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C <br /> Mr. Marshall Cloud <br /> November 27, 2007 <br /> Page 3 <br /> remediation. During benchscale testing it should be noted that the type of tests <br /> performed on the samples can produce varying results (i.e., complete mixing of <br /> sample versus flow-through column testing), so consistency in benchscale <br /> testing methods used is recommended. <br /> 2. DTSC recommends estimating the contaminant mass located in the "source <br /> area" in pounds and should verify that the investigation covers a full lateral and <br /> vertical assessment of the saturated soil matrix, including free-phase product, <br /> and any mass from the smear zone. Contaminant mass calculations should <br /> include both dissolved and sorbed phases of contaminants. <br /> Specific Comments <br /> 1. Page 3-7, section 3.7.3, second bullet; DTSC recommends using EPA <br /> Method 6010B for analysis of metals such as arsenic, barium, cadmium, <br /> chromium, copper, iron, lead, and selenium in the saturated soil matrix rather <br /> than method 6020A. <br /> 2. Page 3-7, section 3.7.3, third bullet; DTSC recommends using EPA <br /> Method 60106 for analysis of total manganese concentrations in saturated soil <br /> matrix. <br /> 3. Page 3-7, section 3.7.3, fourth bullet; DTSC recommends using EPA <br /> Method 7199 for analysis of Hexavalent chromium in post injection matrix <br /> sampling. Method 7196 is susceptible to matrix interference from turbid solutions <br /> and the presence of Hexavalent molybdenum, mercury, and vanadium. <br /> 4. Figure 1-2, Cross-Section D-D', South Balloon; The 100 parts per billion (ppb) <br /> TCE isopleth drawn around MW302B2 is drawn incorrectly and should be <br /> redrawn. As currently drawn, the 100 ppb isopleth encompasses a 39 ppb TCE <br /> concentration located at the middle screen of MW302B2. Please revise the <br /> figure. <br /> 5. Figure 1-3, Proposed Phase I CPT Locations; The figure indicates that Phase I <br /> CPT locations are planned primarily to the east, and southeast of CPT 1063 <br /> location, whereas the highest concentrations of TCE in ground water appear to <br /> the west/northwest surrounding extraction well EWA5 and MW450C. <br /> Additionally, ground water flow directions for the B-zone aquifer indicate a <br /> southwesterly flow direction in the vicinity of CPT 1063. Describe in the report <br />