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02 <br /> JARED ST�TF.s UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br /> A Region 9 <br /> q Y 75 Hawthorne Street <br /> `e+777/ San Francisco CA 94105-3901 <br /> January 21, 2000 <br /> Mr. Dale Clemens <br /> Environmental Protection Office <br /> DD-Tracy <br /> P.O. Box 960001 <br /> Stockton, CA 95296-0250 <br /> RE: Review of the "Well Monitoring Program, Draft 1999 Annual Monitoring <br /> Report" dated December 1999 for Tracy Defense Depot <br /> Dear Dale, <br /> Enclosed is EPA' s evaluation of the "Well Monitoring Program, Draft 1999 <br /> Annual Monitoring Report" (the Report) dated December 1999. <br /> The Report is well written and the data presentation is excellent. However, <br /> some issues and outlined below. In addition, the Report states (Section <br /> 4.8.3, Page 4-9) that "Dieldrin results above the water quality objective of <br /> (0.05 ug/1) were reported at LM003AA (in 4Q98, 1Q99, and 3Q99) and LM015AA. (in <br /> 1Q99 and 3Q99) . Wells will continue to be sampled to monitor performance of <br /> this removal action." Since dieldrin was detected above the water quality <br /> objective in up to three monitoring events, further source removal or <br /> additional groundwater remedies may have to be considered for the area around <br /> these monitoring wells in the future. <br /> It should be noted that the TCE plume in the Upper Horizon extends northeast <br /> of the Annex onto the Robertson property (as identified from concentrations <br /> reported in samples collected from the wells that were installed on the <br /> property in 1999) and appears to extend beyond the Robertson property. <br /> Further investigation northeast of the Robertson property appears to be <br /> warranted. In addition, a small new PCE plume was identified near LM059A in <br /> . the Upper Horizon which may require further investigation in the future. <br /> It should also be noted that the extraction system capture zones presented in <br /> the Report are estimated capture zones and are not based on actual data since <br />