Trees help clean the West’s dumps

Phytoremediation tackles everything from dry-cleaning solvents to formaldehyde

  • Illustration of how trees filter pollution

    EPA
 

MCMINNVILLE, OREGON — George Duvendack looks out over a mountain of garbage. The Riverbend Landfill, which Duvendack manages, is piled 100 feet deep with colorful bits of trash. There are 4.6 million tons of junk here, from four surrounding counties.

While today the sky is a sharp and biting blue, on most days here in western Oregon, rain pours from the sky. All that water filters through the garbage, creating an environmental problem for Duvendack. “It’s not like the Black Death or anything, but that water is contaminated and we can’t just dump it into the river or let it flood into the ground,” he says.

Landfills in arid regions can pump tainted drainage water into open tanks where it evaporates, but the Pacific Northwest is far too soggy for this. Instead, Duvendack is using a cutting-edge cleanup tool: two acres of poplar trees.

Each summer, Duvendack pumps wastewater from a concrete holding pond to irrigate the trees. As the poplars ingest the polluted water, enzymes in the trees’ cells break apart and consume the contaminants, transforming harmful chemicals like trichloroethylene, which is used in dry-cleaning solvents, into common, harmless compounds, contained inside the trees.

Phytoremediation, the use of plants to filter, consume and degrade contaminates, isn’t just used for garbage juice. Throughout the country, and at nearly 100 sites around the West, companies are using the relatively new science to break down a range of pollutants, including pesticides, mercury and formaldehyde.

“Phytoremediation is phenomenal,” says Lee Newman, director of environmental health sciences at the University of South Carolina, who did some of the primary research on the subject at the University of Washington. “It’s doing what needs to be done and it’s doing it naturally.”

A cheaper alternative

Phytoremediation builds on a decades-old technology called bioremediation, which uses bacteria to clean up environmental messes. Bacteria live in the soil, where they feast on carbon, the element that occurs in all organic things, including petroleum products. As these micro-organisms gobble away, they break the bonds between the organic compounds. Colonies of these little PacMen have helped clean up oil spills like Alaska’s Exxon Valdez.

Trees spur bacterial growth by adding nutrients to the soil, and they have the added advantage of roots that extend up to 50 feet underground, allowing them to clean sites where contamination has penetrated deep into soil and groundwater. Traditionally, to clean these sites, companies have had to resort to extremely expensive and labor-intensive techniques, such as excavating entire areas and incinerating contaminated soil. In order to clean up creosote used for treating railroad ties at the former Union Pacific railroad facility in Laramie, Wyo., work crews had to dig up 20 feet of dirt. The company then tried to flush the chemical out of the soil with biodegradable soap.

When that failed to remove residual creosote, Union Pacific planted cottonwoods, poplars, aspens and blue spruce. While the trees and the bacteria clean the contaminants, the site has become a city park.

Built-in limitations

Still, phytoremediation has a way to go before it can be more widely used. There are no consistent standards and guidelines for the relatively new technology, and few people understand how to use it. The U.S. Environmental Protection Agency is developing design manuals for engineers and regulators, but these aren’t expected to be ready for at least two years.

And there are built-in limitations. Phytoremediation requires a lot of space, which is becoming harder to find in the West’s urban areas. It also requires a lot of time — 30 years in some cases — for trees to do their work. Traditional cleaning methods, although expensive, are quicker.

“In places where people or animals are using the groundwater and there are eminent hazards or threats, I don’t have the luxury to sit back and wait and see if it (phytoremediation) works,” says Cliff Walkey, a hydrologist with the Oregon Department of Environmental Quality. “Phytoremediation is becoming mainstream, but it’s just not appropriate to apply in every case.”

But back at the Riverbend Landfill, George Duvendack says he’s found his answer. Monitoring the phytoremediation project costs in excess of $100,000 annually, but, he says “It’s still the cheapest alternative.” He’s also planning to make a few additional dollars by cutting down the trees every 10 years, harvesting an estimated 900,000 board-feet of lumber.

The author writes from Portland, Oregon.

- The Riverbend Landfill: George Duvendack, [email protected]

- To learn more about bioremediation, log onto the EPA’s Web site at www.clu-in.org/remed1.cfm.

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