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ENVIRONMENTAL HEALTH DEPARTMENT <br /> AS�U�'�" c� SAN JOAQUIN COUNTY <br /> G <br /> Unit Supervisors <br /> Donna K Heran,R E H S 304 East Weber Avenue, Third Floor Carl Borgman,R E H S <br /> Director <br /> Mike Huggins,R E H S, <br /> Al Olsen,R E H S Stockton, California 95202-2708 Douglas W Wilson,R E H S <br /> • c �4 • Program Manager Telephone (209) 468-3420 Margaret Lagorio,R F H S <br /> QcrFOR`' Laurie A Cotulia,R E H S <br /> Fax (209) 464-0138 Robert McClellon,R E H S <br /> Program bfanager Mark Barcellos,R E H S <br /> PAUL SUPPLE LIAR 2 2 2804 <br /> ATLANTIC RICHFIELD COMPANY <br /> P O BOX 5549 <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,for ARCO 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 />