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M. Scott Mansholt - 3 - 26 January 2010 Chevron Environmental US Can-Welty Road, Vernalis • Depth to uppermost groundwater occurs between 32 and 51 feet bgs with an easterly gradient, and is consistent with prior information. Based on the investigative findings, SAIC proposes the following: • Destroy monitoring wells (MWs) -1, 2, and 3 in accordance with appropriate San Joaquin County monitoring well guidelines. • Advance two additional borings west-southwest of the Site to collect samples for analysis to delineate the lateral extent of TPH affected soil/groundwater for this area. • Advance two soil borings north-northwest of the Site to collect samples for analysis to define the lateral extent of affected soil downgradient of the Site. • As described above, the affected area west of the Site will be addressed separately as a new project and designated - US Can-Offsite, Vernalis. Central Valley Water Board staff has the following comments: • Due to decreasing groundwater elevations, one or more of the remaining monitoring wells often do not have adequate water for sampling. Additionally, several years of groundwater data exist for the monitoring wells. The three MWs can be destroyed in accordance with appropriate County guidelines and should follow the previously approved workplan. • The additional Site characterization can be completed in conjunction with the monitoring well destruction activities and the findings provided in one report. • A separate workplan for the US Can-Offsite project addressing TPH affected soil and/or groundwater west of the US Can-Welty Road Site can be submitted. • Central Valley Water Board staff concurs with the additional characterization activities proposed in the Report. By 30 July 2010, please provide the investigative report of findings and the MW destruction documentation. By 30 August 2010, please submit a workplan for US Can-Offsite.