Water quality before and after deep tunnel operation in Milwaukee, Wisconsin

The mitigative effects of the deep tunnel for temporary storage of storm wa ter and sewage, on the water qualify of the Milwaukee. Menomonee, and Kinni ckinnic Rivers are investigated. The analysis is based on data from the Mil waukee Metropolitan Sewerage Districts overflow and surface-watts quality m onitoring program. Statistical analysis of water quality parameters (BOD, p hosphorus, suspended solid. fecal coliform counts, zinc, and chloride) in t he three rivers indicates that Menomonee River benefits the most from the d eep tunnel. Fecal coliform counts inside the CSO area, and to a certain ext ent BOD and zinc levels, exhibit the most significant decline after 1994 wh en the tunnel came on line. These conclusions are based on t-test compariso ns of regional averages incorporating spatial and temporal correlations fro m 1991 to 1993 and 1994 to 1997. The results from r-tests are complemented and confirmed with results from Mann-Kendall tests Tor trend. Suspended sol ids and chloride do not decrease after 1994. (C) 2001 Elsevier Science Ltd. All rights reserved.