State inspectors sweeping the Plum subdivision where a massive house explosion last weekend killed six people have detected low levels of combustible gas in the vicinity of the blast. They are awaiting test results to identify the vapor and determine its source.

The mere presence of such gas does not necessarily indicate it was involved in the colossal detonation, which obliterated a house in the Rustic Ridge neighborhood and destroyed two other homes, according to Lauren Camarda, a spokeswoman for the state Department of Environmental Protection’s southwest region.

“It shouldn’t be a signal to anyone that there’s a suspicion of something,” Camarda said Friday.

In the aftermath of the blast, Gov. Josh Shapiro ordered the agency to launch an investigation into what are called “stray” gases such as methane, which could seep from various points underground, including sewers, landfills and active or abandoned oil and gas wells.

The DEP will determine what type of stray gas is present in Rustic Ridge, and then, if relevant, whether any infrastructure under its jurisdiction played a role in the explosion.

“Our emergency response team, geologists and members of the Oil and Gas District Operations will continue to have boots on the ground in the days ahead, as we exhaust every relevant resource in our scope of jurisdiction,” DEP Secretary Rich Negrin said in a statement.

Similarly, the independent state Public Utility Commission, which regulates utilities — including Peoples natural gas company, which provides service to the borough — has kicked off its own probe, sending pipeline safety engineers to Plum.

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The utility said it continues to monitor the area for the presence of natural gas. But the company Friday again refused to divulge whether it had received reports of natural gas odors in Plum’s Rustic Ridge neighborhood in the days before the explosion.

Inspectors wielding handheld gas detectors have been at the site of the blast all week, capturing samples from the soil and buildings in the neighborhood and sending them to a private lab for expedited testing.

Different gases have different telltale signatures that can help inspectors determine their source — a sewer, for instance, as opposed to the type of gas that might be in a distribution line going to a home.

The agency expects to get the results next week, Camarda said.

“It doesn’t give you an exact pinpoint source,” she said. “It can help us rule things out.”

Camarda did not have details about how many samples were taken or from where.

She said the combustible gas that was detected was not enough to merit a warning to residents.

“We have found just enough to take a sample,” Camarda said. “That’s showing there’s a presence. But it does not indicate a level that there is a concern.”

The DEP’s inspectors have examined the oil and gas wells closest to Rustic Ridge and are in contact with the companies that own and operate them and their pipelines. They have begun inspecting abandoned and historic wells in the area.

Inspectors have effectively ruled out one area of concern as a possible source of natural gas: abandoned mines.

But the Allegheny County Fire Marshal’s Office said this week that part of its investigation involved reports of a problematic hot water tank in the house that exploded at 141 Rustic Ridge Drive.

The house was owned by Paul and Heather Oravitz, who both were killed. The four other victims were all in the Oravitz home at the time of the blast.

They were Michael Thomas, the borough’s manager; Kevin Sebunia; and Casey Clontz and his 12-year-old son, Keegan.

A county spokeswoman could not be immediately reached to verify whether investigators continue to pursue information about the hot water tank.

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