Even when you’re done with an oil well, you’re not really done with it. Idle wells could still be leaking methane, a potent greenhouse gas, into the atmosphere, according to a new study carried out on oil wells in Texas.

Amy Townsend-Small, an associate professor of geology and geography in UC’s College of Arts and Sciences, has been studying leaky oil wells for a few years, finding that some of them are still leaking methane years after the activity has been shut down. But this is the first time she was granted access to study wells on private land.

“Nobody has ever gotten access to these wells in Texas,” Townsend-Small said. “In my previous studies, the wells were all on public land,” Townsend-Small says.

There were reasons to suspect that things were not alright in Texas. A 2016 study by Townsend-Small found a similar issue in inactive wells she tested in Colorado, Wyoming, Ohio and, Utah, which leak methane equivalent to burning more than 16 million barrels of oil — and that’s according to conservative government estimates.

In Texas, things were just as bad, if not worse.

“Some of them were leaking a lot. Most of them were leaking a little or not at all, which is a pattern that we have seen across the oil and gas supply chain,” Townsend-Small said. “A few sources are responsible for most of the leaks.”

The average leaking rate was 6.2 grams per hour, although seven had methane emissions of as much as 132 grams per hour. If the same rate were to be consistent across all wells in Texas, it would be the equivalent of releasing 5.5 million kilograms of methane per year, the equivalent of burning 150 million pounds of coal.

In addition to the methane, Townsend-Small discovered another problem: five wells were leaking a brine solution onto the ground, in some cases creating large ponds, wreaking havoc on the nearby environment.

“I was horrified by that. I’ve never seen anything like that here in Ohio,” Townsend-Small said. “One was gushing out so much water that people who lived there called it a lake, but it’s toxic. It has dead trees all around it and smells like hydrogen sulfide.”

This isn’t the first time the problem was highlighted by researchers. Time and time again, studies have revealed that oil wells are leaking methane, and authorities are underestimating the problem. Across the US and Canada alone, there are millions of inactive oil wells, hundreds of thousands of which are undocumented. Many of these are improperly sealed and are continuously leaking methane into the atmosphere.

According to conservative estimates, these uncapped wells are responsible for 4% of the US total methane emissions, but the situation could be much worse, and those responsible for the wells are reluctant to offer external access to monitor the leaks. Even this study, wouldn’t have been possible without media organizations that wanted to explore the environmental impact of oil wells and arranged with property owners to allow Townsend-Small to carry out measurements. But there’s also some good news hidden in this study. The good news is that since a few of these wells are responsible for a majority of emissions, they could be prioritized and capped.

President Joe Biden’s stimulus plan includes $16 billion for capping abandoned oil and gas wells and mitigating abandoned mines. Inactive oil wells produce less methane than active ones, but it’s one way to reduce greenhouse gas emissions. With studies like this one, the more problematic ones could be prioritized. In addition, infrared camera inspections could help identify leaks and monitor wells.

The study was published in the journal Environmental Research Letters.