MADISON, Wis. (WMDX) – Officials with the Madison Metropolitan Sewerage District say that around 34,000 gallons of wastewater flowed into Lake Mendota last week after a sewer line broke open. 

Eric Dundee, Principal Engineer with the MMSD, says that workers were performing routine maintenance on the pipe when a valve broke, spilling a total of around 45,000 gallons of wastewater. Sewerage officials were able to capture around 11,000 gallons and put it back into the sewer system.

The incident happened on a pipe around Universities and Bakers Avenue Thursday. Some wastewater did make its way into the basements of two nearby homes. MMSD is working with the owners of those homes to help address any damage done by the flooding. Dundee says that the break lasted around five to six hours. 

34,000 gallons is about the amount of two to three in-ground swimming pools, and Dundee says that amount won’t have a significant impact on the health of Lake Mendota. As soon as the break occurred, MMSD contacted both the state Department of Natural Resources and the city-county health department to make sure that the area was safe for both people and wildlife. 

Along with pathogens making their way into the water, Dundee says one of the biggest concerns with a wastewater spill of this kind is the creation of an algae bloom. “Luckily, it’s not the middle of summer,” Dundee says. “So there was not a lot of growth in that.”

Dundee says that the rain that came the next day also helped to dilute the wastewater, and kept it from pooling in just one place.  

While MMSD says they always aim for zero breaks, breaks like the one last Thursday do occur, usually after heavy rains. Dundee says that last year, they had three breaks throughout their entire system. In 2022, MMSD had zero breaks. 

Amanda Wegner, Communications and Public Affairs Director with MMSD, says that a combination of aging pipes, and people sending things down the drain that they shouldn’t, are the main culprit in line breaks. 

“Some parts of (our) system are over 100 years old,” Wegner says. “Not only here in the Madison area, but across the nation, we’re dealing with aging infrastructure, and challenges of just things that people choose to put down the toilet and sink that they shouldn’t, all those things… we try to keep the system flowing and moving, preventative maintenance… It really does take everyone in making smart choices in what they put down their drain to prevent blockages and stoppages in the system so we can keep it flowing like it needs to be.”