Phreatophyte influence on reductive dechlorination in a shallow aquifer contaminated with trichloroethene (TCE)

Phytoremediation uses the natural ability of plants to degrade contaminants in groundwater. A field demonstration designed to remediate aerobic shallow ground‐water contaminated with trichloroethene began in April 1996 with the planting of cottonwood trees, a short‐rotation woody crop, over an approximately 0.2‐ha area at the Naval Air Station, Fort Worth, Texas. The project was developed to demonstrate capture of contaminated groundwater and degradation of contaminants by phreatophytes. Analyses from samples of groundwater collected from July 1997 to June 1998 indicate that tree roots have the potential to create anaerobic conditions in the groundwater that will facilitate degradation of trichloroethene by microbially mediated reductive dechlorination. Organic matter from root exudates and decay of tree roots probably stimulate microbial activity, consuming dissolved oxygen. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about 20 years of age and 60 meters southwest of the cottonwood plantings) where degradation products of trichloroethene were measured. Oxidation