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Atlantic Richfield Company 3 ARCO 4932, 16 E Harding Way,Stockton,CA June 7,2002 ' • d vacuums u to 89 feet away, the calculated radii i Based on resulting induce p y, ' of influence ranged between 46 7 feet and 89 2 feet • During feasibility testing, approximately 544 3 pounds of TPHg, 19 5 pounds of benzene, and 440 pounds of MtBE were extracted from the soil ' beneath the site Estimated mass removal quantities were calculated from field flame-ionization detector(FID) readings that consistently exceeded ' 10,000 parts per million by volume (ppmv) and laboratory analytical results MPE feasibility testing activities and findings are summarized in SECOR's report titled Interim Remediation/Multi-Phase Extraction Feasibility Test Report, dated May 4, ' 2001 During July 2001, SECOR advanced two soil borings and installed five groundwater ' monitoring wells to further investigate the lateral and vertical extent of petroleum hydrocarbons in soil and groundwater beneath the site Soil borings SB-1 and SB-2 ' were drilled to 80 feet and 78 feet bgs, respectively Wells MW-5 through MW-9 were completed at 40 feet bgs Results of the investigation indicated that the vertical extent of petroleum hydrocarbons including MtBE in soil was vertically defined beneath the site ' by deep borings SB-1 and SB-2, and off-site by the borings for wells MW-5, MW-7, and MW-8 The presence of MtBE in the deepest soil sample collected from the boring for well MW-6 (8 2 mg/kg) suggested that additional investigation for vertical off-site liedelineation was warranted Based on groundwater analytical results, SECOR concluded that the lateral extent of TPHg and benzene had been defined by wells MW-5 ' through MW-8, however the presence of MtBE in groundwater samples collected from well MW-6 and depth-discrete groundwater samples from boring SB-2 confirmed that further lateral and vertical delineation of the dissolved MtBE plume was required within these areas SECOR further concluded that the presence of TPHg and benzene in upgradient well MW-9 suggested that an additional source(s) of petroleum hydrocarbons might be present in the area Results of this investigation are documented ' in SECOR's Additional Site Assessment Report, dated November 9, 2001 In 2001, SECOR conducted a door-to-door survey of businesses and residences in the area to identify any water supply wells within a 500-foot radius of the site A questionnaire was supplied to those businesses or residences that could not be first- handedly contacted Based on review of verbal and written survey results returned to ' SECOR, there were no water supply wells confirmed within a 500-foot radius of the site According to the SJCEHD in a letter dated November 21, 2000, two water supply ' wells were documented in the vicinity of the site These water supply wells were located in the field, approximately 1/2 mile east of the site at the Stockton State Hospital, and approximately 2,000 feet northwest of the site, at the intersection of Wyandotte and ' Commerce Streets Results of the well survey are included in SECOR's report titled, Additional Site Assessment Report, dated November 9, 2001 ' I1ARCO14932`Reports\Asmt&AgfrTstRpt doc