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g'7 <br /> • <br /> ARCADIS GERAGHTY& MILLER <br /> ARCADIS Geraghty&Miller Inc <br /> 1050 Marina Way South <br /> Richmond <br /> Mr Brett Hunter California 94804 <br /> Chevron Products Company Tel 510 233 3200 <br /> 6001 Bollinger Canyon Road fax 510 233 3204 <br /> San Ramon, California 94583 <br /> Subject WESTERN REGION <br /> Operation of Soil Vapor Extraction and Air Sparging Remediation Systems, First <br /> Quarter 1998, 2905 West Benjamin Holt Drive (Service Station#9-4275), Stockton, <br /> California <br /> Richmond <br /> Dear Mr Hunter 26 May 1998 <br /> This letter summarizes the operation of the soil vapor extraction (SVE) and air Contact <br /> sparging systems in place at the above-referenced site (Figure 1) and provides Aaron O'Brien <br /> recommendations for the enhancement of the remediation program <br /> The extraction well network consists of ten SVE and nine air sparging wells System <br /> installation was completed in February 1997 as reported in the Corrective Action Extension <br /> Plan (Geraghty &Miller, May 1997) Groundwater was encountered at (510) 233-3200 <br /> approximately 17 feet below the ground surface (bgs) when the remediation system <br /> was installed The screened interval for the SVE wells extends from approximately <br /> 10 feet bgs to 17 feet bgs Groundwater was measured during the February 1997 <br /> groundwater monitoring event at approximately 8 to 10 feet bgs following heavy <br /> winter rains This submergence of the screen prevented operation of the SVE system <br /> until the groundwater receded <br /> SVE and Air Sparging Systems Operations <br /> The SVE system was started in September 1997 after groundwater was observed at <br /> approximately 12 to 13 feet bgs A rise in groundwater elevation following the <br /> recent winter necessitated discontinuation of the operation of the SVE system in <br /> February 1998 Low vapor influent concentrations were encountered during <br /> operation of the SVE system which has resulted in low mass removal ARCADIS <br /> Geraghty & Miller optimized the SVE system by extracting from wells with higher <br /> concentrations, however vapor concentrations remained below levels required for <br /> effective mass removal Operational parameters for the SVE system are included in <br /> Table 1 <br /> Operation of the air sparging system began in April 1997 The system operates <br /> cyclically, infecting air alternately into Wells GM-I through GM-5 and Wells GM-6 <br /> Our ref <br /> R0000309 0909!1 stgtr98 doc <br />