Biannual recalibration of two spectral gamma-ray logging systems used for baseline characterization measurements in the Hanford Tank Farms. Vadose Zone Characterization Project at the Hanford Tank Farms

The US Department of Energy`s (DOE`s) Grand Junction Projects Office (GJPO) is engaged in establishing an initial, or baseline, characterization of the gamma-ray-emitting contaminants in the subsurface of the Tank Farms at the DOE Hanford site in the State of Washington. These baseline data are gathered by logging existing monitoring boreholes with two high-resolution passive gamma-ray logging systems informally known as Gamma 1 and Gamma 2. Calibration of the logging systems is crucial to the assurance of data quality. The project document Spectral Gamma-Ray borehole Geophysical Logging Characterization and Baseline Monitoring Plan for the Hanford Single-Shell Tanks (DOE 1995a) specifies that the initial, or base, calibration of both systems must be performed before commencement of field measurements at Hanford and that both systems must be recalibrated every 6 months thereafter using the calibration standards at the Hanford borehole logging calibration center. Data collection for the base calibrations was completed in April 1995; the results were published in Calibration of Two Spectral Gamma-Ray Logging Systems for Baseline Characterization Measurements in the Hanford Tank Farms (DOE 1995b). This report documents the first recalibration of the two systems that was performed in October 1995 at the Hanford Site. Analyses of data collected during the recalibrations are presented