SITE INFORMATION AND CORRESPONDENCE

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C) City of Stockton A68109.01B July 18, 1997 Page 8 k TABLE 4 Summary of Groundwater Analytical Results Soil Probe Locatioa SP December 23,. 1996 Results in mic opww per liter Cz%A) sa�p�e - Iotatioa beasettcurUMM. _ Toluene Eth* Xyk: e-. MISE. TPi;D trI SP-1 `D I 0.7 ti-D D 410 WME = methvl tertiary-bucyt ether TPH-D = total petroleum hydrocarbons-diesel range constituents `-D = not detected at or above detection limit for reporting purposes Detection limits for these analyses are reported on the attached laboratory reports. E 6.0 EVALUATION 6.1 Soil Characterization: Diesel range constituents TPH-D were detected in soil samples collected at soil probe locations SP-1 and SP-2. The greatest concentration of TPH- D (310 mg/kg) was detected in the soil sample collected at 12 feet BSG from soil probe location SP-1. Concentrations of TPH-D at 31 mg/kg were detected in the soil sample collected at 5 feet BSG in soil probe location SP-1 and at 24 mg/kg in the soil sample collected at 16 feet BSG in soil probe location SP-2. Trace concentrations (Iess than 0.10 mg/kg of toluene. ethylbenzene, and xylenes were also detected in the soil sample collected at 16 feet BSG in soil probe location SP-2. } 6.2 Groundwater Characterization: The analytical results of the groundwater sample collected from the soil probe SP-1 indicates that the groundwater sample was impacted by t toluene and TPH-D. Benzene, ethylbenzene, and xylenes were not detected in concentrations above the detection limits in the groundwater sample analyses. Concentrations of TPH-D at 410 micrograms per liter (µg/L) were detected in the groundwater sample collected from soil probe location SP-1. This small concentration suggests that free diesel product does not exist on the groundwater surface at this location. 6.3 Potential Environmental Effects: Potential environmental effects of the soil impacted with TPH-D were evaluated using the "Leaching Potential Analysis for Gasoline and Diesel" from the Lealdna Underground Fuel Tank LUFT Field Manual (California State Water Resources Board, 1989). This analysis provides recommended maximum allowable concentrations of TPH-D and BTEY in soil that can be left in place without threatening j groundwater. Site specific parameters that are considered in this analysis include; depth to groundwater below contaminated soil, subsurface fractures, average annual precipitation, man-made conduits, and unique site features (i.e. recharge area, coarse soil, nearby wells, etc.). 1