HomeMy Public PortalAboutLong-Term Control Plan Exec. Summary 2011Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-1 February 2011
EXECUTIVE SUMMARY
Purpose
The Metropolitan St. Louis Sewer District (MSD) provides wastewater and stormwater service to
approximately 1.4 million people in a 535-square-mile service area encompassing the independent City
of St. Louis and most of St. Louis County. The collection system owned and operated by MSD consists
of over 9,600 miles of pipe, making it the fourth largest in the United States.
Most of MSD’s customers are served by separate sanitary and storm sewers. However, approximately
75 square miles of St. Louis City and adjoining St. Louis County are served by a combined sewer
system, as shown in Figure ES-1. During dry weather, the capacity of the combined sewer system is
sufficient so that wastewater is conveyed to MSD’s wastewater treatment plants. During heavy rainfall,
the combination of stormwater and wastewater may exceed the capacity of the combined sewer system.
The excess flow, called combined sewer overflow (CSO), is discharged directly to the Mississippi River
or to one of the river’s tributary streams through permitted outfall pipes.
Figure ES-1 MSD’s Service Area and Combined Sewer Area
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-2 February 2011
The U.S. Environmental Protection Agency (EPA) issued a CSO Control Policy in 1994 intended to
eventually bring CSOs nationwide into compliance with the Clean Water Act. The goals of CSO control
are to:
• Ensure that if CSOs occur, they are only as a result of wet weather,
• Bring all wet weather CSO discharge points into compliance with the technology-based and water
quality-based requirements of the Clean Water Act, and
• Minimize the impacts of CSOs on water quality, aquatic biota, and human health.
The policy requires agencies with CSOs to prepare a Long-Term Control Plan (LTCP) describing how
they will accomplish these goals. MSD prepared and submitted its original LTCP to the Missouri
Department of Natural Resources (MDNR) in 1999, but due to conflicts between Missouri law and the
federal Clean Water Act, MDNR could not approve the submitted plan. A second, phased-implementation
LTCP was prepared for MDNR in 2004 in accordance with State laws and regulations. This LTCP was
approved by MDNR but was later disapproved by EPA. Following discussions aimed at resolving the
conflicts, EPA and MDNR requested that MSD update its original LTCP. This report describes the
development and selection of MSD’s updated plan for controlling combined sewer overflows. Certain
controls from the 2004 phased-implementation LTCP have been incorporated into the current LTCP,
along with additional control measures to meet the requirements of the Clean Water Act and CSO
Control Policy. The 2004 phased-implementation LTCP is no longer considered to be in effect.
CSO Locations and Impacted Waterways
Within MSD’s combined sewer area there are a total of 199 CSO outfalls. These outfalls are included as
permitted discharge locations in the Missouri State Operating Permits issued to MSD by MDNR. One
permit covers the Bissell Point service area (MO-0025178) while the other covers the Lemay service
area (MO-0025151). During wet weather, these CSOs may discharge to the following waterways:
• Mississippi River (60 CSOs)
• River Des Peres – Lower and Middle (52 CSOs)
• River Des Peres – Upper (39 CSOs)
• Tributaries to the River Des Peres (42 CSOs)
• Maline Creek (4 CSOs)
• Gingras Creek (1 CSO)
• Gravois Creek (1 CSO, recently separated and removed)
The locations of these waterways and CSOs are shown in Figure ES-2. Characteristics of these
waterways, including applicable beneficial designated uses, are described below. None of these
waterways have been identified as meeting the definition of Sensitive Areas contained in the CSO
Control Policy. Sensitive Areas are those that should receive the highest priority for potential
elimination or re-location of CSOs if feasible.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-3 February 2011
Figure ES-2 CSO and Receiving Water Locations
Lower & Middle River Des Peres – The Lower River Des Peres starts at the confluence with Deer Creek
and extends about six miles downstream to the Mississippi River. Flow consists of a small base flow,
and large volumes of intermittent storm drainage from runoff, storm sewers, and combined sewers. The
Lower River Des Peres is subject to backwater from the Mississippi River. This segment of the River
Des Peres is classified for livestock & wildlife watering, warm water aquatic life protection, and
secondary contact recreation1.
The Middle River Des Peres extends approximately seven and one-half miles from the intersection of
Dartmouth and Harvard Streets in University City to the confluence with Deer Creek. The upper four
and one-half mile reach has been enclosed and is a combined sewer. The lower three mile reach,
beginning near the Macklind Pump Station, is an open channel with a concrete base and concrete or rip-
rap slopes. Flow is intermittent, consisting entirely of storm drainage from the Upper River Des Peres
and combined sewers. The Middle River Des Peres is unclassified.
1 Designated uses are based on 10 CSR 20-7.031, Water Quality Standards, July 31, 2008, and revisions approved by
Missouri Clean Water Commission on July 1, 2009.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-4 February 2011
Upper River Des Peres – The Upper River Des Peres extends approximately six miles in the Lemay
service area from near Ashby and Warson Roads to the intersection of Dartmouth and Harvard Streets in
University City. Flow is intermittent, and consists of storm drainage from separate storm sewers and
overflows from combined sewers. The Upper River Des Peres is unclassified.
Maline Creek – Maline Creek extends approximately seven miles from east of Lambert-St. Louis
International Airport through the Bissell Point service area to the Mississippi River. Flow is intermittent,
and consists mostly of storm runoff and drainage from storm sewers. The lower reaches of the creek are
subject to backwater from the Mississippi River. One mile of the creek is classified for livestock &
wildlife watering, warm water aquatic life protection, and recreational uses. The lower half-mile
segment, which receives CSO discharges, is classified for secondary contact recreation. The upper half-
mile segment, above the CSO locations, is classified for whole body contact recreation (Class B).
Mississippi River – The Mississippi River at St. Louis receives significant point and nonpoint source
loads from a 697,000 square mile drainage area encompassing all or part of 13 states, as well as local
discharges from municipal, industrial, and agricultural wastewater treatment facilities located in
St. Louis City and St. Louis County, Missouri, and Madison and St. Clair Counties, Illinois. The
Mississippi River at St. Louis has a daily average flow of approximately 175,000 cubic feet per second.
The segment of the river that receives CSO flows from MSD’s service area is classified for irrigation,
livestock & wildlife watering, warm water aquatic life protection, drinking water supply, industrial
process and cooling water supply, and secondary contact recreation. Two Use Attainability Analyses
have been conducted to support the secondary contact recreation use designation.
Assessment of Current CSO Impacts
To assess the impact of CSOs on these waterways, MSD collected in-stream water quality data and
developed hydraulic models of its combined sewer system. Computer models of the CSO-impacted
portions of the River Des Peres and Maline Creek were also developed. In developing these models, it
was also necessary to model the runoff from portions of these watersheds that are served by separate
stormwater systems. These computer models were calibrated to flow, rainfall, and water quality data
collected over a multi-year period.
A review of existing water quality data was conducted to determine parameters that should be modeled
to assess the impact of CSOs. This review concluded that, for the tributaries receiving CSOs, bacteria
and dissolved oxygen are parameters of concern, and ammonia is a potential parameter of concern. For
the Mississippi River, neither bacteria, dissolved oxygen nor ammonia are parameters of concern that
require modeling to assess the impact of CSOs. Therefore, water quality data alone were used to assess
impacts on the Mississippi River.
CSO planning was based on typical or “average year” conditions, in accordance with EPA guidance.
MSD selected the year 2000 rainfall as representative of system-wide average annual conditions, based
on a detailed statistical analysis of 57 years of hourly rain data from Lambert-St. Louis International
Airport. Year 2000 Mississippi River stage, which influences backwater conditions in the tributaries,
was also deemed to be typical, based on a stage-exceedance analysis using 75 years of daily river data.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-5 February 2011
The hydraulic models of the combined sewer system allowed estimation of CSO overflow volumes and
frequencies to the various waterways for the average year conditions, as summarized in Table ES-1.
Waterway CSO Volume
(billion gallons)
Number of
Overflow Events
River Des Peres and tributaries 6.15 62
Maline Creek 0.15 29
Gingras Creek 0.02 33
Mississippi River 6.95 65
Total 13.3
Table ES-1 Estimated CSO Occurrence for Average Year (Year 2000)
The estimated volumes were used to calculate pollutant loadings from the combined sewer system.
Water quality in the River Des Peres and Maline Creek was modeled for the average year conditions
using the calculated loadings from the CSOs, separate storm runoff, and upstream boundaries. Simulated
water quality parameters included E. coli bacteria, carbonaceous biochemical oxygen demand (CBOD),
nitrogen (organic and ammonia), and dissolved oxygen. The information below summarizes the results
of the model simulations and conclusions from in-stream data.
Lower & Middle River Des Peres – Model calculations demonstrate that ammonia criteria are met
100 percent of the time during a typical year. While exceedances of dissolved oxygen criteria occur
regularly in the Lower River Des Peres, the model indicates that removal of CSOs does not greatly
increase the time of compliance. Most dissolved oxygen exceedances occur during wet weather, but
some occur during dry weather as well, primarily during periods when backwater from high water levels
in the Mississippi River reduce flow velocities and reaeration in the River Des Peres channel. Other
factors influencing dissolved oxygen levels include plant photosynthesis and respiration, stream
temperatures, stormwater discharges, and sediment oxygen demand. Compliance with the secondary
contact recreation criteria in the typical year is not an issue, and complete removal of CSOs has a
relatively minor effect on reducing the geometric mean bacteria densities.
Upper River Des Peres – Model calculations demonstrate that ammonia criteria are met 100 percent of
the time during a typical year. Exceedances of dissolved oxygen criteria occur, partly as a result of
photosynthesis-respiration, but also as a result of CSOs.
Maline Creek – Modeling demonstrates that ammonia criteria are met 100 percent of the time during a
typical year. Exceedances of dissolved oxygen criteria occur regularly; however, removal of CSOs has
no perceptible impact due to their small volume relative to upstream and stormwater sources.
Compliance with the secondary contact recreation criteria in the CSO-impacted segment is not an issue,
and complete removal of CSOs again has a relatively minor effect on reducing the geometric mean
bacteria densities.
Mississippi River – Water quality data indicate that dissolved oxygen concentrations in the river are
generally well above the 5 mg/L standard. Bacteria densities in the river are orders of magnitude less
than bacteria in the other receiving streams and meet the secondary contact recreation standard.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-6 February 2011
Alternatives Evaluation
MSD used a multi-level screening process, depicted in Figure ES-3, to develop and evaluate various
alternatives to control CSOs to meet the goals of the CSO Control Policy and improve water quality in
the impacted waterways.
SOURCE
CONTROL
TECHNOLOGIES
TREATMENT
TECHNOLOGIES
STORAGE
TECHNOLOGIES
COLLECTION
SYSTEM
CONTROLS
LEVEL 1
SCREENING
INTEGRATED
CONTROL
ALTERNATIVES
SPECIFIC TO
MSD’S SYSTEM
AND RECEIVING
WATERS
LEVEL 2
SCREENING
FEASIBLE AND
COST-EFFECTIVE
INTEGRATED
CONTROL
ALTERNATIVES
70+ TECHNOLOGIES 55 ALTERNATIVES 12 ALTERNATIVES
LEVEL3
SCREENING
1 ALTERNATIVE
SELECTED
ALTERNATIVE
FEASIBILITY COST-
PERFORMANCE
PUBLIC INPUT
COST
SOURCE
CONTROL
TECHNOLOGIES
TREATMENT
TECHNOLOGIES
STORAGE
TECHNOLOGIES
COLLECTION
SYSTEM
CONTROLS
LEVEL 1
SCREENING
INTEGRATED
CONTROL
ALTERNATIVES
SPECIFIC TO
MSD’S SYSTEM
AND RECEIVING
WATERS
LEVEL 2
SCREENING
FEASIBLE AND
COST-EFFECTIVE
INTEGRATED
CONTROL
ALTERNATIVES
70+ TECHNOLOGIES 55 ALTERNATIVES 12 ALTERNATIVES
LEVEL3
SCREENING
1 ALTERNATIVE
SELECTED
ALTERNATIVE
FEASIBILITY COST-
PERFORMANCE
PUBLIC INPUT
COST
Figure ES-3 Alternatives Evaluation Process
MSD began by evaluating a wide range of control technologies:
• Source Control Technologies – those technologies that affect the quantity or quality of runoff prior to
entering the collection system.
• Collection System Controls – those technologies that affect CSO flows and loads once the runoff has
entered the collection system.
• Storage Technologies – those technologies that provide for storage of flows from the collection
system for subsequent treatment after the storm is over and conveyance and treatment capacity have
been restored.
• Treatment Technologies – those technologies that provide for either local (at the CSO) or centralized
treatment of CSO flows to reduce the pollutant loading to receiving waters.
More than 70 CSO control technologies were evaluated (Level 1 Screening). Each technology was
screened to determine its feasibility and applicability to the unique characteristics of MSD’s combined
sewer system. Feasible CSO control technologies were then assembled into 55 Integrated Control
Alternatives specific to each receiving water. Each Integrated Control Alternative consists of one or
more of the following components:
• Source Control Technologies that were determined to be applicable to all alternatives.
• Collection System Technologies that were determined to be applicable to all alternatives.
• Long-term CSO controls that have already been implemented by MSD or are currently being
implemented by MSD that will continue to serve an important long-term role in controlling CSOs.
These controls represent an investment of $0.6 billion that has already reduced annual CSO volumes
by 38 percent.
• New long-term CSO controls necessary to meet the established CSO control goals.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-7 February 2011
Each of the 55 Integrated Control Alternatives was then evaluated and screened to develop a short list of
the most feasible and cost effective alternatives for further analysis (Level 2 Screening). Evaluation
criteria included affordability, CSO flow/load reduction, constructability, expandability, operability,
public acceptability, reuse of existing facilities, and infrastructure rehabilitation / upgrade opportunities.
Twelve Integrated Control Alternatives remained after the Level 2 screening process. For each of these
twelve alternatives, MSD:
• evaluated a range of sizes of the 12 Integrated Control Alternatives that would achieve 0, an average
of 1 to 3, an average of 4 to 7, and an average of 8 to 12 overflow events per year;
• analyzed the impact that each of the 12 Integrated Control Alternatives is estimated to have on peak
instantaneous and sustained flows to the Lemay and Bissell Point Treatment Plants;
• estimated project costs, including capital costs, annual operation and maintenance costs, and total
present worth (life-cycle) costs;
• estimated the benefits arising from implementation;
• conducted cost-performance (“knee of the curve”) analyses comparing estimated costs to the
estimated benefits; and
• involved its Stakeholder Advisory Committee and the public in reviewing the analysis results.
This Level 3 screening process resulted in the identification of five CSO control scenarios that consist of
combinations of the 12 Integrated Control Alternatives:
• Scenario 1 – Complete elimination of CSOs
• Scenario 2 – CSO control to the “knee-of-the-curve” on all CSOs
• Scenario 3 – CSO control to the “knee-of-the-curve” on CSOs discharging to urban streams (e.g.,
Maline Creek, the River Des Peres and its tributaries), plus an enhanced green infrastructure program
in areas with CSOs directly tributary to the Mississippi River
• Scenario 4 – CSO control to a uniform minimum level of control (18 overflows per year) on all CSOs
• Scenario 5 – CSOs to urban streams to receive a graduated level of control (higher control on smaller
streams), plus an enhanced green infrastructure program in areas with CSOs directly tributary to the
Mississippi River
These scenarios were discussed with MSD’s Stakeholder Advisory Committee that was created for the
LTCP public participation program, and the general public. Scenario 3 was selected to form the basis of
the CSO control measures for the LTCP. The selection was based on a number of factors including:
• Public and political acceptance of the proposed solutions,
• Total program cost and resulting user rates,
• Costs and benefits of existing controls,
• Costs versus benefits,
• Cascading effect of implementing controls,
• Water quality gains,
• Treatment plant impacts, and
• Technical feasibility.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-8 February 2011
Figure ES-4 depicts the calculated annual system-wide overflow volume with each control scenario
compared to the pre-control and current conditions. Figure ES-5 provides the same information for
the urban streams only. Scenario 1 (complete sewer separation) is neither realistic nor affordable.
Scenario 2 (uniform control everywhere) is significantly more expensive than Scenarios 3 and 5, and
provides little added water quality benefit. Control Scenario 3 provides the maximum benefit on the
urban streams, and the same system-wide benefit as Scenarios 4 and 5, at an affordable cost.
0
5
10
15
20
25
Pre-Control Modeled
Conditions
Scenario 5 Scenario 3 Scenario 4 Scenario 2 Scenario 1Annual CSO Volume (billion gallons) Figure ES-4 Comparison of Scenarios – System-Wide Benefits
0
1
2
3
4
5
6
7
8
9
Pre-Control Modeled
Conditions
Scenario 4 Scenario 5 Scenario 3 Scenario 2 Scenario 1Annual CSO Volume (billion gallons) Figure ES-5 Comparison of Scenarios – Urban Streams
Scenario 1
Complete elimination
Scenario 2
“Knee-of-the-curve”
everywhere
Scenario 3
“Knee-of-the-curve” on
urban streams + enhanced
green program on
Mississippi
Scenario 4
Uniform minimum Level of
Control
Scenario 5
Graduated control on
urban streams + enhanced
green program on
Mississippi
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-9 February 2011
Public Involvement
MSD conducted a focused public involvement program to engage the affected public in the above-
described decision making process to select the long-term CSO controls. The program included the
following components:
• Face-to-face interviews with key stakeholders representing business, community, environmental,
municipal, public health and regional planning organizations. These interviews were used to modify
the public involvement program plan to make it more responsive to the public’s interests and external
realities.
• A Stakeholder Advisory Committee (SAC) comprising 12 municipal, environmental, regional,
business and community representatives. The SAC reviewed program data and technical findings;
increased community awareness of and support for the CSO control program; advanced MSD’s
understanding of their constituents’ concerns, issues, priorities and interests; and served as a sounding
board and connection to the community at-large.
• Stakeholder and community presentations to a wide variety of business, community, environmental,
legislative, municipal and professional groups. The presentations were educational in nature, intended
to raise awareness of the CSO control program.
• Public open houses at 13 locations throughout MSD’s service area. The open houses were designed
to educate the public about CSOs and their impacts, review options for controlling CSOs, identify the
public’s preferred options and explore opportunities for additional action by MSD and the public in
addressing the CSO issue. These public deliberation sessions allowed 451 members of the public to
directly weigh in on the selection of CSO controls.
• A Clean Rivers Healthy Communities web site that provided the public with opportunities to learn
more about the program, participate virtually in the public open houses, and leave feedback for the
CSO control program.
• Outreach to the media, through such activities as tours and briefings, to aid their understanding of
complex issues as they communicated with their audiences.
• Telephone surveys to gauge public understanding of the CSO issue.
The input received from the public during these activities was used by MSD to help define the CSO
control scenarios that were considered during the alternatives evaluation process, and to assist in
selection of the preferred control option. Follow-up public open houses were conducted to present and
discuss the selected control option with the community. MSD intends to continue its public involvement
program throughout the LTCP approval and implementation process.
Selected Plan Details
MSD is committed to continue to improve water quality in the Mississippi River, Maline Creek, and the
River Des Peres and its tributaries. The selected LTCP controls build upon MSD’s previous investments
in CSO control and provide for significant additional reductions in CSO volumes and pollutant loadings.
The selected controls will also allow MSD the financial capability to maintain its existing infrastructure
and tackle significant issues in its separate sewer systems.
The selected LTCP consists of controlling CSOs to MSD’s urban streams to the point where further
expenditures yield significantly diminished returns (the “knee-of-the-curve”), coupled with an enhanced
green infrastructure program in areas with CSOs that discharge directly to the Mississippi River. Source
controls and collection system controls common to all areas are also part of the selected plan, as are the
CSO controls that MSD has already implemented during the planning period.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-10 February 2011
The selected LTCP components are listed in Table ES-2 along with estimated total capital and total present
worth costs. Costs for long-term CSO controls that have already been implemented by MSD, or are currently
being implemented, are not included in the table. The estimated total capital cost of these completed and
ongoing improvements is $634 million. Figure ES-6 depicts the locations of the principal new components.
Cost Opinions ($million)1
LTCP Component Capital Cost Total Present
Worth
System-wide
Source Control Technologies Note 2 Note 2
Collection System Technologies Note 2 Note 2
Maline Creek
Bissell Point Overflow Regulation System Note 2 Note 2
Sewer Separation of Outfalls 053 and 060 Note 2 Note 2
Treatment unit to treat overflows from Outfall 051 and storage tank
to store overflows from Outfall 052 31 41
Gingras Creek
Separation of three storm sewers from combined sewer system and
relocation of Outfall 059 6.0 6.1
Upper River Des Peres
Skinker-McCausland Tunnel to express convey separate sewer
system flows around the combined sewer system Note 2 Note 2
Storage tunnel to store flows from CSO outfalls to the Upper River Des
Peres 183 212
River Des Peres Tributaries
Sewer separation of 15 smaller CSOs Note 2 Note 2
Elimination of all CSO outfalls to tributaries, tunnel to store/convey
flows to the River Des Peres channel 396 434
Lower and Middle River Des Peres
Lemay Overflow Regulation System Note 2 Note 2
Skinker-McCausland Tunnel to express convey separate sewer system
flows around the combined sewer system Note 2 Note 2
Full utilization of excess primary treatment capacity at Lemay
Treatment Plant Note 2 Note 2
Sewer separation of 5 smaller CSOs Note 2 Note 2
Repair of inflow to interceptor sewers under River Des Peres Note 2 Note 2
Upstream CSO controls (Upper River Des Peres) Note 3 Note 3
Flow storage in 29-ft horseshoe sewers under Forest Park and in new
storage tunnel, 100 MGD treatment unit near Outfall 063, removal of
secondary treatment bottlenecks at WWTP
1,103 1,208
Mississippi River
Bissell Point Overflow Regulation System Note 2 Note 2
Separation of two major industrial sources Note 2 Note 2
Full utilization of excess primary treatment capacity, and maximizing
flow pumped to the Bissell Point Treatment Plant Note 2 Note 2
Sewer separation for Outfall 055 Note 2 Note 2
Upstream CSO controls (Maline Creek, River Des Peres) Note 3 Note 3
Enhanced green infrastructure program 100 100
Grand Total 1,819 2,001
Notes: 1. Costs updated to ENR Construction Cost Index of 8580.
2. Costs for controls already implemented or currently being implemented are not included as
LTCP future costs.
3. Costs for upstream CSO controls are reflected under the appropriate upstream components.
Table ES-2 Selected Long-Term Control Plan Components
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-11 February 2011
Figure ES-6 Selected Long-Term Control Plan - Major Future Components
The principal components of the control plan are described below.
System-wide Controls – System-wide source controls include green infrastructure, illicit connection
control, stormwater detention for new developments, catch basin cleaning, solids/floatables control,
illegal dumping control, hazardous waste collection, good housekeeping, street sweeping, construction
erosion and waste control, litter control, industrial pretreatment program, stream teams, community
clean-up programs, recycling programs, pet waste management, proper yard waste disposal, and the
installation and maintenance of warning signage. System-wide collection system controls include
diversion structure maintenance, outfall maintenance, sewer system cleaning and sewer separation for
new developments or redevelopments.
Maline Creek CSO Controls – The CSO controls selected for Maline Creek are estimated to control
overflows to a level of 4 overflows per year in the typical year. The controls include the following
components:
• The existing Bissell Point Overflow Regulation System will continue to be operated to control the
influence of Mississippi River stage on the capture of flows at Bissell Point Outfall 051 to Maline
Creek.
• Infiltration and inflow (I/I) controls will be implemented in the separate sewer systems upstream of
the Maline Drop Shaft as part of MSD’s efforts to eliminate constructed SSOs. Reduced peak flows
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-12 February 2011
resulting from I/I control may allow for greater capture of wet weather flows from the combined
sewer system.
• Bissell Point Outfalls 053 and 060 will be eliminated by sewer separation.
• A 1.0 million gallon storage facility will be constructed to control overflows from Bissell Point
Outfall 052. Control features will include modifications to the existing drop shaft/diversion structure,
flow screening facilities, an above- or below-grade storage tank, a tank dewatering pump station, and
interconnecting piping. Combined sewage will be temporarily stored at the facility during a storm
event until the north leg of the Bissell Point Interceptor Tunnel has capacity to convey the return flow
to the Bissell Point Treatment Plant for secondary treatment.
• A 94 MGD treatment facility will be built to treat CSO flows from Bissell Point Outfall 051 prior to
discharge to Maline Creek. Control features will include a modified diversion structure, pump station
to the treatment facility, and Enhanced High Rate Clarification treatment unit(s) providing screening,
the equivalent of primary treatment and disinfection to the design flows prior to discharge to Maline
Creek.
Gingras Creek CSO Controls – The CSO controls selected for Gingras Creek will eliminate the
occurrence of CSOs. The controls include the following components:
• Three large storm sewers will be disconnected from the existing combined sewer system and
connected to a new separate storm sewer discharging to Gingras Creek.
• Bissell Point Outfall 059 will be eliminated. The existing 66-inch combined sewer will be extended
to the Baden combined sewer system (Gingras Creek Branch of the Baden Trunk Sewer).
Upper River Des Peres CSO Controls – The CSO controls selected for the Upper River Des Peres are
estimated to control overflows to a level of 4 overflows per year in the typical year. The controls include
the following components:
• MSD will continue to operate and maintain the Skinker-McCausland Tunnel to express route separate
sanitary flows around the combined portions of the Upper River Des Peres sewer system, thereby
eliminating the overflow of this separate sanitary flow from the combined sewer system during wet
weather.
• A 30 million gallon deep storage tunnel will be constructed to store flows from the 39 CSO outfalls
to the Upper River Des Peres. The tunnel is estimated to be approximately 24 feet in diameter,
extending approximately 9,000 feet from near Lemay Outfall 090 to a location near Outfall 064. The
existing 39 CSO outfalls will be consolidated to approximately 4 or 5 drop shaft locations along the
tunnel. A tunnel dewatering pump station will pump stored flow back to the Skinker-McCausland
Tunnel and Lemay Treatment Plant for secondary treatment as capacity becomes available.
River Des Peres Tributaries CSO Controls – The CSO controls selected for the River Des Peres
tributaries (Deer, Black, Hampton and Claytonia Creeks) are estimated to control overflows to a level of
4 overflows per year in the typical year. The controls include the following components:
• Fifteen small CSO outfalls will be eliminated by sewer separation.
• A tunnel, approximately 20 feet in diameter and 12,000 feet long, will convey all flows from the
remaining CSOs to a single location on the River Des Peres main channel in the vicinity of its
confluence with Deer Creek. Consequently, the CSO outfalls along the tributaries, remaining after the
above-mentioned sewer separations are completed, will be eliminated. The tunnel size necessary for
total flow conveyance is adequate to provide CSO flow storage to the desired level of control. The
tunnel alignment will generally follow the creek alignment from the confluence of Claytonia and
Hampton Creeks to the River Des Peres main channel. Approximately five or six drop shafts are
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-13 February 2011
anticipated to direct flow from shallow conveyance piping to the deep tunnel. A dewatering pump
station at the tunnel’s downstream end will pump stored flow from the tunnel to the Lemay
Treatment Plant, where it will receive full secondary treatment, as conveyance and treatment capacity
becomes available.
Lower & Middle River Des Peres CSO Controls – The CSO controls selected for Lower and Middle
River Des Peres are estimated to control overflows to a level of 4 overflows per year in the typical year.
The controls include the following components:
• The existing Lemay Overflow Regulation System will continue to be operated to control the
influence of Mississippi River stage on the capture of flows at outfalls along the Lower and Middle
River Des Peres.
• MSD will continue to operate and maintain the Skinker-McCausland Tunnel to express route separate
sanitary flows around the combined portions of the Upper River Des Peres sewer system, thereby
eliminating the overflow of this separate sanitary flow from Lemay Outfall 063 during wet weather.
• MSD will utilize excess primary treatment capacity at the Lemay Treatment Plant to maximize treatment
during wet weather. Upon completion of influent pumping and ongoing plant outfall modifications,
the expanded treatment plant will have the ability to treat 340 MGD through its preliminary and
primary treatment facilities. Flow rates of up to 340 MGD will be pumped and treated during wet
weather events. The current capacity of the secondary treatment facilities is 167 MGD.
• Five small CSO outfalls will be eliminated by sewer separation.
• MSD will correct the excessive inflow problem to the interceptor sewers beneath the Lower River
Des Peres channel that has been hampering MSD’s ability to maximize the capture of wet weather
flows from its combined sewer system. These excessive inflows occur during periods of backwater
due to high Mississippi River stage.
• CSO controls implemented on the Upper River Des Peres and River Des Peres tributaries will benefit
the Lower and Middle River Des Peres by reducing overflow volumes and pollutant loadings.
• The existing dual 29-foot wide horseshoe sewers beneath Forest Park (immediately upstream of
Lemay Outfall 063) will be utilized to store up to 25 million gallons of wet weather flow. This will be
accomplished by the construction of a flow control gate at Outfall 063.
• A 100 MGD Enhanced High Rate Clarification treatment unit will be constructed adjacent to
Outfall 063 to provide for the equivalent of primary treatment and disinfection of up to 100 MGD
of flow from Outfall 063. Treated flow will be discharged to the Middle River Des Peres channel.
• A 206 million gallon deep storage tunnel will be constructed to store flows from the CSO outfalls to
the Lower and Middle River Des Peres. The tunnel is estimated to be approximately 28 feet in
diameter, extending approximately 47,400 feet from Outfall 063 to a location near the Lemay
Treatment Plant. The existing CSO outfalls will be consolidated to approximately 14 drop shaft
locations along the tunnel. A tunnel dewatering pump station will pump stored flow directly to the
Lemay Treatment Plant for secondary treatment as capacity becomes available.
• Flow capacity bottlenecks that currently limit secondary treatment capacity at the Lemay Treatment
Plant to 167 MGD will be removed. It is anticipated that secondary capacity can be increased to
210 MGD. Stress testing will be performed to determine maximum treatable flow rates for the plant.
Mississippi River CSO Controls – The CSO controls described above for the receiving waters that are
tributary to the Mississippi River will complement the significant long-term controls already
implemented on the Mississippi River outfalls. These controls, along with the enhanced green
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-14 February 2011
infrastructure program proposed by MSD, will provide meaningful reductions in overall CSO volumes
and pollutant loadings to the Mississippi River.
• The existing Bissell Point and Lemay Overflow Regulation Systems will continue to be operated to
control the influence of Mississippi River stage on the capture of flows at the CSO outfalls to the
Mississippi River.
• Two significant industrial users currently have their wastewater discharges disconnected from the
combined sewer system and connected directly to the Bissell Point Interceptor Tunnel.
• MSD will utilize excess primary treatment capacity at the Bissell Point Treatment Plant to maximize
treatment during wet weather. The treatment plant has the ability to treat 350 MGD through its
preliminary and primary treatment facilities. Flow rates of up to 350 MGD will be pumped and
treated during wet weather events, except during extremely high river stage conditions, when the
capacity of the effluent pump station limits total plant flow to approximately 250 MGD. The current
capacity of the secondary treatment facilities is 250 MGD.
• Bissell Point Outfall 055 will be eliminated by sewer separation.
• In addition to the above-noted CSO long-term controls that have already been implemented, the CSO
controls implemented along Maline Creek, and the River Des Peres and its tributaries will benefit the
Mississippi River by significantly reducing CSO volumes and pollutant loadings.
• MSD will invest $100 million in an enhanced green infrastructure program focused on its combined
sewer areas with CSOs that are directly tributary to the Mississippi River. The overall objective is to
identify and implement projects and programs that will significantly reduce CSOs and provide
additional environmental benefit. A program goal is to reduce CSO overflow volumes to the
Mississippi River by 10 percent. This goal will be updated based upon the results of initial projects
comprising the pilot phase of the program. MSD has limited direct control over the infrastructure and
policies that impact the magnitude of storm runoff in the combined sewer areas. To address this
challenge, MSD plans to work with local units of government, private developers, and other
stakeholders to implement the program. It is anticipated that MSD’s enhanced green infrastructure
program will comprise the following types of activities:
– Community outreach and education programs.
– Partnering with the Land Reutilization Authority and the St. Louis Development Corporation to
implement green infrastructure on to-be-developed properties in some of the most economically-
distressed portions of the City of St. Louis. Once the pilot program is complete, perform similar
work with like entities in the economically-distressed portions of North St. Louis County located
within the Bissell Point service area.
– Lot-scale and neighborhood-scale stormwater management projects that incorporate green
infrastructure.
– Working with developers to encourage green infrastructure implementation in specific
redevelopment opportunities.
– Support of rain barrel and rain garden implementation programs.
LTCP Benefits and Water Quality Standards Review and Revision
The selected CSO controls are intended to bring CSOs into compliance with technology-based and water
quality-based requirements of the Clean Water Act and to minimize the impact of CSOs on water
quality, aquatic biota and human health. Implementation of the selected LTCP will substantially reduce
the occurrence and magnitude of CSOs to MSD’s urban streams as well as significantly reduce CSO
volumes and loadings to the Mississippi River. For the parameters of concern – ammonia, bacteria and
dissolved oxygen – water quality data and water quality simulations indicate that, with the LTCP
controls implemented:
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-15 February 2011
• Ammonia criteria, acute and chronic, are met for all receiving waters.
• Geometric mean criteria for E. coli bacteria are met for all receiving waters.
• The dissolved oxygen criteria are met in the Mississippi River.
• Exceedances of water quality criteria for dissolved oxygen are predicted to occur in Maline Creek.
CSOs, however, play a very small role, as their volume is very small compared to upstream and
storm flows.
• Exceedances of water quality criteria for dissolved oxygen are predicted to occur in the River Des
Peres, partially due to CSOs.
Despite the significant reductions in pollutant loadings associated with the selected LTCP controls,
these controls are expected to only slightly improve the percent compliance with dissolved oxygen
criteria in the urban streams (Maline Creek and the River Des Peres). Even complete elimination of
CSO and stormwater discharges would not significantly improve dissolved oxygen conditions.
Other contributing factors to the problem include diurnal swings in dissolved oxygen due to plant
photosynthesis-respiration, and backwater conditions caused by high Mississippi River stage. Because
of these factors, a site-specific dissolved oxygen criterion for the River Des Peres and Maline Creek will
be necessary. Preparation of the Use Attainability Analysis necessary to determine the highest attainable
use should not delay agreement on the selected CSO controls because it is clear that even elimination of
the CSOs would not address the stream impairments.
Financial Impacts and Schedule
MSD has evaluated the financial impacts of constructing and operating the improvements contemplated
in its total Capital Improvement and Replacement Program (CIRP). The CIRP comprises not only the
CSO controls described in this LTCP, but also the need to operate and maintain current assets, control
wet weather flows in sanitary sewer systems, construct wastewater treatment plant improvements, and
provide stormwater services.
MSD’s financial analysis is consistent with the principles of EPA’s Guidance on Financial Capability
Assessment and Schedule Development. The assessment is based on determining the amount of net
revenues that may be generated under feasible rate and fee increase scenarios. The feasibility of these
scenarios is based in part on current and projected burden of wastewater and stormwater service costs,
and in part on the unique socio-economic attributes of MSD’s service area. MSD has employed its cash
flow forecasting model to determine the capital project financing capacity under a range of wastewater
and stormwater rate slope scenarios and alternative configurations of the CIRP. The analyses were based
on well documented information on the District’s financial position, and several critical assumptions
such as inflation rates, median household income (MHI) growth rate, and capital financing (bond)
parameters.
The resulting cash-flow projections have allowed MSD to determine the amount and pace of CIRP
spending that can be financed within the District’s capabilities. MSD’s proposed 23-year baseline
schedule for implementing CSO controls, together with other CIRP expenditures, represents an
unprecedented capital investment for MSD’s service area that will require substantial rate increases.
These rate increases build the necessary revenue generation capacity for MSD to aggressively control
CSOs and address other water quality issues (SSO control, wastewater treatment, and stormwater
management). At the same time, these increases will elevate claims on ratepayer income already
strained by recent economic decline, as shown in Figure ES-7.
Metropolitan St. Louis Sewer District
CSO LTCP Update EXECUTIVE SUMMARY
Page ES-16 February 2011
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
2010 2015 2020 2025 2030 2035 2040Residential Bill as % of MHISt. Louis County Combined (Weighted Avg)
St. Louis City Low Income
EPA High Burden Threshold
Figure ES-7 Projected Typical Residential Bills for Proposed Capital Improvement and Replacement Program
The projected rate increases place portions of the MSD ratepayer population at the threshold of “High
Burden” while imposing potentially problematic burdens on low-income ratepayers throughout the
District’s service area.
MSD’s approach to financial capability assessment also contemplates mechanisms to assess and manage
risk should significant adverse changes to its financial circumstances or other financial or budgetary
issues arise. MSD will periodically update projected cash flows and estimated project costs. In the event
that the funding level is significantly less than anticipated, or project costs are significantly higher than
anticipated, MSD may propose adjustments to project scopes and/or timelines consistent with available
funding levels and project costs.
Post-Construction Compliance Monitoring
Post-construction compliance monitoring will be performed to determine the effectiveness of the LTCP
in meeting the plan’s performance objectives, and to assess and document impacts on receiving waters
resulting from implementation of the CSO control measures. Documentation of the monitoring results
will be provided in annual progress reports that will summarize:
• Final design criteria and sizing of the CSO control program elements,
• CSO control measure performance (e.g., CSO activation and flow data),
• Rainfall data,
• Receiving water quality data,
• Progress in updating and calibrating/validating the hydraulic models,
• Status in achieving performance objectives based on continuous simulation modeling for the typical year,
• Identification of variances from expected results, and
• Proposed corrective action of LTCP program element(s), if needed.