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

Pietro Bonetti, Christian Leuz, Giovanna Michelon

Key Takeaways: 

1. The application of hydraulic fracturing to develop oil and natural gas has led to a sharp increase in U.S. energy production and generated enormous benefits. As drilling activity has increased, however, a robust debate has begun regarding the pros and cons at a local level. Advocates point to increased economic activity. Opponents point to possible air and water pollution.
2. Several studies have documented instances of groundwater contamination related to hydraulic fracturing wells, but there is limited evidence linking the practice to surface water impacts. This study provides the first evidence that hydraulic fracturing is related to increased salt concentrations in surface waters for several shales across the United States.
3. The study combines surface water measurements with 46,479 hydraulic fracturing wells to examine whether new drilling and development activities are associated with elevated salt concentrations (bromide, chloride, barium and strontium) in 408 U.S. watersheds over an eleven-year period.
4. The authors found a very small but consistent increase in barium, chloride and strontium, but not bromide, in watersheds with new hydraulic fracturing wells. The elevated levels were well below environmental and health advisory levels. The increases in salt levels were largest during the early phases of production when wells generate large amounts of flowback and produced water.
5. The salt concentrations were most pronounced for wells that produced larger amounts of water and for wells located in areas where the deep formations exhibited higher levels of salinity. This evidence ties the elevated salt concentrations more closely to hydraulic fracturing activities.
6. Salt concentrations were highest when observed within a year from drilling, at monitoring stations that were within 15 kilometers and (likely) downstream from a well.