United States

Environmental Protection

Agency

Office of Water

Washington, D.C.

EPA 832-F-99-042

September 1999

Combined Sewer Overflow

Technology Fact Sheet

Retention Basins

DESCRIPTION

In older communities, where combined sewer

systems are still common, storm water flows often

exceed the sewer system’s hydraulic capacity.

Redevelopment of urban areas can also increase the

impervious area in the sewershed, which, in turn,

increases storm water flows to combined sewers.

Storage is often the best measure for attenuating

peak combined sewer flows. Storage facilities have

been used extensively for Combined Sewer

Overflow (CSO) mitigation (Urbonas and Stahre,

1993; Field, 1997). Specific CSO retention

methods include underground storage (e.g.,

tunnels), in-receiving water storage, and retention

basins (RBs). RBs may be built in-line or off-line.

This fact sheet describes near-surface, off-line RBs.

CSO RBs capture and store some of the excess

combined sewer flow that would otherwise be

bypassed to receiving waters. Stored flows are

subsequently returned to the sewer system during

dry weather periods, when in-line flows are reduced

and capacity is available at the treatment facility.

RBs can be designed to control both flow rate and

water quality. Figure 1 shows an example of a

multi-stage CSO RB with treatment capabilities.

This facility handles peak flows by routing them

through a mechanical bar screen and then pumping

them into the first compartment. The main

function of the first compartment is to allow for

Source: City of Grand Rapids, Michigan, 1992.

FIGURE 1 CITY OF GRAND RAPIDS-MARKET AVENUE CSO RETENTION BASIN
primary settling and grit removal. If the flows

continue to rise, the first compartment fills and then

spills over into the second compartment. This

compartment is designed specifically to store most

of the overflow from the first compartment.

Compartment two is also equipped with a floor

wash system that flushes all settled sediments into

a collection trough. If the flows continue to rise,

the water spills over into a series of troughs where

sodium hypochlorite is applied for disinfection.

The flow is then routed to a contact tank in

compartment three which eventually returns the

water to the Grand River.

In addition to minimizing water quality impacts and

attenuating peak flows, CSO storage eliminates or

reduces sewer backups, improves the efficiency of

existing treatment capacity, and improves effluent

quality at the treatment facility (WEF/ASCE, 1992).

Near-surface storage in open or covered basins is

the most common method of CSO retention. RBs

may be placed online or offline from the combined

sewer. Online RBs are connected in series to the

combined sewer and retain excess flows when the

inlet flow surpasses the outlet capacity. Off-line

RBs are connected in parallel to the combined

sewer and receive flows only during wet weather

periods.

Off-line RBs are typically earthen basins or covered

or uncovered concrete tanks. Covered basins are

widely used because they provide better odor

control and better safety conditions. 

Off-line storage is more costly than online storage

because parallel lines must be constructed and

facilities for pumping the stored wastewater back to

the sewer are usually required. However, off-line

storage is required where head loss in the

downstream sewer is a concern and sedimentation

or other treatment methods are desired. 

Offline RBs may be located at upstream or

downstream locations in the combined sewer

system. Advantages of upstream control include

greater flexibility in selecting sites for facilities and

more efficient control of flows to the downstream

treatment facility. The primary advantage of

downstream storage is that fewer facilities are

required, resulting in lower construction and

operation and maintenance costs. It may be

possible to minimize costs further if storage

capacity is available at the wastewater treatment

plant.

Primary concerns in CSO retention are:

• Managing flows to and from the retention

basin.

• Preventing the combined sewage from

becoming septic (or handling the

wastewater after it has become septic).

• Removing accumulated solids and

floatables.

• Disinfecting basin overflows to receiving

waters.

CSO RBs have been designed to limit these

problems. In offline facilities, flows are regulated

by limiting the amount of flow that is diverted to

the RB (Figure 1). The sidestream flow is regulated

by a device located downstream of the diversion or

at the basin’s outlet. Many types of fixed and

movable flow regulators may be used for CSO

retention basins.

Average BOD concentrations of combined sewage

are usually high enough to promote septic

conditions if the wastewater is retained for an

extended period of time. Therefore, the stored

wastewater must be either aerated at the RB or

returned to the sewer system in a timely manner.

Sedimentation treatment is often incorporated into

the RB design. RBs may be compartmentalized so

that the first flush flow can be retained in one or

more tanks long enough to remove suspended

solids, BOD, and nutrients, while the remainder of

the flow is handled in subsequent compartments. In

some cases, the discharged flow can bypass the

primary sedimentation process at the wastewater

treatment facility.

An RB can remove accumulated solids by inducing

scouring or agitating the stored wastewater during

discharge to the sewer, by flushing with a potable or
effluent water supply, or by using mechanical

scrapers (WEF/ASCE, 1992). Flushing systems

release a wave of water to sweep accumulated

solids and debris to a disposal channel at the end of

the basin.

In cases where CSO flows exceed the capacity of

RBs, an overflow structure diverts the excess flows

to nearby surface waters. Disinfection of RB

overflows may be required to minimize the risk of

pathogens being discharged to receiving waters.

High-rate disinfection is often required to ensure

adequate removal of pathogens from short-term,

high volume overflows. The disinfection process

must be adaptable to intermittent high flows with

variable temperatures, suspended solids

concentrations, and microorganism levels (Field,

1997).

APPLICABILITY

Offline storage is a common structural CSO control

because it is less costly and more easily adapted to

site conditions than other structural approaches

(e.g., storm sewer separation). Several

municipalities, including Boston, MA, Atlanta, GA,

Los Angeles, CA, Wayne County, MI, and

Saginaw, MI, have constructed networks of offline

retention basins to minimize CSOs. Other

municipalities, including Richmond, VA, and

Grand Rapids, MI, are using one or a few large RBs

for CSO control. 

The City of Richmond's RB has a storage capacity

of 36 million gallons (MG). It is designed to

capture the first flush of combined sewage for a

one-month design storm. The basin includes jet

aeration and momentum headers, which prevent the

retained wastewater from becoming septic and keep

solids in suspension. The stored combined sewage

is pumped to the wastewater treatment plant within

48 hours after the end of each event.

Environmental assessments are required to evaluate

the environmental impact of constructing and

operating RBs. The results of these studies can

influence the location and the design of facilities,

and even the decision of whether or not to construct

retention basins (Munger and Toll, 1996).

Experience has shown that public perception is an

important factor in the design of CSO retention

basins. Recent designs of CSO retention basins

have incorporated aesthetic elements, such as parks

or recreational areas, on top of covered basins, as

well as more elaborate odor control systems

(Wayne County, 1997; AMSA, 1994).

Offline retention basins are often used to manage

CSOs after existing storage in the sewer system has

been optimized. Offline RBs are usually

implemented where online facilities are not

practical (e.g., where head loss in downstream

sewers is a concern) or some level of treatment is

required.

Engineering design studies should evaluate

subsurface soil conditions, depth of construction,

constraints on use and access to the site, and

environmental impact. Detailed evaluation should

consider the means of disposal of screenings and

residual solids, handling and storage of chemicals,

capacity and routing of sewer/force main, and the

need for a pump station.

ADVANTAGES AND DISADVANTAGES

The primary limitations of CSO retention basins are

their costs and the environmental impact of

construction. Because retention basin construction

can be expensive, other source control and sewer

optimization measures should be implemented

before considering the addition of storage controls.

Construction of large retention basins may require

the destruction of sensitive habitats for terrestrial

and aquatic life. Environmental assessments are

generally required to select sites that will have the

least impact on the environment and the public. In

some cases, mitigation of unavoidable

environmental impacts may be required.

Construction of RBs can have a significant impact

on the environment. Environmental assessments

are usually performed to identify sites and

construction methods that will minimize damage to

the environment and disturbance of the public.

These assessments will also specify steps that can

be taken to mitigate unavoidable environmental

impacts. 
The elimination or reduction of CSOs can improve

receiving water quality. As shown in Figure 2,

fecal coliform concentrations in the Grand River

below the CSO outfalls and wastewater treatment

plant have exhibited a long-term decline. The

improved water quality appears to be related to the

30 MG retention basin that came online in 1992.

Additional information on the effects of CSO

storage on water quality will become available

when CSO long-term monitoring programs are fully

implemented as part of EPA's CSO Control

Strategy (U.S. EPA, 1994). Recommended

performance measures for the National CSO

Control Program are described by AMSA (1996).

DESIGN CRITERIA

The primary purpose of storage is to optimize

treatment of the combined flow at the downstream

wastewater treatment plant; therefore, RB design

should be developed with consideration of the

treatment capabilities of the wastewater treatment

plant. The RB design should also ensure that stored

wastewater does not become septic and

accumulated solids and floatables are effectively

removed. In some cases, RB overflows to receiving

waters must be disinfected. 

As with all CSO control approaches, the evaluation

of CSO retention basins should start with a detailed

characterization of the sewer system, including a

review of rainfall and sewer flow records,

monitoring of selected CSO locations, receiving

water quality monitoring, and mathematic modeling

(Moffa, 1997). This information is used to

establish a design standard such as the frequency of

RB overflows to surface waters (e.g., one, three, or

five times a year) or the percent reduction in CSO

volume. The size of the basin may be based on data

on rainfall intensity, duration, and frequency;

standard design storms with a specified recurrence

interval (e.g., one, five, or ten years); the

chronologic record of rainfall; or a chronologic

series of measured flows at the site (Urbonas and

Stahre, 1993).

Storage Volume

Several methods for calculating storage volumes

have been summarized by Urbonas and Stahre

(1993). One of the most common is flow route

modeling. These models have become popular for

calculating storage volumes because of their ability

to simulate runoff under a variety of conditions.

Commonly used models include EPA's Storm

Water Management Model (SWMM); the U.S.

Army Corps of Engineers' Storage, Treatment,

Overflow, Runoff Model (STORM); and the

Hydrological Simulation Program-FORTRAN

(HSPF). Useful summaries of these models are

given by Huber and Heaney (1980, 1982). SWMM

is most commonly used to simulate urban runoff

processes and combined sewer systems (EPA,

1985; James, 1993). In addition to estimating

surface runoff, SWMM and other models can

estimate pollutant loads in response to precipitation

and surface pollutant accumulations.

Basin Shape

Rectangular basins are the least expensive to

construct and maintain. Circular and octagonal

basins are more expensive to build, but are

advantageous because they can be configured to

self-clean settled solids.

Inlet Type

The choice of inlet type will depend on whether the

RB is designed to remove solids. If solids removal

0

100

200

300

400

500

600

86 87 88 89 90 91 92 93 94 95 96

Geometric Mean (#/100

ml)

Year

Source: Grand Rapids, 1996.

Source: City of Grand Rapids, Michigan, 1996.

FIGURE 2 TREND OF FECAL COLIFORMS IN

GRAND RAPIDS, MI
is desired, the inflow velocity must be reduced (e.g.,

by using baffles) to prevent resuspension of settled

solids. Alternatively, the inlet can be configured to

create turbulence and circular flow to keep solids in

suspension if sedimentation is not desired.

Bottom Configuration

The bottom configuration of an RB can enhance

cleaning of sand, silt, and other settled solids.

Three types of bottom configuration are used for

rectangular RBs: flat bottoms; parallel longitudinal

grooves; and a single continuous groove. Flat

bottoms are the easiest to construct, but require a

mechanism for solids removal. Urbonas and Stahre

(1993) suggest that flat-bottomed basins should

have a minimum bottom slope of 3 percent and a

width equal to one-half to two-thirds of the length.

A series of parallel, longitudinal grooves may be

constructed to convey solids out of the basin;

however, experience has shown that supplemental

cleaning is occasionally required (Urbonas and

Stahre, 1993). Basins with bottoms that have a

single continuous groove can also be self-flushing.

Outlet Type

Outlet structures must be closely matched to the

specifications of downstream facilities. It is usually

desirable to maintain a constant outlet flow rate to

minimize the effects on downstream structures. RB

outflow can be controlled using a fixed outlet

opening, a choked outlet pipe, adjustable gates,

pumps, and special regulators. Fixed outlet

orifices, flow-restricting pipes, and overflow weirs

are often chosen to regulate the RB outlet flow

because they have predictable hydraulic

characteristics and are simple to design (Field,

1997).

Remotely controlled gates offer more direct control

of the RB outlet flow. These outlets generally

consist of a flow-monitoring system, movable gates

that are adjusted by electrical, hydraulic, or

pneumatic controls, and a data processing and

control unit (Urbonas and Stahre, 1993). Coupled

with the use of a model to estimate runoff from

rainfall, this system can be adjust the gate opening

well in advance of high-flow events. However, gate

systems consist of many moving parts and require

instrumentation, which can be expensive to operate

and maintain.

Pumps are used to regulate RB outflow where the

topography does not allow gravity flow or more

operational control is needed. The primary

disadvantages of this system are the costs of

operating and maintaining the pumps and the

potential for pump failure.

In Europe, several self-regulating outlet systems

have been developed for RBs, including

float-activated gates, floating outlets, and bending

weirs. A float-activated gate developed in

Germany, called the HydroslideTM, restricts outlet

openings during high flow events so that a constant

discharge rate is maintained (Figure 3). A floating

outlet is another self-regulating outlet. This outlet

floats on the water surface and maintains a constant

water depth at the RB outlet. The removal of

surface water helps to trap settled solids in the RB.

Bending weirs also operate automatically without

the use of auxiliary power (Field, 1997). One type

of bending weir used for RBs, called the

HydrobendTM, is a bending flap controlled by a

counterweight and an eccentric control disc. As

shown in Figure 4, the disc is designed to balance

between the forces of water pressure on the

overflow face of the bending weir and the

counterweight (GNA, 1996).

Source: GNA, 1996.

FIGURE 3 HYDROSLIDETM FLOW

REGULATOR
Overflow Structures

RBs are usually equipped with emergency spillways

or outlets. Spillways are sized to pass the

maximum inflow under the worst-case condition of

a clogged or non-operational outlet. Spillways

should be located away from the RB outlet to

minimize the loss of floatables that often collect

near outlets (Urbonas and Stahre, 1993).

Disinfection

In some cases, RB overflows may be disinfected to

prevent the discharge of pathogens to surface

waters. Chlorine gas (Cl2) or sodium chloride

(NaCl) is commonly used for wastewater

disinfection. However, these disinfectants can react

with ammonia (NH3) in the combined sewage to

form chloramine compounds, which are toxic to

aquatic life. Chlorine dioxide (ClO2), a more

rapidly-acting disinfectant, does not react with NH3.

It may be necessary to dechlorinate the RB

overflow to eliminate the potential for instream

toxicity due to chlorine.

Operational Control

CSO retention basins are operated to minimize

overflow and maximize the capacity of the sewer

system and treatment facility. Three levels of

operational control may be practiced:

• Local (closed-loop) control of regulators,

gates, or pumps.

• Regional coordination of several local

controllers. 

• Global control of multiple components,

including rainfall and flow data recorders,

telemetered controllers for regulators, gates,

and pumps, and a computer system for

overall system control.

The City of Grand Rapids (MI) uses a global CSO

monitoring system that consists of sewer level

sensors, a bridged telephone network and telemetry

system, and a PC-based data acquisition and

processing system (Spykerman, 1996).

PERFORMANCE

CSO retention basins can significantly reduce or

eliminate CSO volumes. Construction of a 30 MG

retention and treatment basin by the City of Grand

Rapids (MI) helped to reduce CSO discharge

volumes by about 90 percent (Grand Rapids, 1995).

Similar results have been achieved at other

municipalities. 

Concentrations of coliform bacteria, suspended

solids, nutrients, and BOD can be reduced in RBs

designed to induce sedimentation. Estimated

removal rates of BOD5 and suspended solids are

determined by the detention time and overflow rates

(based on average daily flows). Figure 5 shows the

average percent removal of BOD5 and suspended

solids for municipal wastewaters. However, the

solids characteristics and settling velocities of

CSOs vary by site and it is recommended to

develop a settling velocity distribution for each site

(Field, 1997). Chemicals can be added to improve

solids removal by coagulation (Adams, et. al,

1981).

OPERATION AND MAINTENANCE

Basins, especially those with covered

compartments, are subjected to extreme conditions,

including high humidity, corrosive gases, and

sludge deposits. Operation and maintenance

requirements can be reduced through appropriate

Source: GNA, 1996.

FIGURE 4 HYDROBENDTM FLOW

REGULATOR
planning and design (e.g., using corrosion-resistant

materials and providing adequate ventilation).

However, routine inspection and maintenance

remain necessary to ensure proper operation of the

basin.

Sediment removal systems include traveling bridge

nozzles, fixed nozzles, mechanical mixers, and

water flushing systems. Studies have shown that

flushing systems are the most efficient and costeffective (Novac and Grande, 1992; Parente, et al.,

1995). Two types of flushers have been widely

used: a flip gate flusher such as HydroselfTM or

HydrassTM, and tipping flushers (Field, 1997). The

HydroselfTM system operates by discharging water

through a hydraulically operated flap gate. The gate

creates a flushing wave that sweeps settled solids

and debris from the basin floor (GNA, 1996). More

than 300 HydroselfTM units are used in Europe for

cleaning CSO storage tanks (Field, 1997).

As shown in Figure 6, the tipping flusher is a

cylindrical vessel that is placed above the maximum

water level on the back wall of the retention basin.

The vessel fills with water up to a pre-determined

depth, and then the vessel rotates on a center axis,

spilling the water into the basin and creating a

flushing wave. Tipping flusher units have been

used in North America since the early 1990s.

Access must be provided for basin cleaning and for

removing blockages from the outlet and spillway.

Walkways are also recommended for inspection of

spillways, outlets, and the interior of covered basins

(Urbonas and Stahre, 1993). Monitoring

information is essential for operational control and

future design considerations; therefore, the water

level in the basin should be recorded.

COSTS

Storage and treatment of CSOs is structurally

intensive and costly, and should be used only after

CSO sources have been controlled and sewer use

has been optimized. Costs of CSO controls for

selected communities throughout the U.S are

summarized in Table 1. The cost of basin

construction can also be estimated from standard

cost curves like those provided by Lager, et al.

(1977).

As shown in Table 1, capital costs for CSO

retention basins are significant. Before

implementing CSO controls, a cost-benefit analysis

should be done to compare the costs of the controls

to the anticipated benefits of improved water

Source: GNA, 1996.

FIGURE 6 TIPPING FLUSHER UNIT

Percent Removal

Detention Time, hr

Source: Steel, 1960.

FIGURE 5 PERCENT BOD5 AND

SUSPENDED SOLIDS REMOVAL FOR

VARIOUS OVERFLOW RATES VERSUS

DETENTION TIME IN TREATING MUNICIPAL

WASTEWATERS
TABLE 1 COSTS OF CSO RETENTION BASINS FOR SELECTED MUNICIPALITIES

Municipality Retention

Basin

Year

Constructed

Basin

Capacity

(MG)

Covered/

Uncovered

Type of

Facility

Construction

Cost

O & M

Cost

Design

Criteria

Grand

Rapids, MI

Market

Avenue RB

June 1992 30.5 offline $30 million $40,000 10 yr-1

hr storm

First

Compartment

10.68 covered

Second

Compartment

16.68 uncovered

Third

Compartment

3.14 uncovered

Richmond,

VA

Shockhoe

RB and

Diversion

System

~1988 41 covered and

uncovered

hydraulic

retention,

sediment

return to

sewerage

system, no

disinfection

covered:

$1,077,9002

uncovered:

$343,9002

$500,096 1 month

design

storm,

7500 cfs

first flush

Oakland

County, MI

Acacia

Park

1997 4.5 covered offline with

sedimentation

and

disinfection

capabilities

$13.9 million $207,000 30

minute

detention

for 

1 year/ 

1 hour

storm

Birmingha

m

1997 9.6

(includes

tunnel)

covered offline with

sedimentation

and

disinfection

capabilities

$35.6 million $370,000 30

minute

detention

for 

1 year/ 

1 hour

storm

Bloomfield

Village

1997 10.2 covered offline with

sedimentation

and

disinfection

capabilities

$28.9 million $500,000 30

minute

detention

for 

1 year/ 

 1 hour

storm

San

Francisco,

CA

North

Shore

1984 24 covered

(underground)

transport/

storage box3

$69.08 million not

available

4 CSOs/

year4

Mariposa 1992 0.7 covered

(underground)

transport/

storage box3

$10.17 million not

available

10

CSOs/

year4

Sunnydale 1991 6.2 covered

(underground)

transport/

storage box3

$19.29 million not

available

1 CSO/

year4

Yosemite 1989 11.5 covered

(underground)

transport/

storage box3

$19.16 million not

available

1 CSO/

year4

1 includes operators, time, supplies, chemicals, parts, and utility charges

2 costs adjusted to 1994 costs

3 CSO discharges from transport storage facilities receive flow through treatment with weirs to settle solids and baffles to skim floatables

4 Transport storage facilities were designed in conjunction with pumping and treatment facilities to meet annual average CSO criteria

specified in NPDES permits; local sewers tributary to the transport/storage boxes are designed for the 5 year storm
quality. For example, King County, WA is

currently performing a CSO assessment to identify

the water quality benefits of CSO controls and to

determine the most effective method for improving

water quality (Munger and Toll, 1997).

Novac and Grande (1992) surveyed the costs of

various methods for cleaning CSO storage basins.

Tipping flushers had less capital and operation and

maintenance costs than traveling bridge nozzles,

fixed nozzles, and mechanical mixers. The average

capital cost for tipping flushers was $19.59 per

cubic meter of storage ($14.96 per cubic yard of

storage), compared with $51.66 and $52.44 per

cubic meter of storage ($39.45 and $40.04 per cubic

yard) for traveling bridge nozzles and fixed nozzles

(adjusted to 1998 costs). Parente, et al., (1995)

determined that HydroselfTM, a flushing gate

system, would be cost-effective compared to

tipping flushers and spray methods. Capital and

operation and maintenance costs were $109.38 and

$0.08 per square meter of area ($91.44 and $0.07

per square yard) for HydroselfTM versus $164.08

and $0.12 per square meter of area ($137.17 and

$0.10 per square yard) for tipping flushers (adjusted

to 1998 costs).

Capital and operating costs for high-intensity

chlorination systems are described by Field (1997).

A system with short chlorine contact times and

intense mixing is more economical and can be as

effective as a conventional process with longer

chlorine contact times (Field, 1997).

REFERENCES

1. Adams, C.E., D.L. Ford, and W.W.

Eckenfelder, 1981. Development of Design

and Operational Criteria for Wastewater

Treatment. Enviro Press, Nashville, TN.

2. AMSA, 1994. Approaches to Combined

Sewer Overflow Program Development: A

CSO Assessment Report. Association of

Metropolitan Sewerage Agencies,

Washington, D.C.

3. AMSA, 1996. Performance Measures for

the National CSO Control Program.

Association of Metropolitan Sewerage

Agencies, Washington, D.C.

4. Field, R. and T.P. O'Connor, 1997.

“Control and Treatment of Combined

Sewer Overflows.” In: Control and

Treatment of Combined Sewer Overflows.

P. Moffa (ed), Van Nostrand Reinhold,

New York, NY.

5. GNA, 1996. CSO Equipment Information.

Grande, Novac & Associates, Inc.,

Montreal, Canada.

6. City of Grand Rapids, Michigan, 1992.

Brochure: Grand Rapids Market Avenue

Retention Basin. Grand Rapids Public

Works.

7. City of Grand Rapids, Michigan, 1995.

Brochure: Grand Rapids Reduces

Combined Sewer Overflows Dramatically.

Grand Rapids Public Works.

8. City of Grand Rapids, Michigan, 1996.

Long-term Overflow Monitoring Reports -

1986 to 1996. Grand Rapids Public Works.

9. City of Grand Rapids, Michigan, 1998. C.

Schroeder, Hydraulic Engineer, City of

Grand Rapids Waste Water Treatment

Plant, Grand Rapids, personal

communication with Parsons Engineering

Science, Inc.

10. Greeley & Hanson, 1998. F. Maisch,

personal communication with Parsons

Engineering Science, Inc. regarding City of

Richmond, Schokhoe Retention Basin.

11. Huber, W.C., and J.P. Heaney, 1980.

“Operational Models for Stormwater

Quality Management,” In: Environmental

Impact of Nonpoint Source Pollution. M.R.

Overcash and J.M. Davidson (eds.). Ann

Arbor Science Publications, Ann Arbor, MI.

12. Huber, W.C., and J.P. Heaney, 1982.

“Analyzing Residuals Discharge and

Generation from Urban and Non-urban
Land Surfaces,” In: Analyzing Natural

Systems, Analysis for Regional

Residuals-Environmental Quality

Management. D.J. Basta and B.T. Bowers

(eds.). The Johns Hopkins University

Press, Baltimore, MD.

13. James, W., 1993. “Introduction to the

SWMM Environment,” In: New Techniques

for Modeling the Management of

Stormwater Quality Impacts. Lewis

Publishers, CRS Press, Boca Raton, FL.

14. Lager, J.A. et al. 1977. Urban Stormwater

Managment and Technology: Update and

User’s Guide. EPA 600/8-77-014, U.S.

EPA, Washington, DC.

15. Moffa, P., 1997. “The Combined Sewer

Overflow Problem: An Overview,” In:

Control and Treatment of Combined Sewer

Overflows, P. Moffa (ed), Van Nostrand

Reinhold, New York, NY.

16. Munger, S. and J. Toll, 1997. “King

County Water Quality Assessment,” In:

Seminar Proceedings for Wet Weather

Research Program - Research Findings and

Applications. Water Environment Research

Foundation Seminar, Chicago, IL.

17. Novac, G. and N. Grande, 1992. Cost

Analysis of Different Methods of Cleaning

CSO and Wastewater Equalization Tanks.

Water Environment Federation 65th Annual

Conference & Exposition, New Orleans,

LA. #AC92-067-006.

18. Oakland County, Michigan, 1999. G.P.

Aho, Assistant Chief Engineer, Oakland

County Drain Commisioner, personal

communication with Parsons Engineering

Science, Inc.

19. Parente, M., K.E. Stevens, and C. Eicher,

1995. Evaluation of the New Technology in

the Flushing of Detention Facilities. Water

Environment Federation, 68th Annual

Conference & Exposition, Miami, FL.

#9537001.

20. Reynolds, T. D. and Richards, P. A., 1996.

“Unit Operations and Processes in

Environmental Engineering,” In: Water

Supply and Sewage, E. W. Steel (ed),

McGraw-Hill, Inc.

21. City of San Francisco, California, 1999. B.

Goldstein, Public Utilities Commission,

City of San Francisco, personal

communication with Parsons Engineering

Science, Inc.

22. Spykerman, M., 1996. Real-Time

Combined Sewer Overflow Monitoring.

Michigan Water Environment Association

"Need to Know" Workshop. 

23. Urbonas, B. and P. Stahre, 1993.

Stormwater: Best Management Practices

and Detention for Water Quality, Drainage,

and CSO Management. PTR Prentice Hall,

Englewood Cliffs, NJ.

24. U. S. EPA, 1985. Storm Water

Management Model (SWMM) Bibliography.

EPA/600/3-85/077, Athens, GA.

25. U. S. EPA, 1994. Combined Sewer

Overflows Policy. EPA 830-B-94-001,

Washington, D.C.

26. Wayne County Department of Environment,

1998. “Rouge River National Wet Weather

Demonstration Project: CSO Demonstration

Project.” Internet site a t

http://208.220.235.35/wayne/build/rpo/tec

htop/cso/csocont.html, accessed June, 1998.

27. WEF/ASCE, 1992. Design and

Construction of Urban Stormwater

Management Practices. Water

Environment Federation, Alexandria, VA,

American Society of Civil Engineers,

Washington, D.C.
For more information contact:

Municipal Technology Branch

U.S. EPA

Mail Code 4204

401 M St., S.W.

Washington, D.C., 20460

ADDITIONAL INFORMATION

City of Grand Rapids, Michigan

Chuck Shroeder

Grand Rapids Wastewater Treatment Facility

1300 Market St., SW

Grand Rapids, MI 49503

Milwaukee Metropolitan Sewerage District

Wayne St. John

Director of Operations

260 W. Seeboth St.

Milwaukee, WI 53201

Oakland County, Michigan

Gary R. Aho

Oakland County Drain Commissioner

No.1 Public Works Drive

Waterford, MI 48328

City of Richmond, Virginia

Mac McConico

600 E. Broad St., Rm 831

Richmond, VA 23219

City of San Francisco, California

Beth Goldstein

Public Utilities Commission

1212 Market St., 2nd floor

San Francisco, CA 94102

The mention of trade names or commercial

products does not constitute endorsement or

recommendation for the use by the U.S.

Environmental Protection Agency.