363 million gallons of wastewater untreated

More than 363 million gallons of untreated wastewater — a mix of sewage and stormwater — spilled into local rivers and Lake Michigan after heavy rains June 18 and 19, the Milwaukee Metropolitan Sewerage District said in a report to state environmental officials.

The deep tunnel quickly filled to 74% of capacity within one hour June 18 at the start of a series of storms that dropped more than 4 inches of rain on the city's north side in two days, MMSD water quality protection director Sharon Mertens said in the report.

After the tunnel was closed at 3:50 p.m. June 18, an estimated 360 million gallons of wastewater overflowed from combined sanitary and storm sewers to the local waterways.

MMSD started the overflows to relieve the sewers and reduce the risk of sewage backing up into basements, officials said. Overflows ended before 4 a.m. June 20.

An estimated 3.7 million gallons of untreated wastewater was pumped out of a separate sanitary sewer near North 35th Street and West Roosevelt Drive over three hours June 18 to prevent basement backups in the neighborhood. The overflow volume was directed into a city storm sewer that drained to Lincoln Creek, the MMSD report said.

MMSD also used an emergency storm measure at its Jones Island sewage treatment plant to free up space in the deep tunnel during the storms.

Plant operators pumped 112 million gallons of wastewater from the tunnel directly to the disinfection facility at the end of the treatment process over a 33hour period from 4 p.m. June 18 to 1 a.m. June 20, the report said.