The EPA has proposed to disapprove part of the most recent air quality plan revisions for Maricopa County, Arizona, the so-called "Five Percent Plan." If the disapproval goes into effect, the state will be at risk for sanctions under the Clean Air Act (CAA), including restrictions on federal highway funding, unless deficiencies are corrected to the EPA's satisfaction within two years.

The Maricopa County area, which includes metropolitan Phoenix, has been considered by the EPA to be in "nonattainment" for coarse particulate matter (PM-10) since 1996. In 2007, after falling into "serious nonattainment," the State of Arizona submitted a plan to reduce PM-10 by five percent each year until the applicable National Ambient Air Quality Standard (NAAQS) was attained. The EPA's decision this month to propose disapproval of part of the Five Percent Plan is largely a result of two significant problems with the plan in the EPA's view. First, the EPA says that the state relied on an inadequate inventory of emissions sources, with too heavy a focus on the construction industry to the exclusion of other sources. Second, the EPA disapproved a request by the Arizona Department of Environmental Quality (ADEQ) to treat as "exceptional events" four exceedances of the PM-10 NAAQS at a monitoring station in southwestern Phoenix. ADEQ had concluded that these exceedances, measured at the West 43rd Ave. monitoring station, were caused by dust storms rather than human activity, and as such, should not count against Maricopa County's goal of having no more than three violations of the PM-10 NAAQS during the period from 2008 to 2010. The EPA, in a May 2010 decision that we blogged about here, disagreed with the ADEQ's "exceptional events" determination, thereby dooming the state’s efforts to achieve attainment by 2010.

The CAA's "sanctions clock" will begin to run against the State of Arizona when the EPA's proposed disapproval becomes effective. The proposal was published in the Federal Register Sept. 9, 2010, triggering a thirty-day comment period, and the EPA expects to make a final decision in early January 2011. Under the CAA and its implementing regulations, if a state has not come into attainment or revised its plan to the EPA's satisfaction within 18 months of plan disapproval, the EPA is required to apply the "offset sanction," under which new and modified stationary sources are subject to a 2-to-1 emissions offset, meaning that they must reduce emissions from other sources equal to twice the amount they project to emit. Six months later, at the two-year mark, the state will be at risk for highway funding restrictions if deficiencies remain uncorrected, although the EPA's press release states that transportation projects scheduled from 2011 to 2014 would not be affected.