WASHINGTON — The Supreme Court dealt a setback on Monday to roughly 100 Montana residents who sought to sue Atlantic Richfield Co. to help them restore property contaminated by arsenic and lead.

The source of the toxic waste was a copper smelter near Butte, Montana, which for nearly a century processed ore and released lethal chemicals into the environment, including, according to court records, as much as 62 tons of arsenic and 10 tons of lead each day.

In 1983, a few years after the smelter was shut down, the Environmental Protection Agency designated the 300 square miles surrounding the smelter a Superfund site, requiring the parties responsible for the pollution to take steps to clean it up. Atlantic Richfield, which owns the smelter, says it has spent more than $450 million to fulfill that obligation.

The landowners said more was required, and they proposed their own plans, suing the company to make it pay for them. The company responded that the EPA has to approve the additional remediation sought by the landowners.

Since the agency has not granted approval, the company argued, the Superfund law barred the suit. But the Montana Supreme Court let the case go forward.

Writing for the seven-member majority in the case, Atlantic Richfield Co. v. Christian, No. 17-1498, Chief Justice John G. Roberts Jr. said the agency must play a decisive role. The alternative, he said, was administrative chaos with the potential to create additional environmental problems.

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“Under the landowners’ interpretation,” the chief justice wrote, “property owners would be free to dig up arsenic-infected soil and build trenches to redirect lead-contaminated groundwater without even notifying E.P.A.”

Roberts added that the landowners may have other ways to seek relief.

“Atlantic Richfield remains potentially liable under state law for compensatory damages, including loss of use and enjoyment of property, diminution of value, incidental and consequential damages, and annoyance and discomfort,” he wrote. “The damages issue before the court is whether Atlantic Richfield is also liable for the landowners’ own remediation beyond that required under the act. Even then, the answer is yes — so long as the landowners first obtain E.P.A. approval for the remedial work they seek to carry out.”

In dissent, Justice Neil M. Gorsuch, joined by Justice Clarence Thomas, wrote that the decision gave far too much power to the federal government. “No one may do anything in 300 square miles of Montana, the company insists,” he wrote, “without first securing the federal government’s permission.”

The majority’s interpretation of the Superfund law, Gorsuch wrote, amounted to “paternalistic central planning” and “transforms it from a law that supplements state environmental restoration efforts into one that prohibits them.”

“Along the way,” he wrote, “it strips away ancient common law rights from innocent landowners and forces them to suffer toxic waste in their backyards, playgrounds and farms. Respectfully, that is not what the law was written to do; that is what it was written to prevent.”