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Environmental Geosciences (DEG)

Abstract

DOI:10.1306/eg.08180909012

Structural and stratigraphic control on the migration of a contaminant plume at the P Reactor area, Savannah River site, South Carolina

Antonio E. Cameron Gonzalez,1 Camelia C. Knapp,2 Michael G. Waddell,3 Adrian D. Addison,4 John M. Shafer5

1Department of Earth and Ocean Sciences, University of South Carolina, 701 Sumter St., EWS 617, Columbia, South Carolina 29208; [email protected]
2Department of Earth and Ocean Sciences, University of South Carolina, 701 Sumter St., EWS 617, Columbia, South Carolina 29208
3Earth Sciences and Resources Institute, University of South Carolina, 1233 Washington St., Suite 300, Columbia, South Carolina 29208
4Earth Sciences and Resources Institute, University of South Carolina, 1233 Washington St., Suite 300, Columbia, South Carolina 29208
5Earth Sciences and Resources Institute, University of South Carolina, 1233 Washington St., Suite 300, Columbia, South Carolina 29208

AUTHORS

Antonio Cameron is a Ph.D. candidate in the Department of Earth and Ocean Sciences at the University of South Carolina. He received M.S. and B.S. degrees in geology from the University of Puerto Rico at Mayaguez and worked for 3 years as a researcher in the Puerto Rico Seismic Network. His research interests include exploration and environmental geophysics, earthquake seismology, and geostatistics.

Camelia Knapp received a Ph.D. in geophysics from Cornell University and B.S. and M.S. degrees in geophysical engineering from the University of Bucharest (Romania). She worked with the Romanian State Oil Company and the National Institute for Earth Physics. Currently at the University of South Carolina in the Department of Earth and Ocean Sciences, her research interests include exploration and environmental geophysics, crustal-scale seismology, and gas hydrates.

Michael Waddell completed his graduate studies at Earth Sciences and Resources Institute-University of South Carolina (ESRI-USC), in 1982 and remained at ESRI-USC until 1984 when he became a reservoir geologist in Houston working on petrographic investigations of hydrocarbon reservoirs worldwide. In 1986, he returned to ESRI-USC to start an environmental geophysics group and is presently its manager.

Adrian Addison received his Ph.D. in geological sciences from the University of South Carolina. He received a B.S. degree in geophysics from the University of Oklahoma and worked for 4 years as a geophysicist with the U.S. Geological Survey. He recently joined ESRI-USC as a researcher associate, and his research interests include borehole and near-surface geophysics, environmental geology, and signal processing.

John Shafer received his Ph.D. in civil engineering from Colorado State University, his M.S. degree in resource development from Michigan State University, and his B.S. degree in earth science from Penn State University. His research focus includes integrated site characterization, coupled simulation-optimization approaches to solving groundwater problems, and groundwater susceptibility and contamination potential analysis.

ACKNOWLEDGEMENTS

We thank Duke Brantley from the Earth Sciences and Resources Institute; Susan Hubbard, John Peterson, Michael Kowalsky, and Kenneth Williams from Lawrence Berkeley National Laboratory; and Gregg Flach, Marry Harris, and Margaret Milling from Savannah River National Laboratory. Special thanks go to James Knapp and Jose Manuel Bacale as well as to the Geophysical Exploration and the Tectonics Geophysical Laboratories from the Department of Earth and Ocean Sciences at the University of South Carolina. We also acknowledge Landmark Graphics Corporation, Seismic Micro-Technology Inc., and Environmental Systems Research Institute (ProMaxreg, Kingdomreg Suite and ArcGISTM software packages) for the University Grants Programs. This work was made possible through a grant by the Office of Science-Biological and Environmental Research of the U.S. Department of Energy (grant DE-FG02-06ER64210).

ABSTRACT

Geophysical methods, including a shallow seismic reflection (SSR) survey, surface and borehole ground-penetrating radar (GPR) data, and electrical resistivity imaging (ERI), were conducted at the Savannah River site (SRS), South Carolina, to investigate the shallow stratigraphy, hydrogeophysical zonation, and the applicability and performance of these geophysical techniques for hydrogeological characterization in contaminant areas. The study site is the P Reactor area located within the upper Atlantic coastal plain, with clastic sediments ranging from Late Cretaceous to Miocene in age. The target of this research was the delineation and prediction of migration pathways of a trichloroethylene (TCE) contaminant plume that originates from the northwest section of the reactor facility and discharges into the nearby Steel Creek. This contaminant plume has been migrating in an east-to-west direction and narrowing away from the source in an area where the general stratigraphy along with the groundwater flow dips to the southeast. Here, we present the results from a stratigraphic and hydrogeophysical characterization of the site using the SSR, GPR, and ERI methods. Although detailed stratigraphic layers were identified in the upper approximately 50 m (164 ft), other major findings include (1) the discovery of a shallow (sim23 m [75 ft] from the ground surface) inverse fault, (2) the detection of a paleochannel system that was previously reported but that seems to be controlled by the reactivation of the interpreted fault, and (3) the finding that the hydraulic gradient seems to have a convergence of groundwater flow near the area. The interpreted fault at the study site appears to be of upper Eocene age and may be associated with other known reactivated faults within the Dunbarton Triassic Basin. The coincident use of the SSR and ERI methods in conjunction with the complementary 50-, 100-, and 200-MHz GPR antennas allowed us to generate a detailed geologic model of the shallow subsurface, suggesting that the migration of the TCE plume is constrained by (1) the paleochannel system with respect to its migration direction, (2) the presence of an inverse fault that may also contribute to the paleochannel growth and structural evolution, and (3) the local groundwater flow volume with respect to its longer and narrower shape away from the source updip stratigraphic bedding.

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