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Lee Higgins - 8 - 7 December 2010 Chevron, TAOC Tracy Rail Yard • The fuel fingerprint determinations indicated the TPH present is consistent with biodegraded/weathered San Joaquin Valley crude oil; possibly biodegraded bunker fuel which was noted in one of the samples. San Joaquin Valley crude oil and bunker fuel are associated with the historical use of the OVP/TAOC pipelines and possibly the historic rail yard operations. • The lateral extent of crude oil affected soil, below a depth of 11 feet bgs, has been generally defined onsite with the exception of an area on the central-east side of parcel OU-2; AMEC's Report contends that this affected area may have been associated with the historic rail yard facility. • The vertical extent of affected soil onsite has been defined at a depth of approximately 21.5 feet bgs. • With exception of the central-east area of OU-2 discussed above, affected groundwater has been defined at the Site; it is AMEC's contention this is not related to the historical OVP/TAOC pipelines. • The offsite extent of affected groundwater has not been defined to the east, south, and west of the Site. Chevron will address offsite crude oil impacts separately. • Sufficient shallow oil samples collected for analysis during the current investigation will be included in a site-wide risk assessment and a remedial action workplan which will be prepared by ARCADIS on behalf of UPRR, the property owner. • Concentrations of the chemicals previously/currently detected within OU-3 and 4 will be evaluated (by ARCADIS/UPRR) as part of a future remedial action plan, approved by the DTSC, and with a proposed land use covenant. The former and current conditions identified will be used to assess whether the currently approved remedy is protective of the current land use at sites OU-3 and 4, now owned by the City of Tracy. Based on my review, I have the following comments: • Review of the previous and current findings, onsite soil and groundwater appear to be adequately delineated within units OU-2, 3, and 4 with the exception of the central-east area of OU-2. Provided the gradient is north-northwest consistent with neighboring OVP/TAOC sites, the downgradient extent of affected groundwater has been defined along the north sides of these operable units. • Based on the analytical results, the lateral and vertical extent of crude oil affected soil has been delineated within OU-5. Affected soil was observed in borings at depths up to 21.5 feet bgs. • Groundwater has not been adequately defined in the central area of OU-5, downgradient to the north and northeast of AMEC soil boring TRY-29. Analysis of the TRY-29 groundwater sample submitted for fuel fingerprint determination, reported TPHd at a concentration of 5,600 pg/L. According to the fuel fingerprint evaluation, the