DENVER (CN) – A federal judge on Thursday refused to block public access to a former nuclear facility that has been turned into a wildlife refuge.

Rocky Mountain Peace & Justice Center sued the U.S. Fish and Wildlife Service in May, accusing it of endangering the public by opening land contaminated by plutonium without completing an environmental impact statement that weighs the risks to public safety.

In his 18-page order, U.S. District Judge Philip Brimmer noted the last environmental review completed in 2004 did not deny that trace amounts of plutonium remained on the site. However, Fish and Wildlife said the risk from working on or visiting the refuge is low – the increased cancer risk is 1 in 1 million for a refuge worker and 6 in 10 million for visitors, based on plutonium levels of 7 picocuries per gram of soil.

The plaintiffs’ claim that no plutonium is safe plutonium did not move Brimmer.

“But plaintiffs have not, for example, shown that any of their members will be exposed to a risk that exceeds an established threshold for exposure or produces a health risk beyond the very small, but nonetheless non-zero, risk resulting from exposure to even minute quantities of radioactive materials,” Brimmer wrote. “Regulatory action often involves managing the levels of risk, and plaintiffs have not shown a basis to claim that agencies are required to eliminate every added risk of plutonium exposure or that such mitigation would even be possible.”

Although Rocky Mountain Peace & Justice Center’s request for a preliminary block on opening the refuge was denied, attorney Randall Weiner is ready to continue to argue the case in court.

“Our case will clearly demonstrate that the government does not have an up-to-date assessment of risks to the environment and human health from allowing unlimited public visits to the Refuge,” Weiner said in a statement.

With the refuge scheduled to open on Sept. 15, Weiner said his clients “hope to promptly show the court that the federal government violated the laws it was required to follow, and thus convince the judge to close the refuge soon after it opens.”

The refuge’s 18 miles of trail will connect the Rocky Mountain Arsenal National Wildlife Refuge northeast of Denver with Rocky Mountain National Park just west of Boulder.

The Rocky Mountain Flats Plant was built in 1950 to manufacture nuclear weapon triggers. For four decades, workers filled stainless steel canisters with liquid plutonium to create “plutonium pits,” the core of a nuclear weapon responsible for its detonation.

In 1978, the Rocky Flats Truth Force camped out on the train tracks supplying the plant in a call for nuclear disarmament. Then in 1989, after decades of unreported incidents, an FBI raid exposed criminal mishandling of toxic waste and the U.S. Environmental Protection Agency listed Rocky Mountain Flats as a Superfund site. The plant officially closed two years later.

In 2001, Congress passed the Rocky Flats National Wildlife Refuge Act and allocated $7.7 billion over a decade to clean up the site with plans to open it to the public. Fish and Wildlife has offered guided tours of the site since 2015.

A combined 300,000 children won’t be visiting the refuge, however, as six local school districts passed resolutions banning field trips to the site.