Investigators probe for source of petroleum discharge into Mpls. sewers

A firefighter puts a manhole cover back over a hole in a street.
A half dozen buildings at the University of Minnesota have been evacuated after a sewer crew reported petroleum in a tunnel on Tuesday.
Kerem Yücel | MPR News

Twin Cities authorities say they are talking now to local industrial companies with large petroleum storage tanks in the region as they probe how petroleum ended up in Minneapolis sewers, forcing Tuesday’s evacuations on the University of Minnesota campus.

“Investigators are assessing whether the material was directly discharged” into Minneapolis sewers or lines in the connected regional system, the Metropolitan Council said in a statement Wednesday.

City and regional sewer lines near the university showed “signs of black oily liquid or odor,” the Met Council said, noting that the lines merge and carry sewage to the regional wastewater treatment plant in St. Paul.

A spokesperson for the Minnesota Department of Public Safety said test results indicate the substance was most likely diesel fuel.

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University officials ordered evacuations of six buildings Tuesday after contractors working in the sewer tunnels located around 5th and Oak streets reported their gas monitors had sounded an alarm and that they could see and smell petroleum, the Minneapolis Fire Department said.

Fire crews later flushed out the affected lines and gave the all-clear later in the afternoon.

It’s not clear if Tuesday’s discharge was tied to a fire and reports of gas leaks in the area about a month ago that forced the evacuation of several buildings on campus. The origin of those leaks remains under investigation.

Jim Smith, the state fire marshal, said Tuesday that the region’s sewer system’s complexity — some 640 miles of sanitary sewers and nine treatment plants — makes it extremely difficult to trace.

He added that authorities had reached out to local pipeline operators but they did not appear to be the source.