Board of County Commissioners of Weld County, Colorado v. EPA

Under the Clean Air Act (CAA), the Environmental Protection Agency (EPA) (defendant) regulated ozone levels using a three-step scheme. First, the EPA periodically established National Ambient Air Quality Standards (NAAQS). Second, the EPA divided the country into geographic areas and gave each area an attainment or nonattainment designation. An area was nonattaining if its own atmospheric concentration of pollutants exceeded the NAAQS or if it contributed to a nearby area’s nonattainment. Third, states were required to adopt state implementation plans (SIPs) specifying how their areas would achieve or maintain attainment status. A nonattainment designation triggered more stringent SIP requirements, with the requirements becoming more burdensome the worse the nonattainment status. Also, the CAA imposed statutory deadlines for achieving attainment status. For marginal nonattainment areas, the deadline was three years. Failure to meet the deadline triggered reclassification as a worse nonattainment status and exposed a state to financial and regulatory consequences. In August 2018, the EPA designated El Paso County, Texas (El Paso) as an attainment area. However, the District of Columbia Circuit subsequently deemed that designation arbitrary and remanded it to the EPA for reconsideration. In November 2021, the EPA issued a final rule with a revised designation. Finding that El Paso contributed to neighboring Doña Ana County’s nonattainment, the EPA folded El Paso into the Doña Ana area, which had received a marginal nonattainment designation in August 2018. The EPA declined to assign a new attainment date to El Paso when issuing the revised designation. El Paso was therefore subject to Doña Ana’s three-year attainment deadline, which had expired in August 2021, three months before El Paso was folded into the Doña Ana area. Texas (plaintiff) sued the EPA, seeking a declaration that the EPA’s 2021 nonattainment designation was impermissibly retroactive.