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M. Scott Mansholt - 2 - 12 March 2008 TAOC Tracy Gravel Pits • The extent of elevated TPH compounds in soil occurs in distinct thin layers to about 11-feet; soil below this depth appears to be unaffected; • The lateral extent of affected soil has not been adequately defined at the northwest and southeast ends of the gravel pit excavation and in the area north of the adjacent residence in the southeast corner of the site; • Affected groundwater is limited in extent and appears to be adequately delineated onsite; • Shallow soil samples obtained next to the rail spur and submitted for Title 22 metals analysis reported ND or low concentrations within the range(s) expected for naturally occurring background values; and, • Water supply wells identified by the weir search survey are of sufficient distance upgradient/cross gradient locations and combined with the depths of the sanitary surface seals, indicates it is unlikely dissolved petroleum constituents from the site would have affected these wells. Regional Water Board staff concurs with the investigative report of findings, with the following comments: • Affected-soil from parts of the site where tank bottoms or other debris was disposed of were not sampled for rnetals; TPH-affected soil/material samples from these areas need to be analyzed for Title 22 metals; the number of sampling locations/depths need to statistically represent the portion(s) of the site where those materials were previously disposed of; • Additional soil characterization is needed at the northwest and southeast portions of the gravel pit excavation and for the onsite area north of the adjacent residence at the southeast corner of the site; onsite delineation information is needed and to evaluate if affected soil extends offsite; and, a Additional research needs to be conducted to obtain information regardina ownership of the industrial well west of the UPRR easement which is adjacent the west side of the site. If access is granted, a sample needs to be collected and submitted for the site petroleum hydrocarbon constituents unless previous sample results from others are available; these results can be submitted.