WORKING TOWARDS PERMITTING CSOs in CINCINNATI

In order to satisfy the requirements of a signed Consent Decree, the Metropolitan Sewer District of Greater Cincinnati, MSD, is in the process of completing an update of their Combined Sewer Overflow long-term control plan, LTCP, scheduled for completion in late June 2005. An important challenge posed by the Consent Decree is to develop a defensible technical approach that is both acceptable to state and federal authorities and leads to permitting of all CSOs in the Cincinnati area. In order to meet this challenge, XCG Consultants Limited, the lead consultants on this project, has developed a comprehensive work plan designed to provide the technical support for the development of an appropriate strategy for permitting of area CSOs.To date, the project team has established a clear statement of baseline water quality for all significant Ohio side tributaries and the Ohio River. The development of the LTCP update and final permitting of CSOs will be completed through the month of June 2005.Assessment tools developed and applied for this project were based on US EPAs modeling tools and included:SWMM5-Kinematic Wave model for system hydrology, CSO, sanitary sewer overflows or SSOs, and non-point pollutant sources.SWMM5-Dynamic Wave model for all tributaries.Environmental Fluid Dynamics Code (EFDC) for hydrodynamic modeling of the Ohio River.Water Quality Assessment Program (WASP7) for water quality modeling of all tributaries and the Ohio River.A rigorous analysis of historical water quality, and the results of a 2004 monitoring program led to the conclusion that, relative to current water quality standards, the principal pollutant of concern is E. coli. Continuous modeling results, for existing conditions and a representative rainfall year (1970) indicated that, relative to a seasonal or a 30-day moving-window geometric mean, the Ohio River is generally in compliance with applicable E. coli water quality standards. However, daily maximum E. coli concentrations periodically exceed water quality standards during wet-weather, particularly downstream of Mill Creek. For the Ohio River tributaries investigated, Mill Creek and the Little Miami River, model results indicated that 30-day moving window geometric mean E. coli concentrations exceed applicable water quality standards during wet-weather, particularly in the lower most reaches.