Laying the Foundation for Regulatory Approval for a Wet Weather Chemically Enhanced High Rate Treatment Facility

The Metropolitan Sewer District of Greater Cincinnati (MSD) Sycamore Wastewater Treatment Plant is located in northeast Hamilton County in southwest Ohio adjacent to the Little Miami River. Recent analysis of influent flow rates shows that the plant is frequently operating in excess of its design flow of 6 million gallons per day (mgd). In addition, the plant lacks sufficient capacity to treat all influent wet-weather flows due to excessive rainfall-dependent infiltration and inflow (RDI/I) entering the upstream sanitary sewer collection system.MSD proposes as a first phase the addition of a chemically enhanced high rate separation (CEHRS) system, ultraviolet disinfection (UV), and effluent pumping. These changes to the facility will increase the average capacity to 9 mgd and provide capacity for a projected peak wet weather flow of 50 mgd. During wet weather, flows in excess of 18 mgd will be treated by passing it through the new CEHRS facility, while flows less than 18 mgd will be treated through conventional secondary treatment.The Little Miami River, to which Sycamore Creek discharges, is recognized as an environmentally sensitive stream. The Little Miami River is also designated as a State and National Resource Water for Primary Contact Recreation. MSD wants to develop a permitting strategy that is both technically defensible and recognizes stakeholders concerns. The adopted strategy must demonstrate to Ohio EPA and the interested public through the NPDES permitting process and Anti-Degradation review that the use of CEHRS technology coupled with the addition of conventional treatment technology will reduce the pollutant load entering the Little Miami River, thus improving water quality.