In this March 29, 2013 photo, a worker helps monitor water pumping pressure and temperature, at an Encana Oil & Gas (USA) Inc. hydraulic fracturing and extraction site, outside Rifle, in western Colorado. Hydraulic fracturing, or "fracking," occurs after oil and gas wells are drilled and frequently in between drilling phases. The process uses millions of gallons of water mixed with smaller amounts of fine sand and chemicals to split open oil- and gas-bearing rock often located more than a mile underground. Fracking typically occurs in conjunction with other modern drilling techniques, such as directional drilling. (AP Photo/Brennan Linsley)

Associated Press
In this March 29, 2013 photo, a worker helps monitor water pumping pressure and temperature, at an Encana Oil & Gas (USA) Inc. hydraulic fracturing and extraction site, outside Rifle, in western Colorado. Hydraulic fracturing, or "fracking," occurs after oil and gas wells are drilled and frequently in between drilling phases. The process uses millions of gallons of water mixed with smaller amounts of fine sand and chemicals to split open oil- and gas-bearing rock often located more than a mile underground. Fracking typically occurs in conjunction with other modern drilling techniques, such as directional drilling. (AP Photo/Brennan Linsley)
In this March 29, 2013 photo, a worker helps monitor water pumping pressure and temperature, at an Encana Oil & Gas (USA) Inc. hydraulic fracturing and extraction site, outside Rifle, in western Colorado. Hydraulic fracturing, or "fracking," occurs after oil and gas wells are drilled and frequently in between drilling phases. The process uses millions of gallons of water mixed with smaller amounts of fine sand and chemicals to split open oil- and gas-bearing rock often located more than a mile underground. Fracking typically occurs in conjunction with other modern drilling techniques, such as directional drilling. (AP Photo/Brennan Linsley)
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