This action resolves alleged violations of 40 CFR Part 60, Subpart UUU. The ACO requires Cristal to submit initial notifications, conduct initial performance testing, begin conducting daily visible emission readings, record and maintain records, submit semi-annual reports to EPA, and apply for modifications to its existing permits to incorporate the ACO requirements. This action establishes requirements which will help EPA assure Cristal maintains continuous compliance with Subpart UUU.