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L 'low Lt'elw within the excavation. Soil samples from the soil stockpile reported a maximum concentration of 6.3 ppm TPH-diesel, 0.005 ppm total xylenes, and 38 ppm total lead. 2.3 Regulatory Review The results of the tank removal were reviewed by SJPHS. Based on the detected hydrocarbon concentrations and documented shallow groundwater conditions in the area, SJPHS required a limited subsurface investigation to determine if petroleum hydrocarbons had impacted the soil and groundwater. SJPHS is currently serving as the lead enforcement agency, with copies of all correspondence forwarded to the Central Valley - California Regional Water Quality Control Board (Regional Board). 2.4 Lawrence Livermore National Laboratory Groundwater Investigation Based on documentation provided by LLNL, a site-wide remedial investigation has been implemented at the LLNL facility in response to the initial detection of trichloroethylene L (TCE) in a water supply well. TCE contaminated groundwater had apparently originated from two primary sources: (1) several debris burial trenches, located approximately 350 feet L4101 northeast of the project site, and (2) a dry well pad, located approximately 1200 feet northwest of CRFFS. Other chemicals associated with the TCE release include perchloroethylene L (PCE), 1,2-dichloroethylene (1,2-DCE), 1,1,1-trichloroethane (1,1,1-TCA), benzene, toluene, xylenes, ethylbenzene, various metals (cadmium, copper and zinc) and other chlorinated Lsolvents (LLNL, 1994). LMultiple soil, rock, soil vapor and groundwater investigation have been conducted since 1983 to evaluate the extent of subsurface chemicals in the vicinity of the release areas. The L investigation was extended to the CRFFS facility, located hydraulically down-gradient from the point sources. As shown in Figure 2, five groundwater monitoring wells were installed adjacent to the former CRFFS diesel UST. The wells were installed expressly to track the Lplume of chlorinated solvent contaminated groundwater that migrated from the Livermore property. Relatively low concentrations of TCE, PCE, and 1,2-DCE, generally at <0.1 Lmg/kg concentrations, were reported in soil samples collected in the area. No halogenated volatile organic compounds have been reported in groundwater samples collected from the CRFFS wells. The wells are currently monitored on a monthly basis and sampled on a 6W quarterly basis (LLNL, 1994). 1 TETRA TECH:Castle Rock Forest Fire Station,Preliminary Site Assessment Report Page 5 L 1