MADISON, WIS. – A Madison Metropolitan Sewerage District crew conducting inspections in the wake of heavy precipitation during the weekend of June 16-17 late Wednesday documented a manhole on Madison’s near west side that produced an overflow of diluted wastewater into Lake Wingra.
The manhole, in the UW–Madison Arboretum southwest of Arbor Drive, had its cover tilted slightly and evidence of flow exiting the manhole included bent grass and debris extending to the elevated shoreline of the lake approximately 30 feet away. Observations in the area during the time of the storm indicated a period of peak flow lasting less than two hours, resulting in an estimate of less than 50,000 gallons of wastewater that reached Lake Wingra.
With some areas of the city and surrounding areas receiving approximately 6 inches of rain from the storm in the early morning hours of June 16, flooded streets and basements were commonplace. The intense rainfall and surrounding street elevations compared to Monroe Street contributed to the high water in the area. Unlike street inlet grates that empty into storm sewers, basement floor drains empty into the sanitary sewer system and during street flooding, additional stormwater enters the sanitary sewer system through small openings around manholes.
District staff members have notified the Wisconsin Department of Natural Resources and Public Health Madison and Dane County. No measurable impacts to surface water quality or human health are expected due to the dilute nature of the discharge and high volume of surface water entering from other sources.