MMSD treated 99.8% of wastewater in 2016

The Milwaukee Metropolitan Sewerage District treated 68.2 billion gallons of sewage and storm water in 2016 and fell less than 0.2% short of processing all of the wastewater that flowed into the regional system last year, officials said Thursday.

By year’s end, MMSD had treated 99.84% of all wastewater collected in its regional sewers and deep tunnel, records show.

The score is nearly 1 percentage point higher than its 2015 achievement of 98.9%, and more than 14 points higher than the U.S. Environmental Protection Agency’s goal of 85% for municipalities or regional wastewater utilities with combined sanitary and storm sewers.

Since the first full year of deep tunnel operation in 1994, the district has treated an average of 98.4% of all sewage and storm water collected, according to district records.

“I don’t know of any other community with combined sewers in the country that reaches this 98 to 99% treated on a consistent basis,” MMSD Executive Director Kevin Shafer said Thursday.

A perfect record was not possible last year after a total of 109.4 million gallons of untreated wastewater spilled into local waterways and Lake Michigan in overflows of combined sanitary and storm sewers during two heavy rain storms.

On Sept. 7 and 8, combined sewers in central Milwaukee and eastern Shorewood poured more than 109.2 million gallons of untreated wastewater into local rivers and Lake Michigan to prevent sewage backups into basements and property damage.

The sewer overflows started after the deep tunnel quickly filled to 85% of its capacity on Sept. 7 and gates connecting regional sewers to the tunnel were closed.

In 44 other storms last year, 100% of sewer overflow volumes were stored in the deep tunnel until there was capacity at the Jones Island and South Shore plants to treat the waste.

On Aug. 30, a single combined sewer near N. 35th St. and W. Congress Ave. was briefly filled at the height of an intense storm and overflowed for 7 minutes even though gates to the deep tunnel remained open. An estimated 200,000 gallons of untreated wastewater was discharged to Lincoln Creek that day.

Combined sewers are allowed to overflow up to six times a year, under a state permit.

Since 1994, combined sewers have overflowed an average of 2.3 times a year, records show. When the deep tunnel storage system was designed in the early 1980s, engineers projected combined sewer overflows would be reduced to an average of 1.4 a year.

The district’s goal is 100% treatment with no sewer overflows by 2035, Shafer said.

Apart from the 2016 overflows, MMSD discharged 35.8 million gallons of partially treated wastewater from its Jones Island sewage treatment plant to Lake Michigan over a period of 11 hours during the Sept. 7-8 storm.

During this emergency measure, the district pumped wastewater from the deep tunnel directly to the plant’s disinfection facility. The flow bypassed secondary treatment before it was disinfected to kill bacteria and discharged to the lake.