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MENT <br /> ENVIRONMENTAL HEALTH DEPAR <br /> oPq��N SAN JOAQUIN COUNTY Unit Supervisors <br /> ' ?� Donna K.Henan,R.E.H.S. Car!Borgman,R.E.H.S. <br /> 304 East Weber Avenue,Third Floor <br /> :< Director Mike-Huggins,R.E.H.S.,R.D.T. <br /> en.R.E.H.S: Stockton, Califnrrlla 95202-2708 Douglas W.Wilson,R.E.H.S.r. Al Qls ,. <br /> .Program Manager- Telephone: (209).468-3420 Margaret Lagorio,R.E.H-S. <br /> b `' Laurie A.Cotntla,R.E:I3:5. Robert McClellon,R.E.H.S. <br /> Program Manager' Fax. (209)464-013$.. Mark Bareellos,R.E.H.S. <br /> NOV 17 2003 <br /> PAUL SUPPLE <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 Corrective Action <br /> Plan (CAP), dated 19 September 2003,prepared.by URS Corporation Americas(URS)on your <br /> behalf. The recommended remedial actions in the above referenced CAP,for remediation of <br /> petroleum hydrocarbons and oxygenates present in soil and groundwater beneath the site by a <br /> combination soil vapor extraction(SVE)and an air sparging system is approved as an interim <br /> measure. However,EHD cannot approve the CAP.at.this time as EHD believes that the cross- = <br /> 'sections submitted An the-CAP do not adequately model the,hydiogeology of the site,and the'' ` <br /> vertical delineation of contaminants is still incomplete in the underd storage tank.( <br /> grounUST) <br /> area. Therefore,additional site characterization is needed. Upon receipt of the final'site <br /> characterization materials,the CAP may be resubmitted for approval consideration. <br /> EHD suggests using Cone Penetrometer Testing(CPT)to refine the hydrogeologic model. CPT <br /> may better characterize the fine grain and coarse grain intervals,and groundwater samples taken <br /> during a well-designed CPT investigation may help delineate and/or characterize the plume of <br /> impacted groundwater at the UST site. Information obtained from such a study may demonstrate <br /> the need,or lack of need,for additional groundwater monitoring wells and aid selection'of <br /> advantageous monitoring well locations. <br /> EHD believes that there are three sand-rich intervals beneath this site,identified as Sand 1 at 25 <br /> to 35 feet below surface grade(bsg); Sand 2 at 45 to 60 feet bsg; and Sand 3 at 65 to 75 feet bsg <br /> (all depths approximate);and presents this view of the current state of the site: <br /> y . The three shallow vapor wells encounter Sand 1 in the vadose zone. This may account <br /> for the significant radius of influence found during the SVE test study. <br /> • Apprdximately ten feet of silt lie above and below Sand 1 so its may be necessary to <br /> install additional vapor wells to specifically target these silt zones. <br /> Sand 2 and Sand 3 may be interconnected;however,EHD believes that these sand <br /> intervals are separated and monitoring wells screened across both Sand 2 and Sand 3 may <br /> be providing a vertical conduit for contaminants. <br /> • Insitu air sparging(IAS)may not be a practical remediation method considering the site <br /> geology and current water table. IAS is generally more effective for addressing dissolved <br /> hydrocarbons than MTBE. If implemented,EHD recommends considering placing the <br /> spargers in the silt layers and injecting the air at a slow rate'for the interim remediation. <br /> I <br />