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S E C 0 R a z Conceptual Site Model A March 24, 2004 Page 4 and 1987 (1968 photo revised) Land use illustrated on the reviewed topographic maps, excluding " the 1913 topographic map were consistent with land use depicted on the aerial photographs Topographic maps are presented in Appendix A PMS 3 0 PREVIOUS INVESTIGATIONS n� A summary of previous investigations for the Site is presented below Historical soil and groundwater analytical data tables are presented in Appendix B Site specific historical boring logs and well completion details are presented in Appendix C Assessment excerpts for Chevron service station No 9-2033 are presented in Appendix D _, 31 Groundwater Technology Monitoring Well and Soil Boring Installation, March 1995 In March 1995, Groundwater Technology Inc (GTI) installed three groundwater monitoring wells (MW-1, MW-2, and MW-3) onsite to approximately 50 feet bgs, and one soil boring (SB-1) to approximately 36 feet bgs Total petroleum hydrocarbons as gasoline (TPHg) was reported below laboratory reporting limits in sod samples collected from MW-1 and MW-2 TPHg was detected at 3 8 milligrams per kilogram (mg/kg) and 250 mg/kg in MW-3 at 25 feet bgs and 35 feet bgs, respectively TPHg was detected at concentrations of 4 2 mg/kg and 28 mg/kg in SB-1 at 30 feet • bgs and 35 feet bgs, respectively Benzene was detected at concentrations ranging from 0 012 mg/kg (MW-3 at 30 feet bgs) to 0 46 mg/kg (SB-1 at 35 feet bgs) consistent with the first occurrence of groundwater Chromium, lead, nickel, and zinc were reported at concentrations of 23 mg/kg, 7 8 mg/kg, 21 mg/kg, and 50 mg/kg, respectively in MW-1 at 10 feet bgs and concentrations of 31 mg/kg, 6 5 mg/kg, 42 mg/kg, and 59 mg/kg, respectively in MW-1 at 35 feet bgs , Mese activities are summarized in the summary of previous investigations attachment in SEC OR's 1 ssessment Report ° Dated ib�ski-5;299x' Soil sample analytical results for this ; scope of work are presented in Appendix `f0n' �t��a°ai y'O'kj 4116* 3.2 Touchstone Developments Environmental Management Report, UST Closure Report and Limited Over-excavation Sampling Report, Dated August 7, 1997 On September 9, 1996, Touchstone Developments Environmental Management (Touchstone) supervised the excavation and removal of three USTs, three hydraulic hoists, product dispensers, ; associated product lines and limited over-excavation Soil samples collected from beneath the former USTs, hydraulic hoists, product piping, and dispenser locations were analyzed for petroleum r_ hydrocarbons TPHg was detected at a maximum concentration of 3,000 mg/kg in P6 at 3 5 feet bgs Benzene was detected at maximum concentration 2 8 mg/kg in P5 at 4 feet bgs On September 11, 1996, soil near the former USTs, product dispensers, and product lines was excavated and removed TPHg was detected at concentrations ranging from 1 0 mg/kg (PXS1 at 5 feet bgs) to 1,700 mg/kg (PXB2 at 6 feet bgs) Benzene was detected at concentrations ranging from 0 0052 mg/kg (TXS4 at 15 feet bgs) to 14 mg/kg (PXB7 at 7 feet bgs) The Touchstone report indicated that additional samples collected and analyzed following soil excavation suggested remnant hydrocarbon concentrations underlying the former southern product island These activities '40 are summarized in Touchstone's, UST Closure Report and Limped Over-excavation Sampling Report, Dated August 7, 1997 Excerpts from the Touchstone report are presented in Appendix D i 11Chovron19203,31REPORTSICSMICSi`1 920 U (REV 13)doc