The Ninth Circuit ruled on requirements for standing under the National Environmental Policy Act (NEPA)[1] in a case concerning an exchange of public land in the Las Vegas Valley. In 1996, the Bureau of Land Management (BLM) entered into a non-binding agreement with Del Webb, a private developer, regarding an exchange of 4,975 acres of federal land for private land considered by the agency to be environmentally sensitive. Del Webb planned to build 11,200 homes on the land it received from BLM. In compliance with NEPA, the BLM prepared an environmental assessment (EA). The EA acknowledged that the Las Vegas Valley was a nonattainment area under the Clean Air Act (CAA)[2] for carbon monoxide and particulate matter, and the EA included estimates of the additional emissions the Del Webb development would generate. Based on the EA, BLM returned a finding of no significant impact (FONSI), allowing the land exchange to go forward.

Hall filed suit in federal district court alleging that BLM failed to comply with NEPA and that the exchange would violate the conformity provision of the CAA.[3] BLM moved for summary judgment. In response to BLM's motion, Hall submitted an affidavit averring that he resided in the Las Vegas Valley, that since moving to the area he had developed a persistent cough due to dust and air pollution, that previous BLM land exchanges and private development had resulted in increased emissions, and that he regularly traveled throughout areas of the valley that had registered unsafe levels of air pollution. Because land exchanges are exempted from conformity challenges by EPA regulation,[4] the district court dismissed the CAA claim for lack of jurisdiction. Nationally applicable regulations can be challenged only in the Court of Appeals for the District of Columbia.[5] The district court dismissed Hall's NEPA claim for lack of standing because Hall failed to provide specific facts linking his respiratory ailment to the land to be exchanged. Hall appealed both claims.

On review, the Ninth Circuit concluded that Hall had standing for the following reasons. First, "evidence of a credible threat to the plaintiff's physical well-being from airborne pollutants falls well within the range of injuries to cognizable interests that may confer standing."[6] Second, because the rights Hall asserted under NEPA were procedural rights, the court's inquiry into the imminence of threatened harm was "less demanding."[7] Hall did not have to show that further study and analysis by the government would have resulted in a different conclusion. Third, with regard to the causation issue, the court found that Hall needed only to establish the reasonable probability that the challenged action would threaten his concrete interest, a degree of certainty less than that required to succeed on the merits of a tort claim. Finally, Hall's claim did not rely on conjecture about the behavior of other parties or on conjecture about whether Del Webb's actions would worsen pollutant levels in the valley. For these reasons, in light of his affidavit, Hall's claim that he would be affected negatively by the land exchange was reasonable.

The Ninth Circuit reversed the district court in part, holding that Hall had standing for his NEPA claim, and affirmed in part, holding that the district court lacked subject matter jurisdiction over the CAA claim.