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GEOMATRIX Mr. Philip Isorena California Regional Water Quality Control Board September 14, 2000 Page 2 residents at the site. Chevron should submit another copy of the report that staff can forward to the Office of Environmental Health Hazard Assessment for review. When we finalize the closure request, Chevron will forward an extra copy of the request to the RWQCB for submittal to the Office of Environmental Health Hazard Assessment(OEHHA). The final closure request will contain the human health screening evaluation that was included in the draft closure request. In future submittals, Chevron will provide the RWQCB with an extra copy for submittal to OEHHA if the request document includes a human health screening or risk evaluation. B. Compliance with State Water Resources Control Board Resolution No. 92-49 The Board specifies requirements which responsible parties must meet during investigation and cleanup ofpolluted sites. These requirements are specified in State Water Resources Control Board Resolution No. 92-49 which states that pollution must be cleaned up to return the site to background conditions, unless it is technologically or economically infeasible to do so. Resolution 92-49 also states that the Regional Board shall determine whether water quality objectives (WQOs) can reasonably be achieved within a reasonable period. Staff consider a "reasonable" time frame for a remedy relying on natural attenuation (NA) is a time frame comparable to that which could be achieved through active restoration. The more appropriate timeframe must be determined through an analysis of remedial alternatives. Chevron performed such an evaluation of remedial alternative with estimates of the time it would take for each alternative to remediate the site. However, the time to remediation for NA, air sparging/soil vapor extraction, oxygen releasing compounds, and excavation is so general (such as decades to centuries) that a meaningful comparison of the alternatives is not possible. Chevron should refine the evaluation of each alternative to come up with more accurate time estimates that can be used in comparing the alternatives. Chevron also should look at innovative alternatives, such as chemical oxidation and thermal desorption/ destruction that may be cost effective in remediating its site, if remediation is necessary. In Geomatrix's Draft Site Closure Request, we provided order-of-magnitude remediation time frames for several remedial alternatives, including natural attenuation with no active remediation. The purpose of this analysis was to allow for a relative comparison of time frames for various alternatives. These order-of-magnitude estimates were used because it is very difficult to accurately predict more specific remediation time frames. For purposes of the analysis, we assumed that RWQCB will not consider remediation to be complete until concentrations of biodegradation byproducts in groundwater are permanently below the taste and odor WQO for diesel (e.g. all byproducts degraded to water and carbon dioxide). The analysis showed that only complete removal of all affected soil will likely achieve complete remediation in a relatively short time frame. All other remedial alternatives that were evaluated will not achieve complete remediation for decades, or possibly centuries. As such, the remediation time frames can be considered "comparable."