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CAMBRIA southwest corner of the former UST location Maximum concentrations were 17,000 parts per million (ppm) low/medium boiling point hydrocarbons quantitated against a gasoline standard and 400 ppm benzene, both at a depth of 15 feet below grade (fbg) In June 1990, the former USTs were removed, and Aegis collected six soil samples from beneath the USTs and six soil samples beneath product lines The highest concentrations were from the UST excavation with maximum concentrations of 19,000 ppm petroleum hydrocarbons volatile (PHV) and 280 ppm benzene This investigation is summarized in Aegis' June 18, 1990 Preliminary Subsurface InvestigationlTank Closure Report (Interim Soil Remediation Work Plan) During July 1990, Aegis installed monitoring wells MW-1 through MW-3 and vapor extraction wells VEW-1 and VEW-2 The highest concentrations in soil were from boring VEW-2 at 45 fbg, with 12,000 ppm PHV and 110 ppm benzene During the initial groundwater monitoring event, PHV and benzene were detected in all wells at concentrations ranging from 350 to 500,000 parts per billion (ppb) and 190 to 10,000 ppb, respectively These results are discussed in Aegis' January 4, 1991 Site Assessment Report In late 1991 and early 1992, Aegis performed a 75-day vapor extraction feasibility test at the • subject site using wells VFW-1, VEW-2, and MW-3 Wells VEW-1 and VEW-2 were tested to evaluate their feasibility in addressing petroleum hydrocarbons detected below the former UST location Well MW-3 was selected based on previously detected separate-phase hydrocarbons (SPH) in this well However, SPH has not been detected in well MW-3 since August 1993 In September 1995,Fugro West, Inc (Fugro) of Roseville, California drilled four GeoProbeo soil borings Soil samples from the boring drilled in the former UST location contained total purgeable hydrocarbons as gasoline (TPHg) concentrations up to 7,000 ppm (at 16 fbg) and a benzene concentration of 10 ppm (at 49 fbg) TPHg and benzene were not detected in soil from the other borings Grab groundwater samples collected from these borings contained TPHg ranging from 14,000 to 60,000 ppb and benzene ranging from 4,100 to 9,800 ppb The complete results of this investigation may be found in Fugro's November 29, 1995 Limited Subsurface Investigation Results In July 1997, Cambria drilled four onsite soil borings near the dispenser islands Petroleum constituents were delineated in soil in all the borings except one drilled near the northeastern dispenser In September 1997, Cambria installed monitoring wells MW4 through MW-7 These wells are sampled quarterly During the initial sampling event, TPHg and benzene were detected in wells MW-3-through-MW-7 of concentrations-ranging from 1,300 to 31,000 ppb and 9 1 to 1,900 ppb, respectively MTBE was reported by EPA Method 8020 in wells MW-3 through 0854 2