ightly deeper contamination than plants, typically 10-15 feet, but cannot remediate deep aquifers without further design work . 4.Trees roots grow in the capillary fringe, but do not extend deep in to the aquifer. This makes remediating DNAPL’s in situ with plants and trees not recommended. 5.Plants that absorb toxic materials may contaminant the food chain. 6.Volatization of compounds may transform a groundwater pollution problem to an air pollution problem. 7.Returning the water to the earth after aquaculture must be permitted. 8.Less efficient for hydrophobic contaminants, which bind tightly to soil. Case Studies: 1) At the Naval Air Station Joint Reserve Base Fort Worth, phytoremediation is being used to clean up trichloroethylene (TCE) from a shallow, thin aerobic aquifer. Cottonwoods are being used, and after 1 year, the trees are beginning to show signs of taking the TCE out of the aquifer. (Betts, 1997) 2) At the Iowa Army Ammunitions Plant, phytoremediation is being used as a polishing treatment for explosive-contaminated soil and groundwater. The demonstration, which ended in March, 1997, used native aquatic plant and hybrid poplars to remediate the site where an estimated 1-5% of the original pollutants still remain. A full-scale project is estimated to reduce the contamination by an order of magnitude (Betts, 1997). 3) After investigating using phytoremediation on a site contaminated with hydrocarbons, the Alabama Department of Environmental Management granted a site. The site involved about 1500 cubic yards of soil, and began with approximately 70% of the baseline samples containing over 100 PPM of total petroleum hydrocarbon (TPH). After 1 year of vegetative cover, approximately 83% of the samples contained less than 10-PPM TPH. 4) Phytoremediation was used at the decommissioned Detroit Forge plant to clean up approximately 5,800 cubic yards of lead-impacted soil. Two plantings were completed, the first using sunflow...
