Pennsylvania State University researchers using a new testing protocol have found significantly low levels of methane contamination in water wells across the state that could be linked to natural gas drilling.
The university said researchers used “existing, affordable” water chemistry tests and applied a method described in a peer-reviewed journal last year on a much larger dataset. The latest findings were published in July in the journal of Environmental Science & Technology.
Researchers took samples in the northeast, northwest and southwest parts of the state, where both conventional and unconventional oil and gas drilling are prevalent. They set out to see what percentage of the water wells showed chemical changes indicative of methane contamination caused by drilling for and producing fossil fuels.
Of the 20,751 samples, only 17 or 0.08%, showed possible signs of methane contamination by the extraction process. The researchers divided the water samples into various types. The two types that were defined as those most likely caused by oil and gas drilling contained high methane and sulfate levels, and either low or high iron levels.
Methane in groundwater in the Marcellus Shale and other resource plays is not uncommon. If methane has been in groundwater for a long time, bacteria would have reduced the iron and sulfate. The reduced forms would have precipitated as iron sulfide, indicating naturally occurring methane.
Of the 17 samples that returned positive for new methane, researchers said 13 were from the northeastern part of the state, where unconventional drilling is robust. But none of the samples came from sites within 2,500 feet of “known problematic wells,” the university added.
“The researchers’ findings suggest that methane may migrate farther than previously thought if the new methane was derived from these known problematic gas wells,” Penn State said. “Only intensive field investigations could show whether this happened.”
Under state law, operators are responsible for methane leaks that impact wells within a 2,500-foot area.
“We focus on the Marcellus Shale, but this testing protocol has the potential to be applied to other shale plays in the United States and other countries,” said study co-author Tao Wen, of the university’s Earth and Environmental Systems Institute. “It can benefit the global community.”
The research was funded by the National Science Foundation and the U.S. Geological Survey.