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Lee Higgins -2 - 7 December 2010 TAOC 6th Street Rail Yard Tracy, San Joaquin County In conjunction with investigations completed at the Site for UPRR, Chevron initiated the recent soil, groundwater, and soil vapor investigation to address crude oil leaks associated with the historical OVP/TAOC pipelines with regulatory oversight provided by Central Valley Water Board staff. Since earlier investigations conducted for UPRR included partial delineation of crude oil impacts, AMEC's recent investigation addressed data gaps of the Site where additional borings were needed. Soil, soil vapor, and groundwater samples were collected from OU's 2 through 5 to address better delineation of the impacted areas. According to AMEC's Report, pipelines/equipment associated with the historical OVP/TAOC pipelines were not present in OU-1, thus borings/sampling was not completed in this parcel. Soil and groundwater samples submitted for fuel fingerprint evaluation determined the petroleum hydrocarbons identified at those boring locations was consistent with weathered/degraded San Joaquin Valley crude oil and possibly bunker fuel. Central Valley Water Board staff finds that: • Eleven soil vapor samples were submitted from borings near where elevated TPH concentrations were previously reported in soil and groundwater. Benzene and naphthalene were non-detect; low concentrations of toluene, ethylbenzene, xylenes did not exceed respective environmental screening levels. • With the exception of a portion of the east-northeast side of OU-2, near the approximate terminus of the historical OVP and a former aboveground storage tank, soil and groundwater in this parcel have been delineated. • Additional characterization is needed in the vicinity of OU-2 boring TRY-1 to determine if the TPHc detected in soil (12,000 mg/kg) at six feet bgs is associated with the historical pipelines or is related to the former railroad maintenance facility. The lateral and vertical extent of crude oil affected soil/groundwater needs to be determined. Fuel fingerprint evaluation of TPH affected soil should be considered to determine the nature and source of the petroleum product present. • Crude oil affected soil and groundwater has been adequately defined within parcels OU-3 and 4 and additional characterization is not needed. • Affected soil has been delineated in OU-5. However, impacted groundwater has not been defined in the central-eastern area of OU-5 near AMEC boring TRY-29 (5,600 pg/L TPHd). Additional soil and groundwater investigation, including fuel fingerprint determination, is needed north-northeast of the boring. • Additional groundwater characterization is needed offsite primarily east, south, west, and northwest of the Site. This work is to be addressed separately by Chevron with oversight provided by Central Valley Water Board staff.