Michigan v. EPA
United States Court of Appeals for the District of Columbia Circuit
213 F.3d 663 (2000)
Under the Clean Air Act, states must adopt state implementation plans (SIPs) ensuring in-state pollution sources do not significantly contribute to another state's failure to meet national air-quality standards. Based on extensive scientific and empirical analysis, the EPA (defendant) identified 23 states as significant contributors of nitrogen oxide emissions drifting downwind and required those states to revise their SIPs using a budget approach requiring 'highly cost-effective controls' to reduce ozone-forming emissions. Michigan and 21 other states, along with industry groups and others (plaintiffs), challenged the EPA's approach, arguing the agency's 'contribute significantly' determination improperly factored in cost and that the mandate intruded on states' authority to design their own SIPs.
Whether the EPA may revise state implementation plans to require highly cost-effective controls on nitrogen oxide emissions that contribute significantly to another state's failure to meet air-quality standards.