The Environmental Protection Agency said Thursday that it was weighing whether a controversial refinery on St. Croix posed “an imminent risk to people’s health” after a third incident in the span of three months sickened local residents and forced three schools and the island’s bureau of motor vehicles to close.

Residents across the island — some living as far as 10 miles away from Limetree Bay Refining’s operations on the south shore — began reporting feeling nauseous and ill on Wednesday after gaseous fumes were released from one of its oil refining units. The odor persisted through Friday.

Two primary schools and a technical educational center closed on Thursday, along with the Bureau of Motor Vehicles, and remained shut Friday. Local officials said in a statement the bureau stayed closed because its employees “are affected by the strong, unpleasant gas like odor, in the atmosphere around the BMV.”

“EPA takes very seriously the reports from today and in recent weeks of children, families, and individuals becoming sickened by emissions around the Limetree Bay facility,” the agency said in a statement. “If EPA makes a determination that the facility’s operations present an imminent risk to people’s health, consistent with its legal authorities, it will take appropriate action to safeguard public safety.”

Limetree Bay and territory officials gave shifting accounts of what might have transpired over the course of the week.

The company, which has had two accidents since restarting operations Feb. 1, confirmed in a statement that it had “become aware of an odor affecting areas west of the facility,” adding that maintenance work on a “coker unit,” which processes oil at a high heat level, “has resulted in light hydrocarbon odors.”

“We will continue to monitor the situation, but there is the potential for additional odors while maintenance continues,” the firm said. “We apologize for any impact this may have caused the community.”

On Thursday, when residents contacted Limetree Bay about the fumes, it posted on Facebook that nothing was amiss.

“Limetree Bay has received several community complaints of a strong odor,” it said. “Our preliminary investigations have revealed that units are operating normally and there is no activity that would result in an odor.”

In a phone briefing with reporters Friday, U.S. Virgin Islands Gov. Albert Bryan (D) and his deputies said they were conducting air monitoring “to find out what is causing this stench.”

“I just want to show the public that we’re doing everything to keep the people safe,” Bryan said. “We’ve not ruled out anything. We are looking under every stone to make sure we have the information needed.”

Jean-Pierre Oriol, U.S. Virgin Islands planning and natural resources commissioner, told reporters that after inspecting the plant his office did not believe the refinery was the cause of the persistent odor, but then added, “It hasn’t been ruled out.”

Roughly 100 residents have notified local authorities about the gaseous odor, according to Virgin Islands Territorial Emergency Management Agency Director Daryl Jaschen.

Jelani Ritter, a local blogger who lives 10 miles away from the plant on the island’s west end, said in an email that he was awakened at dawn Thursday by a smell that “was most unbearable.”

“The lack of accountability from Limetree is disheartening, as many individuals reported becoming nauseous, while throbbing headaches have become the norm,” Ritter said.

Jennifer Valiulis, who heads the St. Croix Environmental Association, said in an email that her office has been deluged with calls from residents concerned about the impact of the plant’s operations. In February, an upset at the refinery showered oil on people’s homes, gardens and drinking-water supplies more than two miles away, and last month sulfuric gases escaped from the plant.

“The fumes are inescapable in the areas downwind from the refinery, even with closed doors and windows, and I’m hearing desperation from people who don’t know what to do and frustration at the lack of answers or relief,” she said.

Some, like Ritter, are questioning their support for the plant. The refinery, which used to operate under the name Hovensa before shutting down nearly a decade ago and changing ownership, is a major employer and source of revenue for the territory.

“It is time that our local government applies pressure in its attempts to hold Limetree Bay Terminals responsible, through the enforcement of fines and citations for their continuous contamination of the environment, and the health impacts these mishaps have and continue to have on the citizens of St. Croix,” he said.

On Wednesday the company agreed to start operating five sulfur-dioxide monitoring stations that the previous owner shut down when it shuttered, after the EPA notified Limetree that failing to run the monitors amounted to a legal violation.

The EPA, which sent a team of experts to St. Croix on April 30 to investigate the refinery’s operations along with territory officials, said it will “be bringing monitoring equipment to St. Croix in the coming days, along with personnel to operate the monitors.” Agency officials said they will measure air concentrations of sulfur dioxide and hydrogen sulfide.

John Walke, clean-air director for the Natural Resources Defense Council, said in an email that it was significant that the agency said it was looking into whether the plant posed “an imminent risk to people’s health,” because it alluded to the EPA’s enforcement authority under the Clean Air Act, “which allows the agency to swoop in with special powers when it concludes there is an immediate health threat.”

“This is a shot across Limetree’s bow,” he said, because if that determination is made, the “EPA could go to federal district court to ‘immediately restrain’ the source to stop the responsible emissions.”