ARCHIVED REPORTS XR0011739 - Laserfiche WebLink

Home Browse Search

---------------- Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 22 5.0 HYDROCARBONS IN SOIL AND GROUNDWATER By synthesizing the historic, geologic, hydrostratigraphic and geo-chemical data gathered by the work performed for the site characterization program, together with information obtained by Dietz Irrigation at the time the underground storage tanks and piping were removed from the 7500 West Eleventh Street property, SJC has developed an �_J interpretation of the sources by which, and the distribution and lateral and vertical extent to which the subsurface beneath the subject property and adjacent areas has been affected by petroleum hydrocarbons. This interpretation and the parameters upon which it is based are discussed in the following sections of this report. Note: Analyses performed on selected samples of soil and groundwater also included analysis for total lead in soil and groundwater. The sampling locations and the results of _ those analyses are included in Tables 1 and 2. However, in those cases where lead was detectable, its concentration was well within the range that is known to occur naturally in the alluvial deposits on which the subject property is located. (The San Joaquin Company .3 Inc. 2000.) Also, we note that no EDB or 1,2-DCA were detected in any samples of groundwater that were analyzed. 5.1. Tank Pit No. 1 As was noted in Section 2.1, when the underground storage tanks that had served the fueling station in the years prior to its final closure were removed from Tank Pit No. 1, they were in excellent condition and free of rust. There was no evidence that either the tanks or their adjacent piping had leaked or that there had been any significant release of fueldue to over-filling of the tanks. I_�1 Four soil samples recovered from the walls of Tank Pit No. 1 at the depth of the surface of the groundwater contained, as can be seen in Table 1, no detectable concentrations of gasoline, although MTBE was present in all four samples at very low concentrations. Three of the samples contained low concentrations of one or more of the BTEX compounds. Diesel at a concentration of 2,200 mg/Kg was detected in a soil sample recovered from the west wall at groundwater level in the southwest corner of the pit. Diesel in the three other samples contained either no detectable concentrations of diesel or very low concentrations of that fuel. The sampling locations referred to above are shown on Figure 4. i As was also discussed in Section 2.1, when the tanks from Tank Pit No. 1 were removed, ':_J floating product flowed in from the western wall of the pit. That floating product was skimmed from the water surface until there was no further inflow, and the tank pit was free of floating product. Significantly, although a grab sample of groundwater taken from the pit at that time contained 210,000 µg/L of diesel, it also contained 55,000 µg/L of gasoline, which would be incompatible with the fact that no detectable concentrations of gasoline were detected in samples recovered from the walls of the pit at the depth of the water table, unless the source of the floating product that flowed into Tank Pit No. 1 was located at some point remote from and to the west of the pit. sic