SITE INFORMATION AND CORRESPONDENCE

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Mr. Maurice Benson • February 23, 2010 Page 3 soil vapor extraction (SVE) is planned at SWMU 20 for late 2010 to remediate the vadose zone contamination, yet the report presents no discussion of these more time-critical actions to reduce the groundwater cleanup time. The report should capture the recent analytical results from SWMU 20 indicating that the area is the most significant volatile organic compound source to groundwater at DDJC-Tracy supported by soil gas data, groundwater monitoring well data, and imminent source area controls planned for 2010. 6.) Page 3-5, Summary of Plume Changes, TCE: The sentence "...areal extents of TCE concentrations exceeding the ACL of 5 pg/L remained stable or were reduced from 3Q08 to 3Q09" is inaccurate considering the results from LM193AU-NS reporting 73.1 J+ pg/L in 1Q09 and 104 pg/L in 2Q09. The section should be revised to not mislead the reader into believing statements which are not supported by data. 7.) Page 3-6, section 3.3.3.4: The reason TCE was not detected in groundwater collected in the Upper Hydrologic Zone in 3Q09 is due to LM193AU-NS being last sampled in 2Q09 at 104 pg/L before being destroyed by Warehouse demolition activities at SWMU 20. LM193AU-NS was originally installed on March 1, 2009, and was screened from 10 feet below ground surface (ft. bgs) to 24.5 ft. bgs. The screen interval represents the, Upper Hydrologic Zone referencing the Annual Reports Well Construction Details Table 2.5-1. The report is misleading the reader to believe that the TCE issue at SWMU 20 is either sporadic or is no longer the issue when in reality the monitoring point was destroyed, thus preventing further data collection. The report should be non- biased in presenting the true depiction of contaminant distribution at DDJC-Tracy considering the persistence of inaccurate information refuted and referenced in this comment letter. 8.) Page 3-7, section 3.3.3.8, Horizontal Extent of TCE 2006 through 2009: Results from LM193AU-NS in 2009 show much higher contaminant concentrations (104 pg/L) at SWMU 20 when compared to the 2008 CPT results of 37.7 pg/L. Accordingly, the report should note the results from LM193AU-NS and the implied larger areal extents of the TCE groundwater plume above 5 pg/L based on groundwater plume attenuation mechanisms and the fact that the monitoring well data are more representative of true contaminant conditions compared to CPT data. DTSC reminds DESJC that CPT data are best applied as a characterization tool and should not be used as a substitute for groundwater monitoring well data where available. 9.) Page 3-9, Pesticides and Herbicides: During the March 2009 timeframe, DESJC discovered elevated concentrations of pesticides and herbicides in soil cuttings created from borings as part of SVE well installation efforts at Area