Developing a robust geologic conceptual model using pseudo 3-D P-wave seismic reflection data

Abstract

As part of a multiscale hydrogeophysical and modeling study, a pseudo three-dimensional (3-D) seismic survey was conducted over a contaminant plume at P area, Savannah River site (South Carolina), to enhance the existing geologic model by resolving uncertainties in the lithostratigraphic sequence. The geometry of the dissolved phase trichloroethylene plume, based on initial site characterization, appears to be confined to a narrow corridor within the Eocene sand overlying a clay unit approximately 25 m (82 ft) below land surface. Processing the seismic data as a 3-D data volume instead of a series of closely spaced two-dimensional lines allowed for better interpretation of the target horizons, the lower clay, and the sand above the clay. Calibrating the seismic data with existing borehole geophysical logs, core data as well as vertical seismic profiling (VSP) data allowed the seismic data to be inverted from two-way traveltime 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. The outcome was the production of realistic horizon surface maps that show that two channel complexes are located on the section, which are not present in the conceptual model, and that the upper and middle clays are not laterally continuous as previously thought. The geometry of the primary channel has been transposed over the map view of the plume to investigate potential relationships between the shape of the plume and the presence of the channel.