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i <br /> Mr Nuel Henderson <br /> Page 4 of 4 <br /> Reduce the monitoring and sampling frequency to a semi-annual schedule Gwen the massive quantity <br /> • of historical groundwater monitoring and chemical analysis data at this site, quarterly monitoring and <br /> sampling for this site is not warranted <br /> Vapor Extraction System Operation <br /> The current cost of operating the soil vapor extraction system is not justified by the relatively small <br /> incremental effect on the total hydrocarbon mass removed from the subsurface However, water levels <br /> are on the decline, and it is possible that the San Joaquin Valley is entering a period of normal to <br /> below-normal rainfall which may results in decreasing groundwater levels in the coming years If so, <br /> contaminated soil that is now saturated may become exposed We recommend removing the vapor <br /> extraction/thermal oxidizer equipment from the site, but retaining the vapor wells and associated <br /> conveyance piping for possible resumption of vapor extraction in the future <br /> Fieldwork for the first quarter is scheduled to be conducted in February 2003 EHD will be notified 48 <br /> hours prior to conducting the quarterly fieldwork <br /> If you have any questions or comments regarding tins report,please contact us at your convenience <br /> Respectfully, <br /> Gro d alysis, Inc <br /> ED <br /> rGf O�0 ' <br /> 39cy <br /> Staff Geologist GREGORY P.- 4L STAHL <br /> '{ <br /> /&IyU No. 5023 <br /> Gregory P Stahl, RG 5023 <br /> CA Certified Hydrogeologist No 264 gfct'OF Ckt�F � <br /> Attachments <br /> PC Mr Carl Knowles <br /> Mr Pat Riddle, Esq, Law Offices of Patrick D Riddle <br /> Mr Marty Hartzell,RWQCB Sacramento <br /> Mr Don Roek <br /> 11GZA_FSISYS010ata1GROUNDZEIROEKIQMR1200214gm2002 doe <br /> I <br />