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Fracking: Underground Connections Could Spell Drinking Water Troubles

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It's possible, according to a new study by Duke University researchers, that underground pathways can connect deep rock formations to shallow aquifers.

Water samples in Pennsylvania suggest there may be natural pathways for contamination.

Drinking water contamination from horizontal drilling and hydraulic fracturing — a k a fracking — for natural gas in Pennsylvania, does it occur? No, say the gas companies (and many geologists). A new paper adds a “but.”

Many Say It Can’t Happen There

Extracting natural gas from shale deposits involves fracturing the rock about a mile (or more) beneath the surface by pumping high volumes of water, sand and a mix of chemicals at high pressure into the shale.

The aquifers that provide drinking water in the region lie a mere 30 to 100 yards beneath the surface.

And between the shale and the aquifers lie a mile or more of solid rock.

There’s no way, some argue, that stuff liberated by the fracking way down in the shale can get into the aquifers a mere 100 yards below the surface.

Yeah, but …

The argument seems to make sense and yet there’s this nagging question: Why are so many people in Pennsylvania experiencing problems with their drinking water near where the fracking is occurring? Also, why did a group of scientists from Duke find evidence of significant contamination of thermogenic methane (i.e., gas produced in shale) in water wells near fracked wells?

Can you explain these as mere coincidences with no cause-and-effect relationship? Perhaps, but it seems unlikely to me. Too many coincidences.

Or is it the result of sloppy and careless work (such as the installation of faulty casings) on the part of a few “bad apple” drillers? That seems much more likely.

The one explanation that seems least likely is that there are actual pathways by which gases and/or fluids from the shale formations could migrate upward into the aquifer. However, the findings reported in a paper by Nathanial Warner of Duke University and colleagues recently published in the Proceedings of the National Academy of Sciences suggest that such an explanation is not outside the realm of possibility.

Geochemical Sleuthing Uncovers a Natural Pathway for Contamination

Following up on the team’s earlier work [pdf] documenting methane contamination of drinking water in Pennsylvania, the authors analyzed 426 shallow water samples taken both recently and in the 1980s (well before Pennsylvania’s current natural gas rush) from a six-county region in Pennsylvania. They compared them to 83 Appalachian brine samples from deep formations.

Each water sample underwent a battery of chemical analyses, and the researchers documented concentrations of a myriad of dissolved substances including chloride, bromide, sodium, strontium, manganese, carbonate, and sulfate. Based on these analyses, the authors identified four general categories of surface water: two with low salinity and two with elevated salinity. Of the two with high salinity, one had a composition that was “similar to brines found in deeper Appalachian formations (e.g., the Marcellus brine). This suggests mixing of shallow modern water with deep formation brines.”

Still, No Smoking Gun

The implications of the Warner et al data are striking. It suggests that there are natural pathways by which deep brines from the Marcellus can percolate upward and mix with shallow aquifers. If such pathways exist, then they could, at least in theory, provide a conduit for gases and fluids associated with fracking to eventually find their way into aquifers and then into people’s drinking water.

Theory’s one thing, but has it actually happened? The authors find no evidence of any fluid contamination from fracking via this mechanism. The composition of the surface water samples that look like Marcellus brine are virtually identical to the composition of water samples taken from these sites in the 1980s — well before the fracking in the area began. In other words, the brininess of the sample is not due to recent fracking or any drilling for that matter.

Study Results Leave Door Open to Potential Contamination

However, the Duke team does not rule out the possibility that the methane contamination they have already observed in some drinking water wells may be related to migration through these pathways, and that fluid contamination could eventually occur.

“The possibility of drilling and hydraulic fracturing causing rapid flow of brine to shallow groundwater in lower hydrodynamic pressure zones is unlikely but still unknown. By contrast, the time scale for fugitive gas contamination of shallow aquifers can be decoupled from natural brine movement specifically when gas concentrations exceed solubility (approximately 30 cc∕kg) and forms mobile free phase gases (i.e., bubbles).”

Regardless, the authors point out that their work does suggest the need for a good deal more caution than some have argued as reasonable.

“The coincidence of elevated salinity in shallow groundwater with a geochemical signature similar to produced water from the Marcellus Formation suggests that these areas could be at greater risk of contamination from shale gas development because of a preexisting network of cross-formational pathways that has enhanced hydraulic connectivity to deeper geological formations.”

So it seems possible that the region’s geology is not quite as isolating or separated as some have suggested, and is a lot more connective. The Warner et al study seems to suggest that underground connections could allow contaminants to flow from the deep formations to shallow aquifers. Is it proof positive? Of course not. But maybe it’s enough of a coincidence to suggest that we at least hold off on fracking in regions that are the source of water for millions of people such as the Susquehanna and Delaware River watersheds?