EVALUATION OF IN-STREAM IMPACTS OF CSO CONTROL FACILITIES

Abstract

Is the discharge from a combined sewer overflow (CSO) control facility clean enough to meet water quality standards? What in-stream impacts should be measured? How can the in-stream impacts of CSO be evaluated when there are other sources of wet weather pollution in the watershed? When is there enough data to make decisions? These are the questions being answered by the Rouge River National Wet Weather Demonstration Project in metropolitan Detroit. Nine new facilities for storing and treating CSO discharges have been constructed and placed into operation along the Rouge River since 1997. A detailed evaluation is underway to examine the performance of the facilities and the water quality impacts of their discharges. This paper focuses on the in-stream evaluation of four criteria: • The water quality standard for dissolved oxygen • The physical characteristics standard • The total residual chlorine standard • The health of the biological community (as a surrogate for toxic materials) The evaluation is being performed in the context of a number of watershed restoration efforts on the Rouge River. These other efforts include: illicit discharge elimination, storm water management, abandoned dump remediation, and habitat and recreational improvements. In the Rouge Watershed, CSO discharges are being controlled in three phases: • Phase 1 – public health protection for approximately 30 percent of the combined sewer area • Phase 2 – public health protection for the remaining combined sewer area • Phase 3 – meet water quality standards in the river (not necessarily in the whole effluent) for all combined sewer overflows The nine facilities being evaluated are part of Phase 1. The evaluation of the Phase 1 facilities will lead to the basis of design for Phase 2 and Phase 3. The answers will determine the level of additional investment required for completion of CSO control in Phase 2 and Phase 3.