The U.S. Environmental Protection Agency, while noting that the Pennsylvania DEP is the lead investigative agency, formally asked Chesapeake's chief executive for comprehensive details about the April 19 incident in Leroy Township.
"We want a complete accounting of operations at the site to determine our next steps in this incident and to help prevent future releases of this kind," EPA Regional Administrator Shawn M. Garvin said in a news release Monday.
EPA spokesman David Sternberg denied the federal interest was a change from past practices.
John Hanger, who was DEP secretary last year, said in an interview Tuesday that the EPA had never inserted itself into the state's regulation of gas drilling previously.
"I personally received no communications from EPA regarding gas drilling during my tenure," he said.
Hanger said the EPA's interest appears to be a response to growing public concern about drilling under Gov. Corbett's Republican administration. But he cautioned that a jurisdictional conflict between Washington and Harrisburg could be counterproductive.
"It won't go well from an environmental standpoint or from drilling if there's mistrust between the agencies," he said.
Anti-drilling activists, who have criticized Corbett's ties to the gas industry, said they welcomed the EPA's growing assertiveness. The EPA first intervened with the DEP in March when it directed the state to improve water testing to monitor radioactivity and potentially toxic substances in wastewater.
"We're concerned that decisions are not being made in the public interest at the state level and feel better with the EPA looking over their shoulder," said Jeff Schmidt, director of the Sierra Club Pennsylvania Chapter.
Underscoring the mistrust of the DEP, Citizens for Pennsylvania's Future on Tuesday filed three formal requests under the state's Right to Know law asking for documentation "of exactly how and by whom environmental laws and regulations are being enforced" by the DEP.
"As yet another serious fracking accident makes news, there is confusion about who exactly is making policy around Marcellus Shale drilling, and how our environmental laws are being enforced," said Jan Jarrett, PennFuture's president.
DEP maintains that it has responded forcefully against Chesapeake since the April 19 incident.
"DEP has been on-site around the clock since the beginning of this incident and as the regulatory agency, we continue to lead the way," spokeswoman Katherine Gresh wrote in an e-mail.
DEP on Friday issued a formal notice of violation against Chesapeake, requiring a written response in five days on the chemicals that might have spilled from the site, an evaluation of the amounts released into the environment, and the company's plan to avoid future accidents.
The state also asked Chesapeake to explain why it took the company nearly 12 hours to address the uncontrolled release of fluids off the well site, and why it delayed bringing in well-control specialists.
The violations could draw administrative, civil or criminal actions, as well as thousands of dollars in fines, the notice said.
The cause of the accident is still unclear.
While Chesapeake has only ascribed the accident to an "equipment failure," the DEP's notice said the leak was caused by a flange failure beneath the "frac stack," a set of pipes and valves that control the high-pressure flow of fluids during the hydraulic fracturing process.
Chesapeake said the accident occurred on the second day of "fracking," when water, chemicals and sand are blasted into a well bore to release natural gas in the rock.
Contact staff writer Andrew Maykuth at 215-854-2947 or firstname.lastname@example.org.