Stormwater rivals combined sewer overflows as major pollution source in Lake Michigan
Ann Arbor, MI — In the past decades, we have reduced sewage discharges into Great Lakes waterways. However, urban development also has increased stormwater entering the Great Lakes from impervious surfaces, such as parking lots and buildings. Older areas of Milwaukee, Chicago, Detroit, Toledo, and Cleveland still have combined sewer systems that collect sanitary sewage from houses and buildings in the same pipe as stormwater runoff, with both going to the wastewater treatment plant. During large storm events, excess overflow of untreated sewage and stormwater the goes directly into waterways. This research study compared the impact of stormwater with combined sewage overflows.
Sewage is known to carry harmful bacteria, but the amount of fecal pollution in stormwater is relatively unknown. This contamination is measured according to EPA recommended limits of the fecal bacteria indicator Escherichia coli (E. coli). This study measured levels of E. coli in Milwaukee, Wisconsin, which has three major tributaries that discharge into Lake Michigan.
"We found that stormwater had very high levels of E. coli, 100 to 500 times higher than water quality standards," says Sandra McLellan, an Assistant Scientist at the University of Wisconsin-Milwaukee. The sources of this pollution remain under investigation, but may include pet waste, wildlife, leaking sewer pipes, or cross connections of sanitary pipes into the stormwater system. This work shows that pollution enters the lake every time it rains and in order to improve water quality, both combined sewer overflows and stormwater discharges need to be addressed.
Increasing public awareness about the negative impacts of stormwater also may prompt citizens to examine their own property to find ways to reduce runoff. Disconnecting downspouts, creating rain gardens to retain runoff, and minimizing fertilizer usage are just a few steps people can take to help reduce pollution entering the Great Lakes.
Original Publication Information
Results of this study, "Distribution and Fate of Escherichia coli in Lake Michigan Following Contamination with Urban Stormwater and Combined Sewer Overflows," are reported by Sandra L. McLellan, Erika J. Hollis, Morgan M. Depas, Meredith Van Dyke, Josh Harris and Caitlin O. Scope in the latest issue (Volume 33, No. 3, pp. 566-580) of the Journal of Great Lakes Research, published by the International Association for Great Lakes Research, 2007.
Contacts
For more information about the study, contact Sandra McLellan, Great Lakes WATER Institute, University of Wisconsin-Milwaukee, Milwaukee, WI 53204, mclellan@uwm.edu, (414) 382-1700.
For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; editor@iaglr.org; (608) 692-1076.
Links
Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.
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