Under the Bush Administration, Vice President Dick Cheney helped to pass the Energy Policy Act of 2005, which exempts hydraulic fracturing from federal oversight under the Safe Drinking Water Act of 1974. This gap in the regulation is often referred to as the Halliburton loophole. With such an exemption, companies are not required by the federal government to disclose the chemicals being used in their frac fluid. Some companies are choosing voluntarily to disclose that information, and a few states also require such disclosure for oversight purposes.
Learn more about the Halliburton Loophole, and the EPA regulations on hydraulic fracturing.