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i► _ <br /> z ENVIRONMENTAL HEALTHDEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> v a Donna K.Heran,R.E.H.S. <br /> 304 East Weber Avenue' Third Floor Carl Borgman, R.E.H.S. <br /> Director <br /> Mike Huggins,R.E.H.S.,R.D.l. <br /> • Al Olsen, Stockton, California 95202-2708 <br /> .. �•.• Douglas W. Wilson,R.E.H.S. <br /> e., Foaa�P Program Manager Telephone: (209) 468-3420 Margaret Lagorio, R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209} 464-0138 Mark Barcellos,R.E,H,S, <br /> PAUL SUPPLE _ MAR 2 2 2404 <br /> ATLANTIC RICHFIELD COMPANY <br /> P O BOX 6549 <br /> MORAGA CA 94570 <br /> RE: ARCO Service Station No. 2186 <br /> 3212 North California Street <br /> Stockton, California 94570 <br /> San Joaquin County Environmental Health Department(EHD)has reviewed Work Plan for <br /> Groundwater Monitoring and Remediation Well Installation, dated February 13, 2004, and <br /> prepared by URS Corporation Americas(URS) on your behalf. The work plan includes the <br /> installation of one deep groundwater monitoring well,one soil vapor extraction well, and 10 air- <br /> sparging wells at the above mentioned site. EHD also reviewed the Response to Comments-San <br /> Joaquin County Electronic Mail of March 9, 2004,forARCO Station No. 2186 dated <br /> March 11, 2004. <br /> EHD approves the installation of one monitoring well advanced to approximately 100 feet below <br /> ground surface (bgs). Soil samples will be collected at five-foot intervals,beginning at 5 feet bgs, <br /> and continuous coring will begin at approximately 75 feet bgs to characterize the hydrogeology <br /> and lithology and assess the vertical extent of impacted soil and groundwater. At least one soil <br /> sample will be collected from the capillary fringe area and at least one soil sample will sent to a <br /> California certified laboratory for analysis. <br /> EHD also approves the installation of one soil vapor extraction(SVE)well, advanced to <br /> approximately 40 feet bgs. Soil samples will be collected at 5-foot intervals,beginning at 5 feet <br /> bgs. At least one soil sample will be collected from the capillary fringe area and at least one soil <br /> sample will sent to a California certified laboratory for analysis. <br /> EHD cannot approve the installation of ten air-sparging wells for remediation of petroleum <br /> hydrocarbons and oxygenates beneath the site for the following reason. Site geology raises <br /> concerns that sparged air and entrapped hydrocarbons may not be recovered by the SVE system. <br /> The proposed sparing points are at 65 feet bgs. Current data shows that this sand layer is overlain <br /> by a fine-grained interval, EHD is concerned that the spared air and entrapped petroleum <br /> hydrocarbons will follow the path of least resistance and migrate laterally,rather than vertically, <br /> thereby spreading the contamination. EHD recommends conducting a pilot study designed to test <br /> the insitu air sparing(IAS) system for effectiveness and recovery. Groundwater should be <br /> monitored to detect migration of contaminants; data gathered during this pilot study can be used <br /> to estimate the mass recovery and duration of this remedial effort. <br />