MMSD Reports Overflows of More Than 170 Million Gallons

Heavy rains this week capped by the downpour Tuesday evening caused the Milwaukee Metropolitan Sewerage District to divert 170.5 million gallons of untreated combined stormwater and sanitary sewage overflow to area waterways.

The district also "blended" 26.8 million gallons of partially treated wastewater and released it to Lake Michigan.

According to MMSD's report to the Wisconsin Department of Natural Resources on  sewer overflows resulting from heavy rain on Monday and Tuesday:

Localized flooding resulted from strong storms Monday morning with about 2 inches of rain falling in less than two hours. The Deep Tunnel filled to 288 million gallons out of 521 million gallons capacity. MMSD pumped the tunnel down throughout the day and overnight, getting it to the 150-million-gallon level before several more storms hit.

Shortly after 8 p.m. Tuesday, intense rain delivered a rate of 5.5 billion gallons per day (3.8 million gallons per minute) to the Deep Tunnel system.

To reduce the risk of basement backups and reserve room in the tunnel for separate sewer flows, MMSD started a combined sewer overflow at 8:30 p.m. Tuesday. The combined sewer overflow is estimated at 170.5 million gallons.

Also, to reduce sewer overflows and reserve room in the Deep Tunnel for separate sewer flows from the suburbs and parts of Milwaukee, MMSD blended 26.8 million gallons of stormwater and wastewater at the Jones Island Water Reclamation Facility by pumping it out of the Deep Tunnel, blending it with wastewater that went through the first three stages of treatment and sending the entire flow through the disinfection process before releasing it to Lake Michigan.