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

摘要

Intrusive sampling of buried waste sites is expensive and time consuming and it increasesthe chances of worker exposure to hazardous materials. While noninvasive characterizationtechniques are not a substitute for invasive sampling, they can focus the sampling effort therebyreducing the number of invasive samples required, decreasing the time required to characterize asite, and reducing the risk of worker exposure to hazardous materials. The results of the use ofnoninvasive geophysical techniques for the characterization of Pits 2, 3, 5, and Soil Vaults Rows1–14 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 islocated in the southwestern area of the Idaho National Engineering and EnvironmentalLaboratory (INEEL). The SDA is located in a high desert plateau with approximately 20 feet ofunconsolidated sediment (mainly weathered basalt) underlain by layers of fractured basalt. Thewaste pits and soil vault rows were constructed by excavating to the surface of the basalt. Wastewas placed directly on the basalt or on top of a thin soil layer placed on the basalt. Disposal ofthe waste occurred over a period of approximately 20 years starting in the early 1950s. Thiswaste contains radionuclides (cesium, uranium, americium, plutonium, strontium), hazardouscompounds (beryllium, asbestos, zirconium fines, sodium and potassium salts, mercury, solventsand 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 thathave covered parts of the SDA and provided general information about the sites. However,improvements to geophysical techniques now allow for higher resolution surveys. The purposeof the survey described in this report was to use these improved techniques to better define thelocation of the waste buried in Pits 2, 3, 5, and Soil Vault Rows 1–14. Better definition of the pitand soil vault boundaries and metallic objects within the pits will help in selection of sites forfurther investigation. In addition to providing better definition of the pits and vaults, the purposeof this work was to illustrate the power of combining geophysical techniques. The survey wasconducted in October of 1999.A variety of noninvasive geophysical tools can be used to distinguish the boundaries ofburied waste sites and provide qualitative data of the contents of those sites. Three geophysicaltechnologies: 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 coveringapproximately 15 acres in the SDA.Selection of these technologies was based on the results of previous demonstrations atBrookhaven National Laboratory and the Cold Test Pit at the INEEL. For comparison of thegeophysical data to historical data, Geosoft software was used to merge the geophysical datawith the CAD rendering of the historical pit, trench, and soil vault row locations. The synthesisof the data from the multiple techniques significantly improved the resolution and compositionaldetail delivered by the surveys.Data from the survey provided the locations of geophysical anomalies associated withshallow buried waste. Correlation of these geophysical anomalies to the historical records wasdone in an effort to better determine boundaries of the pits and soil vault rows and verify thereliability of the historical data. Results of this work will be used to facilitate the selection ofsampling locations for contaminants of potential concern and to help locate areas to performdemonstrations of remediation technologies.Geophysical data from three instruments were analyzed individually and as a group andcompared with available historical records to better determine discreet boundaries and thepresence and location of buried waste forms in five pits and fourteen soil vault rows. Using thethree instruments and a more dense data collection method, information was collected thatsuccessfully identified discrete boundaries for most of the pits and soil vault rows and providedenhanced clarity of waste forms over previous surveys. The data collected from this survey wasused in evaluating the accuracy of the historical data and provided additional information on thelocation and content of the pits and trenches. This data will help reduce the number of invasivesamples required to characterize the pits and trenches and will assist operations in planning fieldtreatability studies.