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Mr. Maurice Benson <br /> December 30, 2009 <br /> Page 4 <br /> 6.) Page 4-1, section 4.1; The stakeholders should discuss the concept of potentially <br /> lowering the warning levels concentration for CDCs with similar warning and <br /> MCL values. Lowering the warning level for these 5 COCs would provide greater <br /> awareness of plume migration, trigger more responsive monitoring actions <br /> earlier, and ensures better awareness of the site remediation progress by all <br /> stakeholders. <br /> 7.) Page 4-1, sections 4.1 & 4.2; The Contingency Plan should identify the <br /> timeframe for notification of the regulatory agencies due to successive COC <br /> detections over the MCL. <br /> Conclusion <br /> The off-site potable well contingency plan proposes significant reductions in the <br /> sampling frequencies for off-site potable wells. The rationale for the reductions in <br /> sampling frequencies are to help minimize the groundwater monitoring programs <br /> operational costs and to help reduce Defense Logistics Agency's liability due to regular <br /> sampling of potable wells on private properties. While the report proposes the <br /> significant reductions in sampling frequencies there is not evaluation presented on the <br /> impact to human health or safety considerations for implementing the reduced <br /> sampling. Additionally, The Plan's Warning Levels are equivalent to the MCL for many <br /> contaminants which don't allow for any advanced notice to the agencies until <br /> contaminant concentrations are at the MCL level or higher. The Plan should consider <br /> either reducing the Warning Levels to one-half the MCL where equivalent, or <br /> incorporate the Public Health Goals as Warning Levels for increased protectiveness, <br /> monitoring, and reporting. <br /> The concept of using guard wells as an "early warning" system is an acceptable <br /> approach, but is best applied when the plumes' flow paths are well characterized and <br /> documented, and when there is representative monitoring from guard wells up-gradient <br /> from the at risk potable wells. Typically, at least three lines of evidence should be used <br /> to determine plume stability and guard well protectiveness. Accordingly, DESJC should <br /> apply the 3-dimensional groundwater model predictions as another tool to help <br /> determine whether plume migration is likely or occurring, and whether the guard wells <br /> are providing an adequate "early warning." <br /> DTSC recommends that DESJC provide the regulatory agencies with the <br /> comprehensive hydrologic analysis demonstrating that the guard well cluster locations <br /> are appropriately located and screened in the specific hydrologic zones represented by <br /> the PWs. The hydrologic analysis would allow the regulatory stakeholders to <br /> individually assess the current monitoring well/guard well locations to help gain a higher <br />