Wastewater overflowed into Lake Wingra during last weekend’s flooding, officials say

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Photo courtesy of Brad Bellisle. Floodwaters remain at the UW Arboretum the morning after heavy rainfall. Photo courtesy of Brad Bellisle.

An overflow of diluted wastewater went into Lake Wingra during last weekend’s flooding, Madison Metropolitan Sewerage District officials said.

A crew conducting inspections after heavy precipitation fell over the weekend documented a manhole on Madison’s near west side that produced the overflow, according to a release.

The cover of a manhole in the UW-Madison Arboretum southwest of Arbor Drive was tilted slightly, and crews found evidence of the flow exiting the manhole, including bent grass and debris extending to the elevated shoreline of the lake, about 30 feet away, officials said.

Crews estimate less than 50,000 gallons of wastewater reached Lake Wingra.

Officials said with some areas of the city receiving 6 inches of rain, flooded streets and basements were common, and the intense rainfall and surrounding street elevations compared to Monroe Street contributed to the high water in the area of the overflow.

“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,” officials said in the release.

Officials 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 diluted level of the discharge and high volume of surface water entering from other sources, officials said.

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