Respondent owns a combined-cycle cogeneration power plant facility. From approximately 1991 to December 2013, the Facility was operated as a combined-cycle cogeneration power plant. Beginning in April 2012, the Facility halted full-time operations and began operating one or two days per year in order to conduct ISO-New England capability tests; however, the ammonia refrigeration system at the Facility remained intact and continued to contain ammonia. According to Respondent, during the curtailed operations time period before and after the inspection, the ammonia was stored in the chiller building and not distributed throughout the full system. The associated piping and valves were drained and not in service. On August 8, 2013, EPA performed an inspection to assess Respondent’s compliance with Section 112(r) of the CAA. At the time of the Inspection, the Facility was a building or structure from which an accidental release may occur and was therefore a “stationary source,” as defined at Section 112(r)(2)(C) of the CAA, 42 U.S.C. § 7412(r)(2)(C), and 40 C.F.R. § 68.3. At the time of the Inspection, Respondent used anhydrous ammonia in a refrigeration process (“the Process”), as defined by 40 C.F.R. § 68.3.