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Peter MacNicholl <br /> February 23, 2005 <br /> Page 4 of 4 <br /> 3) Page 5-8, Section 5.8.2 (Conclusions, Recommendations): The GSU concurs with <br /> the recommendations presented here, with the following caveats. Regarding the first <br /> bulleted recommendation, the GSU recommends that future capture zone analyses <br /> follow the forthcoming USEPA guidance (as noted above in the General Comments). <br /> Specifically, the GSU recommends the use of multiple lines of evidence (including <br /> particle tracking analysis) to verify capture with extraction wells EW002AU and <br /> EW004AU. Regarding bulleted recommendation number 5, the GSU questions whether <br /> discontinuing pumping from extraction well EW021A may result in the loss of capture of <br /> the PCE and TCE plumes in the middle hydrologic zone near monitoring well LM058AU, <br /> especially given the current recommendation by the USACOE to discontinue pumping <br /> from extraction well EW031C (Section 5.8.2). Finally, regarding bulleted <br /> recommendation number 7, the GSU questions where specifically the proposed nested <br /> piezometers are to be located. <br /> Recommendation <br /> The GSU recommends revising the Draft 2004 Annual Progress Report to include <br /> a discussion of the effects discontinuing pumping from extraction well EW-021A <br /> may have on the ability of the groundwater extraction system to capture the PCE <br /> and TCE plumes in the middle hydrologic zones near monitoring well LM058AU. <br /> In addition, the GSU recommends including a more detailed discussion of the <br /> locations for the proposed piezometers to be installed near extraction wells EW- <br /> 24B and EW02513. <br /> 4) Page 7-4, Section 7.4.7 (Sampling Recommendations, Recommended Deletions): <br /> The GSU agrees with the recommendation to discontinue the analysis for total <br /> petroleum hydrocarbons (TPH) as diesel from the current sampling program. However, <br /> the GSU questions whether TPH as gasoline has been detected in the wells. If TPH as <br /> gasoline has not been detected in a well for several sampling events, it may be <br /> appropriate to discontinue the analysis for TPH as gasoline. <br /> Recommendation <br /> The GSU concurs with the USACOE's recommendation to discontinue analyzing <br /> for TPH as diesel. Regarding the USACOE's recommendation to eliminate the <br /> analysis for TPH as gasoline, the GSU requests clarification of the historical <br /> trends of TPH as gasoline at the Site prior to offering its concurrence. <br /> If you have any questions, please contact me at 916/255-3695 or at <br /> bduke@dtsc.ca.gov. <br /> Tracy DDD_URS121704_DraftWellMonitoring Prog2004AnnualRpt.doc <br />