© Carle KennedyAuthorities are blocking off areas of a Burnsville neighborhood near River Hills Drive and Hwy. 13 East, after residents reported there seemed to be some type of underground explosion around 1 p.m. Friday.
Authorities are still seeking the cause behind increased carbon monoxide levels that caused the explosion, sending three manhole covers flying into the air.

Apple Valley firefighters on Friday responded to an apparent underground explosion in a Burnsville neighborhood of which authorities still were still seeking the cause on Friday night.

Nobody was hurt in the blast that shook a neighborhood in northeast Burnsville on Friday afternoon, but at least 100 residents were evacuated from the neighborhood near River Hills Drive and Hwy 13 East after an underground sewer line erupted, sending three manhole covers flying between eight and 12 feet in the air.

"Those manholes weigh 100 pounds a piece," said Fire Marshal Lee LaTourelle. "That's a lot of force."

The source of the blast remains unknown. LaTourelle said many residents complained of a distinct smell of gasoline shortly before and after the explosion. On arrival, emergency workers found high levels of carbon monoxide in the sewer lines - up to 1,000 to 1,200 parts per million.

"That's really explosive," LaTourelle said. "We still don't know quite what happened."

LaTourelle said it was possible that somewhere in the system an incomplete combustion produced the onslaught of CO.

When asked if the explosion could be the result of intentional tampering, LaTourelle said, "Your guess is as good as mine. We've seen people pour oil or gas down the sewer before, but there were no signs that that had occurred in the immediate area."

By 8 p.m. CO levels had fallen within the normal range. Officials announced that they were flushing the system, a process that would take several hours.

In the meantime, residents waited in the basement of River Hills United Methodist Church until it was safe to return home.

Duane Harves and his wife were home at the time of the explosion. Harves said he was working in the basement when he heard four distinct booms.

"It rattled the whole house," he said.

Across Hwy 13, resident Ina Kusic was startled by an inexplicable roar.

"I heard a loud noise and at first I thought it was a car accident," she said. "Then I heard all the fire trucks coming down the road. I never expected this."

Residents Joanne Mieling and Michael Mieling said they had only minutes to leave their home on Hayes Drive in the River Hills neighborhood earlier Friday.

"A fireman came to the door and said there had been a chemical spill," Michael Mieling said. "It didn't register in the air, but it had gotten into the sewers."

The fireman told them there had already been a couple of explosions.

Lee Hillis said he was on his way home from the grocery store and was stopped from going to his house on Ridgewood Court. He met up with his wife, Sandy Hillis, when she came home from work.

"Everything was blocked off," she said. "One woman told me it was a gas leak."

Both couples decided to wait it out a Perkins along I-35W.

Officers from the Incident Command Center in Eagan, the Minnesota Collapsed Structure Rescue Team, Dakota County Special Operations and fire departments from Burnsville, Apple Valley, Rosemount, Lakeville, Inver Grove Heights, Eagan and Hastings responded to the scene.

LaTourelle said the City of Burnsville would provide a full explanation as soon as the investigation concluded.