The grandfather clause in the proposed PM2.5 standards is going to get another look-see before the rule goes into effect, the EPA announced Monday in the Federal Register.

The agency provided notice that through a letter signed on April 24, 2009, the EPA has granted a petition for reconsideration dated Feb. 10, 2009, submitted by Earthjustice on behalf of the National Resources Defense Council (NRDC) and the Sierra Club, with respect to the final rule titled, Implementation of the New Source Review (NSR) Program for Particulate Matter Less Than 2.5 Micrometers (PM_2.5), published on May 16, 2008. Effective June 1, 2009, 40 CFR 52.21(i)(1)(xi) is stayed for a period of three months, until Sept. 1, 2009.

In addition, the EPA has administratively stayed one of the provisions to which the petitioners objected – a "grandfathering" provision for PM2.5 contained in the federal prevention of significant deterioration (PSD) program. The EPA said it will publish notification in the Federal Register establishing a comment period and opportunity for a public hearing for the reconsideration proceeding.