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Mr. Marshall Cloud <br /> September 18, 2007 <br /> Page 2 <br /> General Comment <br /> 1. DTSC is pleased with DDJC-Sharpe implementing optimization efforts in its <br /> pump and treat system through focused groundwater extraction in addition to <br /> investigation and remediation of persistent VOC sources for groundwater <br /> contamination. <br /> Specific Comments <br /> 1. Figures 3-7 and 3-8; The potentiometric surface contours provide groundwater <br /> contours but fail to provide groundwater flow directions using the gradient arrows. <br /> The figures should be revised in the Final report for consistency with Figure 3-6 <br /> already showing the gradient arrows along with the Figure's Legends indicating <br /> the symbols are to be used. <br /> 2. Page 2-1, section 2.0.3, last sentence; The text in the report should be revised <br /> to indicate a ten foot screen length from 129.3 to 139.3 feet below ground <br /> surface (bgs). <br /> 3. Page 3-12, section 3.2.3.2; The purpose of the focused extraction tests are to <br /> accelerate mass removal from areas of groundwater with the highest <br /> concentrations of contaminants. According to section 4.3.8 of the DDJC-Sharpe <br /> 2006 FFA Annual Progress Report, focused groundwater extraction at MW437C <br /> removed approximately 9.27 pounds (lbs.) of VOCs in 2006, compared to <br /> 22.32 lbs. removed from EWCC1 in 2005. Please describe in the report the <br /> benefit of focused extraction when only half as much contaminant mass was <br /> removed from MW437C in comparison to the previous year's pumping regime <br /> from EWCC1. <br /> 4. Page 4-1, section 4.0, second bullet; DTSC believes that the contaminant <br /> concentrations observed at MW437C are a result of the up-gradient persistent <br /> source area, P-5A, where analytical groundwater data are showing <br /> Trichloroethene (TCE) concentrations of 1,350 micrograms per litre (Ng/L) at 21 <br /> feet bgs. The higher TCE concentrations seen at MW437C in comparison to <br /> EWCC1 could potentially be a result of MW437C being farther north and closer <br /> to the ground water flow path induced by EWCC3, which has a strong hydraulic <br /> influence on both B & C-zone groundwater flow in the Central Area. TCE <br /> concentrations of 38 pg/L found in EWCC3 influent indicate the extraction well is <br /> likely pulling portions of contaminants from P-5A source area outside the <br /> hydraulic influence of EWCC1. Additionally, TCE concentrations of 28 pg/L were <br />