Water wells close to gas-drilling sites in Pennsylvania had methane levels more than six times higher than more distant wells, evidence that the boost in production is causing leaks, Duke University researchers found.
The chemical fingerprint of the methane, the key component of natural gas, along with the presence of ethane and propane, indicate that much of the gas is from deep underground, such as the Marcellus Shale, according to a study released today. Production in the Marcellus is booming through hydraulic fracturing, or fracking, to break up rock and free trapped gas.
“Distance to gas wells was, by far, the most significant factor influencing gases in the drinking water we sampled,” said Rob Jackson, an environmental sciences professor at Duke in Durham, North Carolina, and the study’s lead author. The evidence “all suggest that drilling has affected some homeowners’ water.”
The peer-reviewed study, released in the Proceedings of the National Academy of Sciences, is a follow-up and extension of a 2011 study by Jackson and his co-authors, which drew criticism from the drilling industry. That study tested drinking water supplies in northeastern Pennsylvania including the town of Dimock, where the state said gas wells failed and leaked. It found no evidence of the chemicals used in fracking in water wells; it did link drilling to elevated methane leaks.
Industry scientists and advocates challenged the results, arguing that the methane appeared to come from more shallow sources, and might be the result of longstanding, natural migration pathways. Scientists affiliated with Cabot Oil & Gas Corp. (COG:US) released research last month from analysis of 1,701 wells in Susquehanna County, in northeastern Pennsylvania, and found no connection between drilling activities and methane levels. Cabot is a gas driller in the region.
“Methane is common in Susquehanna county water wells and is best correlated with topography and groundwater geochemistry, rather than shale-gas extraction activities,” according to the peer-reviewed study published in the journal Groundwater.
Methane can escape from the water at levels detected in some of the wells, and is explosive. Some of the levels found near drilling operations exceed state and federal standards, the Duke study showed.
Gas production in Pennsylvania surged in the past few years as companies expanded their use of fracking, in which water, chemicals and sand are shot underground to break apart the rock and free the gas. The Marcellus Shale is about 5,000 feet underground in Pennsylvania, separated by thick rock layers from water aquifers, which are at most a few hundred feet beneath the surface.
Still, a surge in fracking has been accompanied by a complaints from many homeowners who say their water has been contaminated, resulting in sick children, dead livestock and flammable tap water. Industry groups representing companies such as Cabot say evidence has failed to establish a case of water contamination from fracking. The Duke study doesn’t link the methane found in the water wells to fracking, and instead, Jackson said that faulty drilling procedures could allow some gas to escape from wells and into the aquifer, or free shallower pockets of gas during drilling itself.
“It doesn’t have to be a fracking problem,” Jackson said in an interview. “First and foremost, we think it’s an issue of well integrity.”
Jackson and his colleagues sampled 141 different wells in northeastern Pennsylvania. They found the presence of methane in some levels in 82 percent of the wells. However, the concentration of the gas in wells within one kilometer (0.6 miles) of drilling operations was six times greater. The scientists also looked for ethane and propane in the wells, which indicate gas that has come from older, deeper formations. Ethane presence was 23 times greater near gas wells, and propane was only present in 10 wells near drilling sites.
The researchers also looked at the isotopic signature of the gas, and found it to be either intermediate level or deeper Marcellus style, the paper said. “Not all cases of contamination are coming from the Marcellus,” Jackson said.
The Duke results for Pennsylvania contrast with findings by some of the same researchers from Arkansas, in which they found no evidence of groundwater contamination.
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