NORTH POLE — At least six households near the Flint Hills Resources refinery learned in the past few months that their drinking water is tainted with an industrial chemical whose long-term health effects are largely unknown.

On Monday, about 80 people gathered at North Pole High School to hear from scientists and Flint Hills Resources about how the chemical, sulfolane, got into the water and what is being done about it.

Mark Gregory, vice president of Flint Hills’ Alaska operations, said the leaking of sulfolane into the local water system came as a surprise to Flint Hills. Officials are focused on figuring out how far and wide the chemical has spread.

“We are very much concerned with trying to understand where this plume is at,” he said.

Routine testing by Flint Hills uncovered the groundwater contamination this fall.

Sulfolane, used to make fuel, is not among the hundreds of chemicals normally regulated in drinking water, said Cindy Christian, a state drinking water expert.

It bonds easily with water, which is how a sulfolane spill sometime before 2000 managed to leach into the water table near the refinery, contaminating an unknown number of private wells and one of the wells that feeds the city water system. That well has since been disconnected from North Pole water mains.

“I thought my water was safe,” said Janet Jahn, a schoolteacher who built a house northwest of the refinery in 1979.

Almost two weeks ago, a strange car appeared in her driveway. The occupants, representatives of Flint Hills, asked if they could test her water and provided her a water cooler, advising her not to drink the well water she’d been using for decades.

“When they gave me the water, I switched,” Jahn said. “I do as I’m told.”

Chris Brenner, a 68-year-old retired schoolteacher who lives near Jahn, also switched to bottled water. Flint Hills paid her a similar visit.

Brenner had an ovarian tumor removed in 2002 and a tumor removed from her thyroid earlier this year, she said.

“It could have been the chemical thing, of course I think that,” she said.

Brenner enlisted the help of her son to pull up everything she could about sulfolane on the Internet, she said.

Lori Verbrugge, a toxicologist with the state Division of Public Health, said officials are still trying to determine how much, if any, sulfolane is safe in drinking water. They hope to have a number in a few months.

“It doesn’t accumulate in your body,” she said. “When you get it in your body, it’s metabolized very rapidly.”

Tracy Harmon, a restaurant manager whose family relies on the city water system, said his family has switched to bottled water even though the city’s primary well is purported to be untainted.

“It’s distressing,” he said. “Flint Hills is being proactive, but I hope this doesn’t kill my property value that much.”

Gregory said Flint Hills will work with its neighbors to ensure residents have access to clean water.

“Come spring here, we hope to have a more permanent solution,” he said.

Contact staff writer Amanda Bohman at 459-7544.