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• Monitoring Well Installation Report - Former Chevron Service Station !l9-5775 June 2 1999 centimeter (gm/cc) to 1 97 gm/cc, natural density ranging from 1 66 gm/cc to 2 17 gm/cc, matrix density ranging from 2 67 gm/cc to 2 74 gm/cc, and porosity ranging from 30 1 % to 40 8 % The composite stockpile sample contained 60 ppm TPHg and 0 18 ppm benzene Soil chemical analytical data are summarized in Tables 3 and 4 5.3 Groundwater Analytical Results Groundwater samples collected from wells MW -3 and MW -4 contained TPHg (3,100 ppb and 11,000 ppb, respectively), benzene (3,100 ppb and 6,800 ppb, respectively) and MtBE (4 9 ppb and 1,200 ppb, respectively) ELBE (130 ppb) was detected in the groundwater sample collected from well MW -4, but was not detected in the sample collected from well MW -3 Other oxygenate compounds were not detected in the groundwater samples collected from wells MW -3 and MW -4 Groundwater sample collected from well MW -1 contained benzene (1,400 ppb), MtBE (62,000 ppb), EtBE (2,400 ppb) and tAME (780 ppb) TPHg, ethanol, t -butanol or DIPE were not detected in the sample from well MW -1, however, the detection limit for TPHg was increased for this sample to 10,000 ppb The groundwater sample collected from well MW -2 did not contain TPHg, benzene or oxygenate • compounds Groundwater analytical data are summarized in Table 2 • 6.0 CONCLUSIONS Based on analytical results from soil samples collected and analyzed during this investigation, it appears that soil in the vicinity of boring SB -1 (beneath the eastern end of the former middle gasoline UST ) has been impacted by TPHg (up to 1,200 ppm), MtBE (up to 110 ppm), EtBE (up to 1 3 ppm), benzene (up to 0 81 ppm) and tAME (0 34 ppm) The vertical extent of hydrocarbon impacted soil in this location has been delineated to less than 10 ppm of TPHg and nondetectable level of tAME at a depth of 37 feet bgs, nondetectable level of EtBE at a depth of 65 feet bgs, and low levels of benzene (leas than 0 1 ppm) and MtBE (less than 1 ppm) at a depth of 72 feet bgs The lateral extent of hydrocarbon impacted soil at the subject site has been delineated to nondetectable concentrations of EtBE and nondetectable or low concentrations of TPHg (less than 2 ppm), benzene (less than 0 1 ppm) and MtBE (less than 1 ppm) in borings MW -I through MW -4 Shallow groundwater at the site has been impacted by TPHg (up to 11,000 ppb), benzene (up to 6,800 ppb) and MtBE (up to 62,000 ppb), except the eastern portion of the site (vicinity of well MW -2) Groundwater at the site has been also impacted by EtBE (2,400 ppb in well MWA and 130 ppb in well MW -4) and tAME (780 ppb in well MW -1) The extent of hydrocarbon impacted groundwater has not been delineated 34640804-2 6