HGS RESEARCH HIGHLIGHT – Groundwaters in Northeastern Pennsylvania near intense hydraulic fracturing activities exhibit few organic chemical impacts
Xiong, B., Soriano, M. A., Gutchess, K. M., Hoffman, N., Clark, C. J., Siegel, H. G., De Vera, G. A. D., Li, Y., Brenneis, R. J., Cox, A. J., Ryan, E. C., Sumner, A. J., Deziel, N. C., Saiers, J. E., & Plata, D. L. (2022). Groundwaters in Northeastern Pennsylvania near intense hydraulic fracturing activities exhibit few organic chemical impacts. In Environmental Science: Processes & Impacts (Vol. 24, Issue 2, pp. 252–264). Royal Society of Chemistry (RSC). https://doi.org/10.1039/d1em00124h
“The control volume finite-element hydrologic simulator, Hydrogeosphere, was used to model coupled flow and transport over a 190 km2 area in southeastern Bradford County that encompassed eight of the sampled domestic wells and 30 unconventional well pads.”
Fig. 5. Contaminant transport length-scales are short relative to the distance to nearest oil and gas well over the timescale of unconventional oil and gas well development in Northeastern PA. (A) Gas well drilling age and distance to nearest groundwater well (blue circles) are shown alongside transport distance as a function of time considering a distribution of hydrological conditions in southeastern sub-region of Bradford county, PA and two representative end-members: acrylamide (red, log Koc = 0.55) and bis-2-ethylhexyl phthalate (black/gray, log Koc = 4.99, where Koc is in L kgoc−1). The solid, dashed, dotted, and shaded regions refer groundwater transport velocities that bound the distribution of the results. B (acrylamide) and C (bis-2-ethylhexyl phthalate) illustrate geospatially specific transport distances about 30 gas well pads (gray circles) near 8 groundwater wells (black stars) in southeastern Bradford County after 10 years.
In this comprehensive study, researchers investigated the potential impact of hydraulic fracturing activities on groundwater quality in Northeastern Pennsylvania.
The study focused on analyzing organic contaminants in 94 domestic groundwater sites after a decade of intense hydraulic fracturing in the region. Results revealed that all volatile and semi-volatile compounds analyzed were below the recommended maximum contaminant levels set by the United States Environmental Protection Agency. Integrated concentrations of gasoline range organic compounds (GRO) and diesel range organic compounds (DRO) were also found to be low, indicating minimal organic chemical contamination.
The study utilized HydroGeoSphere (HGS) to simulate the potential movement of contaminants through the region.
“Groundwater velocities were computed from the calibrated model and were used within a Monte Carlo framework to infer the distribution in transport length scales for weakly- and strongly-adsorbing organic contaminants.” - Xiong et al., 2022By leveraging the capabilities of HGS, the researchers were able to assess the transport of organic contaminants from hydraulic fracturing sites to groundwater wells in the region.
Through correlation analyses, researchers found that higher levels of GRO were associated with violations within a 2 km radius, suggesting a link between safety violations and organic compound levels. Additionally, correlations between DRO and certain inorganic species, such as barium and strontium, as well as methane, indicated a potential source of high salinity and organic contamination.
Despite the detection of select organic compounds in some samples, overall contamination rates were low, likely due to short transport distances from gas wells relative to groundwater wells. The study utilized a spatially-resolved hydrogeologic model to estimate transport distances, revealing a low probability of systematic groundwater organic contamination in the region.
Plain Language Summary:
This work illustrates that a large sampling of groundwater wells in Northeastern Pennsylvania have not been substantially contaminated with hydrophobic organic contaminants spanning a spectrum of volatilities (volatile organic, gasoline-, or diesel-range organic compounds) even after a decade of intense hydraulic fracturing activity. The reasons for this can include the relatively protective nature of groundwater flow in the area, long transport times of sorption-retarded chemicals, and a lack of systematic chemical releases from oil and gas well operations. Nevertheless, accidental chemical releases are commonly documented, albeit with limited specificity.
Abstract:
Horizontal drilling with hydraulic fracturing (HDHF) relies on the use of anthropogenic organic chemicals in proximity to residential areas, raising concern for groundwater contamination. Here, we extensively characterized organic contaminants in 94 domestic groundwater sites in Northeastern Pennsylvania after ten years of activity in the region. All analyzed volatile and semi-volatile compounds were below recommended United States Environmental Protection Agency maximum contaminant levels, and integrated concentrations across two volatility ranges, gasoline range organic compounds (GRO) and diesel range organic compounds (DRO), were low (0.13 ± 0.06 to 2.2 ± 0.7 ppb and 5.2–101.6 ppb, respectively). Following dozens of correlation analyses with distance-to-well metrics and inter-chemical indicator correlations, no statistically significant correlations were found except: (1) GRO levels were higher within 2 km of violations and (2) correlation between DRO and a few inorganic species (e.g., Ba and Sr) and methane. The correlation of DRO with inorganic species suggests a potential high salinity source, whereas elevated GRO may result from nearby safety violations. Highest-concentration DRO samples contained bis-2-ethylhexyl phthalate and N,N-dimethyltetradecylamine. Nevertheless, the overall low rate of contamination for the analytes could be explained by a spatially-resolved hydrogeologic model, where estimated transport distances from gas wells over the relevant timeframes were short relative to the distance to the nearest groundwater wells. Together, the observations and modeled results suggest a low probability of systematic groundwater organic contamination in the region.