Anaerobic Biodegradation and Hydrogeochemical Controls on Natural Attenuation of Trichloroethene in an Inland Forested Wetland

ABSTRACT

A field and laboratory investigation of natural attenuation, focusing on anaerobic biodegradation, was conducted in a forested wetland where a plume of trichloroethene discharges from a sand aquifer through organic-rich wetland and stream-bottom sediments. The rapid response of the wetland hydrology to precipitation events altered groundwater flow and geochemistry during wet conditions in the spring compared to the drier conditions in the summer and fall. During dry conditions, partial reductive dechlorination of trichloroethene to cis-1,2-dichloroethene occurred in methanogenic wetland porewater. Influx of oxygenated recharge during wet conditions resulted in a change from methanogenic to iron-reducing conditions and a lack of 1,2-dichloroethene production in the wet spring conditions. During these wet conditions, dilution was the primary attenuation mechanism evident for trichloroethene in the wetland porewater. Trichloroethene degradation was insignificant in anaerobic microcosms constructed with the shallow wetland sediment, and microbiological analyses showed a low microbial biomass and absence of known dehalorespiring microorganisms. Despite the typically organic-rich characteristic of wetland sediments, natural attenuation by anaerobic degradation may not be an effective groundwater remediation for chlorinated solvents at all sites.

KEYWORDS:

• biodegradation
• chlorinated solvents
• groundwater contamination
• natural attenuation
• trichloroethene
• wetlands

ACKNOWLEDGMENTS

Funding for this research was largely provided by the Department of Defense Environmental Security Technology Certification Program (ESTCP). Additional funding was provided by McGuire Air Force Base, and we are grateful for logistical support from John Pohl and King Mak throughout this study. We also thank U.S. Geological Survey personnel Thomas Imbrigiotta and Theodore Ehlke (West Trenton, New Jersey) for assistance with field work and surveying data, and Elizabeth Jones and Mary Voytek (Reston, Virginia) for molecular analyses. This article benefited from reviews of an early draft by Thomas Imbrigiotta and Emily Majcher (USGS) and Michael Rivett (University of Birmingham).

The current address of Linda Jo Dyer is USDA Monitoring Programs Office, Manassas, Virginia, USA.

The current address of David R. Burris is Integrated Science & Technology, Panama City, Florida, USA

Notes

¹The use of trade, product, or firm names in this paper is for descriptive purposes only and does not imply endorsement by the U.S. Government.