The Environmental Protection Agency (EPA) is promulgating a source-specific Federal Implementation Plan (FIP) to regulate emissions from the Navajo Generating Station (NGS), a coal-fired power plant located on the Navajo Indian Reservation near Page, Arizona. EPA proposed the NGS FIP on September 12, 2006, to establish federally enforceable limitations for TSP, SO<INF>2</INF>, and opacity, and control measures for dust. The limits had previously been established in the Arizona SIP. EPA promulgated the Tribal Authority Rule in 1998, clarifying that state air quality regulations generally did not apply to facilities on Indian reservations and that EPA should fill the regulatory gap as necessary or appropriate. This action fills the regulatory gap for the NGS facility.