Approval and Promulgation of Implementation Plans for Arizona; Maricopa County PM-10 Nonattainment Area; Serious Area Plan for Attainment of the 24-Hour and Annual PM-10 Standards

EPA is taking final action under the Clean Air Act (CAA) to approve the Best Available Control Measure (BACM) and the Most Stringent Measure (MSM) demonstrations in the serious area particulate matter (PM-10) plan for the Maricopa County portion of the metropolitan Phoenix (Arizona) nonattainment area (Maricopa County area). EPA is also confirming that it appropriately granted Arizona's request to extend the attainment deadline from 2001 to 2006. EPA originally approved these demonstrations and granted the extension request on July 25, 2002. Thereafter EPA's action was challenged in the U.S. Court of Appeals for the Ninth Circuit. In response to the Court's remand, EPA reassessed the BACM demonstration for the significant source categories of on-road motor vehicles and nonroad engines and equipment exhaust, specifically regarding whether or not California Air Resources Board (CARB) diesel is a BACM and/or MSM. As a result of this reassessment, EPA in 2006 again approved the BACM and MSM demonstrations in the plan and granted the request for an attainment date extension. In light of its 2007 finding that the Maricopa County area failed to attain the 24- hour PM-10 National Ambient Air Quality Standard (NAAQS) by December 31, 2006, EPA has again reassessed the BACM and MSM demonstrations and is again approving these demonstrations.