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Mr. Maurice Benson <br /> November 19, 2008. <br /> Page 4 <br /> Northwest Corner Dieldrin Focused Feasibility Study: <br /> Rationale provided for the OW Rebound Test state in the report that "the dieldrin <br /> groundwater ACL of 0.05 pg/L will be very difficult to achieve due to the <br /> persistence and immobility of this organochlorine pesticide in the saturated <br /> zone." This determination is unsupported, especially due to the fact that a <br /> Focused Feasibility Study evaluating the ability to effectively remediate dieldrin <br /> mass through active pump and treat is forthcoming. Additionally, the Sanitary <br /> Sewer Lagoon or Central Dieldrin Plume at DDJC-Tracy has shown significant <br /> response to the active pump and treat groundwater remedy, resulting in reduced <br /> areal plume extents and contaminant concentrations. <br /> DESJC should await the submittal and results of the Focused Feasibility Study <br /> evaluating diedrin mass removal from the saturated zone prior to proposal of an <br /> OU1 Rebound Test. <br /> Summary: <br /> DTSC considers the proposal to shutdown the OU1 groundwater extraction and <br /> treatment system premature with the ongoing remedial work at DDJC-Tracy. <br /> DESJC-Tracy should focus fieldwork efforts to vertically and horizontally <br /> delineate the NE Banta Road TCE plume. The VOC source areas remaining at <br /> Warehouse 10 and the SVE sites should be remediated to eliminate the <br /> continuing source of groundwater contamination. Finally, the forthcoming <br /> Focused Feasibility Study will be used determine whether dieldrin mass can <br /> effectively be remediated through the selected groundwater pump and treat <br /> remedy and should not be presented or concluded on in this work plan. <br /> If you have any questions or comments regarding this letter, please feel free to contact <br /> me at (916) 255-3713 or e-mail me at pmacnichadtsc.ca.gov. <br /> Sincerely, <br /> �� 0. <br /> Peter MacNicholl, P.E. <br /> Hazardous Substances Engineer <br /> Sacramento Office <br /> Brownfields and Environmental Restoration Program <br />