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Wendy L. Cohen 5 1 December 1993 <br /> Comment: The risk to current and future users of Zone C water also should be evaluated. <br /> 16. Page 30 of the work plan also states that a ground water model will be used to estimate a <br /> time-averaged concentration at the downgradient boundary over the period of exposure. A <br /> vadose zone transport model will be used to estimate mass loadings from the source areas to <br /> the water table. <br /> Comment: The work plan did not explain why the chosen models are suited to the intended <br /> use, whether the models are thoroughly tested and validated for the intended use, or whether <br /> the model documentation is complete and user-friendly. <br /> 17. Page 35 of the work plan states that the soil underneath the former leaking sewer line has been <br /> identified as the currently known prime VOC source area and corresponds to the area of the <br /> highest Zone A ground water concentrations. As an interim remedial measure (IRM), a vapor <br /> extraction system is being proposed in this area. <br /> Comment: As previously stated, the source area near Village Cleaners also should be <br /> remediated as an IRM. <br /> 18. Page 36 of the work plan states that based on the evaluation and screening of potential <br /> available technologies, the IRMs selected include soil vapor extraction and dual extraction <br /> and/or air sparging to treat soil and ground water. <br /> Comment: I concur with the proposed IRMs. However, the evaluation and screening should <br /> be included in the work plan. <br /> 19. Page 40 of the work plan anticipates that the maximum contaminant levels (MCLS) for DCE, <br /> PCE, and TCE will be established as the ground water cleanup goals. <br /> Comment: LVC must comply with State Water Resources Control Board (State Board) <br /> Resolution No. 68-16, the Anti-Degradation Policy. Resolution 68-16 requires that the <br /> existing high quality of the state's waters be maintained. Therefore, returning the ground <br /> water to its initial high quality requires (a) the ground water pollutants to be cleaned up to <br /> background concentrations and (b) the soil contamination to be cleaned up to levels which do <br /> not threaten to degrade the underlying ground water. <br /> Background concentrations in ground water for DCE, PCE, and TCE equal zero because these <br /> compounds are not naturally found in ground water. In reality, background concentrations <br /> must be defined as concentrations which are lower than the detection limits of the standard <br /> U.S. EPA analytical method, i.e., Method 601. While nondetectable levels of the <br /> aforementioned compounds are the goals for cleanup, sometimes these goals cannot be <br /> achieved. If after installing and operating the best available technology for some period of <br /> time, the goal cannot be reached, we can reconsider, but the cleanup level should not be <br /> greater than the MCL for drinking water. <br />