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i 4.0 Conclusions ' 4.1 Soil Contamination The analytical results and the field observations indicate that trace to low levels of BTEX constituents are present in the saturated zone soils in the vicinity of MW-8 TPH-g was not detected in these soils Soil contamination was not detected in the vadose zone in MW-8 or in any sample from MW-9 Higher levels of TPH-g (39 to 140 mg/kg) and BTEX (0 17 to 2 4 wg/kg) were ' detected in soil samples collected by Kleinfelder in 1989 These samples were collected from borings B-1 (approximately 10 feet north of MW-1) and B-2 (in the ' northeast corner of the former location of the UST removed in 1987) The location of the contamination detected in MW-8 correlates with this historical data Soil samples collected by Weston at a depth of 10 feet in MW-4, MW-5, MW-6, and MW-7 borings indicated low levels of toluene and xylenes (1 6 to 37 µg/kg) and concentrations of lead ranging from 7 0 to 15 5 mg/kg Benzene, ethylbenzene, and TPH-g were not detected in soil samples from these well borings According to the LUFT Field Manual, the maximum allowable TPH-g Ievels that can be safely left in place without threatening water quality at the most sensitive site is 10 ppm At concentrations of TPH-g less than 10 ppm, BTEX levels are typically less than detection limits The LUFT Field Manual states that at less ' sensitive sites, levels of 0 3 ppm benzene, 0 3 ppm toluene, 1 ppm ethylbenzene, and 1 ppm total xylenes can be left in place without impacting the groundwater The ' BTEX concentrations detected in soil from MW-8 exceed detection limits but are below the levels for the less sensitive site Based on the analytical results, the ' groundwater at the Stockton Service Center has already been impacted The soil contamination is limited to the saturated zone and the contaminants appear to be in the dissolved phase It appears that sufficient vadose zone soils were excavated ' e, during the UST removal Remediation of the groundwater at the site will likely remediate the soil in the saturated zone as well Any residual soil contamination ' would most likely not be sufficient to be contaminate the groundwater and would likely be naturally biodegraded over time Therefore, soil remediation is not warranted at this site i I 93822 Bast Bay Municipal Utility District 40429SOO asa 10 Stockton Svc Ctr -site Assessment/Remedial Options