With ERG support, EPA, the Pennsylvania Department of Environmental Protection, and the U.S. Department of Justice recently reached a settlement with MarkWest, a midstream oil and gas company, over its alleged Clean Air Act and state-level violations. ERG helped EPA investigate MarkWest facilities in eastern Ohio and western Pennsylvania since 2015. MarkWest is alleged to have failed to apply for, and comply with, required permits and/or recordkeeping requirements for activities that resulted in vented volatile organic compound emissions, which may produce adverse health effects and contribute to ground level ozone formation. ERG conducted field testing and laboratory analyses, worker and public health risk assessments, engineering evaluations, and economic benefit modeling. The settlement will advance the latest technological approaches to minimizing air pollutant emissions at midstream oil and gas facilities and require MarkWest to implement multiple supplemental environmental projects.