Innovative Approach to Double Wet Weather Capacity for CSO and SSO Mitigation in Oneida County, New York

The Oneida County Sewer District (District) is administered through the Oneida County Department of Water Quality and Water Pollution Control (WQ&WPC) which is responsible for the operation and management of the District's facilities and personnel. District facilities include 72.4 kilometers of interceptor sewers, the Sauquoit Creek and the Barnes Avenue Pumping Station, and the Water Pollution Control Plant (WPCP). The District services 15 municipalities including the City of Utica. The New York State Department of Environmental Conservation (NYSDEC) and Oneida County (County) entered into a Consent Order due to sanitary sewer overflow (SSO) at the Sauquoit Creek Pumping Station (SCPS). In addition to the Consent Order with the County, the NYSDEC has required a combined sewer overflow long term control plan (LTCP) as part of the City of Utica's SPDES permit. The LTCP requires the City to increase its percent capture of CSO flows during wet weather. As a result of the County's Consent Order to mitigate SSO at the SCPS, and the City's LTCP to increase the capture of CSO flows, the WPCP will be required to accept and treat flows beyond its existing capacity. The WPCP can currently process a peak flow of approximately 208 megaliters per day (ML/d) (55 million gallons per day (mgd)). Based on preliminary CSO/SSO mitigation requirements as well as projected growth within the District, the WPCP may need to be expanded for a peak capacity of 420 ML/d (111 mgd). A wet weather operating strategy known as “split flow” was evaluated as a solution to double the plant's peak capacity. In this strategy, all sanitary flows are conveyed through the secondary treatment process. Combined sewer flows receive primary sedimentation, and high rate disinfection. This process provides compliance with the USEPA CSO Control Policy for the combined flows, and compliance with the Federal Water Pollution Control Act (Clean Water Act) for secondary treatment of sanitary flows.