USING 2D AND 3D HIGH RESOLUTION P-WAVE REFLECTIVE SEISMIC TO MAP THE NEAR SURFACE STRATIGRAPHY AND HYDROSTRATIGRAPHY IN THE COASTAL PLAIN OF SOUTH CAROLINA: EXAMPLES FROM CHARLESTON NAVAL WEAPONS STATION (CNWS) AND P-AREA, SAVANNAH RIVER SITE

The traditional method for mapping the stratigraphy and hydrostratigraphy in the South Carolina coastal plain is drilling numerous boreholes and correlating the interfaces between holes. As an alternative, noninvasive shallow high-resolution seismic reflection surveys can provide a near continuous record of vertical and spatial geologic/lithologic changes when properly calibrated with a few boreholes.

The Solid Waste Management Unit 12 (SWMU-12) at CNWS, Charleston, South Carolina offered some unique technical problems for applying the seismic reflection technique to map the Quaternary stratigraphy because of the shallow target depth (< 9m). The geology beneath SWMU-12 consists of Quaternary marginal marine sands and clays that overly Eocene marl. Based upon seismic data and core and gamma logs from existing wells, it appears that there are numerous stack channels sequences in the surficial aquifer. These channels are interpreted as a tidal channel sand overlying a clay unit. Using high frequency data we were able to map the gross features such as lithologic boundaries and channels features, plus features within the individual channels.

The P-Area at Savannah River Site is located in the upper coastal plain of South Carolina. P-Area subsurface geology consists of Eocene to Cretaceous age clastic deposits. The gravels, sands, and clays that make up the Eocene section are presumed to be fluvial deposits. A pseudo 3D high resolution seismic survey was conducted over an area approximately 240 meters by 40 meters to map the stratigraphy and hydrostratigraphy zones down to the top of Eocene clay. The maximum target depth was approximately 45 meters below land surface. The pseudo 3D field acquisition techniques allow the data to be process and interpreted as a 3D volume.