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Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, C4, Page 36 r With the exception of a trace of diesel detected in a sample recovered from a depth of 14 f ft, none of the soil samples recovered from PP-2, which was located just west of the dispenser islands, contained any detectable concentrations of TPH(d), TPH(g) or the BTEX compounds. Soil samples recovered from MW-2, located further to the west near the boundary of the 7500 West Eleventh Street property, were also free of any detectable concentrations of TPH(g) or the BTEX compounds. However, a trace of an unidentified k hydrocarbon in the diesel range was detected at a concentration of 1.90 mg/Kg from a soil sample recovered from a depth of 5 ft in that well boring. Except for traces of gasoline in a soil sample recovered from the shallow depth of 4 ft., samples from PP-4 were free of petroleum hydrocarbons. Low concentrations of diesel- range hydrocarbons of up to 122 mg/Kg and gasoline-range hydrocarbons ranging from 3.8 to 170 mg/Kg were detected in soil samples recovered from shallow depths in MW-4. No petroleum hydrocarbons were detected in samples recovered from deeper than 11 ft BGS in either boring. Soil samples recovered from PP-3 and MW-3 revealed concentrations of diesel and gasoline that were generally elevated compared to those detected in the borings located to their east or west along the West Eleventh Street frontage of the subject property. Moreover, particularly in the case of MW-3, petroleum hydrocarbons were found to be present at significantly greater depths in those borings than in borings to their east or west. However, the concentrations detected in the samples recovered from the MW-3 and PP-3 borings are, in absolute terms, very low. The maximum concentration of diesel detected in the samples recovered from PP-3 was only 54 mg/Kg and the corresponding value for gasoline was 15 mg/Kg; similarly, the maximum concentration of diesel detected in samples recovered from MW-3 was 16.9 mg/Kg and the corresponding value for gasoline in a sample from that boring was 18 mg/Kg. The low concentrations of fuel hydrocarbons detected in soil samples recovered from PP- 3 and MW-3 are notable given the close proximity of those borings to the over-excavated =- Dispenser Pit, from which soil affected by high concentrations of petroleum hydrocarbons was removed in December,1998. The absence of significant concentrations of analytes of concern in soil samples recovered from those borings indicates that Dietz Irrigation had over-excavated a sufficient area to successfully remove the soil most severely affected by leakage from the maze of underground pipelines that had fed the fueling station's dispenser pumps. UJ By superimposing onto hydrostratigraphic section B-B' the information discussed above, i::; together with information regarding the presence of visual and olfactory indicators in ``J soils included on the boring and well logs, it is possible to develop a graphic representation of the zone of the subsurface along that section line that is affected by fuels that leaked from the maze of piping. That representation is shown on Figure 15. A shaded, lens-shaped area indicates the presence of a primary plume of diesel and gasoline in the subsurface that has the geometry typical of the distribution of hydrocarbons encountered at sites where leaks from sources located above the groundwater table have occurred. That zone of affected soil has a maximum thickness of some 20 ft, of which the i sic