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Table 1. Site characteristics and scores. <br /> Site characteristic Score <br /> 1. The minimum depth to ground water from the soil sample is 0 <br /> approximately 20 ft. <br /> 2. Subsurface fractures are likely to exist in the bedrock that underlies the 5 <br /> tank excavation. <br /> 3. The average annual precipitation is 10.87 in. 9 <br /> 4. No man-made conduits exist. 10 <br /> 5. A unique site feature such as coarse sand or gravel lenses could exist. 9 <br /> Total 33 <br /> The score of 33 falls under the "high leaching potential" category and corresponds to <br /> acceptable concentrations for TEPH-Diesel of 100 ppm and ND concentrations of BTE and X. <br /> Since the soil in the west end of the tank excavation yielded a TEPH-Diesel concentration of 65 <br /> ppm and ND concentrations of BTE and X, the soil did not exceed the leaching potential criteria. <br /> Therefore, the tank excavation area was backfilled with imported sand. The piping excavation <br /> area was also backfilled with imported sand and paved with asphalt. <br /> Soil Bioremediation <br /> No diesel-containing soil has been transported offsite. The approximately 120 cubic yards of <br /> soil that was removed from the tank and piping excavations has been stockpiled on, and covered <br /> with, 10 mil polyethylene sheeting. Since the concentrations of BTE and X in the soil are below <br /> detection limits, there are no air emissions of volatile organic compounds (VOCs). LLNL is <br /> conducting a benchtest experiment to evaluate the feasibility of using Enhanced Soil <br /> Bioremediation (ESB) to reduce the concentration of diesel in the soil. Preliminary ESB data <br /> demonstrate that bioremediation is an effective alternative to transporting the soil offsite. The <br /> full scale ESB is scheduled for Spring 1991, and should be completed during the summer. Mr. <br /> Mike Higgins of the Central Valley Regional Water Quality Control Board (RWQCB) has been <br /> verbally informed of the bioremediation project, and he will be updated periodically. <br /> Conclusion <br /> The closure activities for the 874-DlU1 Underground Diesel-Fuel System have been <br /> completed according to the Closure Plan. Except for the full scale ESB, no other activities are <br /> required or planned. <br /> 8 <br />