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12 4 milligrams per kilogram in the 13-foot samples collected from the north ends of both tanks, <br /> but was not detected in the samples collected at 16 feet bgs <br /> 1 <br /> 1998 <br />' In 1998, soil samples were collected at 5-foot intervals between about 10 5 and 40 5 feet bgs <br /> from borings B3-1, 133-2, and B3-3 (Figure 2) (Boyajian & Ross, 1998) PHCs were not detected <br />' in the soil samples collected from 10 to 11 feet bgs and from 35 to 40 feet bgs The highest <br /> concentrations of PHCs were detected in the soil sample collected at about 15 5 feet bgs from <br /> boring B3-2 PHCs were detected in some of the grab groundwater samples collected from these <br />' borings <br />' 1999 and Groundwater Monitoring <br /> In 1999, three groundwater monitoring wells (MW3-1, MW3-2, and MW3-3) were installed in <br /> the vicinity of the former UST area (Figure 2) (Ross, 1999) The 35-foot deep wells are <br /> constructed with 25-foot-long screens at the bottom The Port has been monitoring and sampling j <br /> these wells on a quarterly basis since 1999 (Port of Stockton, 2002) <br /> 1 <br /> Groundwater samples collected from the monitoring wells have been analyzed for TPHg, <br /> benzene, toluene, ethylbenzene, and xylenes (BTEX), and on several occasions for methyl <br /> tertiary butyl ether(MtBE) Depth to water in the wells has ranged from about 9 to 16 feet bgs <br />' Horizontal groundwater flow directions have been variable, ranging from northwest clockwise to <br /> southwest Groundwater gradients have also been variable, ranging from about 0 004 to 0 035 <br /> foot per foot No seasonality is apparent in the groundwater flow direction or gradient MtBE <br /> has not been detected in the groundwater samples collected from the monitoring wells TPHg <br />' and BTEX concentrations in the groundwater samples collected from the monitoring wells have <br /> not indicated apparent upward trends <br />' 2001 <br /> An assessment was conducted at the site to delineate the lateral and vertical extent of petroleum <br />' hydrocarbons in soil and groundwater(Geomatnx, 2002b) Four soil borings (133-4 through B3- <br /> 7, Figure 2) were advanced to about 40 feet bgs TPHg and BTEX were detected at low <br /> concentrations in the soil samples collected at 15 to 20 feet bgs from borings B3-5 and B3-6, but <br /> were not detected in soil samples collected from about 40 feet bgs in any of the four borings <br />' High concentrations of TPHg and BTEX were detected in the grab groundwater samples <br /> collected at about 20 feet bgs from borings B3-5 and 133-6 TPHg and BTEX were detected at <br /> . low concentrations in dust one 40-foot sample, which was collected from boring 133-5 <br />' ust s11e3 gtrk2 doc 4 <br /> 1 <br />