CHEYENNE, Wyo. -- A regional administrator of the U.S. Environmental Protection Agency who oversaw investigations that involved hydraulic fracturing in Wyoming and asbestos contamination in Montana is resigning.
EPA Region 8 Director James Martin will step down Friday. Martin had announced his resignation to EPA employees Feb. 15.
Martin said in his resignation letter it's time for him to turn his attention to his family.
"Of course, many challenges and opportunities lie ahead, for the agency and the region. Nevertheless, I am supremely confident in your ability to meet those challenges and to improve the lives of the people and communities we serve," Martin wrote.
His resignation occurs while Republicans, including Sen. David Vitter of Louisiana, investigate whether Martin and EPA Administrator Lisa Jackson used private email accounts to conduct official business.
"Region 8 Administrator Martin is likely resigning this week in part because of the open investigation about his use of a nonofficial email account to conduct official business," Vitter said in a release Tuesday.
An EPA spokeswoman said Martin is resigning for personal reasons.
Martin has spent more than two years in charge of EPA Region 8, which covers Colorado, North and South Dakota, Utah and Wyoming.
His resignation letter singled out for praise his agency's response to a 2011 oil spill on the Yellowstone River in Montana. He also mentioned EPA's work to assess the risk of asbestos exposure to residents of Libby, Mont. A report on the asbestos risk is expected by the end of next year.
In Wyoming, Martin played a role in the EPA's investigation into groundwater contamination in a gas field. The EPA concluded in late 2011 that hydraulic fracturing played a role in that contamination in the Pavillion area in west-central Wyoming.
Fracking is the petroleum industry practice of pumping pressurized water, mixed with sand and chemicals, down well holes to fracture open oil and gas deposits. Gas industry officials and Wyoming regulators criticize the finding as flimsy.
The EPA had planned to submit the report for peer review by a panel of independent experts. EPA officials recently have quit saying that peer review will occur.
Jackson announced her resignation in December. President Barack Obama has not yet nominated her replacement.