ARCHIVED REPORTS SOIL AND GROUNDWATER INVESTIGATION REPORT

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West Byron Road Project -3 - 15 April 2094 ' Tracy, San Joaquin Co. PARS were not detected in the majority of the samples; low concentrations of several PAHs were ' reported in boring SB-34 at 19 feet. The vertical extent of impacted groundwater was defined at 27 feet in SB-26 at 110 µg/L TPH-d. SAIC Recommendations j i Based on the findings, SAIC determined that soil and groundwater has not been delineated at several different locations and additional step-out borings were needed. SAIC recommended step-out borings to ' collect soil and groundwater samples south of the following locations: SB-2, SB-3, and SB-6; • SB-8 through SB-12; ' • SB-19, SB-22 through SB-26 and SB-36; and, • SB-28, SB-30, SB-33 to SB-35. CONCLUSIONS With the exception of the Surland Homes property, soil and groundwater have been adequately delineated on adjacent properties downgradient (north) of the project. Those sites where delineation has been completed have received NFA determinations by the SJCEHD or the Regional Board. Two adjacent upgradient sites have also received NFA determinations. The lateral extent of impacted soil and groundwater has not been adequately delineated at several locations south of West Byron Road. The vertical extent of impacted groundwater has been delineated as defined by SB-26 where TPH-d attenuates to 110 pg/L at 27 feet. Similarly, the vertical extent of TPH impacted soil has been adequately delineated at several locations defined in numerous borings attenuating to less 100 mg/kg to ND at depths between 20 and 36 feet. I concur with SAIC's recommendations for additional step-out borings south of the locations described above with the exception of the additional borings south of SB-34 and 35. Soil and groundwater have been adequately delineated south of borings SB-34 and SB-35 (Monterosso property) previously investigated by PG&B and others. An NFA was granted in September 1996 for the Monterosso residential property south of these borings after the investigations determined the property had not been significantly impacted as a result of leaks from the OVP. ' RECOMMENDATIONS Based on review of the previous and current findings, I would make the following general recommendations regarding proposed additional borings: • One boring south of and midway between SB-2 and SB-3; • One boring south of SB-6; • Two borings - diagonally southwest and southeast of SB-8; • One boring south and midway between SB-1 I and SB-12; 1