Using Pseudo 3-D P-Wave Seismic Reflection Data in Developing a More Robust Geologic Conceptual Model in Site Characterization: From Example from P-Area, Savannah River Site, SC

Michael Waddell¹, Adrian Addison², Daniel Brantley¹, and John M. Shafer^1
1Earth Sciences and Resources Inst., Univerisity of SC, Columbia, SC
²Geological Sciences, University of SC, Columbia, SC

P-area at the Savannah River Site is located in the upper coastal plain of South Carolina. The site consists of approximately 350 meters of unconsolidated sands, clays, and gavels. At P-area there is a contaminant plume of dissolved TCE located in an Eocene sand. The geometry of the plume based on initial site characterization appears to be confined to a narrow corridor in sand overlying a clay unit approximately 23 meters below land surface. Additional borehole investigation suggests that contamination also may be below the clay unit and into underlying sand which suggests the clay unit is not continuous over the study area.. As part of a multi-scale hydrogeophysical and modeling study a pseudo 3D seismic surface seismic survey was conducted over the plume area to enhance the existing geologic model by resolving uncertainty in the litho-stratigraphic sequence at the study site.

The seismic survey area is 34 meters by 170 meters with 2906 shot points located within this area. Processing the data set as a 3D data cube instead of a series of closely spaced 2D lines allowed better interpretation of the target horizons which are the lower clay and the sand directly below the clay. The outcome was the production of realistic horizon surfaces maps. Calibrating the seismic data with existing borehole geophysical logs, core data, as well as VSP data allowed the seismic data to be inverted from two-way travel time to depth, thereby facilitating full integration of the seismic data into a solid earth model that is the basic part of a site conceptual model.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas