MMSD discharged 230M gallons recently
Milwaukee residents saw a record-setting rain event last week for February, dumping more than 2 inches of rain over the course of 24 hours.
The previous single-day record for the month was 1.81 inches set on Feb. 21, 1913.
The rain caused flooding in some places and led to 230 million gallons of wastewater being discharged into local water bodies before heading into Lake Michigan, according to the Milwaukee Metropolitan Sewerage District.
The overflow lasted a total of 44.5 hours from Feb. 27 to March 1.
The Milwaukee, Menomonee and Kinnickinnic Rivers were all potentially impacted during that time.
While overflows have been known to occur this time of year, the area is seeing more heavy rainfall events, said Bill Graffin, the public information office for the sewerage district.
And when one inch of rain falls on the sewerage district’s service area, which includes the city and many suburbs, that’s the equivalent of 7.1 billion gallons of water entering the combined sewer system. The city uses a combined system that includes storm sewers and sewage from homes and businesses.
The sewerage district is working on projects that restore habitat along waterways and create more green infrastructure that helps soak up more rainfall. But when there is too much rain, there is nowhere for it to go when it falls on impervious surfaces, like concrete, before it runs into a storm sewer.
And this rainfall hit icy, frozen ground.
So, when more water is flowing into the treatment plants than can be processed, the sewerage district can allow overflows to prevent sewage backups and flooding in homes and businesses.
By federal law, the sewerage district is allowed six overflows per year, or they must capture and clean 85% of the total rainfall over the course of that year. The district has averaged 98.5% since 1994.
Last year, there was only one overflow. It occurred after nearly five inches of rain fell over the course of 24 hours, which made it the sixth biggest rain event in Milwaukee since the late 1800s. That overflow released 756 million gallons into nearby waterways.
Largely the overflows are made up of groundwater and water from storm sewers, but there is a chance of bacteria flowing into waterbodies that receive the releases then into Lake Michigan. But because the conditions are so harsh in Lake Michigan, the bacteria usually only survive three to 10 days, according to Graffin.
For more information about the overflow, visit www.mmsd.com.