INTEGRATING COLLECTION AND RECEIVING WATER QUALITY MODELS FOR CSO LONG TERM CONTROL PLANNING

The primary purpose for computer modeling is to provide information to assist agency managers to make informed and technically sound decisions. Successful Combined Sewer Overflow (CSO) control planning involves a comprehensive assessment and evaluation of many complex factors associated with collection system performance, pollutant loadings, and receiving water quality. Furthermore, CSO facility planning incorporates a more inclusive watershed management approach recognizing receiving stream use designation, stormwater and other point/non-point sources that contribute to the current state of water quality.The Metropolitan Sewer District of Greater Cincinnati (MSD) is engaged in updating their CSO Long Term Control Plan (CSO LTCP Update) in response to a Consent Decree finalized in May of 2004. The Consent Decree requires MSD to explicitly evaluate control levels of 85%, 90%, 95% and 99% control. Although MSD is required to look at prescribed levels of control they have embarked on a more expansive wet weather management program that incorporates water quality assessment supported by water quality modeling as an integral part of developing and evaluating CSO control alternatives. This paper presents the integrated modeling approach used by MSD in the development of their CSO LTCP Update plan and overall wet weather program strategy.