One of the most iconic symbols of the fracking debate is the video of a man setting his tap water on fire in Colorado.
Fracking, which refers to hydraulic fracturing, is a technique used to extract natural gas, and has become synonymous with all things gas drilling. It involves shooting water, sand and a mix of chemicals at high pressure deep into a wellbore to help split the shale rock and release the gas.
Some worry fracking fluid will leak out of a well and contaminate aquifers. In fact, a recent draft EPA study about water pollution in Pavilion, Wyo., does make that link. Fracking wastewater has also spilled and contaminated surface water.
But fracking does not put methane into tap water. Tap water blow torches, as seen in the documentary film Gasland, result from methane migration. Such movements of gas may or may not be related to drilling. But they do not result from fracking. And that’s an important distinction to make.
Tracing the source of migrating methane, or stray gas, can be complicated and mysterious. Investigators often use isotope identification to get a “fingerprint” of the gas. But just as in law enforcement, fingerprints can be tricky.
In the case of Dimock, Pa., wells drilled by Cabot Oil and Gas were fracked. But the Pennsylvania Department of Environmental Protection did not connect the flaming water taps to fracking; regulators blamed poor well construction and over-pressurization.
When a wellbore is drilled, a steel casing is sent down the hole. Then cement is poured down, and pushed upward to seal the open space between the steel casing, and the rock. That cement seal is supposed to prevent any gas, or fluid, from migrating into or out of the wellbore, and from using that space between the rock and the newly drilled well as a conduit. But that cement job doesn’t always work. And in the case of Dimock, it failed miserably.
Fred Baldassare worked as an inspector for DEP, where he spent six years investigating methane migration and helped out on the Dimock case. He was the guy who looked at the geochemistry of those flaming taps. In other words, he looked at the gas fingerprint. Baldassare says the evidence linking Dimock’s flaming tap water to gas drilling by Cabot is overwhelming.
But where that gas actually came from, whether it was from deep in the Marcellus formation, or whether it was from a more shallow formation, is unclear.
“The gas was nearly an exact match to the gas coming from the Marcellus wells,” said Baldassare. “But we couldn’t say it came from there because there are gas deposits above the Marcellus that have the same fingerprint.”
And that’s where it gets tricky. One big problem in Pennsylvania is this: Without a baseline water test before any drilling activity begins, how does one prove high levels of methane didn’t already exist in the water well i.e. from natural migration? And few residential wells in the state have those pre-drilling readings.
Gas can get into well-water in various ways. Baldassare says drilling, along with a bad cement job, can cause any gas pocket that has been stable for thousands of years to start moving. That’s because methane, under high pressure, wants to go to an area of lower pressure. And drilling, whether it’s a vertical well, horizontal well, deep well, or shallow well, can provide that opportunity.
But other things can, too, such as coal mining. It can also happen naturally. And that’s where the importance of establishing that gas fingerprint comes in. Baldassare says he spent a lot of time tracking methane migration long before the first Marcellus Shale gas well was even drilled.
“There are examples of [methane migration] throughout the Northeast that have nothing to do with gas activity,” says Baldassare. “And there are others that do happen because of drilling or mining activity.”
Reports of methane migrating into water wells date back to the 1800′s. It can originate in a coal bed. A report put out by the Penn State Cooperative Extension Service in 2009 says deep water wells in the northern and western parts of the state are the most susceptible. Still, the study also says natural methane migration is a rare occurrence.
When methane migrates, it will dissolve in water, but once the water reaches a lower pressure zone, the gas wants to get out. That’s why people experiencing methane in their water supplies will first notice a spurting at the tap, or bubbles in a glass of water. If that happens, the concentration is high enough to be combustible and the presence of the colorless, odorless methane becomes a danger.
If it’s above 28 milligrams per liter, it’s considered dangerous, and can collect in a tight space. When triggered, it could explode. That’s what happened when Dimock resident Norma Fiorentino’s water well blew up.
Neither the federal EPA nor the state DEP consider drinking water with methane to be harmful. But there are few studies on the long-term health impacts of drinking water with high levels of methane.
Recent studies on the connection between methane migration and gas drilling has produced conflicting conclusions. Duke University researchers published a report in May, 2011 that found higher concentrations of methane in water wells near gas drilling sites in Pennsylvania. But another study, published by Penn State University in October 2011, found no correlation between the presence of natural gas wells and the presence of methane in drinking water.
The dueling studies have fueled confusion over the link between flaming taps and natural gas drilling. In December 2011, the EPA published a draft report on water pollution in Pavilion, Wyo. In that report, the EPA says methane migration may be due to gas drilling.
“Although some natural migration of gas would be expected above a gas field such as Pavillion, data suggest that enhanced migration of gas has occurred within ground water at depths used for domestic water supply and to domestic wells. Further investigation would be needed to determine the extent of gas migration and the fate and transport processes influencing migration to domestic wells.”
So once methane migrates into a water supply, what then? Baldassare says proper venting and aeration does work. But some homeowners suffering from high levels of methane in their water wells have expressed doubts about the venting systems, as well as filtration systems. Baldassare also says if the source of the stray gas is halted, eventually, the water will be free of the methane through natural processes. But it’s unclear how long that could take.