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Mr. Scott Hooton - 2 - 15 February 2000 <br /> Of particular concern, however, is the fact that the greatest increase in MtBE concentrations is found in <br /> MW-8, an offsite downgradient well. Increases in MW-1 and MW-2 also are of concern since these <br /> two wells are near the site's boundary and approximately upgradient of MW-8, depending on the <br /> particular seasonal flow pattern. There are no obvious sources for new releases near these two wells, <br /> although site maps show two former installations, designated Former Tank A and Former Splash Pond <br /> in their general vicinity. Of active site appurtenances, the loading rack is nearest MW-11. However, <br /> MtBE concentrations in MW-11 have been significantly lower than in MW-1, 2, and 8. and have been <br /> inconsistent in occurrence. This may be due to construction differences in MW-11, or it may suggest <br /> that the loading rack is not, in fact, the source. <br /> I understand your suggestion that the MtBE problem postdates BP's tenure, but I believe that the present <br /> level of information does not allow for definition of the source or sources for the MtBE, TPH-g and <br /> benzene. Therefore, I request that you propose a work plan and time schedule for assessing the <br /> source(s), and for defining the lateral and vertical extent of the offsite plume. <br /> I further request that the neat round of analyses for MtBE include all site wells, and that the analyses be <br /> done using USEPA Method 8260. Please ask the laboratory to analyze for all the oxygenates, and report <br /> all peaks. <br /> Please submit the work plan and proposed time schedule by 15 March 2000. The time schedule should <br /> allow for an investigation report to be submitted by 30 June 2000. This report should include a <br /> proposal and rationale for further assessment or for remedial action as needed. The report should be <br /> supported with fence diagrams of the site based on known subsurface geology and an), new logging that <br /> is done. <br /> Thank you for your frank discussions on this matter. If you have any questions, please call me at <br /> (916) 255-3119. <br /> AIL WIGGETT, C.E.G. <br /> Associate Engineering Geologist <br /> Aboveground Tanks Program <br /> cc: San Joaquin County PHS/EHD, Stockton <br /> Mr. Larry Silva, P.O. Box 2628, 9645 Santa Fe Springs Road, Santa Fe Springs. CA., 90670- <br /> 0628 <br /> GJW/C/BP folder/assess Iv <br />