On August 04, 1997, the U.S. Environmental Protection Agency (EPA) approved the Arizona Department of Environmental Quality's (ADEQ) 1997 plan, known as the "microscale plan" affecting particulate matter sources in the Maricopa County Serious PM10 Nonattainment Area, which includes the Salt River monitoring site (62 FR 41856). In 2002, the U.S. EPA found Arizona's plan inadequate to achieve attainment of the 24-hour National Ambient Air Quality Standards (NAAQS) for PM10 in the Salt River monitoring site area, noting exceedances of the 24-hour PM10 NAAQS in the Salt River area after May 1998, the date by which the plan was supposed to yield attainment of the standard (67 FR 44369 , July 02, 2002).
In response to the U.S. EPA's request for revision of ADEQ's 1997 plan to enhance PM10 controls in the Salt River monitoring area, ADEQ, coordinating with Maricopa County Environmental Services Department (MCESD), U.S. EPA, and others, completed compiling data in the area in 2002, and throughout 2003, analyzed the data and researched appropriate controls. In January 2004, ADEQ submitted preliminary plan revisions to the U.S. EPA to meet U.S. EPA's February 02, 2004, submission deadline. Because all necessary plan commitments and required rulemaking processes had not been completed at that point, ADEQ has continued, since February 2004, to make necessary refinements to emissions inventory and modeling; hold workshops to inform stakeholders, the public, and state, county, and local jurisdictions concerning PM10 control measures needed and to work with them to develop control measure commitments; to participate in Maricopa County rule revision processes; and to gather data on progress toward implementation of prior plan control measures.
On August 02, 2004, ADEQ submitted the most recent plan revision, the Revised PM10 State Implementation Plan for the Salt River Area, to the U.S. EPA. This document replaces the February 2004 submission. The objectives of the Salt River plan are to meet the U.S. EPA requirements to implement adequate control measures by February 02, 2005, and demonstrate attainment of the 24-hour federal standard for PM10 pollution by December 31, 2006, in the Salt River Study Area. In addition, U.S. EPA requires that control measures applied to significant sources of PM10 emissions in the Salt River Study Area be applied to similar sources throughout the Maricopa County Serious PM10 Nonattainment Area.
This latest revision to the Salt River PM10 SIP provides additional details on the effectiveness of control measures and the revisions of Maricopa County Rules 310, 310.01, and 316 that were committed to in the PM10 SIP revision submitted to the U.S. EPA in August 2004. A Public Hearing to receive comments on the this revision was held July 25, 2005.