AQUIFER CHARACTERIZATION AND CONTAMINANT PREDICTION USING SEQUENCE STRATIGRAPHY: AN EXAMPLE FROM TERTIARY STRATA AT THE SAVANNAH RIVER SITE

CASTLE, James W., Dept. of Geological Sciences, Clemson University, Clemson, SC 29634-1908, jcastle@clemson.edu; MILLER, Russell B., Kestrel Management Services, LLC, 25 Woods Lake Road, Greenville, SC 29607; HANN, Crystal L., Dept. of Geological Sciences, Clemson University, Clemson, SC 29634-1908; TEMPLES, Tom J., U.S. Dept. of Energy, Savannah River Site, Aiken, SC 29802

Based on results of detailed core description and interpretation for 26 wells at the Savannah River Site (SRS), sequence-stratigraphic models of Paleocene and Eocene aquifers were developed and applied to predicting groundwater movement and contaminant migration.

In the Upper Three Runs aquifer, contaminants migrate locally downward through an upper interval of transgressive and regressive deposits, across a sequence boundary, and into highstand systems-tract sands. Updip bounding surfaces within the highstand sands are likely to impede downward migration of contaminants, but to only a minor extent because of their discontinuous character.

Low-energy shelf deposits of the Gordon confining unit, which includes a maximum-flooding surface, help to protect the underlying transgressive system-tract sands of the Gordon aquifer from contamination. In the southeastern, downdip part of SRS, these fine-grained shelf deposits tend to be laterally continuous, acting as an effective barrier to downward contaminant migration into the Gordon aquifer. However, in updip areas of the site, transgressive shelf clays are thinner and less continuous due to the more proximal depositional setting. In these areas, there is the potential for contaminants to migrate downward through nondepositional breaches into the underlying aquifer.

The top of the Crouch Branch confining unit generally corresponds to a lower sequence boundary. Evidence of exposure and erosion at this contact indicates that portions of the confining unit have been removed, providing potential pathways for downward migration into the Crouch Branch aquifer. Erosional scour of the confining unit is more extensive in the updip, proximal areas toward the northwestern part of SRS.