(Phytoremediation of TCE-Contaminated Shallow Groundwater)
The U. S. Air Force (USAF) has initiated a field demonstration designed to evaluate the effectiveness of eastern cottonwood trees in remediating shallow groundwater contaminated with trichloroethene (TCE). Using vegetation to remediate contaminated soil and groundwater is known as phytoremediation.
Phytoremediation of groundwater involves planting deep-rooted, water-loving vegetation to reduce contaminant levels in the saturated zone. The USAF's demonstration entails planting and cultivating eastern cottonwood trees over a dissolved TCE plume in a shallow (6 to 11 feet below grade) alluvial aquifer.
The cottonwood trees are expected to bioremediate the contaminated groundwater
and any contaminated soil through one or more of the following mechanisms:
In essence, the trees are expected to serve as a natural pump-and-treat system.
TCE concentrations in the groundwater, soil from the rhizosphere, and tree tissues will be monitored during the demonstration. In general, data will be gathered and interpreted to identify the overall effect of the planted trees on the dissolved TCE plume in the aquifer. Groundwater levels and TCE concentrations in the aquifer will be measured initially to establish baseline conditions and subsequently to map changes in the aquifer throughout the demonstration period. Changes in the flow field and the position of the TCE plume will also be modeled.
TCE concentrations will also be monitored in the soil from the rhizosphere and in the tree tissues. Ratios of daughter and parent compounds will be calculated for groundwater, soil, and tissue samples collected throughout the demonstration period. Microbial activity in the rhizosphere will be monitored and transpiration rates will be measured. These data will be used to determine the fate of the TCE at the site, including those processes that affect its fate.
The USAF's phytoremediation technology may be used to remediate shallow groundwater and soil contaminated with TCE, as well as other contaminants common to USAF installations. Such contaminants include petroleum, munitions, and halogenated hydrocarbons. Costs of the technology are limited to initial site preparation, planting, and occasional maintenance (irrigation).
The technology was accepted into the SITE Demonstration Program in 1996. The USAF is currently demonstrating its phytoremediation technology on a TCE plume near Air Force Plant 4 at the Naval Air Station Ft. Worth, formerly Carswell Air Force Base in Fort Worth, Texas. Initial site characterization and final site selection were completed in January 1996. Site development, which included planting trees and installing the irrigation system, was completed in April 1996. The figure on the previous page details the layout of the site. Baseline sampling began in June 1996, and demonstration sampling is scheduled to continue until 2000. The USAF speculates that the trees may begin transpiring water from the aquifer as early as the summer of 1997.
EPA PROJECT MANAGER:
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
TECHNOLOGY DEVELOPER CONTACT:
U.S. Air Force
Mail Stop ASC-EMR
1801 10th Street, Building 8, Suite 200
Wright Patterson Air Force Base, OH 45433
513-255-7716, ext. 302