STI provided litigation and technical support for the U.S. Department of Justice in legal action against the Westvaco pulp and paper mill in Maryland for violations of the Clean Air Act (CAA) due to excessive sulfur dioxide (SO2) emissions. STI supported the litigation by estimating the air quality impacts from the SO2 emissions using CMAQ modeling simulations at 12-km resolution. STI provided the modeling outputs to other expert witnesses to help quantify the health and ecosystem impacts of the emissions. In the remedy phase of the litigation, STI prepared an expert report in support of relief for Westvaco’s violations that used AERMOD and other analyses to evaluate the air quality benefits of various mitigation alternatives.