Under the Clean Water Act, cities must address the release of untreated wastewater through combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs). In 2002, the Cincinnati sewerage district reached agreement on a Clean Water Act consent decree with the Department of Justice, EPA, and the state of Ohio. A Final Amended Consent Order was approved by the Court in 2010. The sewer district has launched a $1.45 billion Phase 1 Capital Program to comply with its USEPA/Department of Justice Order.
The largest SSO in the Metropolitan Sewer District of Greater Cincinnati is SSO 700, located in Sharonville. SSO 700 serves as a primary collection system relief during storm events. A 30-million-gallon-per-day (MGD) pilot treatment facility was installed in 2006 to evaluate high-rate treatment of this SSO’s discharge for use throughout the sewer district’s system.
The existing pilot plant passes wastewater through three 1.2-million-gallon (4,500-cubic-meter) storage tanks and a high-rate ballasted flocculation and UV treatment facility before the water is discharged into Mill Creek. However, SSO 700 overflow rates exceed the treatment/storage capacity during heavy rains and wastewater backs up from the combined sewer system downstream and overflows at SSO 700.
Recent engineering assessments developed a $230 million plan to manage SSO 700 flows, based upon construction of larger treatment systems. Hamilton County’s concern about the increased program costs, along with other stakeholders concerns about the project’s local impacts, became the basis for further strategic planning.
Since 2010, Mott MacDonald has provided technical analysis, program management, value engineering, and construction management assistance to Hamilton County. These oversight services address capital and operations activities, focusing on the Capital Program. The County’s Director of Utility Oversight — Dave Meyer, PE — advanced our concept of integrated watershed management with the County Commissioners and the USEPA as an alternative to the focused Treatment Facilities Plan.
The Hamilton County Board of Commissioners endorsed resolutions that directed the development of Integrated Watershed Management Plans to manage SSO 700’s overflow. The Integrated Watershed Management approach will consider green infrastructure and watershed strategies in addition to traditional structural solutions to mitigate pollution sources at the lowest possible cost and with the greatest water-quality benefits. Mott MacDonald is now assisting the County implement this plan, including stakeholder communications, technical assessments, and program reviews.
Compared to the previous plan, the IWM approach to the SSO 700 Basin plans is expected to save more than $100 million and achieve greater overflow volume reduction and in-stream water quality.
In addition, these solutions will enable the locally affected communities to address directly related stormwater issues. This Integrated Watershed Management approach has received USEPA’s approval, as well as the written and verbal endorsement of the local Sierra Club, a long-term advocate of SSO 700 abatement.