SNELLING, S.C. (AP) - Higher-than-expected levels of a radioactive material are tainting the groundwater at a Barnwell County nuclear waste dump that's been considered safe by regulators.

Tritium levels in the groundwater beneath the landfill are above the Environmental Protection Agency's standard for safe drinking water, according to records obtained by The (Columbia) State newspaper.

The records show that tritium levels beneath the Chem-Nuclear landfill rival those on parts of the Savannah River Site, a nearby atomic weapons complex.

Exposure to tritium can increase a person's chances of cancer, regulators say.

Leaks of radioactivity have been found before at the Barnwell County site. But the recently released records give new details about the extent, showing the average levels of contamination in monitoring wells and the location of the wells.

Company officials say they comply with federal standards for water pollution.

No one lives directly in the path of the radioactive pollution from the landfill, and area drinking wells are not tainted by the material, according to the South Carolina Department of Health and Environmental Control.

Still, DHEC says they will take a closer look at the wells, and Chem-Nuclear will test wells for anyone concerned about tritium in their drinking water, said Vice President Jim Latham.

The company has acknowledged a leak, traced to the late 1970s, when the company says its disposal practices were not as advanced as today. "Our door has always been open to anybody who may be interested or who has questions about what we do," Latham said.

In an attempt to reduce tritium levels, the company has begun sealing closed landfill trenches to prevent rainwater from getting into the burial pits.

The company is also using a synthetic liner above some of the trenches to repel rainwater that could trickle through the nuclear garbage, into groundwater.

Walter Grubbs, 35, a factory worker who grew up south of the landfill, wants to know why state regulators never told him about the tritium - and whether radioactive waste threatens his family's well.

"It concerns me if I'm drinking this stuff and it's doing harm to me somewhere down the road," Grubbs said. "You'd think the government would be keeping on top of all that. That's what they get paid to do."