The Environmental Protection Agency (EPA) is proposing a source-specific federal implementation plan (FIP) requiring the Navajo Generating Station (NGS), located on the Navajo Nation, to reduce emissions of oxides of nitrogen (NO X) under the Best Available Retrofit Technology (BART) provision of the Clean Air Act (CAA or Act) in order to reduce visibility impairment resulting from NGS at 11 National Parks and Wilderness Areas. NGS, which was built over 35 years ago, is the largest coal-fired power plant in the West in terms of generating capacity. It is central to the economies of the Navajo Nation and Hopi Tribe and supplies power to the states of Arizona, Nevada, and California. Electricity produced by NGS is also used to power the Central Arizona Project, which supplies surface water to three counties and numerous Indian tribes in Arizona. NGS is projected to continue operating at least until 2044.