Lasagna: a new recipe for 'dirty' soils.

Earlier this year, several large manufacturing companies decided to team up with the federal government to solve a common--and currently intractable--environmental problem: how to clean up chemical contaminated of deep clay soils.

Chemicals that seep into the ground and enter the fine pores of a buried layer of clay can become all but impossible to extract, observes Philip H. Brodsky of Monsanto Co. in St. Louis. And that's bad news, he says, because heavy layers of such clay underlie at least half the major chemical spill and toxic waste sites in the United States.

But Brodsky has tested in the laboratory a new cleanup scheme that the industry-government consortium expects to test at a chlorinated-solvent spill site early next year. Brodsky reports that this Lasagna Project - named for the alternating layers of wastes and cleanup zones it involves - will broker a novel marriage of three mature technologies.

Hydraulic fracturing will be used to create a series of treatment sites inches from the clay. In this technique, crews bore holes down to the desired depths. A slurry of guar gum and sand, which breaks up the soil, is injected into each hole. When inserted enzymes later break the goo down into water, there remains a series of pancake-shaped zones of permeable sand some 15 feet or more in diameter and up to one-half-inch thick.

For in-ground cleanup, engineers then deliver into each fracture zone materials that have been tailored to treat the nearby wastes. Microbes and a nutrient cocktail, for example, might be used to break down compounds such as polychlorinated biphenyls (PCBs). Or iron filings could be packed into the zone to foster the catalytic break down of chlorinated solvents, Brodsky notes. Treatment managers could even break down contaminants electrochemically.

The project would then use electroosmosis to release clay-bound contaminants and transport them to treatment sites (degradation zones). The negatively charged surface of clay particles tends to attract water droplets. But when a negative and a positive electrode are put outside the contaminated clay, the water travels toward the negative electrode - with the contaminants in tow (upper diagram).

Electroosmosis should be able to draw buried chemicals to degradation zones (lower diagram) in just a week or two, Brodsky says. And by periodically reversing the electrodes'

polarity, he adds, chemicals could be shunted back and forth between zones until their breakdown is complete.

Last week, officials at Monsanto, EPA, the Energy Department, General Electric Co., and E.I. Du Pont to work out details that will allow each to collaborate fully while retaining rights to any proprietary technologies.