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829-DlU1 Supplemental Information The 829-DlU1 tank system was installed in 1983. It is.located just outside the fence surrounding the high explosives burn facility, approximately forty feet southwest of the fence gate. The tank supplied diesel fuel to the iron horse, a container for burning high explosive waste. The underground diesel fuel tank is constructed with double walls consisting of a 30-gallon steel drum as the outer secondary container, and a 25 to 27-gallon inner primary container of unknown composition. On September 21, 1993, several inches of gravel were removed exposing the top of the tank and the joint connecting the tank to a dear plastic standpipe equipped with a liquid level indicator. The purpose of the excavation was to permit replacement of the standpipe that had become embrittled by sunlight. The excavation revealed diesel fuel contamination in the gravel fill surrounding the top of the tank, and a hole in the top of the tank (drum lid) that was the apparent result of having been punctured by a pick ax at the time of the excavation. This discovery resulted in a verbal report to Bill Snavely of San Joaquin County Public Health Services and a voice mail message to Susan Timm of the Central Valley Regional Water Quality Control Board, both on September 22, 1993. An "Underground Storage Tank Unauthorized Release (Leak)/Contamination Site Report" was submitted to San Joaquin County Public Health Services on September 29, 1993. The contaminated fill material was the probable result of historical tank overfilling. The amount of diesel fuel released is estimated to be one gallon or less. No fuel was released as a result of the excavation. The tank was pumped out the morning of September 22, 1993. The piping was dug up by mistake, but has been retained at the site. Figure 1 (see Appendix B) shows the location of the 829-DlU1 tank system in relation to the Lawrence Livermore National Laboratory (LLNL), Site 300. Figure 2 (Appendix B) shows a plan view of the 829-DlU1 tank system in relation to the high explosives waste burn facility gate and fence. UST 829-DlU1 has not leaked according to previous tank integrity test reports. LLNL contracted Clayton Environmental Consultants to perform tank integrity tests using Horner Ezy-Check test equipment. The annual 1993 test report is included as Appendix C. If soil encountered at the time of closure contains evidence of diesel fuel, the impacted soil will be excavated (maximum of ten cubic yards) and stockpiled on sheets of plastic pending collection and analyses of soil samples collected within the excavation and from the excavated materials. If soil contamination remaining in the excavation appears to be more than minor, or if there is an indication of contaminated ground water, LLNL will perform further