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Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 12 r PP-5 and PP-6 were situated across West Eleventh Street to investigate whether a plume of fuel hydrocarbons in groundwater had reached that down-gradient area and, if such was the case, to explore its lateral and vertical extent. , a It was evident from the information obtained from PP-1 through PP-6 that the leading } edge of a plume of affected groundwater emanating from the 7500 West Eleventh Street property had crossed that street and had advanced further to the north-northeast. Data from PP-2 and PP-6 indicated that the western-most edge of the plume was located to the west of the former boring, but to the east of the latter. The elevated concentrations of gas ' and diesel-range hydrocarbons that amounted to 1,600 µglL and 14,000 µg/L respectively, in the groundwater sample recovered from PP-3 supported a conclusion that fuel hydrocarbons had migrated from the area of the former fueling station's pump islands down the groundwater gradient and under West Eleventh Street. In that boring, which had a total depth of 28 ft., visual and olfactory indicators and early analytical data from soil samples recovered from the boring indicated that soils beneath that area of the site were affected to a depth of some 20 ft. High concentrations of diesel and gasoline at 560 µg/L, and 1,100 µg/L, respectively, were detected in samples of groundwater recovered from PP-5, located at the northwestern comer of the intersection of West Eleventh Street and Chrisman Road. Concentrations of those fuel hydrocarbons, at 400 µg/L and 880 µg/L, respectively, were detected in groundwater samples recovered from PP-4, that was located near the south side curb of West Eleventh Street, a short distance to the west of Chrisman Road. Based on the above information, it would have been logical to drill additional borings to the east of Chrisman Road to explore for the eastern limit of the plume of affected ( groundwater. Unfortunately, such investigation was precluded by the USTCF staff's refusal to fund that work, which had been proposed in the Work Plan for the site 4 characterization program. At an early stage of the subsurface investigation, it became apparent that the distribution of petroleum hydrocarbons in soils beneath the 7500 West Eleventh Street property and neighboring areas was highly complex. Continuing investigation using push-probe technology appeared to indicate that, in addition to the relatively clear presence of the plume of fuel hydrocarbons that has been discussed above, the surficial soils over a wide area at varying depths up to 10 ft. were affected by other petroleum hydrocarbons having a variety of characteristics. (Note: see Tables 1 and 2 for analytical data that includes explanatory footnotes concerning the distribution and types of hydrocarbons detected.) In an attempt to delineate the areas affected by the dispersed hydrocarbons described jabove and to delineate the lateral and vertical extent of the plume emanating from the area where the pump islands had been located when the fueling station was in operation, eight (8) additional push-probe holes were drilled at the locations shown on Figure 8. These included borings located so as to investigate areas of the site from which piping had been removed and where soil samples taken at the time the underground storage sic