Now that it's clear the State of Washington has made its recommendation to include the bulk of the metro area into a Wapato Hills-Puyallup Valley Non-attainment Area for PM2.5, the questions are what will EPA decide to do and by when?
EPA is required (Section 107(d)(1)) of the Clean Air Act to notify states no later than 120 days prior to the signature date for designations if it will modify the states recommendations. Signature on final designations is due by December 18, 2008. Therefore if the Agency (Administrator) modifies designation recommendations, it will send letters to those states where it intends to modify in July of 2008.
States will then have an opportunity to explain why they think EPA's modification is not appropriate (has been by letter, informally in the past). EPA is saying it will not be publishing a proposed notice and soliciting comments. The administrator's signature will be on its final action.
EPA will publish a final rule soon after the Administrator's signature (expect in January 2009 or late December 2008 depending on when the designations are signed). That rule will be effective 90 days later, likely in March 2009.