ELR Citation: 43 ELR 20019
No(s). 10-1413 (D.C. Cir. Jan 22, 2013)

The D.C. Circuit vacated and remanded portions of an EPA rule establishing regulations for particulate matter less than 2.5 micrometers (PM2.5) under CAA §166. The rule established significant impact levels (SILs) and a significant monitoring concentration (SMC) for PM2.5, screening tools EPA uses to determine whether a new source may be exempt from certain requirements under §165 of the Act. EPA acknowledged that portions of the rule establishing SILs did not reflect its intent in promulgating the SILs. The court, therefore, granted the Agency's request to vacate and remand those portions of its PM2.5 SIL regulations. But the court also granted an environmental group's petition to vacate portions of the PM2.5 SMC regulations. CAA §165(e)(2) sets forth an "extraordinarily rigid" mandate that a PSD permit applicant undertake preconstruction monitoring. Accordingly, EPA lacks de minimis authority to promulgate an SMC for PM2.5 that can be used to exempt an owner of a proposed source or modification from undertaking the year-long preconstruction air quality monitoring requirement under §165(e)(2).