Cleaning of CSO Facilities Using Various Flushing Devices – A Case Study for the Midland Avenue Regional Treatment Facility, Onondaga County, New York

In March of 2008, the Onondaga County Department of Water Environment Protection placed into service the Midland Avenue Regional Treatment Facility (RTF) designed to provide storage and treatment of combined sewer overflows (CSOs) originating in the City of Syracuse, New York. The Midland Avenue service area encompasses approximately 2,300 acres of urban residential and commercial areas. The Midland Avenue RTF was designed to store up to 5.1 million gallons (MG) of CSO and treat excess CSO flows up to 330 cubic feet per second (cfs) using coarse screening, vortex separators and high-rate disinfection. The RTF consists of a 12-foot diameter influent conveyance pipeline which is used as a storage conduit, a 2.5 million gallon rectangular underground storage tank, influent pumping facilities, two 42-foot diameter vortex separators and a rectangular 1.0 MG underground disinfection tank.Following a CSO event, the Midland Avenue RTF is dewatered with captured flows directed to the County's main interceptor sewer for subsequent treatment at the downstream Metropolitan Syracuse Wastewater Treatment plant. The County is then faced with the post-storm cleanup of the RTF facilities which includes removing residuals that have accumulated in the influent pipeline, underground storage tank, vortex separators and the underground disinfection tank. In addition to a myriad of wash down hoses to facilitate the cleanup of the large underground facilities, the County has employed the following automated cleaning devices in the Midland Avenue RTF to help minimize the requirement for County operations staff to enter confined spaces for routine clean-up operations:Vacuum Flushing Devices in the 12-foot diameter influent conveyance pipelineFlushing Gates in the 2.5 million gallon underground storage tankTipping Buckets in the 1.0 million gallon underground disinfection tankThis paper provides a detailed overview of the CSO flushing devices installed at the Midland Avenue RTF.In addition, “lessons learned” for the flushing devices and their application to cleaning CSO storage tanks and large diameter conveyances are provided.