Respondent owns a Utilities Plant that maintains the support of steam, refrigeration, compressed air, cooling and process water; wastewater treatment, electricity, and natural gas for a chemical manufacturing complex. The Utilities Plant includes methanol storage and ammonia storage tank operations and distribution systems. Respondent produces, processes, stores, or handles up to a maximum of 51,180,000 pounds of ammonia (anhydrous) at the Facility. Ammonia (anhydrous) is identified at 40 C.F .R. Part 68.130 as a toxic regulated substance with a threshold quantity of 10,000 pounds. On Tuesday, June 16, 2015, the Utilities Plant experienced a high level alarm for the ammonia vapor return line at its ammonia field trap. Utilities Operations staff began responding to the high level alarm by transferring an oil and ammonia mixture from the field trap into totes. The scrubber system was also employed to capture ammonia vapors from the totes. Respondent reported the release of 387 pounds of anhydrous ammonia from the Utilities Plant to the surrounding ambient air. Respondent identified after the incident that excess ammonia liquid accumulated in the field trap, in part, because of limited pump capacity for the ammonia field trap. The associated pump was undersized for the unanticipated upset condition that occurred.