Evaluation of Field-Scale Chemical-Hydrologic Processes in a Large-Scale Phytoremediation Site

A large-scale, integrated, multi-species phytoremediation system including 2000 trees and engineered wetlands were installed in 2005 to remove carbon tetrachloride from impacted groundwater and surface water. In order to evaluate chemical-hydrologic processes at the remediation site, a well-instrumented monitoring network has been implemented for more than 5 years. The extensive data were collected through automated monitoring well system, a weather station, runoff gauges, and sap-flow monitoring system as well as seasonal sampling for chemical and isotope analysis and plant tissue analysis. This paper will present overall results of dynamics of water flow components, removal rate of carbon tetrachloride, and evidences of various chemical-hydrological processes.   

The detailed result of stable isotope ratio measurements of carbon (C) and chlorine (Cl) in dissolved carbon tetrachloride (CCl₄) from the groundwater plume for the last 5 years will be discussed. The possible data interpretation may suggest that CCl₄could be attenuated via evaporation (up to ~90%) in the source area, progressive biodegradation (<10%) within the major plume area before entering phytoremediation area, and significant biodegradation (20%) over lateral and vertically-upward pathways in the phytoremediation planting area.