Last week, the United States Court of Appeals for the District of Columbia invalidated a rule issued by the U.S. Environmental Protection Agency that would have prevented state and locate authorities from supplementing inadequate monitoring requirements for air pollution sources under the Clean Air Act.

The 1990 Amendments to the Clean Air Act compel certain stationary sources of air pollution to obtain permits from state and local authorities that identify all emission limits for the source and also include monitoring requirements sufficient to assure compliance with the permit terms and conditions. Sometimes, the monitoring requirements set forth in the Clean Air Act itself do not assure compliance with the Clean Air Act's emissions standards. For example, some standards require daily compliance with emissions standards but only call for yearly monitoring.

EPA originally issued a guidance document, and attempted to promulgate a rule, that allowed state and local authorities to "fill the gap" left by the Clean Air Act. In other words, EPA allowed state and local governments, such as the Missouri Department of Natural Resources, to require daily emissions monitoring to assure compliance with Clean Air Act emissions standards.

Industry sued the EPA alleging that the EPA had overstepped its authority under the Clean Air Act because the Clean Air Act did not expressly provide for emissions monitoring by state and local governments. Rather than fight the litigation, EPA issued an amended rule prohibiting state and local governments from supplementing the Clean Air Act's emission standards.

As soon as the amended rule became final, the Sierra Club sued EPA, arguing that the amended rule violates the Clean Air Act on its face. The United States District Court for the District of Columbia agreed.

In a two-to-one decision, the District Court found that EPA's amended rule was contrary to the statutory directive that each Clean Air Act permit include adequate monitoring requirements. In other words, if the emissions standard required daily compliance, state and local governments must require daily monitoring in order to assure compliance with the daily emissions standard. Yearly monitoring would be inadequate and contrary to the Clean Air Act.