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ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors Donna K.Heran,R.E.H.S. 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. Director Mike Huggins,R.E.H.S.,R.B.I. •'•. Al Olsen,R.E.H.S. Stockton, California.95202-2708 Douglas W.Wilson,R.E.H.S. �q ._,�•;;:�;.P Program Manager Telephone: (209)468-3420 Margaret_Lagorio,R.E.H.S_ {f FOR Laurie A.Cotuila,R.E.H.S. Fax: (209)464-0138 Robert McClellan,R.E.H.s, Program Afanager Mark Barcellos,R.E.H.S. PAUL SUPPLE MAR 2 Z 2904 ATLANTIC RICHFIELD COMPANY P O sox 6549 MORAGA CA 94570 RE: ARCO Service Station No.2186 3212 North California Street Stockton,California 94570 San Joaquin County Environmental Health Department(EHD)has reviewed Work Plan for Groundwater Monitoring and Remediation Well Installation, dated February 13,2004,and prepared by URS Corporation Americas(URS)on your behalf. The work plan includes the installation of one deep groundwater monitoring well,one soil vapor extraction well,and 10 air- sparging wells at the above mentioned site. EHD also reviewed the Response to Comments-San Joaquin County Electronic Mail of March 9, 1004,for ARCO Station No. 2186 dated March 11,2004. EHD approves the installation of one monitoring well advanced to approximately 100 feet below ground surface(bgs). Soil samples will be collected at five-foot intervals,beginning at 5 feet bgs, and continuous coring will begin at approximately 75 feet bgs to characterize the hydrogeology and lithology and assess the vertical extent of impacted soil and groundwater. At least one soil sample will be collected from the capillary fringe area and at least one soil sample will sent to a California certified laboratory for analysis. EHD also approves the installation of one soil vapor extraction(SVE)well,advanced to approximately 40 feet bgs. Soil samples will be collected at 5-foot intervals,beginning at 5 feet bgs. At least one soil sample will be collected from the capillary fringe area and at least one soil sample will sent to a California certified laboratory for analysis. EHD cannot approve the installation of ten air-sparging wells for remediation of petroleum hydrocarbons and oxygenates beneath the site for the following reason. Site geology raises concerns that sparged air and entrapped hydrocarbons may not be recovered by the SVE system. The proposed sparing points are at 65 feet bgs. Current data shows that this sand layer is overlain by a fine-grained interval. EHD is concerned that the spared air and entrapped petroleum hydrocarbons will follow the path of least resistance and migrate laterally,rather than vertically, thereby spreading the contamination. EHD recommends conducting a pilot study designed to test the insitu air sparing(IAS) system for effectiveness and recovery. Groundwater should be monitored to detect migration of contaminants;data gathered during this pilot study can be used to estimate the mass recovery and duration of this remedial effort.