The connection between energy and water resources was in the spotlight this year as hydraulic fracturing ramped up across the country, along with fears that the toxic fluid produced in the process could pollute drinking water sources.
The process, being used in a number of states from Wyoming to Pennsylvania, involves pumping large volumes of chemically treated water at high pressure into underground shale and sand formations to produce natural gas.
(Read National Geographic News' special series on hydraulic fracturing and the "Great Shale Gas Rush."
About 4 million gallons (15 million liters) of water are pumped thousands of feet underground at each well. (See National Geographic's 3-D Interactive, “Breaking Fuel From Rock.”)
The process has stirred especially great controversy in Pennsylvania, where the industry is growing rapidly since its arrival just three years ago, with 2,100 wells so far.
While natural gas companies assure local residents and environmental officials that fracking fluid is pumped right past groundwater resources through a steel and cement pipe, eliminating the threat of drinking water pollution (20 percent of Pennsylvania residents use groundwater), concerned citizens and scientists point to the fact that about 20 to 50 percent of the drilling fluid migrates back to the surface.
This “produced water,” which includes the frack chemicals, is a super-salty brine, prone to bacterial growth, and potentially contaminated with heavy metals. If not handled correctly, it could pose significant risks to water quality. In at least 130 cases documented since 2008 by Pennsylvania environmental authorities, drilling wastewater has spilled into creeks and tributaries due to holding pond overflows, pump failures, and other errors.
In late November, Exxon Mobil Corp. subsidiary XTO Energy spilled up to 13,000 gallons (49,200 liters) of "produced water" from a Pennsylvania natural gas well site into a nearby stream, according to a news release from the Pennsylvania Department of Environmental Protection.
Given the controversial nature of the fluids, the U.S. government is considering a policy that would require companies to disclose the content of their fracking fluids when they operate on public lands. (Read more: "U.S. Weighs Disclosure Rules for Natural Gas Drillers".) And New York Governor David A. Paterson issued an executive order this month banning all hydraulic fracturing in his state until next July, according to the New York Times.