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The maximum concentration of lead in soil samples collected was 12 mg/kg, well below the California Code of Regulations, Title 22, Total Threshold Limit Concentration (TTLC) of 1,000 mg/kg The common background range of concentrations of lead in soils is 2 to 200 mg/kg with the average being 10 mg/kg (W. Lindsay, 1979), and the concentration of lead in soil detected in the samples collected falls within the average background concentration. 4.4 Groundwater Analytical Results Groundwater samples were collected from the five monitor wells on November 19, 1992 and submitted for laboratory analysis as described previously. A summary of the groundwater sample analytical data is presented in Table 3, and groundwater sample analytical data sheets and chain-of-custody records are included in Appendix III The analytical results indicated that no detectable concentrations of TPH were present in the groundwater samples collected from the five monitor wells at the site. Concentrations of benzene were detected in groundwater samples collected from monitor wells MW2, MW3 and MW4 at 0.58 µg/1, 7.7 ,ug/l and 18 µg/1, respectively. Toluene and ethylbenzene were detected only in the groundwater sample collected from well MW4 at a concentration of 12 µg/l each. Xylenes were detected in groundwater samples collected from MW3 and MW4 at concentrations of 1.2 Mcg/l and 13.5 µg/1, respectively. BTEX concentrations in groundwater samples collected from the monitor wells are also shown on the benzene isoconcentration contour map included as Figure 4 The total lead concentrations in groundwater ranged from 3.4 1 to 13 1,u /1 The lowest ln' g fig/ g concentration was detected in the groundwater sample collected from well MW 1 located at the southern end of the tank excavation and the highest total lead concentration was in the groundwater sample collected from well MW2 located to the west (up gradient) of the underground storage tank excavation The drinking water maximum contaminant levels (MCLS) for BTEX and lead compounds reported in the Staff Report of the Regional Water Quality Control Board Central Valley ' Region are as follows• • Benzene = 1 jug/1 ' Toluene = 1,000 µg/1 • Ethylbenzene = 680 µg/l • Xylene = 1,750 µg/l ' Lead = 50 jzg/l Benzene is the only compound detected in the groundwater samples collected as part of the ' preliminary site assessment that exceeded the MCL iiisicai 14