Geophysical characterization of a fractured-bedrock aquifer and blast-fractured contaminant-recovery trench
- and others
Borehole- and surface-geophysical methods were used to characterize the hydrogeology and the effects of blast fracturing an in-situ recovery trench in a contaminated fractured-bedrock aquifer. The recovery trench is located at the former fire-training area of Loring Air Force Base in Aroostook County, Maine. Borehole-geophysical methods, used in six wells at the site, included video, acoustic televiewer, heat-pulse flowmeter under nonpumping and low-rate pumping conditions, natural gamma, electromagnetic induction, fluid temperature and conductivity, caliper, deviation, and borehole radar. Borehole radar was used in a single-hole reflection configuration with directional and non-directional 60-MHz (me-ahertz) antennas and in a cross-hole tomography configuration with 22- MHz antennas. One surface-geophysical method, azimuthal square-array direct-current resistivity, also was used. Geophysical surveys were conducted before and after blast fracturing the recovery trench. Integrated interpretation of the geophysical data collected before blasting indicates that most transmissive fractures are steeply dipping and are oriented northeast and southwest. Analysis of azimuthal square-array-resistivity data indicates that the secondary porosity of the fractured-bedrock aquifer is about 1 percent. The borehole-geophysical data and cross- hole radar tomography data indicate that more fractures are present in the upper 20 to 25 m (meters) of bedrock than in bedrock below this depth. Interpretation of the Geophysical data collected after blast fracturing the recovery trench indicates that the blast created an intensely fractured zone about 3 m wide, 26 m deep, along the 50-m length of the recovery trench. Blast-induced porosity in the recovery trench is estimated from the borehole-radar data to be 1 3.5 {+-} 5 percent at the midpoint of the trench, decreasing to 7.3 {+-} 6 percent at the northwestern end.
- OSTI ID:
- 381492
- Report Number(s):
- CONF-960477--
- Country of Publication:
- United States
- Language:
- English
Similar Records
Characteristics of fractures in crystalline bedrock determined by surface and borehole geophysical surveys, Eastern Surplus Superfund Site, Meddybemps, Maine
Comparison of heat-pulse flow measurements and vertical gradients in a fractured limestone aquifer