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CLOSURE REPORT FOR UNDERGROUND STORAGE TANK 830-D1 U1 BACKGROUND The underground storage tank (UST) identified as UST 830-D1 U1, was located south of Building 830, at the Lawrence Livermore National Laboratory (LLNL) Site 300, south of Tracy, California, see Figure 2 (Appendix A). A copy of the UST 830-D1 U1 Approved Application for Underground Storage Tank Closure Permit is included as Appendix B. The cylindrical 280-gallon tank had an approximate diameter of 45 inches, a length of 40 inches, and was constructed of single-walled, carbon steel. UST 830-D1 U1 contained diesel fuel to supply a standby emergency generator serving Building 830. The installation date for UST 830-D1U1 is unknown. The most recent precision tank test results for UST 830-D1 U1, from Gary Peters Enterprises in 1987, using the Tank Audit Leak Computer, showed the tank system to be leak tight, see the UST 830-D1 U1 Closure Plan. After the tank test, the tank was emptied and decontaminated. Between May 6, 1993 and October 14, 1993, UST 814-D1 U1 was monitored weekly using manual stick readings. UST 830-D1 U1 was closed because it was no longer in service. SOIL EXCAVATION AND TANK REMOVAL Soil excavation and tank removal were performed by the LLNL Labor Shop on October 14, 1993. The tank disposal site for this project was Erickson Enterprises in Richmond, California. Oxygen displacement using dry ice was the method used to inert the tank. The oxygen level within the tank was measured at <10 parts per million (ppm) by a LLNL Health and Safety Technician before the tank was removed from the excavation. The tank had three holes in the lower part of one of the tank ends, see Photograph 4 (Appendix C). The piping showed no signs of failure. The UST had a tar coating that was relatively undamaged, see Photograph 5 (Appendix C). Figure 3 (Appendix A) shows the tank excavation, which measured 8 feet by 10 feet by 10.5 feet deep, and the soil sample collection points. Excavated soil was stored on and covered with sheets of polyethylene. The LLNL Heavy Equipment Group Leader, Mr. Stan Pereira, determined that no shoring of the excavation was necessary. A summary of the soil types within the excavation is as follows: • 0-1 foot - Roadbase aggregate • 1-10.5 feet - Brown clay Petroleum product odors were detected in the excavated fill material, in the tank excavation, and in native soil beneath the tank. The fuel supply and return lines in the concrete standby emergency generator pad were cut and capped below ground, see Photograph 1 (Appendix C). Groundwater depth in the area is approximately 104 feet, and the groundwater flow direction is assumed to be south, see Figure 4 (Appendix A). UST 830 CLOSURE REPORT