An Integrated Approach to Water Quality Assessment in Support of a Long-Term Control Plan

The Metropolitan Sewer District of Greater Cincinnati, MSDGC, is in the process of developing a comprehensive Long-Term Control Plan, LTCP, addressing combined and sanitary (CSO and SSO) overflows. In support of this plan, an integrated suite of numerical tools was developed to facilitate comparative assessment of alternative solutions. In particular, the numerical tools provided the necessary linkages between reduced CSO and SSO loadings and in-stream water quality benefits. A review of historical monitoring information, in combination with the results of a recent monitoring program, has demonstrated that the sole pollutant of concern is E. coli. Consequently, the scope of the water quality evaluation focused on E. coli, while benefits were defined in terms of reduced risks to human health during the recreation season and increased opportunities for water based recreation. A watershed-approach was followed and benefits were assessed on scales ranging from first-order stream streams, with drainage areas of 50 square miles or less, to the Ohio River.