For the first time, a scientific study has linked natural gas drilling and hydraulic fracturing with a pattern of drinking water contamination so severe that some faucets can be lit on fire.
The peer-reviewed study, published on Monday in the Proceedings of the National Academy of Sciences, stands to shape the contentious debate over whether drilling is safe and begins to fill an information gap that has made it difficult for lawmakers and the public to understand the risks.
The research was conducted by four scientists at Duke University. They found that levels of flammable methane gas in drinking water wells increased to dangerous levels when those water supplies were close to natural gas wells. They also found that the type of gas detected at high levels in the water was the same type of gas that energy companies were extracting from thousands of feet underground, strongly implying that the gas may be seeping underground through natural or manmade faults and fractures, or coming from cracks in the well structure itself.
"Our results show evidence for methane contamination of shallow drinking water systems in at least three areas of the region and suggest important environmental risks accompanying shale gas exploration worldwide," the article states.
The group tested 68 drinking water wells in the Marcellus and Utica shale drilling areas in northeastern Pennsylvania and southern New York State. Sixty of those wells were tested for dissolved gas. While most of the wells had some methane, the water samples taken closest to the gas wells had on average 17 times the levels detected in wells further from active drilling. The group defined an active drilling area as within one kilometer, or about six tenths of a mile, from a gas well.
The average concentration of the methane detected in the water wells near drilling sites fell squarely within a range that the U.S. Department of Interior says is dangerous and requires urgent "hazard mitigation" action, according to the study.
The researchers did not find evidence that the chemicals used in hydraulic fracturing had contaminated any of the wells they tested, allaying for the time being some of the greatest fears among environmentalists and drilling opponents.
But they were alarmed by what they described as a clear correlation between drilling activity and the seepage of gas contaminants underground, a danger in itself and evidence that pathways do exist for contaminants to migrate deep within the earth.
"We certainly didn't expect to see such a strong relationship between the concentration of methane in water and the nearest gas wells. That was a real surprise," said Robert Jackson, a biology professor at Duke and one of the report's authors.
Methane contamination of drinking water wells has been a common complaint among people living in gas drilling areas across the country. A 2009 investigation by ProPublica revealed that methane contamination from drilling was widespread, including in Colorado, Ohio and Pennsylvania. In several cases, homes blew up after gas seeped into their basements or water supplies. In Pennsylvania a 2004 accident killed three people, including a baby.
In Dimock, Pa., where part of the Duke study was performed, some residents' water wells exploded or their water could be lit on fire. In at least a dozen cases in Colorado, methane had infiltrated drinking water supplies that residents said were clean until hydraulic fracturing was performed nearby.
The drilling industry and some state regulators described some of these cases as "anecdotal" and said they were either unconnected to drilling activity or were an isolated problem. But the consistency of the Duke findings raises questions about how unusual and widespread such cases of methane contamination may be.
“It suggests that at least in the region we looked, this is a more general problem than people expected," Jackson told ProPublica.
For those who live in the midst of this problem, the report serves as long-awaited vindication.
"We weren't just blowing smoke. What we were talking about was the truth," said Ron Carter, a Dimock resident whose water went bad when drilling began there in 2008 and was later tested as part of the study. "Now I’m happy that at least something helps prove out our theory."
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 analysis. 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.