SITE INFORMATION AND CORRESPONDENCE FILE 1

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4 receptors. The work plan also described Chevron's subsequent plans to evaluate the necessity of remedial feasibility studies upon its review of the data collected during work plan implementation. The work plan addendum(10/17/96) submitted by Pacific proposed relocating the originally proposed monitoring well such that downgradient contaminant plume definition would be accomplished. The work plan addendum also proposed a soil boring that would obtain soil samples for the purpose of better characterizing exposure pathways beneath the subject site. The work plan addendum described the scope of work as being part of a phased, cost-effective approach toward corrective action that is based on actual risk. The work plan addendum again,emphasized that Chevron would evaluate the feasibility of remedial alternatives as soon as the associated risks were characterized and the appropriate level of remedial action was determined. Submit a map indicating proposed well/boring locations,work plan amendment including feasibility study,and permit applications/fees and encroachment permits. Chevron's consultant,Pacific Environmental Group,Inc.,will submit a revised site map to your agency on April 28, 1997. The revised map will indicate the new locations of the proposed monitoring well and soil boring. On that day Pacific will also submit the necessary well/boring permit applications and associated fees. The encroachment permit application for the proposed monitoring well is still being reviewed by Caltrans. A copy of this permit will be submitted to your agency as soon as it is received. The City of Stockton has deferred all encroachment/permitting issues relating to the proposed monitoring well to Caltrans. However, the City of Stockton will be notified of the proposed well location and of the planned drilling schedule. As discussed above, Chevron feels that it would be premature at this time to perform any feasibility testing of remedial alternatives. As such, there are no plans to amend the existing work plan to include remedial alternative feasibility testing. However, Chevron is committed to performing a feasibility evaluation of remedial alternatives. As results from the proposed scope of work are known and associated risks are characterized, a corrective action plan will be developed which will include a feasibility study of appropriate remedial alternatives. Chevron requests for groundwater monitoring program changes are denied. Prior to making the recommendation to modify the groundwater monitoring program at the subject site, Chevron reviewed the historic site data to answer the following questions.Have all contaminants of concern been identified?Has the extent of contamination in groundwater been adequately defined?Does the groundwater investigation data provide enough information to determine the most cost-effective plan of remedial action?The answers to these questions are provided below. Knowledge about the primary source of contamination combined with seven years of soil and groundwater investigation at the subject site have provided Chevron a thorough understanding about the contaminants of concern. The adequacy of groundwater contaminant plume definition at the subject site should be evaluated in terms of understanding the transport and migrational tendencies of the contaminant with respect to potential receptor locations and health risk. This comes down to knowing the direction,velocity,and distance the contaminant will migrate and knowing where any potential receptors are. The direction of groundwater(contaminant)flow at the subject site has been toward the southeast. This flow direction has been consistent throughout six hydrologic cycles. As such, the migrational direction of the contaminant plume is well understood by Chevron. Considering the soil types within the water bearing zone beneath the subject site, it would be reasonable to estimate a groundwater flow velocity of no more than three feet per year. However at this time, Chevron has little knowledge about the location of sensitive receptors in the vicinity of the subject site.