Mitsubishi Chemical also reached an out-of-court settlement with residents here by agreeing to donate $164,000 to the community’s schools, while denying any responsibility for illnesses.

Osamu Shimizu, the director of Asian Rare Earth, the Mitsubishi Chemical subsidiary that owns the mine, declined to discuss details of the factory’s operation before it closed in 1992. But he said that the company was committed to a safe and complete cleanup.

Workers in protective gear have already removed 11,000 truckloads of radioactively contaminated material, hauling away every trace of the old refinery and even tainted soil from beneath it, down to the bedrock as much as 25 feet below, said Anthony Goh, the consultant overseeing the project for one of Mitsubishi’s contractors, GeoSyntec, an Atlanta-based firm.

To dispose of the radioactive material, engineers have cut the top off a hill three miles away in a forest reserve, buried the material inside the hill’s core and then entombed it under more than 20 feet of clay and granite.

The toughest part of the Bukit Merah cleanup will come this summer, when robots and workers in protective gear are to start trying to move more than 80,000 steel barrels of radioactive waste from a concrete bunker. They will mix it with cement and gypsum, and then permanently store it in the hilltop repository.