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Mr Nuel Henderson <br /> Page 4 of 4 <br /> indicate that these wells have been impacted by the contaminant plume originating from the Top <br /> Filling site <br /> Reduce the monitoring and sampling frequency to a semi-annual schedule Given the massive <br /> quantity of historical groundwater monitoring and chemical analysis data at this site, quarterly <br /> monitoring and 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 <br /> small incremental effect on the total hydrocarbon mass removed from the subsurface However, <br /> water levels are on the decline, and it is possible that the San Joaquin Valley is entering a period <br /> of normal to below-normal rainfall resulting in decreasing groundwater levels in the coming years <br /> If so, contaminated soil that is now saturated may become exposed We recommend removing <br /> the vapor extraction/thermal oxidizer equipment from the site, but retain the vapor wells and <br /> associated conveyance piping for possible resumption of vapor extraction in the future <br /> Fieldwork for the fourth quarter is scheduled to be conducted in November 2002 EHD will be <br /> notified 48 hours prior to conducting the quarterly fieldwork <br /> • If you have any questions or comments regarding this report, please contact us at your <br /> convenience <br /> Respectfully, <br /> Gro d alysis, Inc -�"—� <br /> �C <br /> �} <br /> 44 j ' <br /> �! C" <br /> Se Garvey GFEGQRY P. <br /> Staff Geologist S T AHL <br /> No. 5G23 <br /> Gregory P Stahl, RG 5023 �Tf OF CA'Lk O � <br /> CA Certified Hydrogeologist No 264 <br /> Attachments <br /> I <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 /> I%GLA_FSIbYSOl1D,L,1GROUN'DZE1ROrk\QN[R\2042�3ymZU02 doc <br />