Correspondence/Rebuttal pubs.acs.org/est
Comment on “Impact to Underground Sources of Drinking Water and Domestic Wells from Production Well Stimulation and Completion Practices in the Pavillion, Wyoming, Field” n the article “Impact to Underground Sources of Drinking Water and Domestic Wells from Production Well Stimulation and Completion Practices in the Pavillion, Wyoming, Field” (DOI: 10.1021/acs.est.5b04970),1 the authors Mssrs. DiGiulio and Jackson present their review of groundwater tests and operating records from the Pavillion oilfield in Wyoming and conclude: “We have, for the first time, demonstrated impact to USDWs as a result of hydraulic fracturing.” This finding relies on test results from two monitoring wells installed by the USEPA in 2010, designated MW01 and MW022. Based upon the available data, we have assessed the water quality in the drinking water wells actually utilized by the local community and evaluated the most likely explanation for the apparent water quality anomalies observed in the two monitoring wells. The data show that water wells in this area do not exhibit impacts from hydraulic fracturing activities, as there is no significant difference in the water quality of water wells located near to and far from the gas production wells. Furthermore, comparison of the two monitoring wells shows that they exhibit very different ionic signatures but an identical organic signature - an organic signature that is distinct from that of all other wells, whether water or gas, in this field. This chemistry suggests an irregularity in the two monitoring wells rather than an impact by hydraulic fracturing, which could not reasonably have caused the two monitoring wells to have different ionic signatures but the same organic signature.
I
2. THE IONIC COMPOSITIONS OF WATER FROM MONITORING WELLS MW01 AND MW02 ARE DISTINCTLY DIFFERENT AND DO NOT DEMONSTRATE AN OILFIELD IMPACT The authors rely upon test results from 2 monitoring wells within the 20-square mile Pavillion Field to support their conclusion regarding impacts by hydraulic fracturing. We have compared the ionic composition of these two monitoring wells to samples from water wells (groundwater) and gas wells (produced water and bradenhead water) reported in the Supporting Information. These data show that the ionic composition of water from MW01 is consistent with the water wells, while MW02 is consistent with the gas wells. However, well MW02 is deeper than MW01, and there is no evidence to suggest that MW02 is not representative of natural groundwater conditions at that location. Neither MW01, MW02, or the other water wells have an ionic signature that demonstrates an impact by potassium-chloride fracturing fluids.
3. MONITORING WELLS MW01 AND MW02 SHARE AN ORGANIC CHEMICAL SIGNATURE THAT IS DISTINCTLY DIFFERENT FROM THE WATER WELLS AND GAS WELLS IN THIS AREA, WHICH SUGGESTS AN IRREGULARITY IN THESE TWO WELLS RATHER THAN AN OILFIELD IMPACT Test results show the two monitoring wells to contain several volatile and semivolatile organic chemicals, with approximately 70% of the chemicals detected in MW02 also being detected in MW01, but at lower concentrations. The authors compare this list of chemicals to those used in hydraulic fracturing fluids to suggest an impact by oilfield operations. However, a number of water wells and gas wells in the Pavillion were tested for these same organic chemicals, and none of these wells share the organic chemical signature of the two monitoring wells. The absence of this chemical fingerprint in the water from the gas wells, where the greatest mass of fracturing fluids would have been injected, tells us that these chemicals are likely not associated with hydraulic fracturing. Furthermore, the presence of this organic signature in the two monitoring wells but none of the other water wells in the Pavillion Field shows that these two wells are quite peculiar and not representative of groundwater conditions in the gas field. The two monitoring wells also exhibit a unique pH level compared to the water wells and gas wells. The unique organic signature and unique pH signature are consistent with disturbances related to well construction, as previously discussed by other commenters.
1. THERE IS NO SIGNIFICANT DIFFERENCE IN WATER QUALITY FOR WATER WELLS NEAR TO (1 KM) GAS WELLS To assess the possible effect of oilfield activities on groundwater quality, the authors plot the data for water wells near to and water wells far from gas wells. The data plots presented in the paper show no significant difference in the major ion content of these two sets of wells−showing there to be no regional impact by oilfield operations. Consistent with these facts, the authors do not find impacts by hydraulic fracturing on the domestic water wells or irrigation wells that are actually used by the local community. Rather, their conclusion states that a “USDW” (underground source of drinking water) has been impacted. However, the USDW underlying the Pavillion Field is itself an oil and gas reservoir. Within this USDW, gas wells extract natural gas from the approximate depth interval of 300 m to over 1500 m below ground, while most water wells extract drinking water from depth less than 200 m. The available data show no spatial pattern of impacts by oilfield operations on these actual water wells. © XXXX American Chemical Society
A
DOI: 10.1021/acs.est.6b03829 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Correspondence/Rebuttal
4. HYDRAULIC FRACTURING COULD NOT REASONABLY CAUSE WELLS MW01 AND MW02 TO HAVE DIFFERENT IONIC SIGNATURES BUT THE SAME ORGANIC SIGNATURE The authors conclude that both MW01 and MW02 have been impacted by hydraulic fracturing fluids. They postulate that the difference in the ionic signature of the two wells could be caused by a change in the hydraulic fracturing fluids used over time. However, it is not reasonable to suggest that hydraulic fracturing operations could cause these two wells to have a different ionic content but the same organic content. The simpler explanation is that there are no ionic impacts on these wells by hydraulic fracturing and that the organic chemicals are sourced by something other than oilfield operations.
■
CONCLUSION In sum, we find no evidence of impacts by hydraulic fracturing to the groundwater resources actually being utilized by the local community. The water quality of the two monitoring wells most likely reflects natural salinity conditions combined with organic contaminants that may have been introduced during installation of the monitoring wells. John A. Connor* Kenneth Walker Lisa Molofsky Ernesto Baca Elaine Gie Thomas McHugh GSI Environmental Inc., 2211 Norfolk, Suite 1000, Houston, Texas 77027, United States
■
AUTHOR INFORMATION
Corresponding Author
*Phone: 713-522-6300, e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) DiGiulio, D. C.; Jackson, R. B. Impact to Underground Sources of Drinking Water and Domestic Wells from Production Well Stimulation and Completion Practices in the Pavillion, Wyoming, Field. Environ. Sci. Technol. 2016, 50 (8), 4524−4536. (2) U.S. EPA. Draft Investigation of Ground Water Contamination Near Pavillion, Wyoming, EPA 600/R-00/000; U.S. Environmental Protection Agency, 2011.
B
DOI: 10.1021/acs.est.6b03829 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
