Combined Sewer Overflow (CSO) Facilities 7 Mile CSO Basin Puritan-Fenkell CSO Basin Hubbell-Southfield CSO Basin DWSD recently placed three CSO basins in operation. The basins are an outgrowth of the Rouge River National Wet Weather Demonstration Project, a program initiated in 1992 and made possible from the cooperation of a network of local, state, and federal agencies. One of the Project’s main areas of focus has been the elimination of sources of pollution to the Rouge and its watershed. The end goal is to restore this vast area to its former glory as a community asset. A total of 10 basins - each with a different innovative feature - are located throughout the Rouge River watershed. Three are owned, operated and maintained by DWSD. The remaining seven are operated by other communities located within the watershed. Newer communities have separate sewer systems: one to handle residential and commercial flow, and the other for storm flow. In older metropolitan areas like Detroit, all wastewater from residential, commercial and storms flows through a combined sewer system. When DWSD's Wastewater Treatment Plant was built in 1940, interceptor sewers through which wastewater flowed to the plant included dozens of outfalls along the Detroit and Rouge Rivers. During storm events, flow through the interceptors often exceeded capacity, making it necessary to release untreated wastewater directly into the two rivers in order to reduce the number of sewage backups into the homes of residents. The combined sewer overflow that was released contained human and household waste, in addition to high concentrations of toxic substances used in manufacturing. As the metro area’s population grew and more communities entered the system, demand on the treatment plant increased proportionately. This, in turn, increased the frequency of combined sewer overflows. A CSO Retention Basin temporarily stores wastewater flow that exceeds system capacity. The basin’s contents are released to the Wastewater Treatment Plant only after overall system flow has subsided and the plant is once again able to accept it. During its brief stay in a CSO basin, wastewater is screened and treated with a strong disinfectant. The Decanting feature incorporated into the Department’s basins comes into play on those occasions when basin capacity is exceeded by successive storm flows. A portion of the basin’s contents are released into the river, but only after the wastewater has been subjected to prolonged settling, screening and adequate disinfection procedures. Each of DWSD’s three award-winning basins also uses First Flush and Tipping Bucket technology. First flush refers to the control of wastewater flow that occurs during the first stages of a new storm event. This early runoff is more toxic than that produced during a storm’s later stages due to the washing effect of runoff on pollutants that have accumulated on the land. Tipping Bucket technology is used to remove solids remaining in the basin after a storm event. Large reservoirs above the basin’s floor release water that allows pumps to move the mixture along to the Wastewater Treatment Plant for processing. Because they are demonstration projects - containing unique design features and functions - each basin has been required to undergo a 24-month evaluation period - scheduled to conclude on November 1, 2001 - to determine the effectiveness and suitability of its design for use in other areas of the country. back to Faciliites
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