Congressional Research Service. April 4, 2012.
Hydraulic fracturing is a technique used to free oil and natural gas trapped underground in lowpermeability rock formations by injecting a fluid under high pressure in order to cause cracks in the formations. The composition of a fracking fluid varies with the nature of the formation, but typically contains mostly water; a proppant to keep the fractures open, such as sand; and a small percentage of chemical additives. Some of these additives may be hazardous to health and the environment. This report provides an overview of current and proposed laws at the state and federal levels that require the disclosure of the chemicals added to the fluid used in hydraulic fracturing.
http://www.fas.org/sgp/crs/misc/R42461.pdf [PDF format, 21 pages].