Recently, a study by Nathaniel Warner and others (most at Duke's Nicholas School of the Environment) addressed the natural flow of briny water deep underground to shallow aquifers far overhead. Some commenters saw this study as evidence that shale gas development can damage drinking water aquifers. Salon.com reported "Confirmed: Fracking can Pollute". But others saw the study as giving shale gas in the Marcellus a clean bill of health on this issue - fuelfix.com reported "New research shows no Marcellus Shale pollution". Who's right?
Groundwater pollution from methane, from briny water found in the target formation or above it, or from fracking fluids is a major concern of the public. There is very little information available in the academic literature that addresses these topics empirically. Many studies show that fractures are far too confined and occur at far too deep a level to affect groundwater, and most claims of methane migration from a shale gas well to water wells are debunked on the grounds that methane was present in the water well or in or near the groundwater prior to the drilling process. One of the more controversial papers was by some of the same team members that wrote this new article. In that prior paper they showed that in the northeastern Marcellus, many of the water wells within a mile of a shale gas well showed elevated methane levels, and that wells farther away did not. However, the paper can be criticized because there were no readings before the drilling began, the wells examined were not randomly chosen but were based on complaints, and there were many wells within a mile without methane but no attempt was made to explain why or why not.
Another prior relevant paper by Tom Myers concludes that deep fluids can make it to the surface through natural fractures and fleshes out the mechanisms, but also examines the role fracking can play in speeding upward migration of gas or liquids. He uses groundwater simulation modeling to conclude that fracking widens existing fractures and could allow transport of fracturing fluids and formation water to shallow aquifers in "tens of years or less."
This new study focuses instead on empirical measurements of the migration of brine in the northeastern Marcellus to water wells and finds that brine far below the groundwater is using “naturally occurring pathways” to make its way into the shallow aquifers that feed water wells. But, importantly, no direct link is made from shale gas development to this migration. Indeed, the researchers say that “occurrences of [briny} water do not correlate with the location of shale gas wells,” and also that these brines were present before shale gas development began. In other words, the researchers only found evidence that brine from far below a shallow aquifer can migrate to that aquifer – empirical evidence supporting Myers’ simulations.
The researchers cannot directly link these brines to the Marcellus formation, but they do say that chemical analysis of the brines is consistent with brines from that formation. One can, of course, then infer (as the researchers suggest) that if brine can move in this way, fracking fluid and methane can also move in this way and, using an even broader inference and Meyers’ paper, that possibly the acts of drilling and fracking can increase the probability that these substance can migrate. The researchers also note that the time scale for methane to migrate is much shorter than that of liquids. Unlike Myers, they say that “it is unlikely” that these deeply injected fracking fluids and the formation water found there would reach shallow aquifers in a reasonable time scale.
My judgment is that the most recent study and the Myers study together are a cautionary tale about the damage that shale gas development can do to a shallow aquifer even though no direct link has been found. If migration routes exist it seems reasonable that methane, at least, can find them more easily with than without fracking activity. The key to this conclusion, however, is whether the brine observed is coming from the Marcellus formation (or even deeper). In this, there is only circumstantial evidence and a lot of variability that makes such attribution very difficult. Indeed, as noted in a peer review from PSU geologist Terry Engelder, there is very little water in the Marcellus formation in the northeastern PA part of the Marcellus, which makes such a link far less plausible.
In other words, neither headline is fair. The study gives enough to worry about that it's misleading to say it shows no pollution. But there's not enough evidence to conclude based on this study alone that fracking in the Marcellus can pollute groundwater.