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C/ <br />120 ppm in the samples collected from both 10 and 20 feet bgs MTBE was detected in four of <br />the five samples analyzed from SB -4 The highest detection of benzene was present at a <br />concentration of 16 ppm in the sample collected at 20 feet bgs <br />' 3.2.2 Groundwater <br />Analytical results of the groundwater samples collected from the Geoprobe bonngs indicate that <br />petroleum hydrocarbons have impacted the groundwater beneath the site Analytical results are <br />summarized in Table 4 and laboratory reports are included in Appendix E <br />' The groundwater sample analyzed from SB -3 contained 750 ppb TPH-as-Aviation Gas, 460 ppb <br />TPH-as-Jet Fuel and 2 9 ppb benzene The groundwater sample from SB -4 contained 18,000 <br />' ppb TPH-as-Aviation Gas, 8,500 ppb TPH-as-Jet Fuel and 710 ppb benzene These <br />concentrations of petroleum hydrocarbons in the groundwater are above allowable limits <br />1 <br />4.0 Conclusions and Recommendations <br />' 4.1 Conclusions <br />The environmental site investigation at the Stockton Metropolitan Airport Aviation Fuel Storage <br />Area included the sampling of soil and groundwater from two on-site locations using a Geoprobe <br />DPT rig The project objectives, including a determination of groundwater quality beneath the <br />' site, were successfully accomplished <br />Field observations and laboratory data collected during the investigation indicate that petroleum <br />hydrocarbons did impact the soil and groundwater in the vicinity of the former USTs The <br />' highest detection of TPH-as-Aviation Gas were reported at 8,000 ppm in the soil sample <br />collected at 10 feet bgs on the northwest side of the eastern former tank complex TPH-as-Jet <br />' Fuel was found in soil at the same location at significantly lower concentrations of up to 120 <br />ppm Benzene was found in soil at a maximum concentration of 16 ppm At each of the two <br />' sample locations, the vertical extent of impacted soil was defined It is likely, however, that soil <br />beneath and/or alongside the buried concrete slab may be impacted at greater depths <br />' Analytical results of the groundwater samples indicate that TPH-as-Aviation Gas is present at <br />concentrations of up to 18,000 ppb beneath the site TPH-as-Jet Fuel was found in groundwater <br />SAC/2_22-96/ENG/765436 10 <br />