PSD permits issued to major emitting facilities must include BACT standards for each pollutant subject to regulation under the CAA. These standards must be determined by permitting authorities on a case-bycase basis, subject to EPA review and approval. Step 1 of the EPA’s preferred “top-down” procedure for making these determinations presents difficult interpretive issues, particularly as the Agency struggles to clarify its policy against using BACT to redefine the applicant’s facility.