Using a large-sample statistical approach based on publicly available data, the authors of a recent study investigated the potential impact of unconventional oil and gas development on surface water quality.
Published in Science, the report studied four ions in watersheds across the US.
Bonetti et al. combined a geocoded database of 46,479 hydraulically fractured (HF) wells from 24 shales with 60,783 surface water measurements over 11 years (2006–2016) across 408 watersheds with HF activity. The four ions studied were bromide (Br−), chloride (Cl−), barium (Ba), and strontium (Sr).
The authors noted they estimated their regression model for all US watersheds with HF wells and then separately for Pennsylvania, because Pennsylvania accounted for almost 41% of the sample.
Their findings showed an association between new HF wells and elevated concentrations of Cl−, Ba, and Sr in same-watershed surface waters. Br– results were weaker and often insignificant. The estimated well/ion association was more pronounced when using water measurements from monitors located close to and likely downstream of wells and from the early phases of production, when amounts of flowback and produced water are larger.
The introduction to the report noted: “The small increases appeared 90 to 180 days after new wells were put in and suggest some surface water contamination. The magnitude appears small but may require that more attention be paid to monitoring near-well surface waters.”
The authors wrote, “Although this evidence is based on associations, and as such not causal, the regression analysis controls for a large number of observed and unobserved factors and models background ion concentrations in a flexible and comprehensive manner. Thus, we find it difficult to explain the results by other factors. The confluence of our findings is consistent with unconventional O&G development driving the anomalous surface water ion concentrations identified by our model.”
Large-Sample Evidence on the Impact of Unconventional Oil and Gas Development on Surface Waters by Pietro Bonetti, University of Navarra (Spain); Christian Leuz, University of Chicago and the National Bureau of Economic Research; and Giovanna Michelon, University of Bristol. https://doi.org/10.1126/science.aaz2185.