United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-084 Nov. 1983
&ER& Project Summary
Demonstrate Real Time
Automatic Control of Combined
Sewer Systems
Harold C. Coffee, Donald E. Evenson, Paul R. Giguere,
Gene T. Handa, Christos A. Phanartzis, and Larry A. Roesner
IV'
This study's primary objective was to
develop a real time automatic control
model that could be used in connection
with a combined sewer system to mini-
mize overflows during storms. The
model was applied to the North Shore
Outfall Consolidation Project in San
Francisco. This project consists of a
larger transport-storage facility that in-
tercepts existing outfalls and allows
flows to be pumped to a primary or a
secondary treatment plant depending
on operational strategy. The perfor-
mance of four reactive control strate-
gies and one reactive-predictive strate-
gy were formulated and evaluated for
pollutant removal. The cost effective-
ness of each was then determined.
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
San Francisco has a requirement to
reduce wet weather overflows from a
statistical average of 82 per year to 4 per
year. Part of the overall plan for combined
sewer overflow control involves the North
Shore Outfall Consolidation Project. This
project includes a transport-storage
facility with a total storage volume of 19
million gal. A pumping system for
transporting wet weather flows initially
to the North Point Plant is designed for a
maximum capacity of 150 mgd. Dry
weather capacity is 30 mgd. Eventually
secondary treatment for dry weather
flows would be provided at an expanded
Southwest Plant and wet weather flows
would be pumped to a proposed Southwest
Plant providing primary treatment. The
objective of the project was to develop a
real time automatic control model that
would manage the movement and location
of the water in the system to minimize the
pollution load to the primary treatment
plant.
Summary of the Project Scope
This report presents the findings of the
first phase of the total effort dealing only
with the development and application of
concepts and methods for analyzing real
time automatic control systems. Control
system objectives were to:
1. limit untreated overflows to an
average of less than one per year (this
was later changed to four by the
California Regional Water Quality
Control Board),
2. control the location of overflow
points,
2. provide the best treatment possible to
all flows,
4. make optimal use of all facilities to
avoid higher costs, and
5. provide data logs and reports for
current needs and for historical
records.
To achieve these, three alternative
methods of control were considered in
the study:
1. remote manual control with data
logging,
-------
2. central digital (automatic) control and
data logging, and
3. distributed digital control and data
logging.
Only two types of control philosophies
were applicable to the system:
1. purely reactive control and
2. integrated reactive-predictive control.
Four reactive control strategies and
one reactive-predictive strategy were
formulated and evaluated in the course of
the study:
1. basic operation strategy (this strategy
represents the basic required strategy
to meet the overflow objectives),
2. basic operating strategy with seasonal
constraints,
3. basic operating strategy with minimum
storage constraints,
4. basic operating strategy with season-
al and minimum storage constraints,
and
5. basic operating strategy with rainfall
prediction and seasonal and minimum
storage constraints.
These strategies are first described
generally and then in terms of the basic
philosophy of control they represent and
the types of control devices required to
implement them. The devices include
water level recorders, flow gates, dams,
weirs, pumps, and digital control and
computer hardware.
Four mathematical models were inves-
tigated for application as analytical tools
that could be used for developing and
testing control strategies and for simulat-
ing inflows to the system and its resulting
hydraulic response, based either on
historical or real time conditions. The
three computer models were TREAT and
the RUNOFF and TRANSPORT Blocks of
EPA's Storm Management Model (SWMM).
Each model is described briefly, and its
potential usefulness in this study is
explored. Applications of the models to
the project are described and example
results presented. The fourth model
involves rainfall prediction — a necessary
input for predictive control strategies. The
subjects include alternative techniques
available for rainfall prediction, local
rainfall characteristics and data availability
in the San Francisco area, and the
computer model RAFORT, which was
developed specifically for the project and
is applicable to real time operation
Examples of rainfall predictions made
with RAFORT are included.
After considering the basic analytical
tools need to assess the alternative
control strategies for the project, the
results of the assessment are given. For
each strategy introduced, the computer
model TREAT simulated details of the
system over a 70-year period. The major
inputs and processes modeled included
rainfall/runoff, dry weather flows,
primary and secondary treatment, storage,
and untreated overflows. The TREAT
algorithms were modified so the control
system could operate for each simulated
alternative control strategy. TREAT then
produced a complete statistical frequency
distribution for 12 performance indicators,
including such measures as the annual
number of wet weather events and the
associated amount and duration of
treatment, storage, and untreated over-
flows. A rough measure of the relative
reductions in pollutant load discharged in
each case was also computed.
The annual capital and operation and
maintenance costs for each strategy
were estimated based on the added costs
attributed to the control system. A cost-
effectiveness analysis was then performed
to arrive at conclusions on the best
strategies for the system.
Conclusions and
Recommendations
The conclusions and recommendations
relate to the general concepts and
approaches developed during the study
rather than to the specific operation of the
San Francisco Project. Some of the major
conclusions drawn were:
• Control strategies can have a signifi-
cant impact on the overall performance
of the system and should be considered
during the facilities planning and
design phase.
• For the San Francisco Project and an
overflow objective of one per year, the
best control strategy appears to be
reactive.
• Reactive-predictive strategies have
modest potential for improving system
performance but are limited by
inaccuracies in rainfall prediction
methodology.
• The model TREAT is useful in evaluat-
ing control strategies but is inadequate
for use in real time control if a
predictive strategy is selected.
• The RUNOFF Block of SWMM could
be used in real time control under a
predictive strategy.
• The TRANSPORT Block of SWMM is
too complex and is too subject to
numerical instabilities for use in real
time control.
• The best control strategy depends on
the system design and the control
objectives; changes in either will alter
the control strategy that provides the
best performance.
The full report was submitted in
fulfillment of Cooperative Agreement No.
CS-803743 by the City and County of San
Francisco under the sponsorship of the
U.S. Environmental Protection Agency.
-------
Harold C. Coffee, Gene T. Handa, and ChristosA. Phananzis are with the City and
County of San Francisco. San Francisco, CA 94102; Donald E. Evenson and Paul
R. Giguere are with Camp Dresser and McKee, Inc., Walnut Creek, CA 94596;
and Larry R. Roesner is with Camp Dresser and McKee, Inc., Annandale, VA
22003.
Richard Field is the EPA Project Officer (see below).
The complete report, entitled "Demonstrate Real Time Automatic Control of
Combined Sewer Systems," (Order No. PB 83-259 705.Cost: $ 16.00, 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
irUS GOVERNMENT PRINTING OFFICE 1983-659-017/7228
-------
United States Center for Environmental Research .. _ POSTAGE
Environmental Protection Information
Aaencv Cincinnati OH 45268
a Cincinnati, Ohio
Permit No G35
Official Business
Penalty for Private Use $300
MfcKL00632«0
MJU^TJLLEY
i> OtARBUWN SI
CHICAGO IL 60bO<»
------- |