The Hydraulic Fracturing Water Cycle
The hydraulic fracturing water cycle. Image courtesy US EPA


In cases where drinking-water wells near fracking sites have been contaminated, the problem usually comes from gases released as a result of the process. Researchers think those gases get into drinking water when the casings around wells are faulty. Part one of a two-part story.

By Gabe Rivin

Throughout 2013, Robert Jackson and a staff of fellow scientists fanned across northeastern Pennsylvania, ready to fill buckets with water.

For months, the Duke University scientists and others sampled residents’ well water. The team looked for a number of potential contaminants in the water – including those involved in hydraulic fracturing, the controversial process used to recover oil and natural gas.

Pennsylvania in recent years had seen a rapid influx of natural-gas development. A portion of the state is situated on top of the Marcellus Shale, a massive, multi-state-spanning geological layer that contains a bounty of natural gas. That shale couldn’t be drilled – at least not economically so – until recent years, when engineers developed new techniques for horizontal drilling and hydraulic fracturing, or “fracking,” as it’s also known.

Robert Jackson, Duke University biology professor and geochemist.
Robert Jackson, Duke University biology professor and geochemist. Image courtesy Duke University

Fracking increasingly received scrutiny from the media, provoking deep anxieties about residents’ vulnerability to a relatively unstudied process.

Residents living near fracking sites, as well as environmental advocates, worried that the process could contaminate drinking water. They wondered whether fracking produced methane in kitchen taps, filling houses with an invisible, explosive toxin.

But as recently as 2010, academic literature could scarcely respond to these worries, according to Jackson.

“We looked at the literature and there was a lot of talk and lot of heated rhetoric, and no studies,” he said. So Jackson’s group began their investigation. “We asked a simple question: If you live near a natural-gas well, is your water any different than someone who lives far away?”

The answer, at least in the Pennsylvania samplings, was alarming.

Duke’s team found that, for residents living within one kilometer of gas wells, drinking water from wells tended to have dramatically increased levels of methane, propane and ethane. Using chemical analysis, the Duke scientists found that the gases matched those which were produced from fracking the Marcellus Shale.

The group’s published study, like their more limited study from 2011, renewed the raging public debate about fracking. (The 2011 study, which also included data from New York, was the first to provide “systematic evidence” that gas wells had contaminated drinking-water wells with methane, according to a Duke white paper.)

Environmentalists cited the study as further evidence that fracking was dangerous. Industry groups, in a recurring sort of rebuttal, questioned the study’s methodology. And Duke’s researchers continued to plea for more research, which they said was severely lacking.

Duke doctoral student Nathaniel Warner samples well water in Pennsylvania.
Duke doctoral student Nathaniel Warner samples well water in Pennsylvania. Image courtesy Duke University

“It’s clearly a risk of flammability and explosion if super-saturated methane – of which we found cases – builds up in someone’s basement or in their shed or around their well,” said Jackson. But, he added, “I’ve looked several times over past few years. I can’t find a single study that looks at chronic exposure to methane in a toxicological sense.”

Often buried within this debate, however, was an important but tentative conclusion of Duke’s study: Fracking in itself was probably not to blame for the water contamination.

Instead, the likely culprits were poorly built wells – inadequate steel casing and poor cement jobs.

In other words, the water contamination was avoidable.

As North Carolina prepares for its first-ever gas drilling, beginning as early as next year, Duke’s study has prompted concern about the integrity of the state’s future wells – whether the wells will be required to have strong-enough cement and steel casing, or whether they will fail to seal off groundwater from stray gases.

North Carolina’s drilling regulators are working to finish rules that govern well casing and cementing. In drafting these and other rules, the regulators have debated what constitutes a properly built and operated well.

Implicitly and explicitly too, they have debated risk. Are industry standards strong enough to protect North Carolinians’ health? And with a dearth of rigorous academic research, how can regulators best address fracking’s risks for public health?

How fracking works

The term fracking is often a misnomer in debates about gas drilling. The term refers to the high-pressured injection of water, sand and chemicals into a well, a process that helps to fracture shale rock and release trapped oil and natural gas.

But fracking is only one part of the complete drilling process.

Natural-gas producers begin by drilling their wells into the ground. This happens in several stages, according to David Kelly, a senior analyst at the Environmental Defense Fund.

“You have to think about the well as sort of like a toy light saber, this series of cones where one fits inside the other and they get progressively smaller,” he said.

The Hydraulic Fracturing Water Cycle
The hydraulic fracturing water cycle. Image courtesy US EPA

The well often has several layers of protective casing at the top, all of which are cemented to each other, one at a time. The outermost casing also has an outer layer of cement, which plugs the space between the casing and the natural geological formations, including groundwater.

As the well approaches shale, its casing curves horizontally. A wire is sent through the casing and to the bottom of the well. That wire then delivers miniature explosions that create fissures in the casing, cement and shale. This sets the stage for the actual fracking.

Soon, fracking fluid is pumped into the well at high pressures. The fluid enlarges and props open the fissures, and allows oil and gas to flow through the casing and back to the surface, where it is captured.

According to the Duke study, the water contamination likely would have occurred during that trip back to the surface.

Click to go to industry-created video which explains the process of creating well casings.
Click to go to an industry-created video which explains the process of creating well casings. Screen capture image courtesy Marathon Oil Corp.

To understand why, it helps to remember that, during the fracking process, the well’s casing is under tremendous pressure. If the well were poorly installed and cemented, it could spring a leak, like a full water balloon pricked with a tiny hole.

And that leak could slip past cement and into groundwater, according to Avner Vengosh, one of the coauthors of the 2013 and 2011 Duke studies.

Leaking gases then would eventually find their way into the wells that supply homes with their drinking water.

Whether that will actually happen, however, has much to do with drilling rules that state regulators are currently writing, and with the state’s enforcement of these rules.

Part II of this story will run tomorrow, and will look at the strengths and potential weaknesses of the state’s draft drilling rules.

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Gabe Rivin

Gabe is our former environmental health reporter from 2014-2016. He is a former editor of The Cooperative Business Journal, and a former reporter for Inside Washington Publishers, where he covered federal...