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3.0 Site Investigation Result <br />Results of the field and laboratory activities are discussed in this section <br />3.1 Geology and Hydrogeology <br />In general, the site geology consists of soils composed of interbedded clay, silt and sand mixtures <br />to a depth of at least 55 feet bgs Sand intervals encountered during sampling were less than 5 <br />feet thick and consisted primarily of poorly graded fine- to medium -grained micaceous sand <br />The geologic units are not continous Comparison of the geologist's logs indicate facies changes <br />over short distances across the site This is not uncommon for the area Detailed soil <br />classifications are presented on the boring logs included in Appendix C <br />Groundwater was encountered beneath the site at a depth of approximately 55 feet bgs <br />Groundwater from this first water -bearing zone likely resides under water table conditions Low <br />recharge rates observed qualitatively during groundwater sampling suggests that hydraulic <br />conductivities associated with this water -bearing zone are low <br />3.2 Petroleum Hydrocarbon Distribution <br />All soil and groundwater samples were analyzed for TPH-as-Aviation Gas, TPH-as-Jet Fuel, <br />MTBE and BTEX The results of these analyses are discussed in the following sections <br />3.2.1 Soil <br />Analytical results of the soil samples collected from the two Geoprobe borings indicate that <br />petroleum hydrocarbons have impacted vadose zone soil to a depth of at least 35 feet bgs Soil <br />sample laboratory test results for TPH-as-Aviation Gas, TPH-as-Jet Fuel, MTBE and BTEX are <br />summarized in Table 3 and laboratory reports are included in Appendix D <br />All soil samples analyzed from SB -3 were found to be below reporting limits for all parameters <br />Soil samples analyzed from SB -4 contained detectable concentrations of all parameters TPH-as- <br />Aviation Gas was detected in the three shallowest samples submitted from SB -4 The highest <br />detection of TPH-as-Aviation Gas was present at a concentration of 8,000 ppm in the sample <br />collected at 10 feet bgs TPH-as-Jet Fuel was also detected in the three shallowest samples <br />submitted from SB -4 The highest detection of TPH-as-Jet Fuel was present at a concentration of <br />SAC/2-22-96/ENG/765436 9 <br />