On January 22, 2013, a panel of the DC Circuit vacated EPA's recently promulgated Significant Impact Levels (SILs) and Significant Monitoring Concentrations (SMCs) for PM2.5. These screening tools are designed to allow for a streamlined New Source Review analysis for projects with the potential to cause only a de minimis increase in ambient air concentrations, exempting them from the cumulative modeling and preconstruction monitoring requirements that would otherwise be required under the Clean Air Act. These tools can be essential to obtaining a PSD permit within a reasonable time to achieve business objectives. As a result, the DC Circuit Court decision, and EPA's revisions to the PM2.5 requirements on remand, will have significant ramifications on future PSD permitting.
In the case before the DC Circuit, Sierra Club v. EPA, the Sierra Club challenged EPA's authority to promulgate SILs and SMCs for PM2.5. EPA itself agreed that the language it had used for the SILs went farther than it had intended and joined in Sierra Club's request for vacatur and remand. EPA argued that its SMCs for PM2.5, however, should be preserved under its general authority to exempt de minimis projects from the comprehensive monitoring and modeling requirements of the Clean Air Act. The court vacated both the SILs and the SMCs, finding that EPA had not provided for adequate state discretion in implementing the SILs, and that EPA had overstepped its authority with respect to the SMCs. In doing so, the court acknowledged that EPA held general authority to create de minimis exceptions to statutory requirements, but found that the particular statutory provisions at issue were so "extraordinarily rigid" as to foreclose the breadth of the exceptions created by EPA. The court read the Clean Air Act to require continuous preconstruction ambient monitoring sufficient to perform a “complete and adequate analysis” of the pre-project ambient conditions to enable a determination as to whether the PSD project will result in a violation of the NAAQS. The court left open for further review the extent to which EPA could provide for streamlined monitoring, but determined that EPA could not categorically exempt projects that fell below a specified level from all monitoring obligations.
While this decision is specific to PM2.5, the analysis could be applied to challenge the way that SILs and SMCs are used for other pollutants in areas that do not have local ambient air quality monitoring for the PSD pollutants implicated by a major modification or a new source. As a result, it will be important for any facility considering future modifications that may trigger New Source Review to stay informed of the developing case law on EPA's authority to streamline the permitting process. In the meantime, states will continue to be able to apply state-specific SILs, provided they can demonstrate with monitoring data that there is adequate headroom under the NAAQS to accommodate them. States can also continue to look to EPA’s SO2, NO2, and PM10 SILs as guidance in formulating these state-specific standards.