Congress enacted CERLA to address “the serious environmental and health risks posed by industrial pollution.” The Act seeks “to promote the timely cleanup of hazardous waste sites and to ensure that the costs of such cleanup efforts [are] borne by those responsible for the contamination.” The EPA may clean those sites itself or compel responsible parties to perform the cleanup. If the Government performs the cleanup, it may recover its costs from responsible parties. §9607(a)(4)(A). Responsible parties are jointly and severally liable for the full cost of the cleanup but may seek contributions from other responsible parties. §9613(f)(1). The EPA conducts a remedial investigation and feasibility study to assess the contamination and evaluate cleanup options. Section 122(e)(6) of the Act provides that, once the study begins, “no potentially responsible party may undertake any remedial action” at the site without EPA approval. 42 U. S. C. §9622(e)(6). It requires “substantial and meaningful involvement by each State in initiation, development, and selection” of cleanup actions in that State. §9621(f)(1). And, in most instances, it requires that remedial action complies with “legally applicable or relevant and appropriate” requirements of state environmental law. §9621(d)(2)(A). To insulate cleanup plans from collateral attack, §113(b) of the Act provides federal district courts with “exclusive original jurisdiction over all controversies arising under” the Act, and §113(h) then strips such courts of jurisdiction “to review any challenges to removal or remedial action,” except in five limited circumstances. §§9613(b), (h). The Anaconda Copper Smelter contaminated an area of over 300 square miles with arsenic and lead. The Environmental Protection Agency has worked with the current owner, D, to implement a cleanup plan under CERLA. In the 35 years the EPA has managed an extensive cleanup at the site, working with Atlantic Richfield to remediate more than 800 residential and commercial properties; remove 10 million cubic yards of tailings, mine waste, and contaminated soil; cap in place 500 million cubic yards of waste over 5,000 acres; and reclaim 12,500 acres of land. As of 2015, EPA’s plan anticipated cleanup of more than 1,000 additional residential yards, revegetation of 7,000 acres of uplands, removal of several waste areas, and closure of contaminated stream banks and railroad beds. The EPA projects that the cleanup will continue through 2025. Ps, a group of 98 landowners sued D in Montana state court for common law nuisance, trespass, and strict liability. Ps sought restoration damages, which under Montana law must be spent on rehabilitation of the property. Ps’ proposed restoration plan includes measures beyond those the agency found necessary to protect human health and the environment. In Montana law, property damages are generally measured by the “difference between the value of the property before and after the injury or the diminution in value.” If the damaged property serves as a private residence and the plaintiff has an interest in having the property restored, diminution in value will not return the plaintiff to the same position as before the tort. The plaintiff may seek restoration damages, even if they exceed the property’s diminution in value. Restoration damages can be recovered if the plaintiff has “reasons personal” for restoring the property and that his injury is temporary and abatable, meaning “[t]he ability to repair [the] injury must be more than a theoretical possibility.” The award must be used for restoration. Ps want a soil contamination level of 15 parts per million of arsenic, rather than the 250 parts per million level set by EPA. Ps seek to excavate offending soil within residential yards to a depth of two feet rather than EPA’s chosen depth of one. Ps seek to capture and treat shallow groundwater through an 8,000-foot long, 15-foot deep, and 3-foot wide underground permeable barrier, a plan the agency rejected as costly and unnecessary to secure safe drinking water. Ps cleanup would cost D $50 to $58 million. The court granted judgment for Ps on D's summary judgment motion and allowed the lawsuit to continue. The Montana Supreme Court affirmed. The Montana Supreme Court rejected D’s argument that §113 stripped the Montana courts of jurisdiction over the landowners’ claim for restoration damages. The Montana Supreme Court reasoned that the landowners’ plan was not such a challenge because it would not “stop, delay, or change the work EPA is doing.” The Montana Supreme Court also rejected D’s argument that the landowners were potentially responsible parties (PRPs) prohibited from taking remedial action without EPA approval under §122(e)(6) of the Act. It reasoned that the statute of limitations for a claim against the landowners had run and Ps could no longer be considered PRPs. D appealed.