SITE INFORMATION AND CORRESPONDENCE

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GEOMATRIX Mr. Philip Isorena California Regional Water Quality Control Board September 14, 2000 Page 4 In addition to the four criteria for low risk groundwater, Chevron also should provide the information specified in Table 1 of Appendix B. The information specified in Table 1 of Appendix B is presented in Appendix E of the draft closure request. CEMC will include this information in the text of the final closure request. Conformance of a site to the low risk groundwater criteria relies on existence of NA at each site. For NA to be acceptable to Board staff, its remediation time must be comparable to those ofactive remedial alternatives. Comment addressed in Item B. Site-Specific Evaluation Chevron evaluated the site against the four criteria for low risk groundwater under Appendix B and provides justification as to why the site meets each criterion. Those four criteria and my comments on Chevron's assertions are described below. E. Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass reduction rate of groundwater pollutants discussed in 44 below. Chevron has not estimated the contaminant mass in the vadose zone or groundwater. Therefore, staff cannot determine whether or not mass reduction or its reversal has occurred. Chevron should estimate the mass and show that reduction has occurred or is occurring. The statement that residual hydrocarbons in soil are not adding amounts of soluble constituents to groundwater is incorrect because TPH characterized in the diesel range is being detected in monitoring wells (MWs) 1 and 4. It is possible to estimate the current mass of residual non-dissolved petroleum in soil (both above and below the water table), the current mass of dissolved petroleum in groundwater, and the current mass of degradation byproducts in groundwater. However, it is not possible to estimate what these masses were at the time the release occurred and, accordingly, it is not possible to estimate the historic "mass reduction rate of groundwater pollutants." To address RWQCB's comment in the final closure request, Geomatrix will attempt to obtain information about the composition of fresh San Joaquin Valley crude and compare it to the composition of weathered petroleum in the site subsurface. Qualitative observations will be noted. For example, fresh San Joaquin Valley crude contains measurable concentrations of BTEX, which may have affected groundwater at the time of the release. Since the release occurred, the mass of BTEX in groundwater generally has been reduced to non-detectable concentrations. Because little or no measurable BTEX remains in weathered petroleum at the site;this remaining petroleum will not reverse or threaten to reverse the mass reduction rate of BTEX in groundwater. Additionally,