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2020 Facilities Plan Conveyance Report
Chapter 2: Description of Conveyance Facilities 2.1 Milwaukee Metropolitan Sewerage District System The Milwaukee Metropolitan Sewerage District (MMSD) conveyance system transports wastewater generated by the MMSD satellite municipalities to Jones Island and South Shore Wastewater Treatment Plants (JIWWTP and SSWWTP). The main components of the system, as of 2000, are shown in Figure 2-1 and include the following:
♦ Metropolitan Interceptor Sewer (MIS) System
♦ Near Surface Collector Sewers (NSCS)
♦ Inline Storage System (ISS)
The interaction among these components is shown schematically in Figure 2-2 and is described below.
2.1.1 Metropolitan Interceptor Sewer System The MIS system, shown in Figure 2-3, consists of about 290 miles of interceptor sewers that collect wastewater from MMSD satellite municipalities and convey it to either the treatment plants or the ISS. The MMSD planning area includes both separate and combined sewer areas. The sanitary sewer service area (SSSA) within the planning area is about 381 square miles and the combined sewer service area (CSSA) is about 24 square miles. Small, isolated areas of partially separated sewers exist within the CSSA.
Figure 2-4 shows the portions of the service area that are tributary to each of the wastewater treatment plants, including a portion that can flow to either plant. Under normal operating conditions, flow from the area that is a tributary to either plant is directed to JIWWTP during dry weather so that the delivery of solids to the Milorganite® production facility at JIWWTP is maximized. Flow from this area is diverted to SSWWTP during wet weather periods to relieve JIWWTP-bound segments of the MIS system and to maximize the use of available treatment capacity at SSWWTP.
In the central portion of the MMSD, the MIS system is configured as two separate sewer networks consisting of a low-level and a high-level system. This system, which is referred to as the Central MIS, collects flows primarily from the CSSA and a portion of the SSSA. Flows from the lower topographical areas that are adjacent to the Milwaukee, Menomonee, and Kinnickinnic Rivers are collected by the low-level system. The high-level system is designed to convey flows collected from the higher elevation areas. Both systems convey flows to JIWWTP during dry weather but can be diverted to the ISS during wet weather.
Metropolitan interceptor sewers range in size from 8 to 150 inches in diameter, and most are constructed of reinforced concrete pipe or monolithically constructed reinforced concrete. Currently, eight pumping stations in the MIS system convey flow from lower to higher elevations. The MMSD also owns and maintains a pump station on Lake Drive at Ravine Lane in Bayside that pumps flow within the Bayside local collection system. Table 2-1 summarizes information for the MMSD pumping stations.
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FIGURE 2-1
MMSD CONVEYANCE SYSTEM2020 CONVEYANCE REPORT
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1. RECEIVINGWATERS
5c NEAR
SURFACE
COLLECTOR
5f INLIN
E STORAGE T
UNNEL
3. M.I.S.
COLLECTORNEAR SURFACE
5e DROPSHAFT
5e DROPSHAFT
CSO
CSO
5b DIV
ERSION S
TRUCTURE
5d JUNCTIONCHAMBER
INTERCEPTIN
GSTRUCTURE
2. SEWERCOMBINED
5a MIS DIVERSION CHAMBERSEPARATE
SEWER
AREA
COMBINED S
EWER A
REA
SYSTEMS:RECEIVING WATERS (RIVERS & LAKE)
METROPOLITAN INTERCEPTOR SEWER (MIS)
b - DIVERSION STRUCTURESc - COLLECTORS
e - DROPSHAFTSf - INLINE STORAGE TUNNELg - INLINE PUMP STATION (not shown)h - INLINE SOLIDS HANDLING FACILITY (not shown)
COMBINED SEWERS
MUNICIPAL SEPARATE SEWERSINLINE STORAGE SYSTEMa - DIVERSION CHAMBERS
d - JUNCTION CHAMBERS
1. 2. 3. 4. 5.
4. MUNICIPAL SEPARATE SEWERS
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FIGURE 2-2
ISOMETRIC SCHEMATIC OF MMSD CONVEYANCE/STORAGE SYSTEMS2020 CONVEYANCE REPORT
FIGURE 2-3
METROPOLITANINTERCEPTORSEWER SYSTEM2020 CONVEYANCE REPORT
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FIGURE 2-4
WWTP TRIBUTARY AREAS2020 CONVEYANCE REPORT
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NameIdentification
Number Operation Location
South Howell Avenue
Pump StationPS0101 Relief S. Howell Ave. and E. Citation Way
Greenfield Park Pump Station PS0301 Relief 1500 S. 124th
St.
Underwood Creek
Pump StationPS0302 Relief Underwood Creek Pkwy and W. Potter Rd.
Beach Road Pump Station PS0401 Continuous 7509 N. Beach Dr.
Lake Drive and Ravine Lane
Pump StationPS0402 Continuous 9415 N. Lake Dr.
Port Washington Road
Pump StationPS0501 Continuous N. Port Washington Rd. and W. Marne Ave.
Green Tree Road Pump
StationPS0502 Relief 1300 W. Green Tree Rd.
Mount Vernon Pump Station1
PS0701 Continuous N. 42nd
St. & W. Mount Vernon Ave
Brady Street Pump Station PS0703 Relief N. Water St. & E. Pearson St.
Notes: Data current as of December 2005
1) Proposed to be abandoned
TABLE 2-1
MMSD PUMPING STATIONS2020 CONVEYANCE REPORT
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2020 Facilities Plan Conveyance Report Numerous diversion chambers located throughout the MIS system can be used to divert flow from one part of the system to another. These structures are listed in Table 2-2. As described above, using some of these facilities helps to ensure that the MIS system and treatment plants are used to their maximum conveyance and treatment capacities during wet weather events. Other diversion chambers divert flows for maintenance purposes. Bypasses are located at several points in the MIS system to relieve the system under extreme wet weather conditions. These bypasses are indicated in Table 2–3 and include overflow pipes, gated bypass structures, and bypass pumping stations.
The Northwest Side Relief Sewer (NWSRS) is a major relief facility that was completed during the 2020 facilities planning process. This facility is a 7-mile-long, 20-foot-diameter tunnel that provides relief to portions of the MIS system on the northwest side of the MMSD planning area. The NWSRS can function as either a storage facility or a relief sewer. In storage mode, the NWSRS temporarily stores wet weather flow, which is then drained into the ISS. In relief sewer mode, the NSWRS can operate as a conveyance facility to provide hydraulic relief to the MIS.
2.1.2 Near Surface Collector Sewers
The MIS system collects wastewater from a combined sewer service area of approximately 24 square miles located in the central portion of the city of Milwaukee and in a portion of the village of Shorewood, as shown in Figure 2-5. The low-flow portion of the combined sewer flow is captured by the MIS system at intercepting structures that limit the rate of flow that can be delivered to the MIS system. When the rate of combined sewer flow exceeds the capacity of an intercepting structure, the excess flow continues downstream in the combined sewer to a diversion structure where it is diverted to a near surface collector sewer. The near surface collector sewers capture combined sewer flow from one or more diversion structures and convey the flow to the ISS for temporary storage. If the combined sewer gates to the ISS are closed, flow is diverted to combined sewer outfalls, rather than to the near surface collector sewers.
2.1.3 Inline Storage System The ISS is a 19-mile network of storage tunnels constructed in bedrock about 250 to 300 feet below the ground surface. The ISS temporarily stores and conveys both separate and combined sewer system flow. Flow from the MIS system is delivered to the ISS through 24 dropshafts, 16 of which convey only combined sewer flow; four of which convey only separate sewer flow; and another four that convey both separate and combined flow. The dropshafts are designed to dissipate the energy of the falling flow, thereby preventing damage to the underground structures. The dropshafts are also designed to minimize air entrainment, which can limit the hydraulic capacity of the dropshaft. Flow is pumped out of the ISS at the Inline Pump Station located at JIWWTP. Flow can be pumped to either JIWWTP or SSWWTP.
2.1.4 Control System
Operation of the MIS system and ISS is controlled using a sophisticated real-time control system that maximizes the use of MIS system capacity and controls flow into and out of the ISS. The central computer for the control system is located at JIWWTP. A radio telemetry system is used for communications between the central computer and remote facilities.
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JIWWTP Tributary Area– MIS Flow Diversions
IdentificationNumber Location Diversion To:
DC0306 Greenfield Park Pump Station SSWWTP
DC0406 Interstate Highway 43 and W. Green Tree Rd. SSWWTP
DC0505 N. 51st
Blvd. and W. Hampton Ave. SSWWTP
DC0603 S. 6th
St. and W. Oklahoma Ave. SSWWTP
DC0604 S. 35th
St. and W. Manitoba St. SSWWTP
DC0605 S. 6th
St. and W. Warnimont Ave. SSWWTP
DC0606 S. Kinnickinnic Ave. and S. Barland Ave SSWWTP
70509 Green Tree Road Pump Station SSWWTP
DC0501 E. Brady St. and N. Van Buren St. ISS
DC0502 N. Humboldt Blvd. and W. Capitol Dr. ISS
DC0503 Pillsbury Grain Silos ISS
DC0504 N. 31st
St. and W. Hampton Ave. ISS
DC0506 N. 35th
St. and W. Capitol Dr. ISS
DC0507 N. Lydell Ave. and W. Fairmount Ave. ISS
DC0508 N. Milwaukee River Pkwy and W. Villard Ave. (extended) ISS
DC0509 W. Hampton Ave. and N. Lydell Ave. ISS
DC0602 S. 35th
St. and W. National Ave. ISS
DC0510 N. 37th
St. and W. Juneau Ave. Combined Sewer to MIS
75033 N. Water St. and E. Pearson St. (pumping station) CMIS–low level to high level
DC0601 S. 12th
St. and W. National Ave. CMIS–high level to low level
DC0701 E. Pleasant St. and N. Commerce St. CMIS–low level to ISS
DC0702 N. Marshall St. (vacated) and Milwaukee River CMIS–low level to ISS
DC0703 S. 16th
St. and W. Canal St. CMIS–low level to ISS
DC0704 N. Young St. and E. Erie St. CMIS–low level to ISS
SSWWTP Tributary Area– MIS Flow Diversions
IdentificationNumber Location Diversion To:
DC0101 S. 27th
St. and W. Howard Ave. JIWWTP
DC0102 S. Howell Ave. and E. Layton Ave. JIWWTP
DC0301 S. 84th
St. and W. Walker St. SSWWTP1
DC0302 S. 84th
St. and W. Adler St. SSWWTP1
DC0303 W. Wisconsin Ave. and Windsor Dr. SSWWTP1
DC0305 N. Menomonee River Pkwy. and W. Keefe Ave. SSWWTP1
DC0401 S. Hawley Rd. and CP Rail Road JIWWTP
DC0403 N. 58th
St. and W. State St. JIWWTP
DC0404 N. 58th
St. and W. Roosevelt Ave. JIWWTP
DC0407 W. Dean Rd. and N. Teutonia Ave. JIWWTP
TABLE 2-2 SHEET 1 OF 2
MMSD DIVERSION CHAMBERS2020 CONVEYANCE REPORT
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SSWWTP Tributary Area– MIS Flow Diversions
IdentificationNumber Location Diversion To:
DC0408 N. Green Bay Ave. – North of Beaver Creek JIWWTP
DC0409 N. Sidney Pl. and W. Mill Rd. JIWWTP
DC0103 S. 6th
St. and W. Oklahoma Ave. ISS
DC0304 Milw. County Grounds (about 1500 N. 87th
St) ISS
DC0402 N. 59th
St. Extended and W. Trenton Pl. ISS
DC0405 N. 51st
Blvd. and W. Hampton Ave. ISS
MIS = Metropolitan Interceptor Sewer
CMIS = Central Metropolitan Interceptor Sewer
ISS = Inline Storage System
JIWWTP = Jones Island Wastewater Treatment Plant
SSWWTP = South Shore Wastewater Treatment Plant
Note: Data current as of December 2005
1) Immediate diversion is to another branch of the SSWWTP system; tributary flow can be diverted to JIWWTP if diversions are made at
several diversion chambers.
TABLE 2-2 SHEET 2 OF 2
MMSD DIVERSION CHAMBERS2020 CONVEYANCE REPORT
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2020 Facilities Plan Conveyance Report Table 2–3, page 1 of 2
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TABLE 2-3 SHEET 1 OF 2
MMSD BYPASS STRUCTURES2020 CONVEYANCE REPORT
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TABLE 2-3 SHEET 2 OF 2
MMSD BYPASS STRUCTURES2020 CONVEYANCE REPORT
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2020 Facilities Plan Conveyance Report 2.1.5 Design Criteria
Metropolitan Interceptor Sewer System The criteria for sizing MIS system facilities evolved throughout the years as various planning efforts were undertaken. Previous planning efforts include the Milwaukee Water Pollution Abatement Program (MWPAP) from 1977 to 1994, and the 2010 Facilities Plan that was completed in 1998. Sizing of MIS system facilities during the MWPAP was based on simulated design hydrographs adjusted to represent peak flows for a historic wet weather event that occurred on May 12-13, 1978.(1) This event was chosen because at the time of the planning effort in the late 1970s, it created the largest wastewater flow ever recorded at SSWWTP and produced about three inches of rain in 24 hours.
Sizing of MIS system facilities for the 2010 Facilities Plan was based on a similar approach. A wet weather event that occurred on May 9-10, 1990, produced the largest recorded daily flow at SSWWTP.(2) The maximum 24-hour precipitation for this event was just under three inches, some of which fell as snow but melted within 12 to 18 hours. The recurrence interval of wastewater flows measured during this event was estimated to be about five years. Hydrographs were developed for the May 9-10, 1990, event using flow monitoring records and routed through a dynamic model of the MIS system to determine peak flows throughout the system. Metropolitan interceptor sewer system relief needs were sized to accommodate the simulated peak flows.
Near Surface Collector Sewers The NSCS were sized during the MWPAP to convey the peak flows generated in the combined sewer area for a five-year recurrence interval rainfall event.(3)
Inline Storage System The ISS is a dual-purpose facility that stores wastewater from both separate and combined sewer areas. The concept for a deep tunnel storage facility to address combined sewer overflow abatement was identified in the Southeastern Wisconsin Regional Planning Commission’s (SEWRPC) Milwaukee River Watershed Plan and further addressed in the Regional Water Quality Management Plan for Southeastern Wisconsin.(4,5) The ISS concept evolved during planning for relief of the MIS system and control of combined sewer overflows during the MWPAP. At that time, planners recognized that there was a need to provide major relief interceptors (12 feet in diameter) that paralleled the Milwaukee and Menomonee Rivers and could convey peak flows from the separate sewer areas. The most cost-effective approach to building interceptors of this size was to construct them in bedrock about 300 feet below grade. It was then determined that extra storage could be obtained by “over-sizing” these relief tunnels. The extra storage would shave peak flows and lessen the amount of flow discharged to the wastewater treatment plants, thus reducing the required capacities of these plants while providing treatment for a substantial volume of wet weather flow. As planning to address combined sewer overflows progressed in parallel to the planning for MIS system relief, it was determined that the storage tunnels for separate sewage storage would be used only a few times each year and that the full tunnel volume needed for separate sewage would be used very infrequently. Therefore, it was reasoned that if a means could be provided to accommodate both objectives, the tunnel system could also be used to store combined sewage and reduce combined sewer overflows. Combined sewer flows are generated much more quickly than separate sewer flows, so
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2020 Facilities Plan Conveyance Report successful implementation of the dual-purpose concept required limiting the amount of tunnel volume used for combined sewage so that volume would also be available for storing separate sewage. A prediction algorithm was developed to calculate the volume required for separate sewage inflow (VRSSI) that would need to be stored in the tunnel during a wet weather event so that combined sewage flow to the ISS could be stopped and an appropriate tunnel volume for the separate sewage reserved. The initial algorithm for predicting the required storage volume was based on past and predicted rainfall and recorded decrease in snow pack depth. Experience has shown that accurate rainfall forecasts have been difficult to obtain for large events. Due to difficulties controlling flow to the ISS so that a sufficient volume for separate sewage is reserved and the ISS is not overfilled, MMSD adopted the practice of using past operational experience in conjunction with knowledge of changing conditions throughout wet weather events to establish the VRSSI. Recent practice has resulted in initial VRSSI values ranging from 125 to 250 million gallons (MG). The MMSD is in the process of implementing a new algorithm for predicting the VRSSI.
The ISS was initially sized to contain the volume of sewage from the separate sewer area that needed to be stored for the largest separate sewage storage event simulated for the meteorological conditions that occurred during the period of record available at the time of the planning (1940 through 1979).(6) An event in June 1940 required the largest separate sewage storage volume. The ISS sizing resulted in a projected long-term average frequency of less than two CSOs per year, as determined in the Milwaukee Harbor estuary study.(7)
Long-term simulations were performed during the 2010 facilities planning effort to assess the performance of the ISS for projected 2010 flows. These flows were based on 2010 population and land use conditions and a recommended 5% reduction in infiltration and inflow (I/I). The simulations were based on the assumption that the required volume of storage for separate sewage could be accurately predicted and reserved in the ISS for individual wet weather events. Based on these assumptions, it was concluded that the existing ISS could provide a five-year level of protection against sanitary sewer overflows for the projected 2010 conditions. This level of protection against sanitary sewer overflows was consistent with the estimated five-year wastewater recurrence interval of the design event used for MIS system sizing. It was also concluded that a long-term average combined sewer overflow frequency of less than two CSOs per year would be achieved for the projected 2010 conditions. This combined sewer overflow frequency was consistent with the original sizing criteria for the ISS.
2.1.6 Policies and Programs
The MMSD has numerous policies and programs in place to manage wastewater flow from the municipalities.
Rules and Regulations Chapter 2 of MMSD’s Rules and Regulations addresses requirements for the planning, design, and construction of sewers and ancillary facilities in MMSD’s planning area. Chapter 3 outlines requirements for management of I/I.
Limited Sewer System Evaluation Survey The MMSD recently provided partial funding for a limited sewer system evaluation survey (LSSES) program whereby communities investigated I/I sources in their systems. The goal of the program was to identify local system defects that could be corrected to reduce I/I.
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2020 Facilities Plan Conveyance Report Infiltration and Inflow Demonstration Projects
The MMSD also recently completed several I/I demonstration projects. These projects have identified technologies and costs for rehabilitation methods to reduce I/I. The results of this effort will provide data for use in implementing I/I reduction projects.
Private Property Infiltration and Inflow Study A private property I/I reduction study was conducted in parallel with the 2020 facilities planning effort. The purpose of this study was to assess the significance of I/I from private property sources in the MMSD service area and examine the technical, legal, and financial issues related to the potential implementation of a private property I/I reduction program.
Rainwater Reduction Program The MMSD has undertaken several studies to evaluate the impact of reducing the amount of rainwater that enters the combined sewer system. The goal of these studies is to identify opportunities to reduce direct inflow to the combined system.
Capacity Management Operations and Maintenance The MMSD is currently implementing a Capacity Management, Operations, and Maintenance (CMOM) program. To date, strategies have been developed for the following program components:
♦ Management Plan
♦ Overflow Response Plan (ORP)
♦ System Evaluation and Capacity Assurance Plan (SECAP)
♦ Communications and Program Audit Plan
The MMSD has also funded the development of CMOM readiness reviews and business practice evaluations, as well as limited SECAPs for all 28 of its customer municipalities.
2.2 Municipal Collection SystemsThe MMSD serves 28 satellite municipalities that own and operate local sewer systems. Separate sewers serve most of the MMSD service area and combined sewers serve about 24 square miles of the service area including the central portion of the city of Milwaukee and a portion of the village of Shorewood.
The age of municipal sewers ranges from over 100 years old for some city of Milwaukee sewers to new sewers currently under construction. Various pipe materials have been used in construction over the years including reinforced concrete, clay, brick, and polyvinyl chloride.
The design criteria for sizing the municipal collection systems vary widely. No common design criteria are defined for separate sewers in terms of a wet weather event recurrence interval. Analyses conducted for the MWPAP concluded that existing combined sewers had capacities to convey storm events with recurrence intervals ranging from two to 10 years.(8) Upgrades to combined sewers in the city of Milwaukee are now being sized for a 10-year recurrence interval rainfall.(9)
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2020 Facilities Plan Conveyance Report Bypasses or overflows from 24 of the municipal collection systems are subject to the requirements of a Wisconsin Department of Natural Resources (WDNR) general permit to discharge under the Wisconsin Pollutant Discharge Elimination System (WPDES). Four of the municipal systems are subject to the requirements of individual permits.
Many communities have undertaken infiltration/inflow reduction measures in recent years to reduce the magnitude of I/I in their systems. As outlined above, MMSD is currently funding CMOM program development for each of the municipal systems.
2.3 Private Wastewater Collection Systems Private collection systems are those owned and operated by property owners. Private collection systems include laterals for single- and multi-family residential buildings, and local collection systems on commercial and industrial property. Flow from these systems enters the municipal collection systems and eventually the MIS system.
2.4 Planning Units
The MMSD wastewater service area was divided into planning units called sewersheds to estimate wastewater flows that are tributary to MMSD facilities. The definition of these planning units is presented in Chapter 3, Analytical Methods/Data Sources of this report.
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2020 Facilities Plan Conveyance Report References
(1) Program Management Office, Milwaukee Water Pollution Abatement Program, Sewer
System Evaluation Survey, General Report, Volume 1 (Milwaukee: Milwaukee Metropolitan Sewerage District, 1981)
(2) Milwaukee Metropolitan Sewerage District, 2010 Facilities Plan, Volume 1 (Milwaukee: Milwaukee Metropolitan Sewerage District, 1998)
(3) Milwaukee Water Pollution Abatement Program, Inline Storage System O & M Manual, System Summary (Milwaukee: Milwaukee Metropolitan Sewerage District, June 1992)
(4) Southeastern Wisconsin Regional Planning Commission, Planning Report No. 13, A Comprehensive Plan for the Milwaukee River Watershed, Volume 2, Alternative Plans and Recommended Plan, October 1971
(5) Southeastern Wisconsin Regional Planning Commission, Planning Report No. 30, A Regional Water Quality Management Plan for Southeastern Wisconsin:2000, Volume 3, Recommended Plan, June 1979
(6) Milwaukee Water Pollution Abatement Program, Inline Storage System O & M Manual, System Summary (Milwaukee: Milwaukee Metropolitan Sewerage District, June 1992)
(7) Southeastern Wisconsin Regional Planning Commission, Planning Report No. 37, A Water Resources Management Plan for the Milwaukee Harbor Estuary, Volume 2, Alternative and Recommended Plans, December 1987
(8) Milwaukee Water Pollution Abatement Program, Inline Storage System O & M Manual, System Summary (Milwaukee: Milwaukee Metropolitan Sewerage District, June 1992)
(9) City of Milwaukee, Bureau of Engineers, Sewer Engineering Division, Sewer Design Manual (January 20, 1984)
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