Gary May is awaiting sentencing after pleading guilty to felony conspiracy for impeding federal enforcement efforts while he was the mine superintendent at Upper Big Branch mine in West Virginia.

The 43-year-old entered his plea before Judge Irene Berger at a US district court in Beckley on Thursday.

May has been charged with conspiracy to impede the US Mine Safety and Health Administration in its enforcement efforts at the Raleigh County operation between February 2008 and April 5, 2010, the day of the blast.

Southern District of West Virginia US Attorney Booth Goodwin previously filed a one-count information with May’s charge – a felony under 18 US Code Section 371.

The US attorney said in the charge that May worked “together with others known and unknown” to “unlawfully, willfully and knowingly” conspire to impede the efforts of federal investigators by using code words to provide pre-notification of the presence of inspectors on mine property, and to conceal safety and health violations and falsify examination record books.

“It was further a part of this conspiracy that May … upon learning that an MSHA inspection was about to take place in a certain area of the mine, would and did alter, and authorize and cause the alteration of, the ventilation system of the mine to direct additional air to the area where the inspection was to take place, in order to conceal and cover up the quantity of air that normally reached that area of the mine,” he said in the February documentation.

In February 2010, just two months prior to the explosion, May ordered the alteration of the electrical wiring of a continuous miner methane monitor to override the automatic shutoff of the machine that was typically triggered by high methane levels.

“People who run coal mines have a fundamental obligation to be honest with mine regulators,” Goodwin said on Thursday.

He said: “When mine operators resort to tricks and deceit to keep government officials in the dark, our mine safety system unravels and miners are put in harm’s way. The least we can do for coal miners is protect the integrity of the laws designed to keep them safe.”

He also said the agency was pleased that May is cooperating with its investigation into the explosion and the events leading up to the event.

“We hope he can give us a better picture of what was going on at this company,” Goodwin added. 

May, who faces up to five years in prison and a $US250,000 fine, will be sentenced August 9.

The Federal Bureau of Investigation and the US Department of Labor's Office of Inspector General are handling the criminal portion of the investigation.

Massey, who was the owner of the Upper Big Branch operation at the time of the explosion, was acquired by Alpha Natural Resources in June 2010.

The operation remains closed.