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Turning Brownfields Green
By Lily Auliff
LLT, with support from the Texas Forest Service, is in the process of launching a pilot project that will test phytoremediation, or the use of trees and other vegetation to clean contaminated soil, sludges, sediments, or groundwater. Soliciting business and industry with contaminated sites, LLT will select three sites with varying types of soil contamination for clean up. The Geochemical & Environmental Research Group from Texas A & M will help LLT with the scientific side of the project – testing the contamination, selecting the plants to use, and monitoring results. “We hope to try different plants on the same type of contamination and see what works best,” explains Jennifer Lorenz, director of LLT. Phytoremediation has been tested widely on small plots around the world, although large-scale use has been limited, according to the US Environmental Protection Agency (EPA). Sunflowers absorb radioactive elements near Chernobyl, poplar trees prevent the spread of contaminated groundwater at a military testing facility in Maryland, and grasses and clover break down petroleum at a toxic site in Virginia, among other initiatives. But LLT’s project will be the first of its type in the Houston area, according to Lorenz. Vegetation works in different ways to remove contaminants. Plant roots can absorb metals and radioactive elements from contaminated soils; the plants are then harvested and destroyed or recycled. Roots can also filter groundwater, or act as hydraulic pumps that control groundwater flow. Some plants, or the microorganisms that they attract, actually break down toxic organic compounds into less harmful substances. The usual method of brownfield clean up – removing and burying or incinerating the toxic soil – is expensive, disruptive, and can inadvertently spread the contamination, says Lorenz. “So many of these brownfields are located near homes. The removal process itself is an issue,” she notes. Phytoremediation, which can be used alone or in conjunction with traditional dig and dump strategies, is a relatively inexpensive, aesthetically pleasing, passive technique driven by solar energy. Lorenz also sees phytoremediation as a way to curb the urban heat island effect in Houston. Research shows that downtowns or shopping centers can be as much as 8 to 12 degrees hotter than surrounding suburban or rural areas. The shade and evapotranspiration from added vegetation can alleviate this phenomenon. “So many of the hot spots in the city are brownfields,” she notes. There can be financial benefits as well. In some cases, business and industry receive pollution credits for cleaning up. Subsequently putting the property into a conservation easement – which LLT hopes to do with the pilot plots after clean up is complete – protects the site’s natural features and provides property tax benefits to the owner. And phytoremediated sites provide nearby residents and passers-by with a more aesthetically pleasing environment. “All these things could lead to an improved industry image for any owner of a contaminated site willing to try this new science,” says Lorenz. There are still a few drawbacks to this relatively new technique. Some are concerned that wildlife may consume contaminated plants or that some toxins will evaporate from leaves into the air. Phytoremediation is also slower than mechanical methods and is limited to the depths that roots can reach. Preliminary studies indicate that it works best on shallow sites with low to medium contaminant concentration. Because of these potential problems, many experts still consider phytoremediation experimental and advocate more research before large-scale implementation. For more information on LLT’s pilot project, contact 713-524-2100 or Jennifer.Lorenz@visto.com. |
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Hundreds of brownfields – abandoned, idled, or underused industrial or commercial properties with real or perceived environmental contamination issues - lie within the city of Houston alone. Cleaning them up can be technically difficult and costly, but Legacy Land Trust (LLT), a local conservation organization, hopes to find a way to let plants do the work.