Approval and Promulgation of Air Quality Implementation Plans; State of Colorado; Second Ten-Year PM10

The Environmental Protection Agency (EPA) is proposing to approve State Implementation Plan (SIP) revisions submitted by the State of Colorado. On May 13, 2013, the Governor of Colorado's designee submitted to the EPA a revised maintenance plan for the Lamar area for the National Ambient Air Quality Standards (NAAQS) for particulate matter with an aerodynamic diameter less than or equal to 10 microns (PM 10 ). EPA is proposing to approve the revised maintenance plan with the exception of one aspect of the plan's contingency measures.