Air Force environmental officials are contemplating the cleanup of a site they call the "nasty one," where about 100,000 gallons of hazardous solvents were dumped in the 1960s and '70s.

The solvents had been buried in a trench at the north end of the base's runway. For the most part, they remain there today due to underground clay formations that created something of a natural reservoir, said Capt. Ed Heyse, chief of HAFB's restoration division.The solvents include quantities of trichloroethylene, or TCE, which has been shown to cause cancer in laboratory animals.

The clay formation, however, has prevented most of the solvents from flowing into the water table and winding up in the Weber River, which runs below the runway, he said.

"We've kind of been lucky with that one," Heyse said. "It's the nastiest one, but it's in a low spot in the clay. Most of the 100,000 gallons is still at the site," which is officially called Operable Unit No. 2.

That's the good news. The bad news is that TCE breaks down naturally, first into the less hazardous compound, dichloroethylene, or DCE, but eventually into vinyl chloride, a compound known to cause cancer in humans.

Recent tests have revealed concentrations of DCE.

"What really makes this dangerous is the next step," Heyse told the base's Cleanup Technical Review Committee. "Hopefully, we'll clean everything up before it gets to that point."

Vinyl chloride has been detected at an older landfill southeast of Operable Unit No. 2, Heyse told the committee, which consists of officials from the military, state and federal environmental organizations, and local government leaders.

It is estimated that it will cost between $40 million and $50 million to complete the cleanup.