What are leaky underground storage tanks and how do you clean them?

For more than a decade, some residents of the small Canob Park neighborhood in Richmond, Rhode Island, drank and bathed in tap water contaminated by gasoline leaking from tanks under gas stations a few hundred yards from their homes. They battled oil companies for years, had to boil most of their water every day and feared that they and their children would suffer permanent damage.

The Canob Park disaster sparked a national outcry in the 1980s to clean up and regulate the thousands of underground tanks that stored petroleum, fuel oil and other dangerous chemicals. This program continues to this day, and although more than half a million sites have been remediated, the tanks are a major cause of groundwater contamination.

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EDITOR'S NOTE: This article is a collaboration between The Associated Press and The Uproot Project.

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According to the U.S. Environmental Protection Agency, nearly half of all Americans rely on groundwater for their drinking water, and it's not just well water that's at risk. Even if a city's water supply is treated and processed to ensure it meets federal standards, contaminants from gas leaks can still be picked up on the way to the faucet. In some cases, this can happen if the water comes from an unregulated well—some cities get their drinking water from a mix of surface and groundwater—or through broken pipes.

For private wells that are not regulated by the government, the responsibility for treating and filtering the water lies with the homeowner.

How leaks occur

Environmental experts say even a pinhead-sized hole in an underground tank can leak 400 gallons of fuel a year into the ground, polluting soil and water. Leaks can also destroy habitat and kill wildlife. According to the latest data from the U.S. Environmental Protection Agency (EPA), about 81 million people live within a quarter-mile of an underground storage tank that has experienced at least one leak.

Most tanks were made of steel in the mid-1980s and corroded over time. Modern tanks are made of fiberglass, which is more corrosion-resistant, but all tanks start to leak sooner or later, says Dr. Kelly Pennell, a professor of environmental engineering and water resources at the University of Kentucky. The cylindrical tanks typically hold tens of thousands of gallons of fuel.

Detecting leaks is not easy, she said.

“If a gas station has been in operation for 10 or 15 years, you may not be able to detect these small leaks,” Dr. Pennell said. “You wouldn't lose 1,000 gallons a day – you lose drops – but over time, they become noticeable.”

Leaks can create chemical plumes that move through groundwater and turn into steam that rises through cracks in the foundations of homes and businesses. These fumes can contain cancer-causing chemicals, including benzene, a component of gasoline. They also pose a fire and explosion risk. When contamination was detected in Canob Park, the local fire chief took drinking water samples from one of the gas stations and said it was “almost flammable.”

Cleaning up groundwater contamination is costly, says Anne Rabe, environmental policy director at the New York Public Interest Research Group, a nonprofit that studies environmental problems, including leaking underground storage tanks.

“You really have to do extensive testing to determine when these underground storage tanks are leaking and take immediate action, otherwise the leak will continue to spread every week and that will increase the cost of remediation,” Rabe said.

Since Congress authorized the EPA to regulate underground tanks in 1984, more than 516,000 leaks have been cleaned up, but more than 57,000 known locations still await complete cleanup, the EPA says.

Cost of cleaning

The average cost to clean up such a site is $154,000, according to the Association of State and Territorial Solid Waste Management Officials, an organization that acts as a liaison between state and territorial programs to address leaky underground storage tanks and the EPA. But that cost can be much higher or lower, depending on the amount of work involved.

The owners of the tanks must buy insurance and pay for cleanup, but that doesn't always happen. A trust fund that receives money from a gasoline tax helps – it currently has about $1.5 billion – but the program costs the states and federal government about $1 billion a year in addition to the fund.

While there are leaking underground storage tanks in nearly every city in the U.S., according to the EPA, the people closest to these sites tend to live in lower-income, higher-minority communities.

The EPA requires owners and operators of underground storage tanks to install approved leak detection equipment and test these systems regularly. But they are not foolproof. There are several types of systems, and each type can miss a leak or its extent. Industry groups recommend building a system that uses more than one leak detection method, but that doesn't always happen, and sometimes the method chosen may not be the best for a particular tank. And owners may not maintain them properly.

The EPA estimated that complying with the regulations would cost tank owners and operators a total of $160 million per year in 2015 – or about $715 per facility per year. However, it would mean fewer taxpayer dollars would be needed for cleanup, the agency said.

Some of the properties remediated since the program's inception have been funded through federal and state brownfield remediation programs that encourage the remediation and reuse of contaminated or potentially contaminated sites.

The EPA announced a historic $315 million investment in the Brownfields program last year, with most of the money coming from the bipartisan infrastructure deal that President Joe Biden signed more than two years ago.

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Jordan Gass-poore, The Uproot Project, The Associated Press