Facility Plan Amendment
Introduction
1. Background
2. Supplement

3. Conveyances
4. RTF
5. Schedule
Appendices

Midland Avenue RTF and Conveyances: Facility Plan Amendment, June 2003
by Environmental Engineering Associates, LLP
for Onondaga County Department of Water Environment Protection

3. Midland Avenue conveyances/off-line storage

Quick reference
— 3.1 General
— 3.3 Design flow rates/conveyance sizing
— 3.4 Off-line storage facility
— 3.5 Sequence of operations
— 3.6 CSO volumetric capture

3.1 General

As described in Section 2.5, the recommended CSO abatement plan for the Midland Avenue RTF and Conveyances Project includes the installation of a 330 cfs RTF at the Oxford Street location (east of Onondaga Creek) plus 4.2 MG of in-line conveyances storage plus 2.5 MG of upstream off-line storage. This section provides a brief description of operations, basis of design flows, and preliminary sizing of the Midland Avenue Conveyances and off-line storage facility. Section 4 describes in more detail, the facilities and operation of the Midland Avenue RTF. 3.2 Description of Facilities and Operation

The Midland Avenue Conveyances will consist of CSO transmission pipelines of varying sizes, located along Onondaga Creek in the southern section of the City of Syracuse. The Midland Avenue Conveyances will collect overflows from the existing CSOs 039, 042, and 044, up to the one-year design storm, and all combined sewer flow from CSOs 043, 052, 060 (includes former Overflow 077), 061, 067, 076 [to be permanently closed] and convey these flows to the Midland Avenue RTF.

The Midland Avenue Conveyances and proposed 2.5 million gallon (MG) off-line, underground storage tank (to be located directly upstream and adjacent to the Midland Avenue RTF between Oxford and Blaine Streets) will also provide flow storage and attenuate the peak flow to the Midland Avenue RTF. At CSO locations 039, 042, and 044, the existing regulator structures will be modified to direct overflows up to the one-year design storm event to the new conveyances and, as appropriate, the off-line storage facilities.

For CSO locations 043, 052, 060 (includes former Overflow 077), 061, 067, and 076, the existing outfall pipelines will be permanently closed and all flows will be directed via new pipelines to the conveyances and, as appropriate, the off-line storage facility.

As noted in Section 2.4, overflows from CSOs 038, 040, 041, 045, 046A, 046B, 047, 048, 050, 051, 053, and 054 will not be connected to the Midland Avenue Conveyances/Off-Line Storage Facility or contribute flow to the Midland Avenue RTF, as existing combined sewers in these areas will be separated. This sewer separation program will prevent future CSO discharges from these drainage areas.

The Midland Avenue Conveyances/Off-Line Storage Facility will include the following components:

Tallman Street CSO transmission pipeline from Tallman Street to the Midland Avenue RTF, which will collect and convey combined sewer flow (up to the one-year design storm event) from CSO 039
Midland Avenue CSO transmission pipeline from West Newell Street to the Midland Avenue RTF, which will convey combined sewer flow (up to the one-year design storm event) from CSO 044 and all combined sewer flows from CSOs 043, 060 (includes former Overflow 077), 061, 067, and 076
Bellevue Avenue CSO transmission pipeline, which will convey combined sewer flow (up to the one-year design storm event) from CSO 042 across Onondaga Creek to the underground storage tank and the RTF
Elmhurst Avenue CSO transmission pipeline or siphon (to be determined during design), which will convey all combined sewer flow from CSO 052 across Onondaga Creek to the Midland Avenue Conveyances and RTF.

Figure 2-3 presents the recommended plan layout for the Midland Avenue Conveyances and Off-Line (Underground) Storage Facility.

In addition to the CSO transmission pipelines and off-line storage facility, a connection between the existing Main Interceptor Sewer (MIS) and the Midland Avenue RTF must be provided to allow a portion of the flows in the filled MIS upstream of the RTF to discharge into the RTF. This relief of MIS flows will provide for downstream conveyance capacity in the MIS for the RTF underflow (equal to five percent of the RTF influent pumping/treatment rate).

As noted in Section 2.4, overflows from CSOs 038, 040, 041, 045, 046A, 046B, 047, 048, 050, 051, 053, and 054 will not be connected to the Midland Avenue Conveyances or contribute flow to the Midland Avenue RTF, as existing combined sewers in these areas will be separated. This sewer separation program will prevent future CSO discharges from these drainage areas.

The ACJ established two phases for construction of the Midland Avenue RTF and Conveyances Project. Phase One included construction of the Conveyances with a construction commencement date of May 1, 1999 and a construction completion/begin operation date of May 1, 2004. Phase Two included construction of the RTF with a construction commencement date of May 1, 2004 and a construction completion/begin operation date (major milestone) of May 1, 2007.

In order to comply with the ACJ CSO Construction Milestone Completion Schedule outlined above and to better address constructability impact issues associated with constructing the RTF following construction of the Conveyances in accordance with the ACJ, the County requested and NYSDEC subsequently approved modification to the construction sequencing of the project to initiate the RTF project prior to completion of the Conveyances project. A more thorough discussion of this revised project sequencing is presented in Section 5.

3.3 Design flow rates/conveyance sizing

The Midland Avenue CSO Conveyances have been sized to accommodate additional pipeline storage and conveyance capacity for the one-year design storm event. Specifically, the design flow rates for the Midland Avenue Conveyances have been developed based on the following:

Transmission to the Midland Avenue RTF of the peak discharge from the CSOs to remain in the system upon completion of the Project (i.e., CSOs 039, 042, and 044) up to the one-year design storm event

Necessary service area capture component to result in a minimum 85% capture of the total system-wide overflow volume

Transmission to the Midland Avenue RTF of additional flows above the one-year design storm event for the six CSOs scheduled to be closed upon completion of the Project (i.e., CSOs 043, 052, 060 (includes former Overflow 077), 061, 067, and 076), as discussed in Section 2.4.

Table 3-1 presents the design flow rates and required sizing for each segment of the proposed Midland Avenue Conveyances.

TABLE 3-1. CONVEYANCE DESIGN FLOW RATES/SIZING

CSO transmission conduits (CSO connected) Diameter (inches) Approximate length (ft) Peak flow (cfs)

Midland Transmission Conduits

West Newell Street (CSO 067)/West Brighton Avenue (CSO 076) 42 1,500 26

West Brighton Avenue (CSO 076)/Elmhurst Avenue (CSO 052) 54 600 42

Elmhurst Avenue (CSO 052)/West Colvin Street (CSO 060) 66 850 138

West Colvin Street (CSO 060)/Kirk Avenue 120 1,850 304

Kirk Avenue/South Avenue (CSO 044) 144 1,525 303

South Avenue (CSO 044)/Midland Avenue (CSO 043) 144 1,360 430

Midland Avenue (CSO 043)/Midland RTF 144 295 511

Tallman Transmission Conduits (039)

Tallman Street - East 54 128 255

Tallman Street/Midland RTF 84 886 255

Bellevue Avenue Transmission Conduits (042)

Midland Avenue/Midland RTF 66 200 183

Elmhurst Avenue Transmission Conduits (052)

Elmhurst Avenue (CSO 052)/Midland Transmission Conduits 66 180 100

Connection Conduits

Midland Avenue - East (CSO 043) 72 35 225

West Castle Street/South Avenue (CSO 044) 48 50 65

West Colvin Street (CSO 060 and CSO 077) 60 40 185

Crehange Street/Onondaga Creek (CSO 061) 12 25 8

West Brighton Avenue/Midland Avenue (CSO 076) 54 0 40

MIS TAP 48 40 33

3.4 Off-line storage facility

The proposed 2.5 MG underground, off-line storage facility will be used in conjunction with the 4.2 MG of conveyance storage to provide a total storage volume of 6.7 MG upstream of the RTF. This total storage volume permits the size of the Midland Avenue RTF to be reduced from 667 cfs to 330 cfs.

As shown on Figure 2-3, the 2.5 MG underground, off-line storage facility will be located directly upstream and adjacent to the Midland Avenue RTF, north of Blaine Street, on the east side of Onondaga Creek.

Figure 3-1 shows a preliminary plan of the 2.5 MG underground storage facility between Onondaga Creek and the MIS.

Figure 3-2 depicts a preliminary section of the storage facility.

3.5 Sequence of operations

In order to meet the minimum 85 percent volumetric capture of combined sewage on a system-wide average annual basis pursuant to the ACJ, it is necessary for the Midland Avenue Conveyances/Off-Line Storage Facility and RTF to be operated in a manner that allows for filling and maximizing storage in the conveyances, the underground off-line storage tank, and the influent wet well of the RTF prior to initiating the RTF influent pumps. This would be achieved by setting of the RTF influent pump "on" elevation above the crown of the conveyances at the RTF.

Flow will enter the RTF influent wet well from the conveyances. The influent wet well will fill and, as additional flow enters the wet well, it will back up into the conveyances. Inflatable dams and/or weir structures will be installed in the upper reaches of the conveyances to maximize the conveyances storage (note: these control structures will be more fully developed during Phase Three conveyances design). Conveyances storage will be designed to ensure that no collector sewer surcharging occurs as a result of storage operations.

The 2.5 MG underground storage tank will be located at the downstream end of the proposed Midland Avenue CSO transmission pipeline at its connection into the RTF influent wet well. A side overflow weir to the underground storage tank from the Midland Avenue CSO transmission pipeline will permit flows above a pre-established weir elevation (set to maximize conveyances storage) to enter the storage tank.

As shown in Figure 3-1, the underground storage tank will be composed of multiple cells to permit sequential filling of the storage tank. This will permit use of only those cells necessary for flow storage during smaller, less intense storm events. Upon achieving the maximum storage capacity of the conveyances and underground storage tank (6.7 MG total), the RTF influent pumps will activate to process additional flow through the RTF. The RTF influent pump will be programmed to shut down once the influent flow elevation recedes to the maximum storage elevation for the underground storage tank/conveyances system.

At the conclusion of the CSO event, the RTF dewatering pumps will be used to pump the CSO volume stored in the RTF, disinfection tank, conveyances and underground storage tank to the MIS for transport to, and treatment at, Metro. All stored CSO must be pumped out in 48 hours or less to comply with accepted operating procedures and directive by the NYSDEC. A more detailed description of the separate RTF operations is presented in Section 4.

3.6 CSO volumetric capture

In order to demonstrate compliance with the ACJ-mandated minimum 85 percent volumetric capture of combined sewage in a system-wide average annual basis, EEA retained the services of an independent sewer system modeling consultant, and developer of the County's computerized Storm Water Management Model (SWMM), to execute the County's calibrated SWMM using the various CSO compliance projects that have either been completed or are proposed for implementation pursuant to the ACJ. The SWMM executions were run using a long-term simulation approach based upon over 30 years of precipitation data for the Syracuse Metropolitan area.

For existing conditions, without implementation of any CSO abatement projects, the County Sanitary District trunk and interceptor sewer transports 74% of the average annual volume of combined sewage collected within the City of Syracuse collector and combined sewer system to Metro for treatment. A summary of this volume capture information is presented in Table 3-2.

Table 3-2. CSO volume capture table - existing conditions, 1997

Table 3-2. CSO volume capture table - existing conditions, 1997

Upon implementation of the ACJ CSO abatement projects, as described above, the average annual volume of combined sewage collected within the combined sewer system for transport to Metro for treatment is projected to be in the range of 89% to 91%. A summary of this volume capture information is presented in Table 3-3. These data indicate that the fully-implemented ACJ CSO compliance projects will satisfy the minimum 85 percent capture requirements of the ACJ.

Table 3-3. CSO volume capture table - future conditions, treatment at Metro

Table 3-3. CSO volume capture table - future conditions, treatment at Metro

Table 3-4 presents the CSO volume capture information for the combined treatment of CSO both at Metro and at the completed/proposed ACJ compliance projects, which is projected to be approximately 96%.

Table 3-4. CSO volume capture table - future conditions, treatment at Metro and RTFs

Table 3-4. CSO volume capture table - future conditions, treatment at Metro and RTFs

Appendix 8, prepared by Brown & Caldwell (formerly Moffa & Associates), explains the evolution of the capture tables from 1996 to present.

Based on the most recent modeling and resultant updated volume capture tables, the Midland Project when completed will achieve a total capture with treatment at Metro of 92%, based on the one-year storm and 30-year record of precipitation. Thus, only 8% of the total average annual CSO flow within the Midland CSO service area will require regional treatment, disinfection, dechlorination, and discharge to Onondaga Creek.