By now, most readers of this blog are familiar with the infamous video of a Pennsylvania man turning on his kitchen faucet, flicking a cigarette lighter, and watching the out-pour ignite in a burst of flames. Suspicions have centered around recent natural gas drilling operations in that area, however, no strong evidence existed to back up these suspicions.
But now, a team of Duke University scientists, analyzing shallow groundwater sources near active gas wells, has found that levels of flammable methane (CH4) contamination increased when those water supplies were nearest natural gas wells. The Duke study/analysis is the first to find physical evidence of the connection.
All wells sampled were located in three different areas: two in Northeastern Pennsylvania (the Lockhaven and Catskill formations) and one in upstate New York (the Genesee group).
As to any counter-claims that these findings are coincidental and/or of natural origin, the team performed an isotopic analysis on the methane in order to distinguish between biogenic methane, produced by microbial decay, and thermogenic methane, which occurs in the deeper hydrocarbon layers targeted by drilling operations. The test confirmed that it is the type of methane extracted during natural gas drilling.
Some industry-connected critics claim that not enough wells were sampled (note: 26 wells were sampled over three regions) to make this determination, but the same critics — including one hydrogeologist (see link below) — do not cite how many wells should be sampled to make this linkage valid.
The radius used in the analysis was within 1 kilometer from an active gas well. Water supplies that were furthest from the wells showed higher volumes of natural, biogenic methane, while supplies closer to the rigs showed increasing thermogenic methane levels — many at dangerous levels.
Average and maximum methane concentrations in active drilling areas was 19.2 and 64 mg/L^1 respectively — a potential explosion hazard. The high concentrations of thermogenic methane decreased the farther away from the active cites one sampled, and giving way to biogenic or mixed CH4 concentrations in the outlying areas.
Quoting from the study paper (published May 9 in the Proceedings of the National Academy of Sciences), the authors (Osborn et al) state:
“In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH4 L-1 (n = 26), a potential explosion hazard…”
The team also found evidence of another hydrocarbon gas, ethane (C2H6), which is another component of natural gas, in 81% of drinking water supplies near active drilling sites, while it was found in only 9% of water supplies farther away. Lesser amounts of propane and butane (also constituents of natural gas) were also found in some water supplies near the most active drilling sites.
The distance between the bottom of an aquifer (a drinking water source) and the fractured shale beds (that trap the natural gases) can be up to a mile and mostly made of solid rock. Seepage through this rock, then, tends to follow along new and old fracture lines, or along faults created by the hydraulic fracturing process. It can also occur through physical displacement/pressure and/or through cracked or damaged well casings — which the Duke team believes is the most likely cause of the contamination.
However, the scientist could not rule out wide-ranging, underground migration of the gas “…due to the extensive fracture systems reported for these formations and the many older, uncased wells drilled and abandoned.”
Importantly, but inconclusively, the Duke study did not find evidence of contamination from the hydrauiic fluids used in fracking operations. Such fluids –including diesel fuel — have been found to contain unsafe levels of the cancer-causing B.T.E.X.* family of chemicals.
Quoting from the paper abstract:
“We found no evidence for contamination of drinking-water samples with deep saline brines or fracturing fluids.”
Such chemicals may take longer to seep through cracks in well casings or through fractures (natural and man-made) in the shale, and so, while this negative finding may give comfort to some, only a longer-term, comprehensive study will be able to determine the actual risk of this type of contamination.
In summation, the authors state:
“We conclude that greater stewardship, data, and—possibly—regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.
* B.T.E.X. = benzene, toluene, ethylbenzene and xylene
For a more in depth, investigative article on this topic, check out: ‘Scientific Study Links Flammable Drinking Water to Fracking’
Ref. 1 – Ryder RT, Zagorski WA (2003) Nature, origin, and production characteristics of the Lower Silurian regional oil and gas accumulation, central Appalachian basin, United States. AAPG Bull 87:847–872.
Map and Graph credits: Author’s Paper, supplementary material, PNAS.org