SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Johnson 0 - 2 - 13 October 2010 Mountain House Site#4 anticipates beginning the work within 30 days following acceptance of this work plan and submitting the report by January 2411. Our comments are presented below: 1. We are concerned that the proposed sampling plan may not present the most efficient strategy for achieving the objective of this investigation, which is to delineate the lateral extent of contamination in soil and vertical extent in groundwater. The Work Plan does not identify a reliable method for screening soil encountered in the boreholes for the presence of petroleum, or for collecting discrete samples to determine the maximum depth at which groundwater pollution is encountered. In the event that laboratory analytical tests show that soil and groundwater samples collected in this investigation did not delineate the extent of contamination to non- detect, we may require Chevron to conduct additional sampling. Chevron should consider screening soil samples in the field using a photo-ionization detector, and collecting depth-discrete grab groundwater samples at greater depths. 2. Previous laboratory analytical results showed thzit there are elevated concentrations of petroleum hydrocarbons in soil in the area where sampling is proposed, but the Work Plan does not include laboratory analysis of soil samples. Based on these documented results, we strongly suggest that Chevron revise its proposed sampling program to include the submittal of soil samples for laboratory analysis. The data are needed to laterally delineate the contamination in the vadose zone, and may also be critical for calculating the mass of contamination in soil and assessing ecological and health risks as it becomes necessary to evaluate future remedial or eventual site closure alternatives. 3. The laboratory method identified on Page 5 may be erroneous. The correct laboratory analytical method for tetraethyl lead (TEL) and tetramethyl lead (TML) is Hazardous Materials Laboratory (HMQ 939-M. 4. It is not clear whether comparing the chromatograms from the laboratory analytical results to known standards would serve to elucidate the origin of the contaminants. Chevron and Central Valley Water Board staff have compared chromatograms generated from a previous sampling event to standards. The comparisons show that the weathered residual product generates chromatograms that are distinctly different than the original product and may not match standards. Instead of comparing the chromatograms to a known standard, we request that Chevron submit the laboratory analytical results of equipment blanks for each media and all standards used to create the respective calibration curves for the analytical results. The concerns addressed in the comments above prevent us from concurring with the Work Plan. By 5 November 2010, please submit a revised Work Plan that resolves these comments.