In August 2005, a dispersion modeling analysis showed that Mirant's Potomac River Generating Station (PRGS) was causing or contributing to significant exceedances of the NAAQS. EPA sent a Notice of Violation citing Mirant's failute to immediately shut down the PRGS. EPA approved State Implementation Plan and theefore federally enforceable. EPA negotiated an Administrative Complaince Order. this Order was signed on June 1, 2006