SSO 700 Integrated Watershed Action Plan Collection System Hydraulic Model Calibration: Objectives, Methodology, and Results

Sanitary Sewer Overflow (SSO) 700 is the largest SSO in the Metropolitan Sewer District of Greater Cincinnati’s (MSDGC’s) system. Under MSDGC’s Consent Decree, MSDGC is required to eliminate SSO 700. Addressing this mandate in isolation through the implementation of traditional, end-of -pipe infrastructure may cost ratepayers as much as $230 million, with no enhancement to local communities. Hamilton County and MSDGC have pursued a comprehensive evaluation of the SSO 700 watershed to develop an Integrated Watershed Action Plan (IWAP). The purpose of the IWAP is to identify and evaluate the range of water quality and water quantity issues and opportunities throughout the watershed and ultimately arrive at solutions that cost-effectively achieve compliance with the Consent Decree and the Clean Water Act.To achieve the objectives of the IWAP, the various sources of pollution and the roles they play impairing the various waterways within the watershed will be characterized. Ultimately, an optimum combination of cost-effective and affordable gray infrastructure, sustainable infrastructure, and watershed-based controls for the watershed will be identified. The collection system hydraulic model will be used to perform conceptual planning-level alternative analyses for the mitigation of overflows, to document existing discharges and ultimate achievement of consent decree compliance, and to provide input to the water quality model framework for characterization of instream water quality conditions.The SSO 700 IWAP collection system model calibration and validation was implemented to refine an existing tool using more recent data and more advanced modeling techniques to achieve the objectives of the collection system model and the overall project. The SSO 700 IWAP collection system model was successfully calibrated to MSDGC’s modeling guidelines at the time of project inception. In addition to flow and depth comparisons at all of the flow monitoring locations meeting MSDGC’s calibration guidelines, the collection system model also reflects the conditions at the SSO 700 Storage and Treatment Facility and the CSOs and SSOs within the watershed. Moving ahead, the calibrated and validated collection system hydraulic model will be used to provide input to the IWAP water quality model framework and perform alternative analyses to mitigate overflows during the next phase of the project.