A U.S. judge on May 1 halted nearly 300 oil and gas leases on a large section of federal land in Montana that had been approved by an agency of the Interior Department and ordered the agency to conduct a thorough environmental analysis of the impact of fracking on drinking water.

District Court Judge Brian Morris said in his ruling that the Bureau of Land Management (BLM) did not factor in the environmental risks to Montana's water supply before it made a blanket approval for oil and gas leasing on nearly 150,000 acres of federal land.

"BLM failed to take a hard look at groundwater impacts due to shallow fracturing and due to surface casing depth not extending past drinking water," Morris said in his opinion.

Environmental group Wildearth Guardians, the plaintiff, had sued the BLM after it issued 287 leases in two lease sales, in December 2017 and March 2018. The group argued that the BLM violated the National Environmental Protection Act by failing to properly analyze the risks posed by drilling to drinking water and the climate and examine alternatives.

Morris vacated the leases issued from the two sales, vacated the BLM's finding of "no significant impact" during its environmental assessment of the drilling area and asked the agency to conduct further study of the environmental impacts of widespread drilling.

More than a dozen small companies purchased leases during the two lease sales.

Morris said the problem with the BLM's review of the project was not its flawed analysis but "the absence of analysis."

In a statement, the BLM said it disagreed with Morris's ruling. "The BLM stands by its analysis in following the letter of the law to issue oil and gas leases in Montana."

Just last month, Morris canceled a key permit for the controversial Keystone XL pipeline, which has been ensnared in legal battles for over a decade, because he found that the U.S. Army Corps of Engineers did not adequately consider effects on endangered species in rivers the pipeline would cross.

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Environmental groups praised the decision, seeing it as a victory against the Trump administration's policy of "energy dominance" and its focus on opening up public land for fossil fuel extraction.

“We’re thankful the court has put the brakes on this reckless behavior but we know this is not the end of the attacks on public resources,” said Derf Johnson, clean water program director of the Montana Environmental Information Center.