Rooting out pollution

Trees: The government enlists pines, poplars, willows and oaks to do battle with contaminated ground water at Aberdeen Proving Ground.

November 26, 2001|By Lane Harvey Brown | Lane Harvey Brown,SUN STAFF

Workers from the Army and the Environmental Protection Agency travel past sprawling test ranges and curious deer to the southern tip of Aberdeen Proving Ground's Edgewood peninsula, into the old Dragon's Lair, to fight a stubborn foe.

They are armed with trees - a benign-sounding first line of defense. But don't be fooled.

These 409 loblolly pines, hybrid poplars, willows and oaks are helping to turn the tide in the agencies' fight against a plume, or spread, of contaminated ground water left behind from toxic burn pits nicknamed the Dragon's Lair. The trees drink up the ground water and break down the pollutants naturally.

The pits were used from the 1940s to the 1970s to burn equipment used in chemical warfare experiments. They contain high levels of solvent contamination, ranging from 4,400 parts per million near the now-filled-in pits to traces at the edges of the area, J Field.

"Because of high concentrations here, cleaning [the contaminants] up is very difficult," said Steven R. Hirsh, a remedial project manager for the EPA.

Other difficulties have arisen. The polluted ground water moves too slowly to be pumped and treated effectively. And while much of the soil, contaminated with lead, PCBs and arsenic, has been excavated, removing all of it proved too expensive.

After trying more conventional methods in the 1990s, the EPA and the Army ended up with more pollution than they had anticipated - and millions of dollars in bills, with little conclusive progress.

Those factors began to spur more innovative thinking on the cleanup project. But what really opened the door for trees at J Field was a simple fact: There's no one around for miles. Unlike northern areas of the installation, which border populated areas, J Field is isolated. With the entire peninsula designated a Superfund National Priority List site, the Army, the EPA, the state and the community had to make choices about where to concentrate resources. The boundary areas, near Edgewood, won out.

Relying on trees means cleanup might not be complete for 100 years, Hirsh said, but it's a far less expensive method to stem the spread of contaminated ground water and break down pollutants.

J Field was the last stop for equipment used in chemical labs and tests conducted by the Army. Workers would fill burn-pit trenches with the equipment, along with old pallets and other scrap, an accelerant such as heating oil and a detonator, said John Wrobel, a project manager with the Army's Directorate of Safety, Health and Environment who oversees the J Field project. From a bunker, they would spark fires to burn away the contaminants, then douse the remains with solvent to remove traces of chemicals.

Given such a history, the agencies overseeing the cleanup were surprised by what they didn't find at the site, said John Fairbank, chief of the Federal/National Priority List Superfund Division at the state Department of the Environment, which reviews and comments on J Field reports. "What turns out to be the issue is lead, PCBs and industrial solvents. Chemical warfare material is really not an issue," he said.

Though the agencies and the community agreed that letting nature take its course at J Field was the most feasible option, many people were skeptical when the first trees were planted in the mid-1990s, said Harry R. Compton, an EPA environmental engineer.

"Nobody thought the trees would live," he said.

Those 180 trees, however, are not only alive, they are thriving - most are 50 feet tall or higher. And they are successfully slowing the flow of polluted ground water, and capturing and breaking down contaminants, a process called phytoremediation.

The method is being used at only a few military and civilian sites around the country, including ones in Texas, Florida, Oregon and New Jersey, Hirsh said.

Thirsty trees

Researchers are learning during the growing season that, from about April to November, thirsty trees drink about 20 gallons a day. Sometimes the trees are working so hard to draw the slow-moving water through the roots that the ground around them sinks.

The trees, planted in a U-shape stretching out in front of the underground plume of contamination, are monitored from root to leaf. Researchers bore holes into the trunks to detect traces of contaminants; take sap samples, which are evaluated on the spot to track water flow; and bag branches to measure pollution escaping through the leaves.

Signs of success

These readings reveal traces of solvents, indicating the process is working, Hirsh said. Much of the breaking down of pollutants occurs at the root level, he said, so that by the time the tree emits gases, the contaminants are in parts per billion and dissipate quickly. They can't even be measured, he said, unless the branches are bagged and baked in the sun.

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