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VEGETATM REMEDIATION PXOCE5S OFFEm ADVANTAcEs ovER TRADMONAL Pump-AND-TREAT TEcioioLoc s <br /> contamination of aquifers Due to the low solubility of most heavy metals, <br />' they are nearly impossible to extract via standard pump-and-treat method- <br /> ologies Although it is true that plants generally do not uptake heavy metals <br /> to any great degree,this is somewhat dependent on their lack of availability <br /> I to the plant (Jackson and Alloway, 1992) <br /> Heavy metal availability may explain the following data An evaluation <br /> of heavy metal uptake by several hybrid poplar trees revealed a ten-fold <br /> or more increase in the zinc content of affected trees Zinc concentrations <br /> were as high as 2,900 mg/kg in dry leaf tissue of selected trees and as low <br /> as 170 mg/kg for other trees Although these data are not the result of a <br /> controlled experiment, they illustrate the potential for heavy metal uptake <br /> and the potential fit that TreeMediation has in the remediation of heavy <br /> metals This is especially true where it is acceptable to contain the problem <br /> and limit or eliminate migration of heavy metals to the groundwater <br /> Organics <br /> Organic constituents can be adsorbed by vegetation and metabolized <br /> or otherwise degraded, or they can be affected by contact with the plant <br /> Once sn contact with roots (Shimp et al , 1993) Plant roots are extremely valuable to a wide <br /> the plants'roots, range of microbial populations that thrive, often in a symbiotic relation- <br /> many organic ship, in the area immediately surrounding the roots(the rhizosphere) The <br /> molecules can be rhizosphere provides much of the food, moisture, and oxygen needed by <br /> subjected to microbial microbes to survive in regions of the sod where they would not normally <br /> degradataan or be found(i e ,in the region of a deep aquifer)(Anderson et al , 1993) Once <br /> metabolism. in contact with the plants' roots, many organic molecules can be subjected <br /> to microbial degradation or metabolism <br /> CONCLUSION <br /> Su-ice its inception in 1990,the TreeMediation process has been applied <br /> at six sites in Wisconsin, Illinois,North and South Carolina,and New jersey <br /> Application at the New jersey site was the main focus of this discussion <br /> In Illinois, TreeMediatson was coupled with a standard pump-and-treat <br /> system to alleviate an isnrnediate problem of off-site movement of a <br /> contaminant plume containing nitrogen and pesticides Another site in <br />' Illinois is being treated for organic and inorganic agncultural chemicals, <br /> dramatic reductions have been realized for pesticide levels in the soil(from <br /> 1,000 mg/kg to less than 10 mg/kg thus far) In Wisconsin, nitrogen and <br />' pesticides are being remediated using TreeMediation and surface vegeta- <br /> tion An aquifer in sandy coastal soil in North Carolina is being treated with <br /> TreeMediation for several inorganic agricultural chemicals as a cost- <br /> effective alternative to a pump-and-treat system Finally, TreeMediation is <br /> being applied to mitigate the migration of heavy metals to an aquifer in <br /> westem South Carolina <br /> Each site posed different problems and, except for the New Jersey and <br /> South Carolina sites, standard pump-and-crest typically would have been <br /> the process of choice TreeMediation, however, was chosen for these sites <br />' because of its superior capabilities and much lower costs than traditional <br /> pump-and-creat OR <br /> 351 <br /> REMrMIATION/SUMMER 1994 <br />