Transport and Degradation of a Trichloroethylene Plume Within a Stream Hyporheic Zone
In predicting natural attenuation rates for contaminant plumes, it is vital to determine flow patterns, suitability of chemical and microbial conditions, and seasonality. Savannah River Site’s CMP Pits operated from 1971 until 1979; receiving chemicals, metals, and pesticides. Now a Superfund site, monitoring-wells indicated perchloroethylene (PCE) and trichloroethylene (TCE) had seeped beneath the vadose zone. It was unknown how the plume was entering Pen Branch valley below and whether natural attenuation was degrading the contaminant load. Our study focused on plume transport and exchange within the critical hyporheic zone beneath Pen Branch and helped to ground-truth model the plume borders. We also determined reductive dechlorination of PCE and TCE into dichloroethylene and vinyl chloride. Over forty sampling holes were augered into the hyporheic zone and adjacent floodplain along with 12 stream stations. Chemical conditions linked to natural attenuation (e.g. H2S, Fe+2, and NH3) were monitored to identify reductive dechlorination suitability along with temperature, pH, redox, and dissolved oxygen. Plume flow displayed complex entry patterns, but natural attenuation was documented by higher levels of cis-dichloroethylene (cis-DCE) (61.5 μg/l) compared to PCE or TCE. High means of hyporheic PCE (26.5 μg/l) and TCE (6.7 μg/l) compared to overlying stream water PCE (0.5 μg/l) and TCE (0.2 μg/l) raise new transport pathway questions.
KeywordsVolatile Organic Compound Natural Attenuation Hyporheic Zone Reductive Dechlorination Savannah River Site
The efforts of South Carolina State University student interns: Chris Carter, Stephanie Roach, Landis Chambers, Kendall Simmons, Ta’mara Brown, Lanita Peterson, and Eric Foxworth were greatly appreciated. University and SRS planning assistance were also given generously by Dr. Judith D. Salley, Larry Anderson, and Janelle Jansen.
- Board on Environmental Studies and Toxicology. 2006. Assessing the Human Health Risks of Trichloroethylene. National Research Council of The National Academies, The National Academies Press, Washington, DC, 448 p.Google Scholar
- Harte, P.T., M.J. Brayton, and W. Ives. 2000. Use of Passive Diffusion Samplers for Monitoring Volatile Organic Compounds in Ground Water. USGS Fact Sheet 088-00 4p.Google Scholar
- Maslia, M L., J.B. Sautner, R.E. Faye, R.J. Suárez-Soto, M.M. Aral, W.M. Grayman, W.J.J. Wang, F.J. Bove, P.Z. Ruckart, C. Valenzuela, J.W. Green, Jr., and A.L. Krueger. 2007. Analyses of Groundwater Flow, Contaminant Fate and Transport,and Distribution of Drinking Water at Tarawa Terrace and Vicinity,U.S. Marine Corps Base Camp Lejeune, North Carolina: Historical Reconstruction and Present-Day Conditions. Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services, Atlanta, GA, 116 p.Google Scholar
- SRS Citizen’s Advisory Board, 1999. Chemicals, Metals, And Pesticides (CMP) Pits. SRS Citizen’s Advisory Board Publ. Recommendation No. 83, 2p.Google Scholar
- Wiedemeier, T.H., M.A. Swanson, D.E. Moutoux, E.K. Gordon, J.T. Wilson, B.H. Wilson, D.H. Kampbell, P.E. Haas, R.N. Miller, J.E. Hansen, and F.H. Chapelle. 1998. Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water. United States Environmental Protection Agency, Office of Research and Development, Washington DC, EPA/600/R-98/128.Google Scholar