(CNN) -- The Upper Big Branch coal mine, where 29 people were killed in a blast two years ago Thursday, will be permanently sealed by the summer.
Crews will seal with concrete the portals that allow entry to the mine, plug boreholes and cap mine fan shafts, said the mine's new owners Alpha Natural Resources.
"Though two years have passed, everyone still has vivid memories of the tragedy and the suffering the miners' families endured," said company Chief Executive Officer Kevin Crutchfield. "For all of us in the mining industry, it is a solemn reminder of why we must always put safety first in everything we do at work and at home."
The explosion at the West Virginia mine on April 5, 2010, was the deadliest U.S. mine disaster since 1972, when 91 men died in a fire at the Sunshine Mine in Kellogg, Idaho.
In a December report,the Mine Safety and Health Administration found a methane ignition that set off flammable coal dust was the immediate cause of the 2010 explosion.
But it also blamed the "unlawful policies and practices" of then-mine owner Massey Energy Co., which it said "promoted and enforced a workplace culture that valued production over safety."
Alpha Natural Resources bought Massey in 2011 and has agreed to a $209 million settlement to avoid prosecution. The deal includes payments of $1.5 million to each family that lost a member in the blast.
In March, Gary May, who was in charge of ensuring the safety of miners at the coal mine, pleaded guilty to charges that he helped conceal hazardous conditions from federal inspectors.
May is the highest-ranking Massey executive charged in connection with the explosion.
In court, May admitted to tipping off mine managers that inspectors from the federal Mine Safety and Health Administration were on their way, allowing them to clean up hazards like poor airflow and piles of loose coal that would have led to citations and fines.
He also admitted to falsifying safety records and telling miners to rewire a device that monitored flammable methane gas levels, allowing mine equipment to run illegally, prosecutors said.
Massey kept two sets of books to mislead federal inspectors and its own workers about hazards in the mine, and had twice as many accidents as it reported to regulators, the December MSHA report concluded.
The company failed to conduct adequate inspections, intimidated workers to prevent them from reporting violations and tipped off crews to surprise inspections, the report found.
An earlier state investigation found the mine lacked adequate ventilation; water sprays on equipment were not properly maintained and failed to function as they should have; and the mining company didn't meet federal and state safety standards for the application of rock dust, a crucial tool in keeping highly volatile coal dust from exploding.
Massey Energy -- whose former CEO, Don Blankenship, was an outspoken critic of federal regulators -- disputed that report, saying the blast probably occurred when natural gas flooded into the mine.
MSHA said that investigators considered that explanation but that it didn't fit the facts.