Abandoned oil and gas wells in Pennsylvania emit carcinogens and other harmful pollutants, groundbreaking study shows

The release of cancer-causing benzene and other toxic gases from sites in Pennsylvania raises concerns about millions of other abandoned wells across the U.S.

• By Liza Gross/

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On a cloudy late-winter morning in 2004, Charles and Dorothy Harper were babysitting their 17-month-old grandson, Baelee, when the furnace in their rural Western Pennsylvania home revved up. The newly retired pastor and his wife did not realize that flammable gas had infiltrated the basement of the house, which they had recently built.

Around 9 a.m. that dreary March morning, a massive explosion leveled the house and left three lifeless bodies buried in the rubble along a country road about 80 miles northeast of Pittsburgh.

There were 16 known gas wells within 3,000 feet of the Harpers’ home. Natural gas from a well that was being drilled had entered the basement through the couple’s well water, a marshal with a local fire department told The Pittsburgh Tribune Review at the time. Officials knew this, the marshal said, because they tested the victims’ blood and lung tissue after recovering their bodies and found methane—a potent climate-warming compound that is the main constituent of natural gas.

Yet a new study suggests that residents of the nation’s fossil-fuel producing regions could be facing a different threat: carcinogens and other toxic air contaminants spewing from millions of wells that are no longer even operating.

In a study in the journal ACS Omega, researchers have reported the discovery of harmful volatile organic compounds, or VOCs, leaking from 48 abandoned wells in Western Pennsylvania.

Scientists have long known from studies of active drill sites that oil and gas wells produce a wide range of hazardous air pollutants. Yet until now, no independent researchers had systematically measured toxic air contaminants from any of the more than 3 million abandoned oil and gas wells scattered across the nation.

In the study, researchers with the nonprofit research and policy institute PSE Healthy Energy measured both the emission rates and the concentrations of harmful VOCs coming from abandoned wells in the heart of the nation’s largest gas field, the Marcellus Shale. “Our study is the first to thoroughly identify that there is a benzene hazard associated with abandoned wells,” said the lead author, Seth Shonkoff, the executive editor of the research institute, PSE Healthy Energy.

Many were releasing benzene, a well-established cause of cancer, along with compounds that damage the nervous, immune and respiratory systems, the researchers reported. They found air concentrations as high as 250 parts per million—250,000 times the California safety threshold of 0.001 parts per million, which public health experts use as a gold standard because it tends to protect the most vulnerable populations, such as children.

The U.S. Environmental Protection Agency classifies benzene as a known human carcinogen for every route of exposure, whether inhaled, ingested or absorbed through the skin, and the World Health Organization has concluded that no safe level of exposure to benzene exists.

Decades ago, studies associated benzene with an increased risk of cancer for oil industry workers. VOCs like those found at the abandoned wells are also well-established precursors of smog, or ground-level ozone. Exposure to ozone is linked to diverse health problems, including uncontrolled asthma requiring emergency room visits and hospitalization and cardiovascular and respiratory disease leading to premature deaths.

While some of the abandoned wells investigated for the study are buried in remote areas, 93 percent are within 3,280 feet of buildings and homes, the team found. Nearly a quarter are just 328 feet from buildings and homes—less than the length of a football field.

Joan Casey, an environmental epidemiologist with the University of Washington’s School of Public Health who was not involved in the study, said the article’s findings

were disappointing but not surprising.

“There are measured VOCs coming out of these wells that we know are health-harmful,” said Casey, who serves with Shonkoff on a scientific panel advising the state of California on public health regulations for the oil and gas industry. “Most of our health studies to date have focused on residential proximity to active oil and gas wells and have completely ignored this subset of abandoned wells.”

That means the public health community is missing “this whole other set of exposures” in evaluating the impact of oil and gas wells, she said. “If what is found in this study is generalized to all of our abandoned wells, we definitely don’t want people living near them.”

Often, the Only Option: Testing Wells on Public Lands

The fact that some abandoned wells are releasing a carcinogenic compound at very high levels raises serious concerns about air quality, groundwater quality and people who could be exposed to problems with both, Shonkoff said. And it adds to a larger body of research on what makes up natural gas as it travels through the oil and gas supply chain, from wells to the pipelines that supply homes and buildings.

“What we’ve found across all these studies, which has actually been quite surprising, is that all of this gas is not just methane,” he said. Almost every single sample of gas across the supply chain, including abandoned wells, contains cancer-causing benzene, his studies have found.

Industry research has already identified emissions of benzene and other gases from active oil and gas wells, Kyle Ferrar, a public health expert with the nonprofit FracTracker Alliance, noted. Ferrar, who was not involved in the Pennsylvania study, has long documented uncontrolled well leaks in California.

But it has been hard for independent researchers to get access to old abandoned wells to measure and assess the toxicity of harmful non-methane emissions, he said. So they typically have to locate such wells on public lands. “You don’t have that in a lot of places, but you do in Pennsylvania,” Ferrar said.

Pennsylvania regulators believe that some 200,000 wells that have been abandoned since the first was drilled in the 1850s are missing from state databases. Some remain unaccounted for because they predate modern well permitting and plugging requirements.

For others, historical records indicate that the wells existed but lack coordinates to show where they were, said Neil Shader, a spokesperson for the Pennsylvania Department of Environmental Protection, or DEP.  “We can account, for sure, for about 27,000,” he said. “But the rest are lost to history, buried in dead leaves and dirt, paved over, et cetera.”

Sometimes, according to Shonkoff, all that’s left is a hole in the ground.

Staff members from the DEP helped Shonkoff’s researchers locate the 48 wells so they could collect and analyze gas. Because most were on public land, the team didn’t need permission to gain access to the sites.

Shonkoff said he would have liked to have sampled every known abandoned well in Pennsylvania. But with the lab analysis alone costing $500 a sample, the time and money needed to study thousands of wells would have been prohibitive. So the team focused on 48.

The results demonstrate that the geology underlying the wells affects what comes out of them. When the researchers compared their Pennsylvania readings to spot samples taken in other oil and gas formations across the country, they saw that benzene concentrations varied considerably by location.

Not all abandoned wells pose the same risks, Shonkoff said. Some are leaking more than others. Some are very close to where people live, work and play. Others could contaminate nearby drinking water sources.

“This information should be taken into consideration as we think about which wells to prioritize plugging first, with the limited amount of resources we have to address this massive problem,” he said. That would mean identifying the abandoned wells with the highest emissions of harmful substances and then determining which are closest to communities and their drinking water sources.

In the course of the research, Pennsylvania regulators issued an emergency well-plugging order for a well southeast of Pittsburgh after the team detected levels of methane and benzene at the highest rate measured in the study, 250,000 times California’s safety standard. Residents of a new housing development three-fifths of a mile away had complained of odors. The emissions were so pungent and irritating that the researchers cautioned anyone taking air samples at the site in the future to wear protective respiratory gear.

In another case, the researchers discovered that an unplugged abandoned well sat as little as 33 feet from the rented home of a family that had no idea that the pipe in the backyard was an old gas well. The team did not detect benzene at the site but recorded daily methane emissions high enough to pose the risk of a fire and explosion.

Many residences and buildings in oil- and gas-producing regions across the country are built on top of abandoned wells, unbeknownst to the owner or builder, Shonkoff said. That’s why building codes in the Los Angeles Basin, another major oil-producing region, require methane and VOC mitigation systems to be installed in all buildings within specified zones.

The systems blow gas out of a house to prevent it from accumulating. Such a device could have saved the Harper family.

“Before this study, we would think about the big risks being tied only to explosion hazards,” Shonkoff said. The research shows that governments also need to focus on exposure to air pollutants, he added.

A Trillion-Dollar Problem

Last year the Biden administration announced a $4.7 billion program to clean up abandoned wells under the 2021 Infrastructure Investment and Jobs Act. Shader of the Pennsylvania DEP said the agency had received $25 million so far in federal funds to plug abandoned wells and hoped to secure nearly $400 million in all. But plugging thousands of abandoned wells in the state would likely cost billions.

Operators in Pennsylvania must post a bond of $2,500 to drill a new well (and up to $25,000 to cover all wells they drill). They forfeit the money to the state if they abandon the well without plugging it, Shader said. But state officials estimate that it costs an average of $33,000 to plug a well, and as much as $800,000 if the job requires clearing years of debris.

A new bill proposed in the state assembly would allow regulators to raise bond prices to help support remediation efforts. The Pennsylvania Independent Oil and Gas Association recently objected to the legislation, arguing that there was no evidence that operators have been abandoning wells and leaving taxpayers to foot the remediation bill. The association, which represents about 400 operators in the state, did not respond to requests for comment on the study.

Shonkoff says he appreciates that federal funds are being invested in remediation. But with so many abandoned wells across the country and more to come as drilling continues, he adds, it’s really a multitrillion-dollar national problem. For the time being, “we need to get very clear on how to prioritize wells that need to be remediated with the billions of dollars on the table right now,” he said.

In California, Ferrar has identified hundreds of leaking idle wells and infrastructure in Bakersfield and other oil-producing regions in the state but thinks that’s just a fraction of the true count. Although California regulators have required operators to plug many of them, the fixes are temporary because old wells are so leak-prone, he added.

Acting on clear evidence that living, playing and working near active oil and gas operations causes serious health problems, California legislators passed the strongest setback law in the country last year. Regulators stopped implementing protections after an oil industry effort to reverse the law qualified for a referendum on the 2024 general election ballot, although legal experts say the state could simply stop issuing drilling permits near neighborhoods.

“This research stresses that we need a setback now more than ever,” Ferrar said.

After the Harpers were killed in 2004, the DEP warned residents that high concentrations of methane in water wells and confined spaces can cause explosions. Now the question remains of whether safety guidance should be issued for state residents living near neglected wells.

Given that many of the wells sampled were emitting harmful gases, sometimes at very high rates, near homes, the study’s authors wrote, “further investigation is necessary to determine whether gas emissions pose an inhalation risk to people living, working, or congregating near abandoned wells.”

For Shonkoff, the new evidence that carcinogens and other toxic air contaminants are being released also underscores an urgent need to move from natural gas to clean energy sources.

Until then, he contends, state regulatory agencies should require the monitoring and disclosure of gas composition throughout the nation’s supply chains. That way, public officials would have the information they need to protect people who might be in harm’s way—and move them before it’s too late.

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