SITE INFORMATION AND CORRESPONDENCE

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Mr. Donovan - 2 - • 21 August 1997 geophysical survey of the area to attempt to find another well. It is our understanding that these requirements have been conveyed to Tesoro by EMCON staff, and based on telephone conversation on 18 August 1997, that Tesoro agrees to the videologging and laboratory analysis to identify the product. Staff understands that Tesoro wishes to destroy this well in any case, since it in not in use and raises the same concerns of potentially being a conduit. Staff concurs and will support the well's destruction if the videologging supports the probability that this well is 17A1. Depending on the results of the analyses of the free product, we may request some further actions in addition to, or prior to, destruction of the well. Regardless of whether the product is pump oil, as has been suggested, or something else, staff is concerned that the lateral extent of it is not known. This concern is exacerbated by the well's location near the southern boundary of the Tesoro lease and upgradient of the Santa Fe Pacific Pipeline facility. 3. P;oposed decomrnissioning of monitoring wells: Staff has reviewed the proposed decommissioning of several groups of monitoring wells at the facilities, comprising twenty-four wells in all. Staff review considered the location, available information on the construction, and the monitoring history of the wells in question. In general, most of the wells are shallow and many of them lack surface seals. Eighteen of the proposed wells were installed in 1987-89 for monitoring and product recovery in the northwest part of the STTC site. At present,these wells have free product as an intermittent sheen and further recovery efforts are deemed not practical. Five other wells were installed between 1989-1992 for groundwater monitoring. The twenty-fourth well is not specified in the proposal's justification . From the information available in the proposal and in the files, there are 6 wells out of the twenty-four that have constructions typical of monitoring wells rather than larger diameter recovery wells. The attached memo summarizes staff s analysis and reasoning in reviewing the proposal. Staff concurs with the proposal to decommission the wells designated SP-I through SP-5 along Nary Drive. These are large diameter, shallow wells with a history of floating product, but have none now, and are near the "zero" line. Staff also concurs with decommissioning the wells designated "TO" as listed on Table 1, attached, principally because of their lack of seals. Four of these wells are in the center of the Time Oil lease, near the center of the high-concentration area of the terminals complex. Staff is concerned that removal of these wells leaves a very small number of wells in this area. Regarding the TS series wells, staff would like more information on their construction and condition, particularly confirmation on whether they have seals. Together, the TO and TS wells proposed for removal constitute most of the wells on the western, cross-gradient side of the plume within the high- concentration area. Only six wells will remain in the Time Oil lease in this area of the plume; of these, three are proposed for use as "trigger"wells in the future. Regarding the PS/MW-I 1 and PSIMW 12 wells, these two wells appear to have been constructed as a well pair and construction as reported seems acceptable. They are outside of the present downgradient edge if the dissolved plume, based on recent data. The workplan states that nearby wells currently sampled in the monitoring program provide coverage of this area. However, the currently-monitored wells are approximately 120 to 300 feet away from PS/MW-11 and-12 and are farther east and south into the POSDEF Co-gen area, that is, farther from the edge of A-zone plume. The proposed revision to the monitoring program does not include any of these wells and in fact proposes a"trigger" well west of Stork Road, and no monitoring in the POSDEF area. PS/MW-12 is one of the few "deep zone"