Report to Congress: Combined Sewer Overflows to the Lake Michigan Basin


Courtesy of US EPA - Environmental Protection Agency

The U.S. Environmental Protection Agency (EPA) is transmitting this Report to Congress on combined sewer overflows (CSOs) in the Lake Michigan basin. CSOs can occur in combined sewer systems (CSSs), which are defined as collection systems that carry both wastewater and storm water in the same pipe. A CSO is defined as “the discharge from a CSS at a point prior to the publicly-owned treatment works (POTW) treatment plant.” Points in the collection system at which CSOs occur are called CSO discharge points. Some CSOs discharge infrequently, while others discharge every time it rains. Overflow frequency and duration varies from system to system and from outfall to outfall within a single CSS. Because CSOs contain untreated wastewater and storm water, they contribute microbial pathogens and other pollutants to surface waters. CSOs can impact the environment and human health. Specifically, CSOs can cause or contribute to water quality impairments, beach closures, contamination of drinking water supplies, and other environmental and human health problems.

This report presents EPA’s most recent assessment of the occurrences of CSOs in the Lake Michigan basin, the enforcement of existing regulations concerning such discharges, and the future steps EPA plans to take to minimize such overflows.

Why is EPA Preparing this Report to Congress?

The Committee is concerned about the occurrences of combined sewage overflow from wastewater treatment facilities into Lake Michigan. The committee is also concerned that existing regulations concerning such discharges are not sufficiently enforced so as to prevent negative impacts on the Lake Michigan ecosystem. The committee directs the EPA to report, by September 30, 2005, outlining what future steps it plans to take to minimize such overflows.

What Methodology did EPA Use for this Report to Congress?

The basic study approach for this report was to collect data and report on CSO implementation and enforcement activities in the Lake Michigan basin, which includes parts of Indiana, Michigan, Wisconsin, and Illinois. This approach principally entailed the review of existing state, EPA headquarters, and EPA Region 5 permit and enforcement files, as well as other federal and state databases. This report is centered on a summarization, presentation, and description of existing state and EPA information on CSOs in the Lake Michigan basin.

Data presented in this report were collected from previously published or previously available state, regional, and local data sources (for example, data on overflows into Lake Michigan in Illinois were taken from the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) website at p/default.htm p/default.htm, while data on CSOs in Indiana were compiled from Discharge Monitoring Reports (DMRs) submitted to the Indiana Department of Environmental Management (IDEM) by each CSO community as part of these communities’ National Pollutant Discharge Elimination System (NPDES) requirements; a full discussion of the data collection methodology used in this report is provided in Chapter 3). No attempts were made to interpret data to reconcile differences in reporting methods or data collection timeframes, primarily due to the fact that there is no specific guideline in the CSO Control Policy for CSO data collection, and therefore such comparisons or reconciliation attempts might lead to misrepresentations of the original data. Therefore, readers are cautioned against attempting to draw conclusions between localities because of the differences in data sets. Yet despite the differences between the data sets, EPA believes that the data present general information that is characteristic of the extent of CSOs in the Great Lakes area.

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