Methane is not regulated in drinking water, and while research is limited, it is not currently believed to be harmful to drink. But the methane is dangerous because as it collects in enclosed spaces it can asphyxiate people nearby, or lead to an explosion.
To determine where the methane in the wells they tested came from, the researchers ran it through a molecular fingerprinting process called an isotopic analys
is. Water samples furthest from gas drilling showed traces of biogenic methane—a type of methane that can naturally appear in water from biological decay. But samples taken closer to drilling had high concentrations of thermogenic methane, which comes from the same hydrocarbon layers where gas drilling is targeted. That—plus the proximity to the gas wells—told the researchers that the contamination was linked to the drilling processes.
In addition to the methane, other types of gases were also detected, providing further evidence that the gas originated with the hydrocarbon deposits miles beneath the earth and that it was unique to the active gas drilling areas. Ethane, another component of natural gas, and other hydrocarbons were detected in 81 percent of water wells near active gas drilling, but in only 9 percent of water wells further away. Propane and butane were also detected in some drilling area wells.
The report noted that as much as a mile of rock separated the bottom of the shallow drinking water wells from the deep zones fractured for gas, and identified several ways in which fluids or the gas contaminants could move underground: The substances could be displaced by the pressures underground; could travel through new fractures or connections to faults created by the hydraulic fracturing process; or could leak from the well casing itself somewhere closer to the surface.
The geology in Pennsylvania and New York, they said, is tectonically active with faults and other pathways through the rock. They noted that leaky well casings were the most likely cause of the contamination, but couldn’t rule out long-range underground migration, which they said “might be possible due to both the extensive fracture systems reported for these formations and the many older, uncased wells drilled and abandoned.”
The water was also analyzed for signs that dangerous fluids from inside the gas wells might have escaped into water supplies. The group tested for salts, radium and other chemicals that, if detected, would have signaled that the produced water or natural fluids in the well’s target zone were making it to the aquifers. But those types of fluids were not found. The group did not test for fracking chemicals or hydrocarbons like benzene, relying instead on the saline or radioactive compounds like radium as indicators.
In an interview, Jackson said that gas was more likely to migrate underground than liquid chemicals. Based on his findings, he doesn’t believe the toxic chemicals pumped into the ground during fracturing are likely to end up in water supplies the same way the methane did. “I’m not ready to use the word impossible,” he said, “but unlikely.”
In a white paper the group issued along with the journal article, Jackson and the others acknowledged the uncertainty and called for more research. “Contamination is often stated to be impossible due to the distance between the well and the drinking water,” they wrote. “Although this seems reasonable in most (and possibly all) cases, field and modeling studies should be undertaken to confirm this assumption … Understanding any cases where this assumption is incorrect will be important—when, where, and why they occur—to limit problems with hydraulic fracturing operations.”
The Duke study precedes a national study by the Environmental Protection Agency into the dangers of hydraulic fracturing that is expected to be finished sometime next year. Last year the EPA found that some chemicals known to be used in fracturing were among the contaminants detected in 11 residential drinking water wells in Pavillion, Wy.—where more than 200 natural gas wells have been drilled in recent years—but that investigation is continuing and the scientists haven’t concluded that the contamination is linked with drilling or hydraulic fracturing.
The release of the Duke research could immediately shape the increasingly intense public debate over drilling and hydraulic fracturing, especially in some of the areas where the research was conducted. Pennsylvania, which holds drilling companies liable for drinking water contamination within 1000 feet of a gas well, might consider the fact that the Duke researchers found the contamination extended to about 3,000 feet, Jackson said. New York State has a moratorium in place for hydraulic fracturing of horizontally-drilled wells—which cover more area and require more chemicals—through the end of June to allow for more consideration of the risks. “I would extend that at least temporarily,” Jackson said.
Congress, too, is taking note.
“This study provides eye-opening scientific evidence about methane contamination and the risks that irresponsible natural gas drilling poses for drinking water supplies,” said Congressman Maurice Hinchey, D-NY. “It provides yet another reason why more study of the environmental and health risks associated with hydraulic fracturing is needed.”
Hinchey is one of several Democratic members of Congress who recently re-introduced the FRAC Act, which calls for public disclosure of the chemicals used underground. The bill, which is currently languishing in the House, would remove an exemption in federal law that prohibits the EPA from regulating hydraulic fracturing.
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