In this March 25, 2014 photo, a worker climbs down a from a machine that mixes sand and water, left, before it is pumped underground during a hydraulic fracturing operation at an Encana Corp. well pad... more 
In this March 25, 2014 photo, a worker climbs down a from a machine that mixes sand and water, left, before it is pumped underground during a hydraulic fracturing operation at an Encana Corp. well pad near Mead, Colo. Hydraulic fracturing, or "fracking," is the practice of injecting water, sand and chemicals into source rock to crack it and create escape routes for oil and gas. (AP Photo/Brennan Linsley) less 
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Associated Press | Photo By Brennan Linsley
Thu, Apr 17, 2014 6:06 PM EDT