There are two interesting new reports out the focus more attention on the potential for the natural gas drilling boom to contaminate drinking water supplies.

The first got more attention, including this post on the Climate Progress blog, in part because it was being promoted by the Natural Resources Defense Council, one of the environmental groups that commissioned the report and explained it this way:

An independent scientist has confirmed that fracking has clearly contaminated a drinking water source east of the town of Pavillion, Wyoming, supporting the findings in a draft EPA report published in December.

This is not only important news for residents of the small town with contaminated water-– but it has national significance as well. While oil and gas corporations enjoy exemptions from critical protective environmental provisions in the Safe Drinking Water Act and Clean Water Act, they have continued to publicly claim there has never been any proof that fracking has contaminated drinking water–despite reports of suspected cases from around the country.

Here’s the basic conclusion from that report, written for NRDC and other groups by hydro-geologist Tom Myers:

After consideration of the evidence presented in the EPA report and in URS (2009 and 2010), it is clear that hydraulic fracturing (fracking (Kramer 2011)) has caused pollution of the Wind River formation and aquifer. The EPA documents that pollution with up to four sample events in the domestic water wells and two sample events in two monitoring well constructed by the EPA between the level of the domestic water wells and the gas production zone. The EPA’s conclusion is sound.

Importantly, though, the report adds:

The situation at Pavillion is not an analogue for other gas plays because the geology and regulatory framework may be different.

That’s why, for folks concerned about the Marcellus Shale boom here in West Virginia, this other study — also by Myers, but published in a peer-reviewed journal — might turn out to be much more important.  Abrahm Lustgarten, the great reporter at ProPublica, broke the story:

A new study has raised fresh concerns about the safety of gas drilling in the Marcellus Shale, concluding that fracking chemicals injected into the ground could migrate toward drinking water supplies far more quickly than experts have previously predicted.

 More than 5,000 wells were drilled in the Marcellus between mid-2009 and mid-2010, according to the study, which was published in the journal Ground Water two weeks ago. Operators inject up to 4 million gallons of fluid, under more than 10,000 pounds of pressure, to drill and frack each well.

Scientists have theorized that impermeable layers of rock would keep the fluid, which contains benzene and other dangerous chemicals, safely locked nearly a mile below water supplies. This view of the earth’s underground geology is a cornerstone of the industry’s argument that fracking poses minimal threats to the environment.

But the study, using computer modeling, concluded that natural faults and fractures in the Marcellus, exacerbated by the effects of fracking itself, could allow chemicals to reach the surface in as little as “just a few years.”

“Simply put, [the rock layers] are not impermeable,” said the study’s author, Tom Myers, an independent hydrogeologist whose clients include the federal government and environmental groups.

“The Marcellus shale is being fracked into a very high permeability,” he said. “Fluids could move from most any injection process.”

The research for the study was paid for by Catskill Mountainkeeper and the Park Foundation, two upstate New York organizations that have opposed gas drilling and fracking in the Marcellus.

Much of the debate about the environmental risks of gas drilling has centered on the risk that spills could pollute surface water or that structural failures would cause wells to leak.

Though some scientists believed it was possible for fracking to contaminate underground water supplies, those risks have been considered secondary. The study in Ground Water is the first peer-reviewed research evaluating this possibility.

Here’s a summary of the study, which is available online here:

Hydraulic fracturing of deep shale beds to develop natural gas has caused concern regarding the potential for various forms of water pollution. Two potential pathways—advective transport through bulk media and preferential flow through fractures—could allow the transport of contaminants from the fractured shale to aquifers. There is substantial geologic evidence that natural vertical flow drives contaminants, mostly brine, to near the surface from deep evaporite sources. Interpretative modeling shows that advective transport could require up to tens of thousands of years to move contaminants to the surface, but also that fracking the shale could reduce that transport time to tens or hundreds of years. Conductive faults or fracture zones, as found throughout the Marcellus shale region, could reduce the travel time further. Injection of up to 15,000,000 L of fluid into the shale generates high pressure at the well, which decreases with distance from the well and with time after injection as the fluid advects through the shale. The advection displaces native fluids, mostly brine, and fractures the bulk media widening existing fractures. Simulated pressure returns to pre-injection levels in about 300 d. The overall system requires from 3 to 6 years to reach a new equilibrium reflecting the significant changes caused by fracking the shale, which could allow advective transport to aquifers in less than 10 years. The rapid expansion of hydraulic fracturing requires that monitoring systems be employed to track the movement of contaminants and that gas wells have a reasonable offset from faults.