SAND2000-2094
Unlimited Release
Printed August 2000
Christopher A. Rautman
Underground Storage Technology Department
Sandia National Laboratories
P. O. Box 5800
Albuquerque, New Mexico 87185-0706
Portions of the SmartSampling™ analysis methodology have been applied to the evaluation of radioactive contaminated landscape soils at Brookhaven National Laboratory. Specifically, the spatial, volumetric distribution of cesium-137 (137Cs) contamination within Area of Concern 16E-1 has been modeled probabilistically using a geostatistical methodology, with the purpose of identifying the likelihood of successfully reducing, with respect to a pre-existing, baseline remediation plan, the volume of soil that must be disposed of offsite during clean-up. The principal objective of the analysis was to evaluate the likelihood of successful deployment of the Segmented Gate System (SGS), a novel remediation approach that emphasizes real-time separation of clean from contaminated materials during remediation operations. One primary requirement for successful application of the segmented gate technology investigated is that a variety of contaminant levels exist at the deployment site, which would enable to the SGS to discriminate material above and below a specified remediation threshold value.
The results of this analysis indicate that there is potential for significant volume reduction with respect to the baseline remediation plan at a threshold excavation level of 23 pCi/g 137Cs. A reduction of approximately 50 percent, from a baseline volume of approximately 1,064.7 yd3 to less than 550 yd3, is possible with acceptance of only a very small level of engineering risk. The vast majority of this volume reduction is obtained by not excavating almost all of levels 3 and 4 (from 12 to 24 inches in depth), which appear to be virtually uncontaminated, based on the available data. Additional volume reductions related to soil materials on levels 1 (depths of 0–6 inches) and 2 (6–12 inches) may be possible, specifically through use of the SGS technology. Level-by-level evaluation of simulation results suggests that as much as 26 percent of level 1 and as much as 65 percent of level 2 soils may actually be uncontaminated. Additionally, numerical experiments have been conducted to investigate the effects of selective excavation on the volume and average activity of the remediated materials. These numerical experiments indicate that nonselective excavation may result in mixing of contaminated and uncontaminated materials such that the total volume of material above the threshold excavation level of 23 pCi/g may exceed the baseline volume, thus defeating volume-reduction efforts.
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