UNIVERSITY PARK, Pa. -- A researcher in Penn State's College of Agricultural Sciences recently discovered a way to revive sterile soil from an Environmental Protection Agency (EPA) Superfund site using lawn trimmings from community waste.

Richard Stehouwer, assistant professor of environmental soils, under contract with U.S. EPA, developed a mix of composted leaves and grass to make a once sterile soil healthy enough to support plantings. "By adding compost, we didn't have to haul in new soil," Stehouwer says. "We didn't rob prime farmlands of valuable topsoil, which also saved dollars and added less truck traffic to the community's roads.

"Instead of hauling in 2,000 tons of soil per acre, we used 150 tons per acre of compost," he explains. "We also made use of a residential waste product -- leaves and grasses -- from suburban Washington, D.C."

The 10-acre Drake Chemical Superfund site in Lock Haven, Pa., contained 300,000 tons of contaminated soil that needed to be cleaned up, Stehouwer explains. Because of the type of contaminants present, EPA chose to incinerate the soil in an on-site kiln.

The incineration -- which took place from spring 1998 until spring 1999 -- broke down the toxins to harmless carbon dioxide and water.

Until fall 1981, Drake Chemical manufactured chemicals for use in dyes and other organic compounds. The chemicals entered the soil because they weren't properly handled and stored. "The most extensive hazardous contaminant was beta-naphthylamene, a bladder carcinogen," Stehouwer says.

After incineration, the Drake cleanup team backfilled the site with the ash, which they planned to stabilize with a no-maintenance, permanent plant cover. But they knew plants weren't likely to grow in this material.

"The ash wasn't really a soil any longer," Stehouwer says. "All of the organic matter -- the carbon-containing material that holds water in the soil and provides the energy for the microbes that cycle nutrients -- had been burned off. EPA's original plan was to haul in new, clean soil fill and topsoil to cover the site to a depth of 24 inches. But we wanted to see if there was something we could do directly to the ash to get plants to grow."

The three biggest problems, Stehouwer explains, were the lack of organic matter, alkalinity and salinity. During incineration, the cleanup team added quicklime to drive moisture from the soil, which made the ash alkaline. "The soil had a pH of 8 1/2, the pH of pure limestone," Stehouwer says. "Typical agricultural soils in Pennsylvania run from 6 1/2 to 7. Forest soils are even more acidic."

The crew also sprayed the hot ash with scrubber water to cool it, which added high concentrations of sodium chloride (table salt). "Sodium and chloride both are detrimental to plants at high concentrations," Stehouwer says.

"We had three hurdles to clear before we could get plants to grow. Compost seemed like a good amendment, because we know it adds organic matter, dilutes salts and generates acid as it decomposes, which lowers the alkalinity. It might also bind sodium and make it less available to the plants."

Organic material also provides pore spaces in soil, which allows water to soak down rather than run off the surface. "Because the ash was purely mineral, the surface was hard and compact," Stehouwer says. "By amending the soil with compost, we hoped to encourage water to flow through the pile. This would allow nature to start flushing the salts from the rooting zone."

To determine how much compost to add, Stehouwer and research associate Kirsten Macneal performed greenhouse trials. They mixed the ash with various concentrations of composted yard trimmings and inorganic fertilizer, and simulated plowing methods that might be used in the field. They planted a grass (tall fescue) and legume (birdsfoot trefoil) and monitored their growth. "We also simulated the worst-case scenario of no rain, adding only enough water to moisten the soil, but not leach the salts," Stehouwer says.

The researchers found that as they increased the compost and fertilizer, plant growth improved. As expected, nothing grew on the straight soil ash. Stehouwer recommended that the cleanup team work four inches of compost into the ash, in two stages, along with some inorganic fertilizer. "They blended the materials with a chisel plow to about 12 inches, to provide an adequate depth for plant roots," he says.

Based on the recommendations of Peter Landschoot, Penn State professor of turfgrass science, the site was seeded with a mix of grasses and legumes known to be tolerant of high salt and alkalinity, including tall and red fescue, two legumes (birdsfoot trefoil and red clover) and fast-growing perennial ryegrass.

"We learned there can be alternatives to cleaning up Superfund sites that make more sense than bringing in new soil -- both economically and environmentally," Stehouwer says.

The Drake cleanup team included the EPA, Pennsylvania Department of Environmental Protection (DEP), the U.S. Army Corps of Engineers, OHM Remediation Services Corp., various subcontractors and vendors and the Penn State personnel.

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EDITORS: For more information, Richard Stehouwer can be reached at 814-863-7640.

Contacts: Kim Dionis KDionis@psu.edu 814-863-2703 814-865-1068 fax