"Congressional interest in U.S. energy policy has often focused on ways through which the United States could secure more economical, reliable, and cleaner fossil fuel resources both domestically and internationally. Recent expansion in natural gas production, primarily as a result of new or improved technologies (e.g., hydraulic fracturing, directional drilling) used on unconventional resources (e.g., shale, tight sands, and coalbed methane) has made natural gas an increasingly significant component in the U.S. energy supply. This expansion, however, has prompted questions about the potential impacts of natural gas systems on human health and the environment, including impacts on air quality."
CRS Report for Congress, R42986
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html