Until fall 1981, the Drake Chemical Company in Lock Haven manufactured chemicals for use in dyes and other organic compounds. Because the chemicals weren’t properly handled and stored, they ended up in the soil, creating a 10-acre toxic mess.

In 1980, the U.S. Congress established the Superfund Program to clean up the most contaminated sites in the nation. The program, administered by the Environmental Protection Agency in cooperation with state and tribal governments, targeted 117 sites in Pennsylvania.

“The Drake Chemical Superfund site contained 300,000 tons of contaminated soil that needed to be cleaned up,” says environmental soil scientist Rick Stehouwer. “The most extensive hazardous contaminant was betanaphthylamene, which can cause bladder cancer.”

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 into harmless carbon dioxide and water. The cleanup team then backfilled the site with the ash, which they planned to stabilize with a no-maintenance, permanent plant cover.

But there was a big problem.

“The ash wasn’t really a soil any longer,” Stehouwer says. “All of the organic matter—the 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,” he says. “But we wanted to see if there was something we could do directly to the ash to get plants to grow.”

Stehouwer set out to make the sterile soil healthy enough to support plantings. The three biggest problems were the lack of organic matter, alkalinity, and salinity.

The city of Lock Haven now stores road salt in this facility on the former Drake Chemical Superfund site.

“During incineration, the cleanup team added quicklime to drive moisture from the soil, which made the ash alkaline,” he says. “The soil had a pH of 8.5, the same as pure limestone. Typical agricultural soils in Pennsylvania run from 6.5 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.

“So, we had three hurdles to clear before we could get plants to grow. We thought compost might be a good amendment, because 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 in compost also provides pore spaces in soil, which allows water to soak in rather than run off the surface. “Because the ash was purely mineral, its 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, then simulated plowing methods that might be used in the field. They planted a grass, tall fescue, and a legume, birdsfoot trefoil, and monitored their growth. “We also simulated the worst-case scenario of no rain, adding enough water to moisten the soil, but not enough to 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 untreated soil ash.

Stehouwer recommended that the EPA cleanup team work 4 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 turfgrass scientist Pete Landschoot, the site was then seeded with a mix of grasses and legumes that tolerate 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 that make more sense than bringing in new soil to clean up Superfund sites, both economically and environmentally,” Stehouwer says.

“By using compost, we didn’t have to 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 of compost per acre.”
Using compost also allowed them to make use of a community waste. “We used a residential waste product—leaves and grasses—from suburban Washington, D.C.,” he says.

—Kim Dionis