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ENVIRONMENTAL HEALTH DEPARTMENT <br /> PQu � <br /> SAN J�OAQUIN COUNTY <br /> t i Unrl Suptrwsors <br /> Donna K.Horan,R.E H S <br /> Drrmfor 304 East Weber Avenue, Third Floor Carl Borgman,R E H S <br /> Al Olsen,R E H S Stockton, California 95202-2708 Mike Huggins,R E Fl S,R D I <br /> o �P Pragrarrr Manager Douglas W Wilson,R E N S <br /> 4< r ED) Laurie A Cotulisk,R E N S Telephone (209) 468-3420 Margaret Lagorio,R E H S <br /> Prog►aru htrurager Fax (209) 464-0138 Robert McClellan,R E H S <br /> Mark Barcellos, R E 11 5 <br /> BOB DENINO MAY 2 4 2005 <br /> SOUTHLAND CORPORATION <br /> 10220 SW GREENBURG RA SUITE 270 <br /> PORTLAND OR 97223 <br /> RE 7-Eleven Store No 19976 SITE CODE 1435 <br /> 1399 North Main Street RO 675 <br /> Manteca, CA 95336 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Quarterly <br /> Groundwater Monitoring and Remediation Progress Report First Quarter 1005, dated <br /> May 4, 2005, prepared and submitted by Secor International Incorporated (Secor) on your <br /> behalf for the above-referenced site This comment letter is in response to a telephone <br /> conversation between Secor and EHD, followed by an email from Damon Brown of <br /> Secor on May 16, 2005 <br /> Upon reviewing the analytical data from the first quarter 2005 monitoring event, EHD <br /> concurs with Secor that groundwater contamination is vertically defined in the source <br /> area EHD suspects that groundwater results from deep well samples MW-IA, MW-4A, <br /> and MW-5A collected dunng the December 2004 monitoring event may be due to cross <br /> contamination The thin sand monitored by the deeper wells does not appear to be <br /> impacted, therefore, EHD does not require the installation of a monitoring well located <br /> between borehole GP-3 and MW-lIMW-IA Please sample MW-4A quarterly to <br /> confirm non-detect results following recoveries for benzene, toluene, ethyl benzene, and <br /> total xylenes reported during the fourth quarter sampling event <br /> i <br /> By letter dated May 3, 2005, EHD requested documentation that groundwater mounding <br /> is not occumng during oxygen injection at this site By email dated May 16, 2005, Secor <br /> suggested taking depth-to-water measurements in the injection wells and adjacent wells <br /> before and after the oxygen injections to document groundwater elevation changes EHD <br /> recommends depth-to-water measurements be initiated several hours prior to oxygen <br /> injection, during, and after oxygen injection at monitoring wells MW-2 (adjacent and <br /> down gradient to sparge wells SP-1/SP-I A), MW-5/MW-5A (down gradient to SP-IISP- <br /> 1 A), and MW-4 (up gradient to SP-l ISP-I A) for background control <br /> Q -IQUM9IF � <br /> i MAY 2 5 2905 <br />