RECEIVING WATER QUALITY MONITORING IN SUPPORT OF LONG-TERM CSO CONTROL PLAN

In 1999, the Detroit Water and Sewerage Department (DWSD) implemented a Detroit River water quality monitoring program to establish a basis for determining the effectiveness of three pilot combined sewer overflow (CSO) facilities and to help define what other CSO controls should be undertaken as part of the Long Term CSO Control Plan. In addition to protecting public health and eliminating raw sewage, a major concern of the Michigan Department of Environmental Quality (MDEQ) was whether CSOs along the Detroit River are causing a depression of the dissolved oxygen (DO) in the river to below the state's cold water fishery standard of 7 milligrams per liter (mg/l) (MDEQ 1994).The key issues identified by the Long-Term CSO Control Plan's Water Quality Work Group (WQWG) that this paper focuses on are:The presence and extent of dissolved oxygen (DO) levels that are below the cold water fisheries standard and that can be attributed to upstream CSOs on the Detroit River.The extent of aesthetic impairments, if any, directly resulting from CSOs.The extent of other use impairments, if any, directly resulting from CSOs (recreational water contact, water supply, etc.).The ecological impacts of untreated and treated CSO discharges on aquatic communities, especially benthic macroinvertebrates.The extent of the CSO discharge plumes.Specific water quality monitoring and survey activities were developed and have been implemented to investigate these issues. The collection of water quality data began several years before construction of the first pilot CSO control facility was completed, and will continue until 2 years after the third pilot facility is completed.The monitoring performed since 1999 has shown DWSD's CSO discharges are not causing DO in the Detroit River to fall below the standard, indicating that future controls for Detroit River CSOs may not need to be designed to reduce suspended solids and biochemical oxygen demand. This could allow the use of screening and disinfection facilities instead of retention treatment basins, resulting in considerable capital, as well as O&M cost savings and using much less of the valuable shoreline property. Collecting water quality data before the construction of these pilot facilities has provided the opportunity to demonstrate whether the receiving water's baseline conditions and capacity for assimilating oxygen-demanding material require the additional capture that CSO basins provide. DWSD will need to gain the acceptance of MDEQ for future proposed levels of CSO control and treatment technologies.