The Energy Policy Act of 2005 basically exempts hydraulic fracturing activities from the Underground Injection Control Program established under the Safe Drinking Water Act (SDWA).  (The Wikipedia entry on the Energy Policy Act of 2005 is here, and a pdf version of it is here.) The relevant entry from the Energy Policy Act of 2005 states


Paragraph (1) of section 1421(d) of the Safe Drinking Water Act (42 U.S.C. 300h(d)) is amended to read as follows:
‘‘(1) UNDERGROUND INJECTION.—The term ‘underground injection’— ‘‘(A) means the subsurface emplacement of fluids by well injection; and
‘‘(B) excludes—
‘‘(i) the underground injection of natural gas for purposes of storage; and
‘‘(ii) the underground injection of fluids or propping agents (other than diesel fuels) pursuant to hydraulic fracturing operations related to oil, gas, or geothermal production activities.’’.

(At times, legal definitions can defy logic :  injection is not injection if it is injection … of things related to certain activities.  Of course, the definition here is for regulatory purposes, and so the logic lapse is at least explainable.)

Some are calling this exemption the “Haliburton Loophole,” and the National Resources Defense Council (NRDC) has been calling for its repeal.