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r <br /> % <br /> down criteria. However, since this system is relatively small and can be easily re- <br /> deployed, DTSC does not object to the proposed approach. As specified in Section 4.2.5 <br /> of Volume 3, sample results from VMWs and additional data points will be used to <br /> validate if the ROD clean-up levels have been achieved. <br /> 4. Section 4 of Volume 3 also provides information on the rebound evaluation and specifies <br /> that the rebound period should extend for at least one week. Based on DTSC experience, <br /> we believe the minimum rebound period should be on the order of months, not weeks as <br /> proposed. <br /> Specific Comments: Volume 1 <br /> 1. Pg 4-1, Sec. 4.2. So as not to confuse the reader, DTSC recommends that text be added <br /> stating that the effective radius of influence and determination of clean-up will be based <br /> on the observed reduction of contaminant concentrations at VMWs. <br /> 2. Pg 6-6, Sec 6.7.2. The design document states that"If a permeable lithologic unit is not <br /> encountered within 1 foot of assigned depth, the contractor shall inform the contracting <br /> officer and the VMW may not be installed at that location." The cross-sections for <br /> SWMU20 - SB204 (Figures 3-16 and 3-17) show extensive clay (low permeability) <br /> zones. Given the proposed location of VMWs at SWMU20-SB204, some of the VMWs <br /> will likely not meet the criteria. DTSC is not opposed to allowing field decisions, but <br /> please provide the decision logic/criteria that will be used to determine if the boring is to <br /> be completed as a VMW. <br /> Specific Comments: Volume 3 <br /> 3. Pg 5-2, Sec. 5.4.1. Prior to performing the respiration test, DTSC recommends that the <br /> oxygen and carbon dioxide levels be measured so as to provide a baseline prior to <br /> injection of air. <br />