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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, B3-2, and B3-3 (Figure 2) (Boyajian & Ross, 1998) PHCs were not detected <br /> in the soil samples collected from 10 toll 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 <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 <br />' these wells on a quarterly basis since 1999 (Port of Stockton, 2002) <br /> Groundwater Monitoring <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 bonngs (B3-4 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 B3-6 TPHg and BTEX were detected at <br /> low concentrations in dust one 40-foot sample, which was collected from boring B3-5 <br />' 2002 <br /> An assessment was conducted at the site to further delineate the lateral extent of petroleum <br /> hydrocarbons in soil and groundwater(Geomatnx, 2002a) Six soil borings (B3-8 through <br /> B3-13, Figure 2) were advanced to about 40 feet bgs TPHg and BTEX were not detected in any <br /> of the soil or groundwater samples collected <br /> Based on the results of these assessments, significant impact to soil and groundwater at the site <br /> • appears to be limited to the 20-foot depth zone The lateral extent of soil and groundwater <br />' u[--3 gir13 doc 3 <br /> 1 <br />