Business, Government Legal News from throughout WVEPA examining Marcellus drilling in southwestern Pa.

EPA spokeswoman Bonnie Smith tells the Pittsburgh Post-Gazette that the agency began investigations in late September.

"The EPA is assessing the findings of our air, water and hazardous waste investigations in Washington County," said Smith, an EPA spokeswoman in Philadelphia. The agency will not disclose the names of the facility or facilities where testing has been done until the investigation is complete, which will take several more months.

Washington County, just south of Pittsburgh, is a hotbed of Marcellus Shale gas development. It has more wells and compressor stations — which pump natural gas through pipelines — than any other county in the region.

The hydraulic fracturing drilling technique involves the high-pressure injection of mixture of water, sand and chemicals deep underground to free the trapped gas. And emissions of air pollutants by compressor stations — including nitrogen oxides, sulfur dioxide, airborne particulates and carbon monoxide — have the potential to adversely affect air quality, the newspaper reports.

Federal investigations that assess air, water and land impacts are not common in Pennsylvania or other states that enforce their own environmental laws. But they are a long-standing part of the EPA "tool box," Smith said. The investigations can target single facilities, multiple facilities or environmental problems in a given area.

Katy Gresh, a Pennsylvania DEP spokeswoman, declined to comment on the EPA probe or say if the state is participating in it.

Range Resources, which owns the vast majority of the wells in Washington County, and MarkWest Energy Partners, which owns most of the compressor stations, did not immediately respond to requests for comment.