Public arguments about fracking (at least among those who have heard of the natural gas production technique) have become contentious—a situation not helped by the technical and complicated topic. Lots of information and claims fly around, but there's little in the way of an established framework to help make sense of them.

Claims that fracking has contaminated water can be difficult to resolve, and some turn out to be unrelated to fracking. Geology differs from place to place in important ways that have to be taken into consideration when analyzing water. Regulations governing fracking vary from state to state, too. And the practice has been scrutinized at a level we haven’t subjected conventional oil and gas production to, meaning we might be discovering problems that are common to other techniques.

The illusion of simplicity

Still, we occasionally get a relatively simple case, even if its broader implications are minimal. In the summer of 2010, three nearby homes in northeast Pennsylvania started having disturbing problems with their water wells. Methane was seeping up—in one case accumulating to levels that necessitated evacuating a home due to the explosion risk—and the wells were muddy and foaming. (A nearby river even began bubbling a few months later.)

Methane sometimes makes its way into wells without help from humans and can go unnoticed until proper sampling takes place, but the concentrations here were pretty high. Foaming isn’t a great sign, either. One of the water wells had even been tested before the gas drilling began, and there were no signs of methane.

Over several months leading up to this, ten gas wells had been drilled and fracked within a couple kilometers of these homes. The Pennsylvania Department of Environmental Protection tested the affected wells, inspected the gas wells, and determined that the gas company (Chesapeake Appalachia LLC) was culpable. After replacement water wells had the same problems, the company eventually bought out the homes as part of a settlement with the owners.

Even so, the water well tests didn’t yield unambiguous evidence of how they were contaminated. Nothing much was detected beyond the methane (which is an explosion risk but not otherwise a health hazard), leaving the foam a mystery.

A group of Penn State researchers led by environmental consultant Garth Llewellyn (who worked for the affected homeowners during their lawsuit) decided to turn some bigger analytical guns on the question. They subjected water samples collected during the investigation to a type of testing capable of revealing many more compounds, even at concentrations lower than one part per trillion. For comparison, they also got 30 samples of water used to frack gas wells in the area—though they didn’t have any samples from the suspect gas wells near the affected homes.

Complex measures

The testing allowed the researchers to fingerprint the water samples based on the many faintly present organic compounds they contained. All of the fracking water samples had a similar fingerprint (which is good). The impacted water wells shared that same fingerprint, while local, uncontaminated water wells did not.

The researchers also looked for a particular compound that has been used before to infer the presence of fracking fluids—2-butoxyethanol, a surfactant common in cleaning products. They detected 2-butoxyethanol in some of the frack water samples as well as one of the three affected water wells, where it was present at less than 0.5 parts per trillion. When 8 of the 10 natural gas wells were re-fracked in 2012, 2-butoxyethanol was among the chemicals the company reported using (via the Frac Focus website).

Although it wasn’t detected in two of the three water wells (which, to be clear, doesn’t guarantee it wasn’t there), 2-butoxyethanol is a good candidate to have caused the foaming in those wells as methane bubbled up. It’s also possible that some of the other low-level organic compounds were responsible, instead.

The researchers also analyzed the isotopic composition of the methane from the water and gas wells and the ratio of chlorine to bromine in the various water samples. The results told them that the methane in the drinking water wells matched the methane in the gas wells, but it was unlikely that fracking fluid had mixed with the deep, salty water and come back up to reach the wells. Instead, the fracking fluid that contaminated the water wells was probably just on its way down.

So how did this happen? It turns out that while the gas wells were surrounded by a protective seal of concrete and steel down along the top 300 meters and down at the business end below 2,000 meters, there was no such seal in between. Pennsylvania has since tightened up their regulations, but that methodology was legal at the time the wells were drilled.

Contrary to public concern that fracking fluid or natural gas will travel upward through the rock to reach drinking water aquifers, the protective seals around gas wells are the real sources of risk. In this case, the gas pressure in that unsealed space around several of the well pipes was measured to be higher than regulations allowed before the problems with the water wells began—so we know gas escaped the confines of the well pipe and could have been pushing outward into the rock.

While stray gas like that has been suspected of reaching water wells in other places, hints of fracking fluid reaching water wells is rare. The researchers think that during the pressurized injection of the frack water, some may have leaked through that unsealed portion of the borehole and taken the same path as the escaping natural gas—perhaps traveling through fractures.

The case for contamination from the fracked wells is pretty tight, although there was also a leak of frack water from a surface holding pit that could potentially have provided a more traditional source for some of the contaminants. The good news is that it was preventable; these gas wells weren’t constructed carefully enough. Conventional gas wells, sans fracking, would probably also have allowed methane to leak upwards. (Though without the foaming, perhaps.) There’s a reason why the integrity of that protective seal around the well has been the focus of so much regulatory attention. It’s critical, and it can be done right—or wrong.

PNAS, 2015. DOI: 10.1073/pnas.1420279112 (About DOIs).