SITE INFORMATION AND CORRESPONDENCE

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• �.av:ra r - a:xxfr�se Mr. Robert Mihalovich Chevron Environmental Management Company April 4, 2002 Page 2 )INVESTIGATION APPROACH Geomatrix reviewed locations where petroleum hydrocarbons were detected during the Con- dor investigation and grouped them into six separate sites. Borings were grouped together based primarily on their proximity to each other and the potential issues in each area. Sites 1 and 2, although relatively close together, were designated as separate sites because Site 1 may have unique ecological considerations due to its close proximity to the Mountain House Creek, which will be widened during development. Site 2 likely will not have significant ecological considerations. The remainder of the sites were designated where borings with affected soil were close together and were bounded on either side by unaffected soil that con- tinued for a considerable distance. The northernmost boring in which petroleum hydrocarbons were detected was not designated as a site nor considered for further evaluation because TPHc was detected at only 13 milli- grams per kilogram (mg/kg) and no staining was observed(Boring GP-108; Figure 2). It is our opinion that this negligible detection does not warrant further investigation. Sites will be investigated in accordance with the Consistent Technical Approach (CTA)' that is typically applied at ChevronTexaco's OVP sites. The major components of the CTA are: delineation of the vertical and lateral extent of affected soil; • delineation of the lateral extent of affected groundwater; and • an assessment of the potential health risks associated with constituents present in site soil and groundwater. REGULATORY APPROACH Geomatrix proposes to meet with the Regional Water Quality Control Board, Central Valley Region (RWQCB) prior to commencing work to discuss implementation of a self-directed approach for these sites. The key elements of this approach are as follows: • A work plan for each phase of investigation will be submitted to the RWQCB for informational purposes only. With the exception of work plans that include monitor- ing well installation, it is anticipated that RWQCB staff approval will not be required to obtain permits and implement the proposed work. • A brief data summary following each phase of investigation will be submitted to the RWQCB. If additional work is needed, recommendations will be made in the data summary. No response from RWQCB will be required. Geomatrix Consultants,Inc.,2001,Draft Revised Technical Approach to Site Evaluation and Decision- Making,Old Valley Pipeline Sites—Central Valley Region, October; and Geomatrix Consultants,Inc., 1997, Technical Approach to Site Evaluation and Decision-Making,Old Valley Pipeline Sites—Central Valley Region,March 19.