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5400-5606 Pacific Avenue • 2 - • 3 May 2005 <br /> Stockton, San Joaquin County <br /> Ethylbenzene(E), 890 µg/L; Toluene(T), 1,200 gg/L; and Xylenes (X),2,800 µg/L. With the exception of <br /> Benzene detected at 2.2 lig/L on 18 October 2004, MW-23S (located north of MW-3 across Robinhood Drive) <br /> has been non-detect for four of the last five quarters. The Workplan proposes sampling AS-33 soil and <br /> groundwater for TPHg,BTEX, MtBE, Ethylene Dibromide and 1,2-Dichlorethane. <br /> The Remedial Alternatives Report presents a Remedial Alternatives Screening Matrix,which is similar to a <br /> feasibility study table, for six alternatives (No Further Action,Natural Attenuation&Monitoring, Air Sparging <br /> with Soil Vapor Extraction(SVE),Enhanced In-Situ Bioaugmentation, Groundwater Recovery and Treatment, <br /> and In-situ Chemical Oxidation(Ozone)). The Remedial Alternatives Report choice is AS and states the <br /> proposed modifications(one new AS well and one MW modified into an AS well)are cost effective and do not <br /> entail a major revision to the existing treatment system. <br /> I concur to the proposed Workplan with the following modifications: <br /> • Add the following analytes to the fuel oxygenate(MtBE) list: tertiary butyl alcohol (TBA), tertiary <br /> amyl methyl ether(TAME), di-isopropyl ether(RIPE), and ethyl tertiary butyl ether(ETBE). <br /> All work must be done in accordance to Appendix A -Reports, Tri-Regional Board Staff Recommendation for <br /> Preliminary Investigations and Evaluation of Underground Tank Sites, April 2004,which may be downloaded <br /> from the Internet website in the header of this letter. Please procure the appropriate permits from San Joaquin <br /> County Environmental Health Department(SJCEHD), and provide SJCEHD and myself at least 3 working days <br /> notice prior to starting fieldwork. Also provide a report(electronic submittal to GeoTracker and paper copy to <br /> this office) of the soil and groundwater sampling and modifications to the AS system in the next monitoring <br /> report,due 1 August 2005. <br /> You may call me at(916)464-4615 for questions or additional information. <br /> JAMES L. BARYON,P.G. <br /> Engineering Geologist <br /> Enclosure <br /> cc: Mr. Mark Owens,UST Cleanup Fund, SWRCB, Sacramento <br /> Mr.Mike Infuma, San Joaquin County Environmental Health Division, Stockton <br /> Ms. Jill Tracy,Esq.,UNOCAL, Brea <br /> Mr.Ben Heningburg,ENSR International, Sacramento <br /> Mr. Gary Hall, GHH Engineering,Inc.,Auburn, CA <br />