Fracking wells in Pennsylvania’s Marcellus Shale region are disproportionately located in poor rural communities, which bear the brunt of associated pollution, according to a new study.

The study bolsters concerns that poor people are more likely to deal with hydraulic fracturing in their community and raises concerns that such vulnerable populations will suffer the potential health impacts of air and water pollution associated with pulling gas from the ground.

“This trend is not one we’re surprised by, we see this in a lot of industries,” said Mike Ewall, founder and director of Energy Justice Network, a nonprofit organization that works with U.S. communities dealing with pollution from energy.

However industry groups say hydraulic fracturing is in rural farming regions of Pennsylvania out of necessity and is providing some much needed economic stimulus.

Researchers from Clark University mapped areas in Pennsylvania, West Virginia and Ohio to identify areas with a lot of Marcellus Shale hydraulic fracturing wells and then examined some local demographics: age, poverty and education levels, and race.

The Marcellus Shale is a large rock formation—almost 95,000 square miles—that stretches across parts of New York, Pennsylvania, Ohio and West Virginia and holds trillions of cubic feet of natural gas. It’s experienced a surge of drilling as techniques have advanced. The most common method, hydraulic fracturing or “fracking”, works by drilling and injecting fluid at high pressure, which fractures rocks and releases the natural gas.

One thing was clear from the Clark University study: poverty levels are strongly associated with active fracking wells in Pennsylvania.

“Our analysis shows that environmental injustice was observed only in Pennsylvania, particularly with respect to poverty: in seven out of nine analyses, potentially exposed [census] tracts had significantly higher percent of people below poverty level than non-exposed tracts,” the authors wrote.

The researchers used different tests to estimate exposure to potential gas well pollution—varying the distance from the wells since there is no definitive distance that makes someone safe or exposed. “No matter how you estimate proximity, it always came up as exposure was significantly, much higher” in poor Pennsylvania communities, said lead author of the study Yelena Ogneva-Himmelberger, a Clark University assistant professor of Geographic Information Sciences for Development and Environment.

She said the study raises environmental justice concerns as people under the poverty line often “have less mobility and access to information” about the potential ills of fracking, especially since the communities she looked at were rural areas without the amenities of larger cities and towns.

She also found local clusters of gas wells disproportionately impacting the poor, elderly and those with lower education in West Virginia, and children in Ohio.

Most concern about proximity to gas wells stems from the potential for air pollution from drilling and leaks, and water pollution from the mix of chemicals pumped into the ground, radiation from the fractured rocks, or methane.

And recent headlines have only stoked alarm in Pennsylvania fracking communities.

This week the Proceedings of the National Academies of Sciences released a study that found traces of a common fracking chemical in water from three homes in Bradford County, Pennsylvania, where the median household income is 10 percent lower than the rest of the state’s.

In addition, last month researchers reported that radon—the world’s second leading cause of lung cancer—is much more prevalent in Pennsylvania buildings near natural gas development than in other parts of the state.

And a week after the radon study, the state released data that showed sulfur dioxide emissions soared 57 percent from 2012 to 2013 at Pennsylvania natural gas sites. Sulfur dioxide harms the respiratory system and can cause or worsen illnesses such as asthma.

Industry has long maintained that fracking is environmentally safe and cleaner than other fossil fuels. In response to the new study, Joe Massaro, a spokesman for the Independent Petroleum Association of America's outreach program called Energy in Depth, said in an email that industry presence is helping poor Pennsylvania communities.

"A majority of people living in these rural areas are hardworking, generational farmers. According to the Pennsylvania farm Bureau the average net cash income per farm is $18,567, just below the poverty line," Massaro said. "By signing leases with oil and natural gas operators here in the Commonwealth, these farmers have been able to buy new state of the art equipment and pay off debt which has made their lives that much easier."

Massaro added that the oil and gas industry also provides local tax revenue and jobs.

But Energy Justice’s shale gas program coordinator, Alex Lotorto, disagrees and said that small farmers may have seen a short-term boost from oil and gas leases but the negative impacts of the industry far outweigh any perceived benefits.

He said that the new study just reinforces what his group has been seeing on the ground for years.

“Residents in these poor counties have been under assault for generations,” he said.

“Rural poverty is real in the shale fields.”

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.