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i <br /> ENSR International <br /> tl nal <br /> • __,_._�. _ _�_ � . ,-�_ � -,.r �t:,�� .��_ � <br /> 10411 Old Placerville Road <br /> i <br /> August 30, 2004 Suite 210�� Sacramento,CA 95827 2508 <br /> `+ (916)362 7100 <br /> FAX (916)362 8100 <br /> www ensr com <br /> Ms Margaret Lagorro <br /> County of San Joaquin <br /> Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, CA 95202-2708 <br /> RE Response to Agency Request for Additional Subsurface Data <br /> Former Unocal Station No 2859 <br /> 1665 Pacific Avenue, Stockton, California <br /> Dear Ms Lagorro <br /> On behalf of the Union Oil Company of California (Unocal), ENSR Corporation (ENSR) has <br /> prepared this letter in response to the December 30, 2003 letter from the San Joaquin County <br /> Environmental Health Department (SJCEHD) A copy of the above-referenced letter is included <br /> as Attachment A <br /> As requested by SJCEHD, ENSR conducted an internal file review and found additional soil <br /> data concerning 1,2-Dichloroethane (1,2-DCA) ENSR is presenting additional soil data <br /> concerning lead As stated in the letter from the SJCEHD, a soil sample was taken from <br /> beneath the former waste oil underground storage tank following removal activities on <br /> March 29, 1988 The sample was analyzed for 1,2-DCA with a result of less than <br /> 0 03 milligrams per kilogram (mg/kg) An additional soil sample collected on March 30, 1988 <br /> from beneath the former underground storage tanks at a depth of 26 feet was analyzed for <br /> organic lead with a result of less than 10 mg/kg The certified analytical report for these <br /> samples is included as Attachment B <br /> A composite soil sample was collected from soil cuttings generated during the drilling operations <br /> related to piezometer well NP-1 on March 31, 1999 NP-1 is located approximately 20 feet to <br /> the east of the former dispenser islands and next to monitoring well MW-10 NP-1 was drilled <br /> and installed from January 4 through January 6, 1999 to a total depth of 90 feet below ground <br /> surface The sample was analyzed for lead for disposal purposes and was reported by the lab <br /> to have a concentration of 20 parts per million The certified analytical report for the composite <br /> soil sample is included as Attachment C <br /> A composite soil sample obtained from of soil cuttings from monitoring wells MW-12, MW-14, <br /> MW-16, MW-18, and MW-19, was collected on March 8, 2002 and analyzed for disposal <br /> purposes The previously listed monitoring wells were drilled on May 21 through May 23, 2001 <br /> Monitoring wells MWA2, MWA4, and MWA6 are located onsite while MWA8 and MWA9 are <br /> offsite wells The laboratory reported a total lead concentration of 8 2 mg/kg from the composite <br /> sample No additional soil sample results were found regarding lead or 1,2-DCA The certified <br /> analytical report for the latter composite soil sample is included as Attachment D <br /> J kProjects1o6940V859-35TFinaRCorrespondenoe12859 BLtr 083004 doc <br /> 35 Years of Excellence in Environmental Services <br />