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Mr. Maurice Benson • <br /> February 23, 2010 <br /> Page 2 <br /> Annual Report or representative primary documents due to consistency, <br /> enforceability, and disputability. The regulatory agencies met with DESJC and <br /> discuss the DDJC-Tracy Proposed 2010 Monitoring Program Sampling <br /> frequencies on February 4`h, 2010. The decisions made during the meeting and <br /> agreed upon sampling frequencies will be captured in meeting minutes prepared <br /> by the contractor, HDR/e2M. <br /> 2.) Page 2-7, section 2.5.5.3, Vertical Hydraulic Gradients: Downward vertical <br /> gradients from the Upper to Middle zones are the most common gradients at <br /> DDJC-Tracy. The report notes that eight (8) of the fourteen (14) well pairs show <br /> a downward vertical gradient in all four quarters, but fails to discuss the <br /> mechanism for these gradients; for example, can these gradients be attributed to <br /> operating extraction wells screened in the Middle zone? The report should <br /> identify the cause of these vertical downward gradients and if these current <br /> gradients are consistent with previous years' data. <br /> 3.) Page 2-11, section 2.8.2, first paragraph, last sentence: DTSC is aware that <br /> DESJC has conducted several rounds of cone-penetrometer testing (CPT) for <br /> the East Banta Road tricholorethene (TCE) plume since 1996 in order to better <br /> characterize the lateral and vertical extents. DTSC does not believe the report's <br /> statement is accurate considering the more recent CPT data from 2008 <br /> identifying that the TCE toe-of-plume has migrated further down-gradient and <br /> prompted DESJC to plan the installation of guard wells to monitor the plume's <br /> leading edge. The report should clearly identify the previous fieldwork efforts <br /> made to delineate the East Banta Road TCE plume and not ignore 14 years' <br /> worth of groundwater analytical data. <br /> 4.) Page 3-1 , section 3.1.2, Nature and Extent of CDCs in Groundwater: The <br /> statement that "...COC plumes exceeding the aquifer cleanup level (ACL) are <br /> stable or shrinking and COC concentrations are decreasing at DDJC-Tracy" is <br /> somewhat misleading taking into account the recent discovery and delineation of <br /> the Solid Waste Management Unit (SWMU) 20 TCE groundwater plume. The <br /> SWMU 20 TCE plume represents a footprint of approximately 20,000 square <br /> feet of groundwater contaminated over the ACL of 5 pg/L and also reported the <br /> highest TCE concentration in a monitoring well with 104 pg/L recorded in 2Q09. <br /> The report should be revised to consider the more recent CPT fieldwork <br /> conducted in 2008 in conjunction with the monitoring results from LM193AU-NS <br /> in 2Q09 to present a more accurate depiction of COC plumes at DDJC-Tracy. <br /> 5.) Page 3-3, section 3.3.1, VOC Source Areas: Similar to comment #4, the report <br /> should identify the persistent groundwater source emanating from SWMU 20 <br /> and how monitoring results from LM193AU-NS are approximately four (4) times <br /> higher than any other TCE concentration reported at DDJC-Tracy. Additionally, <br />