BURLINGTON, Vt.— Oct. 26, 2015 — The hydraulic fracturing process can create fractures underground that connect to abandoned oil and gas wells, leading to methane escaping into the atmosphere, according to a press release.

A study by the University of Vermont funded by the National Science Foundation found that abandoned wells near fracking sites can allow methane release which is not currently being measured, noted the release.

Publishing their findings in the Proceedings of the National Academies of Science, the researchers said that methane leaks measured at some abandoned wells near fracking sites are significant, although they did not investigate the source of the gas, stated the release.

“Our paper shows that fracking sites don’t exist in isolation; They’re part of a system that includes a network of abandoned wells that can effectively pipeline methane to the surface,” said lead author James Montague, an environmental engineering Ph.D. student at the University of Vermont, in the release.

The study focused on an area of the Marcellus Shale in New York State which was fracked until the controversial drilling technique was banned across the state in the summer of 2015, shared the release. The formation, composed of layers of shale and hydrocarbons, is beneath land that has been used for conventional oil and gas drilling since the 1880s.

According to the university, official records show the location of about 40,000 existing wells in New York, 30,000 of which are located within the footprint of the Marcellus formation, but the state’s Department of Environmental Conservation estimates that as many as 70,000 wells have been drilled.

With the location of so many wells unknown, the researchers used a mathematical model to predict the likelihood that the fracking-induced fractures of a randomly placed new well in the Marcellus formation would connect to an existing wellbore. This put the probability at between 0.03 percent and 3 percent.

After the paper was published last week, industry-sponsored information emerged which increased assumptions about the area impacted by a set of six to eight fracking wells known as a well pad, raising the probabilities cited in the paper by a factor of 10 or more.

Methane can only escape via abandoned wells that are damaged, for example when the concrete that buffers the well from the surrounding earth loses integrity.

But given the large number of abandoned wells, even a small percentage of damaged wellbores can potentially pose an environmental risk, warned the study’s co-author George Pinder, professor of environmental engineering.

Extensive due diligence by oil and gas companies to identify all nearby wells will have the greatest effect in reducing the probability of leaks between wells, the researchers concluded.

You can find the entire release here.