On July 13, 2021, the Director of the Enforcement and Compliance Assurance Division of EPA-Region III issued an administrative compliance order (ACO) under the federal Clean Air Act to Magnesita Refractories Company (Magnesita) to address Magnesita?s violations of requirements to have continuous opacity monitoring systems (COMS) installed, maintained, calibrated, and operated at two lime kilns and their associated coolers at Magnesita?s York, Pennsylvania lime manufacturing plant. The COMS are required by 40 CFR Part 63, Subpart AAAAA, the national emission standards for hazardous air pollutants for lime manufacturing plants. The ACO requires Magnesita to achieve and demonstrate full compliance with the requirements as expeditiously as practicable but no later than 180 calendar days from the effective date of the ACO. EPA-Region III consulted with the Pennsylvania Department of Environmental Protection (PADEP) prior to issuing the ACO and PADEP supported its issuance.