Relative low cost. Since contaminated soil can be treated on-site, there are no transportation expenses or disposal fees.

No need to excavate soil

Disadvantages of the biological approach

Microbes will have to achieve close to 100 percent destruction before the bioremediation is considered to have wide acceptance. It remains essentially unproved.

The regulatory agencies are slow to embrace bioremediation. "We don't see it as a panacea," said Robert Meacham of the EPA. "You have to look at each site separately and see which contaminants are involved."

Alternatives to hazardous waste disposal

Each year, about 264 metric tons of liquid and solid hazardous waste are generated in the United States. Just how to get rid of it has become an expensive and complex public problem. Among the methods:

Dumps - Rising costs, lack of protection for land and for underground water facilities, the pubic attention on the environmental inadvisability of dumping hazardous substances in landfills are all increasingly making this a bad alternative, even at the few approved sites.

Incineration - Burning waste at high temperatures has been criticized for producing toxic by-products, including dioxins. Still, only about half of the nation's incineration capacity is being used to destroy liquid hazardous wastes.

Ocean incineration - Waste placed aboard ocean-going incineration ships can be burned at much higher temperatures than on land, eliminating most hazardous by-products. The procedure is used in Europe but has not yet become widespread in the United States, in part because it has not been believed economical. There are some environmental concerns and fear of shoreline spills.

Waste reduction - The Environmental Protection Agency's preferred solution is to reduce waste at the source. The agency seems to support installation of cleanup procedures and equipment at industrial and commercial sites.