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1 1 SECOR w ' 5.0 PETROLEUM HYDROCARBON DISTRIBUTION AND CONCENTRAITON TRENDS ' S1 Distribution of Petroleum Hydrocarbons Soil 5 1 1 Distribution of Hydrocarbons in Soil Concentrations of TPHg, benzene, MtBE, and 1,2-DCA and the approximate extent of adsorbed hydrocarbons in soil is also illustrated on Figure 4 Maximum adsorbed concentrations are t located in the vicinity of the pump islands and beneath the southern portion of the UST pit The maximum adsorbed concentrations were detected beneath the dispensers at approximately 60 feet bgs (4,780 mg/kg TPHg in MW-6 at 60 feet bgs) 5 1 1 1 Lateral Distribution of Hydrocarbons in Shallow Soil. The lateral distribution of hydrocarbons in shallow soil has been delineated by wells MW-1 through MW-4 which all reported no detectable concentrations of TPHg, benzene, MtBE, or 1,2- DCA in soil samples analyzed to 45 feet bgs 51 1,2 Lateral Distribution of Hydrocarbons in Deep Soil. ' During vertical assessments conducted in July 2000 (GP-1 through GP-3) and the installation of deep onsite wells MW-5 through MW-10 between November 2000 and September 2001, '. hydrocarbon impacts to sod at depth ranging from 60 to 80 feet bgs were reported Maximum concentrations of TPHg and benzene were reported at a depth of 60 feet bgs in wells MW-5 through MW-10 Four additional deep wells (MW-10 through MW-14) were installed in June and July 2003 to delineate deep soil impacts No detectable concentrations of TPHg, benzene, MtBE, or 1,2-DCA were reported in soil samples from MWA 1 through MW-14 with the exception of 1,2-DCA (0 0071 mg/kg) in well MWA2 at 70 feet The installation of wells MWA0 through MWA4 completed lateral delineation of hydrocarbon impacted soil in the deeper zone The detection of 1,2-DCA in MW-12 at 70 is crass-to-up gradient from the Former 76 Station 51 13 Vertical Delineation of Hydrocarbons in Soil Vertical delineation of TPHg, benzene, MtBE, and 1,2-DCA in soil was completed in May of 2004 by drilling two (SB-1 D and S13-2D) onsite, deep, sonic borings (dual-hole) to 120 feet bgs Soil samples were collected continuously from 80 to 120 feet bgs and selected soil samples at ' 10 foot intervals were submitted for laboratory analysis The vertical extent of TPHg, benzene, MtBE, and 1,2-DCA in soil was delineated at 90 feet bgs by samples SB-1 D@90' and SB- 2D@90' which reported no detectable concentrations of petroleum hydrocarbons ' 62 Petroleum Hydrocarbons in Groundwater Concentrations of TPHg, benzene, MtBE, and 1,2-DCA dissolved in shallow and deep ' groundwater on April 26, 2004, are illustrated on Figures 5 through 12 5 2 1 Lateral Distribution of TPHg in Shallow and Deep Groundwater ' 6 2 1 1 Shallow Groundwater. Historically, TPHg had not been reported in any of the shallow wells (MW-1 through MW- 4) prior to the fourth quarter of 2003 with the exception of one detection in well MW-3 at a concentration of 67 ppb during the first quarter 2001 During the second quarter of 2004 TPHg was reported Updated SCM doc 7 August 13,2004 77CP 64409 05 0005