When the warehouse of Westchem Agriculture Chemicals Inc. in Minot, N.D., caught on fire in April 1987, fire crews rushed in and hosed down the flames. Unfortunately, their quick response only led to more problems.As it turned out, barrels of pesticides had been stored inside the warehouse, and the water that squelched the fire also washed the toxic chemicals into the soil, posing a threat to the local drinking water supply.

At first, it seemed that the only solution was to haul the contaminated soil to a landfill.

But upon reflection, Westchem's general manager, Harold Schultz, realized that course of action only would have moved the toxic chemicals from his back yard to someone else's. Schultz had grown up in a farming community and felt strong ties to the land.

"Sooner or later," he said, "five or 10 centuries down the road, when we're all dead and gone, it's (dumping toxic materials) going to cause some problems on this earth."

As the excavation was still going on, a business associate told Schultz about a company that could clean up the contamination by stimulating microogranisms already present in the soil to munch away at the chemicals. The soil-dwelling organisms would do the job thoroughly and for a much lower price.

By June, a team from Ecova Corp., based in Redmond, Wash., was in place, ready to clean up the mess, using this biological method.

Within three months, the bacteria had destroyed 96 percent of the hazardous chemicals in the soil. Pesticide levels of substances such as 2,4,D and MCPA plummeted from 800 to 10 parts per million.

Using microbes to break down wastes isn't a novel idea. Knowingly or not, people have been doing it for centuries. When you bury an apple in the back yard, it decomposes as soil organisms gobble it up. Such creatures also keep busy at sewage plants, digesting the endless streams of waste.

Only in the last few decades, however, have scientists begun to tap the greater potential of microbes using them to destroy hazardous substances.

In the '60s, scientists discovered that microbes living in the soil could be used to clean up petroleum waste products, although it wasn't until the early '70s that the new technology was put to work.

One of the first cleanups took place in Ambler, Pa., where a pipeline broke and contaminated the community drinking water supply with 130,000 gallons of high octane gasoline from the spill. By adding nutrients and oxygen, the microbes in just over a year reduced the level of contamination to under 100 parts per billion - the level considered safe at the time. Without intervention, it might have taken 50 to 100 years, or more, to reach that level.

This technique, called bioremediation, has been used for many years on simple carbon-based petroleum compounds. But only in the last three or four years has the field entered a new arena.

Companies today are using microbes to degrade more complex chemicals, such as pesticides and solvents, although heavy metals and complex petroleum byproducts continue to present a challenge.

About 20 companies in the United States now offer bioremediation on a commercial basis, according to John Glaser, a chemist, in the Environmental Protection Agency's hazardous waste engineering research laboratory. He said he is "very optimistic" about bioremediation, despite its limits.

Dick Raymond, the man who patented bioremediation for gasoline-contaminated groundwater, conceded that "there are going to be a lot of people trying to sell the process for things that won't work.

About 20 years ago, Raymond's methods were first used to clean up oil spills. Now scientists have identified microorganisms that can destroy more complicated chemicals. Some companies now are even beginning to tackle Superfund sites that typically contain a long list of chemical contaminants. Such sites have been designated by the government as priority cleanup areas because of their threat to humans.

Karen Arnstein, marketing communications manager of the environmental engineering company ERT, said her firm has just received EPA approval to clean up one such Superfund site, the French Ltd., site in Crosby, Texas. The site looks like a scenic pond on the surface, but beneath the water is an array of hazardous materials, including benzene, chloroform, toluene and vinyl chloride.

Initially, the EPA had planned to incinerate the wastes, at an estimated cost of nearly $150 million. ERT proposed bioremediation as a less expensive alternative saying it could do the job for less than $50 million by using microbes already living in the pond to destroy the hazardous chemicals.

The firm has completed a demonstration project, on a one-third-acre plot at the French lagoon, and the EPA has given it the go-ahead to clean up the rest of the site.

Though cleaning up of combination of chemicals offers promise for dealing with Superfund sites, Gaylen Brubaker of International Technology, one of the county's largest environmental management companies, said these projects move very slowly.

Both the regulatory agencies and the responsible companies have had limited experience with bioremediation, Brubaker said. The approval process can easily be stalled at any stage in the game.

As an example, Brubaker pointed out that ARS, the bioremediation group within International Technology, did a feasibility study for a proj-ect 21/2 years ago. "But (because of) the permitting, the bureaucracy and the litigious nature of this kind of a business, very little has progressed beyond the feasibility phase."

The regulatory agencies admittedly are slow to embrace bioremediation. "We don't see it as a panacea," Roger Meacham of the EPA said. "It has potential for being a scientifically sound, safe remedy for Superfund sites. But you have to look at each site separately and see which contaminants are involved."

Brubaker believes the hesitancy of the EPA stems mostly from lack of familiarity. He said, "Up until three years ago, everyone assumed landfill was the answer and so there hasn't been that much motivation to look at innovative methods." Bioremediation has not been done on a wide scale, however, and few people are willing to take a risk with an unproven method.

Westchem was willing to take that risk. The Ecova team came to the North Dakota warehouse knowing that the job would entail more than simply sprinkling microbes onto the "hot spots."

Before taking any action, they had to assess the damage and determine which microorganisms would clean the area most effectively. They found that bacteria already living in the soil would prove most useful.

Once they began, workers constructed a 5-acre treatment bed on the site. The bed, which resembled a large pond, was lined with a thick layer of clay to prevent the contaminants from leaching through.

When the bed was completed, workers dug up the contaminated soil and moved it to the treatment bed where they mixed in microbes that had been chosen for the task - bacteria indigenous to the soil.

Those single-celled, primitive organisms didn't do the job unassisted, however.

Like a garden compost pile, the microbes needed nutrients, oxygen and water to stimulate them to devour hazardous chemicals.

The low cost of using microbes to break down hazardous waste is another appealing aspect of bioremediation. Since contaminated soil can be treated on-site, there are no transportation expenses or disposal fees.

And if the microbes can work effectively right in the ground - without the need to excavate soil - there is an additional savings.

But the notion that nature can do the job free is misguided. "It's just less expensive than (other methods)," Bourquin said.

Scientists say that waste-eating microbes offer great promise for the future, although they will not replace present methods. "Everybody wants biodegradation to work," Unterman said. "There's nothing better than letting Mother Nature recycle all of the world's effluent."