The D.C. Circuit Court of Appeals has remanded portions of the U.S. Environmental Protection Agency’s (EPA’s) rules under the Clean Air Act (CAA) Prevention of Significant Deterioration (PSD) program to the agency, because they violated statutory duties. Sierra Club v. EPA, No. 10-1413 (D.C. Cir. 1/22/13). Under the PSD program, to modify or construct an emission source in areas that EPA has determined are in attainment status for specific pollutants, the source must obtain a permit, after demonstrating that its emissions will not exceed a specific allowable incremental increase for the relevant pollutants. The issue before the court involved EPA’s efforts to focus monitoring requirements for ambient levels of fine particulates (PM2.5) during the pre-application process on locations that demonstrate some chance of exceeding the attainment limit.

The rule as EPA originally wrote it allowed facilities expected to have PM2.5 emissions below the “Significant Impact Level” (SIL) to skip the otherwiserequired one year of monitoring before they could apply for a permit. In effect, this created a de minimis exemption from more stringent air-monitoring requirements. EPA’s rule also exempts from the one-year monitoring requirement proposed sources in locations where the PM2.5 levels are below the “Significant Monitoring Concentration” (SMC), which was set at twice the detection level of the monitoring equipment. EPA has used the SMC concept to exempt facilities from emission monitoring for other pollutants since 1980.

The Sierra Club sued, challenging EPA’s authority to implement SILs and SMCs. Due to the possibility that a facility in an area that was just barely in attainment could avoid monitoring because its emissions were under the SIL but could still cause the area to fall out of attainment, EPA agreed that the regulation was flawed and proposed vacating it with a remand to EPA. Although the Sierra Club argued that EPA lacked any authority to promulgate SIL under any potential revision to the rule, the court declined to rule on that issue. Similarly, the court left in place EPA’s SILs under the PSD program, because that regulatory language did not present the possibility of foreclosing the monitoring needed to assess compliance with the law.

The court rejected EPA’s argument that any challenge to its authority to incorporate an SMC into the regulations should have occurred after it first enacted SMCs in 1980. Saying it had not decided the issue before, the court assessed EPA’s authority to incorporate an emission exemption based on an SMC for PM2.5 and ruled that the statute so clearly required ambient air monitoring before applying for a permit that EPA had no room to assert implicit authority to exempt de minimis conditions from the statutory requirements. The court therefore vacated EPA’s SMC for PM2.5.