Coal mining companies and state regulators are struggling to figure out the impact of U.S. EPA's new greenhouse gas emission rules on mines. While much of the policy debate has centered on power plants and large industrial emitters, the mining industry has been trying to understand how new regulatory systems apply to them. After all, some mines release more methane than large conventional emitters. "There's a lot of confusion right now," said Alex Bond, air quality director at the National Mining Association.