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1 <br /> 2A Excavation and Backfllling <br /> ' 10 and 11 1993 approximately 500 cubic yards of contaminated soil were removed <br /> On May � PP Y <br /> from tank pit #1 Soil was removed from the excavation to a depth of 35 feet at the <br /> tsouthern end of the excavation Field screening with a photo-ionization detector (PID) <br /> detected organic vapors at the floor of the enlarged excavation. In subsequent verbal <br /> communication, the PHS/EHD notified Pacific Gas that, due to seasonal high groundwater <br /> ' of approximately 45 feet, a groundwater investigation involving the installation of three <br /> monitoring wells would be required. <br /> ' On May 12 and 13, 1993, the excavation was partially backfilled Crushed rock and pea <br /> gravel were used to backfill the southern portion of the excavation The entire excavation <br /> was then backfilled and compacted to a depth of 5 feet below surface grade <br /> 2.5 Monitoring Well Installation and Assessment <br /> ' From November 3 to 5, 1993, five soil borings were drilled at the site Borings B-10 and 13- <br /> 11 were placed in the excavation (approximately 5 feet below surface grade), advanced to <br /> ' depths of 75 and 70 feet respectively and backfilled with portland cement Three other <br /> borings were advanced to 88 feet and completed as 2-inch groundwater monitoring wells <br /> (MW-1, MW-2 and MW-3) A total of 14 soil samples were analyzed for total petroleum <br /> ' hydrocarbons (TPH as gasoline) and volatile aromatics (BTE&X) Three samples were also <br /> analyzed for TPH as diesel <br /> Hydrocarbon odors were noted in soil samples from borings B-10, B-11 and MW-1 at depths <br /> between 45 and 65 feet Laboratory analysis detected TPH as gasoline in 5 of the 14 samples <br /> analyzed The highest concentration of gasoline was detected in B-10 at a depth of 40 feet <br /> ' (1310-40) Toluene was detected only in sample 1311-55, at the detection limit of 0 005 pal is <br /> per million (ppm) Ethylbenzene and xylenes were detected in three samples at <br /> concentrations up to 0 018 ppm (MW1-45) No benzene or diesel were detected in any of <br /> ' the samples <br /> ' 2.6 Groundwater Monitoring <br /> TPH as diesel was has been detected in all three monitoring wells at concentrations from <br /> ' 90AgIL (parts per billion, ppb) to 400 ppb TPH as gasoline has been detected in MW-2 and <br /> at concentrations from 53 ppb to 67 ppb Benzene has been detected in MW-2 and MW-3 <br /> at concentrations of 13 ppb and 0 58 ppb, respectively Toluene has been detected in MW-1 j <br /> ' and MW-3 at concentrations of 199 ppb and 2 4 ppb, respectively Ethylbenzene or xylene <br /> has not been detected in any of the monitoring wells <br /> ' Groundwater depth has been measured at approximately 72 feet The groundwater flow <br /> direction has been measured in the northeast direction <br /> G-60-3 Audra Se—I— <br /> N.G.0.s OR442 9W2 S <br /> 1 <br />