EPA DOCUMENT AC-06
RETURN TO MARTHA SEGALL
ROOM 206, BLDG. A
0050
LITERATURE SUMMARIES
PREPARED FOR A
CSO GUIDANCE DOCUMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C.
September 28,1989
1. An Analysis of the United States Environmental Protection Agency's Needs
Survey (American Public Works Association), 1975.
2. Analyzing the Existing Collection System (Pisano), 1978-1981.
3. Assessment of Benefits Resulting from Control of Combined Sewer Overflows
(Driscoll and Mancini), 1978.
4. Benefit Analysis for Combined Sewer Overflow Control (USEPA - Environmental
Research Information Center), 1979.
5. Combined Sewer Overflow Abatement Alternatives - Washington, D.C.
(Weston), 1970.
6. Combined Sewer Overflow Abatement Program, Rochester, New York
(Drehwig, Murray, Carleo, Jordan), 1981.
7. Combined Sewer Regulator Overflow Facilities (American Public Works
Association), 1970.
8. Control of Combined Sewer Overflows in Minneapolis-St.Pau! (Tucker), 1971.
9. Countermeasures for Pollution from Overflows: The State-of-the-Art (Field,
Lager), 1974.
10. Dry-Weather Deposition and Flushing for Combined Sewer Overflow Pollution
Control (Pisano), 1979.
11. Methodology of Analysis for a Combined Sewer Overflow Abatement Program
(Murphy), 1978.
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12. Prevention and Correction of Excessive Infiltration and Inflow into Sewer
Systems (American Public Works Association), 1971.
13. Relationship Between Diameter and Height for the Design of a Swirl
Concentrator as a Combined Sewer Overflow Regulator (Sullivan, Conn, lire,
Parkinson, Galiama), 1974.
14. Remote Control of Combined Sewer Overflows (Anderson, Gallery), 1974.
15. Retention Basin Control of Combined Sewer Overflows (Springfield Sanitary
District), 1970.
16. Sewer Flow Measurement: A State-of-the-Art Assessment (EG & G Washington
Analytical Services Center, Inc.), 1975.
17. Storage and Treatment of Combined Sewer Overflow (Liebenow, Beiging),
1972.
18. A Strategy for Integrating Storage Treatment Options with Management
Practices (Heany, Nix), 1978.
19. Stream Pollution and Abatement From Combined Sewer Overflows (Burgess,
Niple), 1969.
20. Surface and Sub-Surface Detention in Developed Urban Areas: A Case Study
(Walesh, Schoeffmann), 1984.
21. The Swirl Concentrator as a Combined Sewer Overflow Regulator Facility
(Field), 1972.
22. Swirl and Helical Bend Pollution Control Devices (Sullivan, lire, Parkinson,
Zielinski), 1982.
23. Urban Runoff Pollution Control Technology Overview (Brunner, Field, Masters,
Tafuri),1977.
24. Use of Street Cleaning Operations in Reducing Urban Runoff Pollution (Pitt),
1978.
25. Useful Technologies Information on Sewer Flushing (Pisano), 1978.
26. Water Quality Characteristics of Storm and Combined Sewer Overflow (Ministry
of Construction - Japanese Government), 1977.
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AN ANALYSIS OF THE UNITED STATES
ENVIRONMENTAL PROTECTION AGENCY'S
NEEDS SURVEY
AMERICAN PUBLIC WORKS ASSOCIATION
August 1975
Public Law 93-243 directed the U.S. Environmental Protection Agency to conduct a
survey in 1974 to determine the cost of wastewater facilities eligible for funding under
PL 92-500. The National Commission on Water Quality retained the APWA Research
Foundation to make an independent study of the procedures used by states and
selected metropolitan communities to assess and report the cost estimates and to
assemble data concerning industrial use of municipal treatment facilities, sludge
disposal, and proposed financing of the construction program. The APWA study was
not intended either to duplicate or to validate the results of the USEPA survey. Rather,
the study was designed to add interpretation to the 1974 Needs Survey. This report
presents the findings of the APWA study.
The APWA study reviewed state policies and procedures on non-federal financing of
local sewer systems and treatment facilities, industry-municipal inter-relations on
wastewater handling, private industry waste handling and disposal, non-utility private
wastewater treatment needs, cost factors not included in the 1974 needs estimates but
requiring consideration up to and after 1983, and opinions of state officials on the ability
of public agencies to complete needed sewer system and treatment facilities by the
deadlines established by PL 92-500. The APWA study also explored potential impacts
of the major water quality controls stipulated by the Act on the state's surface water,
groundwater, air, and land resources. In addition, the reported needs of representative
metropolitan governmental units and their financing of required construction work were
examined. The study identified areas where the 1974 Needs Survey reflects realistic
Construction costs for projects required by PL 92-500 and ascertained how the states
determined their needs. The study also evaluated the reasons for changes between the
1974 Survey and a previous survey conducted in 1973.
The study conducted by APWA included in-person interviews with 18 states and three
(3) metropolitan areas. In addition, mail surveys were conducted in the remaining 32
states, the District of Columbia, Puerto Rico, the Virgin Islands, American Samoa, and
the trust territory of the Pacific Islands.
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The same needs categories which were used in the USEPA National Needs Survey for
1974 were used for this study. They include the following:
Category I - Secondary Treatment and Best Practicable Waste Treatment
Technology
Category II - More Stringent Degrees of Treatment
Category IIIA - Infiltration/Inflow Correction
Category IIIB - Major Sewer System Rehabilitation
Category IVA - New Collector Sewers and Appurtenances
Category IVB - New Interceptor Sewers and Appurtenances
Category V - Correction of Combined Sewer Overflows
Category VI - Treatment and/or Control of Stormwater Discharges
The APWA study interviews and surveys covered the following information:
Estimate of methods used by local authorities to develop cost estimates for the
1974 Needs Survey: for facilities with no needs, facilities for which 1973 cost
estimates were reported, and facilities with updated or newly estimated needs
for all categories.
Reasons for new or updated costs in 1974 survey not included in the 1973
survey, increased facility capacities required, new facility processes required,
other reasons for new or updated 1974 costs for all categories.
Methods used by states for cost estimates and evaluation procedures: USEPA
guidelines, state modifications of USEPA guidelines, state-developed guidelines
for all categories.
Basis for state variances from USEPA Guidelines for each category I - VI.
Basis for state variances from engineering report estimates of local authorities
for each category.
Basis for 1974 Needs estimates: cost-effective analyses, engineering studies,
USEPA guidelines, rough local estimates-for all categories.
Anticipated needs not included in the 1974 Needs Survey but required to meet
1983 criteria, based on 1990 population estimates: upgrading of water quality
standards, land needs for treatment facilities and disposal areas for effluent and
sludge application, system rehabilitation needs (including treatment facilities),
needs for privately owned (non-industrial) treatment system facilities, and
facilities with undetermined needs--for ail categories.
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State policies on disposal and treatment of industrial wastes: encouragement
by states of joint municipal-industrial treatment facilities, requiring cost recovery
systems for industrial waste handling to qualify municipal facilities for state aid,
invoking USEPA guidelines on industrial wastes cost-recovery arrangements,
status of cost-recovery arrangements in the states.
Wastewater character and volumes produced by the ten major industries in
each state: listing of major industries in order of importance, MGD flow, BOD
and Suspended Solids loadings.
Estimated trends in industrial wastes production - 1974/1977/1983: volumes of
wastewaters produced, volumes anticipated to be handled by municipal
facilities - for each of the ten major industries of each authority.
Estimated construction cost of probable industrial wastewater treatment facilities
- 1974 to 1983: for publicly owned plants handling industrial wastes, for
industry-owned facilities, dependent upon whether cost of municipal systems
handling industrial wastes was included in 1974 needs and percentage of
Category I needs included in the 1974 survey.
Basis for population estimates for 1990 by local authorities: USEPA regional
estimates (Series E, Department of Commerce); state own population
estimates, local or regional planning agency population studies and projections,
or any combination of methods for estimating population trends.
State estimates on progress in meeting goals of PL 92-500 for Categories I and
II: numbers and capacities of facilities already completed, numbers and
capacities of facilities to be completed by 1977, numbers and capacities of
facilities to be under construction in 1977, numbers and capacities of facilities
not yet begun in 1977, estimated cost of facilities to be completed between 1974
and 1977, and estimated cost of facilities to be under construction or not yet
begun in 1977.
State authorization of local financing requirements for Category I and Category
II facilities: state aid arrangements, funds allocated for local water pollution
control needs, types of taxes and/or other local funding methods for sewer
systems and treatment works.
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Detailed information on state and local infiltration/inflow control actions
(Category I1IA): allowable infiltration rates set by states for sewer design,
estimates of actual infiltration rates experienced in sewer systems, amounts of
infiltration that can cause sewer system and treatment plant problems, state
regulations prohibiting inflow into sanitary sewers, status of local studies of
infiltration/inflow problems, types of local corrective actions taken or
contemplated to correct infiltration/inflow conditions - including sewer system
rehabilitation, excess treatment facilities, percent of systems studied to
determine cost of correction actions, and percent of total sewer systems
requiring infiltration corrective actions.
Miles of sewers in state requiring major rehabilitation {Category IIIB), due to:
age of sewer system, defective workmanship or materials, chemical
deterioration, establishment of state guidelines or criteria for major
rehabilitation, and other causes.
State policies and experiences on combined sewer overflows and corrective
actions (Category V): state criteria on quality of combined sewer overflows,
provisions to prevent or minimize overflows, state policies on elimination of
combined sewer overflows, number of enforcement actions taken, methods and
costs planned by the state for correction of overflow - sewer separation,
treatment equivalent to primary plus disinfection, treatment equivalent to
secondary, storage off- system or in-system, flow routing and other means,
state policies permitting new or extensions of combined sewers, and amounts
built from 1970 to 1974.
State policies and procedures on storm water discharge elimination (Category
VI): states' estimates for 1974 needs in terms of quality of storm water runoff,
rainfall events covered by storm sewer design, establishment of state
stormwater control criteria to guide local governments, state requirements for
stormwater discharge control or treatment - including storage and controlled
release, storage in-system with release to treatment equivalent to secondary
treatment or other means.
States' evaluation of the potential environmental impact of compliance with the
goals of PL 92-500: as envisioned by the 1974 needs estimates on surface
water, groundwater, air and land resources.
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The findings of the APWA study by needs category are as follows:
Category I- Secondary Treatment and Best Practicable Wastewater Treatment
Technology
Population estimates seem high
The extent of municipal facility use by industry is uncertain
The cost of adequate sludge handling and disposal facilities has not been
included in all cost estimates.
High I/I flows may be included as the basis of facility design
Costs for the facilities appear to be based generally upon engineering studies
with well defined treatment requirements
Category II - More Stringent Treatment Required by Water Quality
Population estimates seem high
Assumptions concerning the level of treatment required are preliminary
The extent of use of facilities of industry is uncertain
High I/I flows may be included as the basis of facility design
The cost of adequate sludge handling and disposal facilities has not been
included in all cost estimates
Uncertainty as to which facilities will be required to meet water quality
requirements suggests that reported costs are questionable; costs may be high,
low or accurate
Category IMA - Correction of Infiltration/Inflow
Few local authorities have conducted I/I studies
Correctional cost versus cost of excess treatment capacity has not been
determined for most systems.
Where relatively high I/I rates are allowed, the cost of Category I and II facilities
will be higher than where more strict standards are in effect.
Total costs for Category IIIA appear to be low due to number of authorities not
reporting costs for 1974
Category IIIB - Major Sewer Rehabilitation
Total costs will not be known until I/I studies have been conducted
Since many local authorities did not report costs in 1974, they are probably
understated
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Category IVA - New Collector Sewers
Methods used to obtain cost estimates appear reliable; however, some sewers
reported in the Needs Survey may not be eligible for inclusion and high population
estimates could have produced overstated costs.
Category IVB - New Interceptor Sewers
Methods used to obtain cost estimates appear reliable; however, the size and cost of
systems is dependent upon the accuracy of population and industrial flow estimates for
Category I and II facilities.
Category V - Correction of Combined Sewer Overflows
Cost estimates may be high where they are based on sewer separation
Many small local authorities apparently did not report their needs
Sludge handling requirements were not always considered
Control or treatment objectives are needed
The net effect of the above factors could not be estimated
Category VI - Treatment and/or Control of Stormwater
Estimates were missing from three states
Control or treatment objectives are needed
A significant portion of the costs reported were for storm sewers
Costs are to be considered speculative and a first estimate
The analysis for state-reported data concerning the status of plans for construction of
Category i and II treatment facilities indicated that 66 percent of the facilities would not
be completed by 1977, but 24 percent of them would be under construction. In terms
of capacity, 43 percent could be completed by 1977, 30 percent would be under
construction, and 27 percent would not be started.
Adequate methods were not available to evaluate the potential environmental impacts
of the pollution control program. However, the opinion of the key officials participating
in the survey was that receiving surface waters would be generally improved and that
groundwater and air resources would not be degraded by the construction of new
facilities.
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ANALYZING THE EXISTING COLLECTION SYSTEM
by
DR. WILLIAM C. PISANO
ENVIRONMENTAL DESIGN AND PLANNING, INC.
presented at
EPA TECHNOLOGY TRANSFER SEMINARS ON
COMBINED SEWER OVERFLOW
ASSESSMENT AND CONTROL PROCEDURES
1978-1981
The objective of this combined sewer management study was to study in fine detail the
impact of potential structural and non-structural control options for an old combined
sewer collection system and then to select the least cost program for that system. The
same problem was analyzed from three alternative points of view: a) remedial system
fixes; b) the vogue and prevailing 208 orientation of street sweeping/sewer
flushing/roof top inflow control; and c) end-of-line detention storage. Beforehand It
was believed that significant control of combined sewer overflows can in fact be
accomplished through a purposeful effort in restoring the condition of the existing
system and jointly maximizing any system control.
The principal motivation and emphasis of the study method was to demonstrate the
feasibility and practicality of developing low-cost, non-structural solutions for mitigating
the number and magnitude of combined sewer overflows from the prototype study
area.
This study was extremely well-received by USEPA as a hallmark problem-solving
investigation which demonstrated the clear and unmistakable need to thoroughly
understand the piping system, optimize its performance and then consider additive
control measures. The study was presented at several Combined Sewer Overflow
Technology Transfers EPA sponsored between 1978-1981.
This project was described in the 1978 report to Congress on Control of Combined
Sewer Overflow in the United States. It best signifies Environmental Design and
Planning's cost-effective philosophical approach to combined sewer management
planning. The following is excerpted from the report to Congress:
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"The major objective of collection system management is to implement a continual
remedial repair and maintenance program to provide maximum transmission of flows
for treatment and disposal while minimizing overflow, bypass, and local flooding. It
requires an understanding of how the collection system works and patience to locate
unknown malfunctions of all types, poorly optimized regulators, unused in-line storage,
and pipes clogged with sediments in old combined sewer systems.
The first phase of analysis in a sewer system study is an extensive inventory of data and
mapping of flowline profiles. This information is then used to conduct a detailed
physical survey of regulator and storm drain performance. In this detailed study,
Pisano found that minor repairs of four overflow structures and several small alterations
of storm sewer piping obtained a 43.9 percent reduction of the present BOD load due
to combined sewer overflow at a cost of $26,000. An additional 23 percent BOD
reduction was obtained at a cost of $4,678,000 using sewer flushing, street sweeping,
inflow correction and storage. This type of sewer system inventory and study should
be the first objective of any combined sewer overflow pollution abatement project."
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ASSESSMENT OF BENEFITS RESULTING FROM
CONTROL OF COMBINED SEWER OVERFLOWS
by
EUGENE D. DRISCOLL AND JOHN L MANCINI
HYDROSCIENCE, INC.
presented at
EPA TECHNOLOGY TRANSFER SEMINARS ON
COMBINED SEWER OVERFLOW
ASSESSMENT AND CONTROL PROCEDURES
1978
The nature of surface water quality problems present around metropolitan areas is quite
varied. Local factors have a predominant influence on the class of problem, its severity,
and the specific source or sources which are contributing to the problem. The local
factors which affect water quality include climate, geography, population, population
concentration, the nature and degree of industrialization in an area, the receiving water
system, its nature, size and hydrology; and the nature of the surrounding area - both
upstream and downstream of the urban area itself.
The objective of water quality management, particularly facilities planning activities, is
improvement in water use. The definitions of water quality problems used in 201
studies should be related to water uses. This type of water quality problem definition
will provide a sound basis for focusing pollution control activities, facility evaluations
and efforts to benefit estimates.
Facility plans must provide answers to three implicit questions which are raised by
public administrators and citizens. These are:
Why commit any resources at all to these water quality management
activities?
Why commit these resources now?
Why commit these resources in the way recommended?
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Estimates of water quality and water use benefits provides part of the information
needed to answer these questions. The reason a community, a state or EPA would
want to commit resources to water quality management activities, regardless of time
frame, would be that the perceived benefits are larger than the anticipated costs.
A common element of all levels of benefit estimates is the ability to quantitatively project
water quality impacts of pollution control activities. There are several methods of
estimating the benefits of water quality management.
The first is Application of Available Technology. The essence of this approach is a
fundamental assumption that the benefits to be derived from the proposed activities are
so large that they will automatically justify the allocation of the required resources. The
controlling factor is assumed to be the availability of technology for obtaining the water
quality benefits.
A second measure which can be considered in benefit estimates concerns
achievement of "water quality standards." The basic assumption is that standards are
somehow tied to protection of certain water uses. A major requirement of this type of
an evaluation is the ability to directly relate proposed pollution control activities to
improvements in receiving water quality.
An additional level of resolution may be obtained through translating improvements in
water quality into "Estimates of Increased Water Use Potential." Physical scales such
as useable beach length and water surface area can be related to the number of
individuals that could utilize those resources. Once the level of water quality
improvement has been defined as suggested above, these factors may be used to
estimate the potential increased water resource utilization that could be
accommodated.
The final level of benefit analysis is the classical cost benefit analysis in which each
anticipated water usage is assigned a dollar value as a measure of unit worth or
willingness to pay. The actual projected usage in each water use category is multiplied
by the unit value and the sum represents an estimate of the value of the total benefits.
The benefit total value is compared to total costs.
The analysis of receiving water impacts is a common element to each of the benefit
estimating techniques previously discussed.
Streams and rivers can often be characterized as one-dimensional flowing systems
where dispersion of mass can be neglected. For a complete specification of stream
responses to pollutant loads under these assumptions, the initial pollutant
concentration, the reaction rate, and the river flow and cross-sectional areas must be
defined. Concentrations are assumed to be constant throughout the depth and across
the width of the receiving water. The receiving water geometry is, therefore,
approximated by a series of constant geometry and constant flow segments. For a first
assessment, a single segment model should be used with a spatially aggregated
average stormwater load.
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One or two spatial dimensions may be of importance in estuaries, although initial
assessments may simplify the problem to a one-dimensional analysts. The primary
difference between estuaries and the one-dimensional river flow situation is the
dispersive mass transport due to tidal mixing. This forms an important transport
phenomena in combination with to the net freshwater flow through the estuary and, as
such, must be included specifically in the analysis.
Lakes and reservoirs can involve either two or three spatial dimensions. Initial
assessments of long-term stormwater impacts in lakes and reservoirs may be made
with a few simplifying assumptions. To determine the average concentration of slowly
reactive constituents (i.e., dissolved solids, persistent organics, etc.), the water body
may be assumed to be completely mixed.
The objective of a 201 Facilities Plan for CSOs should include the following elements.
First, the need for controlling waste loads from each source should be assessed. The
need should be defined in terms of sufficient impacts on receiving water quality which
violate water quality standards and as a consequence impair or deny desired beneficial
uses of the receiving water body. Secondly, where a need for CSO control has been
established, the 201 planning effort should identify a control strategy for which cost-
effectiveness is justified in terms of the receiving water benefits expected to accrue.
In order to determine receiving water impacts, it is necessary to identify the magnitude
of the waste loads which enter the receiving water. The determination of point source
continuous loads is straightforward, being defined by the volume and quality of the
discharge. However, intermittent waste loads, which result from the rainfall process,
are more difficult to characterize. The intermittent nature of rainfall, the number and
wide spatial distribution of overflow points, and the variability in both size of storm event
and pollutant concentrations found in runoff, make a definitive determination of such
loads impractical, if not virtually impossible.
Once the magnitude of stormwater impacts on receiving water quality are estimated,
control strategies for the reduction of these impacts may be analyzed. A variety of
stormwater control alternatives are available. These are generally grouped into two
types of approaches:
1. Structural, end-of-pipe treatment devices
2. Management practices
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Structural, end-of-pipe alternatives include devices which capture and store runoff, such
as interceptors and retention basins, and devices which reduce the pollutant
concentration of runoff or overflows, such as screens, filters, concentrators, and
disinfection systems. Management practices include source controls, such as street
sweeping and erosion control; and collection system management techniques, such as
sewer flushing and polymer injection to increase the flow capacity of the sewerage
system. The projected improvement in receiving water quality due to the modification
of stormwater loads represents the benefit of potential stormwater control actions.
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BENEFIT ANALYSIS FOR COMBINED SEWER OVERFLOW CONTROL
TECHNOLOGY TRANSFER SEMINAR PUBLICATION
ENVIRONMENTAL RESEARCH INFORMATION CENTER
CINCINNATI, OHIO 45268
EPA-625/4-79-013
April 1979
Approximately 40 million people (one-fifth of the nation's population) are served by
combined sewers. There are between 1,100 and 1,300 combined sewer systems,
covering an area of more than 2 and one-half million acres. Seventy-seven major cities,
including 10 of the country's 14 largest have combined sewer overflow control needs of
$50 million or more. They account for 96 percent of urbanized area combined sewer
overflow control needs and 64 percent of national needs.
Some of the options for controlling combined sewer overflows, especially those
involving the division of the combined sewers into separate storm and sanitary
systems, necessitate monumental expenditures that severely strain local budgets and
state construction grant allocations.
As a tool to relate proposed expenditure to anticipated benefit, a properly executed
benefit analysis helps a municipality, and thus the U.S. government, avoid unnecessary
costs. A benefit analysis provides justification for funding requested from the state and
EPA, and it demonstrates to the taxpayers that their tax dollars are being used to
achieve desirable objectives.
To succeed in obtaining approval and funding assistance for a combined sewer
overflow (CSO) project, it is necessary to know the regulations and policies that have
an impact on ultimate grant application approvals. A clear understanding should be
developed at the beginning of the process, because the plans must provide special
outputs and must meet a number of criteria peculiar to combined sewer overflow
control planning.
In any well executed planning process in the public realm, there are two general
principles regarding the preparation of objectives. First, the effort to define them should
begin early in the project. Second, though decisions on objectives can be facilitated by
the technicians and consultants who can suggest alternatives and indicate the range of
choices, the actual choices must be made by elected officials. A third principle has
applicability to many types of projects but is of critical importance to planning for
control of pollution from combined sewer overflows. The tasks of developing a
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combined sewer overflow control program that will qualify for EPA approval and funding
and then obtaining the funding as well as local support for the proposal will be
immensely easier if the combined sewer overflow control objectives are related to
benefits and expressed in such a way that measurement of benefit is made possible. It
is the benefits that are the results of pollution abatement - the improvements expected
in receiving water uses - that must be demonstrated. Because this is the case, it makes
sense to select as pollution control objectives the maintenance of or improvement in
specific beneficial uses.
The determination of both required and desired uses of local receiving water is only the
beginning of the analysis necessary to plan for combined sewer overflow control
projects that are to be funded by the federal government. One criterion for federal
approval of combined sewer overflow projects is that the analysis must have
"...demonstrated that the level of pollution control provided will be necessary to protect
a beneficial use of the receiving water even after technology-based standards...are
achieved by industrial point sources and at least secondary treatment is achieved for
dry weather municipal flows in the area." Combined sewer overflow control must also
be shown to be more cost effective than "the addition of treatment higher than
secondary treatment for dry weather municipal flows in the area." Taken together,
these criteria mean among other things, that in order for a CSO project to qualify for
federal funding, the pollutants to be controlled must be identified with a specific
beneficial use and that a primary contributor of that pollutant must be demonstrated to
be combined sewer overflows.
Selecting from among the alternatives available for controlling combined sewer
overflows does not enter the planning process until many decisions about desired
benefits have been made and data gathering is quite far advanced. The water quality
parameters associated with the desired beneficial uses provide the link between
objectives and control alternatives. The objectives must first be translated into the
water quality criteria necessary to protect the uses. Then the reductions in specific
pollutant inputs required to meet the criteria can be calculated. With this work
completed, two tasks remain: the development of a control strategy and the selection
of control alternatives.
Technologies to control pollution from combined sewer overflow, many of which are
also applicable to urban stormwater runoff, can be grouped in three main categories:
source controls to reduce the amounts of pollutants entering the sewer system,
collection system control to improve the system's effectiveness in storing and handling
the flows, and off-line storage and treatment to remove pollutants from combined sewer
flows. The control alternative selected for any given situation may include techniques
from one or more of these groups.
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Most source controls are non-structural in nature. The principle common to all of them
is reduction of pollutant accumulation on impervious surfaces in the drainage basin or
in portions of the collection system itself, so that pollutant loadings in combined sewer
flows during storm events are lowered. Included under the category of source controls
are: street cleaning, combined sewer flushing, and catch basin cleaning.
Techniques of collection system controls are intended to ensure that the sewer system
operates as efficiently as possible and that maximum advantage is taken of any
opportunities it offers for combined sewer overflow pollution reduction. All of these
measures require detailed knowledge of the sewer system. Some are structural and
some are nonstructural. Included under collection system controls are the following:
existing system management, flow reduction techniques, sewer separation and in-line
storage.
When the list of control alternatives has been narrowed down to those that look most
promising, each should be tested again for effectiveness in providing the desired
benefit-that is, in meeting the criteria to protect that benefit.
The analysts and planning for combined sewer overflow correction has rested solidly on
a determination of desired or required beneficial uses of a receiving water body and the
most cost effective controls that will result in these beneficial uses. The culmination of
this process in a decision to proceed depends on the presentation of the answers to
three basic questions:
What are the benefits?
How costly is the project?
Do the benefits expected justify the commitment of public funds and other
resources?
The key to a successful outcome of this stage is that the questions be answered in a
clear, logical, and realistic manner. The dollar amounts involved in combined sewer
overflow control projects are invariably large enough to attract more than casual
interest. If it is not possible to demonstrate to the taxpayers a favorable relationship of
benefits to costs, it is not likely that they will lend their support to the undertaking.
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COMBINED SEWER OVERFLOW ABATEMENT ALTERNATIVES
WASHINGTON, D.C.
by
ROY F. WESTON, INC.
ENVIRONMENTAL SCIENTISTS AND ENGINEERS
WEST CHESTER, PENNSYLVANIA
for
THE WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
August 1970
Most United States cities today are served both by combined sewers and by separate
sanitary and storm sewer systems. As determined from a 1967 survey sponsored by
the Water Quality Office of the Environmental Protection Agency, approximately 29
percent of the total sewered population of the United States is served by combined
sewer systems. Approximately three percent of the total annual flow of sewage and as
much as 95 percent of the sewage produced during periods of rainfall is carried with
combined sewer overflows to the surface waters.
The District of Columbia follows this pattern, with an area of approximately 20 square
miles (one-third of the total area of the District) being served by combined sewers. The
hydraulic capacity of the system is often exceeded during periods of precipitation, and
raw sewage mixed with surface runoff is discharged to the watercourses of the District.
The Potomac Estuary is polluted and continues to experience problems with low
dissolved oxygen, excessive algae growths, sediments, high concentrations of fecal
bacteria and repulsive floating matter. All of these problems, except sediments, are
complicated by combined sewers. Although combined sewer overflow adds to the
sediment load, the primary source of sediment is the heavy silt load included in the
runoff from areas with significant agricultural and construction activity. In addition to
the effects of combined overflow on the Potomac River, overflows into Rock Creek
detract from the natural and recreational features of this small, scenic stream flowing
through the District.
After review and interpretation of pertinent information, four methods of abating
pollution from combined sewer overflows appeared to offer sufficient promise to justify
consideration as alternative approaches for the District:
1- Sewer Separation
This alternative would completely separate storm and sanitary sewers.
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2. Storage Reservoirs
Sufficient underground storage volume would be provided to hold the
combined sewer overflows caused by each storm until the storm
subsides and stored wastewater would then be pumped the back into
the sewerage system for conveyance to a centralized treatment plant.
3. Treatment at Overflow Points
A treatment facility would be located at each existing overflow point,
except where conditions either prevent this or dictate that certain
overflow points be combined.
4. Tunnels and Mined Storage
Combined sewer overflow would drop through a vertical shaft down to
an underground system of tunnels and mined storage. The tunnels
would convey the overflow at high velocity to mined storage. After the
storm subsides, the retained overflow would be pumped back into the
regular sewers.
Cost is an essential factor in selecting the appropriate alternative for abating combined
sewer overflows. In summary, the costs for each alternative were as follows:
1. Storage Reservoirs
2. Treatment at Overflow Points
3. Conveyance Tunnels and Mined Storage
4. Sewer Separation
$5,560,000
$6,820,000
$3,500,000
Considerably greater than
the above 3
To determine which of the feasible alternative approaches would offer the best
opportunity for abatement of the combined sewer overflow problem requires careful
consideration of many factors. Cost comparison obviously is essential, but there are
other factors which also have a significant bearing on the selection of the most
favorable plan. The most important of these other factors are reliability, flexibility, land
requirements, public convenience, implementation, and solids disposal and gas
production.
Each strategy offers a different level of costs, pollutant loadings, and benefits. While
the selection of the appropriate strategy rested partially on factors beyond the scope of
this study, the information presented within this article indicated that the appropriate
District-wide solution would utilize mined storage and conveyance tunnels. The total
project costs of the recommended alternative was estimated to be $318,000,000 in
1970.
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COMBINED SEWER OVERFLOW ABATEMENT PROGRAM, ROCHESTER, N.Y.
VOLUME I: ABATEMENT ANALYSIS
by
FRANK J.DREHWIG
CORNELIUS B. MURRAY, JR.
DAVID J. CARLEO
THOMAS A. JORDAN
O'BRIEN & GERE ENGINEERS, INC.
SYRACUSE, NEW YORK
July 1981
EPA NO. 600/2-81-113
Pollution abatement analyses, conducted in conjunction with system network modeling
studies and supported by combined sewer overflow (CSO) monitoring and sampling,
were initiated with the ultimate goal of formulating a cohesive and workable Master Plan
for CSO reduction and control in Rochester, New York. The Master Plan was
developed in light of fiscal constraints, sewer system complexities, necessity for
optimized benefits from minimal capital and operating expenditures, and best use
policies for the affected receiving waters. The present methodology is considered
applicable to other urban areas.
Overflow monitoring and sampling data from thirteen CSO locations within the
Rochester, New York Pure Waters District collected during the period January through
December, 1985 served as the basis for network modeling studies. Within each of
these overflow discharge conduits, an electronic flow measuring system was installed
to determine the hydrograph and thus the quantity of combined sewer overflow
discharged from the tributary drainage area.
To collect the samples, samplers were installed at each of the overflow
locations. Samples were collected at approximately 15-minute intervals unless the
pumping distance dictated suction and purge times greater than 15 minutes. At the
completion of an overflow event, the samples were collected and transported to the
laboratory for analyses.
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A system of 12 rain gauges was installed within the Rochester Pure Waters District. The
location of each gauge was selected by dividing the District into 12 units of equal area.
Within each of the units, a building of significant height {school, firehouse, pump
station) with no observable influences from adjacent buildings or trees was selected for
installation. The total system of gauges allowed an evaluation of differences of rainfall
patterns and their possible effect on the intercepting sewer system.
The flow, analytical, and rainfall data that were monitored and recorded served two
main purposes. First, the data was used directly in the calibration and verification
process associated with the application of the SWMM. Secondly, much of the data was
used for developing valuable relationships between rainfall and overflow quantity and
quality through the use of statistical procedures.
In the overall effort to develop an abatement and management program for the
combined sewer overflows, the physical characteristics of the entire study area were
defined. A brief description of the scope of work outlined for the drainage areas
surveys follows:
1} Each of the 13 CSO locations were divided into a maximum of sixty
subcatchments ranging in size from ten to fifty acres. Division was made
on the basis of land slope and zoning classifications such as residential,
commercial, industrial, or open.
2) Each drainage area subcatchment was characterized by determining the
average ground slope, percent of the area that is pervious and
impervious, total area, average drainage width, total length of gutters,
total number of catch basins and stored volume of each, the BOD5
contained in the volume of stored water in those catch basins, and any
available surface storage capacities.
3) The estimation of dry-weather flow for each subcatchment was made by
collecting statistics as to the number of dwelling units, average number
of people per unit, market value of average units, average family income,
percent of units with garbage grinders, and information as to industrial
process flows.
4) Other information required to complete the characterization of the
drainage basin included total population, street cleaning frequency,
average number of sweeper passes, and location of inlet manholes.
5) Information was obtained to characterize the sewer network including
length of sewer conduits, conduit slope, type, size and roughness, and
manhole invert and ground elevations.
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The two models selected for demonstration and use in the evaluation of various
combined sewer overflow abatement alternatives proposed under this program were
the SWMM (II) and the Simplified Storm Model (7). The Simplified Stormwater Model
was developed by Metcalf & Eddy, Inc. Each model was selected for a specific
purpose. Preliminary screening of various abatement alternatives was accomplished
with the use of the Simplified Stormwater Model, whereas, the SWMM was used to
evaluate specific alternatives under the application of varying design storms.
There are three general approaches available for the control of Stormwater and CSO
discharges. A combination of storage and treatment can be applied through the use of
structurally intensive measures to attain defined water quality standards. Secondly, the
sources of the pollutants discharged into the sewer system can be addressed through
the application of the Best Management Practices (BMP) concept. Thirdly, a
combination of the two can be applied. In general, the most cost-effective abatement
alternative will be the application of structural and nonstructural (BMP) measures.
For this article, the alternatives that were evaluated can be classified as nonstructural,
minimal structural, and structurally intensive. The first two classes of abatement
alternatives are those generally considered in developing a BMP program.
Nonstructural Alternatives
1) - Land Use Policies
- Land use policies and sewer system maintenance procedures can
significantly affect both the quantity and quality of combined sewer
overflows.
2) - Street Cleaning Practices
3) - Increased Sewer Maintenance
- Sewer maintenance has potential for not only reducing system
flooding but also minimizing first flush effects.
4) - Land Use Planning
- Increased imperviousness adversely affects the quantity and quality of
Stormwater and combined sewer overflow.
5) - Surface Storage
Minimal Structural Alternatives
1) Abandoned Treatment Facilities
2) Multi-Purpose Upstream Impoundment for Overflow Control
3) Use of In-System Regulators and Control Structures for Increased In-
System Storage
4) Upgrading the Existing St. Paul Interceptor
5) Selective Blockage of High Impacting Combined Sewer Overflows
6) Selective Overflow Weir Evaluation
7) Regulator Capacity Evaluation
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Structural intensive Alternatives
Alternative 1: This alternative considered capturing the first-flush from all the river
overflow sites and treating all post first-flush flows with primary swirl devices. The
temporarily stored first-flush volume would be released back into the interceptor system
on termination of system overflows.
Alternative 2: This alternative involved evaluating various storage and treatment
options for capturing the total overflow to the Genesee River.
Alternative 3: The only difference between Alternatives 2 and 3 was the location of the
treatment facility.
Alternative 4: This alternative is similar to Alternate 1 with the exception that the post
first-flush would not be treated, but directly discharged to the river.
Alternative 5: Primary swirl concentrators would be located on each of the river
overflow locations for treatment of the entire overflow volume.
Alternative 6: This alternative involved construction of an interceptor to convey
overflows from the western portion of the collection system to the Cross-lrondequoit
Tunnel. The latter facility served the eastern portion of the city and had in-system
storage available.
Cost benefit analyses of all structurally intensive alternatives were conducted using
optimum treatment process train configurations developed from pilot plant evaluations,
as reported in Volume II of the project's report.
Based on the results of this investigation, the following conclusions were made.
General
1. A rigorous definition of the existing system of CSO and stormwater
facilities is fundamental to the development of an abatement program.
This definition includes the identification of major drainage basins, major
trunk and intercepting sewers, and CSO and stormwater relief points.
2. The installation and proper maintenance of overflow monitoring
instrumentation is essential for both receiving water problem definition
and any subsequent sewer network and water quality model calibration
and verification.
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3. Accurate rainfall data collection and subsequent statistical analyses,
including design storm definition and formulation, is essential in
evaluating the response of the existing system as well as the
effectiveness of various abatement alternatives.
4. Development of a methodology of approach and definition of applicable
abatement alternatives early in the program ensures that the purpose of
the study is not lost, and all data collection activities are conducted
according to the required analyses.
5. SSM is capable of providing a preliminary screening of potential
abatement alternatives involving a balance between storage and
treatment.
6. SWMM (USEPA Stormwater Management Model-Version II) can project
the urban storm runoff and quantities within acceptable confidence limits
but is presently limited in its ability to simulate overflow quality.
7. Overflow quality can be better simulated through the application of
statistical techniques using actual monitoring overflow data.
8. The ability to abate CSO pollution resulting from an infrequent design
storm event will require 1he implementation of structurally intensive
facilities, minimal structural improvements to the existing sewer system,
or the implementation of nonstructural abatement alternatives, known as
BMPs.
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COMBINED SEWER REGULATOR
OVERFLOW FACILITIES
AMERICAN PUBLIC WORKS ASSOCIATION
DEPARTMENT OF THE INTERIOR
July 1970
PROGRAM NO. 11022 DMU
An in-depth investigation of combined sewer regulator practices was carried out by the
American Public Works Association. The focus of this investigation was on design
application, performance, operation and maintenance practices, and equipment. The
study provided information upon which to base recommendations on the more effective
use and management of existing regulator facilities and on maximizing the quality of
wastes discharged to receiving waters. This report was dedicated entirely to regulator
facilities and was not concerned with other aspects of combined sewer systems.
The findings and major recommendations of this study included the following:
It is economically infeasible to apply expensive and sophisticated
regulator devices in small regulator structures which handle flows of 2 cfs
or less. Consolidation of small regulator-overflow locations would make
it feasible to provide more effective control facilities.
Regulators should be designed to control both quantity and quality of
overflows. Too often, design is concerned only with the quantity of the
overflow.
Management of control for an entire sewer system could result in less
overflows than would be seen in a system which has all independently
controlled devices.
Control systems should have the ability to direct excess flow in one part
of a system to another part of the system which may have available
capacity to handle the excess flow.
Dynamic-type regulators, while more costly for initial installation, are
better able to reduce overflows than static devices. This is a result of the
dynamic regulators' ability to react to sewer system hydraulic conditions.
896RHG7.WS5
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Many existing dynamic-type regulators have been removed or disabled
because of maintenance and repair costs. Each type of regulator should
be given the attention required to achieve maximum performance
(instead of being neglected).
Regulator facilities should be designed such that they are easily
accessible for routine maintenance purposes. Inaccessible regulator
stations tend to discourage the frequency and effectiveness of
inspections and maintenance.
Training is extremely important for the proper operation of an overflow
control device. Maintenance crews should be adequately staffed and
provided with the necessary equipment and tools to service the
equipment.
Corrosion and wear can shorten the life of overflow control equipment.
Adequate specifications must be prepared to address existing
environmentai conditions.
Tide gates are often poorly located for maintenance purposes. Design
should provide sufficient access.
State water pollution control agencies have not exerted enough regulator
control over sewer overflows.
Manufacturers, officials, and designers should communicate more often
on overflow matters. This would produce a better knowledge base for
reducing overflows.
A Manual of Practice has been developed on the design, operation, and
maintenance of combined sewer overflow regulators and tide gates, as
part of this study.
Clogging is the most frequent cause of regulator malfunction.
Maintenance should be designed to reduce these effects.
Local jurisdictions should gather information on the frequency and extent
of overflow events.
European practices have been effective and should be studied for use in
the United States and Canada.
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CONTROL OF COMBINED SEWER OVERFLOWS
IN MINNEAPOLIS-SAINT PAUL
SCOTT L TUCKER
DEPARTMENT OF THE INTERIOR
October 1971
NTISPB-212903
This report represented one phase of a larger scale study which was designed to
develop criteria and a rationale for the establishment of centralized metropolitan water
intelligence systems in urbanized and urbanizing areas. This particular phase of the
overall project (Phase I) was focused on real-time automation and control facilities for
combined sewers. Basic objectives of Phase I were to:
Investigate and describe modern automation and control systems for
combined sewer systems,
Develop criteria for managers, planners, and designers for the operation
of combined sewer systems, and
Study the feasibility of automation and control systems for combined
sewer systems.
This report was prepared in connection with one task of Phase L which examined
existing planned automation and control systems. The planning, design, operation,
and maintenance of computer controlled systems was studied. Regulators were
redesigned and rebuilt; rainfall, water level, and water quality data were monitored and
transmitted to computer based data logging and processing centers; and regulators,
gates, and pumps were remotely controlled. These controls were not designed as
integral parts of complete metropolitan systems, but were implemented to demonstrate
concepts and hardware.
Existing overflow regulators were replaced with power operated gates at 16 key
diversion locations. The new regulators will control flows and levels in the sewers by
adjusting gate position (tied to a telemetering system). River water quality was also
monitored at five (5) locations. The CSO control system had basically five (5) functions:
Scan and print readings of river quality, regulator activities, interceptor
conditions, and rainfall;
896RHG6.WS5
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Control regulator gate positions;
Perform analyses of data;
Provide an operational model that could aid the operator during
rainstorm events; and
Perform any other functions for management that would not affect
performance during rainstorm events.
Data acquisition for the system program emphasized providing immediate information
on river quality, including dissolved oxygen, chloride, ORP, pH, and temperature.
Additionally, depth of flow in the trunk sewers, depth of flow in the overflow pipe,
position of the regulator, and rainfall data were immediately available. Control functions
included operating gates to predetermined set points based on system conditions. The
main concerns of the operator were to prevent:
surcharging of the trunk sewers
excessive pressure buildup on the inflatable dams and gates.
Operation of the system, as of 1971, consisted only of deflating system dams (allowing
an overflow) if system pressures became too high. No attempts were made to utilize
the control system as a storage area for excessive combined sewer flows.
The demonstration project discussed in this article was a definite success insofaras
demonstrated the feasibility of controlling of combined sewer overflows. Overflow
regulators could be remotely controlled based on parameters monitored throughout
the interceptor system. The conclusions stated, however, that the demonstration
project was not being used up to its potential. No attempts were being made to
optimize storage of combined sewage overflows in the interceptor system and the
prediction model developed to assist an operator was not being used.
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COUNTERMEASURES FOR POLLUTION FROM OVERFLOWS
THE STATE OF THE ART
by
RICHARD FIELD
STORM AND COMBINED SEWER SECTION (EDISON, JEW JERSEY)
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
NATIONAL ENVIRONMENTAL RESEARCH CENTER
CINCINNATI, OHIO 45268
and
JOHN A. LAGER
METCALF & EDDY, INC.
PALO ALTO, CALIFORNIA 94303
December") 974
Control and/or treatment of stormwater discharges and combined sewer overflows
from urban areas are problems of importance in the field of water quality management.
Over the previous decade, much research effort was expended and a large amount of
data was generated, primarily through the actions and support of the U.S.
Environmental Protection Agency's Storm and Combined Sewer Research and
Development Program.
Combined sewer overflows are major sources of water pollution, but even discharges
of stormwater alone can seriously affect water quality. Current approaches involve
control of overflows, treatment and combinations of the two. Control may involve
maximizing treatment with existing facilities, control of infiltration and extraneous
inflows, surface sanitation and management, as well as flow regulation and storage.
Examples of source controls include flow attenuation, erosion control, restrictions on
chemical use {deicing compounds, pesticides), and improved neighborhood sanitation
practices. The theory behind source controls is to limit the supply of contaminants.
The benefits are not only reduced water pollution but also cleaner and healthier
environments.
896CMS9.WS5
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Examples of collection system controls include flushing, polymer feed, inflow/infiltration
control, improved regulator devices, sewer separation, and remote monitoring/control
systems. The emphasis, with the exception of sewer separation, is upon optimal
utilization of the existing facilities.
Storage facilities possess characteristics which are also beneficial in stormwater
treatment: 1) they are capable of providing flow equalization or attenuation and, in the
case of tunnels, flow transmission; 2) they are simple to design and operate; 3) they
respond without difficulty to intermittent and random storm behavior; 4) they are
relatively unaffected by flow and quality changes; and 5) frequently they can be
operated in concert with regional dry weather flow treatment plants for benefits during
both dry and wet-weather conditions. Disadvantages of storage facilities include their
large size, high cost, and dependency on other treatment facilities for dewatering and
solids disposal.
Physical treatment processes in many ways are well suited to stormwater applications,
particularly with respect to solids removal. These processes include sedimentation,
dissolved air flotation, screening, filtration, and flow regulation. Handicaps appear to
be sensitivities to flows and loadings, high maintenance requirements, and the absence
of effective utilization between storms.
Biological treatment of storm wastewaters must overcome some serious drawbacks: 1)
the biomass used to assimilate the waste constituents must either be kept alive during
times of dry weather or allowed to develop for each storm event; and 2) once
developed, the biomass is highly susceptible to washout by hydraulic surges or
overload.
Physical/chemical processes are of particular importance to stormwater treatment
because of their adaptability to automated operation, rapid startup and shutdown
characteristics, and very good resistance to shock-loads. Drawbacks to
physical/chemical treatment include high initial costs, high chemical requirements, and
increased sludge (by dry weight) to be disposed of.
By far the most promising approaches to urban stormwater management involve the
integrated use of control and treatment with an areawide, multidiscipltnary perspective.
Integrated approaches are notably demonstrated in programs underway in Chicago,
San Francisco, Seattle, Washington, D.C., and Rochester, New York.
896CMS9.WS5
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Two directions for further study were suggested: 1) Characterization and Evaluation:
Simulation Models, Nationwide Assessment of Urban Runoff Impacts, Combined
Sewage Sludge, Uniform Procedures for Analysis and Evaluation of Storm Flow
Characteristics and Treatability, Flow Measurement, Consideration of Trace Pollutants,
and Pathogen Detection, and 2) Control Methodology: New Sewer Design, Upstream
Impoundment, Catch Basins, Runoff Attenuation by Porous Pavement, Dual Use
Facilities, Swirl and Helical Separators, Comparisons of Screening Devices,
Hydrologic-Hydraulic Design Rationale, and Beneficial Use of Stormwater.
A nationwide characterization and evaluation of the impact of new methods for the
determination of pathogenic pollution would be required in addition to a reevaluation of
disinfection requirements. Methods of controlling and treating heavy metals and
organics found in runoff should be developed. Detention, both in-line and upstream,
needs further development to optimize its effectiveness as a pollution abatement
procedure.
Multi-billion dollar treatment plant upgrading and expansion programs now in progress
throughout the country will do much to alleviate water pollution. However, means of
mitigating the effects of urban runoff must also be found if we hope to abate the
pollution in an optimal manner.
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DRY WEATHER DEPOSITION AND FLUSHING
FOR COMBINED SEWER OVERFLOW POLLUTION CONTROL
by
DR. WILLIAM C. PISANO, et. al.
NORTHEASTERN UNIVERSITY AND
ENVIRONMENTAL DESIGN AND PLANNING, INC.
August 1979
EPA NO. 600/2-79-133
This report summarizes the results of a two-year study aimed at addressing the
feasibility, cost-effectiveness and ease of application of upstream solids control as an
integral part of overall combined sewer management. The project was functionally
divided into four major phases. The first three phases were intensive field engineering
investigations, while the fourth phase was relegated to data reduction and desk-top
analytical efforts.
In the first phase of field work, four test segments on different streets in the Boston
sewerage system were field flushed over an extended period using different flushing
methods. External sources of fresh water, as well as treated sewage, were used. The
experiments were aimed at quantifying the effectiveness of flushing deposition
accumulations from a single pipe segment on a routine basis, as well as roughly
estimating deposition characteristics within collection system laterals. Removals of 75
to 90 percent for grit, organic and nutrient contaminants can be expected for single
manhole to manhole small diameter combined and separated sewer laterals. All
flushing methods yielded comparable flushing pollutant removals. The most effective
flushing method was an application of about 50 cubic feet (1.42 cubic meters) of water,
injected at discharge rates exceeding 0.5 cfs (14.4 liters per second).
The second phase of field work was concerned with the problem of flushing a long flat
stretch of combined sewer laterals. Flushes were injected into the uppermost manhole
and pollutant levels in the flush wave passing three downstream manholes were
monitored. Work was divided into two subphases. Initially, pollutant removals over the
three segments were determined for different flushing conditions established in the first
manhole, providing insights into flushing effectiveness over three segments of pipe.
The results of these experiments indicated that a single flushing at the upper end of the
street was reasonably effective in removing most of the deposited load along the 675-
foot (206 m.) stretch of 12-inch (30.5 cm.) combined sewer lateral. Next, settleability
tests were performed for the purpose of crudely extrapolating how far beyond the
896RHG10.WS5
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flushing monitoring manholes the materials would be carried. The experiments showed
that heavier grit fractions would quickly resettle, leaving the lighter solid fractions in
suspension. Roughly 20 to 30 percent of suspended solids and about half of the BOD
and nutrient loads would remain in suspension after 30 minutes of settling time.
Analysis of the heavy metals results from the settleability experiments indicated that
about 20 to 40 percent of the heavy metals would not settle within two hours of settling.
In the final phase of field operation, an automatic sewer flushing module was designed,
fabricated, installed, and operated on a single segment for an extended period.
Flushed pollutant loads were determined for seven flushing events, and were
comparable to removals noted in the first phase of work, where flushing was
accomplished by manual means using a flush truck. The purpose of this work was to
begin to develop operational experience using automated flushing equipment. The
state-of-the-art with respect to operational automated flushing methods, equipment,
and sensing interfaces has not been fully demonstrated at this point in time. The effort
in this study is viewed as a pilot prototype investigation.
In the fourth phase, various predictive deposition loading and flushing criteria were
generated from the large data base developed during the field programs. These
formalisms allow for scanning of large-scale sewer systems to identify problem pipes
with respect to deposition. The refined tools will allow for comparative analysis of
upstream solids control vs. selected structural options to compare program
efficiencies.
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THE METHODOLOGY OF ANALYSIS FOR A
COMBINED SEWER OVERFLOW ABATEMENT PROGRAM
CORNELIUS B. MURPHY, JR.
U.S. ENVIRONMENTAL PROTECTION AGENCY
TECHNOLOGY TRANSFER PROGRAM
CHICAGO, ILLINOIS
July 25-26,1978
The Fifth Annual International Joint Commission (UC) Report on Great Lakes Water
Quality acknowledged the impact of urban runoff in the Great Lakes Basin:
"The Commission believes that combined sewer overflows and
stormwater flows from urban areas are reaching serious proportions and
contribute significant amounts of a wide range of harmful substances in
the Great Lakes."
Urban runoff is composed of two major components, stormwater and combined sewer
overflow. Stormwater discharges consist of runoff from various impervious areas which
have been contaminated by pollutants accumulated on the various surfaces due to
chemical spillage, air pollution, atmospheric washout, the application of highway
deicing agents, fecal matter of animal origin, and the accumulation of surface debris
and litter. The combined sewer overflows contain stormwater and sanitary sewerage.
The problem of combined sewer overflows is extensive insofaras one-fifth of the
nation's population is served by combined sewer systems. Furthermore, ten (10) of the
nation's fourteen (14) largest cities are served by a combined system in whole or in
part.
The objective of facilities planning is the development of cost effective, environmentally
sound and implementable conveyance and treatment systems which will meet
applicable requirements of Sections 201 (g), 301, and 302 of PL 92-500.
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Consistent with 40 CFR Part 35, Subpart E (Grants for Construction of Treatment Works
- Federal Water Pollution Control Act Amendments of 1972) a facilities plan is to
include:
A description of the treatment works for which construction drawings and
specifications are to be prepared,
A description of the selected wastewater treatment system covering all
elements of the system,
Infiltration/inflow documentation,
A cost-effectiveness analysis of the alternatives,
Identification of effluent limitations (permit),
Required comments or approvals of relevant state, interstate, regional
and local agencies,
Brief summary of pertinent public hearings or meetings, and
Brief statement demonstrating the implementability of the project.
The facilities planning activities are essentially the same for conventional treatment
facilities as for combined sewer overflow facilities. However, there were some
difficulties in the planning process. As a result, EPA established certain specific
policies (PRM 75-34 and PRM 77-4) which described how these issues were to be
addressed in the facility planning for combined sewer overflow abatement facilities.
PRM 77-4 outlined a cost allocation procedure for multiple purpose projects, allowing
EPA and the applicant to select the abatement alternative which offers the highest cost-
effectiveness relative to pollution control. PRM 75-34 outlines the procedure to select
the alternative and the sizing necessary to optimize the marginal cost/marginal benefit
ratio of the abatement options.
In the process of conducting the Rochester, New York CSO study, a methodology for
the analysis of CSO abatement alternatives was developed. The abatement alternative
analysis involved the logical development of a data base which analyzed activities in
fifteen major categories.
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A number of points were stressed in the development of the methodology sequence.
The first of these points was the need to define the applicable abatement alternatives
very early in the program. This process ensure that the purpose of the study is not lost
and all data gathering activities be conducted according to the required analyses.
Another important step was the calibration and verification of all models that were used
for CSO analysis in the study area. The models selected for application were based on
the urban area and collection system requirements as well as the objectives defined in
the initial phase of the program. The Simplified Stormwater Model was used in the
Initial screening of alternatives. The final analysis was conducted on a selected number
of abatement alternatives with the use of SWMM Version II. In conducting the network
model activity, it became apparent that one should not use models which are more
complex than the analysis requires. One should be certain to utilize the simplest model
which will attain the defined objectives. It is for this reason that the Simplified
Stormwater Model or an equivalent planning tool was recommended in the initial
screening of alternatives, while the use of SWMM Version II was recommended in the
final analysis of a select number of abatement alternatives.
The following major tasks are considered to be most important in the methodology
necessary to develop a combined sewer overflow master plan: definition of program
objectives, definition of existing conveyance and treatment systems, definition of
drainage areas and their characteristics, review of the meteorological data base,
selection of detailed network model to be utilized in the hydraulic analysis of the
existing system and the proposed alternatives, initiation of the overflow and
meteorological monitoring program necessary to augment the existing data base,
establishing relevant abatement alternatives, use of a simplified Stormwater model to
evaluate the existing system - long-term simulation, initial evaluation of
storage/treatment - capital intensive alternatives using the simplified Stormwater model,
calibration and verification of the detailed network model, application of the detailed
network model to the preliminary evaluation of non-structural alternatives, selection and
verification of wet weather quality predictive models, evaluations of applicable treatment
processes, detailed analysis of the prime alternatives, development of the CSO
abatement Master Plan.
In light of the very significant capital and operating costs associated with the
implementation of capital intensive storage/treatment alternatives, a more exacting
system analysis is necessary to evaluate the application of less capital intensive
measures which may be particularly effective in optimizing the performance of the
existing system. The methodology and tools of analysis are presently available which
allow the development of a comprehensive and cost-effective combined sewer overflow
abatement program.
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PREVENTION AND CORRECTION OF EXCESSIVE INFILTRATION
AND INFLOW INTO SEWER SYSTEMS
MANUAL OF PRACTICE
by the
AMERICAN PUBLIC WORKS ASSOCIATION
January 1971
As a result of a national study of the sources and prevention of infiltration and inflow, a
Manual of Practice was proposed. The Manual is intended to serve as a guide to local
officials in evaluating their construction practices, conducting surveys to determine the
extent and location of infiltration and inflow, the making of economic analyses of the
cost of excessive infiltration/inflow waters, and instituting corrective action.
"Infiltration" covers the volume of groundwater entering sewers and building sewer
connection from the soil, through defective joints, broken or cracked pipe, improper
connections, manhole wails, etc.
"Inflow" covers the volume of any kinds of water discharged into sewer tines from such
sources as roof leaders; cellar and yard area drains; foundation drains; commercial and
industrial so-called "clean water" discharges; drains from springs and swampy areas;
etc. It does not include, and is distinguished from, "infiltration".
"Infiltration/Inflow" is the volume of both infiltration water and inflow water found in
existing sewer systems, where the indistinguishability of the two components of
extraneous waters makes it possible to ascertain the amounts of both or either.
Infiltration and inflow conditions have two characteristics in common, in that each
problem is divided into two parts: prevention of excessive extraneous flows, and
correction of conditions already imposed on existing sewer systems.
In the case of infiltration, prevention of excessive entries into new sewer systems
depends on effective design; choice of effective materials of sewer construction;
imposition of rigid specifications limiting infiltration allowances; and alert and
unremitting inspection and testing of construction projects to assure tightness of
sewers and minimization of infiltration waters.
896CMS2.WS5
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Correction of infiltration conditions in existing sewer systems involves evaluation and
interpretation of sewage flow conditions to determine the presence and extent of
excessive extraneous water flows from sewer system sources, the location and gauging
of such infiltration flows, and the elimination of these flows by various corrective, repair
and replacement methods.
Prevention of excessive inflow volumes is a matter of regulating sewer uses and
enforcement of such precepts and codes by means of vigilant surveys and surveillance
methods. Correction of existing inflow conditions involves location of points of inflow
connections; determination of their legitimacy or illicit nature; evaluation of the
responsibility for correction of such conditions; establishment of inflow control policies
where none have been in effect; institution of corrective policies and measures, backed
up by investigative and enforcement procedures to make such policies potent.
The initial area of concern in reducing or eliminating infiltration involves the production
of a pipe system and appurtenances which are water-tight and do not permit ground-
water leakage. The realization of this objective begins during design. A number of
preliminary activities are necessary to provide vital background information before any
design decisions are made. Soil and groundwater conditions must be considered if the
design for a proposed sewer system is to avoid infiltration. The four methods of
obtaining the necessry design information include: reconnaissance (the gathering of
available information on soils and groundwater conditions), subsurface investigations,
lab testing, and in-situ testing.
Also, the above concern is important to improvements in pipe material which ensure
that the designer can provide proper materials to meet rigid infiltration allowances.
The most critical factor relative to the prevention of infiltration in new sewers is
construction. All of the currently manufactured pipes and joints are capable of being
assembled into sewer systems with minimal infiltration. This capability must be
coupled with good workmanship and adequate inspection.
The correction of infiltration involves a lengthy, systematic approach. The first step is to
identify the system by obtaining maps of the sewer system. The maps should be
analyzed to develop a series of small drainage areas. Next, identify the scope of
infiltration by obtaining actual dry-weather and wet-weather flow measurements at key
manholes. If the infiltration/inflow problem has been identified as rain-connected and
the system is supposedly separate, a rainfall simulation in the storm sewers can help
pinpoint the source. It is also very important that a physical survey of the sewer system
be taken to check for the effects of poor soil conditions and groundwater conditions.
Next, a planned sewer cleaning program should be established. Clean sewers are a
necessary prerequisite for any television inspection program and also for any correction
sealing procedures. As a result of the findings of the previous stages, the best
utilization of television or photographic inspection can now be determined. Based on
the results and recommendations of the inspection report, sound budgeting and
planning for the restoration of the system can now be achieved.
896CMS2.WS5
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Control of inflow, like control of infiltration, resolves itself into two practices: prevention
of new inflows, and correction of existing inflows. Prevention involves exclusion of
inflow connections by edict, and the rejection of any such flows when new structures
are built, or when existing building operations are modified. Correction involves the
location of existing sources and their elimination by physical separation of any such
connections in accordance with set policies of the jurisdictions.
Guidelines have been given for the control of infiltration and inflow conditions. Each
jurisdiction must determine its own policies and practices, using these indicators as to
what can be accomplished by new criteria and actions.
896CMS2.WS5
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RELATIONSHIP BETWEEN DIAMETER AND HEIGHT
FOR THE DESIGN OF A SWIRL CONCENTRATOR
AS A COMBINED SEWER OVERFLOW REGULATOR
RICHARD H. SULLIVAN, MORRIS M. COHN
JAMES E. URE, FRED E. PARKINSON
GEORGE GALIAMA
AMERICAN PUBLIC WORKS ASSOCIATION
July 1974
EPA 670/2-74-039
This report is a supplement to the report entitled "The Swirl Concentrator as a
Combined Sewer Overflow Regulator Facility" which was published in September of
1972. The 1972 studies demonstrated that the swirl device was capable of removing
floatable and suspended solids from sanitary sewage and stormwater. They
established a suitable relationship between chamber depth and diameter and their
effect on solids removal efficiencies. The purpose of this supplemental report was to
investigate the depth to width ratio established by the 1972 report and to define the
dimensions which would provide optimum construction economy and operating
efficiency in terms of solids.
The studies for this report were conducted on a hydraulic model of the swirl
concentrator at the LaSaile Hydraulics Laboratory in Montreal. The concentrator
configuration was similar to that which was used in the 1972 study. The model
diameter remained constant at 36 inches with a 20-inch diameter clear liquid overflow
weir and a 24-inch diameter scum ring.
The variable factors chosen to provide the chamber depth-to-width relationships were
weir height and the inlet pipe diameter. The study covered five rates of discharge,
including the probable ranges that would be imposed on a full-scale unit. These
fiowrates on a 1:12 scale of laboratory model to prototype, were: 50; 100; 150; 200; and
300 cfs. Four inlet pipe diameters were studied: 3; 4; 5; and 6 foot. The inlet
wastewater line was set at a slope of 1:1,000 to provide tangential flow of incoming
liquid in the swirl concentrator chamber.
At least three weir heights, or chamber depths, were tested for each inlet pipe diameter.
The range selected for the hydraulic study was: 6; 7; 9;, 11; and 13 feet.
896RBS3.WS5
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The incoming wastewater was composed of water supplied from a constant level tank
in the laboratory, and synthetic solids of proper composition injected into the inflow
stream by a vibrating feed unit.
The clear water outlet from the swirl concentrator was through a 6-inch diameter pipe
which was installed upward through the bottom of the model centerline. The height
could be varied at will by adding or removing segments to or from the top of the pipe.
The foul outlet consisted of a 2-inch diameter flexible tube, leading to a solids settling
tower fitted with an adjustable level outlet pipe which could be raised or lowered to
regulate the rate of discharge of the solids flow.
The grit increment of the synthetic solids injected into the stream flow to the swirl was
assumed to have a specific gravity of 2.65 and a straight line grain size distribution was
selected as a representative average of samples taken from existing combined sewer
systems - from No. 70 to No. 10 sieve sizes. The concentration range was 20 to 360
mg/l.
The organic material contained in the flow to the swirl concentrator, was defined as
having a specific gravity of 1.2 and a grain size distribution from less than 0.1 to 5 mm.
The floatable increment injected in the flow had a specific gravity of 0.9 to 0.998 and a
size range from 5 to 25 mm. The concentration range was 10 to 80 mg/l.
The hydraulic model could not duplicate the variations in inflow rates and in combined
wastewater solids concentration, which normally occurs in sewer system operations.
The pilot study which evaluated solids recovery for four sizes of inlet pipes and various
weir heights produced the following conclusions:
Design parameters can be definitively established, covering swirl
concentrator chamber diameter, inlet pipe dimensions, and internal
chamber facilities, to provide specific solids removal efficiencies for
prototype combined sewer overflow systems.
For chambers having a ratio of chamber diameter to chamber depth of 4 : 1
it was found that the depth had little effect on recovery rate. The same
condition was found when the ratio of chamber diameter to inlet dimension
was in the range of 6 : 1 or 7.2 : 1. When the ratio of chamber diameter to
inlet dimension was increased to 9 : 1 or 12 : 1, the depth or weir height had
more influence on recovery rates.
896RBS3.WS5
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For any given discharge the use of a smaller ratio of chamber diameter to
inlet dimension results in lower inlet velocity and lower chamber area and
volume. Hence for economy reasons, the designer should attempt to
reduce this ratio as close to six as is possible with the use of the design
curves given in this report.
Where circumstances are not favorable for the standard design with a ratio
of chamber diameter to depth of 4 : 1, it is possible to decrease the
chamber depth to a value equal to the inlet dimension. This also results in
an increase in the chamber diameter and chamber area. The chamber
volume may also be somewhat affected either up or down by this change.
The report recommended that the swirl concentrator principle be utilized more
extensively for the removal of solids pollutants of both inorganic and organic nature
which are contained in combined sewer overflow wastes.
896RBS3.WS5
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REMOTE CONTROL OF COMBINED SEWER OVERFLOWS
JAMES J. ANDERSON AND ROBERT L GALLERY
JOURNAL OF THE WATER POLLUTION CONTROL FEDERATION
November 1974
Vol 46, No. 11 pp. 2555-2564
The Minneapolis - St. Paul combined sewer system was modified with the installation of
a computer-assisted, real-time monitoring and remote control to reduce number and
volume of combined sewer overflows. The combined sewers service area, some of
which has been partially separated, is approximately 30 sq. miles (77.7 sq. km.). Initial
sewer gauging had indicated that the 30 mile interceptor system conveyance capacity
was not fully utilized during wet weather events. This was because of inflexible
regulator devices, and non-uniform distribution of rainfall over the service area.
The control system was designed to provide variable flow control to the interceptor
system, based on current conditions in the sewer system. Rain gauges, level sensors,
and gate and dam sensing devices transmit information to a central control system
over leased telephone wires. The amount of flow diverted to the interceptor is
controlled by inflatable fabric dams and hydraulicaily operated gates.
Gates and dams may be controlled remotely by an internal program, or manually by an
operator at a console. The position or pressure of each dam and gate is addressed,
and brought back to the proper value if the position or pressure has changed. This
control system has a mathematical model to assist the operator in anticipating sewer
flow conditions, based on rainfall location and intensity, and to test a change in
operation before initiating it. The control system cannot operate independently,
because it does not have a feedback routine in the model. The operational strategy is
to maximize downstream interceptor capacity, while preventing surcharging of trunk
sewers. Costs for the system in 1969 included $500,000 for regulator modifications;
$185,000 for the underground control vaults, polemount cabinets, telephone and the
level gauging system; and $370,000 for the central computer, level transducers,
telemetry, and supervisory contact equipments.
During 1969 and 1970, overflow events were reduced by 58 and 52 percent
respectively. Duration was reduced by 88 and 84 percent. Snowmelt overflow events
were virtually eliminated.
896BJK5.WS5
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RETENTION BASIN CONTROL OF COMBINED SEWER OVERFLOWS
by
SPRINGFIELD SANITARY DISTRICT
SPRINGFIELD, ILLINOIS
for the
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
August 1970
Storm overflow from combined sewers discharged through the Cook Street Pumping
Station of the Springfield Sanitary District into Sugar Creek has resulted in repeated fish
kills during previous years. A study was undertaken to evaluate the ability of a retention
basin to prevent such deterioration of water quality. Anticipated possible effects of the
basin include attenuation of peak flows, sedimentation, and biological degradation. An
anticipated adverse effect of the retention basin was the discharge of algae synthesized
in the basin. Performance of the lagoon during the 20-month period of observation
indicated that it was successful in preventing severe deterioration of downstream water
quality due to combined sewer overflows.
Performance of the lagoon was monitored by daily collection of composite samples
from the lagoon influent and effluent and by grab sampling of stations in Sugar Creek
above and below the point of lagoon discharge. Interpretation of the capabilities and
limitations of the facility was limited by the lack of capability for measuring influent flow
rate and the lack of influent and effluent samples collected at various periods during
storms. Hence, it was not possible to conduct mass balance computations on the
basin to determine its overall effectiveness. Best evidence of the efficiency of the facility
was afforded by observation of the fact that incidence of fish kills was limited following
installation of the retention basin.
While the movement of individual storm flows through the lagoon could not be traced, it
was observed that the average annual reduction of BOD was 27 percent and total
coliform reduction averaged 72 percent. However, during the period from June through
October 1969, production of algae in the basin caused the effluent BOD to consistently
exceed that of the influent. This observation was substantiated by the increase in
suspended solids in the effluent during these periods, increased effluent pH and
supersaturation of dissolved oxygen during periods of high radiant energy. It would
appear that the suitability of retention basins of the type used at Springfield should be
considered on an individual basis because of the possibility of adverse water quality
conditions being created as a result of the release of high concentrations of algae
during parts of the year.
896CMS1.WS5
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Considerable reductions in the concentration of indicator organisms occurred in the
retention basin, averaging 72 percent. However, influent total coliform density was high
(averaging 1,250,000/100 ml) and thus the effluent coliform density was significant
(353,000/100 mi).
While the analysis of the performance of the basin is limited on a quantitative basis, it
was shown to be an adequate solution for the existing problem at Springfield, Illinois.
Only one fish kill occurred during the period of study, and it happened during a period
when the basin was drained for repair.
It was not possible to quantitatively determine the relative effect of the various
mechanisms which could account for the basin's performance. Sedimentation can
reasonably be accredited with some water quality improvement since sludge
accumulated in the basin. However, the contribution of bacteria and algae synthesized
in the basin to this sediment is not known. Similarly, the amount of biological
degradation of soluble and colloidal organic material has not been established. It is
postulated that an appreciable amount of the observed improvement could be
attributed to retention of storm flow with slow release at diminished rates to the
receiving stream.
The analysis of basin performance could not provide a rational basis for determining
the desirable size of storm water retention facilities at other installations. This is
because the available instrumentation did not afford a measure of influent flow rate and
because a portion of high storm water overflows were bypassed and did not enter the
retention facility. On the basis of an increase in biochemical oxygen demand during
summer months, it was anticipated that difficulty might be experienced at certain
installations because of deterioration of downstream water quality or because of
aesthetic objection to the high algae densities. Sizing retention facilities clearly
depends upon the water quality objective involved. For example, where appreciable
reductions in the density of indicator organisms is necessary, retention times
approximating those provided at Springfield would not be sufficient. An additional
consideration in determining basin volume is the requirement for storage of solids
retained in the basin.
896CMS1 .WS5
896CMS1.WS5
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SEWER FLOW MEASUREMENT
A STATE-OF-THE-ART ASSESSMENT
by
PHILIP E. SHELLEY
GEORGE A. KIRKPATRICK
EG & G WASHINGTON ANALYTICAL SERVICES CENTER, INC.
ROCKVILLE, MARYLAND 20850
November*! 975
In order to characterize stormwater and combined sewer overflows and to facilitate the
development, demonstration, and evaluation of treatment and control systems for
combating the problem, it is necessary to have accurate and reliable determinations of
the quantity and quality of the flows. Both the quantity and quality of urban stormwater
runoff are highly variable and transient in nature, because of meteorological and
climatological factors, topography, hydraulic characteristics of the surface and
subsurface conduits, and land use activities. Conventional flow measurement devices
and techniques have been developed mainly for the relatively steady-state flows as
found in irrigation canals, sanitary sewers, and large streams rather than the highly
varying surges encountered in storm and combined sewers.
Measurements of quantity of flow, usually in conjunction with sampling for flow quality,
are essential to nearly all aspects of water pollution control. Research, planning,
design, operation and maintenance, and enforcement of pertinent laws are activities
which rely on flow measurement to be effective. For some activities, very precise, time
synchronized, continuous flow records are needed. With others, occasional, fairly
rough estimates of flow may suffice.
The various flow measuring devices and techniques are summarized in Table 1. These
evaluations were made with a storm or combined sewer application in mind and will not
necessarily be applicable for other types of flows.
A second table offers a comparison of some of the primary devices or techniques that
are used to measure storm and combined sewer discharges. Each method is
numerically evaluated in terms of its percent of achievement of several desirable
characteristics. Dilution techniques as a class promise accuracy in a number of
applications. They are probably most useful as a tool for in-place calibration of other
primary devices. They have also been extremely useful for general survey purposes
and have found some application when added to other primary devices during periods
of extreme flow such as pressurized flow in a conduit that is normally open channel.
896CMS10.WS5
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Acoustic open channel devices are dependent on the velocity profile a resultant
requirement for several sets of transducers. They are presently justifiable for very large
flows because of the expense involved.
The Parshall flume is a commonly used flow measurement device. The requirement for
a drop in the flow is a disadvantage, and submerged operation may present problems
at some sites. Known uncertainties in the head-discharge relations (possibly up to 5
percent), together with possible geometric deviations, make calibration in place a
requirement for high accuracy. Palmer-Bowlus type flumes are very popular overall.
They can be used as portable as well as fixed devices in many instances, are relatively
inexpensive, and can handle solids in the flow without great difficulty.
All point velocity measuring devices were included in the current meter category. In the
hands of an experienced operator, good results can be obtained. They are often used
to calibrate primary devices in place or for general survey work. They are generally not
suited for unattended operation in storm and combined sewer flows, however.
Electromagnetic flowmeters show considerable promise where pressurized flow is
assured as do closed pipe acoustic devices. Neither can be considered portable if one
requires that the acoustic sensors be wetted, a recommended practice for most
wastewater applications.
Open flow nozzles and sharp-crested weirs are often used where the required head
drop is available. Weirs will require frequent cleaning and are best used as temporary
installations for calibration purposes. Flow tubes and venturies are only suitable for
pressurized flow sites such as might be encountered, for example, at the entrance to a
treatment plant.
Trajectory coordinate techniques, such as the California pipe or Purdue methods,
require a pipe discharging freely into the atmosphere with sufficient drop to allow a
reasonably accurate vertical measurement to be made, a situation not often
encountered in storm or combined sewers. Slope area methods, as explained earlier,
must generally be considered as producing estimates only and, consequently, should
be considered as the choice of last resort.
896CMS10.WS5
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STORAGE AND TREATMENT OF COMBINED SEWER OVERFLOW
WILBUR R. LEIBENOW, BEIGING, JAMES, K.,
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND MONTIRONIG
October 1972
122 pages.
EPA-R2-72-070
The objective of this study was to demonstrate the feasibility and economic
effectiveness of a combined wastewater overflow detention basin. Wastewater in
excess of existing transportation/treatment system capacities overflows to a detention
basin during wet weather, and is later treated during periods of low flow.
A paved asphalt detention basin with a storage volume of 8.66 acre feet was
constructed at Chippewa Falls, Wisconsin to receive overflow from a 90 acre combined
sewer area including all of the central business district. The system was designed so
that the stored combined sewage could be pumped to the wastewater treatment plant
when precipitation subsided.
Project construction began in October of 1967 and was completed in March of 1969.
Total capital cost for the demonstration project was approximately $610,000. This cost
can be subdivided into the following components:
Detention Pond Construction
Pumping Station, Pond Structures, Piping
Combined Relief Sewer and Separate Sewer
Electrical Work
Treatment Plant Revisions
Land
$ 60,000
158,000
223,000
21,000
117,000
2,000
Total
$610,000
896RHG3.WS5
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This study was conducted over the two-year time frame of 1969 and 1970. Results
indicated several positive effects from installation of this basin. During 1969, due to dry
weather, the pond received flow during only 16 events, but completely filled twice and
overflow to the river occurred. During 1970, there were 46 discharges to the pond with
only one overflow to the river. Over the study period, 37.75 million gallons of combined
sewage (93.7 percent of the total discharge volume) were withheld from the river for
subsequent treatment. This included 49,520 pounds of BOD5 and 90,390 pounds of
suspended solids which were withheld from the river and were subsequently treated.
These loads represented 98.2 percent of the total BOD5 and 95.8 percent of the total
suspended solids which were contained in the overflows from the existing
transport/treatment system.
There were no observed detrimental effects on treatment plant operation due to the
increased intermittent flows from the detention pond. Although the basin is located in
close proximity to the business district, no complaints were received regarding any
phase of the pond operation. The overflow basin stored combined sewage for periods
up to 14 hours without odors developing. Substantial relief from basement flooding in
the downtown area was also observed as a result of the basin.
The estimated average operating and maintenance cost attributed to the storage basin
system was $7,300 per year over the two year period. The largest portion of this annual
cost (75 percent) was attributed to additional treatment plant operations while pumping
and pond cleaning accounted for the remaining portions (7.5 percent and 17.5 percent
respectively).
896RHG3.WS5
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A STRATEGY FOR INTEGRATING STORAGE TREATMENT OPTIONS
WITH MANAGEMENT PRACTICES
JAMES P. HEANY, STEPHEN J. NIX
USEPA - TECHNOLOGY TRANSFER SEMINAR ON
COMBINED SEWER OVERFLOW ASSESSMENT AND CONTROL PROCEDURES
WINDSOR LOCKS, CONNECTICUT
May 18 and 19,1978
A methodology was presented to provide planners with a tool to develop preliminary
cost estimates and strategies for wet-weather poflution control facilities. The primary
emphasis was placed on procedures to integrate storage/treatment options with other
management practices.
Previous assessments published by the authors indicated that nationwide capital costs
for wet-weather pollution control ranged from $2.5 billion at 25 percent BOD control to
$41.9 billion at 85 percent BOD control. The plotted curve of function of percent BOD
removal is an exponential type curve. Graphical solutions were used by the authors to
evaluate a wide range of wet-weather control options.
Wet-weather pollution control costs were estimated based on production theory and
marginal cost analysis from economics. A seven-step graphical procedure was
developed to produce this estimate. Production functions were established for street
sweeping, combined sewer flushing, and storage treatment. A unit cost of $7.00 per
curb mile was established for street sweeping and $11.78 per foot of sewer was
established as a unit cost for sewer flushing. Unit costs for storage treatment were
taken from existing EPA publications.
The methodology was applied to a hypothetical city of 1,000,000 people. Pollutant
loads were estimated, and a control network consisting of street sweeping, sewer
flushing and storage/treatment was analyzed. The results demonstrated that other
management practices used in conjunction with storage/treatment can give a savings
of 5 to 45 percent over storage/treatment alone.
The results of the paper represent simplified estimates of system savings and pollution
control, however they do suggest that management practices should be considered as
part of a stormwater pollution control package. The methodology was stated to be
capable of estimating the costs and cost savings of pollution control management
practices.
896RHG4.WS5
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STREAM POLLUTION AND ABATEMENT
FROM COMBINED SEWER OVERFLOWS
BUCYRUS, OHIO
FEDERAL WATER QUALITY ADMINISTRATION
DEPARTMENT OF THE INTERIOR
by
BURGESS AND NIPLE, LIMITED
November 1969
This report presents the findings of a study conducted to evaluate the pollutional effects
from combined sewer overflows on the Sandusky River at Bucyrus, Ohio. It also
presents the benefits, economics, and feasibility of abating pollution from combined
sewer overflows. The study compares physical sewer separation to alternate methods
of reducing or eliminating the pollution resulting from combined sewer overflows. This
study focuses on determining if there are methods of abating pollution from combined
sewer overflows which would accomplish the task better than physical separation and
at a lesser cost.
One of the primary objectives of the study was to determine the relationship of rainfall
events to overflow events and the volume of flow in the Sandusky River. Historical
records of rainfall and flow in the Sandusky River were evaluated along with data
collected during the one-year study period. Weirs for measuring overflow volumes
were installed at three locations. Samples were also collected at these locations to
determine overflow characteristics and effects on the stream. From this information a
two-year, one-hour design storm was selected for use in sizing intercepting devices and
treatment facilities.
The city of Bucyrus is located near the upper end of the Sandusky River Basin which is
tributary to Lake Erie. Bucyrus has an incorporated area of about 2,340 acres, a
population of 13,000, and a combined sewer system with an average dry weather
wastewater flow of 2.2 million gallons per day.
896RBS6.WS5
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The results of the study show that any 20 minute rainfall greater than 0.05 inches will
produce an overflow. The combined sewers will overflow about 73 times each year
discharging an estimated annual volume of 350 million gallons containing 350,000
pounds of BOD and 1,400,000 pounds of suspended solids. The combined sewer
overflows had an average BOD of 120 mg/l, suspended solids of 470 mg/l, total
conforms of 11,000,000 per 100 ml and fecal conforms of 1,600,000 per 100 ml. The
BOD concentration of the Sandusky River, immediately downstream from Bucyrus,
varied from an average 6 mg/l during dry weather to a high of 51 mg/l during overflow
discharges. The total conforms varied from an average of 400,000 per 100 ml during
dry weather to a high of 8,800,000 per 100 ml during overflow discharges.
Six methods of controlling the pollution from combined sewer overflows were evaluated
for degree of protection, advantages, disadvantages and estimated costs. The
methods evaluated are presented below with their associated costs.
Complete Separation of Sanitary Wastewater and Stormwater
- New Sanitary Sewer System $9,300,000
- New Storm Sewer System $8,800,000
Interceptor Sewer and Lagoon System
- Interceptor, Pump Station and Aerated Lagoon $5,220,000
- Holding Tanks, Interceptor, Pump Station $5,860,000
and Aerated Lagoon
Stream Flow Augmentation $5,000,000
Primary Treatment of Overflows $8,810,000
Chlorination of Overflows $3,000,000
Off-Stream Treatment $1,700,000
Sewer separation was the most costly alternative to controlling combined sewer
overflows and would only reduce the pollutants discharged to the river by 50 percent.
In this report it was shown that the stormwater runoff from urban areas contains a
significant amount of contaminants harmful to stream water quality. The degree of
pollution from stormwater varies from that of very dilute sewage to strong sewage.
Construction and operation of the Interceptor and Lagoon System or Off-Stream
Treatment would be the most economicaf method of reduction or controlling pollution
from overflows.
896RBS6.WS5
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The interceptor and lagoon system would be designed to protect the stream from all
overflows from storms less than the two-year, one-hour storm. The lagoon could also
provide tertiary treatment for effluent from the existing wastewater treatment plant. The
Off-Stream Treatment Alternative involves construction of a pump station to divert the
flow in the Sandusky River to lagoons for treatment during combined sewer overflows.
This alternative would only provide downstream water quality protection and would not
change the water quality in the river reach within the city.
Stream flow augmentation is a method of controlling pollution from overflows by
providing sufficient dilution water from storage impoundments to maintain a desired
concentration of dissolved oxygen downstream during overflows. This is not feasible at
Bucyrus due to the lack of suitable reservoir sites.
Primary treatment of overflows is very costly and it would only reduce the waste loads
discharged to the river by 50 to 70 percent.
Chlorination of overflows would reduce the bacteria count discharged to the river but
would not significantly reduce the concentration of any of the other pollutants present in
the combined sewer flows.
The study recommended two phases of construction. The first phase would involve
construction of Off-Stream Treatment to include construction of a pump station, a low
head dam, and a lagoon system. When it has been adequately demonstrated that the
lagoon treatment is capable of providing the water quality protection required, the
second phase would be constructed. The second phase would involve construction of
the interceptor. The first phase would provide downstream water quality protection.
The second phase would provide water quality protection for entire stream reach within
Bucyrus and downstream.
This alternative is less costly than complete sewer separation and it provides treatment
for storm runoff as well as sanitary flow. Sewer Separation would result in all urban
storm runoff being directly discharged to the river.
896RBS6.WS5
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SURFACE AND SUB-SURFACE DETENTION IN
DEVELOPED URBAN AREAS:
A CASE STUDY
by
STUART G. WALESH, P.E.
and
MARK L. SCHOEFFMANN, P.E.
PRESENTED AT THE AMERICAN SOCIETY OF
CIVIL ENGINEERS CONFERENCE
"URBAN WATER-84"
BALTIMORE, MARYLAND
May 28-31,1984
Stormwater detention facilities are technically sound, economically attractive, and
environmentally acceptable elements in urban stormwater control systems serving
newly developing areas. A potential, fundamentally different approach is retrofitting
detention into an existing stormwater system. A carefully engineered runoff control
system (RCS) including on-street storage and subsurface tank storage may be
implemented to control the stormwater flow into a combined sewer system to mitigate
basement flooding and control stormwater runoff to mitigate surface flooding.
Presented in this article is the process leading to and the status of an ongoing project
incorporating surface and subsurface detention to prevent sewer surcharging and
basement flooding in a completely urbanized 1,200-acre combined sewer service area
in Skokie, Illinois. The Village of Skokie, Illinois, a northern suburb of Chicago, is within
the service area of the Metropolitan Sanitary District of Greater Chicago (MSDGC). The
1200-acre Howard Street Sewer District (HSSD) is on the south side of the Village.
The fully developed district contains approximately 80 percent residential land use, 15
percent industrial and 5 percent commercial. The gross population density is
approximately 15 people per acre. Average annual precipitation is about 34 inches and
all seasons are marked by occasional intense storms. Runoff from these storms,
particularly in the spring and summer, cause severe surcharging and basement
flooding. For 1 hour, 1-, 10-, and 100-year recurrence interval rainfall events, rainfall
amounts are 1.19, 1.94, and 2.80 inches respectively. For a 24-hour period, the 1-, 10,
and 100-year amounts are 2.21, 3.86, and 6.70 inches respectively.
896CMS11.WS5
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The HSSD slopes generally eastward along Howard Street, the main east-west artery,
towards the North Shore Channel. Slopes vary from 0.1 to 1 percent and the overall
slope of the district is 0.2 percent.
Surface drainage moves from front lawns, driveways, and alleys to the streets.
Stormwater moves in gutters along the curb lines to the nearest inlets which are located
at mid-block points and immediately outside of intersections.
Stormwater and sewage from the HSSD are conveyed to an interceptor owned and
maintained by the MSDGC. Interception takes place at the east end of the HSSD near
the North Shore Channel. The MSDGC has completed Phase I of the Tunnel and
Reservoir Plan (TARP) which was scheduled to go into operation in early 1985. TARP
was to increase the interceptor capacity and reduce overflows into the North Shore
Channel. Although TARP will improve the outlet conditions for runoff events from the
HSSD, it will not change flow capacities or conditions in most of the HSSD.
The MSDGC obtained funding for TARP form the USEPA and it appeared Skokie may
be eligible for similar funding to be used for a conveyance system within the Village.
The estimated cost for the conveyance system was $78,000,000 for the entire Village.
By 1981, it was evident that EPA funds for this plan would not be available. Another
study was undertaken and it concluded with the idea of a system which would
incorporate runoff control with surface and subsurface storage within the developed
area.
The following design criteria were established at the beginning of the engineering
process or evolved during the course of the process.
Use the 10-year recurrence interval storm.
Make maximum utilization of existing sewer system but reduce sewer
surcharging to prevent sewage backup caused by overloading of the sewer
system.
Make maximum utilization of available street storage capacity without causing
flood damage to adjacent property.
Minimize flooding on state and county highways.
Assume TARP is completed and the HSSD discharges into it.
Utilize a gravity-operated system, in preference to a pumped system, and make
minimal use of electrical and mechanical controls and equipment.
896CMS11.WS5
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Watershed modeling and analysis was used to diagnose the hydrologic-hydraulic
behavior of the HSSD. A three-phased approach was used in the watershed modeling
and analysis.
Phase I was a static condition analysis which determined if flood levels on the North
Shore Channel would cause basement flooding solely as a result of backwater. The
analysis was conducted to determine if there were portions of the HSSD in which flood
control could not be achieved by in-HSSD runoff control. The analysis concluded that
there were no significant areas in which basement flooding would result solely from
backwater of the North Shore Channel.
The intent of Phase II. Sewer Capacity Analysis, was to determine the maximum rate in
which stormwater runoff could be released into the combined sewer system without
exceeding the established surcharge level The sewer capacity analysis was carried
out using the computer program System Analysis Model (SAM), which permitted
simulation of the entire HSSD and provided the computational means of accounting for
system surcharges and hydraulic grade lines for each trunk and branch sewer.
Street Ponding Analysis, Phase III, determined the street ponding which would occur as
a result of regulating the rate at which stormwater runoff could enter the combined
sewer system. Overall, the street ponding analysis indicated that keeping water out of
basements via surface and subsurface ponding was feasible but the number of streets
subject to ponding would increase.
The recommended Runoff Control System consists of:
425 flow regulators functioning in conjunction with 215 berms.
12 subsurface storage facilities.
9,500 feet of 30-inch to 72-inch separate relief sewer for the commercial,
downstream end of the HSSD.
The system would perform such that the average maximum depth of street ponding is
approximately 0.7 feet measured from the gutter at the lowest point in the block and the
average ponding duration is 5 hours under the design 10-year storm condition. The
estimated late 1983 cost for the recommended runoff control system was $8.1 million
or about 20 percent of the cost of a conventional runoff control system.
The recommended runoff control system was tailored to the unique combination of
topographic, land use, hydrologic and hydraulic characteristics of the combined sewer
service area in Skokie. However, the analytic techniques used, particularly the
hydrologic-hydraulic computer models, and the surface and subsurface facilities and
hardware employed are likely to be applicable to other fully developed urban areas
experiencing sewer surcharging and other flooding problems.
896CHS11.WS5
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THE SWIRL CONCENTRATOR AS
A COMBINED SEWER OVERFLOW
REGULATOR FACILITY
RICHARD FIELD
September 1972
EPA-R2-72-008
In 1969-70 The American Public Works Association (APWA) Research Foundation
carried out a national investigation of the means by which municipal jurisdictions in the
U.S. and Canada regulate and control overflows from combined sewer systems, and of
methods by which the pollutional effects of these discharges into receiving waters can
be minimized.
The major finding of the study was that in American practice, little or no effort was made
to improve the quality of the overflow liquids and, thereby, to reduce the pollutional
impact on receiving waters. Regulators were only capable of controlling the quantity of
overflows; and even this function had been carried out with only limited success. The
investigation also disclosed that European practices emphasized improvement of the
quality of storm overflows from combined sewers by various mechanical-hydraulic
means. One of the methods of quality control being used in Bristol, England, was the
so-called "vortex" device. The APWA study recommended that further research be
conducted on new devices which could induce separation of solids from the liquid.
This led to the study of the swirl concentrator which is a modified version of the "vortex"
device. This study found that a vortex flow pattern should be avoided when working
with larger flows in minimum-sized chambers. However, it showed that inducing a swirl
action in the wastewater was very effective in causing a liquid-solids separation.
The American Public Works Association, under contract with the City of Lancaster, PA,
completed this study with the intent that Lancaster would construct a demonstration or
prototype swirl concentrator. The study included hydraulic modeling studies
conducted at the LaSalle Hydraulic Laboratory in Canada; and mathematical modeling
to determine design relationships and the degree of efficiency which might be
associated with construction of such facilities. The objectives of the study were to
determine swirl concentration configurations, flow patterns, and settleable solids
removal efficiency.
896RBS4.WS5
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The device, as developed by the study, consists of a circular channel in which rotary
motion of the sewage is induced by the kinetic energy of the sewage entering the
chamber. Settleable solids underflow discharges through an orifice called the foul
sewer outlet, located at the bottom and near the center of the chamber. Clarified liquid
discharges over a circular weir around the center of the tank and is conveyed to storage
treatment devices as required or to receiving waters. The concept is that the rotary
motion causes the sewage to follow a long spiral path through the circular-chamber. A
free surface vortex was eliminated by using a flow deflector, preventing flow completing
its first revolution in the chamber from merging with inlet flow. Some rotational
movement remains, but in the form of a gentle swirl, so that water entering the chamber
from the inlet pipe is slowed down and diffused with very little turbulence. The particles
entering the basin spread over the full cross section of the channel and settle rapidly.
Solids are entrained along the bottom, around the chamber, and are concentrated at
the foul sewer outlet.
The following conclusions were drawn from the hydraulic and mathematical modeling:
The swirl concentrator is a practical, simple facility which offers a high
degree of performance in reducing the amount of settleable solids
contained in combined sewer overflows.
The swirl concentrator is very efficient in separating both grit and settleable
solids in their middle (>0.2 mm) and larger grain size ranges. By weight,
these fractions represent about two-thirds of the respective materials in the
defined combined sewer. Separation of the small grain sizes was less
efficient, although still appreciable.
The floatables trap and storage arrangements should capture most of the
lighter than water pollutants and convey them to the foul sewer. Its
dimensions are such that oversize floating objects would not be captured,
and would tend to go over the effluent weir rather than stay in the chamber
to clog the foul outlet.
Both the floatables trap and foul outlet are easy to inspect and clean out if
necessary, during dry weather flows.
There must be sufficient hydraulic head available to allow flows to pass
through the swirl concentrator facility without causing backups or flooding
upstream in the system. Sufficient head should be available to operate the
foul sewer discharge by gravity. If sufficient head is not available, the foul
sewer discharge may require continuous pumping.
896RBS4.WS5
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SWIRL AND HELICAL BEND
POLLUTION CONTROL DEVICES
RICHARD H. SULLIVAN, JAMES E. URE,
FRED PARKINSON, AND PAUL ZIELINSKI
AMERICAN PUBLIC WORKS ASSOCIATION
CHICAGO, ILLINOIS
prepared for
MUNICIPAL ENVIRONMENTAL RESEARCH LAB
CINCINNATI, OHIO
July 1982
EPA NO. 600/8-82-013
In 1970, an EPA state-of-the-art report on regulators indicated that two British devices
showed possibilities for application as combined sewer overflow regulators in the
United States. These were the vortex-flow regulator, later called the swirl
regulator/separator, and the helical bend regulator/separator. Both have been
modified for adaptation to North American treatment practice.
The design criteria used for the English regulators differ from those used in North
American practice, primarily in the ratio of wet-weather flow to dry-weather flow allowed
to enter the interceptor for treatment. Thus, it was necessary to conduct hydraulic
model studies to develop units for United States practice.
The swirl combined sewer overflow regulator/separator is of simple annular-shaped
construction and requires no moving parts to achieve a relatively high degree of
separation of settleable and floatable solids from a waste stream. While accomplishing
the separation of solids, it also regulates the flow to the interceptor sewer system.
Wastes are concentrated into what should be a more economical method to treat the
waste stream. Treatment of the concentrate could be with either conventional
wastewater treatment facilities or special combined sewer overflow treatment units.
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The device consists of a circular channel in which rotary motion of the sewage is
induced by the kinetic energy of the incoming sewage. Flow to the treatment plant is
deflected and discharged through an orifice called the foul sewer outlet, located at the
bottom and near the center of the chamber. Excess flow in storm periods discharges
over a circular weir around the center of the tank and is conveyed to storage treatment
devices as required or to receiving waters. The concept is that the rotary motion
causes the sewage to follow a long spiral path through the circular chamber. A flow
deflector prevents flow completing its first revolution in the chamber from merging with
inlet flow. Some rotational movement remains, but in the form of a gentle swirl, so that
water entering the chamber from the inlet pipe is slowed down and diffused with very
little turbulence. The particles entering the basin spread over the full cross section of
the channel and settle rapidly. Solids are entrained along the bottom, around the
chamber, and are concentrated at the foul sewer outlet. Flow through the foul sewer
outlet is limited to the hydraulic capacity of downstream facilities.
The device is essentially without moving parts and performs well under a variety of flow
conditions. The primary features of the unit include: Inlet Ramp, Row Deflector, Scum
Ring, Overflow Weir and Weir Plate, Gutters, Downshaft and Secondary Overflow Weir.
Three flow quantities must be considered in the design: 1) the peak dry-weather flow;
2) the design flow, i.e., the flow for which the optimum treatment is desired; and 3) the
maximum flow likely to occur through the chamber.
The following procedure should be used when designing a swirl regulator/separator.
1. Select design discharge
2. Select the recovery efficiency desired:
- One of four performance efficiencies can be chosen -
either 100,90,80 or 70 percent recovery of settleable solids
3. Find the inlet dimension--D1, and chamber diameter--D2
4. Check discharge range covered
5. Recovery rates
6. Foul discharge
7. Find dimensions for the whole structure
8. Geometry modifications
9. Foul discharge modifications
The location of the swirl regulator/separator is dependent upon the elevation of the
combined sewer and the location of the interceptor sewer. In some instances, it may
be feasible to construct the facility underground in the public right-of-way. The site
should minimize construction of transition sewers from the collector and the clear
overflow discharge to receiving waters.
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The operation and maintenance requirements for swirl regulators/separators has been
assumed to be constant for all sizes of units. Cleaning of the unit may be done with
automatic washdown facilities. With these washdown facilities, only one or two special
site visits to remove large objects can be anticipated.
Results from three demonstration units are available which have tended to validate the
laboratory testing. The units which have been constructed include those by Onondaqa
County (Syracuse), New York; Lancaster, Pennsylvania; and Boston, Massachusetts.
The experience of all three agencies with the operation of the swirl unit has been very
good. Generally, operational problems which have become apparent have been due to
design deficiencies.
Monitoring for treatment evaluation has been performed at the Syracuse facility.
Efficiency has been calculated on the values based upon the laboratory work.
Relatively good SS removal efficiencies were determined over the entire storm flow
range at the Syracuse prototype. Total mass loading and concentration removal
efficiencies ranged from 33 to 82 percent and 18 to 55 percent, respectively, with
flowrates from 0.54 cu m/min (0.2 mgd) to 20.5 cu m/min (7.6 mgd). Suspended
solids influent concentrations greater than 250 mg/l generally resulted in removals of
better than 50 percent of the total mass loading to the swirl.
Care must be taken in evaluating swirl solids treatability since under dry-weather flow
conditions, all regulators are designed to deliver the entire flow volume and associated
solids to the intercepting sewer until a predetermined overflow rate is reached.
If the swirl regulator was replaced by a conventional flow regulator, the net mass
loading reductions (attributable to the SS conventionally going to the intercepted
underflow) would have ranged from 17 to 64 percent as compared to a more effective
range of 33 to 82 percent for the swirl.
Prototype analyses indicated BOD5 removals of 50 to 82 percent for mass loading, and
29 to 79 percent in terms of concentration.
The helical bend combined sewer overflow regulator/separator consists of an enlarged
section of the sewer which acts as a solids and floatables trap prior to diversion of the
overflow to additional treatment or receiving waters. The device requires considerable
space to construct. Operation and maintenance are minimized as there are no
mechanical or moving parts within the device. The channel is curved to develop helical
secondary motions within the flow. The helical motion effectively captures particles
which have a greater settling velocity than the upward velocity of the helical motion.
Relatively high velocities are achieved as the chamber empties to treatment at the end
of the storm event which will remove deposited solids. Thus, the helical bend separator
is unique in that most of the removed solids are released at the end of the storm event.
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The helical bend combined sewer overflow separator was developed in Great Britain.
The design developed for USEPA was based upon English experience as well as
hydraulic and mathematical model studies. A demonstration unit has been installed
(September 1979) in Boston, Massachusetts, where it was to be tested on both
combined sewage and separate stormwater flows.
Available data indicates that the helical bend separator can be as efficient as the swirl
separator/regulator. The helical bend separator compared to the swirl separator
should have less head loss, may require less acquisition of additional right-of-way, and
allows the short period of time at the end of the storm event. However, the cost of the
device may be up to 50 percent more than an equivalent swirl separator/regulator and
almost 3 times more than a swirl unit designed to remove 80 to 90 percent of the solids.
The location and depth of the combined sewer will determine the area required for its
installation. The depth of the sewer may suggest that an underground chamber is
appropriate. If this is the case or if adjacent land is expensive, it may be desirable to
construct a chamber for the separator along the existing right-of-way of the sewer.
The available head at a specific site may be a critical factor in the choice of the specific
type of combined sewer regulator to be used. The head loss must be considered for
two conditions: 1) for periods of dry-weather flow, and 2) for periods of wet-weather
flow. The available head during dry-weather flow will depend on the difference in
elevation between the combined sewer and the interceptor that will convey the flow to
the wastewater treatment plant. The available head during wet-weather flow will
depend on the difference in elevation between the combined sewer and the water
surface of the receiving stream.
The helical bend separator was tested extensively in Nantwich, England. The first full
size unit has been built in Boston, Massachusetts. A purpose of the demonstration
project was to compare the efficiency of the unit as compared to a swirl
separator/regulator. The unit was to be tested on combined sewer overflows and
stormwater discharges. Test results were not available at the time of preparation of the
article. Construction costs were very low due to the fact that the unit was prefabricated
from wood and is not intended for permanent use.
It appears that the principal advantages of the helical bend separator are the low head
requirements and the discharge to treatment of the captured solids at the end of the
storm event. The swirl regulator/separator in turn requires less space and should be
less expensive to construct. Use of the swirl regulator/separator where insufficient
hydraulic head is available for its normal mode of operation may require dry weather
bypassing the device. As both units have been designed to minimize the cost of
operation and maintenance problems, they are considered comparable.
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URBAN RUNOFF POLLUTION CONTROL TECHNOLOGY OVERVIEW
C.B. BRUNNER, R.I. FIELD
H.E. MASTERS, A.N. TAFUR1
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO
PROCEEDINGS
5TH UNITED STATES/JAPAN CONFERENCE ON
SEWAGE TREATMENT TECHNOLOGY
TOKYO, JAPAN
December 1977
USEPA 600/9-77-027
Control and treatment of stormwater discharges and combined sewage overflows from
urban areas are problems of increasing importance in the field of water quality
management. Over the past decade much research effort has been expended and a
large amount of data has been generated, primarily through the actions and support of
the U.S. Environmental Protection Agency's Storm and Combined Sewer Research and
Development Program.
The program starts with "Problem Definition" broken into "Characterization" and
"Solution Methodology".
The average BOD concentration in combined sewer overflow is approximately one-half
the raw sanitary sewage BOD. However, storm discharges must be considered in
terms of their shockloading effect due to their great magnitude. A not uncommon
rainfall intensity of 1 inch/hour will produce urban flowrates 50 to 100 times greater than
the dry-weather flow from the same area.
Approximately one-half of the stream miles in this country are water quality limited and
30 percent of these stream lengths are polluted to a certain degree with urban runoff.
Therefore, secondary treatment of dry-weather flow is not sufficient to produce required
receiving water quality; and control of runoff pollution becomes an alternate for
maintaining stream standards. Accordingly, both water quality planning and water
pollution abatement programs need to be based on an analysis of the total urban
pollution loads.
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Until the urban stormwater situation is analyzed and efficient corrective measures
taken, there may be no point to seeking higher levels of treatment efficiency in existing
plants.
The second area under Problem Definition, "Solution Methodology" naturally followed
initial "Characterization" for providing a uniform and necessary background for the user
community.
The first and most fundamental approach should be a more accurate assessment of
the problem. Ideally, this should involve acquiring data on a city-wide basis for both
dry-weather flow and wet-weather flow.
Integrated with a more accurate assessment is the consideration of cost-effective
approaches to wet-weather flow pollution control.
User Assistance Tools are divided into "Instrumentation" and "Simulation Models".
The qualitative and quantitative measurement of storm overflows is essential for
planning, process design, control, evaluation, and enforcement. "Urban intelligence
systems" require real-time data from rapid remote sensors in order to achieve remote
control of a sewerage network. Sampling devices do not provide representative
aliquots, and in-line measurement of suspended solids and organics is needed.
Conventional rate-of-flow meters have been developed mainly for relatively steady-state
irrigational streams and sanitary flows and not for the highly varying surges
encountered in storm and combined sewers.
The electromagnetic, ultra-sound, and passive sound flowmeters have been developed
to overcome these adverse storm flow conditions. Passive sound instruments offer the
additional benefit of extremely low power requirements rendering them amenable to
installation at remote overflow locations and integration into city-wide, in-sewer,
sensing, and control systems.
Math models are needed to predict complex dynamic responses to variable and
stochastic climatological phenomena. Models have been subcategorized into three
groups: 1) simplified for preliminary planning, 2) detailed for planning and design, and
3) operational for supervisory control.
The Storm Water Management Model (SWMM) provides a detailed simulation of the
quantity and quality of stormwater during a specified precipitation event. Its benefits for
detailed planning and design have been demonstrated and the model is widely used.
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Wet-weather flow control can be assumed to involve aspects as follows. First, there is
the choice as to where to attach the problem: at the source (e.g., the street, gutters,
and catchment areas) by land management, in the collection system, or off-line by
storage. Second, there is the choice of how much control or degree of treatment to
introduce. Third, there is the impact assessment, public exposure, and priority ranking
with other needs.
Land Management includes all measures for reducing urban and construction site
stormwater runoff and pollutants before they enter the downstream drainage system.
On-site measures include structural, semi-structural and non-structural techniques that
affect both the quantity and quality of runoff.
Structural and semi-structural control measures require physical modifications in a
construction or urbanizing area and includes such techniques as on-site storage,
porous pavement, overland flow modifications and solids separation.
Non-structural control measures involve surface sanitation, chemical use control, urban
development resource planning, use of natural drainage, and certain erosion/
sedimentation control practice.
The next category, collection system control pertains to those management alternatives
concerned with wastewater interception and transport. These alternatives include
sewer separation; improved maintenance and design of catch basins, sewers,
regulators, and tide gates; and remote flow monitoring and control. The emphasis, with
the inception of sewer separation, is on optimum utilization of existing facilities and fully
automated control. Because added use of the existing system is employed, the
concepts generally involve cost-effective, low-structurally intensive control alternatives.
Storage is perhaps the most cost-effective method available for reducing pollution
resulting from combined sewer overflows and managing urban stormwater runoff.
Furthermore, it is the best documented abatement measure in present practice.
Storage facilities possess many of the favorable attributes desired in combined sewer
overflow control: 1) they are basically simple in structural design and operation; 2) they
respond without difficulty to intermittent and random storm behavior; 3) they are
relatively unaffected by flow and quality changes; and 4) they are capable of providing
flow equalization and, in the case of sewers and tunnels, transmission.
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THE USE OF STREET CLEANING OPERATIONS
IN REDUCING URBAN RUNOFF POLLUTION
ROBERT PITT
EPA - TECHNOLOGY TRANSFER SEMINAR SERIES ON
COMBINED SEWER OVERFLOW ASSESSMENT AND
CONTROL PROCEDURES
1978
In many cases, street cleaning operations can be used to reduce the amount of
pollutants entering urban runoff. This paper described the effectiveness and cost
characteristics of street cleaning operations. Information was summarized from many
different studies conducted over the last 20 years, but was mostly based upon the
results of a study completed for the Storm and Combined Sewer Section of the USEPA
(Edison, New Jersey) entitled, Demonstration of Non-Point Pollution Abatement
Through Improved Street Cleaning Practices.
This demonstration project included several hundred street cleaning tests conducted
over a period of a year in San Jose, California. More than 20,000 samples were
collected and analyzed in describing street surface loading conditions during specially
scheduled street cleaning operations. Five different study areas were examined
ranging from downtown commercial areas to suburban residential areas. The study
areas ranged in size from 50 to 200 acres. This study was unique in that it measured
the effectiveness of street cleaning over large areas under the influence of many real-
world conditions, such as different land uses, variable street dirt loadings, changing
weather characteristics, varying parked car conditions and different street surface
pavement conditions. Previous street cleaning effectiveness studies only examined
street cleaning equipment operating under very strictly controlled conditions in strip test
or very small scale (about 40 foot cleaning paths) actual street and curb tests.
Therefore, these results typically show the effectiveness of street cleaning operations to
be somewhat less effective than under the earlier more controlled tests. However,
street cleaning practices can be used to significantly reduce the quantities of some
street surface contaminants in urban runoff, if the street cleaning program is adequately
designed.
The type of street contaminants present are generally a function of local geological
conditions, motor vehicle emissions and wear, and inputs from surrounding areas.
Accumulation rates of street surface contaminants vary widely with geographical
location, season, land use, traffic, and other conditions. Nationwide accumulation rates
vary from 3 to 2700 Ib/curb-mile/day with an average around 150 Ib/curb-mile/day.
896RHG5.WS5
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This study showed that higher concentrations of contaminants are seen with
decreasing particle size. Additionally, typical street sweeping activities are most
effective at removing larger size particles. Street cleaning is still an important control
measure because the larger size particles are typically the most abundant and contain
significant quantities of contaminants. The largest particles (>6370>() had removal
rates as high as 55 percent during this study.
Another important aspect of an effective street sweeping operation is to implement
measures to eliminate parking interferences. This study found that the percent of total
street solids loading removed by sweeping was negatively impacted by the percentage
of curb length occupied by parked cars. Under most conditions, removal of parked
cars during street sweeping operations can significantly improve the street cleaning
effectiveness.
The San Jose study found the following removal rates and costs for several
contaminants during the street cleaning operations:
Average Removal
(!b/curb-mile)
Average Unit Cost
($/lb removed)
Total Solids
TSS
BOD5
Lead
Cadmium
200
100
12
0.80
0.002
0.08
0.16
1.34
20
8000
As shown, removal rates and costs vary widely for different types of surface
contaminants.
Information from this study was presented in a generic manner that should be
applicable to most areas of the country. Specific local monitoring activities are
necessary before final design of an adequate street cleaning program can be
completed.
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USEFUL TECHNOLOGICAL INFORMATION ON
SEWER FLUSHING
by
DR. WILLIAM C. PISANO
ENVIRONMENTAL DESIGN AND PLANNING, INC.
Presented at
EPA TECHNOLOGY TRANSFER SEMINARS ON
COMBINED SEWER OVERFLOW ASSESSMENT AND
CONTROL PROCEDURES
1978
Combined sewer systems are generally old, well constructed, but often because of
neglect, function poorly, particularly during wet weather flow conditions, in the past,
overflow regulation was often set to minimize retained wet weather flows for treatment
even though there was ample hydraulic conveyance capacity. Many repairs and
patchwork such as the connection of new separated areas into combined systems over
the years have greatly confounded piping complexity. Understanding how the system
works is no simple task. Sewer maps are generally old, piece meal, out-of-date, and
difficult to use. Detailed operational information in a simple concise form simply does
not exist.
Municipal maintenance funds are generally limited and are largely relegated to reaction
policies such as cleaning clogged sewers. Active maintenance programs aimed at
ensuring proper collection system performance during both dry and wet weather
conditions are almost non-existant for most communities. The maintenance issue is
further compounded by the fact that in many cities there is a functional division of
responsibility and authority between upstream collection system control and
management, and downstream overflow collection, conveyance, and treatment. The
downstream authority generally views its mission as abating combined sewer overflows
within the spatial limits of their jurisdiction. Downstream control generally means
expensive structural programs. Institutional differences often preclude the downstream
authority from assuming the role for active management of the upstream areas. The
net result in many cases, is that both known and unknown upstream system problems
having a high pollution control cost-effectiveness, often go undetected and
uncontrolled, and management is focused instead on downstream solutions resulting
in high program costs.
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Putting aside institutional and jurisdictional issues, it is the author's belief that the
financial interests of the federal government would be best served if in fact, Step 1 201
Combined Sewer Facilities Planning both mandated and funded for each and every
facility study in reasonably sized communities, thorough and comprehensive sewer
mapping activities, intensive physical surveys and measurement programs during all
flow conditions for the entire sewerage system of concern. This assertior is based on
the belief that there are unknown malfunctions of all types, poorly optimized regulators,
unused in-line storage and pipes clogged with sediments in old combined sewer
systems. Furthermore, detection and correction of these maladies would in fact, result
in extremely cost-effective solutions for partial if not significant control of combined
sewer overflow emissions. It is a further belief that wet weather emissions/water quality
response measurement programs should then be instituted to ascertain whether further
planning and additional control is necessary. In some situations it will be clear that
additional control is necessary. In some situations it will be clear that additional
management and control will be immediately necessary. For many small communities
already faced with taxed financial resources for dry weather treatment, the
measurement and wait/see option will be meaningful.
In short, combined sewer management planning should be "front-end" loaded with
intensive mapping and field sleuthing and measurement activities. This proposition
represents a fairly radical departure from current planning methodologies where often
the orientation seems to be heading toward heavy "back-end" loaded SWMM modeling
and "desk top" analysis efforts with inventory and survey efforts kept to a minimum.
The author believes that a change in the opposition direction would be in the long run,
be more cost-effective to the government, provided that the institutional and funding
mechanisms can be resolved.
The findings of a recent section 208 combined sewer management study for portions of
the sewerage system in the City of Fitchburg, MA demonstrate this viewpoint. The
results showed that sewerage system remedial repairs and slight piping modifications
were an order of magnitude less expensive than the nominal BMP practices of sewer
flushing, street sweeping and catchbasin cleaning, and several orders of magnitude
less than alternative structural options.
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WATER QUALITY CHARACTERISTICS OF
STORM AND COMBINED SEWER OVERFLOW
April 26-28,1977
TOKYO, JAPAN
MINISTRY OF CONSTRUCTION
JAPANESE GOVERNMENT
PROCEEDINGS
5TH UNITED STATES/JAPAN CONFERENCE ON
SEWAGE TREATMENT TECHNOLOGY
TOKYO, JAPAN
December 1977
USEPA 600/9-77-027
In Japan as of 1975, 583 municipalities had sewage works. In 1976, 65 new
municipalities were expected to begin wastewater treatment.
In Japan, many cities have combined sewer systems. According to a 1972 survey
conducted by the Ministry of Construction, combined sewer systems acbounted for 73
percent of the total sewered area, covering 69 percent of the total sewered population.
Many municipalities which have combined sewer systems have adopted separate
sewer systems in new sewered areas, so the proportion of combined sewer systems is
decreasing gradually. Nevertheless, the significance of the combined sewer overflow
on the contribution to pollution loads in waters has not yet been reduced significantly.
In large cities where steps toward improvement through secondary treatment have
been made, the contribution for water pollution by combined sewer overflow will be
increased more and more.
Large costs have stood in the way of changing combined systems to separate systems.
Narrow width of road in densely populated areas, and the fact that stormwater from
storm sewers itself is populated, have also limited separation. Converting 1o a separate
system is not always considered to be the best solution. >
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Most of the measures taken or being planned to control the water pollution by
combined sewer overflow are either detention or sedimentation of wet-weather
overflow.
In Japan, there are three practical examples of measures to control water pollution due
to combined sewer overflow, two in Osaka and one in Yokohama.
In 1975, the Osaka Municipal Government constructed a stormwater sedimentation
tank consisting of two basins. The dimensions of each basin is 3.5m in width, 20.2m in
length and 4.5m to 5.0m in depth. Four additional basins were to have been
constructed. With all the basins complete, the storage capacity was estimated at
2,000m3. This facility is the only example in Japan of measures against wet-weather
overflow. In Osaka, flooding frequently occurs in lowlands because of marginal use of
catch basins and settling due to excessive use of groundwater. In order to solve this
problem, installation of a new interceptor was planned and has been underway since
1973. This trunk sewer is planned to control water pollution due to wet-weather
overflow without detriment to the original purpose of flood control.
The Yokohama Municipal Government was in the process of constructing a stormwater
sedimentation tank consisting of 18 6.0m wide by 35m long by 6.0m deep basins with a
total capacity of 22,680m3. These tanks are expected to reduce the pollution loads by
10 percent or more in SS and almost the same degree in BOD compared to sewer
separation.
For the purpose of collecting extensive data on the characteristics of wet-weather
combined sewage, 12 drainage areas different in drainage system and land use were
selected as the study areas in 11 member municipalities.
Following is a list of survey areas and a brief explanation of each.
Combined Sewer Survey Areas:
A. Single-family residential area apart form the city's center
B. Populated urban area with a mixed variety of residential houses and stores
C. Area with small to medium factories, residential houses and stores
D. Area with residential zones and shopping quarters
E. Residential area on a terrace bordering on an urban area
F. Area with low-story and medium-story shopping quarters and amusement
quarters
G. Area with low-story shopping quarters, amusement quarters, and medium-story
business quarters.
H. Dense area packed with low-story residential houses, stores and factories
mainly of textile and dyeing
I. Typical high-story civic and business center
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J. Area with residential quarters, commercial quarters, wholesale markets and
small factories along a trunk road
K. Suburban residential area on a terrace with many company-owned residential
houses.
L. Amusement quarters
Separate Sewer Survey Areas:
M. Tier on the sea, with business quarters, commercial quarters, hotels, public
facilities, government institutions, multi-family residential houses
O. Newly developed residential area on a suburban terrace, with single-family
houses
In each survey area sewage flow was measured and once every 30 minutes sampling
was conducted for water quality analysis.
Following are the water quality characteristics of respective survey areas in dry-weather
and the factors which are considered attributable to them.
C. Industrial quarters count for 75 percent of total area, discharging high
concentrations of heavy metals
E. Residential, but high in BOD, COD and SS
H. A good number of textile and dyeing factories in the area resulting in high BOD,
COD and SS
I. Typical business quarters discharging weak effluents having a soluble-to-total
BOD ratio of 14.4 percent
K. Low BOD; quantities of pipeline deposits are suspected
L. Densely built amusement quarters generating a large volume of sludge for the
area; high BOD
While these areas have different characteristics, they also have something in common
with each other:
a. VSS/SS is in the range of 0.63 to 0.88, except for one survey area.
b. Three survey areas (F, G, and L) show flow rate 10 to 30 percent less in winter
than in summer, and an increase in BOD of 30 to 40 percent on the average in
winter over summer.
c. No definite differences by land use are noticed.
Wet-weather surveys were conducted two to four times in each survey area.
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The runoff coefficient is largely influenced by the impervious area ratio. Some survey
areas had a large impervious area ratio of more than 90 percent. In these areas, the
runoff coefficient is high. Taken altogether, the runoff coefficient lies in the range of 40
to 80 percent.
After a light rainfall, BOD, T-P and K-N become far larger in concentration than in dry
weather. In the case of a large scale storm, the concentrations are reduced by dilution
effects and the loadings are held within several times those in dry weather. Regarding
SS, the reduction in concentration is far less than others even in the case of a large-
scale rainfall. It remains almost the same as in dry weather. This shows that the bulk of
SS was conveyed into the sewer from the ground surfaces.
The surveys on combined sewer overflow in the 12 representative cities in Japan have
disclosed the following:
1. In wet weather, BOD, T-P and T-K are diluted significantly while SS remains the
same.
2. In wet weather, water quality in the combined sewers seriously decreases.
3. In wet weather the combined sewers experience an increase in inorganic SS
and at the same time an increase in refractory organics.
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