concen-
tration, and mass loads, was used to evalu-
ate the frequency, volume, and pollutant
load of overflows and treatment plant dis-
charges.

Plant Operation Frequency
  Once the storage and treatment capaci-
ties were established, it was necessary to
estimate the length of time the wet-weather
portion of the plant would operate for each
storm and the time available between storm
events to drain and clean sedimentation
tanks and grit chambers.
  HISTO was run on EPAMAC output during
a year of typical rainfall. The time between
storms was determined for each event Thus
it was possible to determine a representa-
tive number of times the tanks would be
clean at the start of a storm and also the
number of times the tanks would still con-
tain water or sediment at the start of the
next storm event.

Model Description
  The EPAMAC model (Figure 4) computes
the runoff and eventual discharge to the re-
ceiving water. Multiple lateral inflows, dry-
weather flows, pumping rates, and storage
operation modes are included in the model.
HISTO prints summary tables and graphs
from EPAMAC results for statistical analy-
sis. The VDAY program features include
coliform concentration calculation in re-
ceiving water (including die-off overtime),
a statistical analysis of overflow events and
violation days,  and the option to select
specific time periods for analysis.


Technical Basis and Assumptions
  The fundamental theory behind EPAMAC
is the  rational method of computing
runoff. The  rational method relates flow
to the  contributing  area,  rainfall,  and
runoff coefficient for the area to determine
the runoff volume for each  time step.
                   Maximum
                    Storage
                    Capacity
              Pollutant
              Removals
                                  Receiving Water
                    Receiving Water
Figure 4.    EPAMAC schematic.


  By using continuous rainfall records,
the method can be used to approximate a
continuous simulation model.

  The rational method is most appropriate-
ly used  in urban areas of less than 100
acres (41  ha) or where runoff is spread
over the surface and collected in numer-
ous inlets. The method is somewhat sim-
plistic; but the simplicity is appropriate for
EPAMAC, since it is a broad-scale model
for use in  estimating long-term  results
rather than simulating individuals storm
events.

  Another  theory used  in EPAMAC
involves mixing in storage. The complete
mix theory assumes  that flow and the
associated pollutants are immediately
dispersed throughout storage. The parti-
cles then  leave  in  proportion  to  the
average concentration and flow volume
removed from storage at any time step.
  Sedimentation  theory is involved in
estimating  the effect of storage on the
percent removal of solids from storage
overflows. The ideal, theoretical settling
velocity  of a material in water is  a
function of  particle size, shape,  and
specific weight.  Other factors such as
turbulence and horizontal velocity affect
how a particle will actually settle in a
transport or storage facility. The detailed
procedure  for making the estimate  is
included as Appendix C.

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  Several  assumptions were chosen to
maintain the EPAMAC model simplicity
and serviceability. The major assumptions
are:
 • Pollutants are conservative  and do
   not degrade.
 • Suspended solids removal efficiencies
   that are due to  settling overflow
   volumes in storage are constant over
   varying flowrates.
 • Three wet-weather flow quality
   concentrations  can be  input as
   separate values for the first  hour,
   second hour, and all  subsequent
   hours of a storm to simulate first flush
   effects.

  The HISTO program  is simply a data
transformation program: It takes the
input data and prints  them  in a new
format — namely, histogram plots and
range summary tables.
  The fundamental theory behind VDAY
is that the time variation of  the coliform
concentration in the receiving water after
an overflow event follows Chick's law (i.e.,
the longer the time since the end of the
overflow,  the greater the die-off of the
organisms).
  The user should keep in mind that the
values for  the coliform die-off decay rate
were determined through regression
analysis of data specific to San Francisco.
The  user  should determine, whenever
possible, the appropriate values for these
coefficients for any other location where
the program is applied. The decay rates
for San Francisco can be used as default
values,  if necessary;  but  the  results
should then be used for relative compari-
sons only.

Limitations
    As a consequence of the simplifying
assumptions  used in  the program, the
programs  should be executed  with at
least  10 to 20 year's worth of rainfall
records to provide results that represent
the actual  ranges that can be expected to
occur. Shorter periods of record can be
used,  but the  results may be less
representative of what can actually be
expected.

Other limitations of EPAMAC include:
 • BOD and SS are the only pollutants
   modeled.
 • Wet-weather flow quality for  each
   pollutant  is based on  three  input
   values: One for the first hour, one for
   the second hour, and one for the third
   and any subsequent hours of a storm.
 • Printout is in units of-Mgal, klb, and
   mg/L only for the appropriate time
   period  selected.
 • A  maximum  of four lateral inflows
   (flows from  previously  simulated
   adjacent areas) is allowed.
 • Values from  monthly and annual
   summaries are considered represen-
   tative of the actual periods simulated.
   Values from hourly and daily summaries
   cannot be considered truly represen-
   tative of actual storm events because
   of simplifying assumptions used  in
   the model.

Limitations of the VDAY program include:
 • The attenuation  rate of coliforms  in
   receiving water can be a default value
   based on the overflow volume (included
   in program) or a  user-supplied value
   developed for the specific area being
   simulated.
 • Printout  is in units of  Mgal  and
   violation days.
 • Printout is on an annual basis and is
   only  generally  representative  of
   conditions being modeled. Values
   from shorter  time periods (less than
   20 years) will produce an  incomplete
   statistical analysis based on the
   ranked values only.

Benefits
  The major benefits from application of
EPAMAC were the ability to evaluate a
large number of alternatives,  the ease of
understanding the results, the quickness
of obtaining  results, and the acceptance
of results in  decision-making processes.
  The use of EPAMAC met the planning
objectives of examining a large number of
alternatives  (58 in  the case of  San
Francisco) at a technical level sufficient to
determine differences  in  the  water
quality effects and the overflow frequen-
cies. System configurations were identi-
fied and used as a basis for comparing the
cost-effectiveness of the alternatives.
EPAMAC results were  also  used  to
achieve the  objective of establishing
reasonable allowable overflow frequency
limits.
  For planning and comparing alternatives,
EPAMAC is sufficiently accurate. Verifica-
tion  indicated that the real situation  is
adequately modeled. As with all models,
the accuracy of the  results  depends
strongly on the input data.
  Applying a model to San Francisco can
become unreasonably complex because
of the size and intricacy of the sewerage
system. But  the  EPAMAC adequately
handled the task. Results were understand-
able, and the volume of computer output
was  under user  control. The  overflow
event data and mass balance summaries
provided sufficient detail without generat-
ing  a volume of data that would be
impossible to review or comprehend. The
model was a tool for comprehending a
complex system without obscuring the
goals. The  results could  be used to
determine further implications of storage
and treatment balances. The postprocess-
ors also provided necessary information
and understandable results.
  The EPAMAC algorithm is simple and
straightforward, unlike those used in
some detailed, single-event simulation
models. An extensive educational program
is not needed to help the user comprehend
the model and its required input.
  The most significant benefit of EPAMAC
application was  not just in analysis of
alternatives in the facilities plan. Informa-
tion  developed was also used by the
regional  water quality enforcement
agency to evaluate appropriate, allowable
overflow frequency levels to be included
in NPDES regulations. Pollutant loadings
developed from EPAMAC simulation
runs and violation day data from VDAY
were used in cost/benefit  analyses to
determine allowable overflow frequency
levels consistent with beneficial uses of
the shoreline, ocean, and bay waters. In
conclusion,  the model results were
accepted at several levels of the decision-
making process and  were  used to
establish policy.
Model Documentation and
User's Guide
  The report  includes  a section  that
provides EPAMAC documentation and
serves as a user's guide. This section
includes (1) general description, (2) user
instruction, (3) technical concepts, and
(4) program documentation.
  The general description includes the
capabilities,  features, restrictions, and
limitations of the EPAMAC and postproc-
essor programs.
  User instructions are provided for the
program processing steps, system schemat-
ics,  alternative analysis,  execution
logistics and  input  data preparation.
Example input data sets, example outputs,
and interpretation of the results are also
described. The theory, assumptions, and
limitations for EPAMAC, HISTO,  and
VDAY are presented in the technical
concepts section of the report.
  Program documentation for EPAMAC
and the postprocessor programs includes
the mode of operation, program functions
and  internal algorithms, and  program
segments and subroutines. A section on
job control statements and input/output
file descriptions is provided for the
EPAMAC program.

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  A list of each program and a description
of the variables are included in Appendix
A.

Summary and Recommendations
 • The EPAMAC is a generalized version
   of the  SFMAC used during the
   development of  San Francisco's
   Southwest Water Pollution Control
   Plant Facility Plan and Master Plan.
 • EPAMAC is a special purpose, contin-
   uous simulation  model  of  surface
   runoff with minimal input data
   requirements, broad areal and tempor-
   al coverage, and both flexibility and
   ease of application.
 • In addition to quantity and quality
   analyses for stormwater flows, capabil-
   ities  of  the model include dry-
   weather flow, hourly simulation,
   overflow event analysis, pollutant
   removal as a result of sedimentation
   in storage,  and lateral inflows.
   Postprocessor programs can also
   provide  histogram plots of flow and
   quality as well as analyses of  violation
   days for  coliform  limits in receiving
   water for several coliform standards.
 • Information developed by the model
   was used by decision-makers  for
   establishing allowable overflow fre-
   quency limitations for NPDES permits
   for wet-weather discharges.
 • The overall effectiveness of the model
   in this  application was  high. The
   client and consultant were both able
   to contribute significantly to the
   model application process. Also, the
   flow and quality concerns in a
   combined sewer system were adequate-
   ly addressed. In addition, the  planning
   objectives were met, and preliminary
   sizing of a large number of diversified
   alternatives was accomplished.
 • The EPAMAC and  postprocessor
   programs should be implemented as
   a  preliminary design and planning
   tool.
 • The EPAMAC should be used repeated-
   ly to analyze various combinations of
   storage  capacities and treatment
   plant rates to determine  possible
   optimum conditions. The EPAMAC
   should be used to examine seasonal
   and yearly periods.

  The full report was submitted  in partial
fulfillment of Contract No. 68-03-2877
by  Metcalf &  Eddy, Inc., under the
sponsorship of the  U.S. Environmental
Protection Agency.
William G. Smith and Marianne  E. Strickfaden  are  with  Metcalf  & Eddy,
  Engineers, Inc., Palo Alto, CA 94303.
Richard Field is the EPA Project Officer (see below).
The complete report, entitled "EPA  Macroscopic Planning Model (EPAMAC) for
  Stormwater and Combined Sewer Overflow Control: Application Guide and
  User's Manual," (Order No. PB 83-259 689; Cost: $26.50, subject to change)
  will be available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield. VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Storm and Combined Sewer Program
        Municipal Environmental Research Laboratory—Cincinnati
        U.S. Environmental Protection Agency
        Edison,  NJ 08837

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