City officials say they have concluded their inquiry into a that shook a quiet neighborhood near River Hills Drive West in . The underground explosion rattled homes and sent manhole covers shooting up into the air, prompting the evacuation of over 100 residents.
The exact cause is still shrouded in mystery, though investigators were able to conclude that an unidentified flammable chemical entered the sewage system through the sewer drain of an existing home or business. It is believed that emanations from the chemical traveled through the sewage pipes and up through a dry basement drain in a neighboring home. Officials suspect that the flame of a gas water heater or furnace ignited the fumes, causing the explosion.
City workers have been monitoring the system, probing two miles of sewer line beneath the neighborhood with a subterranean camera. Since that time, the city has not discovered anything abnormal. It appears that the explosion was a one-time occurrence, officials said in a press release Thursday afternoon.
The Burnsville Fire Department cautioned residents to use care when disposing of household chemicals. For information regarding proper disposal go here. They also advised residents to keep all drains in their home wet. Water acts as a sealant that keeps sewer gases out.