4. Clinton Street CSO abatement approaches, Onondaga Lake Improvement

Clinton Street CSO Abatement Project Facility Plan (Nov 2005)
by Environmental Engineering Associates, LLP
for Onondaga County Department of Water Environment Protection

4. Clinton Street CSO abatement approaches

4.1 Introduction

As presented in Section 2.4, the following CSO treatment technologies/approaches are determined to be the most feasible for achieving compliance with the Clinton Street CSO service area ACJ requirements.

Recognizing that there may be potential cost savings if partial sewer separation of select smaller individual CSO drainage basins were combined with a smaller-size regional storage facility or regional storage and treatment facility with disinfection (RTF), it was determined appropriate to evaluate the individual CSO discharge characteristics within the service area to assess the feasibility of partial sewer separation. This section presents the results of this evaluation.

4.2 Sewer system modeling and service area flows

Environmental Engineering Associates, LLP (EEA) coordinated with modeling consultant Brown and Caldwell to execute the previously developed sewer system model for the Clinton Street CSO service area. The purpose of this model execution was to develop individual flow hydrographs for each of the Clinton Street CSO drainage basins for the 1-year design storm condition, consistent with ACJ requirements. Pursuant to previous County discussions with the NYSDEC concerning the definition of a 1-year design storm event for the purposes of the ACJ, the 1-year design storm is defined to be a 1-year frequency, 2-hour duration, 15-minute rainfall interval storm event. Copies of the individual flow hydrographs for the Clinton Street CSOs are presented in Appendix E.

Click here for Appendix E. One-year design storm individual CSO flow hydrographs.

A summary listing the individual service area CSOs, associated drainage areas, and 1-year design storm peak flow rates is presented in Table 4-1.

Table 4-1. CSO outfall 1-yr peak flow rates
CSO	Basin area, acres	Peak flow rate*, CFS
027	134	86
028	24	9
029	8	12
030	312	216
031	25	14
032	25	16
033	18	16
034	214	264
035	23	16
036	188	135
*Peak flow rate based upon one-year frequency, two-hour duration, 15-minute rainfall interval storm event with free-outlet design condition. CFS = cubic feet per second

4.3 CSO service area groupings

Using the information presented in Table 4-1 and on Figure 4-1, the most reasonable groupings of CSO outfalls, to be considered in conjunction with partial sewer separation, were developed. These groupings were established based on individual CSO outfall proximity to one another, the size of the respective CSO drainage basins, and the CSO outfall discharge locations relative to Onondaga Creek and the MIS. In general, CSO drainage basins located west of Onondaga Creek and of relatively small size were determined to be the most appropriate for consideration of sewer separation. This is due to the fact that separation of the west side drainage basins will reduce the quantity of flow that will require crossing of Onondaga Creek to discharge to the MIS. In addition, as stated previously, sewer separation has been shown to be cost-effective in smaller drainage basins.

Using the above basis for grouping the CSO outfalls, the following most beneficial CSO groupings were selected for further evaluation:

A. Sewer separation of CSO drainage basins west of Onondaga Creek (excluding 036)—028, 031, 032, 033, and 035—with conveyance and storage or storage/treatment of the remaining service area CSOs (027, 029, 030, 034, and 036) at a CSO abatement facility to be located at a final preferred site.

B. Sewer separation of CSO drainage basins west of Onondaga Creek and north of Tully Street (excluding 036)—028, 031, and 032—with conveyance and storage or storage/treatment of the remaining service area CSOs (027, 029, 030, 033, 034, 035, and 036) at a CSO abatement facility to be located at a final preferred site.

4.4 Most viable CSO abatement approaches

In addition to the partial sewer separation CSO abatement approaches identified in Section 4.3, the following two CSO abatement approaches were previously identified as being appropriate for further evaluation for the abatement of Clinton Street service area CSOs.

A. Sewer separation of the entire Clinton Street CSO service area.

B. Conveyance and storage or storage/treatment of all Clinton Street CSOs at a single service area storage facility or storage/RTF using either vortex separators (with disinfection) or ORF (with disinfection).

A summary matrix of the four most viable CSO abatement approaches for the Clinton Street CSO service area is presented in Table 4-2.

Table 4-2. Most viable CSO abatement approaches
	Abatement method (CSO basin nos.)
Description	Overflow conveyed to RTF	Separated
1. RTF* at preferred site with no sewer separation	027, 028, 029, 030, 031, 032, 033, 034, 035, 036
2. RTF* at preferred site with sewer separation west of Onondaga Creek (excluding 036)	027, 029, 030, 034, 036	028, 031, 032, 033, 035
3. RTF* at preferred site with sewer separation west of Onondaga Creek and north of Tully Street (excluding 036)	027, 029, 030, 033, 034, 035, 036	028, 031, 032
4. Full sewer separation		027, 028, 029, 030, 031, 032, 033, 034, 035, 036
*RTF (Regional Treatment Facility) includes either (a) Vortex Separation with High-Rate Disinfection or (b) Overflow Retention Facility with High-Rate Disinfection.