BOREHOLE GEOPHYSICS FOR CONTAMINATION INVESTIGATIONS IN FRACTURED SEDIMENTARY BEDROCK

Borehole geophysics provides critical information for contamination investigations in fractured sedimentary bedrock. The application of borehole geophysics at several sites contaminated with volatile organic compounds (VOCs) and underlain by shale, sandstone, and carbonate rock in the Northeast and California will be presented. The borehole-geophysical methods applied at the sites included gamma and induction logging; borehole imaging (acoustic and optical televiewer); and fluid property logging (specific conductance and temperature), flowmeter testing (heat pulse and electromagnetic), and VOCs point sampling under ambient and pumped conditions. Integrated analysis of the borehole geophysical logs helped to delineate lithology and correlate stratigraphy and to define the distribution and orientation of bedding and fractures. The log analysis also helped to characterize the distribution of fracture-flow zones, quantify vertical flow between zones in open boreholes under ambient and pumped conditions, and estimate zone transmissivity, head, and connectivity. The geohydrologic information gained through borehole geophysics was useful for general site characterization as well as the evaluation of VOCs sampling programs that utilized open boreholes and discrete-zone packer systems.