GEOPHYSICAL SURVEY OF BURIED WASTE AT THE IDAHO NATIONAL ENGINEERING AND ENVIRONMENTAL LABORATORY: A CASE STUDY

摘要

Intrusive sampling of buried waste sites is expensive and time consuming and it increases the chances of worker exposure to hazardous materials. While noninvasive characterization techniques are not a substitute for invasive sampling, they can focus the sampling effort thereby reducing the number of invasive samples required, decreasing the time required to characterize a site, and reducing the risk of worker exposure to hazardous materials. The results of the use of noninvasive geophysical techniques for the characterization of Pits 2, 3, 5, and Soil Vaults Rows 1–14 in the Subsurface Disposal Area (SDA) are presented as a case study. The SDA is a part of the Radioactive Waste Management Complex (RWMC), which is located in the southwestern area of the Idaho National Engineering and Environmental Laboratory (INEEL). The SDA is located in a high desert plateau with approximately 20 feet of unconsolidated sediment (mainly weathered basalt) underlain by layers of fractured basalt. The waste pits and soil vault rows were constructed by excavating to the surface of the basalt. Waste was placed directly on the basalt or on top of a thin soil layer placed on the basalt. Disposal of the waste occurred over a period of approximately 20 years starting in the early 1950s. This waste contains radionuclides (cesium, uranium, americium, plutonium, strontium), hazardous compounds (beryllium, asbestos, zirconium fines, sodium and potassium salts, mercury, solvents and degreasing agents, solidified acids and bases), and general debris (metal, wood, paper, cloth, plastic). Previous characterization activities have included compilation of historical data (photographs, waste disposal manifests), soil and gas sampling, and geophysical surveys that have covered parts of the SDA and provided general information about the sites. However, improvements to geophysical techniques now allow for higher resolution surveys. The purpose of the survey described in this report was to use these improved techniques to better define the location of the waste buried in Pits 2, 3, 5, and Soil Vault Rows 1–14. Better definition of the pit and soil vault boundaries and metallic objects within the pits will help in selection of sites for further investigation. In addition to providing better definition of the pits and vaults, the purpose of this work was to illustrate the power of combining geophysical techniques. The survey was conducted in October of 1999. A variety of noninvasive geophysical tools can be used to distinguish the boundaries of buried waste sites and provide qualitative data of the contents of those sites. Three geophysical technologies: the Rapid Geophysical Surveyor (RGS), the Geonics EM 61, and the Geophex (GEM2) were used to characterize Pits 2, 3, 5, and Soil Vault Rows 1–14 covering approximately 15 acres in the SDA. Selection of these technologies was based on the results of previous demonstrations at Brookhaven National Laboratory and the Cold Test Pit at the INEEL. For comparison of the geophysical data to historical data, Geosoft software was used to merge the geophysical data with the CAD rendering of the historical pit, trench, and soil vault row locations. The synthesis of the data from the multiple techniques significantly improved the resolution and compositional detail delivered by the surveys. Data from the survey provided the locations of geophysical anomalies associated with shallow buried waste. Correlation of these geophysical anomalies to the historical records was done in an effort to better determine boundaries of the pits and soil vault rows and verify the reliability of the historical data. Results of this work will be used to facilitate the selection of sampling locations for contaminants of potential concern and to help locate areas to perform demonstrations of remediation technologies. Geophysical data from three instruments were analyzed individually and as a group and compared