WASHINGTON (Reuters) - The U.S. Interior Department has been unable to adequately explain why it canceled a $1 million study on the public health impacts of mountaintop removal coal mining, the agency’s inspector general office said in a report released on Tuesday.

FILE PHOTO: U.S. Secretary of the Interior Ryan Zinke testifies in front of the Senate Committee on Energy and Natural Resources on Capitol Hill in Washington, U.S. March 13, 2018. REUTERS/Eric Thayer

Interior Secretary Ryan Zinke canceled the government-funded study on the health impacts of the controversial mining technique used in Appalachia last August as part of what officials said was an agency-wide review of grants in excess of $100,000. The study was by the National Academies of Sciences, Engineering, and Medicine.

Mountaintop removal is a form of surface mining in which explosives are used to extract coal from mountaintops and ridgelines. It has raised concern about impacts on rivers and streams, and on human health in surrounding communities.

When the Interior Department was asked by the inspector general to detail the reasons for its decision to cancel the study, it could not produce any evidence of a formal review, the watchdog said in its report.

“Departmental officials were unable to provide specific criteria used for their determination whether to allow or cease certain grants and cooperative agreements,” the report said. It added the cancellation “wasted” some $455,110 that had already been spent on research and that the remaining $548,443 would be returned to the Treasury in 2021.

Interior Department spokeswoman Heather Swift defended the decision, saying the coal study was “duplicative” and was drawing money away from more important efforts “like rebuilding public lands infrastructure and securing public lands along the U.S.-Mexico border.”

“It may not sound like a lot of money to House Democrats who continually look for ways to spend us into obliteration,” she told Reuters in an email.

The Obama administration had launched the study shortly before leaving office.

The inspector general probe was triggered by a request from U.S. Representative Raul Grijalva, the top Democrat on the House Natural Resources Committee, who has accused the Interior Department of lying and mishandling taxpayer money.

A report this week by magazine Pacific Standard showed that Katharine MacGregor, deputy assistant secretary for land and minerals management at Interior, was pushing for the study to be suspended after meetings with coal industry groups, according to public records it obtained.

Efforts to reach MacGregor were not successful.

The National Mining Association called the NAS report “unnecessary” and said existing literature on mountaintop mining shows it poses no public health hazards.