Remediation of TCE-contaminated groundwater by a permeable reactive barrier filled with plant mulch (Biowall)

Abstract

A pilot-scale permeable reactive barrier filled with plant mulch was installed at Altus Air Force Base in Oklahoma, USA to treat trichloroethylene (TCE) contamination in groundwater emanating from a landfill. The barrier was constructed in June 2002. It was 139 meters long, 7 meters deep, and 0.5 meters wide. The barrier is also called a Biowall because one of the mechanisms for removal of TCE is anaerobic biodegradation. This study aimed at evaluating the performance of the pilot-scale Biowall after its installation. Data from over four years' monitoring indicated that the Biowall greatly changed geochemistry in the study area and stimulated TCE removal. The concentration of TCE in the Biowall and downgradient of the Biowall was greatly reduced as compared to that in ground water upgradient of the Biowall, while the concentration of cis-DCE in the Biowall and downgradient of the Biowall was much higher than that observed upgradient of the Biowall. Over time, the concentration of vinyl chloride in the Biowall and downgradient of the Biowall increased. Dehalococcoides DNA was detected within and downgradient of the Biowall, corresponding to the observation that vinyl chloride was produced at these locations. Results from a tracer study indicated that the regional groundwater flow pattern ultimately determined the flow direction in the area around the Biowall. The natural groundwater velocity was estimated at an average of 0.060 ± 0.015 m/d.

Keywords:

• Trichloroethylene
• remediation
• Biowall
• geochemistry
• Dehalococcoides DNA
• groundwater
• interface

Acknowledgments

This work was performed while the first author (Xiaoxia Lu) held a National Research Council Research Associateship Award at the U.S. Environmental Protection Agency (U.S. EPA). The U.S. EPA through its Office of Research and Development partially funded and collaborated in the research described here under an in-house project (Task 3674, MNA of Chlorinated Solvents). Portions of this work were supported through IAG # RW-57939566 “Identification of Processes that Control Natural Attenuation at Chlorinated Solvent Spill Sites” and IAG # RW57939929 “Identification of Mineral Substances that Enhance Natural Non-Biological Attenuation of Chlorinated Organic Contaminants in Ground Water” between U.S. EPA and the U.S. Air Force Center for Environmental Excellence. The authors thank Cherri Adair (U.S. EPA) for her assistance with field sampling, and are grateful to the reviewers for their comments on this paper.

This paper was presented at the SETAC Asia/Pacific 2006 conference held at Peking University, China on September 18–20, 2006.