SITE INFORMATION AND CORRESPONDENCE

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ENVIRONMENTAL HEALTH VEPARTMENT SAN JOAQUIN COUNTY f: Unit Supervisors Donna K.Reran,R.E.H.S. 304 East Weber Avenue, Third Floor g� ac .� Carl Bor an,R.E.H.S. Director Mike Huggins,R.E.H.S.,R.D.I. At Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. • Cq(,FQpN�P , Program Manager Laurie ,R.E.H.S. Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. Program raamm Manager Fax: (209) 464-0138 Robert McClellan,R.E.H.S. Mark Barcellos,R.E.H.S. SEP 1 3 2005 DENIS L BROWN SUKH C & PERMINDER K SINGH SHELL OIL PRODUCTS 880 VICTOR RD 20945 S WILMINGTON AVE LODI, CA 95240 CARSON CA 90810 RE: SHELL SERVICE STATION SITE CODE: 1746 880 VICTOR ROAD LODI CA 95240 San Joaquin County Environmental Health Department(EHD) has reviewed Subsurface Investigation Work Plan(work plan) dated August 26,2005,and Soil Vapor Extraction Reevaluation Report(SVE Report),dated July 27,2005,prepared by Cambria Environmental Technology,Inc. (Cambria) for the above-referenced site. In the work plan,Cambria,proposes installing three monitoring wells MW-12,MW-13,MW-14,with screen intervals from approximately 5 feet above and 10 feet below first encountered groundwater, and one deep monitoring well,MW-15,with the screened interval from approximately 90 to 100 feet below surface grade (bsg). The work plan states that a conductor casing may be installed during construction of MW-15. Please note that if the conductor casing is to be left in place it must have a two inch annular grout seal placed around the outside of it. The work plan does not detail the diameter or length of the conductor casing. It does state that the monitoring well will be constructed with 4-inch casing. Typically,4-inch diameter monitoring well casing is installed in a 10.25-inch diameter auger. In order to use a 10.25-inch auger,the conductor casing would have to be at least 12 inches in diameter. If a 12-inch conductor casing is to remain in place with a two inch annular seal, the bore hole would have to be 16 inches in diameter. Hollow stem auger drilling is not typically used for borings where conductor casing is to be removed during grouting of the monitoring well casing. If hollow stem auger drilling will not be used for installation of MW-15, then the type of drilling to be used must be provided to EHD and if the same drilling company does not perform both types of drilling, separate well permits must be obtained for each drilling company. The necessity of installation of conductor casing should be evaluated. The work plan is approved as adequate and necessary,with the condition that details on the conductor casing installation are submitted with the EHD well permit application(s) and$89 permit fee(s). Cambria requested that the report of the investigation be submitted to EHD within 75 days after completion of the work instead of within 60 days after completion of the work. EHD approves of this schedule for submittal of the report of the investigation. The work is to be completed within 60 days of the date of this letter. Based on the data presented in the SVE Report, EHD agrees that the SVE wells were set within the area of known soil contamination by MTBE and,with a 20-ft radius of influence, the SVE test should have affected the areas shown to have MTBE-impacted soil. Cambria interprets the SVE test data and SVE boring soil data to indicate degradation or migration of MTBE to account for much of the lack of detectable MTBE concentrations in the soil samples collected from the SVE well borings, but other factors may have influenced the soil concentrations.