Approval and Promulgation of Air Quality Implementation Plans; Arizona; Regional Haze State and Federal Implementation Plans; Reconsideration

The Environmental Protection Agency (EPA) is approving a source-specific revision to the Arizona State Implementation Plan (SIP) that establishes an alternative to best available retrofit technology (BART) for Steam Units 2 and 3 (ST2 and ST3) at Arizona Electric Power Cooperative's (AEPCO) Apache Generating Station (Apache). Under the BART Alternative, ST2 will be converted from a primarily coal-fired unit to a unit that combusts pipeline-quality natural gas, while ST3 will remain as a coal-fired unit and would be retrofitted with selective non-catalytic reduction (SNCR) control technology. The SIP revision also revises the emission limit for nitrogen oxides (NO<INF>X</INF>) applicable to Apache Steam Unit 1 (ST1), when it is operated in combined-cycle mode with Gas Turbine 1 (GT1). EPA has determined that the BART Alternative for ST2 and ST3 would provide greater reasonable progress toward natural visibility conditions than BART, in accordance with the requirements of the Clean Air Act (CAA) and EPA's Regional Haze Rule (RHR). Accordingly, we are approving all elements of the SIP revision, with the exception of a provision pertaining to affirmative defenses for malfunctions. In conjunction with this final approval, we are withdrawing those portions of the Arizona Federal Implementation Plan (FIP) that address BART for Apache.