COMPLIANCE INFO_FILE 3 - Laserfiche WebLink

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Presumably, the operational piping consisted of two lines, a supply line and a return line, that linked the tank and the generator. The tank was removed from the ground in 1985 during a site-wide maintenance project. As shown in Figure 2, the tank excavation is located on a steep hillside just south of Building 850. The unpaved hillside slopes to the north at 10 to 40 degrees. The elevation of the base of the tank was approximately 20 ft above the generator. The tank excavation is approximately 10 ft wide and 20 ft long with the longitudinal axis oriented east-west. The tank excavation has not been backfilled and averages approximately 5 ft deep. The average elevation of the base of the tank excavation is 1,324 ft. A layer of'approximately 2.5 ft of sloughed soil from the walls of the excavation forms the floor of the tank excavation. Soil removed from around the tank during its excavation has been stockpiled near the southwest comer of the tank excavation. The volume of the excavated soil pile is approximately 26 yd3. During tank excavation in 1985, the piping that was connected to the underside of the tank was broken (R. Ambrosino, personal communication). The broken piping was sealed almost immediately after it was broken. An attempt had been made to pump out the tank before it was removed, but the pumping was unsuccessful due to the large amount of sludge in the tank. The sludge, which was approximately 2.5 in. thick, had accumulated because the tank had not been used for several years. The tank was visually inspected after it was removed from the excavation. No perforations or holes were evident. The tank was cleaned and shipped offsite by Universal Engineering (Appendix B). The amount of diesel fuel that was released via the broken piping is not known but is estimated by the tank removal laborer to be only a few gallons. The diesel fuel drained from the broken piping on to the eastern floor of the tank excavation (M. Heaton, personal communication). It is not possible to infer that the diesel fuel released during the tank removal operation is the sole source of all the diesel fuel in the soil because neither the tank nor the piping were precision tested or periodically monitored while the system was in service (R. Henry, personal communication). solo91 'e Setting Building 850 is situated on the northern flank of the Patterson Anticline in the eastern side of the Altamont Hills. Located within the Coast Range Physiographic Province, the topography of Site 300 is marked by steep canyons and hills. The surficial soils at the tank excavation are derived from colluvium and are classified as Linne clay loam (Cole et al., 1943). Soil composition ranges from clayey silt to silty, fine- to medium-grain sand. Prominent shrinkage cracks, indicative of a highly expansive clay content, have been observed to form locally in this soil during the dry season (Taffet et al., 1990). The bedrock underlying the soil varies from a well indurated siltstone to a moderately indurated and moderately well sorted, silty sandstone that varies from fine to coarse grained. The bedrock is extensively jointed and the bedding dips approximately 10 degrees east. The near-surface bedrock at Building 850 has been mapped as the Miocene Neroly Formation (Lamarre et al., 1990). Figure 3 depicts the ground water elevation of the uppermost water-bearing zone in the vicinity of Building 850. Five monitor wells are located within 350 ft of the 850-D1U1 excavation. This water-bearing zone, which is within the Neroly Formation interbedded 4