Methane seeping up underground pathways caused concentrated plumes of gas in the air in Bradford County, PA, where the state and a natural gas drilling company are investigating the cause of stray methane bubbling in streams and water wells, according to a study.
The 3½-hour survey conducted for the environmental organization by Gas Safety Inc. in Leroy Twp. on June 8 found average ground-level methane concentrations in a roughly 2-square-mile area at nearly twice normal background levels for the region’s air.
The methane concentration in the air spiked to 22 parts per million – more than 10 times the highest background level of 1.95 parts per million – during a roadside survey north of Route 414 and Rockwell Road. The concentration and size of the plume “clearly indicate that one or more methane emissions were present and releasing substantial amounts of methane into the atmosphere,” according to the report. The scientists ruled out nearby farm or other natural sources of biogenic methane, like animal manure, and found no elevated levels downwind of a nearby Chesapeake Energy natural gas well pad that might have indicated leaking from above-ground infrastructure at the site.
The methane levels were much higher than amounts that naturally seep through the earth or caused by the breakdown of biological material in wetlands, the researchers said.
“The amount of methane that had to come out at that point to generate that plume, that’s a lot of methane,” said Bryce Payne, Ph.D., the report’s author and an environmental scientist at Gas Safety Inc. “The preponderance of evidence here is that this is a nonbiogenic source.”
The researchers just did surveys along public roads and on a few properties where landowners gave them permission to take air samples and so could not track the precise emissions points for the gas.
The average concentration of methane found in the air during the sampling would not pose a health risk but it is a notable source of a greenhouse gas, Payne said. The highest concentration of gas nearest to the points where it is escaping from the ground could potentially pose an explosion risk, he said.
Methane bubbling in water wells and creeks outside the airborne plume but close to it also indicate the spread of methane is greater underground than above ground in the area, the study found.
“The underground extent of methane contamination is significantly greater than the plume we identified,” Dr. Payne said.
The state and Chesapeake have been investigating the source of methane in at least three water wells, two streams and a wetland in the same area of Leroy Twp. since May 19, when residents reported changes in their water. Two Chesapeake natural gas wells on a pad a half-mile from the affected water wells are under investigation as a potential source of the stray gas.
The state has not determined the cause of the methane, which does occur naturally in some water wells in the state and also tracks to faulty cemented barriers in natural gas wells in Bradford, Susquehanna and other regional counties.
Methane bubbling in one tributary to Towanda Creek unsettled the rocky streambed and turned it the consistency of pudding. As of the end of May, officials vented three water wells and the homes got water treatment units or replacement bulk water and methane monitoring alarms. A fourth home got bottled water as a precaution.
A Department of Environmental Protection spokesman said the agency received the Clean Air Council report on Tuesday afternoon and would have to review it before commenting. Oil and gas enforcement staff were out of the regional office on business and were not available to provide an update on the status of the state’s investigation, he said.