ARCHIVED REPORTS_XR0011832 - Laserfiche WebLink

Home Browse Search

Subsurface Investigation and Well Installation Report ARCO FacilityNo 6100 Tracy, California • Page 7 to have a strike of N15°E, with bedding observed to be dipping towards the east- southeast at 19° from horizontal The regional surface topography in the vicinity of the site dips toward the east and southeast (Figure 1) Based on the interpretation of subsurface conditions presented in Cross-Section B-B', the strata beneath the site appear to dip toward the southeast Using the top of the sand stratum encountered at approximately 82 feet bgs in boring B-33, 75 feet bgs in boring B-35, and 77 feet bgs in boring B-38, a strike of N17°E with a dip of 5° from horizontal toward the east was calculated The differences in dip measured beneath the site and at the outcrop 1 mile away are likely caused by deformation related to formation of the adjacent Coast Range Well MW-2 is the only newly installed well that contains rechargeable quantities of groundwater A Delta representative bailed groundwater from well MW-2 on September 17, 2001, and measured recovery rates of groundwater in the well for approximately 7 5 hours The field data sheet showing depth to groundwater measurements is included in Appendix D Laboratory Results Petroleum hydrocarbons were detected in soil samples collected from borings B-33, B-34, and B-36 through B-38 at various depths between 17 and 105 feet bgs Petroleum hydrocarbons were not detected in soil samples collected at depths greater than 105 feet bgs The highest concentrations of TPHG (1,200 milligrams per kilogram [mg/kg]) and benzene (13 mg/kg) were detected in the sample collected from boring B-37 at 55 feet bgs The highest concentrations of TPHG and BTEX in bonngs B-33, B-34, B-36, and B-37 were detected in samples collected at depths ranging between 55 and 64 feet bgs The highest concentrations of TPHG and BTEX in boring B-38 were detected in the sample collected from 34 feet bgs Petroleum hydrocarbons were not detected in soil samples collected from boring B-35 MTBE was the only oxygenate compound detected during this investigation, and was only detected in the soil sample collected from 63 feet bgs (boring B-33) at a concentration of 0 12 mg/kg Methanol was detected in the soil sample from 35 feet bgs in boring B-36 (7 1 mg/kg) Ethanol, TBA, DIPE, TAME, ETBE, EDB, and 1,2-DCA were not detected in any of the soil samples TPHG, benzene, and MTBE concentrations in soil are included on the geologic cross sections (Figures 3 and 4) Soil analytical results are presented in Table 1 TPHG (100 micrograms per liter [µg/1]) and benzene (4 7 µg/L) were detected in the groundwater sample collected from well MW-2 Other BTEX constituents or oxygenate compounds were not detected in the groundwater sample P 1ARCO\61001REPORTS16100-well install report doe