Environment

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In this photo taken April, 18, 2014, a home's foundation stands in a empty neighborhood where houses once were in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Greensburg's population stands at about 850. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, a new community center rises in the distance beyond stairs leading to where a house once stood in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Greensburg's population is around 850 residents. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, street signs and stretches of roads are all that remain of a trailer park built by the Federal Emergency Management Agency to provide temporary housing for displaced residents displaced in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Greensburg's population is around 850 residents. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, economic development director Sue Greenleaf-Taylor has a view of empty lots and a temporary Post Office where businesses once stood in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Greensburg is struggling like many rural communities to maintain its population base. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, a large photo of tornado damage hangs in a hallway of the rebuilt high school in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Greensburg's population is around 850 residents. (AP Photo/Charlie Rieel)

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In this photo taken April, 18, 2014, Mayor Bob Dixson stands with a soon-to-be completed community theater at right, and the only downtown building to survive a massive tornado in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Dixson believes most of the town's current 850 residents are ready to move on and deal with the same sort of problems that plague most rural communities. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, Mayor Bob Dixson stands with a soon-to-be completed community theater at right, and the only downtown building to survive a massive tornado in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, Dixson believes most of the town's current 850 residents are ready to move on and deal with the same sort of problems that plague most rural communities. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, Mark DelGrosso, visiting from Oklahoma, tours the rebuilt Big Well Museum in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, many of the town's destroyed civic buildings have been rebuilt but a rebound in population is slow in coming. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, wind turbines rise beyond a sign welcoming visitors to Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community, Greensburg is one of the greenest towns in the country but struggles to regain residents that were displaced by the disaster. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, museum director Stacy Barnes looks out over scattered rebuilt homes and business from a viewing deck at the rebuilt Big Well Museum in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, many of the town's destroyed civic buildings have been rebuilt but a rebound in population is slow in coming. (AP Photo/Charlie Riedel)

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In this photo taken April, 18, 2014, museum director Stacy Barnes looks out over scattered rebuilt homes from a viewing deck at the rebuilt Big Well Museum in Greensburg, Kan. Seven years after an EF-5 tornado destroyed most of the community of 1,500, many of the town's destroyed civic buildings have been rebuilt but a rebound in population is slow in coming. (AP Photo/Charlie Riedel)

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Desiree McCaslin, a Sioux City Public Works department employee, displays a hydrogen sulfide meter similar to one that would be suspended in the wet well, left, at the Riverside sewage lift station on May 1, 2014. The city is continuing its struggle with sewage odors in Sioux City's Riverside neighborhood. The injection of chemicals into a sewer line has produced mixed results and some mixed opinions from people who live near the Riverside lift station. (AP Photo/The Sioux City Journal, John Quinlan)

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Desiree McCaslin, a Sioux City Public Works department employee, demonstrates how a hydrogen sulfide meter is used to measure the gas in the wet well at the Riverside sewage lift station on May 1, 2014. The city is continuing its struggle with sewage odors in Sioux City's Riverside neighborhood. The injection of chemicals into a sewer line has produced mixed results and some mixed opinions from people who live near the Riverside lift station. (AP Photo/The Sioux City Journal, John Quinlan)