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Page 2 <br /> 2. In addition to completing horizontal delineation discussed above,the TPH-d plume needs <br /> to be stable or declining. H&H plans to demonstrate through trend analysis that MW-3 <br /> and MW-4 are stable and/or declining. Included with this will be an assessment of <br /> watertable elevations related to fluctuating contaminant concentrations. This may be <br /> useful in establishing a correlation of contaminant levels and watertable elevations. A <br /> minimum of four quarters of data will be needed to establish such trends. Therefore, an <br /> estimated number of additional quarterly sampling events is undetermined at this time. <br /> 3. Upon successful establishment of declining trends, a risk assessment approach will be <br /> employed to identify when the TPH-d contamination would be gone and water quality <br /> objectives(WQOs) achieved. Since only partial risk assessment information has been <br /> previously submitted by Geomatrix, a complete risk assessment regarding potential <br /> receptors will be completed at this time utilizing the San Francisco ESLs. <br /> 4. H&H will evaluate the possibility of a recirculation system as suggested by Harlin Knoll. <br /> However, due to the fine grained materials,this may be problematic, inefficient, and not <br /> cost-productive, and H&H is not proposing this activity at this time. <br /> 5. To fulfill the requirements of the Central Valley Water Board, hydrocarbon vapors as a <br /> pathway will be considered and evaluated. In order to demonstrate there are no potential <br /> health risks associated with vapors, soil gas samples via summa canisters or development <br /> of a model, i.e. Johnson/Ettinger,will be completed. Currently, based on site information <br /> including soil type and contaminant type that shows a general lack of volatile <br /> constituents,modeling is the route H&H proposes to demonstrate this. <br /> An updated site figure that includes the locations of the proposed borings/monitoring wells is <br /> included with this letter. <br /> Therefore, we are anxious to move this site toward closure in the very near future and appreciate <br /> written concurrence regarding the proposed activities. <br /> Our office has recently moved so please note my new telephone number (630) 584-4401. I will <br /> contact you to arrange a convenient time to discuss this site. <br /> Sincerely yours, <br /> Linda L.Huff,P.E. <br /> President <br /> Enclosure <br /> cc: James Taylor, ContiGroup Companies,Inc. <br /> Central Valley Regional Water Board <br /> Robert Marty,AGE <br /> RAOONTGRAWtockton12007 Correspondeneelltr to H Knoll Aug 07.doc <br />