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IV Fourth Quarter 2001 Mondonng and Sampling Report 3 Remediation Well Installationllntenm Remediation Report January 31 2002 7-Eleven Inc Store#19976,1399 North Main Street Manteca CA ' Remediation Well Installationllnterim Remediation ' One double-nested sparge well was installed as shown on Figure 2 to a total depth of 50 feet below grade, perforated from 30 to 35 feet and 45 to 50 feet below grade The well was Installed using 12-Inch diameter hollow stem augers The well segments were constructed using 2-inch diameter Schedule 40 poly-vinyl ' chloride (PVC) casing with flush threads and 0 020-inch-slot well screen Sand filter packing was placed around the well screen to a height of 1 foot above the top of the screen In the shallowest segment During drilling of the deeper segment, flowing sand mixed with filter packing sand resulting in a filter pack installed ' 8 feet above the top of the screened interval The filter packs were sealed with 2-3 feet of bentonite (hydrated in place), followed by a neat-cement grout to grade The wellheads are protected at the surface by locking, expandable caps and a traffic-rated street box(with a watertight bolted ltd)set In concrete Well construction details and soil boring logs are Included with field notes in Attachment 3 ' During drilling,soil samples were collected at five foot intervals from surface grade to the total depth of drilling and logged using the Unified Soil Classification System by an IT geologist working under the supervision of a California registered geologist Selected sod samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory for analysis for BTEX and TPH-G using Environmental Protection Agency(EPA) method 8020/modified 8015 and for oxygenates TBA, MTBE, DIPE, ETBE and TAME using EPA method 8260 The highest benzene,TPH-G, and MTBE concentrations were detected in the soil sample collected at 24 feet below grade at 0 6 milligrams per kilogram (mg/Kg),23 mg/kg, and 0 29 mg/kg, respectively(Table 2) ' Soil MTBE concentrations attenuated vertically with increasing depth to 0 0051 mg/kg at 49 feet below grade (the deepest sample collected) Laboratory reports are Included in Attachment 4 ' Interim remediation conducted during the quarter consisted of two episodes of soil vapor extraction, conducted using well MW-2 A mobile 150-cfm thermal oxidizer was used, permitted through the local air quality management district Influent concentrations were generally low(Attachment 3) Subsequent ' interim remediation episodes will be conducted using the horizontal vapor extraction wells In addition, an air sparge test will be conducted during the first quarter 2002, results will be submitted with the first quarter 2002 report Sod Cuttings/Purge Water Transportation and Disposal All soil cuttings and purge water generated during this quarter's events were stored In 55-gallon ' Department of Transportation (DOT)-approved drums pending characterization and proper disposal by a licensed waste hauler for appropriate recycling as non-hazardous waste • ' 19976014 DOC 1