Cumulative frequency of unconventional well density. Cumulative frequency of unconventional well density (km^–2) within 2.5 km of the sampling locations with more than 1 well within 2.5 km in Southwestern PA (blue), Northeastern PA in 2012, (green), and Northeastern PA in 2015 (black). DOI: https://doi.org/10.1525/elementa.182.f7