Long-Term Changes in Ground-Water Chemistry at a Texas Phytoremediation Site (Abstract)

摘要

A field-scale demonstration project was conducted in Fort Worth, Texas, to evaluate the effectiveness of eastern cottonwood trees at attenuating low-level trichloroethene (TCE) contamination in ground water. After 6 years, trees planted in areas where depth to water typically is less than 3 meters caused several changes in ground-water chemistry: enough dissolved organic carbon was delivered to the underlying aquifer to substantially lower dissolved oxygen concentrations, create iron-reducing conditions along the center- line of the plume of TCE, create sulfate-reducing or methanogenic conditions locally, and initiate in-place reductive dechlorination of TCE. Degradation rates for TCE along the plume centerline beneath the site increased almost 100-fold during the first 6 years after planting. A 60-fold increase in attenuation capacity in ground water along the centerline of the plume has increased the potential for a reduction in plume migration. Results from the 8th and 9th years of sampling indicate that reducing conditions achieved at the site were capable of altering the reduction-oxidation state of water, resulting in the modifica- tion of transport of inorganic elements such as uranium, chromium, manganese, and arsenic. The mobility of uranium and chromium was decreased, and the mobility of arsenic and manganese was increased. Transition metal bioavailability and mobility are important issues when promoting the reductive dechlorination of chlorinated solvents in ground-water remediation schemes.