Supplementing the greenhouse gas ("GHG") reporting regulations issued in October 2009, on June 28, 2010, U.S. EPA imposed annual reporting requirements on four additional GHG sources: underground coal mines; industrial water treatment systems; industrial waste landfills; and magnesium production facilities. The magnesium facilities' principal GHG emission of concern is sulfur hexafluoride, which has been reported as having a global warming potential of 22,800 times that of carbon dioxide ("CO2"). The other three new reporting sources have methane as their principal GHG emission. Methane has 20 times the global warming potential of CO2. These four new source categories must begin collecting emissions data on January 1, 2011, and submit their first annual reports to the EPA on March 31, 2012. EPA's final rule on the new source categories for GHG reporting can be found here. EPA's October 2009 rule requiring GHG reporting can be found here.