Environment

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In this March 25, 2014 photo, a worker adjusts hoses during a hydraulic fracturing operation at an Encana Corp. gas well, near Mead, Colo. The first experimental use of hydraulic fracturing was in 1947, and more than 1 million U.S. oil and gas wells have been fracked since, according to the American Petroleum Institute. The National Petroleum Council estimates that up to 80 percent of natural gas wells drilled in the next decade will require hydraulic fracturing. (AP Photo/Brennan Linsley)

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In this March 25, 2014 photo, a worker watches over a hydraulic fracturing operation at an Encana Corp. gas well, near Mead, Colo. In the background is a tall canvas wall around the perimeter of the extraction site, which mitigates noise, light and dust coming from the operation during the drilling and completion phase, which generally takes a few weeks. (AP Photo/Brennan Linsley)

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In this April 15, 2014 photo is a fence surrounding the barren site of the West, Texas, Fertilizer Company that was destroyed by an explosion one year earlier. On April 17, 2013, a fire at the plant caused a blast that caved in walls at nearby schools and homes, and sent debris flying for miles. (AP Photo/Waco Tribune Herald, Rod Aydelotte)

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In this April 9, 2014 photo is a wooden cross near the site of the former West, Texas, Fertilizer Company that was destroyed by an explosion one year earlier. On April 17, 2013, a fire at the plant caused a blast that caved in walls at nearby schools and homes, and sent debris flying for miles. (AP Photo/Waco Tribune Herald, Rod Aydelotte)

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In this April 15, 2014 aerial photograph is a property that was damaged by the West, Texas, Fertilizer Company explosion one year earlier. On April 17, 2013, a fire at the plant triggered an ammonium nitrate explosion that killed 15 people and injured hundreds. (AP Photo/The Dallas Morning News, G.J. McCarthy)

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In this April 15, 2014 aerial photograph is an overall view of the area affected by the West, Texas, Fertilizer Company explosion one year earlier. On April 17, 2013, a fire at the plant triggered an ammonium nitrate explosion that killed 15 people and injured hundreds. (AP Photo/The Dallas Morning News, G.J. McCarthy)

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In this April 15, 2014 aerial photograph are properties under construction in an area damaged by the West, Texas, Fertilizer Company explosion one year earlier. On April 17, 2013, a fire at the plant triggered an ammonium nitrate explosion that killed 15 people and injured hundreds. (AP Photo/The Dallas Morning News, G.J. McCarthy)

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In this April 15, 2014 photo letters of hope are attached to a tree at the site of the old West Rest Haven nursing home that was destroyed in the West, Texas, Fertilizer Company a year earlier. On April 17, 2013, a fire at the plant caused a blast that caved in walls at nearby schools and homes, and sent debris flying for miles. (AP Photo/Waco Tribune Herald, Rod Aydelotte)