On May 30, 2014, the United States Environmental Protection Agency (EPA) approved Maricopa County’s proposed plan to meet federal air quality standards for particulate matter measuring ten microns or less (i.e., dust), known as PM-10. The approval of the plan—titled the 2012 Five Percent Plan for PM-10 in the Maricopa County Non-Attainment Area (the Five Percent Plan)—is a significant accomplishment for Arizona, Maricopa County and local businesses given Arizona’s previous inability to satisfy federal PM-10 standards since 1970.

In Maricopa County, the presence of PM-10 is primarily attributed to dust from paved and unpaved roads, construction activity, high winds, vehicle exhaust and tire wear. PM-10 can cause adverse health effects by penetrating the human respiratory tract and aggravating the cardiopulmonary system. 

EPA established a National Ambient Air Quality Standard (NAAQS) under the Clean Air Act that regulates the levels of PM-10 in the air. The current PM-10 NAAQS allows only one exceedance per year of the established PM-10 threshold: 150 ug/m3 averaged over a 24-hour period. When an area fails to meet an established NAAQS, it must develop a State Implementation Plan (SIP) to explain how it will achieve compliance. Here, Maricopa County was required to develop and receive EPA approval for its proposed SIP that described emissions limits, control measures and emission source inventories that demonstrate that the applicable standard is attainable. 

The approved Five Percent Plan is a significant step for Arizona, Maricopa County and the regulated community, particularly given EPA’s partial disapproval of Maricopa County’s previously proposed 2007 SIP. Because of EPA’s acceptance of the Five Percent Plan, Maricopa County can avoid the implementation of a Federal Implementation Plan, which would impose significant additional emission reduction requirements on local businesses. Further, EPA’s acceptance of the Five Percent Plan assures the continued flow of federal highway funds to the state.   

A critical aspect of EPA’s approval of the Five Percent Plan was the agency’s concurrence that 25 exceedances of daily PM-10 thresholds—attributable to uncontrollable area dust storms that frequently occur during Arizona’s monsoon season—constituted “Exceptional Events” rather than violations of the NAAQS. These Exceptional Event demonstrations were the first in the nation to be approved under EPA’s newly revised Exceptional Event policy.

As recently approved, the Five Percent Plan describes the various control measures for attaining the PM-10 NAAQS as well as demonstrating annual five percent reductions in PM-10 emissions. These measures include state and county regulations governing PM-10 emissions, such as the recently implemented dust action general permit. This dust action general permit identifies a series of best management practices businesses may have to implement on days with a high risk of dust generation. 

Many of the Five Percent Plan’s PM-10 control measures have been in effect for several years prior to EPA’s recent approval. Regardless, Arizona businesses should consider ensuring their operations comply with state and local PM-10 regulations implemented as part of the approved Five Percent Plan.