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Characteristics for the diesel-containing bedrock beneath the tank excavation are scored in Table 4. The bedrock sample with the maximum reported TEPH-diesel concentration is used to characterize all the bedrock at the tank excavation. This sample was collected from borehole U850-DlUl-13 at an elevation of 1,303 ft and yielded the a TEPH-diesel concentration of 29 ppm. The score of 39 for diesel-containing bedrock falls into the "high leaching potential" classification and permits an acceptable TEPH-diesel concentration of 100 ppm and ND concentrations of BTEX. Since all the bedrock samples yielded TEPH-diesel concentrations below these values, the bedrock can be left in place without its threatening the ground water. However, as shown in Figures 5 and 6, it is conservatively assumed that the uppermost few feet of bedrock for which samples are not available (immediately beneath the tank excavation) may contain concentrations of TEPH-diesel greater than 100 ppm. Conclusion The characterization of soil and bedrock with detectable concentrations of TEPH-diesel and BTEX has been completed at the 850-DlUl tank excavation. Soil contamination is limited to the eastern area of the tank excavation. As shown on Figure 9, the estimated volume of soil, and possibly bedrock, with concentrations of TEPH-diesel greater than the LUFT maximum allowable concentration of 100 ppm is approximately 19 yd3 and is confined to elevations above approximately 1,310 ft. All of the soil with detectable concentrations of BTEX is contained within this volume. The elevation of ground water beneath the tank excavation is 1,275 ft. Diesel fuel has not reached ground water. The approximate 19 yd3 of soil will be remediated. Remediation will probably include the excavation of the soil. Soil or bedrock at the base of this new excavation will be sampled to ensure that all the diesel-containing soil and bedrock is removed. The approximate 26 yd3 of soil in the excavated soil pile located at the southwest corner of the present tank excavation will also be remediated along with the newly removed soil and bedrock. The total volume of soil and bedrock to be remediated is approximately 45 yd3 and will be remediated by either onsite bioremediation or offsite disposal. Enhanced Soil Bioremediation (ESB) may be used to remediate the soil and bedrock after being removed from the hillside. LLNL is currently conducting a benchtest experiment to evaluate the feasibility of using ESB to reduce the concentration of diesel-fuel in the soil which was removed from the vicinity of Building 874. Preliminary ESB data demonstrate that bioremediation is an effective cleanup alternative (Lamarre, 1990). The selected remediation alternative will be discussed further in the forthcoming Feasibility Study of the Building 850 and the East Firing Areas,Lawrence Livermore National Laboratory Site 300. 18