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ENVIROI* Y NTAL INVESTIGATION REPORT <br /> Unocal Service Station No 5886 <br /> 2701 West March Lane <br /> Stockton California <br /> ' Delta Project No D095-066 <br /> Page 18 <br /> ' 4 9 Monitonng Well Locations <br /> On November 22, 1995, Delta submitted a Well Box Locatcon letter to SJCEHD proposing the installation <br /> ' of two monitoring well boxes Delta proposed the installation of two 24-inch square boxes to allow for <br /> Installation of ground water monitoring wells following the resurfacing of the site The installation of <br /> ' one box west of Geoprobe location GP-18 and one box southwest of GP-17 was proposed An additional <br /> well is proposed in the area south of GP-21 On November 28, 1995, Delta received verbal approval <br /> ' from SJCEHD to install the well boxes at the proposed locations The well boxes were installed in early <br /> December 1995 <br /> ' 5.0 RESIDUAL HYDROCARBONS IN SOIL <br /> ' 5.1 Residual Total Petroleum Hydrocarbons as Gasoline <br /> Soil samples collected from residual soil during the canopy footing sampling, geoprobe installation, and <br /> UST removal were partitioned into three stratigraphic intervals, three to five feet bsg, six to ten feet bsg, <br /> and greater than ten feet bsg Soil sample concentrations quantified as TPH as gasoline and TPH as <br /> ' diesel were plotted for residual soil samples Benzene was reported in one residual soil sample only, <br /> (GP-3-9) at a concentration of 0 0093 trig/kg (Table 4) Soil in the vicinity of soil samples D-7-3 5 and <br /> ' T-5-4 5 (Table 1) was removed during the southern canopy footing sampling and during the tank cavity <br /> enlargement, respectively <br /> ' Residual TPH as gasoline was not present in soil samples collected from the three to five foot interval <br /> The locations of the residual soil samples collected from this interval are shown on Figure 11 (Residual <br /> ' TPH (Gasoline) Concentrations in Soil from 3 to 5 Feet) Concentrations ranging from C 10 to <br /> 29 mg/kg were detected in residual soil samples collected from six to ten feet bsg All concentrations <br /> ' detected above the laboratory's limits of detection were located in the vicinity of the former northern and <br /> southern dispenser islands (Figure 12, Residual TPH (Gasoline) Concentrations in Soil from 6 to <br /> ' 10 Feet) No detectable concentrations of TPH as gasoline was reported in residual soil samples collected <br /> from ten feet bsg or greater (below ground water) These soil samples were collected during the <br /> installation of the Geoprobes and during the confirmation soil sampling performed under the former <br /> tRPT160 SIS <br />