Martin was a top official in the Colorado state government under former Gov. Bill Ritter (D) before coming to EPA, serving as executive director of the state's Natural Resources department.
"[It] has come time to leave public service after six wonderful but challenging years, first serving Governor Ritter and then the President and the Administrator. It is time that I turn my attention to my family, and to considering my next step in life," he told colleagues in announcing his departure from EPA.
An EPA spokeswoman told Greenwire in late January that Martin did not use the account to conduct official business.
Martin's email announcing the resignation lists several areas in which he said the region has taken strides in recent years.
"We have fundamentally changed the way in which we work with our tribal partners, in a positive way. The region's relationships with our state partners have never been better," he said.
Another portion of the message claims progress in carrying out the National Environmental Policy Act (NEPA).
"Our NEPA team has pioneered ways in which we can work with our sister federal agencies in finding ways to facilitate energy production while protecting the environment, one of the President's priorities," he said, while also lauding the agency's work in responding to Exxon's July 2011 oil spill into Montana's Yellowstone River and other initiatives.
—This post was updated at 4:04 p.m.