Definition Of A Critical Confining Zone Using Surface Geophysical Methods

Definition of the hydrogeologic framework in layered sediments of fluvial and deltaic origin is a difficult challenge<br>for environmental characterization and remediation programs due to the lithologic and stratigraphic heterogeneities<br>inherent in these settings. These heterogeneties often control contaminant transport ,and the effectiveness of<br>remediation alternatives. Surface geophysical surveys can be cost-effective methods for characterization, but<br>individual methods have inherent limitations in resolution and sensitivity. A synergistic approach, utilizing two<br>geophysical survey methods was applied, to define and examine the nature and extent of a deep confining zone of<br>reguiatory importance, the Crouch Branch Confining Unit, in Coastal Plain sediments at the Savannah River Site.<br>TDEM accurately maps the overall conductance (product of thickness and electrical conductivity) of a confining<br>zone clay facies; from variation in conductance, changes in lithology of the confining zone can be inferred.. Shear<br>wave seismic reflection surveys map the depth to the clay layers, and the clay layer thickness, but provides little<br>information on the lithologic nature of the confining zone. Integrated interpretation of the combined data set<br>(including all available borehole logs) allows for delineation of the lateral and vertical extent of clay-dominated<br>zones, sand-dominated zones, key stratigraphic horizons, and erosional features associated with unconformities.<br>This approach has resulted in the collection of critical information that will be used to optimize remedial system<br>design, representing a significant cost savings to environmental restoration programs at the Savannah River Site.