The chemical-laced water used in hydraulic fracturing can migrate through fractures and faults up to overlying aquifers in as little as tens of years. Published in the peer-reviewed Ground Water, this study raises renewed questions about the potential for hydraulic fracturing to fundamentally alter shale rock formations and the hydrogeologic cycle in ways that could affect freshwater drinking supplies.
There are also concerns that improperly sealed or unsealed abandoned drilling wells and naturally occurring fractures and faults will offer a path to connect gas bearing shale layers with overlying freshwater aquifers.
A common response by the oil/gas industry to this concern is that upward migration of deep, thermogenic methane gas and chemicals used in the fracturing process is impossible, due to layers and layers of impermeable rock that prevent such movement.
The problem, some hydrogeologists say, is the industry is offering little to no data to support this argument. While the ability of shale to transmit fluids (its permeability) is about 1,000 times less than that of sandstone aquifers, hydrogeologists say the entire purpose of hydraulic fracturing is to increase the permeability of shale rock to allow the "trapped" methane gas to leak out, mainly into the more permeable overlying rock layers. Pre-existing fractures provide such a pathway.
In addition to the above concerns and debates, up to a third of the toxic fluid used in hydraulic fracturing will resurface, as well as naturally occurring and extremely salty brine, or "produced water." The high amounts of the resulting contaminated wastewater has raised its own challenges around disposal and treatment, as well as the potential for water contamination from spills.
Some think that what is already known about well casing failures is enough to put a hold on unconventional drilling: "Why would anyone risk our aquifers for a few years of profits?