Federal prosecutors today charged a Massey superintendent with conspiring to impede the Mine Safety and Health Administration enforcement efforts at the Upper Big Branch (UBB) mine, which was the site of an April 2010 blast that killed 29 miners.

Carl May of Bloomingrose, West Virginia is the third and most senior mine supervisor to be charged in the disaster. May was the mine's Superintendent at the time of the explosion.

An Information filed by United States Attorney Booth Goodwin alleges that May conspired to defraud the United States by impeding MSHA in carrying out its lawful functions, a felony violation of 18 U.S.C. § 371. The offense charged in the Information carries a potential penalty of up to five years' imprisonment.

May is charged with giving advance notice of MSHA inspections, "knowing and intending that the persons receiving this advance notice would conceal and cover up violations of mine health and safety laws that otherwise would result in citations and orders issued by MSHA." May allegedly used code phrases to give this advance notice of inspections, in order to conceal from MSHA the fact that such advance notice was being given.

Upon learning of impending MSHA inspections, May allgedly concealed or aided in the concealment of violations of mine health and safety laws that otherwise would result in citations and orders issued by MSHA. One violation: upon learning that an MSHA inspection was about to take place in a certain area of UBB, May allegedly altered 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.

The Justice Department document says that when a legally mandated methane monitor on a continuous mining machine at the mine stopped operating properly -- which caused the continuous mining machine to be automatically deactivated as required by law -- May ordered the electrical wiring in the methane monitor to be altered to defeat the legally mandated automatic shut-off mechanism, allowing the continuous mining machine to be operated for several hours without a functioning methane monitor.

He is also accused of falsifying examination record books at UBB.

"Mine safety and health laws were routinely violated at UBB, in part because of a belief that that following those laws would decrease coal production," notes the charging document.

Goodwin said the investigation into the tragedy remains ongoing, although he called today's charge against May "a significant step."

The Federal Bureau of Investigation and the United States Department of Labor's Office of Inspector General are handling the investigation.