Some types of water can now sustain fires, instead of putting them out.

A team of Duke researchers has found high levels of leaked methane in well water collected near hydrofracking and shale-gas drilling sites, according to a study funded by the Nicholas School of the Environment and the Center for Global Change. The 60 samples were gathered from private groundwater wells from five counties in Pennsylvania and New York.

“Eighty five percent of samples contained detectable levels of methane,” said Stephen Osborn, an earth and ocean sciences research associate at the Nicholas School. “We noticed that, on average, natural gas concentrations in homeowners’ wells where there is natural gas extraction is 17 times higher [than areas where there is not natural gas extraction].”

Although nine of the 26 water wells located within one kilometer of a gas well had hazardous methane concentrations, none of the 34 wells located more than a kilometer away did, Robert Jackson, Nicholas professor of global environmental change and director of the Center on Global Change, wrote in a email Monday.

Hydrofracking, a method that extracts natural gas from shale rock formations, involves injecting over seven million gallons of highly-pressurized, chemically-treated water into the Appalachian basin, Osborn said.

“The whole object is to increase fluid flow between geologic formations and the gas wells,” he said.

By extending underground natural fractures, hydrofracking creates conditions that facilitate gas flow back into the gas wells, where it is subsequently harvested.

Last July, the researchers began collecting groundwater samples and analyzing them for dissolved gas concentrations and major inorganic components. Although the analyses showed no evidence of contamination from the chemically-treated water, many samples contained methane levels as high as 64 milligrams per liter—enough to pose a flammability hazard.

Prior to the study, some homeowners in Pennsylvania had contacted the Nicholas School because they were concerned about the quality of their water after natural gas wells were drilled and fracked.

“In some cases, [the homeowners] noticed that they’ve been able to light their water on fire,” Osborn said.

Methane accumulates naturally in water systems in concentrations less than 1 milligrams per liter. Concentrations greater than 28 milligrams per liter are sufficient to generate cause for concern, as they may pose an explosion hazard.

The gas can act as an asphyxiant in enclosed spaces, but the effects of consuming methane are currently unknown.

Approximately 44 million Americans rely on a private water supply for household and agricultural use, Jackson said, adding that his team has called for a medical review of chronic, low-level exposure to methane through ingestion or breathing.

Nathaniel Warner, a doctoral student at the Nicholas School, said though the study is the first of its kind to examine the relationship between proximity to a gas well and the likelihood of having contaminated water, it is uncertain whether the relationship between methane levels and proximity to a gas well extends elsewhere.

“It would be difficult to produce usable gas without hydraulic fracturing [so] I think [the results] just point to more research needing to be done [on this type of technology],” he said.