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Mr. Marshall Cloud <br /> February 6, 2008 <br /> Page 2 <br /> 3. Page 3-1, Section 3.1.2; The report states that "the western (leading) edge of <br /> the Contaminants of Concern (CDCs) plumes above the Aquifer Cleanup <br /> Level are stable and shrinking and COC concentrations in most wells are <br /> decreasing at DESJC-Sharpe." DTSC does not consider this an accurate <br /> statement due to the fact that off-site extraction well (EW) EWCC3 has <br /> recorded the highest TCE concentration at that location in the last seven <br /> years with a 3Q07concentration of 47.1 micrograms per liter (Ng/L). In <br /> addition, off-site monitoring well MW510C, located approximately 900 feet <br /> down-gradient, outside the hydraulic influence of EWCC3, is now showing <br /> TCE concentrations ranging from 0.37 pg/L, first detected in March 2005, to <br /> 0.34 pg/L recorded in August 2007. DTSC believes that incomplete capture <br /> is occurring at EWCC3 and allowing the toe of the Central Area TCE plume to <br /> migrate further westward. The section should identify the TCE detections in <br /> down-gradient monitoring well MW510C and the highest TCE concentrations <br /> observed in off-site extraction well EWCC3 in the last seven years. <br /> 4. Page 3-2, Section 3.3.1.5; The results from the December 2007 Cone- <br /> Penetrometer Testing (CPT) fieldwork for sites P-5A and P-2A were <br /> submitted to regulatory agencies in a report dated December 13, 2007 and <br /> should be included in this section to provide the most recent sampling results <br /> for P-5A. <br /> 5. Page 3-3, Section 3.3.1.6; See comment#4. <br /> 6. Page 3-4, Table 3.3.3.2; The table should identify that the highest <br /> concentration of tetrachloroethene (PCE) was detected in MW445C with a <br /> concentration of 45.2 pg/L in 1Q07 and that PCE detections were also found <br /> in MW497, located approximately 20 feet from the western base boundary at <br /> concentrations at approximately 2.0 pg/L. The SB PCE plume is not fully <br /> delineated laterally or vertically to the west of MW497 due to the lack of <br /> monitoring points. DTSC recommends that DESJC delineate the SB PCE <br /> plume to the west of base boundary, down-gradient of MW497 to the Aquifer <br /> Cleanup Level of 0.5 pg/L. <br /> 7. Page 3-5, Section 3.3.4.1, The section states that TCE concentrations in <br /> 2007 have steadily increased in MW418AR and MW418B compared to <br /> concentrations measured in 2005 and 2006. The report should acknowledge <br /> 2007 CPT fieldwork results in the SB recording a maximum TCE <br /> concentration of 1200 pg/L at CP1200 boring at 69 feet below ground surface, <br /> indicating that a persistent source remains and is contributing to the ground <br />