The Environmental Protection Agency will send investigators to the U.S. Virgin Islands as early as this week, the agency announced Tuesday, as part of a larger probe into a series of accidents at a St. Croix oil refinery that residents worry has exposed them to dangerous levels of noxious fumes and poisoned their drinking water.

The investigation, which will be done in conjunction with U.S. Virgin Islands officials, will look into recent mishaps at the Limetree Bay refinery, including an accidental flare last week that released large amounts of sulfuric gases, causing three schools to shut down on Friday and prompting local officials to issue a warning for those with breathing issues to stay indoors.

The fumes also forced the island’s Covid-19 vaccination center on the University of the Virgin Islands campus to close Friday, the Washington Post reported last week.

“We smell it outside, we smell it inside. It irritates your eyes, your throat,” said Olasee Davis, an ecology professor at the university, which is located about two and a half miles west of the refinery. “People are concerned about their health.”

It’s the second flaring incident, in which a refinery burns off gases or releases steam as a safety precaution, since the plant reopened in February under new ownership. An accidental flare on Feb. 4 covered more than 130 homes in the nearby Clifton Hill neighborhood with specks of oil and contaminated the drinking water for dozens of residents.

“The executive management of Limetree Bay sincerely apologizes on behalf of the entire organization for the unpleasant odor that came from the refinery yesterday and for its impact on our neighbors and the community,” Limetree said in a statement on Saturday.  “We are committed to investigating fully the reasons for this event in cooperation with local regulators, and to implement improvements to prevent it from happening again.”

EPA’s announcement Tuesday was a sign that the agency may be ramping up its investigation into possible violations by Limetree and is the latest in a series of developments that have cast doubt on the future of the refinery.

In March, the agency withdrew a key air pollution permit for the plant that would have allowed the company to expand its refining operations in the future, citing environmental justice concerns and a need to further review how to best safeguard the community. The refinery also shut down operations for about three weeks earlier this month due to an undisclosed mishap, and several top Limetree executives announced they were stepping down, according to reports from Reuters.

The refinery closed in 2012 after its previous owner agreed a year earlier to a $700 million consent decree with the EPA mandating various environmental and pollution control improvements, most of which were never made. The plant, which the previous owner took into bankruptcy in 2015, reopened earlier this year under a permit granted by the Trump administration in 2018.

Environmentalists say permitting the plant’s reopening was a clear example of Trump’s unfettered and irresponsible deregulatory agenda and his administration’s penchant for granting sweetheart deals to well-connected corporate interests late in his term. In Limetree’s case, the administration ignored decades of precedent when considering the new permits and expressed a willingness in emails to the refinery’s new owners to do almost anything they needed to restart it.

Last week’s incident also raised questions about what exactly was released into nearby communities. On Friday, the U.S. Virgin Islands Department of Planning and Natural Resources said in a statement that “an exceedance of hydrogen sulfide” at the refinery had caused the foul odor. Limetree disputed that claim, saying in its own statement over the weekend that a buildup of hydrogen sulfide was sent to a flaring unit where it was “safely burned” and converted into sulfur dioxide.

Both sulfur dioxide and hydrogen sulfide can be harmful—and even deadly—to humans in high concentrations, causing lung and eye irritation and complicating breathing. Acute exposure to hydrogen sulfide can lead to serious injuries, including causing comas, according to the Center for Disease Control.

St. Croix’s 56-year-old refinery has a long history of spills and environmental violations, including leaking more than 43 million gallons of oil into St. Croix’s only aquifer between 1982 and 2011. Many residents have expressed distrust in the local government, which they say has been too lenient with the refinery’s owners when conducting oversight, often at the expense of the mostly Black and Latino neighborhoods that surround the facility.

In its Tuesday press release, the EPA said it would work with the U.S. Virgin Islands government to transparently distribute information to the community and channel residents’ concerns to the proper authorities.

“The incidents have been distressing and, in some cases, caused members of this already overburdened community to become ill,” the agency said.