SITE INFORMATION AND CORRESPONDENCE_FILE 1

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i Wendy Cohen,SLIC Unit -5- 1 February 1996 concentrations. The higher analytical quantitation limits of the recent four sampling periods may have masked an existing problem at MW-24. Well logs of these borings could also help clarify the marked differences between results from these two wells. My Recommendations To move this case toward closure, I recommend that the following actions be taken by the discharger: 1) Submit the items identified in the enclosed Appendix B, Requests for Closure, to the Tri- Regional Board Staff Recommendationsfor Preliminary Investigation and Evaluation of Underground Tank Sites that have not already been submitted. Materials that have already been submitted should be referenced in this submittal. Substitute "pipeline" for all references to "tank systems" in the wording of Appendix B. 2) To more clearly delineate subsurface hydrogeology at the site, submit well boring logs for all wells and a hydrologic cross section in the direction parallel to the pipeline and extending from monitoring well MW-7 through well MW-15. 3) Perform two additional quarters of ground water monitoring—I recommend the first and second quarters of 1996=for all wells sampled during 1994 and 1995 plus wells MW-16, MW-17, MW-18, and MW-19. Samples should be analyzed for diesel-range and gasoline- range petroleum hydrocarbons by GC-FID and for BTEX by USEPA Method 8020 without filtration. Centrifugation and silica gel cleanup of diesel-range hydrocarbon samples are acceptable, but not necessary. Diesel-range (extractable) hydrocarbons should be limited to hydrocarbons with C1O through C23 chain lengths. Gasoline-range (purgeable) hydrocarbons should be limited to hydrocarbons with C4 through C 12 chain lengths. Analytical quantitation limits should match those of the Tri-Regional Recommendations. 4) Based on the results of the additional monitoring performed under Recommendation#3 above, a decision on the need for future monitoring would be made. Future monitoring (in addition to that recommended in Recommendation#3) may be able to be eliminated if appropriate source removal activities are conducted, such as removal and treatment of contaminated soils in the areas of monitoring wells MW-13 and-MW-23. Enclosure