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F-a <br /> St&urface investigation Results <br /> 6131 Pacific Ave., Stockton, CA. <br /> Aegis Project No. 90.020 <br /> Page 21 <br /> f <br /> 4.4 S03:L YMPLINGI OF EXCAVATED MATERIAL <br /> �pproximately 150 cubic yards of soil were generated by the tank <br /> replacement activities. Soils were stockpiled and covered by <br /> visquene at the location shown on Figure 7. Four soil samples <br /> i were collected from the stockpiled soils and composited into one <br /> sample at the laboratory. Soil samples were collected by digging <br /> ,�. approximately 1.5 feet below the surface of the soil pile and <br /> advancing a clean brass sampling tube into the soil sui.oh that no <br /> head space was left in the tube. <br /> Table 3C presents the analytical results from samples collected <br /> from the excavated material. <br /> '"" YSCUSSION OF RESULTS <br /> i , <br /> The following subsections discuss the results of the preliminary <br /> subsurface investigation and tank closure activities. <br /> 5.1 PETROLEVM HYDROCAR3ONS IN SOIL: ORIGINAL TANK BAS <br /> Gasoline odor observations, PID readings and soil sample <br /> analytical laboratory results indicate impact tri the native sails <br /> adjacent to`'the original tank basin Soil samplas collected from <br /> B-3 .indicate1 the presence of petroleum hydrocarbons at.a depth <br /> of 50 feet bilow grade ,beneath the original tank basin. <br /> 5.2 PE'T'ROLEUM HYDROCARBONS IN SOIL: NEW TANK BASIN <br /> Gasoline odor observations and soil sample analytical laboratory <br /> results indicate that petroleum hydrocarbons are not present in <br /> the area of the new tank location at depths less than 21.5 feet <br /> below grade. <br /> w 5.3 PETROLEUM HYDROCARBONS IN SOIL: PRODUCT LINES <br /> Gasoline odor observations and soil sample analytical laboratory <br /> results indicate that petroleum hydrocarbons exist beneath the <br /> location of the product line trenches. The product lines are <br /> located adjacent to the footings <br /> for the canopy and with in three <br /> feet of the building. Excavation of soils containing petroleum <br /> hydrocarbons adjacent tD the footings may endanger the structural <br /> integrity of the canopy footings. and .the building foundation. <br /> i, . <br /> 5.4 HORIZONTAL EXTENT OF PETROLRUM HYDROCARBONS IN SOIL <br /> Figures 8A , 8B and 8C present benzene iso-contours in soils at <br /> the 101--201, 251-35' and 40' to 50' foot levels. <br /> As shown by the figures the highest concentrations of petroleum <br /> constituents are .located around the location of tank #3. An <br /> a` inferred zero line of benzene in the soil indicates that the <br /> migration of petroleum hydrocarbons is confined to the area <br /> adjacent to the original underground fuel storage tanks. <br />