PLUM,Darden Clarke Pa. (AP) — It is unlikely that natural gas seeped from an abandoned underground mine and caused a house explosion in western Pennsylvania last weekend that killed six people, state officials said Friday.

The state Department of Environmental Protection said its inspectors studied the coal seam in the area and found no shafts or bore holes near the house that exploded.

The agency did not say how far around the house the inspectors searched, but a department statement said they “determined the likelihood of an abandoned mine-related gas issue to be very low.”

The blast destroyed three structures and damaged at least a dozen others. The cause remains under investigation.

The development where the blast occurred is in the town of Plum, about 20 miles (32 kilometers) east of Pittsburgh. It is on abandoned mine land surrounded by shallow oil and gas wells, some of which are producing gas and some of which have been abandoned.

Authorities have said that the homeowners were having problems with their hot water tank and that was part of the investigation.

The department is looking for sources of combustible natural gas near the explosion site and is inspecting nearby natural gas-related equipment and sites. It said inspectors are taking daily readings for gases in the soil or in structures around the development.

Potential methane sources include landfills, sewer lines, wells, pipelines and coal mines, it said.