3 million gallons of wastewater spilled into Lake Michigan after Jones Island power outage

Don Behm | Milwaukee Journal Sentinel

An estimated 3.17 million gallons of wastewater spilled into Lake Michigan on Saturday during a temporary power outage at the Jones Island sewage treatment plant, Milwaukee Metropolitan Sewerage District officials said Thursday.

A portion of the plant flooded during the power outage and wastewater entered a channel that diverted the flow to chlorine disinfection tanks before spilling into the lake, MMSD said in a report to the state Department of Natural Resources.

Power was out at the state's largest wastewater plant for nearly three hours Saturday, from 1:47 p.m. to 4:30 p.m., the report said. No pumps were operating during that time.

The cause of the power outage has not been determined.

At the time the main electric power feed failed, turbines that ordinarily burn landfill gas to generate a portion of the plant's power and serve as a backup in case of an emergency were not available, officials said. The turbines had been shut down for repairs.

Separately, on Monday, MMSD started overflows of combined sanitary and storm sewers to local waterways after intense rains quickly filled combined sewers and the deep tunnel. It was the third combined sewer overflow of this year.

RELATED: Combined sewers overflowed to rivers and Lake Michigan in wake of Monday's heavy rains

The overflows began at 11:30 p.m. Monday as an emergency measure to prevent sewage backups into residences and businesses. The overflows ended around 8 a.m. Tuesday.

An estimate of the overflow volume was not available Thursday.