1887

Abstract

A major obstacle to the remediation of contaminated aquifers at the Savannah River Site in Aiken, South Carolina is<br>the presence of discontinuous sand and clay lenses that are difficult to map effectively using geologic and geophysical<br>well logs. In order to map these discontinuous sand and clay lenses we acquire two perpendicular nine-component<br>(9C) seismic lines, a 9C Vertical Seismic Profile, (VSP) and p-wave and s-wave sonic logs in a borehole south of the<br>Old Burial Ground at the Savannah River Site within which were available natural gamma ray and interpreted geology<br>logs. P-wave reflections are interpreted as originating from water table, the Tan Clay, the Green Clay, the top of<br>the Ellenton Clay, and a calcareous sediment layer within the Barnwell/McBean aquifer. Along the east-west trending<br>line, reflectors are generally continuous except for the occurrence of a discontinuity in the upper reflectors near the<br>east end of the line. This discontinuity could be interpreted as a sediment slump feature possibly related to the dissolution<br>of the calcareous sediment layer, or as the eastern terminus of a large scour feature. Along the north-south<br>trending line, reflectors are spatially less continuous and are interpreted as being cut by several channel/scour features.<br>The shear-wave stacks are interpreted as mapping the top of the Tan Clay and the calcareous sediment layer and show<br>evidence of azimuthal anisotropy. Using Alford rotations to maximize the energy in the fast and slow shear directions<br>gives a magnitude of anisotropy of 3% with a direction of anisotropy agreeing, near the center of the east-west trending<br>line, with the regional stress direction. Although the most consistent anisotropy is observed near the center of the<br>line, systematic variations along the line suggest that the observed anisotropy is not related solely to the regional<br>stress field. Other mechanisms that could be responsible include grain orientation, stacked stratigraphic features, and<br>depositional or erosional lineations. None of these mechanisms can be excluded until further analysis of the 9C VSP<br>and until laboratory measurements of core samples have been completed.

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/content/papers/10.3997/2214-4609-pdb.205.1996_012
1996-04-28
2024-06-18
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