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Mr. Carl Navarra <br /> 7500 W. Eleventh Street <br /> Page 2 of 2 <br /> Another important technical justification for the proposed extraction trench would be to <br /> demonstrate a reasonable potential to achieve an effective reduction of -the dissolved <br /> contaminant mass to either sufficiently remediate the site directly or -to enable natural <br /> attenuation to complete the remedial action in a reasonable time frame. This requires estimates <br /> of the dissolved contaminant mass and the portion that can be removed through the proposed <br /> extraction technique. These estimates are necessary to calculate the appropriate volume of <br /> impacted groundwater to extract, which in turn affects the optimum number of extraction events <br /> and costs. TSJCI anticipates two extraction events based on their experience with the <br /> excavation on the subject site; however that excavation was at the up-gradient portion of the <br /> plume, very likely with relatively unimpacted groundwater that come into the excavation from the <br /> south. The proposed excavation'trench has impacted groundwater and possibly LNAPL both <br /> up-gradient and down-gradient of the excavation, which may alter individual extraction event <br /> effectiveness. A mass reduction rate through natural attenuation has already been calculated. <br /> If you have,any questions or comments you may contact Nuel Henderson at (209)468-3436. <br /> Donna Heran, RENS, Director <br /> Environmental Health Department <br /> Nuel C. Henderson, Jr., PG Mar�Lagorlo, REH <br /> 7 <br /> Engineering Geologist Program Coordinator <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> cc: James L.L. Barton, CVRWQCB <br /> Dai Watkins, TSJCI <br />