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Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 25 >si No detectable concentrations of gasoline or MTBE were found in any of the samples from Pipe Trench No. 2, although some of them contain very low concentrations of one or more of the BTEX compounds. Two of the five samples contained very low concentrations of diesel, ranging from 1.0 to 3.1 mg/Kg. At the time it was removed, the purpose of the pipeline in Pipe Trench No. 2 was not apparent. However, as can be seen in Figure 3, its alignment suggests that, at some time in the past, it may have continued in the direction of Tank Pit No. 1 or, possibly, Tank Pit No. 2. At the time it was removed, Dietz Irrigation's Field Superintendent also reported that the ground around its southwestern end, near the former truck service bay, appeared to be disturbed, suggesting that a tank or some other structure, might, at some time, have been located there. However, no such feature has been discovered at that location. 5.5 Lateral and Vertical Extent of Hydrocarbons in the Subsurface As is described in Section 3.0, the distribution of petroleum hydrocarbons in soil and groundwater beneath the 7500 West Eleventh Street property and beneath an adjacent portion of West Eleventh Street was investigated by observation and analysis of soil and groundwater samples recovered from temporary borings and groundwater-quality monitoring wells. That information was used to evaluate the lateral and vertical extent of petroleum hydrocarbons in the subsurface and to identify separate sources of hydrocarbons formerly present on the site. 5.5.1 Primary Plume of Diesel and Gasoline Examination of the results of analyses of groundwater (as presented in Table 2) from push-probe boring PP-3 and monitoring well MW-3, which, as shown on Figure 8, are located near the West Eleventh Street frontage of the former fueling station, reveals that there are moderate- to-high concentrations of petroleum hydrocarbons, the molecular chains of which are in both the diesel and gasoline range, a short distance down-gradient from the former location of the fueling station dispenser islands. Those concentrations amount to 14,000 pg/L and 2,800 µg/L of diesel-range product in groundwater recovered from PP-3 and MW-3, respectively. The corresponding concentrations of gasoline-range product were 1,600 µg/L and 11,000 pg/L, respectively. To the west of PP-3 and MW-3, the concentration of diesel-range hydrocarbons in ..', groundwater recovered from PP-2 was only 190 pg/L and the corresponding value for gasoline-range hydrocarbons was only 300 gg/L. Further to the west there were no detectable concentrations of either diesel or gasoline in the groundwater recovered from MW-2, located near the western boundary of the subject property. Directly to the east of PP-3 and MW-3, the concentrations of diesel- and gasoline-range hydrocarbons in groundwater recovered from PP-4 and MW-4 are significantly reduced, compared to those in the former locations that are close to the area where the fuel dispensing pumps had been located. The concentrations of diesel-range fuel in sic i