SAMPLING OF WET SANITARY COLLECTION SYSTEMS: HOW IT COMPARES TO CSO

Within Southeastern Michigan, the regulations for controlling excess flows from wet sanitary collection systems are very different as compared to control of flows from combined collection systems. Communities with wet separated collection systems are facing the future construction of facilities to retain all flow generated from a 25-year, 24-hour design storm. Retention of flows from combined systems is at a significantly smaller design storm, and discharge of treated effluent from treatment facilities is allowable. The purpose of this project was to characterize the pollutant quality of flows within wet sanitary collection systems during wet weather and to compare the observed pollutant quality to previously observed data from combined collection systems. This information may be useful to further the discussion with the regulatory agency on selection of a smaller design storm criteria for sizing facilities to control wet weather induced sanitary sewer overflows (SSOs) or wet sanitary sewer excess flows (flows in excess of a community's purchase capacity, which may not result in an SSO). The selection of the design storm criteria can have a significant impact on the size and cost of required facilities to control excess flows within wet sanitary collection systems.