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Vegetation that helps break down toxins debuts at manufactured gas plant site.
Planting swaths of rye grass and mulberry trees and sowing the soil with bacteria are hardly standard operating procedure when it comes to cleaning up manufactured gas plant sites. But if Bill Bogan has his way, it just might be.
Bogan is an environmental microbiologist at the Gas Technology Institute. For the past year and a quarter, he has been working with Washington Gas in an experiment to see whether phytoremediation-using plants and biological materials to sequester or metabolize toxic materials from polluted soil and water-can work to clean up some of the 1,500 to 5,000 manufactured gas plant (MGP) sites scattered across the country.
If the experiment succeeds, remediation costs at some MGP sites could be halved, at least if Ford Motor Co.'s experience is any guide. Ford used phytoremediation at its River Rouge site to clean up 30 acres polluted with polyaromatic hydrocarbons (PAHs). Those PAHs, the byproduct of coke production on the site many years ago, are very similar to the waste produced by MGPs. Ford spent more than $900,000 on its phytoremediation project, but the company says it would have spent another $1 million on cleanup had it used traditional remediation methods. Rather than carting away 5,700 cubic yards of soil, Ford needed only to dispose of a few cubic yards of toxic plants.
It's too soon to say whether the Washington Gas site will see similar results, since the project won't be completed for nearly two years. Even assuming a highly successful experiment, Bogan points out that phytoremediation is not quite as cheap as the costs for plant material and labor for planting. "Still, phytoremediation is likely to be much cheaper" than traditional remediation methods, he says. There would, for example, be no need to pay for equipment to dig up tons of tainted soil and transport them to approved waste facilities, with the accompanying disposal fees.
The list of plants suited to phytoremediation is growing. Tomato plants, for example, absorb zinc, copper, and lead from surrounding soil. Sunflowers thrived in the radioactive waters near Chernobyl, and concentrated pollutants in their roots. The brake fern, native to the Southeast and California, drinks arsenic like a baby drinks milk. And many prairie grasses soak up hydrocarbons and speed up pollutant degradation.
Bogan's approach at the Washington Gas site was to try 10 different treatments combining various trees, grasses, and bacteria to see what, if anything, worked to reduce site toxicity. Midway into the second growing season, he says some combinations are having a significant impact on site toxicity.
But getting some plants and trees to grow at the site has been a problem in about half the experimental plots, Bogan says. That's not due to site toxicity, but the heavy clay soil that lines much of the mid-Atlantic, including the Washington Gas site. Clay soil is mineral rich, but without amendments of organic materials to help water and oxygen permeate it, many plants can't hack the dense ground. Bogan says the site's dogwoods have