Evaluating a groundwater supply contamination incident attributed to Marcellus Shale gas development.
Evaluating a groundwater supply contamination incident attributed to Marcellus Shale gas development
- Garth T. Llewellyna,1,
- Frank Dormanb,
- J. L. Westlandb,
- D. Yoxtheimerc,
- Paul Grievec,
- Todd Sowersc,
- E. Humston-Fulmerd, and
- Susan L. Brantleyc,1
Edited by Stephen Polasky, University of Minnesota, St. Paul, MN, and approved April 2, 2015 (received for review October 22, 2014)
New techniques of high-volume hydraulic fracturing (HVHF) are now used to unlock oil and gas from rocks with very low permeability. Some members of the public protest against HVHF due to fears that associated compounds could migrate into aquifers. We report a case where natural gas and other contaminants migrated laterally through kilometers of rock at shallow to intermediate depths, impacting an aquifer used as a potable water source. The incident was attributed to Marcellus Shale gas development. The organic contaminants—likely derived from drilling or HVHF fluids—were detected using instrumentation not available in most commercial laboratories. More such incidents must be analyzed and data released publicly so that similar problems can be avoided through use of better management practices.
High-volume hydraulic fracturing (HVHF) has revolutionized the oil and gas industry worldwide but has been accompanied by highly controversial incidents of reported water contamination. For example, groundwater contamination by stray natural gas and spillage of brine and other gas drilling-related fluids is known to occur. However, contamination of shallow potable aquifers by HVHF at depth has never been fully documented. We investigated a case where Marcellus Shale gas wells in Pennsylvania caused inundation of natural gas and foam in initially potable groundwater used by several households. With comprehensive 2D gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS), an unresolved complex mixture of organic compounds was identified in the aquifer. Similar signatures were also observed in flowback from Marcellus Shale gas wells. A compound identified in flowback, 2-n-Butoxyethanol, was also positively identified in one of the foaming drinking water wells at nanogram-per-liter concentrations. The most likely explanation of the incident is that stray natural gas and drilling or HF compounds were driven ∼1–3 km along shallow to intermediate depth fractures to the aquifer used as a potable water source. Part of the problem may have been wastewaters from a pit leak reported at the nearest gas well pad—the only nearby pad where wells were hydraulically fractured before the contamination incident. If samples of drilling, pit, and HVHF fluids had been available, GCxGC-TOFMS might have fingerprinted the contamination source. Such evaluations would contribute significantly to better management practices as the shale gas industry expands worldwide.
Author contributions: G.T.L., F.D., D.Y., and S.L.B. designed research; G.T.L., F.D., J.L.W., D.Y., P.G., T.S., and S.L.B. performed research; F.D. contributed new reagents/analytic tools; G.T.L., F.D., J.L.W., D.Y., P.G., T.S., E.H.-F., and S.L.B. analyzed data; and G.T.L. and S.L.B. wrote the paper.
Conflict of interest statement: G.T.L. and Appalachia Consulting provided litigation support and environmental consulting services to the impacted households.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1420279112/-/DCSupplemental.