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. 2017 Aug 23;125(8):086004. doi: 10.1289/EHP1535

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EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted.

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Map of USA classifying the regions based on active well counts. The regions are stratified as follows: well count from 1 to 100, from 101 to 1000, from 1001 to 5000, greater than 5000, and no active wells. — Confirmed active well counts by U.S. county. Well data are from DrillingInfo (http://info.drillinginfo.com/). Administrative boundaries are from the U.S. Census Bureau (2014).