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City of Stockton A68109.01B July 18, 1997 Page 8 ' C TABLE 4 :. Summary;:of Gro l;�ndwater Analytical Results Soil Probe Location SP 1 December 23, 1996 Results m wwri grams per lricr L Serrene Talucae Pthyl- Xyleaes -: MIBE AYH D } � 6emetx SP-1 ND 0.7 ND M? itis 410 " MT13E = methyl tertiary-butyl ether TPH-D = total petroleum hydrocarbons-diesel range constituents ND = not detected at or above detection limit for reporting purposes Detection limits for these analyses are reported on the attached laboratory reports. 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 (less 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. l4 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 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 Leaking Underground Fuel Tank (LUFT) Field Manual (California State Water {` Resources Board, 1989). This analysis provides recommended maximum allowable concentrations of TPH-D and BTEX in soil that can be left in place without threatening groundwater. Site specific parameters that are considered in this analysis include; depth to s 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.). i�