Large-Sample Evidence on the Impact of Unconventional Oil and Gas Development on Surface Waters

The impact of unconventional oil and gas development on water quality is a major environmental concern. We built a large, geo-coded database that combines surface water measurements with horizontally drilled wells stimulated by hydraulic fracturing (HF) for several shales to examine whether temporal and spatial well variation is associated with anomalous salt concentrations in U.S. watersheds. We analyzed four ions that could indicate water impact from unconventional development. We found very small concentration increases associated with new HF wells for barium, chloride and strontium, but not bromide. All ions showed larger, but still small-in-magnitude increases 91-180 days after well spudding. Our estimates were most pronounced for wells with larger amounts of produced water, wells located over high-salinity formations, and wells closer and likely upstream from water monitors