Authorities have resumed investigation into the cause of a fatal house explosion in Columbia Falls earlier this month.

Standing in a steady drizzle Thursday, representatives from NorthWestern Energy, the Columbia Falls Fire Department and multiple insurance companies watched as an excavator removed debris from the foundation of the home at 1206 Second Ave. W.

According to NorthWestern Energy spokeswoman Claudia Rapkoch, authorities hypothesize gas migrated into the home, found an ignition point and exploded May 6 while NorthWestern Energy employees were repairing an underground service line that had been damaged earlier that day by Flathead Electric Cooperative.

The blast killed veteran NorthWestern Energy worker Jim Hilton, 53, of Kalispell.

It is still unclear what ignited the gas and how the gas entered the home belonging to Ted and Myrtle Langton, since the ruptured service line served the home behind the house that exploded.

The purpose of the investigation, said Rapkoch, is to “determine factually how that

happened” by examining the makeup of the soil and trying to determine the particular path the gas followed through onsite testing and evacuating the pipes, then sending the soil and pipes to a lab for testing.

Rapkoch called the process that resumed Thursday “very much a scientific forensics investigation.”

She said authorities waited until Thursday to resume investigation due to scheduling conflicts with all of the interested parties because everyone had to be available to observe at the same time.

Rapkoch speculated it will be a couple of months before the investigation is concluded.

The area around the site, including a portion of 12th Street West, has been fenced and secured during the investigation. All of the neighbors can reach their houses off the portions of the street that will remain open.

Residents of 11 nearby houses that were evacuated are now back in their homes.