On March 20, 2017, the Environmental Protection Agency (EPA) issued further delay of effective date for the EPA's Guideline on Air Quality Models (Guideline). The purpose of the delay is to allow recently-appointed government officials an opportunity to perform an initial review of the Guideline and determine whether an additional, substantive review of the Guideline is required. Note that while the new effective date for the Guideline is currently established as May 22, 2017, should officials choose to perform a substantive review, the effective date may be further delayed.
EPA's Guideline on Air Quality Models provides direction to EPA, states, tribes, and industry with regards to conducting air dispersion modeling and is a legally binding regulation. The Guideline was updated for the first time since November 2005, finalized on December 20, 2016, and published in the Federal Register (FR) on January 17, 2017.
The further delay of effective date is not subject to public comment. The documentation of further delay, as published in the FR Volume 82, Number 52 is available here.