The CSO 077 regulator upsize highlights the County’s opportunistic approach for CSO abatement. Via routine inspections by the County, it was determined that the existing 15” CSO regulator between the West Colvin Trunk Sewer (077) and the Midland Ave. Trunk Sewer was in poor condition and in danger of failure in the near future. Rather than simply replace the pipe with a pipe of the same diameter, the County viewed the combined sewer system holistically and completed a SWMM analysis for upsizing the regulator pipe. Based on the SWMM analysis, a 24” pipe was found to provide the greatest CSO reduction benefit to CSO 077, essentially eliminating all overflows from both the intermediate overflow from CSO 077 and the ultimate overflow to Onondaga Creek, CSO 060/077. An average total of 6.8 million gallons of combined sewer overflow and 22 overflow events from CSO 060/077 are eliminated by this change (SWMM calculations for the 1991 typical year). The combined sewer flow is now conveyed via the Midland Avenue Trunk Sewer to the Midland Avenue Regional Treatment Facility for treatment prior to discharge to Onondaga Creek.
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