Laserfiche WebLink
Mr. Maurice Benson - 2 - 3 December 2008 <br /> Defense Logistics Agency <br /> 2. Attachments 2 and 3 present the TCE concentration trend in monitoring well LM165A. <br /> Between 1997 and 1999, concentrations ranged between approximately 6 and 8 µg/L, <br /> which was similar to the trend at LM147A. However, between 2000 and 2007 <br /> concentrations were less than 2 pg/L. The rapid and stepped decline of TCE may have <br /> been the result of injection of treated groundwater into nearby injection galleries. DESJC <br /> should drill borings southwest and west of LM165A. <br /> 3. The center of the TCE plume may have extended from LM147A (Attachment 1) through <br /> LM176A (Attachment 4), LM076A (Attachment 5), EW020A (Attachment 6), EW019A <br /> (Attachment 7), PWO01 (Attachment 9), and LM150A (Attachment 10). The trend graphs <br /> shown on the Attachments indicate that TCE concentrations between 2000 and 2004 <br /> were very similar in these wells. Also, concentrations in CPT borings drilled near these <br /> wells during October 2001 were similar: CP0793, located approximately 270 feet south of <br /> LM176A was 5.9 µg/L, CP0792, located approximately 120 feet north of LM076A was <br /> 7.4 µg/L, and CP0791, located a few feet east of EW020A was 5 gg/L. Also of note, the <br /> concentration of TCE in CP0392 drilled in October 1999 was 11 µg/L. CP0392 was drilled <br /> approximately 200 feet northeast of LM150A and 300 feet northeast of PW001. <br /> Concentrations of TCE in EW018A (Attachment 8), LM152A (Attachment 11), and <br /> LM154A (Attachment 12) between 2000 and 2004 suggest that these are side-gradient <br /> wells. <br /> Attachments 13 and 14 show concentration trends in monitoring wells LM156A and <br /> LM157A, respectively. The results suggest that the center of the plume continued <br /> beyond LM150A northeast to these wells. In addition, the most recent CPT borings <br /> installed in this area in October 1999 were CP0392 with a TCE concentration of 11 µg/L <br /> and CP0394 with a TCE concentration of 7.1 µg/L. To complete the characterization of <br /> TCE concentrations in groundwater, DESJC should drill borings along the apparent <br /> northeast-trending plume axis between LM150A and LM156A. Based on the results, <br /> DESJC should install monitoring wells in this area. <br /> 4. The downgradient extend of the TCE plume has not been determined because TCE <br /> concentrations are present in downgradient monitoring wells LM156A and LM157A. In <br /> fact, concentrations have not declined since they were installed (Attachments 13 and 14) <br /> and continue to be greater than the aquifer cleanup level of 5 µg/L specified in the <br /> Record of Decision for the DDJC Site. DESJC should install monitoring wells <br /> downgradient of LM 156A and LM157A. <br /> If you have any questions, please contact me at (916) 464-4675, or by email at <br /> jbrownell@waterboards.ca.gov. <br /> �&Zrj� <br /> James R. Brownell, P.G. <br /> Associate Engineering Geologist <br />