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lose <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. <br /> 304 East Weber Avenue, Third Floor <br /> Director Mike Huggins,R.E.H.S-,R.D.I. <br /> ='' s Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> e • Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> S. <br /> Laurie A.Cotulla,R.E.H.S. Fax: (209) 4{74-0138 Robert McClelfon,R.E.H.Mark Barcellos,R.E.H.S.. <br /> Program Manager <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 in the CAP do not adequately model the hydrogeology of the site, and the <br /> vertical delineation of contaminants is still incomplete in the underground storage tank(UST) <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 /> ained <br /> rom such a study may <br /> impacted gr la k of ndwaneed , for additional grou dwat r mr at the UST site. Information tdemonstrate <br /> ng wells and aid selection f <br /> the need, or <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 /> • 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 /> • Approximately ten feet of silt lie above and below Sand 1 so it 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 />