The U.S. Environmental Protection Agency (EPA) is challenging a Pennsylvania policy for measuring air emissions, including those from Marcellus Shale development.

The EPA believes that new Pennsylvania Department of Environmental Protection (DEP) guidelines for deciding whether to aggregate emissions from interconnected industrial sites runs against existing state and federal laws, Diana Esher, director of the air protection division for EPA Region 3, wrote in a comment letter on Nov. 21.

"The draft guidance appears to alter the conventional way in which aggregation determinations have been made federally and by [DEP]," Esher wrote.

Regulators considering whether to aggregate emissions from various sources must consider whether the activities come from the same industry, the same entity and are "contiguous or adjacent," a vague phrase without a firm definition on the books. In an October technical guidance, the DEP defined those words literally as "the distance or spatial relationships between locations" (see Shale Daily, Oct. 14).

"Over time, there was a tendency by some regulators to morph the meaning of 'contiguous' or 'adjacent' properties to mean only that operations on the properties be 'interdependent,'" DEP Secretary Michael Krancer said at the time, saying the expanded definition wasn't supported by case law or existing state and federal regulations.

That definition is important for the oil and gas industries, because well pads and compressor stations connected by pipelines can cover many square miles. If the emissions from aggregated facilities hit a threshold, they trigger additional regulations.

Although Krancer said each determination would continue to be "applied on a case-by-case basis," Esher said the new definition constituted a "bright line," or a set measurement standard that could overshadow the specific factors in any given case.

In making its change, the DEP pointed to the "quarter-mile rule of thumb" that states like Texas, Oklahoma and Louisiana use to measure "contiguous or adjacent."

The issue is bigger than a spat between the state and federal regulators. Under the Bush administration, the EPA attempted to simplify the aggregation process by using a "proximity" definition for "contiguous or adjacent," but the Obama administration withdrew that guidance and said decisions should be case-by-case.

The EPA and DEP have previously locked horns on shale gas development, particularly water quality and wastewater management issues (see Shale Daily, May 16; March 9).

The EPA letter is one of many comments the DEP received on the guidance. The DEP said it would address all the comments in its official response document.