Milwaukee Metropolitan Sewerage District Executive Director Kevin Shafer was sitting high and dry, without a bit of bad news or drastic rain storms, for quite a while. 

“Until this June, we’d gone 22 months without an overflow,” he says

An overflow occurs when the MMSD’s Deep Tunnel — all 521 million gallons of its massive capacity — gets so filled with storm water and sewage that the system must let some of that polluted water overflow into the rivers, which eventually flow into Lake Michigan. 

Back before the Deep Tunnel was built and came on line in 1993, Milwaukee averaged 50 to 60 overflows a year. Since then the average has been just 2.3 per year.