After an underground explosion sent manhole covers flying on University of Minnesota campus streets Thursday afternoon, the Metropolitan Council is reminding people that it's a really bad idea release flammable materials into the sewer system.
"It is a stark reminder that the only thing that should go down the sewer besides human waste is toilet paper," the Met Council said Friday. "We are warning residents, businesses, and industries not to put gas or other flammable materials down the sewer."
Thursday's explosion and corresponding fire happened led numerous blocks being evacuated around 3 p.m. Thursday. Residence hall along 17th Ave. near the University Ave. intersection was the scene of a fire, while the evacuation area stretched between 15th Ave. and Oak St. and 4th St. and Pillsbury Dr.
While working to extinguish a fire in the basement of the residence hall, fire crews were informed of the underground sewer explosion that had blown manhole covers off the streets in the area, possibly all the way down to 10th Ave.
According to the Met Council, an environmental services team is attempting to figure out the cause of the explosion and the preliminary answer is "believed to be a release of gasoline into the sanitary sewer system."
It's unclear how gasoline was released into the sewer, but investigators are trying to find out if it was flushed down a toilet or released through a sink drain or floor drain.
"There was a release into the sewer system and we don’t yet know how or where," Met Council spokesperson Bonnie Kollodge told Bring Me The News. "Businesses and industrial users also release into the sewer system so those options have to be explored."
The Met Council says a regional sewer merges with a city sewer in the area and flows into the Metropolitan Wastewater Treatment Plant in Saint Paul. The city sewer system is 15-20 feet underground, while the regional sanitary sewer intercepter pipe is about 70 feet down.
An all-clear was given around 9 p.m. Thursday, with residents in the area allowed to return to their homes. However, anyone who suspects a gas odor should still call 911.