SITE INFORMATION AND CORRESPONDENCE

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GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company July 12, 2001 Page 5 Estimated Duration of Remediation Using ORC at the Site The estimate of duration of remediation time for using ORC at the site is based on the fol- lowing site constraints: (1) the majority of the residual petroleum at the site is entrained within the inaccessible fine-grained soil beneath Grant Line Road' and (2) the ORC will be place downgradient and outside the area of residual petroleum in the existing monitoring wells at the site (wells MW-6, MW-7, MW-8, and MW-12; Figure 3). Initially, the existing dissolved-phase petroleum hydrocarbons in groundwater in the immedi- ate vicinity of these wells are anticipated to be biodegraded relatively quickly with available oxygen supply from the ORC. However, in the long-term, the overall rate of biodegradation would be on the order of the rate for NA due to the limitations of transport mechanisms that govern the migration of dissolved-phase petroleum hydrocarbons from the source area(i.e., the fine-grained soil beneath Grant Line Road) to the immediate vicinity of these wells. Since this is the same transport mechanism that governs the migration(and subsequent degradation) of dissolved petroleum via NA, the result is similar estimated remediation times for EISB using ORC (i.e., Alternative 3) and NA. A discussion of these transport mechanisms is pre- sented in Appendix B. Based on this information, the use of ORC is not anticipated to significantly shorten the remediation duration estimated for NA (17 years). For cost estimating purposes, benzene concentrations in groundwater at MW-6 were qualitatively estimated to reach 0.5 µg/1 in about 15 years for Alternative 3. It should also be noted that the remediation duration may be exactly the same as that for NA, for the reasons mentioned above. ORC PILOT STUDY The RWQCB requested that Chevron conduct an ORC pilot study to obtain information per- taining to (1) the amount of ORC needed per year and (2) the time to remediate the site using ORC, so that a direct cost comparison with MNA can be made (RWQCB, 2001). Based on the limited effectiveness of ORC to significantly reduce, if at all, the remediation time com- pared to NA, a pilot study does not seem warranted. However, a conceptual pilot study to address these issues is presented below for evaluation purposes. • A pilot study work plan would be prepared and submitted to the RWQCB for approval. • ORC would be placed in four existing onsite monitoring wells (MW-6, MW-7, MW-8, and MW-12). • Dissolved oxygen, oxidation-reduction potential, and pH would be monitored in these wells once per month. Access to the residual petroleum is limited by the presence of Grant Line Road and by its proximity to Chevron's active pipeline.